Method for manufacturing a chip

Abstract

Provided is a method for manufacturing a chip that can suppress a decrease in quality of the chip. The method for manufacturing a chip that is divided into a plurality of chips along a division predetermined line includes: a wafer holding step of holding a wafer on a first surface side by a chuck table to expose a second surface side of the wafer; a modification layer forming step of forming a modification layer including a plurality of modification regions arranged along the division predetermined line by irradiating a laser beam that has a transmissivity with respect to the wafer and is condensed at a first condensing point and a second condensing point from the second surface side of the wafer in such a manner that the first condensing point and the second condensing point are positioned inside the wafer, and forming modification regions in regions where the first condensing point and the second condensing point are positioned, respectively; and a division step of dividing the wafer into the plurality of chips along the division predetermined line by applying an external force to the wafer.

Description

TECHNICAL FIELD

[0001] The present application relates to a manufacturing method of a chip, which divides a wafer into a plurality of chips. BACKGROUND

[0002] In a manufacturing process of a device chip, a wafer in which devices such as ICs (Integrated Circuits) are respectively formed in a plurality of regions divided by a plurality of division- scheduled lines (streets) crossing each other is used. By dividing the wafer along the division-scheduled lines, a plurality of device chips each having a device are manufactured.

[0003] In the division of the wafer, a cutting device is mainly used, which has a chuck table that holds the wafer and a spindle (rotary shaft) that is installed with a ring-shaped cutting tool that cuts the wafer. By rotating the cutting tool and cutting into the wafer held by the chuck table, the wafer is cut along the division-scheduled lines and is divided.

[0004] On the other hand, in recent years, a technique of dividing the wafer by laser processing has also been attracting attention. For example, a method is proposed in which a laser beam that is transparent to the wafer is condensed inside the wafer, and a modified layer (modified layer (altered layer)) is formed inside the wafer along the division-scheduled lines (see Patent Document 1). The region of the wafer in which the modified layer is formed becomes brittle compared to other regions. Therefore, when an external force is applied to the wafer in which the modified layer is formed, the wafer is divided from the modified layer as a starting point.

[0005] However, depending on the thickness, material, and the like of the wafer, even if only one modified layer is formed on the wafer and an external force is applied, the wafer can not be properly divided from the modified layer as a starting point. In this case, a plurality of modified layers are formed along each division-scheduled line in the thickness direction of the wafer (see Patent Document 2). For example, a plurality of times of laser beams are each irradiated along each division-scheduled line while the height of the condensing point of the laser beam is changed in stages, thereby forming a plurality of modified layers on the wafer.

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-179302

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2009-10105

[0008] In the formation process of the modified layer, a plurality of modified regions are formed inside the wafer at a prescribed interval along the division-scheduled lines, for example, by irradiating a laser beam. In this case, the modified layer corresponds to a layer that includes a plurality of modified regions arranged along the division-scheduled lines.

[0009] When the modified region is formed, a crack (cleavage plane) is generated in the modified region. Also, when the crack developing from the modified region reaches a region in which the modified region is to be formed next, upon irradiation of the laser beam to the region thereafter, diffuse reflection of the laser beam occurs due to the crack.

[0010] When the diffuse reflection of the laser beam occurs in the inside of the wafer, it is difficult to properly form the modified region in the region irradiated with the laser beam, and the modified layer sometimes cannot sufficiently function as a starting point of division of the wafer. Also, due to the diffuse reflection of the laser beam, the crack generated in the modified region easily develops radially in an unintended direction, or a longer crack is easily formed contrary to the expectation. Due to this irregular crack, it is possible that the breakage of the wafer is directed in an undesirable direction when the wafer is divided in a later process.

[0011] As described above, if the diffuse reflection of the laser beam occurs when the modified region is formed, the wafer is difficult to be properly divided along the division predetermined line when an external force is applied to the wafer. As a result, it is possible that the chip is broken or a concave-convex is formed on the side surface (division surface) of the chip at the time of division of the wafer, and the quality of the chip is reduced. SUMMARY

[0012] The present application has been achieved in view of the above-described problems, and an object thereof is to provide a method of manufacturing a chip capable of suppressing reduction in quality of the chip.

[0013] According to one embodiment of the present application, there is provided a method of manufacturing a chip by dividing a wafer along a division predetermined line into a plurality of chips, wherein the method of manufacturing a chip includes: a wafer holding step of holding a first surface side of the wafer with a chuck table to expose a second surface side of the wafer; a modified layer forming step of forming a modified region in a region in which a first focal point and a second focal point are positioned by irradiating a laser beam having transmissivity with respect to the wafer and condensed at the first focal point and the second focal point from the second surface side of the wafer so that the first focal point and the second focal point are positioned inside the wafer, and forming a modified layer including a plurality of the modified regions arranged along the division predetermined line; and a division step of applying an external force to the wafer to divide the wafer along the division predetermined line into a plurality of the chips, wherein, in the modified layer forming step, a crack generated in the modified region formed in the region in which the first focal point is positioned is connected to a crack generated in the modified region formed in the region in which the second focal point is positioned.

[0014] Further, it is preferable that the modification layer forming process has a first modification layer forming process of forming a first modification layer including a plurality of the modification regions arranged along the division predetermined line by irradiating the laser beam from the second surface side of the wafer, and a second modification layer forming process of forming a second modification layer including a plurality of the modification regions arranged along the division predetermined line at a position closer to the first surface side of the wafer than the first modification layer by irradiating the laser beam from the second surface side of the wafer.

