OHMIC CONTACTS TO N-TYPE INDIUM PHOSPHIDE
BY
P-J-TOPHAM
Thesis
submitted
and Electrical
for
the
degree
to
the
Engineering,
of Doctor
Department
University
of Electronic
of
Surrey,
of Philosophy.
September
1983.
SUMMARY
have been studied
Two methods
Indium
high
Phosphide
results
to explain
behaviour
of
than
resistance
reference
following
laser
and these
selenium
are
between
Data
ions
correlated
theory
these
is
with
has been
alloying
and
calculations
presented
implanted
and
have been
alloying
to laser
phenomena relating
annealing.
metallisation
A simple
contacts.
(ii)
and
metal
by furnace
of the
properties
to
contacts
the
on
and annealed
over
comparable
or
lower
The
relative
merits
discussed
with
conditions.
Both methods
problems
followed
has been found
of
ohmic
a deposited
observations.
experimental
a range
on
the
agreement
annealing
selenium
techniques
of
forming
alloying
semiconductor
electrical
reasonable
and
of
by a variety
developed
laser
and electrical
underlying
studied
the
:
dose implantation
The structural
the
(i)
for
of
the
to their
have produced
techniques.
existing
two
contacts
methods
suitable
are
device
of
applications.
particular
and
ACKNOWLEDGMENTS
The author
throughout
advice
the
for
Jim Wilde
and
for
and Engineering
Ltd
are
gratefully
the
device
Research
this
to Mike
Hales
Sanders-for
acknowledged
his
for
his
their
are
whilst
Alan
I.
Research
financial
and
extending
ion
thanked
enthusiasm
of appendix
and Plessey
help
The
support
to Ramish Varma,
for
for
project.
their
processing
Council
for
technicians
university
thanks
Sealy
K. G. Stephens
to
Thanks
Ian
Brian
and Prof.
and
Particular
thesis.
Dr.
facilities
patience.
Blunt
thank
work
laboratory
their
to Roy
this
this
departmental
implantation
to
wishes
and
writing
Hughes
and
The Science
(Caswell)
assistance.
CONTENTS
(1)
(2)
Introduction
(1.1)
Literature
(1.2)
Metal-Semiconductor
(1-3)
Measurement of contact
Metallurgy
Review
laser
of
Experimental
(2-2)
Alloying
(2-3)
Optical
(2-4)
RBS observation
of contacts
microscopy
of metal
(3.2)
Metallisation
(3-3)
Doping
of
of
of
Implantation
(4.2)
Annealing
(4-3)
Recovery
by ion
contact
composition
resistivity
the
semiconductor
selenium
(4-1)
diffusion
layers
of alloyed
Analysis
Doping
method
theory
(3.0
Annealing
resistivity
alloying
(2.1)
Properties
contacts
implants
details
methods
of
damage
implantation
(5.1)
Measurement
(5-2)
Electrical
(5-3)
Summary of doping
techniques
results
by implantation
(6) Measurements on contacts
(6.1)
Non-linear
(6.2)
Ohmic alloyed
contacts
(6-3)
Ion
implanted
contacts
Discussion
contacts
and Conclusions
(7-1)
Discussion
of
laser
(7.2)
Discussion
of
implantation
(7-3)
Comparison
of
contacts
(7-4)
Conclusions
(7.5)
Further
alloying
work
References
Appendices
I:
II
Devices
: Material
fabricated
properties
of
InP
results
results
1
(1)
INTRODUCTION
The aim of
making
in
ohmic
this
to
contacts
InP compared
using
1.1.1,
section
together
fabricating
devices
in
in
section
shown
entirely
improved
1.1.2
a deposited
heavily
or to
metal
doped
techniques
ohmic
and the
following
contact
resistivity.
metallurgical
layer.
laser
section
2.2
alloying.
measurements
in
three.
The results
effects
Again
aspects
of
the
of
of
of
ion
these
implantation.
the
of
a
experimental
presented
two chapters
damage and the
a
and
problems
these
1.2
to
devoted
metal
are
with
model
.
with
the
of its
a
in
The
presented
the
particularly
four
the
the
with
observations
chapters
deals
thin
measuring
simple
samples
in
form
deposited
a
irradiated
irradiate
for
deals
two
to
section
Chapter
not
this
in
are
implantation,
are
to
for
methods
and
are
basis
explained
derivation
on the
annealing,
first
for
account
electrical
chapter
the
to
two and three
irradiating
of
is
them
solutions
to use a laser
reviews
Chapters
and includes
to
formation
to
methods
theoretical
in
problem
contacts
existing
in
devices
of
major
implantation
The
(1-3)
section
effects
pulsed
ion
of
summarised
results
possible
was either
contact
laser
of
that
two
employ
surface
of
technique
here
ohmic
making
The
investigated
are
A
properties.
InP is
satisfactory.
problem
semiconductors
methods
The advantages
Phosphide.
some experimental
with
these
is
other
two novel
study
Indium
n-type
with
utilising
it
has been to
work
and five.
physical
removal
by
2
latter
chapter
measurements
upon the
The
annealing.
electrical
The final
the
chapter
each of
the
two
relating
to laser
with
the
the
for
in
contacting
alloyed
two techniques
contacts
formed
specifically
appendix
is
7.2.
is
by
related
aim
ion
to
in
of
this
contacts
to
the
2,3,6.1
7.1.
the
of
follow
sections
and
The use of
4,5,
6.2
ion
and 6.3
and
merits
of
relative
devices
some
study,
As these
are
results
have been
they
are
7-3.
chapter
implantation.
ohmic
simpler
chapters
A discussion
in
methods
chapters
chapter
covered
both
all
placed
had
not
in
I.
(1.1)Literature
Review
(1.1.1)Advantages
of
Indium
has
Phosphide
properties
compared
advantages
with
(i)
in
and
contacts
separately,
are
to be found
the
not
methods
contacts
contacts
by
made
may be found
contained
chapter
Although
As it
the
contains
layers.
annealed
contacts
six.
discussion
implantation
discussed
the
on
in
assembled
five)
has been to make ohmic
objective
measurements
(chapter
Both
support
Indium
with
gallium
Phosphide
many
It
shares
and these
InP and GaAs have the
Gunn oscillations.
in
advantages
silicon.
arsenide
devices
correct
are
fundamental
some
of
these
:
band
structure
to
3
(ii)
The low field
InP and GaAs than
in
greater
(iii)
and peak electron
mobility
Whereas
direct
are
silicon.
has an indirect
silicon
compounds have
in
velocity
bandgaps
these
bandgap,
is
which
III-V
for
useful
optical
devices.
(iv)
It
widely
is
varying
the
was
optical
with
GaAs, these
in
(ii)
of
developing
the
devices
are
advantages
are
GaAs
development
advantages
now widely
of Gunn
out
in
microwave
by
shown
InP.
importance.
assumed
used
of
and
InP
and
compared
are:.
The ratio
greater
other
oscillators
for
spurred
the
Further
systems.
(i)
reason
have
GaAs
result,
microwave
reason
same
Only more recently
As a
simple.
original
the
subsequently
form
heterostructures
epitaxial
upon InP and GaAs.
properties
to
The ability
diodes
to grow
possible
the
of
InP than
peak to
in
valley
velocity
electron
is
GaAs.
The InP peak electron
is
velocity
higher
than
that
of
GaAs.
(iii)
The thermal
conductivity
of
InP is
than
greater
that
of GaAs.
(iv)
InP than
(v)
and hole
The electron
for
Dielectrics
be deposited
ionisation
rates
are
lower
for
GaAs.
yielding
onto
InP.
low interface
state
densities
can
4
These advantages
with
to
regard
the
improvements
The velocity
of
conductivity.
enabled
InP
for
be
will
Semiconductor
The
ion-implanted
dB at
GaAs
associated
gain
6 dB for
of
the
(6)
of
this
have
GHz
which
InP FET's
GaAs devices.
which
power
even lower
might
frequency
cut-off
GaAs (2)
this
has
( due to
been
results
(5)
noise
figures
are
same
was 7.5
dB
on InP Metal
of
2.4
8
GHz
dB
to
but
geometry,
at
the
observed
identical
almost
the
of
performances
in
have given
has
sensitivity.
the
compared
GaAs device.
rates
given
an efficiency
level
recent
are
an important
These have been fabricated
and
with
most
higher
the
with
The
and
efficiency
superior
(1).
InP than
MESFET's
the
The ionisation
devices.
12
the
in
together
exhibit
)
(MESFET's)
FET's
at 8 GHz and 3.5
in
velocity
(3,4).
experimentally
with
higher
peak electron
greater
to
GaAs devices
similar
InP devices.
temperature
reduced
detail,
in more
factor
This,
oscillators
to
bring
an important
and
Gunn
with
FET's
they
oscillators.
thermal
compared
is
ratio
diode
Gunn
now be discussed
will
peak pulse
of
14% which
An advantage
be important
level
a Gunn oscillator
noise
level.
parameter
for
by ion-implantation
of 5W at
power outputs
is
of
in
a similar
the
is
some applications,
is
an alternative
into
InP
10.8
GHz
to
efficiency
InP device
IMPATT
the
that
low noise
although
which
at
has an
5
It
been found
has recently
a low density
creating
(7).
semiconductor
Insulator
of
This
makes
comparable
manner
mode FET's
with
(MISFET's)
frequency
a good low
of
16 GHz have been reported
(8).
the
gate
in MESFET's due to the
low
an insulator
under
barrier
diodes.
should
be useful
the
InP has
suppression
the
is
for
of
to
inferior
greater
very
shallow
traps
traps
might
is
InP,
than
the
channel
which
noise
figure
Noise
oxide
to
cause
(13)
and the
application
InP charge-coupled
low
best
devices
propagation
paralleling
device
(CCD)
delay
of
partly
by
and these
deposition.
the
surface
of
mode MISFET's
have
mobilities
five
(12)
are
opening
fabricated
the
has
up
the
The simplest
gates.
MOS structures
which
8 GHz (8)
be introduced
at
logic
limit
is
dielectric
channel
power
to
interface
has been entirely
inverter,
an
silicon
speed,
and the
of 8 dB at
enhancement
gate
devices
GaAs act
invertion
strong
The
those'of
Schottky
conductivity
semiconductor
the
leakage
which
may also
a
The use of
n-InP
for
in
a
as
well,
GaAs MESFET's and this
best
by improving
of high
possibilities
Another
thermal
(10,11).
greater
substrate
a high
GaAs, and as a result
been fabricated
gate,
the
at
(4)
FET's
in
an insulated
of
of
length.
gate
possible
unlike
logic
the
of
be reduced
also
times
in
of
voltage
the
gate
of
problem
height
power
The reported
that
the
It
InP high
domains
(9).
barrier
breakdown
advantages
current
due to
The high
the
overcomes
and
Depletion
on silicon.
as
cut-off
InP
InP
performance
frequency
onto
of Metal
formation
using
MOSFET's fabricated
to
dielectric
the
possible
FET's
Semiconductor
the
between
states
S'02
to deposit
possible
gate
on an InP
was 350
on silicon
been
is
ps.
the
operated
6
sucessfully
(14).
and higher
speed:
The
the
advantages
test
InP are
of
device
lower
had a frequency
dark
current
limit
of
over
InP
(15)
which
50 MHz.
Light
diodes
emitting
have a narrow
doubler
phosphors
which
greater
interest
is
InP substrates
lasers
Both
and
for
the
the
uniformity
possible
for
opening
integrating
them
InP FET's
In all
contact
required.
only
the
is
devices
The specification
resistance.
to
keep.
been
most
on
wavelength
systems.
with
The
A
promising.
by ion-implantation
is
in
on one substrate,
(18).
devices
is
which
ohmic
In
unwanted
above
devices
least
at
two ohmic
(TED's, MISFET's)
devices
the
layers
(16,17).
to be
reported
produced
of
implanted
photodiodes
mentioned
IMPATT oscillators
oscillators,
necessary
of
have
and photodetectors
and for
material
micron
area
formation
contact
The unipolar
An
communication
GaAlAs optoelectronic
required
to n-type
parasitic
LED's
with
as has been done with
(1-1.2)Ohmic
were
1.3
optic
layers
response
frequency
exciting
light.
of
junction
p/n
in
of GaInAsP quaternary
fibre
n-type
produce
and photo
blue-green
manufacture
for
for
suitable
growth
photodetectors
to
width
produce
InP and quaternary
beryllium
can also
line
spectral
be produced
the
area
contact
large
signal
dissipation
this
are
contacts
thesis.
includes
operation
and LASERs the
power
in
ohmic
contacts
require
studied
always
one
a
such as Gunn
low resistance
to
low
a minimum.
is
In
7
small
signal
is
resistance
contacts
for
required
are
(e-g-
such as that
operation
often
300'C
for
TED's)
The conventional
and GaAs is
the
on the
dopant.
be obtained
a thin
Contact
As far
resistance
of
the
heavily
doped layer.
process
and rapid
diffusion
diffuse
interface
between
to dope
metal
the
:
InP
usually
a
eutectic
a
for
InP is
out
must
the best
with
be
and
of
metal
the
is
the
not
the
dopant
germanium
chapter
method
The
adequate.
is
a
certainly
contacts
InP to
well
can occur
on the
at
conventional
the
can
Alloyed
in
reported
dissolve
solution
ohm. cm2
explained
alloyed
metal
of
on
resistivity
and semiconductor
restrictions
the
higher
contacts
is
and-
(19,20).
perfectly
with
melt
germanium
n-type
heat
concentration
10-6
InP
concerned
The dissolution
places
a high
reasons
to
seem
the
semiconductor
somewhat
difficulties
because
During
of around
on
(21,22)
would
The
a problem.
of
InP
suitable
a
recrystallises
method
as n-type
parasitic
to form-
for
to both
contacts
and incorporating
InP have
ohm-cm2
contacts
contact
Ias
area,
p-type).
layer
resistivities
this
of making
not
temperatures
containing
and Zn for
n-type
substrate
by
10-4
1.2-2.
in
ohmic
layer
metal
semiconductor
to p-type
contacts
about
In addition
at high
defined
of making
a
dissolves
metal
regrowing
the
be stable
closely
method
Ge for
down
cooling
of
to
and
by alloying
(e. g.
the
cycle
speed and low noise.
required
low
and photodiodes
in'FET's.
example,
dopant
high
of FET's
occur
form
controlled
in
resulting
(21).
metals
and gold
and dissolve
the
a
The need
used
is
the
for
the
employed
InP and
a
commonly either
Tin
has
been
also
A major
gold.
InP at
with
above
ohmic
with
to alloy
the
advantages
to
inhibit
balling
and better
(28,29).
which
It
should
be
would
for
GaAs,
this
aluminium
type
to
is
is
analysed
successful
on
short
laser
heating
in
edges
these
alloyed
high
The
in
greater
resistivity
point
melting
the
also
,
contact
a
cycle
to smoother
results
to use high
GaAs, is
Possible
(27).
lower
Based on
for
leading
anneal
reacts
also
laser.
smoother
alloy
been used for
(26).
pulsed
the
InP
furnace
alloys
without
encouraging
the
results
to
contacts
InP are
thesis.
A standard
silicon
the
to
measurements
in
presented
is
be possible
into
photo-engraved
producing
decomposing.
semiconductor
of
diffuses
reported
that
are
reaction
interface
a
with
violent
silver
the metallisation
during
difficult
but
agent.
conjunction
has also
already
with
alloying
dopant
its
a diffuse
problems,
in
rapidly
(25)
interface
the
of
in
retention
reached
solubility
Silver-tin
up of
metal-semiconductor
temperature
(24).
metal
furnace
over
surfaces
and gold
these
contact
is
gold
(23),
InP resulting
(19)
dopant
using
"wetting"
added as a
to Gunn oscillators
An approach
will
400*C
temperature
contacts
strongly
with
problem
is
as the
used
around
this
or indium
nickel
technique
production
implant
evaporated
in
the
(30)
GaAs
on
a heavily
forming
next
as the
for
doped surface
a field
section.
large
ohmic
emission
This
barrier
layer
onto
method
which
of
the
not
very
means
that
contact,
height
to
contacts
is
9
high
very
contact
carrier
much
problem
damage.
InP
the
in
encapsulation
electrical
activity
are
the
carried
is
implantation
of
(5,39)-
FET's
surface
the
of
give
Low
carrier
contact
InP
limited
can
a low
donors
concentration
resistivity
produce
resistance
liquid
of
of
the
alloyed
contact
contacts.
have
carrier
in
(38).
growth
used
have been used
is
implants
(37)
holes/cm3
been
as this
than
maximum
has already
(5,40)
silicon
Acceptors
epitaxial
a sufficiently
ohmic
1018
the
when the
(36).
and
or hot,
mobilities
phase
implants
(35)
room temperature
the
have
precentage
However,
around
ions
similar
most marked
but
namely
Sulphur
greater
is
InP
to
energy
a
temperature
into
results
with
at
significantly
the
agreement
give
to
or provision
donor
(32),
750*C.
around
InP,
(37)
Si
N4
or
3
Silicon
the
out
decomposition
in
of
One
techniques
this
A range
implanted
an elevated
implanted
concentration
Ion
at
Similar
ions
two and this
other
out
been
have
to GaAs.
(32)
has
electron
anneal
cause
are
three
whether
layers
of
also
All
to
need
low
reported.
required
(34).
these
temperatures
annealing
either
InP,
high
being
prevent
S'02
pressure
into
(33).
to
implantation
obtaining
the
manner
either
over
Selenium
implanted
is
used
donor
1019/cm3
over
The temperatures
using
been implanted
for
well
a similar
a phosphorus
in
to achieve
necessary
by
InP
success
on GaAs are
used
are
of
ion-implantation
of
radiation
those
greater
(31),
concentrations
of
Doping
resistivity.
produced
of
concentrations
to
thought
Donor
to
make
raise
the
to
reduce
implantation
high
carrier
concentration
(see
section
1.2)
without
to
the
10
need for
in
alloying
designed
for
can be controlled
of non alloyed
horizontal
creep.
to
ability
self
the
is
(1-2)
the
source
high
(1-2-1)
The Schottky
Several
authors
be
should
derived
from
Om and
an
affinity
electron
levels
Fermi
contact
given
OB
and the
with
of
InP as a FET
some
with
1.1a)
are
1.1b).
work
brought
For
of work
function
into
function
0.
contact
and
the
to the
semiconductor
xs
given
can be
a rectifying
the metal
is
references
OM > OS
.
potential
contacts
quantities
useful
when a metal
:
from
these
analysis
1ý
diffusion
and is
capacitance
semiconductor
metal
complete
(fig.
The barrier
by
=0m-
(fig.
coincide
ensues.
dealt
semiconductor
XS
the
by use of
model
situation
n-type
and
mode MISFET the
regions
performance
However,
a simple
case
contacts
more
consulted.
the
for
fully.
have
a
enhancement
parasitic
frequency
of
diffusion
vertical
and drain
reduces
to be utilised
and for
the
without
dimensions
accuracy
allows
of
Metal-Semiconductor
(41,42,43)
is
case
align
if
essential
material
the
as a mask greatly
metal
gate
In
greater
with
as melting
contacts,
the
In addition
much
can be
which
temperatures
at high
a dopant.
a
allows
metallisation,
stability
metallurgical
contact
of
choice
the need to incorporate
the
This
metallisation.
the
in
freedom
greater
the
by
11
vd
bias
(T2 exp
A*
where
is
ohmic
contact
Ionically
simple
to
the
should
bonded
model.
the
Richardsons
modified
result
on n-type
for
the
As a result
barrier
n-type
height
InP.
(42)
the
and
The depletýon
example
by
region
in
(fig.
of
the
an
1.1c).
to this
surfaces
of
Si, GaAs, InP)
are
states.
pins
has very
virtually
then
ZnS, conform
(e. g.
of surface
metal
0m<0s
semiconductor
properties
semiconductors
density
if
theory
Schottky
This
surface.
given
constant
1-5
simple
However,
by a high
controlled
1-4
semiconductors,
bonded
covalently
e4B)
kT
47r
e M*e k2
h3
A*=
According
1-3
charge
external
j0=A*
-over
barrier
exp K-kT )-11
electronic
V=
the
le vjý
I
JO
e
emission
(41)
density
a current
gives
by thermionic
transport
Current
1-2
OB
=0m-
the
little
Fermi
level
effect
at
the
on
the
all
metals
form
a barrier
to
the
semiconductor
under
the
12
metal
be
can
obtain
obtained
Hence the
For
termed
current
over
occurs
produces
a
semiconductor
permittivity
is
width
1-7
doped material
flow
(figs.
increases,
the
is
field
and this
well
an effectively
is
in
to permit
in
tunnelling
and
fig.
occurs
termed
field
either
direction
ohmic
width
contact.
is
by thermionic
As
& 1.2b).
depletion
emission
flow
current
1.2a
enough
illustrated
the
equally
the
the barrier
thermionic
barrier
and
OB
can become thin
concentrations
the
ND
of
e2 ND
concentration
barrier
to
1-6
depletion
EsE0
lightly
emission
equation
2esco
doping
,'=ý.,
(41)
2ND (X-W)2
a uniform
ESC-0 -
Poisson-s
barrier:
a parabolic
EM =8
for
by integrating
the
top
the
near
tunnelling
position
1.2c.
At
high
through
the
bottom
(figs.
of
the
this
:
the
emission.
carrier
is
of maximum
Field
1-2a
carrier
10% of
emission
& 1.2b)
and
13
(1-2.2)
Ohmic contacts
To be useful
be capable
that
the
is
of
It
is
defining
desirable
that
the
v
PC
so that
specific
V is
the
semiconductor
incremental
drop
alone,
J
these
contact
dominated
requires
the
(ii)
(iii)
Uv)
(v)
the
the
by
formation
in
Alloy
contact
reverse
can be used
a contact
the
resistivity
1.8
0
is
which
is
the
not
through
density
current
to
attributable
the
characteristics
a
field
is
emission
of a heavily
following
doped
metal
the
the
surface
ways
implantation
Diffusion
laser
and electron
semiconductor
necessary
regrowth
Pulse
of
part
and
same contact
Epitaxy
Ion
active
forward
For-such
drop
a voltage
6A.
To achieve
(i)
the
should
contact
V-0
voltage
area
can be achieved
with
across
polarities.
6A,
where
current
voltage
supply
is
parameter
required
similar
to both
connection
an ohmic
the
with
also
are
fabrication
the
supplying
characteristics
for
device
compared
small
device.
in
beam alloying
and
layer.
this
This
14
common technique
The most
which
relies
metal
(which
include
may
active
electrically
doped layer
may also
it
implants
by furnace
has
regions.
deposited
without
compound
necessary
can
a very
It
to
mV was
to
The
for
Pulse
expression
substituted
dose ion
doped
not
used
temperatures
electron
and
dopant
the
is
a metal
is
laser
under
influence
that
is
high
and
metallisation
for
The calculations
bias,
voltage.
reverse
into
current
the
and reverse
this
equality
To obtain
density
expression
employed,
in
for
reverse
currents
extends
to
voltage
The result
are
small
from
resistivity
a bias
-
Stratton
concentrations
were performed
forward
applied
is
emission
carrier
and
on
flow
current
Padovanni
of
doping
surface
the
for
field
for
approximation
zero
of
used
contact
for
if
high
the
of
(44).
heavily
Diffusion
the
an
high
result
as
theory
"ohmic"
an
reverse
and
epitaxy
thin
contacts
the
barrier
at
anneal
A heavily
phase
treatment.
expression
that
the
incorporating
create
devices.
in
(45).
