Work function control of metal gates by interdiffused Ni-Ta with high thermal stability

By using the Ni-Ta alloys fabricated by interdiffusing stacks of Ni and Ta, we have experimentally investigated the work function (φ_m) controllability and thermal stability required for the advanced metal gate MOSFETs. The capacitance-voltage (C-V) measurement of the interdiffused Ni/Ta and Ta/Ni stacks revealed that the φ_m of the Ni-Ta alloy was changed from that of pure Ni and Ta samples. The φ_m uniformity of the interdiffused Ni-Ta alloy was found to be comparable to that of the pure Ni by observing the microscopic φ_m by scanning Maxwell-stress microscopy. The excellent thermal stability of the interdiffused Ta/Ni stack was revealed up to 900°C. From these experimental results, the Ni-Ta alloy is promising candidate for the metal-gate MOSFETs.