Method for separating wafers

Abstract

The present application provides a wafer separation method capable of stably separating a wafer having a chamfered peripheral portion. In the present application, the wafer is processed in a manner that a portion of the wafer is removed along a curved portion of the peripheral surface (chamfered peripheral portion) before a separation starting point is formed in the interior of the wafer. Thus, a modified layer and a crack as the separation starting point can be formed in the interior of the wafer without causing diffuse reflection of a laser beam in the curved portion of the peripheral surface and / or deviation of a condensing point. As a result, the wafer can be stably separated.

Description

Technical Field

[0001] This invention relates to a method for separating wafers. Background Technology

[0002] Chips containing power devices such as inverters or converters are typically manufactured by dividing a wafer, on which a large number of power devices are formed on the front side, into regions containing each power device. Regarding the wafer, for example, after thinning the back side to a specified thickness using a grinding machine, it is divided into individual chips using processing equipment such as cutting equipment and laser processing equipment.

[0003] In recent years, silicon carbide (SiC) has attracted much attention as a next-generation material for power devices. However, silicon carbide is extremely hard. Therefore, various problems arise when using silicon carbide wafers to manufacture chips containing power devices.

[0004] For example, when grinding wafers made of silicon carbide using a grinding machine, the wear of the grinding tools used in the grinding process may increase. In this case, the grinding tools need to be replaced frequently, which leads to reduced chip manufacturing efficiency and increased manufacturing costs.

[0005] As a method for thinning wafers, a method using a laser beam is also known (see, for example, Patent Document 1). In this method, after the wafer is irradiated with a laser beam to form a modified layer and cracks inside the wafer, an external force is applied to the wafer, thereby separating the wafer from the modified layer and cracks as the separation starting point.

[0006] Furthermore, during the transport of wafers processed in various steps, breakage and defects may occur on the outer periphery of the wafer. As a method to prevent such breakage and defects, a method is known to chamfer the outer periphery of the wafer, that is, to scrape the outer periphery in a manner that bends outward from the outer periphery of the wafer in a convex shape (see, for example, Patent Document 2).

[0007] Patent Document 1: Japanese Patent Application Publication No. 2017-28072

[0008] Patent Document 2: Japanese Patent Application Publication No. 2017-183503

[0009] When separating a wafer with a chamfered outer periphery using the method disclosed in Patent Document 1, the laser beam may be diffusely reflected due to the unevenness present on the outer periphery. In this case, the laser beam may not be able to converge to the interior of the outer periphery of the wafer, thus failing to form a modified layer and cracks as the separation starting point inside the outer periphery.

[0010] Furthermore, when the outer peripheral surface is curved, the location of the laser beam's focal point (depth from the front surface of the wafer) may deviate from the hypothetical location. In this case, even if a separation origin is formed inside the outer peripheral portion, the separation origin formed on the outer peripheral portion will be formed at a different location (depth from the front surface of the wafer) than separation origins formed on other parts.

[0011] Therefore, when a laser beam is applied to the chamfered outer periphery of a wafer, the wafer may not separate, or the wafer may separate into two wafers with different thicknesses in the outer periphery and other parts. Summary of the Invention

[0012] In view of this, the object of the present invention is to provide a method for separating wafers that can stably separate wafers with chamfered outer periphery.

[0013] According to the present invention, a method for separating a wafer is provided, the wafer having a first surface, a second surface opposite to the first surface, and an outer peripheral surface located between the first surface and the second surface, the outer peripheral surface having a curved portion that convexly curves outward, the method for separating the wafer into two wafers having the first surface side and the second surface side, wherein the method for separating the wafer includes the following steps: a processing step, processing the wafer in such a way that a portion of the wafer is removed along the curved portion; a separation starting point forming step, after the processing step, irradiating the wafer with the laser beam while positioning a focal point of a laser beam of a wavelength that is transparent to the wafer inside the wafer and maintaining the focal point inside the wafer, thereby forming a separation starting point inside the wafer; and a separation step, after the separation starting point forming step, applying an external force to separate the wafer from the separation starting point into a wafer having the first surface and a wafer having the second surface.

[0014] Preferably, the curved portion has a first portion extending in an arc shape and a second portion extending in a straight line. In this processing step, the wafer is processed in such a way that a portion of the wafer is removed in an arc shape along the first portion and a portion of the wafer is removed in a straight line or an arc shape along the second portion.

[0015] In addition, it is preferable to remove all of the bent portion from the wafer during this processing step.

