Boron and phosphorus ions are implanted in order to control the internal stress and Young’s modulus of 200‐nm‐thick silicon nitride and polycrystalline silicon films prepared by low‐pressure chemical vapor deposition. These ions are implanted into the middle layer of the films at doses of 1×1014 and 1×1015/cm2, then the films are annealed at 900 °C. The internal stress and Young’s modulus of these films are measured by a rectangular membrane load deflection technique [Tech. Digest, IEEE Micro Electromechanical Systems Workshop, IEEE, Salt Lake City, UT, 1989, p. 152]. Both internal stress and Young’s modulus of the silicon nitride film decrease with dose, while those of the polycrystalline silicon film do not necessarily decrease.