JP2022024591A - Wafer processing method and system - Google Patents

Abstract

To provide a wafer processing method and a system, capable of suppressing entry of a grinding dust into a gap caused between chips after a wafer is cut.SOLUTION: A wafer processing method comprises: a laser processing step of forming a laser processing region (R1 and R2) along a division schedule line (CL) of a wafer (W) in an inner part of a substrate of the wafer in which a device layer is laminated onto a front surface of the substrate; and a grinding step of dividing the wafer into individual chips (C) by setting a thickness of the wafer at a target thickness (Ht) by grinding a back surface of the wafer. The laser processing step contains: a position setting step of setting a position in a thickness direction of the wafer of the laser processing region (R2) at a position of the target thickness; and a laser processing region formation step of forming the laser processing region at the position set in the position setting step by collecting a laser beam (L) in an inner part of the wafer.SELECTED DRAWING: Figure 1

Description

The present invention relates to a wafer processing method and system, and relates to a wafer processing method and system for dividing a wafer from a laser processing region formed inside the wafer.

Conventionally, laser processing is performed by aligning a condensing point inside a wafer such as silicon and irradiating laser light along the planned division line to form a laser processing region inside the wafer along the planned division line, which is the starting point of cutting. A device (also referred to as a laser dicing device) is known. The wafer on which the laser processing region is formed is then divided by a division process such as expansion or braking at a division schedule line and divided into individual chips (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2020-057743

In the wafer cutting process, the load (pressure) applied to the wafer when grinding the back surface side of the wafer using a grinder is used to develop cracks from the laser processing region and cut the wafer.

8A and 8B are partial cross-sectional views showing a wafer cutting process, FIG. 8A shows a wafer W before grinding, and FIG. 8B shows a state in which cracks have grown inside the wafer W due to a load during grinding. 8 (c) shows a state in which the wafer W is cut along the crack. FIG. 9 is a partially enlarged view of the region XI of FIG. 8 (c).

First, as shown in FIG. 8A, the wafer W has a back grind tape (not shown in FIG. 8; BG in FIG. 10) attached to the surface Wa on which a device such as an electronic circuit is formed. It is placed on a suction stage (not shown) with the surface Wa facing down and held by suction. Laser processing regions R1 and R2 are formed inside the wafer W by laser processing. The laser processing regions R1 and R2 serve as starting points of cracks K inside the wafer W, and are formed in two stages at different positions in the depth direction (Z direction) of the wafer W. Although a plurality of laser processing regions R1 and R2 are formed along the planned division line of the wafer W, they are simplified to two in FIG.

Next, the back surface Wb of the wafer W is ground by the grinder 50. A grindstone 54 is attached to the rotary grinding machine 52 of the grinding machine 50, and the grindstone 54 is brought into contact with the back surface Wb of the wafer W to rotate the rotary grindstone 52 to grind the wafer W.

As the grinding of the wafer W progresses, the crack K propagates in the depth direction of the wafer W as shown in FIG. 8B due to the load applied to the back surface Wb of the wafer W via the grindstone 54. Then, after reaching the front surface Wa and the back surface Wb of the wafer W, as shown in FIG. 8C, the wafer W is divided along the planned division line, and the divided chips C1 and C2 are expanded. A minute gap Gap is generated.

As shown enlarged in FIG. 9, the grinding debris (also referred to as sludge) SL generated by grinding may enter the gap Gap between the chips C1 and C2 and reach the surfaces of the chips C1 and C2. (See FIG. 10).

FIG. 10 is an image showing the surface of the back grind tape after picking up the chip after cutting. As shown in FIG. 10, the grinding chips SL adhere to the surface of the back grind tape BG in a substantially grid pattern along the planned division line of the wafer W. Such grinding debris SL causes contamination of the device formed on the surfaces of the chips C1 and C2.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a wafer processing method and system capable of suppressing the intrusion of grinding chips into the gaps generated between chips after wafer cutting. ..

