Wafer Separation Method

Abstract

To provide a wafer separation method capable of stably separating a wafer whose outer periphery is chamfered.SOLUTION: Prior to forming a separation initiation point inside a wafer, the wafer is processed so that a portion of the wafer is removed along a curved portion of the outer surface (chamfered outer surface). This makes it possible to form a modified layer and cracks inside the wafer that serve as a separation initiation point without causing diffuse reflection of a laser beam and / or a shift in the focus point at the curved portion of the outer surface. As a result, the wafer can be stably separated.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for separating a wafer. [Background technology]

[0002] Chips including power devices such as inverters or converters are generally manufactured by dividing a wafer having a large number of power devices formed on its surface into regions including individual power devices. For example, the wafer is thinned to a predetermined thickness by grinding the back side using a grinding device, and then divided into individual chips using a processing device such as a cutting device and a laser processing device.

[0003] In recent years, silicon carbide (SiC) has been attracting attention as a material for next-generation power devices. However, silicon carbide has a very high hardness. Therefore, when manufacturing chips including power devices using wafers made of silicon carbide, various problems can occur.

[0004] For example, when a wafer made of silicon carbide is ground using a grinding device, the grinding wheel used for grinding may be worn down, which may result in frequent replacement of the grinding wheel, resulting in a decrease in chip manufacturing efficiency and an increase in manufacturing costs.

[0005] A method using a laser beam is also known as a method for thinning a wafer (see, for example, Patent Document 1). In this method, a laser beam is irradiated onto a wafer to form a modified layer and cracks inside the wafer, and then an external force is applied to the wafer to separate the wafer using the modified layer and cracks as separation starting points.

[0006] In addition, when the wafer is transported to be processed in various steps, the wafer may be cracked or chipped at its outer periphery. As a method for preventing such cracking and chipping, a method of chamfering the outer periphery of the wafer, that is, a method of grinding the outer periphery so that the outer periphery of the wafer is curved convexly outward, is known (for example, see Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2017-28072 A [Patent Document 2] JP 2017-183503 A Summary of the Invention [Problem to be solved by the invention]

[0008] When a wafer having a chamfered outer periphery is separated using the method disclosed in Patent Document 1, the laser beam may be diffusely reflected due to the unevenness on the outer periphery. In this case, the laser beam may not be focused inside the outer periphery of the wafer, and modified layers and cracks that serve as separation starting points may not be formed inside the outer periphery.

[0009] In addition, if the outer peripheral surface is curved, the position of the focal point of the laser beam (depth from the surface of the wafer) may deviate from the expected position. In this case, even if a separation starting point is formed inside the outer peripheral portion, the separation starting point formed on the outer peripheral portion will be formed at a different position (depth from the surface of the wafer) from the separation starting points formed in other portions.

[0010] Therefore, when a laser beam is irradiated to the chamfered outer periphery of a wafer, the wafer may not be separated, or the wafer may be separated into two wafers having different thicknesses between the outer periphery and the remaining portion. In view of this, an object of the present invention is to provide a wafer separation method capable of stably separating a wafer having a chamfered outer periphery. [Means for solving the problem]

[0011] According to one aspect of the present invention, there is provided a wafer separation method for separating a wafer having a first surface, a second surface opposite to the first surface, and an outer circumferential surface located between the first surface and the second surface, the outer circumferential surface comprising a curved portion curved convexly outward, into two pieces, a first surface side and a second surface side, the method comprising: a processing step of processing the wafer so as to remove a part of the wafer along the curved portion; a separation origin forming step of, after the processing step, positioning a focal point of a laser beam having a wavelength that is transparent to the wafer inside the wafer, and irradiating the wafer with the laser beam while moving the focal point and the wafer relatively so that the focal point is maintained inside the wafer, thereby forming a separation origin inside the wafer; and a separation step of, after the separation origin forming step, applying an external force to separate the wafer from the separation origin into a wafer having the first surface and a wafer having the second surface, wherein in the processing step, The wafer is cut into by a cutting blade.According to another aspect of the present invention, there is provided a wafer separation method for separating a wafer having a first surface, a second surface opposite to the first surface, and an outer circumferential surface located between the first surface and the second surface, the outer circumferential surface being curved convexly outward, into two pieces, one on the first surface side and the other on the second surface side, the method including the steps of: processing the wafer so as to remove a part of the wafer along the curved portion; a separation step of forming a separation origin inside the wafer by irradiating the laser beam while moving the wafer relative to the wafer, and a separation step of applying an external force after the separation origin forming step to separate the wafer from the separation origin into a wafer having the first surface and a wafer having the second surface, wherein in the processing step, a part of the first surface side of the curved portion is removed from the first surface side of the wafer, and in the separation origin forming step, the focal point is positioned at a depth between the first surface of the wafer and the remaining curved portion.

