阅读说明：本技术 晶片的加工方法 (Method for processing wafer ) 是由 古田健次 于 2020-02-14 设计创作，主要内容包括：提供晶片的加工方法,能够抑制由激光束的照射而引起的器件的损伤。一种晶片的加工方法,该晶片在由多条第1分割预定线和多条第2分割预定线划分的多个区域的正面侧形成有器件,该晶片的加工方法具有如下的步骤：第1改质层形成步骤,在使激光束的聚光点的高度与晶片的内部中的位于晶片的正面侧的第1区域的高度一致的状态下照射激光束,从而在第1区域中形成第1改质层；以及第2改质层形成步骤,在使激光束的聚光点的高度与晶片的内部中的位于晶片的背面侧的第2区域的高度一致的情况下照射激光束,从而在第2区域中形成第2改质层,并且形成从晶片的正面至背面的龟裂,沿着多条第1分割预定线和多条第2分割预定线对晶片进行分割。(Provided is a wafer processing method capable of suppressing damage to a device caused by irradiation with a laser beam. A method for processing a wafer having devices formed on a front surface side of a plurality of regions defined by a plurality of first planned dividing lines 1 and a plurality of second planned dividing lines 2, the method comprising the steps of: a 1 st modified layer forming step of irradiating the wafer with the laser beam in a state where a height of a condensed point of the laser beam is made to coincide with a height of a 1 st region located on a front surface side of the wafer in the wafer, thereby forming a 1 st modified layer in the 1 st region; and a 2 nd modified layer forming step of irradiating the wafer with a laser beam while matching a height of a converging point of the laser beam with a height of a 2 nd region located on a back surface side of the wafer in the wafer, thereby forming a 2 nd modified layer in the 2 nd region, forming a crack from a front surface to a back surface of the wafer, and dividing the wafer along the plurality of 1 st planned dividing lines and the plurality of 2 nd planned dividing lines.)

1. A method for processing a wafer having devices formed on the front surface side of a plurality of regions defined by a plurality of lines to divide 1 st and a plurality of lines to divide 2 nd intersecting the lines to divide 1 st,

the processing method of the wafer comprises the following steps:

a protective member attaching step of attaching a protective member to the front surface side of the wafer;

a 1 st modified layer forming step of forming a 1 st modified layer in the 1 st region by irradiating the wafer with the laser beam from the back surface side thereof along the 1 st planned dividing line and the 2 nd planned dividing line while matching a height of a converging point of the laser beam having transparency with respect to the wafer with a height of a 1 st region on the front surface side of the wafer in the wafer held by the chuck table through the protective member;

a 2 nd modified layer forming step of forming a 2 nd modified layer in the 2 nd region by irradiating the wafer with the laser beam from the back side thereof along the 1 st planned dividing line and the 2 nd planned dividing line in a state where the height of the converging point of the laser beam is made to coincide with the height of the 2 nd region in the wafer on the back side thereof after the 1 st modified layer forming step is performed, forming a crack from the front side to the back side of the wafer, and dividing the wafer along the 1 st planned dividing line and the 2 nd planned dividing line; and

and a grinding step of grinding the back surface side of the wafer to reduce the thickness of the wafer to a predetermined thickness after the 2 nd modified layer forming step is performed.

2. The method of processing a wafer according to claim 1,

in the 1 st modified layer forming step, cracks are generated from the 1 st modified layer to the front surface of the wafer.

3. The method of processing a wafer according to claim 1 or 2,

in the 1 st modified layer forming step, the 1 st modified layer is formed so that the distance between the front surface of the wafer and the 1 st modified layer is larger than the predetermined thickness,

in the grinding step, the 1 st modified layer is removed by thinning the wafer to the prescribed thickness.

Technical Field

The present invention relates to a method for processing a wafer on which a device is formed.

Background

In a manufacturing process of a device chip, a wafer is used in which devices such as an IC (Integrated Circuit) and an LSI (Large scale integration) are formed in each of a plurality of regions defined by a plurality of planned dividing lines (streets) crossing each other. By dividing the wafer along the lines to divide, a plurality of device chips each having a device can be obtained.

For dividing a wafer, for example, a cutting apparatus having a spindle (rotary shaft) to which an annular cutting tool for cutting the wafer is attached is used. The wafer is cut and divided along the planned dividing lines by rotating the cutting tool and cutting into the wafer along the planned dividing lines.

On the other hand, in recent years, attention has been paid to a technique of dividing a wafer by laser processing. For example, the following methods are proposed (see patent document 1): a laser beam having transparency to the wafer is condensed inside the wafer, and a modified region (modified layer) is formed inside the wafer along the lines to be divided. The region where the modified layer is formed is more fragile than the other regions of the wafer. Therefore, when an external force is applied to the wafer on which the modified layer is formed, the wafer is divided along the lines to be divided with the modified layer as a starting point.

