JP2020074454A - Laser processing system and laser processing method for improving chip strength - Google Patents

Abstract

To improve the chip strength.SOLUTION: A laser processing device includes modified region forming means that irradiates the inside of a wafer with pulsed laser light emitted from a laser oscillator from the back surface side of a semiconductor wafer via a condenser lens to form a modified region having an independent minute hole at regular intervals inside the wafer, and modified region position control means that adjusts the modified region forming position to a position where a crack extending from the minute hole in the modified region develops and becomes a starting point of cutting of the semiconductor wafer when the modified region is ground and removed from the back surface of the semiconductor wafer, and the modified region position control means includes relative Z direction position adjustment means of the semiconductor wafer by a table, and condensed lens position control means by Z fine movement means constituted by a piezoelectric element.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for cleaving a wafer having a modified region formed therein with a laser beam.

  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, an expand tape is attached to the back surface of the semiconductor substrate, and a knife is applied from above the expand tape. It is described that a semiconductor substrate is cut into chips by applying an edge and breaking the substrate with the modified region as a base point.

  Further, in Patent Document 1, a semiconductor substrate mounted with the back surface facing upward is irradiated with a laser to form a modified region inside the substrate, and then the substrate is ground to be thinned and expanded on the back surface of the semiconductor substrate. It is described that a substrate is mounted and a expandable tape is stretched to split the substrate from the modified region as a base point.

  In Patent Document 2, by irradiating a semiconductor substrate mounted with the back surface facing upward with a laser to form a modified region inside the substrate, a crack is generated in the thickness direction of the semiconductor substrate, and the back surface of the substrate is It is described that a semiconductor substrate is cut into chips by exposing cracks on the back surface by grinding and chemical etching. Further, in Patent Document 2, cracks are generated in the thickness direction from the modified region by causing thermal stress by giving a natural or relatively small force, for example, an artificial force or a temperature difference to the substrate. It is described that it occurs.

Japanese Patent No. 3624909 Japanese Patent No. 3762409

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

  Therefore, there is a problem that variations occur in the cracks of the substrate, and if the cracks do not progress slowly, the substrate is broken even in the chip. In addition, when stress is sequentially applied locally to the part to be cut into the substrate, for example, when many chips are collected from one substrate, there are many cutting lines. However, there is a problem that productivity is extremely reduced.

  Further, when an external force is applied to break the substrate, a very large stress is required when breaking the wafer unless the substrate is thinly processed.

  In particular, when the substrate thickness is sufficiently thick 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 neatly and vertically due to the effect of the sudden external force. Therefore, it may be necessary to irradiate several laser pulses in multiple steps in the thickness direction of the substrate.

  Further, in the inventions described in Patent Documents 1 and 2, the modified region formed inside the substrate by the laser irradiation is finally left on the cross section of the chip. Therefore, dust may be generated from the modified region of the chip cross section. Further, 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 becomes small.

  In the invention described in Patent Document 2, it is described that the crack naturally occurs in the thickness direction from the modified region, but on the other hand, when the crack naturally breaks, the crack may not necessarily crack naturally. In order to inevitably obtain the stable effect of breaking, it is sometimes necessary to take an arbitrary means, and when it naturally breaks, it is not an arbitrary means.

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

  Further, in the invention described in Patent Document 2, after the semiconductor substrate is ground, chemical etching is performed on the back surface. However, after grinding, a grinding streak due to fixed abrasive grains remains on the surface after grinding, and accompanying minute cracks. Are formed, and the work-affected layer remains. When the surface is chemically etched, a portion having a large lattice strain such as a microcrack is selectively etched. Therefore, the microcracks are instead promoted to become large cracks. Therefore, not only the cutting start region, but sometimes the micro cracks formed by grinding and etching may break, which poses a problem that stable cutting is difficult.

  Further, since the unevenness of the substrate surface is promoted by etching, the substrate surface is not mirror-finished. As a result, since unevenness is left in the divided chips as well, it is sufficiently possible to break the chip from large unevenness, that is, minute cracks, and there is a problem that the bending strength of the chip becomes low.

  Further, when the etching solution acts on the modified portion after laser processing, the modified portion is once melted, recrystallized, and solidified, so that a large grain boundary is formed.

  When the etching liquid acts on such a grain boundary portion, the etching progresses so that the silicon grains are peeled off from the grain boundary, so that the unevenness is further promoted.

  Specifically, in the cited document, p.12_1 line, it is described that the polishing step is a grinding step and performing chemical etching on the back surface. In the case of chemical etching, even if the chemical etching is left as it is, the chemical etching liquid penetrates into the cracks and has a function of melting the cracked portions.

  In particular, when the cracks extend to the surface of the substrate, the etching liquid penetrates between the chips and the film to which the chips are adhered, causing a problem of peeling the chips from the film.

  Moreover, even if the crack does not extend to the surface of the substrate, the etching proceeds along the crack. Especially when etching is performed in a thinned state after grinding, the etching solution penetrates into the cracks by a capillary phenomenon, deepens the microcracks while melting the crack tips, and a new etching solution further enters there. Become. In this case, when the etching liquid acts on the vicinity of the device surface, the vicinity of the device surface may be melted, and the etching may proceed to the inside of the element. 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 and secondary problems associated therewith may be induced.

  Further, in such a case, as a result, a crack may advance to the surface, and an etching solution may partially enter between the chip and the film, causing a problem that the chip is peeled off during the process. In particular, when the substrate becomes thin after grinding, cracks are likely to proceed with a small external force, and chip peeling occurs when the crack reaches the surface. It must be processed so that it does not proceed any further.

  Although Patent Document 2 describes that a crack is generated from the modified region by grinding the back surface of the substrate, Patent Document 2 does not describe a method of fixing the substrate when grinding the substrate. .. When the outer circumference 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 adsorbed as shown in FIG. In such a case, cracking does not occur in the modified region even if the back surface of the substrate is ground because it is not restrained.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method of cleaving a semiconductor substrate that can efficiently obtain chips of stable quality.

  In order to achieve the above object, one aspect of a method for cleaving a semiconductor substrate according to the present invention is a wafer cleaving method for cleaving a wafer having a modified region formed therein with a laser beam, wherein the wafer surface is uniformly tabled. In the step of vacuum adsorption to, the wafer backside is removed by grinding in a state of vacuum adsorbing the wafer, while advancing the microcracks extending from the modified region in the wafer depth direction, leaving the advanced microcracks. A grinding step of grinding and removing the modified region, a grinding step of performing a chemical mechanical polishing of the back surface of the wafer after the grinding step, and a step of cleaving the wafer after the mirroring step. Characterize.

  In one aspect of the method for cleaving a semiconductor substrate according to the present invention, in the grinding step, the back surface of the wafer is removed by grinding from a portion before the modified region, and a microcrack extending from the modified region is formed in the wafer depth. It is preferable to include a first grinding step of advancing in a direction and a second grinding step of grinding and removing the modified region formed inside the wafer while leaving the advanced microcracks.

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

  According to the semiconductor substrate cleaving method of the present invention, the cleaving can be performed reliably and efficiently, and chips of stable quality can be efficiently obtained.

