Laser beam processing methods for wafers

Abstract

Laser beam processing method for a wafer (W) having a device (D) in each of the regions which are subdivided by a plurality of provided division lines (R) formed in a grid, the method comprising: a first groove processing training step for emitting a pulsed laser beam (L) along the intended division line (R) in such a way that the overlap rate of the concentrated beam spots (C1, C2) of the pulsed laser beam, which is concentrated onto the wafer (W), is identical or less than 95%, in order to form a first laser beam processing groove (S1); and a second groove processing training step after the execution of the first groove processing training step for emitting the pulsed laser beam (L) along the first laser beam processing groove (S1) in such a way that the overlap rate of the concentrated beam spots (C1, C2) of the pulsed laser beam, which is concentrated on the wafer (W), is identical or more than 97%, in order to form a second laser beam processing groove (S2) on a bottom region of the first laser beam processing groove (S1), wherein the depth of the second laser beam processing groove (S2) is greater than the depth of the first laser beam processing groove (S1), and debris generated in the second groove processing step is deposited within the first laser beam processing groove (S1) so that it does not protrude to a surface of the wafer (W).

Description

Background of the invention: Technical field

[0001] The present invention relates to a laser beam processing method for a wafer, in which a surface of a wafer, which is equipped with a plurality of devices, is irradiated with a laser beam to perform an ablation processing. State of the art

[0002] Semiconductor devices such as memory, CPUs, etc., and optical devices such as LEDs (light-emitting diodes), etc., are manufactured by a process in which a laser beam is emitted through a laser beam processing device along predetermined division lines of a wafer, which is formed with semiconductor devices such as ICs (integrated circuits), LSIs (large integrations), etc., or optical devices such as LEDs, etc., and the wafer is divided along the predetermined division lines.

[0003] In this laser beam processing method, the wafer was split into setup chips by complete cutting with a cutting blade after grooves were formed by the laser beam, or by fracturing the wafer after modified layers were formed by the laser beam. A method was also investigated in which grooves were formed deeply by the laser beam, and the wafer was subsequently split. In this case, it was found that if the flattening (degree of flatness) of the elliptical spot diameter of the laser beam is increased, a deep groove can be formed by a single laser beam irradiation sequence, and the desired processing can be carried out efficiently (see, for example, Japanese patent application JP 2007-275912A and US patent 2007 / 0264799A1, which relates to a wafer processing method for forming a groove in a wafer).US 2006 / 0255022A1 relates to a laser processing method for a wafer to form a groove by applying a pulsed laser beam to a rear surface of a wafer. Description of the invention

[0004] During processing, where grooves are formed in a wafer using a laser beam, melt products from the wafer, known as debris, can be deposited at both sides of the groove, depending on the amount of wafer removed. Whether a deep groove is formed by a single laser scan or by multiple laser scans of the same location to create a deep groove, debris of considerable height is formed in essentially the same way. Such debris would clog the pick-up mechanism (a component used to hold a chip by suction) for chip lifting in the subsequent step, which is a very serious problem.

[0005] Accordingly, it is an object of the present invention to provide a laser beam processing method for a wafer in which the melt products of the wafer, so-called debris, can be retained from being exposed to the surface of the wafer.

[0006] According to one aspect of the present invention, a laser beam processing method for a wafer is provided, comprising a device in each of the regions which are delimited by a plurality of provided division lines which are configured in a grid, wherein the method comprises: a first groove processing formation step for emitting a pulsed laser beam along the provided division line in such a way that the overlap rate of concentrated beam spots of the pulsed laser beam which is concentrated on the wafer is identical or less than 95%, in order to form a first laser beam processing groove;and a second groove training step, after the execution of the first groove training step, for emitting the pulsed laser beam along the first laser beam training groove in such a way that the overlap rate of the concentrated beam spots of the pulsed laser beam focused onto the wafer is identical or greater than 97%, in order to form a second laser beam training groove at a bottom region of the first laser beam training groove, wherein the depth of the second laser beam training groove is greater than the depth of the first laser beam training groove, and debris generated in the second groove training step is deposited within the first laser beam training groove so as not to protrude from a surface of the wafer.

[0007] Preferably, the concentrated beam spot of the pulsed laser beam is elliptical in shape, the pulsed laser beam is emitted onto the wafer in the first groove training step and the second groove training step in such a way that a principal axis of the concentrated beam spot is arranged along the intended division line, and the length of the principal axis of the concentrated beam spot in the second groove training step is greater than the length of the principal axis of the concentrated beam spot in the first groove training step.

