Selective etching of silicon in preference to germanium and Si0.5Ge0.5

摘要

At 50 °C and 760 mTorr, Si may be etched in preference to Ge and SiGe with an essentially infinite Si:Ge etch rate ratio (ERR), while for Si:SiGe, the ERR is also infinite at 22 °C and 760 mTorr. XPS data shows the selectivity is due to differential suppression of etching by a ~2 ML thick CHF layer formed by the H/CF/Ar plasma on Si and Ge or SiGe. The data is consistent with the less exothermic reaction of fluorine radicals with Ge or SiGe being strongly suppressed by the CHF layer, while on Si the CHF layer is not sufficient to completely suppress etching. Replacing H with D in the feed gas results in an inverse kinetic isotope effect (IKIE) where the Si and SiGe etch rates are increased by ~42× with retention of significant etch selectivity. The use of D/CF/Ar instead of H/CF/Ar results in less total carbon deposition and eliminates fluorocarbon deposition on Si and SiGe, and gives less Ge enrichment of SiGe. This is consistent with the selectivity being due to the differential suppression of etching by an angstrom scale carbon layer.