THE USE OF LOW PRESSURE IN THE EPITAXIAL GROWTH OF Si, GaAs, GaAlAs, InP, GaInAs, GaInAsP AND InAlAs

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THE USE OF LOW PRESSURE IN THE EPITAXIAL GROWTH OF Si, GaAs, GaAlAs, InP, GaInAs,

GaInAsP AND InAlAs

J. Duchemin

To cite this version:

J. Duchemin. THE USE OF LOW PRESSURE IN THE EPITAXIAL GROWTH OF Si, GaAs,

GaAlAs, InP, GaInAs, GaInAsP AND InAlAs. Journal de Physique Colloques, 1982, 43 (C5), pp.C5-

87-C5-92. �10.1051/jphyscol:1982511�. �jpa-00222230�

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JOURNAL DE PHYSIQUE

CoZZoque C5, suppZ6ment au n012, Tome 43, d&cembre 1982 page C5-87

THE USE O F LOW PRESSURE I N THE EPITAXIAL GROWTH O F Si, GaAs, GaAlAs, InP, GaInAs, GaInAsP AND InAlAs

J.P. Duchemin

Thornson-CSF, Laboratoire Central de Recherches, Domaine de CorbeuiZZe, B.P. N 0 l O , 91401 Orsay cedex, France

d6sum6.

-

^{I 1 a}

e t e

montrd que 1 ' u t i l i s a t i o n de l a pression r & d u i t e dans l a

-

croissance e p i t a x i a l e du s i 1 ic i u m p e r m e t t a i t de r d d u i r e l e phenomene d ' a u t o - dopage q u i accompagne I 1 ' u t i l i s a t i o n des s u b s t r a t s fortement dooes. f l a aussi

@ t e

montre que l ' a d s o r o t i o n de 11hydroq6ne e t a i t r e d u i t e I basse pression, ce q u i a u t o r i s e l a croissance de c o u c h e m o n o c r i s t a l l i n ~ i i t r e s basse temperature.

En se basant s u r ces r e s u l t a t s , une agproche I basse p r e s s i o n a aussi

e t e

u t i l i s e e pour l a croissance des composes b i n a i r e s 1 I I . V . I 1 appa- r a f t a l o r s qu 'il y a peu d ' a d s o r p t i o n de 1 'hydrogCne e t que l a temperature minimum pour une croissance m o n o c r i s t a l l i n e n ' e s t pas a f f e c t e e p a r l a pression.

Cependant, l ' e f f e t des decompositions p a r a s i t e s peut S t r e r e d u i t en t r a v a i l l a n t I basse pression. La p l u s qrande v i t e s s e de passage des gaz q u i r e s u l t e de l ' u t i l i s a t i o n de l a basse pression e t l a r d d u c t i o n de l'auto-dopage o n t c o n d u i t I l ' o b t e n t i o n des i n t e r f a c e s t r & s abruptes.

Abstract.

-

The use o f a low pressure i n t h e e p i t a x i a l growth of s i l i c o n has been shown t o reduce t h e ?henomenon o f autodoping which accompanies t h e use o f h e a v i l y doped substrates. Also i t was found t h a t hydrogen adsorotion was reduced a t low pressure a l l o w i n g t h e growth o f good-quality s i n g l e - c r y s t a l m a t e r i a l t o be c a r r i e d o u t a t a lower temperature than was p o s s i b l e i n an atmospheric nressure system.

Based on these r e s u l t s a low pressure approach was a l s o used f o r growth o f t h e 111-V b i n a r y comoounds. I n t h i s case t h e r e anpeared t o be l i t t l e hydrogen a d s o r p t i o n and t h e minimum temperature f o r monocrystal 1 i ne growth was n o t a f f e c t e d by pressure. However t h e occurence o f o a r a s i t i c d e c o m ~ o s i t i o n i n t h e gas phase was pressure deaendent and has been v i r t u a l l y e l i m i n a t e d by t h e use of low pressure. The h i g h e r gas s ~ e e d s which r e s u l t from t h e use o f a low aressure have allowed us t o achieve v e r y abrunt h e t e r o i n t e r f a c e s , f o r examole a t t h e GaInAs/InP h e t e r o i n t e r f a c e grown by low aressure OM VPE a

l o c a l l i s e d e l e c t r o n gas e x h i b i t i n g two dimensional p r o p e r t i e s has been measured.