4.1018/cm3.
noting
their
heat
calculate
a reasonable
or
ohmic
a furnace
to activate
semiconductors
period
their
forward
cases
to
semiconductor
Only
and
(31)
regrowth
metallisation.
possible
the
Schottky
equal
found
by melting
a
bias,
grown
diffusion
useful
of
liquid
rapid
through
excess
by
achieve
resistivity.
is
be
n-type
contact
which
the
further
short
is
(46).
and
of
detrimental
are
solubility
for
regrowing
annealing
both
In
beams
during
(20)
dissolving
semiconductor
of
component
been
Recently
alloy
a dopant),
epitaxially
subsequently
with
on
amount
on a small
is
InP
of
W
was then
15
into
substituted
A second
of
the
bias
For
agreement
was
voltage.
The results
presented
in
used are
given
the
obtained
1.3
figure
in
concentrations.
contact
resistivity
than
would
The
in
result
(1-3-1)
levels
means
parasitic
of
are
effective
of
a
gives
the
ohm. cm2 whilst
same hole
10-4
about
p-InP
less
are
to
contacts
non-alloyed
of
practical
1019 electrons/cm3
obtained'in
given
mass
for
resistivity
contact
InP,
n-type
The agreement
resistivities
10-6
are
n-GaAs
to n-InP.
and
bias
The constants
with
for
bias
p-InP
resistance.
contact
resistance
and resistivity
Techniques
The contact
semiconductor
alone.
can be rewritten
PC =
has previously
resistivity
of a contact
resistance
example,
doping
which
Measurement
For
a
highest
a high
contact
good
lower
mV
InP.
comparison
height
low
the
10
for
constants
about
in
results
1019 holes/cm3
(1-3)
(1-8),
of
for
(47)
Sze
and
barrier
in
carrier
ohm. cm2 .
For
linearity
the
presented,
and p-type
II.
identical
results
concentration
n-type
appendix
The small
reasonable.
InP
for
resistivity.
check
results
calculatios
by Changjang
calculated
n-type
the
the
to
concentrations
with
of
as n-GaAs has almost
is
carrier
for
a value
100 mV was tried
of
voltage
contact.
values
1.8 yielding
equation
not
attributable
Contact
for
11M
I Rc.BA 1
6A- 0
linear
been defined
to
the
defined
resistivityRc,
contacts
resistance
in
as
of
the
the
equation
as
1-9
16
for
which
with
a contact
density
current
uniform
to
simplifies
pc = Rc. A
types
Two distinct
dealt
the
with
bulk
flows
of
the
semiconductor,
(fig.
the
bulk
(48)
Strack
top
is
plane
semiconductor.
contacts
LP-C
=
of
flow
resistance
is
In
several
the
vertical
method
are
contact
to
of
surfaces
principally
diameters
one
of
the
first
third
term
the
For
+
term
the
the
the
smaller
than
denoted
by RS , is
ps
2d
is
resistance
is
term
f-d4L)
Arctan
f
-Ls
7rd
7rd2
where
readily.
the
on both
formed
&
Cox
of
deposited
the
on
ground
shown to be :
Rfoial
second
current
layer.
are
contacts
and current
and the
one substrate
the
when
flow
1-4a)
of
through
vertically
secondly
surface
current
techniques
flows
be
will
measurement
current
and
a thin
Vertical
wafer
resistance
when the
through
these
through
contact
firstly
(1-3-2)
the
of
:-
laterally
In
1.10
the
of
spreading
common case
contact
the
back
Rr
resistance
contact
resistance
of
the
thickness
sample
given
+
plus
which
contact
the
required
and the
wiring.
The
can be calculated
diameter
spreading
being
much
resistance,
by
1-12
17
hence,
4pc
Rtotal -
let
7rd2
Ri
Rs;
=
-
Rtotal
Ri=i
hence
7r
a plot
intercept
Ps
Pc
arrangement
in
effect
the
resistance
in
equivalent
the
in
addition
probe
in
small,
approximately
0-37ps
-'ý
For both
techniques
negligible
(e. g.
of bulk
varying
on the
back
contact,
not
the
previous
semiconductor
surface
the
effect
which
requires
is
only
the
the
error
the
of
Hence
accurately.
method
removes
the
However,
fixed
contacts
to
and partially
resistance.
is
the
The resistance
identical
a probe
resistivity
diameter
contact
are
an
and
2
I/d
Ri vs.
plotting
by this
given
4 pc / 7r
of
measurement
calculated
For small
semiconductor.
a slope
1-4b was developed.
of
the
be
obtained
is
for
geometry
cannot
the
circuit
spreading
the
yields
figure
the
resistance
Pc
need
of
resistivity
is
1/d2
any effect
of
because
1-14
An error
shown
resistance
Rr
vs.
the
but
analysis
removes
interface
show up as a curve
To avoid
values
Ri
of
the
,
+
d2
of Rr.
would
1-13
+ Rr + Rs
valid
use
in
of
if
spreading
the
the
low
contact
contact
spreading
resistivity
resistivity
by
d
1-15
the
metallisation
by ele. ctroplating
resistance
gold).
can
be
made
18
(1-3-3)
Lateral
technique
This
structures.
layer
epitaxial
InP.
A
is
of
is
mesa
potential
on
distance,
as shown,
give
the
structure
often
etched
are
of width
of
the
1-5)
to
ensure
end
on
fingers
Vc.
on an
semi-insulating
1 and spacing
back
potential
fabricated
perpendicularcurrent
w, length
sampling
device
planar
is
Rs grown
and extrapolated
contact
testing
(fig.
resistivity
each
to
suited
sheet
The contacts
flow.
well
typical
A
flow
current
to
is
against
plotted
the
to
end
contact
The contact
The
s.
is
resistance
simply
Rc- = VC/I
1-16
The sheet
Rs=m.
w/I
where
m is
resistivity
(1-3-4)
the
epitaxial
1
slope
is
area,
of
not,
the
graph
in
general,
be derived
will
The transmission
A simplified
length
and
layer
by
given
1-17
which
by the
multiplied
is
resistance
planar
width
of
line
contact
w,
negligible
and
of
(fig
in
1-5)the
the
model
consists
of
contact
thickness
contact
next
(TIM)
The
sheet
resistance
section.
metallisation
resistivity
and
contact
/Oc
resistivity
of
on an
RB
19
(fig.
1.6).
and current
V(x)
under
il.
ax-
cOsh
characteristic
z=
ý Rspc
-L
w
attenuation
are
situation
by
given
Z. sinh
by the
the voltage
and has shown that
:
ax1.18
V2 /Z sinh
-ax-
this
has modelled
1.6b)
contact
the
where
and the
the
= V, cosh
i2
(fig
line
transmission
lossy
(49,50)
Berger
1-19
c( x
impedance
is
given
by
:
1-20
constant
is
Rs
1-21
ce
PC
For
'2 ý 0,,
an end contact
planar
then
test
(fig.
structure
defined
and V,
may
be
measured
The contact
1-5)-
using
resistance
the
is
:
RC =
1i,Vil
1-22
i -0
:F
hence
Rc =Z
The term
For
For
coth
al controls
al<0.5,
aI>2,
1-22a
a1
the
Rc a i/d,
Rc=
Z,
resistance
contact
PC=Rcwd
=
cRc
W2
Rs
2
as follows:
1-23
1-24
20
from
substituting
(1-17)
eqn.
and noting
VC/Ic
m=
1-25
Pc = Rs w ic
lc
The length
the
is
the
Furthermore
as a consequence
contact
length
contact
resistance.
specific
contact
not
the
in
achieved
the
specific
contact
junctions).
drain
contacts
the
planar
width.
contact
the
contact
must
the
3-3)
width
as
in
this
turn
rapid
of
be
neglected.
for
devices
the
Hence
in
which
Gunn devices',
predicts
be
current
fraction
design
the
can
vertical
such as the
useful
In
met.
devices,
gate
at high
(49)
(e. g.
the
which
Berger
the bulk
FET,
particularly
is
through.
may
meaningful
a
introduced
parameter
is
planar
resistance
This
error
by
be
a small
only
for
of
per unit
is
the
is
However
resistance
depth
melt
beam annealed
(section
-In
in
evaluate
be shown that
will
doping
region.
melted
to
it
melts
to
been used
under
unlikely
of
resistivity
flow
current
is
the
improvement
noted
resistivity
constant.
extending
and electron
a condition
level
thickness
semiconductor
laser
semiconductor
as the
measurement,
for
if
contact
were
(1.221
method has often
altered,
and a
interface
equation
sheet
high
the
of
show no significant
However,
the
where
of
resistivity
semiconductor
diffusion
the
This
be significantly
cases
the
21c will
(25).
layers
that
beyond
length
contact
throughout
density
current
metal
effective
source
p-n
and
is
parameter
the
affects
parasitic
performance,
frequencies.
termed
the
resistance
end resistivity
(eqn.
1.22)
and has
multiplied
the
by the
value
of
contact
PAGE
NUMBERING
AS
ORIGINAL
22
Vac.ley
.1
Ec
EF
EFý
777/777
cu
S
U-j
metal
In-type
Ev
s/c
b
Vd
ee.,
E
Ec
F
EF
Ev
EF
/////
I '//"
(0 orn) e
(X,
e -
Ec
---EF
Ev
Fig.
1.1
Contact
between
metal
and semiconductor
23
Thermionic emission
a
forwardbias
Thermionic
field emission
EF
Field emission
EF 7
b
Thermionicenission
bias
reverse
Thermionic ffeld emission
Field emission
EF
EF
Fig. 1-2a,b Current transport mechanisms
Dominant
transport
current
Thermionic IT-F
I r:
-I-i
1
*8
m
*6
-4
a2
01016
id"n/crrf-1
10
is
id,
Fig.1-2cPosition of maximumtransrWisslionthrough barrier
24
lu -4
4r,
lo-5
Ob=)0-4
00--%
c**.
ýj
Li
10-6
Qý
lo-7
10
18
19
10
np
20
10
cm-3)
Fig.1-3 Specific contact resistivity to
n-InP
p-InP
n-GaAs after ref-47
25
1< d >1
II
s/c resistivity=
PS
R, = backcontact
resistance
Fig.
1.4a Arrangement
to measure contact
method of Cox & Strack.
resistance
by the
I
(1)3
(2)
Rmeta[
Rc
additional
probe
Rs
ýRr
Fig.
1-4b Modified
resistance,
to measure contact
the resistance
of the back contact.
eliminating
arrangement
26
V__
HSH
It
4.
180ym
41.
4
40ym
H--*i
x
k 2k
Fig-1-5 Arrangement
planar
to measure contact resistance
structure.
on a
27
ViT
TV2
/OC
12
PS
x-=O
Fig.
.
1.6a
Contact
structure
Yv
modelled
by the
TLM method.
t
v
.
Gdx
Rdx
>1
i,
12
x=O
Fig.
1.6b
Equivalent
circuit
of
the
contact
used in
thelanalysis.
28
(2)
METALLURGY OF LASER ALLOYING
two
The following
irradiating
to
the
test
before
metal,
the
experimental
Three
types
was bulk
grown,
on
side
boiling
in
table
donor
into
2.1
with
was repeated
Tin
An
in
sizes
the
and also
the
res. > 10
deposited
electrical
by
were
the
substrates
for
study
its
which
layer
ohm. cm
(100)
of
After
used are
and so
gold
the
a
electrical
was found
silver
of nickel,
listed
combining
can be used for
of
by
were cleaned
simplicity,
on GaAs (50)
A composition
7
the manufacturer.
was chosen
a previous
these
crystal
single
The metallisations
additional
on InP.
deals
chapter
on
solvents.
connection
a metallic
measurements.
beneficial
.
one
suitable
organic
some experimental
16 3
7cm
2.10
5.1
015
n=
-
the
cleaved
a
and
n-1018/cm3
Fe doped semi-insulating,
being
This
method
have beeen employed,
(iii)
polished
laser.
method
Undoped n-type,
orientation
ruby
of
InP.
substrate
material
effects
The next
model.
alloying,
Sn doped n-type,
(ii)
All
of
with
measurements
laser
underlying
(2-1)
(i)
together
electrical
the
experimental
the
of
after
and
of
properties
in
the
with
principally
the
process
validity
a pulsed
with
of
the
of
model
mathematical
metal
details
contains
chapter
data
deposited
a
investigate
chapters
to be
practice
and germanium
29
is
used in
already
InP,
will
which
germanium
to achieve
the
one pump down of
being
the
were stuck
samples
n-type
Ni-Au-Ge
by
hence
gold
with
(i. e.
to
in
glass
entire
by photoengraving
in
in
lift-off
photo
the
the
the
and
wax
case of
of
case
The
InP).
then
were
in
metal
named
with
Contacts
case
out
"Apiezon-W"
with
surface.
In the
first
contact
slides
density
was carried
the
low
a
energy
density.
energy
absorbed
the
has
it
the
reducing
and
alloying
as
vacuum system,
samples
or
layer
metallisation,
their
over
metallised
top
laser
of
case
laser
between
deposition
first
evaporated
on the
with
a given
multi-layer
the
to GaAs and
contact
an ohmic
comparison
the
as
compared
reflectivity
of
In
was deposited
form
direct
a
allow
alloying.
conventional
required
to
industry
defined
the
Sn and
the
Sn-Ag
metallisation.
The samples
ruby
(wavelength
laser
otherwise
laser
were then
stated
quartz
beam to produce
with
profile
a
further
incident
of
'Ismearing
large
energy
scale
the
sample
density
monitor
on
an energy
entire
the
beam
out"
of
4-5% over
aperture.
of properties
energy
density
somewhat
integrating
The
small
Unless
duration.
the
the
sample
density
larger
the
scale
as one sample
than
irradiance
variations
has
areas
with
As a
scale.
energy
that
The
area.
profile
on a smaller
the
density
energy
uniform
non-uniformity
is
Q-switched
a
using
was used to homogenise
approximately
beam has a Gaussian
variations
of
an
air
25 ns pulse
wave guide
uniformity
non-homogenised
result
694 rim) of
a
in
irradiated
density
measured
over
cause
irradiated
by
the
a
30
with
a
the
range
results
those
with
the
the
the
homogenised
tin
surplus
removed
using
It
alloy
laser
insoluble
Table
beam,
anneals.
photoengraving.
following
laser
multi-mode
later
all
alloying
in
the
densities.
energy
with
for
adopted
different
of
was
not
beam are
hence
less
the
these
the
same
for
due to
either
the
tin
than
homogeniser
as
had
the
for
the
remove
formation
or
was
samples
etchants
to
possible
reasons
accurate
The semi-insulating
presumeably
etchants
For
Ag-Sn
of
silver.
2-1
Su bst rate
Sn doped
Undoped
Fe doped
(n+)
(n)
(SO
Metalrisaýtion
lisa i
1000 A
Sn
2000 A
Sn
010
101010
1000 A Sn+1500 A Ag
101010
50 Ä Ni + 1000 Ä Au
+400 Ä Ge
111
0
an
31
(2-2)
theory
Alloying
The processes
by
explained
in
parameter
is
the
during
occurring
a
simple
mathematical
which
diffusion
length
is
which
given
and the
to be used
ID
2-1
of
the
pulse
is
given
diffusivity
thermal
are
&t
duration
time
important
The
conditions
by
K
2-2
PS
where
It
is
capacity
K
thermal
p
density
S
specific
found
vary
that
only
conductivity
heat
the
slowly
(
KKT
T
300 300
n
)
capacity
values
can be described
conductivity
be
may
by :
IDD,
where At=
alloying
model.
boundary
considering
thermal
laser
with
of
density
and
temperature
by an equation
of
heat
specific
but
the
the
form
thermal
(82)
2-3
32
temperature
T=
where
= 1.2 for
conBtant
K300 ý thermal
Using
when irradiated
melting
the
typical
the
with
the
bulk
during
is,
surface
the
laser
after
length
sample
et.
the
the
except
for
range,
given
incident
R=
metallisation
In this
the
Ke
temperatures
much
only
the
case the
is
surface
initial
the
at
than
less
temperature
rise
0-5
2-4
reflectivity
is
given
by
2-5
subtrate
temperature
assumed to be
mean thermal
independant
conductivity
over
of
temperature
the
temperature
by (53)
Ke
where
are
is
InP
the
at
density
energy
Tp = TM + Ts
Ts = initial
constants
is
(52)
al.
temperature
peak surface
where
All
ei=
microns
remaining
I
161t
Tm -ý 2 ei (1 - R)
7r? S Ke
where
0.5
length
25 ns duration
of
0.4 mm therefore
pulse.
Liau
pulse
diffusion
of
the
of
diffusion
thermal
re and about
thermal
thickness
the
laser
room temperatu
at
sample
temperature
Q-switched
a
300K
at
II
appendix
Hence the
point.
heated
at
with
1.0 microns
about
conductivity
from
constants
InP
the
=
N/KS
subscripts
respectivly.
Kp
2-6
"s"
and "p"
Employing
refer
to
equation
the
initial
(2.3)
and
peak
and rearranging
33
gives
:
0-5
mm
Ts TP
Tm =21-R
where
It
m=n/2
be
in
possible,
the
after
n
"(300
300
s*
7r
should
temperatures
that
noted
Liau,
start
of
to
the
Tm H/
the
of
excess
after
T=
2-7
the
semiconductor
the
calculate
is
equation
melting
temperature
not
valid
point.
It
at
for
is
alsc
t,
time,
a given
pulse:
At ) +Ts ;t<At
2-8
ý
T=T,,
By setting
the
two
solutions
the metal
is
temperature
times
melt
hence
the
the
surface
required
the
in
metallisation
time
the
Again
molten.
difference
the
parameter
melt
readily
depth.
observed
(53)
thermal
diffusion
layer
to bring
are
to be at
the
This
calculation
much
greater
a uniform
surface
to
the
is
is
period
is
during
relies
on the
temperature.
point
peak
point.
estimate
the
which
the
an
than
for
solving
that
melting
sufficiently
the melting
and
is
restriction
calculated
length
+Ts ; t>&t
point
melting
must not exceed the semiconductor
A further
semiconductor
[t / At
-1]
[t / At
T to
0-5 ý
of
fact
the
that
duration
pulse
to
consider
The energy
density
great
has been calculated
34
let
previously,
to melt
available
depth,
it
I is
xf
AHf is
(i)
the
Significant
Vaporisation
(iii)
Thermal
have heated
of
the
metal
achieve
melt
2-9
latent
the
layer
point
a temperature
rise
metal
in
the
the
heat
of
fusion.
as an upper
limit
as
is
to absorb
There
the
Tr
semiconductor
layer
molten
the
modified
is
Es + cm ein d Tr
1-R
and/or
i. e.
all
the
liquid
same temperature
reduce
semiconductor.
melting
Ei =
to
act
metal
the
the
conditions
is
thickness
gradient
these
the
these
energy
have been neglected:
has been assumed to be at
of
Under
above may be regarded
metal
(ii)
effect
.
further
all
Ef
specific
factors
Each of
Therefore
by :
calculated
following
tf
semiconductor.
ei- (1-A)äHf p
,
The value
the
the
given
Xf =
where
be denoted
given
melted
some of
are
three
energy
thickness.
layer
the
energy
cases
density
:
which
firstly
required
The
would
below
to
by :
2-10
35
where
cm = metal
and
calculated
density
pm= metal
density
d=
thickness
metal
the
is
es
heat
specific
Above
Es +cm
Ei Z
Finally,
the
For
the
place
gold-germanium
calculations
melting
semiconductor,
the
point
energy
which
are
latent
heat
2-11
of fusion
melting
point
:
2-12
1+AHfxfp
2-11
eq n.
silver-tin
takes
forms,
metal
semiconductor
(1-R)fi=I
reaction
the
the
ein dTr + äHm pmd
1-R
AHm= metal
above
For the
to heat
reqired
is
required
where
density
energy
previously.
capacity
melts
has
it
metallisation
between
the
layer
it
has been
about
30C.
at
summarised
in
metals,
figures
been
hence
assumed
The
2.1,2.2
assumed
they
that
results
and 2.3.
melt
the
of
that
no
separately.
eutectic
all
the
36
(2-3)
Optical
microscopy
The samples
to
microscopy
in
contacts,
laser
the
to
in
a change
the
masking
steps
(i. e.
gaps
gap
devices,
and
as
FET's)
the
ruin
the
so
increased
gradually
topull-back"
becoming
j/cm2
the
metal
has not
of
back
pulled
The surrounding
rippled.
under
the
under
the
it
suggest
edges
the
should
melt
at
has
this
accurate
with
It
not
melted
energy
to
density
(fig.
melted
clear
more
the
0.38
of
2.4c).
and is
The
finely
as has the
the
whether
InP
InP
The calculations
but
with
0-ý5 j/cm2 have a similar
is
and
density
or not.
predict
the
becomes
extent
density
fine
with
mottled
changes
is
in
subsequent
energy
finely
any significant
contact.
contact
alloyed
to
contacts
from
to bridge
alloying
InP has obviously
whole
sufficiently
contacts
of
the
is
problem
structures
At an energy
more serious.
shows
of melting
between
laser
the
becoming
metal
appearance
the
2
J/cm.
0-33
2-4b)
sufficiently
As
2
is
J/cm
0.14
a serious
For
maintained.
can flow
of
tin
metallisation
alignment
device.
the
with
is
phenomenon
metal
to
pronounced
not
be
cannot
the
by
the
InP nor
hypothesis
of
precise
tin
or less
j/cm2
(fig.
micrograph
The
This
edges.
fabricating
and the
"pull-back"
by the
the
density
energy
contrast
unaffected
of 0.096
neither
metallisation.
supported
deposited
laser
tin
were
density
density
A
the
squares,
energy
energy
melt.
to melt
calculated
further
an
phase
The 2000 A thick
roughness.
200 micron
of
At this
expected
the
form
Nomarski
using
surface
using
2.4a).
contacts
examined
highlight
alloying
(fig
is
were
of
the
model
is
certainty.
