PURPOSE: To facilitate polishing which can reconcile uniformization of a polishing quantity in a semiconductor wafer surface and flattening to a step difference by forming a groove on the reverse side of a polishing surface by leaving a prescribed thickness.

CONSTITUTION: When a surface of a semiconductor wafer 5 is polished, a groove 19 formed in a first layer part 17 is formed between it and a polishing surface 17a by leaving a prescribed thickness, and since a surface of a polishing surface 17a is continuously connected, a condition such as horizontal directional force acts and a side surface 19a part of the groove 19 contacts with a recessed part 13b of a second insulating film 13 can be avoided, so that flatness is not impaired. A pitch of the groove 19 is sufficiently smaller than a diameter of the semiconductor wafer 5, and since the first layer part 17 bends in a part of the groove 19, it can easily run along a surface of the second insulating film 13, and since deformation by running along the surface of the second insulating film 13 is absorbed by a flexible second layer part 18, excellent uniformity of a polishing quantity can be secured over the whole surface of the semiconductor wafer 5.