Wafer processing method

Abstract

To provide a wafer processing method that enables relatively readily removal of a circumference excessive region including a chamfering part from an active area of a wafer.SOLUTION: A wafer processing method includes: a holding step of holding a wafer on a chuck table while exposing a back surface; a grinding step of grinding the back surface of the wafer, after positioning a grinding wheel having a diameter smaller than a diameter of the wafer to the inside of a circumference excessive region, and grinding an active area to a predetermined thickness and at the same time, forming a ring-shaped protruding part in the circumference excessive region; a separation-start-point forming step of forming a separation-start point for separating the circumference excessive region from the active area, before or after the grinding step; and a chamfering-part removing step of applying external force to the ring-shaped protruding part of the wafer having the separation-start point formed therein to remove the chamfering-part together with circumference excessive region from the wafer.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a wafer processing method for grinding the back surface of a wafer having an effective area on its front surface, an outer peripheral surplus area surrounding the effective area, and a chamfered portion formed in the outer peripheral surplus area. [Background technology]

[0002] A wafer has a device area on its front surface, where a plurality of devices such as ICs and LSIs are partitioned by planned division lines. The back surface of the wafer is ground to thin it to the desired thickness, and then the wafer is divided into individual device chips using a cutting device or laser processing device. These chips are then used in electrical devices such as mobile phones and personal computers.

[0003] In addition, a chamfer is formed on the outer periphery of the wafer, and when the back surface of the wafer is ground to thin it, the chamfer becomes as sharp as a knife edge, which can cause injury to an operator handling the wafer, or can cause cracks to form from the outer periphery of the wafer to the inside, damaging the device.

[0004] Therefore, a technology has been proposed in which, before grinding the back surface of the wafer, a focal point of a laser beam having a wavelength that is transparent to the wafer is positioned inside the chamfer and irradiated, forming a ring-shaped modified layer inside the wafer, and then removing the chamfer using the modified layer as the starting point for dividing the wafer (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2022-174036 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, since the thickness of the wafer to be processed is relatively large at 700 to 800 μm, there is a problem in that even if the modified layer as described above is formed, it is not easy to remove the chamfered portion.

[0007] Furthermore, even with the above-mentioned methods, it is possible that the chamfered portion cannot be completely removed, and a small portion of the chamfered portion may remain. This may result in problems such as the remaining portion falling off in a later process and becoming a source of contamination, or causing chipping of the device chips when the wafer is divided into individual device chips.

[0008] The present invention has been made in consideration of the above-mentioned circumstances, and its main technical object is to provide a wafer processing method that makes it possible to relatively easily remove the peripheral excess area including the chamfered portion from the effective area of ​​the wafer, and also solves problems such as a small amount of the chamfered portion remaining and falling off in a later process to become a source of contamination or causing chipping of the device chips when the wafer is divided into individual device chips. [Means for solving the problem]

[0009] In order to solve the above-mentioned main technical problem, according to the present invention, there is provided a wafer processing method for grinding the back surface of a wafer having an effective area on its front surface and an outer circumferential surplus area surrounding the effective area, the method comprising: a holding step of holding the wafer on a chuck table with the back surface exposed; a grinding step of positioning a grinding wheel having a diameter smaller than that of the wafer inside the outer circumferential surplus area and grinding the back surface of the wafer to grind the effective area to a predetermined thickness and form a ring-shaped protrusion in the outer circumferential surplus area; a separation origin forming step of forming a separation origin for separating the outer circumferential surplus area from the effective area before or after the grinding step; and a chamfer removing step of applying an external force to the ring-shaped protrusion of the wafer on which the separation origin has been formed, thereby removing the chamfer from the wafer together with the outer circumferential surplus area. A wafer processing method comprising the steps of:

[0010] In the chamfer removing step, the wafer is held on a spinner table and rotated, and an external force is applied to the ring-shaped protrusion by centrifugal force to remove the chamfer together with the outer peripheral surplus region from the wafer. If the separation starting point forming step is performed before the grinding step, the chamfer removing step may be performed by applying an external force to the ring-shaped protrusion by the grinding wheel in the grinding step to remove the chamfer together with the outer peripheral surplus region from the wafer.

[0011] The wafer may be a laminated wafer in which the effective area side faces another wafer. In the separation starting point forming step, it is preferable to irradiate the wafer with a focusing point of a laser beam having a wavelength that is transparent to the wafer at the boundary between the effective area and the peripheral excess area, and form a ring-shaped modified layer at the boundary. Furthermore, after the chamfer removing step is performed, a finish grinding step may be performed in which the back surface of the wafer is further ground to a desired thickness. The effective area of ​​the wafer is preferably a device area in which a plurality of devices are partitioned by a planned dividing line. Effect of the Invention