A sheet (expansion sheet) which can be expanded by applying an external force, for example, is attached to the wafer on which the modified layer is formed. By expanding the sheet, an external force is applied to the wafer, and the wafer is divided along the lines to be divided. Further, the following method is proposed (see patent document 2): the wafer having the modified layer formed thereon is subjected to grinding, whereby cracks are generated from the modified layer, and the wafer is divided.

Patent document 1: japanese patent laid-open publication No. 2011-

Patent document 2: japanese patent laid-open publication No. 2015-37172

As described above, when the wafer is divided by laser processing, a plurality of modified layers may be formed in the thickness direction of the wafer along each line to be divided depending on the thickness, material, and the like of the wafer. The multilayer modified layer is formed by, for example, irradiating the wafer with a laser beam from the upper surface side (back surface side) of the wafer a plurality of times along a single line to divide while the position (height) of the converging point of the laser beam in the vertical direction is changed stepwise from the lower surface side to the upper surface side of the wafer. Thus, for example, even when the wafer is relatively thick, the wafer is appropriately divided with the modified layer as a starting point.

Here, when a plurality of modified layers are formed along the 1 st line and the 2 nd line intersecting each other, the plurality of modified layers along the 1 st line are usually formed from the lower surface side to the upper surface side of the wafer, and then the plurality of modified layers along the 2 nd line are usually formed from the lower surface side to the upper surface side of the wafer. Therefore, when forming the modified layers along the 2 nd planned dividing line, a plurality of modified layers have been formed from the lower surface side to the upper surface side of the wafer in the intersection region of the 1 st planned dividing line and the 2 nd planned dividing line.

When the modified layer is formed along the 2 nd division lines, a laser beam is irradiated to the intersection region. Then, the laser beam is irradiated on the modified layer formed in the intersection region, and diffuse reflection (scattering) of the laser beam occurs, and the laser beam may be exposed from the 2 nd planned dividing line. As a result, the laser beam is irradiated on the device formed on the lower surface side (front surface side) of the wafer, and the device may be damaged.

In particular, when forming the modified layer on the lower surface side of the wafer along the 2 nd dividing lines, the laser beams are irradiated to the plurality of modified layers formed from the lower surface to the upper surface of the wafer in the intersection regions. Therefore, diffuse reflection of the laser beam is easily generated, and damage to the device is also easily generated.

Disclosure of Invention

The present invention has been made in view of the above problems, and an object thereof is to provide a wafer processing method capable of suppressing damage to a device caused by irradiation with a laser beam.

According to one aspect of the present invention, there is provided a method of processing a wafer having devices formed on a front surface side of a plurality of regions defined by a plurality of lines to divide 1 and a plurality of lines to divide 2 intersecting the lines to divide 1, the method comprising the steps of: a protective member attaching step of attaching a protective member to the front surface side of the wafer; a 1 st modified layer forming step of forming a 1 st modified layer in the 1 st region by irradiating the wafer with the laser beam from the back surface side thereof along the 1 st planned dividing line and the 2 nd planned dividing line while matching a height of a converging point of the laser beam having transparency with respect to the wafer with a height of a 1 st region on the front surface side of the wafer in the wafer held by the chuck table through the protective member; a 2 nd modified layer forming step of forming a 2 nd modified layer in the 2 nd region by irradiating the wafer with the laser beam from the back side thereof along the 1 st planned dividing line and the 2 nd planned dividing line in a state where the height of the converging point of the laser beam is made to coincide with the height of the 2 nd region in the wafer on the back side thereof after the 1 st modified layer forming step is performed, forming a crack from the front side to the back side of the wafer, and dividing the wafer along the 1 st planned dividing line and the 2 nd planned dividing line; and a grinding step of grinding the back surface side of the wafer to reduce the thickness of the wafer to a predetermined thickness after the 2 nd modified layer forming step is performed.

In addition, it is preferable that, in the 1 st modified layer forming step, a crack is generated from the 1 st modified layer to the front surface of the wafer. In addition, it is preferable that in the 1 st modified layer forming step, the 1 st modified layer is formed such that a distance between the front surface of the wafer and the 1 st modified layer is larger than the predetermined thickness, and in the grinding step, the 1 st modified layer is removed by thinning the wafer to the predetermined thickness.

In a wafer processing method according to an aspect of the present invention, first, a 1 st modified layer is formed in a 1 st region located on the front surface side (lower surface side) of the wafer in the wafer along the 1 st planned dividing line and the 2 nd planned dividing line. Then, the 2 nd modified layer is formed in the 2 nd region located on the back surface side (upper surface side) of the wafer in the inside of the wafer along the plurality of 1 st planned dividing lines and the plurality of 2 nd planned dividing lines 13 b.

In the above wafer processing method, when the 1 st modified layer is formed in the 1 st region along the 1 st division lines and the 2 nd division lines, the modified layer is not formed in the 2 nd region. Therefore, when the wafer is irradiated with the laser beam while locating the converging point of the laser beam in the 1 st region, diffuse reflection (scattering) of the laser beam is less likely to occur in the 2 nd region. Thus, irradiation of the laser beam to the device is not easily generated, and breakage of the device is suppressed.

Drawings

Fig. 1 is a perspective view showing a wafer.

