TEM AND RBS STUDIES OF THE REGROWTH OF ARSENIC IMPLANTED POLYSILICON DUE TO AN OXIDATION DRIVE-IN

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TEM AND RBS STUDIES OF THE REGROWTH OF ARSENIC IMPLANTED POLYSILICON DUE TO AN

OXIDATION DRIVE-IN

M. Wilson, P. Ashburn, B. Soerwirdjo, G. Booker, P. Ward

To cite this version:

M. Wilson, P. Ashburn, B. Soerwirdjo, G. Booker, P. Ward. TEM AND RBS STUDIES OF THE REGROWTH OF ARSENIC IMPLANTED POLYSILICON DUE TO AN OXIDATION DRIVE- IN. Journal de Physique Colloques, 1982, 43 (C1), pp.C1-253-C1-258. �10.1051/jphyscol:1982135�.

�jpa-00221792�

JOURNAL DE PHYSIQUE

CoZbque C l , suppZ6ment au nO1O, Tome 43, octobre 1982 page C1-253

TEM AND RBS STUDIES OF THE REGROWTH OF ARSENIC IMPLANTED POLYSILICON DUE T O AN OXIDATION DRIVE-IN

M.C. ~ i l s o n * , P. ~shburn*: B. ~oerwirdjo*: G.R. ~ o o k e r * and P. ward""*

*Department of MetaZZurgy & Science of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, England

**Department of Electronics, The University, Southampton SO9 SNH, England

***PZessey Research (CasweZZ) LM, !The AZZen Clark Research Centre, CasweZZ, Toweester, Northants N N I Z 8EQ, England

R6sume Des couches d e s i l i c i u m p o l y c r i s t a l l i n d e 140nm d'6paisseur o n t 6 t 6 d6posBes s u r d e s lames d e s i l i c i u m d ' o r i e n t a t i o n

( l o o ) ,

implantses avec d e s i o n s a r s e n i c (40keV, 5 x 10" ~ m - ~ ) e t r e c u i t e s sous atmosphere seche d10xyg8ne 2L 1000°C. Des etudes par microscopic Blectronique en transmission e t par r 6 t r o d i f f u s i o n de p a r t i c l e s a o n t montrs q u ' i n i t i a l e m e n t l e s g r a i n s c r o i s s e n t , p u i s q u ' e n s u i t e i l s r e c r i s t a l l i s e n t en donnant un materiau monocrystallin. Le temps pendant l e q u e l l a r e c r y s t a l l i s a t i o n s ' e f f e c t u e depend du t r a i t e m e n t applique

a

l a lame d e s i l i c i u m h s d i a t e m e n t avant l a d s p o s i t i o n du s i l i c i u m p o l y c r i s t a l l i n . Les s t r u c t u r e s obtenues e t l e s d i s t r i b u t i o n s en a r s e n i c sont d e c r i t e s e t d i s c u t e e s .

Abstract P o l y s i l i c o n l a y e r s 140nm t h i c k were deposited onto (100) s i l i c o n s l i c e s , implanted with 5 x

lo1'

~ r n - ~ , 4OkeV a r s e n i c ions, and given a d r y oxygen drive-in a t 100O0C. TEM and RBS s t u d i e s showed t h a t t h e p l y c r y s t a l l i n e g r a i n s i n i t i a l l y coarsened and subsequently regrew t o g i v e s i n g l e - c r y s t a l material.

The time taken f o r t h e regrowth t o occur depended on t h e treatment given t o t h e s i l i c o n s l i c e inanediately p r i o r t o t h e p o l y s i l i c o n deposition. The r e s u l t i n g structuresand a r s e n i c d i s t r i b u t i o n s a r e described and discussed.

