Development of Si (100) surface roughness at the initial stage of etching in F2 and XeF2 gases:: ellipsometric study

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 XeF2 gases. It was observed that the roughness increases during etching in XeF2 gas and decreases during etching in F-2 gas, indicating that F-2 gas polishes an Si surface unlike XeF2. 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 XeF2, the formation of SiF2 and SiF3 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 XeF2 exposure. (C) 1999 Elsevier Science B.V. All rights reserved.