JP2020025142A - Wafer processing device and wafer processing method for obtaining chip with high transverse intensity - Google Patents

Abstract

To provide a wafer processing device and a wafer processing method, capable of efficiently obtaining chips with stable quality.SOLUTION: A wafer processing device for obtaining a chip with high transverse intensity includes: modified area forming means for forming independent modified areas with fixed intervals at the inside of a wafer by focusing pulsed laser light at a deeper position from a rear face side of the wafer; grinding means for grinding and removing a laser transmission portion from the rear face of the wafer to a focus point while leaving fine cracks extending down from the focus point of the pulsed laser light; and polishing means for removing processing distortion due to the grinding while leaving the fine cracks, after the grinding.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for cleaving a wafer in which a modified region is formed with a laser beam.

  Patent Document 1 discloses that a semiconductor substrate placed with its back surface facing upward is irradiated with a laser to form a modified region inside the substrate, an expand tape is attached to the back surface of the semiconductor substrate, and a knife is placed from above the expand tape. It describes that the semiconductor substrate is cut into chips by applying an edge to the substrate and dividing the substrate with the modified region as a base point.

  Further, in Patent Document 1, a semiconductor substrate placed with its back surface facing upward is irradiated with a laser to form a modified region inside the substrate, and then the substrate is ground and thinned, and an expanded surface is formed on the back surface of the semiconductor substrate. It describes that a substrate is cracked with a modified area as a base point by mounting a tape and expanding an expand tape.

  Patent Literature 2 discloses that a semiconductor substrate placed with its back surface facing upward is irradiated with a laser to form a modified region inside the substrate, thereby causing cracks in the thickness direction of the semiconductor substrate and causing the back surface of the substrate to It describes that a semiconductor substrate is cut into chips by exposing cracks on the back surface by grinding and chemical etching. Patent Document 2 discloses that a crack is generated in the thickness direction from the modified region by generating a thermal stress by applying a natural or relatively small force, for example, an artificial force or a temperature difference to the substrate. It is stated that it occurs.

Japanese Patent No. 3624909 Japanese Patent No. 3762409

  In the invention described in Patent Literature 1, the substrate is cracked by applying an external force locally by a knife edge, but a bending stress or a shear stress is applied to the substrate to apply the external force locally. However, it is difficult to distribute bending stress and shear stress uniformly over the entire surface of the substrate. For example, when a bending stress or a shear stress is applied to a substrate, the stress concentrates on a weak point, and it is impossible to efficiently and uniformly apply a minimum necessary stress to a desired portion.

  Therefore, there is a problem that the cracks in the substrate vary, and if the cracks do not progress slowly, the substrate is broken even in the chip. In addition, when a portion to be cut into a substrate is cut by applying stress locally in order, for example, when collecting a large number of chips from a single substrate, there are many cut lines. However, there is a problem that productivity is extremely reduced.

  Further, when the substrate is cracked by applying an external force, if the substrate is not thinned, a very large stress is required when the wafer is cracked.

  In particular, when the substrate thickness is sufficiently large with respect to the modified depth width of the laser processing, even if an external force is applied, it is not always possible to cut the substrate perpendicularly to the substrate due to the sudden external force. Therefore, it may be necessary to irradiate several laser pulses in the thickness direction of the substrate in multiple stages.

  In the inventions described in Patent Literatures 1 and 2, the modified region formed inside the substrate by the laser irradiation ultimately remains on the chip cross section. Therefore, there is a case where dust is generated from a portion of the modified region of the chip cross section. In addition, as a result of local crushing of the chip cross section, the crushed cross section may trigger the chip to break. As a result, there is a problem that the bending strength of the chip is reduced.

  In the invention described in Patent Document 2, it is described that cracks naturally occur in the thickness direction from the modified region. On the other hand, when the cracks occur naturally, there are cases where the cracks do not necessarily occur naturally. In order to inevitably obtain the stable effect of breaking, it is sometimes necessary to take arbitrary measures, and if it breaks naturally, it is not an arbitrary means.

  It is also conceivable to generate a thermal stress by giving a temperature difference as a relatively small force to generate a crack in the thickness direction from the modified region. In this case, there is a problem that it is very difficult to provide a uniform thermal gradient in the plane of the substrate. That is, even if a thermal gradient is artificially applied, heat is dispersed in the substrate by heat conduction so as to partially reduce the thermal gradient. Therefore, there is an extremely difficult problem in how to constantly generate a stable thermal gradient (stable temperature difference) enough to cut a certain substrate.

  Further, in the invention described in Patent Document 2, after the semiconductor substrate is ground, the back surface is subjected to chemical etching. However, after the grinding, a grinding streak due to fixed abrasive grains remains on the ground surface, and accompanying minute cracks. Are formed, and the damaged layer remains. When the surface is chemically etched, a portion having a large lattice distortion such as a minute crack is selectively etched. Therefore, the minute cracks are rather promoted and become large cracks. For this reason, not only the cutting starting region but also a small crack formed by grinding and etching sometimes breaks, and there is a problem that stable cutting is difficult.

  Further, since the unevenness of the substrate surface is promoted by the etching, the substrate surface is not mirror-finished. For this reason, since the unevenness remains in the divided chip, it is sufficiently considered that the chip is broken from a portion having a large unevenness, that is, a minute crack, and there is a problem that the bending strength of the chip decreases.

  In addition, when the etching liquid acts on the laser-processed and modified portions, the modified portions are once melted, recrystallized, and solidified, so that large grain boundaries are formed.

  When an etching solution acts on such a grain boundary, the etching proceeds so that silicon grains are peeled off from the grain boundary, so that the etching is performed so as to further promote unevenness.

  Specifically, in the cited document, line p. 12_1, the polishing step describes that the grinding step and the backside are subjected to chemical etching. In the case of chemical etching, even if left as it is, the chemical etching solution permeates into the crack and has an effect of melting the crack portion.

  In particular, when the crack runs ahead on the surface of the substrate, a problem occurs in that the etchant penetrates between the chips and the film adhering the chips, and peels the chips from the film.

  Further, even if the crack does not run on the surface of the substrate, the etching proceeds along the crack. In particular, when performing etching in a thinned state after grinding, the etchant penetrates into the cracks by capillary action, dissolving the crack tip, further deepening the microcracks, and further entering a new etchant there. Become. In this case, if an etchant acts on the vicinity of the device surface, it may melt the vicinity of the device surface, and the etching may progress to the inside of the element. Further, even if there is no problem at that time, the etching solution left on the wall surface of the wafer may enter the inside of the device and cause a defect thereafter. Therefore, while removing the processing strain on the wafer surface, cracks may be further promoted, which may cause secondary problems.

  Further, in such a case, as a result, the crack may precede on the surface, and an etching solution may partially enter between the chip and the film, causing a problem that the chip may be peeled off during processing. In particular, when the substrate becomes thin after grinding, cracks are likely to progress with a small amount of external force, and chip peeling occurs when the crack reaches the surface. You must take action to prevent further progress.

  Patent Document 2 describes that a crack is generated from a modified region by grinding the back surface of the substrate, but Patent Document 2 does not describe a method of fixing the substrate when grinding the substrate. . When the outer periphery of the substrate is supported by fitting the substrate into a retainer or the like as shown in FIG. 20, or when only a part of the substrate is sucked as shown in FIG. Since it is not constrained, in such a case, even if the back surface of the substrate is ground, no crack is generated from the modified region.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method of cutting a semiconductor substrate, which can efficiently obtain a chip of stable quality.

  In order to achieve the above object, an aspect of a method for cutting a semiconductor substrate according to the present invention is a wafer cutting method for cutting a wafer having a modified region formed therein by a laser beam, wherein the wafer surface is uniformly set on a table. The step of vacuum suction and grinding the back surface of the wafer in a state where the wafer is vacuum suctioned, while developing the micro crack extending from the modified region in the depth direction of the wafer, leaving the advanced micro crack. A grinding step of grinding and removing the modified region, after the grinding step, a mirror finishing step of performing chemical mechanical polishing of the back surface of the wafer, and after the mirror finishing step, a step of cutting the wafer, Features.

  In one aspect of the method for cleaving a semiconductor substrate according to the present invention, the grinding step grinds and removes a small crack extending from the back surface of the wafer to a portion before the reformed region and extending from the reformed region to the wafer depth. Preferably, the method includes a first grinding step of extending in the direction, and a second grinding step of grinding and removing the modified region formed in the inside of the wafer while leaving the extended fine crack.

  In one aspect of the method for cleaving a semiconductor substrate according to the present invention, it is preferable that, in the mirror-finish step, mirror-finish is performed by removing the work-affected layer introduced in the grinding step while leaving the microcracks. .

  ADVANTAGE OF THE INVENTION According to the cutting method of the semiconductor substrate of this invention, cutting can be performed reliably and efficiently, and the chip of stable quality can be obtained efficiently.