1. General The d e p o s i t i o n of a p l y s i l i c o n l a y e r onto a s i n g l e - c r y s t a l s i l i c o n s l i c e , followed by ion implantation of a dopant and an oxidation drive-in, i s of i n t e r e s t with regard t o both MOS and b i p o l a r i n t e g r a t e d c i r c u i t f a b r i c a t i o n . I n t h e p r e s e n t work, n-type (100) s i l i c o n s l i c e s were given a blanket boron d e p o s i t i o n treatment s i m i l a r t o t h a t used in t h e f a b r i c a t i o n of standard b i p o l a r t r a n s i s t o r s . The r e s u l t i n g s l i c e s were subjected t o e i t h e r a 1 0 s e t c h i n a CF4 plasma o r a

loss

dip-etch i n buffered HF, and t h i s was immediately followed by t h e d e p o s i t i o n a t 620°C of an undoped p o l y s i l i c o n l a y e r s 0.14pm t h i c k using a low-pressure chemical vapour d e p o s i t i o n method. The aim of t h e s e etching treatments was t o remove any t h i n sur- f a c e oxide f i l m s t h a t may have been p r e s e n t on t h e s l i c e s . The p l y s i l i c o n l a y e r s were implanted a t room temperature w i t h 5 x

lo1'

40keV a r s e n i c i o n s (LSS range 0.027 f 0.012pm). The a r s e n i c was then driven-in a t 1000°C i n d r y oxygen f o r e i t h e r 5, 20 o r 40 m i n , producing a s u r f a c e oxide l a y e r and reducing t h e t h i c k n e s s of t h e i n i t i a l p o l y s i l i c o n layer. For example, a f t e r t h e 40 m i n drive-in, t h e s u r f a c e oxide l a y e r was % 0.07pm t h i c k and t h e i n i t i a l p o l y s i l i c o n l a y e r was % O.1Opm t h i c k . TEM examinations were made with a P h i l i p s EM300 operated a t lOOkeV using e i t h e r plan-view o r cross-section specimens. Rutherford b a c k s c a t t e r i n g s t u d i e s were performed with a 1.5MeV helium ion-beam i n i t i a l l y a l i g n e d along one of t h e c r y s t a l d i r e c t i o n s i n t h e s i n g l e - c r y s t a l s i l i c o n s l i c e (channelled spectrum), and then with t h e beam misaligned

(random spectrum).

2. TEM Results For t h e p o l y s i l i c o n l a y e r s as-deposited onto t h e s i l i c o n s l i c e , TEM plan-view specimens showed t h a t t h e g r a i n s were of mean l a t e r a l s i z e 0.05pm (Fig.la).

TEM cross-section specimens revealed t h a t t h e g r a i n s we*colurnnar and extended com- p l e t e l y through t h e 0.14pm t h i c k l a y e r , and t h a t i n d i v i d u a l l a y e r s were reasonably uniform in t h i c k n e s s (Fig.lb). Selected-area transmission e l e c t r o n d i f f r a c t i o n p a t t e r n s i n d i c a t e d t h a t t h e g r a i n s w e r e randomly o r i e n t a t e d c r y s t a l l o g r a p h i c a l l y . For t h e p o l y s i l i c o n l a y e r s t h a t had been implanted, cross-section specimens showed t h a t t h e l a y e r s had been converted t o amorphous m a t e r i a l t o a uniform depth of

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982135

C1-254 JOURNAL DE PHYSIQUE

0.07um ( F i g . 1 ~ ) . I n each of F i g s . l b and c , t h e lower arrow i n d i c a t e s t h e s i l i c o n s l i c e / p l y s i l i c o n l a y e r i n t e r f a c e , and t h e upper arrow i n d i c a t e s t h e p o l y s i l i c o n l a y e r s u r f a c e .

For t h e specimens t h a t had been plasma-etched p r i o r t o t h e p l y s i l i c o n l a y e r d e p s i - t i o n , and t h e n g i v e n a n o x i d a t i o n d r i v e - i n , t h e r e s u l t s were a s follows. For a specimen given a 20 rnin d r i v e - i n , and a l s o a specimen given a 40 min d r i v e - i n , a l l a r e a s of t h e i n i t i a l p l y s i l i c o n l a y e r were p o l y c r y s t a l l i n e (Figs.2a and b ) . The mean l a t e r a l g r a i n s i z e was 0.15um, and t h e g r a i n s extended completely through t h e l a y e r . The g r a i n s were randomly o r i e n t a t e d c r y s t a l l o g r a p h i c a l l y and were h e a v i l y twinned. I n Fig.2b (and a l s o Figs.3b, 3c, 4b and 4 c ) , t h e lower arrow i n d i c a t e s t h e s i l i c o n s l i c e / i n i t i a l p l y s i l i c o n l a y e r i n t e r f a c e (termed i n t e r f a c e 1 1 , and t h e upper arrow i n d i c a t e s t h e i n i t i a l p o l y s i l i c o n l a y e r / s u r f a c e o x i d e l a y e r i n t e r f a c e (termed i n t e r f a c e 2 ) .

