High temperature oxidation of Si(100) by neutral oxygen cluster beam:: Coexistence of active and passive oxidation areas

We report the study of Si(100) oxidation by oxygen clusters with an average size of 2000 molecules at substrate temperatures ranging from 850 to 1100 degreesC. It has been found that at T<1000 degreesC two areas corresponding to passive and active oxidation of silicon coexist within the same impact spot on the surface. In the central part of the impact spot, no surface etching occurs due to the formation of a protective oxide layer. In the area surrounding the central part, a circular groove with a steep inner and slightly sloping outer walls is formed as a result of surface etching via the reaction 2Si+O-2-->2SiO(gas). The reactive sticking coefficient of oxygen obtained from the etch rate in active oxidation area is significantly higher than that for oxidation by molecular oxygen. The coexistence of the two areas is attributed to a quasi-Gaussian flux density distribution in the beam cross section. The observed abrupt drop of the etch rate at the inner wall of the groove marks the transition from active to passive oxidation. Silicon oxidation by an oxygen cluster beam shows specific features that have not been observed in previous works with molecular oxygen. The critical flux density corresponding to the transition does not, for instance show an Arrhenius behavior. Besides, this study shows the crucial role of the beam spatial parameters when supersonic sources are used to study surface reactions. (C) 2002 American Institute of Physics.