Grinding method

Abstract

To provide a grinding method that can remove at least a portion of a chamfered outer peripheral region of a wafer while suppressing a crack from being formed in the chamfered outer peripheral region or the outer peripheral region from being broken into pieces, during grinding of a wafer included in a laminate wafer.SOLUTION: A grinding method comprises: a holding step of holding a laminate wafer so that a wafer is exposed; a first grinding step of partially removing a central region of the wafer and grinding the wafer along a thickness direction of the wafer so that an outer peripheral region surrounding the central region remains, after the holding step; and a second grinding step of grinding the wafer along the thickness direction of the wafer so that at least a portion of the outer peripheral region of the wafer is removed, after the first grinding step. Loads generated on the laminate wafer in the second grinding step are smaller than loads generated on the laminate wafer in the first grinding step.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a grinding method for grinding a laminated wafer including a chamfered wafer.

Background Art

[0002] Chips of devices such as ICs (Integrated Circuits) are essential components in various electronic devices such as mobile phones and personal computers. Such chips are manufactured, for example, by grinding the back side of a wafer having a plurality of devices formed on the front side of its central region and then dividing the wafer along the boundaries of the plurality of devices.

[0003] Cracks are likely to occur in the outer peripheral region surrounding the central region of the wafer. Therefore, in the chip manufacturing process, the outer peripheral region of the wafer is often chamfered prior to various processes. However, if the back side of the wafer is ground until the thickness of the wafer becomes less than half, the chamfered outer peripheral region becomes knife-edge-like.

[0004] When the back side of the wafer having such a shape is continuously ground, stress concentrates in the outer peripheral region and cracks are likely to occur. Therefore, in the chip manufacturing process, the wafer may be cut to remove the front side of the chamfered outer peripheral region and then the back side of the wafer may be ground (see, for example, Patent Document 1).

[0005] Furthermore, chips may be manufactured by dividing a plurality of laminated wafers (hereinafter also referred to as "laminated wafers") along the boundaries of a plurality of devices for the purpose of high integration and the like. Such a laminated wafer is formed, for example, in the following order.

[0006] First, the wafer is bonded to a support wafer through an adhesive provided on the surface of the wafer. Next, with the support wafer held, the chamfered outer peripheral region of the wafer is cut and removed. Next, the back side of the wafer is ground to form a thinned wafer (hereinafter also referred to as the "first thinned wafer").

[0007] Next, another wafer is bonded to the first thinned wafer through an adhesive provided on the surface of the other wafer. Next, with the support wafer held, the chamfered outer peripheral region of the other wafer is cut and removed. Next, the back side of the other wafer is ground to form a thinned wafer (hereinafter also referred to as the "second thinned wafer").

[0008] Furthermore, by repeating the above-described processes, that is, bonding the wafer to the thinned wafer and cutting and grinding the wafer, a stacked wafer including three or more thinned wafers and a support wafer is formed. Then, by dividing this stacked wafer along the boundaries of a plurality of devices, for example, highly integrated chips are manufactured.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] Cutting and grinding of the wafer are generally performed in separate processing apparatuses, that is, a cutting apparatus and a grinding apparatus, respectively. Therefore, when a stacked wafer is formed as described above, it is time-consuming and the required time becomes long.

[0011] On the other hand, when the wafer is not cut, that is, when the chamfered outer peripheral region is not removed, cracks are likely to occur in the outer peripheral region during wafer grinding. Further, when the adhesive is not sufficiently provided on the surface of the wafer, the outer peripheral region of the wafer may become fragments during wafer grinding, and these fragments may scatter.

[0012] When the scattered fragments collide with the central region of the wafer, there is a risk that large cracks that divide the wafer are formed in the wafer. Also, when the scattered fragments collide with a component of the grinding apparatus (for example, a grinding wheel for grinding the wafer or a gauge for measuring the thickness of the wafer), there is a risk that this component is damaged.

[0013] In view of these points, an object of the present invention is to provide a grinding method capable of removing at least a part of the outer peripheral region of a wafer while suppressing the formation of cracks in the chamfered outer peripheral region or the outer peripheral region becoming fragments during grinding of the wafer included in the laminated wafer.

