Quality and Reliability of Quality and Reliability of
Semiconductor DevicesSemiconductor Devices
Daniel R. LoughmillerDaniel R. Loughmiller
Product Engineering ManagerProduct Engineering Manager
Network and Communications GroupNetwork and Communications Group
Micron Technology, Inc.Micron Technology, Inc.
What are Quality and Reliability and What are Quality and Reliability and
how are they measured?how are they measured?
Quality is typically defined as the “time zero” Quality is typically defined as the “time zero”
failure rate and is measured in DPM (Defects failure rate and is measured in DPM (Defects
Per Million) or PPM (Parts Per Million).Per Million) or PPM (Parts Per Million).
Reliability typically refers to the “intrinsic Reliability typically refers to the “intrinsic
failure rate” over time and is measured in failure rate” over time and is measured in
FITS (Failures In Time per billion device FITS (Failures In Time per billion device
hours).hours).
The The BathTub BathTub CurveCurve
BathTub Curve
Log Time
Failure Rate
What factors contribute to
What factors contribute to
semiconductor device failures?semiconductor device failures?
Packaging related failures:Packaging related failures:
Thermal/mechanical stress.Thermal/mechanical stress.
Moisture induced corrosion.Moisture induced corrosion.
Alpha radiation.Alpha radiation.
Silicon related failures:Silicon related failures:
Sensitive to thermal and voltage stress.Sensitive to thermal and voltage stress.
Particle contamination.Particle contamination.
Silicon lattice defects.Silicon lattice defects.
Thin film (oxide) integrity.Thin film (oxide) integrity.
Examples of Package Related
Examples of Package Related
Failures Failures –– Lifted Ball BondsLifted Ball Bonds
Examples of Package Related
Examples of Package Related
Failures Failures –– Lifted Ball BondsLifted Ball Bonds
Example of Silicon Related
Example of Silicon Related
FailureFailureParticle ContaminationParticle Contamination
Example of Silicon Related
Example of Silicon Related
FailureFailureSilicon Crystal DefectSilicon Crystal Defect
How do semiconductor How do semiconductor
manufacturers provide quality manufacturers provide quality
and reliability?and reliability?
The testing of semiconductor devices is The testing of semiconductor devices is
aimed at detecting defective units before aimed at detecting defective units before
shipment to customer.shipment to customer.
BURNBURNIN (high voltage/high temperature IN (high voltage/high temperature
stress) is used to accelerate the failure of stress) is used to accelerate the failure of
defective components.defective components.
The effectiveness of these processes is The effectiveness of these processes is
monitored through accelerated testing.monitored through accelerated testing.
How are reliability failure rates
How are reliability failure rates
calculated?calculated?
It is very impractical to determine failure rates It is very impractical to determine failure rates
using “real time” data.using “real time” data.
Predicted failure rates must be validated before Predicted failure rates must be validated before
product release which would impact time to product release which would impact time to
market.market.
Semiconductor devices are subjected to Semiconductor devices are subjected to
“accelerated” stress conditions.“accelerated” stress conditions.
Statistical models are applied to accelerated data Statistical models are applied to accelerated data
to calculate predicted failure rates.to calculate predicted failure rates.
FIT Rate ComputationFIT Rate Computation
Where:Where:
FIT Rate = FIT Rate = Failures per billion device hours
Pn Pn = = Poisson Statistic at 60% confidence (can be referenced in
statistical tables based on sample size/failure rate).
Device Hours = Device Hours = Sample size X test hours at accelerated
conditions. Typically must have over a million device hours for
statistical significance.
AF = AF = Acceleration factor between stress environment and typical
operating conditions.
910E
AF
s
DeviceHour
Pn
FITRate
Voltage Acceleration FactorVoltage Acceleration Factor
Where:
V
s
=Accelerated Stress Voltage
V
o
=Typical Operating Voltage
= Experimentally determined constant based on dielectric
integrity data.
