Investigation of Cl2 etch in view of extremely low temperature selective epitaxial processes

Abstract

A Cl2 etch of different group IV materials in a low temperature range (260–600 °C) is presented. It is shown that in general the Cl2 etching behavior is very similar to that of HCl: Si is etched slowest, Ge fastest with SiGe being between these two cases. Activation energies for Cl2 etching of Si, SiGe and Ge are very low and show that neither Cl nor H surface passivation are limiting factors for the etch. The etching rate is strongly affected by the choice of the carrier gas (He, H2 and N2) and by the process pressure which gives high flexibility for its application. As compared to HCl, Cl2 allows decreasing of the etching process temperatures down to ∼400 °C for Si and ∼250 °C for Ge. Although it is not clear if co-flow selective processes are visible due to possible exothermic chain reaction of radicals in the presence of group IV hydrides, cyclic approaches can be relatively easily achieved at temperatures below 500 °C.