Mesoscopic mechanical characterization of hydrogenated silicon thin film and the intrinsic relationship with the microstructure

Abstract

Hydrogenated silicon films were deposited on glass and single crystalline silicon substrate in a capacitively coupled radio-frequent plasma enhanced vapor deposition system aided by direct current bias excitation. Hydrogenated silicon films are used to realize a silicon material that consists of a two-phase mixture of amorphous and ordered silicon. Micro-Raman scattering is employed to investigate the thin film microstructure. The crystalline volume fraction (Xc) is obtained from the Raman spectra. Mesoscopic mechanical characterization of the thin film is done by nanoindentation based on the conventional depth-sensing indentation method. An analytical relation between Xc and elastic modulus is established. It is shown that the elastic modulus of the film on glass substrate is lower than that on silicon with the the same Xc. The grain size of phosphorus doped thin film is smaller than that of the intrinsic one and more ordered. The Xc is usually above 40%. The film with diborane doping is on the opposite, the Xc of which is usually below 40%. For P-doped, intrinsic and B-doped fims, when the Xc values are 45%, 30% and 15%, respectively, the values of elastic modulus are minimal.