Fig. 2 is a side view, partly in section, showing a laser processing apparatus.

Fig. 3 (a) is an enlarged cross-sectional view showing a part of the wafer in the 1 st modified layer forming step, and fig. 3 (B) is an enlarged cross-sectional view showing a part of the wafer after the 1 st modified layer forming step.

Fig. 4 (a) is an enlarged cross-sectional view showing a part of the wafer in the 2 nd modified layer forming step, and fig. 4 (B) is an enlarged cross-sectional view showing a part of the wafer after the 2 nd modified layer forming step.

Fig. 5 is a side view showing the grinding apparatus.

Fig. 6 is an enlarged cross-sectional view showing a part of the wafer after the grinding step.

Description of the reference symbols

11: a wafer; 11 a: a front side; 11 b: a back side; 11 c: region 1; 11 d: a 2 nd region; 13 a: a 1 st division predetermined line; 13 b: a 2 nd division predetermined line; 13 c: a crossover region; 15: a device; 17: a protective member; 19: modified layer (altered layer); 21: a device layer (functional layer); 23 a: a 1 st altered layer (1 st altered layer); 23 b: a 2 nd altered layer (2 nd altered layer); 25a, 25 b: cracking (crazing); 27: cracking (crazing); 2: a laser processing device; 4: a chuck table (holding table); 4 a: a holding surface; 6: a laser irradiation unit; 8: a laser beam; 12: a grinding device; 14: a chuck table (holding table); 14 a: a holding surface; 16: a grinding unit; 18: a main shaft; 20: a mounting seat; 22: grinding the grinding wheel; 24: a base station; 26: and grinding the grinding tool.

Detailed Description

Hereinafter, an embodiment of one embodiment of the present invention will be described with reference to the drawings. First, a description will be given of a configuration example of a wafer that can be processed by the wafer processing method according to the present embodiment. Fig. 1 is a perspective view showing a wafer 11.

The wafer 11 has a front surface 11a and a back surface 11b, and is formed into a disk shape using a material such as silicon. The wafer 11 is divided into a plurality of regions by a plurality of lines to divide (streets) arranged in a grid shape so as to intersect each other.

Specifically, a plurality of lines to divide 1, 13a, and lines to divide 2, 13B are set on the wafer 11, the plurality of lines to divide 1, 13a being aligned such that the longitudinal direction is along the 1 st direction (the direction indicated by the arrow a), and the lines to divide 2, 13B being aligned such that the longitudinal direction is along the 2 nd direction (the direction indicated by the arrow B) substantially perpendicular to the 1 st direction. The 1 st line 13a and the 2 nd line 13b are arranged so as to intersect each other, and the wafer 11 is divided into a plurality of regions by the 1 st line 13a and the 2 nd line 13 b.

On the front surface 11a side of the plurality of regions defined by the 1 st line 13a and the 2 nd line 13b, devices 15, such as ICs (Integrated circuits) and LSIs (Large Scale Integrated circuits), are formed. When the wafer 11 is divided along the 1 st line 13a and the 2 nd line 13b, a plurality of device chips each having a device 15 can be obtained.

The material, shape, structure, size, and the like of the wafer 11 are not limited. For example, the wafer 11 may be formed of a material such as a semiconductor other than silicon (GaAs, SiC, InP, GaN, or the like), sapphire, glass, ceramic, resin, or metal. The type, number, shape, structure, size, arrangement, and the like of the devices 15 are not limited.

When the wafer 11 is divided, for example, division start points are formed along the 1 st line 13a and the 2 nd line 13 b. The division starting point functions as a starting point of division (a trigger of division) when the wafer 11 is divided. For example, the starting points for division are formed by modifying (modifying) the interior of the wafer 11 along the 1 st line 13a and the 2 nd line 13b by laser processing the wafer 11.

The modified region (modified layer) inside the wafer 11 is more fragile than the other regions of the wafer 11. Then, if an external force is applied to the wafer 11 on which the modified layer is formed, for example, outward in the radial direction of the wafer 11, cracks extend from the modified layer in the thickness direction of the wafer 11, and the wafer 11 is divided with the modified layer as a starting point. That is, the modified layer functions as a division start point of the wafer 11. Thus, the wafer 11 is divided along the 1 st line 13a and the 2 nd line 13b, and a plurality of device chips each having the device 15 can be obtained.

When the division starting points are formed on the wafer 11 by laser processing, first, the protective member 17 is attached to the front surface 11a side of the wafer 11 (protective member attaching step). As the protective member 17, for example, a film-like tape made of resin or the like and formed in a circular shape having substantially the same diameter as the wafer 11 is used. The plurality of devices 15 formed on the front surface 11a side of the wafer 11 are covered and protected by the protection member 17.

In addition, the wafer 11 may be supported by an annular frame in order to facilitate processing and transportation of the wafer 11. Specifically, a circular protective member 17 having a larger diameter than the wafer 11 is attached to the front surface 11a side of the wafer 11, and a ring-shaped frame having a circular opening having a larger diameter than the wafer 11 is attached to the outer peripheral portion of the protective member 17. This constitutes a frame unit in which the wafer 11 is supported by an annular frame via the protective member 17.

