Composition, structure, and electrical characteristics of HfO_2 gate dielectrics grown using the remote- and direct-plasma atomic layer deposition methods

摘要

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 HfO_2 gate dielectric to examine their electrical characteristics. The as-deposited RPALD HfO_2 layer exhibited an amorphous structure, while the DPALD HfO_2 layer exhibited a polycrystalline structure. Medium-energy ion scattering measurement data indicate that the interfacial layer consisted of interfacial SiO_(2-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 SiO_(2-x). The as-deposited RPALD HfO_2 films had better interfacial layer characteristics, such as an effective fixed oxide charge density (Q_(f,eff)) and interfacial roughness than the DPALD HfO_2 films did. A MOS capacitor fabricated using the RPALD method exhibited an equivalent oxide thickness (EOT) of 1.8 nm with a Q_(f,eff) = -4.2 x 10~(11) q/cm~2 (where q is the elementary charge, 1.6022 x 10~(-19) C), whereas a MOS capacitor fabricated using the DPALD method had an EOT=2.0 nm and a Q_(f,eff) = -1.2 x 10~(13) q/cm~2. At a power=0:6 MV/cm, the RPALD n-type metal-oxide semiconductor field-effect transistor (nMOSFET) showed μ_(eff)=168 cm~2/V s, which was 50% greater than the value of the DPALD nMOSFET (μ_(eff) = 111 cm~2/V s). In the region where V_g-V_t=2.0 V, 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.