An impurity region is formed in a surface of a substrate by exposing the substrate to a plasma generated from a gas containing an impurity in a vacuum chamber. In this process, a plasma doping condition is set with respect to a dose of the impurity to be introduced into the substrate so that a first one of doses in a central portion and in a peripheral portion of the substrate is greater than a second one of the doses during an initial period of doping, with the second dose becoming greater than the first dose thereafter.