Composition, structure, and electrical characteristics of HfO2 gate dielectrics grown using the remote- and direct-plasma atomic layer deposition methods

Hafnium oxide thin films were deposited using both the remote-plasma atomic layer deposition (RPALD) and direct-plasma atomic layer deposition (DPALD) methods. Metal-oxide semiconductor (MOS) capacitors and transistors were fabricated with HfO2 gate dielectric to examine their electrical characteristics. The as-deposited RPALD HfO2 layer exhibited an amorphous structure, while the DPALD HfO2 layer exhibited a polycrystalline structure. Medium-energy ion scattering measurement data indicate that the interfacial layer consisted of interfacial SiO2−x and silicate layers. This suggests that the change in stoichiometry with depth could be related to the energetic plasma beam used in the plasma ALD process, resulting in damage to the Si surface and an interaction between Hf and SiO2−x. The as-deposited RPALD HfO2 films had better interfacial layer characteristics, such as an effective fixed oxide charge density (Qf,eff) and interfacial roughness than the DPALD HfO2 films did. A MOS capacitor fabricated using the RPALD method exhibited an equivalent oxide thickness (EOT) of 1.8nm with a Qf,eff=−4.2×1011q∕cm2 (where q is the elementary charge, 1.6022×10−19C), whereas a MOS capacitor fabricated using the DPALD method had an EOT=2.0nm and a Qf,eff=−1.2×1013q∕cm2. At a power=0.6MV∕cm, the RPALD n-type metal-oxide semiconductor field-effect transistor (nMOSFET) showed μeff=168cm2∕Vs, which was 50% greater than the value of the DPALD nMOSFET (μeff=111cm2∕Vs). In the region where Vg-Vt=2.0V, the RPALD MOSFET drain current was about 30% higher than the DPALD MOSFET drain current. These improvements are believed to be due to the lower effective fixed charge density, and they minimize problems arising from plasma charging damage.