TWI868313B - Chip manufacturing method - Google Patents

Abstract

The subject of the present invention is to provide a chip manufacturing method that can suppress the degradation of chip quality. The solution is a chip manufacturing method, which is a chip manufacturing method for dividing a wafer into a plurality of chips along a predetermined dividing line, and comprises: a wafer holding process, which is to hold the first side of the wafer with a suction cup and expose the second side of the wafer; a modified layer forming process, which is to irradiate from the second side of the wafer by positioning a laser beam that is transmissive to the wafer and focused at a first focal point and a second focal point in the interior of the wafer, and to form modified areas in the areas where the first focal point and the second focal point are positioned, respectively, to form a modified layer including a plurality of modified areas arranged along the predetermined dividing line; and a dividing process, which is to apply external force to the wafer to divide the wafer into a plurality of the chips along the predetermined dividing line.

Description

Chip manufacturing method

The present invention relates to a chip manufacturing method for dividing a wafer into a plurality of chips.

In the manufacturing process of device chips, a wafer is used in which a plurality of regions divided by a plurality of predetermined dividing lines (slicing streets) intersecting each other are respectively formed with devices such as ICs. By dividing the wafer along the predetermined dividing lines, a plurality of device chips each having a device can be manufactured.

For wafer division, a cutting device is mainly used, which has a suction table for holding the wafer and a main shaft (rotating axis) on which a circular cutting blade for cutting the wafer is mounted. The cutting blade is rotated to cut into the wafer held by the suction table, so as to cut and divide the wafer along a predetermined dividing line.

On the other hand, in recent years, attention has also been paid to the technology of dividing wafers by laser processing. For example, a method has been proposed in which a laser beam that is transparent to the wafer is focused inside the wafer to form a modified layer (modified layer (modified layer)) inside the wafer along a predetermined dividing line (see patent document 1). The area of the wafer where the modified layer is formed is more fragile than other areas. Therefore, if an external force is applied to the wafer with the modified layer formed, the wafer can be divided starting from the modified layer.

However, depending on the thickness and material of the wafer, only one modified layer is formed on the wafer, and even if an external force is applied, the wafer will not be properly divided starting from the modified layer. At this time, multiple modified layers are formed along each predetermined dividing line in the thickness direction of the wafer (see Patent Document 2). For example, by gradually changing the height of the focal point of the laser beam, the laser beam is irradiated multiple times along each predetermined dividing line to form multiple modified layers on the wafer. [Prior Technical Document] [Patent Document]

[Patent Document 1] Japanese Patent Publication No. 2004-179302 [Patent Document 2] Japanese Patent Publication No. 2009-10105

[The problem that the invention wants to solve]

In the process of forming the modified layer, for example, by irradiating a laser beam, a plurality of modified regions (modified regions) are formed at predetermined intervals along a predetermined dividing line inside the wafer. In this case, the modified layer is equivalent to a layer including a plurality of modified regions arranged along the predetermined dividing line.

When a modified region is formed, a crack (cleavage plane) will occur in the modified region. If the crack propagating from the modified region reaches the region where the modified region is to be formed, when the laser beam is subsequently irradiated to the region, the crack will cause diffuse reflection of the laser beam.

If diffuse reflection of the laser beam occurs inside the wafer, it becomes difficult to properly form a modified area in the area irradiated with the laser beam, and the modified layer cannot fully function as the starting point for wafer division. In addition, due to diffuse reflection of the laser beam, the cracks generated in the modified area may extend radially in unexpected directions or may easily exceed expectations and form excessively long cracks. Due to these irregular cracks, there is a risk that the wafer may be induced to break in an unexpected direction when the wafer is divided in the subsequent process.

As described above, if diffuse reflection of the laser beam occurs when forming the modified area, it will become difficult to properly divide the wafer along the predetermined dividing line when an external force is applied to the wafer. As a result, the wafer may be damaged when dividing the wafer, or the side surface (dividing surface) of the wafer may become uneven, which may lead to a decrease in the quality of the wafer.

The present invention is invented in view of the related problems, and its purpose is to provide a chip manufacturing method that can suppress the quality degradation of the chip. [Means for solving the problem]

According to one aspect of the present invention, a chip manufacturing method is provided, which is a chip manufacturing method for dividing a wafer into a plurality of chips along a predetermined dividing line, comprising: a wafer holding process, in which a first side of the wafer is held by a suction cup and a second side of the wafer is exposed; a modified layer forming process, in which a laser beam having transmissivity to the wafer and focused at a first focal point and a second focal point is positioned inside the wafer, and a modified layer is formed from the second side of the wafer. Irradiation is performed to form modified regions respectively in the regions where the first focal point and the second focal point are positioned, so as to form a modified layer including a plurality of modified regions arranged along the predetermined dividing line; and a dividing process is performed to apply external force to the wafer to divide the wafer into a plurality of chips along the predetermined dividing line; in the modified layer forming process, the cracks generated in the modified region formed in the region where the first focal point is positioned are connected with the cracks generated in the modified region formed in the region where the second focal point is positioned.

Furthermore, it is ideal that the modified layer forming process comprises: a first modified layer forming process, which is performed by irradiating the laser beam from the second side of the wafer to form a first modified layer including a plurality of modified regions arranged along the predetermined dividing line; and a second modified layer forming process, which is performed by irradiating the laser beam from the second side of the wafer to form a second modified layer including a plurality of modified regions arranged along the predetermined dividing line on the first side of the wafer closer to the first side than the first modified layer.

