JP7463035B2 - Stacked wafer processing method - Google Patents

Description

The present invention relates to a method for processing a stacked wafer, which includes multiple stacked wafers.

In the device chip manufacturing process, a wafer is used in which devices are formed in multiple areas partitioned by multiple planned division lines (streets) arranged in a grid pattern. By dividing this wafer along the planned division lines, multiple device chips, each equipped with a device, are obtained. The device chips are mounted on various electronic devices such as mobile phones and personal computers.

A cutting device is used to divide the wafer. The cutting device is equipped with a chuck table that holds the workpiece, and a cutting unit to which an annular cutting blade that cuts the workpiece is attached. The cutting blade is rotated and cuts into the wafer along the planned division lines, dividing the wafer into multiple device chips.

At the planned dividing line of the wafer, a portion of the functional layer, which is made up of a laminate of various films (insulating film, conductive film, etc.) that make up the device, remains. Therefore, when the wafer is cut along the planned dividing line with a cutting blade, the film contained in the functional layer may be caught in the rotating cutting blade and peeled off. If the peeling of the film that occurs at the planned dividing line reaches the device, there is a risk of damaging the device.

Therefore, before cutting the wafer with a cutting blade, a process is sometimes performed in which the functional layer remaining on the intended dividing line is divided by irradiating it with a laser beam (see Patent Document 1). When this method is used, even if the film peels off along the intended dividing line when cutting the wafer with the cutting blade, the peeling does not reach the device, preventing damage to the device.

JP 2005-64230 A

In recent years, technology for manufacturing device chips in which multiple devices and wiring are stacked has been attracting attention, with the aim of improving the processing speed and miniaturization of device chips. To manufacture this type of device chip, a stacked wafer is used, which is formed by bonding two wafers together and connecting the devices and other elements formed on each wafer. By cutting the stacked wafer with a cutting blade, a device chip equipped with, for example, stacked devices can be obtained.

However, the above-mentioned laminated wafer has a structure in which two wafers are bonded together via a functional layer. Therefore, after the wafers are laminated, the functional layer is covered by the wafer, making it difficult to process the functional layer along the planned division line. As a result, it is not possible to stop the progression of film peeling that occurs when cutting the laminated wafers with a cutting blade, making it easy for damage to the device to occur.

The present invention was made in consideration of these problems, and aims to provide a method for processing stacked wafers that can prevent damage to devices.

According to one aspect of the present invention, there is provided a method for processing a laminated wafer, which includes a functional layer constituting a device arranged in each of areas partitioned by a plurality of planned division lines, and a first wafer and a second wafer stacked on each other via the functional layer, the method comprising: a protective member attachment step for attaching a protective member to the laminated wafer; a functional layer modification step for irradiating the functional layer along the planned division lines through the first wafer with a laser beam that is transparent to the first wafer and absorbent to the functional layer, thereby forming a modified part in the functional layer along the planned division lines; and a cutting step for cutting the laminated wafer along the planned division lines by inserting a cutting blade between both ends of the modified part in the width direction after the protective member attachment step and the functional layer modification step are performed.

Preferably, in the functional layer modification step, two modified regions are formed along both ends of the width direction of the planned division line, and in the cutting step, the cutting blade is inserted between the two modified regions. Also, preferably, in the functional layer modification step, the focal point of the laser beam is positioned inside the functional layer. Also, preferably, the laminated wafer processing method further includes a grinding step of grinding the first wafer to a predetermined thickness before carrying out the functional layer modification step.

In a method for processing a laminated wafer according to one aspect of the present invention, a laser beam is irradiated onto a functional layer through a first wafer to form a modified portion in the functional layer. Therefore, even in a laminated wafer in which the functional layer is covered by a first wafer and a second wafer, the functional layer can be appropriately modified. This makes it possible to prevent peeling of the film contained in the functional layer from reaching the device, thereby preventing damage to the device.

