Oxidation of Ni(Pt)Si by molecular vs. atomic oxygen

摘要

X-ray photoelectron spectroscopy (XPS) has been used to characterize the oxidation of a clean Ni(Pt)Si surface under two distinct conditions: exposure to a mixed flux of atomic and molecular oxygen (O + O_2; P_(O+O2) =5 × 10~(-6)Torr) and pure molecular oxygen (O_2: P_(O_2) =10~(-5)Torr) at ambient temperatures. Formation of the clean, stoichiometric (nickel monosilicide) phase under vacuum conditions results in the formation of a surface layer enriched in PtSi. Oxidation of this surface in the presence of atomic oxygen initially results in formation of a silicon oxide overlayer. At higher exposures, kinetically limited oxidation of Pt results in Pt silicate formation. No passivation of oxygen uptake of the sample is observed for total O + O_2 exposure <8 x 104 L, at which point the average oxide/silicate overlayer thickness is 23 (3) A (uncertainty in the last digit in parentheses). In contrast, exposure of the clean Ni(Pt)Si surface to molecular oxygen only (maximum exposure: 5 × 10~5 L) results in slow growth of a silicon oxide overlayer, without silicate formation, and eventual passivation at a total average oxide thickness of 8(1) A, compared to a oxide average thickness of 17(2) A (no silicate formation) for the as-received sample (i.e., exposed to ambient.) The aggressive silicon oxidation by atomic oxygen, results in Ni-rich silicide formation in the substrate and the kinetically limited oxidation of the Pt.