Nondestructive inspection of patterns formed on inner surfaces of small diameter pipes

Inspection of patterns formed on inner surfaces of copper pipes with a small diameter of 2 mm was investigated. At first, space patterns with widths of 20-30 μm were lithographically formed using a handmade laser-scan exposure system. The exposure system was equipped with a monitoring system of a laser beam spot irradiated on the inner surface of pipe for the exposure. Pattern inspection was executed utilizing this monitoring system. In the case of exposure for patterning, the beam monitor was used for confirming the position and size of the laser beam. However, being prevented by the bright beam spot, background views were not clearly observed. For this reason, the pinhole that is initially inserted for reshaping the laser beam and making an appropriately small spot was removed, and the brightness of the beam spot was mitigated. In addition, inspected camera images were stored as video images in a personal computer using a video capture. As samples for the inspection, space patterns in resist films and groove patterns etched in copper pipes were used. As a result, resist space patterns were observed quite clearly, and pattern widths were measurable. In addition, the measured pattern widths almost agreed with the ones measured using a scanning electron microscope after cutting a half of the pipe off. On the other hand, etched groove patterns were not so clear as resist patterns. However, it was clarified that fatal pattern defects such as kinks, shifts, and breaks were detected, if the pattern images stored in the computer were carefully investigated. The new nondestructive inspection method is effective.