Issue Providing a silicon film which can prevent damage of electronic devices formed on a substrate from occurrence, can prevent apparatus arrangement from becoming large-scale one, can improve coherency of a silicon thin film to a substrate, and is hardly happened crack and/or flaking, and providing a method for forming the silicon thin film.Solving Means A method for forming a silicon thin film according to the present invention is a method for forming a silicon thin film having isolation function or barrier function, on a substrate K using CVD method, and comprises a step for forming a first thin film on the substrate using plasma CVD method employing gas containing hydrogen element and a gas containing silicon element; a step for forming a second thin film using plasma CVD method employing a gas containing nitrogen element and a gas containing silicon element; and a step for forming a third thin film using plasma CVD method employing a gas containing oxygen element and a gas containing silicon element.