Means for Solving the Problems

[0014] According to the present invention, there is provided a grinding method for grinding a laminated wafer including a chamfered wafer, the method including a holding step of holding the laminated wafer so that the wafer is exposed, and after the holding step, partially removing a central region of the wafer and leaving an outer peripheral region surrounding the central region, a first grinding step of grinding the wafer along the thickness direction of the wafer, and after the first grinding step, a second grinding step of grinding the wafer along the thickness direction of the wafer so as to remove at least a part of the outer peripheral region of the wafer, and a grinding method is provided in which the load generated in the laminated wafer during the second grinding step is smaller than the load generated in the laminated wafer during the first grinding step.

[0015] In the second grinding step, it is preferable that a step formed by a circular lower step and an annular upper step surrounding the lower step or a step formed by a circular upper step and an annular lower step surrounding the upper step is formed on the surface to be ground, or the wafer is ground so that the surface to be ground is flush.

[0016] Alternatively, in the second grinding step, it is preferable that the wafer is ground so as to remove all of the outer peripheral region of the wafer. In this case, the laminated wafer further includes an adhesive provided on the back surface of the surface to be ground of the wafer, and the second grinding step preferably ends when the value of a physical quantity that changes depending on the load generated in the laminated wafer becomes equal to or greater than a predetermined threshold value.

Advantages of the Invention

[0017] The grinding method of the present invention includes a first grinding step of partially removing the central region of the wafer along the thickness direction of the wafer so as to partially remove the central region of the wafer and leave the outer peripheral region. And in this first grinding step, since only the central region of the wafer is ground instead of the entire area of the wafer, an excessive load does not occur in the outer peripheral region of the wafer.

[0018] Further, the grinding method of the present invention includes a second grinding step of grinding the wafer along the thickness direction of the wafer so as to remove at least a part of the outer peripheral region of the wafer after the first grinding step. And in this second grinding step, since the load generated in the laminated wafer is smaller than the load generated in the laminated wafer during the first grinding step, an excessive load does not occur in the outer peripheral region of the wafer.

[0019] That is, in the grinding method of the present invention, at least a part of the outer peripheral region of the wafer can be removed without causing an excessive load on the outer peripheral region of the wafer. Therefore, in the grinding method of the present invention, while suppressing the formation of cracks in the chamfered outer peripheral region or the outer peripheral region becoming fragments during the grinding of the wafers included in the stacked wafer, at least a part of the outer peripheral region of the wafer can be removed.

Brief Description of the Drawings

[0020]

Figure 1

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DETAILED DESCRIPTION OF THE INVENTION

[0021] Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1(A) is a top view schematically showing an example of a wafer, and FIG. 1(B) is a cross-sectional view schematically showing the wafer shown in FIG. 1(A).

[0022] The wafer 11 shown in FIGS. 1(A) and 1(B) is made of, for example, a semiconductor material of silicon (Si). The dotted line shown in FIG. 1(A) schematically indicates the boundary between the central region 11a and the outer peripheral region 11b of the wafer 11, and does not exist in the actual wafer 11.

[0023] On the surface side of the central region 11a of this wafer 11, a plurality of devices 13 are formed. Each of the plurality of devices 13 includes, for example, an element for constituting an IC, a semiconductor memory, or a CMOS (Complementary Metal Oxide Semiconductor) image sensor. Further, the plurality of devices 13 are arranged in a matrix. That is, the boundaries of the plurality of devices 13 extend in a lattice pattern.

[0024] Furthermore, the wafer 11 may be provided with wirings such as through-silicon vias (TSVs). This TSV is provided, for example, inside a groove formed on the surface side of the wafer 11 or inside a through-hole extending from the front surface to the back surface. In addition, the outer peripheral region 11b surrounding the central region 11a of the wafer 11 is chamfered. In other words, the side surface of the wafer 11 is curved so as to be convex outward.

[0025] Note that there are no restrictions on the material, shape, structure, size, etc. of the wafer 11. The wafer 11 may be made of, for example, a semiconductor material other than silicon (e.g., silicon carbide (SiC) or gallium nitride (GaN), etc.). Similarly, there are no restrictions on the type, quantity, shape, structure, size, or arrangement, etc. of the device 13.

[0026] FIG. 2 is a cross-sectional view schematically showing an example of a stacked wafer including the wafer 11. The stacked wafer 15 shown in FIG. 2 includes the wafer 11, an adhesive 17 provided on the surface of the wafer 11, and a support wafer 19 bonded to the wafer 11 via the adhesive 17.

