Target material pathways model for high power pulsed magnetron sputtering

The potential of high power pulsed magnetron sputtering (HPPMS) has created growing interest, because it can generate a dense plasma with high target material ion content. However, reported deposition rates are significantly lower than for dc or midfrequency ac sputtering at the same average power in most cases. The fraction of target material arriving at the workpiece, which is ionized, ranges from 5% to 70% as reported so far by workers in the field, even though optical emission spectroscopy suggests a highly metallic plasma. A simple pathways model has been developed to explain these experimental results. In addition, evaluation of the model for various interesting materials suggests target material characteristics which are desirable in order to achieve higher deposition rates and a greater ionized fraction of target material reaching the substrate. The model will be presented, with representative characteristic results and implications on HPPMS processes. In addition, insights from approximate model equations will be presented.