Next, the wafer 11 is held by the laser processing apparatus. Fig. 2 is a side view, partly in section, showing the laser processing apparatus 2. The laser processing apparatus 2 includes: a chuck table (holding table) 4 for holding the wafer 11; and a laser irradiation unit 6 that irradiates a laser beam 8.

The chuck table 4 is connected to a rotation drive source (not shown) such as a motor, and the rotation drive source rotates the chuck table 4 about a rotation axis substantially parallel to the vertical direction (Z-axis direction, vertical direction). Further, a moving mechanism (not shown) for moving the chuck table 4 in the machining feed direction (X-axis direction, 1 st horizontal direction) and the indexing feed direction (Y-axis direction, 2 nd horizontal direction) is provided below the chuck table 4.

The upper surface of the chuck table 4 constitutes a holding surface 4a for holding the wafer 11. The holding surface 4a is formed in a circular shape corresponding to the shape of the wafer 11. However, the shape of the holding surface 4a can be changed as appropriate depending on the shape of the wafer 11 and the like. The holding surface 4a is connected to a suction source (not shown) via a flow path (not shown) formed inside the chuck table 4.

A laser irradiation unit 6 is provided above the chuck table 4. The laser irradiation unit 6 includes: a laser oscillator that pulses a laser beam having a predetermined wavelength; and a condenser that condenses the laser beam oscillated from the laser oscillator at a predetermined position. The laser irradiation unit 6 irradiates the laser beam 8 toward the wafer 11 held by the chuck table 4.

In addition, the wavelength of the laser beam 8 is set so that the laser beam 8 shows transmissivity with respect to the wafer 11. Therefore, the laser beam 8 transmitted through the wafer 11 (having transparency to the wafer 11) is irradiated from the laser irradiation unit 6 to the wafer 11.

The rotation drive source and the movement mechanism connected to the chuck table 4, and the laser irradiation unit 6 are connected to a control unit (not shown) that controls each component constituting the laser processing apparatus 2. The control unit controls the position of the chuck table 4 and the irradiation conditions of the laser beam 8 (position of the focal point, power, spot diameter, repetition frequency, and the like).

The wafer 11 is held by the chuck table 4 via the protective member 17. Specifically, the wafer 11 is disposed on the chuck table 4 such that the front surface 11a side (the protective member 17 side) of the wafer 11 faces the holding surface 4a of the chuck table 4. In this state, if a negative pressure from a suction source is applied to the holding surface 4a, the wafer 11 is sucked and held by the chuck table 4.

Next, the laser beam 8 is irradiated from the laser irradiation unit 6 toward the wafer 11. At this time, the laser beam 8 is condensed inside the wafer 11 (the region between the front surface 11a and the back surface 11b of the wafer). Further, the irradiation conditions (power, spot diameter, repetition frequency, etc.) of the laser beam 8 are adjusted so that the inside of the wafer 11 is modified (altered) by multiphoton absorption.

By moving the chuck table 4 in the horizontal direction (X-axis direction in fig. 2) while irradiating the wafer 11 with the laser beam 8, a linear modified layer (modified layer) 19 is formed inside the wafer 11. The region where the modified layer 19 is formed is more fragile than the other regions of the wafer 11. When an external force is applied to the wafer 11 on which the modified layer 19 is formed, for example, fractures extend from the modified layer 19 in the thickness direction of the wafer 11, and the wafer 11 is divided with the modified layer 19 as a starting point. That is, the modified layer 19 functions as a division start point.

Further, depending on the thickness, material, and the like of the wafer 11, a plurality of modified layers 19 may be formed in the thickness direction of the wafer 11. By forming the plurality of modified layers 19, even when the wafer 11 is relatively thick, for example, the wafer 11 can be appropriately divided from the modified layers 19.

In the case of forming the modified layers 19, usually, the modified layers 19 are formed along the 1 st line 13a (see fig. 1) from the lower surface side (front surface 11a side) to the upper surface side (back surface 11b side) of the wafer 11, and then the modified layers 19 are formed along the 2 nd line 13b (see fig. 1) from the lower surface side to the upper surface side of the wafer. Therefore, when the modified layer 19 is formed along the 2 nd planned dividing line 13b, the modified layer 19 is already formed in a plurality of layers from the lower surface side to the upper surface side of the wafer 11 in the intersection region 13c (see fig. 1) of the 1 st planned dividing line 13a and the 2 nd planned dividing line 13 b.

When the modified layer 19 is formed along the 2 nd line 13b, the laser beam 8 is irradiated to the intersection region 13 c. Then, the laser beam 8 is irradiated onto the modified layer 19 formed in the intersection region 13c, so that diffuse reflection (scattering) of the laser beam 8 occurs, and the laser beam 8 may be exposed from the 2 nd line to divide 13 b. As a result, the laser beam 8 is irradiated on the device 15 (see fig. 1) formed on the lower surface side (front surface 11a side) of the wafer 11, and the device 15 may be damaged.

