quality assurance of silicon strip detectors and monitoring of manufacturing process
Download
Skip this Video
Download Presentation
Quality Assurance of Silicon Strip Detectors and Monitoring of Manufacturing Process

Loading in 2 Seconds...

play fullscreen
1 / 34

Quality Assurance of Silicon Strip Detectors and Monitoring of Manufacturing Process - PowerPoint PPT Presentation


  • 100 Views
  • Uploaded on

Quality Assurance of Silicon Strip Detectors and Monitoring of Manufacturing Process. Thomas Bergauer Institute f. High Energy Physics HEPHY, Vienna SiLC meeting @ ILC Workshop Vienna, Nov 18 th , 2005. Outline of Talk. Characterization of Silicon Strip Detectors for Quality Assurance

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Quality Assurance of Silicon Strip Detectors and Monitoring of Manufacturing Process' - paloma


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
quality assurance of silicon strip detectors and monitoring of manufacturing process

Quality Assurance of Silicon Strip Detectors and Monitoring of Manufacturing Process

Thomas Bergauer

Institute f. High Energy Physics HEPHY, Vienna

SiLC meeting @ ILC Workshop Vienna, Nov 18th, 2005

outline of talk
Outline of Talk
  • Characterization of Silicon Strip Detectors for Quality Assurance
  • Characterization of “standardized” test-structures to monitor manufacturing process

6” wafer:

Characterization of Strip Detector

  • global measurements (IV, CV)
  • strip-by-strip tests (Ileak, Cac, Rpoly and Idiel)

Characterization of test structures

with 9 different measurements

Thomas Bergauer, HEPHY Vienna

sensor characterization basics
Silicon Sensors for future high-energy experiments will have many strips to achieve a high spatial resolution.

Large Tracker will use enormous area of silicon sensors

Efficient Quality Assurance mandatory

Automated test system is necessary to determine the electrical parameters of each strip.

What do we test?

Global parameters:

IV-Curve:

Dark current

Breakthrough

CV-Curve:

Depletion voltage

Total Capacitance

Strip Parameters

strip leakage current Istrip

poly-silicon resistor Rpoly

coupling capacitance Cac

dielectric current Idiel

Sensor Characterization Basics

Thomas Bergauer, HEPHY Vienna

ac coupled silicon strip detector
AC-coupled Silicon Strip Detector
  • What do we test?
    • Si Strip Sensors for the CMS Tracker
    • n bulk
    • p+ implanted strips
      • connected to bias ring via polysilicon resistors
    • AC-coupled Aluminium readout strips
    • Dielectric Oxide SiO2 + Si3N4

Thomas Bergauer, HEPHY Vienna

ac coupled silicon strip detector1
AC-coupled Silicon Strip Detector

Strip Pitch

80-170μm

Corner of a typical CMS Silicon Strip Detector

Thomas Bergauer, HEPHY Vienna

sensor test setup
Sensor Test Setup
  • Light-tight Box, Instruments, Computer
  • vacuum support carrying the sensor
    • Mounted on freely movable table in X, Y and Z
  • Needles to contact sensor bias line
    • fixed relative to sensor
  • Needles to contact:
    • DC pad (p+ implant)
    • AC pad (Metal layer)
    • Can contact ever single strip while table with sensor is moving

Thomas Bergauer, HEPHY Vienna

sensor test schematics
Sensor Test Schematics
  • Instruments (HV source, Amp-Meter, LCR-Meter,…) on the left are connected via a cross-point switching matrix to the needles which contact the sensor to perform different measurements

Thomas Bergauer, HEPHY Vienna

example measurements cv iv
Example Measurements: CV, IV
  • Combined voltage ramp up to 500-800V
    • Dark current (blue) and
    • total capacitance (red, plotted 1/C2) is recorded.
  • Depletion voltage is extracted

Thomas Bergauer, HEPHY Vienna

example measurements stripscan
Example Measurements: Stripscan
  • After IV-CV ramp, bias voltage is adjusted to stable value (e.g. 400 V) and stripscan is started
  • 4 parameters tested for each strip:
    • dielectric current Idiel
    • coupling capacitance Cac
    • poly-silicon resistor Rpoly
    • strip leakage current Istrip
  • For each test, the switching matrix has to be reconfigured
    • Full characterization of detector with 512 strips: 3h

