Laser processing method

Abstract

To provide a laser processing method capable of suppressing deflection of cracks extending from a modified region while narrowing the width of a groove formed in an object.SOLUTION: A laser processing method includes the steps of irradiating a wafer 20 with a laser beam L to form a first groove M1 in the wafer 20 along a line 15, irradiating the wafer 20 with a laser beam L to form a second groove M2 in the wafer 20 along the line 15 such that the widthwise end of the first groove M1 overlaps with the first groove M1, and irradiating the wafer 20 with the laser beam L0 to form a modified region 11 along the line 15 inside the wafer 20 after forming a composite groove MH including the first groove M1 and the second groove M2 in the wafer 20, and extending a crack 9 from the modified region 11.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] One aspect of the present invention relates to a laser processing method.

Background Art

[0002] When cutting an object along a line, for example, grooving may be performed to remove the surface layer side of the object along the line (see, for example, Patent Documents 1 and 2). In such grooving, a groove is formed in the object along the line by irradiating the object with laser light.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described technology, after forming a groove, the object may be irradiated with laser light to form a modified region inside the object along the line, and cracks may be extended from the modified region to cut the object along the line. In this case, in order to improve the yield of the cut object (for example, chip yield), it is desirable to narrow the width of the groove formed in the object. However, if the width of the groove is narrowed, cracks are likely to extend so as to deviate from the groove, and the cracks may deviate greatly from the line, which may deteriorate the cutting quality.

[0005] Therefore, an object of one aspect of the present invention is to provide a laser processing method capable of suppressing the deviation of cracks extending from a modified region while narrowing the width of a groove formed in an object.

Means for Solving the Problems

[0006] A laser processing method according to one aspect of the present invention comprises the steps of: irradiating an object with laser light to form a first groove in the object along a line; irradiating an object with laser light to form a second groove in the object along the line such that the widthwise end of the first groove overlaps with the first groove; and after forming a composite groove including the first groove and the second groove in the object, irradiating the object with laser light to form a modified region inside the object along the line and to propagate a crack from the modified region.

[0007] This laser processing method forms a composite groove in the object, including a first groove and a second groove whose ends overlap. This allows for a wider groove width in the object while inducing crack propagation toward these two grooves, thereby enhancing the crack induction effect compared to when a single groove is formed, and suppressing crack propagation that deviates from the groove. In other words, it is possible to narrow the width of the groove formed in the object while suppressing crack deviation extending from the modified region.

[0008] A laser processing method according to one aspect of the present invention may further include a step of cutting the object along a line by expanding a tape attached to the object when the end of the crack reaches the inner surface of the first groove or the inner surface of the second groove, after forming a modified region. In this case, it becomes possible to cut the object with high precision along the line.

[0009] In a laser processing method according to one aspect of the present invention, the object to be processed includes a substrate and a functional element layer on the substrate, and the composite groove may be provided on the functional element layer side of the object to be processed such that both the bottom of the first groove and the bottom of the second groove reach the substrate. In this case, the crack induction effect by the first groove and the second groove can be further enhanced.

[0010] In a laser processing method according to one aspect of the present invention, the object to be processed comprises a substrate and a functional element layer on the substrate, and the composite groove may be provided on the functional element layer side of the object to be processed such that neither the bottom of the first groove nor the bottom of the second groove reaches the substrate. In this case, it becomes possible to make the depths of the first groove and the second groove shallower.

[0011] In a laser processing method according to one aspect of the present invention, the object to be processed comprises a substrate and a functional element layer on the substrate, and the composite groove may be provided in the functional element layer of the object such that either the bottom of the first groove or the bottom of the second groove reaches the substrate. In this case, the crack induction effect by the first groove and the second groove can be further enhanced.

[0012] A laser processing method according to one aspect of the present invention may include a step of forming a protective film on the functional element layer before forming the composite groove. In this case, the functional element layer can be effectively protected by the protective film.

[0013] In a laser processing method according to one aspect of the present invention, the composite groove may have a W-shape in a cross-sectional view perpendicular to the line. In this case, the above effect of suppressing the deviation of cracks extending from the modified region while narrowing the width of the groove formed in the object is significantly enhanced.

[0014] A laser processing method according to one aspect of the present invention may include a step of grinding and thinning the workpiece before forming the composite groove. In this case, the workpiece can be thinned by grinding before forming the composite groove.

[0015] A laser processing method according to one aspect of the present invention may include a step of grinding and thinning the workpiece after forming a modified region. In this case, the workpiece can be thinned by grinding after the formation of a composite groove.

[0016] In the laser processing method according to one aspect of the present invention, a plurality of lines are set on the object, and the step of forming the modified region may include a step of correcting the formation position of the modified region so as to match the center position in the width direction of the composite groove when the deviation amount of the formation position of the modified region from the center position of the composite groove is larger than half of the groove width of the composite groove. In this case, it is possible to correct the formation position of the modified region by using the groove width of the composite width.

Effects of the Invention

[0017] According to one aspect of the present invention, it is possible to provide a laser processing method capable of suppressing the deviation of cracks extending from the modified region while narrowing the width of the groove formed in the object.

Brief Description of the Drawings

[0018] [Figure 1] It is a configuration diagram of a laser processing apparatus for forming a modified region inside a wafer. [Figure 2] It is a configuration diagram of a laser processing apparatus for performing grooving. [Figure 3] It is a plan view of a wafer to be processed. [Figure 4] It is a cross-sectional view of a part of the wafer shown in FIG. 3. [Figure 5] It is a plan view of a part of the street shown in FIG. 3. [Figure 6] It is a diagram showing an example of the positions of the condensing points of the first branched laser light and the positions of the condensing points of the second branched laser light when viewed from the Z direction. [Figure 7] (a) is a cross-sectional view of a wafer for explaining a laser processing method according to an embodiment. (b) is a cross-sectional view of the wafer showing the continuation of FIG. 7(a). (c) is a cross-sectional view of the wafer showing the continuation of FIG. 7(b). [Figure 8] (a) is a cross-sectional view of the wafer showing the continuation of FIG. 7(c). (b) is a cross-sectional view of the wafer showing the continuation of FIG. 8(a). (c) is a cross-sectional view of the wafer showing the continuation of FIG. 8(b). [Figure 9](a) is a cross-sectional view of a wafer showing the continuation of FIG. 8(c). (b) is a cross-sectional view of a wafer showing the continuation of FIG. 9(a). [Figure 10] It is an enlarged cross-sectional view of a part of the wafer in FIG. 9(b). [Figure 11] (a) is a cross-sectional view corresponding to FIG. 10 of a wafer according to a modified example. (b) is a cross-sectional view corresponding to FIG. 10 of a wafer according to another modified example. (c) is a cross-sectional view corresponding to FIG. 10 of a wafer according to still another modified example. [Figure 12] It is a cross-sectional view of a wafer showing the continuation of FIG. 9(b). [Figure 13] It is a cross-sectional view corresponding to FIG. 10 of a wafer according to a conventional example. [Figure 14] It is a diagram showing another example of the positions of the respective condensing points of the first branched laser beam and the positions of the respective condensing points of the second branched laser beam when viewed from the Z direction. [Figure 15] (a) is a diagram showing an example of the positions of the respective condensing points of the first branched laser beam, the positions of the respective condensing points of the second branched laser beam, and the positions of the respective condensing points of the third branched laser beam when viewed from the Z direction. (b) is a cross-sectional view of a wafer showing a composite groove according to a modified example. [Figure 16] (a) is a cross-sectional view of a wafer showing a composite groove according to a modified example. (b) is a cross-sectional view of a wafer showing a composite groove according to a modified example. (c) is a cross-sectional view of a wafer showing a composite groove according to a modified example. [Figure 17] (a) is a cross-sectional view of a wafer showing a composite groove according to a modified example. (b) is a cross-sectional view of a wafer showing a composite groove according to a modified example. (c) is a cross-sectional view of a wafer showing a composite groove according to a modified example. [Figure 18] It is a diagram showing the test results evaluating the deviation of cracks when a composite groove is formed. [Figure 19] (a) is a cross-sectional view of a wafer showing another example of a method for forming a composite groove. (b) is a cross-sectional view of a wafer showing the continuation of FIG. 19(a). [Figure 20] (a) is a cross-sectional view of a wafer showing still another example of a method for forming a composite groove. (b) is a cross-sectional view of a wafer showing the continuation of FIG. 20(a). [Figure 21] This flowchart illustrates an example of laser processing that includes a step to correct the formation position of the modified region. [Figure 22] This is a perspective view showing a laser processing apparatus equipped with optical systems for grooving and optical systems for forming modified regions. [Figure 23] (a) is a cross-sectional view of a wafer illustrating a modified laser processing method. (b) is a cross-sectional view of a wafer continuing from Figure 23(a). (c) is a cross-sectional view of a wafer continuing from Figure 23(b). [Figure 24] (a) is a cross-sectional view of the wafer, continuing from Figure 23(c). (b) is a cross-sectional view of the wafer, continuing from Figure 24(a). (c) is a cross-sectional view of the wafer, continuing from Figure 24(b). [Figure 25] This is a cross-sectional view of the wafer, continuing from Figure 24(c). [Modes for carrying out the invention]

