JP7290843B2 - Crack growth device and crack growth method - Google Patents

Description

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

In Patent Document 1, a semiconductor substrate placed with its back surface facing upward is irradiated with a laser to form a modified region inside the substrate, an expanding tape is attached to the back surface of the semiconductor substrate, and a knife is cut from above the expanding tape. It describes cutting a semiconductor substrate into chips by applying an edge and splitting the substrate with the modified region as a base point.

Further, in Patent Document 1, a semiconductor substrate placed with its back surface facing upward is irradiated with a laser to form a modified region inside the substrate, then the substrate is ground to be thinned, and expanded on the back surface of the semiconductor substrate. It is described that the tape is attached and the expanded tape is stretched to split the substrate with the modified region as a base point.

In Patent Document 2, a semiconductor substrate placed with its back surface facing upward is irradiated with a laser beam to form a modified region inside the substrate, thereby generating cracks in the thickness direction of the semiconductor substrate, thereby cracking the back surface of the substrate. It describes cutting a semiconductor substrate into chips by exposing cracks on the back surface by grinding and chemical etching. Patent Document 2 discloses that cracks occur in the thickness direction from the modified region by generating thermal stress by applying a natural or relatively small force, such as an artificial force or a temperature difference, to the substrate. described to occur.

Japanese Patent No. 3624909 Japanese Patent No. 3762409

In the invention described in Patent Document 1, the substrate is cracked by applying an external force locally with a knife edge, and bending stress and shear stress are applied to the substrate in order to apply the external force locally. However, it is difficult to uniformly distribute bending stress and shear stress over the entire surface of the substrate. For example, when bending stress or shearing stress is applied to the substrate, the stress is concentrated on some weak point, and the minimum required stress cannot be uniformly applied to the desired portion efficiently.

Therefore, there is a problem that the cracking of the substrate varies, and if the cracking does not progress slowly, the substrate will break even in the chip. In addition, in the case where stress is applied locally and sequentially to the portion to be cut of the substrate, for example, in the case of collecting a large number of chips from a single substrate, there are many cutting lines. , there is a problem that the productivity is very low.

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

In particular, when the thickness of the substrate is sufficiently thick relative to the width of the modified depth of laser processing, even if an external force is applied, it is not always possible to cleanly cut the substrate vertically due to the influence of the sudden external force. Therefore, it may be necessary to irradiate several laser pulses in multiple steps in the thickness direction of the substrate.

In addition, in the inventions described in Patent Documents 1 and 2, the modified region formed inside the substrate by laser irradiation eventually remains on the cross section of the chip. Therefore, dust may be generated from the modified region of the chip cross section. In addition, as a result of local fracture of the chip cross-section, the fractured cross-section may trigger the chip to break. As a result, there is a problem that the bending strength of the chip is reduced.

The invention described in Patent Document 2 describes that cracks naturally occur in the thickness direction from the modified region. In order to inevitably obtain the stable effect of breaking, it is sometimes necessary to take arbitrary means, and if it breaks naturally, it does not correspond to arbitrary means.

It is also conceivable to generate thermal stress by applying a temperature difference as a relatively small force to cause cracking in the thickness direction from the modified region. In this case, there is a problem of how to give a uniform thermal gradient in the plane of the substrate. That is, even if a thermal gradient is artificially provided, heat is dispersed in the substrate by heat conduction so as to partially alleviate the thermal gradient. Therefore, there is a very difficult problem in how to continuously form a stable thermal gradient (stable temperature difference) sufficient to cut a given substrate.

In addition, in the invention described in Patent Document 2, after the semiconductor substrate is ground, the back surface is chemically etched. is formed, and a work-affected layer remains. When the surface is chemically etched, portions with large lattice distortion such as microcracks are selectively etched. As a result, microcracks are rather encouraged to become large cracks. For this reason, not only the cutting starting point region but also the microcracks formed by grinding and etching may occasionally cause fracture, which poses a problem that stable cutting is difficult.

In addition, the substrate surface is not mirror-finished because the etching promotes unevenness on the substrate surface. As a result, since unevenness remains even in the divided chips, it is highly possible that the chip will be broken from a portion with large unevenness, that is, a microcrack, and the die strength of the chip will be low.

Furthermore, when an etchant is applied to a portion that has been modified by laser processing, the modified portion is once melted, recrystallized, and solidified, so that large grain boundaries are formed.

When the etchant acts on such grain boundaries, the etching progresses so that the silicon grains are peeled off from the grain boundaries.

As for the polishing process, specifically, p.12_1 line of the cited document describes that the grinding process and the back surface are subjected to chemical etching. In the case of chemical etching, even if the crack is left as it is, the chemical etchant penetrates into the crack and has the effect of dissolving the crack.

In particular, when the cracks extend to the surface of the substrate, the etchant permeates between the chip and the film bonding the chips, causing a problem of peeling the chip from the film.

Etching proceeds along the crack even if the crack does not reach the surface of the substrate. In particular, when etching is performed in a thin state after grinding, the etchant permeates into the cracks by capillary action, melting the crack tips and deepening the microcracks, and furthermore, new etchant enters there. Become. In this case, if the etchant acts on the vicinity of the device surface, the vicinity of the device surface may be dissolved, and etching may proceed to the inside of the element. Moreover, even if there is no problem at that time, the etchant left on the wall surface of the wafer may enter the inside of the device and cause defects later. Therefore, while the processing strain on the wafer surface is removed, cracks may be further promoted and secondary problems associated therewith may be induced.

Moreover, in such a case, cracks may eventually extend to the surface, and the etchant may partially enter between the chip and the film, causing the chip to peel off during processing. In particular, when the substrate becomes thinner after grinding, cracks tend to progress even with a small amount of external force, and when the crack reaches the surface, chip separation occurs. You have to do something to prevent it from progressing any further.

Patent Document 2 describes that cracks are generated from the modified region by grinding the back surface of the substrate, but Patent Document 2 does not describe a method for fixing the substrate when the substrate is ground. . In the case where the outer periphery of the substrate is supported by fitting the substrate into a retainer or the like as shown in FIG. 17, or in the case where only a part of the substrate is sucked as shown in FIG. In such a case, even if the rear surface of the substrate is ground, cracks do not occur from the modified region because they are not restrained.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wafer processing apparatus and a wafer processing method capable of efficiently obtaining chips of stable quality.

