TWI879940B - Wafer processing method - Google Patents

Abstract

[Topic] Provide a wafer processing method so that deteriorated products generated by laser beam irradiation will not remain on the periphery of the wafer and the wafer will not be damaged when the wafer is transported. [Solution] A wafer processing method, comprising the following steps: a modified layer forming step, in which the focal point of the laser beam LB having a wavelength that is penetrating to the wafer 2 is positioned inside the wafer 2 corresponding to the peripheral residual area 10 from the back side 2b of the wafer 2, and the laser beam LB is irradiated to the wafer 2 to form a ring-shaped modified layer 24 at a position that does not reach the finished thickness of the wafer 2; a protective component placement step, in which the protective component 14 is placed on the back side 2b of the wafer 2. The front side 2a of the wafer 2; a modified layer removal step, which positions the cutting blade 34 at the area corresponding to the modified layer 24 from the back side 2b of the wafer 2 to cut the wafer 2 and remove the modified layer 24, while making the cleavage surface 38 reach the front side 2a of the wafer 2; an outer ring removal step, which removes the outer ring 40 of the peripheral residual area 10 with the cleavage surface 38 as the starting point; and a grinding step, which grinds the back side 2b of the wafer 2 until the finished thickness of the wafer 2 is reached.

Description

Wafer processing method

The present invention relates to a wafer processing method, wherein the wafer has a component area on the front side which is divided into a plurality of components by predetermined dividing lines and a peripheral residual area surrounding the component area.

The wafer has a component area on the front side that is divided into multiple components such as ICs and LSIs by predetermined dividing lines, and a peripheral residual area surrounding the component area. After being ground to a predetermined thickness by a grinding device on the back side, it is divided into individual component chips by a cutting device or a laser processing device. The divided component chips are used in electronic devices such as mobile phones and personal computers.

When grinding the back of the wafer to make it thinner, the chamfered portion formed on the outer peripheral end of the wafer will become as sharp as a knife edge, and there is a problem that chipping will occur during grinding and the cracks will reach the component area and damage the component. Therefore, the applicant of the present invention proposes a technology that irradiates the outer peripheral residual area with the chamfered portion with laser light before grinding the back of the wafer to remove the outer peripheral residual area (for example, see patent document 1).

[Learning Technology Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Publication No. 2006-108532

However, there is the following problem: the deteriorated products generated by the irradiation of laser beams remain on the periphery of the wafer, and the wafer may be damaged when it is transported due to the deteriorated products.

The subject of the present invention completed in view of the above facts is to provide a wafer processing method, which prevents the deteriorated products generated by the irradiation of laser light from remaining on the periphery of the wafer and prevents the wafer from being damaged when transporting the wafer.

The present invention provides the following wafer processing method to solve the above-mentioned problem. That is, a wafer processing method, wherein a wafer has a component area divided into a plurality of components by a predetermined dividing line and a peripheral residual area surrounding the component area on the front side, and the wafer processing method comprises the following steps: a modified layer forming step, wherein a focal point of a laser beam having a wavelength penetrating the wafer is positioned from the back side of the wafer at the inside of the wafer corresponding to the peripheral residual area, and the wafer is irradiated with laser beam to form a ring-shaped modified layer at a position that does not reach the finished thickness of the wafer; The modified layer is formed by a protective member arrangement step, which arranges the protective member on the front side of the wafer before or after the modified layer formation step; the modified layer removal step, which positions the cutting blade at the area corresponding to the modified layer from the back side of the wafer to cut the wafer and remove the modified layer, while making the cleavage surface reach the front side of the wafer; the outer ring removal step, which removes the outer ring of the peripheral residual area starting from the cleavage surface; and the grinding step, which grinds the back side of the wafer until the finished thickness of the wafer is reached.

Preferably, the following steps are included: a transfer step, in which after the grinding step, a dicing film is adhered to the back of the wafer, and the periphery of the dicing film is supported by a frame having an opening for accommodating the wafer, and a protective member is removed from the front of the wafer; and a splitting step, in which the wafer is processed along a predetermined splitting line to split the wafer into individual component chips.