For a second specimen given a 40 rnin d r i v e - i n , i n some a r e a s t h e i n i t i a l p l y s i l i c o n l a y e r was completely p l y c r y s t a l l i n e a s in Fig.2, w h i l e i n o t h e r a r e a s t h e l a y e r w a s p a r t l y p o l y c r y s t a l l i n e (P) and p a r t l y s i n g l e c r y s t a l (S) (Figs.3a and b), w i t h t h e s i n g l e c r y s t a l r e g i o n s being t y p i c a l l y l u m a c r o s s . The a r e a s of t h i s l a y e r t h a t were p a r t l y p o l y c r y s t a l l i n e and p a r t l y s i n g l e - c r y s t a l showed pronounced l o c a l v a r i a t i o n s i n t h i c k n e s s ( F i g . 3 ~ ) . A band of f i n e damage 5 t o 30nm t h i c k and c o n s i s t i n g of small d i s l o c a t i o n l o o p s and c l u s t e r s was p r e s e n t a t i n t e r f a c e 1 ( F i g . 3 ~ ) . T h i s damage o c c u r r e d b o t h where t h e i n i t i a l p l y s i l i c o n l a y e r was s t i l l p l y c r y s t a l l i n e and where it had regrown a s s i n g l e c r y s t a l .

For t h e specimens t h a t had been dip-etched p r i o r t o t h e p l y s i l i c o n l a y e r d e p o s i t i o n , t h e r e s u l t s were a s follows. For specimens g i v e n e i t h e r a 20 o r 40 rnin d r i v e - i n , a l l a r e a s of t h e i n i t i a l p o l y s i l i c o n l a y e r s were s i n g l e c r y s t a l ( F i g s - l a and b). The l a y e r s contained d e f e c t s ( D ) , e.g, d i s l o c a t i o n s , s t a c k i n g f a u l t s and micro-twin l a m e l l a e , of d e n s i t y + 2 x 10' cm ( a s r e f e r r e d t o plan-view specimens) and t h e s e t h r e a d e d completely through t h e l a y e r . A band of f i n e damage was p r e s e n t a t i n t e r - f a c e 1 ( F i g . 4 ~ ) . The specimen given a 5 min d r i v e - i n was n o t a v a i l a b l e f o r TEM examination.

For t h e l a y e r of Fig.4 t h a t was completely s i n g l e c r y s t a l , p a r t i c u l a r d i f f r a c t i o n c o n d i t i o n s were used s o a s t o r e v e a l t h e d e f e c t s p r e s e n t , and t h e c o n t r a s t f o r t h e i n d i v i d u a l s t a c k i n g f a u l t s and micro-twin l a m e l l a e w a s e s p e c i a l l y pronounced. For t h e l a y e r of Fig.3 t h a t was p a r t l y p o l y c r y s t a l l i n e and p a r t l y s i n g l e c r y s t a l , d e f e c t s

(D) o c c u r r e d i n t h e s i n g l e c r y s t a l r e g i o n s s i m i l a r t o t h o s e shown i n Fig.4. However, f o r Fig.3 d i f f e r e n t d i f f r a c t i o n c o n d i t i o n s were used s o t h a t t h e s e d e f e c t s were n o t r e v e a l e d , t h i s being done s o t h a t t h e d i s t i n c t i o n between t h e p o l y c r y s t a l l i n e and s i n g l e - c r y s t a l r e g i o n s could b e more r e a d i l y made. D i f f e r e n t d i f f r a c t i o n c o n d i t i o n s were mainly a l s o r e s p o n s i b l e f o r t h e d i f f e r e n t appearances of t h e s u r f a c e o x i d e l a y e r

( t h a t a r o s e from t h e o x i d a t i o n d r i v e - i n ) i n t h e v a r i o u s c r o s s - s e c t i o n specimens.

