[OPTICAL REVIEW Vol. 8, No. 6 (2001) 416-421]
Diffractive Phase Element for Shrinking Focal Spot Diameter: Design, Fabrication and Application to Laser Beam Lithography
Yusuke OGURA1,*, Jun TANIDA1, Yoshiki ICHIOKA2, Yoshiaki MOKUNO3,4 and Katsunori MATSUOKA3,4
1Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka, 565-0871 Japan, 2Nara National College of Technology, 22 Yata-cho, Yamatokoriyama, Nara, 639-1080 Japan, 3Osaka National Research Institute, 1-8-31 Midorigaoka, Ikeda, Osaka, 563-8577 Japan
(Received December 27, 2000; Accepted August 30, 2001)
A diffractive phase element (DPE) capable of shrinking the main-lobe of the focal spot of an incident beam has been developed. The DPE is expected to be used in laser beam lithography to improve the resolution. Special constraints, which force the focal spot to be small while permitting increase of the side-lobes, are introduced in the design of the DPE using an iterative method based on the Gerchberg-Saxton algorithm. Two kinds of DPEs are fabricated by a laser beam lithography system of our own composition and their performances are experimentally measured. The minimum line width obtained by the system is improved from 1.2μm to 1.0μm with the fabricated DPE. Focal depth of the focusing system is discussed.
Key words : diffractive phase element, laser beam lithography, focusing system, spot diameter, focal depth