Direct Simulation Monte Carlo – DSMC

The DSMC simulation is especially well suited for pressure ranges below 100 Pascal. CFD methods cannot be used in this pressure range since particle dynamics no longer meet the continuum assumptions here.

Sample application I: Optimization of thermal vaporiser sources

Direct Simulation Monte Carlo DSMC of thermal vaporisation
© Fraunhofer IST

Thermal vaporisation is an important alternative to plasma-assisted precipitation processes, for example with substrates or precursors that are sensitive to high-energy particle bombardment. The uniform sputtering of large areas at high rates is a special challenge here.

Recent literature shows that simple superposition models are still being used in the model-based optimization of thermal vaporiser sources. Only the particle trajectories leading from a source term to the substrate surface are superimposed with these models. Collective effects due to interactions between the particle species are disregarded here by definition. Comparisons with experiments have shown that only models that consider the interactions between all particle species lead to reliable results. This is assured with the DSMC simulation – assuming the corresponding cross-section parameters were transferred correctly.

Two-dimensional DSMC simulations are performed to investigate the above-mentioned collective effects on the layout of a line source. Since the influences of the source geometry and thermal vapour pressure on the layer profile in the simulation align with experimental observations, they could be taken into account for the layout.

Sample application II: Sputter simulation for aperture optimization

Simulated metal absorption profile on the inner walls of the EOSS® sputtering chamber.
© Fraunhofer IST, Andreas Pflug

Simulated metal absorption profile on the inner walls of the EOSS® sputtering chamber.

Measured and simulated deposition rate.
© Fraunhofer IST

Measured and simulated deposition rate.

High-precision optical filters are a core element of many special applications, such as optical precision measuring instruments for the aerospace sector, high-performance optical fibres or UV photolithography. The progressive requirements for the performance characteristics of these filters require increasingly complex layer stacks with a rising number of individual layers. This simultaneously imposes higher standards on the homogeneity and reproducibility of the individual layers.

DSMC simulations of the gas dynamics and particle transport in a sputtering process have been carried out in order to identify the relevant influencing variables in layer deposition. Among other things, this made it possible to quantify the influence of the system and aperture geometry on the coating profile. This enabled aperture optimization on a purely virtual basis and led to an experimentally validated coating homogeneity that is clearly superior to experimental aperture optimization.