JP6300763B2 - Workpiece processing method - Google Patents

Description

  The present invention relates to a workpiece processing method for dividing a plate-like workpiece into a plurality of device chips.

  In an electronic device typified by a mobile phone or a personal computer, a device chip including an electronic circuit (device) is an essential component. In the device chip, for example, the surface of a wafer made of a semiconductor material such as silicon is partitioned by a plurality of scheduled division lines (streets), an electronic circuit is formed in each region, and then the wafer is divided along the planned division lines. Manufactured by.

  One method of dividing a wafer is to focus a transparent laser beam inside the wafer to form a modified region (modified layer) by multiphoton absorption, and use the modified region as a starting point for the division. Stealth dicing (SD: Stealth Dicing) is known (see, for example, Patent Document 1).

  In stealth dicing, since it is not necessary to form grooves in the wafer by cutting or the like, the width of the line to be divided can be reduced to increase the number of device chips. On the other hand, this stealth dicing has a problem that the bending strength of the device chip tends to be lowered due to the remaining modified region.

  In order to solve this problem, after forming a modified region at a depth that does not reach the finished thickness of the device chip from the back side of the wafer, the modified region is removed by grinding the back side of the wafer. However, SDBG (Stealth Dicing Before Grinding) that is divided into device chips has been studied (see, for example, Patent Document 2 and Patent Document 3).

  By the way, when the wafer is ground, grinding distortion occurs on the back surface, which is the surface to be ground, and the bending strength of the device chip is lowered. Therefore, after grinding the wafer, the wafer is polished by a method such as CMP (Chemical Mechanical Polishing) to remove grinding distortion.

JP 2002-192370 A International Publication No. 2003/77295 JP 2006-12902 A

  However, when a wafer ground and divided by the above-mentioned SDBG is polished by CMP, free abrasive grains contained in the polishing liquid enter the gaps between adjacent device chips and adhere to the side surfaces. If the abrasive grains adhere to the side surfaces of the device chip, problems are likely to occur in subsequent processes.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a method of processing a workpiece that prevents adhesion of abrasive grains to a device chip.

  According to the present invention, there is provided a processing method for a workpiece by dividing a plate-like workpiece into a plurality of device chips along a predetermined division line, and a laser beam having a wavelength having transparency to the workpiece. A modified layer forming step of forming a modified layer on the back surface side from a position corresponding to the finished thickness of the device chip, After performing the layer forming step, after grinding the back surface of the workpiece and processing the workpiece to the finished thickness of the device chip, and after performing the modified layer forming step, After performing the dividing step of dividing the work piece into the individual device chips along the division line on which the modified layer is formed, the back surface grinding step, and the dividing step, no abrasive grains are included. Polishing including abrasive grains while supplying polishing liquid to the workpiece And a polishing step of removing grinding distortion on the back surface of the work piece by polishing the back surface of the work piece using a lid. The

In the present invention, it is preferable to further include a gettering layer forming step of forming a gettering layer on the back surface of the workpiece after performing the polishing step. In the present invention, it is preferable that in the polishing step, a part of the grinding strain on the back surface of the workpiece is left to form a gettering layer.

  Further, in the present invention, the hardness (Asker-C) of the polishing pad is 55 degrees to 90 degrees, and the compressibility of the polishing pad is 2% to 15%, and the abrasive contained in the polishing pad The material of the grains is diamond, green carborundum, white alundum, ceria or zirconia, and the grain size of the abrasive grains contained in the polishing pad is preferably 0.01 μm to 10 μm.

  In the present invention, the polishing liquid is preferably an alkaline solution.

  In the workpiece processing method according to the present invention, in the polishing step, the workpiece is polished using a polishing pad containing abrasive grains while supplying a polishing liquid not containing abrasive grains to the workpiece. The abrasive grains do not adhere to the side surfaces of the device chip as in the conventional method using the polishing liquid containing.

It is a perspective view which shows a workpiece etc. typically. It is a perspective view which shows a modified layer formation process typically. FIG. 3A and FIG. 3B are partial cross-sectional side views schematically showing the back grinding step and the dividing step. 4A is a partial cross-sectional side view schematically showing the polishing process, and FIG. 4B is a cross-sectional view schematically showing the workpiece after the polishing process.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The processing method of the workpiece according to this embodiment includes a modified layer forming step (see FIG. 2), a back grinding step (see FIGS. 3A and 3B), and a dividing step (see FIG. 3A). ) And FIG. 3B), a polishing step (see FIG. 4A and FIG. 4B), and a gettering layer forming step.

