Photoelectron spectroscopy (PES) and temperature-programmed desorption (TPD) studies investigated the chemistry of Cia on Si/Cu(100). Si deposition was carried out by exposing Cu(100) to SiH4 at 420 K. PES showed that the exposure of this Si-saturated surface to Cia resulted in the formation of SiCl, SiCl2, and SiCl3 species at 120 K, with the latter species becoming more prevalent at higher Cl coverages. Heating of the chlorinated surface between 120 and 500 K increased the concentration of SiCl3 species. TPD studies of Cl-2/Si/Cu(100) as a function of Si coverage showed primarily SiCl3 (and probably SiCl2) desorption at the lower Si coverages and SiCl4 at the highest Si coverage. The majority of the Si was not removed from the surface as chlorosilane product, but instead diffused into the Cu bulk at temperatures above 500 K