[0012] Preferably, the curved portion has a first portion extending in an arc shape and a second portion extending in a straight line, and in the processing step, the wafer is moved along the first portion. The curved portion A portion of the wafer is removed in an arc shape, and the second portion of the wafer is removed along the arc shape. The curved portion The wafer is processed so that a portion is removed in a linear or arc shape.

[0016] Furthermore, the processing step preferably includes cutting a cutting blade into the wafer to remove a portion of the wafer. Effect of the Invention

[0017] In the present invention, prior to forming a separation starting point inside the wafer, the wafer is processed so as to remove a part of the wafer along the curved portion (chamfered outer periphery) of the outer periphery. This makes it possible to form a modified layer and a crack that will become a separation starting point inside the wafer without causing diffuse reflection of the laser beam at the curved portion of the outer periphery and / or shifting of the focal point. As a result, the wafer can be stably separated. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1(A) is a top view that typically shows a wafer, and FIG. 1(B) is a cross-sectional view that typically shows the wafer. [Diagram 2] FIG. 2 is a flow chart showing an example of a wafer separation method. [Diagram 3] FIG. 3 is a partial cross-sectional side view that illustrates a processing step of full-cut trimming a wafer. [Figure 4] FIG. 4 is a partial cross-sectional side view that illustrates a processing step of half-cut trimming a wafer. [Diagram 5] FIG. 5 is a partial cross-sectional side view that illustrates a processing step for forming a groove along a curved portion in a wafer. [Figure 6] Each of FIG. 6(A), FIG. 6(B), and FIG. 6(C) is a cross-sectional view that typically shows a wafer processed in a processing step. [Figure 7] FIG. 7 is a partial cross-sectional side view illustrating a separation start point forming step of forming a separation start point on a full-cut trimmed wafer. [Figure 8] FIG. 8 is a partial cross-sectional side view that illustrates a separation start point forming step of forming a separation start point on a half-cut trimmed wafer. [Figure 9] FIG. 9 is a partial cross-sectional side view that illustrates a separation start point forming step of forming a separation start point on a wafer in which a groove is formed along a curved portion. [Figure 10] FIG. 10 is a partial cross-sectional side view that illustrates a separation step for separating the wafer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] An embodiment of the present invention will be described with reference to the accompanying drawings. Figures 1(A) and 1(B) are a top view and a cross-sectional view, respectively, that show a wafer to be separated into two wafers. The wafer 11 shown in Figures 1(A) and 1(B) is made of, for example, silicon carbide (SiC).

[0020] The wafer 11 has a first surface (front surface) 11a, a second surface (back surface) 11b opposite to the first surface 11a, and an outer peripheral surface 11c located between the first surface 11a and the second surface 11b. The first surface 11a side of the wafer 11 is divided into a plurality of regions by a plurality of intended division lines 13 that intersect with each other, and a device 15 such as an inverter or a converter is formed in each region.

[0021] Two flat portions indicating crystal orientation, so-called primary orientation flat (orientation flat) 17a and secondary orientation flat 17b, are formed on the outer peripheral surface 11c of wafer 11. That is, the portion of outer peripheral surface 11c where primary orientation flat 17a and secondary orientation flat 17b are formed extends linearly, and the other portion extends in an arc shape.

[0022] The outer periphery of wafer 11 is chamfered so that outer periphery surface 11c is curved outwardly and convexly. As a result, outer periphery surface 11c has a curved portion formed by the chamfer. This curved portion extends linearly in the area where primary orientation flat 17a and secondary orientation flat 17b are formed, and extends in an arc shape in the other areas.

[0023] There are no limitations on the material, shape, structure, size, etc. of the wafer 11. The wafer 11 may be made of other materials such as semiconductors such as silicon (Si), ceramics, resin, metal, etc. Also, the outer peripheral surface 11c of the wafer 11 may have a V-shaped notch, a so-called notch, formed thereon to indicate the crystal orientation instead of an orientation flat.

[0024] Furthermore, the entire outer periphery of wafer 11 does not have to be chamfered. For example, the portions of the outer periphery of wafer 11 where primary orientation flat 17a and secondary orientation flat 17b are formed may not be chamfered, and only the remaining portions may be chamfered. In this case, outer periphery 11c includes a curved portion formed by chamfering and a non-chamfered portion that is not chamfered.

[0025] Similarly, there is no limitation on the type, number, shape, structure, size, arrangement, etc. of the device 15. For example, the device 15 may be an IC (Integrated Circuit) or an LSI (Large Scale Integration), etc. Also, the device 15 does not have to be formed on the wafer 11.

