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 SiH₄, NH₃ and H₂ 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 SiN _x films were improved by the increase of NH₃/SiH₄ and H₂/SiH₄ mixing ratios and substrate temperatures. H₂ treatment was attempted to improve the breakdown voltage further. A breakdown voltage as high as 6.6 MV/cm was obtained after H₂ annealing at 180 °C. The defect states inside the SiN _x 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 H₂ 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.