[0016] Alternatively, preferably, in the processing step, a portion of the first side of the bend is removed from the first side of the wafer, and in the separation starting point forming step, the focusing point is positioned at the depth between the first side of the wafer and the remaining bend.

[0017] Alternatively, preferably, in this processing step, a portion of the first surface of the wafer is removed to form a groove, and in the separation starting point forming step, the focusing point is positioned at a depth between the first surface of the wafer and the bottom surface of the groove, and the laser beam is irradiated onto the region of the wafer that is closer to the inside of the groove.

[0018] Alternatively, in this processing step, it is preferable to have a cutting tool cut into the wafer to remove a portion of it.

[0019] In this invention, before forming a separation starting point inside the wafer, the wafer is processed by removing a portion of the wafer along the curved portion (the chamfered outer periphery) of its outer peripheral surface. This allows the formation of a modified layer and cracks serving as a separation starting point inside the wafer without causing diffuse reflection of the laser beam in the curved portion of the outer peripheral surface or a shift in the focusing point. As a result, the wafer can be stably separated. Attached Figure Description

[0020] Figure 1 (A) is a schematic top view of the wafer. Figure 1 (B) is a schematic cross-sectional view of the wafer.

[0021] Figure 2 This is a flowchart illustrating an example of a wafer separation method.

[0022] Figure 3 It is a partial cross-sectional side view schematically illustrating the processing steps of a full-cut and trimmed wafer.

[0023] Figure 4 It is a partial cross-sectional side view schematically illustrating the processing steps of partially cutting and trimming a wafer.

[0024] Figure 5 This is a partial cross-sectional side view schematically illustrating the processing steps of forming a groove along a bend on a wafer.

[0025] Figure 6 (A) Figure 6 (B) and Figure 6 (C) are schematic cross-sectional views showing the wafers processed in the processing steps.

[0026] Figure 7 This is a partial cross-sectional side view schematically illustrating the separation origin formation step in a wafer after full dicing and trimming.

[0027] Figure 8 This is a partial cross-sectional side view schematically illustrating the separation origin formation step in a wafer after half-cutting and trimming.

[0028] Figure 9This is a partial cross-sectional side view schematically illustrating the separation origin formation step in a wafer with grooves formed along the bend.

[0029] Figure 10 This is a partial cross-sectional side view schematically illustrating the separation steps of separating a wafer.

[0030] Label Explanation

[0031] 11: Wafer; 11a: First side (front); 11b: Second side (back); 11c: Outer peripheral surface; 11d: Modified layer; 11e: Crack; 11f: Residual bend; 11g: Groove; 13: Pre-cutting line; 15: Device; 17a, 17b: Orientation plane; 19, 21: Belt; 2: Cutting device; 4: θ stage; 6: Chuck stage; 6a: Frame; 8: Cutting unit; 10: Spindle; 12: Cutting tool; 20: Laser beam irradiation device; 22: Table base; 24: Chuck stage; 26: Head; 30: Ultrasonic irradiation device; 32: Liquid tank; 34: Mounting stage; 36: Ultrasonic irradiation unit. Detailed Implementation

[0032] The embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 (A) and Figure 1 (B) is a schematic top view and cross-sectional view of a wafer to be separated into two wafers. Figure 1 (A) and Figure 1 The wafer 11 shown in (B) is formed, for example, from silicon carbide (SiC).

[0033] The wafer 11 has a first surface (front side) 11a, a second surface (back side) 11b opposite to the first surface 11a, and an outer peripheral surface 11c located between the first surface 11a and the second surface 11b. Furthermore, the first surface 11a side of the wafer 11 is divided into multiple regions by a plurality of intersecting predetermined dividing lines 13, and devices such as inverters or converters are formed in each region.

[0034] Two planar portions representing crystal orientation, namely a primary orientation plane 17a and a secondary orientation plane 17b, are formed on the outer peripheral surface 11c of the wafer 11. That is, the portion of the outer peripheral surface 11c in which the primary orientation plane 17a and the secondary orientation plane 17b are formed extends in a straight line, and the portion outside of them extends in an arc shape.

[0035] Furthermore, the outer periphery of the wafer 11 is chamfered in a manner that curves outward in a convex shape along the outer peripheral surface 11c. As a result, the outer peripheral surface 11c has a curved portion formed by the chamfer. Moreover, this curved portion extends in a straight line in the portion where the primary orientation plane 17a and the secondary orientation plane 17b are formed, and extends in an arc shape in the portion outside of them.

