Abstract
N-channel metal gate metal oxide semiconductor field effect transistors (MOSFET) with Ta2O5 gate oxide are fabricated. The Ta2O5 films are deposited by plasma enhanced chemical vapor deposition system. The Capacitance-Voltage, Drain current-Drain voltage and Drain voltage-gat voltage characteristics are measured. The electron mobility obtained from gm plot was 333 cm^2/V·s at gate voltage is 0.35V. The subthreshold swing was 73 mV/dec.The hot carrier effects are studied now. The barrier potential height of Ta2O5/Si is determined by using the lucky electron model. A value of barrier height = 0.86 eV is obtained by assuming an impact ionization energy of impact ionization is 1.3 eV. And Ta2O5/Si electron barrier height equation is: Φb=0.86-(1.94×10^-4)Eox^0.5-(6×10^-6)Eox^2/3。Meanwhile, there are two different slope values in log (gate current / drain current) vs. log (substrate current/ drain current) plot. The slope of log (gate current / drain current) vs. log (substrate current/ drain current) plot m = 0.44 ~ 0.6.When drain voltage is below the transition point, the gate current is dominated by thermionic emission current due to the electron barrier height of Ta2O5/silicon is only 0.86 eV. When drain voltage is above the transition point, the impact ionization probability increase in the velocity saturation region and the gate current increases due to impact ionization hot electron. The slope of log (gate current / drain current) vs. log (substrate current/ drain current) plot m = 0.92 ~ 1.08. The interface trapped charge, the surface recombination velocity and the minority carrier lifetime in the field-induced depletion region measured from gated-diodes are 9.5×10^12cm^-2 eV-1, 780 cm/s and 3×10^-6 s, respectively. Comparison with conventional MOSFETs with SiO2 gate oxide was made. It shows that the surface properties of Ta2O5 transistors are worse than SiO2 transistors. Two comparison experiments are also carried out for MOSFETs with and without (i) a rapid thermal annealing at 800 oC and (ii) a channel hot carrier stress. The degradation of the interface trapped charge density and the surface recombination velocity due to RTA at 800 oC for 1 min. and the stress were studied.