Open Air Fabrication Process of Cu Thin Films on Teflon Surface Using ArF Excimer Laser Irradiation
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electroless plating of copper is carried out on the un-ablated surface[i-3]. Alternatively, Teflon has been modified by an ArF excimer laser irradiation in gaseous N2H 4 with electroless plating of copper or nickel performed on the photo-modified surface[4]. On the other hand, we have reported on photochemical modification of a Teflon surface: the C-F bonds on the photo-excited surface are easily defluorinated by boron, aluminum or hydrogen atoms, having a binding energy with fluorine atom higher than the C-F binding energy; dangling bonds of the defluorinated carbon atoms are bonded with a functional group[5-7]. In this study, with our photochemical modification technique, fluorine atoms of the surface were replaced by copper atoms. The Cu thin films were grown on the Cu nuclei on the photomodified Teflon surface. PHOTOCHEMICAL REACTION The principle of the surface modification is illustrated in Fig. 1. In order to fabricate the Cu thin films on a Teflon surface, it is needed to defluorinate the C-F bonds of the surface. Therefore, the ArF laser having a photon energy of 147kcal higher than the C-F binding energy of 128kcal/mol is employed for the modification. Namely, the C-F bonds can be cut directly by the ArF laser photons. Even though the C-F bonds are cut, fluorine atoms immediately recombine with the carbon atoms of the surface because of the high electronegativity of fluorine atoms. Thus, we have reported that the fluorine atoms of photo-excited C-F bonds can be defluorinated effectively by boron, aluminum or hydrogen atoms because the B-F bonds of 184kcal/mol, the Al-F bonds of 159kcal/mol and the H-F 655 Mat. Res. Soc. Symp. Proc. Vol. 397 ©1996 Materials Research Society
By this photochemical reaction, the bonds of 135kcal/mol with higher binding energy. defluorination easily takes place, with substitution of a functional group successfully carried out on the defluorinated surfrace. In this study, ArF laser light passes through an Cu electroless plating solution and irradiates a Teflon surface. The resin surface is then defluorinated by the hydrogen atoms which are photodissociated from the Cu solution. Dangling bonds of carbon atoms are combined with the oxygen and the copper atoms which are also photodissociated. As a result, C-OCu bonds are produced on the surface and function as Cu nuclei for an electroless plating. Electroless plating can be carried out only on the photomodified parts. Consequently, the deposition of Cu thin films can be carried out in an open air process.
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F 0I F F I
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ArF excimer laser (193nm)
C - C -C-C . .........
Cu electroless-plating solution Teflon film
H-F : 135kcal/mol > C-F : 128kcaI/mol < ArF laser photon : 147kcal
Principle of the surface modification. Fluorine atoms of the C-F bonds excited by ArF laser Fig. 1 are effectively pulled out by the hydrogen atoms which are photodissociated from the Cu elctroless plating solution. Dangling bonds of carbon atoms are combined with the oxygen and the copper atoms which are also photo
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