[0036] Furthermore, there are no restrictions on the material, shape, structure, and size of the wafer 11. The wafer 11 can be formed from materials such as silicon (Si) or other semiconductors, ceramics, resins, and metals. In addition, a V-shaped notch, or so-called notch, indicating crystal orientation, can be formed on the outer peripheral surface 11c of the wafer 11 instead of an orientation plane.

[0037] Alternatively, the entire outer periphery of the wafer 11 may not be chamfered. For example, the portion of the outer periphery of the wafer 11 with the primary orientation plane 17a and the secondary orientation plane 17b may not be chamfered, but only the portion other than those planes may be chamfered. In this case, the outer peripheral surface 11c includes a curved portion formed by chamfering and a non-chamfered portion.

[0038] Similarly, there are no restrictions on the type, quantity, shape, structure, size, and configuration of the device 15. For example, the device 15 can be an IC (Integrated Circuit) or an LSI (Large Scale Integration). Alternatively, the device 15 may not be formed on the wafer 11.

[0039] Figure 2 It shows that Figure 1 (A) and Figure 1 A flowchart illustrating an example of a method for separating wafer 11 shown in (B) into two wafers (a wafer having a first surface 11a and a wafer having a second surface 11b) with a first surface side and a second surface side. Figure 2 In the wafer separation method shown, the wafer 11 is first processed by removing a portion of the wafer 11 along the curved portion of the outer peripheral surface 11c (processing step: S1).

[0040] In processing step S1, the entire curved portion can be removed from the wafer 11 (full cutting trimming) to flatten the outer peripheral surface of the wafer 11, or a portion of the curved portion on the first surface 11a side of the wafer 11 can be removed (partial cutting trimming) to form a step difference on the outer periphery of the wafer 11. Alternatively, in processing step S1, a portion of the first surface 11a side of the wafer 11 can be removed to form a groove along the curved portion on the outer peripheral surface 11c. That is, in processing step S1, at least a portion of the first surface 11a side of the wafer 11 is removed along the curved portion on the outer peripheral surface 11c.

[0041] The following is for reference Figures 3-5The following steps are described in sequence: step S1-1, which involves fully cutting and trimming the wafer 11 to flatten its outer peripheral surface; step S1-2, which involves partially cutting and trimming the wafer 11 to form a stepped difference on its outer peripheral portion; and step S1-3, which involves removing a portion of the first surface 11a of the wafer 11 to form a groove along the curved portion of the outer peripheral surface 11c.

[0042] Figure 3 This is a partial cross-sectional side view schematically illustrating the processing step S1-1, which involves fully dicing and trimming the wafer 11 to planarize its outer peripheral surface. Specifically, in Figure 3 In the processing step S1-1 shown, the cutting device 2 completely removes the bent portion from the side of the first surface 11a on which the wafer 11 with the strip 19 is attached to the second surface 11b. Additionally, Figure 3 The Z-axis direction shown is approximately parallel to the vertical direction.

[0043] The cutting device 2 has a cylindrical θ stage 4. A disk-shaped chuck stage 6, which holds the wafer 11 across a belt 19, is provided on the upper part of the θ stage 4. The θ stage 4 is connected to a rotary drive source (not shown) such as an electric motor. When the rotary drive source is activated, the θ stage 4 and the chuck stage 6 rotate about a straight line passing through the center of the chuck stage 6 and along the Z-axis.

[0044] The chuck worktable 6 has a frame 6a made of metal such as stainless steel. The frame 6a has a disc-shaped bottom wall and an annular side wall extending upward from the outer periphery of the bottom wall, defining a recess. A disc-shaped perforated plate (not shown) is fixed in the recess. The disc-shaped perforated plate is made of porous ceramic and has a diameter approximately the same as the inner diameter of the recess.

[0045] The perforated plate of the chuck stage 6 is connected to a suction source (not shown) such as a vacuum pump via a flow path formed in the frame 6a. When the suction source is activated, a negative pressure is generated on the upper surface of the perforated plate (the holding surface of the chuck stage 6). By generating this negative pressure, the wafer 11 placed on the chuck stage 6 is attracted and held by the chuck stage 6 through the belt 19.

[0046] Additionally, the θ stage 4 and the chuck table 6 are connected to an X-axis moving mechanism (not shown). When this X-axis moving mechanism is activated, the θ stage 4 and the chuck table 6 move in a direction perpendicular to the Z-axis (X-axis direction).

