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Optical lithography with 157-nm light is expected to bridge the gap between 193-nm technology and next-generation lithography. One important practical difficulty facing the implementation of 157-nm technology is gas absorption of 157-nm light. The exposure process for 193-nm technology is carried out in air. However, oxygen and water vapor attenuate 157-nm radiation. Alternatively, the exposure can be carried out in a nitrogen-purged environment. The purification of the volume trapped between the reticle and the hard pellicle is challenging because of the delicate pellicle geometry. In this paper, experimental results are presented that support the design and development of pellicle purge processes for 157-nm optical lithography. Specifically, a hard pellicle was installed in the Pressure Bulge Tool (at the UW Computational Mechanics Center) and experimental measurements of the pressure-induced pellicle distortion were obtained. The pressure loads imposed on the pellicle are representative of those expected during in-tool purge processes. Separate testing quantified the pellicle fracture stress and the flow characteristics of the pellicle/reticle geometry for a particular vent configuration (i.e., frame vent hole size and number, and filter system). These flow characteristics are important, as they ultimately dictate the pressure difference imposed on the pellicle during any purging process. These various experimental measurements, when taken together, facilitate the assessment of the feasibility and requirements associated with alternative pellicle purging strategies for 157-nm lithography.
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