[0008] In the laser beam processing method for a wafer according to the present invention, the pulsed laser beam is emitted with an overlap rate that is identical to or less than 95% to provisionally form the first laser beam processing groove, after the pulsed laser beam is emitted with an overlap rate that is identical to or more than 97% to form the deep second laser beam processing groove on a bottom region of the first laser beam processing groove, and the wafer is divided into chips.In such processing, debris of a lower height is generated at an overlap rate of 95% or less, while deep grooves can be formed at an overlap rate of 97% or more. The greater height debris generated at the latter overlap rate is captured within the first laser beam processing groove, thus preventing it from being exposed to the wafer surface. Therefore, in cases where the wafer is processed to a relatively deep depth or completely cut, the laser beam processing method for a wafer according to the present invention enables efficient processing with a reduced number of laser beam scans, while preventing the debris from being exposed to the wafer surface.

[0009] The above and other tasks, features and advantages of the present invention and the way in which they are implemented will become clearer, and the invention itself will be better understood by studying the following description and the attached claims with reference to the accompanying drawings, which show some preferred embodiments of the invention. Brief description of the drawings Fig. Figure 1 is a perspective view showing an exemplary embodiment of a laser beam processing device with which the laser beam processing method for a wafer can be carried out according to an embodiment of the present invention; Fig. 2 is a perspective view of at least one wafer which is to be laser beam processed by the laser beam processing method for a wafer according to the embodiment; Fig. Figure 3 is a perspective view of the wafer, which is to be laser-processed by the laser beam processing method for a wafer according to the embodiment in the state in which it is supported by a ring-shaped frame; Fig. Figure 4A is an illustration of the design of a condenser of laser beam emission means, wherein a concentrated beam spot has an elliptical shape, the laser beam processing device according to the present embodiment in a Y-axis direction; Fig. 4B is an illustration of the condenser of the laser beam emitting means, wherein the concentrated beam spot has an elliptical shape, of the laser beam processing device according to the embodiment in an X-axis direction; Fig. 4C is a top view of a concentrated beam spot formed into an elliptical shape by the condenser of the laser beam emitting means of the laser beam processing device according to the embodiment; Fig. Figure 5A is an illustration of the design of a condenser of the laser beam emission means, wherein a concentrated beam spot has a circular shape, of the laser beam processing device according to the embodiment in a Y-axis direction; Fig. Figure 5B is an illustration of the design of the condenser of the laser beam emission means, wherein the concentrated beam spot has a circular shape, of the laser beam processing device according to the embodiment in an X-axis direction; Fig. 5C is a top view of a concentrated beam spot which is formed into a circular shape by the condenser of the laser beam emitting means of the laser beam processing device according to the embodiment; Fig. Figure 6A is a schematic illustration of a side cross-sectional surface of the laser beam processing device according to the embodiment in a state where a first laser beam processing groove is formed; Fig. 6B is a cross-sectional view along line VIb-VIb in Fig. 6A; Fig. Figure 7A is a schematic illustration of a side cross-sectional surface of the laser beam processing device according to the embodiment in a state where a second laser beam processing groove is formed; Fig. 7B is a cross-sectional view along line VIIb-VIIb in Fig. 7A; Fig. Figure 8 is a flowchart of the laser beam processing method for a wafer according to the embodiment; and Fig. Figure 9 is a visualization of the overlap rate of the concentrated beam spot in the laser beam processing method for a wafer according to the embodiment. Detailed description of the preferred embodiment

[0010] A preferred embodiment of the present invention is described in detail below with reference to the drawings. The present invention is not limited to the content described in the following embodiment. Furthermore, the components described below include those that a person skilled in the art might encounter and those that are essentially the same as those described below. Moreover, the embodiments described below can be combined as required. In addition, various omissions, substitutions, and adaptations are possible without departing from the core message of the present invention.

[0011] The laser beam processing method for a wafer W according to the embodiment is carried out by a laser beam processing device 1, which is located in Fig. The laser beam processing device 1 is configured to perform a method in which a pulsed excitation laser beam L (pulsed laser beam) is emitted onto the wafer W along designated division lines R, while a clamping table 10 for holding the wafer W on it and laser beam emitting means 20 are moved relative to each other, thereby applying ablation processing to the wafer W to create laser beam processing grooves S (shown in Figure 1). Fig. 7A and Fig. 7B) to form in the wafer W.

