Investigation of mechanisms shifting metal effective workfunction towards P+ for various Al incorporation scenarii

Al incorporation in the High-κ/metal gate stack is studied for pMOS transistors application. Al is here incorporated before or after high-k deposition, or during the metal deposition. Using bevelled oxides and Internal photoemission (IPE), we discriminate and quantify the three key mechanisms shifting the effective metal workfunction WF_Meff: (1) a dipole (up to ~1 eV!) build up at the SiO₂/High-κ interface induced by Al diffusion; (2) a reduction of this dipole for small interfacial SiO₂ layer; (3) an opposite shift of the metal workfunction WF_M towards N+ for Metal-Al compounds.