Preparation of Pure and Doped Silicon Carbide by Pyrolysis of Silane Compounds

8/14/2019 Preparation of Pure and Doped Silicon Carbide by Pyrolysis of Silane Compounds

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2 9 4 J. Electroehem. Soc.: SOLI D- STATE SC I ENC E AND TEC HNOLOGY February 1978One point commonly overlooked is the question ofhow to define current density. The phosphor crystal-l i tes are exposed to an instantane ous current densitygiven by (assuming a "pill-box" current dis tr ibution)

4j _ - - [ 1 4 ]d ~A common erro r is to call

j ' = - [15]A(where A is the raster area) the curren t density, whilein actuality i t is the t ime-averaged current density.This is not the value to which the phosphor responds.The inst anta neou s value j, or the integ ral ~ = f j dr,are the only meani ngful quantit ies if one wishes tostudy phosphor physics.

ConclusionThus we have seen that in a raster excitation ex-periment, multi excitati on can cause a considerable ef-fect. Any experime nt which permits multiexcita tion tooccur will yield misleading results, as the current den-sity of the excitation pulse will be unknown and the

number of excitation pulses per frame will vary asthe beam current, and hence beam diameter , varies.

It s~hould be pointed out that a rast er- sca nnin g ex-per iment wherein only raster b r igh tness measurementsare made cannot be properly used even for crudeevaluation experiments, for the degree of nonlinea ritydiffers for various phosphors, preventing any compari-son, even if the same excitation means (electron gun,deflection yoke, etc.) are used. Hence raster br ightne ssmeasurements are a poor way to characterize cathodo-lumines cent phosphors: a much more mean ingfu l tech-nique is a spot brightness measurement as a functionof beam excitation density on a single l ine scan raster ,or on a stationary pulsed beam (meeting the criter iadiscussed above) as a functi on of cur ren t density.

A c k n o w l e d g m e n tThe author acknowledges helpful discussions withH. N. Hersh and L. Ozawa, the assistance of G. Ban,and the encourageme nt of G. E. Weibel in the workpresented here.Manuscript submitted July 15, 1977; revised manu-script received Oct. 5, 1977.Any discussion of this pape r wi ll appear in a Discus-sion Section to be published in the December 1978JOURNAL. All discuss ions for the Dec emb er 1978 Disc us-sion Section shoul d be s ubmi tted by Aug. 1, 1978.Publication costs of this article were assisted byZenith Radio Corporation.

Prep arat ion of P ure and D oped Si licon Carb ideby Py rolysis of S ilan e Comp ounds

W . v o n M u e n c h * a n d E . P e t t e n p a u lInstitut A fur WerkstofJkunde, Technische Universit~t, D-3000 Hannover, Germany

ABSTRACTPolycrystall ine #-SIC is prepared from three different silane compounds(methyl-tr ichloros ilane, dimethyl-dichlorosilane, and tr imethyl -chlorosil ane)by the van Arkel process. The influence of the growt h pa ramet ers (flowrates, vapor pressures, and deposition temperat ure) on the growth rate andthe stoichiometry of the deposit is investigated. The most satisfactory resultsin terms of stoichi ometry are obtai ned in the 1400~176 tem pera tur e range.Doping is accomplishect by adding tr i met hyl -al umi num and diborane. The6H silicon carbide crystals are grown by the sublimati on technique usingdoped and undoped polycrystall ine material .

The 6H polytype of silicon carbide is considered apotentially useful material for special semiconductordevices, e.g., for l ight-e mittin g diodes, high t empera-ture rectifiers, and av alanc he diodes. The 6 H siliconcarbide crystals for electronic applications are pro-duced by sublimation of polycrystall ine sil icon car-bide or elementary sil icon and carbon at temperaturesaro und 2500~ (Lel y proces s). In most cases, so far,commercial (green or black) grinding powder hasbeen used as a feed materi al (1-3) ; the sy nthesis fromthe elements is generally less efficient in terms ofcrystal size and perfection. With th e gr indi ng powder,however, a large amo unt of various impurities is intro-duced into the growth system. The resulting (n- orp-type): crystal s, therefore, contain compensating (ac-ceptor or donor) impurities and also deep traps: Thesecrystals cannot be directly used for junction forma-tion in most applications. They may serve as a sub-strate material for VPE or LPE processes; some im-purity transfer (autodoping) from the substrate to