The wafer processing method of the present invention includes the following steps: a modified layer forming step, in which the focal point of the laser light of a wavelength penetrating the wafer is positioned from the back side of the wafer to the inside of the wafer corresponding to the peripheral residual area, and the wafer is irradiated with laser light to form a ring-shaped modified layer at a position that does not reach the finished thickness of the wafer; a protective member arranging step, in which the protective member is arranged on the front side of the wafer before or after the modified layer forming step; and a modified layer removing step, in which the modified layer is removed from the wafer. The back of the wafer is positioned to position the cutting blade in the area corresponding to the modified layer to cut the wafer and remove the modified layer, while the cleavage surface reaches the front of the wafer; the outer ring removal step, which uses the cleavage surface as a starting point to remove the outer ring of the peripheral residual area; and the grinding step, which grinds the back of the wafer until the finished thickness of the wafer is reached, so that the periphery of the wafer will be covered by the cleavage surface, so that the deteriorated products generated by the irradiation of the laser beam will not remain on the periphery of the wafer, and the wafer will not be damaged when the wafer is transported.

2: Wafer

2a: Front side of the wafer

2b: Back side of the wafer

4: Components

6: Split the predetermined line

8: Component area

10: Peripheral remaining area

14: Protective components

24: Modified layer

38: Split surface

40: Outer ring of the remaining peripheral area

58: Cutting film

60:Framework

60a: Opening of the frame

78: Component chip

Figure 1 is a three-dimensional diagram showing the state of the protective component installation step.

Figure 2 is a three-dimensional diagram showing the state of the chuck table holding the wafer.

Figure 3 is a three-dimensional diagram showing the state of the modified layer forming step.

FIG4(a) is a three-dimensional view of a wafer having a ring-shaped modified layer formed thereon, and FIG4(b) is a cross-sectional view of the wafer shown in FIG4(a).

Figure 5(a) is a three-dimensional diagram showing the state of the modified layer removal step, and Figure 5(b) is a cross-sectional diagram of the wafer after the modified layer has been removed.

Figure 6 is a three-dimensional diagram showing the state of implementing the outer ring removal step.

FIG7(a) is a three-dimensional diagram showing the state of the grinding step, and FIG7(b) is a three-dimensional diagram of the wafer after the grinding step.

FIG8(a) is a three-dimensional diagram showing a state where the dicing film is attached to the back of the wafer in the transfer step, and FIG8(b) is a three-dimensional diagram showing a state where the protective member has been removed from the front of the wafer in the transfer step.

Figure 9 is a three-dimensional diagram showing the state of using a cutting device to implement the splitting step.

Figure 10 is a three-dimensional diagram showing the state of performing the segmentation step using a laser processing device.

Figure 11 is a three-dimensional diagram showing the state of the picking step.

Below, the preferred implementation of the wafer processing method of the present invention is described while referring to the drawings.

FIG. 1 shows a wafer 2 processed by the wafer processing method of the present invention. The wafer 2 is a disk-shaped wafer 2 with a thickness of about 700 μm, and is formed of silicon or the like. The front surface 2a of the wafer 2 is formed with a component area 8 for dividing a plurality of components 4 such as IC and LSI by a grid-like predetermined dividing line 6, and a peripheral residual area 10 surrounding the component area 8. In FIG. 1, for the sake of convenience, a boundary 12 between the component area 8 and the peripheral residual area 10 is represented by a two-point chain line, but there is actually no line representing the boundary 12.

In the wafer processing method of the illustrated embodiment, as shown in FIG1 , first, a protective member arrangement step of arranging the protective member 14 on the front surface 2a of the wafer 2 is implemented. As the protective member 14, for example, a circular adhesive film having the same diameter as the diameter of the wafer 2 can be used.

After the protective member arrangement step is performed, the modified layer formation step described below is performed: the focal point of the laser light of a wavelength penetrating the wafer 2 is positioned inside the wafer 2 corresponding to the peripheral residual area 10 from the back side 2b of the wafer 2, and the laser light is irradiated on the wafer 2 to form a ring-shaped modified layer at a position that does not reach the finished thickness of the wafer 2. Incidentally, in the illustrated implementation method, although the protective member arrangement step is performed before the modified layer formation step, the protective member arrangement step can also be performed after the modified layer formation step.

