As the insulating film 102, a single layer structure or a multilayer structure of insulating films containing nitrogen or oxygen such as silicon oxide (SiOx), silicon nitride (SiNx), silicon oxynitride (SiOxNy) (x>y), or silicon nitride oxide (SiNxOy) (x>y) formed by a sputtering method, an LPCVD method, a plasma CVD method or the like, can be employed.