1. I n t r o d u c t i o n .

-

Over t h e l a s t pass years, sharper and sharper i m p u r i t y o r o f i l e s o r c o n c e n t r a t i o n g r a d i e n t s have been r e q u i r e d . Abrunt i m p u r i t y o r o f i l e s a r e needed f o r c e r t a i n microwave devices such as m i 11 im e t e r Schottky diodes and I m p a t t diodes.

Abrupt c o m ~ o s i t i o n changes have become necessary f o r s i n g l e quantum w e l l o r super- l a t t i c e l a s e r diodes and f o r two dimensional e l e c t r o n qas f i e l d e f f e c t t r a n s i s t o r s .

, - - -

- - - .

Whatever t h e m a t e r i a l ( S i (1) GaAs(2) GaA1As (3) (4) InP(5) GaInAs(6) GaInAsP(7) t h e LP 110 CVD technique has emerged as a convenient method o f producing sharp i n t e r f a c e s .

The reasons which make an i m p u r i t y o r composition t r a n s i t i o n n o t as sharp as

.Zt

should be a r e many, however t h e f o l l o w i n g ones t o some e x t e n t c o n t r o l most o f t h e i n t e r f a c e s .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982511

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JOURNAL DE PHYSIQUE

. out-diffusion

. a u t o d o ~ i n g

. adsorption

. dead spaces.

The paper discusses these four phenomena and concludes t h a t i n each case, a s i g n i f i c a n t imnrovement can be obtained by ooerating a reactor a t low pres- sure.

2.

O u t diffusion. - The so-called out-diffusion i s the phenomenon where the s o l i d s t a t e diffusion of impurities from the s u b s t r a t e through a c t i v e layers or from one active layer t o another one i s involved. Diffusion p r o f i l e s obey Fick' Law which depends upon the diffusion c o e f f i c i e n t , so t h a t the i m ~ u r i t y diffusion i s minimized i f growth temoerature i s lowered. The e f f e c t s of diffusion a r e more strongly obser- ved f o r s i l i c o n eoitaxy than f o r 111-V Compound epitaxy because diffusion coeffi- c i e n t s a r e higher f o r s i l i c o n imourities than f o r most 111-V Eompound imnurities.

For t h a t reason a larqe e f f o r t has been devoted t o making s i l i c o n epitaxy oossible a t a lower temperature. In a arevious ~ u b l i c a t i o n (1) we showed t h a t hydrogen mole- cules were strongly adsorbed on s i l i c o n s i t e s a s proved by t h e f a c t t h a t growth r a t e was inversely a r o ~ o r t i o n a l to the square root of hydroqen oressure. Therefore the temperature l i m i t below which growth becomes o o l u c r i s t a l l i n e was lowered when oee- rating a s i l i c o n reactor a t reduced nressure. Tyoical data a r e l i s t e d i n t a b l e 1

:

A t 10 Torr the growth remained monocrystalline down t o 800°C. Hydrogen adsorption on group I11 and group

V

elements i s l e s s than on s i l i c o n which r e s u l t s i n no e f f e c t of hydrogen nressure on the growth temnerature behaviour

