KINETICS OF INITIAL OXIDATION OF THE SI(111)-7X7 SURFACE NEAR THE CRITICAL CONDITIONS

The kinetics of the initial oxidation of Si(111)-7 x 7 by oxygen at pr essures from 5 x 10(-9) to 1 x 10(-6) Torr are investigated with optic al second-harmonic generation at surface temperatures near T-tr, where T-tr is the transition temperature from oxide growth to Si etching. T he initial reactive sticking coefficient, obtained from the rate of ox ide growth, decreases gradually to zero at T-tr with increasing temper ature. The pressure dependence of the reaction rate constants derived by using a precursor model shows the key role of the interaction in th e layer of chemisorbed precursor species for initial silicon oxidation near T-tr. It is shown that the pressure and temperature dependence o f the reaction rate constants of the precursor species determines the boundary for oxide nucleation.