JP7313775B2 - Wafer processing method - Google Patents

Description

The present invention relates to a wafer processing method used for processing wafers typified by silicon wafers.

In the process of manufacturing device chips, a wafer is used in which devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integration) are formed on the surface side of areas partitioned by dividing lines (streets). A plurality of device chips each having a device is obtained by dividing the wafer along the planned division lines. Device chips are mounted on various electronic devices such as mobile phones and personal computers.

Along with the miniaturization and thinning of electronic equipment, there is a demand for thinning of device chips. Therefore, a method of thinning the wafer by grinding the back side of the wafer before splitting is used. A grinding apparatus including a chuck table for holding the wafer and a grinding unit for grinding the wafer is used for grinding the wafer. The grinding unit is equipped with a grinding wheel to which a plurality of grinding wheels are fixed.

Also, in recent years, a technique for processing a plurality of stacked wafers has been proposed (see Patent Document 1). For example, a technology has been put into practical use in which wafers on which a plurality of devices are formed are stacked, and the devices are connected to each other by a through electrode (TSV: Through-Silicon Via) penetrating vertically through the wafers. Compared to the case of using wire bonding or the like, the use of these through electrodes makes it possible to shorten the wiring that connects the devices, so that it is possible to reduce the size of the device chip and improve the processing speed.

Further, in the manufacturing process of a back side illumination (BSI) type complementary metal oxide semiconductor (CMOS) sensor, the front side of a first wafer on which a photodiode is formed and the front side of a second wafer on which a wiring layer is formed are bonded to form a bonded wafer including a photodiode and a wiring layer that are laminated to each other. This bonded wafer is thinned by grinding and then divided into a plurality of chips.

JP 2016-4795 A

When thinning a bonded wafer in which a first wafer and a second wafer are stacked, wet etching using a chemical solution may be performed on the back side of the first wafer after the back side of the first wafer is ground. This wet etching uniformly planarizes the back side of the first wafer. After that, the second wafer is thinned by grinding the back side of the second wafer.

However, when the chemical solution is supplied to the rear surface side of the first wafer, the chemical solution may run along the outer peripheral edge of the first wafer and enter between the first wafer and the second wafer. In this case, the chemical solution is supplied to the bonding area (interface) between the first wafer and the second wafer in the outer peripheral portion of the bonded wafer, thereby weakening the bonding between the first wafer and the second wafer. If the back surface of the second wafer is ground in a state in which the bonding between the first wafer and the second wafer is insufficient in the outer peripheral portion of the bonded wafer, processing defects such as chipping and breaking (cracks) are likely to occur in the outer peripheral portion of the bonded wafer.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wafer processing method capable of suppressing the occurrence of defective processing.

According to one aspect of the present invention, a first cutting step of cutting the chamfered portion into an annular shape by cutting the chamfered portion into an annular shape from the surface side of a first wafer having a chamfered portion on the outer peripheral portion, a device region in which a plurality of devices are formed, and an outer peripheral surplus region surrounding the device region on the front surface side of the outer peripheral surplus region to a region on the outer peripheral edge side of the first wafer in the outer peripheral surplus region, and cutting the chamfered portion annularly after performing the first cutting step. a first grinding step of grinding the back side of the first wafer to make the thickness of the first wafer the finished thickness after performing the bonded wafer forming step; a wet etching step of supplying a chemical solution to the back side of the first wafer ground in the first grinding step to wet-etch the back side of the first wafer; A second cutting step in which a cutting blade of No. 2 is cut with a depth of cut from the side of the first wafer to the second wafer to circularly cut a region of the outer peripheral portion of the bonded wafer to which the chemical solution has adhered; a protective member disposing step of disposing a protective member on the side of the first wafer of the bonded wafer after the second cutting step; a step of disposing a protective member on the first wafer side of the bonded wafer; and a thinning second grinding step.

In addition, preferably, in the second cutting step, of the peripheral surplus region of the first wafer, the region remaining after the first cutting step is performed is cut and removed. Preferably, the device is a photodiode, a plurality of wiring layers are formed on the surface side of the second wafer, and in the bonded wafer forming step, the first wafer and the second wafer are bonded together so that the photodiode and the wiring layer are connected.

In a wafer processing method according to an aspect of the present invention, after wet etching is performed by supplying a chemical solution to the back surface side of the first wafer, the region of the outer peripheral portion of the bonded wafer to which the chemical solution is adhered is cut into an annular shape. As a result, the region where the bonding between the first wafer and the second wafer is weakened by the chemical solution is removed from the outer peripheral portion of the bonded wafer, and processing defects are less likely to occur when the second wafer is subsequently ground.

