Study on the third harmonic diagnosis and etching distribution analysis according to the phase change between the upper and lower RF electrodes in a 60 MHz capacitively coupled plasma triode reactor based high aspect ratio contact dry etching process

The high aspect ratio contact dry etching process generally uses source frequencies of tens of MHz or more and high power of thousands of watts or more to generate high plasma density under low pressure conditions of 10 Pa or less in capacitively coupled plasma (CCP). This intensifies the problem of plasma density distribution such as high density of reactor centers caused by coupling phenomenon between harmonic based plasma series resonance and spatial wave resonance caused by nonlinear characteristics of plasma. In this study, the same 60 MHz source frequency was applied to the upper and lower electrodes of the triode CCP reactor, and the analysis was performed between the third harmonic plasma series resonance measured and the calculated quality factor value according to the voltage phase change between the electrodes. In order to measure the change rate of 180 MHz electromagnetic waves, which is the third harmonic of fundamental frequency, a coli-type electromagnetic wave pickup antenna was mounted on a viewport on the side of the near reactor wall to measure the radiation current, and the etching distribution of the SiO2 blanket wafer was measured to confirm the correlation with the process result. As a result, it was confirmed that the third harmonic ratio to the fundamental frequency was measured to be the lowest near 90° compared to the phase 0° and 180° between electrodes, and the etching distribution near the center of the SiO2 blanket wafer was improved. This phenomenon could be explained through the average value for the time of the total sheath capacitance calculated as a sum for the upper electrode, the lower electrode, and the wall ground sheath according the phase difference, and the quality factor calculation value inversely proportional to the total sheath capacitance. That is, under the experimental process conditions, the time average total sheath capacitance value was calculated as the maximum value and the quality factor was calculated as the minimum value from the upper and lower radio frequency source perspectives near the 90° phase difference, and it was estimated that the third harmonic plasma series resonance phenomenon was reduced.