Thus, t h i s l a y e r i s n o t r e a d i l y seen i n Fig.2b, appears g r e y i n Figs.3b, 4b and 4c, and appears b r i g h t i n F i g . 3 ~ .

3. RBS R e s u l t s For t h e RBS s p e c t r a o b t a i n e d and shown i n Fig.5, t h e main c u r v e s corresponded t o b a c k s c a t t e r i n g by s i l i c o n atoms, b u t a d d i t i o n a l peaks a r o s e from b a c k s c a t t e r i n g by oxygen and a r s e n i c atoms. For t h e plasma-etched specimens, t h e r e s u l t s were a s follows. For t h e specimen g i v e n a 20 min d r i v e - i n (Fig.5a), t h e channelled y i e l d was l e s s t h a n t h e random y i e l d f o r e n e r g i e s l e s s t h a n 0.75MeV, b u t was t h e same f o r e n e r g i e s between 0.78 and 0.83MeV. The former e n e r g i e s corresponded t o t h e s i l i c o n s l i c e , and t h e lower y i e l d was expected because o f t h e c h a n n e l l i n g o c c u r r i n g i n t h e s i n g l e - c r y s t a l s i l i c o n s l i c e . The l a t t e r e n e r g i e s corresponded t o t h e i n i t i a l p l y s i l i c o n l a y e r , and t h e same y i e l d i n d i c a t e d t h a t t h e l a y e r was s t i l l completely p l y c r y s t a l l i n e . The a d d i t i o n a l peaks were explained a s follows. The narrow peak a t 0.56MeV corresponded t o t h e oxygen p r e s e n t i n t h e s u r f a c e o x i d e l a y e r a r i s i n g from t h e o x i d a t i o n d r i v e - i n . The s l i g h t shoulder a t 0.85MeV corresponded t o t h e s i l i c o n p r e s e n t i n t h e s u r f a c e o x i d e l a y e r . The s e p a r a t e broad peak a t 1.08 t o 1.20MeV corresponded t o t h e a r s e n i c p r e s e n t i n t h e s u r f a c e o x i d e l a y e r , t h e i n i t i a l p l y s i l i c o n l a y e r and t h e s i l i c o n s l i c e .

For t h e plasma-etched specimen given a 4Omin d r i v e - i n t h a t was shown by TEM t o p o s s e s s a p a r t l y p o l y c r y s t a l l i n e and p a r t l y s i n g l e - c r y s t a l l a y e r , t h e c h a n n e l l e d y i e l d between 0.78 and 0.83MeV, which corresponded t o t h e i n i t i a l p o l y s i l i c o n l a y e r ,

showed a pronounced p l a t e a u a t a h e i g h t intermediate t o t h a t expected f o r completely p l y c r y s t a l l i n e m a t e r i a l and completely s i n g l e - c r y s t a l m a t e r i a l (Fig.5b). This r e s u l t i n d i c a t e d t h a t t h e l a y e r had p a r t l y regrown. For t h i s specimen, t h e s i l i c o n i n t h e s u r f a c e oxide l a y e r gave a shoulder i n t h e random y i e l d a t 0.85MeV a s before, but now produced a d e f i n i t e peak i n t h e channelled y i e l d a t t h i s p o s i t i o n . The

second plasma-etched specimen given a 40 min drive-in t h a t was shown by TEM t o possess a completely p o l y c r y s t a l l i n e l a y e r was n o t a v a i l a b l e f o r RBS s t u d i e s . For t h e dip-etched specimens, t h e r e s u l t s were a s follows. For t h e specimen given a

5 rnin drive-in, t h e s p e c t r a were s i m i l a r t o t h o s e of Fig.5a i n d i c a t i n g t h a t t h e i n i t i a l p o l y s i l i c o n l a y e r was s t i l l completely p l y c r y s t a l l i n e . For t h e specimens given e i t h e r a 20 o r 40 min d r i v e - i n , t h e s p e c t r a were a s i n F i g . 5 ~ . The channelled y i e l d between 0.78 and 0,85MeV, which corresponded t o t h e i n i t i a l p l y s i l i c o n l a y e r , was now continuous with t h e y i e l d from t h e lower energies, which corresponded t o t h e s i n g l e - c r y s t a l s l i c e . This i n d i c a t e d t h a t t h e l a y e r had completely regrown.