[0012] The wafer processing method of the present invention includes a holding step of holding the wafer on a chuck table with the back surface exposed, a grinding step of positioning a grinding wheel having a diameter smaller than the diameter of the wafer and arranged in a ring shape inside the outer circumferential surplus region to grind the back surface of the wafer, grinding the effective region to a predetermined thickness and forming a ring-shaped convex portion in the outer circumferential surplus region, a separation starting point forming step of forming a separation starting point for separating the outer circumferential surplus region from the effective region before or after the grinding step, and a chamfer removing step of applying an external force to the ring-shaped convex portion of the wafer on which the separation starting point has been formed, thereby removing the chamfer portion from the wafer together with the outer circumferential surplus region. Therefore, it becomes possible to relatively easily remove the convex portion formed from the outer circumferential surplus region including the chamfer, and the problem of it being difficult to remove the outer circumferential surplus region including the chamfer is solved. In addition, because the chamfered portion can be easily removed, the chamfered portion is prevented from remaining on the outer periphery of the wafer, which solves the problem that the remaining portion falls off in a later process and becomes a source of contamination, or that the remaining portion becomes a cause of chipping of the device chips when the wafer is divided into individual device chips. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2A is a perspective view of a stacked wafer serving as a workpiece in this embodiment, and FIG. 2B is a perspective view of a single wafer serving as a workpiece in this embodiment. [Diagram 2] FIG. 2A is a perspective view showing a manner in which a wafer is held on a chuck table of a laser processing apparatus that performs a separation start point forming step; FIG. 2B is a perspective view showing a manner in which a separation start point is formed by the laser processing apparatus shown in FIG. [Diagram 3] (a) A schematic cross-sectional view showing the morphology of a modified layer (Type 1) that serves as the starting point of separation, (b) a schematic cross-sectional view showing the morphology of another modified layer (Type 2) that serves as the starting point of separation, and (c) a schematic cross-sectional view showing the morphology of yet another modified layer (Type 3) that serves as the starting point of separation. [Figure 4] FIG. 11 is a perspective view showing an embodiment in which a chamfered portion removing step is performed together with a grinding step. [Diagram 5]FIG. 11 is a perspective view showing an aspect of a grinding step performed before a separation start point forming step is performed. [Figure 6] FIG. 1A is a perspective view showing an embodiment of a separation start point forming step carried out after a grinding step, and FIG. 1B is a schematic cross-sectional view showing the form of a separation start point formed by the separation start point forming step shown in FIG. [Figure 7] FIG. 1A is a schematic side view, partially in cross section, showing an embodiment in which a ring-shaped protrusion is accommodated in an external force applying means that applies an external force to the ring-shaped protrusion formed on the stacked wafer; FIG. 1B is a schematic side view showing an embodiment in which the external force applying means shown in FIG. 1A is tilted down to remove a chamfered portion from the stacked wafer. [Figure 8] 1 is an overall perspective view of a chamfer removing device that applies an external force to a ring-shaped protrusion formed on a laminated wafer to remove the chamfer. FIG. [Figure 9] 9 is a side view showing an embodiment of a chamfer removing step with a part of the chamfer removing device shown in FIG. 8 in cross section. [Figure 10] FIG. 13 is a perspective view showing an embodiment of a finish grinding step. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a wafer processing method according to the present invention will be described in detail with reference to the accompanying drawings.

[0015] FIG. 1(a) shows a laminated wafer W to be processed by the wafer processing method of the present embodiment. The laminated wafer W is a wafer in which a first wafer 10A and a second wafer 10B are laminated and integrated as shown in the figure. The first wafer 10A is, for example, a silicon wafer having a diameter of 300 mm and a thickness of 700 μm, and a plurality of devices 12A are formed on the front surface 10Aa by dividing the wafer into sections by dividing lines 14A. The wafer 10A has a front surface 10Aa and a back surface 10Ab, and includes an effective area 16A near the center where the devices 12A to be used as products are formed, a chamfered portion 17A formed at the end of the outer periphery of the outer periphery surplus area 18A surrounding the effective area 16A, and a boundary portion 15A between the effective area 16A and the chamfered portion 17A, which divides the effective area 16A from the outer periphery surplus area 18A. The boundary 15A is added for convenience of explanation, and is not actually added to the first wafer 10A. The boundary 15A is not a region limited to a circular line as shown in the figure, but a region having a certain width in the radial direction. The second wafer 10B also has a similar configuration to the first wafer 10A, and although not shown, is a silicon wafer in which a plurality of devices are formed by dividing lines on the surface 10Ba facing the lower side in the figure. The laminated wafer W is, for example, integrated by siloxane bonding by bonding the effective area 16A of the surface 10Aa of the first wafer 10A and the surface 10Ba of the second wafer 10B face to face and heat treating them.

[0016] FIG. 1(b) shows another wafer 10C to be processed by the wafer processing method of the present embodiment. The wafer 10C is a single wafer, and a protective tape T is attached to the surface 10Ca of the wafer 10C. The illustrated wafer 10C has the same configuration as the above-mentioned wafer 10A, for example, and is a silicon wafer with a diameter of 300 mm and a thickness of 700 μm, and a plurality of devices 12C are formed on the surface 10Ca by dividing the wafer by a division line 14C. The wafer 10C has a surface 10Ca and a back surface 10Cb, and includes an effective area 16C near the center where the devices 12C to be used as products are formed, a chamfered portion 17C formed at the outer edge of the outer periphery of the outer periphery surplus area 18C surrounding the effective area 16C, and a boundary portion 15C between the effective area 16C and the chamfered portion 17C, which divides the effective area 16C from the outer periphery surplus area 18C. Like the above-described boundary 15A, the boundary 15C is provided for convenience of explanation and is not actually provided on the wafer 10C. When processing is performed by the wafer processing method of the present embodiment, the protective tape T attached to the front surface 10Ca functions as a protective member that protects the devices 12C in the effective region 16C.

