Variation of Radial Plasma Density Profile with the Excitation Frequency in a Magnetron-Type Plasma
Abstract
The variation of the radial profile of plasma density with the excitation frequency was investigated using a magnetron-type plasma source. The plasma source is comprised of a cylindrical shaped rf electrode and two annular magnets attached to the outer surface of the rf electrode. As the excitation frequency of the plasma, 13.56 MHz, 40 MHz and 60 MHz were used. The radial profile of plasma density was observed in the downstream at 12 cm below the axial center of the rf electrode. Measurements were carried out for Ar plasma for pressures < 10 mTorr. The applied rf power varied from 200 W to 1500 W. The radial profile of the plasma density at a given distance from the axial center of the rf electrode changes with the change of excitation frequency. When the excitation frequency is 40 MHz, a radially uniform plasma could be obtained 12 cm below the axial center of the rf electrode. The nonuniformity of this plasma over an area of 300 mm diameter is <±5% regardless of the applied rf power. A change of pressure slightly affects the radial uniformity of the plasma. Plasmas produced by two other frequencies show a higher nonuniformity at the same distance from the axial center.
- Publication:
-
Japanese Journal of Applied Physics
- Pub Date:
- April 1998
- DOI:
- 10.1143/JJAP.37.2035
- Bibcode:
- 1998JaJAP..37.2035W