[0019] Hereinafter, an embodiment according to one aspect of the present invention will be described in detail with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0020] In this embodiment, a modified region is formed inside the wafer (object). As an apparatus for forming a modified region inside the wafer, for example, the laser processing apparatus 100 shown in Figure 1 can be used. As shown in Figure 1, the laser processing apparatus 100 includes a support unit 102, a light source 103, an optical axis adjustment unit 104, a spatial light modulator 105, a focusing unit 106, an optical axis monitor unit 107, a visible light imaging unit 108A, an infrared imaging unit 108B, a moving mechanism 109, and a management unit 150. The laser processing apparatus 100 is an apparatus that forms a modified region 11 in the wafer 20 by irradiating the wafer 20 with laser light L0. In the following description, the three mutually orthogonal directions are referred to as the X direction, Y direction, and Z direction, respectively. For example, the X direction is the first horizontal direction, the Y direction is the second horizontal direction perpendicular to the first horizontal direction, and the Z direction is the vertical direction.

[0021] The support unit 102 supports the wafer 20, for example, by adsorbing the wafer 20. The support unit 102 is movable along the X and Y directions. The support unit 102 is rotatable about a rotation axis along the Z direction. The light source 103 emits laser light L0, for example, by a pulse oscillation method. The laser light L0 is transparent to the wafer 20. The optical axis adjustment unit 104 adjusts the optical axis of the laser light L0 emitted from the light source 103. The optical axis adjustment unit 104 is composed of, for example, a plurality of reflective mirrors whose position and angle can be adjusted.

[0022] The spatial light modulator 105 is located inside the laser processing head H. The spatial light modulator 105 modulates the laser light L0 emitted from the light source 103. The spatial light modulator 105 is a reflective liquid crystal on silicon (LCOS) spatial light modulator (SLM). The spatial light modulator 105 can modulate the laser light L0 by appropriately setting the modulation pattern displayed on its display unit (liquid crystal layer). In this embodiment, the laser light L0 that travels downward along the Z direction from the optical axis adjustment unit 104 enters the laser processing head H, is reflected by the mirror MM1, and enters the spatial light modulator 105. The spatial light modulator 105 modulates the laser light L0 that has entered in this manner while reflecting it.

[0023] The focusing unit 106 is attached to the bottom wall of the laser processing head H. The focusing unit 106 focuses the laser light L0 modulated by the spatial light modulator 105 onto the wafer 20 supported by the support unit 102. In this embodiment, the laser light L0 reflected by the spatial light modulator 105 is reflected by the dichroic mirror MM2 and incident on the focusing unit 106. The focusing unit 106 focuses the incident laser light L0 onto the wafer 20. The focusing unit 106 is configured such that a focusing lens unit 161 is attached to the bottom wall of the laser processing head H via a drive mechanism 162. The drive mechanism 162 moves the focusing lens unit 161 along the Z direction, for example, by the driving force of a piezoelectric element.

[0024] Within the laser processing head H, an imaging optical system (not shown) is positioned between the spatial light modulator 105 and the focusing unit 106. The imaging optical system constitutes a bilateral telecentric optical system in which the reflective surface of the spatial light modulator 105 and the entrance pupil surface of the focusing unit 106 are in an imaging relationship. As a result, the image of the laser light L0 on the reflective surface of the spatial light modulator 105 (the image of the laser light L0 modulated by the spatial light modulator 105) is transferred (imaged) onto the entrance pupil surface of the focusing unit 106. A pair of distance measuring sensors S1 and S2 are mounted on the bottom wall of the laser processing head H so as to be positioned on both sides of the focusing lens unit 161 in the X direction. Each distance measuring sensor S1 and S2 emits distance measuring light (e.g., laser light) toward the laser light incident surface of the wafer 20 and acquires displacement data of the laser light incident surface by detecting the distance measuring light reflected from the laser light incident surface.

[0025] The optical axis monitor unit 107 is located inside the laser processing head H. The optical axis monitor unit 107 detects a portion of the laser light L0 that has passed through the dichroic mirror MM2. The detection result by the optical axis monitor unit 107 shows, for example, the relationship between the optical axis of the laser light L0 incident on the focusing lens unit 161 and the optical axis of the focusing lens unit 161. The visible light imaging unit 108A emits visible light V0 and acquires an image of the wafer 20 as a visible light V0 image. The visible light imaging unit 108A is located inside the laser processing head H. The infrared imaging unit 108B emits infrared light and acquires an infrared image of the wafer 20 as an infrared light image. The infrared imaging unit 108B is attached to the side wall of the laser processing head H.

[0026] The moving mechanism 109 includes a mechanism for moving at least one of the laser processing head H and the support part 102 in the X, Y, and Z directions. The moving mechanism 109 drives at least one of the laser processing head H and the support part 102 by the driving force of a known drive device such as a motor so that the focal point C of the laser beam L0 moves in the X, Y, and Z directions. The moving mechanism 109 includes a mechanism for rotating the support part 102. The moving mechanism 109 rotates the support part 102 by the driving force of a known drive device such as a motor.

[0027] The management unit 150 includes a control unit 151, a user interface 152, and a storage unit 153. The control unit 151 controls the operation of each part of the laser processing apparatus 100. The control unit 151 is configured as a computer device including a processor, memory, storage, and communication devices. In the control unit 151, the processor executes software (programs) loaded into memory, etc., and controls the reading and writing of data in memory and storage, as well as communication by the communication devices. The user interface 152 displays and inputs various types of data. The user interface 152 constitutes a GUI (Graphical User Interface) with a graphics-based operating system.

[0028] The user interface 152 includes at least one of the following: a touch panel, keyboard, mouse, microphone, tablet terminal, monitor, etc. The user interface 152 can accept various types of input, such as touch input, keyboard input, mouse operation, and voice input. The user interface 152 can display various types of information on its display screen. The user interface 152 corresponds to an input receiving unit that accepts input and a display unit that can display a settings screen based on the received input. The storage unit 153 is, for example, a hard disk and stores various types of data.

[0029] In the laser processing apparatus 100 configured as described above, when laser light L0 is focused into the wafer 20, the laser light L is absorbed in the portion corresponding to the focal point (at least a part of the focal area) C of the laser light L0, and a modified region 11 is formed inside the wafer 20. The modified region 11 is a region whose density, refractive index, mechanical strength, and other physical properties differ from the surrounding unmodified region. Examples of modified regions 11 include melting regions, crack regions, dielectric breakdown regions, refractive index change regions, etc. The modified region 11 includes a plurality of modified spots 11s and cracks extending from the plurality of modified spots 11s.

[0030] As an example, the operation of the laser processing apparatus 100 will be described when a modified region 11 is formed inside the wafer 20 along a line 15 for cutting the wafer 20.

