PURPOSE: To keep not only a polishing process high in controllability but also a semiconductor device high in characteristics by a method wherein a carbon film is provided as a polishing stop layer in a polishing process wherein a buried insulating film used for isolating devices from each other is flattened.
CONSTITUTION: Carbon films 10 and 14 are made to serve as a polishing stop layer, and silicon oxide films 4 and 7 and a silicon nitride film 11 are polished with cerium oxide as abrasive material. A carbon film used as a polishing stopper can be set 20 times or above as low in polishing rate as a silicon oxide, so that polishing can be stopped at a required position. Then, silicon oxide films 4 and 7 and the silicon nitride film 11 are thermally treated for 30 minutes in an atmosphere of water vapor and oxygen at a temperature of 650°C and successively thermally treated for 30 minutes in an atmosphere of oxygen at a temperature of 1050°C. By these thermal treatments, the silicon oxide film 7 is enhanced in density, and the carbon films 10 and 14 can be removed by burning, so that processes can be lessened in number.
TSUNASHIMA YOSHITAKA
OKANO HARUO
