157-nm lithography for 100-nm generation and beyond : Progress and status photomask focus

157-nm has emerged as the most favorable post 193-nm lithography choice. Significant progress has been made since it was initiated at MIT-LL in 1997. Material is perhaps the most critical issue of 157-nm lithography in all areas of concern: optics, resist, and mask. CaF 2 is the only material currently shown to be feasible for 157-nm lens though other materials namely BaF 2 are being developed as secondary material. Due to limited availability of materials in conjunction with the difficulty in developing line-narrowed F 2 laser, optics design is limited. Catadioptric lens design is being considered by most major exposure tool suppliers. Meanwhile, most conventional organic materials are opaque at 157-nm. New fluorinated polymers have been discovered and currently being developed for both resist and pellicle applications. Good progress in this area has been reported at the Sematech's First 157-nm Symposium at Dana Point, California, May 9-11, 2000. Alternative approaches are also being developed. One example is thin layer resist process using conventional chemistry to overcome high absorption issue at 157-nm. Another is the so-called hard pellicle, i.e., a ∼300-um thick film of the newly developed dry-fluorine doped fused silica is used instead of the typical 1-um thin organic membrane. On the other hand, major accomplishment has been reached in the field of mask blank material to replace the existing one for 157-nm application. The new dry and fluorine-doped fused silica has been shown to have good transmittance and radiation durability. Blank and reticle making using this newly developed material have been reported to be satisfactory even with current processes. High absorption at 157-nm also leads to other requirements such as surface molecular contamination removal and system purging. Therefore, reticle handling has become critical in that reticle purging, In-Situ cleaning and ESD prevention must be considered. While recognized to be issues, possible technical solutions have been proposed. This paper will provide an overview of 157-nm lithography development. Results will be presented to show progress. Critical issues covering exposure tool, resist and mask will be discussed.