  In the modified layer forming step, the workpiece is irradiated with a laser beam having a wavelength having transparency, thereby forming a modified layer along the planned division line. In the back surface grinding process, the back surface of the workpiece is ground to process the workpiece to the finished thickness of the device chip. In the dividing step, the workpiece is divided into device chips along the planned dividing line.

  In the polishing step, the back surface of the workpiece is polished using a polishing pad containing abrasive grains while supplying a polishing liquid not containing abrasive grains to the workpiece. Thereby, grinding distortion on the back surface of the workpiece is removed. In the gettering layer forming step, a gettering layer is formed on the back surface of the workpiece. Hereinafter, the processing method of the workpiece which concerns on this embodiment is explained in full detail.

  FIG. 1 is a perspective view schematically showing a workpiece to be processed in the present embodiment. As shown in FIG. 1, the workpiece 11 is a disk-shaped wafer made of a semiconductor material such as silicon, for example, and the surface 11 a side is divided into a central device region and an outer peripheral surplus region surrounding the device region. It is divided. The device region is further divided into a plurality of regions by a plurality of division lines (streets) 13 arranged in a lattice pattern, and devices 15 such as ICs and LSIs are formed in each region.

  In this embodiment, a wafer made of a semiconductor material such as silicon is used as the workpiece 11. However, the material, shape, etc. of the workpiece 11 are not limited. For example, a substrate made of a material such as ceramic, resin, or metal can be used as the workpiece 11. Similarly, there is no restriction on the arrangement of the division lines 13 and the type of the device 15.

  In the workpiece dividing method according to the present embodiment, first, the protective member 21 is attached to the surface 11 a side of the workpiece 11. The protective member 21 is, for example, a pressure-sensitive adhesive tape, a resin substrate, a wafer of the same or different type as the workpiece 11, and the first surface 21 a side, which is made of an adhesive or the like. A layer is provided.

  Therefore, the protection member 21 can be attached to the workpiece 11 by bringing the first surface 21 a side of the protection member 21 into contact with the surface 11 a side of the workpiece 11. By sticking the protective member 21 to the workpiece 11 in this manner, the device 15 can be prevented from being damaged by a load applied during grinding.

  After the protective member 21 is attached to the workpiece 11, a modified layer forming step is performed in which the workpiece 11 is irradiated with a laser beam having a wavelength having transparency to form a modified layer along the planned division line. To do. FIG. 2 is a perspective view schematically showing the modified layer forming step. 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 4 that sucks and holds the workpiece 11. The chuck table 4 is connected to a rotation drive source (not shown) such as a motor, and rotates around a rotation axis substantially parallel to the vertical direction. A table moving mechanism (not shown) is provided below the chuck table 4, and the chuck table 4 is moved in the horizontal direction by the table moving mechanism.

  The upper surface of the chuck table 4 serves as a holding surface that sucks and holds the second surface 21 b side of the protection member 21 attached to the workpiece 11. A negative pressure of a suction source (not shown) acts on the holding surface through a flow path (not shown) formed inside the chuck table 4 to generate a suction force for sucking the protection member 21.

  A laser processing unit 6 is disposed above the chuck table 4. A camera 8 for imaging the workpiece 11 is installed at a position adjacent to the laser processing unit 6. The laser processing unit 6 irradiates the laser beam L pulsed by a laser oscillator (not shown) downward. The laser oscillator is configured to be able to pulse-oscillate a laser beam L having a wavelength that is difficult to be absorbed by the workpiece 11 (wavelength having transparency).

  In the modified layer forming step, first, the second surface 21b of the protective member 21 attached to the workpiece 11 is brought into contact with the holding surface of the chuck table 4 to apply a negative pressure of the suction source. Thereby, the workpiece 11 is sucked and held by the chuck table 4 with the back surface 11b side exposed upward.

  Next, the chuck table 4 holding the workpiece 11 is moved and rotated so that the laser processing unit 6 is aligned with the end of the division line 15 to be processed. Then, while irradiating the laser beam L from the laser processing unit 6 toward the back surface 11 b of the workpiece 11, the chuck table 4 is moved in a direction parallel to the division line 13 to be processed. That is, the laser beam L is irradiated along the division line 13 from the back surface 11 b side of the workpiece 11.

