TWI767009B - Wafer processing method - Google Patents

Abstract

[Subject] To provide a wafer processing method, which can irradiate a wafer with a device area on the front side and a remaining area surrounding the outer periphery of the device area by irradiating a laser beam from the back side of the wafer through a dicing tape. The same modified layer is formed in the device regions, which are regions where each device has metal bumps. [Solution] A method for processing a wafer, the wafer has a device area on the front side and a remaining area surrounding the outer periphery of the device area, and the device area is formed by a plurality of predetermined dividing lines formed in a lattice shape by a functional layer laminated on the front side. Divide and form a device area with electrode bumps in each of the divided areas. The processing method of the wafer is to irradiate a laser beam from the front side of the wafer and ablate to form along the The annular groove on the inner circumference of the remaining outer circumference area and the linear laser processing groove along the dividing line. Next, the front and back sides of the frame unit are turned over and the front side of the wafer is held by a work chuck, and a laser beam is irradiated from the back side of the wafer to form a ring-shaped modified layer located in the ring-shaped groove inside the wafer. . When the annular modified layer is formed inside the wafer, the cracks extend from the annular modified layer in the direction of the annular groove, and the wafer is divided into a peripheral remaining region and a device region. After the step of dividing the remaining peripheral region, a laser beam is irradiated from the back side of the wafer through a dicing tape to form a modified layer along the line to be divided inside the wafer.

Description

Wafer processing method

Field of Invention

The present invention relates to a wafer processing method for dividing a wafer into individual device wafers by irradiating a laser beam.

Background of the Invention

When assembling a semiconductor device chip on a motherboard, although the electrodes of the semiconductor device chip and the electrodes of the motherboard are generally connected by wire bonding, recently flip-chip bonding (flip-chip bonding) Also commonly used, this flip-chip bonding method uses a spherical metal bump (bump) formed of copper or the like on the front surface of a semiconductor device as an electrode, and flips the semiconductor device wafer to connect the metal bump to a host. on the electrodes of the plate.

As a method of dividing a semiconductor wafer into individual device wafers, in addition to a method of dicing with a dicing blade, a dividing process by a laser beam is also known. In dicing by a dicing blade, a low-dielectric-constant insulating film (Low-k film) as an interlayer insulating film, which may be peeled off from the wafer, can be reliably performed by ablation processing with a laser beam. segmentation.

In addition, the following processing method is also known: irradiating the wafer with a laser beam of a wavelength which is penetrating to the wafer, so that the After forming a modified layer that serves as the starting point of fracture, an external force is applied to the wafer to divide the wafer into individual device chips.

In Japanese Patent Laid-Open No. 2011-187479, a method is disclosed in which laser processing grooves are formed by irradiating a laser beam having a wavelength absorbing the wafer from the front side of the wafer along a line to be divided. A modified layer is formed inside the wafer by irradiating a laser beam having a wavelength that penetrates the wafer from the back side of the wafer along the line to be divided, and then an external force is applied to the wafer so that the front surface has a Low-k The film wafer is divided into individual device wafers.

In the method of processing the front and back sides of such a wafer with a laser beam, there is a problem in that when a modified layer is formed inside a wafer with electrode bumps, the height of the electrode bumps is difficult to remove from the work clamp. The remaining area of the outer periphery where the holding surface of the table is suspended will sag due to the pull-down of the dicing tape, resulting in a change in the position (depth direction) where the modified layer is formed, and resulting in failure to break.

In order to prevent this situation, Japanese Patent Laid-Open No. 2017-050461 has disclosed a special work chuck, which is used to support the remaining area of the outer periphery of the wafer with an annular elastic member such as resin or rubber, And the laser beam is irradiated from the back of the wafer through the dicing tape.

prior art literature Patent Literature

Patent Document 1: Japanese Patent Laid-Open No. 2011-187479

Patent Document 2: Japanese Patent Laid-Open No. 2017-050461

Summary of Invention

However, the height of the electrode bumps varies slightly depending on the device, and it is difficult to support the entire wafer flat with the height of one type of annular elastic member. In particular, when the wafer is supported by a ring-shaped elastic member having a height different from that of the electrode bumps, the remaining peripheral region of the wafer is slightly bent, and it becomes impossible to form a modified layer on the entire wafer. at the same depth, and there is a problem of causing defective wafer breakage.

