Paul D. Pochan

and electron temperatures near 4 eV. The electron density peaked on axis with typical full-width at half maximum of 7 cm to 9 cm. Discharges in chlorine and nitrogen had bimodal operation that was clearly evident from optical emission intensity. A dim mode occurred at low power and a bright mode at high power. The transition between modes had hysteresis. After many hours of high-power operation, films formed on electrodes and walls of one Cell. These deposits affected the dim-to-bright mode transition, and also apparently caused generation of hot electrons and increased the plasma potential.

Period doubling and concomitant subharmonic generation have been reported in rf-excited plasmas. We show that this phenomenon is caused by the nonlinear interaction of the plasma-sheath capacitance with the external rf power circuits. As a result, changes in the external circuits can be used to control period doubling. Sheath capacitance can be derived from electrical measurements of period doubling.

The initial interlaboratory comparison of Reference-Cell plasmas emphasized rf voltage and current measurements. Plasma properties were found to be dependent on rf circuit impedances at harmonics of the 13.56-MHz excitation frequency as well as on power, pressure, etc. The dependence was due to the nonlinear interaction of the plasma with the rf generator, cables, and matching network. This finding led to studies of performance problems common to industrial etching reactors. Electrical diagnostics and methodologies that had been developed with the Reference Cell were applied to the production problems. The authors developed understanding of and control over subharmonic generation and they developed cures for chamber-to-chamber variability in etch rate and dc bias.