Threshold voltage shift instability induced by plasma charging damage in MOSFETs with high-k dielectric

Polarities of plasma charging damage in n- and p-channel MOSFETs with Hf-based high-k gate stack (HfAlOx/SiO₂) were studied for two different plasma sources (Ar-and Cl-based gas mixtures), and found to depend on plasma conditions, in contrast to those with conventional SiO₂. For Ar-plasma, which was confirmed to induce a larger charging damage, both n- and p-ch MOSFETs with high-k gate stacks suffer from negative charge trapping, whereas for Cl-plasma confirmed to induce less damage, both n- and p-ch MOSFETs with high-k gate stacks suffer from positive charge trapping, i.e., the direction of threshold voltage (V_t) shift depends on plasma sources and a amount of charging damage. From the results of constant-current stress tests, the present unique V_t shifts were attributed to the characteristic hole and electron trapping phenomena, implying the necessity of taking the intrinsic charge trapping process into consideration for accurate evaluations of charging damage on high-k gate dielectrics.