The present invention has been made in view of such problems, and an object of the present invention is to provide a wafer processing method capable of processing a wafer having a device region on the front surface and a remaining region surrounding the outer periphery of the device region from the wafer. The back side of the device is irradiated with a laser beam through a dicing tape, and the same modified layer can be formed in the device region, where the device region is the region where each device has metal bumps.

According to the present invention, a method for processing a wafer can be provided, the wafer has a device region on the front surface and a remaining region surrounding the outer periphery of the device region, and the device region is divided into a plurality of strips formed by a grid of functional layers laminated on the front surface. The wafer processing method is characterized by comprising: a frame unit forming step, forming a frame unit, the frame The unit is that the back of the wafer is attached to the dicing tape, and the aforementioned dicing tape is Installed on the annular frame to block the opening of the annular frame; the first holding step is to hold the wafer of the frame unit with the holding surface of the working chuck of the laser processing device across the dicing tape; the laser In the process groove forming step, the wafer held in the first holding step is irradiated from the front side of the wafer with a first laser beam having a wavelength that is absorbing to the wafer to form a ridge on the front side of the wafer. A linear groove along the planned dividing line and an annular groove along the inner circumference of the remaining area of the outer circumference; in the second holding step, after the laser processing groove forming step is performed, the front side surface of the wafer faces the holding surface and is the working chuck holds the frame unit; in the step of forming an annular modified layer, a second laser beam with a wavelength that is penetrating to the wafer and the dicing tape is along the annular groove and across the dicing tape The wafer held in the second holding step is irradiated to form a ring-shaped modified layer serving as a ring-shaped fracture origin in the inside of the wafer; the outer peripheral remaining region is divided in a step of dividing the ring-shaped modified layer from the ring-shaped modified layer. extending to the fissure of the annular groove, and dividing the remaining area of the outer periphery of the wafer and the device area in the state of being attached to the dicing tape as it is; the step of forming a modified layer is to separate the second laser beam from the second laser beam. The dicing tape irradiates the device area of the wafer whose peripheral remaining area has been divided, so as to form a modified layer inside the wafer along the planned dividing line; and the dividing step is performed when the modified layer is formed After the step, an external force is applied to the wafer through the dicing tape, so as to divide the device area of the wafer into individual device chips.

Preferably, the wafer processing method further has annular grooves. In the detection step, after the second holding step is performed and before the ring-shaped modified layer forming step is performed, the ring-shaped groove of the wafer is detected with an infrared camera, and in order to form the ring-shaped groove The modified layer is set so that the position where the second laser beam is irradiated is aligned with the annular groove.

In the wafer processing method of the present invention, the front side of the wafer is attracted and held by the work chuck, and the wafer is irradiated with a laser beam through the dicing tape attached to the back side of the wafer, and the inner When forming the modified layer, in order to suppress the deflection of the remaining peripheral region, an annular groove separating the remaining peripheral region from the device region and an annular modified layer located in the annular groove are formed.

In this way, the crack extending from the annular reforming layer can reach the annular groove, and the wafer can be separated into the remaining peripheral region and the device region, and the influence caused by the deflection of the remaining peripheral region can be eliminated. The modified layer is formed at the same position in the depth direction in the device region held flat.

