Accurate position measurement of a high-density beam spot array in digital maskless lithography

Since patterns in digital maskless lithography are formed by accumulating the exposure energy of a high-density beam spot array, the accurate position measurement of the spot array is essential for the precise operation of the system. We propose a measurement technique for detecting the position of a high-density, subpixel size beam spot array with a charge-coupled device (CCD). In order to determine the position of each beam spot with a small number of CCD pixels, we assign 3×3 pixels of the CCD for each spot and scan the CCD to determine the signal of a center pixel. We numerically analyze the measurement uncertainty in the pixel position for various scanning conditions. We set up an experimental system for proof of concept and to detect the position of a 10×10 beam spot array with an uncertainty less than 100 nm. Additionally, the measurement uncertainty quantitatively matches the numerical analysis results.