FIG. 1 is a diagram showing an outline configuration of a laser dicing apparatus 1. FIG. 2 is a conceptual configuration diagram illustrating a configuration of a driving unit of the laser dicing device 1. FIG. 2 is a plan view illustrating a configuration of a driving unit of the laser dicing apparatus 1. FIG. 2 is a diagram showing an outline configuration of a grinding device 2. FIG. 2 is a partially enlarged view of the grinding device 2. FIG. 2 is a partially enlarged view of the grinding device 2. FIG. 2 is a schematic diagram of a polishing stage of the grinding device 2. It is a figure which shows the detail of the chuck of the grinding device 2, (a) is a top view, (b) is sectional drawing, (c) is a partial enlarged view. The side view of the tape peeling apparatus 3. FIG. 4 is a side cross-sectional view showing a state of the cleavage. FIG. 4 is a side cross-sectional view showing a state of a pressed elastic body. FIG. 3 is a perspective view showing a state of cleavage. FIG. 3 is a perspective view showing a method of attaching a tape. FIG. 2 is a flowchart showing a method for cutting a semiconductor substrate according to the present invention. The figure explaining a grinding removal process. It is a figure explaining crack propagation in a grinding removal process, (a) is a schematic diagram at the time of grinding, (b) is a state of the back surface of wafer W, (c) is a state of surface of wafer W, (d) is a state of wafer W Sectional view. The figure explaining the surface state of the back surface of the wafer W after a grinding removal process. The figure which showed about the conditions of a crack growth evaluation. The figure which showed the evaluation result of the crack growth evaluation. The figure which shows the fixed state at the time of the conventional board | substrate grinding. The figure which shows the fixed state at the time of the conventional board | substrate grinding.

  Hereinafter, preferred embodiments of a method for cutting a semiconductor substrate according to the present invention will be described in detail with reference to the accompanying drawings.

  The present invention relates to a laser dicing device 1, a grinding device 2, a tape peeling device 3, and a transport device (not shown) for transporting a wafer processed by the laser dicing device 1 to the grinding device 2 or the tape peeling device 3. And an expanding device that separates the wafer that has been cut by the tape peeling device 3.

<About the device configuration>
(1) Regarding Laser Dicing Apparatus 1 FIG. 1 is a diagram showing an outline configuration of the laser dicing apparatus 1. As shown in FIG. 1, the laser dicing apparatus 1 according to the present embodiment mainly includes a wafer moving unit 11, a laser head 40 including a laser optical unit 20 and an observation optical unit 30, a control unit 50, and the like. .

  The wafer moving unit 11 includes a suction stage 13 for holding the wafer W by suction, and an XYZθ table 12 provided on the main body base 16 of the laser dicing apparatus 1 for moving the suction stage 13 precisely in the XYZθ direction. The wafer W is precisely moved in the XYZθ directions in the figure by the wafer moving unit 11.

  A back grinding tape (hereinafter, referred to as a BG tape) B having an adhesive is attached to the surface on which the devices are formed by a tape attaching device (not shown), and the wafer W is placed on the suction stage 13 so that the back surface faces upward. You.

  In addition, the wafer W may be configured such that a dicing sheet having an adhesive on one surface is attached thereto, and the wafer W may be placed on the suction stage 13 while being integrated with the frame via the dicing sheet. In this case, it is placed on the suction stage 13 so that the surface faces upward.

  The laser optical unit 20 includes a laser oscillator 21, a collimating lens 22, a half mirror 23, a condensing lens (condensing lens) 24, a driving unit 25 for finely moving a laser beam parallel to the wafer W, and the like. The laser light oscillated from the laser oscillator 21 is focused on the inside of the wafer W via an optical system such as a collimator lens 22, a half mirror 23, and a condensing lens 24. The position of the condensing point in the Z direction is adjusted by the Z direction fine movement of the condensing lens 24 by the Z fine movement means 27 described later.

  The conditions for the laser beam are as follows: the light source is a semiconductor laser-pumped Nd: YAG laser, the wavelength is 1064 nm, the laser beam spot cross section is 3.14 × 10 −8 cm 2, the oscillation mode is a Q switch pulse, the repetition frequency is 100 kHz, and the pulse width is Is 30 ns, the output is 20 μJ / pulse, the laser light quality is TEM00, and the polarization characteristic is linearly polarized light. The conditions of the condensing lens 24 are as follows: a magnification of 50 times; A. Is 0.55, and the transmittance for the laser light wavelength is 60%.

  The observation optical unit 30 includes an observation light source 31, a collimating lens 32, a half mirror 33, a condensing lens 34, a CCD camera 35 as an observation unit, an image processing unit 38, a television monitor 36, and the like.

  In the observation optical unit 30, the illumination light emitted from the observation light source 31 irradiates the surface of the wafer W through an optical system such as a collimator lens 32, a half mirror 33, and a condensing lens 24. Light reflected from the surface of the wafer W is incident on a CCD camera 35 as observation means via a condensing lens 24, half mirrors 23 and 33, and a condensing lens 34, and a surface image of the wafer W is captured.

  The image data is input to the image processing unit 38, used for alignment of the wafer W, and is displayed on the television monitor 36 via the control unit 50.

  The control unit 50 includes a CPU, a memory, an input / output circuit unit, and controls the operation of each unit of the laser dicing apparatus 1.

  The laser dicing apparatus 1 includes a wafer cassette elevator (not shown), a wafer transfer unit, an operation plate, an indicator light, and the like.

  The wafer cassette elevator moves a cassette in which wafers are stored up and down to position it at a transfer position. The transfer means transfers the wafer between the cassette and the suction stage 13.

  Switches and a display device for operating each part of the dicing apparatus 10 are attached to the operation plate. The indicator lights indicate the operation status of the dicing apparatus 10 during processing, processing completion, emergency stop, and the like.

  FIG. 2 is a conceptual diagram illustrating details of the driving unit 25. The driving unit 25 includes a lens frame 26 that holds the condensing lens 24, a Z fine movement unit 27 that is attached to the upper surface of the lens frame 26, and that slightly moves the lens frame 26 in the Z direction in the drawing, and a holding frame 28 that holds the Z fine movement unit 27. , PZ1, PZ2, etc., which are linear fine movement means for finely moving the holding frame 28 in parallel with the wafer W.

  As the Z fine movement means 27, a piezoelectric element which expands and contracts by applying a voltage is used. The condensing lens 24 is minutely fed in the Z direction by the expansion and contraction of the piezoelectric element, so that the position of the condensing point of the laser beam in the Z direction is precisely positioned.

  The holding frame 28 is supported by two pairs of parallel springs composed of four piano wires (not shown), is movable in the X and Y directions, and is restricted from moving in the Z direction. The method of supporting the holding frame 28 is not limited to this. For example, the holding frame 28 may be sandwiched vertically by a plurality of balls to restrict the movement in the Z direction and to support the movement in the XY directions.

  A piezoelectric element is used for the linear fine movement means PZ1 and PZ2, similarly to the Z fine movement means 27. One end is fixed to the case body of the laser head 40, and the other end is in contact with the side surface of the holding frame.

  FIG. 3 is a plan view of the driving unit 25. As shown in FIG. 3, two linear fine movement means PZ1 and PZ2 are arranged in the X direction. One end is fixed to the case body of the laser head 40, and the other end is in contact with the side surface of the holding frame 28. . Therefore, the condensing lens 24 can be finely reciprocated in the X direction by controlling the applied voltage, and the laser beam can be finely reciprocated in the X direction or vibrated.

  Note that a piezoelectric element may be used for one of the linear fine movement means PZ1 and PZ2, and the other may be an elastic member such as a spring material. Further, three linear fine movement means may be arranged on the circumference.

  Laser light L is emitted from the laser oscillator 21, and the laser light L is applied to the inside of the wafer W via an optical system such as a collimator lens 22, a half mirror 23, and a condensing lens 24. The Z-direction position of the converging point of the irradiated laser beam L is accurately adjusted to a predetermined position inside the wafer by adjusting the Z-direction position of the wafer W by the XYZθ table 12 and controlling the position of the condensing lens 24 by the Z fine movement means 27. Is set.

  In this state, the XYZθ table 12 is processed and fed in the X direction which is the dicing direction, and the condensing lens 24 is reciprocated minutely by the linear fine movement means PZ1 and PZ2 provided on the laser head 40, so that the laser light L The laser light L is vibrated in the X direction or an arbitrary XY direction in parallel, and the converging point of the laser light L is minutely vibrated inside the wafer to form the modified region K. Thereby, one modified region K by multiphoton absorption is formed inside the wafer W along the cutting line of the wafer W.

  If necessary, vibration in the Z direction by the Z fine movement means 27 may be applied. Also, by sending the wafer W in the X direction while slowly reciprocating finely sending the laser light L in the X direction which is the processing direction, the laser light L is repeatedly irradiated in a back-and-forth state like a perforation. Is also good.

  When one line of the modified region is formed along the cutting line, the XYZθ table 12 is indexed and fed by one pitch in the Y direction, and the modified line is similarly formed on the next line.

  When the reformed regions are formed along all the cutting lines parallel to the X direction, the XYZθ table 12 is rotated by 90 °, and all the lines orthogonal to the previous line are formed in the same manner.

(2) Regarding the Grinding Apparatus 2 FIG. 4 is a perspective view showing an outline configuration of the grinding apparatus 2. The main body 112 of the grinding device 2 is provided with an alignment stage 116, a coarse grinding stage 118, a fine grinding stage 120, a polishing stage 122, a polishing cloth cleaning stage 123, a polishing cloth dressing stage 127, and a wafer cleaning stage 124.

  The coarse grinding stage 118, the fine grinding stage 120, and the polishing stage 122 are partitioned by a partition plate 125 (omitted in FIG. 4) as shown in FIG. 5, and the working fluid used in each of the stages 118, 120, 122 is adjacent. It is prevented from scattering on the stage.

  As shown in FIG. 5, the partition plate 125 is fixed to the index table 134, and is formed in a cross shape so as to partition the four chucks 132, 136, 138, and 140 installed on the index table 134. .

