Shogo URA, Kenji KINTAKA¹, Hideyuki AWAZU, Yasuhiro AWATSUJI, and Junji NISHII²

Department of Electronics, Kyoto Institute of Technology, Kyoto 606-8585, Japan
¹Photonics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568, Japan
²Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0020, Japan

(Received May 28, 2010; Revised August 4, 2010; Accepted August 5, 2010)

An interference exposure system using a phase-shifting mask was proposed for generating periodic sawtooth optical intensity profile with chirp in period. Multiple space-harmonic waves are launched from the mask by diffraction, and the sawtooth optical intensity is formed by interference based on Fourier synthesis after propagation through an air gap. The design concept merely utilizing positive diffraction-order harmonics with tilt illumination of an exposure light and a design algorithm based on time-reversed configuration for calculating required phase shift amount were proposed and discussed. A phase-shifting mask for a blazed grating of very high chirp rate was designed to demonstrate its potential and feasibility. The grating period changes from 2.2 to 3.1 μm gradually within 0.3 mm length. Sawtooth-like optical intensity profile was confirmed by theoretical simulation as well as preliminary experimental results.

Key words: diffractive optics, blazed gratings, chirp gratings, optical interference, interference exposure, Fourier synthesis