PURPOSE: To manufacture a high quality silicon crystal film at a temperature lower than the conventional case, without using a film forming equipment applying high vacuum.

CONSTITUTION: Mixed gas of SiH4, SiH2F2 and Ar are supplied to the inside of a film forming chamber 11 set in the state of vacuum, and an epitaxial silicon thin film is continuously formed on a silicon single crystal substrate 14 heated at about 650°C. Since the SiH2F2 is easy to be thermally decomposed in the high temperature region in the vicinity of the substrate where a heat filament 20 is arranged, and the decomposition is accelerated by the radical components of SiH4, high density fluorine based radicals locally exist in this region. Hence impurities mixed in a substrate or a growing silicon film are eliminated by the etching action of the fluorine based radicals, so that the substrate heating temperature can be lowered by synergistic effect with the heat filament. On the other hand, since SiH2F2 is hard to be thermally decomposed as compared with SiH4 in the region which is distant from the substrate and of low temperature distribution, generation of floating foreign matter caused by corrosion action of the fluorine based radicals can be restrained.