Krypton as filter for ions, debris and useless radiation in EUV projection lithography systems

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Abstract

The life time of the first multilayer mirror (the condenser) in optical systems for projection Extreme Ultra-Violet (EUV) lithography based on Laser Produced Plasmas (LPP) is limited both by the debris bombardment and by the EUV radiation photoablation. These problems can be dramatically reduced by using krypton as debris stopper, exploiting its high atomic weight (21 times the helium value) and its high transparency in the EUV region only between 60 and 90 eV. We demonstrate both theoretically and experimentally that by filling the laser-target interaction chamber with krypton at low pressure (a few mbar) it is possible to stop efficiently the small debris (having a size smaller than 1 micron, including ions, neutrals and clusters) while keeping a reasonable transmission of the EUV radiation in the 60-90 eV range (> 80%). In particular, this is experimentally demonstrated for a solid target LPP based on a tantalum or copper tape target and pumped by a large energy (4 J - 120 ns) XeCl excimer laser. The poor transmission of krypton, out of the above mentioned spectral window, significantly reduces the exposition of the condenser mirror to useless radiation. As far as the larger size debris is regarded, a dramatic reduction of their flux has been obtained by decreasing the laser intensity on the target, still keeping a laser to EUV energy conversion as high as 0.7%/eV/sr at 70 eV, from a Ta target, together with a shot to shot EUV pulse energy stability better than 1%.
Original languageEnglish
DOIs
Publication statusPublished - 2001
Externally publishedYes
EventApplications of X-Rays Generated from Lasers and Other Bright Sources II - , United States
Duration: 1 Jan 2001 → …

Conference

ConferenceApplications of X-Rays Generated from Lasers and Other Bright Sources II
CountryUnited States
Period1/1/01 → …

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All Science Journal Classification (ASJC) codes

  • Electrical and Electronic Engineering
  • Condensed Matter Physics

Cite this

Flora, F., Mezi, L., Bollanti, S., Bonfigli, F., Di Lazzaro, P., Letardi, T., & Zheng, C. (2001). Krypton as filter for ions, debris and useless radiation in EUV projection lithography systems. Paper presented at Applications of X-Rays Generated from Lasers and Other Bright Sources II, United States. https://doi.org/10.1117/12.448452