JP7527728B2 - How the chip is manufactured - Google Patents

Description

The present invention relates to a method for manufacturing chips.

Chips for devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integration) are essential components in various electronic devices such as mobile phones and personal computers. These chips are manufactured, for example, in the following order:

First, a disk-shaped substrate made of a semiconductor material is prepared. Next, functional layers including conductive and insulating films are laminated on the surface of the substrate so that devices are formed in areas partitioned by a number of streets set in a grid pattern. Next, the wafer is divided along the streets to manufacture individual chips.

Here, when a functional layer is laminated on the surface of the substrate, a TEG (Test Element Group) for evaluating the performance of the device is generally provided on one of the multiple streets. In addition, an insulating film (e.g., a low-dielectric constant insulating film (Low-k film)) used to form the device is often provided over the entire surface of the substrate and then remains on multiple streets without being removed by etching or the like.

Therefore, when manufacturing chips, it is necessary to divide the wafer using a method that can remove not only the substrate but also the functional layers including the TEG and low-k film. A method using a laser beam, for example, is known for this purpose (see Patent Document 1).

In this method, a laser beam with a wavelength absorbed by the functional layer is first irradiated from the exposed front side of the functional layer to cause ablation, thereby removing the functional layer present in the multiple streets. Next, a modified layer is formed inside the substrate present in the multiple streets by irradiating the substrate from the rear side with a laser beam with a wavelength that passes through the substrate, with the focal point positioned inside the substrate. Next, an external force is applied to the wafer including the substrate on which the modified layer has been formed, and the wafer is divided along the multiple streets, with the modified layer serving as the dividing point.

JP 2007-173475 A

When manufacturing chips as described above, it is common to process multiple wafers in succession under the same conditions. However, if the thicknesses of the multiple wafers are different (or the average thickness if there is in-plane variation in the thickness of each wafer), it may not be possible to divide all of them as intended.

Specifically, when multiple wafers have different thicknesses, processing defects may occur, such as the wafer cracking in the area containing the device or not being divided. Such problems can be prevented by changing processing conditions, such as the average output of the laser beam and the position where the laser beam is focused when forming a modified layer inside the substrate (the depth of the focal point of the laser beam from the back surface of the substrate), according to the thickness of the wafer. However, changing processing conditions in this way may result in quality defects, such as variation in the quality of the resulting chips.

In view of the above, the object of the present invention is to provide a chip manufacturing method that can manufacture chips without causing processing defects and quality defects, even when multiple wafers have different thicknesses.

According to the present invention, a method for manufacturing chips includes a first wafer and a second wafer thicker than the first wafer, each of which has a substrate and a functional layer laminated on the surface of the substrate, and a device is formed by a part of the substrate and a part of the functional layer included in an area partitioned by a plurality of streets set in a lattice pattern, and the first wafer and the second wafer are divided along the plurality of streets to manufacture individual chips. The method includes a laser processing groove forming step of forming a laser processing groove that penetrates the functional layer and exposes the substrate by irradiating a laser beam having a wavelength absorbed by at least one of the substrate and the functional layer from the exposed surface side of the functional layer along the plurality of streets, and a laser processing groove forming step of forming a laser processing groove that penetrates the functional layer and exposes the substrate after the laser processing groove forming step. and a modified layer forming step in which a modified layer that serves as a splitting starting point is formed on the substrate by irradiating the substrate with a laser beam from the rear side of the substrate with a focal point positioned inside the substrate, and the laser beam is irradiated to the first wafer and the second wafer in the laser groove forming step such that the laser groove formed on the first wafer is shallower than the laser groove formed on the second wafer, with the distance between the focal point of the laser beam on the first wafer and the rear side of the substrate being equal to the distance between the focal point of the laser beam on the second wafer and the rear side of the substrate in the laser groove forming step.

Preferably, in the laser groove formation step, a laser beam having a wavelength that is absorbed by the functional layer is irradiated from the surface side of the functional layer along the multiple streets, and then a laser beam having a wavelength that is absorbed by the substrate is irradiated from the surface side of the functional layer along the multiple streets.