[0027] This stacked wafer 15 is formed, for example, by providing an adhesive 17 on the surface of the wafer 11 and then pressing the wafer 11 against the support wafer 19 with the surface of the wafer 11 facing the surface of the support wafer 19. Note that the adhesive 17 is, for example, an acrylic-based adhesive or an epoxy-based adhesive.

[0028] Further, the support wafer 19 has a diameter approximately equal to that of the wafer 11 and is made of, for example, a semiconductor material such as silicon. Also, the support wafer 19 is, for example, a bare wafer or a mirror wafer. Alternatively, the support wafer 19 may be a wafer on which some device is formed. For example, when a BSI (Back Side Illumination) type CMOS image sensor is manufactured from this stacked wafer 15, a pixel circuit of the image sensor may be formed on the surface side of the support wafer 19.

[0029] FIG. 3 is a perspective view schematically showing an example of a grinding apparatus for grinding the stacked wafer 15. The grinding apparatus 2 shown in FIG. 3 includes a chuck table 4 and a grinding unit 10 provided above the chuck table 4. FIG. 4(A) is a cross-sectional view schematically showing the chuck table 4, and FIG. 4(B) is a partial cross-sectional side view schematically showing the grinding unit 10.

[0030] The chuck table 4 has a disk-shaped frame body 6 made of, for example, ceramics or the like. This frame body 6 has a disk-shaped bottom wall and a cylindrical side wall that stands upright from the outer peripheral portion of this bottom wall and whose inner diameter is slightly smaller than the diameter of the support wafer 19. And, on the upper side of the frame body 6, there is a disk-shaped recess defined by the bottom wall and the side wall.

[0031] A disk-shaped porous plate 8 made of porous ceramics or the like is fixed in this recess, and this porous plate 8 includes a large number of through holes that open on its upper surface. Also, the upper surface of the chuck table 4 (that is, the upper surface of the side wall of the frame body 6 and the upper surface of the porous plate 8) has a shape corresponding to the side surface of a cone whose generatrix length is slightly larger than the radius of the support wafer 19.

[0032] Also, a flow path 6a that opens on the upper surface of the bottom wall of the frame body 6, that is, the bottom surface of the recess and penetrates the bottom wall is formed. This flow path 6a is connected to a suction source (not shown) and a fluid supply source (not shown) via a valve (not shown) or the like.

[0033] Note that this suction source includes, for example, an ejector or the like. Also, the fluid supply source includes, for example, a tank for storing high-pressure gas, a filter for removing foreign matter mixed in the gas supplied from the tank, and a regulator for adjusting the pressure of the gas supplied from the tank.

[0034] Furthermore, the chuck table 4 is connected to a horizontal movement mechanism (not shown). This horizontal movement mechanism includes, for example, a ball screw and a motor connected to this ball screw. Alternatively, the horizontal movement mechanism may include a turntable that supports the chuck table and a motor for rotating this turntable. And, when this horizontal movement mechanism is operated, the chuck table 4 moves along the horizontal direction.

[0035] Further, the chuck table 4 is connected to a rotation mechanism (not shown). This rotation mechanism includes, for example, a motor and pulleys. When this rotation mechanism is operated, the chuck table 4 rotates about a straight line passing 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 the rotation axis.

[0036] Also, the chuck table 4 is connected to an inclination adjustment mechanism (not shown). This inclination adjustment mechanism includes, for example, two movable shafts and one fixed shaft that are arranged at generally equal angular intervals along the circumferential direction of the chuck table 4. When at least one of the two movable shafts moves the chuck table 4 up and down partially, the inclination of its rotation axis is adjusted.

[0037] The grinding unit 10 has a columnar spindle 12 extending along the vertical direction. The upper surface of a disc-shaped wheel mount 14 made of stainless steel or the like is fixed to the tip end portion (lower end portion) of the spindle 12. Further, an annular grinding wheel 16 having an outer diameter approximately equal to the diameter of the wheel mount 14 is detachably mounted on the lower portion of the wheel mount 14.

[0038] The grinding wheel 16 has an annular wheel base 18. This wheel base 18 is made of, for example, stainless steel or the like, and a plurality of grinding wheels 20 are arranged at generally equal angular intervals along the circumferential direction of the wheel base 18 on the lower surface side thereof. Each of the plurality of grinding wheels 20 has abrasive grains such as diamond or cBN dispersed in a binder such as vitrified bond or resin bond.

[0039] Also, the base end portion (upper end portion) of the spindle 12 is connected to a rotational drive source (not shown) such as a motor. When this rotational drive source is operated, the spindle 12, the wheel mount 14, and the grinding wheel 16 rotate about a straight line passing through the center of the spindle 12 and along the vertical direction as the rotation axis.