[0031] First, the laser processing apparatus 100 rotates the support unit 102 so that the line 15 set on the wafer 20 is parallel to the X direction. Based on the image acquired by the infrared imaging unit 108B (for example, an image of the functional element layer on the wafer 20), the laser processing apparatus 100 moves the support unit 102 along the X and Y directions so that the focal point C of the laser beam L0 is located on the line 15 when viewed from the Z direction. Based on the image acquired by the visible imaging unit 108A (for example, an image of the laser beam incident surface of the wafer 20), the laser processing apparatus 100 moves the laser processing head H (i.e., the focusing unit 106) along the Z direction so that the focal point C of the laser beam L0 is located on the laser beam incident surface (height setting). Using that position as a reference, the laser processing apparatus 100 moves the laser processing head H along the Z direction so that the focal point C of the laser beam L0 is located at a predetermined depth from the laser beam incident surface.

[0032] Next, the laser processing apparatus 100 emits laser light L0 from the light source 103 and moves the support part 102 along the X direction so that the focal point C of the laser light L0 moves relative to the line 15. At this time, the laser processing apparatus 100 operates the drive mechanism 162 of the focusing part 106 so that the focal point C of the laser light L0 is located at a predetermined depth from the laser light incident surface, based on the displacement data of the laser light incident surface acquired by one of the pair of distance measuring sensors S1 and S2, which is located on the front side in the processing direction of the laser light L0.

[0033] As a result, a row of modified regions 11 is formed along line 15 and at a certain depth from the laser light incident surface of wafer 20. When laser light L0 is emitted from light source 103 by pulse oscillation, multiple modified spots 11s are formed so as to be aligned in a row along the X direction. Each modified spot 11s is formed by irradiation with one pulse of laser light L0. A row of modified regions 11 is a collection of multiple modified spots 11s aligned in a row. Adjacent modified spots 11s may be connected to each other or separated from each other depending on the pulse pitch of the laser light L0 (the value obtained by dividing the relative movement speed of the focal point C with respect to wafer 20 by the repetition frequency of the laser light L0).

[0034] In this embodiment, a grooving process is performed to form grooves in the wafer 20 along the line 15 by irradiating the street with laser light along the line 15 so that the surface layer of the street on the wafer 20 is removed. As the apparatus for performing the grooving process, for example, the laser processing apparatus 1 shown in Figure 2 can be used.

[0035] As shown in Figure 2, the laser processing apparatus 1 comprises a support unit 2, an irradiation unit 3, an imaging unit 4, and a control unit 5. The support unit 2 supports the wafer 20. The support unit 2 holds the wafer 20, for example by adsorption, so that the surface of the wafer 20, including the streets, faces the irradiation unit 3 and the imaging unit 4. For example, the support unit 2 is movable along the X and Y directions and rotatable about an axis parallel to the Z direction as its centerline.

[0036] The irradiation unit 3 irradiates the street of the wafer 20, which is supported by the support unit 2, with laser light L. The irradiation unit 3 includes a laser light source 31, a shaping optical system 32, a dichroic mirror 33, and a focusing unit 34. The laser light source 31 emits laser light L. The shaping optical system 32 adjusts the laser light L emitted from the laser light source 31. The shaping optical system 32 includes a spatial light modulator 132 that modulates the phase of the laser light L.

[0037] The spatial light modulator 132 has a display unit 132A into which the laser light L emitted from the laser light source 31 is incident. The spatial light modulator 132 modulates the laser light L according to the modulation pattern displayed on the display unit 132A. The shaping optical system 32 may include an imaging optical system that constitutes a bilateral telecentric optical system in which the modulation plane of the spatial light modulator and the entrance pupil plane of the focusing unit 34 are in an imaging relationship. The shaping optical system 32 may further include an attenuator for adjusting the output of the laser light L and a beam expander for expanding the diameter of the laser light L.

[0038] The dichroic mirror 33 reflects the laser light L emitted from the shaping optical system 32 and directs it into the focusing unit 34. The focusing unit 34 focuses the laser light L (laser light L modulated by the spatial light modulator 132) reflected by the dichroic mirror 33 onto the street of the wafer 20 supported by the support unit 2.

[0039] The irradiation unit 3 further includes a light source 35, a half mirror 36, and an image sensor 37. The light source 35 emits visible light V1. The half mirror 36 reflects the visible light V1 emitted from the light source 35 and directs it into the focusing unit 34. The dichroic mirror 33 transmits the visible light V1 between the half mirror 36 and the focusing unit 34. The focusing unit 34 focuses the visible light V1 reflected by the half mirror 36 onto the street of the wafer 20 supported by the support unit 2. The image sensor 37 detects the visible light V1 that has been reflected by the street of the wafer 20 and transmitted through the focusing unit 34, the dichroic mirror 33, and the half mirror 36. In the laser processing apparatus 1, the control unit 5 moves the focusing unit 34 along the Z direction, for example, so that the focusing point of the laser beam L is located on the street of the wafer 20, based on the detection result by the image sensor 37.

[0040] The imaging unit 4 acquires street image data of the wafer 20 supported by the support unit 2. The imaging unit 4 is an internal observation camera that observes the inside of the wafer 20 in which the modified region 11 has been formed by the laser processing device 100. The imaging unit 4 emits infrared light onto the wafer 20 and acquires an image of the wafer 20 as image data using infrared light. An InGaAs camera can be used as the imaging unit 4.

[0041] The control unit 5 controls the operation of each part of the laser processing apparatus 1. The control unit 5 includes a processing unit 51, a storage unit 52, and an input receiving unit 53. The processing unit 51 is a computer device including a processor, memory, storage, and communication devices. In the processing unit 51, the processor executes software (programs) loaded into memory, etc., and controls the reading and writing of data in memory and storage, as well as communication by the communication devices. The storage unit 52 is, for example, a hard disk, and stores various types of data. The input receiving unit 53 is an interface unit that receives input of various types of data from the operator. As an example, the input receiving unit 53 is at least one of a keyboard, mouse, or GUI (Graphical User Interface).

[0042] The laser processing apparatus 1 performs grooving. In grooving, the control unit 5 controls the irradiation unit 3 so that laser light L is irradiated along the line 15 to each street of the wafer 20 supported by the support unit 2, and the control unit 5 controls the support unit 2 so that the laser light L moves relative to the line 15 (details will be described later).

[0043] As shown in Figures 3 and 4, the wafer 20 has a semiconductor substrate (substrate) 21 and a functional element layer 22. The thickness of the wafer 20 is, for example, 775 μm. The semiconductor substrate 21 has a front surface 21a and a back surface 21b. The semiconductor substrate 21 is, for example, a silicon substrate. The semiconductor substrate 21 is provided with notches 21c indicating the crystal orientation. The semiconductor substrate 21 may be provided with orientation flats instead of notches 21c. The functional element layer 22 is formed on the front surface 21a of the semiconductor substrate 21. The functional element layer 22 includes a plurality of functional elements 22a. The plurality of functional elements 22a are arranged two-dimensionally along the front surface 21a of the semiconductor substrate 21. Each functional element 22a is, for example, a light-receiving element such as a photodiode, a light-emitting element such as a laser diode, a circuit element such as a memory, etc. Each functional element 22a may also be configured three-dimensionally by stacking multiple layers.

[0044] Multiple streets 23 are formed on the wafer 20. The multiple streets 23 are regions exposed to the outside between adjacent functional elements 22a. In other words, the multiple functional elements 22a are arranged adjacent to each other via the streets 23. For example, the multiple streets 23 extend in a grid pattern between adjacent functional elements 22a arranged in a matrix. As shown in Figure 5, an insulating film 24 and multiple metal structures 25, 26 are formed on the surface of the streets 23. The insulating film 24 is, for example, a low-k film. Each metal structure 25, 26 is, for example, a metal pad. Metal structures 25 and 26 differ from each other in at least one of the following respects: thickness, area, or material.

