Plasma Quest Limited
Magnetic Data Storage Materials
Plasma Quest Perspective
Barry Holton
Managing Director
January 16th 2006
Tel: +44(0) 1256 740680
www.plasmaquest.co.uk
e-mail: sales@plasmaquest.co.uk
Objectives:
 To tell you who we are!
 To present what PQL sees as the
challenges for deposition technologies
 To indicate where PQL is directing its
materials deposition developments
 To indicate where PQL sees the potential
 To listen
Introduction
PQL is a small R&D company with 7 years experience of
developing, using - and promoting - Remote Plasma Sputtering
as a solution to a wide range of materials and applications,
providing unique solutions and benefits in most cases.
- high rate, low temperature deposition of low stress thin film
coatings with near ideal physical properties
-significantly increased process scope – ‘enabling technology’
- deposition of metals, alloys, insulators and ferromagnetics*
- stable reactive sputter deposition for dielectric thin films
- deposition of high quality transparent conducting oxides (TCO)
- deposition of DLC with high optical transmission
- deposition of polycrystalline silicon for electronic devices
- new waveguide materials and system options for opto-electronics
[*remote plasma allows thick (6mm+) target use]
Hard Disc Developments
Already well established with large companies and their
R&D operations investing heavily.
PQL will not look DIRECTLY at developing in this area,
but it will look to promote its technologies where appropriate
Currently working with Universities of York and Manchester
in a LINK ISD programme to:
“demonstrate the potential of HiTUS technology for the
production of thin films of magnetic materials and other films
suitable for application in the field of magnetic information storage”
(a number of papers have been generated from this project)
What will PQL develop?
PQL seeks to concentrate on “specialist” activities,
where the key characteristics of its technology offer
new opportunities, for example:




High target utilisation
Sputtering from thick ferromagnetic targets
Thin film properties close to bulk
Ability readily to control grain size
PLUS





Readily controllable stress
High rate deposition at low temperature
Stoichiometric deposition from compound targets
Very smooth films
High rate, stable reactive sputtering
Plasma Density Amplification through Magnetic Confinement
Diode Sputtering
(no magnetic field)
Target : -ve bias
Gnd
Low ionisation
efficiency
= low sputter rates,
high pressure
Target current density
0.1 – 2.0 mA/cm2
Plasma Density Amplification through Magnetic Confinement
Diode Sputtering
(no magnetic field)
Target : -ve bias
‘Magnetron’ confinement at target
Target : -ve bias
Gnd
High local ionisation
efficiency
= high local sputter
rates (‘racetrack’)
Target current density
up to 100 mA/cm2
locally
Gnd
Low ionisation
efficiency
= low sputter rates,
high pressure
Target current density
0.1 – 2.0 mA/cm2
Plasma Density Amplification through Magnetic Confinement
Diode Sputtering
(no magnetic field)
Target : -ve bias
‘Magnetron’ confinement at target
Target : -ve bias
Gnd
High local ionisation
efficiency
= high local sputter
rates (‘racetrack’)
Target current density
up to 100 mA/cm2
locally
Remote Plasma
Gnd
Low ionisation
efficiency
= low sputter rates,
high pressure
Target current density
0.1 – 2.0 mA/cm2
Target : -ve bias
Gnd
High remote
ionisation efficiency
= high sputter rates
over full target
Target current density
up to 100 mA/cm2
over full target
Standard System Schematic
SIDE ARM
PLASMA SOURCE
DEPOSITION
CHAMBER
Substrate Holder
Assembly, Shutter,
etc.
Plasma
Path in
Chamber
Source
Electromagnet
Target Electromagnet
Multiple Indexable
Target System
Plasma Source Basics
• External RF antenna (13.56, 40MHz) produces initial low density plasma.
• Combined RF and DC electromagnetic fields accelerate electrons; magnetic
field constrains electron paths and increases average path length.
• A significant proportion of electrons are accelerated to c. 50eV (probe
measurements) – optimum for ionisation of argon gas.
• Combination of long path and high ionisation efficiency results in plasma
density amplification towards plasma source exit – visible by OES.
• Plasma densities in excess of 1013 cm-3 may be achieved at source exit,
limited by ambient gas pressure (90% ionised by OES).
