L. Wilken

Erosion rate measurements for GD-OES

For GD-OES the sputtering rate of standard reference materials is needed for calibration purposes. A modern optical profilometer is used to measure 3D crater profiles. The crater volume, the erosion and the sputtering rate is calculated. A series of measurements was performed at reference materials and different plasma conditions. The plot of the reduced sputtering rates versus voltage proves the validity of the Boumans formula.

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%.

Comparison of modeling calculations with experimental results for rf glow discharge optical emission spectrometry

Abstract A model developed recently for a radio-frequency glow discharge, is applied to experimental Grimm-type discharge conditions, to check the validity of the model calculations. The calculated electrical characteristics (rf voltage, d.c. bias voltage, electrical power, peak-to-peak current, as well as the time-profiles of voltage and current), and the calculated erosion rates are compared with the measured values for an rf frequency of 3.5 MHz. The electrical characteristics are found to be in fairly good agreement. The calculated and measured erosion rates show larger discrepancies. Compared to the d.c. Grimm-type glow discharge, where similar quantities were compared and were found in excellent agreement, the agreement is less satisfactory in the rf discharge. This illustrates that the rf discharge is much more complicated than a d.c. discharge, and that more fundamental studies are required.

Comparison of modeling calculations with experimental results for direct current glow discharge optical emission spectrometry

Abstract A comparison is made between numerical modeling and experimental results for the electrical characteristics, the erosion rates and the optical emission intensities of various argon and copper lines in a direct current glow discharge, to verify the model calculations and to illustrate some features and limitations of the model. In order to reach good agreement with the current–voltage characteristics, the gas temperature, which was treated as an adjustable parameter, was assumed to increase slightly as a function of voltage and pressure. This assumption is in accordance with theoretical predictions and experimental observations in the literature. The erosion rates and optical emission intensities, calculated as a function of voltage and pressure, were also found to be in reasonable agreement with the experimental data. However, it appeared that still better agreement with the measured data could be reached when the gas temperature was assumed to be constant as a function of voltage. This illustrates that the effect of voltage cannot yet be completely correctly predicted for both the electrical current and the erosion rates and optical emission intensities at the same time, and that, therefore, the glow discharge behavior is not yet perfectly described in the model. This is not unexpected in view of the complexity of the model calculations and the uncertainties of some input data. However, in general, the agreement between model results and experimental data is satisfactory, so that it can be concluded that the model gives already a realistic picture of the direct current glow discharge.

In situ depth measurements for GD-OESPresented at the 2003 European Winter Conference on Plasma Spectrochemistry, Garmisch-Partenkirchen, Germany, January 12?17, 2003.

For a glow discharge source we present a new instrument to measure the depth during sputtering. The developed system is based on a laser interferometer and a Grimm type GD source. We developed a mathematical model, which corrects the signal disturbances due to the thermal expansion of GD source and sample surface. Another model describes dependence of the sample surface temperature on discharge power, material constants and position. The in situ depth measurement instrument is used to measure the thickness of zinc layers in the micrometer range.

Radio frequency glow discharge source with integrated voltage and current probes used for evaluation of discharge parameters

A radio frequency (rf) Grimm-type glow discharge source for the chemical analysis of solid samples, with integrated voltage and current probes, was developed. All elements of a plasma equivalent circuit are determined from the measured current-voltage characteristics. The procedure is based on the independent evaluation of the ion current and electron current region. The physical meaning of the parameters is investigated by comparisons with measurements from dc glow discharges. We found that the reduced rf current of the powered electrode is comparable to the reduced current in dc discharges. A formula is developed that corrects the reduced current due to gas heating. The sheath thickness at the powered rf electrode is evaluated and is between 75 and 1100μm. The voltage of the bulk plasma is in the range 2–15V, and the resistance is between 30 and 400Ω. The bulk plasma consumes about 3% of the total power, and the reduced voltage is comparable to the reduced electrical field in the positive column of dire...