* Electrochemical Society Active Member.Key words: silicon carbide, van Arkel process, methyltrichloro-$ilane, dimethyl-dlchlorosilane, trimethyl-chlorosilane.

the epitaxial layer then must be taken into account(4).The realization of blue light-emitting diodes with arather high efficiency has prompted the prese nt inve sti-gation on the preparation of polycrystall ine sil iconcarbide as a starting material in the Lely process (5).Previous studies on vapor-phase reactions involvingsilicon carbide were performed with emphasis onsingle crystal growth of different polytypes (6-13).Knippenberg, Kapteyns, and Hagen were the f irst tointroduce presynthesized (CVD) sil icon carbide in theLely process (14, 15); this material was obtained witha met hyl-dichlorosil ane source at a low deposition rate(3g/hr) . The main purpose of this study is the optimi-zation of the growth rate, the yield, and the stoichiom-etry of the vapor-grown material . This has been ac-complished by proper reactor design, choice of reac-tants, and deposition conditions. In addition, some ob-servations on the surface morphology are included.

A major problem in the Lely process is the repro-ducibili ty of the incorporation of acceptors (mainl yalu min um and boron). Previously, these dopants havebeen added in solid form to the (undoped) feed mate-


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Vol. 125, No. 2 P R E P A R A T I O N O F S iC B Y P Y R O L Y S I S 295r i a l i n t h e L e l y p r o c e s s . I t i s d i f fi c u l t, h o w e v e r , t o o b -t a i n u n i f o r m l y d o p e d c r y s t a ls in t h i s m a n n e r , b e c a u s eo f l a r g e d i f f e r e n c e s i n t h e v a p o r p r e s s u r e s o f t h ed o p a n t s a n d t h e d i s s o c i a t i o n p r o d u c t s o f s il i c o n c a r -b i d e. T h is p r o b l e m c a n b e o v e r c o m e b y i n t r o d u c t i o no f d o p a n t s d u r i n g t h e p y r o l y s i s o f t h e s i l a n e c o m -p o u n d s . D o p i n g w i t h d i b o r a n e a n d t r i m e t h y l - a l u -m i n u m h a s b e e n i n v e s t i g a t e d i n t hi s s tu d y .

ExperimentalT h e p r i n c i p l e o f t h e v a n A r k e l p r o c e s s i s s h o w n i nF i g . l a . D e t a i l s o f t h e r e a c t i o n c h a m b e r c a n b e s e e ni n F ig . lb . T h e ( w a t e r - c o o l e d ) b a s e p l a t e is m a d e f r o ms i l v e r - p l a t e d co p p e r , t h e c u r r e n t l e a d s a n d t h e g a si n l e t ( n o z z l es ) a r e o f p u r e s i lv e r . It is i m p o r t a n t t h a tt h e g a s s t r e a m s e j e c t e d f r o m t h e n o z z l es a r e h i t t i n gb o t h c a r b o n , h e a t e r r o d s u n i f o r m l y a n d w i t h h i g hv e l o ci ty . T h is c a n b e a c c o m p l i sh e d b y a p p r o p r i a t es h a p i n g a n d a d j u s t m e n t o f t h e n o zz le s . T h e c a r b o nr o d s ( 6 m m d i a m , 1 50 -3 0.0 m m l e n g t h ) a r e h e a t e d w i t ha .c . u n d e r c o n s t a n t v o l t a g e c o n d i t i o n s . E x a c t m e a s u r e -m e n t s o f t h e t e m p e r a t u r e ( b y p y r o m e t r y ) a r e p o s s ib l eo n l y i n t h e i n i t i a l s t a g e o f t h e g r o w t h e x p e r i m e n t ,s i n c e r e a c t i o n b y - p r o d u c t s a r e d e p o s i t e d a t th e i n s i d eo f t h e q u a r t z b e l l j a r . I t is e s t i m a t e d t h a t t h e s u r f a c et e m p e r a t u r e o f t h e s i li c o n c a r b i d e d e c r e a s e s b y a b o u t

