The Research Data Center Ruhr at the RWI (FDZ Ruhr im RWI)

Relationship between center-peaked plasma density profiles and harmonic electromagnetic waves in very high frequency capacitively coupled plasma reactors

“…Experimental measurements of the electron density profile and higher harmonic content of the electric field in VHF-CCP sources revealed that the confined sharp center peak superimposed on the broad center peak strongly correlates with the presence of UHF waves (400 MHz-1 GHz), although the frequencies of these waves are affected by the plasma density and chamber configuration. These results reproduce the experimental results obtained by Hebner et al 2) Complementing the experiments, precise numerical simulations of simple cavities and a full representation of our test-bench experiments indicate which harmonics are amplified in the plasma and produce the center peak. Power, pressure, frequency, and geometry determine the detailed profile, but it can be concluded that the center-peak evolution requires the amplification of the UHF wave content.…”

“…In addition, the fundamental, 2nd-4th harmonics, and UHF waves (>400 MHz) are prominent. Recall that Hebner et al 2) reported that 4th and 5th (704-880 MHz) harmonics UHF waves exist only in the center region in the case 176 MHz discharge and noted the correlation of the location of these UHF waves with a center-peaked plasma profile. Our simulation results are very likely a reproduction of the phenomena observed by Hebner et al…”

“…Numerous experimental reports on the radial distribution of plasma density or the associated physical properties in simple-structure parallel-plate CCP sources have shown that center-peaked plasma properties (density, current, and optical emission) occur when the driving frequency exceeds tens of MHz. Induction probe measurements of the RF current profile reported by Hebner and coworkers 2,3) showed that the RF current at the center is higher for a high driving frequency of 176 MHz than for 13.56 MHz. Sung and coworkers 4,5) measured the profile of Ar line (750 nm) emission intensity in a 100 MHz CCP source.…”