Effect of Al doping on the reliability of ALD HfO₂

This work has demonstrated a high quality HfO₂ based gate stack by depositing atomic layer deposited (ALD) HfAlO_x along with HfO₂ in a layered structure. In order to get multifold enhancement of the gate stack quality both Al percentage and distribution were observed by varying the HfAlO_x layer thickness and it was found that < 2% Al/(Al+Hf)% incorporation can result in up to 18% reduction in average EOT along with up to six fold reduction in gate leakage current as compared to the dielectric with no Al content. On the other hand, excess Al presence in the interfacial layer moderately increased the interface state density (D_it). When devices were stressed in the gate injection mode at a constant field stress dielectrics with Al/(Hf+Al)% ∼ 2% showed resistance to stress induced flatband voltage shift (δV_FB), and stress induced leakage current (SILC). The time dependent dielectric breakdown (TDDB) characteristics of these devices showed a reduced charge to breakdown and an increase in the extracted Weibull slope (β]) that further confirms an enhanced dielectric reliability.