3D sensors
Sherwood Parker (U. of Hawaii)
Collaborators: High Energy Physics Projects
C. Kenney * (Molecular Biology Consortium)
C. Da Via, J. Hasi *, A. Kok, S. Watts (Brunel University)
S. Seidel, M. Hoeferkamp, I. Gorelov (University of New Mexico)
Members of the TOTEM, Czech Technical Univ. and FP420 groups
Kevin Einsweiler, Maurice Garcia-Sciveres (LBL)
G. Anelli, P. Jarron, M. Despeisse (CERN – Microelectronics group)
J. Morse (European Synchrotron Radiation Facility), E. Perozziello
* Collaborators: Structural Molecular Biology
E. Westbrook, A. Thompson (MBC), D. Gnani (LBL)
Outline:
Pixels – replacement / upgrade
•
•
•
•
•
•
•
•
•
•
1. what is needed
2. basic 3D properties
3. how they help
4. results – first irradiation
5. results – speed, active edges
6. results – ATLAS front end chip
7. results – second irradiation
8. improved yield: planar/3D active edges
9. improving yield: current run
10. ongoing measurements
From:
B-Layer Replacement Proposal, Goals
K. Einsweiler, LBNL
December Pixel Week, 2004
Scope:
•Therefore propose that new B-layer have design goal of
3 times design luminosity both for total dose lifetime and
for instantaneous luminosity tolerance. For total dose,
assume that a similar several year lifetime is needed, so
this would translate to about 3 x 1015 n equivalent NIEL
dose and 150 MRad ionizing dose.
•Of course if this proves too difficult, we can always
build several B-Layers using the present technology, and
change them each year or two.
Material Reduction:
•Basic cooling services would remain unchanged, so
reductions must come from electrical services, and from
minimizing overlap fractions by maximizing the active
fraction of the pixel module.
•Present module has active fraction of 71%. With larger FE
die size, a design optimized to minimize non-active region
at bottom of FE chip, and an edgeless sensor technology,
could increase the active fraction to about 90%.
ATLAS Pixel B-Layer Replacement Proposal
ATL-IP-ER-0015 Modified: 30/12/2004 Rev. No.: 2.0
3.3 Sensor technology:
. . . .We expect that, including the effects of charge
sharing between pixels, a minimum signal size of 8-10Ke
will be required in order to achieve greater than 99%
single-hit efficiency for the B-Layer.
Outline:
Pixels – replacement / upgrade
•
•
•
•
•
•
•
•
•
•
1. what is needed
2. basic 3D properties
3. how they help
4. results – first irradiation
5. results – speed, active edges
6. results – ATLAS front end chip
7. results – second irradiation
8. improved yield: planar/3D active edges
9. improving yield: current run
10. ongoing measurements
INTRODUCTION
3D silicon detectors were proposed in 1995
by S. Parker, and active edges in 1997 by C. Kenney.
Combine traditional VLSI processing and
MEMS (Micro Electro Mechanical Systems)
technology.
1.
2.
3.
4.
5.
6.
7.
8.
NIMA 395 (1997) 328
IEEE Trans Nucl Sci 46 (1999) 1224
IEEE Trans Nucl Sci 48 (2001) 189
IEEE Trans Nucl Sci 48 (2001) 1629
IEEE Trans Nucl Sci 48 (2001) 2405
CERN Courier, Vol 43, Jan 2003, pp 23-26
NIMA 509 (2003)86-91
NIMA 524 (2004) 236-244
Electrodes are processed inside the detector
bulk instead of being implanted on the
Wafer's surface.
The edge is an electrode! Dead volume at the
Edge < 2 microns! Essential for
-Large area coverage
-Forward physics
n
n
p
n
n
100
µm
n
134
µm
n
p
n
n
200
µm
n-type bulk
100
µm
+
(signal strength from infra red light beam)
Speed: planar
3D
4.
4.
4.
1. 3D lateral cell size can be smaller than wafer thickness, so
1.
shorter collection distance
2. in 3D, field lines end on cylinders rather than on circles, so
2.
3. most of the signal is induced when the charge is close to the
electrode, where the electrode solid angle is large, so planar
signals are spread out in time as the charge arrives, and
higher average fields for any
given maximum field (price:
larger electrode capacitance)
3.
3D signals are concentrated
in time as the track arrives
4. Landau fluctuations along track arrive sequentially and may
cause secondary peaks (see next slide)
4.
