JP2024068263A - Wafer processing method and laminated wafer processing method - Google Patents

Abstract

[Problem] To provide a wafer processing method capable of promoting spontaneous cutting of each of a plurality of grinding wheels when grinding the backside of a wafer included in a stacked wafer. [Solution] A wafer processing method for processing a wafer to form a thinned wafer having a finishing thickness, comprising a groove forming step for forming a groove on the backside of the first wafer to a depth less than the distance obtained by subtracting the finishing thickness from the initial thickness of the first wafer, and a grinding step for grinding the backside of the first wafer after the groove forming step so as to remove a portion of the backside of the first wafer that defines the groove, to form a thinned wafer having a finishing thickness, and in the grinding step, the grinding wheel is rotated so that each of the plurality of grinding wheels in contact with the backside of the first wafer moves from the center of the backside of the first wafer toward the outer periphery. [Selected Figure] Figure 12

Description

The present invention relates to a wafer processing method for processing a wafer to form a thinned wafer having a finishing thickness, and a laminated wafer processing method for processing a first wafer included in a laminated wafer comprising a first wafer and a second wafer having a front surface bonded to the front surface side of the first wafer to form a thinned wafer having a finishing thickness.

Chips for devices such as integrated circuits (ICs) are essential components in various electronic devices such as mobile phones and personal computers. Such chips are manufactured, for example, by grinding a wafer with multiple devices formed on its front side to the desired thickness, and then dividing the wafer along the boundaries between the multiple devices.

Cracks are likely to occur on the outer edge of a wafer. For this reason, in the chip manufacturing process, the outer edge 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 is reduced to less than half, the chamfered outer edge takes on a knife-edge shape. Stress is then concentrated in this area, making it prone to cracks.

Therefore, in the chip manufacturing process, the wafer may be cut to remove the front side of the chamfered outer periphery, and then the back side of the wafer may be ground (see, for example, Patent Document 1). Furthermore, chips may be manufactured, for example, by dividing multiple stacked wafers (hereinafter also referred to as "stacked wafers") along the boundaries of multiple devices.

This laminated wafer is formed, for example, in the following order. First, the front side of the support wafer and the front side of the wafer are bonded. Next, while the back side of the support wafer is held, the chamfered outer edge 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"). Next, the back side of the first thinned wafer is polished and flattened.

The back side of the first thinned wafer is then bonded to the front side of another wafer. Next, while the back side of the support wafer is being held, the chamfered outer edge 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"). Next, the back side of the second thinned wafer is polished and flattened.

Furthermore, by repeating the same process, a stacked wafer containing three or more thinned wafers and a support wafer is formed. Then, by dividing this stacked wafer along the boundaries of multiple devices, it becomes possible to manufacture, for example, highly integrated chips.

JP 2000-173961 A

Wafer grinding is generally performed using a grinding wheel that has multiple grinding stones arranged in a ring shape, each with a large number of abrasive grains dispersed inside. When this grinding wheel is used to grind the back side of a wafer, each of the multiple grinding stones wears out (specifically, the abrasive grains exposed on the grinding surface of the grinding stones become worn).

For this reason, grinding of the back side of the wafer is usually carried out in such a way that each of the multiple grinding wheels creates its own cutting edge (specifically, by grinding the grinding surface side of the grinding wheel to expose new abrasive grains on the grinding surface).

For example, this grinding is performed by bringing the grinding wheel and the front side of the wafer closer together while rotating both the grinding wheel and the wafer so that each of the multiple grinding stones in contact with the back side of the wafer moves from the outer periphery of the back side of the wafer toward the center (hereinafter, this type of grinding is also referred to as "outer-inner grinding").

In this case, the grinding surfaces of the multiple grinding wheels collide with different points on the outer periphery of the back side of the wafer, grinding the back side of the wafer until it reaches the center. In this case, the collision of the grinding surfaces of the multiple grinding wheels with different points on the outer periphery of the back side of the wafer can promote the spontaneous sharpening of each of the multiple grinding wheels.

However, when grinding the back side of a wafer included in a stacked wafer in this manner, there is a risk that the wafer may be peeled off from the stacked wafer due to the collision. For this reason, this grinding is sometimes performed with the rotation direction of the grinding wheel reversed from the rotation direction used for external and internal grinding.

In other words, this grinding is sometimes performed by bringing the grinding wheel and the front side of the wafer closer together while rotating both the grinding wheel and the wafer so that each of the multiple grinding stones in contact with the back side of the wafer moves from the center of the back side of the wafer toward the outer periphery (hereinafter, this type of grinding is also referred to as "inner and outer grinding").

In this case, the grinding surfaces of the multiple grinding wheels come into contact with the center of the back side of the wafer and then grind the back side of the wafer until they reach different locations on the outer periphery. In this case, the grinding surfaces of the multiple grinding wheels come into contact with the center of the back side of the wafer in sequence, making it difficult for the collisions described above to occur. As a result, in internal and external grinding, there is a risk that the self-sharpening of each of the multiple grinding wheels will be insufficient.

In view of the above, the object of the present invention is to provide a wafer processing method capable of promoting the spontaneous sharpening of each of multiple grinding wheels when grinding the backsides of wafers included in a stacked wafer.

According to one aspect of the present invention, a wafer processing method for processing a wafer to form a thinned wafer having a finishing thickness includes a first holding step of holding the front side of a first wafer by a first chuck table that can rotate about a straight line passing through the center of a first holding surface as a rotation axis, a groove forming step of forming a groove on the back side of the first wafer after the first holding step, the groove having a depth that does not reach the distance obtained by subtracting the finishing thickness from the initial thickness of the first wafer, a bonding step of bonding the front side of the first wafer to the front side of a second wafer after the groove forming step, and a second chuck table that can rotate about a straight line passing through the center of a second holding surface that has a shape corresponding to the side surface of a cone as a rotation axis after the bonding step. A method for processing a wafer is provided, which includes a holding step, and a grinding step in which, after the second holding step, both a grinding wheel having a plurality of grinding wheels arranged in an annular shape and the second chuck table are rotated, and with at least one of the plurality of grinding wheels in contact with the back side of the first wafer, the grinding wheel and the second chuck table are brought closer together to grind the back side of the first wafer so that a portion of the back side of the first wafer that defines the groove is removed to form the thinned wafer having the finished thickness, and in the grinding step, the grinding wheel is rotated so that each of the plurality of grinding wheels in contact with the back side of the first wafer moves from the center of the back side of the first wafer toward the outer periphery.

Furthermore, in the groove forming step, it is preferable that the groove is formed by rotating the first chuck table at least once while an annular cutting blade that rotates about a straight line parallel to the first holding surface as its axis of rotation is cut into the front surface side of the first wafer.

Alternatively, the first holding surface has a shape corresponding to the side surface of a cone, and in the groove forming step, the groove is preferably formed by bringing the groove forming grinding wheel and the first chuck table close together while both the groove forming grinding wheel, which has a plurality of groove forming grinding wheels arranged in a ring and has an outer diameter shorter than the radius of the first wafer, and the first chuck table rotate and at least one of the plurality of groove forming grinding wheels is in contact with the back side of the first wafer. In this case, it is more preferable that the first chuck table is the same as the second chuck table.

According to another aspect of the present invention, a method for processing a laminated wafer, which includes a first wafer and a second wafer having a front surface bonded to the front surface side of the first wafer, includes processing the first wafer included in the laminated wafer to form a thinned wafer having a finishing thickness, the method including: a first holding step of holding the back surface side of the second wafer by a first chuck table that can rotate about a straight line passing through the center of a first holding surface as a rotation axis; a groove forming step of forming a groove on the back surface of the first wafer by rotating the first chuck table at least once while an annular cutting blade that rotates about a straight line parallel to the first holding surface as a rotation axis is cut into the front surface side of the first wafer, the groove forming step being performed after the groove forming step, by rotating the first chuck table at least once. A method for processing laminated wafers is provided, which includes a second holding step of holding the back side of the second wafer by a second chuck table that can rotate around a straight line as a rotation axis, and a grinding step of forming the thinned wafer having the finishing thickness by grinding the back side of the first wafer so that a portion of the back side of the first wafer that defines the groove is removed by moving the grinding wheel and the second chuck table close to each other while both rotating a grinding wheel having a plurality of grinding wheels arranged in an annular shape and at least one of the plurality of grinding wheels contacting the back side of the first wafer after the second holding step, and the grinding wheel is rotated so that each of the plurality of grinding wheels contacting the back side of the first wafer moves from the center of the back side of the first wafer toward the outer periphery.

