JP2015201585A - Processing method of wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a processing method of a wafer capable of preventing a corner of a chip from being broken.SOLUTION: The processing method includes: a protection member arranging step of arranging a protection member (21) on a surface (11a) of a wafer (11); a modification layer forming step of forming a modification layer (23) within the wafer by irradiating the wafer with a laser beam (L) of a wavelength having permeability; a holding step of holding the wafer with holding means (14) via the protection member; and a grinding step of grinding the wafer with grinding means including an abrasive grindstone (40), thinning the wafer into predetermined thickness and forming a plurality of divided chips (27) along the modification layer. In the modification layer forming step, a modification layer (23b) along a street (17) is formed and the modification layer (23b) that is rectangular in a planar view is formed in a crossing area of streets, such that cutoff parts (27a) of which the corners are cut off are formed in the plurality of chips.

Description

  The present invention relates to a wafer processing method for dividing a wafer to form a plurality of chips.

  In recent years, in order to realize a small and lightweight device, it is required to thinly process a wafer made of a material such as silicon by grinding. For this grinding, for example, a grinding apparatus including a chuck table for sucking and holding a wafer and a grinding wheel disposed above the chuck table and having a grindstone (grinding grindstone) fixed to the lower surface is used.

  The wafer can be thinned by grinding the wafer by lowering the grinding wheel and pressing the grinding wheel against the work surface of the wafer while rotating the chuck table and the grinding wheel. By the way, when a wafer having reduced rigidity due to this thinning is cut with a cutting blade or the like in order to divide it into a plurality of chips, problems such as chipping (cracking) and cracking (cracking) are likely to occur.

  Therefore, in recent years, a laser beam having a wavelength that is difficult to be absorbed by the wafer (having transparency) is condensed inside the wafer to form a modified region (modified layer) that serves as a starting point of division, and then the wafer is formed. A grinding method has been put to practical use (see, for example, Patent Document 1). In this processing method, an external force applied during grinding is used to divide the wafer into a plurality of chips while thinning the wafer, so that it is not necessary to cut a wafer with reduced rigidity.

International Publication No. 03/077795

  However, in the above-described processing method, since the plurality of chips formed by division are close to each other, the formed chips are in contact with each other during grinding, and in particular, there is a high possibility that the corners of the chip are missing. If the chip corner is chipped, the chip will start from the chipping and the device will be damaged.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a wafer processing method capable of preventing chipping of chips.

  According to the present invention, there is provided a wafer processing method in which a device is formed in each region of a surface partitioned by a plurality of streets, the protective member disposing step of disposing a protective member on the surface of the wafer, A modified layer forming step in which a modified layer is formed inside the wafer by irradiating a laser beam having a wavelength having transparency to the wafer before or after the protective member arranging step, and the protecting member arranging step And the modified layer forming step, the holding step for holding the wafer via the protective member by the holding means, and after the holding step, the wafer is ground by a grinding means including a grinding wheel. And a grinding step of forming a plurality of chips divided along the modified layer, and thinning the wafer to a predetermined thickness. A reformed layer is formed along the street, and a rectangular modified layer is formed in a plan view with apexes positioned on the street, or a circular modified layer is formed in a crossing region of the street in a plan view. Thus, a wafer processing method is provided, in which a plurality of chips formed in the grinding step are formed with cut-off portions with corners cut off.

  In the wafer processing method of the present invention, a modified layer is formed along the street of the wafer, and a modified layer having a rectangular shape in a plan view in which each apex is positioned on the street, or a circular modified layer in a plan view. Are formed in the street intersection region, and then, by dividing the wafer along the modified layer, it is possible to form a plurality of chips having cut-off portions with corners cut off.

  In other words, if a rectangular or circular modified layer for forming the cut-off portion is provided, the corners of the chip are cut off during grinding of the wafer. There is no end to it. Thus, according to the present invention, it is possible to provide a wafer processing method capable of preventing chipping of chip corners.

