Physical Characterization of the Metal/High-k Layer Interaction upon Annealing

The replacement of poly-silicon by metallic compounds in the gate stack leads to the search of metals with suitable work function. However, it is observed that thermal budget has a large influence on the effective work functions of several metals. In this paper, we investigated the possible modification of the chemical states by physical analysis techniques (XPS, XRR, MEIS, TOF-SIMS) by studying the chemistry of the high-k oxide/metal interface. We show that in the case of the TiN/TaN/HfO2/SiO2/Si stack, several modifications occur upon 1000oC N2 annealing: Increase of the nitrogen content of the TaN, interdiffusion of the Ti and TaN, and formation of Ta2O5 at the TaN/HfO2 interface.