10, 20: Ball screw

11: Semiconductor wafer (wafer)

11a: Front

12, 22: Pulse motor

13: Substrate

14: Y-axis feeding mechanism (Y-axis feeding equipment)

15: Functional layer

16, 6: Rails

17: Divide the scheduled line

18: X-axis moving block

19: Devices

2: Laser processing device

21: Electrode bumps

23: Device area

24, 24A: work clamp table

24a: Attraction and retention

25: Peripheral remaining area

26, 56: Fixtures

27: Frame Unit

28: X-axis feeding mechanism (X-axis feeding equipment)

29: Annular groove

30: Cylindrical support member

31: Linear laser processing groove

32: Pillar

33: Sheet member

34: Laser beam irradiation unit

35: Annular modified layer

36: Cover

37: Rift

38: Condenser (laser head)

39: Dividing Line

4: Static abutment (base)

40: Shooting unit

41: Modified layer

43: Device Wafer

44: Ring support member

46: Ring-shaped elastic member

50: Split expansion device

52: outer cylinder

54: Cylindrical pressing member

8: Y-axis moving block

A, R, X, Y, X1: Arrow

F: Ring frame

T: cutting tape

LB1: 1st laser beam

LB2: 2nd laser beam

X, Y, Z: direction

FIG. 1 is a perspective view of a laser processing apparatus.

FIG. 2 is a front perspective view of a semiconductor wafer having a plurality of electrode bumps for each device.

3 is a perspective view of a frame unit.

4(A) is a perspective view showing a step of forming an annular groove by ablation, and FIG. 4(B) is a perspective view showing a step of forming a linear laser-processed groove by ablation.

FIG. 5 is a cross-sectional view showing a step of forming an annular modified layer.

6 is a cross-sectional view showing a step of forming a modified layer.

FIG. 7 is a cross-sectional view showing a second embodiment of the step of forming an annular modified layer.

FIG. 8 is a cross-sectional view showing a second embodiment of the step of forming a modified layer.

FIG. 9 is a cross-sectional view showing the dividing step.

Form for carrying out the invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 is a schematic configuration diagram of a laser processing apparatus 2 suitable for implementing the wafer processing method according to the embodiment of the present invention. The laser processing apparatus 2 includes a pair of guide rails 6 mounted on the stationary base 4 and extending in the Y-axis direction.

The Y-axis moving block 8 is moved in the indexing feeding direction (ie, the Y-axis direction) by the Y-axis feeding mechanism (Y-axis feeding device) 14 composed of the ball screw 10 and the pulse motor 12 . A pair of guide rails 16 extending in the X-axis direction are fixed to the Y-axis moving block 8 .

The X-axis moving block 18 uses an X-axis feeding mechanism (X-axis feeding device) 28 composed of a ball screw 20 and a pulse motor 22 , and is guided by the guide rail 16 and moves in the processing feeding direction (ie, the X-axis). direction) move.

The table 24 is mounted on the X-axis moving block 18 through a cylindrical support member 30 . A plurality of (four in this embodiment) clamps 26 capable of clamping the ring frame F shown in FIG. 3 are arranged on the work clamp table 24 .

A pillar 32 is erected at the rear of the base 4 . A cover 36 of the laser beam irradiation unit 34 is fixed on the pillar 32 . housed in housing 36 There is a laser beam oscillation device including a YAG laser oscillator or the like, and a condenser (laser head) 38 for condensing the laser beam on a wafer for processing is mounted on the front end of the cover 36 .

A photographing unit 40 is installed at the front end of the cover 36 of the laser beam irradiation unit 34 , and the photographing unit 40 photographs the wafer 11 held on the work chuck 24 . The photographing unit is provided with a photographing element corresponding to infrared light. The condenser 38 and the imaging unit 40 are arranged in a row in the X-axis direction.

Referring to FIG. 2 , there is shown a front perspective view of a semiconductor wafer (hereinafter, simply referred to as a wafer) 11 suitable for processing by the wafer processing method according to the embodiment of the present invention.

