Fabrication of Crystalline HfO2 High-κ Dielectric Films Deposited on Crystalline γ-Al2O3 Films

Crystalline HfO2/γ-Al2O3 gate stacks were successfully fabricated by evaporating the HfO2 film on crystalline γ-Al2O3/Si substrates at 500°C. In the fabrication, crystalline γ-Al2O3 assisted the crystallization of the HfO2 film, which was deposited without the degradation of surface morphology. The electrical characteristics of the crystalline HfO2/γ-Al2O3 stacked dielectric and amorphous HfO2 unstacked dielectric were compared. The leakage current density of the stacked dielectric was lower than that of the unstacked dielectric. The HfO2 layer deposited on the crystalline γ-Al2O3/Si showed a higher dielectric constant than the amorphous HfO2 unstacked dielectric. It was also observed that the frequency dependence of the flat-band voltage shift of the stacked dielectric was negligible and different from that of the unstacked dielectric. These results indicate that crystalline γ-Al2O3 films prevented the formation of an interface layer between HfO2 and Si substrates. The crystalline γ-Al2O3 films work well as buffer layers and may be available for future high-κ gate stack application.