Growth of Noble Metal Ru Thin Films by Liquid Injection Atomic Layer Deposition

Ru thin films were deposited by liquid injection atomic layer deposition (LIALD) with tris(2,2,6,6-tetramethyl-3,5-heptanedionato)ruthenium dissolved in ethylcyclohexane (ECH) and oxygen at growth temperatures of 330 and 380 degrees C. The film thickness is clearly saturated with increasing the injected volume of Ru solution. However, the value of the saturated film thickness at a certain cycle decreased when decreasing the concentration of a Ru solution from 0.05 to 0.01 M. Additionally, the film thickness decreased with increasing the flow rate and feeding time of O(2). All films that were deposited at 380 degrees C were metallic Ru films not RuO(2). Even at a low temperature of 330 degrees C, a very large amount and long time feeding of O(2) was required to form a detectable amount of RuO(2) phase. This phenomenon, which is unique for the LIALD Ru process, is consistently explained by a reduction of adsorbed oxygen atoms by ECH during feeding of the Ru solution. The adsorbed oxygen atoms are removed from the subsurface because the equilibrium oxygen partial pressure for oxidation of noble metals such as Ru is relatively high. Therefore, LIALD is effective in reducing the content of the corresponding oxides in noble metal films.