[0045] As shown in Figures 3 and 4, the wafer 20 has multiple lines 15. The wafer 20 is intended to be cut along each of the lines 15 for each functional element 22a (i.e., chipped for each functional element 22a). Each line 15 passes through each street 23 when viewed from the thickness direction of the wafer 20. For example, each line 15 extends through the center of each street 23 when viewed from the thickness direction of the wafer 20. Each line 15 is a virtual line set on the wafer 20 by the laser processing apparatus 1,100. Each line 15 may also be a line actually drawn on the wafer 20.

[0046] In this embodiment, the modulation pattern displayed on the display unit 132A of the spatial light modulator 132 includes a branching pattern that branches the laser beam L into a plurality (in this case, two) of first branched laser beams that form a first groove and a plurality (in this case, two) of second branched laser beams that form a second groove. As shown in Figure 6, in this embodiment, in the X direction along the line 15, the focal points SA1 and SA2 of the two first branched laser beams are aligned from one side of the line 15 to the other, and then the focal points SB1 and SB2 of the two second branched laser beams are aligned. In the Y direction, which corresponds to the width direction of the groove to be formed, the positions of the focal points SA1 and SA2 of the first branched laser beams are equal to each other. In the Y direction, the positions of the focal points SB1 and SB2 of the second branched laser beams are equal to each other.

[0047] The positions of the focal points SA1 and SA2 of the first branched laser beam are also referred to as the first processing points, and the positions of the focal points SB1 and SB2 of the second branched laser beam are also referred to as the second processing points. In the X direction, the distance between the position of adjacent focal point SA2 of the first branched laser beam and the position of focal point SB1 of the second branched laser beam is defined as the interval d23. In other words, the interval d23 is the distance in the X direction between adjacent first and second processing points. In the Y direction, which corresponds to the width direction of the groove to be formed, the distance between the positions of the focal points SA1 and SA2 of the first branched laser beam and the positions of the focal points SB1 and SB2 of the second branched laser beam is defined as the interval Y1.

[0048] The spacing d23 is greater than the spacing Y1. The spacing d23 is greater than the pulse pitch of the laser beam L. The spacing d23 is, for example, 20 μm or more. In the X direction along line 15, the spacing d12 between the positions of the focal points SA1 and SA2 of the multiple first branched laser beams is greater than the pulse pitch of the laser beam L. The spacing d12 is smaller than the spacing d23. In the X direction, the spacing d34 between the positions of the focal points SB1 and SB2 of the multiple second branched laser beams is greater than the pulse pitch of the laser beam L. The spacing d34 is smaller than the spacing d23. The branching pattern branches the laser beam L so that the focal points SA1, SA2, SB1, and SB2 are arranged in a one-dimensional array along line 15 (including substantially one-dimensional arrays, substantially one-dimensional arrays, and approximately one-dimensional arrays; the same applies hereinafter).

[0049] As shown in Figure 8(b), the first groove M1 formed by the first branched laser beam LA and the second groove M2 formed by the second branched laser beam LB constitute a composite groove MH. The composite groove MH is a W-shaped groove (W groove) in a cross-sectional view perpendicular to line 15. The composite groove MH is a groove with a shape having two valleys and one peak on the bottom side in a cross-sectional view perpendicular to line 15. The first groove M1 and the second groove M2 are V-shaped grooves (V grooves) in a cross-sectional view perpendicular to line 15. The end of the second groove M2 in the Y direction overlaps that of the first groove M1. In other words, the first groove M1 and the second groove M2 extend in the X direction with their ends in the Y direction overlapping. The first groove M1 and the second groove M2 are provided so that their peripheral edges are in contact. The first groove M1 and the second groove M2 are grooves of the same depth and width.

[0050] The composite groove MH is provided on the wafer 20 on the functional element layer 22 side, such that both the bottom of the first groove M1 and the bottom of the second groove M2 reach the semiconductor substrate 21. The bottoms of the first groove M1 and the bottom of the second groove M2 reach the functional element layer 22 side of the semiconductor substrate 21. The overlapping ends of the first groove M1 and the second groove M2 (the peak portion on the bottom side of the composite groove MH) reach the semiconductor substrate 21 side of the functional element layer 22. The grooving width, which is the groove width on the widest side of the composite groove MH, is set to, for example, 12 μm. The grooving width can be input as appropriate via the input receiving unit 53 (see Figure 2). The grooving width is narrower than the width of the street 23.

[0051] Note that the intervals d12 and d34 may be equal or different. For example, if the pulse pitch is 0.5 μm, the interval d12 may be 10 μm, the interval d23 may be 20 μm, the interval d34 may be 10 μm, and the interval Y1 may be 5 μm. The interval Y1 is the interval at which the composite groove MH can form a W shape in cross-section, and may be smaller than the grooving width.

[0052] Next, the laser processing method using the laser processing device 100 and the laser processing device 1 will be explained with reference to Figures 7 to 11.

[0053] First, a wafer 20 is prepared as shown in Figure 7(a). A grinding tape 28 is attached to the surface of the wafer 20 on the functional element layer 22 side. As shown in Figure 7(b), the back surface 21b of the semiconductor substrate 21 of the wafer 20 is ground in a grinding apparatus to thin the wafer 20 to the desired thickness (grinding process). As shown in Figure 7(c), the grinding tape 28 is removed, and a protective film 29 is applied to the surface of the wafer 20 on the functional element layer 22 side to protect the functional element layer 22 (functional element 22a).

[0054] Next, as shown in Figure 8(a), the laser processing apparatus 1 holds the wafer 20 in place by adsorption using the support unit 2, and then performs grooving on the wafer 20. In grooving, the control unit 5 controls the irradiation unit 3 so that the laser beam L is irradiated along the line 15 onto the street 23 of the wafer 20, and the control unit 5 controls the support unit 2 so that the laser beam L moves relative to the line 15. As a result, as shown in Figure 8(b), the surface layer of the street 23 on the wafer 20 is removed, and a composite groove MH including the first groove M1 and the second groove M2 is formed.

[0055] Specifically, in the grooving process, a laser beam L is emitted, and the emitted laser beam L is incident on the display unit 132A (see Figure 2) of the spatial light modulator 132 (see Figure 2). The modulation pattern displayed on the display unit 132A causes the laser beam L to be split into a first branched laser beam LA and a second branched laser beam LB, and the first branched laser beam LA and the second branched laser beam LB are focused onto the wafer 20. In the grooving process, for example, in the Z direction, the focusing unit 34 (see Figure 2) is moved or the spatial light modulator 132 is modulated so that the first branched laser beam LA and the second branched laser beam LB are focused onto the surface of the functional element layer 22. The first groove M1 is formed by focusing the first branched laser beam LA, and the second groove M2 is formed by focusing the second branched laser beam LB.

[0056] As described above, the modulation pattern includes a branching pattern. The branching pattern can be appropriately generated by the control unit 5 based on the grooving width input via the input receiving unit 53 (see Figure 2). For example, the branching pattern can be automatically generated by the control unit 5 using various known methods such that the focal points SA1, SA2, SB1, SB2 of the first branched laser beam LA and the second branched laser beam LB are located in a one-dimensional array as shown in Figure 6, and a composite groove MH of the grooving width is realized.

[0057] The processing conditions for forming the composite groove MH are not particularly limited and can be set based on various known findings. The processing conditions for forming the composite groove MH can be appropriately input via the input receiving unit 53. For example, the processing conditions for forming the composite groove MH may be the following conditions. In the following example conditions, burst pulses are not used, but burst pulses may be used, for example, to suppress film peeling (the same applies below). Wavelength of laser light L: 515nm Laser beam L pulse width: 600 fs Laser beam L pulse pitch: 0.5 μm Processing energy (total energy at each focal point): 4.0 μJ Number of scans: 1 pass Position of the bottom of the composite groove MH: 3 μm from the surface 21a of the semiconductor substrate 21

[0058] Next, as shown in Figure 8(c), the wafer 20 is removed from the support 2, and the protective film 29 is removed using, for example, a chemical solution. As shown in Figure 9(a), a transparent dicing tape (tape) DC with a ring frame RF is attached to the back surface 21b of the semiconductor substrate 21 of the wafer 20. The transparent dicing tape DC is also called an expanded film.

