Laser processing methods

Abstract

A laser processing method comprises: a step to form a first groove in an object along a line by irradiating the object with laser light; a step to form a second groove in the object along the line by irradiating the object with laser light, wherein the second groove overlaps an end part of the first groove in the width direction of the first groove; and a step to form a modified area in the object along the line by irradiating the object with laser light and extending a crack from the modified area after forming the compound groove comprising the first groove and the second groove in the object.

Description

Technical area

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

[0002] For example, when cutting an object along a line, grooving processing can be performed to remove the surface layer side of the object along the line (see, for example, Patent Literatures 1 and 2). In such grooving processing, a groove is formed in the object along the line by irradiating the object with laser light. Reference listPatent literature Patent Literature 1: Unexamined Japanese Patent Publication No. 2007-173475 Patent Literature 2: Unexamined Japanese Patent Publication No. 2017-011040 Summary of the inventionProblem

[0003] In the techniques described above, after forming the groove, a modified region can be formed in the object along the line by irradiating the object with laser light, and the object can be cut along the line by expanding a crack from the modified region. In this case, in order to increase the yield (e.g., chip yield) of the object after cutting, it is desirable to reduce the width of the groove formed in the object. However, if the width of the groove is reduced, the crack tends to expand and thus deviate from the groove. For this reason, the crack deviates greatly from the line, which may degrade the cutting quality.

[0004] It is therefore an object of an object of the present invention to provide a laser processing method capable of suppressing a deviation of a crack extending from a modified portion and simultaneously reducing the width of a groove formed in an object. Problem solving

[0005] A laser processing method according to one aspect of the present invention includes: a step of forming a first groove in an object along a line by irradiating the object with laser light; a step of forming a second groove in the object along the line by irradiating the object with laser light, the second groove overlapping an end part of the first groove in the width direction of the first groove; and a step of forming a modified region in the object along the line by irradiating the object with laser light and expanding a crack from the modified region after forming a composite groove including the first groove and the second groove in the object.

[0006] In this laser processing method, a compound groove comprising the first groove and the second groove whose end parts overlap with each other is formed in the object. And because expansion of a crack into two grooves, namely the first groove and the second groove, is induced while simultaneously suppressing an increase in the width of the groove formed in the object, the effect of inducing the crack can be increased compared to a case where only a single groove is formed. In this way, it is possible to suppress the crack from expanding deviating from the groove. Thus, it is possible to suppress deviation of the crack expanding from the modified region and simultaneously reduce the width of the groove formed in the object.

[0007] The laser processing method according to one aspect of the present invention may further include a step of cutting the object along the line by stretching a tape attached to the object when an end of the crack reaches an inner surface of the first groove or an inner surface of the second groove after forming the modified region. In this case, the object can be cut accurately along the line.

[0008] In the laser processing method according to one aspect of the present invention, the object may include 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 such that a bottom of the first groove and a bottom of the second groove both reach the substrate. In this case, the crack-inducing effect of the first groove and the second groove can be further enhanced.

[0009] In the laser processing method according to one aspect of the present invention, the object may include 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 such that a bottom of the first groove and a bottom of the second groove both do not reach the substrate. In this case, the depths of the first groove and the second groove can be reduced.

[0010] In the laser processing method according to one aspect of the present invention, the object may include 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 such that a bottom of the first groove or a bottom of the second groove reaches the substrate. In this case, the crack-inducing effect of the first groove and the second groove can be enhanced.

[0011] In the laser processing method according to one aspect of the present invention, a step of forming a protective film on the functional element layer may be included before forming the composite groove. In this case, the functional element layer can be effectively protected by the protective film.

[0012] In the laser processing method according to one aspect of the present invention, the compound groove may have a W shape in a cross-sectional view perpendicular to the line. In this case, the above-described effect of suppressing deviation of the crack extending from the modified region can be achieved, and at the same time, the width of the groove formed in the object can be reduced.

[0013] In the laser processing method according to one aspect of the present invention, a step of grinding the object to make the object thin may be included before forming the compound groove. In this case, the object may be made thin by grinding before forming the compound groove.

[0014] In the laser processing method according to one aspect of the present invention, after forming the modified region, a step of grinding the object to make the object thin may be included. In this case, the object may be made thin by grinding after the compound groove is formed.

[0015] In the laser processing method according to one aspect of the present invention, a plurality of lines may be 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 to correspond to a center position of the compound groove when the deviation amount of the formation position of the modified region from the center position of the compound groove in the width direction of the compound groove is greater than half the groove formation width of the compound groove. In this case, the formation position of the modified region may be corrected using the groove formation width of the compound groove. Advantageous effects of the invention

[0016] According to one aspect of the present invention, there can be provided a laser processing method that can suppress deviation of the crack extending from the modified region and at the same time reduce the width of the groove formed in the object. Brief description of the drawings Fig. 1 is a configuration diagram of a laser processing apparatus for forming a modified region in a wafer. Fig. 2 is a configuration diagram of a laser processing apparatus for performing grooving processing. Fig. 3 is a plan view of a wafer to be processed. Fig. 4 is a cross-sectional view of a portion of the Fig. 3 wafers shown. Fig. 5 is a plan view of a part of a Fig. 3 shown street. Fig. 6 is a schematic view of an example in which the position of each focusing point of the first branched laser light and the position of each focusing point of the second branched laser light are shown from a Z direction. Fig. 7(a) is a cross-sectional view of a wafer for explaining a laser processing method according to an embodiment. Fig. 7(b) is a cross-sectional view of the wafer and a continuation of Fig. 7(a). Fig. 7(c) is a cross-sectional view of the wafer and a continuation of Fig. 7(b). Fig. Figure 8(a) is a cross-sectional view of the wafer and a continuation of Fig. 7(c). Fig. 8(b) is a cross-sectional view of the wafer and a continuation of Fig. 8(a). Fig. Figure 8(c) is a cross-sectional view of the wafer and a continuation of Fig. 8(b). Fig. 9(a) is a cross-sectional view of the wafer and a continuation of Fig. 8(c). Fig. 9(b) is a cross-sectional view of the wafer and a continuation of Fig. 9(a). Fig. 10 is an enlarged cross-sectional view of a portion of the wafer of Fig. 9(b). Fig. 11(a) is a Fig. 10 corresponding cross-sectional view of a wafer according to a modification example. Fig. 11(b) is a Fig. 10 corresponding cross-sectional view of a wafer according to another modification example. Fig. 11(c) is a Fig. 10 corresponding cross-sectional view of a wafer according to another modification example. Fig. 12 is a cross-sectional view of the wafer and a continuation of Fig. 9(b). Fig. 13 is a Fig. 10 corresponding cross-sectional view of a wafer according to a conventional example. Fig. 14 is a schematic view of another example in which the position of each focusing point of the first branched laser light and the position of each focusing point of the second branched laser light from the Z direction are shown. Fig. 15(a) is a schematic view of an example in which the position of each focusing point of the first branched laser light, the position of each focusing point of the second branched laser light, and the position of each focusing point of the third branched laser light are shown from the Z direction. Fig. 15(b) is a cross-sectional view of a wafer showing a compound groove according to a modification example. Fig. 16(a) is a cross-sectional view of a wafer showing a compound groove according to a modification example. Fig. 16(b) is a cross-sectional view of a wafer showing a compound groove according to a modification example. Fig. 16(c) is a cross-sectional view of a wafer showing a compound groove according to a modification example. Fig. 17(a) is a cross-sectional view of a wafer showing a compound groove according to a modification example. Fig. 17(b) is a cross-sectional view of a wafer showing a compound groove according to a modification example. Fig. 17(c) is a cross-sectional view of a wafer showing a compound groove according to a modification example. Fig. 18 is a table showing test results for evaluating the deviation of a crack when a compound groove is formed. Fig. 19(a) is a cross-sectional view of a wafer showing another example of a method for forming a compound groove. Fig. 19(b) is a cross-sectional view of the wafer and a continuation of Fig. 19(a). Fig. 20(a) is a cross-sectional view of a wafer showing another example of the method for forming a compound groove. Fig. 20(b) is a cross-sectional view of the wafer and a continuation of Fig. 20(a). Fig. 21 is a flowchart showing an example of laser processing including a step of correcting the formation position of a modified region. Fig. 22 is a perspective view of a laser processing apparatus in which an optical system for grooving processing and an optical system for forming a modified region are mounted. Fig. 23(a) is a cross-sectional view of a wafer for explaining a laser processing method according to a modification example. Fig. 23(b) is a cross-sectional view of the wafer and a continuation of Fig. 23(a). Fig. 23(c) is a cross-sectional view of the wafer and a continuation of Fig. 23(b). Fig. 24(a) is a cross-sectional view of the wafer and a continuation of Fig. 23(c). Fig. 24(b) is a cross-sectional view of the wafer and a continuation of Fig. 24(a). Fig. 24(c) is a cross-sectional view of the wafer and a continuation of Fig. 24(b). Fig. 25 is a cross-sectional view of the wafer and a continuation of Fig. 24(c). Description of embodiments

