Wafer processing method and grinding apparatus

Abstract

The present invention provides a wafer processing method that allows for easy removal of the chamfered portion of the first wafer from a bonded wafer formed by joining a first wafer and a second wafer. [Solution] The wafer processing method includes a modified layer formation step in which the second wafer 84 of the bonded wafer 86 is held on a holding table, the focal point of a laser beam is positioned on the inside adjacent to the chamfered portion 98 formed on the outer circumference of the first wafer 82 of the bonded wafer 86, and the laser beam is irradiated to form a ring-shaped modified layer 108; a loading step in which the bonded wafer 86 is loaded into a grinding device for grinding the first wafer 82 of the bonded wafer 86; and a grinding step in which the first wafer 82 is ground to thin it and the chamfered portion 98 formed on the outer circumference of the first wafer 82 is removed by the grinding force. In the loading step or the grinding step, a fluid supply step is performed in which a fluid that weakens the bonding force is supplied to the interface of the chamfered portion 98 where the first wafer 82 and the second wafer 84 are bonded.

Description

Technical Field

[0001] The present invention relates to a wafer processing method for processing a first wafer of a bonded wafer in which a first wafer and a second wafer are bonded, and a grinding apparatus for grinding the first wafer of the bonded wafer in which the first wafer and the second wafer are bonded.

Background Art

[0002] A wafer on which a plurality of devices such as ICs and LSIs are partitioned by a dicing line and formed on the surface is ground on the back surface to a predetermined thickness and then divided into individual device chips by a dicing apparatus or a laser processing apparatus. Each of the divided device chips is used in an electric device such as a mobile phone or a personal computer.

[0003] When the back surface of the wafer is ground and thinned, a chamfer is formed on the outer periphery of the wafer, so that the chamfer becomes a sharp knife edge. Therefore, there is a problem that cracks are likely to enter from the outer periphery to the inside of the wafer, increasing the risk of device damage. In addition, when the chamfer becomes a sharp knife edge, the operator must take more care in handling the wafer. Therefore, a technique for removing the chamfer has been proposed by the present applicant (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] There is a technique to improve the functionality of a device by bonding a first wafer to a second wafer, and then grinding the back surface of the first wafer to form a desired thickness. However, this technique has the problem that it is relatively difficult to remove the chamfered portion from the first wafer. That is, wafers bonded by siloxane bonds or the like have strong bonding forces, and even if a modified layer is formed inside the first wafer by irradiating it with a laser beam whose wavelength is transparent to the wafer, with the focal point positioned inside adjacent to the chamfered portion, it is difficult to remove the chamfered portion.

[0006] Furthermore, when removing the chamfered portion from the first wafer with a cutting blade, there is a risk of damaging the second wafer.

[0007] The object of the present invention is to provide a wafer processing method and grinding apparatus that can easily remove the chamfered portion of the first wafer from a bonded wafer formed by joining a first wafer and a second wafer. [Means for solving the problem]

[0008] According to the present invention, the following wafer processing method is provided that solves the above problems. That is, A wafer processing method comprising processing the first wafer of a bonded wafer formed by joining a first wafer and a second wafer, A modification layer formation step involves holding the second wafer of the bonded wafer on a holding table, positioning the focal point of a laser beam on the inside adjacent to the chamfered portion formed on the outer circumference of the first wafer of the bonded wafer, and irradiating the laser beam to form a ring-shaped modification layer. A loading step of loading the bonded wafer into a grinding apparatus for grinding the first wafer of the bonded wafer, The process includes a grinding step of thinning the first wafer by grinding and removing the chamfered portion formed on the outer circumference of the first wafer by the grinding force, A wafer processing method is provided, comprising a fluid supply step in which a fluid that weakens the bonding force is supplied to the interface of the chamfered portion where the first wafer and the second wafer are joined, during the loading step or the grinding step.

[0009] Preferably, in the fluid supply step, a fluid supply nozzle equipped with a tip for injecting the fluid is used. The fluid is preferably water. The first wafer and the second wafer are joined by Si-O-Si siloxane bonds, and in the fluid supply step, the Si-O-Si bonds can be changed to Si-OH-OH-Si bonds by a fluid that weakens the bonding force, thereby weakening the bonding force.

[0010] Furthermore, the present invention provides the following grinding apparatus that solves the above problems. That is, A grinding apparatus for grinding the first wafer of a bonded wafer formed by joining a first wafer and a second wafer, A grinding apparatus is provided, which includes a chuck table for holding the bonded wafer, a grinding means rotatably mounted on the chuck table, a grinding wheel on which grinding wheels for grinding the first wafer of the bonded wafer held on the chuck table are arranged in an annular pattern, and a fluid supply means for supplying a fluid to weaken the bonding force at the interface of the chamfered portion where the first wafer and the second wafer are joined.

