Space-Limited Crystal Growth Mechanism of TiO2 Films by Atomic Layer Deposition

In this paper, a novel space-limited crystal growth mechanism of TiO2 films on a Si substrate by ALD is presented. The results show that two distinct grain-growth behaviors are observed at two different growth temperature ranges. At 300-500 degrees C, grain growth of the films has a conventional temperature dependence with an activation energy of about 12.39 kJ/mol. However, the grain growth has an unconventional temperature dependence, as the grain size decreases with increasing growth temperature for films grown at temperatures between 150 and 250 degrees C. This TiO2 growth is dominated by the surface nucleation of the films. It is suggested that this interesting phenomenon may also occur for other materials grown by ALD. In addition, the nucleating kinetics of ALD-TiO2 films has also been investigated, and the nucleating activation energy of films is approximately 48.25 kJ/mol.