the method of polishing a copper layer of a substrate is capable of improving a stock removal rate , etc . the method comprises the steps of : supplying a substrate onto an polishing pad of an polishing plate with a copper layer facing the polishing pad ; pressing the substrate onto the polishing pad , with a backing pad , by a press head ; relatively rotating the press head with respect to the polishing plate , with supplying polishing slurry onto the polishing pad . the backing pad is made of a material whose asker c hardness is 75 - 95 and whose compressibility is 10 % or less . the polishing slurry includes a chelating agent for chelating copper , an etching agent for etching the surface of copper layer , an oxidizing agent for oxidizing the surface of copper layer , and water .