The growth of glow discharge hydrogenated amorphous silicon

Journal of Non-Crystalline Solids 97&98 (1987) 1383-1386 North-Holland, Amsterdam

THE

GROWTH

P.K.

OF G L O W

BHAT

, H.

DISCHARGE

CHATHAM

1383

HYDROGENATED

, and Y.H.

AMORPHOUS

SHING

and

SILICON

J.W.

PERRY

,

G l a s s t e c h S o l a r , Inc. Wheatridge, Colorado

(GSI), 80033,

1244] W e s t U.S.A.

49th

Jet P r o p u l s i o n L a b o r a t o r y , 4800 Oak G r o v e Pasadena, California 91109, U . S . A .

Avenue,

Drive,

We p r e s e n t new r e s u l t s on the s t u d y of p l a s m a by o p t i c a l e m i s s i o n s p e c t r o s c o p y , m a s s s p e c t r o s c o p y and c o h e r e n t a n t i Stokes Raman spectroscopy in an rf glow d i s c h a r g e s y s t e m u s e d for s o l a r c e l l s h a v i n g d e v i c e c o n v e r s i o n e f f i c i e n c l e s c l o s e to 11%. U n d e r optimum deposition conditions in the silane plasma, neither OES nor CARS show emission lines associated with H and SiH 2 r a d i c a l s . The temperature d e p e n d e n c e of e m i s s i o n s p e c i e s s u g g e s t s a c t i v a t i o n e n e r g i e s a s s o c i a t e d w i t h s o m e of the r e a c t i o n s at the g r o w i n g s i l i c o n s u r f a c e in the r a n g e 0 . 0 2 to 0 . 0 7 eV.

I.

INTRODUCTION Despite

advances

technologies, processes (PECVD) about

involved

of film

probably

little

in

PECVD.

chemistry

have

has

been

emission

spectroscopy

plasma

physical

has

deposition

different

silane

spectroscopy

Si:H

films.

growth under

of

(OES)

laser-induced coherent

experiments order

and

r.f.

PECVD

are

usually

optimum In

a-Si:H

films

using

devlce-quallty Diagnostics

of

a-Si:H

the

silanes

in

plasma

with

for

in-situ

and

the

CARS,

a-Si:H

0022-3093/87/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

a-Si:H

OES

ion

mass

spectroscopy of

H,

SiH2,

plasma

Plasma

some

including

absorption

silane

producing

deposition

for

and

Raman

process

present

plasma

(3),

presence

reactors.

we

film

plasma

and

of

techniques

neutral

anti-Stokes

conditions report,

(I),

deposited

nature

fluorescence

reveal

performed

this

of

information

microstructural,

films

the

by a v a r i e t y

higher

from

the

deposition

the

from

of

of

and

d.c.

inferred

based

formation

vapor

of

Diagnostics

(4)

both

been

film

chemical majority

properties

pursued

These

measurements

the

complex

(CARS)

and

enhanced

past,

(a-Si:H)

thin

the

spectroscopy

S i 2 H 6,

the

to

(2),

SiH3,

silicon

about

significance

(MS)

(5).

amorphous

known

In the

growth and

in is

in

a-Si:H.

electronic

optical

little

diagnostic

parameters

very

device-quality results and

in

MS

on

athe

performed

conditions.

films

with

good

opto-

P.K. Bhat et al, / Glow discharge hydrogenated amorphous silicon

1384

electronic glow

properties

discharge

(GSI).

The

chambers

2.

RESULTS

AND

Figure optimized

observe

The

silane

the

OES

depletion

decreasing

r.f.

power.

flow

and

process in

In-situ

whereas rf

for

increase than

of

and

with

SiH 4

increase

of

atoms

and

shown

linearly 106

flow both

2,

to

and

increasing

emissive SiH*

suggest

do

la).

non-linearly

with

cm -3

related

species emission

that

the

neutral

SiH*

species

films.

the

plasma

shows

production

of

at

powers

low

Figure

between

a-Si:H of

in

for

we

(Figure

increase

would

clearly

spectroscopy

(~657nm)

(-414nm)

correlation

are

SiH 4

H*

used

conditions,

r.f.

quantities

that

SI2H 6

is linear

both

increase

(i

30mW/cm2),

with

increasing

power. Neutral

mostly

with

migrate If

reaction

accesses

conditions

process

by CARS,

more

deposition

mass

the

Inc.

(6).

under

with

parameters

OES

the

of

non-linearly

and

the

intensity

depletion

custom-designed

these

emission

not

for

r.f.

Solar,

instrumental

signals

Under

rate

plasma,

seen

OES

Although the

responsible

state-of-the-art Glasstech

experiments

associated

SiH*

in

species

and

as m e a s u r e d

for

with

exist

plasma

material. emission

signal

have

optical

diagnostics

I shows

any

in by

DISCUSSION

a-Si:H

not

systems

direct

in-situ

deposited

manufactured

deposition

with

performing

were

systems

to

one

SiH 4 the

the

produced

molecules

substrate

presumes

substrate,

radicals

parent

surface

that

by

initial

and

before

changing

gas

phase

in

the

the

plasma

resultant

condensing

the

into

a-Si:H.

temperature

nucleation

react

products

is

of

not

the

affected *

during could

film

growth,

provide

Figure

3

measured SI2H 6

as

shows

the

measured

of

the

emission

SiH*

energies

are of

SiH 4

very .07

the

by

range

MS.

