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Abstract

A method is provided for depositing on a substrate a layer of fine-grained copper especially adapted for the making of masters for optical information storage discs, comprising the steps of placing a substrate in an electroplating bath comprising from about 180 to about 220 grams/liter of copper sulfate, from about 40 to about 80 grams/liter of sulfuric acid, from about 30 to about 60 ppm of chloride ion, from about 1.0 to about 15 grams/liter of a polyether having a molecular weight from about 4,000 to about 10,000, from about 1.0 to about 100 milligrams/liter of a sulfonated, sulfurized benzene compound, and from about 3.5 to about 30 milligrams/liter of 1-lower alkyl-2-mercapto imidazole; and passing electric current through the bath to deposit copper on the substrate. Also disclosed is a method of using high performance liquid chromatography techniques to quantitatively measure 1-lower alkyl-2-mercapto imidazole concentration and to control the same.

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First Claim