Applications of rapid thermal process to nitridation of tungsten and denudation of WNx 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_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_x/poly-Si gate has been achieved. The purpose of this paper is to report a study of tungsten nitridation and WN_x denudation using RTP in various gas ambients, including N₂, Ar, forming gas (10% H₂ in Ar), wet H₂ (16% H₂O in H₂) and NH₃. RTA in a spike fashion in NH₃ or wet H₂ for only 2 seconds was used to convert 50 nm WN_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_x.