• Measurements show high ion densities, but low ion bias (tens of V) – no
sputtering of unbiassed components.
• Electrodeless system, highly robust and tolerant of reactive gases.
Remote Plasma Sputtering Basics
• DC magnetic field produced by the Source and Target electromagnets
continues to constrain electron paths, essentially ‘directing’ the plasma to
the target – a ‘cascade’ generation process.
• Despite magnetic field variations (30-300G range) and increasing distance
from the source, high ionisation efficiencies are maintained – producing a
high density plasma in front of the target surface.
• In the absence of target bias no sputtering occurs. Increasing (negative)
target bias up to ~100V draws increasing ion current from the plasma.
Sputtering begins during this time for most materials.
• Above -100V bias, the ion current ‘limits’ at a value dependent on process
conditions (Source Power, magnetic field strength, gas pressure). Sputter
rate therefore depends on bias voltage from hereon (approx. linearly to 2kV)
• The plasma itself is unaffected by target bias – giving an inherently stable
basis for the sputtering process. Independent Source and Target operation
allows stable coating over 5 orders of magnitude of deposition rate.
Some Indicative Deposition Rates
 Reactive Al2O3
 Reactive Ta2O5
 Reactive SiO2
 Reactive TiO2
 Fe/Co
240nm/min
125nm/min
100nm/min
100nm/min
200mm Ø target
100mm Ø target
100mm Ø target
100mm Ø target
120nm/min 6mm x 100mm Ø target
Plasma Quest’s Base Technology
High Density Plasma Launch System
(Some Benefits)
•Plasma Densities 1010 to 1013 cm-3
•Plasma Assisted High Rate Reactive Deposition
•High Target Utilisation
•Control of Grain Size
•Sputter from thick ferromagnetic targets
•Exceptional Film Properties eg
•Low Stress Films
•Refractive Index near bulk
•Low absorption
•Very Smooth
•Stoichiometry of compound targets maintained
•Control of Properties
•System retrofittable to existing vacuum processes
•Deposition onto Organic Substrates
•Plasma Clean Facility
AN ENABLING TECHNOLOGY
Some Magnetic Materials Information
University of York - 2005
PQL/UoY 2005
120nm Fe deposited onto 25µm Kapton
<D> (nm)
30000
100
CoFe 20nm films
20000
M (kilogauss)
80
60
40
sample KAP4
10000
0
-10000
20
-20000
200
400
600
800
1000
-30000
-1000
Bias Voltage (-V)
-500
0
H (Oe)
Trinity College Dublin - 2001
Origins of the films
Sample reference
Roughness
Ra (nm)
PQL
MTA-100
0.5 nm
PQL
MTA-101 (A)
0.5 nm
PQL
MTA-104
1.6 nm
Coey et al.
Janko-Si-1
2.4 nm
Coey et al.
Janko-Si-2
2.5 nm
500
1000
Si /Cr /FeCo-2.5nm Cr with different voltage levels for seed
M (kG)
30
20
Cr seed shows good MS
10
AND lower HC ~ 11 Oe
0
29050501
29050502
03050501
04050501
04050502
04050503
-10
-20
-30
-600
-400
-200
0
200
400
600
Field (Oe)
Sample
29050501
29050502
03050501
04050501
04050502
04050503
BP
mbar
5.0e-6
1.6e-6
7.5e-6
1.0e-6
8.5e-6
8.0e-6
Bias
-V
200
250
300
400
500
600
Volume
(cm3)
2.2x10-5
2.1x10-5
2.0x10-5
2.2x10-5
1.5x10-5
2.0x10-5
Ms
EMU
4.1x10-2
3.68x10-2
3.71x10-2
3.7x10-2
2.63x10-2
3.481x10-2
Ms
EMU/cm3
1865
1754
1858
1685
1744
1744
Ms
kG
23.4
22
23.3
21.2
21.9
21.9
Hc
Oe
21
41
11
33
60
64
Production Systems ‘Scale Up’ Issues
• The ‘standard’ HiTUS technology requires a source of similar diameter
to the target diameter to be used. Typically 7.5cm to 20cm diameter
targets are used in our systems (application dependent)
• We have successfully demonstrated Plasma Source operation to 20cm
diameter – potentially allowing use with 30cm targets.