From t h e broad peaks of t h e channelled s p e c t r a a t 1.08 t o 1.20MeV, t o t a l a r s e n i c con- c e n t r a t i o n v depth curves were deduced and t h r e e of t h e s e a r e shown i n Fig.6. These p r o f i l e s were a l l of t h e same general shape with peaks occurring a t both i n t e r f a c e 1 and i n t e r f a c e 2. The shapes depended on t h e oxidation drive-in times, but n o t s i g n i f i c a n t l y on whether t h e i n i t i a l s i l i c o n s l i c e s had been given a plasma-etch o r a dip-etch. The p r o f i l e s showed t h a t a progressive movement of i n t e r f a c e 2 towards i n t e r f a c e 1 occurred a s t h e oxidation drive-in time increased from 5 t o 20 t o 40 min, corresponding t o t h e progressive growth of t h e s u r f a c e oxide l a y e r . From t h e por- t i o n s of t h e p r o f i l e s which corresponded t o t h e s i l i c o n s l i c e , approximate v a l u e s f o r t h e depth of t h e p-n junction below i n t e r f a c e 1 were deduced. The p r o f i l e s showed t h a t f o r a 5 min drive-in, t h e a r s e n i c concentration a t i n t e r f a c e 1 was % 6.0 x 1020 cm-3 and t h e junction depth was s 0.07pm. For a 20 rnin drive-in, t h e analogous values were s 3.8 x

l o z 0

and % 0. llpm, and f o r a 40 rnin drive-in, t h e y were

% 3.0 x

lo2'

and % 0.18pm. A c a l c u l a t e d LSS t o t a l a r s e n i c concentration p r o f i l g corresponding t o t h e d i s t r i b u t i o n of t h e a r s e n i c i n t h e i n i t i a l p o l y s i l i c o n l a y e r inanediately p r i o r t o t h e oxidation drive-in, i s a l s o included i n Fig.6.

4. Discussion The TEM and RBS r e s u l t s taken t o g e t h e r i n d i c a t e t h a t t h e i n i t i a l p o l y s i l i c o n l a y e r s , implanted with a r s e n i c ions, regrow during t h e subsequent oxida- t i o n drive-in a s follows. The regrowth occurs i n two stages. F i r s t , t h e r e i s a r a p i d coarsening of t h e p l y c r y s t a l l i n e grains. I n p a r t i c u l a r , t h e g r a i n s change from columnar of l a t e r a l width 0.05pm t o e q u i a x i a l of l a t e r a l width 0.15pm, t h e l a t t e r dimension corresponding approximately t o t h e p o l y s i l i c o n l a y e r thickness.

This behaviour r e p r e s e n t s t h e growth of some g r a i n s a t t h e expense of o t h e r s , and i s n o t d i r e c t l y r e l a t e d t o t h e f a c t t h a t t h e p l y s i l i c o n l a y e r was deposited onto a s i n g l e - c r y s t a l s i l i c o n s l i c e . (The same g r a i n coarsening behaviour was observed i n analogous experiments simultaneously performed but n o t reported above using s i m i l a r p l y s i l i c o n l a y e r s t h a t had been deposited onto t h i c k s u r f a c e oxide layers.)

Second, a f t e r t h e e l a p s e of a c e r t a i n t h r e s h o l d time, new g r a i n s s t a r t t o form a t a number of c e n t r e s a t t h e i n i t i a l p l y s i l i c o n l a y e r / s i l i c o n s l i c e i n t e r f a c e with t h e same c r y s t a l l o g r a p h i c o r i e n t a t i o n a s t h e s i l i c o n s l i c e . These new g r a i n s grow up- wards and sideways t o form small s i n g l e - c r y s t a l r e g i o n s extending completely through t h e l a y e r , and t h e s e r e g i o n s eventually j o i n up t o produce a complete s i n g l e c r y s t a l l a y e r of t h e same c r y s t a l l o g r a p h i c o r i e n t a t i o n a s t h e s i l i c o n s l i c e . For t h e plasma- etched specimen given a 40 rnin drive-in which contained both s i n g l e - c r y s t a l and p l y c r y s t a l l i n e regions (Fig.3a), t h e mean spacing between t h e s i n g l e - c r y s t a l regions was 3pm i n d i c a t i n g t h a t i n t h i s c a s e t h e number of c e n t r e s nucleating t h e new g r a i n s a t t h e i n t e r f a c e was s

