Development of a radio-frequency glow discharge source with integrated voltage and current probes

Radio-frequency glow discharge optical emission spectroscopy is routinely used for the chemical analysis of solid samples. Correct plasma voltage and current signals are needed to quantify depth-profile measurements. Therefore, a glow discharge source with integrated current and voltage probes has been developed. The main source feature is the small disturbance of the current signal by displacement currents and the independence of the current signal from leak currents of the water cooling. The special probe design results in a wide bandwidth and good phase stability. Plasma disturbances caused by harmonics of the radio-frequency generator are reduced by the use of a resistive–capacitive low-pass filter. With this new technique current–voltage characteristics are measured even for samples with insulating layers. A new procedure allows the determination of the plasma bias voltage for insulating samples. Though the insulating layer thickness on metal is usually unknown, it is possible to calculate the effective plasma voltage and also the quantitative RF-GD-OES depth-profile using an iterative procedure. We present current–voltage characteristics for conducting and nonconducting samples for different materials, pressures and voltages. The estimated errors for the voltage, current and power measurement are smaller than 8%.