Simple maskless lithography tool with a desk-top size using a liquid-crystal-display projector

Abstract

A very simple and low-cost maskless exposure tool with a desk-top size was developed for applying to fabrications of various micro electro mechanical systems (MEMS) and bio-devices. A commercial projector with three liquid crystal display (LCD) panels of red, green, and blue colors was utilized as it was, except attaching a macro-lens for a camera after removing the magnification optics of the original projector. Therefore, the sizes were as small as 300 wide×400 deep×500 high mm3, and the system was fabricated at a very small expense (¥500,000≈€3500). Pixel pitches on the LCD panel were 8.5μm, and the 7.4-μm square pixels were projected onto a wafer in a magnification ratio of 1.65. Efficient pixel numbers were 1024×768, and the exposure field sizes were 14.3×10.7mm2. Using the system, isolated line patterns with a width corresponding to one pixel size of approximately 14μm, and 1:1 lines-and-spaces (L&S) patterns with a width of two pixel sizes of 28μm were stably printed. Not only line patterns in orthogonal directions, but also radial oblique patterns were clearly and smoothly printed, and complicated arbitrary patterns were also printed. These projection ratio and pattern widths were decided considering the present applications to fabrications of micro-fluidic devices and lens arrays. If smaller patterns are required, the minimum pattern size and the projection ratio are conformably changed in principle. Because arbitrary patterns designed on a personal computer are directly printed on a wafer, preparations of expensive reticles are not necessary. Accordingly, besides the system cost and footprint are drastically saved, working expenses are much saved.