Auger electron spectroscopy was employed to characterize the diffusion barrier properties of molybdenum in the CrSi2/Mo/Au metallization system. The barrier action of Mo was demonstrated to persist even after 2000 hours annealing time at 300 C in a nitrogen ambient. At 340 C annealing temperature, however, rapid interdiffusion was observed to have occurred between the various metal layers after only 261 hours. The presence of controlled amounts of oxygen in the Mo layer is believed to be responsible for suppressing the short circuit interdiffusion between the thin film layers. Above 340 C, its is believed that the increase in the oxygen mobility led to deterioration of its stuffing action, resulting in the rapid interdiffusion of the thin film layers along grain boundaries

Boah, J. K.

Russell, V.

Smith, D. P.

English

NASA Technical Reports Server

STUFFEO MO LAYER AS A DIFFUSION BARRIER IN METALLIZATIONS FOR HIGH TEMPERATURE ELECTRONICS 
John K. Boah, General E lec t r ic  Company, EP-7, Syracuse, New York, 13221 
Virginia Russell, General Electr ic  Company, EP-3. Syracuse, New York, 13221 
Olvid P. Smith, General E le r t r i c  Company, EP-7, Syracuse, New York, 1322! 
Abstract 
Auger electron spectroscopy (AES) was employed to  
ch rac te r l ze  the d l f fus ion  bar r ie r  properties o f  
molytdenum i n  the CrSl2/Mo/Au metal l izat ion system. 
The barr ler  action of Mo was dmonstrated to  pers ist  
even a f te r  2000 hours annealing time a t  300°C i n  a 
nitrogen ambient. 
At 340°C annealing temperature, however, rapid 
i n ~ r d i f f u s i o n  was cbserved to  have occurred between 
the various metal layers a f t e r  only 261 b u r s .  
At 450'6, the ne ta l l  izat ion degraded a f t e r  only 
trro hours o f  annealing. 
The need fo r  high temperature (up to  300°C) micro- 
electronics appl ications i n  such diverse f i e l ds  as 
a i r c r a f t  engine controls, nuclear reactor core 
mn i to r i ng  fnstrumentation and o i l  and gas well 
downhole instrumentation has further lmposed 
str ingeqt r e l i a b i l i t y  requirenents on microelectronic 
interconnections. Oifftbsion barr ier  protection o f  
the o h i c  contact layer and metal conductor layer thus 
assuws new importance. This paper w i l l  discuss the 
enhh.r.d high temperature di f fus ion bar r ie r  properties 
achieved through the introduction o f  control led 
amounts o f  oxygen i n  the Ho bar r ie r  layer o f  the 
Cr/HD/Au metal 1 i za t  .on system. 
The presence o f  control led amounts o: oxygen i n  the A bar r ie r  metal l izat ion systen. i s  show scheinatically 
bb layer i s  be1 ieved to  be responsible f o r  suppressing i n  Figure 1. I t  consists of an o h i c  contact layer 
the short c i r c u i t  tnterdiffusion between the th in  (CrSiz), a d i f fus ion bar r ie r  layer (stuffed HD) and an 
f i l m  layers. Above 340°C, i t  i s  believed that  the interconnect o r  conductor layer (Au). Figure 2 
increase i n  the oxygen r,ubil i t y  led to  deter iorat ion i l l us t ra tes  a tr i-metal system where d i f fus ion  barr ier  
o f  i t s  s tu f f ing  action, resul t ing i n  the rapid protection i s  l o s t  during heat treatment. 
interdi f fus ion o f  the th in  f i l m  layers along grain 
boundaries. Experimental Procedur? 
The CrSi2/A/Au barr ier  metal l izat ion syctem l e n t  
i t s e l f  eas i ly  to f i ne  l i n e  patterning. 
Introduction 
Thin f i l m  metal l izations play a c r i t i c a l  r o le  i n  the 
re1 i a b i l  i t y  o f  microelectronic devices. The 
deleteridus ef fects o f  aluminum a l loy  penetrationl-2 
and the "purple plagueU3-4 i n  gold-aluminum th in  
f i l m  couples are well -known examples. Thin f i l m  
metal l izations are made up o f  very small grairs, 
high densit ies o f  grain boundaries and dislocations. 
