Crack development method

Abstract

To provide a wafer processing device and wafer processing method that can efficiently obtain a chip of stable quality.SOLUTION: A method for developing a crack inside a wafer is for performing a modified layer forming process with laser and for performing a grinding process from a backside to a target surface by combining rough grinding, fine grinding, and chemical mechanical polishing to remove a modified layer. In the rough grinding, the backside of the wafer is ground while a water supply is stopped, a wafer crack is developed due to thermal expansion, and the wafer is attached to expand tape, and the wafer is separated by a stretching process.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a technique for cleaving a wafer having a laser modified region therein. [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 onto the substrate 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 naturally or by a relatively small force, such as an artificial force or by 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 splitting the substrate by applying an external force, if the substrate is not thinned, a very large stress is required to split the wafer, which is a problem.

[0009] In particular, when the substrate is thick enough 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 the substrate with several laser pulses in multiple stages in the thickness direction.

[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 left on the wall of the wafer 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. 17, or when only a portion of the substrate is attracted to the substrate as shown in Fig. 18, 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 an object of the present invention is to provide a wafer processing apparatus and a wafer processing method that can efficiently obtain chips of stable quality. [Means for solving the problem]

[0023] A wafer processing apparatus for achieving the object of the present invention processes a wafer having a modified region formed therein by laser light, and includes a grinding unit that grinds the back surface of the wafer with a grinding wheel while adsorbing the front surface of the wafer, removing the modified region while leaving microcracks extending from the modified region, and a polishing unit that polishes the back surface of the wafer with an abrasive cloth after grinding.

[0024] According to this device, the grinding heat generated by the grinding causes the wafer surface to expand radially together with the wafer being ground, but the wafer vacuum chuck, which has a large thermal capacity, tries to prevent the wafer from expanding.

[0025] As a result, the back surface of the wafer expands due to thermal expansion, while the chucked front surface of the wafer does not expand due to the vacuum chuck and tries to maintain its original state. As a result, the modified region formed inside the wafer acts to further expand depending on the difference in expansion between the front surface and the back surface of the wafer, and the cracks grow further. The modified region has large crystal grains and is brittle because some parts were irradiated with laser light and melted once and then recrystallized. If such a modified region 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 from the side of the chip. However, since the microcracks that grow from the modified region are pure crystal faces, even if this face 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.

[0026] In this way, the wafer is ground and removed by the grinding process, and the microvoids are propagated in the thickness direction of the wafer to remove the modified regions. Next, in order to highlight the process-induced 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-induced layer. As a result, only the microvoids remain on the surface, and the remaining area becomes a perfect mirror surface without any processing distortion.

[0027] The unbroken wafer is then placed on a wafer-cutting mechanism, bending stress is applied to the wafer to cut it, and the expand film is then pulled 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 problems such as chip cracking and dust generation from the chip cross section, and makes it possible to efficiently obtain chips of stable quality.

[0028] 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 significantly different from the etching process in the polishing step shown in Reference 2.

[0029] 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, so that the modified layer formed by the laser is further enlarged. 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.

[0030] 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.

[0031] 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 problems with the conventional technology, such as the abrasive penetrating and peeling the chip off the film, or the abrasive getting around to the chip surface and corroding the chip, causing the chip device to stop functioning.

[0032] 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.

[0033] For example, in the case of 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:

[0034]

number

[0035] 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 surface of the silica particles.

[0036] 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.

[0037] 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.

[0038] 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).

[0039] As a result, most of the process-induced layers on the wafer surface are removed. The wafer surface that is formed has a mirror finish. The principle of this mirror finish is as follows, in comparison with the chemical etching described in Reference 2.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] After the chemical mechanical polishing, the chip is not yet completely cracked. Only small voids developed from the modified layer remain on the surface after the chemical mechanical polishing. The modified layer has already been removed in the previous grinding process.

[0044] 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.

[0045] 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.

