Atomic layer deposition of HfO2 thin films on ultrathin SiO2 formed by remote plasma oxidation

Abstract

An ultrathin SiO2 layer was grown on a H-terminated Si substrate by using remote plasma oxidation. The subsequent HfO2 deposition on the ultrathin SiO2 was achieved by a remote plasma atomic layer deposition (RPALD). During the HfO2 film deposition and rapid thermal annealing (RTA), the ultrathin SiO2 buffer layer effectively suppressed the formation of Hf silicate layers in the interfacial region. The Hf silicate layer in the interfacial region grew with increasing RTA temperature. The positive fixed oxide charges in the HfO2 film were reduced with increasing RTA temperature. The thickness of the HfO2 films with an ultrathin SiO2 buffer layer showed a lower effective fixed oxide charge density (Q(f),(e) (f) (f)) due to the shift of the flat band voltage (V-FB) toward the positive direction, compared to those with H-terminated Si. The thin interfacial layer of the HfO2 films with a thin SiO2 buffer layer resulted in a low equivalent oxide thickness (EOT) value. The leakage current densities of the HfO2 films increased because of the crystallization of the HfO2 film after RTA.