MECHANISM OF SURFACE-REACTION IN THE DEPOSITION PROCESS OF ALPHA-SI-H BY RF GLOW-DISCHARGE

Hydrogenated amorphous Si (a-Si:H) films are deposited by the rf glow discharge of SiH4. The mechanism of the surface reaction of the incident SiH3 radical produced by the glow discharge to form the a-Si:H network was studied in this work. The hydrogen concentration was investigated by IR absorption in a-Si:H films deposited under various conditions of the substrate temperature Ts and the SiH4 partial pressure Ps in the reactant gases. The hydrogen concentration in the films was divided into SiH and SiH2 configurations by spectral deconvolution. While the SiH concentration S1 was not influenced very much by variation of the deposition conditions, the SiH2 concentration S2 was remarkably influenced. S2 increased with an increase in the deposition rate of the film at a different rate by the variation of Ts and Ps. The following reaction scheme of the radicals adsorbed on the growing surface is proposed to explain these changes in S2 and S1. The dehydrogenation and Si-Si bond formation into the network are made by two kinds of processes, the fast process and the slow process. The fast process occurs predominantly in high-rate depositions and incorporates SiH2 into the network. The slow process occurs predominantly in low-rate depositions and incorporates some SiH. The fast process takes place by interactions of two adsorbed radicals and the slow process takes place at steplike sites after migration on the surface. The observed variations in S2 with Ts and Ps are analyzed by this model and the rate constants of each process are determined. The activation energy in the slow process is obtained to be 0.3 eV, which is considered to be due to the migration of the SiH3 radical on the growing surface. The data of the S1 variation are also analyzed and the minimum concentration of H atom is found to be about 10 at. %, in agreement with experiments. Variation of the dangling-bond density with deposition condition is found to have similarities with that of S1 and S2. The features of the surface reaction mechanism are successfully explained by this model. © 1995 The American Physical Society.