The chemical distribution of oxide-masked polycrystalline Si0.45Ge0.55 structures etched using gas mixtures of Cl-2, HBr, and O-2 has been investigated by x-ray photoelectron spectroscopy (XPS). The 200 mm diam wafers were etched in a low-pressure, high-density plasma helicon source. The chemical constituents present on the tops, sidewalls, and bottoms of the etched features were determined by XPS. As for polysilicon, a silicon oxide-like film is formed on the sidewalls of the features when etching with HBr/Cl-2/O-2 and Cl-2/O-2, plasmas, whereas there is no germanium oxide-like formation. Using XPS, the silicon oxide-like layer was estimated to be 11 Angstrom thick on the sidewalls of the poly Si0.45Ge0.55, with both mixtures. The thinner oxide-like layer measured on the sidewalls of polycrystalline Si0.45Ge0.55(11 Angstrom) compared to that on the sidewalls of polycrystalline Si (30 Angstrom) demonstrates that the oxide like layer thickness depends on the germanium con centration in the alloy. XPS also shows that by using the Cl-2/O-2 gas mixture, the germanium of the polycrystalline SiGe sidewalls spontaneously reacts with oxygen to form volatile etching species.