Projection Lithography using Light Emitting Diodes and Minimal Square Optical Fibers

A new inexpensive optical lithography system using light-emitting diodes (LEDs) and a minimal optical fiber matrix was investigated for printing two-dimensional code marks, and other rough patterns easily. Circular 125-µm optical fibers were squared and arranged in a matrix, and each optical fiber was connected to each LED with a wavelength of 465 nm in a matrix with 8 rows and 8 columns. Thus, blight and dark arrangements at the fiber ends were used as a binary mask. Patterns were printed on silicon wafers coated with a 1-µm thick positive resist using a handmade 1/10 reduction projection exposure system. As a result, good checker patterns with sizes of almost 12 µm square were printed. However, it was found that pattern sizes were increased due to stray light when adjacent fibers were bright simultaneously. To address this issue, the stray light intensity was measured, and a compensation method of the stray light was investigated. Using the original method, arbitrary patterns were successfully printed.