Investigation of the extinction coefficient of PECVD hydrogenated amorphous silicon nitride films

In order to study the infrared absorption characteristics of hydrogenated amorphous silicon nitride (a-SiNx:H) films prepared by plasma-enhanced chemical vapor deposition (PECVD), the influence of process parameters on the extinction coefficient (EC) of a-SiNx:H films is investigated in the spectrum from 714 to 1250 cm−1. In our experiments, the EC at Si–N stretching frequency ranges from 1.32 to 2.27 and the corresponding peak wave number shifts from 828 to 890 cm−1 by adjusting process parameters. The results show that the enhanced HF power and substrate temperature are the most important parameters for increasing the EC of the film, and increased NH3/SiH4 gas flow ratio is the key to the blueshift of peak wave number. Finally, the adjusted process parameters of a-SiNx:H film for application in an infrared focal plane array are selected: SiH4:NH3:N2 = 2:3:100, HF power: 45 W, LF power: 35 W, pulse time: HF/LF pulse time = 0.6, temperature: 350 and pressure: 650 mTorr.