Keiko Chiba

Development of ArF immersion exposure tool

Immersion lithography systems with a 193 nm light source are being pursued in the industry. This paper presents the results of the study we have made on various aspects of the exposure system, and gives the status of exposure system development together with the challenges involved. If there are fluctuations in the flow rate of immersion fluid, i.e. ultrapure water, the positioning accuracy of the wafer stage may be affected. Similarly, temperature changes in the fluid can significantly influence imaging performance of the projection optics. We have developed an ultrapure water supply control system which allows direct connection to the ultrapure water line of the existing fabs and enables constant-temperature, constant-flow rate control of the water with high stability. The evaluation results of this system will be shown. Photoresist materials such as photo-acid generator, PAG, dissolved into the water are a cause of concern for lens contamination. The challenge for exposure tool suppliers in terms of contamination control is to specify the permissible dissolution amount. To this end, wet contamination tests are in progress, and the findings to date will be discussed in this paper. Two verification tools for immersion exposure are built: a two-beam interference exposure tool and a full-field alpha-site scanner. Using the alpha tool, the evaluation results of full wafer CD uniformity including edge dies will be presented. Also, defect analysis results will be shown, specifically the impact of air bubbles on patterning.