According to yet another aspect of the present invention, a method for processing a laminated wafer, which includes a first wafer and a second wafer having a front surface bonded to the front surface side of the first wafer, includes a holding step of holding the back surface side of the second wafer by a chuck table that can rotate about a straight line passing through the center of a holding surface shaped to correspond to the side surface of a cone as a rotation axis, and after the holding step, a groove forming grinding wheel having a plurality of groove forming grinding wheels arranged in a ring shape and having an outer diameter shorter than the radius of the first wafer and the chuck table are both rotated, and at least one of the plurality of groove forming grinding wheels is in contact with the back surface side of the first wafer, and the groove forming grinding wheel and the chuck table are brought close to each other to subtract the finishing thickness from the initial thickness of the first wafer. A method for processing laminated wafers is provided, which includes a groove forming step for forming a groove on the back side of the first wafer having a depth that does not reach the distance obtained by grinding the back side of the first wafer by rotating a thinning grinding wheel having a plurality of thinning grinding wheels arranged in an annular shape and the chuck table after the groove forming step, and by bringing the thinning grinding wheel and the chuck table closer together while at least one of the plurality of thinning grinding wheels is in contact with the back side of the first wafer, the back side of the first wafer is ground so that a portion of the back side of the first wafer that defines the groove is removed, thereby forming the thinned wafer having the finishing thickness. In the grinding step, the thinning grinding wheel is rotated so that each of the plurality of thinning grinding wheels in contact with the back side of the first wafer moves from the center of the back side of the first wafer toward the outer periphery.

In one aspect of the present invention, a groove is formed on the back side of a first wafer to a depth less than the distance obtained by subtracting the finished thickness from the initial thickness of the wafer, and then the front side of the first wafer and the front side of the second wafer are joined to form a laminated wafer. The back side of the first wafer included in this laminated wafer is then internally and externally ground to form a thinned wafer having the finished thickness.

In this case, from the time when grinding of the back side of the first wafer is started until the grinding progresses and the outer wall defining the groove is removed, the grinding surface of each of the multiple grinding wheels collides with different points on the inner circumference of the upper surface side of the outer wall. Therefore, in this method, the self-sharpening of each of the multiple grinding wheels can be promoted as the grinding surface of each of the multiple grinding wheels collides with different points on the inner circumference of the upper surface side of the outer wall defining the groove.

FIG. 1A is a top view that shows a schematic diagram of an example of a wafer, and FIG. 1B is a cross-sectional view that shows a schematic diagram of the wafer shown in FIG. 1A. FIG. 2 is a flow chart that illustrates a schematic diagram of an example of a wafer processing method for processing a wafer to form a thinned wafer having a finish thickness. FIG. 3 is a perspective view illustrating an example of a cutting device. FIG. 4 is a perspective view that illustrates a cutting blade included in the cutting device. FIG. 5(A) is a partially cross-sectional front view showing a schematic diagram of how the first holding step S1 is performed in the cutting device, and FIG. 5(B) is a partially cross-sectional front view showing a schematic diagram of how the groove forming step S2 is performed in the cutting device. FIG. 6A is a cross-sectional view that typically shows how the bonding step S3 is performed, and FIG. 6B is a cross-sectional view that typically shows the laminated wafers formed in the bonding step S3. FIG. 7 is a perspective view showing a schematic example of a grinding and polishing apparatus. Figure 8(A) is a cross-sectional view showing a schematic diagram of a chuck table included in the grinding and polishing apparatus, Figure 8(B) is a partially cross-sectional side view showing a schematic diagram of a grinding wheel and the like included in the grinding and polishing apparatus, and Figure 8(C) is a cross-sectional view showing a schematic diagram of a polishing pad and the like included in the grinding and polishing apparatus. FIG. 9(A) is a partially cross-sectional side view showing a schematic diagram of the second holding step S4 being performed in the grinding and polishing apparatus, and FIG. 9(B) is a partially cross-sectional side view showing a schematic diagram of the grinding step S5 being performed in the grinding and polishing apparatus. FIG. 10(A) is a partially cross-sectional side view showing a schematic diagram of how grinding step S5 is performed in a grinding and polishing apparatus, and FIG. 10(B) is a partially cross-sectional side view showing a schematic diagram of a thinned wafer etc. formed from a wafer in grinding step S5. FIG. 11 is a cross-sectional view showing a schematic view of a polishing step being performed in the grinding and polishing apparatus. FIG. 12 is a flow chart that illustrates a schematic diagram of another example of a wafer processing method for processing a wafer to form a thinned wafer having a finish thickness. FIG. 13(A) is a partially cross-sectional front view showing a schematic diagram of how the first holding step S11 is performed in the cutting device, and FIG. 13(B) is a partially cross-sectional front view showing a schematic diagram of how the groove forming step S12 is performed in the cutting device. Figure 14(A) is a partially cross-sectional side view showing a schematic diagram of how the first holding step S11 is performed in the grinding and polishing apparatus, and Figure 14(B) is a partially cross-sectional front view showing a schematic diagram of how the groove forming step S12 is performed in the grinding and polishing apparatus. FIG. 15A is a cross-sectional view that typically shows how the bonding step S13 is performed, and FIG. 15B is a cross-sectional view that typically shows the laminated wafers formed in the bonding step S13. FIG. 16(A) is a partially cross-sectional side view showing a schematic diagram of how the second holding step S14 is performed in the grinding and polishing apparatus, and FIG. 16(B) is a partially cross-sectional side view showing a schematic diagram of how the grinding step S15 is performed in the grinding and polishing apparatus. FIG. 17 is a flow chart that illustrates an example of a method for processing laminated wafers.

An embodiment of the present invention will be described with reference to the attached drawings. Fig. 1(A) is a top view showing an example of a wafer, and Fig. 1(B) is a cross-sectional view showing the wafer shown in Fig. 1(A). The wafer 11 shown in Figs. 1(A) and 1(B) has a front surface 11a and a back surface 11b that are roughly parallel, and is made of, for example, silicon (Si).

A plurality of devices 13 are formed on the front surface 11a of the wafer 11. Each of the plurality of devices 13 includes elements for constituting, for example, an IC, a semiconductor memory, or a CMOS (Complementary Metal Oxide Semiconductor) image sensor.

The multiple devices 13 are arranged in a matrix. That is, the boundaries between the multiple devices 13 extend in a lattice pattern. Furthermore, the wafer 11 may have grooves formed therein in which wiring such as through-silicon electrodes (TSVs (Through-Silicon Vias)) is provided. The outer periphery of the wafer 11 is chamfered. In other words, the side surface 11c of the wafer 11 is curved so as to be convex outward.

There are no limitations on the material, shape, structure, or size of the wafer 11. The wafer 11 may be made of a semiconductor material other than silicon (e.g., silicon carbide (SiC) or gallium nitride (GaN)). Similarly, there are no limitations on the type, number, shape, structure, size, or arrangement of the devices 13.

Figure 2 is a flow chart showing a schematic example of a wafer processing method for processing a wafer 11 to form a thinned wafer having a finishing thickness. In this method, first, the back surface 11b side of the wafer 11 is held (first holding step S1), and then a groove having a depth exceeding the finishing thickness is formed on the front surface 11a side of the wafer 11 (groove forming step S2).

Figure 3 is a perspective view showing a schematic example of a cutting device for performing the first holding step S1 and the groove forming step S2. Note that the +X axis direction (forward direction) and the +Y axis direction (left direction) shown in Figure 3 are directions perpendicular to each other on a horizontal plane, and the +Z axis direction (upward direction) is a direction perpendicular to each of the +X axis direction and the +Y axis direction.

In addition, the -X-axis direction (rearward) shown in FIG. 3 is the opposite direction to the +X-axis direction, the -Y-axis direction (rightward) is the opposite direction to the +Y-axis direction, and the -Z-axis direction (downward) is the opposite direction to the +Z-axis direction. In addition, hereinafter, the +X-axis direction and the -X-axis direction are collectively referred to as the X-axis direction, the +Y-axis direction and the -Y-axis direction are collectively referred to as the Y-axis direction, and the +Z-axis direction and the -Z-axis direction are collectively referred to as the Z-axis direction.

The cutting device 2 shown in FIG. 3 includes a base 4 that supports each component. A recess 4a extending along the X-axis direction is formed on the top surface of the base 4. Inside the recess 4a, a flat table cover 6 and a bellows-shaped dust-proof and drip-proof cover 8 that expands and contracts as the table cover 6 moves are provided.

