Shape positional accuracy optimization via writing order correction

Abstract

Shape positional accuracy is a ubiquitous challenge when writing critical features using electron beam (e-beam) lithography. Positional accuracy can be particularly important when patterning for dense pattern arrays often found in plasmonic device structures. These arrays contain structures critically placed within a few tens or hundreds of nanometers apart from one another, whereby poor positional accuracy on the same order of magnitude would impact overall device performance. The sources of positional accuracy are varied on an e-beam lithography system and can include, but are not limited to beam drift, surface charging, environmental noise, and temperature to name a few. This work demonstrates the impact of shape writing order on sub-100 nm features to tolerate these potential sources of shape positional errors. The shape positional accuracy of both proximity effect corrected (PEC) and non-PEC array patterns are studied using a 20 MHz fixed clock 50 keV Gaussian spot electron beam lithography system exposing at 1 nA with a 60 μm final aperture, and a 20 nm beam step size using 200 nm of ZEP520A from ZEON Chemicals atop a bulk Si substrate. The patterns are transferred via etch or metal deposition. The authors find that both pattern design and data preparation impacts positional accuracy by way of the designed shape order or the reshuffling of shapes, respectively. Resorting the shapes within the arrays allows the beam to continuously raster or meander through the array along the X- or Y-axis, row by row or column-by-column, respectively, while exposing abutting shapes yields optimal shape placement with a negligible impact on writing time.