A wafer processing apparatus for achieving the object of the present invention is a wafer processing apparatus for processing a wafer having a modified region formed therein by a laser beam, wherein the back surface of the wafer is ground with a grinding wheel while the front surface of the wafer is being sucked. and a grinding section that removes the modified region while leaving microcracks extending from the modified region, and a polishing section that polishes the back surface of the wafer with a polishing cloth after grinding.

According to this apparatus, due to grinding heat generated by grinding, the surface of the wafer undergoing grinding expands due to thermal expansion in the radial direction. However, on the other hand, a wafer vacuum chuck with a large heat capacity tries to prevent the wafer from spreading due to its expansion.

As a result, while the rear surface of the wafer expands due to thermal expansion, the front surface of the wafer being chucked does not expand due to the vacuum chuck and tries to maintain the same state. As a result, the modified region formed inside the wafer acts to further expand the modified region according to the difference in expansion between the front and back surfaces of the wafer, and the crack progresses further. The modified region has large crystal grains and is fragile because there is a part that was once melted and recrystallized by irradiation with the laser beam. When such a modified region appears on the side surface of a chip in the future, dust may be generated from the side surface of the chip, and large crystal grains may be chipped from the side surface of the chip. However, since the microcracks that develop from the modified region are pure crystal planes, even if these planes appear on the chip side in the future, they may generate dust from the chip side or become large crystal grains and chip. There is no such thing as.

In this way, the wafer is scraped and removed by the grinding process, and the modified region is removed by extending the minute holes in the thickness direction of the wafer. Next, in order to make the work-affected layer formed by grinding and the microvoids that have developed stand out, the entire surface of the wafer is subjected to chemical mechanical polishing (details will be described later) to completely remove the work-affected layer. do. As a result, only microvoids remain on the surface, and the remaining area becomes a perfect mirror surface without machining strain.

Thereafter, the unbroken wafer is placed on a wafer breaking mechanism to apply a bending stress to the wafer to break the wafer, and then the expand film is pulled to separate the chips from each other. As a result, the modified region formed by the laser beam can be prevented from remaining on the cross section of the chip. Therefore, it is possible to prevent defects such as cracking of the chip and generation of dust from the cross section of the chip, and to efficiently obtain chips of stable quality.

Moreover, since the back surface of the ground wafer is chemically and mechanically polished before the wafer is divided, the die strength of the chips can be increased. Here, the chemical mechanical polishing is largely distinguished from the etching process in the polishing process described in Cited Document 2.

First, the chemical solution in the present application is different from the etching solution in Cited Document 2. The etchant in Cited Document 2 has the effect of naturally dissolving the substrate, that is, etching the substrate by the action of the liquid on the surface of the substrate. As a result, the etchant permeates even the cracked portion and naturally etches the surroundings, which has the effect of further enlarging the modified layer formed by the laser. Further, in the case of the conventional etchant, as described above, the etchant penetrates too much into the cracks, propagating the cracks, and finally penetrates into the portion between the chip and the film. As a result, the etchant flows to the chip surface, and the chip surface is corroded by the etchant, and each chip device may not function.

On the other hand, the polishing agent (slurry) used in the chemical mechanical polishing of the present application has no etching action under static conditions. That is, even if only the abrasive is supplied to the wafer, the etching does not proceed at all, and the wafer surface is merely modified. Therefore, even if the abrasive gets into the cracks on the planned cutting line of the wafer, it does not melt the surrounding silicon, so the cracks do not progress any further.

As a result, cracks may grow in the polishing process, that is, the etching process in Cited Document 2, but in the polishing process of the present application, the wafer is not etched at all even if the abrasive is left to stand, so cracks hardly grow. . As a result, the polishing agent permeates and the chip is arbitrarily peeled off from the film, and the polishing agent flows around the chip surface and erodes the chip, causing the chip device to stop functioning. There is no

Here, the mechanism of chemical mechanical polishing is as follows. That is, in polishing, an abrasive is first supplied to the wafer, which only chemically modifies the wafer surface. Next, since the modified surface is softer, the abrasive grains contained in the slurry act on the wafer surface in this state, and even with a very small stress, the wafer surface can be removed efficiently. be.

For example, for processes that remove silicon, silica-based slurries are used. When using a silica-based slurry, the following reactions occur on the wafer surface.

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

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

At this time, the silica sol and silica particles that permeate the cracks do not have the effect of further propagating the cracks. This is because the polishing pad does not enter into the cracks, so that no mechanical action works and, as a result, no chemical removal action occurs.

As a result, the work-affected layer on the substrate surface generated during grinding is supplied with a chemical slurry containing silica sol and silica particles, and the polishing pad comes into contact with the substrate to create a mechanical friction effect. Together with this, only the substrate surface is chemically and mechanically polished and removed (Edited by Toshiro Doi: Detailed explanation of semiconductor CMP technology (Kogyo Chosakai) (2001) pp.40-42).

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

In the case of chemical etching, as described above, lattice strain and crystal defect portions in crystals such as silicon are selectively etched. As a result, etch pits may be formed and large hollows may occur along the grain boundaries, which cannot be avoided in principle.

On the other hand, in the case of chemical-mechanical polishing, as mentioned above, the chemical removing action does not work unless the mechanical action works. The mechanical action, which here is the rubbing of the wafer surface by the polishing pad, has nothing to do with the crystalline state of the substrate surface and occurs with equal probability on all substrate surfaces. . Therefore, all surfaces are uniformly removed regardless of the crystal state, and chemical action works, so that the surface becomes a uniform surface with no crystal defects and a mirror surface. Here, the term "mirror surface" is ambiguous from a relative point of view, so in the present application, it is defined as a mirror surface obtained by chemical mechanical polishing.

By performing such chemical mechanical polishing, it is possible to obtain an ideal mirror surface state, which is greatly different from that in Cited Document 2, and to prevent erosion due to penetration of the etchant between the chip and the film.

It should be noted that the chips are not yet completely cracked after chemical mechanical polishing. Only microvoids developed from the modified layer remain on the surface part after chemical mechanical polishing. Note that the modified layer has already been removed by the previous grinding process.

If the state in which the microvoids developed from the modified layer are left, for example, in the surface state after grinding and etching as shown in Cited Document 2, the microvoids developed from the modified layer and It is no longer possible to clearly distinguish from the unevenness promoted by the etching treatment after grinding. Therefore, when breaking the chip, the chip is not necessarily broken from the microvoids, but depending on the case, it is conceivable that the chip may be broken from the irregularities formed by further enhancing the grinding streaks by etching.