[0011] The apparatus includes a cassette table on which a cassette containing multiple bonded wafers is placed; a transport means for transporting the bonded wafers from the cassette placed on the cassette table to a temporary receiving table for centering; a transport means for transporting the bonded wafers from the temporary receiving table to a chuck table located in the loading / unloading area; and a transport means for moving the chuck table from the loading / unloading area to a processing area where the first wafer is ground by the grinding means. The fluid supply means is preferably located in the loading / unloading area or the processing area. The fluid may be water. The first wafer and the second wafer are bonded by a Si-O-Si siloxane bond, and the bond can be weakened by a fluid that changes the Si-O-Si bond to a Si-OH-OH-Si bond. [Effects of the Invention]

[0012] The wafer processing method of the present invention is A wafer processing method comprising processing the first wafer of a bonded wafer formed by joining a first wafer and a second wafer, A modification layer formation step involves holding the second wafer of the bonded wafer on a holding table, positioning the focal point of a laser beam on the inside adjacent to the chamfered portion formed on the outer circumference of the first wafer of the bonded wafer, and irradiating the laser beam to form a ring-shaped modification layer. A loading step of loading the bonded wafer into a grinding apparatus for grinding the first wafer of the bonded wafer, The process includes a grinding step of thinning the first wafer by grinding and removing the chamfered portion formed on the outer circumference of the first wafer by the grinding force, In the loading process or the grinding process, a fluid supply process is carried out to supply a fluid that weakens the bonding force to the interface of the chamfered portion where the first wafer and the second wafer are joined, so that the chamfered portion of the first wafer can be easily removed from the joined wafer formed by joining the first wafer and the second wafer.

[0013] The grinding apparatus of the present invention is A grinding device for grinding the first wafer of a bonded wafer in which a first wafer and a second wafer are bonded, a chuck table for holding the bonded wafer, and grinding means rotatably mounting a grinding wheel in which a grinding stone for grinding the first wafer of the bonded wafer held on the chuck table is annularly arranged, and fluid supply means for supplying a fluid for weakening the bonding force to the interface of the chamfered portion where the first wafer and the second wafer are bonded. Therefore, the chamfered portion of the first wafer can be easily removed from the bonded wafer in which the first wafer and the second wafer are bonded.

Brief Description of the Drawings

[0014] [Figure 1] Perspective view of the grinding device according to the present invention. [Figure 2] (a) Perspective view of the bonded wafer, (b) Partial cross-sectional view of the bonded wafer shown in (a). [Figure 3] (a) Perspective view showing the modified layer forming process, (b) Partial cross-sectional view of the bonded wafer in which a ring-shaped modified layer is formed on the first wafer. [Figure 4] Plan view of a wafer in which a radial modified layer extending radially outward from the ring-shaped modified layer is formed. [Figure 5] (a) Perspective view showing the fluid supply process, (b) Partial cross-sectional view of the bonded wafer in which fluid is supplied to the interface of the chamfered portion. [Figure 6] (a) Perspective view showing rough grinding in the grinding process, (b) Perspective view of the bonded wafer from which the chamfered portion of the first wafer has been removed. [Figure 7] (a) Perspective view showing finish grinding in the grinding process, (b) Perspective view of the bonded wafer in which the back surface of the first wafer has been finish ground.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, preferred embodiments of a wafer processing method and a grinding device according to the present invention will be described with reference to the drawings.

[0016] (Grinding device 2) As shown in Figure 1, the grinding apparatus 2 of this embodiment includes a chuck table 4 for holding a bonded wafer, a grinding means 6 rotatably mounted on a grinding wheel having grinding wheels arranged in an annular pattern for grinding the first wafer of the bonded wafer held on the chuck table 4, and a fluid supply means 8 for supplying a fluid to weaken the bonding force at the interface of the chamfered portion where the first wafer and the second wafer are joined.

[0017] (Chuck table 4 of grinding device 2) A circular suction chuck 10 is positioned at the upper end of the chuck table 4. The suction chuck 10 is made of a porous material such as porous ceramics. The suction chuck 10 is connected to a suction means (not shown). The chuck table 4 generates a suction force on the upper surface of the suction chuck 10 using the suction means, and holds the bonding wafer placed on the upper surface of the suction chuck 10 by suction. The chuck table 4 is rotated vertically around its axis by a chuck table motor (not shown).

[0018] The grinding apparatus 2 of this embodiment is equipped with three chuck tables 4. The three chuck tables 4 are mounted on the upper surface of a circular turntable 12 at equal intervals in the circumferential direction. The turntable 12 is rotatably supported on the upper surface of the base 14 of the grinding apparatus 2. The three chuck tables 4 are then sequentially positioned in the loading / unloading area A, the rough machining area B, and the finishing area C as the turntable 12 rotates.

[0019] (Grinding means 6 of grinding device 2) The grinding means 6 includes a first grinding unit 6a for rough grinding a bonded wafer located in the rough machining area B, a first grinding feed unit 6b for grinding feed the first grinding unit 6a, a second grinding unit 6c for finish grinding a bonded wafer located in the finishing machining area C, and a second grinding feed unit 6d for grinding feed the second grinding unit 6c.

