Method of manufacturing semiconductor integrated circuit device

Disclosed is a method to achieve the planarization of a BPSG film and reduction of micro-scratches on a BPSG film by the CMP method. A BPSG film is deposited over a main surface of a substrate on which MISFETs have been formed, and then, a surface of the BPSG film is planarized by the CMP method. Thereafter, a thermal treatment is performed to the substrate to reflow the BPSG film, thereby removing the micro-scratches on the surface of the BPSG film caused by the polishing. At this time, the amount of polishing of the surface of the BPSG film is controlled within a range of 90 to 300 nm, preferably 100 to 250 nm, and more preferably 120 to 200 nm.