The modified layer formation step can be implemented, for example, using a laser processing device 16 partially shown in FIG. 2 and FIG. 3. The laser processing device 16 includes: a chuck table 18 that attracts and holds the wafer 2; a condenser 20 that irradiates the pulsed laser beam (laser beam) LB to the wafer 2 attracted and held on the chuck table 18; and a camera (not shown) that photographs the wafer 2 attracted and held on the chuck table 18.

As shown in FIG2 , a porous circular adsorption chuck 22 connected to a suction means (not shown) is disposed at the upper end of the chuck table 18. The chuck table 18 generates a suction force on the upper surface of the adsorption chuck 22 by the suction means, thereby attracting and holding the wafer 2 carried on the upper surface of the adsorption chuck 22.

The chuck table 18 is configured to be able to rotate freely with an axis extending in the vertical direction through the radial center of the adsorption chuck 22 as the rotation center, and is configured to be able to move forward and backward freely in the X-axis direction indicated by the arrow X in FIG. 2 and the Y-axis direction perpendicular to the X-axis direction (in the direction indicated by the arrow Y in FIG. 2). Incidentally, the XY plane defined by the X-axis direction and the Y-axis direction is substantially horizontal.

The condenser 20 has a condensing lens (not shown) that focuses the pulsed laser beam LB oscillated by the laser beam oscillator (not shown) of the laser processing device 16. The imaging means of the laser processing device 16 include (all of which are not shown): a general imaging element (CCD) that photographs the object to be processed by visible light; an infrared irradiation means that irradiates infrared rays to the object to be processed; an optical system that captures the infrared rays irradiated by the infrared irradiation means; and an imaging element (infrared CCD) that outputs an electronic signal corresponding to the infrared rays captured by the optical system.

In the modified layer formation step, as shown in FIG2 , first, the back side 2b of the wafer 2 is facing upward, and the upper surface of the chuck table 18 is used to attract and hold the wafer 2. At this time, the radial center of the wafer 2 is aligned with the radial center of the adsorption chuck 22 (the rotation center of the chuck table 18).

Next, the wafer 2 is photographed from above by the imaging means of the laser processing device 16, and based on the image of the wafer 2 photographed by the imaging means, the focal point of the pulsed laser beam LB of a wavelength penetrating the wafer 2 is positioned inside the wafer 2 corresponding to the peripheral residual area 10 from the back side 2b of the wafer 2. In addition, the vertical position of the focal point is adjusted to a position that does not reach the finished thickness of the wafer 2 (for example, about 50μm from the front side 2a of the wafer 2).

Incidentally, when photographing the wafer 2 by means of photography, the back side 2b of the wafer 2 is facing upward and the front side 2a on which the components 4 and the predetermined dividing line 6 are formed is facing downward. However, as mentioned above, since the photography means includes infrared irradiation means, an optical system for capturing infrared rays, and an imaging element (infrared CCD) that outputs electronic signals corresponding to infrared rays, the components 4 and the predetermined dividing line 6 on the front side 2a can be photographed through the back side 2b of the wafer 2. In this way, the focal point of the pulsed laser beam LB can be positioned inside the wafer 2 corresponding to the peripheral residual area 10 from the back side 2b of the wafer 2.

Next, as shown in FIG3 , the chuck table 18 is rotated at a predetermined rotation speed, and the focal point of the pulsed laser beam LB is moved relative to the wafer 2 along the peripheral residual area 10, while the pulsed laser beam LB is irradiated to the wafer 2 from the condenser 20. Thus, as shown in FIG4 (a) and FIG4 (b), a ring-shaped modified layer 24 with a relatively small strength can be formed along the peripheral residual area 10 inside the wafer 2 corresponding to the peripheral residual area 10, that is, the position that does not reach the finished thickness of the wafer 2.

This annular modified layer formation step can be performed, for example, under the following conditions.

Wavelength of pulsed laser light: 1342nm

Repetition frequency: 60kHz

Average output: 1.6W

Chuck table rotation speed: 0.5 rotations/second

After the modified layer forming step is performed, the modified layer removal step described below is performed: the dicing blade is positioned at the area corresponding to the modified layer 24 from the back side 2b of the wafer 2 to cut the wafer 2 and remove the modified layer 24, while the cleavage surface reaches the front side 2a of the wafer 2.