FIG. 2 is a perspective view showing a first wafer and a second wafer. FIG. 2 is a perspective view showing a laminated wafer. FIG. 2 is a perspective view showing a laminated wafer to which a protective member is attached. FIG. 2 is a partial cross-sectional front view showing the grinding device. FIG. 5A is a partially sectional front view showing the laser processing apparatus, and FIG. 5B is an enlarged sectional view showing a part of the laminated wafer to be irradiated with a laser beam. FIG. 6A is a partially sectional front view showing the cutting device, and FIG. 6B is an enlarged sectional view showing a part of the laminated wafers being cut by the cutting blade.

Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. First, an example of the configuration of a laminated wafer that can be processed by the laminated wafer processing method according to this embodiment will be described. The laminated wafer is formed by stacking a first wafer and a second wafer.

Figure 1 is a perspective view showing wafer 11 and wafer 19. For example, wafer 11 is a disk-shaped wafer made of a semiconductor material such as silicon, and has a front surface 11a and a back surface 11b that are generally parallel to each other. A functional layer (device layer) 13 including multiple laminated thin films is formed on the front surface 11a side of wafer 11.

The functional layer 13 constitutes devices 15 such as ICs (Integrated Circuits) and LSIs (Large Scale Integration) formed on the front surface 11a side of the wafer 11. Specifically, the functional layer 13 is a laminate including various films (functional films) for forming a plurality of devices 15. For example, the functional layer 13 includes conductive films that constitute the electrodes, wiring, etc. of the devices 15, and insulating films that constitute the interlayer insulating films, passivation films, etc. of the devices 15.

A low-dielectric constant insulating film (low-k film) can be used as the interlayer insulating film of the device 15. The low-dielectric constant insulating film is an insulating film made of inorganic materials such as SiOF, SiOC, BSG (SiOB), etc., or organic materials such as polyimide-based and parylene-based polymers. The passivation film is an insulating film made of silicon nitride film, silicon oxide film, etc., and is formed to cover multiple devices 15.

The areas of the functional layer 13 that do not form the devices 15 form a plurality of planned division lines 17 that intersect with each other. That is, the functional layer 13 forms a plurality of devices 15 and a grid-like planned division line 17. The devices 15 are each arranged in a rectangular area partitioned by the planned division lines 17.

There are no limitations on the material, shape, structure, size, etc. of the wafer 11. For example, the wafer 11 may be a substrate of any size and shape made of a semiconductor other than silicon (GaAs, InP, GaN, SiC, etc.), glass, ceramics, resin, metal, etc. Furthermore, there are no limitations on the type, number, shape, structure, size, arrangement, etc. of the devices 15 formed on the wafer 11.

Wafer 19 is a wafer that is laminated and bonded to wafer 11. For example, wafer 19 is made of the same material as wafer 11 and has a front surface 19a and a back surface 19b that are generally parallel to each other.

There are no limitations on the configuration of the wafer 19. For example, a plurality of electrodes, wiring, circuits, etc. connected to the device 15 may be formed on the surface 19a side of the wafer 19. A functional layer having a configuration similar to that of the functional layer 13 may also be formed on the surface 19a side of the wafer 19. In other words, a plurality of devices connected to the device 15 may be formed on the surface 19a side of the wafer 19.

Figure 2 is a perspective view showing a laminated wafer 21. By bonding the wafer 11 and the wafer 19 together, a laminated wafer 21 is formed, which includes the wafers 11 and 19 stacked on top of each other. For example, the front surface 11a of the wafer 11 and the front surface 19a of the wafer 19 are bonded together via the functional layer 13. This connects the device 15 formed on the wafer 11 to the devices formed on the wafer 19, etc.

The method for bonding wafer 11 and wafer 19 can be selected as appropriate. Specifically, wafer 11 and wafer 19 are bonded by direct bonding or indirect bonding. For example, an adhesive is applied to surface 11a of wafer 11 or surface 19a of wafer 19, and wafer 11 and wafer 19 are bonded via this adhesive.

By dividing the laminated wafer 21 along the planned division lines 17 (see FIG. 1), for example, multiple device chips having stacked devices are manufactured. The specific processing method for the laminated wafer 21 is described below.

First, a protective member is attached to the laminated wafer 21 (protective member attachment step). Figure 3 is a perspective view showing the laminated wafer 21 to which the protective member 23 is attached.