  The coarse grinding stage 118 is a stage for performing coarse polishing, and is surrounded by a side surface of the main body 112, a top plate 128, and a partition plate 125, as shown in FIG. The fine grinding stage 120 is a stage for performing fine polishing, and is surrounded by the side surface of the main body 112, the top plate 129, and the partition plate 125, like the rough polishing stage 118. Brushes (not shown) are provided on the upper and side surfaces of the partition plate 125 to isolate the coarse grinding stage 118 and the fine grinding stage 120 from the outside. The top plates 128 and 129 have through holes 128A and 129A into which the heads of the respective stages are inserted.

  The polishing stage 122 performs chemical mechanical polishing, and is covered by a casing 126 having a top plate 126A as shown in FIG. 5 in order to isolate the polishing stage 122 from other stages. The top plate 126A has a through hole 126C through which the head of each stage is inserted.

  As shown in FIG. 6, a brush 126B is attached to a side of the casing 126 through which the partition plate 125 passes, and the brush 126B is attached to the upper surface 125A of the partition plate 125 when the chuck 140 is located at the processing position. It contacts the side surface 125B. Thus, when the chuck 140 is located at the processing position, the casing 126, the partition plate 125, and the brush 126B are held in a substantially airtight state.

  Since the polishing stage 122 performs chemical mechanical polishing, the polishing liquid contains a chemical polishing agent. When the grinding processing liquid is mixed with such a polishing processing liquid, the concentration of the chemical polishing agent decreases, and a problem that the processing time becomes longer occurs. By keeping the polishing stage 122 in a substantially confidential state, it is possible to prevent the grinding fluid and processing chips used in the fine grinding stage 120 from entering the polishing stage 122, and to prevent the polishing fluid used in the polishing stage 122. Can be prevented from scattering from the polishing stage 122. Therefore, it is possible to prevent processing defects caused by mixing of both processing liquids.

  FIG. 7 is a structural diagram of the polishing stage 122. In the polishing stage 122, polishing is performed by the polishing cloth 156 and the slurry supplied from the polishing cloth 156, and a damaged layer generated on the back surface of the wafer W is removed by rough polishing and fine polishing. The work-affected layer is a general term for, for example, streaks and work strains (crystals are altered) caused by grinding.

  The polishing cloth 156 of the polishing stage 122 is attached to a polishing head 161 connected to an output shaft 160 of a motor 158. Guide blocks 162, 162 constituting a linear motion guide are provided on the side surface of the motor 158, and the guide blocks 162, 162 are vertically movably engaged with guide rails 166 provided on the side surface of the support plate 164. Have been. Therefore, the polishing cloth 156 is attached to the support plate 164 together with the motor 158 so as to be vertically movable.

  The support plate 164 is provided at the tip of an arm 168 that is arranged horizontally. A base end of the arm 168 is connected to an output shaft 174 of a motor 172 disposed inside the casing 170. Therefore, when the motor 172 is driven, the arm 168 can rotate around the output shaft 174. Thus, the range of the polishing cloth 56 at the polishing position (see the solid line in FIG. 3), the polishing cloth cleaning position by the polishing cloth cleaning stage 123 (see the two-dot chain line in FIG. 3), and the dress position by the polishing cloth dressing stage 127 are shown. Can be moved within. When the polishing pad 156 is moved to the polishing pad cleaning position, the surface thereof is cleaned by the polishing pad cleaning stage 123 to remove polishing debris and the like adhering to the surface. As the polishing cloth 156, foamed polyurethane, polishing cloth, or the like can be exemplified. The polishing cloth cleaning stage 123 is provided with a removing member such as a brush for removing polishing debris. The removing member is driven to rotate when the polishing pad 156 is washed, and the polishing pad 156 is also driven to rotate by the motor 158. The same material as the polishing cloth 156, for example, foamed polyurethane, is employed for the polishing cloth dressing stage 127.

  Guide blocks 176 and 176 constituting a linear motion guide are provided on the side surface of the casing 170, and the guide blocks 176 and 176 are vertically movable on guide rails 180 provided on the side surface of the housing 178 for the screw feeder. Is engaged. In addition, a nut member 179 protrudes from a side surface of the casing 170. The nut member 179 is screwed to a screw rod 181 of a screw feeder provided in the housing 178 through an opening (not shown) formed in the housing 178. The output shaft 184 of the motor 182 is connected to the upper end of the screw rod 181. Therefore, when the motor 82 is driven and the screw rod 181 is rotated, the casing 70 is moved up and down by the feeding action of the screw feeder and the straight-moving action of the guide block 176 and the guide rail 180. Thus, the polishing pad 156 is largely moved in the vertical direction, and the interval between the polishing head 161 and the wafer W is set to a predetermined interval.

  The piston 188 of the air cylinder device 186 is connected to the upper surface of the motor 158 via a through hole 169 of the arm 168. In addition, a regulator 190 that controls the internal pressure P of the cylinder is connected to the air cylinder device 186. Therefore, when the internal pressure P is controlled by the regulator 190, the pressing force (pressing force) of the polishing pad 156 against the wafer W can be controlled.

  In this embodiment, the polishing cloth 156 is used as the polishing body. However, the present invention is not limited to this. For example, if the affected layer can be removed, electrophoresis of a grinding wheel or abrasive grains may be used. May be applied. When electrophoresis of a polishing grindstone or abrasive grains is applied, it is preferable to perform quantitative polishing.

  Returning to the description of FIG. The alignment stage 116 is a stage for aligning the wafer W transferred from the laser dicing apparatus 1 by a transfer device (not shown) to a predetermined position. The wafer W positioned by the alignment stage 116 is suction-held by a transfer robot (not shown), then transferred to an empty chuck 132, and suction-held by the suction surface of the chuck 132.

  The chuck 132 is installed on an index table 134, and chucks 136, 138, and 140 having the same function are installed on a circumference around the rotation axis 135 of the index table 134 at intervals of 90 degrees. . A spindle (not shown) of a motor (not shown) is connected to the rotating shaft 135.

  The chuck 136 is located on the rough grinding stage 118 in FIG. 4, and the sucked wafer W is roughly ground here. The chuck 138 is located on the fine grinding stage 120 in FIG. 4, and the attracted wafer W is subjected to finish grinding (fine grinding, spark out) here. The chuck 140 is positioned on the polishing stage 122 in FIG. 4, and the chucked wafer W is polished here to remove a damaged layer generated by the grinding and a variation in the thickness of the wafer W.

  Here, the chucks 132, 136, 138, and 140 will be described. Since the chucks 136, 138, and 140 have the same configuration as the chuck 132, the chuck 132 will be described, and the description of the chucks 136, 138, and 140 will be omitted.

  8A and 8B are diagrams showing details of the chuck 132, where FIG. 8A is a plan view of the chuck 132, FIG. 8B is a cross-sectional view taken along the line AA ′ in FIG. 8A, and FIG. FIG.

  The chuck 132 is configured by fitting a mounting table 132a formed of a porous material (for example, porous ceramics) into a chuck body 132b formed of a dense body. On the lower side of the chuck body 132b where the mounting table 132a is fitted, a suction hole 132c is formed for vacuum suction. The chuck 132 is desirably formed of a material having low thermal conductivity.

  As shown in FIG. 8C, the wafer W is mounted on the mounting table 132a via the BG tape B. As shown in FIG. 8C, the mounting table 132a is formed such that a part of the outer periphery of the wafer W protrudes from the mounting table 132a when the wafer W is mounted on the mounting table 132a, and has a width x. Is about 1.5 mm. The wafer W used in the present embodiment has a diameter of about 12 inches and a thickness t of about 775 μm.

  As shown in FIGS. 8A and 8B, the suction holes 132c are arranged so as to cover substantially the entire area of the mounting table 132a. A fluid coupling (not shown) is connected to the suction hole 132c, and a suction pump (not shown) connected to the fluid coupling sucks air. Therefore, substantially the entire surface of the wafer W is firmly suctioned to the surface of the mounting table 132a. Thus, the wafer W and the mounting table 132a can be brought into close contact with each other without causing a positional shift.

  As shown in FIG. 7, the chucks 132, 136, 138, and 140 have a spindle 194 and a motor 192 connected to the lower surface thereof, respectively, and are rotated by the driving force of these motors 192. The motor 192 is supported by the index table 134 via a support member 193. Thus, every time the chucks 132, 136, 138, 140 are moved by the motor 137, the spindle 194 is separated from the chucks 132, 136, 138, 140, or the chucks 132, 136 are attached to the spindle 194 installed at the next movement position. , 138 and 140 can be omitted.

  The piston 119 of the cylinder device 117 is connected to a lower portion of the motor 192. When this piston 119 is extended, it is fitted and connected to a concave portion (not shown) formed at the lower part of the chucks 132, 136, 138, 140. Then, the chucks 132, 136, 138, 140 are moved upward from the index table 134 by the continuous extension operation of the piston 119, and are positioned at the grinding positions by the grindstones 146, 154.

  The control unit 100 includes a CPU, a memory, an input / output circuit unit, and controls the operation of each unit of the grinding device 2.

  The thickness of the wafer W sucked and held by the chuck 132 is measured by a pair of measurement gauges (not shown) connected to the control unit 100. Each of these measurement gauges has a contact, and the contact is in contact with the upper surface (back surface) of the wafer W, and the other contacts are in contact with the upper surface of the chuck 132. These measurement gauges can detect the thickness of the wafer W with the upper surface of the chuck 132 as a reference point, as a difference between in-process gauge read values. Note that the thickness measurement by the measurement gauge may be performed in-line. Further, the method of measuring the thickness of the wafer W is not limited to this.