The semiconductor wafer 11 has a functional layer 15 laminated on the front surface of a substrate 13 formed of silicon or the like, and on the functional layer 15 is a plurality of regions demarcated by a plurality of planned dividing lines 17 formed in a lattice shape A device 19 having a plurality of electrode bumps 21 is formed in each of them. The semiconductor wafer 11 has a device region 23 on which a plurality of devices 19 are formed, and a remaining region 25 surrounding the outer periphery of the device region 23 on the front surface 11 a.

As shown in FIG. 3 , when the wafer processing method according to the embodiment of the present invention is carried out, the back surface of the wafer 11 is attached to the outer peripheral portion and mounted on the ring frame F to block the opening of the ring frame F The frame unit 27 is formed on the dicing tape T, and the frame unit 27 is put into the laser processing apparatus 2 .

As shown in FIG. 4(A) , after the frame unit 27 is formed, a first holding step of holding the frame unit 27 via the dicing tape T with the table 24 of the laser processing apparatus 2 is carried out. Wafer 11.

In the first holding step, after holding the wafer 11 on the table 24, after detecting the coordinates of the edge of the wafer 11 at three or more points to detect the center position of the wafer 11, the wafer 11 may be placed again. The center of the circle 11 is aligned with the pre-registered center coordinates of the holding surface of the work chuck 24 , and the work chuck 24 holds the wafer 11 .

Then, the wafer 11 held in the first holding step is irradiated with the first laser beam LB1 having a wavelength (for example, 355 nm) that is absorbing to the wafer 11 from the front surface 11 a side of the wafer 11 , and the work clamp is 24 is rotated in the direction of arrow R, thereby forming an annular groove 29 along the remaining area 25 of the outer periphery of the wafer 11 .

Next, as shown in FIG. 4(B), by irradiating the first laser beam LB1 along the line to be divided 17 from the front surface 11a side of the wafer 11, the table 24 is processed and fed in the direction of the arrow X, Linear laser processing grooves 31 are formed along the line to be divided 17 by ablation processing.

The table 24 is sequentially indexed and fed in the direction of the arrow Y according to the pitch of the planned dividing lines to form linear laser processing grooves 31 along all the planned dividing lines 17 extending in the first direction. .

Next, after rotating the table 24 by 90°, the same linear laser processing is formed by ablation along all the planned dividing lines 17 extending in the second direction orthogonal to the first direction. Ditch 31.

In the above-described embodiment, after the annular groove 29 is formed, the linear laser processing groove 31 is formed, but this order may be reversed. In this specification, the annular groove forming step and the straight line The laser-processed groove forming steps are collectively referred to as a laser-processed groove forming step.

As shown in FIG. 5, after the laser processing groove forming step is performed, the front and back sides of the frame unit 27 are turned over so that the front side 11a of the wafer 11 of the frame unit 27 faces the suction and holding portion 24a of the work chuck 24, and the work The chuck table 24 sucks and holds the wafer 11 through the sheet member 33 that protects the front surface 11a side of the wafer 11, and clamps and fixes the ring frame F of the frame unit 27 with the clamps 26 of the work chuck table 24 (second holding step).

Next, the annular groove 29 is detected by imaging the remaining area 25 of the outer periphery of the wafer 11 with the infrared imaging element of the imaging unit 40 through the dicing tape T. Align the position of the annular groove 29, and irradiate the laser beam LB2 with a wavelength (for example, 1064 nm) that is transparent to the wafer 11 and the dicing tape T through the dicing tape T from the condenser 38, The table 24 is rotated at a low speed to form a pair of annular modified layers 35 located in the annular grooves 29 as the origin of fracture in the inside of the wafer 11 .

Preferably, in the case where the annular groove 29 is formed by aligning the center of the wafer 11 with the center of the holding surface of the table 24 to hold the wafer 11, the same is true when the annular modified layer 35 is formed on the wafer 11. The modified layer 35 is formed by holding the center of the wafer 11 aligned with the center of the holding surface of the stage 24 .