A chuck table 10 is provided above the table cover 6. The chuck table 10 has a disk-shaped frame 10a made of ceramics or the like. The frame 10a has a disk-shaped bottom wall and a cylindrical side wall that stands upright from the bottom wall.

In addition, a disk-shaped porous plate 10b made of, for example, porous ceramics is fixed to the recess defined by the bottom wall and side wall of the frame body 10a. This porous plate 10b has a diameter roughly equal to the inner diameter of the side wall of the frame body 10a.

The porous plate 10b is connected to a suction source (not shown) such as an ejector provided inside the recess 4a through a through hole formed in the bottom wall of the frame 10a. The chuck table 10 has an upper surface perpendicular to the Z-axis direction, and this upper surface functions as a holding surface for holding the wafer 11.

Specifically, when the suction source communicating with the porous plate 10b is operated while the wafer 11 is placed on the upper surface of the chuck table 10, a suction force acts on the underside of the wafer 11. As a result, the underside of the wafer 11 is held by the chuck table 10.

The chuck table 10 is also connected to an X-axis direction movement mechanism (not shown) provided inside the recess 4a. This X-axis direction movement mechanism includes, for example, a ball screw and a motor connected to the ball screw. When this X-axis direction movement mechanism is operated, the chuck table 10 moves along the X-axis direction. Furthermore, in conjunction with these movements, the table cover 6 moves along the X-axis direction and the dust-proof and drip-proof cover 8 expands and contracts.

The chuck table 10 is also connected to a rotary drive source (not shown) provided inside the recess 4a. This rotary drive source includes, for example, a spindle and a motor connected to the spindle. When this rotary drive source is operated, the chuck table 10 rotates around a rotation axis that passes through the center of the upper surface of the porous plate 10b and is aligned in the Z-axis direction.

A support structure 16 is provided in the area of the upper surface of the base 4 near the recess 4a. This support structure 16 has an erected portion 16a extending from the upper surface of the base 4 along the +Z axis direction, and an arm portion 16b extending from the upper end of the erected portion 16a along the -Y axis direction so as to cross the recess 4a. A Y axis direction movement mechanism 18 is provided on the front side of the arm portion 16b.

This Y-axis direction movement mechanism 18 has a pair of Y-axis guide rails 20 that are fixed to the front surface of the arm portion 16b and extend along the Y-axis direction. A Y-axis movement plate 22 is connected to the front surface of the pair of Y-axis guide rails 20 in a manner that allows it to slide along the pair of Y-axis guide rails 20.

A screw shaft 24 extending along the Y-axis direction is disposed between the pair of Y-axis guide rails 20. A motor (not shown) for rotating the screw shaft 24 is connected to one end of the screw shaft 24. A nut (not shown) that houses a large number of balls that roll on the surface of the rotating screw shaft 24 is provided on the surface of the screw shaft 24 on which the spiral groove is formed, forming a ball screw.

In other words, when the screw shaft 24 rotates, many balls circulate inside the nut, causing the nut to move along the Y-axis direction. This nut is also fixed to the rear side of the Y-axis moving plate 22. Therefore, when the screw shaft 24 is rotated by a motor connected to one end of the screw shaft 24, the Y-axis moving plate 22 moves along the Y-axis direction together with the nut.

A Z-axis direction moving mechanism 26 is provided on the front side of the Y-axis moving plate 22. This Z-axis direction moving mechanism 26 is fixed to the front side of the Y-axis moving plate 22 and has a pair of Z-axis guide rails 28 that extend along the Z-axis direction. A Z-axis moving plate 30 is connected to the front side of the pair of Z-axis guide rails 28 in a manner that allows it to slide along the pair of Z-axis guide rails 28.

A screw shaft 32 extending along the Z-axis direction is disposed between the pair of Z-axis guide rails 28. A motor 34 for rotating the screw shaft 32 is connected to one end (upper end) of the screw shaft 32. A nut (not shown) that houses a large number of balls that roll on the surface of the rotating screw shaft 32 is provided on the surface of the screw shaft 32 on which the spiral groove is formed, forming a ball screw.

In other words, when the screw shaft 32 rotates, many balls circulate inside the nut, causing the nut to move along the Z-axis direction. This nut is also fixed to the rear side of the Z-axis moving plate 30. Therefore, when the screw shaft 32 is rotated by the motor 34, the Z-axis moving plate 30 moves along the Z-axis direction together with the nut.

A cutting unit 36 is fixed to the lower part of the Z-axis moving plate 30. This cutting unit 36 has a cylindrical spindle housing 38 extending along the Y-axis direction and a cutting blade 40 exposed from the spindle housing 38. Figure 4 is a perspective view showing the cutting blade 40 and other components.

The spindle housing 38 of the cutting unit 36 contains a cylindrical spindle 42 that extends along the Y-axis direction. The spindle 42 is supported by the spindle housing 38 in a rotatable manner. The tip of the spindle 42 protrudes outside the spindle housing 38, and an annular cutting blade 40 is attached to this tip.

The cutting blade 40 includes a cutting edge formed of an electroformed grinding wheel in which abrasive grains made of diamond or cubic boron nitride (cBN) are fixed with a binder such as nickel. The base end of the spindle 42 is connected to a motor built into the spindle housing 38.

When this motor is operated, the cutting blade 40 rotates together with the spindle 42 around a straight line along the Y-axis direction as the axis of rotation. The cutting blade 40 is attached to the spindle 42 so that the straight line that serves as the axis of rotation of the spindle 42 passes through the center of the cutting blade 40.

When the motor connected to one end of the screw shaft 24 is operated, the cutting unit 36 moves along the Y-axis direction. When the motor 34 connected to one end of the screw shaft 32 is operated, the cutting unit 36 moves along the Z-axis direction.

As shown in FIG. 3, an imaging unit 44 is provided in the +X-axis direction as viewed from the cutting unit 36. This imaging unit 44 includes, for example, an objective lens and an imaging element such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor, and captures an image of a structure present below it.

Figure 5 (A) is a partial cross-sectional front view showing a schematic diagram of the first holding step S1 being performed in the cutting device 2. When performing the first holding step S1 in the cutting device 2, first, the wafer 11 is placed on the upper surface of the chuck table 10 with the front surface 11a of the wafer 11 facing up.

Then, in this state, the suction source communicating with the porous plate 10b is operated. This causes a suction force to act on the back surface 11b of the wafer 11. As a result, the back surface 11b of the wafer 11 is held on the upper surface of the chuck table 10, completing the first holding step S1.

Figure 5 (B) is a partial cross-sectional front view that shows a schematic diagram of the groove forming step S2 being performed in the cutting device 2. In this groove forming step S2, first, in a plan view, the chuck table 10 is moved along the X-axis direction and/or the cutting unit 36 is moved along the Y-axis direction so that the cutting blade 40 is positioned directly above a predetermined area of the wafer 11.

This specified region is located in the +Y-axis direction when viewed from the center of the wafer 11, and is located outside the multiple devices 13 formed on the front surface 11a side of the wafer 11 and inside the chamfered outer edge.

Next, while rotating the cutting blade 40, the cutting unit 36 is lowered so that the cutting blade 40 cuts into the wafer 11 until the bottom end of the cutting blade 40 reaches a depth from the surface 11a of the wafer 11 that exceeds the finishing thickness.

Then, the chuck table 10 is rotated at least once while the rotating cutting blade 40 is cutting into the wafer 11. As a result, a groove 15 having an annular bottom surface of the predetermined depth is formed on the front surface 11a side of the wafer 11, completing the groove forming step S2.

After the groove forming step S2, the front surface 11a of the wafer 11 is bonded to the front surface of the support wafer (bonding step S3). FIG. 6(A) is a cross-sectional view that shows the bonding step S3, and FIG. 6(B) is a cross-sectional view that shows the stacked wafers formed in the bonding step S3.

The support wafer 17 bonded to the wafer 11 has, for example, the same shape as the wafer 11. Also, like the wafer 11, multiple devices may be formed on the front surface 17a of the support wafer 17.

When bonding the surface 11a of the wafer 11 to the surface 17a of the support wafer 17, first, an adhesive 19 containing an acrylic adhesive or an epoxy adhesive is applied to the surface 17a of the support wafer 17.

The adhesive 19 is provided not only near the center of the support wafer 17 but also near the outer periphery so that the surface 11a of the wafer 11 and the surface 17a of the support wafer 17 can be bonded not only inside but also outside the grooves 15 formed on the surface 11a of the wafer 11.