[0017] The wafer processed by the wafer processing method of the present invention is not limited to the above-mentioned stacked wafer W in which two wafers are stacked, and the single silicon wafer 10C, but includes various wafers having an effective area and a chamfered portion at the edge of the outer periphery surrounding the effective area. For example, it may be a gallium nitride (GaN) wafer, a gallium arsenide (GaAs) wafer, a lithium tantalate (LiTaO3) wafer, or a lithium niobate (LiNbO3) wafer, or it may be a wafer (e.g., a glass wafer) in which no device is formed in the central area called the effective area, and the central area is processed later and used as a product. In the embodiment described below, a wafer processing method using the above-mentioned stacked wafer W as the workpiece will be described.

[0018] The wafer processing method of this embodiment performed on the above-mentioned stacked wafer W includes a holding step of holding the stacked wafer W on a chuck table while exposing the back side of the stacked wafer W, i.e., the back surface 10Ab of the first wafer 10A; a grinding wheel having a diameter smaller than the diameter of the stacked wafer W and having grinding stones arranged in an annular shape, which will be described later, positioned inside the region corresponding to the outer peripheral excess region 18A, i.e., inside the boundary portion 15A, to grind the back surface 10Ab of the first wafer 10A; The method includes a grinding process in which the area corresponding to the effective area 16A is ground to a predetermined thickness and a ring-shaped convex portion is formed in the outer peripheral surplus area 18A, a separation starting point forming process in which a separation starting point for separating the outer peripheral surplus area 18A including the chamfered portion 17A from the effective area 16A is formed before or after the grinding process, and a chamfered portion removing process in which an external force is applied to the ring-shaped convex portion of the stacked wafer W in which the separation starting point is formed, thereby removing the chamfered portion 17A together with the outer peripheral surplus area 18A from the stacked wafer W.

[0019] The wafer processing method of the present invention can be carried out by appropriately changing the order of the above-mentioned steps, and an example of a specific procedure of the wafer processing method included in the present invention will be described below with reference to the drawings.

[0020] In this embodiment, before the grinding process is performed, a separation starting point forming process is performed to form a separation starting point for separating the outer peripheral excess area 18A from the effective area 16A. When performing the separation starting point forming process, the stacked wafer W is first transported to a laser processing device 20 (only a part of which is shown) shown in Figs. 2(a) and (b). The laser processing device 20 at least includes a chuck table 21 shown in Fig. 2(a) and a laser beam application means 22 shown in Fig. 2(b). The chuck table 21 includes an adsorption chuck 21a formed of a breathable member constituting a holding surface, and a frame body 21b surrounding the adsorption chuck 21a. The laser beam application means 22 includes a laser oscillator (not shown) that oscillates a laser beam having a wavelength that is transparent to the first wafer 10A constituting the stacked wafer W, and a condenser 23 that condenses and irradiates the laser beam LB oscillated by the laser oscillator. Furthermore, the laser processing device 20 is equipped with a moving means for moving the chuck table 21, a rotary drive means for rotating the chuck table 21, a suction means for generating negative pressure in the suction chuck 21a, and the like (all of which are omitted from the drawings).

[0021] 2(a), the stacked wafers W are placed on a chuck table 21 with the first wafer 10A forming the back surface of the stacked wafers W facing upward and the second wafer 10B facing downward, and a suction means (not shown) is operated to hold the stacked wafers W by suction. Alignment is performed on the stacked wafers W held by the chuck table 21 using an alignment means and a height detection means (both not shown) provided in the laser processing device 20 to detect the position of the outer circumferential end portion where the chamfered portion 17A of the first wafer 10A is formed and the center position of the first wafer 10A, and the height of the back surface 10Ab of the first wafer 10A is detected to detect the processing position to be irradiated with the laser beam LB set corresponding to the boundary portion 15A described above.

[0022] Meanwhile, the form of the separation starting point formed by the separation starting point forming step carried out in the present invention includes, for example, types 1 to 3 described below.

[0023] (Dip 1) By detecting the position of the edge of the outer periphery where the chamfered portion 17A of the first wafer 10A is formed and the center position of the first wafer 10A, for example, a position that is inside the outer periphery marginal region 18A (for example, a region 0.5 mm from the edge of the outer periphery) where the chamfered portion 17A is formed from the edge of the outer periphery of the first wafer 10A and has a radius of 147 mm from the center point of the first wafer 10A, which is set in a ring shape corresponding to the above-mentioned boundary portion 15A, is detected as a predetermined processing position for forming a modified layer by laser processing. Position information of the processing position detected in this way is stored in a control means (not shown).

