Etch rate and plasma density radial uniformity measurements in a cusped field helicon plasma etcher

Experiments on the University of Wisconsin helicon etcher were conducted to study the effects on uniformity of applying a cusped magnetic field to the etching chamber. Also a comparison was made between long and short antenna/substrate separation distances. The plasma radial density uniformities, measured using a Langmuir probe over the inner 10 cm diameter of the chamber, gave maximum density variations of +/- 22% with the cusp off and +/- 1.28% at the zero field region of the cusp. The maximum SiO2 etch rate in CF4/Ar plasmas occurred at 50% Ar concentration in the long source configuration. Etch rate uniformity of SiO2 etching in a CF4/Ar/O-2 plasma improved from +/- 8.1% to +/- 2.6% for a 82.5 mm wafer by shortening the antenna-substrate separation distance from 108 to 47 cm. Azimuthal asymmetry of the plasma produced from the Nagoya type III antenna was observed in the shea source configuration in which the SiO2 etch rate uniformity varied from +/- 1.5% across the vertical axis of a 150-mm-diam wafer to +/- 12% across the horizontal axis of the wafer. (C) 1996 American Vacuum Society.