CDF/DOC/TRACKING/PUBLIC/6283
V1.0
January 24, 2003

Silicon Sensor Quality Assurance for
the CDF Run2b Silicon Detector
N. Bacchetta1, G. Bolla4, D. Bortoletto4, A. Canepa4, B. Flaugher1, K. Hara6, D-H. Kim5,
S. Kim6, M. Hoeferkamp3, D. Pellet2, A. Roy4, S. Seidel3, Y. Takei6, I. Yu5
1

Fermilab, Batavia, Illinois, USA
University of California at Davis, Davis, California, USA
3
University of New Mexico, Albuquerque, New Mexico, USA
4
Purdue University, West Lafayette, Indiana, USA
5
CDF-Korean Group (Syungpook U, Sungkyunkwan U)
6
University of Tsukuba, Tsukuba, Ibaraki, Japan
2

Abstract
This document describes in detail the quality assurance (QA) program for the CDF
Run2b silicon sensors. The scope of the QA program, the responsibilities of theparticipating institutions and the measurement procedures are defined.

1. Introduction
The CDF collaboration is building a new silicon tracker system for Tevatron collider
Run2b, replacing the present L00 and SVXII detectors. The new silicon system will be a
six-layer device located between 2.1 cm and 16 cm radius, consisting of ~2300 single
sided silicon sensors. The planned silicon detector is expected to become operational in2005.
A thorough, reliable, and efficient silicon sensor probing and characterization, definedin a well-organized silicon quality assurance (QA) program, are critical for the sensor
quality and hence the success of the silicon detector. This document describes theprocedures, responsibilities and the organization of the silicon sensors quality control forRun2b. In particular this includes:ooooOrganization and responsibility of testing
Testing procedures and acceptance criteria
Testing setups
Accounting, documentation and database

2. General CDF Run2b silicon sensor QA organization issues
Quality assurance will be a collaborative effort and is shared among different
institutes. The Procurement Institutes and other institutes (Testing Institutes), which are1participating in the QA program, have to perform the quality checks in a consistentmanner as defined in the QA program described here. The responsibility for the complete
QA program implementation will be the task of the local coordinator of each of Testing
and Procurement Institutes. Before a Testing Institute will start to take part in the silicon
QA program, it has to be certified by the Run2b silicon group.
The Procurement and Testing Institutes presently foreseen are listed with the names of
local coordinators:
Procurement and Testing Instituteso University of Tsukuba, Japan. Local coordinator: Kazuhiko Harao Kyunpook National University, Korea. Local coordinator: Dong-Hee Kim
Procurement Instituteo Fermilab, Batavia, USA. Local coordinator: Nicola Bacchetta
Testing Instituteso University of New Mexico: S. Seidelo Purdue University: D. Bortolettoo University of California at Davis: D. Pellet
The three Procurement Institutes, University of Tsukuba, Fermilab, and Kyunpook
National University, perform dedicated testing and coordinating tasks. Its main tasks willbe:(1) Initial registration of the sensors(2) Visual inspection on and I-V measurement of the sensors(3) - Distribution of the sensors to outside Testing Institutes, or- Performance of an additional sensor characterization measurement programon sensor sub-samples(4) Shipping and handling of the rejects which are returned to the supplier(5) Overall monitoring of the QA program
The sensor characterization in Item (3) is carried out by Testing Institutes, and hence thesensors procured by Fermilab will be tested by outside institutes, Purdue University andUniversity of New Mexico. University of California at Davis will conduct irradiation
programs.
The qualified sensors will be gathered to Fermilab where sensors are assembled to thestaves. As the Assembly Institute, Fermilab will perform:(6) Collection of the test data and grading of the sensors(7) Visual inspection and I-V measurement of the sensors just before assembling
into the module
The above items (1) to (7) require coordinated work between the Procurement andTesting Institutes and their completion will be the responsibility of the appointed Run2b
silicon sensor coordinators together with the local coordinators at these institutes.
Among the above items, item (2) can be skipped later once the quality production isestablished. Such changes in the described procedures have to be agreed by the Run2b
silicon group. Figure 1 shows a graphical representation of the QA program with thesilicon sensor flow.

2

reject

Kyungpook

U. Tsukuba

Supplier

Supplier

UC Davis• manufacture QA• QA datasheet

Procurement Institutes

Fermilab

Purdue U.

Sensor registration
Visual inspection, I-V
QA on sub-sample, orcoordinate sub-sample tests
with Testing Institutes

Testing Institutes

U. NM

QA on sub-sample

n irradiation

Fermilab, assembly center
visual inspection, I-V

3. Overview of Sensor Design, Specifications and Terms of Acceptance3.1. General
All silicon detectors are p+n type single sided sensors, with AC coupling and biased
through polysilicon resistors. The silicon sensors will have a guard ring with peripheral nwell design. We envision three sensor types for Run2b:

Type

ActiveLength(mm)

ActiveWidth(mm)

