Resolution, overlay, and field-size for lithography systems

Resolution, overlay, and field size limits for U.V., x-ray, electron beam and ion beam lithography are described. Economic trade-offs between the methods, and their suitability for particular thin film device applications, are not considered. The following are some of the conclusions that are discussed. 1) At 1µ linewidth, contrast for optical projection can be higher than that for electron beam. 2) X-ray lithography offers the highest contrast and resist aspect ratio for linewidths above about 0.1µ, but for dimensions below 0.1µ, highest aspect ratio is obtained with electron beam. 3) With electron beam exposure on a bulk sample, contrast for 50nm linewidth is the same as that for 1µ linewidth, provided the resist is thin. 4) Ultimately the range of secondary electrons limits resolution in E/B lithography, just as the range of photoelectrons limits resolution in x-ray lithography. In both cases, minimum linewidth and spacing in dense patterns is about 20nm.