Sn Etching of Extreme Ultraviolet (EUV) Mirror Surface Using Ar-H₂ Atmospheric Pressure Arc Plasma Jet

An Ar-H-2 arc plasma jet under atmospheric pressure was used to etch the tin (Sn) contamination deposited on the multi-thin film surface of the Extreme ultraviolet (EUV) mirror. Sn was deposited on a multilayer of ZrO2/SiO2/Si to prepare a sample. The Sn was removed by hydrogen radical (H) to form a gaseous compound in the form of SnH4. The compound has the advantage of being easy to remove from the system via exhaust. Among methods for removing Sn using H, the reason why an atmospheric pressure Ar-H-2 plasma jet is particularly used is that the device has the advantage of being simple in configuration compared to other methods. By varying the discharge conditions such as the content of H-2 in mixture gas, applied power, and treatment time, the plasma characteristics and the degree of Sn removal were investigated. The basic plasma characteristics were identified by electron density and electron temperature through optical emission spectroscopy (OES). In particular, the generation of Ar* (argon excitation species) has been estimated for the parameter for H generation. To avoid thermal effect, we measure the temperature of sample surfaces with an infrared camera. For surface analysis of Sn etching, we used scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). In this experiment, the optimal case of Ar-H-2 atmospheric pressure arc plasma jet was found to be treated for at least 1 min in the removal of Sn contamination under applied power of 500 W using 5% of H-2 mixed content.