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DØ-note 4120
July 2003
Silicon Sensor Quality Assurance for the D0 Run IIb Silicon
Detector: Procedures and Equipment
A. Bean1, T. Bolton2, M. Demarteau3, R. Demina4, D.Karmanov5, S. Korjenevski4, F.
Lehner6, R. Lipton3, M. Mao3, M. Merkin5, R.L.McCarthy7, R. Sidwell2 and R.P Smith3
1 Kansas University, Lawrence, USA
2 Kansas State University, Manhattan, USA
3 Fermi National Accelerator Laboratory, USA
4 University of Rochester, USA
5 Moscow State University, Russia
6 University of Zurich, Switzerland
7 State University of New York at Stony Brook, USA
Abstract
This documents describes in detail the quality assurance (QA) program for the D0 Run
IIb silicon sensors. The scope of the QA program, the responsibilities of the participating
institutions, and the testing and measurement procedures are defined.
1. Introduction
Preparation for the Run IIb silicon tracking system for the D0 detector is underway. The
design of the new system relies profoundly on the experience gained with the Run IIa
silicon tracker and the quality assurance program established for the Run IIb silicon
sensors themselves likewise builds on the Run IIa experience. The new tracking system
incorporates ~ 2400 single-sided sensors in six barrel layers located at radii from 1.8 cm
to 16 cm from the interaction point. The Run IIb detector is scheduled to be ready for
installation by midyear 2006 and must maintain efficient tracking performance after
experiencing the radiation damage expected (up to 1014 1 MeV equivalent neutrons/cm2)
over its Run IIb lifetime (~10-15 fb-1 integrated Tevatron collider luminosity).
A thorough, reliable, and efficient silicon sensor probing and characterization effort,
defined in a well-organized silicon quality assurance (QA) program is critical for the
confirmation that only sensors of desired quality are procured and incorporated into the
detector. This document describes the procedures, responsibilities and organization of the
QA program established by the D0 collaboration for the silicon sensors for the RunIIb
silicon tracking system. In particular the program includes:



Organization and responsibility for testing
Testing procedures and acceptance criteria
Testing equipment
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
Inventory control, documentation and database
In addition to incorporating prior experience gained during the fabrication of the Run IIa
detector, the Run IIb QA program also incorporates testing procedures developed for the
ATLAS SCT sensors and the CMS silicon sensors. Finally, it incorporates the consensus
of many discussions within the D0 Run IIb silicon group while the design and
performance parameters of the new system were developed.
In Section 2 of this document the general silicon sensor QA organization is described and
its responsibilities are defined. Section 3 summarizes the silicon sensor specifications and
terms of acceptance. Section 4 describes the silicon sensor QA program in detail. The
inventory and testing database design and its requirements are described in section 6, and
in Section 7 there is a list of measurement instrumentation and probing equipment which
have been found useful by D0 and have been installed at the several silicon testing
centers. The specifications for the sensors are given in Section 8
This document is also available on the D0 Run IIb sensor web page
http://www.physik.unizh.ch/~lehnerf/dzero/run2b.html. This web page contains also links
to updated probing and testing information as well as results.
2. General D0 Run IIb Silicon Sensor QA Organization Issues
Quality assurance for the D0 Run IIb silicon sensors will be carried out at three primary
D0 institutions and two secondary D0 institutions. The four primary testing centers and
the corresponding coordinators are:




Fermilab, Batavia, USA. Local coordinator: Marcel Demarteau, Ron Lipton and
Madame Mao
Kansas State University, Manhattan, USA. Local coordinator: Tim Bolton and
Robin Sidwell
State University of New York, Stony Brook, USA. Local coordinator: Bob
McCarthy
University of Rochester, USA. Local Coordinator: Regina Demina and Sergey
Korjenevski
In the event of testing schedule backlogs additional QA activities are foreseen to occur at
two secondary institutions:


Moscow State University, Moscow, Russia. Local coordinator: Michael Merkin
University of Zurich, Zurich, Switzerland. Local coordinator: Frank Lehner
The QA program defines a collaborative activity that provides for shared responsibility
among the different institutions with defined testing procedures followed rigorously at all
testing centers. Local coordinators at each institution are charged with the responsibility
to determine that the local QA program is implemented consistently and that all tests are
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performed in accordance with this document. Prior to the performance of QA testing on
production sensors at any institution, the capabilities and performance of that institution
will be certified by the Run IIb silicon sensor coordinators.
Fermilab will serve as a central distribution and control center with dedicated testing and
coordinating tasks. Its main tasks will be:








The initial registration of each sensor upon receipt from the vendor
The visual inspection of each sensor
The two key characterization measurements (I-V and C-V) on each sensor
The distribution of the sensors to the two other primary testing centers
The performance of additional sensor characterization measurements on subsamples of the sensors as described in this document
The handling and shipping of sensors rejected by the QA program that are
returned to the vendor
The overall monitoring of the QA program
The final acceptance and grading of the sensors
The last two items are coordinating and managing tasks and their completion will be the
responsibility of the two RunIIb silicon sensor coordinators together with the local
coordinator(s) at Fermilab.
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Figure 1 shows a graphical representation of the QA program with the silicon sensor
flow.
Figure 1: A graphical representation of the QA organization and silicon sensor flow.
3. Overview of Sensor Design, Specifications and Terms of Acceptance
3.1. General
The Run IIb silicon detectors are p+n type single-sided sensors, with AC coupling and
biased through polysilicon resistors. The silicon sensors will have a single-guard ring
with peripheral n-well feature as designed by Hamamatsu Photonics. There are three
sensor types required for the RunIIb detector:
Layers
Active
Length
(mm)
Active
Width
(mm)
Strip pitch /readout pitch
(m)
# readout
channels
# of sensors + spares
0
77.36
12.8
25/50
256
144+50%=216
1
77.36
22.272
29/58
384
144+50%=216
4
2-5
98.33
38.34
30/60
639
1896+20%=2280
Layer 2-5 sensors will be manufactured on 6-inch wafers. Layer 0 and 1 sensors are
compatible with a production on 4, 5 or 6-inch wafers.
The web page http://www.physik.unizh.ch/~lehnerf/dzero/run2b.html provides links to
the detailed mechanical drawings of the sensors. These drawings are given wide
circulation throughout D0 so that all testing personnel become familiar with the exact
sensor or test structure geometry in precise detail. This detail comprises the location and
character of fiducial marks, the location and character of bonding and testing pads, the
on-sensor strip numbering keys, and the multiple-field scratchpad for unique sensor
identification, vendor information and for QA pass/fail marks done by the testing centers.
3.2. Specifications
The detailed sensor specifications are reproduced in Section 8 of this note. The following
table summarizes the mechanical and electrical specifications critical to the QA program:
Specifications:
Wafer thickness
Depletion voltage
Leakage current
Junction breakdown
Implant width
Al width
Coupling capacitance
Coupling capacitor breakdown
Interstrip capacitance
Polysilicon bias resistor
Defective strips
Layer 0/1
32020m, wafer warp less than
m
40<V<300V
<100nA/cm2 at RT and
FDV+20V, total current < 4A at
700V
>700V
7m
2-3 m overhanging metal
>10pF/cm
>100V
<1.2pF/cm
0.80.3 M
<1% per sensor
Layer 2-5
32020m, wafer warp less than
m
40<V<300V
<100nA/cm2 at RT and
FDV+20V, total current < 16A
at 350V
>350V
8m
2-3 m overhanging metal
>12pF/cm
>100V
<1.2pF/cm
0.80.3 M
<1% per sensor
3.3. Terms of acceptance
The silicon Distribution and Control Center (i.e. Fermilab) will receive all sensors from
the vendor and record them as in preliminary compliance if the specified QA
documentation received from the vendor indicates that all vendor-required tests meet the
specification.
