Process for producing silicon substrate

The purpose is to provide a process for easily producing at low cost a silicon substrate for use in solar cell production and an acidic etchant for silicon wafers. In the process, uniform irregularities suitable for solar cells are formed in a surface of a wafer of polycrystalline silicon to thereby make a contribution to an improvement in photoelectric conversion efficiency due to the resultant reduction in reflectance, and the polycrystalline-silicon wafer is prevented from staining when etched. This process for producing a silicon substrate for solar cell production is characterized by etching a silicon wafer with an acidic etchant comprising (a) at least one compound selected from the group consisting of halooxoacids and salts thereof, (b) at least one compound selected from the group consisting of hydrogen fluoride and salts thereof, (c) nitric acid and/or hydrogen peroxide, and (d) water to thereby form irregularities in the surface of the silicon wafer. The acidic etchant for silicon wafers comprises the ingredients (a) to (d).