Testing of Test Structures in Vienna

4 May 2010

Thomas Bergauer (HEPHY Vienna)

Testing of Test Structures in Vienna

CMS Sensor-TUPO

CMS Sensor-TUPO

HISTORY

CMS Process Qualification Center 2001-2007

2Thomas Bergauer (HEPHY Vienna)4 May 2010

CMS Sensor-TUPO

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– Some parameters are not accessible on

main detector (e.g. flatband voltage of MOS), but important for proper operation

• Worked extremely well during CMS sensor production

– Several problems have been identified during CMS quality assurance tests

TS-CAP

sheet

GCD

CAP-TS-AC CAP-TS-AC

baby diode

MOS 1

MOS 2


CMS Sensor-TUPO

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: Cross-point switching box, used to switch instruments to different needles


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Three Setups have been installed


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Mechanical support (Vienna)

Microscope

Probecard (green) in support

TS fixed with vacuum onto support

XY-Table for alignment


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Probe-Card to switching matrix

2nd Version

Individual shielded cables


Probe-card

4 pcs. Keithley 1x10 multiplexer cards(part of switching system)

CMS Sensor-TUPO

Instruments available in Vienna

• Source Measure Unit:– Keithley 237 and 2410

• LCR Meter– Keithley 595 (quasistatic)

– Agilent 4274A (10Hz-100kHz)

– Agilent 4285A (75kHz to

30MHz)

• Switching System– Keithley 7002

– 4x5 pt. matrix cards 7153

– 1x10 pt multiplexer cards 7154


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Yellow Fields: Limits and cuts for qualification

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

Software: Labview

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


CMS Sensor-TUPO

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 Tracker Construction database (Oracle)


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Example of identified problems

• Limit: Rint > 1GΩ to have a good separation of neighbouring strips

• Each dot in the left plot shows one measurement

• Value started to getting below limit

• We reported this to the company• Due to the long production

pipeline, a significant amount of ~1000 sensors were affected

Inter strip resistance issue during CMS sensor production


CMS Sensor-TUPO

• In total, more than 4500 Half moons have been tested in the three labs

• Different problems of several sensor batches have been discovered, 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


Solved Problems

CMS Sensor-TUPO

ACTUAL SETUP FOR SLHC UPGRADE

Instruments and Cold Chuck


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Setup today

Picture above shows the current status of the setup• Unchanged (wrt. CMS sensor production): SMU, LCR-Meter and

other instruments• New: cold chuck for testing irradiated structures• Different: currently no probe-card, but individual needles


CMS Sensor-TUPO

Cold Chuck

• 2x 240W water cooled Peltier modules• Chiller filled with alcohol/water mixture

to remove heat from back of Peltier modules

• 2-channel power supply from Vienna Cold box connected to peltier elements

• HEPHY-made TRHX System for monitoring of temperatures and relative humidity


CMS Sensor-TUPO

Cold Chuck in Measurement Box


Acrylic glas box for minimizing of dry volume;Flooded with dry air (DP -60 deg.C)

“glovebox” with gloves

Opening with cover to change sensor/halfmoon

CMS Sensor-TUPO

Individual needles instead of probe-card

• Although a probe-card is very handy for doing repeated measurements on thousands of test structures, the layout of halfmoon is fixed and other measurements cannot be performed

• Thus, we will keep individual needles for the moment


CMS Sensor-TUPO

Measurements performed for CMS• 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

sheet

GCD

CAP-TS-AC CAP-TS-AC

baby diode

MOS 1

MOS 2


CMS Sensor-TUPO

Measurements performed so far

• In November 2009 we have received one proton-irradiated CMS halfmoon from Karlsruhe

• The structures were irradiated with protons to 5.24E14 n(equiv) and are annealed (80min at 60°C).

• Measurements performed so far:– IV on baby, diode– CV Diode and Baby with comparison– CV MOS– C_int, R_int


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Measurements: IV

Non-irradiated irradiated


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Measurements CV

Comparison Unirradiated vs.Irradiated sample


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Measurements MOS

Non-irradiated irradiated


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Strip scans at room temperature

• We can also perform strip-by strip measurements of unirradiated sensors only (other setup without cold chuck)– Single strip current– Poly-silicon resistors– Coupling capacitance– Dielectric current


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Test Structures of new LayoutLayout of new HPK wafer:

Diode GCD

TS

_cap

Cap-TS-AC f. C_int measurement

Sheet

MOSVia-TS

Cap

-TS

-DC


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Manpower / Timing

• Time Estimate for full half moon: 4h– Manual measurements, no

probe-card

• Time estimate with probe-card: 30 minutes– But: effort necessary to

design und buy probe-card

– Large effort to modify setup

– Setup not flexible for other measurements anymore

Available manpower• Technicians

– 0-2 FTE as necessary

• Physicist – 0-2 FTE as necessary

• Students– 0.2 - 1 FTE


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Planning/Summary

• Currently: We are re-measuring all parameters of irradiated/not irradiated structures that our student gets familiar with it

• Necessary modification of software – improve fits– DB interaction (once TrackerDB stuff gets settled)

• We will perform n-irradiation in our own reactor for testing purposes in near future

• We are ready for the delivery from HPK


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THE ENDBackup slides follow

28Markus Friedl (HEPHY Vienna)20 October 2009

CMS Sensor-TUPO

Test Structures of new LayoutLayout of new HPK wafer and position of possible probe-card

Cap-TS-AC f. C_int measurement


Documents

Testing of Test Structures in Vienna