Post deposition UV-induced O2 annealing of HfO2 thin films

UV-assisted annealing processes for thin oxide films is an alternative to conventional thermal annealing and has shown many advantages such as low annealing temperature, reducing annealing time and easy to control. We report in this work the deposition of ultra-thin HfO(2) films on silicon substrate by two CVD techniques, namely thermal CVD and photo-induced CVD using 222 nm excimer lamps at 400 degrees C. As-deposited films of around 10 nm in thickness with refractive indices from 1.72 to 1.80 were grown. The deposition rate measured by ellipsometry was found to be about 2 nm/min by UV-CVD, while the deposition rate by thermal CVD is 20% less than that by UV-CVD. XRD showed that the as-deposited HfO(2) films were amorphous. This work focuses on the effect of post deposition UV annealing in oxygen on the structural, optical and electrical properties of the HfO(2) films at low temperature (400 degrees C). Investigation of the interfacial layer by FTIR revealed that thickness of the interfacial SiO(2) layer slightly increases with the UV-annealing time and UV annealing can convert sub-oxides at the interface into stoichiometric SiO(2), leading to improved interfacial qualities. The permittivity ranges in 8-16, are lower than theoretical values. However, the post deposition UV O(2) annealing results in an improvement in effective breakdown field and calculated permittivity, and a reduction in leakage current density for the HfO(2) films. (c) 2004 Elsevier Ltd. All rights reserved.