When the remaining slurry and polishing residue are removed by cleaning with a cleaning liquid (preferably a cleaning liquid containing a surfactant), organic matter in the cleaning liquid containing a surfactant seeps into the interlayer insulating film 3. Therefore, the substrate is subsequently washed with an organic solvent or a solution containing an organic solvent, thus washing away the organic matter that has seeped into the interlayer insulating film 3. Although the interlayer insulating film 3 is subjected to a hydrophobic treatment, since the solvent used is an organic solvent, this solvent is able to seep into the interlayer insulating film 3, dissolve the organic matter, and wash the organic matter away without being affected by this hydrophobic treatment. Afterward, the substrate 1 is dried, and the organic solvent or solution containing an organic solvent that is adhering to the surface is removed.