Strip pitch /readout
pitch (µm)# readoutchannels# of sensors + spares

0 /Axial

77.36

12.8

25/50

256

144+30%=190

1-5 /Axial

94.35

38.5

37.5/75

512

1512+20%=1800

2-4 /Stereo

94.35

39.0

40/80

512

648+23%=800

Layers/All the sensors will be manufactured on 6’’ wafers.
Schematic drawings of the sensors, on which the location of strips, fiducial marks,
bonding pads as well as the strip numbering definition and other features are indicated,exist on http://hep-www.px.tsukuba.ac.jp/~hara/run2bsi.html. The sensors carry a 16-field
scratchpad for unique sensor identification1.
3.2. Specifications
The detailed sensor specifications are attached in the appendix of this note. The
following table gives an overview:
1

The serial numbers are given in BCD codes (each group of 4 digits represents one decimal number).
3

Specifications:
Wafer thickness
Full depletion voltage
Leakage current
Junction breakdown
Implant width
Al width
Coupling capacitance
Coupling capacitor breakdown
Interstrip capacitance
Polysilicon bias resistor
Defective strips

Inner Axial
320±15µm
wafer warp less than 130µm
120<Vdep<250V<50nA/cm2 at RT and at 500V
>500V
7 µm
1-3 µm overhanging metal>12pF/cm>100V<1.2pF/cm
1.5±0.5 MΩ<1%Outer Axial/Small Stereo
320±15µm
wafer warp less than 130µm
120<Vdep<250V<50nA/cm2 at RT and at 500V
>500V
8 µm
2-3 µm overhanging metal>12pF/cm>100V<1.2pF/cm
1.5±0.5 MΩ<1%

3.3. Terms of Acceptance
The silicon sensors will be delivered to three procurement institutes: University ofTsukuba (64% of Outer Axial and 44% of Outer SAS), Fermilab (36% of Outer Axial,
56% of Outer SAS, and a% of Inner Axial), and Kyungpook National University (100a% of Inner Axial)2. The procurement institutes will initially accept the silicon sensors
delivered by the supplier and preliminary qualify them as good according to the test
results of the supplier, if the criteria described in the sensor specifications are fulfilled.
These institutes will carry out on every delivered sensor an electrical I-V measurement
and a visual inspection. For a sub-sample of the delivered sensors, thoroughmeasurements of the QA program will be performed to confirm the specifications.
Fermilab will distribute the sensors to outside institutes for this program. Based upon the
results of these measurements, the procurement institutes will reject a sensor within 6months after delivery. The supplier will be notified and upon request the sensors will be
returned for re-measurements. The supplier and the procurement institutes together with
the Run2b silicon sensor coordinators can agree upon the acceptance of individual
sensors if specifications are missed only marginally.

4. The QA Program
We describe in the following the complete QA program for the Run2b silicon sensor
testing. The QA program consists of three main parts:
1. The visual inspection and I-V measurement are most critical and yet can be done in areasonable time. These tests are to be performed on every received sensor at theProcurement Institutes. The same tests are carried out at Fermilab prior to assembling
the sensors into modules. As we gain the experience and if the QA group agrees, thetests at the Procurement Institutes could be skipped: We maintain the tests at
Fermilab prior to assembling.
2

The percentage a is under discussion, while we aim it to be 0.
4

2. The tests on subsets of the sensors will be conducted on a certain fraction ofdelivered sensors. The fraction depends on the quality of the products and the stageof production but keeps at least one senor per batch. The main goal of the subset tests
is to verify the specifications more in detail. The subset tests are mostly done in an
automatic electrical measurement procedure on an automatic probe station at Testing
Institutes. The mechanical test measurements are also included to verify themechanical tolerances. Fermilab will conduct the mechanical tests for their delivery.
3. Diagnostic tests are to be performed primarily on the sensors with observed
irregularities. The tests on irradiated samples are also included. The diagnostic tests
may measure in much more detail complex electrical parameters, depending on theirregularity, in order to get a deeper insight into the sensor qualities.

4.1. General Conditions/Requirements of Testing
4.1.1. Clean Room Conditions and Handling of Sensors
A clean room or a clean room housing is necessary at the Testing Institute. The
temperature and humidity (50+/−20%) must be controlled and recorded appropriately.
The recommended testing systems/methods described in this document are our guideline,
hence Testing Institutes can adopt them depending on the availability.
Before handling prototype or production type sensors at the Testing Institutes, a certain
amount of practice and experience of the testing personnel is required. Protective clothes,masks and gloves shall be used always near exposed silicon detectors. When setting thesensors on the stage, use the protective paper provided by the supplier to slide in/out theprobe stage. When vacuum tweezers is used, verify that it will not create damages to thesensor3. Anti-electrostatic procedure must be always obeyed. The sensors should only be
stored in dry storage containers.
4.1.2. QA Database and Color Coded Classification
The supplier will provide Excel-based datasheets. The items for each sensor will be
Lot Number, Serial Number, Leakage Currents at 0 to 1000 V in steps of 10 V, Full
Depletion Voltage, and a list of dead channels. On a lot basis, polysilicon resistance
range is measured. Procurement Institutes must add five columns (C through G, keeping
separately the original file) of Location (C), QA (D), Assembled (E), V.I. (F), and I-V(G). Visual Inspection and I-V results are recorded in columns “V.I.” and “I-V”. The
overall QA pass/fail judgment should be provided in column “QA” based on the criteria
described below. It is a responsibility of Procurement Institutes to track the location until
the tested sensors are gathered to Fermilab updating column “Location”. It is a
responsibility of Testing Institutes to crosscheck the shipment and update the column“QA”. The test data used for the updates are also to be recorded in an Excel and attachedwhen the sensors are shipped to Fermilab. Any new data of mechanical or electricalmeasurements of the QA program should contain the following data appropriately:3

