New Pixel Detector Concepts - Arno E. Kompatscher, Tobias Wittig, Alexander Lawerenz, Ralf Röder - CERN Indico
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Competence in Silicon
FuTuRe 2018
Workshop on the Future of
Silicon Detector Technologies
Erfurt
Mar. 5th-6th, 2018
New Pixel Detector Concepts
- Arno E. Kompatscher, Tobias Wittig, Alexander Lawerenz, Ralf Röder -
CONTENTS
1. TENSOR:
Bias grid optimization for quality control of pixel sensors.
2. LAT:
Large area thinned pixel sensors via KOH etching.
3. TRIDENT:
Trenches as isolation for planar pixel sensors.
Processing of 3D-pixel-sensors.
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 2
TENSOR | introduction
• Bias grids are used to short circuit all pixels in
order to do reliable quality assessment (IV-
curves).
• Standard in ATLAS: punch-through structures to Pixel matrix with bias grid
isolate pixels from each other during normal
operation.
• Problem: bias grids act parasitic (unwanted
charge loss) after heavy irradiation.
“Punch-through”:
Troska, Georg, Development and operation of a testbeam setup for
qualification studies of ATLAS Pixel Sensors, Dissertation. - TU Dortmund, 2012 Punch-through
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 3
TENSOR | precursors
w/ bias rail w/o bias rail
• layout modifications
• technological processing steps stay the same
• 1 FE-I4 SCS which houses different variants Ref: Y.Unno, Latest
status of the KEK/HPK
pixel sensor and
understanding with
TCAD simulation. -
Presentation, ITk-
Week, CERN, February
26, 2015.
std
1
Ref: C.Nellist et al. Test beam and clean room studies of ATLAS PPS 2 var
modules with alternative bias rail geometries; 28th RD50 Workshop,
Torino, Italy 3
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 4
TENSOR | objectives
• implementation of „fuses“
• very thin metal traces on top of the final
passivation
• sensor test with short-cut pixel matrix
Removal of fuses afterwards:
• very short etching step
• melting by applying high
currents
punch-through proposed solution
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 5
TENSOR | dummy wafer run
• fuse dummy wafer run finished
• FE-I4 like test matrices
• test structures
• implementation of different fuse widths
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 6
TENSOR | dummy fuse tests
• first tests of “burning” fuses successful
• but: problems with thickness of metal layer
– 25, 50, 150, 300 nm thickness
– too thin for needle: sometimes metal
melted/scratched contact point
– no issue though: pads were only for proof
of principle
• additional test on prototype (2nd wafer run):
wet etching!
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 7
TENSOR | etching tests
not etched etched over-etched
Metal rail (fuse) clearly Fuse etched away Twice the etching time
visible of „etched“
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 8
TENSOR | etching results
• Etching successful
• Very promising: even with
significant over etching acceptable
• With new layout promising cheap
alternative
• More reproducible and cleaner
than burning out (as expected)
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 9
TENSOR | sensor wafer run
Bias rail over bump Bias rail opposite of With pads for needle
openings bump openings (same prober access
position as punch
through in conventional
FE-I4)
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 10TENSOR | summary • Burning tests with dummy wafer run expectedly not very reliable • Etching tests very promising: reproducible results with low risk of failure • Sensor wafer run being finished this week Outlook: • Initial characterization: is temporary metal suitable for IV- measurements? • Flip chipping with FEs and glass wafer dummies • Tests with x-ray source © 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 11
CONTENTS
1. TENSOR:
Bias grid optimization for quality control of pixel sensors.
2. LAT:
Large area thinned pixel sensors via KOH etching.
3. TRIDENT:
Trenches as isolation for planar pixel sensors.
Processing of 3D-pixel-sensors.
