Method of processing a wafer

Abstract

Provided is a wafer processing method in which a laser light irradiation-induced modification does not remain on the outer periphery of a wafer, and the wafer is not damaged during conveyance. The method includes: a modification layer forming step of positioning a focal point of laser light (LB) of a wavelength that is transmissive to the wafer on the inside of the wafer corresponding to a remaining area (10) of the outer periphery from the back surface (2b) side of the wafer (2) and irradiating the laser light to form a ring-shaped modification layer (24) at a position where a finished thickness is not reached; a protective member attaching step of attaching a protective member (14) to the front surface (2a) of the wafer; a modification layer removing step of performing cutting with a cutting tool (34) positioned on the back surface of the wafer at a region corresponding to the modification layer to remove the modification layer and bring a cleavage surface (38) to the front surface of the wafer; a ring removing step of removing a ring (40) of the remaining area of the outer periphery from the cleavage surface; and a grinding step of performing grinding on the back surface of the wafer until the finished thickness is reached.

Description

TECHNICAL FIELD

[0001] The present application relates to a wafer processing method in which a plurality of device regions divided by a dicing line and a peripheral remaining region surrounding the device regions are formed on a front surface of the wafer. BACKGROUND

[0002] A wafer in which a plurality of devices such as ICs, LSIs, and the like are divided by a dicing line and a peripheral remaining region surrounding the device regions are formed on a front surface is thinned by grinding a back surface of the wafer with a grinding device, and then the wafer is divided into individual device chips by a cutting device or a laser processing device. The divided device chips are used for electronic devices such as mobile phones, personal computers, and the like.

[0003] When the back surface of the wafer is ground to thin the wafer, there is a problem that a chamfer portion formed at a peripheral end of the wafer becomes sharp like a blade, a defect is generated in grinding, and a crack reaches the device region to damage the device. Therefore, the present applicant has proposed a technique in which the peripheral remaining region having the chamfer portion is removed by irradiating laser light before the back surface of the wafer is ground (for example, refer to Patent Document 1).

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-108532

[0005] However, a deteriorated substance generated by the irradiation of the laser light remains at the periphery of the wafer, and there is a problem that the wafer is broken during conveyance of the wafer due to the deteriorated substance. SUMMARY

[0006] The present application has been achieved in view of the above-described fact, and an object is to provide a wafer processing method in which a deteriorated substance generated by irradiation of laser light does not remain at the periphery of the wafer, and the wafer is not broken during conveyance of the wafer.

[0007] A wafer processing method according to the present application includes: a modification layer forming step of forming a ring-shaped modification layer in a position that does not reach a finished thickness of the wafer by irradiating laser light from a back surface side of the wafer with a focal point of the laser light of a wavelength that is transparent to the wafer positioned inside the wafer corresponding to a peripheral remaining region; a protective member attaching step of attaching a protective member to a front surface of the wafer before or after the modification layer forming step; a modification layer removing step of removing the modification layer by cutting the wafer with a cutting tool positioned in a region corresponding to the modification layer from the back surface of the wafer, and reaching a cleavage plane to the front surface of the wafer; a ring removing step of removing a ring of the peripheral remaining region from the cleavage plane; and a grinding step of grinding the back surface of the wafer until the finished thickness of the wafer is reached.

[0008] The wafer processing method preferably includes: a transfer step of removing the protective member from the front surface of the wafer by sticking a dicing tape to the back surface of the wafer and supporting a periphery of the dicing tape with a frame having an opening portion in which the wafer is accommodated after the grinding step; and a dicing step of dicing the wafer into individual device chips by processing the wafer at a dicing line.

[0009] The wafer processing method according to the present application includes: a modification layer forming step of forming a ring-shaped modification layer in a position that does not reach a finished thickness of the wafer by irradiating laser light from a back surface side of the wafer with a focal point of the laser light of a wavelength that is transparent to the wafer positioned inside the wafer corresponding to a peripheral remaining region; a protective member attaching step of attaching a protective member to a front surface of the wafer before or after the modification layer forming step; a modification layer removing step of removing the modification layer by cutting the wafer with a cutting tool positioned in a region corresponding to the modification layer from the back surface of the wafer, and reaching a cleavage plane to the front surface of the wafer; a ring removing step of removing a ring of the peripheral remaining region from the cleavage plane; and a grinding step of grinding the back surface of the wafer until the finished thickness of the wafer is reached. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is a perspective view showing a state in which the protective member attaching step is performed.