TABLE

1. -

Hydrogen pressure

(TorrJ 1050'C 100O.C 95D'C 900'C 8m'C 800'C

760 mono mono poly poly poly poly 250 mono mono poly poly

70 mono mono mono poiy

:% : ::f

30 mono mono mono mono mono poly 10 mono mono mom mono mono mono

3. Auto-dooing. - Some of t h e d i f f e r e n t e f f e c t s which make the impurity p r o f i l e l e s s sharp than

i t

should be were analysed quantitatively i n t h e case of s i l i c o n epitaxy but the possible mechanisms a r e t h e same f o r a l l vapour phase epitaxy techniques and a l s o f o r other materials. The d i f f e r e n t phenomena responsible f o r the experimental impurfty profiles appear i n f i g u r e

1.

a ) For high f r e e c a r r i e r concentration from a few times 1018 t o a few times lo1' cm-3 the impurity y o f i l e f i t s well u i t h a curve com~uted assuming t h a t i m ~ u r i t i e s obey Fick'Law.

b) For f r e e c a r r i e r concentration from a few times 1017 t o a few times 1016 an-3 the measured impurity p r o f i l e no longer s a t i s f i e s Fick's laws.

Impurities exaoinq from the f r o n t side of the substrate, which a r e d i s t r i b u t e d within the qas r~hase and reincoroorated inside the qrowinn film a r e resoonsdble f o r t h i s o a r t of the imourity p r o f i l e whose sloae i s s o f t , several thousands

A

f o r a decade. The r e s u l t of t h i s contamination can be decreased by reducing the Dressure and thus enhancing the diffusion constants f o r a l l imnurities contained i n the gas phase, giving them l e s s chance of being reincoroorated.

c ) For f r e e c a r r i e r concentration lower than a few times 1016 cnr3,

there i s another break i n t h e curve of f i g . 1 whose slooe becomes q u i t e f l a t . The

f r e e c a r r i e r concentration r e s u l t s from imourities f r m t h e gas ohase (back ground

doping l e v e l ) plus impurities from the back side of the substrate where the growth

r a t e i s generally lower than f o r the f r o n t s i d e on very heavily dooed substrates

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thG auto-dopinq from t h e back s i d e can be very s i g n i f i c a n t and must be reduced t h i s can be acheived by c o a t i n g i t w i t h a lower c o n c e n t r a t i o n e p i l a y e r p r e v i o u s l y grown o r w i t h a pre-deposited d i e l e c t r i c f i l m o f Si3N4 o r Si02

.

The mechanism (b) i s r e s p o n s i b l e f o r i m p u r i t y p r o f i l e s which a r e n o t as sharp as they should be. The o n l y way t o reduce t h i s e f f e c t i s t o lower t h e pressure i n o r d e r t o increase gas ~ h a s e d i f f u s i o n c o e f f i c i e n t s o f s?ecies which have escaped and t o ' remove these i m p u r i t i e s . By o p e r a t i n g a s i l i c o n o r a g a l l i u m a r s e n i - de r e a c t o r a t 76 T o r r i n s t e a d o f 760 T o r r one can measure p r o f i l e s as sharp as t h e d i f f u s i o n l e n g t h allows.

FIG. 1

4. Adsorption.- As t h e two f i r s t l i m i t a t i o n s a r e due t o t h e growth surface o r t o p r o p e r t i e s of t h e gas l a y e r l o c a t e d c l o s e t o i t , t h e r e are two o t h e r l i m i t a t i o n s which a r e caused by t u b i n q o r q u a r t z surfaces and by t h e gas p a t t e r n s i n s i d e t h e growth c e l l . One o f these l i m i t a t i o n s i s t h e a d s o r p t i o n on Langnuir surfaces. Any i n n e r surface o f a vapour ohase r e a c t o r can adsorb a q u a n t i t y m o f any m a t e r i a l ~ n s i - de t h e gas ohase, given b y

a' P i + b mi =

c P i + d

la"

a,b,c, and c are constants, P i i s t h e p a r t i a l pressure o f an i m p u r i t y (i

.

I f t h e

l i g h t l y contaminated mi = a Pi+b

- ." 1

surface i s h e a v i l y p o l l u t e d P i >7 b o r

$

^{and m i}⁼^{c s t ,} ^{I f}on t h e con r a r y i t i s d

UyJriJ' qrw.