The <100> sensors are easier to charge up than <111> sensors because the inversion potential is smaller.
5Measurement data, Temperature/humidity, Date, Testing Institutes, Comments
Table 1 summarizes the new columns and color codes to help understand the status. The
cells of the Excel files are originally not colored when the sensors are delivered. As the
QA is underway, the color of cell “QA” is updated based on the QA result. The column“Assembled” shows sensor usage: Fermilab colors in blue when the sensor is used,
Testing Institutes color in gray when the sensor is spent for destructive tests, andProcurement Institutes color in red if the sensor is rejected and sent back to the supplier.
Table 1: New Excel cells and color codes. Note that Columns A and B are filled with Lot
Number and Serial Number by the supplierCol. Column title Maintained by
C
Location
Procurement Institutes (Fermilab when received from Japan/Korea)
D
QA
Coded by Procurement Institutes and Testing Institutes
Red
QA failed
Green QA passed
E
Assembled Coded by Fermilab, Testing Institutes, or Procurement Institutes
Blue
Assembled: Fermilab
Gray
Used for destructive tests: Testing Institutes
Red
Rejected and sent back to supplier: Procurement Institutes
F
V.I.
Procurement Institutes /Fermilab
G
I-V
Procurement Institutes /Fermilab

Table 2: An example of Page-1 of Excel datasheet. The leakage current and other data
columns continue further to the right.
Lot No.
Serial No.
SWA61457
0002
SWA61457
0010
SWA61457
0011
SWA61457
0016
SWA61457
0020
SWA61457
0021
SWA61457
0023
SWA61457
0026
SWA61457
0027
SWA61457
0032

Location
Tsukuba
Tsukuba
Tsukuba
Tsukuba
Tsukuba
Tsukuba
Tsukuba
Tsukuba
Tsukuba
Tsukuba

QA
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK

assembled

V.I.
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK

I-V
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK

Leakage Current[nA]
0V
10V
4.982
40.59
4.919
40.66
4.784
47.6
4.944
38.86
4.934
43.35
4.935
38.64
4.899
41.32
14.443
51.93
4.948
41.64
5.574
37.15

One Excel file will be created including all the sensors in the same delivery container.
Each container must be labeled properly such that one-to-one correspondence is clear
between the container label and Excel file name. The container and the Excel file must be
always carried together. When sensors are shipped to outside institutions, both have to be
shipped. If only a part of the sensors are to be shipped, create a new Excel file including
only those sensor data. Adding/updating the test results is to be made directly to the6

Excel file attached. Testing Institutions have to record the most updated data. Whendifferent Testing Institutes add a new set of data, add new page (I-V (2), for example) tothe same book. The MainPage, though, has to be updated directly under the responsibilityof Test Institute where the latest QA is carried out.
The provisional Excel file name is030122_SVX2B-OUT0-SSD_TKB_to_FNAL_14.xls
indicating the shipping date, project name (SVX2B), sensor type (OUT0 for outer axials,
OUTS for outer stereos, and IN0 for inner axials), shipping institute, receiving institute,and the number of sensors packaged.

4.2. Tests performed by Procurement Institutes
Procurement Institutes perform on every sensor a visual inspection and I-V
measurement. The initial sensor registration includes checking of the supplier datasheet
and color code classification of the delivered sensors.

4.2.1 Initial Sensor Registration
This task is performed at each of Procurement Institutes. The procedure is as follows:(1) On receiving the supplier’s datasheet in Excel, copy the original Excel file to a newone and add new five columns as described in Table 1. This page is referred to Page1 or Main Page.
(2) The shipment of the sensor batch is checked for the content with the supplier’s
datasheet. Cell “Location” is filled with the name of the Procurement Institute withchecking:
 batch/lot number serial ID-number of sensor(3) Cell “QA” is colored based on examination of the supplier’s data on
 leakage current values up to 1000V in a step of 10V (less than 2µA at 500V)
 depletion voltage (120V to 250V)
 number of bad channels/strips as claimed by vendor (less than 6)
 polysilicon resistor values (1 MΩ to 2 MΩ: data given on a lot basis)
The examination must be done automatically using Excel by checking the leakage
current at 500V, depletion voltage range, and number of dead channels. The
polysilicon resister values measured on a lot basis are provided on a separate paper,
which are also to be checked.
(4) It is mandatory to create a plot showing I-V curves and check irregular sensors.
The sensors with irregular I-V characteristics are selected for I-V stability test
described below.