Furthermore, according to another aspect of the present invention, a chip manufacturing method is provided, which is a chip manufacturing method for dividing a wafer into a plurality of chips along a predetermined dividing line, and comprises: a wafer holding process, in which a suction cup is used to hold the first side of the wafer and the second side of the wafer is exposed; a modified layer forming process, in which a laser beam that is transmissive to the wafer and focused at a first focal point or even a fourth focal point is irradiated from the second side of the wafer in a manner that the first focal point and the second focal point are positioned at the first area inside the wafer, and the third focal point and the fourth focal point are positioned at the second area closer to the first side of the wafer than the first area inside the wafer, so as to irradiate the first focal point from the second side of the wafer. The light spot and even the area where the fourth light-converging point is positioned form modified areas respectively to form a first modified layer and a second modified layer including a plurality of the modified areas arranged along the predetermined dividing line; and a splitting process is to apply external force to the wafer to split the wafer into a plurality of the chips along the predetermined dividing line; in the modified layer forming process, the cracks generated in the modified area formed in the area where the first light-converging point is positioned are connected to the cracks generated in the modified area formed in the area where the second light-converging point is positioned, and the cracks generated in the modified area formed in the area where the third light-converging point is positioned are connected to the cracks generated in the modified area formed in the area where the fourth light-converging point is positioned. [Effect of the invention]

In a chip manufacturing method of one aspect of the present invention, a laser beam focused at a plurality of focal points is irradiated onto the wafer, and modified regions are formed in the regions where the focal points are located, respectively, to connect the cracks generated in one modified region with the cracks generated in other modified regions.

According to the above-mentioned chip manufacturing method, the focal point of the laser beam can be positioned at the region inside the wafer where no cracks are formed to form a modified region, while cracks connecting adjacent modified regions are formed. In this way, diffuse reflection of the laser beam can be suppressed and a modified layer can be appropriately formed. As a result, the wafer becomes easy to be split along a predetermined splitting line, and the quality degradation of the chip can be suppressed.

Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. First, a structure example of a wafer that can be used in the chip manufacturing method of the present embodiment will be described. FIG1(A) is a perspective view showing a wafer 11.

The wafer 11 is formed into a disk shape using a material such as silicon, and has a substantially parallel front surface (first surface) 11a and a rear surface (second surface) 11b. The wafer 11 is divided into a plurality of rectangular regions by a plurality of predetermined dividing lines (dicing streets) 13 arranged in a grid pattern in a manner intersecting each other.

Devices 15 such as IC (Integrated Circuit), LSI (Large Scale Integration), and MEMS (Micro Electro Mechanical Systems) are formed on the surface 11a of the plurality of regions divided by the predetermined dividing lines 13. When the wafer 11 is divided along the predetermined dividing lines 13, a plurality of chips (device chips) each having the device 15 can be obtained.

Furthermore, the material, shape, structure, size, etc. of the wafer 11 are not limited. For example, the wafer 11 may be a substrate made of semiconductors other than silicon (GaAs, SiC, InP, GaN, etc.), sapphire, glass, ceramics, resin, metal, etc. Also, the type, quantity, shape, structure, size, and arrangement of the device 15 are not limited, and the device 15 may not be formed on the wafer 11.

A splitting starting point is formed on the wafer 11, which functions as a splitting starting point (a splitting trigger point) when the wafer 11 is split in a subsequent process. For example, laser processing is applied to the wafer 11 to modify (change quality) the inside of the wafer 11 along a predetermined splitting line 13, thereby forming a splitting starting point.

The region (modified region) inside the wafer 11 where the splitting starting point is formed is weaker than other regions of the wafer 11. Therefore, if an external force is applied to the wafer 11 where the splitting starting point is formed, the wafer 11 will break along the predetermined splitting line 13 starting from the splitting starting point. In this way, a plurality of device chips each having a device 15 are obtained.

When forming the splitting starting point on the wafer 11 by laser processing, for example, a laser beam is irradiated from the back side 11b of the wafer 11. At this time, a protective member 17 is attached to the front side 11a of the wafer 11. FIG1(B) is a perspective view showing the wafer 11 to which the protective member 17 is attached.

As the protective member 17, a sheet (tape) having a circular film-shaped substrate and an adhesive layer (paste layer) provided on the substrate can be used. For example, the substrate is made of a resin such as polyolefin, polyvinyl chloride, polyethylene terephthalate, etc., and the adhesive layer is made of an epoxy-based, acrylic-based, or rubber-based adhesive. In addition, the adhesive layer may be made of an ultraviolet-curing resin that is cured by ultraviolet irradiation.

For example, the protection member 17 is formed into a circular shape having substantially the same diameter as the wafer 11, and is attached to the surface 11a side of the wafer 11 so as to cover the plurality of devices 15. The protection member 17 protects the plurality of devices 15.

The separation starting point is formed by using a laser processing device that processes the wafer 11 by irradiating a laser beam. Fig. 2 is a front view showing a part of a cross section of the laser processing device 2. The laser processing device 2 includes a chuck table (holding table) 4 that holds the wafer 11 and a laser irradiation unit 6 that irradiates a laser beam 8.

A rotation drive source such as a motor (not shown) and a ball screw type moving mechanism (not shown) are connected to the suction cup table 4. The rotation drive source rotates the suction cup table 4 around a rotation axis roughly parallel to the Z-axis direction (vertical direction, up and down direction). In addition, the moving mechanism moves the suction cup table 4 along the X-axis direction (processing feed direction, first horizontal direction) and the Y-axis direction (indexing feed direction, second horizontal direction).

