Surface Kinetics of Titanium Isopropoxide in Chemical Vapor Deposition of Titanium Dioxide and Barium Titanate

Abstract

All chemical vapor deposition (CVD) processes rely on the adsorption and decomposition of precursors on a substrate to deposit the desired material. The growth rate of the film is determined by the surface kinetics of the utilized precursor molecules and generally dependent on precursor concentration and substrate temperature. Investigation of surface kinetics is challenging in CVD techniques as precise quantification of the precursor concentration (or precursor flux) is difficult. Furthermore gas-phase reactions can influence the film growth. In this thesis we develop a method to characterize precursor surface kinetics during deposition processes using high vacuum chemical vapor deposition (HV-CVD). In a high vacuum environment precursor transport takes place in the molecular flow regime and gas phase reactions are efficiently suppressed. Furthermore precursor impinging rates can be calculated using a relatively simple mathematical model. Relating the number of impinging precursor molecules to the absolute amount of deposited material allows investigating the deposition kinetics in a very precise manner. We apply this method to characterize titanium isopropoxide and water in chemical vapor deposition conditions over large parameter range. Fitting a surface kinetic model to experimental data enabled us to derive activation energies for desorption, hydrolysis and pyrolysis. The surface kinetic model is then applied to characterize the TTIP based HV-CVD and ALD process of titanium dioxide in detail. Furthermore, we have studied the surface kinetics of TTIP when the substrate is additionally exposed to barium precursors aiming to deposit barium titanate. We demonstrate that HV-CVD is capable of growing epitaxial barium titanate films on magnesium oxide, strontium titanate and strontium titanate buffered silicon substrates at 400°C process temperature; this is the lowest reported substrate temperature for epitaxial growth of barium titanate by CVD. Finally, we investigate two experimental techniques to selectively grow titanium dioxide: a lift-off technique based on shading masks and a surface passivation technique, based on the local modification of surface reactions. We will demonstrate, that the surface kinetics of TTIP are not optimal for the local deposition of titanium dioxide in the first case, but that HV-CVD is capable of enhancing selectivity compared to previously reported values in the latter approach.