In the protective member attachment step, for example, a circular protective member 23 having a diameter larger than that of the wafer 11 is attached to the back surface 11b side of the wafer 11. As a result, the back surface 11b side of the wafer 11 is covered and protected by the protective member 23.

For example, a film-like tape is used as the protective member 23. This tape includes a circular substrate and an adhesive layer (glue layer) provided on the substrate. For example, the substrate is made of a resin such as polyolefin, polyvinyl chloride, or polyethylene terephthalate, and the adhesive layer is made of an epoxy-, acrylic-, or rubber-based adhesive. The adhesive layer may also be made of an ultraviolet-curing resin that hardens when exposed to ultraviolet light.

The outer periphery of the protective member 23 is attached to an annular frame 25 made of metal or the like. A circular opening 25a with a diameter larger than that of the stacked wafers 21 is provided in the center of the frame 25. The stacked wafers 21 are attached to the center of the protective member 23 so that they are positioned inside the opening 25a of the frame 25. As a result, the wafer 11 side of the stacked wafers 21 is supported by the frame 25 via the protective member 23.

Next, the wafer 19 is ground until it has a predetermined thickness (grinding step). In the grinding step, the wafer 19 is ground and thinned by a grinding device. FIG. 4 is a partial cross-sectional front view showing the grinding device 2. The grinding device 2 includes a chuck table (holding table) 4 that holds the stacked wafers 21, and a grinding unit 8 that grinds the stacked wafers 21 held by the chuck table 4.

The upper surface of the chuck table 4 constitutes a flat holding surface 4a that holds the stacked wafers 21. The holding surface 4a is connected to a suction source (not shown) such as an ejector via a suction passage (not shown) and a valve (not shown) formed inside the chuck table 4.

The chuck table 4 is connected to a ball screw type movement mechanism (not shown) that moves the chuck table 4 in the horizontal direction, and a rotation drive source (not shown) such as a motor that rotates the chuck table 4 around a rotation axis that is roughly parallel to the vertical direction. In addition, a number of clamps 6 are provided around the periphery of the chuck table 4 to grip and secure the frame 25 that supports the stacked wafers 21.

A grinding unit 8 is disposed above the chuck table 4. The grinding unit 8 includes a cylindrical spindle 10 disposed vertically. A disk-shaped mount 12 is fixed to the tip (lower end) of the spindle 10. A rotational drive source (not shown), such as a motor, that rotates the spindle 10 is connected to the base (upper end) of the spindle 10.

A grinding wheel 14 for grinding the laminated wafer 21 is attached to the underside of the mount 12. The grinding wheel 14 is provided with an annular base 16 made of a metal such as stainless steel or aluminum and formed to have roughly the same diameter as the mount 12. In addition, a plurality of grinding wheels 18 are fixed to the underside of the base 16. For example, the plurality of grinding wheels 18 are formed in a rectangular parallelepiped shape and are fixed at roughly equal intervals along the outer periphery of the base 16.

The grinding wheel 14 rotates around a rotation axis roughly parallel to the vertical direction by power transmitted from a rotary drive source via the spindle 10 and mount 12. A ball screw type movement mechanism (not shown) is connected to the grinding unit 8, and this movement mechanism raises and lowers the grinding unit 8 in the vertical direction. Furthermore, a nozzle 20 is provided near the grinding unit 8 to supply a grinding fluid 22, such as pure water, to the stacked wafers 21 held by the chuck table 4 and the multiple grinding wheels 18.

In the grinding step, first, the stacked wafers 21 are held by the chuck table 4. Specifically, the stacked wafers 21 are placed on the chuck table 4 so that the back surface 11b (protective member 23 side) of the wafers 11 faces the holding surface 4a and the back surface 19b of the wafers 19 is exposed upward. In addition, the frame 25 is gripped and fixed by multiple clamps 6. In this state, when negative pressure from a suction source is applied to the holding surface 4a, the wafer 11 side of the stacked wafers 21 is suction-held by the chuck table 4 via the protective member 23.

Next, the chuck table 4 is moved below the grinding unit 8. Then, while the chuck table 4 and the grinding wheel 14 are rotated in a predetermined direction at a predetermined rotation speed, the grinding wheel 14 is lowered toward the chuck table 4. The speed at which the grinding wheel 14 is lowered is adjusted so that the multiple grinding stones 18 are pressed against the stacked wafers 21 with an appropriate force.