[0026] Fig. 2 is a flow chart showing an example of a wafer separation method for separating the wafer 11 shown in Fig. 1(A) and Fig. 1(B) into two pieces (a wafer having a first surface 11a and a wafer having a second surface 11b) of the first surface side and the second surface side. In the wafer separation method shown in Fig. 2, first, the wafer 11 is processed so as to remove a part of the wafer 11 along the curved portion of the outer circumferential surface 11c (processing step: S1).

[0027] In the processing step (S1), the entire curved portion may be removed from the wafer 11 (full cut trim) to flatten the outer peripheral surface of the wafer 11, or a part of the curved portion on the first surface 11a side of the wafer 11 may be removed from the first surface 11a side of the wafer 11 (half cut trim) to form a step on the outer peripheral portion of the wafer 11. Furthermore, in the processing step (S1), a part of the first surface 11a side of the wafer 11 may be removed from the first surface 11a side to form a groove along the curved portion of the outer peripheral surface 11c. That is, in the processing step (S1), at least a part of the first surface 11a side of the wafer 11 is removed along the curved portion of the outer peripheral surface 11c.

[0028] Below, the processing step (S1-1) of full-cut trimming the wafer 11 to flatten the outer peripheral surface of the wafer 11, the processing step (S1-2) of half-cut trimming the wafer 11 to form a step on the outer peripheral portion of the wafer 11, and the processing step (S1-3) of removing a portion of the first surface 11a side of the wafer 11 to form a groove along the curved portion of the outer peripheral surface 11c will be described in order with reference to Figures 3 to 5.

[0029] Fig. 3 is a partial cross-sectional side view that shows a processing step (S1-1) of fully cutting and trimming the wafer 11 to flatten the outer peripheral surface of the wafer 11. Specifically, in the processing step (S1-1) shown in Fig. 3, the cutting device 2 cuts and removes all of the curved portion from the first surface 11a side of the wafer 11 having the tape 19 attached to the second surface 11b. The Z-axis direction shown in Fig. 3 is approximately parallel to the vertical direction.

[0030] The cutting device 2 has a cylindrical θ table 4. A disk-shaped chuck table 6 on which the wafer 11 is placed via a tape 19 is provided on the upper portion of the θ table 4. The θ table 4 is also connected to a rotation drive source (not shown) such as a motor. When the rotation drive source is operated, the θ table 4 and the chuck table 6 rotate about an axis that is a straight line passing through the center of the chuck table 6 along the Z-axis direction.

[0031] The chuck table 6 has a frame 6a made of a metal such as stainless steel. The frame 6a has a disk-shaped bottom wall and an annular side wall extending upward from the outer periphery of the bottom wall, and a recess is defined by the side wall. A disk-shaped porous plate (not shown) made of porous ceramics and having a diameter approximately the same as the inner diameter of the recess is fixed in the recess.

[0032] The porous plate of the chuck table 6 is connected to a suction source (not shown) such as a vacuum pump through a flow path formed in the frame 6a. When this suction source is operated, negative pressure is generated on the upper surface of the porous plate (the holding surface of the chuck table 6). Due to the generation of this negative pressure, the wafer 11 placed on the chuck table 6 is sucked and held to the chuck table 6 via the tape 19.

[0033] Furthermore, the θ table 4 and the chuck table 6 are connected to an X-axis direction moving mechanism (not shown). When this X-axis direction moving mechanism is operated, the θ table 4 and the chuck table 6 move in a direction perpendicular to the Z-axis direction (the X-axis direction).

[0034] A cutting unit 8 is provided above the chuck table 6. The cutting unit 8 is connected to a Y-axis direction moving mechanism (not shown) and a Z-axis direction moving mechanism (not shown). When the Y-axis direction moving mechanism is operated, the cutting unit 8 moves in a direction (Y-axis direction) perpendicular to the Z-axis direction and perpendicular to the X-axis direction. When the Z-axis direction moving mechanism is operated, the cutting unit 8 moves in the Z-axis direction, i.e., the cutting unit 8 moves up and down.

[0035] The cutting unit 8 has a cylindrical spindle 10 extending in the Y-axis direction. A cutting blade 12 having an annular cutting edge is attached to one end of the spindle 10. The cutting blade 12 is a hub-type cutting blade that is integrally formed with an annular base made of, for example, a metal or the like and an annular cutting edge that runs along the outer periphery of the base.