1 00 ~ d u r i n g t h e 6 h r g r o w t h p e r i o d . T h e r e a c t i o nc h a m b e r i s c a r e f u l l y e v a c u a t e d a n d f lu s h e d w i t h p u r eh y d r o g e n ( 50 m i n , a t l e a s t ) b e f o r e e a c h r u n . T h ed e p o s i t io n t a k e s p l a c e i n h y d r o g e n a t a t m o s p h e r i cp r e s s u r e .T h e c a r r i e r g a s ca n b e s a t u r a t e d w i t h s i l a n e c o m -p o u n d s k e p t a t ( t h e r m o s t a t i c a l ly c o n tr o l l ed ) t e m p e r a -t u r e s i n t h e 1 3 ~1 7 6 r a n g e . T h e fo l l o w i n g c o m p o u n d sh a v e b e e n u s e d : m e t h y l - t r i c h l o r o s i l a n e , C H sS iC 1 3

REACTIONCHAMBER

EX -SILANE (CH3)3AI / HAUS TC O M P O U N D 6 1 0 H 2 2 (PU MP)B 2 H 6 / A r H 2

F i g . la . A p p a r a t u s f o r t h e g ro w t h o f d o p e d a n d u n d o p e d s i li co nc a r b i d e b y t h e v a n A r k e l p r o ce s s .

Q U A R T Z ~

G A S I N L E T s - -

i

m C A R B ON/ H E A T E R

NOZZLE~

G A S O U T L E TF ig . l b . D e s i g n o f r e a c t io n c h a m b e r

1 03 /[i"/Torr

T C H 3 S i H C I 2 ( H MuJ 1 0 2 '( 0 H s )s S i C I ( M 3 / ~ / ~ /=

n-uJ , / / ~ ( ~ H 3 S iC I 3 ( M 1 )r r C H3)2Si lC I 2 (M 2)0 101a .

, o o / / /2 0 0 2 4 0 2 8 0 3 2 0 K 3 6 0

T E M P E R A T U R E "F i g . 2 . V a p o r p r e s s u re o f s i l a n e c o m p o u n d s . F r o m L a n d o l t - B i i r n -s t e i n ( 1 6 ) .

( M 1 ) ; d i m e t h y l - d i c h l o r o s i l a n e , ( CH 3 )2 S IC 1 2 ( M 2 ) ;a n d t r i m e t h y l - c h l o r o s i l a n e , ( C H ~ )3 S iC 1 ( M 3 ) . T h ev a p o r p r e s s u r e s o f th e s e c o m p o u n d s a r e s h o w n i n F ig .2 . T h e u s e o f m e t h y l - d i c h l o r o s i l a n e ( H _ M ) a p p e a r s t ob e im p r a c t i c a l , d u e t o t h e h i g h v a p o r p r e s s u r e a t r o o mt e m p e r a t u r e .D o p i n g o f p o l y c r y s t a l l in e m a t e r i a l w i t h b o r o n i sa c c o m p l i sh e d b y a d d i n g a m e t e r e d f lo w o f d i b o r a n e( d i l u t e d i n a r g o n ) d u r i n g t h e d e p o s i t i o n c y cl e . As e p a r a t e b u b b l e r c o n t a i n i n g a 1 0 -2 0 % s o l u t i o n o ft r i m e t h y l - a l u m i n u m i n n - d e ca n e (C10H22) serves a st h e s o u rc e fo r a l u m i n u m d o p i n g ; t h e v a p o r p r e s s u r e o fn - d e c a n e is n e g l ig i b l e i n t h e t e m p e r a t u r e r a n g e i n -v o l v e d .T h e c a r b o n r o d s a n d e x c e s s c a r b o n ( i f a n y ) a r e r e -m o v e d b y h e a t - t r e a t m e n t i n o x y g e n . A n y e x c e s s o fs i li c o n i s r e m o v e d b y e v a p o r a t i o n i n v a c u u m . T h u s ,b o t h a n e x c e s s o f c a r b o n a n d a n e x c e s s o f si l i co n c a nb e d e t e r m i n e d q u a n t i t a t iv e l y b y s i m p l e g r a v i m e t r i cm e a n s .T h e s i l ic o n c a r b i d e r o d s ( d o p e d a n d u n d o p e d ) a r eb r o k e n i n t o l u m p s o f s u i t a b l e s iz e a n d c l e a n e d i n h y -d r o f l u o r i c a c id . T h e s e l u m p s s e r v e a s a fe e d m a t e r i a lf o r th e m o d i f i e d L e l y p r o c e s s d e s c r i b e d p r e v i o u s l y ( 5,1 4 ). T h e 6 H s i l ic o n c a r b i d e c r y s t a l s a r e o b t a i n e d i n t h ef o r m o f p l a t e l e t s w i t h f l at s u r f a c e p e r p e n d i c u l a r t o t h ec - a x i s. H a l l a n d r e s i s t i v i t y m e a s u r e m e n t s a r e p e r -f o r m e d b y t h e v an d e r P a u w m e t h o d .

