AB-INITIO MOLECULAR-ORBITAL STUDY ON THE SURFACE-REACTIONS OF METHANEAND SILANE PLASMA CHEMICAL-VAPOR-DEPOSITION

Hydrogen-elimination reactions on the substrate surface of methane pla sma are studied on the basis of an ab initio molecular-orbital method. The activation energy of the reaction of the rate determining step (b y MP2/3-21G//HF/3-21G) is much higher than the analogous reaction in s ilane plasma. In the case of carbon surface reactions, the activation energy becomes larger; as the model cluster size becomes larger, while in the case of silicon surface reactions,the activation energy become s lower as the model cluster size becomes larger. Thermodynamically, t he relative stability of the reactant and the product of the hydrogen elimination reaction on the substrate surface of methane plasma are si milar to that of silane plasma. Thus the methane plasma surface reacti ons are expected to be qualitatively different from silane plasma surf ace reactions at low substrate temperatures, while they are expected t o be similar at high substrate temperatures.