The
appearance,
and
37
it
is
only
after
clearly
visible
melting
of
alloying
the
through
The InP-Sn
from
At a laser
energy
density
j/cm2
the
surface
is
laser
alloying
2.5b)
although
polish
lines
InP
where
are
(fig
pits
is
surface
pits
is
energy
density
increases
the
2
the
J/cm
surface
is
almost
completely
energy
density
At
surface
the
increasing
visible
in
allowing
ripples
greater
for
the
in
are
reflectivity
be
alloy
regrowth.
due
to
the
fine
ripples
0.55
j/cm2
and further
ripples
energy
with
the
to
in
results
and
pits
j/cm2
0.38
due to
2.5d)
the
of
covered
2
J/cm
0.75
the highest
to
is
fine
(fig.
concluded
of
by very
depth
and
this
is
(fig.
smooth
frequency
density
to
still
during
whether
After
InP.
so are
density
the
clearly
of
0.92
even larger.
behaviour
the
tin
energy
density
At
are
roughness
the
a micrograph.
Similar
but
covered
energy
ripples
the
textured
or whether
a
by the
laser
a
Increasing
in
j/cm2
The pits
0.096
and
appeared
is
surface
the
completely
increasing
have
dissolved
clear.
results
the
of
2-5a)
of untreated
pits
the
on
has been removed.
been
overlapping
not
that
fine
majority
tin
has
2.5c).
that
clearly
2
(fig.
J/cm
to
j/cm2
more
the
all
0-058
identical
seen
visible.
0.33
are
2.4d)confirming
still
Increasing
and at
the
which
of
0.14
with
be
can
samples
deep ripples
place.
interface
semi-insulating
that
j/cm2
(fig.
contact
InP has taken
the
0.75
with
is
greater
of
the
shown
by
the
silver-tin
contacts,
thermal
mass
silver.
Up to an energy
of
the
contact
and the
density
of
38
0.27
j/cm2
little
The first
contacts.
density
of
j/cm2
fine
deeper
2.
J/cm
rippling
of
the highest
surface
the
of
from
metal
0.92
evidence
back
from
an energy
have an
with
dark
0.33
alloying
micrograph
in
At
.
2
the
J/cm
important
"pull-back"
that
the
of
visible,
for
0.92
at
appearance.
One
not
become
observed
rippled.
can be maintained
germanium
agreement
fine
so
densities
energy
is
the
marked
deposited
2
J/cm
to
(fig.
2.6b)
of
are
much smoother
and the
j/cm2
colour
with
which
InP is
little
purple
coloration
is
energy
be
taken.
density
(fig
2.6c)
of
0.38
clearly
j/cm2
showing
the
pulled
calculated
to
back
and
results
in
from
absent
AuGe
at
unfortunatly
results
an
the
occurs
pull
surface
of
2
J/cm
change
A similar
The
of
0.20
phase
in
again
The pitting
formation
of
j/cm2
and has severely
A second
0.27
micrographs.
the
density
of
2.6a),
model.
energy
edges.
purple
attractive
theoretical
0.096
only
(fig.
be visible
to be due to
At a laser
density
with
the
presumed
strongly
require
contacts
to
with
The contacts
melt.
is
edges
alloying
phase.
is
very
gold
of
surface
metal
is
and 1.54
is
to 0.55
ripples
1.24
of
energy
increases
change
contact
laser
and less.
j/cm2
eutectic
phase
the
edges of
a
these
occurs,
becomes grossly
structures
reasonable
the
at
density
densities
composite
the
at
evident
energy
surface
deposited
The nickel
for
except
become much smoother
contacts
the
lithographic
As the
energy
the
advantage-of
is
A second
contacts
laser
seen
change
the
2.
J/Cm
when the
j/cm2
phase
0.33
0.75
at
is
change
alloying
after
laser
allowing
the
relativly
a
39
smooth
surface
energy
density
formation
suspected
the
increasing
in
results
1.24
fairly
irradiance
laser
(fig.
but
untreated
are
for
material
the
to
0.75
j/cm2
the
j/cm2
by
the
with
Further
RBS.
by
j/CM2
0.92
and
energy
densities
contacts
are
of
still
from
the
identical
to
InP
of
waves
and
surface
correlates
observed
swamped
were visible.
j/cm2
taken
,
is
substrate
in
j/cm2
to
progressivly
the
as might
agreement
calculations
energy
densities
up to 0.20
had
obviously
melted,
be
fine
evidence
of
to melt
and the
Increasing
produces
fine
very
just
are
pits
appearance.
laser
ripples
these
The
at
0.38
more pronounced
with
increasing
alloying
maximum irradiance
shows the
be expected
of
found
the
as the
metal
InP
marked
a
to
density
clearly
become
ripples
density
energy
J/cm2-
the
contacts
of
existence
between
previous
1.54
of
examination
clearly
is
of
the
become
laser
0.27
at
had
energy
and
of
no signs
although
contacts
the
J/cm2-.
visible
alloying
2
J/cm .
The optical
interface
Very
calculated
for
visible
laser
is
by etching,
exposed
contacts
metal
alloying
up to
a roughened
as
and 1.54
interface,
The metal-InP
0.33
in
substrate.
surrounding
Although
Increasing
At the highest
contacts.
2-6d)
smooth
NiP
laser
the
back.
which
contact
of
smooth
j/cm2
change
the
of
pull
j1CM2 results
0-55
to
contraction
severe
from
and freedom
and
these
section.
and
two major
InP
melt.
observations
The
metal-InP
phase
changes
Qualitative
and
calculations
the
make
40
simplifying
several
for
the
exact
phase
densities
the
In particular
metal
the
and
are
changes
energy
so the
assumptions
only
could
from
evidence
the
the micrographs.
from
of the
appearance
interface
exposed
etch
be derived
the
Furthermore
approximate.
not
derived
densities
energy
was
remaining
in
not
complete
agreement.
(2-4)
RBS observation
Once the
remaining
to those
close
is
elements
of
Because
However
poor.
were He+ ions
a take
angle
laser
j/cm2
impurity
substrate,
not
a significant
it
but
expected
germanium
Ni-Au-Ge
less
0.27
were
detector
this
lower
in
the
in
the
energy
lack
the
for
edge
After
densities
levels
the
the
indium.
is
laser
(fig.
position
backscattered
the
of
metal
diffusion
at
of
of melting
molten
no gold
spectrum
than
150 -
Increasing
Unfortuneatly
latter
1.5mm and
of
energy
from
contact.
very
indium
significant
regrowth
j1CM2 results
of
with
with
is
the
size
a spot
no
any
The experimental
1000A.
metallisation
alloy
for
germanium.
of
up to
indium.
the
from
separated
InP,
by Rutherford
for
sensitivity
correlates
peak occurs
are
mass of
barrier
there
process
to
atomic
1.5 MeV with
at
seems that
a slight
for
depths
surface
This
density
energy
from
or
present.
the
the
the
alloying
of 0.20
2-7)
to
observed
the
is
gold
for
conditions
off
the
the
off
be
can
and tin
silver
can be resolved
and so
has been etched
components
(RBS).
Back Scattering
diffusion
metal
metal
indiffused
remaining
of
ions
in
the
41
so
matrix
definite
no
of germanium is
concentration
A high
melts.
could be
low resistivity
contacts.
the InP
is
which
Further
increasing
j/cm2 does
result
in
The doping
effect
other
interesting
peak which
feature
as the two materials
strongly
react
phospherous
at the
because of
the
Gold is
this
in
present
the
that
does in similar
of
the
contacts
in
of this
measuremment
with
large
The
nickel
a small peak corresponding
to
to
due
the
length
is
large
is present
(fig.
at
The
higher
2-9).
Again
from these spectra.
near to the surfaces
of
less
it
than
as a diffusion
GaAs (53).
background
is not certain.
identification
is acting
these samples.
resolved
can be
to
high concentrations
to
2.8)
energy corresponding
of Nip is possible
nickel
0.38
6.1020/CM3.
around
spectrum is
at the surface
these samples but the diffusion
may be
to
the InP (fig.
into
of 0.45 j/cm2 and 0.55 j/cm2
identification
no positive
but
of nickel
energy densities
energy density
of such a high concentration.
exhibits
surface
indium,
high concentration
the laser
of this
The spectrum
to the InP than the
down closer
at the a backscattered
occurs
the surface.
effect
for
necessary
is not known so no inference
gold
drawn on the electrical
germanium
into
concentration
of
the InP
diffused
diffusing
gold
a peak impurity
producing
doped layer
a
not
above 400 C and the gold was laid
germanium.
as
such
The gold has still
surprising
for
spectrum
energy density
impurity
to produce a heavily
expected
A high
made.
the
At this
of an
concentration
in
present
0.33 j/cm2-
with
sample alloyed
be
can
confirmation
No
1000A.
barrier
germanium
as it
can
However, due to the poor sensitivity
regard
to
germanium,
sufficient
be
42
to
concentrations
being
without
0.92
j/cm2
is
these
following
etch
an
the
2.10)
more than
1
the
large,
the
micron
the
In
The
the
Germanium
on
substrate
remains
substrate
melts
expected,
but
layer
in
phosphide.
At
21/cm3
which
electrical
still
suggest
or
yield
diffusion
is
most
solid
the
to
1.54
the
InP
2-3)
is
into
some
1.54
30%
about
near
and
are
coefficients
At
the
behaviour
complex
no
to
an
high
properties.
be
thin
expected
of
the
in
process
is
the
gold
j/cm2
of
surface
and
possibly
by
the
to
have
surface.
the
the
indium
is
reduced
Nickel
place.
rapidly
gold
a
remains
When
be
thin
The
at
dissolved
dramatic
the
as might
formation
is
Gold
When the
alloyed.
layer.
surface
role
densities
energy
might
takes
important
concentrations
laser
diffuse
not
a
of
when
alloying
does
gold
confined
plays
high
diffusion
21,3
6.10 7cm
the
(section
liquid
gold.
during
gold.
InP
is
melt
the
of
indium
the
summary,
surface
lengths
about
concentration.
to accomodate
the
and
movement
is
concentration
estimated
diffused
depth
that
combined
1.24
of
deeply
gold
possible
be removed
densities
has
the
be chemically
may not
energy
gold
diffusion
inhibiting
nickel
laser
is
It
acting.
nickel
but
and
1000A deep indicating
compound and so could
considering
although
the
the
0.75
of
2.9)
than
less
still
anneals
resistant
(fig.
j/cm2
6.10
is
At the highest
etch.
to
restricted
barrier
irradianceB
(fig.
be present
could
effect
greater
can be resolved
still
a diffusion
in
At still
observed.
no nickel
diffusion
doping
a heavy
produce
the
InP
of
the
up
eff ect
to
on
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b
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C
0-38 jcm-2
0-75 j cm-2
Fig. 2-4
Sn coiitacts
2000
on InP
a
0 .058jc m-2
b
0.14 jcm-2
C14
0-33 jcm-2
-.
", 4..,.,..
0-75 Jcm 2
W4,41
Fig. 2-S 20004
Sri on Sl
InP after
0-096 jcm-2
b
0-20 jcm-2
14
0-38 jcm-2
d
1-24 jcm -2
Fig.
2-6
NiAuGe contacts on InP
etching
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50
PROPERTIES OF ALLOYED LAYERS
(3-1)
Analysis
An electron
laser
after
250 x
250
microns
in
that
is
the
separate
the
For
In
first
this
ensures
in
the
although
The
of
the
density
the
is
peaks
problem
tin
detector
silver
the
electron
that
the
InP
and
to
unable
the
also
analysis
3.1a).
InP is
of
thick
gold
volume
a
If
and
tin
0.2
j/cm2
not
thought
the
is
is
peak
is
peak
This
the
beam
(fig.
observed
peak
is
a rough
at
the
lowest
removed
(fig.
3-1b)
Even
is
kV
the
within
removed
phosphorus
to melt.
5
of a phosphorus
remaining.
some
entirely
was
to
energy
some tin
tin
circles
technique
in
lack
phosporus
of
tin
qualitative
as shown by the
and
amount
a
A
beam was reduced
amplitude
of
1000
of
homogeniBer,
spectrum
the
and
was
to be a
One
radius.
particularly
of samples
the
(fig.
3.1b, c, d).
energy
set
layer
penetrates
measure
tin
tin
1000 A thick
the
with
dispersive
energy
spot
overlap.
without
annealed
used.
the
50 x 50
can be considered
metallisations,
indium.,
peaks
phosphorus
which
that
The
an
about
to
1mm circles
circles.
analysed
compared
the
analysing
the
of
over
from
varied
area
micron
volume
depth
small
100
contacts
beam was scanned
this
case
the
analyse
electron
the
the
to
used
contacts,
the
case of
so
silver-tin
the
in
microns
of
with
The
of
centre
composition
was
microprobe
the
defocused
cylinder
contact
annealing.
the
in
area
of
may be due to
the
51
large
more tin
the
integralB
a
density
2
JAM
to
that
samples
peak.
the
in
presented
InP does not
may be related
of tin
to
the melting
is
the
phosphorus
to
fall
vapour
phosphorus
of
increasing
with
0.8
these
only
about
results
it
may
for
anneals
layers
of
tin
in
20% of
be
be
the
that
pressure.
the
continues
as
expected
of 0.5
and that
beneficial
to
contacts
the
density
energy
From
remains.
insufficient
2
J/cM
molten
system
remaining
is
at
this
about
of
tin
original
energy
tin-GaAs
the
occurs
apparent
InP at
At a laser
concluded
excess
would
for
which
increases.
pressure
remain
density
this
evaporation
The amount of tin
energy
j/cm2
forced
loss
vapour
phosphorus
as occurs
(56).
studied
previously
vapour,
of the
A
2000
the
for
The loss
melt.
the
separate
For
suggested
by the
was used to
less.
The mechanism
(fig.
homogenised
and
a large
the
increased
the
with
Little
in
below
spectrum
3.2.
resulting
tin
the
figure
density,
energy
is
The results
2
J/cm
0-3
of
density
j/cm2
annealed
each elemental
are
well
of InP alone.
algorithm
densities
range
0.8
deconvolution
layer
energy
energy
and at
identical
under
tin
thick
3.1c)
remaining
beam,
laser
laser
InP
over
phosphorus
As the
virtually
For
of
(fig-*
lost
is
is
3.1d)
0.4
(55).
point
melting
for
pressure
vapour
metal
even
may
thicker
intended
for
devices.
The silver-tin
alloying
for
energy
process
densities
contacts
(fig.
are
3-3)
up to 0.4
with
more
resistant
no tin
j/cm2.
At
to
the
laser
or silver
being
removed
higher
laser
energy
52
densities
the
results
thought
to melt
for
Almost
with
all
the
0.75
j/cm2
laser
but
but
intact.
surface
0.9
on
a different
but
the
layer
from
metal
remains
half
the
below
0.8-0.9
J/cm2-
sample
annealed
from
anneal
the
of
large
the
scatter
removed
during
the
with
up to
anneals
to
the
same
most
the
of
importance
the
of
detailed
precludes
that
not
the
leaves
is
for
InP is
exactly
substrate,
conclusion
being
beneficial
be
should
overall
the
highlights
The
analysis
tin
j/cm2
difference
preparation.
although
densities
energy
the
This
the
scattered
has been removed
metal
metallisation,
metal
become
inhibits
silver
and more than
anneal
1.2
This
j/cm2.
properties
of
the
only
the
gold
and
microprobe,
for
electrical
contacts.
Due to the
layers
germanium
density
edges of the
but
remains
of
is
liquid
at
about
rises
0.5
after
the
highest
to
the
gold
the
molten
Ge
As the
350 C and. this
would
gold
falls
energy
the
used
is
of
1.6
suitable
the
contact
is
sharply
removed
original
during
and germanium
temperature
the
the
3-4).
is
seem to be as
sustrate
if
from
gold
half
laser
NiAuGe
laser
(fig.
area
2
the
J/cm
than
property
yield
back"
a smaller
more
The
.
of
the
increasing
with
"pulling
gold
and
a desireable
density
the
excess
results
use.
energy
yield
extent
adhering
obviously
practical
laser
even
in
as silver
by the
and so occupying
in
From these
J/cm2.
This
contact
Au
layer
nickel
due to
probably
to a limited
only
amount
the
densities
At energy
the
of
can be resolved
Initially
contacts.
energy
thinness
anneal.
to
with
increasing
form
a eutectic
attained
for
be
an
53
irradiance
estimated
two components
the
is
Ge
As the
is
beyond
be
to
levels.
Therefore
of
the
laser
the
thick
the
was
germanium
(3.2)
of most of
1
very
only
small
are
experiment,
to
achieve
high
the
Ge does not
metalisations
doping
prevent
the
also
may not
layer
of
of
between
durable
quite
were removed
expected
the
results
was
substrate
the
metals.
and
the
layer.
The
the
to
be
possible
based
gold
preferential
the
with
felt
and
by
2000
improved
One problem
which
the
the
1000 A thick
overlayer
considerably.
variation
interface
than
silver
contamination
loss
of
of
the
be a problem.
Metallisation
An alternative
thick
significant
studied
be
durable
more
tin
results
As might
A
1500
a
was the
of
the
of
was
surface
oxidation
InP
microprobe
process.
the
layer
due to
contact
of
of
adhesion
silver
each
layer
The addition
the
removal
this
of
to
2
J/cm
formation.
alloying
tin
resolution.
quantities
up
as a dopant
the
Obviously
significant
densities
energy
that
manner.
a similar
but
in
be expected
might
present
dissolved
To summarise
quantities
only
the
contact
successful
laser
using
germanium
required
in
preferentially
anneals
quantities,
it
j/CM2
be removed
would
removed
for
remain
0.1
of
resistivity
method
of
investigating
the
condition
54
metal
layer
sheet
resistivity
droplets)
by
and
formation
of
directly
in
used
to
layer
reversing
the
current
source
and
flow.
probes
are
through
the
tin
should
perform
of
is
the
blown
be noted
the
advantage
into
or
that
the
of
it
is
contact
is
that
alloying
X-ray
off
quite
resistance
its
contacts
observed
by
on
the
met by any laboratory
and
stable
and lowered
reproducible
times
several
the
are used
in
one
conduction
negligable.
the
of
1000
n-type
(fig.
i
thick
substrates
3-5).
microprobe
during
this
with
requirements
easily
case.
This
analysis
the
a non-homogenised
in
associated
action
this
in
which
probe
the
substrates
or
density
energy
the
the
make low
are
are
resistivity
semi-insulating
results
oxidation
rectifying
raised
semiconductor
The sheet
the
by
problems
Hence
readings
When semi-insulating
increasing
either
point
the
no
voltmeter
and the
the
with
place.
either
Of
resistivity
formed
has
four
The probes
metal
even when
the
performance
of many of
the
instruments
cannot
(e. g.
texture
change,
used was the
free
is
current
their
electrical
use on semiconductors.
to
as
its
of
remaining
metal
method
The method
the
by measurement
a device.
The technique
application
this
chemical
phosphides.
relevant
when
by
of
amount
by
affected
is
alloying
exact
determined
is
films
The
.
be accurately
thin
laser
following
laser
laser
tin
rise
is
in
and
alloying
beam
layer
on
rapidly
with
agreement
with
confirms
that
process.
was
used
It
to
55
The sheet
less
(fig.
sharply
laser
At low
contacts.
been blown
in
off
the metal.
At
disappears
which
The
adhesion.
These
behaviour.
X-ray
for
the
of
extent
The silver
tin
The
3.7).
than
greater
the
inter-diffusion
found
for
that
pure
silver
2
J/cm
correlate
of
around
20%
of
0.5
resistivity
it
during
of
this
problem
substrate
improving
the
an
at
to
the
alloying
well
the
with
the
threshold
2
J/cm
and in
0.4
-
for
remains
metal
2J/cm
of
From the
and hence
of
of
related
in
in
0.3
has a less
resistivity
resistivity
both
around
adhesion
,
also
measurements
of metal
behaviour
is
a change
3.2)
to
discontinuity
a
which
due
the
interface
had
layer
the
of
and hence
(fig.
excess
occurs
the
0.
j/cm2
-5
:
expected.
chemical
poor
shows
substrate
initial
causing
real
large
be
to
the
at
of
tin
thought
melting
removal
in
the
which
to
the
during
had
samples
be related
results
densities
energy
the
tin
thinner
formation
0.5
0.4
removal
the
above
electrical
microprobe
irradiance
substrate
resistivity
the
of
is
inter-diffusion
around
melting
This
rises
more durable
densities
sheet
density
energy
may
for
beam from
the
of
is
layer
the
case for
some of
the
tin
thick
layer
densities
one piece.
rapid
allows
which
thicker
of
energy
was the
important
centre
contamination
surface
the
is
energy
the
near
than
the
which
alloying
areas
3.6)
shows that
This
layer.
the
of
resistivity
i
2000
the
R. B. S.
clear
layer
results
silver
cut
a factor
and
that
appears
the
is
(fig.
trend
of
four
from
also
significant
of
alloys
are
much greater
than
probable
explanation
of
seems a
the
metal.
It
is
deposition
56
the
greater
less
but
certain,
irradiance
at
behaviour
for
a
such as oxygen
the
substrate
show
densities
in
more than
exact
alloy
this
be
may
be
which
is
The
melt.
densities
greater
Ag/Sn
the
the
of
alloy
layer
of
system
the
of
0.5
for
gold
rise
in
metal
balling
up
The
above
for
these
sheet
the
energy
that
j/cm2
well
with
the
As with
the
suggest
observed
to
energy
with
densities.
is
gold.
phosphide
anneals
does not
the
0.3
-
indium,
correlates
resistivity
remaining
into
0.2
sheet
(fig-3-8),
value
about
for
which
initial
components
sharply
j/cm2
characteristics
expected
density
energy
of
but
ascertained
similar
other
rise
rises
excess
has
the
of
shows a smooth
loss
same fraction
twice
due to diffusion
estimated
the
analysis
& (iii)
metallisation.
is
observes
a low conductivity
of
metal,
laser
droplets.
of Ni/Au/Ge
system
the
formation
remaining
unconnected
resistivity
in
the
for
microprobe
cannot
are
The resistivity
the
at
electrical
times
discrepancy
into
of
ten
of
this
silver-tin
resistivity
The
further
The ternary
the
resistivity
(i)
to
and contamination
Without
oxidation
metal
layers
whilst
than
sensitivity
interfaces.
1 j/cm2
of
laser
The alloying
a greater
remaining.
causes
the
in
for
2.
J/cm
of metal
for
(ii)
the
silver/tin
increase
excess
in
is
more complicated
to
is
metallisation
results
inevitably
may lead
content
and
an
25%
cause
possible
to
and this
the
0-5
above
data
microprobe
variable
densities
is
the
with
indicate
rather
system
metal
data
of
2
J/cm
with
energy
single
results
of
sets
of a binary
factors
both
both
up to 0-5
stable
Agreement
resistivity.
the
by X-ray
57
that
the
of
pull-back
the
X-ray
is
that
(3-1)
the
from
the
indicates
of
added
multicomponent
systems.
metallisations
is
laser
for
that
(3-3)
Doping
the
When all
alloy
for
of
the
described,
any
may have,
the
substrates
were of
could
possible
on these
not
for
in
the
all
three
metal
rises
sharply
the
2
J/cm .
