Engineering strained silicon on insulator wafers with the Smart Cut™ technology

Strained silicon on insulator wafers are today envisioned as a natural and powerful enhancement to standard SOI wafers and/or bulk-like strained Si layers. This paper is intended to demonstrate through miscellaneous structural results how a layer transfer technique such as the Smart Cut(TM) technology can be used to obtain good quality tensile-strained silicon on insulator wafers. Such a technique uses preferentially hydrogen implantation to peel-off the very top part of an epitaxial stack and transfer it onto another silicon substrate. The formation of an insulator, prior to the bonding onto a new silicon substrate enables the formation of a "semiconductor on insulator" structure. Two approaches based on the Smart Cut technique are considered in this paper. The first one relies on the formation by layer transfer of a relaxed SiGe on insulator ("SGOI") substrate on which a tensile-strained Si layer is then grown. The second one is based oil the transfer of a SiGe relaxed buffer/Si cap stack. A SiGe-free tensile-silicon on insulator (sSOI) substrate is then obtained after the selective etching of the top SiGe layer. The epitaxial layers Studied in this article are of two kinds: (i) the thick, nearly fully relaxed SiGe layers (with Or Without tensile-strained Si layers on top depending on the final structure targeted: SGOI or sSOI) used as the donor wafers in layer transfer operations, and (ii) the thin, relaxed SiGe layers and the thin, tensile-strained Si epitaxial films grown on SGOI substrates. In-depth physical characterizations of these epitaxial layers are used to evaluate the quality of the transferred layers in terms of thickness uniformity, Ge content, Strain control, dislocation densities etc... Detailed experiments are also used to demonstrate that these final substrates are compatible with future CMOS applications. The sSOI approach is particularly challenging in this respect as the strain needs to be maintained during many technological operations such as layer transfer, selective removal of the SiGe, high temperature thermal treatments etc. First results showing how the strain is changing during such operations are presented. (C) 2004 Elsevier Ltd. All rights reserved.