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17 December 2003 Development of phase-shift and transmittance metrology system for 157-nm PSMs
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Direct phase-shift measurement is one of the key technologies to realize Phase-Shift-Mask (PSM) application. Most mask makers are developing practical PSMs for 157nm lithography. Final tuning of the optical parameters and quality assurance of them require accurate measurement tool of phase-shift and transmittance with 157nm light illumination. In this paper, we will report the development of the system, which measures the phase-shift and transmittance of 157nm PSM at wavelength. This system has a 157nm F2 laser as a light source of the illumination and CaF2 optics with a CCD camera for the imaging. Key component is the interferometer, which has a function of lateral image shearing and phase modulation. The same technology is used in the current UV and DUV tools already exist. N2 purge and vacuum environments are newly introduced for the optical path to minimize attenuation of 157nm light by O2 and H2O. A fluctuation of the attenuation in the optical path significantly affects the short-term measurement repeatability. A new measurement algorithm, which uses two measurement spots on a PSM image, gives better repeatability than using single measurement spot under such unstable condition. Because most fluctuations are common elements to both of the two spots, they can be canceled out by the new calculation algorithms for phase-shift and transmittance measurements. The system with new techniques shows enough performance for the requirement of 157nm PSM measurements with new techniques.
© (2003) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Hal Kusunose, Takashi Yasui, and Iwao Higashikawa "Development of phase-shift and transmittance metrology system for 157-nm PSMs", Proc. SPIE 5256, 23rd Annual BACUS Symposium on Photomask Technology, (17 December 2003);

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