Chuck table, grinding apparatus, and workpiece grinding method

Abstract

A chuck table used while grinding a flat plate-shaped workpiece having four or more corners in plan view, the chuck table including a holding surface partitioned into a circular first region surrounded by a polygonal second region that has an outer periphery having four or more corners, in plan view, in which the holding surface is shaped such that the center of the first region is the lowest point and the height increases as the distance from the center increases, and the angle formed between the reference tangent plane of the holding surface at the center of the first region and the first tangent plane of the holding surface at points other than the center that are included in the first region is smaller than the angle formed between the reference tangent plane and a second tangent plane of the holding surface at points included in the second region.

What is claimed is: 
     
         1 . A chuck table used at a time of grinding a flat plate-shaped workpiece having four or more corners in plan view, the chuck table comprising:
 a holding surface partitioned into a circular first region and a polygonal second region that surrounds the first region and that has an outer periphery having four or more corners, in plan view, wherein   the holding surface has such a shape that a center of the first region is a lowest point and a height increases as a distance from the center increases, and   an angle formed between a reference tangent plane of the holding surface at the center of the first region and a first tangent plane of the holding surface at points other than the center that are included in the first region is smaller than an angle formed between the reference tangent plane and a second tangent plane of the holding surface at points included in the second region.   
     
     
         2 . A grinding apparatus for grinding a flat plate-shaped workpiece having four or more corners in plan view, the grinding apparatus comprising:
 a chuck table that includes a holding surface partitioned into a circular first region and a polygonal second region surrounding the first region and having an outer periphery having four or more corners, in plan view, and that is rotatable about a straight line passing through a center of the first region, as a rotational axis; and   a spindle having a distal end portion to which a grinding wheel including a plurality of grindstones disposed annularly at predetermined intervals is mounted, wherein   an outer diameter of a trajectory of the plurality of grindstones that is followed when the spindle is rotated is larger than a distance between the center of the first region of the holding surface and each of the four or more corners,   the holding surface has such a shape that the center of the first region is a lowest point and a height increases as a distance from the center increases, and   an angle formed between a reference tangent plane of the holding surface at the center of the first region and a first tangent plane of the holding surface at points other than the center that are included in the first region is smaller than an angle formed between the reference tangent plane and a second tangent plane of the holding surface at points included in the second region.   
     
     
         3 . A workpiece grinding method of grinding a flat plate-shaped workpiece having four or more corners in plan view, in a grinding apparatus including a chuck table that has a holding surface partitioned into a circular first region and a polygonal second region surrounding the first region and having an outer periphery having four or more corners, in plan view, and that is capable of rotating about a straight line passing through a center of the first region, as a rotational axis, and a spindle having a distal end portion to which a grinding wheel including a plurality of grindstones disposed annularly at predetermined intervals is mounted, an outer diameter of a trajectory of the plurality of grindstones that is followed when the spindle is rotated being larger than a distance between the center of the first region of the holding surface and each of the four or more corners, the workpiece grinding method comprising:
 holding a face side of the workpiece on the holding surface of the chuck table in a state in which each of the four or more corners included in the workpiece is positioned in a same direction as any of the four or more corners included in the second region as viewed from the center of the first region;   after the holding, moving the chuck table and the spindle relative to each other such that the center of the first region and the trajectory overlap with each other in a predetermined direction; and,   after the moving, causing the chuck table and the spindle to approach each other along the predetermined direction such that a reverse side of the workpiece and the plurality of grindstones come into contact with each other, while rotating both the chuck table and the spindle, wherein   the holding surface has such a shape that the center of the first region is a lowest point and a height increases as a distance from the center increases, and   an angle formed between a reference tangent plane of the holding surface at the center of the first region and a first tangent plane of the holding surface at points other than the center that are included in the first region is smaller than an angle formed between the reference tangent plane and a second tangent plane of the holding surface at points included in the second region.