Debris mitigation and cleaning strategies for Sn-based sources for EUV lithography

摘要

The EUV source is an essential part of an EUV lithography exposure tool. All EUVL sources, and especially Sn-basedsources, not only generate the desired radiation at a wavelength of 13.5 nm but also produce debris that limits thelifetime of the collecting optics in the lithographic system. In order to increase the lifetime of these optics we havesuccessfully demonstrated the feasibility of both debris mitigation and cleaning strategies.In this paper, we show the experimental results for different debris mitigation schemes as performed in cooperation withPhilips Extreme UV. We performed our experiments under realistic conditions: samples that closely resemble the opticsin the EUV lithography set-up and positioned at realistic distances and orientation to the Sn-based EUV source. Usingthese schemes we were able to suppress both atomic debris and Sn-particles generated by the Sn-based EUV sourcewith 4-5 orders of magnitude. Based on our experiments, we found a significant improvement in the lifetime of the EUVoptics.In addition to avoiding the contamination of EUV optics, one can also clean the contaminated EUV optics. To do this,we have developed a technology for removing Sn (and C) using atomic hydrogen. We demonstrated Sn removal at arate >200 nm/hour under a variety of experimental conditions (temperature, pressure).Our results demonstrate that combining debris mitigation schemes with cleaning schemes could lead to an EUVlithography system with acceptable operational lifetimes.