0.5
device
This
is
of
contact.
be
etched
doping
can
the
using
lithographic
the
effect
be measured
semi-insulating
,
indiffUBed
that
noting
material.
off,
such measurements
see
if
As the
were not
samples.
As a preliminary
contacts
irradiance
from
has been removed
components
silver-tin
laser
higher
clear
a practical
metalisation
original
and the
layers
Substrate
metal
previously
The
reactions
of
above
be
cannot
the
of
resistivity
section
composition.
following
is
densities
energy
measurements
a contact
its
deposited
alloy
Ni/Au/Ge.
the
previous
of
of
What
the
the
of
noting
,
resistivity
analysis
the
ation
for
performance
complexity
significance
particular
etches
the
of
explan
these
measurements
resistivity
expected
the
strongly
comparing
elec trical
resistance
excessive
occurs
microprobe
determined
accurately
than
metal
from
The conclusion
with
may be
The same causes
microprobe.
test,
Van-der-Pauw
to
measurements
,
it
the
was
four
worth
point
making
probe
was
58
As
used.
the
the
probes
for
readings
fluctuations,
so
to
subject
tin
process
for
the
thought
to melt
2
J/cm which
is
magnitude
with
of
values
the
3-6)
of
Hall
irradiated
the
is
for
phase
fall
hence
laser
the
an energy
density
.
regrowth.
density
of
these
is
is
is
metal
of
to
the
energy
This
no correction
energy
required
indiffusion
50 ohms/0
of
tin
by alloy
increasing
with
tin.
density
an order
of
samples
coated
required
to
the
resistivity.
resistivity
measurements
Little
measurements.
with
layer.
only
energy
resistivity
the metallisation
observed
the
of about
than
(fig.
the Van-der-Pauw
mobility
to
thick
is
occurs
liquid
allowing
value
The results
samples
conductivity
using
satisfactory,
for
incorporation
not
figure
conductive
which
The
as shown in
1
2000
2
J/cm. for
0.15
continues
greater
metal
of
in
is
samples
the
dice.
-
methods
resistance
approximately
substrate
lowest
two
lower
5.1
are
were made
samples
error
chapter
significantly
in
The resistivity
a
the
of
resistances
square
the
of
large
showed
higher
the
of
in
semiconductor
samples
on the
corners
and so dopant
increase
the
the
removal
excess
the
The Van-der-PaUW
discussed
the
are
in
with
is
to
resistance
consideration
InP. after
samples
A great
to
between
densities
melt
measurements
dots
for
particularly
0.4
the
samples
Agreement
Some
higher
the
and
cloverleaf
3.9
the
some inaccuracies.
by alloying
directly
make contact
less
typical
than
of
the
0.4
doping
2
(fig.
J/cm
iron
are
doped
confirmed
occurs
3.10)
substrate.
by
for
and the
At
59
densities
energy
to high
a
in
fall
alloy
regrowth
then
increases
as
the
the
allow
the
in
is
levels
in
the
may be the
crystal
poor
with
For
loss
of
(fig.
of melting
sheet
in
up to
is
in
less
than
layers.
from
the
energy
depth
carrier
to
the
5.
chapter
100 Cm2/V/s
for
The reason
leading
layer
melted
1
for
similar
shown
of
excess
the
0.3
j/cm2
substrate
0.4
falls
no
measureable
these
does not
j/cm2
,
sharply
for
the
which
but
occur.
the
begins
for
an
densities,
At energy
substrate
to
in
change
evidence
energy
seem to
coated
behav iour.
different
with
at
been
had
which
correlates
regrowth
of
samples
has an entirely
This
by alloy
resistivity
the
of
occurs
densities
ion-implanted
phosphorus
for
volume
This
at
to
as
great
melt
indicating
as
diffusion
The maximum sheet
The calculated
doped layer
3.11)
densities
doping
the
of
so
1015/cm2
1019/cm3.
of
expected
quality.
Ni/Au/Ge
absence
the
that
resistivity
resistivity
hence
to
The sheet
energy
.
between
is
the
is
is
The doping
which
that
of
excess
microns
of
mechanism
phase
ion-implantation
mobility
inferior
far
to
,
by
of
to be saturated.
I j/cm2
excess
reason
density,
this
for
the
InP
2
J/cm
0-5
substrate.
noting
in
0.5
the
of
liquid
depth
of
around
obtained
However,
the
is
excess
concentrations
this
in
melted
entire
densities
is
tin
change
energy
increases,
concentration
electron
j/cm2
depth
the
melting
increasing
with
of
to
the
dopes
to
density
energy
concentration,
actual
and
melt
coefficient
carrier
tin
the
and greater,
the
may be related
known but
not
j/cm2
Increasing
levels.
causes
0.4
of
rise
melts
with
60
increasing
and hence
the
increase
with
clarified
by the
thickness
densities
0.9
has
semiconductor
has
conductivity
HF+HN03)
(table
of
3-1).
layer
which
which
is
This
doping
component
concentration
causes
energy
laser
is
1.54
j/cm2
did
to
expected
the
densities.
by
sharp
fall
tin
an order
of magnitude
layers
but
lower.
as
in
such
using
energy
the
of
of
the
to
the
a
dopant.
the
similar
sheet
as
sheet
InP
NiP
germanium
The
resistivity
is
the
the
the breakdown
The mobility
alloyed
etch
doping
barrier
likely
observing
alloying
act
the
a
remeasuring
as a diffusion
be
not
of
seem
produce
may be due to
the
of
cause
a chemical
laser
energy
would
would
and
Hall
nickel-phosphide
confirmed
(using
The
samples.
seems to act
laser
R. B. S.
be
with
The
the
is
no
:
resistivity
but
to
situation
doping
no
depth.
spectroscopy
and
doping
the
phosphide
1.24
the
substrate
highest
the
is,
discovered
by
The
annealed
sheet
melt
could
Auger
of
densities
nickel
with
resistivity
samples
depth
expected
measurement
That
been
hypothesis
the
of
removal
for
identified
This
cause.
Hall
the
on
not
tentatively
layer
the
so the
occurred
be
would
density.
j/cm2
depend
to
of
as the melt
surprising
energy
results
to
is
of a doped layer
measureable
Up
expected
This
increasing
is
coefficient
of
density.
energy
at
to
the
that
carrier
61
Table 3.1
---------------Energy
-----------------
density
ns
-------------
--------------
6.0.1012
79
1.32.10
1.54
14
1.45-10
55
782
1.. 54
14
1.54-10
52
762
on laser
these
alloying
the
InP,
but
microprobe
the
exhibit
have
will
(section
silver
superior
resistivity
the
3-1)
it
lower
is
component
the
contact
resistivity.
that,
more
on
metal
metallisations
has
whilst
the
doping
of
the
with
tin
3.2)
less
pure
and so might
However,
were
is
The X-ray
durable
(section
of
which
that
compared
performance.
the
cause
be expected
were
electrical
in
to
has revealed
contacts
surface
result
layer,
a conductive
results
tin
does not
cases
It
process.
dope the
4
information
obtain
forming
contact
can heavily
measurements
the multi-
the
most
produces
From these
uncertain.
contacts
tin
in
NiAuGe metallisation
has been to
measurements
regarding
that
been found
that
(ohm/ 0
1.24
The aim of
tin,
PS
(cm2/V/s).
-----------------
----------------
------------
lis
(cli2)
(j/cm2)
the
---------------
have
the
shown
conductive
62
than
in
expected.
interpreting
chapters
6.1
Therefore
the
and 6.2.
electrical
all
these
data
measurements
on the
contacts,
can only
assist
presented
in
63
1
1
0
1000
23
A SnI InP
4
234
KeV
Fig.
3.1
Microprobe
analyser
X-ray
spectra
for
1000A tin
contacts
to
InP.
64
Sn / InP
12-ONO
m
CD
V-%-. 0
WNW
k
0
u
C=
V)
L
now
0a
1
-2 -4 -6. ' -8
E (jcm-2)
Fig.
3.2
Microprobe
yield
of
tin
on InP vs.
laser
energy
density.
65
I.
Ag Sn / InP
0
0
AN.
g
m
CD
V)
0
u
Sn
.
01
V)
0-5
Fig-
3.3
Microprobe
laBei
energy
1.0
E(i cm-2)
yield
of silver
density..
and tin
1-5
on InP vs.
66
GeAuNi/InP
2(
0
11
o
ell
Au
0-11-ý
V)
4-
. ---ft%
ý-
DI
111.0-
.v%.,
(A
Ge
I1
40
0
ý--
11
0-5
1.0
E(i cm-2)
Fig.
3.4
Microprobd
laser
energy
yield
of
density.
gold
and
-ýý_;
germanium
Im%Lo
1-5
on InP
VB-
67
0
Cd
94
Fig.
3.5 Metallisation
laser
08
J cV2
resistivity
energy density.
1-2
of 1000k tin
on Inp vs.
68
-0
2.000A Sn
(I,
10
Pm
0
expected vatue
L
0-2 0-4 0-6 0-9- 1
1-2 1-4
E(i cm-2
Fig.
3.6
Metallisation
laser
energy
resistivity
density.
of
2000A tin
on InP vs.
69
HR
AgSn / InP
0I0
0
0
0-5 ---11.5
E(j cm-2)
Fig.
3.7 Metallisation
laser
energy
resistivity
density.
of silver-tin
on InP vs.
70
Ni Au 5e
10
E
Qý
00
expectedvalue
0
0-4
E(j
Fig
3.8
Metallisation
laser
energy
1-2
0-8
cm-2
resistivity
density.
of
NiAuGe on InP vs.
i
71
HR
CC
)5
3
04
os
03
02
0
Fig-
0-4
0.8
.E(j cm-2)
3-9. Sheet resisitivity
of InP after
has been etched off.
1.2
2000i tin
layer
72
Sn / InP
1015[
o0
E
Li
1014
400
100
W
CN
E
0
00
0
Fig.
0-5
3.10 Sheet carrier
by laser
1-5
1
E(jc rjf2)
concentration
alloying
2000i
tin
and mobility
on InP.
produced
73
Ni Au Ge
IR
p
be
ro
05
V- dP
104
0
Q1,
103
&
0
0-4
Ej
Fig-
3.11
Sheet
resistivity
of
0-8
cm-2
InP after
1-2
NiAuGe has been etched
off.
74
SELENIUM IMPLANTATION OF InP
The next
two chapters
heavily
thin,
doped
in
the
with
the
and
experiment
of
removal
preparation
techniques
a
polished
on
implants
the
sample
The
surface
one
substrates
one
close
to
monitored
hour
annealing
are
deals
chapter
observed
the
describes
and the
ion
the
annealing,
five
of
details
this
of
sample
the
of
results
by
Hall
5.2.
implantation
greater
a resistivity
contamination
out
either
to
hence
the
to minimise
normal
were
with
with
the
temperature
with
a thermocouple.
the
unheated
200+20 C.
the
ion
sample
of
the
The
was
Fe-doped
than
107 ohm. cm
The
orientation.
by the manufacturer.
side
or heated
temperature,
about
for
(100)
carried
surface
by
5-1),
section
of
avoid
were.
after
a
of
means
chapter
section
Chapter
'having
InP
to
was Se(78)
by
this
damage
used
semi-insulating
surface
formation
details
material
and with
The third
in
given
the
surfaces
(section
(4.1)Implantation
The
of
crystal
backscattering.
are
section
resulting
Rutherford
measurements
the
4.2.
section
with
concerned
at
layer
The first
implantation.
analysed
are
The ion
molecular
slices
were
species
used
beam inclined
effects
and
mounting
7
at
from
of
channeling.
remained
at
heating
temperature
The
argon.
process
room
took
was assumed to be
plate
which
was
75
To achieve
implanted
samples
were
schedule
and
25 keV
Se+ was
Se2
impurity
lies
(fig.
(S'3N,
nitride
5-1)
section
the
this
peak
on the
')
was
is
hence
peak
was
estimated
by
enough
differences
concentration.
as
the
was
of
interference
in
thickness
profile
the
silicon
the
under
thickness
profile
surface
and
used
the
.
previously
atomic
pyrolytically
optimum
the
a
dielectric
dielectric
grown
The
of
the
The
below.
small
impurity
between
which
accurate
peak
quite
have
little
(see
700ý
colour
is
The
species
a high
through
implant
4.1
molecular
obtaining
implant
the
4.2).
described
conditions
that
such
figure
the
with
of
in
some
the
energies,
shown
are
to
concentration
several
method
is
interface
the
of
implanting
An alternative
semiconductor
layer,
by
obtained
dielectric
at
ions
LSS profile
concentration
deposited
impurity
surface
with
expected
50 kV.
at
high
a
flat
of
the
near
effect
76
(4.2)
Annealing
ion
of
implanted
InP
A major problem of annealing
360*C (55),
(33).
implants
selenium
during
decomposition
for
temperatures
whilst
A horizontal
as 1% in either
supplied
diluted
further
with
temperatures
to be adequate for
indium
temperatures
these
but
4-3a)
hydrogen
filled
by
prevented
.
raising
concentration
to
1%.
Lowering
the PH3 concentration
decomposition
occurring
at lower
temperatures
under PH3 concentrations
annealing
4.3c.
in figure
Clawson et al
the
was
(57) is valid
decomposition
prevent
of
It
it
the
approximately
highlights
surface
the mechanism for
liquidus
filled
inclusions
damage or handling,
then lose
the
at higher
the
PH3
results
in
and the results
temperatures
of
Samples
pressure
show
phosphorus
present
decomposition
over
filled
to
with
which
From this
is that
pits
pressure
,
due to growth defects,
adjacent
by
in excess
annealed
( fig-4-3b).
of the indium
that
and
to use a pressure
liquidus.
melt and dissolve
phosphorus
(fig.
the mechanism suggested
damage and scratches
in 'the absence of sufficient
indium
found that
the formation
higher
from 0.09% to 1% are presented
is necessary
Indium-Phosphorus
At
on the surface
occurred
a
produce
This was found
up to about 800'C
pits
be
could
This was
to
of 0.25%.
used
was used with
hydrogen or nitrogen.
in the furnace
concentration
phosphine
anneal
was the method
zone furnace
diffused
palladium
to
needed
ambient can be used to prevent
(34) and this
annealing
decomposes above
it
of 750 C are
A PH3
most of the samples.
the PH3
InP is that
indium
minute
polish
phosphide
to the atmosphere and are then able to
77
dissolve
further
material.
Even with
sufficient
deterioration
1015 Se+/cm2 at
with
occurs
the
during
occurs
above
with
a
increasing
dose
the
4.5a, b, c)
The "grain"
a substrate
during
place
no
(fig.
annealing
a
to
finish
depends
on the
annealed
damage is
at
a
by
given
by implanting
into
introduced
deterioration
observable
4.4d)
mirror
1015 Se+/cm2 produces
be shown,
will
fine,
very
damage produced
being
As
200*C much less
at
and correspondingly
crystal
Increasing
roughening
is
deterioration
after
4.4a, b, c).
surface
eye of
1013 Se+/cm2
from
(fig.
temperature
the
of
surface.
more deterioration
progressivly
to
.
surface
implanted
samples
some
The amount
the
of
state
For
some
temperature
an appearance
haze.
slight
crystalline
into
(fig.
having
samples
pressure
annealing.
room
7WC
over
phosphorus
the
takes
implantation
even after
of
1015 Se+/cm2.
An alternative
the
encapsulate
about
10
20
is
minutes
above
deterioration
annealed
the
decomposition
preventing
a
dielectric
a
onto
to
mixture
the
of
samples
used
deposit.
the
on the
strip
surface
heater
deposited
ammonia
and
which
are
and
Although
decomposition
of
silane
temperature
heated
on a
1000A
took
the
deposition
of
can be observed.
for
a further
to
prevents
nitride
550*C
was
is
which
used was silicon
The temperature
to
were then
with
from
decomposed
strip.
temperature
visible
sample
CVD process
pyrolytically
carbon
of
The dielectric
out-diffusion.
by the
method
ten
InP
no
Samples
minutes.
78
The silicon
nitride
temperature
in
nitride
two
HF
concentrated
holes
Pin
minutes.
in
annealing
at
temperatures
indium
filled
pits
form
beneath
and
increase
the
the
indium
deteriorate
not
of
surfaces
annealed
samples
(compare
temperature
The samples
PH anneals
3
which
4-5d)
without
a cap under
but
in
through
does
not
more
much
the
between
than
PH3 at
the
a dielectric
zone furnace
the
a hydrogen
only
As the
better
and is
excess
the
same
4.5b).
implanted
were
silicon
them.
in
surface
room
in
holes
pin
(fig.
at
the
become
beneath
phosphide
figure
with
number of
pits
were annealed
nitride
silicon
but
However,
does
the
increased
is
markedly
extensive.
(4-3)
three
in
after
temperature
anneal
to
removed
became visible
of 700 C
pits
was then
cap of
for
the
substrates
at
used
was used.
atmosphere
Recovery of damage
doses
Implanting
room temperature
are
layer
(61)
temperature
an
amorphisation
an
the
the
and
necessary
temperature
asymptotic
of
InP
layer
amorphous
thickness
and ion
energy
during
The substrate
reaches
& 4-7)
heated
amorphous
implant
4.6
ion
increasing
which
produces
(figs.
R. B. S.
1014 Se+/cm2 into
1015 or
of
dose.
implant
these
Implanting
prevents
authors
increases
required
limit
of.
even
when
increases
of which
with
formation
have
shown
maintain
about
150 C,
with
with
substrates
the
to
implanted
into
larger
by
observed
as
ion
of
that
an
the
doses.
crystallinity
which
large
prevents
doses.
79
Implants
of
200*C
have
implants
be expected
would
damage,
4.8.
The
which
is
'b').
thickness
layer
the
is
The surface
'c')
although
but
temperature
'e')
material
original
827'C
that
the
for
dechanneling
the
the
under
implant
a
rate
at
a
is
'f').
'e')
To achieve
in
lower
by the
implant
increasing
to
anneal
827*C
of
that
for
the
Unimplanted
material
annealed
at
produces
a spectrum
identical
to
therefore
substrates,
(curve
611'C
at
temperature
identical
not
the
5.2.
section
annealing
with
a
(curve
The electrical
damage introduced
reduce
'a')
560"C reduces
in
after
figure
507C
at
to
at
(curve
layer
discussed
an anneal'at
grown
prevent
and
shown in
amorphous.
is
to
continues
The damage produced
anneals
layers
the
temperature
which
conditions
remains
same conditions
as
implantation.
it
spectrum
PH is
3
temperature
much of
(curve
the
annealing
after
annealing
amorphous
even after
the
under
longer
The disorder
remains.
(curve
but
amorphous
no
than
temperature,
room
by R. B. S.,
after
anneal
further
of
conduction
(curve
sample
the
4-8)
has an amorphous
reduced
Increasing
&
at
more easily.
ten minutes
as implanted
substantially
at
held
substrates
4.7
substrates
observed
for
temperatures
various
into
to anneal
The implant
(figs.
damage
less
much
corresponding
1014 Se+/cm2 into
1015 or
either
is
due to residual
complete
excess
the
increased
disorder
recrystallisation
827*C is
of
from
of
necessary,
this
under
any decomposition.
by a similar
tempFrature
(fig.
implant
4-9)
of
than
1014
the
Se+/cm2
1015Se+/cm2
80
implant.
The surface
PH for
3
ten
damage
peak
is
(also
considerably
658*C (curve
of
'd').
1014 Se+/cm2 is
thickness
degree
by a
with
of
the
implants
by RBS.
disorder
greater
is
by the
RBS spectrum
The rate
of
times
amorphous
layers
all
the
at
damage.
This
contrasts
suggesting
dependent
in
that
of
the
in
range
in
occurs
the
same temperature
lack
of
the
strong
the
on anneal
5-25
five
to
the
minutes
rather
duration
than
may
anneal
the
layer.
even at
at
about
remaining
(fig.
on temperature
properties
in
rapid
The
has no observable
dependence
temperature
is
the
produced
was annealed
thickness
similar
amorphous
minutes.
first
Se+/cm2
masked
layer
of
more deeply
may extend
implant
807'C
that
layer
amorphous
surface
'd')
at
of
the
amorphous
sensitivity
electrical
layer
are
the
in
(curve
1015
is
to
by a dose
of
disorder
a
returned
explanations
this
the
dose
disorder
identical
are
the
with
but
at
an anneal
amorphous
Two
anneal
introduced
a
an
The 1015 Se+/cm2
regrowth
annealing
for
dechannelling
regrowth
low temperatures.
555C for
than
and the
758*C
for
in
anneal
'b')
is.
of
occurs
also
dose implant
an
The material
within
Se+/cm2 implant,
higher
after
produce
as observed
1015
reduced
the*disorder
less
markedly
both
although
of
an
(curve
a temperature
at
Therefore
after
562'C
decomposition
observable
curve
amorphous
'c').
by an anneal
crystal
and no
no longer
at a temperature
minutes
t emperature
single
is
4.10)
hence
further
and
on the
effect
of
the
(fig.
also
anneal
4-9)
be
duration.
more
81
The 1015 Se+/cm2 implant
annealed
a
at
PH the
3
of a
R. B. S.
single
by RBS
summary,
the
this
work
200 keV implants
750 .*C and
800*C
for
it
550 C could
not
five
first
Se+/cm2
heated
removed
could
to
all
minutes
not
200 C
amorphise
during
by annealing
at
the
the
the
450 C.
anneal
Prolonged
that
regrowth
did
In
anneal.
surface
implant
if
and all
next
is
about
annealing
contrast
2
at
produced
was
occur
the
at
Se+/cm
1014
layer
the
layer.
surface
of
amorphous
the
temperature
room
recrystallisation
the
of
to
are
implant.
an amorphous
respectivly.
the
hot
the
ions
temperatures
low
the
in
to that
shown in
be
necessary
was
recrystallise
1015 Se+/cm2 indeed
the
created
complete
and 1015 Se+/cm2 implants
all
room
implanted
damage at
that
similar
damage observed
of
the
of
200*C
identical
will
activation
RBS has shown
in
used
the
of
annealing
electrical
with
implants
For
the
it
at
10 minutes
451 C for
annealing
that
However,
active.
correlated
In
infer
the
than
practically
The complete
necepsarily
that
is
held
substrate
at
annealing
spectrum
aligned
electrically
chapter
After
crystal.
does
a
temperature
lower
much
implant.
temperature
into
by
during
even 1015
substrate
damage could
was
be
82
Fig. 4-1
L.S.S. profile of multiple implant
1021
E
Li
I- I
lol
0
400
800
depth(A)
@ 200KeV
1015
1-82.1014 @ 100
1-55.1014 @ 50
7-4 1013@ 25
.
1200
83
m
E
Li
ai
V)
lo20
InP
Si3N47-1
--=
1019
500
1000
0
depth ( A)
Fig.