Grow th of P olycrystalline SiCT h e g r o w t h o f p o l y c r y s t a l l in e s i li c on c a r b i d e f r o ms i l a n e c o m p o u n d s c a n b e d e s c r i b e d i n t e r m s o f t h ef o l l o w i n g r e a c t i o n s ( 1 7 ). A t l o w t e m p e r a t u r e s ( ~1 2 0 0 ~

C H ~ SiC 18 4 - 2H 2 - ~ S i + C H 4 + 3 H C 1(CH3)2SiC12 4- 2H2-> Si q- 2CH4+ 2HCI(CI-I3)3SiCI - 2H2- > Si 4- 3C H4 + HC I

CH4-> C + 2H2S i + C ~ S i C

A t h i g h t e m p e r a t u r e s ( ~ 1 80 0~2C H~S iCI3 + H 2 ~ 2S t + C2H2 -~ - 6HC 1

(CHs)2SiCl2 -F H2"-> Si + C2H 2 + 2H CI 4- 2H2


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2 9 6 J . E lec t rochem. Sac . : S O L I D - S T A T E S C I E N C E A N D T E C H N O L O G Y February 19782( C H ~ ) 3 S i C I - p H 2 - ~ 2S t + 3C 2H 2 - F 2H C I - F 61-12

C~H~-* 2C + H2S i + C - ~ S i C

I n th e i n t e r m e d i a t e t e m p e r a t u r e r a n g e b o t h m e t h a n ea n d a c e t y l e n e c a n b e f o r m e d .T h e a m o u n t o f e x c e s s s i l ic o n o r c a r b o n r e s u l t i n gf r o m t h e a b o v e r e a c t i o n s i s d e p e n d e n t o n t h e s i l a n e

c o m p o s i t i o n a n d t h e g r o w t h t e m p e r a t u r e . A s s h o w ni n F i g . 3, a n e s s e n t i a l l y s t o i c h i o m e t r i c g r o w t h o f s i li c o nc a r b i d e i s p o s s i b l e w i t h a l l t h r e e s i l a n e c o m p o u n d si n t h e 1 45 0~ 17 6 t e m p e r a t u r e r a n g e . M e t h y l - t r i -c h l o r o s i l a n e ( M 1 ) y i e l d s a r e l a t i v e l y l a r g e e x c e s so f s i li c o n a t t e m p e r a t u r e s b e l o w 1 4 0 0~ T h e r e s u l t so b t a i n e d w i t h d i m e t h y l - d i c h l o r o s i l a n e (1 Vi2 ) a n d t r i -m e t h y l - c h l o r o s i l a n e ( M 3 ) a r e q u i t e s i m i l a r i n t h e1 4 00 ~ 17 6 t e m p e r a t u r e r a n g e .T h e t e m p e r a t u r e d e p e n d e n c e o f th e o v e r - a l l g r o w t hr a t e i s s h o w n i n F i g . 4 . W i t h t h e p r o c e s s p a r a m e t e r sf i x ed a s f o l lo w s : b u b b l e r t e m p e r a t u r e , 1 2 ~ b u b b l e rf l o w r a t e , 6 0 l i t e r s / h r ; a n d t o t a l f lo w r a t e , 3 00 l i t e r s / h r ;o n e o b t a i n s t h e h i g h e s t d e p o s i t i o n r a t e w i t h s i l a n e M 3( 15 g / h r a t 16 0 0~ d u e to t h e h i g h v a p o r p r e s s u r eo f t h i s c o m p o u n d ( s e e F ig . 2 ). T h e d e p o s i t i o n r a t e s

