Anisotropic Initial Stage of Laser-Induced Chlorine Reaction on Si(111) Observed by Surface-Sensitive Optical Methods

Abstract

We investigate chlorine chemisorption and the initial stage of laser-induced reaction on Si(111) using second-harmonic generation (SHG) and reflectance difference spectroscopy (RDS). SHG signals that originate from direct bulk transition, generated by 1.6 and 1.7 eV probe light, show good threefold symmetry reflecting the symmetry of bulk Si, and SHG signals that originate from the surface, generated by 2.0 eV probe light, show threefold symmetry that intensifies in the [211] direction after chlorine chemisorption. The difference in reflectivity between the [211] direction and the [011] direction in the initial stage of the reaction is observed. In both clean Si surface and chlorinated Si surface, the RDS signal gradually changes with the progress of etching reaction, and the anisotropic initial stage of the reaction that depends on the direction of the atomic steps is observed.