Patent ID: 8562390

Claim:
A double-disc grinding apparatus having at least: a rotatable ring-shaped holder for supporting a sheet-like wafer having a notch for indicating a crystal orientation from an outer circumference side along a radial direction, the holder having a protruding portion to be engaged with the crystal-orientation-indicating notch; and a pair of grindstones for simultaneously grinding both surfaces of the wafer supported by the holder, wherein the holder is provided with at least one protruding portion separately from the protruding portion to be engaged with the crystal-orientation-indicating notch, the both surfaces of the wafer are simultaneously ground by the pair of the grindstones while the wafer is supported and rotated with the at least one protruding portion being engaged with a notch formed on the wafer separately from the crystal-orientation-indicating notch, and a position of the at least one protruding portion provided for supporting the wafer includes at least a position that is circularly symmetric about a central axis of the holder, with respect to a position of the protruding portion to be engaged with the crystal-orientation-indicating notch.