[0024] Based on the information of the processing position detected by the above-mentioned alignment, the chuck table 21 is moved to position the above-mentioned predetermined processing position directly below the condenser 23 of the laser beam application means 22 as shown in Fig. 2(b). Next, a laser beam LB having transparency to the first wafer 10A is irradiated from the back surface 10Ab side of the first wafer 10A at a focused point positioned within the boundary portion 15A between the effective area 16A and the outer peripheral excess area 18A including the chamfered portion 17A, and the chuck table 21 is rotated in the direction indicated by the arrow R1 to form a modified layer 100, which serves as a separation starting point of the present invention, all around the chamfered portion 17A of the first wafer 10A.

[0025] As shown in FIG. 3(a), the modified layer 100 described above has cracks 101 formed by forming the modified layer 100, and the cracks 101 are formed at a relatively deep position leading to the front surface 10Aa side of the first wafer 10A. Furthermore, the modified layer 100 is formed in a plurality of layers in the vertical direction, and is composed of, for example, four modified layers in the vertical direction. When forming such a modified layer 100, first, the focal point of the laser beam LB is positioned at a position set deep inside the front surface 10Aa side of the boundary portion 15A of the first wafer 10A, and the laser beam LB is irradiated, and the chuck table 21 is rotated as described above to form a first annular modified layer along the boundary portion 15A. Thereafter, while rotating the chuck table 21, the focal point is raised toward the back surface 10Ab side (upward) three times, and a total of four annular modified layers are formed along the boundary portion 15A. Such a modified layer 100 is referred to as Type 1.

[0026] (Dive 2) The type 2 separation starting point described below is, for example, as shown in FIG. 3(b), formed by positioning the focal point of the laser beam LB at an adjacent position on the outside of the modified layer 100 and irradiating the laser beam LB, and rotating the chuck table 21 to form annular modified layers 102 and 103 at different depth positions, in addition to the modified layer 100 of type 1 described above. As shown in FIG. 3(b), the annular modified layers 102 and 103 are formed by a plurality of modified layers adjacent to each other in the radial direction at the same depth position, and are formed by irradiating the modified layer 100 of type 1 with the focal point of the laser beam LB moving in the horizontal direction at a position adjacent to the outside of the modified layer 100 of type 1 while rotating the chuck table 21 in the direction indicated by the arrow R1 described above. As a result, a type 2 separation starting point composed of the modified layers 100, 102, and 103 is formed.

[0027] (Type 3) The separation starting point of type 3 described below is different from the modified layers of types 1 and 2 described above. As shown in FIG. 3(c), the focal point of the laser beam LB is positioned at the deepest part inside the boundary portion 15A, the chuck table 21 is rotated, and the first annular modified layer is formed along the chamfered portion 17A, and then the focal point is moved to the back surface 10Ab side (upper surface side) of the wafer 10A several times and the focal point is moved to the center side (left side in the figure) of the wafer 10A. As a result, the modified layer 104 inclined toward the center side of the wafer 10A is formed in an annular shape along the chamfered portion 17A. Furthermore, as shown in the figure, modified layers 105 and 106 inclined similarly to the modified layer 104 are formed at positions adjacent to the outside of the modified layer 104 (the chamfered portion 17A side). As a result, the separation starting point of type 3 composed of the modified layers 104, 105, and 106 is formed.

[0028] The laser processing conditions when carrying out the above-mentioned separation start point forming step are set, for example, as follows. Wavelength: 1099nm Repetition frequency: 80kHz Average power output: 2.0W Machining feed speed: 450mm / s or Wavelength: 1342nm Repetition frequency: 90kHz Average power output: 1.9W Machining feed speed: 400mm / s

[0029] The separation starting point formed by the present invention is not limited to the forms shown in the above types 1 to 3, and may function as a separation starting point for removing the chamfered portion 17A in the chamfered portion removing step described later. For example, the modified layers of the above types 1 to 3 may be appropriately combined, or may be in a different form. In the following description, an example is described in which a laminated wafer W is processed on the first wafer 10A, in which the above type 1 consisting of the modified layer 100 is formed as a separation starting point.

[0030] After the above-mentioned separation starting point forming step is performed, the laminated wafers W are transported to a grinding device 30 (only a part of which is shown) shown in Fig. 4 in order to perform a grinding step on the laminated wafers W. The grinding device 30 includes a chuck table 31 capable of rotating while holding the laminated wafers W, and a grinding means 32 for performing a grinding process on the laminated wafers W. The grinding means 32 includes a rotatable and vertically movable spindle 33, a wheel mount 34 attached to the tip of the spindle 33 and rotating with the rotation of the spindle 33, and a grinding wheel 35 attached to the lower surface of the wheel mount 34 and having a diameter smaller than the diameter of the laminated wafers W and having a grinding wheel 36 arranged in an annular shape on the lower surface side.

[0031] Once the stacked wafers W are transported to the grinding device 30 described above, the back surface 10Ab of the first wafer 10A to be ground is exposed upward and placed on the chuck table 31, and the suction means (not shown) is activated to hold the wafer by suction (holding process).