  The index table 134 is rotated by 90 degrees in the direction of arrow R in FIG. 4 by the control unit 100, so that the wafer W whose thickness has been measured is positioned on the coarse grinding stage 118, and the wafer W is moved by the cup-type grindstone 146 of the coarse grinding stage 118. The back surface of W is roughly ground. As shown in FIG. 4, the cup-type grindstone 146 is connected to an output shaft (not shown) of a motor 148, and is attached to a grindstone feeder 152 via a support casing 150 of the motor 148. The grindstone feeding device 152 moves the cup-shaped grindstone 146 up and down together with the motor 148, and the cup-shaped grindstone 146 is pressed against the back surface of the wafer W by this downward movement. Thereby, rough grinding of the back surface of the wafer W is performed. The control unit 100 sets the amount of downward movement of the cup-type grindstone 146 and controls the motor 148. The amount of downward movement of the cup-shaped grindstone 46, that is, the amount of grinding by the cup-shaped grindstone 146, is set based on the reference position of the cup-shaped grindstone 146 registered in advance and the thickness of the wafer W detected by the measurement gauge. Is done. Further, the control unit 100 controls the number of rotations of the cup-type grindstone 146 by controlling the number of rotations of the motor 148.

  The thickness of the wafer W whose back surface has been roughly ground by the coarse grinding stage 118 is measured by a measurement gauge (not shown) connected to the control unit 100 after the cup-shaped grindstone 146 retreats from the wafer W. When the index table 134 is rotated by 90 degrees in the direction of arrow R in FIG. 4 by the control unit 100, the wafer W whose thickness has been measured is positioned on the fine grinding stage 120, and the thickness of the wafer W is finely adjusted by the cup-type grindstone 154 of the fine grinding stage 120. Grinding and sparking out. The structure of the fine grinding stage 120 is the same as the structure of the coarse grinding stage 118, and a description thereof will be omitted. The amount of grinding by the cup-shaped grindstone 154 is set by the control unit 100, and the moving amount and the number of rotations of the cup-shaped grindstone 154 are controlled by the control unit 100.

  The thickness of the wafer W whose back surface has been finely ground by the fine grinding stage 120 is measured by a measurement gauge (not shown) connected to the control unit 100 after the cup-shaped grindstone 154 is retracted and moved from the wafer W. When the index table 134 is rotated by 90 degrees in the direction of arrow R in FIG. 4 by the control unit 100, the wafer W whose thickness has been measured is positioned on the polishing stage 122, and chemical mechanical polishing is performed by the polishing cloth 156 of the polishing stage 122. Then, the rear surface of the wafer W is mirror-finished. The vertical movement distance of the polishing pad 156 is set by the control unit 100, and the position of the polishing pad 156 is controlled by controlling the motor 182 by the control unit 100. The control unit 100 controls the rotation speed of the motor 158, that is, the rotation speed of the polishing pad 156.

  After the arm 168 is rotated by the control unit 100 and the polishing pad 156 is retracted from the position above the wafer W, the wafer W polished by the polishing stage 122 is moved by a hand (not shown) of a robot (not shown). And carried to the wafer cleaning stage 124. As the wafer cleaning stage 124, a stage having a rinsing cleaning function and a spin drying function is applied. The polished wafer W is not easily damaged because the deteriorated layer is removed, and therefore is not damaged during transfer by the robot and during cleaning in the wafer cleaning stage 124.

  The wafer W that has been cleaned and dried in the wafer cleaning stage 124 is suction-held by a hand (not shown) of a robot (not shown) and stored in a predetermined shelf of a cassette (not shown).

(3) Tape peeling device 3 FIG. 9 is a side view showing the configuration of the tape peeling device 3. The bonding of the BG tape B or the expanding tape E to the wafer W is performed by the tape peeling device 3. Further, the wafer W ground and polished by the grinding device 2 is cleaved by the tape peeling device 3.

  The tape peeling device 3 includes a table 211 rotatably provided by a driving device (not shown). An elastic body 212 on which the wafer W is placed is attached to the upper surface of the table 211.

  A supply reel 213 and a peeling roller 214 are provided above the table 211, and a peeling film 215 for peeling the BG tape B adhered to the surface of the wafer W is fed out from the supply reel 213, and the guide rollers 216, 217 Through the take-up reel 218.

  A pressing member 219 for cleaving the wafer W is provided near the peeling roller 214 (for example, above the outer peripheral portion of the table 211).

  The elastic body 212 attached to the upper surface of the table 211 is an elastic body having a small compression set and having no void, and is formed in a lattice shape or at a space equal to or less than the size of the chip C formed on the wafer W as shown in FIG. Grooves 212a are formed in parallel. The elastic body 212 is connected to a vacuum generating source (not shown), the BG tape B is adhered to the front surface by grooves 212a, 212a, and the like, and the elastic body 212 is mounted on the frame F via the expanding tape E adhered to the back surface. The formed wafer W is formed so as to be able to be fixed by suction.

  As a material of the elastic body 212, for example, SBR (styrene butadiene rubber), NBR (nitrile butadiene rubber) or the like can be preferably used. The groove 212a may have a hole shape or an uneven shape.

  For example, when a sponge-like elastic body 212B in which a large number of small gaps are formed as shown in FIG. 11A is used at the time of cleaving the wafer W, the gap becomes small or the compression set due to the flattening of the gaps. Distortion occurs. For this reason, when the elastic body 212B is used repeatedly, the elastic coefficient gradually changes due to deformation, and stable cutting cannot be performed.

  Further, as shown in FIG. 11B, in the elastic body 212C having no grooves, holes, irregularities, etc., when a part of the elastic body is pushed in, since the volume is constant, a part around the pushed-in body rises. It will be. In this case, even if the wafer is locally pressed to sink the wafer, the stress is dispersed and it is difficult to efficiently cut the wafer.

  On the other hand, as shown in FIG. 11 (c), since the elastic body 212 has room for lateral deformation due to the groove 212a when pressed from above, uniform deformation occurs, and the cutting line desired to be cut. Stress is concentrated on S, and the cutting can be performed reliably and efficiently.

  As shown in FIG. 10, the pressing member 219 has a radius R smaller than the interval L between the cutting lines S on which the modified layer P is formed. When the radius R is smaller than the interval L, the pressing member 219 does not press another cutting line S when pressing one cutting line S. As a result, stress is concentrated on the cutting line S where cutting is desired, and cutting can be performed reliably and efficiently.

  As shown in FIG. 12, the cutting of the wafer W is performed by attaching a BG tape B to the front surface of the wafer W on which the modified layer P is formed along the cutting line S and an expanding tape E to the back surface side. The tape peeling apparatus 3 adjusts the position of the wafer W by rotating the table 211 so that the pressing member 219 is parallel to one of the cutting lines S formed in a lattice as shown in FIG.

  In this state, the pressing member 219 is pressed against the wafer W and rolled, and the wafer W is cut along one cutting line S. After cutting one of the cutting lines S, the table 211 on which the wafer W is placed is rotated by 90 degrees by a driving unit (not shown) so that the other cutting line S and the pressing member 219 are arranged in parallel. In this state, the pressing member 219 is pressed against the wafer W and rolled, so that the wafer W is cut along the other cutting line S.

  Since the BG tape B and the expanding tape E are attached to the front and back surfaces of the wafer W, the BG tape B and the expanding tape E are used to cut one cutting line S and then cut the adjacent cutting line S. The position is constrained, and the chip interval does not greatly increase in the cut line S that has already been cut. Accordingly, local stress of the pressing member 219 is not dispersed by not only vertical deformation due to the elastic body 212 but also horizontal deformation due to a large gap between the chips C, and the stress is concentrated. Cutting can be performed efficiently and reliably.

  In addition, since the BG tape B and the expanding tape E are adhered to the front surface and the back surface, debris generated when the wafer W is cut does not adhere to the elastic body 212, and the next wafer W is elastically bonded. Even if it is placed on 212, no detrimental effect is caused by the fragments.

  The peeling roller 214 is formed of an elastic body softer than the elastic body 212. The BG tape B has, for example, an ultraviolet-curable adhesive on the bonding surface, and is irradiated with ultraviolet light by an ultraviolet irradiation device (not shown) provided inside or outside the tape peeling device 3 to reduce the adhesive force. . The peeling film 215 is rolled in the lateral direction (the direction of arrow A shown in FIG. 9) while pressing the peeling roller 214 downward as shown in FIG. Affixed.

  After the peeling film 215 is adhered, the winding unit 218A including the take-up reel 218 and the guide roller 217 winds the peeling film 215 together with the peeling roller 214 in the horizontal direction (the direction of arrow B shown in FIG. 9). ), The BG tape B is peeled off from the wafer W.

  When the peeling film 215 is adhered by the peeling roller 214 or the BG tape B is peeled, the cutting line S for dividing the chip C is moved with respect to the peeling roller 214 as shown in FIG. By rotating the table 211 by 45 degrees, the wafers W arranged in parallel are arranged so that the cutting line S is inclined and intersects the peeling roller 214 as shown in FIG. 13B.

  Thereby, the position of the chip C which has been cut at the time of attaching the release film 215 or the peeling of the BG tape B does not shift, and does not adversely affect the subsequent processes such as the pickup of the expanded chip C. .

(4) Expanding Device Next, an expanding device (not shown) will be described. As the expanding device, a conventional ordinary expanding device can be used. For example, an expanding device having the following configuration, which is disclosed in JP-A-2007-173587, can be used.