l o 7

The c r y s t a l l o g r a p h i c d e f e c t s p r e s e n t i n t h e f i n a l s i n g l e - c r y s t a l l a y e r probably a r o s e both a s t h e new s i n g l e - c r y s t a l g r a i n s grew sideways along t h e i n i t i a l p l y s i l i c o n l a y e r / s i l i c o n s l i c e i n t e r f a c e , possibly because of i n t e r a c t i o n s with t h e d i s l o c a t i o n loops and c l u s t e r s present i n t h e narrow band of damage l o c a t e d a t t h i s i n t e r f a c e , and a s t h e i n d i v i d u a l new s i n g l e - c r y s t a l regions joined with oreanother, possibly due t o small c r y s t a l l o g r a p h i c m i s - matches between them.

The TEM and RBS r e s u l t s show t h a t t h e t h r e s h o l d time f o r t h e plasma-etched specimens i s s l i g h t l y g r e a t e r than 40 min, but f o r t h e dip-etched specimens i s between 5 and 20 min. This d i f f e r e n c e i n threshold time was c o n s i s t e n t l y obtained when f u r t h e r specimens were s i m i l a r l y prepared and examined. The reason f o r t h i s d i f f e r e n c e i s

C1-256 JOURNAL DE PHYSIQUE

considered t o b e a s follows. A f t e r t h e s i l i c o n s l i c e s a r e plasma- o r dip-etched, a t h i n o x i d e f i l m remains o r i s formed on t h e s u r f a c e o f t h e s l i c e . When a p l y s i l i c o n l a y e r i s d e p o s i t e d on t h e s l i c e , t h i s o x i d e f i l m i s t r a p p e d a t t h e p o l y s i l i c o n l a y e r / s i l i c o n s l i c e i n t e r f a c e . During t h e s u b s e q u e n t o x i d a t i o n d r i v e - i n , t h e o x i d e f i l m p r o g r e s s i v e l y d i s p e r s e s due t o l o c a l i s e d d i f f u s i o n , and e v e n t u a l l y s m a l l ' h o l e s ' begin t o form i n t h e f i l m . It i s a t t h e s e ' h o l e s ' t h a t t h e new g r a i n s i n t h e poly- s i l i c o n l a y e r n u c l e a t e w i t h t h e same c r y s t a l l o g r a p h i c o r i e n t a t i o n a s t h e u n d e r l y i n g s i l i c o n s l i c e . The t h r e s h o l d time f o r n u c l e a t i o n w i l l depend on t h e i n i t i a l t h i c k - n e s s of t h e o x i d e film. The f i l m t h i c k n e s s i s considered t o be g r e a t e r f o r t h e plasma-etched specimens, and s o t h e t h r e s h o l d t i m e i s g r e a t e r f o r t h e s e specimens.

The narrow band o f damage l o c a t e d a t t h e p o l y s i l i c o n l a y e r / s i l i c o n s l i c e i n t e r f a c e which i s p r e s e n t f o l l o w i n g t h e o x i d a t i o n d r i v e - i n f o r b o t h t h e plasma- and dip-etched specimens i s thought t o a r i s e from t h i s t h i n o x i d e film. A s e p a r a t e examination /1/

has now been made of t h e s e specimens p r i o r t o t h e o x i d a t i o n d r i v e - i n u s i n g t h e Auger a n a l y s i s method. The r e s u l t s confirmed t h a t f o r a l l of t h e specimens an o x i d e f i l m was p r e s e n t a t t h e p o l y s i l i c o n l a y e r / s i l i c o n s l i c e i n t e r f a c e , and showed t h a t t h e f i l m s ranged i n t h i c k n e s s up t o l.Onm and were t h i c k e r f o r t h e plasma-etched specimens.