The modified layer removal step can be implemented, for example, using a cutting device 26 partially shown in FIG. 5( a ). The cutting device 26 includes: a chuck table 28 that attracts and holds the wafer 2; and a cutting means 30 that cuts the wafer 2 attracted and held on the chuck table 28 .

The circular chuck table 28 that attracts and holds the wafer 2 on the upper surface is configured to be rotatable with an axis that passes through the radial center of the chuck 28 and extends in the vertical direction as the rotation center, and is also configured to be movable in the X-axis direction. The cutting means 30 includes: a spindle 32 that is configured to be rotatable with the Y-axis direction as the axis center; and an annular cutting blade 34 that is fixed to the front end of the spindle 32.

Now, referring to Figure 5(a), in the modified layer removal step, first, the back side 2b of the wafer 2 is facing upward, and the upper surface of the chuck table 28 is used to attract and hold the wafer 2. At this time, the radial center of the wafer 2 is aligned with the rotation center of the chuck table 28.

Next, the cutting blade 34 is positioned above the modified layer 24, and the tip of the cutting blade 34 rotating at high speed is cut from the back side 2b of the wafer 2 to a position that does not reach the finished thickness of the wafer 2, and the chuck table 28 is rotated at a predetermined rotation speed. Thus, as shown in FIG. 5(b), in the area corresponding to the modified layer 24, a cutting groove 36 can be formed from the back side 2b of the wafer 2 to a position that does not reach the finished thickness of the wafer 2, thereby removing all the modified layer 24. Since all the modified layer 24 is removed in this way, the deteriorated product generated by the irradiation of the pulsed laser beam LB will not remain on the periphery of the wafer 2.

Furthermore, when the wafer 2 with the modified layer 24 is cut by the dicing blade 34, the crack will extend from the modified layer 24 to the thickness direction of the wafer 2, so the cleavage surface 38 formed by the crack will reach the front surface 2a of the wafer 2 from the bottom surface of the cutting groove 36. Therefore, the outer ring 40 corresponding to the peripheral residual area 10 will be cut out from the wafer 2. Incidentally, 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 60μm.

After the modified layer removal step is performed, the outer ring removal step described later is performed as shown in FIG6 : the outer ring 40 of the peripheral residual area 10 is removed starting from the cleavage surface 38 .

After the outer ring removal step is performed, the grinding step described below is performed: grinding the back side 2b of the wafer 2 until the finished thickness of the wafer 2 is reached. The grinding step can be performed, for example, using a grinding device 42 partially shown in FIG. 7(a). The grinding device 42 includes: a chuck table 44 that attracts and holds the wafer 2; and a grinding means 46 that grinds the wafer 2 attracted and held on the chuck table 44.

The chuck table 44 that attracts and holds the wafer 2 in the upper surface is configured to be rotatable with an axis extending in the vertical direction as the rotation center. The grinding means 46 includes: a spindle 48 that extends in the vertical direction and can rotate; and a wheel frame 50 that is fixed to the lower end of the spindle 48. An annular grinding wheel 54 is fixed to the lower surface of the wheel frame 50 by bolts 52, and a plurality of grinding stones 56 are fixed to the outer peripheral portion of the lower surface of the grinding wheel 54 in an annular shape with spaced intervals in the circumferential direction.

Now, referring to FIG. 7(a), the explanation continues. In the grinding step, first, the back side 2b of the wafer 2 is facing upward, and the wafer 2 is held by the upper surface of the chuck table 44. Then, the chuck table 44 is rotated counterclockwise when viewed from above, and the spindle 48 is rotated counterclockwise when viewed from above. Then, the spindle 48 is lowered so that the grinding stone 56 contacts the back side 2b of the wafer 2, and then the spindle 48 is lowered at a predetermined grinding feed speed. Thus, as shown in FIG. 7(b), the back side 2b of the wafer 2 can be ground to form the finished thickness of the wafer 2 (for example, about 50μm), and the back side 2b of the wafer 2 is made flat. In addition, the outer periphery of the wafer 2 formed to the finished thickness is covered by the cleavage surface 38.