[0017] An embodiment according to one aspect of the present invention will be described in detail below with reference to the figures. Like or corresponding parts in the figures are designated by like reference numerals, and a repeated description of these parts will be omitted here.

[0018] In this embodiment, a modified region is formed in a wafer (object). For example, a Fig. 1 can be used as a device for forming a modified region in a wafer. As shown in Fig. 1, the laser processing apparatus 100 includes a holding unit 102, a light source 103, an optical axis adjusting unit 104, a spatial light modulator 105, a condensing unit 106, an optical axis monitoring unit 107, a visible light image pickup unit 108A, an infrared image pickup unit 108B, a moving mechanism 109, and a management unit 150. The laser processing apparatus 100 is an apparatus for forming a modified region 11 on a wafer 20 by irradiating the wafer 20 with laser light L0. In the following description, three mutually perpendicular directions are referred to as an X direction, a Y direction, and a Z direction, respectively. For example, the X direction is a first horizontal direction, the Y direction is a second horizontal direction perpendicular to the first horizontal direction, and the Z direction is a vertical direction.

[0019] The holding unit 102 holds the wafer 20, for example, by adsorbing the wafer 20. The holding unit 102 can be moved along each of the X-direction and the Y-direction. The holding unit 102 can be rotated about a rotation axis along the Z-direction. The light source 103 emits the laser light L0 using, for example, 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 by the light source 103. The optical axis adjustment unit 104 consists, for example, of a plurality of reflection mirrors whose positions and angles can be adjusted.

[0020] The spatial light modulator 105 is arranged in a 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 liquid crystal on silicon (LCOS) spatial light modulator (SLM). In the spatial light modulator 105, the laser light L0 can be modulated by appropriately setting a modulation pattern for display on a display unit (liquid crystal layer). In this embodiment, the laser light L0 traveling 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 is incident on the spatial light modulator 105. The spatial light modulator 105 modulates the thus incident laser light L0 and reflects the laser light L0.

[0021] The condensing unit 106 is mounted on the bottom wall of the laser processing head H. The condensing unit 106 condenses the laser light L0 modulated by the spatial light modulator 105 onto the wafer 20 held by the holding unit 102. In this embodiment, the laser light L0 reflected by the spatial light modulator 105 is reflected by a dichroic mirror MM2 to be incident on the condensing unit 106. The condensing unit 106 condenses the thus incident laser light L0 onto the wafer 20. The condensing unit 106 is formed by mounting a condensing lens unit 161 on the bottom wall of the laser processing head H via a drive mechanism 162. The drive mechanism 162 moves the condensing unit 161 along the Z direction, for example, by the driving force of a piezoelectric element.

[0022] Furthermore, in the laser processing head H, an image pickup optical system (not shown) is arranged between the spatial light modulator 105 and the condensing unit 106. The image pickup optical system forms a double-sided telecentric optical system in which the reflection surface of the spatial light modulator 105 and the entrance pupil plane of the condensing unit 106 are in an image pickup relationship. Therefore, the image of the laser light L0 on the reflection surface of the spatial light modulator 105 (the image of the laser light L0 modulated by the spatial light modulator 105) is transferred (formed) onto the entrance pupil plane of the condensing unit 106. A pair of distance sensors S1 and S2 are mounted on the bottom wall of the laser processing head H so as to be arranged on both sides of the condensing lens unit 161 in the X direction.Each of the distance sensors S1 and S2 obtains displacement data of the laser light incident surface by emitting light for distance detection (for example, a laser light) to the laser light incident surface of the wafer 20 and detecting the light for distance detection from the laser light incident surface.

[0023] The optical axis monitoring unit 107 is arranged in the laser processing head H. The optical axis monitoring unit 107 detects a part of the laser light L0 that has passed through the dichroic mirror MM2. The detection result of the optical axis monitoring unit 107 indicates, for example, a relationship between the optical axis of the laser light L0 incident on the condensing lens unit 161 and the optical axis of the condensing lens unit 161. The visible light image pickup unit 108A emits visible light V0 and obtains an image of the wafer 20 through the visible light V0 as an image. The visible light image pickup unit 108A is arranged in the laser processing head H. The infrared image pickup unit 108B emits infrared light and obtains an image of the wafer 20 through the infrared light as an infrared image. The infrared image pickup unit 108B is mounted on the side wall of the laser processing head H.

[0024] The movement mechanism 109 includes a mechanism that moves the laser processing head H and / or the holding unit 102 in the X direction, the Y direction, and the Z direction. The movement mechanism 109 drives the laser processing head H and / or the holding unit 102 with the driving force of a known driving device such as a motor, so that the focusing point C of the laser light L0 moves in the X direction, the Y direction, and the Z direction. The movement mechanism 109 includes a mechanism that rotationally drives the holding unit 102 with the driving force of a known driving device such as a motor.

[0025] 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 unit of the laser processing device 100. The control unit 151 is configured as a computer device including a processor, a RAM, a storage, a communication device, etc. In the control unit 151, the processor executes software (a program) or the like read into the RAM to control the reading and writing of data in the RAM and storage and communication through the communication device. The user interface 152 displays and inputs various types of data. The user interface 152 is a graphical user interface (GUI) with a graphically based operating system.

[0026] The user interface 152 includes, for example, a touch screen, a keyboard, a mouse, a microphone, a tablet terminal, a monitor, and / or the like. The user interface 152 can receive various inputs, for example, through 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 receives input and a display unit that can display a set screen content based on the received input. The storage unit 153 is, for example, a hard disk and stores various types of data.

[0027] In the laser processing apparatus 100 having the above-described configuration, when the laser light L0 is condensed in the wafer 20, the laser light L is absorbed in a portion corresponding to the focusing point (at least a portion of the focusing region) C of the laser light L0, and the modified region 11 is formed in the wafer 20. The modified region 11 is a region whose density, refractive index, mechanical strength, and other physical properties are different from those of the surrounding unmodified region. Examples of the modified region 11 include a melt treatment region, a crack region, a dielectric breakdown region, and a refractive index change region. The modified region 11 includes a plurality of modified points 11s and cracks extending from the plurality of modified points 11s.

[0028] The following describes, by way of example, the operation of the laser processing apparatus 100 for forming the modified region 11 in the wafer 20 along a line 15 for cutting the wafer 20.

[0029] First, the laser processing apparatus 100 rotates the holding unit 102 such that the line 15 set on the wafer 20 is parallel to the X direction. The laser processing apparatus 100 moves the holding unit 102 along the X direction and the Y direction, respectively, based on the image obtained by the infrared image pickup unit 108B (for example, an image of the functional element layer in the wafer 20), so that the focusing point C of the laser light L0 is positioned on the line 15 as viewed from the Z direction. The laser processing apparatus 100 moves the laser processing head H (i.e., the condensing unit 106) along the Z direction based on the image obtained by the visible light image pickup unit 108A (for example, an image of the laser incident surface of the wafer 20), so that the focusing point C of the laser light L0 is positioned on the laser light incident surface (height adjustment).With the position as a reference, the laser processing apparatus 100 moves the laser processing head H along the Z direction so that the focusing point C of the laser light L0 is positioned at a predetermined depth from the laser light incident surface.