The Distribution and Control Center will expeditiously perform the sensor key tests
described in detail below before distributing any sensors to the other testing sites. In
addition, Fermilab will perform additional subset tests described below on a fraction of
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the sensors that pass the key tests. The subset tests focus on confirming the compliance
of all sensors within a production batch.
Non-compliance of any sensor will be determined by Fermilab within 90 days of receipt
of the sensor. The vendor will be notified of the non-compliance and if the vendor
requests the opportunity for remeasurement, the noncompliant sensor(s) will be returned
to the vendor. The Run IIb silicon sensor coordinators and the vendor can agree upon the
acceptance of sensors that fail only marginally to meet specifications.
4. The QA program
The QA program for the Run IIb sensors consists of four main parts:
1. Key Tests: The silicon sensor key tests are performed on every received sensor.
The measurements/procedures belonging to the key tests are the most important
ones because they confirm acceptable minimum performance of the sensor as an
entity. The key tests are carried out at the Distribution and Control Center, i.e. at
Fermilab.
2. Subset Tests: The silicon sensor subset tests are conducted on a defined fraction
of sensors which pass the key tests. The main goal of the subset tests is to verify
compliance with the specifications in depth. The fraction of sensors which were
subject to these tests was large during the prototyping stage. For production
sensors, the fraction will depend on the overall quality of the subset test data and
its corroboration of the vendor QA data. The subset tests are nearly all done in
automatic probe stations under computer program control.
3. Diagnostic Tests: The silicon sensor diagnostic tests are routinely performed on
a fraction of sensors selected at random from those passing the key tests,
continuously throughout the sensor delivery period, as well as on sensors with
irregularities revealed in the key or subset sensor tests. The diagnostic tests
measure in much more detail complex electrical parameters to provide a deeper
insight into sensor quality and to monitor the vendor production process from
batch to batch.
4. Mechanical Measurements: The mechanical measurements are routinely
performed throughout the production period on a fraction of sensors selected at
random from those which satisfy the key tests. The measurements have been
crucial in the prototyping phase to validate the mask design, and they can reveal
wafer and production problems that might arise during production.
The current definition of the fractions of sensors which will be subject to the subset,
diagnostic and mechanical tests is maintained in the D0 Run IIb Silicon Sensor QA
Part Flow document. The fractions listed in this document will be updated on a
continuing basis as the overall quality of the received sensors warrant. This document can
be found on the web page http://www.physik.unizh.ch/~lehnerf/dzero/run2b.html.
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4.1. General Conditions/requirements of Testing/probing
4.1.1. Clean Room conditions and handling of sensors
All personnel who handle sensors shall undergo training and practice in the handling of
sensors that exposes them to all phases of the manipulation of the sensors required by the
QA program. Sensors not being tested shall be stored in clean containers in a dry storage
area with restricted access.
All production sensors shall be handled at the testing centers in a clean room or a clean
room housing with temperature (21 +/- 2oC) and humidity (40+/-10%) control. The clean
room class is not specified, but personnel access to the area must be strictly limit and
non-silicon activities (e.g. soldering, use of chemical reagents, use of power tools, etc.)
prohibited. Note the actual humidity in the work environment should not fall below 30%
so that electrostatic discharges don’t become a problem.
.
Protective clothes, masks, and gloves shall be worn by all personnel who handle sensors.
While vacuum tweezers have customarily been the preferred method of lifting sensors,
recent testing experience indicates that the tweezers may leave a temporary “footprint” on
the detector that enhances the strip leakage currents where the vacuum cup of the
tweezers contacts the sensor. Until this phenomenon is better understood, the use of
vacuum tweezers should be limited. Because the sensors are packaged between two thin
layers of cardboard, it is generally possible to gently and safely slide the sensors from the
packaging to probe chucks, and back again, completely avoiding the use of tweezers.
In chapter 7 of this document are described the recommended test and measurement
equipment that has been found to facilitate this QA program. A detailed guideline to
cleanroom conditions and sensor handling can be found on the web
(http://www.physik.unizh.ch/~lehnerf/dzero/qa/qa.html)
4.1.2. Testing conditions
All electrical tests should be carried out in the specified clean room or clean room
housing described in section 4.1.1. The electrical tests must be made in a light-tight dark
box. To contact the sensors for probing, the probe tips must be placed only on special
contact pads which are not used for production bonding during the assembly process
(except bias line contact pads). These “test pads” or “probe pads” (either AC- or DCpads) are indicated on the mechanical sensor drawings, which are available at
http://www.physik.unizh.ch/~lehnerf/dzero/drawings/drawings.html.
We suggest covering the chuck of the probe station with a special conductive rubber film
prior to usage to prevent damage on the sensor backside during the positioning of the
sensor on the chuck. If a conductive rubber sheet is not used, then great care has to be
used in keeping the chuck clean, not to damage the sensors.
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4.1.3. Sensor Database
A general database system for parts and components as well as for production and
assembly of the entire Run IIb detector is being prepared at Fermilab. The database
design and architecture is adopted from the ATLAS SCT group1. This database is a
relational database in ORACLE and follows a client/server model. The database server is
located at Fermilab. The web-interfaces for easy storage and retrieval of data are being
developed. The database usage is part of the sensor QA program, and the database will be
utilized to identify and track sensors and to store and retrieve sensor quality and grading
information data for each silicon sensor.
Whenever testing data is logged to the database, the record must contain the following
items:





Measurement data
Temperature/humidity
Date
Testing center
Comments
As noted in section 2, one of the tasks of the Run IIb silicon sensor coordinators will be
to monitor the conformance of database entries to these requirements. The utility of the
database is strongly a function of the clarity and comprehensivity of the data logged in it.
4.2. Key Sensor Tests: Performed on every Sensor
The key sensor test program represents the most important quality control test of the QA
program. The key tests shall be performed on all sensors promptly at Fermilab upon their
receipt from the vendor. The tests are not complex and they serve as a valuable firstinspection for sensor acceptance and performance grading. The key tests include an
initial registration of the sensor in the database, a visual inspection, and I-V and C-V
electrical measurements.
4.2.1 Initial Registration into the Database
This task is done at the central distribution center (Fermilab). Each shipment of sensors is
checked for content and QA documentation from the vendor. For each sensor the test
structure piece (“half moon”) for each wafer must be present. The vendor QA
measurements are provided in both an electronic format (i.e. EXCEL spreadsheet) and
printed copy. This material is verified for completeness and the data is inspected to
ensure that each sensor it documents meets specification.
1
The Atlas SCT designers kindly agreed to provide us their designer file
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Specifically, the material is checked for:

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








serial ID-number of sensor
batch/lot number
wafer thickness
leakage current values at the range of specified voltages
depletion voltage
number of bad channels/strips
polysilicon resistor mean value and standard deviation or min/max
Aluminium resistance value on monitor structure
Implant resistance value on monitor structure
typical coupling capacitor mean value and breakdown value
eventually further measurement information based on teststructures
If any of the required information or the teststructure “half moon” for a sensor is missing,
such omission shall be specifically flagged in the database and the sensor marked as
noncompliant in the database. If any of the data indicates that the sensor does not meet
specifications, the offending information is unambiguously flagged in the database and
the sensor marked as noncompliant. The arrival date and present location (i.e. testing
institute) of each sensor is entered.
