Realization of high quality silicon nitride deposition at low temperatures

This work demonstrates the low temperature thin-film deposition of silicon nitride (SiNx) for III-nitride-based high electron mobility transistors using inductively coupled plasma chemical vapor deposition. It is observed that the nonlinear dependency of the deposition temperature and gas flow rates have a profound impact on the film quality. The process parameter space is scanned and the optimum film quality is achieved, which is verified with physical and electrical characterizations. The best quality film is achieved at a deposition temperature of 380 degrees C demonstrating near ideal stoichiometry with negligible hydrogen (<5%) and oxygen (<3%) concentrations. In addition, the optimized film is found to have zero pinholes even at a thickness of 10 nm and is uniform over a large area with an rms roughness of 0.58 nm. The deposited films are characterized by atomic force microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The dielectric strength and dielectric constant of these films are determined from current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the metal-insulator-metal structure, respectively. For the best quality film, the values of dielectric strength and dielectric constant are measured to be similar to 8 MV/cm and similar to 7.5, respectively. A metal-insulator-semiconductor-heterostructure (metal/SiNx/AlGaN/GaN) capacitor is fabricated with the optimized recipe for interface characterization. The density of slow traps is determined from the hysteresis in the C-V curve and found to be 7.38x1010 cm-2. The frequency dependent conductance method is also used to investigate the trap density. The trap state density is found to be 1.67x1012 cm-2 eV-1 at 0.29 eV below conduction band.