[0046] In addition, a wafer processing method for achieving the object of the present invention is a wafer processing method for processing a wafer having a modified region formed therein by laser light, the method comprising: a grinding step in which the back surface of the wafer is ground with a grinding wheel while the front surface of the wafer is adsorbed, thereby removing the modified region while leaving microcracks extending from the modified region; and a polishing step in which, after grinding, the back surface of the wafer is polished with an abrasive cloth. Effect of the Invention

[0047] According to the present invention, chips of stable quality can be obtained efficiently. [Brief description of the drawings]

[0048] [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] 4 is a flowchart showing a process flow of a semiconductor substrate cutting method. [Figure 10] FIG. 2 is a diagram illustrating a laser modification process. [Figure 11] FIG. [Figure 12] FIG. [Figure 13] 1A to 1D are diagrams illustrating 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 14] 11 is a diagram for explaining the surface state of the rear surface of the wafer W after the grinding and removing process. [Figure 15] FIG. 4 is a diagram illustrating a dividing and separating process. [Figure 16] FIG. 4 is a diagram illustrating a dividing and separating process. [Figure 17] FIG. 13 is a diagram showing a conventional fixed state during substrate grinding. [Figure 18] FIG. 13 is a diagram showing a conventional fixed state during substrate grinding. [Figure 19] FIG. 1 shows the conditions for crack growth evaluation. [Figure 20] FIG. 13 shows the results of crack growth evaluation. [Figure 21] FIG. 3 is a diagram showing an outline of a splitting device 300. [Figure 22] FIG. 11 is an explanatory diagram showing another embodiment of the chuck deflection means. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0050] The present invention is performed by a cutting device composed of a laser dicing device 1, a grinding device 2, a transport device (not shown) that transports the wafer processed by the laser dicing device 1 to the grinding device 2, and a dividing device that divides the wafer ground by the grinding device 2 into chips.

[0051] <About the device configuration> (1) Laser dicing machine 1 1 is a diagram showing the overall configuration of a laser dicing device 1. As shown in the figure, the laser dicing device 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.

[0052] 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 apparatus 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.

[0053] The wafer W has a BG tape B having an adhesive attached to one surface of the front surface, and is placed on the suction stage 13 with the back surface facing upward.

[0054] 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.

[0055] 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 oscillated 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.

[0056] The laser light conditions were as follows: light source was a semiconductor laser pumped Nd:YAG laser, wavelength was 1064 nm, and the cross-sectional area of ​​the laser light spot was 3.14 × 10 -8 cm 2 The oscillation form is a Q-switched pulse, the repetition frequency is 100 kHz, the pulse width is 30 ns, the output is 20 μJ / pulse, the laser light quality is TEM00, and the polarization characteristics are linearly polarized. The conditions of the condenser lens 24 are a magnification of 50 times, an NA of 0.55, and a transmittance of 60 percent for the laser light wavelength.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] The control unit 50 is made up of a CPU, a memory, an input / output circuit unit, etc., and controls the operation of each unit of the laser dicing apparatus 1.

[0061] 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.

[0062] The wafer cassette elevator moves a cassette containing wafers up and down to position it at a transfer position. The transfer means transfers the wafer between the cassette and the suction stage 13.

[0063] The operation panel is equipped with switches and display devices for operating each part of the dicing device 10. The indicator lights display the operating status of the dicing device 10, such as when processing is in progress, processing is completed, and emergency stop.

[0064] 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 finely 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 finely in parallel with wafer W.

[0065] 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.

[0066] 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.

[0067] 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 .

[0068] Fig. 3 is a plan view of driving means 25. As shown in Fig. 3, two linear fine movement means PZ1, 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 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 laser light can be finely moved back and forth in the X direction or vibrated.

[0069] 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.

[0070] Laser light L is emitted from a laser oscillator 21, and 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. 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 the XYZθ table 12 and controlling the position of the condenser lens 24 using the Z fine movement means 27.

[0071] In this state, the XYZθ table 12 is 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 P. As a result, a line of modified region P due to multiphoton absorption is formed inside the wafer W along the cutting line of the wafer W.