In the present invention, while maintaining a constant distance between the focal point of the laser beam and the back surface of the substrate in the laser groove forming step, a laser beam is irradiated onto each of the thin wafer (first wafer) and the thick wafer (second wafer) so that the laser groove formed in the thin wafer (first wafer) is shallower than the laser groove formed in the thick wafer (second wafer).

As a result, in the present invention, even when the modified layer formation step is performed under the same conditions so that the modified layer is formed at a predetermined depth from the back surface of the substrate, without setting separate processing conditions for the thin wafer and the thick wafer, the bottom surface of the laser-processed groove can be positioned near the modified layer. Therefore, when an external force is applied to each of the thin wafer and the thick wafer, there is a high probability that a crack originating from the modified layer will progress toward the laser-processed groove.

In other words, in the present invention, the difference in thickness between the region of the substrate (unprocessed region) that overlaps with the laser-processed groove in the thickness direction of the thin wafer and the unprocessed region of the thick wafer can be made smaller than the difference in thickness between the thin wafer and the thick wafer. Therefore, even when the modified layer formation step is performed under the same conditions for each of the thin wafer and the thick wafer, the substrates of both wafers can be in the same processed state.

As a result, all of the multiple wafers can be divided without causing processing defects, and individual chips can be manufactured from each wafer. Furthermore, in the present invention, all of the multiple wafers can be divided without changing processing conditions according to the wafer thickness, such as the average output of the laser beam and the position where the laser beam is focused when forming a modified layer inside the substrate (the depth of the focal point of the laser beam from the back surface of the substrate), thereby preventing the occurrence of quality defects.

FIG. 1(A) is a perspective view showing an example of a wafer, FIG. 1(B) is a cross-sectional view showing an example of a thin wafer, and FIG. 1(C) is a cross-sectional view showing an example of a thick wafer. FIG. 2 is a flow chart showing an example of a method for manufacturing a chip. FIG. 3 is a perspective view that shows a schematic diagram of a laser processing apparatus and a wafer that perform the laser groove forming step. FIG. 4(A) is a cross-sectional view showing a schematic example of a thin wafer having a laser-processed groove formed therein, and FIG. 4(B) is a cross-sectional view showing a schematic example of a thick wafer having a laser-processed groove formed therein. FIG. 5(A) is a cross-sectional view showing a schematic example of a thin wafer on which a modified layer is formed, and FIG. 5(B) is a cross-sectional view showing a schematic example of a thick wafer on which a modified layer is formed. FIG. 6(A) is a cross-sectional view showing a schematic of the expanding apparatus and the wafer before the division step is performed, and FIG. 6(B) is a cross-sectional view showing a schematic of the expanding apparatus and the wafer after the division step is performed.

The embodiments of the present invention will be described with reference to the attached drawings. Fig. 1(A) is a perspective view showing an example of a wafer to be divided to manufacture chips, Fig. 1(B) is a cross-sectional view showing an example of a thin wafer (first wafer) having the structure shown in Fig. 1(A), and Fig. 1(C) is a cross-sectional view showing an example of a thick wafer having the structure shown in Fig. 1(A).

The wafer 11 shown in FIG. 1(A) has a disk-shaped substrate 13 with a notch formed on the outer edge to indicate the crystal orientation. The substrate 13 is made of, for example, silicon (Si), and a portion of its surface (top surface) side is provided with an impurity region doped with impurities.

There are no limitations on the material, shape, structure, size, etc. of the substrate 13. The substrate 13 may be made of materials such as semiconductors other than silicon, ceramics, resins, and metals. The substrate 13 may not have an impurity region. The outer edge of the substrate 13 may have a flat portion indicating the crystal orientation, a so-called orientation flat, instead of a notch.

A functional layer 15 including multiple insulating films and multiple conductive films is laminated on the surface of the substrate 13. The wafer 11 is composed of the laminated substrate 13 and functional layer 15, and has a thickness of, for example, 275 μm to 325 μm.

In addition, in the wafer 11, devices (ICs, etc.) 19 are formed from parts of the substrate 13 (intrinsic semiconductor regions and impurity regions where no impurities exist) and parts of the functional layer 15 (insulating films and conductive films) contained in the areas partitioned by a plurality of streets 17 set in a lattice pattern. There are no limitations on the type, quantity, shape, structure, size, arrangement, etc. of the devices 19.

