Crack propagation device and crack propagation method

Abstract

To enable good wafer cleavage. [Solution] A crack propagation device that propagates cracks inside a wafer, equipped with a crack propagation means that changes the degree of crack propagation by changing the water supply conditions when the back surface of the wafer is ground.

Description

[Technical Field]

[0001] The present invention relates to a technique for cleaving a wafer in which a modified region has been formed 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 upward 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 placed with its back side facing upward is irradiated with a laser to form a modified region inside the substrate, and then the substrate is ground to make it thinner, and an expandable tape is attached to the back side of the semiconductor substrate and stretched to split the substrate using the modified region as a base point.

[0004] Patent Document 2 describes a method of irradiating a semiconductor substrate placed with its back surface facing up with a laser 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 in the thickness direction from the modified region can be generated naturally or by a relatively small force, such as an artificial force or by generating thermal stress by applying a temperature difference to the substrate. [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, a substrate is broken by applying a localized external force using a knife edge, but this localized application of external force imparts bending stress or shear stress to the substrate. However, it is difficult to distribute bending stress or shear stress uniformly over the entire surface of the substrate. For example, when bending stress or shear stress is applied to a substrate, the stress tends to concentrate at weak points, making it impossible to efficiently and uniformly apply the minimum necessary stress to the desired portion.

[0007] Therefore, there is a problem that cracks in the substrate vary, and if the cracks do not progress slowly, the substrate may break even within the chip. Furthermore, when cutting the substrate by applying stress locally and sequentially to the cutting portion, for example, when collecting many chips from a single 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 has not been thinned, there is a problem that a very large stress is required to split the wafer.

[0009] In particular, when the substrate is thick enough relative to the depth of modification to be achieved by laser processing, applying an external force may not always result in a clean perpendicular cleavage to the substrate due to the effect of a sudden external force. Therefore, it may be necessary to irradiate the substrate with several laser pulses in multiple stages in the thickness direction.

[0010] Furthermore, 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. This can cause dust to be emitted from the modified region on the chip cross section. Furthermore, localized fractures on the chip cross section can trigger the chip to break, which can result in a problem of reduced die strength.

[0011] The invention described in Patent Document 2 states that cracks naturally occur in the thickness direction from the modified region, but on the other hand, natural cracks do not necessarily occur naturally. In order to necessarily achieve the stable effect of cracking, it is sometimes necessary to take arbitrary measures, but natural cracks do not fall under the category of arbitrary measures.

[0012] It is also possible to generate thermal stress by applying a relatively small force, a temperature difference, and thereby generate cracks in the thickness direction from the modified region. In this case, it is extremely difficult to create a uniform thermal gradient across the surface of the substrate. In other words, even if a thermal gradient is artificially created, heat will be dispersed within the substrate by thermal conduction, partially mitigating the thermal gradient. Therefore, it is extremely difficult to consistently create a stable thermal gradient (stable temperature difference) sufficient to cut a certain amount of substrate.

[0013] In addition, in the invention described in Patent Document 2, after grinding a semiconductor substrate, chemical etching is performed on the back surface. However, after grinding, grinding marks from the fixed abrasive grains remain on the ground surface, accompanied by the formation of microcracks and a process-affected layer. When chemically etching the surface, areas with large lattice distortion, such as microcracks, are selectively etched. As a result, the microcracks are actually promoted and become larger cracks. As a result, fracture can sometimes occur not only in the cutting starting area but also from microcracks formed by grinding and etching, making stable cutting difficult.

[0014] Furthermore, since etching increases the surface roughness of the substrate, the surface is not mirror-finished, and as a result, the separated chips are still uneven, which means that breakage is likely to occur from the most uneven areas, i.e., from microcracks, resulting in a problem of reduced die strength.

[0015] Furthermore, when an etching solution acts on a laser-processed and modified portion, the modified portion is melted once, recrystallized, and solidified, resulting in the formation of large grain boundaries.

[0016] When the etching solution acts on such grain boundary portions, etching proceeds in such a way that silicon grains peel off from the grain boundaries, resulting in etching that further promotes unevenness.

[0017] Specifically, the polishing process is described on page 12, line 1 of the cited document as a grinding process followed by chemical etching on the backside. In the case of chemical etching, even if the product is left as is, the chemical etching solution will penetrate into the cracks and dissolve the cracked areas.

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

[0019] Furthermore, even if the cracks do not extend all the way to the substrate surface, etching continues along the cracks. Particularly when etching is performed on a thinned substrate after grinding, the etchant penetrates the cracks by capillary action, dissolving the crack tips and deepening the microcracks, allowing new etchant to penetrate further into the cracks. In this case, if the etchant acts near the device surface, it may dissolve the device surface and cause etching to progress into the device's interior. Even if there are no problems at the time, etchant remaining on the wafer wall may penetrate into the device and cause subsequent defects. Therefore, while removing processing strain on the wafer surface, it may further promote cracks and induce secondary problems.