[0030] Subsequently, the laser processing apparatus 100 emits the laser light L0 from the light source 103 and moves the holding unit 102 along the X direction so that the focusing point C of the laser light L0 moves relatively along the line 15. At this time, the laser processing apparatus 100 operates the drive mechanism 162 of the condensing unit 106 based on the displacement data of the laser light incident surface obtained by one of the pair of distance sensors S1 and S2 arranged on the front side in the processing progress direction of the laser light L0, so that the focusing point C of the laser light L0 is located at a predetermined depth from the laser light incident surface.

[0031] In this way, a row of modified regions 11 is formed along line 15 and at a fixed depth from the laser light incident surface of wafer 20. When laser light L0 is emitted from light source 103 using a pulse oscillation method, a plurality of modified spots 11s are formed aligned in a row along the X direction. A modified spot 11s is formed by emitting a single pulse of laser light L0. The modified regions 11 in a row are a set of a plurality of modified spots 11s arranged 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 (a value obtained by dividing the relative moving speed of the focusing spot C with respect to the wafer 20 by the repetition frequency of the laser light L0).

[0032] In this embodiment, a groove forming process is performed to form a groove in the wafer 20 along the line 15 by emitting a laser light onto the road along the line 15 so that the surface layer of the road on the wafer 20 is removed. For example, the Fig. 2 can be used as an apparatus for performing grooving processing.

[0033] As in Fig. 2, the laser processing apparatus 1 includes a holding unit 2, an irradiation unit 3, an image pickup unit 4, and a control unit 5. The holding unit 2 holds the wafer 20. The holding unit 2 holds the wafer 20 such that the surface of the wafer 20 faces the street of the irradiation unit 3 and the image pickup unit 4, for example, by adsorbing the wafer 20. For example, the holding unit 2 can move along each of the X-direction and the Y-direction, and can rotate with an axis parallel to the Z-direction as a center line.

[0034] The irradiation unit 3 irradiates the street of the wafer 20 held by the holding unit 2 with the laser light L. The irradiation unit 3 includes a laser light source 31, a shaping optical system 32, a dichroic mirror 33, and a condensing unit 34. The laser light source 31 emits the laser light L. The shaping optical system 32 adjusts the laser light L emitted by 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.

[0035] The spatial light modulator 132 has a display unit 132A onto 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 a modulation pattern displayed on the display unit 132A. The shaping optical system 32 may include an image pickup optical system and may be a double-sided telecentric optical system in which the modulation surface of the spatial light modulator and the entrance pupil plane of the condensing unit 34 are in an image pickup 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 increasing the diameter of the laser light L.

[0036] The dichroic mirror 33 reflects the laser light L emitted from the forming optical system 32 and makes the reflected laser light L incident on the condensing unit 34. The condensing unit 34 condenses the laser light L reflected by the dichroic mirror 33 (the laser light L modulated by the spatial light modulator 132) onto the wafer 20 held by the holding unit 2.

[0037] The irradiation unit 3 further includes a light source 35, a half mirror 36, and an image pickup element 37. The light source 35 emits the visible light V1. The half mirror 36 reflects the visible light V1 emitted by the light source 35 and allows the reflected visible light V1 to be incident on the condensing unit 34. The dichroic mirror 33 transmits the visible light V1 between the half mirror 36 and the condensing unit 34. The condensing unit 34 condenses the visible light V1 reflected by the half mirror 36 onto the street of the wafer 20 held by the holding unit 2. The image pickup element 37 captures the visible light V1 reflected by the street of the wafer 20 and transmitted through the condensing unit 34, the dichroic mirror 33, and the half mirror 36.In the laser processing apparatus 1, the control unit 5 moves the condensing unit 34 along the Z direction based on the detection result of the image pickup element 37, for example, such that the focusing point of the laser light L is positioned on the street of the wafer 20.

[0038] The image acquisition unit 4 obtains image data of the wafer 20 held by the holding unit 2. The image acquisition unit 4 is an internal observation camera for observing the interior of the wafer 20 on which the modified region 11 has been formed by the laser processing apparatus 100. The image acquisition unit 4 emits infrared light toward the wafer 20 and obtains an image of the wafer 20 using the infrared light as image data. An InGaAs camera can be used as the image acquisition unit 4.

[0039] The control unit 5 controls the operation of each unit of the laser processing device 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, a RAM, a memory, a communication device, and so on. In the processing unit 51, the processor executes software (program) or the like read into the RAM to control the reading and writing of data in the RAM and the memory and communication through the communication device. 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.For example, the input receiving unit 53 is a keyboard, a mouse and / or a graphical user interface (GUI).

[0040] The laser processing device 1 performs grooving processing. In the grooving processing, the control unit 5 controls the irradiation unit 3 such that the laser light L is emitted along the line 15 to each street on the wafer 20 held by the holding unit 2, and the control unit 5 controls the holding unit 2 such that the laser light L moves relatively along the line 15 (described in more detail below).

[0041] As in Fig. 3 and Fig. As shown in Figure 4, the wafer 20 includes 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. A notch 21c indicating the crystal orientation is provided in the semiconductor substrate 21. Instead of the notch 21c, an alignment surface may be provided in the semiconductor substrate 21. 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, or a circuit element such as a memory. Each functional element 22a can be formed three-dimensionally by stacking a plurality of layers.

[0042] A plurality of streets 23 are formed on the wafer 20. The plurality of streets 23 are regions exposed to the outside between the mutually adjacent functional elements 22a. The plurality of functional elements 22a are thus arranged adjacent to one another with the street 23 in between. In one example, the plurality of streets 23 extend in a lattice shape so that they pass between the adjacent functional elements 22a for the plurality of functional elements 22a arranged in a matrix. As shown in Fig. As shown in Figure 5, an insulating film 24 and a plurality of metal structures 25 and 26 are formed on the surface layer of the road 23. The insulating film 24 is, for example, a low-k film. Each of the metal structures 25 and 26 is, for example, a metal pad. The metal structure 25 and the metal structure 26 are different in thickness, area, and material, for example.

[0043] As in Fig. 3 and Fig. 4, a plurality of lines 15 are provided on the wafer 20. The wafer 20 is to be cut into the functional elements 22a along the plurality of lines 15 (i.e., processed into chips corresponding to the respective functional elements 22a). Each line 15 extends through a street 23 as viewed from the thickness direction of the wafer 20. For example, each line 15 extends through the center of the street 23 as viewed from the thickness direction of the wafer 20. Each line 15 is a virtual line provided on the wafer 20 by the laser processing devices 1 and 100. Each line 15 may also be a line actually drawn on the wafer 20.

[0044] In this embodiment, the modulation pattern displayed on the display unit 132A of the spatial light modulator 132 includes a branching pattern for branching the laser light L into a plurality of (here: two) first branched laser light components for forming a first groove and a plurality of (here: two) second branched laser light components for forming a second groove. As shown in Fig. As shown in Figure 6, in this embodiment, focusing points SA1 and SA2 of two first branched laser light components are aligned, and then focusing points SB1 and SB2 of two second branched laser light components are aligned from one side of line 15 to the other side in the X direction along line 15. In the Y direction corresponding to the width direction of a groove to be formed, the positions of the focusing points SA1 and SA2 of the first branched laser light components are the same. In the Y direction, the positions of the focusing points SB1 and SB2 of the second branched laser light components are the same.

