April 30, 2014 1

Combination of Multiple Mechanism for Post-Silicon

Reliability Prediction

April 30, 2014

Joseph B. Bernstein Ofir Delly,

Moti GabbayAriel University

Yizhak Bot (BQR)josephbe@ariel.ac.il

April 30, 2014 2

We always try learning from the past in order to improve the Future.

One Problem..…Everyone sees the past

differently !

April 30, 2014 3

“It is possible to fail in many ways...while to succeed is

possible only in one way…” Aristotle

If We don’t learn from the past, We are condemned to repeat

it…George Santayana, 1952

April 30, 2014 4

SO, WHAT’S THE BIG PROBLEM ???

WHY IS LIFETIME PREDICTION

SO DIFFICULT???

April 30, 2014 5

The Semiconductor Test Industry Today

We test the parts “blindly” and then “see how they run”…

April 30, 2014 6

Field Data Analysis Results

= 1 ± .2 for all systemsField Failures are generally Constant Rate Occurrences, Beta = 1 is Poisson.

Cumulative data for over 10,000,000 Military Electronic Systems

Physics of Failure

MTBF Region

So, we should keep MTBF and FIT

April 30, 2014 7

•Modern Electronics have nearly constant failure rate

•Few (very rare) exceptions•Keep the idea of Constant Rate and

work within the framework of Failure-In-Time (FIT)

Some Observations:

April 30, 2014 8

So what’s the problems with FIT ?Handbooks are Pretty outdated

oMIL 217 is OLD and USELESS.oFIDES is updated but only applies a

single mechanism approach.oPhysics of Failure (PoF) approach

looks to TTF and not FIT.oProbabilistic DfR requires unique

distributions for each mechanism.oHALT/HASS cannot predict l.

April 30, 2014 9

JEDEC Publication JEP 122G Rev. Oct. 2011 I Bet You didn’t know JEDEC says this:

2 Terms and definitions (cont’d) quoted failure rate: The predicted failure rate for typical

operating conditions. (This is the FIT)NOTE: The quoted failure rate is calculated from the observed

failure rate under accelerated stress conditions multiplied by an accelerated factor; e.g..…

“When multiple failure mechanisms and thus multiple acceleration factors are involved, then a proper summation technique, e.g., sum-of-

the-failure rates method, is required”.

April 30, 2014 10

Semiconductor Industry ‘Joke’ The Magical Mysterious Decreasing FIT

Intel

Maxim

1 FIT = 1 Failure per 10,000 parts in 12 years.If ONLY this were true!

PLX

April 30, 2014 11

Measured Component FIT (l) vs. Year Produced

•Compared to previous avionic system data, the trend continues at a much greater than expected rate.

•Bernstein’s Law: ~10x increase in FIT every 10 years

Field Return Data

0.25 m : ~20-50 FIT

90 nm : ~ 150 - 300 FITACTUAL Failures per Billion Part-Hours 65nm:~ 300-450 FIT

Avionic and Military

Expectation!

130 nm : ~90-120 FIT

45-22 nm??? :

April 30, 2014 12

Reliability

Performance

Benefits to Accurate Prediction !!Performance is

Designed for a required Reliability specification

A small reduction in performance

can bring a huge gain in reliability

(illustrative)

1 .X

X 2.

Suggestion:Two products;

One design

More customers for the same

Design

More applications means more Sale$

Multiple Accelerated Test Matrix for Reliability Prediction 12

April 30, 2014 13

Performance vs. Reliability

•I could double the speed for free If I KNOW the reliability, maybe I CAN improve performance?!?!

Why not operate here?

0.5 1 1.5 2 2.5 3 3.50.00E+00

1.00E+07

2.00E+07

3.00E+07

4.00E+07

5.00E+07

6.00E+07

7.00E+07

8.00E+07

9.00E+07

1.00E+0821 inverter RO

Core Voltage (V)

Freq

. (Hz

)

Nominal Voltage

April 30, 2014 14

Qualification TODAY Industry ‘Standard’ FIT (failures in time) model:

Acceleration Factor (AF) is the product of Voltage and Temperature acceleration factors.

