Study of reactive electron beam deposited tantalum penta oxide thin films with spectroscopic ellipsometry and atomic force microscopy

Abstract

The optical and surface morphological properties of thin films are profoundly influenced by the deposition technique and the various process parameters employed. In present work, several tantalum penta oxide thin films have been fabricated using reactive electron beam evaporation at varying oxygen (O2) pressures, ranging from 3 × 10−3 Pa to 8 × 10−2 Pa. Refractive index, extinction coefficient, and voids in thin film microstructure were determined through the analysis of spectroscopic ellipsometric measurements. The refractive index, which exhibits a decreasing trend, varies between 1.859 and 2.067, with the exception being the lowest O2 pressure. The variation has been explained in terms of varying oxygen content and voids in the thin films. The extinction coefficient exhibits a decreasing trend due to the increasing oxidation of tantalum, except at O2 pressure of 8 × 10−2 Pa. Increase in the extinction coefficient at this pressure could be due to porous film microstructure, resulting in dominant light scattering. Variation of film density which is similar to that of refractive index, has been attributed to the varying oxidation of tantalum (Ta) and film porosity. Surface root mean square (rms) roughness, correlation length and Hurst parameter, have been derived from suitable analysis of atomic force microscopy measurements. Variations of correlation length and rms roughness have been explained in terms of varying surface shadowing effects and oxidation of Ta with varying O2 pressure.

Keywords

• Tantalum penta oxide thin films
• Electron beam deposition
• Spectroscopic ellipsometry
• Atomic force microscopy
• Grazing incidence X-ray reflectivity