[0012] Here, the wafer W is a processing object that is laser-processed by the laser beam processing device 1. In the present embodiment, the wafer W is a circular disk-shaped semiconductor wafer or optical setup wafer whose base material is silicon, sapphire, gallium, or the like. As in Fig. 2 and Fig. As shown in Figure 3, the wafer W is formed on its end-face surface WS with features D in regions that are delimited into a grid by a multitude of predefined division lines R. As shown in Fig. Figure 3 shows a back surface on the side of the wafer W, which is opposite the front surface WS, which is formed with a plurality of features D, attached to a pressure-sensitive adhesive strip T, and an annular frame F is attached to the pressure-sensitive adhesive strip T, which is attached to the wafer W, thereby fixing the wafer W to the annular frame F.

[0013] As in Fig. Figure 1 shows the laser beam processing device 1 comprising the clamping table 10, the laser beam emitting means 20, image acquisition means 30, and control means not shown. The laser beam processing device 1 also includes: an X-axis movement means 40, by which the clamping table 10 and the laser beam emitting means 20 are movable relative to each other in an X-axis direction; a Y-axis movement means 50, by which the clamping table 10 and the laser beam emitting means 20 are movable relative to each other in a Y-axis direction; and a Z-axis movement means 60, by which the clamping table 10 and the laser beam emitting means 20 are movable relative to each other in a Z-axis direction.

[0014] The clamping table 10 has a circular, disc-shaped form, the surface of which is made of porous ceramic or the like; it is connected to a vacuum suction source (not shown) via a vacuum suction passage (not shown), whereby the wafer W is attached to it before laser processing, and the clamping table holds the wafer W in place by suction. The clamping table 10 can also be disassembled and mounted on a table trolley 3 (shown in Fig. 1) is attached to a main body 2 of the laser beam processing device 1. The table carriage 3 can be moved in the X-axis direction by the X-axis motion means 40, in the Y-axis direction by the Y-axis motion means 50, and rotated about a central axis (parallel to the Z-axis) by a carriage drive source (not shown).

[0015] The laser beam emitting means 20 is a means by which the end-face surface WS of the wafer W is irradiated with a pulsed laser beam L (see Fig. 4A to 5C). The laser beam emitter 20 can be moved in the Z-axis direction relative to the wafer W, which is held on the clamping table 10, by the Z-axis motion device 60. The laser beam emitter 20 comprises laser beam oscillators (not shown) and a condenser 21, through which the pulsed laser beam L, which has been set into oscillation by the laser beam oscillators, is emitted onto the end-face surface WS of the wafer W.

[0016] The laser beam oscillator, which converts the pulsed laser beam L into a pulsed oscillation at a wavelength that is absorbed within the wafer W, can be suitably selected according to the type of wafer W, the processing method, and the like. For example, a YAG laser oscillator, a YVO4 laser oscillator, or the like can be used as the laser beam oscillator. The laser beam oscillator converts the laser beam L into a pulsed oscillation with a repetition frequency of, for example, 10 kHz. As shown in Fig. 4A and Fig. As shown in Figure 4B, the condenser 21 comprises a first cylindrical lens 22 and a second cylindrical lens 23, through which the pulsed laser beam L, which has been set into oscillation by the laser beam oscillator, is passed, and a condenser lens 24 for concentrating the pulsed laser beam L. The first cylindrical lens 22 forms a convex lens, while the second cylindrical lens 23 forms a concave lens.

[0017] Furthermore, the condenser 21 is designed such that the second cylindrical lens 23 is moved by a driving force (not shown) of a motor between a position in which the first cylindrical lens 22 and the second cylindrical lens 23 come into contact with each other, as shown in Fig. 5A and Fig. 5B shown, and a position in which the second cylindrical lens and the first cylindrical lens 22 are spaced apart from each other, as in Fig. 4A and Fig. 4B shown, can be moved. When the first cylindrical lens 22 and the second cylindrical lens 23 are brought into contact with each other, as shown in Fig. 5A and Fig. As shown in Figure 5B, the condenser 21 forms a concentrated beam spot C1 of the pulsed laser beam L into a circular shape, as shown in Figure 5B. Fig. 5C shown. On the other hand, if the first cylindrical lens 22 and the second cylindrical lens 23 are arranged at a distance from each other, as in Fig. 4A and Fig. As shown in Figure 4B, the condenser 21 forms a concentrated beam spot C2 of the pulsed laser beam L into an elliptical shape, as shown in Fig. 4C shown.