In order to solve the above problems, the wafer processing method according to the first aspect of the present invention has a laser processing region inside a wafer substrate in which a device layer is laminated on the surface of the substrate along a planned division line of the wafer. The laser processing step is provided with a laser processing step for forming a wafer and a grinding step for grinding the back surface of the wafer to target the thickness of the wafer and dividing the wafer into individual chips. The laser processing step is in the thickness direction of the wafer in the laser processing region. The position setting step of setting the position of the target thickness to the position of the target thickness, and the laser processing area forming step of forming the laser processing area at the position set in the position setting step by condensing the laser beam inside the wafer. Be prepared.

In the wafer machining method according to the second aspect of the present invention, a plurality of layers of laser machining regions are formed in the thickness direction of the wafer in the laser machining region forming step of the first aspect, and a plurality of layers of lasers are formed in the positioning step. Of the machining areas, the laser machining area on the back surface side is set at the position of the target thickness.

In the wafer processing method according to the third aspect of the present invention, in the position setting step of the first or second aspect, the position of the target thickness is in the range from the back surface side of the laser processing region to one third. Set the position of the laser machining area so that they overlap.

In the wafer processing method according to the fourth aspect of the present invention, in the position setting step of the first or second aspect, the position of the target thickness is 3 minutes from the back surface side of the region excluding the void at the lower end of the laser processing region. The position of the laser machining area is set so as to overlap the area up to 1.

The wafer processing system according to the fifth aspect of the present invention includes a laser processing apparatus that forms a laser processing region along a planned division line of a wafer inside a wafer substrate in which a device layer is laminated on the surface of the substrate. It is equipped with a grinding device that grinds the back surface of the wafer to make the thickness of the wafer the target thickness and divides the wafer into individual chips. It is provided with a position setting unit set to 1 and a laser processing unit that forms a laser processing region at a position set by the position setting unit by condensing the laser beam inside the wafer.

According to the present invention, by forming the laser processing region according to the target thickness of the wafer, it is possible to suppress the intrusion of grinding chips into the gaps of the chips after the wafer is cut.

FIG. 1 is an image showing a machined cross section of a chip after dividing a wafer. FIG. 2 is a block diagram showing a configuration of a laser processing apparatus in a wafer processing system according to an embodiment of the present invention. FIG. 3 is a block diagram showing a configuration of a grinding device in the wafer processing system according to the embodiment of the present invention. FIG. 4 is a cross-sectional view showing the relationship between the laser machining region and the target thickness Ht. FIG. 5 is an image showing a processed cross section of the chip. FIG. 6 is an image showing a machined cross section of the chip after grinding. FIG. 7 is an image showing the surface of the back grind tape after picking up the chip after cutting. FIG. 8 is a partial cross-sectional view showing a wafer cutting process. FIG. 9 is a partially enlarged view of the region XI of FIG. 8 (c). FIG. 10 is an image showing the surface of the back grind tape after picking up the chip after cutting.

Hereinafter, embodiments of the wafer processing method and system according to the present invention will be described with reference to the accompanying drawings.

[Outline of Embodiment]
FIG. 1 is an image showing a machined cross section of a chip after dividing a wafer.

As shown in FIG. 1, when the laser machining regions R1 and R2 are left on the machining cross section (side wall) CW of the chip C after dividing the wafer W, the grinding debris (sludge) SL generated by the grinding process is upward (+ Z). It can be seen that the wafer is collected in the laser processing region R2 on the side, the back surface Wb (see FIG. 2) of the wafer W, and does not invade the front surface Wa side of the laser processing region R2. From this, it is considered that the laser processing regions R1 and R2 have a function of collecting the grinding debris SL invading from the surface side to be ground of the wafer W like a net. Specifically, since the surfaces of the laser processing regions R1 and R2 have more irregularities than the surfaces cut by the cracks extending from the laser processing regions R1 and R2, the irregularities collect the grinding chips SL. It is considered to have the function of.

In the present embodiment, the grinding debris SL is laser-machined by making the Z-direction position of the laser machining region R2 on the back surface Wb side of the wafer W correspond to the target value (hereinafter referred to as the target thickness) Ht of the thickness of the chip C. It is prevented from entering the surface Wa side of the region R2 (see FIG. 4).

