TWI833762B - Processing method of the workpiece - Google Patents

Abstract

The object is to prevent grinding chips from adhering to the side surfaces of the wafer in a processing method that divides the workpiece using the modified layer inside the workpiece as a starting point. The solution is a processing method of the processed object, including: A laser beam (LB1) that is transparent to the workpiece (W) is irradiated from the back surface (Wb) side along the line to be divided (S), so that cracks will not occur from the top to the bottom and the lower end will be located at a ratio corresponding to the wafer. Complete the steps of the first modified layer (M1) whose thickness position (Z1) is slightly closer to the back (Wb) side; A laser beam (LB2) that is transparent to the workpiece (W) is irradiated from the back surface (Wb) side along the line to be divided (S), and is located on the back surface (Wb) of the first modified layer (M1). The step of forming a second modified layer (M2) that generates cracks (Mb, Ma) on the upper and lower sides; and The step of grinding the back surface (Wb) of the workpiece (W) to form the finished thickness (H1) of the wafer, and dividing the workpiece (W) into wafers (C) using the second modified layer (M2) as a starting point. .

Description

Processing method of the workpiece

The present invention relates to a processing method for dividing a workpiece into individual wafers along a planned dividing line.

In the semiconductor device manufacturing process, a plurality of areas are defined on the surface of a roughly disk-shaped semiconductor workpiece by a plurality of planned dividing lines called dividing lines arranged in a lattice. The area forms circuits (functional components) such as ICs and LSIs. Then, the semiconductor workpiece is cut along the planned dividing line, thereby dividing the area where the circuit is formed, and manufacturing individual semiconductor wafers.

As a method of cutting the semiconductor workpiece along the line to be divided, there is a method that involves using a pulsed laser light with a wavelength that is transparent to the workpiece and aligning the light collection point with the area to be divided of the workpiece. A method of laser processing in which pulsed laser light is irradiated from inside is known (for example, see Patent Document 1).

The method of dividing a workpiece using this laser processing is to align the light collection point inward from one surface side of the workpiece and irradiate a pulse laser with a wavelength in the infrared region that is transparent to the workpiece. The light ray continuously forms a modified layer along the planned dividing line inside the workpiece, and grinds the back side of the workpiece along the planned dividing line whose intensity is reduced by forming this modified layer. The stress generated will break and divide the workpiece. [Advanced technical documents] [Patent Document]

[Patent Document 1] Japanese Patent No. 4733934

(The problem that the invention aims to solve)

However, in the dividing method described in Patent Document 1, gaps are generated between the divided wafers. Therefore, if the workpiece is ground to the finished thickness after the wafers are divided, the grinding water containing grinding chips (used during grinding) The water used to cool and clean the contact point between the grinding stone and the workpiece) will penetrate into the gap between the wafers, and the grinding chips will adhere to the sides of the wafers. The grinding debris attached to the side of the wafer is very difficult to remove even if it is cleaned by the cleaning mechanism of the grinding device.

Therefore, an object of the present invention is to provide a processing method for dividing the workpiece into wafers by continuously forming a modified layer along a planned division line inside the workpiece, and using the modified layer as a starting point to divide the workpiece into wafers. A processing method in which grinding chips adhere to the workpiece on the side of the wafer. (Means used to solve problems)

According to the present invention, there is provided a processing method of a workpiece in which functional elements are formed in each area divided by a plurality of planned division lines formed on a surface along a planned division line. The processing method of dividing the processed object into individual wafers has the following characteristics: The first modified layer forming step is to irradiate laser light of a wavelength that is transparent to the workpiece from the back side of the workpiece along the line to be divided, so that cracks will not occur at the upper and lower ends. a first modified layer located slightly closer to the back side than a height corresponding to the completed thickness of the wafer; The second modified layer forming step is to irradiate laser light of a wavelength that is transparent to the workpiece from the back side of the workpiece along the planned dividing line to form a second modified layer on the back side of the workpiece. The formation of cracks on the back side of the first modified layer formed in the step will occur in the upper and lower second modified layers; and The backside grinding step is to grind the backside of the workpiece on which the first modified layer and the second modified layer are formed, to form the workpiece into the completed thickness of the wafer, and to use the second modified layer with cracks. Using the layer as the starting point, the workpiece is divided into individual wafers. In the back grinding step, the first modified layer remains until the back grinding is completed, thereby preventing grinding water containing grinding chips from penetrating into the gap between the wafers.

