Fabrication of poly-Si thin film transistors using sputter-deposited gate SiO2 films

Physical and electrical properties of sputter-deposited SiO2 films were investigated. Quality of SiO2 film is substantially improved using Ar and O-2 mixture as a sputtering gas. Effective dielectric breakdown strength appears to be enhanced by reducing oxide thickness, probably due to the reduction of roughness of poly-Si/SiO2 interfaces. The breakdown electric field in thin oxides (similar to 100 Angstrom) is about 8 MV/cm, which is comparable with that of thermally grown SiO2. The poly-Si TFT's using sputter-deposited gate SiO2 were fabricated with low temperature processes (<600 degrees C), and their device performances were investigated as a function of gate oxide thickness. The reduction of gate oxide thickness linearly lowers the threshold voltage and subthreshold slope, which can be explained in terms of increased oxide capacitance. The poly-Si TFT's with 100 Angstrom-thick gate oxides shows good device characteristics; threshold voltage of 4 V, substreshold slope of 500 mV/dec, and field effect mobility of 35 cm(2)/Vs. The improvement of TFT performance by thin gate oxide is considered to be amplified, when it comes along with enhancement of crystalline quality of active poly-Si layers.