A mechanism for SiCl2 formation and desorption during the etching of Si(100) (2 x 1) surfaces at low Cl coverages was analyzed by using first-principles calculations. It was found that the 2 monochlorinated Si atoms of a surface dimer could rearrange themselves into a metastable SiCl2 adsorbed species, plus a Cl-free Si atom. The desorption of SiCl2 occurred via a 2-step mechanism in which the adsorbed species was first stabilized by the diffusion away of the free Si atom. The energy barrier to the formation of adsorbed SiCl2 was lower at a dimer next to a dimer vacancy than at an undamaged point of the surface. This conclusion was consistent with scanning tunnelling microscopic observations of the preferential linear growth of etch pits along dimer rows.

G.A.De Wijs, A.De Vita, A.Selloni: Physical Review Letters, 1997, 78[25], 4877-80