High Resolution Copper Lines by direct Imprinting
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C.M. Hong, X. Sun, S. Wagner, S.Y. Chou Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544 ABSTRACT One-micrometer wide copper lines are patterned by direct imprinting and thermolysis. First, a layer of plastic copper hexanoate is spun on a substrate and patterned by direct imprint. Then the copper hexanoate line pattern is converted to copper metal lines by thermal and hydrogen anneals. The converted copper film resistivity is - 8 LtQcm. The direct imprinting of a fine metal pattern points the way to the direct patterning of device materials at high resolution.
INTRODUCTION Fine metal lines are becoming ever more important to the technology of integrated circuits (ICs). Interconnecting the devices now is the most costly step in fabricating a silicon IC. The metal lines on a large-area circuit such as active-matrix liquid crystal displays soon could be a mile long. The performance of these circuits depends critically on having metals with high conductivity. The need to reduce cost while raising conductivity has stoked the interest in the direct writing of lines of metal, particularly of copper. Direct writing is a mass production technique that could eliminate many process steps from circuit fabrication. Similar motives have stimulated experiments on the direct printing of other active device materials for transistors [1-4] and organic light emitting diodes [5,6]. These experiments have drawn on conventional printing techniques including screen printing and inkjet printing, whose present line pair resolution however lies considerably above - 10 ýtm. Here we report patterning by direct imprint experiments in which we achieved a copper linewidth of 1 gm by the imprinting of a precursor film followed by its conversion to copper metal. This technique is capable of printing even finer copper lines, because it is closely related to the nanoimprint lithography technique [7,8] that has attained a feature size of 6 nm.
EXPERIMENTS During experiments on the writing of copper lines by exposing copper hexanoate, Cu 2 (OH2 )2(O2 CR) 4 where R = (CH 2 ) 4 CH 3 , to UV radiation [9,10], we had discovered that this compound can be decomposed and reduced to metallic copper with a simple annealing sequence [3]. Upon heating, the organic ligand and CO 2 or CO are split off and ejected from the surface of the film. The film that remains on the substrate consists of a mixture of copper and copper(I) oxide. Annealing the film in forming gas (H2 + N2) reduces Cu 2 O to copper metal. Copper hexanoate is plastic by virtue of its high aliphatic content and thus is easily molded by imprinting. Figure 1 shows the steps involved in the patterning of copper lines by imprinting. I g of copper hexanoate prepared according to Graddon [11 ] is dissolved in 5 ml isopropyl alcohol by
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Mat. Res. Soc. Symp. Proc. Vol. 624 © 2000 Materials Research Society
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