[0032] Next, the spindle 33 is rotated in the direction indicated by the arrow R2 at a predetermined rotation speed (for example, 6000 rpm), and the chuck table 31 is rotated in the direction indicated by the arrow R3 at a predetermined rotation speed (for example, 300 rpm). Then, the grinding wheel 34 rotated together with the spindle 33 is lowered in the direction indicated by the arrow R4 to bring the grinding wheel 36 into contact with the back surface 10Ab of the first wafer 10A of the laminated wafer W. The grinding wheel 36 is brought into contact with a region of the back surface 10Ab corresponding to the above-mentioned device region 16A, and is fed for grinding at a speed of, for example, 1.0 μm / sec in the direction indicated by the arrow R4. In this grinding process, the inner region is ground along the boundary portion 15A where the above-mentioned modified layer 100 is formed, and the outer portion of the device region 16A, i.e., the region corresponding to the outer peripheral excess region 18A including the chamfered portion 17A, is not ground. As a result, as shown on the left side of Figure 4, a recess 19A is formed in the central region of the back surface 10Ab corresponding to the ground device region 16A, and a ring-shaped protrusion 19B having a step between itself and the bottom surface of the recess 19A is formed in the region corresponding to the above-mentioned peripheral excess region 18A (grinding process).

[0033] In this embodiment, as described above, before the grinding step is performed, the first wafer 10A of the laminated wafer W is subjected to a separation starting point forming step, and a modified layer 100 serving as a separation starting point for separating the effective area 16A and the outer circumferential surplus area 18A including the chamfered portion 17A is formed at the boundary portion 15A between the effective area 16A and the outer circumferential surplus area 18A including the chamfered portion 17A. Then, as the grinding step described above is performed and the grinding process progresses, a recess 19A is formed on the back surface 10Ab of the first wafer 10A, and a ring-shaped protrusion 19B is formed so as to surround the recess 19A. As a result, an external force is effectively applied to the ring-shaped protrusion 19B by the grinding wheel 35 equipped with the grinding wheel 36. As a result, the outer circumferential surplus area 18A including the chamfered portion 17A constituting the protrusion 19B is destroyed and separated from the effective area 16A with the modified layer 100 described above as a separation starting point, and the chamfered portion 17A is removed together with the outer circumferential surplus area 18A as shown on the right side of FIG. 4 (chamfered portion removing step).

[0034] In the above embodiment, an example is shown in which the separation starting point forming step is performed before the grinding step, and the chamfer removing step is performed together with the grinding step, but the present invention is not limited to this. For example, the separation starting point forming step can be performed after the grinding step, and then the chamfer removing step can be performed. A wafer processing method in which the separation starting point forming step and the chamfer removing step are performed after the grinding step is described below.

[0035] Once the unprocessed stacked wafers W described with reference to Fig. 1 have been prepared, they are transported to a grinding device 30 (only a portion of which is shown) shown in Fig. 5. The grinding device 30 shown in Fig. 5 is the same as the grinding device 30 described with reference to Fig. 4, and detailed description thereof will be omitted. Once the stacked wafers W have been transported to the grinding device 30, the back surface 10Ab of the first wafer 10A constituting the stacked wafers W is exposed upward and placed on a chuck table 31, and a suction means (not shown) is operated to hold the stacked wafers W by suction (holding step).

[0036] Next, as shown in FIG. 5, the spindle 33 is rotated in the direction indicated by the arrow R2 at a predetermined rotation speed (for example, 6000 rpm), and the chuck table 31 is rotated in the direction indicated by the arrow R3 at a predetermined rotation speed (for example, 300 rpm). Then, the grinding wheel 35 rotated together with the spindle 33 is lowered in the direction indicated by the arrow R4, and the grinding wheel 36 is brought into contact with the back surface 10Ab of the first wafer 10A of the laminated wafer W. The grinding wheel 36 is brought into contact with the region of the back surface 10Ab corresponding to the above-mentioned device region 16A, and is fed for grinding at a speed of, for example, 1.0 μm / sec in the direction indicated by the arrow R4. Then, as shown in FIG. 5, a recess 19A having a desired thickness is formed in the center region corresponding to the ground device region 16A, and a region corresponding to the outer peripheral excess region 18A including the chamfered portion 17A is not ground, and a ring-shaped protrusion 19B having a step between the recess 19A and the region is formed (grinding process).

[0037] After carrying out the grinding step described above, the laminated wafer W on which the recess 19A and the ring-shaped protrusion 19B are formed is transferred to a laser processing device 20 (only a part of which is shown) shown in Fig. 6, where a separation start point forming step is carried out. Note that the laser processing device 20 is the same device as the laser processing device 20 described based on Fig. 2, and detailed description thereof will be omitted.

[0038] 6(a), the stacked wafers W on which the grinding process has been performed are placed on the chuck table 21 with the back surface 10Ab of the first wafer 10A on which the recess 19A and the ring-shaped protrusion 19B are formed facing upward and the second wafer 10B facing downward, and the stacked wafers W are suction-held by operating the suction means (not shown). Alignment is performed on the stacked wafers W suction-held on the chuck table 21 using an alignment means and a height detection means (not shown) arranged on the laser processing device 20 to detect the position of the outer circumferential end portion on which the chamfered portion 17A of the first wafer 10A is formed and the center position of the first wafer 10A, and the height of the upper surface of the back surface 10Ab of the first wafer 10A is detected, and the step portion formed by the recess 19A and the ring-shaped protrusion 19B is detected as the processing position to be irradiated with the laser beam LB. The machining position is set on the outer periphery of the recess 19A in a region in contact with the protrusion 19B.