*r'1apr

L e t us sunnose t h a t t h e i n n e r surfaces have reached a steady s t a t e and mi = mio. A t t h a t t i m e t h e doping mole f r a c t i o n o f t h e i m p u r i t y i, which may be, f o r i n s t a n c e a dopant, i s increased t o a value m i l . The e q u i l i b r i u m c o n d i t i o n s w i l l change and some i m p u r i t i e s w i l l be adsorbed on surfaces ; f o r a c e r t a i n t i m e t h e ,concentration o f umnurity i which reaches t h e growth area i s then lower than Pio. I t takes sometime b e f o r e new steady c o n d i t i o n s a r e obtained.

T. d o p d

<ukt&

L e t us now su pose t h e opposite t h a t t h e i m o u r i t y i i s decreased t o a v a l u e m i 2 l o w e r t h a t pio, t i e surfaces release some i m p u r i t i e s and t h e i m p u r i t y concentration which reaches t h e growth area i s then h i q h e r than P i (o); new steady

s t a t e c o n d i t i o n s are obtained o n l y a f t e r some time.

This e f f e c t can be s t r o n g . Examoles i n v o l v i n g i t have a l r e a d y been r e p o r t e d : when growing C r doped Semi-insulating GaAs u s i n g MO CVD and (C0)6Cr, M. BONNET ( 8 ) has r e p o r t e d t h a t t h e steady s t a t e doping i s n o t reached u n t i l a f t e r 20 minutes growth. Mhen growing GaAlAs/GaAs i n a b a f f l e MO CVD r e a c t o r S t r i n - g f e l low (9) has observed a memory e f f e c t due t o A1 (CH3)3 a d s o r p t i o n on t h e b a f f l e g r a p h i t e r e s u l t i n g i n an enlarged t r a n s i t i o n .

JJ7,en

r+. evn $rwk

*pily.r

-Id'

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C5-90 JOURNAL DE PHYSIQUE

By reducing the t o t a l pressure one can reduce the d i f f e r e n t Fartial pressures which a r e proportional t o xi

P

where xi i s the mole f r a c t i o n .

5. Dead spaces. - Gilling reported t h a t what ever the flow r a t e the gas flow pattern i s always laminar when the c a r r i e r gas i s hydrogen

( 1 0 ) .

However entrance e f f e c t s resulting i n turbulent flow (area) can be observed. A t any place where the flow i s turbulent, there are dead spaces which a r e not renewed as f a s t as the laminar part of t h e flow. The dead spaces a c t a s isolated bubbles which s t o r e some gas material f o r some time. In addition t o that,homogeneoas nucleation i s i n i t i a t e d inside those bubbles. After some delay dead spaces a r e swept by t h e general circulation of gas, stored material i s d i s t r i b u t e d and small nucleites resulting from homogenous nu- cleations are released. This r e s u l t s f i r s t i n broader i n t e r f a c e and second i n a depletion of the gas phase due t o t h e f a c t t h a t nucleites , when created, can grow quickly consuming the s t a r t i n g material. I t i s d i f f i c u l t o t make a theoretical analysis of the entrance e f f e c t s which e x i s t a t reduced pressure. Never theless experimental data show t h a t sham interfaces and scaled up reactors can be made a t reduced pressure.

6. Results - The purpose of t h i s paper i s not t o qive an extended l i s t of the r e s u l t s

whichhave been published

;

t a b l e

2

give a sumnary of some of the most s i g n i f i c a n t

ones.