Thomas Bergauer, HEPHY Vienna

example results depletion voltage dark current sensors for cms
Example Results: Depletion Voltage, Dark current (Sensors for CMS)

Depletion Voltage

Dark current @ 450V

Thomas Bergauer, HEPHY Vienna

results stripscan
Results: Stripscan
  • Total number of bad strips
    • Total = sum of Istrip , Rpoly, Cac, Idiel )
    • Bad = outside specified cuts
  • CMS requires less than 1% of strips are outside cuts for at least one of the strip parameters
  • Average bad strips per sensor:
    • 0,37

Thomas Bergauer, HEPHY Vienna

2 monitoring of manufacturing process

2. Monitoring of Manufacturing Process

“PQC”…. Process Quality Control

motivation and assumptions
Motivation and Assumptions
  • Full Characterization of Strip Detector has some disadvantages
    • takes a lot of time (if every strip is checked)
    • Only sample tests possible (assumption that production batch behave similar)
    • Some interesting parameters are not accessible on standard detector or would require destructive tests
  • Remedy: Doing similar measurements on standardized test-structures
    • Assumption: Test structures behave identical to main sensor, since produced on the same wafer
    • Measure many parameter, each on a dedicated test structure
    • Destructive Tests possible
    • Fast measurement possible

Thomas Bergauer, HEPHY Vienna

standardized set of test structures

baby

diode

MOS out

TS-CAP

GCD

sheet

CAP-TS-AC

CAP-TS-AC

MOS in

StandardizedSet of Test Structures

“Standard Half moon”

  • 9 different structures
  • individually described in the next slides

Company test-structures

Thomas Bergauer, HEPHY Vienna

test structures
TS-CAP:

Coupling capacitance CAC to determine oxide thickness

IV-Curve: breakthrough voltage of oxide

Sheet:

Aluminium resistivity

p+-impantresistivity

Polysilicon resistivity

GCD:

Gate Controlled Diode

IV-Curve to determine surface current Isurface

Characterize Si-SiO2 interface

CAP-TS-AC:

Inter-strip capacitance Cint

Baby-Sensor:

IV-Curve for dark current

Breakthrough

CAP-TS-DC:

Inter-strip Resistance Rint

Diode:

CV-Curve to determine depletion voltage Vdepletion

Calculate resistivity of silicon bulk

MOS:

CV-Curve to extract flatband voltage Vflatband to characterize fixed oxide charges

(details on next slide)

Test Structures

Thomas Bergauer, HEPHY Vienna

slide17
MOS
  • Metal Oxide Semiconductor
  • Oxide composition represents configuration of
    • Thick dielectric in inter-strip region
    • Thin dielectric underneath strips (right)
  • Extraction of flatband voltage Vfb
    • Seen by sharp decrease of Capacitance (between accumulation and inversion)
    • to determine fixed positive charges in Oxide
  • Limit defined experimental after test beam

Thomas Bergauer, HEPHY Vienna

setup description
Setup Description
  • Probe-card with 40 needles contacts all pads of test structures in parallel
    • Half moon fixed by vacuum
    • Micropositioner used for Alignment
    • In light-tight box with humidity and temperature control
  • Instruments
    • Source Measurement Unit (SMU)
    • Voltage Source
    • LCR-Meter (Capacitance)
  • Heart of the system: Crosspoint switching box
    • Used to switch instruments to different needles
  • PC with Labview used to control instruments and switching system
  • GPIB Bus for communication

Thomas Bergauer, HEPHY Vienna

pqc setup
PQC Setup

Thomas Bergauer, HEPHY Vienna

software

Yellow Fields:

Limits and cuts for

qualification

Blue Fields:

Obtained results

extracted from graph

by linear fits (red/green lines)

Software

After run:

Before run:

  • Self-developed LabVIEW program
  • Fully automatic measurement procedure (~30 minutes)
    • Except alignment of Half moon and placement of probecard
  • Automatic extraction of parameters

Thomas Bergauer, HEPHY Vienna

examples of identified problems
Examples of identified problems

Interstrip Resistance

  • Limit: Rint > 1GΩ to have a good separation of neighbouring strips
  • Value started to getting below limit
  • We reported this to the company
  • Due to the long production pipeline, a significant amount of ~1000 sensors were affected
  • These sensors will not be used for CMS Tracker!

