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The first slide shows what happens to lithography when you expose through a pellicle that's been contaminated. This particular pellicle was contaminated by a finger print and no one would be happy with that kind of distortion and side walls. This is on a wafer, by the way, and I think a mask would similar. You can really see the distortion at 1000X total magnification. Essentially, there are two types of contamination problems relating to pellicles. Obviously, most particles that we find in a typical mask shop or wafer fab are not going to really be a problem. Anything sixty microns and below is not going to bother lithography on most any kind of equipment you use. However, fingerprints from handling, operator, and can moisture from present problems either the nitrogen lines or from the operator, can present problems. At SSEC we have been working for quite some time developing cleaning techniques for these types of pellicles. There have been some things written in the industry saying that you can't expose pellicles to water or water-based detergents because it creates problems. However, we have devised a technique using our mask cleaning equipment that is consistently reliable. The process that we have developed is a very simple detergent cleaning using an oscillating low-pressure dispense arm, that can be programmed back and forth over the plate surface while it's spinning. The detergent rinse is Microclean, followed by water rinse, which is followed by a very high speed 5000 rpm spin dry. One of the key elements in this cleaning process is the ability to oscillate the dispense arm over the plate, making contact with the detergent over each part of the pellicle, rather than dispense in the center of the plate and allowing the centrifugal force, caused by the plate's spinning, to just glaze over the top of the surface. That tends to leave some film on the plate.
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