JP2019087751A - Laser processing device and laser processing method - Google Patents

Abstract

To provide a laser processing device and laser processing method, capable of highly efficiently acquiring a chip with stable quality.SOLUTION: The laser processing device, condensing laser beam into the inside of a wafer to form a modified region, includes: a condenser lens for condensing laser beam into the inside of the wafer; control means for controlling a condensing point position of laser beam by the condensing lens so that the wafer is not broken into chips when reverse face grinding of the wafer has been performed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for cleaving a wafer having a laser modified region inside the wafer.

  In Patent Document 1, a semiconductor substrate placed with the back surface facing upward is irradiated with a laser to form a modified region inside the substrate, and an expand tape is mounted on the back surface of the semiconductor substrate, and a knife is placed on the expand tape. It is described that the semiconductor substrate is cut into chips by applying an edge and dividing the substrate based on the modified region.

  Further, according to Patent Document 1, a semiconductor substrate placed 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 and thinned and expanded on the back surface of the semiconductor substrate. It is described that the substrate is divided with the modified region as a base point by mounting the tape and stretching the expanded tape.

  In Patent Document 2, the semiconductor substrate placed with the back surface facing upward is irradiated with a laser to form a modified region inside the substrate to generate a crack 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 the cracks to the back surface by grinding and chemical etching. In Patent Document 2, cracks are generated in the thickness direction from the modified region by generating thermal stress by applying a relatively small force, for example, an artificial force or a temperature difference to the substrate. It is described that it occurs.

Patent 3624909 Patent No. 3762409

  In the invention described in Patent Document 1, the substrate is divided by applying an external force locally by the knife edge, but in order to apply the external force locally, a bending stress or a shear stress is applied to the substrate. However, it is difficult to uniformly distribute bending stress and shear stress over the entire surface of the substrate. For example, when a bending stress or a shear stress is applied to the substrate, the stress is concentrated at a weak point, and the necessary minimum stress can not be efficiently applied uniformly to the desired portion.

  Therefore, there is a problem that the substrate is unevenly cracked, and the substrate is broken even in the chip if the crack does not progress gradually. In addition, in the case where stress is sequentially applied locally to a portion where a substrate is to be cut for cutting, for example, in the case of collecting a large number of chips from a single substrate, a large number of cutting lines exist. There is a problem that productivity is greatly reduced.

  In addition, when an external force is applied to break the base, if the substrate is not processed thin, there is a problem that a very large stress is required when the wafer is broken.

  In particular, in the case where the substrate thickness is sufficiently large with respect to the modification depth width of laser processing, even if an external force is applied, it is not always possible to cut neatly perpendicular to the substrate under the influence of rapid external force. Therefore, it may be necessary to apply several laser pulses in multiple stages 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 irradiation of the laser finally remains in the chip cross section. Therefore, dust may be generated from the portion of the reformed area of the chip cross section. Moreover, as a result of the chip cross-sectional portion being locally broken, the chip may be broken due to the broken cross section. As a result, there is a problem that the chipping strength of the chip is reduced.

  In the invention described in Patent Document 2, although it is described that a crack naturally occurs in the thickness direction from the reformed region, there is also a case where it does not necessarily fracture naturally when it is broken naturally. In order to necessarily obtain a stable effect of breaking, sometimes it is necessary to take arbitrary measures, and if it can be broken naturally, it does not fall under any arbitrary means.

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

  In the invention described in Patent Document 2, the semiconductor substrate is ground and then chemically etched on the back surface, but after grinding, the surface after grinding remains with a grinding mark due to the fixed abrasive and concomitantly a minute crack Is formed, and the damaged layer remains. When the surface is chemically etched, portions with large lattice distortion such as micro cracks are selectively etched. Therefore, micro cracks are rather promoted and become large cracks. Therefore, not only the cutting starting point region, but sometimes the microcracks formed by grinding and etching sometimes cause breakage, and there is a problem that stable cutting processing is difficult.

  Moreover, since the unevenness of the substrate surface is promoted by the etching, the substrate surface is not mirror-polished. Therefore, since the unevenness remains even in the divided chips, it is sufficiently considered that the chip is broken from a portion with large unevenness, that is, a micro crack, and there is a problem that the die strength of the chip becomes low.

  Furthermore, when the etching solution acts on the laser-processed and reformed portion, the reformed portion is once melted, recrystallized, and solidified, so that large grain boundaries are formed.

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

  As the polishing process, specifically, it is described that the chemical etching is applied to the grinding process and the back surface in the cited document p. 12_1 line. In the case of chemical etching, even if it is left as it is, the chemical etching solution penetrates into the crack and has an effect of melting the crack portion.

  In particular, when the crack has advanced to the surface of the substrate, the etchant penetrates between the chip and the film adhering the chip, causing a problem of peeling the chip from the film.

  Also, even if the crack does not extend to the surface of the substrate, the etching proceeds along the crack. In particular, when etching is performed in a thinned state after grinding, the etchant penetrates into the crack by capillary action, and while the tip of the crack is melted, the micro crack is further deepened, and a new etchant is further introduced into it. Become. In this case, when the etching solution acts in the vicinity of the device surface, the vicinity of the device surface may be melted and etching may proceed to the inside of the element. In addition, even if there is no problem at that time, the etching solution left on the wafer wall may enter the inside of the device and then cause a failure. Therefore, while the processing strain on the wafer surface is removed, the crack may be further promoted, and a concomitant secondary problem 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 may be peeled off during processing. In particular, when the substrate becomes thin after the grinding progresses, the crack is likely to progress with a slight external force, and chip peeling occurs when the crack reaches the surface, so the crack is generated when the substrate becomes thin. It must be processed to prevent further progress.

  Although patent document 2 describes that a crack generate | occur | produces from a modification | reformation area | region by grinding the back surface of a board | substrate, patent document 2 does not describe the fixing method of the board | substrate at the time of grinding a board | substrate. . When the outer periphery of the substrate is supported by fitting the substrate into a retainer or the like as shown in FIG. 17 or when only a part of the substrate is adsorbed as shown in FIG. In this case, even if the back surface of the substrate is ground, no cracking occurs from the modified region.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a wafer processing apparatus and a wafer processing method capable of efficiently obtaining a chip of stable quality.

  A wafer processing apparatus for achieving the object of the present invention is a wafer processing apparatus for processing a wafer having a reformed region formed therein with laser light, wherein the back surface of the wafer is ground with a grinding wheel in a state where the surface of the wafer is adsorbed. And a grinding unit for removing the modified region leaving micro cracks extending from the modified region, and a grinding unit for grinding the back surface of the wafer with a polishing cloth after grinding.

  According to this device, the grinding heat generated by grinding causes thermal expansion and spreading in the radial direction with the wafer surface being ground. However, on the other hand, the wafer tries to prevent its expansion due to the wafer vacuum chuck having a large heat capacity.

