Work Function Engineering Within a Single Metal Gate Stack: Manipulating Terbium- and Aluminum-Induced Interface Dipoles of Opposing Polarity

In this paper, a systematic study on combining n-type and p-type interface dipoles for metal gate work function (Phi_m) engineering within the same gate stack was conducted. Ultrathin terbium (Tb) and aluminum (Al)-based interlayers (ILs) were utilized for n- and p-type dipole formation, respectively, to modulate the net interface dipole magnitude and polarity within a metal gate stack. By controlling the net interface dipole through Tb- and Al-based ILs, continuous TaN Phi_m tunability of ~ 0.7-0.8 eV (after either a 500degC or 950degC anneal) on SiO₂ dielectric was attained. The reversal of net interface dipole polarity was demonstrated using both TaN/SiO2 and TaN/high-kappa gate stacks by varying IL metal species and anneal conditions. A convenient way in reversing a Tb-induced (n-type) dipole through Al-incorporation via the TaN metal gate using a ldquogate-firstrdquo process is also shown. The dominant dipole that results in the metal gate stack hinges critically on the reactions of Al and Tb with SiO₂ (or underlying SiO₂ for high-kappa stacks) for Al-O-(Si) and Tb-O-Si bond formation, respectively. This concept of manipulating interface dipoles of opposing polarity for metal gate Phi_m tunability could open up new avenues for achieving multiple Phi_m using a single metal gate and a simple integration scheme.