JP2018142717A - Wafer processing method and wafer processing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer processing method and a wafer processing system capable of efficiently obtaining a chip with stable quality.SOLUTION: The wafer processing method includes: a modified region formation process for forming a laser-modified region between a target surface set in a wafer and a rear surface of the wafer; and a grinding process for grinding the wafer from the rear surface of the wafer to the target surface to thin the wafer without dividing the wafer for every chip.SELECTED DRAWING: Figure 9

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

  Further, Patent Document 1 discloses that a semiconductor substrate placed with the back surface facing upward is irradiated with laser to form a modified region inside the substrate, and then the substrate is ground and thinned. It is described that the substrate is divided based on the modified region by attaching the tape and extending the expanded tape.

  In Patent Document 2, a semiconductor substrate placed with the back surface facing upward is irradiated with a laser to form a modified region inside the substrate, thereby generating a crack in the thickness direction of the semiconductor substrate. It describes that a semiconductor substrate is cut into chips by exposing cracks to the back surface by grinding and chemical etching. Patent Document 2 discloses that a natural stress or a relatively small force, for example, an artificial force or a thermal stress is generated by applying a temperature difference to the substrate, thereby causing a crack in the thickness direction from the modified region. 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 applying an external force locally with a knife edge. In order to apply the external force locally, bending stress or shear stress is applied to the substrate. However, it is difficult to distribute bending stress and shear stress uniformly over the entire surface of the substrate. For example, when bending stress or shear stress is applied to the substrate, the stress is concentrated at some weak point, and the necessary minimum stress cannot be uniformly applied to a desired portion efficiently.

  Therefore, there is a problem in that the substrate breaks and the substrate breaks even in the chip when the crack does not proceed slowly. In addition, when cutting a portion of the substrate by applying stress locally in order, for example, when collecting a large number of chips from a single substrate, there are a large number of cutting lines. There is a problem that productivity is greatly reduced.

  In addition, when an external force is applied and the substrate is cracked, if the substrate is not processed thinly, there is a problem that a very large stress is required when the wafer is cracked.

  In particular, when the substrate thickness is sufficiently thick with respect to the modified depth of laser processing, even if an external force is applied, it is not always possible to cleave the substrate cleanly perpendicularly to the substrate due to the influence of the abrupt external force. Therefore, it may be necessary to irradiate 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 in the substrate by the laser irradiation finally remains in the chip cross section. Therefore, dust may be generated from the modified region of the chip cross section. In addition, as a result of the chip cross-sectional portion being locally crushed, the crushed cross section may be a trigger to break the chip. As a result, there is a problem that the bending strength of the chip is reduced.

  In the invention described in Patent Document 2, it is described that cracks naturally occur in the thickness direction from the modified region, but there are cases where cracks do not necessarily occur naturally when they crack naturally. In order to inevitably obtain the stable effect of cracking, it is sometimes necessary to take arbitrary measures, and if it breaks naturally, it does not fall under arbitrary measures.

  In addition, as a relatively small force, it is conceivable to generate a thermal stress by giving a temperature difference 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 give a uniform thermal gradient in the plane of the substrate. That is, even if a thermal gradient is artificially applied, heat is dispersed in the substrate so as to alleviate the partial thermal gradient by heat conduction. Therefore, there is a very difficult problem in how to constantly form a stable thermal gradient (stable temperature difference) enough to cut a certain substrate.

  In the invention described in Patent Document 2, the semiconductor substrate is ground and then chemically etched on the back surface. However, after grinding, the ground surface is left with grinding streaks due to fixed abrasive grains and accompanied by minute cracks. Is 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, micro cracks are promoted and become large cracks. For this reason, there is a problem that not only the cutting start region but also a small crack formed by grinding and etching sometimes breaks, and it is difficult to perform stable cutting.

  Further, since the unevenness of the substrate surface is promoted by etching, the substrate surface is not mirror-finished. For this reason, since the unevenness remains in the divided chips, it can be considered to be broken from a large unevenness portion, that is, a micro crack, and there is a problem that the bending strength of the chip is lowered.

  Further, when the etching solution is applied to the modified portion that has been laser processed, the modified portion is once melted and recrystallized, so that a large grain boundary is formed.

  When an etching solution acts on such a grain boundary portion, etching proceeds so that silicon grains are peeled off from the grain boundary.

  Specifically, as the polishing process, it is described in the cited document p.12_1 line that the grinding process and chemical etching are performed on the back surface. In the case of chemical etching, even if it is left as it is, the chemical etching solution penetrates into the cracks and has the effect of dissolving the cracks.

  In particular, when the crack has advanced to the surface of the substrate, the etching solution permeates between the chip and the film adhering the chip, thereby causing a problem of peeling the chip from the film.

  Even if the crack does not run to the surface of the substrate, the etching proceeds along the crack. Especially when etching in a thin state after grinding, the etching solution penetrates into the crack by capillary action, deepens the micro crack while melting the crack tip, and further enters a new etching solution there Become. In this case, if the etching solution acts in the vicinity of the device surface, the vicinity of the device surface is melted, and 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 distortion on the wafer surface, the crack may be further promoted and the accompanying secondary problems may be induced.

  Further, in such a case, as a result, the crack may be advanced to the surface, and an etching solution may partially enter between the chip and the film, and the chip may be peeled off during processing. In particular, when grinding progresses after grinding, cracks tend to progress with a slight external force, and chip peeling occurs when the cracks reach the surface. It must be processed so that it does not progress further.

  Patent Document 2 describes that a crack is generated from the modified region by grinding the back surface of the substrate, but Patent Document 2 does not describe a method for fixing the substrate when grinding the substrate. . When the outer periphery of the substrate is supported by fitting the substrate into a retainer or the like as shown in FIG. 17 or when only a part of the substrate is adsorbed as shown in FIG. Since it is not restrained, in such a case, even if the back surface of the substrate is ground, cracks do not occur 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 stable quality chips.

