Electrical and structural properties of hafnium silicate thin films

Thin (∼4 nm) hafnium silicate (HfO2)x(SiO2)1−x/SiO2 gate stacks (0 < x < 1) grown by metal organic chemical vapour deposition (MOCVD) are investigated in this study. The focus is on extracting the optical constants, and hence bandgaps as well as dielectric constants. The VUV (vacuum ultraviolet) spectroscopic ellipsometry (VUV-SE) technique in the spectral range 140–1700 nm, together with current–voltage and capacitance–voltage techniques were used for studying the optical and electrical properties of the layers, respectively. The bandgap was found to increase from 5.24 eV for HfO2 to 6 eV for Hf-silicate with 30% Hf. The permittivity was reduced from ∼21 for HfO2 layers to ∼8 for Hf-silicate with x = 0.3. The results suggest that the optimal Hf content is above 0.6, for which the permittivity higher than 10 can be achieved.