The t o t a l a r s e n i c c o n c e n t r a t i o n p r o f i l e s o b t a i n e d from t h e RBS s t u d i e s show t h a t a f t e r a n o x i d a t i o n d r i v e - i n o f o n l y 5 min, t h e r e i s a d r a m a t i c r e d i s t r i b u t i o n of t h e a r s e n i c . Before o x i d a t i o n t h e r e is an a r s e n i c peak o f

*

1.7 x

lo2'

cm-3 j u s t below t h e p o l y s i l i c o n s u r f a c e . A f t e r o x i d a t i o n for 5 min t h e r e a r e a r s e n i c peaks of 4.0 x

l o z 0

cme3 a t t h e s u r f a c e o x i d e l a y e r / i n i t i a l p o l y s i l i c o n i n t e r f a c e ( i n t e r f a c e 2 ) , and s 6.2 x

l o z 0

a t t h e i n i t i a l p o l y s i l i c o n l a y e r / s i l i c o n s l i c e i n t e r f a c e ( i n t e r f a c e 1 ) . This a r i s e s because of t h e r a p i d d i f f u s i o n of t h e a r s e n i c a l o n g t h e boundaries of t h e i n i t i a l p o l y s i l i c o n g r a i n s t o t h e two i n t e r f a c e s . A s t h e o x i d a t i o n d r i v e - i n c o n t i n u e s t o 20 and t h e n 40 min, t h e a r s e n i c peaks a t t h e two i n t e r f a c e s p r o g r e s s i v a y d e c r e a s e , and a r s e n i c d i f f u s e s i n t o t h e underlying s i l i c o n s l i c e t o g i v e a progres- s i v e l y deeper p-n j u n c t i o n . O u r f i n d i n g t h a t t h i s d i f f u s i o n behaviour does n o t depend s i g n i f i c a n t l y o n whether t h e specimen w a s given a plasma- o r d i p - e t c h is thought t o be mainly due t o t h e i n i t i a l r a p i d d i f f u s i o n of t h e a r s e n i c t o i n t e r f a c e l , b e f o r e t h e p o l y s i l i c o n l a y e r regrows, g i v i n g a l a r g e a r s e n i c peak a t t h i s i n t e r f a c e . The subsequent l a y e r regrowth behaviour t h e n h a s l i t t l e e f f e c t on t h e d i f f u s i o n o f t h e a r s e n i c i n t o t h e underlying s i l i c o n s l i c e . I n a d d i t i o n it i s p o s s i b l e t h a t some of t h e a r s e n i c p r e s e n t i n t e r a c t s w i t h t h e narrow band of damage l o c a t e d a t i n t e r f a c e 1. T h i s may cause slower d i f f u s i o n i n t o t h e underlying s i l i c o n s l i c e t h a n would o t h e r w i s e occur because it h a s t o 'break away' from t h e damage.

The TEM r e s u l t s a l s o show t h a t no d e t e c t a b l e c r y s t a l l o g r a p h i c d e f e c t s had formed i n t h e u n d e r l y i n g s i l i c o n s l i c e s a f t e r t h e specimens had been given o x i d a t i o n d r i v e - i n s . This was t h e expected r e s u l t and i s one o f t h e r e a s o n s f o r implanting t h e a r s e n i c i n t o a p o l y s i l i c o n l a y e r r a t h e r t h a n d i r e c t l y i n t o t h e s i l i c o n s l i c e , when a p p r e c i - a b l e c r y s t a l l o g r a p h i c d e f e c t s a r i s e following an o x i d a t i o n d r i v e - i n . Our measure- ments of 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 of b i p o l a r t r a n s i s t o r s have shown t h a t much b e t t e r performances o c c u r when t h e t r a n s i s t o r s a r e made u s i n g p o l y s i l i c o n t h a n when made by t h e conventional method (Soerowirdjo e t a l , t o be p u b l i s h e d ) . However, when f a b r i c a t i n g b i p o l a r t r a n s i s t o r s w i t h p o l y s i l i c o n it i s n e c e s s a r y t h a t t h e presence of s u r f a c e o x i d e f i l m s on t h e i n i t i a l s i l i c o n s l i c e s and t h e regrowth behaviour of t h e p o l y s i l i c o n l a y e r s be under s t r i c t c o n t r o l o r v a r i a b l e d e v i c e c h a r a c t e r i s t i c s w i l l occur, and t h e r e s u l t s o f t h e p r e s e n t work have helped t o r e v e a l some of t h e f a c t o r s t h a t a r e important f o r t h i s t o be achieved.