  As a result, the back surface of the wafer expands due to thermal expansion, while the surface of the wafer being chucked does not expand by the vacuum chuck and tries to maintain the state as it is. As a result, the modified region formed inside the wafer acts 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 is irradiated with laser light and there is a portion that is once melted and recrystallized, crystal grains are large and fragile. If such a modified region appears on the side of the chip in the future, dust may be generated from the side of the chip and large grains may be missing from the side of the chip. However, the microcracks developed from the modified region are pure crystal faces, so even if this face appears on the side of the chip in the future, dust may be generated from the side of the chip or large crystal grains may be chipped. There is no such thing.

  Thus, the grinding process removes the wafer while shaving it, and the microvoids are developed in the thickness direction of the wafer to remove the modified region. Next, chemical mechanical polishing is performed on the entire surface of the wafer (to be described in detail later) in order to highlight the processing-altered layer formed by grinding and the developed microvoids, and the processing-altered layer is completely removed. Do. As a result, only the microvoids remain on the surface, and the remaining area becomes a perfect mirror surface with no processing distortion.

  After that, the wafer which has not been cracked is placed on a mechanism for cutting the wafer, bending stress is applied to the wafer to cut the wafer, and then the expanded film is pulled to separate the chips from each other. Thereby, it is possible to prevent the modified region formed by the laser light from remaining in the cross section of the chip. Therefore, it is possible to prevent a defect such as cracking of the chip or dust generation from the cross section of the chip, and to efficiently obtain a chip of stable quality.

  In addition, since the back surface of the ground wafer is subjected to chemical mechanical polishing and then the wafer is divided, it is possible to increase the chip bending strength. Here, chemical mechanical polishing is largely distinguished from the etching process in the polishing process shown in the cited reference 2.

  First, the chemical solution in the present application is different from the etching solution in Patent Document 2. The etching solution in Patent Document 2 has an action of spontaneously dissolving the substrate, that is, etching, when the solution acts on the substrate surface. As a result, the etching solution penetrates and naturally etches the periphery even in the part where the crack has occurred, so that the modified layer formed by the laser is made larger. Further, in the case of the conventional etching solution, as described above, the etching solution penetrates too much in the crack to propagate the crack, and finally penetrates to a portion between the chip and the film. As a result, the etching solution may flow to the chip surface, the chip surface may be eroded by the etching solution, and the respective chip devices may not function.

  On the other hand, the abrasive (slurry) used in the chemical mechanical polishing of the present invention has no etching action under static conditions. That is, even if only the polishing agent is supplied to the wafer, the etching does not proceed at all, but merely modifies the wafer surface. Therefore, even if the abrasive gets into the crack in the wafer cutting line, the surrounding silicon is not melted, so that the crack does not progress further.

  As a result, although cracks may develop in the polishing process, ie, the etching process in reference document 2, in the polishing process of the present application, the cracks hardly progress because the wafer is not etched at all even if the abrasive is added and left . As a result, the conventional problem occurs that the abrasive penetrates and the chip is detached from the film by hand, and the abrasive goes around the chip surface to erode the chip and the chip device does not function. There is no.

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

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

  That is, usually, the wafer surface immediately after polishing contains Si atoms. The Si atom is hydrated on the surface in water, and -OH is present on the surface of the Si atom. The OH groups attached to the surface of the Si substrate are connected to SiOH of the silica sol present in the liquid and SiOH present on the surface of the silica particles.

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

  At this time, the effect of further developing the crack does not work by the silica sol or the silica particle that has penetrated the crack. Since the polishing pad does not enter into the cracks, no mechanical action occurs, and as a result, no chemical removal action occurs.

  As a result, the process-altered layer on the substrate surface generated during grinding is supplied with a slurry having a chemical property having silica sol and silica particles, and a mechanical friction action is exerted by the polishing pad contacting the substrate. At the same time, only the substrate surface is chemically and mechanically polished and removed (Toshio Tohi, editor: Detailed Description of Semiconductor CMP Technology (Industrial Survey Committee) (2001), p. 40-42).

  As a result, most of the damaged layer on the wafer surface is removed. Also, the formed wafer surface is a mirror surface. The principle of this mirror surface is as follows in comparison with the chemical etching in the cited reference 2.

  In the case of chemical etching, as described above, lattice distortions and crystal defects are selectively etched in crystals such as silicon. As a result, etch pits are formed, or large etching occurs along grain boundaries, which can not be avoided in principle.

  On the other hand, in the case of chemical mechanical polishing, as mentioned above, chemical removal does not work unless mechanical action works. A mechanical action, here rubbing the wafer surface with the polishing pad, is one that occurs equally on all substrate surfaces, regardless of the crystalline state of the substrate surface at all. . Therefore, since all the surfaces are uniformly removed regardless of the crystalline state, the surface functions chemically, so that the surface is a uniform surface, with no crystal defects, and becomes a mirror surface. Here, since a mirror surface is vague from a relative viewpoint, 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 largely different from the cited document 2, and to prevent the erosion due to the penetration of the etching solution between the chip and the film.

  Incidentally, after chemical mechanical polishing, the chip is not completely broken yet. It only leaves microvoids developed from the modified layer on the surface part after chemical mechanical polishing. The modified layer has already been removed in the previous grinding process.

  When the state in which the microvoids developed from the modified layer are left is formed in the surface state subjected to grinding and etching as shown in, for example, cited reference 2, the microvoids developed from the modified layer, It becomes impossible to distinguish clearly from the unevenness promoted by the etching process after grinding. Therefore, when the chip is cut, it may be considered that breakage does not necessarily occur from the microvoids, and in some cases, the ground grinding streak may be broken from the uneven portion further promoted by the etching.

  As in the present application, when chemical mechanical polishing is applied to the surface, there are few irregularities on the surface of the wafer after processing, and only microvoids developed from the modifying layer are left. Therefore, when the cutting process is performed in this state, the crack further propagates from the microvoids and is cut.

  Further, a wafer processing method for achieving the object of the present invention is a wafer processing method for processing a wafer having a reformed region formed therein by laser light, wherein the grinding wheel grinds the back surface of the wafer in a state where the surface of the wafer is adsorbed. Grinding in which the modified area is removed leaving microcracks extending from the modified area, and a grinding process in which the rear surface of the wafer is polished with a polishing cloth after grinding.

  According to the present invention, it is possible to efficiently obtain a chip of stable quality.

