Andrew Herschberg


The Tin Removal EXperiment (T-REX) aims to remove tin on the collection mirror of an extreme ultraviolet (EUV) source used for advanced lithography. This is extremely important for the semiconductor industry as tin deposition on the collection mirror drastically reduces the reflectivity, mirror lifetime, and tool availability. Tin is removed by an annular hydrogen surface wave plasma (SWP) source at the cone and perimeter of the collection mirror. SWPs are ideal for this application as they have high ion and radical densities and have electron temperatures low enough to not cause any damage to the collection mirror. Measurements of the radical density, done with a radical probe, and ion density and electron temperature, measured with a Langmuir probe, are used to characterize the plasma at various flow rates, pressures, powers, and temperatures. In addition, optical and stylus profilometry are used to measure etch rates, while a scanning electron microscope is used to measure surface morphology as a result of the SWP. The SWP source can also operate in-situ and provide etch rates that exceed that of the collection mirror contamination rate, which will reduce tool downtime and increase mirror lifetime.