The figure which shows the general structure of the laser dicing apparatus 1. FIG. 3 is a conceptual configuration diagram showing a configuration of a driving unit of the laser dicing device 1. FIG. 3 is a plan view showing a configuration of driving means of the laser dicing device 1. The figure which shows the general structure of the grinding device 2. The elements on larger scale of the grinding device 2. The elements on larger scale of the grinding device 2. 3 is a schematic view of a polishing stage of the grinding device 2. FIG. It is a figure which shows the detail of the chuck | zipper of the grinding device 2, (a) is a top view, (b) is sectional drawing, (c) is a partially expanded view. The side view of the tape peeling apparatus 3. The side sectional view showing the state of cleaving. FIG. 4 is a side sectional view showing a state of the pressed elastic body. The perspective view which showed the mode of cleaving. The perspective view which showed the attachment method of a tape. The flowchart which showed the cutting method of the semiconductor substrate which concerns on this invention. The figure explaining a grinding removal process. It is a figure explaining crack progress 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 the front surface of wafer W, (d) is the state of wafer W Sectional view. The figure explaining the surface state of the wafer W back surface after a grinding removal process. The figure shown about the conditions of crack growth evaluation. The figure which showed the evaluation result of crack growth evaluation. The figure which shows the fixed state at the time of the conventional substrate grinding. The figure which shows the fixed state at the time of the conventional substrate grinding.

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

  The present invention includes a laser dicing device 1, a grinding device 2, a tape peeling device 3, and a carrying device (not shown) for carrying a wafer processed by the laser dicing device 1 to the grinding device 2 or the tape peeling device 3. The cutting device is composed of an expanding device that separates the wafers cut by the tape peeling device 3.

<About device configuration>
(1) About Laser Dicing Device 1 FIG. 1 is a diagram showing a general configuration of the laser dicing device 1. As shown in the figure, the laser dicing apparatus 1 of 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 that holds the wafer W by suction, and an XYZθ table 12 that is provided on the main body base 16 of the laser dicing apparatus 1 and that moves the suction stage 13 precisely in the XYZθ directions. The wafer moving unit 11 precisely moves the wafer W in the XYZθ directions in the drawing.

  A back grinding tape (hereinafter, BG tape) B having an adhesive material is attached to the surface of the wafer W on which the device is 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. It

  The wafer W may be mounted on the suction stage 13 in such a state that a dicing sheet having an adhesive material is attached to one surface of the wafer W and the wafer W is integrated with the frame via the dicing sheet. In this case, it is placed on the suction stage 13 with its surface facing upward.

  The laser optical unit 20 includes a laser oscillator 21, a collimator lens 22, a half mirror 23, a condensation lens (condensing lens) 24, a driving unit 25 that slightly moves the laser light in parallel to the wafer W, and the like. The laser light emitted from the laser oscillator 21 is focused inside the wafer W through an optical system such as a collimator lens 22, a half mirror 23, and a condensation lens 24. The position of the focal point in the Z direction is adjusted by the Z direction fine movement of the condensation lens 24 by the Z fine movement means 27 described later.

  The conditions of the laser light are as follows: the light source is a semiconductor laser-excited Nd: YAG laser, the wavelength is 1064 nm, the laser light spot cross-sectional area 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 beam quality is TEM00, and the polarization characteristic is linear polarization. The conditions of the condensation lens 24 are that the magnification is 50 times and N. 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 collimator lens 32, a half mirror 33, a condensation lens 34, a CCD camera 35 as an observation means, 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 the optical system such as the collimator lens 32, the half mirror 33, and the condensation lens 24. The reflected light from the surface of the wafer W is incident on a CCD camera 35 as an observation means via the condensation lens 24, the half mirrors 23 and 33, and the condensation lens 34, and a surface image of the wafer W is captured.

  The imaged data is input to the image processing unit 38, used for alignment of the wafer W, and also 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 the like, and controls the operation of each unit of the laser dicing device 1.

  The laser dicing apparatus 1 is composed of a wafer cassette elevator, a wafer transfer means, an operation plate, an indicator lamp and the like, which are not shown.

  The wafer cassette elevator vertically moves a cassette in which wafers are stored and positions the cassette at a transfer position. The transfer unit transfers the wafer between the cassette and the suction stage 13.

  Switches and a display device for operating each part of the dicing device 10 are attached to the operation plate. The indicator lamp displays the operating status of the dicing device 10, such as during processing, processing completion, and emergency stop.

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

  A piezoelectric element that expands and contracts when a voltage is applied is used for the Z fine movement means 27. Due to the expansion and contraction of the piezoelectric element, the condensation lens 24 is slightly moved in the Z direction, and the position of the laser light focusing point in the Z direction is precisely positioned.

  The holding frame 28 is supported by two pairs of parallel springs made up of four piano wires (not shown), is movable in the XY directions, and is restrained from moving in the Z direction. The supporting method of the holding frame 28 is not limited to this, and may be sandwiched by a plurality of balls in the vertical direction to restrain the movement in the Z direction and support the holding frame 28 so as to be movable in the XY directions.

  Piezoelectric elements are used for the linear fine movement means PZ1 and PZ2, like 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 28.

  FIG. 3 is a plan view of the driving means 25. As shown in FIG. 3, two linear fine movement units PZ1 and PZ2 are arranged in the X direction, one end of each 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, by controlling the applied voltage, the condensation lens 24 can be reciprocated in the X direction and the laser beam can be reciprocated in the X direction or oscillated.

  A piezoelectric element may be used for either one of the linear fine movement units 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 condensation lens 24. The Z-direction position of the focused point of the irradiated laser light 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 condensation 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 condensation lens 24 is finely moved back and forth by the linear fine movement means PZ1 and PZ2 provided in the laser head 40, and the laser light L is transferred to the wafer W. The laser light L is oscillated in parallel in the X direction or in any XY direction, and the modified point K is formed while the focusing point of the laser light L slightly vibrates inside the wafer. As a result, one line of the modified region K due to multiphoton absorption is formed inside the wafer W along the cutting line of the wafer W.

  If necessary, the Z fine movement means 27 may apply vibration in the Z direction. Further, the laser light L is slowly and reciprocally moved in the X direction, which is the processing direction, and the wafer W is sent in the X direction, so that the laser light L is repeatedly irradiated in a back and forth state like perforations. Good.

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

  When the modified region is formed along all the cutting lines parallel to the X direction, the XYZθ table 12 is rotated by 90 °, and the modified region is also formed on all the lines orthogonal to the previous line.

(2) Grinding Device 2 FIG. 4 is a perspective view showing the general configuration of the grinding device 2. The main body 112 of the grinding device 2 is provided with an alignment stage 116, a rough 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 rough grinding stage 118, the fine grinding stage 120, and the polishing stage 122 are partitioned by a partition plate 125 (not shown in FIG. 4) as shown in FIG. 5, and the machining liquids used in the respective stages 118, 120, 122 are adjacent to each other. 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, 140 installed on the index table 134. ..

  The rough grinding stage 118 is a stage for performing rough polishing, and is surrounded by the side surface of the main body 112, the top plate 128, and the 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 arranged on the upper surface and the side surfaces of the partition plate 125 to isolate the rough grinding stage 118 and the fine grinding stage 120 from the outside. Further, the top plates 128 and 129 are formed with through holes 128A and 129A through which the heads of the respective stages are inserted.

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

  As shown in FIG. 6, a brush 126B is attached to the side surface of the casing 126 through which the partition plate 125 passes, and this brush 126B has an upper surface 125A and a top surface 125A of the partition plate 125 when the chuck 140 is in the processing position. The side surface 125B is contacted. As a result, when the chuck 140 is located at the processing position, it is held in a substantially airtight state by the casing 126, the partition plate 125, and the brush 126B.