7

The sensors are now ready for visual inspection and I-V measurement.
4.2.2 Visual Inspection
A visual inspection on all arrived sensors is a key sensor test especially at early stageof production, which will ensure that the sensor is free from physical defects andscratches. The results of the visual inspections in case of sensor flaws should point to thestrip regions, guard/bias ring regions or edges, which look bad and doubtful, so thatfurther electrical measurements have to be conducted.
The visual inspection is carried out at Procurement Institutes on an x-y moving tableequipped with a microscope having high magnification optics (5x-50x). A camera hooked
up to the microscope and a monitor with recording capability are necessary.
Procedure:
1. Ensure that the x-y table is completely clean.
2. Remove sensor from its envelope/shipping container.
3. Search for any signs of silicon debris in the sensor envelope. If debris is present, besure 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 with placing the sensor on the protective paper,
which can be found in the envelope. If there are indications of edge chipping, or any
blemishes or scratches, place the sensor on the x-y stage without removing theprotective paper. Measure the size of the defect and take a picture if appropriate.
5. Place the sensor with the strip side up on the x-y stage. It is recommended to use theprotective paper under the sensor.
6. Check that the serial number scratched on the identification pads matches the serial
number on the sensor envelope.
7. At high magnification, scan along all four edges, searching for edge chipping,scratching or other damage.
8. Check the visibility and quality of the fiducial marks
9. With the same high magnification, scan along the bias resistors, searching for breaks,
signs of processing defects or non-uniformity.
10. Scan along the AC-bonding pads.
11. At lower magnification, scan the full area of the sensor, taking note (and taking
pictures where appropriate) of blemishes, scratches or other non-standard features.
12. Comments and findings from visual inspections are recorded in an appropriate way ina separate sheet (Page-2 or VI Page) in the same Excel book.
Acceptance:
The sensor should be flagged “Fail” in Column “V.I.”, if any edge chipping (front orback) exceeds 50µm, or if there is severe scratching or other gross defects, or there aresigns of a processing abnormality. If in doubt, select the sensor for a full strip test to
confirm any defects electrically.

4.2.3. I-V Curve and Leakage Current Determination

8

This measurement is carried out by Procurement Institutes for every sensor. The test
requires a power supply and a pico-ammeter such as a Keithley-486/487. The sensor
backside is placed on the chuck of a probe station and probe needle is put on the biasring.
The I-V characteristic between the biasring and the backside is measured. The current ismeasured every 10V step up to 1000V with a 5 second delay between steps. A current
limit of 50µA is imposed throughout the measurement. The temperature of the probestation environment should be recorded as well. The measurement schematic is sketchedin Figure 2.
The obtained leakage current values and temperature have to be stored in Page-3 (or VI
Page). Select the sensors with irregular I-V curve, which are to be checked for leakage
current stability and DC scan described later.
Biasring+ Vb _
0.1M

GND

Ib
Back plane
1M

Figure 2: I-V measurement setup.
The sensor is vacuum chucked,
where positive voltage is applied.

Acceptance:
The leakage current is below 2 µA at RT up to 500 V.
At this stage, the sensor is ready for assembly or further QA tests. An example Excel
datasheet at this stage is shown in Table 2. Note that Cell “QA” on Page-1 must be final
and should be updated as other QA measurements are performed.

4.3. Tests on Sensor Subsets
The tests on sensor subsets are conducted on a sampling basis by Testing Institutes.
The tests should allow us to evaluate the general quality of the sensor batches and toverify the sensor specifications in much more detail. The tests should primarily be carriedout on those sensors which showed significant deviations in the I-V curve from that in the
supplier’s datasheet, showed non standard I-V curve, and have relatively large number ofdefective strips. We also test the sensors that are doubtful in visual inspections.

9Intensive probing to verify detailed characteristics may have a risk of damaging thesensor. We therefore minimize this risk once we are confident that sensors with uniformcharacteristics are being delivered. The guideline of the sampling fraction is as follows:o Prototype phase: the subset sample is about 30-50% of all delivered prototypes.
All the candidate Testing Institutes should examine their testing system and makeefforts to increase this fraction.
o Pre-production phase: the subset sample is about 10-20% plus the sensors withirregular I-V and visual inspection results.
o Production phase: the subset sample will be decreased to about 5% or at least one
sensor per batch. The sensors with irregular I-V and visual inspection results
should be tested in addition, where the definition of “irregularity” should be
updated from that in the pre-production phase after gaining experiences.
o Irradiation test: neutron irradiation will be carried out at a rate of 3-4 sensors
every two months.

4.3.1 I-V Curve Stability
This I-V curve stability test should verify that the sensor shows a consistent and small
leakage current characteristics over a 10-hour period. As described in 4.2.3, the current ismeasured every 10V step up to 1000V with a 5 second delay between steps. Thismeasurement is repeated every 30 min whereas the bias voltage is set to the operation
voltage (full depletion voltage plus 20V, or 200 V typically) between the I-V
measurements. A current limit of 50µA is imposed throughout the measurement period.
A good selection of sensors for this test is to pick a sensor with irregular I-V curve
and/or visual inspection results. The data should be recorded in Page-4 of Excel book.
Acceptance:
The leakage current after correction of the temperature variation should be constant to20%. In case a tendency of increase in the current is observed, the sensor has to be tested
further longer.