[0011] Figure 2 is a perspective view showing a state in which the wafer is held to a chuck table.

[0012] Figure 3 It is a three-dimensional view showing the state of the modified layer formation process.

[0013] Figure 4 (a) is a three-dimensional view of a wafer with a ring-shaped modified layer. Figure 4 (b) is Figure 4 (a) is a cross-sectional view of the wafer.

[0014] Figure 5 (a) is a perspective view showing the state of the modified layer removal process. Figure 5 (b) is a cross-sectional view of the wafer after the modified layer has been removed.

[0015] Figure 6 This is a perspective view showing the state of the ring removal process.

[0016] Figure 7 (a) is a perspective view showing the state of the grinding process being performed. Figure 7 (b) is a three-dimensional view of the wafer after the grinding process has been performed.

[0017] Figure 8 (a) is a perspective view showing the state of attaching a scribe strip to the back of the wafer during the transfer process. Figure 8 (b) is a perspective view showing the state in which the protective component has been removed from the front side of the wafer during the transfer process.

[0018] Figure 9 This is a perspective view showing the state of using a cutting device to carry out the division process.

[0019] Figure 10 This is a perspective view showing the state of performing the division process using a laser processing device.

[0020] Figure 11 It is a three-dimensional view showing the state of the picking process.

[0021] Label Explanation

[0022] 2: Wafer; 2a: Front side of wafer; 2b: Back side of wafer; 4: Device; 6: Pre-defined dicing line; 8: Device area; 10: Remaining peripheral area; 14: Protective component; 24: Modified layer; 38: Cleavage surface; 40: Ring of remaining peripheral area; 58: Dicing strip; 60: Frame; 60a: Opening of the frame; 78: Device chip. Detailed Implementation

[0023] Hereinafter, a preferred embodiment of the wafer processing method of the present invention will be described with reference to the accompanying drawings.

[0024] exist Figure 1The diagram shows a wafer 2 processed using the wafer processing method of the present invention. The wafer 2, a circular plate-shaped wafer with a thickness of approximately 700 μm, can be formed, for example, from silicon. The front side 2a of the wafer 2 has a device region 8 divided by lattice-shaped dividing lines 6 for multiple devices 4 such as ICs and LSIs, and a remaining peripheral region 10 surrounding the device region 8. Figure 1 For convenience, a double-dotted line is used to represent the boundary 12 between the device region 8 and the remaining outer region 10, but in reality, there is no line representing the boundary 12.

[0025] In the wafer processing method of this embodiment, such as Figure 1 As shown, firstly, a protective component placement process is performed to place a protective component 14 on the front side 2a of the wafer 2. For example, a circular adhesive tape with the same diameter as the wafer 2 can be used as the protective component 14.

[0026] After the protective component placement process, a modifier layer formation process is performed. A laser beam of a wavelength transparent to the wafer 2 is focused from the back surface 2b side of the wafer 2 onto the interior of the wafer 2, corresponding to the remaining peripheral region 10, and the wafer 2 is irradiated with the laser beam. An annular modifier layer is formed at a location where the finished thickness of the wafer 2 is not reached. In the illustrated embodiment, the protective component placement process is performed before the modifier layer formation process, but it can also be performed after the modifier layer formation process.

[0027] The modified layer formation process can be used, for example, in... Figure 2 and Figure 3 The laser processing apparatus 16 shown in the figure is used to implement this process. The laser processing apparatus 16 includes: a chuck stage 18 for attracting and holding a wafer 2; a concentrator 20 for irradiating the wafer 2 held on the chuck stage 18 with pulsed laser beams LB; and an imaging unit (not shown) for imaging the wafer 2 held on the chuck stage 18.

[0028] like Figure 2 As shown, a porous, circular suction chuck 22 connected to a suction unit (not shown) is disposed at the upper end of the chuck stage 18. The chuck stage 18 uses the suction unit to generate an attractive force on the upper surface of the suction chuck 22 to attract and hold the wafer 2 placed on the upper surface of the suction chuck 22.