[0015] Further, according to another aspect of the present application, there is provided a method of manufacturing a chip by dividing a wafer along a division predetermined line into a plurality of chips, wherein the method of manufacturing a chip has a wafer holding process of holding a first surface side of the wafer with a chuck table to expose a second surface side of the wafer, a modification layer forming process of forming a first modification layer including a plurality of modification regions arranged along the division predetermined line by irradiating a laser beam having transmittance with respect to the wafer and condensed at a first focal point, a second focal point, a third focal point, and a fourth focal point from the second surface side of the wafer in such a manner that the first focal point and the second focal point are positioned in a first region inside the wafer and the third focal point and the fourth focal point are positioned in a second region at a position closer to the first surface side of the wafer than the first region, and forming the modification regions in the regions where the first to fourth focal points are positioned, respectively, and forming the first and second modification layers including a plurality of the modification regions arranged along the division predetermined line, and a division process of dividing the wafer into a plurality of the chips along the division predetermined line by applying an external force to the wafer, and in the modification layer forming process, a crack generated in the modification region formed in the region where the first focal point is positioned is connected to a crack generated in the modification region formed in the region where the second focal point is positioned, and a crack generated in the modification region formed in the region where the third focal point is positioned is connected to a crack generated in the modification region formed in the region where the fourth focal point is positioned.

[0016] In the method of manufacturing a chip of one embodiment of the present application, the modification regions are formed in the regions where the focal points are positioned by irradiating the laser beam condensed at a plurality of focal points with respect to the wafer, and a crack generated in one modification region is connected to a crack generated in another modification region.

[0017] According to the method of manufacturing a chip described above, the focal points of the laser beam can be positioned in the regions inside the wafer where no cracks are formed to form the modification regions, and a crack connecting adjacent modification regions can be formed. Thus, the modification layer is formed appropriately with suppression of diffuse reflection of the laser beam. As a result, the wafer is easily divided along the division predetermined line, and thus the quality of the chips is less likely to be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1(A) is a perspective view showing a wafer, Figure 1 (B) is a perspective view showing a wafer to which a protective member is attached.

[0019] Figure 2 (A) is a partial cross-sectional front view showing a laser processing apparatus.

[0020] Figure 3 (B) is a schematic view showing a structure example of a laser irradiation unit.

[0021] Figure 4 (A) is a cross-sectional view showing a part of a wafer to which a laser beam is irradiated, Figure 4 (B) is a cross-sectional view showing a modified region.

[0022] Figure 5 (A) is a cross-sectional view showing a part of a wafer in which a second layer of a modified layer is formed, Figure 5 (B) is a cross-sectional view showing a part of a wafer in which a plurality of modified layers are formed.

[0023] Figure 6 (A) is a perspective view showing a wafer to which an expansion tape is attached.

[0024] Figure 7 (B) is a perspective view showing an expansion apparatus.

[0025] Figure 8 (A) is a cross-sectional view showing an expansion apparatus that holds a wafer, Figure 8 (B) is a cross-sectional view showing an expansion apparatus that expands an expansion tape.

[0026] Figure 9 (A) is a partial cross-sectional front view showing a laser processing apparatus having a laser irradiation unit that irradiates a laser beam condensed at four focal points.

[0027] Figure 10 (B) is a cross-sectional view showing a part of a wafer to which a laser beam condensed at four focal points is irradiated.

[0028] Figure 11 (A) is an image view showing a side surface of a chip of a comparative example, Figure 11 (B) is an image view showing a side surface of a chip of an embodiment.

[0029] Explanation of Reference Signs

[0030] 11: wafer; 11a: front surface (first surface); 11b: back surface (second surface); 13: division- scheduled line (spacer); 15: device; 17: protective member; 19, 19a, 19b, 19c, 19d: modified region (altered region); 21, 21a, 21b: crack (crack); 23: modified layer (altered layer); 25: propagation band; 27: frame; 27a: opening; 29: chip (device chip); 31: chip; 33: modified layer (altered layer); 35: crack (crack); 37: division mark; 41: chip; 43: modified layer (altered layer); 2: laser processing apparatus; 4: chuck table (holding table); 4a: holding surface; 6: laser irradiation unit; 8: laser beam; 8a, 8b: condensing point (condensing position); 10: laser oscillator; 12: mirror; 14: laser branching portion; 16: condensing lens; 22: propagation device (division device); 24: roller; 26: frame holding unit; 28: support table; 30: jig; 32: rod; 34: air cylinder; 36: base; 40: laser irradiation unit; 42: laser beam; 42a, 42b, 42c, 42d: condensing point (condensing position). DETAILED DESCRIPTION

[0031] Hereinafter, an embodiment of one mode of the present application will be described with reference to the drawings. First, a structure example of a wafer which can be used for a manufacturing method of a chip of the present embodiment will be described. Figure 1 (A) of FIG. 1 is a perspective view showing a wafer 11.

[0032] The wafer 11 is formed in a disc shape using a material such as silicon, for example, and has a front surface (first surface) 11a and a back surface (second surface) 11b which are substantially parallel to each other. The wafer 11 is divided into a plurality of rectangular regions by a plurality of division-scheduled lines (spacers) 13 which are arranged in a lattice shape in a manner of intersecting each other.

[0033] A device 15 such as an IC (Integrated Circuit), an LSI (Large Scale Integration), a MEMS (Micro Electro Mechanical Systems), or the like is formed on the front surface 11a side of each of the plurality of regions divided by the division-scheduled lines 13. When the wafer 11 is divided along the division-scheduled lines 13, a plurality of chips (device chips) each having the device 15 are obtained.

[0034] Further, the material, shape, configuration, size, and the like of the wafer 11 are not limited. For example, the wafer 11 can be a substrate composed of a semiconductor other than silicon (GaAs, SiC, InP, GaN, or the like), sapphire, glass, ceramic, resin, metal, or the like. Further, the kind, number, shape, configuration, size, arrangement, and the like of the devices 15 are not limited, and the devices 15 can not be formed on the wafer 11.

[0035] On the wafer 11, a division starting point that functions as a starting point of division (a trigger of division) when the wafer 11 is divided in a later process is formed. For example, laser processing is performed on the wafer 11, and the inside of the wafer 11 is modified (altered) along a division predetermined line 13, whereby the division starting point is formed.

