GRINDING METHOD

BACKGROUND OF THE INVENTION
Field of the Invention

The present invention relates to a grinding method of grinding a laminated wafer including a beveled water.

Description of the Related Art

Chips of devices such as integrated circuits (ICs), for example, are indispensable elements in various electronic appliances such as cellular phones and personal computers. Such chips are fabricated from a wafer by grinding a reverse side of the wafer that has a plurality of devices constructed in a central region of a face side thereof and then dividing the wafer along boundaries between the devices.

A wafer is likely to crack in an outer circumferential region thereof that surrounds its central region. Hence, in order to prevent the outer circumferential region of the wafer from cracking, the outer circumferential region of the wafer is often beveled prior to the various steps of a process of manufacturing chips from the wafer. When the reverse side of the wafer is then ground to a thickness that is equal to or less than one-half of the original thickness of the wafer, the beveled outer circumferential region is shaped into a knife edge.

Continued grinding of the reverse side of the wafer applies stresses primarily to the outer circumferential region, tending to cause the outer circumferential region to crack. One solution in the chip fabrication process is to remove the face side of the beveled outer circumferential region and to subsequently grind the reverse side of the wafer (see, for example, Japanese Patent Laid-open No. 2000-173961).

According to another chip fabrication process, chips are produced from a laminated wafer including a plurality of stacked wafers, by dividing the laminated wafer along boundaries between a plurality of devices on the laminated wafer for the purpose of achieving a higher level of circuit integration. The laminated wafer is produced as follows.

First, a wafer is joined to a support wafer by an adhesive on a face side of the wafer. Then, while the support wafer is being held in position, a beveled outer circumferential region of the wafer is cut off. Thereafter, the wafer is thinned down by being ground on the reverse side. The wafer thus thinned down will be referred to as a “first thinned wafer.”

Then, another wafer is joined to the first thinned wafer by an adhesive on a face side of the other wafer. Then, while the support wafer is being held in position, a beveled outer circumferential region of the other wafer is cut off. Thereafter, the other wafer is ground on the reverse side to be thinned down. The other wafer thus thinned down will be referred to as a “second thinned wafer.”

The above processing cycle of joining a wafer to a thinned wafer and cutting and grinding the wafer is repeated to construct a laminated wafer including three or more thinned wafers and a support wafer. The laminated wafer is then divided along boundaries of a plurality of devices on the wafers, thereby producing individual chips with highly integrated circuits.

SUMMARY OF THE INVENTION

Wafers are generally cut and ground by different apparatuses, i.e., a cutting apparatus and a grinding apparatus. Consequently, fabricating laminated wafers in the manner described above involves a lot of time and labor.

If a wafer is not cut, i.e., if a beveled outer circumferential region of a wafer is not removed, then the outer circumferential region is likely to crack while the wafer is being ground. Moreover, if a sufficient amount of adhesive is not provided on the face side of the wafer, the outer circumferential region tends to break into fragments that may be scattered around while the wafer is being ground.

If the scattered fragments impinge upon the central region of the wafer, then they may possibly cause the wafer to develop cracks large enough to split the wafer. The scattered fragments may also damage components of the grinding apparatus, e.g., grindstones that grind the wafer and a gauge for measuring the thickness of the wafer.

In view of the above drawbacks, it is an object of the present invention to provide a grinding method that is capable of removing at least a portion of a beveled outer circumferential region of a wafer included in a laminated wafer while at the same time preventing the beveled outer circumferential region from cracking and breaking into fragments while the wafer is being ground.

In accordance with an aspect of the present invention, there is provided a grinding method of grinding a laminated wafer including a beveled wafer, including a holding step of holding the laminated wafer such that the wafer is exposed, after the holding step, a first grinding step of grinding the wafer thicknesswise with respect to the wafer to remove part of a central region of the wafer and leave an outer circumferential region of the wafer that surrounds the central region unremoved, and after the first grinding step, a second grinding step of grinding the wafer thicknesswise with respect to the wafer to remove at least a portion of the outer circumferential region of the wafer, in which the load imposed on the laminated wafer in the second grinding step is smaller than the load imposed on the laminated wafer in the first grinding step.