[0040] In the grinding wheel 16, a plurality of grinding grains 20 are provided such that the outer diameter of the locus of the plurality of grinding grains 20 when the grinding wheel 16 is rotated is slightly smaller than the radius of the wafer 11 and slightly larger than the radius of the central region 11a thereof.

[0041] Furthermore, the grinding unit 10 is connected to a vertical movement mechanism (not shown). This vertical movement mechanism includes, for example, a ball screw and a motor connected to this ball screw. When this vertical movement mechanism is operated, the grinding unit 10 moves along the vertical direction.

[0042] In addition, the grinding apparatus 2 includes a controller for controlling the above-described components. FIG. 4(C) is a block diagram schematically showing an example of this controller. The controller 22 shown in FIG. 4(C) includes a processor 22a and a memory 22b.

[0043] The processor 22a is constituted by, for example, a CPU (Central Processing Unit) or the like. Then, the processor 22a controls the components of the grinding apparatus 2 so as to read out and execute a program for grinding the stacked wafer 15 from the memory 22b.

[0044] The memory 22b is constituted by, for example, a volatile memory such as a DRAM (Dynamic Random Access Memory) or an SRAM (Static Random Access Memory), and a non-volatile memory such as an SSD (Solid State Drive) (NAND type flash memory) or an HDD (Hard Disk Drive) (magnetic storage device).

[0045] Then, the memory 22b stores various types of information (specifically, data, programs, etc.) used in the processor 22a. For example, the memory 22b stores a threshold value of a physical quantity that changes depending on the load generated in the stacked wafer 15. Note that examples of this physical quantity include the current supplied to the rotational drive source connected to the proximal end portion of the spindle 12 or the load applied to the chuck table 4.

[0046] FIG. 5 is a flowchart schematically showing an example of a grinding method for grinding the stacked wafer 15 in the grinding apparatus 2. In this method, first, the stacked wafer 15 is held so that the wafer 11 is exposed (holding step S1). FIG. 6 is a partial cross-sectional side view schematically showing the state of the holding step S1.

[0047] In this holding step S1, first, the stacked wafer 15 is carried into the chuck table 4 so that the center of the support wafer 19 and the center of the chuck table 4 overlap in the vertical direction. Next, an aspiration source communicating with the flow path 6a formed in the bottom wall of the frame body 6 of the chuck table 4 is operated.

[0048] Thereby, an aspiration force acts on the stacked wafer 15 through the flow path 6a and the porous plate 8. As a result, the stacked wafer 15 is held in a state where the wafer 11 is exposed, and the holding step S1 is completed.

[0049] After the holding step S1, the wafer 11 is ground along the thickness direction of the wafer 11 so as to partially remove the central region 11a of the wafer 11 and leave the outer peripheral region 11b (first grinding step S2). FIG. 7 is a partial cross-sectional side view schematically showing the state of the first grinding step S2.

[0050] In this first grinding step S2, first, the inclination of the chuck table 4 is adjusted so that a line segment connecting the highest point on the outer periphery of the holding surface of the chuck table 4 and the center of the holding surface is perpendicular to the vertical direction. If the chuck table 4 is already inclined so that this line segment is perpendicular to the vertical direction, this adjustment is unnecessary.

[0051] Next, in a plan view, the chuck table 4 is moved horizontally so that the outer periphery of the trajectories of the plurality of grinding wheels 20 when the grinding wheel 16 is rotated and the boundary between the central region 11a and the outer peripheral region 11b of the wafer 11 are inscribed at a point on the boundary that overlaps with the above-mentioned line segment.

[0052] Next, each of the chuck table 4 and the grinding wheel 16 is operated under predetermined grinding conditions. That is, with each of the chuck table 4 and the grinding wheel 16 rotating at a predetermined rotational speed, the grinding wheel 16 is lowered at a predetermined grinding feed rate.

[0053] As a result, the plurality of grinding wheels 20 are pressed against the central region 11a of the wafer 11, and the central region 11a is ground along the thickness direction of the wafer 11. As a result, the central region 11a of the wafer 11 is partially removed without removing the outer peripheral region 11b of the wafer 11, and a concave portion 11c having a circular bottom surface is formed on the upper surface (back surface) of the wafer 11.