[0018] The image acquisition device 30 serves to acquire an image of the end face WS of the wafer W, which is held on the clamping table 10. The image acquisition device 30 is designed so that it can be moved in the Z-axis direction relative to the wafer W, which is held on the clamping table 10, together with the laser beam emission device 20 by the Z-axis movement device 60. The image acquisition device 30 outputs the image of the end face WS of the wafer W, which is held on the clamping table 10, to the control device.

[0019] The control means serves to control the aforementioned components of the laser beam processing device 1 in order to cause the laser beam processing device 1 to perform a processing operation on the wafer W. The control means causes the laser beam emitters 20 to emit a pulsed laser beam L onto the end face WS of the wafer W in order to form first laser beam processing grooves S1 and subsequently second laser beam processing grooves S2 on the base region of the first laser beam processing grooves S1, thereby forming the laser beam processing grooves S in the wafer W. The control means also includes, as a secondary component, a microprocessor (not shown), comprising a processor consisting of a CPU or the like, and a ROM, RAM, or the like.The control medium is linked to a display medium (not shown) for displaying the status of the processing operation and operating resources (not shown) which are used at the time by an operator to register information regarding the processing content or the like.

[0020] The laser beam processing method for a wafer W according to the present embodiment is described below. This method involves emitting a laser beam L, which is pulsed, along the defined division lines R formed on the end-face surface WS of the wafer W to perform ablation processing and thereby form the laser beam processing grooves S. The laser beam processing method for a wafer W comprises at least a first groove formation step and a second groove formation step.

[0021] In the laser beam processing method for a wafer W, information regarding the processing content is registered in the control means by a user, and the laser beam processing device 1 begins a processing operation when a processing operation start command is provided by the user. In the processing operation, the wafer W, which adheres to the annular frame F by the pressure-sensitive adhesive strip T, is secured on the clamping table 10; subsequently, the control means cause the wafer W to be held in suction on the clamping table 10 in step ST1. Fig. 8, and the control progresses to step ST2.

[0022] The control means now cause the clamping table 10 to move via the X-axis motion means 40 and the Y-axis motion means 50 in order to position the wafer W, which is held on the clamping table 10, on the underside of the image acquisition means 30, and to cause the image acquisition means 30 to acquire an image. The image acquisition means 30 outputs the acquired image to the control means. Subsequently, the control means performs image processing, such as raster adjustment to align the intended division line R on the wafer W, which is held on the clamping table 10, with the condenser 21 of the laser beam emission means 20, thereby aligning the laser beam emission means 20, and the control proceeds to step ST3.

[0023] Subsequently, in step ST3, the control device causes the pulsed laser beam L to be emitted along the intended division line R, while the clamping table 10 moves in the direction of arrow X1 (shown in Fig. 6A) is moved by the X-axis motion means 40 in such a way that the overlap rate of the elliptical concentrated beam spots C2 of the pulsed laser beam L, which is concentrated on the wafer W, is within the range of 50% to 95%. The control means forms the first laser beam processing groove S1 (which forms the laser beam processing groove S), as in Fig. 6A and Fig. Figure 6B shows the first laser beam processing groove S1 in a comparatively flat shape, and debris DB1 (illustrated by closely spaced parallel oblique lines in Figure 6B). Fig. 6B), which consists of melt products of wafer W generated during the formation of the first laser beam processing groove S1, are formed as small protrusions on both inclined surfaces of the first laser beam processing groove S1. Step ST3 corresponds to the first groove processing formation step, after which the control system proceeds to step ST4.

[0024] Subsequently, in step ST4, the control means causes the pulsed laser beam L to be emitted along the first laser beam processing groove S1, while the clamping table 10 moves in the direction of arrow X2 (shown in Fig. 7A), opposite arrow X1, is moved by the X-axis motion means 40 in such a way that the overlap rate of the concentrated beam spots C2 of the pulsed laser beam L, which is concentrated on the wafer W, is identical or greater than 97% and less than 100%. The control means forms the second laser beam processing groove S2 (which forms the laser beam processing groove S) on the bottom region of the first laser beam processing groove S1, as shown in Fig. 7A and Fig. 7B shown.

