Identification of sub-band-gap absorption features at the HfO2/Si(100) interface via spectroscopic ellipsometry

Spectroscopic ellipsometry is used to characterize charge trapping defect states in thin HfO2 gate dielectric films deposited by atomic layer deposition on chemically oxidized p-type Si (100) substrates. The intensity of specific absorption features detected below the band gap of HfO2 at 2.9 and 4.75 eV is clearly distinguished from the Si critical points; however, repeating this spectroscopic evaluation for identical HfO2 films deposited and annealed on fused silica substrates results in no defect features detected. The HfO2/Si(100) results, therefore, suggest these oxygen deficient defects are not intrinsic to HfO2 but reside primarily at the interface with the silicon substrate. The feasibility of utilizing spectroscopic ellipsometry to identify stoichiometric variations at the SiO2/Si(100) interface and the corresponding changes associated with the electrical performance is presented.