Low Electron Temperature Plasma Diagnosis: Revisiting Langmuir Electrostatic Probes

This article describes a method of measurement of the current-to-probe voltage characteristic curve of a Langmuir electrostatic probe immersed in a plasma characterized by a low electron temperature that is only one order of magnitude higher than room temperature. These plasmas are widely used in industrial processes related to surface technology, polymers, cleaning, nanostructures, etc. The measurement method complies with the strict requirements to perform representative plasma diagnosis, particularly in the ion saturation zone when the probe is polarized much more negatively that the potential of the plasma bulk surrounding the probe and allows to diagnose the plasma very quickly and locally, making it possible to better monitor and control the plasma discharge uniformity and time drift. The requirements for the Langmuir probe design, the data acquisition and data treatment are thoroughly explained and their influence on the measurement method is also described. Subsequently, the article describes different diagnostic methods of the magnitudes that characterize the plasma, based on theoretical models of that characteristic curve. Each of these methods is applied to different zones of the measured characteristic curve, the obtained results being quite similar, which guarantees the quality of the measurements. The advantages and disadvantages of each method are discussed. A series of measurements of the plasma density for different plasma conditions shows that the method is sensitive enough that the temperature of the ions needs to be taken into account in the data processing. Finally, a Virtual Instrument is included in the LabView environment that performs the diagnosis process with sufficient speed and precision, which allows the scientist to control the parameters that characterize the plasma to increase the quality and performance of the industrial processes in which the plasma diagnosis is to be used. The Virtual Instrument can be downloaded for free from a link that is included, in order to be easily adapted to the usual devices in a plasma laboratory.

Characterization of SiO2 Etching Profiles in Pulse-Modulated Capacitively Coupled Plasmas

Although pulse-modulated plasma has overcome various problems encountered during the development of the high aspect ratio contact hole etching process, there is still a lack of understanding in terms of precisely how the pulse-modulated plasma solves the issues. In this research, to gain insight into previously observed phenomena, SiO2 etching characteristics were investigated under various pulsed plasma conditions and analyzed through plasma diagnostics. Specifically, the disappearance of micro-trenching from the use of pulse-modulated plasma is analyzed via self-bias, and the phenomenon that as power off-time increases, the sidewall angle increases is interpreted via radical species density and self-bias. Further, the change from etching to deposition with decreased peak power during processing is understood via self-bias and electron density. It is expected that this research will provide an informative window for the optimization of SiO2 etching and for basic processing databases including plasma diagnosis for advanced plasma processing simulators.

DC Glow Discharge Plasma Characteristics in Ar/O2 Gas Mixture

In this article, the effects of the O2 ratio on the electrical characteristics, including the I-V characteristic curve, Panchen’s curve, and I-P curve, were tested in a sample of O2/Ar gaseous mixture . The sample was produced by plasma-based DC magnetron sputtering with niobium metal as a target material. The inter-electrode spacing value was 4 cm. Plasma diagnosis via the Optical Emission Spectroscopy (OES) method was used to achieve Te and Ne mixture values of 20 %, 30 %, 50%, and 70% in the Ar/O2 system. The results showed that the discharge is operating in the abnormal glow region and the discharge current was decreased by increasing O2 percentage. In addition, the experimental results showed that the discharge is optimal at 30% gas ratio. It was found that the electron temperature was decreased with increasing working pressure and increased with increasing the O2 percentage, while electron density was increased with increasing both working gas pressure and O2 percentage.