Direct evidence of localized states in high-k materials for gate insulator - Cathode luminescence study of HfO2 films -

Abstract

pp.762-763 silica subsffates. 3. Results and Discussion Annealing technique is important to modiff or improve material properties and an inevitable process for device fabrications. To detect the change of localized states in FIfO, we have performed CL as a function of annealing temperature from 300"C to 800'C. CL spectra of an as-deposited sample and of samples with Tu = 400"C, 600"C, and 800"C are plotted in Fig. 1. CL spectra changed&astically depending on T.. This shows that the localized states in FlfOrfilms sensitively changes with Tu, because the luminescence spectra are generally sensitive to localized states in the gap. This is the first observation indicating a change of the localized states in high-k materials with annealing. Since the leakage cunent also depen& on the annealing temperature, it is likely that a change of leakage current is caused mainly by a change of localized states distribution. As seen in Fig. 1, CL spectra have two peaks at 4.3 eY (290 nm) and 3.4 eV (370 nm). The peak intensities af,e plotted as a function of T. in Fig. 2. The 4.3 eV peak monotonously increases with annealing temperatures, while the 3.4 eV peak has a maximum intensity around 400 "C. Excited electrons and holes recombine through radiative and non-radiative processes as schematically shown in Fig. 3. Radiative processes are generally dre to band edge recombination, band tail recombination, or recombination through defects. On the other han4 there are non-radiative recombination processes through defect states.