Ablation Lithography for TFT-LCD
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Ablation Lithography for TFT-LCD Kenkichi Suzuki, Nobuaki Hayashi, Hiroshi Masuhara1 and Thomas K. Lippert2 Displays, Hitachi, Ltd., 3300 Hayano, Mobara, Japan 1 Applied Physics Department, Osaka University, Suita, Osaka, Japan 2 Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland ABSTRACT
Ablation lithography is based on the photo-decomposition ablation of polymer materials by excimer laser. It is a self-development process, and accordingly possible to reduce the throughput time and manufacturing cost of TFT-LCD. The major alterations from the conventional photolithography are the resist material and the mask. Developing both the technologies and using an experimental exposure& aligner, we fabricated a TFT pattern on 300 x 400 mm2 glass substrate. The result proves the feasibility of EAL as an high throughput lithography suitable for a-Si TFT. INTRODUCTION The LCD (liquid crystal display) has been almost a synonym of FPD (flat panel displays), and the industry has been extended to the scale of nearly one tenth of that of semiconductor for recent 10 years. It is mainly due to a-Si TFT (thin film transistor)-LCD, which realized high display quality comparable to the conventional CRT, and the productions has increased concurrently with the enlargement of PC (personal computer) market. However there has been always discrepancy between the manufacturing cost and the price the market demands. The price has gone down regularly when the quantity increases (“crystal cycle”), and the manufacturers have coped with by reducing the cost and increasing sales by productions of larger sized and higher definition displays. Such circumstances are now changing, as rapid developments of information technologies demands variety of the displays, from small sizes for mobiles to larger sizes. Among them, especially large and high definition FPDs, e.g. more than 40” size, are very essential for expansion of FPD industry, because the new information system is fundamentally a combination of PC and TV. Although PC is still a large application field of TFT-LCD, it is very important to steer the development toward such displays, because they are actual drives to grow up the display market much more. A question arises; is a-Si TFT-LCD competent to such displays with reasonable cost? Actually other displays, such as PDP (plasma display panel) and the low temperature p-Si (LTP)TFT, have started the productions. At present, PDP has a limitation in resolution and the cost reduction is not easy. LTP-TFT is most promising, especially its combination with organic EL, but its technical status is rather preliminary, far from low cost manufacturing meanwhile. On the other hand, a-Si TFT needs only slight improvements in the materials, processes, and designs to achieve the target performances. However, the production technology of a-Si TFT-LCD is almost matured, and the cost reduction is only achieved by reduction of the throughput time. The present throughput-up scheme is to use larger sized glass substrates, which resemble larger wafer in D1.2.1
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