Mechanical properties of thin films of hydrogenated silicon and their relationship with microstructure

Thin films of hydrogenated silicon were deposited on glass and single-crystalline silicon substrates using a capacitively coupled radio-frequency plasma-enhanced vapor-deposition system with the help of direct-current bias stimulation. Micro-Raman scattering was applied to investigate the microstructure of the thin films obtained. The crystalline volume fraction, X c, was obtained from the Raman spectra. Microscopic mechanical characterization of the thin films was carried out by nanoindentation based on the conventional depth-sensing indentation method. An analytical relation between X c and the elastic modulus was thereby established. The elastic modulus of the film on a glass substrate was found to be lower than that of the film on a monocrystalline silicon substrate with the same X c. The grain size of a phosphorus-doped thin film was smaller than that of the intrinsic one, with greater ordering of the grains and X c was found to be usually above 40%. A film with boron doping was on the opposite side, with X c usually below 40%. In the phosphorus-doped, intrinsic, and boron-doped films, the elastic moduli were lower when the X c values were 45%, 30%, and 15%, respectively.