FIG. 1 is a view showing an outline configuration of a laser dicing apparatus 1; FIG. 2 is a conceptual block diagram showing the configuration of drive means of the laser dicing apparatus 1. FIG. 2 is a plan view showing the configuration of drive means of the laser dicing apparatus 1; FIG. 2 is a view showing an outline configuration of a grinding device 2; The elements on larger scale of grinding device 2. The elements on larger scale of grinding device 2. FIG. 5 is a schematic view of a polishing stage of the grinding device 2; It is a figure which shows the detail of the chuck | zipper of the grinding apparatus 2, (a) is a top view, (b) is sectional drawing, (c) is a partially expanded view. The flowchart which shows the flow of processing of the cutting method of a semiconductor substrate. A figure explaining a laser modification process. The figure explaining a cutting line. The figure explaining a grinding removal process. It is a figure explaining crack growth in a grinding removal process, (a) is a schematic diagram at the time of grinding, (b) is a state of wafer W back surface, (c) is a state of wafer W surface, (d) is wafer W Cross section. Diagram for explaining the surface condition of the back surface of the wafer W after the grinding and removing process Diagram explaining the division and separation process Diagram explaining the division and separation process Diagram showing the fixed state during conventional substrate grinding Diagram showing the fixed state during conventional substrate grinding Diagram showing conditions for crack growth evaluation Figure showing the evaluation results of crack growth evaluation The figure which shows the outline of the dividing device 300 Explanatory drawing which shows other embodiment of a chuck | zipper bending means

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

  According to the present invention, a laser dicing apparatus 1, a grinding apparatus 2, a transfer apparatus (not shown) for transferring a wafer processed by the laser dicing apparatus 1 to the grinding apparatus 2, and a chip obtained by grinding the wafer ground by the grinding apparatus 2 It is performed by the cutting device comprised with the dividing device which divides | segments into.

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

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

  The wafer W is mounted on the suction stage 13 with the BG tape B having an adhesive material attached to one surface of the front surface and the back surface facing upward.

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

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

As the laser light conditions, the light source is a semiconductor laser pumped 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 Q switch pulse, and the repetition frequency is 100 kHz. The pulse width is 30 ns, the output is 20 μJ / pulse, the laser light quality is TEM00, and the polarization characteristic is linear polarization. The condition of the condensing lens 24 is that the magnification is 50 ×, N.V. A. Is 0.55, and the transmittance to the laser light wavelength is 60 percent.

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

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

  The imaging data is input to the image processing unit 38 and used for alignment of the wafer W, and is 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 apparatus 1.

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

  The wafer cassette elevator moves the cassette in which the wafer is stored up and down and positions it at the transfer position. The transfer means transfers the wafer between the cassette and the suction stage 13.

  Switches and display devices for operating each part of the dicing apparatus 10 are attached to the operation plate. The indicator lights indicate the operation status such as processing end, emergency stop, etc. during processing of the dicing apparatus 10.

  FIG. 2 is a conceptual view for explaining the details of the drive means 25. As shown in FIG. The driving means 25 includes a lens frame 26 for holding the condensing lens 24, a Z fine movement means 27 mounted on the upper surface of the lens frame 26 for slightly moving the lens frame 26 in the Z direction in the figure, and a holding frame 28 holding the Z fine movement means 27. It is composed of PZ1, PZ2 and the like which are linear fine moving means for slightly moving the holding frame 28 in parallel with the wafer W.

  The Z fine movement means 27 uses a piezoelectric element that expands and contracts by voltage application. The expansion and contraction of the piezoelectric element minutely feeds the condensing lens 24 in the Z direction, so that the position in the Z direction of the focusing point of the laser light can be precisely positioned.

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

  The linear fine moving means PZ1 and PZ2 use the same piezoelectric element as the Z fine moving means 27. One end is fixed to the case main 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 drive means 25. As shown in FIG. As shown in FIG. 3, two linear fine moving means PZ1 and PZ2 are arranged in the X direction, one end of which is fixed to the case main body of the laser head 40 and the other end abuts on the side surface of the holding frame 28. . Therefore, by controlling the applied voltage, the condensing lens 24 can be finely moved in the X direction, and the laser beam can be finely moved in the X direction or oscillated.

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

  A laser beam L is emitted from the laser oscillator 21 and the laser beam L is applied to the inside of the wafer W via an optical system such as a collimator lens 22, a half mirror 23, and a condensing lens 24. The Z-direction position of the condensing point of the laser light L to be irradiated is accurately at a predetermined position inside the wafer by the Z-direction position adjustment of the wafer W by the XYZθ table 12 and the position control of the condensing lens 24 by the Z fine movement unit 27 It is set.

  In this state, the XYZθ table 12 is processed and fed in the X direction which is the dicing direction, and the condensing lens 24 is slightly moved back and forth by the linear fine moving means PZ1 and PZ2 provided on the laser head 40. The modified region P is formed while being vibrated in parallel in the X direction or in any XY direction, and the focusing point of the laser light L minutely vibrates inside the wafer. Thereby, along the cutting line of the wafer W, one line of the modified region P by multiphoton absorption is formed inside the wafer W.

  In addition, you may add the vibration of the Z direction by Z fine movement means 27 as needed. In addition, by sending the wafer W in the X direction while slowly reciprocating the laser beam L in the X direction which is the processing direction, the laser beam L is repeatedly irradiated in a back and forth state like a perforation. It is also good.

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

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

(2) Grinding Device 2 FIG. 4 is a perspective view showing an outline configuration of the grinding device 2. 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 are provided on the main body 112 of the grinding apparatus 2.

  The rough grinding stage 118, the fine grinding stage 120, and the polishing stage 122 are separated by a partition plate 125 (not shown in FIG. 4) as shown in FIG. 5, and the working fluid used in each of the stages 118, 120 and 122 is adjacent. Scattering on the stage is prevented.

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

  The rough grinding stage 118 is a stage for rough grinding 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 fine grinding, and is surrounded by the side surface of the main body 112, the top plate 129, and the partition plate 125, similarly to the rough grinding stage 118. Brushes (not shown) are disposed on the top and side surfaces of the partition plate 125 to isolate the rough grinding stage 118 and the fine grinding stage 120 from the outside. Further, through holes 128A, 129A through which the heads of the stages are inserted are formed in the top plates 128, 129.

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

  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 when the chuck 140 is in the processing position, the brush 126B is mounted on the upper surface 125A of the partition plate 125 and It contacts the side surface 125B. Thus, when the chuck 140 is at the processing position, the casing 126, the partition plate 125, and the brush 126B are held substantially airtight.

  Since the polishing stage 122 performs chemical mechanical polishing, the polishing fluid contains a chemical polishing agent. When the grinding fluid is mixed into such a polishing fluid, the concentration of the chemical polishing agent is reduced, which causes a problem that the processing time becomes long. By keeping the polishing stage 122 in a substantially classified state, it is possible to prevent the grinding fluid and the work debris used in the fine grinding stage 120 from entering the polishing stage 122, and the polishing fluid used in the polishing stage 122 Can be prevented from scattering from the polishing stage 122. Therefore, processing problems caused by the mixing of both processing fluids can be prevented.

  FIG. 7 is a structural view of the polishing stage 122. As shown in FIG. In the polishing stage 122, polishing is performed by the polishing pad 516 and the slurry supplied from the polishing pad 156, and the damaged layer formed on the back surface of the wafer W is removed by rough polishing and fine polishing. The processing-deteriorated layer is a generic term such as streaks and processing distortion (crystals are degraded) or the like generated by grinding.