Next, while the back surface 17b of the support wafer 17 is supported, the front surface 11a of the wafer 11 is pressed against the front surface 17a of the support wafer 17 via the adhesive 19. This forms a laminated wafer 1 including the wafer 11 and the support wafer 17 whose front surface 17a is bonded to the front surface 11a of the wafer 11, completing the bonding step S3.

After the bonding step S3, the back surface 17b of the support wafer 17 is held (second holding step S4), and then the back surface 11b of the wafer 11 is ground to form a thinned wafer having a finishing thickness and an excess ring surrounding the thinned wafer (grinding step S5).

Figure 7 is a perspective view showing a schematic example of a grinding and polishing device for performing the second holding step S4 and the grinding step S5. Note that the U-axis direction (forward direction) and the V-axis direction (left direction) shown in Figure 7 are directions perpendicular to each other on a horizontal plane, and the W-axis direction (upward direction) is a direction (vertical direction) perpendicular to the U-axis direction and the V-axis direction.

The grinding and polishing apparatus 102 shown in FIG. 7 includes a base 104 that supports each component. A recess 104a is formed in the front of the top surface of the base 104, and a transport mechanism 106 that transports the stacked wafer 1 while holding it by suction is provided in this recess 104a. Furthermore, the transport mechanism 106 can also turn the stacked wafer upside down while holding it.

In addition, cassette tables 108a and 108b are provided in front of the recess 104a. Cassettes 110a and 110b capable of accommodating multiple laminated wafers 1 are placed on these cassette tables 108a and 108b, respectively. In addition, a position adjustment mechanism 112 for adjusting the position of the laminated wafers 1 is provided diagonally behind the recess 104a.

This position adjustment mechanism 112 includes, for example, a table 112a configured to support the central portion of the laminated wafer 1, and a plurality of pins 112b configured to move toward and away from the table 112a on the outer side of the table 112a. For example, the laminated wafer 1 transferred from the cassette 110a by the transfer mechanism 106 is transferred onto this table 112a.

Then, the position adjustment mechanism 112 aligns the laminated wafer 1 that has been loaded onto the table 112a. Specifically, the multiple pins 112b are moved closer to the table 112a until they come into contact with the side of the laminated wafer 1 that has been loaded onto the table 112a. This aligns the center of the laminated wafer 1 to a predetermined position on a plane parallel to the U-axis and V-axis directions (UV plane).

In addition, a transport mechanism 114 is provided near the position adjustment mechanism 112, which rotates and transports the laminated wafer 1 while holding it by suction. This transport mechanism 114 has a suction pad that can suck the top side of the laminated wafer 1, and transports the laminated wafer 1, whose position has been adjusted by the position adjustment mechanism 112, backward. In addition, a disk-shaped turntable 116 is provided behind the transport mechanism 114.

The turntable 116 is connected to a rotary drive source (not shown) such as a motor. When the rotary drive source is operated, the turntable 116 rotates around a straight line that passes through the center of the turntable 116 and is parallel to the W-axis direction as its axis of rotation. In addition, on the upper surface of the turntable 116, multiple (e.g., four) chuck tables 118 are provided at approximately equal angular intervals along the circumferential direction of the turntable 116.

Then, the transport mechanism 114 transports the stacked wafers 1 from the table 112a of the position adjustment mechanism 112 to the chuck table 118 arranged at a load/unload position near the transport mechanism 114. The turntable 116 also rotates, for example, in the direction of the arrow shown in FIG. 7, and moves each chuck table 118 to the load/unload position, rough grinding position, finish grinding position, and polishing position in that order.

Figure 8 (A) is a cross-sectional view showing a schematic diagram of the chuck table 118. The chuck table 118 has a frame 118a made of ceramics or the like. The frame 118a has a disk-shaped bottom wall and an annular side wall extending upward from the periphery of the bottom wall.

In addition, a disk-shaped porous plate 118b made of, for example, porous ceramics is fixed to the recess defined by the bottom wall and side wall of the frame. This porous plate 118b has a diameter roughly equal to the inner diameter of the side wall of the frame.

The porous plate 118b is connected to a suction source (not shown) such as an ejector through a through hole 118c formed in the bottom wall of the frame 118a. The chuck table 118 has an upper surface shaped to correspond to the side surface of the cone, and this upper surface functions as a holding surface for holding the stacked wafers 1.

Specifically, when the stacked wafer 1 is placed on the upper surface of the chuck table 118 and a suction source communicating with the porous plate is operated, a suction force acts on the underside of the stacked wafer 1. As a result, the underside of the stacked wafer 1 is held by the chuck table 118.

Furthermore, the chuck table 118 is connected to a rotational drive source (not shown). This rotational drive source includes, for example, a pulley and a motor connected to the pulley. When this rotational drive source is operated, the chuck table 118 rotates around a straight line passing through the center of the upper surface of the chuck table 118 as the rotation axis.

The chuck table 118 is supported by a tilt adjustment mechanism (not shown). This tilt adjustment mechanism includes two movable shafts and one fixed shaft that are spaced at approximately equal angles along the circumferential direction of the chuck table 118. When at least one of the two movable shafts partially raises or lowers the chuck table 118, the tilt of the chuck table 118, more specifically, the tilt of its rotation axis, is adjusted.

As shown in FIG. 7, a columnar support structure 120 is provided behind each of the rough grinding position and the finish grinding position (behind the turntable 116). A W-axis direction movement mechanism 122 is provided on the front surface of the support structure 120 (the surface facing the turntable 116). This W-axis direction movement mechanism 122 is fixed to the front surface of the support structure 120 and has a pair of W-axis guide rails 124 that extend along the W-axis direction.

A W-axis moving plate 126 is connected to the front side of the pair of W-axis guide rails 124 in a manner that allows it to slide along the pair of W-axis guide rails 124. A screw shaft 128 extending along the W-axis direction is disposed between the pair of W-axis guide rails 124. A motor 130 for rotating the screw shaft 128 is connected to the upper end of the screw shaft 128.

A nut (not shown) that accommodates a large number of balls that roll on the surface of the rotating screw shaft 128 is provided on the surface of the screw shaft 128 where the helical grooves are formed, forming a ball screw. In other words, when the screw shaft 128 rotates, a large number of balls circulate inside the nut, and the nut moves along the W-axis direction.

The nut is also fixed to the rear surface (back surface) of the W-axis moving plate 126. Therefore, when the screw shaft 128 is rotated by the motor 130, the W-axis moving plate 126 moves along the W-axis direction together with the nut. Furthermore, a fixing device 132 is provided on the surface (front surface) of the W-axis moving plate 126.

The fixture 132 supports the grinding unit 134. The grinding unit 134 has a spindle housing 136 that is fixed to the fixture 132. The spindle housing 136 contains a spindle 138 that extends along the W-axis direction in a rotatable manner.

The upper end of the spindle 138 is connected to a rotary drive source (not shown) such as a motor, and the spindle 138 can rotate around a straight line parallel to the W-axis direction as a rotation axis by the power of this rotary drive source. The lower end of the spindle 138 is exposed from the underside of the spindle housing 136, and a disk-shaped mount 140 is fixed to this lower end.

A grinding wheel 142 for rough grinding is attached to the underside of the mount 140 of the grinding unit 134 on the rough grinding position side. Similarly, a grinding wheel 142 for finish grinding is attached to the underside of the mount 140 of the grinding unit 134 on the finish grinding position side.

Figure 8 (B) is a partial cross-sectional side view showing the grinding wheel 142 and other components. The grinding wheel 142 includes an annular wheel base 142a made of a metal such as stainless steel or aluminum. In addition, a number of grinding stones 142b are fixed to the underside of the wheel base 142a at roughly equal angular intervals along the circumferential direction.

Each of the grinding wheels 142b contains a binder such as vitrified or resinoid, and abrasive grains such as diamond dispersed in the binder. The average grain size of the abrasive grains contained in the grinding wheels 142b of the grinding wheel 142 for finish grinding is generally smaller than the average grain size of the abrasive grains contained in the grinding wheels 142b of the grinding wheel 142 for rough grinding.

In addition, a grinding fluid supply nozzle (not shown) is disposed near the grinding wheel 142 to supply liquid (grinding fluid) such as pure water to the processing point. Alternatively, instead of or in addition to this grinding fluid supply nozzle, an opening for supplying the grinding fluid may be provided in the grinding wheel 142, and the grinding fluid may be supplied to the processing point through this opening.