• The Plasma Source requires an RF supply of similar rating to the target
supply – a cost disadvantage.
• Substrate size and deposition rate trade off = bigger targets or multiple
targets are required for large throughput applications. Remote Plasma
systems are disadvantaged due to multiple plasma source cost
implications.
Scale Up Development – ‘Linear’ System
Trials passing the plasma ‘beam’ along a rectangular target show
improved area coating as expected, but …………..
………….we also discovered that a cylindrical target can be placed
within the plasma beam without compromising the beam in any way.
Substantial in-house R&D over the last year has shown that this
configuration has many benefits:
•
•
•
•
•
More efficient use of plasma source – one tenth the power
required
Eliminates need to scale source with target
Greatly increased coating area
Greatly increased coating rates
Retains all HiTUS advantages – improves reactive stability.
Linear System Schematic
Substrate Carrier
Or Web Feed (1)
Cylindrical Target
Plasma Source
Launch
Electromagnet
Substrate Carrier
Or Web Feed (2)
(Note: system shown rotated 90 degrees for clarity)
Target
Electromagnet
Fundamentals of Linear Source Operation
• Critical understanding: the plasma beam from our Plasma Source
essentially comprises two regions:
• A tubular cross section ‘generation’ region
• A more extensive ‘cylindrical’ cross section plasma region
• The former is the main ‘glow discharge’ that visually defines the
apparent plasma ‘beam’ – this must not be obstructed.
• The latter (may be invisible) can be obstructed.
• Thus a target may be placed within the plasma generation tube and
thereby surrounded by plasma without detriment to the plasma itself.
• In addition, the generation tube appears to act as a ‘conduit’ for the RF
energy – plasma generation efficiency is maintained, providing a
uniform plasma density for sputtering from the whole target surface.
Linear System - Target Size Comparison
Linear Source 35cm
20cm
10cm
50cm x 7.5cm dia. Linear Target System
Linear System - High Rate Deposition onto Thin
Plastic Sheet for Flexible Electronics
• A wide range of thin films , from metals to dielectrics, have been
successfully deposited onto 50µm Kapton and 25µm PET
• Films are low stress, controllable from tensile through to compressive
• Film properties are near ideal and unchanged from those achieved on
e.g. glass, and silicon wafers
• Examples of thin film depositions onto plastics (35cm linear target):
•Stainless steel – 80 nm/min at 30cm separation
•Titanium –
100 nm/min at 26cm separation
•Iron –
45 nm/min at 30cm separation
•Aluminium –
100 nm/min at 22cm separation
•Alumina –
115 nm/min at 22cm separation
• System limited – extrapolated potential rates are 2-3 times this.
• Target wall thickness ~ 1.5cm for all targets – including magnetics.
Stress control
800nm Permalloy (NiFe) on 25µm Kapton sheet
Linear System - High Rate Deposition of Ferromagnetic
Materials onto thin plastic film – M-H Loop Data
• 15mm wall thickness low purity iron (mild steel) 35cm linear target
• Target - substrate separation 30cm
• Substrate : 25µm Kapton sheet
• Deposition rate : 45nm/min; Total film thickness : 120nm; Deposition area : 0.2m2
• Zero stress film
30000
M (kilogauss)
20000
sample KAP4
10000
0
-10000
-20000
-30000
-1000
-500
0
H (Oe)
500
1000
Linear System - High Rate Dielectric Deposition
• Linear System uses the same ‘reactive sputtering’ technique as
standard HiTUS – inherently stable process without feedback control
• Uses metallic sputtering target, e.g. Al for alumina, Si for silica. This
allows high rate sputtering – and cheaper DC supplies for metallics.
• Introduce appropriate flow (and distribution) of reactive gas during the
sputter process, e.g. O2 for oxides, N2 for nitrides – or appropriate
mixture for oxy-nitrides.
• High density plasma assists reaction (gas phase or surface) resulting
in deposition of high quality, densified dielectrics at room temperature.
• Fully reacted coatings for optimised process – no free metal inclusion.
•Coatings are generally amorphous (low light scatter).