The upper surface of the suction cup table 4 constitutes a holding surface 4a for holding the wafer 11. The holding surface 4a is a flat surface that is roughly parallel to the X-axis direction and the Y-axis direction. For example, the holding surface 4a is formed into a circular shape corresponding to the shape of the wafer 11. However, the shape of the holding surface 4a can be appropriately changed according to the shape of the wafer 11, etc. The holding surface 4a is connected to a suction source (not shown) such as a vacuum generator through a flow path (not shown) and a valve (not shown) formed inside the suction cup table 4.

A laser irradiation unit 6 is provided above the chuck stage 4. The laser irradiation unit 6 irradiates a laser beam 8 toward the wafer 11 held by the chuck stage 4. The irradiation conditions of the laser beam 8 are set so that a region (modifying region) that is qualitatively changed by multiphoton absorption modification is formed in the region of the wafer 11 irradiated with the laser beam 8.

Specifically, the wavelength of the laser beam 8 is set in such a way that the laser beam 8 is transmissive to the wafer 11. Therefore, the laser beam 8 at least partially transmits the wafer 11 (is transmissive to the wafer 11) and is irradiated to the wafer 11 from the laser irradiation unit 6. In addition, other irradiation conditions (output, pulse width, spot diameter, repetition frequency, etc.) of the laser beam 8 are also appropriately set in such a way that a modified region is formed on the wafer 11.

Furthermore, the laser irradiation unit 6 is configured to focus the laser beam 8 at least at two focusing points (focusing positions). FIG2 shows an example in which the laser beam 8 is focused at two focusing points (focusing positions) 8a and 8b.

FIG3 is a schematic diagram showing an example of the structure of the laser irradiation unit 6. The laser irradiation unit 6 is provided with a laser oscillator 10 for pulse oscillating a laser beam. As the laser oscillator 10, for example, a YAG laser, a _YVO4 laser, a YLF laser, etc. are used. The laser beam 8 pulsed and oscillated from the laser oscillator 10 is reflected by the lens 12 and enters the laser branching section 14, and is branched into a plurality of (two in FIG3 ) beams by the laser branching section 14. Thereafter, the branched laser beam 8 is focused at a predetermined position by the focusing lens 16.

The structure of the laser diverging portion 14 is not limited as long as it can diverge the laser beam 8. For example, the laser diverging portion 14 is formed by LCOS-SLM (Liquid Crystal On Silicon - Spatial Light Modulator), a diffractive optical element (DOE), etc.

The components of the laser processing device 2 shown in FIG. 2 (the rotation drive source and the moving mechanism connected to the suction cup table 4, the laser irradiation unit 6, etc.) are respectively connected to a control unit (not shown) that controls the operation of each component of the laser processing device 2. The position of the suction cup table 4, the irradiation conditions of the laser beam 8, etc. are controlled by the control unit.

The control unit is constituted by, for example, a computer, and includes a processing unit that performs various processes (calculations, etc.) required for the operation of the laser processing device 2, and a memory unit that stores various information (data, programs, etc.) used for the processes performed by the processing unit. The processing unit is constituted by, for example, a processor including a CPU (Central Processing Unit). In addition, the memory unit is constituted by a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory).

When the laser processing device 2 is used to process the wafer 11, first, the wafer 11 is held by the suction cup table 4 (wafer holding process). Specifically, the wafer 11 is placed on the suction cup table 4 in such a manner that the surface 11a side (protective member 17 side) faces the holding surface 4a and the back side 11b is exposed upward. In this state, if the negative pressure of the suction source is applied to the holding surface 4a, the surface 11a side of the wafer 11 will be sucked and held by the suction cup table 4.

Next, the laser beam 8 is irradiated onto the wafer 11 to form a modified layer on the wafer 11 (modified layer forming process). In the modified layer forming process, first, the chuck table 4 is rotated to align the length direction of a predetermined dividing line 13 (refer to FIG. 1 (A) and FIG. 1 (B)) with the X-axis direction. In addition, the position of the chuck table 4 in the Y-axis direction is adjusted in such a way that the focal points 8a and 8b of the laser beam 8 are arranged on the extension line of the predetermined dividing line 13.

Then, while the laser irradiation unit 6 irradiates the laser beam 8, the chuck stage 4 is moved along the X-axis direction (processing feed). Thereby, the chuck stage 4 holding the wafer 11 and the laser irradiation unit 6 are relatively moved along the X-axis direction, and the laser beam 8 is scanned along a predetermined dividing line 13. At this time, the focal points 8a and 8b of the laser beam 8 are positioned in a manner adjacent to each other along a direction parallel to the moving direction of the chuck stage 4 (the direction indicated by the arrow A in FIG. 2 ).

FIG. 4(A) is a cross-sectional view showing a portion of the wafer 11 irradiated with the laser beam 8. In the modified layer formation process, the focal points 8a and 8b of the laser beam 8 are positioned inside the wafer 11 in a manner adjacent to each other along a predetermined dividing line 13 (see FIG. 1(A) and FIG. 1(B)). Then, if the laser beam 8 is irradiated from the back side 11b of the wafer 11, a modified region (qualitatively changed region) 19 is formed in the region of the wafer 11 irradiated with the laser beam 8. The modified region 19 is equivalent to a region qualitatively changed by multiphoton absorption modification.

