Acoustic streaming effects in megasonic cleaning of EUV photomasks: A continuum model

Vivek Kapila, Pierre A. Deymier, Hrishikesh Shende, Viraj Pandit, Srini Raghavan, Florence O. Eschbach

Research output: Contribution to journalConference articlepeer-review

18 Scopus citations


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 participates 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.

Original languageEnglish (US)
Article number59923X
JournalProceedings of SPIE - The International Society for Optical Engineering
Issue number2
StatePublished - 2005
Event25th Annual BACUS Symposium on Photomask Technology - Monterey, CA, United States
Duration: Oct 4 2005Oct 7 2005


  • Acoustic streaming
  • Euv lithography
  • Megasonic cleaning

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


Dive into the research topics of 'Acoustic streaming effects in megasonic cleaning of EUV photomasks: A continuum model'. Together they form a unique fingerprint.

Cite this