LASER VOLTAGE PROBING (LVP)

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Nov 2, 2013 (3 years and 8 months ago)

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YARIİLETKEN OPTOELEKTRONİĞİ

LASER VOLTAGE PROBING (LVP)

İsmail CANTÜRK
12504201



CASE STUDY AND GENERAL REVIEW


Laser

Voltage

Probing

in

Failure

Analysis

of


Advanced

Integrated

Circuits

on

Silicon

on

Insulator

(
SOI
)



19
th

International

Symposium

on

the

Pyhsical

and

Failure

Analysis

of

Integrated

Circuits

(IPFA)


2
-
6

July

2012
,

Singapore

Laser Voltage Probing


Laser

voltage

probing

is

the

newest

generation

of

tools

that

perform

timing

analysis

for

electrical

fault

isolation

in

advanced

failure

analysis

facilities
.

This

paper

uses

failure

analysis

case

studies

on

SOI

to

showcase

the

implementation

of

laser

voltage

probing

in

the

failure

analysis

flow

and

highlight

its

significance

in

root
-
cause

identification

X

LVP


Failure

analysis

(FA)

at

advanced

technology

nodes

has

become

increasing

difficult

because

of

smaller

g
eometries

and

increased

sensitivity

to

subtle

defects
.

This

increases

the

need

for

successful

electrical

fault

isolation

(EFI)

X

Classic techniques


E
lectric

F
ault

isolation

utilizes

laser
-
intrusive

or

emission
-
based

techniques

that

exploit

anomalous

signals

coming

from

the

defect
.



The

device

under

test

(DUT)

may

be

biased

statically

using

simple

source

meters

for

techniques

like

thermal
-
induced

voltage

alteration

(TIVA)

or

photo/thermal
-
emission

microscopy

(EM)
.

DUTs

with

defects

that

do

not

have

an

electric

path

between

the

static

supplies

go

through

dynamic

testing

using

automated

test

equipment

(ATE)

by

running

patterns

that

exercise

the

defective

circuitry
.

Techniques

like

soft

defect

localization

(SDL)

or

dynamic

EM

are

then

employed,

depending

on

the

failing

symptoms
.


LVP


EFI

is

inadequate

with

the

techniques

already

described,

and

there

is

a

need

to

study

the

actual

behavior

of

transistors

while

they

are

toggled

during

the

tests
.

This

is

called

timing

analysis

or

waveform

analysis
.

The

common

technique

used

in

the

last

decade

worked

by

collecting

photons

released

during

the

toggling

events

and

statistically

accumulating

them

into

a

waveform

Why we need LVP?


The

technique

has

been

extremely

useful

in

the

past,

but

with

voltage

scaling

and

shrinking

transistor

sizes,

the

number

of

photons

being

released

has

decreased

dramatically
.

In

addition,

signals

between

two

transistors

in

the

collection

window

of

a

few

microns

are

indistinguishable,

leading

to

cross
-
talk


LVP









absorption coefficient

amplitude modulation

refractive index

phase modulation


modulated reflected laser is collected by a photodetector

for translation from an optical
signal into an electrical

signal. This resultant electrical signal is then amplified and

finally fed to an oscilloscope to reassemble the original

transitions on the transistor

X

LVP


Laser

voltage

probing

(LVP)

is

the

latest

generation

of

timing

tools

that

perform

well

against

voltage

scaling

while

accommodating

a

much

smaller

collection

window
.

The

technique

employs

the

Franz
-
Keldysh

effect

(i
.
e
.
,

decoding

the

optical

modulation

caused

by

changes

in

the

electrical

field

in

a

transistor’s

space
-
charge

regions)
.

Both

continuous

wave

(CW)

and

femtosecond

pulsed

near
-
infra
-
red

(NIR)

lasers

have

been

used

to

implement

equipment

using

this

effect
.