In this embodiment, multiple wafers of different thicknesses are divided to manufacture individual chips as shown in Figures 1(B) and 1(C). The thin wafer (first wafer) 11a shown in Figure 1(B) and the thick wafer (second wafer) 11b shown in Figure 1(C) have the same structure, except that the substrate 13a shown in Figure 1(B) is thinner than the thick substrate 13b shown in Figure 1(C).

Figure 2 is a flowchart showing an example of a method for manufacturing a chip according to this embodiment. In this method, a laser beam is first irradiated onto the exposed surface side of the functional layer 15 to form a laser groove that penetrates the functional layer 15 and exposes the substrate 13 (13a, 13a) (laser groove formation step: S1).

Figure 3 is a perspective view that shows a schematic diagram of a laser processing device and a wafer 11 that perform the laser groove forming step (S1). Note that the X-axis direction and the Y-axis direction shown in Figure 3 are directions that are perpendicular to each other on a horizontal plane, and the Z-axis direction is a direction (vertical direction) that is perpendicular to the X-axis direction and the Y-axis direction.

The laser processing device 2 shown in FIG. 3 has a circular holding surface that is roughly parallel to the X-axis and Y-axis directions, and has a chuck table 4 that can hold a wafer 11 (11a, 11b) on this holding surface. The chuck table 4 is connected to a suction mechanism (not shown).

The suction mechanism has an ejector or the like and is capable of generating negative pressure on the holding surface of the chuck table 4. When the suction mechanism operates with the wafer 11 (11a, 11b) placed on the holding surface, the wafer 11 (11a, 11b) is suction-held to the chuck table 4.

Furthermore, the chuck table 4 is connected to an X-axis direction moving mechanism (not shown) and a Y-axis direction moving mechanism (not shown). The X-axis direction moving mechanism and the Y-axis direction moving mechanism have, for example, a ball screw and a motor. When the X-axis direction moving mechanism and/or the Y-axis direction moving mechanism operates, the chuck table 4 moves along the X-axis direction and/or the Y-axis direction.

The chuck table 4 is also connected to a rotation mechanism (not shown). The rotation mechanism includes, for example, a spindle and a motor. When the rotation mechanism operates, the chuck table 4 rotates around a straight line along the Z-axis direction that passes through the center of the holding surface.

A head 8 of the laser beam irradiation unit 6 is provided above the chuck table 4. The head 8 is provided at the tip (one end) of a connecting part 10 that extends along the X-axis direction. The head 8 houses an optical system such as a focusing lens and a mirror, and the connecting part 10 houses an optical system such as a mirror and/or a lens.

The other end of the connecting part 10 is connected to a Z-axis direction movement mechanism (not shown). The Z-axis direction movement mechanism includes, for example, a ball screw and a motor. When the Z-axis direction movement mechanism operates, the head 8 and the connecting part 10 move along the Z-axis direction.

The laser beam irradiation unit 6 also has a laser oscillator (not shown) that generates a laser beam with a wavelength (e.g., 355 nm) that is absorbed by at least one of the substrate 13 (13a, 13a) and the functional layer 15.

The laser oscillator has a laser medium such as Nd:YAG. When a laser beam is generated by the laser oscillator, the laser beam is irradiated onto the holding surface side of the chuck table 4 via the optical system of the connection part 10 and the head 8.

An imaging unit 12 capable of imaging the holding surface side of the chuck table 4 is provided on the side of the connecting portion 10. The imaging unit 12 has a light source such as an LED (Light Emitting Diode) that emits visible light or infrared light, an objective lens, and an imaging element such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor. The objective lens of the imaging unit 12 is provided at a position separated along the Y-axis direction from the focusing lens housed in the head 8.

The laser processing groove formation step (S1) using the laser processing device 2 is performed, for example, in the following order. First, the wafer 11 (11a, 11b) is placed on the holding surface of the chuck table 4 with the functional layer 15 facing up. Next, the suction mechanism is operated so that the wafer 11 (11a, 11b) is suction-held on the chuck table 4.

