THERMAL AND DIRECT ETCHING MECHANISMS OF SI(100) WITH A HYPERTHERMAL CHLORINE BEAM

The etching of Si(100) with hyperthermal beams of atomic and molecular chlorine has been studied in the temperature range between 130 and 200 K. The dominant etch product, SiCl4, is evolved in two parallel reaction pathways, only one of which is thermally activated. It is shown that the nonactivated pathway, which has an appreciable rate only when hyperthermal chlorine atoms are incident upon the surface, is due to collision-induced desorption of weakly bound SiCl4. By increasing the normal component of the chlorine incident translational energy, the efficiency of converting incident Cl into SiCl4 can be increased to 0.6% in the nonthermal channel, at temperatures for which the thermal etching rate is negligible. The normal energy scaling and the observed energy threshold suggest that this process should result in highly anisotropic etching.