Crack propagation device and crack propagation method

Abstract

To enable good cutting of a workpiece.SOLUTION: A crack propagation device for propagating a crack inside a workpiece includes crack propagation means for changing the degree of propagation of the crack by controlling the water supply when the back surface of a workpiece is ground.SELECTED DRAWING: Figure 18

Description

[Technical field]

[0001] The present invention relates to a technique for cleaving a wafer having a modified region formed therein by laser light. [Background technology]

[0002] Patent Document 1 describes a method of cutting a semiconductor substrate into chips by irradiating a laser onto a semiconductor substrate placed with its back side facing upwards to form a modified region inside the substrate, attaching an expandable tape to the back side of the semiconductor substrate, and applying a knife edge from above the expandable tape to split the substrate using the modified region as a base point.

[0003] Patent document 1 also describes a method in which a semiconductor substrate is placed with its back side facing up, a laser is irradiated to form a modified region inside the substrate, the substrate is then ground to make it thinner, an expandable tape is attached to the back side of the semiconductor substrate, and the expandable tape is stretched to split the substrate using the modified region as a base point.

[0004] Patent Document 2 describes a method of irradiating a laser onto a semiconductor substrate placed with its back surface facing up to form a modified region inside the substrate, thereby generating cracks in the thickness direction of the semiconductor substrate, and then grinding and chemically etching the back surface of the substrate to expose the cracks on the back surface, thereby cutting the semiconductor substrate into chips. Patent Document 2 also describes that cracks are generated in the thickness direction from the modified region by natural or relatively small forces, such as artificial forces or applying a temperature difference to the substrate to generate thermal stress. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3624909 [Patent Document 2] Patent No. 3762409 Summary of the Invention [Problem to be solved by the invention]

[0006] In the invention described in Patent Document 1, the substrate is broken by applying an external force locally with a knife edge, but this application of external force locally causes bending stress or shear stress to be applied to the substrate. However, it is difficult to distribute bending stress or shear stress uniformly over the entire substrate. For example, when bending stress or shear stress is applied to the substrate, the stress will be concentrated at a weak point somewhere, and it is not possible to efficiently apply the minimum necessary stress uniformly to the desired part.

[0007] Therefore, there is a problem that the cracking of the substrate varies, and if the cracking does not progress slowly, the substrate may break even within the chip. In addition, when cutting the substrate by applying stress locally and sequentially to the portion to be cut, for example, when collecting many chips from one substrate, there is a problem that productivity is significantly reduced because there are many cutting lines.

[0008] Furthermore, when an external force is applied to split the substrate, if the substrate is not thinned, a very large stress is required to split the wafer.

[0009] In particular, when the substrate thickness is sufficiently large compared to the depth width of the laser processing, even if an external force is applied, it is not always possible to cut the substrate cleanly and perpendicularly due to the influence of a sudden external force. Therefore, it may be necessary to irradiate several laser pulses in multiple stages in the thickness direction of the substrate.

[0010] In addition, in the inventions described in Patent Documents 1 and 2, the modified region formed inside the substrate by laser irradiation ultimately remains on the chip cross section. Therefore, dust may be generated from the modified region on the chip cross section. In addition, as a result of the chip cross section being locally fractured, the fractured cross section may trigger the chip to break. As a result, there is a problem that the flexural strength of the chip is reduced.

[0011] In the invention described in Patent Document 2, it is described that cracks naturally occur in the thickness direction from the modified region, but on the other hand, there are cases where the cracks do not necessarily occur naturally. In order to necessarily obtain the stable effect of cracking, it is sometimes necessary to take arbitrary measures, but when the cracks occur naturally, they do not fall under arbitrary measures.

[0012] It is also possible to apply a relatively small force, a temperature difference, to generate thermal stress, which can cause cracks to form in the thickness direction from the modified region. In this case, there is a problem in that it is very difficult to provide a uniform thermal gradient within the surface of the substrate. In other words, even if a thermal gradient is artificially applied, heat will disperse within the substrate through thermal conduction so as to partially alleviate the thermal gradient. Therefore, there is an extremely difficult problem in terms of how to constantly create a stable thermal gradient (stable temperature difference) sufficient to cut a certain substrate.

[0013] In addition, in the invention described in Patent Document 2, after grinding the semiconductor substrate, chemical etching is performed on the back surface. However, after grinding, grinding marks caused by fixed abrasive grains remain on the ground surface, and microcracks are formed accompanying the grinding, leaving a process-affected layer. When the surface is chemically etched, the part with large lattice distortion such as microcracks is selectively etched. Therefore, the microcracks are promoted and become larger. Therefore, not only the cutting starting area but also sometimes breaks from the microcracks formed by grinding and etching, which makes it difficult to perform stable cutting.

[0014] In addition, the etching process increases the unevenness of the substrate surface, so the substrate surface is not mirror-finished. As a result, the unevenness remains in the separated chips, and it is quite possible that the chips will break from the most uneven parts, i.e., from microcracks, resulting in a problem of reduced flexural strength of the chips.

[0015] Furthermore, when an etching solution acts on a portion that has been laser processed and modified, the modified portion is once melted, then recrystallized and solidified, and large grain boundaries are formed.

[0016] When an etching solution acts on such grain boundaries, etching proceeds in such a way that silicon grains peel off from the grain boundaries, resulting in etching that further promotes the formation of irregularities.

[0017] Specifically, the polishing process is described in the cited reference on page 12, line 1 as a grinding process and chemical etching on the back side. In the case of chemical etching, even if the product is left as it is, the chemical etching solution will penetrate into the cracks and dissolve the cracked parts.

[0018] In particular, if the cracks extend onto the surface of the substrate, the etching solution may penetrate between the chip and the film bonding the chip, causing the chip to peel off from the film.

[0019] Even if the cracks do not reach the surface of the substrate, etching will proceed along the cracks. In particular, when etching is performed after grinding, the etching solution will penetrate the cracks by capillary action, melting the tip of the crack and deepening the microcracks, and new etching solution will enter the cracks. In this case, if the etching solution acts on the vicinity of the device surface, it may dissolve the vicinity of the device surface and the etching may proceed to the inside of the element. Even if there is no problem at that time, the etching solution remaining on the wafer wall may enter the inside of the device and cause a defect later. Therefore, while the processing distortion on the wafer surface is removed, the cracks may be further promoted and the associated secondary problems may be induced.

[0020] In such cases, the cracks may eventually progress to the surface, causing the etching solution to get in between some of the chips and the film, resulting in the chips peeling off during processing. In particular, when the substrate becomes thinner as a result of grinding, the cracks tend to progress with even a small external force, and when the cracks reach the surface, chip peeling occurs. Therefore, when the substrate becomes thinner, processing must be carried out to prevent the cracks from progressing any further.

[0021] Patent Document 2 describes that grinding the back surface of the substrate causes cracks to occur in the modified region, but does not describe a method for fixing the substrate when grinding the substrate. When the periphery of the substrate is supported by fitting it into a retainer or the like as shown in Fig. 20, or when only a portion of the substrate is attracted to the substrate as shown in Fig. 21, the substrate is not uniformly constrained all over, and in such cases, cracks do not occur in the modified region even if the back surface of the substrate is ground.

[0022] The present invention has been made in view of the above circumstances, and has an object to provide a method for cutting a semiconductor substrate, which can efficiently obtain chips of stable quality. [Means for solving the problem]

[0023] In order to achieve the above-mentioned object, one aspect of the semiconductor substrate cutting method of the present invention is a wafer cutting method for cutting a wafer having a modified region formed therein by laser light, the method comprising the steps of: uniformly vacuum-adsorbing the front surface of the wafer to a table; grinding a back surface of the wafer while the wafer is vacuum-adsorbed, and grinding away the modified region while leaving behind microcracks extending from the modified region and propagating the microcracks in the wafer depth direction; a mirror-finishing step of chemically and mechanically polishing the back surface of the wafer after the grinding step; and a step of cutting the wafer after the mirror-finishing step.

[0024] In one embodiment of the semiconductor substrate cutting method of the present invention, the grinding process preferably includes a first grinding process in which the back surface of the wafer is ground to a portion just before the modified region and microcracks extending from the modified region are propagated in the depth direction of the wafer, and a second grinding process in which the modified region formed inside the wafer is ground to be removed while leaving the propagated microcracks.

