SBIR-STTR Award

In response to AF95-135, we propose to determine the feasibility of enhancing the resolution of current excimer lithography systems by employing spatial filter and phase mask of novel designs. The spatial filter (which is a diffractive optical element) will be specially designed for edge enhancement to improve on the high frequency contents of the images illuminating the photoresist and the resolution performance of the excimer lithography system. The phase mask (which is another diffractive optical element) will be special designed for controlling the illumination direction of the mask (or reticle) in the excimer lithography system to achieve superresolution performance (or the performance of a larger effective aperture than the actual lens aperture). These two approaches will result in low cost add-on accessories (with mechanism similar to reticle or color filter changers) readily insertable to the production lithography system, one for each system model. They will overcome the disadvantage in the existing method of using phase shifting masks, which require custom design and fabrication specific to each integrated circuit; they will not require redesigning the lamp housing for illumination control. To demonstrate the feasibility of resolution enhancement, NIPT will work closely with ANVIK to ensure that the designs and the fabricated spatial filter and phase mask will function properly in their excimer lithography systems.

Keywords:
Excimer Laser Excimer Laser Lithography Lithography Spatial Filter Spatial Filter

The minimum feature size achievable with lithographic systems is one of he most critical parameters for the semiconductor industry, since it directly impacts the performance and yield of integrated circuits (IC). Currently high performance IC manufacturing employs i-line optical projection aligners. We proposed and deomonstrated the feasibility of enhancing the resolution of optical projection aligners, for SBIR Phase I contract 95-C-1673, by employing (a) a phase mask (PM, e.g. an axicon) to control the illumination direction on the reticle without requiring the lamp housing be redesigned to achieve super-resolution performance, and (b) a high-pass spatial filter (SF) to improve on the contrast of the high spatial frequency contents of an image. The PM and the SF will be add-on accessories readily insertable to a production lithography system. They will overcome the cost disadvantage in using custom phase shifting masks in photolithography. Preliminary experimental results obtained in Phase I provided us with good confidence in our approach and we are ready to proceed to Phase II.In Phase II we propose to modify our PM design that will lead to 150% resolution enhancement, instead of 100%, i.e. enhancement by a factor of three instead of two. The PM modified sesign can be employed together with the SF for further enhancing the edge fidelity in IC images. While the combination of PM and SF is applicable to all i-line stepper systems as well as excimer lithography systems, we propose to work closely with Anvik and design the PM and SF specifically for their large area, high-throughput patterning and via-etching system. Feasibility demonstrations of our PM and SF in an Anvik system will first be carried out in Wright Laboratory, then at an industrial laboratory, such as MCC, to helop overcome the new technology insertion barrier that may exist. We will also investigate in Phase II the replications of PM and SF to reduce their unit cost.Success in Phase III demonstrating resolution enhancement on an Excimerlithography system in an industrial lab environment and developing good techniques ofr replicatons of PM and SF will lay a solid foundation for their employment in other production photolithography systems in Phase III.

Keywords:
Resolution Enhancement Phase Mask Photolithography Diffractive Optical Element Spatial Filter