Copper Pattern Formation on Fluorocarbon Film by Single Shot of ArF Laser
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Copper Pattern Formation on Fluorocarbon Film by Single Shot of ArF Laser T. Mochizuki and M. Murahara Department of electrical engineering, Tokai University 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan ABSTRACT Copper nuclei have been photo-che mically patterned on the fluorocarbon film surface in copper sulfate atmosphere via the reticle with just one shot of the ArF laser. Previously, we have reported that it required more than 3,000 shots of the ArF laser to substitute the Cu atoms on the fluorocarbon surface. Fluorocarbon is regarded as promising as a printed wiring board material in the high- frequency band. However, the fluorocarbon is chemically stable making it difficult to bond to copper foil. Generally, a copper foil is formed on the fluorocarbon surface by electroless plating with a catalyst core. In this method, however, the surface is made rough in pretreatment, which impairs its characteristics. Using the catalysts also causes differences in the dielectric constant, generating a high frequency noise. Thus, we demonstrated the direct formation of copper nuclei on the fluorocarbon surface photo-chemically by using the Xe2 excimer lamp and the ArF excimer laser. The sample surface was first irradiated by Xe2 excimer lamplight to make it hydrophilic. The surface was then irradiated with circuit patterned ArF laser light in the presence of copper-sulfate (CuSO4 ) aqueous solution to substitute the Cu atom. The modified sample was immersed in the electroless plating solution at 60 degrees Celsius for 15 minutes, and the copper foil was locally formed on the areas exposed to light. INTRODUCTION Fluorocarbons such as polytetrafluoroethylene (PTFE), have excellent properties including heat resistance, chemical resistance, and water or oil repellency. Besides high electrical insulation, a low dielectric constant of 2.1 is required for a printed circuit substrate for a high frequency bond. Thus, the fabrication of metal films such as a copper on the fluorocarbon surface is needed. On electric circuit printed boards, the copper foils have been generally produced by electroless plating after making the sample rough and using palladium (Pd) or platinum (Pt) catalyst cores for adhesion. Fluorocarbons are mainly composed of C-F bonds. However, the
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chemical stability of the fluorocarbons makes it difficult to create a chemical bond on the surface. Thus a surface modification of fluorocarbons is required to improve the formation of copper thin foil. Many studies have been done in the polymer surface modification with plasma or laser- light for electroless plating or electroplating treatment. Weber and co-workers tried to deposit of the titanium nitride (TiN) on the PTFE surface with electron cyclotron resonance (ECR) plasma in low temperature [1]. Zhao and co-workers tried to modify the polymide surface with KrF laser abrasion. The modified surface was deposited on the Pd catalyst by immersing in Pd solution [2]. Wang demonstrated that Q-switched Nd:YAG laser induced deposition of Cu atoms o
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