FIG. 1A is a perspective view schematically showing a configuration example of a wafer, and FIG. 1B is a perspective view schematically showing a protective member disposing step. 2A is a partial cross-sectional side view schematically showing the modified layer forming step, and FIG. 2B is a plan view schematically showing the modified layer formed on the wafer. It is a perspective view which shows a holding step and a grinding step typically. It is a top view which shows typically the shape of the chip | tip formed. FIG. 5A is a plan view schematically showing a modified layer formed on the wafer in the first modification, and FIG. 5B is a modified layer formed on the wafer in the second modification. It is a top view which shows typically. It is a top view which shows typically the shape of the chip | tip formed in the 1st modification.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The wafer processing method according to the present embodiment includes a protective member disposing step (FIG. 1B), a modified layer forming step (FIGS. 2A and 2B), and a holding step (FIG. 3). And a grinding step (FIGS. 3 and 4).

  In the protective member disposing step, a protective member is disposed on the front surface side of the wafer. In the modified layer forming step, a laser beam having a wavelength that is difficult to be absorbed by the wafer (wavelength having transparency) is irradiated to form a modified layer inside the wafer. In this modified layer forming step, a straight modified layer is formed along the street in plan view, and a rectangular modified layer in the plan view is formed in an intersection region (near the intersection) of the street.

  In the holding step, the front side of the wafer is sucked and held by the chuck table (holding means). In the grinding step, the back surface is ground to thin the wafer, and the wafer is divided along the modified layer to form a plurality of chips. Hereinafter, the wafer processing method according to the present embodiment will be described in detail.

  FIG. 1A is a perspective view schematically showing a configuration example of a wafer processed by the wafer processing method according to the present embodiment. As shown in FIG. 1A, the wafer 11 is a disk-shaped semiconductor wafer made of a material such as silicon, for example, and the surface 11a has a central device region 13 and an outer peripheral surplus region 15 surrounding the device region 13. And divided.

  The device region 13 is further divided into a plurality of regions by streets (scheduled cutting lines) 17 arranged in a lattice pattern, and a device 19 such as an IC is formed in each region. The outer periphery 11c of the wafer 11 is chamfered, and the cross-sectional shape is an arc shape.

  In the wafer processing method according to the present embodiment, first, the protective member disposing step of disposing a protective member on the surface 11a side of the wafer 11 is performed. FIG. 1B is a perspective view schematically showing the protective member disposing step. As shown in FIG. 1B, the protection member 21 is formed in a disk shape that is substantially the same shape as the wafer 11. As the protective member 21, for example, a resin substrate, an adhesive tape, a semiconductor wafer, or the like can be used.

  In the protection member disposing step, the wafer 11 and the protection member 21 are overlapped with the front surface 11 a side of the wafer 11 facing the front surface 21 a side of the protection member 21. At this time, an adhesive or the like is interposed between the surface 11 a of the wafer 11 and the surface 21 a of the protective member 21. Thereby, the protection member 21 is fixed to the surface 11a side of the wafer 11 via an adhesive or the like.

  After the protective member disposing step, a modified layer forming step for forming a modified layer inside the wafer 11 is performed. FIG. 2A is a partial cross-sectional side view schematically showing the modified layer forming step, and FIG. 2B is a plan view schematically showing the modified layer formed on the wafer 11. . The modified layer forming step is performed by, for example, the laser processing apparatus 2 shown in FIG.

  The laser processing apparatus 2 includes a chuck table (not shown) that holds the wafer 11 by suction. The chuck table is connected to a rotation mechanism (not shown) such as a motor, and rotates around a rotation shaft extending in the vertical direction. A moving mechanism (not shown) is provided below the chuck table, and the chuck table moves in the horizontal direction by the moving mechanism.

  The upper surface of the chuck table is a holding surface that sucks and holds the front surface 11a side (the back surface 21b side of the protective member 21) of the wafer 11. A negative pressure of a suction source acts on the holding surface through a channel formed inside the chuck table, and a suction force for sucking the wafer 11 is generated. A laser processing head 4 is disposed above the chuck table.