[0025] In addition, in one aspect of the semiconductor substrate cleaving method according to the present invention, it is preferable that the mirror finishing step removes a process-affected layer introduced in the grinding step while leaving the microcracks, thereby achieving a mirror finish. Effect of the Invention

[0026] According to the method for cutting a semiconductor substrate of the present invention, cutting can be performed reliably and efficiently, and chips of stable quality can be obtained efficiently. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a diagram showing an overall configuration of a laser dicing apparatus 1. [Diagram 2] FIG. 2 is a conceptual diagram showing the configuration of a driving means of the laser dicing device 1. [Diagram 3] FIG. 2 is a plan view showing the configuration of a driving means of the laser dicing apparatus 1. [Figure 4] FIG. 2 is a diagram showing an overall configuration of a grinding device 2. [Diagram 5] FIG. [Figure 6] FIG. [Figure 7] 3 is a schematic diagram of a polishing stage of the grinding device 2. FIG. [Figure 8] 3A to 3C are diagrams showing details of a chuck of the grinding device 2, in which (a) is a plan view, (b) is a cross-sectional view, and (c) is a partially enlarged view. [Figure 9] FIG. [Figure 10] FIG. [Figure 11] FIG. 11 is a side cross-sectional view showing the state of a pressed elastic body. [Figure 12] FIG. [Figure 13] FIG. [Figure 14] FIG. 2 is a flow diagram showing a method for cutting a semiconductor substrate according to the present invention. [Figure 15] FIG. [Figure 16] 1A to 1D are diagrams explaining the progression of cracks during the grinding removal process, where (a) is a schematic diagram during grinding, (b) is the state of the back surface of the wafer W, (c) is the state of the front surface of the wafer W, and (d) is a cross-sectional view of the wafer W. [Figure 17] FIG. 4 is a diagram for explaining the surface state of the back surface of the wafer W after the grinding and removing process. [Figure 18] FIG. 1 shows the conditions for crack growth evaluation. [Figure 19] FIG. 13 shows the results of crack growth evaluation. [Figure 20] FIG. 13 is a diagram showing a conventional fixed state during substrate grinding. [Figure 21] FIG. 13 is a diagram showing a conventional fixed state during substrate grinding. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a method for cutting a semiconductor substrate according to the present invention will now be described in detail with reference to the accompanying drawings.

[0029] The present invention is performed by a cutting device composed of a laser dicing device 1, a grinding device 2, a tape peeling device 3, a transport device (not shown) that transports the wafer processed by the laser dicing device 1 to the grinding device 2 or the tape peeling device 3, and an expanding device that separates the wafer cut by the tape peeling device 3.

[0030] <About the device configuration> (1) Laser dicing device 1 1 is a diagram showing an overview of a laser dicing apparatus 1. As shown in the figure, the laser dicing apparatus 1 of this embodiment is mainly composed of a wafer moving unit 11, a laser head 40 consisting of a laser optical unit 20 and an observation optical unit 30, a control unit 50, etc.

[0031] The wafer moving unit 11 is composed of a suction stage 13 that suction-holds the wafer W, and an XYZθ table 12 that is provided on a main body base 16 of the laser dicing device 1 and that precisely moves the suction stage 13 in the XYZθ directions. The wafer moving unit 11 precisely moves the wafer W in the XYZθ directions in the figure.

[0032] A backgrind tape (hereinafter, BG tape) B having an adhesive is attached to the surface of the wafer W on which the devices are formed by a tape attachment device (not shown), and the wafer W is placed on the suction stage 13 with the back surface facing upward.

[0033] The wafer W may be mounted on the suction stage 13 in a state where a dicing sheet having an adhesive is attached to one surface of the wafer W and the wafer W is integrated with the frame via the dicing sheet. In this case, the wafer W is mounted on the suction stage 13 with the front surface facing upward.

[0034] The laser optical unit 20 is composed of a laser oscillator 21, a collimator lens 22, a half mirror 23, a condenser lens (light-collecting lens) 24, and a driving means 25 for minutely moving the laser light parallel to the wafer W. The laser light emitted from the laser oscillator 21 is condensed inside the wafer W via an optical system including the collimator lens 22, the half mirror 23, and the condenser lens 24. The Z-direction position of the focal point is adjusted by minutely moving the condenser lens 24 in the Z direction by a Z minute movement means 27 described later.

[0035] The laser light conditions are as follows: light source is a semiconductor laser pumped Nd:YAG laser, wavelength is 1064 nm, laser light spot cross-sectional area is 3.14×10-8 cm2, oscillation form is Q-switched pulse, repetition frequency is 100 kHz, pulse width is 30 ns, output is 20 μJ / pulse, laser light quality is TEM00, and polarization characteristics are linearly polarized. The condenser lens 24 conditions are: magnification is 50 times, NA is 0.55, and transmittance for the laser light wavelength is 60 percent.

[0036] The observation optical section 30 comprises an observation light source 31, a collimator lens 32, a half mirror 33, a condenser lens 34, a CCD camera 35 as an observation means, an image processing section 38, a television monitor 36, and the like.

[0037] In the observation optical section 30, illumination light emitted from an observation light source 31 passes through an optical system including a collimator lens 32, a half mirror 33, and a condenser lens 24, and illuminates the surface of the wafer W. Light reflected from the surface of the wafer W passes through the condenser lens 24, the half mirrors 23 and 33, and the condenser lens 34 and enters a CCD camera 35 as an observation means, and an image of the surface of the wafer W is captured.

[0038] This image 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.

[0039] The control unit 50 is made up of 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.

[0040] The laser dicing device 1 is composed of a wafer cassette elevator, a wafer transport means, an operation panel, and indicator lights, which are not shown.

[0041] The wafer cassette elevator moves a cassette containing wafers up and down to position it at a transfer position. The transfer means transfers the wafers between the cassette and the suction stage 13.

[0042] The operation panel is equipped with switches and a display device for operating each part of the dicing device 10. The indicator lamps display the operating status of the dicing device 10, such as when processing is in progress, processing is completed, and emergency stop.

[0043] 2 is a conceptual diagram illustrating the details of driving means 25. Driving means 25 is made up of lens frame 26 which holds condenser lens 24, Z fine movement means 27 which is attached to the upper surface of lens frame 26 and moves lens frame 26 slightly in the Z direction in the figure, holding frame 28 which holds Z fine movement means 27, and linear fine movement means PZ1 and PZ2 which move holding frame 28 slightly parallel to wafer W.

[0044] A piezoelectric element that expands and contracts when a voltage is applied is used for the Z fine movement means 27. The expansion and contraction of this piezoelectric element causes the condenser lens 24 to be slightly moved in the Z direction, so that the position of the focal point of the laser light in the Z direction can be precisely positioned.

[0045] The holding frame 28 is supported by two pairs of parallel springs made of four piano wires (not shown), allowing it to move freely in the X and Y directions but restricting its movement in the Z direction. Note that the method of supporting the holding frame 28 is not limited to this, and it may be supported by, for example, multiple balls above and below to restrict its movement in the Z direction while allowing it to move freely in the X and Y directions.

[0046] Like Z fine movement means 27, linear fine movement means PZ1, PZ2 use piezoelectric elements, one end of which is fixed to the case body of laser head 40 and the other end of which is in contact with the side surface of holding frame .

[0047] Fig. 3 is a plan view of driving means 25. As shown in Fig. 3, two linear fine movement means PZ1 and PZ2 are arranged in the X direction, one end of each of which is fixed to the case body of laser head 40 and the other end of which abuts against a side surface of holding frame 28. Therefore, by controlling the applied voltage, condenser lens 24 can be finely moved back and forth in the X direction, and laser light can be finely moved back and forth in the X direction or vibrated.

[0048] It is also possible to use a piezoelectric element for one of the linear fine movement means PZ1, PZ2, and to use an elastic member such as a spring for the other. Also, three linear fine movement means may be arranged on a circumference.

[0049] Laser light L is emitted from a laser oscillator 21, and the laser light L passes through an optical system including a collimator lens 22, a half mirror 23, and a condenser lens 24, and is then irradiated onto the inside of a wafer W. The Z-direction position of the focal point of the irradiated laser light L is accurately set to a predetermined position within the wafer by adjusting the Z-direction position of the wafer W using the XYZθ table 12 and controlling the position of the condenser lens 24 using the Z fine movement means 27.

[0050] In this state, the XYZθ table 12 is processed and fed in the X direction, which is the dicing direction, while the condenser lens 24 is moved slightly back and forth by the linear micro-movement means PZ1, PZ2 provided on the laser head 40, the laser light L is vibrated in the X direction or any XY direction parallel to the wafer W, and the focal point of the laser light L vibrates slightly inside the wafer to form a modified region K. As a result, a line of modified region K due to multiphoton absorption is formed inside the wafer W along the cutting line of the wafer W.

[0051] If necessary, vibration in the Z direction may be applied by the Z fine movement means 27. In addition, the laser light L may be repeatedly irradiated back and forth like a perforation by feeding the wafer W in the X direction while slowly finely feeding the laser light L back and forth in the X direction, which is the processing direction.

[0052] When one line of modified regions is formed along the cutting line, the XYZθ table 12 is indexed and fed by one pitch in the Y direction, and a modified region is formed on the next line in the same manner.

[0053] When modified regions have been formed along all of the cutting lines parallel to the X direction, the XYZθ table 12 is rotated by 90°, and modified regions are similarly formed along all of the lines perpendicular to the previous lines.

[0054] (2) Grinding device 2 4 is a perspective view showing an outline of the configuration of the grinding apparatus 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, an abrasive cloth cleaning stage 123, an abrasive cloth dressing stage 127, and a wafer cleaning stage 124.

[0055] The rough grinding stage 118, the fine grinding stage 120, and the polishing stage 122 are separated by a partition plate 125 (omitted in FIG. 4) as shown in FIG. 5, to prevent the machining fluid used in each stage 118, 120, 122 from splashing onto the adjacent stages.

[0056] 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 separate the four chucks 132, 136, 138, and 140 mounted on the index table 134.