a c h i e v e d w i t h t h e s i l an e c o m p o u n d s M 1 a n d M 2 a r eq u i t e s i m i l a r ( 6 g / h r . a p p r o x i m a t e l y ) . T h e s e f ig u r e sa r e v a l i d f o r a s i m u l t a n e o u s d e p o s i t i o n o n t w o c a r -b o n r o d s o f 15 0 m m l e n g t h e a c h . T h e y i e l d c a n b ei n c r e a s e d b y 5 0 % , a p p r o x i m a t e l y , b y u s i n g c a r b o nr o d s o f 3 00 m m l e n g t h .A h i g h e r g r o w t h r a t e c a n a ls o b e a c h i e v e d b y i n -c r e a s i n g t h e b u b b l e r f l o w r a te , a t t h e e x p e n s e o f th eb y p a s s . fl o w . A n e x a m p l e i s s h o w n i n F ig . 4 ( t o p c u r v e )f o r s i li c o n c a r b i d e g r o w t h u s i n g s i l a n e M 2 ( b u b b l e rf lo w r a t e 1 00 l it e r s / h r , n o b y p a s s ) .F i g u r e 5 d e m o n s t r a te s t h e i n f l u e n ce o f t h e g r o w t ht e m p e r a t u r e o n t h e m o r p h o l o g y o f si li c o n c a rb i d e( w i t h e x c e s s s i li c o n o r c a r b o n ) p r o d u c e d f r o m d i -m e t h y l - d i c h l o r o s i l an e . H i g h d e n s i t y m a t e r i a l w i t h

s m a l l g r a i n s i ze a n d u n i f o r m l y d i s t r i b u t e d e x c e sss i li c o n i s o b t a i n e d a t l o w t e m p e r a t u r e s . T h e g r a i ns iz e i n c r e a s e s w i t h i n c r e a s i n g g r o w t h t e m p e r a t u r e .T h e e x c e s s c a r b o n w h i c h is f o r m e d a t t e m p e r a t u r e sa b o v e 16 00 ~ i s c o n c e n t r a t e d m a i n l y b e t w e e n p a r -wt?/o

I 2 oz0rn0 0U.l0XW 2 0790_ . . JcO 40I

w t . %6 0

M 1- - ~ - - M 2- - - o - - M 3

/ ///

/

~/

/ /

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1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 ~ 1 8 0 0G R O W T H T E M P E R A T U R E

Fig. 3. De vi a t i on f r om stoich l emet r y (excess car bon or silicon)Ys. grow th temp erature. A rrows are point ing f rom the in it ia l growtht em per a t u r e t o t h e (es t i m a t ed ) t em per a t u r e a t t h e en d o f t h egrowth process.

2 , Ig / h M 2 /

2 0 w / o b y p a s s /

1 6 ~ . ~" / /-


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Vol. 125, No. 2 PR EPA R ATI ON OF S iC B Y PYR OLYSI S 29 7

Fig. 5 . Morphology of si l icon carbide grown by the van Arke l process a t d i f fe rent tem peratures (s i !ane M2) . (a ) 1200~ (b) 1400~(c ) 1600~ (d) 1800~ ( in i t ia ! temperatures).

