A method for cleaning a polishing pad includes dispensing a first amount of deionized water on the polishing pad; cleaning the polishing pad with an acidity/alkalinity solution after dispensing the first amount of deionized water on the polishing pad; rinsing the polishing pad with a second amount of deionized water after cleaning the polishing pad with the acidity/alkalinity solution; removing the acidity/alkalinity solution from the polishing pad. In a subsequent CMP process, the method includes polishing a GST material device for obtaining an improved performance of the GST material device.