Pecvd Process Parameters And The Annealing Technique On The Properties Of Silicon Nitride Thin Films

Because of its anti-wearing, high mechanical strength, good insulation, and strong ability to resisitance to alkali metal ions and water erosion, silicon nitride thin films are used as passivation layers, dielectric layers and support layers in MEMS. Plasma enhanced chemical vapor deposition (PECVD) is used as one of the commonly used methods for depositing thin films due to its low deposition temperature, good step coverage capability and high process repeatability.Influences of pressure and power on refractive index (RI), density and stress of silicon nitride films prepared by low frequency (380KHZ) PECVD were thoroughly studied. At the same time, Fourier transform infrared spectrometry (FTIR) were employed to analyze thin film’s components under different preparation conditions. And then the dielectric constants of silicon nitride films, which deposited under four conditions such as different gas flow ratio (SiH4/NH3), power, gas pressure, substrate temperature, are studied, too. In order to improve the performance of silicon nitride films, it is annealed in vacuum. And influences of vacuum annealing on properties of silicon nitride films, including the thickness, refractive index (RI) of silicon nitride films and the etch rate in HF, were studied. Results showed that dielectric constants of PECVD silicon nitride films changed very little at different gas pressure, which maintained at7. But in other deposition conditions dielectric constants of PECVD silicon nitride films changed differently due to its different composition and structure; the thickness of PECVD silicon nitride films after vacuum annealing was related to deposition conditions, the RI of silicon nitride films increased after vacuum annealing, and the etch rate in HF decreased rapidly after that. The results before and after vacuum annealing were analyzed with FTIR.