Surface Kinetics of Titanium Isopropoxide in High Vacuum Chemical Vapor Deposition
Understanding the surface kinetics of precursor decomposition during thin film formation represents a key aspect in the understanding and engineering of chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes. The determination of activation energies of the surface reaction steps, however, is often challenging because it requires precise knowledge of precursor impinging rates. Afterward, the kinetics can be investigated by comparing the amount of deposited material with the absolute precursor flow. Ideally, the experimental equipment allows a distinction between gas phase and surface reactions. Both are difficult to achieve in conventional CVD processes. A high vacuum environment, however, enables the quantitative prediction of precursor impinging rates due to the ballistic nature of precursor transport; additionally precursor gas phase reactions do not occur. We investigated the surface reaction kinetics of titanium isopropoxide (TTIP) in the high vacuum CVD of titanium dioxide. Additionally, we have investigated the addition of water as a reactani to the deposition process. In this way, even surface kinetics relevant for ALD processes could be investigated. Here, we propose a comprehensive surface kinetic model of titanium isopropoxide surface reactions including hydrolytic and pyrolytic reactions. The surface kinetic model was fitted to 363 data points taken from combinatorial experiments covering a wide range of deposition parameters (substrate temperature, 175-610 degrees C; TTIP impinging rate, 0.1 x 10(15)-6.0 x 10(15)cm(-2) s(-1); water impinging rate, 4.5 x 10(16)cm(-2) s(-1)), which enabled us to derive activation energies for desorption, hydrolysis, and pyrolysis.