4.2.2 Visual inspection
When the registration process is completed all sensors not marked as noncompliant are
subject to visual inspection.
This key sensor test is also performed at the central distribution center, and its purpose is
to identify sensors for which mechanical imperfection might impair electrical
performance. The visual inspection identifies physical defects, damage, and edge
chipping, and records the sensor region where the damage is located so that further
electrical measurements can focus on that region. If edge damage is identified, the sensor
must be sent for mechanical measurements when the visual inspection is complete.
The visual inspection is carried out on an x-y moving table equipped with a microscope
having different objectives with magnification from 3x to 50x. A video camera
connected to the microscope with a video monitor and video printing capability is
required. A detailed guide to sensor visual inspections including some illustrative sensor
defect pictures is on the web (http://www.physik.unizh.ch/~lehnerf/dzero/qa/qa.html)
Procedure for visual inspection:
1. Ensure that the x-y table is completely clean and clear of any debris.
2. Remove sensor from its envelope/shipping container.
3. Search for any signs of silicon debris in the sensor envelope or within the shipping
box. If debris is present, be sure to remove it before eventually returning the sensor to
the envelope, and identify the source of the debris during the visual scans of the
sensor.
4. Examine the back surface by eye. Take note of any blemishes or scratches.
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5. If there are indications of edge chipping, place the sensor on the probe station chuck
(with the sensor still strip-side down on the shipping cardboard unless the chuck is
covered with the recommended pad) and measure the width of the chipping. Take a
picture if appropriate.
6. Remove the sensor from the chuck and replace it on the chuck with the strip side
facing upwards.
7. Check that the serial number scratched on the identification pads matches the serial
number on the sensor envelope.
8. At high magnification, scan along all four edges, searching for edge chipping,
scratching or other damage.
9. Check the visibility and quality of the fiducial marks.
10. With the same high magnification, scan along the bias resistors, searching for breaks,
signs of processing defects or non-uniformity. Check for alignment of metalization
with implant.
11. Scan along the AC-bonding pads (the ones which will be used for the hybrid bonds)
and verify that they are clean and not probed.
12. At lower magnification, scan the full area of the sensor, making notes (and taking
pictures where appropriate) of blemishes, scratches or other non-standard features.
13. Update the database, recording the completion of visual inspection and enter all
comments and findings.
Acceptance:
The sensor should be flagged in the database as having failed visual inspection if any
edge chipping (front or back) exceeds 50m, or if there is severe scratching or other
gross defects, or there are signs of a processing abnormality. If in doubt, flag the sensor
for a full strip test so that potential defects are confirmed electrically.
4.2.3. C-V Curve and Sensor Depletion Voltage Determination
This key sensor test is done at Fermilab on every sensor and requires an LCR-meter with
an external bias adapter and a bias voltage source. Place the sensor with the backside on
the chuck of a probe station and contact the bias rail with a probe needle. Connect the
LCR meter, bias supply, probe and chuck as shown in Fig. 2, with external bias adapter.
Ensure that the bias adapter has suitable blocking capacitors with appropriate voltage
withstand and low current leakage. (It is good practice to make and record the specified
test periodically with no sensor connected, to verify the performance of the system and
determine the size of “background” signals).
Measure and record the capacitance in 10V steps up to 350V (for L0 & L1 sensors) or up
to 200V (for L2-L5 sensors) with a 10 second delay between voltage increments. Use
10kHz with the LCR meter in SERIES mode (Cs-Rs), 1.0 V amplitude. Alternatively,
one can also use 1 kHz and a level of 500mV.
In order to determine the full depletion voltage (FDV), the data have to be represented in
a way 1/C2 versus bias voltage. The FDV is then determined as the lowest voltage, where
the increase of 1/C2 is found to be less than 2%. This method of determining FDV is
actually performed by Hamamatsu. We decided in the Run IIb group to change the FDV
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determination to this method. Compared to our old method of fitting the appropriate
lower and upper sections of the 1/C2 data independently with two straight lines and taking
the intersection of the two straight lines, the previous method tends to give slightly larger
depletion voltages.
Log the measured FDV and date of measurement in that part of the excel spreadsheet,
which will later then uploaded to the database.
Acceptance criteria:
 Full Depletion Voltage (FDV) is in the region 40--150V for L2-L5.
 FDV is in the region 40--300V for L0&L1.
HV source
Test chuck
Probe to
-HV
+HV
bias line
GND
С1=1μF
С2=1μF
H
L
LCR-meter, 1kHz
Fig.2: The setup for the C-V measurement and Full Depletion Voltage.
4.2.4. I-V Curve and Leakage Current Determination
This key sensor test is carried out at the central testing center for every sensor. The test
requires a power supply and a pico-Ampmeter. The best choice is a sensitive source
measurement unit (SMU) with high voltage isolation and current limitation such as a
Keithley-487/237. The sensor backside is placed on the chuck of a probe station and
probe needle is put on the bias line contact pad. Connect the probe, chuck, and SMU as
shown in Fig. 3.
Measure the total leakage current between the bias rail and the sensor backside in 10V
steps up to 800V (for L0&L1 sensors) or up to 500V (for L2-L5 sensors) with a 5 second
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delay between voltage increments. A current limit of 50A must be imposed throughout
the measurement. The temperature of the probe station environment should be recorded
as well. The leakage current data have to go into the excel spreadsheet, which will then
be uploaded.
Acceptance:
 bias current below 100 nA/cm2 at 1.1FDV and R.T. (for L0,L1,L2-L5)
 L0: 1 A at 1.1 x FDV
 L1: 1.7 A at 1.1 x FDV
 L2-L5: 3.8 A at 1.1 x FDV
 bias current below 4 A at 700V (for L0, L1) or below 16 A at 350V (for L2-L5).
SMU
HV source
Test chuck
Probe on the
bias line
-HV
+HV
pA
GND
Fig.3: The setup for the leakage current measurement (I-V).
4.3. Sensor Subset Tests
As described in section 4, the sensor subset tests are conducted routinely on a fraction of
sensors only. The tests are designed to allow better evaluation of the general quality of
the sensor batches and to verify the sensor specifications in much more detail. The tests
must also be carried out on particular sensors if there are significant deviations between
the electrical parameters measured by the manufacturer and results from the testing
center, for example in the leakage currents.
The local coordinators determine which sensors are to be subject to the sample tests.
They may decide for example that it is advisable to carry out these tests specifically on a
sample of sensors with non-critical visible defects found during visual inspection (see
4.2.2.).
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After any sensor has been subject to any of the sensor subset tests described below, the IV measurement as listed in Section 4.2.3, must be repeated.
4.3.1. Definition of the subsets
The size of the fraction of sensors subject to the subset tests will be determined by the
Run IIb sensor coordinators and recorded in the parts flow document. They will choose a
sufficiently large fraction to enable firm conclusions to be drawn from the subset tests.
Generally, the appropriate subset fractions have been (are expected to be) determined as:



During prototype phase of all sensor types: the subset sample should consist of
75% of all delivered prototype sensors.
During pre- or pilot-production phase of all sensor types: the subset sample
should be ~35-50% of all delivered sensors.
