SUBSTRATE ORIENTATION DEPENDENCE OF SELF-LIMITED ATOMIC-LAYER ETCHINGOF SI WITH CHLORINE ADSORPTION AND LOW-ENERGY AR+ IRRADIATION

The self-limited atomic-layer etching of Si(100), (111), (110) and (21 1) has been investigated by alternated chlorine adsorption and low-ene rgy Ar+ ion irradiation using an ultraclean electron cyclotron resonan ce apparatus. The etch rate per cycle is described by a Langmuir-type equation with the etch rate in saturation and the chlorine adsorption rate for each substrate orientation. There is a possibility that the e tch rate per cycle in saturation is expressed by a well-regulated frac tional number of the atomic-layer thickness. It has been found that th e chlorine radicals are dominant adsorption species in the present exp erimental conditions, and that the sticking probabilities of chlorine radicals are almost independent of the substrate orientation. In XPS m easurements, peaks of Si+ have been observed, but neither of Si2+ nor Si3+ on the chlorine adsorbed surface and the adsorbed chlorine layer has been estimated to be as thin as about one monolayer. It has been p roposed that the atomic-layer etch rate per cycle in saturation is exp lained by a simple equation considering the bond structure of each sub strate surface.