Model-dielectric-function analysis of ion-implanted Si(100) wafers

Abstract

Optical properties of Si+, P+, and Ar+ ion-implanted Si(100) wafers have been studied using spectroscopic ellipsometry. The Si+, P+, and Ar+ ions are implanted at 150 keV with fluences ranging from 1×1014 to 2×1015 cm−2 at room temperature. A model dielectric function (MDF), which was developed for modeling the optical constants of perfectly crystalline semiconductors, has been applied to investigate the optical response of the ion-implanted Si(100) wafers. The MDF analysis indicates a distinct structural transition from the crystalline to amorphous phase at some ion fluences around 1014–1015cm−2. Since the critical points do not have any validity in amorphous material, the band gaps used in the MDF are not a result of the Bragg gaps at the Brillouin-zone boundaries, but are considered to arise from the short-range order determined by the covalent bonding. Using these results, we obtain an expression, D=(1.6×108/M)2.2 cm−2 which enables us to estimate the crystalline-amorphous phase transition fluence D for silicon wafers implanted with optional ion species of mass number M. No clear change in the morphology of silicon surface after ion implantation has also been confirmed by atomic force microscopy.