Furthermore, when the modified region 19 is formed, a crack 21 (see FIG. 4(B) ) is generated in the modified region 19 and spreads radially from the modified region 19. The modified region 19 and the crack 21 function as a starting point for dividing the wafer 11 in a subsequent process.

Here, the laser beam 8 is simultaneously irradiated on the areas where the focal points 8a and 8b of the wafer 11 are positioned, and the modified areas 19a and 19b are formed simultaneously. The modified areas 19a and 19b are formed along the predetermined dividing line 13 (see FIG. 1(A) and FIG. 1(B)) at intervals corresponding to the distance between the focal points 8a and 8b.

FIG4(B) is a cross-sectional view showing the modified regions 19a and 19b. FIG4(B) shows the modified regions 19a and 19b formed in the region where the focal points 8a and 8b of the wafer 11 are positioned, and the cracks (cracks) 21a and 21b extending from the modified regions 19a and 19b in the thickness direction of the wafer 11 (the vertical direction of FIG4(B)) and the radial direction of the wafer 11 (the horizontal direction of FIG4(B)).

The distance between the focal points 8a and 8b is set in such a way that the torsion 21a extending from the modified region 19a is connected to the torsion 21b extending from the modified region 19b. Therefore, if the modified regions 19a and 19b are formed simultaneously by irradiation with the laser beam 8, the torsion 21a and the torsion 21b are connected, and the modified regions 19a and 19b are connected through the torsion 21a and 21b. As a result, the division starting point is continuously formed along the predetermined division line 13 inside the wafer 11. For example, the distance between the focal points 8a and 8b is set to be greater than 3μm and less than 16μm, and ideally greater than 4μm and less than 8μm.

Then, when the laser beam 8 focused at the focal points 8a and 8b is scanned along the predetermined dividing line 13, a pair of modified regions 19a and 19b are sequentially formed one group at a time along the predetermined dividing line 13. As a result, a modified layer (modified layer) 23 including a plurality of modified regions 19 arranged along the predetermined dividing line 13 is formed inside the wafer 11.

Furthermore, each modified region 19a, 19b is formed at a position closer to the front side of the scanning direction of the laser beam 8 (the rear side of the moving direction (arrow A in FIG. 2 ) of the suction table 4) than the modified region 19a, 19b just formed previously. Therefore, a new modified region 19a or a modified region 19b will not be formed repeatedly at the same place as another modified region 19 already formed on the wafer 11.

Here, when the laser beam 8 is simultaneously focused at the focal points 8a and 8b, the focal point 8b is positioned at a position further away from the other modified regions 19 (especially, the modified region 19b formed just before) formed on the wafer 11 than the focal point 8a. Therefore, the focal point 8b is easily positioned in a region where the gob crack 21 extending from the other modified region 19 formed on the wafer 11 does not exist. As a result, diffuse reflection of the laser beam 8 that may occur when the laser beam 8 is focused in a region where the gob crack 21 exists can be suppressed.

If diffuse reflection of the laser beam 8 inside the wafer 11 is suppressed, the modified region 19 becomes easy to form in the intended region, and the phenomenon that the turtle crack 21 extends in an unexpected direction and the turtle crack 21 is formed beyond expectation and becomes too long becomes difficult to occur. As a result, a modified layer 23 including the appropriately formed modified region 19 and suppressing the occurrence of irregular turtle cracks 21 is formed on the wafer 11.

Furthermore, it is preferred that the modified region 19a is formed at a position where the tortoise crack 21a extending from the modified region 19a is connected to the tortoise crack 21 extending from other modified regions 19 (especially, the modified region 19b formed just before) formed on the wafer 11. In this way, two sets of modified regions 19a and 19b formed at different times can be connected through the tortoise crack 21, and an uninterrupted starting point for division can be formed inside the wafer 11.

Furthermore, it is preferred that the focal point 8b of the laser beam 8 is positioned in a region where there are no cracks 21 extending from other modified regions 19 formed on the wafer 11. In this way, diffuse reflection of the laser beam 8 can be further suppressed.

The interval of the area irradiated with the laser beam 8 (corresponding to the interval between the modified areas 19a and the interval between the modified areas 19b) can be adjusted by controlling the moving speed (processing feed speed) of the chuck table 4 and the repetition frequency of the laser beam 8. For example, the interval of the area irradiated with the laser beam 8 is set to be greater than 6μm and less than 32μm, and preferably greater than 8μm and less than 16μm.

Then, after the modified layer 23 is formed along one predetermined dividing line 13, the same procedure is repeated to form the modified layer 23 along other predetermined dividing lines 13. Thus, the wafer 11 is obtained in which the modified layer 23 is formed in a grid pattern along all the predetermined dividing lines 13.

The region of the wafer 11 where the modified layer 23 is formed is weaker than other regions of the wafer 11. Therefore, if an external force is applied to the wafer 11 where the modified layer 23 is formed, the wafer 11 will break along the predetermined dividing line 13 starting from the modified layer 23.

Furthermore, it is preferred to form a plurality of modified layers 23 in the thickness direction of the wafer 11, depending on the thickness and material of the wafer 11. For example, when the wafer 11 is a silicon wafer having a thickness of 200 μm or more, by forming two or more modified layers 23, it is easy to appropriately divide the wafer 11. When forming a plurality of modified layers 23, the modified layers 23 are further formed along the predetermined dividing lines 13 where the modified layers 23 have been formed.

