Relaxed Si0.7Ge0.3 buffer layers grown on patterned silicon substrates forSiGe n-channel HMOSFETs

For a successful fabrication of hetero-MOSFETs (HMOSFETs) the compatibility of the epitaxial growth of the heterostructures with the standard CMOS pro cess is an important factor. For this reason, we demonstrate for the first time the growth of relaxed SiGe buffer layers with a Ge content up to 30% b y differential molecular beam epitaxy (MBE) after the definition of the act ive device areas of n-channel HMOSFETs by lateral oxide isolation. The infl uence of lateral dimensions and the composition of the epitaxial layer stac ks on the surface topography, relaxation and defect density has been invest igated. Scanning electron microscopy (SEM) and differential interference co ntrast (DIC) micrographs were applied to characterize the quality of the di fferential epitaxy and the surface topography. The degree of relaxation in the patterned areas was determined using micro-Raman spectroscopy. The anal ysis of the dislocations was carried out by transmission electron microscop y (TEM). The reduction of the surface cross-hatch with decreasing lateral d imensions was clearly seen. Further, we found, that the increase of the rel axation corresponds to a higher density of misfit dislocations; confined at the interface SiGe buffer/Si buffer. To our surprise, we also observed a s trong influence of the pure Si channel (10 nm tensile-strained Si layer) on the SiGe buffer layer. This indicates that the investigation of the qualit y of the relaxed SiGe buffer layers should be only done with the whole epit axial layer stack of the device structure. (C) 2000 Elsevier Science S.A. A ll rights reserved.