Photoemission investigation of Ge and SiGe alloy surfaces after reactive ion etching

Photoemission spectra were obtained from Ge surfaces after reactive ion etching with CF4 and CF4/H2 mixtures. These measurements indicate a surface layer of fluorinated Ge species as well as adsorbed carbon and CFx species. The shifted intensity in the Ge(2p3/2) core level suggests a layer of about 1 to 2 layers of GeFx, with x∼2–3. The accumulation of CFx overlayer increases with increasing H2 to CF4, but comparisons with Si etched under identical conditions indicate that there is less steady-state film deposition of Ge during reactive ion etching than on Si. Thus, an increased thickness of carbonaceous overlayer on Ge compared to Si is unlikely to be the explanation for the observed drop in the selectivity toward etching Ge over Si with increasing hydrogen addition. Reactive ion etching of a Si35Ge65 alloy was also investigated. Here, photoemission indicated a surface layer of GeFx similar to that found on pure Ge, but little evidence of SiFx species. The composition of the surface is enriched in Ge for about 3–5 layers.