Spectroscopic ellipsometry of SixGe1-x/Si: a tool for composition and profile analysis in strained heterostructures used in the microelectronics industry

SixGe1-x/Si strained-layer heterostructures play a primary role in today's developments in Si-based fast electronics. Either real-time epitaxial growt h control of this alloy or ex situ on-line characterization of the processe d wafers is required. Indeed, spectroscopic ellipsometry (SE) is a fast and non-destructive technique compared to secondary ion mass spectroscopy (SIM S) and/or X-ray diffraction XRD X-ray analysis. The heterostructure-base-tr ansistor (HBT) ellipsometry studies, with either graded or abrupt profiles, have been reported. The analysis presented herein was based on an optical database of indices currently provided in the literature for relaxed materi als. For strained pseudomorphic structures, using a calibration procedure t o access the actual x alloy composition, the in-depth variation x could be determined even with the presence of a silicon capping layer. Achievement w as completed for a dummy-load of test wafers, as well as for patterned proc essed wafers, where analysis required minimum areas of 30 x 30 mum. (C) 200 0 Elsevier Science S.A. All rights reserved.