[0025] The depth D2 of the second laser beam processing groove S2 is greater than the depth D1 of the first laser beam processing groove S1 because the overlap rate in step ST4 is greater than the overlap rate in step ST3, as shown in Fig. 7A and Fig. 7B is shown. In addition, the debris DB2 (characterized by closely spaced parallel diagonal lines in Fig. 7B), which consists of melt products of wafer W generated in step ST4, is formed as protrusions on both inclined surfaces of the second laser beam processing groove S2 and deposited within the first laser beam processing groove S1; thus, the debris DB2 does not protrude from the end-face surface WS of wafer W. Furthermore, in the present embodiment, the second laser beam processing grooves S2 penetrate wafer W. Incidentally, step ST4 corresponds to the second groove processing step, and the debris DB1 and DB2 is in Fig. 6A and Fig. 7A omitted.

[0026] In steps ST3 and ST4 of the present embodiment, the control means causes the cylindrical lenses 22 and 23 of the condenser 21 to be spaced apart from each other in the laser beam emission means 20. The pulsed laser beam L is emitted such that the concentrated beam spot C2 has an elliptical shape, and the principal (longitudinal) axis of the concentrated beam spot C2 is arranged along the intended division line R and the X-axis, as shown in Fig. 4C shown. Furthermore, the control means causes the laser beam emitter 20 to oscillate the laser beam L in a pulsed form, whereby the concentrated beam spots C2 of the pulsed laser beam L, which is concentrated on the end-face surface WS of the wafer W, which is moved by the X-axis motion means 40, only partially overlap with each other (and are not overlapped at the other parts), as shown by the solid line and the two-dot dashed line in Fig. 9 shown.

[0027] The overlap rate in the present invention can be expressed by the following formula 1: Overlap rate (%) - ((MA-1) / MA) × 100 ... Formula 1, where MA is the diameter in the principal (longitudinal) axis of the concentrated beam spot C2 of the laser beam L, which is set into a pulsed oscillation and concentrated onto the end-face surface WS of the wafer W, and 1 is the length in the central principal (longitudinal) axis of the non-overlapping part (represented by parallel oblique lines in Fig. 9) the concentrated radiation spots C2 are adjacent to each other.

[0028] Furthermore, in steps ST3 and ST4 of the present embodiment, the laser beam emitter 20 emits the pulsed laser beam L with the same frequency and repetition rate, such that the pulsed laser beam L is concentrated into elliptical concentrated beam spots C2 of the same shape on the end-face surface WS of the wafer W. For example, the diameter MA (shown in Fig. C) in the main (longitudinal) axis of the concentrated radiation spot C2 100 to 800 µm and the diameter MB (branched into Fig. C) in the secondary axis (short side) of the concentrated beam spots C2 50 to 10 µm. Furthermore, in the present embodiment, the movement speed of the clamping table 10 in step ST4 is lower than the movement speed of the clamping table 10 in step ST3.

[0029] After step ST4, the control system proceeds to step ST5. In step ST5, the control system determines whether the first laser beam processing grooves S1 and the second laser beam processing grooves S2 have been formed along all of the intended division lines R; more precisely, whether the laser beam processing grooves S have been formed along all of the intended division lines R. If it is determined that the first laser beam processing grooves S1 and the second laser beam processing grooves S2 have not been formed along all of the intended division lines R, the control system returns to step ST3.

[0030] Subsequently, when the first laser beam processing grooves S1 and the second laser beam processing grooves S2 have been formed along all the designated division lines R, the first laser beam processing grooves S1 and the second laser beam processing grooves S2, which have been formed along all the designated division lines R, have penetrated the wafer W, and the wafer W has been subdivided into chips, each comprising the device D. When it is determined that the first laser beam processing grooves S1 and the second laser beam processing grooves S2 have been formed along all the designated division lines R, the control means stop the laser beam processing process by the laser beam processing emitter 20 and retract the clamping table 10 from the position on the underside of the laser beam processing device 20 by the X-axis motion means 40.The wafer W, which has been subjected to the laser beam processing procedure, is removed from the clamping table 10. If a wafer W is clamped onto the clamping table 10 before laser processing, the control means ensure that the laser beam processing applied to the wafer W is carried out in the same manner as in the previously described procedure.

