Optical lithography onto inside surfaces of small-diameter pipes

Lithography onto inside surfaces of small-diameter pipes was investigated. Two types of exposure rod for inserting into the pipes were developed. One has a chip of light emitting diode (LED) at the rod end, and the other transmits the exposure light through an optical fiber. In the latter case, LED was used as a source, too. Aluminum pipes with an inner diameter of 5 mm were coated with a positive resist PMER P-AR900. The resist thickness was controlled to be approximately 10 μm, and the pipes were exposed to the light beam from the inserted exposure rods. The exposure light beams were narrowed using handmade pinholes with hole-sizes of 170 μm and 100 μm. Patterns were delineated rotating and moving the pipes. As a result, space patterns with a width of less than 200 μm were printed. Not only simple linear patterns but also helicoids and character patterns were successfully printed. The novel “inside lithography” is feasible and will be useful for carving various fine grooves onto the inside surfaces of small-diameter pipes and cylinders.