When chemical mechanical polishing is applied to the surface as in the present application, there is almost no unevenness on the surface of the wafer after processing, and only microvoids developed from the modified layer remain. Therefore, when the cutting treatment is performed in this state, the cracks are further propagated from the microvoids, resulting in the cutting.

Further, 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 a laser beam, wherein the back surface of the wafer is ground with a whetstone while the front surface of the wafer is being sucked. and removing the modified region leaving microcracks extending from the modified region, and a polishing step of polishing the back surface of the wafer with an abrasive cloth after grinding.

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

1 is a diagram showing an overview configuration of a laser dicing apparatus 1; FIG. 2 is a conceptual configuration diagram showing the configuration of driving means of the laser dicing apparatus 1. FIG. 2 is a plan view showing the configuration of driving means of the laser dicing apparatus 1; FIG. FIG. 2 is a diagram showing an overview configuration of a grinding device 2; FIG. 2 is a partially enlarged view of the grinding device 2; FIG. 2 is a partially enlarged view of the grinding device 2; 4 is a schematic diagram of a polishing stage of the grinding device 2; FIG. It is a figure which shows the detail of the chuck|zipper of the grinding device 2, (a) is a top view, (b) is sectional drawing, (c) is the elements on larger scale. 4 is a flow chart showing the flow of processing of a method for cutting a semiconductor substrate. The figure explaining a laser modification process. The figure explaining a cutting line. The figure explaining a grinding removal process. It is a diagram for explaining the crack growth in the grinding removal process, (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 the state of the wafer W. Cross section. FIG. 4 is a diagram for explaining the surface state of the back surface of the wafer W after the grinding removal process; Diagram explaining the division/separation process Diagram explaining the division/separation process Diagram showing a fixed state during conventional substrate grinding Diagram showing a fixed state during conventional substrate grinding Figure showing conditions for crack growth evaluation Figure showing evaluation results of crack growth evaluation Schematic diagram of the splitting device 300 Explanatory drawing showing another embodiment of the chuck bending means

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

The present invention comprises a laser dicing device 1, a grinding device 2, a transfer device (not shown) for transferring a wafer processed by the laser dicing device 1 to a grinding device 2, and a wafer ground by the grinding device 2 into a chip. It is performed by a cutting device composed of a dividing device that divides into two.

<About device configuration>
(1) About laser dicing apparatus 1 FIG. As shown in the figure, the laser dicing apparatus 1 of this embodiment mainly includes a wafer moving section 11, a laser head 40 comprising a laser optical section 20 and an observation optical section 30, a control section 50, and the like. .

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

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

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

The laser optical unit 20 is composed of a laser oscillator 21, a collimating lens 22, a half mirror 23, a condensing lens (condensing lens) 24, driving means 25 for finely moving the laser light parallel to the wafer W, and the like. A laser beam oscillated from a laser oscillator 21 is condensed inside the wafer W through an optical system such as a collimating lens 22, a half mirror 23, a condensing lens 24, and the like. The position of the focal point in the Z direction is adjusted by finely moving the condenser lens 24 in the Z direction by means of Z fine movement means 27, which will be described later.

The conditions of the laser beam are as follows: the light source is a semiconductor laser-excited Nd:YAG laser, the wavelength is 1064 nm, the laser beam spot cross-sectional area is 3.14×10 ⁻⁸ cm ² , the oscillation mode is Q-switch pulse, the repetition frequency is 100 kHz, The pulse width is 30 ns, the output is 20 μJ/pulse, the laser light quality is TEM00, and the polarization property is linear polarization. Further, the conditions for the condensed lens 24 are a magnification of 50 times, N.O. A. is 0.55, and the transmittance for the laser light wavelength is 60 percent.

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

In the observation optical unit 30 , the illumination light emitted from the observation light source 31 irradiates the surface of the wafer W through an optical system such as a collimate lens 32 , a half mirror 33 and a condensed lens 24 . Reflected light from the surface of the wafer W passes through the condensed lens 24, the half mirrors 23 and 33, and the condensed lens 34 and enters a CCD camera 35 as an observation means, and an image of the surface of the wafer W is captured.

This imaging data is input to the image processing unit 38 , used for alignment of the wafer W, and displayed on the television monitor 36 via the control unit 50 .

The control unit 50 includes a CPU, a memory, an input/output circuit unit, etc., and controls the operation of each unit of the laser dicing apparatus 1 .

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

The wafer cassette elevator vertically moves the cassette in which the wafers are stored and positions it at the transfer position. The carrier means carries the wafer between the cassette and the suction stage 13 .

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

FIG. 2 is a conceptual diagram illustrating the details of the driving means 25. As shown in FIG. The drive means 25 includes a lens frame 26 that holds the condensed lens 24, a Z fine movement means 27 that is attached to the upper surface of the lens frame 26 and finely moves the lens frame 26 in the Z direction of the drawing, and a holding frame 28 that holds the Z fine movement means 27. , PZ1, PZ2, etc., which are linear fine movement means for finely moving the holding frame 28 in parallel with the wafer W. As shown in FIG.

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 the piezoelectric element slightly moves the condenser lens 24 in the Z direction, so that the focal point of the laser beam is precisely positioned in the Z direction.

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

The linear fine movement means PZ1 and PZ2 use a piezoelectric element like the Z fine movement means 27, one end of which is fixed to the case body of the laser head 40 and the other end of which is in contact with the side surface of the holding frame 28.

3 is a plan view of the driving means 25. FIG. As shown in FIG. 3, two linear fine movement means PZ1 and PZ2 are arranged in the X direction, one end of which is fixed to the case body of the laser head 40, and the other end is in contact with the side surface of the holding frame 28. . Therefore, by controlling the applied voltage, the condensing lens 24 can be reciprocally finely fed in the X direction, and the laser beam can be reciprocally finely fed in the X direction or oscillated.

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

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

In this state, the XYZ.theta. It is vibrated in parallel in the X direction or arbitrary XY directions, and the focal point of the laser beam L forms a modified region P while vibrating minutely inside the wafer. As a result, one line of the modified region P by multiphoton absorption is formed inside the wafer W along the cutting line of the wafer W. As shown in FIG.

