Cryogenic aerosol cleaning of photomasks

S. Banerjee; C. C. Lin; S. Su; H. F. Chung; W. Brandt; K. Tang

doi:10.1117/12.617081

28 June 2005 Cryogenic aerosol cleaning of photomasks

S. Banerjee, C. C. Lin, S. Su, H. F. Chung, W. Brandt, K. Tang

Proceedings Volume 5853, Photomask and Next-Generation Lithography Mask Technology XII; (2005) https://doi.org/10.1117/12.617081
Event: Photomask and Next Generation Lithography Mask Technology XII, 2005, Yokohama, Japan

Abstract

This paper describes the mechanism and cleaning results of a dry cleaning technology using CO₂ cryogenic aerosols. The cleaning mechanism relies on momentum transfer from the aerosol particles to overcome the force of adhesion of the contaminant particles on the surface. Particle removal is possible without degradation or etching of underlying film or the need for drying with IPA as in wet cleaning. A theoretical model of particle removal based on momentum transfer is described, predicting higher removal efficiency for sub-micron particles compared to larger particles. Experimental results with Si₃N₄ particles on silicon wafers show that removal of sub-micron particles is 10% higher than larger particles up to 30 μm, as predicted by the model. The paper also shows experimental results of various types of contaminant particle removal in photomask cleaning. Results of post mechanical repair cleaning of photomasks show effective removal of the quartz particles without damage to the adjacent chrome lines. Inorganic contaminants such as ammonium sulphate, commonly known as "haze", is removed by cryogenic aerosol cleaning with 99% efficiency as seen using optical inspection tool. The effect of cleaning on the phase and transmission of the mask is measured with multiple cleaning. The results show that over 16 cleaning cycles, the change in transmission is 0.04% an the change in phase is 0.37°. Thus a non-invasive cleaning for sub-micron particles from photomasks is possible with CO₂ cryogenic aerosols.

Citation Download Citation

S. Banerjee, C. C. Lin, S. Su, H. F. Chung, W. Brandt, and K. Tang "Cryogenic aerosol cleaning of photomasks", Proc. SPIE 5853, Photomask and Next-Generation Lithography Mask Technology XII, (28 June 2005); https://doi.org/10.1117/12.617081

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