[0020] (First grinding unit 6a of the grinding means 6) The first grinding unit 6a includes a lifting plate 18 that is vertically movable and supported by a support wall 16 extending upward from the end of the base 14 (the rear end in Figure 1), a protruding member 20 that protrudes from the lifting plate 18, a spindle housing 22 mounted on the protruding member 20, a spindle 24 that is rotatably supported by the spindle housing 22, and a motor 26 that rotates the spindle 24. A disc-shaped wheel mount 28 is fixed to the lower end of the spindle 24, as shown in Figure 6(a). An annular grinding wheel 32 is fastened to the lower surface of the wheel mount 28 by bolts 30. Multiple rough grinding wheels 34a are fixed to the lower surface of the grinding wheel 32, arranged in an annular pattern at intervals in the circumferential direction.

[0021] (First grinding feed unit 6b of the grinding means 6) As shown in Figure 1, the first grinding feed unit 6b has a ball screw 36 that extends vertically along one side of the support wall 16 and a motor 38 that rotates the ball screw 36. The nut portion (not shown) of the ball screw 36 is connected to the lifting plate 18. The first grinding feed unit 6b converts the rotational motion of the motor 38 into linear motion using the ball screw 36 and transmits it to the lifting plate 18, thereby feeding the first grinding unit 6a vertically along the guide rail 16a of the support wall 16.

[0022] (Second grinding unit 6c of grinding means 6) The second grinding unit 6c performs finish grinding on the bonded wafer. The grinding wheel 34b of the second grinding unit 6c (see Figure 7(a)) is a grinding wheel for finish grinding and is made up of abrasive grains with a smaller grain size than the grinding wheel 34a (a grinding wheel for rough grinding) of the first grinding unit 6a. The second grinding unit 6c can have the same configuration as the first grinding unit 6a, except for the grinding wheel 34b, so the same reference numerals as the components of the first grinding unit 6a are used and the explanation is omitted.

[0023] (Second grinding feed unit 6d of the grinding means 6) The second grinding feed unit 6d feeds the second grinding unit 6c in the vertical direction. The second grinding feed unit 6d may have the same configuration as the first grinding feed unit 6b, so it is given the same reference numerals as the first grinding feed unit 6b and its description is omitted.

[0024] (Fluid supply means 8 of grinding device 2) The fluid supply means 8 comprises a fluid supply source (not shown) and a fluid supply nozzle 40 equipped with a tip for injecting fluid (e.g., pure water) supplied from the fluid supply source. As shown in Figure 1, in this embodiment, the fluid supply nozzle 40 is installed in both the loading / unloading area A and the rough machining area B, but it is sufficient to install it in either the loading / unloading area A or the rough machining area B. The fluid supplied by the fluid supply means 8 is not limited to a liquid form, but may also be in the form of vapor or mist.

[0025] Furthermore, the fluid supply means 8 may be configured to supply fluid that weakens the bonding force to the interface of the chamfered portion by submerging the bonded wafer in a water tank (not shown) that stores fluid. The water tank of the fluid supply means 8 can be installed so as to be able to move up and down around the cassette table 44 or the temporary support table 46 shown below. When the water tank is installed around the cassette table 44, after the cassette 42 shown below is placed on the cassette table 44, the water tank is positioned at an operational position where fluid can be stored, and as fluid is stored inside the water tank, the bonded wafer in the cassette 42 is submerged, and fluid is supplied to the interface of the chamfered portion. Also, when the water tank is installed around the temporary support table 46, after the bonded wafer is placed on the temporary support table 46, the water tank is positioned at an operational position where fluid can be stored, and as fluid is stored inside the water tank, the bonded wafer on the temporary support table 46 is submerged, and fluid is supplied to the interface of the chamfered portion.

[0026] As shown in Figure 1, the grinding apparatus 2 of this embodiment further includes a cassette table 44 on which a cassette 42 containing a plurality of bonded wafers is placed, a transport means 48 for transporting the bonded wafers from the cassette 42 placed on the cassette table 44 to a temporary receiving table 46 for centering, a transport means 50 for transporting the bonded wafers from the temporary receiving table 46 to a chuck table 4 positioned in the loading / unloading area A, and a move means like a turntable for moving the chuck table 4 from the loading / unloading area A to a processing area where the first wafer is ground by the grinding means 6.

[0027] (Cassette table 44 of grinding device 2) The cassette table 44 comprises a first cassette table 44a on which a first cassette 42a containing a bonded wafer before grinding is placed, and a second cassette table 44b on which a second cassette 42b containing a bonded wafer after grinding is placed.

[0028] (Temporary support table 46 of grinding device 2) The temporary support table 46 comprises a base plate 52 supported on the upper surface of the base 14, and a circular support base 54 positioned in the center of the upper surface of the base plate 52 and having a diameter smaller than the diameter of the bonded wafer. Multiple elongated holes 52a extending radially from the support base 54 are formed in the base plate 52 at intervals around the support base 54. Multiple pins 56 protruding upward are movably provided in the elongated holes 52a. A pin moving mechanism (not shown) is also attached to the base plate 52 for synchronously moving the multiple pins 56 along the elongated holes 52a. The temporary support table 46 then aligns the center of the bonded wafer with the center of the support base 54 by synchronously moving the multiple pins 56 with the outer circumference of the bonded wafer placed on the support base 54 and bringing the multiple pins 56 into contact with the outer circumference of the bonded wafer.