[Wafer processing system]
The wafer processing system 10 according to the present embodiment includes a laser processing device 10-1 (see FIG. 2) and a grinding device 10-2 (see FIG. 3). The laser processing apparatus 10-1 forms a laser processing region inside the wafer W along the planned division line of the wafer W (laser processing step). The grinding device 10-2 grinds the back surface Wb of the wafer W to make the thickness of the wafer W the target thickness Ht, and uses the load applied to the wafer W during the grinding process to grind the wafer W into individual chips C. Divide into (grinding steps).

(Laser processing)
FIG. 2 is a block diagram showing a configuration of a laser processing apparatus in a wafer processing system according to an embodiment of the present invention.

As shown in FIG. 2, the laser processing apparatus 10-1 includes a control unit 12, a wafer moving unit 14, and a laser processing unit 16.

The control unit 12 includes a CPU (Central Processing Unit), a memory (for example, ROM (Read Only Memory), RAM (Random Access Memory), etc.), storage (for example, HDD (Hard Disk Drive), SSD (Solid State Drive), etc.). ) And an input / output circuit unit, etc., and controls the operation of each unit of the laser processing apparatus 10-1. The control unit 12 is realized by, for example, a personal computer or a workstation.

The wafer moving unit 14 includes a suction stage T1 that sucks and holds the wafer W, and an XYZθ table that is provided on the main body base (not shown) of the laser processing apparatus 10-1 and moves the suction stage T1 in the XYZθ direction.

The wafer W is, for example, a disk-shaped semiconductor wafer made of silicon. The surface Wa of the substrate of the wafer W is divided into grid-like regions by, for example, a plurality of scheduled division lines extending in the XY directions, and devices (device layers) such as electronic circuits are respectively in the grid-like regions. It is formed (laminated).

When dividing the wafer W into individual chips C, first, a back grind tape (protective tape) BG is attached to the surface Wa of the wafer W, and the surface is attached to the holding surface of the table T of the laser processing apparatus 10-1. Place it with Wa facing down. Then, the wafer W is sucked and held by the suction stage T1. The wafer W may be adsorbed and held without attaching the back grind tape BG.

The laser processing unit 16 includes an optical element such as a laser light source and a condensation lens, and a driving means for finely moving the laser beam L in the Z direction with respect to the wafer W. As the laser light source, for example, a semiconductor laser-excited Nd: YAG (Yttrium Aluminum Garnet) laser is used. The laser beam L emitted from the laser light source is focused inside the wafer W by the condensation lens. As a result, the laser processing regions R1 and R2 are formed inside the wafer W.

Here, the laser processing regions R1 and R2 are regions in which the internal density, refractive index, mechanical strength, and other physical characteristics of the wafer W are different from those of the surroundings due to irradiation with laser light, and the strength is lower than that of the surroundings. It means that. The laser processing regions R1 and R2 include, for example, a crack region.

When the laser processing regions R1 and R2 are formed on the wafer W, the laser beam L is emitted from the laser processing unit 16 and irradiates the wafer W via an optical system such as a condensation lens. The Z-direction position of the condensing point FP of the irradiated laser beam L is accurately set to a predetermined position inside the wafer W by adjusting the Z-direction position of the wafer W by the XYZ θ table and controlling the position of the condensation lens.

In this state, the XYZθ table is machined and fed in the X direction, which is the dicing direction. As a result, one line of laser processing regions R1 and R2 is formed along the planned division line of the wafer W. Then, when one laser machining region R1 and R2 are formed along the scheduled division line, the XYZθ table is indexed and fed by one pitch in the Y direction, and the laser machining regions R1 and R2 are also formed on the next scheduled division line. Laser beam machining. Next, when the laser machining regions R1 and R2 are formed along all the planned division lines in the X direction, the XYZθ table is rotated by 90 ° around the Z axis, and the same applies to the rotated X-direction scheduled division line. The laser processing regions R1 and R2 are formed.