Though

LVP

has

existed

for

a

long

while,

the

current

implementations

make

the

technique

a

lot

more

usable

X

LVP


This

effect

is

also

used

to

perform

frequency

mapping

(FM)

or

laser

voltage

imaging

(LVI)
.

This

technique

has

been

shown

to

isolate

broken

scan

fails

successfully
.

LVP

and

FM

have

made

the

difference

between

failing

to

find

the

cause

and

successful

root
-
cause

identification

THE FRANZ
-
KELDYSH EFFECT


LVP

works

on

the

principles

of

the

Franz
-
Keldysh

effect

on

the

space
-
charge

region

of

a

MOSFET

.

Also

known

as

the

depletion

region,

the

space
-
charge

region

refers

to

the

junctions

between

the

source,

drain,

or

channel

of

the

transistor

and

its

body
.


Two

optical

properties

of

this

region

and

of

interest

to

us

vary

with

the

applied

electric

field
:

the

absorption

coefficient

and

the

refractive

index

LVP Basics


When

a

laser

of

uniform

amplitude

and

phase

is

incident

onto

the

space
-
charge

region,

some

of

the

photons

are

absorbed

(function

of

the

absorption

coefficient)

and

the

rest

are

reflected
.

The

reflected

photons

are,

hence,

“amplitude

modulated”

by

changes

to

the

absorption

coefficient,

which

means

changes

in

the

electric

field

due

to

toggling

of

the

logic

state

of

the

transistor

are

mapped

onto

the

amplitude

modulated

reflected

las
er

X

LVP Basics


While

changes

to

the

absorption

coefficient

cause

amplitude

modulation

of

the

reflected

laser,

changes

to

the

refractive

index

cause

a

“phase

modulation”

that

changes

the

phase

of

the

reflected

laser
.

On

the

CW

LVP

implementation,

detection

is

based

on

changes

to

the

absorption

coefficient

only
.

On

the

pulsed

LVP

implementation,

detection

is

based

on

both

absorption

coefficient

modulation

and

phase

changes

X

LVP Basics


The

modulated

reflected

laser

is

collected

by

a

photodetector

for

translation

from

an

optical

signal

into

an

electrical

signal
.

This

resultant

electrical

signal

is

then

amplified

and

finally

fed

to

an

oscilloscope

to

reassemble

the

original

transitions

on

the

transistor

X

LVP Basics


The

sample

is

exercised

continuously

using

the

pattern

of

interest

on

an

automated

test

equipment

(
ATE
)
,

and

a

trigger

pulse

is

generated

at

a

precise

vector,

which

is

then

fed

into

the

LVP

system
.

This

pulse

triggers

the

oscilloscope

at

the

window

of

interest

and

the

resultant

waveform

is

averaged

millions

of

times

to

reproduce

the

logic

states

of

the

transistor

in

that

interval
.



The

output

of

the

amplifier

electronics

can

also

be

sent

into

a

spectrum

analyzer

to

identify

frequency
.

The

tool

can

then

be

made

to

search

for

this

frequency

over

an

area
;

this

technique

is

called

frequency

mapping

(FM)
.

LVP Basics


Pulsed

LVP

is

implemented

in

a

different

way

but

utilizes

the

same

basic

principles

of

the

Franz
-
Keldysh

effect
.

Below
,

a

femtosecond

laser

pulse

is

shot

at

the

transistor

at

precise

intervals

from

the

trigger,

recollected

into

bins,

and

accumulated

into

a

waveform
.

This

implementation,

however,

does

not

accommodate

FM

LVP Basics


Though

there

are

several

applications

for

LVP

and

FM,

the

focus

here

is

to

isolate

defects

on

SOI
-
based

advanced

integrated

circuits
.

LVP

is

particularly

effective

when

used

with

structural

tests

like

scan

or

JTAG

because

the

behavior

can

be

predicted

from

the

transistors

of

interest

TYPES OF LVP


Continuous Waveform
Laser Voltage Probing
(CW LVP)



Lase waveforms are sent
in a continuous manner


PULSE LVP




Laser waveforms are sent
as a sequence of pulses

Case Study (CW LVP)


This

case

discusses

SOI

qualification

reject

that

failed

scan

logic

tests
.

