Strain relaxed high quality silicon-germanium-on-insulator substrates formed by pulsed laser irradiation technology

Abstract

We report the impact of pulsed laser annealing on the relaxation of strain in SiGe-on-insulator (SGOI) substrates formed by Ge condensation. Ge condensation process results in a partially strained SiGe layer, whose mechanism of stress release is governed by the onset of defects formation. The strain developed in the SiGe layer as condensation proceeds is systematically studied, to identify the critical phase where defects form. The SGOI layer is then irradiated with an excimer laser. The laser annealing repairs any existing defects and relaxes the compressive strain in the crystalline SiGe layer to -0.28% when irradiated with an optimized laser fluence of 450 mJ/cm2 for seven consecutive pulses. Spectroscopic ellipsometry and atomic force microscopy (AFM) measurements of the laser-annealed surface revealed the excellent crystallinity and improved surface roughness (∼0.42 nm). Etch pit density measurements revealed a threading dislocation density of about 4 × 105 cm-2. A clear understanding of the correlation between strain evolution with excimer laser energy density and pulse number enables the SGOI substrate fabrication to be tailored according to the requirements of strain engineering for application in high mobility metal oxide semiconductor field effect transistors (MOSFETs). © 2008 The Japan Society of Applied Physics.