AVS 57th International Symposium & Exhibition
    Thin Film Wednesday Sessions
       Session TF+EM-WeM

Paper TF+EM-WeM12
Depth Resolved Cathodoluminescence Spectroscopy of Amorphous High-k Dielectric LaLuO3

Wednesday, October 20, 2010, 11:40 am, Room Dona Ana

Session: High K Dielectrics for Si Electronics
Presenter: S. Shen, Ohio State University
Authors: S. Shen, Ohio State University
Y. Liu, Harvard University
R.G. Gordon, Harvard University
L.J. Brillson, Ohio State University
Correspondent: Click to Email
We have used depth-resolved cathodoluminescence spectroscopy (DRCLS) to measure the native point defects and reaction-induced defects within ultrathin LaLuO3 dielectric films. The rare earth oxide LaLuO3 is gaining much attention because of its high dielectric constant (28 ~ 32) and its potential application to replace SiO2 as a gate dielectric for Si microelectronics, requiring both sub-nanometer thick gate oxide layers and low leakage currents. LaLuO3 deposited by atomic layer deposition (ALD) provides films with high crystallization temperature and relatively high conduction band offset, but they have non-negligible leakage currents that are attributed to electronic trap states in the band gap. Annealing can partially reduce these traps but can also induce diffusion/reaction at the LaLuO3 interfaces. We used DRCLS to determine the changes in defect levels of WN/20 nm LaLuO3/Si gate structures as a function of annealing and the introduction of an Al2O3 diffusion barrier at the Si interface. A 10 nm WN/20nm LaLuO3/Si structure as-grown exhibits defect emissions at 2.4, 3.2, 3.8, 4.2 and 4.7 eV as well as a 5.48 eV band gap. With 300ºC cyclic annealing, 10 nm WN/20nm LaLuO3/Si, the band gap emission is absent and high energy emissions at 4.2 and 4.7 eV shift to 3.8 eV. A 10 nm WN/20nm LaLuO3/0.4 nm Al2O3/Si interlayer structure exhibits negligible difference from the interlayer-free stack without anneal. However, with annealing, the WN/20nm LaLuO3/0.4 nm Al2O3/Si defects at high energy and the band gap remain unchanged while the lower energy defects are suppressed. The 5.48 eV band gap emission agrees with an internal photoemission gap of 5.3 eV measured previously. The 4.2 and 4.7 eV emissions are consistent with weighted density function approximation calculations showing two oxygen-vacancy-related states at similar energies near the LaLuO3 conduction band edge. The DRCLS–measured degradation of optical features with annealing of the interlayer-free structure is attributed to Si diffusion and reaction with LaLuO3 as observed by cross sectional TEM. This degradation is suppressed with the Al2O3 barrier layer. Furthermore, the annealing of the interlayer structure reduces all the low energy defect emissions. Finally, the highest lying state at 4.7 eV above the valence band (0.78 eV below the conduction band) agrees reasonably well with the 0.6-0.7 eV electrical measurements of leakage current. These results highlight the importance of annealing with a diffusion barrier at the Si interface to suppress defects within LaLuO3 without Si reaction at the LaLuO3 interface.