Spectroscopic ellipsometry characterization of strained and relaxed Si1−xGex epitaxial layers

Abstract

Spectroscopic ellipsometry has been used to study thick, relaxed and thin, strained epilayers of Si_1−xGe_x on Si in the range 0.1<x0.87Ge_0.13 and Si_0.8Ge_0.2 have been obtained and long‐wavelength absorption coefficient values, required for interference fringe fitting, shown to be higher than measured previously. The dielectric function of strained Si_0.78Ge_0.22 has been measured for the first time and the effects of strain on the critical points shown to be consistent with deformation potential theory. An interpolation procedure has been developed for the fitting of layer composition and thickness, and excellent agreement with conventional techniques obtained for a series of uncapped single epilayers. The surface roughness of Si_1−xGe_x epilayers has been studied as a function of time and deposition temperature and shown to play an important role in the modeling. The application of the technique to the characterization of buried strained layers is discussed.