Patent ID: 8035801
Filing Date: 2011-10-11
Classification: G03F

Abstract:
1. A method for in-situ aberration measurement in an optical imaging system of lithographic tools, the optical imaging system comprising: a light source for producing light beams; an illumination system for adjusting the intensity distribution of the beams radiated by the light source; an optical imaging apparatus for imaging a reticle pattern formed on a reticle onto a wafer; a reticle stage for supporting and accurately positioning the reticle; a wafer stage for supporting and accurately positioning the wafer, characterized in that the method comprises the steps of: (a) imaging the reticle pattern to form an imaged pattern by transmitting the beams through the reticle via the optical imaging system, the imaged reticle pattern being shaped to have plural groups of imaged linewidths; (b) measuring the plural groups of imaged linewidths of the imaged pattern using either of an image sensor, a CD-SEM and a microscope by modifying the intensity distribution at an exit pupil plane of the optical imaging system; (c) calculating the asymmetry and ununiformity of the imaged linewidths and calculating aberrations of the optical imaging system.