2, 1 1 ,2 _ _g / h

2 0

I 6 - -LLII'--,


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298 J. E[ectrochem. Sac. : S O LID -S TA TE S CIEN CE A N D TECH N O LO G Y F e b r u a r y 1978

1 2g / h - -

1 0

w 8I -


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Vol. 125, No. 2 P R E P A R A T I O N O F S iC B Y P Y R O L Y S I S 2 9 9i n c o r p o r a t i o n i s t h e o n l y r e a s o n f o r t h e o c c u r r e n c e o ft h i s p e a k ; c r y s t a l d e f e c t s m a y a l s o c o n t r i b u t e t o t h e6 40 n m e m i s s io n . T h e l a t t e r p r o c e s s i s s u g g e s t e d b yt h e r e s u l ts o b t a i n e d w i t h c r y s t a l s o f e x t r e m e l y h i g hp u r i t y .

ConclusionP u r e a n d d o p e d p o l y c r y s t a l l i n e s i li c o n c a r b i d e c a nb e p r o d u c e d b y t h e v a n A r k e l p r o c e s s u s i n g s i l a n ec o m p o u n d s . A re a s o n a b l e g r o w t h r a t e ( in th e o r d e r

o f 4 0 g / h r ) c a n b e a c h i e v e d b y p r o p e r c h o i c e o f t h eg r o w t h c o n d i t i o n s ; a s t o i c h i o m e t r i c d e p o s i t i s o b -t a i n e d i n t h e 1 4 0 0~ 1 7 6 t e m p e r a t u r e r a n g e . T h ep o l y c r y s t a l l i n e S i C m a t e r i a l c a n s e r v e a s f e e d m a t e -r i a l f o r t h e L e l y p r o c e s s , i.e., f o r th e g r o w t h o f 6 Hs i li c o n c a r b i d e c r y s t a l s . A s u b s t a n t i a l i m p r o v e m e n t o ft h e e l e c t r i c a l p r o p e r t i e s (i.e., h i g h e r c a r r i e r m o b i l i t y )h a s b e e n a c h i e v e d . T h e p r o c e s s i s p a r t i c u l a r l y u s e f u lf o r d o p i n g w i t h a l u m i n u m ; h o l e c o n c e n t r a t i o n s i n t h e1 01 6-1 0 i s c m - 3 r a n g e a r e o b t a i n e d r e p r o d u c i b l y i nt h i s m a n n e r .M a n u s c r i p t s u b m i t t e d J u n e 1 7, 1 97 7; r e v i s e d m a n u -s c r i p t r e c e i v e d S e p t . 7 , 1 97 7.A n y d i s c u s s i o n o f t h i s p a p e r w i l l a p p e a r i n a D i s c u s -

s i o n S e c ti o n to b e p u b l i s h e d i n t h e D e c e m b e r 1 97 8J O U R na L . A l l d i s c u s s i o n s f o r t h e D e c e m b e r 1 97 8 D i s c u s -s i o n S e c t i o n s h o u l d b e s u b m i t t e d b y A u g . 1, 19 78 .Pub l i ca t ion cos t s o ] t h i s a r t i c l e w e r e a s s i s t ed b y t h eI n s t i tu t A ] ~ r W e r k s t o f ] k u n d e d e r T e c hn i s c h e U n i v e r -s it~Lt Ha nn ove r.