During production phase of all sensor types, the subset sample is ~20% with a
later reduction to 10% if the measurement results are consistent with each other
within production batches and with the vendor QC reports.
.
4.3.2. Leakage Current Stability – I vs. time Curve
This sensor subset stability test I(t) verifies that any variation in sensor leakage currents
over a 24-hour period is within acceptable limits. The stability test is carried out at the
central distribution center. A light-tight enclosure housing several sensors, a (multichannel) power supply, pico-Ampmeter(s) and a temperature/humidity monitor are
required for the test. The sensors may be placed in individual holders that permit them to
be conveniently biased through wire-bonded wire leads.
The bias voltage is ramped to the test voltage (FDV+20V). Then the bias currents and
temperature/humidity are measured and logged every 15 minutes over a 24 hour period.
A current limit of 50A must be imposed throughout the measurement. The schematic of
this measurement is the same as for Fig.3. An appropriate choice of sensors for the I(t)
stability test is selecting from each batch one representative sensor and/or one sensor with
relatively high but acceptable leakage currents.
The sensors which are subject to this leakage current stability test must be identified in
the database, and the temperature, humidity, test voltage, maximum leakage current,
maximum leakage current variation, and date of the tests also logged in the database. The
raw data file of the individual voltages and currents measured during 24 hours is also
uploaded to the database.
Acceptance:
The leakage current stability of the sensors at high voltage was not explicitly specified.
However a variation in leakage current during 24 hours of less than 20% after correction
for temperature variation is expected and desired.
4.3.3 Full Strip Test (AC scan)
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This sensor subset test probes every (readout) strip of the sensor in order to determine the
coupling capacitance of the readout strip, to check the capacitor dielectric for pinholes,
and to look for strip metal and implant shorts and opens. The AC-scan is a crucial sensor
subset test and every testing center having an automatic probe station must be able to
perform it.
Procedure and Equipment:
The test requires that all readout strips be separately probed while the sensor is partially
depleted via contacts to the sensor bias rail and backside. The test requires a separate bias
voltage source to deplete the sensor, a voltage source with current limit and a pA-meter
(e.g. a Keithly 487/237 SMU) to check for pinholes. Moreover, an LCR-meter and
external adaptor for the coupling capacitance measurement is required as well as an
automatic computer controlled probe station to effect the precise movement of the probetip from pad to pad. Connect the electrical test equipment, sensor, and probe chuck as
shown in Figure 4. (The bias may be connected by use of a chuck-mounted probe which
contacts the bias rail, by a probe on the “arm” of the probe station which contacts the
“long window” in the passivation on the bias line, or by an auxiliary connection
wirebonded to the sensor via a special sensor holder).
Only the AC-contact pads designated for probing should be probed during the
measurements. Set the current limit of the SMU to a maximum of 50uA during all
phases of the testing. Mount the sensor backside down on the chuck and align it carefully
to the axes of the probestation, and set the vertical elevation of the sensor to ensure
complete but careful contact of the probe to the sensor.
After selecting all appropriate operating parameters for the probe station control
computer program (previously written and debugged for such measurements), probe all
readout strips according to the following protocol:
1. Apply +20V from the bias voltage source to the sensor backside with the bias rail at
ground potential in order to partially deplete the detector and step to strip N.
2. Raise the chuck to contact the AC probe pad on the strip.
3. Increase the test voltage to +80V (with ramp, current limit always applied), wait 1
second and recheck the current.
4. Decrease the test voltage to 0V (with ramp).
5. Wait 1 second and measure C (at 1kHz, with the LCR meter set to Cs-Rs mode).
6. Lower the chuck to disconnect the probe from the pad.
7. Return to step 2 and repeat the measurement cycle for strip N+1.
Acceptance:
The specification requires <1% defective strips for all sensor types. The definition of a
defective or bad strip is provided in the appended D0 Run IIb Detector Specification.
Defective or bad strips in general have:
 Pinholes – current through the capacitor >10 nA at 80 V and RT
 Short – coupling capacitor >1.2 times the typical value
 Open - coupling capacitor <0.8 times the typical value
 Strip leakage current in excess of 10nA measured at RT and FDV
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 Bias resistor not consistent with 0.8  0.3 M, or interstrip resistance < 2 G
The first three defects can be detected with the AC-scan. If for any strip an open or short
is detected, a visual inspection of the strip at high magnification must be made to attempt
to verify the defect visually.
LCR-meter
H
L
С2=1μF
С1=1μF
Probe on the
bias line
R=300 kOhm
Probe on the
AC contact
pad
Bias voltage
source
(~20V)
+HV
-HV
GND
Test chuck
+V
-V
pA
pA-meter
Test voltage source
(1-100V)
SMU
Fig.4: The setup for the full AC strip test (AC-test).
The mean over all strips of the measured coupling capacitor value, the date of
measurement, and the strip number of any bad strips, must be recorded in the database.
The raw measurement file must also be uploaded to the database.
4.3.4. Strip leakage current test (DC-scan)
It is appropriate to schedule for a DC-Scan any sensor for which the bias current from the
I-V test (see 4.2.4) is significantly different from the bias current data reported by the
vendor, or the leakage current stability test (see 4.3.2.) gives unacceptable or unstable
results, or the visual inspection identifies a strip region with significant flaws. The DC
scan measures the individual strip leakage currents.
15
Procedure and Equipment:
This sensor subset test requires an automatic probe station with high moving accuracy
and good repeatability since the DC-pads on the sensor are very small. A voltage source,
two pA-meters (called "strip" and "bias") are also required.
The equipment is connected as shown in Fig 5. The bias to the sensor may be connected
in the same manner as described in 4.3.3 above.
Under computer control, probe all DC readout strips according one of the two following
procedures. Which of the two procedures to follow depends on the type of the contact to
the bias line. If the bias line is continuously connected Procedure A, which leaves the
bias voltage on throughout the tests, is used. If the bias line is connected and
disconnected for each strip (i.e. if the bias line is contacted by a probe which rides on the
arm and which touches the “long window” in the bias passivation), the bias voltage must
be ramped anew for each strip and decreased to zero before the probe is lifted from the
DC pad under test. For this case, Procedure B is used.
Procedure A (continuous contact with the sensor bias line):
1. Set (with ramp) the bias voltage at max(1.1FDV,FDV+20V).
2. Step to strip N and raise the chuck, i.e. contact the pad with the probe.
3. Measure the bias current with the "bias" pA-meter. If the bias current is significantly
lower than in the previous step, stop the measurement, turn off the bias voltage,
switch on the light in the dark box and check the contact to the bias line.
4. If step 3 was OK, then measure the strip current by the "strip" pA-meter.
5. Lower the chuck, i.e. lift the probe tip from the pad.
6. Repeat the measurement cycle from step 1 onward for strip N+1.
7. After the last strip measurement has been performed, decrease the bias voltage source
to 0V (no ramp).
Procedure B:
If the sensor bias is interrupted at each measurement (e.g. a probe mounted on the probe
station “arm” is used to contact the "long window" in the bias line passivation.
1. Step to strip N and raise the chuck, i.e. contact the pads
2. Set (with ramp) the bias voltage to max(1.1xFDV,FDV+20V) and wait 1 second.
3. Measure the bias current with the "bias" pA-meter. If the bias current is significantly
lower than in the previous step, stop the measurement, turn off the bias voltage,
switch on the light in the dark box and check the contact of probe to the bias line.