FIG. 1A is a perspective view showing the first wafer, and FIG. 1B is a perspective view showing the second wafer. FIG. 2(A) is a front view showing the first wafer in the first cutting step, and FIG. 2(B) is a plan view showing an enlarged part of the peripheral surplus region of the first wafer. It is a front view which shows a bonded wafer. FIG. 4 is a front view showing the bonded wafer in the first grinding step; FIG. 4 is a front view showing the bonded wafer in the polishing step; FIG. 4B is a front view showing the bonded wafer in a wet etching step; FIG. 10 is a front view showing the bonded wafer in the second cutting step; FIG. 4 is a front view showing a bonded wafer on which a protective member is arranged; FIG. 11 is a front view showing the bonded wafer in the second grinding step; FIG. 10 is a front view showing the bonded wafer after the second grinding step;

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, a configuration example of a wafer that can be processed by the wafer processing method according to the present embodiment will be described. FIG. 1A is a perspective view showing a wafer 11 (first wafer 11), and FIG. 1B is a perspective view showing a wafer 21 (second wafer 21). By bonding the wafer 11 and the wafer 21 together, a bonded wafer 31 (see FIG. 3), which will be described later, is formed.

The wafer 11 shown in FIG. 1A is, for example, a disk-shaped SOI (Silicon On Insulator) substrate, and includes a front surface 11a, a back surface 11b, and an outer peripheral edge (side surface) 11c connected to the front surface 11a and the back surface 11b. The wafer 11 is subjected to a so-called chamfering process to remove corners formed on the outer peripheral edge 11c of the wafer 11. As shown in FIG. Therefore, the outer peripheral edge 11c of the wafer 11 is curved from the front surface 11a to the back surface 11b of the wafer 11 (see FIG. 2A, etc.).

The wafer 11 is partitioned into a plurality of regions by a plurality of dividing lines (streets) 13 arranged in a grid pattern so as to intersect each other. Devices 15 such as ICs (Integrated Circuits) and LSIs (Large Scale Integration) are formed on the surface 11a side of the plurality of regions.

Further, the wafer 11 has, on its surface 11a side, a device region 17a in which a plurality of devices 15 are formed, and an outer peripheral surplus region 17b surrounding the device region 17a and in which no device 15 is formed. For example, the device region 17a has a circular shape in plan view, and the peripheral surplus region 17b corresponds to an annular region surrounding the device region 17a.

The structure, material, etc. of the wafer 21 shown in FIG. 1B are the same as those of the wafer 11 . Specifically, the wafer 21 has a front surface 21a, a back surface 21b, and an outer peripheral edge (side surface) 21c. Note that the wafer 21 is also chamfered in the same manner as the wafer 11 .

The wafer 21 is partitioned into a plurality of regions by a plurality of division lines (streets) 23 arranged in a grid pattern so as to intersect each other, and devices 25 are formed on the surface 21a side of each region. Further, the wafer 21 has, on its front surface 21a side, a device region 27a in which a plurality of devices 25 are formed, and an outer peripheral surplus region 27b surrounding the device region 27a and in which no device 25 is formed.

The material, shape, structure, size, etc. of the wafers 11 and 21 are not limited. For example, the wafers 11 and 21 may be substrates made of materials such as semiconductors (Si, GaAs, InP, GaN, SiC, etc.), glass, ceramics, resins, and metals. Moreover, there are no restrictions on the type, number, shape, structure, size, arrangement, etc. of the devices 15 and 25 .

The wafer 11 and the wafer 21 are bonded to each other and stacked in a bonded wafer forming step, which will be described later. Thereby, a bonded wafer 31 (see FIG. 3) including the wafer 11 and the wafer 21 that are stacked is formed. When the wafer 11 and the wafer 21 are bonded together, the devices 15 of the wafer 11 and the devices 25 of the wafer 21 are connected.

For example, when manufacturing a Back Side Illumination (BSI) type CMOS (Complementary Metal Oxide Semiconductor) sensor, a photodiode is formed on the wafer 11 as the device 15, and a wiring layer is formed on the wafer 21 as the device 25. The wiring layer formed on the wafer 21 corresponds to a layer including wiring for supplying signals to the photodiodes, wiring for outputting signals from the photodiodes, circuits (driving circuits) for driving the photodiodes, and the like. By bonding the wafer 11 and the wafer 21 together, the photodiode and the wiring layer are connected.

By dividing the bonded wafers 11 and 21 along, for example, dividing lines 13 and 23, a plurality of device chips each having stacked devices 15 and 25 are manufactured. For dividing the wafers 11 and 21, for example, a cutting device is used which includes a chuck table (holding table) for holding the wafers 11 and 21 and a cutting unit to which an annular cutting blade for cutting the wafers 11 and 21 is mounted.

By thinning the wafers 11 and 21 before dividing the wafers 11 and 21, thinned device chips can be obtained. In the wafer processing method according to the present embodiment, the wafers 11 and 21 are thinned by grinding the back surface 11b side of the wafer 11 and the back surface 21b side of the wafer 21, respectively. A specific example of the wafer processing method according to the present embodiment will be described below.

First, a first cutting blade is caused to cut into the wafer 11 from the front surface 11a side of the wafer 11, and the outer peripheral portion of the wafer 11 is cut into an annular shape (first cutting step). FIG. 2A is a front view showing the wafer 11 in the first cutting step. The cutting of the wafer 11 is performed using the cutting device 2, for example.