[0057] The rough grinding stage 118 is a stage for performing rough grinding, and is surrounded by the side surface of the main body 112, a top plate 128, and a partition plate 125, as shown in Fig. 5. The fine grinding stage 120 is a stage for performing fine grinding, and is surrounded by the side surface of the main body 112, a top plate 129, and a partition plate 125, similar to the rough grinding stage 118. Brushes (not shown) are provided on the upper surface and side surface of the partition plate 125 to isolate the rough grinding stage 118 and the fine grinding stage 120 from the outside. Furthermore, the top plates 128 and 129 are formed with through holes 128A and 129A through which the heads of the respective stages are inserted.

[0058] The polishing stage 122 performs chemical mechanical polishing, and in order to isolate it from the other stages, it is covered by a casing 126 having a top plate 126A as shown in Fig. 5. The top plate 126A is formed with through holes 126C through which the heads of each stage are inserted.

[0059] 6, a brush 126B is attached to the side surface of the casing 126 through which the partition plate 125 passes, and this brush 126B comes into contact with the upper surface 125A and the side surface 125B of the partition plate 125 when the chuck 140 is located at the processing position. As a result, when the chuck 140 is located at the processing position, the casing 126, the partition plate 125, and the brush 126B are maintained in a substantially airtight state.

[0060] Since the polishing stage 122 performs chemical mechanical polishing, the polishing liquid contains a chemical abrasive. If the grinding liquid is mixed into such a polishing liquid, the concentration of the chemical abrasive decreases, causing a problem that the processing time becomes longer. By keeping the polishing stage 122 in a substantially airtight state, it is possible to prevent the grinding liquid used in the fine grinding stage 120 and processing debris from entering the polishing stage 122, and also to prevent the polishing liquid used in the polishing stage 122 from scattering from the polishing stage 122. Therefore, processing defects caused by mixing of the two processing liquids can be prevented.

[0061] 7 is a structural diagram of the polishing stage 122. In the polishing stage 122, the wafer W is polished by the polishing cloth 156 and the slurry supplied from the polishing cloth 156, and a process-damaged layer occurring on the back surface of the wafer W is removed by rough polishing and fine polishing. The process-damaged layer is a general term for scratches and process distortions (crystals are altered) and the like occurring due to grinding.

[0062] The polishing cloth 156 of the polishing stage 122 is attached to a polishing head 161 connected to an output shaft 160 of a motor 158. Guide blocks 162, 162 constituting a linear guide are provided on the side of the motor 158, and the guide blocks 162, 162 are engaged with a guide rail 166 provided on the side of a support plate 164 so as to be vertically movable. Therefore, the polishing cloth 156, together with the motor 158, is attached to the support plate 164 so as to be vertically movable.

[0063] The support plate 164 is provided at the tip of an arm 168 arranged horizontally. The base end of the arm 168 is connected to an output shaft 174 of a motor 172 arranged in a casing 170. Therefore, when the motor 172 is driven, the arm 168 can rotate around the output shaft 174. This allows the polishing cloth 56 to be moved within a range between a polishing position (see solid line in FIG. 3), a polishing cloth cleaning position (see two-dot chain line in FIG. 3) by the polishing cloth cleaning stage 123, and a dressing position by the polishing cloth dressing stage 127. When the polishing cloth 156 is moved to the polishing cloth cleaning position, the surface of the polishing cloth 156 is cleaned by the polishing cloth cleaning stage 123 to remove polishing debris and the like adhering to the surface. Examples of the polishing cloth 156 include polyurethane foam and polishing cloth, and the polishing cloth cleaning stage 123 is provided with a removal member such as a brush for removing polishing debris. This removal member is rotated when the polishing cloth 156 is cleaned, and the polishing cloth 156 is also rotated by the motor 158. The polishing cloth dressing stage 127 is made of the same material as the polishing cloth 156, for example, polyurethane foam.

[0064] Guide blocks 176, 176 constituting a linear guide are provided on the side of the casing 170, and these guide blocks 176, 176 are engaged with a guide rail 180 provided on the side of a housing 178 for a screw feed device so as to be movable up and down. A nut member 179 is provided protrudingly on the side of the casing 170. The nut member 179 is screwed to a screw rod 181 of a screw feed device disposed in the housing 178 through an opening (not shown) formed in the housing 178. An output shaft 184 of a motor 182 is connected to the upper end of the screw rod 181. Therefore, when the motor 82 is driven to rotate the screw rod 181, the casing 70 is moved up and down by the feeding action of the screw feed device and the linear action of the guide block 176 and the guide rail 180. As a result, the polishing cloth 156 is moved largely in the vertical direction, and the interval between the polishing head 161 and the wafer W is set to a predetermined interval.

[0065] A piston 188 of an air cylinder device 186 is connected to the upper surface of the motor 158 via a through hole 169 of the arm 168. A regulator 190 that controls the internal pressure P of the cylinder is also connected to the air cylinder device 186. Therefore, when the internal pressure P is controlled by this regulator 190, the pressing force (pressure contact force) of the polishing cloth 156 against the wafer W can be controlled.

[0066] In this embodiment, the polishing cloth 156 is used as the polishing body, but the present invention is not limited to this, and as long as it is possible to remove the processing-affected layer, for example, a polishing stone or electrophoresis of abrasive grains may be used. When a polishing stone or electrophoresis of abrasive grains is used, it is preferable to perform fixed quantity polishing.

[0067] Returning to the explanation of Fig. 4, the alignment stage 116 is a stage that aligns the wafer W transferred from the laser dicing device 1 by a transfer device (not shown) to a predetermined position. The wafer W aligned on this alignment stage 116 is sucked and held by a transfer robot (not shown), and then transferred to an empty chuck 132 and sucked and held on the suction surface of this chuck 132.

[0068] Chuck 132 is mounted on index table 134, and chucks 136, 138, and 140 having the same function are mounted at 90 degree intervals on a circumference centered on rotation shaft 135 of index table 134. A spindle (not shown) of a motor (not shown) is connected to rotation shaft 135.

[0069] The chuck 136 is positioned at the rough grinding stage 118 in Fig. 4, where the adsorbed wafer W is roughly ground. The chuck 138 is positioned at the fine grinding stage 120 in Fig. 4, where the adsorbed wafer W is finish ground (fine grinding, spark out). The chuck 140 is positioned at the polishing stage 122 in Fig. 4, where the adsorbed wafer W is polished, and the process-induced layer caused by grinding and the variation in thickness of the wafer W are removed.

[0070] Here, a description will be given of the chucks 132, 136, 138, and 140. Since the chucks 136, 138, and 140 have the same configuration as the chuck 132, only the chuck 132 will be described and a description of the chucks 136, 138, and 140 will be omitted.

[0071] FIG. 8 shows details of the chuck 132, where (a) is a plan view of the chuck 132, (b) is a cross-sectional view taken along line A-A' in (a), and (c) is an enlarged view of part B in (b).

[0072] The chuck 132 is constructed by fitting a mounting table 132a made of a porous material (for example, porous ceramics) into a chuck body 132b made of a dense body. A suction hole 132c is formed for vacuum suction on the underside of the chuck body 132b where the mounting table 132a is fitted. The chuck 132 is desirably formed of a material with low thermal conductivity.

[0073] As shown in Fig. 8(c), the wafer W is placed on the mounting table 132a via the BG tape B. As shown in Fig. 8(c), the mounting table 132a is formed so that when the wafer W is placed on the mounting table 132a, a part of the outer periphery of the wafer W protrudes from the mounting table 132a, but the width x is about 1.5 mm. The wafer W used in this embodiment has a diameter of about 12 inches and a thickness t of about 775 µm.

[0074] 8(a) and (b), 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 holes 132c, and a suction pump (not shown) connected to the fluid coupling sucks in air. Therefore, substantially the entire surface of the wafer W is firmly vacuum-sucked to the surface of the mounting table 132a. This allows the wafer W and the mounting table 132a to be in close contact with each other without causing misalignment.

[0075] 7, a spindle 194 and a motor 192 are respectively connected to the bottom surface of the chucks 132, 136, 138, 140, and the chucks 132, 136, 138, 140 are rotated by the driving force of the motor 192. The motor 192 is supported by the index table 134 via a support member 193. This makes it possible to eliminate the need to disconnect the spindle 194 from the chucks 132, 136, 138, 140 and to connect the chucks 132, 136, 138, 140 to the spindle 194 installed at the next movement position every time the chucks 132, 136, 138, 140 are moved by the motor 137.

[0076] A piston 119 of a cylinder device 117 is connected to the lower part of the motor 192. When the piston 119 is extended, it is fitted into and connected to recesses (not shown) formed in the lower parts of the chucks 132, 136, 138, and 140. Then, as the piston 119 continues to extend, the chucks 132, 136, 138, and 140 are moved upward from the index table 134 and positioned at a grinding position by the grinding wheels 146 and 154.

[0077] The control unit 100 includes a CPU, a memory, an input / output circuit unit, and the like, and controls the operation of each unit of the grinding device 2.

[0078] The thickness of the wafer W held by suction on 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, one of which is in contact with the upper surface (rear 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 the difference between in-process gauge readings, with the upper surface of the chuck 132 used as a reference point. Note that thickness measurement using the measurement gauges may be performed in-line. Also, the method of measuring the thickness of the wafer W is not limited to this.