The procedure for forming the laser processing regions R1 and R2 is not particularly limited. For example, as shown in FIG. 2, the laser processing region R1 of the first layer may be formed on the entire surface of the wafer W, and then the laser processing region R2 of the second layer (the back surface Wb side of the wafer W) may be formed. In this case, the laser machining conditions for forming the laser machining regions R1 and R2 may be different from each other or may be the same. Alternatively, by providing a branching portion (for example, a beam splitter or the like) for branching the laser beam L and condensing the light on two condensing points having different positions (depths) in the Z direction inside the wafer W, once. The two layers of laser processing regions R1 and R2 may be formed by the scan.

The wafer W on which the laser processing regions R1 and R2 are formed is conveyed from the laser processing apparatus 10-1 to the grinding apparatus 10-2, the back surface of the wafer W is ground, and a part of the laser processing region R2 on the back surface side is formed. It is removed and split into individual chips (see Figure 3).

(Grinding)
FIG. 3 is a block diagram showing a configuration of a grinding device in the wafer processing system according to the embodiment of the present invention. FIG. 3 shows a state in which the back surface Wb of the wafer W is ground to Wb1.

As shown in FIG. 3, the grinding apparatus 10-2 according to the present embodiment includes a grinding control unit 18, a thickness measuring unit 20, a wafer moving unit 22, and a grinding machine (grinder) 50. The grinding machine 50 includes a rotary grinding machine 52 and a grindstone 54 attached to the rotary grinding machine 52.

The grinding control unit 18 includes a motor for rotating the rotary grinding machine 52 around the shaft. The grinding control unit 18 adjusts the Z-direction position of the rotary grinding machine 52 while supplying the slurry to the back surface Wb of the wafer W from the slurry supply port (not shown) in response to a command from the control unit 12, and the wafer W The grindstone 54 is brought into contact with the back surface Wb of the above and rotated.

The wafer moving unit 22 includes a chuck table T2 that attracts and holds the wafer W, and an XY table (not shown) that moves the chuck table T2 in the XY directions in the grinding apparatus 10-2.

The wafer W is transferred to the grinding apparatus 10-2 after the laser processing regions R1 and R2 are formed in the laser processing apparatus 10-1. Then, the wafer W is placed on the holding surface of the chuck table T2 with the surface Wa facing down, and is adsorbed and held by the chuck table T2. Next, while the chuck table T2 is moved in the XY direction by the wafer moving unit 22, the grinding wheel 54 is brought into contact with the back surface Wb of the wafer W and rotated by the grinding control unit 18, so that the entire surface of the back surface Wb of the wafer W is formed. Be ground.

The thickness measuring unit 20 is a means for measuring the thickness of the wafer W. The thickness measuring unit 20 can measure the thickness of the wafer W in-situ while grinding the back surface Wb of the wafer W. As the thickness measuring unit 20, a contact-type means for measuring by bringing a contact-type height gauge into contact with the back surface Wb of the wafer W may be used. Further, the thickness measuring unit 20 is a non-contact type means (for example,) in which a laser beam from a laser light source (for example, a semiconductor laser) is applied to the back surface Wb of the wafer W to measure the distance to the back surface Wb of the wafer W. ToF (Time-of-Flight) method) may be used.

The grinding control unit 18 grinds the back surface Wb of the wafer W while calculating the thickness of the wafer W based on the output from the thickness measuring unit 20. Thereby, the thickness of the wafer W can be set to the target thickness Ht.

In the example shown in FIG. 3, the grinding device 10-2 is controlled by the same control unit 12 as the laser processing device 10-1, but a control unit different from the laser processing device 10-1 ( For example, it may be controlled by a personal computer or a workstation). That is, the laser processing device 10-1 and the grinding device 10-2 may be separate and independent devices. In this case, the control unit of the grinding apparatus 10-2 receives information on the positions and sizes of the laser processing regions R1 and R2 and information on the target thickness Ht of the thickness of the wafer W from the control unit 12 of the laser processing apparatus 10-1. It may be shared via a communication line, a storage device, or the like.

[Laser processing area]
Next, the relationship between the laser processing region R2 and the target thickness Ht of the chip C will be described. FIG. 4 is a cross-sectional view showing the relationship between the laser machining region and the target thickness Ht, and FIG. 5 is an image showing the machining cross section of the chip. Note that FIG. 4 shows only the laser processing region R2 on the back surface Wb side of the wafer W for the sake of simplicity.