Then, based on an image of the exposed surface of the functional layer 15 formed by imaging with the imaging unit 12 using visible light, the rotation mechanism rotates the chuck table 4 so that the multiple streets 17 are parallel to the X-axis direction or the Y-axis direction. Next, the X-axis direction movement mechanism and the Y-axis direction movement mechanism move the chuck table 4 so that some of the multiple streets 17 are positioned directly under the head 8.

Then, while the X-axis direction moving mechanism or the Y-axis direction moving mechanism moves the chuck table 4, the laser beam irradiation unit 6 irradiates a laser beam having a wavelength that is absorbed by at least one of the substrate 13 (13a, 13a) and the functional layer 15.

The laser beam is a pulsed laser beam with an average output of 0.1 W to 50.0 W (typically 1.0 W to 1.5 W) and a repetition frequency of 10 kHz to 50 MHz (typically 40 kHz to 160 kHz). The movement speed (processing feed speed) of the chuck table 4 in the X-axis or Y-axis direction is, for example, 50 mm/s to 1000 mm/s.

As a result, ablation occurs in the functional layer 15 and the substrate 13 (13a, 13a) that overlap in the Z-axis direction with the street 17 irradiated with the laser beam, and a laser groove 21 is formed that penetrates the functional layer 15 and exposes the substrate 13 (13a, 13a). Furthermore, by sequentially irradiating the remaining streets 17 with this laser beam, laser grooves 21 are formed in all of the multiple streets 17.

Figure 4(A) is a cross-sectional view that shows a schematic of a thin wafer 11a with a laser-machined groove 21a formed therein, and Figure 4(B) is a cross-sectional view that shows a schematic of a thick wafer 11b with a laser-machined groove 21b formed therein.

In the laser processing groove forming step (S1), for example, while maintaining the height of the head 8 of the laser beam irradiation unit 6 constant with respect to the holding surface of the chuck table 4 as a reference (i.e., maintaining the height of the focal point F1 of the laser beam L1 constant with respect to the holding surface of the chuck table 4 as a reference), the laser beam L1 is irradiated onto the thin wafer 11a and the thick wafer 11b so that the laser processing groove 21a formed in the thin wafer 11a is shallower than the laser processing groove 21b formed in the thick wafer 11b.

In other words, while maintaining a constant distance d1 between the focal point F1 of the laser beam L1 focused by the focusing lens 8a and the rear surface of the substrate 13 (13a, 13b), the laser beam L1 is irradiated onto the thin wafer 11a and the thick wafer 11b so that the laser processed groove 21a formed in the thin wafer 11a is shallower than the laser processed groove 21b formed in the thick wafer 11b.

In the manufacturing method of the chip shown in FIG. 2, after the laser groove forming step (S1), a laser beam is irradiated onto the back side of the substrate 13 (13a, 13a) to form a modified layer that will be the starting point for splitting in the substrate 13 (13a, 13a) (modified layer forming step: S2).

In the chip manufacturing method shown in FIG. 2, the order in which the laser groove formation step (S1) and the modified layer formation step (S2) are performed on the thin wafer 11a and the thick wafer 11b is not limited.

For example, the laser groove forming step (S1) and the modified layer forming step (S2) may be performed consecutively on one of the thin wafer 11a and the thick wafer 11b, and then the laser groove forming step (S1) and the modified layer forming step (S2) may be performed consecutively on the other.

Alternatively, the laser groove formation step (S1) may be performed consecutively on both the thin wafer 11a and the thick wafer 11b, and then the modified layer formation step (S2) may be performed consecutively on both.

The modified layer forming step (S2) is performed, for example, by using a laser irradiation device having a structure similar to that of the laser processing device 2 shown in FIG. 3. However, in the modified layer forming step (S2), a laser beam having a wavelength (for example, 1099 nm) that is transmitted through the substrate 13 (13a, 13a) is used.

Therefore, the laser irradiation device used in the modified layer formation step (S2) has a laser oscillator that generates a laser beam of this wavelength. In addition, if such a laser oscillator is included in the laser processing device 2 shown in FIG. 3, the modified layer formation step (S2) may be performed using the laser processing device 2.

