Status and challenges in electrical diagnostics of processing plasmas

Eugen Stamate (Invited author)

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Reactive plasmas produced in oxygen, nitrogen, hydrogen and other complex gas mixture are used for various applications including thin films, etching, ion implantation, ashing, particles growth, oxidation and other surface functionalization processes. Most of the reactive gases are also electronegative so that, the role of negative ions cannot be neglected. The continuous decrease of the features size in micro- and nanoelectronic industry requires a precise control of plasma parameters including the negative ions. Despite of a good progress in plasma diagnostics, yet more is to be done for developing techniques compatible with the strict requirements for device-making setups. Moreover the properties and possibilities to control the electronegative discharges are not completely understood. The aim of this work is to review the main electrical diagnostics techniques available to investigate reactive plasmas. Electrostatic probes have been used to diagnose electronegative plasma since 70’s. While this technique can give good results for density ratios of negative ion to electron higher than 10 its applicability for lower density ratios is questionable. In this context is was demonstrated that double hump structures observed in the electron energy probability function close to plasma potential cannot be associated with negative ion parameters because those structures are produced by a particular change in the work function over the probe surface as a result of discrete ion focusing. Another way to detect the plasma parameters in the presence of negative ions is to use the sensibility of the test function in the mid and high energy tail of the distribution function. The presence of negative ions is also associated with a lower heat flux to the probe, a fact that led to the development of a thermal probe that allows one to record at the same time not only the current bias, but also a temperature bias characteristic. The recent discovery of the discrete and modal focusing effects, associated with three-dimensional plasma-sheath-lenses has created the possibility to detect even low densities of negative ions using the sheath-lens probe. The positive ion extraction from reactive plasmas is rather easy. However, this is not the case for negative ions. The influence of biased electrodes, of small or large dimensions on plasma parameters in electronegative discharges can give more information about the possibility to control and use these plasmas for processing. Development of reactive plasma sources for both applications and basic science is rather challenging and some of these efforts will be presented in direct correlation with diagnostic approaches.
Original languageEnglish
Publication date2014
Publication statusPublished - 2014
Event41st International Conference on Metallurgical Coatings and Thin Films - San Diego, CA, United States
Duration: 28 Apr 20142 May 2014
Conference number: 41


Conference41st International Conference on Metallurgical Coatings and Thin Films
Country/TerritoryUnited States
CitySan Diego, CA
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