Si-H VIBRATIONAL PROPERTIES IN CRYSTALLIZED HYDROGENATED SILICON FABRICATED BY REACTIVE SPUTTERING IN H2 ATMOSPHERE

HAL Id: jpa-00220916

https://hal.archives-ouvertes.fr/jpa-00220916

Submitted on 1 Jan 1981

HAL

is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire

HAL, est

destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Si-H VIBRATIONAL PROPERTIES IN CRYSTALLIZED HYDROGENATED SILICON FABRICATED BY REACTIVE SPUTTERING IN H2

ATMOSPHERE

A. Hiraki, T. Imura, K. Mogi, M. Tashiro

To cite this version:

A. Hiraki, T. Imura, K. Mogi, M. Tashiro. Si-H VIBRATIONAL PROPERTIES IN CRYSTALLIZED HYDROGENATED SILICON FABRICATED BY REACTIVE SPUTTERING IN H2 ATMOSPHERE. Journal de Physique Colloques, 1981, 42 (C4), pp.C4-277-C4-280.

�10.1051/jphyscol:1981459�. �jpa-00220916�

Si-H VIBRATIONAL PROPERTIES IN CRYSTALLIZED HYDROGENATED SILICON FABRI- C A T E D B Y REACTIVE SPUTTERING IN H2 ATMOSPHERE

A. Hiraki, T. Imura, K. Mogi and M. Tashiro Dept. of E.E., Osaka Univ., Suita, Osaka 565, Japan

Abstract.- Crystallized hydrogenated silicon (c-Si:H) films are fabricated by rf-sputtering in pure H2 atmosphere. Their sharp

-

and fine structured infrared spectra have enabled us to assign accurately the vibrational configurations between Si and H.

The results are applicable to the amorphous hydrogenated silicon (a-Si:H) where the Si-H vibrational configurations are not yet well understood.

We have found that rf-sputtering in H2 atmosphere can fabricate films of crystallized hydrogenated silicon (c-Si:H) [l]. The films thus obtained reveal several interesting features and properties.

Due to crystalline nature of the film, the infrared (IR) spectra of Si-H vibrations are composed of well separated peaks.

Present paper aims to describe a contribution of the IR spectra for better understanding of the Si-H vibration in amorphous hydro- genated silicon (a-Si:H)

.

The c-Si:H films were prepared by rf-sputtering in a NEVA FP-21 diode sputtering apparatus under H2 pressure (3-5) x 10-I Torr with

n

rf-power ranging from 1.2 to 3.6 w/cmL. The Si crystalline substrates were water cooled or heated up to 250°C.

Depending upon these parameters, c-Si:H films with variety of IR properties can be fabricated. As an example, IR spectrum of a c-Si:H film deposited on a water cooled substrate is shown in Fig.1 together with that of an a-Si:H film for comparison. The a-Si:H film was fabricated by conventional sputtering in Ar+H2 atmosphere.

-

In addition to sharp and fine structured spectrum of c-Si:H

100

--- . .

\

',

_\

stretch~ng band

-

_bendlnq ^I-/"

and 4

Fig.1 : IR spectra of c-Si:H and a-Si:H.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981459

JOURNAL DE PHYSIQUE

I I I

2300 2100 Wavenumber (cm-I)

Fig.3 : Schematic of Si-H bond configurations in c-Si:H.

Fig.2 : Stretching mode region of c-Si':H (a) as deposited,

(b) annealed at 400°C for 30 min.

compared with br~ader~structure-less one of a-Si:H, complete absence of the absorption at 2000 cm-' is found in the c-Si:H.

In the stretching vibration region, at least six peaks are clearly seen as shown in Fig. 2 (a)

.

For the assignment of these peaks, the above situation is of great help since, if one assumes the absorption at 2000 cm-l is due to an isolated ESi-H bond stretching, we only have to consider =Si=H 2' -SiEH3 and their combinations, namely, seven configurations (five

=Si=H2 related and two - S ~ E H ~ related ones) as illustrated in Fig.3.

An IR study [2] on Si-H stretching modes in substituted silane molecules has indicated that the stretching frequency

v ~

can be

~ - ~

expressed by the following empirical equation:

3

%i-H = a + b Z E(Ri) i=l

where a and b are constants, E(Ri) is a measure of the electro- negativity of the i-th substituted atom or group R

i'

The applicability of the empirical relationship to the Si-H stretchig frequency in a-Si:H has been claimed by Lucovsky [3] who has

-

1

estimated YSi-H(in cm ) through under written expressions in the following three types of substituted silane molecules: SiHXYZ, SiH2XY and SiH3X, where X I Y and Z represent substituted atoms or groups.

calculated the SR(R)'s in the seven configurations and from equations (2)and (3) estimated USi-H'~ which are listed in Table 1 with

assigned experimental values taken from the peak positions in Fig.2.