I t i s  well established that grain boundaries and 
dislocations increase atomic b l i t y  by acting as 
short c i r c u i t  d i f fus ion paths?-&. ~ j o s t e i n 6  has 
shown that  f o r  face centered cubic metals, t h i n  f i l m  
interdi f fus ion i s  control led by dislocation pipe 
d i f fus ion  and grain boundary di f fus ion i n  the 
temperature range 30-60 percent o f  the me1 t i ng  
point. Below th i s  temperature range, i , . terdiffusion 
i s  not very signif icant. Above t h i s  temperature 
range, 1 t t i c e  d i f fus ion  predoniinates. Diffusion 9 barr iers such as stuffed barriers, passive barriers, 
sac r i f i c i a l  barr iers and themdynamicall y stable 
barriers, are intended to suppress short c i r c u i t  
control led interdi f fus ion.  The purple plague 
mentioned ear l  l e r  can be ascribed to Kirkendall 
voiding through short c i r c u i t  in terdi f fus ion.  
I la r r ls  e t  a18 reported that  the d i f fus ion  o f  T i  i n  Mo 
was inhib i ted by the presence of oxygen i n  tq Mo 
layer o f  a Tl/bb/Au system. Nowicki and Wang 
observed the suppression o f  Au-Sl intermixing i n  
Si/Mo/Au system i f  the bb layer was react ively 
sputtered i n  N2-Ar mixture. They a t t r ibu ted the 
enhanced Ho barr ier  action to  N2 occupation o f  the 
octahedral s i tes around th9 bb aLms. Neither o f  
the above studies deal t  wi th prolonged annealing 
ef fects a t  high temperatures. 
Srquen'-ial deposition o f  the th in  f i l m  layers o f  Cr ,  
HD, and Au on (111)-oriented, N-type s i l i con  single 
crystal  wafers was carr ied out using planar r.f. 
magnetron sputtering ( Perkin-Elmr Ul tec Model 2400- 
8SA). Sputtering pressures were less than 10 mtorr 
using Irgcn. Oxygen-arcon gas mixtures were u t i l i z e d  
fo r  reactive sputtering o f  the Fb. Prior  to sputtering, 
the s i l i con  wafers were etched I n  d i l u t e  HF, rinsed 
thc !~ugh ly  i n  de-ionized water. a i r  dried and trans- 
ferred imed ia t c l y  in to  the sputtering chamber. 
After sequentially depositins the Cr/tm/Au system, 
sintering was performed i n  a quartz tube i n  a flowing 
nitrogen ambient a t  450°C fo r  I 5  minutes to a f f ec t  
CrSi2 f o w l t i o n .  
dnneal ing experimeats were subsequent1 y carr ied out 
a t  300°C. 340°C and 450°C. The 300°C anneal; were 
performed i n  nitrogen ambients i n  a quartz tube fo r  
168 hours, 1000 hcurs and 2000 hours. 
Annealing experiments above 300-C were carried out  i n  
vacuum,. BCS was employed to study the extent o f  t h i n  
f i l m  interdi f fus ion between the various :atal layers. 
Fine l i n e  pattarn def in i t ion  was evaluated using a 
combination of pmtol i thographic and chemical etching 
techniques. 
Results and Discussions 
AES p ro f i l es  o f  the Cr/b/Au system before and a f te r  
sinterlng a t  30a°C are shown i n  Figures 3-6. There 
was l im i ted  penetration o f  the C r  layer by the Mo layer 
during the sputter deposition. Af ter  anneal ing a t  
300°C fo r  2000 hours, the di f fus40n bar r ie r  properties 
of the Ma layer were found to be intact .  &I# re-  
d is t r ibu t ion  o f  thc oxygen i n  ttr* Ho layei- occurred 
during tb? 300°C annealing. The suppresslon o f  the 
exw-ted grain boundary in terd i f fus ion  may be 
https://ntrs.nasa.gov/search.jsp?R=19820007462 2020-03-21T15:50:18+00:00Z
r w r i b e d  t o  the oxygen incorporated i n t o  the Ho 
I r y e r .  The s tu f f i ng  behavior o f  oxygen may be 
s i m l l a r  t o  tha t  of n i t rogen i n  T i - W  observed by 
b w i c k i  gt a l l 0  irl the AlITi-WIAU system. Nowicki 
and Wang a lso reported t h a t  con t ro l led  incorporat ion 
of n i  troqen i n t o  n~ lybdcnun  s i g n i f i c a n t l y  reduced the 
r a t e  o f  g ra in  boundary t n t e r d i f f u s i o n  i n  MoIAu 