[0039] As described above, when the processing position to be irradiated with the laser beam LB is detected, the chuck table 21 is moved to position the processing position directly below the condenser 23 of the laser beam application means 22 as shown in Fig. 6(a). Next, the condensing point of the laser beam LB is positioned inside the processing position from the back surface 10Ab side of the first wafer 10A and irradiated, and the chuck table 21 is rotated in the direction indicated by the arrow R1 to form the above-mentioned type 1 modified layer 100 that serves as a separation starting point over the entire circumference along the processing position as shown in Fig. 6(b) (separation starting point forming step). Note that the separation starting point formed here is not limited to the above-mentioned type 1 modified layer 100, and may be the above-mentioned type 2 or 3 modified layer, or may be a modified layer of another form.

[0040] As described above, after the grinding process is performed and then the separation starting point forming process is performed, a chamfer removing process is performed in which an external force is applied to the ring-shaped convex portion 19B of the stacked wafer W in which the separation starting point is formed, thereby removing the outer peripheral excess region 18A including the chamfered portion 17A from the stacked wafer W.

[0041] In the chamfered portion removing step performed after the separation start point forming step, the means for applying an external force to the ring-shaped protrusion 19B is not particularly limited, but for example, an external force applying means 40 as shown in FIG. 7 can be used. The external force applying means 40 has claws 41a and 41b at its tip, and the claws 41a and 41b form a storage section 43 for storing the protrusion 19B. The length of one of the claws 41b is set short in accordance with the depth of the recess 19A, and the length of the other claw 41a is set relatively longer than the claw 41b so as to support the chamfered portion 17A of the first wafer 10A from the outside. As shown in FIG. 7(a), the external force applying means 40 is lowered in the direction indicated by the arrow R5 with respect to the protrusion 19B of the stacked wafer W that has been subjected to the grinding step and the separation start point forming step, and the protrusion 19B is stored in the storage section 43. 7(b), the external force applying means 40 is tilted in the direction indicated by the arrow R6 in the figure, so that the claws 41a and 41b apply an external force to the convex portion 19B, destroying the convex portion 19B along the separation starting point (modified layer 100), and the convex portion 19B can be separated from the outer peripheral edge 10Ac of the first wafer 10A. Note that, since the convex portion 19B separated from the outer peripheral edge 10Ac of the first wafer 10A is only a part of it when viewed in the circumferential direction as shown in the figure, the above-mentioned external force applying means 40 is applied while rotating the chuck table 21 holding the stacked wafers W by a predetermined angle, for example, 45° at a time, so that the convex portion 19B can be sequentially separated from the outer peripheral edge 10Ac of the first wafer 10A as described above, and the convex portion 19B can be completely removed over the entire circumference of the first wafer 10A.

[0042] In the chamfer removing step of the present invention, the means for applying an external force to the protrusion 19B is not limited to the external force applying means 40 described above, and for example, a chamfer removing device 50 can be used which holds and rotates the stacked wafers W on a spinner table 52 as shown in Figures 8 and 9, and applies an external force to the ring-shaped protrusion 19B by centrifugal force to remove the chamfer 17A together with the outer peripheral excess region 18A from the stacked wafers W.

[0043] As shown in FIG. 8, the chamfer removing device 50 includes a spinner table 52 and a cover part 51 that surrounds the entire side of the spinner table 52 and has a circular opening 51a at the top. For convenience of explanation, FIG. 8 shows a cutaway part of the front side of the cover part 51. The spinner table 52 is composed of an adsorption chuck 52a formed of a porous material having air permeability, and a frame part 52b that surrounds the adsorption chuck 52a. The adsorption chuck 52a is connected to a suction means (not shown) to generate negative pressure on the upper surface of the adsorption chuck 52a. A rotating shaft 53 is connected to the spinner table 52, and the rotating shaft 53 is driven by a motor 54 to rotate the spinner table 52. A plurality of air pistons 55 are arranged on the outer periphery of the motor 54. The spinner table 52, the rotating shaft 53, and the motor 54 can be raised and lowered together by moving a rod 56 up and down by the air piston 55. The above-mentioned rotating shaft 53 and motor 54 function as a base that supports the spinner table 52 .

[0044] As can be seen from Fig. 8, the cover part 51 has an annular bottom wall 51c, an outer wall 51d erected on the outer periphery of the bottom wall 51c, and an inner wall 51e erected on the inner periphery of the bottom wall 51c to form an internal space 58, and also has a plurality of legs 51b supporting the cover part 51. The outer wall 51d is gradually reduced in diameter toward the top to form a curved shape, and the circular opening 51a is formed with dimensions slightly larger than the outer dimensions of the frame part 52b of the spinner table 52. A skirt part 57 is disposed on the rotating shaft 53 and rotates together with the rotating shaft 53 below the spinner table 52. The chamfer removing device 50 has a configuration generally as described above, and the procedure for performing the chamfer removing process using the chamfer removing device 50 will be described with reference to Fig. 8 and Fig. 9. In FIG. 9, for convenience of explanation, the cover portion 51 and the skirt portion 57 are shown in cross section, and the leg portion 51b of the cover portion 51 and the air piston 55 are omitted.