[0029] (Conveying means 48 of the grinding device 2) The transport means 48 comprises a multi-joint arm 58 supported on a base 14, an actuator (not shown) for operating the multi-joint arm 58, and a holding piece 60 attached to the tip of the multi-joint arm 58. Multiple suction holes (not shown) are formed on one side of the holding piece 60. Each suction hole is connected to a suction means (not shown). The transport means 48 generates suction force at the suction holes of the holding piece 60 using the suction means, and holds the bonded wafer by suction on one side of the holding piece 60. The transport means 48 also operates the multi-joint arm 58 with the actuator to transport the bonded wafer before grinding from the first cassette 42a to the temporary receiving table 46, and transports the bonded wafer after grinding from the cleaning means 70 (described later) to the second cassette 42b.

[0030] (Means 50 for loading the grinding device 2) The loading means 50 includes a rotating shaft 62 mounted on a base 14 so as to be rotatable and vertically movable, an arm 64 extending substantially horizontally from the upper end of the rotating shaft 62, a suction piece 66 attached to the lower surface of the tip of the arm 64, a rotating shaft motor (not shown) for rotating the rotating shaft 62, and a lifting means (not shown) such as an air cylinder for raising and lowering the rotating shaft 62. Multiple suction holes (not shown) are formed on the lower surface of the suction piece 66. Each suction hole is connected to a suction means (not shown). The loading means 50 generates suction force at the suction holes of the suction piece 66 using the suction means, and holds the bonded wafer on the temporary receiving table 46 with the suction piece 66. The loading means 50 also uses the lifting means and the rotating shaft motor to raise, lower and rotate the rotating shaft 62, loading the bonded wafer from the temporary receiving table 46 to the chuck table 4 located in the loading / unloading area A.

[0031] (Means of transport for grinding device 2) The moving means of this embodiment comprises the turntable 12 and a turntable motor (not shown) for rotating the turntable 12. The moving means rotates the turntable 12 to sequentially move the chuck table 4 to the loading / unloading area A, the rough machining area B, and the finishing machining area C. The moving means is not limited to the above-described form. For example, if there is one chuck table 4, one grinding unit and one grinding feed unit of the grinding means 6, the moving means may be a ball screw type moving means that moves the chuck table 4 linearly between the loading / unloading area and the machining area.

[0032] The grinding apparatus 2 further includes an unloading means 68 for unloading the bonded wafer after grinding from the chuck table 4 located in the unloading / unloading area A, and a cleaning means 70 for cleaning the unloaded bonded wafer after grinding.

[0033] (Discharge means 68 of grinding device 2) The unloading means 68 includes a rotating shaft 72 mounted on a base 14 so as to be rotatable and vertically movable, an arm 74 extending substantially horizontally from the upper end of the rotating shaft 72, a suction piece 76 attached to the lower surface of the tip of the arm 74, a rotating shaft motor (not shown) for rotating the rotating shaft 72, and a lifting means (not shown) such as an air cylinder for raising and lowering the rotating shaft 72. Multiple suction holes (not shown) are formed on the lower surface of the suction piece 76. Each suction hole is connected to a suction means (not shown). The unloading means 68 generates suction force at the suction holes of the suction piece 76 using the suction means, and uses the suction piece 76 to suction and hold the bonded wafer after grinding on the chuck table 4 located in the unloading area A. Furthermore, the unloading means 68 raises and lowers and rotates the rotating shaft 72 using a lifting means and a motor for the rotating shaft to unload the bonded wafer after grinding from the chuck table 4 located in the unloading / unloading area A.

[0034] (Cleaning means 70 of the grinding device 2) The cleaning means 70 includes a spinner table 78 for suction holding the bonded wafer, a spinner table motor (not shown) for rotating the spinner table 78, a cleaning water nozzle (not shown) for spraying cleaning water onto the bonded wafer held by the spinner table 78, and an air nozzle (not shown) for spraying drying air onto the bonded wafer held by the spinner table 78. The cleaning means 70 rotates the spinner table 78 holding the bonded wafer by suction, sprays cleaning water from the cleaning water nozzle to clean the bonded wafer, and after cleaning with cleaning water, sprays drying air from the air nozzle to dry the bonded wafer.

