There is a need for pristine vacuum environments free of carbon contamination in many lithography tools. Carbon is a
particularly irksome contaminant due to its ubiquity and its reactivity with energetic electron or EUV photon beams.
When residual hydrocarbons land on a surface that is being impinged by an energetic beam, they will crack and reform
as less mobile deposits. Carbon buildup cause loss in image resolution resulting in line width measurement increases
during multiple CD-SEM scans, and on EUV optics it can lead to lower reflectivity and throughput of a lithography
system. A new downstream plasma cleaner has been developed to clean larger chambers at lower pressures and higher
RF plasma power (50W) and operates efficiently with current turbomolecular pumps. Cleaning rates can be measured
by using a quartz crystal microbalance (QCM) with its surface previously contaminated with hydrocarbons. Rates have
been measured at over 1 nm/minute at a distance of over 0.5 m from the plasma source. The cleaner can be used with
room air, oxygen gas mixtures, and hydrogen gas. Although it is slightly larger than the currently available Evactron®
De-Contaminator, it still has a compact footprint which allows it to be easily installed on lithography tools. This paper
will explore the operation of the new plasma cleaner, examining the effect of the cleaning rate due to changes in various
conditions including power, pressure and distance from the plasma source.
The problem of carbon contamination on extreme ultraviolet (EUV) optics, causing unacceptably low reflectivity in
mirrors, must be solved before industry will adopt the technology on a production scale. Breaking vacuum, removing
and then cleaning mirrors is a time-consuming and expensive method for dealing with the problem. A safe yet effective
in situ method for cleaning EUV optics and maintaining vacuum chamber cleanliness is important for progress in EUV
lithography. Carbon contamination has also been a problem for the scanning electron microscopes (SEMs) leading to
reduced image quality. The use of low power downstream plasma cleaner has been shown to be effective in removing
carbon contamination from SEMs. The plasma dissociates oxygen molecules into neutral oxygen radicals. These
radicals flow throughout the SEM vacuum chamber and chemically remove the carbon contamination. Since the process
works by chemical etch and not by sputter etch, the capping layer on EUV mirrors will not be damaged by the cleaning
process. The production of chemically etching oxygen radicals by plasma cleaning was measured using a quartz crystal
microbalance. The effectiveness of the downstream plasma cleaning process was also tested on EUV mirrors.
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