[0036] The region (modified region) of the wafer 11 in which the division starting point is formed becomes brittle compared to other regions of the wafer 11. Therefore, when an external force is applied to the wafer 11 in which the division starting point is formed, the wafer 11 breaks along the division predetermined line 13 with the division starting point as a starting point. Thus, a plurality of device chips each having the device 15 is obtained.

[0037] When the division starting point is formed on the wafer 11 by laser processing, for example, a laser beam is irradiated from the back surface 11b side of the wafer 11. In this case, a protective member 17 is attached to the front surface 11a side of the wafer 11. Figure 1 (B) is a perspective view showing the wafer 11 to which the protective member 17 is attached.

[0038] As the protective member 17, a sheet (tape) having a thin film-shaped base material formed in a circular shape and an adhesive layer (paste layer) provided on the base material can be used. For example, the base material is formed of a resin such as polyolefin, polyvinyl chloride, polyethylene terephthalate, and the like, and the adhesive layer is formed of an adhesive such as an epoxy-based, acrylic-based, or rubber-based adhesive or the like. Further, the adhesive layer can use a resin of an ultraviolet-curable type that is cured by irradiation of ultraviolet rays.

[0039] For example, the protective member 17 is formed in a circular shape substantially the same diameter as the wafer 11, and is attached to the front surface 11a side of the wafer 11 in a manner to cover the plurality of devices 15. The plurality of devices 15 is protected by the protective member 17.

[0040] In order to form the division starting point, a laser processing apparatus that processes the wafer 11 by irradiation of a laser beam is used. Figure 2 is a partial cross-sectional front view showing a laser processing apparatus 2. The laser processing apparatus 2 has a chuck table (holding table) 4 that holds the wafer 11, and a laser irradiation unit 6 that irradiates a laser beam 8.

[0041] A rotary drive source (not shown) such as a motor and a ball screw type moving mechanism (not shown) are connected to the chuck table 4. The rotary drive source rotates the chuck table 4 about a rotary shaft that is substantially parallel to the Z-axis direction (vertical direction, up-down direction). In addition, the moving mechanism moves the chuck table 4 in the X-axis direction (machining feed direction, first horizontal direction) and the Y-axis direction (index feed direction, second horizontal direction).

[0042] The upper surface of the chuck table 4 constitutes a holding surface 4a that holds the wafer 11. The holding surface 4a is a flat surface that is substantially parallel to the X-axis direction and the Y-axis direction. For example, the holding surface 4a is formed in a circular shape in correspondence with the shape of the wafer 11. However, the shape of the holding surface 4a can be appropriately changed depending on the shape of the wafer 11 or the like. The holding surface 4a is connected to a suction source (not shown) such as an ejector via a flow path (not shown) formed in the inside of the chuck table 4 and a valve (not shown).

[0043] A laser irradiation unit 6 is provided above the chuck table 4. The laser irradiation unit 6 irradiates a laser beam 8 toward the wafer 11 held by the chuck table 4. The irradiation conditions of the laser beam 8 are set so as to form a region in which a modification by multi-photon absorption is induced (modified region (altered region)) in a region of the wafer 11 irradiated with the laser beam 8.

[0044] Specifically, the wavelength of the laser beam 8 is set so that the laser beam 8 exhibits transmissivity with respect to the wafer 11. Therefore, at least a part of the laser beam 8 that transmits through the wafer 11 (has transmissivity with respect to the wafer 11) is irradiated from the laser irradiation unit 6 toward the wafer 11. In addition, other irradiation conditions (output, pulse width, spot diameter, repetition frequency, etc.) of the laser beam 8 are also appropriately set in a manner so as to form a modified region on the wafer 11.

[0045] In addition, the laser irradiation unit 6 is configured so that the laser beam 8 is condensed at least at two or more condensing points (condensing positions). Figure 2 An example in which the laser beam 8 is condensed at two condensing points (condensing positions) 8a, 8b is shown.

[0046] Figure 3 is a schematic view showing an example of the configuration of the laser irradiation unit 6. The laser irradiation unit 6 has a laser oscillator 10 that pulses and oscillates a laser beam. As the laser oscillator 10, for example, a YAG laser, a YVO4 laser, a YLF laser, or the like is used. The laser beam 8 that is pulsed and oscillated from the laser oscillator 10 is reflected by a mirror 12 to be incident to a laser branching portion 14, and is branched into a plurality of (two in Figure 3 the example) beams by the laser branching portion 14. Then, the branched laser beams 8 are condensed at prescribed positions by a condensing lens 16.

[0047] The structure of the laser branching portion 14 is not limited as long as it is capable of branching the laser beam 8. For example, the laser branching portion 14 is configured by an LCOS-SLM (Liquid Crystal On Silicon-Spatial Light Modulator), a diffractive optical element (DOE), or the like.

[0048] Configurations Figure 2 The structural elements of the laser processing apparatus 2 (a rotation drive source and a moving mechanism coupled to the chuck table 4, the laser irradiation unit 6, and the like) are respectively connected to control sections (not shown) that control the operation of each of the structural elements of the laser processing apparatus 2. Through the control sections, the position of the chuck table 4, the irradiation conditions of the laser beam 8, and the like are controlled.

[0049] The control sections are configured by, for example, a computer, and include a processing section that performs various processes (computations and the like) required for the operation of the laser processing apparatus 2, and a storage section that stores various information (data, programs, and the like) used for the processes performed by the processing section. The processing section is configured to include, for example, a processor such as a CPU (Central Processing Unit). In addition, the storage section is configured by a memory such as a ROM (Read Only Memory) and a RAM (Random Access Memory).

