Semiconductor device, wiring substrate forming method, and substrate processing apparatus

aaaaaabbbA substrate support having a flat supporting surface is prepared, and a semiconductor substrate is fixed to the substrate supporting surface by attaching a wiring forming surface to the supporting surface by suction, for example, by vacuum suction. On this occasion, the wiring forming surface is forcibly flattened by being attached to the supporting surface by suction, and therefore the wiring forming surface becomes a reference plane for planarization of a back surface. In this state, planarization processing is performed by mechanically grinding the back surface to grind away projecting portions of the back surface. Hence, variations in the thickness of the substrate (especially, semiconductor substrate) are made uniform, and high-speed planarization is realized easily and inexpensively without disadvantages such as dishing and without any limitation on a wiring design.