  The laser processing head 4 focuses the laser beam L oscillated by a laser oscillator (not shown) inside the wafer 11 sucked and held by the chuck table. The laser oscillator is configured to be able to oscillate a laser beam L having a wavelength that is difficult to be absorbed by the wafer 11 (wavelength having transparency). For example, when the modified layer is formed on the wafer 11 made of silicon, a YAG or YVO 4 pulse laser oscillator capable of oscillating a laser beam L having a wavelength of 1064 nm may be used as the laser oscillator.

  In the modified layer forming step, first, the front surface 11a side (the back surface 21b side of the protective member 21) of the wafer 11 is brought into contact with the holding surface of the chuck table, and negative pressure of the suction source is applied. Thus, the wafer 11 is sucked and held on the chuck table with the back surface 11b side exposed upward.

  Next, the chuck table is moved and rotated to align the laser processing head 4 with the street 17 to be processed. After alignment, the laser processing head 4 irradiates the laser beam L toward the back surface 11b of the wafer 11, and moves (processes) the chuck table in a first direction parallel to the street 17 to be processed. That is, the wafer 11 and the laser processing head 4 are relatively moved in parallel with respect to the street 17 to be processed.

  Here, the condensing point of the laser beam L is positioned inside the wafer 11 at a position where the distance from the surface 11 a is larger than the finished thickness of the wafer 11. The power of the laser beam L is set high enough to cause a crack (crack) to occur from the vicinity of the condensing point toward the surface 11 a of the wafer 11. As described above, the wavelength of the laser beam L is a wavelength that is difficult to be absorbed by the wafer 11 (a wavelength having transparency). However, the irradiation condition of the laser beam L is not necessarily limited to this.

  When such a laser beam L is condensed inside the wafer 11, the wafer 11 is modified by multiphoton absorption generated in the vicinity of the condensing point. Therefore, by irradiating the laser beam L while relatively moving as described above, a straight modified layer 23a is formed along the street 17 to be processed in a plan view as shown in FIG. 2B. it can. Since the power of the laser beam L is set high, as shown in FIG. 2A, a crack layer 25 is formed between the modified layer 23a and the surface 11a.

  After forming the modified layer 23a along the street 17 to be processed, the irradiation of the laser beam L is stopped, and the chuck table is moved (indexed feed) in the second direction perpendicular to the street 17 to be processed. That is, the wafer 11 and the laser processing head 4 are moved vertically relative to the street 17 to be processed. Thereby, the laser processing head 4 is aligned with the adjacent street 17.

  After the alignment, a similar modified layer 23 a is formed along the adjacent street 17. After repeating this operation and forming the modified layer 23a along all the streets 17 extending in the first direction, the chuck table is rotated 90 ° around the rotation axis extending in the vertical direction to be orthogonal to the first direction. The modified layer 23a is formed along the street 17 extending in the second direction.

  After forming the modified layer 23a along all the streets 17, the irradiation of the laser beam L is stopped, and the laser processing head 4 is positioned above the intersection region (near the intersection) where the streets 17 intersect. That is, the chuck table and the laser processing head 4 are moved relative to each other so that the laser processing head 4 is positioned above a region where the modified layer 23a extending in the first direction and the modified layer 23a extending in the second direction intersect.

  Next, a laser beam L is irradiated while the wafer 11 and the laser processing head 4 are moved relative to each other to form a modified layer 23b that cuts off the corners of a rectangular area defined by the streets 17 (modified layer 23a). Specifically, as shown in FIG. 2B, a rectangular modified layer 23b is formed on the street 17 (modified layer 23a) in a plan view with apexes positioned.

  After the modified layer 23b is formed in the intersection region to be processed, the laser processing head 4 is positioned in another adjacent intersection region, and the similar modified layer 23b is formed. When this operation is repeated and the modified layer 23b is formed in all the intersecting regions, the modified layer forming step ends. In this embodiment, the rectangular modified layer 23b is formed after all the linear modified layers 23a are formed. However, the modified layers 23 (modified layers 23a and 23b) are formed. The order is not particularly limited.

