Influence of pressure on sputter yield in DC magnetron discharge with PIC simulation

We explore the dependence of the sputter yield in planar DC magnetron discharge (DCMD) on the neutral gas pressure using 2D-RZ particle-in-cell (PIC) simulations. Magnetron discharge is the most widely used technique to deposit metallic and compound thin films. These discharges rely on an external magnetic field, applied perpendicular to the electric field, in order to reduce the necessary gas pressure and discharge voltage. The reduced pressure enables increased deposition rates due to decreased scattering of the sputtered atoms. In this work, we find that the pressure also influences the voltage profile along the discharge axis, which controls the ion bombardment energy. The ion bombardment energy is important because it determines the sputtering yield, which directly scales the deposition rate. We find that nearly all of the ionization occurs in the quasineutral plasma (outside of the cathode sheath). The ions are, therefore, accelerated by at least the sheath voltage gain, and up to the full discharge voltage. We provide a theoretical explanation of this behavior and also explore other pressure dependent phenomena in DCMD.