When the rotating grinding wheels 18 come into contact with the back surface 19b of the wafer 19, the back surface 19b of the wafer 19 is scraped off. This grinds the wafer 19 to thin it. In addition, the grinding fluid 22 supplied from the nozzle 20 while the wafer 19 is being ground cools the wafer 19 and the grinding wheels 18, and washes away any debris (grinding debris) generated by grinding the wafer 19. Then, when the wafer 19 has been thinned to a predetermined thickness (finishing thickness), grinding of the wafer 19 is stopped.

Although the above describes the case where the wafer 19 is ground, the wafer 11 may also be ground in the grinding step. In this case, first, in the protective member attachment step (see FIG. 3), the protective member 23 is attached to the back surface 19b of the wafer 19. The stacked wafers 21 are held by the chuck table 4 so that the back surface 11b of the wafer 11 is exposed upward and the back surface 19b (protective member 23 side) of the wafer 19 faces the holding surface 4a. Then, the grinding wheel 18 is brought into contact with the back surface 11b of the wafer 11, thereby grinding and thinning the wafer 11 to a predetermined thickness (finishing thickness).

Next, a laser beam is irradiated onto the functional layer 13 through the wafer 11 or wafer 19 to form a modified portion in the functional layer 13 (functional layer modification step). In the functional layer modification step, the laser processing is performed on the functional layer 13 by a laser processing device, and the functional layer 13 is modified (altered).

Figure 5 (A) is a partial cross-sectional front view showing the laser processing device 30. The laser processing device 30 includes a chuck table (holding table) 32 that holds the laminated wafer 21, and a laser irradiation unit 36 that irradiates a laser beam 38.

The upper surface of the chuck table 32 constitutes a flat holding surface 32a that holds the stacked wafers 21. The holding surface 32a is connected to a suction source (not shown) such as an ejector via a suction passage (not shown) and a valve (not shown) formed inside the chuck table 32.

The chuck table 32 is connected to a ball screw type movement mechanism (not shown) that moves the chuck table 32 along the processing feed direction (left-right direction in FIG. 5(A)) and the indexing feed direction (front-back direction in FIG. 5(A)), and a rotation drive source (not shown) such as a motor that rotates the chuck table 32 around a rotation axis that is roughly parallel to the vertical direction. In addition, a number of clamps 34 that grip and fix the frame 25 that supports the stacked wafers 21 are provided around the periphery of the chuck table 32.

A laser irradiation unit 36 is provided above the chuck table 32, which irradiates a laser beam 38 toward the laminated wafer 21 held by the chuck table 32. The laser irradiation unit 36 includes a laser oscillator, such as a YAG laser, a _YVO4 laser, or a YLF laser, which oscillates a laser in a pulsed manner, and a focusing lens which condenses the laser pulsed from the laser oscillator.

In the functional layer modification step, first, the stacked wafers 21 are held by the chuck table 32. Specifically, the stacked wafers 21 are placed on the chuck table 32 so that the back surface 11b (protective member 23 side) of the wafers 11 faces the holding surface 32a and the back surface 19b of the wafers 19 is exposed upward. In addition, the frame 25 is gripped and fixed by a number of clamps 34. In this state, when negative pressure from a suction source is applied to the holding surface 32a, the wafer 11 side of the stacked wafers 21 is suction-held by the chuck table 32 via the protective member 23.

Next, the chuck table 32 is rotated to align the length direction of the planned division line 17 (see FIG. 1) with the processing feed direction (left-right direction in FIG. 5(A)). Also, the position of the chuck table 32 in the indexing feed direction (front-back direction in FIG. 5(A)) is adjusted so that the focal point of the laser beam 38 is positioned at a position overlapping with the extension line of the planned division line 17.

Then, while irradiating the laser beam 38 from the laser irradiation unit 36, the chuck table 32 is moved along the processing feed direction (processing feed), and the chuck table 32 and the laser irradiation unit 36 are moved relatively along the processing feed direction. As a result, the laser beam 38 is irradiated along the planned division line 17 onto the back surface 19b side of the wafer 19.