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

  The support plate 164 is provided at the tip of the horizontally arranged arm 168. The proximal end of the arm 168 is connected to the output shaft 174 of the motor 172 disposed in the casing 170. Thus, when the motor 172 is driven, the arm 168 can pivot about the output shaft 174. Thus, the range between the polishing position (see the solid line in FIG. 3) of the polishing pad 56, the polishing position (the two-dot chain line in FIG. 3) by the polishing pad cleaning stage 123, and the dress position by the polishing pad dressing stage 127 It can be moved within. When the polishing pad 156 is moved to the polishing pad cleaning position, the polishing pad cleaning stage 123 cleans the surface thereof and removes polishing debris and the like adhering to the surface. In addition, as the polishing pad 156, foamed polyurethane, a polishing pad, etc. can be illustrated, and the polishing pad cleaning stage 123 is provided with a removal member such as a brush for removing polishing debris. The removing member is driven to rotate when the polishing pad 156 is cleaned, and the polishing pad 156 is also driven to rotate by the motor 158 as well. For the polishing pad dressing stage 127, the same material as the polishing pad 156, for example, foamed polyurethane is adopted.

  Guide blocks 176, 176 constituting a linear motion guide are provided on the side surface of the casing 170, and the guide blocks 176, 176 can move up and down vertically on a guide rail 180 provided on the side surface of the housing 178 for a screw feeder. Is engaged. In addition, a nut member 179 is provided on the side surface of the casing 170 so as to protrude. The nut member 179 is screwed into a threaded rod 181 of a screw feeder disposed 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 threaded 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 operation of the screw feeder and the rectilinear operation of the guide block 176 and the guide rail 180. Thus, the polishing pad 156 is moved largely 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 top surface of the motor 158 through the through hole 169 of the arm 168. Further, a regulator 190 that controls the internal pressure P of the cylinder is connected to the air cylinder device 186. Therefore, when the internal pressure P is controlled by the regulator 190, the pressing force (pressure contact force) of the polishing pad 156 against the wafer W can be controlled.

  In the present embodiment, although the polishing pad 156 is applied as the polishing body, the present invention is not limited to this. For example, if removal of the processing-altered layer is possible, electrophoresis etc. It may apply. In the case where a polishing stone, electrophoresis of abrasive grains, or the like is applied, quantitative polishing is preferably performed.

  It returns to the explanation of FIG. The alignment stage 116 is a stage which aligns the wafer W transferred from the laser dicing apparatus 1 by a transfer apparatus (not shown) at a predetermined position. The wafer W aligned by the alignment stage 116 is held by suction by a transfer robot (not shown), and then conveyed toward the empty chuck 132 and held by suction on the suction surface of the chuck 132.

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

  The chuck 136 is positioned on the rough grinding stage 118 in FIG. 4, and the chucked wafer W is rough ground here. The chuck 138 is positioned on the fine grinding stage 120 in FIG. 4, and the wafer W thus adsorbed is finish ground (fine grinding, spark out) here. The chuck 140 is positioned on the polishing stage 122 in FIG. 4 and the chucked wafer W is polished here to remove variations in thickness of the damaged layer and the wafer W caused by grinding.

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

  FIG. 8 is a view showing details of the chuck 132, in which (a) is a plan view of the chuck 132, (b) is a cross-sectional view taken along the line AA 'in (a), and (c) is an enlarged B part in (b). FIG.

  The chuck 132 is configured by fitting a mounting table 132 a formed of a porous material (for example, porous ceramic) into a chuck body 132 b formed of a dense body. At the lower side of the mounting table 132a of the chuck body 132b, suction holes 132c are formed for vacuum suction. The chuck 132 is desirably formed of a material having a low thermal conductivity.

  As shown in FIG. 8C, the wafer W is mounted on the mounting table 132a via the BG tape B. The mounting table 132a is formed such that when the wafer W is mounted on the mounting table 132a, as shown in FIG. 8C, 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 the present embodiment has a diameter of about 12 inches and a thickness t of about 775 μm.

  As shown in FIGS. 2A and 2B, the suction holes 132c are arranged to cover substantially the entire area of the mounting table 132a. A fluid coupling (not shown) is connected to the suction hole 132c, and a suction pump (not shown) connected to the fluid coupling sucks air. Therefore, substantially the entire surface of the wafer W is firmly vacuum-adsorbed on the surface of the mounting table 132a. As a result, the wafer W and the mounting table 132a can be in close contact with each other without causing positional deviation.

  As shown in FIG. 7, the chucks 132, 136, 138, and 140 have the lower surfaces thereof respectively connected to a spindle 194 and a motor 192, and are rotated by the driving force of these motors 192. The motor 192 is supported by the index table 134 via the support member 193. As a result, each 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 chucks 132, 136 on the spindle 194 installed at the next moving position. , 138, 140 can be omitted.

  The piston 119 of the cylinder device 117 is connected to the lower part of the motor 192. When the piston 119 is extended, it is inserted into and connected to a recess (not shown) formed in the lower part of the chuck 132, 136, 138, 140. Then, the chucks 132, 136, 138, and 140 are moved upward from the index table 134 by the continued extension operation of the piston 119, and are positioned at the grinding position by the cup-type grinding wheels 146 and 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 apparatus 2.

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

  The index table 134 is rotated by 90 degrees in the direction of arrow R in FIG. 4 by the control unit 100, so that the wafer W whose thickness is measured is positioned on the rough grinding stage 118, and the cup type 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 attached to the grindstone feeder 152 via a support casing 150 of the motor 148. The grinding wheel feeder 152 moves the cup-shaped grinding wheel 146 up and down together with the motor 148, and the cup-shaped grinding wheel 146 is pressed against the back surface of the wafer W by this downward movement. Thereby, the rough grinding of the back surface of the wafer W is performed. The control unit 100 sets the amount of downward movement of the cup-shaped grindstone 146 and controls the motor 148. The amount of descent 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. Be done. Further, the control unit 100 controls the number of rotations of the cup-shaped grinding wheel 146 by controlling the number of rotations of the motor 148.

  The thickness of the wafer W whose back surface is roughly ground in the rough grinding stage 118 is measured by a measurement gauge (not shown) connected to the control unit 100 after the cup-shaped grindstone 146 is moved away from the wafer W. The index table 134 is rotated by 90 degrees in the direction of arrow R in FIG. 4 by the control unit 100, so that the wafer W whose thickness is measured is positioned on the fine grinding stage 120, and the cup type grindstone 154 of the fine grinding stage 120 Grinded, 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 is omitted here. Further, the amount of grinding by the cup-shaped grindstone 154 is set by the control unit 100, and the amount of movement and the number of rotations of the cup-shaped grindstone 154 are controlled by the control unit 100.

  The thickness of the wafer W whose back surface is finely ground in the precision grinding stage 120 is measured by a measurement gauge (not shown) connected to the control unit 100 after the cup-shaped grindstone 154 retracts from the wafer W. When index table 134 is rotated 90 degrees in the direction of arrow R in FIG. 4 by controller 100, wafer W whose thickness is measured is positioned on polishing stage 122, and chemical mechanical polishing is performed by polishing cloth 156 of polishing stage 122. And the back surface of the wafer W is mirror-polished. The vertical movement distance of the polishing pad 156 is set by the control unit 100, and the motor 182 is controlled by the control unit 100, whereby the position of the polishing pad 156 is controlled. Further, the control unit 100 controls the number of rotations of the motor 158, that is, the number of rotations of the polishing pad 156.

