Polishing method using ceria slurry, and method of manufacturing semiconductor device

Polishing processes are separated into a plurality of phases; that is, an early polishing phase, a planarization phase, and a post-planarization phase. Polishing is effected by means of changing polishing requirements from phase to phase. Since polishing is effected under appropriate polishing requirements which vary from phase to phase, a polishing time is shortened by means of increasing a polishing rate in each phase. By means of polishing a wafer through use of highly-selective ceria slurry having superior smoothness, high smoothness and high productivity can be achieved simultaneously.