[0036] The cutting edge of the hub-type cutting blade is made of an electroformed grinding stone in which abrasive grains made of diamond or cubic boron nitride (cBN) are fixed with a binder such as nickel. Also, a washer-type cutting blade made of an annular cutting edge in which abrasive grains are fixed with a binder such as metal, ceramic, or resin may be used as the cutting blade 12.

[0037] The other end of the spindle is connected to a rotary drive source (not shown) such as a motor. When the rotary drive source operates, the cutting blade 12 rotates together with the spindle 10 around an axis that is a straight line passing through the center of the spindle 10 along the Y-axis direction.

[0038] In the processing step (S1) shown in FIG. 3, for example, the arc-shaped outer peripheral surface 11c of wafer 11, i.e., all of the curved portions of outer peripheral surface 11c other than the portions where primary orientation flat 17a and secondary orientation flat 17b are formed, are removed, and then all of the curved portions of outer peripheral surface 11c in the portions where primary orientation flat 17a and secondary orientation flat 17b are formed are removed.

[0039] For example, first, the chuck table 6 and / or the cutting unit 8 are positioned so that the lower end of the cutting blade 12 is located directly above the arc-shaped outer circumferential surface 11c of the wafer 11. Next, the cutting unit 8 is lowered until the cutting blade 12 comes into contact with the tape 19 while the cutting blade 12 is rotating.

[0040] Next, the chuck table 6 is rotated at least one revolution while the cutting blade 12 is being rotated. This removes all of the curved portions of the arc-shaped outer peripheral surface 11c of the wafer 11. That is, all of the curved portions extending in an arc shape are removed in an arc shape.

[0041] Next, chuck table 6 is rotated so that primary orientation flat 17a or secondary orientation flat 17b is parallel to the X-axis direction. Next, chuck table 6 is moved along the X-axis direction so that cutting blade 12 is separated from wafer 11. Next, cutting unit 8 is moved along the Y-axis direction so that cutting blade 12 is positioned in the X-axis direction when viewed from primary orientation flat 17a or secondary orientation flat 17b.

[0042] Next, the cutting unit 8 is lowered so that the bottom end of the cutting blade 12 is lower than the top surface of the tape 19 and higher than the bottom surface of the tape 19. Next, while the cutting blade 12 is rotating, the chuck table 6 is moved along the X-axis direction so that the wafer 11 passes from one end of the cutting blade 12 to the other end in the X-axis direction.

[0043] As a result, all of the curved portions of outer circumferential surface 11c where primary orientation flat 17a and secondary orientation flat 17b are formed are removed, that is, all of the curved portions that extend linearly are removed linearly.

[0044] Fig. 4 is a partial cross-sectional side view that typically shows a processing step (S1-2) of half-cut trimming the wafer 11 to form a step on the outer periphery of the wafer 11. Note that the cutting device 2 shown in Fig. 4 is the same as the cutting device 2 shown in Fig. 3, and therefore a description thereof will be omitted.

[0045] In the processing step (S1-2) shown in FIG. 4, for example, a portion of the curved portion of the arc-shaped outer peripheral surface 11c of the wafer 11 on the side of the first surface 11a is removed, and then a portion of the curved portion of the outer peripheral surface 11c on the side of the first surface 11a where the primary orientation flat 17a and the secondary orientation flat 17b are formed is removed.

[0046] For example, first, the chuck table 6 and / or the cutting unit 8 are positioned so that the lower end of the cutting blade 12 is located directly above the arc-shaped outer peripheral surface 11c of the wafer 11. Next, while the cutting blade 12 is rotating, the cutting unit 8 is lowered until the lower end of the cutting blade 12 reaches a position lower than the first surface 11a and higher than the second surface 11b.

[0047] Next, the chuck table 6 is rotated at least one revolution while the cutting blade 12 is being rotated. This removes a part of the first surface 11a side of the curved portion of the arc-shaped outer peripheral surface 11c of the wafer 11. That is, a part of the first surface 11a side of the curved portion extending in an arc shape is removed in an arc shape.

[0048] Next, chuck table 6 is rotated so that primary orientation flat 17a or secondary orientation flat 17b is parallel to the X-axis direction. Next, chuck table 6 is moved along the X-axis direction so that cutting blade 12 is separated from wafer 11. Next, cutting unit 8 is moved along the Y-axis direction so that cutting blade 12 is positioned in the X-axis direction when viewed from primary orientation flat 17a or secondary orientation flat 17b.

[0049] Next, the cutting unit 8 is lowered so that the lower end of the cutting blade 12 is lower than the first surface 11a and higher than the second surface 11b. Next, while the cutting blade 12 is rotating, the chuck table 6 is moved along the X-axis direction so that the wafer 11 passes from one end of the cutting blade 12 to the other end in the X-axis direction.