Preferably, the second grinding step includes grinding a surface of the outer circumferential region of the wafer to form thereon a step that includes a circular lower surface and an annular upper surface that extends around the circular lower surface or to form thereon a step that includes a circular upper surface and an annular lower surface that extends around the circular upper surface. Alternatively, the second grinding step preferably includes grinding a surface of the outer circumferential region of the wafer to form an even upper surface entirely thereon.

Alternatively, the second grinding step preferably includes grinding a surface of the outer circumferential region of the wafer to eliminate the outer circumferential region of the wafer in its entirety. Preferably, the laminated wafer further includes an adhesive provided on a surface of the wafer that is opposite a ground surface, and the second grinding step is preferably terminated when a value of a physical quantity that varies depending on the load imposed on the laminated wafer becomes equal to or higher than a predetermined threshold value.

As described above, the grinding method includes the first grinding step that grinds the central region of the wafer thicknesswise with respect to the wafer to remove part of the central region and leave the outer circumferential region unremoved. In the first grinding step, since the wafer is ground only in the central region thereof, and not in its entirety, no excessive load is applied to the outer circumferential region of the wafer.

The grinding method also includes, after the first grinding step, the second grinding step that grinds the wafer thicknesswise with respect to the wafer to remove at least a portion of the outer circumferential region thereof. In the second grinding step, since the load imposed on the laminated wafer in the second grinding step is smaller than the load imposed on the laminated wafer in the first grinding step, no excessive load is applied to the outer circumferential region of the wafer.

Consequently, the grinding method is able to remove at least a portion of the outer circumferential region of the wafer without imposing an excessive load on the outer circumferential region. According to the grinding method, while the wafer included in the laminated wafer is being ground, at least a portion of the outer circumferential region that is beveled can be removed while at the same time the beveled outer circumferential region is prevented from cracking and breaking into fragments.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view schematically illustrating a wafer by way of example;

FIG. 1B is a cross-sectional view schematically illustrating the wafer illustrated in FIG. 1A;

FIG. 2 is a cross-sectional view schematically illustrating a laminated wafer that includes the wafer illustrated in FIGS. 1A and 1B;

FIG. 3 is a perspective view schematically illustrating by way of example a grinding apparatus for grinding the laminated wafer illustrated in FIG. 2;

FIG. 4A is a cross-sectional view schematically illustrating a chuck table of the grinding apparatus illustrated in FIG. 3;

FIG. 4B is a side elevational view, partly in cross section, schematically illustrating a grinding unit of the grinding apparatus illustrated in FIG. 3;

FIG. 4C is a block diagram schematically illustrating a controller of the grinding apparatus illustrated in FIG. 3;

FIG. 5 is a flowchart schematically illustrating an example of a grinding method that grinds the laminated wafer illustrated in FIG. 2 on the grinding apparatus illustrated in FIG. 3;

FIG. 6 is a side elevational view, partly in cross section, schematically illustrating the manner in which a holding step of the grinding method illustrated in FIG. 5 is carried out;

FIG. 7 is a side elevational view, partly in cross section, schematically illustrating the manner in which a first grinding step of the grinding method illustrated in FIG. 5 is carried out;

FIG. 8 is a side elevational view, partly in cross section, schematically illustrating the manner in which a second grinding step of the grinding method illustrated in FIG. 5 is carried out;

FIG. 9A is a cross-sectional view schematically illustrating the laminated wafer in which the wafer illustrated in FIGS. 1A and 1B has been ground to a first profile in the second grinding step of the grinding method illustrated in FIG. 5;

FIG. 9B is a cross-sectional view schematically illustrating the laminated wafer in which the wafer illustrated in FIGS. 1A and 1B has been ground to a second profile in the second grinding step of the grinding method illustrated in FIG. 5;