The

failure

is

gross

at

different

temperature,

frequency,

and

voltage

conditions
.

No

anomalous

signals

were

observed

with

other

fault

isolation

techniques,

including

TIVA

and

static

or

dynamic

EM

(Figure

2
),

and

the

area

is

too

big

for

direct

physical

analysis
.

Case Study


FM

is

performed

on

the

unit
.

The

scan

test

is

looped

continuously

using

the

ATE

with

a

50
-
MHz

clock

frequency
.

The

area

of

interest

is

frequency
-
mapped
.

Unlike

in

a

chain

test,

in

a

scan

logic

test

the

output

of

scan

flops

usually

do

not

toggle

at

the

same

frequency

as

the

supplied

clocks,

though

they

could

be

a

harmonic
.

Case Study (CW LVP)

Case Study


Figure

3

is

an

overlay

of

the

FM

with

the

aligned

CAD

layout
.

Strong

and

unexpected

FM

signals

are

observed

at

one

of

the

call
-
out

circuitries
.

The

other

red

sites

belong

to

the

clock

drivers

and

should

be

ideally

present


Figure

4

shows

the

CW

LVP

waveforms

collected

from

the

circuitries

of

interest
.

The

horizontal

axis

is

in

units

of

time

and

the

vertical

axis,

though

arbitrary,

is

in

fact

an

indication

of

the

state

of

the

transistor
.

For

practical

purposes,

it

can

assume
d

that

a

high

on

the

waveforms

indicates

that

the

transistor

is

turned

on

Case Study


The

first

pair

of

waveforms

indicates

clock

transitions

and

in

this

case

toggles

at

100

MHz
.

It

is

observe
d

that

two

clock

pulses

in

the

window

of

interest
.

Signals

are

collected

from

a

reference

circuitry,

which

is

expected

to

have

toggles

similar

to

the

circuitry

of

interest

and

are

shown

as

the

second

pair

of

waveforms
.

Signals

at

the

reference

circuitry

indicate

flat

states

and

sharp

transitions

between

low

and

high,

which

is

expected
.


The

third

pair

of

waveforms

is

collected

from

the

transistors

flagged

by

FM

and

diagnostics
.

The

waveforms

collected

are

much

bigger

in

amplitude

and

do

not

have

the

flat

states

or

sharp

transitions

that

it

is

observed

that

on

the

reference

circuitry
.

This

signal

indicates

an

abnormal

amplitude

modulation

of

laser

and

is

probably

due

to

an

anomaly

in

the

active

regions

of

the

transistor
.

Case Study


Following

EFI,

the

sample

is

deprocessed

layer

by

layer

looking

for

anomalies

at

each

metal

and

via

level
.

No

physical

defect

was

observed

until

M
1
.

Nanoprobing

performed

subsequently

on

the

flagged

instance

(Figure

5
)

indicates

a

short

between

the

drain

and

gate

of

the

NMOS

transistor
.



The

NMOS

is

then

cross
-
sectioned,

and

the

scanning

transmission

electron

microscope

(STEM)

analysis

shown

on

Figure

6

exposed

a

silicide

short

between

the

gate

and

the

drain,

which

explains

the

root

cause

for

the

failure
.

Case Study (Pulse LWP)


This

analysis

is

also

performed

on

a

scan

failure

that

fails

gross

at

different

temperatures,

voltage,

and

frequency
.

Referring

to

Figure

7
,

the

schematic

of

the

failing

circuits,

the

inverter

driving

the

signal

launch

is

flagged

as

defective

by

diagnostics
.

This

signal

fans

out

to

multiple

multiplexers

(
Mux
1
,

Mux
2
,

Mux
3
)
.

Case Study


The

CAD

layout

is

shown

in

Figure

8

and

the

signal

direction

is

marked

in

yellow
.

