Amorphous silicon nitride thin films were deposited at low temperature using the inductively coupled plasma enhanced chemical vapor deposition (ICP-CVD). $N_2$ and $SiH_4$ gases were used as reactant gases for deposition of the films in order to reduce the hydrogen content. The hydrogen content in the films were quatitatively analyzed using FTIR. The variation of refractive index and optical absorption of the films as a function of deposition parameter were investigated.
As $N_2$ flow rate and RF power increase and substrate temperature is lowered, N/Si ratio is reduced producing higher refractive index and optical band gap of the films. The variation of $N_2$ flow rate and RF power mainly induces the increase of N-H bond causing the increase of Urbach energy without significant change of the total hydrogen content. Hydrogen content of the films are much less than those of the films deposited by conventional PECVD using $SiH_4$/$N_2$ gases since $N_2$ gas is used for $NH_3$ gas. However, all the hydrogen configurations and total hydrogen content decrease with increasing substrate temperature due to the release of hydrogen at high temperature. Therefore, Urbach energy decreases with increasing substrate temperature.
