JP7519884B2 - Wafer Processing Method - Google Patents

Description

The present invention relates to a wafer processing method.

Conventionally, the most common method for manufacturing semiconductor device chips such as memory and LSI (Large Scale Integration) has been to form devices on the surface of a semiconductor wafer, grind it down to the finishing thickness, and then dice it along the streets (planned division lines) with a cutting blade.

In response to this, a process known as SDBG (Stealth Dicing Before Grinding) has been devised, in which a modified layer is formed inside the wafer using a laser beam, and then the wafer is divided into chips while being ground from the backside (see, for example, Patent Document 1). SDBG processing narrows the streets more than conventional processes, increasing the number of chips that can be obtained from each wafer, and also improving the flexural strength of the chips, which is reduced by chipping caused by dicing.

JP 2004-349623 A

In SDBG processing, if the cracks that start from the modified layer and propagate become meandering, the flexural strength will decrease and the chip shape will change, so it is necessary to form a modified layer of a certain thickness or more with a laser beam of a certain level of power. However, as the power of the laser beam increases, the flexural strength of the chip may decrease, especially in processing methods that leave the modified layer on the side of the chip.

The present invention was made in consideration of these problems, and its purpose is to provide a wafer processing method that can extend the cracks that occur when dividing the wafer using the modified layer as the fracture starting point along the thickness direction of the wafer.

In order to solve the above-mentioned problems and achieve the object, the wafer processing method of the present invention is a method for processing a wafer having a surface on which devices are formed in areas partitioned by planned division lines, and includes a protective tape application step of applying a protective tape to the surface side of the wafer on which the devices are formed, a groove formation step of forming grooves in areas of the exposed surface of the protective tape corresponding to the planned division lines after the protective tape application step is performed, a modified layer formation step of irradiating a laser beam having a wavelength that is transparent to the wafer from the back side of the wafer along the planned division lines to form a modified layer inside the wafer after the groove formation step is performed, and a grinding step of holding the protective tape side of the wafer on a chuck table, grinding the back side of the wafer with a grinding wheel to thin it to a finishing thickness, and dividing the wafer along the planned division lines after the modified layer formation step is performed, and is characterized in that the direction of the cracks extending from the modified layer in the grinding step is guided in the thickness direction of the wafer by the grooves of the protective tape.

In addition, in the wafer processing method of the present invention, in the grinding step, the grinding wheel, which is fed from the back surface of the wafer in the thickness direction of the wafer, may end grinding before it reaches the modified layer.

In addition, in the wafer processing method of the present invention, the groove may be formed by cutting blade or laser processing.

The present invention allows the cracks that occur when the wafer is divided using the modified layer as the fracture starting point to extend along the thickness direction of the wafer.

FIG. 1 is a flowchart showing a flow of a wafer processing method according to an embodiment of the present invention. FIG. 2 is a perspective view showing an example of the protective tape attaching step shown in FIG. FIG. 3 is a perspective view showing the wafer after the protective tape application step. FIG. 4 is a perspective view showing an example of the groove forming step shown in FIG. FIG. 5 is a side view, partly in section, showing one state of the groove forming step. FIG. 6 is a side view, partially in section, showing another example of the groove forming step shown in FIG. 1 . FIG. 7 is a side view, partly in section, showing one state of the modified layer forming step shown in FIG. FIG. 8 is a cross-sectional view showing a main part of the wafer after the modified layer forming step. FIG. 9 is a side view, partially in section, showing an example of the grinding step shown in FIG. 2 . FIG. 10 is a cross-sectional view showing a portion of the wafer after the grinding step.

The following describes in detail the form (embodiment) for carrying out the present invention with reference to the drawings. The present invention is not limited to the contents described in the following embodiment. The components described below include those that a person skilled in the art can easily imagine and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. Various omissions, substitutions, or modifications of the configuration can be made without departing from the spirit of the present invention.

[Embodiment]
A method for processing a wafer 10 according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a flow chart showing the flow of the method for processing a wafer 10 according to the embodiment. The method for processing a wafer 10 includes a protective tape attachment step 1, a groove formation step 2, a modified layer formation step 3, and a grinding step 4.

(Protective tape application step 1)
Fig. 2 is a perspective view showing an example of protective tape application step 1 shown in Fig. 1. Fig. 3 is a perspective view showing the wafer 10 after protective tape application step 1. Protective tape application step 1 is a step of applying a protective tape 20 to the front surface 12 side of the wafer 10 on which the devices 14 are formed.

