Applications of rapid thermal process to nitridation of tungsten and denudation of WN/sub x/ for poly-Si/Metal gates

To reduce gate RC delay in sub-100 nm CMOS devices, a poly-Si/metal gate electrode stack, consisting of W/barrier/poly-Si layers has become an attractive candidate. Recent studies show that rapid thermal annealing (RTA) of amorphous WN/sub x//poly-Si resulted in denudation of nitrogen atoms with simultaneous in situ formation of low resistivity W and highly reliable barrier layer. This process indicated some advantages, i.e. there is no need for barrier interface, yet device properties superior to those of conventional W/WN/sub x//poly-Si gate has been achieved. The purpose of this paper is to report a study of tungsten nitridation and WN/sub x/ denudation using RTP in various gas ambients, including N/sub 2/, Ar, forming gas (10% H/sub 2/ in Ar), wet H/sub 2/ (16% H/sub 2/O in H/sub 2/) and NH/sub 3/. RTA in a spike fashion in NH/sub 3/ or wet H/sub 2/ for only 2 seconds was used to convert 50 nm WN/sub x/ to pure W. Auger electron spectroscopy (AES) studies indicated that the in situ interface barrier formation with high nitrogen content was completed during the denudation of WN/sub x/.