  At this time, the position of the condensing point of the laser beam L is set to the back surface 11b side from the position corresponding to the finished thickness of the device chip inside the workpiece 11. Thereby, the vicinity of the condensing point of the laser beam L can be modified by multiphoton absorption, and the modified layer 17 along the division line 15 to be processed can be formed. That is, the modified layer 17 is formed on the back surface 11b side from the position corresponding to the finished thickness of the device chip. When the modified layer 17 is formed along all the division lines 15, the modified layer forming process ends.

  After the modified layer forming step, a back surface grinding step for grinding the back surface 11b of the workpiece 11 and a dividing step for dividing the workpiece 11 into device chips are performed. FIG. 3A and FIG. 3B are partial cross-sectional side views schematically showing the back grinding step and the dividing step. The back grinding process and the dividing process are performed by, for example, the grinding apparatus 12 illustrated in FIGS. 3A and 3B.

  The grinding device 12 includes a chuck table 14 that sucks and holds the workpiece 11. The chuck table 14 is connected to a rotation drive source (not shown) such as a motor, and rotates around a rotation axis substantially parallel to the vertical direction. A table moving mechanism (not shown) is provided below the chuck table 14, and the chuck table 14 is moved in the horizontal direction by the table moving mechanism.

  The upper surface of the chuck table 14 is a holding surface 14 a that sucks and holds the second surface 21 b side of the protective member 21 attached to the workpiece 11. A negative pressure of a suction source (not shown) acts on the holding surface 14a through a flow path (not shown) formed inside the chuck table 14, and a suction force for sucking the protection member 21 is generated. .

  A grinding unit 16 is disposed above the chuck table 14. The grinding unit 16 includes a spindle housing 18 supported by a grinding unit lifting mechanism (not shown). A spindle 20 is accommodated in the spindle housing 18, and a disc-shaped mount 22 is fixed to the lower end portion of the spindle 20.

  A grinding wheel 24 having substantially the same diameter as the mount 22 is mounted on the lower surface of the mount 22. The grinding wheel 24 includes a wheel base 26 made of a metal material such as stainless steel or aluminum. A plurality of grinding wheels 28 are annularly arranged on the lower surface of the wheel base 26.

  A rotation drive source (not shown) such as a motor is connected to the upper end side (base end side) of the spindle 20. The grinding wheel 24 rotates around a rotation axis substantially parallel to the vertical direction by the rotational force transmitted from the rotational drive source.

  In the back grinding step and the dividing step, first, the second surface 21b of the protection member 21 attached to the workpiece 11 is brought into contact with the holding surface 14a of the chuck table 14 to apply a negative pressure of the suction source. Thereby, the workpiece 11 is sucked and held on the chuck table 14 with the back surface 11b side exposed upward.

  Next, the chuck table 14 is moved below the grinding wheel 24. Then, as shown in FIG. 3A, the spindle table 18 and the grinding wheel 24 are rotated to lower the spindle housing 18 while supplying a grinding fluid such as pure water. The descending amount of the spindle housing 18 is adjusted so that the lower surface of the grinding wheel 28 is pressed against the back surface 11 b of the workpiece 11.

  Thereby, the back surface 11b side of the workpiece 11 can be ground. This grinding is performed, for example, while measuring the thickness of the workpiece 11. In the present embodiment, since the modified layer 17 is formed along the planned division line 13, the workpiece 11 is broken at the starting point of the modified layer 17 by the pressure applied during grinding, and becomes the planned division line. Divided along.

  As shown in FIG. 3 (B), when the workpiece 11 is thinned to the finished thickness and divided into a plurality of device chips 19 along all the planned dividing lines 13, the back grinding step and the dividing step are completed. .

  In this embodiment, since the modified layer 17 is formed on the back surface 11b side from the position corresponding to the finished thickness of the device chip 19, if the workpiece 11 is thinned to the finished thickness of the device chip, the modified layer 17 is formed. Layer 17 is completely removed from workpiece 11. Therefore, the bending strength of the device chip 19 does not decrease due to the remaining modified layer 17.

  After the dividing step, a polishing step for polishing the back surface 11b of the workpiece 11 is performed. FIG. 4A is a partial cross-sectional side view schematically showing the polishing step. The polishing step is performed, for example, by a polishing apparatus 32 shown in FIG. The polishing apparatus 32 includes a chuck table 34 that sucks and holds the workpiece 11.

