Nanometer-level stitching in raster-scanning electron-beam lithography using spatial-phase locking

Pattern-placement inaccuracy is a persistent, Problem in scanning-electron-beam lithography (SEBL) despite the high-resolution obtained in SEBL systems. Pattern-placement errors stem from a variety of environmental and system. variations; however, the fundamental issue is the open-loop nature of the system, i.e., the beam location on the substrate is not monitored during exposure. In contrast, spatial-phase-locked electron-beam lithography (SPLEBL) provides closed-loop control of the beam position by monitoring the signal from a fiducial grid on the substrate. By detecting the spatial phase of the grid signal one can estimate the beam position within a small fraction of the grid period. We have implemented SPLEBL by adding real-time signal processing, feedback control, and raster-scan exposure capability to an inexpensive SEBL system. Using a 246 nm period, electron-transparent fiducial grid that covers the entire substrate, we have exposed patterns that exhibit global placement accuracy with respect to the grid and field-stitching precision better than 1.3 nm (one standard deviation). (C) 2003 American Vacuum Society.