[0050] This removes a portion of first surface 11a side of the curved portion of outer peripheral surface 11c at the portion where primary orientation flat 17a and secondary orientation flat 17b are formed. That is, a portion of first surface 11a side of the curved portion extending linearly is removed linearly.

[0051] 5 is a partial cross-sectional side view that shows a processing step (S1-3) of forming a groove along a curved portion of the outer circumferential surface 11c by removing a part of the first surface 11a side of the wafer 11 from the first surface 11a side. Note that the cutting device 2 shown in FIG. 5 is the same as the cutting device 2 shown in FIG. 3 and FIG. 4, and therefore the description thereof will be omitted.

[0052] In the processing step (S1-3) shown in FIG. 5, for example, a groove extending in an arc shape along the curved portion of the arc-shaped outer peripheral surface 11c of wafer 11 is formed, and then a groove extending in a straight line along the curved portion of outer peripheral surface 11c in the portion where primary orientation flat 17a and secondary orientation flat 17b are formed is formed.

[0053] For example, first, the chuck table 6 and / or cutting unit 8 are positioned so that the lower end of the cutting blade 12 is located directly above an area whose distance from the center of the wafer 11 is shorter than the distance between the arc-shaped outer peripheral surface 11c and the center of the wafer 11 and longer than the shortest distance between the primary orientation flat 17a and the secondary orientation flat 17b and the center of the wafer 11.

[0054] Next, while the cutting blade 12 is rotating, the cutting unit 8 is lowered until the lower end of the cutting blade 12 reaches a position lower than the first surface 11a and higher than the second surface 11b. Next, while the cutting blade 12 is rotating, the chuck table 6 is rotated at least one revolution.

[0055] This forms a groove extending in an arc shape along the curved portion of the arc-shaped outer circumferential surface 11c of the wafer 11. That is, a part of the first surface 11a side of the wafer 11 is removed in an arc shape along the curved portion extending in an arc shape.

[0056] Next, chuck table 6 is rotated so that primary orientation flat 17a or secondary orientation flat 17b is parallel to the X-axis direction. Next, chuck table 6 is moved along the X-axis direction so that cutting blade 12 is separated from wafer 11. Next, cutting unit 8 is moved along the Y-axis direction so that cutting blade 12 is positioned slightly offset from the X-axis direction toward wafer 11 when viewed from primary orientation flat 17a or secondary orientation flat 17b.

[0057] Next, the cutting unit 8 is lowered so that the lower end of the cutting blade 12 is lower than the first surface 11a and higher than the second surface 11b. Next, while the cutting blade 12 is rotating, the chuck table 6 is moved along the X-axis direction so that the wafer 11 passes from one end of the cutting blade 12 to the other end in the X-axis direction.

[0058] This forms a groove that extends linearly along the curved portion of outer circumferential surface 11c where primary orientation flat 17a and secondary orientation flat 17b are formed. In other words, a portion of first surface 11a of wafer 11 is removed linearly along the linearly extending curved portion.

[0059] Alternatively, in the processing step (S1-3) shown in Fig. 5, a portion of first surface 11a side of wafer 11 may be removed from first surface 11a side to form an annular groove. That is, in the processing step (S1-3) shown in Fig. 5, a groove may be formed that extends in an arc shape along the curved portion of arc-shaped outer peripheral surface 11c of wafer 11 and that extends in an arc shape along the curved portion of outer peripheral surface 11c in the portion where primary orientation flat 17a and secondary orientation flat 17b are formed.

[0060] For example, first, the chuck table 6 and / or the cutting unit 8 are positioned so that the lower end of the cutting blade 12 is located directly above an area whose distance from the center of the wafer 11 is shorter than the shortest distance between the primary orientation flat 17a and the secondary orientation flat 17b and the center of the wafer 11.

[0061] Next, while the cutting blade 12 is rotating, the cutting unit 8 is lowered until the lower end of the cutting blade 12 reaches a position lower than the first surface 11a and higher than the second surface 11b. Next, while the cutting blade 12 is rotating, the chuck table 6 is rotated at least one revolution. As a result, an annular groove is formed on the first surface 11a side of the wafer 11.

[0062] That is, a portion of the first surface 11a side of the wafer 11 is removed in an arc shape along the curved portion that extends in an arc shape (the curved portion of the arc-shaped outer peripheral surface 11c), and a portion of the first surface 11a side of the wafer 11 is removed in an arc shape along the curved portion that extends in a straight line (the curved portion of the outer peripheral surface 11c where the primary orientation flat 17a and the secondary orientation flat 17b are formed).