  After the modified layer forming step, a holding step is performed in which the front surface 11a side (back surface 21b side of the protection member 21) of the wafer 11 is sucked and held by the chuck table (holding means) of the grinding apparatus. FIG. 3 is a perspective view schematically showing a holding step and a grinding step performed after the holding step.

  As shown in FIG. 3, the grinding device 12 used in the present embodiment includes a chuck table (holding means) 14 that holds the wafer 11 by suction. The chuck table 14 is connected to a rotation mechanism (not shown) such as a motor, and rotates around a rotation shaft extending in the vertical direction.

  The upper surface of the chuck table 14 is a holding surface that sucks and holds the front surface 11 a side (the back surface 21 b side of the protection member 21) of the wafer 11. A negative pressure of a suction source acts on the holding surface through a flow path formed inside the chuck table 14 to generate a suction force that sucks the wafer 11.

  A grinding mechanism (grinding means) is disposed above the chuck table 14. The grinding mechanism includes a spindle 16 that rotates about a rotation axis extending in the vertical direction. The spindle 16 is lifted and lowered by a lifting mechanism (not shown). A disc-shaped wheel mount 18 is fixed to the lower end side of the spindle 16.

  A grinding wheel 20 having substantially the same diameter as the wheel mount 18 is mounted on the lower surface of the wheel mount 18. The grinding wheel 20 includes a wheel base 22 made of a metal material such as stainless steel. A plurality of grinding wheels 24 are fixed to the annular lower surface of the wheel base 22 over the entire circumference.

  In the holding step, first, the back surface 21b side of the protective member 21 disposed on the wafer 11 is brought into contact with the holding surface of the chuck table 14 to apply a negative pressure of the suction source. As a result, the wafer 11 is sucked and held on the chuck table 14 via the protective member 21. That is, in this state, the back surface 11b side of the wafer 11 is exposed upward.

  After the holding step, the back surface 11b side is ground to thin the wafer 11, and a grinding step for dividing the wafer 11 along the modified layer 23 (modified layers 23a and 23b) is performed. In the grinding step, the spindle 16 is lowered while rotating the chuck table 14 and the spindle 16 in predetermined directions, respectively, and the grinding wheel 24 is brought into contact with the back surface 11b side of the wafer 11 as shown in FIG.

  The spindle 16 is lowered at an arbitrary grinding feed rate suitable for grinding the wafer 11. As described above, the modified layer 23 serving as the starting point of the division is formed inside the wafer 11. Therefore, by lowering the spindle 16 and applying an external force to the wafer 11, the wafer 11 can be divided along the modified layer 23 to form a plurality of chips corresponding to each device 19.

  FIG. 4 is a plan view schematically showing the shape of the chip formed in the grinding step. The wafer 11 is divided along a straight modified layer 23a in plan view and a rectangular modified layer 23b in plan view, and includes a plurality of cut-out portions 27a with corners cut off as shown in FIG. A chip 27 is formed.

  When the wafer 11 (chip 27) is ground to the finished thickness, the grinding step ends. In this embodiment, since the modified layer 23 is formed by positioning the condensing point of the laser beam L at a position where the distance from the surface 11a is larger than the finished thickness of the wafer 11, the finished thickness of the wafer 11 is increased. When the grinding is performed, the modified layer 23 is completely removed. Thereby, the bending strength of the tip 27 can be increased.

  As described above, in the wafer processing method according to the present embodiment, the modified layer 23a is formed along the street 17 of the wafer 11 and the apexes are positioned on the street 17 (modified layer 23a). Since the visually modified rectangular layer 23b is formed in the intersecting region of the street 17 (modified layer 23a), the wafer 11 is ground and divided along the modified layer 23 (modified layers 23a and 23b). Thus, it is possible to form a plurality of chips 27 including cut-out portions 27a with corners cut off.