The cutting device 2 includes a chuck table (holding table) 4 that holds the wafer 11 . The upper surface of the chuck table 4 constitutes a holding surface 4a for holding the wafer 11. As shown in FIG. The holding surface 4 a is connected to a suction source (not shown) such as an ejector through a suction path (not shown) formed inside the chuck table 4 .

The chuck table 4 is connected to a rotary drive source (not shown) such as a motor, and this rotary drive source rotates the chuck table 4 around a rotary shaft substantially parallel to the vertical direction. A moving mechanism (not shown) is provided below the chuck table 4, and this moving mechanism moves the chuck table 4 along the processing feed direction (first horizontal direction).

A cutting unit 6 is arranged above the chuck table 4 . The cutting unit 6 has a cylindrical housing (not shown), which accommodates a cylindrical spindle 8 arranged along a direction generally parallel to the holding surface 4a and generally perpendicular to the machining feed direction.

A tip portion (one end side) of the spindle 8 is exposed from the housing, and an annular cutting blade 10 (first cutting blade 10) is attached to the tip portion of the spindle 8 . The cutting blade 10 is formed, for example, by fixing abrasive grains made of diamond, cubic boron nitride (cBN) or the like with a bonding material made of metal, ceramics, resin or the like.

A rotational drive source (not shown) such as a motor is connected to the base end (the other end) of the spindle 8 . A cutting blade 10 mounted on a spindle 8 is rotated by a force transmitted through the spindle 8 from this rotational drive source. A moving mechanism (not shown) is connected to the cutting unit 6, and this moving mechanism moves the cutting unit 6 along the indexing feed direction (second horizontal direction) perpendicular to the processing feed direction and the vertical direction.

In the first cutting step, first, the wafer 11 is arranged on the chuck table 4 so that the back surface 11b side of the wafer 11 faces the holding surface 4a. In this state, when a negative pressure from a suction source is applied to the holding surface 4a, the wafer 11 is suction-held by the chuck table 4 with the front surface 11a exposed upward.

As described above, the wafer 11 is chamfered, and the outer peripheral edge 11c of the wafer 11 is curved. Therefore, a chamfered portion 19 is formed on the outer peripheral portion of the wafer 11 so that the thickness of the wafer 11 decreases toward the radially outer side of the wafer 11 .

Next, the cutting blade 10 cuts the peripheral surplus region 17b of the wafer 11 held by the chuck table 4 . In the first cutting step, the cutting blade 10 is cut into a part of the peripheral surplus region 17b on the side of the outer peripheral edge 11c of the wafer 11 .

FIG. 2B is a plan view showing an enlarged portion of the peripheral surplus region 17b of the wafer 11. FIG. The outer peripheral surplus region 17 b includes an annular region 17 c located on the outer peripheral edge 11 c side of the wafer 11 . This area 17c corresponds to, for example, the area on the surface 11a side of the chamfered portion 19 (see FIG. 2A).

In the first cutting step, the position of the cutting unit 6 is adjusted so that the cutting blade 10 cuts from the front surface 11a side of the wafer 11 into the region 17c of the outer peripheral surplus region 17b with a depth of cut exceeding the first finish thickness. The first finished thickness corresponds to the thickness of the wafer 11 after being thinned by grinding in the first grinding step (see FIG. 4) described later.

Specifically, first, the height of the cutting unit 6 is adjusted so that the lower end of the cutting blade 10 is positioned below the front surface 11a of the wafer 11 and above the rear surface 11b. At this time, the cutting blade 10 is arranged so that the difference in height between the surface 11a of the wafer 11 and the lower end of the cutting blade 10 (cutting depth of the cutting blade 10) exceeds the first finish thickness. As the cutting blade 10, a cutting blade having a thickness equal to or greater than the width of the region 17c is used.

In addition, the position of the cutting unit 6 in the index feed direction (horizontal direction in FIG. 2(A)) is adjusted so that the cutting blade 10 and the region 17c overlap when viewed from the front. Then, while rotating the cutting blade 10, the chuck table 4 is moved in the processing feed direction (the front-rear direction in FIG. 2(A)) to move the chuck table 4 and the cutting blade 10 relatively. As a result, the cutting blade 10 cuts into the region 17c from the surface 11a side to a predetermined cutting depth.

With the cutting blade 10 cutting into the region 17c, the movement of the chuck table 4 is stopped and the chuck table 4 is rotated. As a result, the cutting blade 10 cuts into the region 17c along the circumferential direction of the wafer 11 . As a result, the chamfered portion 19 is cut into an annular shape, and a stepped portion 19a (see FIG. 3) is formed in the chamfered portion 19. As shown in FIG.

The stepped portion 19a includes an annular bottom surface (bottom portion) that is substantially parallel to the front surface 11a and the rear surface 11b of the wafer 11 and is located closer to the rear surface 11b than the front surface 11a, and an annular side surface that is substantially parallel to the thickness direction of the wafer 11 and formed from the front surface 11a to the bottom surface of the wafer 11. The depth (height of the side surface) of this stepped portion 19a is equal to the depth of cut of the cutting blade 10 and larger than the first finish thickness.