It

is

and

is

of

and

eV

of

important

of

the

the

of

SiH

reaction

SiH 4 and

300-500K,

temperature .02

surface

dependence

independent

signal

dependence

the

depletion

studied,

weakly eV

on

temperature

and

depletion

signal

temperature

information

by OES,

temperature

the

to

SIH* the note

while

relative dependent,

respectively.

emission

as

production

of

that

the

substrate

emission processes.

for

the

change

in

temperature,

magnitude having

of

Si2H 6

activation

Therefore,

these

P.K. Bhat et al. / Glow discharge hydrogenated amorphous silicon

thermally with

activated

weak Of

bonding

the

species,

only

at

the

growing

surface

radicals

on

the

constitute The

fact

that

temperature

the

emission

SiH

increasing

the

However,

it

is

changing

efficiency

of

the

Disilane

they

on

react

The

to

in

a major

SIH*

emission

the

electron

form

a weak

bond

that

SIH 3

known

plasmas

independent changes

production reactions

a

of

at

of

the

observed SI2H 6 or

in with

near

the

in

the

observations

hop

SiH*

(I).

in

the

increase

in

when or

+ H2

decrease may

line

occurs and

the two

density

excitation

plasma. silyl

diffuse

gas

the

on

(SiH 3)

the

radicals

surface

until

S i 2 H 6,

~ Si2H 6 (surface) energy

Fig.

3

surface

influence

~ Si2H 6 (gas)

(-0,02eV)

is

compatible

processes on

the

(2).

associated with

described

properties

of

with

SI2H 6

reaction

in

this

PECVD

(2).

paper

a-Si:H

could

films.

REFERENCES

I)

A. M a t s u d a

2)

G.

Y.

and

Turban,

67,

5)

that

temperature

activation

the

4)

unpaired

in s i l a n e

S i H 4 is

these

÷ 2H 2 ~-

possible

form

Therefore,

3)

to

gas

surface

production

4.

radicals

is

species

the

due

it

that

interpret

production

the

2 SiH 3 ( s u r f a c e )

have

involve

model:

to

adsorb

will

the of

and

H + SiH 4 ~ S i H 3 + H 2 ÷ SiH

due

of

suggest

are

one

film

Moreover,

intensity

We

with

the

depletion

would

surface.

following

of

majority

temperature

substrate

radicals

surface.

the

substrate

should

surface.

the

hydrogen

(7).

to

processes

all

arriving with

surface

1385

K.

Y.

(]980),

T.

Hayashi,

Technol.

4A,

P.B.

Davies,

N.A.

Chem.

Phys.

Hata,

1872.

A.

Thin and

Solid B.

Films

92,

Grolleau,

Thin

(1982),

171.

Solid

Films

309.

Matsuml,

Sci.

N.

Tanaka,

Catherlne

83,

H.

(1986)

Issacs,

(1985)

Matsuda

Yoshlkawa,

and

and

S.

Konlya,

J.

Vac.

1786. S.A.

Johnson,

D.K.

Russell,

J.

2060. K.

Tanaka,

J.

Appl.

Phys.

59

(1986)

P.K. Bhat et al. / Glow discharge hydrogenated amorphous silicon

1386

(6)

Y.H.

(7)

R.

Shing,

19th

IEEE

J. W.

PV Spec.

Robertson

3412.

R°

Appl.

Phys.

and

Perry, Conf., A.

Robertson, Lett.

and

A.M.

Hermann,

New O r l e a n s ,

Gallagher, D.

Hils,

4 3 (1983)

J.

H.

Presented

U.S.A., Appl.

Chatham

May,

Phys. and

the

1987. 59

A.

at

(1986)

Gallagher,

544.

i

414

657

X1 z

t,u

XIO

_1 tu

a ~'~

XlO0

WAVELENGTH (NM)

Flg. I measured produce and (b) density

SiH 4 p l a s m a OES s p e c t r a for c o n d i t i o n s used to (a) good q u a l i t y a - S i : H a - S i : H w i t h h i g h e r defect of s t a t e s .

>-19

FLOW RATE (sccm)

2o

~

h-

80

Sill 4

z

e-elO--i i - - r e -

uJ )-z

30 Z

~20

==

-J

,U

20

IO

.J i,u

I

~o~I

~

_

1.5 RF POWER (W)

Fig. 2 SiH 4 d e p l e t i o n as m e a s u r e d by C A R S as a f u n c t i o n of RF power and flow rate.

3 IO/T

I

2.5 -1 (K)

1

3.5

Flg. 3 The ~ e m p e r a t u r e d e p e n dence of SIH emission intensity, p r o d u c t i o n of S12H6, and the d e p l e t i o n of SiH 4.