Dose control for fabrication of grayscale structures using a single step electron-beam lithographic process

Many optoelectronic devices include multidimensional (grayscale) semiconductor structures such as diffractive optical elements (DOE's), blazed gratings, and photonic band gap (PBG) crystals. Their performance is known to be highly sensitive to dimensional accuracy of features in the multidimensional structure. Therefore, it is essential to have a tight control of the feature size in the fabrication process. Grayscale electron (e) -beam lithography enables a single step lithographic process for fabrication of such multidimensional structures and therefore has several advantages over using a binary lithographic process multiple times. As the feature size decreases, proximity effect in the e-beam lithographic process can make dimensions of the written features in a device substantially different from the ideal ones so that performance of the device is significantly degraded. In this paper, an efficient dose control scheme for grayscale e-beam lithography, which attempts to minimize the difference between the spatial exposure distribution and the "shape" of a multidimensional structure, is described along with results from an extensive computer simulation. (C) 2003 American Vacuum Society.