Next, the front surface 11a side of the wafer 11 and the front surface 21a side of the wafer 21 are bonded to form a bonded wafer (bonded wafer formation step). FIG. 3 is a front view showing a bonded wafer (laminated wafer) 31. FIG.

In the bonded wafer forming step, the wafers 11 and 21 are bonded and stacked such that the front surface 11a side of the wafer 11 and the front surface 21a of the wafer 21 are in contact with each other. At this time, the devices 15 formed on the wafer 11 (see FIG. 1A) and the devices 25 formed on the wafer 21 (see FIG. 1B) are connected. For example, when the device 15 is a photodiode and the device 25 is a wiring layer, the photodiode and the wiring layer are connected by performing the bonded wafer forming step.

The wafer 11 and the wafer 21 are bonded by direct bonding, for example. However, the method of bonding the wafers 11 and 21 is not limited, and indirect bonding may be used. For example, an adhesive may be applied to the front surface 11a side of the wafer 11 or the front surface 21a side of the wafer 21, and the wafers 11 and 21 may be bonded via the adhesive.

Next, the back surface 11b side of the wafer 11 is ground (first grinding step). FIG. 4 is a front view showing the bonded wafer 31 in the first grinding step. Grinding of the bonded wafer 31 is performed using the grinding device 20, for example.

The grinding device 20 includes a chuck table (holding table) 22 that holds the bonded wafer 31 . The upper surface of the chuck table 22 forms a holding surface 22a for holding the bonded wafer 31. As shown in FIG. The holding surface 22 a is connected to a suction source (not shown) such as an ejector through a suction path (not shown) formed inside the chuck table 22 .

The chuck table 22 is connected to a rotary drive source (not shown) such as a motor, and this rotary drive source rotates the chuck table 22 around a rotary shaft substantially parallel to the vertical direction. A moving mechanism (not shown) is provided below the chuck table 22, and this moving mechanism moves the chuck table 22 in the horizontal direction.

A grinding unit 24 is arranged above the chuck table 22 . The grinding unit 24 has a cylindrical housing (not shown) supported by a lifting mechanism (not shown). A cylindrical spindle 26 is accommodated in this housing, and the tip (lower end) of the spindle 26 is exposed from the housing.

A disk-shaped mount 28 is fixed to the tip of the spindle 26 . An annular grinding wheel 30 having approximately the same diameter as the mount 28 is attached to the lower surface of the mount 28 . The grinding wheel 30 has an annular base 32 made of metal such as stainless steel or aluminum. A plurality of rectangular parallelepiped grinding wheels 34 are annularly arranged along the outer circumference of the base 32 on the lower surface side of the base 32 .

A rotational drive source (not shown) such as a motor is connected to the base end of the spindle 26 . Grinding wheel 30 mounted on mount 28 is rotated by force transmitted from this rotational drive source through spindle 26 and mount 28 .

A nozzle 36 for supplying a grinding liquid 38 such as pure water to the bonded wafer 31 held by the chuck table 22 and the plurality of grinding wheels 34 is provided near the chuck table 22 and the grinding unit 24 . When the bonded wafer 31 is ground by the plurality of grinding wheels 34 , the grinding liquid 38 is supplied from the nozzle 36 to the bonded wafer 31 and the plurality of grinding wheels 34 .

In the first grinding step, first, the bonded wafer 31 is held by the chuck table 22 . Specifically, the bonded wafer 31 is arranged on the chuck table 22 so that the back surface 21b side of the wafer 21 faces the holding surface 22a and the back surface 11b side of the wafer 11 is exposed upward. In this state, the bonded wafer 31 is suction-held by the chuck table 22 by applying the negative pressure of the suction source to the holding surface 22 a of the chuck table 22 .

Next, the chuck table 22 holding the bonded wafer 31 is moved below the grinding unit 24 . Then, the grinding wheel 30 is lowered toward the chuck table 22 while rotating the chuck table 22 and the grinding wheel 30 in predetermined directions at predetermined rotation speeds. The descending speed of the grinding wheel 30 at this time is adjusted so that the plurality of grinding wheels 34 are pressed against the back surface 11b side of the wafer 11 with an appropriate force.

When a plurality of rotating grinding wheels 34 come into contact with the rear surface 11b side of the wafer 11, the rear surface 11b side of the wafer 11 is scraped off. As a result, the wafer 11 is ground and thinned. Then, when the thickness of the wafer 11 reaches a predetermined target value (first finished thickness), the grinding of the wafer 11 is stopped.

Also, when the wafer 11 is ground by the plurality of grinding wheels 34 , the grinding fluid 38 is supplied from the nozzle 36 to the wafer 11 and the plurality of grinding wheels 34 . The grinding liquid 38 cools the wafer 11 and the plurality of grinding wheels 34 and washes away debris (grinding debris) generated by grinding the wafer 11 .

When the thickness of wafer 11 reaches the first finish thickness, chamfered portion 19 (see FIG. 3) of wafer 11 is removed. The outer peripheral edge 11c of the wafer 11 after grinding becomes a flat surface substantially parallel to the thickness direction of the wafer 11 (see FIG. 5, etc.).