[0079] The index table 134 is rotated 90 degrees in the direction of the arrow R in FIG. 4 by the control unit 100, so that the wafer W whose thickness has been measured is positioned on the rough grinding stage 118, and the back surface of the wafer W is roughly ground by the cup-shaped grindstone 146 of the rough grinding stage 118. As shown in FIG. 4, the cup-shaped grindstone 146 is connected to an output shaft (not shown) of a motor 148, and is attached to a grindstone feeder 152 via a support casing 150 for the motor 148. The grindstone feeder 152 moves the cup-shaped grindstone 146 up and down together with the motor 148, and the cup-shaped grindstone 146 is pressed against the back surface of the wafer W by this downward movement. This allows the back surface of the wafer W to be roughly ground. The control unit 100 sets the amount of downward movement of the cup-shaped grindstone 146 and controls the motor 148. The amount of downward movement of the cup-shaped grindstone 46, i.e., the amount of grinding by the cup-shaped grindstone 146, is set based on a reference position of the cup-shaped grindstone 146 registered in advance and the thickness of the wafer W detected by the measurement gauge. The control unit 100 also controls the number of rotations of the motor 148, thereby controlling the number of rotations of the cup-shaped grindstone 146.

[0080] After the cup-shaped grinding wheel 146 is retracted from the wafer W, the thickness of the wafer W, which has been roughly ground on the rough grinding stage 118, is measured by a measuring gauge (not shown) connected to the control unit 100. The control unit 100 rotates the index table 134 by 90 degrees in the direction of the arrow R in FIG. 4, so that the wafer W, whose thickness has been measured, is positioned on the fine grinding stage 120, where it is fine ground and sparked out by the cup-shaped grinding wheel 154 of the fine grinding stage 120. The structure of the fine grinding stage 120 is the same as that of the rough grinding stage 118, and therefore a description thereof will be omitted here. The amount of grinding by the cup-shaped grinding wheel 154 is set by the control unit 100, and the processing movement amount and rotation speed of the cup-shaped grinding wheel 154 are controlled by the control unit 100.

[0081] After the cup-shaped grinding wheel 154 is retracted from the wafer W, the thickness of the wafer W, which has been precision ground on the precision grinding stage 120, is measured by a measuring gauge (not shown) connected to the control unit 100. 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, so that the rear surface of the wafer W is mirror-finished. The vertical movement distance of the polishing cloth 156 is set by the control unit 100, and the control unit 100 controls the motor 182 to control the position of the polishing cloth 156. The control unit 100 also controls the rotation speed of the motor 158, i.e., the rotation speed of the polishing cloth 156.

[0082] After the control unit 100 rotates the arm 168 and the polishing cloth 156 is retracted from the position above the wafer W, the wafer W polished on the polishing stage 122 is attracted and held by a hand (not shown) of a robot (not shown) and transported to the wafer cleaning stage 124. A stage having a rinse cleaning function and a spin drying function is used as the wafer cleaning stage 124. Since the polished wafer W has had its process-affected layer removed, it is not easily damaged, and therefore is not damaged during transportation by the robot or cleaning on the wafer cleaning stage 124.

[0083] The wafer W that has been cleaned and dried on the wafer cleaning stage 124 is suction-held by a hand (not shown) of a robot (not shown) and stored on a predetermined shelf of a cassette (not shown).

[0084] (3) Tape peeling device 3 9 is a side view showing the configuration of the tape peeling device 3. The BG tape B or the expand tape E is attached to the wafer W by the tape peeling device 3. Furthermore, the wafer W ground and polished by the grinding device 2 is cleaved by the tape peeling device 3.

[0085] The tape separation device 3 includes a table 211 that is rotatable by a driving device (not shown). On the upper surface of the table 211, an elastic body 212 on which the wafer W is placed is attached.

[0086] A supply reel 213 and a peeling roller 214 are provided above the table 211, and a peeling film 215 for peeling off the BG tape B adhered to the surface of the wafer W is unwound from the supply reel 213 and taken up by a take-up reel 218 via guide rollers 216 and 217.

[0087] A pressing member 219 for cutting the wafer W is provided near the peeling roller 214 (for example, above the outer periphery of the table 211).

[0088] 10 are formed at intervals equal to or smaller than the size of the chips C formed on the wafer W. The elastic body 212 is connected to a vacuum generating source (not shown), and is formed so that the grooves 212a, 212a... etc. can adsorb and fix the wafer W mounted on a frame F via an expandable tape E attached to the back surface and a BG tape B attached to the front surface.

[0089] For example, SBR (styrene butadiene rubber) or NBR (nitrile butadiene rubber) can be suitably used as the material of the elastic body 212. The grooves 212a may be in the shape of holes or in the shape of projections and recesses.

[0090] For example, when a sponge-like elastic body 212B having many small voids as shown in Fig. 11(a) is used to cleave a wafer W, the voids become smaller and flatten, causing permanent compression set. For this reason, when the elastic body 212B is used repeatedly, the elastic modulus gradually changes due to deformation, making it impossible to cleave the wafer W stably.

[0091] 11(b), in the case of an elastic body 212C that does not have grooves, holes, or unevenness, when a part of the elastic body is pressed in, the volume is constant and the surrounding part rises up. In this case, even if an attempt is made to press locally to sink the wafer and cut it, the stress is dispersed, making it difficult to cut it efficiently.

[0092] In contrast, as shown in FIG. 11(c), the elastic body 212 has room for lateral deformation due to the grooves 212a when pressed from above, so that uniform deformation occurs and stress is concentrated on the cutting line S along which cutting is desired, thereby ensuring reliable and efficient cutting.

[0093] 10, the pressing member 219 is formed with a radius R smaller than the interval L of the cutting lines S where the modified layer P is formed. Since the radius R is smaller than the interval L, when the pressing member 219 presses one cutting line S, it does not press other cutting lines S. As a result, stress is concentrated on the cutting line S where cutting is desired, and cutting can be performed reliably and efficiently.

[0094] The wafer W is cut by adhering a BG tape B to the front side of the wafer W on which a modified layer P has been formed along a cutting line S, and an expandable tape E to the back side of the wafer W, as shown in Fig. 12. The tape peeling device 3 adjusts the position of the wafer W by rotating the table 211 so that a pressing member 219 is parallel to one side of the cutting line S formed in a lattice pattern, as shown in Fig. 12.

[0095] In this state, the pressing member 219 is pressed against the wafer W and rolled, thereby cutting the wafer W along one of the cutting lines S. After cutting one of the cutting lines S, the table 211 on which the wafer W is placed is rotated 90 degrees by a driving means (not shown), thereby disposing the table 211 so that the other cutting line S and the pressing member 219 are parallel to each other. In this state, the pressing member 219 is pressed against the wafer W and rolled, thereby cutting the wafer W along the other cutting line S.

[0096] Since the BG tape B and the expandable tape E are attached to the front and back surfaces of the wafer W, after one cutting line S is cut, when the adjacent cutting line S is cut, the position is restrained by the BG tape B and the expandable tape E, and the chip intervals do not increase significantly at the already cut cutting line S. This prevents the local stress of the pressing member 219 from being dispersed not only by the vertical deformation caused by the elastic body 212 but also by the horizontal deformation caused by the large increase in the intervals between the chips C, and the stress is concentrated to ensure efficient cutting.

[0097] In addition, by attaching the BG tape B and the expand tape E to the front and back surfaces, fragments generated when the wafer W is cut do not adhere to the elastic body 212, and even if the next wafer W is placed on the elastic body 212, there is no adverse effect due to the fragments.

[0098] The peeling roller 214 is formed of an elastic body that is softer than the elastic body 212. The BG tape B has, for example, an ultraviolet-curing adhesive on its adhesion surface, and its adhesive strength is reduced by irradiating it with ultraviolet light from an ultraviolet irradiation device (not shown) provided inside or outside the tape peeling device 3. A peeling film 215 is affixed onto the BG tape B whose adhesive strength has been reduced by rolling the peeling roller 214 laterally (in the direction of arrow A shown in FIG. 9) while pressing it downward, as shown in FIG. 9.

[0099] After the peeling film 215 is attached, a winding unit 218A including a winding reel 218 and a guide roller 217 moves laterally (in the direction of arrow B shown in FIG. 9 ) together with the peeling roller 214 while winding up the peeling film 215, thereby peeling the BG tape B from the wafer W.

[0100] When applying the peeling film 215 using the peeling roller 214 or peeling off the BG tape B, the wafer W, in which the cutting line S for dividing the chips C is arranged parallel to the peeling roller 214 as shown in FIG. 13(a), is rotated by 45 degrees by the table 211 so that the cutting line S intersects the peeling roller 214 at an angle as shown in FIG. 13(b).

[0101] This prevents the position of the cleaved chip C from shifting when the peeling film 215 is attached or when the BG tape B is peeled off, and does not adversely affect subsequent processes such as picking up the chip C after expansion.

[0102] (4) Expanding device Next, the expanding device (not shown) will be described. A conventional expanding device can be used as the expanding device. For example, an expanding device having the following configuration, as disclosed in Japanese Patent Application Laid-Open No. 2007-173587, can be used.