3 KILLER problems:.1This does NOT fit with KNOWN failure models.

.2When ZERO failures are reported, there is NO statistical meaning to the acceleration factor.

.3Uncertainty is assumed for 0/1 fails, while AF has ZERO uncertainty; no accounting for error in AF!!

April 30, 2014 15

Multiple Mechanisms Are Here to Stay

• Traditional Reliability approach fails to predict Field Failures .

• Modeling, Simulation and Acceleration alone will NOT yield true results without Accurate Failure Analysis.

• HOWEVER: We CAN model and PREDICT Failure Rate under Known Conditions with a

more complete picture of the mechanisms???

April 30, 2014 16

Multiple Mechanisms Don’t Add Up!!! Single Mechanism Model:

–AFsystem = AFThermal* AFElectrical

–So, 1/MTTFuse = 1/(MTTFtest *AFMM)

Multiple Mechanism Model:–1/MTTFuse = P1/(MTTFtest *AFmech1) + P2/(MTTFtest *AFmech2)

–Therefore, the effective AF for multiple mechanisms is:AFMM = 1

P1P2AFmech1AFmech2

•The True acceleration factor is the SMALLER one, not the one which exposes a failure at accelerated test.

+

April 30, 2014 17

Traditional Methodology•Single Mechanism Model (old JEDEC Standard):

–77 Devices tested for 1000 hours with 0 failures…•For Example: AFT = 100 and AFV = 130

AFS= 100*130 = 13000 !!

Zero failures at High V and High T

Assume 1 failure after 1000 hours :Thus FIT: 109 / (77 * 1000 * 13000) = 1 FIT!!

•NICE! Now, we have done a great job and can go home and celebrate our success !!! NOT!!!

April 30, 2014 18

The Reality of Multiple Mechanisms•BUT….Multiple Mechanisms Compete!

•Same Example: AFV from HCI and AFT from EM –EM has Ea = 1 eV and voltage g ~ 1.

–HCI has Ea ~ 0 eV and voltage g ~ 14

•NOW, AFS = 2/(1/100 + 1/130) = 163

•So our correct calculation for the same data:

FIT: 109 / (77 * 1000 * 163) = 113 FIT!!This is compared to 1 FIT based on HTOL.

Traditional FIT is ALWAYS too low as compared to considering multiple mechanisms

April 30, 2014 19

Failure Rate Estimation at System LevelNew System Reliability Model

Replacement Program (collaboration)

FM1 FM2 FM3

Nth Component

Each component is comprised of several sub-components in

proportion to their function and relative reliability stress.

Base Failure rate can be determined at various accelerated conditions in order to normalize the matrix and

make physics based reliability assessment from test data combined

with knowledge of the application

April 30, 2014 20

FIXtress™ : A MORE ACCURATE FIT

Time to Fail (years)24681012

Calculated PDF

(FIT)

l

l~S(1/MTTF1+1/MTTF2+…+1/MTTFn)The manufacturers have the data, we can make the

prediction (BQR Software Tool)!

λTDDB

λHCI

λNBTI

λEM

λPackage

April 30, 2014 21

“It is better to be roughly right than precisely

wrong”. ―John Maynard Keynes

Our Guiding Principle:

April 30, 2014 22

How can we match data from reliability Models with experimentally obtained AF from HTOL?

PROPOSAL: Run Multiple Tests at different conditions while monitoring degradation.

