Utilizing tertiary butyl iodide as an effective film quality enhancing agent for atomic layer deposition of HfO2 dielectric thin films

Abstract

The effects of the initial pulse of tert-butyl iodide as a surfactant in atomic layer deposition of HfO2 using cyclopentadienyl tris(dimethylamino) hafnium, CpHf(NMe2)3, and ozone, O3, are investigated at 320, 300, and 250 °C. The formation of 2-methylpropene and hydrogen iodide from tert-butyl iodide via elimination reactions is the key idea of our effective approach for improving film conformality, film quality, and leakage current simultaneously. Our predicted growth mechanisms, supported by experimental results, suggest that different blocking probabilities by 2-methylpropene and hydrogen iodide on the top and bottom sides of the trench feature with an aspect ratio of 22.6:1 lead to 10% improvement in film conformality. In addition, ligand exchanges between the Hf precursor and hydrogen iodide lead to effective removal of large portions of carbon-containing ligands, resulting in a significant reduction in carbon residues, 76% at 320 °C and 40% at 250 °C, as evidenced by secondary ion mass spectrometry results. An increase in film density is also observed partly due to better completion of surface reactions between –I of Hf–I and O3. In terms of electrical properties, a significant improvement of 95% in leakage current is achieved due to the improvement in the film quality when tert-butyl iodide is employed. The deposited HfO2 film has superior leakage properties of 5.18 × 10−8 A/cm2 at 3 MV/cm, which is below the dynamic random access memory leakage current limit.