[0035] (Bonded wafer 86) Figure 2 shows a bonded wafer 86 formed by bonding a first wafer 82 and a second wafer 84. The first wafer 82 and the second wafer 84 are made of silicon (Si) and can be formed, for example, with a diameter of 300 mm and a thickness of 775 μm. The surface 84a of the second wafer 84 has a device region 92 in which multiple devices 88 such as ICs and LSIs are demarcated by grid-like division lines 90, and an outer peripheral surplus region 94 surrounding the device region 92. In Figure 2(a), a ring-shaped boundary 96 between the device region 92 and the outer peripheral surplus region 94 is shown by a dashed line for convenience, but in reality, there is no line indicating the boundary 96. Although not shown, the surface 82a of the first wafer 82 has the same configuration as the surface 84a of the second wafer 84. Furthermore, as shown in Figure 2(b), curved chamfered portions 98 are formed on the outer periphery of the first wafer 82 and the second wafer 84. The width of the chamfered portion 98 is, for example, about 2 mm to 3 mm. In addition, notches 100 indicating the crystal orientation are formed on the outer periphery of the first wafer 82 and the second wafer 84 (see Figure 2(a)).

[0036] When forming the bonded wafer 86, the notches 100 of the first wafer 82 and the notches 100 of the second wafer 84 are aligned, and the surface 82a of the first wafer 82 and the surface 84a of the second wafer 84 are bonded together. After bonding the first wafer 82 and the second wafer 84, it is preferable to apply heat treatment to tightly bond the first wafer 82 and the second wafer 84 together using siloxane bonds. Siloxane bonds are Si-O-Si bonds in which silicon (Si) and oxygen (O) are alternately bonded, and a strong bond can be maintained even at high temperatures.

[0037] (Wafer processing method) Next, a method for processing the first wafer 82 of the bonded wafer 86 will be described.

[0038] (Modified layer formation process) In this embodiment, first, the second wafer 84 of the bonded wafer 86 is held on a holding table, and the focal point of the laser beam is positioned on the inside adjacent to the chamfered portion 98 formed on the outer circumference of the first wafer 82 of the bonded wafer 86, and the laser beam is irradiated to perform a modified layer formation process to form a ring-shaped modified layer.

[0039] (Laser processing device 102) The modified layer formation process can be carried out, for example, using the laser processing apparatus 102 shown in Figure 3(a). The laser processing apparatus 102 includes a holding table 104 for holding the wafer by suction, an oscillator (not shown) that emits a pulsed laser beam LB with a wavelength that is transparent to the bonded wafer 86, and a concentrator 106 that focuses the laser beam LB emitted by the oscillator and irradiates the first wafer 82 with it.

[0040] In the modified layer formation process, first, the second wafer 84 of the bonded wafer 86 is held on the holding table 104. At this time, the back surface 84b of the second wafer 84 is facing downwards, and the bonded wafer 86 is placed on the upper surface of the holding table 104. The rotation center of the holding table 104 is also aligned with the center of the bonded wafer 86. Then, a suction force is generated on the upper surface of the holding table 104 by a suction means (not shown), and the back surface 84b of the second wafer 84 is held in place by suction on the upper surface of the holding table 104.

[0041] Once the second wafer 84 of the bonded wafer 86 is held on the holding table 104, the processing line to be irradiated with the laser beam LB is set. At this time, the imaging means (not shown) of the laser processing apparatus 102 is used to image the first wafer 82 from above, and the outer circumference and center position of the first wafer 82 are detected based on the image of the first wafer 82 captured by the imaging means. Then, based on the detected outer circumference and center position of the first wafer 82, a ring-shaped line located inside (outer circumference excess area 94 or boundary 96) adjacent to the chamfered portion 98 formed on the outer circumference of the first wafer 82 is set as the processing line.

[0042] Once the processing line to which the laser beam LB should be irradiated is set, the focal point of the laser beam LB is positioned at the required height on the processing line. At this time, the height detection means (not shown) of the laser processing apparatus 102 detects the height of the back surface 82b of the first wafer 82 (the height of the top surface of the bonded wafer 86). Then, using the detected height of the back surface 82b as a reference, the focal point of the laser beam LB is positioned at the required height on the processing line (inside the outer peripheral excess area 94).

[0043] Once the focal point of the laser beam LB is positioned at the required height on the processing line, the laser beam LB, with a wavelength that is transparent to the bonding wafer 86, is irradiated onto the first wafer 82 to form a ring-shaped modified layer 108 along the chamfered portion 98. That is, by rotating the holding table 104 at a predetermined rotational speed in the direction indicated by arrow R1 in Figure 3(a) while irradiating the first wafer 82 with the laser beam LB, a ring-shaped modified layer 108 is formed around the entire circumference of the ring-shaped processing line.

[0044] Once one ring-shaped modified layer 108 (one full circle) is formed, the height of the focal point of the laser beam LB is changed to a shallower position, and the laser beam LB is irradiated onto the first wafer 82 in the same manner as above. By repeating the change in the height of the focal point and the irradiation of the laser beam LB in this manner, multiple ring-shaped modified layers 108 are formed at intervals in the vertical direction (see Figure 3(b)). Note that adjacent modified layers 108 in the vertical direction are connected by cracks (not shown) extending from the modified layer 108.