Here, if the wafer 11 does not have the stepped portion 19a, if the back surface 11b side of the wafer 11 is ground in the grinding step, the outer peripheral portion (chamfered portion 19) of the wafer 11 after grinding becomes sharply pointed radially outward of the wafer 11, that is, a so-called knife edge shape. If the outer peripheral portion of the wafer 11 has a knife-edge shape, the outer peripheral portion of the wafer 11 is likely to be damaged, such as chipped or cracked.

On the other hand, if so-called edge trimming is performed to form a stepped portion 19a along the outer peripheral portion of the wafer 11, the outer peripheral edge 11c of the wafer 11 after grinding does not have a knife-edge shape and becomes flat. As a result, the peripheral portion of the wafer 11 is less likely to be damaged.

Next, the back surface 11b side of the wafer 11 is polished (polishing step). FIG. 5 is a front view showing the bonded wafer 31 in the polishing step. Polishing of the bonded wafer 31 is performed using a polishing apparatus 40, for example.

The polishing apparatus 40 includes a chuck table (holding table) 42 that holds the bonded wafer 31 . The upper surface of the chuck table 42 constitutes a holding surface 42 a that holds the bonded wafer 31 . The holding surface 42 a is connected to a suction source (not shown) such as an ejector through a suction path (not shown) formed inside the chuck table 42 .

The chuck table 42 is connected to a rotation drive source (not shown) such as a motor, and this rotation drive source rotates the chuck table 42 around a rotation axis substantially parallel to the vertical direction. A moving mechanism (not shown) is provided below the chuck table 42, and this moving mechanism moves the chuck table 42 along the horizontal direction.

A polishing unit 44 is arranged above the chuck table 42 . The polishing unit 44 has a cylindrical housing (not shown) supported by an elevating mechanism (not shown). A cylindrical spindle 46 is accommodated in this housing, and the tip (lower end) of the spindle 46 is exposed from the housing.

A disk-shaped mount 48 is fixed to the tip of the spindle 46 . A disk-shaped polishing pad 50 having approximately the same diameter as the mount 48 is attached to the lower surface of the mount 48 . The polishing pad 50 has a disk-shaped base 52 made of metal such as stainless steel or aluminum. A disk-shaped polishing layer 54 is fixed to the lower surface of the base 52 .

A rotational drive source (not shown) such as a motor is connected to the base end of the spindle 46 . The polishing pad 50 mounted on the mount 48 is rotated by force transmitted from this rotational drive source via the spindle 46 and mount 48 .

Further, inside the polishing unit 44, a polishing liquid supply path 56 that opens at the center of the lower surface of the polishing layer 54 is formed along the vertical direction. When polishing the bonded wafer 31 , the polishing liquid is supplied from the polishing liquid supply path 56 toward the bonded wafer 31 and the polishing layer 54 .

The polishing layer 54 is formed, for example, by dispersing abrasive grains (fixed abrasive grains) in nonwoven fabric or urethane foam. As abrasive grains, for example, silica having a grain size of about 0.1 μm to 10 μm can be used. However, the grain size, material, etc. of the abrasive grains are appropriately changed according to the material, etc. of the wafer 11 .

When the polishing layer 54 contains abrasive grains, the polishing liquid supplied from the polishing liquid supply path 56 is a polishing liquid that does not contain abrasive grains. As the polishing liquid, for example, an alkaline solution in which sodium hydroxide, potassium hydroxide, or the like is dissolved, or an acidic liquid such as permanganate can be used. Pure water can also be used as the polishing liquid.

On the other hand, the polishing layer 54 may not contain abrasive grains. In this case, a chemical solution (slurry) in which abrasive grains (loose abrasive grains) are dispersed is used as the polishing liquid supplied from the polishing liquid supply path 56 . The material of the chemical liquid, the material of the abrasive grains, the grain size of the abrasive grains, and the like are appropriately selected according to the material of the wafer 11 and the like.

In the polishing step, first, the bonded wafer 31 is held by the chuck table 42 . Specifically, the bonded wafer 31 is arranged on the chuck table 42 so that the back surface 21b side of the wafer 21 faces the holding surface 42a and the back surface 11b side of the wafer 11 is exposed upward. In this state, when a negative pressure of a suction source is applied to the holding surface 42a of the chuck table 42, the bonded wafer 31 is held by the chuck table 42 by suction.

Next, the chuck table 42 holding the bonded wafer 31 is moved below the polishing unit 44 . Then, the chuck table 42 and the polishing pad 50 are rotated in predetermined directions at predetermined rotation speeds, and the polishing pad 50 is lowered toward the chuck table 42 while supplying the polishing liquid from the polishing liquid supply path 56 toward the bonded wafer 31. The lowering speed of the polishing pad 50 at this time is adjusted so that the lower surface of the polishing layer 54 is pressed against the back surface 11b side of the wafer 11 with an appropriate force.

When the rotating polishing layer 54 contacts the rear surface 11b side of the wafer 11, the rear surface 11b side of the wafer 11 is polished. This polishing removes the grinding marks formed on the back surface 11b side of the wafer 11 by performing the above-described first grinding step, and the back surface 11b side of the wafer 11 is flattened. Then, when the thickness of the wafer 11 reaches a predetermined thickness, the polishing of the wafer 11 is stopped.

