Abstract: A method for forming a smooth borophosphosilicate glass film on a semiconductor substrate is described, in which a semiconductor substrate having at least one stepped portion thereon is formed with one side of the substrate a borophosphosilicate glass layer having a defined boron content and a defined phosphorus content with a defined total content of the boron and phosphorus. The layer is subjected to thermal treatment under conditions of a temperature of not lower than 940.degree. C. and a time of not shorter than 15 minutes in an atmospheric gas supplied at a flow rate of not lower than 19 liters/minute. As a result, the BPSG glass layer is smoothed on the surface thereof without formation of undesirable grains on the surface. This thermal treatment is particularly suitable for fabrication of a semiconductor element or device using an insulating film of the borophosphosilicate glass.

Abstract: According to the present invention, an SOI film of a monocrystalline silicon film is formed by making solid phase epitaxial growth of an amorphous silicon layer formed on an oxide film. A through hole portion formed in the oxide film is formed in such a shape that an epitaxial growth region growing with the through hole portion as a nucleus covers the entire region of the amorphous silicon layer. After the SOI film is formed, oxygen ions are ioin-implanted into the through hole portion in the oxide film, to be embedded by an oxide film layer by thermal processing.