In particular, when the modified layer 19 is formed on the lower surface side (front surface 11a side) of the wafer 11 along the 2 nd dividing lines 13b, the laser beam 8 is irradiated to the plurality of modified layers 19 that have been formed from the lower surface to the upper surface of the wafer 11 in the intersection regions 13 c. Therefore, the diffuse reflection of the laser beam 8 is easily generated, and the damage of the device 15 is also easily generated.

Therefore, in the wafer processing method according to the present embodiment, the modified layer is formed in the 1 st region 11c (see fig. 3a and the like) of the wafer 11 on the front surface 11a side of the wafer 11 in the wafer 11 along the plurality of 1 st planned dividing lines 13a and the plurality of 2 nd planned dividing lines 13b, and then the modified layer is formed in the 2 nd region 11d (see fig. 3a and the like) of the wafer 11 on the back surface 11b side of the wafer 11 in the wafer 11 along the plurality of 1 st planned dividing lines 13a and the plurality of 2 nd planned dividing lines 13 b.

Specifically, first, the 1 st modified layer (1 st modified layer) 23a is formed in the 1 st region 11c of the wafer 11 along the plurality of 1 st lines 13a and the plurality of 2 nd lines 13b (1 st modified layer forming step). Fig. 3 (a) is an enlarged cross-sectional view showing a part of the wafer 11 in the 1 st modified layer forming step.

A protective member 17 is attached to the front surface 11a of the wafer 11 with a device layer (functional layer) 21 interposed therebetween. The device layer 21 corresponds to a layer including various functional films (a conductive film, an insulating film, and the like) constituting the plurality of devices 15 (see fig. 1) formed on the front surface 11a side of the wafer 11.

In the 1 st modified layer forming step, first, the chuck table 4 (see fig. 2) is rotated so that the longitudinal direction of the 1 st line to divide 13a (see fig. 1) coincides with the processing feed direction of the chuck table 4. In addition, the height of the converging point of the laser beam 8 is made to coincide with the height of the 1 st region 11c of the wafer 11. Then, the chuck table 4 is moved in the processing feed direction while the laser beam 8 is irradiated from the laser irradiation unit 6 toward the wafer 11, and the laser beam 8 is irradiated along the 1 st line to divide 13 a.

By irradiation with the laser beam 8, a linear 1 st modified layer 23a is formed along the 1 st line 13a in the 1 st region 11c of the wafer 11, and a crack 25a extends from the 1 st modified layer 23a in the thickness direction of the wafer 11. The crack 25a may be formed from the 1 st modified layer 23a toward one of the front surface 11a and the rear surface 11b, or may be formed from the 1 st modified layer 23a toward both of the front surface 11a and the rear surface 11 b.

Next, the converging point of the laser beam 8 is moved toward the back surface 11b side of the wafer 11, and the laser beam 8 is similarly irradiated onto the 1 st region 11 c. As a result, a plurality of 1 st modified layers 23a overlapping in a plan view are formed in the 1 st region 11c along one 1 st line to divide 13 a. Fig. 3 (a) shows a case where 2 modified layers 23a of the 1 st layer are formed, but the number of the modified layers 23a of the 1 st layer can be changed depending on the thickness and the material layer of the wafer 11, and can be set to any number of 1, 3 or more.

When the plurality of modified layers 1a are formed, the crack 25a extending from one modified layer 1a is connected to the crack 25a extending from the other modified layer 1 23 a. In fig. 3a, a crack 25a extending from the 1 st modified layer 23a of the 1 st layer (the 1 st modified layer 23a on the front surface 11a side) toward the rear surface 11b side and a crack 25a extending from the 1 st modified layer 23a of the 2 nd layer (the 1 st modified layer 23a on the rear surface 11b side) toward the front surface 11a side are connected to each other.

Thereafter, the 1 st modified layer 23a is similarly formed along the other 1 st lines 13 a. As a result, the 1 st modified layer 23a is formed in the 1 st region 11c of the wafer 11 in a linear shape along all the 1 st planned dividing lines 13 a.

Next, the chuck table 4 is rotated so that the longitudinal direction of the 2 nd line to divide 13b (see fig. 1) coincides with the processing feed direction of the chuck table 4. Then, the 1 st modified layer 23a is formed along all the 2 nd planned dividing lines 13b by the same procedure. As a result, the 1 st modified layer 23a is formed in the 1 st region 11c of the wafer 11 in a lattice shape along the 1 st line to divide 13a and the 2 nd line to divide 13 b.

In addition, when the 1 st modified layer 23a is formed along the 2 nd planned dividing line 13b, the laser beam 8 is irradiated to the 1 st region 11c through the 2 nd region 11 d. Here, if a modified layer is formed in the 2 nd region 11d, the laser beam 8 may be irradiated to the modified layer to be diffusely reflected (scattered), and may be irradiated to the device 15 included in the device layer 21. This may cause the device 15 to break.