2, the wafer 10 is a disk-shaped semiconductor wafer, an optical device wafer, or the like, having a substrate 11 made of silicon (Si), sapphire (Al ₂ O ₃ ), gallium arsenide (GaAs), silicon carbide (SiC), or the like. The wafer 10 has a plurality of planned division lines 13 formed on a front surface 12 of the substrate 11, and devices 14 formed in each region partitioned by the plurality of planned division lines 13 intersecting in a lattice pattern. The surface of the wafer 10 opposite the front surface 12 on which the devices 14 are formed is referred to as a back surface 15.

The device 14 is, for example, an integrated circuit such as an IC (Integrated Circuit) or an LSI, a memory, an image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), or a MEMS (Micro Electro Mechanical System). The wafer 10 is divided along the planned division lines 13 to be singulated into individual chips.

In the protective tape application step 1 of the embodiment, the protective tape 20, which is a disk-shaped tape having the same diameter as the wafer 10, is applied to the surface 12 side of the wafer 10 on which the devices 14 are formed. The protective tape 20 protects the devices 14 on the surface 12 side of the wafer 10 held on the chuck tables 31, 41, 51 of the cutting device 30 (see Figures 4 and 5), the laser processing device 40 (see Figures 6 or 7), or the grinding device 50 (see Figure 9), which will be described later, from damage caused by adhesion of foreign matter or contact. The protective tape 20 includes a base layer 21 made of a synthetic resin and an adhesive layer 22 having adhesiveness laminated on at least one of the front and back surfaces of the base layer 21 (see Figures 8 and 10). The protective tape 20 is applied to the surface 12 of the wafer 10 with the surface on the side of the adhesive layer 22 as the application surface.

(Groove formation step 2)
Fig. 4 is a perspective view showing an example of the groove forming step 2 shown in Fig. 1. Fig. 5 is a side view showing, in partial cross section, one state of the groove forming step 2. The groove forming step 2 is performed after the protective tape attaching step 1. The groove forming step 2 is a step of forming grooves 23 in areas corresponding to the planned division lines 13 on the exposed surface of the protective tape 20.

In groove forming step 2 shown in Figures 4 and 5, grooves 23 are formed in the protective tape 20 by cutting using a cutting device 30. The cutting device 30 includes a chuck table 31 having a holding surface 32, a cutting unit 33, a moving unit (not shown) that moves the chuck table 31 and the cutting unit 33 relative to each other, and an imaging unit (not shown).

The cutting unit 33 comprises a disk-shaped cutting blade 34, a spindle 35 that serves as the axis of rotation of the cutting blade 34, and a mount flange 36 that is attached to the spindle 35 and to which the cutting blade 34 is fixed. The cutting blade 34 and spindle 35 have an axis of rotation that is parallel to the holding surface 32 of the chuck table 31 that holds the wafer 10 to be cut. The cutting blade 34 is attached to the tip of the spindle 35.

In groove formation step 2 shown in Figures 4 and 5, first, the back surface 15 side of the wafer 10 is suction-held on the holding surface 32 of the chuck table 31. Next, the cutting unit 33 and the wafer 10 are aligned. Specifically, a moving unit (not shown) moves the chuck table 31 to the processing area below the cutting unit 33, and an imaging unit (not shown) photographs and aligns the wafer 10, thereby aligning the processing point of the cutting blade 34 with the planned dividing line 13 of the wafer 10.

In the groove forming step 2 shown in FIG. 4 and FIG. 5, the supply of cutting water is then started toward the front surface 12 side of the wafer 10. Next, the chuck table 31 and the cutting blade 34 of the cutting unit 33 are moved relatively along the planned division line 13 by a moving unit (not shown), cutting into the protective tape 20 until a predetermined amount of groove 23 is formed in the protective tape 20, thereby forming the groove 23 in the protective tape 20.

In the groove forming step 2, the grooves 23 may be formed in the protective tape 20 by a laser beam 45. FIG. 6 is a side view showing, in partial cross section, another example of the groove forming step 2 shown in FIG. 1.

In the groove forming step 2 shown in FIG. 6, a groove 23 is formed in the protective tape 20 by ablation processing using a laser processing device 40. The laser processing device 40 includes a chuck table 41 having a holding surface 42, a laser beam application unit 43, a moving unit (not shown) that moves the chuck table 41 and the laser beam application unit 43 relative to each other, and an imaging unit (not shown).

In groove formation step 2 shown in FIG. 6, first, the back surface 15 side of the wafer 10 is sucked and held on the holding surface 42 of the chuck table 41. Next, the laser beam application unit 43 and the wafer 10 are aligned. Specifically, a moving unit (not shown) moves the chuck table 41 to the processing position, and an imaging unit (not shown) images and aligns the wafer 10, thereby aligning the irradiation portion 44 of the laser beam application unit 43 with the planned division line 13 of the wafer 10.