[0072] If necessary, vibration in the Z direction may be applied by Z fine movement means 27. In addition, the laser light L may be repeatedly irradiated back and forth like a perforation by slowly finely moving the laser light L back and forth in the X direction, which is the processing direction, while moving the wafer W in the X direction.

[0073] 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.

[0074] 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.

[0075] (2) Grinding device 2 4 is a perspective view showing an 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.

[0076] 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.

[0077] 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.

[0078] The rough grinding stage 118 is a stage where rough grinding is performed, 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 where fine grinding is performed, and is surrounded by the side surface of the main body 112, a top plate 129, and a partition plate 125, just like 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 7 is a structural diagram of the polishing stage 122. In the polishing stage 122, the wafer W is polished by the polishing cloth 516 and the slurry supplied from the polishing cloth 156, and a process-affected layer occurring on the rear surface of the wafer W is removed by rough polishing and fine polishing. The process-affected layer is a general term for scratches and process distortions (crystals are altered) and the like occurring due to grinding.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] Returning to the explanation of Fig. 4, the alignment stage 116 is a stage that aligns the wafer W transferred from the laser dicing apparatus 1 by a transfer device (not shown) to a predetermined position. The wafer W aligned on this alignment stage 116 is attracted and held by a transfer robot (not shown), and then transferred to an empty chuck 132 and attracted and held on the suction surface of this chuck 132.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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).

[0093] 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.

[0094] 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.

[0095] 2(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.

[0096] 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.

[0097] 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 cup-shaped grinding wheels 146 and 154.

[0098] 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.

[0099] 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.

[0100] 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 rotation speed of the motor 148, thereby controlling the rotation speed of the cup-shaped grindstone 146.

[0101] After the cup-shaped grinding wheel 146 is retracted from the wafer W, the thickness of the wafer W, whose back surface 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 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 by the cup-shaped grinding wheel 154 of the fine grinding stage 120 and sparked out. The structure of this 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.

[0102] After the cup-shaped grinding wheel 154 is retracted from the wafer W, the thickness of the wafer W, whose back surface 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 the 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 back 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.

[0103] After the arm 168 is rotated by the control unit 100 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 rinsing function and a spin drying function is used as the wafer cleaning stage 124. Since the wafer W after polishing 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.

[0104] The wafer W that has been cleaned and dried on the wafer cleaning stage 124 is attracted and held by a hand (not shown) of a robot (not shown) and stored on a predetermined shelf of a cassette (not shown).

[0105] (3) Splitting device Next, the splitting device (not shown) will be described. A conventional splitting device can be used as the splitting device. For example, a splitting device having the following configuration, as disclosed in US Pat. No. 2004-100240, can be used.

[0106] That is, the peripheral portion of the dicing tape is fixed to a frame. A ring member is in contact with the lower surface of the inner portion of the peripheral portion of the dicing tape. The outer peripheral edge of the upper surface of this ring member is smoothly chamfered with a R. A UV light source (UV light irradiation means) is disposed below the dicing tape.

[0107] The dicing tape is irradiated with UV light from a UV light source while the frame is pressed downward. By irradiating the dicing tape with UV light, the adhesive on the dicing tape can be hardened and the adhesive strength of the tape can be changed.

[0108] At the same time, a downward force is applied to the frame, pushing it down. This causes the dicing tape to expand, widening the gap between the chips. At this time, the dicing tape S expands smoothly because the outer periphery of the top surface of the ring member is smoothly chamfered.

[0109] 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.

[0110] The irradiation conditions such as the UV light irradiation intensity (power), wavelength region, and irradiation time can be appropriately selected depending on the adhesive material of the dicing tape S, the size of the wafer, the size of the chips after cleavage, and the like.

[0111] Here, a UV light source is not necessarily required, and it is possible to appropriately cut the chips by adjusting the adhesive strength of the dicing tape.