4.3.2 Full Strip Test (AC scan)This test probes the AC pad of every readout strip in order to evaluate the coupling
capacitance (this provides information on strip metal shorts and opens), to check thepinholes in capacitor dielectric, and to evaluate the uniformity of the polysilicon
resistances. The AC scan should be made with an automatic probe station.
Procedure:
The test requires a separate bias voltage source (Vb) to deplete the sensor, and a
voltage source (Vcp) and pico-ammeter system to check for pinholes. An LCR-meter in
Cs-Rs mode is used for measuring the coupling capacitance and resistance in series. Twoprobe-tips on an automatic probe station (probes move relative to the sensor) are used to10

contact the every readout AC pad (probe A) and baisring (probe B) while the bias voltage
is provided via contact to the backside.
The schematic of the measurement is presented in Fig.3. A current limit in the power
supply of 50nA should be always applied while charging or discharging the capacitors.
Under computer control, probe all readout strips according to the following instructions.
1. Ramp up the bias voltage (Vb) to the operation voltage.
2. Step to strip N and contact both probes A and B.
3. Increase the test voltage Vcp to +10V, wait 0.5 seconds. If the current runs into thecurrent limit of 50nA, a pinhole is found. Skip step 4 and go to step 5.
4. Increase the test voltage Vcp to +100V, wait 1 second and measure the current toverify the coupling capacitor insulation.
5. Decrease the test voltage to 0V and wait for 0.5 seconds.
6. (Switch the relays on.) Measure C and R at 1kHz and in Cs-Rs mode. (Switch therelays off)
7. Repeat the measurement cycle from point 2 above for strip N+1.
Acceptance:
We require <1% defective strips. Defective or bad strips in general have: Pinholes – current through the capacitor >10 nA at 100 V and RT
 Short – coupling capacitor >1.2 times the typical value Open – coupling capacitor <0.8 times the typical value
 Polysilicon resistor out of specs
The first three defects can be detected with the AC-scan. If you detect metal short oropen, try to verify the defect by visual inspection of the bad strip. The measured value ofR (Step 7) represents the polysilicon resistance in series and the implant resistance. The
Biasring
ProbeA+ Vcp _

Icp
ProbeB

GND+ Vb _

10M

LCR

0.1M

Cs-Rs

GND

Ib
1 µF

Back plane
1M

Figure 3: Setup for the full strip scan (AC scan)11

polysilicon resistance is typically 0.4-0.5 MΩ smaller than the measured R. Although thepolysilicon value is not directly measured, uniform R implies a good uniformity inpolysilicon resistances. For the strips with irregular R, the polysilicon resistance shouldbe measured directly as described in 4.4.2.
Note that the relays are used to protect the LCR meter at Icp measurement: Step 6.
These relays could create paths to ground, which adds finite leakage current to Icp value.
The protection resistors (10MΩ and 1MΩ) limit the Icp to a 10 µA level for complete
pin-holes. The delay of 1 sec in Step 4 may not be long enough compared to the decay
time due to possible residual impedance. The 1 sec delay should be taken as acompromise from the total measurement time.
The measured data should be stored in Page-5 of Excel book. The newly founddefective strips should be added to the list in Page-1 and the corresponding Cell “QA” isupdated accordingly.

4.3.3 Total Capacitance (C-V curve)
The total capacitance is measured with the system shown in Fig.4. Measurement withsmaller LCR frequency results in actual total capacitance. Positive bias voltage isprovided to the backplane as usual. The Nsub pad (See drawing) and the biasring which
is set to GND are used to measure the bulk capacitance: The biasring and Nsub padprobes are connected to L and H, respectively, of LCR-meter through capacitors of 1 µF.
The LCR frequency can be as low as 100Hz with this configuration. The frequency
should be optimized when the bias is supplied from the backplane. Measure and record
the capacitance in 10V steps up to 500V. The full depletion voltage is defined as theintersection of two straight lines when the data are plotted in1/C2 versus bias voltage. The
fit rang should be optimized such that χ2/NDF is minimum in each range. Data are stored
in Page-6. Note that this system can also be used for I-V measurement.
Acceptance:
The full depletion voltage should be in the range 120 to 250V.