For a device that typically operates at 2.7V and is stressed at
3.7V: AFAF
VV
= 20.09= 20.09
)(
os
VV
V
eAF
Thermal Acceleration FactorThermal Acceleration Factor
Where:
T
s
=Accelerated Stress Temperature in Kelvins
T
o
=Typical Operating Temperature in Kelvins
E
a
= Activation Energy in eV. Activation energy for typical oxide
defects has been experimentally determined to be 0.3eV.
k = Boltzmann’s Const (8.617E5 eV/
o
K)
For a device which typically operates at 50’C and is stressed at
125’C: AFAF
T T
= 7.623= 7.623
)
11
(
so
a
TTk
E
T
eAF
Overall Acceleration FactorOverall Acceleration Factor
To determine the overall acceleration factor To determine the overall acceleration factor
used in the FIT Rate calculation, the temperature used in the FIT Rate calculation, the temperature
and voltage stress factors are multiplied and voltage stress factors are multiplied
together.together.
AFAF
TT
= AF= AF
VV
X AFX AF
TT
= 20.09 X 7.623 = 153= 20.09 X 7.623 = 153
FIT Rate Calculation ExampleFIT Rate Calculation Example
A device typically operates at 2.7V and 50’C. 18,386
devices are stressed for 168 hours at 3.7V and 125’C.
There are 10 failures. What is the FIT rate?
Pn = Based on the number of failures in the sample size,
Pn is found to be 11.51 at 60% confidence.
Device Hours = 18,386 X 168 = 3.09 X 10
6
AF=153
FIT Rate=11.51(10FIT Rate=11.51(10
99
)/(3.09 X 10)/(3.09 X 10
66
)(153) = 24 FITS)(153) = 24 FITS
Or one could expect 24 failures every billion hours.
What would the MTBF be???
Thin Film (Dielectric) IntegrityThin Film (Dielectric) Integrity
TDDB (Time Dependent Dielectric Breakdown) is a TDDB (Time Dependent Dielectric Breakdown) is a
principal failure mechanism in semiconductor devices.principal failure mechanism in semiconductor devices.
1.1.Defect related breakdown (caught at BURNDefect related breakdown (caught at BURNIN).IN).
Asperities at Asperities at SiSiSiO2 interfaceSiO2 interface
Crystal defects/pinholes.Crystal defects/pinholes.
2.2.Intrinsic breakdown (Intrinsic breakdown (wearoutwearout).).
Hot electrons/charge trapping causes eventual Hot electrons/charge trapping causes eventual
rupture of dielectric.rupture of dielectric.
How are these modeled?How are these modeled?
TDDB failures exhibit a lognormal distribution that can TDDB failures exhibit a lognormal distribution that can
be approximated by:be approximated by:
)
ln
(
2
1
2
1
)(
t
e
t
tf
Where:Where:
sigma = standard deviation of the samplesigma = standard deviation of the sample
mumu = mean of the distribution= mean of the distribution
TDDB is a strong function of electric field stress and a TDDB is a strong function of electric field stress and a
weak function of thermal stress with an Activation weak function of thermal stress with an Activation
Energy of 0.3eV.Energy of 0.3eV.
Other accelerated tests typically Other accelerated tests typically
performed to measure device performed to measure device
reliability:reliability:
THB (Temp/Humidity/Bias) THB (Temp/Humidity/Bias) –– 85’C/85% RH/3.6V85’C/85% RH/3.6V
Autoclave Autoclave –– 121’C/100% RH/3.6V121’C/100% RH/3.6V
Temp Cycle Temp Cycle  40’C to +85C/1008 cycles40’C to +85C/1008 cycles
Thermal Shock Thermal Shock  55’C to + 125’C55’C to + 125’C
High Temp Storage High Temp Storage  +150’C for 1008 hours+150’C for 1008 hours
ESD ESD –– Based on MIL STD 3015Based on MIL STD 3015
Latchup Latchup
Electromigration Electromigration StudiesStudies
Questions?Questions?
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