Landau fluctuations arrive
nearly simultaneously
5. if readout has inputs from both n+ and p+ electrodes,
5.
drift time corrections can be
made
6.
track locations within the
pixel can be found
6. for long, narrow pixels and fast electronics,
Potential 3D features from preliminary calculations:
1 ns
p
8 µm
n
50 µm
50 µm
3 ns
3. Fast pulses. Current to the p electrode and the other 3
n electrodes.
(The track is parallel to the electrodes through a cell center and a
null point. V – bias = 10V. Cell centers are in center of any
quadrant. Null points are located between pairs of n electrodes.)
Outline:
Pixels – replacement / upgrade
•
•
•
•
•
•
•
•
•
•
1. what is needed
2. basic 3D properties
3. how they help
4. results – first irradiation
5. results – speed, active edges
6. results – ATLAS front end chip
7. results – second irradiation
8. improved yield: planar/3D active edges
9. improving yield: current run
10. ongoing measurements
Useful properties of 3D radiation sensors:
1 Long tracks can have short drift distances.
2 They can be depleted, and have full sensitivity,
at lower bias voltages.
3 The geometric nature of this means there will
be a low increase of depletion voltage with
radiation damage.
4 They have rapid charge collection, and charges
from perpendicular tracks come in together,
rather than one at a time from the track ends,
so they can make order-of-magnitude shorter
pulses.
5. This speed is maintained, as expected, in
heavily irradiated sensors, and is useful in
reducing capture losses regardless of amplifier
speeds.
6. With fields directed away from, rather than
along pixel or strip boundaries, they have
reduced charge-sharing.
Charge-sharing may be used to improve spatial
resolution, but may also take tracks below
threshold in radiation damaged silicon,
particularly with planar sensors.
7. Active edges provide full sensitivity to within
a few microns of the physical edges, in contrast
with the large dead regions of standard planar
technology (1.1 mm in the Atlas and CMS pixel
sensors which must allow for many concentric
guard rings).
8. Bias voltages can be made to vary across 3D
sensors. (useful if radiation damage and so
depletion voltages are much higher at, for
example, sensor edges near the beam)
BUT
they require more fabrication work.
Outline:
Pixels – replacement / upgrade
•
•
•
•
•
•
•
•
•
•
1. what is needed
2. basic 3D properties
3. how they help
4. results – first irradiation
5. results – speed, active edges
6. results – ATLAS front end chip
7. results – second irradiation
8. improved yield: planar/3D active edges
9. improving yield: current run
10. ongoing measurements
Probe point
R - probe
C - probe
C - sensor
V - bias
3D performance after irradiation
90-Sr β signal in 3D sensor irradiated
by 10e15 SPS protons / sq cm, fully
reverse annealed, no implanted
oxygen, room temperature.
Both sensors 181 µm thick, 100 µm × 134
µm cells, joined in rows for readout.
IR µbeam signal vs. V-bias, 3D
sensor 10e15 55 MeV protons / sq.
cm ≈ 1.8 10e15 1 MeV neutrons.
Measured at room temp. Stored at
low temp. No beneficial or reverse
annealing, no oxygen.
Outline:
Pixels – replacement / upgrade
•
•
•
•
•
•
•
•
•
•
1. what is needed
2. basic 3D properties
3. how they help
4. results – first irradiation
5. results – speed, active edges
6. results – ATLAS front end chip
7. results – second irradiation
8. improved yield: planar/3D active edges
9. improving yield: current run
10. ongoing measurements
planar sensor pulse shape
0.13 µm chips now fabricated – rise, fall times expected to be ≈ 1.5 ns
rise times ≈ 3.5 ns
fall times ≈ 3.5 ns
Resistive (transistor channel) feedback, and so a current amplifier.