R E F E R E N C E S1 . J . A . L e l y , B e t . D eu t s ch . K e r a m . G e s . , 32, 229( 1 9 5 5 ) .2 . W . F . K n i p p e n b e r g , Ph i l i p s Res . Rep . , 18, 205( 1 9 6 3 ) .3 . R . M . P o t t e r a n d J . H . S a t t e l e , J . C r y s t . G r o w t h , 12 ,245 ( 1972 ) .4 . W . v o n M u e n c h , W . K u e r z i n g e r , a n d I . P f a f f e n e d e r ,S o l i d - S t a t e E l e c t r on . , 19 , 871 ( 197 6 ) .5 . W . v o n M u e n c h , J . E lec t ron . Ma ter . , 6 , 449 ( 1 977 ) .6 . J . T . K e n d a l l , J . C h em . P h y s . , 21 , 821 ( 1 953 ) .7 . R . F . A d a m s k y a n d K . M . M e r z , Z . Kr i s ta l log r . , 111,350 ( 1959 ) .8 . V . E . S t r a u g h a n a n d E . F . M a y e r , i n " S i l i c o n C a r -b i d e , J. R . O ' C o n n o r a n d J . S m i l t e n s , E d i t o r s, p .9 4, P e r g a m o n P r e s s , N e w Y o r k ( 1 9 6 0) .9 . S . S u s m a n , R . A . S p r i g g s , a n d H . S . W e b e r , i n ibid.,p. 94.1 0. H : W . H u g g i n s a n d C . H . P i t t , A m . C e r a m . S o c .Bul l . , 46 , 266 ( 19 67 ) .1 1. I. B e r m a n a n d C . E . R y a n , J . C r y s t . G r ow t h , 9, 314( 1 9 7 1 ) .1 2. A . W . C. v a n K e m e n a d e a n d C . F . S t e m f o o r t , ibid.,12 , 13 ( 1972 ) .1 3. F . K o b a y a s h i , K . I k a w a , a n d K . I w a m o t o , ib id . , 28 ,395 ( 1975 ) .1 4. C . 3 . K a p t e y n s a n d W . F . K n i p p e n b e r g , ibid., 7, 20( 1 9 7 0 ) .1 5. S . H . H a g e n a n d C . J . K a p t e y n s , Ph i l i p s Res . Rep . ,25 , 1 ( 1970 ) .16 . " L a n d o l t - B o e r n s t e i n , Z a h l e n w e r t e u n d F u n k -t i o n e n , " V o l . I L 2 a , p . 44 S p r i n g e r - V e r l a g , B e r l i n( 1 9 6 0 ) .17 . P . R a i - C h o u d h u r y a n d N . P . F o r m i g o n i , T h i sJou r n a l , 116, 1440 (1969) .

O p t ic a l R e f le c t a n c e M e t h o d f o r D e t e r m i n i n g t h e S u r f a c eQ u a l i t y o f S a p p h i r e ( A I O )

P . J . Z a n z u c c h i , * M . T . D u f f y , * a n d R . C . A l i gR C A L a b or a t o r i e s , P r i n c e t on , N ew J e r s e y 0 8 54 0

A B S T R A C TP o l i s h e d s a p p h i r e w a f e r s a r e u s e d as s u b s t r a t e s f o r t h e g r o w t h o f c r y s -t a l l i n e s i li c o n . T h e q u a l i t y o f t h e s u b s t r a t e s u r f a c e i s a n i m p o r t a n t f a c t o r i nd e t e r m i n i n g t h e c r y s t a l l i n e q u a l i t y o f t h e s i l i c o n f i lm a n d , i n t u r n , r e l a t e s t os i li c o n d e v i c e p e r f o r m a n c e a n d r e l i ab i l i ty . T o i m p r o v e s i l i c o n - o n - s a p p h i r ed e v i c e m a n u f a c t u r e , a s e n s i t iv e a n d n o n a e s t r u c t i v e G p t ic a l r e f l ec t a n c e t e c h -n i q u e h a s b e e n d e v e l o p e d t o d e t e r m i n e t h e q u a l i t y o f p o l i s h e d s a p p h i r e s u r -f a ce s . T h e c o r r e l a t i o n b e t w e e n s u r f a c e d a m a g e a n d s i n g l e o r m u l t i p l e s p e c u l a rr e f l e ct a n c e o f s a p p h i r e i n t h e l a t t i c e m o d e r e g i o n , 9 0 0- 30 0 c m - 1 , i s r e p o r t e d .A s a r e s u l t o f su r f a c e d a m a g e , t h e A 1 2 03 v i b r a t i o n a l m o d e s o f s a p p h i r e a r ed i s t o r t e d a n d t h e o p t i c a l c o n s t a n t s a s s o c i a te d w i t h t h e s e m o d e s c h a n g e . T oi n t e r p r e t t h e s i n g l e a n d m u l t i p l e r e f l e c t a n c e s p e c t r a t h e o p t i c a l c o n s t a n t s o f