[0045] When performing the chamfered portion removing step, the above-mentioned air piston 55 is operated to raise the spinner table 52 in the internal space 58 of the cover part 51, and the spinner table 52 is positioned in the vicinity of the opening 51a of the cover part 51, which is the loading / unloading position for loading / unloading the laminated wafers W, as shown in Fig. 8. Then, the laminated wafer W which has been subjected to the grinding step and the separation start point forming step and has the recessed portion 19A and the ring-shaped protruding portion 19B formed therein and the modified layer 100 serving as the separation start point is transported and placed on the spinner table 52 with the first wafer 10A side facing upward and the second wafer 10B side facing downward, and the suction means (not shown) is operated to suction and hold the laminated wafer W on the spinner table 52.

[0046] Next, the air piston 55 is operated to lower the spinner table 52 and position it at the lower chamfer removal position in the internal space 58 as shown in Fig. 9. At this time, the skirt portion 57 is in a state of covering the outside of the inner wall 51e of the cover portion 51.

[0047] Next, the motor 54 is operated to rotate the rotating shaft 53 for rotating the spinner table 52 at high speed for a predetermined time in the direction indicated by the arrow R7 in FIG. 9. The rotation speed of the rotating shaft 53 is set to, for example, 1000 to 3000 rpm. By rotating the spinner table 52 at high speed in this manner, a strong centrifugal force effectively acts on the convex portion 19B of the first wafer 10A. As a result, the convex portion 19B is broken starting from the separation origin (modified layer 100) formed by the above-mentioned separation origin forming step, separated from the effective area 16A, and scattered from the outer peripheral end 10Ac of the first wafer 10A into the internal space 58 of the cover part 51. As a result, the convex portion 19B constituted by the outer peripheral excess area 18A including the chamfered portion 17A is removed from the effective area 16A of the first wafer 10A, and the chamfered portion removing step is completed. At this time, since the outer wall 51d of the cover part 51 is formed so as to have a smaller diameter going upward as described above, the scattered convex parts 19B fall along the inner surface of the outer wall 51d of the cover part 51, and are prevented from scattering to the outside of the cover part 51. The convex parts 19B removed from the first wafer 10A accumulate on the bottom wall 51c of the cover part 51, and are periodically collected after this chamfer removing step is performed on the multiple stacked wafers W.

[0048] After the above-mentioned chamfered portion removing step is completed, a finish grinding step may be performed in which the back surface 10Ab of the first wafer 10A of the stacked wafers W is further ground to a desired thickness. In the following description, a mode for performing the finish grinding step in which the back surface 10Ab of the first wafer 10A of the stacked wafers W from which the convex portion 19B has been removed by the above-mentioned chamfered portion removing step is ground to a desired finishing thickness will be described.

[0049] The stacked wafers W that have been subjected to the chamfered portion removing process are transported to a grinding device 60 (only a part of which is shown) shown on the right side of Fig. 10. As shown in the figure, the grinding device 60 is equipped with a grinding means 62 for thinning a workpiece that is suction-held on a chuck table 61. The grinding means 62 is equipped with a rotating spindle 62a that is rotated by a rotation drive mechanism (not shown), a wheel mount 62b that is attached to the lower end of the rotating spindle 62a, and a grinding wheel 62c that is attached to the lower surface of the wheel mount 62b, and a plurality of grinding stones 62d are annularly arranged on the lower surface of the grinding wheel 62c.

[0050] As shown in the figure, the stacked wafers W are transported to a grinding device 60, placed on a chuck table 61 with the second wafer 10B side facing downward, and suction-holding is performed by operating a suction means (not shown). Next, the rotating spindle 62a of the grinding means 62 is rotated in the direction indicated by an arrow R8 in FIG. 10 at, for example, 6000 rpm, while the chuck table 61 is rotated in the direction indicated by an arrow R9 at, for example, 300 rpm. Then, while supplying grinding water onto the back surface 10Ab of the first wafer 10A by a grinding water supplying means (not shown), the grinding wheel 62c is lowered in the downward direction indicated by an arrow R10, and the grinding stone 62d is brought into contact with the back surface 10Ab of the first wafer 10A, and is fed for grinding in the direction indicated by the arrow R10 at a grinding feed rate of, for example, 1.0 μm / sec. At this time, grinding can be performed while measuring the thickness of the stacked wafers W by a contact or non-contact measuring gauge (not shown). When the back surface 10Ab of the first wafer 10A is ground by a predetermined amount to obtain the desired finishing thickness of the laminated wafers W, the grinding means 62 is stopped and retreated upward, completing the finish grinding process. After the finish grinding process is completed, cleaning, drying, and other processes (details of which are omitted) are appropriately performed.