[0063] Each of Figures 6(A), 6(B), and 6(C) is a cross-sectional view showing a wafer 11 that has been processed in processing step (S1) to remove a portion of the wafer 11 along the curved portion of the outer circumferential surface 11c.

[0064] Specifically, Fig. 6(A) is a cross-sectional view showing a wafer 11 whose outer circumferential surface has been flattened in a processing step (S1-1). Fig. 6(B) is a cross-sectional view showing a wafer 11 whose outer circumferential portion has a step formed thereon in a processing step (S1-2). Fig. 6(C) is a cross-sectional view showing a wafer 11 whose outer circumferential surface 11c has a groove formed thereon along a curved portion thereof in a processing step (S1-3).

[0065] In the wafer separation method shown in FIG. 2, after a processing step (S1), a laser beam is irradiated onto the wafer 11 to form separation start points inside the wafer 11 (separation start point forming step: S2).

[0066] Below, the separation starting point forming step (S2-1) of forming a separation starting point inside the wafer 11 having a flattened outer circumferential surface, the separation starting point forming step (S2-2) of forming a separation starting point inside the wafer 11 having a step formed on the outer circumferential surface, and the separation starting point forming step (S2-3) of forming a separation starting point inside the wafer 11 having a groove formed along the curved portion of the outer circumferential surface 11c will be described in order with reference to Figures 7 to 9.

[0067] Fig. 7 is a partial cross-sectional side view that shows a schematic diagram of a separation starting point forming step (S2-1) for forming a separation starting point inside the wafer 11 whose outer circumferential surface has been flattened in the processing step (S1-1). Specifically, in the separation starting point forming step (S2-1) shown in Fig. 7, a laser beam irradiation device 20 irradiates a laser beam from the second surface 11b side of the wafer 11 having a tape 21 attached to the first surface 11a to form a separation starting point inside the wafer 11. The Z-axis direction shown in Fig. 7 is approximately parallel to the vertical direction.

[0068] The laser beam irradiation device 20 has a cylindrical table base 22. On the upper part of the table base 22, a disk-shaped chuck table 24 is provided on which the wafer 11 is placed with the tape 21 interposed therebetween.

[0069] The chuck table 24 has a frame 24a made of a metal such as stainless steel. The frame 24a has a disk-shaped bottom wall and an annular side wall extending upward from the outer periphery of the bottom wall, and a recess is defined by the side wall. A disk-shaped porous plate (not shown) made of porous ceramics and having a diameter approximately the same as the inner diameter of the recess is fixed in the recess.

[0070] The porous plate of the chuck table 24 is connected to a suction source (not shown) such as a vacuum pump through a flow path formed in the frame 24a. When this suction source is operated, negative pressure is generated on the upper surface of the porous plate (the holding surface of the chuck table 24). Due to the generation of this negative pressure, the wafer 11 placed on the chuck table 24 is sucked and held to the chuck table 24 via the tape 21.

[0071] Furthermore, the table base 22 and the chuck table 24 are connected to a horizontal movement mechanism (not shown). When this horizontal movement mechanism is operated, the table base 22 and the chuck table 24 move in a plane (horizontal plane) perpendicular to the Z-axis direction.

[0072] A head 26 of a laser beam irradiation unit (not shown) is provided above the chuck table 24. The head 26 is connected to a Z-axis direction moving mechanism (not shown). When this Z-axis direction moving mechanism is operated, the head 26 moves in the Z-axis direction, that is, the head 26 moves up and down.

[0073] The laser beam irradiation unit has a laser oscillator that generates a laser beam L having a wavelength that is transparent to the wafer 11. The laser oscillator has a laser medium, such as Nd:YAG, that is suitable for laser oscillation. The laser beam irradiation unit also has an optical system that includes a condenser lens that positions the focal point of the laser beam L at a predetermined height. The condenser lens is housed in the head 26.

[0074] 7, the optical system of the laser beam irradiation unit, for example, the height of the head 26, is set so that the focal point of the laser beam L is positioned inside the wafer 11, and then the chuck table 24 is moved in the horizontal plane while the laser beam L is irradiated. As a result, a modified layer 11d and a crack 11e that become the separation starting points are formed inside the wafer 11.

[0075] Fig. 8 is a partial cross-sectional side view that shows a separation starting point forming step (S2-2) for forming separation starting points inside the wafer 11 having a step formed on the outer periphery in the processing step (S1-2). Note that the laser beam irradiation device 20 shown in Fig. 8 is the same as the laser beam irradiation device 20 shown in Fig. 7, and therefore the description thereof will be omitted.

