Effect of HCl catalyst in the formation of flat structures of Ta2O5 thin films by sol-gel technique

Ta 2 O 5 thin films have been prepared from tantalum ethoxide solutions [Ta(C2H5O)5] by sol-gel spin coating technique on Si (100) substrates and annealed at different temperatures ranging from 500 to 800 °C for 1 h. The physical, chemical and morphological characteristics of both fine powders and thin films have been characterized by bulk techniques like N2 adsorption and He porosimetry, thermogravimetry, differential thermal analysis and surface techniques like x-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM), and x-ray photelectron spectroscopy (XPS). Additions of acid catalyst (HCl) and proper thermal treatment enable the formation of highly dense flat like films of Ta2O5, as observed by AFM observations. Films prepared from neutral precursor solutions show a micrometer-range porous network and a strongly marked rough polycrystalline surface structure. HCl catalyst resulted in a decrease of the crystallization temperature to 630 °C, with respect to a crystallization temperature of 732 °C found for the neutral prepared films. The evolution of dense structures upon HCl treatment has been confirmed by surface area and density measurements on the fine powders. XPS measurements have confirmed the formation of stoichiometric Ta2O5 for the HCl prepared films. The pH of the precursor solution as well as the annealing thermal treatment have resulted in the key process parameters for controlling the microstructural characteristics of the deposited films.