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

Abstract

Recently, vacuum ultra-violet (VUV) radiations emitted from plasmas have been of particular interest for semiconductor device fabrication because of the effects of their high energy photons such as induced damage or curing on low-k materials. Due to the difficulty to implement 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 spectrometer, the system shows considerable implementation potential thanks to its compact size, higher detection accuracy and time resolution below 200 ns. VUV radiations emitted by continuous and pulsed hydrogen plasmas generated at low pressure were investigated using the developed system. Using various filters, we were able to compare the VUV photons intensity in different wavelength ranges. It was found that VUV photons 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 radiations such as Lyman and Werner bands observed in low-pressure hydrogen plasmas.