[0076] In the separation starting point formation step (S2-2) shown in FIG. 8, the optical system of the laser beam irradiation unit, for example, the height of the head 26, is set so that the focal point of the laser beam L is positioned at a depth between the first surface 11a of the wafer 11 and the remaining curved portion 11f, and then the laser beam L is irradiated while moving the chuck table 24 in the horizontal plane.

[0077] Specifically, in the separation starting point formation step (S2-2) shown in FIG. 8, the optical system is set to position the focal point of the laser beam L between a first imaginary plane that passes through a portion of the step formed in the outer periphery that is closest to the first surface 11a and is generally parallel to the first surface 11a and the second surface 11b, and a second imaginary plane that passes through a portion of the step that is closest to the second surface 11b and is generally parallel to the first surface 11a and the second surface 11b.

[0078] As a result, a modified layer 11d and a crack 11e, which serve as separation starting points, are formed at a depth between the first surface 11a of the wafer 11 and the remaining curved portion 11f (i.e., between the first imaginary surface and the second imaginary surface).

[0079] 9 is a partially sectional side view that shows a schematic diagram of a separation starting point forming step (S2-3) for forming a separation starting point inside the wafer 11 in which a groove 11g is formed along the curved portion of the outer circumferential surface 11c in the processing step (S1-3). Note that the laser beam irradiation device 20 shown in FIG. 9 is the same as the laser beam irradiation device 20 shown in FIG. 7 and FIG. 8, and therefore a description thereof will be omitted.

[0080] In the separation starting point formation step (S2-3) shown in FIG. 9, the optical system of the laser beam irradiation unit, for example, the height of the head 26, is set so that the focal point of the laser beam L is positioned at a depth between the first surface 11a of the wafer 11 and the bottom surface of the groove 11g, and then the laser beam L is irradiated while moving the chuck table 24 in the horizontal plane so that the focal point is maintained in the area of ​​the wafer 11 inside the groove 11g.

[0081] Specifically, in the separation starting point formation step (S2-3) shown in FIG. 9, the optical system is set to position the focal point of the laser beam L between a third imaginary plane that passes through a portion of the groove 11g closest to the first surface 11a and is generally parallel to the first surface 11a and the second surface 11b, and a fourth imaginary plane that passes through a portion of the groove 11g closest to the second surface 11b and is generally parallel to the first surface 11a and the second surface 11b.

[0082] As a result, a modified layer 11d and a crack 11e, which will become the starting point of separation, are formed at a depth between the first surface 11a of the wafer 11 and the bottom surface of the groove 11g (that is, between the third imaginary surface and the fourth imaginary surface).

[0083] In the wafer separation method shown in FIG. 2, after the separation starting point formation step (S2), an external force is applied to separate the wafer 11 into two pieces (a wafer having a first surface 11a and a wafer having a second surface 11b) having a first surface side and a second surface side (separation step: S3).

[0084] Fig. 10 is a partial cross-sectional side view that shows a separation step (S3) for separating the wafer 11 in which the modified layer 11d and the crack 11e that become the separation starting points are formed in the separation starting point forming step (S2). Specifically, in the separation step (S3) shown in Fig. 10, an external force is applied to the wafer 11 using an ultrasonic irradiation device 30 to separate the wafer 11 into two wafers.

[0085] The ultrasonic irradiation device 30 has a liquid tank 32 that contains a liquid such as water. A disk-shaped mounting table 34 on which the wafer 11 is placed is provided on the bottom surface of the liquid tank 32. Furthermore, the ultrasonic irradiation device 30 has an ultrasonic irradiation unit 36 ​​that irradiates the liquid contained in the liquid tank 32 with ultrasonic waves.

[0086] 10, for example, an ultrasonic irradiation unit 36 ​​irradiates ultrasonic waves to the liquid contained in the liquid tank 32, thereby applying an external force to the wafer 11 placed on the mounting table 34. As a result, the wafer 11 is separated into two wafers with a surface including the separation starting points of the modified layer 11d and the crack 11e as a separation surface.

[0087] In the wafer separation method of this embodiment, prior to forming a separation starting point inside the wafer 11, the wafer 11 is processed so as to remove a portion of the wafer 11 along the curved portion (chamfered outer periphery) of the outer periphery 11c.

[0088] This makes it possible to form modified layers and cracks that serve as separation starting points inside the wafer 11 without causing diffuse reflection of the laser beam at the curved portion of the outer circumferential surface 11c and / or shifting of the focal point. As a result, the wafer 11 can be stably separated.

[0089] It should be noted that the wafer separation method according to the above-described embodiment is merely one aspect of the present invention, and the present invention also includes wafer separation methods having features different from the above-described wafer separation method.

[0090] For example, in the above-mentioned processing step (S1), the cutting blade 12 is caused to cut into the wafer 11 to remove a portion of the wafer 11, but the method of removing a portion of the wafer 11 is not limited to this.