[0020] In such cases, the cracks may eventually progress to the surface, allowing the etching solution to get in between some of the chips and the film, causing the chips to peel off during processing. In particular, when the substrate becomes thinner as grinding progresses, 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 a substrate causes cracks to occur in the modified region, but does not describe a method for fixing the substrate when grinding it. When the periphery of the substrate is supported by fitting it into a retainer or the like as shown in Figure 20, or when only a portion of the substrate is sucked as shown in Figure 21, the substrate is not uniformly restrained 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 as its object to provide a method for cutting a semiconductor substrate that 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 cleaving method according to the present invention is a wafer cleaving method for cleaving a wafer having a modified region formed therein by laser light, characterized in that it comprises the steps of: a step of uniformly vacuum-sucking the front surface of the wafer to a table; a grinding step of grinding away the back surface of the wafer while the wafer is vacuum-sucked, and grinding away the modified region while leaving behind microcracks extending from the modified region while propagating the microcracks in the wafer depth direction; a mirror-finishing step of chemically mechanically polishing the back surface of the wafer after the grinding step; and a step of cleaving the wafer after the mirror-finishing step.

[0024] In one aspect of the semiconductor substrate cleaving 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, 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 the process-affected layer introduced in the grinding step while leaving the microcracks. [Effects 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 explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a diagram showing the overall configuration of a laser dicing device 1. [Figure 2] FIG. 2 is a conceptual diagram showing the configuration of a driving means of the laser dicing device 1. [Figure 3] FIG. 2 is a plan view showing the configuration of a driving means of the laser dicing device 1. [Figure 4] FIG. 2 is a diagram showing the overall configuration of a grinding device 2. [Figure 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. 10 is a side cross-sectional view showing the state of the elastic body being pressed. [Figure 12] FIG. [Figure 13] FIG. [Figure 14] 1 is a flow diagram showing a method for cutting a semiconductor substrate according to the present invention. [Figure 15] FIG. [Figure 16] 1A and 1B are diagrams explaining crack propagation 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. 10 is a diagram illustrating the surface state of the rear surface of the wafer W after the grinding removal process. [Figure 18] FIG. 1 shows the conditions for crack propagation evaluation. [Figure 19] FIG. 10 is a diagram showing the evaluation results of crack growth evaluation. [Figure 20] FIG. 10 is a diagram showing a conventional fixed state during substrate grinding. [Figure 21] FIG. 10 is a diagram showing a conventional fixed state during substrate grinding. DETAILED DESCRIPTION OF THE INVENTION

[0028] A preferred embodiment of the method for cutting a semiconductor substrate according to the present invention will be described in detail below with reference to the accompanying drawings.

[0029] The present invention is performed by a cutting device comprising 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] <Device configuration> (1) Laser dicing device 1 1 is a diagram showing the overall configuration 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 the 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 back grinding tape (hereinafter referred to as BG tape) B having an adhesive material is attached to the surface of the wafer W on which the device is formed by a tape 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 with a dicing sheet having an adhesive attached to one surface thereof and integrated with the frame via the dicing sheet. In this case, the wafer W is mounted on the suction stage 13 with its 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 slightly moving the laser light parallel to the wafer W. The laser light emitted from the laser oscillator 21 passes through an optical system including the collimator lens 22, half mirror 23, and condenser lens 24 and is then focused inside the wafer W. The Z-direction position of the focusing point is adjusted by slightly moving the condenser lens 24 in the Z direction using a Z-direction fine movement means 27, which will be 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 mode 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 conditions for the condenser lens 24 are a magnification of 50x, 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 observation means, an image processing section 38, a television monitor 36, and the like.

[0037] In the observation optical unit 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 serving as 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 includes a CPU, a memory, an input / output circuit unit, and the like, and controls the operation of each unit of the laser dicing device 1.

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

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

[0042] The operation panel is fitted with switches and display devices for operating each part of the dicing device 10. Indicator lights display the operating status of the dicing device 10, such as when processing is in progress, processing is complete, and when there is an emergency stop.

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

[0044] A piezoelectric element that expands and contracts when a voltage is applied is used for Z fine movement means 27. The expansion and contraction of this piezoelectric element causes 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 also be supported by, for example, multiple balls sandwiching it from above and below, restricting its movement in the Z direction while allowing it to move freely in the X and Y directions.

[0046] The linear fine movement means PZ1 and PZ2 use piezoelectric elements, similar to the Z fine movement means 27, with one end fixed to the case body of the laser head 40 and the other end abutting against the side surface of the 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, with one end of each fixed to the case body of laser head 40 and the other end abutting against the 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 the 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 use an elastic member such as a spring for the other.Also, three linear fine movement means may be arranged on the circumference.

[0049] Laser light L is emitted from a laser oscillator 21, and 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 inside the wafer by adjusting the Z-direction position of the wafer W using an XYZθ table 12 and controlling the position of the condenser lens 24 using a Z fine movement means 27.

[0050] In this state, the XYZθ table 12 is fed in the X direction, which is the dicing direction, while the condenser lens 24 is slightly moved back and forth by the linear micro-motion means PZ1 and PZ2 provided on the laser head 40, the laser light L is vibrated in the X direction or any X or Y 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. Furthermore, the wafer W may be sent in the X direction while the laser beam L is slowly finely moved back and forth in the X direction, which is the processing direction, so that the laser beam L is repeatedly irradiated back and forth like a perforation.

[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 modified regions are formed on the next line in the same manner.

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

[0054] (2) Grinding device 2 4 is a perspective view showing the overall 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, which prevents the machining fluid used in each stage 118, 120, 122 from splashing onto 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 installed on the index table 134.

