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Proceedings Article

Controlling contamination in Mo/Si multilayer mirrors by Si surface capping modifications

[+] Author Affiliations
Michael E. Malinowski, Chip Steinhaus, W. Miles Clift, Leonard E. Klebanoff

Sandia National Labs. (USA)

Stanley Mrowka

Lawrence Berkeley National Lab. (USA)

Regina Soufli

Lawrence Livermore National Lab. (USA)

Proc. SPIE 4688, Emerging Lithographic Technologies VI, 442 (July 5, 2002); doi:10.1117/12.472320
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From Conference Volume 4688

  • Emerging Lithographic Technologies VI
  • Roxann L. Engelstad
  • Santa Clara, CA | March 03, 2002

abstract

The performance of Mo/Si multilayer mirrors (MLMs) used to reflect UV (EUV) radiation in an EUV + hydrocarbon (NC) vapor environment can be improved by optimizing the silicon capping layer thickness on the MLM in order to minimize the initial buildup of carbon on MLMs. Carbon buildup is undesirable since it can absorb EUV radiation and reduce MLM reflectivity. A set of Mo/Si MLMs deposited on Si wafers was fabricated such that each MLM had a different Si capping layer thickness ranging form 2 nm to 7 nm. Samples from each MLM wafer were exposed to a combination of EUV light + (HC) vapors at the Advanced Light Source (ALS) synchrotron in order to determine if the Si capping layer thickness affected the carbon buildup on the MLMs. It was found that the capping layer thickness had a major influence on this 'carbonizing' tendency, with the 3 nm layer thickness providing the best initial resistance to carbonizing and accompanying EUV reflectivity loss in the MLM. The Si capping layer thickness deposited on a typical EUV optic is 4.3 nm. Measurements of the absolute reflectivities performed on the Calibration and Standards beamline at the ALS indicated the EUV reflectivity of the 3 nm-capped MLM was actually slightly higher than that of the normal, 4 nm Si-capped sample. These results show that he use of a 3 nm capping layer represents an improvement over the 4 nm layer since the 3 nm has both a higher absolute reflectivity and better initial resistance to carbon buildup. The results also support the general concept of minimizing the electric field intensity at the MLM surface to minimize photoelectron production and, correspondingly, carbon buildup in a EUV + HC vapor environment.

© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Citation

Michael E. Malinowski ; Chip Steinhaus ; W. Miles Clift ; Leonard E. Klebanoff ; Stanley Mrowka, et al.
"Controlling contamination in Mo/Si multilayer mirrors by Si surface capping modifications", Proc. SPIE 4688, Emerging Lithographic Technologies VI, 442 (July 5, 2002); doi:10.1117/12.472320; http://dx.doi.org/10.1117/12.472320


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