A method for forming an amorphous thin film comprises: forming a seed layer on a surface of a base by supplying aminosilane-based gas on the base; forming the first boron-doped amorphous thin film by supplying the first source gas including boron-based gas on the seed layer; and forming the second boron-doped amorphous thin film by supplying the second source gas including boron-based gas on the first amorphous thin film.