  After the arm 168 is rotated by the control unit 100 and the polishing pad 156 retracts from the upper position of the wafer W, the wafer W polished by the polishing stage 122 is moved by the hand of a robot (not shown) (not shown) The wafer is held by suction and transferred 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 polished wafer W is not easily broken because the damaged layer is removed, and therefore, it is not broken during transport by the robot and cleaning at the wafer cleaning stage 124.

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

(3) Division Device Next, the division device (not shown) will be described. The splitting device can use a conventional, conventional splitting device. For example, it is possible to use a dividing device having the following configuration, which is disclosed in Table 2004-100240.

  That is, the peripheral edge portion of the dicing tape is fixed to the frame-like frame. A ring member is in contact with the lower surface of the inner portion of the peripheral portion of the dicing tape. The upper peripheral edge of the ring member is chamfered smoothly by R-chamfering. Below the dicing tape, a UV light source (UV light irradiation means) is disposed.

  The UV light is directed to the dicing tape from the UV light source and the frame is pushed downward. By irradiation with UV light, the pressure-sensitive adhesive of the dicing tape can be cured or the adhesion of the tape can be changed.

  At the same time, a force is applied downward to the frame and pushed downward. Thereby, the dicing tape is expanded and the distance between the chips is expanded. At this time, since the upper outer peripheral edge of the ring member is R-chamfered smoothly, the dicing tape S is expanded smoothly.

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

  As irradiation conditions such as UV light irradiation intensity (power), wavelength region, irradiation time, appropriate values can be selected according to the material of the pressure-sensitive adhesive of dicing tape S, the size of the wafer, the size of the chip after cutting, and the like.

  Here, it is not necessary to have a UV light source, and it is possible to appropriately cut the chip by adjusting the adhesion of the dicing tape.

(4) Another Embodiment of Splitting Device FIG. 21 is a schematic view of the splitting device 300. As shown in FIG. In FIG. 21, (A) is a plan view of the dividing device 300, and (B) is a side view of the dividing device 300. The dividing device 300 mainly includes a wafer chuck 304 for suction-fixing the wafer 302, a bending means 306 for bending the wafer chuck 304, and a vacuum pump 308.

  The wafer chuck 304 mainly includes an independent suction chuck 310 having independent suction holes and a communication groove chuck 312 having a spiral groove communicating with the independent suction holes, and the independent suction chuck 310 and the communication groove chuck It overlaps with 312.

  The thickness of the communication groove chuck 312 and the thickness of the independent suction chuck 310 are about 1 mm, respectively, and become approximately 2 mm by overlapping each other. It is preferable to manufacture resin materials, such as an acryl, as a member, respectively. However, the material is not limited to the resin material, and other materials such as ceramic may be used, and any material may be selected as long as the wafer chuck can be bent after vacuum suction of the wear. Further, the material itself of the wafer chuck 304 does not necessarily have to be bent, as long as the entire wafer chuck 304 is bent.

  The bending means 306 is a rod-like body whose tip is rounded, and can push the central portion of the back surface of the wafer chuck 304 upward to bend the wafer chuck 304 in a hemispherical shape.

  The wafer 302 is placed on the wafer chuck 304 and vacuum-sucked while the wafer 302 is stuck on the expanded film 314 whose outer periphery is fixed by a frame such as metal. It is preferable that the expanded film 314 be somewhat breathable, and the wafer 302 itself is directly attracted to the wafer chuck 304 by vacuum force.

  The wafer chuck 304 is bent into a hemispherical shape by the bending means while holding the wafer 302 in a suctioned state. Thereby, the wafer 302 is divided along the cutting line.

  Next, another embodiment of the chuck bending means will be described with reference to FIG. FIG. 22 is an explanatory view showing another embodiment of the chuck bending means. In this figure, the components other than the chuck bending means 320 are the same as those in FIG.

  As shown in FIG. 22, the chuck bending means 320 has a semicylindrical shape. The dividing device 300 also comprises means (not shown) for rotating the chuck deflection means 320 relative to the wafer 302.

  The dividing lines formed on the wafer 302 are often in the X-axis direction and the Y-axis direction in consideration of the X-axis and Y-axis which are perpendicular to the difference in the wafer surface. Therefore, the wafer 302 is divided as follows. That is, the position of the chuck bending means 320 is aligned so that one side of the chuck bending means 320 is parallel to the X axis. Next, the wafer 302 is placed on the alignment wafer chuck 304 and vacuum-sucked so that the dividing line is parallel to the X axis.

  By pressing the chuck bending means 320 against the lower surface of the wafer chuck 304, the wafer 302 is bent together with the wafer chuck 304 and divided in the X direction. Next, the chuck bending means 320 is released from the wafer chuck 304 and rotated 90 degrees so that the one side is parallel to the Y axis, and the wafer 302 is pressed again against the lower surface of the wafer chuck 304. Split in the direction. Thus, the wafer 302 can be divided along the dividing line in both the X and Y directions.

  Here, in the case where the wafer 302 is not sucked by vacuum and is pushed by the chuck bending means 320 via a dicing film which is an elastic film to bend the wafer 302, if the wafer is broken first at a certain portion, the crack Since the wafer bends sharply in the other part where the curvature of the chuck bending means 320 is absorbed, the wafer may not partially bend and may follow the chuck bending means 320 without being divided.

  Therefore, first, the wafer 302 is vacuum-sucked to the wafer chuck 304, the wafer chuck 304 corrects the wafer 302 to a flat surface, and then the entire wafer chuck 304 is bent. Correspondingly, since the wafer 302 is copied while being adsorbed, a uniform constant bending stress is applied in the plane of the wafer 302, so that the wafer 302 can be divided without any division residue.

<Method of cutting semiconductor substrate>
Next, a method of cutting a semiconductor substrate will be described. FIG. 9 is a flow chart showing the flow of processing of the semiconductor substrate cutting method.

(1) Laser reforming process (step S10)
The wafer W on which the BG tape B is attached to the front surface is mounted on the suction stage 13 of the laser dicing apparatus 1 such that the back surface is upward. The following processing is performed by the laser dicing apparatus 1 and is controlled by the control unit 50.

  When the laser beam L is emitted from the laser oscillator 21, the laser beam 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 the inside of the wafer W is modified. A quality region P is formed.

  In the present embodiment, since the thickness of the finally generated 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, as shown in FIG. In order to break the front surface (device surface) of the wafer W efficiently, the laser modification area is located relatively deep near the reference surface, which is the surface located on the back side by the thickness of the chip T from the front surface of the wafer W It is necessary to form.

