Optical Limitation in Fine Pattern Photolithography

The limitation of the photolithographic formation of fine patterns is investigated. It is shown that the minimum pattern width is limited by the interference of the Fresnel diffracted light at the mask edge. Consequently, the finest resolvable pattern is determined by the wavelength of the exposing light and by the optical length between the mask and the sample surface. Experiments with the contact printer are performed to verify the analysis. The selection of suitable exposure conditions and the optical length makes it possible to form a pattern as narrow as 0.3 µm, which is shorter than the exposing light wavelength.