Development of Si(100) surface roughness at the initial stage of etching in F 2 and XeF 2 gases: ellipsometric study

Abstract

The evolution of roughness on the Si(100) surface has been investigated in the initial stage of etching in a molecular flow of F 2 and XeF 2 gases. It was observed that the roughness increases during etching in XeF 2 gas and decreases during etching in F 2 gas, indicating that F 2 gas polishes an Si surface unlike XeF 2. This is explained by the kinetics of the formation of adsorption layer, which was studied by ellipsometry. It is supposed that F 2 gas exposure leads to a layer-by-layer etching and polishing of the surface at an atomic scale. For XeF 2, the formation of SiF 2 and SiF 3 complexes is a non-activated process — therefore, their formation is not surface site dependent. Si atoms are removed from random sites on the surface, and the surface roughness increases during etching with XeF 2 exposure.