[0029] The chuck table 18 is configured to rotate freely about an axis extending vertically through the radial center of the suction chuck 22, and is configured to... Figure 2 The X-axis direction indicated by the middle arrow X and the Y-axis direction perpendicular to the X-axis direction ( Figure 2The wafer 2 is moved in the X-axis direction and the Y-axis direction (indicated by arrows Y) by the wafer stage 12. In addition, the XY plane defined by the X-axis direction and the Y-axis direction is substantially horizontal.

[0030] The condenser 20 has a condensing lens (not shown) that condenses the pulsed laser beam LB oscillated by a laser beam oscillator (not shown) of the laser processing device 16. The imaging unit of the laser processing device 16 includes (none of which is shown) a general imaging element (CCD) that images the workpiece with visible light, an infrared ray irradiation unit that irradiates the workpiece with infrared rays, an optical system that captures the infrared rays irradiated by the infrared ray irradiation unit, and an imaging element (infrared ray CCD) that outputs an electric signal corresponding to the infrared rays captured by the optical system.

[0031] In the modification layer forming process, as shown in Figure 2 , first, the back surface 2b of the wafer 2 is oriented upward, and the wafer 2 is suction-held by the upper surface of the chuck table 18. At this time, the radial center of the wafer 2 is aligned with the radial center of the suction chuck 22 (the rotational center of the chuck table 18).

[0032] Next, the wafer 2 is imaged from above by the imaging unit of the laser processing device 16, and based on the image of the wafer 2 imaged by the imaging unit, the condensing point of the pulsed laser beam LB having a wavelength that is transmissive to the wafer 2 is positioned inside the wafer 2 corresponding to the outer peripheral remaining region 10 from the back surface 2b side of the wafer 2. In addition, the position in the up-down direction of the condensing point is adjusted to a position that does not reach the finished thickness of the wafer 2 (for example, about 50 μm from the front surface 2a of the wafer 2).

[0033] In addition, when the wafer 2 is imaged by the imaging unit, the back surface 2b of the wafer 2 is oriented upward, and the front surface 2a in which the device 4 and the division predetermined line 6 are formed is oriented downward, but as described above, the imaging unit includes the infrared ray irradiation unit, the optical system that captures the infrared rays, and the imaging element (infrared ray CCD) that outputs an electric signal corresponding to the infrared rays, and thus it is possible to image the device 4 and the division predetermined line 6 of the front surface 2a from the back surface 2b of the wafer 2. Thus, it is possible to position the condensing point of the pulsed laser beam LB inside the wafer 2 corresponding to the outer peripheral remaining region 10 from the back surface 2b side of the wafer 2.

[0034] Next, as shown in Figure 3 , the chuck table 18 is rotated at a prescribed rotational speed, and thus the condensing point of the pulsed laser beam LB is relatively moved along the outer peripheral remaining region 10 with respect to the wafer 2, and the pulsed laser beam LB is irradiated from the condenser 20 to the wafer 2. Thus, as shown in Figure 4 (a) and Figure 4As shown in (b) of FIG. 2, the ring-shaped modification layer 24 having a small strength can be formed along the outer peripheral remaining region 10 at a position inside the wafer 2 corresponding to the outer peripheral remaining region 10 and not reaching the finished thickness of the wafer 2.

[0035] Such a ring-shaped modification layer forming process can be performed, for example, under the following conditions.

[0036] Wavelength of pulsed laser light: 1342 nm

[0037] Repetition frequency: 60 kHz

[0038] Average output: 1.6 W

[0039] Rotational speed of chuck table: 0.5 revolutions / second

[0040] After the modification layer forming process is implemented, a modification layer removing process is implemented, the cutting tool is positioned at a region corresponding to the modification layer 24 from the back surface 2b of the wafer 2, the wafer 2 is cut to remove the modification layer 24, and the cleavage plane reaches the front surface 2a of the wafer 2.