4. If step 3 was OK, then measure the strip current by "strip" pA-meter.
5. Decrease the bias voltage source to 0V (no ramp).
6. Lower the chuck, i.e. lift the probe tip from the pad.
7. Repeat the measurement cycle from point 1 above for strip N+1.
16
Strip pA-meter
Probe on the
DC contact
pad
pA
Bias pA-meter
pA
Probe on the
bias line
Bias voltage
source
+HV
-HV
GND
Test chuck
Fig.5: Setup for the full strip test (DC-scan).
Acceptance:
The specification requires <1% defective strips in any sensor type. If the strip current
exceeds 10nA at FDV and RT, the strip is designated a defective strip. After the DC-scan
has been performed, the database should be updated and the bad strip numbers as
obtained from the DC-scan should be stored in the database.
4.4. Diagnostic Tests
The sensor diagnostic tests comprise special tests which provide more detailed evaluation
of the electrical parameters of the sensors. The diagnostic tests are either done on single
strips of the sensors or on the corresponding test structure which is delivered with each
wafer. The test structure layout (“halfmoon”) and the structures implemented on it are
described in http:///www.physik.unizh.ch/~lehnerf/dzero/teststructure/teststructure.html.
The diagnostic tests are a set of detailed electrical measurements of complex sensor/wafer
properties. The results of the sensor diagnostic tests will give comprehensive information
of the overall silicon sensor performance. The RunIIb silicon sensor coordinators will
routinely cause these tests to be performed on a small sample of sensors selected at
random.
After each sensor diagnostic test, the I-V measurement on the sensor as described in
Section 4.2.4 must be repeated.
17
4.4.1 Polysilicon Resistance
On the test structure:
This test requires a voltage source, a pA-meter and the appropriate resistor bank structure
on the test structure. Place the test structure backside down on the chuck of a probe
station. Contact the two contact pads of the polysilicon resistor piece on the test-structure
and step a testing voltage from -1V to + 1V in 0.1V increments and record the current.
Plot the I-V data and fit to a straight line to obtain the value of the polysilicon resistor
from the I-V curve. Note, that there are several polysilicon arrays on the teststructure,
which all should have the same mean resistor value, but some of them could deviate from
linearity at applied voltages higher (lower) than 3 V (–3V).
On the sensor:
Place the sensor backside down on the chuck of a probe station and contact the bias rail,
chuck and DC-pad of any strip according to the schematic in Fig.6. Beside the bias
supply you need an additional small test voltage supply to apply a testing voltage across a
polysilicon resistor. The detector does not need to be fully depleted so set the bias voltage
to10V. Step the testing voltage from -1V to + 1V in 0.1V increments and record the strip
current. Fit the I-V curve with a straight line to obtain the value of the polysilicon
resistor. Measure at least 5 strips on the sensor to get a representative sample.
Note that you can get a mistakenly low resistance if the strip has extremely high leakage
current (>100nA@10V). Note also, that the recorded value of the polysilicon resistance
can be affected if the interstrip resistance is much lower than specified. Since the strips
act then as an extended resistive network a low value for the bias resistor is then
mistakenly extracted from the measurements.
.
Acceptance:
The polysilicon resistor values must satisfy 0.8+0.3 Mohm.
18
Fig.6: Setup for the polysilicon bias resistor measurements on the sensor.
Remark 1:
The “true” polysilicon resistor on the sensor is only measured if there is in fact a
polysilicon resistor between the contacted DC–pad and the bias rail. If the polysilicon
resistor is on the other end of the strip, i.e. separated from the DC-pad, then the implant
resistance is measured as well and the observed resistance is a summed series resistance
of the two. The measurement of the implant resistance alone is described in section 4.4.4.
Remark 2:
HPK has suggested another setup to measure the polysilicon resistors on sensors. This
setup requires a second probe tip. Set the bias voltage of the detector to 10V. Contact the
strip under test and its neighbor strip at their DC-pads. Connect the DC-pad of the
neighbor strip to the bias rail and apply a test voltage from 0V to –1V. Measure the DC
current of the strip under test through a pA-meter. Then, calculate the resistance by
simply dividing the voltage by the currents.
19
4.4.2 Strip and Interstrip Capacitance
This test consists of two measurements with the objective of determining the total strip
and interstrip capacitance. The total strip capacitance is the capacitance to ground, which
represents a total load capacitance for the preamplifier and hence determines the noise in
the front-end. The total strip capacitance consists of the interstrip capacitance, i.e. the
contribution from one strip to the neighbor strips and the capacitance of one strip to the
sensor backplane. Typically, for the Run IIb detectors, the total strip capacitance is
dominated by the interstrip capacitance due to the narrow strip spacing and the backplane
capacitance contributes only 15-25% to the total. For that reason the interstrip
capacitance of the sensor is the more important quantity.
In this measurement we are only interested in readout strips, i.e strips having an AC-pad.
The intermediate strips are floating with respect to the virtual ground of the preamplifier
and will not be contacted with probe tips in these measurements. The capacitance tests
require an LCR-meter and a voltage source, as well as up to four probe manipulators. An
external adaptor (with decoupling capacitors) is required to protect the input terminals of
the LCR meter from the bias voltage as shown in Fig. 7.
This strip capacitance measurement has a very important impact on the noise estimations
for silicon ladders and this test as been performed very carefully and thoroughly on
prototype sensor samples for up to 5 strips per sensor. It is also very important to perform
this measurement on irradiated sensors.
4.4.2.1 Procedure for Interstrip capacitance Cint
Place the sensor on the chuck of a probe station, and contact the bias rail by a probe
needle. Following the schematic of Fig. 8, the backside and the bias rail should be
connected to the high and grounded-low sides respectively of the voltage source. Turn on
the bias voltage to FDV+20V. Place two coaxial (if available) probes on the AC-contact
pads according to the schematics of Fig.9.a, and measure the capacitance value. This
value is to a good approximation the Interstrip capacitance Cint to one neighbor strip
only. For each capacitance measurement sweep the test frequency from 1kHz to a few
MHz with the LCR meter in Cs-Rs mode at oscillator amplitude 1V. The measured
capacitance will flatten off towards higher frequency.
In addition to the frequency scan, a voltage scan of the capacitance is required, i.e. fixing
the frequency to 1MHz and ramping the bias voltage from 0V to FDV+20V.
20
LCR-meter
H pot.
Ext. adapter
to probe 1
L pot.
A
100 nF
curr.
100 nF
curr.
H curr.
L curr.
Screens @ shields of
ext. adapter and cables
to different combination of
probes and to chuck,
according the schematics
GND
Fig.7: External adapter for the LCR meter for the strip capacitance measurements.
Bias voltage source
Probe on the bias line
-HV
+HV
R=1MOhm
R=1MOhm
Test chuck
Fig.8: Biasing the detector for the strip capacitance measurement.
21
Fig.9.a: Measurement of the interstrip capacitance Cint.
22
Fig.9.b: Measurement of the total strip capacitance Ctot.
4.4.2.2 Procedure for total strip capacitance Ctot
It is useful to make an additional measurement, which determines the total strip
capacitance, i.e. the total capacitance of one strip as seen by the preamplifier. Figure 9b
shows the setup, with the intermediate strips omitted from the drawing. An external
adaptor (with blocking capacitors) protects the LCR from the bias voltage, and the sensor
is biased up to FDV+20V. As it is in the case of the interstrip capacitances, it is important
to probe the AC-pads of the readout strips only. The capacitance value at a frequency of
1MHz is taken as representative. A four-probe connection to the LCR yields greatest
precision.
