A New Simple Method for Fabrication of Fine Metal Patterns
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A New Simple Method for Fabrication of Fine Metal Patterns Yasuyuki Hotta, Koji Asakawa, Shigeru Matake, and Toshiro Hiraoka Advanced Materials and Devices Laboratories, Corporate Research & Development Center, Toshiba Corporation, 1 Komukai Toshiba-cho, Saiwaiku, Kawasaki 212-8582, Japan
ABSTRACT We developed a new method for easy fabrication of micrometer-scale fine metal patterns on substrates. The patterns can be fabricated at low cost, at low processing temperature, and on uneven substrates as well as on plane surfaces. The method involves, first, forming hydrophilic and hydrophobic patterns on the substrates, and, second, depositing metal by electroless plating on the hydrophilic area. Hydrophilic and hydrophobic patterns were formed on a sensitizer containing naphthoquinonediazide (NQD) units coated on the substrates by the exposure. In the exposed areas, metal particles that are catalysts for electroless copper plating were adsorbed in the ion-exchange reaction and then the reduction treatment was performed. Copper was selectively deposited by the self-catalyst mechanism, according to the exposed patterns. All experimental processes can be carried out at room temperature. Using this new method, copper line patterns of 25 µm and copper dot patterns of 15 µm diameter were fabricated on the substrate.
INTRODUCTION In order to manufacture high- performance electronic equipment, a technology for fabricating fine conductor wiring on printed wiring boards (PWBs) is indispensable. At present, in the mainstream method of wiring fabrication on PWBs, patterned resists are used, and subtractive and additive processes are performed. This conventional method of metal pattern fabrication involves complicated processes and, moreover, requires the use of large amounts of environmentally harmful chemicals. On the other hand, for the manufacturing of high-performance electronic equipment, the PWB substrate is required to have a low dielectric constant and thermal stability. To satisfy these requirements, polyimide (PI) and poly(tetrafluoroethylene) (PTFE) are widely used as substrates. In the present work, resist patterning was not used and the technology for forming metallic wiring directly on these substrates was investigated. In the case of one candidate technology, the surface of the substrates was partially modified by laser, and metal was deposited by plating on the surfaces [1-6]. In the case of another candidate technology, the surface of the PI substrates was modified by carboxylation, and metallic nuclei were selectively formed by photolithography [7]. We propose a method of metal pattern formation that lowers fabrication cost and extends applicability to other substrate materials. In this method, a thin layer of photosensitizers is coated on the substrates, and the required patterns are formed by UV light exposure. Metal particles are adsorbed on the exposed area, then metal patterns are formed by electroless plating on the metal particles, which serve as a nucleus. For this technology, we used a photosensitizer c
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