  That is, the peripheral portion of the expanding tape E is fixed to the frame F. A ring member is in contact with the lower surface of the inner portion of the peripheral portion of the expand tape E. The outer periphery of the upper surface of this ring member is smoothly chamfered. A downward force is applied to the frame F, and the frame F is pushed downward. Thereby, the dicing tape is expanded, and the interval between the chips is widened. At this time, since the outer peripheral edge of the upper surface of the ring member is smoothly chamfered, the expanding tape E is smoothly expanded.

  As a mechanism for pushing down the frame F, various known linear motion devices can be adopted. For example, a linear motion device including a cylinder member (by hydraulic pressure, pneumatic pressure, or the like), a motor, and a screw (a combination of a male screw as a shaft and a female screw as a bearing) can be employed.

<Semiconductor substrate cutting method>
Next, a method for cutting the semiconductor substrate will be described. FIG. 14 is a flowchart showing a processing flow of a method of cutting a semiconductor substrate.

(1) BG tape attaching process (step S1)
In the method for cutting a semiconductor substrate according to the present invention, first, a BG tape B is attached to the front surface of the wafer W on which a circuit pattern and the like are formed (step S1).

  The bonding of the BG tape B to the wafer W is performed by a tape bonding device (not shown). When attaching the BG tape B, the table 211 is rotated 45 degrees so that the cutting line S dividing the chip C is inclined and intersects with the attaching roller to which the tape is attached. This prevents the wafer W from being cut along the cutting line S by the pressing force of the sticking roller while the BG tape B is being stuck to the wafer W.

(2) Laser reforming step (Step S2)
The wafer W having the BG tape B attached to the front surface is placed on the suction stage 13 of the laser dicing apparatus 1 so that the back surface faces upward. The following processing is performed by the laser dicing apparatus 1 and is controlled by the control unit 50.

  When the laser light L is emitted from the laser oscillator 21, the laser light L is applied to the inside of the wafer W via an optical system such as a collimating lens 22, a half mirror 23, and a condensing lens 24, and the laser light L is changed inside the wafer W. The quality region K is formed.

  In the present embodiment, since the thickness of the finally generated chip is approximately 50 μm, the laser light is irradiated to a depth of approximately 60 μm to approximately 80 μm from the surface of the wafer W. In order to efficiently break the surface (device surface) of the wafer W, the laser modified region should be placed at a relatively deep position near the reference surface, which is a surface located on the back surface by the thickness of the chip C from the surface of the wafer W. This is because it needs to be formed.

  The control unit 50 scans the pulsed processing laser light L in parallel with the surface of the wafer W, and forms a plurality of discontinuous modified regions K in the wafer W side by side. Micropores (hereinafter, referred to as cracks) are formed inside the modified region K. Hereinafter, a region formed by arranging a plurality of discontinuous modified regions K,... Is referred to as a modified layer.

  When the modified layer is formed along all of the cutting lines S shown in FIG. 10, the process of step S2 ends.

(3) Grinding removal step (Step S3)
When the modified region K is formed along the cutting line S in the laser reforming step (Step S2), the wafer W is transferred from the laser dicing device 1 to the grinding device 2 by a transfer device (not shown). The following processing is performed by the grinding device 2 and is controlled by the control unit 100.

  The transported wafer W is placed on a chuck 132 (eg, chucks 136, 148, and 140 are also possible) with the back surface facing upward, that is, the BG tape B attached to the front surface of the wafer W facing downward. The entire surface is vacuum-sucked on the chuck 132.

  The index table 134 is rotated around the rotation shaft 135 to carry the chuck 132 into the rough grinding stage 118, and the wafer W is roughly polished.

  The rough polishing is performed by rotating the chuck 132 and the cup-shaped grindstone 146. In the present embodiment, for example, Vitrified # 325 manufactured by Tokyo Seimitsu is used as the cup-shaped grindstone 146, and the rotation speed of the cup-shaped grindstone 146 is approximately 3000 rpm.

  After the rough polishing, the index table 134 is rotated about the rotation shaft 135 to carry the chuck 132 into the fine grinding stage 120, and the chuck 132 is rotated and the cup-type grindstone 154 is rotated to precisely polish the wafer W. In the present embodiment, for example, resin # 2000 manufactured by Tokyo Seimitsu Co., Ltd. is used as the cup-shaped grindstone 154, and the rotation speed of the cup-shaped grindstone 154 is approximately 2400 rpm.

  In the present embodiment, as shown in FIG. 15, grinding is performed to the target surface, that is, to a depth of approximately 50 μm from the surface of the wafer W by combining the rough polishing and the fine polishing. In the present embodiment, the rough polishing is performed to approximately 700 μm, and the fine polishing is performed to approximately 30 to 40 μm. However, it is not strictly determined, and the times of the rough polishing and the fine polishing are substantially the same. The grinding amount may be determined so as to be as follows.

  Therefore, as shown in FIG. 15, the modified layer is removed in the grinding step, and the modified region K by the laser beam does not remain on the cross section of the chip C which is the final product. Therefore, it is possible to prevent the modified layer from being crushed from the cross section of the chip, the chip C from being broken from the crushed portion, and the generation of dust from the crushed portion.

  Further, in the present embodiment, in this grinding and removing step, a crack propagation step of causing cracks in the modified layer to propagate in the thickness direction of wafer W is included. FIGS. 16A and 16B are diagrams for explaining the mechanism of crack propagation. FIG. 16A is a schematic diagram at the time of grinding, FIG. 16B is a diagram of the back surface of the wafer W, FIG. 16C is a diagram of the front surface of the wafer W, and FIG. FIG. 4 is a cross-sectional view of the wafer W during grinding.

  By the grinding, the ground surface shown in FIG. 16A, that is, the back surface of the wafer W is expanded by the grinding heat as shown in FIG. 16B. On the other hand, almost the entire surface of the surface opposite to the ground surface, that is, the surface of the wafer W is depressurized and adsorbed by the vacuum chuck as shown in FIG. Is physically constrained against displacement.

  In other words, as shown in FIG. 16D, the back surface (ground surface) of the wafer W tends to spread in the outer peripheral direction (displacement due to thermal expansion) in the case of a disk shape due to thermal expansion, while the front surface ( The suction surface is constrained so as not to physically displace each point in the wafer surface to be expanded. For this reason, a strain is generated inside the wafer, and a crack propagates in the thickness direction of the wafer W due to the internal strain. This internal strain acts equally between the portion expanded by thermal expansion and each point in the wafer surface which is physically constrained. Crack growth due to internal strain is most efficient at the beginning of grinding, that is, at the time of rough polishing, in which the amount of grinding and the frictional force are large, that is, the frictional heat is also large.

  The laser modified region is formed at a relatively deep position close to the thickness of the chip. Therefore, in the initial stage of grinding, the distance from the ground surface to the laser modified layer is relatively long, but the target surface from the modified layer is relatively close to the extent that the cracks can propagate. Therefore, in order to propagate the crack, it is preferable that the thermal expansion of the wafer W be promoted by the grinding heat at the beginning of the rough polishing.

  Even if grinding is performed under conditions for thermally expanding the wafer W, that is, under conditions for generating a good amount of frictional heat (e.g., reducing the amount of grinding fluid), the shear stress of the grinding is immediately applied to the modified layer. Not even a thing. In the present embodiment, the crack does not grow due to the shear stress caused by the grinding, but the thermal expansion due to the grinding heat is the dominant factor in the crack growth.

  In the case where a crack is propagated due to internal strain, the crack can be uniformly propagated at each point in the wafer W regardless of the rigidity variation in the surface of the wafer W regardless of the type of the wafer W. . Therefore, it is possible to prevent the stress from being concentrated on a portion having low rigidity due to the presence of a defect in the surface of the wafer W as in the case of applying an artificial stress.

  Further, when an external force is artificially applied, stress concentrates on a weak portion of the material, so that it is difficult to control cracks to develop uniformly and slowly, and the wafer is completely cut. On the other hand, in the case of crack propagation due to internal strain in the present embodiment, the crack can be delicately propagated because the internal strain is due to the degree of thermal expansion. That is, the crack can be propagated between the target surface and the surface of the wafer W. Therefore, it is possible to efficiently divide the wafer in the wafer cutting step (step S6) described later.

  Note that internal strain due to thermal expansion of the wafer W is distinguished from so-called thermal stress caused by a temperature difference. Although the thermal stress is generated in proportion to the temperature gradient, in the present embodiment, the generated heat escapes to the chucks 132, 136, 138, and 140, so that no thermal stress is generated.

(4) Chemical mechanical polishing step (Step S4)
This step is performed by the grinding device 2 and is controlled by the control unit 100.

  After the fine polishing, the index table 134 is rotated about the rotation shaft 135 to carry the chuck 132 into the polishing stage 122, and the chemical mechanical polishing is performed by the polishing cloth 156 of the polishing stage 122, and in the grinding and removing step (step S 3). The affected layer formed on the back surface of the wafer W is removed, and the back surface of the wafer W is mirror-finished.

  In this embodiment, a non-woven cloth impregnated with polyurethane (for example, TS200L manufactured by Tokyo Seimitsu) is used as the polishing cloth 156, colloidal silica is used as the slurry, and the rotation speed of the polishing cloth 156 is approximately 300 rpm.

  As a result of the grinding and removing step (step S3), many irregularities as shown in FIG. 17 are formed on the back surface of the wafer W. When polishing is performed by chemical etching, since the surface shape is kept as it is, there is a possibility that cracks may occur from the concave portions, and the surface is not mirror-finished. On the other hand, in the present embodiment, since chemical mechanical polishing is performed, the processing distortion generated by the processing is removed, and the unevenness on the surface is removed, and the surface is mirror-finished.

