Two dimensional code marks are often used for the production management. In particular, in the production lines of liquid-crystal-display panels and others, data on fabrication processes such as production number and process conditions are written on each substrate or device in detail, and they are used for quality managements. For this reason, lithography system specialized in code mark printing is developed. However, conventional systems using lamp projection exposure or laser scan exposure are very expensive. Therefore, development of a low-cost exposure system using light emitting diodes (LEDs) and optical fibers with squared ends arrayed in a matrix is strongly expected. In the past research, feasibility of such a new exposure system was demonstrated using a handmade system equipped with 100 LEDs with a central wavelength of 405 nm, a 10×10 matrix of optical fibers with 1 mm square ends, and a 10X projection lens. Based on these progresses, a new method for fabricating large-scale arrays of finer fibers with squared ends was developed in this paper. At most 40 plastic optical fibers were arranged in a linear gap of an arraying instrument, and simultaneously squared by heating them on a hotplate at 120°C for 7 min. Fiber sizes were homogeneous within 496±4 μm. In addition, average light leak was improved from 34.4 to 21.3% by adopting the new method in place of conventional one by one squaring method. Square matrix arrays necessary for printing code marks will be obtained by piling the newly fabricated linear arrays up.
There are great advantages in cost and simplicity, if exposure sources in lithography systems for printing two dimensional code marks are changed from ultra-high-pressure mercury lamps to light emitting diodes (LEDs). For this reason, a prototype exposure system was developed, and it was demonstrated that two dimensional code marks were successfully printed using LEDs as exposure sources and a squared plastic optical fiber matrix as code-mark cells. In addition, it was also verified that suitably printed code marks were directly readable using a commercially available code-mark reader. However, readability for various marks has not been investigated sufficiently. For this reason, the readability was investigated in detail by variously changing lighting maps of LEDs, here. Readable ratios of code marks printed under short exposure-time conditions were investigated in particular to clarify the redundancy and margin for the exposure dose and mark-quality degradation. As test code marks, 6 figure numbers such as 111111, 222222,…777777 were used. This is because not to make LEDs which are not lightened. As a result, all the code marks printed with good profiles and almost no resist residues were correctly read. In addition, code marks with slight resist residues were also readable. It was clarified that amount of resist residues in the data area greatly influenced the readability.
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