Fig. 5(A) is a cross-sectional view showing a portion of the wafer 11 on which a plurality of modified layers 23 are formed. When the plurality of modified layers 23 are formed on the wafer 11, first, a modified layer 23 (the first modified layer 23) is formed (the first modified layer forming process), and then another modified layer 23 (the second modified layer 23) is formed in a region different from the first modified layer (the second modified layer forming process).

Here, it can be confirmed that the cracks 21 (see FIG. 4(B)) generated from the modified region 19 tend to extend toward the direction (back surface 11b side) where the laser beam 8 is incident. Therefore, when forming a plurality of modified layers 23 on the wafer 11, it is preferred to form the modified layers 23 sequentially from the back surface 11b side of the wafer 11 toward the surface 11a side.

Specifically, in the second modified layer formation process, the focal points 8a and 8b of the laser beam 8 are positioned closer to the surface 11a side (lower side) of the wafer 11 than when the first modified layer 23 is formed. Then, the second modified layer 23 is formed closer to the surface 11a side of the wafer 11 than the first modified layer 23 by the same procedure as when the first modified layer 23 is formed.

At this time, the laser beam 8 for forming the second modified layer 23 is focused in the region (surface 11a side of the wafer 11) where the cracks 21 generated in the first modified layer 23 are difficult to propagate. As a result, the laser beam 8 becomes difficult to focus in the region where the cracks 21 exist, and diffuse reflection of the laser beam 8 can be suppressed.

Furthermore, as described above, the first modified layer 23 is formed under the condition that the irregular cracks 21 are unlikely to occur. Therefore, when the second modified layer 23 is formed, even if the laser beam 8 passes through the first modified layer 23 and irradiates the area where the second modified layer 23 is formed, it is unlikely that the laser beam 8 will be unexpectedly reflected in the first modified layer 23. Thus, the second modified layer 23 can be easily and appropriately formed.

FIG5(B) is a cross-sectional view showing a portion of the wafer 11 on which a plurality of modified layers 23 are formed. As shown in FIG5(B), by forming a plurality of modified layers 23 on the wafer 11, for example, even when the wafer 11 is relatively thick, the wafer 11 can be appropriately divided. Furthermore, the number of modified layers 23 formed on the wafer 11 is not limited and can be appropriately set according to the thickness and material of the wafer 11.

Next, an external force is applied to the wafer 11 to separate the wafer 11 into a plurality of chips along the predetermined separation lines 13 (splitting process). For example, the splitting process is performed by attaching the wafer 11 to a stretch tape and expanding the stretch tape. FIG. 6 is a three-dimensional view of the wafer 11 attached with the stretch tape 25.

The stretch tape 25 is a tape that can be expanded by applying an external force (a tape with stretchability). For example, as the stretch tape 25, a sheet having a base material formed into a circular film shape and an adhesive layer (paste layer) provided on the base material can be used. Examples of materials for the base material and the adhesive layer are the same as those for the protective member 17 (see FIG. 1(B)). However, as long as the stretch tape 25 has stretchability and can be attached to the wafer 11, the structure and material are not limited.

For example, a circular stretch tape 25 having a larger diameter than the wafer 11 is attached to the back surface 11b of the wafer 11. Also, the outer periphery of the stretch tape 25 is attached to a ring-shaped frame 27 made of metal or the like and having a circular opening 27a in the center. Furthermore, the diameter of the opening 27a is larger than the diameter of the wafer 11, and the wafer 11 is arranged inside the opening 27a. When the stretch tape 25 is attached to the wafer 11 and the frame 27, the wafer 11 is supported by the frame 27 via the stretch tape 25.

After that, the protective member 17 is peeled off from the surface 11a side of the wafer 11. Thus, the surface 11a side (device 15 side) of the wafer 11 is exposed. In this state, if the stretching tape 25 is stretched outward in the radial direction, an external force is applied to the wafer 11, and the wafer 11 is divided into a plurality of chips.

The expansion of the stretching tape 25 is performed, for example, using an expansion device for expanding the stretching tape 25. Fig. 7 is a perspective view showing the expansion device (dividing device) 22. The expansion device 22 expands the stretching tape 25 by stretching to divide the wafer 11 on which the modified layer 23 is formed.

The expansion device 22 includes a cylindrical drum portion 24 having a diameter larger than that of the wafer 11, and a frame holding unit 26 that holds a frame 27 (see FIG. 6 ) for supporting the wafer 11. The frame holding unit 26 includes an annular support table 28 that supports the frame 27. The support table 28 is provided to surround the upper end of the drum 24, and is arranged so that the height of the upper surface of the support table 28 is substantially the same as the height of the upper end of the drum portion 24.

A plurality of clamps 30 are fixed to the outer periphery of the support platform 28. The plurality of clamps 30 are arranged at approximately equal intervals along the circumferential direction of the support platform 28, and hold and fix the frame 27 arranged on the support platform 28. The frame 27 is arranged on the support platform 28, and the frame 27 is fixed by the plurality of clamps 30, and the frame 27 is held by the frame holding unit 26.

The support platform 28 is supported by a plurality of rods 32 that move (rise and fall) in the vertical direction (up and down direction), and an air cylinder 34 that moves the rod 32 up and down is connected to the lower end of each rod 32. Furthermore, the plurality of air cylinders 34 are supported by a ring-shaped base 36. When the rod 32 is lowered by the air cylinder 34, the support platform 28 moves downward together with the frame 27.

In the separation process, first, the air cylinder 34 is operated to adjust the height of the support table 28 so that the height of the upper end of the drum 24 is consistent with the height of the upper surface of the support table 28. Then, the frame 27 (see FIG. 6 ) supporting the wafer 11 is arranged on the support table 28. At this time, the wafer 11 is arranged on the inner side of the outer periphery of the drum 24 in a plan view. Thereafter, the frame 27 arranged on the support table 28 is fixed by a plurality of clamps 30.

