The effect of nitrogen pre-annealing on the sidewall oxidation of WSix and on the related electrical properties of WSix /poly Si gate structure

N₂ pre-annealing at 900°C for 20 minutes was effective to suppress undesirable sidewall oxidation of WSi_x in a tungsten polycide gate structure during post oxidation processing. Contact resistance measurements show that the N₂ pre-annealing improved the metal contact resistance on the gate while it degraded the tungsten polycide contact resistance on the gate. The contradictory effects on two contact resistances on the gate are attributed to Si out-diffusion from dichlorosilane-based tungsten silicide (DCS-WSi_x) during N₂ pre-annealing. From experiment and simulation data, it is verified that the additional thermal budget of N₂ pre-annealing does not affect the device parameters of n- or p-MOSFETs at gate length L=10 μm. It is considered that the segregation of fluorine (F) atoms from DCS-WSi_x on to the gate oxide caused the increase in threshold voltage (V _T), the reduction of saturation current (I_DSAT), and the increase in subthreshold slope of n-MOSFETs. However, no significant changes were observed in p-MOSFETs. On the other hand, the gate oxide characteristics were not degraded by N₂ pre-annealing