  In other words, in order to improve the quality of the chip C, which is the final product, two processes, a grinding and removing process using a grindstone and a chemical mechanical polishing process using free abrasive grains containing a chemical solution using a polishing cloth, are indispensable. .

(5) Expanding tape attaching step (Step S5)
An expand tape E is attached to the back surface of the wafer W that has been subjected to the chemical mechanical polishing step (Step S4). The expand tape is a kind of elastic tape, and is expandable and contractible.

  The bonding of the expand tape E to the wafer W is performed by a tape bonding device (not shown) in the same manner as the bonding of the BG tape B in step S1. When attaching the expanding tape E, the table 211 is rotated by 45 degrees so that the cutting line S for dividing the chip C, as in the case of the BG tape B, obliquely intersects the attaching roller to which the tape is attached. Let it.

  This prevents the wafer W from being cut along the cutting line S by the pressure of the sticking roller while the expanding tape E is being stuck to the wafer W.

(6) Wafer cutting process (Step S6)
The wafer W to which the expanding tape E is adhered is transported to the tape peeling device 3, presses the pressing member 218 against the wafer W, and cuts the wafer W along the cutting line S, so that the wafer W becomes individual chips C. Divided.

  In the cutting of the wafer W, the elastic body 212 is provided on the upper surface of the wafer W such that the pressing member 219 is parallel to one of the cutting lines S, which are cutting lines formed in a lattice shape as shown in FIG. Placed on the table 211. In this state, the pressing member 219 is pressed against the wafer W and rolled, and the wafer W is cut along one cutting line S. After the cutting of one cutting line S, the table 211 on which the wafer W is placed is rotated 90 degrees by a driving unit (not shown), and the other cutting line S and the pressing member 219 are arranged so as to be parallel to each other. The wafer W is cut along the cutting line S.

  The elastic body 212 attached to the upper surface of the table 211 is an elastic body having a small compression set and having no void, and is formed in a lattice shape or at a space equal to or less than the size of the chip C formed on the wafer W as shown in FIG. Grooves 212a are formed in parallel. As a result, as shown in FIG. 11 (c), the elastic body 212 has a room for lateral deformation due to the groove 212a when pressed from above, so that uniform deformation occurs and the cutting line S desired to be cut. , Stress is concentrated, and the cutting can be performed reliably and efficiently.

  As shown in FIG. 10, the pressing member 219 is formed such that the radius r is smaller than the interval 1 between the cutting lines S in which the modified regions K are formed. When pressing, other cutting lines S are not pressed. As a result, stress is concentrated on the cutting line S where cutting is desired, and cutting can be performed reliably and efficiently.

  In the cutting of the wafer W, the BG tape B and the expanding tape E are attached to the front surface and the back surface. Therefore, when cutting one cutting line S and then cutting the adjacent cutting line S, the BG tape B and the expanding tape are used. The position of the chip is restricted by E, so that the chip interval does not greatly increase in the cutting line S that has already been cut. This prevents local stress of the pressing member 218 from being dispersed by not only vertical deformation due to the elastic body 212 but also horizontal deformation due to a large gap between the chips C, thereby concentrating the stress. Cutting can be performed efficiently and reliably.

  In addition, since the BG tape B and the expanding tape E are adhered to the front surface and the back surface, debris generated when the wafer W is cut does not adhere to the elastic body 212, and the next wafer W is elastically bonded. Even if it is placed on 212, no detrimental effect is caused by the fragments.

(7) BG tape peeling step (Step S7)
With respect to the cut wafer W, the peeling film 215 is adhered to the BG tape B by the peeling roller 214, and the BG tape B is peeled.

  The peeling roller 214 is formed of an elastic body softer than the elastic body 212. The BG tape B has, for example, an ultraviolet-curable adhesive on the bonding surface, and is irradiated with ultraviolet light by an ultraviolet irradiation device (not shown) provided inside or outside the tape peeling device 3 to reduce the adhesive force. . The peeling film 215 is rolled in the lateral direction (the direction of arrow A shown in FIG. 9) while pressing the peeling roller 214 downward as shown in FIG. Affixed.

  After the peeling film 215 is adhered, the winding unit 218A including the two take-up reels 18 and the guide rollers 217 winds the peeling film 215 together with the peeling roller 214 in the horizontal direction (arrow B shown in FIG. 9). Direction), the BG tape B is peeled off from the wafer W.

  When the peeling film 215 is adhered by the peeling roller 214 or the BG tape B is peeled, the cutting line S for dividing the chip C is moved with respect to the peeling roller 214 as shown in FIG. By rotating the table 211 by 45 degrees, the wafers W arranged in parallel are arranged so that the streets S are inclined and intersect with the peeling rollers 214 as shown in FIG. 13B.

  Thereby, the position of the chip C which has been cut at the time of attaching the release film 215 or the peeling of the BG tape B does not shift, and does not adversely affect the subsequent processes such as the pickup of the expanded chip C. .

(8) Wafer separation process (Step S8)
After peeling the BG tape B, the wafer W is placed on an expand table (not shown) with the expand tape E down, and the frame F is pushed down or the frame F is fixed and the table is raised to raise the expand tape E. And the distance between the chips C is increased.

  The expanded wafer W is picked up from the expanded tape E for each chip C and transported to various subsequent processes.

<< Crack growth evaluation by polishing >>
Next, evaluation of crack growth by polishing in the grinding and removing step (step S3) will be described with reference to FIGS. The polishing method, the division and separation method, their conditions, and the like are basically as described in steps S1 to S8. FIG. 18 is a diagram showing the conditions of the crack growth evaluation, and FIG. 19 is a diagram showing the evaluation results of the crack growth evaluation.

  18A, 18B, and 18C, the horizontal axis is common, each position corresponds to each other, and indicates the polishing time (s). The vertical axis of (A) in FIG. 18 indicates the cutting speed (polishing rate) (μm / s), the vertical axis of (B) indicates ON and OFF of the water supply to the grindstone during polishing, and (C) The vertical axis indicates the temperature (° C.) of the back surface of the wafer W during polishing.

  As shown in FIG. 18A, the rough polishing was performed for a total of 710 μm while changing the polishing rate, then the fine polishing was performed for 13 μm (not shown), and the chemical mechanical polishing (not shown) was performed for 2 μm. In the case of the wafer, as shown in FIG. 18 (B), an interruption period for supplying water to the grindstone or the wafer was provided during the rough polishing. Water supply was stopped after elapse of t1 seconds after the start of polishing, and water supply was restarted after elapse of t2 seconds after the start of polishing. Water was supplied at a flow rate of 10 L / min. Thereafter, the steps S5, S6, and S7 were performed to cut the wafer, and the cut state was observed and evaluated. The results are summarized in FIG. 19, in which the case where the chip was broken well without cracking or dusting was marked as ○, and the one where the chip was cracked or dusted was marked as x.

  As shown in FIG. 18C, the back surface temperature of the wafer W suddenly starts rising after t1 seconds from the start of polishing when the supply of water is stopped, and decreases immediately after t2 seconds after the start of polishing when the supply of water is restarted. Began to do.

  As shown in FIG. 19, when the back surface temperature of the wafer W became 70 ° C. or higher by polishing, the wafer was favorably cut. This is presumably because the cracks formed by the laser developed due to the heat of polishing.

  Therefore, the grinding apparatus according to the present invention includes a means for measuring the temperature of the wafer, a means for turning on / off the water supply to the grindstone or the wafer during the grinding, and a method for setting the wafer temperature to a predetermined value after a predetermined time has elapsed from the start of the grinding. Means for controlling so that the water supply to the wafer is turned off until the time is shorter. As a result, cracks formed by the laser can be propagated, and the wafer can be cut well.

  As described above, according to the present embodiment, the crack in the modified region formed by the laser light by grinding can be propagated, and therefore, the modification formed by the laser light on the cross section of the chip C can be performed. An area can be prevented from remaining. Therefore, it is possible to prevent a problem that the chip C is broken or dust is generated from a cross section of the chip C. Therefore, chips of stable quality can be obtained efficiently. Further, the stress of the pressing member is concentrated on the cutting line of the wafer, so that the cutting can be reliably and efficiently performed. Further, the contamination at the time of cutting is not left on the elastic body on which the wafer is placed, and even if the cutting is continuously performed, the wafer is not adversely affected.

(Note)
As will be understood from the description of the embodiments described in detail above, the present specification includes disclosure of various technical ideas including the following inventions.

  (Supplementary Note 1) A step of adhering a back grinding tape to the front surface of the wafer, and a step of applying a laser beam from the back surface along a cutting line of the wafer to which the back grinding tape is adhered, and entering the inside of the wafer. A modified region forming step of forming minute holes in the modified region by forming the modified region, and substantially the entire surface of the wafer on which the modified region is formed in the modified region forming step is formed in each region. A vacuum suction step of independently and uniformly vacuum suctioning the table, and grinding the wafer from the back surface, the substantially entire surface of which has been suctioned to the table in the suction step, to remove the modified region and remove the micro holes. A grinding step of expanding the wafer in the thickness direction of the wafer, and after the grinding step, the micropores are chemically and mechanically polished on the wafer that has been developed in the thickness direction of the wafer in the grinding step. And a step of attaching an expand tape to the back surface of the wafer polished chemically and mechanically, and pressing the wafer with the expand tape attached to the back surface with a pressing member via the back grinding tape. A cleaving step of cleaving the wafer, a peeling tape for peeling the back grind tape, and a peeling step of peeling the back grind tape with a peel roller, and the cleaved wafer, A method of cutting a semiconductor substrate, comprising: a separating step of dividing an expandable tape into a plurality of chips by stretching the expandable tape.

