This paper reports nanostructural characteristics and mechanical properties of the PECVD silicon nitride thin films deposited at relatively low temperatures. Nanostructures of the films were examined using high resolution transmission electron microscopy. Chemical bonding structures of the films were studied using Fourier Infrared Transmission Spectrum (FTIR) analysis. Mechanical properties of the films, such as creep behavior and frictional resistance, were investigated using nanoindentation and nanoscratch. The results showed that the variation in deposition temperature significantly affected the mechanical properties of the films, though all the films exhibited to have similar homogenous amorphous structures with no physical defect observed even at atomic scale. There existed strong correlations between the mechanical properties and the hydrogen concentration in the thin films.