[0041] The modification layer removing process can be implemented, for example, using the cutting device 26 shown in part in (a) of FIG. 3. The cutting device 26 has a chuck table 28 that suction-holds the wafer 2 and a cutting unit 30 that cuts the wafer 2 suction-held on the chuck table 28. Figure 5

[0042] The circular chuck table 28 that suction-holds the wafer 2 on the upper surface is configured to be rotatable about an axis extending through the radial center of the chuck table 28 and in the vertical direction as a rotation center, and is configured to be movable in the X-axis direction. The cutting unit 30 includes a spindle 32 configured to be rotatable about the Y-axis direction as an axis, and a ring-shaped cutting tool 34 fixed to the front end of the spindle 32.

[0043] Referring to (a) of FIG. 3, in the modification layer removing process, first, the back surface 2b of the wafer 2 is oriented upward, and the wafer 2 is suction-held by the upper surface of the chuck table 28. At this time, the radial center of the wafer 2 is aligned with the rotation center of the chuck table 28. Figure 5

[0044] Next, the cutting tool 34 is positioned above the modification layer 24, the cutting tool 34 is rotated at high speed, the blade tip of the cutting tool 34 is cut into the wafer 2 from the back surface 2b to a position not reaching the finished thickness of the wafer 2, and the chuck table 28 is rotated at a predetermined rotational speed. Thus, as shown in (b) of FIG. 3, the modification layer 24 is removed by the cutting tool 34, and the cleavage plane reaches the front surface 2a of the wafer 2. Figure 5 ​​As shown in (b), a cutting groove 36 is formed in the region corresponding to the modified layer 24, from the back surface 2b of the wafer 2 to a position where the finished thickness of the wafer 2 has not been reached, so that the modified layer 24 can be removed. Since the modified layer 24 is removed in this way, the deterioration products generated by the irradiation of the pulsed laser beam LB will not remain on the outer periphery of the wafer 2.

[0045] Furthermore, when the wafer 2 with the modified layer 24 is cut using the cutting tool 34, cracks propagate from the modified layer 24 in the thickness direction of the wafer 2. Therefore, the cleavage surface 38 from which the crack forms extends from the bottom surface of the cutting groove 36 to the front surface 2a of the wafer 2. Thus, a ring 40 corresponding to the remaining peripheral region 10 is segmented from the wafer 2. In addition, the dimension from the bottom surface of the cutting groove 36 to the front surface 2a of the wafer 2 is thicker than the finished thickness of the wafer 2, for example, it can be about 60 μm.

[0046] After the modified layer removal process is implemented, such as Figure 6 As shown, a ring removal process is performed to remove the ring 40 of the remaining peripheral region 10 starting from the cleavage surface 38.

[0047] After the ring removal process, a grinding process is performed to grind the back surface 2b of wafer 2 until the finished thickness of wafer 2 is achieved. The grinding process can be used, for example, in... Figure 7 A portion of the grinding apparatus 42 is shown in (a) to implement this process. The grinding apparatus 42 includes: a chuck stage 44 that attracts and holds the wafer 2; and a grinding unit 46 that grinds the wafer 2 that is attracted and held on the chuck stage 44.

[0048] The chuck stage 44, which attracts and holds the wafer 2 on its upper surface, is configured to rotate freely about an axis extending in the vertical direction. The grinding unit 46 includes a rotatable spindle 48 extending in the vertical direction and a grinding wheel mount 50 fixed to the lower end of the spindle 48. An annular grinding wheel 54 is fixed to the lower surface of the grinding wheel mount 50 by bolts 52, and a plurality of grinding tools 56 arranged in a ring at circumferential intervals are fixed to the outer periphery of the lower surface of the grinding wheel 54.

[0049] Reference Figure 7 Continuing with explanation (a), in the grinding process, firstly, the back surface 2b of the wafer 2 is facing upwards, and the wafer 2 is held by the upper surface of the chuck stage 44. Next, the chuck stage 44 is rotated counterclockwise when viewed from above, and the spindle 48 is also rotated counterclockwise when viewed from above. Then, after the spindle 48 is lowered to bring the grinding wheel 56 into contact with the back surface 2b of the wafer 2, the spindle 48 is lowered at a predetermined grinding feed rate. Thus, as... Figure 7As shown in (b), grinding the back surface 2b of wafer 2 to form a finished thickness of wafer 2 (for example, about 50 μm) can flatten the back surface 2b of wafer 2. In addition, the outer periphery of wafer 2, which has been formed to the finished thickness, is covered by cleavage surface 38.