  Since the polishing stage 122 performs chemical mechanical polishing, the polishing liquid contains a chemical polishing agent. When the grinding liquid is mixed with such a polishing liquid, the concentration of the chemical polishing agent is lowered and the processing time becomes long. By keeping the polishing stage 122 in a substantially airtight state, it is possible to prevent the grinding processing liquid or processing waste used in the fine grinding stage 120 from entering the polishing stage 122, and the polishing processing liquid used in the polishing stage 122 can be prevented. Can be prevented from scattering from the polishing stage 122. Therefore, it is possible to prevent processing defects due to the mixing of both processing liquids.

  FIG. 7 is a structural diagram of the polishing stage 122. On the polishing stage 122, polishing is performed by the polishing cloth 156 and the slurry supplied from the polishing cloth 156, and the work-affected layer formed on the back surface of the wafer W by the rough polishing and the fine polishing is removed. The work-affected layer is a general term for striations, work strain (the crystal is altered) and the like caused by grinding.

  The polishing cloth 156 of the polishing stage 122 is attached to the polishing head 161 connected to the output shaft 160 of the motor 158. Guide blocks 162, 162 forming a linear guide are provided on the side surface of the motor 158, and the guide blocks 162, 162 are vertically movably engaged with a guide rail 166 provided on the side surface of the support plate 164. Has been done. 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 the horizontally arranged arm 168. A base end portion of the arm 168 is connected to an output shaft 174 of a motor 172 arranged inside the casing 170. Therefore, when the motor 172 is driven, the arm 168 can rotate about the output shaft 174. Thereby, the range between the polishing position of the polishing cloth 56 (see the solid line in FIG. 3), the polishing cloth cleaning position by the polishing cloth cleaning stage 123 (see the chain double-dashed line in FIG. 3), and the dressing position by the polishing cloth dressing stage 127. Can be moved within. When the polishing cloth 156 is moved to the polishing cloth cleaning position, the polishing cloth cleaning stage 123 cleans the surface of the polishing cloth 156 and removes polishing dust and the like adhering to the surface. The polishing cloth 156 can be exemplified by foamed polyurethane, a polishing cloth, etc., and the polishing cloth cleaning stage 123 is provided with a removing member such as a brush for removing polishing dust. The removing member is rotationally driven when the polishing cloth 156 is washed, and the polishing cloth 156 is also rotationally driven by the motor 158. The polishing cloth dressing stage 127 is made of the same material as the polishing cloth 156, for example, foamed polyurethane.

  Guide blocks 176 and 176 forming a linear guide are provided on a side surface of the casing 170, and the guide blocks 176 and 176 are vertically movable on a guide rail 180 provided on a side surface of a housing 178 for a screw feeder. Is engaged with. Further, a nut member 179 is provided on the side surface of the casing 170 so as to project. The nut member 179 is screwed to the screw rod 181 of the screw feeder arranged 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 feeding device and the rectilinear action of the guide block 176 and the guide rail 180. Thereby, the polishing cloth 156 is largely moved in the vertical direction, and the distance between the polishing head 161 and the wafer W is set to a predetermined distance.

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

  In the present embodiment, the polishing cloth 156 is applied as the polishing body, but the present invention is not limited to this, and if the work-affected layer can be removed, for example, a polishing grindstone or an electrophoresis of abrasive grains or the like can be used. You may apply. When a polishing grindstone or electrophoresis of abrasive grains is applied, quantitative polishing is preferably performed.

  Returning to the explanation of FIG. The alignment stage 116 is a stage for aligning the wafer W transferred from the laser dicing device 1 by a transfer device (not shown) to a predetermined position. The wafer W aligned by the alignment stage 116 is adsorbed and held by a transfer robot (not shown), and then conveyed toward an empty chuck 132, and adsorbed and held on an adsorption surface of the chuck 132.

  The chuck 132 is installed on the index table 134, and chucks 136, 138, 140 having the same function are installed at intervals of 90 degrees on the circumference around the rotation axis 135 of the index table 134. .. A spindle (not shown) of a motor (not shown) is connected to the rotary 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 adsorbed wafer W is finally ground (fine grinding, spark out) here. The chuck 140 is positioned on the polishing stage 122 in FIG. 4, and the adsorbed wafer W is polished here, and the work-affected layer caused by grinding and the variation in the thickness of the wafer W are removed.

  Here, the chucks 132, 136, 138, 140 will be described. The chucks 136, 138, and 140 have the same configuration as the chuck 132, so 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. FIG. 8A is a plan view of the chuck 132, FIG. 8B is a sectional view taken along line AA ′ in FIG. 8A, and FIG. It is a figure.

  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. A suction hole 132c for vacuum suction is formed on the lower side of the chuck body 132b into which the mounting table 132a is fitted. The chuck 132 is preferably formed of a material having low thermal conductivity.

  On the mounting table 132a, as shown in FIG. 8C, the wafer W is mounted via the BG tape B. As shown in FIG. 8C, the mounting table 132a is formed such that when the wafer W is mounted on the mounting table 132a, a part of the outer periphery of the wafer W protrudes from the mounting table 132a. Is about 1.5 mm. The wafer W used in this 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) coupled to the fluid coupling sucks air. Therefore, the substantially entire surface of the wafer W is firmly vacuum-adsorbed on the surface of the mounting table 132a. As a result, the wafer W and the mounting table 132a can be brought into close contact with each other on the surface without displacement.

  As shown in FIG. 7, the chucks 132, 136, 138, 140 are connected at their lower surfaces with a spindle 194 and a motor 192, 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. Accordingly, 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. It is possible to save the trouble of connecting 138, 140.

  The piston 119 of the cylinder device 117 is connected to the lower portion of the motor 192. When the piston 119 is extended, the piston 119 is fitted into a recess (not shown) formed in the lower portion of the chucks 132, 136, 138, 140 and connected. 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 the like, 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 measuring gauges (not shown) connected to the control unit 100. Each of these measuring gauges has a contact, and the contact is in contact with the upper surface (back surface) of the wafer W and the other contact is in contact with the upper surface of the chuck 132. These measurement gauges can detect the thickness of the wafer W as a difference between in-process gauge readings with the upper surface of the chuck 132 as a reference point. The thickness may be measured in-line with a measuring gauge. The method of measuring the thickness of the wafer W is not limited to this.

  By rotating the index table 134 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 rough grinding stage 118, and the wafer W is moved by the cup-shaped grindstone 146 of the rough grinding stage 118. The back surface of W is roughly ground. As shown in FIG. 4, the cup-shaped grindstone 146 is connected to an output shaft (not shown) of the motor 148, and is attached to the grindstone feeding device 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 by this downward movement, the cup-shaped grindstone 146 is pressed against the back surface of the wafer W. As a result, the back surface of the wafer W is roughly ground. The controller 100 sets the descending movement amount of the cup-shaped 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. To be done. The control unit 100 also controls the rotation speed of the cup-shaped grindstone 146 by controlling the rotation speed of the motor 148.