  The control unit 50 scans the pulsed laser light L for processing parallel to the surface of the wafer W, and forms a plurality of discontinuous modified regions P, P,... Inside the wafer W. Inside the modified region P, microvoids (hereinafter, referred to as cracks) K are formed. Hereinafter, a region formed by arranging a plurality of discontinuous reforming regions P, P, ... is referred to as a reforming layer.

  When the modified layer is formed along all the cutting lines L shown in FIG. 11, the process of step S10 is ended.

(2) Grinding removal process (step S12)
After the reformed region is formed along the cutting line L in the laser reforming step (step S10), the wafer W is transported from the laser dicing device 1 to the grinding device 2 by the transport device (not shown). The following processing is performed by the grinding device 2 and is controlled by the control unit 100.

  The back surface of the transferred wafer W is placed on the upper side, that is, the BG tape B attached to the front surface of the wafer W is on the lower side and placed on the chuck 132 (exemplified by the chucks 136, 148, and 140). The entire surface is vacuum attracted to the chuck 132.

  The index table 134 is rotated about the rotation axis 135 to carry the chuck 132 onto the rough grinding stage 118, and the wafer W is roughly ground.

  Rough grinding is performed by rotating the chuck 132 and rotating the cup-shaped grinding wheel 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 rotational speed of the cup-shaped grindstone 146 is approximately 3000 rpm.

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

  In the present embodiment, as shown in FIG. 12, the rough grinding and the fine grinding are combined and grinding is performed to the target surface, that is, to a depth of approximately 50 μm from the surface of the wafer W. In this embodiment, approximately 700 μm is ground by rough grinding, and approximately 30 to 40 μm is ground by fine grinding, but it is not strictly determined, and the time for rough grinding and fine grinding is approximately the same. The grinding amount may be determined to be

  Therefore, as shown in FIG. 12, the modified layer is removed in the grinding process, and the modified region P by laser light does not remain on the cross section of the chip T which is the final product. Therefore, the reforming layer can be broken from the chip cross section, and the chip T can be prevented from being broken from the broken portion and dusting from the broken portion.

  Further, in the present embodiment, the grinding and removing step includes a crack extension step of causing the crack in the modified layer to propagate in the thickness direction of the wafer W. FIG. 13 is a view for explaining the mechanism of crack development, in which (a) is a schematic view at the time of grinding, (b) is a back surface of the wafer W, (c) is a surface of the wafer W, (d) is It is sectional drawing of the wafer W at the time of grinding.

  By grinding, the grinding surface shown in FIG. 13A, that is, the back surface of the wafer W is expanded by the grinding heat as shown in FIG. 13B. On the other hand, the surface opposite to the grinding surface, that is, the surface of the wafer W, has its entire surface vacuum-adsorbed by the vacuum chuck as shown in FIG. 13C, so that no lateral displacement occurs due to thermal expansion. Physically constrained against displacement.

  That is, as shown in FIG. 13D, the back surface (ground surface) of wafer W tends to expand in the outer peripheral direction (displacement due to thermal expansion) in the case of a disk due to thermal expansion. The suction surface is constrained so as not to physically shift each point on the wafer surface where the spreading is going to occur. Therefore, strain occurs inside the wafer, and the crack develops in the thickness direction of the wafer W due to the internal strain. This internal strain works equally between the portion that expands due to thermal expansion and each point in the wafer plane that is physically constrained. Crack growth due to internal strain is the most efficient at the initial stage of grinding where the amount of grinding is large and the frictional force is also large, that is, the frictional heat can be large, that is, rough grinding.

  The laser modified region is formed at a relatively deep position close to the thickness of the chip. Therefore, although the distance from the grinding surface to the laser modification layer is relatively long at the initial stage of grinding, the target surface from the modification layer is at a position relatively close to the extent to which a crack is to be developed. Therefore, for the crack growth, the thermal expansion of the wafer W may be promoted by the grinding heat at the beginning of the rough grinding.

  Even if grinding is performed under the conditions for thermal expansion of the wafer W, that is, the conditions for generating a large amount of frictional heat (for example, reducing the amount of grinding fluid), the shear stress of the grinding immediately reaches the modified layer. It is not something to be done. In the present embodiment, the crack does not progress due to the shear stress due to grinding, but the thermal expansion due to the grinding heat is the dominant factor of the crack progress.

  In the case where a crack is caused to progress by internal strain, the crack can be made to progress uniformly at each point in the wafer W regardless of any wafer W without causing stiffness variation in the wafer W, etc. . Therefore, as in the case of applying artificial stress, it is possible to prevent stress from concentrating on a portion of low rigidity caused by the presence of a defect or the like in the wafer W plane.

  In addition, when an external force is artificially applied, stress concentrates on the weak portion of the material, so it is difficult to control the crack to propagate uniformly and gently, and the wafer is completely cut. On the other hand, in the case of the progress of the crack due to the internal strain in the present embodiment, since the internal strain is due to the degree of the thermal expansion, it is possible to finely develop the crack. That is, the crack can be advanced to between the target surface and the surface of the wafer W. Therefore, it becomes possible to divide efficiently in the dividing / separating step (step S18) 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. 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, and 140, and thus no thermal stress is generated.

(3) Chemical mechanical polishing process (step S14)
This process is performed by the grinding device 2 and is controlled by the control unit 100.

  After the fine grinding, the index table 134 is rotated about the rotary shaft 135 to carry the chuck 132 onto the polishing stage 122, chemical mechanical polishing is performed by the polishing cloth 156 of the polishing stage 122, and in the grinding removal step (step S12). The damaged layer formed on the back surface of the wafer W is removed, and the back surface of the wafer W is mirror-polished.

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

  A large number of asperities as shown in FIG. 14 are formed on the back surface of the wafer W in the grinding and removing step (step S12). When polishing is performed by chemical etching, since the surface shape is maintained as it is, there is a possibility that a crack may be generated from the recess, and the surface is not mirror-polished. On the other hand, in the present embodiment, since the chemical mechanical polishing is performed, the processing strain generated by the processing is removed, and the surface asperity is removed and the mirror surface is formed.

  That is, in order to improve the quality of the final product chip T, two steps, a grinding and removing process using a grindstone and a chemical mechanical polishing process using free abrasive grains containing a chemical liquid using a polishing cloth, are indispensable. .

(4) Expanding tape sticking process (step S16)
The expand tape F is attached to the back surface of the wafer W on which the chemical mechanical polishing process (step S14) has been performed. Expanded tape is a type of elastic tape and is stretchable.

  In the present embodiment, the back surface of the wafer W is mirror-polished in the chemical mechanical polishing step (step S14), so the adhesion between the expanded tape F and the wafer is also significantly improved. In addition, it is possible to increase the bending strength of the chip T which is finally generated.

(5) Division / separation process (step S18)
The surface of the wafer W is placed on the dividing device as shown in FIG. 15, with the wafer W having the expanded tape F attached to the back in the expanded tape attaching step (step S16), as shown in FIG. In the grinding removal step (step S12), since the crack has progressed to the surface side from the target surface, as shown in FIG. 15, the crack which has progressed is formed on the side to which expand tape F of wafer W is attached. There is.

