Quantification of VUV photon and particle fluxes in low pressure plasmas for surface treatment

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Photon fluxes in the ultraviolet (UV) and in particular in the vacuum-ultraviolet spectral range (VUV) within low pressure plasmas for surface treatment can have a decisive impact on the material's surface. Energy resolved quantification and if necessary tuning of these fluxes is elementary for optimizing the respective plasma processes. Therefore, VUV spectrometers need to be applied, which require direct access to the plasma chamber and whose complex intensity calibration needs to be performed on-site. Hence, up to now fundamental studies exist only for very specific applications or are limited to simulations. This project aims at the systematic wavelength-resolved quantification of the UV and VUV photon fluxes in plasmas used for surface treatment and their correlation to the occurring particle fluxes. A portable measurement device is to be developed in a second step, in order to make relevant VUV/UV photon fluxes at process plasmas accessible. The investigations are conducted at a dedicated laboratory experiment equipped with the appropriate diagnostics for the flux characterization: intensity calibrated emission spectroscopy from the VUV through to the NIR spectral range, a moveable Langmuir probe as well as energy resolved mass spectrometry. The measurements are assisted by collisional-radiative modelling including the effects of reabsorption of photons within the plasma, in order to determine the main influencing plasma parameters on the emitted radiation. In parallel a prototype for a compact measurement device to quantify energy resolved VUV/UV photon fluxes at process plasmas will be developed. The instrument is based on a VUV sensitive photodiode and interchangeable filters, which are to be selected with regard to the particular process gases. The laboratory setup gives the unique opportunity to benchmark the device against the absolutely calibrated VUV spectrometer. In order to demonstrate its applicability to process plasmas the device will conclusively be tested at three different experiments related to surface treatment.