Mux
1

and

Mux
2

are

closer

to

signal

launch

and

Mux
3

is

further

downstream
.

No

anomaly

is

observed

through

static

FI

techniques


LVP

(Figure

9
)

is

used

to

isolate

the

failure

Case Study


P
ulsed

LVP

(Figure

9
)

is

used

to

isolate

the

failure,

though

either

system

could

have

provided

similar

results
.

The

transitions

of

interest

happen

in

the

period

marked

by

the

dotted

rectangle
.

As

the

clock

goes

high,

the

active

of

signal

launch

transitions

from

a

high

to

low

on

the

NMOS

and

its

inverse

is

observed

on

the

PMOS
.



This

signal

fans

out

to

Mux
1
,

Mux
2
,

and

Mux
3

at

the

same

time
.

The

data

collected

within

Mux
1

and

Mux
2

show

clear

high
-
to
-
low

transition

on

the

PMOS

and

a

corresponding

low

to
-

high

on

the

NMOS
.

Mux
3
,

on

the

other

hand,

does

not

have

a

clear

transition

on

either

NMOS

or

PMOS
.

This

could

mean

that

there

is

no

signal

entering

Mux
3
;

there

could

be

an

anomaly

in

connecting

metal

lines

between

Mux
2

and

Mux
3

Case Study


Mux
3
,

on

the

other

hand,

does

not

have

a

clear

transition

on

either

NMOS

or

PMOS
.

This

could

mean

that

there

is

no

signal

entering

Mux
3
;

there

could

be

an

anomaly

in

connecting

metal

lines

between

Mux
2

and

Mux
3

Conclusion


The

technique

has

contributed

significantly

to

the

success

rates

of

F
I
,

improving

root
-
cause

identification

and

resulting

in

earlier

process

fixes,

therefore

improving

yield

and

reliability
.

It

also

gives

us

an

opportunity

to

understand

test

results

and

correlate

the

defect

to

the

failing

symptoms


Introduction

to

Laser

Voltage

Probing

(LVP)

of

Integrated

Circuits

Siva

Kolachina,

Texas

Instruments

Inc,

Stafford,

TX,

USA
,

Chapter

10
:

Laser

and

Particle

Beam
-
Based

Localization

Techniques,

Microelectronics

Failure

Analysis

Desk

Reference

Fifth

Edition


Investigation

of

laser
-
beam

modulations

induced

by

the

operation

of

electronic

devices,

vorgelegt

von

Dipl
.
-
Ing
.

Ulrike

Kindereit

aus

Berlin,

Von

der

Fakultat

IV

-

Elektrotechnik

und

Informatik
,

Doktorin

der

Ingenieurwissenschaften


Laser

Voltage

Probe

(LVP)
:

A

Novel

Optical

Probing

Technology

for

Flip
-
Chip

Packaged

Microprocessors,

Wai

Mun

Yee,

Mario

Paniccia*,

Travis

Eiles*,

Valluri

Rao*

Intel

Technology

Sdn
.

Bhd
.
,

Bayan

Lepas

Free

Industrial

Zone,

1

1900

Penang,

Malaysia

;

*

Intel

Corporation,

Santa

Clara,

USA
.


Laser

Voltage

Probing

in

Failure

Analysis

of

Advanced

Integrated

Circuits

on

SOI

Ravikumar,

V
.
K
.
1
,

Wampler,

R
.
2
,

Ho,

M
.
Y
.
1
,

Christensen,

J
.
2
,

Phoa,

S
.
L
.
1

Advanced

Micro

Devices

Singapore

Pte

Ltd
1
,

508

Chai

Chee

Lane,

Singapore

469032
,

Advanced

Micro

Devices,

Inc
.
2
,

7171

Southwest

Pkwy,

Austin

TX

78735
,

USA


www.aku.edu.tr

;
www.dcgsystems.com

;
www.yarbis.yildiz.edu.tr/tkiyan

;
www.sciencedirect.com









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