Effect of gas flow ratio in PE-CVD on elastic properties of sub-micron thick silicon nitride films for MEMS

This paper focuses on revealing the effect of gas flow ratio in PE-CVD on elastic properties of sub micron-thick silicon nitride (SiN_x) films for surface-micromachined MEMS. SiN_x films having a thickness of 0.1 μm to 0.7 μm are deposited on single crystal silicon (SCS) specimens of 10 μm in thickness by changing the gas flow ratio of NH₃´ to SiH₄ in PE-CVD. The atomic force microscope (AFM) tensile testing technique is employed to characterize Young´s modulus and Poisson´s ratio of SiN_x films. The Young´s modulus of SiN_x films range from 102 GPa to 143 GPa, independent of film thickness. A Poisson´s ratio ranging from 0.2 to 0.26 is also obtained from tensile and nano-indentation combined tests. Auger spectroscopy makes it clear that an increase of the atomic content ratio of nitrogen to silicon in SiN_x film yields its higher elastic mechanical properties.