Suppression of electrical breakdown in silicon nitride films deposited by catalytic chemical vapor deposition at temperatures below 200 °C

Silicon nitride (SiN _x) films for a gate dielectric layer of thin film transistors were deposited by catalytic chemical vapor deposition at a low temperature (≤200 °C). A mixture of SiH ₄, NH ₃ and H ₂ was used as a source gas. Metal-insulator-semiconductor (MIS) capacitor structures were fabricated for current-voltage (I-V) and capacitance-voltage (C-V) measurements. The breakdown voltage characteristics of the SiNx films were improved by the increase of NH ₃/SiH ₄ and H ₂/SiH ₄ mixing ratios and substrate temperatures. H ₂ treatment was attempted to improve the breakdown voltage further. A breakdown voltage as high as 6.6 MV/cm was obtained after H ₂ annealing at 180 °C. The defect states inside the SiNx films were analyzed by photoluminescence spectra. Silicon dangling bonds (2.5 eV) and nitrogen dangling bonds (3.1 eV) were observed. These defect states inside the SiN _x films disappeared after H ₂ annealing. Flat band voltage shifts were observed in C-V curves, and their magnitudes decreased as the defect states inside the SiN _x films decreased.