Patent ID: 7455939
Filing Date: 2008-11-25
Classification: G03B,G03F

Abstract:
1. A method of making a process monitor grating pattern for use on a mask to be used in a lithographic imaging system comprising: determining minimum resolvable pitch of a plurality of spaced, adjacent line elements, wherein each of the line elements are separately resolvable when projected by the lithographic imaging system; selecting a process monitor grating period P wherein λ is the exposure wavelength, NA is the numerical aperture value, and σ max is the maximum illumination coherence of the lithographic imaging system; and designing a process monitor grating pattern having a plurality of adjacent sets of grouped line elements spaced from each other, each set of grouped line elements comprising a center line and adjacent lines spaced on each side of the center line, and wherein the center line has a width greater than the widths of the adjacent lines, the number of line elements in each set of grouped line elements in a process monitor grating pattern being the smallest odd integer greater than or equal to M, each set of grouped line elements being spaced from and parallel to an adjacent set of grouped line elements by the process monitor grating period, such that when the process monitor grating pattern is projected by the lithographic imaging system the line elements in each set are unresolvable from each other and Fourier coefficients of diffracted orders m created by the line elements in the range of 1<|m|≦M are zero, a solution set of the Fourier coefficients being selected to be compatible with the fabrication capability of the mask to be made and the wafer process, the designing of the grouped line elements including correcting widths of the line elements and spaces in the process monitor grating pattern for electromagnetic field (EMF) effects in the mask to be used in the lithographic imaging system.