Note that the first grinding step and the polishing step may be performed using one processing apparatus including the grinding unit 24 (see FIG. 4) and the polishing unit 44 (see FIG. 5). In addition, if there is no problem even if the wafer 11 is not polished, such as when the influence of the grinding marks formed in the first grinding step is small, the polishing step can be omitted.

Next, a chemical solution is supplied to the back surface 11b side of the wafer 11 to wet-etch the back surface 11b side of the wafer 11 (wet etching step). FIG. 6 is a front view showing the bonded wafer 31 in the wet etching step. Wet etching of the bonded wafer 31 is performed using an etching apparatus 60, for example.

The etching apparatus 60 includes a chuck table (holding table) 62 that holds the bonded wafer 31 . The upper surface of the chuck table 62 constitutes a holding surface 62 a that holds the bonded wafer 31 . The holding surface 62 a is connected to a suction source (not shown) such as an ejector through a suction path (not shown) formed inside the chuck table 62 .

The chuck table 62 is connected to a rotation drive source (not shown) such as a motor, and this rotation drive source rotates the chuck table 62 around a rotation axis substantially parallel to the vertical direction. A nozzle 64 for supplying a chemical solution (etching solution) 66 for etching the bonded wafer 31 is arranged above the chuck table 62 .

In the wet etching step, first, the bonded wafer 31 is held by the chuck table 62 . Specifically, the bonded wafer 31 is arranged on the chuck table 62 so that the back surface 21b side of the wafer 21 faces the holding surface 62a and the back surface 11b side of the wafer 11 is exposed upward. In this state, when a negative pressure of a suction source is applied to the holding surface 62a of the chuck table 62, the bonded wafer 31 is held by the chuck table 62 by suction.

Next, while the chuck table 62 is being rotated, the chemical solution 66 is jetted (dripped) from the nozzle 64 toward the chuck table 62 side. As a result, the chemical solution 66 is supplied to the entire rear surface 11b side of the wafer 11, and the rear surface 11b of the wafer 11 is subjected to wet etching.

The material of the chemical liquid 66 is appropriately selected according to the material of the wafer 11 and the like. For example, when the wafer 11 is made of silicon, an acidic mixed solution containing hydrofluoric acid and nitric acid can be used as the chemical solution 66 . This wet etching removes processing marks formed on the back surface 11b side of the wafer 11 by grinding or polishing, and the back surface 11b side of the wafer 11 is uniformly flattened.

When the chemical solution 66 is supplied from the nozzle 64 to the bonded wafer 31 , the chemical solution 66 enters between the wafer 11 and the wafer 21 along the outer peripheral edge 11 c from the back surface 11 b side of the wafer 11 . As a result, the chemical solution 66 is supplied to the bonding area (interface) between the wafers 11 and 21 in the outer peripheral portion of the bonded wafer 31, and the bonding between the wafers 11 and 21 is weakened.

Next, the second cutting blade is cut into the bonded wafer 31 with a depth of cut from the wafer 11 side to the wafer 21 to cut the outer peripheral portion of the bonded wafer 31 in an annular shape (second cutting step). FIG. 7 is a front view showing the bonded wafer 31 in the second cutting step.

In the second cutting step, for example, the cutting device 2 used in the first cutting step is used. A cutting blade 12 (second cutting blade 12 ) is attached to the cutting unit 6 . The material, structure, etc. of the cutting blade 12 are the same as those of the cutting blade 10 (see FIG. 2A). The cutting blade 12 may be the same as or different from the cutting blade 10 .

In the second cutting step, first, the bonded wafer 31 is held by the chuck table 4 . Specifically, the bonded wafer 31 is arranged on the chuck table 4 so that the back surface 21b side of the wafer 21 faces the holding surface 4a and the back surface 11b side of the wafer 11 is exposed upward. In this state, when a negative pressure of a suction source is applied to the holding surface 4a of the chuck table 4, the bonded wafer 31 is held by the chuck table 4 by suction.

Next, the cutting blade 12 cuts the outer peripheral portion of the bonded wafer 31 held by the chuck table 4 . At this time, the cutting blade 12 is caused to cut into the bonded wafer 31 with a cutting depth from the rear surface 11b side of the wafer 11 to the wafer 21, and the outer peripheral portion of the bonded wafer 31 is cut into an annular shape.

Specifically, first, the height of the cutting unit 6 is adjusted so that the lower end of the cutting blade 12 is arranged below the front surface 21a of the wafer 21 and above the rear surface 21b. At this time, the cutting blade 12 is arranged so that the height difference between the surface 21a of the wafer 21 and the lower end of the cutting blade 12 (the cutting depth of the cutting blade 12 into the wafer 21) exceeds the second finish thickness. The second finished thickness corresponds to the thickness of the wafer 21 after being ground and thinned in the second grinding step (see FIG. 9) described later.