Vibration in the Z direction may be applied by the Z fine movement means 27 as required. In addition, by feeding the wafer W in the X direction while slowly reciprocating the laser light L in the X direction, which is the processing direction, the laser light L is repeatedly irradiated in a back-and-forth state like perforations. good too.

When one line of the modified region is formed along the cutting line, the XYZθ table 12 is indexed and fed by one pitch in the Y direction, and the next line is similarly formed with the modified region.

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

(2) Grinding Device 2 FIG. 4 is a perspective view showing the general configuration of the grinding device 2 . The main body 112 of the grinding device 2 is provided with an alignment stage 116 , a rough grinding stage 118 , a fine grinding stage 120 , a polishing stage 122 , a polishing cloth cleaning stage 123 , a polishing cloth dressing stage 127 and a wafer cleaning stage 124 .

Rough grinding stage 118, fine grinding stage 120, and polishing stage 122 are partitioned by a partition plate 125 (not shown in FIG. 4) as shown in FIG. It is prevented from scattering on the stage.

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

The rough grinding stage 118 is a stage that performs rough grinding, and as shown in FIG. The fine grinding stage 120 is a stage that performs fine grinding, and is surrounded by the side surface of the main body 112 , the top plate 129 and the partition plate 125 like the rough grinding stage 118 . Brushes (not shown) are provided on the top and side surfaces of the partition plate 125 to isolate the rough grinding stage 118 and fine grinding stage 120 from the outside. Through holes 128A and 129A through which the heads of the respective stages are inserted are formed in the top plates 128 and 129, respectively.

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

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

Since the polishing stage 122 performs chemical mechanical polishing, the polishing liquid contains a chemical polishing agent. If the grinding liquid is mixed with such a polishing liquid, the concentration of the chemical polishing agent is lowered, resulting in an increase in processing time. By keeping the polishing stage 122 in a substantially airtight state, it is possible to prevent the grinding fluid and processing debris used in the fine grinding stage 120 from entering the polishing stage 122, and also prevent the grinding fluid used in the polishing stage 122 from entering the polishing stage 122. can be prevented from scattering from the polishing stage 122 . Therefore, it is possible to prevent machining problems caused by mixing of both machining liquids.

FIG. 7 is a structural diagram of the polishing stage 122. As shown in FIG. In the polishing stage 122, the wafer W is polished with a polishing cloth 516 and a slurry supplied from the polishing cloth 156, and a process-affected layer formed on the rear surface of the wafer W is removed by rough polishing and fine polishing. The work-affected layer is a general term for streaks and work strain (crystal is altered) caused by grinding.

A 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 linear motion guides are provided on the side surface of the motor 158, and the guide blocks 162, 162 are engaged with guide rails 166 provided on the side surface of the support plate 164 so as to be vertically movable. It is Therefore, the polishing cloth 156 is attached to the support plate 164 together with the motor 158 so as to be vertically movable.

A support plate 164 is provided at the tip of an arm 168 arranged horizontally. A base end of the arm 168 is connected to an output shaft 174 of a motor 172 arranged within the casing 170 . Therefore, when the motor 172 is driven, the arm 168 can rotate about the output shaft 174 . As a result, the range of the polishing position of the polishing cloth 56 (see the solid line in FIG. 3), the cleaning position of the polishing cloth by the polishing cloth cleaning stage 123 (see the two-dot chain line in FIG. 3), and the dressing position of the polishing cloth dressing stage 127 is determined. can be moved inside. When the polishing cloth 156 is moved to the polishing cloth washing position, the surface of the polishing cloth 156 is washed by the polishing cloth washing stage 123 to remove polishing dust and the like adhering to the surface. Examples of the polishing cloth 156 include foamed polyurethane, polishing cloth, etc. The polishing cloth cleaning stage 123 is provided with a removing member such as a brush for removing polishing debris. This removal member is rotationally driven when cleaning the polishing cloth 156 , and the polishing cloth 156 is similarly rotationally driven by the motor 158 . The polishing cloth dressing stage 127 employs the same material as the polishing cloth 156, such as polyurethane foam.

Guide blocks 176, 176 constituting linear motion guides are provided on the side surface of the casing 170. These guide blocks 176, 176 are vertically movable on a guide rail 180 provided on the side surface of a housing 178 for the screw feeder. is engaged in Also, a nut member 179 protrudes from the side surface of the casing 170 . The nut member 179 is screwed through an opening (not shown) formed in the housing 178 to a threaded rod 181 of a screw feeder provided 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 82 is driven and the threaded rod 181 is rotated, the casing 70 is moved up and down by the feeding action of the screw feeder and the rectilinear action of the guide block 176 and the guide rail 180 . As a result, the polishing cloth 156 is largely moved in the vertical direction, and the gap between the polishing head 161 and the wafer W is set to a predetermined gap.

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

In the present embodiment, the polishing cloth 156 is used as the polishing body, but the present invention is not limited to this, and as long as the work-affected layer can be removed, for example, a polishing grindstone or electrophoresis of abrasive grains can be used. may apply. When a polishing grindstone, electrophoresis of abrasive grains, or the like is applied, it is preferable to perform quantitative polishing.

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

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

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

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

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

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. A suction hole 132c for vacuum suction is formed on the lower side of the chuck body 132b into which the mounting table 132a is fitted. The chuck 132 is desirably made of a material with low thermal conductivity.

The wafer W is mounted on the mounting table 132a with the BG tape B interposed therebetween, as shown in FIG. 8(c). As shown in FIG. 8C, the mounting table 132a is formed such that when the wafer W is mounted on the mounting table 132a, part of the outer periphery of the wafer W protrudes from the mounting table 132a. is about 1.5 mm. The wafer W used in this embodiment has a diameter of approximately 12 inches and a thickness t of approximately 775 μm.

As shown in FIGS. 2A and 2B, the suction holes 132c are arranged so as to cover substantially the entire mounting table 132a. A fluid coupling (not shown) is connected to the suction hole 132c, and a suction pump (not shown) connected to this 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. As a result, the wafer W and the mounting table 132a can be brought into close contact with each other without any positional deviation.

