Wafer processing method

Abstract

To provide a wafer processing method with which the occurrence of cracks and chipping can be prevented in removing a ring-shaped reinforcement part from a wafer formed with a circular recess.SOLUTION: A wafer processing method includes: a circular recess forming step 1 of, on a rear face of a wafer having a device area and an outer peripheral excess area surrounding the device area on a front face, forming a circular recess in an area corresponding to the device area, and forming an annular projection including an area corresponding to the outer peripheral excess area on an outer peripheral side of the circular recess; and a separation step 2 of radiating a laser beam along a boundary area between the circular recess and the annular projection to separate the circular recess and the annular projection from each other. The separation step 2 includes: a first laser beam radiation step 2-1 of radiating the laser beam along the boundary area at a first power density to form a processing groove; and a second laser beam radiation step 2-2 of radiating the laser beam along the processing groove at a second power density different from the first power density.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Semiconductor devices are generally manufactured by grinding the back surface of a wafer, which has devices formed on its front surface, to thin it to a predetermined thickness, and then dividing it into individual devices using a cutting device that uses a cutting blade or a laser processing device that processes the wafer by irradiating it with a laser beam.

[0003] For example, a method is known in which a region of the back surface of a wafer corresponding to a device region in which devices are formed is ground to form a circular recess, and a ring-shaped reinforcing portion is formed on the outer periphery of the circular recess to reinforce the wafer during handling, known as TAIKO grinding (registered trademark). This method prevents cracking or chipping of the thinned wafer after grinding.

[0004] On the other hand, when dividing a wafer into individual chips, the ring-shaped reinforcing part becomes an obstacle to division, so it is necessary to remove the ring-shaped reinforcing part beforehand, and a method has been proposed in which an annular division groove is formed in the boundary region between the circular recess and the ring-shaped reinforcing part, and the ring-shaped reinforcing part is then removed by detaching it (see Patent Document 1).When forming the division groove, for example, a method has been proposed in which the front side of the wafer is held by a chuck table with a convex shape corresponding to the step between the circular recess and the ring-shaped reinforcing part (see Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-061137 A [Patent Document 2] JP 2010-016146 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when forming the dividing groove and removing the ring-shaped reinforcing portion, there is a problem that cracks and chipping occur in the ring-shaped reinforcing portion and the device region.

[0007] The present invention has been made in consideration of such problems, and its object is to provide a wafer processing method that can suppress the occurrence of cracks and chipping when removing a ring-shaped reinforcing portion from a wafer having a circular recess formed therein. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, the wafer processing method of the present invention is a wafer processing method for processing a wafer having, on its surface, a device region in which a plurality of devices are formed and a peripheral excess region surrounding the device region, and includes a circular recess formation step of forming a circular recess in a region corresponding to the device region on the back surface of the wafer, and forming an annular convex portion including a region corresponding to the peripheral excess region on the outer circumferential side of the circular recess, and a separation step of irradiating a laser beam along a boundary region between the circular recess and the annular convex portion to separate the circular recess and the annular convex portion along the boundary region, the separation step including a first laser beam irradiation step of irradiating a laser beam along the boundary region at a first power density to form a processed groove, and a second laser beam irradiation step of irradiating a laser beam along the processed groove formed in the first laser beam irradiation step at a second power density different from the first power density.

[0009] In addition, in the wafer processing method of the present invention, in the second laser beam irradiation step, a laser beam may be irradiated toward the circular recess side from the center in the width direction of the processed groove formed in the first laser beam irradiation step.

[0010] In addition, in the wafer processing method of the present invention, in the second laser beam irradiation step, a laser beam may be irradiated toward the annular convex portion from the center of the width direction of the processed groove formed in the first laser beam irradiation step.

[0011] Furthermore, in the wafer processing method of the present invention, the separation step may involve branching the laser beam to form a first beam spot having the first power density and a second beam spot having the second power density, thereby simultaneously carrying out the first laser beam irradiation step and the second laser beam irradiation step.