[0050] When the wafer 11 is processed by the laser processing apparatus 2, first, the wafer 11 is held by the chuck table 4 (wafer holding step). Specifically, the wafer 11 is disposed on the chuck table 4 in a manner that the front surface 11a side (the protection member 17 side) faces the holding surface 4a and the back surface 11b side is exposed upward. In this state, when the negative pressure of the suction source is applied to the holding surface 4a, the front surface 11a side of the wafer 11 is held by the chuck table 4 by suction.

[0051] Next, the laser beam 8 is irradiated to the wafer 11, and a modification layer is formed in the wafer 11 (modification layer forming step). In the modification layer forming step, first, the chuck table 4 is rotated so that the length direction of one of the division predetermined lines 13 (refer to (A) of FIG. 1 and (B) of FIG. 2) coincides with the X-axis direction. In addition, the position of the chuck table 4 in the Y-axis direction is adjusted so that the focal points 8a and 8b of the laser beam 8 are disposed on the extension line of one of the division predetermined lines 13. Figure 1 Figure 1

[0052] ​​Then, while irradiating the laser beam 8 from the laser irradiation unit 6, the chuck stage 4 is moved along the X-axis (processing feed). As a result, the chuck stage 4, which holds the wafer 11, and the laser irradiation unit 6 move relative to each other along the X-axis, and the laser beam 8 scans along a predetermined dividing line 13. At this time, the focusing points 8a and 8b of the laser beam 8 are positioned along the direction of movement of the chuck stage 4 (…). Figure 2 The direction indicated by arrow A is adjacent to the direction parallel to it.

[0053] Figure 4 (A) is a cross-sectional view showing a portion of a wafer 11 irradiated by a laser beam 8. During the modification layer formation process, the focusing points 8a and 8b of the laser beam 8 are aligned along a predetermined dividing line 13 (see reference 1). Figure 1 (A) and Figure 1 The (B) side is positioned adjacent to the interior of the wafer 11. Moreover, when the laser beam 8 is irradiated from the back side 11b of the wafer 11, a modified region (deteriorated region) 19 is formed in the region of the wafer 11 irradiated by the laser beam 8. This modified region 19 is equivalent to a region that is modified and deteriorated by multiphoton absorption.

[0054] Additionally, when the modified region 19 is formed, cracks 21 are generated within the modified region 19 (see reference). Figure 4 (B)) and develops radially from the modified region 19. When the wafer 11 is diced in a subsequent process, the modified region 19 and the crack 21 function as the starting point for dicing.

[0055] Here, laser beam 8 is simultaneously irradiated into the regions located at the focusing points 8a and 8b of the wafer 11, thereby forming modified regions 19a and 19b. These modified regions 19a and 19b are spaced along a predetermined dividing line 13 (see reference 13) at intervals corresponding to the distance between the focusing points 8a and 8b. Figure 1 (A) and Figure 1 (B) is formed.

[0056] Figure 4 (B) is a cross-sectional view showing the modified regions 19a and 19b. Figure 4 (B) shows the modified regions 19a and 19b formed in the regions located at the focusing points 8a and 8b of the wafer 11, and the regions extending from the modified regions 19a and 19b toward the thickness direction of the wafer 11. Figure 4 (B) in the vertical direction) and the radial direction of wafer 11 ( Figure 4 Cracks (fissures) developing in the left and right directions of (B) 21a, 21b.

[0057] The distance between the focusing points 8a and 8b is set in such a way that the cracks 21a and 21b developing from the modified region 19a and 19b can be connected. Therefore, when the modified regions 19a and 19b are simultaneously formed by irradiating the laser beam 8, the cracks 21a and 21b connect, and the modified regions 19a and 19b are connected via the cracks 21a and 21b. As a result, slitting start points are continuously formed inside the wafer 11 along the predetermined slitting line 13. For example, the distance between the focusing points 8a and 8b is set to be 3 μm or more and 16 μm or less, preferably 4 μm or more and 8 μm or less.

[0058] Furthermore, when the laser beam 8, which is focused at the focal points 8a and 8b, scans along the predetermined dividing line 13, a pair of modified regions 19a and 19b are formed sequentially along the predetermined dividing line 13. As a result, a modified layer (modified layer) 23 containing a plurality of modified regions 19 arranged along the predetermined dividing line 13 is formed inside the wafer 11.

[0059] Furthermore, each modified region 19a and 19b is formed on the front side of the laser beam 8 scanning direction (in the moving direction of the chuck table 4) compared to the newly formed modified regions 19a and 19b. Figure 2 The location is on the rear side of arrow A). Therefore, the new modified region 19a or modified region 19b will not be repeatedly formed in the same location as other modified regions 19 already formed on wafer 11.

[0060] Here, when the laser beam 8 is simultaneously focused at focal points 8a and 8b, focal point 8b is positioned further away from other modified regions 19 already formed on the wafer 11 (especially the newly formed modified region 19b) compared to focal point 8a. Therefore, focal point 8b is easily positioned in areas where cracks 21 do not develop from other modified regions 19 already formed on the wafer 11. As a result, diffuse reflection of the laser beam 8 that may occur when focused in areas where cracks 21 exist is suppressed.

[0061] When diffuse reflection of the laser beam 8 inside the wafer 11 is suppressed, the modified region 19 is easily formed in the desired area, and the phenomenon of cracks 21 developing in an unexpected direction or forming longer cracks 21 contrary to expectations is less likely to occur. As a result, a modified layer 23 containing appropriately formed modified regions 19 and suppressing the formation of irregular cracks 21 is formed on the wafer 11.

[0062] Further, it is preferable that the modified region 19a be formed at a position at which a crack 21a developing from the modified region 19a is linked with a crack 21 developing from another modified region 19 (particularly, the modified region 19b just formed) already formed in the wafer 11. Thereby, it is possible to link two groups of modified regions 19a, 19b formed at different timings via the cracks 21, and thus it is possible to form a seamless division starting point inside the wafer 11.