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

A piston 119 of the cylinder device 117 is connected to the lower portion of the motor 192 . When the piston 119 is extended, it is inserted into recesses (not shown) formed in the lower portions of the chucks 132, 136, 138, and 140 to be connected. Then, the chucks 132 , 136 , 138 , 140 are lifted from the index table 134 by the continued extension of the piston 119 and positioned at grinding positions by the cup-shaped grindstones 146 , 154 .

The control unit 100 includes a CPU, a memory, an input/output circuit unit, etc., and controls the operation of each unit of the grinding apparatus 2 .

The thickness of the wafer W sucked and held by the chuck 132 is measured by a pair of measurement gauges (not shown) connected to the controller 100 . Each of these measurement gauges has a contact, one of which is in contact with the upper surface (back surface) of the wafer W, and the other contact with the upper surface of the chuck 132 . These measurement gauges can detect the thickness of the wafer W as a difference in in-process gauge readings with the upper surface of the chuck 132 as a reference point. In addition, the thickness measurement by the measuring gauge may be performed in-line. Also, the method of measuring the thickness of the wafer W is not limited to this.

The index table 134 is rotated 90 degrees in the direction of arrow R in FIG. The back surface of W is rough ground. As shown in FIG. 4, the cup-shaped grindstone 146 is connected to an output shaft (not shown) of a motor 148 and attached to a grindstone feeder 152 via a casing 150 for supporting the motor 148 . The grindstone feeder 152 vertically moves the cup-shaped grindstone 146 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. Thereby, the back surface of the wafer W is 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, that is, the amount of grinding by the cup-shaped grindstone 146 is set based on the pre-registered reference position of the cup-shaped grindstone 146 and the thickness of the wafer W detected by the measurement gauge. be done. The control unit 100 also controls the rotation speed of the cup-shaped grindstone 146 by controlling the rotation speed of the motor 148 .

After the cup-shaped grindstone 146 is retracted from the wafer W, the thickness of the wafer W whose back surface has been roughly ground on the rough grinding stage 118 is measured by a measurement gauge (not shown) connected to the controller 100 . The control unit 100 rotates the index table 134 by 90 degrees in the direction of arrow R in FIG. Grinded and sparked out. Since the structure of the fine grinding stage 120 is the same as that of the rough grinding stage 118, the description thereof is omitted here. The amount of grinding by the cup-shaped grindstone 154 is set by the controller 100 , and the processing movement amount and the number of revolutions of the cup-shaped grindstone 154 are controlled by the controller 100 .

After the cup-shaped grindstone 154 is retracted from the wafer W, the thickness of the wafer W whose back surface has been finely ground by the fine grinding stage 120 is measured by a measurement 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. Then, the back surface of the wafer W is mirror-finished. The vertical movement distance of the abrasive cloth 156 is set by the controller 100, and the position of the abrasive cloth 156 is controlled by controlling the motor 182 by the controller 100. FIG. Further, the control unit 100 controls the rotation speed of the motor 158 , that is, the rotation speed of the polishing pad 156 .

The wafer W polished on the polishing stage 122 is transferred to the hand (not shown) of the robot (not shown) 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. , and transferred to the wafer cleaning stage 124 . A stage having a rinse cleaning function and a spin drying function is applied as the wafer cleaning stage 124 . The polished wafer W is free of the process-affected layer, so that it is not easily damaged during transportation by the robot and during cleaning on the wafer cleaning stage 124 .

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

(3) Splitting Device Next, a splitting device (not shown) will be described. The dividing device can be a conventional normal dividing device. For example, it is possible to use a splitting device having the following configuration, which is disclosed in Table No. 2004-100240.

That is, the peripheral portion of the dicing tape is fixed to a frame-like frame. A ring member is in contact with the lower surface of the inner portion of the dicing tape peripheral portion. The outer periphery of the upper surface of this ring member is smoothly rounded. A UV light source (UV light irradiation means) is arranged below the dicing tape.

While irradiating the dicing tape with UV light from the UV light source, the frame is pushed downward. By irradiation with UV light, the adhesive of the dicing tape can be cured and the adhesive force of the tape can be changed.

At the same time, a downward force is applied to the frame, pushing it downward. As a result, the dicing tape is expanded to increase the distance between chips. At this time, the dicing tape S is expanded smoothly because the outer periphery of the upper surface of the ring member is smoothly rounded.

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

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

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

(4) Other Embodiments of Dividing Apparatus FIG. 21, (A) is a plan view of the dividing device 300, and (B) is a side view of the dividing device 300. FIG. The dividing device 300 mainly includes a wafer chuck 304 for holding a wafer 302 by suction, bending means 306 for bending the wafer chuck 304 , and a vacuum pump 308 .

The wafer chuck 304 mainly includes an independent suction chuck 310 having independent suction holes and a communication groove chuck 312 having spiral grooves communicating with the independent suction holes. 312 are superimposed.

The thickness of the communicating groove chuck 312 and the independent suction chuck 310 is about 1 mm each, and the thickness becomes about 2 mm when the two are overlapped. It is preferable that each member is made of a resin material such as acrylic. However, the material is not limited to the resin material, and other materials such as ceramics may be used, and any material may be selected as long as the wafer chuck can be deflected after the wafer is vacuum-sucked. Moreover, the material of the wafer chuck 304 itself does not necessarily need to be bent, and any configuration or structure that allows the wafer chuck 304 as a whole to bend is sufficient.

The bending means 306 is a rod-shaped body with a rounded end, and can bend the wafer chuck 304 in a hemispherical shape by pushing up the central portion of the back surface of the wafer chuck 304 from below.

The wafer 302 is placed on a wafer chuck 304 while being attached to an expand film 314 whose outer circumference is fixed by a frame made of metal, for example, and is vacuum-sucked. The expand film 314 preferably has air permeability to some extent, and the air permeability allows the wafer 302 itself to be directly sucked to the wafer chuck 304 by vacuum force.

The wafer chuck 304 is deflected in a hemispherical shape by the deflecting means while holding the wafer 302 . Thereby, the wafer 302 is divided along the cutting lines.

Next, another embodiment of chuck deflection means will be described with reference to FIG. FIG. 22 is an explanatory diagram showing another embodiment of the chuck bending means. 21 except for the chuck bending means 320, the description thereof is omitted.

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

Considering the X-axis and Y-axis that are perpendicular to each other within the wafer surface, the dividing lines formed on the wafer 302 are often in the X-axis direction and the Y-axis direction. Therefore, the wafer 302 is divided as follows. That is, the chuck deflecting means 320 is positioned so that one side of the chuck deflecting means 320 is parallel to the X-axis. Next, the wafer 302 is placed on the alignment wafer chuck 304 and vacuum-sucked so that the dividing line is parallel to the X-axis.