coup1 es. 
Annealing above 300°C revealed tha t  oxygen s t u f f i n g  
does not  complete1 y suppress short c i r c u i t  contro l  l e d  
i n t e r d i f f u s i o n  such as shown i n  the AES p r o f i l e  o f  
Figures 7 and 8. I n  fact,  a t  450°C. the oxygen 
m o b i l i t y  uas so h igh tha t  s t u f f i n g  ac t ion  nas l o s t  
w i t h  a resu l tan t  loss  o f  Ho b a r r i e r  ac t ion  a f t e r  
on ly  2 hours o f  annealing. This observat ion i s  
consis tent  wi'h the equations o f  ~ j o s t e i n 6  and 
other  recen t l y  observed t h i n  f i l m  i n t e r d i f f u s i o n  
phenomena6. Fine 1 ine  pat tern ing was accompl ished 
using photo1 i thography and chemical e tch ing such as 
shown i n  Figure 9. The f i n e  l i n e s  a re  two microns 
i n  width. 
The diffusion b a r r i e r  ac t ion  o f  s tu f fed  Ho layers 
has been de~mnstrated t o  be re1 i a b l e  a t  300°C f o r  
a t  l e a s t  2000 hours i n  a n i t rogen asbient.  Thc 
incorporat ion of oxygen i n  the Ho l aye r  i s  believed 
t o  be responsible f o r  the enhanced d i f f u s i o n  bar r ie r  
a c t i o n  o f  the Cr/Mo/Au metal1 i z a t i o , ~  system a t  
temperatures below 300°C. Above 300°C. the Mo 
b a r r i e r  ac t ion  rapid1 y deter iorates.  
The coaperation o f  Or. Joseph Peng ( fo rn~er l y  o f  
ARACOR. Sunnyvai~.  Cal i forn ia ,  and now w i th  
F a i r c h i l d )  and Dr. A r i s t o t e l i s  Christou (NRL. 
Washington, 0. C.) i n  the AES analys is  i s  
g ra te fu l  1 y acknowlecged. Our tharks a1 so t o  
Dr.  Christou f o r  many helpfu l  d~sucss ions.  
L i s t  o f  References 
-
1 . C. J, Santoro. J. Electrochem. Soc. 116 
361 -3M ( 1 9691. 
2. H. hsenberg. j. 2. S ~ l l  ivan and J. K. Howard 
i n  Thin F i lms- Interc l i f fus ion and Reactions 
edi ted by J. M. Poate, K. N. Tu and 
J. W. Mayer (John Wiley and Sons, NY. 1978). 
3. J. F .  E. Bagl in and J. M. Poate, i b i d .  
4. J. A. Cunningham, Sol i d  State Electron. 8 
735 (1965). 
5. R. W. B a l l u f f i  and J. M. Blakely, Thin So l id  
Films. 25, 363-392 (1975). 
6. N. A. ~ s s t e i n .  i n  Dif fusion, Pm. Soc. Metals, 
Metals Park, Ohio, 1973, pg 241. 
7. M. A. Nicolet,  D i f fus ion  Bar r ie rs  i n  Thin Films, 
Thin Sol id  Films. 52, 415-443, 1978. 
8. J. M. Harris, E. Luguj jo, S. U. Campisano, 
M. A. N ico le t  and R. Shim, J. Va. Sci. 
Technol. 12 (1). 524-527 (1978). 
9. R. S. NowEki and I. Wang, J. Vac. Sci. Technol ., 
15 (2). 235-237, (1978). 
10. R. S. Nowicki, J. M. Harr is,  M. A. N ico le t  and 
I .  V. M i t che l l ,  Thin So l id  Films, 53, 195-205 
(1 978). 
-- 
Fiaure 1 : 
Figure '?-i':P'l. I:: \ : ? 1 : 1 3 .  14 A I R I  \ I 1 1 A I  )I)?:'  ;.',I*[ 
JA.'.'I,. +'H I1 I!',. I \  ! \ , \ I  : . ( l ~ . l . t ~ l A l  :,,tlr':L'.I 
I A S C V I P O ( U ~ E 0  
m i ,  
Figure 3: 
AES SPUTTER PROFILE OF THE Cr/Mo/Au SYSTEM AFTER 
Cr S i FORMAT I ON 
F i g u r e  4: AES SPUTTER PROFILE OF THE Cr/Ho/Au 
SYSTEM AFTER A 168 HOUR ANNEAL AT 300°C FOLLOWING 
THE CrS i2  FORMATION 
F i g u r e  5: AES SPUTTER PROFILE OF THE Cr/Fb/Au 
SYSTEM AFTER A 1000  HOUR AiINEAL AT 300°C FOLLOWING 
TtiE C r S i 2  FORMATION 
F i g u r e  6: AES SPUTTER PROFILE OF THE Cr,'MolAu 
SYSTEM AFTER A 2000 HOUR ANNEAL AT 300°C FOLLOWING 
M E  CrS i2  FORMATION 
F i g u r e  8: A X  SPUTTER PROFILE OF THE Cr/Mo/Au 
SYSTEM AFTER VACUUM SINTTRIN? AT 4 5 0 ' f  FOR 
2 HOURS 
F i g u r e  9: PHOTOMICROGRAFH OF FINE LINE PATTERNING 
OF THE Cr/Mo/Au SYSTEM. THE FINE LINE., 
ARE 2 MICRONS I N  WIDTH. 
F i g u r e  7:  AES SPUTTER PXOFILE OF THE Cr/Mo/Au SYSTEM AFTEQ VACUUM SINTERIKG AT 3 4 0 ° C  FOR 264 HOURS 


Stuffed MO layer as a diffusion barrier in metallizations for high temperature electronics

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