FIG. 9C is a cross-sectional view schematically illustrating the laminated wafer in which the wafer illustrated in FIGS. 1A and 1B has been ground to a third profile in the second grinding step of the grinding method illustrated in FIG. 5; and

FIG. 9D is a cross-sectional view schematically illustrating the laminated wafer in which the wafer illustrated in FIGS. 1A and 1B has been ground to a fourth profile in the second grinding step of the grinding method illustrated in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A grinding method according to an embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1A schematically illustrates in plan a wafer 11 by way of example, and FIG. 1B schematically illustrates in cross section the wafer 11 illustrated in FIG. 1A.

The wafer 11 illustrated in FIGS. 1A and 1B is made of a semiconductor material such as silicon (Si), for example. The wafer 11, which is of a circular shape, includes a central region 11a and an outer circumferential region 11b surrounding the central region 11a. The central region 11a and the outer circumferential region 11b are set apart from each other by a circular boundary that is schematically indicated by a dotted line that does not, in reality, exist on the wafer 11.

The central region 11a of the wafer 11 has a face side where a plurality of devices 13 are constructed. Each of the devices 13 includes components that make up an IC, a semiconductor memory, or a complementary-metal-oxide-semiconductor (CMOS) image sensor, for example. The devices 13 are arranged in a matrix, i.e., are separated from each other by a grid of boundaries.

The wafer 11 may also include interconnects such as through-silicon vias (TSVs) disposed in through holes extending from either slits defined in the face side of the wafer 11 or the face side to a reverse side of the wafer 11 that is opposite the face side, for example. The outer circumferential region 11b that surrounds the central region 11a of the wafer 11 has its outer side edge beveled, i.e., curved into a radially outwardly protruding shape.

The wafer 11 is not limited to having any particular material, shape, structure, and size. The wafer 11 may, for example, be made of a semiconductor material other than silicon, e.g., silicon carbide (Sic) or gallium nitride (GaN). Similarly, the devices 13 are not limited to any kind, number, shape, structure, size, and layout.

FIG. 2 schematically illustrates a laminated wafer 15 including the wafer 11 in cross section by way of example. As illustrated in FIG. 2, the laminated wafer 15 includes the wafer 11, an adhesive 17 provided on the face side, which is depicted as a lower surface in FIG. 2, of the wafer 11, and a support wafer 19 joined to the wafer 11 by the adhesive 17 interposed therebetween.

The laminated wafer 15 is fabricated by providing the adhesive 17 on the face side of the wafer 11 and thereafter pressing the wafer 11 against the support wafer 19 with the face side of the wafer 11 confronting a face side, which is depicted as an upper surface in FIG. 2, of the support wafer 19. The adhesive 17 is, for example, an acryl-base adhesive or an epoxy-base adhesive.

The support wafer 19 is of a circular shape substantially equal in diameter to the wafer 11 and is made of a semiconductor material such as silicon, for example. The support wafer 19 is a bare wafer or a mirror wafer, for example. Alternatively, the support wafer 19 may be a wafer with some devices constructed thereon. In a case where a back-side-illumination (BSI) CMOS image sensor is to be manufactured from the laminated wafer 15, for example, the image sensor may have pixel circuits fabricated on the face side of the support wafer 19.

FIG. 3 schematically illustrates in perspective by way of example a grinding apparatus 2 for grinding the laminated wafer 15. As illustrated in FIG. 3, the grinding apparatus 2 includes a chuck table 4 and a grinding unit 10 disposed above the chuck table 4. FIG. 4A schematically illustrates the chuck table 4 in cross section, and FIG. 4B schematically illustrates the grinding unit 10 in side elevation, partly in cross section.

The chuck table 4 has a disk-shaped frame 6 made of ceramics, for example. The frame 6 has a disk-shaped bottom wall and a hollow cylindrical side wall extending vertically upwardly from an outer circumferential portion of the bottom wall. The side wall has an inside diameter that is slightly smaller than the diameter of the support wafer 19. The bottom wall and the side wall jointly define a circular recess above the bottom wall of the frame 6.