Acknowledgements The a u t h o r s wish t o thank Mrs J E D u f f i l l f o r u s e f u l d i s c u s s i o n s , t h e s t a f f of t h e M i c r o e l e c t r o n i c s F a b r i c a t i o n F a c i l i t y a t t h e U n i v e r s i t y of

Southampton f o r a s s i s t a n c e w i t h t h e s l i c e f a b r i c a t i o n , and SERC f o r s u p p o r t i n g t h e p r o j e c t .

References

/1/ D u f f i l l , J.E., ' I n v e s t i g a t i o n o f i n t e r f a c i a l o x i d e t h i c k n e s s e s between s i l i c o n and p l y s i l i c o n ' , a c c e p t e d f o r ESSDERC, Munich, September 1982.

Micrographic TEM

Figs.la,lb. Silicium polycristallin non implants, m e du plan et vue de cotk.

Fig.1~. Silicium polycristall+ implant6, vue de cotk.

TEM Micrographs

Figs.la,lb. Unimplanted polysilicon, plan view and cross-section.

Fig.1~. Implanted polysilicon, cross-section.

Echelle de

grandissement = 200nm

d

Magnification bar = 200nm

Figs.2at2b. Traitement au plasma, recuit de 40 min (echantillon no. l), vue du plan et vue de cote.

Figs.2a,2bS Plasma-etched, 40 min drive-in (specimen I), plan view and cross-section.

Figs.3aI3b. Traitement au plasma, recuit de 40 rnin (echantillon no. 21, m e du plan et vue de cots.

Fig.3~. ~ & n e chose que Fig.3bt fort grandissement, vue de cot6.

Figs.3a,3b. Plasma-etched, 40 min drive-in (specimen 2), plan view and cross-section.

Fig.3~. As 3b, high magnification cross-section.

C1-258 JOURNAL DE PHYSIQUE

FigsS4a,4b. Traitement chimique, r e c u i t d e 40 min, vue du p l a n e t m e d e cotd.

F i g . 4 ~ . ~ 8 m e chose que Fig.4b, f o r t grandissement, m e d e cotd.

Figss4a,4b. Dip-etched, 40 min d r i v e - i n , p l a n view and c r o s s - s e c t i o n . F i g . 4 ~ . A s 4b, h i g h m a g n i f i c a t i o n c r o s s - s e c t i o n .

S p e c t r e s RBS

- m

\., ^?, 5a-

.

R

5

, ' : ;

3

'.

- 8 ^--.

Fig. 5a. Traitement a u plasma, r e c u i t d e 20 min.

Fig. 5b. Traitement au plasma, r e c u i t d e 40 min ( e c h a n t i l l o n no.2).

Fig. 5c. Traitement chimique, r e c u i t d e 40 min.

RBS S p e c t r a

Fig.5a. Plasma-etched, 20 min d r i v e - i n . Fig. 5b. Plasma-etched, 40 min d r i v e - i n . Fig. 5c. Dip-etched, 40 min d r i v e - i n .

',

-., _..,:

^{; fi I} _\

5 b

, '.

R

-.. ..

P r o f i l s d ' A r s e n i c Fig.6a. Implantg, LSS.

Fig. 6b. Traitement chimique r e c u i t d e 5 min.

F i g . 6 ~ . Traitement au plasma, r e c u i t d e 20 m i n . Fig.6d. Traitement chimique,

r e c u i t d e 40 min.

-

'... .. _.

^, _{, ,}

::

^t

-4 8

5c

<... R '">,

0.3 0.6 .9 1.2 0.3 0 6 p.9 1.2

Arsenic P r o f i l e s

- C

%

^MeV

0.3 0.6 c.9 1.2

Fig.6a. As-implanted, LSS.

Pig.6b. Dip-etched, 5 min d r i v e - i n . F i q . 6 ~ . Plasma-etched, 20 min

d r i v e - i n .

Fig.6d. Dip-etched, 40 min d r i v e - i n .