[0057] 5, the rough grinding stage 118 is a stage for performing rough grinding, and is surrounded by the side surfaces of the main body 112, a top plate 128, and a partition plate 125. The fine grinding stage 120 is a stage for performing fine grinding, and like the rough grinding stage 118, is surrounded by the side surfaces of the main body 112, a top plate 129, and a partition plate 125. Brushes (not shown) are disposed on the top and side surfaces of the partition plate 125, isolating 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 has through holes 126C formed therein, through which the heads of the respective stages are inserted.

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

[0060] The polishing stage 122 performs chemical mechanical polishing, and therefore the polishing fluid contains a chemical abrasive. If the grinding fluid is mixed into this polishing fluid, the concentration of the chemical abrasive decreases, causing problems such as longer processing time. By keeping the polishing stage 122 in a substantially airtight state, the grinding fluid used in the fine grinding stage 120 and processing debris can be prevented from entering the polishing stage 122, and the polishing fluid used in the polishing stage 122 can be prevented from scattering from the polishing stage 122. This prevents processing problems caused by mixing of the two processing fluids.

[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 distortion (crystal deformation) caused by 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 guide rails 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 so as to be vertically movable relative to the support plate 164.

[0063] The support plate 164 is provided at the tip of a horizontally disposed arm 168. The base end of the arm 168 is connected to an output shaft 174 of a motor 172 disposed within a casing 170. Therefore, when the motor 172 is driven, the arm 168 can rotate about the output shaft 174. This allows the abrasive cloth 56 to be moved within a range between a polishing position (see the solid line in FIG. 3 ), a abrasive cloth cleaning position (see the two-dot chain line in FIG. 3 ) operated by the abrasive cloth cleaning stage 123, and a dressing position operated by the abrasive cloth dressing stage 127. When the abrasive cloth 156 is moved to the abrasive cloth cleaning position, the surface of the abrasive cloth 156 is cleaned by the abrasive cloth cleaning stage 123 to remove abrasive debris and the like adhering to the surface. Examples of the abrasive cloth 156 include foamed polyurethane and abrasive cloths. The abrasive cloth cleaning stage 123 is provided with a removal member, such as a brush, for removing abrasive debris. This removal member is rotated when the abrasive cloth 156 is cleaned, and the abrasive cloth 156 is similarly 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 guide rails 180 provided on the side of a housing 178 for a screw feed device so as to be freely movable up and down. A nut member 179 protrudes from the side of the casing 170. The nut member 179 is threadedly engaged with a threaded rod 181 of the screw feed device disposed within 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 threaded rod 181. Therefore, when the motor 182 is driven to rotate the threaded rod 181, the casing 170 is moved up and down by the feeding action of the screw feed device and the linear movement of the guide blocks 176 and guide rails 180. This causes the polishing cloth 156 to move significantly up and down, and the distance between the polishing head 161 and the wafer W is set to a predetermined distance.

[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 in 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) 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 any other polishing stone or electrophoresis of abrasive grains may be used as long as it is possible to remove the processing-affected layer. 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 Figure 4, the alignment stage 116 is a stage that aligns the wafer W, which has been transferred from the laser dicing apparatus 1 by a transfer device (not shown), to a predetermined position. The wafer W, which has been aligned on this alignment stage 116, is sucked and held by a transfer robot (not shown), and then transferred to an empty chuck 132, where it is sucked and held by 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. Rotation shaft 135 is connected to a spindle (not shown) of a motor (not shown).

[0069] In Fig. 4, the chuck 136 is positioned at the rough grinding stage 118, where the adsorbed wafer W is rough-ground. In Fig. 4, the chuck 138 is positioned at the fine grinding stage 120, where the adsorbed wafer W is finish-ground (fine grinding, spark-out). In Fig. 4, the chuck 140 is positioned at the polishing stage 122, where the adsorbed wafer W is polished, and any process-affected layer caused by grinding and variations in the 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] 8A and 8B are diagrams showing the details of the chuck 132, in which (a) is a plan view of the chuck 132, (b) is a cross-sectional view taken along line AA' in (a), and (c) is an enlarged view of part B in (b).

[0072] The chuck 132 is configured 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. Adsorption holes 132c are formed on the underside of the chuck body 132b where the mounting table 132a is fitted, for vacuum adsorption. It is desirable that the chuck 132 be made of a material with low thermal conductivity.

[0073] As shown in Fig. 8(c), a wafer W is placed on the mounting table 132a via a 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, 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] As shown in Figures 8(a) and 8(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 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 coupled to the underside of the chucks 132, 136, 138, and 140, and the chucks 132, 136, 138, and 140 are rotated by the driving force of the motor 192. The motor 192 is supported on the index table 134 via a support member 193. This eliminates the need to disconnect the spindle 194 from the chucks 132, 136, 138, and 140 and to couple the chucks 132, 136, 138, and 140 to the spindle 194 installed at the next movement position every time the chucks 132, 136, 138, and 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 the 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. These measurement gauges each have a contact, one of which is in contact with the top surface (back surface) of the wafer W, and the other contact is in contact with the top surface of the chuck 132. These measurement gauges can detect the thickness of the wafer W as the difference between in-process gauge readings, using the top surface of the chuck 132 as a reference point. Note that thickness measurement using the measurement gauges may be performed in-line. Also, the method for measuring the thickness of the wafer W is not limited to this.

