Method for Grinding Plate-Formed Workpiece and Grinding Apparatus

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2024-047442 filed on Mar. 25, 2024, and No. 2024-185633 filed on Oct. 22, 2024; the entire contents of which are incorporated herein by reference.

The present disclosure relates to a method for grinding a plate-formed workpiece and a grinding apparatus using a chuck table to hold the workpiece.

Japanese Patent Laid-Open Publication No. 2021-062460 discloses a grinding method for grinding a plate-formed warped workpiece with a rotating grindstone. According to the publication, for holding the plate-formed warped workpiece on a chuck table, a tape may be adhered to an outer circumferential surface of the plate-formed workpiece, which is in a concave form due to the warpage. When the tape is adhered, a closed space is formed between the tape and the concave surface of the workpiece, and the chuck table may hold the plate-formed workpiece through the tape with the space formed underneath the workpiece.

As such, when adhering the tape to the workpiece, adhering the tape and forming of the closed space with the workpiece may be performed simultaneously, which may be burdensome and may lower working efficiency.

In view of the above, one of purposes of the present disclosure is to provide a method for grinding a plate-formed workpiece and a grinding apparatus that may improve working efficiency for grinding a plate-formed workpiece which is warped at a center thereof.

According to an aspect of the present disclosure, a method for grinding a plate-formed workpiece having a raised center with a grindstone includes a first holding process including suctioning and holding the plate-formed workpiece against a holder surface of a first chuck table, which is in a shape where a center is raised with respect to an outer circumference thereof; a reaction-force reducing grinding process including grinding a central part of the plate-formed workpiece with the grindstone to reduce a reaction force against a flattening force to be applied to the plate-formed workpiece; a second holding process including suctioning and holding the plate-formed workpiece against a holder surface of a second chuck table, which spreads in parallel to a lower surface of the grindstone; and a finish-grinding process including grinding to finish the plate-formed workpiece with the grindstone.

According to another aspect of the present disclosure, a grinding apparatus configured to grind the plate-formed workpiece in the above method includes at least the first chuck table including the holder surface where the center is raised toward the lower surface of the grindstone; the second chuck table including the holder surface spreading in parallel to the lower surface of the grindstone; and a grinding assembly configured to grind the plate-formed workpiece suctioned and held with one of the first chuck table or the second chuck table.

According to another aspect of the present disclosure, a method for grinding a plate-formed workpiece having a raised center with a grindstone includes a first holding process including suctioning and holding the plate-formed workpiece, in a state where a center of the plate-formed workpiece is raised, against a holder surface of a chuck table, which spreads in parallel to a lower surface of the grindstone; a reaction-force reducing grinding process including grinding a central part of the plate-formed workpiece with the grindstone to reduce a reaction force against a flattening force to be applied to the plate-formed workpiece; a second holding process including suctioning and holding the plate-formed workpiece against the holder surface of the chuck table without forming a gap between the holder surface and a lower surface of the plate-formed workpiece; and a finish-grinding process including grinding to finish the plate-formed workpiece with the grindstone.

According to another aspect of the present disclosure, a grinding apparatus configured to grind the plate-formed workpiece in the above method includes at least the chuck table including the holder surface; a suction path connecting the holder surface and a suction source; a pressure adjuster device arranged in the suction path and configured to adjust a negative pressure value of the holder surface; and a grinding assembly configured to grind the plate-formed workpiece suctioned and held with the chuck table.

According to another aspect of the present disclosure, a grinding apparatus configured to grind the plate-formed workpiece in the above method includes at least the chuck table having at least two holder surfaces including a central holder surface and an outer circumferential holder surface, which are concentric; a central suction path connecting the central holder surface and a suction source; an outer circumferential suction path connecting the outer circumferential holder surface and the suction source; an area changeable device configured to change an area of the at least two holder surfaces; and a grinding assembly configured to grind the plate-formed workpiece suctioned and held with the chuck table.

According to the present disclosure, the central part of the plate-formed workpiece may be ground after the plate-formed workpiece is held on the holder surface, which is raised to be higher at the center than the outer circumference thereof, or after the plate-formed workpiece in a form where the center thereof is raised is held on the holder surface. As such, before the plate-formed workpiece is flattened for finish-grinding, a reaction force that may be produced against flattening force may be reduced. Therefore, without the conventional process to adhere a tape to a workpiece forming a closed space therewith, the plate-formed workpiece with the raised center may be ground. As such, according to the present disclosure, working efficiency for grinding a plate-formed workpiece, which is warped to rise at the center thereof, may be improved.