As shown in FIG. 7, a support structure 144 is provided to the side of the polishing position (to the side of the turntable 116). A U-axis direction movement mechanism 146 is provided on the side of the support structure 144 facing the turntable 116. This U-axis direction movement mechanism 146 is fixed to the side of the support structure 144 facing the turntable 116, and has a pair of U-axis guide rails 148 that extend along the U-axis direction.

A U-axis moving plate 150 is connected to the turntable 116 side of the pair of U-axis guide rails 148 in a manner that allows it to slide along the pair of U-axis guide rails 148. A screw shaft 152 extending along the U-axis direction is disposed between the pair of U-axis guide rails 148. A motor 154 for rotating the screw shaft 152 is connected to the front end of the screw shaft 152.

A nut (not shown) that accommodates a large number of balls that roll on the surface of the rotating screw shaft 152 is provided on the surface of the screw shaft 152 on which the helical grooves are formed, forming a ball screw. In other words, when the screw shaft 152 rotates, a large number of balls circulate inside the nut, causing the nut to move along the U-axis direction.

The nut is fixed to the surface (back surface) of the U-axis moving plate 150 that faces the support structure 144. Therefore, when the screw shaft 152 is rotated by the motor 154, the U-axis moving plate 150 moves along the U-axis direction together with the nut. Furthermore, a W-axis direction moving mechanism 156 is provided on the surface (front surface) of the U-axis moving plate 150 facing the turntable 116.

This W-axis direction movement mechanism 156 has a pair of W-axis guide rails 158 that are fixed to the surface of the U-axis movement plate 150 and extend along the W-axis direction. In addition, a W-axis movement plate 160 is connected to the turntable 116 side of the pair of W-axis guide rails 158 in a manner that allows it to slide along the pair of W-axis guide rails 158.

A screw shaft 162 extending along the W-axis direction is disposed between the pair of W-axis guide rails 158. A motor 164 for rotating the screw shaft 162 is connected to the upper end of the screw shaft 162. A nut (not shown) that houses a large number of balls that roll on the surface of the rotating screw shaft 162 is provided on the surface of the screw shaft 162 on which the spiral groove is formed, forming a ball screw.

In other words, when the screw shaft 162 rotates, a large number of balls circulate inside the nut, causing the nut to move along the W-axis direction. This nut is also fixed to the surface (back surface) of the W-axis moving plate 160 that faces the U-axis moving plate 150. Therefore, when the screw shaft 162 is rotated by the motor 164, the W-axis moving plate 160 moves along the W-axis direction together with the nut.

Furthermore, a fixture 166 is provided on the face (front surface) of the W-axis moving plate 160 facing the turntable 116. This fixture 166 supports a polishing unit 168. The polishing unit 168 has a spindle housing 170 fixed to the fixture 166.

The spindle housing 170 accommodates a spindle 172 extending along the W-axis direction in a rotatable manner. A rotational drive source such as a motor (not shown) is connected to the upper end of the spindle 172, and the spindle 172 rotates by the power of the rotational drive source.

The lower end of the spindle 172 is exposed from the underside of the spindle housing 170, and a disk-shaped mount 174 is fixed to this lower end. A disk-shaped polishing pad 176 is attached to the underside of the mount 174.

Figure 8 (C) is a cross-sectional view showing the polishing pad 176 and other components. The polishing pad 176 has a disk-shaped pad base 176a with roughly the same diameter as the mount 174. A disk-shaped polishing layer 176b with roughly the same diameter as the mount 174 is fixed to the underside of the pad base 176a.

This polishing layer 176b is flexible and elastically deforms in response to the pressure applied during polishing. Specifically, the polishing layer 176b is a fixed abrasive layer with abrasive grains dispersed therein. For example, the polishing layer 176b is manufactured by impregnating a polyester nonwoven fabric with a urethane solution in which abrasive grains are dispersed, and then drying it.

The abrasive grains dispersed inside the polishing layer 176b are made of materials such as SiC, cBN, diamond, or metal oxide fine particles, etc. As the metal oxide fine particles, fine particles made of _SiO2 (silica), _CeO2 (ceria), _ZrO2 (zirconia), _Al2O3 (alumina) _, etc. are used.

The radial center positions of the spindle 172, mount 174, and polishing pad 176 are generally aligned, and a cylindrical through hole 178 is formed through these center positions. This through hole 178 is connected to a polishing liquid supply source (not shown) that supplies liquid (polishing liquid) such as pure water to the processing point.

This polishing liquid supply source has a polishing liquid storage tank and a liquid supply pump. The polishing liquid supply source also supplies the polishing liquid to the chuck table 118 positioned at the polishing position through a through hole 178 formed in the spindle 172, etc. The polishing liquid may or may not contain abrasive grains.

As shown in FIG. 7, a transport mechanism 180 is provided to the side of the transport mechanism 114, which rotates and transports the laminated wafer 1 while holding it by suction. This transport mechanism 180 has a suction pad that can suck the top side of the laminated wafer 1, and transports the laminated wafer 1 placed on the chuck table 118 positioned at the loading/unloading position forward.

In addition, a cleaning mechanism 182 configured to clean the top side of the laminated wafer 1 carried out by the transport mechanism 180 is disposed in front of the transport mechanism 180 and behind the recess 104a. The laminated wafer 1 cleaned by this cleaning mechanism 182 is transported by the transport mechanism 106 and stored in, for example, a cassette 110b.

Figure 9 (A) is a partial cross-sectional side view showing the state in which the second holding step S4 is performed in the grinding and polishing device 102. When the second holding step S4 is performed in the grinding and polishing device 102, first, the stacked wafers 1 that have been transferred from the cassettes 110a and 110b are transferred to the chuck table 118 positioned at the transfer position, using the transfer mechanisms 106 and 114, etc., so that the back surface 11b side of the wafer 11 faces up.

Then, in this state, the suction source communicating with the porous plate 118b is operated. This causes a suction force to act on the back surface 17b of the support wafer 17. As a result, the back surface 17b of the support wafer 17 is held on the upper surface of the chuck table 118, completing the second holding step S4.

Figures 9(B) and 10(A) are each a partial cross-sectional side view that shows the grinding step S5 being performed in the grinding and polishing device 102, and Figure 10(B) is a partial cross-sectional side view that shows the thinned wafer etc. formed from the wafer 11 in the grinding step S5.

When performing the grinding step S5 in the grinding and polishing device 102, first, the turntable 116 is rotated so that the chuck table 118 that holds the back surface 17b side of the support wafer 17 is positioned at the rough grinding position. Specifically, the turntable 116 is rotated so that the trajectory of the multiple grinding stones 142b when the grinding wheel 142 for rough grinding is rotated and the center of the upper surface of the chuck table 118 overlap in the W-axis direction.

Next, the inclination of the chuck table 118 is adjusted so that the line segment connecting the center of the top surface of the chuck table 118 and a specific point on its periphery is approximately horizontal. Specifically, the inclination of the chuck table 118 is adjusted so that the rotation axis of the grinding wheel 142 for rough grinding and the line segment overlap in the W-axis direction.

Next, while both the grinding wheel 142 for rough grinding and the chuck table 118 are rotating, the grinding wheel 142 is lowered until at least one of the grinding stones 142b contacts the back surface 11b of the wafer 11 (see FIG. 9(B)). This starts rough grinding of the back surface 11b of the wafer 11.

This rough grinding is an inside and outside grinding. That is, during this rough grinding, the grinding wheel 142 rotates so that each of the multiple grinding stones 142b in contact with the back surface 11b of the wafer 11 moves from the center of the back surface 11b of the wafer 11 toward the outer periphery.

As this rough grinding continues, the wafer 11 is divided at the groove 15 to form the thinned wafer 21 and the surplus ring 23 surrounding the thinned wafer 21 (see FIG. 10(A)). From this point on, the grinding surfaces of the multiple grinding wheels 142b collide with different points on the inner circumference of the upper surface side of the surplus ring 23.

This rough grinding is continued, for example, until the thinned wafer 21 reaches the finishing thickness. Then, when the thinned wafer 21 reaches the finishing thickness, the rotation of both the grinding wheel 142 for rough grinding and the chuck table 118 is stopped, and the grinding wheel 142 and the thinned wafer 21 are separated from each other, that is, the grinding wheel 142 is raised (see FIG. 10(B)). This completes the grinding step S5.