[0045] Each position of the focusing points SA1 and SA2 of the first branched laser light components is also referred to as a first processing point, and each position of the focusing points SB1 and SB2 of the second branched laser light components is also referred to as a second processing point. In the X direction, the distance between the position of the focusing point SA2 of the first branched laser light and the adjacent position of the focusing point SB1 of the second branched laser light is defined as a distance d23. In other words, the distance d23 is a distance in the X direction between the first processing point and the adjacent second processing point.In the Y direction, which corresponds to the width direction of the groove to be formed, the distance between the positions of the focusing points SA1 and SA2 of the first branched laser light components and the positions of the focusing points SB1 and SB2 of the second branched laser light components is defined as a distance Y1.

[0046] The distance d23 is greater than the distance Y1. The distance d23 is greater than the pulse pitch of the laser light L. The distance d23 is, for example, 20 µm or more. The distance d12 between the positions of the focusing points SA1 and SA2 of a plurality of first branched laser light components in the X direction along the line 15 is greater than the pulse pitch of the laser light L. The distance d12 is smaller than the distance d23. The distance d34 between the positions of the focusing points SB1 and SB2 of a plurality of second branched laser light components in the X direction is greater than the pulse pitch of the laser light L. The distance d34 is smaller than the distance d23.The branching pattern branches the laser light L such that the focusing points SA1, SA2, SB1 and SB2 are aligned in a one-dimensional arrangement (including an approximately one-dimensional arrangement, a substantially one-dimensional arrangement and an approximately one-dimensional arrangement; the same also applies below) along the line 15.

[0047] As in Fig. As shown in Figure 8(b), the first groove M1 formed by the first branched laser light LA ​​and the second branched groove M2 formed by the second branched laser light LB constitute a composite groove MH. The composite groove MH is a W-shaped groove (W-groove) in a cross-sectional view perpendicular to the line 15. The composite groove MH is a groove having a shape with two valley parts and a mountain part on the bottom side in a cross-sectional view perpendicular to the line 15. The first groove M1 and the second groove M2 are each a V-shaped groove (V-groove) in a cross-sectional view perpendicular to the line 15. The second groove M2 overlaps an end part of the first groove M1 in the Y direction. In other words, the first groove M1 and the second groove M2 extend in the X direction, while their end parts in the Y direction overlap each other. The first groove M1 and the second groove M2 are provided such that their peripheral edges are in contact with each other.The first groove M1 and the second groove M2 are grooves that each have the same depth and width.

[0048] The compound groove MH is provided on the functional element layer 22 side of the wafer 20 so that the bottom of the first groove M1 and the bottom of the second groove M2 reach the semiconductor substrate 21. The bottom 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 end parts of the first groove M1 and the second groove M2 (a peak part on the bottom side of the compound groove MH) reach the functional element layer 22 side of the semiconductor substrate 21. The groove width, which is the groove formation width of the compound groove MH on the most open side, is, for example, 12 μm. An appropriate groove formation width can be determined via the receiving unit 53 (see Fig. 2). The groove formation width is smaller than the width of road 23.

[0049] Furthermore, the distance d12 and the distance d34 can be the same or different. For example, if the pulse pitch is 0.5 µm, the distance d12 can be 10 µm, the distance d23 can be 20 µm, the distance d34 can be 10 µm, and the distance Y1 can be 5 µm. The distance Y1 is a distance that allows the compound groove MH to have a W shape in a cross-sectional view and can be smaller than the groove formation width.

[0050] Hereinafter, a laser processing method using the laser processing apparatus 100 and the laser processing apparatus 1 will be described with reference to Fig. 7 to 11.

[0051] First, as in Fig. 7(a), the wafer 20 is prepared. A grinding belt 28 is applied to the surface of the wafer 20 on the side of the functional element layer 22. As shown in Fig. As shown in Fig. 7(b), the rear surface 21b side of the semiconductor substrate 21 of the wafer 20 is ground using a grinder to make the wafer 20 thin to a desired thickness (grinding step). As shown in Fig. 7(c), the grinding tape 28 is removed and a protective film 29 for protecting the functional element layer 22 (functional element 22a) is applied to the surface of the wafer 20 on the side of the functional element layer 22.

[0052] Then, as in Fig. 8(a), in the laser processing apparatus 1, after the wafer 20 has been adsorbed and held by the holding unit 2, a groove formation processing is performed on the wafer 20. In the groove formation processing, the control unit 5 controls the irradiation unit 3 such that the laser light L is emitted to the street 23 of the wafer 20 along the line 15, and the control unit 5 controls the holding unit 2 such that the laser light L moves relatively along the line 15. Thereby, as shown in Fig. 8(b)), the surface layer of the street 23 on the wafer 20 is removed to form the composite groove MH including the first groove M1 and the second groove M2.

[0053] Specifically, in the groove forming processing, the laser light L is emitted, the emitted laser light L is caused to be directed to the display unit 132A (see Fig. 2) of the room light modulator 132 (see Fig. 2), the laser light L is branched into the first branched laser light LA ​​and the second branched laser light LB by the modulation pattern displayed on the display unit 132A, and the first branched laser light LA ​​and the second branched laser light LB are condensed onto the wafer 20. In the groove formation processing, the condensation unit 34 (see Fig. 2) is moved or modulated by the spatial light modulator 132, so that the first branched laser light LA ​​and the second branched laser light LB are condensed onto the surface of the functional element layer 22, for example, in the Z direction. The first groove M1 is formed by condensing the first branched laser light LA, and the second groove M2 is formed by the second branched laser light LB.

[0054] As described above, the modulation pattern includes a branching pattern. The branching pattern can be appropriately determined by the control unit 5 based on the information received via the input receiving unit 53 (see Fig. 2) input groove formation width. For example, the branching pattern can be automatically generated by the control unit 5 using various known methods, so that the focusing points SA1, SA2, SB1 and SB2 of the first branched laser light LA ​​and the second branched laser light LB are arranged in a one-dimensional arrangement as shown in Fig. 6 are positioned to realize the compound groove MH with the groove formation width.

[0055] No particular restrictions are imposed here on the processing conditions for forming the compound groove MH, so they can be set based on various known techniques. Appropriate processing conditions for forming the compound groove MH can be input via the input receiving unit 53. The processing conditions for forming the compound groove MH can be, for example, the following conditions. In the following exemplary conditions, burst pulses are not used. However, burst pulses can be used, for example, for suppressing film peeling (see below). Wavelength of laser light L: 515 nm Pulse width of the laser light L: 600 fs Pulse distance of the laser light L: 0.5 µm Processing energy (total energy of each focusing point): 4.0 µJ Number of rounds: 1 round Position of the bottom of the compound groove MH: 3 µm from the front surface 21a of the semiconductor substrate 21

[0056] Then, as in Fig. As shown in Fig. 8(c), the wafer 20 is removed from the holding unit 2 and the protective film 29 is removed using, for example, a chemical solution. As shown in Fig. As shown in Figure 9(a), a dicing tape (tape) DC provided with a ring frame RF is attached to the rear surface 21b of the semiconductor substrate 21 of the wafer 20. The transparent dicing tape DC is also called a stretch film.

[0057] Then, as in Fig. As shown in Fig. 9(b), in the laser processing apparatus 100, the wafer 20 is irradiated with the laser light L0 along the line 15, thereby forming the modified region 11 in the wafer 20 along the line 15. At this time, the wafer 20 is adsorbed and held by the holding unit 102, with the transparent dicing tape DC attached to the back surface 21b of the semiconductor substrate 21. Then, the focusing point of the laser light L0 in the semiconductor substrate 21 is aligned by the transparent dicing tape DC, so that the wafer 20 is irradiated with the laser light L0 with the back surface 21b as the laser light incident surface.