[0045] The modified layer formation process can be carried out, for example, under the following processing conditions. The defocus shown below is the amount of movement when the light concentrator 106 is moved toward the bonded wafer 86, starting from a state where the focal point of the laser beam LB is positioned on the back surface 82b (exposed surface) of the first wafer 82. Laser beam wavelength: 1099nm~1342nm Repetition frequency: 80kHz Holding table rotation speed: 60 rpm Average output: 2W Defocus: 650μm, 500μm, 350μm, 200μm

[0046] In the modified layer formation step, a modified layer 110 extending radially from the ring-shaped modified layer 108 may also be formed (see Figure 4). That is, multiple linear modified layers 110 extending radially outward from the ring-shaped modified layer 108 to the outer circumference of the first wafer 82 may be formed radially inside the first wafer 82 at equal intervals in the circumferential direction (three in this embodiment). Similar to the ring-shaped modified layer 108, it is preferable to form multiple radial modified layers 110 at intervals in the vertical direction. By forming such radial modified layers 110, the chamfered portion 98 can be finely divided and removed effectively in the grinding step described later.

[0047] (Carry-in process) After the modified layer formation process is carried out, a loading process is performed in which the bonded wafer 86 is loaded into a grinding apparatus that grinds the first wafer 82 of the bonded wafer 86. In this embodiment, an example of loading the bonded wafer 86 into the grinding apparatus 2 described above will be explained.

[0048] In the loading process, first, the first and second cassettes 42a and 42b are placed on the first and second cassette tables 44a and 44b. At this time, multiple bonded wafers 86, each having a ring-shaped modified layer 108 formed on the first wafer 82, are placed in the first cassette 42a. Then, the first cassette 42a containing the multiple bonded wafers 86 is placed on the first cassette table 44a. In addition, an empty second cassette 42b for containing the bonded wafers 86 after grinding is placed on the second cassette table 44b.

[0049] Once the first and second cassettes 42a and 42b are placed on the first and second cassette tables 44a and 44b, the bonded wafer 86 is loaded from the first cassette 42a onto the chuck table 4. First, the unground bonded wafer 86 is transported from the first cassette 42a to the support base 54 of the temporary receiving table 46 using the transport means 48. At this time, the bonded wafer 86 is placed on the support base 54 with the first wafer 82 on top and the second wafer 84 on the bottom. Next, the multiple pins 56 of the temporary receiving table 46 are moved synchronously, and the multiple pins 56 are brought into contact with the outer circumference of the bonded wafer placed on the support base 54, thereby aligning the center of the bonded wafer with the center of the support base 54. Then, the bonded wafer 86 is loaded onto the chuck table 4 located in the loading / unloading area A using the transport means 50, and the bonded wafer 86 is placed on the upper surface of the chuck table 4. Then, suction force is generated in the suction chuck 10 of the chuck table 4, and the bonded wafer 86 is held in place by suction at the chuck table 4. The loading process is carried out in this manner.

[0050] (Fluid supply process) In this embodiment, during the above-described loading process, a fluid supply process is carried out to supply a fluid that weakens the bonding force to the interface of the chamfered portion 98 where the first wafer 82 and the second wafer 84 are joined.

[0051] The fluid supply process in the loading process can be performed, for example, after the first cassette 42a is placed on the first cassette table 44a, but before the bonded wafers 86 are transported from the first cassette 42a to the temporary receiving table 46. In this case, after the first cassette 42a is placed on the first cassette table 44a, the water tank installed around the first cassette table 44a is raised and lowered to position the water tank in an operational position where fluid can be stored. Next, fluid that weakens the bonding force at the interface of the chamfered portion 98 is stored inside the water tank, submerging the multiple bonded wafers 86 in the first cassette 42a. This allows fluid that weakens the bonding force at the interface of the chamfered portion 98 to be supplied. After that, the water tank is positioned in a non-operating position and the fluid is discharged from inside the water tank, and the bonded wafers 86 are loaded onto the chuck table 4 as described above.

[0052] Furthermore, the fluid supply process in the loading process can also be performed after the bonded wafer 86 is placed on the support base 54 of the temporary receiving table 46, but before the centering of the bonded wafer 86 is performed. In this case, after the bonded wafer 86 is placed on the support base 54 of the temporary receiving table 46, the water tank installed around the temporary receiving table 46 is raised and lowered to position the water tank in an operational position where fluid can be stored. Next, fluid that weakens the bonding force at the interface of the chamfered portion 98 is stored inside the water tank, submerging the bonded wafer 86 on the support base 54. This allows fluid that weakens the bonding force at the interface of the chamfered portion 98 to be supplied. After that, the water tank is positioned in a non-operating position and the fluid is discharged from inside the water tank, the centering of the bonded wafer 86 is performed, and then the bonded wafer 86 is loaded onto the chuck table 4 as described above.