When the annular modified layer 35 is formed inside the wafer 11, as shown in the partially enlarged view of FIG. As shown, the peripheral remaining area 25 and the device area 23 are attached to the dicing tape T as they are, and are divided along the Line 39 is divided or separated (peripheral remaining area division step).

After the step of dividing the remaining peripheral area is performed, the second laser beam LB2 is irradiated along the planned dividing line 17 to the device area 23 of the wafer 11 from which the remaining peripheral area 25 has been divided through the dicing tape T, and the working chuck is moved. 24 is processed and fed in the direction of arrow X1, whereby the modified layer 41 along the line to be divided 17 is formed inside the wafer 11 (modified layer forming step).

In this modified layer forming step, the table 24 is gradually indexed and fed at intervals of the planned dividing line 17 in the Y-axis direction orthogonal to the processing feed direction X1, and is extended in the first direction along the All of the planned dividing lines 17 form the modified layer 41 inside the wafer 11 .

Next, after rotating the table 24 by 90 degrees, the same modified layer 41 is formed inside the wafer 11 along all the planned dividing lines 17 extending in the second direction orthogonal to the first direction.

Next, referring to FIGS. 7 and 8 , a description will be given of a ring-shaped modified layer forming step and a modified layer forming step of the second embodiment, which are carried out using the work jig 24A for wafers with bumps.

As shown in the partially enlarged views of FIGS. 7 and 8 , the remaining outer peripheral region 25 of the wafer 11 is in contact with an annular elastic member 46 serving as a support portion for the remaining outer peripheral region, and the annular elastic member 46 corresponds to the electrode protrusion The height of the block 21 is arranged so as to protrude from the upper surface of the table 24 . The ring-shaped elastic member 46 is supported by the ring-shaped support member 44 fixed to the work table 24A.

According to the work table 24A having such a configuration, because The electrode bump 21 side of the wafer 11 is held by the holding surface of the suction holding portion 24a, and the outer peripheral remaining region 25 is supported by the annular elastic member 46, whereby the annular elastic member 46 holds the wafer 11 and suction Since the holding surfaces of the portions 24a are sealed to ensure sufficient negative pressure, the device region 23 of the wafer 11 including the electrode bumps 21 can be stably held from the electrode bump 21 side.

In addition, since the front surface 11 a of the wafer 11 is protected by the sheet member 33 , the front surface 11 a of the wafer 11 can be sufficiently protected when the wafer 11 is sucked and held. However, when the height of the electrode bump 21 is changed according to the type of the device, a height difference is generated between the annular holding member 46 and the electrode bump, so that the annular elastic member becomes, for example, as shown in FIG. 7 . The outer periphery of the wafer is deflected higher than the electrode bumps, but by performing the step of dividing the remaining peripheral region, the deflection of the outer periphery of the wafer does not become a problem.

In the second embodiment using the work table 24A shown in FIGS. 7 and 8 , the annular modified layer forming step, the outer peripheral remaining area dividing step, and the The step of forming the modified layer. Thereby, the outer periphery of the device region does not become high due to the deflection of the outer periphery of the wafer, and a modified layer having an appropriate height can be formed up to the outer periphery of the device region.

After the annular modified layer forming step, the peripheral remaining area dividing step, and the modified layer forming step are performed, a dividing step is performed. The dividing step is to apply an external force to the wafer 11 through the dicing tape T to separate the devices of the wafer 11. The region 23 is divided into individual device wafers.

In this dividing step, as shown in FIG. 9(A) , the annular frame F of the frame unit 27 is supported by the outer cylinder 52 of the divided expansion device 50 , and the annular frame F is clamped and fixed by the clamp 56 . Then, the upper end of the cylindrical pressing member 54 having a diameter smaller than the opening of the ring frame F and larger than the outer diameter of the wafer 11 is brought into contact with the dicing tape T.

