Electrophotographic Patterning of a-Si:H
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H. GLESKOVA*, S. WAGNER* AND D.S. SHEN** *
Princeton University, Department of Electrical Engineering, Princeton, NJ 08544
** University of Alabama in Huntsville, Department of Electrical and Computer Engineering, Huntsville, AL 35899
ABSTRACT A novel laser-printing method for the manufacturing of the backplane circuits of activematrix liquid-crystal displays (AMLCD) is proposed and demonstrated. Xerographic toner is used as an etch mask for amorphous silicon (a-Si:H) and for the seeding of metal lines. We also demonstrate for the first time the direct-print patterning of silicon on - 50 gam thick glass foil. INTRODUCTION The photolithographic patterning techniques used in the AMLCD manufacturing were developed for the manufacturing of integrated circuits on silicon wafers, and are correspondingly expensive. Typically, six to nine thin film layers are used in the manufacturing of the backplane circuit, with photolithography required at each step [1]. The typical design rule for the channel of a thin-film transistor (TFT) is 3-5 pm [1]. Exposure by stepper requires stitching, which is accurate to -1 jIm [2], and is slow. In order to decrease the price of AMLCDs, new alternative and cheaper methods for color filter manufacturing are being investigated. Among them are electrodeposition and printing, e.g. screen printing and offset printing [1]. We have been exploring direct-printing techniques for semiconductor patterning and for metallization. Such techniques could revolutionize the largearea capability and the manufacturing throughput of the backplane for AMLCDs and other large-area displays. In our current project we use laser printing. Commercial laser printers already can print over an area of 11 x 17 sq. in. with a resolution of 1,800 dots per inch (dpi), which is equivalent to a design rule of'- 14.5 gim. Toner particles currently available have - 3 pim diameter, with long-term prospects of reaching a minimum size of-- I nm by using fullerene (C60 ) as the toner [3]. The lateral resolution limit is set by optical diffraction of a laser diode, which lies around 1 pgm. The limit set by the photoconductor is comparable to its thickness, which is of the order of 10 to 20 gim at present. With smaller toner particles, the voltage across the photoconductor can be reduced, and so can be its thickness, promising an increase in resolution to allow design rules of 5 gpm or less. This means that the laser-printing technique could be applied to the production of the backplane of large-area displays. In this paper we report our first experimental results on the patterning of a-Si:H by laser printing. PATTERNING PROCEDURES AND RESULTS To use a laser-printed toner as a photolithographic mask, the following steps are necessary: (1) pattern generation using computer software, (2) transfer of the pattern to the desired surface, and (3) selective etching. 719 Mat. Res. Soc. Symp. Proc. Vol. 377 0 1995 Materials Research Society
Pattern generation We evaluated computer software for pattern generation, considering the resolutio
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