[0112] (4) Other embodiments of the splitting device Fig. 21 is a diagram showing an outline of the dividing apparatus 300. In Fig. 21, (A) is a plan view of the dividing apparatus 300, and (B) is a side view of the dividing apparatus 300. The dividing apparatus 300 is mainly configured to include a wafer chuck 304 for suction-fixing a wafer 302, a bending means 306 for bending the wafer chuck 304, and a vacuum pump 308.

[0113] The wafer chuck 304 is mainly composed of an independent suction chuck 310 having independent suction holes and a communicating groove chuck 312 having a spiral groove communicating with the independent suction holes, and the independent suction chuck 310 and the communicating groove chuck 312 are overlapped.

[0114] The thickness of the communication groove chuck 312 and the independent suction chuck 310 is about 1 mm each, and when the two are stacked together, the thickness becomes about 2 mm. Each is preferably made of a resin material such as acrylic. However, the material is not limited to a resin material, and other materials such as ceramics may be used, and any material may be selected as long as it can bend the wafer chuck after the wafer is vacuum-attached. In addition, the material of the wafer chuck 304 itself does not necessarily need to bend, and it is sufficient that the wafer chuck 304 as a whole has a configuration and structure that allows it to bend.

[0115] The deflection means 306 is a rod-like body with a rounded tip, and can deflect the wafer chuck 304 into a hemispherical shape by pushing the center of the back surface of the wafer chuck 304 upward from below.

[0116] The wafer 302 is placed on the wafer chuck 304 with the outer periphery of the expand film 314 attached thereon, for example, by a metal frame, and is vacuum-adsorbed. It is preferable that the expand film 314 has some breathability, because the breathability allows the wafer 302 itself to be directly adsorbed to the wafer chuck 304 by the vacuum force.

[0117] The wafer chuck 304 is bent into a hemispherical shape by a bending means while still holding the wafer 302. As a result, the wafer 302 is divided along the cutting lines.

[0118] Next, another embodiment of the chuck deflection means will be described with reference to Fig. 22. Fig. 22 is an explanatory diagram showing another embodiment of the chuck deflection means. In this figure, except for the chuck deflection means 320, the components are the same as those in Fig. 21, so the description will be omitted.

[0119] 22, the chuck bending means 320 is in a semi-cylindrical shape. The dividing apparatus 300 also includes a means (not shown) for rotating the chuck bending means 320 relative to the wafer 302.

[0120] When considering the X-axis and Y-axis that are perpendicular to the surface of the wafer, the dividing lines formed on the wafer 302 are often in the X-axis and Y-axis directions. Therefore, the wafer 302 is divided as follows. That is, the position of the chuck bending means 320 is adjusted so that one side of the chuck bending means 320 is parallel to the X-axis. Next, the wafer 302 is aligned so that the dividing line is parallel to the X-axis, and is placed on the wafer chuck 304 and vacuum-adsorbed.

[0121] The chuck deflection means 320 is pressed against the lower surface of the wafer chuck 304 to deflect the wafer 302 together with the wafer chuck 304 and divide it in the X direction. Next, the chuck deflection means 320 is removed from the wafer chuck 304, rotated 90 degrees, and pressed against the lower surface of the wafer chuck 304 again so that the one side surface is parallel to the Y axis, dividing the wafer 302 in the Y direction. This allows the wafer 302 to be split along the division lines in both the X and Y directions.

[0122] Here, if the wafer 302 is not vacuum-adsorbed but is bent by being pressed against the chuck bending means 320 via a dicing film, which is an elastic film, and the wafer cracks first in a certain part, the wafer bends sharply at the cracked part, and the curvature of the chuck bending means 320 is absorbed there, so that part of the wafer does not bend and may follow the shape of the chuck bending means 320 without being divided.

[0123] Therefore, wafer 302 is first vacuum-attached to wafer chuck 304, which then straightens wafer 302 to a flat surface. Then, wafer chuck 304 is bent together with wafer chuck 304. Each part of wafer 302 conforms to the bending of wafer chuck 304, and wafer 302 follows the bending while still attached to wafer chuck 304. As a result, a constant bending stress is applied uniformly across the surface of wafer 302, and wafer 302 can be divided without leaving any remaining part.