Next, as shown in FIG. 9(B), the cylindrical pressing member 54 is pushed in the direction of the arrow A, so that the dicing tape T on which the wafer 11 is attached is expanded in the radial direction, and the wafer 11 is formed along the The device wafers 43 are divided into individual device wafers 43 by the line 17 with the modified layer 41 to be divided, and gaps are formed between the wafers.

In the above-mentioned embodiment, when the annular frame F of the frame unit 27 is clamped and pulled down by the clamps 26 of the work clamp table 24, in order to suppress the deflection of the outer peripheral remaining area 25, the outer peripheral remaining area 25 is formed from The laser processing trench 29 and the annular modified layer 35 are separated from the device region 23 . In order to prevent the annular remaining area from suppressing expansion, for example, a reforming layer may be formed in the form of dividing the remaining area on the outer periphery in the east-west, north-south direction.

In this way, the crack 37 extending from the annular modified layer 35 can reach the annular laser processing groove 29 , the wafer 11 can be separated into the peripheral remaining region 25 and the device region 23 , and the residual peripheral region 25 can be eliminated. Due to the influence of the deflection, the same modified layer is formed in the depth direction of the wafer in the device region 23 held flat by the work chuck 24, and an external force is applied to the wafer 11 to carry out the dividing step. Thus, the wafer 11 can be surely divided into the individual device wafers 43 .

11‧‧‧Wafer

15‧‧‧Functional layer

17‧‧‧Separation Schedule

24‧‧‧Working table

24a‧‧‧Attraction and Retention

26‧‧‧ Fixtures

29‧‧‧Annular groove

33‧‧‧Sheet member

35‧‧‧Annular modified layer

37‧‧‧Fissure

38‧‧‧Concentrator

F‧‧‧Ring frame

T‧‧‧Cutting Tape

LB2‧‧‧2nd laser beam

Claims (2)

A method for processing a wafer, the wafer has a device area on the front side and a remaining area around the outer periphery of the device area, the device area is a functional layer laminated on the front side is divided by a plurality of predetermined dividing lines formed in a lattice shape, and The wafer processing method is characterized by comprising: a frame unit forming step of forming a frame unit, wherein the frame unit is a back surface of the wafer Attached to a dicing tape, the outer periphery of the dicing tape is installed on the annular frame to block the opening of the annular frame; The first holding step is separated by the holding surface of the working table of the laser processing device. the dicing tape holds the wafer of the frame unit; the laser processing groove forming step, the first laser beam having a wavelength absorbing to the wafer is oriented from the front side of the wafer to the wafer held in the first holding step The wafer is irradiated to form a straight groove along the planned dividing line and an annular groove along the inner circumference of the remaining area of the outer circumference on the front surface of the wafer; in the second holding step, the laser processing groove forming step is performed After that, make the front side of the wafer face the holding surface and hold the frame unit with the working chuck; in the step of forming a ring-shaped modified layer, a second laser with a wavelength that is penetrating to the wafer and the dicing tape irradiating the wafer held in the second holding step with a light beam along the annular groove and through the dicing tape, so as to form a ring-shaped modified layer that becomes a ring-shaped fracture origin in the inside of the wafer; The step of dividing the remaining peripheral region is to divide the remaining peripheral region and the device region of the wafer in the state of being attached to the dicing tape from the annular modified layer to the crack extending from the annular groove; modifying In the step of forming a mass layer, the second laser beam is irradiated to the device area of the wafer whose peripheral remaining area has been divided through the dicing tape, so as to form a modification along the dividing line in the inside of the wafer. A quality layer; and a dividing step, after the forming step of the modified layer is performed, an external force is applied to the wafer through the dicing tape, so as to divide the device area of the wafer into individual device chips. The wafer processing method according to claim 1, further comprising an annular groove detection step, the annular groove detection step is performed after the second holding step is performed and before the annular modified layer forming step is performed, The annular groove of the wafer is detected with an infrared camera, and the position where the second laser beam is irradiated is set to the annular groove in order to form the annular modified layer.

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