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

Here, if the wafer 302 is not vacuum-sucked but is pushed to the chuck bending means 320 through the dicing film, which is an elastic film, and the wafer 302 is bent, if the wafer cracks first at a certain part, the crack Since the wafer bends steeply at the edge portion, and the curvature of the chuck bending means 320 is absorbed there, the wafer may not bend partially and may follow the chuck bending means 320 without being divided.

Therefore, the wafer 302 is first vacuum-sucked by the wafer chuck 304 , and after the wafer 302 is flattened by the wafer chuck 304 , the wafer chuck 304 is bent. Since the wafer 302 follows while being sucked, a constant bending stress is uniformly applied to the surface of the wafer 302, so that the wafer 302 can be divided without leaving any division residue.

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

(1) Laser modification step (step S10)
A wafer W having a BG tape B attached to its surface is placed on the suction stage 13 of the laser dicing apparatus 1 so that the back surface faces upward. The following processing is performed by the laser dicing apparatus 1 and controlled by the controller 50 .

When the laser beam L is emitted from the laser oscillator 21, the laser beam L is irradiated inside the wafer W via an optical system such as a collimator lens 22, a half mirror 23, a condensing lens 24, etc., and is reflected inside the wafer W. A quality region P is formed.

In the present embodiment, since the thickness of the finally produced chip is approximately 50 μm, the laser beam is applied to a depth of approximately 60 μm to approximately 80 μm from the surface of the wafer W, as shown in FIG. In order to efficiently break the front surface (device surface) of the wafer W, a laser-modified region is formed at a relatively deep position close to the reference surface, which is a surface located on the back surface side by the thickness of the chip T from the front surface of the wafer W. This is because it is necessary to form

The controller 50 scans the surface of the wafer W with a pulsed processing laser beam L in parallel to form a plurality of discontinuous modified regions P, P, . . . Inside the modified region P, minute holes (hereinafter referred to as cracks) K are formed. A region formed by arranging a plurality of discontinuous modified regions P, P, . . . is hereinafter referred to as a modified layer.

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

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

The transferred wafer W is placed on a chuck 132 (eg, chucks 136, 148, and 140 are also acceptable) with the rear surface of the wafer W facing upward, that is, with the BG tape B attached to the front surface of the wafer W facing downward. The entire surface is vacuum-sucked to the chuck 132 .

The index table 134 is rotated around the rotary shaft 135 to load the chuck 132 onto the rough grinding stage 118, and the wafer W is roughly ground.

Rough grinding is performed by rotating the cup-shaped grindstone 146 while rotating the chuck 132 . In this embodiment, Vitrified #325 manufactured by Tokyo Seimitsu Co., Ltd. is used as the cup-shaped grindstone 146, and the rotation speed of the cup-shaped grindstone 146 is approximately 3000 rpm.

After rough grinding, the index table 134 is rotated around the rotary shaft 135 to carry the chuck 132 onto the fine grinding stage 120, and the wafer W is fine ground by rotating the chuck 132 and the cup-shaped grindstone 154. In this embodiment, resin #2000 manufactured by Tokyo Seimitsu Co., Ltd. is used as the cup-shaped grindstone 154, and the rotational speed of the cup-shaped grindstone 154 is approximately 2400 rpm.

In this embodiment, as shown in FIG. 12, rough grinding and fine grinding are combined to perform grinding to the target surface, that is, to a depth of approximately 50 μm from the surface of the wafer W. As shown in FIG. In the present embodiment, roughly 700 μm is ground in rough grinding, and approximately 30 to 40 μm is ground in fine grinding. You may determine the amount of grinding so that it may become.

Therefore, as shown in FIG. 12, the modified layer is removed in the grinding process, and the modified region P by the laser beam does not remain in the cross section of the chip T as the final product. Therefore, it is possible to prevent the modified layer from being crushed from the cross section of the chip, the chip T from being broken from the crushed portion, and dust from the crushed portion.

Further, in the present embodiment, the grinding removal step includes a crack propagation step for propagating cracks in the modified layer in the thickness direction of the wafer W. As shown in FIG. 13A and 13B are diagrams illustrating the mechanism of crack propagation, in which (a) is a schematic diagram during grinding, (b) is the back surface of the wafer W, (c) is the front surface of the wafer W, and (d) is the surface of the wafer W. 4 is a cross-sectional view of wafer W during grinding; FIG.

Due to the grinding, the ground surface shown in FIG. 13(a), that is, the back surface of the wafer W expands due to grinding heat as shown in FIG. 13(b). On the other hand, as shown in FIG. 13C, the surface opposite to the ground surface, that is, the surface of the wafer W is vacuum-adsorbed by a vacuum chuck over its entire surface, and is laterally moved so as not to cause misalignment due to thermal expansion. is physically constrained against displacement to

That is, as shown in FIG. 13(d), the back surface (grinding surface) of the wafer W tends to expand in the outer peripheral direction due to thermal expansion (displacement due to thermal expansion) in the case of a disk shape, whereas the front surface of the wafer W ( The attraction surface) is constrained so that each point on the wafer surface to be spread is not physically displaced. As a result, strain occurs inside the wafer, and cracks develop in the thickness direction of the wafer W due to this internal strain. This internal strain acts evenly between the portion 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 at the initial stage of grinding, that is, during rough grinding, when the amount of grinding is the largest and the frictional force is large, ie, the frictional heat can be large.

The laser-modified region is formed at a relatively deep position close to the thickness of the chip. Therefore, in the early stages of grinding, the distance from the ground surface to the laser modified layer is relatively long, but the target surface is relatively close to the modified layer to the extent that cracks are propagated. Therefore, in order to promote crack growth, it is preferable to promote the thermal expansion of the wafer W by the grinding heat in the early stages of rough grinding.

Even if grinding is performed under conditions that cause the wafer W to thermally expand, that is, conditions for generating a large amount of frictional heat (for example, using less grinding fluid), the shear stress of grinding will immediately affect the modified layer. Nor will it be done. In the present embodiment, cracks are not propagated by shear stress due to grinding, but thermal expansion due to grinding heat is the dominant factor in crack propagation.

