| Abstract
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1988 |
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Active Mask UV Lithography System for MEMS and µ-TAS Applications |
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Equipment, Machines & Instruments: MEMS, LIGA & Nanotechnology |
| Primary
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| Organization |
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| Content |
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Layer manufacturing is utilized for fabrication of micro-electromechanical systems (MEMS) and micro total analysis systems (µ-TAS). Layer manufacturing process generally required for the repetitive exposure procedure. Both the preparation of multiple mask and repetitive exposure procedure prevents quick fabrication of three dimensional micro structures. In order to simplify the fabrication process of layer manufacturing, the active mask fabrication technique was thus proposed such as lithography technique utilized liquid crystal device (LCD) as an electrically controllable photomask. The computer generated mask patterns displayed on the LCD has a role of multiple photomasks.
However, it is difficult to develop the LCD lithography system used UV light as a light source in order to fabricate microstructure using commercially available UV photoresist. Since UV light exposure caused serious damage to the LCD.
We therefore developed a prototype system of UV photolithography system using LCD as active mask. The design for utilizing UV light as a light source was investigated. In order to prevent the damage and to reduce the dark current noise in UV exposure procedure using LCD mask, the UV light irradiation should be decreased to the TFT substrate part. The LCD with microlens array made by EPSON Corp. has high numerical aperture (NA) of 54% as compared to conventional LCD without microlens array. It has advantage for decreasing UV light irradiation to the TFT substrate of poli-Si part near the electrode, and the dark current noise could be reduced. The loss of UV light through the LCD mask also becomes lower in case of using LCD with high NA.
This system can be also applied for the gray-scale lithography, which doesn't need repetitive procedure of mask alignment, exposure and development for fabricating 3D structures, by using gray-scale picture as a computer generated photomask. The intensity calibration for gray-scale exposure was easily performed by controlling the gray level of LCD equivalent to the computer generated photomask. The gray-scale lithography could be applied for fabrication of micro lens array and micro channels with tapered shape.
Using this system, the patterning characteristics for UV photoresist are evaluated by exposing two-dimensional line and space patterns. A step shape is then fabricated in order to verify the feasibility of the gray-scale lithography using our designed system. The shape with different height can be fabricated without any repetition exposure and developing procedures.
This report describes in the following results: first, the LCD mask exposure system using the ultraviolet light source is developed, second, high resolution such as 11µm is experimentally confirmed in the case of exposure using grid patterns and, third, fabrication of 3D step shapes is realized using the LCD as a gray-scale photomask.
It is expected that this system can quickly and precisely fabricate complicated 3D structure such as µTAS tip and the MEMS devices in case of small-lot production. The production time and cost of micro device is expected to be greatly improved using this method.
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