Monitoring of radio-frequency glow-discharge plasma

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Abstract
The optical emission profile (OEP) between anode and cathode electrodes is examined for monitoring planar rf discharges of H2, N2, and Ar gases. Form the OEP we can easily find the boundary of the ion sheath and the plasma region and accordingly the ion sheath width at the cathode electrode. The plasma parameters are measured by the Langmuir probe method, and the relative mean electron energy Te in H2 and N2 plasmas is found to be evaluated by the ion sheath width ls with a relationship Te∝ls. The plasma density can also be estimated by both the cathode negative potential Vc and ls. A charge-coupled device (CCD) image sensor with a 105-mm macro lens is employed to measure the OEP within a very short time. Although the CCD measurement shows a somewhat deviated OEP, this is very useful to measure the precise ion sheath width.