In the groove forming step 2 shown in FIG. 6, a laser beam 45 is irradiated from the front surface 12 side of the wafer 10 with a focal point 46 positioned on the protective tape 20 attached to the wafer 10 while the chuck table 41 is moved relative to the laser beam application unit 43. The laser beam 45 is a laser beam with a wavelength that is absorbent for the protective tape 20. In the groove forming step 2, the laser beam 45 with a focal point 46 positioned on or near the surface of the protective tape 20 is irradiated along the planned division line 13 to form a groove 23 in the protective tape 20 along the planned division line 13.

In the groove forming step 2, the groove 23 is formed only in the base layer 21 of the protective tape 20, and is formed so as not to reach the adhesive layer 22 (see Figures 8 and 10). The groove 23 is formed to have a groove width of 50 μm or more, preferably 100 μm or more. It is also desirable that the groove width of the groove 23 is equal to or less than the width of the planned division line 13.

(Modified layer forming step 3)
Fig. 7 is a side view, partially in cross section, showing one state of the modified layer forming step 3 shown in Fig. 1. Fig. 8 is a cross-sectional view showing a main part of the wafer 10 after the modified layer forming step 3. The modified layer forming step 3 is performed after the groove forming step 2. The modified layer forming step 3 is a step in which a laser beam 45 having a wavelength that is transparent to the wafer 10 is irradiated from the back surface 15 side of the wafer 10 along the intended division lines 13 to form a modified layer 16 inside the wafer 10.

The modified layer 16 refers to a region whose density, refractive index, mechanical strength, or other physical properties are different from those of the surrounding area. The modified layer 16 is, for example, a melting process region, a crack region, an insulation breakdown region, a refractive index change region, or a mixture of these regions. The modified layer 16 has a lower mechanical strength, etc. than other parts of the wafer 10.

In the modified layer formation step 3, a modified layer 16 is formed inside the substrate 11 of the wafer 10 by stealth dicing using a laser processing device 40. The laser processing device 40 may be the same device as that used in the groove formation step 2 shown in FIG. 6.

In the modified layer formation step 3, first, the front surface 12 side of the wafer 10 is suction-held on the holding surface 42 of the chuck table 41 via the protective tape 20. Next, the chuck table 41 is moved to the processing position by a moving unit (not shown), and the wafer 10 is imaged and aligned by an imaging unit (not shown) to align the irradiation portion 44 of the laser beam irradiation unit 43 with the planned division line 13 of the wafer 10.

In the modified layer forming step 3, a pulsed laser beam 45 is then irradiated from the back surface 15 side of the wafer 10 with a focal point 46 positioned inside the substrate 11 while the chuck table 41 is moved relative to the laser beam application unit 43. By irradiating the laser beam 45 with the focal point 46 positioned inside the substrate 11 along the planned division line 13, a modified layer 16 is formed inside the substrate 11 along the planned division line 13. That is, as shown in FIG. 8, a modified layer 16 is formed along the groove 23 of the protective tape 20 formed in the groove forming step 2.

(Grinding step 4)
Fig. 9 is a side view, partially in cross section, showing an example of the grinding step 4 shown in Fig. 2. Fig. 10 is a cross-sectional view showing a main part of the wafer 10 after the grinding step 4. The grinding step 4 is performed after the modified layer forming step 3. The grinding step 4 is a step of grinding the back surface 15 of the wafer 10 to thin it to a finishing thickness 17, and dividing the wafer 10 along the planned dividing lines 13.

In grinding step 4, the wafer 10 is ground from the back surface 15 side by a grinding process using a grinding device 50 to thin the wafer 10 to a finishing thickness 17. The grinding device 50 includes a chuck table 51 having a holding surface 52, and a grinding unit 53. The grinding unit 53 includes a spindle 54 which is a rotating shaft member, a wheel base 55 attached to the lower end of the spindle 54, a grinding wheel 56 attached to the underside of the wheel base 55, and a grinding water supply nozzle 57. The wheel base 55 rotates on an axis parallel to the axis of the chuck table 51.

In grinding step 4, first, the front surface 12 side of the wafer 10 is suction-held on the holding surface 52 of the chuck table 51 via the protective tape 20. Next, while the chuck table 51 is rotated about its axis, the wheel base 55 is rotated about its axis. Grinding water 58 is supplied from the grinding water supply nozzle 57, and the grinding wheel 56 attached to the underside of the wheel base 55 is brought closer to the chuck table 51 at a predetermined feed rate, so that the wafer 10 is ground from the back surface 15 side by the grinding wheel 56.

