Effect of Using Ethanol as the Oxygen Source on the Growth and Dielectric Behavior of Atomic Layer Deposited Hafnium Oxide

Abstract

Use of common atomic layer deposition (ALD) oxygen sources such as oxygen, ozone or water often causes uncontrolled oxidation of the silicon surface by diffusion through the growing HfO2 film during the ALD process. This results in thick interfacial layer (IL) that is detrimental to future transistor scaling if further thinning of the IL is desired. In order to minimize the uncontrolled oxidation at the interface, we explored the use of ethanol as the ALD oxygen source in the ALD HfO2 process. The effect of using ethanol on the growth, composition and electrical behavior of ALD HfO2 films was studied and compared against films prepared using water based ALD process. Ethanol showed good reactivity with the hafnium precursor tetrakis(diethylamino)hafnium and displayed typical ALD growth behavior of linear film growth within a wide ALD process temperature window (200-280 °C). The ethanol based ALD process exhibited HfO2 growth rate of 0.05 nm/cycle which was less than 0.15 nm/cycle obtained when water was used as the ALD oxygen source. X-ray photoelectron spectroscopy (XPS) showed the deposition of stoichiometric HfO2 with trace amount of carbon in the film. SiO2 interfacial layer was not observed in as-deposited samples, whereas annealed samples showed SiO2 XPS features. Films prepared using the ethanol based ALD process showed comparable dielectric performance to that of water based ALD process films and displayed well behaved C-V and I-V curves with as-deposited (ethanol) HfO2 samples showing the lowest leakage current density of 5 x 10-8 A/cm2 at 1 V gate bias.