Influence of Gas Flow Ratio in PE‐CVD Process on Mechanical Properties of Silicon Nitride Film

This paper investigates the influence of gas flow ratio in the preparation of submicron‐thick silicon nitride (SiN_x) films on their elastic properties. SiN_x films with a thickness ranging from 0.14 to 0.69 µm were deposited by plasma‐enhanced chemical vapor deposition (PE‐CVD) onto 10‐µm‐thick single‐crystal silicon (SCS) specimens by changing the gas flow ratio of monosilane (SiH₄) to ammonia (NH₃) to nitrogen (N₂). A uniaxial tensile tester operated under an atomic force microscope (AFM) characterized the Young's modulus of SiN_x films and the fracture strength of SiN_x/SCS laminated specimens. The Young's modulus of SiN_x films ranged from 99.5 to 144.3 GPa, which increased with the gas flow ratio but was independent of the film thickness. Nano‐indentation tests were also carried out to examine the Poisson's ratio of SiN_x films in addition to the tensile tests. The Poisson's ratio was found to be 0.19 to 0.27, on average. Auger spectroscopy revealed that an increase of the atomic content ratio of nitrogen (N) to silicon (Si) in SiN_x films yielded higher elastic constants of the films. © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.