Gaseous discharge light sources are leading candidates for generating 13.5 nm wavelengths needed for next-generation optical lithography. Electrode debris reaching the first collector optic is a serious concern for device lifetime and cost of ownership. This paper describes the experimental setup and initial data obtained for testing secondary-plasma-based debris mitigation for EUV gas discharge light sources. Operation of a dense plasma focus, secondary RF debris mitigation system, and several in-situ diagnostics were successfully tested, achieving first measurements for debris attenuation. It was also found that fast ion and fast neutral particle erosion processes at the optical mirror location dominate over deposition of sputtered metal if a collimator or “foil trap” is positioned between the hot pinch plasma and the first collector optic.
RF plasma based mitigation has been studied as an improved debris mitigation scheme for extreme ultraviolet (EUV) sources. The RF plasma ionizes sputtered neutral debris and, when used in conjunction with a collimator (also known as a foil trap), inhibits that debris from reaching the collector optics. An ionization fraction of 61±3% has been measured. In addition, increased scattering of the ion component of the debris has led to a decrease in erosive flux reaching the diagnostics. Results from in-situ high-precision quartz crystal oscillators, ex-situ surface characterization (Auger, XPS), and secondary plasma characterization is presented for a series of mitigation schemes, including a foil trap in conjunction with the RF plasma.