Abstract: This invention relates to a surface smoothing method for smoothing the surface of a semiconductor film and insulating film, etc, and a method of forming and SOI substrate by using this surface smoothing method. In this surface smoothing method, the surface of a semiconductor film or an insulating film formed on a substrate is irradiated with an ion beam at an incident angle of about 85.degree. or more, to the normal direction of the surface, while revolving the substrate, whereby the surface is smoothed easily without any contamination thereof or physical deformation of the surface layer.

Abstract: The present invention relates to a method of forming a single crystalline magnesia spinel film on a single crystalline silicon substrate by the use of the vapor-phase epitaxial method.According to the method of the present invention, at first a first single crystalline magnesia spinel layer having a compositional ratio of magnesium maintained at a nearly stoichiometric compositional ratio is epitaxially grown in a vapor-phase on the single crystalline silicon substrate, and then a second single crystalline magnesia spinel layer having a compositional ratio of magnesium which decreases upward is epitaxially grown in a vapor-phase on the first single crystalline magnesia spinel layer. In the event that a Si film is grown on the single crystalline magnesia spinel film formed by the method of the present invention, out of atoms of Mg and Al taken in the Si film in the initial growth stage of the Si film, a concentration of Mg atoms which react more actively upon Si can be reduced.