The modified layer forming step (S2) using the laser irradiation device is performed, for example, in the following order. First, the wafer 11 (11a, 11b) is placed on the holding surface of the chuck table with the substrate 13 (13a, 13b) facing up. Next, the suction mechanism is operated so that the wafer 11 (11a, 11b) is suction-held on the chuck table.

Then, based on an image of the surface of the substrate 13 (13a, 13b) formed by imaging with an imaging unit using infrared rays, the rotation mechanism rotates the chuck table so that the multiple streets 17 are parallel to the X-axis direction or the Y-axis direction. Next, the Z-axis movement mechanism moves the head of the laser beam irradiation unit, which has an optical system such as a focusing lens, so that the distance between the head and the back surface of the substrate 13 (13a, 13b) is a predetermined distance.

Then, the X-axis direction movement mechanism and the Y-axis direction movement mechanism move the chuck table so that some of the multiple streets 17 are positioned directly under the head. Next, while the X-axis direction movement mechanism or the Y-axis direction movement mechanism moves the chuck table, the laser beam irradiation unit irradiates a laser beam with a wavelength that passes through the substrate 13 (13a, 13b). At this time, the focal point of the laser beam is positioned inside the substrate 13 (13a, 13b).

The laser beam is a pulsed laser beam with an average output of 0.5 W to 3.0 W (typically 1.5 W) and a repetition frequency of 80 kHz to 150 kHz (typically 100 kHz). The movement speed (processing feed speed) of the chuck table in the X-axis or Y-axis direction is, for example, 50 mm/s to 1000 mm/s.

As a result, modified layers are formed inside the substrates 13 (13a, 13b) that overlap in the Z-axis direction with the street 17 irradiated with the laser beam. Furthermore, by sequentially irradiating the remaining streets 17 with the laser beam, modified layers are formed inside all of the substrates 13 (13a, 13b) on the multiple streets 17.

Figure 5(A) is a cross-sectional view that shows a schematic of a thin wafer 11a on which a modified layer 23a is formed, and Figure 5(B) is a cross-sectional view that shows a schematic of a thick wafer 11b on which a modified layer 23b is formed.

In the modified layer formation step (S2), for example, the laser beam L2 is irradiated onto the thin wafer 11a and the thick wafer 11b without changing the head height based on the back surface of the substrate 13 (13a, 13b). In other words, the laser beam L2 is irradiated onto the thin wafer 11a and the thick wafer 11b while maintaining a constant distance d2 between the focal point F2 of the laser beam L2 focused by the focusing lens 8b and the back surface of the substrate 13 (13a, 13b).

In this case, modified layers 23a and 23b can be formed on wafers 11 (11a and 11b) so that the distance between modified layer 23a formed on thin wafer 11a and the bottom surface of laser-processed groove 21a is approximately equal to the distance between modified layer 23b formed on thick wafer 11b and the bottom surface of laser-processed groove 21b.

In the chip manufacturing method shown in FIG. 2, after the modified layer forming step (S2), an external force is applied to divide the wafer 11 (11a, 11b) (division step: S3). FIG. 6(A) is a cross-sectional view showing the expanding device and the wafer 11 before the division step (S3), and FIG. 6(B) is a cross-sectional view showing the expanding device and the wafer 11 after the division step (S3).

In the division step (S3), first, an annular frame 27 is attached to the peripheral region of the upper surface of the disk-shaped expanding tape 25, and the substrate 13 (13a, 13b) of the wafer 11 (11a, 11b) is attached to the central region (see FIG. 6(A)). Then, the expanding tape 25 is expanded by the expanding device 14 shown in FIG. 6(A) and FIG. 6(B).

The expanding device 14 has a cylindrical drum 16 and a support unit 18. The support unit 18 has an annular support base 20 that is arranged to surround the upper end of the drum 16. The support base 20 is capable of supporting the peripheral area of the expanding tape 25 and the frame 27.

The support unit 18 also has a number of clamps 22 arranged at approximately equal intervals along the circumferential direction of the support base 20. The clamps 22 can grip and fix the peripheral area of the expandable tape 25 and the frame 27 together with the support base 20.

