Method for forming film and manufacture of semiconductor device

The present invention relates to a film forming method for forming a planarized interlayer insulating film to cover wiring layers, etc. of a semiconductor integrated circuit device, and a semiconductor device manufacturing method using such film forming method. The film forming method comprises the steps of forming on a substrate 206, a phosphorus-containing insulating film 45a which contains P2O3 by using a film forming gas in which an oxidizing gas is added into a gas mixture including phosphorus-containing compound, which has III valence phosphorus and in which oxygen is bonded to at least one bond of the III valence phosphorus, and silicon-containing compound, or by using said film forming gas from which the oxidizing gas removed, heating the phosphorus-containing insulating film 45a while applying acceleration to the phosphorus-containing insulating film 45a to fluidize the phosphorus-containing insulating film and thus planarize a surface of the phosphorus-containing insulating film 45b while the phosphorus-containing insulating film 45a has a predetermined viscosity, and heating further the phosphorus-containing insulating film 45b after the surface of the phosphorus-containing insulating film 45b has been planarized, to sublimate P2O3 in the phosphorus-containing insulating film 45b and thus solidify the phosphorus-containing insulating film 45b.