Statistical comparison of field height correction by Z-stage movement versus height-correction hardware in a modern electron-beam lithography tool

Modern electron-beam lithography tools are expected to operate within very tight specifications [S. Babin, S. Borisov, V. Militsin, T. Komagata, and T. Wakatsuki, Proc. Soc. Photo-Opt. Instrum. 9984, 998406 (2016)], in order to meet lithographic requirements for today’s and tomorrow’s cutting-edge electronic and photonic device fabrication. Specifications for linewidth fidelity, field stitching, and absolute feature placement accuracy demand the highest levels of performance. In this work, the performance of the hardware height compensation mechanism in a modern Gaussian-beam, vector-scan lithography tool is statistically compared with the use of the Z stage to correct for height on a field-by-field basis, in order to determine the method most likely to yield the best writing performance on a nonflat substrate. A test sample is prepared by writing an array of square marks on a 4 in. Si wafer. Four marks per field are written, using the four corners of the writing field. After development, the wafer is coated with metal and the resulting marker array is formed via lift-off. The test wafer is then reloaded into the lithography tool. For each writing field, the positions of each of the four marks are found, with respect to the center of the field. The fields are visited in a spiral-out order, beginning near the center of the wafer. Location of the marks can be performed under two different conditions: fixed Z position with normal height compensation active or with Z position adjusted to bring the substrate to reference the height before locating marks in each field. No height compensation is used in the latter case. Subsequent statistical and graphical analysis of the collected data provides insight into the dynamics of the tool’s height correction capabilities and helps to inform the choice of Z-drive motion versus hardware height correction. In addition, should anomalies be observed, the analysis provides useful diagnostic information.