4.2
LSS profile
of
implant
through
700i
S'3N4'
84
Co
1Z3
tko
:1
0)
m
Me)[Ndl
-4
r-4
ca
CD
Lr)
CZ)
C)
4D
co
04
72
a)
0
1ý
0
a)
41
Ln
0)
10
Ile
Ln
4-)
cn
ca
ý4
co
04
9
0
44
0
F-4
q)
04
>
so
E-4
0"'
, Pol
'A
9
ý,
Wo
41
C-
Q)
Q
Co r4-11
rý cm
$.4 a:)
ca
Q
Co
Ký
40
to
C:
rco
Co
-H
p4
c:
Co pý
-4
V-4
0
85
ef
I
z
mc
V)
.
I--,
C)
Ln
Ln
10
CYI
-rm
ai
r
m
PU
-01
C)
C
m
CL
cn
C,
m
mT
a-
-t
LL
C)
10
10
(01
C)
CC)
-I
*/
*
"
*
"***
1"
C
kj
C)
V)
Ln
C)
I
ml
-01
E
E
cu
c
ýu
%A
C26
I
(Z
(U
CD
vi
ml
cn
0
86
1015Set/CM2
(I)
200keVRT
100
keVRT
rl
_0
Gi
>1
200keV,2OCrC
I
300
Fig.
4.6
RBS spectra
200 100
depth (nm)
for
1015 Se+/CM2 implanted
0
at various
energies.
87
+Se/cM2
I
200keV
0-1-%
V)
4-
100keV,RT
ru
13
---0
50keV,RT
200keV,200"C
300
Fig.
4.7
RBS spectra
for
0
200 100
depth (nm)
1014 Se+/cm2
implanted
at
various
energies.
88
I
5'Seý,
10
200keV,RT
Random
a
b
:: 3
ru
c
d
cli
e
300
Fig.
4.8
RBS spectra
200 100
depth (nm)
0
1015 Se+/cm2 annealed
for
a=
as implanted,
e=
827 C, f=
b=
single
507*C, c=
crystal
at
various
611*C, d=
temperatures:
738*C,
89
104Seý,200 keV, RT
2
4-
E
b
ro
-D
w
.>
C
d
300
Fig.
4.9
RBS spectra
for
as implanted,
200 100
depth (nm)
T014 Se+/cm2
b=
562'C,
annealed
c=
0
at
658'C,
various
d=
temperatures.
758 & 807'C
90
0C
25 min, 55S
(I)
4-
15min
'0ýý
-0
eru
10
min
v
_0
5min
10
15
ai
Sej200keVRT
300
200 100
depth (nm)
0
Fig 4-10RBS spectra for various annealingtimes
555"C
at
91
Doping
(5.1)
point
particularly
have
for
with
in
routine
The Hall
checking
to
similar
dots
Small
four
for
tin
in
detail:
cut
from
wire
is
flushed
with
on and
takes
reveals
should
ohmic
order
of
GaAs but
in
input
prove
process.
The method
n-type
the
measurement.
method
four
sample
the
measurement
probe
that
usual.
presented
of
point
into
that
with
a stable
a production
the
of
used
and so is
respects
(1)
that
compared
in
implants.
ensures
Pauw resistivity
requires
as is
donor
material
result
is
measurement
of
resistance
of
periphery
Pauw geometry,
n-type
to
the
technique
the
on
placed
small
hence
good agreement,
to
Van der
resistivity
evaluation
voltmeter
the
of
rapid
height
the
Comparison
useful
method
sufficiently
of
is
probe
suited
resistance
der
techniques
The low barrier
probes
Implantation
Measurement
The four
InP.
by Ion
are
to
be
contacts
the
employ
forming
differs
contacts
in
placed
on
Van
important
the
four
corners.
(2)
The heating
(3)
The heater
reach
(4)
the
About
by bubbling
ensures
(5)
tin
stage
is
turned
melting
before
forming
good wetting
As soon as all
gas.
two
about
to
minutes
point.
15 seconds
the
forming
of
the
the
dots
gas through
the
dots
tin
melt
HC1 gas is
hydrochloric
the
InP.
have melted
the
onto
HU
introduced
acid,
this
step
is
turned
off
92
and the heating
continued
does not
300 C-
(6)
to
exceed
in
cool
This
to
fragile
are
cloverleafs
have been
I
(fig.
samples
micron
high.
All
the
of resistivity
values
the
In
to
order
it
and mobility
obtain
is
the
Cloverleafs
photoresist
and etching
(about
small
measured
for
and
sheet
carrier
depth
profiles
of
forms
a
and cloverleaf
square
is
are
this
acid,
samples
presented
sandblasted
breakage.
of
error
of
Etchants
Although
were studied.
amounts
of InP,
solvent
Therefore
the
with
square
9%)
and
the
same
hence
samples
are
concentration
only
and
sheet
it
based
attacked
also
methanol
measurements
are
amounts
of
bromine-iodine-methanol
to
possible
was considered
the
concentration
small
away
on
found
was
carrier
etch
use of methanol
evaporated,
contacts
to
necessary
reliably.
material
the
InP with
InP,
ohmic
optimistic.
slightly
the
results
to
forming
of
softness
Comparison
comparison
geometry.
in
hydrochloric
shows that
invalidate
does not
the
the
concentrated
5-1)
allowed
are
samples
reliable
subject
in
seconds
mesa about
and
by masking
formed
five
Due to
InP.
n-type
temperature
gas.
has been highly
procedure
contacts
for
forming
flowing
and the
off
the
ensuring
one minute
turned
then
is
The heater
for
black
wax
posed
a
presented.
remove
small
undesirable
used
to
flammable
as
protect
hazard.
93
To avoid
that
the
subjected
devices
the
to
this
the
anneal
,
as FET's.
5.1)
formation
for
is
conduction
substrate
fabricated
devices
When similar
(table
5-2).
The
for
degradation
deposition
the
of
cap
of
So far
deposition.
amount
introduces
effect
of
even a thin
degraded
planar
device
the
high
nitride
density
pin-holes
is
be overcome
either
both
the
sides
by etching
of
the
or
an encapsulant
of
it
to
visible
would
nitride
of
InP
during
the
first
are
At anneal
preclude
Another
problem
the
away the
in
back
the
so
the
concerned
could
the
the
few seconds
temperatures
would
The
above
and
error
layer
the
growth.
at a temperature
samples
the
that
seem
temperature
of
occurred
700*C was the
of
were not
surface
sample.
samples
resistivity
silicon
decomposition
Hall
with
a negligible
as a FET.
as an encapsulant.
encapsulant
capping
of
for
of
Hall
conduction
Therefore
surface.
material.
rich
as the
of
such
the
either
was performed
have become indium
may
surface
to
temperature
the
decomposition
non-stoichiometric
corresponds
data
limited
during
occurred
825*ýC
pin-holes
which
the
From
eye.
at
over
a
a PH3 ambient
up
degradation
at
in
temperatures
were annealed
anneal
for
required
anneal
semi-insulating
substrates
temperature
highest
naked
in
pits
a problem
significant
nitride
silicon
not
also
when
for
resistivity
filled
necessary
resistive
annealed
resistivity
of
indium
of
is
condition
is
highly
remains
The substrates
their
retained
it
measurements
substrate
to SOO'C and degradation
the
sheet
semi-insulating
such
(table
in
errors
use
using
surface
decomposed
,
however
the
influence
a
above 700*C
of
silicon
a dielectric
which
layer
could
or
by
94
TABLE 5.1.
Resistivity
of Fe-doped after
Anneal
('C)
annealing
in PH3
Sheet Resistivity
(ýi/sq)
>109
760
1.4.109
800
1.6.109
822
6.105 - 3.107
TABLE 5.2.
Resistivity
of Fe-doped after
Anneal
5500/10 min
-11-
-it-
under Si3N4
R. (2/sq. )
(*C)
+700*/10
annealing
min
n. (cm-2)
HR
2.2.105
-8.3.109
2.9.105
-5.9.109
3.2.105
-6.2.109
95
(5.2)
Electrical
(5.2.1)
results
Results
After
atmosphere
a temperature
Se+/cm2 implanted
(fig.
5.2)
At
furnace
annealed
fact
of
to
much
and
InP.
4-3).
to
rise
and then
falls
dependant
Hence for
donor
implanted
shown by
RBS,
should
in
than
on the
InP
the
at
still
taken
of
of
to
The sheet
achieved
as a method
for
of
low
despite
activity
electrical
to
at
comparatively
amorphous
removal
evidence
be
not
promise
great
up
begins
mobility.
that
750, C
slightly
decomposition
shows that
This
not
is
donors
is
room temperature
at
15% electrical
'layer
1015
continues
greater
showed
a dose of
about
reduction
a
and
at
Annealing
surface
(section
R. B. S.
is
the
in
was chosen
activity
surface
550*C produces
the
that
mobility
for
GaAs
contacts
temperature
a substrate
of Boo cm2/Vs,
may account
minutes
Annealing
.
InP
annealing
ten
of
800'C
-
temperature,
concentration
on
electrical
the
a value
carrier
making
550'C
maximum of
this
which
occur
a time
although
800*C, reaching
825*C.
(31,34)
200 keV into
at
a broad
produces
literature
of
range
annealing
the
of
a review
phosphine
capless
of
the
as observed
by
activation
of
implantation
damage.
damage,
crystal
for
as a criterion
as
finding
conductivity..
In
order
to
study
the
effect
temperature
on this
implant,
a
annealed
at higher
temperatures
of varying
of
the
annealing
550*C was chosen
were almost
completely
time
as samples
annealed
96
the
during
to
5 minutes
constant
only
significant
giving
carrier
sheet
with
this
three
any given
temperature.
of
excess
of
80%
(fig.
5-4).
of
The
550'C
to
keeping
the
activity
is
the maximum
concentrations
its
slightly
implant
ene rgy
activity
of
at
to about
of 760'C.
final
25% (fig.
about
be
the
excess
700*C
smaller
expected
at
in
sensitive
the
The
give
doped
50 keV
sharply
this
of
value
electrical
and peaks
to
higher
the
with
maximum
the
over
200 keV to
range
750'C
of
more heavily
from
5.5)
1019/cm3.
further
all
with
the
reduced
(53)
700*C
magnitude
1014 Se+/cm2 the
Due to
would
is
of
than
of
recovery
in
by
value
this
activities
contrast
greater
dose constant
reduced
In
of
time
temperature
an order
and
at
a
for
used
electrical
by
times
a time
at
electrical
more
The
annealing
that
annealing
much
750*C.
the
annealing
temperatures
at
is
varying
only
When the
a temperature
annealed
reaches
layer.
produces
dose,
mobility
the
by
mobility
any
minutes
was
anneal
resistivity,
for
complete
Se+/cm2
shortest
has been shown that
ten
of
activity
range
2/Vs
900CM
It
sufficient
to
when
higher
temperature
the
1014
for
times
minutes.
longer
complete
implant.
is
the
all
three
the
of
limited
may be concluded
to
sufficient
A dose
dose
It
being
for
same values
time
anneal
is
the
5-3)
minutes
annealing
than
was about
sufficient
for
the
and so
which
(fig.
the
is
temperature
than
time
concentration.
ten minutes
less
shortest
occurs
practically
The range
minutes.
difference
5 minutes
of
the
furnace,
the
of
ten
of
25 minutes,
time
time
time
standard
at
implant
peak electron
activity
falls
97
significantly
being
800 C
at
to
more sensitive
Based on these
640 to
range
of
600'C
carrier
maximum values.
The sheet
implanted
(fig.
samples
ions
energy
the
electrical
5.6)
are
implant,
single
has not
very
the
the
degraded
temperatures
compared
of
the
of
in
the
multiply
those
implantation
activation
loss
with
the
of
to
similar
activity,
a marked
properties
so
in
annealing
have
in
results
reduction
At
multiple
temperature
anneal
conductivity
and sheet
with
restricted
implants
1014
the
concentration
1015 Se+/cm2
800*C for
implant.
shallow
below
and
the
over
and a corresponding
the
of
particularly
implant
shallower
implanted
samples
Exceeding
decomposition
surface
the
annealed
790*C.
the
to
decomposition.
surface
results
were
selenium
energy
due
possibly
the
of
the
lower
principal
implant.
less
The implants
into
damage than
similar
damage anneals
of
the
lower
out
The final
implant
1015 Se+/cm2
a slight
peak in
known.
The sheet
further
increase
2.1014/cm2 which
is
achieved
activity
carrier
in
is
the
at
implants
be tried
should
value
500*C for
almo. st
a
which
falls
temperature
factor
of
this
In view
was felt
and the
5-7)
that
400 to
range
for
activity
at 450*C (fig.
cause
and
4-3).
it
of electrical
concentration
annealing
implants,
(section
temperature
room temperature
temperatures
annealing
temperature
room
on the
results
have been shown to
substrates
a lower
at
750*C was chosen.
is
heated
and there
is
no explanation
slightly
to a value
two less
than
a
with
of
the
a
about
same
98
into
implant
damage does not
to
the
the
of
seems that
it
at
is
22
about
resistivity
into
similar
after
implant
annealed
at
750*C.
of
self
and gate
Se+/cm2 into
hot
a
concentration
reaches
(fig.
the
and higher
anneal
mobility
of
implant
temperature
The implant
shows a
that
excess
hot
similar
a higher
of
to
that
carriers
The mobility
all
yield
is
annealing
1014 Se+/CM2 at
pattern
percentage.
to
of
in with
implant
at
5-8).
fits
temperatures
the
(fig.
the
electrical
is
as the
A similar
anneals
that
damage
will
higher
activity
energy
is
,
radiation
be
no improvement.
50 keV into
550, C
temperature
idea
that
temperatures
carrier
above
room
than
1014
of
The sheet
the
for
dielectric
2/V.
1500 cm
s for
greater
gives
importance
an implant
the
as the
results
200'C
treatment.
for
for
sheet
a room temperature
great
anneal
600*C
of
lowest
at
MISFET's
value
similar
of
results
plateau
dose.
smaller
a
the
the
This
is
gate
substrate
5-4).
damage produces
with
fact
aligned
from
being
the maximum value
implant
This
its
held
600*C to
at
excess
the
is
implant.
From these
a substrate
annealing
may be drawn
conclusion
to
implants.
have to withstand
metal
a plateau
1100cm2/V. s
in
anneals
similar
room temperature
an implant
fabrication
for
is
ohms/0
reaches
over
at
contribute
of a room temperature
constant
iesults
the
600 .C and
that
suggests
may even
The mobility
maximum mobility
resistivity
at
and
the
to
The sheet
an anneal
This
InP but
in
concentration.
following
superior
donors
compensate
electron
value
room temperature.
at
a substrate
less
a 600*C
Again
the
the
room
of
studied.
a
hot
hot
substrate
implants,
achieved
at
in
low
99
implants
at
implant
has
all
(fig.
electrical,
implants.
This
may
active
The sheet
electrical
the
of
200 ohms/C3 .
implant
energy
for
concentrations
(5.2.2)
Results
gives
using
higher
in
annealed
in
the
of
encapsulant
properties
sheet
the
values
energy
within
different
ions.
experimental
a sheet
electron
1200cm 2/V. s
of
and
and less
make this
implant
together
hot
substrates
for
suitable
surface
a
carrier
silicon
at
these
measured
filled
by the
as the
a
have
greater
in
pin-holes
produce,
Van-der-Pauw
implant
investigated
The results
pits
keV
encapsulant
similar
temperatures
when
200
at
The non-uniformity
problem.
indium
the
5.10).
700 C
Se+/cm2
nitride
than
all
(fig.
above
a
1015
of
activities
550-800*C
become
annealing
pyrolytic
a PH3 atmosphere
that
lower
high
implant
particularly
scatter,
the
the
activity
giving
capped
electrical
range
than
a 550 C anneal.
A room temperature
annealed
into
200
The higher
should
implants
energy
multiple
,
the
the
due to
with
mobility
energy
whilst
activity
constant
550-756'C,
range
temperature
annealing
higher
are
13
2
7cm.
3.10
of
be
by the
produced
parameters
about
resistivity
critical
defects
temperature
concentration
5-5)
hot
than
greater
(fig.
lower
the
The low
slightly
implant
for
greater
5.9).
had slightly
electrically
over
is
activity
room temperature
room temperature
with
temperatures
a peak electrical
implants
keV hot
sheet
mobility
and
anneal
corresponding
error
the
temperatures,
annealing
of
electrical
means that
technique
the
are
the
subject
100
to
increasing
a
result
temperature
high
of
the
iemperatures
The
surface.
lower
the
may be due to
the
between
the
growing
silicon
the
continuing
time
10 minutes
is
(fig.
atmosphere.
over
the
without
nitride
The mobility
is
range
concentration,
carrier
annealing
out
of
stress
expansion
of
the
silicon
The implant
profile
either
silicon
nearer
hot
through
the
ýnaffected
one
the
surface
nitride
cap.
silicon
nitride
was removed
is
1015
substrates.
in
HF acid.
550*C
then
30 minutes
sheet
is
extended
beyond
14
2
2.5-10 7cm
which
the
carrier
in
a
the
by the
used
to
Se+/cm2 at
After
The results
the
fall
is
cause
PH
3
time
annealing
known for
caused
by
The
possible
nitride,
was
or room temperature
which
expansion
annealed
by
however,
surface,
somewhat
PH
3
up to
of
implant
same
reason
in
anneal
value
No
studied.
in
at
for
growth
a constant
the
are
minutes
when the
than
at
investigated
was
40 minutes.
of
slightly
greater
still
ten
to
mobility
InP substrate.
for
5.11)
in
decomposition
major
annealed
nitride
of
550-C
increase
in
of mobility
anneal
at
falls
concentration
with
the
anneal
a total
.
samples
and the
dependence
The fall
anneal
caused by differential
stress
nitride
an
As
-
with
than
values
the
for
surface
silicon
The time
giving
maximum
above 700'C
activity
other
correlates
800 cm2/V. s than
at
trend
up to 700*C
temperature
annealing
of
variations
show no particular
with
temperatures
annealing
the
this,
of
mobility
for
error
in
the
differential
shift
the
200 keV into
anneal
for
the
the
room
101
temperature
taken
are
the half
of
650*C and the high
than
greater
temperatures
that
fact
implanted
the
room
in
excess
profile,
bare
annealing
are
as
750*C when post
implant
definitly
be ascribed
nitride
silicon
a
The implant
substrate
the
bare
gives
implant
an
anneal
and dielectric
aligned
the
anneal
when account
is
gate
to be
MISFET,
than
between
might
noted
that
the
in
the
that
of
The improved
be useful
where
when
using
the
all
pinholes,
the
with
be caused
example
implanted
particularly
was badly
this
as the
silicon
similar
at
annealing
range
200*C.
is
at
by the
pitted
effect
cannot
quality
CVD
of
from run to run.
through
a
a
around
agrees
for
implantation
The maximum amount
dielectric.
with
the
activity
for
is
experiment
into
The mobility
shorter
nitride
control
implant
behaviour
form
deposited
to
varies
to
the
implant
method
was
of a tendancy
Without
anneal.
this
It
mask.
500'C.
and at
undesireable,
a
at
compensation
of
nitride
in
damage would
room temperature
at
had less
nitride
of
is
bare
dip
a
the
much of
When account
silicon
the
This
has
-
the
bare
600'C.
The level
implants
photo-resist
note
profile
so
implants
the
of activation
of
5.12
with
temperature
damage
low temperature
hot
level
nitride.
silicon
in
removed
particular
the
the
figure
correspondance
In
substrate.
in
given
profile
have a greater
curves
hot
implant
500*C.
present
this
low
taken
of
the
activation
is
can
necessary
during
temperature
the
ions
for
anneal,
annealing
heated
a
(fig.
characteristic
of
As it
into
nitride
5.13)
to
in
the
trapped
be
the
achieved
gate
for
under
metal
a
self
silicon
102
is
nitride
of
and hence
mobility,
(fig.
5.13)
necessary
(5-3)
The results
of
encourageing.
25%
particular
in
concentration
Both
4.2
the
whilst
implant
peak of
for
nitride
at
the
A
further
the
-electrical
with
.
through
pin-holes.
bare
of
has yielded
implant
implants,.
nitride
was
for
low
is
carrier
(section
5.2.1).
contrast
also
shifted
maintained
temperature
of
this
to
microscopy
up
develop
reduced
to
8007C
pin-holes
the
the
density
of
was that
the
whilst
the
surface
or even improved
anneals
the
Performing
implant
the
the
maintained
700ýC-
above
In
sheet
a
did
encapsulant
profile
than
temperatures
significance
activation
phase
annealing
annealing
silicon
greater
have maintained
techniques
temperatures
been
tried.
conditions
14
4.10 electrons/cm2
The PH ambient
3
silicon
annealing
implant
annealing
resistivity
substrate
implant
as seen by Nomarski
morphology
section
after
excess
and capless
capped
surface
in
1015 Se+/cm2
the
the
have
InP
to achieve
possible
the
all
possible
650*C
of
implanted
ion
annealing
of
activation
and the
is
pip-holes.
has been found
It
values
by implantation
doping
Summary of
final
At a temperature
cap had no visible
nitride
their
resistivity
contact
dielectric.
of the
deterioration
silicon
lowest
the
between
The
fabrication.
6501C and so a compromise
at
anneal
an
device
attain
resistivity
sheet
after
for
interest
particular
(section
compared
5.2.2).
103
The high
for
importance
of
gold
level
ohmic
contacts
6.3
to
HoweVer,
considerable
doping,
some of
despite
on the
section
at
Contact
resistance
electrical
these
layers
these
in
4.3
the
particularly
contacts.
damage remained
by RBS in
seen
as
,
effects
of
good
electrical
many samples
.
properties
The role
are
this
discussed
in
section
results
even after
of
of
measurements
presented
are
is
surface,
annealing
damage and its
in
section
7.2
104
cli
Lru
Cr
V)
1014
Z
IC(
1013
1013
Fig.
5-1
1014
)I
(cloverteaf
cm-2
n
Comparison
with
of
Hall
two different
measurements
geometries.
made on samples
105
5
1()l (,- P+ 700 KPV PT
4.101
E
Li
V)
c lol
BOO
400
LI)
>
E
U
200
(1)
81
34
r2
q2
1111111
600
Fig.
5.2
Sheet
carrier
resisitivity
temperature.
700
Ta(oc)
concentration,
of
1015 Se+/cm2
mobility
implant
800
and
vs.
annealing
106
1015
Se+@200KeV, RT
Ta=553"C
E
L)
........................
(I,
14
14
p
aI
tJ)
+00
>
(J
E
Li
200
0
(1)
400
200
100
lk I
05
10 15
20 25
30
fa (min )
Fig.
5-3 Electrical
function
activity
of
annealing
of
1015 Se+/cm2
time.
implant
as a
107
RT
1ý4 Seý20OKeV,
1111
1014
ez
C%4
le
01
1100
E
(A
r-
1013
0----0
800,ri-
(A
400
4-00
Li
(n
200
200
1oc
600
700
800
(0 c)
TC-3
Fig.