  The chuck table 34 is connected to a rotation drive source (not shown) such as a motor, and rotates around a rotation axis substantially parallel to the vertical direction. A table moving mechanism (not shown) is provided below the chuck table 34, and the chuck table 34 is moved in the horizontal direction by the table moving mechanism.

  The upper surface of the chuck table 34 is a holding surface 34 a that sucks and holds the second surface 21 b side of the protective member 21 attached to the workpiece 11. A negative pressure of a suction source (not shown) acts on the holding surface 34a through a channel (not shown) formed inside the chuck table 34, and a suction force for sucking the protection member 21 is generated. .

  A polishing unit 36 is disposed above the chuck table 34. The polishing unit 36 includes a spindle housing 38 supported by a polishing unit lifting mechanism (not shown). A spindle 40 is accommodated in the spindle housing 38, and a disc-shaped mount 42 is fixed to the lower end portion of the spindle 40.

  A polishing pad 44 having the same diameter as that of the mount 42 is attached to the lower surface of the mount 42. The polishing pad 44 is composed of, for example, a polishing cloth made of non-woven fabric or foamed urethane, and abrasive grains fixed to the polishing cloth. The thickness of the polishing pad 44 is, for example, 3 mm or more, and grooves having a depth of 2.5 mm or more are formed in a lattice pattern on the entire lower surface (polishing surface) of the polishing pad 44.

The hardness (Asker-C) of the polishing pad 44 is desirably 55 degrees to 90 degrees, and the compression rate of the polishing pad 44 is desirably 2% to 15%. The compression rate is expressed as (t1−) where t1 is the thickness of the polishing pad 44 when a load of 300 g / cm ² is applied, and t2 is the thickness of the polishing pad 44 when a load of 2000 g / cm ² is applied. t2) / t1 × 100. By setting the compression rate of the polishing pad 44 to 2% to 15%, chipping of the edge of the workpiece 11 can be suppressed while maintaining a high polishing rate.

  The material of the abrasive grains is, for example, diamond, green carborundum, white alundum, ceria, zirconia, etc. The grain size of the abrasive grains is, for example, 0.01 μm to 10 μm, preferably 0.1 μm to 2 μm. It is. However, the material of the abrasive grains and the grain size of the abrasive grains can be arbitrarily changed according to the material of the workpiece 11 and the like.

  A rotation drive source (not shown) such as a motor is connected to the upper end side (base end side) of the spindle 40. The polishing pad 44 rotates around a rotation axis substantially parallel to the vertical direction by the rotational force transmitted from the rotational driving source.

  When polishing the back surface 11 b of the workpiece 11, first, the second surface 21 b of the protection member 21 attached to the workpiece 11 is brought into contact with the holding surface 34 a of the chuck table 34, thereby Apply pressure. Thereby, the workpiece 11 is sucked and held on the chuck table 34 with the back surface 11b side exposed upward.

  Next, the chuck table 34 is moved below the polishing pad 44. Then, as shown in FIG. 4A, the chuck table 34 and the polishing pad 44 are rotated to lower the spindle housing 38 while supplying the polishing liquid. The descending amount of the spindle housing 38 is adjusted so that the lower surface (polishing surface) of the polishing pad 44 is pressed against the back surface 11 b of the workpiece 11. As a result, the back surface 11b of the workpiece 11 can be polished to remove grinding distortion.

  As the polishing liquid, for example, an alkaline solution containing no abrasive grains is used. This is because if abrasive grains are included in the polishing liquid, the abrasive grains easily remain in the gaps between adjacent device chips 19. In the present embodiment, since the polishing pad 44 including abrasive grains is used, the workpiece 11 can be appropriately polished without including abrasive grains in the polishing liquid. In addition, as an alkaline solution, potassium hydroxide, sodium hydroxide, tetramethylammonium hydroxide (TMAH), potassium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, etc. can be used.

  FIG. 4B is a cross-sectional view schematically showing the workpiece 11 after the polishing process. In the polishing process of the present embodiment, as described above, the workpiece 11 is polished using a polishing liquid that does not contain abrasive grains, so that the abrasive grains adhere to the side surfaces of the device chip 19 corresponding to the dividing grooves 15. There is no.