  The thickness of the wafer W whose back surface is roughly ground by the rough grinding stage 118 is measured by a measuring gauge (not shown) connected to the control unit 100 after the cup-shaped grindstone 146 is retreated from the wafer W. By rotating the index table 134 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 finely moved by the cup-shaped grindstone 154 of the fine grinding stage 120. Grinded and sparked out. Since the structure of the fine grinding stage 120 is the same as the structure of the rough grinding stage 118, the description thereof will be omitted here. The amount of grinding by the cup-shaped grindstone 154 is set by the control unit 100, and the processing movement amount and the rotation speed 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 measuring gauge (not shown) connected to the control unit 100 after the cup-shaped grindstone 154 is retracted from the wafer W. When the index table 134 is rotated 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 placed on the polishing stage 122, and chemical mechanical polishing is performed by the polishing cloth 156 of the polishing stage 122. The back surface of the wafer W is mirror-finished. The vertical movement distance of the polishing pad 156 is set by the controller 100, and the position of the polishing pad 156 is controlled by controlling the motor 182 by the controller 100. Further, the control unit 100 controls the rotation speed of the motor 158, that is, the rotation speed of the polishing cloth 156.

  For the wafer W polished by the polishing stage 122, the arm 168 is rotated by the controller 100 and the polishing cloth 156 is retracted from the position above the wafer W, and then the hand (not shown) of the robot (not shown). Then, the wafer is sucked and held by and is transported to the wafer cleaning stage 124. As the wafer cleaning stage 124, a stage having a rinse cleaning function and a spin drying function is applied. The wafer W that has been polished does not easily break because the work-affected layer has been removed, and therefore does not break during transportation by the robot and during cleaning in the wafer cleaning stage 124.

  The wafer W, which has been cleaned and dried by 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 tape peeling device 3 adheres the BG tape B or the expanded tape E to the wafer W. Further, the wafer W ground and polished by the grinding device 2 is cut 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 off the BG tape B attached to the surface of the wafer W is fed from the supply reel 213 to guide rollers 216, 217. After that, it is wound around 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 has a lattice shape or a lattice shape as shown in FIG. 10 at intervals equal to or smaller than the size of the chip C formed on the wafer W. .. are formed in parallel with each other. The elastic body 212 is connected to a vacuum generating source (not shown), the BG tape B is attached to the front surface by the grooves 212a, 212a, etc., and the elastic body 212 is mounted on the frame F via the expand tape E attached to the back surface. The formed wafer W is formed so that it can be fixed by suction.

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

  For example, when the sponge-like elastic body 212B shown in FIG. 11A in which a large number of small voids are formed is used for cleaving the wafer W, the voids become small and the compression permanent due to the flattening of the voids. Distortion occurs. For this reason, when the elastic body 212B is repeatedly used, the elastic coefficient gradually changes due to deformation, and stable cleaving cannot be performed.

  In addition, as shown in FIG. 11B, in the elastic body 212C having no groove, hole, or unevenness, when a part of the elastic body is pushed in, the volume around the elastic body 212C is constant, so that the portion around the pushed up portion rises. It will be. In this case, even if an attempt is made to locally squeeze the wafer by sinking it, the stress is dispersed and it becomes difficult to efficiently sever the wafer.

  On the other hand, as shown in FIG. 11C, the elastic body 212 has room for lateral deformation due to the groove 212a when pressed from above, so that uniform deformation occurs and a cutting line desired to be cleaved. Stress concentrates on S, and reliable and efficient cutting can be performed.

  As shown in FIG. 10, the pressing member 219 is formed so that the radius R is smaller than the interval L between the cutting lines S where the modified layer P is formed. Since 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 concentrates on the cutting line S desired to be cleaved, and reliable and efficient cleaving can be performed.

  As shown in FIG. 12, the cleavage of the wafer W is performed by adhering the BG tape B on the front surface of the wafer W on which the modified layer P is formed along the cutting line S and the expanding tape E on the rear surface side. As shown in FIG. 12, the tape peeling device 3 rotates the table 211 and adjusts the position of the wafer W so that the pressing member 219 is parallel to one of the cutting lines S formed in a lattice shape.

  In this state, the pressing member 219 is pressed against the wafer W and is rolled, so that the wafer W is cut along the one cutting line S. After the cutting of one of the cutting lines S, the table W on which the wafer W is placed is rotated 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 is 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 surface and the back surface of the wafer W, when the cutting line S is cut after cutting one cutting line S, the BG tape B and the expanding tape E are used. The position is restrained, and the chip interval does not greatly expand in the already cut cutting line S. As a result, not only the vertical deformation due to the elastic body 212 but also the lateral deformation due to the large distance between the chips C is prevented from locally distributing the stress of the pressing member 219, and the stress is concentrated. Cleavage can be performed reliably and efficiently.

  In addition, since the BG tape B and the expanding tape E are attached to the front surface and the back surface, fragments or the like generated when the wafer W is cleaved do not adhere to the elastic body 212, and the next wafer W is elastic. Even if it is placed on 212, no adverse effect due to the fragments will occur.

  The peeling roller 214 is formed of an elastic body that is softer than the elastic body 212. The BG tape B has, for example, an ultraviolet-curable adhesive on the adhered surface, and its adhesive strength is reduced by being irradiated with ultraviolet rays by an ultraviolet irradiation device (not shown) provided inside or outside the tape peeling device 3. .. As shown in FIG. 9, the peeling film 215 is rolled on the BG tape B having the reduced adhesive force by rolling the peeling roller 214 in the lateral direction (direction of arrow A in FIG. 9) while pressing the peeling roller 214 downward. It is attached.

  After the peeling film 215 is attached, 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 lateral direction (direction of arrow B shown in FIG. 9). ), The BG tape B is peeled from the wafer W.

  When the peeling film 215 is attached by the peeling roller 214 or when the BG tape B is peeled off, the cutting line S for dividing the chip C into the peeling roller 214 is divided 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 inclines with respect to the peeling roller 214 as shown in FIG. 13B.

  As a result, the position of the cleaved chip C is not displaced when the peeling film 215 is attached or when the BG tape B is peeled off, and it does not adversely affect subsequent steps such as picking up the chip C after expansion. ..

(4) Expanding Device Next, an expanding device (not shown) will be described. As the expander, a conventional normal expander can be used. For example, an expanding device having the following configuration disclosed in Japanese Patent Laid-Open No. 2007-173587 can be used.

  That is, the peripheral portion of the expand tape E is fixed to the frame F having a frame shape. A ring member is in contact with the lower surface of the inner portion of the peripheral edge of the expanded tape E. The outer peripheral edge portion 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. As a result, the dicing tape is expanded and the distance between the chips is widened. At this time, since the outer peripheral edge portion of the upper surface of the ring member is smoothly chamfered, the expand tape E is expanded smoothly.

  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, etc.), a motor and a screw (combination of a male screw as a shaft and a female screw as a bearing) can be adopted.

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

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

  The BG tape B is attached to the wafer W by a tape attaching device (not shown). When adhering the BG tape B, the table 211 is rotated by 45 degrees so that the cutting line S dividing the chip C intersects the adhering roller for adhering the tape at an angle. This prevents the wafer W from being cut along the cutting line S by the pressure of the sticking roller while the BG tape B is stuck to the wafer W.

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

  When the laser light L is emitted from the laser oscillator 21, the laser light L is irradiated to the inside of the wafer W via the optical system such as the collimator lens 22, the half mirror 23, and the condensation lens 24, and is re-introduced into the inside of the wafer W. A quality region K is formed.

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

  The controller 50 scans the surface of the wafer W in parallel with a pulsed laser beam L for processing to form a plurality of discontinuous modified regions K ... Inside the wafer W. Inside the modified region K, minute holes (hereinafter referred to as cracks) are formed. 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)
After the modified region K is formed along the cutting line S by the laser modification process (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 controlled by the control unit 100.