  According to the invention described in Supplementary Note 1, the backing tape for protection is attached to the surface of the wafer by the mechanism for attaching the tape. After attaching the back grind tape, laser light is incident from the back surface of the wafer along the cutting line to form a modified region inside the wafer, thereby forming minute holes in the modified region. The modified surface is removed by grinding the wafer from the back surface in a state where substantially all of the surface of the wafer having the modified region formed thereon is independently and uniformly adsorbed on the table.

  At this time, the grinding heat generated by the grinding tends to expand in the radial direction together with the surface of the wafer being ground. However, on the other hand, the wafer tends to be prevented from spreading due to its expansion by a wafer vacuum chuck having a large heat capacity.

  As a result, the front surface of the wafer expands due to thermal expansion, while the back surface of the wafer being chucked does not expand due to the vacuum chuck, and attempts to maintain the state as it is. As a result, the modified region formed inside the wafer acts to further expand the modified region in accordance with the difference in expansion between the front surface and the back surface of the wafer, and the cracks further develop. Since the modified region is irradiated with laser light and has a portion that is once melted and recrystallized, crystal grains are large and brittle. When such a modified region appears on the side surface of a chip in the future, dust is generated from the side surface of the chip, and large crystal grains may be chipped from the side surface of the chip. However, since the micro-crack portion that has propagated from the modified region is a pure crystal surface, even if this surface appears on the chip side in the future, it will be dusted from the chip side or chipped as large crystal grains. There is no such thing.

  In this way, the wafer is removed while being ground by the grinding process, and the micro holes are developed in the thickness direction of the wafer to remove the modified region. Next, in order to highlight the work-affected layer formed by grinding and the developed micropores, the entire surface of the wafer is subjected to chemical mechanical polishing (detailed later), and the work-affected layer is completely removed. I do. As a result, only the minute holes remain on the surface, and the remaining area becomes a perfect mirror surface without processing strain. Thereafter, an expanded film is adhered to the back surface of the wafer that has not yet been broken by a mechanism for attaching a tape.

  The wafer to which the expanded film is adhered is turned over and placed on a table provided in a mechanism for peeling off the back grinding tape. Subsequently, one of the cutting lines is cut by a pressing member provided in the peeling mechanism and positioned parallel to the cutting line. After all the cutting lines have been cut, the wafer is rotated 90 degrees and the other cutting line is cut.

  After the cleaving, the adhesive force of the back grinding tape is reduced by ultraviolet irradiation or heating. The peeling tape is adhered to the back grinding tape having the reduced adhesive strength by the peeling roller to be peeled off. On the wafer from which the back grinding tape has been peeled, the expanded film is expanded to separate the chips. As a result, it is possible to prevent the modified region formed by the laser beam from remaining on the cross section of the chip. For this reason, it is possible to prevent a problem that the chip is broken or generate dust from the cross section of the chip, and to efficiently obtain a chip of stable quality.

  Further, since the wafer is divided after the back surface of the ground wafer is subjected to chemical mechanical polishing, the die strength of the chip can be increased. Here, the chemical mechanical polishing is largely distinguished from the etching process in the polishing step shown in the cited document 2.

  First, the chemical liquid in the present application is different from the etching liquid in Reference 2. The etching solution in the cited document 2 has a function of dissolving the substrate spontaneously, that is, etching, when the liquid acts on the substrate surface. Thereby, even in a portion where a crack has occurred, the etching liquid penetrates and the surroundings are naturally etched, so that the modified layer formed by the laser is further enlarged. Further, in the case of the conventional etching solution, as described above, the etching solution excessively penetrates inside the cracks, causes the cracks to propagate, and finally penetrates into the portion between the chip and the film. As a result, the etchant may reach the chip surface, and the chip surface may be eroded by the etchant, so that each chip device may not function.

  On the other hand, the abrasive (slurry) used in the chemical mechanical polishing of the present application has no etching action under a static condition. That is, even if only the polishing agent is supplied to the wafer, the etching does not proceed at all, but merely modifies the wafer surface. For this reason, even if the abrasive enters a crack at a line where the wafer is to be cut, the surrounding silicon is not melted, and the crack does not further develop.

  As a result, cracks may develop in the polishing step, ie, the etching step, in Reference 2, but in the polishing step of the present application, cracks hardly progress because the wafer is not etched at all even if the abrasive is left alone. . As a result, the conventional problem that the abrasive penetrates the chip from the film due to penetration of the abrasive and the abrasive wraps around the chip surface and erodes the chip, causing the chip device to not function. There is no.

  Here, the mechanism of chemical mechanical polishing is as follows. That is, in polishing, an abrasive is first supplied to the wafer, but only the surface of the wafer is chemically modified. Next, since the modified surface is softened, the abrasive grains contained in the slurry act on the wafer surface in this state, so the wafer surface can be efficiently removed even with very small stress. is there.

  For example, in the case of a process for removing silicon, a silica-based slurry is used. When a silica-based slurry is used, the following reaction occurs on the wafer surface.

[Equation 1]
Si (-OH) + SiOH = SiO2 + H2O
That is, the wafer surface immediately after polishing usually has Si atoms. This Si atom is hydrated on the surface in water, and -OH exists on the surface of the Si atom. The OH groups attached to the surface of the Si substrate are combined with SiOH of silica sol existing in the liquid and SiOH existing on the surface of the silica particles.

  However, this alone does not allow the etching to proceed. As a result, in this state, the polishing pad containing a large amount of silica particles is moved relative to the substrate, and the silica particles act on the substrate surface under a certain amount of momentum, so that a certain temperature is obtained. Under the environment and pressure environment, the chemical reaction proceeds and is mechanically removed.

  At this time, the silica sol or silica particles that have permeated the cracks do not have the effect of further promoting the cracks. This is because the polishing pad does not enter into the crack, so that no mechanical action works, and as a result, no chemical removing action occurs.

  As a result, a chemically modified slurry containing silica sol and silica particles is supplied to the work-affected layer on the substrate surface generated during grinding, and a mechanical friction action acts when the polishing pad comes into contact with the substrate. In combination with this, only the substrate surface is chemically and mechanically polished and removed (Toshiro Dohi, edited by Semiconductor CMP Technology (Industrial Research Group) (2001) pp. 40-42).

  As a result, most of the work-affected layer on the wafer surface is removed. Further, the surface of the formed wafer becomes a mirror surface. The principle of the mirror surface is as follows when compared with the chemical etching described in the cited document 2.

  In the case of chemical etching, as described above, lattice distortion and crystal defect portions in a crystal such as silicon are selectively etched. As a result, etch pits are formed or the holes are greatly eclipsed along the crystal grain boundaries, and this is in principle unavoidable.

  On the other hand, in the case of the chemical mechanical polishing, as described above, the chemical removing action does not work unless the mechanical action works. Mechanical action, here rubbing the wafer surface with a polishing pad, this mechanical action occurs with equal probability on all substrate surfaces, irrespective of the crystalline state of the substrate surface . For this reason, since all the surfaces are uniformly removed regardless of the crystal state, a chemical action is effected, so that the surfaces are uniform, have no crystal defects, and have a mirror surface. Here, since a mirror surface is ambiguous from a relative viewpoint, in this application, it is defined as a mirror surface obtained by chemical mechanical polishing.

  By performing such chemical mechanical polishing, it is possible to obtain an ideal mirror surface state, which is significantly different from that of the cited document 2, and to prevent erosion due to the penetration of the etching solution between the chip and the film.

  After the chemical mechanical polishing, the chips are not completely broken yet. Only the micropores that have evolved from the modified layer are left on the surface after partial chemical mechanical polishing. The modified layer has already been removed in the previous grinding process.

  When the state in which the micropores that have evolved from the modified layer are left is formed in a surface state that has been subjected to grinding and etching as shown in, for example, Patent Document 2, micropores that have evolved from the modified layer, The unevenness promoted by the etching treatment after the grinding cannot be clearly distinguished. Therefore, when the chip is cut, the chip is not necessarily broken from the minute hole, but depending on the case, the ground streak may be broken from the uneven portion further promoted by etching.

  When the surface is subjected to chemical mechanical polishing as in the present application, there is almost no unevenness on the wafer surface after the treatment, and only micropores extending from the modified layer are left. Therefore, when the cutting process is performed in this state, the cracks are further developed from the minute holes, and the cutting is performed.

  As described above, in the method of the present invention, even after the grinding and the chemical mechanical polishing, the micropores are enlarged and the crack is propagated, but the substrate is not completely divided. If cracks develop during grinding or chemical mechanical polishing and the substrate is completely divided, chips on the outer peripheral part of the wafer, in particular, cannot withstand the shear stress during grinding and polishing, and are separated from the suction table. There is a problem of causing chipping.

  However, in the invention of the present application, even after grinding and polishing, the cracks are propagated but not completely divided. In order to further propagate the crack from a state where it is not completely divided and completely cleave it, a step of further fracturing is required. In the cleaving process, after an expand tape is attached to the back surface of the wafer, a pressing member is pressed through the tape to locally apply a bending stress to the wafer. This makes it possible to cut efficiently with the cracks developed by grinding as starting points.

  Here, when the expand tape is not stuck, the wafer is directly pressed by the pressing member, and when the wafer is cut, the vibration of the crack is propagated in the wafer surface. The propagated vibration may cause other parts of the cutting line to be incidentally split, or may split parts other than the cutting line.

