Correspondence relation between [N-H]/[Si-H] ratio and their optical loss properties in silicon nitride thin films

This work reports a detailed study of hydrogen bonds in the silicon nitride (SiN_x:H) thin films. Plasma-enhanced chemical vapor deposition was used to produce the films under different values of gas flow ratio and radio frequency power, in which SiH₄ and N₂ as the precursors. Hydrogen content of silicon nitride (SiN_x:H) thin films have been investigated by fourier transform infrared spectroscopy. The amount of bonded was calculated from N-H and Si-H infrared absorption bands. When gas flow ratio or radio frequency power changed, the trends of NH bond density and Si-H bond density are exactly opposite, which is explained by a competitive process the formation of N-H and Si-H bonds during the growth of the film. The corresponding optical measurement of waveguides showed the optical propagation loss was lowest at the minimized the sum of hydrogen. It was found that the [N-H]/[Si-H] is nearer to stoichiometric ( [N]/[Si]=1.3), the hydrogen content in the films was lower. The rule of hydrogen content with the ratio of [NH]/[Si-H] is very useful to controlling the films growing for optical material, solar cell and so on.