Study on Monitoring of Radio Frequency Glow Discharge Plasma

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Optical emission profile (OEP) between parallel cathode and anode electrodes was proposed for monitoring and characterizing radio frequency (rf) glow discharge plasma, and H_2, N_2 and Ar glow discharges were examined. The cathode sheath width was evaluated quite easily by the OEP, because the boundary of the ion sheath and the plasma lay just at a peak position in the OEP. Only H_2 discharge has a doublet peak and a second peak corresponded to the boundary. The plasma parameters are measured by the Langmuir probe method, and the relative mean electronenergy Te in H_2 and N_2 plasmas is found to be evaluated by the ion sheath width Is with a relationship Te Is. The plasma density can also be estimated by both the cathode negative potential Vc and Is.The quick measurement of the OEP using a CCD image sensor was also examined for the practical palsma processings. Although the CCD technique brought the somewhat deviated OEP because of the difficulty in the representation of the parallel electrodes at a two dimentional image through an optical lens, the precise ion sheath widths were also to be evaluated, especially for relatively narrow sheath widths. The CCD image sensor combined with a macro-lens with the focal distance of 105mm was quite successful for measuring the sheath width.