Hereinbelow, a grinding method and a grinding apparatus for a plate-formed workpiece according to a first embodiment will be described with reference to the accompanying drawings. First, a plate-formed workpiece W to be ground as shown inis described. The plate-formed workpiece W is, for example, a disk-shaped wafer having a thickness of 2.5 mm.is a cross-sectional view of the plate-formed workpiece W before grinding. As shown in, the plate-formed workpiece W is warped to rise at a center thereof, where a first surface Won one side in a direction of thickness is convex, and a second surface Won the other side in the direction of thickness is concave. For the plate-formed workpiece W in the present embodiment, although not specifically limited, a workpiece with resiliency that may exert a reaction force against a flattening force, when the flattening force to correct warpage is applied thereto before grinding, is used. For example, in a plate-formed workpiece W with a thickness of 2.5 mm, an amount of warpage, at a central part where the warpage is at its maximum extent, may be 2 mm.

Next, a grinding apparatusfor grinding the plate-formed workpiece W will be described.is a schematic perspective view of the grinding apparatus according to the first embodiment. An X-axis direction, a Y-axis direction, and a Z-axis direction shown in the drawings are orthogonal to one another. The X-axis direction and the Y-axis direction are substantially horizontal directions, and the Z-axis direction is an up-down direction (vertical direction). A +X side and a −X side, which are one and the opposite sides as pointed by a bidirectional arrow along the X-axis direction, are a rightward side and a leftward side, respectively. A +Y side and a −Y side, which are one and the opposite sides as pointed by a bidirectional arrow along the Y-axis direction, are a rearward side and a frontward side, respectively. A +Z side and a −Z side, which are one and the opposite sides as pointed by a bidirectional arrow along the Z-axis direction, is an upper side and a lower side, respectively.

The grinding apparatusis configured to perform a series of operations including a loading process, a grinding process, a cleaning process, and an unloading process with the plate-formed workpiece W fully automatically. The plate-formed workpiece W may be fed to the grinding apparatusin a state where the plate-formed workpiece W is stored in a cassette.

On the −Y direction side of a baseof the grinding apparatus, two cassettesthat may each store a plurality of plate-formed workpieces W are placed. One of the cassettesmay store the plate-formed workpieces W before grinding, and the other of the cassettesmay store the plate-formed workpieces W after grinding. At a rearward position with respect to the cassettes, a robot handthat may pick up the plate-formed workpiece W from the one of the cassettesor may place the plate-formed workpiece W back in the other of the cassettesis provided.

The grinding apparatushas a controller, including a processor to execute various processes and a memory storing programs. The grinding apparatusis configured to perform the series of operations including the loading process, the grinding process, the cleaning process, and the unloading process with the plate-formed workpieces W fully automatically according to the programs stored in the memory of the controllerand controlling signals transmitted from the controllerto each component.

At a rightward-rear position and a leftward-rear position with respect to the robot hand, respectively, provided are a positioning assembly, on which the plate-formed workpiece W before grinding is placed, and a spinner-cleaning device, which may clean the plate-formed workpiece W after grinding. The robot handmay convey the plate-formed workpiece W before grinding from the cassetteto the positioning assemblyand convey the plate-formed workpiece W after grinding from the spinner-cleaning deviceto the cassette.

The positioning assemblyincludes a plurality of positioning pins, which are arranged around a temporary placement tableand are movable inward toward or outward from a center of the temporary placement table. While the plate-formed workpiece W is on the temporary placement tablein the positioning assembly, by moving the plurality of positioning pinsto respectively contact an outer circumferential edge of the plate-formed workpiece W, a center of the plate-formed workpiece W is located at the center of the temporary placement table.

The spinner-cleaning devicemay clean the plate-formed workpiece W having been ground by supplying a cleaning solution from a cleaning nozzleto the plate-formed workpiece W and rotating a spinner tableholding the plate-formed workpiece W at a high speed by a motor, which is not shown.

At a position between the positioning assemblyand the spinner-cleaning deviceon the base, a supporting blockextending in the Y-axis direction is provided, and at a rearward position on the base, a columnis provided to stand vertically. Moreover, the grinding apparatusincludes a conveyer assemblyarranged on the supporting blockand a holder devicelocated between the conveyer assemblyand the columnon the base. The holder deviceincludes a first chuck tableand a second chuck tablearranged on a turntable.