[0058] The laser light L0 is transparent to the transparent dicing tape DC and the semiconductor substrate 21. When the laser light L0 is condensed in the semiconductor substrate 21, the laser light L0 is adsorbed at a part corresponding to the focusing point of the laser light L0, and accordingly, the modified region 11 is formed in the semiconductor substrate 21, and a crack 9 expands from the modified region 11. Regarding the processing conditions for forming the modified region 11, no particular requirements are made here, so they can be set based on various known findings. Appropriate processing conditions for forming the modified region 11 can be set via the user interface 152 (see Fig. 1). The processing conditions for forming the modified region 11 may be, for example, the following conditions. Wavelength of laser light L0: 1099 nm Pulse width of the laser light L0: 700 ns Pulse spacing of the laser light L0: 6.5 µm Processing energy: 22 µJ Number of rounds: 8 rounds

[0059] An extension of the crack 9 extending from the modified region 11 to the side of the functional element layer 22 is induced to two grooves of the composite groove MH, namely the first groove M1 and the second groove M2, so that its end reaches the inner surface of the first groove M1 or the inner surface of the second groove M2. For example, in the Fig. 10, there is essentially no deviation of the modified region 11 from the line 15 in the Y-direction, so that in this case the induced crack 9 reaches the inner surface of the first groove M1 on the side of the second groove M2. Alternatively, for example, in the example shown in Fig. 11(a) there is a deviation of the modified region 11 from the line 15 in the Y direction, the induced crack 9 can reach the bottom of the first groove M1. Alternatively, for example, in the example shown in Fig. 11(b), there is a deviation of the modified region 11 from the line 15 in the Y direction, the induced crack 9 can reach the inner surface of the first groove M1 on a side opposite to the second groove side. Alternatively, for example, if, as in the example shown in Fig. 11(c), there is a deviation of the modified region 11 from the line 15 in the Y direction, the induced crack 9 can reach the inner surface of the first groove M1 on the side of the second groove M2.

[0060] Then, as in Fig. 12, by stretching the attached transparent dicing tape DC with a stretching device (not shown), the crack in the thickness direction of the wafer 20 from the modified region 11 formed inside the semiconductor substrate 21 is extended along each line 15 to cut the wafer 20 along the line 15. As a result, the wafer 20 is divided into chips corresponding to the respective functional elements 22a, and a plurality of chips T1 are obtained.

[0061] For example, instead of the transparent dicing tape DC, a protective tape may be attached to the functional element layer 22 side, and laser light L0 may be emitted from the back surface 21b of the semiconductor substrate 21 to form the modified region 11. Then, the transparent dicing tape DC may be attached to the back surface 21b of the semiconductor substrate 21, and the protective tape on the functional element layer 22 side may be peeled off, and the transparent dicing tape DC may be stretched and divided. For example, using a holding material, laser processing (grooving processing and formation of the modified region 11) may be performed with a protective film attached. Then, the protective film may be removed, the transparent dicing tape DC may be attached, and the transparent dicing tape DC may be stretched and divided.

[0062] By the way, as in Fig. As shown in Figure 13, when a single V-groove M0 is formed in the wafer 20 along the line 15, the crack 9 extends from the modified region 11, which is formed further inside than the V-groove M0 in the Z direction in the wafer 20, to an extension deviated from the V-groove M0. For this reason, the crack 9 deviates significantly from the line 15. In this case, the cutting quality when cutting the wafer 20 is reduced. This increases the likelihood of deterioration in the division quality, occurrence of cracking, and the occurrence of cracks.

[0063] Therefore, in this embodiment, the composite groove MH including the first groove M1 and the second groove M2 whose end portions overlap with each other is formed in the wafer 20. Since expansion of the crack 9 into two grooves, namely the first groove M1 and the second groove M2, is induced while suppressing an increase in the groove formation width, the effect of inducing the crack 9 can be increased compared to a case where only a single V-groove M0 is formed. This can suppress aberration of the crack 9 expanding. Therefore, deviation of the crack 9 expanding from the modified region 11 can be suppressed while reducing the groove formation width. The deviation of the crack 9 can be kept within the groove formation width. Because the division quality can be improved, all the chips can be reliably divided. The width of the street 23 can be reduced.

[0064] This embodiment further includes a step of cutting the wafer 20 along the line 15 by stretching the transparent dicing tape DC attached to the wafer 20, wherein 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 forming the modified region 11. In this case, the wafer 20 can be cut accurately along the line 15.

[0065] In this embodiment, the wafer 20 includes the semiconductor substrate 21 and the functional element layer 22. The composite groove MH is provided on the functional element layer 22 side of the wafer 20, so that the bottom of the first groove M1 and the bottom of the second groove M2 reach the semiconductor substrate 21. In this case, the effect of inducing the crack 9 by the first groove M1 and the second groove M2 can be further enhanced.

[0066] This embodiment includes a step of forming the protective film 29 on the functional element layer 22 before forming the compound groove MH. In this case, the functional element layer 22 can be effectively protected by the protective film 29. In this embodiment, the compound groove MH has a W shape in a cross-sectional view perpendicular to the line 15. In this case, the above-described effect of suppressing deviation of the crack 9 while reducing the groove formation width is enhanced. This embodiment includes a step of grinding the wafer 20 to make the wafer 20 thin before forming the compound groove MH. In this case, the wafer 20 can be made thin by grinding before forming the compound groove MH.

[0067] In the laser processing apparatus 1 and the laser processing method according to the present embodiment, the distance d23 between the first processing point and the adjacent second processing point (between the position of the focusing point SA2 of the first branched laser light and the position of the focusing point SB1 of the second branched laser light) 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 allows the first processing point and the second processing point to be separated so far that the first processing point and the second processing point hardly influence each other. Examples of influence include disturbance of the preceding processing point and influence of processing in a heat-characterized state.Furthermore, the first processing point and the second processing point can be separated from each other to such an extent that any influence substantially disappears. Therefore, 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 formed distinctly so that their bottoms are clearly defined. Therefore, with the laser processing apparatus 1 and the laser processing method for branching the laser light L into a plurality of branched laser light components and irradiating the wafer 20 with the branched laser light components, the first groove M1 and the second groove M2 can be satisfactorily formed in the wafer 20 along the line 15.

[0068] In this embodiment, the second groove M2 overlaps the end portion of the first groove M1 in the width direction of the first groove M1. The composite groove MH including the first groove M1 and the second groove M2 can be formed in the wafer 20. Such a composite groove MH can effectively induce expansion of the crack 9 from the modified region 11 formed in the wafer 20.

[0069] In this embodiment, the distance d23 in the X direction is larger than the pulse pitch of the laser light L. In this case, because the occurrence of a situation in which the distance between the first processing position and the second processing position is too short and accordingly their influence on each other becomes considerable is suppressed, the first groove M1 and the second groove M2 can be satisfactorily formed in the wafer 20.

[0070] In this embodiment, the distance d12 between a plurality of first processing positions in the X direction is larger than the pulse pitch of the laser light L. In this case, because the occurrence of a situation in which the distance d12 between the plurality of first processing positions is too short and accordingly their influence on each other becomes considerable can be suppressed, the first groove M1 can be satisfactorily formed.

[0071] In this embodiment, the distance d12 between the plurality of first processing positions in the X direction is smaller than the distance d23. In this case, the distance between the plurality of first processing positions can be set to a range where they influence each other, so that the generation of a heat-affected zone around the first groove M1 can be suppressed.

[0072] In this embodiment, the distance d34 between a plurality of second processing positions in the X direction is larger than the pulse pitch of the laser light L. In this case, because the occurrence of a situation in which the distance between the plurality of second processing positions is too short and accordingly their influence on each other becomes considerable can be suppressed, the second groove M2 can be satisfactorily formed.

[0073] In this embodiment, the distance d34 between the plurality of second processing positions in the X direction is smaller than the distance d23. In this case, the distance between the plurality of second processing positions can be set to a range where they interfere with each other, so that the generation of a heat-affected zone around the second groove M2 can be suppressed.

[0074] In this embodiment, the branching pattern branches the laser light L into two first branched laser light components LA and two second branched laser light components LB. Because the energy at each of the focusing points SA1, SA2, SB1, and SB2 can be reduced in this case, a heat-affected zone can be suppressed.