5.4
Electrical
annealing
activity
temperature.
of
1014 Se+/cm2 implant
vs.
---L
108
1014
Se, 50 KeV,RT
4.1013
a
014
1
E
u
Ln
0
103
800
"T
W
0
000
400
0-4
E
u
: 3,
\,
200
I
co
0
.
-. 1
BQO
vi40C
co
600
Fig.
700
1- (00
C-3
5-5-Electrical
1014Se+/cm2
activity
vs.
of
800
50 keV implant
annealing
temperature.
of
109
implant
multiple
4.1014
C134
f=u
1014
8QC
0
40C
64
E
Li
0
Ln
Q---
700
T3(00
c
600
Fig.
5.6
800
E16ctrical
annealing
activity
temperature.
of multiple
implant
vs.
110
1015Sý+@200KeV,20.OOC
4
Li
:_0
0
V)
C:
104
800
oý
/0
oc
N-I
r'-4
f=Li
0
0C
0
::
4
G
10
400
500
600
TZ
a(00
Fig.
5.7
Sheet
carrier
resistivity
function
of
concentration,
mobility
is
for 10
Se+/cm2 implanted
annealing
temperature.
700'
and
hot'as
a
ill
Se+@200:KeV,2000C
1014
1014
pp
"00
2101"0
0--%
00______Q
Ir-,
0
0
10.
IT
0
40,
10
0
13
3
40
Fig.
500
600
)
Ta(OC
___
700
5.8 Electrical
for a 1014 Se+/cm2, hot
activity
implant vs.
annealing temperature.
112
14
()
200
c
50
KeV,.
Se'
10
1
-
-11
C"-4
1,1013
E
U
1013
>
1500
c4
E
1000
800
Li
It)
400
0
0
200
0
ci
0
1
500
600
700
100
800
(oc)
TC--3
Fig.
5.9 Electrical
for a 50 keV, hot implant of
activity
1014 Se+/cm2 as a function of annealing temperature.
113
lds
101E
Se, 200.kev,RT
E
L)
t/-I
T
I>
14
10
800
E
.u
400
=3,
Ln
4(
,
0
--,
Iv
A
600
S'3N4
700
T,a ( *C)
AG
A800
only
Fig.
5.10 Eldctrical
various
activity
temperatures
for
1015 Se+/cm2 annealed
under silicon
nitride.
at
114
1015,
105Seý,RT, 550'C
2-
--
1014
103
-8-
E
Li
VI
I
100
/1000ý
vl-
S'3N4growth
1 00L
Fig.
10
5-11
20
Electrical
varous
30
activity
times
under
of
40 -tca
/ min
1015 Se+/cm2
silicon
nitride.
annealed
for
115
0
AS
RTrm-1000
i3N4
1015Se'@20OKeV,
ý4
)00
C,4
E
u
+00
ýjo]3
1000
600
400
0
ZO
CN
E
200
.
500
400
Fig.
5.12
Sheet
function
carrier
of
1015 Se+/cm2
700
600
Ta(OC)
concentration
annealing
through
and mobility
temperature
silicon
nitride.
for
as a
implant
of
i
116
()
*
/In
P,200C
1015Se', 20OKeV:ý' Si3N4
S
E
Li
I
/
I
/
:
:
:
ý014
.
.
?.103
BOO
400
200
:: L
100
400
Fig.
5-13 Sheet*carrier
.
500
600
(oc )
TC-3
concentration
15
10 Se+/cm2, implanted
hot
and mobility
through
silicon
for
nitride.
117
(6)
MEASUREMENTSON CONTACTS
(6.1)
Non linear
the
Some of
between
existed
barrier
this
laser
had I-V
energies,
contacts
the
by laser
caused
diodes.
The back
eutectic
alloy
contact
(n-1016)
low barrier
from
ideal
hence
still
is
less
had an I-V
(fig.
present
energy
densities
mechanically
6-ic)
densities,
linear
I-V
including
no
weak
when
I-V
of
used
a
on leaky
liquid
tin
energy
was far
densities
of
a barrier
to
contacts
laser
These
lack
all
of
6.1b),
reliably.
InP melts,
for
so the
measurements
height
laser
characteristics
anneal.
due to
(fig.
two
contacts
the
undoped
characteristic
indicating
all
which
C-V
a barrier
with
the
characteristic
about
characteristic
whilst
to
made
I-V
quantify
probed
latter
and
indium-gallium
which
alloyed
for
current-voltage
contacts
forward
The 2000 A thick
characteristics.
had almost
6.1a)
to
laser
contacts
tin
factor
possible
in
changes
measurements
with
reverse
the
an ideality
not
the
or
greater
soft
(fig.
height
with
it
A few of
j/cm2
a
still
plane.
ground
Furthermore
unreliable.
made
a barrier
The
allows
which
1000 A thick
had
both
were made.
was
on a copper
that
low
with
To investigate
annealing,
meter
The as deposited
the
InP.
measurements
capacitance
material
and the
metal
annealed
indicating
characteristics
capacitance-voltage
"Boonton"
contacts,
alloyed
0.3
was
alloyed
with
had linear
I-V
undoped
InP
laser
contacts
rectifying
energy
were
action
118
may be due to a tin
the
of
oxide
evaporation
to a poor
The silver-tin
the
of
samples
behaviour
used
6.2).
anneal
this
laser
have
I-V
the
of
presence
energy
almost
of
the
broadly
little
density
linear,
effect
but
Due to
at
reverse
current
be
taken
the
non ideal
alloyed
from
to 0.27
j/cm2
leakage
flow.
current
results
being
in
limited
a
:
at
grpater
alloying
with
energy
of
0.20
deviation
indicates
than
of
the
increasing
bulk
(fig.
densities
to
by other
contact
less
is
sensitive
the
by the
a
properties
Further
The C-V measurements
picture
which
line
straight
V (fig.
j/cm2
energy
although
The
for
observable
laser
a
on
reverse
occurred
highly
no change
with
a
of
The electrical
obviously
effect
to
0.14
of
metal.
causes
current
a fixed
density
reverse
semi-conductor.
similar
in
to
the
to
0.5
barrier
a slight
the
reduced
bias
the
characteristic
but
effect.
which
even greater
diameter)
factors
of barrier
are
The contacts
techniques.
ideality
had
as a measure
energy
interface
alloying
due
also
an alternative
current
even to melt
metal-InP
gentle
j/cm2
an
same
tin
barriers
increase
with
not
calculated
the
was reverse
InP
n-type
densities.
energy
was used
A significant
laser
undoped
and poor
Schottky
current
quantity
of
these
of
saturation
low
the
of
C-V measurements
allowing
with
annealed
the
(100 micron
size
resistance
series
to
characteristics
contact
smaller
the
cause.
contacts
diode
reverse
soft
the
vacuum was not
surface
in
out
so oxidation
sound
mechanically
were
the
on
to n+ InP carried
The contacts
InP.
formed
heterojunction
oxide
resistance
6.3b)
0.1
the
is
which
give
j/cm2
a
has
diffusion
119
is.
potential
For the
soft
diodes
results
are
not
deposited
is
(n-1018
/cm3)
some of
the
A
a
densities
the
saturation
of
resistivity
contact
1018/cm3
electron
substrate
(section
formation
of
a
3c)
very
already
alloyed
NiAuGe
laser
on heavily
energy
characteristics
densities
did
the
All
more
not
than
deviate
would
to
a
give
dope the
height
doped substrates.
current
NiAuGe does not
barrier
to produce
8 A/cm2 after
InP of
low
tend
energy
n-type
mechanism
contacts
which
V which
contact
explains
may be the
saturation
the
This
(fig.
j/cm2
higher
reaching
ohm. cm2
As the
concentration.
doped InP.
only
10-4
about
0.1
At
of
particularly
action
rectifying
of 0.3
potential
characteristics
6.4a)
This
doped
Sn
onto
around
2
J/cm.
0.33
to a barrier
corresponds
(fig.
increases
current
with
I-V
heterojunction.
germanium
anneal
the
this
of
cause
possible
as
yielding
slope
deposited
densities
energy
the
the
/cm3.
However
with
alloying
of
laser
with
were non-linear
formation
a
6.3a)
the
anneals
1/C2 vs V for
of
only
were
substrates.
contacts
laser
6.4b).
contacts
laser
a plot
6.4.1015
of
conditions.
surface
energy
(fig.
linear
concentration
The Ni-Au-Ge
but
reliable
in
a change
by high
produced
very
contact
a carrier
after
indicating
reduced
to
seems
Schottky
diode
by
to
the
(69)
observation
low
be
resistivity
that
contacts
the
contacts
alloyed
with
0.4
j/cm2
had
I-V
measureable
from
linear.
120
(6.2)
Laser
The laser
InP
that
even
resistance
back
contact
A
The 2000
(fig.
6-5),
to
sharply
0.3
a value
j/cm2
producing
a heavily
tunnelling
contact.
with
increasing
the
lowest
of
estimate
1.6.10-6
error
probably
measured
contact
does
alloy
resistance
for
resistivity
for
of
the
exceed
8.10-7
step
0.6
200
with
ohm. cm2.
fall
that
the
the
sheet
Using
the
the
gives
micron
contacts
a
produces
ohm-cm2.
1.3.2
InP,
to
j/cm2
chapter
100 micron
the
of
for
indicates
10-6
the
of
continues
with
of about
density
energy
resistivity
be
drops
necessary
in
the
would
melting
which
to
resistivity
an
increases
resistivity
not
low
a
UP t. 0 0-3'j/cm2
layer
alloying
due
contacts
the
with
density
Laser
ohm. cm2 whilst
the
surface
concentration
minimum measurable
densities
ohm. cm2 at
contact
energy
spreading
was such
liquid
ohmic
were
of
well
The
contact
was
and
In/Ga
The contact
3.10-6
doped
concentration.
electron
contacts
ohmic
the
energy
melts.
around
laser
electron
surface
tin
tin
material
substrate
were
to
some alloying
correlates
which
the
the
of
contacts
laser
a
the
because
expected
starting
with
contacts
tin
although
series
by the
measured
the
of
doped
plane.
ground
for
heavily
on
resistivity
level
was formed
thick
doping
substrate
deposited
as
copper
in
The doping
the
the
coating
contact
resistance
as possible.
as small
fabricated
The low resistivity
bulk
the
that
ensured
their
had
method.
probe
contacts
contacts
alloyed
(n-1018/cm3)
third
ohmic
alloyed
contacts
the worst
Hence
the
as
case
lowest
121
is
resistivity
the
and this
laser
contact
resistance
form
number
It
all
laser
these
device
the
tin
a large
the
at
the
higher
have
of
more uncertain
as the
as
even when
of
furnace
alloyed
between
will
surface
makes the
may
the
result
the
of
no
original
is
allowance
contact
resistivity
(19,20)
and 0.8
low resistance
sufficiently
during
off
contacts
0.3
0.8
contact
a
be a fraction
values
than
the
of
densities
these
The
phospherus
energy
that
densities
energy
been blown
and
sized
values.
compensation
may only
best
different
greater
amount
areas
resistance
the
with
having
The
experiment.
measured
alloyed
be"noted
should
Hence
j/cm2-
to be
for
useful
in
pure
tin
applications.
The silver-tin
layer,
as
This
was
the
contacts.
of
properties
the
reason
The sharp
far
more durable
than
analysis
and sheet
drop
melting
occurs
greater
than
in
for
for
the
improve
The as deposited
energy
contact
density
but
above,
given
to
expected
a low laser
with
annealed
is
layer
was shown by microprobe
measurements.
for
the
cause
area
with
contacts
results
unconnected
spreading
comparable
tin
of
metal
are
for
measurement
active
made for
may
of
electrically
area.
of
contacts
which
The loss
a
of
As a result,
have been lost
the
resolution
in
may be due to
anneal.
donors.
two sets
for
rises
resistivity
the
confidence
gives
contacts
j/cm2
the
between
agreement
to
close
an
energy
tin.
layer,
but
are
ohmic
to
0.4
of
this
electrical
and those
contacts
due
-density
resistivity
the
show no tendancy
resistivity',
the
is
(fig.
6.6)
to alloy
the
substrate
2
J/cm
which
expected
in.
as
is
the
122
has
silver
a
2
J/cM
0.4
reflectivity.
The contact
about
10-5
and
is
laser
energy
which
produces
Thus
the
increasing
1.6
higher
j/CM2
ohm. cm2.
than
resistivity
density.
silver
is
required
is
made for
for
the
the
of
less.
This
4.10-6
ohm-cm2,
device
with
presence
higher
the
energy
formation
advantage
as wire
density
causes
severe
to be protected
reducing
the
contact
is
not
the
may
be
with
0.5
sufficient
required
to
decomposition
is
bare
away.
would
of
this
on
have
a
greater
the
left
to
is
that
about
a
allow
the
contact
InP which
A
and
into
successful
the
etched
required
of
problem
achieve
of
by the
incorporating
metal
is
j/cm2
resisivity
for
the
effect
by irradiance
One slight
effect
this
found
value
is
affect
was
bonding.
density
It
well.
would
method
of
be to place
the
tin
durability
of
the
known.
The Ni-Au-Ge
which
that
When allowance
but
a contact
the
density
layer
or subsequently
energy
on top but
layer
low
energy
of
might
silver
tin
produces
a usefully
of
energy
density.
silver-tin
little
density
energy
the
contact
reflectivity
reasonably
active
The
range
of
1.5.10-6
about
laser
energy
of
irradiance
a greater
this
greater
agree
electrically
such operations
have
two curves
with
of
incident
absorbed
to be affected
microprobe
the
steadily
highest
have
over
a greater
secondary.
the
contacts
due to
mainly
for
falls
resistivity
contacts
a given
this
incorporation
obviously
tin
is
that
expected
a contact
means that
which
up to
density
silver-tin
the
This
ohm. cm2
resisitivity
due
samples
to a slightly
lower
initial
substrate
resistivity,
doping
level
or
123
due to
formation
the
measurements
are
(fig.
which
6-7)
resistivity
was for
the
produces
a
previously
by
not
a
shows
barrier
height
contact
resistivity
in
rise
j/cm2.
0.2
above
contact
by the
and 0.1
densities
energy
a greater
confirmed
of 0.06
densities
is
of
j/cm2
of
correlates
with
of
contact
suggested
(chapter
formation
of
nickel-phosphide
3)
the
field
a
interface
layer..
on
the
alloying
conditions
layer,
and
not
by doping
of
is
so
depends
not
around
value
0.5
j/cm2.
irradiating
on the
Further
doping
the
of
Ni-Au-Ge
after
However,
the
laser
surface
are
and
the
damage to
furnace
surrounding
whilst
alloying
about
after
effect
be noted
two sets
coated
density
may
contact
contact
InP.
It
not
that
of
the
samples
with
cause
metal.
heavy
resistivity.
more
does
to a
substrates
producing
,
The
substrate.
no significant
entirely
of
resistivity
than
improve
removal
the
metallisation,
so
interface
greater
the
a
resistivity
with
should
energy
by
density
for
were
but
energy
it
different
As
laser
produces
j/cm2
formation
contact
the
1 j/cm2
in
as it
0.4
this
producing
of
fall
contact
contact
so the
laser
resistivity.
Hence the
InP,
energy
at
the
barrier
melting
samples
InP
emission
semi-insulating
were
the
with
of
the
resistivity.
increasing
method
irradiance
of
more than
semi-insulating
considerable
contacts
doping
conditions
Disadvantages
the
The
laser
as abrupt
ohm. cm2
increasing
with
ohm. cm2 for
contact
the
the
10-5
with
irradiation
as the
fall
values
measured
to
sensitive
not
for
Irradiating
2.10-5
about
is
change
diode
measurement
resistance
two metallisations.
other
.
The melting
the
although
The
metal
and
must be concluded
adequate
give
usefully
device
low
124
resistivity
the
behaviour
type
layer,
interface
of
the
of
Ni-Au-Ge
the
One such
irradiated
with
by
five
four
contours
top
and
follow
contacts
density
laser
the
the beam.
a
Indeed,
that
modification
spread
the
by
produced
inferred
density
energy
reflects
resistivity
a
improved
the
of
in
the
in
laser
anneal
homogeniser
contact
on
constant
that
obvious
greater
resistance
the
the
6.8
bare
example,
the
mean
energy
falls
with
in
variation
density
energy
the
resistivity.
sample
at
that
on
of
for
of
resistivity
figure
defined
The contacts
At
laser
for
measurements
immediatly
suggesting
in
in
result
the
on
contours
pattern.
contact
pattern
of
is
It
uniformity
values
in
and left.
variation
this
of well
these
have significantly
bottom
2
J/cm
0.38
of
increasing
smaller
at
ohmic
process
sets
of
plotted
defined
edges
should
was measured
6.8.
the
after
photo-engraving
The results
figure
a well
nickel
had complete
are
for
because
two metallisations.
other
contacts
J/cm2.
in
right-hand
the
of
array
resistivity
the
pattern
0.38
the
samples
set
the
be
may
formed
properly
out
developed
the
contacts.
than
to
well
of
some
in
not
Leaving
characteristics
Due to
contact
is
contacts,
This
alloying.
seems to be responsible
which
treatment.
laser
a similar
the
laser
after
contacts
across
the
resembles
InP.
laser
will
It
may be
beam,
result
by
in
a
125
(6-3)Contacts
The ion
implanted
the
by
measured
metal
deposition
the
areas.
photoresist
was
was performed,
although
the
was measured
resistivity
at
almost
also
as does the
sheet
the
is
length
flow
current
flow
all
much greater
contacts
is
over
to
for
the
However
the
100 milliohm.
end
expense
of
contact
to
increasing
the
the
used in
end
vertical
is
resistivity
summarised
in
of
table
layers.
jo15
laser
the
end
reduced
parallel
are
the
the
effective
contact
the
The
be
can
are
parameters
best
1.3.4,
contact
specific
the
section
influences
contacts
for
cases.
as it
without
rise
all
at
no
for
probes
resistivity.
The
ion-implanted
resistivity
than
contacts.
the
and
between
end
length.
used
These
contacts
The contact
alloyed
then
in
layer,
implanted
ion
devices
the
be
can
gold
in
which
of
to define
resistance
a thicker
dimension
importance.
paramount
for
which
the
resistivity
contact
minimum
If
resistivity.
current
effective
pure
separate
important
by implanting
the
using
is
for
some temperature
as noted
importance
is
will
increasing
contacts,
planar
technique
1mA was used
of
1.3-4).
evaporation
The
evaporation.
A current
resistivity
contact
6.1
used
resistivity
chapter
using
metallisation
of greater
parameter
method
(see
off
fingers
In comparing
contact
lift
and current.
voltage
their
fabricated
and the
during
of
each pair
line
was
alloying
layers
had
samples
pattern
The
was inevitable
implanted
transmission
The multi-finger
deliberate
ion
to
Se+/cm2 hot
alloyed
resistivity
cm and so in
implant
is
or conventionally
of
conventi
a FET structure
onal
this
126
length
The contact
for
used
geometries
resistivities
which
concentration
is
for
these
keV
surface
carrier
The
reason
room temperature
so the
due
resistivity
would
a
gives
implant
a
leads
to
the
nitride
Again,
of
a high
to
surface
the
end
carrier
greater
than
noted
that
be
should
alloyed
contacts
the
and large
layer
in
the.
increasing
metal
The
and so
contacts
This
for
the
of
this
a planar
compared
with
poor
carrier
so
lower
the
to
results
large
nitride
surface
200
adhesion
a silicon
demonstrates
was
for
scatter
surface.
the
may indicate
had poor
The metal
resistivity
substrate.
than
damage
through
optimum
suggesting
known but
not
greater
to alloyed
1015 Se+/cm2
the
at
resistivity
end resistivity
contact
of
is
this
contaminated
a bare
adhesion
packing
and
concentration
resistivity
be inferior
superior
into
it
contact
implant.
high
to
The implant
for
due to
compensation
be
the
annealed
although
has a lower
sample
alone
implant
760*C
of
contact
conventionally
a high
surface
energy,
to
high
a
resistivity
sheet
present
The contacts
as
However,
the
structures.
planar
keV implant.
may
and the
comparable
allow
higher
expected
resistance.
than
less
circuit.
has
temperature
it
to be
implant.
are
The 50
this
is
source
far
would
have
smaller
contacts
when used in
that
implant
1015 Se+/cm2
the
and
an integrated
hot
Se+/cm2
1014
is
microns
contacts
to be used in
density
17
at
in
improvement
show a marked
would
contact
sheet
implant
device.
layer
a similar
benefit
of
concentration.
improved
surface
127
preparation
The high
to be
The
room
temperature
implant
is
of 750'C
the
from
expected
for
necessary
The epitaxial
finger
masked
produce
heavily
doped regions
this
regions,
contact
the
For
contacts.
true
the
the
and
of
the
area
for
value
calculated
gives
a
smaller
due to
the
apparently
is
not
affected
resistivity
25% in
the
differences
it
is
the
values
in
end
surface
of
of
greater
significantly
conditions.
that
transmission
For
the
value
between
all
implant
on
three
is
the
times
difference
illustrates
useful
an
The end
resistivity.
example
is
However,
may be due to very
This
the
this
over,
correct.
and the
of
resistivity
in
resistivity
sheet
drain
the
area
contact
end resistivity
resistivity
is
to
process
and
sheet
that
selective
value
area
of
as
the
source
the
the
of
unimplanted
testing
FET
measured
the
adjacent
with
implanted
sample
resistivity
contact
to
measure
same
the
of
is
implantation
measurement.
a true
part
the
an artefact
the
this
a temperature
had
contacts
implantation
be
must
contact
the
under
addition
be
end
silicon
but
implant
during
In
to
resistivity
through
sample
resistivity
contact
large
annealing.
demonstrates
sample
of
method
under
area
selective
inaccurate.
a
shows that
which
pattern
elsewhere.
material
the
line
a
hot
the
on semi-insulating
surface
for
data
complete
by
epitaxial
than
Hall
is
to
leads
results
Van-der-Pauw
TLM measurement
resistivity
poorer
the
than
sheet
produced
nitride
the
The
resistivity.
of
value
resistivity.
contact
much greater
that
suggesting
again
value
is
resistivity
sheet
measured
even lower
to
lead
might
of
small
that
measurement
128
parameter.
implanted
The multiply
temperature
optimum
similar
gave
resulted
in
5.2-1).