The conveyer assemblymay load the first chuck tableor the second chuck tablewith the plate-formed workpiece W and unload the plate-formed workpiece W from the first chuck tableor the second chuck table. The conveyer assemblymay convey the plate-formed workpiece W among the first chuck tableor the second chuck table, which is located frontward at a load/unload position, the temporary placement table, and the spinner table.

The conveyer assemblyincludes a conveyer pad, which may suction and hold an upper surface of the plate-formed workpiece W, and a rotating device, which may rotate (pivot) the conveyer padon an axis extending in the Z-axis direction. Moreover, the conveyer assemblyincludes a lift/lower assembly, which supports the conveyer padmovably upward or downward in the Z-axis direction, and a Y-axis movable assembly, which may move the conveyer padin the Y-axis direction. The rotating deviceis supported by the lift/lower assembly, and the lift/lower assemblyis supported by a Y-axis movable deviceof the Y-axis movable assembly, which will be described further below. The conveyer padis supported at an end of an arm, which extends horizontally from a lower end of the rotating device. The rotating deviceand the lift/lower assemblyare each driven by a driving force from a motor and an actuator, which are not shown, to cause the armto rotate and move vertically.

The Y-axis movable assemblyincludes a pair of guide railsarranged on a surface of the supporting blockon the +X direction side and extending in the Y-axis direction, a Y-axis movable devicesupported by the supporting blockthrough the pair of guide railsmovably in the Y-axis direction, a ball screwextending in the Y-axis direction and screwed to a screw thread (not shown) in the Y-axis movable device, and a motorto rotate the ball screw. As the motordrives the ball screwto rotate, the Y-axis movable devicemoves in the Y-axis direction. As the Y-axis movable devicemoves in the Y-axis direction, the armsupported by the Y-axis movable devicethrough the rotating deviceand the lift/lower assemblymoves in the Y-axis direction, and as a result, the position of the conveyer padmay change in the Y-axis direction.

The conveyer assemblymay operate the rotating deviceto rotate and the Y-axis movable assemblyto move in the Y-axis direction, thereby moving the conveyer padin the horizontal direction. Moreover, the conveyer assemblymay operate the lift/lower assemblyto move the conveyer padup or down in the Z-axis direction. With these operations, the plate-formed workpiece W may be conveyed among the first chuck tableor the second chuck table, which is located frontward at the load/unload position, the temporary placement table, and the spinner table.

The turntablein the holder deviceis in a shape of a disk and is supported on the baserotatably about an axis extending in the Z-axis direction. The turntablemay be driven to rotate by a motor in a turntable rotating assembly (not shown).

The first chuck tableand the second chuck tableare located symmetrically with respect to a rotation center of the turntable(a center of the first chuck tableand a center of the second chuck tableare apart from each other bydegrees in a rotating direction of the turntable). The first chuck tableand the second chuck tablemay be located at a grinding position, which is on the +Y direction side and the −X direction side with respect to the rotation center of the turntable, or the load/unload position, which is on the −Y direction side and the +X direction side with respect to the rotation center of the turntable. The grinding position is a position where a grinding assembly, which will be described later, may grind the first surface Wof the plate-formed workpiece W.

The grinding apparatusfurther includes a lift/lower assemblyarranged on the columnand the grinding assemblymovable up or down in the Z-axis direction.

The lift/lower assemblyincludes a pair of guide railslocated on a frontward surface of the columnand extending in the Z-axis direction, a lift/lower tablearranged movably in the Z-axis direction with respect to the pair of guide rails, and a ball screwextending in the Z-axis direction and screwed to a screw thread (not shown) in the lift/lower table. As a motor, which is coupled to one end of the ball screw, drives the ball screwto rotate, the lift/lower tablemoves in the Z-axis direction.

The grinding assemblysupports a spindlerotatably with respect to a spindle housing, which is attached to a frontward surface of the lift/lower tablevia a holderand supported by the holder. The spindleis driven by a driving force of a spindle motorto rotate on an axis extending in the Z-axis direction.

A mountis connected to a lower end of the spindle, and a grinding wheelis attached to the mount. On a lower surface of the grinding wheel, an annular grindstone, including a plurality of grindstones arranged annularly, is provided. The grinding assemblymay grind the first surface Wof the plate-formed workpiece W suctioned and held by the first chuck tableor the second chuck tablewith the grindstone.

are schematic cross-sectional views of the first chuck table and surrounding thereof according to the first embodiment.are schematic cross-sectional views of the second chuck table and surrounding thereof according to the first embodiment. The first chuck tableand the second chuck tablehave a substantially similar configuration except for shapes of holder surfaces,.

