Fabrication of SiN films at low temperature by RF biased coaxial-line microwave plasma CVD

This paper discusses the influence of ion bombardment on the characteristics of SiN films. In this study, the double-tube coaxial-line microwave plasma CVD system, which is suitable for the investigation of ion bombardment, is used to deposit SiN films. The ion bombardment energy is varied by varying the RF bias at constant ion density. As the RF bias is increased, the film density increases and the hydrogen concentration decreases, but the dangling bond density increases. The increase in the film density and decrease of hydrogen concentration are caused by the increase in film surface temperature, while the increase of the dangling bond density is caused by bond breakage due to the N⁺ ion implantation. When the substrate temperature is 200°C and the RF bias is -175 V, the film density is 3 g/cm³ and the hydrogen concentration is 9 at.% because of the film surface heating effect of ion bombardment and also due to substrate heating. Substrate heating at 200°C suppresses the increase in the dangling bond density. It is also demonstrated that the film surface temperature is about 200°C when RF bias is -70∼-80 V and the substrate is unheated by any heater.