Enhanced etching of Si(100) by neutral oxygen cluster beam

We present the study of high temperature (800-1250 degreesC) oxidation of Si(100) by large neutral oxygen clusters (600 and 4000 molecules per cluster). The coexistence of passive and active oxidation areas on the surface under cluster beam impact allows studying simultaneously both reactive etching via the reaction 2Si + O-2 --> 2SiO(g) and onset of SiO2 formation. The reactive sticking coefficient of oxygen in the active oxidation area is significantly higher than that for molecular oxygen and exhibits a strong dependence on the cluster flux. We suggest that the enhancement of active oxidation results from multiple collisions of cluster molecules with the surface. While in the case of the larger clusters the flux dependence of the etch rate may be partly explained by etching-induced surface misorientation, for the smaller clusters it is obviously a clusters-related effect, presumably related to the capture of oxygen scattered from the surface by oncoming clusters. The analysis of the critical conditions for oxide growth indicates that SiO2 nucleation is also enhanced for the smaller clusters. (C) 2002 Elsevier Science B.V. All rights reserved.