The direct readability of code marks printed using a new exposure system was investigated. In the new exposure system, code-mark patterns were printed using LEDs as exposure sources and squared optical-fiber ends as code-mark elements. A 10 ' 10 fiber matrix was fabricated, and light emitted from each LED was led to each fiber. Because gaps appeared between the code-mark cells, a long exposure time was adopted, and the gaps between cells were eliminated by giving an overdose of light. After code-mark patterns were stably printed, their readability was investigated using a commercial code-mark reader. It was found that all the printed code marks were readable without errors. In concrete, same 100 identical marks printed on a wafer were readable. Moreover, six kinds of marks were repeatedly detected more than 100 times with no reading errors.
Capability of stereophonic projection lithography on arbitrarily but gently curved surfaces was demonstrated using plastic spoons as a reticle and specimens to be patterned. It had already been clarified that the patterned area size was drastically enlarged by illuminating the transparent reticle obliquely upward by collimated light from one side. Here, it was confirmed at first that 200 μm line-and-space patterns in 10 mm square area on a flat reticle were stably replicated on Si wafers with large exposure-time and focus margins. Next, reticle patterns on a spoon concave were successfully replicated on convex surfaces of specimen spoons. On the other hand, it was clarified that resist pattern field was distorted in a warped trapezoid, and pattern sizes were also varied similarly. However, because the distortions are regular and systematic, they are probably no problem, if critical overlays are not required. And, the distortions can be compensated by modifying the reticle, if necessary.
The feasibility of a novel economical and environmentally friendly exposure system using a light-emitting diode (LED) array as a light source was demonstrated. Such an exposure system is especially useful for printing two-dimensional code marks for the production management of semiconductor devices and liquid crystal display panels. The new system also uses an optical fiber matrix array connected to the LED array. The tips of the plastic optical fibers of 1 mm diameter are heated and deformed into a square shape, and the square fiber ends are projected by a 1/10 reduction lens. Using LEDs with a central wavelength of 405 nm and an output power of 40 mW/cm 2 , quasi-square code mark patterns are printed with good size repeatability in a practically feasible short time of less than 2 s.
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