SUPERFICIAL-ENHANCED THERMAL NITRIDATION OF SiO2 THIN FILMS

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SUPERFICIAL-ENHANCED THERMAL NITRIDATION OF SiO2 THIN FILMS

A. Glachant, B. Balland, A. Ronda, J. Bureau, C. Plossu

To cite this version:

A. Glachant, B. Balland, A. Ronda, J. Bureau, C. Plossu. SUPERFICIAL-ENHANCED THERMAL

NITRIDATION OF SiO2 THIN FILMS. Journal de Physique Colloques, 1988, 49 (C4), pp.C4-413-

C4-416. �10.1051/jphyscol:1988487�. �jpa-00227985�

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JOURNAL DE PHYSIQUE

Colloque C4, supplement au n 0 9 , Tome 49, septembre 1988

SUPERFICIAL-ENHANCED THERMAL NITRIDATION OF Si02 THIN FILMS

A. GLACHANT, B. BALLAND*

,

A. RONDA( ) , J. C. BUREAU* and C. PLOSSU*

~ ~ ~ ~ ~ - ~ & p a r t e m e n t d e Physique. Facult6 des Sciences de Luminy, Case 901, F-13288 Marseille Cedex 9, France

" ~ a b o r a t o i r e de Physique d e la Matiere (CNRS-UA 358), Bat. 502, INSA d e Lyon, 20, Av. A. Einstein, F-69621 Villeurbanne Cedex, France

Resume

-

La n i t r u r a t i o n s u p e r f i c i e l l e de f i l m s minces (Q 13 nm) de Si02 peut 6 t r e stiniul6e en p r a t i a u a n t des r e c u i t s r e p e t i t i f s e n t r e 900°C e t 1200°C dans une f a i b l e pression (4 10-' mbar) d'amrioniac de purete contr6lge. La zone s u p e r f i c i e l l e n i t r u r e e s ' e t e n d a l o r s s u r 3

a

4 nlri avec une decroissance r a p i d e de l a c o n c e n t r a t i o n d'azote en f o n c t i o n de 1 a profondeur. Les r e s u l t a t s experimentaux suggerent que l e s especes asines NH, ( 0 < x < 3) s o n t e s s e n t i e l l e s dans l e processus de n i t r u r a t i o n de SiOp par NH3. Des s&uctur.?s A1/Si02 n i t r u r 6 e / S i ( l O O ) p o n t 6 t 6 fabriquees i n s i t u ou non.

~n

o p t i m i s a n t

-

l e s c o n d i t i o n s de n i tr u r a t i o n . l e s mesures G l e c t r i a u e s r e v e l e n t une f a i b l e densi t 6 d ' e t a t s d ' i n t e r f a c e (10"

a

10" e v - l cm-2), une bonne tenue

a

1 'i n j e c t i o n d ' e l e c t r o n s c a r a c t e r i s e e par un e a u i l i b r e e n t r e piegeage e t depiegeage dans l a r e g i o n n i t r u r e e e t un champ d e s t r u c t i f p a r f o i s s u p e r i e u r

a

10 MV cn-1.

A b s t r a c t

-

S u p e r f i c i a l n i t r i d a t i o n o f t h i n (% 13 nm) Si02 f i l m s can be enhanced u s i n g annealing c y c l e s o f s h o r t d u r a t i o n a t h i g h temperatures (900°C-1200°C) i n low pure ammonia pressures (d 1 0 - I mbar). The n i t r i d e d surface r e g i o n i s 3 t o 4 nm wide w i t h a r a p i d l y decreasing n i t r o g e n c o n c e n t r a t i o n versus depth. The experimental data suggest t h a t amine NHx (0 < x < 3 ) species a r e e s s e n t i a l i n t h e n i t r i d a t i o n process o f Si02 using NIi3 gas. A l - g a t e / n i t r i d e d Si02/Si (100)p c a p a c i t o r s have been prepared i n s i t u o r not. E l e c t r i c a l measurements show t h a t a low i n t e r f a c e - s t a t e d e n s i t y (10" t o 1011 ev-' cmm2), a good s t a b i l i t y d u r i n g e l e c t r o n i n j e c t i o n due t o a balance between t r a p p i n g and d e t r a p p i n g i n the n i t r i d e d r e g i o n o f Si02 and a d e s t r u c t i v e breakdown f i e l d as h i g h as

