PIC-MCC Simulation of DC Magnetron Sputtering using High-order Methods
Direct Current (DC) Magnetron Sputtering is an effective method used in thin film deposition processes to create, e.g., a metallic coating on an object. The material used for the coating is released or sputtered from a target (cathode) by bombarding that surface with energetic ions and then condensates on the substrate (anode) surface. To increase the deposition rate on the substrate, a magnet configuration is used to confine electrons in front of the target. In the following the benefits of a magnetron simulation are shown.
3D Simulation Setup
The simulation setup is adapted from Pflug et al., see details below. The simulation domain with target (pink) and magnetic field that is created by the coaxial permanent magnets below the target (outside of the simulation domain) is shown. The chamber is filled with Ar with a pressure of approx. 0.3 Pa and the voltage that is applied to the target is -300 V.
The Particle-In-Cell (PIC) method is applied to simulate the interaction between charged particles and electromagnetic fields and the collisions between the charged particles and the Ar gas are considered by the Monte Carlo Collisions (MCC) model, which assumes a background gas with constant properties over the course of the simulation.
Prediction of plasma instabilities: Spokes
Typical physical phenomena that occur directly in front of the target surface are so-called spokes, waves of high electron density that rotate in a specific direction due to the trapped electrons in the magnetic field. The simulation (left) is compared with an experimental result given in Pflug et al., see details below. For a given magnetic field distribution and applied voltage, the number of spokes and their rotating velocity depends on the background gas pressure (Pflug et al.).
Prediction of impact rates
The impact pattern on the target reveals temporally and spatially resolved information regarding, among others, the impact momentum, energy and angle of ions and electrons. From these simulations, the erosion of the target surface can be determined and influences of the gas mixture and pressure, applied voltage, surface material, etc. can be quantified and used for optimization. In the picture above, the impact energy pattern of singly charged ions is shown and the effect of the occurring spokes can clearly be seen, which increases the impact energy of the ions at the current position of the spoke.
Statistics from the target impacts give information about the distribution function of each species. The histogram plots above indicates the angle and energy bandwidth of the bombarding Argon ions. Again, the influence of the process parameters can be investigated by these simulations. Furthermore, details on the chemical composition of the plasma, the main chemical reactions that dominate the process and formation of radicals and tracer species are possible simulation outputs.
More information about the underlying theory and modelling can be found here:
- Pflug, A. & Vergöhl, M. (2019). Modelling of Thin Film Deposition Processes as a Service Proceedings of the 10th International Conference on Power Electronics for Plasma Engineering, 73(1-12), 978-83-930983-9-2 .