90Sr.20v.bias3.1
4.00E-03
30ns
2.00E-03
0.00E+00
1
23 45 67
89 111 133 155 177 199 221 243 265 287 309 331 353 375 397 419 441 463 485 507 529 551 573 595 617 639 661 683 705 727 749 771 793
-2.00E-03
v
5ns
-4.00E-03
-6.00E-03
-8.00E-03
-1.00E-02
time (62.5 ps / point)
Time Pts:
channel 1
channel 2
channel 3
0.13 µm transimpedance amplifier, 90-Sr β source, no collimation
channel 1 self-triggers, other two channels are left, right neighbors
90Sr.20v.bias3.2
3.00E-03
30ns
2.00E-03
1.00E-03
0.00E+00
23
45
67 89 111 133 155 177 199 221 243 265 287 309 331 353 375 397 419 441 463 485 507 529 551 573 595 617 639 661 683 705 727 749 771 793
v
1
-1.00E-03
5ns
-2.00E-03
-3.00E-03
-4.00E-03
-5.00E-03
time (62.5 ps / point)
Time Pts:
channel 1
channel 2
channel 3
0.13 µm transimpedance amplifier, 90-Sr β source, no collimation
channel 1 self-triggers, other two channels are left, right neighbors
90Sr.20v.bias3.3
2.00E-03
30ns
1.00E-03
0.00E+00
1
23
45
67
89 111 133 155 177 199 221 243 265 287 309 331 353 375 397 419 441 463 485 507 529 551 573 595 617 639 661 683 705 727 749 771 793
-1.00E-03
v
5ns
-2.00E-03
-3.00E-03
-4.00E-03
-5.00E-03
time (62.5 ps / point)
Time Pts:
channel 1
channel 2
channel 3
0.13 µm transimpedance amplifier, 90-Sr β source, no collimation
channel 1 self-triggers, other two channels are left, right neighbors
90Sr.20v.bias3.4
2.00E-03
30ns
1.00E-03
0.00E+00
v
1
-1.00E-03
23
45
67 89 111 133 155 177 199 221 243 265 287 309 331 353 375 397 419 441 463 485 507 529 551 573 595 617 639 661 683 705 727 749 771 793
5ns
-2.00E-03
-3.00E-03
-4.00E-03
time (62.5 ps / point)
Time Pts:
channel 1
channel 2
channel 3
4.00E-03
2.00E-03
0.00E+00
-2.00E-03 1 25 49 73 97 121 145 169 193 217 241 265 289 313 337 361 385 409 433 457 481 505 529 553 577 601 625 649 673 697 721 745 769 793
5ns
-4.00E-03
-6.00E-03
-8.00E-03
-1.00E-02
-1.20E-02
Amplifier output, 0.8 ns rise-time step pulse applied to input.
Reasons for dead borders on standard planar
technology sensors
a
b
d
c
a.
b.
c.
d.
space for guard rings
sawed edges connecting top and bottom are conductors
chips and cracks are also conducting and can reach inside the
edges
the field lines bulge out, and should be kept away from b and
cs
Active
Edges
1. etch border trenches
oxide
2. diffuse in dopant
p
p
n
n
3. grow protective oxide
cover
4. fill trench with poly
5. vertical, directed etch
(to dotted lines)
sensor wafer
support wafer
6. turn off sidewall
protection step
oxide
p
p
n
n
7. isotropic etch to oxide
stop
8. additional steps are not
included on this slide
(and note, bonding
oxide to support wafer
not colored )
9.
support wafer
oxide
n and p electrodes can be
reversed
Some work on deep etching:
d
D
0. An old hole (filled).
D/d = 121 µm /11µm.
1. Process steps to improve depth / diameter ratios, and to make holes
and trenches at the same time (middle). Note: s(↕) = s(↔) × cos 20º.
2. True diameter from an angled saw cut: (right). D/d, top holes ≈ 18 / 1.
3. A second, newer STS etcher has just been installed at Stanford. It is
faster and should make somewhat narrower holes and trenches.
4. The old etcher will become a “dirty” one, allowing us to make trench
“dicing” etches on wafers with indium bumps.
X-ray microbeam results for a 3D sensor
40
30
20
inter-strip
boundaries
edge
10
0
0
100
200
300
400
X-ray micro-beam scan, in 2 µm steps, of a 3D, n bulk and edges, 181
µm thick sensor. The left curve is for the edge p channel. The
horizontal scale is in µm; the vertical is arbitrary. The small dip in each
center is from nearby 3D electrodes. The left edge tail is from
reflected gold x-rays and from leakage current.
45-54
36-45
27-36
18-27
9-18
54
45
0
0-9
36
60
27
18
9
0
120
180
microns
240
300
360
Current from scan in an x-ray microbeam, of another 3D sensor with
a photomicrograph of the corresponding part on the right. Grid lines
are spaced 10µm apart.
Some results from the CERN X5 beam test
(120 GeV muons)
Measured hit position in 3D
sensor plane #3 vs. predicted
position from beam telescope.
Fitted 3D sensor width = 3,203 ±4 µm.
Drawn width = 3,195 µm.
Sensor
efficiency = 98%. System efficiency less
due to DAQ, triggering electronics.
Outline:
Pixels – replacement / upgrade
•
•
•
•
•
•
•
•
•
•
1. what is needed
2. basic 3D properties
3. how they help
4. results – first irradiation
5. results – speed, active edges
6. results – ATLAS front end chip
7. results – second irradiation
8. improved yield: planar/3D active edges
9. improving yield: current run
10. ongoing measurements
More typical spectrum
TOT spectrum for the best looking pixel
Possible steps for improvement of fabrication yields:
• Improvement of fabrication steps (as was done for planar / 3D active edge sensors).
