Effect of Hf Sources, Oxidizing Agents, and NH_3/Ar Plasma on the Properties of HfAlO_x Films Prepared by Atomic Layer Deposition

摘要

The effect of Hf sources, oxidizing agents, and NH_3/Ar plasma on the properties of HfO_2 and HfAlO_x films prepared by atomic layer deposition (ALD) have been investigated. The use of tetrakis(ethylmethylamino)hafnium: Hf(NEtMe)_4 (TEMAHf) as a source of hafnium has avoided the problems associated with hafnium tetrachloride (HfCl_4), such as poor throughput and the generation of a large number of particles. This source has also been effective in reducing the level of residual chlorine (Cl). However, the level of residual carbon (C) increased. Hydrolysis was found to be more effective than oxidation using O_3 in removing ligands from the TEMAHf and/or trimethylaluminum (TMA); the film formed using O_3 contained a higher level of C than that using H_2O, resulting in the deterioration in field-effect transistor (FET) properties, such as the subthreshold swings and the mobilities. The total levels of residual impurities (C+Cl) were successfully reduced through the combination of TEMAHf and NH_3/Ar plasma, leading to improvements in FET properties, particularly in the reduction of the gate leakage current.