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'semi conductor

S i

GaAs

GaAl As GaAs

I n

GaInAs 0.48 0.52

GaInAsP

S t a r t i n g materi a1 s

z 4 9 H2 AsH3, B2H6 5b C I S Ga(CH3I3

ASH H -3

*

2

SiH4,Zn(C2H5)2

1 ~ ( C 2 H 5 ) 3

%3 H2-N2 H2S Zn(2H5I2 Ga(C2H5)3

As--

' 4 2 " ' ~ H2S Ga(C2H5)3 1n(C2H5)3 -3 ASH -3 PH

N2H2 H2S,Zn(C2H5)

Pressure and temperature

50 Torr 930°C

76 Torr

250 Torr 750°C

76 T o r r 550-650

76 Torr 550°C

76 Torr 650°C

Device Characteristics

Impatt diodes a t 94 GHz 60hW i n CW 17 6.5%.

Schottky diodes F E T G.R.1.N.-SCH Laser diodes Jth= 230 ~ c m - ~ f o r 413 um

c a v i t y 1 ength Jth- 121 Acm-2 f o r 1788 vm c a v i t y length To = 160°C.

800-1000 A/min

1000 A/min

300 A/min.

175 A/min

p300=7800

u~~~ 5200

~ 7 7 258000

350 A/min

350 A/min.

an v - l s - l

p300 11800 65000 V772

'" "

-1

'- I

A two dimentio- nal e l e c t r o n gas conductivi- t y has been observed a t an GaInAs/InP i n t e r f a c e

cm V' S-

cw

Laser a t 1 . 3 m J h

830 mA CU Laser a t 1 . 4 8 ~ 1 J h

266 m~

L i f e time >7000 hours a t 16'C.

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C5-92 JOURNAL DE PHYSIQUE

6. Conclusion.

-

ble have described some c u r r e n t a o p l i c a t i o n s o f LP CVD growth where pressure can be used as a v a r i a b l e Darameter. Growth a t low pressure has t h e advantages o f reducing auto-dooing, thereby improving t h e abruptness o f doping changes, and reducing t h e incidence o f p a r a s i t i c gas phase decomposition.

Devices f a b r i c a t e d from these m a t e r i a l s , e.g. S i impatts, GaAlAs/GaAs aml GaInAsP/InP DH l a s e r s have shown s t a t e - o f - t h e - a r t performance.

7- References.

-

1.J.P. Duchemin, 4 . Bonnet,

F.

Koelsch J. Electrochem. Soc.

125

(1978) 637

2.J.P. Duchemin, Y. Bonnet, F. Koelsch and D. Huyghe J. Electrochem. Soc.

120

(1979) 1134

3.J.P. H i r t z , Bui Dinh-Vuong, J.P. Duchemin, P. H i r t z , B. de Cremoux, R. B i s a r o and P. Merenda.

Appl. Phys. L e t t . 36 (10) 15 May 1980.

4.S.Hersee, !I. Baldy, P.Assenat, B. de Cremoux, J.P. Duchemin E l e c t r o n i c s L e t t e r s Vol. 18 (1982) 618.

5.J.P. Duchemin, !I. Bonnet, 6 . BEUCHET and F. Koelsch I n s t . Phys. Conf. Ser. No45 Chapter 1 (1979).

6 3 . Razeghi, V.A. Poisson, J.P. L a r i v a i n , B. de Cremoux, J.P. Duchemin, M. Voos E l e c t r o n i c s L e t t e r s Vo1.18 (1982) 339.

7.Y. Razeghi, P. H i r t z , R. Blondeau, J.P. t a r i v a i n , L.NoP1, B. de Cremoux, J.P. Duchemin.

E l e c t r o n i c s L e t t e r s Vol. 18 (1982) 132.

8.M.Bonnet, J .?. Duchemin, A.9. Huber and 6 . ? t o r i l l o t .

Proceeding of Semi-insulating 111-\! m a t e r i a l s nottingham 1980 e d l t e d by

6.J

Rees.

9.D.W. K i s l e r and J.N. Y i l l e r , G.B. S t r i n g f e l l o w . Apolied Phys. L e t t .

-

40 (1982) 614.

10.L.J. G i l l i n g Proc of V I I I i n t . Conference on C.V.D. (1981) 199.