[0051] As described above, in the laminated wafer W that has been subjected to the grinding process and the separation starting point formation process in the wafer processing method of this embodiment, a thinned recess 19A is formed in the area corresponding to the effective area 16A, and the chamfered portion 17A and the peripheral surplus area 18A are left on the outer periphery to form a ring-shaped protrusion 19B. Therefore, it becomes possible to relatively easily remove the protrusion 19B composed of the peripheral surplus area 18A including the chamfered portion 17A from the recess 19A, thereby eliminating the problem that it is difficult to remove the peripheral surplus area 18A including the chamfered portion 17A.

[0052] In addition, since the chamfered portion 17A can be easily removed, the chamfered portion 17A is prevented from remaining on the outer periphery of the first wafer 10A, which eliminates problems such as the remaining portion falling off in a later process and becoming a source of contamination, or causing chipping of the device chips when the stacked wafers W are divided into individual device chips.

[0053] In the above embodiment, an example of processing a laminated wafer W by applying the wafer processing method of the present embodiment is shown, but the wafer processed by the present invention is not limited to the laminated wafer W described above, and may be a single wafer 10C as shown in FIG. 1(b), and may include various wafers having an effective area and a chamfered portion at the edge of the outer periphery surrounding the effective area. The wafer processed by the present invention may be, for example, a gallium nitride (GaN) wafer, a gallium arsenide (GaAs) wafer, a lithium tantalate (LiTaO3) wafer, or a lithium niobate (LiNbO3) wafer, or may be a wafer (e.g., a glass wafer) in which no device is formed in the central area called the effective area, and the central area is processed later and used as a product. [Explanation of symbols]

[0054] 10A: First wafer 10Aa: Surface 10Ab: Back 12A: Device 14A: Planned division line 15A: Border 16A: Effective area 17A: Chamfered part 18A: Surplus outer area 19A: Recess 19B: Convex 10B: Second wafer 10Ba: Surface 10Bb: Back side 10C: Wafer (single wafer) 10Ca: surface 10Cb: Back side 12C:Device 14C: Planned division line 15C: Border 16C: Effective area 17C: Chamfered part 18C: Surplus outer area 20: Laser processing equipment 21: Chuck table 22: Laser beam irradiation means 23: Concentrator 30: Grinding equipment 31: Chuck table 32: Grinding means 33: Rotating spindle 34: Wheel mount 35: Grinding wheel 36: Grinding wheel 40: External force application means 41a, 41b: Claw part 43: Storage unit 50: Chamfer removal device 51: Cover part 51a: Opening 51b: Legs 51c: Bottom wall 51d: Exterior wall 51e:Inner wall 52: Spinner table 53: Rotating shaft 54: Motor 55: Air piston 56: Rod 57: Skirt Club 58: Interior space 60: Grinding equipment 61: Chuck table 62: Grinding means 62a: Rotating spindle 62b: Wheel mount 62c: Grinding wheel 62d: Grinding wheel 100: Modified layer 101: Crack 102, 103: Modified layer 104, 105, 106: Modified layers W: Stacked wafer

Claims

1. A wafer processing method for grinding a back surface of a wafer having an effective area on a front surface and an outer peripheral surplus area surrounding the effective area, the back surface of the wafer being formed with a chamfered portion in the outer peripheral surplus area, comprising: a holding step of holding the wafer on a chuck table with the back surface exposed; a grinding process in which a grinding wheel having a diameter smaller than that of the wafer is positioned inside the outer peripheral excess region to grind the back surface of the wafer, thereby grinding the effective region to a predetermined thickness and forming a ring-shaped protrusion in the outer peripheral excess region; a separation starting point forming step of forming a separation starting point for separating the outer peripheral excess area from the effective area before or after the grinding step; a chamfer removing step of applying an external force to the ring-shaped protrusion of the wafer on which the separation starting points are formed, thereby removing the chamfer from the wafer together with the outer peripheral excess region; A wafer processing method comprising the steps of:

2. 2. The wafer processing method according to claim 1, wherein in the chamfer removing step, the wafer is held on a spinner table and rotated, and an external force is applied to the ring-shaped convex portion by centrifugal force to remove the chamfer from the wafer together with the peripheral excess region.

3. When the separation starting point forming step is performed before the grinding step, The wafer processing method according to claim 1, wherein in the grinding step, the chamfer removing step is carried out by applying an external force to the ring-shaped convex portion with the grinding wheel to remove the chamfer from the wafer together with the peripheral excess region.

4. 2. The method for processing a wafer according to claim 1, wherein the wafer is a laminated wafer in which the effective region side of the wafer is laminated on another wafer so as to face each other.

5. A wafer processing method as described in claim 1, wherein in the separation starting point formation step, a focal point of a laser beam having a wavelength that is transparent to the wafer is positioned at the boundary between the effective area and the peripheral excess area and irradiated to form a ring-shaped modified layer at the boundary.

6. 2. The wafer processing method according to claim 1, further comprising the step of: performing a finish grinding step of further grinding the back surface of the wafer to a desired thickness after the chamfer removing step is performed.

7. 2. The wafer processing method according to claim 1, wherein the effective area of ​​the wafer is a device area in which a plurality of devices are partitioned by planned division lines.

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