  The transferred wafer W is placed on the 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-adsorbed by the chuck 132.

  The index table 134 is rotated about the rotating shaft 135, and the chuck 132 is carried into the rough grinding stage 118 to roughly polish the wafer W.

  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 Co., Ltd. is used as the cup-shaped grindstone 146, and the rotation speed of the cup-shaped grindstone 146 is about 3000 rpm.

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

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

  Therefore, as shown in FIG. 15, the modified layer is removed in the grinding step, and the modified region K due to 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 crushing from the cross section of the chip, cracking the chip C from the crushed portion, and generating dust from the crushed portion.

  In addition, in the present embodiment, the grinding and removing step includes a crack developing step of causing cracks in the modified layer to propagate in the thickness direction of the wafer W. 16A and 16B are views for explaining a mechanism in which a crack propagates. FIG. 16A is a schematic diagram at the time of grinding, FIG. 16B is a state of the back surface of the wafer W, FIG. 16C is a state of the front surface of the wafer W, and FIG. It is sectional drawing of the wafer W at the time of 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, the surface opposite to the ground surface, that is, the surface of the wafer W, is substantially vacuum-adsorbed by the vacuum chuck as shown in FIG. 16C, and is laterally moved so as not to be displaced due to thermal expansion. Is physically constrained against displacement to.

  That is, as shown in FIG. 16D, when the back surface (grinding surface) of the wafer W is disk-shaped due to thermal expansion, it tends to expand in the outer peripheral direction (displacement due to thermal expansion), whereas the front surface of the wafer W (displacement due to thermal expansion). The suction surface) is constrained so as not to physically displace each point on the wafer surface which is about to spread. Therefore, strain is generated inside the wafer, and the crack propagates in the thickness direction of the wafer W due to this internal strain. This internal strain acts equally between the portion that expands due to thermal expansion and each point in the wafer surface that is physically constrained. The crack growth due to the internal strain is most efficient at the initial stage of grinding, that is, at the time of rough polishing, where the grinding amount is the largest and the frictional force is also large, that is, the friction heat can be large.

  The laser modified region is formed at a relatively deep position near the thickness of the chip. Therefore, in the initial stage of grinding, the distance from the grinding surface to the laser modified layer is relatively large, but the modified layer is relatively close to the target surface to the extent of crack propagation. Therefore, in order to propagate cracks, it is advisable to promote the thermal expansion of the wafer W by the grinding heat at the initial stage of rough polishing.

  Even if grinding is performed under the condition of thermally expanding the wafer W, that is, under the condition of generating a large amount of frictional heat (for example, using less grinding liquid), the shearing stress of grinding is immediately exerted on the modified layer. Not even a thing. In the present embodiment, the crack does not propagate due to the shear stress due to grinding, but the thermal expansion due to the grinding heat is the dominant factor for crack propagation.

  When the cracks are propagated by the internal strain, the cracks can be uniformly propagated at each point in the wafer W plane regardless of the rigidity variation in the wafer W plane. .. Therefore, it is possible to prevent stress from concentrating on a portion having a low rigidity due to the presence of defects in the surface of the wafer W as in the case where artificial stress is applied.

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

  The internal strain due to the thermal expansion of the wafer W is distinguished from so-called thermal stress caused by the temperature difference. The thermal stress is generated in proportion to the temperature gradient, but in the present embodiment, the generated heat escapes to the chucks 132, 136, 138, 140, so that the thermal stress is not generated.

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

  After the precise polishing, the index table 134 is rotated about the rotary 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. In the grinding removal step (step S3). The work-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, polyurethane-impregnated non-woven cloth (for example, TS200L manufactured by Tokyo Seimitsu Co., Ltd.) is used as the polishing cloth 156, colloidal silica is used as the slurry, and the rotation speed of the polishing cloth 156 is about 300 rpm.

  By the grinding and removing step (step S3), the back surface of the wafer W has many irregularities as shown in FIG. When polishing is performed by chemical etching, the surface shape is maintained as it is, so cracks may occur from the recesses, and the surface is not mirror-finished. On the other hand, in the present embodiment, since the chemical mechanical polishing is performed, the processing strain caused by the processing is removed, and the unevenness on the surface is removed to give a mirror surface.

  That is, in order to improve the quality of the final product, the chip C, two processes, that is, 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) Expand tape attaching step (step S5)
The expand tape E is attached to the back surface of the wafer W that has undergone the chemical mechanical polishing step (step S4). Expanded tape is a type of elastic tape that can expand and contract.

  Adhesion of the expanded tape E to the wafer W is performed by a tape attachment device (not shown) as in the case of attaching the BG tape B in step S1. When the expanded tape E is attached, the table 211 is rotated 45 degrees so that the cutting line S that divides the chip C, like the BG tape B, is inclined and intersects the attachment roller to which the tape is attached. Let

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

(6) Wafer cleaving process (step S6)
The wafer W to which the expand tape E is attached is conveyed to the tape peeling device 3, the pressing member 218 is pressed against the wafer W, and the wafer W is cut along the cutting line S, so that the wafer W is cut into individual chips C. Will be divided.

  In the cutting of the wafer W, the elastic member 212 is provided on the upper surface of the wafer W so that the pressing member 219 is parallel to one of the cutting lines S, which is a cutting line formed in a lattice shape as shown in FIG. It is placed on the table 211. In this state, the pressing member 219 is pressed against the wafer W and is rolled, so that the wafer W is cut along the one cutting line S. After the cutting of one cutting line 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, and the other cutting line S is arranged. 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 has a lattice shape or a lattice shape as shown in FIG. 10 at intervals equal to or smaller than the size of the chip C formed on the wafer W. .. are formed in parallel with each other. As a result, as shown in FIG. 11C, the elastic body 212 has room for lateral deformation due to the groove 212a in response to pressure from above, so that uniform deformation occurs and the cutting line S desired to be cleaved. The stress concentrates on the and reliable cutting can be performed efficiently.

  As shown in FIG. 10, the pressing member 219 is formed so that the radius r is smaller than the interval l between the cutting lines S in which the modified region K is formed, so that the pressing member 19 forms one cutting line S. When pressing, it is not necessary to press another cutting line S. As a result, stress concentrates on the cutting line S desired to be cleaved, and reliable and efficient cleaving can be performed.

  In the cutting of the wafer W, since the BG tape B and the expanding tape E are attached to the front surface and the back surface, when cutting one cutting line S and then cutting the adjacent cutting line S, the BG tape B and the expanding tape E are cut. The position of the chip is restrained by E, and the chip interval does not greatly expand in the cutting line S that has already been cut. As a result, not only the vertical deformation due to the elastic body 212 but also the lateral deformation due to the large distance between the chips C is prevented from distributing the local stress of the pressing member 218, so that the stress is concentrated. Cleavage can be performed reliably and efficiently.

  In addition, since the BG tape B and the expanding tape E are attached to the front surface and the back surface, fragments or the like generated when the wafer W is cleaved do not adhere to the elastic body 212, and the next wafer W is elastic. Even if it is placed on 212, no adverse effect due to the fragments will occur.

(7) BG tape peeling process (step S7)
The peeling film 215 of the cleaved wafer W is attached 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 that is softer than the elastic body 212. The BG tape B has, for example, an ultraviolet-curable adhesive on the adhered surface, and its adhesive strength is reduced by being irradiated with ultraviolet rays by an ultraviolet irradiation device (not shown) provided inside or outside the tape peeling device 3. .. As shown in FIG. 9, the peeling film 215 is rolled on the BG tape B having the reduced adhesive force by rolling the peeling roller 214 in the lateral direction (direction of arrow A in FIG. 9) while pressing the peeling roller 214 downward. It is attached.

