Thin-film UV–vis spectroscopy as a chemically-sensitive monitoring tool for copper etching bath

Abstract Subtractive copper etching is a central process in fabricating advanced printed circuit boards, where ever-shrinking features demand precise control of etch rate and etch factor. Copper etching baths, using cupric chloride, involve complex chemical equilibria that the currently used semi-chemical monitoring tools, including oxidation–reduction potential, conductivity, and specific gravity, can have difficulty controlling precisely. We report a new monitoring tool, thin-film UV–vis spectroscopy, to support and enhance the existing monitoring parameters. UV–vis can distinguish specific chemical contributions to the etch bath performance and to monitoring parameters, and can contribute to significant improvements in the control of the copper etching system.

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