On the other hand, in the 1 st modified layer forming step described above, the 1 st modified layer 23a is formed only in the 1 st region 11c along the 1 st line to divide 13 a. Therefore, when the 1 st modified layer 23a is formed along the 2 nd planned dividing line 13b, no modified layer is formed in the 2 nd region 11d, and diffuse reflection of the laser beam 8 is less likely to occur in the 2 nd region 11 d. Thus, irradiation of the laser beam 8 to the device 15 is less likely to occur, and breakage of the device 15 is suppressed.

In the case of forming the 1 st modified layer 23a in a plurality of layers along the 1 st line 13a and the 2 nd line 13b, the order of forming the 1 st modified layer 23a is not limited. For example, after a plurality of 1 st modified layers 23a are formed along the 1 st line 13a, a plurality of 1 st modified layers 23a may be formed along the 2 nd line 13b, or the step of forming the 1 st modified layers 23a in one layer along the 1 st line 13a and the 2 nd line 13b may be repeated.

Fig. 3 (B) is an enlarged cross-sectional view showing a part of the wafer 11 after the 1 st modified layer forming step. In the 1 st region 11c of the wafer 11, a 1 st modified layer 23a extending in the longitudinal direction of the 1 st line to divide 13a (the left-right direction of the paper surface in fig. 3B) and a 1 st modified layer 23a extending in the longitudinal direction of the 2 nd line to divide 13B (the front-back direction of the paper surface in fig. 3B) are formed. Fig. 3 (B) shows an example of the wafer 11 in which 21 st modified layers 23a are formed along the 1 st planned dividing lines 13a and the 2 nd planned dividing lines 13B, respectively.

When the 1 st modified layer 23a is formed, the region of the wafer 11 where the 1 st modified layer 23a is formed may expand, and the wafer 11 may be warped due to the expansion. When the wafer 11 is warped, the positions of the lines to divide 1 st 13a and the lines to divide 2 b are changed, and it is difficult to irradiate the laser beam 8 along the lines to divide 1 13a and the lines to divide 2 b. In particular, when the number of the 1 st lines 13a and the 2 nd lines 13b is large and the distance therebetween is narrow (for example, 5mm or less), the variation in the positions of the 1 st lines 13a and the 2 nd lines 13b due to the expansion of the wafer 11 is likely to increase.

Therefore, in the 1 st modified layer forming step, as shown in fig. 3 (a), fractures 25a preferably occur from the 1 st modified layer 23a to the front surface 11a of the wafer 11. Specifically, in forming the 1 st modified layer 23a closest to the front surface 11a of the wafer 11, the irradiation conditions of the laser beam 8 are set so as to form the crack 25a reaching the front surface 11a of the wafer 11 from the 1 st modified layer 23 a.

For example, in the case of using a silicon wafer having a diameter of 12 inches and a thickness of 775 μm as the wafer 11, the focal point of the laser beam 8 is positioned at a point at a distance (depth) of 200 μm or less from the front surface 11a of the wafer 11. Then, the laser beam 8 is irradiated along the plurality of lines to divide 1 st 13a and the plurality of lines to divide 2 nd 13 b. The irradiation conditions of the laser beam 8 are set as follows, for example.

Light source: YAG pulse laser

Wavelength: 1064nm

Repetition frequency: 60kHz

Average output: 1.8W

Processing feed speed: 900mm/s

When the laser beam 8 is irradiated under the above conditions, the crack 25a reaching the front surface 11a of the wafer 11 from the 1 st modified layer 23a closest to the front surface 11a of the wafer 11 is continuously formed. As a result, a partial region on the front surface 11a side of the wafer 11 is divided along the 1 st line 13a and the 2 nd line 13 b.

When the front surface 11a side of the wafer 11 was thus divided, it was confirmed that even if the 1 st modified layer 23a was formed, warpage of the wafer 11 was not easily generated. This suppresses deformation of the 1 st line 13a and the 2 nd line 13b, and facilitates irradiation of the laser beam 8 along the 1 st line 13a and the 2 nd line 13 b.

At the time of forming the 1 st modified layer 23a, the back surface 11b side (the 2 nd region 11d side) of the wafer 11 is connected without being divided. Therefore, even if the front surface 11a side (the 1 st region 11c side) of the wafer 11 swells due to the formation of the 1 st modified layer 23a, the entire wafer 11 is less likely to be deformed or warped, and the variation in the positions of the 1 st line to divide 13a and the 2 nd line to divide 13b is suppressed.

Next, a 2 nd modified layer (modified layer) 23b is formed in the 2 nd region 11d of the wafer 11 along the plurality of 1 st lines 13a and the plurality of 2 nd lines 13b (2 nd modified layer forming step). Fig. 4 (a) is an enlarged cross-sectional view showing a part of the wafer 11 in the 2 nd modified layer forming step.

In the 2 nd modified layer forming step, the laser beam 8 is irradiated along the plurality of 1 st lines 13a and the plurality of 2 nd lines 13b in the same step as the 1 st modified layer forming step. However, when the wafer 11 is irradiated with the laser beam 8, the height of the converging point of the laser beam 8 coincides with the height of the 2 nd region 11d of the wafer 11.