  A wafer processing apparatus for achieving an object of the present invention is a wafer processing apparatus for processing a wafer in which a modified region is formed inside by a laser beam, and grinding the back surface of the wafer with a grinding wheel while adsorbing the surface of the wafer. And a grinding unit that removes the modified region leaving a microcrack extending from the modified region, and a polishing unit that polishes the back surface of the wafer with a polishing cloth after grinding.

  According to this apparatus, due to the grinding heat generated by grinding, the wafer expands in the radial direction along with the surface of the wafer being ground. However, on the other hand, the wafer tends to be prevented from spreading due to expansion by a wafer vacuum chuck having a large heat capacity.

  As a result, the wafer back surface expands due to thermal expansion, while the chucked wafer surface does not expand due to the vacuum chuck and tries to maintain the state as it is. As a result, the modified region formed in the wafer acts so that the modified region further expands according to the difference in expansion between the front surface and the back surface of the wafer, and further cracks progress. The modified region is irradiated with laser light, and there are portions that are once melted and recrystallized, so that the crystal grains are fragile. When such a modified region appears on the side surface of a future chip, dust is generated from the side surface of the chip, and large crystal grains may be chipped from the side surface of the chip. However, since the microcracked part that has developed from the modified region is a pure crystal surface, even if this surface appears on the future chip side surface, dust is generated from the chip side surface or chipped as large crystal grains. There is no such thing.

  In this way, the wafer is removed while being ground by the grinding process, and the micropores 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 advanced micropores stand out, the entire surface of the wafer is subjected to chemical mechanical polishing (detailed later) to completely remove the work-affected layer. To do. As a result, only the minute holes remain on the surface, and the remaining region becomes a complete mirror surface with no processing distortion.

  Thereafter, the wafer that has not yet been cracked is placed on a mechanism for cleaving the wafer, the wafer is cleaved by applying a bending stress to the wafer, and then the expanded film is pulled to separate the chips. Thereby, it is possible to prevent the modified region formed by the laser light from remaining on the cross section of the chip. Therefore, it is possible to prevent a problem that the chip is broken or generate dust from the cross section of the chip and efficiently obtain a chip having a stable quality.

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

  First, the chemical solution in the present application is different from the etchant of the cited document 2. The etching solution in the cited document 2 has an action of dissolving the substrate naturally by the action of the solution on the substrate surface, that is, etching. Thereby, even in the cracked portion, the etching solution penetrates and naturally etches the surroundings, so that the modified layer formed by the laser is further enlarged. Further, in the case of the conventional etching solution, as described above, the etching solution penetrates too much into the cracks to cause the cracks to progress, and finally penetrates to the portion between the chip and the film. As a result, the etching solution may flow to the chip surface, and the chip surface may be eroded by the etching solution, so that each chip device may not function.

  In contrast, 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, the etching does not proceed at all, and the wafer surface is simply modified. For this reason, even if the abrasive enters the crack in the cutting line of the wafer, the surrounding silicon is not melted, so that the crack does not further develop.

  As a result, cracks may progress in the polishing process, ie, the etching process in the cited document 2, but in the polishing process of the present application, the wafer is not etched at all even if the abrasive is put in, so the cracks hardly progress. . As a result, the conventional problem that the abrasive penetrates and peels the chip from the film on its own, or the abrasive wraps around the chip surface and erodes the chip, causing the chip device to fail. 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, which only chemically modifies the wafer surface. Next, since the modified surface is soft, the abrasive grains contained in the slurry act on the wafer surface in this state, so the wafer surface can be efficiently removed even with a very small stress. is there.

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

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

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

  At this time, the effect of further developing the crack does not work due to the silica sol or silica particles that have penetrated the crack. This is because the polishing pad does not enter the crack, so that the mechanical action does not work and consequently no chemical removal action occurs.

  As a result, the process-affected layer on the substrate surface generated during grinding is supplied with a chemical slurry containing silica sol and silica particles, and a mechanical frictional action occurs when the polishing pad comes into contact with the substrate. As a result, only the substrate surface is removed by chemical mechanical polishing (edited by Toshiro Toi: Detailed explanation on semiconductor CMP technology (Industry Research Committee) (2001) p.40-42).

  As a result, most of the work-affected layer on the wafer surface is removed. The formed wafer surface is a mirror surface. The principle of this mirror surface is as follows when compared with the chemical etching disclosed in Cited Document 2.

  In the case of chemical etching, as described above, lattice strain and crystal defects are selectively etched in a crystal such as silicon. For this reason, etch pits are formed, or large pits 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 removal action does not work unless the mechanical action works. The mechanical action, here the rubbing of the wafer surface by means of the polishing pad, will occur with equal probability on all substrate surfaces, irrespective of the crystalline state of the substrate surface. . Therefore, since all the surfaces are uniformly removed regardless of the crystal state, the chemical action is exerted, so that the surface is uniform and free of crystal defects and becomes a mirror surface. Here, since the mirror surface is ambiguous from a relative viewpoint, in this application, it is defined as a mirror surface obtained by chemical mechanical polishing.

  By performing such chemical mechanical polishing, an ideal mirror surface state can be obtained, which is greatly different from the cited document 2, and erosion due to penetration of the etching solution between the chip and the film can be prevented.

  Note that after chemical mechanical polishing, the chip is not yet completely broken. It only leaves the micropores that have developed from the modified layer on the surface portion after partial chemical mechanical polishing. The modified layer has already been removed by the previous grinding process.