[0075] In this embodiment, the branching pattern branches the laser light L such that the focusing points SA1, SA2, SB1, and SB2 are aligned in a one-dimensional array along line 15. Therefore, the narrow compound groove MH can be formed in the wafer 20. Furthermore, the bending strength of the wafer 20 can be improved.

[0076] Even if there is no deviation of the position of the modified region 11 from the position of the line 15 in the Y direction, a problem may occur when forming a single V-groove M0 if the crack 9 extending from the modified region 11 meanders. Because the composite groove MH is formed as a W-groove in this embodiment, this problem can be suppressed.

[0077] In this embodiment, the branching pattern may branch the laser light L into three first branched laser light components LA for forming the first groove M1 and three second branched laser light components LB for forming the second groove M2. In this case, for example, as shown in Fig. 14, in the X direction along line 15 from one side of line 15 to the other side, the focusing points SA1, SA2, and SA3 of the three first branched laser light components are aligned, and then the focusing points SB1, SB2, and SB3 of the three second branched laser light components are aligned. In the Y direction, which corresponds to the width direction of a groove to be formed, the positions of the focusing points SA1, SA2, and SA3 of the first branched laser light components are the same. In the Y direction, the positions of the focusing points SB1, SB2, and SB3 of the second branched laser light components are the same. With such a branching pattern, since the energy at each of the focusing points SA1, SA2, SA3, SB1, SB2, and SB3 can be further reduced, the heat-affected zone can be further suppressed.

[0078] In this embodiment, the branching pattern displayed on the display unit 132A of the spatial light modulator 132 may branch the laser light L into one or more (here: two) first branched laser light components LA to form the first groove M1, one or more (here: two) second branched laser light components LB to form the second groove M2, and one or more (here: two) third branched laser light components to form the third groove M3. In this case, for example, as shown in Fig. As shown in Figure 15(a), in the X direction along line 15 from one side of line 15 to the other, the focusing points SA1 and SA2 of the two first branched laser light components are aligned, the focusing points SB1 and SB2 of the two second branched laser light components are aligned, and then the focusing points SC1 and SC2 of the two third branched laser light components are aligned. In the Y direction, which corresponds to the width direction of a groove to be formed, the positions of the focusing points SC1 and SC2 of the third branched laser light components are the same.

[0079] In the X direction, the distance between the position of the focusing point SB2 of the second branched laser light and the adjacent position of the focusing point SC1 of the third branched laser light is defined as a distance d45. The distance d45 is equal to the distance d23. In the Y direction, the distance between each of the positions of the focusing points SB1 and SB2 of the second branched laser light components and each of the positions of the focusing points SC1 and SC2 of the third branched laser light components is defined as a distance Y2. The distance Y2 is equal to the distance Y1. The distance d45 is greater than the distance Y1. The distance d45 is greater than the pulse pitch of the laser light L. The distance d56 between the positions of the focusing points SC1 and SC2 of a plurality of third branched laser light components in the X direction along the line 15 is greater than the pulse pitch of the laser light L.The distance d56 is smaller than the distance d23. The branching pattern branches the laser light L such that the focusing points SA1, SA2, SB1, SB2, SC1, and SC2 are aligned in a one-dimensional array along line 15. In this case, as shown in . Fig. 15(b) a wide compound groove MH1 can be formed.

[0080] The first groove M1 formed by the first branched laser light LA, the second groove M2 formed by the second branched laser light LB, and the third groove M3 formed by the third branched laser light constitute the composite groove MH1. The composite groove MH1 is a groove having a shape with three valley parts and two peak parts on the bottom side in a cross-sectional view perpendicular to the line 15. The first groove M1, the second groove M2, and the third groove M3 are each a V-groove in a cross-sectional view perpendicular to the line 15. The second groove M2 overlaps an end part of the first groove M1 in the Y direction. In other words, the first groove M1 and the second groove M2 extend in the X direction while their end parts in the Y direction overlap each other. The first groove M1 and the second groove M2 are provided such that their peripheral edges are in contact with each other.An end portion of the third groove M3 in the Y direction overlaps an end portion of the second groove M2 in the Y direction. In other words, the second groove M2 and the third groove M3 extend in the X direction, while their end portions in the Y direction overlap each other. The second groove M2 and the third groove M3 are provided such that their peripheral edges are in contact with each other. The first groove M1, the second groove M2, and the third groove M3 have the same depth and width.

[0081] The compound groove MH1 is provided on the functional element layer 22 side of the wafer 20, so that the bottom of the first groove M1, the bottom of the second groove M2, and the bottom of the third groove M3 all reach the semiconductor substrate 21. The bottom 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 end portions of the first groove M1, the second groove M2, and the third groove M3 (two peak portions on the bottom side of the compound groove MH1) reach the functional element layer 22 side of the semiconductor substrate 21.

[0082] By the way, in this embodiment, as in Fig. 16(a), a compound groove MH2 may be provided on the functional element layer 22 side of the wafer 20. The compound groove MH2 is a W-groove formed by the first groove M1 and the second groove M2. The second groove M2 overlaps an end portion of the first groove M1 in the Y direction. The compound groove MH2 is provided such that the bottom of the first groove M1 and the bottom of the second groove M2 both reach the semiconductor substrate 21. The overlapping end portions of the first groove M1 and the second groove M2 (a peak portion on the bottom side of the compound groove MH) reach the functional element layer 22 side of the semiconductor substrate 21. The bottoms of the first groove M1 and the second groove M2 of the compound groove MH2 are separated from each other in the Y direction compared to the compound groove MH (see Fig. 8(b)). Even with such a compound groove MH2, the same effect is achieved as with the compound groove MH.

[0083] In this embodiment, as in Fig. As shown in Fig. 16(b), a compound groove MH3 may be provided on the functional element layer 22 side of the wafer 20. The compound groove MH3 is a W-groove formed by the first groove M1 and the second groove M2. The second groove M2 overlaps an end part of the first groove M1 in the Y direction. The first groove M1 is a groove deeper than the second groove M2. The compound groove MH3 is provided such that the bottom of the first groove M1 reaches the semiconductor substrate 21 and the bottom of the second groove M2 does not reach the semiconductor substrate 21. That is, either the bottom of the first groove M1 or the bottom of the second groove M2 is provided such that it reaches the semiconductor substrate 21. The overlapping end parts of the first groove M1 and the second groove M2 (a mountain part on the bottom side of the composite groove NH3) reach the side of the semiconductor substrate 21 of the functional element layer 22.Even with such a composite groove MH3, the same effect as with the composite groove MH is achieved. The effect of inducing the crack 9 by the first groove M1 and the second groove M2 can be further improved.

[0084] In this embodiment, as in Fig. As shown in Figure 16(c), a compound groove MH4 may be provided on the functional element layer 22 side of the wafer 20. The compound groove MH4 is a W-groove formed by the first groove M1 and the second groove M2. The second groove M2 overlaps an end portion of the first groove M1 in the Y direction. The first groove M1 is a groove deeper than the second groove M2. The compound groove MH4 is provided such that the bottom of the first groove M1 reaches the semiconductor substrate 21, and the bottom of the second groove M2 does not reach the semiconductor substrate 21. That is, either the bottom of the first groove M1 or the bottom of the second groove M2 is provided such that it reaches the semiconductor substrate 21. The overlapping end portions of the first groove M1 and the second groove M2 (a peak portion on the bottom side of the compound groove MH4) reach the surface side of the functional element layer 22.The bottoms of the first groove M1 and the second groove M2 of the compound groove MH4 are separated from each other in the Y direction compared to the compound groove MH3 (see . Fig. 16b). Even with such a composite groove MH4, the same effect as with the composite groove MH is achieved. The effect of inducing the crack 9 by the first groove M1 and the second groove M2 can be further improved.

