Reactions of the Silicon (100) Crystal Surface with Hyperthermal Chlorine Molecules and Radicals.

This dissertation discusses the etching and scattering reactions of Cl_2 and Cl neutrals at high kinetic energies with Si(100). The particle beam is generated by passing pulsed laser light through a cryogenically condensed film of chlorine gas. Energy is absorbed into the film via electronic transitions and then converted to translational kinetic energy. The process is photothermal, resulting in beam energies which vary with total photon flux rather than photon energy. The energy of the beam is continuously variable by changing the thickness of the cryogenic film. The beam is composed primarily of Cl _2 molecules, and up to 10% Cl radicals. Maximum translational kinetic energies of 6 eV are achieved for Cl_2, with a mean energy of 2.69 eV and a full width at half maximum of 2 eV. The technique is also applied successfully to condensed films of ICl. Using the chlorine hyperthermal beam, SiCl _{rm x} (x = 1 to 4) etch products are observed. The largest raw signal observed is from SiCl_sp{3}{+} and this species is monitored for etch rate studies. Chlorine beams with <{rm E}> >= 2 eV, and with reasonable flux above 3 eV, show a factor of 3.6 +/- 1 increase in the production of SiCl_sp {3}{+} over lower energy hyperthermal beams. The fast beams show a factor of at least 30 increase in etch rate over thermal chlorine. At elevated surface temperatures the product distribution shifts to favor the less chlorinated species, SiCl and SiCl_2 . Scattering of Cl_2 is examined for velocity-selected beams at various energies. The fraction of the incident beam which is scattered from silicon decreases with increasing incident energy, from 75% at < {rm E}> = 0.5 eV to 18% at <{rm E}> = 2.7 eV. The scattering fraction increases with increasing exposure of the surface to the chlorine beam. Comparison of the scattering data to Auger analysis of the surface shows that the fraction of the incident beam which is not scattered, for high Cl_2 mean energies, is also not observed on the surface. This suggests that part of the flux in the high energy beams is being consumed by etch product formation and supports results found in the etching studies above.