In the illustrated implementation method, after the grinding step is performed, the transfer step described below is performed: the dicing film is adhered to the back side 2b of the wafer 2, and the periphery of the dicing film is supported by a frame having an opening for accommodating the wafer 2, and the protective member 14 is removed from the front side 2a of the wafer 2.

Referring to FIG. 8(a) and FIG. 8(b) for explanation, the periphery of the dicing film 58 of the illustrated embodiment is supported by a ring-shaped frame 60 having an opening 60a for accommodating the wafer 2. As shown in FIG. 8(a), In the transfer step, first, the dicing film 58 supported by the frame 60 is adhered to the back side 2b of the wafer 2. Then, as shown in FIG. 8(b), the protective member 14 is peeled off from the front side 2a of the wafer 2.

After the transfer step is performed, the following division step is performed: the predetermined division line 6 of the wafer 2 is processed to divide the wafer 2 into individual component chips. The division step can be performed using the above-mentioned cutting device 26.

Referring to FIG. 9 for explanation, in the splitting step, first, the front side 2a of the wafer 2 is facing upward, and the wafer 2 is held by the upper surface of the chuck table 28 (omitted in FIG. 9) of the cutting device 26. Then, the predetermined splitting line 6 is aligned in the X-axis direction, and the predetermined splitting line 6 and the cutting blade 34 are aligned at the same time. Then, the tip of the high-speed rotating cutting blade 34 is cut from the front side 2a into the predetermined splitting line 6 aligned in the X-axis direction, and the chuck table 28 is fed relative to the cutting means 30 in the X-axis direction, thereby performing the splitting groove forming process of forming the splitting groove 62 along the predetermined splitting line 6.

Then, the indexing feeding and the above-mentioned splitting groove forming processing are repeated to form splitting grooves 62 along all the splitting predetermined lines 6 aligned in the X-axis direction; wherein the indexing feeding is to make the cutting blade 34 index the splitting predetermined lines 6 relative to the chuck table 28 in the Y-axis direction. In addition, the chuck table 28 is first rotated 90 degrees, and then the splitting groove forming processing is repeated while indexing and feeding, so that the splitting grooves 62 are formed along all the splitting predetermined lines 6 perpendicular to the previously formed splitting grooves 6. The splitting step is implemented in this way, and the wafer 2 is split into component chips of individual components 4 along the splitting predetermined lines 6.

In the splitting step, the laser processing device 16 can also be used to irradiate the pulse laser beam LB along the predetermined splitting line 6 to split the wafer 2 into individual component chips. When the laser processing device 16 is used, as shown in FIG. 10, the focal point of the pulse laser beam LB with a wavelength that is penetrating to the wafer 2 is positioned inside the predetermined splitting line 6 and the pulse laser beam LB is irradiated to the wafer 2, thereby forming a lattice-shaped modified layer 63 inside the wafer 2 along the predetermined splitting line 6. Afterwards, the wafer 2 is given an external force by expanding the dicing film 58, so that the wafer 2 can be split into individual component chips.

The laser processing device used to implement the splitting step is not limited to the laser processing device 16 described above, and may also be a laser processing device of the type described below: the focal point of the laser light of a wavelength that absorbs the wafer 2 is positioned on the front surface 2a of the wafer 2 and the laser light is irradiated to the wafer 2, and a grid-shaped processing groove is formed along the predetermined splitting line 6 by ablation processing. Alternatively, the laser processing device of the type described below can also be used in the splitting step: the focal point of the laser light of a wavelength that penetrates the wafer 2 is positioned on the predetermined splitting line 6 and the laser light is irradiated to the wafer 2, and the shield channel is formed into a grid along the predetermined splitting line 6; Wherein, the shield channel has fine holes extending in the thickness direction of the wafer 2 and amorphous surrounding the fine holes.

After the separation step is performed, a picking step of picking up the component wafer from the dicing film 58 is performed. The picking step can be performed, for example, using a picking device 64 partially shown in FIG. 11 . The picking device 64 includes: an expansion device 66 that expands the dicing film 58 to expand the interval between adjacent component wafers; and a picking collet 68 that absorbs and transports the component wafer.