The first chuck tableas shown inincludes a first frameand a first porous sheetin a shape of a disk mounted in a recess formed on an upper side of the first frame, and an upper surface of the first porous sheetforms the holder surface. The second chuck tableas shown inincludes a second frameand a second porous sheetin a shape of a disk mounted in a recess formed on an upper side of the second frame, and an upper surface of the second porous sheetforms the holder surface. The first and second porous sheets,are made of a porous material such as ceramics and have fine pores formed throughout.

The holder devicefurther includes a first table-rotating assemblyand a second table-rotating assembly. The first and second table-rotating assemblies,are each composed of, for example, a motor and a pulley mechanism, which are not shown. The first table-rotating assemblymay drive the first chuck tableto rotate on a center axis Cof the holder surface, and the second table-rotating assemblymay drive the second chuck tableto rotate on a center axis Cof the holder surface.

The holder deviceincludes a suction source, a first suction path (suction path)connected to the first porous sheetof the first chuck tableand continuous with the holder surface, and a second suction path (suction path)connected to the second porous sheetof the second chuck tableand continuous with the holder surface. The suction sourcemay be composed of, for example, a vacuum generator such as a vacuum pump or an ejector.

The first suction pathis connected to the suction sourcethrough a first open/close valve, and the second suction pathis connected to the suction sourcethrough a second open/close valve. When the first open/close valveis open, the suction sourceand the holder surfaceof the first chuck tablecommunicate through the first suction path, and the air is suctioned through the holder surfaceto generate negative pressure, thereby the plate-formed workpiece W may be suctioned and held against the holder surface. When the second open/close valveis open, the suction sourceand the holder surfaceof the second chuck tablecommunicate through the second suction path, and the air is suctioned through the holder surfaceto generate negative pressure, thereby the plate-formed workpiece W may be suctioned and held against the holder surface. Optionally, the suction sourcemay be a common configuration to be connected with both the first and suction paths,, or may be provided separately to each of the first and second suction paths,.

Next, shapes of the holder surfaceof the second chuck tableand the holder surfaceof the first chuck tablewill be described below in this given order.

The holder surfaceof the second chuck tableis formed as a conical surface, of which apex is located on the center axis Cthat is a rotation axis of the second chuck table, and which descends gradually toward an outer periphery of the second chuck table. An inclination of the holder surfaceis slight enough not to be visually recognizable. A radial range in the plate-formed workpiece W held on this holder surfaceis a grinding range, where the plate-formed workpiece W contacts the annular grindstone. At an area directly below the grinding range, the holder surfaceis formed to be parallel to a lower surfaceof the grindstone.

The holder surfaceof the first chuck tablehas a central areaand a circumferential areaformed on an outer side of the central area. The central areaforms a conical surface, of which apex is located on a center axis Cthat is a rotation axis of the first chuck table, and which descends gradually toward an outer circumference of the first chuck table. An inclination of the holder surfaceis substantially equal to the inclination of the holder surface. The circumferential areaforms a conical surface, which descends gradually toward the outer circumference of the first chuck table, of which taper angle is different from a taper angle of the conical surface of the central area. In particular, the circumferential areaforms a smaller taper angle than the taper angle of the central area.

As such, compared to the holder surfaceof the second chuck table, the holder surfaceof the first chuck tableis in a form such that the center is raised steeply than the circumference. Moreover, the holder surfaceof the first chuck tableis in a positional relation such that the circumferential areais farther from the lower surfaceof the grindstonethan the central area(see), so that the holder surfaceis raised toward the lower surfaceof the grindstone.

Operations of the components in the grinding apparatusare controlled by the controller(see). The memory device in the controllermay store, as a part of controlling programs, for example, programs for controlling the operations of the holder deviceand the grinding assembly. For example, the controllermay control open/close behaviors of the first and second open/close valves,and suctioning behaviors with the holder surfaces,. For the operation of each component in the grinding apparatusdescribed below, when no explicit entity is specified as a subject to control the operation, it is assumed that the operation is controlled by signals output from the controller.

Hereinbelow, a method for grinding a plate-formed workpiece according to the present embodiment will be described. The method for grinding the plate-formed workpiece according to the present embodiment may be implemented by performing steps including a first holding process, a reaction-force reducing grinding process, a second holding process, and a finish-grinding process in this given order.illustrates the first holding process,illustrates the reaction-force reducing grinding process,illustrates the second holding process, andillustrates the finish-grinding process.