  When the state of leaving the microvoids that have advanced from the modified layer is formed in a surface state that has been subjected to grinding and etching as shown in, for example, cited document 2, micropores that have advanced from the modified layer; It becomes impossible to clearly distinguish the unevenness promoted by the etching process after grinding. Therefore, when the chip is cleaved, the chip does not necessarily break from the minute holes, and in some cases, the ground grinding trace may be broken from the uneven portion further promoted by etching.

  When the surface is subjected to chemical mechanical polishing as in the present application, there is almost no unevenness on the surface of the wafer after processing, and only the microscopic voids that have advanced from the modified layer are left. Therefore, when the cleaving process is performed in this state, cracks further develop from the minute holes and cleave.

  Further, a wafer processing method for achieving the object of the present invention is a wafer processing method for processing a wafer in which a modified region is formed inside with a laser beam. And a grinding step of removing the modified region leaving a microcrack extending from the modified region, and a polishing step of polishing the back surface of the wafer with a polishing cloth after grinding.

  According to the present invention, stable quality chips can be obtained efficiently.

The figure which shows the general-view structure of the laser dicing apparatus. 1 is a conceptual configuration diagram showing a configuration of driving means of a laser dicing apparatus 1. FIG. FIG. 3 is a plan view illustrating a configuration of a driving unit of the laser dicing apparatus 1. The figure which shows the general-view structure of the grinding device. The elements on larger scale of the grinding apparatus 2. FIG. The elements on larger scale of the grinding apparatus 2. FIG. FIG. 3 is a schematic diagram of a polishing stage of the grinding apparatus 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 partial enlarged view. The flowchart which shows the flow of a process of the cutting method of a semiconductor substrate. The figure explaining a laser modification process. The figure explaining a cutting line. The figure explaining a grinding removal process. It is a figure explaining the crack progress in a grinding removal process, (a) is the schematic at the time of grinding, (b) is the state of the wafer W back surface, (c) is the state of the wafer W surface, (d) is the state of the wafer W Sectional drawing. The figure explaining the surface state of the wafer W back surface after a grinding removal process The figure explaining the division / separation process The figure explaining the division / 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 apparatus 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 accompanying drawings.

  The present invention includes a laser dicing apparatus 1, a grinding apparatus 2, a transport apparatus (not shown) for transporting a wafer processed by the laser dicing apparatus 1 to the grinding apparatus 2, and a wafer ground by the grinding apparatus 2 as a chip. It is performed by a cutting device constituted by a dividing device that divides into two.

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

  The wafer W is placed on the suction stage 13 such that a BG tape B having an adhesive material is attached to one surface of the wafer W, and the back surface faces upward.

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

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

The laser light conditions are as follows: 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 a Q switch pulse, 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 linearly polarized light. The condition of the condensation lens 24 is that the magnification is 50 times, N.I. A. Is 0.55, and the transmittance with respect to the wavelength of the laser beam 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 an optical system such as a collimating lens 32, a half mirror 33, and a condensation lens 24. Reflected light from the surface of the wafer W enters the CCD camera 35 as 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.

  This 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 through 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 includes a wafer cassette elevator (not shown), a wafer transfer means, an operation plate, an indicator lamp, and the like.

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

  On the operation plate, switches for operating each part of the dicing device 10 and a display device are attached. The indicator lamp displays an operation status such as processing end, emergency stop, etc. during processing of the dicing apparatus 10.

  FIG. 2 is a conceptual diagram illustrating details of the driving means 25. The driving means 25 includes a lens frame 26 that holds the condensation lens 24, a Z fine movement means 27 that is attached to the upper surface of the lens frame 26 and moves the lens frame 26 in the Z direction in the drawing, and a holding frame 28 that holds the Z fine movement means 27. , PZ1, PZ2, etc., which are linear fine movement means for finely 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 when a voltage is applied. Due to the expansion and contraction of the piezoelectric element, the condensation lens 24 is finely fed in the Z direction, and the position of the laser light condensing point in the Z direction is precisely positioned.

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

  For the linear fine movement means PZ1 and PZ2, a piezoelectric element is used similarly to the Z fine movement 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 driving means 25. As shown in FIG. 3, two linear fine movement means PZ 1 and PZ 2 are arranged in the X direction, one end of which 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 finely fed back and forth in the X direction, and the laser beam can be finely fed back and forth in the X direction or oscillated.

  A piezoelectric element may be used for one of the linear fine movement means PZ1 and PZ2, and the other may be an elastic member such as a spring material. Also, 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 irradiated to the inside of the wafer W through an optical system such as a collimating lens 22, a half mirror 23, a condensation lens 24, and the like. The position of the condensing point of the irradiated laser beam L in the Z direction is accurately adjusted to a predetermined position inside the wafer by adjusting the position of the wafer W in the Z direction 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 reciprocally moved by the linear fine movement means PZ1 and PZ2 provided in the laser head 40. The modified region P is formed while being vibrated in the X direction or in an arbitrary XY direction in parallel and the condensing point of the laser light L is vibrated minutely inside the wafer. Thereby, one line of the modified region P by multiphoton absorption is formed inside the wafer W along the cutting line of the wafer W.

  In addition, you may add the vibration of the Z direction by the Z fine movement means 27 as needed. In addition, the laser beam L is repeatedly reciprocated in the X direction, which is the processing direction, and the wafer W is sent in the X direction, so that the laser beam L is repeatedly irradiated in a state of going back and forth like a perforation. Also good.

  When one line of the 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 formed in the same manner for all the lines orthogonal to the previous line.

(2) About Grinding Device 2 FIG. 4 is a perspective view showing a general configuration of the grinding device 2. The main body 112 of the grinding apparatus 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.

  As shown in FIG. 5, 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), and the processing liquid used in each stage 118, 120, 122 is adjacent. It is prevented from splashing 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 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 that performs 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 upper surface and side surfaces of the partition plate 125 to isolate the rough grinding stage 118 and the fine grinding stage 120 from the outside. The top plates 128 and 129 have 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 has a through hole 126C through which the head of each stage is inserted.