10 MV cm-' can be achieved by o p t i m i z i n g n i t r i d a t i o n c o n d i t i o n s .

1

-

INTRODUCTION

S u p e r f i c i a l n i t r i d a t i o n o f t h i n Si02 f i l m s grown on S i would modify t h e i n s u l a t o r s t r u c t u r e i n such a way t o make i t impervious t o contaminant d i f f u s i o n and l e s s s u s c e p t i b l e t o degradation d u r i n g VLSI processes and h i g h - f i e l d stresses, w i t h o u t damaging t h e e l e c t r i c a l c h a r a c t e r i s t i c s o f t h e SiD2/Si i n t e r f a c e . The n i t r i d a t i o n o f Si07 t h i n f i l m s i s g e n e r a l l y accomplished i n h i g h ammonia pressures ( P >/ 1 b a r ) and a t h i g h temperatures (9C0°C < T < 1200°C) /1/ u s i n g excessi- v e l y l o n g furnace times o r plasma-enhanced processes. Rapid thermal n i t r i d a t i o n a t h i g h temperatures /2,3/ has been a l s o proposed t o reduce n i t r o g e n i n t e r f a c i a l concentration, increase surface n i t r i d a t i o n and overcome t h e d i f f i c u l t y o f dopant r e d i s t r i b u t i o n . However, these various processes s u f f e r from t h e i n a b i l i t y t o c o n t r o l t h e s p a t i a l n i t r o g e n d i s t r i b u t i o n i n t h e oxide f i l m and consequently the d e f e c t d e n s i t y i n t h e oxide b u l k and a t t h e Si02/Si

( 1 ) Present address : Llbt, Facul t e s U n i v e r s i t a i r e s N.D. de l a Paix, 6 1 r u e de Bruxelles, 8-5000 Namur, Belgium.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988487

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C4-414 JOURNAL DE PHYSIQUE

i n t e r f a c e . We show here t h a t s u p e r f i c i a l n i t r i d a t i o n o f very t h i n SiO, f i l m s ( t h i c k n e s s o f

~ 1 3 nm) t h e r m a l l y grown on p-Si(100) can be achieved i n low ammonia Lressures (P

r

10-'mbar) by thermal a c t i v a t i o n (950°C 6 T

<

1150°C) u s i n g annealing c y c l e s o f s h o r t d u r a t i o n (sequen- t i a l mode). The purpose o f o u r study i s t o understand t h e changes i n e l e c t r i c a l p r o p e r t i e s c o r r e l a t e d w i t h t h e composition o f t h e i n s u l a t i n g f i l m s d u r i n g t h e n i t r i d a t i o n process. More- over, t h i s study should l e a d t o a b e t t e r understanding o f t h e n i t r i d a t i o n mechanisms o f t h i n thermal Si02 f i l m s and then t o a l i m i t a t i o n o f n i t r o g e n i n c o r p o r a t i o n i n t h e s u r f a c e r e g i o n .

2

-

EXPERIMENTAL METHODS

-

The n i t r o g e n c o n t e n t o f t h e thermal oxides as a f u n c t i o n o f n i t r i d a t i o n parameters (T, P, annealing d u r a t i o n At, t o t a l n i tr i d a t i o n t i m e t ) has been i n v e s t i g a t e d u s i n g several a n a l y t i - c a l techniques. N i t r o g e n depth p r o f i l e s i n t h e n i t r i d e d f i l m were measured by AES i n con- j u n c t i o n w i t h argon i o n - s p u t t e r i n g and SIMS. The elemental composition and chemical bonding were s t u d i e d by AES, XPS. Raman ( R S ) and i n f r a - r e d (IRS) spectroscopies. Some e l e c t r i c a l measurements by use o f I(V), C(V ,a)-G(V,w) and DLTS techniques, time-dependent breakdown and t r a p p i ng-detrappi ng measurements have been performed on A1 gate RIS devices prepared i n s i t u o r n o t w i t h t h e r m a l - n i t r i d e d oxide gate i n s u l a t o r s t o r e l a t e t h e e l e c t r i c a l p r o p e r t i e s t o t h e elemental composition.

3

-

RESULTS AND DISCUSSIOti

Enhancement o f surface r e a c t i o n was observed f o r s u f f i c i e n t l y 1 arge n i tr i d a t i o n times ( 4 h 4 t 6 10 h), T 5 950°C and P 10-3 mbar /4,6/ as shown i n f i g u r e 1. Moreover, t h e r e a c t i o n r a t e d u r i n g t h e f i r s t n i t r i d a t i o n stages increased f o r t h e s h o r t e s t annealing periods ( A t 4 10 mjn). I n these c o n d i t i o n s , a temperature r i s e above % 950aC d i d n o t a f f e c t markedly t h e r e a c t i o n r a t e . The experimental data suggest t h a t amine NHx ( 0 < x < 3) species