[0103] That is, the peripheral edge of the expanding tape E is fixed to a frame-shaped frame F. A ring member abuts the underside of the inner part of the peripheral edge of the expanding tape E. The outer peripheral edge of the upper surface of this ring member is smoothly chamfered with a radius. A downward force is applied to the frame F, which pushes it downward. This expands the dicing tape and increases the space between the chips. At this time, since the outer peripheral edge of the upper surface of the ring member is smoothly chamfered with a radius, the expanding tape E expands smoothly.

[0104] Various known linear motion devices can be used as the mechanism for pushing down the frame F. For example, a linear motion device made up of a cylinder member (hydraulic, pneumatic, etc.), a motor, and a screw (a combination of a male screw as a shaft and a female screw as a bearing) can be used.

[0105] <Method of cutting semiconductor substrate> Next, a method for cutting a semiconductor substrate will be described with reference to a flowchart shown in FIG 14.

[0106] (1) BG tape attachment process (Step S1) In the method for cutting a semiconductor substrate of the present invention, first, a BG tape B is attached to the front surface side of a wafer W on which a circuit pattern and the like are formed (step S1).

[0107] The BG tape B is adhered to the wafer W by a tape adhering device (not shown). When adhering the BG tape B, the table 211 is rotated 45 degrees so that the cutting line S for dividing the chips C intersects at an angle with respect to the adhering roller that adheres the tape. This prevents the wafer W from being broken along the cutting line S by the pressure of the adhering roller while the BG tape B is being adhered to the wafer W.

[0108] (2) Laser modification process (step S2) The wafer W with the BG tape B attached to its front surface is placed with its back surface facing upward on the suction stage 13 of the laser dicing apparatus 1. The following processing is performed by the laser dicing apparatus 1 and is controlled by the control unit 50.

[0109] When laser light L is emitted from a laser oscillator 21, the laser light L is irradiated onto the inside of a wafer W via an optical system including a collimator lens 22, a half mirror 23, and a condenser lens 24, and a modified region K is formed inside the wafer W.

[0110] In this embodiment, since the thickness of the chips that are finally produced is approximately 50 μm, the laser light is irradiated to a depth of approximately 60 μm to approximately 80 μm from the front surface of the wafer W. This is because, in order to efficiently break the front surface (device surface) of the wafer W, it is necessary to form a laser modified region at a relatively deep position close to the reference surface, which is the surface located on the back side of the front surface of the wafer W by the thickness of the chip C.

[0111] The control unit 50 scans the surface of the wafer W with a pulsed processing laser light L in parallel to form a plurality of discontinuous modified regions K... in the wafer W. Micropores (hereinafter referred to as cracks) are formed inside the modified regions K. Hereinafter, the region in which a plurality of discontinuous modified regions K... are formed in an array is referred to as a modified layer.

[0112] When the modified layers are formed along all of the cutting lines S shown in FIG. 10, the process of step S2 ends.

[0113] (3) Grinding and Removal Process (Step S3) After the modified region K is formed along the cutting line S by the laser modification process (step S2), the wafer W is transported by a transport device (not shown) from the laser dicing device 1 to the grinding device 2. The following processing is performed in the grinding device 2 and is controlled by the control unit 100.

[0114] The transported wafer W is placed on the chuck 132 (for example, chucks 136, 148, and 140 are also acceptable) with its back surface facing up, i.e., with the BG tape B attached to the front surface of the wafer W facing down, and approximately the entire surface of the wafer W is vacuum-adsorbed to the chuck 132.

[0115] The index table 134 is rotated about a rotation axis 135 to carry the chuck 132 into the rough grinding stage 118, and the wafer W is roughly polished.

[0116] Rough polishing is performed by rotating the chuck 132 and the cup-shaped grindstone 146. In this embodiment, for example, Vitrified #325 manufactured by Tokyo Seimitsu is used as the cup-shaped grindstone 146, and the rotation speed of the cup-shaped grindstone 146 is about 3000 rpm.

[0117] After the rough polishing, the index table 134 is rotated about the rotation axis 135 to carry the chuck 132 into the fine grinding stage 120, and the chuck 132 and the cup-shaped grindstone 154 are rotated to fine polish the wafer W. In this embodiment, a rough grindstone, for example, Resin #2000 manufactured by Tokyo Seimitsu, is used as the cup-shaped grindstone 154, and the rotation speed of the cup-shaped grindstone 154 is approximately 2400 rpm.

[0118] 15, rough polishing and fine polishing are combined to grind down to the target surface, that is, to a depth of about 50 μm from the surface of the wafer W. In this embodiment, roughly 700 μm of grinding is performed in rough polishing, and about 30 to 40 μm of grinding is performed in fine polishing, but this is not strictly determined, and the grinding amount may be determined so that the time for rough polishing and fine polishing are approximately the same.

[0119] 15, the modified layer is removed in the grinding process, and no modified region K by the laser light remains on the cross section of the final product, the chip C. This prevents the modified layer from fracturing from the chip cross section, causing the chip C to crack from the fracturing parts, and prevents dust from being generated from the fracturing parts.

[0120] In this embodiment, the grinding removal step includes a crack propagation step of propagating the cracks in the modified layer in the thickness direction of the wafer W. Fig. 16 is a diagram for explaining the mechanism by which the cracks propagate, in which (a) is a schematic diagram during grinding, (b) is the state of the back surface of the wafer W, (c) is the state of the front surface of the wafer W, and (d) is a cross-sectional view of the wafer W during grinding.

[0121] During grinding, the grinding surface shown in Fig. 16(a), i.e., the back surface of the wafer W, expands due to grinding heat as shown in Fig. 16(b). On the other hand, the surface opposite to the grinding surface, i.e., the front surface of the wafer W, is almost entirely vacuum-adsorbed by a vacuum chuck as shown in Fig. 16(c), and is physically restrained from lateral displacement so as to prevent positional deviation due to thermal expansion.

[0122] That is, as shown in Fig. 16(d), the back surface (grinding surface) of the wafer W, if it is disk-shaped, tends to expand in the outer periphery direction due to thermal expansion (displacement due to thermal expansion), whereas the front surface (adsorption surface) of the wafer W is physically restrained so that each point on the wafer surface that is expanding does not shift position. As a result, distortion occurs inside the wafer, and this internal distortion causes cracks to propagate in the thickness direction of the wafer W. This internal distortion acts evenly between the part that expands due to thermal expansion and each point on the wafer surface that is physically restrained. Crack propagation due to internal distortion is most efficient in the initial stage of grinding, i.e., during rough polishing, when the amount of grinding is largest and the frictional force is also large, i.e., the frictional heat can also be large.

[0123] The laser modified area is formed at a relatively deep position close to the thickness of the chip. Therefore, the distance from the grinding surface to the laser modified layer is relatively far in the early stage of grinding, but the modified layer is located relatively close enough to the target surface to cause cracks to grow. Therefore, in order to cause cracks to grow, it is advisable to promote thermal expansion of the wafer W by using grinding heat in the early stage of rough polishing.

[0124] Even if grinding is performed under conditions that cause thermal expansion of the wafer W, that is, conditions that generate a large amount of frictional heat (for example, by reducing the amount of grinding fluid), the shear stress of grinding is not immediately applied to the modified layer. In this embodiment, the cracks do not grow due to the shear stress caused by grinding, but the thermal expansion caused by the grinding heat is the dominant factor in the growth of the cracks.

[0125] When the crack is propagated by internal strain, the crack can be propagated uniformly at each point on the surface of the wafer W regardless of the type of wafer W, regardless of the variation in rigidity of the wafer W. Therefore, it is possible to prevent stress from concentrating on parts with weak rigidity due to the presence of defects on the surface of the wafer W, as in the case of applying artificial stress.

[0126] Furthermore, when an external force is applied artificially, stress is concentrated in weak parts of the material, making it difficult to control the crack to grow uniformly and slowly, and the wafer is completely cleaved. In contrast, in the case of crack growth due to internal strain in this embodiment, the internal strain is caused by the degree of thermal expansion, so it is possible to delicately grow the crack. In other words, the crack can be grown to between the target surface and the surface of the wafer W. This makes it possible to efficiently divide the wafer in the wafer cleaving process (step S6) described later.

[0127] The internal distortion caused by the thermal expansion of the wafer W is to be distinguished from the so-called thermal stress caused by the temperature difference. Thermal stress occurs in proportion to the temperature gradient, but in this embodiment, the generated heat escapes to the chucks 132, 136, 138, and 140, so no thermal stress occurs.

[0128] (4) Chemical mechanical polishing process (step S4) This process is carried out by the grinding device 2 and is controlled by the control unit 100.

[0129] After the fine polishing, the index table 134 is rotated around the rotation axis 135 to load the chuck 132 into the polishing stage 122, where chemical mechanical polishing is performed using the polishing cloth 156 of the polishing stage 122. In the polishing removal process (step S3), the processed layer formed on the back surface of the wafer W is removed, and the back surface of the wafer W is mirror-finished.

[0130] In this embodiment, a polyurethane-impregnated nonwoven fabric (for example, TS200L manufactured by Tokyo Seimitsu) is used as the polishing cloth 156, colloidal silica is used as the slurry, and the rotation speed of the polishing cloth 156 is approximately 300 rpm.

[0131] As a result of the grinding removal step (step S3), the back surface of the wafer W has numerous irregularities as shown in FIG. 17. When polishing is performed by chemical etching, the surface shape is maintained as is, so there is a risk of cracks occurring from the recesses, and the surface is not mirror-finished. In contrast, in the present embodiment, chemical mechanical polishing is used, so processing distortions caused by processing are removed, and the surface irregularities are removed to form a mirror-finished surface.

