Thermal expansion coefficients and composition of sputter-deposited silicon oxynitride thin films

Modern technology is heavily reliant on silicon dioxide and silicon nitride thin films. These films have many electronic and optical applications, and in some cases silicon oxynitride films of intermediate composition are desirable. We have systematically deposited several SiOxNy films by magnetron sputter deposition and thoroughly investigated their composition with Rutherford backscattering spectrometry and optical measurements. The as-deposited stress in these thin films was also measured and all were found to be compressive. Temperature-dependent stress measurements up to 450 °C were then used to extract the biaxial modulus and coefficient of thermal expansion for each SiO_xN_y . The SiO₂-like films exhibit negative thermal expansion, which is consistent with a strong but porous structure. Increasing the nitrogen content results in the thermal expansion coefficient increasing towards values reported elsewhere for Si₃N₄.