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Proceedings Paper

Acoustic streaming effects in megasonic cleaning of EUV photomasks: a continuum model
Author(s): Vivek Kapila; Pierre A. Deymier; Hrishikesh Shende; Viraj Pandit; Srini Raghavan; Florence Odile Eschbach
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Paper Abstract

Removal of nano-scale contaminant particles from the photomasks is of critical importance to the implementation of EUV lithography for 32nm node. Megasonic cleaning has traditionally been used for photomask cleaning and extensions to sub 50nm particulates removal is being considered as a pattern damage free cleaning approach. Several mechanisms for removal are believed to be active in megasonic cleaning systems, e.g., cavitation, and acoustic streaming (Eckart, Schlichting, and microstreaming). It is often difficult to separate the effects of these individual mechanisms on contamination removal in a conventional experimental setup. Therefore, a theoretical approach is undertaken in this work with a focus on determining the contribution of acoustic streaming in cleaning process. A continuum model is used to describe the interaction between megasonic waves and a substrate (fused silica) immersed in a fluid (water). The model accounts for the viscous nature of the fluid. We calculate the acoustic vibrational modes of the system. These in turn are used to determine the acoustic streaming forces that lead to Schlichting streaming in a narrow acoustic boundary layer at the substrate/fluid interface. These forces are subsequently used to estimate the streaming velocities that may in turn apply a pressure and drag force on the contaminant particles adhering to the substrate. These effects are calculated as a function of angle of incidence, frequency and intensity of the megasonic wave. The relevance of this study is then discussed in the context of the cleaning efficiency and pattern damage in competing megasonic cleaning technologies, such as immersion, and nozzle-based systems.

Paper Details

Date Published: 8 November 2005
PDF: 10 pages
Proc. SPIE 5992, 25th Annual BACUS Symposium on Photomask Technology, 59923X (8 November 2005); doi: 10.1117/12.633378
Show Author Affiliations
Vivek Kapila, Univ. of Arizona (United States)
Pierre A. Deymier, Univ. of Arizona (United States)
Hrishikesh Shende, Univ. of Arizona (United States)
Viraj Pandit, Univ. of Arizona (United States)
Srini Raghavan, Univ. of Arizona (United States)
Florence Odile Eschbach, Intel Corp. (United States)

Published in SPIE Proceedings Vol. 5992:
25th Annual BACUS Symposium on Photomask Technology
J. Tracy Weed; Patrick M. Martin, Editor(s)

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