[0079] The control unit 100 rotates the index table 134 by 90 degrees in the direction of arrow R in FIG. 4, whereby 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 a cup-shaped grinding wheel 146 on the rough grinding stage 118. As shown in FIG. 4, the cup-shaped grinding wheel 146 is connected to an output shaft (not shown) of a motor 148 and is attached to a grinding wheel feeder 152 via a support casing 150 for the motor 148. The grinding wheel feeder 152 moves the cup-shaped grinding wheel 146 up and down together with the motor 148, and this downward movement presses the cup-shaped grinding wheel 146 against the back surface of the wafer W. This performs rough grinding of the back surface of the wafer W. The control unit 100 sets the amount of downward movement of the cup-shaped grinding wheel 146 and controls the motor 148. The amount of downward movement of the cup-shaped grinding wheel 46, i.e., the amount of grinding by the cup-shaped grinding wheel 146, is set based on a pre-registered reference position of the cup-shaped grinding wheel 146 and the thickness of the wafer W detected by the measurement gauge. The control unit 100 also controls the rotation speed of the motor 148, thereby controlling the rotation speed of the cup-shaped grinding wheel 146.

[0080] After the cup-shaped grinding wheel 146 is retracted from the wafer W, the thickness of the wafer W, whose backside has been roughly ground by 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 arrow R in FIG. 4, whereby 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 this fine grinding stage 120 is the same as the structure 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, whose backside has been precision-ground by 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, thereby polishing the backside of the wafer W to a mirror finish. 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 retreats from the position above the wafer W, the wafer W polished on the polishing stage 122 is held by suction on a hand (not shown) of a robot (not shown) and transported to the wafer cleaning stage 124. A stage having a rinse function and a spin-dry function is used as the wafer cleaning stage 124. Since the polished wafer W has had its process-damaged 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 sucked and 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 expandable tape E is attached to the wafer W by the tape peeling device 3. Furthermore, the wafer W that has been ground and polished by the grinding device 2 is cleaved by the tape peeling device 3.

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

[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] The elastic body 212 attached to the upper surface of the table 211 is a void-free elastic body with small compression set, and has grooves 212a, 212a... formed in a grid pattern or arranged 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. The elastic body 212 is connected to a vacuum generating source (not shown), and is formed so that the BG tape B is attached to the front surface through the grooves 212a, 212a..., etc., and the wafer W mounted on a frame F can be suction-fixed via expandable tape E attached to the back 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] 11(a), when a sponge-like elastic body 212B having many small voids formed therein is used to cleave a wafer W, the voids become smaller and flattened, causing permanent compression set. Therefore, when the elastic body 212B is used repeatedly, the elastic modulus gradually changes due to deformation, making stable cleavage impossible.

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

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

[0093] 10, the pressing member 219 is formed so that its radius R is smaller than the interval L between the cutting lines S where the modified layer P is formed. Because 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. This allows stress to be concentrated on the cutting line S where cutting is desired, ensuring reliable and efficient cutting.

[0094] 12, the wafer W is cleaved 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. The tape peeling device 3 adjusts the position of the wafer W by rotating the table 211 so that the pressing member 219 is parallel to one side of the cutting lines S formed in a grid pattern, as shown in FIG.

[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 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), thereby positioning 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, 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 expandable tape E, and the chip spacing does not increase significantly along the already cut cutting line S. This prevents the local stress of the pressing member 219 from being dispersed not only by vertical deformation caused by the elastic body 212 but also by horizontal deformation caused by the large increase in spacing between the chips C, and allows the stress to be concentrated, ensuring reliable and efficient cutting.

[0097] Furthermore, by adhering the BG tape B and the expandable tape E to the front and back surfaces, fragments generated when the wafer W is cleaved do not adhere to the elastic body 212, and even when the next wafer W is placed on the elastic body 212, no adverse effects are caused by 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. As shown in Figure 9, the peeling roller 214 is pressed downward and rolled laterally (in the direction of arrow A in Figure 9) onto the BG tape B whose adhesive strength has been reduced, thereby adhering a peeling film 215.

[0099] After the peeling film 215 is attached, the winding unit 218A, which includes the winding reel 218 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.

[0100] 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 line S for dividing the chips C is arranged parallel to the peeling roller 214 as shown in Figure 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 Figure 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. 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 against the underside of the inner portion of the peripheral edge of the expanding tape E. The outer peripheral edge of the top surface of this ring member is smoothly chamfered with a radius. A downward force is applied to the frame F, pushing it downward. This expands the dicing tape and increases the spacing between the chips. At this time, because the outer peripheral edge of the top 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 consisting of a cylinder member (hydraulic, pneumatic, etc.) or a motor and screw (a combination of a male screw as a shaft and a female screw as a bearing) can be used.

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

[0106] (1) BG tape application 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 of the 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 that divides the chips C intersects at an angle with respect to the adhering roller that adheres the tape. This prevents the wafer W from being split 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 the laser oscillator 21, the laser light L is irradiated onto the inside of the 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 surface of the wafer W. This is because, in order to efficiently fracture the 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 wafer W surface by the thickness of the chip C.