[0063] Further, it is preferable that the focal point 8a of the laser beam 8 be positioned at a region in which there is no crack 21 developing from another modified region 19 already formed in the wafer 11. Thereby, it is possible to further suppress the diffuse reflection of the laser beam 8.

[0064] The interval of the regions irradiated with the laser beam 8 (corresponding to the interval of the modified regions 19a from each other and the interval of the modified regions 19b from each other) can be adjusted by controlling the moving speed (machining feed speed) of the chuck table 4 and the repetition frequency of the laser beam 8. For example, the interval of the regions irradiated with the laser beam 8 is set to 6 μm or more and 32 μm or less, and preferably 8 μm or more and 16 μm or less.

[0065] Further, after the modified layer 23 is formed along one division predetermined line 13, the same step is repeated to form the modified layer 23 along another division predetermined line 13. Thereby, the wafer 11 in which the modified layer 23 is formed in a lattice shape along all the division predetermined lines 13 is obtained.

[0066] The region of the wafer 11 in which the modified layer 23 is formed is brittle compared to other regions of the wafer 11. Therefore, when an external force is applied to the wafer 11 in which the modified layer 23 is formed, the wafer 11 is broken along the division predetermined line 13 with the modified layer 23 as a starting point.

[0067] Further, depending on the thickness, material, and the like of the wafer 11, it is preferable that a plurality of modified layers 23 be formed in the thickness direction of the wafer 11. For example, in the case where the wafer 11 is a silicon wafer having a thickness of 200 μm or more, by forming two or more modified layers 23, the wafer 11 is easily and appropriately divided. In the case where a plurality of modified layers 23 are formed, the modified layer 23 is further formed along the division predetermined line 13 in which the modified layer 23 has already been formed.

[0068] Figure 5 FIG. 1 is a cross-sectional view showing a part of a wafer 11 in which a plurality of modified layers 23 are formed. In the case where a plurality of modified layers 23 are formed in the wafer 11, first, one modified layer 23 (a first modified layer 23) is formed (a first modified layer forming step), and then, another modified layer 23 (a second modified layer 23) is formed in a region different from the first modified layer (a second modified layer forming step).

[0069] Here, crack 21 originating from modified region 19 is confirmed (refer to...). Figure 4 (B) tends to extend toward the direction of incident of the laser beam 8 (back side 11b). Therefore, when forming multiple modified layers 23 on the wafer 11, it is preferable to form the modified layers 23 sequentially from the back side 11b of the wafer 11 toward the front side 11a.

[0070] Specifically, in the second modified layer formation process, the focusing points 8a and 8b of the laser beam 8 are positioned closer to the front side 11a (lower surface side) of the wafer 11 than when the first modified layer 23 was formed. Then, through the same steps as when forming the first modified layer 23, the second modified layer 23 is formed at a position closer to the front side 11a of the wafer 11 than when the first modified layer 23 was formed.

[0071] In this case, the laser beam 8 used to form the second modified layer 23 is focused on the region (the front side 11a side of the wafer 11) where the crack 21 generated by the first modified layer 23 is less likely to develop. As a result, the laser beam 8 is less likely to be focused on the region where the crack 21 exists, thereby suppressing diffuse reflection of the laser beam 8.

[0072] Furthermore, as described above, the first modified layer 23 is formed under conditions where irregular cracks 21 are not easily generated. Therefore, when the second modified layer 23 is formed, even if the laser beam 8 irradiates the area where the second modified layer 23 is formed via the first modified layer 23, unexpected reflections of the laser beam 8 are not easily generated in the first modified layer 23. As a result, the second modified layer 23 can be formed easily and appropriately.

[0073] Figure 5 (B) is a cross-sectional view showing a portion of a wafer 11 having multiple modified layers 23 formed thereon. Figure 5 As shown in (B), by forming multiple modification layers 23 in the wafer 11, the wafer 11 can be appropriately divided, for example, even when the wafer 11 is relatively thick. In addition, there is no limit to the number of modification layers 23 formed in the wafer 11, and they can be appropriately set according to the thickness, material, etc. of the wafer 11.

[0074] Next, an external force is applied to the wafer 11 to divide it into multiple chips along the predetermined dicing line 13 (dicing process). For example, the dicing process is performed by attaching the wafer 11 to an extension tape and expanding the extension tape. Figure 6 This is a perspective view showing a chip 11 with an extension strip 25 attached.

[0075] The expansion strip 25 is a strip that can be expanded by applying external force (a strip with expandability). For example, as the expansion strip 25, a sheet having a substrate formed in the shape of a circular film and an adhesive layer (paste layer) disposed on the substrate can be used. Examples of the materials of the substrate and adhesive layer are the same as those of the protective component 17 (see). Figure 1The same as the wafer 11 (B). However, the extension tape 25 is not limited in configuration and material as long as it is extensible and can be attached to the wafer 11.

[0076] For example, a circular extension tape 25 having a larger diameter than the wafer 11 is attached to the back surface 11b side of the wafer 11. In addition, the outer peripheral portion of the extension tape 25 is attached to a ring-shaped frame 27 made of metal or the like and having a circular opening 27a in the central portion. In addition, the diameter of the opening 27a is larger than the diameter of the wafer 11, and the wafer 11 is disposed inside the opening 27a. When the extension tape 25 is attached to the wafer 11 and the frame 27, the wafer 11 is supported by the frame 27 with the extension tape 25 interposed therebetween.

[0077] Then, the protective member 17 is peeled from the front surface 11a side of the wafer 11. Thereby, the front surface 11a side (device 15 side) of the wafer 11 is exposed. In this state, if the extension tape 25 is stretched toward the radial direction outside to extend the extension tape 25, an external force is applied to the wafer 11, and the wafer 11 is divided into a plurality of chips.

