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Abstract

An object of the invention is to remove organic materials and metal impurities on a silicon-based semiconductor substrate while preventing regrowth of a natural oxide film and thermal diffusion of the metal impurities from occurring. In order to achieve the object, H.sub.2 gas that can maintain a reductive atmosphere is consistently used, as a carrier gas, through a whole process, the organic materials in attachment is decomposed by HF gas and the metal impurities are transformed into metal chlorides by HCl gas. In any of treatments, since products whose vapor pressures are higher than those of respective starting materials are obtained, the products are respectively vaporized in a H.sub.2 gas atmosphere at higher temperatures than those at which the decomposition and the transformation are performed. The whole process can be performed in a low temperature range whose upper limit is 1000.degree. C. or lower. In a case where the impurities attach to an oxide film, the oxide film can be removed by HF gas treatment, in a preceding step of a process described above, in the temperature range of lower than 100.degree. C. in which water adsorbed on or occluded in the oxide film can be retained, and in the case, if the HF treatment or the HCl treatment is performed from the initial stage of a process at a temperature of 100.degree. C. or higher with no preceding step, the oxide film can be retained.

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First Claim