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Proceedings Paper

Advances in post AFM repair cleaning of photomask with CO2 cryogenic aerosol technology
Author(s): Charles Bowers; Ivin Varghese; Mehdi Balooch; Werner Brandt
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Paper Abstract

As the mask technology matures, critical printing features and sub-resolution assist features (SRAF) shrink below 100 nm, forcing critical cleaning processes to face significant challenges. These challenges include use of new materials, oxidation, chemical contamination sensitivity, proportionally decreasing printable defect size, and a requirement for a damage-free clean. CO2 cryogenic aerosol cleaning has the potential to offer a wide process window for meeting these new challenges, if residue adder issues and damage can be eliminated. Some key differentiations of CO2 cryogenic aerosol cleaning are the non-oxidizing and non-etching properties compared to conventional chemical wet clean processes with or without megasonics. In prior work, the feasibility of CO2 cryogenic aerosol in post AFM repair photomask cleaning was demonstrated. In this paper, recent advancements of CO2 cryogenic aerosol cleaning technology are presented, focusing on the traditional problem areas of particle adders, electrostatic discharge (ESD), and mask damage mitigation. Key aspects of successful CO2 cryogenic aerosol cleaning include the spray nozzle design, CO2 liquid purity, and system design. The design of the nozzle directly controls the size, density, and velocity of the CO2 snow particles. Methodology and measurements of the solid CO2 particle size and velocity distributions will be presented, and their responses to various control parameters will be discussed. Adder control can be achieved only through use of highly purified CO2 and careful materials selection. Recent advances in CO2 purity will be discussed and data shown. The mask cleaning efficiency by CO2 cryogenic aerosol and damage control is essentially an optimization of the momentum of the solid CO2 particles and elimination of adders. The previous damage threshold of 150 nm SRAF structures has been reduced to 70nm and data will be shown indicating 60 nm is possible in the near future. Data on CO2 tribocharge mitigation, the main cause of ESD, will also be presented and application to current technology nodes discussed.

Paper Details

Date Published: 11 May 2009
PDF: 8 pages
Proc. SPIE 7379, Photomask and Next-Generation Lithography Mask Technology XVI, 73791I (11 May 2009); doi: 10.1117/12.824295
Show Author Affiliations
Charles Bowers, Eco-Snow Systems LLC, Linde AG (United States)
Ivin Varghese, Eco-Snow Systems LLC, Linde AG (United States)
Mehdi Balooch, Eco-Snow Systems LLC, Linde AG (United States)
Werner Brandt, Eco-Snow Systems LLC, Linde AG (United States)

Published in SPIE Proceedings Vol. 7379:
Photomask and Next-Generation Lithography Mask Technology XVI
Kunihiro Hosono, Editor(s)

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