[0047] A cutting unit 8 is disposed above the chuck table 6. The cutting unit 8 is connected to a Y-axis moving mechanism (not shown) and a Z-axis moving mechanism (not shown). When the Y-axis moving mechanism is activated, the cutting unit 8 moves in the Y-axis direction, which is perpendicular to both the Z-axis and X-axis directions. Furthermore, when the Z-axis moving mechanism is activated, the cutting unit 8 moves in the Z-axis direction, i.e., the cutting unit 8 moves up and down.

[0048] The cutting unit 8 has a cylindrical spindle 10 extending along the Y-axis. A cutting tool 12 with an annular cutting edge is mounted at one end of the spindle 10. The cutting tool 12 is, for example, a hub-type cutting tool, which is constructed by integrating an annular base made of metal or the like and an annular cutting edge along the outer periphery of the base.

[0049] The cutting edge of the hub-type cutting tool is made of an electroformed abrasive, which is formed by fixing abrasive grains made of diamond or cubic boron nitride (cBN) with a bonding material such as nickel. Alternatively, as the cutting tool 12, a washer-type cutting tool with an annular cutting edge can also be used, which is formed by fixing abrasive grains with a bonding material such as metal, ceramic, or resin.

[0050] Additionally, the other end of the spindle is connected to a rotary drive source (not shown) such as an electric motor. When the rotary drive source is activated, the cutting tool 12 and the spindle 10 rotate together about a straight line along the Y-axis passing through the center of the spindle 10.

[0051] exist Figure 3 In the processing step S1 shown, for example, after all the curved portions of the outer peripheral surface 11c of the wafer 11, except for the portion where the primary orientation plane 17a and the secondary orientation plane 17b are formed, are removed, all the curved portions of the outer peripheral surface 11c where the primary orientation plane 17a and the secondary orientation plane 17b are formed are removed.

[0052] For example, the chuck stage 6 and / or cutting unit 8 are first positioned such that the lower end of the cutting tool 12 is positioned directly above the arc-shaped outer peripheral surface 11c of the wafer 11. Then, the cutting unit 8 is lowered until the cutting tool 12 contacts the belt 19 while the cutting tool 12 is rotating.

[0053] Next, while the cutting tool 12 is rotating, the chuck table 6 is rotated at least one revolution. This removes all the curved portion of the arc-shaped outer peripheral surface 11c of the wafer 11. In other words, all the curved portion extending along the arc shape is removed in an arc shape.

[0054] Next, the chuck stage 6 is rotated so that either the primary orientation plane 17a or the secondary orientation plane 17b is parallel to the X-axis direction. Next, the chuck stage 6 is moved along the X-axis direction so that the cutting tool 12 leaves the wafer 11. Next, the cutting unit 8 is moved along the Y-axis direction so that the cutting tool 12 is positioned in the X-axis direction when viewed from the primary orientation plane 17a or the secondary orientation plane 17b.

[0055] Next, the cutting unit 8 is lowered such that the lower end of the cutting tool 12 is lower than the upper surface of the belt 19 but higher than the lower surface. Then, the chuck table 6 is moved along the X-axis such that the wafer 11 passes from one end of the cutting tool 12 in the X-axis direction to the other end while the cutting tool 12 is rotating.

[0056] Therefore, the curved portion of the outer peripheral surface 11c of the part having the primary orientation plane 17a and the secondary orientation plane 17b is completely removed. That is, the curved portion extending in a straight line is completely removed in a straight line.

[0057] Figure 4 This is a partial cross-sectional side view schematically illustrating processing steps S1-2, in which a step difference is formed on the outer periphery of wafer 11 by performing a partial dicing trimming. Additionally, Figure 4 The cutting device 2 shown is Figure 3 The cutting device 2 shown is the same, so the description is omitted.

[0058] exist Figure 4 In the processing steps S1-2 shown, for example, after removing a portion of the first surface 11a side of the curved portion of the arc-shaped outer peripheral surface 11c of the wafer 11, a portion of the first surface 11a side of the curved portion of the outer peripheral surface 11c where the primary orientation plane 17a and the secondary orientation plane 17b are formed is removed.

[0059] For example, the chuck stage 6 and / or cutting unit 8 are first positioned such that the lower end of the cutting tool 12 is positioned directly above the arc-shaped outer peripheral surface 11c of the wafer 11. Then, while the cutting tool 12 is rotating, the cutting unit 8 is lowered until the lower end of the cutting tool 12 reaches a position lower than the first surface 11a and higher than the second surface 11b.

