Adsorption of precursor molecules in the CVD process of (Ba;Sr)titanate simulated by ab-initio calculations

Ab-initio simulations with the quantum chemistry code DMOL have been perfor med to investigate the adsorption behaviour of two possible titanium precur sors for SrTiO3 deposition, TiO(thd)(2) (titanyl-bis-[tetramethyl-heptan-di onato]) and TTIP (titan-tetraisopropoxy). We have developed a cluster repre sentation of 3 x 3 elementary cells which proved to be a model system for t he adsorption at a 2-D (100) SrO terminated surface. Moder calculations for TiO2 and CH4 adsorption at this and a variety of modified clusters allowed an estimation of the errors introduced by the use of a finite cluster inst ead of the infinite surface. Our calculations show that the TTIP precursor has a much higher energy of adsorption, a closer distance of the adsorbed s tate to the surface as well as a higher dissociation energy than the TiO(th d)(2) molecule. From these results it is rather straightforward to expect a higher sticking probability and a lower surface mobility for TTIP than for TiO(thd)(2). This is in good agreement with experimental results on edge c overage of BST films deposited by the MOCVD method from the respective Ti p recursors. (C) 2000 Elsevier Science S.A. Ail rights reserved.