Electrical and structural properties of TaN gate electrodes fabricated by wet etching using NH₄OH/H₂O₂ solution and Hf metal hard mask

We fabricated TaN gate electrodes on SiO₂ film by wet etching using NH₄OH/H₂O₂ solution and investigated the electrical and structural properties of the TaN/SiO₂ interfacial layer. Hf metal was used as a hard mask for the wet etching of the TaN film. It was found that the gate patterning of the TaN film was successfully achieved by wet chemical etching, which should be applicable for dual-metal-gate fabrication. The effective fixed charge density (Q_eff) into the SiO₂ film and the effective work function (Φ_m,eff) of TaN remained constant after N₂ annealing at temperatures of up to 750°C but increased after annealing at 900°C. The analysis by X-ray photoelectron spectroscopy (XPS) indicated that Ta oxide was formed near the TaN/SiO₂ interface after the annealing at 900°C. The increases in Q_eff and Φ_m,eff are discussed on the basis of the XPS results.