This
the
Hall
much
less
is
very
The
concentration.
mainly
in
layer
annealed
in
or vertical
devices.
would
is
(21).
contact
far
were
resistivity
The values
much less
slight
alloying
mirror
finish
device
fabrication.
so
than
the
spread
measured
(fig.
than
during
this
is
values
found
of
for
mean of
the
evaporation.
alloying-
The ýmportant
either
7
at
circuit
the
tabulated
seventeen
the
not
1cm x 1cm dice.
spread
of values.
ohm-cm2 may
All
electrical
planar
more closely
1.8.10-6
would
of
a marked
contacts
all
best
contacts
has a tight
the
the
alloyed
random across
6.9)
to
the
an order
integrated
of values
at
to
offers
these
of
for
in
spread
smaller
The contact
to
the
greater
for
over
contacts
length
a
resistivity
process
this
of
comparable
contacting
packing
carrier
in
is
for
contact
resistivity
is
when making
dense
higher
as
results
but
(chapter
surface
end resistivity
The effective
To investigate
sets
sheet
temperature
resistance
Also
the
The contact
and the
allow
applications.
parameters
high
is
temperature,
mobility,
Hence this
improvement
microns
lower
implant
50 keV implant
to
resistivity.
smaller.
magnitude
its
(20)
contacts
alloyed
lower
640*C which
of
resistivity
greater
much
the
at
contact
the
either
complete
the
sensitive
due to
end
the
of
the
at
annealed
resistivity
difference
why the
explains
samples
sample,
activation
at
a temperature
for
results
annealed
were
760*C or at
of
sheet
samples
the
present
contacts
be
were
a problem
parameter
if
due
to
this
129
contact
were
excess
than
resistance.
twice
the
in
a
All
the
if
then
chosen
comments apply
6.10).
The
is
spread
the
similar
on which
tempbrature
with
ten
one
values
is
can be drawn
sets
of
measurements
be useful
or metals
even
if
it
present
the
less,
data
ohm. cm2
"test".
this
(fig.
with
no contact
on end resistivity
should
sample
were made.
were necessary
on the
less
selection
of end resistivity
It
for
pass
on
of
3.10-6
such as
would
No comparison
contacts.
resistance
as a suitable
contact
histogram
be a limit
would
a
value
the
to
alloyed
would
dielectrics
an absolute
of
conclusions
had
be taken
might
mean by 50%.
for
available
structure
contacts
but
all
Similar
exceeding
vertical
mean which
Similarly
criterion.
were
used
surface.
be
noted
annealed
at
The lower
to
heat
that
640*C
anneal
treat
130
6-la Curve trace
Fig.
IOOOA tin contact,
as
deposited.
of
3mA-2-
8V
642
-4V
-3
.2
ý-2
.,
lu
16ý
I/A
n=2
16
6.1b Forward I vs V for
Fig.
the as deposited
contact.
10
3mA
II
0
200
Vf IV
400
2
6V
42
-2
V
-3
6-1c Curve trace of
Fig.
1000A tin contact, laser
alloyed with 0.29 J/cm2-
131
I
I
I
-
0
0-
102
-
-
0
0
8
0
0
10
8
0
-
E
U
-
1<
IC-
10-1
-
0
-
8
0
o
0
-
I
I
I
0.1
0
in-2
IV
03
0-2
E(j CM-2)
Fig.
-6.2
Current
silver-tin
density
at
contacts.
a reverse
bias
of
0-5V for
132
0
%.
00
CN
-It
00-
CN4
Ln
0
000
0
.
PA
(A)
4J
m
4-3
0 'a
P
0
4-3
CH
0
P4
(1)
0
r-I
4-3
(1)
rj
4-3
0
0
4-3
4-"
cc
%0
Ln
0
P4
IL4
0
0
rj
4;
>
>0
M
>
C-4
4-4
-01
0
Q
A
P
4
0
0
A4
Ln
(Z_jd) Z_D
0
0
ca
Ký
m
1
P4
-7
E
u
Ln
UJ
133
co
C2
ca
0
m
6
00
4-3
Cýl
00
C-,4
E
91.0)
00
. 14
4-3
0
ca
P
(D
4-3
co
ul
ca
r-i
00
0
ui
0
00
4-4
0
00
0
. r4
4-3
P4
CL)
NAj
(
CNIJ
--T
v)
z-w3
sr
>
C-4
C=)
T6
I
*ri >.ä
C-4
-t
%ýo
0
C"j
CU
>
cö
-4-3 -P C)
0
ci -ý
cö Co h-i
.
6D
-ri
p4
9.4 4J
ej 91 CZ 0C) 0 CD
134
1
Sn/ InP
lu
"
20OPm
li
loopm o
lo-
C11.4
F=
u
10
-01
Fig.
0-4
E (j cm-2)
6.5
Specific
contact
function
of
laser
resistivity
energy
4
of 2000A tin
density.
as a
135
AgSnI InP
III
I
I
I-.
10-4
:
0---%
C*14
E-=
u
u
Qý
10-5
.
:
-
10
'. 1I
01
Fig.
lI
0-4
E (j cM-2)
6.6
Specific
laser
contact
energy
resistivity
density.
of
silver-tin
vs.
136
1
I
I
III
10-3
E
10-4
U
Qý
10-5
I
I
1
-1
*2
-4 -6 -8
E(i cm-2)
-02
Fig.
II
6.7
Specific
density
codtact
resistivity
vs.
for NiAuGe metallisation.
laser
energy
137
; -o
0
3.1
"
I
S
0
"
0
0
0
'. 3
1.6
2. o
2.5
nCm2)
C(jO-5.
Fig.
6.8 Map of
chip
specific
for
contact
NiAuGe laser
resistivity
alloyed
with
across
0.38
a 5x5mm
j/CM2.
138
10
W
-4L-)
ro
4c_0
Li
40
Lcu
-0
E
2
pC
Fig -
6.9
Distribution
the
multiple
( 1CF6.nCM2)
of specific
contact
resisitivity
implant
annealed at 70C.
for
139
10
W
4-
u
ru
-4-C:
0
U
40
-0
0246
(mn-cm)
jOe
Fig.
6.10
Distribution
implant
of
annealed
end resistivity
at
700C.
for
multiple
140
(3)
::I,
+1
+1
2, c)
+1
00
-
C;
C14
-, T
-
+1
(n --T co
1ý C--
CY)
C14
CN
r--
Lý
04
C4
00
U-1
--t
o
-
7
co
Cý
CD
-cp
C'ý
t
C14
C)6
o
+1
+1
CD
+1
7.-
76
TV
(D
(Ij
C
C
<
06
ta
a-
E
C)
(D
C)
(o
0
C.
t1-1
-
+1
+1
00
4;
J)
a)
(1)
CIO
t-
Ln
to
CD
LO
-1
(1)
0
)
C14
-
(::
10
C'47
0
Lo
co
1ý0
0
0
-C
LO
L--
(0
+1
+1
m
Ln
6,1 6
6
+1 +1 +1
L-(D
co
&
LO
Lo
Lr)
ý
'o
"7
It
co
M
C:)
ý: -
C;
c:,
C4
10
00
C:)
C?
o
+1
o
+1
m
C4ý
00
0
(o
t-
c)
C)
C,4
(f)
*T*
Lol
C'14
u,
V)
t
Ln
_j*
-.
-C: -0
0
+1
+1
10
-
jZ
+1
CY)
--T
10
Lb
+1
T
a)
CY)
+1
--:
-
LO
t-
+1
m
64
LO
+1
+1
6
:ý C;
VC*f)
(D
L--
LO
0
cr-
-4.1
-C
6
0
0
04
-0
cq
0
0
-C
0
0
04
Ln
cr)
)
0
*1-1
0
M
-
oc:
C)
0
00
0
CY)
-ýt
0
0
CY)
(9
o
(D 6
o
c1r)
CY)
-ýr
LO
+1 +1
T
c)
co
+1 +1
a) cx)
clý4
Q
<jU
-
(D
0')
(0
LI)
E
E
CY)
LO
(D
+1
(3)
+1
+1
+1
+1
C)
6
o
C-ý +1
M
Cý
Ln
+1
U-)
Cj
m
t-ý
C3
cy')
0)
M
(D
0
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-t
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1-1
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CN
w
Ul
0
0
141
(7)
DISCUSSION AND CONCLUSIONS
making
have produced
The structural
firstly
in
resistivity
on the
suitability
(7.1)
Discussion
The novelty
in
of
time
the
understanding
the
which
is
metal
due to the
the
visible
planar
source
semiconductor
this
model
effects
metallisations
not
large
is
may melt
energy
into
the
due to
density
emphasis
is
point
required
and a
of
metals
to
considered
and both
of
to melt
in
wholly
all
for
density
energy
of
a
step
densities
energy
then
absorbtion
does
formulation
laser
semiconductor
an
was an important
various
The
as it
melting
the
2.2,
metal
makes
involving
coefficient
the
each
categories.
assumed to be absorbed
The
of
contact
InP
section
attenuation
spectrum.
of heat
metal
the
seen at
merits
particular
difficult,
studied.
reflected
the
in
contact
results
As a consequence
model,
these
and
measured
device
a
of
excess
scale.
theoretical
each of
alloying
the mechanisms
in
temperatures
nano-second
laser
with
alloying
be discussed
7.2,
relative
'particular
laser
of
of
grasp
simple
each for
of
7.4
Both
resistance.
will
the
the
of
Phosphide.
and
with
section
methods
electrical
7.1
Finally
.
new
properties
sections
in
be discussed
will
low
of
correlated
7.3
section
method
intuitive
be
then
will
results
Indium.
electrical
in
each method
two
study
n-type
contacts
bulk
and
for
both
to
contacts
ohmic
techniques
work has been to
this
The aim of
metal
the
in
be a
and
energy.
Based on
just
metal
the
or
142
the
density
energy
semiconductor
which
correspond
with
Agreement
with
the
energy
density
At
calculations.
by
observed
tin
phase
very
X-ray
at
remains
also
occurred
at
point
this
temperature.
low
(section
InP.
the
which
measured
parameters.
(section
3-3)
Other
changes
particularly
are
is
for
phosphorus
to
melt
assumed
high
temperatures
forming
at
place
of
phosphides
may
InP.
contact
:
as
the
account
energy
In
the
between
the
with
the
for
the
theoretical
metals
in
to
the
all
the
InP
of
mechanism
by
the
to
The
is
nature
of
a
strong
metallisation.
additional
changes
excess
of
those
model
no
reactions
the
high
than
so
reactive
contact
and
metal,
point.
lead
attained
has
The
more
The
is
formation.
melting
metal.
densities
the
caused
sharply,
the
InP
in
loss
contacts.
InP
as
underlying
to
rises
the
appearance
take
also
loss
reactions
to
at
pressure
lost
reaction
occur
benefit
evaporation
in
over
raised
the
such
made
because
no
is
changes
tin
was
resistivity
that
dopes
pure
the
of
the
the
by
and
possibility
of
forced
of
resistivity
accounted
heavily
so benevolent
for
vapour
metallisation
tin
is
pressure
density
dramatic
the
of
was
metallisation
energy
were
required
This
indicating
obviously
not
that
phosphorus
contact
is
the
melts,
The
serious
suggested
Chemical
As
3-1).
The
and
melting
no metal
phosphorus
3.2)
InP
which
the
and
tin
assumptions
density
energy
the
contacts
the
simplifying
(section
232*C
at
the
with
this
microprobe
melts
small
the
considering
good
and
the
the
of
appearance
2-3)
surprisingly
the
in
metal
firstly
(section
observed
metal.
the
Considering
changes
contacts,
both
melt
calculated.
was
silver-tin
to
required
InP,
that
in
needed
are
is
the
143
and the
metal
InP are
have no
effect
Regarding
the
a great
energy
the
less
than
In the
which
components.
is
seen
as
For
theory.
resistivity
in
visible
the
Au-Ge
does not
due
increased
the
as shown in
heavily
but
the
poor
contacts
almost
irradiation.
the
to,
InP
poor
InP melts
3.3,
This
3.2)
It
(fig-2.6)
The
the
the
accuracy
by
the
in
the
that
due to
is
but
germanium
a conducting
clearly
energy
still
layer
to be nickel
of
densities
energy
is
by
formation
for
the
and
doping
lost
thought
substrate
up to
a reaction
semiconductor
is
of
appear
of
As
although
layer
is
melting
temperatures
probably
3-1)
adhesion.
but
at
would
No gold
(section
the
change
Evidence
occur.
alloy.
section
surface.
laser
again
no
point.
micrographs
melt
probably
tin
pure
probably
manufacture.
reflect
reasonable
(section
observed
eutectic
do not
InP very
energy
with
metallisation
InP melting
regrowth
the
the
of
would
device
cm2/Vs
contacts,
predicted
this
the
exceeding
which
for
dopes
100
case
Ni-Au-Ge
the
was
tin
become
surfaces
were much more durable.
was
metallisation
2.5d)
fig.
by high
removed
contacts
to
the
unsuitable
the
is
metal
(see
densities
quality.
Turning
on the
other
assumption
densities
energy
densities
of
mobilities
silver-tin
that
the
of
this
phosphorus
rippled
energy
crystalline
the
of
laser
and
these
alloy
behaviour
reactivity
pitted
At these
all
thermal
components
simplification.
render
the
as
on the
At the highest
very
distinct
considered
is
lost,
density
not
is
is
doped,
present
phosphide
144
although
no
metallisation
although
densities
used,
indium
the
tin
contacts
All
during
device
for
employed,
Only
the
diffusion
for
study,
it
of
of
the
interface
is
most
than
a
InP
the
possibly
than
inbetween
the
1000 i
formation
the
of
for
serious
metal
vertical,
thick)
micron
layers
and IMPATT diodes.
contact
2.4
chapter
only
or
energy
was
Surprisingly
-
thick
of
at
a
the
the
gold
surface
nickel
may have had an influence
to
amenable
and
phosphide
on the
movement
laser
alloyed
gold.
The loss
contacts
metal
in
laser
by movement
based
gold
that
the
other
much smoother
Gunn oscillators
a layer
within
the
at
the
given
has been suggested
layer
in
example
reasons
was contained
(less
as thin
remain
affected
diffusion
This
the
of
the
density.
energy
are
to
phosphorus
than
smoother
structures
devices
at most
the
with
highest
the
lost
The
given.
manner
a similar
The contacts
cause.
alloying.
two terminal
reaction
and also
even at
is
gold
again
the
is
contacts,
are
little
be
can
in
rises
resistivity
contacts
the
identification
positive
of metal
to
are
is
adhesion
of
composition
germanium
as
the
interpretation
or
the
an
of
a
serious
by
contact
complex
difficult.
a
layer
reactions
of
This
improvement
composite
may be possible
to minimise
absorbing
A marked
use.
using
so it
gold
if
problem
practical
obtained
silver
containing
although
be
is
this
metallisation
to
loss.
NiAuGe contact
principle
could
the
optimise
The
seems to have been
the
in
use
of
successful,
makes
be applied
exact
to
145
other
metallisations
given
alloying
adjacent
to
(7.2)
of
implantation
in
using
The main problem
the
common
damage.
the
semiconductors
With
a large
of
the
InP implanted
at
layer
surface
case
for
(section
Se+/cm2
but
conductivity
temperature
that
the
ion
dose it
is
carriers
is
far
hardly
implanted
less
suprising
dopant
amorphous
dopant
are
order
present
is
helium
ions
used
required
reasonable
to
five
compensated.
than
the
active
not
requirement
remove
the
a
observe
RBS.
Very
between
the
for
the
the
InP has negligible
low
comparatively
figure
The
value
5.2)
implanted
indicating
mobility,
of
layer
at
the
containing
Some restructuring
by the
permit
little
fact
the
channelling
restructuring
selenium
atom
and
to
300
1500 cm2/V. s but
Apparently
donor
is
electrical
1015 Se+/cm2
the
evidenced
to
form bonds
to
amorphous.
sufficient
for
1014
the
when implanted.
turn
of
surface
has occurred
to
dose
to
expected
the
radiation
with
(see
not
of
and this
necessary
at
140 ohm/[]
as
the
amorphous
order
minutes
completely
layer
not
was
is
of
The as implanted
of
a
any
may be possible
usually
in
dope
introduction
annealing
550*C for
for
damage to
to
room temperature
after
of
cm2/V. S, is
this
the
It
has a resistivity
layer
is
dopant.
the
of
activation
density
results
semiconductor
4-3).
the
reducing
ion-implantation
damage by annealing
radiation
the
enough
energy
InP.
of
areas
Discussion
incident
thereby
treatment,
unmetallised
the
reduce
the
give
of
that
amount
of
would
the
of
the
be
matrix,
up a free
a
146
to the
electron
the
on
resides
could
be tested
site,
and
However, tin
the
with
being
heavily
conductive
or
techniques
electron
might
be expected
the
A
level.
of
spectroscopy
photon
this
is
(63)
suggests
suggested
this
annealing
seem plausible
either
level.
implants
sub-lattice
Significant
(e. g.
ion
be
a
the
bulk
should
give
is
donor
activity
Ar, Kr)(35,65)
to
is
although
supporting
this
donor
other
and
work
The
vacancy.
the
support
produced
are
band
conduction
of
by X-ray
observed
producing
two
loss
shallow
to a similar
rise
latter
induced
the
tend
damage
by pulse
observations
vacancy
would
highly
also
these
states
a
InP.
amorphous
These
to be due to a phosphorus
observations
not
preferential
All
eV from
is
produced
(44,61).
an indium
alloying,
is
milling
a damage
0.15
crystal.
considerable
the
of
indium
the
location
doping
donor
the
by laser
lattice
produce
location
on
damaged layer
to
damage seen by
indicating
beam
of
at
level
that
that
surface
(62)
to
layers
component.
postulation
density
amorphise
annealing
volatile
by the
satisfied
will
heavily
the
beam
phosphorus,
It
as is
ion
the
by
produced
(60)
resides
suggests
influencing
InP
which
the
selenium
lattice
of
tin,
of
the
the
whereas
InP when introduced
mobilities
factor
Amorphous
pulse
dopes
that
The effect
heavy
damage and this
dominant
sub-lattice
sub-lattice.
a
be noted
should
by implanting
poor
lattice
laser
phosphorus
indium
on the
RBS is
It
lattice.
latter.
vacancies
shallow
by
hypothesis.
inert
on
donor
gas
147
An alternative
implantation,
high
(64)
in
results
ohm. cm is
produced
sufficiently
high
when
n-type
dose of
protons
levels
together
levels
matches
the
formation
of
the
explain
may be
thin
of
to
Schottky
barrier
voltage
around
103
InP
p-type
band
of
donor
of
shallow
may explain
ion
acceptor
difficulty
The
complexes
may even
observed
for
acceptor
-
the
implantation.
concentrations
devices,
film
flash
to
similar
possible
when
103 ohm. cm resistivity.
by
InP
size
dope
solar
all
would
the
solar
for
It
cell.
stoichiometric
InP
to
form
films.
Subsequent
annealing
at
for
used
defect
polycrystalline
be offset
interest
great
evaporate
those
cell
of
principally
and reduce
the
InP is
amorphous
polycrystalline
crystal
cell
doping
or
increase
only
(38,66).
to
temperatures
InP
and when a
into
shallow
levels
hole
possible
amorphous
into
protons
irradiated
around
vacancy
low maximum
in
application
produce
observations.
such donor
phosphorus
The donor
to
of
concentration
doped p-type
techniques
growth
devices
implanted
fairly
a
experimental
heavily
forming
is
a smaller
of
proton
material
is
InP
of
that
with
The presence
in
n-type
demonstrate
The authors
by
A maximum resistivity
becomes
the material
is
of
ohm. cm) resistivity
irradiated.
InP is
p-type
(>107
high
implantation
The
layers.
damage
GaAs and GaAlAs
used in
commonly
resistivity
introducing
of
method
would
have
by the
implanted
layers
densities.
If
InP with
acceptors
to be employed.
higher
operating
it
should
is
not
then
The
a
low
temperature
148
than
by
silicon
thin
(67)
with
good
be used
to
used
might
into
substrates
that
a
5.7
-
The
difference
is
most
700'C
concentration
disorder
than
is
more
by
like
That
donor
be of
defects
is,
in
the
single
the
but
the
defect
the
in
number
the
deep donors
so as
to
and causing
the
ionised
figures
at
that
mobility
This
levels
band
transfer
can still
that
the
defects
of
be
prevent
defects
deep acceptors,
impurity
can be
to
to
the
like
the
crystalline
damage.
necessary
room
above,
to
the
given
annealing
perturbation
acceptor
allow
compensate
for
induced
only
a
noted
In addition
is
obtained,
implanted
is
non-ionised
it
is
marked
conduction
carriers.
behaviour,
It
implanting
as shown in
observed
the
oxide,
crystals
for
sensitive
GaAs.
cells
tin
by
result
But as
less
the
bandgap
centres
for
from
exceed
the
two charged
result.
of
far
with
clearly
ionisation
scattering
aranged
case
removed
significant
InP
crystal
damaged.
is
considering
sufficiently
all
the
the
when
heavily
still
indium.
necessary
greater,
electron
not
is
are
is
of
The expected
temperature
solar
reduced
mobilities
below
making
voltage.
the
temperature
cause
output
considerably
200'C.
at
anneal
temperatures
explained
the
and
and 5.8
correlates
of
cost
on p-type
increase
held
lower
activation
efficiency
damage is
The amount of
low
A heterojunction
techniques.
film
already
the
and
cells
solar
may
donor
and are
electrons.
producing
scattering
as a
149
feature
The most curious
the
in
peak
(fig.
500'C
around
deep donors
out
anneal
out
the
absorbs
the
of
silicon
the
compensation,
(fig.
5.12),
(7-3)
is
For
have
damage
profile
the
only
be
also
being
5-5).
in
Conversely
during
implantation
correspondingly
and
room temperature
implant
be
to
about
i
100
70
in
specific
the
10-6
L
this
without
The
depth
the
use
as the
etch
specific
contact
This
Hall
etch
depth
depletion
becoming
cannot
order
of
produces
compete
with
resistivity
requires
and strip
has
resistivity.
to
contacts
and so the
of
one
contact
ohm. cm2-
1019 electrons/cm3
a
concentration
implanted
contacts
around
in
concentration
roughly
carrier
drop
ion
carrier
Very
surface
or
alloyed
surface
I.
chapter
in
alloyed
of about
unreliable
below
in
of magnitude
conventional
only
overlayer
a high
for
increase
laser
doping
centres
Comparison of contacts
orders
will
to
reduced.
been demonstrated
three
deep acceptors
damage resulting
(fig.
nitride
of
the
acceptors
greatest
implants
particularly
The requirement
magnitude
the
of
majority
of
some
acceptor
the
of
shallow
the
is
temperatures
at
The damage may
with
regions
implants
that
these
750'C.
above
in
of
compensation
is
allowing.
and
dependent,
created
addition
500'C
donors
temperatures
at
preferentially
greater
above
hot
Se+/cm2
An explanation
shallow
deposition
energy
the
5-7).
anneal
the
compensate
Io15
when annealing
activity
the
of annealing
a surface
is
width
measurementý'are
be reduced
inaccurate.
This
much
is
150
the
due to
probably
oxide.