Biasring

backplane+ Vb _

Nsub
0.1M

Ib
1M

GND

LCR
1 µF

Figure 4: Setup for C-V
curve measurement124.3.4 Mechanical Tests
The warp of single-sided sensors is substantially larger than of double-sided sensors.
We recommend that several mechanical measurements on silicon sensors should be
performed at a random sampling. The measurements should verify the mechanicalspecification of wafer warp and cutting accuracy on an optical metrology system. The
data has to be stored in Excel Page-7 in an appropriate format.
4.3.4.1 Sensor Warp
The sensor warp is measured in a free state of the sensor on an optical metrology
machine. Measurement should be made at grids of every 1 cm including four positions inclose vicinity to the corners. The measured data are expressed as deviations from thereference plane that is defined by the data at three of the four corners. The maximum
deviation, RMS of the deviation, and twist (deviation of the corner which are not used forthe reference plane definition) are recorded. The maximum deviation must be smaller
than 130 µm.
4.3.3.2 Sensor Cutting Accuracy
The cutting accuracy is surveyed with an optical metrology machine. The nominal
distance from the fiducial mark to the edge is 330 µm for outer sensors. Measure thisdistance at four corners (in total 8 data points). They have to be accurate to ±20µm.
4.3.3.3 Wafer Thickness
The wafer thickness is measured at the sides by ensuring that the detector is touching
the stage of the metrology machine. Use a vacuum chuck. The thickness is determined as
the height difference between the stage and the sensor surface. The thickness should be in
the range 320 ±20µm (5µm is added to the specification accounting for possible
uncertainty in this measurement procedure). If the Z resolution of the system is limited,measure the thickness with holding the sensors vertically. Take data at middle of the two
shorter sides.

4.4. Diagnostic Tests
This subsection lists recommended procedures for a more detailed evaluation of theelectrical parameters of the sensors. The tests are either done on single strips of thesensors with irregularities or every strip for detailed overall performance evaluation suchas for irradiation tests. We recommend that the Testing Institutes perform these tests
routinely keeping a rate at least one per batch even if no irregular sensor is found fromother tests. After each diagnostic test, the I-V measurement on the sensor should be
repeated. The data has to be stored in the Excel datasheet appropriately.
4.4.1 Strip Leakage Current (DC-scan)
If the I-V test shows irregularly large leakage currents or the IV stability test gives
unstable results, it is recommended to perform the strip leakage current test (DC scan) inorder to try to find out the source of the big or unstable leakage.
13

The schematic of measurement is presented in Fig.5. Under computer control, probe all
readout/intermediate strips according to the following instructions.
Procedure:
1. Ramp up the bias voltage Vb to the operation voltage or the voltage to test.
2. Step to Strip N and contact the biasring (probe A) and DC pad (probe B).
3. Measure the bias current Ib with the pico-ammeter Ibias. The bias current reading
must be consistent with the known value, otherwise check the contacts.
4. If Step 3 is OK, then measure the strip current Istrip with the pico-ammeter.
5. Repeat the measurement cycle from Step 1 onward for Strip N+1.
6. Ramp down the bias voltage to 0V.
Acceptance:
If the strip current exceeds 100 nA at the operation voltage and RT, the strip is counted
as defective. The newly found defective strips are added to the defective strip list on Page
1 and “QA” Cell is updated accordingly. The DC scan data are stored in a separate page
appropriately.

Biasring
ProbeA

IstripDC padProbeB+ Vb _
0.1M

Ib

GND

Back plane

Figure 5: Setup for strip leak current measurement (DC scan).

14

4.4.2 Polysilicon Resistance
The sensors which show irregular R values in the AC scan are subjected to check thepolysilicon resistance. Since this measurement is sensitive to detect sensor charge-up,
testing at a constant rate is recommended depending on the achievable frequency of AC
scan. Also a random sampling test must be made to evaluate directly the polysilicon
resistance. The schematic is given in Fig.6. The resistance is evaluated by probing the DC
pad and biasring and by measuring the resistance with an LCR meter. The sensor isbiased such that the surface isolation is established. Recommendation is 200V to fully
deplete. Note that the resulting resistance will be substantially smaller than the realpolysilicon resistance if the strip leakage current is extremely high (irradiated sensors forexample). In this case, a system of DC power supply and current meter provides reliablevalues. Subtract the measured current with no external voltage from that with external
voltage applied.
Measure neighboring strips as well for comparison. At a random sampling test,
measure the strips at different (at least five) locations to detect possible non-uniformity.
Biasring
ProbeA

LCR
ProbeB

Cp-Rp
1 µF

+ Vb
0.1M
Ib

Back plane

1M

Figure 6: Setup for the polysilicon bias resistor measurement. A system based on
external voltage source and ampere meter is an alternative, which can be
configured from the interstrip resistance measurement setup (Fig. 8).
Acceptance:
The polysilicon resistor values have to be within 1.5+0.5 Mohms.

4.4.3 Interstrip Capacitance
The major contributions to the total strip capacitance, which represents the total load
capacitance for the preamplifier, are the interstrip capacitance, i.e. the contribution from15

one strip to the neighbor strips, and the capacitance of one strip to the backplane. Amongthese, the interstrip capacitance is measured with a system shown in Fig 7.
Procedure:
Place the sensor with the backplane and biasring connected to the high and grounded-low
sides respectively of the voltage source. Ramp up the bias to the operation voltage. Place
two coaxial probes on the AC pads as shown in Fig.6, and measure the capacitance value
at 1 MHz frequency. Note a certain contribution of the strip capacitance to the backplane
is present in so measured capacitance. We take the measured capacitance as the interstrip
capacitance.
Acceptance:
The interstrip capacitance has to be less than 11.2 pF (1.2 pF/cm).
Biasring+ V_

Probe A
0.5M
Probe B

1M

Back plane

LCR
Probe C

1 µF

Figure 7: Setup for interstrip capacitance measurement.