[0078] In the extension of the extension tape 25, for example, an extension device that extends the extension tape 25 is used. Figure 7 is a perspective view showing the extension device (dicing device) 22. The extension device 22 stretches the extension tape 25 to extend the extension tape 25, and dices the wafer 11 on which the modified layer 23 is formed.

[0079] The extension device 22 has a cylindrical roller 24 having a larger diameter than the wafer 11, and a frame holding unit 26 that holds the frame 27 that supports the wafer 11 (see Figure 6 see). The frame holding unit 26 has a ring-shaped support table 28 that supports the frame 27. The support table 28 is provided so as to surround the upper end portion of the roller 24, and is disposed so that the height of the upper surface of the support table 28 is substantially the same as the height of the upper end of the roller 24.

[0080] A plurality of jigs 30 are fixed to the outer peripheral portion of the support table 28. The plurality of jigs 30 are disposed substantially at equal intervals along the circumferential direction of the support table 28, and hold and fix the frame 27 disposed on the support table 28. By disposing the frame 27 on the support table 28 and fixing the frame 27 with the plurality of jigs 30, the frame 27 is held by the frame holding unit 26.

[0081] The support table 28 is supported by a plurality of rods 32 that are moved (raised and lowered) along the vertical direction (upward and downward direction), and a cylinder 34 that raises and lowers the rod 32 is connected to the lower end portion of each rod 32. In addition, the plurality of cylinders 34 are supported by a ring-shaped base 36. When the rod 32 is lowered by the cylinder 34, the support table 28 moves downward together with the frame 27.

[0082] In the dividing process, first, the cylinder 34 is operated to adjust the height of the support table 28 so that the height of the upper end of the roller 24 coincides with the height of the upper surface of the support table 28. Then, the frame 27 (see FIG. 1) supporting the state of the wafer 11 is placed on the support table 28. At this time, the wafer 11 is placed inside the outer periphery of the roller 24 in plan view. Then, the frame 27 placed on the support table 28 is fixed by the plurality of jigs 30. Figure 6 ) is placed on the support table 28. At this time, the wafer 11 is placed inside the outer periphery of the roller 24 in plan view. Then, the frame 27 placed on the support table 28 is fixed by the plurality of jigs 30.

[0083] Thus, the wafer 11 is held by the frame holding unit 26 via the expansion tape 25 and the frame 27. Figure 8 (A) is a cross-sectional view showing the expansion device 22 that holds the wafer 11. In addition, a modified layer 23 is formed in a lattice shape on the wafer 11 along the division predetermined line 13 (see (A) of FIG. 1). Figure 1

[0084] Next, the cylinder 34 is operated to pull down the support table 28, and the frame 27 is moved to the lower side. Thus, the expansion tape 25 supported by the upper end of the roller 24 is stretched to the outer side in the radial direction to expand. As a result, an external force toward the outer side in the radial direction of the wafer 11 is applied to the wafer 11.

[0085] Figure 8 (B) is a cross-sectional view showing the expansion device 22 that expands the expansion tape 25. When the wafer 11 is applied with the external force by the expansion of the expansion tape 25, the wafer 11 is broken along the modified layer 23 to be divided into a plurality of chips (device chips) 29. That is, the modified layer 23 functions as a division starting point. In this way, the wafer 11 is divided, and the chips 29 are manufactured. In addition, after the wafer 11 is divided, each chip 29 is picked up by a collet (not shown), for example, and mounted on a prescribed substrate (wiring substrate or the like).

[0086] As described above, in the chip manufacturing method of the present embodiment, the modified regions 19a, 19b are formed in the regions positioned by the focal points 8a, 8b of the laser beam 8, respectively, and the cracks 21a generated in the modified region 19a are connected to the cracks 21b generated in the modified region 19b.

[0087] According to the chip manufacturing method described above, it is possible to form the modified regions 19a, 19b by positioning the focal points 8a, 8b of the laser beam 8 in the regions inside the wafer 11 where the cracks 21 are not formed, and it is possible to form the cracks that connect the adjacent modified regions 19a, 19b. Thus, the diffuse reflection of the laser beam 8 is suppressed, and the modified layer 23 is appropriately formed. As a result, the wafer 11 is easily divided along the division predetermined line 13, and thus the quality reduction of the chips 29 is suppressed.

[0088] ​Further, in the above-described embodiment, an example in which the modified layer 23 is formed using the laser beam 8 that is condensed only at two condensing points 8a, 8b is described, but the number of condensing points of the laser beam for forming the modified layer 23 can be three or more. In this case, the modified regions 19 are formed at three or more places at the same time, and the cracks 21 that develop from the adjacent modified regions 19 are connected to each other.

[0089] Further, in a case where the laser beam is condensed at four or more condensing points, the laser beam can be irradiated to the wafer 11 in a state where two or more condensing points are positioned at different depth positions inside the wafer 11. In this case, two or more modified layers 23 can be formed in a simultaneous manner.

[0090] Figure 9 is a partial cross-sectional front view of the laser processing apparatus 2 that shows the laser irradiation unit 40 having the laser beam 42 that is irradiated so as to be condensed at four condensing points (condensing positions) 42a, 42b, 42c, 42d. As shown in Figure 9 , the laser irradiation unit 40 causes the laser beam 42 to be condensed at the condensing points 42a, 42b, 42c, 42d.

[0091] The laser irradiation unit 40 can be configured similarly to the laser irradiation unit 6 (refer to Figure 3 ). However, the laser branching portion 14 is configured to branch the laser beam oscillated from the laser oscillator 10 into four. For example, as the laser branching portion 14, an LCOS-SLM that branches the laser beam into four is used.

[0092] As shown in Figure 9 , the laser irradiation unit 40 irradiates the laser beam 42 in a state where the condensing points 42a, 42b and the condensing points 42c, 42d are positioned at different depth positions inside the wafer 11. Specifically, the condensing points 42a, 42b are positioned at a first region inside the wafer 11, and the condensing points 42c, 42d are positioned at a second region that is positioned at a position closer to the front surface 11a of the wafer 11 than the first region. Then, by irradiating the laser beam 42 to the wafer 11, two modified layers 23 are formed on the wafer 11 in a simultaneous manner.