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

  Since the polishing stage 122 performs chemical mechanical polishing, the polishing liquid contains a chemical abrasive. When a grinding process liquid is mixed in such a polishing process liquid, the concentration of the chemical abrasive is lowered, resulting in a problem that the processing time becomes longer. By maintaining the polishing stage 122 in a substantially confidential state, it is possible to prevent the grinding fluid and processing waste used in the precision 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, it is possible to prevent a processing failure caused by mixing of both processing liquids.

  FIG. 7 is a structural diagram of the polishing stage 122. In the polishing stage 122, polishing is performed by the polishing cloth 516 and the slurry supplied from the polishing cloth 156, and the work-affected layer generated on the back surface of the wafer W is removed by rough polishing and fine polishing. The work-affected layer is a general term for streaks and work strains (crystals are altered) generated 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 and 162 constituting a linear guide are provided on the side surface of the motor 158, and the guide blocks 162 and 162 are engaged with a guide rail 166 provided on the side surface of the support plate 164 so as to be movable up and down. Has been. Therefore, the polishing pad 156 is attached to the support plate 164 together with the motor 158 so as to be movable up and down.

  The support plate 164 is provided at the tip of the arm 168 arranged horizontally. A base end portion of the arm 168 is connected to an output shaft 174 of a motor 172 disposed in the casing 170. Therefore, when the motor 172 is driven, the arm 168 can rotate around the output shaft 174. As a result, the polishing cloth 56 is polished (see the solid line in FIG. 3), the polishing cloth cleaning stage 123 is in the polishing cloth cleaning position (see the two-dot chain line in FIG. 3), and the polishing cloth dressing stage 127 is in the dress position. 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. Examples of the polishing cloth 156 include polyurethane foam and polishing cloth. The polishing cloth cleaning stage 123 is provided with a removing member such as a brush for removing polishing debris. This removal member is rotationally driven when the polishing cloth 156 is cleaned, and the polishing cloth 156 is also rotationally driven by the motor 158. The abrasive cloth dressing stage 127 is made of the same material as the abrasive cloth 156, for example, polyurethane foam.

  Guide blocks 176 and 176 constituting linear motion guides are provided on the side surface of the casing 170, and the guide blocks 176 and 176 are movable up and down on a guide rail 180 provided on a side surface of the housing 178 for the screw feeder. Is engaged. A nut member 179 protrudes from the side surface of the casing 170. The nut member 179 is screwed into a screw rod 181 of a screw feeding device 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 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 linear movement action of the guide block 176 and the guide rail 180. As a result, the polishing pad 156 is greatly moved in the vertical direction, and the interval between the polishing head 161 and the wafer W is set to a predetermined interval.

  The piston 188 of the air cylinder device 186 is connected to the upper surface of the motor 158 through the through hole 169 of the arm 168. 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. However, the present invention is not limited to this. For example, if the work-affected layer can be removed, for example, grinding wheel or abrasive gel electrophoresis may be performed. You may apply. When applying a grinding wheel or electrophoresis of abrasive grains, it is preferable to perform quantitative polishing.

  Returning to the description of FIG. The alignment stage 116 is a stage that 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 sucked and held by a transfer robot (not shown), then transferred toward the empty chuck 132, and sucked and held on the suction surface of the chuck 132.

  The chuck 132 is installed on the index table 134, and chucks 136, 138, and 140 having the same function are installed on the circumference around the rotation shaft 135 of the index table 134 at an interval of 90 degrees. . A 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 attracted wafer W is roughly ground here. The chuck 138 is positioned on the precision grinding stage 120 in FIG. 4, and the attracted wafer W is finish-ground (fine grinding, spark out) here. The chuck 140 is positioned on the polishing stage 122 in FIG. 4, and the attracted wafer W is polished here, and the work-affected layer generated by grinding and the variation in the thickness of the wafer W are removed.

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

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

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

  As shown in FIG. 8C, the wafer W is placed on the mounting table 132a via the BG tape B. As shown in FIG. 8C, the mounting table 132a is formed so that a part of the outer periphery of the wafer W protrudes from the mounting table 132a when the wafer W is mounted on the mounting table 132a. 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 hole 132c is disposed so as to cover substantially the entire area of the mounting table 132a. A fluid coupling (not shown) is connected to the suction hole 132c, and a suction pump (not shown) connected to the fluid coupling sucks air. Accordingly, substantially the entire surface of the wafer W is firmly vacuum-sucked on the surface of the mounting table 132a. Thus, the wafer W and the mounting table 132a can be brought into close contact with each other without causing positional displacement.

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

  A piston 119 of the cylinder device 117 is connected to the lower part of the motor 192. When the piston 119 is extended, the piston 119 is inserted into and connected to a recess (not shown) formed in the lower part of the chucks 132, 136, 138, and 140. The chucks 132, 136, 138, and 140 are moved upward from the index table 134 by the continuous extending operation of the piston 119, and are positioned at the grinding positions by the cup-type grindstones 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 attracted and held by the chuck 132 is measured by a pair of measurement gauges (not shown) connected to the control unit 100. Each of these measurement gauges has a contact, and the contact is in contact with the upper surface (back surface) of the wafer W, and the other 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. In addition, you may implement the thickness measurement by a measurement gauge in-line. The method for measuring the thickness of the wafer W is not limited to this.

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

  The thickness of the wafer W whose back surface has been roughly ground by the rough grinding stage 118 is measured by a measurement gauge (not shown) connected to the control unit 100 after the cup-type grindstone 146 has retreated from the wafer W. The index table 134 is rotated 90 degrees in the direction of arrow R in FIG. 4 by the control unit 100, whereby the wafer W whose thickness has been measured is positioned on the fine grinding stage 120, and is precisely adjusted by the cup-type 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 that of the rough grinding stage 118, the description thereof is omitted here. The amount of grinding by the cup-type grindstone 154 is set by the control unit 100, and the processing movement amount and the rotation speed of the cup-type grindstone 154 are controlled by the control unit 100.

