Double-disc grinding apparatus and workpiece double-disc grinding method
The invention is directed to a double-disc grinding apparatus including: a rotatable ring holder configured to support a sheet workpiece along a circumferential direction from an outer circumference side of the workpiece; a pair of grinding wheels for grinding surfaces of the workpiece supported by the ring holder; and a hydrostatic bearing for supporting the ring holder without contact from both of a direction of a rotational axis of the ring holder and a direction perpendicular to the rotational axis by hydrostatic pressure of fluid supplied from both directions, wherein supply pressures at which the fluid is supplied from the direction of the rotational axis and from the direction perpendicular to the rotational axis can be independently controlled. The invention provides a double-disc grinding apparatus and a workpiece double-disc grinding method that can improve variation in nanotopography depending on the lot of workpieces or grinding wheels to obtain nanotopography stably.
1. A double-disc grinding apparatus comprising:
a rotatable ring holder configured to support a sheet workpiece along a circumferential direction from an outer circumference side of the workpiece;
a pair of grinding wheels configured to simultaneously grind two surfaces of the workpiece supported by the ring holder; and
a hydrostatic bearing configured to support the ring holder without contact from both of a direction of a rotational axis of the ring holder and a direction perpendicular to the rotational axis by hydrostatic pressure of fluid supplied from both the directions, wherein
supply pressures at which the fluid is supplied from the direction of the rotational axis and from the direction perpendicular to the rotational axis are independently controlled, and
the supply pressures at which the fluid is supplied are controlled such that a degree of rigidity A is 200 gf/μm or less and a degree of rigidity B is 800 gf/μm or more, where the rigidity A represents division of a load by a displacement when the load is applied to the ring holder from one direction of the rotational axis with the fluid supplied from an other direction, and the rigidity B represents division of a load by a displacement when the load is applied to the ring holder from a direction perpendicular to the rotational axis with the fluid supplied from an opposite direction.
2. A workpiece double-disc grinding method comprising:
supporting a sheet workpiece along a circumferential direction from an outer circumference side of the workpiece by a ring holder;
simultaneously grinding two surfaces of the workpiece supported by the ring holder with a pair of grinding wheels while rotating the ring holder, wherein
fluid is supplied from both of a direction of a rotational axis of the ring holder and a direction perpendicular to the rotational axis at independently controlled supply pressures, and both the surfaces of the workpiece are simultaneously ground while the ring holder is supported without contact from both the directions by hydrostatic pressure of the supplied fluid with a hydrostatic bearing, and
the supply pressures at which the fluid is supplied are controlled such that a degree of rigidity A is 200 gf/μm or less and a degree of rigidity B is 800 gf/μm or more, where the rigidity A represents division of a load by a displacement when the load is applied to the ring holder from one direction of the rotational axis with the fluid supplied from an other direction, and the rigidity B represents division of a load by a displacement when the load is applied to the ring holder from the direction perpendicular to the rotational axis with the fluid supplied from an opposite direction.