[0085] In this embodiment, as in Fig. As shown in Fig. 17(a), a compound groove MH5 may be provided on the functional element layer 22 side of the wafer 20. The compound groove MH5 is a W-groove formed by the first groove M1 and the second groove M2. The second groove M2 overlaps an end part of the first groove M1 in the Y direction. The first groove M1 and the second groove M2 are grooves having the same depth and width. The compound groove MH2 is provided such that the bottom of the first groove M1 and the bottom of the second groove M2 both do not reach the semiconductor substrate 21. Even with such a compound groove MH5, the same effect as with the compound groove MH is achieved. The depths of the first groove M1 and the second groove M2 can be reduced.

[0086] In this embodiment, as in Fig. As shown in Figure 17(b), a compound groove MH6 may be provided on the functional element layer 22 side of the wafer 20. The compound groove MH6 is a W-groove formed by the first groove M1 and the second groove M2. The second groove M2 overlaps an end portion of the first groove M1 in the Y direction. The first groove M1 and the second groove M2 are grooves having the same depth and width. The compound groove MH6 is provided such that the bottom of the first groove M1 and the bottom of the second groove M2 both do not reach the semiconductor substrate 21. The overlapping end portions of the first groove M1 and the second groove M2 (a peak portion on the bottom side of the compound 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 compound groove MH6 are separated from each other in the Y direction compared to the compound groove MH5 (see Fig. 17(a)). Even with such a composite groove MH6, the same effect as with the composite groove MH is achieved. The effect of inducing the crack 9 by the first groove M1 and the second groove M2 can be further improved.

[0087] Fig. Figure 18 is a table showing the test results for evaluating the deviation of the crack 9 during the formation of the compound groove MH. In the table, the digging depth corresponds to the position of the bottom of the compound groove MH, and the penetration depth into the semiconductor substrate 21 extends from the front surface 21a of the semiconductor substrate 21. The displacement amount corresponds to the deviation amount between the formed modified region 11 and the center of the compound groove MH in the width direction of the compound groove MH. "○" means that the end of the induced crack 9 reaches the inner surface of the first groove M1 or the inner surface of the second groove M2. "Deviation" means that the crack 9 deviates from the compound groove MH, and 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 the test shown in the table, the groove formation width is 12 μm. As shown in Fig. As shown in Figure 18, with the compound groove MH, even if the formed modified portion 11 deviates from the compound groove MH in the width direction, the effect of inducing the crack 9 can be obtained as long as the deviation amount falls within a predetermined range. Furthermore, it is clear that with a greater digging depth, a more effective effect of inducing the crack 9 can be achieved in terms of the displacement amount.

[0088] In the groove formation processing of this embodiment, the first groove M1 and the second groove M2 are formed simultaneously by the first branched laser light LA ​​and the second branched laser light LB formed by branching the laser light L with the branching pattern displayed on the display unit 132A of the spatial light modulator 132. However, the present invention is not limited to this. The groove formation processing may include a step of forming the first groove M1 in the wafer 20 along the line 15 by irradiating the wafer 20 with the laser light L, and a step of forming the second groove M2 in the wafer 20 along the line 15 by irradiating the wafer 20 with the laser light L.

[0089] For example, as in Fig. As shown in Figure 19(a), the surface layer of the wafer 20 on the side of the functional element layer 22 is removed by condensing the laser light L onto the functional element layer 22 by the condensation unit 34, thereby forming the first groove M1. Thereafter, as shown in Fig. 19(b), the surface layer of the wafer 20 on the side of the functional element layer 22 can be removed by the condensation unit 34 and / or the holding unit 2 (see Fig. 2) is moved by a predetermined amount in the Y direction (width direction of the first groove M1) and the laser light L is condensed by the condensing unit 34 onto the functional element layer 22 to thereby form the second groove M2.

[0090] In addition, for example, as in Fig. 20(a), the surface layer of the wafer 20 on the side of the functional element layer 22 is removed by condensing the laser light L onto the functional element layer 22 by the condensing unit 34, thereby forming the first groove M1. Thereafter, the surface layer of the wafer 20 on the side of the functional element layer 22 can be removed by displaying a shift pattern on the display unit 132A of the spatial light modulator 132 for shifting the focusing point of the laser light L by a predetermined amount in the Y direction (width direction of the first groove M1) and condensing the laser light L onto the functional element layer 22 by the condensing unit 34 as shown in Fig. 20(b) to thereby form the second groove M2.

[0091] In this embodiment, the step of forming the modified portion 11 may include a step of correcting the formation position of the modified portion 11 to correspond to the center position when the deviation amount (hereinafter referred to as "width direction deviation amount") of the formation position of the modified portion 11 from the center position of the composite groove MH in the width direction of the composite groove MH is greater than half the value of the groove width. For example, the following in Fig. 21 steps shown.

[0092] In the step of forming the modified region 11, first, in the Y direction corresponding to the width direction of the compound groove MH, the formation position of the modified region 11 (the position at which the modified region 11 is to be formed) is ensured to correspond to the center position of the compound groove MH, which is a reference processing position (step S11). The center position of the compound groove MH can be checked, for example, based on an image captured by the infrared image pickup unit 108B (see Fig. 1). Subsequently, the modified region 11 is formed along the line 15 as described above (step S12).

[0093] When the formation of the modified region 11 along the entire line 15 in the X direction is completed (YES in step S13), it is determined that the laser processing has been completed and the processing is ended, and then the process proceeds to the next step. On the other hand, when the formation of the modified region 11 along the entire line 15 in the X direction is not completed (NO in step S13), the formation position of the modified region 11 is moved by a predetermined distance (a distance corresponding to the distance between the two adjacent lines 15) in the Y direction, and the laser processing head H and / or the holding unit 102 (see Fig. 1) is moved in the Y direction (step S14).

[0094] It is determined whether the deviation amount in the width direction of the modified region 11 is greater than half the value (1 / 2 value) of the groove formation width (step S15). The deviation amount in the width direction of the modified region 11 can be checked, for example, based on an image captured by the infrared image pickup unit 108B (see Fig. 1). If YES in step S15, the formation position of the modified area 11 in the Y direction is corrected (step S16). In step S16, the position of the laser processing head H and / or the holding unit 102 (see Fig. 1) in the Y direction so that the formation position of the modified region 11 corresponds to the center position of the compound groove MH in the Y direction. If NO in step S15 or step S16, the process returns to the processing of step S12. In the laser processing method according to the modification example described above, the formation position of the modified region 11 can be corrected using the groove formation width. Modification examples

[0095] One aspect of the present invention is not limited to the embodiment described above.

[0096] In the above-described embodiment, the laser processing device 1 for performing groove formation processing and the laser processing device 100 for forming the modified region 11 in the wafer 20 are separate devices, but the present invention is not limited thereto. For example, a device for groove formation processing and a device for forming the modified region 11 may be integrated by connecting them to each other by a transfer arm. For example, in a Fig. In the laser processing apparatus 200 shown in FIG. 22, a stage 202 can be used jointly for mounting an optical system 210A corresponding to a processing apparatus for grooving processing and an optical system 210B corresponding to a processing apparatus for forming the modified region 11. Furthermore, such a laser processing apparatus 200 includes a moving mechanism 205 for moving the stage (holding unit) 202 and a moving mechanism 206 for moving the optical systems 210A and 210B.

[0097] The laser processing method using the laser processing device 100 and the laser processing device 1 is not limited to the method described above and may be, for example, the following method. First, as shown in Fig. 23(a), the wafer 20 is prepared. The protective film 29 is applied to the surface of the wafer 20 on the side of the functional element layer 22. Subsequently, as shown in Fig. 23(b), in the laser processing apparatus 1, the wafer 20 is adsorbed and held by the holding unit 2, and then the groove formation processing is performed on the wafer 20. In the groove formation processing, the control unit 5 controls the irradiation unit 3 such that the street 23 of the wafer 20 is irradiated with the laser light L along the line 15, and the control unit 5 controls the holding unit 2 such 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 to form the compound groove MH.

