title: Through-focus technique for nano-scale grating pitch and linewidth analysis.
abstract: We report results of experimental investigations into a through-focus method relevant to sub-wavelength feature dimension measurement. The method linearizes the partial derivative values of a focus indicator with respect to minimum intensity order, and hence permits determination of pitch using a classical linear method. By evaluating the variations in focus indicator of the different captured images obtained at various focal positions, the through-focus curves show a response to sub-resolution changes in the grating structure. The results suggest that sub-wavelength feature dimensions can be evaluated using regular optical microscopes by implementing the through focus method.
authors.forename: Yi-Sha
authors.initials: YS
authors.lastname: Ku
authors.forename: An-Shun
authors.initials: AS
authors.lastname: Liu
authors.forename: Nigel
authors.initials: N
authors.lastname: Smith