Composition, structure, and electrical characteristics of HfO ₂ 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 Hf O2 gate dielectric to examine their electrical characteristics. The as-deposited RPALD Hf O2 layer exhibited an amorphous structure, while the DPALD Hf O2 layer exhibited a polycrystalline structure. Medium-energy ion scattering measurement data indicate that the interfacial layer consisted of interfacial Si O2-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 Si O2-x. The as-deposited RPALD Hf O2 films had better interfacial layer characteristics, such as an effective fixed oxide charge density (Qf,eff) and interfacial roughness than the DPALD Hf O2 films did. A MOS capacitor fabricated using the RPALD method exhibited an equivalent oxide thickness (EOT) of 1.8 nm with a Qf,eff =-4.2× 1011 q cm2 (where q is the elementary charge, 1.6022× 10-19 C), whereas a MOS capacitor fabricated using the DPALD method had an EOT=2.0 nm and a Qf,eff =-1.2× 1013 q cm2. At a power=0.6 MVcm, the RPALD n -type metal-oxide semiconductor field-effect transistor (nMOSFET) showed μeff =168 cm2 V s, which was 50% greater than the value of the DPALD nMOSFET (μeff =111 cm2 V s). In the region where Vg - Vt =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.