[0012] In the wafer processing method of the present invention, the first power density may be set to be larger than the second power density. Effect of the Invention

[0013] The present invention can suppress the occurrence of cracks and chipping when removing a ring-shaped reinforcing portion from a wafer having a circular recess formed therein. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view showing an example of a wafer to be processed by the wafer processing method according to the embodiment. [Diagram 2] FIG. 2 is a flowchart showing a flow of the wafer processing method according to the embodiment. [Diagram 3] FIG. 3 is a perspective view showing one state of the circular recess forming step shown in FIG. [Figure 4] FIG. 4 is a schematic diagram showing a laser processing apparatus for carrying out the separation step shown in FIG. [Diagram 5] FIG. 5 is a side view, partly in section, showing one state of the separation step shown in FIG. [Figure 6] FIG. 6 is a plan view of the wafer at the separation step shown in FIG. [Figure 7]FIG. 7 is an enlarged plan view of a portion of the wafer showing the beam spot in the separation step shown in FIG. [Figure 8] FIG. 8 is an enlarged plan view of a portion of the wafer showing the beam spot in the separation step shown in FIG. [Figure 9] FIG. 9 is an enlarged plan view of a portion of the wafer showing the beam spot in the separation step shown in FIG. [Figure 10] FIG. 10 is an enlarged plan view of a portion of the wafer showing the beam spot in the separation step shown in FIG. [Figure 11] FIG. 11 is a side view, partially in section, showing one state of the separation step according to the modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The form (embodiment) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiment. Furthermore, the components described below include those that a person skilled in the art can easily imagine and those that are substantially the same. Furthermore, the configurations described below can be appropriately combined. Furthermore, various omissions, substitutions, or modifications of the configurations can be made without departing from the gist of the present invention.

[0016] [Embodiment] A method for processing a wafer 10 according to an embodiment of the present invention will be described with reference to the drawings. First, the wafer 10 to be processed will be described. Fig. 1 is a perspective view showing an example of the wafer 10 to be processed in the method for processing a wafer 10 according to the embodiment.

[0017] The wafer 10 shown in Fig. 1 is a disk-shaped semiconductor wafer, an optical device wafer, or the like, having a substrate 11 made of silicon (Si), sapphire (Al2O3), gallium arsenide (GaAs), silicon carbide (SiC), or the like. The wafer 10 has a device layer on the surface 12 side of the substrate 11, the device layer including a device region 13 and a peripheral surplus region 14 surrounding the device region 13. Note that, for the sake of convenience, the boundary between the device region 13 and the peripheral surplus region 14 is shown by a dotted line in Fig. 1, but in reality, no line exists at the boundary.

[0018] The device region 13 has a plurality of planned division lines 15 set in a grid pattern on the surface 12 of the substrate 11, and devices 16 formed in each region partitioned by the planned division lines 15. The peripheral excess region 14 is a region that surrounds the device region 13 all around and in which no devices 16 are formed. The devices 16 are, for example, integrated circuits such as ICs (Integrated Circuits) or LSIs (Large Scale Integration), image sensors such as CCDs (Charge Coupled Devices) or CMOSs ​​(Complementary Metal Oxide Semiconductors), or MEMS (Micro Electro Mechanical Systems).

[0019] With the protective member 30 attached to the front surface 12, the wafer 10 is thinned by grinding an area corresponding to the device area 13 on the back surface 17 side, and then the device area 13 and the peripheral excess area 14 are separated and the wafer is divided into individual devices 16 along the division lines 15 to be singulated into chips. The protective member 30 is in the form of a sheet having substantially the same shape as the outer shape of the wafer 10. The protective member 30 may be configured to include, for example, a base layer made of a synthetic resin and a glue layer made of an adhesive synthetic resin laminated on the base layer, or may be configured of a thermoplastic resin without a glue layer.

[0020] Next, the flow of the method for processing the wafer 10 will be described. Fig. 2 is a flow chart showing the flow of the method for processing the wafer 10 according to the embodiment. As shown in Fig. 2, the method for processing the wafer 10 according to the embodiment includes a circular recess forming step 1 and a separation step 2. The separation step 2 includes a first laser beam irradiation step 2-1 and a second laser beam irradiation step 2-2.

[0021] (Circular recess formation step 1) Fig. 3 is a perspective view showing one state of the circular recess forming step 1 shown in Fig. 2. The circular recess forming step 1 is a step of forming a circular recess 18 in a region corresponding to the device region 13 on the back surface 17 of the wafer 10, and forming an annular protrusion 19 including a region corresponding to the outer periphery excess region 14 on the outer periphery side of the circular recess 18.