[0060] Next, while the cutting tool 12 is rotating, the chuck table 6 is rotated at least one revolution. This removes a portion 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 portion of the first surface 11a side of the curved portion extending in an arc shape is removed in an arc shape.

[0061] Next, the chuck stage 6 is rotated so that either the primary orientation plane 17a or the secondary orientation plane 17b is parallel to the X-axis direction. Next, the chuck stage 6 is moved along the X-axis direction so that the cutting tool 12 leaves the wafer 11. Next, the cutting unit 8 is moved along the Y-axis direction so that the cutting tool 12 is positioned in the X-axis direction when viewed from the primary orientation plane 17a or the secondary orientation plane 17b.

[0062] Next, the cutting unit 8 is lowered such that the lower end of the cutting tool 12 is lower than the first surface 11a and higher than the second surface 11b. Then, the chuck table 6 is moved along the X-axis such that the wafer 11 passes from one end of the cutting tool 12 in the X-axis direction to the other end while the cutting tool 12 is rotating.

[0063] Therefore, a portion of the curved portion on the first surface 11a side of the outer peripheral surface 11c of the portion having the primary orientation plane 17a and the secondary orientation plane 17b is removed. That is, a portion of the curved portion on the first surface 11a side, which extends in a straight line, is removed in a straight line.

[0064] Figure 5 This is a partial cross-sectional side view schematically illustrating processing steps S1-3, in which a portion of the first surface 11a of the wafer 11 is removed to form a groove along the outer peripheral surface 11c. Additionally, Figure 5 The cutting device 2 shown is Figure 3 and Figure 4 The cutting device 2 shown is the same, so the description is omitted.

[0065] exist Figure 5 In the processing steps S1-3 shown, for example, after forming a groove that extends in an arc shape along the curved portion of the outer peripheral surface 11c of the wafer 11, a groove that extends in a straight line along the curved portion of the outer peripheral surface 11c where the primary orientation plane 17a and the secondary orientation plane 17b are formed is formed.

[0066] For example, the chuck stage 6 and / or cutting unit 8 are first positioned directly above the region where the lower end of the cutting tool 12 is positioned at a distance from the center of the wafer 11 that 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 plane 17a and the secondary orientation plane 17b and the center of the wafer 11.

[0067] Next, while the cutting tool 12 is rotating, the cutting unit 8 is lowered until the lower end of the cutting tool 12 reaches a position lower than the first surface 11a and higher than the second surface 11b. Then, while the cutting tool 12 is rotating, the chuck table 6 is rotated at least one revolution.

[0068] Thus, a groove is formed that extends in an arc shape along the curved portion of the arc-shaped outer peripheral surface 11c of the wafer 11. 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.

[0069] Next, the chuck stage 6 is rotated so that either the primary orientation plane 17a or the secondary orientation plane 17b is parallel to the X-axis direction. Next, the chuck stage 6 is moved along the X-axis so that the cutting tool 12 leaves the wafer 11. Next, the cutting unit 8 is moved along the Y-axis so that, when viewed from the primary orientation plane 17a or the secondary orientation plane 17b, the cutting tool 12 is positioned slightly offset from the X-axis towards the wafer 11.

[0070] Next, the cutting unit 8 is lowered such that the lower end of the cutting tool 12 is lower than the first surface 11a and higher than the second surface 11b. Then, the chuck table 6 is moved along the X-axis such that the wafer 11 passes from one end of the cutting tool 12 in the X-axis direction to the other end while the cutting tool 12 is rotating.

[0071] Thus, a groove is formed that extends in a straight line along the curved portion of the outer peripheral surface 11c where the primary orientation plane 17a and the secondary orientation plane 17b are formed. That is, a portion of the first surface 11a side of the wafer 11 is removed in a straight line along the curved portion that extends in a straight line.

[0072] Or, in Figure 5 In the processing steps S1-3 shown, a portion of the first surface 11a of the wafer 11 can be removed from the first surface 11a side to form an annular groove. That is, in Figure 5 In the processing steps S1-3 shown, a groove can be formed that extends in an arc shape along the curved portion of the arc-shaped outer peripheral surface 11c of the wafer 11 and extends in an arc shape along the curved portion of the outer peripheral surface 11c where the primary orientation plane 17a and the secondary orientation plane 17b are formed.

