Control of the Harmonics Generation in a Capacitively Coupled Plasma Reactor

The resonant growth of harmonics was observed in a dual-frequency capacitively coupled plasma etcher. The resonances of the second, third, and fourth harmonics of the bias RF were observed through current and voltage measurements. A fine tuning of the wafer-electrode reactance revealed that the reactance is the dominant factor controlling harmonic amplitude. The resonances take place when the sum of the wafer-electrode and plasma reactances reaches its minimum value at the harmonic frequency. A simple nonlinear equivalent circuit model well reproduces the experimental result. Significant changes in the radial distribution of electron density and the resultant etching rate were observed at resonance.