22

Physics of Failure Models (JEDEC)

AF from Burn-in at different T, V

Matrix solution can match

Post-Silicon Test Strategy

April 30, 2014 23

JEDEC or TSMC Physics models

MTBF / FIT

DOE Burn-In

Relative AF Relative MTBF/FIT

System (TEST) measurements

DPPM per Fmax limit (real FIT at V, T test)

Matrix solution

24 failure mechanisms

over 4 categories

TDDB

HCI

BTI

EM

T1,V1

λTDDB λHCI λBTI λEM

T2,V2

T3,V3

T4,V4

Rel. AF

=

X

Reliability solution: FIT, DPPM

Output

Proportionality parameter X

Input Input

Input

Our New Approach (ARIEL)

April 30, 2014 24

45nm

Temp Volt TDDB HCI BTI EM FIT200 1.2 2.93E+03 8.35E+00 4.26E+04 2.40E+05 242750140 1.2 3.71E+02 1.59E-01 4.55E+02 9.71E+03 9710

-35 2.4 3.19E+08 2.12E+13 9.08E+07 8.16E-05 9710000140 2.4 5.10E+13 5.13E+11 2.20E+13 9.71E+03 703975

30 1.2 1.00 1.00 1.00 1.00 185 1.2 30 0.67 34 399.00 Use

120 1.8 5305442428 739966 42398594 5362 HTOL

Contributions from JEDEC ModelsDifferent Dominant Mechanism at

each test condition

April 30, 2014 25

HTOL is OVERWHELMINGLY measuring only TDDB

•This is very convenient when Zero failures arise during the 1000 hour HTOL test.

•Foundries design the gate oxides very well so there WILL be NO TDDB failures during HTOL testing.

•3 other mechanisms are just ignored during final test and qualification.

April 30, 2014 26

Separation of Mechanisms•Failure Mechanisms can be separated by

properly selecting test conditions.•High Voltage and Low Voltage tests EM

•High Temperature and High Voltage tests for NBTI and for TDDB

•Low Temperature and High Voltage tests for HCI

April 30, 2014 27

Two Distinct Mechanisms! •HCI frequency dependence

•See at LOW T and High V•NBTI No Freq. dependence

•Seen at High T and High V

0 50 100 150 200 250 300 350 400 4500

0.001

0.002

0.003

0.004

0.005

0.006

0 100 200 300 400 500 600 7000

0.001

0.002

0.003

0.004

0.005

0.006

F(MHz) F(MHz)

-35°C2.4 V

140° C2.4 V

Note: -35°C has >2.5X failure rate as at 140°C for the same Voltage!!

April 30, 2014 28

TDDB from NBTI

0.5 1 1.5 2 2.5 3 3.50

100000000

200000000

300000000

400000000

500000000

600000000

700000000

21-stage RO Frequency vs. Voltage

Voltage-core

Soft breakdownPerf

orm

ance

(fre

q.)

Time-Dependent Dielectric Breakdown (TDDB)

Neg. Bias-Temperature Instability (NBTI)

April 30, 2014 29

Prediction for 28nm

30 40 50 60 70 80 90 1001101201

10

100

1000 FIT for f=1GHz

Temperature °C

FIT

per

Billi

on G

ates

Voltage

1.2

1.1 1.0

0.8 0.9

30 40 50 60 70 80 90 100 110 1201

10

100

1000 FIT for V=1.0 V

Temperature °C

FIT

per

billi

on G

ates

Dominant Mechanisms are EM and BTI, so strong T and Freq. dependence but weak V dependence.

2 GHz1.5

1.0 0.5

0.1

April 30, 2014 30

Observation

•Increase voltage by 20%•Increase performance by 20%

•Increases FIT by only factor of 2•Increased customer satisfaction

•Increased sales for FREE!!!

April 30, 2014 31

Main Observations.1 Dominant Mechanism at HTOL test is Never

the dominant mechanism at USE conditions.2Acceleration Factor based on 1 mechanism

model Significantly Overestimates Reliability.3Foundry models today are quite

sophisticated and consider N- and P-MOS based on their own data AND companies trust these models.

.4The chip companies WANT to consider the true contributions of EACH mechanism.

April 30, 2014 32

Conclusions

•We have developed a prediction model that is based on 4 failure mechanisms

•Our model is more accurate than the single failure model currently in use

•Collaboration with Industry is Necessary to Verify our Models and to keep pace with advancing technology

April 30, 2014 3333

Thank You