Surface Reaction Kinetics of Titanium Isopropoxide and Water in Atomic Layer Deposition
In atomic layer deposition processes (ALD), surface reactions of adsorbed precursor species lead to the formation of thin films. In order to achieve a well-controlled, self-limiting process, the substrate is sequentially exposed to different precursor molecules, each one until the surface is completely saturated. The necessary time of exposure depends on precursor transport and on surface kinetics of which the latter are determined by the respective activation energies for the surface reactions. In this contribution, we apply a surface kinetic model and surface reaction rates to describe the ALD process for the deposition of titanium dioxide utilizing titanium isopropoxide and water as reactive precursor combination. We examine in detail precursor surface coverages and investigate the influence of substrate temperature and exposure time on the hydrolytic decomposition of the adsorbed titanium precursor. In this way, we can quantify the deposition rate in each deposition cycle and examine the contribution of desired hydrolytic surface reactions and undesired pyrolytic decomposition reactions that limits ALD processes. We identify ALE) threshold temperatures and discuss the influence of pulse durations on the so-called ALD window: Finally, we examine the influence of precursor and water residual pressure remaining in the reactor after their respective exposure pulses on the thin film growth behavior, which can arise either from limited pumping capacities in an ALD vacuum system or insufficient purging times in particular for high complex geometries.