[0124] <Method of cutting semiconductor substrate> Next, a method for cutting a semiconductor substrate will be described with reference to a flowchart shown in FIG 9.

[0125] (1) Laser modification process (step S10) 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.

[0126] When laser light L is emitted from a 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 P is formed inside the wafer W.

[0127] In this embodiment, since the thickness of the chips that are finally generated 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, as shown in Fig. 10. 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 wafer W front surface by the thickness of the chip T.

[0128] 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 P, P, ... arranged side by side within the wafer W. Micropores (hereinafter referred to as cracks) K are formed within the modified region P. Hereinafter, the region formed with a plurality of discontinuous modified regions P, P, ... arranged side by side is referred to as a modified layer.

[0129] When the modified layers are formed along all of the cutting lines L shown in FIG. 11, the process of step S10 ends.

[0130] (2) Grinding and Removal Process (Step S12) After the modified region is formed along the cutting line L by the laser modification process (step S10), 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 by the grinding device 2 and is controlled by the control unit 100.

[0131] The transported wafer W is placed on the chuck 132 (for example, chucks 136, 148, and 140 are also acceptable) with the back surface of the wafer W 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.

[0132] The index table 134 is rotated about the rotation axis 135 to carry the chuck 132 into the rough grinding stage 118, and the wafer W is roughly ground.

[0133] Rough grinding 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.

[0134] After the rough grinding, the index table 134 is rotated about the rotation axis 135 to carry the chuck 132 into the precision grinding stage 120, and the chuck 132 and the cup-shaped grindstone 154 are rotated to precision grind the wafer W. In this embodiment, for example, Tokyo Seimitsu's Resin #2000 is used as the cup-shaped grindstone 154, and the rotation speed of the cup-shaped grindstone 154 is approximately 2400 rpm.

[0135] 12, rough grinding and fine grinding are combined to grind to the target surface, that is, to a depth of approximately 50 μm from the surface of the wafer W. In this embodiment, rough grinding is performed to a depth of approximately 700 μm, and fine grinding 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 time for rough grinding and fine grinding are approximately the same.

[0136] 12, the modified layer is removed in the grinding process, and no modified region P by the laser light remains on the cross section of the chip T, which is the final product. This prevents the modified layer from fracturing from the chip cross section, causing the chip T to crack from the fractured parts, and prevents dust from being generated from the fractured parts.

[0137] 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. 13 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.

[0138] During grinding, the grinding surface shown in Fig. 13(a), i.e., the back surface of the wafer W, expands due to grinding heat as shown in Fig. 13(b). On the other hand, the surface opposite 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. 13(c), and is physically restrained from lateral displacement so as to prevent positional deviation due to thermal expansion.

[0139] That is, as shown in Fig. 13(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 grinding, when the amount of grinding is largest and the frictional force is also large, i.e., the frictional heat can also be large.

[0140] The laser modified region 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 the grinding heat in the early stage of rough grinding.

[0141] Even if grinding is performed under conditions that cause thermal expansion of the wafer W, that is, conditions for generating 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.

[0142] 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 on 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 on the surface of the wafer W, as in the case of applying artificial stress.

[0143] 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 broken. 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, making it 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 dividing and separating step (step S18) described later.

[0144] 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.

[0145] (3) Chemical mechanical polishing process (step S14) This process is carried out by the grinding device 2 and is controlled by the control unit 100.

[0146] After the precision grinding, 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 by the polishing cloth 156 of the polishing stage 122. In the polishing removal process (step S12), the processed altered layer formed on the back surface of the wafer W is removed, and the back surface of the wafer W is mirror-finished.

[0147] 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.

[0148] As a result of the grinding removal step (step S12), the back surface of the wafer W has numerous irregularities as shown in Fig. 14. 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.

[0149] In other words, in order to improve the quality of the final product, the chip T, 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.

[0150] (4) Expandable tape application process (step S16) An expandable tape F is attached to the rear surface of the wafer W that has been subjected to the chemical mechanical polishing step (step S14). The expandable tape is a type of elastic tape and is freely stretchable.

