Effect of External Substrate Heating on Properties of RF Sputter Deposited Silicon Nitride Films

A silicon nitride film was prepared using RF magnetron sputtering. The influence of the sputtering parameters such as RF power, sputtering pressure and external substrate heating (during deposition) on deposition rate, etch rate and residual stress in the films has been investigated. The mechanical properties such as hardness (H) and Young's modulus (E) of silicon nitride film were evaluated using nano-indentation techniques. The highest value of H and E were found to be 33 and 309 GPa respectively, when a load of 5 mN was applied. For this purpose, silicon nitride film was deposited at 300 W RF power and 5 mTorr sputtering pressure with external substrate heating at 250°C. Also, effect of sputtering parameters, especially external substrate heating, was investigated for their effect on structural and optical properties of silicon nitride film. The optical and structural properties of the films were evaluated by ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD) and atomic force microscopy (AFM). To demonstrate the application of prepared silicon nitride film, it was used as a masking layer during boron and phosphorus diffusion process. It was demonstrated through present work that even 50 nm thin film of sputter-deposited silicon nitride can be successfully used as diffusion mask for shallow junction formation. Also, suspended microstructures such as cantilever beams, diaphragms, and bridges were fabricated using silicon nitride films as structural layer for MEMS application.