PYRAMID-a hierarchical, rule-based approach toward proximity effect correction. I. Exposure estimation

One of the major limiting factors in electron beam (e-beam) lithography is the undesired development of circuit area caused by electron scattering (the proximity effect). Since the proximity effect imposes a severe limitation on the ultimate resolution attainable with electron beam lithography, it is important to examine ways in which the proximity effect can be reduced. In order to develop a fast and efficient proximity effect correction scheme it is necessary to have a fast and accurate technique for finding the exposure (energy) deposited at any given point in the circuit pattern. In this paper we present the hierarchical digital signal processing (DSP) model utilized by PYRAMID (our proximity effect correction scheme) to estimate these exposures. Our approach employs a two part hierarchical estimation technique which is several orders of magnitude faster than a direct (spatial domain or FFT-based) convolution yet is able to predict the result of an exposure with a high degree of accuracy. A detailed description of our method of exposure estimation is followed by a thorough analysts of its performance through simulation and experimental results.