WET and Siconi® cleaning sequences for SiGe epitaxial regrowth

Abstract

SiGe channels can be used to boost the hole mobility and tailor the threshold voltage shift in advanced p-type Metal Oxide Semiconductor Field Effect Transistors. An efficient removal of SiGe oxides prior to the low temperature Selective Epitaxial Growth (SEG) of SiGe:B in the Sources/Drains regions of such devices is then mandatory. The H2 bake that precedes SEG, carried out at temperatures typically lower than 650 °C to avoid islanding or shape change, requires a very efficient removal of surface contaminants (such as C, F, O…), beforehand. As germanium is very reactive in the air, Siconi® in-situ surface preparation schemes are likely to be of use on SiGe surfaces with such thermal budget constraints. Recently, a new surface preparation strategy based on i) a wet chemical oxide formation followed by ii) a standard NH3/NF3 remote plasma Siconi® process was evaluated. In order to use such a scheme for the fabrication of devices, we study here the impact of that surface preparation on the epitaxial regrowth of Si0.60Ge0.40 on Si0.60Ge0.40 films (in terms of oxygen removal efficiency, resulting morphology and so on). We show that such surface preparations yield drastically reduced interfacial contamination, with surfaces which can be rough after epitaxial re-growth, however. Thanks to an in-depth analysis of the interplay between surface preparation and growth parameters, an innovative process sequence is proposed that yields smooth, high-quality films.