[0054] Note that the grinding of the central region 11a of the wafer 11 is continued, for example, until the depth of the concave portion 11c reaches a desired depth. When the depth of the concave portion 11c reaches the desired depth, the rotation of both the chuck table 4 and the grinding wheel 16 is stopped and the grinding wheel 16 is raised, and the first grinding step S2 is completed.

[0055] After the first grinding step S2, the wafer 11 is ground along the thickness direction of the wafer 11 so as to remove at least a part of the outer peripheral region 11b of the wafer 11 (second grinding step S3). FIG. 8 is a partial cross-sectional side view schematically showing the state of the second grinding step S3.

[0056] In this second grinding step S3, first, in a plan view, the outer periphery of the trajectories of the plurality of grinding wheels 20 when the grinding wheel 16 is rotated and the boundary between the central region 11a and the outer peripheral region 11b of the wafer 11 are circumscribed at a point where the boundary overlaps with the above-mentioned line segment. The chuck table 4 is moved horizontally.

[0057] Next, the chuck table 4 and the grinding wheel 16 are each operated under predetermined grinding conditions. Note that the grinding conditions in the second grinding step S3 (for example, the respective rotational speeds of the chuck table 4 and the grinding wheel 16 and the grinding feed rate of the grinding wheel 16, etc.) are set so that the load generated on the stacked wafer 15 is smaller than the load generated on the stacked wafer 15 in the first grinding step S2.

[0058] For example, when the radius of the central region 11a of the wafer 11 is larger than the length in the radial direction of the wafer 11 in the outer peripheral region 11b, the grinding conditions in the second grinding step S3 may be set the same as the grinding conditions in the first grinding step S2.

[0059] As a result, the plurality of grinding wheels 20 are pressed against the outer peripheral region 11b of the wafer 11, and the outer peripheral region 11b is ground along the thickness direction of the wafer 11. As a result, at least a part of the outer peripheral region 11b of the wafer 11 is removed, and the second grinding step S3 is completed.

[0060] Each of FIGS. 9(A), 9(B), 9(C), and 9(D) is a cross-sectional view schematically showing the stacked wafer 15 after the second grinding step S3. In this second grinding step S3, for example, the wafer 11 is ground so as to leave the concave portion 11c (see FIG. 9(A)).

[0061] In other words, in the second grinding step S3, for example, the wafer 11 is ground so that a step 21 composed of a circular lower step 21a and an annular upper step 21b surrounding the lower step 21a is formed on the surface to be ground. In this case, it is preferable in that the probability of forming cracks in the central region 11a of the wafer 11 can be reduced in the second grinding step S3.

[0062] Alternatively, in the second grinding step S3, for example, the wafer 11 may be ground so as to eliminate the concave portion 11c (see FIGS. 9(B), 9(C), and 9(D)). In this case, it is preferable in that subsequent handling of the stacked wafer 15, for example, bonding to the thinned wafer 11 via an adhesive (not shown) of another wafer (not shown) different from the wafer 11 becomes easier.

[0063] Specifically, in the second grinding step S3, the wafer 11 may be ground so that the surface to be ground becomes flat (see FIG. 9(B)). Further, in the second grinding step S3, the wafer 11 may be ground so that a step 23 composed of a circular upper step 23a and an annular lower step 23b surrounding the upper step 23a is formed on the surface to be ground (see FIG. 9(C)).

[0064] Furthermore, in the second grinding step S3, the wafer 11 may be ground so as to remove all of the outer peripheral region 11b of the wafer 11 (see FIG. 9(D)). Note that when all of the outer peripheral region 11b of the wafer 11 is ground and a plurality of grinding wheels 20 come into contact in the second grinding step S3, the load generated on the stacked wafer 15 increases.

[0065] Therefore, in this case, the processor 22a of the controller 22 may determine whether to end the second grinding step S3 with reference to a physical quantity that changes depending on the load generated on the stacked wafer 15. Specifically, the processor 22a may end the second grinding step S3 when this physical quantity becomes equal to or greater than a threshold value stored in the memory 22b.

[0066] The grinding method shown in FIG. 5 includes a first grinding step S2 of partially removing the central region 11a of the wafer 11 along the thickness direction of the wafer 11 so as to partially remove the central region 11a of the wafer 11 and leave the outer peripheral region 11b. In this first grinding step S2, only the central region 11a of the wafer 11 is ground, not the entire area of the wafer 11, so that an excessive load does not occur in the outer peripheral region 11b of the wafer 11.

