H. Badorreck
M. Jupé
D. Ristau

Analysis of HfO2 virtual materials for different discrete deposition energies and saturation rates

SPIE Optical Systems Design
14. Mai
Frankfurt am Main
Type: Konferenzbeitrag
Virtual Materials are created using the Virtual Coater concept, which facilitates the complete theoretical description of real deposition processes. The concept is based on the combination of different simulation models on multiple scales, where each model describes the process dynamics on its own scale. For each model different techniques regarding special requirements can be applied. The simulation of the material transport in the coating plant is modelled by Direct Simulation Monte Carlo (DSMC) resulting in energy and angle distributions of particles approaching the substrate. Here, discrete deposition energies under vertical incidence are used for the subsequently performed atomistic growth simulation of the thin layers by Molecular Dynamics (MD). This allows for studying the dependence on the deposition energy in particular, while specific discrete energies still can be associated to different coating processes. The Molecular Dynamics gives insight into the structural properties like density, surface roughness, stoichiometry and structural inhomogeneities. The non-stoichiometric growth of metal oxides by Physical Vapor Deposition (PVD) processes can be compensated by saturation with additional oxygen, which is accordingly applied in the simulation. The results of the MD are needed to calculate the electronic and optical properties of the Virtual Materials by Density Functional Theory (DFT). In the course of this, a small supercell of about 100 atoms extracted from the atomistic grown structure representing the properties on this small scale is utilized. Larger structural properties like inhomogeneities in the structure can be treated by DFT in only very limited cases. The DFT delivers the dielectric function and therefore allows the deduction of the refractive index and the absorption. Besides the structural properties with respect to different deposition energies, the investigation of HfO2 thin layers is especially interesting regarding the stoichiometry, due to the strongly increasing absorption already for marginal imbalances in the Hf:O ratio. Here, the limited number of atoms, that can be handled by the DFT, also restricts the calculation for non-stoichiometric Virtual Materials to above roughly 1\% in the deviation from ideal stoichiometric ratio. Therefore one aspect of this work is to determine if the extrapolation to values below 1\% is applicable.