Aberration measurement of projection optics in lithographic tools by use of an alternating phase-shifting mask
As a critical dimension shrinks, the degradation in image quality caused by wavefront aberrations of projection optics in lithographic tools becomes a serious problem. It is necessary to establish a technique for a fast and accurate in situ aberration measurement. We introduce what we believe to be a novel technique for characterizing the aberrations of projection optics by using an alternating phase-shifting mask. The even aberrations, such as spherical aberration and astigmatism, and the odd aberrations, such as coma, are extracted from focus shifts and image displacements of the phase-shifted pattern, respectively. The focus shifts and the image displacements are measured by a transmission image sensor. The simulation results show that, compared with the accuracy of the previous straightforward measurement technique, the accuracy of the coma measurement increases by more than 30% and the accuracy of the spherical-aberration measurement increases by approximately 20%.
- OSTI ID:
- 20779258
- Journal Information:
- Applied Optics, Vol. 45, Issue 2; Other Information: DOI: 10.1364/AO.45.000281; (c) 2006 Optical Society of America; Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-6935
- Country of Publication:
- United States
- Language:
- English
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