Chemistry and band offsets of HfO2 thin films for gate insulators

Interfacial chemistry and band offsets of ${\mathrm{HfO}}_2$ films grown on Si(100) substrates are investigated using high-resolution angle-resolved photoelectron spectroscopy and are correlated with interfacial structures revealed by transmission electron microscope. Hf $\text{4f}$ and O $\text{1s}$ spectra show similar chemical shifts indicating the existence of a double layer structure consisting of a ${\mathrm{HfO}}_2,$ upper layer and a ${\mathrm{SiO}}_2$ -rich ${\mathrm{Hf}}_{\text{1−x}}{\mathrm{Si}}_x{\mathrm{O}}_2$ lower layer. Two types of valence band offsets are clearly determined by a double subtraction method to be 3.0 and 3.8 eV that can be attributed to ${\mathrm{\Delta Ev}}^1$ for the upper layer ${\mathrm{HfO}}_2/\mathrm{Si}$ and ${\mathrm{\Delta Ev}}^2$ for the lower layer ${\mathrm{Hf}}_{\text{1−x}}{\mathrm{Si}}_x{\mathrm{O}}_2/\mathrm{Si},$ respectively.