Note, that Cint as it is measured in figure 9a is defined as the capacitance to only one
neighbor. The total interstrip capacitance is twice as much and is specified in the
acceptance criteria. Note also, that we extract the strip capacitance values at a frequency
of 1MHz.
Acceptance:
Only the interstrip capacitance is explicitly stated in the specification, and the following
values are expected:
23
 The capacitance from the strip to the backside should be less than 0.3 pF/cm at
FDV+20V bias.
 The interstrip capacitance (here: interstrip capacitance to left and right neighbor) must
be less than 1.2 pF/cm at FDV+20V bias, i.e. less than 9.2 pF for L0&L1 and less
than 11.8 pF for L2&L5.
4.4.3 Metal Series Resistance
A series resistance in front of the preamplifier adds noise to the electronics. Although the
ENC noise contribution due to the metal resistance on our silicon detectors is not
dominating, the metal resistance should be checked. This test requires a voltage source a
pA-meter and a test structure. Apply a voltage between the two ends of the appropriate
metal line test-structure (if available) or to either end of one of the detector metal strips
(if no test-structure is available). Set the testing voltage from -0.5V to + 0.5V in 0.1V
step and read the current. Calculate the resistance value per 1cm of the metallization from
the I-V curve.
Acceptance:
The series resistance should be less than 20 Ohmcm for L2&L5 and less than 30
Ohm/cm for L0&L1.
4.4.4 Implant resistance (on the test structure only)
This test requires a voltage source, a pA-meter and a special test structure. Place the
piece of the wafer with the test structure with the backside on the chuck. Apply a voltage
between the two ends of the contact pads of the test structure. Set the testing voltage from
–1V to +1V in 0.1V step and read the current. Calculate the resistance value per 1cm of
implantation from the I-V curve.
Acceptance:
The implant resistance is not explicitly specified, since it depends on the exact doping
concentration. However we expect values of less than 200 KOhm/cm.
4.4.5 Flat band voltage (on the test structure only)
This test requires an LCR-meter with an internal DC voltage source. Also a MOS teststructure is necessary. Place the piece of wafer with the MOS test structure with the
backside on the chuck of the probe station and contact the MOS pad with a probe needle.
Connect the MOS metal to the H-output of the LCR-meter and the backside to the Loutputs of the LCR-meter. Measure the capacitance across the MOS as a function of the
internal DC bias from -20V to +20V with a step of 1V and delay 1s (before the
measurement). Set the following parameters on the LCR-meter: test frequency 1kHz;
mode Cs-Rs; AC test voltage value 0.1V.
24
Acceptance:
There are no defined acceptance criteria. The flat band voltage is used as a monitor of the
processing consistency and measures mainly the fixed oxide charge density.
4.4.6. Interstrip Resistance.
This test requires a pA-meter and two voltage sources. Place the detector backside on the
chuck of a probe station and contact the bias rail, chuck and DC-pads of strips N and N+1
according the schematics of Fig.10.
Set the bias voltage on the sensor by ramping up to FDV+20V. Then execute the
following procedure:
1. Step the testing voltage (Vt) from -1V to +1V in 0.1V increments with a delay not less
then 5s at each step;
2. Read the strip current (Istr).
Fit a straight line to the I(V) data to obtain the interstrip resistance
Rintrstr = V/Istrip.
Note that for a non-irradiated sensors the interstrip resistance can be very high with
values of about 100 GOhm, so the setup must allow to measure small changes of strip
currents (10 pA). The delay before the actual strip current measurement must be long
enough to stabilize the strip current.
Acceptance:
The interstrip resistance must be higher than 2 GOhm.
Test voltage source
+V
Probe on the DC
contact pad N+1
-V
Probe on the
DC contact pad N
pA
Probe on the bias line
Bias voltage source
+HV
-HV
GND
Test chuck
25
Fig.10: Interstrip resistance measurement.
4.4.7. Coupling Capacitance
4.4.7.1. Coupling capacitor value (on the test structure only)
Although the AC strip test measures the coupling capacitors, a precise determination of
the coupling capacitor value is done on a test structure. The measurement requires an
LCR-meter and a special test structure, which should have a single AC-coupled strip
similar to the ones, which are on the sensors. Place the piece of the wafer with the test
structure backside on the chuck of a probe station and contact the AC and DC contact
pads of the strip with probe needles to the LCR-meter outputs. Measure the capacitance
between the metallization (AC-pads) and implantation (DC-pads) at several frequencies
down to 500Hz in Cs-Rs mode. Determine the true value of the coupling capacitance in
the low frequency limit.
Acceptance:
The coupling capacitance should be higher than 12 pF/cm.
4.4.7.2. Strip capacitors breakdown voltage (on the test structure only)
This (destructive) test requires a voltage source/pA-meter (e.g. Keithley 487/237 SMU)
and the special test structure with a single AC-coupled implantation.
Place the piece of the wafer with the test structure backside down on the chuck of a probe
station and contact the AC and DC contact pads of the strip with probe needles to the
SMU. Use a serial resistor with 10MOhm value in series with the input of the SMU pAmeter. Measure the leakage current through the strip capacitor by ramping the testing
voltage from 1V to 100V in steps of 5V and with a delay of 1s (at least) between steps.
The capacitor breakdown is defined at the voltage when the current reaches 100nA or
more.
Acceptance:
The breakdown voltage of the coupling capacitors must exceed 100V.
4.5 Mechanical tests
A number of mechanical measurements on silicon sensors will be routinely performed on
a fraction of sensors from each production batch. The measurements verify the
mechanical specification of wafer thickness, wafer warp and cutting accuracy and will be
carried out at the central distribution center (i.e. at Fermilab) primarily on an optical
metrology system. The Run IIb sensor coordinators will specify the size of the fraction of
sensors routinely measured. During production, 10% of the sensors per production batch
are probably sufficient for this QA procedure. In the prototype phase however, the tested
26
sensor number is generally higher. Exact numbers of sensor fractions are given in the part
flow document.
4.5.1. Sensor thickness
The wafer thickness can be easily measured on the test structure pieces with the help of a
screw micrometer. The thickness of the test structure pieces are measured at several
positions and averaged. The resulting value and its RMS is stored into the database. The
accepted sensor thickness must lie within 32020 m.
4.5.2. Sensor warp
The sensor warp is measured with the sensor in a free state on an optical metrology
machine (e.g. OGP). The best-fit plane is determined, and the RMS and the maximum
deviation are recorded into the database. The acceptance criterion was originally that the
flatness of the wafer should be within 25 m, but this criterion is on a best effort base
and it may be relaxed to 50 m.
4.5.3. Sensor cut dimensions and cutting accuracy
The cutting length and width are determined on an optical metrology machine (e.g.
OGP). The accuracy of the cutting line with respect to the nominal cutting line must be
better than 20m and its parallelism to the datum line defined by the fiducial targets
must be better than 10m.
27
5. A short summary of the QA-program.
This section summarizes the QA-program with the four main parts.