Thomas Bergauer, HEPHY Vienna

examples of identified problems 2
Examples of identified problems (2)

Flatband Voltage

  • Limit of 10V determined during irradiation campaign
  • We observed values up to 40V for early deliveries
  • Some batches from later deliveries suffer from contamination of production line

Thomas Bergauer, HEPHY Vienna

examples of identified problems 3
Examples of identified problems (3)

Aluminium resistivity

  • Aluminium resistivity too high for some delivered batches
  • Limit: <30mΩ/sq.
  • Affects noise behaviour of readout chip
  • After discovery of this issue we requested to increase thickness of Al layer

=> Problem disappeared

Thomas Bergauer, HEPHY Vienna

summary
Summary
  • Future experiments with a large tracker will require a huge number of silicon strip sensors.
    • Compare with CMS Silicon Strip Tracker: 206 m2 is equal to
      • 24.244 pieces of sensors and
      • 9.316.352 channels
  • Its fabrication will last many months (years) and a stable production during the whole production time is mandatory.
  • Strip-by-strip test of detectors is necessary but not sufficient
    • Slow, reduced set of parameters to test
  • Measurements on dedicated test-structures is a powerful possibility to monitor the fabrication process
    • During a long production time
    • Also on parameters which are not accessible on the main sensor (e.g. MOS, GCD,... )
    • Destructive tests possible
    • Fast measurement allows high throughput

Thomas Bergauer, HEPHY Vienna

outlook and future plans
Outlook and Future Plans
  • We have to optimize our test structures
    • We learned during the CMS QA that some things can be improved:
      • Smaller structures
      • Better design of some structures (e.g. diode, sheet)
  • We want to offer this standardized set of test structures to all interested groups in the future
    • To put it on unused space of their wafer design

Thanks.

Thomas Bergauer, HEPHY Vienna

ts cap
TS CAP
  • Array of 26 AC-coupled strips
  • Test of Coupling Capacitance
    • Oxide Thickness can calculated
  • Test of dielectric breakdown
    • Destructive !

Thomas Bergauer, HEPHY Vienna

sheet
Sheet
  • Combination of
    • Three polysilicon resistors
    • Three Aluminium Strips (10, 20, 50 um thickness)
    • Three p+ Strips (10, 20, 50 um thickness)
  • Used to determine resistivity of implant, Aluminium and polysilicon
  • These Parameters have influence on noise behavior of readout chip

Thomas Bergauer, HEPHY Vienna

slide30
GCD
  • Gate controlled diodes
    • Two circles ones (not used)
    • Two squares ones with comb-shaped p+-Diodes and comb-shaped MOS structures alternately arranged
  • Used to extract surface current
    • by applying a constant reverse bias voltage through the diode
    • while varying the gate voltage of the MOS structure.
    • Sharp decrease of dark current in the inversion region gives the surface current
  • Important Parameter to monitor oxide and Si-SiO2 interface quality
  • Limit determined experimental by irradiation

Thomas Bergauer, HEPHY Vienna

cap ts ac
CAP-TS-AC
  • Measurement of inter-strip capacitance
    • Between single central strip and two neighboring ones
    • Outer strips on top and bottom are shorted and connected to ground (directly on the structure)
    • While biasing of structure is mandatory
  • Parameter related to noise and SNR of readout chip

Thomas Bergauer, HEPHY Vienna

baby sensor
Baby Sensor
  • Structure with 192 AC-coupled strips
  • Identical to main detector
  • Used to measure IV-curve up to 700 V
    • Breakthrough voltage is determined

Thomas Bergauer, HEPHY Vienna

cap ts dc
CAP-TS-DC
  • Used to determine inter-strip resistance
  • Similar structure like CAP-TS-AC (used for C_int) but with exceptions
    • no polysilicon resistor (strips do not have a connection to bias ring)
    • p+ strips are directly connected to Aluminium strips
  • High value of inter-strip resistance necessary to have a good electrical separation of strips

Thomas Bergauer, HEPHY Vienna

diode
Diode
  • Simple square diode
  • Voltage scan is used to measure Capacitance and to extract
    • total bulk thickness
    • Bulk resistivity

Thomas Bergauer, HEPHY Vienna

ad