PLASMA UNIFORMITY OF MICROWAVE ION SOURCES

The ion saturation current uniformities of two different type plasma sources, a coaxial and a Lisitano coil type, are studied using a moveable Langmuir probe. They both operate under off-resonance microwave discharge. H//2 or Ar is used as the discharge gas. The coaxial source provides better uniformities for ion saturation current, electron temperature, and electron density than the Lisitano coil, independent of the discharge gas species. The ion saturation current with the coaxial source is uniform within about 15% inside a 40-mm-diam circle for a 0. 17 Pa H//2 discharge. However, with the Lisitano coil, uniformity is limited to a 20-mm-diam circle. Furthermore, the Lisitano coil easily suffers from heat distortion because of difficulties in realizing a cooled system. It is also experimentally verified that the coaxial-type source is more appropriate for obtaining high density plasma under continuous operation.