As shown in FIG. 11 , the expansion means 66 includes: a cylindrical expansion roller 70; a plurality of cylinders 72 arranged around the expansion roller 70; an annular retaining member 74 connecting the upper ends of each of the cylinders 72; and a plurality of clamps 76 arranged at intervals in the circumferential direction on the outer peripheral portion of the retaining member 74.

Each cylinder 72 causes the retaining member 74 to rise and fall relative to the expansion roller 70 between the reference position and the expansion position; wherein the reference position is when the upper surface of the retaining member 74 is at a height substantially equal to that of the upper end of the expansion roller 70, and the expansion position is when the upper surface of the retaining member 74 is located below the upper end of the expansion roller 70. Incidentally, in FIG. 11 , the expansion roller 70 is indicated by a solid line when the retaining member 74 is located at the reference position, and the expansion roller 70 is indicated by a two-point chain when the retaining member 74 is located at the expansion position.

The pickup clamp 68 is configured to be movable in the horizontal direction and the vertical direction. A suction device is connected to the pickup clamp 68, and the component chip is adsorbed by the lower surface of the front end of the pickup clamp 68.

Now, referring to FIG. 11, in the picking step, first, the wafer 2 divided into individual component chips 78 is facing upward, and the frame 60 is placed on the upper surface of the holding member 74 at the reference position. Then, the frame 60 is fixed with a plurality of clamps 76. Then, by lowering the holding member 74 to the expanded position, radial tension is applied to the dicing film 58. In this way, as shown by the two-point chain in FIG. 11, the intervals between the component chips 78 attached to the dicing film 58 are expanded.

Next, the pick-up clamp 68 is positioned above the component wafer 78 to be picked up. Next, the pick-up clamp 68 is lowered, and the upper surface of the component wafer 78 is adsorbed by the lower surface of the front end of the pick-up clamp 68. Next, the pick-up clamp 68 is raised, and the component wafer 78 is peeled off from the dicing film 58 and picked up. Next, the picked-up component wafer 78 is transported to a predetermined transport position of a tray, etc. Then, this picking operation is performed sequentially for all component wafers 78.

As described above, according to the wafer processing method of the illustrated embodiment, since the periphery of the wafer 2 is covered by the cleavage surface 38, the deteriorated product generated by the irradiation of the laser beam LB will not remain on the periphery of the wafer 2, so the wafer 2 will not be damaged when the wafer 2 is transported.

2: Wafer

2a: Front side of the wafer

2b: Back side of the wafer

4: Components

10: Peripheral remaining area

14: Protective components

24: Modified layer

26: Cutting device

28: Chuck table

30: Cutting method

32: Main axis

34: Cutting blade

36: Cutting groove

38: Split surface

40: Outer ring of the remaining peripheral area

Claims (2)

A wafer processing method, wherein a component area divided into a plurality of components by a predetermined dividing line and a peripheral residual area surrounding the component area are formed on the front side of the wafer, and the wafer processing method comprises the following steps: A modified layer forming step, wherein the focal point of a laser beam having a wavelength penetrating the wafer is positioned from the back side of the wafer to the inside of the wafer corresponding to the peripheral residual area, and the wafer is irradiated with laser beam to form a ring-shaped modified layer at a position that does not reach the finished thickness of the wafer; A protective member arranging step, wherein the protective member is arranged on the front side of the wafer before or after the modified layer forming step; A modified layer removal step, which positions the cutting blade at the area corresponding to the modified layer from the back side of the wafer to cut the wafer and remove all the modified layers, while making the cleavage plane reach the front side of the wafer; An outer ring removal step, which uses the cleavage plane as a starting point to remove the outer ring of the peripheral residual area; and A grinding step, which grinds the back side of the wafer after the modified layer removal step and the outer ring removal step until the finished thickness of the wafer is reached. The wafer processing method of claim 1, wherein the following steps are included: A transfer step, in which after the grinding step, a dicing film is adhered to the back of the wafer, and the periphery of the dicing film is supported by a frame having an opening for accommodating the wafer, and a protective member is removed from the front of the wafer; and A splitting step, in which the wafer is processed along a predetermined splitting line to split the wafer into individual component chips.