Photon and Ion Beam-Induced Chemistry of Palladium Acetate Films
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PHOTON AND ION BEAM-INDUCED CHEMISTRY OF PALLADIUM ACETATE FILMS M. E. GROSS,* W. L. BROWN,* J. LINNROS,* L. R. HARRIOTT,* K. D. CUMMINGS,* AND H. 0. FUNSTEN** *AT&T Bell Laboratories, Murray Hill, NJ 07974 **School of Engineering and Applied Sciences, University of Virginia, Charlottesville, VA 22901 and AT&T Bell Laboratories, Murray Hill, NJ 07974 ABSTRACT Electrically conducting palladium features have been produced by laser and ion beam irradiation of thin palladium acetate films. The photothermal reaction induced by scanned continuous wave Ar+ laser irradiation leads to metal lines that may exhibit periodic structure. This results from repeated propagation of "explosive" reaction fronts generated by coupling of the heat from the absorbed laser radiation with the heat of the decomposition reaction of the film. In contrast, 2 MeV He' ion irradiation produces smooth metallic-looking features that contain up to 20% of the original carbon and 5% of the original oxygen content of the film. Films irradiated with 2 MeV Ne+ ions contain slightly lower amounts of carbon and oxygen residues, but fully exposed thick films (0.90 pm) appear black rather than metallic silver. In addition to having significantly higher purity, the laser-written features have lower resistivities than the ion beam-irradiated features. Infrared spectroscopy of the ion beam-irradiated films as a function of dose indicates a progressive loss in intensity of the characteristics acetate (COO-) vibrations. This occurs at doses lower than those associated with major C and 0 loss from the films. Partially ion-exposed films continue to decompose to metallic-looking material over a period of weeks after irradiation. Metallic palladium particles apparently catalyze this process. INTRODUCTION Direct-write metallization in solid films of metallo-organic [11 compounds has recently been demonstrated using lasers [2,31, ion [4,51 and electron [61 beams. The choice of direct-write beam depends on the ultimate desired resolution coupled with a consideration of the decomposition chemistry of the precursor materials induced by that particular beam. The materials requirements for applications such as customization and repair of integrated circuits and lithographic masks vary from materials of high electrical conductivity to those having high opacity to specific radiation. Alternatively, the direct-write process can be used to define a template of a material such as palladium that will then serve as a catalyst for electrolessly plating copper [71 or other materials. Laser direct-writing of palladium from thin films of palladium acetate in a photothermal process has recently been demonstrated [8]. A schematic of this process is shown in Figure 1. The palladium features may exhibit a periodic structure when written on quartz, a thermally insulating substrate. On a better thermal conductor such as silicon, little structure is observed. In either case, the deposited metal is relatively pure. 2 MeV He' and Ne+ ion beam-induced reactions of palladium acetate are striking
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