Abstract: A coating solution for forming a silica-based film, having a given viscosity, is coated on a substrate such as a silicon wafer, this coating solution is dried to form a silica-based film, and this silica-based film is exposed to ultraviolet radiation in an atmosphere containing ozone at room temperature or while heating it preferably at a temperature of not more than 300.degree. C., particularly at a temperature of from 50.degree. to 200.degree. C., by means of a heating member such as a hot plate.The film quality of the silica-based film can be improved by exposing it to ultraviolet radiation in the atmosphere containing ozone.

Abstract: The adhesiveness of a silicone-based coating film on a substrate to an overcoating layer, e.g., a photoresist layer, can be improved without causing cracks when the silicone-based coating film is subjected to a plasma treatment at a temperature of 120.degree. C. or below in an atmosphere of a gas mainly composed of oxygen. Similar conditions of plasma treatment are applicable when patterning of a silicone-based coating film is desired in a procedure comprising the steps of forming a photoresist layer thereon, patterning of the photoresist layer in a photolithographic method, selectively etching the silicone-based coating film with the patterned resist layer serving as a mask and removing the photoresist layer by the plasma treatment.

Abstract: The coating solution of the invention is useful for forming a silica-based coating layer on a substrate such as semiconductor silicon wafers in the manufacturing process of semiconductor devices such as VLSIs. The coating solution is particularly advantageous to smooth a substrate surface having a difference in levels by completely filling the recessed areas. The coating solution is an organic solution of a cohydrolyzate of an alkoxy silane mixture composed of at least two kinds of di-, tri- and tetraalkoxy silane compounds such as a combination of methyl trimethoxy silane and tetramethoxy silane in a specified molar ratio and can be prepared by adding water to an organic solution of these alkoxy silane compounds without using any acid catalyst to effect the cohydrolysis of the silane compounds.