Investigation of MEM sensors
by typical methods of
semiconductor failure
analysis
Dr. Claudia Keller
May 2008
Presentation Overview
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FA Munich organization
Basic failure analysis flow
SAR 10 Angular Rate Gyro
Case Study A of SAR 10
Case Study B of SAR 10
Summary
Presentation Overview
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FA Munich organization
Basic failure analysis flow
SAR 10 Angular Rate Gyro
Case Study A of SAR 10
Case Study B of SAR 10
Summary
Overview of Failure analysis in Munich
n failure analysis lab
- analysis of customer returns and internal qualification
- method development and evaluation
n ~ 90 people working in 5 groups for all business units
n MEMs are within business unit sensors in the automotive part
n examples for sensors at IFX:
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pressure sensors
hall sensors
angular rate gyro sensors
radar sensors at 9 GHz
Presentation Overview
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FA Munich organization
Basic failure analysis flow
SAR 10 Angular Rate Gyro
Case Study A of SAR 10
Case Study B of SAR 10
Summary
Basic failure analysis flow for “normal” devices
Process
Result
Equipment
Verification of Failure
Test Result, U-I-Curves
Tester, UTI
Decapsulation of IC
Access to Die Surface
or Backside
Jetty, Wet Etching
Fault Localization
Area of problem:
Block, Cell, Transistor
Emission Microscopy,
Laser Voltage Probing
Characterization
of Primitive
Access to Primitive
I-V-Curves
Probe station,
Parameter Analyzer
Physical
Failure Analysis
Preparation
& Image
Wet, dry etching, FIB
SEM, AFM ,TEM
Presentation Overview
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FA Munich organization
Basic failure analysis flow
SAR 10 Angular Rate Gyro
Case Study A of SAR 10
Case Study B of SAR 10
Summary
Description of
SAR 10 Angular Rate Gyro
decapsulated
device
n Applications:
-
rollover detection
dynamic Stability Control
n operating principle:
detection of Coriolis force by
capacity measurements
n two-chip solution
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ASIC for logic operations
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Sensor
MEMS
in detail
SAR10 - Gyro Chip Design
Photo through
top glass
R12
C15
LSON
Electrode pattern
on glass
6
5
4
3
2
1
Press contacts
Wire bond
pads
1 micron gap
Triple stack
structure
Glass
ss
a
l
g
Si
ss
a
l
g
Glass
pads
Presentation Overview
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FA Munich organization
Basic failure analysis flow
SAR 10 Angular Rate Gyro
Case Study A of SAR 10
Case Study B of SAR 10
Summary
case study A
analysis of press contact within SAR 10
n failure description:
- the device failed due to wrong measurement data of sensor
- detailed investigation showed failure located on sensor
- needle measurement of characteristic lines indicate problem at o ne press
contact
n optical inspection at corresponding area shows no irregularity
fail contact
reference contact
Schematic of press contact
top view through
top glass
cross section
needed
mechanical polishing
for thinning
Electrode glass
view in
image
Ti/TiN
Aluminium
press contact
Oxide
Silicon
mechanical cross section not
possible because contact
cannot be stabilized
-> Backside FIB
Basic Information on Backside FIB
n Navigation through silicon
with co-axial IR and ion
column
n 10..30keV, 1pA..20nA
beam
n <10nm FIB resolution,
<100nm positioning
accuracy
Backside FIB cross section
overview
of press
contact
failing press contact
result:
missing layer
due to
structuring
fault
reference press contact
Presentation Overview
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FA Munich organization
Basic failure analysis flow
SAR 10 Angular Rate Gyro
Case Study A of SAR 10
Case Study B of SAR 10
Summary
case study B
analysis of press contact at edge of sensor
failure description:
LogIV QN800017063010 die 90
- the device failed due to wrong
measurement data
- detailed investigation showed
problems on the sensor
- needle measurement of characteristic
lines indicate no current at pad 6
n
Current (A)
n
1,0E-04
1,0E-05
1,0E-06
1,0E-07
1,0E-08
1,0E-09
1,0E-10
1,0E-11
1,0E-12
-19 -17 -15 -13 -11 -9
Pad6
Pad5
Pad2
Pad1
-7
-5
-3 -1
1
Voltage (V)
optical inspection at corresponding area shows no irregularity
Backside FIB not possible due to glass edge
Mechanical cross section
n Embedded mechanical cross section perpendicular to press
contact is performed
n For embedding a fluorescent epoxy glue is used
- to see cracks in contact - no crack was visible
- to stabilize press contact during polishing process
fail contact
reference contact
embedded cross section
SEM investigation of cross section
SEM overview of
press contacts
fail contact
reference contact
no layer missing
no crack visible
FIB cross section perpendicular to mechanical
cross section
Electrode glass
view in
image
electode metal
Aluminium
press contact
Oxide
Fib cross section
Silicon
middle of press contact
30 µm
mechanical cross section
FIB cross section perpendicular to mechanical
cross section
fail contact
reference contact
result:
no opening
in oxide
Presentation Overview
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FA Munich organization
Basic failure analysis flow
SAR 10 Angular Rate Gyro
Case Study A of SAR 10
Case Study B of SAR 10
Summary
Summary
n MEMS can be analyzed with standard methods for “normal “
semiconductor products
n a standard analysis flow is not possible, e.g. depending on the
position of the press contact the analysis flow has to be varied
and adapted to every special product/case.