AVS 45th International Symposium
    Plasma Science and Technology Division Thursday Sessions
       Session PS-ThA

Paper PS-ThA4
An ICP Source Design with Improved Azimuthal Symmetry@footnote 1@

Thursday, November 5, 1998, 3:00 pm, Room 318/319/320

Session: Diagnostics II
Presenter: M.H. Khater, University of Texas, Dallas
Authors: M.H. Khater, University of Texas, Dallas
L.J. Overzet, University of Texas, Dallas
B.E. Cherrington, University of Dayton
Correspondent: Click to Email
The geometry of an inductively coupled plasma (ICP) source impacts the plasma and processing uniformity. A reasonably uniform source design does not always guarantee uniform plasma, however, because transmission line effects also impact its performance.@footnote 2@ These cause the current to vary along the coil length producing azimuthal asymmetries in the RF fields of planar sources, a non-uniform power deposition in the plasma and non-uniform processing rates. The azimuthal uniformity for planar coils can be improved somewhat but with significant drawbacks. A source geometry that is inherently uniform and is not adversely impacted by transmission line effects would be preferred. We will present what we think is just such an ICP source design. The geometry is three dimensional rather than planar and consists of two (or more) layers of full and semicircular loops with the RF current generally flowing in opposite directions. Typically, the "bottom" layer consists of full circular loops, while the "top" layer consists of semicircular loops. The length of the new source is greater than that of a similarly sized planar coil, nevertheless, both have inductances near 3 µH. We have measured the free space magnetic fields produced by one of these sources in the (r,@theta@) plane using a B-dot probe. It generated fields of higher azimuthal symmetry than the planar coil despite a larger current variation (I@sub out@/I@sub in@) along the source length. The average value of the peak azimuthal electric field for the new source was E@sub theta@/I@sub out@=0.24 V/(cm A) with a standard deviation of @sigma@=0.0085. The planar coil produced 0.32 V/(cm A) with @sigma@=0.027. The new source has been used to produce high density (10@super 11@-10@super 12@ cm@super -3@) Ar and SF@sub 6@ discharges at low pressures (5-20 mTorr) and to etch poly silicon. @FootnoteText@ @footnote 1@ This material is based upon work supported by Beta Squared Inc. under Grant No. UTD96-56 and by the State of Texas Advanced Research Program under Grant No. 009741-043. @footnote 2@ M. Kushner, et al., J. Appl. Phys. 80, 1337 (1996).