[0111] The control unit 50 scans a pulsed processing laser beam L parallel to the surface of the wafer W to form a plurality of discontinuous modified regions K... arranged side by side within the wafer W. Microvoids (hereinafter referred to as cracks) are formed within the modified regions K. Hereinafter, the region formed by arranging a plurality of discontinuous modified regions K... 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 is completed.

[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 may also be used) with the 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 the rotation axis 135 to carry the chuck 132 into the rough grinding stage 118, where 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, a vitrified #325 grindstone manufactured by Tokyo Seimitsu is used as the cup-shaped grindstone 146, and the rotation speed of the cup-shaped grindstone 146 is approximately 3000 rpm.

[0117] After the rough grinding, the index table 134 is rotated about the rotation axis 135 to load 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, in this embodiment, rough polishing and fine polishing are combined to grind down to the target surface, that is, to a depth of approximately 50 μm from the surface of the wafer W. In this embodiment, roughly polishing is performed to a depth of approximately 700 μm, and fine polishing is performed to a depth of approximately 30 to 40 μm, but this is not strictly determined, and the grinding amount may be determined so that the rough polishing and fine polishing times 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 being fractured from the chip cross section, causing the chip C to crack from the fractured parts, and preventing dust from being generated from the fractured parts.

[0120] In this embodiment, the grinding removal process includes a crack propagation process for propagating cracks in the modified layer in the thickness direction of the wafer W. Figure 16 is a diagram for explaining the mechanism by which cracks propagate, 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 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 the grinding heat as shown in Fig. 16(b). In contrast, the surface opposite the grinding surface, i.e., the front surface of the wafer W, is almost entirely vacuum-sucked by a vacuum chuck as shown in Fig. 16(c), and is physically restrained from lateral displacement to prevent positional displacement due to thermal expansion.

[0122] That is, as shown in Figure 16(d), the back surface (grinding surface) of the wafer W, if disk-shaped, tends to expand in the outer periphery 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, strain is generated inside the wafer, and this internal strain causes cracks to propagate in the thickness direction of the wafer W. This internal strain acts equally 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 strain is most efficient in the early stages of grinding, i.e., during rough polishing, when the amount of grinding is greatest and the frictional force is also greatest, i.e., frictional heat is also greatest.

[0123] The laser-modified region is formed at a relatively deep position close to the thickness of the chip. Therefore, although the distance from the grinding surface to the laser-modified layer is relatively long in the early stages of grinding, the modified layer is located relatively close enough to the target surface to propagate cracks. Therefore, to propagate cracks, it is advisable to promote thermal expansion of the wafer W by using the grinding heat in the early stages of rough polishing.

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

[0125] When cracks are propagated by internal strain, cracks can be propagated uniformly at each point on the surface of the wafer W regardless of the type of wafer W, regardless of variations in rigidity within the surface of the wafer W. Therefore, it is possible to prevent stress from concentrating on parts with weak rigidity due to the presence of defects within the surface of the wafer W, as occurs when artificial stress is applied.

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

[0127] Note that the internal strain caused by the thermal expansion of the wafer W is to be distinguished from the so-called thermal stress caused by a 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 precision 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 damaged 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), numerous irregularities are formed on the back surface of the wafer W, as shown in FIG. 17. When polishing is performed by chemical etching, the surface shape is left intact, which may result in cracks occurring from the recesses, and the surface is not mirror-finished. In contrast, in this embodiment, chemical mechanical polishing is used, which removes processing strain caused by processing, removes surface irregularities, and results in 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 stone, and a chemical mechanical polishing process using abrasive cloth and free abrasive grains containing a chemical liquid.

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

[0134] The expanding tape E is adhered to the wafer W by a tape adhering device (not shown), similar to the application of the BG tape B in step S1. When adhering the expanding tape E, the table 211 is rotated 45 degrees so that the cutting lines S that divide the chips C intersect at an angle with respect to the adhering roller that applies the tape, similar to the BG tape B.

[0135] This prevents the wafer W from being split along the cutting line S due to the pressure of the joining roller while the expanding tape E is being joined to the wafer W.

[0136] (6) Wafer cleaving process (step S6) The wafer W with the expanding tape E attached thereto is transported to the tape peeling device 3, where 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 a 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, 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) 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 grid pattern or arranged 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 to deform laterally when pressed from above by the grooves 212a, 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 its radius r is smaller than the interval 1 between the cutting lines S along which the modified regions K are formed. This prevents the pressing member 19 from pressing one cutting line S while pressing other cutting lines S. This allows stress to be concentrated on the cutting line S along which cutting is desired, ensuring reliable and efficient cutting.

[0140] When cutting the wafer W, since the BG tape B and the expandable tape E are adhered 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 expandable tape E, and the chip spacing does not increase significantly along the already cut cutting line S. This prevents the local stress of the pressing member 218 from being dispersed not only by vertical deformation caused by the elastic body 212 but also by horizontal deformation caused by the large increase in spacing between the chips C, and allows the stress to be concentrated, ensuring reliable and efficient cutting.