In addition, the position of the cutting unit 6 in the index feed direction (horizontal direction in FIG. 7) is adjusted so that the cutting blade 12 and the outer peripheral portion of the bonded wafer 31 overlap each other when viewed from the front. At this time, the position of the cutting unit 6 is adjusted so that at least a portion of the peripheral surplus region 17b of the wafer 11 (see FIG. 1A) and the peripheral surplus region 27b of the wafer 21 (see FIG. 1A) are cut.

In the above-described first cutting step, of the outer peripheral surplus region 17b of the wafer 11, the region 17c (see FIG. 2B) located on the outer peripheral edge 11c side of the wafer 11 was cut, so that the other region of the outer peripheral surplus region 17b (annular region located on the central side of the wafer 11) remains. For example, in the second cutting step, the position of the cutting unit 6 is adjusted so that the cutting blade 12 cuts into the remaining portion of the peripheral surplus region 17b.

Then, while rotating the cutting blade 12, the chuck table 4 is moved in the processing feed direction (the front-rear direction in FIG. 7), and the chuck table 4 and the cutting blade 12 are moved relative to each other. As a result, the cutting blade 12 cuts the wafer 11 side of the bonded wafer 31 with a predetermined cutting depth, and the outer peripheral portion of the bonded wafer 31 (the outer peripheral surplus region 17b of the wafer 11 and the outer peripheral surplus region 27b of the wafer 21) is cut.

With the cutting blade 12 cutting into the outer peripheral portion of the bonded wafer 31, the movement of the chuck table 4 is stopped and the chuck table 4 is rotated. As a result, the outer peripheral portion of the bonded wafer 31 is cut annularly by the cutting blade 12 to form a stepped portion 31a (see FIG. 8) on the outer peripheral portion of the bonded wafer 31 .

The stepped portion 31a includes an annular bottom surface (bottom portion) that is substantially parallel to the front surface 21a and the rear surface 21b of the wafer 21 and positioned closer to the rear surface 21b than the front surface 21a, and an annular side surface that is substantially parallel to the thickness direction of the wafer 21 and formed from the front surface 21a to the bottom surface of the wafer 21. The height of this side is equal to the depth of cut of the cutting blade 12 into the wafer 21 and is greater than the second finish thickness.

After the above-described wet etching step is performed, an area where the bonding between the wafers 11 and 21 is weakened due to the adhesion of the chemical solution 66 (see FIG. 6) remains on the outer periphery of the bonded wafer 31. However, by cutting the outer peripheral portion of the bonded wafer 31 in an annular shape in the second cutting step, the region to which the chemical liquid 66 adheres is removed. As a result, the bonded wafer 31 is in a state in which the wafer 11 and the wafer 21 are firmly bonded even at the outer peripheral portion.

Next, a protective member is arranged on the wafer 11 side of the bonded wafer 31 (protective member arranging step). FIG. 8 is a front view showing the bonded wafer 31 on which the protective member 33 is arranged.

The protective member 33 is a highly rigid substrate made of glass, silicon, ceramics, or the like. For example, the protective member 33 is formed in a disc shape having approximately the same diameter as the wafer 11 . This protective member 33 is fixed to the rear surface 11b side of the wafer 11 via an adhesive, for example. However, there is no limitation on the method of disposing the protective member 33 on the wafer 11 .

By disposing the protective member 33 on the bonded wafer 31, deformation (bending or the like) of the thinned wafer 11 is suppressed. As a result, the wafer 11 is prevented from being damaged, and the bonded wafer 31 can be easily held and transported. Also, the plurality of devices 15 (see FIG. 1A) formed on the wafer 11 are protected by the protective member 33 .

The material of the protective member 33 is not limited as long as it can protect the wafer 11 and the device 15 . For example, a protective tape made of flexible resin may be used as the protective member 33 . The masking tape includes a circular base material and an adhesive layer (glue layer) provided on the base material. The base material is made of a resin such as polyolefin, polyvinyl chloride, polyethylene terephthalate, etc., and the adhesive layer is made of an epoxy, acrylic or rubber adhesive. In addition, an ultraviolet curable resin that is cured by being irradiated with ultraviolet rays can also be used for the adhesive layer.

Next, the back surface 21b side of the wafer 21 is ground to thin the bonded wafer 31 (second grinding step). FIG. 9 is a front view showing the bonded wafer 31 in the second grinding step. In the second grinding step, for example, the grinding device 20 used in the first grinding step is used.

In the second grinding step, first, the bonded wafer 31 is held by the chuck table 22 . Specifically, the bonded wafer 31 is placed on the chuck table 22 so that the protective member 33 side (back surface 11b side of the wafer 11) faces the holding surface 22a and the back surface 21b side of the wafer 21 is exposed upward. In this state, when the negative pressure of the suction source is applied to the holding surface 22 a of the chuck table 22 , the chuck table 22 holds the bonded wafer 31 on the protective member 33 side by suction.

Then, the rear surface 21b side of the wafer 21 is ground by a plurality of grinding wheels 34 in the same procedure as the first cutting step. Thereby, the wafer 21 is thinned. Then, when the thickness of the wafer 21 reaches a predetermined target value (second finished thickness), the grinding of the wafer 21 is stopped.