[0031] As previously mentioned, according to the laser beam processing method for a wafer according to the present embodiment, irradiation with the pulsed laser beam L is carried out with an overlap rate of 95% or less, whereby the narrower first laser beam processing grooves S1 are initially formed, after which the deeper second laser beam processing grooves S2 are formed at the bottom regions of the first laser beam processing grooves S1 with an overlap rate of 97% or more. In such processing, debris DB1 with a small height is produced at an overlap rate of 95% or less, whereby the deeper grooves can be formed with an overlap rate of 97% or more, with the result that the debris DB2 with a greater height is produced in such a way that it is contained within the first laser beam processing grooves S1.Thus, the large height of the DB2 debris generated during the formation of the second laser beam processing groove S2 can be retained from being exposed to the end-face surface WS of the wafer W. Accordingly, in cases where the wafer W is processed relatively deeply or completely cut, the laser beam processing method for a wafer W according to the present embodiment enables efficient processing with a reduced number of laser beam L scans, while the DB2 debris is retained from being exposed to the end-face surface WS of the wafer W.

[0032] Furthermore, according to the laser beam processing method for a wafer W according to the present embodiment, the overlap rate in step ST3 is set to be identical or greater than 50%. This allows the first laser beam processing grooves S1 to be formed with a uniform width, ensuring that the second laser beam processing grooves S2 can be reliably formed at the bottom of the first laser beam processing grooves S1. Additionally, the overlap rate in step ST4 is set to less than 100%. This allows the second laser beam processing grooves S2 to be reliably formed at the bottom of the first laser beam processing grooves S1.

[0033] In the embodiment described above, after the first laser beam processing groove S1 has been formed along a single provided division line R, the second laser beam processing groove S2 is formed on the bottom region of the first laser beam processing groove S1. In the present embodiment, however, a different configuration can be adopted in which the first laser beam processing grooves S1 are formed along all the provided division lines R before the second laser beam processing grooves S2 are formed on the bottom regions of the first laser beam processing grooves S1.

[0034] In the embodiment described above, the second laser beam processing groove S2 is formed in step ST4 after the first laser beam processing groove S1 has been formed in step ST3. In the present embodiment, however, an alternative configuration can be adopted in which at least one laser beam processing groove is also formed on a bottom region of the second laser beam processing groove S2. In this case, the overlap rate during the formation of the latter laser beam processing groove can be improved, or the overlap rate during the formation of the latter laser beam processing groove can be identical to the overlap rate during the formation of the second laser beam processing groove S2. Furthermore, in the present invention, the second laser beam processing groove S2 can be formed after the first laser beam processing groove S1 has been formed several times.

[0035] In the embodiment described above, the concentrated beam spot C2 in step ST3 is the same in shape as the concentrated beam spot C2 in step ST4. In the present invention, however, the length of the principal axis of the concentrated beam spot C2 of the laser beam L can be greater in step ST4 than in step ST3.

[0036] While the second laser beam processing grooves S2 were designed to penetrate through the wafer W in the embodiment described above, the second laser beam processing grooves S2 in the present invention do not necessarily have to penetrate through the wafer W.

Claims

[1] Laser beam processing method for a wafer (W) having a device (D) in each of the regions which are subdivided by a plurality of provided division lines (R) formed in a grid, the method comprising: a first groove processing training step for emitting a pulsed laser beam (L) along the intended division line (R) in such a way that the overlap rate of the concentrated beam spots (C1, C2) of the pulsed laser beam, which is concentrated onto the wafer (W), is identical or less than 95%, in order to form a first laser beam processing groove (S1); and a second groove processing training step after the execution of the first groove processing training step for emitting the pulsed laser beam (L) along the first laser beam processing groove (S1) in such a way that the overlap rate of the concentrated beam spots (C1, C2) of the pulsed laser beam, which is concentrated on the wafer (W), is identical or more than 97%, in order to form a second laser beam processing groove (S2) on a bottom region of the first laser beam processing groove (S1), wherein the depth of the second laser beam processing groove (S2) is greater than the depth of the first laser beam processing groove (S1), and debris generated in the second groove processing formation step is deposited within the first laser beam processing groove (S1) so that it does not protrude to a surface of the wafer (W). [2] Laser beam processing method for a wafer (W) according to claim 1, where the concentrated beam spot (C2) of the pulsed laser beam (L) has an elliptical shape, the pulsed laser beam (L) is emitted onto the wafer (W) in the first groove training step and the second groove training step in such a way that a principal axis of the concentrated beam spot (C2) is arranged along the intended division line (R), and the length of the principal axis of the concentrated beam spot (C2) in the second groove forming step is greater than the length of the principal axis of the concentrated beam spot (C2) in the first groove forming step.

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