The present invention has as an object, the provision of a manufacturing method for a
semiconductor gas-phase epitaxial
wafer which achieves the extremely high
wafer flatness demanded in line with making wafers larger in size and heightening device
process integration levels, and which forms either a backside CVD film or a
thermal oxide film required as a gas-phase epitaxial
wafer, and solves problems related thereto. More particularly, it achieves the high flatness and low
processing deformation required by a large-
diameter wafer, and makes it possible to enhance yield in the device process. In a manufacturing method for a
semiconductor gas-phase epitaxial wafer, which enables a thin, disc-shaped wafer to be sliced from a single-
crystal ingot, a required surface to be finished to a mirror surface, and an epitaxial layer to be formed on the main surface, that introducing into the above-mentioned manufacturing method a two-sided
polishing process for
polishing both the front and back surfaces of a wafer; a process for forming either a CVD film or a
thermal oxide film on the backside of a wafer; and a one-sided mirror-finish
polishing process for polishing the main surface of a wafer enables the realization of the extremely high wafer flatness demanded by a large-
diameter wafer, while preventing autodoping.