Si(100)-(2x1) etching with fluorine: Planar removal versus three dimensional fitting

The morphologies achieved by thermally activated reactions of adsorbed F wi th Si(100)-(2 X 1) were studied with scanning tunneling microscopy. Dimer v acancies were produced in the top layer but, more significantly, there was a new reaction pathway that gave rise to multilayer pitting even when the s urface concentration was very low. This pathway can be linked to the atomic structure of the exposed layer and the formation of SiF2 in that layer. It accounts for surface roughening, and it is very effective.