  After the polishing step, a gettering layer forming step for forming a gettering layer on the back surface of the workpiece 11 is performed. The gettering layer forming step is performed, for example, by the same method as the polishing step using the polishing apparatus 32 used in the polishing step. However, in this gettering layer forming step, the lower surface (polishing surface) of the polishing pad 44 is brought into contact with the back surface 11b of the workpiece 11 without being pressed against it. That is, no pressure is applied from the polishing pad 44 to the workpiece 11.

  In this way, a gettering layer including a fine strain is formed by slightly rubbing the back surface 11 b of the workpiece 11 with the polishing pad 44. This gettering layer can prevent the device 15 from being contaminated by a metal element or the like. It should be noted that the gettering layer can also be obtained by leaving a slight amount of grinding strain formed in the back grinding process. In this case, it is not necessary to perform the gettering layer forming step after the polishing step.

  As described above, in the workpiece processing method according to the present embodiment, in the polishing step, the workpiece is processed using the polishing pad 44 containing abrasive grains while supplying the polishing liquid not containing abrasive grains to the workpiece 11. Since the object 11 is polished, the abrasive grains do not adhere to the side surfaces of the device chip 19 as in the conventional method using a polishing liquid containing abrasive grains.

  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 back grinding step and the dividing step are performed simultaneously, but the back grinding step and the dividing step may be performed separately.

  Specifically, for example, after performing the dividing step, the back surface grinding step can be performed. In this case, for example, a method of expanding the expanded tape attached to the workpiece 11 or a method of pressing the workpiece 11 along the scheduled division line 13 with a pressing blade can be employed for the dividing step.

  Of course, after performing the back surface grinding step and the dividing step according to the above embodiment, a dividing step for expanding the expanded tape and a dividing step for pressing with a pressing blade may be additionally performed as necessary.

  In addition, the structure, method, and the like according to the above-described embodiment can be appropriately modified and implemented without departing from the scope of the object of the present invention.

11 Workpiece 11a Front surface 11b Back surface 13 Scheduled line (street)
DESCRIPTION OF SYMBOLS 15 Device 17 Modified layer 19 Device chip 21 Protection member 21a 1st surface 21b 2nd surface L Laser beam 2 Laser processing apparatus 4 Chuck table 6 Laser processing unit 8 Camera 12 Grinding device 14 Chuck table 14a Holding surface 16 Grinding unit 18 Spindle housing DESCRIPTION OF SYMBOLS 20 Spindle 22 Mount 24 Grinding wheel 26 Wheel base 28 Grinding wheel 32 Polishing device 34 Chuck table 34a Holding surface 36 Polishing unit 38 Spindle housing 40 Spindle 42 Mount 44 Polishing pad

Claims (5)

A workpiece processing method for dividing a plate-like workpiece into a plurality of device chips along a planned division line,
A laser beam having a wavelength that is transmissive to the workpiece is irradiated from the back side of the workpiece along the planned dividing line, and modified from the position corresponding to the finished thickness of the device chip to the back side. A modified layer forming step of forming a layer;
After performing the modified layer forming step, grinding the back surface of the workpiece to process the workpiece into a finished thickness of the device chip; and
After performing the modified layer forming step, a dividing step of dividing the workpiece into individual device chips along the division line on which the modified layer is formed;
After carrying out the back grinding step and the dividing step, polishing the back surface of the workpiece using a polishing pad containing abrasive grains while supplying a polishing liquid not containing abrasive grains to the workpiece, A polishing step for removing grinding distortion on the back surface of the workpiece;
The processing method of the to-be-processed object characterized by providing.   The method for processing a workpiece according to claim 1, further comprising a gettering layer forming step of forming a gettering layer on the back surface of the workpiece after performing the polishing step. 2. The processing method for a workpiece according to claim 1, wherein in the polishing step, a part of the grinding strain on the back surface of the workpiece is left to form a gettering layer. The polishing pad has a hardness (Asker-C) of 55 degrees to 90 degrees,
The compression rate of the polishing pad is 2% to 15%,
The material of the abrasive grains contained in the polishing pad is diamond, green carborundum, white alundum, ceria or zirconia,
The abrasive grains having a grain size contained in the polishing pad, a processing method of a workpiece according to claims 1 to claim 3, characterized in that the 0.01 to 10 m. The processing method for a workpiece according to any one of claims 1 to 4 , wherein the polishing liquid is an alkaline solution.

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