Spretrochimica Acta, Vol. 39B, No. 12. pp. 1579-1581, 1984. PrintedinGnatBritain.

Surface- and microanalysis

0584-8547/84 so3.00+.00 0 1984.Pergamotl Press Ltd.

as a tool for studying the corrosion of aluminium

M. J. A. VAN CRAEN,* F. C. ADAMS,* L. J. A. VAN Bsstct and R. A. L. VANDEN BERoust *University of Antwerp (U.I.A.), B-2610 Wilrijk, Belgium and tBel1 Telephone Manufacturing Company, B9OOO

Gent, Belgium

(Received 27 March 1984)

Ahatraet-Corrosion phenomena of Al-l % Si bond wires, observed after life testing of certain transistors, are studied. The following information is derived from laboratory simulation tests: the kinetics of the corrosion process, information about the corrosion mechanism and critical parameters, especially the influence of the environmental gas and Si content and finally the identification of the corrosion products and their comparison with those found for the transistor. It is demonstrated, using a combination of several surface. analytical techniques, that the Al pitting corrosion is induced and enhanced by the presence of water as a transport medium and surface electrolyte in an oxygen-rich atmosphere, with chloride ions as a stimulating and activating species. The effect of 1 y0 Si in the wire consists in acceleration of the corrosion rate, and is probably due to grain boundary effects. All critical corrosion parameters could be traced in the transistor system by electron microscopy, laser microprobe mass analysis and residual gas (and moisture) analysis by mass spectrometry.

IN ORDER to obtain a fair reliability, integrated circuits (I.C.) are protected against the environment by an insulating material and an hermetically sealed package. However, it has been shown that this does not prevent corrosion of conductor tabs and wire bond connections. Life testing of transistors indicated that air should be avoided as a sealing gas.

For the study of the corrosion phenomena of Al wire bonds and for the identification of the critical parameters and their influence, corrosion simulation tests were performed. An analytical procedure as presented in Table 1, using several surface-sensitive methods was necessary to provide the required information on the corrosion process. The equipment used and their specifications are summarised in Table 2. Also included are the specific advantages, shortcomings and the information obtained using these methods especially as related to this study of Al corrosion and its simulation testing.

Some typical examples of the analytical results and information provided by the used methods are: -LAMMA indicated that the corrosion products formed on the Al/Ni contact interface

consist of aluminium sulphate, -oxide and -hydroxides, -chlorides and of alkali- and earth alkaline rich particles.

-EPMA/SEM showed the layered structure of the corrosion products on the Al wire bonds and provided the (microscopic) information on the influence of various corrosion para- meters.

-AES in-depth profiling revealed the structure and composition of the alumina, aluminium metal and substrate layers.

-EMPA provided quantitative information on the composition of the corrosion products. -SIMS showed that the activator was concentrated both at the oxide layer/atmosphere and

at the alumina/metal substrate interface. -ESCA determination of the modified Auger parameters and peak shapes resulted in the

identification of the chemical species present in the corrosion products. Using this combination of several advanced surface-sensitive and micro-analytical

techniques it was shown that the corrosion of the aluminium-1 % silicon samples and subsequent pitting formation in reactive atmospheres was caused by the presence of water as a transport medium and surface electrolyte in an oxygen-rich atmosphere, with chloride ions as stimulating species.

Acknowledgement-This work was carried out under research grant 80/85-10 of the Interministrial Commission for Science Policy, Belgium.

SA(B) 39:12-v 1579

1580 M. J. A. VAN CRAEN et al.

Table 1. Scheme of the principle steps in the study of the corrosion phenomena of Al in integrated circuits (KC.) using electron probe microanalysis (EPMA), scanning electron microscopy (SEM), electron spectroscopy for chemical analysis (ESCA), Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS) and laser

microprobe mass analysis (LAMMA)

Micro-electronic devices

I I.C. Life testing I

9 wire bond corrosq

I EPMA SEM

1

ESCA AES SIMS

Microscopic Surface analysis analysis

In-depth analysis

Influence or corrosion parameters

Corrosion phenomena

Tab

le 2

. Sp

ecif

icat

ions

an

d ch

arac

teri

stic

s of

the

sur

face

- an

d m

icro

anal

ytic

al

met

hods

us

ed t

o st

udy

the

Al

corr

osio

n ph

enom

ena

SEM

E

PMA

A

ES

ESC

A

SIM

S L

AM

MA

Type

Spec

ific

atio

ns

Jeol

35

25 k

eV e

- C

AN

BE

RR

A

com

pute

r

Adv

anta

ges

mic

rosc

opy

with

hig

h la

tera

l re

solu

tion

Info

rmat

ion

obta

ined

st

ruct

ure

of c

orro

sion

pr

oduc

ts/m

icro

scop

ic

anal

ysis

Jeol

733

Ph

ysic

al

Ele

ctro

nics

Su

perp

robe

59

0 25

keV

e-

5keV

e-

elem

ent

map

ping

(0

.5 rA

) X

-ray

mic

roan

alys

is

4 ke

V A

r+

TR

AC

OR

T

M-2

000

CM

A (

0.6

% r

esol

co

mpu

ter

utio

n)

f SE

M/a

naly

tical

su

rfac

e se

nsiti

vity

/in-

poss

ibili

ties

dept

h an

alys

is

mic

rosc

opy/

quan

ti-

tativ

e an

alys

is o

f co

r-

rosi

on

prod

ucts

dist

ribu

tion

of 0

, A

l an

d Si

at

surf

ace

and

in-d

epth

ch

argi

ng

effe

cts/

de

tect

ion

limits

D

isad

vant

ages

f

char

ging

of

ins

ulat

ing

oxid

e fi

lms/

high

de

tect

ion

limits

/O,

Na,

Cl

not

dete

ctab

le

Phys

ical

E

lect

roni

cs

W-K

m

10 k

eV

(40

mA

) do

uble

-pas

s C

MA

(1

.2 y

0 re

solu

tion)

su

rfac

e se

nsiti

vity

/ ch

emic

al

info

rmat

ion

chem

ical

ana

lysi

s us

ing

Aug

er

para

met

er

sens

itivi

ty/lo

ng

anal

ysis

tim

es

requ

ired

CA

ME

CA

IM

S-30

0

6 ke

V A

r+

Ele

ctro

stat

ic

Sect

or

Ana

lyse

r PD

P/l

l-04

co

mpu

ter

extr

eme

dete

ctio

n se

nsiti

vity

/intr

insi

c in

-dep

th

prof

iling

in

-dep

th

dist

ribu

tion

of 0

, N

a, A

I an

d Si

in

the

oxid

e fi

lms

limite

d ch

emic

al

info

rmat

ion/

quan

ti-

fica

tion

very

dif

icul

t

Ley

bold

-Her

eaus

50

0

Q-s

witc

hed

Nd-

YA

G

lase

r t

= 2

65 n

m

MIN

K-c

ompu

ter

rapi

dnes

s/ch

emic

al

spec

iatio

n/m

icro

- an

alys

is

iden

tific

atio

n of

co

rros

ion

prod

ucts

repr

oduc

ibili

ty,

sam

ple

prep

arat

ion