[0053] Furthermore, the fluid supply process in the loading process may be performed after the bonded wafer 86 is held by suction on the chuck table 4 located in the loading / unloading area A. In this case, after the bonded wafer 86 is held by suction on the chuck table 4 located in the loading / unloading area A, the chuck table 4 is rotated in the direction indicated by arrow R2 in Figure 5(a), and fluid is sprayed from the fluid supply nozzle 40 installed in the loading / unloading area A toward the outer circumference of the bonded wafer 86. This allows a fluid that weakens the bonding force to be supplied to the interface of the chamfered portion 98.

[0054] As described above, the bonded wafer 86 in this embodiment is bonded by siloxane bonds (Si-O-Si bonds). Therefore, when fluid is supplied to the interface of the chamfered portion 98, the fluid gradually penetrates from the outer circumference of the bonded wafer 86 to the bonding surface, and the region into which the fluid has penetrated changes to a Si-OH-OH-Si bond. As a result, the bonding force in the region into which the fluid has penetrated is weakened, and a bond weakening region 112 is formed in a ring shape at the interface of the chamfered portion 98 (outer circumference side of the bonding surface) (see Figure 5(b)).

[0055] (Grinding process) After the loading process is carried out, the first wafer 82 is ground to thin it, and a grinding process is performed to remove the chamfered portion 98 formed on the outer circumference of the first wafer 82 by the force of grinding.

[0056] (Rough grinding in the grinding process) In the grinding process, rough grinding is first performed on the back surface 82b of the first wafer 82. When rough grinding is performed, first the turntable 12 is rotated 120 degrees to position the chuck table 4, which is holding the bonded wafer 86 by suction, from the loading / unloading area A to the rough processing area B. Next, the chuck table 4 is rotated at a predetermined rotational speed (for example, 300 rpm) in the direction indicated by arrow R3 in Figure 6(a). Also, the spindle 24 of the first grinding unit 6a is rotated at a predetermined rotational speed (for example, 6000 rpm) in the direction indicated by arrow R4. Next, the spindle 24 is lowered by the first grinding feed unit 6b, bringing the grinding wheel 34a for rough grinding into contact with the back surface 82b of the first wafer 82, and grinding water is supplied to the part of the back surface 82b of the first wafer 82 into contact with the grinding wheel 34a. Then, the spindle 24 is lowered at a predetermined grinding feed rate (for example, 1.0 μm / s). This rough grinding is performed on the back surface 82b of the first wafer 82, thereby thinning the first wafer 82. In addition, the grinding force acting on the bonded wafer 86 from the first grinding unit 6a removes the chamfered portion 98 formed on the outer circumference of the first wafer 82 (see Figures 6(a) and 6(b)).

[0057] Furthermore, a fluid supply process may be performed during the rough grinding stage of the grinding process. In this case, after positioning the chuck table 4 from the loading / unloading area A to the rough machining area B, before rough grinding is performed on the back surface 82b of the first wafer 82, fluid is sprayed from the fluid supply nozzle 40 installed in the rough machining area B toward the outer circumference of the bonded wafer 86 while rotating the chuck table 4. This allows a fluid that weakens the bonding force to be supplied to the interface of the chamfered portion 98. Alternatively, while rough grinding is performed on the back surface 82b of the first wafer 82, fluid may be sprayed from the fluid supply nozzle 40 installed in the rough machining area B toward the outer circumference of the bonded wafer 86 to supply a fluid that weakens the bonding force to the interface of the chamfered portion 98.

[0058] (Finish grinding in the grinding process) After rough grinding is performed on the back surface 82b of the first wafer 82, finish grinding is performed on the back surface 82b of the first wafer 82. When performing finish grinding, first, the turntable 12 is rotated 120 degrees to position the chuck table 4, which is holding the bonded wafer 86 by suction, from the rough machining area B to the finish machining area C. Next, the chuck table 4 is rotated at a predetermined rotational speed (for example, 300 rpm) in the direction indicated by arrow R5 in Figure 7(a). Also, the spindle 24 of the second grinding unit 6c is rotated at a predetermined rotational speed (for example, 6000 rpm) in the direction indicated by arrow R6. Next, the spindle 24 is lowered by the second grinding feed unit 6d, bringing the grinding wheel 34b for finish grinding into contact with the back surface 82b of the first wafer 82, and grinding water is supplied to the part of the back surface 82b of the first wafer 82 into contact with the grinding wheel 34b. Then, the spindle 24 is lowered at a predetermined grinding feed rate (for example, 0.1 μm / s). This allows finish grinding to be performed on the back surface 82b of the first wafer 82 (see Figure 7(b)). After that, the turntable 12 is rotated 120 degrees to position the chuck table 4, which is holding the bonded wafer 86 by suction, from the finishing processing area C to the loading / unloading area A.

[0059] (Washing process) After the grinding process, a cleaning process is performed to clean the bonded wafer 86. In the cleaning process, first, the bonded wafer 86 is unloaded from the chuck table 4 located in the loading / unloading area A to the spinner table 78 of the cleaning means 70 by the unloading means 68. Next, the bonded wafer 86 is held by suction on the upper surface of the spinner table 78. Then, while rotating the spinner table 78, cleaning water is sprayed from the cleaning water nozzle to clean the bonded wafer 86. Next, while rotating the spinner table 78, drying air is sprayed from the air nozzle to dry the bonded wafer 86. After the cleaning process is completed, the cleaned bonded wafer 86 is transported to the second cassette 42b by the transport means 48.