  The thickness of the wafer W whose back surface has been precisely ground by the precision grinding stage 120 is measured by a measurement gauge (not shown) connected to the control unit 100 after the cup-type grindstone 154 moves away 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 positioned 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 control unit 100, and the position of the polishing pad 156 is controlled by controlling the motor 182 by the control unit 100. Further, the control unit 100 controls the rotation speed of the motor 158, that is, the rotation speed of the polishing pad 156.

  The wafer W polished by the polishing stage 122 is rotated by the control unit 100 so that the arm 168 is rotated and the polishing cloth 156 is retracted from the upper position of the wafer W, and then a hand (not shown) of a robot (not shown). Is sucked and held 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. Since the damaged layer is removed, the polished wafer W is not easily damaged. Therefore, the wafer W is not damaged during transfer by the robot and during cleaning in the wafer cleaning stage 124.

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

(3) Dividing device Next, a dividing device (not shown) will be described. As the dividing apparatus, a conventional normal dividing apparatus can be used. For example, a dividing apparatus having the following configuration disclosed in Tables 2004-100240 can be used.

  That is, the peripheral edge 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 outer peripheral edge of the upper surface of this ring member is smoothly rounded. A UV light source (UV light irradiation means) is arranged below the dicing tape.

  While irradiating the UV light from the UV light source toward the dicing tape, the frame is pushed down. By irradiation with UV light, the adhesive of the dicing tape can be cured or the adhesive strength of the tape can be changed.

  At the same time, a downward force is applied to the frame and pushed downward. As a result, the dicing tape is expanded, and the interval between the chips is widened. At this time, since the outer peripheral edge of the upper surface of the ring member is smoothly rounded, the dicing tape S is smoothly expanded.

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

  Irradiation conditions such as UV light irradiation intensity (power), wavelength region, and irradiation time can be selected according to the material of the adhesive of the dicing tape S, the size of the wafer, the size of the chip after cleaving, and the like.

  Here, the UV light source is not necessarily required, and the chip can be appropriately cleaved by adjusting the adhesive strength of the dicing tape.

(4) Other Embodiments of Dividing Device FIG. 21 is a diagram showing an outline of the dividing device 300. 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 apparatus 300 mainly includes a wafer chuck 304 for attracting and 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. The independent suction chuck 310 and the communication groove chuck 312 is superimposed.

  The thicknesses of the communication groove chuck 312 and the independent suction chuck 310 are about 1 mm, respectively. It is preferable that each material is made of a resin material such as acrylic. However, the material is not limited to the resin material, and other materials such as ceramics may be used. Any material may be selected as long as the wafer chuck can be bent after the vacuum suction of the wear. Further, the material itself of the wafer chuck 304 does not necessarily have to be bent, and any structure or structure that can be bent as a whole may be used.

  The bending means 306 is a rod-shaped body having a rounded tip, and can bend the wafer chuck 304 into a hemispherical shape by pushing up the center of the back surface of the wafer chuck 304 from below.

  The wafer 302 is placed on the wafer chuck 304 while being attached to an expanded film 314 whose outer periphery is fixed by a frame such as metal, and is vacuum-sucked. The expanded film 314 is preferably slightly air permeable, and the air permeable allows the wafer 302 itself to be directly attracted to the wafer chuck 304 by a vacuum force.

  The wafer chuck 304 is bent into a hemispherical shape by the bending means while adsorbing the wafer 302. 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 parts 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 kamaboko shape. The dividing device 300 also includes means (not shown) for rotating the chuck bending 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 when the X-axis and Y-axis that are perpendicular to each other on the wafer surface are considered. Therefore, the wafer 302 is divided as follows. That is, the position of the chuck bending means 320 is adjusted so that one side surface 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 moved away from the wafer chuck 304 and rotated by 90 degrees, and the wafer 302 is moved to the Y side by pressing again against the lower surface of the wafer chuck 304 so that the one side surface is parallel to the Y axis. Split in direction. Thereby, the wafer 302 can be divided along the dividing line in both the X direction and the Y direction.

  Here, when the wafer 302 is bent by being pushed by the chuck bending means 320 via the dicing film which is an elastic film without vacuum-adsorbing the wafer 302, if the wafer is cracked first in some part, the crack Since the wafer bends sharply at the part where the curvature of the chuck deflecting means 320 is absorbed, the wafer is not partially bent and may follow the chuck deflecting means 320 without being divided.

  Therefore, when the wafer 302 is first vacuum-sucked to the wafer chuck 304 and the wafer 302 is corrected to a flat surface by the wafer chuck 304 and then bent together with the wafer chuck 304, each part in the wafer 302 is bent by the wafer chuck 304. Accordingly, since the wafer 302 is copied while being attracted, a constant bending stress is uniformly applied to the surface of the wafer 302, so that the wafer 302 can be divided without any remaining division.

<Semiconductor substrate cutting method>
Next, a method for cutting the semiconductor substrate will be described. FIG. 9 is a flowchart showing a process flow of the semiconductor substrate cutting method.

(1) Laser modification process (step S10)
The wafer W with the BG tape B attached to the front surface is placed on the suction stage 13 of the laser dicing apparatus 1 so that the back surface faces upward. The following processing is performed by the laser dicing apparatus 1 and controlled by the control unit 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 an optical system such as the collimating lens 22, the half mirror 23, and the condensation lens 24, and is modified to the inside of the wafer W. A quality region P is formed.