are e s s e n t i a l i n t h e n i t r i d a t i o n process (Fig. 2) : these species have t o d i f f u s e through t h e s u r f a c e l a y e r t o r e a c t w i t h Si02. The thermal r e a c t i o n proceeds v i a t h e replacement o f oxygen atoms f o l l o w i n g probably successive r e a c t i o n s p r e d i c t e d i n t h e l i t e r a t u r e : t h e f i n a l products expected a r e e v e n t u a l l y n i t r i d e and/or h i g h e r o r d e r amine groups w i t h t h e l o s s o f oxygen i n t h e form o f water. The n i t r o g e n p i l e - u p a t t h e SiO / S i i n t e r f a c e was h a r d l y d e t e c t a b l e and t h e r e a c t i o n was e s s e n t i a l l y l o c a l i z e d i n the surface 6egion o f Si02. I n our case, surface reac- t i o n enhancement can be a t t r i b u t e d t o various conplelnentary f a c t o r s , i n c l u d i n g a d r y ammonia ambient, a low c o n c e n t r a t i o n g r a d i e n t o f n i t r i d i n g species and a r a p i d decrease o f t h e d i f f u s i o n c o e f f i c i e n t o f WHx groups when i n c r e a s i n g t h e n i t r o g e n concentration.

>

.-

C

V) p-Si( 100)

5

0.5

C K interface

.- t

Z

0,

0 0.5 1.0 1.5 2.0 2.5 normalized depth

(a)

h

.

^*^(I)(I) 3 0 N

z

-

>,

*

.-

_(I)

+. a,

.-

depth (nm)

(b)

Fig.1

-

^{( a )}N Auger depth p r o f i l e s from a n i t r i d e d Si02 f i l m (P = 10-lmbar

-

T = 1024°C

-

t = 10h) u s i n g d i f f e r e n t s p u t t e r i n g r a t e s ( 1 nm.min-1 : and 0.2 nm.min-1 : o) ; ( b ) SIMS p r o f i l e s o f Si-N and N-0 from a Si02 f i l m r e a c t e d a t T = 1045OC (P = 10-3 mbar) d u r i n g t = 4h and t h e corresponding i n t e r f a c i a l - s t a t e d e n s i t y vs. energy. The n i t r o g e n c o n c e n t r a t i o n i s q u i t e n e g l i g i b l e i n t h e i n t e r f a c i a l region.

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Fig.2

-

( a ) N l s and Si2p photoemission l i n e s (T = 1024°C

-

^{P =} ^mbar

-

t = 5h) f o r two v e r t i c a l sampled depths (about 2 nm ( 0 = 20") and 4 nm ( 8 = 45") w i t h r e s p e c t t o t h e N l s l i n e ) ; ( b ) I n f r a - r e d spectrum o f the same r e a c t e d sample. N i t r i d e species a r e mostly l o c a - l i z e d near t h e i n s u l a t o r surface.

The e f f e c t o f n i t r i d a t i o n on t h e f l a t - b a n d v o l t a g e s h i f t AVFB was analysed by comparison o f simulated i d e a l and a c t u a l C-V curves. AVFB was i n t h e range -1 t o 0.8 V depending on n i t r i - d a t i o n c o n d i t i o n s and was r e l a t e d t o t h e n i t r o g e n d i s t r i b u t i o n w i t h i n t h e n i t r o x i d e . The small p o s i t i v e charge d e n s i t y created ( n e g a t i v e AVFB) was generated r a p i d l y d u r i n g t h e i n i t i a l n i t r i d a t i o n process and i s c o r r e l a t e d w i t h t r a p p i n g by Si-OH o r Si-H groups r e s u l t i n g from Si-0 bond breaking and/or S i - d a n g l i n g bonds generated by i n - d i f f u s i o n o f H species (as shown by SIMS, XPS and IRS a n a l y s i s ) . A f t e r a l o n g n i t r i d a t i o n time ( t > 90 min), t h e C-V characte- r i s t i c was s h i f t e d i n p o s i t i v e b i a s d i r e c t i o n due t o e i t h e r a l o n g e r h e a t c y c l e o r an increase o f n i t r o g e n concentration. The amphoteric and deep %Si centers produce a d e n s i t y o f s t a t e s peak near midgap ( e l e c t r o - o p t i c a l measurements : UV p h o t o - i o n i s a t i o n ) ; they w i l l thus show two l e v e l s : a lower +/O(tSio) trapped h o l e l e v e l and a h i g h e r 0 / - ( A i - ) trapped e l e c t r o n l e v e l . The i n t e r f a c e d e n s i t i e s a r e evaluated from C (V,w) and G(V,w) curves o r from DLTS.

