Design and investigation of a maskless lithography system for printing patterns on the inside surface of a long pipe

A new lithography optics designed and fabricated for printing 300-μm patterns on inside surfaces of pipes with an inner diameter of 10 mm and a length of 300 mm was investigated. Such patterning is required for giving textures to heat pipes, graving bearing grooves, and fabricating electrode and wiring patterns on inside surfaces of pipes. Although the pattern size is far larger than those used for semiconductor device fabrication, patterning onto non-flat surfaces in narrow spaces has hardly been researched anywhere else. Here, a linear optical fiber array composed of 500-μm fibers with squared ends were used for leading exposure light from light emitting diodes and designating pattern shapes. Then, the fiber array end was contacted to the inlet of a taper-conduit, and the pattern shapes were reduced in 1/2.25 at the outlet of the conduit. The conduit was composed of densely contacted fine optical fibers, and each fiber diameter was gradually reduced in the longitudinal direction keeping each fiber position invariably. The reduced pattern shapes were projected by a ratio of 1.25/1 using a simple convex lens on the inside surface of a pipe. Here, the performances of the projection optics were investigated by printing patterns on wafers used temporarily in place of the inside wall of a pipe. As a result, hole and linear space patterns with sizes or widths of approximately 300 μm were successfully formed.