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
© 2006 Optical Society of America
(110.3000) Imaging systems : Image quality assessment
(110.5220) Imaging systems : Photolithography
(120.3940) Instrumentation, measurement, and metrology : Metrology
(220.4840) Optical design and fabrication : Testing
Instrumentation, Measurement, and Metrology
Fan Wang, Xiangzhao Wang, Mingying Ma, Dongqing Zhang, Weijie Shi, and Jianming Hu, "Aberration measurement of projection optics in lithographic tools by use of an alternating phase-shifting mask," Appl. Opt. 45, 281-287 (2006)