[0073] For example, the chuck stage 6 and / or cutting unit 8 are first positioned such that the lower end of the cutting tool 12 is positioned directly above the region that is shorter than the shortest interval between the primary orientation plane 17a and the secondary orientation plane 17b and the center of the wafer 11.

[0074] Next, while the cutting tool 12 is rotating, the cutting unit 8 is lowered to a position where the lower end of the cutting tool 12 is lower than the first surface 11a and higher than the second surface 11b. Then, while the cutting tool 12 is rotating, the chuck stage 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.

[0075] That is, a portion of the first surface 11a side of the wafer 11 is removed in an arc shape along the arc-shaped curved portion (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 straight curved portion (the curved portion of the outer peripheral surface 11c where the primary orientation plane 17a and the secondary orientation plane 17b are formed).

[0076] Figure 6 (A) Figure 6 (B) and Figure 6 (C) are schematic cross-sectional views of the wafer 11, showing that a portion of the wafer 11 was removed in the processing step S1 by means of a bend along the outer peripheral surface 11c.

[0077] Specifically, Figure 6 (A) is a cross-sectional view showing the wafer 11 whose outer peripheral surface is planarized through processing step S1-1. Additionally, Figure 6 (B) is a cross-sectional view showing a wafer 11 with a stepped difference formed on its outer periphery through processing steps S1-2. Additionally, Figure 6 (C) is a cross-sectional view of a wafer 11 having a groove formed along the outer peripheral surface 11c by processing steps S1-3.

[0078] exist Figure 2 In the wafer separation method shown, after processing step S1, a laser beam is irradiated onto wafer 11 to form a separation starting point inside wafer 11 (separation starting point formation step: S2).

[0079] The following is for reference Figures 7-9 The separation start point formation step S2-1, which forms a separation start point inside the wafer 11 with a planarized outer peripheral surface, the separation start point formation step S2-2, which forms a separation start point inside the wafer 11 with a stepped difference formed on the outer peripheral portion, and the separation start point formation step S2-3, which forms a separation start point inside the wafer 11 with a groove formed along the curved portion of the outer peripheral surface 11c, will be described in sequence.

[0080] Figure 7 This is a schematic partial cross-sectional side view illustrating the separation start point formation step S2-1, which involves forming a separation start point inside the wafer 11 whose outer peripheral surface is planarized through processing step S1-1. Specifically, in Figure 7 In the separation starting point formation step S2-1 shown, the laser beam irradiation device 20 irradiates a laser beam from the second surface 11b side of the wafer 11 on which the strip 21 is attached, thereby forming a separation starting point inside the wafer 11. Additionally, Figure 7 The Z-axis direction shown is approximately parallel to the vertical direction.

[0081] The laser beam irradiation device 20 has a cylindrical worktable base 22. A disc-shaped chuck worktable 24 is provided on the upper part of the worktable base 22, which holds the wafer 11 through a belt 21.

[0082] The chuck worktable 24 has a frame 24a made of a metal such as stainless steel. The frame 24a has a disc-shaped bottom wall and an annular side wall extending upward from the outer periphery of the bottom wall, through which a recess is defined. A disc-shaped porous plate (not shown) made of porous ceramic with a diameter approximately the same as the inner diameter of the recess is fixed in the recess.

[0083] The perforated plate of the chuck stage 24 is connected to a suction source (not shown) such as a vacuum pump via a flow path formed in the frame 24a. When the suction source is activated, a negative pressure is generated on the upper surface of the perforated plate (the holding surface of the chuck stage 24). By generating this negative pressure, the wafer 11 placed on the chuck stage 24 is attracted and held by the chuck stage 24 through the belt 21.

[0084] In addition, the worktable base 22 and the chuck worktable 24 are connected to a horizontal moving mechanism (not shown). When the horizontal moving mechanism is activated, the worktable base 22 and the chuck worktable 24 move on a plane (horizontal plane) perpendicular to the Z-axis direction.

[0085] A laser beam irradiation unit (not shown) head 26 is disposed above the chuck table 24. The head 26 is connected to a Z-axis moving mechanism (not shown). When the Z-axis moving mechanism is activated, the head 26 moves in the Z-axis direction, that is, the head 26 rises and falls.

[0086] The laser beam irradiation unit includes a laser oscillator that generates a laser beam L with a wavelength that is transparent to the wafer 11. This laser oscillator may have a laser medium such as Nd:YAG suitable for laser irradiation. Furthermore, the laser beam irradiation unit includes an optical system comprising a focusing lens that positions the focusing point of the laser beam L at a predetermined height. The focusing lens is housed within the head 26.