[0151] In this embodiment, the back surface of the wafer W is mirror-finished in the chemical mechanical polishing process (step S14), so that the adhesion between the expandable tape F and the wafer is significantly improved. In addition, the flexural strength of the chips T that are finally produced can also be increased.

[0152] (5) Dividing and separating step (step S18) The wafer W with the expandable tape F attached to its back surface in the expandable tape attachment step (step S16) is placed with its front surface facing up in a dividing device as shown in Fig. 15. Since the crack has progressed from the target surface toward the front surface side in the grinding and removing step (step S12), a progressed crack has formed on the side of the wafer W where the expandable tape F is attached as shown in Fig. 15.

[0153] 16, when the expandable tape F is expanded outward, the wafer W is broken based on the developed crack. That is, the wafer W is broken along the cutting lines and divided into multiple chips T. When the expandable tape F is then further expanded, the individual chips T are separated.

[0154] In this embodiment, by propagating the crack below the target surface in the grinding and removing step (step S12), it becomes possible to efficiently divide the wafer W into chips T simply by pulling the expandable tape F in the dividing and separating step. In addition, since the wafer is not completely cut when the crack is propagated, the work efficiency is good.

[0155] In addition, in this embodiment, the back surface of the wafer W is mirror-finished in the chemical mechanical polishing process (step S14), so that the expanding tape F and the chips T do not become misaligned and partially peel off during expansion.

[0156] <<Evaluation of crack growth due to grinding>> Next, the evaluation of crack growth due to grinding in the above grinding removal step (step S12) will be described with reference to Fig. 19 and Fig. 20. The grinding method, the dividing and separating method, and the conditions thereof are basically the same as those in steps S10 to S18. Fig. 19 is a diagram showing the conditions for the crack growth evaluation, and Fig. 20 is a diagram showing the evaluation results of the crack growth evaluation.

[0157] 19(A), (B), and (C), the horizontal axis is the same and each position corresponds to each other, and indicates the grinding time (s). The vertical axis of Fig. 19(A) indicates the cutting speed (grinding 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 grinding.

[0158] As shown in FIG. 19(A), rough grinding was performed by changing the grinding speed to a total of 710 μm, then fine grinding was performed by 13 μm (not shown), and chemical mechanical polishing (not shown) was performed by 2 μm. In the case of the wafer, as shown in FIG. 19(B), a period of interruption of water supply to the grindstone or wafer was provided during rough grinding. Water supply was stopped after t1 seconds had elapsed after the start of grinding, and water supply was resumed after t2 seconds had elapsed after the start of grinding. Water supply was performed at a flow rate of 10 L / min. Then, the above steps S16 and S18 were performed to break the wafer, and the broken state was observed and evaluated. The results are summarized in FIG. 20, with ○ indicating that the chip broke well without cracking or generating dust, and × indicating that the chip broke or generated dust.

[0159] As shown in FIG. 19(C), the back surface temperature of the wafer W suddenly began to rise t1 seconds after the start of grinding when the water supply was stopped, and began to fall immediately t2 seconds after the start of grinding when the water supply was resumed.

[0160] 20, when the back surface temperature of the wafer W became 70° C. or higher due to grinding, the wafer was successfully cleaved. This is believed to be because the cracks formed by the laser propagated due to the heat of grinding.

[0161] 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 a predetermined time after the start of grinding. This allows the cracks formed by the laser to grow, and the wafer to be successfully cut.

[0162] As described above, according to this embodiment, the cracks in the modified region formed by the laser light can be advanced by grinding, so that the modified region formed by the laser light does not remain on the cross section of the chip T. This makes it possible to prevent problems such as the chip T cracking or dust generation from the cross section of the chip T. Therefore, chips of stable quality can be obtained efficiently.

[0163] (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.

