Fundamentals and applications of dry CO2 cryogenic aerosol for photomask cleaning

Ivin Varghese; Mehdi Balooch; Charles W. Bowers

doi:10.1117/12.877555

24 September 2010 Fundamentals and applications of dry CO₂ cryogenic aerosol for photomask cleaning

Ivin Varghese, Mehdi Balooch, Charles W. Bowers

Proceedings Volume 7823, Photomask Technology 2010; 78232Y (2010) https://doi.org/10.1117/12.877555
Event: SPIE Photomask Technology, 2010, Monterey, California, United States

Abstract

There is a dire need for the removal of all printable defects on lithography masks. As the technology node advances, smaller particles need to be efficiently removed from smaller features without any damage or adders. CO₂ cryogenic aerosol cleaning is a dry, residue-free and chemically inert technique that doesn't suffer from disadvantages of conventional wet cleaning methods such as transmission/reflectivity loss, phase change, CD change, haze/progressive defects, and/or limitation on number of cleaning cycles. Ultra-pure liquid CO₂ when dispensed through an optimally designed nozzle results in CO₂ clusters that impart the required momentum for defect removal. Historically nanomachining debris removal has been established with this technique. Several improvements have been incorporated for cleaning of advanced node masks, which has enabled Full Mask Final Clean, a new capability that has been successfully demonstrated. The properties of the CO₂ clusters can be captured utilizing the Phase Doppler Anemometry (PDA) and effect of varying process and design parameters can be verified. New nozzles have been designed to widen the cleaning process window for advanced node optical masks, without any damage to the weak primary features and/or sub-resolution assist features (SRAFs). This capability has been experimentally proven for high aspect ratio SRAFs e.g. 2.79 (52nm wide by 145 nm tall) as well as SRAFs 45nm wide by 73 nm tall. In this paper, 100% removal of soft defects that would have printed on advanced node masks is demonstrated. No printed defects larger than 50nm is observed after the CO₂ cleaning. Stability of the cleaning and handling mechanisms has been demonstrated over the last 4.5 months in a production environment. The CO₂ cleaning technique is expected to be effective for more advanced masks and Extreme Ultra-Violet (EUV) lithography.

Citation Download Citation

Ivin Varghese, Mehdi Balooch, and Charles W. Bowers "Fundamentals and applications of dry CO₂ cryogenic aerosol for photomask cleaning", Proc. SPIE 7823, Photomask Technology 2010, 78232Y (24 September 2010); https://doi.org/10.1117/12.877555

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