[0059] Next, as shown in Figure 9(b), in the laser processing apparatus 100, a modified region 11 is formed inside the wafer 20 along the line 15 by irradiating the wafer 20 with laser light L0 along the line 15. Here, with the transparent dicing tape DC attached to the back surface 21b of the semiconductor substrate 21, the wafer 20 is supported by adsorption using the support part 102. Then, the focal point of the laser light L0 is aligned inside the semiconductor substrate 21 via the transparent dicing tape DC, and the back surface 21b is used as the laser light incident surface to irradiate the wafer 20 with laser light L0.

[0060] The laser beam L0 is transparent to the transparent dicing tape DC and the semiconductor substrate 21. When the laser beam L0 is focused into the semiconductor substrate 21, the laser beam L0 is absorbed at the point of focus, forming a modified region 11 inside the semiconductor substrate 21, and a crack 9 extends from the modified region 11. The processing conditions for forming the modified region 11 are not particularly limited and can be set based on various known findings. The processing conditions for forming the modified region 11 can be appropriately input via the user interface 152 (see Figure 1). The processing conditions for forming the modified region 11 may be, for example, the following conditions. Wavelength of laser light L0: 1099nm Laser beam L0 pulse width: 700 nsec Laser beam pulse pitch L0: 6.5 μm Processing energy: 22 μJ Number of scans: 8 passes

[0061] Cracks 9 extending from the modified region 11 toward the functional element layer 22 are induced to extend toward the two first grooves M1 and second grooves M2 of the composite groove MH, and their ends reach the inner surface of the first groove M1 or the inner surface of the second groove M2. For example, in the example shown in Figure 10, there is virtually no displacement of the modified region 11 from the line 15 in the Y direction, and in this case, the induced cracks 9 reach the inner surface of the first groove M1 on the side of the second groove M2. Alternatively, for example, as shown in Figure 11(a), if there is displacement of the modified region 11 from the line 15 in the Y direction, the induced cracks 9 may reach the bottom of the first groove M1. Alternatively, for example, as shown in Figure 11(b), if there is displacement of the modified region 11 from the line 15 in the Y direction, the induced cracks 9 may reach the inner surface of the first groove M1 on the side opposite to the second groove. Alternatively, as shown in the example in Figure 11(c), if there is a displacement of the modified region 11 from the line 15 in the Y direction, the induced crack 9 may reach the inner surface of the second groove M2 side of the first groove M1.

[0062] Next, as shown in Figure 12, in an expanding apparatus (not shown), the attached transparent dicing tape DC is expanded, causing cracks to extend in the thickness direction of the wafer 20 from the modified regions 11 formed inside the semiconductor substrate 21 along each line 15, and the wafer 20 is cut along the lines 15. This separates the wafer 20 into chips for each functional element 22a, obtaining multiple chips T1.

[0063] In the above, for example, instead of the transparent dicing tape DC, a protective tape may be attached to the functional element layer 22 side, a modified region 11 may be formed by irradiating the back surface 21b of the semiconductor substrate 21 with laser light L0, then the transparent dicing tape DC may be attached to the back surface 21b of the semiconductor substrate 21, the protective tape on the functional element layer 22 side may be peeled off, and the transparent dicing tape DC may be expanded and divided. Alternatively, for example, laser processing (grooving and formation of the modified region 11) may be performed with a protective film attached using a support material, then the protective film may be removed, the transparent dicing tape DC may be attached, and the transparent dicing tape DC may be expanded and divided.

[0064] Incidentally, as shown in Figure 13, when a single V-groove M0 is formed in the wafer 20 along line 15, cracks 9 from the modified region 11 formed inward in the Z direction from the V-groove M0 in the wafer 20 tend to extend in a direction that deviates from the V-groove M0. As a result, the cracks 9 deviate significantly from line 15. In this case, the cutting quality when the wafer 20 is cut deteriorates. This increases the likelihood of poor cutting quality, tearing, and remaining cracks.

[0065] In this embodiment, a composite groove MH including a first groove M1 and a second groove M2 whose ends overlap is formed on the wafer 20. This allows for the induction of crack 9 toward these two first grooves M1 and second grooves M2 while keeping the grooving width from becoming too wide, thereby increasing the crack induction effect compared to when a single V groove M0 is formed, and suppressing the deviation of crack 9 from extending in a divergent direction. In other words, it is possible to suppress the deviation of crack 9 extending from the modified region 11 while narrowing the grooving width. The deviation of crack 9 can be contained within the grooving width. This improves the division quality and ensures that all chips are divided reliably. It is also possible to narrow the width of the street 23.

[0066] This embodiment further includes a step of cutting the wafer 20 along the line 15 by expanding a transparent dicing tape DC attached to the wafer 20 when the end of the crack 9 reaches the inner surface of the first groove M1 or the inner surface of the second groove M2, after the modified region 11 has been formed. In this case, it becomes possible to cut the wafer 20 along the line 15 with high precision.

[0067] In this embodiment, the wafer 20 has a semiconductor substrate 21 and a functional element layer 22. The composite groove MH is provided on the functional element layer 22 side of the wafer 20 such that both the bottom of the first groove M1 and the bottom of the second groove M2 reach the semiconductor substrate 21. In this case, the crack induction effect of the first groove M1 and the second groove M2 can be further enhanced.

[0068] This embodiment includes a step of forming a protective film 29 on the functional element layer 22 before forming the composite groove MH. In this case, the functional element layer 22 can be effectively protected by the protective film 29. In this embodiment, the composite groove MH has a W-shape in a cross-sectional view perpendicular to the line 15. In this case, the above effect of suppressing the deviation of cracks 9 while narrowing the grooving width is significantly enhanced. This embodiment includes a step of grinding and thinning the wafer 20 before forming the composite groove MH. In this case, the wafer 20 can be thinned by grinding before forming the composite groove MH.

[0069] In the laser processing apparatus 1 and laser processing method according to this embodiment, the distance d23 between adjacent first and second processing points (the position of the focal point SA2 of the first branched laser beam and the position of the focal point SB1 of the second branched laser beam) in the X direction is greater than the distance Y1 between the first processing position and the second processing position in the Y direction. This makes it possible to separate the first and second processing points until their mutual influence is minimized. Influences include, for example, interference with a preceding processing point and effects such as processing while thermal effects remain. Furthermore, it is possible to separate the first and second processing points until these effects are substantially eliminated. As a result, the first groove M1 and the second groove M2 can be reliably formed as independent grooves in the wafer 20. The first groove M1 and the second groove M2 can be firmly formed so that their respective bottoms are clearly defined. Therefore, in a laser processing apparatus 1 and laser processing method that splits a laser beam L into multiple branched laser beams and irradiates a wafer 20 with it, it becomes possible to form a first groove M1 and a second groove M2 well on the wafer 20 along the line 15.

[0070] In this embodiment, the second groove M2 overlaps the widthwise end of the first groove M1 with the first groove M1. A composite groove MH including the first groove M1 and the second groove M2 can be formed on the wafer 20. Such a composite groove MH can effectively induce cracks 9 that extend from, for example, a modified region 11 formed inside the wafer 20.

[0071] In this embodiment, the spacing d23 in the X direction is greater than the pulse pitch of the laser beam L. In this case, it is possible to suppress the problem of the spacing between the first processing position and the second processing position being too narrow and causing significant mutual influence, thereby enabling the formation of the first groove M1 and the second groove M2 well on the wafer 20.

[0072] In this embodiment, the spacing d12 between the multiple first processing positions in the X direction is greater than the pulse pitch of the laser beam L. In this case, it is possible to suppress the effect of excessively narrow spacing d12 between the multiple first processing positions on each other, thereby enabling the formation of the first groove M1 effectively.