Alternatively, the rough grinding may be completed before the thinned wafer 21 reaches the finishing thickness. In this case, after the rough grinding, the grinding step S5 is completed by performing a finish grinding on the top side (back side) of the thinned wafer 21 until the finishing thickness is reached.

This finish grinding is performed by rotating the turntable 116 so that the chuck table 118 holding the back surface 17b of the support wafer 17 is positioned at the finish grinding position, and then operating the grinding unit 134 etc. on the finish grinding position side in the same manner as the grinding unit 134 etc. on the rough grinding position side described above.

In the wafer processing method shown in FIG. 2, a groove 15 with a depth exceeding the finishing thickness is formed on the front surface 11a of the wafer 11, and then the front surface 11a of the wafer 11 is joined to the front surface 17a of the support wafer 17 to form a laminated wafer 1. Then, the back surface 11b of the wafer 11 included in this laminated wafer 1 is ground internally and externally to form a thinned wafer 21 having the finishing thickness.

In this case, as grinding of the back surface 11b of the wafer 11 progresses and the wafer 11 is divided at the groove 15, the grinding surfaces of the grinding wheels 142b collide with different locations on the inner circumference of the upper surface of the surplus ring 23. Therefore, in this method, the collision of the grinding surfaces of the grinding wheels 142b with different locations on the inner circumference of the upper surface of the surplus ring 23 can promote the spontaneous sharpening of each of the grinding wheels 142b.

Furthermore, in the wafer processing method shown in FIG. 2, a polishing step may be performed after the grinding step S5 to polish the top side (back side) of the thinned wafer 21. FIG. 11 is a cross-sectional view that shows a schematic diagram of the polishing step being performed in the grinding and polishing device 102.

In this polishing step, first, the turntable 116 is rotated so that the chuck table 118, which holds the back surface 17b side of the support wafer 17, is positioned at the polishing position. Specifically, the turntable 116 is rotated so that an area of the polishing pad 176 slightly inside the outer periphery and the center of the top surface of the chuck table 118 overlap in the W-axis direction. If necessary, the polishing pad 176 may be moved along the U-axis direction while rotating the turntable 116.

Next, the inclination of the chuck table 118 is adjusted so that the line segment connecting the center of the top surface of the chuck table 118 and a specific point on its periphery is approximately horizontal. Specifically, the inclination of the chuck table 118 is adjusted so that the rotation axis of the polishing pad 176 and the line segment overlap in the W-axis direction. If necessary, the polishing pad 176 may be moved along the U-axis direction while the inclination of the chuck table 118 is adjusted.

Next, while both the polishing pad 176 and the chuck table 118 are rotating, the polishing pad 176 is lowered so that the lower surface (polished surface) of the polishing layer 176b is pressed against the upper surface of the thinned wafer 21. This causes the upper surface of the thinned wafer 21 to be polished and flattened.

Here, the polishing layer 176b is pressed not only against the upper surface of the thinned wafer 21, but also against the upper surface of the surplus ring 23. In this case, the polishing layer 176b elastically deforms so as to slightly enter the gap between the thinned wafer 21 and the surplus ring 23, but the polishing layer 176b is prevented from elastically deforming so as to come into contact with the side surface of the thinned wafer 21.

Therefore, in this case, the area near the side of the thinned wafer 21 can be prevented from being excessively thinned compared to other areas. Furthermore, the underside of the polishing layer 176b can be dressed by rotating the polishing pad 176 while elastically deforming the polishing layer 176b so that it slightly enters the gap.

Figure 12 is a flow chart that shows a schematic diagram of another example of a wafer processing method for processing a wafer 11 to form a thinned wafer having a finishing thickness. In this method, first, the front surface 11a side of the wafer 11 is held (first holding step S11), and then a groove is formed on the back surface 11b side of the wafer 11 with a depth that does not reach the distance obtained by subtracting the finishing thickness from the initial thickness of the wafer 11 (groove forming step S12).

The first holding step S11 and the groove forming step S12 are performed, for example, in the cutting device 2 shown in FIG. 3 or other known cutting devices. FIG. 13(A) is a partially sectional front view that shows a schematic diagram of the first holding step S11 being performed in the cutting device 2. When performing the first holding step S11 in the cutting device 2, first, the wafer 11 is placed on the upper surface of the chuck table 10 with the back surface 11b of the wafer 11 facing up.

Prior to the first holding step S11, a protective tape may be applied to the surface 11a of the wafer 11 to prevent damage to the device 13. Then, in this state, the suction source communicating with the porous plate 10b is operated. This causes a suction force to act on the surface 11a side of the wafer 11. As a result, the surface 11a side of the wafer 11 is held on the upper surface of the chuck table 10, completing the first holding step S11.

Figure 13 (B) is a partial cross-sectional front view showing the groove forming step S12 being performed in the cutting device 2. In this groove forming step S2, first, in a plan view, the chuck table 10 is moved along the X-axis direction and/or the cutting unit 36 is moved along the Y-axis direction so that the cutting blade 40 is positioned directly above a predetermined area of the wafer 11. Note that this predetermined area is an area located in the +Y-axis direction when viewed from the center of the wafer 11, and located inside the chamfered outer periphery.

Next, while rotating the cutting blade 40, the cutting unit 36 is lowered so that the cutting blade 40 cuts into the wafer 11 until the lower end of the cutting blade 40 reaches a predetermined depth from the back surface 11b of the wafer 11. Note that this predetermined depth is a depth that does not reach the distance obtained by subtracting the finished thickness from the initial thickness of the wafer 11.

Then, the chuck table 10 is rotated at least once while the rotating cutting blade 40 is cutting into the wafer 11. This forms a groove 25 having an annular bottom surface and the specified depth on the back surface 11b side of the wafer 11, completing the groove forming step S12.

In the groove forming step S12, multiple grooves having different diameters and each center located at the center of the back surface 11b of the wafer 11 may be formed on the back surface 11b of the wafer 11. These multiple grooves are formed, for example, by repeating the above-mentioned operation while shifting the position of the cutting blade 40 that cuts into the wafer 11 along the Y-axis direction.

Alternatively, in the groove forming step S12, a groove having a spiral bottom surface may be formed on the back surface 11b of the wafer 11. This groove is formed, for example, by cutting the wafer 11 with a rotating cutting blade 40 and moving the cutting blade 40 along the Y-axis direction while rotating the chuck table 10.

The first holding step S11 and the groove forming step S12 may be performed, for example, in the grinding and polishing device 102 shown in FIG. 7 or in other known grinding devices. FIG. 14(A) is a partially sectional side view that shows a schematic diagram of the first holding step S11 being performed in the grinding and polishing device 102.

When performing the first holding step S11 in the grinding and polishing device 102, first, the wafer 11 that has been removed from the cassettes 110a and 110b is loaded onto the chuck table 118 positioned at the loading/unloading position, using the transport mechanisms 106 and 114, etc., so that the back surface 11b of the wafer 11 faces up.

Prior to the first holding step S11, a protective tape may be applied to the surface 11a of the wafer 11 to prevent damage to the device 13. In this state, the suction source communicating with the porous plate 118b is then operated. This causes a suction force to act on the surface 11a of the wafer 11. As a result, the surface 11a of the wafer 11 is held on the upper surface of the chuck table 118, completing the first holding step S11.

Figure 14 (B) is a partial cross-sectional side view that shows a schematic diagram of the groove forming step S12 being performed in the grinding and polishing device 102. Prior to this groove forming step S12, a grinding wheel (groove forming grinding wheel) 184 with an outer diameter shorter than the radius of the wafer 11 is attached to the mount 140 of the grinding unit 134 on the rough grinding position side of the grinding and polishing device 102.

When performing the groove forming step S12 in the grinding and polishing device 102, first, the turntable 116 is rotated so that the chuck table 118 that holds the front surface 11a side of the wafer 11 is positioned at the rough grinding position. Specifically, the turntable 116 is rotated so that the trajectory of the multiple grinding stones 184a when the grinding wheel 184 is rotated and the center of the upper surface of the chuck table 118 overlap in the W-axis direction.

Next, the inclination of the chuck table 118 is adjusted so that the line segment connecting the center of the top surface of the chuck table 118 and a specific point on its periphery is approximately horizontal. Specifically, the inclination of the chuck table 118 is adjusted so that the rotation axis of the grinding wheel 184 and the line segment overlap in the W-axis direction.