[0067] Further, this grinding method includes a second grinding step S3 of grinding the wafer 11 along the thickness direction of the wafer 11 so as to remove at least a part of the outer peripheral region 11b of the wafer 11 after the first grinding step S2. In this second grinding step S3, since the load generated on the laminated wafer 15 is smaller than the load generated on the laminated wafer 15 in the first grinding step S2, an excessive load does not occur in the outer peripheral region 11b of the wafer 11.

[0068] That is, in this grinding method, at least a part of the outer peripheral region 11b of the wafer 11 can be removed without causing an excessive load on the outer peripheral region 11b of the wafer 11. Therefore, in this grinding method, while suppressing the formation of cracks in the chamfered outer peripheral region 11b or the outer peripheral region 11b becoming fragments during the grinding of the wafer 11 included in the laminated wafer 15, at least a part of the outer peripheral region 11b of the wafer 11 can be removed.

[0069] Note that the above-described content is one aspect of the present invention, and the present invention is not limited to the above-described content. For example, in the present invention, the grinding of the wafer 11 in the second grinding step S3 may be performed using a grinding wheel (second grinding wheel) different from the grinding wheel 16. The grinding wheel 16 and the second grinding wheel differ, for example, in the size of the abrasive grains included in each of the plurality of grinding wheels or the outer diameter size of the locus of the plurality of grinding wheels.

[0070] In this case, for example, an exchange step of replacing the grinding wheel 16 attached to the tip of the spindle 12 with a second grinding wheel is carried out between the first grinding step S2 and the second grinding step S3. Alternatively, in this case, a moving step of moving the chuck table 4 to a position where the wafer 11 can be ground using a grinding unit having a spindle different from the spindle 12 and having a second grinding wheel attached to the tip thereof may be carried out between the first grinding step S2 and the second grinding step S3.

[0071] Further, when the second grinding step S3 of the present invention is carried out so that the laminated wafer 15 shown in FIG. 9(A) or FIG. 9(B) is formed, the second grinding step S3 may be carried out in a state where the trajectories of the plurality of grinding grains 20 when the grinding wheel 16 is rotated overlap with the central region 11a of the wafer 11 in the Z-axis direction.

[0072] In addition, the structures and methods according to the above-described embodiments can be appropriately modified and implemented without departing from the scope of the object of the present invention.

Explanation of Reference Numerals

[0073] 2: Grinding apparatus 4: Chuck table 6: Frame body (6a: Flow path) 8: Porous plate 10: Grinding unit 11: Wafer (11a: Central region, 11b: Outer peripheral region, 11c: Concave portion) 12: Spindle 13: Device 14: Wheel mount 15: Laminated wafer 16: Grinding wheel 17: Adhesive 18: Wheel base 19: Support wafer 20: Grinding grain 21: Step (21a: Lower stage, 21b: Upper stage) 22: Controller (22a: Processor, 22b: Memory) 23: Step difference (23a: upper step, 23b: lower step)

Claims

1. A grinding method for grinding a laminated wafer including a chamfered wafer, comprising: a holding step of holding the laminated wafer so that the wafer is exposed; after the holding step, a first grinding step of grinding the wafer along the thickness direction of the wafer so as to partially remove a central region of the wafer and leave a peripheral region surrounding the central region; after the first grinding step, a second grinding step of grinding the wafer along the thickness direction of the wafer so as to remove at least a part of the peripheral region of the wafer, and a grinding method in which a load generated on the laminated wafer during the second grinding step is smaller than a load generated on the laminated wafer during the first grinding step.

2. The grinding method according to claim 1, wherein in the second grinding step, the wafer is ground so as to form a step constituted by a circular lower stage and an annular upper stage surrounding the lower stage on a surface to be ground.

3. The grinding method according to claim 1, wherein in the second grinding step, the wafer is ground so as to make the surface to be ground flat.

4. The grinding method according to claim 1, wherein in the second grinding step, the wafer is ground so as to form a step constituted by a circular upper stage and an annular lower stage surrounding the upper stage on a surface to be ground.

5. The grinding method according to claim 1, wherein in the second grinding step, the wafer is ground so as to remove all of the peripheral region of the wafer.

6. The laminated wafer further includes an adhesive provided on a surface on the back side of the surface to be ground of the wafer, and the second grinding step ends when a value of a physical quantity that changes depending on a load generated on the laminated wafer becomes equal to or greater than a predetermined threshold value.

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