Pulsed–light Crystallization of Thin Film Silicon, Germanium, and Silicon Germanium Alloy

Abstract

We report the recent progress of crystallization of amorphous silicon (a-Si), amorphous germanium (a-Ge) and amorphous silicon germanium alloy (a-SiGe) using a pulsed-Xenon-lamp system with multiple lamps. The precursor materials were deposited using a sputtering machine on display glass substrates maintained on a rotary holder. The RF powers on the silicon and germanium targets were varied to control the Ge/Si ratio in the materials. The film thickness was in the range of 50-100 nm, targeting the application in thin film transistors (TFT). The samples were pre-heated to 350-450°C in a conveyer chamber with nitrogen flow before the crystallization. The materials were characterized using AFM, Raman and Spectroscopic Ellipsometry. We demonstrated that we can uniformly crystallize a-Si, a-SiGe, and a-Ge with a single-pulse or multiple-pulse process on 10×5 cm² glass substrates. We found that the required crystallization power for a-Ge is much lower than for a-Si. The power needed to crystallize a-SiGe is between the power required for a-Ge and a-Si crystallizations, and it increased with increasing Si fraction. No Raman signal was measurable in the as-deposited films. Strong Raman peaks at 520 cm^-1 and 290 cm^-1 were observed in the pulsed-lamp crystallized poly-Si and poly-Ge films, respectively. Distinct Ge-Ge, Si-Ge, and Si-Si vibration modes were observed at ~285 cm^-1, ~390 cm^-1, and ~470 cm^-1, respectively, in the poly-SiGe films formed after the pulsed-light treatments. Their intensity ratios and the peak positions depended on the Ge/Si ratio and the light intensity used for the crystallization. AFM images showed the formation of large grains with increased surface roughness.