In the grinding step 4, the wafer 10 is ground from the back surface 15 until the wafer 10 has a finishing thickness 17. Grinding stress is applied to the wafer 10 from the wheel base 55 of the grinding unit 53. This grinding stress refers to stress in a direction such as pressing toward the chuck table 51. Since the groove 23 of the protective tape 20 is formed at a position overlapping the planned division line 13 in the thickness direction, the bottom of the groove 23 is pressed toward the chuck table 51 by the above-mentioned grinding stress, and the grinding stress is concentrated on the modified layer 16 inside the wafer 10. Therefore, in the wafer 10, as shown in FIG. 10, the grinding stress causes the crack 18 to extend from the modified layer 16 as a fracture starting point. At this time, the direction of the crack 18 extending from the modified layer 16 is guided in the thickness direction of the wafer 10 by the groove 23 of the protective tape 20. In this way, the wafer 10 is divided into individual chips along the planned division line 13.

As described above, in the processing method for the wafer 10 according to the embodiment, the grooves 23 are formed in the protective tape 20 in the area corresponding to the planned division line 13 of the wafer 10, so that the cracks 18 that break from the modified layer 16 as the fracture origin extend along the thickness direction of the wafer 10. In particular, the method is highly effective in guiding the extension direction of the cracks 18 that extend toward the grinding surface (rear surface 15) beyond the modified layer 16, and is effective in suppressing a decrease in flexural strength even in the case of processing conditions that leave the modified layer 16 on the side of the chip after division.

In the processing method of the wafer 10 according to the embodiment, the groove 23 has a groove width of 50 μm or more, preferably 100 μm or more, and is equal to or less than the width of the planned division line 13. If the groove width is less than 100 μm, there may be some places where it is difficult to concentrate the grinding stress on the modified layer 16, and if the groove width is less than 50 μm, it may be difficult to concentrate the grinding stress on the modified layer 16. If the groove width of the groove 23 exceeds the width of the planned division line 13, the grinding stress may be dispersed inside the wafer 10 and not concentrated on the modified layer 16. Therefore, by making the groove 23 have a groove width of 50 μm or more, preferably 100 μm or more, and is equal to or less than the width of the planned division line 13, the grinding stress can be reliably concentrated on the modified layer 16, and the wafer 10 can be reliably divided into chips.

The present invention is not limited to the above embodiment. In other words, various modifications can be made without departing from the gist of the present invention. For example, when the grooves 23 are formed in the protective tape 20 by cutting in the groove forming step 2, the cutting blade 34 is not limited to the disk-shaped cutting blade 34 of the embodiment, and a blade shaped like a cutter blade may be used. In this case, the effect of suppressing the occurrence of burrs is achieved. In addition, the protective tape 20 may be a type formed from a thermoplastic resin having only the base layer 21 and no adhesive layer 22, and fixed to the wafer 10 by thermocompression.

REFERENCE SIGNS LIST 10 wafer 11 substrate 12 front surface 13 planned division line 14 device 15 back surface 16 modified layer 17 finished thickness 18 crack 20 protective tape 23 groove 30 cutting device 40 laser processing device 45 laser beam 50 grinding device 51 chuck table 56 grinding wheel

Claims (3)

1. A method for processing a wafer having a surface on which devices are formed in areas defined by dividing lines, comprising the steps of:
a protective tape application step of applying a protective tape to the surface side of the wafer on which the device is formed;
a groove forming step of forming grooves in areas of the exposed surface of the protective tape corresponding to the division lines after the protective tape applying step is performed;
a modified layer forming step of irradiating a laser beam having a wavelength that is transparent to the wafer from the back side of the wafer along the intended dividing line to form a modified layer inside the wafer after the groove forming step is performed;
a grinding step in which, after the modified layer forming step, the protective tape side of the wafer is held on a chuck table, the back surface of the wafer is ground with a grinding wheel to thin the wafer to a finish thickness, and the wafer is divided along the planned division lines;
Equipped with
a groove in the protective tape that guides a direction of a crack extending from the modified layer in the grinding step in a thickness direction of the wafer; In the grinding step, the grinding wheel, which is fed from the back surface of the wafer in the thickness direction of the wafer, ends the grinding before reaching the modified layer.
The wafer processing method according to claim 1 . The grooves are formed by a cutting blade or laser processing.
3. The wafer processing method according to claim 1 or 2.

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