  After the peeling film 215 is attached, the take-up unit 218A including the two-winding reel 18 and the guide roller 217 winds the peeling film 215 together with the peeling roller 214 in the lateral direction (arrow B shown in FIG. 9). BG tape B is peeled from the wafer W by moving in the direction).

  When the peeling film 215 is attached by the peeling roller 214 or when the BG tape B is peeled off, the cutting line S for dividing the chip C into the peeling roller 214 is divided 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 incline with respect to the peeling roller 214 as shown in FIG. 13B.

  As a result, the position of the cleaved chip C is not displaced when the peeling film 215 is attached or when the BG tape B is peeled off, and it does not adversely affect subsequent steps such as picking up the chip C after expansion. ..

(8) Wafer separation step (step S8)
After the BG tape B is peeled off, the wafer W is placed on the expanding table (not shown) with the expanding tape E facing down, and the frame F is pushed down or the frame F is fixed and the expanding tape E is raised. And the distance between the tips C is widened.

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

<< Evaluation of crack growth by polishing >>
Next, with reference to FIG. 18 and FIG. 19, description will be made on the evaluation of crack growth due to polishing in the grinding removal step (step S3). The polishing method, the division and separation method, and the conditions thereof are basically the same as those in steps S1 to S8. FIG. 18 is a diagram showing conditions for crack growth evaluation, and FIG. 19 is a diagram showing evaluation results of crack growth evaluation.

  In (A), (B), and (C) of FIG. 18, the horizontal axis is common, the positions correspond to each other, and the polishing time (s) is shown. The vertical axis of (A) of FIG. 18 shows the cutting speed (polishing speed) (μm / s), the vertical axis of (B) shows ON / OFF of the water supply to the whetstone during polishing, (C) The vertical axis indicates the temperature (° C.) on the back surface of the wafer W during polishing.

  As shown in (A) of FIG. 18, rough polishing was performed for a total of 710 μm while changing the polishing rate, then fine polishing was performed for 13 μm (not shown), and further chemical mechanical polishing (not shown) was performed for 2 μm. In the case of a wafer, as shown in FIG. 18B, an interruption period of water supply to the grindstone or the wafer was provided during the rough polishing. Water supply was stopped after t1 seconds had elapsed after the start of polishing, and water supply was resumed after t2 seconds had elapsed after the start of polishing. Water was supplied at a flow rate of 10 L / min. After that, the above steps S5, S6, and S7 were performed to cleave the wafer, and the cleaved state was observed and evaluated. The results are summarized in FIG. 19, in which the chip was satisfactorily cracked without dusting or dusting, and the chip was cracking or dusting.

  As shown in (C) of FIG. 18, the back surface temperature of the wafer W starts to rise abruptly after t1 seconds have passed since the start of polishing when water supply was stopped, and immediately after t2 seconds have elapsed since the start of polishing when water supply was restarted. Started to do.

  As shown in FIG. 19, when the back surface temperature of the wafer W was 70 ° C. or higher due to polishing, the wafer was satisfactorily cleaved. It is considered that this is because the crack formed by the laser developed due to the heat of polishing.

  Therefore, the grinding apparatus according to the present invention, means for measuring the temperature of the wafer, means for turning ON / OFF the water supply to the grindstone or the wafer during grinding, and the wafer temperature to a predetermined value after a predetermined time has elapsed from the start of grinding. And means for controlling to turn off the water supply to the wafer. Thereby, the cracks formed by the laser can be propagated and the wafer can be satisfactorily cut.

  As described above, according to the present embodiment, since the crack in the modified region formed by the laser light can be propagated by grinding, the modification formed by the laser light on the cross section of the chip C can be performed. You can avoid leaving any areas. Therefore, it is possible to prevent a problem that the chip C is broken or dust is generated from the cross section of the chip C. Therefore, a chip of stable quality can be efficiently obtained. Further, the stress of the pressing member is concentrated on the wafer cutting line, and the cutting can be surely and efficiently performed. Furthermore, no contamination is left on the elastic body on which the wafer is placed when the wafer is cut, and even if the wafer is continuously cut, the wafer is not adversely affected.

(Appendix)
As can be understood from the description of the embodiments detailed above, the present specification includes disclosure of various technical ideas including the following inventions.

  (Supplementary Note 1) A step of adhering a back grind tape to the front surface of the wafer, and a laser beam is incident from the back surface along the cutting line of the wafer having the back grind tape adhered to the front surface to the inside of the wafer. A modified region forming step of forming minute holes in the modified region by forming the modified region, and a substantially entire surface of the wafer on which the modified region is formed in the modified region forming step Independently and uniformly vacuum-adsorbing on the table, a vacuum adsorption step, and by removing the modified region by grinding the back surface of the wafer whose substantially entire surface is adsorbed on the table in the adsorption step, and removing the minute holes. And a grinding step for advancing in the thickness direction of the wafer, and after the grinding step, the micropores are chemically mechanically polished in the grinding step in which the microscopic holes have progressed in the thickness direction of the wafer. A step of attaching an expand tape to the back surface of the wafer that has been chemically mechanically polished, and pressing the wafer having the expand tape attached to the back surface with a pressing member via the back grind tape. And a cleaving step of cleaving the wafer, affixing a peeling tape for peeling the back grind tape, a peeling step of peeling the back grind tape with a peeling roller, and the divided wafer, A method of cutting a semiconductor substrate, comprising a step of dividing and separating the expanded tape into a plurality of chips by stretching.

  According to the invention described in appendix 1, a backgrinding tape for protection is attached to the surface of the wafer by a mechanism for attaching the tape. After adhering the back grinding 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 microscopic holes in the modified region. The wafer is ground from the back surface to remove the modified region while the substantially entire surface of the wafer on which the modified region is formed is adsorbed uniformly on the table with the respective values of the substrate independently.

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

  As a result, the front surface of the wafer is expanded by thermal expansion, while the back surface of the chucked wafer is not expanded by the vacuum chuck and tries to maintain the same state. As a result, the modified region formed inside the wafer acts so as to further expand the modified region according to the difference in expansion between the front surface and the back surface of the wafer, and cracks further develop. Since the modified region has a portion which is once re-crystallized by being irradiated with laser light, the crystal grains are large and fragile. When such a modified region appears on the side surface of the chip in the future, in addition to dust generation from the side surface of the chip, large crystal grains may be chipped from the side surface of the chip. However, since the microcrack portion that has evolved from the modified region is a pure crystal plane, even if this plane appears on the side surface of the chip in the future, dust will be generated from the side surface of the chip or large crystal grains will be generated and chipped. There is no such thing.

  In this way, the wafer is removed by grinding in the grinding step, and the microscopic holes are developed in the thickness direction of the wafer to remove the modified region. Next, in order to make the work-affected layer formed by grinding and the developed micropores stand out, chemical mechanical polishing is performed on the entire surface of the wafer (described in detail later) to completely remove the work-affected layer. To do. As a result, only minute pores remain on the surface, and the remaining area becomes a perfect mirror surface with no machining strain. After that, the expand film is attached to the back surface of the wafer which is not yet broken by the mechanism for attaching the tape.