[0050] In the illustrated embodiment, after the grinding process, the following transfer process is performed: a scribe strip is attached to the back side 2b of the wafer 2, and the outer periphery of the scribe strip is supported by a frame having an opening for receiving the wafer 2, and the protective member 14 is removed from the front side 2a of the wafer 2.

[0051] Reference Figure 8 (a) and Figure 8 (b) will be described in the illustration. The outer periphery of the dicing strip 58 in the illustrated embodiment is supported by an annular frame 60, which has an opening 60a for receiving the wafer 2. Figure 8 As shown in (a), in the transfer process, firstly, the dicing tape 58 supported on the frame 60 is attached to the back surface 2b of the wafer 2. Then, as... Figure 8 As shown in (b), the protective component 14 is peeled off from the front side 2a of the wafer 2.

[0052] After the transfer process, a dicing process is performed: the wafer 2 is diced into individual device chips by processing the dicing lines 6 of the wafer 2. The dicing process can be performed using the cutting apparatus 26 described above.

[0053] Reference Figure 9 To explain, in the dicing process, firstly, the front side 2a of the wafer 2 is oriented upwards, and the chuck stage 28 of the dicing device 26 is used (in... Figure 9 The upper surface (not shown in the figure) attracts and holds the wafer 2. Next, the pre-defined dividing line 6 is aligned with the X-axis direction, and the pre-defined dividing line 6 is aligned with the cutting tool 34. Next, the tip of the high-speed rotating cutting tool 34 cuts into the pre-defined dividing line 6 aligned with the X-axis direction from the front side 2a, and the chuck table 28 is fed relative to the cutting unit 30 in the X-axis direction, thereby performing the dividing groove forming process to form the dividing groove 62 along the pre-defined dividing line 6.

[0054] Then, the indexing feed and the aforementioned sizing groove forming process are repeated to form sizing grooves 62 along all the predetermined sizing lines 6 aligned with the X-axis direction. This indexing feed moves the cutting tool 34 relative to the chuck table 28 in the Y-axis direction at intervals along the predetermined sizing lines 6. Furthermore, after rotating the chuck table 28 90 degrees, the sizing groove forming process is repeated while performing the indexing feed, forming sizing grooves 62 along all the predetermined sizing lines 6 perpendicular to the previously formed sizing grooves 62. This sizing process divides the wafer 2 into device chips for each device 4 along the predetermined sizing lines 6.

[0055] In the dicing process, the aforementioned laser processing apparatus 16 can also be used to irradiate pulsed laser light LB along the predetermined dicing line 6 to dic the wafer 2 into individual device chips. When using the laser processing apparatus 16, such as... Figure 10 As shown, the pulsed laser beam LB of a wavelength that is transparent to the wafer 2 is positioned inside the dicing predetermined line 6 and the pulsed laser beam LB is irradiated onto the wafer 2. A modified layer 63 is formed in a grid pattern inside the wafer 2 along the dicing predetermined line 6. Then, by extending the dicing tape 58, an external force is applied to the wafer 2, which can divide the wafer 2 into individual device chips.

[0056] The laser processing apparatus used to perform the dicing process is not limited to the laser processing apparatus 16 described above. It can also be a laser processing apparatus of the following type: a laser beam of wavelength that is absorbent to the wafer 2 is focused on the front surface 2a of the wafer 2 and the wafer 2 is irradiated with laser beam, and a processing groove is formed in a grid pattern along the predetermined dicing line 6 by ablation processing. Alternatively, a laser processing apparatus of the following type can also be used in the dicing process: a laser beam of wavelength that is transmittant to the wafer 2 is focused on the predetermined dicing line 6 and the wafer 2 is irradiated with laser beam, and a shield tunnel is formed in a grid pattern along the predetermined dicing line 6. The shield tunnel has fine holes extending in the thickness direction of the wafer 2 and amorphous material surrounding the fine holes.

