Simulation of Neutral Gas Dynamics for PVD DC-MSIP and HPPMS Processes
Kirsten Bobzin, Nazlim Bagcivan, Sebastian Theiß, Ricardo Henrique Brugnara, Marcel Schäfer, Ralf Peter Brinkmann, Thomas Mussenbrock, Jan Trieschmann
40th International Conference on Metallurgical Coatings and Thin Films (ICMCTF 2013), San Diego (California), USA, 29 April - 03 May
PVD processes such as DC Magnetron Sputtering Ion Plating (DC-MSIP) and High Power Pulse Magnetron Sputtering (HPPMS) are commonly used to produce hard protective coatings for corrosion and wear resistance applications. A uniform layer of coating material is an essential requirement for an effective protection of the coated parts. It is therefore important to understand the gas dynamic processes inside the reactor chamber to optimize the quality of the coatings. In particular, the dynamics of the process gas as well as of the film forming particles sputtered from the target material are of interest. In complex industrial scale coating units the spatial distribution of particles can only be predicted using numerical models. Depending on the geometry of the reactor chamber and the process pressure, different computational models can be used. The flow regime and in consequence the appropriate numerical model is determined by the Knudsen number (Kn) equal to the mean free path over the typical length scale. For Kn < 0.01, continuum models such as computational fluid dynamics (CFD) models allow for a precise description of the gas flow. In contrast, in pressure regimes with Kn > 2 only kinetic models provide an accurate description, e.g. the Direct Simulation Monte-Carlo (DSMC) method. Generalized limits for the validity of the different models in the transition regime 0.01 < Kn < 2 cannot be found.
In this work we investigate an industrial scale hybrid magnetron sputtering coating unit operated at pressures around 500 mPa. Due to the low pressure, the magnetron discharge operates in the already mentioned transition regime. In consequence, both CFD as well as DSMC simulations may provide an appropriate physical description. For our analysis we employ the commercially available FLUENT software V14 and the freely available OpenFOAM simulation package. Results obtained using the CFD and the DSMC approach are compared to investigate the applicability of the different models. The CFD simulations reveal all the principle flow characteristics at relatively low computational costs. The computationally costly DSMC method, however, provides a more detailed picture of the flow dynamics inside the reactor chamber, in particular in regions where Kn ? 1. The kinetic approach provides a more precise description especially at small features of the geometry. In addition, the DSMC routines provided with OpenFOAM can easily be extended with respect to a kinetic description of the coating forming particles sputtered from the target materials. Resulting, this allows for an analysis of the coating formation on the substrates.