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 12LAT | introduction
• Large areas of Silicon detectors
Morettini, ITk pixel:status report, Joint Pixel Sensor Meeting, TU Dortmund,
• Possible areas at ATLAS: 11.06.2015
– Pixel detector: 8.2 m²
– Strip detector: 193 m²
• Thinner sensors have advantages:
– Higher field strengths
– Lower trapping probability
– Increased charge collection
• Problem: wafers very unstable/brittle
whenLAT | reduction of thickness
• Alternaitives to support wafers
• Cavity etching
• Expertise present from MEMS
• Smaller areas
• Smaller thicknesses
• Transferability to radiation
detectors
• Increased stability due to thicker
frames on sensor edge
• Active area inside membrane
• Thicknesses down to 50 µm realistic
• Dicing on membrane edges possible
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 14LAT | dummy wafer run
• Prototype-run with MPP München
• Starting thickness 525µm
• Target thickness 150/100µm
• IR-thin-film measurements confirm:
~125±5µm
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 15LAT | 4“ sensor wafer run
• Cooperation with MPP Munich
• n-in-p ATLAS pixel sensors
– FE-I4 Quad-Sensors
(~4x4cm²)
– FE-I4 SCS
• diodes, test structures
• starting thickness 525µm,
target thicknesses 150/100µm
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 16LAT | 4“ sensor wafer run
• results of dummy wafers could
be reproduced
• large fraction of the area quite
homogeneous
• however, significantly thinner
values still present close to
the membrane edges
• possible improvement with
rotating stage
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 17LAT | 6“ wafer run
Dummy run: Sensor run:
• Similar results to 4“-studies • Big variations in thickness
• ±8 µm variation • Fluctuations within 50 µm range
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 18LAT | SIMS measurements
• SIMS measurements of the doping
profile have been performed on the
membrane and on the four slopes
• Slopes are doped lower than the
membrane itself:
• can be explained by the tilted
angle between the slopes and the
penetrating ion beam
• measured orthogonally to the
slope surface Mem-
brane
• Doping concentration at the slopes is
still high enough to guarantee sensor frame
functionality
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 19LAT | stress tests
• Shear stress is measured by the polarisation state of a reflected
(linearly polarised) laser beam
• Shear stress for different thicknesses are similar
shear stress
(unit DU)
100µm membrane thickness 150µm membrane thickness
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 20LAT | surface roughness
• small scale (AFM measurements)
• Very satisfying results
• average fluctuations in the order of a
few 10 nm
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 21LAT | bump tests
flip chip done at IZM Berlin
data by A.Macchiolo, MPP • mostly very good bump
yield
• just one failed assembly
• remaining assemblies
have (if any) only some
missing bumps in the
corners
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 22LAT | double sided processes
Future developments:
• Continuation project: DLAT
• Transfer of LAT thinning processes
to double sided sensors (e.g. ATLAS
n+-in-n)
• Challenge: lithography in the cavity
• Preliminary tests promising, slight
complication only: quality of
photoresist adhesion on oxide
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 23LAT | summary
• Successful thinning of 4“- and 6“-wafers from 525 µm down to
100 µm.
• SIMS and AFM measurements very satisfying: only slight variations
in implantation quality and surface roughness.
• Sensor wafer runs successful: sensors operable after thinning.
• New project: LAT applied to double sided sensors (e.g. n+-in-n).
• Process also being used for TREX: see presentation by T. Wittig,
„Alternative Implantation Techniques“, today at 15:50.
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 24CONTENTS
1. TENSOR:
Bias grid optimization for quality control of pixel sensors.
2. LAT:
Large area thinned pixel sensors via KOH etching.
3. TRIDENT:
Trenches as isolation for planar pixel sensors.
Processing of 3D-pixel-sensors.
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 25TRIDENT | objectives
• Production of planar and 3D sensors
• “Trenched” planar: pixel isolation
via 30-50 µm trenches between
pixels
• 3D-sensors: control production of
known technology
CERN EDMS document 903424, ATU-RD-MN-0012
Aim:
• make trenched planar sensors for
easy prototyping and enable
variable geometries
• Cost reduction for quick
prototyping © Tobias Wittig
(TU Dortmund, CiS)
© Sonia Fernandez-Perez
(CERN, DECTRIS)
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 26TRIDENT | 3D vs. trenched planar
Lithographic steps
3D-sensors Trenched planar sensors
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 27SUMMARY
TENSOR:
Alternatives to permanent bias grids being
investigated; promising results with a posteriori
etching of metal rails.
To be done: analysis and characterization of sensors.
LAT:
Large area KOH-thinning successful; promising
technology for numerous applications.
Technology being applied to double sided processes.
TRIDENT:
3D-processing being investigated: 3D-sensors, 3D-
structured planar sensors.
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH 28Thank you for your attention!
Arno E. Kompatscher
akompatscher@cismst.de
Konrad-Zuse-Str. 14 Telefon: +49 361 6631410
© 2018 CiS Forschungsinstitut für Mikrosensorik GmbH
99099 Erfurt, Germany Telefax: +49 361 6631413 Copyright: All rights, especially the right of reproduction
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