[0093] Figure 10 is a cross-sectional view of a portion of the wafer 11 that is irradiated with the laser beam 42 that is condensed at the four condensing points 42a, 42b, 42c, 42d. For example, the condensing points 42a, 42b, 42c, 42d are positioned along the division predetermined line 13 (refer to Figure 1The light condensing points 42a, 42b are positioned at a prescribed interval. In addition, the light condensing points 42a, 42b are positioned in a region (first region) in which the modified layer 23 of the first layer is to be formed inside the wafer 11. Further, the light condensing points 42c, 42d are positioned in a region (second region) in which the modified layer 23 of the second layer is to be formed inside the wafer 11.

[0094] In this state, the laser beam 42 is irradiated toward the back surface 11b side of the wafer 11. Thereby, the modified regions (modified regions) 19a, 19b are formed simultaneously in the regions in which the light condensing points 42a, 42b are positioned, and the modified regions (modified regions) 19c, 19d are formed simultaneously in the regions in which the light condensing points 42c, 42d are positioned.

[0095] In addition, the interval of the light condensing points 42a, 42b is set in a manner that the cracks 21 generated from the modified region 19a and the cracks 21 generated from the modified region 19b can be connected. Likewise, the interval of the light condensing points 42c, 42d is set in a manner that the cracks 21 generated from the modified region 19c and the cracks 21 generated from the modified region 19d can be connected.

[0096] Therefore, when the modified regions 19a, 19b, 19c, 19d are formed, the cracks generated in the modified regions 19a, 19b are connected to each other, and the cracks generated in the modified regions 19c, 19d are connected to each other (refer to FIG. 6B). Figure 4 The distance between the light condensing points 42a, 42b and the distance between the light condensing points 42c, 42d are set to, for example, 3 μm or more and 16 μm or less, and preferably set to 4 μm or more and 8 μm or less, respectively.

[0097] As described above, by positioning the light condensing points 42a, 42b and the light condensing points 42c, 42d at different depth positions inside the wafer 11, it is possible to form the two layers of the modified layer 23 in a simultaneous manner. Thereby, in the case where a plurality of the modified layers 23 are formed on the wafer 11, it is possible to achieve simplification of the process and shortening of the processing time.

[0098] Next, the results of evaluating the chips manufactured by the chip manufacturing method of the present embodiment will be described. In the present evaluation, chips obtained by a conventional chip manufacturing method (comparative example) and chips obtained by the chip manufacturing method of the present embodiment (example) were compared.

[0099] In the comparative example, a modified layer was formed by irradiating a laser beam (nanosecond pulse laser) condensed at one point from the back surface side (upper surface side) of a silicon wafer (diameter: 200 mm, thickness: 300 μm). Then, by applying an external force to the silicon wafer (refer to FIG. 1A and FIG. 1B), cracks were generated in the modified layer. Figure 8 of (A) and Figure 8The silicon wafer was divided by (A) and (B) of FIG. 1, and the chip of the comparative example was manufactured.

[0100] In the manufacturing process of the chip of the comparative example, a modification layer including a plurality of modification regions was formed along each of the division predetermined lines by scanning the laser beam in a state where the focal point (1) of the laser beam was positioned inside the silicon wafer. Then, the same process was repeated, and a silicon wafer on which three modification layers were formed was obtained.

[0101] Further, the irradiation conditions of the laser beam in the comparative example were set as follows.

[0102] Laser oscillator: LD-excited Q-switched Nd:YVO4 laser

[0103] Wavelength: 1342 nm

[0104] Output: 1.2 W

[0105] Repetition frequency: 90 kHz

[0106] Spot diameter: 3 μm

[0107] Processing feed rate: 340 mm / s

[0108] On the other hand, in the example, a modification layer was formed by irradiating a laser beam (nanosecond pulse laser) focused at a plurality of positions to the back surface side (upper surface side) of a silicon wafer (200 mm in diameter and 300 μm in thickness). Then, the silicon wafer was divided by (A) and (B) of FIG. 1, and the chip of the example was manufactured. Figure 8 Figure 8 In the manufacturing process of the chip of the example, a modification layer including a plurality of modification regions was formed along each of the division predetermined lines by scanning the laser beam in a state where the focal points (2) of the laser beam were positioned at the same depth inside the silicon wafer (refer to (A) and (B) of FIG. 1). Further, the interval of the two focal points positioned at the same depth inside the silicon wafer was set to 5 μm in consideration of the length of a crack developed from the modification region. Then, the same process was repeated, and a silicon wafer on which seven modification layers were formed was obtained.

[0109] In the manufacturing process of the chip of the example, a modification layer including a plurality of modification regions was formed along each of the division predetermined lines by scanning the laser beam in a state where the focal points (2) of the laser beam were positioned at the same depth inside the silicon wafer (refer to (A) and (B) of FIG. 1). Further, the interval of the two focal points positioned at the same depth inside the silicon wafer was set to 5 μm in consideration of the length of a crack developed from the modification region. Then, the same process was repeated, and a silicon wafer on which seven modification layers were formed was obtained. Figure 4

[0110] Further, the irradiation conditions of the laser beam in the example were set as follows.

[0111] Laser oscillator: LD-excited Q-switched Nd:YVO4 laser

[0112] Wavelength: 1342 nm

[0113] Output: 1.5 W (before branching)

[0114] ​​Repetition frequency: 60kHz

[0115] Spot diameter: 3μm

[0116] Machining feed rate: 600 mm / s

[0117] Next, observe the side surface (segmentation surface) of the chip in the comparative example and the chip in the embodiment. Figure 11 Image (A) is a side view of the comparative example chip 31. Figure 11 (B) is an image showing the side of the chip 41 of the embodiment.

