Suppression of abnormal oxidation of WSi_x/P-doped Si stack gate electrode during gate re-oxidation by additional nitrogen ion implantation

We developed an additional nitrogen ion implantation process to suppress the abnormal oxidation of polycrystalline WSi_x/P-doped Si stack gate electrode during gate re-oxidation around 750°C. The abnormal oxidation was attributed to oxidation during gate re-oxidation, resulting in deformation of the gate electrode profile. A method to suppress the abnormal oxidation is to employ pre-annealing in nitrogen ambient over 850°C before gate re-oxidation; however, it leads to unstable pMOSFETs due to high thermal budget. Thus, we introduced the nitrogen implantation (N⁺ 10 keV/5×10¹⁵ cm^-2) prior to gate re-oxidation to improve the oxidation resistance of WSi_x. The abnormal oxidation of WSi_x was effectively suppressed by nitrogen ion implantation. Moreover, the additional nitrogen ion implantation did not degrade gate oxide integrity (GOI)