[0057] After the dicing process, a pick-up process is performed to retrieve the device chips from the dicing tape 58. This pick-up process can be used, for example, in... Figure 11 A portion of the pickup device 64 is shown for implementation. The pickup device 64 includes: an extension unit 66 that extends the dicing tape 58 to increase the spacing between adjacent device chips; and a pickup chuck 68 that picks up and transports the device chips.

[0058] like Figure 11As shown, the expanding unit 66 includes a cylindrical expanding drum 70, a plurality of air cylinders 72 arranged around the expanding drum 70, an annular holding member 74 coupled to upper ends of the air cylinders 72, and a plurality of clamps 76 arranged at intervals in the circumferential direction at an outer peripheral portion of the holding member 74.

[0059] Each air cylinder 72 relatively raises and lowers the holding member 74 with respect to the expanding drum 70 between a reference position at which the upper surface of the holding member 74 is substantially the same height as the upper end of the expanding drum 70 and an expanded position at which the upper surface of the holding member 74 is located lower than the upper end of the expanding drum 70. Further, in Figure 11 In the drawing, the expanding drum 70 is shown in the case where the holding member 74 is at the reference position by a solid line, and the expanding drum 70 is shown in the case where the holding member 74 is at the expanded position by a double-dot chain line.

[0060] The pickup chuck 68 is configured to be movable in the horizontal direction and the vertical direction. An attracting unit is connected to the pickup chuck 68, and a device chip is adsorbed by the lower surface of the tip end of the pickup chuck 68.

[0061] Referring to Figure 11 Continuing the explanation, in the pickup process, first, the wafer 2 divided into the respective device chips 78 is oriented upward, and the frame 60 is placed on the upper surface of the holding member 74 at the reference position. Next, the frame 60 is fixed by the plurality of clamps 76. Next, the holding member 74 is lowered to the expanded position, and a radial tension is applied to the dicing tape 58. Then, as shown by the double-dot chain line in the drawing, Figure 11 the device chips 78 adhered to the dicing tape 58 are expanded apart from each other.

[0062] Next, the pickup chuck 68 is positioned above the device chip 78 that is the object of pickup. Next, the pickup chuck 68 is lowered, and the upper surface of the device chip 78 is adsorbed by the lower surface of the tip end of the pickup chuck 68. Next, the pickup chuck 68 is raised, and the device chip 78 is peeled off and picked up from the dicing tape 58. Next, the picked-up device chip 78 is carried to a prescribed carrying position such as a tray. Then, the pickup operation is sequentially performed on all of the device chips 78.

[0063] As described above, according to the wafer processing method of the illustrated embodiment, the outer periphery of the wafer 2 is covered by the cleavage plane 38, and the metamorphic substance generated by the irradiation of the laser light LB does not remain at the outer periphery of the wafer 2, so the wafer 2 is not broken during the carrying of the wafer 2.

Claims

1. A method for processing a wafer, the wafer having multiple device regions defined by predetermined lines and a remaining peripheral region surrounding the device regions formed on its front side, wherein, The wafer fabrication method includes the following steps: In the modified layer formation process, a laser beam of wavelength that is transparent to the wafer is focused on the interior of the wafer corresponding to the remaining area of ​​the outer periphery from the back side of the wafer, and the wafer is irradiated with laser beam to form an annular modified layer at the position where the wafer's finished thickness has not been reached. The protective component placement process involves placing a protective component on the front side of the wafer before or after the modification layer formation process. In the modification layer removal process, the cutting tool is positioned from the back side of the wafer to the area corresponding to the modification layer and cuts the wafer to remove the entire modification layer, so that the cleavage surface reaches the front side of the wafer. The ring removal process removes the ring from the remaining outer periphery region, starting from the cleavage plane; as well as The grinding process involves grinding the back side of the wafer after the modification layer removal process and the ring removal process until the wafer reaches its final thickness.

2. The wafer processing method according to claim 1, wherein, The wafer fabrication method includes the following steps: In the transfer process, after the grinding process, a scribe strip is attached to the back side of the wafer, and the outer periphery of the scribe strip is supported by a frame having an opening for receiving the wafer, thereby removing the protective component from the front side of the wafer; and The dicing process involves processing the pre-defined dicing lines on the wafer to divide it into individual device chips.

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