Electrical measurements at radio frequency glow discharges for spectroscopy

This paper presents a review of the electrical radio frequency measurement techniques used in glow discharge optical emission spectrometry (GD-OES). In the introduction we show that for accurate quantitative chemical measurements reproducible electrical measurements are necessary. In the main part we introduce the techniques to generate the radio frequency (RF) and to measure voltage, current and power of the RF discharges. The required bandwidth of a RF current probe is estimated. Directional couplers used for the power measurement are introduced and their properties and limits are discussed. An overview of the different numerical and electronic evaluation methods for the voltage, current and power signals is given. New electrical measurements at the start up of a RF discharge and of a microsecond pulsed RF discharge show the benefit of the glow discharge source with integrated voltage and current probes. We present the use of the evaluated parameters to describe the dependence of the sputtering rate and the optical emission on RF discharge voltage and current using the model of Boumans and Bengtson. We also discuss the techniques to measure thick insulating materials and thin insulating layers with RF-GD-OES. Especially the evaluation of discharge voltage and current is presented in detail.