Nanometrology Using a Quasiperiodic Pattern Diffraction Optical Ruler

This paper presents a nanometrology optical ruler imaging system to enable rapid wafer-scale nanometrology, particularly for scanning probe microscopes. The ruler is generated by the diffraction of a 10^-8 stabilized laser by a metal thin-film pattern. Microfabrication techniques create a high-count quasiperiodic aperture array in the film which generates a translationally asymmetric feature-dense optical diffraction pattern well suited for the nanometrology application. An imager array samples the optical ruler and calculates its position by Fourier transform cross-correlation methods. Numerically, it is found that improving the imager by pixel count and size can reduce positioning errors down to 1/120th of the pixel size, after which further improvements yield no reduction in error. Experiments using a modest complementary metal-oxide-semiconductor imager demonstrate a positioning accuracy of 1/124th of the pixel size, or 29 nm. This system will enable high-precision high-throughput metrology and fabrication of nano- and microelectromechanical systems.