  In the present embodiment, since the thickness of the finally produced chip is about 50 μm, the laser beam is irradiated to a depth of about 60 μm to about 80 μm from the surface of the wafer W as shown in FIG. In order to efficiently break the 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 T from the 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 the pulsed laser beam L for processing, and forms a plurality of discontinuous modified regions P, P,. Inside the modified region P, microvoids (hereinafter referred to as cracks) K are formed. Hereinafter, a region in which a plurality of discontinuous modified regions P, P,... Are formed side by side is referred to as a modified layer.

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

(2) Grinding removal process (step S12)
When the modified region is formed along the cutting line L by the laser modification process (step S10), the wafer W is transferred from the laser dicing apparatus 1 to the grinding apparatus 2 by a transfer apparatus (not shown). The following processing is performed by the grinding apparatus 2 and controlled by the control unit 100.

  The transferred wafer W is placed on a chuck 132 (eg, chucks 136, 148, 140 are also acceptable) with the back surface of the wafer W on the upper side, that is, the BG tape B attached to the front surface of the wafer W on the lower side. The entire surface is vacuum-adsorbed to the chuck 132.

  The index table 134 is rotated about the rotation shaft 135 to bring the chuck 132 into 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-type grindstone 146. In the present embodiment, for example, Vitrified # 325 manufactured by Tokyo Seimitsu is used as the cup-type grindstone 146, and the rotational speed of the cup-type grindstone 146 is approximately 3000 rpm.

  After the rough grinding, the index table 134 is rotated around the rotation shaft 135 to bring the chuck 132 into the precision grinding stage 120, and the chuck 132 is rotated and the cup-type grindstone 154 is rotated to precisely grind the wafer W. In the present embodiment, for example, resin # 2000 manufactured by Tokyo Seimitsu is used as the cup-type grindstone 154, and the rotational speed of the cup-type grindstone 154 is approximately 2400 rpm.

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

  Therefore, as shown in FIG. 12, the modified layer is removed by the grinding process, and the modified region P by the laser beam does not remain in the cross section of the chip T which is the final product. Therefore, it can be avoided that the modified layer is crushed from the chip cross section, the chip T is broken from the crushed portion, and dust is generated from the crushed portion.

  Further, in the present embodiment, this grinding removal step includes a crack propagation step in which the cracks in the modified layer propagate in the thickness direction of the wafer W. FIGS. 13A and 13B are diagrams for explaining the mechanism by which cracks progress. FIG. 13A is a schematic diagram during grinding, FIG. 13B is a state of the back surface of the wafer W, FIG. 13C is a state of the surface of the wafer W, and FIG. 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 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 is adsorbed almost at a reduced pressure by a vacuum chuck as shown in FIG. 13 (c), so that the position shift due to thermal expansion does not occur. Is physically constrained to displacement

  That is, as shown in FIG. 13D, the back surface (grinding surface) of the wafer W tends to spread in the outer circumferential direction due to thermal expansion (displacement due to thermal expansion) when it is disk-shaped (displacement due to thermal expansion). The suction surface is constrained so that each point in the wafer surface to be spread is not physically displaced. For this reason, distortion occurs in the wafer, and cracks propagate in the thickness direction of the wafer W due to the internal distortion. This internal strain works equally between the portion that expands due to thermal expansion and each point in the wafer surface that is physically constrained. Crack growth due to internal strain is most efficient at the initial stage of grinding, ie, during rough grinding, where the amount of grinding is the largest and the frictional force is increased, that is, the frictional heat is increased.

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

  Even if grinding is performed under conditions for thermally expanding the wafer W, that is, conditions for generating a large amount of frictional heat (for example, reducing the amount of grinding fluid), the shear stress of the grinding immediately affects the modified layer. It is not what is done. 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 element of the crack propagation.

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

  In addition, when an external force is applied artificially, stress concentrates on a weak part of the material, so that it is difficult to control the cracks to uniformly and slowly progress, and the wafer is completely cleaved. On the other hand, in the case of the progress of the crack due to the internal strain in the present embodiment, it is possible to cause the crack to be advanced slightly because it is the internal strain due to the degree of thermal expansion. That is, it is possible to propagate the crack to the target surface and the surface of the wafer W. Therefore, it is possible to efficiently divide in the dividing / separating step (step S18) described later.

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

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

  After the fine grinding, the index table 134 is rotated around the rotation shaft 135 to bring the chuck 132 into the polishing stage 122, and chemical mechanical polishing is performed by the polishing cloth 156 of the polishing stage 122, and in the grinding removal step (step S12). 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, a polyurethane-impregnated non-woven cloth (for example, TS200L manufactured by Tokyo Seimitsu) is used as the polishing cloth 156, colloidal silica is used as the slurry, and the rotational speed of the polishing cloth 156 is approximately 300 rpm.

  Due to the grinding and removing process (step S12), the back surface of the wafer W has a large number of irregularities as shown in FIG. In the case of polishing by chemical etching, the surface shape is maintained as it is, so that there is a possibility that cracks are generated from the recesses, and the surface is not mirror-finished. On the other hand, in this embodiment, since chemical mechanical polishing is used, the processing distortion caused by the processing is removed, and the surface irregularities are removed to make a mirror surface.

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

(4) Expanding tape attaching process (step S16)
The expanded tape F is attached to the back surface of the wafer W on which the chemical mechanical polishing step (step S14) has been performed. The expanded tape is a kind of elastic tape and can be expanded and contracted.

  In the present embodiment, since the back surface of the wafer W is mirror-finished in the chemical mechanical polishing step (step S14), the adhesion between the expanded tape F and the wafer is also greatly improved. In addition, the bending strength of the finally generated chip T can be increased.

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

  Thereafter, as shown in FIG. 16, when the expanded tape F is expanded outward (expanded), 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 expanded tape F is further expanded, the individual chips T are separated.