The support unit 18 also has multiple rods 24 arranged at approximately equal intervals along the circumferential direction under the support base 20. The multiple rods 24 support the support base 20 and the multiple clamps 22, and are raised and lowered by a lifting mechanism (not shown) such as an air cylinder.

When expanding the expanding tape 25, first, the rods 24 are raised and lowered so that the upper surface of the support table 20 is positioned on the same plane as the upper end of the drum 16. Next, the peripheral area of the expanding tape 25 and the frame 27 are fixed by the clamps 22 so that the substrates 13 (13a, 13b) of the wafers 11 (11a, 11b) face downward (see FIG. 6(A)).

Next, the rods 24 are lowered together with the support table 20 and the clamps 22. This causes the central region of the expand tape 25 to expand in the planar direction of the wafers 11 (11a, 11b) by the amount that the upper end of the drum 16 and the support table 20 are separated from each other. At this time, a force acts on the wafers 11 (11a, 11b) attached to the expand tape 25 to expand them in the planar direction.

As a result, the modified layers 23a, 23b present in the substrate 13 (13a, 13b) of the wafer 11 (11a, 11b) become the starting point for splitting, causing cracks in the substrate 13 (13a, 13b), which then extend to the laser-machined grooves 21a, 21b. As a result, the wafer 11 (11a, 11b) is split at the multiple streets 17 to produce individual chips (see FIG. 6B).

In the chip manufacturing method shown in FIG. 2, while maintaining a constant distance between the focal point F1 of the laser beam L1 and the back surface of the substrate 13 (13a, 13b) in the laser groove forming step (S1), the laser beam L1 is irradiated onto each of the thin wafer 11a and the thick wafer 11b so that the laser groove 21a formed in the thin wafer 11a is shallower than the laser groove 21b formed in the thick wafer 11b.

As a result, in the chip manufacturing method shown in FIG. 2, even when the modified layer forming step (S2) is performed under the same conditions so that the modified layers 23a, 23b are formed at a predetermined depth from the back surface of the substrate 13 (13a, 13b) without setting individual processing conditions for each of the thin wafer 11a and the thick wafer 11b, the bottom surfaces of the laser processed grooves 21a, 21b can be positioned near the modified layers 23a, 23b. Therefore, when an external force is applied to each of the thin wafer 11a and the thick wafer 11b, there is a high probability that cracks starting from the modified layers 23a, 23b will progress toward the laser processed grooves 21a, 21b.

In other words, in the chip manufacturing method shown in FIG. 2, the difference in thickness between the region (unprocessed region) of the substrate 13a that overlaps the laser-processed groove 21a in the thickness direction of the thin wafer 11a and the unprocessed region of the thick wafer 11b can be made smaller than the difference in thickness between the thin wafer 11a and the thick wafer 11b. Therefore, even when the modified layer formation step (S2) is performed under the same conditions for each of the thin wafer 11a and the thick wafer 11b, the substrates 13 (13a, 13b) of both wafers 11 (11a, 11b) can be made to have the same processed state.

As a result, the thin wafer 11a and the thick wafer 11b can be divided into individual chips without causing processing defects. In addition, in the chip manufacturing method shown in FIG. 2, the thin wafer 11a and the thick wafer 11b can be divided into individual chips without changing the processing conditions such as the average output of the laser beam L1 used in the laser groove formation step (S1) and the laser beam L2 used in the modified layer formation step (S2) and the position where the laser beam L2 is focused in the modified layer formation step (S2) (the depth of the focusing point F2 of the laser beam L2 from the back surface of the substrate 13 (13a, 13b)) according to the thickness of the wafer 11 (11a, 11b), thereby preventing the occurrence of quality defects.

The above-mentioned method for manufacturing chips is one aspect of the present invention, and the present invention also includes methods for manufacturing chips that have different characteristics from this method.

