In-cycle evolution of thickness and roughness parameters during oxygen plasma enhanced ZnO atomic layer deposition using in situ spectroscopic ellipsometry

Abstract

We investigate the time evolution of ZnO thin film growth in oxygen plasma-enhanced atomic layer deposition using in situ spectroscopic ellipsometry. The recently proposed dynamic-dual-box-model approach [Kilic et al., Sci. Rep. 10, 10392 (2020)] is used to analyze the spectroscopic data post-growth. With the help of this model, we explore the in-cycle surface modifications and reveal the repetitive layer-by-layer growth and surface roughness modification mechanisms during the ZnO ultrathin film deposition. The in situ complex-valued dielectric function of the amorphous ZnO thin film is also determined from the model analysis for photon energies of 1.7–4 eV. The dielectric function is analyzed using a critical point model approach providing parameters for bandgap energy, amplitude, and broadening in addition to the index of refraction and extinction coefficient. The dynamic-dual-box-model analysis reveals the initial nucleation phase where the surface roughness changes due to nucleation and island growth prior to film coalescence, which then lead to the surface conformal layer-by-layer growth with constant surface roughness. The thickness evolution is resolved with Angstrom-scale resolution vs time. We propose this method for fast development of growth recipes from real-time in situ data analysis. We also present and discuss results from x-ray diffraction, x-ray photoelectron spectroscopy, and atomic force microscopy to examine crystallographic, chemical, and morphological characteristics of the ZnO film.