The design of immersion photoresists with improved resolution capabilities requires access to an exposure tool that is capable of printing patterns at the desired dimensional scale. Such exposure tooling must be available years in advance of semiconductor manufacturing so that sufficient time is available for refinement and optimization of the resist material. At IBM’s Almaden Research Center we have designed and constructed such an exposure tool for internal photoresist research. This system, nicknamed "NEMO" after the fictional character Captain Nemo in Jules Verne's novel Twenty Thousand Leagues Under the Sea, combines interferometric lithography using 193 nm light with an immersion exposure configuration.

A schematic of the interferometer is shown below. 193-nm light enters from the top of the figure and is split into two beams by diffraction from a fused silica grating. These beams overlap at the wafer surface after reflecting from two mirrors and passing through a custom fused- silica prism. A small amount of liquid is introduced between the final prism face and the resist-coated wafer.

The interferometer is mounted at the front of a rigid structure anchored on a granite slab (Figure 4). A photoresist-covered silicon wafer is held by a vacuum chuck on top of a "puck" that floats on an air cushion while it moves in two horizontal dimensions, and is held firmly against the granite surface by vacuum during the periods of laser exposure.

The NEMO tool is capable of nanoscale lithographic imaging. The scanning electron micrographs depict photoresist patterns exposed using NEMO. The widths of the lines and spaces in this resist image are less than 30 nm.