[0141] Furthermore, by adhering the BG tape B and the expandable tape E to the front and back surfaces, fragments generated when the wafer W is cleaved do not adhere to the elastic body 212, and even when the next wafer W is placed on the elastic body 212, no adverse effects are caused by 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. As shown in Figure 9, the peeling roller 214 is pressed downward and rolled laterally (in the direction of arrow A in Figure 9) onto the BG tape B whose adhesive strength has been reduced, thereby adhering a peeling film 215.

[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 line S for dividing the chips C is arranged parallel to the peeling roller 214 as shown in Figure 13(a), is rotated by 45 degrees by the table 211 so that the street S intersects the peeling roller 214 at an angle as shown in Figure 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 downward, 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 propagation evaluation by polishing in the above-mentioned grinding and removal step (step S3) will be described with reference to Fig. 18 and Fig. 19. The polishing method, dividing and separating method, and their conditions are basically the same as those in steps S1 to S8 above. Fig. 18 is a diagram showing the conditions for the crack propagation evaluation, and Fig. 19 is a diagram showing the evaluation results of the crack propagation evaluation.

[0150] 18(A), (B), and (C), the horizontal axis is common and each position corresponds to another 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 Fig. 18(B) indicates the ON / OFF state of the water supply to the grinding stone during polishing, and the vertical axis of Fig. 18(C) indicates the temperature (°C) of the backside of the wafer W during polishing.

[0151] As shown in Figure 18(A), rough polishing was performed to a total of 710 μm while varying the polishing rate. This was followed by 13 μm of fine polishing (not shown), followed by 2 μm of chemical mechanical polishing (not shown). For the wafer, as shown in Figure 18(B), water supply to the grinding wheel or wafer was interrupted during rough polishing. Water supply was stopped t1 seconds after the start of polishing and resumed t2 seconds after the start of polishing. Water supply was performed at a flow rate of 10 L / min. The wafer was then cleaved by performing steps S5, S6, and S7 described above, and the cleavage state was observed and evaluated. A good cleavage without chip cracking or dust generation was marked with a circle, while a poor cleavage without chip cracking or dust generation was marked with an X. The results are summarized in Figure 19.

[0152] As shown in Figure 18 (C), the backside temperature of the wafer W began to rise suddenly 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 Figure 19, when the backside temperature of the wafer W reached 70°C or higher due to polishing, the wafer was successfully cleaved. This is thought to be because the cracks formed by the laser propagated due to the heat of polishing.

[0154] Therefore, the grinding apparatus according to the present invention can be provided with a means for measuring the wafer temperature, a means for turning on and off the water supply to the grinding wheel or wafer during grinding, and a means for controlling the water supply to the wafer so that it is turned off until the wafer temperature reaches a predetermined value after a predetermined time has elapsed since the start of grinding. This allows the crack formed by the laser to grow and the wafer to be successfully cleaved.

[0155] As described above, according to this embodiment, since the cracks in the modified region formed by the laser beam can be propagated by grinding, it is possible to prevent the modified region formed by the laser beam from remaining on the cross section of the chip C. This prevents problems 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 cutting reliably and efficiently. Furthermore, no contamination is left on the elastic body on which the wafer is placed during cutting, and continuous cutting does not adversely affect the wafer.

[0156] (Addendum) As can be understood from the above detailed description of the embodiments, 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 irradiating a laser beam from the back surface along a cutting line of the wafer with the backgrind tape adhered to the front surface to form modified regions inside the wafer, thereby forming microvoids in the modified regions; a vacuum suction process of vacuum-sucking the substantially entire front surface of the wafer on which the modified regions have been formed in the modified region forming process independently and uniformly to a table in each region; a grinding process of grinding the wafer, whose substantially entire front surface has been adsorbed to the table in the suction process, from the back surface to remove the modified regions and propagate 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 propagated in the thickness direction of the wafer by a step of polishing the wafer by chemical mechanical polishing; a step of applying an expanding tape to the back surface of the wafer that has been chemically and mechanically polished; a step of pressing the wafer with the expanding tape applied to the back surface with a pressing member through the back-grinding tape to thereby cleave the wafer; a step of applying a peeling tape for peeling the back-grinding tape and peeling the back-grinding tape with a peeling roller; and a dividing and separating step of dividing 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 using a tape application mechanism. After the backgrind tape is applied, a laser beam is applied from the back surface of the wafer along the cutting line to form a modified region inside the wafer, thereby forming micropores in the modified region. With substantially the entire surface of the wafer on which the modified region has been formed being held uniformly and independently by suction at each position of the substrate on a table, the wafer is ground from the back surface to remove the modified region.

[0159] At this time, the grinding heat generated by the grinding causes the wafer surface to thermally expand in the radial direction, but the wafer vacuum chuck, which has a large heat capacity, tries to prevent this expansion.

[0160] As a result, the wafer's front surface expands due to thermal expansion, while the chucked back surface of the wafer tends to maintain its original state without expanding due to the vacuum chuck. As a result, the modified region formed inside the wafer acts to further expand in response to the difference in expansion between the front and back surfaces of the wafer, causing further crack propagation. The modified region is large and brittle because some parts were irradiated with laser light and then melted and recrystallized. If such a modified region appears on the side of a future chip, it may cause dust to be emitted from the chip side and large crystal grains to be chipped off from the chip side. However, because the microcracks that propagate from the modified region are pure crystal planes, even if these planes appear on the side of a future chip, they will not cause dust to be emitted from the chip side or become large crystal grains that will chip off.

