Both the electrical conductivity of silicon nitride films at room temperature and the radius of curvature of a silicon wafer with a silicon nitride film are fairly independent of the deposition temperature and NH3/SiCl4 ratio during silicon nitride deposition. When a certain amount of hydrogen is added to the nitrogen carrier gas, the electrical conductivity decreases. The radius of curvature of a wafer with a film deposited by the SiCl4-NH3 reaction is smaller than that of a wafer with a film deposited by the SiH4-NH3 reaction.