[0022] In the circular recess forming step 1 of the embodiment, the back surface 17 side of the device region 13 of the wafer 10 is ground by a grinding apparatus 100 shown in Fig. 3. The grinding apparatus 100 includes a holding table 110, a grinding unit 120, a moving mechanism (not shown) for relatively moving the holding table 110 and the grinding unit 120 in the radial direction of the holding table 110, and a lifting mechanism (not shown) for relatively moving the holding table 110 and the grinding unit 120 in the vertical direction.

[0023] The holding table 110 is, for example, disk-shaped and made of porous ceramics or the like, and holds the wafer 10 on a horizontal, flat holding surface 111. The holding surface 111 is connected to a vacuum suction source via a vacuum suction path, for example, and holds the placed wafer 10 by suction. During grinding, the holding table 110 is rotated within a horizontal plane around a vertical axis by a rotation drive mechanism (not shown).

[0024] The grinding unit 120 grinds the back surface 17 side of the wafer 10 whose front surface 12 side is held on the holding table 110. The grinding unit 120 has a spindle 121 that rotates about a vertical axis, a motor (not shown) that rotates the spindle 121, and a grinding wheel 122 that is attached to the lower end of the spindle 121 and rotates together with the spindle 121 about the vertical axis. The grinding wheel 122 includes a wheel base 123 and a grinding wheel 124 supported on the lower surface side of the wheel base 123. The grinding wheel 124 is disposed in a ring shape whose diameter is equal to or less than the radius of the wafer 10.

[0025] In the circular recess forming step 1, first, the front surface 12 side of the wafer 10 is suction-held on the holding surface 111 of the holding table 110 via the protective member 30. Next, the grinding unit 120 is positioned by a moving mechanism (not shown) at a position where the surface ground by the grinding wheel 124 is inscribed in the inner periphery of the outer peripheral excess region 14 on the back surface 17 of the wafer 10. That is, the surface ground by the grinding wheel 124 is opposed to an area on the back surface 17 of the wafer 10 corresponding to the device region 13.

[0026] In the circular recess forming step 1, next, while the holding table 110 is rotated about its axis, the spindle 121 of the grinding unit 120 is rotationally driven to rotate the grinding wheel 122 about its axis. Grinding fluid is supplied to the grinding surface, and the grinding wheel 122 is brought close to the holding table 110 at a predetermined feed rate by a lifting mechanism (not shown) and the wafer 10 is pressed by the grinding wheel 124, whereby the back surface 17 side of the wafer 10 is ground by the grinding wheel 124 of the grinding wheel 122.

[0027] In the circular recess forming step 1, the back surface 17 of the wafer 10 is ground along the grinding surface of the grinding wheel 124 to form a ground surface on the back surface 17 of the wafer 10 parallel to the grinding surface, and only the region corresponding to the device region 13 is ground and thinned. This performs so-called TAIKO (registered trademark) grinding, which forms a circular recess 18 and an annular protrusion 19 surrounding the circular recess 18 on the back surface 17 of the wafer 10.

[0028] (Separation step 2) Fig. 4 is a schematic diagram showing a laser processing apparatus 200 performing the separation step 2 shown in Fig. 2. Fig. 5 is a side view, partially in cross section, showing one state of the separation step 2 shown in Fig. 2. Fig. 6 is a plan view of the wafer 10 in the separation step 2 shown in Fig. 2. The separation step 2 is a step of irradiating a laser beam 230 along a boundary region 20 between the circular recess 18 and the annular protrusion 19 to separate the circular recess 18 and the annular protrusion 19 along the boundary region 20.

[0029] In the separation step 2 of the embodiment, a processed groove 21 is formed along the boundary region 20 of the wafer 10 by a laser processing apparatus 200 shown in Figures 4 and 5. The laser processing apparatus 200 includes a holding table 210, a laser beam irradiation unit 220, and a moving mechanism (not shown) that moves the holding table 210 and the laser beam irradiation unit 220 relatively.

[0030] The holding table 210 is, for example, disk-shaped and made of porous ceramics or the like, and holds the wafer 10 on a horizontal, flat holding surface 211. The holding table 210 has a convex holding surface 211 that corresponds to the step between the circular recess 18 and the annular protrusion 19 formed on the wafer 10. The holding surface 211 is connected to a vacuum suction source, for example, via a vacuum suction path, and suction-holds the placed wafer 10. A plurality of clamps 212 that clamp an annular frame 40 that supports the wafer 10 are arranged around the holding table 210.

