experience with silicon detectors and module construction

13./4. July 2008 Super-Belle proto-collaboration meeting

Experience with silicon microstrip detectors and module

construction at HEPHY Vienna

Thomas BergauerInstitute for High Energy Physics (HEPHY)

of theAustrian Academy of Sciences


Contents

• Introduction• Silicon microstrip sensors

– Sensor design– Sensor characterization– Process monitoring– Logistics for mass production

• Module construction– Module assembly– Bonding– Testing

• Test beam experience– One example of last test beam


Introduction• Austrian Academy of

Sciences– Largest non-university research

organization in Austria– 70 institutes, commissions and

research units with ~1100 staff

• Institute of High Energy Physics (HEPHY)– Located in Vienna– Founded in 1966 as the

Austrian contribution to CERN– 55 persons staff plus some

students

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Institute of High Energy Physics

Participation in Experiments (Hardware & Analysis):


Institute of High Energy PhysicsOrganizational structure:

• Projects– BELLE Experiment (Christoph Schwanda)– CMS Analyse (Wolfgang Adam)– CMS Inner Tracker (Josef Hrubec)– CMS Trigger (Claudia-Elisabeth Wulz)– DELPHI (Wolfgang Adam)– International Linear Collider (Winfried Mitaroff)– Theory: Supersymmetry (Helmut Eberl)– Public Relations and Outreach (Wolfgang Lucha)– VCI Conference (Manfred Krammer)

• Departments– Algorithm- and Software Development (Rudolf Frühwirth)– Electronics 1 (Anton Taurok)– Electronics 2 (Markus Friedl)– Semiconductor Detectors (Thomas Bergauer)– Computing (Gerhard Walzel)– Mechanical Workshop (Anton Taurok)


History of Semiconductor Detector Research at HEPHY Vienna

• HEPHY Vienna participated in construction of– DELPHI Si Vertex Detector– CMS Tracker

• Moreover, we participated in different CERN R&D collaborations– RD20– RD42 (Diamond detectors)

• Therefore we have large expertise with silicon detectors and their mass production

• However: Expertise is limited to strip detectors (no pixel sensors)


Available manpower

• Manpower available in Semiconductor Group:– 2 FTE scientists– 1,5 FTE students– 1,5 FTE technicians

• Long term contracts with technicians have shown to be an advantage (e.g. during CMS module construction:– huge effort necessary in short time– other institutes hired people on short term basis (“hire & fire”)– Disadvantage: lack of experience caused higher failure rate)

Part of HEPHY semiconductor group staff


Sensor Design

• ICStation from Mentor Graphics available as Design tool

• Design is not drawn but actually “programmed”– using simple programming

language (C like)

• Therefore, it is easy to changeany parameter and re-createthe full sensor within minutes– e.g. width of metal overhang


Design processed at fab

• Design of test structures (based on CMS Design) was successfully fabricated by Institute for Electron Technology (Warsaw, Poland)

• They have experience with SOI and chip production, but not with fully depleted devices yet.

• Goals:– Develop improved test structures

based on CMS– Develop sensor with dual metal layer

to test in-sensor routing

• Three 4” wafers received from first processing batch, results look promising


Characterization = electric measurements• Performed in HEPHY cleanroomMeasurement procedure:• Sensor held by vacuum on motorized table

– Motorized table is movable in XYZ• First set of Needles are used to connect Bias

and Guard ring– Fixed in respect to the sensor

• Second set of Needles are contacting:– DC Pad (p- or n- implant of strip)– AC Pad (Aluminum strip)– By movement of the table each strip can be

contacted to these needles– Full measurement (all strips) takes approx.3 h

per sensor

• 2 „global“ measurements per detector– IV- Curve (Dark current, Breakthrough voltage)– CV- Curve (Detector capacitance, „full

depletion“-voltage)

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Sensors Characterization


4 measurements per strip:

11

• Open Strip:

• Shorted Strip:

Dielectric current:

Coupling capacitance:

Poly-Silicium Bias-resistor:

Single strip current:

• “Pinhole” (short between implant and metal):

Characterization: Strip-by-Strip


Leakage Current at 450VSpecification: max 10µA

Full Depletion VoltageSpecification: 100 V – 300 V

Mean: 576 nA

Mean: 1865 nA

Characterization: IV and CV Results


Number of bad strips per sensor (pinhole, bad polyresistor, Al short,broken Al, open implant, leaky strip,….)