Linear System - High Rate Deposition of Alumina
onto thin plastic film – Transmission Data
• Reactive deposition from aluminium 35cm linear target
• Target - substrate separation 22cm
• Substrate : 25µm PET sheet
• Deposition rate : 115nm/min; Total film thickness : 1000nm; Deposition area : 0.2m2
• Very low stress film. RI = 1.7
110
Transmission (%)
105
100
95
90
85
80
200
400
600
800
Wavelength (nm)
1000
1200
Linear System – 50cm Target Development
Preliminary Results - tbc
•Prototype system in test, driven by 15cm diameter Plasma Source.
• Target diameter is 7cm – this has proven undersize for the Plasma
Source as expected. Estimated maximum is 12cm.
• System power limited at present (60kW target supply requirement).
(RF requirement is 5kW).
• Achieving full utilisation of target length – i.e. plasma propagates over
0.5m.
• Scaling data according to prior target dependencies indicates that
target rates of 400nm/min will be exceeded – potentially 900nm/min.
• Data shows expected scaling of rate with target size increase – a 10cm
target could therefore further raise this rate to 1400nm/min or more.
(Separation = 25cm)
Concept In-Line Linear Source Coating System Schematic
Plasma Sources
Carrier Plate
9 off 4” dia substrates
Load Lock
Deposition Chambers
Dynamic Deposition Rate > 1000nm m/min
(Continuous feed, Web or carrier plates
(Batch and multi-component target systems also in development)
Load Lock
Contacts:
Professor Michael Thwaites (CEO)
Tel: +44 (0) 1256 740682
e-mail: mike.thwaites@plasmaquest.co.uk
Barry Holton (MD)
Tel: +44 (0) 1256 740680
e-mail: barry.holton@plasmaquest.co.uk
Website:
www.plasmaquest.co.uk
Tel: +44(0) 1256 740680
www.plasmaquest.co.uk
e-mail: sales@plasmaquest.co.uk
LINK Programme Materials
 Rigid Disc Materials
Cr, CoPt, FePt
 Soft Magnetic Films and Interlayers
CoFe
 Antiferromagnetic Materials
FeMn, IrMn, PtMn
 Tunnel Junctions
Al2O3, MgO
Tel: +44(0) 1256 740680
www.plasmaquest.co.uk
e-mail: sales@plasmaquest.co.uk
The Hardware
No Racetrack
Magnetron
Racetrack
HiTUS
Full surface erosion
>90% UTILISATION
Copper
Tel: +44(0) 1256 740680
6mm Cobalt
www.plasmaquest.co.uk
e-mail: sales@plasmaquest.co.uk
“Driving” the HiTUS
Target current/voltage relationship
Target current (A)
1.0
0.8
2.0 kW
1.5 kW
1.0 kW
0.5 kW
0.6
0.4
0.2
0.0
0
200
400
600
800
1000
Applied target voltage (V)
Tel: +44(0) 1256 740680
www.plasmaquest.co.uk
e-mail: sales@plasmaquest.co.uk
Target Current (A)
Range of the HiTUS
0
HiTUS Only
0
Target Voltage (V)
Minimum magnetron plasma
striking voltage and current
(Not applicable to HiTUS)
HiTUS + Magnetron
HiTUS Only
BUT: HiTUS INDEPENDENT of gas pressure !!
Tel: +44(0) 1256 740680
www.plasmaquest.co.uk
e-mail: sales@plasmaquest.co.uk
Comparison of theoretical and actual transmittance vs wavelength for
a 14-layer diagnostic filter
Theoretical
Actual
Tel: +44(0) 1256 740680
www.plasmaquest.co.uk
e-mail: sales@plasmaquest.co.uk
Waveguide action in Ta2O5
Tel: +44(0) 1256 740680
www.plasmaquest.co.uk
e-mail: sales@plasmaquest.co.uk
Optical Emission Spectra for Remote Plasma Source
434.8 nm
Ar+
25000
ni ~ 1013 cm-3
20000
15000
Emission
Intensity
(arb units)
420.0 nm
Ar
10000
Wavelength (nm)
Optical emission at antenna
Optical emission at source exit
438.8
437.3
435.8
434.4
432.9
431.4
429.9
428.4
426.9
425.5
424.0
422.5
421.0
419.5
418.0
416.5
0
415.0
5000