[0031] The laser beam irradiation unit 220 is an optical system unit that irradiates a laser beam 230 onto the wafer 10 held on the holding surface 211 of the holding table 210. The laser beam irradiation unit 220 includes an oscillator 221, a condenser 222, a power adjustment unit 223, a branching unit 224, and a mirror 225.

[0032] The oscillator 221 emits a laser beam 230 having a predetermined wavelength for processing the wafer 10. The laser beam 230 irradiated by the laser beam irradiation unit 220 is a laser beam having a wavelength that is transparent or absorbent to the wafer 10, and in an embodiment in which groove processing is performed, is a laser beam having an absorbent wavelength.

[0033] The condenser 222 is a condenser lens that condenses the laser beam 230 emitted from the oscillator 221 at a predetermined position on the wafer 10 held on the holding surface 211 of the holding table 210 and irradiates the wafer 10 with the laser beam.

[0034] The power adjustment unit 223 is provided on the optical path between the oscillator 221 and the condenser 222, and adjusts the output of the laser beam 230. The power adjustment unit 223 includes, for example, an attenuator. When the oscillator 221 has a function of adjusting the output of the laser beam 230, the power adjustment unit 223 does not need to be provided.

[0035] The splitter unit 224 is provided after the power adjustment unit 223 on the optical path between the oscillator 221 and the condenser 222, and splits the laser beam 230 into split beams. The split beams include a first laser beam 231 (see FIGS. 7 to 10) and a second laser beam 232 (see FIGS. 7 to 10), which will be described later. The splitter unit 224 includes a λ / 2 wave plate, a Wollaston prism, and a λ / 4 wave plate. The λ / 2 wave plate changes the linear polarization direction of the incident laser beam 230 according to the rotation angle, and controls the power balance of the split beams by controlling the polarization. The Wollaston prism splits the incident laser beam 230 into two orthogonal linearly polarized split beams, and controls the width of the split beams by rotation. The λ / 4 wave plate gives a phase difference to the incident orthogonal linearly polarized split beams, converting the linearly polarized light into circularly polarized light.

[0036] The mirror 225 reflects the laser beam 230 toward the wafer 10 held on the holding surface 211 of the holding table 210. In the embodiment, the mirror 225 reflects the laser beam 230 branched by the branching unit 224 toward the collector 222.

[0037] In the separation step 2, the wafer 10 is transported and processed while being supported by the frame 40 and the tape 41. The frame 40 is an annular plate-like object made of metal or resin, and has an inner diameter larger than the outer shape of the wafer 10. The tape 41 is in the form of a sheet having a diameter larger than the inner diameter of the frame 40. The tape 41 includes, for example, a base layer made of a synthetic resin having elasticity, and an adhesive layer made of a synthetic resin having elasticity and adhesiveness, laminated on the base layer. The tape 41 may be a thermocompression sheet made of a thermoplastic resin having flexibility, non-adhesiveness, and thermoplasticity, and not including an adhesive layer having adhesiveness.

[0038] The wafer 10 is positioned at a predetermined position in the opening of the frame 40, and the back surface 17 is attached to the tape 41, thereby fixing the wafer 10 to the frame 40 and the tape 41. The tape 41 is attached along the bottom surface of a circular recess 18 formed on the back surface 17 of the wafer 10, a side wall which is the boundary between the circular recess 18 and an annular protrusion 19, and along the annular protrusion 19. The wafer 10 is transported and processed while being supported in the opening of the frame 40.

[0039] In the separation step 2, first, the bottom surface of the circular recess 18 on the back surface 17 side of the wafer 10 is sucked and held on the holding surface 211 of the holding table 210 via the tape 41, and the frame 40 is clamped by the clamping part 212. Next, the wafer 10 and the condenser 222 of the laser beam irradiation unit 220 are aligned. Specifically, the holding table 210 is moved to the irradiation area below the laser beam irradiation unit 220 by a moving unit (not shown). Next, the wafer 10 is photographed and aligned by an imaging unit (not shown), and the irradiation part of the laser beam irradiation unit 220 is vertically opposed to the boundary area 20 of the wafer 10, and then the focal point (beam spot 240) of the laser beam 230 is set on the front surface 12 of the wafer 10. The diameter of the beam spot 240 is about 1 μm or more and 20 μm or less.