[0164] (Additional Note 1) A method for cutting a semiconductor substrate according to a first aspect of the present invention includes a modified area forming step of irradiating laser light from the back surface of the wafer along a cutting line to form modified areas inside the wafer, thereby forming microvoids in the modified areas; a suction step of independently and uniformly adsorbing to a table substantially the entire surface of the wafer on which modified areas have been formed in the modified area forming step; a grinding step of grinding the wafer, the entire surface of which has been adsorbed to the table in the suction step, from the back surface to remove the modified areas and propagate the microvoids in the thickness direction of the wafer; a chemically and mechanically polishing step of the wafer in which the microvoids have propagated in the thickness direction of the wafer in the grinding step; a cutting step of cutting along the cutting line based on the microvoids remaining in the substrate; and a dividing step of dividing the substrate into a plurality of chips after cutting.

[0165] According to the method for cutting a semiconductor substrate of this first embodiment, laser light is incident on the back surface of the wafer along a cutting line to form a modified region inside the wafer, thereby forming microvoids in the modified region, and the wafer is ground from the back surface while substantially the entire surface of the wafer on which the modified region has been formed is adhered independently and uniformly to a table at each position of the substrate, thereby removing the modified region.

[0166] (Note 2) A method for cutting a semiconductor substrate according to a second aspect of the present invention includes a modified region forming step of forming modified regions inside the wafer by irradiating a laser beam from the back surface of the wafer along a cutting line, thereby forming micropores in the modified regions; a step of adsorbing substantially the entire surface of the wafer on which modified regions have been formed in the modified region forming step, uniformly and independently within each region, to a table; and a step of grinding and removing the wafer up to a portion just before the modified regions formed inside the wafer by irradiating the laser beam while the wafer is adsorbed, thereby removing the portions extending from the modified regions. The method includes a first grinding step of propagating the microcracks in the depth direction of the substrate, a second grinding step of grinding away the modified regions formed inside the wafer, a step of removing the process-affected layers introduced in the first and second grinding steps to make the surface mirror-finished while performing chemical mechanical polishing using a chemical slurry and a polishing pad that modifies the wafer surface, leaving behind microcracks extending from the modified regions, a step of cleaving the wafer into wafers based on the microcracks that have propagated in the wafer thickness direction, and a step of separating the cleaved chips after cleaving.

[0167] According to the second aspect of the method for cutting a semiconductor substrate, a modified region is initially formed deep inside the wafer, and removal processing is performed while generating grinding heat in the initial first grinding step, thereby making it possible to propagate cracks formed in the modified region to an even deeper position inside the wafer.

[0168] However, if the laser-modified area is also ground and removed in the first grinding step with the same volume as the unmodified area, the modified area has large crystal grains, so large crystal grains may chip off and these crystal grains may cause further fatal cracks to develop. Therefore, in the first grinding step, it is recommended to grind up to the part just before the modified area where the crystallinity is constant.

[0169] 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.

[0170] After the laser-modified region is removed, chemical mechanical polishing is finally performed, in which a chemical liquid 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.

[0171] 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 surface of the pad, scratches will occur due to the chipped crystal grains during polishing. In such a case, the polished surface will be covered with scratches without achieving the purpose of removing the process-affected layer and creating a mirror finish.

[0172] 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.

[0173] (Appendix 3) A method for cutting a semiconductor substrate according to a third aspect of the present invention is characterized in that, in the method for cutting a semiconductor substrate according to the second aspect, the modified region forming step forms the modified region at a depth of approximately 60 μm to approximately 80 μm from the surface of the wafer, and the first grinding step extends the microvoids to between a depth of approximately 50 μm from the surface of the wafer and the surface of the wafer.

[0174] As a result, a modified region is formed at a depth of about 60 μm to about 80 μm from the surface of the wafer, and microvoids are developed to a depth of about 50 μm from the surface of the wafer and between the surface of the wafer. Therefore, even if the workpiece is ground so that the modified region formed by the laser light does not remain on the cross section of the chip, the microvoids can be left in the workpiece.