Here, the irradiation conditions of the laser beam 38 are set so that the area of the functional layer 13 irradiated with the laser beam 38 melts and is modified (altered). Specifically, the wavelength of the laser beam 38 is set so that at least a portion of the laser beam 38 passes through the wafer 19 and is absorbed by the functional layer 13.

That is, the laser beam 38 is transparent to the wafer 19 and absorptive to the functional layer 13. More specifically, the transmittance of the laser beam 38 through the wafer 19 is higher than the transmittance of the laser beam 38 through the functional layer 13. Also, the absorptance of the laser beam 38 through the functional layer 13 is higher than the absorptance of the laser beam 38 through the wafer 19.

Other irradiation conditions of the laser beam 38 are also set appropriately so as to appropriately modify the functional layer 13. For example, the irradiation conditions of the laser beam 38 can be set as follows.
Wavelength: 500nm to 1300nm
Average power output: 0.5W
Repetition frequency: 100kHz
Processing feed speed: 300 mm/s

The specific wavelength of the laser beam 38 is set taking into consideration the materials of the functional layer 13 and the wafer 19. For example, if the wafer 19 is a silicon wafer and the object to be modified by the laser beam 38 is a low dielectric constant insulating film contained in the functional layer 13, a laser beam with a wavelength of 1064 nm or 1300 nm can be used.

The laser beam 38 is irradiated onto the functional layer 13 through the wafer 19 (transmitting through the wafer 19) and scanned along the intended division lines 17. This causes the functional layer 13 to melt and be modified along the intended division lines 17.

Figure 5 (B) is an enlarged cross-sectional view showing a portion of the laminated wafer 21 onto which the laser beam 38 is irradiated. The functional layer 13 sandwiched between the wafers 11 and 19 includes an area corresponding to the device 15 and an area corresponding to the planned division line 17 provided between the adjacent devices 15. The laser beam 38 is then irradiated onto the functional layer 13 along the planned division line 17.

As a result, modified areas 27 corresponding to linear (strip-like) regions modified by irradiation with the laser beam 38 are formed in the functional layer 13 along the planned division line 17. The modified areas 27 are formed between both ends of the planned division line 17 in the width direction (inside the planned division line 17). In other words, the width of the modified areas 27 is narrower than the width of the planned division line 17.

Here, in the functional layer modification step, it is preferable to form two modified regions 27a, 27b. The modified regions 27a, 27b are formed inside the planned division line 17 along both ends of the planned division line 17 in the width direction. Specifically, the modified region 27a is formed linearly along the length of the planned division line 17 at one end of the planned division line 17 in the width direction. The modified region 27b is formed linearly along the length of the planned division line 17 at the other end of the planned division line 17 in the width direction.

In this case, one end of the modified portion 27 in the width direction corresponds to the modified region 27a, and the other end of the modified portion 27 in the width direction corresponds to the modified region 27b. That is, the modified portion 27 includes modified regions 27a and 27b and a non-modified region sandwiched between the modified regions 27a and 27b.

The two modified regions 27a, 27b can be formed, for example, by irradiating the functional layer 13 with a laser beam 38 that is split into two. Specifically, the laser irradiation unit 36 is equipped with an optical element that splits the laser beam 38. As the optical element, a diffractive optical element (DOE), a liquid crystal on silicon - spatial light modulator (LCOS-SLM), or the like is used. This generates the laser beam 38 that is focused at two points.

With the two focusing points of the laser beam 38 positioned at one end and the other end in the width direction of the planned division line 17 (see FIG. 5(B)), the laser beam 38 is scanned along the planned division line 17. As a result, two modified regions 27a and 27b are simultaneously formed along the planned division line 17.

However, there is no limitation on the method of forming the two modified regions 27a, 27b. For example, the two modified regions 27a, 27b may be formed separately by scanning a laser beam 38 focused at one point twice along the intended division line 17. Depending on the width and spacing of the modified regions 27a, 27b, the modified regions 27a, 27b may be connected to each other. In this case, a modified section 27 is formed in which there is no unmodified region between the modified regions 27a, 27b.