4.4.4 Interstrip Resistance
The interstrip resistance is determined by measuring the induced currents while
applying voltages to the neighboring intermediate strips, as shown in Fig.8. Two probe
needles connected to a voltage source are added to the strip leak current measurement
system (Fig.5).
Procedure:
1. Ramp up the bias voltage to the operation voltage.
2. Set the testing voltage (VDC) from -1V to +1V with 0.5V step.
3. Read the strip current (IDC) after reading is stabilized, typically 1s.
4. Calculate a value of interstrip resistor from the I(V) curve: Rintrstr = ∆IDC/VDC, where∆IDC is the difference of the readings with respect to IDC at VDC= 0V.
16

5. Repeat Steps 2 to 4 for other readout strips.
Acceptance:
The interstrip resistance should be higher than 1 Gohms, while it must be much higher for
non-irradiated sensors. Note the supplier checks the every interstrip resistance. If theresistance turned out to be small, surface charge-up is a most probable cause. Put thesensor back in the original envelope. Keeping such sensors in the envelope should
remove the surface charge in a day. Or illuminate the sensor with UV to remove thesurface charge.
Biasring
ProbeAIDC+ Vb _

VDC

0.1M

GND

I
Back plane

Figure 8: Setup for interstrip resistance measurement.

17

5. Summary of the QA Program.
The following table summarizes the QA program. The frequency is for the prototype
deliveries and numbers in parentheses are for the deliveries after production is stabilized.
The fractions at the pre-production phase are between the two numbers. Items (8) through(11) are performed whenever problems are found, while the rate of at least one detector
per batch has to be maintained even if no such problem is found. Items (2) and (3) will be
replaced with Item (12) after quality sensor delivery is established. Neutron irradiation iscarried out at a rate of 3-4 sensors every two months.
QA item

QA
Frequency
Comments
performed by (production)

Excel bookpage number(1) Initial registration

Procur. Inst.

100%

Page-1(2) Visual Inspection

Procur. Inst.

100%

Page-2(3) I-V

Procur. Inst.

100%

Page-3(4) IV-stability

Testing Inst.

30% (5%)

Sensor subsets

Page-4(5) AC-scan

Testing Inst.

30% (5%)

Sensor subsets

Page-5(6) C-V

Testing Inst.

30% (5%)

Sensor subsets

Page-6(7) Mechanical Tests

Testing Inst.

10% (5%)

Sensor subsets

Page-7(8) DC-scan

Testing Inst.

10% (5%)

Diagnostic+subsets(9) Polysilicon resistor

Testing Inst.

10% (5%)

Diagnostic+subsets(10) Interstrip capacitance

Testing Inst.

10% (5%)

Diagnostic+subsets(11) Interstrip resistance

Testing Inst.

10% (5%)

Diagnostic+subsets(12) IV, visual inspection

Fermilab100%

Neutron irradiation

Testing Inst.

3-4 /2 mon

Page-1
destructive

18

Appendix Diagram of a switch box+ Vb _

to Backplane
0.1M+ Vcp _

GND

Icp

Ib

1M

a

10M

b
Switch to b
(Rint)

to AC pad (AC scan)
to Nsub (C-V)
to DC pad (R-poly)

to Biasringto DC pads
(Rint.)

1 µF+5V+VDC _

AC scan (Icp)
C-V
R-polyto AC pads
(Cint)IDC
H

to LCRL
to DC pad
(Rint/DC scan)

The probes are coaxial with the connections provided through Lemo connectors. The
inputs to the LCR meter are switched, switching being controlled by a computer.
Additional switch is used to by-pass 1MΩ resistor for interstrip resistance (Rint)
measurement. Two voltage and pico-ammeter systems can be replaced with source
meters.

19

Appendix

Run2b Silicon Sensor Specifications
Introduction:
The CDF detector at Fermilab (Batavia, Illinois USA) will undergo a new upgrade for theRun2b data taking period (2006-2008).
CDF will replace most of the present silicon detector system (the SVXII and L00 parts)
with a new detector capable of coping with a substantial increase in the Tevatron Collider
luminosity.
The new detector employs microstrip silicon sensors with single sided (p+ implant), ACcoupled, poly-silicon biased, <100> 6” n-type wafers with different geometry andpitches. The total number of Run2b silicon sensors is about 2,300.
The required number of sensors, outer dimensions, and pitches are summarized in thefollowing table for the three types of the sensors.
type
Outer Axial
Small Angle Stereo
Inner Axial
TOTAL

Production
Quantity
1512
648
144
2,304

Dimensions(mm)
96.392x40.550
96.392x43.100
78.5x14.850

Readout Pitch/pitch(µm)
75/37.5
80/40
50/25

The requirements on the wafer are summarized in the following:
Thickness
Wafer diameter
Wafer type (orientation)
Resistivity
Wafer warp

320 µm ± 15 µm
6 inchn-type (<100>)(see depletion voltage specs)<130 µm

The sensors need to withstand a dose of 1x1014 1 MeV equivalent neutrons/cm2 and an
ionizing dose of 10 Mrad, consequently they should be operational at voltages up to 500
V. All sensors have one floating intermediate strip between readout strips: The readout
strip pitch is twice the value of the strip pitch. All sensors have 3 µm overhanging metal
except for the inner axial where this value is ~1µm.
– The outer axial sensors have a strip pitch of 37.5 µm (readout pitch of 75 µm).
– The small angle sensors have strips at an angle of about 1.2 degrees with respect tothe axial (long side of the detector). Strips not reaching the short edge of the sensor
are properly terminated at the other side of the shorter edge.
– Inner axial sensors have a pitch of 25 um (readout pitch is 50 µm).

