FORMATION OF FILM

PURPOSE:To obtain a thin film at an arbitrary high impurity concentration by executing the following alternately: a process where a gas for film formation use and a gas for doping use are supplied to an atmosphere to be treated and a low-concentration layer whose impurity concentration is low is formed; and a process where a high- concentration layer whose impurity concentration is high is formed. CONSTITUTION:A process to supply a gas for film formation use and a process to stop the gas are executed alternately. Then, a polysilicon film 14 as a low- concentration phosphorus layer with which phosphorus at a low concentration has been doped and whose film thickness is at 2500Angstrom , a high-concentration phosphorus layer 15 which is composed of only phosphorus in this example and whose film thickness is thin at a thickness of, e.g. several Angstrom and a polysilicon film 16 as a low- concentration layer whose film thickness is at 500Angstrom are laminated on the surface of an SiO2 film 13 on a semiconductor wafer W as an object to be treated. This laminated body is heat-treated in an annealing furnace at 900 deg.C for 20 minutes. Then, the phosphorus inside the high-concentration phosphorus layer 15 is diffused to the low-concentration phosphorus layers 14, 16 on both sides, and a high-concentration phosphorus-doped polysilicon film whose film thickness is at 3000Angstrom can be obtained.