As described above, when forming two modified regions 27a and 27b, the output of the laser beam 38 can be significantly reduced compared to when the entire modified portion 27 is modified by a single scan of the laser beam 38. This reduces damage to the laminated wafer 21 caused by irradiation with the laser beam 38.

The irradiation of the laser beam 38 onto the functional layer 13 is preferably performed with the focal point of the laser beam 38 positioned inside the functional layer 13 (between the upper and lower surfaces of the functional layer 13) (see FIG. 5(B)). This makes it easier to modify the inside of the functional layer 13, and ensures the formation of the modified portion 27.

Then, the same procedure is repeated to sequentially form modified areas 27 along the other planned dividing lines 17. As a result, a laminated wafer 21 is obtained in which modified areas 27 have been formed along all of the planned dividing lines 17.

In the functional layer modification step, the laser beam 38 is irradiated to the functional layer 13 through the wafer 19 that has been thinned by carrying out the grinding step (see FIG. 4). This suppresses absorption of the laser beam 38 inside the wafer 19, and promotes absorption of the laser beam 38 in the functional layer 13. In addition, for example, the laser irradiation unit 36 includes a focusing lens for focusing the laser beam 38 inside or near the functional layer 13. When the wafer 19 is thinned, the focusing lens can be positioned closer to the functional layer 13. This allows the diameter of the focusing lens to be reduced, and the laser irradiation unit 36 to be made more compact.

Although the above describes an example in which the laser beam 38 is irradiated to the functional layer 13 through the wafer 19, the laser beam 38 may be irradiated to the functional layer 13 through the wafer 11. In this case, the wafer 11 is ground and thinned in the grinding step (see FIG. 4). In addition, in the functional layer modification step, the wavelength of the laser beam 38 is set so that the laser beam 38 is transparent to the wafer 11 and absorbent to the functional layer 13. The laser beam 38 then passes through the wafer 11 and is irradiated to the functional layer 13, forming a modified portion 27 in the functional layer 13.

However, if the transmittance of the laser beam 38 through the wafer 11 or wafer 19 is sufficiently high and there is no problem in modifying the functional layer 13, the grinding step may be omitted. In this case, the reduction in the number of steps improves processing efficiency and reduces the costs required for preparation and operation of the grinding device 2 (see FIG. 4).

Next, a cutting blade is inserted between both ends of the modified portion 27 in the width direction to cut the laminated wafer 21 along the intended division line 17 (cutting step). In the cutting step, the laminated wafer 21 is cut by a cutting device to divide the laminated wafer 21.

Figure 6 (A) is a partial cross-sectional front view showing the cutting device 40. The cutting device 40 includes a chuck table (holding table) 42 that holds the laminated wafers 21, and a cutting unit 46 that cuts the laminated wafers 21.

The upper surface of the chuck table 42 constitutes a holding surface 42a that holds the stacked wafers 21. The holding surface 42a is connected to a suction source (not shown) such as an ejector via a suction passage (not shown), a valve (not shown), etc. formed inside the chuck table 42.

The chuck table 42 is connected to a ball screw type moving mechanism (not shown) that moves the chuck table 42 along the processing feed direction (front-back direction in FIG. 6(A)) and a rotation drive source (not shown) such as a motor that rotates the chuck table 42 around a rotation axis that is roughly parallel to the vertical direction. In addition, a number of clamps 44 are provided around the periphery of the chuck table 42 to grip and fix the frame 25 that supports the stacked wafers 21.

Above the chuck table 42, there is provided a cutting unit 46 that cuts the laminated wafers 21 held by the chuck table 42. The cutting unit 46 has a cylindrical spindle 48 that is generally parallel to the holding surface 42a and arranged along a direction generally perpendicular to the processing feed direction. An annular cutting blade 50 that cuts the laminated wafers 21 is attached to the tip (one end) of the spindle 48.

For example, a hub-type cutting blade (hub blade) is used as the cutting blade 50. The hub blade is composed of an annular base made of metal or the like and an annular cutting edge formed along the outer periphery of the base. The cutting edge of the hub blade is composed of an electroformed grinding stone in which abrasive grains made of diamond or the like are fixed by a binder such as a nickel plating layer. A washer-type cutting blade (washer blade) may also be used as the cutting blade 50. A washer blade is composed of an annular cutting edge in which abrasive grains are fixed by a binder made of metal, ceramics, resin, or the like.

