ABSTRACT
SiGe alloys are used extensively for their electrical properties (bandgap engineering by adjusting the Ge
content, carriers mobility improvement). With the progress in deposition by epitaxial growth, a new
application is emerging, based on the crystalline properties of the material. Indeed, from pure Si (x¼ 0) to pure Ge (x¼ 1), any Si1xGex alloy can be deposited on Si with the same crystal structure and the same lattice constant (in the growth plane) as the substrate, provided that it does not exceed the critical
thickness for plastic relaxation (Ec). As a consequence, SiGe can be buried between mono-Si layers
without modifying their conduction properties. This method is used in several advanced microelec-
tronics architectures that require a thin single-crystal Si-film isolated from the substrate by a cavity:
the SiGe layer is used as a sacrificial layer for lateral etching. In this approach, the selectivity is crucial
because both similar materials are exposed to the complete etching process whereas only one has to be
removed.