When a crack is propagated by internal strain, the crack can be uniformly propagated at each point in the wafer W surface regardless of the wafer W without being caused by variations in rigidity in the wafer W surface. . Therefore, it is possible to prevent stress from concentrating on a portion with weak rigidity due to the presence of defects in the surface of the wafer W, as in the case of applying an artificial stress.

In addition, when an external force is applied artificially, the stress is concentrated on the weak portion of the material, so it is difficult to control the crack to grow uniformly and gently, and the wafer is completely cleaved. On the other hand, in the case of propagation of cracks due to internal strain in the present embodiment, the cracks can be subtly propagated because the internal strain is caused by the degree of thermal expansion. That is, the crack can grow between the target surface and the wafer W surface. Therefore, it is possible to efficiently divide in the dividing/separating step (step S18) to be described later.

Internal strain due to thermal expansion of the wafer W is distinguished from so-called thermal stress caused by temperature differences. Thermal stress is generated 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 is generated.

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

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

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

Due to the grinding and removing step (step S12), the rear surface of the wafer W is formed with a large number of irregularities as shown in FIG. When polishing is performed by chemical etching, since the surface shape is maintained as it is, there is a risk that cracks may occur from the concave portions, and the surface cannot be mirror-finished. On the other hand, in the present embodiment, since chemical mechanical polishing is performed, processing distortion caused by processing is removed, and irregularities on the surface are removed to make the surface mirror-finished.

In other words, in order to improve the quality of the chip T, which is the final product, two processes are indispensable: a grinding removal process using a grindstone and a chemical mechanical polishing process using free abrasive grains containing a chemical liquid using a polishing cloth. .

(4) Expanding tape attaching step (step S16)
An expanding tape F is attached to the back surface of the wafer W that has undergone the chemical mechanical polishing step (step S14). An expandable tape is a type of elastic tape and is stretchable.

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

(5) Division/Separation Step (Step S18)
The wafer W having the expanding tape F attached to the rear surface thereof in the expanding tape application step (step S16) is placed face up on the dividing device as shown in FIG. In the grinding and removing step (step S12), the crack has grown from the target surface to the front surface side, so as shown in FIG. there is

Thereafter, as shown in FIG. 16, when the expanding tape F is expanded (expanded), the wafer W is broken based on the developed cracks. That is, the wafer W is broken along the cutting lines and divided into a plurality of chips T. As shown in FIG. After that, when the expand tape F is further expanded, the individual chips T are separated.

In this embodiment, in the grinding removal step (step S12), the cracks are allowed to grow below the target surface, so that the wafer W can be efficiently placed on the chips T simply by pulling the expanding tape F in the dividing/separating step. can be split. Moreover, since the wafer is not completely broken when the crack is propagated, the work efficiency is good.

In addition, in the present embodiment, since the back surface of the wafer W is mirror-finished in the chemical mechanical polishing step (step S14), the expanding tape F and the chip T are not partially peeled off due to misalignment during expansion. There is no

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

In (A), (B), and (C) of FIG. 19, the horizontal axis is common, 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 ON/OFF of water supply to the grindstone during polishing, and (C). indicates the temperature (° C.) of the back surface of the wafer W during grinding.

As shown in FIG. 19A, while changing the grinding speed, rough grinding was performed for a total of 710 μm, fine grinding was performed for 13 μm (not shown), and chemical mechanical polishing (not shown) was performed for 2 μm. During wafer grinding, as shown in FIG. 19B, water supply to the grindstone or wafer was interrupted during rough grinding. After t1 seconds passed after the start of grinding, the water supply was stopped, and after t2 seconds passed after the start of grinding, the water supply was resumed. Water was supplied at a flow rate of 10 L/min. After that, the above steps S16 and S18 were performed to cut the wafer, and the state of cutting was observed and evaluated. The results are summarized in FIG.

As shown in FIG. 19C, the back surface temperature of the wafer W suddenly begins to rise after t1 seconds have elapsed since the water supply was stopped and grinding has started, and has fallen immediately after the lapse of t2 seconds after the water supply has resumed and the grinding has started. began to

As shown in FIG. 20, when the back surface temperature of the wafer W reached 70° C. or higher due to grinding, the wafer was cleaved satisfactorily. This is probably because the cracks formed by the laser propagated due to the heat of grinding.

Therefore, the grinding apparatus according to the present invention comprises means for measuring the temperature of the wafer, means for turning on and off the water supply to the grindstone or wafer during grinding, and the wafer temperature reaching a predetermined value after a predetermined time has elapsed from the start of grinding. means for controlling the water supply to the wafer to be turned off until the As a result, the crack formed by the laser can be propagated, and the wafer can be cleaved satisfactorily.

As described above, according to the present embodiment, cracks in the modified region formed by laser light by grinding can be propagated. You can make sure that no space is left over. Therefore, problems such as cracking of the chip T and generation of dust from the cross section of the chip T can be prevented. Therefore, chips with stable quality can be efficiently obtained.

(Appendix)
As understood from the description of the embodiments detailed above, this specification includes disclosure of various technical ideas including the inventions described below.

(Appendix 1) In the method for cutting a semiconductor substrate according to the first aspect of the present invention, a laser beam is incident from the rear surface of a wafer along a cutting line to form a modified region inside the wafer. A modified region forming step of forming micro-holes in the region, and adsorption for uniformly adsorbing substantially the entire surface of the wafer on which the modified regions are formed in the modified region forming step independently and uniformly on the table. a grinding step of removing the modified region by grinding from the rear surface of the wafer whose surface has been adsorbed to the table in the adsorption step, and extending the microvoids in the thickness direction of the wafer; a step of chemically mechanically polishing the wafer in which the minute voids have been developed in the thickness direction of the wafer in the grinding step; and a dividing step of dividing into a plurality of chips after cutting.

According to the method for cutting a semiconductor substrate according to the first aspect, a laser beam is incident from the rear surface of the wafer along the cutting line to form the modified region inside the wafer, thereby forming microvoids in the modified region. is formed, and the modified region is removed by grinding the wafer from the back surface in a state in which substantially the entire surface of the wafer on which the modified region is formed is independently and uniformly adsorbed on the table.