  In the present embodiment, in the grinding and removing step (step S12), the wafer is efficiently transferred to the chip T simply by pulling the expanded tape F in the dividing / separating step by causing the crack to propagate downward from the target surface. It becomes possible to divide. Moreover, since the wafer is not completely cleaved when the crack is advanced, the work efficiency is good.

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

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

  In (A), (B), and (C) of FIG. 19, the horizontal axis is common, and each position corresponds to each other, and indicates the grinding time (s). The vertical axis of (A) in FIG. 19 indicates the cutting speed (grinding speed) (μm / s), and the vertical axis in (B) indicates ON / OFF of water supply to the grindstone being polished, (C) The vertical axis indicates the temperature (° C.) of the back surface of the wafer W during grinding.

  As shown in FIG. 19A, a total of 710 μm of rough grinding was performed while changing the grinding speed, and then 13 μm (not shown) of fine grinding was performed, followed by 2 μm of chemical mechanical polishing (not shown). At the time of wafering, as shown in FIG. 19B, an interruption period of water supply to the grindstone or the wafer was provided during the rough grinding. Water supply was stopped after lapse of t1 seconds from the start of grinding, and water supply was resumed after lapse of t2 seconds from the start of grinding. Water supply was performed at a flow rate of 10 L / min. Then, the said step S16, S18 process was performed, the wafer was cleaved, and the cleaved state was observed and evaluated. The results are summarized in FIG. 20, where the case where the chip did not crack or generate dust and was cracked satisfactorily was marked as ◯, and that where the chip cracked or dusted was marked as x.

  As shown in FIG. 19 (C), the back surface temperature of the wafer W starts to rise suddenly after elapse of t1 seconds after the start of grinding when water supply is stopped, and decreases immediately after elapse of t2 seconds after the start of grinding when 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 higher by grinding, the wafer was cleaved satisfactorily. This is presumably because cracks formed by the laser progressed due to the heat of grinding.

  Therefore, the grinding apparatus according to the present invention includes a means for measuring the temperature of the wafer, a means for turning on / off water supply to the grindstone or the wafer during grinding, and the wafer temperature to a predetermined value after a predetermined time has elapsed since the start of grinding. And a means for controlling the water supply to the wafer to be turned off. Thereby, the crack formed with the laser can be advanced and the wafer can be cleaved satisfactorily.

  As described above, according to the present embodiment, since the crack in the modified region formed by the laser beam can be propagated by grinding, the modified component formed by the laser beam on the cross section of the chip T. It is possible to prevent the area from remaining. For this reason, it is possible to prevent a problem that the chip T is broken or dust is generated from the cross section of the chip T. Therefore, a stable quality chip can be obtained efficiently.

(Appendix)
As can be understood from the description of the embodiment described in detail above, the present specification includes disclosure of various technical ideas including the invention described below.

  (Additional remark 1) The semiconductor substrate cutting method according to the first aspect of the present invention is such that the modified region is formed inside the wafer by entering laser light from the back surface of the wafer along the cutting line. A modified region forming process for forming minute vacancies in the region, and an adsorption for substantially uniformly adsorbing the entire surface of the wafer on which the modified region has been formed in the modified region forming step to the table independently in each region A grinding step of grinding the wafer having substantially the entire surface adsorbed on the table in the adsorption step from the back surface to remove the modified region and causing the micropores to propagate in the thickness direction of the wafer; Cleaving along the cutting line based on the step of chemically and mechanically polishing the wafer in which the micropores are developed in the thickness direction of the wafer in the grinding step, and the micropores left in the substrate Process and multiple chips after cleaving 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, a laser beam is incident from the back surface of the wafer along the cutting line to form a modified region inside the wafer, thereby forming micropores in the modified region. The modified region is removed by grinding the wafer from the back surface in a state where substantially the entire surface of the wafer on which the modified region has been formed is adsorbed uniformly and independently on each surface of the substrate.

  (Supplementary Note 2) The method for cutting a semiconductor substrate according to the second aspect of the present invention includes forming a modified region in the wafer by entering laser light from the back surface of the wafer along the cutting line, A modified region forming step for forming micropores in the modified region, and a substantially entire surface of the wafer on which the modified region is formed in the modified region forming step is uniformly and independently settable in each region. And in a state where the wafer is adsorbed, the laser beam is incident to grind and remove to a portion before the modified region formed inside the wafer, and microcracks extending from the modified region are removed from the depth of the substrate. A first grinding process that progresses in the vertical direction, a second grinding process that grinds and removes the modified region formed inside the wafer, and chemical mechanical polishing using a chemical slurry and a polishing pad that modify the wafer surface. While performing the reforming region Cleaved on the wafer based on the process of removing the work-affected layer introduced in the first and second grinding processes to make the surface mirror-finished and the micro-cracks that have developed in the wafer thickness direction And a step of separating the cleaved chip after cleaving.

  According to the method for cutting a semiconductor substrate according to the second aspect, the modified region is initially formed at a deep position inside the wafer, and is initially removed while generating grinding heat in the first grinding step. Thus, the crack formed in the modified region can be advanced to a deeper position on the wafer.

  However, in the first grinding step, if the laser-modified region is ground and removed with the same capacity as the unmodified region, the modified region has a large grain boundary, so that large crystal grains may be lost. In addition, more fatal cracks may develop along with these crystal grains. Therefore, in the first grinding step, it is preferable to perform grinding to a portion before the modified region where the crystallinity is constant.

  In the second grinding step, the region modified mainly by the laser is ground. At this time, the grinding wheel also has a high count, that is, a grinding wheel having a finer particle size than the first grinding process is used, and fatal cracks and defects derived from the modified region compared to the first grinding process. Gently grind so that it doesn't trigger. The second grinding step is only the modified region, and the grinding rate is set to a low condition even when compared with 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 chemical solution for modifying a wafer is supplied, and a polishing pad such as a polymer or nonwoven fabric is pressed against the wafer to perform chemical and mechanical polishing.