• Use solder bumps at wafer scale.
• 2-3 month fabrication run rather than 5 week run.
• Use of P- type bulk so diode junctions always at signal electrodes so one bad
junction does not short bias supply.
• Probably won’t need to reduce signal electrode capacitance using poly-resistor
isolation of bias electrodes, but it remains a possibility.
Outline:
Pixels – replacement / upgrade
•
•
•
•
•
•
•
•
•
•
1. what is needed
2. basic 3D properties
3. how they help
4. results – first irradiation
5. results – speed, active edges
6. results – ATLAS front end chip
7. results – second irradiation
8. improved yield: planar/3D active edges
9. improving yield: current run
10. ongoing measurements
total
n
p
other
charged
hadrons
Displacement Damage in Silcon for Different Particles
1.0E+04
1.0E+03
protons
D/(95MeVmb)
1.0E+02
1.0E+01
1.0E+00
pions
1.0E-01
electrons
1.0E-02
neutrons
1.0E-03
1.0E-04
1.0E-05
1.0E-10
1.0E-08
1.0E-06
1.0E-04
1.0E-02
particle energy [MeV]
1.0E+00
1.0E+02
1.0E+04
Second Irradiation
Irradiation and thermal history of the samples. The samples were irradiated with
10MeV reactor neutrons. The integration and scaling of the spectrum gave a 1MeV
equivalent damage factor of 1.8. The required, resulting, measured by the dosimeter,
and the corrected fluences are respectively:
requested
[n/cm^2]
1e16
5e15
3e15
1e15
5e14
resulting
[n/cm^2]
4.78e15
3.32e15
2.08e15
8.19e14
3.57e14
corrected
[n1MeV eq/cm2]
8.6 e15
5.98 e15
3.74 e15
1.47e15
6.43 e14
7D
7A
7F
7E (unstable before irradiation)
1B
Vladimir Linhart, Tomas Slavicek and Tomas Horadzov: Praha. C. Da Via’, Brunel.
Sample fabricated and checked by J. Hasi and C. Kenney at Stanford
Irradiation organised by S. Pospisil, Praha, . Useful discussions with S. Parker,
Hawaii and S. Watts, Brunel.
Sensor dimensions (7F): 1.855 mm x 0.96 mm x 235 µm.
0.64 3.7 6.0 8.6 x e15
Preliminary calculation of the α parameter
for a volume of 0.418 mm2 is 3.8 x10-17.
This assumes the leakage current to be
generated by the device full physical
volume.
Oscilloscope trace of an alpha particle with the corresponding histogram
(generated automatically by the oscilloscope), measured at –15C using the
sample 7F with 140V bias. The vertical scale is 500mV/div.
90Sr source, self triggered. 7F at –15C. at 140V bias (3.74e15 n/cm^2).
Oscilloscope traces of 3 beta particles measured under the same conditions
and with the same detector. The vertical scale is 50mV/div.
Outline:
Pixels – replacement / upgrade
•
•
•
•
•
•
•
•
•
•
1. what is needed
2. basic 3D properties
3. how they help
4. results – first irradiation
5. results – speed, active edges
6. results – ATLAS front end chip
7. results – second irradiation
8. improved yield: planar/3D active edges
9. improving yield: current run
10. ongoing measurements
Figure 6. Stanford clean room near diffusion
furnaces, looking in the direction of the red arrow.
Pictures of clean rooms like the one preceding
are familiar, but many other things are needed
for high yield, for example: specific, careful
checking of the results of each of the 37 main
steps and of the many sub-steps, cleanliness not
just of the room and air, but of everything used –
tools, chemicals, cassettes, etc.
The deep etching may leave an uneven surface
that makes it difficult to spin on a uniform layer
of photoresist for a following lithography step. If
this step is a deep etch, a thick resist is needed.
They seem to have a higher level of particulates
and clumps of resist.
Active edge fabrication requires support wafers,
which must be oxide-bonded to the sensor wafer
under extremely clean conditions.
The following specific steps were added to the fabrication
procedure for the two-order-of-magnitude larger, 9 cm2 planar /
3D active edge Totem sensors:
1. The wafers were carefully inspected after every litho step. If
defects were seen, the resist was removed, new resist was
applied, and the wafers were re-spun and re-exposed.
2. Defects in the thick resist used for the trench etch were
covered with polyimide.
3. The surface planarity in the region of the dips at the centers of
the poly-filled electrodes was improved by etching the poly off
the top surface, and then repeating the fill and etch procedure.