Next, while both the grinding wheel 184 and the chuck table 118 are rotating, the grinding wheel 184 is lowered until the lower ends of the multiple grinding stones 184a included in the grinding wheel 184 reach a predetermined depth from the back surface 11b of the wafer 11. Note that this predetermined depth is a depth that does not reach the distance obtained by subtracting the finished thickness from the initial thickness of the wafer 11.

As a result, the central region of the back surface 11b of the wafer 11 is ground and removed. In other words, a groove 27 having a circular bottom and a depth less than the distance obtained by subtracting the finished thickness from the initial thickness of the wafer 11 is formed on the back surface 11b of the wafer 11. This completes the groove formation step S12.

After the groove forming step S12, the front surface 11a of the wafer 11 and the front surface 17a of the support wafer 17 are bonded together (bonding step S13). FIG. 15(A) is a cross-sectional view that shows a schematic diagram of the bonding step S13 that uses a wafer 11 with a groove 25 formed on its back surface 11b, and FIG. 15(B) is a cross-sectional view that shows a schematic diagram of the stacked wafers formed in this bonding step S13.

When bonding the surface 11a side of the wafer 11 to the surface 17a side of the support wafer 17, first, an adhesive 19 containing an acrylic adhesive or an epoxy adhesive is applied to the surface 17a of the support wafer 17. Note that the adhesive 19 used in the bonding step S13 may be applied in any manner as long as it can bond the surface 11a side of the wafer 11 and the surface 17a side of the support wafer 17.

Next, while the back surface 17b of the support wafer 17 is supported, the front surface 11a of the wafer 11 is pressed against the front surface 17a of the support wafer 17 via the adhesive 19. This forms a laminated wafer 3 including the wafer 11 and the support wafer 17 whose front surface 17a is bonded to the front surface 11a of the wafer 11, completing the bonding step S13.

After the bonding step S3, the back surface 17b of the support wafer 17 is held (second holding step S14), and then the back surface 11b of the wafer 11 is ground so that the portion of the back surface 11b of the wafer 11 that defines the groove 25 is removed to form a thinned wafer having a finishing thickness (grinding step S15).

The second holding step S14 and the grinding step S15 are performed, for example, in the grinding and polishing device 102 shown in FIG. 7. FIG. 16(A) is a partially cross-sectional side view that shows a schematic diagram of the second holding step S14 being performed in the grinding and polishing device 102.

When performing the second holding step S14 in the grinding and polishing device 102, first, the stacked wafers 3 that have been removed from the cassettes 110a and 110b are loaded onto the chuck table 118 positioned at the loading/unloading position using the transport mechanisms 106, 114, etc., so that the back surface 11b side of the wafer 11 faces up.

Then, in this state, the suction source communicating with the porous plate 118b is operated. This causes a suction force to act on the back surface 17b of the support wafer 17. As a result, the back surface 17b of the support wafer 17 is held on the upper surface of the chuck table 118, completing the second holding step S14.

Figure 16 (B) is a partial cross-sectional side view showing the grinding step S15 being performed in the grinding and polishing apparatus 102. When performing the grinding step S15 in the grinding and polishing apparatus 102, the turntable 116 is first rotated so that the chuck table 118 holding the back surface 17b side of the support wafer 17 is positioned at the rough grinding position. Specifically, the turntable 116 is rotated so that the trajectory of the multiple grinding stones 142b when the grinding wheel 142 for rough grinding is rotated and the center of the upper surface of the chuck table 118 overlap in the W-axis direction.

Next, the inclination of the chuck table 118 is adjusted so that the line segment connecting the center of the top surface of the chuck table 118 and a specific point on its periphery is approximately horizontal. Specifically, the inclination of the chuck table 118 is adjusted so that the rotation axis of the grinding wheel 142 for rough grinding and the line segment overlap in the W-axis direction.

Next, while rotating both the rough grinding wheel 142 and the chuck table 118, the grinding wheel 142 is lowered until at least one of the multiple grinding stones 142b contacts the back surface 11b of the wafer 11.

This starts rough grinding of the back surface 11b side of the wafer 11. This rough grinding is internal and external grinding. That is, during this rough grinding, the grinding wheel 142 rotates so that each of the multiple grinding stones 142b in contact with the back surface 11b side of the wafer 11 moves from the center of the back surface 11b side of the wafer 11 toward the outer periphery.

In addition, from the time when rough grinding begins, the grinding surfaces of the multiple grinding wheels 142b collide with different locations on the inner circumference of the upper surface side of the outer wall that defines the groove 25. This collision continues until grinding of the back surface 11b side of the wafer 11 progresses and the outer wall that defines the groove 25 is removed.

Furthermore, this rough grinding is continued, for example, until a thinned wafer having a finishing thickness is formed. Then, when this thinned wafer is formed, the rotation of both the grinding wheel 142 for rough grinding and the chuck table 118 is stopped, and the grinding wheel 142 and the thinned wafer are separated, that is, the grinding wheel 142 is raised. With the above, the grinding step S15 is completed.

Alternatively, the rough grinding may be completed before a thinned wafer having a finishing thickness is formed. In this case, after the rough grinding, the grinding step S5 is completed by performing a finish grinding on the back surface 11b side of the wafer 11 until a thinned wafer having a finishing thickness is formed.

This finish grinding is performed by rotating the turntable 116 so that the chuck table 118 holding the back surface 17b of the support wafer 17 is positioned at the finish grinding position, and then operating the grinding unit 134 etc. on the finish grinding position side in the same manner as the grinding unit 134 etc. on the rough grinding position side described above.

In the wafer processing method shown in FIG. 12, a groove 25 is formed on the back surface 11b side of the wafer 11 with a depth less than the distance obtained by subtracting the finished thickness from the initial thickness of the wafer 11, and then the front surface 11a side of the wafer 11 and the front surface 17a side of the support wafer 17 are joined to form a laminated wafer 3. Then, the back surface 11b side of the wafer 11 included in this laminated wafer 3 is ground internally and externally to form a thinned wafer having the finished thickness.

In this case, from the time when grinding of the back surface 11b of the wafer 11 is started until the grinding progresses and the outer wall defining the groove 25 is removed, the grinding surface of each of the multiple grinding wheels 142b collides with different locations on the inner circumference of the upper surface of the outer wall. Therefore, in this method, the collision of the grinding surface of each of the multiple grinding wheels 142b with different locations on the inner circumference of the upper surface of the outer wall defining the groove 25 can promote the spontaneous sharpening of each of the multiple grinding wheels 142b.

In addition, in this method, even if a groove having a spiral bottom surface or a groove having a circular bottom surface 27 (see FIG. 14(B)) is formed on the back surface 11b side of the wafer 11 instead of the groove 25 having an annular bottom surface, the self-sharpening of each of the multiple grinding wheels 142b can be promoted as described above.

In the present invention, the front surface 11a side of the wafer 11 and the front surface 17a side of the support wafer 17 may be joined to form a laminated wafer before the grooves 25, 27 are formed on the back surface 11b side of the wafer 11. In other words, the present invention may be a method for processing a laminated wafer in which the wafers 11 included in the laminated wafer are processed to form thinned wafers.

Figure 17 is a flow chart that shows a schematic example of a method for processing laminated wafers. In this method, first, the back surface 17b of the support wafer 17 is held (first holding step S21), and then grooves 25, 27 are formed on the back surface 11b of the wafer 11 to a depth that is less than the distance obtained by subtracting the finished thickness from the initial thickness of the wafer 11 (groove forming step S22).

The first holding step S21 and the groove forming step S22 are performed in the same manner as the first holding step S11 and the groove forming step S12 shown in FIG. 12, except that, for example, the back surface 17b side of the support wafer 17 is held by the chuck tables 10, 118, rather than the front surface 11a side of the wafer 11. Therefore, a detailed description of the first holding step S21 and the groove forming step S22 will be omitted.

If the groove formation and the wafer thinning are performed while the wafer is held on different chuck tables (step S23: NO) (for example, if the first holding step S21 and the groove formation step S22 are performed on the cutting device 2), the back surface 17b of the support wafer 17 is held on the upper surface of the chuck table 118 of the grinding and polishing device 102 (second holding step S24), and then the back surface 11b of the wafer 11 is ground so that the portion of the back surface 11b of the wafer 11 that defines the groove 25 is removed, thereby forming a thinned wafer having a finishing thickness (grinding step S25).