[0087] exist Figure 7 In the separation starting point formation step S2-1 shown, after setting the optical system of the laser beam irradiation unit, for example, the height of the head 26, in a manner that positions the focusing point of the laser beam L inside the wafer 11, the laser beam L is irradiated while the chuck stage 24 is moved on a horizontal plane. As a result, a modified layer 11d and a crack 11e, serving as the separation starting point, are formed inside the wafer 11.

[0088] Figure 8This is a schematic partial cross-sectional side view illustrating step S2-2, in which a separation start point is formed inside the wafer 11, whose outer periphery has a stepped difference, formed through processing steps S1-2. Additionally, Figure 8 The laser beam irradiation device 20 shown is Figure 7 The laser beam irradiation device 20 shown is the same, so its description is omitted.

[0089] exist Figure 8 In the separation starting point formation step S2-2 shown, after setting the height of the optical system of the laser beam irradiation unit, such as the head 26, in a way that the focusing point of the laser beam L is positioned at the depth between the first surface 11a of the wafer 11 and the remaining curved portion 11f, the laser beam L is irradiated while the chuck stage 24 is moved on the horizontal plane.

[0090] Specifically, in Figure 8 In the separation starting point formation step S2-2 shown, the optical system is configured to position the focusing point of the laser beam L between the first imaginary surface and the second imaginary surface. The first imaginary surface passes through the part of the step difference formed on the outer periphery that is closest to the first surface 11a and is substantially parallel to the first surface 11a and the second surface 11b. The second imaginary surface passes through the part of the step difference that is closest to the second surface 11b and is substantially parallel to the first surface 11a and the second surface 11b.

[0091] Thus, a modified layer 11d and a crack 11e, serving as the separation starting point, are formed at the depth between the first surface 11a and the remaining curved portion 11f of the wafer 11 (i.e., between the first imaginary surface and the second imaginary surface).

[0092] Figure 9 This is a schematic partial cross-sectional side view illustrating step S2-3, in which a separation starting point is formed inside a groove 11g with a curved portion along the outer peripheral surface 11c, formed through processing steps S1-3. Additionally, Figure 9 The laser beam irradiation device 20 shown is Figure 7 and Figure 8 The laser beam irradiation device 20 shown is the same, so its description is omitted.

[0093] exist Figure 9 In the separation starting point formation step S2-3 shown, after setting the height of the optical system of the laser beam irradiation unit, such as the head 26, in a way that the focal point of the laser beam L is positioned at the depth between the first surface 11a of the wafer 11 and the bottom surface of the groove 11g, the laser beam L is irradiated while the chuck stage 24 is moved on the horizontal plane in a way that the focal point is maintained in the region of the wafer 11 that is closer to the inside of the groove 11g.

[0094] Specifically, in Figure 9In the separation starting point formation step S2-3 shown, the optical system is set to position the focusing point of the laser beam L between the third imaginary surface and the fourth imaginary surface. The third imaginary surface passes through the part of the groove 11g closest to the first surface 11a and is approximately parallel to the first surface 11a and the second surface 11b. The fourth imaginary surface passes through the part of the groove 11g closest to the second surface 11b and is approximately parallel to the first surface 11a and the second surface 11b.

[0095] Thus, a modified layer 11d and a crack 11e, serving as the separation starting point, are formed at a depth between the first surface 11a of the wafer 11 and the bottom surface of the trench 11g (i.e., between the third imaginary surface and the fourth imaginary surface).

[0096] exist Figure 2 In the wafer separation method shown, after the separation starting point formation step S2, an external force is applied to separate the wafer 11 into two wafers (a wafer with a first surface 11a and a wafer with a second surface 11b) (separation step: S3).

[0097] Figure 10 This is a partial cross-sectional side view schematically illustrating the separation step S3, in which the wafer 11, having formed a modified layer 11d as a separation starting point and a crack 11e, is separated via the separation starting point formation step S2. Specifically, in Figure 10 In the separation step S3 shown, the wafer 11 is separated into two wafers by applying external force to the wafer 11 using an ultrasonic irradiation device 30.

[0098] The ultrasonic irradiation device 30 includes a liquid tank 32 for holding liquids such as water. A disc-shaped mounting stage 34 for holding the wafer 11 is provided on the bottom surface of the liquid tank 32. In addition, the ultrasonic irradiation device 30 includes an ultrasonic irradiation unit 36 ​​for irradiating ultrasonic waves onto the liquid held in the liquid tank 32.