4. The plasma dice lane was widened from 50 microns to 120
microns. The more open trench prevented the formation of
silicon chips along the trench edges. This seems to have
eliminated this defect class, which caused a 25% loss for the first
batch.
5. Evaporated aluminum instead of sputtered gold was used for
the backside contact.
In the first Totem fabrication run of full-size sensors, only 1 of
28 sensors had 99% or more good strips. After the 5 yield
enhancement steps were added,13 of 20 sensors from the
next run had at least 99% good strips:
RESULTS: full-sized, 512-strip, planar / 3D active-edge sensors, 60V
sensor
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
t4 – 4c
t4 – 5c
t4 – 7c
t4 – 4a
t4 – 5b
t4 – 6c
t4 – 8b
t4 – 7a
t4 – 7b
t4 – 4b
t4 – 8a
t4 – 8c
t4 – 8d
t4 – 5d
t4 – 7d
t4 – 4d
t4 – 5a
t4 – 6a
t4 – 6b
t4 – 6d
leakage current
(µA)
0.7
0.8
0.7
0.7
0.8
0.6
0.9
1.1
0.7
0.8
1.2
1.6
1.9
1.3
0.7
1
-
strips with
defects
0
0
0
1
1
1
1
2
2
3
3
3
3
>5
8
>10
-
% good
strips
100
100
100
99.8
99.8
99.8
99.8
99.6
99.6
99.4
99.4
99.4
99.4
~ 99.0
98.4
<98.0
-
comments
100% at 30V
defect is on back
100% at 30V
testing stopped at 255
hole etched through chip
hole etched through chip
not tested
not tested
Now we must produce similar results for full 3D sensors.
Outline:
Pixels – replacement / upgrade
•
•
•
•
•
•
•
•
•
•
1. what is needed
2. basic 3D properties
3. how they help
4. results – first irradiation
5. results – speed, active edges
6. results – ATLAS front end chip
7. results – second irradiation
8. improved yield: planar/3D active edges
9. improving yield: current run
10. ongoing measurements
Add Yield Improvement Steps – First 10 of 107 steps:
2) CLEAN at WBNONMETAL - YIELD FACTOR: Change chemicals/ Do at
least two spins on the spin dryer
3) CLEAN at WBDIFF - YIELD FACTOR: Change chemicals/ Do at least two
spins on the spin dryer
5) FIELD IMPLANT BOTH THE FRONT AND BACK SURFACES OF THE
WAFERS - YIELD FACTOR : When picking up the double-sided device
wafers, only pick up from the laser edged area of the wafer and Use clean
tweezers
6) CLEAN at WBNONMETAL - YIELD FACTOR: Change chemicals / Do at
least two spins on the spin dryer
7) CLEAN at WBD - YIELD FACTOR: Change chemicals / Do at least two
spins on the spin dryer
8) GROWN THERMAL OXIDE USING TYLAN1-4 - YIELD FACTOR: Load with
delrin tweezers and let wafers cool down before unloading the wafers from
the furnace with the delrin tweezers.
9) PREPARE SURFACES FOR FUSION BONDING AT WBDIFF - YIELD
FACTOR: Change chemicals, definitely for the HCL step prior to fusion
bonding the wafers.
10) FUSION BOND - YIELD FACTOR: Wear face shield to reduce particle
generation. Perform after hours or on weekend when there aren’t many
people around.
Outline:
Pixels – replacement / upgrade
•
•
•
•
•
•
•
•
•
•
1. what is needed
2. basic 3D properties
3. how they help
4. results – first irradiation
5. results – speed, active edges
6. results – ATLAS front end chip
7. results – second irradiation
8. improved yield: planar/3D active edges
9. improving yield: current run
10. ongoing measurements
1. Univ. of New Mexico (following talk)
2. Praha: Cinzia Da Via will travel there next week to continue her
measurements on the irradiated ATLAS pixel spacing sensors:
a. add a trigger for 90-Sr betas after the sensors
b. measurements with flood beam, pulsed, infrared laser illumination
3. infrared laser flood beam measurements: (note: ir diode also ok)
a. pulse time long compared to collection times, short compared to
trapping times and to R (probe) x C (probe + electrode)
b. pulse generator triggers digital scope
c. sweep is long enough to get:
noise and baseline (for subtraction) from trace ahead of trigger,
trapped-charge release signals after trigger
d. on-time average V-signal vs. V-bias gives depleted volume, collection
efficiency
e. RC fall time gives C (electrode); tail gives charge capture information
f. systematic checks will be needed (results should be independent of
laser intensity, exact aim of beam, etc.)