  However, by applying the stress by the pressing member through the tape by attaching the expand tape, the tape absorbs the vibration of the crack when the wafer is cut, so that unnecessary vibration is not generated. Further, since the expanded tape is adhered in a stretched state without wrinkles or deviations, a constant tension is constantly applied to the wafer, and the wafer is in a restrained state. When the wafer is cleaved when the wafer is cleaved, the bending deformation of various parts of the wafer is restrained, and the pressing force of the pressing member is bent against the advanced crack portion, which is a weak rigid portion inside the wafer. Instead, it concentrates as shear stress. As a result, only the portion to be cut is cut efficiently, and the portion other than the cutting line is protected and does not break.

  In particular, when the tape is attached to both sides of the wafer, the vibration of the cracks is completely contained, and the bending of the wafer is further restrained, so that efficient cleaving becomes possible.

  (Supplementary Note 2) A step of attaching a back grinding tape to the front surface of the wafer, and a laser beam is incident from the back surface along a cutting line of the wafer on which the back grinding tape is attached to the front surface to enter the inside of the wafer. By forming the modified region, a modified region forming step of forming minute holes in the modified region and the substantially entire surface of the wafer on which the modified region is formed in the modified region forming step are performed. And a step of independently adsorbing to the table in each area, and in a state where the wafer is adsorbed, grinding the laser beam to a portion before the modified area formed inside the wafer to remove the wafer. A first grinding step for growing microcracks extending from the quality region in the depth direction of the substrate, a second grinding step for grinding and removing a modified region formed inside the wafer, and a chemical process for modifying the wafer surface. While performing chemical mechanical polishing using a polishing pad and a polishing pad, leaving a micro-crack extending from the modified region, removing the work-affected layer introduced in the first and second grinding steps to make the surface mirror-finished. And a step of attaching an expand tape to the back surface of the wafer whose front surface is mirror-finished, and pressing the wafer with the expand tape attached to the back surface with a pressing member via the back grinding tape. A cutting step of cutting the wafer, and a peeling tape to which the back grinding tape is peeled off, and a peeling step of peeling the back grinding tape with a peeling roller. A method of cutting a semiconductor substrate, comprising: a separating step of dividing an expandable tape into a plurality of chips by stretching the expandable tape.

  According to the invention described in Supplementary Note 2, the reforming region is initially formed at a deep position inside the wafer, and the removal processing is performed while generating the grinding heat in the first grinding step at the initial stage, whereby the reforming is performed. It is possible to propagate the crack formed in the region to a deeper position in the wafer.

  However, in the first grinding step, if the region modified by laser is also ground and removed with the same capacity as the region not modified, the modified region has a large grain boundary, so large crystal grains are chipped off, More fatal cracks may develop with these grains. Therefore, in the first grinding step, it is preferable to perform grinding up to a portion before the modified region where the crystallinity is constant.

  In the second grinding step, the region modified mainly by the laser is ground. At this time, the grinding wheel also has a high count, that is, a grinding wheel having a finer grain size than the first grinding process is used. Perform gentle grinding to avoid inducing In the second grinding step, only the modified region is used, and the grinding rate is set to be smaller than that in the first grinding step, and the material is finely cut off.

  After the laser modified region is removed, chemical mechanical polishing is finally performed. In the chemical mechanical polishing, a polishing liquid such as a polymer or a nonwoven fabric is pressed against a wafer while supplying a chemical liquid for modifying the wafer, and the wafer is chemically and mechanically polished.

  If chemical mechanical polishing is performed on the modified region, large crystal grains may be chipped off in the modified region. In the chemical mechanical polishing, a polishing pad such as a nonwoven fabric or a foamed polyurethane is used. Therefore, if the chipped crystal grains enter the surface of the pad, the chipped crystal grains constantly generate a scratch during polishing. In such a case, the polished surface is full of scratches without removing the work-affected layer in the grinding process and achieving the purpose of mirror finishing.

  For this reason, in the state of being introduced into the chemical mechanical polishing step, the modified layer introduced by the laser in the previous second grinding step must be completely removed.

  (Supplementary Note 3) A modified layer is formed by laser light along the cutting line, the back grind tape is adhered to the front surface, and the elastic body is attached to the upper surface of the wafer on which the expand tape is adhered to the back surface. Placed on a table, and rotating the table so that the pressing member is parallel to the cutting line, pressing and rolling the pressing member against the wafer to cut the cutting line. 3. The method for cutting a semiconductor substrate according to Supplementary Note 1 or 2.

  According to the invention described in Supplementary Note 3, in the cleavage of the wafer, a back grinding tape is attached to the front surface, and the wafer on which the modified layer is formed by the laser light incident from the back surface is ground and polished after the back surface is polished. The expanding tape is stuck on the back surface by the tape sticking mechanism.

  The wafer to which the back grinding tape and the expand tape are attached on both sides is placed on a table provided with a mechanism for peeling the back grinding tape and having an elastic body attached to the upper surface. Subsequently, a pressing member provided in the peeling mechanism is positioned parallel to the cutting line, pressed and rolled, and one of the cutting lines is cut.

  After all the cutting lines have been cut, the wafer is rotated 90 degrees and the other cutting line is cut. The adhesive strength of the back-grinding tape is reduced by irradiating ultraviolet rays or heating the cleaved wafer. The peeling tape is adhered to the back grinding tape having the reduced adhesive strength by the peeling roller to be peeled off. On the wafer from which the back grinding tape has been peeled, the expanded film is expanded to separate the chips. As a result, the cutting is reliably and efficiently performed, and even if the cutting is performed continuously, the cutting can be performed continuously without adversely affecting the subsequent wafer.

  (Supplementary Note 4) The method for cutting a semiconductor substrate according to Supplementary Note 3, wherein the pressing member is formed to have a radius smaller than an interval between the cutting lines.

  According to the invention described in Supplementary Note 4, the radius of the pressing member is formed to be smaller than the interval between the cutting lines formed on the wafer to be pressed. Since the radius is smaller than the interval between the cutting lines, the pressing member does not press the plurality of cutting lines at once and the stress is not dispersed. As a result, stress can be concentrated on one cutting line to act on it, and the cutting can be reliably and efficiently performed.

  (Supplementary Note 5) The cutting of the semiconductor substrate according to Supplementary Note 3 or 4, wherein the elastic body has grooves, holes, or irregularities formed at intervals equal to or smaller than the size of the chip formed on the wafer. Method.

  According to the invention described in Supplementary Note 5, the elastic body on which the wafer is placed has grooves, holes, or irregularities formed on the surface. The elastic body is preferably an elastic body having a small compression set and having no void so that a change in the initial elastic modulus and the elastic modulus after several uses are small. Since grooves, holes, or irregularities are formed in the elastic body at intervals equal to or smaller than the size of the chips formed on the wafer, the wafer can be locally deformed, and the cutting can be reliably and efficiently performed.

  (Supplementary Note 6) When sticking the back grinding tape or the expanding tape, the sticking roller is rolled in a direction intersecting obliquely with respect to the cutting line formed in a lattice shape and sticking. 6. The method for cutting a semiconductor substrate according to any one of Supplementary Notes 3 to 5, wherein:

  According to the invention described in Supplementary Note 6, when the back grinding tape or the expanding tape is attached to the front surface and the back surface of the wafer, the table on which the wafer is mounted is rotated by about 45 degrees, thereby forming a grid. After pressing the sticking roller in a direction obliquely crossing the cut line, the tape is stuck by being rolled.

  If the cutting line is cut by the pressing force of the tape application roller, it becomes difficult to apply the tape with high accuracy due to air bubbles entering the application surface and collapse in the chip direction. By moving the tape application roller so as to cross the cutting line so as to be inclined, the cutting can be reliably and efficiently performed without adversely affecting subsequent steps.

  DESCRIPTION OF SYMBOLS 1 ... Laser dicing apparatus, 2 ... Grinding apparatus, 3 ... Tape peeling apparatus, 11 ... Wafer moving part, 13 ... Suction stage, 20 ... Laser optical part, 30 ... Observation optical part, 40 ... Laser head, 50 ... Control part, 118: coarse grinding stage, 120: fine grinding stage, 122: polishing stage, 132, 136, 138, 140: chuck, 146, 154: cup-shaped grindstone, 156: polishing cloth, 211: table, 212: elastic body, 212a ... groove, 213 ... supply reel, 214 ... peeling roller, 215 ... peeling tape, 216, 217 ... guide roller, 218 ... take-up reel, 219 ... pressing member, B ... BG tape, C ... chip, E ... expand Tape, F: Frame, K: Modified area, L: Laser beam, S: Cutting line, W: Work

Claims (2)

In wafer processing equipment to obtain chips with high bending strength,
Concentrating the pulsed laser light at a position deeper than half the thickness of the wafer from the back side of the wafer, modified area forming means for forming independent modified areas at regular intervals inside the wafer,
Grinding means for grinding and removing a laser transmitting portion from the back surface of the wafer to the focal point, leaving a small crack extending downward from the focal point of the pulsed laser light,
After the grinding, polishing means for removing the processing strain of the grinding while leaving the micro-cracks,
Wafer processing device for obtaining chips with high bending strength. In the wafer processing method to obtain chips with high bending strength,
Concentrating the pulsed laser light at a position deeper than half the thickness of the wafer from the back side of the wafer, a modified region forming step of forming independent modified regions at regular intervals inside the wafer,
A grinding step of grinding and removing a laser light transmitting portion from the back surface of the wafer to the focal point, leaving a small crack extending downward from the focal point of the pulsed laser light,
After the grinding, a polishing step of removing the processing strain of the grinding while leaving the micro-cracks,
Wafer processing method for obtaining chips with high bending strength having

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