Structural and optical characteristics of tantalum oxide grown by pulsed Nd:YAG laser oxidation

Tantalum pentoxide $(Ta2O5)$ thin films $(20–50nm)$ have been grown by $1064nm$ Nd:YAG laser oxidation of Ta film deposited on Si. The chemical bonding, structure, and optical properties of the films have been studied by Fourier transform infrared spectroscopy, x-ray diffraction, and reflectance measurements at normal light incidence in the spectral range of $350–800nm$⁠. The effect of the substrate temperature $(250–400°C)$ during oxidation and its optimization with respect to the used laser beam energy density (⁠$3.2–3.4J∕cm2$ per pulse) is discussed. It is established that the substrate temperature is a critical factor for the effectiveness of the oxidation process and can be used to control the composition and amorphous status of the films. The film density explored by refractive index is improved with increasing film thickness. The refractive index of the layers grown under the higher laser beam energy density and at substrate temperature of $350–400°C$ was found to be close to the value of bulk $Ta2O5$⁠. The films are amorphous at substrate temperature below $350°C$ and possessed an orthorhombic $(β-Ta2O5)$ crystal structure at higher temperatures. The thinner layers crystallize at a little higher temperature.