Dependence of electrical properties on nitrogen profile in ultrathin oxynitride gate dielectrics formed by using oxygen and nitrogen radicals

We studied nitrogen incorporation in ultrathin oxynitride films by using ox ygen and nitrogen radicals, and investigated the dependence of the electric al properties on the nitrogen profile. We found that the nitrogen position in the films could be controlled by using different processing sequences, a nd that the N concentration could be controlled at values up to 16%. In thi s process, the interface roughness depends on nitrogen position and nitroge n concentration: the interface roughness tends to increase as the N positio n close to the SiO2-Si interface and increase with N concentration. The res ults of an analysis of the electrical properties of these oxynitride films indicated that the best way to form the film was by radical nitridation aft er radical oxidation. These results show that the nitrogen position should be kept away from the SiO2-Si interface and nitrogen amount should be local ized at the surface. Using this process, we have successfully achieved a lo w-leakage 1.5 nm oxynitride (equivalent oxide thickness) and maintained goo d device performance. This 1.5-nm-thick oxynitride has a leakage current tw o orders of magnitude less than that of 1.5-nm-thick SiO2 without decreasin g the drain current. Radical oxynitridation should thus be very useful in m aking high-quality ultrathin gate-insulator films. (C) 2001 American Instit ute of Physics.