[0175] (Appendix 4) A method for cutting a semiconductor substrate according to a fourth aspect of the present invention is characterized in that, in the method for cutting a semiconductor substrate according to the first aspect, the grinding step includes a step of interrupting the supply of water to the grinding wheel during grinding until the temperature of the wafer being ground reaches 70°C or higher.

[0176] According to the method for cutting a semiconductor substrate according to the fourth aspect, the temperature of the wafer during grinding can be controlled, which allows the micropores to develop in the thickness direction of the wafer.

[0177] (Appendix 5) A method for cutting a semiconductor substrate according to a fifth aspect of the present invention is characterized in that, in the method for cutting a semiconductor substrate according to the second or third aspect, the first grinding step includes a step of interrupting the supply of water to the grindstone during grinding until the temperature of the wafer being ground reaches 70°C or higher.

[0178] According to the semiconductor substrate cutting method of the fifth aspect, the temperature of the wafer during grinding can be controlled, which allows the micropores to develop in the thickness direction of the wafer.

[0179] (Appendix 6) A sixth aspect of the present invention relates to a method for cutting a semiconductor substrate, and is characterized in that, in the method for cutting a semiconductor substrate according to the first or fourth aspect, the dividing step includes a step of attaching an elastic tape to a surface of the wafer, and a step of expanding the elastic tape.

[0180] According to the method for cutting a semiconductor substrate according to the sixth aspect, the wafer can be divided into a plurality of chips by attaching an elastic tape to the surface of the wafer and expanding it.

[0181] (Appendix 7) A seventh aspect of the present invention provides an apparatus for cutting semiconductor substrates, comprising: a laser dicing means for irradiating a laser beam from a back surface of a wafer along a cutting line to form a modified region inside the wafer; a grinding means for grinding the wafer from the back surface to remove the modified region; a transporting means for transporting the wafer from the laser dicing means to the grinding means; and a dividing means for dividing the wafer along the cutting line, wherein the laser dicing means comprises a table on which the wafer is placed with the front surface facing downward; an irradiation means for irradiating a laser beam toward the wafer to form the modified region; and a first control means for controlling the irradiation means so as to change the position to which the laser beam is irradiated, and the grinding means comprises an adsorption table on which the wafer is placed with the front surface facing downward and which adsorbs substantially the entire surface of the wafer; a grinding wheel for grinding the wafer; and a second control means for controlling the height and rotation speed of the grinding wheel.

[0182] This makes it possible to prevent the modified region formed by the laser beam from remaining on the cross section of the chip, thereby preventing problems such as chip cracking and dust generation from the chip cross section, and making it possible to efficiently obtain chips of stable quality.

[0183] (Appendix 8) The semiconductor substrate cutting apparatus according to an eighth aspect of the present invention is characterized in that, in the semiconductor substrate cutting apparatus according to the seventh aspect, the first control means controls the irradiation means so as to form the modified region at a depth of approximately 60 μm to approximately 80 μm from the surface of the wafer, and the second control means controls the height and rotation speed of the grindstone so as to propagate microvoids in the modified region to between a depth of approximately 50 μm from the surface of the wafer and the surface of the wafer.

[0184] This makes it possible to leave minute holes in the workpiece even when the workpiece is ground so that no modified region formed by the laser light remains on the cross section of the chip.

[0185] (Appendix 9) The semiconductor substrate cutting apparatus according to a ninth aspect of the present invention is characterized in that, in the semiconductor substrate cutting apparatus according to the seventh or eighth aspect, it further comprises a means for measuring the temperature of the wafer being ground, a means for turning on and off the supply of water to the grinding wheel or the wafer during grinding, and a means for controlling the supply of water 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.

[0186] This allows the micropores to develop in the thickness direction of the wafer. [Explanation of symbols]

[0187] 1...laser dicing device, 2...grinding device, W...work, B...BG tape, F...expand tape, 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, 300...division device

Claims

[Claim 1] 1. A method for propagating a crack inside a wafer, comprising: a crack propagation step of propagating the crack by grinding the back surface of the wafer with water supply stopped; Crack growth methods.

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