  Thereafter, as shown in FIG. 16, when the expand tape F is expanded outward (expanding), the wafer W is broken based on the developed crack. That is, the wafer W is broken at the cutting line and divided into a plurality of chips T. Thereafter, when the expand tape F is further expanded, the individual chips T are separated.

  In the present embodiment, the wafer W is efficiently cut into chips T only by pulling the expand tape F in this dividing / separating process by causing the crack to extend below the target surface in the grinding and removing step (step S12). It becomes possible to divide. In addition, since the wafer is not completely cut when developing the crack, the working efficiency is good.

  Further, in the present embodiment, since the back surface of the wafer W is mirror-polished in the chemical mechanical polishing step (step S14), the expand tape F and the chip T are displaced and partially peeled off when expanding. There is no

<< Evaluation of crack growth by grinding >>
Next, crack growth evaluation by grinding in the grinding and removing step (step S12) will be described with reference to FIGS. The grinding method, the division and separation method, the conditions thereof, and the like are basically as described in steps S10 to S18. FIG. 19 is a view showing conditions of crack growth evaluation, and FIG. 20 is a view showing an evaluation result of crack growth evaluation.

  In (A), (B) and (C) in FIG. 19, the horizontal axes are common, the respective positions correspond to each other, and the grinding time (s) is indicated. The vertical axis in (A) of FIG. 19 shows the cutting speed (grinding speed) (μm / s), and the vertical axis in (B) shows ON and OFF of the water supply to the grinding wheel during polishing (C) The vertical axis of represents the temperature (° C.) of the back surface of the wafer W during grinding.

  As shown in FIG. 19A, rough grinding was performed for a total of 710 μm while changing the grinding speed, then fine grinding was performed for 13 μm (not shown), and chemical mechanical polishing (not shown) was performed for 2 μm. In the case of a wafer, as shown in FIG. 19 (B), an interruption period of water supply to the grindstone or wafer was provided in the middle of the rough grinding. The water supply was stopped after t1 seconds after the start of grinding, and was restarted after t2 seconds after the start of grinding. Water supply was performed at a flow rate of 10 L / min. Thereafter, the above steps S16 and S18 were performed to cut the wafer, and the cut state was observed and evaluated. The results are summarized in FIG. 20, with 場合 being a case where the chip was cracked or not broken without causing dust, and a case where the chip was broken or dusted was indicated as ×.

  As shown in FIG. 19C, the back surface temperature of the wafer W starts to rise sharply after lapse of t1 seconds after the start of grinding when the water supply is stopped, and drops immediately after elapse of t2 seconds after the start of grinding when the water supply is resumed. Began to do.

  As shown in FIG. 20, when the back surface temperature of the wafer W became 70 ° C. or more by grinding, the wafer was favorably cut. This is considered to be because the crack formed by the laser has been developed by the heat of grinding.

  Therefore, in the grinding apparatus according to the present invention, the means for measuring the temperature of the wafer, the means for turning on and off the water supply to the grinding wheel or 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 so as to turn off the water supply to the wafer until it becomes possible. Thereby, the crack formed by the laser can be advanced, and the wafer can be favorably cut.

  As described above, according to the present embodiment, since the crack in the modified region formed by the laser light can be made to propagate by grinding, the modification formed by the laser light on the cross section of the chip T It is possible not to leave an area. Therefore, it is possible to prevent the problem that the chip T is broken or dust is generated from the cross section of the chip T. Therefore, chips of stable quality can be obtained efficiently.

(Supplementary note)
As can be appreciated from the description of the embodiments detailed above, the present specification includes the disclosure of various technical ideas including the invention described below.

  (Supplementary Note 1) In the method of cutting a semiconductor substrate according to the first aspect of the present invention, the reformed region is formed by injecting a laser beam from the back surface of the wafer along the cutting line to form a modified region inside the wafer. In the modified area forming step of forming microvoids in the area, and the substantially entire surface of the wafer on which the modified area is formed in the modified area forming step is adsorbed on the table uniformly in each area independently. Grinding the wafer having the substantially whole surface of the surface adsorbed on the table in the suction step from the back surface to remove the modified region and advancing the microvoids in the thickness direction of the wafer; A step of chemical-mechanically polishing the wafer, in which the microvoids are developed in the thickness direction of the wafer in the grinding step, and cutting along a cutting line based on the microvoids remaining in the substrate. Process and multiple chips after cutting Characterized in that it comprises a a dividing step of dividing the.

  According to the method for cutting a semiconductor substrate according to the first aspect, the laser light is incident from the back surface of the wafer along the cutting line to form the modified region in the inside of the wafer, thereby forming the microvoids in the modified region. The wafer is ground from the back surface to remove the reformed region in a state where each value of the substrate is adsorbed uniformly on the table substantially on the entire surface of the wafer where the reformed region is formed.

  (Supplementary Note 2) The method of cutting a semiconductor substrate according to the second aspect of the present invention is characterized in that laser light is incident from the back surface of the wafer along the cutting line to form a modified region inside the wafer, The modified region forming step of forming microvoids 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 uniformly and independently table in each region In the step of adsorbing to the wafer, and with the wafer adsorbed, the laser light is incident to grind and remove a portion before the modified region formed inside the wafer, and the microcracks extending from the modified region are deep of the substrate Chemical mechanical polishing using a first grinding process that develops in the vertical direction, a second grinding process that grinds and removes the modified region formed inside the wafer, and a chemical slurry and a polishing pad that modify the wafer surface While performing the above-mentioned reforming area Cutting the wafer based on the step of mirror-finishing the surface by removing the processing-altered layer introduced in the first and second grinding steps while leaving the elongated micro cracks, and based on the micro cracks developed in the wafer thickness direction And a step of separating the cut chips after cutting.

  According to the method of cutting a semiconductor substrate according to the second aspect, the modified region is initially formed at a deep position inside the wafer, and removal processing is performed while generating grinding heat in the first grinding step in the initial stage. Thus, it is possible to propagate the crack formed in the modified region to a deeper position of the wafer.

  However, in the first grinding process, if the area modified by laser is also ground and removed with the same volume as the area not modified, large grain boundaries may be chipped off because the modified area has large grain boundaries. Also, along with these grains, more fatal cracks may develop. Therefore, in the first grinding process, grinding may be performed to a portion before the reforming region where the crystallinity is constant.

  In the second grinding step, the mainly laser-modified area is ground. At this time, the grinding wheel also has a higher count, that is, a grinding wheel having a finer grain size than the first grinding process, and fatal cracks and defects derived from the modified region as compared to the first grinding process. Do a gentle grinding so as not to induce. The second grinding process is only in the reforming region, and the grinding rate is set to be smaller than the first grinding process, and the grinding is finely cut.

  Then, after the laser modified region is removed, chemical mechanical polishing is finally performed. In chemical mechanical polishing, a polishing pad made of polymer, non-woven fabric, or the like is pressed against a wafer while supplying a chemical solution for modifying the wafer to perform chemical and mechanical polishing.

