Method of removing smear from via holes

摘要

An aqueous solution containing sulfuric acid and hydrogen peroxide is used for a soft etchant in a soft etching step in a smear removing process performed prior to a catalyst applying process for chemical copper plating after formation of via holes through an insulating layer of a multi-layer substrate by irradiation of laser. The concentration of sulfuric acid is 1.4 times or less higher than the concentration of hydrogen peroxide. Preferably, the concentration of sulfuric acid is in a range of 5 to 50 g/l, and the concentration of sulfuric acid is lower than the concentration of hydrogen peroxide. More preferably, the concentration of sulfuric acid is in a range of 5 to 10 g/l, and the concentration of hydrogen peroxide is in a range of 30 to 35 g/l. As a result, smear can be certainly removed without excessively etching a conductive layer in the smear removing process.