Silicon Germanium as a novel mask for silicon deep reactive ion etching

This paper reports on the use of p-type polycrystalline Silicon Germanium (poly-Si_1-xGe_x) thin films as a new masking material for cryogenic silicon deep reactive ion etching (DRIE). The proposed masking material can be deposited at CMOS backend compatible temperatures and demonstrates high etching selectivity towards silicon (>;1:270). Moreover, SiGe etches 37 times faster than SiO₂ or SiN masks in SF₆/O₂ plasma resulting in a major reduction in the processing time without the need for a dedicated etcher. Selectivity tests revealed that the etching selectivity of the SiGe mask towards silicon strongly depends on the Ge content, boron concentration and etching temperature. This was attributed to chemical and thermodynamic stability of the SiGe film, as well as the electronic properties of the mask.