Analysis of the through-focus images with boundary-element method in high resolution optical metrology

Abstract

For through-focus focus metric we build a measurement system, in which a single diffraction-limited micro lens is used for imaging and a grating with a few pitches is used as a target. In this system, the optical field is calculated by the boundary-element method, in which a new algorithm is developed to reduce the dimension of a matrix. As a result, the memory capacity required in this calculation is much reduced up to 83% in our simulation case. An optimization of the grating structure is made to obtain the highest sensitivity for the critical dimension metrology. With the optimized grating structure the simulation shows a sensitivity of less than 1 nm in the through-focus focus metric. (c) 2006 American Institute of Physics.