[0132] In other words, in order to improve the quality of the final product, chip C, two processes are essential: a grinding removal process using a grinding wheel and a chemical mechanical polishing process using a polishing cloth with free abrasive grains containing a chemical liquid.

[0133] (5) Expandable tape application process (step S5) An expandable tape E is attached to the back surface of the wafer W that has been subjected to the chemical mechanical polishing step (step S4). The expandable tape is a type of elastic tape and is stretchable.

[0134] The expanding tape E is applied to the wafer W by a tape application device (not shown) in the same manner as the application of the BG tape B in step S1. When applying the expanding tape E, the table 211 is rotated 45 degrees so that the cutting lines S for dividing the chips C, like the BG tape B, intersect at an angle with respect to the application roller for applying the tape.

[0135] This prevents the wafer W from being cut along the cutting line S due to the pressure of the adhesive roller while the expandable tape E is being applied to the wafer W.

[0136] (6) Wafer cutting process (Step S6) The wafer W with the expanding tape E attached thereto is transported to the tape peeling device 3, and a pressing member 218 is pressed against the wafer W to cut the wafer W along the cutting line S, thereby dividing the wafer W into individual chips C.

[0137] 12, the wafer W is placed on a table 211 having an elastic body 212 on its upper surface so that the pressing member 219 is parallel to one of the cutting lines S, which are cutting lines formed in a grid pattern. In this state, the pressing member 219 is pressed against the wafer W and rolled, so that the wafer W is cut along one of the cutting lines S. After cutting along one of the cutting lines S, the table 211 on which the wafer W is placed is rotated 90 degrees by a driving means (not shown) so that the other cutting line S and the pressing member 219 are parallel to each other, and the wafer W is cut along the other cutting line S.

[0138] The elastic body 212 attached to the upper surface of the table 211 is an elastic body with little permanent compression set and no voids, and has grooves 212a, 212a... formed in a lattice pattern or in parallel as shown in Fig. 10 at intervals equal to or smaller than the size of the chips C formed on the wafer W. As a result, the elastic body 212 has room for lateral deformation due to the grooves 212a when pressed from above, as shown in Fig. 11(c), so that uniform deformation occurs and stress is concentrated on the cutting line S along which cutting is desired, thereby enabling reliable and efficient cutting.

[0139] 10, the pressing member 219 is formed so that the radius r is smaller than the interval 1 of the cutting lines S where the modified regions K are formed, so that when the pressing member 19 presses one cutting line S, it does not press other cutting lines S. This allows stress to be concentrated on the cutting line S where cutting is desired, ensuring efficient cutting.

[0140] In cutting the wafer W, since the BG tape B and the expand tape E are attached to the front and back surfaces, when cutting one cutting line S and then cutting the adjacent cutting line S, the position is constrained by the BG tape B and the expand tape E, and the chip intervals do not increase significantly at the already cut cutting line S. This prevents the local stress of the pressing member 218 from being dispersed not only by the vertical deformation caused by the elastic body 212 but also by the horizontal deformation caused by the large increase in the intervals between the chips C, and the stress is concentrated, allowing for reliable and efficient cutting.

[0141] In addition, by attaching the BG tape B and the expand tape E to the front and back surfaces, fragments generated when the wafer W is cut do not adhere to the elastic body 212, and even if the next wafer W is placed on the elastic body 212, there is no adverse effect due to the fragments.

[0142] (7) BG tape peeling process (step S7) The peeling film 215 of the cleaved wafer W is attached to the BG tape B by a peeling roller 214, and the BG tape B is peeled off.

[0143] The peeling roller 214 is formed of an elastic body that is softer than the elastic body 212. The BG tape B has, for example, an ultraviolet-curing adhesive on its adhesion surface, and its adhesive strength is reduced by irradiating it with ultraviolet light from an ultraviolet irradiation device (not shown) provided inside or outside the tape peeling device 3. A peeling film 215 is affixed onto the BG tape B whose adhesive strength has been reduced by rolling the peeling roller 214 laterally (in the direction of arrow A shown in FIG. 9) while pressing it downward, as shown in FIG. 9.

[0144] After the peeling film 215 is attached, the winding unit 218A, which includes the two winding reels 18 and the guide roller 217, moves laterally (in the direction of arrow B shown in Figure 9) together with the peeling roller 214 while winding up the peeling film 215, thereby peeling the BG tape B from the wafer W.

[0145] When applying the peeling film 215 or peeling off the BG tape B using the peeling roller 214, the wafer W in which the cutting lines S for dividing the chips C are arranged parallel to the peeling roller 214 as shown in FIG. 13(a) is rotated by 45 degrees by which the table 211 is positioned so that the streets S intersect at an angle with respect to the peeling roller 214 as shown in FIG. 13(b).

[0146] This prevents the position of the cleaved chip C from shifting when the peeling film 215 is attached or when the BG tape B is peeled off, and does not adversely affect subsequent processes such as picking up the chip C after expansion.

[0147] (8) Wafer Separation Process (Step S8) After peeling off the BG tape B, the wafer W is placed on an expanding table (not shown) with the expanding tape E facing down, and the expanding tape E is stretched by pushing down the frame F or by fixing the frame F and raising the table, thereby widening the spacing between the chips C.

[0148] After expansion, the wafer W is picked up by each chip C from the expanding tape E and transported to various subsequent processes.

[0149] <<Evaluation of crack growth by polishing>> Next, the crack growth evaluation by polishing in the above-mentioned grinding and removing step (step S3) will be described with reference to Fig. 18 and Fig. 19. The polishing method, the dividing and separating method, and the conditions thereof are basically the same as those in the above-mentioned steps S1 to S8. Fig. 18 is a diagram showing the conditions of the crack growth evaluation, and Fig. 19 is a diagram showing the evaluation results of the crack growth evaluation.

[0150] 18(A), (B), and (C), the horizontal axis is the same and each position corresponds to each other, and indicates the polishing time (s). The vertical axis of Fig. 18(A) indicates the cutting speed (polishing speed) (μm / s), the vertical axis of (B) indicates the ON / OFF of the water supply to the grindstone during polishing, and the vertical axis of (C) indicates the temperature (°C) of the back surface of the wafer W during polishing.

[0151] As shown in FIG. 18(A), rough polishing was performed by changing the polishing speed to a total of 710 μm, then fine polishing was performed to 13 μm (not shown), and further chemical mechanical polishing (not shown) was performed to 2 μm. When polishing the wafer, as shown in FIG. 18(B), a period in which water supply to the grindstone or wafer was interrupted was provided during rough polishing. Water supply was stopped after t1 seconds had elapsed after the start of polishing, and water supply was resumed after t2 seconds had elapsed after the start of polishing. Water supply was performed at a flow rate of 10 L / min. Then, the above steps S5, S6, and S7 were performed to cleave the wafer, and the cleavage state was observed and evaluated. The results are summarized in FIG. 19, with ○ indicating that the chip was cleaved well without cracking or generating dust, and × indicating that the chip was cleaved or generating dust.

[0152] As shown in FIG. 18(C), the back surface temperature of the wafer W suddenly began to rise t1 seconds after the start of polishing when the water supply was stopped, and began to fall immediately t2 seconds after the start of polishing when the water supply was resumed.

[0153] As shown in Fig. 19, when the back surface temperature of the wafer W reached 70°C or higher due to polishing, the wafer was successfully cleaved. This is believed to be because the cracks formed by the laser propagated due to the heat of polishing.

[0154] Therefore, the grinding device according to the present invention can include a means for measuring the temperature of the wafer, a means for turning on and off the water supply to the grindstone or wafer during grinding, and a means for controlling the water supply to the wafer to be turned off until the wafer temperature reaches a predetermined value after a predetermined time has elapsed since the start of grinding. This allows the cracks formed by the laser to grow, and the wafer to be successfully cleaved.

[0155] As described above, according to this embodiment, the cracks in the modified region formed by the laser beam can be advanced by grinding, so that the modified region formed by the laser beam does not remain on the cross section of the chip C. This makes it possible to prevent defects such as the chip C cracking or dust generation from the cross section of the chip C. Therefore, chips of stable quality can be efficiently obtained. In addition, the stress of the pressing member can be concentrated on the cutting line of the wafer, making it possible to perform the cleavage reliably and efficiently. Furthermore, no contamination is left on the elastic body on which the wafer is placed during cleavage, and the wafer is not adversely affected even if cleavage is performed continuously.

[0156] (Additional Note) As will be understood from the detailed description of the embodiments above, this specification includes disclosure of various technical ideas including the inventions described below.

