Impact of in situ NH3 preannealing on sub-100 nm tungsten polymetal gate electrode during the sealing nitride formation

Abstract

We investigated the effects of in situ NH3 preannealing immediately before sealing nitride deposition on the wordline sheet resistance (R-s) of a tungsten polymetal gate electrode (W/WNx/poly-Si). While in situ NH3 preannealing is very effective for the suppression of W-O whisker formation, it was found that excessively long-time NH3 preannealing could cause an unexpectedly abnormal increase in the wordline R, of short gate length electrodes, typically < 100 nm. Since X-ray diffraction (XRD) and secondary ion mass spectroscopy (SIMS) analyses reveal that long-time NH3 preannealing results in the nitridation of tungsten sidewall surfaces. the wordline R-s increase in a small-gate-length sample subjected to Iong-time NH3 preannealing is mainly due to tungsten sidewall nitridation, which is localized at the surface region of the tungsten sidewall. In addition, at a Iona-time NH(3-)preannealed gate electrode, an abnormal inflation of the tungsten sidewall occurred due to a slight increment in lattice spacing by tungsten nitridation.