[0098] Then, as in Fig. As shown in Fig. 23(c), the wafer 20 is removed from the holding unit 2 and the protective film 29 is removed using, for example, a chemical solution. As shown in Fig. As shown in Figure 24(a), the abrasive tape 28 is attached to the surface of the wafer 20 on the side of the functional element layer 22. In the laser processing apparatus 100, the modified region 11 is formed in the wafer 20 along the line 15 by irradiating the wafer 20 with the laser light L0 along the line 15. With the wafer 20 adsorbed and held by the holding unit 102, a scan in which the wafer 20 is irradiated with the laser light L0 from the back surface 21b while aligning the focusing point of the laser light L0 in the semiconductor substrate 21 is repeatedly performed by changing the position of the focusing point in the Z direction. As a result, a plurality of rows of modified regions 11 are formed in the Z direction in the semiconductor substrate 21, and the cracks 9 extend from the modified regions 11.

[0099] Then, as in Fig. 24(b), the back surface 21b side of the semiconductor substrate 21 of the wafer 20 is ground using a grinder to thin the wafer 20 to a desired thickness where the modified region 11 has been removed. As shown in Fig. As shown in Fig. 24(c), the transparent dicing tape DC is attached to the ring frame RF on the back surface 21b of the semiconductor substrate 21 of the wafer 20. Then, as shown in Fig.25, by stretching the attached transparent dicing tape DC by means of a stretching device (not shown), the crack 9 is expanded in the thickness direction of the wafer 20 along each line 15, thereby cutting the wafer 20 along the line 15. In this way, the wafer 20 is divided into chips corresponding to the respective functional elements 22a, and a plurality of chips T1 are obtained. In the laser processing method according to such a modification example, the wafer 20 can be made thin by grinding it after forming the compound groove MH.

[0100] In the above-described embodiment and modification example, the imaging unit 4 may include a camera for obtaining image data of the street of the wafer 20 using visible light. In the above-described embodiment and modification example, information for controlling the irradiation conditions (laser on / off control, laser power) of the laser light L in each area of ​​the street 23 may be generated using an image of at least the surface layer of the street 23 after cutting and a perspective image using infrared rays, and groove formation processing may be controlled based on this information. In the above-described embodiment and modification example, the surface layer of the street 23 may be removed by scanning the street 23 with the laser light L a plurality of times.In the above-described embodiment and the above-described modification example, only the holding unit 102 may be controlled such that the laser light L0 moves relatively along each line 15, or only the laser processing head H may be controlled such that the laser light L0 moves relatively along each line 15, or both the holding unit 102 and the laser processing head H may be controlled such that the laser light L0 moves relatively along each line 15.In the above-described embodiment and the above-described modification example, only the control unit 2 may be controlled such that the laser light L moves relatively along each road 23, or only the irradiation unit 3 may be controlled such that the laser light L moves relatively along each road 23, or both the holding unit 2 and the irradiation unit 3 may be controlled such that the laser light L moves relatively along each road 23.

[0101] In the above-described embodiment and modification example, the energy at each focusing point of a plurality of branched laser light components obtained by branching the laser light L may be the same, or may be made stronger or weaker by changing the branching ratio. In the above-described embodiment and modification example, the positions of the focusing points SA1, SA2, and SA3 of the first branched laser light components in the Y direction are the same, but at least one of the positions of the focusing points SA1, SA2, and SA3 of the first branched laser light components in the Y direction may be shifted in the Y direction within a range smaller than the distance Y1.The positions of the focusing points SB1, SB2, and SB3 of the second branched laser light components in the Y direction are the same, but at least one of the positions of the focusing points SB1, SB2, and SB3 of the second branched laser light components in the Y direction can be shifted in the Y direction within a range smaller than the distance Y1. The positions of the focusing points SC1 and SC2 of the third branched laser light components in the Y direction are the same, but at least one of the positions of the focusing points SC1 and SC2 of the third branched laser light components in the Y direction can be shifted in the Y direction within a range smaller than the distance Y1 or the distance Y2. The distance Y1 can be the same as or different from the distance Y2.

[0102] In the above-described embodiment and modification example, the bottom of the first groove M1 and the bottom of the second groove M2 may be arranged on the front surface 21a of the semiconductor substrate 21. In the above-described embodiment and modification example, no particular restrictions are imposed on the number of branches into which the laser light L is branched by the branching pattern, and there may be a plurality of them. In the above-described embodiment and modification example, 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 step after the modified region 11 is formed.In the above-described embodiment and the above-described modification example, “the end of the crack 9 reaches the inner surface of the first groove M1 or the inner surface of the second groove M2,” for example, also includes a case where 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 as long as the processing is performed to process the wafer 20 into chips in a subsequent step. List of reference symbols

[0103] 1: Laser processing device; 2: Holding unit; 9: Crack; 11: Modified area; 15: Line; 20: Wafer (object); 21: Semiconductor substrate (substrate); 22: Functional element layer; 29: Protective film; 31: Laser light source; 34: Condensation unit; 100: Laser processing device; 132: Spatial light modulator; 132A: Display unit; 200: Laser processing device; 202: Stage (holding unit); d12: Distance; d23: Distance; d34: Distance; d45: Distance; d56: Distance; DC: Transparent dicing tape; L: Laser light; L0: Laser light; LA: First branched laser light; LB: Second branched laser light; M1: First groove (groove), M2: Second groove (groove); M3: Third groove (groove); MH, MH1, MH2, MH3, MH4, MH5, MH6: compound groove; SA1, SA2, SA3: focusing point of the first branched laser light; SB1, SB2, SB3: focusing point of the second branched laser light; SC1, SC2: focusing point of the third branched laser light; Y1, Y2: distance.

Claims

[1] Laser processing method comprising: a step of forming a first groove in an object along a line by irradiating the object with laser light, a step of forming a second groove in the object along the line by irradiating the object with laser light, the second groove overlapping an end part of the first groove in the width direction of the first groove, and a step of forming a modified region in the object along the line by irradiating the object with laser light and expanding a crack from the modified region after forming a composite groove including the first groove and the second groove in the object. [2] The laser processing method according to claim 1, further comprising: a step of cutting the object along the line by stretching a tape attached to the object, wherein an end of the tear reaches an inner surface of the first groove or an inner surface of the second groove, after forming the modified portion. [3] Laser processing method according to claim 1 or 2, wherein the object comprises a substrate and a functional element layer on the substrate, and the composite groove is provided on the functional element layer side of the object such that a bottom of the first groove and a bottom of the second groove both reach the substrate. [4] Laser processing method according to claim 1 or 2, wherein the object comprises a substrate and a functional element layer on the substrate, and the composite groove is provided on the functional element layer side of the object such that a bottom of the first groove and a bottom of the second groove both do not reach the substrate. [5] Laser processing apparatus according to claim 1 or 2, wherein the object comprises a substrate and a functional element layer on the substrate, and the composite groove is provided in the functional element layer of the object such that either a bottom of the first groove or a bottom of the second groove reaches the substrate. [6] The laser processing apparatus according to any one of claims 3 to 5, wherein, before forming the composite groove, a step of forming a protective film on the functional element layer is included. [7] The laser processing method according to any one of claims 1 to 6, wherein the compound groove has 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, wherein, before forming the compound groove, a step of grinding the object to make the object thin is included. [9] The laser processing method according to any one of claims 1 to 7, wherein after forming the modified region, a step of grinding the object to make the object thin is included. [10] Laser processing method according to one of claims 1 to 9, where a plurality of lines are placed on the object, and the step of forming the modified region comprises a step of correcting a formation position of the modified region to correspond to a center position of the compound groove when a deviation amount of the formation position of the modified region from the center position of the compound groove in the width direction of the compound groove is greater than a half value of a groove formation width of the compound groove.

Images