First-principles study of chlorine adsorption and reactions on Si(100)

First-principles local-density-functional calculations on the interaction of chlorine with the Si(100)-2x1 surface are presented. Cl-2 adsorption and a number of reactions relevant to etching via desorption of SiCl2 species are considered, both at the defect-free surface, and in the presence of small surface defects. The formation of SiCl2 species via an isomerization-mechanism, their stabilization and desorption are studied. Whereas this is a likely route towards spontaneous etching of the surface in the limit of low Cl coverage (theta(Cl)), at theta(Cl)similar to 1 it is energetically very costly. In the high coverage limit the formation of SiCl2 by either a Cl atom reacting with a monochloride surface species or by dissociative chemisorption of hyperthermal Cl-2 molecules is investigated. For the latter, a barrier for dimer-bond breaking of 0.5-1 eV is estimated. Our results show that both the Cl-2 adsorption energy and the SiCl2 desorption energy decrease significantly with increasing the local chlorine concentration above one monolayer. [S0163-1829(98)08015-1].