For example, in the laser groove forming step (S1), the back surface of the substrate 13 (13a, 13b) of the wafer 11 (11a, 11b) is attached to the central region of a tape, and the laser beam L1 may be irradiated to the wafer 11 (11a, 11b) in a state where the wafer 11 (11a, 11b) is integrated with an annular frame attached to the peripheral region of the tape. That is, in the laser groove forming step (S1), the wafer 11 (11a, 11b) may be irradiated with the laser beam L1 in a state where the wafer 11 (11a, 11b) is suction-held to the chuck table 4 via the tape.

Similarly, in the modified layer forming step (S2), the exposed surface of the functional layer 15 of the wafer 11 (11a, 11b) may be attached to the central region of the tape and the laser beam L2 may be irradiated to the wafer 11 (11a, 11b) in a state where the wafer 11 (11a, 11b) is integrated with an annular frame attached to the peripheral region of the tape. That is, in the modified layer forming step (S2), the laser beam L2 may be irradiated to the wafer 11 (11a, 11b) in a state where the wafer 11 (11a, 11b) is suction-held on the chuck table via the tape.

Alternatively, in the modified layer forming step (S2), the back surface of the wafer 11 (11a, 11b) may be attached to the central region of the tape, and the laser beam L2 may be irradiated to the wafer 11 (11a, 11b) in a state where the wafer 11 (11a, 11b) is integrated with an annular frame attached to the peripheral region of the tape. That is, in the modified layer forming step (S2), the laser beam L2 may be irradiated to the wafer 11 (11a, 11b) through the tape.

When the wafer 11 (11a, 11b) is integrated with the frame in this manner, it is preferable in that the wafer 11 (11a, 11b) can be easily handled. In addition, when tape is applied to the exposed surface of the functional layer 15 in the modified layer formation step (S2), it is preferable in that damage to the device 19 due to contact with the chuck table can be prevented.

On the other hand, when the wafer 11 (11a, 11b) is directly suction-held on the chuck table, this is preferable in that the chip manufacturing process is simplified. Furthermore, when the wafer 11 (11a, 11b) with tape attached to its back surface is used in the modified layer formation step (S2), this is preferable in that it is not necessary to peel off the tape attached to the back surface of the wafer 11 (11a, 11b) and transfer it to the front surface of the wafer 11 (11a, 11b) in the laser-machined groove formation step (S1).

The laser groove forming step (S1) may also be composed of a first step (S1-1) of forming a laser groove that divides the functional layer 15, and a second step (S1-2) of forming a laser groove that extends into the interior of the substrate 13 (13a, 13b) and has a narrower width than the laser groove formed in the first step (S1-1).

The width of the laser groove formed can be adjusted, for example, by controlling the diameter of the laser beam using an optical element such as a beam expander. Alternatively, the width of the laser groove formed on the wafer 11 (11a, 11b) can be adjusted by adjusting the distance between the point on the wafer 11 (11a, 11b) where the laser beam is irradiated (the irradiated portion) and the focal point of the laser beam.

Specifically, the distance between the irradiated portion and the focal point of the laser beam in the second step (S1-2) may be made shorter than the distance between the irradiated portion and the focal point of the laser beam in the first step (S1-1), so that the width of the laser processed groove formed in the second step (S1-2) is narrower than the processed groove formed in the first step (S1-1).

In the first step (S1-1), for example, a laser beam having a wavelength that is absorbed by the functional layer 15 is irradiated along the multiple streets 17 from the exposed surface side of the functional layer 15. In the second step (S1-2), a laser beam having a wavelength that is absorbed by the substrate 13 (13a, 13b) is irradiated along the multiple streets 17 from the surface side of the substrate 13 (13a, 13b) where the functional layer 15 is cut and exposed.

Here, in the first step (S1-1), the focal point of the laser beam may be set arbitrarily. That is, in the first step (S1-1), the laser beam may be irradiated onto the thin wafer 11a and the thick wafer 11b while maintaining a constant distance between the focal point of the laser beam and the back surface of the substrate 13 (13a, 13b), or the laser beam may be irradiated onto the thin wafer 11a and the thick wafer 11b while maintaining a constant distance between the focal point of the laser beam and the exposed surface of the functional layer 15.