  If chemical mechanical polishing is performed on the modified region, large crystal grains may be lost in the modified region. In chemical mechanical polishing, a polishing pad such as a nonwoven fabric or polyurethane foam is used. Therefore, when crystal grains dropped off on the surface of the pad, scratches are generated due to the crystal grains constantly dropped during polishing. In such a case, it is necessary to remove the work-affected layer in the grinding process and achieve a mirror finish, and the polished surface is full of scratches.

  Therefore, in the state introduced into the chemical mechanical polishing process, the modified layer introduced by the laser in the second grinding process must be completely removed.

  (Supplementary Note 3) The method for cutting a semiconductor substrate according to the third aspect of the present invention is the method for cutting a semiconductor substrate according to the second aspect, wherein the modified region forming step is about 60 μm to about 80 μm from the surface of the wafer. The modified region is formed at a depth of about 5 μm, and the first grinding step causes the minute holes to extend from the surface of the wafer to a depth of about 50 μm and the surface of the wafer. .

  As a result, a modified region is formed at a depth of about 60 μm to about 80 μm from the surface of the wafer, and 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 beam does not remain on the cross section of the chip, minute holes can be left in the workpiece.

  (Supplementary Note 4) The semiconductor substrate cutting method according to the fourth aspect of the present invention is the semiconductor substrate cutting method according to the first aspect, wherein the grinding step is performed until the temperature of the wafer being ground reaches 70 ° C. or higher. The method includes the step of interrupting the supply of water to the grindstone during grinding.

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

  (Supplementary Note 5) The semiconductor substrate cutting method according to the fifth aspect of the present invention is the semiconductor substrate cutting method according to the second aspect or the third aspect, wherein the first grinding step is a temperature of the wafer being ground. The method includes a step of interrupting the supply of water to the grindstone during grinding until the temperature reaches 70 ° C. or higher.

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

  (Supplementary Note 6) The method for cutting a semiconductor substrate according to the sixth aspect of the present invention is the method for cutting a semiconductor substrate according to the first aspect or the fourth aspect, wherein the dividing step includes attaching an elastic tape to the surface of the wafer. And a step of expanding the elastic tape.

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

  (Appendix 7) A semiconductor substrate cutting device according to a seventh aspect of the present invention includes laser dicing means for forming a modified region in the wafer by making laser light incident from the back surface of the wafer along the cutting line; Grinding means for grinding the wafer from the back surface to remove the modified region, conveying means for conveying the wafer from the laser dicing means to the grinding means, and dividing means for dividing the wafer along a cutting line The laser dicing means forms the modified region by irradiating a laser beam toward the wafer and a table on which the surface of the wafer is placed downward. And a first control means for controlling the irradiation means so that a position irradiated with the laser light is changed, and the grinding means includes the wafer A suction table having a surface mounted downward and sucking substantially the entire surface of the wafer; a grinding wheel for grinding the wafer; and a second control means for controlling the height and rotation speed of the grinding stone. It is characterized by.

  Thereby, it is possible to prevent the modified region formed by the laser light from remaining on the cross section of the chip. For this reason, it is possible to prevent a problem that the chip is broken or generate dust from the chip cross section, and it is possible to efficiently obtain a chip having a stable quality.

  (Supplementary Note 8) The semiconductor substrate cutting device according to the eighth aspect of the present invention is the semiconductor substrate cutting device according to the seventh aspect, wherein the first control means is approximately 60 μm to approximately 80 μm from the surface of the wafer. The irradiation unit is controlled so as to form the modified region at a depth of about 2 μm, and the second control unit is configured such that the modified region extends from the surface of the wafer to a depth of about 50 μm and the surface of the wafer. The height and the number of rotations of the grindstone are controlled so as to advance the minute holes in the inside.

  Thereby, even if the workpiece is ground so that the modified region formed by the laser beam does not remain on the cross section of the chip, the minute holes can be left in the workpiece.

  (Supplementary Note 9) A semiconductor substrate cutting device according to a ninth aspect of the present invention is the semiconductor substrate cutting device according to the seventh aspect or the eighth aspect, wherein the means for measuring the temperature of the wafer being ground, A means for turning on / off the water supply to the grindstone or the wafer, and a means for controlling to turn off the water supply to the wafer until the wafer temperature reaches a predetermined value after a predetermined time has elapsed since the start of grinding. Features.

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

  DESCRIPTION OF SYMBOLS 1 ... Laser dicing apparatus, 2 ... Grinding apparatus, W ... Workpiece, B ... BG tape, F ... Expanding tape, 11 ... Wafer moving part, 13 ... Adsorption stage, 20 ... Laser optical part, 30 ... Observation optical part, 40 ... Laser head 50... Control unit 118 118 Coarse grinding stage 120 Fine grinding stage 122 Polishing stage 132 136 136 140 Chuck 146 154 Cup grinder 156 Polishing cloth 300 Splitting device

Claims (4)

A modified region forming step of forming a laser modified region between a target surface set inside the wafer and the back surface of the wafer;
Grinding the wafer by grinding from the back surface of the wafer to the target surface without dividing the wafer into chips, and
A wafer processing method comprising: A step of dividing the wafer into chips by applying an external force to the wafer after the grinding step is performed;
The wafer processing method according to claim 1. Modified region forming means for forming a laser modified region between a target surface set inside the wafer and the back surface of the wafer;
Grinding means for thinning the wafer by grinding from the back surface of the wafer to the target surface without dividing the wafer into chips.
A wafer processing system comprising: Dividing means for dividing the wafer into chips by applying an external force to the wafer thinned by the grinding means;
The wafer processing system according to claim 3.

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