Pressure dependence of DC magnetron discharges with 2D PIC simulation

We compare the voltage versus pressure (V-P) dependence of direct-current magnetron discharges (DCMD) in our particle-in-cell (PIC) simulations with experimental measurements. DCMD are crossed-field discharges that are widely used for thin film deposition. A magnetic field, applied perpendicular to the electric field, enables low operating pressures and voltages, which increases the deposition rate. For a fixed current, the discharge voltage decreases with increasing pressure, declining steeply below ~3 mTorr and gradually above. This consistentently-seen experimental behavior has not previously been obtained with PIC simulation or adequately explained. Our 2D-RZ PIC simulations agree well with experiment and provide detailed measurement of the discharge structure near the cathode. In particular, we find that the fraction of emitted electrons that get reabsorbed at the cathode without contributing to the discharge (i.e. recaptured) varies linearly with pressure. This pressure dependence of recapture explains the initial steep decline and later saturation of the V-P curve. We also develop a 1D cascade model of ionization in the presheath that explains the energy distribution of the bombarding ions.