QA-item
QAsubprogram
Initial
registration
Key test
Visual
Inspection
C-V
I-V
QA-test
performed
where
Frequency of
QA-test
100%
Key test
Central
Distribution
Center (CDC)
CDC
Key test
Key test
CDC
CDC
100%
100%
I(T)-stability
AC-scan
Subset test
Subset test
CDC
TC
DC-scan
Subset test
TC
Polysilicon
resistor
Strip
Capacictance
Metal series
Resistance
Implant sheet
resistance
Flat band
Diagnostic test
TC
Diagnostic test
TC
Diagnostic test
TC
Diagnostic test
TC
Diagnostic test
TC
Interstrip
resistance
Coupling
Capacitor
Wafer thickness
Wafer warp
Wafer cut
accuracy
Diagnostic test
TC
Diagnostic test
TC
Mechanical test
Mechanical test
Mechanical test
CDC
CDC
CDC
100%
Sensor subsets
(e.g. 10%)
Sensor subsets
(e.g. 10%)
Sensor subsets
(e.g. 10%)
e.g. 10% per
batch
e.g. 10% per
batch
e.g. 10% per
batch
e.g. 10% per
batch
e.g. 10% per
batch
e.g. 10% per
batch
e.g. 10% per
batch
10% per batch
10% per batch
10% per batch
28
6. Requirements for the Database.
6.1 Proposal for Table definitions
Our general D0 Run IIb detector testing and assembly database is adopted from the
ATLAS SCT and will be redesigned at Fermilab. We will follow in our proposed table
definitions very closely the ATLAS SCT design ideas. The exact format details of the
database for silicon sensors has not been finalized, but for production sensors it may
prove convenient to divide the sensor QA data records into several tables (with data type
as indicated). We propose to store only summary information on sensors in tables. The
raw data from the sensor QA measurements (e.g. leakage current of a sensor in 10V
steps) are stored in separate test raw data tables, called “TEST_RAWDATA” in the
ATLAS SCT design. Every sensor table, to which raw data exist, has a special test
number so that the raw data can be referenced to.
We propose to have the following main tables:
1. Vendor information table (“TSTDETMFRS”)
 Test_Number for referencing the raw data: Long Integer
 Sensor-ID: Long Integer, e.g. 9847463
 Manufacturer: Characters, e.g. Hamamatsu
 Sensor type: characters, e.g. L0 or L1 or L2-L5
 Production type: characters, e.g. prototype or pre-production or production
 Arrival date at central distribution center: date format, e.g. 9/30/02
 Wafer lot/batch information: characters, e.g. SW4751
 Wafer thickness in µm: Float, e.g. 320
 Depletion voltage (V): float, e.g. 147
 Leakage current at 100V in A: float e.g. 1.2
 Leakage current at 300V in A: float e.g. 2.4
 Leakage current at 500V in A: float e.g. 3.0
 Leakage current at 700V in A: float e.g. 3.8 (this field is only active is the
sensor type is L0 or L1
 Number of bad channels/strips: integer, i.e. 2
 Strip numbers and type of defects: integer and characters: e.g. 3 pinhole, 182
metal open. Type of defects are: pinhole, metal open, metal short and leaky
strip
 Polysilicon average resistor value in MOhm: float, e.g. 1.15
 Polysilicon upper resistor value in Mohm: float
 Polysilicon lower resistor value in Mohm: float
 Aluminium trace resistance value in Ohm: float, e.g. 170
 Implant resistance value in MOhm: float, e.g. 1.6
 Average Coupling Capacitor value in pF: float, e.g. 120
 Coupling capacitor breakdown value in V: float, e.g. 240
29




Comments for other measurements: characters
Owning institute at time of record, character
Date record of last modified, date format
Flag (checkbox) for potential missing vendor information: Boolean
The vendor raw data, in particular the leakage current values of the sensors in
20V steps should be uploaded to a raw data test table in a special raw format.
Furthermore, a web-interfaced program is necessary which allows entering the
complete vendor information data for one individual sensor once.
2. Key Test Table (propose the name “TSTDETKEY” or similar, for I-V curves, CV curves and for the visual inspection.)
 Test_number for referencing raw data
 Sensor-ID
 Sensor type
 Visual inspection: Characters for comments
 C-V curve: measurement record indicating:
o Depletion voltage
o Date and location of measurement
o Temperature and humidity
o comments
 I-V curve: measurement record indicating:
o Leakage current in µA at 100V, 200V, 300V, 400V and 500V for L2-L5
or leakage current at 100V, 200V, 300V, 400V, 500V, 600V and 700V
for L0&L1
o breakdown value
o Date and location of measurement
o Temperature and humidity
o Comments
 Sensor marked for 1=subset tests (1a=I(t), 1b=AC, 1c=DC), 2=diagnostic
tests, 3=mechanical tests, 4=irradiation test (only baby detector is being
irradiated)
 Owner
 Last modified
Again, we need raw data tables, which are linked to the key test table for each individual
sensor. If several I-V or C-V curves are taken, then the database has to keep track of this.
3. Sensor Subset Test Block (Note, that this table for one sensor is only created if
the sensor flag in the previous table key test is set to 1=subset tests)
 Test_number
 sensor-ID
30




sensor-type
leakage current stability:
o measurement record should contain bias voltage setting
 min/max current deviation over 24h
 Date and location of measurement
 Temperature and humidity range
 Comments
 AC-scan: measurement record should contain:
 Number of bad strips, e.g. 3
 Bad strip list with fail criteria: e.g. 35 pinhole, 67, 236 metal open
 Date and location of measurement
 Temperature and humidity
 Comments
 DC-scan: measurement record should contain
o bias setting
o number of leaky strips, e.g. 1
o Bad strip list with fail criteria: e.g. 134, I_strip=20nA
o Date and location of measurement
o Temperature and humidity
o Comments
Owner
Last modified
4. Diagnostic Tests Block. (Note that this block is only created if the sensor flag in
the previous table key test is set to 2=diagnostic tests)






Test_Number
Sensor-ID
Sensor type
Polysilicon value: measurement record
i.
Value in MOhm
ii.
Date and location of measurement
iii. Temperature and humidity
iv.
Comments
Strip and interstrip capacitance: measurement record
i.
Value of interstrip capacitance and backplane capacitance in
pF/cm at three different frequencies (1kHz, 10kHz and 100kHz)
ii.
Date and location of measurement
iii. Temperature and humidity
iv.
Comments
Metal series resistance: measurement record
i.
Value of metal series resistance in Ohm/cm
ii.
Date and location of measurement
iii. Temperature and humidity
iv.
Comments
31




Implant Sheet resistance: measurement record
i.
Value of implant sheet resistance in kOhm/cm
ii.
Date and location of measurement
iii. Temperature and humidity
iv.
Comments
Interstrip resistance: measurement record
i.
Value of interstrip resistance in MOhm
ii.
Date and location of measurement
iii. Temperature and humidity
iv.
Comments
Coupling Capacitor breakdown: measurement record
i.
Value of coupling capacitor in pF/cm
ii.
Value of coupling capacitor breakdown in V
iii. Date and location of measurement
iv.
Temperature and humidity
v.
Comments
Flatband voltage: measurement record
i.
Value of flatband shift in V
ii.
Date and location of measurement
iii. Temperature and humidity
iv.
Comments
5. Mechanical test table. (Note that this block is only created if the sensor flag in the
previous table key test is set to 3=mechanical tests).





1.
