Real-time VUV radiation monitoring in low-pressure hydrogen plasma based on fluorescence of sodium salicylate

Recently, vacuum ultra-violet (VUV) radiation emitted from plasmas has been of particular interest in semiconductor device fabrication because of the effects of its high-energy photons, such as induced damage or curing on low-k materials. Due to the difficulty of implementing conventional spectroscopic methods to monitor VUV radiation with high accuracy and time resolution in current plasma processing equipment, novel monitoring methods must be investigated. Therefore, in this work, we developed a compact VUV radiation monitoring system based on a scintillator, i.e. sodium salicylate (NaSal), for real-time VUV measurements. Compared to conventional VUV spectrometers, the system shows considerable implementation potential thanks to its compact size, higher detection accuracy and high time resolution. VUV radiation emitted by continuous and pulsed hydrogen plasmas generated at low pressure was investigated using the developed system. Using various filters, we were able to compare the VUV photon intensity in different wavelength ranges. It was found that the VUV photon intensity between 115 and 250 nm was about 2.5 times higher than in the region below 115 nm due to intense Lyman-α and molecular radiation, such as Lyman and Werner bands observed in low-pressure hydrogen plasmas.