Number of Bad StripsSpecification: max 1% of 512/768 Channels

Percentage of bad strips: 0.018% 0.305%

Mean: 0.1 strip/sensor Mean: 1.9 strip/sensor

Characterization: Strip-Scan Results


TS-CAP

sheet

GCD

CAP-TS-AC CAP-TS-AC

baby diode

MOS 1

MOS 2

Process Monitoring on Test Structures

• What is Process monitoring?– Each wafer hosts additional test

structures around main detector– “standard” set of test structures is called

“half moon” (because of its shape)– Test structures used to determine one

parameter per structure– Assuming that sensor and test structures

behave identically

• Worked extremely well during CMS sensor production

– Several problems have been identified during CMS quality assurance tests

– Some parameters are not accessible on main detector (e.g. flatband voltage of MOS), but important for proper operation


Test Structures Measurements• TS-CAP:

– Coupling capacitance CAC to determine oxide thickness

– IV-Curve: breakthrough voltage of oxide

• Sheet:– Aluminium resistivity– p+-impant resistivity– Polysilicon resistivity

• GCD:– Gate Controlled Diode– IV-Curve to determine surface

current Isurface– Characterize Si-SiO2 interface

• CAP-TS-AC:– Inter-strip capacitance Cint

• Baby-Sensor:– IV-Curve for dark current– Bulk breakthrough voltage

• CAP-TS-DC:– Inter-strip Resistance Rint

• Diode:– CV-Curve to determine depletion

voltage Vdepletion– Calculate resistivity of silicon bulk

• MOS:– CV-Curve to extract flatband voltage

Vflatband to characterize fixed oxide charges

– For thick interstrip oxide (MOS1)– For thin readout oxide (MOS2)

TS-CAP

sheetGCD

CAP-TS-AC CAP-TS-ACbaby diode

MOS 1

MOS 2


Test structures Measurement Setup

• Probe-card with 40 needles contacts all pads of test structures in parallel

– Half moon fixed by vacuum– Micropositioner used for Alignment– In light-tight box with humidity and

temperature control

• Instruments– Source Measurement Unit (SMU)– Voltage Source– LCR-Meter (Capacitance)

• Heart of the system: Crosspointswitching box, used to switch instruments to different needles

• Labview and GPIB used to control instruments and switching system


Process Monitoring Setup


Yellow Fields:Limits and cuts for qualification

Blue Fields:Obtained resultsextracted from graphby linear fits (red/green lines)

Process Monitoring DAQ Software

Fully automatic measurement procedure takes approx. 30min per half moon to produce this:


Passed/Not Passed Lights

• After all measurements finished

• Window pops up• One light for each test

– Green: within limits– Red: out of limits

• Allows immediate judgment about quality

• Pressing “OK” button writes data directly into central database (CMS used Oracle)

20

Process Monitoring Results (1)

• Different problems of several sensor batches (production lots) have been discovered during CMS sensor QA program, e.g.:– Too high flatband voltage– Too high poly-Si resistor– Too high Al sheet resistivity– Too low inter-strip resistance– Too high bulk resistivity

• Most of the issues have been solved by the vendors after an intervention from us


3.5 kOhm

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Process Monitoring Results (2)

• In fairness, I have to say that the majority of monitored parameters were pretty stable vs. time

• For example:– Coupling capacitance (top)– Breakthrough of dielectric

(bottom)


Specification requires > 100 V

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Long term/Coldbox• Long term IV setup for sensor

stability tests– Used to measure dark currents of

10 sensors in parallel vs. time– Discovered corrosion of aluminum

lines on sensor– Needs air moisture and HV– Caused by Potassium

contamination of sensor production line which caused production of (non-conduction) alumina (Al2O3)

• Coldbox for aging studies– Driven by Peltier elements– Discovered issue with conductive

glue on sensor backside(Solution: Backplane bonding)



• For large scale production, an relational database system is necessary to– Keep track of each object– Store measurement results

centrally• Each action (shipment,

assembly, integration, test, repair) is recorded

• CMS Tracker Construction DB uses Oracle to manage >200.000 objects– Sensors, hybrids, modules– Cables (with cabling info)

Logistics for mass production (1)


Database can be used to• Store full history of each

component– Allowed us to produce nice

statistics, e.g. distribution of failures of modules (right)

• Plot histograms of measurement results– E.g. full depletion voltage of

silicon sensors as output of process monitoring tests

The logistics effort in an distributed sensor QA and module production must not be under-estimated!