As shown in FIG. 4, the laser machining region R2 includes a void R20 located at the lower end thereof and a void upper region R22 formed above (rear surface side) of the void R20.

For example, when the laser light L is a pulse laser, the laser light L focused inside the wafer W is locally absorbed in the light collecting point FP and the laser light absorption region in the vicinity thereof. At this time, the temperature of the condensing point FP and the laser light absorption region in the vicinity thereof rises momentarily (for example, about 10,000 K), and the silicon in the laser light absorption region evaporates at once, resulting in voids (vacancy). ) R20 is formed.

Next, the high temperature portion rapidly extends as a thermal shock wave on the upper side of the void R20, that is, on the irradiation side of the laser beam L. At this time, the temperature difference between the high temperature portion and the surrounding low temperature portion becomes very large, the thermal expansion of the high temperature portion is suppressed by the surrounding low temperature portion, and the high temperature portion receives very strong compression. Therefore, a high dislocation density layer is formed in the high temperature portion without melting.

After that, when the next pulse wave is irradiated, the dislocations in the high dislocation density layer in the high temperature portion become nuclei and the crack K grows from the void upper region R22 to the low temperature portion of the single crystal.

The upper void region R22 is a region above the void R20 where laser machining marks (high dislocation density layer, microcracks, etc.) can be confirmed.

As described above, it is considered that the laser processing regions R1 and R2 have a function of collecting the grinding debris SL invading from the surface side to be ground of the wafer W like a net. Therefore, it is conceivable to grind a part of the laser processing region R2 to expose the laser processing region R2 on the back surface side and the side wall CW of the chip C.

In this regard, the inventor of the present invention, when grinding a part of the laser processing region R2, when grinding is performed up to the vicinity of the void R20 of the laser processing region R2, is on the back surface side (upper side in the figure) of the chip C. It was discovered that debris and meandering are likely to occur. Therefore, in the present embodiment, a part of the void upper region R22 of the laser processing region R2 is ground (without grinding the vicinity of the void R20), and the void upper region R22 is formed on the back surface side of the chip C and the side wall CW. Is exposed. As a result, the function of collecting the grinding dust SL by the laser processing region R20 can be enhanced without causing debris and meandering on the back surface side of the chip C.

Therefore, in the present embodiment, as shown in FIG. 4, laser machining is performed so that the void upper region R22 of the laser machining region R2 is formed at the position of the target thickness Ht from the surface Wa of the chip C.

The control unit 12 adjusts the laser processing conditions of the laser processing unit 16 to set the position and size of the laser processing region R2 (void R20 and void upper region R22) (position setting step). Specifically, first, laser processing is performed for each material of the wafer W, and for each laser processing condition such as the position of the condensing point FP during laser processing and the intensity, frequency, numerical aperture, and irradiation time of the laser beam L. Laser processing data of the position and size of the region R2 (void R20 and void upper region R22) are obtained experimentally or by simulation in advance. Then, the control unit 12 performs laser machining so that the void upper region R22 of the laser machining region R2 overlaps the position of the target thickness Ht based on the material of the wafer W and the target thickness Ht and the laser machining data. The position of the focusing point FP and the laser processing conditions such as the intensity, frequency, numerical aperture, and irradiation time of the laser beam L are adjusted. Here, the control unit 12 functions as a position setting unit.

The laser machining unit 16 forms the laser machining region R2 inside the wafer W along the planned division line of the wafer W according to the command from the control unit 12 (laser machining region formation step).

Here, when the wafer W is ground to the target thickness Ht, the range is from a part of the upper end portion of the laser processing region R2 (for example, from the upper side (back surface side) of the laser processing region R2 to about one third). It is preferable to set the formation position of the laser processing region R2 so that the region) is ground. More specifically, when the dimension of the laser processing region R2 in the Z direction is H1, the distance Δ from the upper end portion of the laser processing region R2 in the figure to the position of the target thickness Ht is 0 <Δ≤H1 / 3. It is preferable to adjust the laser processing conditions so as to be.

