In situ real-time spectroscopic ellipsometry study of HfO₂ thin films grown by using the pulsed-source metal-organic chemical-vapor deposition

The HfO₂ thin-film growth process is investigated by using in situ real-time spectroscopic ellipsometry (SE) technique combined with the first-principles molecular-orbital (MO) calculations of the electronic states. The HfO₂ films are grown on the silicon substrate by using the pulsed-source metal-organic chemical-vapor deposition method. Particular attention is paid to the formation of an interfacial layer at the early stage of the growth process by monitoring energy-dependent dielectric constants of the film. The energy dependence of the electronic polarizabilities and dielectric constants is calculated for the amorphous HfO₂, SiO₂, and HfSiO₄ films based on the electronic states and density of states obtained using the discrete-variational Xα MO method with the unit cluster model. The measured SE spectra show that the average dielectric constants of the film vary gradually from those for SiO₂ to those for HfO₂ when the number of deposition cycles increases. By comparing the varied dielectric constants during the film growth with the calculated results, we find that the HfO₂ film growth process can be divided into two stages with different growth mechanisms: SiO₂ and Hf_xSi_yO_z layers are grown at the first stage, which are regarded as the interfacial layers, and the HfO- ₂ layer formation becomes predominant at the second stage.