Nitriding of Silicon in RE Discharge

Abstract

Nitriding of silicon wafer was carried out in a nitrogen or nitrogen-hydrogen plasma generated by an rf discharge. The specimen of 20×10 cm2 cut from p type (100) oriented CZ wafer of 400μm in thickness was set in the quartz tube and reacted with nitrogen or nitrogenhydrogen plasma. The specimen was set apart from the coil and heated at 800°C with an electric furnace. The pressure and the rf power were maintained at 10 Torr and 300 W, respectively.
When silicon wafer was reacted with nitrogen plasma for specified period up to 8 h, no nitriding was observed and SiO₂ was formed on the surface. The film thickness formed on the silicon wafer fluctuated between 60∼500Å and the refractive index was 1.5∼1.6. When the silicon wafer was reacted with nitrogen-hydrogen plasma up to 8 h, the nitriding was succeeded. The refractive index was 2.0±0.1 and was approximately equal to that of silicon nitride obtained by the chemical vapor deposition. Infrared spectra of films obtained after the nitriding were measured. For the sample obtain-e-d- by nitriding with nitrogenhydrogen plasma, only peaks based on Si-N bonds were observed. The peaks based on Si-0bonds observed in the film obtained with the nitrogen plasma was disappeared.
The kinetics of nitriding of silicon wafer with nitrogen hydrogen plasma varied in course of nitriding. The reaction between the gas phase and the silicon wafer may be the rate determining step in the early stage of the reaction. In the case of longer reaction time, the diffusion of nitrogen may be the rate determining step.
From the plasma diagnostics, N₂ and N, + were identifi ed in the nitrogen plasma and N₂N₂+, NH and H were identified in the nitrogen-hydrogen plasma. When hydrogen w as added into the nitrogen plasma, N₂+ ion was substantially decreased by the formation of nitrogen-hydrogen molecules or molecular ions and the sputtering of SiO₂ by N₂+ was suppressed and the nitriding of silicon was successful.