Cylindrical magnetron discharges. I: Current-voltage characteristics for dc- and rf-driven discharge sources

Direct current magnetron discharge sources are often characterized by current-voltage characteristics of the form I∝V n where n is typically in the range from 4 to 10. Similar I-V characteristics are found for dc hollow cathode discharges where the cathode configuration effectively provides electrostatic confinement of the primary electrons. Therefore, by analogy, it has been suggested that the exponent n provides an index to the effectiveness of the magnetic electron confinement in a magnetron discharge. When magnetron discharge sources are driven at rf frequencies, the I-V characteristics typically yield n values in the range 1–3. We have examined the I-V characteristics of cylindrical-post magnetron discharge sources of various diameters driven dc and at rf frequencies of 1.8 and 13.56 MHz. The rf-driven discharges yielded n values which, in most cases, were less than 2.5. Electrostatic probe measurements of the interelectrode voltage distribution showed that the low n values, that is, poor confinement, could be explained by the effect of the magnetic field on the electron transport during that portion of the rf cycle when the post electrode is serving as the anode.