Ultraviolet laser-induced liquid-phase palladium seeding on polymers
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Ultraviolet laser-induced liquid-phase palladium seeding on polymers K. Korda´s, J. Be´ke´si, K. Bali, R. Vajtai, and L. Na´nai Department of Experimental Physics, Jo´zsef Atilla University H-6720 Szeged, Do´m te´r 9, Hungary
Thomas F. George Office of the Chancellor/Departments of Chemistry and Physics & Astronomy, University of Wisconsin—Stevens Point, Stevens Point, Wisconsin 54481-3897
S. Leppa¨vuori Microelectronics and Material Physics Laboratories, University of Oulu, SF-90570 Oulu, Finland (Received 4 November 1998; accepted 15 June 1999)
Excimer laser pulses with wavelength of 308 nm, repetition rates of 1–10 Hz, pulse energies of 300– 400 mJ, and pulse width of 20 ns are used to selectively seed palladium aggregates from a liquid-phase solution on polymer (polyimide) surfaces. The precursors used are PdCl2 in hydrochloric acid and Pd(CH3CO2)2 in acetic acid. The coverage of the polyimide with palladium aggregates is determined by the analysis of scanning electron microscopy measurements. Qualitative and quantitative analyses of seeded particles on polyimide (PI) are investigated by x-ray diffraction and transmission measurements. The amount of deposited palladium showed a quadratic dependence on the laser fluence reaching the surface. On the other hand, the coverage versus number of laser shots shows a square-root-like dependence. The palladium deposits also appear as amorphous and Pd[111] crystallites forms depending on the number of laser pulses. The roughness of a PI surface prior to seeding is modified mechanically and characterized by its fractal dimension. The fractal dimension of the samples varies between 2.3 and 2.7 for all the parameters applied, and the palladium deposition is found to be dependent on this dimension of the PI film.
I. INTRODUCTION
Laser-induced metal deposition onto semiconductors1,2 and insulators3– 6 has been well studied. However, some difficulties occur in the case of polymer targets because of their thermal properties (melting and thermal decomposition). Basically, there are three methods for depositing materials onto these substrates. One of them is laser-induced forward transfer (LIFT). 7,8 The next method is laser-induced chemical vapor-phase deposition (LCVD).9 The third one, which we report on here, is a method by which the surface is activated (by seeding10) before the actual metal deposition (e.g., electroless plating11,12). In all cases, lasers are used as localized energy sources. The key process of Pd LIFT is thermal and/or photolitic decomposition of an organometallic compound by absorption of ultraviolet (UV) laser light.13 In the case of LCVD, a well-focused laser beam heats the surface for the decomposition of a thermosensitive gas-phase metal compound. These methods require many pretreatments and expensive vacuum, exhaust, and pipe equipment. The seeding method does not require any pretreatment 3690
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J. Mater. Res., Vol. 14, No. 9, Sep 1999 Downloaded: 14 Mar 2015
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