To provide a flattening apparatus that grinds and polishes the backside of a semiconductor substrate at high throughput to thin and flatten the substrate and manufactures the semiconductor substrate with less contamination sticking thereto, and to provide a temporary placement surface plate used for the flattening apparatus.

The flattening apparatus 1 includes a loading/unloading stage chamber 11a for the semiconductor device, a backside polishing stage chamber 11c, and a backside grinding stage chamber 11b, each stage chamber housing each mechanical element. The flattening apparatus 1 is so designed that a backside polishing stage 70 capable of polishing two substrates at the same time achieves a throughput time twice as high as a throughput time of a backside polishing stage 20 polishing one substrate at a time.