[0073] In this embodiment, the interval d12 between the multiple first machining positions in the X direction is smaller than the interval d23. In this case, the interval between the multiple first machining positions can be set to a range where they influence each other in order to suppress the HAZ (Heat-Affected Zone) such as heat influences that occur around the formed first groove M1.

[0074] In this embodiment, the spacing d34 between the multiple second processing positions in the X direction is greater than the pulse pitch of the laser beam L. In this case, it is possible to suppress the effect of the multiple second processing positions on each other becoming too close together, thereby enabling the formation of the second groove M2 effectively.

[0075] In this embodiment, the interval d34 between the multiple second machining positions in the X direction is smaller than the interval d23. In this case, the intervals between the multiple second machining positions can be set to a range that influences each other so that the HAZ, such as thermal influences, generated around the formed second groove M2 is suppressed.

[0076] In this embodiment, the branching pattern branches the laser beam L into two first branched laser beams LA and two second branched laser beams LB. In this case, the energy at each focal point SA1, SA2, SB1, and SB2 can be reduced, and the HAZ can be suppressed.

[0077] In this embodiment, the branching pattern branches the laser beam L so that the focal points SA1, SA2, SB1, and SB2 are arranged in a one-dimensional array along line 15. This makes it possible to form narrow composite grooves MH on the wafer 20. Furthermore, it is possible to improve the flexural strength of the wafer 20.

[0078] Even if there is no displacement of the modified region 11 from the position of line 15 in the Y direction, if a single V groove M0 is formed, a defect may occur as a result of the crack 9 extending from the modified region 11 meandering. In this embodiment, however, since a composite groove MH is formed as a W groove, it is possible to suppress such defects.

[0079] In this embodiment, the branching pattern may involve branching the laser beam L into three first branched laser beams LA that form the first groove M1 and three second branched laser beams LB that form the second groove M2. In this case, for example, as shown in Figure 14, the three focal points SA1, SA2, SA3 of the first branched laser beams are aligned in the X direction along the line 15, moving from one side of the line 15 to the other, followed by the three focal points SB1, SB2, SB3 of the second branched laser beams. In the Y direction, which corresponds to the width direction of the groove to be formed, the positions of the focal points SA1, SA2, SA3 of the first branched laser beams are equal to each other. In the Y direction, the positions of the focal points SB1, SB2, SB3 of the second branched laser beams are equal to each other. With such a branching pattern, the energy at each focal point SA1, SA2, SA3, SB1, SB2, SB3 can be further reduced, and the HAZ can be further suppressed.

[0080] In this embodiment, the branching pattern displayed on the display unit 132A of the spatial light modulator 132 may be obtained by branching the laser beam L into one or more (here, two) first branched laser beams LA that form the first groove M1, one or more (here, two) second branched laser beams LB that form the second groove M2, and one or more (here, two) third branched laser beams that form the third groove M3. In this case, for example, as shown in Figure 15(a), in the X direction along the line 15, moving from one side of the line 15 to the other, the focal points SA1 and SA2 of the two first branched laser beams are aligned, followed by the focal points SB1 and SB2 of the two second branched laser beams, and then the focal points SC1 and SC2 of the two third branched laser beams. In the Y direction corresponding to the width direction of the grooves to be formed, the positions of the focal points SC1 and SC2 of the third branched laser beams are equal to each other.

[0081] In the X direction, the distance between the focal point SB2 of adjacent second-branched laser beams and the focal point SC1 of the third-branched laser beam is defined as interval d45. Interval d45 is equal to interval d23. In the Y direction, the distance between the focal points SB1,SB2 of the second-branched laser beams and the focal points SC1,SC2 of the third-branched laser beam is defined as interval Y2. Interval Y2 is equal to interval Y1. Interval d45 is greater than interval Y1. Interval d45 is greater than the pulse pitch of the laser beam L. In the X direction along line 15, the interval d56 between the focal points SC1,SC2 of multiple third-branched laser beams is greater than the pulse pitch of the laser beam L. Interval d56 is smaller than interval d23. The branching pattern branches the laser beam L so that the focal points SA1,SA2,SB1,SB2,SC1,SC2 are arranged in a one-dimensional array along line 15. In this case, as shown in Figure 15(b), it becomes possible to form a wide composite groove MH1.

[0082] The first groove M1 formed by the first branched laser beam LA, the second groove M2 formed by the second branched laser beam LB, and the third groove M3 formed by the third branched laser beam constitute a composite groove MH1. The composite groove MH1 is a groove with a shape having three valleys and two peaks on the bottom side in a cross-sectional view perpendicular to line 15. Each of the first groove M1, second groove M2, and third groove M3 is a V-groove in a cross-sectional view perpendicular to line 15. The end of the second groove M2 in the Y direction overlaps that of the first groove M1. In other words, the first groove M1 and the second groove M2 extend in the X direction with their ends in the Y direction overlapping. The first groove M1 and the second groove M2 are provided so that their peripheral edges are in contact. The end of the third groove M3 in the Y direction overlaps that of the second groove M2. In other words, the second groove M2 and the third groove M3 extend in the X direction with their ends in the Y direction overlapping. The second groove M2 and the third groove M3 are provided so that their peripheral edges are in contact. The first groove M1, the second groove M2, and the third groove M3 are grooves of the same depth and width.

[0083] The composite groove MH1 is provided on the wafer 20 on the functional element layer 22 side such that the bottoms of the first groove M1, the second groove M2, and the third groove M3 all reach the semiconductor substrate 21. The bottoms of the first groove M1 and the second groove M2 reach the functional element layer 22 side of the semiconductor substrate 21. The overlapping ends of the first groove M1, the second groove M2, and the third groove M3 (the two peaks on the bottom side of the composite groove MH1) reach the semiconductor substrate 21 side of the functional element layer 22.

[0084] Incidentally, in this embodiment, as shown in Figure 16(a), a composite groove MH2 may be provided on the functional element layer 22 side of the wafer 20. The composite groove MH2 is a W groove composed of a first groove M1 and a second groove M2. The end of the second groove M2 overlaps with the first groove M1 in the Y direction. The composite groove MH2 is provided such that both the bottom of the first groove M1 and the bottom of the second groove M2 reach the semiconductor substrate 21. The overlapping ends of the first groove M1 and the second groove M2 (the peak portion on the bottom side of the composite groove MH2) reach the surface side of the functional element layer 22. The bottoms of the first groove M1 and the second groove M2 of the composite groove MH2 are separated in the Y direction compared to the composite groove MH (see Figure 8(b)). The same effects as those of the composite groove MH are achieved in such a composite groove MH2.

[0085] In this embodiment, as shown in Figure 16(b), a composite groove MH3 may be provided on the functional element layer 22 side of the wafer 20. The composite groove MH3 is a W groove composed of a first groove M1 and a second groove M2. The end of the second groove M2 overlaps with the first groove M1 in the Y direction. The first groove M1 is a groove that is deeper than the second groove M2. The composite groove MH3 is provided such that the bottom of the first groove M1 reaches the semiconductor substrate 21, but the bottom of the second groove M2 does not reach the semiconductor substrate 21. In other words, it is provided so that either the bottom of the first groove M1 or the bottom of the second groove M2 reaches the semiconductor substrate 21. The overlapping ends of the first groove M1 and the second groove M2 (the peak portion on the bottom side of the composite groove MH3) reach the semiconductor substrate 21 side of the functional element layer 22. The same effects as those of the composite groove MH are achieved with such a composite groove MH3. This makes it possible to further enhance the crack induction effect of the first groove M1 and the second groove M2.

[0086] In this embodiment, as shown in Figure 16(c), a composite groove MH4 may be provided on the functional element layer 22 side of the wafer 20. The composite groove MH4 is a W groove composed of a first groove M1 and a second groove M2. The end of the second groove M2 overlaps with the first groove M1 in the Y direction. The first groove M1 is a groove that is deeper than the second groove M2. The composite groove MH4 is provided such that the bottom of the first groove M1 reaches the semiconductor substrate 21, but the bottom of the second groove M2 does not reach the semiconductor substrate 21. In other words, it is provided so that either the bottom of the first groove M1 or the bottom of the second groove M2 reaches the semiconductor substrate 21. The overlapping ends of the first groove M1 and the second groove M2 (the peak portion on the bottom side of the composite groove MH4) reach the surface side of the functional element layer 22. In composite groove MH4, the bottoms of the first groove M1 and the second groove M2 are separated in the Y direction compared to composite groove MH3 (see Figure 16(b)). Even in such composite groove MH4, the same effect as composite groove MH is achieved. It becomes possible to further enhance the crack induction effect 9 by the first groove M1 and the second groove M2.

