Collector Optic In-Situ Sn Removal Using Hydrogen Plasma

The presence of Sn on the collector optic of an extreme ultraviolet (EUV) light lithography tool continues to be a concern for source manufacturers. A mere nanometers deposition results in reduction of EUV light reflectivity to unacceptable levels. It has been shown previously that hydrogen radical etching of Sn provides a promising technique for in-situ cleaning of the collector optic. One concern in this technique is the redeposition by radicalized SnH4 breaking apart after making contact with a surface. To address this concern, large scale etching measurements were made using a metallic antenna as the substrate. Optimized etch rates approaching 7.5+/-1 nm/min have been achieved with a flow rate of 500 sccm at a pressure of 80 mTorr. The effect of variations in the Sn cleaning environment will be investigated with respect to temperature increases as well as air, oxygen, and methane contamination gasses. Furthermore, the effect of Sn located away from the cleaning location will also be presented.