Plasma modeling for optical coating devices
Benjamin Schröder, Ralf Peter Brinkmann
DPG Frühjahrstagung der Sektion AMOP, March 8-12, 2010, Hannover, Germany (talk)
In manufacturing optical layers by vapor deposition it is useful to use energetic ions to assist the deposition. By doing this, the optical properties of the coating is being controlled and im- proved. The energy spectrum of ions impinging the surface is a crucial factor for the growth of the film.
As such coating devices work at pressures below 0.1 Pa, diffusive fluid dynamical models can hardly be applied due to the low collisional frequencies with the background gas - typically, the mean free path is on the spatial scale of the coating device, which is approximately 1m. Yet, collisions play an important role concerning the shape of the energy distribution. We developed a plasma beam model that comprises the most important collisional effects in this regime: charge exchange collisions and elastic collisions with the background gas to derive macroscopic features such as the electric field and charge densities. To obtain the energy distribution of the ions at the substrate, a hybrid particle simulation is being developed to determine the potential, inject beam particles with a certain energy spectrum and calculate ion-neutral collisions and the response to the electric field to describe the transport of the ions to the surface.