[0087] In this embodiment, as shown in Figure 17(a), a composite groove MH5 may be provided on the functional element layer 22 side of the wafer 20. The composite groove MH5 is a W groove composed of a first groove M1 and a second groove M2. The end of the second groove M2 overlaps the first groove M1 in the Y direction. The first groove M1 and the second groove M2 are grooves of the same depth and width. The composite groove MH2 is provided so that neither the bottom of the first groove M1 nor the bottom of the second groove M2 reaches the semiconductor substrate 21. The same effects as those of the composite groove MH are achieved in such a composite groove MH5. It becomes possible to make the depths of the first groove M1 and the second groove M2 shallower.

[0088] In this embodiment, as shown in Figure 17(b), a composite groove MH6 may be provided on the functional element layer 22 side of the wafer 20. The composite groove MH6 is a W groove composed of a first groove M1 and a second groove M2. The end of the second groove M2 overlaps with the first groove M1 in the Y direction. The first groove M1 and the second groove M2 are grooves of the same depth and width. The composite groove MH6 is provided so that neither the bottom of the first groove M1 nor the bottom of the second groove M2 reaches the semiconductor substrate 21. The overlapping ends of the first groove M1 and the second groove M2 (the peak portion on the bottom side of the composite groove MH6) reach the surface side of the functional element layer 22. The bottoms of the first groove M1 and the second groove M2 of the composite groove MH6 are further apart in the Y direction compared to the composite groove MH5 (see Figure 17(a)). The same effects as those of the composite groove MH are achieved in such a composite groove MH6. This makes it possible to further enhance the crack induction effect of the first groove M1 and the second groove M2.

[0089] Figure 18 shows the test results evaluating the deviation of cracks 9 when a composite groove MH is formed. In the figure, the amount of excavation is the position of the bottom of the composite groove MH and the amount that penetrates the semiconductor substrate 21 from the surface 21a of the semiconductor substrate 21. The amount of shift corresponds to the amount of displacement between the formed modified region 11 and the center of the composite groove MH in the width direction of the composite groove MH. "○" means that the end of the crack 9 was induced to reach the inner surface of the first groove M1 or the inner surface of the second groove M2. "Deviation" means that the crack 9 deviated from the composite groove MH and the end of the crack 9 did not reach the inner surface of the first groove M1 or the inner surface of the second groove M2. In the test shown in the figure, the grooving width is 12 μm. As shown in Figure 18, it can be seen that with a composite groove MH, even if the formed modified region 11 is displaced in the width direction relative to the composite groove MH, a crack induction effect of 9 can be obtained within a certain range. Furthermore, it can be seen that the larger the amount of excavation, the more effectively the crack induction effect of 9 can be exerted relative to the amount of shift.

[0090] In the grooving process of this embodiment, the first groove M1 and the second groove M2 are simultaneously formed by a first branched laser beam LA and a second branched laser beam LB, which are obtained by branching the laser beam L by displaying a branching pattern on the display unit 132A of the spatial light modulator 132, but the process is not limited to this. The grooving process may include the steps of irradiating the wafer 20 with laser beam L to form a first groove M1 in the wafer 20 along the line 15, and irradiating the wafer 20 with laser beam L to form a second groove M2 in the wafer 20 along the line 15.

[0091] For example, as shown in Figure 19(a), the laser beam L is focused onto the functional element layer 22 via the focusing unit 34 to remove the surface layer on the functional element layer 22 side of the wafer 20 and form the first groove M1. Then, as shown in Figure 19(b), at least one of the focusing unit 34 and the support unit 2 (see Figure 2) may be moved by a predetermined amount in the Y direction (width direction of the first groove M1), and the laser beam L is focused onto the functional element layer 22 via the focusing unit 34 to remove the surface layer on the functional element layer 22 side of the wafer 20 and form the second groove M2.

[0092] Alternatively, as shown in Figure 20(a), the laser beam L is focused onto the functional element layer 22 via the focusing unit 34 to remove the surface layer on the functional element layer 22 side of the wafer 20 and form the first groove M1. Then, a shift pattern is displayed on the display unit 132A of the spatial light modulator 132 to shift the focal point of the laser beam L by a predetermined amount in the Y direction (width direction of the first groove M1), and as shown in Figure 20(b), the laser beam L is focused onto the functional element layer 22 via the focusing unit 34 to remove the surface layer on the functional element layer 22 side of the wafer 20 and form the second groove M2.

[0093] In this embodiment, the step of forming the modified region 11 may include a step of correcting the formation position of the modified region 11 to match the center position if the amount of deviation of the formation position of the modified region 11 from the center position of the composite groove MH in the width direction of the composite groove MH (hereinafter also referred to as the "width direction deviation amount") is greater than half the grooving width. For example, the following step shown in Figure 21 may be included.

[0094] In the process of forming the modified region 11, first, the formation position of the modified region 11 (the position where the modified region 11 is planned to be formed) is aligned with the center position of the composite groove MH, which is the reference processing position, in the Y direction corresponding to the width direction of the composite groove MH (step S11). The center position of the composite groove MH can be determined, for example, based on an image captured by the infrared imaging unit 108B (see Figure 1). Subsequently, the modified region 11 is formed along the line 15 as described above (step S12).

[0095] If the formation of the modified region 11 is completed along all of the lines 15 extending in the X direction (YES in step S13), the laser processing is considered complete and the process ends, and the next step is initiated. On the other hand, if the formation of the modified region 11 is not completed along all of the lines 15 extending in the X direction (NO in step S13), at least one of the laser processing head H and the support part 102 (see Figure 1) is moved in the Y direction by a predetermined distance (corresponding to the distance between two adjacent lines 15) to move the formation position of the modified region 11 (step S14).

[0096] Step S15 determines whether the amount of widthwise displacement of the modified region 11 is greater than half the grooving width (1 / 2 value). The amount of widthwise displacement of the modified region 11 can be determined, for example, based on an image captured by the infrared imaging unit 108B (see Figure 1). If the result in step S15 is YES, the formation position of the modified region 11 in the Y direction is corrected (step S16). In step S16, at least one of the laser processing head H and the support unit 102 (see Figure 1) is adjusted in the Y direction so that the formation position of the modified region 11 aligns with the center position of the composite groove MH. If the result in step S15 is NO, or after step S16, the process returns to step S12. According to the modified laser processing method described above, it is possible to correct the formation position of the modified region 11 using the grooving width.

[0097] [Differentiation] One aspect of the present invention is not limited to the above embodiments.

[0098] In the above embodiment, the laser processing apparatus 1 that performs grooving and the laser processing apparatus 100 that forms a modified region 11 inside the wafer 20 are separate devices, but the invention is not limited to this. For example, the device for grooving and the device for forming the modified region 11 may be connected by a transport arm to form a single unit. As an example, as shown in Figure 22, the laser processing apparatus 200 may have a common stage 202 and be equipped with an optical system 210A corresponding to the processing apparatus for grooving and an optical system 210B corresponding to the processing apparatus for forming the modified region 11. Such a laser processing apparatus 200 includes a moving mechanism 205 for moving the stage (support part) 202 and a moving mechanism 206 for moving the optical systems 210A and 210B.