Logistics for mass production (2)

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Module Construction

• HEPHY Vienna built 650 out of 16.000 silicon detector modules for the CMS Tracker– Ring 2 of Tracker Endcaps– Two geometries: R2N and

R2S

• Production Steps:– Assembly: gluing of hybrid

and sensor to CF frame– Wire bonding– Testing



Module Assembly• Module assembly for CMS was

manual process:– CF frame was fixed with vacuum

support– Glue dispensed manually by

operator– Sensor put onto frame using

gallows– Glue curing– Using 3D coordinate

measurement machine (Mitutoyo) for measurement of assembly precision (<10 micron)

• Throughput: 4 modules per day


Wire bonding• Fully automatic large-area wire

bonding machine used for bonding of CMS modules– Model Delvotec 6400– Bond rate 5Hz– Takes 10 minutes for ~800 bonds

per module (if everything works well)

• Bond pull test machine– To verify bond quality– Pull strength: ~8g

• Manual wire bonding machine Kulicke & Soffa– Enhanced by motorized XY-table

for “semi-automatic” use– Bond rate 0.2 Hz– Used for quick single bonds

28

Testing/Repair• Intensive testing of modules

after assembly and bonding using dedicated setup

• Thermal Cycle to speed up aging process– Cold box

• Module repair:– Re-bonding of “touched

bonds”– Disassembly of sensor from

module with faulty hybrid– Mostly time-consuming,

manual work


29

Test beams

Last 5 slides


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Test BeamsGoal of last testbeam (June 08):

evaluate the best strip geometry of silicon strip sensors with 50 micron pitch to determine the highest possible spatial resolution

• Using CERN’s SPS beam (120 GeV pions) [low multiple scatt.]

• Using EUDET pixel telescope as reference

• For this purpose we were using a dedicated mini sensor with different zones, each with a different strip geometry:– Different strip widths– 0, 1 or 2 intermediate strips

TESTAC:

SiLC Sensor:

31

Test Beam: SensorsDUT sensors have been intensively tested in Vienna, e.g.:• IV curves on all sensors• CV curves to determine full depletion voltages

– approx. 60V

Measurement of the inter-strip capacitance reveal different values for each zone:• Capacitance scales linearly with strip width• Different offset for region with one or two intermediate strips

0 100 200 300 400 500 600 700 800

100n

1µ

10µ

curre

nt

voltage

01 02 03 04 05 06 07 10 12 13 17 19 20 21 23 24 26 27 28 29 30 31 32 34 35 36 37 38

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Test Beam: Modules

9 modules have been built using•Multi-geometry test sensor

•APV25 readout chip

•SVD3 readout system developed by Markus Friedl et al. in Vienna

Module Front: back:

Modules have been screwed together to form a kind of “telescope” for tracking purpose

33

Test beam results (1)

Measurement plan:• High-statistics run covering each zone

– Must have enough tracks passing through each zone

• HV scan• Angle scan

Low level data processing already done using Vienna’s testbeam software (electronics group)

• Pedestal subtraction• Common mode correction• Hit finding, Clustering• Peak time reconstruction


34

Test beam results (2)


Width -> +

Analysis started very recently using both:

• EUDET LCIO Analysis (Marlin), because telescope data is already in this format

• standard analysis chain (software developed by Prague colleagues), comprising – hit reconstruction– track identification– alignment and track fitting – calculation of detector

residuals and resolution

35

Summary

• Semiconductor group at HEPHY Vienna completed CMS Tracker construction, testing, installation and commissioning recently

• Large experience with sensor design, electric characterization; module assembly, bonding, testing, repair, logistics

• Schedule:– CMS upgrade:

small (pixel only) 2013, large (full Tracker) 2018– ILC: postponed to later future

• Therefore, we are interested in a mid-term project – Super-Belle would fit perfectly ;-)


36

The End.

(Backup slides follow)


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Test Beam: Zone Description


experience with silicon detectors and module construction

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