On the other hand, if the groove formation and the wafer thinning are performed while the wafer is held on different chuck tables (step S23: YES) (for example, when the first holding step S21 and the groove formation step S22 are performed on the grinding and polishing device 102), the back surface 17b side of the support wafer 17 is held on the upper surface of the chuck table 118, and the back surface 11b side of the wafer 11 is ground so that the portion of the back surface 11b side of the wafer 11 that defines the groove 25 is removed, forming a thinned wafer having a finishing thickness (grinding step S25).

The second holding step S24 and the grinding step S25 are performed in the same manner as the second holding step S14 and the grinding step S15 shown in FIG. 12. Therefore, a detailed description of the second holding step S24 and the grinding step S25 will be omitted.

The present invention may also be a wafer processing method for processing a wafer 11 having a groove 15 (see FIG. 5(B)) formed on the front surface 11a side and grooves 25, 27 (see FIG. 13(B) and FIG. 14(B)) formed on the back surface 11b side to form a thinned wafer having a finishing thickness.

Specifically, the present invention may be a wafer processing method in which, after performing the first holding step S1 and the groove forming step S2 shown in FIG. 2, all steps S11 to S15 shown in FIG. 12 are performed. Alternatively, the present invention may be a wafer processing method in which, after performing the first holding step S11 and the groove forming step S12 shown in FIG. 12, all steps S1 to S5 shown in FIG. 2 are performed.

In addition, the structures and methods of the above-described embodiments can be modified as appropriate without departing from the scope of the present invention.

1: Stacked wafer 2: Cutting device 3: Stacked wafer 4: Base (4a: recess)
6: Table cover 8: Dust-proof/water-proof cover 10: Chuck table (10a: frame, 10b: porous plate)
11: Wafer (first wafer) (11a: front surface, 11b: back surface, 11c: side surface)
13: Device 15: Groove 16: Support structure (16a: standing portion, 16b: arm portion)
17: Support wafer (second wafer)
18: Y-axis direction moving mechanism 19: Adhesive layer 20: Y-axis guide rail 21: Thinned wafer 22: Y-axis moving plate 23: Surplus ring 24: Screw shaft 25: Groove 26: Z-axis direction moving mechanism 27: Groove 28: Z-axis guide rail 30: Z-axis moving plate 32: Screw shaft 34: Motor 36: Cutting unit 38: Spindle housing 40: Cutting blade 42: Spindle 44: Measurement unit 102: Processing device 104: Base (104a: recess)
106: Transport mechanism 108a, 108b: Cassette table 110a, 110b: Cassette 112: Position adjustment mechanism (112a: table, 112b: pin)
114: Transport mechanism 116: Turntable 118: Chuck table
(118a: frame, 118b: porous plate, 118c: through hole)
120: Support structure 122: W-axis direction movement mechanism 124: W-axis guide rail 126: W-axis movement plate 128: Screw shaft 130: Motor 132: Fixture 134: Grinding unit 136: Spindle housing 138: Spindle 140: Mount 142: Grinding wheel (142a: Wheel base, 142b: Grinding stone)
144: Support structure 146: U-axis direction movement mechanism 148: U-axis guide rail 150: U-axis movement plate 152: Screw shaft 154: Motor 156: W-axis direction movement mechanism 158: W-axis guide rail 160: W-axis movement plate 162: Screw shaft 164: Motor 166: Fixture 168: Polishing unit 170: Spindle housing 172: Spindle 174: Mount 176: Polishing pad (176a: pad base, 176b: polishing layer)
178: Through hole 180: Transport mechanism 182: Cleaning mechanism

Claims (6)

1. A method of processing a wafer to form a thinned wafer having a finish thickness, comprising:
a first holding step of holding a front surface side of the first wafer by a first chuck table rotatable about a rotation axis that is a straight line passing through a center of the first holding surface;
a groove forming step of forming a groove on the back surface side of the first wafer, the groove having a depth less than a distance obtained by subtracting the finishing thickness from the initial thickness of the first wafer after the first holding step;
a bonding step of bonding the front surface side of the first wafer to the front surface side of a second wafer after the groove forming step;
a second holding step of holding the back side of the second wafer by a second chuck table rotatable about a rotation axis that is a straight line passing through a center of a second holding surface having a shape corresponding to a side surface of a cone, after the bonding step;
a grinding step in which, after the second holding step, a grinding wheel having a plurality of grinding stones arranged in an annular shape and the second chuck table are both rotated, and the grinding wheel and the second chuck table are brought closer together while at least one of the plurality of grinding stones is in contact with the back side of the first wafer, thereby grinding the back side of the first wafer so that a portion of the back side of the first wafer that defines the groove is removed to form the thinned wafer having the finished thickness,
In the grinding step, the grinding wheel is rotated so that each of the multiple grinding stones in contact with the back side of the first wafer moves from the center of the back side of the first wafer toward the outer periphery. The wafer processing method according to claim 1, wherein in the groove forming step, the groove is formed by rotating the first chuck table at least once while an annular cutting blade that rotates about a straight line parallel to the first holding surface as a rotation axis is cut into the front surface side of the first wafer. The first support surface has a shape corresponding to a side surface of a cone,
2. The wafer processing method of claim 1, wherein in the groove forming step, the groove is formed by rotating both the groove forming grinding wheel having a plurality of groove forming grinding wheels arranged in a ring and having an outer diameter shorter than the radius of the first wafer and the first chuck table, and by bringing the groove forming grinding wheel and the first chuck table closer together while at least one of the plurality of groove forming grinding wheels is in contact with the back side of the first wafer. The wafer processing method according to claim 3, wherein the first chuck table is the same as the second chuck table. A laminated wafer processing method comprising: a first wafer and a second wafer having a front surface side bonded to a front surface side of the first wafer; processing the first wafer included in the laminated wafer to form a thinned wafer having a finish thickness, the method comprising:
a first holding step of holding the back side of the second wafer by a first chuck table rotatable about a rotation axis that is a straight line passing through a center of a first holding surface;
a groove forming step of, after the first holding step, rotating the first chuck table at least once while an annular cutting blade, which rotates about a straight line parallel to the first holding surface as a rotation axis, is caused to cut into the front side of the first wafer, thereby forming a groove on the back side of the first wafer having a depth that does not reach a distance obtained by subtracting the finished thickness from the initial thickness of the first wafer;
a second holding step of holding the back side of the second wafer by a second chuck table rotatable about a rotation axis that is a straight line passing through a center of a second holding surface having a shape corresponding to a side surface of a cone, after the groove forming step;
a grinding step in which, after the second holding step, a grinding wheel having a plurality of grinding stones arranged in an annular shape and the second chuck table are both rotated, and the grinding wheel and the second chuck table are brought closer to each other while at least one of the plurality of grinding stones is in contact with the back side of the first wafer, thereby grinding the back side of the first wafer so that a portion of the back side of the first wafer that defines the groove is removed to form the thinned wafer having the finished thickness,
In the grinding step, the grinding wheel is rotated so that each of the multiple grinding wheels in contact with the back side of the first wafer moves from the center of the back side of the first wafer toward the outer periphery. A laminated wafer processing method comprising: a first wafer and a second wafer having a front surface side bonded to a front surface side of the first wafer; processing the first wafer included in the laminated wafer to form a thinned wafer having a finish thickness, the method comprising:
a holding step of holding the back side of the second wafer by a chuck table that is rotatable about a rotation axis that is a straight line passing through the center of a holding surface that has a shape corresponding to a side surface of a cone;
a groove forming step in which, after the holding step, a groove forming grinding wheel having a plurality of groove forming grinding stones arranged in an annular shape and an outer diameter of which is shorter than a radius of the first wafer and the chuck table are both rotated, and at least one of the plurality of groove forming grinding stones is in contact with the back surface side of the first wafer, and the groove forming grinding wheel and the chuck table are brought closer together to form a groove on the back surface side of the first wafer having a depth that does not reach a distance obtained by subtracting the finished thickness from the initial thickness of the first wafer;
a grinding step in which, after the groove forming step, a thinning grinding wheel having a plurality of thinning grinding stones arranged in an annular shape and the chuck table are both rotated, and in a state in which at least one of the plurality of thinning grinding stones is in contact with the back side of the first wafer, the thinning grinding wheel and the chuck table are brought closer to each other, thereby grinding the back side of the first wafer so that a portion of the back side of the first wafer that defines the groove is removed, thereby forming the thinned wafer having the finished thickness,
In the grinding step, the method for processing stacked wafers rotates the thinning grinding wheel so that each of the multiple thinning grinding stones in contact with the back side of the first wafer moves from the center of the back side of the first wafer toward the outer periphery.

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