Thus, the wafer 11 is held by the frame holding unit 26 via the expansion tape 25 and the frame 27. Fig. 8(A) is a cross-sectional view showing the expansion device 22 holding the wafer 11. In addition, on the wafer 11, the reformed layer 23 is formed in a lattice shape along the predetermined dividing lines 13 (see Fig. 1(A)).

Next, the air cylinder 34 is operated to lower the support table 28 and move the frame 27 downward. As a result, the stretch tape 25 supported by the upper end of the drum 24 is stretched and expanded radially outward. As a result, an external force is applied to the wafer 11 to stretch and expand radially outward.

FIG8(B) is a cross-sectional view showing the expansion device 22 for expanding the stretching tape 25. When an external force is applied to the wafer 11 by the expansion of the stretching tape 25, the wafer 11 will break along the modified layer 23 and be divided into a plurality of chips (device chips) 29. That is, the modified layer 23 has the function of serving as a starting point for division. In this way, the wafer 11 is divided to produce the chips 29. Furthermore, after the wafer 11 is divided, each chip 29 is picked up, for example, by a suction nozzle (not shown) and mounted on a predetermined substrate (wiring substrate, etc.).

As described above, in the chip manufacturing method of the present embodiment, the laser beam 8 focused at the focal points 8a and 8b is irradiated onto the wafer 11, and modified regions 19a and 19b are formed in the areas where the focal points 8a and 8b are positioned, respectively, connecting the cracks 21a generated in the modified region 19a and the cracks 21b generated in the modified region 19b.

According to the aforementioned chip manufacturing method, the focal points 8a and 8b of the laser beam 8 can be positioned at the region inside the wafer 11 where the cracks 21 are not formed to form the modified regions 19a and 19b, while the cracks connecting the adjacent modified regions 19a and 19b are formed. In this way, the diffuse reflection of the laser beam 8 can be suppressed, and the modified layer 23 can be appropriately formed. As a result, the wafer 11 becomes easy to be divided along the predetermined dividing line 13, and the quality reduction of the chip 29 can be suppressed.

Furthermore, in the above-mentioned embodiment, an example of forming the modified layer 23 using the laser beam 8 focused only at two focal points 8a and 8b has been described, but the number of focal points of the laser beam used to form the modified layer 23 may be 3 or more. In this case, the modified regions 19 are formed at three or more locations simultaneously, and the cracks 21 extending from the adjacent modified regions 19 are connected to each other.

Furthermore, when the laser beam is focused at four or more focal points, the laser beam may be irradiated to the wafer 11 while positioning two or more focal points at different depths inside the wafer 11. In this case, two or more modified layers 23 may be formed simultaneously.

Fig. 9 is a partial cross-sectional front view of a laser processing device 2 having a laser irradiation unit 40 for irradiating a laser beam 42 focused at four focal points (focusing positions) 42a, 42b, 42c, and 42d. As shown in Fig. 9, the laser irradiation unit 40 focuses the laser beam 42 at the focal points 42a, 42b, 42c, and 42d.

The laser irradiation unit 40 may be configured similarly to the laser irradiation unit 6 (see FIG. 3 ). However, the laser branching unit 14 is configured to branch the laser beam oscillated from the laser oscillator 10 into four. For example, an LCOS-SLM that branches the laser beam into four is used as the laser branching unit 14 .

As shown in FIG. 9 , the laser irradiation unit 40 irradiates the laser beam 42 while positioning the focal points 42a, 42b and the focal points 42c, 42d at different depths inside the wafer 11. Specifically, the focal points 42a, 42b are positioned at a first region inside the wafer 11, and the focal points 42c, 42d are positioned at a second region located closer to the surface 11a of the wafer 11 than the first region. Then, by irradiating the laser beam 42 to the wafer 11, two modified layers 23 are formed on the wafer 11 simultaneously.

FIG. 10 is a cross-sectional view showing a portion of a wafer 11 irradiated with a laser beam 42 focused at four focal points 42a, 42b, 42c, and 42d. For example, the focal points 42a, 42b, 42c, and 42d are positioned at predetermined intervals along a predetermined dividing line 13 (see FIG. 1(A)). Furthermore, the focal points 42a and 42b are positioned in a region (first region) inside the wafer 11 where a first layer of a modified layer 23 is to be formed. Furthermore, the focal points 42c and 42d are positioned in a region (second region) inside the wafer 11 where a second layer of a modified layer 23 is to be formed.

In this state, the laser beam 42 is irradiated to the back side 11b of the wafer 11. Thus, modified regions (qualitatively changed regions) 19a and 19b are simultaneously formed in the regions where the focal points 42a and 42b are positioned, and modified regions (qualitatively changed regions) 19c and 19d are simultaneously formed in the regions where the focal points 42c and 42d are positioned.

Furthermore, the interval between the focal points 42a and 42b is set so that the torsion 21 generated from the modified region 19a is connected to the torsion 21 generated from the modified region 19b. Similarly, the interval between the focal points 42c and 42d is set so that the torsion 21 generated from the modified region 19c is connected to the torsion 21 generated from the modified region 19d.