The chuck table 4 also includes a disk-shaped porous plate 8 fixedly disposed in the recess. The porous plate 8, which is made of porous ceramics, for example, has a multiplicity of interconnected pores defined therein, some of which are open at its upper surface. The chuck table 4 has an upper surface including the upper surface of the side wall of the frame 6 and the upper surface of the porous plate 8. The upper surface of the chuck table 4 acts as a holding surface for holding the laminated wafer 15 thereon. The upper surface of the chuck table 4 represents the lateral surface of a cone whose generating lines are slightly longer than the radius of the support wafer 19 that is to be placed on the chuck table 4.

The bottom wall of the frame 6 has a fluid channel 6a defined centrally therein that extends vertically therethrough and that has an upper end open at the upper surface of the bottom wall, i.e., the bottom surface of the recess. The fluid channel 6a has a lower end fluidly connected through an unillustrated valve to an unillustrated suction source and an unillustrated fluid supply source.

The suction source includes an ejector, for example. The fluid supply source includes, for example, an unillustrated tank that stores gas under high pressure, an unillustrated filter for removing foreign matter from the gas supplied from the tank, and an unillustrated regulator for regulating the pressure of the gas supplied from the tank.

The chuck table 4 is mechanically connected to an unillustrated horizontally moving mechanism. The horizontally moving mechanism includes a ball screw and an electric motor coupled to the ball screw, for example. Alternatively, the horizontally moving mechanism may include a turntable that supports the chuck table thereon and an electric motor for rotating the turntable. When the horizontally moving mechanism is actuated, it moves the chuck table 4 horizontally.

The chuck table 4 is also mechanically connected to an unillustrated rotating mechanism. The rotating mechanism includes an electric motor, pulleys, and an endless belt, for example. When the rotating mechanism is actuated, it rotates the chuck table 4 about a straight line that extends through the center of the upper surface of the chuck table 4, i.e., the center of the upper surface of the porous plate 8, as a rotation axis.

The chuck table 4 is further mechanically connected to an unillustrated tilt adjusting mechanism. The tilt adjusting mechanism includes, for example, two movable shafts and one fixed shaft that are operatively coupled to the chuck table 4 and disposed at substantially equal angular intervals circumferentially around the chuck table 4. The tilt of the central axis of the chuck table 4 is adjusted when at least one of the movable shafts is axially moved to lift or lower the chuck table 4.

The grinding unit 10 has a vertical cylindrical spindle 12 rotatable about its central axis. The spindle 12 has a lower distal end fixed to the upper surface of a disk-shaped wheel mount 14 made of stainless steel, for example. An annular grinding wheel 16 with an outside diameter substantially equal to a diameter of the wheel mount 14 is removably mounted on the lower surface of the wheel mount 14.

The grinding wheel 16 includes an annular wheel base 18 made of stainless steel, for example. The wheel base 18 has a lower surface on which there is mounted an annular array of grindstones 20 that are disposed at substantially equal angular intervals circumferentially around the wheel base 18. Each of the grindstones 20 is made of abrasive grains of diamond or cubic boron nitride (cBN) dispersed in a binder such as a vitrified bond or a resin bond, for example.

The spindle 12 has an upper proximal end coupled to an unillustrated rotary actuator, such as an electric motor. When the rotary actuator is energized, it rotates the spindle 12 about its central axis that extends straight vertically, thereby rotating the wheel mount 14 and the grinding wheel 16 about their central axes in alignment with the central axis of the spindle 12.

The grindstones 20 of the grinding wheel 16 that work on the wafer 11 to grind the wafer 11 are provided such that the outside diameter of a circular track followed by the grindstones 20 upon rotation of the grinding wheel 16 is slightly smaller than the radius of the wafer 11 but slightly larger than the radius of the central region 11a of the wafer 11.

