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 WFMeff: (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 WFM towards N+ for Metal-Al compounds.