Kaname Okada

Development of hard pellicle for 157 nm

Projection photolithography at 157 nm is now under research as a possible extension of current 248 nm and planned 193 nm technologies .We have found that a thin-film fused silica glass pellicle would be available to 157nm lithography because of its high durability to F2 laser irradiation . In this paper, we present the performance of the hard pellicle made of AQF. Transmission is 97.6 percent when AR films are coated on both surfaces, and its uniformity at 157.6 nm is better than +/- 0.2 percent, and birefringence is within 1 nm. We developed a new evaluation system of a hard pellicle bending in horizontal position and in vertical position. We achieved less than 1um sagging with 800um thickness membrane and glass frame made of modified fused silica in horizontal position.

Hard pellicle study for 157-nm lithography

Identifying a functional pellicle solution for 157-nm lithography remains the most critical issue for mask technology. Developing a hard pellicle system has been a recent focus of study. Fabrication and potential pellicle-induced image placement errors present the highest challenges to the technology for meeting the stringent error budget for manufacturing devices in the 65-nm regime. This paper reports the results of a comprehensive proof-of-concept study on the state-of-art hard pellicle systems, which feature 800-mm thick modified fused silica pellicles and quartz frames. Pellicles were fabricated to ensure optical uniformity and flatness. Typical intrinsic warpage of these pellicles was close to the theoretical limit of 4.0 mm under a gravitational load. Quartz frames had bows less than 1.0 mm. The advantage of quartz frames with matched thermal expansion was demonstrated. An interferometric facility was developed to measure the flatness of the mask and pellicle system before and after pellicle mounting. Depending on the mounting process as well as mounting tool characteristics and techniques, variations were observed from pellicle to pellicle, mount to mount, and mask to mask. A redesign of the mounter and mounting process has significantly improved pellicle flatness. Finite element models were also generated to characterize the relative importance of the principal sources of pellicle-induced photomask distortions. Simulation results provide insightful guidance for improving image quality when employing a hard pellicle.

Fluorine-doped silica fiber with high transparency and resitivity to deep ultra violet light

Transmittance exceeding 92 %m-1 at 266 nm and its permanence after 4 G pulses of laser irradiation are realized in fluorine-doped silica fiber due to the optimized fiber-manufacturing processes such as perform-fabrication and fiber-drawing.