A rotary drive source such as a motor (not shown) is connected to the base end (other end) of the spindle 48. The cutting blade 50 rotates around a rotation axis that is approximately perpendicular to the machining feed direction by the power transmitted from the rotary drive source through the spindle 48.

A ball screw type movement mechanism (not shown) is connected to the cutting unit 46. The movement mechanism moves the cutting unit 46 along the index feed direction (left and right direction in FIG. 6(A)) and the vertical direction. This movement mechanism adjusts the position of the cutting blade 50 in the index feed direction and the height (cut depth) of the cutting blade 50.

In the cutting step, first, the stacked wafers 21 are held by the chuck table 42. Specifically, the stacked wafers 21 are placed on the chuck table 42 so that the back surface 11b (protective member 23 side) of the wafers 11 faces the holding surface 42a and the back surface 19b of the wafers 19 is exposed upward. In addition, the frame 25 is gripped and fixed by a number of clamps 44. In this state, when negative pressure from a suction source is applied to the holding surface 42a, the wafer 11 side of the stacked wafers 21 is suction-held by the chuck table 42 via the protective member 23.

Next, the chuck table 32 is rotated to align the length direction of the planned division line 17 (see FIG. 1) with the processing feed direction (front-to-back direction in FIG. 6(A)). The position of the chuck table 32 in the indexing feed direction (left-to-right direction in FIG. 6(A)) is also adjusted so that the cutting blade 50 is positioned on an extension of the planned division line 17. Furthermore, the height position of the bottom end of the cutting blade 50 is positioned lower than the height position of the bottom end of the stacked wafers 21 (the back surface 11b of the wafer 11).

In this state, the chuck table 42 is moved along the processing feed direction while the cutting blade 50 is rotated. This causes the cutting blade 50 to cut into the stacked wafers 21 along the planned division line 17, cutting the wafers 11 and 19 simultaneously.

The difference in height between the top surface of the stacked wafers 21 (the back surface 19b of the wafers 19) and the bottom end of the cutting blade 50, i.e., the cutting depth of the cutting blade 50 into the stacked wafers 21, is greater than the thickness of the stacked wafers 21. Therefore, the cutting blade 50 cuts the stacked wafers 21 to a cutting depth that reaches the protective member 23. As a result, the stacked wafers 21 are cut along the planned division lines 17.

Figure 6 (B) is an enlarged cross-sectional view of a portion of the laminated wafer 21 cut by the cutting blade 50. In the cutting step, a cutting blade 50 that is thinner than the width of the modified portion 27 formed in the functional layer 13 is used. The cutting blade 50 then cuts between both ends of the modified portion 27 in the width direction (inside the modified portion 27) and cuts the functional layer 13 along the planned division line 17 together with the wafer 11 and the wafer 19. For example, when two modified regions 27a, 27b are formed as shown in Figure 6 (B), the cutting blade 50 cuts into the region of the functional layer 13 located between the modified regions 27a, 27b.

The functional layer 13 contains various films, and when the rotating cutting blade 50 comes into contact with the functional layer 13, the films contained in the functional layer 13 may be caught in the cutting blade 50 and peeled off. In particular, when the functional layer 13 contains a low dielectric constant insulating film (Low-k film), peeling of the low dielectric constant insulating film is likely to occur. If the peeling of the film reaches the device 15 from the planned division line 17, there is a risk that the device 15 may be damaged.

However, in this embodiment, a modified portion 27 is formed in the functional layer 13, and the functional layer 13 is divided at the modified portion 27. More specifically, the connection between the functional layer 13 existing on the outside and inside of the two modified regions 27a, 27b is severed by the modified regions 27a, 27b. Then, in the cutting step, the cutting blade 50 cuts into the inside of the modified portion 27 (between the modified regions 27a, 27b). Therefore, even if the film contained in the functional layer 13 is peeled off by the cutting blade 50 within the planned division line 17, the peeling is stopped by the modified regions 27a, 27b and does not reach the device 15. This prevents damage to the device 15.

