Atomic layer deposition of noble metals:: Exploration of the low limit of the deposition temperature

The low limit of the deposition temperature for atomic layer deposition (ALD) of noble metals has been studied. Two approaches were taken; using pure oxygen instead of air and using a noble metal starting surface instead of Al2O3. Platinum thin films were obtained by ALD from MeCpPtMe3 and pure oxygen at deposition temperature as low as 200 degreesC, which is significantly lower than the low-temperature limit of 300 degreesC previously reported for the platinum ALD process in which air was used as the oxygen source. The platinum films grown in this study had smooth surfaces, adhered well to the substrate, and had low impurity contents. ALD of ruthenium, on the other hand, took place at lower deposition temperatures on an iridium seed layer than on an A1(2)O(3) layer. On iridium surface, ruthenium films were obtained from RuCp2 and oxygen at 225 degreesC and from Ru(thd)(3) and oxygen at 250 degreesC, whereas no films were obtained on Al2O3 at temperatures lower than 275 and 325 degreesC, respectively. The crystal orientation of the ruthenium films was found to depend on the precursor. ALD of palladium from a palladium beta-ketoiminate precursor and oxygen at 250 and 275 degreesC was also studied. However, the film-growth rate did not saturate to a constant level when the precursor pulse times were increased.