Projection Exposure Technology Using a Cone Mirror for Printing Patterns in a Lump on Inner Surfaces of Cylindrical Pipes

Machining to the inner surface of a cylinder is generally performed by machine cutting or pultrusion. However, machining of complex patterns in pipes with a small diameter has been difficult. In this research, concentric circular patterns on a flat reticle were projected onto the inner surface of a cylindrical pipe placed on the axis of the concentric circles using a cone mirror, and circumferential line-and-space patterns were printed. An observation optics was introduced to the exposure system for checking the pattern images on the monitor and adjusting the sample pipe position before the exposure. It was considered that finer patterns were printed, and patterning on opaque pipes became possible by improving alignment accuracy. At first, transparent glass pipes with an outer diameter of 16.5 mm and an inner diameter of 14 mm coated with a negative 10-µm thick resist were used. In this case, projected pattern images were observable from the outside and, 50 µm line-and-space (L&S) patterns were formed in all circumferential directions. Next, patterns were projected on metal (SUS304) pipes, with the same inner diameter. As a result, 100 µm L&S patterns were printed. However, pattern width and height distributed in the axial direction of pipes caused by the non-uniformity of circumferential pattern image intensity. Grayscale reticle may be effective for homogenizing patterns in the axial direction of the cylindrical pipe.