u n d a m a g e d a n d d a m a g e d (1 1 02 ) s a p p h i r e s u r fa c e s h a v e b e e n c a l c u l a t e d f r o mr e f l e ct a n c e d a t a u s i ng t h e K r a m e r s - K r o n i g m e t h o d . F r o m t h is a n a l y s is , th er e f l e c ta n c e o f s a p p h i r e a t a b o u t 6 00 c m - 1 i s f o u n d t o b e v e r y s e n s i t i v e t os u r f a c e q u a l i t y . I n t h i s s p e c t r a l r e g i o n m u l t i p l e r e f le c t a n c e c a n b e u s e d t om e a s u r e t h e s u r f a c e q u a l i t y o f s a p p h i r e w i t h a h i g h d e g r e e o f s e n s i ti v i ty . . T h et e c h n i q u e c a n , in p r i n c i p l e , b e u s e d t o m e a s u r e t h e q u a l i t y o f a n y s e m i c o n -d u c t o r o r d i e l e c t r i c s u r fa c e i n s p e c t r a l r e g i o n s o f h i g h r e f l e ct a n c e , s u c h a sr e g i o n s o f l a t t i c e b a n d o r b a n d g a p a b s o r p t i o n .

T h e c r y s t a l l i n e p e r f e c t i o n o f t h in , e p i t a x i a l l a y e r s i ss t r o n g l y i n f l u e n c e d b y t h e c r y s t a l l i n e p e r f e c t i o n o f t h es u b s t r a t e s u r f a ce . F r o m s t u d i e s o f t h e g r o w t h o f s i l ic o nf i lm s ( 1, 2) o n s i li c o n s u b s t r a t e s i t i s w e l l k n o w n t h a td e f e c t s o n t h e s u b s t r a t e s u r f a c e l e a d t o c r y s t a l g r o w t hd e f e c t s i n th e e p i t a x i a l l a y e r . B y t h e u s e o f L a n g t o p o -g r a p h i c te c h n iq u e s , M c F a r l a n e a n d W a n g ( 3 ) h a v es h o w n t h a t t h e c r y s t a l l i n e p e r f e c t i o n o f I I I - V s e m i c o n -

* E l e c t r o c h e m i c a l S o c i e t y Act ive M ember.Key words : qua l i ty cont rol , (1~02) sapphi r e , mu l t ip l e r e f l e c -t a n c e , K r a m e r s - K r o n i g m e t h o d .

d u c t o r f i lm s o n s a p p h i r e o r s p i n e l s u b s t r a t e s i s s i g n i fi -c a n t l y a l t e r e d b y d e f e c t s o n t h e s u b s t r a t e s u r f a ce .T h e s e d e f e c t s, w h i c h o f t e n a r e n o t v i s i b l e , a r e u s u a l l ys c r a t c h e s i n t r o d u c e d i n t h e p o l i s h i n g o f t h e s u b s t r a t e .D e f e c t s c a n c a u s e ~ he e p i t a x i a l f il m to b e m i s o r i e n t e d i nl o c a l i z e d r e g i o n s . A s a c o n s e q u e n c e , t h i s i n t r o d u c e s l a t -t i c e i m p e r f e c t i o n s i n t h e e p i t a x i a l f il m a n d t h e s e i m p e r -f e ct io n s a r e p a r t i c u l a r l y e v i d e n t w h e n t h e e p i t a x i a lf i lm i s r e l a t i v e l y t h in , i.e., a m i c r o m e t e r o r l e ss int h i c k n e s s . W i t h t h e i n c r e a s e d u s e o f s e m i c o n d u c t o r sa n d d i e le c t r i c s p r e p a r e d a s t h i n e p i t a x i a l f il m s b y

Preparation of Pure and Doped Silicon Carbide by Pyrolysis of Silane Compounds

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