The grinding unit 10 is mechanically connected to an unillustrated vertically moving mechanism. The vertically moving mechanism includes a ball screw and an electric motor coupled to the ball screw, for example. When the vertically moving mechanism is actuated, it moves the grinding unit 10 vertically.

The grinding apparatus 2 includes a controller for controlling its components that have been described above. FIG. 4C schematically illustrates the controller, denoted by 22, in block form by way of example. As illustrated in FIG. 4C, the controller 22 includes a processor 22a and a memory 22b.

The processor 22a is a central processing unit (CPU), for example. The processor 22a reads programs for grinding the laminated wafer 15, specifically the wafer 11, from the memory 22b and executes the program to control the components of the grinding apparatus 2.

The memory 22b includes a volatile memory such as a dynamic random access memory (DRAM) or a static RAM (SRAM), for example, and a nonvolatile memory such as a solid state drive (SSD) also referred to as a Not AND (NAND)-type memory or a hard disk drive (HDD) also referred to as a magnetic storage unit.

The memory 22b stores various items of information, specifically data and programs, to be used by the processor 22a. For example, the memory 22b stores as the data a threshold value for the value of a physical quantity that varies depending on the load on the laminated wafer 15, for example. The physical quantity may represent an electric current to be supplied to the rotary actuator connected to the upper proximal end of the spindle 12 or a load imposed on the chuck table 4.

FIG. 5 is a flowchart schematically illustrating an example of a grinding method that grinds the laminated wafer 15 on the grinding apparatus 2, i.e., the grinding method according to the present embodiment. In the grinding method, first, the laminated wafer 15 is held on the chuck table 4 such that the wafer 11 is exposed upwardly (holding step S1). Specifically, the wafer 11 has a reverse side exposed upwardly that is opposite the face side to which the adhesive 17 is applied. FIG. 6 schematically illustrates in side elevation, partly in cross section, the manner in which the holding step S1 is carried out.

In the holding step S1, specifically, the laminated wafer 15 is introduced and placed on the upper surface of the chuck table 4 such that the center of the support wafer 19 and the center of the chuck table 4 are vertically aligned with each other. Then, the suction source fluidly connected to the fluid channel 6a in the bottom wall of the frame 6 of the chuck table 4 is actuated to generate a suction force, i.e., a negative pressure.

The generated suction force is transmitted through the valve, the fluid channel 6a, and the porous plate 8 and acts on the laminated wafer 15 held on the upper surface of the chuck table 4. As a result, the laminated wafer 15 with the wafer 11 exposed upwardly is held under suction on the chuck table 4. The holding step S1 now comes to an end.

After the holding step S1, the wafer 11 is ground thicknesswise with respect to the wafer 11 in order to remove part of the central region 11a of the wafer 11 while leaving the outer circumferential region 11b unremoved (first grinding step S2). FIG. 7 schematically illustrates in side elevation, partly in cross section, the manner in which the first grinding step S2 is carried out.

In the first grinding step S2, specifically, the tilt of the chuck table 4 is adjusted in order to orient a line segment interconnecting a highest point on the outer circumference of the holding surface of the chuck table 4 and the center of the holding surface perpendicularly to a vertical direction. If the chuck table 4 has already been tilted such that the line segment is oriented perpendicularly to the vertical direction, then the tilt of the chuck table 4 does not need to be adjusted.

Then, the chuck table 4 is moved horizontally until the circular track followed by the grindstones 20 upon rotation of the grinding wheel 16 has an outer circumferential edge inscribed on the boundary between the central region 11a and the outer circumferential region 11b of the wafer 11 at a point where the boundary and the line segment referred to above overlap each other, as viewed in plan.

Then, the chuck table 4 and the grinding wheel 16 are actuated under predetermined grinding conditions. Specifically, while the chuck table 4 and the grinding wheel 16 are being rotated about their respective rotation axes at respective rotational speeds, the grinding wheel 16 is lowered at a predetermined grinding feed speed.