[0118] On the side of the comparative example chip 31, a modified layer (remodeled layer) 33 and multiple long cracks (fissures) 35 irregularly developed from the modified layer 33 were observed. It was confirmed that the cracks 35 propagated a long distance particularly toward the back side (upper surface side, the side side irradiated by the laser beam) of the chip 31.

[0119] As described above, when a laser beam focused at one location is scanned during the manufacturing process of chip 31, diffuse reflection of the laser beam occurs inside the silicon wafer, making it difficult to properly form the remodeling layer 33. Furthermore, the silicon wafer without a properly formed remodeling layer is difficult to break along the remodeling layer, and excessive external force is easily applied to the silicon wafer during dicing. As a result, it is speculated that the remodeling layer 33 will form on the side of chip 31. Figure 11 As shown in (A), multiple cracks 35 reduce the quality of chip 31.

[0120] Furthermore, when forming the second and subsequent modified layers 33, the spacing between the modified layers 33 is set so that the focal point of the laser beam is not positioned on the cracks that develop from the already formed modified layers 33. Here, when the modified layers 33 are formed by irradiating a laser beam focused at one point, longer cracks are formed due to diffuse reflection of the laser beam; therefore, the spacing between the modified layers 33 is set to be wider. As a result, it is difficult for silicon wafers to break between the modified layers 33, and residues are more likely to remain on the side of the chip 31. Figure 11 The dividing line 37 is shown in (A).

[0121] On the other hand, in the chip 41 of the embodiment ( Figure 11 A modified layer (modified layer) 43 was observed on the side of (B). However, no irregularly developed long cracks were found around the modified layer 43, resulting in a high-quality chip 41. It is speculated that this is because a laser beam focused at multiple focal points was used in the formation of the modified layer 43, which suppressed diffuse reflection of the laser beam, appropriately formed the modified layer 43 in the desired area, and suppressed the generation of cracks.

[0122] In addition, when the cracks developing from the modified layer 43 are suppressed, the interval of the modified layer 43 can be made narrow. As a result, the silicon wafer is easily properly broken, and it is not easy for the chips 41 to remain Figure 11 a relatively thick division mark like the division mark 37 shown in (A).

[0123] As described above, it is confirmed that when the modified layer is formed on the silicon wafer by irradiating the laser beam condensed at a plurality of condensing points, the silicon wafer is easily properly divided and the quality reduction of the chips is suppressed.

[0124] In addition, the configuration, method, and the like of the above-described embodiments can be appropriately changed and implemented within a range not departing from the object of the present application.

Claims

1. A method of manufacturing a chip by dividing a wafer into a plurality of chips along a division predetermined line, characterized by comprising: a wafer holding step of holding a first surface side of the wafer with a chuck table to expose a second surface side of the wafer; a modification layer forming step of forming a modification layer including a plurality of modification regions arranged along the division predetermined line, by irradiating a laser beam having transmissivity to the wafer and converging at a first focal point and a second focal point from the second surface side of the wafer in such a manner that the first focal point and the second focal point are positioned inside the wafer, and forming the modification regions in regions where the first focal point and the second focal point are positioned, respectively; and a division step of dividing the wafer into the plurality of chips along the division predetermined line by applying an external force to the wafer, wherein the modification layer forming step includes: a first modification layer forming step of forming a first modification layer including a plurality of the modification regions arranged along the division predetermined line, by irradiating the laser beam from the second surface side of the wafer; and a second modification layer forming step of forming a second modification layer including a plurality of the modification regions arranged along the division predetermined line at a position closer to the first surface side of the wafer than the first modification layer, by irradiating the laser beam from the second surface side of the wafer after the first modification layer forming step, and wherein a crack generated in the modification region formed in the region where the first focal point is positioned is connected to a crack generated in the modification region formed in the region where the second focal point is positioned.

2. A method of manufacturing a chip by dividing a wafer into a plurality of chips along a division predetermined line, characterized by comprising: a wafer holding step of holding a first surface side of the wafer with a chuck table to expose a second surface side of the wafer; a modification layer forming step of forming a first modification layer and a second modification layer including a plurality of modification regions arranged along the division predetermined line, by irradiating a laser beam having transmissivity to the wafer and converging at a first focal point, a second focal point, a third focal point, and a fourth focal point from the second surface side of the wafer in such a manner that the first focal point and the second focal point are positioned in a first region inside the wafer and the third focal point and the fourth focal point are positioned in a second region at a position closer to the first surface side of the wafer than the first region, and forming the modification regions in regions where the first focal point to the fourth focal point are positioned, respectively; and a division step of dividing the wafer into the plurality of chips along the division predetermined line by applying an external force to the wafer, wherein the modification layer forming step includes: a first modification layer forming step of forming a first modification layer including a plurality of the modification regions arranged along the division predetermined line, by irradiating the laser beam from the second surface side of the wafer; and a second modification layer forming step of forming a second modification layer including a plurality of the modification regions arranged along the division predetermined line at a position closer to the first surface side of the wafer than the first modification layer, by irradiating the laser beam from the second surface side of the wafer after the first modification layer forming step, and wherein a crack generated in the modification region formed in the region where the first focal point is positioned is connected to a crack generated in the modification region formed in the region where the second focal point is positioned. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ a second modification layer forming step of forming a second modification layer including a plurality of the modification regions arranged along the division predetermined line at a position on the first surface side of the wafer by irradiating the laser beam from the second surface side of the wafer after the first modification layer forming step, in the modification layer forming step, the cracks generated in the modification regions formed in the region where the first focal point is positioned and the cracks generated in the modification regions formed in the region where the second focal point is positioned are linked, and the cracks generated in the modification regions formed in the region where the third focal point is positioned and the cracks generated in the modification regions formed in the region where the fourth focal point is positioned are linked.

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