Dual-surface polishing device and dual-surface polishing method

A dual-surface polishing device comprising:

• an upper plate and a lower plate in the shape of a doughnut, each having a center hole in the central part thereof, rotates the plates by a sun gear which is installed in the respective center holes in the upper plate and the lower plate and an internal gear which is installed on respective outer peripheral parts of the upper plate and the lower plate while sandwichingly holding carriers which hold a wafer by the upper plate and the lower plate and thereby simultaneously polishes both surfaces of the wafers,
• wherein:
• an inner-periphery-side cutoff part X1 where a polishing surface of the upper plate inclines upward toward an inner periphery part of the upper plate and an inner-periphery-side cutoff part Y1 where a polishing surface of the lower plate inclines downward toward an inner periphery part of the lower plate are respectively formed on the respective inner periphery parts of the upper plate and the lower plate, and an outer-periphery-side cutoff part X2 where the polishing surface of the upper plate inclines upward toward the outer periphery part of the upper plate and an outer-periphery-side cutoff part Y2 where the polishing surface of the lower plate inclines downward toward the outer periphery part of the lower plate are respectively formed on the respective outer periphery parts of the upper plate and the lower plate,
• the inner-periphery-side cutoff parts X1, Y1 and the outer-periphery-side cutoff parts X2, Y2 are respectively disposed in the form of a ring along the respective inner periphery parts and the respective outer periphery parts of the upper plate or the lower plate,
• the dual-surface polishing device is controlled in such a manner that when vertical-direction cutoff amounts of the inner-periphery-side cutoff parts X1, Y1 are designated by A1, B1 (μm) respectively, the A1, B1 (μm) satisfy a range of 10 μm≤A1+B1≤70 μm, and
• the dual-surface polishing device is controlled in such a manner that when vertical-direction cutoff amounts of the outer-periphery-side cutoff parts X2, Y2 are designated by A2, B2 (μm) respectively, the A2, B2 (μm) satisfy a range of 10 μm≤A2+B2≤70 μm.