20

Specifications:
Axial: Active area dimensions4
Axial: Overall dimensions
Axial: Strip Pitch
Axial: Readout Pitch
Axial: Number of Strips
Axial: Number of Readout Strips~ 40.5 x 95.4 mm2
40.550 x 96.392 mm2 (2 detectors per 6” wafer)37.5 µm
75 µm
1024
512

Stereo: Active area dimensions
Stereo: Overall dimensions
Stereo: Strip Pitch
Stereo: Readout Pitch
Stereo: Number of Strips
Stereo: Number of Readout Strips~ 42.1 x 95.4 mm243.100 x 96.392 mm2 (2 detectors per 6” wafer)
40 µm
80 µm
>1024
512

Inner Axial: Active area dimensions
Inner Axial: Overall dimensions
Inner Axial: Strip Pitch
Inner Axial: Readout Pitch
Inner Axial: Number of Strips
Inner Axial: Number of Readout Strips~12.9x78.5 mm2
14.850x96.392 mm2 (6-7 detectors per 6” wafer)
25 µm
50 µm
512
256

Common Specifications:
Depletion Voltage
Biasing scheme
Poly-silicon resistor values
Passivation
Implant strip width
Implant depth
Doping of implant
Width of aluminum strip6
Thickness of Al strips
Resistivity of Al strips
Coupling Capacitor value
Coupling capacitor breakdown voltage
Interstrip resistance
Total interstrip capacitance
Total sensor current7 at T=20o C
Bad channels for grade “A”

From 120 to 250 V (200V as upper limit preferable)
Poly silicon resistor (see drawings)5
1.5 ± 0.5 MΩ (<10% variation within a sensor)
SiO2 0.5 ~ 1.0 µm thick~9 µm>1.2 µm> 1x1018 ions/cm3~15 µm (~11 µm for the inner axials)>1 µm<30 Ω/cm>10 pF/cm>100 V> 1 GΩ<1.2 pF/cm (<1.5pF/cm total for the 90dgr)
grade “A”: <50 nA/cm2 at 500V
grade “B”: < 4uA/ cm2 at 350V and < 10uA/ cm2 at 500V
<1% (No more than 5 per sensor)

4

1 mm is allowed from the active area to the physical edge of the sensor, but the active area can growlarger if less space is needed between the end of the active area and the physical edge of the sensor.
5
Resistor on one side only is an equivalent option but has to be agreed with the customer because it canhave an impact on the active area dimensions and the positioning of the small angle stereo sensors.
6
Only readout strips will be metallized and will have bonding pads. Intermediate strips will have only DC
pad (see drawings for details).
7
For the grade “A” we would like to consider the option of a lower breakdown voltage value of 350V if itcomes with some cost saving. In other words the optional specs for the grade “A” detectors would read
350V instead of 500V.
21

Bad channels for grade “B”<5% (No more than 25 per sensor)

Bad channels definition:
Parameter
Single strip leakage current at 500 V 8
Coupling capacitor
Coupling capacitor
Coupling capacitor
Current through the Coupling capacitor with
80 V across the dielectric

Rule> 10 nA> 1.1 times the typical value< 0.9 times the typical value>1.1 times the typical value but theneighbors are normal>1 nA

ID of the defect
Leaky
Short
Open
PH (pin hole)
PH (pin hole)

Above bad channel definition is based on measuring the coupling capacitance on each
strip. We will consider other means of determining bad strips count based on vendor’s
proposal. Please attach a description of what measurement you would propose in order todetermine the bad strip count and location for each sensor.

Quality Control by manufacturer:
Value of the poly resistor
Value of the depletion voltage
Visual inspection, verifying that no significant scratches, blemishes
and/or edge chipping are present
Total leakage current up to 1000 V9 (or until current=20 µA)10 insteps of 10 V.
Bad strips identification and count

Measured on Test Structures oneach wafer
Measured on Test Structures oneach wafer
Performed on each sensor
Measured on each sensor
Measured on each sensor

Quality Control results have to be provided to the customer on an electronic format
as well as on a paper format.

8

The measurement of strip leakage current of individual sensors is foreseen only for the prototypes. For
mass-production, based on the prototype data, the measurement will be made only for those sensors withthe total leakage current exceeding some criterion to be agreed upon.
9
Or lower value if there is some instrumental limit. In any case at least up to 500V.
10
We can accept other values of voltage and/or current if more convenient for the manufacturer.
22