It
value,
the
is
that
current
carrier
concentration
If
level,
the
all
surface
compensation,
near
for
the
deep donor
as
the
the
greater
(chapter
6-3).
acceptor
compensated
a
very
band
and
higher
energy
3kT
the
the
of
region,
be
might
samples
contact
the
little
depletion
but
on the
exists
valence
the
This
thin
of
has
within
surface
higher
is
which
ionised.
had
also
material
the
near
of
surface
profile.
contacts,
resistivity
contact
may be that
It
fully
are
damage
the
as the
resistivity
carrier
to
gets
bend in
bands
donors
had the
level
level
contact
properties
electrical
sheet
deep
ohmic
non-alloyed
Capacitance
Therefore
a given
native
an anomolous
doping
by assuming
to improve
barrier
this
for
possible
from
the
of
responsible.
be derived
expected
level
being
must
the
implants.
yields
step
signal.
importance
on
first
capacitance
Unfortunately
effect
the
thickness
swamps the
or estimated
measurements
greatest
not
a 20-30
of
again
is
leakage
Fermi
found
oxide
surface
profiling
then
growth
also
voltage
Fermi
rapid
i
which
resisitivity
layer
of
surface,
strongly
the
pinning
effectively
the
raising
height.
Another
formation
of
problem
the
spread
grown
barriers
Schottky
in
native
introducing
semi-conductor
deliberately
with
contact
to
to InP
resistivity
non-alloyed
layer
oxide
ohmic
between
(68).
the
It
is
the
and the
barrier.
an additional
improve
contacts
rectifying
was noticeable
was produced
by the
metal
This
oxide
properties
that
layers
the
the
is
of
lowest
on which
151
the
gold
adhesion
did
not
adhere
well
contacts
also
alloyed
in
necessity
the
using
resistivity
measurements.
is
to
expected
In
dope the
technique
is
employed
a vertical
contact
for
Strack
the
laser
Heavy doping
in
the
the
and for
is
semiconductor
of
contacts
to
observed
densities
effect
at which
(section
dopant
and the
doped to
the
on
measurements
tunnelling
the
(section
6.2).
is
mechanism
(21).
Lowering
of
contacts
no doping
the
of
At higher
can diffuse
in,
solubility
limit
the
tin
from
producing
The
the
contact
metallisation
contacts)
this
reason
that
work
Cox
of
&
the
the
presence
metal
known that
reduced
other
barrier
melting
low contact
this
the
the
energy
Hall
InP melts
thick
layer
point.
' Hall
model
and so
high
resistivities
in
is
by
measured
a relatively
through
for
the
by
systems
height
6.1)
densities
confirm
silver
is
for
is
the
at
mechanism
be
(section
producing
of
the
surface
only
It
InP can
energy
contacts
the
suspected
Sn and Ag/Sn
can occur
surface
silver
3-3).
for
not
height
both
method
in
contacts.
barrier
for
discussed
to
alloying.
such as nickel
the
and
problem
similar
structure
the
unambiguously
this
by laser
on InP
laser
alloyed
contacts
and this
the
where
ohmic
(81)
Some of
highlights
(i. e.
suitable
alloyed
of
particular
forming
sintering
at
not
gold
contacts
correct
semiconductor
TLM
the
for
Another
the
of
the
to determine
resistivity
use
which
and this
surfaces
concentration.
the
to
scatter.
adhesion
clean
contact
one was
layers
a greater
had poor
carrier
surface
chapter
had
obtaining
in
problems
the
was good whilst
layers
field
region
observed
grown
from
152
the
dual
hence
It
than
achieved
tin
dopant
to promote
was.
how
The
use of
nickel
The reason
for
adding
the
and
adhesion
line
so this
well
study
of
the
would
seem
of
contact
seem
would
of
of
what
as a "wetting"
is
based
silver
loss
regardless
it
be
might
may reduce
activity
same effect
and
contact
However,
the
the
tin
minimum
metallisations
increase
dopant.
the
doping
source.
and other
hence
and
tin
a pure
factor
the
greater
may have
as it
equally
adhere
from
of
solubility
and increase
obvious
other
or
undesireable
the
loss
the
level
not
a major
phosphorus
dissolved
is
diffusing
is
phosphorus
doping
the
reduce
resistivity.
the
may inhibit
metallisation
agent
to
appears
to
be
the
most profitable.
(7.4)
Conclusions
and
contacts.
However
competi tion.
heats
diffusion
in
The
devices
detectors.
fabrication
which
could
is
stuck
a
down
is
most
a
for
formed
support.
techniques
in
is
alloying
the
at
the
the
bulk
very
whilst
thin
of
the
The major
back
it
can
be
dopants
and optical
device
cool
may
wave devices
millimetre
the
that
so
acceptor
such as LED/lasers
direct
surface
surface
for
serious
resistance
not
laser
laser
of
low
are
a micron)
junction
advantage
to
produce
beneath
to keep
have contacts
can
of
than
deeper
p/n
The ability
be a
(less
diffusion
with
the
advantage
major
dopants
This
both
techniques
two
the
layer
a thin
of
eliminated.
implantation
ion
alloying
only
that
has been demonstrated
It
of
the
disadvantage
contact
of
laser
153
laser
or indeed
alloying,
decomposition
the
of
devices
planar
On the
furnace
forming
regions
both
employ
implantation
top
contact
or
techniques
implanted
laser
problem
for
out
application
fabrication
form
the
p/n
laser
formation
of
ion
implantation
suitable
for
are
is
are
a
ohmic
successful,
device
being
promising
has
to
be
Also
any
to
the
subsequent
implanted
proton
might
usefully
IMPATT's
forming
using
the
ohmic
alloying.
differing
already
but
in
MISFET
above.
InP
of
suitable
problem
which
junctions
using
a
implanted
the
of
the
the
alloying
carried
by
maintained
layer
whole
noted
is
p-type
contacts
application.
One
ion
an all
resistivity
lost.
the
summary,
alloying
high
to
to
not
with
problems
to
have
techniques
ion
In
diffusion
the
the
be
would
areas
topographical
no
However, the
would
or
anneal
whilst
to
is
are
layers
and recently
(69).
leading
serious
surfaces
implanted
there
devices
isolation
proton
ion
of
has been reported
annealed
finish
mirror
Therefore
planar
the
those
be a
could
is
general,
particularly
This
contrary,
encapsulant.
in
as FET's.
such
annealing
final
surface,
by metallisation.
covered
InP
annealing
used
solution
by
contacts
but
laser
complementary
Ion
structures.
for
actual
looking
devices
for
an
154
(7-5)
Further
as
Further
and laser
implantation
Both
results
work
ohmic
regards
on the
information
by combining
anodic
the
to
etching
profiles.
The
importance
for
measurement
actual
Hall
to
n-type
could
be
successive
is
the
and
with
derived
and
concentration
carrier
InP.
chemical
concentration
be compared
usefully
encouraging
or
mobility
of
critical
of
results
resistance
this
results
on
contacts
half
of
the
at
degree
of
of
measurement.
native
will
sintering
occur
Once the
conditions
been
self-aligned
contacts
might
formed
anyway in
thermo-compression
for
bonding
producing
these
non-alloyed
gate
MISFET-s.
(see
have advantages
for
This
processes
to
contact
I).
be
through
surface.
mounting
contacts
appendix
the
might
metal
the
lowest
the
complicate
and soldering
the
probe
although
the
on
monitor
point
resistivity
device
many
found
also
contact
to diffuse
contacts
inevitably
oxide
such as
have
in
carrier
to
four
of
does
remove
peak
etching,
substrate
improvement
the
steps
by
of material
conducting
Further
the
be possible
should
sucessive
with
by sintering
obtained
It
to
be used
could
revealing
surface.
etching
a
etching
profile,
and removal
measurements
presence
or anodic
implant
an
concentration
any
carrier
resistivity
The same chemical
the
with
measurements
contact
could
layers
ion-implanted
surface
given
formation
contact
produce
near
have
alloying
a package.
resistivity
should
benifit
These non-alloyed
Gunn oscillators
with
an
155
ohmic
than
rather
an injecting
to be investigated
do remain
damage resulting
effect
in
presented
is
under
operating
field,
device
I are
to
necessary
temperature
dopant
intentional
chromium,
The problems
in
dopants
temperatures
to
appear
implants.
The problems
several
(75),
for
strip
or
volume
might
be
stoichiometry
in
a similar
tried
in
the
raising
by implanting
manner
to
scanning
(77)
the
lamp bulb
the
hole
phosphorus
use of
electron
from
to
the
the
are
the
most
Another
concentration
is
gallium
with
for
of
a
laser
promising
approach
to maintain
example,
selenium
of
with
or
heating.
with,
order
order
beam (76)
which
donor
with
decomposition
surface
annealing
of
p-type
significant
compared
a furnace
or
anneal
for
reduced
rapid
source
is
is
for
higher
poor
both
iron
as
severe
(73)
and,
for
(74),
production
more
high
of
substrates.
in
employed
light
diffusion
tin-doped
time
electric
implantation
such
diffusion
available
incoherent
the
impurities
also
migrate
The
remove
by
still
annealing
heater
to
necessary
is
of
commonly
Methods
seconds.
graphite
the
if
minutes
be
might
and high
Furthermore
which
activity
lessened
are
(16,31,72).
InP
electrical
are
in
diffusion
of
Extended
reBect.
defects
epi-layer
have been found
which
respults
performance.
unwanted
and
this
temperature
necessary
the
degrade
damage may itself
initial
remaining
microwave
cycle
annealing
in
the
whether
has a de trimental
although
of high
the
seen
dose implants
if
out
conditions
degrade
to
to be
encouraging
find
Some problems
contact..
remains
performance
appendix
study
It
such high
from
the
on
cathode
cadmium
for
GaAs
156
(78,79).
A further
those
class
for
damage,
of
the
in
a level
be
could
investigated
This
material.
example
protons,
using
of
centre
the
bandgap
are
used
are
be
can
oxygen
InP can be doped with
the
Alternativly
gases.
which
semi-insulating
producing
production
ions
of
or
by
noble
an impurity
having
by Fe, Cr and
as possessed
Co.
higher
If
temperatures
short
are
increased.
for
doping
a double
temperatures
has proved
successful
of pin-holes
is
is
an
amorphous
found
is
in
layer(chapter
both
a dielectric
The encouraging
up.
Further
However
4-3).
work is
some guidelines
results
dioxide
encapsulants
a
Some
and
However
ambient
for
Other
The formation
problem.
so good with
a
even higher
and silicon
this
particularly
is
phosphorus
For
dielectric
with
eliminates
quite
without
be developed.
and could
encapsulant,
surface
using
not
and
nitride
silicon
encapsulant
up to 750'C.
up to 800'C.
a common fault
quality
with
(35)
a PH3 ambient
use of
surface
cap of
Used
nitride
silicon
with
temperatures
annealing
the
of
quality
temperatures
dioxide
even if
annealing,
shown that
InP for
for
have used silicon
workers
the
work has
This
encapsulant
useful
demands on the
the
times,
for
for
the
as it
annealing
sample
with
advantage
may
an
be
and a PH3 ambient.
of
necessary
can be
laser
to
alloying
find
the
offered
:
should
optimum
the
be followed
metallisation.
use
of
a
low
157
the energy
reduces
thereby
melt,
in
a
the
the
as
InP
surroundine
actually
conventional
high
temperatures
forming
composition
or gold
found
but
magnesium,
in
to
going
Another
major
the
problem
of
should
more control
profitable
sputtering
give
to
use
combined
compositional
metal
with
data.
benefit
InP as conventionally
(20).
alloyed
If
alloyed
Initially
the
such as gold-zinc
be
might
reliability
is
contacts
diffusion
technique
electron
the
Laser
may be variable.
this
Auger
the
contacts.
which
profiling
Again,
may be of great
in
a
the
alloyed
some benifit
over
6 pulse
to be
alloys
of
the
to
akin
melts.
to existing
based
platinum
penetration
give
again
more
mixtures
resistivity
contact
be similar
could
alloying
to p-type
ohmic contacts
have a high
contacts
of
use
novel
may allow
laser
be
with
to
The InP may not
the metal
only
which
reached
The
laser
the
platinum
damage
reduce
ruby
may
mechanism
in
alloying
sucessfully.
in
the
with
forming
up to a millisecond.
extending
but
melt
may
again
interesting
silicon
of
aim
to use a free-running
is
duration
envelope
the
which
approach
and
The
results
gold,
A particularly
platinum
with
absorber
Another
silicide.
use
silver
and
to
InP.
compared with
required.
to
is
InP
underlying
robust
mass contact
density
energy
the
damage to the surrounding
the
thermal
considerably
germanium,
for
was particularly
of development
silicon
work
necessary
reducing
lower
much
reducing
line
density
based contact
silver
this
in
layer,
top
reflectivity
and
such
spectroscopy
such a sophisticated
it
as
depth
of
alloying
will
ion
be
beam
(AES)
to
technique
is
158
not
a cross
available
sawing
or
it
A final
a
as
simple
even
features.
as for
to deposit
a
ion
metallisation
the
or
lattice
matched
the
to
InP,
work
been
techniques,
higher
performance
integrating
amplifiers
areas
small
needs
for
will
selectivly
From the
above
the
it
GaInAs
contacts
ability
of
prove
InP
and
The
and the
to
relating
in
Almost
highly
with
may
no
compounds
Although
ion
a
families
these
substrate
ion
to
applicable
cost
same
off
anneal.
GaInAsP.
out
lower
existing
necessitate
as the
implantation
optical
to
dope
invaluable.
can be gathered
to
and
be
would
and etch
can be fabricated
the
the
and quaternary
carried
and
in
a metal
isolation.
to be done to understand
forming
are
on
contact.
InP both
ternary
lasers
onto
case
for
alloying
proton
and
this
the
has
detectors
In
to
look
contacts
metal
subjected
is
successful
devices.
a
be
the
to
alloy
not
that
of
exception
laser
need
laser
to
is
the
and
metallurgical
The procedure
then
developed
extent
to
implantation
with
not
techniques
lesser
greater
layers.
potting
the
alloying
depositing
is
as
reveal
and form
dopant
and relating
such
laser
dopant.
of
the
subsequent
ion
implanted
that
are
implantation
for
before
advantages
may
technique
layer
thin
dopant
of
cleaving
doping
same manner
All
method
alternative
surface
any remaining
sectioning
fully
related
that
much
and optimise
compounds.
exciting
the
work
conditions
159
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A1665
163
APPENDIX I Devices
Two
fabricated
have
structures
been
as an integral
implantation
fabricated
the
of
part
current
flow
device
and one a planar
was a
Gunn
diode
oscillator
contact
(VPE)
epitaxy
phase
silver
is
contact
together
field
which
layer
was implanted
layer
was
ten
surface
with
a
"Miller"
of
of
diffusion
0.04
the
Se+/cm2
micron
hot
concentration
the
when
account
is
for
1016
and
giving
confidence
after
barrier
are
the
carrier
the
implant
taken
at
implantation
that
at
electrons/cm3)
visible
doped
a
seen
762 C for
layer
at
the
(78)
and
depth
is
of
of
between
little
damage
the
the
has
a
high
evidence
length
(around
implant
0.3
the
(fig.
C-V method
Debye
either
profile
indicates
there
the
the
.
surface
(excluding
implant
at
epi
whilst
height
on the
and
of
surface
concentration
based
profiler
of
before
the
keV
a PH3 ambient
injection.
which
The usual
50
at
The
a high
(81 ).
highly
electron
to obtain
differences
significant
in
effective
activation
"spike"
thin
thin
the
automatic
The carrier
level
1.7-1012
vapour
height
creates
with
by
substrate.
barrier
electron
a silver
grown
(n-1018/cm3)
injection
the necessary
was possible
layer
hot
a
device
made by alloying
the
annealed
one a vertical
:
The vertical
"spike"
doped
created
It
1.0.
reduce
reduces
which
achieves
to
and then
This
minutes.
doped
heavily
causes
heated
on a tin
sintered
a thin
with
device.
(n-1015/cm3)
doped
to a lightly
process
normally
ion
employing
or
of
No
micron.
taken
profiles
surface
been
doping)
annealed
and
164
that
the
annealing
have
conditions
impaired
not
the
epitaxial
layer.
the
anneal
the
same manner
as for
ordinary
at
300 C
Following
in
the
contact
was
sintered
injection
required
ratio
in
processed
sinters
diffusion
of
silver,
be much less
in
the
dose
implant
the
desired
These results
devices
processed
at
growth
and
excellent
results
on
be applicable
that
the
cathode
implanted
but
five,
required
in
sample.
minute
the
InP
(21),
By
increasing
it
energy
lowering
otherwise
Obviously
problem
ion
the
of
one
current.
the
the
produce
not
implanted
will
be
should
to
give
the
best
an efficiency
of
required
the
encouraging
7-4W with
was
better
slightly
same time.
device
the
than
ion
silver
need no longer
contacts.
have
could
be
One further
be made of
silver
given
(1)
Optimisation
better
give
in
devices
devices.
conditions
conventional
improvements
alloyed
implanted
and
the
which
conventionally
to
and
Subsequent
processing,
performance
alloyed
highly
GHz
and annealing
microwave
conventionally
are
were
epitaxial
improve
to
piece
barrier
17.4
at
of implantation
cathode
another
reducing
results
result
also
silver
ratio.
12.2%.
should
devices
However
a serious
exact
and the
minute
similar
the
of
the
injection
RF
is
and/or
The microwave
pulsed
a
give
case
I
manner
which
to produce
possible
the
to
390 C
for
was
identical
an
at
which
into
were processed
devices
30%.
of
sample
same epitaxial
layers
expected
uniformity
advantage
(to
give
to
than
is
the
165
required
Shottky
soft
metallurgical
implantation
an enhancement
FET (MISFET).
to
are
that
by
a
The structure
reduces
is
CVD process,
and
InP.
implantation
in
an anneal
a PH3 ambient
(section
to produce
formation
of
of
dioxide
in
over
the
oxygen
source
dioxide
silicon
The
600 C.
drain
over
how the
rises
gain
drain
with
parasitic
ideal
regions
was
drain
for
contact
to
metals
an aluminium
gate
holes
then
of
was aligned
opened
were
layer
a
in
the
and drain.
has
with
of
in,
the
identical
decomposition
Finally
by
has been shown
by pyrolytic
I-2b)
per millimetre,
were
deposited
source
milliSiemens
"wells"
and alloyed
device
(fig.
and
200 keV followed
processing
gap and contact
the
problem
implant
and
doped
deposited
340'C.
at
This
doped
Source
was
fabricated
characteristics
source
at
Further
InGeAu were
of
silicon
silane
1014 Se+/cm2 at
deposited
iron
and drain
of
heavily
be
isolation
The source
is
and
differences
but
can
the
by ion
I. 2a
significant
substrate
elimenates
substrates.
consisting
figure
The most
the
5-2)
contacts.
non-implanted
for
chosen
semiconductor
grown by oxidation
not
This
insulator
in
shown
capacitance.
parasitic
by hot
formed
is
dielectric
semi-insulating
be
can
has been fabricated
mode metal
MOSFET.
silicon
a
the
that
structure
planar,
is
but
sintering)
on InP.
stability
The other,
similar
on
gate
increasing
resistance.
the
a
maximum
In
width.
gate
bias
This
transistor
usual
gain
of
particular
about
8
note
requires
a low
demonstrates
the
which
166
beneficial
drain
regions.
(fig.
I. 2c)
the
to
required
the
oxide
form
the
tracer
Apparently
annealing
has
in
in
:
the
Some of
as
sodium
voltage,
the
on
the
edge of
in
these
has
the
curve
effects
no
are
effect
or
damage
to
an implant
mask to
frequency
is
gain
is
much
shown recently
the
a
no
reduced
improvement
RF
is
a self
that
and
results
to
use
a
the
use of
to
aligned
give
useful
are
available
even
higher
gain
improvement
is
improvement
The
parasitic
It
transistor
to
dose
can
as
high
capacitance
structure.
gate
in
metallisation
structure.
sensitive
molybdenum
gate
gain,
the
A great
aligned
by a self
increased
this
and
implantation
outstanding
have
device.
the
particularly
treatment
annealing
create
(69)
possessing
considerably
implanted
ion
using
deposition
accompany
should
of
not
dielectric
ion
the
performance
although
the
active
feasibility
whilst
devices
conventional
which
but
either
and
threshold
such as loops
electrically
shows the
MISFET's
improvements
expected
the
reduced
device
This
of
damage
also
level.
negligible
InP
the
low
such
up to
be expected
is
potential
right
effects,
might
characteristics,
abscent.
for
extend
and so damage induced
channel
the
negative
a
and
implantation
ions
in
source
surface.
by positive
to
regions
the
that
a shift
channel,
leakage
semi-conductor
causing
implanted
The
gate.
the
may have been caused
in
drain
source
may be presumed
degraded
not
implanted
resistance
bias
zero
and so it
leakage
trapped
4
The
has
annealing
low
the
of
effects
has been
withstand
the
characteristics,
date.
implants
A
further
and produce
167
non-alloyed
In
produced
alloyed
is
ohmic
summary,
results
contacts.
to be expected
conditions
should
contacts.
both
these
comparable
ion
to
As both. these
that
structures
conventional
devices
devices
first
optimisation
produce
implanted
even better
were
of implantation
performance.
produced
have
by
attempts
and annealing
it
04
ý--l
_0
N)
CD
M
C3-
C)
-pC)
C)
.
pi
c+
0
C3rD
0i
tA
c:: )
U3
CD
kj.
F(D
0
F-t
>0
oN
CD
c:: )
CD
m
CO
CD
m
C+
0
Ul
cylý
n( cm-3)
--1
Source
ohmic
S'O2
Gate
Drain
ohmic
rL--j
n+
71
P-type or Semi-insulating
Fig.
I. 2a Cross-section
Fig.
I-2b&c
Source-drain
implanted
of
a self
aligned
characteristics
MISFET.
gate
for
MISFET.
an ion
170
APPENDIX II
Physical
Material
properties
of
InP
constants
Value
Quantity
Molecular
Units
145-79
weight
Density
4.79
g/cm3
Atomic density
3.96.1022
atoms/cm3
Lattice
constant
5.87
A
Thermal
constants
Value
Units
1058
C
594
jIg
Quantity
Melting
Latent
point(at
21 atm. )
heat of fusion
Thermal conductivitY(300K)
0.68
Specific
0.31
J/g. K
4.5-10-6
per C
Coeff.
heat
of expansion
--- J/cm. K
171
Electronic
properties
Quantity
Value
Units
Band gap (30OK)
1-35
eV
Dielectric
const.
Effective
LF
12-35
Optical
9.6
mass
electron
0.069
M
e
light
hole
0.078
Me
heavy
hole
0.4
Me
electron
4600
CM2/Vs
hole
150
CM2/Vs
Value
Units
Lattice
mobility
Optical
constants
Quantity
Refractive
index
Reflectivity
(at
694nm)
3.41
30
%
Absorption
coeff.
3.5-104
per cm
Absorption
edge
0.92
micron