Copper Pattern Formation on Fluorocarbon Film by Single Shot of ArF Laser

Abstract

ABSTRACTCopper nuclei have been photo-chemically 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 ma ke 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.