(Appendix 2) A method for cutting a semiconductor substrate according to the second aspect of the present invention is such that a laser beam is incident from the back surface of a wafer along a cutting line to form a modified region inside the wafer, thereby A modified region forming step of forming microscopic holes in the modified region, and a table that is uniform and independent in each region on substantially the entire surface of the wafer on which the modified region is formed in the modified region forming step. and, while the wafer is adsorbed, the laser beam is incident to grind and remove the portion before the modified region formed inside the wafer, and the microcrack extending from the modified region is removed deep into the substrate. a first grinding step for growing in a vertical direction; a second grinding step for grinding and removing the modified region formed inside the wafer; and chemical mechanical polishing using a chemical slurry and a polishing pad for modifying the wafer surface. removing the work-affected layer introduced in the first and second grinding steps to mirror-finish the surface while leaving microcracks extending from the modified region; and a step of separating the cut chips after the cutting.

According to the method for cutting a semiconductor substrate according to the second aspect, the modified region is formed at a deep position inside the wafer at the initial stage, and the first grinding step initially performs the removing process while generating grinding heat. , it is possible to extend the crack formed in the modified region to a deeper position in the wafer.

However, in the first grinding step, if the laser-modified region is also ground and removed with the same volume as the unmodified region, large crystal grains may be chipped off due to the large crystal grain boundaries in the modified region. In addition, fatal cracks may develop along with such grains. Therefore, in the first grinding step, it is preferable to grind up to the portion before the modified region where the crystallinity is constant.

The second grinding step primarily grinds the laser-modified region. At this time, the grinding wheel also has a high count, that is, a grinding wheel with a finer grain size than in the first grinding process is used, and compared to the first grinding process, fatal cracks and defects derived from the modified region are used. Grind gently so as not to induce The second grinding process is only for the modified region, and the grinding rate is set to be smaller than that of the first grinding process, so that the area is finely ground.

Then, after the laser-modified region is removed, chemical-mechanical polishing is finally performed. In chemical mechanical polishing, a polishing pad such as a polymer or non-woven fabric is pressed against the wafer while supplying a chemical solution that modifies the wafer to chemically and mechanically polish the wafer.

If chemical mechanical polishing is applied to the above-mentioned modified region, large crystal grains may chip off in the modified region. Since chemical mechanical polishing uses a polishing pad such as non-woven fabric or foamed polyurethane, if chipped crystal grains enter the surface of such a pad, the chipped crystal grains will constantly cause scratches during polishing. In such a case, the polished surface is full of scratches without fulfilling the purpose of mirror-finishing while removing the work-affected layer in the grinding process.

For this reason, the modified layer introduced by the laser in the previous second grinding step must be completely removed when introduced into the chemical-mechanical polishing step.

(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 has a thickness of about 60 μm to about 80 μm from the surface of the wafer. and forming the modified region at a depth of about 50 μm from the surface of the wafer and the surface of the wafer in the first grinding step. .

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

(Appendix 4) A method for cutting a semiconductor substrate according to a fourth aspect of the present invention is the method for cutting a semiconductor substrate according to the first aspect, wherein the grinding step is performed until the temperature of the wafer during grinding reaches 70° C. or higher. , interrupting the supply of water to the grindstone during grinding.

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

(Appendix 5) A method for cutting a semiconductor substrate according to a fifth aspect of the present invention is the method for cutting a semiconductor substrate according to the second aspect or the third aspect, wherein the first grinding step reduces the temperature of the wafer during grinding. until the temperature reaches 70° C. or higher, stopping the supply of water to the grindstone during grinding.

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

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

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

(Appendix 7) A semiconductor substrate cutting apparatus according to a seventh aspect of the present invention includes laser dicing means for forming a modified region inside the wafer by applying a laser beam from the rear surface of the wafer along a cutting line, Grinding means for grinding the back surface of the wafer to remove the modified region, transport means for transporting the wafer from the laser dicing means to the grinding means, and dividing means for dividing the wafer along cutting lines. wherein the laser dicing means includes a table on which the wafer surface is placed facing downward, and a laser beam directed toward the wafer to form the modified region. and first control means for controlling the irradiation means so as to change the position where the laser beam is irradiated, wherein the grinding means is mounted with the surface of the wafer facing downward, and the The apparatus is characterized by comprising a suction table for sucking substantially the entire surface of a wafer, a grindstone for grinding the wafer, and second control means for controlling the height and number of revolutions of the grindstone.

As a result, the modified region formed by the laser beam can be prevented from remaining on the cross section of the chip. Therefore, it is possible to prevent defects such as cracking of the chip and generation of dust from the cross section of the chip, and to efficiently obtain chips of stable quality.

(Supplementary Note 8) A semiconductor substrate cutting apparatus according to an eighth aspect of the present invention is the semiconductor substrate cutting apparatus according to the seventh aspect, wherein the first control means has a thickness of approximately 60 μm to approximately 80 μm from the surface of the wafer. and the second control means controls the irradiation means to form the modified region to a depth of about 50 μm from the surface of the wafer and the surface of the wafer to the modified region. It is characterized by controlling the height and rotation speed of the grinding wheel so as to advance the micro-voids inside.

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

(Appendix 9) A semiconductor substrate cutting apparatus according to a ninth aspect of the present invention is the semiconductor substrate cutting apparatus according to the seventh aspect or the eighth aspect described above, wherein means for measuring the temperature of the wafer during grinding; The apparatus further comprises means for turning on and off water supply to the grindstone or wafer, and means for controlling water supply to the wafer to be turned off until the wafer temperature reaches a predetermined value after a predetermined time has elapsed from the start of grinding. Characterized by

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

DESCRIPTION OF SYMBOLS 1... Laser dicing apparatus, 2... Grinding apparatus, W... Workpiece, B... BG tape, F... Expanding tape, 11... Wafer moving part, 13... Adsorption stage, 20... Laser optical part, 30... Observation optical part, 40... Laser head 50 Control unit 118 Rough grinding stage 120 Precise grinding stage 122 Polishing stage 132, 136, 138, 140 Chuck 146, 154 Cup-shaped grindstone 156 Polishing cloth 300 splitter

Claims (2)

A crack propagation device for propagating a crack from a laser-modified region formed inside a wafer,
Crack propagating means for propagating the crack by grinding the back surface of the wafer while water supply is stopped;
Crack growth device. A crack propagation method for propagating a crack from a laser-modified region formed inside a wafer,
A crack growing step of growing the crack by grinding the back surface of the wafer while water supply is stopped;
Crack growth method.

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