[0040] In the separation step 2, next, while rotating the holding table 210 around a vertical axis, a pulsed laser beam 230 is irradiated from the laser beam irradiation unit 220 onto the front surface 12 side of the wafer 10. That is, the laser beam 230 is annularly irradiated along the boundary region 20 of the wafer 10. At this time, in the separation step 2 of the embodiment, the laser beam 230 is branched by the branching unit 224, so that a first laser beam irradiation step 2-1 and a second laser beam irradiation step 2-2 are performed simultaneously.

[0041] The first laser beam irradiation step 2-1 is a step of irradiating the first laser beam 231 with a first power density along the boundary region 20 to form the machined groove 21. The first laser beam 231 forms a first beam spot 241 having a first power density. The first laser beam 231 is irradiated along the boundary region 20 to form the machined groove 21 along the boundary region 20. The machined groove 21 is a through hole that penetrates from the front surface 12 side of the wafer 10 toward the outer periphery of the circular recess 18 on the back surface 17 side. As a result, the wafer 10 is separated into the circular recess 18 corresponding to the device region 13 and the annular protrusion 19 corresponding to the outer periphery excess region 14.

[0042] The second laser beam irradiation step 2-2 is a step of irradiating a second laser beam 232 at a second power density different from the first power density along the processed groove 21 formed in the first laser beam irradiation step 2-1. The second laser beam 232 forms a second beam spot 242 having the second power density. By irradiating the second laser beam 232 along the processed groove 21, processing debris generated by the irradiation of the first laser beam 231 is removed, and cracks and chipping are suppressed.

[0043] 7 to 10 are partially enlarged plan views of the wafer 10 showing the beam spot 240 in the separation step 2 shown in Fig. 2. In the separation step 2, the position of the second beam spot 242 relative to the position of the first beam spot 241 can be set in various ways, as shown in Figs. 7 to 10.

[0044] 7, in the second laser beam irradiation step 2-2, the second laser beam 232 may be irradiated toward the circular recess 18 from the center in the width direction of the processed groove 21 formed in the first laser beam irradiation step 2-1. That is, the laser beam 230 is branched so that the second beam spot 242 is located radially inward of the first beam spot 241 of the wafer 10.

[0045] The branch interval is preferably in a range in which the first beam spot 241 and the second beam spot 242 do not completely overlap, but are not completely separated. The overlap rate between the first beam spot 241 and the second beam spot 242 is set to 10% or more and 90% or less, preferably 50% or more and 70% or less, in the radial direction of the wafer 10. The overlap rate in the circumferential direction of the wafer 10 is preferably 0%.

[0046] In this case, the first power density is set to be larger than the second power density. The output ratio of the first laser beam 231 and the second laser beam 232 is set in the range of 6:4 to 9:1. For example, when a 10 W laser beam 230 is incident, the first laser beam 231 is 6 W or more and 9 W or less, and the second laser beam 232 is 4 W or less and 1 W or more.

[0047] 8, in the second laser beam irradiation step 2-2, the second laser beam 232 may be irradiated to the annular convex portion 19 side from the center in the width direction of the processed groove 21 formed in the first laser beam irradiation step 2-1. That is, the laser beam 230 is branched so that the second beam spot 242 is located on the outer side in the radial direction of the wafer 10 than the first beam spot 241.

[0048] The branching interval (overlap rate) and power density are the same as those in the example shown in Fig. 7. That is, the overlap rate between the first beam spot 241 and the second beam spot 242 is set to 10% or more and 90% or less, preferably 50% or more and 70% or less, in the radial direction of the wafer 10. The overlap rate in the circumferential direction of the wafer 10 is preferably 0%. In addition, the first power density is set to be larger than the second power density, and the output ratio between the first laser beam 231 and the second laser beam 232 is set to be in the range of 6:4 to 9:1.

