A time-modulated and time-averaged two-dimensional (2D) profile of the net excitation rate of Ar(3p5) and Ar+(4p4D7/2) was observed in capacitively coupled plasma (CCP) in Ar as a function of the driving frequency (1-100 MHz) through the use of 2D-t optical emission spectroscopy (OES). A significant improvement in the detection efficiency was achieved for the time-resolved OES. Results are presented for the basic characteristics of 2D and 2D-t profiles of the net excitation rate in Ar from 1 to 100 MHz at 1.0 Torr. For comparison, 2D profiles in CCP between high frequency (13.56 MHz) and very high frequency (100 MHz) at 0.1 Torr and 25 mTorr under the same power dissipation are discussed. The advantages of VHF operation are described and discussed based on the radial uniformity and high density in CCP at low pressure. The appearance of a local emission peak at the edge of the rf electrode is observed in CCP, which is caused by changes in the sustaining mechanism due to increases in the driving frequency.
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