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27 December 1996 Phase measurement using Hg-Xe lamp and KrF excimer laser
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We have developed a new system to measure the phase shift caused by the phase shift mask (PSM) for a deep-UV stepper. The system uses two types of 248 nm wavelength deep-UV light sources. One is an Hg-Xe lamp, and the other is a KrF excimer laser. These are interchangeable to match the illumination light source of the stepper. The phase is measured with a polarizing shearing interferometer. It has two wollaston prisms, a condenser lens, and an objective. The objective has a long working distance of more than 7 mm. This is necessary in order to measure the PSM with a pellicle. A light beam is separated into two orthogonal polarized light beams and sheared on the PSM, and then recombined on a sensor. The transmission beams through a shifter and a substrate interfere each other. Then the phase difference from the shifter is obtained from the difference between the two beams. We evaluated phase measurement repeatability and the measurable minimum pattern width. In the measurement of a halftone PSM, the repeatability was +/- 1 degree over several months, and the minimum pattern width was 2 micrometers or less.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Katsuki Oohashi, Takeshi Fujiwara, Takehiko Nomura, and Akira Ono "Phase measurement using Hg-Xe lamp and KrF excimer laser", Proc. SPIE 2884, 16th Annual BACUS Symposium on Photomask Technology and Management, (27 December 1996);

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