Note that the bonded wafer 31 is in a state where the area where the chemical solution 66 adheres, that is, the area where the bonding between the wafer 11 and the wafer 21 is weak, has been removed by performing the second cutting step described above. Therefore, even if the bonded wafer 31 is ground in the second grinding step, processing defects such as chips and cracks are less likely to occur in the peripheral portion of the bonded wafer 31 .

FIG. 10 is a front view showing the bonded wafer 31 after the second grinding step. After the wafer 21 is ground to the second finished thickness, the stepped portion 31a (see FIG. 9) of the bonded wafer 31 is removed. Then, the outer peripheral edge 21c of the wafer 21 after the grinding process does not have a knife-edge shape and becomes flat. As a result, the peripheral portion of the wafer 21 is less likely to be damaged. That is, the above-described second cutting step (see FIG. 7) also serves as a step of edge trimming the wafer 21 .

After the second grinding step, a polishing step (see FIG. 5) and a wet etching step (see FIG. 6) are performed as necessary, and the rear surface 21b side of the wafer 21 is subjected to polishing and wet etching. As a result, the back surface 21b side of the wafer 21 is flattened.

Through the above steps, a bonded wafer 31 in which the thinned wafer 11 and the wafer 21 are bonded together is obtained. By dividing the bonded wafer 31, for example, along the dividing lines 13 and 23 (see FIGS. 1A and 1B), thin device chips in which the devices 15 and 25 are stacked are obtained.

As described above, in the wafer processing method according to the present embodiment, after wet etching is performed by supplying the chemical solution 66 to the back surface 11b side of the wafer 11, the area of the outer peripheral portion of the bonded wafer 31 to which the chemical solution 66 adheres is cut into an annular shape. As a result, the region where the bonding between the wafer 11 and the wafer 21 is weakened by the chemical solution 66 is removed from the outer periphery of the bonded wafer 31, and processing defects are less likely to occur when the wafer 21 is subsequently ground.

It should be noted that the structure, method, and the like according to the above-described embodiments can be modified as appropriate without departing from the scope of the object of the present invention.

REFERENCE SIGNS LIST 11 wafer 11a front surface 11b back surface 11c outer edge (side surface)
13 Planned division line (street)
15 device 17a device region 17b outer peripheral surplus region 17c region 19 chamfered portion 19a stepped portion 21 wafer 21a front surface 21b back surface 21c outer peripheral edge (side surface)
23 Planned division line (street)
25 device 27a device region 27b peripheral surplus region 31 bonded wafer (laminated wafer)
31a stepped portion 33 protective member 2 cutting device 4 chuck table (holding table)
4a holding surface 6 cutting unit 8 spindle 10 cutting blade (first cutting blade)
12 cutting blade (second cutting blade)
20 grinding device 22 chuck table (holding table)
22a holding surface 24 grinding unit 26 spindle 28 mount 30 grinding wheel 32 base 34 grinding wheel 36 nozzle 38 grinding liquid 40 polishing device 42 chuck table (holding table)
42a holding surface 44 polishing unit 46 spindle 48 mount 50 polishing pad 52 base 54 polishing layer 56 polishing liquid supply path 60 etching device 62 chuck table 62a holding surface 64 nozzle 66 chemical (etching liquid)

Claims (3)

A first cutting step of cutting the chamfered portion into an annular shape by cutting the chamfered portion into an annular shape by cutting a first cutting blade into a region on the outer peripheral edge side of the first wafer in the outer peripheral surplus region from the surface side of the first wafer, which has a chamfered portion on the outer peripheral portion and has a device region in which a plurality of devices are formed and an outer peripheral surplus region surrounding the device region on the surface side;
a bonded wafer forming step of forming a bonded wafer by bonding the front surface side of the first wafer and the front surface side of the second wafer after performing the first cutting step;
After performing the bonded wafer forming step, a first grinding step of grinding the back side of the first wafer to make the thickness of the first wafer the finished thickness;
a wet etching step of supplying a chemical solution to the back side of the first wafer ground in the first grinding step to wet-etch the back side of the first wafer;
After the wet etching step is performed, a second cutting blade is cut into the bonded wafer with a depth of cut from the side of the first wafer to the second wafer, and a second cutting step of annularly cutting a region of the outer peripheral portion of the bonded wafer to which the chemical solution is attached;
After performing the second cutting step, a protective member disposing step of disposing a protective member on the first wafer side of the bonded wafer;
A wafer processing method comprising: a second grinding step of holding the protective member side of the bonded wafer by a chuck table of a grinding device and grinding the back side of the second wafer to thin the bonded wafer. 2. The method of processing a wafer according to claim 1, wherein, in said second cutting step, of said peripheral surplus region of said first wafer, a region remaining after said first cutting step is performed is cut and removed. the device is a photodiode;
A plurality of wiring layers are formed on the surface side of the second wafer,
3. The wafer processing method according to claim 1, wherein in said bonded wafer forming step, said first wafer and said second wafer are bonded together so that said photodiode and said wiring layer are connected.

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