Therefore, when the modified regions 19a, 19b, 19c, and 19d are formed, the cracks generated in the modified regions 19a and 19b are connected to each other, and the cracks generated in the modified regions 19c and 19d are connected to each other (refer to FIG. 4(B)). The distance between the focal points 42a and 42b and the distance between the focal points 42c and 42d are set to, for example, 3 μm or more and 16 μm or less, and preferably 4 μm or more and 8 μm or less.

As described above, by positioning the focal points 42a, 42b and the focal points 42c, 42d at different depths inside the wafer 11, two modified layers 23 can be formed simultaneously. Thus, when forming a plurality of modified layers 23 on the wafer 11, the process can be simplified and the processing time can be shortened.

Next, the results of the evaluation of the chips manufactured using the chip manufacturing method of the present embodiment are described. In this evaluation, the chips obtained by the previous chip manufacturing method (comparison example) and the chips obtained by the chip manufacturing method of the present embodiment (embodiment example) are compared.

In the comparative example, a modified layer is formed by irradiating a laser beam (nanosecond pulse laser) focused at one point from the back side (upper side) of a silicon wafer (diameter 200mm, thickness 300μm). Then, an external force is applied to the silicon wafer (see Figure 8(A) and Figure 8(B)) to split the silicon wafer and manufacture the chips of the comparative example.

In the manufacturing process of the chip of the comparative example, the laser beam is scanned while the focal point (1 point) of the laser beam is positioned inside the silicon wafer, so that a modified layer including a plurality of modified regions is formed along a predetermined dividing line. Thereafter, the same process is repeated to obtain a silicon wafer having three modified layers.

Furthermore, the irradiation conditions of the laser beam in the comparative example are set as follows. Laser oscillator: LD excitation Q switch Nd: YVO ₄ Laser wavelength: 1342nm Output: 1.2W Repetition frequency: 90kHz Spot diameter: 3μm Processing feed speed: 340mm/s

On the other hand, in the embodiment, a modified layer is formed by irradiating the back side (upper side) of a silicon wafer (diameter 200 mm, thickness 300 μm) with a laser beam (nanosecond pulse laser) focused at multiple locations. Then, an external force is applied to the silicon wafer (see FIG. 8 (A) and FIG. 8 (B)) to split the silicon wafer and manufacture the chip of the embodiment.

In the manufacturing process of the chip of the embodiment, the laser beam is scanned while the focal points (2 places) of the laser beam are positioned at the same depth inside the silicon wafer, so that a modified layer including a plurality of modified regions is formed along each predetermined dividing line (refer to FIG. 4 (A) etc.). Furthermore, the interval between the two focal points positioned at the same depth inside the silicon wafer is set to 5 μm in consideration of the length of the crack extending from the modified region. Afterwards, the same process is repeated to obtain a silicon wafer with 7 modified layers.

Furthermore, the irradiation conditions of the laser beam of the embodiment are set as follows. Laser oscillator: LD excitation Q switch Nd: YVO ₄ Laser wavelength: 1342nm Output: 1.5W (before branching) Repetition frequency: 60kHz Spot diameter: 3μm Processing feed speed: 600mm/s

Then, the side surfaces (dividing surfaces) of the aforementioned comparative example chip and the embodiment chip are observed. FIG11(A) is a pictorial diagram showing the side surface of the comparative example chip 31, and FIG11(B) is a pictorial diagram showing the side surface of the embodiment chip 41.

On the side surface of the comparative chip 31, a modified layer (qualitatively altered layer) 33 and numerous cracks (cracks) 35 extending irregularly from the modified layer 33 were observed. It was confirmed that the cracks 35 propagated over a long distance, particularly toward the back side (upper side, the side irradiated with the laser beam) of the chip 31.

As described above, when a laser beam focused at one point is scanned during the manufacturing process of the chip 31, diffuse reflection of the laser beam will occur inside the silicon wafer, making it difficult to properly form the modified layer 33. Then, it is difficult to see the cracks in the modified layer of the silicon wafer without properly forming the modified layer, and it is easy to apply excessive external force to the silicon wafer when it is divided. As a result, many tortoise cracks 35 are formed on the side of the chip 31 as shown in Figure 11 (A), which can be inferred to be a quality deterioration of the chip 31.

Furthermore, when forming the modified layer 33 after the second layer, the interval of the modified layer 33 is set so that the focal point of the laser beam is not positioned on the cracks extending from the already formed modified layer 33. Here, when the modified layer 33 is formed by irradiation with a laser beam focused at one point, a long crack is formed due to diffuse reflection of the laser beam, so the interval of the modified layer 33 is set to be wider. As a result, it becomes difficult for the silicon wafer to break between the modified layers 33, and the division mark 37 shown in FIG. 11 (A) is likely to remain on the side surface of the wafer 31.

On the other hand, a modified layer (modified layer) 43 was observed on the side of the chip 41 (FIG. 11(B)) of the embodiment. However, no irregularly extended long cracks were confirmed around the modified layer 43, and a high-quality chip 41 was obtained. This is presumably because the diffuse reflection of the laser beam was suppressed by using a laser beam focused at a plurality of focal points in the formation of the modified layer 43, and the modified layer 43 was appropriately formed in the intended area, and the occurrence of cracks was suppressed.

Furthermore, if the cracks extending from the modified layer 43 are suppressed, the interval of the modified layer 43 can be reduced. As a result, the silicon wafer can be broken appropriately and it is difficult for an excessively thick division mark such as the division mark 37 shown in FIG. 11(A) to remain on the chip 41.

As described above, it has been confirmed that if a modified layer is formed on a silicon wafer by irradiating a laser beam focused at a plurality of focal points, the silicon wafer can be easily divided appropriately, and the quality degradation of the chip can be suppressed.