[0049] 9, in the second laser beam irradiation step 2-2, the second laser beam 232 may be irradiated to both the circular recess 18 side from the center in the width direction of the processed groove 21 formed in the first laser beam irradiation step 2-1 and the annular protrusion 19 side from the center in the width direction of the processed groove 21. That is, the laser beam 230 is branched so that two second beam spots 242 are located radially inward and radially outward of the wafer 10 from the first beam spot 241, respectively.

[0050] The branch interval (overlap rate) is the same as the example shown in Fig. 7 and Fig. 8. That is, the overlap rate between the first beam spot 241 and each of the second beam spots 242 is set to 10% or more and 90% or less, preferably 50% or more and 70% or less, in the radial direction of the wafer 10. The overlap rate in the circumferential direction of the wafer 10 is preferably 0%. In addition, the first power density is set to be larger than the second power density, and the output ratio between the first laser beam 231 and the two second laser beams 232 is set in the range of 6:2:2 to 9:0.5:0.5.

[0051] 10, in the second laser beam irradiation step 2-2, the second laser beam 232 may be irradiated along the center of the processed groove 21 formed in the first laser beam irradiation step 2-1. That is, the laser beam 230 is branched so that the second beam spot 242 is formed at a position following the first beam spot 241. That is, the laser beam 230 is branched in parallel in the circumferential direction of the wafer 10. The overlap rate between the first beam spot 241 and the second beam spot 242 is set to 0%.

[0052] In this case, the first power density is set to be smaller than the second power density. The output ratio of the first laser beam 231 and the second laser beam 232 is set to be in the range of 1:4 to 9:6. For example, when a 10 W laser beam 230 is incident, the first laser beam 231 is 1 W or more and 4 W or less, and the second laser beam 232 is 9 W or less and 6 W or more.

[0053] 7 to 10, the first laser beam irradiation step 2-1 and the second laser beam irradiation step 2-2 are performed simultaneously by branching the laser beam 230, but the second laser beam irradiation step 2-2 may be performed after forming the processed groove 21 all around the boundary region 20 in the first laser beam irradiation step 2-1. That is, the separation step 2 may be performed in multiple passes. In this case, the irradiation of the first laser beam 231 and the irradiation of the second laser beam 232 may each be performed in multiple passes.

[0054] When the first laser beam irradiation step 2-1 and the second laser beam irradiation step 2-2 are not performed simultaneously, the first power density and the second power density may be larger than each other as long as they are different power densities even when the beam spot 240 is set in any of the modes shown in Fig. 7 to Fig. 10. In addition, the second laser beam 232 may be irradiated in a defocused state.

[0055] [Table 1]

[0056] Table 1 shows whether or not cracks occur in the device region 13 and the peripheral excess region 14 of the wafer 10 after the separation step 2 is performed under each condition. In the first to fourth examples, as shown in Figs. 7 to 10, the laser beam 230 is branched and the first laser beam irradiation step 2-1 and the second laser beam irradiation step 2-2 are performed simultaneously. The magnitude of each power density at this time is as shown above. In the fifth example, the first laser beam irradiation step 2-1 and the second laser beam irradiation step 2-2 are not performed simultaneously but are performed in multiple passes. The comparative example is a case where only the first laser beam irradiation step 2-1 is performed.

[0057] As shown in Table 1, no cracks occur in any of the embodiments shown in the first to fourth examples. In the fifth example, even if a crack occurs when forming the machined groove 21 in the first laser beam irradiation step 2-1, the crack is repaired by melting and then solidifying around the crack in the second laser beam irradiation step 2-2. In contrast, cracks occur in the comparative example in which only the first laser beam irradiation step 2-1 is performed.

[0058] [Modifications] Fig. 11 is a side view partially in cross section showing one state of the separation step 2 according to the modified example. In the separation step 2 of the modified example, a processed groove 21 is formed along the boundary region 20 of the wafer 10 by a laser processing apparatus 200-1 shown in Fig. 11. The laser processing apparatus 200-1 includes a holding table 210-1, a laser beam irradiation unit 220-1, and a moving mechanism (not shown) for relatively moving the holding table 210-1 and the laser beam irradiation unit 220-1.

[0059] The holding table 210-1 of the modified example has a holding surface 211-1 on the lower surface. The holding table 210-1 holds the wafer 10 on the holding surface 211-1 with the irradiated surface of the wafer 10 exposed downward. That is, in the laser processing apparatus 200-1 of the modified example, the laser beam irradiation unit 220-1 irradiates the wafer 10 held on the holding surface 211-1 facing downward with a laser beam 230 from below.