[0099] The laser processing method using the laser processing apparatus 100 and the laser processing apparatus 1 is not limited to the method described above, but may also be the following method, for example. First, a wafer 20 is prepared as shown in Figure 23(a). A protective film 29 is applied to the surface of the wafer 20 on the functional element layer 22 side. Next, as shown in Figure 23(b), the wafer 20 is supported by the support unit 2 in the laser processing apparatus 1, and then grooving is performed on the wafer 20. In grooving, the control unit 5 controls the irradiation unit 3 so that laser light L is irradiated along the line 15 on the street 23 of the wafer 20, and the control unit 5 controls the support unit 2 so that the laser light L moves relatively along the line 15. As a result, the surface layer of the street 23 on the wafer 20 is removed, and composite grooves MH are formed.

[0100] Next, as shown in Figure 23(c), the wafer 20 is removed from the support unit 2, and the protective film 29 is removed using, for example, a chemical solution. As shown in Figure 24(a), a grinding tape 28 is attached to the surface of the wafer 20 on the functional element layer 22 side. In the laser processing apparatus 100, the wafer 20 is irradiated with laser light L0 along the line 15 to form a modified region 11 inside the wafer 20 along the line 15. Here, after the wafer 20 is adsorbed and supported by the support unit 102, the focal point of the laser light L0 is aligned with the inside of the semiconductor substrate 21, and the scanning of the laser light L0 irradiating the wafer 20 from the back surface 21b is repeated multiple times, changing the position of the focal point in the Z direction. As a result, multiple rows of modified regions 11 are formed in the Z direction inside the semiconductor substrate 21, and cracks 9 extend from the modified regions 11.

[0101] Next, as shown in Figure 24(b), the back surface 21b of the semiconductor substrate 21 of the wafer 20 is ground in a grinding apparatus to thin the wafer 20 to a desired thickness in which the modified region 11 is removed. As shown in Figure 24(c), a transparent dicing tape DC with a ring frame RF is attached to the back surface 21b of the semiconductor substrate 21 of the wafer 20. Then, as shown in Figure 25, the attached transparent dicing tape DC is expanded in an expanding apparatus (not shown) to extend cracks 9 in the thickness direction of the wafer 20 along each line 15, and the wafer 20 is cut along the lines 15. In this way, the wafer 20 is chipped for each functional element 22a, and multiple chips T1 are obtained. In this modified laser processing method, the wafer 20 can be thinned by grinding after the formation of the composite groove MH.

[0102] In the above embodiments and modifications, the imaging unit 4 may include a camera that acquires image data of the streets of the wafer 20 using visible light. In the above embodiments and modifications, information can be created to control the irradiation conditions of the laser beam L in each region of the street 23 (laser ON / OFF control, laser power) using an image of at least the surface layer of the street 23 after cutting, or a see-through image using infrared light, and the grooving process can be controlled based on that information. In the above embodiments and modifications, the surface layer of the street 23 may be removed by scanning the street 23 with the laser beam L multiple times. In the above embodiments and modifications, only the support unit 102 may be controlled, only the laser processing head H may be controlled, or both the support unit 102 and the laser processing head H may be controlled so that the laser beam L0 moves relatively along each line 15. In the above embodiments and modifications, only the support unit 2 may be controlled, only the irradiation unit 3 may be controlled, or both the support unit 2 and the irradiation unit 3 may be controlled so that the laser beam L moves relatively along each street 23.

[0103] In the above embodiments and modifications, the energy at each focal point of the multiple branched laser beams obtained by branching the laser beam L may be equal, or the branching ratio may be changed to create varying energies. In the above embodiments and modifications, the focal points SA1, SA2, and SA3 of the first branched laser beam are the same in the Y direction, but at least one of them may be shifted in the Y direction within a range narrower than the interval Y1. The focal points SB1, SB2, and SB3 of the second branched laser beam are the same in the Y direction, but at least one of them may be shifted in the Y direction within a range narrower than the interval Y1. The focal points SC1 and SC2 of the third branched laser beam are the same in the Y direction, but at least one of them may be shifted in the Y direction within a range narrower than the interval Y1 or interval Y2. The interval Y1 may be equal to or different from the interval Y2.

[0104] In the above embodiments and modifications, both the bottom of the first groove M1 and the bottom of the second groove M2 may be located on the surface 21a of the semiconductor substrate 21. In the above embodiments and modifications, the number of branches used to branch the laser light L in the branching pattern is not limited and may be multiple. In the above embodiments and modifications, the end of the crack 9 may reach the inner surface of the first groove M1 or the inner surface of the second groove M2 when the modified region 11 is formed, or the end of the crack 9 may reach the inner surface of the first groove M1 or the inner surface of the second groove M2 in a process after the modified region 11 has been formed. In the above embodiments and modifications, "the end of the crack 9 reaching the inner surface of the first groove M1 or the inner surface of the second groove M2" includes cases where, for example, processing is performed in a later process for the purpose of chipping the wafer 20, the end of the crack 9 does not reach the inner surface of the first groove M1 or the inner surface of the second groove M2 in a part of the line 15. [Explanation of symbols]

[0105] 1...Laser processing device, 2...Support part, 9...Crack, 11...Modification area, 15...Line, 20...Wafer (object), 21...Semiconductor substrate (substrate), 22...Functional element layer, 29...Protective film, 31...Laser light source, 34...Focusing part, 100...Laser processing device, 132...Spatial light modulator, 132A...Display unit, 200...Laser processing device, 202...Stage (support part), d12...Spacing, d23...Spacing, d34...Spacing, d45...Spacing, d56...Spacing, DC...Transparent die Single tape (tape), L...laser beam, L0...laser beam, LA...first branch laser beam, LB...second branch laser beam, M1...first groove, M2...second groove, M3...third groove, MH, MH1, MH2, MH3, MH4, MH5, MH6...composite groove, SA1, SA2, SA3...focusing point of the first branch laser beam, SB1, SB2, SB3...focusing point of the second branch laser beam, SC1, SC2...focusing point of the third branch laser beam, Y1, Y2...interval.

Claims

1. A step of irradiating an object with laser light to form a first groove in the object along a line, A step of irradiating the object with laser light and forming a second groove in the object along the line, such that the end of the first groove in the width direction overlaps with the first groove, The process includes forming a composite groove including the first groove and the second groove in the object, irradiating the object with laser light to form a modified region along the line inside the object and to propagate a crack from the modified region, A laser processing method comprising the step of extending the crack from the modified region, wherein the composite groove induces the extension of the crack from the modified region toward the first groove and the second groove.

2. The laser processing method according to claim 1, further comprising the step of, after forming the modified region, expanding a tape attached to the object while the end of the crack has reached the inner surface of the first groove or the inner surface of the second groove, thereby cutting the object along the line.

3. The object comprises a substrate and a functional element layer on the substrate. The laser processing method according to claim 1 or 2, wherein the composite groove is provided on the functional element layer side of the object such that both the bottom of the first groove and the bottom of the second groove reach the substrate.

4. The object comprises a substrate and a functional element layer on the substrate. The laser processing method according to claim 1 or 2, wherein the composite groove is provided on the functional element layer side of the object such that neither the bottom of the first groove nor the bottom of the second groove reaches the substrate.

5. The object comprises a substrate and a functional element layer on the substrate. The laser processing method according to claim 1 or 2, wherein the composite groove is provided in the functional element layer of the object such that either the bottom of the first groove or the bottom of the second groove reaches the substrate.

6. The laser processing method according to any one of claims 3 to 5, further comprising the step of forming a protective film on the functional element layer before forming the composite groove.

7. The laser processing method according to any one of claims 1 to 6, wherein the composite groove exhibits a W-shape in a cross-sectional view perpendicular to the line.

8. The laser processing method according to any one of claims 1 to 7, further comprising the step of grinding and thinning the object before forming the composite groove.

9. A laser processing method according to any one of claims 1 to 7, comprising the step of grinding and thinning the object after forming the modified region.

10. Multiple lines are set on the object, The laser processing method according to any one of claims 1 to 9, wherein the step of forming the modified region includes, if the amount of deviation of the formation position of the modified region from the center position of the composite groove in the width direction of the composite groove is greater than half the groove width of the composite groove, the step of correcting the formation position of the modified region to match the center position.

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