Furthermore, the structures, methods, etc. of the aforementioned embodiments may be implemented with appropriate modifications as long as they do not deviate from the scope of the purpose of the present invention.

2: Laser processing device 4: Suction table (holding table) 4a: Holding surface 6: Laser irradiation unit 8: Laser beam 8a, 8b: Focusing point (focusing position) 10: Laser oscillator 11: Wafer 11a: Surface (first surface) 11b: Back (second surface) 12: Lens 13: Predetermined dividing line (cutting path) 14: Laser divergence part 15: Device 16: Focusing lens 17: Protective member 19, 19a, 19b, 19c, 19d: Modified area (qualitative change area) 21, 21a, 21b: Crack (crack) 22: Expansion device (dividing device) 23: Modified layer (quality change layer) 24: Drum 25: Stretching tape 26: Frame holding unit 27: Frame 27a: Opening 28: Support table 29: Chip (device chip) 30: Clamp 31: Chip 32: Rod 33: Modified layer (quality change layer) 34: Air cylinder 35: Turtle crack (crack) 36: Base 37: Dividing mark 40: Laser irradiation unit 41: Chip 42: Laser beam 42a, 42b, 42c, 42d: Focusing point (focusing position) 43: Modified layer (quality change layer)

[Figure 1] Figure 1 (A) is a perspective view of a wafer, and Figure 1 (B) is a perspective view of a wafer with a protective member attached. [Figure 2] A front view of a section of a laser processing device. [Figure 3] A schematic diagram of a structure example of a laser irradiation unit. [Figure 4] Figure 4 (A) is a cross-sectional view of a portion of a wafer irradiated with a laser beam, and Figure 4 (B) is a cross-sectional view of a modified region. [Figure 5] Figure 5 (A) is a cross-sectional view of a portion of a wafer forming a second modified layer, and Figure 5 (B) is a cross-sectional view of a portion of a wafer forming multiple modified layers. [Figure 6] A perspective view of a wafer with a stretching tape attached. [Figure 7] A perspective view of an expansion device. [Figure 8] Figure 8 (A) is a cross-sectional view of an expansion device for holding a wafer, and Figure 8 (B) is a cross-sectional view of an expansion device for expanding a stretching tape. [Figure 9] A front view of a portion of a laser processing device having a laser irradiation unit for irradiating a laser beam focused at four focal points. [Figure 10] A cross-sectional view of a portion of a wafer irradiated with a laser beam focused at four focal points. [Figure 11] Figure 11 (A) is a side view of a chip of a comparative example, and Figure 11 (B) is a side view of a chip of an embodiment.

2: Laser processing equipment

4: Suction cup table (holding table)

4a: Keep the face

6: Laser irradiation unit

8: Laser beam

8a,8b: Spotlight

11: Wafer

11a: Surface

11b: Back

17: Protective components

Claims (2)

A chip manufacturing method is a chip manufacturing method for dividing a wafer into a plurality of chips along a predetermined dividing line, and is characterized by: a wafer holding process, in which a suction cup is used to hold the first side of the wafer and the second side of the wafer is exposed; a modified layer forming process, in which a laser beam having transmissivity to the wafer and focused at a first focal point and a second focal point is irradiated from the second side of the wafer in a manner that the first focal point and the second focal point are positioned inside the wafer, and a modified region is formed in the region where the first focal point and the second focal point are positioned, respectively, so as to form a modified layer including a plurality of the modified regions arranged along the predetermined dividing line; and a dividing process, in which an external force is applied to the wafer to divide the wafer along the predetermined dividing line. The wafer is divided into a plurality of wafers along a dividing line; the modified layer forming process comprises: a first modified layer forming process, which forms a first modified layer including a plurality of modified regions arranged along the predetermined dividing line by irradiating the laser beam from the second surface side of the wafer; and a second modified layer forming process, which forms a second modified layer including a plurality of modified regions arranged along the predetermined dividing line on the first surface side of the wafer closer to the first modified layer than the first modified layer by irradiating the laser beam from the second surface side of the wafer; in the modified layer forming process, the cracks generated in the modified region formed in the region where the first focal point is positioned are connected to the cracks generated in the modified region formed in the region where the second focal point is positioned. A chip manufacturing method is a chip manufacturing method for dividing a wafer into a plurality of chips along a predetermined dividing line, and is characterized by: a wafer holding process, in which a suction cup is used to hold the first side of the wafer and the second side of the wafer is exposed; a modified layer forming process, in which a laser beam having transmissivity to the wafer and focused at a first focal point or even a fourth focal point is irradiated from the second side of the wafer in such a manner that the first focal point and the second focal point are positioned at the first area inside the wafer, and the third focal point and the fourth focal point are positioned at the second area closer to the first side of the wafer than the first area inside the wafer, and the modified layer is formed at the first focal point or even the fourth focal point. The regions where the 4 focal points are located respectively form modified regions to form a first modified layer and a second modified layer including a plurality of the modified regions arranged along the predetermined dividing line; and a dividing process is to apply external force to the wafer to divide the wafer into a plurality of the chips along the predetermined dividing line; in the modified layer forming process, the cracks generated in the modified region formed in the region where the first focal point is located are linked to the cracks generated in the modified region formed in the region where the second focal point is located, and the cracks generated in the modified region formed in the region where the third focal point is located are linked to the cracks generated in the modified region formed in the region where the fourth focal point is located.

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