Then, the same procedure is repeated, cutting the cutting blade 50 sequentially along the other planned division lines 17 to cut the laminated wafer 21. Then, when the laminated wafer 21 has been cut along all of the planned division lines 17, the laminated wafer 21 is divided into a plurality of device chips, each of which includes a device 15.

As described above, in the laminated wafer processing method according to this embodiment, the laser beam 38 is irradiated onto the functional layer 13 via the wafer 11 or the wafer 19 to form a modified portion 27 in the functional layer 13. Therefore, even in the laminated wafer 21 in which the functional layer 13 is covered by the wafer 11 and the wafer 19, the functional layer 13 can be appropriately modified. This makes it possible to prevent peeling of the film contained in the functional layer 13 from reaching the device 15, and to prevent damage to the device 15.

In the above embodiment, an example has been described in which the protective member 23 is attached to the wafer 11, and the cutting blade 50 cuts into the stacked wafers 21 so as to reach the protective member 23 from the rear surface 19b of the wafer 19 (see FIG. 6(A)). However, there is no limitation on the method for cutting the stacked wafers 21 in the cutting step.

For example, after the functional layer modification step (see FIG. 5(A)), the laminated wafers 21 may be peeled off from the protective member 23, and a new protective member may be attached to the back surface 19b of the wafer 19 (protective member attachment step). The laminated wafers 21 are then held by the chuck table 42 (see FIG. 6(A)) of the cutting device 40 so that the back surface 11b of the wafer 11 is exposed upward. Thereafter, the cutting blade 50 is caused to cut into the laminated wafers 21 from the back surface 11b of the wafer 11 to the protective member attached to the back surface 19b of the wafer 19, and the laminated wafers 21 are cut.

In the above embodiment, the laminated wafer 21 has two wafers 11 and 19, but the laminated wafer 21 may have three or more wafers. If the laminated wafer 21 includes two or more functional layers 13, a functional layer modification step is performed on each functional layer 13.

In addition, the structures, methods, etc. relating to the above embodiments can be modified as appropriate without departing from the scope of the purpose of the present invention.

11 Wafer 11a Front surface 11b Back surface 13 Functional layer (device layer)
15 Device 17 Planned division line (street)
19 Wafer 19a Front surface 19b Back surface 21 Stacked wafer 23 Protective member 25 Frame 25a Opening 27 Modified portion 27a, 27b Modified region 2 Grinding device 4 Chuck table (holding table)
4a Holding surface 6 Clamp 8 Grinding unit 10 Spindle 12 Mount 14 Grinding wheel 16 Base 18 Grinding stone 20 Nozzle 22 Grinding fluid 30 Laser processing device 32 Chuck table (holding table)
32a: Holding surface 34: Clamp 36: Laser irradiation unit 38: Laser beam 40: Cutting device 42: Chuck table (holding table)
42a: Holding surface 44: Clamp 46: Cutting unit 48: Spindle 50: Cutting blade

Claims (4)

A processing method for a laminated wafer, the method including: a functional layer constituting a device arranged in each of areas partitioned by a plurality of planned dividing lines; and a first wafer and a second wafer stacked on each other via the functional layer, the method comprising the steps of:
a protective member attaching step of attaching a protective member to the laminated wafer;
a functional layer modifying step of irradiating the functional layer along the planned dividing lines through the first wafer with a laser beam that is transparent to the first wafer and absorbent to the functional layer, thereby forming modified portions in the functional layer along the planned dividing lines;
A method for processing a laminated wafer, comprising, after performing the protective member attachment step and the functional layer modification step, a cutting step of inserting a cutting blade between both widthwise ends of the modified portion and cutting the laminated wafer along the planned division line. In the functional layer modification step, two modified regions are formed along both ends of the width direction of the division line,
2. The method for processing laminated wafers according to claim 1, wherein in the cutting step, the cutting blade is inserted between two of the modified regions. The method for processing a laminated wafer according to claim 1 or 2, characterized in that in the functional layer modification step, the focal point of the laser beam is positioned inside the functional layer. The method for processing laminated wafers according to any one of claims 1 to 3, further comprising a grinding step of grinding the first wafer to a predetermined thickness before carrying out the functional layer modification step.

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