”Atomistic simulations of reactive deposition processes”
Marco Jupé and Holger Badorreck
Laser Zentrum Hannover e. V., Hannover, Germany
The manufacturing of optical high quality components is based on the physical deposition of dielectric material. Independently on the coating process, a reactive gas is added during the sputtering. The process parameters and the understanding of the processes are typically developed on the basis of experimental studies and empirical models, because theoretical modeling of the processes did not appear possible. Within the increase of computational power and the development of novel multiple scale models a much more detailed view of the fundamental processes can be achieved. The combination of different simulation techniques allows to study effects which are difficult to measure. One example is the sticking and the reflection of oxygen atoms on the surface. The investigation of such effects are of growing interest, and different simulation techniques are applied to study the behavior. The contribution is focused on the theoretical studies of oxidation and stoichiometry’s of the resulting materials. Here the results of different group using different techniques are compared. In addition, the multiple scale model of the virtual coater is applied to describe the complete coating processes. According to this issue the flexibility of the multiple scale modulation will be presented. In the virtual coater model various simulations are combined to compute the processes on the meter scale with temporal range of few micro second to millisecond up to the sub atomistic processes applying time steps of sup-femtoseconds and ensemble sizes of approximately one hundred atoms. Depending on the problem, the techniques can be combined optimally in a modular system. This procedure allows to implement the process parameters of real coating processes. The main focus here is on the sputtering process, such as sputtering Ion Beam or Magnetron Sputtering. It is also possible to simulate other physical processes such as e-beam or IAD.
For the description of the surface processes the application of atomistic simulations delivers the most detailed view of the processes. Both, kinetic Monte Carlo (kMC) as well as classical molecular dynamic (MD) simulations allows to study the movement and the nucleation at the surface of the solid. With respect to the computational power the kMC is optimized to describe the atomic diffusion, but the possible positions of the atoms are predefined. The simulation is fast comparison to the MD simulation, and can manage several millions of atoms. The implementation of oxygen is defined by the displacement energy of the deposited atom with respect to the next neighbors. In contrast to the kMC the classic MD simulation uses the interatomic forces between all atoms of the ensemble. The movement and the position of the atoms are fully defined by the interatomic force, and consequently, the MD delivers a realistic description of nucleation. In this simulations, the dependency on the kinetic energy, the angle of as well as from the stoichiometry are analyzed. In addition, the influence of different materials is discussed. And finally, the correlation to experimental studies are given.