[0099] exist Figure 10 In the separation step S3 shown, for example, the ultrasonic irradiation unit 36 ​​irradiates the liquid contained in the liquid tank 32 with ultrasonic waves, thereby applying external force to the wafer 11 placed on the mounting stage 34. As a result, the wafer 11 is separated into two wafers using the surface containing the separation initiation point of the modified layer 11d and the crack 11e as the separation surface.

[0100] In the wafer separation method of this embodiment, before forming a separation starting point inside the wafer 11, the wafer 11 is processed in such a way that a portion of the wafer 11 is removed along the curved portion (the chamfered outer peripheral portion) of the outer peripheral surface 11c.

[0101] Therefore, it is possible to ensure that diffuse reflection of the laser beam at the curved portion of the outer peripheral surface 11c and / or shift of the focusing point do not occur, thus preventing the formation of a modified layer and cracks inside the wafer 11 that serve as the separation starting point. As a result, the wafer 11 can be stably separated.

[0102] Furthermore, the wafer separation method described in the above embodiments is only one aspect of the present invention, and wafer separation methods having features different from the wafer separation method described above are also included in the present invention.

[0103] For example, in the processing step S1 described above, the cutting tool 12 cuts 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.

[0104] Specifically, in processing step S1, a portion of the wafer 11 can be removed by laser ablation caused by irradiating a laser beam of a wavelength absorbed by the wafer 11.

[0105] In addition, in the separation starting point formation step S2 described above, the laser beam is irradiated onto the wafer 11 from the second surface 11b side, but the laser beam can also be irradiated onto the wafer 11 from the first surface 11a side.

[0106] In this case, it is preferable that the separation start point formation step S2 can be performed in processing step S1 without separating the tape 19 attached to the second surface 11b and without reattaching the tape 21 to the first surface 11a. On the other hand, it is preferable that when the laser beam is irradiated onto the wafer 11 from the second surface 11b side, the effect of the laser beam irradiation on the device 15 can be reduced.

[0107] Furthermore, in the separation starting point formation step S2 described above, the laser beam L is irradiated onto the wafer 11 while the chuck stage 24 is moved horizontally. However, the laser beam L can also be irradiated onto the wafer 11 while the head 26 is moved horizontally. Alternatively, the laser beam L can be irradiated onto the wafer 11 while both the chuck stage 24 and the head 26 are moved.

[0108] Furthermore, in the separation step S3 described above, the wafer 11 is separated into two wafers by applying external force to the wafer 11 using the ultrasonic irradiation device 30. However, the method of applying external force to the wafer 11 is not limited to using ultrasonic waves. For example, tensile stress can be applied to the wafer 11 in a direction perpendicular to the first surface 11a and the second surface 11b to separate the wafer 11 into two wafers.

[0109] In addition, the above-described embodiments and variations can be appropriately modified and implemented as long as they do not depart from the scope of the present invention.

Claims

1. A method for separating a wafer, the wafer having a first surface, a second surface opposite to the first surface, and an outer peripheral surface located between the first surface and the second surface, the outer peripheral surface having a curved portion that convexly curves outward, the method separating the wafer into two wafers, one with the first surface and the other with the second surface, characterized in that, The wafer separation method comprises the following steps: The processing steps involve removing a portion of the wafer along the bend. In the separation start point formation step, after the processing step, the laser beam is irradiated while the focus point of the laser beam with a wavelength that is transparent to the wafer is positioned inside the wafer and the focus point is maintained inside the wafer, thereby forming a separation start point inside the wafer. as well as In the separation step, following the separation starting point formation step, an external force is applied to separate the wafer from the separation starting point into a wafer having the first surface and a wafer having the second surface. In this processing step, a portion of the bent portion is removed from the first side of the wafer to form a step difference on the outer periphery of the wafer. In the separation starting point formation step, the focusing point is positioned at the depth between the first surface of the wafer and the remaining bend.

2. The wafer separation method according to claim 1, wherein, The curved portion has a first part that extends in an arc shape and a second part that extends in a straight line. In this processing step, the wafer is processed in such a way that a portion of the curved portion of the wafer is removed in an arc shape along the first part and a portion of the curved portion of the wafer is removed in a straight line or an arc shape along the second part.

3. The wafer separation method according to claim 1 or 2, characterized in that, In this processing step, a cutting tool is brought into the wafer to remove a portion of it.

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