In the first holding process, the conveyer assembly(see) is operated to convey and place the plate-formed workpiece W onto the first chuck table. The plate-formed workpiece W with warpage is, as shown in, set in an orientation such that the convex first surface Wfaces upward, and the concave second surface Wfaces downward. Next, the first open/close valveis opened to connect the suction sourcewith the holder surfaceof the first chuck table, and the air is suctioned through the holder surfaceto generate negative pressure, thereby suctioning and holding the plate-formed workpiece W against the holder surface.

The holder surfaceof the first chuck tableis in the form such that the center is raised, and the second surface Wof the plate-formed workpiece W faces downward; therefore, in the state where the plate-formed workpiece W is placed on the holder surface, the second surface Wof the plate-formed workpiece W generally fits with the holder surface. Moreover, as the negative pressure from the holder surfaceacts on the plate-formed workpiece W, the holder surfaceand the second surface Wof the plate-formed workpiece W being suctioned and held thereon contact each other by the surfaces, and the shape of the plate-formed workpiece W with the center being raised may be maintained.

After the first holding process, the reaction-force reducing grinding process, for reducing a reaction force that may be generated when flattening the plate-formed workpiece W, is performed. The reaction-force reducing grinding process is, as shown in, performed by grinding the first surface W, which is the upper surface of the plate-formed workpiece W, with the grinding assembly.

In the reaction-force reducing grinding process, by rotating the turntable(see), the first chuck tableis located below the grinding wheelin the grinding assembly. In this location, the annular grindstoneis arranged such that an outer circumferential edge thereof passes through the center axis Cof the first chuck table.

In this state, the first table-rotating assemblyis operated to rotate the first chuck tableand the plate-formed workpiece W held thereon, and the lift/lower assembly(see) is operated to lower the grinding assemblyand rotate the grindstonevia the spindle. As such, the grindstoneand the plate-formed workpiece W suctioned and held against the first chuck tableapproach and contact each other while rotating respectively.

In this arrangement, the holder surfaceof the first chuck tableand the plate-formed workpiece W are raised at the center thereof; therefore, the grinding range where the plate-formed workpiece W contacts the grindstoneis a partial range that coincides straight above with the central area. In other words, the area coinciding straight above with the circumferential areaof the holder surfacehas the smaller taper angle and thereby is not in contact with the lower surfaceof the grindstone. Therefore, in the reaction-force reducing grinding process, the plate-formed workpiece W is ground partly, i.e., at a central part Wof the first surface W, and is not ground at the outer area outside the central part W. Accordingly, the central part Wof the plate-formed workpiece W is ground to be thinner than the outer area, and the reaction force that may be produced against the flattening correcting force may be reduced.

After the reaction-force reducing grinding process, the second holding process, in which the chuck table to hold the plate-formed workpiece W is changed from the first chuck tableto the second chuck table, is performed. In the second holding process, the plate-formed workpiece W on the first chuck tableis picked up by the conveyer padof the conveyer assembly(see), the turntableis operated to rotate by 180 degrees, and the plate-formed workpiece W is placed on the second chuck table. When placed on the second chuck table, the plate-formed workpiece W is maintained in the orientation where the first surface Wfaces upward and the second surface Wfaces downward. Thereafter, the second open/close valveis opened, the suction sourceand the holder surfaceof the second chuck tablecommunicate, and the air is suctioned through the holder surfaceto generate negative pressure, thereby suctioning and holding the plate-formed workpiece W against the holder surface.

The holder surfaceof the second chuck tablespreads parallel to the lower surfaceof the grindstone; therefore, in the state where the plate-formed workpiece W is held on the holder surface, the second surface Wmay be in the convex shape, which may create a space between the holder surfaceand the second surface W. In such a case, by suctioning the air through the holder surface, a force to attract the second surface Wtoward the holder surfaceis applied to the plate-formed workpiece W, and moreover, the reaction force against this attracting force is reduced as the result of grinding the central part W. Therefore, the second surface Wof the plate-formed workpiece W may contact the holder surfaceby the surface to be suctioned and held thereon.

After the second holding process, as shown in, the finish-grinding process is performed. The finish-grinding process is performed with the grinding assembly, in the same manner as the reaction-force reducing grinding process except that the chuck table to hold the plate-formed workpiece W has been changed from the first chuck tableto the second chuck table. In the finish-grinding process, the plate-formed workpiece W is ground by the grindstoneto a predetermined even thickness.