Alternatively, when the wafer W is ground to the target thickness Ht, it is about one-third from a part of the upper end portion of the laser processing region R2 (for example, from the upper side (back surface side) of the void upper region R22 of the laser processing region R2). The formation position of the laser processing region R2 may be set so that the region up to) is ground. That is, when the dimension in the Z direction of the void upper region R22 of the laser processing region R2 is H2, the distance Δ from the upper end portion of the void upper region R22 of the laser processing region R2 to the position of the target thickness Ht is 0. The laser processing conditions may be adjusted so that <Δ≤H2 / 3.

In the present embodiment, the laser processing region has two layers of R1 and R2, but the present invention is not limited to this. The laser processing region may be formed with only one layer or a plurality of three or more layers. When forming three or more layers of the laser machining region, the laser machining region on the back surface side (closest to the back surface Wb of the wafer W) of the laser machining regions may be formed so as to overlap the positions of the target thickness Ht.

FIG. 6 is an image showing a processed cross section of the chip after grinding, and FIG. 7 is an image showing the surface of the backgrinding tape after picking up the chip after cutting.

As shown in FIG. 6, when grinding is completed in about one-third from the upper side (back surface side) of the laser processing region R2 and the wafer W is divided, the back grind tape BG is shown in FIG. Almost no grinding debris SL was detected on the surface of the surface.

According to the present embodiment, by forming the laser machining region R2 so as to overlap the position of the target thickness Ht, it is possible to suppress the invasion of the grinding dust SL into the gap Gap of the chip C after the wafer W is cut.

[others]
When performing grinding, if a number 6000 or higher or a fine count such as polish is used, surface burning is likely to occur. On the other hand, if a coarse count is used, chipping or small debris is likely to occur. Therefore, it is preferable to use a coarse count such as 3600.

10 ... Wafer processing system, 10-1 ... Laser processing equipment, 10-2 ... Grinding equipment, 12 ... Control unit, 14 ... Wafer moving unit, 16 ... Laser processing unit, 18 ... Grinding control unit, 20 ... Thickness measuring unit, 22 ... Wafer moving part, 50 ... Grinding machine, 52 ... Rotating grinding machine, 54 ... Grindstone, T1 ... Suction stage, T2 ... Chuck table

Claims (5)

A laser machining step of forming a laser machining region along a planned division line of the wafer inside the substrate of a wafer in which a device layer is laminated on the surface of the substrate.
A grinding step is provided in which the back surface of the wafer is ground to make the thickness of the wafer a target thickness, and the wafer is divided into individual chips.
The laser machining step
A position setting step of setting the position of the laser processing region in the thickness direction of the wafer to the position of the target thickness, and
A laser processing region forming step for forming the laser processing region at a position set in the position setting step by condensing the laser light inside the wafer, and a laser processing region forming step.
Wafer processing method. In the laser processing region forming step, a plurality of layers of laser processing regions are formed in the thickness direction of the wafer.
The wafer processing method according to claim 1, wherein in the position setting step, the laser processing region on the back surface side of the laser processing regions of the plurality of layers is set at the position of the target thickness. In the position setting step, the position of the laser processing region is set so that the position of the target thickness overlaps the region in the range from the back surface side of the laser processing region to one-third. The wafer processing method described in 1. In the position setting step, the position of the laser processing region is set so that the position of the target thickness overlaps the region of the laser processing region from the back surface side of the region excluding the void at the lower end to one third. The wafer processing method according to claim 1 or 2, which is set. A laser processing device that forms a laser processing region along the planned division line of the wafer inside the substrate of the wafer in which the device layer is laminated on the surface of the substrate.
A grinding device for grinding the back surface of the wafer to make the thickness of the wafer a target thickness and dividing the wafer into individual chips is provided.
The laser processing device is
A position setting unit that sets the position of the laser processing region in the thickness direction of the wafer to the position of the target thickness.
A laser processing unit that forms the laser processing region at a position set by the position setting unit by condensing laser light inside the wafer, and a laser processing unit.
Wafer processing system equipped with.

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