[0091] Specifically, in the processing step (S1), a part of the wafer 11 may be removed by irradiating the wafer 11 with a laser beam having a wavelength that is absorbed by the wafer 11 to cause laser ablation.

[0092] In the above separation start point forming step (S2), the wafer 11 is irradiated with a laser beam from the second surface 11b side. However, the wafer 11 may be irradiated with a laser beam from the first surface 11a side.

[0093] In this case, it is preferable that the separation start point forming step (S2) can be performed without separating the tape 19 attached to the second surface 11b in the processing step (S1) and without newly attaching the tape 21 to the first surface 11a. On the other hand, when the laser beam is irradiated to the wafer 11 from the second surface 11b side, it is preferable that the influence of the laser beam irradiation on the device 15 can be reduced.

[0094] In the above separation start point forming step (S2), the laser beam L is irradiated onto the wafer 11 while the chuck table 24 is moved in the horizontal direction, but the laser beam L may be irradiated onto the wafer 11 while the head 26 is moved in the horizontal direction. Alternatively, the laser beam L may be irradiated onto the wafer 11 while both the chuck table 24 and the head 26 are moved.

[0095] In the above-mentioned separation step (S3), the wafer 11 is separated into two wafers by applying an external force to the wafer 11 using the ultrasonic irradiation device 30, but the method of applying an external force to the wafer 11 is not limited to the method using ultrasonic waves. For example, the wafer 11 may be separated into two wafers by applying a tensile stress to the wafer 11 in a direction perpendicular to the first surface 11a and the second surface 11b.

[0096] In addition, the structures and methods according to the above-described embodiments and modifications can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0097] 11: Wafer 11a: First surface (front surface) 11b: Second side (back side) 11c: Outer surface 11d: Modified layer 11e: Crack 11f: Remaining curved section 11g: Groove 13: Planned division line 15: Device 17a, 17b: Orientation flat (Orifura) 19,21: Tape 2:Cutting device 4: θ table 6: Chuck table 6a: Frame 8: Cutting unit 10: Spindle 12: Cutting blade 20: Laser beam irradiation device 22: Table base 24: Chuck table 26: Head 30:Ultrasonic irradiation device 32:Liquid tank 34: Placement table 36: Ultrasonic irradiation unit

Claims

1. A wafer separation method for separating a wafer having a first surface, a second surface opposite to the first surface, and an outer circumferential surface located between the first surface and the second surface, the outer circumferential surface having a curved portion that is curved convexly outward, into two pieces on a first surface side and a second surface side, the method comprising the steps of: processing the wafer to remove a portion of the wafer along the curvature; a separation starting point forming step of forming a separation starting point within the wafer by positioning a focal point of a laser beam having a wavelength that is transparent to the wafer inside the wafer and irradiating the wafer with the laser beam while moving the focal point and the wafer relatively so that the focal point is maintained within the wafer; a separation step of applying an external force after the separation origin forming step to separate the wafer from the separation origin into a wafer having the first surface and a wafer having the second surface, The method for separating a wafer, wherein the processing step includes cutting the wafer with a cutting blade to remove all of the curved portion from the wafer.

2. A wafer separation method for separating a wafer having a first surface, a second surface opposite to the first surface, and an outer circumferential surface located between the first surface and the second surface, the outer circumferential surface having a curved portion that is curved convexly outward, into two pieces on a first surface side and a second surface side, the method comprising the steps of: processing the wafer to remove a portion of the wafer along the curvature; a separation starting point forming step of forming a separation starting point within the wafer by positioning a focal point of a laser beam having a wavelength that is transparent to the wafer inside the wafer and irradiating the wafer with the laser beam while moving the focal point and the wafer relatively so that the focal point is maintained within the wafer; a separation step of applying an external force after the separation origin forming step to separate the wafer from the separation origin into a wafer having the first surface and a wafer having the second surface, In the processing step, a part of the curved portion on the first surface side of the wafer is removed from the first surface side of the wafer; A wafer separation method, wherein in the separation start point forming step, the light focusing point is positioned at a depth between the first surface and the remaining curved portion of the wafer.

3. The curved portion has a first portion extending in an arc shape and a second portion extending in a straight line, In the processing step, the wafer is processed so as to remove a part of the curved portion of the wafer in an arc shape along the first portion, and to remove a part of the curved portion of the wafer in a linear or arc shape along the second portion.

3. The method for separating a wafer according to claim 2.

4. The processing step is characterized in that a cutting blade is cut into the wafer to remove a portion of the wafer.

4. The method for separating a wafer according to claim 2 or 3.

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