Before n i tr i d a t i o n , the midgap s u r f a c e - s t a t e d e n s i t y a t t h e Si02/Si i n t e r f a c e i s 1 0 l 0 ev-1.

cm-2 ; a s u f f i c i e n t l y low i n t e r f a c e - s t a t e d e n s i t y ( 1 t o 10.1010 ev-l.cm-2) can be achieved by o p t i m i z i n g n i t r i d a t i o n c o n d i t i o n s ( F i g . l b ) . As observed from conduction and I - V c h a r a c t e r i s - t i c s , a t h i g h e l e c t r i c f i e l d , t h e Fowler-Nordheim (FN) t u n n e l i n g remains t h e dominant

mechanism i n n i t r i d e d oxide, s i m i l a r t o t h e oxide (Fig.3). E l e c t r o n i n j e c t i o n from metal gate o r from t h e s u b s t r a t e i n t o i n s u l a t i n g l a y e r s was accomplished by FN t u n n e l i n g : t h e n i t r i d e d oxide having t h e h i g h e s t n i t r i d a t i o n r a t e s d i d n o t show c a t a s t r o p h i c d i e l e c t r i c breakdown ( b e f o r e reaching s a t u r a t i o n ) b u t r a t h e r e x h i b i t e d a balance between i n j e c t e d e l e c t r o n t r a p p i n g and tunnel detrapping (Fig.4). The f i n a l d e s t r u c t i v e breakdown f i e l d was measured by a p p l y i n g a negative b i a s voltage t o t h e A1 e l e c t r o c e a t a d e f i n i t e sweep r a t e : i t v a r i e d from

2 M V . C ~ - 1 t o > 10 M V . C ~ - 1 depending on t h e n i t r i d a t i o n parameters.

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C4-416 JOURNAL DE PHYSIQUE

gate voltage (V)

( a )

.'..

oxides

Fig.3

-

( a ) I ( V ) c h a r a c t e r i s t i c s f o r d i f f e r e n t MIS s t r u c t u r e s (o,r : n i t r i d e d oxides, o:oxide).

( b ) J / E ~ vs. 1/E f o r d i f f e r e n t MIS s t r u c t u r e s ( J = c u r r e n t d e n s i t y ; E = e l e c t r i c f i e l d across t h e f i l m ) : t h e FN t u n n e l i n g i s t h e dominant conduction mechanism.

b r e a k d o w n

Fig.4

-

( a ) Flat-band v o l t a g e s h i f t vs. i n j e c t e d e l e c t r o n number (curves A,B,C,D). ( b ) F i a t band v o l t a g e r e l a x a t i o n (curves C,D). ( A ) : n i t r o g e n t o oxygen r a t i o r = 0.5 (1045"C, 10- mbar, 7.5h), (B): r = 0.45 (1045OC, 5.10-qmbar, 4h), (C) and (Dl: r = 2.3 (1045OC, 10-3mbar, 4h).

4, CONCLUSION

Superficial-enhanced thermal n i t r i d a t i o n o f SiO2 t h i n f i l m s has been c a r r i e d o u t by thermal a c t i v a t i o n i n low pure ammonia pressures. Amine NHx.species have t o d i f f u s e through t h e s u r f a - ce l a y e r t o r e a c t w i t h Si02. The e l e c t r i c a l p r o p e r t i e s measured w i t h A1 gate MIS s t r u c t u r e s show t h a t n i t r i d e d oxide f i l m s w i l l be good q u a l i t y gate i n s u l a t o r s f o r f u t u r e scaled-down VLSI devices

.

REFERENCES

/1/ Kato,I.,

.

_133.^{r m} Ito,T., Inoue,S. I., Nakamura,T. and Ishikawa,H., Jpn. J. Appl. Phys.

2

⁽¹⁹⁸²⁾

/2/ Moslehi,M.M. and Saraswat,K.C., IEEE Trans. E l e c t r o n Devices ED2 (1985) 106.

/3/ Moslehi ,M.M., Saraswat,C.K. and Shatas,S.C., Appl. Phys. L e t t . 7 (1985) 1113.

/4/ Ronda,A., Glachant,A., Plossu,C. and Balland,B., Appl. Phys. L e B . 50 (1987) 171.

/5/ Balland,B., Dupuy,J.C., Glachant,A. and Ronda,A., Phys. S t a t . Sol. mO(1987) 187.

/6/ Benamar,A., Bureau, J.C., Balland,B., Ronda,A. and Glachant,A., A p p l X r f . Sci

. 30

(1987) 216.