  The wafer to which the expand film is attached is turned over and placed on the table provided in the mechanism for peeling the back grinding tape. Then, one of the cutting lines is cut by the pressing member provided in the peeling mechanism, which is positioned parallel to the cutting line. After all the one cutting lines are cleaved, the wafer is rotated 90 degrees and the other cutting line is cleaved.

  After cleaving, the adhesive force of the back grind tape is reduced by UV irradiation or heating. The peeling tape is adhered to the back grind tape having the reduced adhesive force by the peeling roller to perform peeling. The expand film is expanded on the wafer from which the back grinding tape has been peeled off, and the chips are separated from each other. This can prevent the modified region formed by the laser beam from remaining on the cross section of the chip. Therefore, it is possible to prevent a defect that the chip is broken or dust is generated from the cross section of the chip and efficiently obtain a chip of stable quality.

  Further, since the back surface of the ground wafer is chemically mechanically polished and then the wafer is divided, the bending strength of the chip can be increased. Here, the chemical mechanical polishing is largely distinguished from the etching treatment in the polishing step shown in the cited document 2.

  First, the chemical liquid used in the present application is different from the etching liquid disclosed in Reference 2. The etching liquid in the cited document 2 has a function of naturally melting the substrate, that is, etching by the action of the liquid on the surface of the substrate. As a result, the etching liquid permeates even in the portion where the crack is generated and the surrounding area is naturally etched, which has the effect of further increasing the size of the modified layer formed by the laser. Further, in the case of the conventional etching solution, as described above, the etching solution penetrates too much into the cracks to develop the cracks, and finally penetrates into the portion between the chip and the film. As a result, the etching solution may reach the surface of the chip, and the surface of the chip may be corroded by the etching solution, 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 static conditions. That is, even if only the polishing agent is supplied to the wafer, etching does not proceed at all, and the surface of the wafer is simply modified. Therefore, even if the polishing agent enters into the cracks in the planned cutting line of the wafer, it does not melt the surrounding silicon, and the cracks do not progress any further.

  As a result, cracks may develop in the polishing step or the etching step in the reference document 2, but in the polishing step of the present application, the wafer is not etched at all even if an abrasive is put and left, so the cracks hardly progress. .. As a result, the conventional problem that the abrasive penetrates and peels the chip from the film without permission, or the abrasive wraps around the chip surface and erodes the chip, causing the chip device to stop functioning There is no.

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

  For example, for processes that remove silicon, silica based slurries are used. When using a silica-based slurry, the following reactions occur on the wafer surface.

[Equation 1]
Si (-OH) + SiOH = SiO2 + H2O
That is, usually, there are Si atoms on the wafer surface immediately after polishing. This Si atom is hydrated on the surface in water, and -OH exists on the Si atom surface. 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 silica particles.

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

  At this time, the effect of further developing the crack does not work due to silica sol or silica particles that have penetrated into the crack. This is because the polishing pad does not enter the cracks, so that the mechanical action does not work and, as a result, the chemical removing action does not occur.

  As a result, the work-affected layer on the surface of the substrate generated during grinding is supplied with a chemical slurry containing silica sol and silica particles, and the polishing pad comes into contact with the substrate to cause mechanical friction. Together with this, only the substrate surface is chemically mechanically polished and removed (edited by Toshio Dohi: Detailed Semiconductor CMP Technology (Industrial Research Society) (2001) p.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 in the cited document 2.

  In the case of chemical etching, as described above, lattice strain and crystal defect portions are selectively etched in crystals such as silicon. As a result, etch pits may be formed, and large cuts may occur along the crystal grain boundaries, which cannot be avoided in principle.

  On the other hand, in the case of chemical mechanical polishing, as described above, the chemical removing action does not work unless the mechanical action works. The mechanical action, here the rubbing of the wafer surface by the polishing pad, has nothing to do with the crystalline state of the substrate surface, but it occurs with equal probability on all substrate surfaces. .. Therefore, since all surfaces are uniformly removed regardless of the crystalline state, a chemical action is exerted, so that the surface is a uniform surface and has no crystal defects, and becomes a mirror surface. Here, since the mirror surface is ambiguous from a relative point of view, in the present 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 very different from the reference document 2, and it is possible to prevent erosion due to the penetration of the etching solution between the chip and the film.

  After the chemical mechanical polishing, the chips were not completely broken. It only leaves micropores that have evolved from the modified layer 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 remain is formed in a surface state that is subjected to grinding and etching as shown in the cited document 2, for example, the microvoids that have evolved from the modified layer, It becomes impossible to clearly distinguish the unevenness promoted by the etching treatment after the grinding. Therefore, when the chip is cleaved, it is not always fractured from the minute holes, and in some cases, the ground striations that are ground may be fractured 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 surface of the wafer after the treatment, and only micropores that have evolved from the modified layer are left. Therefore, when the cleaving process is performed in this state, the cracks further develop from the minute holes and cleave.

  As described above, in the method of the present invention, even after the grinding and the chemical mechanical polishing, the micropores become large and the cracks propagate, but the substrate is not completely divided. If a crack develops during grinding or chemical mechanical polishing and the substrate is completely divided, the chips on the outer periphery of the wafer in particular cannot withstand the shearing stress during grinding or polishing and are peeled off from the adsorption table. There is a problem of causing chipping.

  However, in the present invention, although the cracks propagate even after grinding and polishing, they are not completely divided. In order to further develop the crack from the state where the crack is not completely broken and to completely break the crack, a step of further breaking is necessary. In the cleaving step, after the expanded tape is attached to the back surface of the wafer, the pressing member is pressed through the tape to locally apply bending stress to the wafer. As a result, it is possible to efficiently fracture the crack starting from the crack propagated by grinding.

  Here, when the expand tape is not attached, the wafer is directly pressed by the pressing member, and when the wafer is cleaved, the vibration of the crack propagates in the wafer surface. The propagating vibration may be incidentally broken by other parts of the cutting line or may break parts other than the cutting line.

  However, by attaching the expand tape and applying stress by the pressing member via the tape, the tape absorbs the vibration of the crack when the wafer is cleaved, so that unnecessary vibration is not generated. Further, since the expanded tape is attached in a stretched state without wrinkles or deviations, a constant tension is constantly applied to the wafer and the wafer is restrained. When the wafer is constrained when it is cleaved, the bending deformation of various parts of the wafer is constrained, and the pressing force of the pressing member bends against the developed crack part where the rigidity is weak inside the wafer. Instead, it concentrates as shear stress. As a result, only the part to be cut is efficiently cut, and the part other than the cutting line is protected and is not broken.

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

  (Supplementary Note 2) A step of adhering a back grind tape to the front surface of the wafer, and a step of applying laser light from the back surface along the cutting line of the wafer having the back grind tape adhered to the front surface to the inside of the wafer. By forming the modified region, the 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 formed. In the same manner, the step of independently adsorbing to the table in each region, and in the state where the wafer is adsorbed, the laser beam is incident to grind and remove the portion before the modified region formed inside the wafer, First grinding step for propagating microcracks extending from the quality region in the depth direction of the substrate, second grinding step for grinding and removing the modified region formed inside the wafer, and chemical polishing for modifying the wafer surface. While performing chemical mechanical polishing using a polishing pad and a polishing pad, leaving the microcracks extending from the modified region, the work-affected layer introduced in the first and second grinding steps is removed to mirror the surface. Step, a step of attaching an expand tape to the back surface of the wafer whose surface is mirror-finished, and the wafer in which the expand tape is attached to the back surface are pressed by a pressing member via the back grind tape. And a cleaving step of cleaving the wafer, affixing a peeling tape for peeling the back grind tape, a peeling step of peeling the back grind tape with a peeling roller, and the divided wafer, A method of cutting a semiconductor substrate, comprising a step of dividing and separating the expanded tape into a plurality of chips by stretching.

