Faceting and nanostructure effects in Si and SiGe epitaxy

Epitaxy in Si technologies has to be integrated in the flow of fabrication; in most cases, it has to be selective and deposition takes place in extremely small patterns.In a first part, Si or SiGe epitaxy faceting is presented and discussed. Today, the global view is that, at first order, faceting is a kinetic phenomenon, controlled by deposition kinetic anisotropies. On the contrary, in a second part we show that highly faceted structures tend to decrease their surface energy by thermal rounding and that this phenomenon is very important when considering very small (20–40 nm) patterns.The main part reports on the combination of faceting with small size effects. Experiments consist in depositing Si0.72Ge0.28 selectively in very narrow (35–80 nm) lines oriented either along < 110 > or < 100 > crystal axis on (100) Si wafers. Preliminary observations clearly demonstrate an important {100} faceting that is often not observed or reported in literature. Our results also evaluate the lateral overgrowth of selective epitaxies. < 110 >-oriented lines lead to a certain lateral epitaxial overgrowth that is limited by {111} facets whereas epitaxies in < 100 > lines present a much larger (> 2 times) overgrowth bordered by {100} facets.Finally, we demonstrate that the edge effects have to be taken into account. Firstly, the amount of epitaxial material deposited in narrow lines depends on the line orientation, and then we propose the concept of “anisotropic loading effect”. Secondly, we found that deposition rates in small patterns are not constant with time. This corresponds to “time-nonlinear loading effects” that were never conceptualized in literature.