[0060] The procedure of the separation step 2 in the modified example is the same as that in the embodiment except that the holding table 210-1 and the laser beam irradiation unit 220-1 are upside down, and therefore the description will be omitted. When the laser beam 230 is irradiated from below, it is possible to suppress the processing waste generated by the irradiation of the laser beam 230 from falling and scattering on the wafer 10.

[0061] As described above, in the processing method of the wafer 10 according to the embodiment and the modified example, when removing the annular convex portion 19 by irradiating the laser beam 230, the second laser beam 232 having a weaker output than the first laser beam 231 for separating along the boundary region 20 is simultaneously irradiated to at least one of the circular concave portion 18 side and the annular convex portion 19 side, or the second laser beam 232 having a stronger output than the first laser beam 231 is simultaneously irradiated along the center of the processed groove 21. Alternatively, the second laser beam 232 having an output different from that of the first laser beam 231 is irradiated after the processed groove 21 is formed all around the boundary region 20.

[0062] The above-mentioned processing can suppress the crack from spreading toward the device region 13 or the outer circumferential excess region 14 when removing the annular convex portion 19. Also, by simultaneously performing the first laser beam irradiation step 2-1 and the second laser beam irradiation step 2-2 as in the embodiment, the bending strength can be improved, and therefore the occurrence of cracks or chipping when removing the annular convex portion 19 can be suppressed. Also, by simultaneously performing the first laser beam irradiation step 2-1 and the second laser beam irradiation step 2-2, the processing time can be shortened, and the productivity can be improved.

[0063] It should be noted that the present invention is not limited to the above-described embodiment and modifications, and can be practiced in various forms without departing from the spirit of the present invention.

[0064] For example, in the separation step 2, the laser beam 230 is irradiated from the front surface 12 side of the wafer 10, but it may be irradiated from the back surface 17 side. Also, before the laser beam 230 is irradiated, a protective film may be applied to the irradiated surface of the wafer 10.

[0065] Furthermore, the branching unit 224 is not limited to the embodiment, and may include a diffractive optical element, a phase conversion element, or the like. [Explanation of symbols]

[0066] 10 wafers 11 Substrate 12 Surface 13 Device Area 14 Surplus outer area 15 Division line 16 Devices 17 Back side 18 Circular recess 19 Annular protrusion 20 Boundary area 21 Machining groove 100 Grinding equipment 200, 200-1 Laser processing equipment 230 Laser Beam 231 First Laser Beam 232 Second Laser Beam 240 beam spots 241 First Beam Spot 242 Second beam spot

Claims

1. A wafer processing method for processing a wafer having, on a surface thereof, a device region in which a plurality of devices are formed and a peripheral excess region surrounding the device region, comprising: a circular recess forming step of forming a circular recess in a region corresponding to the device region on the back surface of the wafer, and forming an annular protrusion including a region corresponding to the outer circumferential excess region on the outer circumferential side of the circular recess; a separation step of irradiating a laser beam along a boundary region between the circular recess and the annular protrusion to separate the circular recess and the annular protrusion along the boundary region, The separation step comprises: a first laser beam irradiation step of irradiating a laser beam at a first power density along the boundary region to form a groove; A second laser beam irradiation step of irradiating a laser beam at a second power density different from the first power density along the processed groove formed in the first laser beam irradiation step. A wafer processing method comprising the steps of:

2. In the second laser beam irradiation step, A laser beam is irradiated from the center of the width direction of the processed groove formed in the first laser beam irradiation step toward the circular recess.

2. The wafer processing method according to claim 1 .

3. In the second laser beam irradiation step, A laser beam is irradiated from the center of the groove in the width direction formed in the first laser beam irradiation step toward the annular convex portion.

2. The wafer processing method according to claim 1 .

4. In the separation step, The laser beam is split to form a first beam spot having the first power density and a second beam spot having a second power density, thereby simultaneously performing the first laser beam irradiation step and the second laser beam irradiation step.

4. The wafer processing method according to claim 1, wherein the wafer is processed by a process comprising the steps of:

5. The first power density is set to be greater than the second power density.

4. The wafer processing method according to claim 1, wherein the wafer is processed by a process comprising the steps of:

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