Adsorption Kinetic Approximation of a Mixed Alkylamido-Cyclopentadienyl Hafnium Precursor in HfO₂ Atomic Layer Deposition

In this study, the growth kinetics of HfO₂ via the atomic layer deposition (ALD) using a mixed alkylamido-cyclopentadienyl hafnium precursor are proposed based on experimental data. The hydroxyl concentration on the targeted surface, which is sensitive to the surface condition prior to the ALD, governs the saturated growth per cycle (GPC) values. Moreover, we found that the bulkiness of remaining ligands on adsorbed species hinders the adsorption of CpHf(N(CH₃)₂)₃ (Cp-Hf) molecules.<br/>Considering this phenomena, we proposed a kinetic model by calculating the energetic terms to quantify the “steric hindrance effect” of the first elementary surface reaction of precursor Cp-Hf. The targeted Si substrates were hydroxylated at several levels to evaluate the reliance of saturated GPC and steric hindrance effect on the nature of the surface. According to the experimental ALD process, the film growth was found to be influenced by the steric hindrance factor, especially at the temperature range from 150 ^oC to 250 ^oC, but the hindrance effect decreases with increasing temperature and disappears at 300 ^oC. The effective activation energy of the adsorption of Cp-Hf molecules on Si substrates was estimated to be 0.2 eV. Although our present model is limited to the ALD of HfO₂, we foresee that the kinetic model could potentially assist the study of metal oxide ALD which utilizes a wide range of precursors.