Projection lithography using 125-µm square optical fibers and an LED matrix

Qualities of liquid crystal display panels are controlled using two-dimensional code marks in the manufacturing processes. The code marks are printed conventionally by projection lithography using a two dimensional reflection switching device and a laser diode or laser delineation lithography. However, both the specialized projection system, and the laser delineation system are expensive. For this reason, a new inexpensive optical lithography system using an optical fiber matrix and light-emitting diodes (LEDs) were investigated here. Circular 125-μm optical fibers were squared and arranged in a matrix, and a LED matrix with 8 rows and 8 columns was prepared as a light source. The central wavelength of the LED was 465 nm. Each optical fiber was connected to each LED one-to-one, and bright and dark arrangements at the fiber end 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. Fairly good checker patterns with sizes of almost 12 μm square were printed using the alternately lit fiber ends. On the other hand, printed arbitrary patterns showed some irregularities. The irregular shapes and sizes of element patterns, and notches and steps at the stitched parts should be improved by adjusting the light intensities of LEDs more carefully and precisely in the next stage.