A study of stacked PECVD silicon nitride films used for surface micromachined membranes

Silicon nitride stacked films containing three layers differing in mechanical-chemical properties are synthesized using plasma enhanced chemical vapor deposition method from monosilane (SiH4) and ammonia (NH3) mixture. The composition is analyzed using X-ray Photoelectron Spectroscopy and stress is measured using a substrate bending method. The ability to obtain stacked films with the custom tensile stress in the overall structure was demonstrated by the series of experiments. The tensile stress in the top and bottom films was obtained between 200 and 300 MPa whereas the stress in the middle film could be adjusted from compressive 60 MPa to tensile 300 MPa. Since the appropriate stress value is important in achieving required mechanical properties of the membranes, the results obtained are discussed in the context of surface micromachined membrane structures