[0161] In this way, the wafer is removed by grinding, and the microvoids are propagated in the thickness direction of the wafer, eliminating the modified region. Next, to highlight the process-affected layer formed by grinding and the propagated 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 expandable film is attached to the backside of the unbroken wafer using 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. Next, one of the cutting lines is cut by a pressing member installed in the peeling mechanism, which is positioned parallel to the cutting line. After one cutting line is completely cut, the wafer is rotated 90 degrees and the other cutting line is cut.

[0163] After cleaving, the adhesive strength of the backgrind tape is reduced by ultraviolet irradiation, heating, or the like. A peeling tape is then applied to the backgrind tape with reduced adhesive strength using a peeling roller, and the tape is peeled off. After the backgrind tape is peeled off from the wafer, the expand film expands, separating the chips. This prevents the modified region formed by the laser beam from remaining on the chip cross section. This prevents problems such as chip cracking and dust generation from the chip cross section, and allows chips of consistent quality to be obtained efficiently.

[0164] Furthermore, since the backside of the ground wafer is chemically mechanically polished before being divided, the die strength can be increased. Here, chemical mechanical polishing is significantly different from the etching treatment in the polishing process shown in Cited Document 2.

[0165] First, the chemical solution in the present application is different from the etching solution in Reference 2. The etching solution in Reference 2 acts on the substrate surface, naturally dissolving the substrate, i.e., etching it. As a result, even in areas where cracks have occurred, the etching solution penetrates and naturally etches the surrounding area, further enlarging the modified layer formed by the laser. Furthermore, as mentioned above, with conventional etching solutions, the etching solution penetrates too far into the cracks, causing them to grow and eventually penetrate into the area between the chip and the film. This can lead to the etching solution reaching the chip surface, eroding the chip surface and causing each chip device to cease 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; it simply modifies the wafer surface. Therefore, even if the abrasive penetrates into a crack along the planned cutting line of the wafer, it does not dissolve the surrounding silicon, and the crack does not grow any further.

[0167] As a result, cracks may grow during 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 grow. As a result, the conventional problems of the abrasive penetrating and peeling the chip off the film or the abrasive moving toward the chip surface and eroding the chip, causing the chip device to stop functioning, do not occur.

[0168] The mechanism of chemical mechanical polishing is as follows: First, an abrasive is supplied to the wafer, which only chemically modifies the wafer surface. Then, because the modified surface is soft, the abrasive particles contained in the slurry act on the wafer surface, effectively removing the wafer surface even with very little stress.

[0169] For example, in the case of a silicon removal process, 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 contains Si atoms. These Si atoms are hydrated in water, and -OH groups exist on the surface of the Si atoms. The OH groups attached to the Si substrate surface bond with the SiOH groups in the silica sol present in the liquid and the SiOH groups present on the surfaces of the silica particles.

[0171] However, this alone does not result in etching. 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 under a certain momentum, and a chemical reaction occurs under a certain temperature and pressure environment, resulting in mechanical removal.

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

[0173] As a result, the altered layer formed on the substrate surface during grinding is removed by chemically polishing only the substrate surface, due to the supply of a slurry containing silica sol and silica particles, and the mechanical friction caused by the polishing pad coming into contact with the substrate (Dohi Toshiro (ed.): Detailed Explanation of Semiconductor CMP Technology (Industrial Research Association) (2001) pp. 40-42).

[0174] As a result, most of the damaged layer on the wafer surface is removed. The resulting wafer surface has a mirror finish. The principle behind this mirror finish is as follows, compared to chemical etching in Reference 2.

[0175] As mentioned above, chemical etching selectively etches lattice distortions and crystal defects in crystals such as silicon, which can lead to the formation of etch pits and 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, the rubbing of the wafer surface with a polishing pad, occurs with equal probability on all substrate surfaces, regardless of the crystalline state of the substrate surface. Therefore, while the entire surface is uniformly removed regardless of the crystalline state, a chemical action is applied, resulting in a uniform surface, free of crystal defects, and a mirror-like finish. Here, the term "mirror surface" is ambiguous from a relative perspective, so in this application, it is defined as a mirror surface obtained by chemical mechanical polishing.

[0177] By performing 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 chemical mechanical polishing, the chip is not completely broken. Only small voids remain on the surface after chemical mechanical polishing, which have developed from the modified layer. The modified layer has already been removed in the previous grinding process.

[0179] If the surface is left with microvoids that have developed from this modified layer, for example, after grinding and etching as shown in Patent Document 2, it will be impossible to clearly distinguish between the microvoids that have developed from the modified layer and the irregularities that have been promoted by the etching process after grinding. Therefore, when the chip is fractured, it is possible that the fracture will not necessarily occur from the microvoids, but in some cases, the fracture will occur from the irregularities that have been further promoted by etching the grinding marks.

[0180] When chemical mechanical polishing is performed on the surface as in the present invention, the surface of the wafer after the polishing is almost free of irregularities, and only microvoids that have developed from the modified layer remain. Therefore, if the wafer is subjected to a cleaving process in this state, cracks will further develop from the microvoids and cause the wafer to cleave.

