X-RAY PHOTOELECTRON-SPECTROSCOPY ANALYSES OF OXIDE-MASKED POLYCRYSTALLINE SIGE FEATURES ETCHED IN A HIGH-DENSITY PLASMA SOURCE

The chemical distribution of oxide-masked polycrystalline Si0.45Ge0.55 structures etched using gas mixtures of Cl-2, HBr, and O-2 has been i nvestigated by x-ray photoelectron spectroscopy (XPS). The 200 mm diam wafers were etched in a low-pressure, high-density plasma helicon sou rce. The chemical constituents present on the tops, sidewalls, and bot toms 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 i s no germanium oxide-like formation. Using XPS, the silicon oxide-like layer was estimated to be 11 Angstrom thick on the sidewalls of the p oly Si0.45Ge0.55, with both mixtures. The thinner oxide-like layer mea sured on the sidewalls of polycrystalline Si0.45Ge0.55(11 Angstrom) co mpared to that on the sidewalls of polycrystalline Si (30 Angstrom) de monstrates that the oxide like layer thickness depends on the germaniu m 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 sp ontaneously reacts with oxygen to form volatile etching species.