Silicon-hydrogen bonds in silicon oxide films were detected for the first time by applying surface-sensitive X-ray photoelectron spectroscopy and were confirmed by measuring infrared absorption. The areal density of silicon-hydrogen bonds in native oxides formed in a hot solution of HNO3 is estimated to be nearly 2×1014 cm-2, and is much larger than that formed in a solution with a composition of NH4OH:H2O2:H2O=1:1.4:4.
SWhile investigating the surface dependence of the dry cleaning technique using Cl radicals generated with UV irradiation (UV/Cl,), we found that silicon chlorides [SiCl (x = 1 to 4)], etching products created from a reaction between Si and C1 radicals, can remove Fe contaminants. SiCl 4 gas removes Fe contaminants existing on both Si and SiO, surfaces without surface dependence. The surface residue due to the adsorption of SiCl, is insignificant. We also found that a small addition of Cl, to SiC1 4 is advantageous for dry cleaning Si surfaces. Surface flatness and composition are maintained after cleaning with C1, + SiCl 4 (5:195 ml/min) gas mixture. Dry cleaning technology has been significantly improved by the use of an SiCl,-based system instead of Cl1 alone.
The authors propose a new photoexcited silicon-wafer cleaning technique, in which ultraviolet light irradiates the wafer through chlorine gas, followed by thermal treatment in a hydrogen ambient, to grow a high-quality epitaxial layer. The surface metal contaminants were removed through a thin native oxide without damaging the surface by photoexcited cleaning, and the remaining volatile chloride after the photoexcited cleaning at 150°C was removed by thermal treatment at 900°C. Further thermal treatment at 980°C removed even the thin native oxide and then made it possible to grow an epitaxial silicon layer. The SiO2 film formed using a conventional technique on the epitaxial silicon layer showed improved breakdown fields and a decrease of fixed-charge density. The results mean that a high-quality silicon-epitaxial layer has been realized by the cleaning procedure.
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