Test_number
Sensor-ID
Sensor-type
Average and RMS wafer thickness in µm measurement record:
i. Average wafer thickness value in µm
ii. RMS value in µm
iii. Date and location
iv. Temperature and humidity
v. comments
Sensor warp measurement record:
vi. RMS in µm
vii. Maximum deviation in µm
viii. Date and location
ix. Temperature and humidity
x. Comments
Sensor cutting accuracy measurement record:
xi. Parallelism in µm
xii. Cutting accuracy in µm
xiii. Date and location
xiv. Temperature and humidity
xv. Comments
32
6. Irradiation table (only created to a sensor, if the sensor flag in the key test table is
set to 4=irradiation)
o Test_number
o Sensor-IDs
o sensor-type
o Date and time of first irradiation session
o Data and time of second irradiation session
o fluence of first irradiation session 1 MeV neutrons/cm-2
o fluence of second irradiation session 1 MeV neutrons/cm-2
o annealing procedure
o initial depletion voltage
o depletion voltage after 1st session
o depletion voltage after 2nd session
o leakage current at depletion voltage (T=20C) after 1st session
o leakage current at depletion voltage (T=20C) after 2nd session
o breakdown voltage after 2nd session
o comments and other measurements
7. Shipping tables. These tables should be filled whenever a sensor is shipped from
the central distribution center to the testing centers and vice versa. The ATLAS
SCT database design foresees two special tables a SHIP table for the details of
the shipment and a SHIP_ITEMS table to map certain items onto a shipment.
8. Reject table. This table lists failed or “trashed” (=broken) sensors
o Sensor-ID
o Sensor-type
o Source of failure: 1=vendor information, 2=key test, 3=subset test,
4=diagnostic test, 5=mechanical test, 6=irradiation test, 7=damaged
o Detailed failure mode comments:
o Sent back to vendor: date
o Owner
o Last Modified
A final summary table for each sensor includes the most important sensor properties and
information. The table should also contain grading information for the assembly process.
We propose to use 4 grades: A, B, C, and D-grade or “excellent”, “good”, “bad” and
“trashed”. The summary table could be automatically filled and updated.
9. Sensor summary table
o sensor-ID
o sensor-type
o present location
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o assembled? yes/no
o leakage currents at 100V, 300V, 500V and 700V (700V in case of L0 and
L1)
o breakdown voltage
o depletion voltage
o comments from visual inspection
o number of bad channels/strips
o list of bad channels and type of defects
o results from diagnostic tests
o final sensor grade: A, B, C, D
o Owner
o Last Modified
Grade A and B sensors have to fulfill all outlined specifications. Grade A sensors are
defined by less than 0.5% bad channels, grade B sensors by 0.5%<N_bad<1%.
Grade C sensors fail either the 1% spec on the bad channels marginally or show slightly
higher leakage currents/lower breakdown voltage as specified. Grade C is given to
sensors by an individual judgment of the Run2b silicon sensor coordinators. Such graded
sensors are not subject for an reject.
Grade D sensors are sensors, which either have missing vendor information, or have
clearly failed the specs, or have been broken by accident or trashed during the QA
program. In the case of the missing vendor information or vendor information, which is
non-compliant with specs, the sensors have to be treated as rejects.
6.2 Proposal for a common data format at the testing center
We propose a common data format for the sensor probing results. After several
discussions the testing centers agreed on such a common data format, so that the raw data
files can simply be uploaded into corresponding raw data tables for each of the sensor
tests by using the same client software. We are proposing an Excel based spreadsheet,
which contains the sensor probing information from the testing centers. To every sensor
an excel spreadsheet file will be generated. A simple filter program allows then an
insertion of the raw data into the database.
The excel spreadsheet has seven worksheets labeled as follows:
1. Summary – summary information:
a. Sensor serial number and type
b. Testing site
c. Operator’s name
d. Temperature and humidity
e. Depletion voltage FDV
f. Leakage current at FDV+20V
g. List of bad channels by category:
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h.
i. Pinholes (current through capacitor is >10nA at
ii. Shorts (Coupling capacitor is greater than typical)
iii. Opens (Coupling capacitor is less than typical)
iv. Leaky strips (I leak > 10 nA/strip)
v. Bad R poly (outside 0.80.3 MOhm window)
vi. Other bas strips (low interstrip resistance etc)
Detector grade( to be defined on the above data)
80V)
2. Special – this is to be defined and is reserved for later purposes
3. Test – contains mainly teststructure data
4. Rint – interstrip resistance value versus strip number from the full
strip test
5. Cint - interstrip capacitance value versus strip number from the full
strip test
6. Rpoly – polysilicon resistor value versus strip number
7. Ileak – strip leakage current value versus strip number
8. Cac – coupling capacitor value versus strip number
9. Idiel – leakage current through coupling capacitor at 80V versus strip
number
10. C-V – 1/C2 bulk capacitance versus bias voltage in 10 V steps
11. I-V – standard I-V curve in 10 V steps
An example of the standard excel spreadsheet file for the testing centers is available on
http://www.physik.unizh.ch/~lehnerf/dzero/db/db.html
7. Required and Recommended Equipment for the Testing Centers.
A list of required laboratory equipment for the testing centers which are participating in
the D0 RunIIb sensor QA program is shown below. The recommendations for the
equipment indicate that such equipment has proven adequate in the past. Alternative
equipment is acceptable if the equipment specifications are comparable. The
measurement devices and automatic probe stations should be readout by a PC. The
preferred computer control software is Labview communicating with the test
instrumentation using the GPIB (IEEE488) bus protocol and cables.
1. Automatic (computer controlled) probe station with at least 5 probes
(3 coaxial and 2 ordinary) on a vacuum or magnetic base (preferable).
Typical models: Wentworth AWP-1050/1080, Summit 10K, Alessi 6100,
Rucker & Kolls 680/683, Electroglas 1034A6 etc.
The chuck must accomodate 6-inch wafers.
2. High Magnification Optics with a Video Capture Card or Digital Camera
e.g. Leica Microzoom II, up to x500 for the automatic probe station.
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3. Additional Stereo-Zoom Microscope with zoom ~50-100.
Models: Olympus, Nikon, Leica, Microlite, Bausch&Lomb or other types,
which provide the necessary magnification for visual inspections.
4. Probe needles with radius ~2m, ~10m, ~20m.
Type: appropriate for the probe station
Number: at least 50 for each size.
5. Pico-amperemeter with Voltage source (SMU).
Models: Keithley 487, Keithley 6517, Keithley 237.
Number: at least 3.
The best choice: 2 dev. Keitheley 487/6517 and 1 dev. Keithley 237
6. LCR meter.
Models: HP4263B, HP4284
7. Temperature Monitor.
Model: temperature monitor (thermocouple is included) in the SMU
Keithley 487/6517 is preferable.
Number: at least 2.
8. Humidity Monitor.
Model: any digital humidity monitor.
9. Dark box.
Model: any commercial or "home-made" metal black box large enough to
enclose the automatic probe station.
10. Networked PC with GPIB card and appropriate LabView control software.
.
11. Vacuum pump.
Model: according to the recommendations of the automatic probe station
vendors.
12. Vacuum pincers or vacuum pencils.
Model: see "Techni-tool" catalog (www.techni-tool.com):
#784PR444 - "Vampire Vacuum tool" or
#612PT702 - "Pace Handipic", or
#847PR902 - "Pen-Vac Deluxe Kit".
13. Conductive rubber.
Type: 40-10-1010-1221 or 40-20-1010-1273 or 40-10-1010-1285.
For more details see: http://www.chomerics.com
Quantity: at least 2 sheets with size 6"6".
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Fig. 12: A typical (here at KSU) probestation setup (w/o enclosure).
8. Silicon Sensor Specifications
This part is gone since version 4.0. The specifications are available on the www:
http://www.physik.unizh.ch/~lehnerf/dzero/specs/specs.html
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