The grindstones 20 are pressed against the central region 11a of the wafer 11 in abrasive contact therewith, thereby grinding the central region 11a thicknesswise with respect to the wafer 11. As a result, whereas the outer circumferential region 11b of the wafer 11 remains unremoved, the central region 11a is partially removed, forming a cavity 11c with a circular bottom in the upper surface, i.e., the reverse side, of the wafer 11.

The central region 11a is continuously ground until the cavity 11c is deepened to a desired depth. When the depth of the cavity 11c has reached the desired depth, the chuck table 4 and the grinding wheel 16 stop being rotated, and the grinding wheel 16 is lifted. The first grinding step S2 is now finished.

After the first grinding step S2, the wafer 11 is ground thicknesswise in order to remove at least a portion of the outer circumferential region 11b thereof (second grinding step S3). FIG. 8 schematically illustrates in side elevation, partly in cross section, the manner in which the second grinding step S3 is carried out.

In the second grinding step S3, specifically, the chuck table 4 is moved horizontally until the circular track followed by the grindstones 20 upon rotation of the grinding wheel 16 has its outer circumferential edge circumscribed on the boundary between the central region 11a and the outer circumferential region 11b of the wafer 11 at the point where the boundary and the line segment referred to above overlap each other, as viewed in plan.

Then, the chuck table 4 and the grinding wheel 16 are actuated under predetermined grinding conditions. Specifically, the grinding conditions in the second grinding step S3 include the respective rotational speeds of the chuck table 4 and the grinding wheel 16 and the grinding feed speed of the grinding wheel 16, for example. These grinding conditions are set to such values that the load imposed on the laminated wafer 15 in the second grinding step S3 is smaller than the load imposed on the laminated wafer 15 in the first grinding step S2.

For example, if the radius of the central region 11a of the wafer 11 is larger than the radial length of the outer circumferential region 11b thereof, then the grinding conditions in the second grinding step S3 may be the same as the grinding conditions in the first grinding step S2.

The grindstones 20 are abrasively pressed against the outer circumferential region 11b of the wafer 11, thereby grinding the outer circumferential region 11b thicknesswise with respect to the wafer 11. As a result, at least a portion of the outer circumferential region 11b is removed, whereupon the second grinding step S3 is completed.

FIGS. 9A through 9D schematically illustrate in cross section the laminated wafer 15 in which the wafer 11 illustrated in FIGS. 1A and 1B has been ground to first through fourth profiles, respectively, that are different from each other in the second grinding step S3.

According to the first profile illustrated in FIG. 9A, the wafer 11 is ground to leave part of the outer circumferential region 11b and the cavity 11c in the second grinding step S3. More specifically, the upper surface of the outer circumferential region 11b of the wafer 11 is ground in the second grinding step S3 to form thereon a step 21 that includes a circular lower surface 21a and an annular upper surface 21b that extends around the circular lower surface 21a and is higher than the circular lower surface 21a. The circular lower surface 21a represents the circular bottom of the cavity 11c, and the annular upper surface 21b represents the ground upper surface of the outer circumferential region 11b of the wafer 11. The first profile achieved in the second grinding step S3 is advantageous in that the probability of cracking of the central region 11a of the wafer 11 is reduced.

According to the second, third, and fourth profiles illustrated in FIGS. 9B, 9C, and 9D, the wafer 11 is ground to eliminate the cavity 11c in the second grinding step S3. The second, third, and fourth profiles achieved in the second grinding step S3 are advantageous in that the laminated wafer 15 can easily be handled in a subsequent step, e.g., an unillustrated other wafer different from the wafer 11 can easily be joined in a subsequent step by an unillustrated adhesive to the wafer 11 that has been thinned down in the second grinding step S3.

More specifically, according to the second profile illustrated in FIG. 9B, the upper surface of the outer circumferential region 11b of the wafer 11 is ground to form an even upper surface entirely thereon in the second grinding step S3. The even upper surface represents the circular bottom of the cavity 11c and the ground upper surface of the outer circumferential region 11b that lie flush with each other.