Table 1 :

VSi-H

calculated and experimental.

Si-H sum of

Ys~-H

^{( cm-I )}

con£ iguration SR (R) calculated experimental

Fig.4 : psi-, versus SR sum. modes at 2085'cm -1 and 2100 cm-l, The error bars indicate respectively, against the exposure standard deviations. to the air or oxidation.

The appropriateness of the assignment and also effectiveness of (2) and (3) are recognized from the apparent linear~relation between electronegativity sunCSR(R) and VSi-B(SiH2XY and SiH3X)shown in Fig.4

-

open circles represent p Si-H 's in substituted silane molecules reported in the reference [ 3 ] .

From equation (1) and taking X, Y and Z as sole Si atoms, V , i - ~ for an isolated ZSi-H configuration is calculated to be 2013 cm-l, which supports the above made assumption of to the an isolated absorption ESi-H at within 2000 cm-I experi- due mental error.

Further, an annealing experiment On the c-Si:H film at 400°C for 30 min. confirmed the assignment of the -SiZH3 related stretching

%,-,,

(SiH3 K )

.

Namely, as shown in Fig.2 (b)

,

three peaks at 2105, 2135 and 2155

-

¹

cm disappeared indicating that -SiEH3 configuration was destroyed by the annealing.

-

_i-

E V

-

^22c3

II b

5

*loo-

0 5 10 Another interesting fact is a

~ t ~ b i l i t ~ - ~ ~ t i ~ ~ l ~ ~ t ~ ~ ~ ~ ~ ~ t i ~ i t ~

sum

quite remarkable difference be tween the two =Si=H, related stretching

-

^{I -}

-

^{l o}

/:)/

( C H d F 0 CIz

,

O CH3 (CH$(CH$O

/jb.'%

cH42--xc~3

-

A=14cm-1 /0(%?l~%H3

i c -

-Si

H,

^{by d.}

-

-

JOURNAL DE PHYSIQUE

References.

[l] IMURA T., MOGI K., HIRAKI A,, NAKASHIMA S. & MITSUISHI A., Sol. St. Comm., to be published.

[2] SMITH L. & ANGELOTTI C., Spectrochimica Acta

15

(1959) 412.

[3] LUCOVSKY G., Sol. St. Comm. 29 (1979) 571.

[4] IMURA T., USHITA K. & HIRAKI A., Jap. J. App. Physics 19 (1980) L65.

Intensity of the 2100 cm-I stretch- ing assigned to configuration b. in

Fig.3, decreased upon the exposure and 2000-

at the same time new absorpton at 2270 -.- 2SP

,,

²¹⁰⁰

-

¹

cm developed. However, the absorption at 2085 cm-l assigned to an isolated

=Si=H2 (or a. in Fig.3) changed little, if any, and consequently no development

-

of the new absorption at 2270 cm-I which was calculated to be due to the attach- ¹⁰⁰⁰ ment of electronegative oxygen atom to

the 2100 cm-l con£ iguration.

With this information it is possible to predict the stability of a-Si:H films to the degradation by the oxidation or oxygen-inclusion [4].

In fact, unstable films exhbit intense absorption at 2100 cm-l, while tne films with 2085 cm-l like films fabricated by glow discharge technique

are certainly stable. Fig.5 : IR spectra of To show this, two a-Si:H films, a-Si:H films deposited whose IR spectra are shown in Fig.5, by diode and triode were exposed to the air. One specimen sputtering

.

(2SP) which indicates obvious peak at

2100 cm'l was fabricated by diode sputtering in Ar+H2 atmosphere and suffered severe degradation in its photoconductivity due to oxygen- inclusion [41, which resulted in both the decrease in 2100 cm-' and the development of 2270 cm-' absorptions. However, the other one

(4SP) fabricated by tetrode sputtering did show no detectable effect.

We have shown that the present c-Si:H films provide good opportunities for the detailed study of Si-H vibrational configu- rations in solid which helped to understand IR spectra of a-Si:H films

in more realistic way than did the study of the substituted silane molecules-mainly the stretching vibrations are reported and the detailed information on the bending and wagging vibrations is soon published elsewhere.

We express sincere thanks to Prof. S.Minomura of Institute for Solid State Physics, the Univ. of Tokyo for his encouragement and helps for the study.