On the other hand, in the second step (S1-2), for example, while maintaining the height of the head 8 of the laser beam irradiation unit 6 constant with respect to the holding surface of the chuck table 4 (i.e., maintaining the height of the focal point of the laser beam constant with respect to the holding surface of the chuck table 4), the laser beam is irradiated onto the thin wafer 11a and the thick wafer 11b so that the laser processed grooves formed in the thin wafer 11a are shallower than the laser processed grooves formed in the thick wafer 11b.

In other words, while maintaining a constant distance between the focal point of the laser beam and the back surface of the substrate 13 (13a, 13b), the laser beam is irradiated onto the thin wafer 11a and the thick wafer 11b so that the laser processed groove 21a formed in the thin wafer 11a is shallower than the laser processed groove 21b formed in the thick wafer 11b.

When the laser groove forming step (S1) is thus composed of a first step (S1-1) and a second step (S1-2), this is preferable in that it makes it easier to reliably divide the functional layer 15 in the first step (S1-1) and to form a laser groove of the desired depth in the second step (S1-2). On the other hand, when the laser groove forming step (S1) is composed of a single step, this is preferable in that it simplifies the chip manufacturing process.

In addition, in the modified layer forming step (S2), the irradiation of the laser beam L2 onto the multiple streets 17 may be repeated multiple times. For example, the laser beam L2 may be irradiated onto the multiple streets 17 in a state where the distance between the focal point F2 of the laser beam L2 and the rear surface of the substrate 13 (13a, 13b) is a predetermined value, and then the laser beam L2 may be irradiated onto the multiple streets 17 again in a state where the distance is a value that is slightly increased or decreased from the predetermined value.

In this case, modified layers 23a, 23b can be formed in a wide area of substrate 13 (13a, 13b) along the thickness direction of wafer 11 (11a, 11b). This further reduces the likelihood of processing defects occurring when wafer 11 (11a, 11b) is divided to manufacture individual chips.

In addition, in the division step (S3), the wafer 11 (11a, 11b) may be divided into individual chips by pressing a blade against the multiple streets 17 on which the laser-machined grooves 21a, 21b are formed to impart bending stress, a process known as breaking.

In addition, the structures and methods of the above-described embodiments and variations can be modified as appropriate without departing from the scope of the present invention.

11 (11a, 11b): Wafer 13 (13a, 13b): Substrate 15: Functional layer 17: Street 19: Device 21a, 21b: Laser processed groove 23a, 23b: Modified layer 25: Expanded tape 27: Frame 2: Laser processing device 4: Chuck table 6: Laser beam irradiation unit 8: Head 8a, 8b: Condenser lens 10: Connection part 12: Imaging unit 14: Expanding device 16: Drum 18: Support unit 20: Support stand 22: Clamp 24: Rod

Claims (2)

A method for manufacturing chips, comprising the steps of: dividing a first wafer and a second wafer thicker than the first wafer, each of which has a substrate and a functional layer laminated on a surface of the substrate, the first wafer and the second wafer having a thickness greater than the first wafer, the first wafer and the second wafer being formed on the substrate along a plurality of streets defined in a lattice pattern, to manufacture individual chips;
a laser groove forming step of irradiating a laser beam having a wavelength absorbed by at least one of the substrate and the functional layer from the exposed surface side of the functional layer along the plurality of streets to form a laser groove penetrating the functional layer and exposing the substrate;
and a modified layer forming step of forming a modified layer serving as a splitting starting point in the substrate by irradiating a laser beam having a wavelength that transmits the substrate from the rear side of the substrate with a focusing point positioned inside the substrate after the laser groove forming step,
a laser beam is irradiated onto the first wafer and the second wafer in the laser groove forming step such that the distance between the focal point of the laser beam in the laser groove forming step for the first wafer and the rear surface of the substrate is equal to the distance between the focal point of the laser beam in the laser groove forming step for the second wafer and the rear surface of the substrate, and the laser groove formed in the first wafer is shallower than the laser groove formed in the second wafer. The method for manufacturing a chip according to claim 1, wherein in the laser groove forming step, a laser beam having a wavelength absorbed by the functional layer is irradiated from the surface side of the functional layer along the multiple streets, and then a laser beam having a wavelength absorbed by the substrate is irradiated from the surface side of the functional layer along the multiple streets.

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