  According to the invention described in appendix 2, the reforming region is initially formed at a deep position inside the wafer, and is removed and processed in the first grinding step while generating the grinding heat. It is possible to propagate the crack formed in the region to a deeper position in the wafer.

  However, in the first grinding step, when the laser-modified region having the same capacity as the unmodified region is ground and removed, the modified region has a large crystal grain boundary, and thus large crystal grains are chipped off, With such crystal grains, a fatal crack may further develop. Therefore, in the first grinding step, it is preferable to grind up to the portion before the modified region where the crystallinity is constant.

  In the second grinding step, the laser-modified region is mainly ground. At this time, the grinding wheel also has a high count, that is, a grinding wheel having a finer grain size is used as compared with the first grinding step, and fatal cracks or defects derived from the modified region are obtained as compared with the first grinding step. A gentle grinding process is carried out so as not to induce. The second grinding step is performed only on the modified region, and the grinding rate is set to be smaller than that of the first grinding step, and the fine grinding is performed.

  Then, after the laser modified region is removed, chemical mechanical polishing is finally performed. In chemical mechanical polishing, a polishing pad such as a polymer or a non-woven fabric is pressed against a wafer while supplying a chemical liquid that modifies the wafer to perform chemical and mechanical polishing.

  If chemical mechanical polishing is performed on the modified region, large crystal grains may drop off in the modified region. Since a polishing pad made of non-woven fabric or polyurethane foam is used in chemical mechanical polishing, scratched crystal grains constantly generate scratches during polishing if such dropped crystal grains enter the pad surface. In such a case, it is necessary to remove the work-affected layer in the grinding process and achieve the mirror-finished surface, and the scratched surface is covered with scratches.

  Therefore, in the state of being introduced into the chemical mechanical polishing step, the modified layer introduced by the laser in the above 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 having the expand tape adhered to the back surface. It is placed on a table, and the table is rotated so that the pressing member is parallel to the cutting line, and the pressing member is pressed against the wafer and rolled to cut the cutting line. The method for cutting a semiconductor substrate according to Supplementary Note 1 or Supplementary Note 2.

  According to the invention described in appendix 3, a back grinding tape is adhered to the front surface of the wafer when cleaving the wafer, and the back surface of the wafer having the modified layer formed by the laser light incident from the rear surface is ground and polished. The expanding tape is attached to the back surface by the tape attaching mechanism.

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

  After all the one cutting lines are cleaved, the wafer is rotated 90 degrees and the other cutting line is cleaved. The adhesive force of the back grind tape is reduced on the cleaved wafer by UV irradiation or heating. The peeling tape is adhered to the back grind tape having the reduced adhesive force by the peeling roller to perform peeling. The expand film is expanded on the wafer from which the back grinding tape has been peeled off, and the chips are separated from each other. As a result, the cleaving is surely and efficiently performed, and even if the cleaving is continuously performed, the cleaving can be continuously performed 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 with a radius smaller than an interval between the cutting lines.

  According to the invention described in appendix 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, it is possible to concentrate the stress on one cutting line and act it, so that the cutting can be performed reliably and efficiently.

  (Supplementary note 5) The semiconductor substrate according to Supplementary note 3 or Supplementary note 4, wherein 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. Method.

  According to the invention described in appendix 5, the surface of the elastic body on which the wafer is placed is grooved, holed, or roughened. The elastic body is preferably an elastic body having a small compression set and having no voids so that the elastic modulus at the initial stage and the elastic modulus after being used a few times are small. Since the groove, the hole, or the unevenness is formed in the elastic body at intervals equal to or smaller than the size of the chip formed on the wafer, the wafer can be locally deformed, and the cutting can be surely and efficiently performed.

  (Supplementary Note 6) When applying the back grind tape or the expanding tape, the applying roller is applied by rolling in a direction that intersects the cutting lines formed in a grid with an inclination. 6. The method for cutting a semiconductor substrate according to any one of appendices 3 to 5, characterized in that.

  According to the invention described in appendix 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 placed is rotated by about 45 degrees to form a lattice shape. After pressing the sticking roller in a direction intersecting with the cut line inclined, it is rolled to stick the tape.

  If the cutting line is broken by the pressing force of the tape sticking roller, it becomes difficult to stick the tape with high accuracy because of bubbles entering the sticking surface and collapsing in the chip direction. By moving the tape adhering roller so as to intersect with the cutting line so as to be inclined, the cutting can be surely and efficiently performed, and the subsequent steps are not adversely affected.

  DESCRIPTION OF SYMBOLS 1 ... Laser dicing device, 2 ... Grinding device, 3 ... Tape peeling device, 11 ... Wafer moving part, 13 ... Adsorption 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 grindstone, 156 ... Polishing cloth, 211 ... Table, 212 ... Elastic body, 212a ... Groove, 213 ... Supply reel, 214 ... Separation roller, 215 ... Separation 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 light, S ... Cutting line, W ... Work

Claims (2)

In a laser processing system that improves chip strength,
A semiconductor wafer having a protective sheet attached to protect the device surface, a wafer holding unit for holding the protective sheet side to a wafer chuck,
Alignment means for irradiating illumination light emitted from an observation light source from the back surface side of the semiconductor wafer via a condenser lens, observing the front surface of the semiconductor wafer having the device surface, and aligning the semiconductor wafer When,
Pulsed laser light emitted from a laser oscillator is irradiated to the inside of the wafer from the back surface side of the semiconductor wafer via the condenser lens, and a modified region having independent minute holes at regular intervals is formed inside the wafer. A modified region forming means to be formed,
When the modified region is ground and removed from the back surface of the semiconductor wafer, the modified region is located at a position where a crack extending from the micropores in the modified region is a starting point of cutting of the semiconductor wafer. Reforming area position control means for adjusting the formation position of
Equipped with
The modified region position control means has a relative Z direction position adjustment means for the semiconductor wafer by a table and a condensation lens position control means by a Z fine movement means composed of a piezoelectric element.
Laser processing system that improves chip strength. In the laser processing method for improving the chip strength,
A wafer holding step of holding the protective sheet side of the semiconductor wafer with the protective sheet attached to protect the device surface on the wafer chuck,
An alignment step of aligning the semiconductor wafer by illuminating illumination light emitted from an observation light source from the back side of the semiconductor wafer via a condenser lens, observing the front surface of the semiconductor wafer having the device surface. When,
Pulsed laser light emitted from a laser oscillator is irradiated to the inside of the wafer from the back surface side of the semiconductor wafer via the condenser lens, and a modified region having independent minute holes at regular intervals is formed inside the wafer. A modified region forming step to be formed,
When the modified region is ground and removed from the back surface of the semiconductor wafer, the modified region is located at a position where a crack extending from the micropores in the modified region is a starting point of cutting of the semiconductor wafer. A modified region position control step for adjusting the formation position of
Equipped with
The modified region position control step includes a relative Z direction position adjustment step of the semiconductor wafer by a table, and a condensation lens position control step by a Z fine movement unit composed of a piezoelectric element.
Laser processing method to improve chip strength.

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