[0157] (Note 1) A process of adhering a backgrind tape to the front surface of a wafer; a modified region forming process of forming microvoids in the modified region by irradiating a laser beam from the rear surface along a cutting line of the wafer with the backgrind tape adhered to the front surface of the wafer; a vacuum suction process of vacuum-adhering substantially the entire front surface of the wafer in which the modified region has been formed in the modified region forming process to a table independently and uniformly in each region; a grinding process of grinding the wafer, the entire front surface of which has been adsorbed to the table in the suction process, from the rear surface to remove the modified region and to extend the microvoids in the thickness direction of the wafer; and a step of chemically and mechanically polishing the wafer in which the microvoids have been developed in the thickness direction of the wafer by the above-mentioned step; a step of attaching an expanding tape to the back surface of the chemically and mechanically polished wafer; a step of pressing the wafer with the expanding tape attached to the back surface thereof with a pressing member via the back-grind tape to thereby cleave the wafer; a step of attaching a peeling tape for peeling the back-grind tape and peeling the back-grind tape with a peeling roller; and a step of dividing and separating the cleaved wafer into a plurality of chips by stretching the expanding tape.

[0158] According to the invention described in Appendix 1, a protective backgrind tape is applied to the front surface of the wafer by a tape application mechanism. After the backgrind tape is applied, a laser beam is applied from the rear surface of the wafer along the cutting line to form a modified region inside the wafer, thereby forming micropores in the modified region. With substantially the entire surface of the wafer on which the modified region has been formed being held independently and uniformly by adsorption at each position of the substrate on a table, the wafer is ground from the rear surface to remove the modified region.

[0159] At this time, the grinding heat generated by the grinding causes the wafer surface to expand radially along with the grinding surface, but the wafer vacuum chuck, which has a large thermal capacity, tries to prevent this expansion.

[0160] As a result, the wafer surface expands due to thermal expansion, while the chucked wafer backside does not expand due to the vacuum chuck and tries to maintain its original state. As a result, the modified area formed inside the wafer acts to further expand according to the difference in expansion between the wafer surface and backside, and the cracks grow further. The modified area is irradiated with laser light, and some parts are once melted and recrystallized, so the crystal grains are large and brittle. If such a modified area appears on the side of a future chip, dust will be emitted from the side of the chip, and large crystal grains may be chipped off from the side of the chip. However, since the microcracks that grow from the modified area are pure crystal planes, even if this surface appears on the side of a future chip, dust will not be emitted from the side of the chip, and large crystal grains will not be chipped off.

[0161] In this way, the wafer is removed while being ground by the grinding process, and the microvoids are expanded in the thickness direction of the wafer to remove the modified regions. Next, in order to highlight the process-affected layer formed by grinding and the expanded microvoids, the entire wafer is subjected to chemical mechanical polishing (described in detail later) to completely remove the process-affected layer. 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, an expand film is attached to the back side of the wafer, which is still unbroken, by a tape-applying mechanism.

[0162] The wafer with the expand film attached is inverted and placed on a table installed in a mechanism for peeling off the backgrind tape. Then, one of the cutting lines is cut by a pressing member installed in the peeling mechanism, which is positioned parallel to the cutting lines. After the entire cutting line on one side is cut, the wafer is rotated 90 degrees and the other cutting line is cut.

[0163] After fracturing, the adhesive strength of the backgrind tape is reduced by ultraviolet irradiation, heating, etc. A peeling tape is applied to the backgrind tape with reduced adhesive strength by a peeling roller, and peeling is performed. After the backgrind tape is peeled off from the wafer, the expand film is expanded to separate the chips. This makes it possible to prevent the modified region formed by the laser light from remaining on the chip cross section. This prevents defects such as chip cracking and dust generation from the chip cross section, and makes it possible to efficiently obtain chips of stable quality.

[0164] In addition, since the back surface of the ground wafer is chemically mechanically polished before the wafer is divided, the die strength can be increased. Here, the chemical mechanical polishing is largely different from the etching treatment in the polishing process shown in the cited document 2.

[0165] First, the chemical liquid in the present application is different from the etching liquid in Reference 2. The etching liquid in Reference 2 has the effect of naturally dissolving the substrate by acting on the substrate surface, i.e., etching. As a result, even in the area where a crack has occurred, the etching liquid penetrates and naturally etches the surrounding area, which has the effect of further enlarging the modified layer formed by the laser. Also, in the case of conventional etching liquids, as mentioned above, the etching liquid penetrates too much into the crack, causing the crack to progress, and finally penetrates into the area between the chip and the film. As a result, the etching liquid may reach the chip surface, causing the chip surface to be eroded by the etching liquid, causing each chip device to stop functioning.

[0166] In contrast, the abrasive (slurry) used in the chemical mechanical polishing of the present invention has no etching effect under static conditions. In other words, even if only the abrasive is supplied to the wafer, no etching occurs, and the wafer surface is simply modified. Therefore, even if the abrasive gets into a crack on the wafer's intended cutting line, the surrounding silicon is not dissolved, and the crack does not progress any further.

[0167] As a result, cracks may develop in the polishing process, i.e., the etching process, in Reference 2, but in the polishing process of the present application, the wafer is not etched at all even if an abrasive is added and left, so cracks hardly develop at all. As a result, there are no conventional problems that the abrasive penetrates and peels the chip off from the film, or that the abrasive gets around to the chip surface and corrodes the chip, causing the chip device to stop functioning.

[0168] The mechanism of chemical mechanical polishing is as follows: In polishing, an abrasive is first supplied to the wafer, which only chemically modifies the wafer surface. The modified surface is then softened, and the abrasive particles contained in the slurry act on the wafer surface, allowing the wafer surface to be efficiently removed even with very small stress.

[0169] For example, in a process for removing silicon, a silica-based slurry is used. When a silica-based slurry is used, the following reaction occurs on the wafer surface:

[0170] [Number 1] Si(-OH)+SiOH=SiO2+H2O That is, the wafer surface immediately after polishing usually has Si atoms. These Si atoms are hydrated on the surface in water, and -OH exists on the surface of the Si atoms. The OH groups attached to the surface of the Si substrate bond with the SiOH of the silica sol in the liquid and the SiOH present on the surfaces of the silica particles.

[0171] However, this alone does not allow etching to proceed. As a result, a polishing pad containing a large amount of silica particles is moved relative to the substrate in this state, and the silica particles are applied to the substrate surface with a certain momentum, and the silica particles are mechanically removed while a chemical reaction proceeds under a certain temperature and pressure environment.

[0172] In this case, the silica sol or silica particles that have penetrated into the cracks do not have the effect of expanding the cracks further. Because the polishing pad does not penetrate into the cracks, no mechanical action occurs, and as a result, no chemical removal action occurs.

[0173] In this way, the altered layer on the substrate surface that occurs during grinding is removed by the supply of a slurry having chemical properties of silica sol and silica particles, and combined with the mechanical friction caused by the polishing pad coming into contact with the substrate, the substrate surface is chemically and mechanically polished away (Dohi Toshiro (ed.): Detailed Explanation of Semiconductor CMP Technology (Kogyo Chosakai) (2001) pp. 40-42).

[0174] As a result, most of the damaged layers on the wafer surface are removed. The wafer surface is mirror-finished. The principle of this mirror-finish is as follows, in comparison with the chemical etching described in Reference 2.

[0175] In the case of chemical etching, as mentioned above, lattice distortion and crystal defects in crystals such as silicon are selectively etched, which can lead to the formation of etch pits or large gouges along the grain boundaries, which cannot be avoided in principle.

[0176] In contrast, in the case of chemical mechanical polishing, as mentioned above, no chemical removal action occurs unless a mechanical action is applied. The mechanical action, in this case, is the rubbing of the wafer surface with a polishing pad, and this mechanical action occurs with equal probability on all substrate surfaces, regardless of the crystalline state of the substrate surface. Therefore, since the chemical action is applied while all surfaces are uniformly removed regardless of the crystalline state, the surface becomes uniform, free of crystal defects, and mirror-like. Here, the term "mirror surface" is ambiguous from a relative perspective, and is therefore defined in this application as a mirror surface obtained by chemical mechanical polishing.

[0177] By carrying out such chemical mechanical polishing, an ideal mirror surface can be obtained, which is significantly different from that in Reference 2, and erosion caused by penetration of the etching solution between the chip and the film can be prevented.

[0178] After the chemical mechanical polishing, the chip is not yet completely cracked. Only small voids developed from the modified layer remain on the surface part after the chemical mechanical polishing. The modified layer has already been removed in the previous grinding process.

[0179] If the state in which the microvoids developed from this modified layer remain is formed in a surface state that has been subjected to grinding and etching as shown in, for example, Reference 2, it becomes impossible to clearly distinguish between the microvoids developed from the modified layer and the irregularities promoted by the etching process after grinding. Therefore, when the chip is broken, it is not necessarily broken from the microvoids, but in some cases, it is considered that the chip may break from the irregularities that have been further promoted by etching the grinding marks.

[0180] When the surface is subjected to chemical mechanical polishing as in the present application, the surface of the wafer after the polishing has almost no irregularities, and only micropores that have developed from the modified layer remain. Therefore, if the wafer is subjected to a cleaving process in this state, cracks will develop further from the micropores and break the wafer.

[0181] Thus, in the method of the present invention, even after grinding and chemical mechanical polishing, the microvoids become larger and the cracks grow, but the substrate is not completely divided. If the cracks grow during grinding or chemical mechanical polishing and the substrate is completely divided, the chips, especially those on the periphery of the wafer, will not be able to withstand the shear stress during grinding or polishing, and will be peeled off from the suction table, causing chipping.