According to the third profile illustrated in FIG. 9C, the upper surface of the outer circumferential region 11b of the wafer 11 is ground to form thereon a step 23 in the second grinding step S3. The step 23 includes a circular upper surface 23a and an annular lower surface 23b that extends around the circular upper surface 23a. The circular upper surface 23a represents the circular bottom of the cavity 11c and the annular lower surface 23b represents the ground upper surface of the outer circumferential region 11b that is lower than the circular upper surface 23a.

According to the fourth profile illustrated in FIG. 9D, the upper surface of the outer circumferential region 11b of the wafer 11 is ground in the second grinding step S3 to eliminate the outer circumferential region 11b in its entirety while leaving a circular upper surface that represents the circular bottom of the cavity 11c.

If the grindstones 20 contact the adhesive 17 after grinding off the outer circumferential region 11b in its entirety in the second grinding step S3, then the grindstones 20 impose an increased undue load on the laminated wafer 15. To avoid the increased undue load on the laminated wafer 15, the processor 22a of the controller 22 may determine whether the second grinding step S3 is to be terminated or not, by referring to the value of the physical quantity that varies depending on the load on the laminated wafer 15. Specifically, the processor 22a may terminate the second grinding step S3 when the value of the physical quantity becomes equal to or higher than the threshold value stored in the memory 22b.

As described above, the grinding method illustrated in FIG. 5 includes the first grinding step S2 that grinds the central region 11a of the wafer 11 thicknesswise with respect to the wafer 11 to remove part of the central region 11a and leave the outer circumferential region 11b unremoved. In the first grinding step S2, since the wafer 11 is ground only in the central region 11a thereof, but not in its entirety, no excessive load is applied to the outer circumferential region 11b of the wafer 11.

The grinding method also includes, after the first grinding step S2, the second grinding step S3 that grinds the wafer 11 thicknesswise with respect to the wafer 11 to remove at least a portion of the outer circumferential region 11b thereof. In the second grinding step S3, since the load imposed on the laminated wafer 15 in the second grinding step S3 is smaller than the load imposed on the laminated wafer 15 in the first grinding step S2, no excessive load is applied to the outer circumferential region 11b of the wafer 11.

Consequently, the grinding method is able to remove at least a portion of the outer circumferential region 11b of the wafer 11 without imposing an excessive load on the outer circumferential region 11b. According to the grinding method, while the wafer 11 included in the laminated wafer 15 is being ground, at least a portion of the beveled outer circumferential region 11b can be removed while at the same time the beveled outer circumferential region 11b is prevented from cracking and breaking into fragments.

The embodiment described above is illustrated by way of example only, and the present invention is not limited to the details of the embodiment. According to the present invention, the wafer 11 may be ground in the second grinding step S3 with use of a grinding wheel, i.e., a second grinding wheel, different from the grinding wheel 16. The grinding wheel 16 and the second grinding wheel have respective sets of grindstones, and the sizes of the abrasive grains contained in those sets of grindstones and the outside diameters of the tracks followed by those sets of grindstones, for example, are different from each other.

In a case where the second grinding wheel is used, the grinding method additionally includes, between the first grinding step S2 and the second grinding step S3, a replacing step of replacing the grinding wheel 16 mounted on the distal end of the spindle 12 with the second grinding wheel. Alternatively, a moving step may be carried out between the first grinding step S2 and the second grinding step S3 to move the chuck table 4 with the laminated wafer 15 held thereon to a position where the wafer 11 can be ground by another grinding unit that has a spindle and the second grinding wheel mounted on the distal end of the spindle.

In a case where the wafer 11 is ground to produce the first profile illustrated in FIG. 9A or the second profile illustrated in FIG. 9B, the wafer 11 may be ground in second grinding step S3 while the track followed by the grindstones 20 upon rotation of the grinding wheel 16 is overlapping the central region 11a of the wafer 11 as viewed in plan, i.e., along the vertical direction.

The structural and methodical details of the above embodiment may be changed or modified without departing from the scope of the present invention.

The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.

GRINDING METHOD

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