[0060] As described above, in this embodiment, a fluid that weakens the bonding force is supplied to the interface of the chamfered portion 98 where the first wafer 82 and the second wafer 84 are joined, thereby forming a ring-shaped bonding force weakening region 112 at the interface of the chamfered portion 98. Therefore, when the first wafer 82 is ground and thinned, the chamfered portion 98 of the first wafer 82 can be easily removed. Furthermore, since there is no need to remove the chamfered portion 98 with a cutting blade, the second wafer 84 is not damaged.

[0061] In this embodiment, siloxane bonding was used as an example to describe the bonding of the bonded wafer 86, but it is not limited to siloxane bonding; for example, SiCN bonding, TEOS bonding, or ThOx bonding may also be used. Even with these types of bonding, the bonding force of the bonded wafer 86 can be weakened by supplying a fluid that weakens the bonding force to the interface of the chamfered portion 98 where the first wafer 82 and the second wafer 84 are bonded. Furthermore, even if O2 plasma or N2 plasma is applied as a pretreatment to the bonding surface of the bonded wafer 86, the bonding force of the bonded wafer 86 can be weakened. [Explanation of Symbols]

[0062] 2: Grinding equipment 4: Chuck Table 6: Grinding method 6a: First grinding unit 6b: First grinding feed unit 6c: Second grinding unit 6d: Second grinding feed unit 8: Fluid supply means 32: Grinding Wheel 34a: Grinding wheel for rough grinding 34b: Grinding wheel for finishing 40: Fluid supply nozzle 42: Cassette 42a: First cassette 42b: Second cassette 44: Cassette Table 44a: First cassette table 44b: Second cassette table 46: Temporary support table 48: Conveying means 50: Delivery method 82: The First Wafer 82a: Surface of the first wafer 82b: Reverse side of the first wafer 84: The Second Wave 84a: Surface of the second wafer 84b: Reverse side of the second wafer 86: Bonded wafer 98: Chamfered section 108: Ring-shaped modified layer A: Loading / unloading area B: Rough machining area C: Finishing area

Claims

1. A wafer processing method comprising processing the first wafer of a bonded wafer formed by joining a first wafer and a second wafer, A modification layer formation step involves holding the second wafer of the bonded wafer on a holding table, positioning the focal point of a laser beam on the inside adjacent to the chamfered portion formed on the outer circumference of the first wafer of the bonded wafer, and irradiating the laser beam to form a ring-shaped modification layer. A loading step of loading the bonded wafer into a grinding apparatus for grinding the first wafer of the bonded wafer, The process includes a grinding step of thinning the first wafer by grinding and removing the chamfered portion formed on the outer circumference of the first wafer by the grinding force, A wafer processing method comprising a fluid supply step in which a fluid that weakens the bonding force is supplied to the interface of the chamfered portion where the first wafer and the second wafer are joined, during the loading step or the grinding step.

2. The wafer processing method according to claim 1, wherein a fluid supply nozzle equipped with a tip for spraying the fluid is used in the fluid supply step.

3. The wafer processing method according to claim 1, wherein the fluid is water.

4. The first wafer and the second wafer are joined by a Si-O-Si siloxane bond. The wafer processing method according to claim 1, wherein in the fluid supply step, the Si-O-Si bond is changed to a Si-OH-OH-Si bond by a fluid that weakens the bonding force, thereby weakening the bonding force.

5. A grinding apparatus for grinding the first wafer of a bonded wafer formed by joining a first wafer and a second wafer, A grinding apparatus comprising: a chuck table for holding the bonded wafer; a grinding means rotatably mounted on the chuck table, the grinding wheel having grinding wheels arranged in an annular pattern for grinding the first wafer of the bonded wafer held on the chuck table; and a fluid supply means for supplying a fluid to weaken the bonding force at the interface of the chamfered portion where the first wafer and the second wafer are joined.

6. The system includes a cassette table on which a cassette containing multiple bonded wafers is placed, a transport means for transporting the bonded wafers from the cassette placed on the cassette table to a temporary receiving table for centering, a loading means for loading the bonded wafers from the temporary receiving table into a chuck table positioned in the loading / unloading area, and a moving means for moving the chuck table from the loading / unloading area to a processing area where the first wafer is ground by the grinding means. The grinding apparatus according to claim 5, wherein the fluid supply means is disposed in the loading / unloading area or the processing area.

7. The grinding apparatus according to claim 5, wherein the fluid is water.

8. The first wafer and the second wafer are joined by a Si-O-Si siloxane bond. The grinding apparatus according to claim 5, wherein the Si-O-Si bond is changed to a Si-OH-OH-Si bond by a fluid that weakens the bonding force, thereby weakening the bonding force.

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