Metal-gate work function modulation using hafnium alloys obtained by the interdiffusion of thin metallic layers

Abstract

Metal-gate work function m modulation using Hf alloys was achieved by the interdiffusion of bilayer metallic films each with a thickness of less than or equal to 10 nm. For a bilayer stack comprising a Hf layer on a Ni layer, varying the HfNi metal thickness ratio from 0 (single-layer Ni stack) to 1.4 achieved m tunability from 4.74 to 4.2 eV after forming gas anneal (FGA) at 420°C. Interdiffusion in HfPt stack and PtPt-Hf stack was also explored, and the largest m shift of ∼0.5 eV from single-layer Pt and Pt-Hf stack, respectively, was obtained after annealing at 700°C for 30 s. The observed m shift correlated to the extent of metal interdiffusion and was found to be strongly dependent on the metal thickness and anneal temperature. The HfPt stack was further employed to demonstrate m tunability of thin interdiffused metal layers on HfO2 and HfLaOx high- k gate dielectrics. Through process optimization, the interdiffusion of thin metallic layers allows precise dual-gate m control for advanced transistors. © 2007 The Electrochemical Society.