Oxidation study of hydrogenated amorphous silicon carbide films
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Oxidation study of hydrogenated amorphous silicon carbide films W.K. Choi, L.P. Lee and C.C. Leoy Microelectronics Laboratory, Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 ABSTRACT We present results of an oxidation study of a-Si1-xCx:H films prepared by the plasma enhanced chemical vapor deposition of silane and acetylene. The composition (i.e. x) of the samples was determined by the flow rates of silane and acetylene. Oxidation was carried out at 400 to 850°C in dry oxygen ambient. The infrared (IR) spectra of the as-prepared films showed the intensity of the Si-C peak decreases and the Si-CH3 peak increases as x increases. The Si-H peak shifts to higher frequency as x increases. Note that the incorporation of CH3 radicals in a-Si1-xCx:H films has shown to introduce voids and increased the porosity of the films. The IR spectra of the oxidized samples showed clear Si-O stretching and rocking/wagging modes for all films. We suggest that the growth of oxide on a-Si1-xCx:H is a result of voids that facilitate the diffusion of oxidants into the film. We shown that the activation energy, obtained from the linear rate region of the oxide growth, was far less than the dissociation energies of the Si-Si, Si-C and Si-H bonds. We suggest that this could be due to the amorphous nature of the samples that caused the various chemical bonds to be weaker during oxidation. INTRODUCTION Hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films have attracted considerable research interests in recent years mainly due to (i) their potential applications in electronics and optical devices and (ii) it provides an interesting system for the fundamental study of amorphous material with different degrees of disorder. As the potential of this material is basically in the optoelectronics area, the optical and structural properties of a-Si1-xCx:H films have been extensively studied [1]. It should be noted that there are other applications of a-Si1-xCx:H films that have been suggested in the literature. These include: as passivation of electrical devices [2], coating material for glass and metal for ultraviolet optics [3] and as a masking material for micromechanical devices [4]. As the majority of these applications involve high temperature process in inert or oxidizing ambient, an understanding on the effect of annealing or oxidation processes on a-Si1-xCx:H films is important for these applications. There are comparatively more research in the effect of annealing on a-Si1-xCx:H films [5-8] as compare to the oxidation study of this material. We have recently reported oxidation results of a-Si0.2C0.8:H films [9]. It was found that the oxidation process proceeded very rapidly at a relatively low temperature of 400°C. The Si-CH3 bonds provide the necessary porous structure for the significant oxide growth. In this paper, we present more detailed oxidation results of a-Si1-xCx:H films with x = 0.3, 0.5 and 0.8 at different oxidation temperature and duration. EXPERI
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