  If chemical mechanical polishing is performed in the above-described modified region, large grains may be chipped off in the modified region. Since chemical mechanical polishing uses a polishing pad such as non-woven fabric or foamed polyurethane, if such broken crystal grains enter the surface of the pad, scratches will be generated by the constantly broken crystal grains during polishing. In such a case, the polished surface will be covered with scratches, without the purpose of achieving a mirror finish while removing the damaged layer in the grinding process.

  As such, in the state of being introduced into the chemical mechanical polishing process, the modified layer introduced by the laser in the previous second grinding process must be completely removed.

  (Supplementary Note 3) The method of cutting a semiconductor substrate according to the third aspect of the present invention is the method of cutting a semiconductor substrate according to the second aspect, wherein the modified region forming step is approximately 60 μm to approximately 80 μm from the surface of the wafer. Forming the modified region at a depth of about 50 .mu.m, and the first grinding step is characterized in that the microvoids are developed from the surface of the wafer to a depth of about 50 .mu.m and between the surface of the wafer. .

  As a result, the modified region is formed at a depth of about 60 μm to about 80 μm from the surface of the wafer, and the microvoids are developed from the surface of the wafer to a depth of about 50 μm and the surface of the wafer. Therefore, even if the workpiece is ground so that the modified region formed by the laser light does not remain in the cross section of the chip, the microvoids can be left in the workpiece.

  (Supplementary Note 4) In the method of cutting a semiconductor substrate according to the fourth aspect of the present invention, in the method of cutting a semiconductor substrate according to the first aspect, the grinding step is performed until the temperature of the wafer being ground becomes 70 ° C. or higher. , Interrupting the supply of water to the grinding wheel during grinding.

  According to the method of cutting a semiconductor substrate according to the fourth aspect, the temperature of the wafer being ground can be controlled. As a result, the microvoids can be advanced in the thickness direction of the wafer.

  (Supplementary Note 5) In the method of cutting a semiconductor substrate according to the fifth aspect of the present invention, in the method of cutting a semiconductor substrate according to the second or third aspect, the temperature of the wafer being ground is the first grinding step. Interrupting the supply of water to the grinding wheel during grinding until the temperature reaches 70.degree. C. or higher.

  According to the method of cutting a semiconductor substrate according to the fifth aspect, the temperature of the wafer during grinding can be controlled. As a result, the microvoids can be advanced in the thickness direction of the wafer.

  (Supplementary Note 6) In the semiconductor substrate cutting method according to the sixth aspect of the present invention, in the semiconductor substrate cutting method according to the first aspect or the fourth aspect, in the dividing step, an elastic tape is attached to the surface of the wafer. And expanding the elastic tape.

  According to the method of cutting a semiconductor substrate according to the sixth aspect, the wafer can be divided into a plurality of chips by sticking and expanding the elastic tape on the surface of the wafer.

  (Supplementary Note 7) A semiconductor substrate cutting apparatus according to a seventh aspect of the present invention includes: laser dicing means for forming a modified region in the inside of the wafer by causing laser light to be incident from the back surface of the wafer along the cutting line; Grinding means for grinding the wafer from the back side to remove the modified region; transfer means for transferring the wafer from the laser dicing means to the grinding means; dividing means for dividing the wafer along a cutting line The apparatus for cutting a semiconductor substrate comprising: a table on which a surface of the wafer is placed downward, and a laser beam is irradiated to the wafer to form the modified region. Irradiation means, and first control means for controlling the irradiation means so as to change the position to which the laser beam is irradiated, and the grinding means comprises the wafer It has a suction table mounted with its surface facing downward and suctioning substantially the entire surface of the wafer, a grinding wheel for grinding the wafer, and a second control means for controlling the height and the number of revolutions of the grinding wheel. It is characterized by

  Thereby, it is possible to prevent the modified region formed by the laser light from remaining in the cross section of the chip. Therefore, it is possible to prevent a defect such as cracking of the chip or dust generation from the cross section of the chip, and to efficiently obtain a chip of stable quality.

  (Supplementary Note 8) The apparatus for cutting a semiconductor substrate according to the eighth aspect of the present invention is the apparatus for cutting a semiconductor substrate according to the seventh aspect, wherein the first control means measures approximately 60 μm to approximately 80 μm from the surface of the wafer. Controlling the irradiation unit to form the modified region at a depth of about 50 .mu.m from the surface of the wafer to the surface of the wafer. The height and the number of revolutions of the grinding wheel are controlled so as to develop microvoids in the inside.

  As a result, even if the work is ground so that the modified region formed by the laser light does not remain in the cross section of the chip, microvoids can be left in the work.

  (Supplementary Note 9) The semiconductor substrate cutting apparatus according to the ninth aspect of the present invention is the semiconductor substrate cutting apparatus according to the seventh aspect or the eighth aspect, including means for measuring the temperature of the wafer being ground, and grinding. It further comprises means for turning on and off the water supply to the grindstone or wafer, and means for controlling the water supply to the wafer to be off until the wafer temperature reaches a predetermined value after a predetermined time has elapsed from the start of grinding. It features.

  As a result, the microvoids can be advanced in the thickness direction of the wafer.

  DESCRIPTION OF SYMBOLS 1 ... Laser dicing apparatus, 2 ... Grinding apparatus, W .. Work, B .. BG tape, F ... Expanded tape, 11 ... Wafer moving part, 13 ... Adsorption stage, 20 ... Laser optical part, 30 ... Observation optical part, 40 ... Laser head, 50: Control unit, 118: Rough grinding stage, 120: Fine grinding stage, 122: Polishing stage, 132, 136, 138, 140: Chuck, 146, 154: Cup type grinding wheel, 156: Polishing cloth, 300 ... Splitter

Claims (6)

A laser processing apparatus which condenses laser light on the inside of a wafer to form a modified region, and
A condensing lens for condensing the laser beam on the inside of the wafer;
A control unit that controls a position of a focusing point of the laser beam by the focusing lens so that the wafer is not divided into chips when back grinding of the wafer is performed;
A laser processing apparatus comprising: The control means controls the focus position so that microcracks extending from the modified region have a length that does not reach the surface of the wafer.
The laser processing apparatus according to claim 1. The control means controls the focus position so that the modified region is removed by back grinding the wafer.
The laser processing apparatus of Claim 1 or 2. A laser processing method of condensing a laser beam on the inside of a wafer to form a modified region,
Collecting the laser light inside the wafer;
A control step of controlling a position of a focusing point of the laser beam in the focusing step so that the wafer is not divided into chips when back grinding of the wafer is performed;
A laser processing method comprising: The control step controls the position of the focusing point so that microcracks extending from the modified region have a length that does not reach the surface of the wafer.
The laser processing method according to claim 4. The control step controls the position of the focusing point so that the modified region is removed by back grinding the wafer.
The laser processing method of Claim 4 or 5.

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