FTIR Analysis of Microwave-Excited PECVD Silicon Nitride Layers

This paper presents infrared absorption (FTIR) measurements of SiN layers and correlates them to their ability to passivate silicon wafer surfaces. The best passivation was obtained for films having a nitrogen to silicon atomic composition in the proximity of N/Si=1.2, together with a high concentration of Si-N bonds (approximately 1times10²³ cm^-3) and a refractive index in the vicinity of n=2. The total hydrogen concentration in these films remained practically unchanged after a high temperature firing cycle, which indicates a good thermal stability. In contrast, silicon rich layers (higher refractive index and lower Si-N bond density) suffered a large reduction in the total hydrogen content. These results support the suggestion by ECN researchers that the Si-N bond concentration can be a good indicator of the ultimate electronic impact of the SiN layers