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ABSTRACT The characterization of hydrogen in hydrogenated nano-crystalline silicon (nc-Si:H) films with various crystallinity has been studied using FTIR absorption spectroscopy and gas effusion spectroscopy. In gas effusion spectrum of a nc-Si:H, three evolution peaks of H 2 are found near 400, 500 and 600 'C. From the deconvolution of the gas effusion spectra, the hydrogen concentration in amorphous region dose not depend on the volume fraction of crystalline. The surface density of hydrogen at the interface and in the grain boundaries of nano-crystalline grains decreases with the volume fraction of crystalline. The properties of hydrogen in nc-Si:H films are discussed with the results of FTIR absorption spectroscopy. INTRODUCTION Hydrogenated nano-crystalline silicon (nc-Si:H) films can be prepared by PECVD method using high dilution of SiH 4 in H2 . The nc-Si:H films are more stable by light irradiation than a-

Si:H films.

The hydrogen concentration in nc-Si:H films is almost same as that in a-Si:H films.

In the growth and the properties of nc-Si:H, the role of hydrogen is very important. The properties of hydrogen in nc-Si:H films, however, have not been understood in detail yet. In this report, nc-Si:H films with various crystallinity were prepared at RF-power range between 9 and 76 W. The thermal evolution and the bonding states of hydrogen in nc-Si:H films have been studied by using gas effusion spectroscopy and FTIR absorption spectroscopy. From these results, the properties of hydrogen in nc-Si:H films are discussed. EXPERIMENT The samples were prepared on sapphire and c-Si substrates by PECVD at 13.56 MHz using SiH 4 and H2 . The total gas pressure was 4 Torr with the ratio R=H 2 /SiH 4 of 40. The substrate temperature was -250 'C and the RF-power was varied from 9 to 76 W. The film thickness was from 0.9 to 1.4 min. A hydrogenated amorphous silicon (a-Si:H) film was prepared by the same method at RF-power of 70 W with R=9 to compare to nc-Si:H films. The film thickness was -0.9 pm. The crystallinity of the sample was investigated using Raman spectroscopy and X-ray diffraction (XRD). Raman spectra were measured using He-Ne laser at a wavelength of 633 nm. 317 Mat. Res. Soc. Symp. Proc. Vol. 557 © 1999 Materials Research Society

(W)

" ý76

(220) (311) 76

9

239

99 400

350

300

450

500

600

550

1'0

650

20

...

40

50

60

Fig. 2. XRD patterns of the samples prepared at various RF-power.

Fig. 1. Raman spectra of the samples prepared at various RF-power. 0.7...

30

2e (degree)

Raman shift (cm- )

200

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........

0.6

0.5

'1150

0

o (220) S0.4 0.3 0.43

100 .(111)

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50

0.1 6

0

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60 40 Power (W)

1

80

100

0

0

20

60 40 Power (W)

0"

80

100

Fig. 3 (b). RF-power dependence of grain size in the samples.

Fig. 3 (a). RF-power dependence of volume fraction of crystalline in the samples.

The volume fraction of crystalline X, was estimated as the ratio Ic/(lc+Ia), where la and Ic 1 corresponds to the integrated intensities of Raman peaks near 488 and 520 cm- , respectively