Local Bonding Structure of High-Stress Silicon Nitride Film Modified by UV Curing for Strained Silicon Technology beyond 45 nm Node SoC Devices

摘要

Silicon nitride films (p-SiN) with different high stresses were formed by changing the monosilane-to-ammonia source gas ratio, RF power, and deposition temperature in a conventional plasma-enhanced chemical vapor deposition (PECVD). PECVD was used to deposit p-SiN films with high-stresses because it can flexibly change the stress of the film to be formed from tensile to compressive direction. The formed films were analyzed by Fourier transform-infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), nanoindentation, and positron-beam annihilation to obtain data on local bonding structure, mechanical properties and the behavior of vacancies in the p-SiN films. In this study, to clarify the local bonding structure of high stress SiN films, we investigated p-SiN films with and without ultraviolet (UV) curing that is effective in tensile stress. It has been confirmed that total hydrogen (Si-H + N-H) concentration decreases with increasing film stress of p-SiN films. It has been found that UV curing promotes Si-N-Si crosslinking due to dehydrogenization, leading to the formation of a stoichiometric silicon nitride, Si_3N_4, network structure, and the vacancies in the p-SiN films shrink during UV curing. Finally, we proposed a structural model for the local bonding arrangement in p-SiN films with UV curing.