As a result, the 2 nd modified layer 23b is formed in the 2 nd region 11d of the wafer 11 along the plurality of 1 st lines 13a and the plurality of 2 nd lines 13b, and fractures (cracks) 25b are formed from the 2 nd modified layer 23b in the thickness direction of the wafer 11. In the 2 nd modified layer forming step, as shown in fig. 4 (a), irradiation conditions of the laser beam 8 are set so as to form fractures 25b from the 2 nd modified layer 23b to the back surface 11b of the wafer 11.

Fig. 4 (B) is an enlarged cross-sectional view showing a part of the wafer 11 after the 2 nd modified layer forming step. Fig. 4 (B) shows an example of the wafer 11 in which 2 nd modified layers 23B are formed along the 1 st line 13a and the 2 nd line 13B, respectively. Further, the crack 25b extending from the 2 nd modified layer 23b of the 1 st layer (the 2 nd modified layer 23b on the front surface 11a side) toward the rear surface 11b side and the crack 25b extending from the 2 nd modified layer 23b of the 2 nd layer (the 2 nd modified layer 23b on the rear surface 11b side) toward the front surface 11a side are connected to each other.

The number of modified layers 23b of the 2 nd region 11d can be set as appropriate in the same manner as the number of modified layers 23a of the 1 st region. In the case of forming a plurality of modified layers 23b along the line to divide 1 and the line to divide 2 13b, the order of forming the modified layers 2 23b can be appropriately set in the same manner as in the modified layer forming step 1. The crack 25b extends in the same manner as the crack 25a formed in the 1 st region 11 c.

When the 2 nd modified layer forming step is performed, the fracture 25a formed in the 1 st modified layer forming step is connected to the fracture 25b formed in the 2 nd modified layer forming step, and a plurality of fractures (cracks) 27 extending from the back surface 11b to the front surface 11a of the wafer 11 are continuously formed along the 1 st line 13a and the 2 nd line 13 b. As a result, the wafer 11 is divided along the 1 st line 13a and the 2 nd line 13b, and a plurality of device chips each having a device 15 (see fig. 1) can be obtained.

In addition, the fractures 25a formed in the 1 st region 11c in the 1 st modified layer forming step may not reach the front surface 11a of the wafer 11. However, if the crack 25b reaching the back surface 11b of the wafer 11 is formed in the modified layer 2 forming step, the crack 25a spreads so as to reach the front surface 11a of the wafer 11 when the crack 25b is formed.

When the wafer 11 is divided, the protective member 17 is attached to the front surface 11a side of the wafer 11. Therefore, after the wafer 11 is divided into a plurality of device chips, the arrangement of the respective device chips is also maintained by the protective member 17.

The number of the 1 st modified layers 23a formed in the 1 st region 11c and the number of the 2 nd modified layers 23b formed in the 2 nd region 11d are preferably adjusted according to the thickness, material, and the like of the wafer 11. For example, in the case where the wafer 11 is a silicon wafer having a diameter of 12 feet and a thickness of 775 μm, when 2 modified layers 1, 23a are formed in the 1 st region 11c and 5 modified layers 2, 23b are formed in the 2 nd region 11d, it is confirmed that the wafer 11 is properly divided.

In addition, the number of the 1 st modified layers 23a formed in the 1 st region 11c is preferably smaller than the number of the 2 nd modified layers 23b formed in the 2 nd region 11 d. This confirmed that the wafer 11 was less likely to warp.

Next, the back surface 11b side of the wafer 11 is ground to thin the wafer 11 to a predetermined thickness (grinding step). In the grinding step, the wafer 11 is ground using, for example, a grinding apparatus. Fig. 5 is a side view showing the grinding device 12.

The grinding device 12 includes a chuck table (holding table) 14 that holds the wafer 11. The chuck table 14 is connected to a rotation drive source (not shown) such as a motor, and the rotation drive source rotates the chuck table 14 about a rotation axis substantially parallel to the vertical direction. Further, a moving mechanism (not shown) for moving the chuck table 14 in the machining feed direction is provided below the chuck table 14.

The upper surface of the chuck table 14 constitutes a holding surface 14a for holding the wafer 11. The holding surface 14a is formed in a circular shape corresponding to the shape of the wafer 11. However, the shape of the holding surface 14a can be changed as appropriate depending on the shape of the wafer 11 and the like. The holding surface 14a is connected to a suction source (not shown) via a flow path (not shown) formed inside the chuck table 14.

A grinding unit 16 is disposed above the chuck table 14. The grinding unit 16 includes a spindle housing (not shown) supported by an elevating mechanism (not shown). A spindle 18 is housed in the spindle case, and a disk-shaped mount 20 is fixed to a lower end portion of the spindle 18.

