Abstract: For manufacturing a master for the replication of optical discs a plate of fine-grained copper is coated with a photoresist and exposed by a laser beam which is turned on and off in accordance with information to be recorded on the disc. After developing the photoresist, the exposed portions of the copper layer is etched to a predetermined depth and the photoresist stripped from the etched copper surface.

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.