[0182] However, in the present invention, even after grinding and polishing, the crack continues to grow but is not completely cut. In order to make the crack grow from a state in which it is not completely cut to a complete cleavage, a further cleaving step is required. In the cleaving step, an expandable tape is attached to the back surface of the wafer, and then a pressing member is pressed through the tape to locally apply bending stress to the wafer. This makes it possible to efficiently cleave the wafer, starting from the crack that has grown due to grinding.

[0183] If the expandable tape is not attached, the wafer is directly pressed by the pressing member, and when the wafer is cut, the vibration of the crack propagates within the wafer surface. The propagated vibration may cause other parts of the cutting line to crack incidentally, or may cause parts other than the cutting line to crack.

[0184] However, by applying an expandable tape and applying stress by a pressing member through the tape, the tape absorbs the vibration of the crack when the wafer is cut, so no unnecessary vibration is generated. In addition, since the expandable tape is applied in a stretched state without wrinkles or buckling, a constant tension is constantly applied to the wafer, and the wafer is in a restrained state. If the wafer is restrained when it is cut, the bending deformation of various parts of the wafer is restrained, and the pressing force of the pressing member is concentrated as a shear stress, not a bending stress, on the advanced crack part, which is a part of the wafer with weak rigidity. As a result, only the part that should be cut is efficiently cut, and the parts other than the cutting line are protected and do not crack.

[0185] In particular, when tape is applied to both sides of the wafer, the vibrations that cause the cracking are completely contained and the bending of the wafer is further restricted, making it possible to efficiently cut the wafer.

[0186] (Note 2) A process of adhering a backgrind tape to the front surface of a wafer; a modified region forming process of forming micropores in the modified region by irradiating a laser beam from the rear surface of the wafer along a cutting line of the wafer with the backgrind tape attached to the front surface; a process of adsorbing substantially the entire surface of the wafer on which the modified region is formed in the modified region forming process to a table uniformly and independently in each region; a first grinding process of irradiating the laser beam while the wafer is adsorbed to grind and remove the modified region formed inside the wafer up to a portion in front of the modified region, and causing microcracks extending from the modified region to progress in the depth direction of the substrate; a second grinding process of grinding and removing the modified region formed inside the wafer; and a chemical process for modifying the wafer surface. a step of removing the process-affected layer introduced in the first and second grinding steps while performing chemical mechanical polishing using a slurry and a polishing pad, leaving microcracks extending from the modified region, to make the surface mirror-finished; a step of attaching an expandable tape to the backside of the wafer whose surface has been mirror-finished; a step of pressing the wafer with the expandable tape attached to its backside with a pressing member via the back-grinding tape to thereby cleave the wafer; a step of attaching a peeling tape for peeling off the back-grinding tape and peeling off the back-grinding tape with a peeling roller; and a step of dividing and separating the cleaved wafer into a plurality of chips by stretching the expandable tape.

[0187] According to the invention described in Appendix 2, a modified region is initially formed deep inside the wafer, and removal processing is performed while generating grinding heat in the first grinding step at an early stage, thereby making it possible to propagate cracks formed in the modified region to an even deeper position inside the wafer.

[0188] However, if the laser-modified area is also ground and removed in the first grinding process with the same volume as the unmodified area, the modified area has large crystal grains, so large crystal grains may chip off and cause fatal cracks to grow along with these crystal grains. Therefore, in the first grinding process, it is recommended to grind up to the part just before the modified area where the crystallinity is constant.

[0189] In the second grinding process, the area modified by the laser is mainly ground. In this case, the grinding wheel is also high-grit, i.e., a grinding wheel with a finer grain size than the first grinding process is used, and compared to the first grinding process, the grinding process is gentler so as not to induce fatal cracks or defects derived from the modified area. The second grinding process is only for the modified area, and the grinding rate is smaller than that of the first grinding process, and the area is finely ground.

[0190] After the laser-modified region is removed, chemical mechanical polishing is finally performed, in which a chemical solution for modifying the wafer is supplied while a polishing pad made of polymer or nonwoven fabric is pressed against the wafer to perform chemical and mechanical polishing.

[0191] If chemical mechanical polishing is performed on the modified area, large crystal grains may chip off from the modified area. Since chemical mechanical polishing uses polishing pads made of nonwoven fabric or polyurethane foam, if the chipped crystal grains get into the pad surface, they will constantly cause scratches during polishing. In such cases, the polished surface will be covered with scratches without achieving the purpose of removing the process-affected layer and creating a mirror finish.

[0192] For this reason, the modified layer introduced by the laser in the previous second grinding step must be completely removed before the material is introduced into the chemical mechanical polishing step.

[0193] (Appendix 3) A method for cutting a semiconductor substrate according to appendix 1 or 2, characterized in that a modified layer is formed along the cutting line by laser light, the backgrind tape is attached to the front surface of the wafer, and the expand tape is attached to the back surface of the wafer, the wafer being placed on a table having an elastic body attached to its upper surface, the table being rotated so that the pressing member is parallel to the cutting line, and the pressing member is pressed against the wafer and rolled to break the cutting line.

[0194] According to the invention described in Appendix 3, when the wafer is fractured, a backgrind tape is attached to the front surface, and after the rear surface of the wafer on which a modified layer is formed by the laser light incident from the rear surface is ground and polished, an expand tape is attached to the rear surface by a tape application mechanism.

[0195] The wafer with the backgrind tape and the expand tape attached on both sides is placed on a table with an elastic body attached to the upper surface, which is provided in a mechanism for peeling off the backgrind tape. Next, a pressing member provided in the peeling mechanism is positioned parallel to the cutting line, and is pressed and rolled to break one of the cutting lines.

[0196] After all the cutting lines on one side have been cut, the wafer is rotated 90 degrees and the other cutting line is cut. The adhesive strength of the backgrind tape on the cut wafer is reduced by UV irradiation or heating. A peeling tape is applied to the backgrind tape with reduced adhesive strength by a peeling roller, and peeling is performed. After the backgrind tape has been peeled off, the expand film on the wafer is expanded to separate the chips. This ensures reliable and efficient cutting, and makes it possible to perform successive cuttings without adversely affecting subsequent wafers.

[0197] (Appendix 4) The method for cutting a semiconductor substrate according to appendix 3, wherein the pressing member is formed with a radius smaller than the interval between the cutting lines.

[0198] According to the invention described in Appendix 4, the radius of the pressing member is formed to be smaller than the interval between the cutting lines formed on the wafer to be pressed. Since the radius is smaller than the interval between the cutting lines, the pressing member does not press multiple cutting lines at once, which prevents the stress from being dispersed. This makes it possible to concentrate the stress on one cutting line, ensuring efficient cutting.

[0199] (Appendix 5) The method for cutting a semiconductor substrate according to appendix 3 or appendix 4, characterized in that the elastic body has grooves, holes, or irregularities formed at intervals equal to or smaller than the size of the chips formed on the wafer.

[0200] According to the invention described in Appendix 5, the elastic body on which the wafer is placed has a surface with grooves, holes, or projections and recesses. The elastic body is preferably a void-free elastic body with small compression set so that the initial elastic modulus and the change in elastic modulus after several uses are small. By forming grooves, holes, or projections and recesses in the elastic body at intervals equal to or smaller than the size of the chips formed on the wafer, the wafer can be locally deformed, and the cutting can be performed reliably and efficiently.

[0201] (Appendix 6) The method for cutting a semiconductor substrate according to any one of Appendices 3 to 5, characterized in that when the backgrind tape or the expand tape is applied, an application roller is rolled in a direction that intersects at an angle with respect to the cutting lines formed in a grid pattern to apply the tape.

[0202] According to the invention described in Appendix 6, when the backgrind tape or the expand tape is applied to the front and back surfaces of the wafer, the table on which the wafer is placed is rotated by about 45 degrees, and the application roller is pressed in a direction that crosses the cutting lines formed in a grid pattern at an angle, and then the tape is applied by rolling.

[0203] If the cutting line were to be cut by the pressure of the tape application roller, air bubbles would be trapped on the application surface, and the chip direction would be distorted, making it difficult to apply the tape accurately. By moving the tape application roller so that it crosses the cutting line at an angle, the cutting can be performed reliably and efficiently, and there is no adverse effect on subsequent processes. [Explanation of symbols]

[0204] 1...laser dicing device, 2...grinding device, 3...tape peeling device, 11...wafer moving section, 13...suction stage, 20...laser optical section, 30...observation optical section, 40...laser head, 50...control section, 118...rough grinding stage, 120...fine grinding stage, 122...polishing stage, 132, 136, 138, 140...chuck, 146, 154...cup-shaped grinding wheel, 156...polishing cloth, 211...table, 212...elastic body, 212a...groove, 213...supply reel, 214...peeling roller, 215...peeling tape, 216, 217...guide roller, 218...take-up reel, 219...pressing member, B...BG tape, C...chip, E...expanded tape, F...frame, K...modified area, L...laser light, S...cutting line, W...work

Claims

1. A crack propagation device for propagating a crack inside a workpiece, comprising: a crack propagation means for controlling the water supply when the back surface of the workpiece is ground to change the degree of propagation of the crack; Crack propagation device.

2. A crack propagation method for propagating an internal crack of a workpiece, comprising: A crack propagation step is provided in which the degree of propagation of the crack is changed by controlling the water supply when the back surface of the workpiece is ground. Crack growth methods.

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