A grinding wheel 22 having substantially the same diameter as the mount 20 is attached to the lower surface of the mount 20. The grinding wheel 22 has an annular base 24 made of a metal material such as stainless steel or aluminum. A plurality of grinding stones 26 formed in a rectangular parallelepiped shape are fixed to the lower surface side of the base 24. A plurality of grinding stones 26 are arranged in a ring shape along the outer periphery of the base 24.

A rotation drive source (not shown) such as a motor is connected to the upper end side (base end side) of the main shaft 18. The grinding wheel 22 is rotated about a rotation axis substantially parallel to the vertical direction by a force transmitted from the rotary drive source. A grinding fluid supply path (not shown) for supplying a grinding fluid such as pure water is provided inside the grinding unit 16. When the wafer 11 is ground, a grinding fluid is supplied to the wafer 11 and the grinding wheel 26.

In the grinding step, first, the wafer 11 is disposed on the chuck table 14 so that the front surface 11a side (the protective member 17 side) of the wafer 11 faces the holding surface 14 a. In this state, if a negative pressure from the suction source is applied to the holding surface 14a, the wafer 11 is sucked and held by the chuck table 14 while the rear surface 11b side is exposed upward.

Next, the chuck table 14 is moved and disposed below the grinding unit 16. Then, the chuck table 14 and the grinding wheel 22 are rotated to lower the spindle 18 while supplying the grinding liquid to the back surface 11b side of the wafer 11. The lowering speed of the spindle 18 is adjusted so that the lower surface of the grinding stone 26 is pressed against the back surface 11b of the wafer 11 with an appropriate force.

When the grinding stone 26 is brought into contact with the back surface 11b side of the wafer 11, the back surface 11b side of the wafer 11 is ground and the wafer 11 is thinned. Then, grinding of the wafer 11 is continued until the thickness of the wafer 11 becomes a predetermined thickness (finishing thickness). The finish thickness corresponds to the final thickness of the device chip obtained by dividing the wafer 11.

Fig. 6 is an enlarged cross-sectional view showing a part of the wafer 11 after the grinding step. When the grinding step is performed, the wafer 11 divided along the 1 st line 13a and the 2 nd line 13b is thinned to a finish thickness.

Further, if the 1 st modified layer 23a remains on the wafer 11 after the grinding process (see fig. 3a and the like), the bending strength of the device chip obtained by dividing the wafer 11 is lowered. Therefore, in the 1 st modified layer forming step, the 1 st modified layer 23a is preferably formed such that the distance between the front surface 11a of the wafer 11 and the 1 st modified layer 23a in the thickness direction of the wafer 11 is larger than the finishing thickness. That is, it is preferable that the 1 st modified layer 23a is not formed in a region where the distance (depth) from the front surface 11a of the wafer 11 is equal to or less than the finishing thickness.

In the above case, when the wafer 11 is ground in the grinding step until the thickness of the wafer 11 becomes the finish thickness, the 1 st modified layer 23a is entirely removed. Therefore, the 1 st modified layer 23a does not remain on the wafer 11 after the grinding process, and the reduction in the bending strength of the device chip is suppressed.

As described above, the wafer processing method according to the present embodiment includes: a 1 st modified layer forming step of forming a 1 st modified layer 23a in the 1 st region 11c along the 1 st and 2 nd lines 13a and 13 b; and a 2 nd modified layer forming step of forming a 2 nd modified layer 23b in the 2 nd region 11d along the 1 st predetermined dividing line 13a and the 2 nd predetermined dividing line 13 b.

In the above-described wafer processing method, when the 1 st modified layer 23a is formed in the 1 st region 11c along the 1 st planned dividing line 13a and the 2 nd planned dividing line 13b, no modified layer is formed in the 2 nd region 11 d. Therefore, when the laser beam 8 is irradiated onto the wafer 11 with the focal point of the laser beam 8 positioned in the 1 st region 11c, the laser beam 8 is less likely to be diffusely reflected (scattered) in the 2 nd region 11 d. Thus, irradiation of the laser beam 8 to the device 15 is less likely to occur, and breakage of the device 15 is suppressed.

In addition, when a method of dividing a wafer having a modified layer formed thereon by using a conventional expanding sheet or a method of dividing a wafer by grinding the wafer having a modified layer formed thereon is used, a desired external force may not be applied to the entire wafer, and the wafer may not be appropriately divided. Further, at the time of performing the step of forming the modified layer on the wafer, it is difficult to confirm whether or not the modified layer is properly formed along the planned dividing line, and it is difficult to predict whether or not the wafer is properly divided in the subsequent step.

On the other hand, in the wafer processing method of the present embodiment, the wafer 11 is divided by a crack generated by forming the modified layer from the front surface 11a side to the back surface 11b side of the wafer 11. Thereby, the wafer 11 is appropriately divided along the 1 st line 13a and the 2 nd line 13 b. Further, since the dividing step of the wafer 11 is already completed at the time when the 1 st modified layer forming step and the 2 nd modified layer forming step are performed, it is possible to easily confirm whether or not the wafer 11 is appropriately divided before performing the subsequent steps (grinding step and the like).

The structure, method, and the like of the above embodiments can be modified as appropriate without departing from the object of the present invention.