[0181] Thus, in the method of the present invention, even after grinding and chemical mechanical polishing, the microvoids grow larger and cracks propagate, but the substrate is not completely divided. If the cracks propagate 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 peel 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 split. To further propagate the crack from a state where it is not completely split to completely split the wafer, a further splitting step is required. The splitting step involves attaching an expandable tape to the backside of the wafer, and then applying pressure with a pressing member through the tape to locally apply bending stress to the wafer. This allows for efficient splitting, starting from the crack that has grown due to grinding.

[0183] If no expanding tape is attached, the wafer is directly pressed by the pressing member, and when the wafer is cut, the vibrations of the cracks are propagated within the wafer surface. The propagated vibrations may cause incidental cracks in other parts of the cutting line or may crack parts other than the cutting line.

[0184] However, by applying an expanding tape and applying stress via the tape using a pressing member, the tape absorbs the vibrations of the crack when the wafer is cleaved, preventing unnecessary vibrations. Furthermore, because the expanding tape is applied in a stretched state without wrinkles or warping, it constantly applies a constant tension to the wafer, constraining it. When the wafer is constrained during cleavage, bending deformation in various parts of the wafer is constrained, and the pressing force of the pressing member is concentrated as shear stress, rather than bending, on the advanced crack, which is a weak area inside the wafer. This ensures that only the areas that should be cut are efficiently cut, while areas outside the cutting line are protected and do not crack.

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

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

[0187] According to the invention described in Appendix 2, the modified region is initially formed deep inside the wafer, and by initially performing the removal process while generating grinding heat in the first grinding step, it is possible to propagate the cracks formed in the modified region to even deeper positions inside the wafer.

[0188] However, if the laser-modified area is also ground away with the same volume as the unmodified area in the first grinding process, the modified area has large crystal grain boundaries, which can cause large crystal grains to chip off and further develop fatal cracks. Therefore, it is recommended that the first grinding process be performed up to the area just before the modified area, where the crystallinity is constant.

[0189] The second grinding process mainly removes the laser-modified area. A higher-grit grinding wheel, i.e., a finer-grained wheel than that used in the first grinding process, is used, and the grinding process is gentler than in the first grinding process to avoid inducing fatal cracks or defects derived from the modified area. The second grinding process is limited to the modified area, and the grinding rate is slower than in the first grinding process, allowing for fine grinding.

[0190] After the laser-modified region is removed, chemical mechanical polishing (CMP) is finally performed, in which a chemical solution that modifies the wafer is supplied while a polishing pad made of polymer or nonwoven fabric is pressed against the wafer to chemically and mechanically polish it.

[0191] If chemical mechanical polishing were to be performed on the modified region, large crystal grains could chip off from the modified region. Chemical mechanical polishing uses polishing pads made of nonwoven fabric or polyurethane foam, and if the chipped crystal grains get into the pad surface, they will constantly create scratches during polishing. In such cases, the polished surface will end up covered in scratches, rather than achieving the goal of removing the altered layer and achieving 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, and the wafer is placed on a table having an elastic body attached to its upper surface, the table is rotated so that the pressing member is parallel to the cutting line, and the pressing member is pressed against the wafer and rolled to break the cutting line.

[0194] According to the invention described in Appendix 3, when the wafer is cleaved, 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 laser light incident from the rear surface is ground and polished, an expand tape is attached to the rear surface by a tape-attaching mechanism.

[0195] The wafer with backgrind tape and expand tape attached to both sides is placed on a table with an elastic body attached to its 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 one cutting line is completely 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 ultraviolet light irradiation or heating. A peeling roller applies peeling tape to the backgrind tape with reduced adhesive strength, and the wafer is peeled off. After the backgrind tape is peeled off, the expand film on the wafer is expanded, separating the chips. This ensures efficient cutting, and allows for successive cutting 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 spacing 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 spacing between the cutting lines formed on the wafer being pressed. Because the radius is smaller than the spacing between the cutting lines, the pressing member does not press multiple cutting lines at once, preventing the stress from being dispersed. This makes it possible to concentrate the stress on one cutting line, ensuring reliable and efficient cutting.

[0199] (Appendix 5) A 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 grooves, holes, or irregularities formed on its surface. 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 repeated use are small. By forming grooves, holes, or irregularities 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, ensuring reliable and efficient cleaving.

[0201] (Appendix 6) A 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 the cutting lines formed in a grid pattern at an angle to apply the tape.

[0202] According to the invention described in Appendix 6, when backgrinding tape or expanding tape is adhered to the front and back surfaces of a wafer, the table on which the wafer is placed is rotated by about 45 degrees, and the adhering roller is pressed in a direction that intersects the cutting lines formed in a grid pattern at an angle, and then the tape is adhered 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 tape would be misaligned, making it difficult to apply the tape accurately. By moving the tape application roller so that it crosses the cutting line at an angle, cutting can be done reliably and efficiently, without adversely affecting 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...pressure 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 wafer, comprising: a crack propagation means for varying the degree of propagation of the crack by changing the water supply conditions when the back surface of the wafer is ground; Crack propagation device.

2. A crack propagation method for propagating a crack inside a wafer, comprising: a crack propagation step of changing a water supply condition when the back surface of the wafer is ground to change a degree of propagation of the crack; Crack propagation method.

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