  That is, if the rectangular modified layer 23b for forming the cut-off portion 27a is provided, the corners of the chip 27 are cut off during grinding of the wafer 11, so that even if the adjacent chips 27 come into contact with each other, the chip 27 The corners of the are never missing. Thus, according to the present embodiment, it is possible to provide a wafer processing method capable of preventing chipping of the corners of the chip 27.

  In addition, this invention is not limited to description of the said embodiment, A various change can be implemented. For example, in the above embodiment, the modified layer 23b having a rectangular shape in plan view is formed in the intersecting region of the streets 17, but the shape of the modified layer formed in the intersecting region is not limited to this. FIG. 5A is a plan view schematically showing a modified layer formed on the wafer 11 in the first modification.

  As shown in FIG. 5A, in the first modification, a straight modified layer 23c is formed along the street 17 in plan view, and a circular modified layer 23d is formed in the street 17 ( It is formed in the intersecting region of the modified layer 23c). FIG. 6 is a plan view schematically showing the shape of the chip 27 formed in the first modification. As shown in FIG. 6, also in the first modification, a plurality of chips 27 including cut-off portions 27b with corners cut off can be formed.

  Further, in the above-described embodiment and the first modification, the modified layers 23a and 23c that are linear in a plan view are also formed in the intersecting region of the street 17, but the present invention is not necessarily limited thereto. FIG. 5B is a plan view schematically showing a modified layer formed on the wafer 11 in the second modification. As shown in FIG. 5B, a straight modified layer 23e is formed in a plan view on a street 17 excluding an intersecting region, and a rectangular (or circular) modified layer 23f is intersected with the street 17 in a plan view. It may be formed in a region.

  In the above embodiment, the modified layer forming step is performed after the protective member disposing step, but the modified layer forming step may be performed before the protective member disposing step. Moreover, in the said embodiment, although the modified layer formation step is implemented on the conditions that the crack layer 25 is formed between the modified layer 23 and the surface 11a, the modified layer is formed on the condition that the crack layer 25 is not formed. A layer forming step may be performed.

  Moreover, in the said embodiment, although the laser beam L is irradiated to the back surface 11b side of the wafer 11 in which the device 19 was formed, you may irradiate the laser beam L to the surface 11a side of the wafer 11. FIG.

  In addition, the configurations, methods, and the like according to the above-described embodiments can be changed as appropriate without departing from the scope of the object of the present invention.

DESCRIPTION OF SYMBOLS 11 Wafer 11a Front surface 11b Back surface 11c Outer periphery 13 Device area | region 15 Outer periphery excess area | region 17 Street (division plan line)
19 Device 21 Protective member 21a Front surface 21b Back surface 23, 23a, 23b, 23c, 23d, 23e, 23f Modified layer 25 Crack layer 27 Chip 27a, 27b Cut-off portion 2 Laser processing device 4 Laser processing head 12 Grinding device 14 Chuck table ( Holding means)
16 Spindle 18 Wheel mount 20 Grinding wheel 22 Wheel base 24 Grinding wheel L Laser beam

Claims (1)

A method of processing a wafer in which devices are formed in each region of a surface partitioned by a plurality of streets,
A protective member disposing step of disposing a protective member on the surface of the wafer;
A modified layer forming step in which a modified layer is formed in the wafer by irradiating a laser beam having a wavelength having transparency to the wafer before or after the protective member disposing step;
A holding step of holding the wafer by a holding means via the protection member after performing the protection member disposing step and the modified layer forming step;
After carrying out the holding step, the wafer is ground by a grinding means including a grinding wheel to thin the wafer to a predetermined thickness and form a plurality of chips divided along the modified layer And comprising
In the modified layer forming step, a modified layer is formed along the street, and a modified layer having a rectangular shape in a plan view in which a vertex is positioned on the street, or a circular modified layer in a plan view. Is formed in a crossing region of the streets, thereby forming a cut-off portion with corners cut off in a plurality of chips formed in the grinding step.

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