quality assurance for the radiation hard atlas pixel sensors · c-v analysis f p-spray = c ox ·(v...
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![Page 1: Quality assurance for the radiation hard ATLAS pixel sensors · C-V Analysis f p-spray = C ox ·(V th-V fb) / e under depleted over depleted. Pixel 2000, June 2000, Genova QA for](https://reader033.vdocument.in/reader033/viewer/2022050416/5f8c62b11066715c0876224b/html5/thumbnails/1.jpg)
Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors,J.M. Klaiber-Lodewigs - Univ. Dortmund
Quality assurance
for the
radiation hard ATLAS pixel sensors
Contents: - Why is systematic QA necessary?
- Procedures and design features- Measurements before irradiation- Measurements after irradiation
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 2
Introduction
• large number of detector parts(2228 modules fitted with one sensortile and 16 front-end chips each)
• parts not easily accessible afterassembly (central position, coolingand radiation)
• every bad pixel degradesperformance
• ≈ 1.4·108 pixel channels in total
Why systematic quality assurance for theATLAS pixel sensor?
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 3
Important steps for QA
Setting technical specifications
Designing according to specifications
Identifying relevant qualities
Defining reliable measurement procedures
Calibrating involved test sites
Archiving measurement data in data base
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 4
Pixel design requirements
• pixel size 50µm x 400µm50 µm pitch12µm diameter bump connection
• total active area 2.3m2 (2228 modules)high yieldtestability
• 10 years operationfault tolerance
• harsh radiation environmentup to 1015 cm-2 (1 MeV neutron eq.)radiation hard technology and design
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 5
Isolation techniquesOptimizing performance before and
after type-inversion and ensuring testability
p-stop p-spray moderated p-spray
For p-spray testing of worst caseof breakdown before irradiation
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 6
Testability
I-V tests on test pixels using punch-through
current throughsingle pixel
current throughpunch-through array
Leakage current indicative for quality of every pixel
1.00E-04
1.00E-03
1.00E-02
1.00E-01
1.00E+00
1.00E+01
1.00E+02
0 20 40 60 80 100 120 140 160 180 200
bias voltage [V]
curr
ent
[nA
]
defective pixel
good pixel
1.00E-01
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
0 20 40 60 80 100 120 140 160 180 200
bias voltage [V]
curr
ent
[nA
]
good pixel matrix
matrix with defective pixels
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 7
Testability
• Punch-through effect across a biasgrid allows testing of all pixels usingonly two probes on wafer p-side
I-V tests before bonding using bias grid
groundp-side bias
punch-through
guard ring
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 8
Leakage current
• I-V measurements ofleakage current show pixel quality
• breakdown voltageindicates type of defect
• tile classification possible
Tile classification by pixel quality
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 9
Leakage currentYield analysis based on I-V curves
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 10
Sensor depletion
• Test diodes on production waferfor well defined capacitancemeasurements
• Full depletion visible by levellingout of C vs. V-1/2 curve (suppression of possible constantstray capacitances)
Diagnostic measurement bydiode capacitance
Defined n-Bulk area
p+
n+
guard ring
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 11
Oxide characteristicsDiagnostic measurements on
MOS and GCD
• oxide breakdown and capacitancemeasured in I-V and C-V curves onMOS pads
• interface generation currentmeasured on gate controlled diodesas I-V curve around flat-band casewith identical gate and diode voltage
• current step indicates chargedensity on interface
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 12
P-spray dose
• source - drainmeasurement on MOSFETon depleted bulk
• p-spray inverts at highergate voltage: threshold Vth
• source-drain current risesrapidly at Vth
backside voltage Vb
Vgate SourceDrain Vdrain= 0.1V I
n+ n+
p-sprayp+
n-Bulk
Method of measurement
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 13
P-spray dose
• after Vth is identified p-spraydose is given by
using flat-band voltage andoxide capacitance from MOSC-V
Analysis
φp-spray = Cox· (Vth-Vfb) / e
under depleted over depleted
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 14
Radiation hardness tests
Bulk damage testing• after irrad. with 3.1⋅1014cm-2
neutron equivalent protons
• after irrad. with 1015cm-2 neutronequivalent protons (design fluence)
Surface damage testing• after irrad. with 500 kGray lowenergetic electrons (design dose)
• depletion measurement on diode
• I-V measurements on mini chipand diode (small structures)
• interface generation currentmeasurement on GCD• p-spray measurement onMOSFET
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 15
Testing responsibilities
vendor• providing process data
• testing pixel quality on sensortiles on wafer level
• performing diagnostic tests onwafer level for depletion, oxidequality and capacitance, and p-spray dose
ATLAS institutes• checking process data
• testing pixel quality on sensorstiles, single chips and mini chips
• performing all diagnostic testson wafer level and on diced teststructures
• measuring irradiated structures
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Pixel 2000, June 2000, Genova QA for rad. hard ATLAS pixel sensors, J.M. Klaiber-Lodewigs - Univ. Dortmund 16
Summary
• technical specifications completed and approved• sensor design completed and approved
• quality test for every pixel on sensor defined and demonstrated• diagnostic tests for relevant qualities defined and demonstrated
• cross calibration of test sites in progress
• data base for test results under construction
Progress of quality assurance process