Preferably, in the back grinding step, the second modified layer formed in the second modified layer forming step is cracked on the upper and lower sides by the grinding stress generated in the workpiece to break the workpiece. things. [Effects of the invention]

According to the present invention, in the back surface grinding step, the first modified layer remains until the back surface grinding is completed, thereby preventing grinding water containing grinding chips from intruding into the gaps between the wafers formed by the division.

That is, in addition to the second modified layer that serves as a starting point for dividing the workpiece into wafers, the first modified layer is formed in the vicinity of a position corresponding to the completed thickness of the wafer. In the back grinding step, even if After the workpiece is divided into wafers starting from the second modified layer, there is also a first modified layer with thin and wide cutting grooves. The first modified layer prevents grinding water containing grinding chips from entering the wafer. The side immersion task suppresses the adhesion of grinding chips on the side of the wafer. In addition, since the first modified layer formed in the first modified layer forming step is formed by irradiating laser light with a low output that does not cause cracks in the upper and lower directions, the first modified layer During formation, the scattering of the laser light through the cracks is prevented, the attack of the laser light on the functional components on the surface of the workpiece is suppressed, and the functional components are not damaged. Therefore, even if the first modified layer is formed near a position corresponding to the completed thickness of the wafer, no problem occurs. The first modified layer remaining until the grinding is completed can prevent grinding chips from intruding into the side surface of the wafer. In addition, since both the first modified layer and the second modified layer are formed on the back side of the position corresponding to the completed thickness of the wafer, the workpiece is ground to the completed thickness in the back surface grinding step. Both modified layers will be removed. Therefore, it is possible to prevent the strength of the wafer from decreasing due to the remaining modified layer.

Hereinafter, steps for dividing the workpiece W shown in FIG. 1 into wafers each including the functional elements D along the planned dividing line S will be described regarding the processing method of the workpiece according to the present invention.

The workpiece W shown in FIG. 1 is, for example, a semiconductor wafer having a circular plate shape and using silicon as a base material. In FIG. 1 , the surface Wa facing downward is formed with a plurality of orthogonally intersecting planned division lines S. , functional elements (devices) D are respectively formed in each area divided into a grid shape by the planned division lines S. For example, the surface Wa of the workpiece W is protected by a protective tape T. In addition, the base material of the workpiece W may be composed of gallium arsenide, sapphire, gallium nitride, silicon carbide, etc., in addition to silicon.

The laser processing device 1 shown in FIG. 1 is a device in which a laser beam irradiation means 6 irradiates a workpiece W held on a holding table 30 with a laser beam. The holding base 30 that holds the workpiece W has a circular outer shape in plan view and is made of a porous member or the like. It has a flat holding surface 300 that attracts and holds the workpiece W. The holding surface 300 is connected to a suction surface (not shown). source. The holding base 30 is rotatable around an axis in the vertical direction (Z-axis direction), and can be reciprocated in the X-axis direction and the Y-axis direction by a moving means not shown in the figure.

The laser beam irradiation means 6 is provided, for example, with a cylindrical housing 60 extending horizontally in the Y-axis direction above the holding surface 300 . A laser light oscillator 61 is disposed inside the housing 60 . The laser light oscillator 61 is, for example, an Nd:YVO4 laser, and can oscillate a laser light (pulse laser) of a predetermined wavelength (for example, a wavelength of 1342 nm) that is transparent to the workpiece W.

A laser head 62 having a collecting lens 62 a inside is disposed at the front end of the housing 60 . The laser light irradiation means 6 uses a reflection mirror (not shown) provided inside the housing 60 and the laser head 62 to reflect the laser light oscillating in the −Y-axis direction from the laser light oscillator 61 so that it enters the laser beam irradiation device 6 . The light reaches the light collecting lens 62 a, whereby the laser light directed in the −Z direction can be accurately collected and irradiated to a predetermined height position of the workpiece W held on the holding table 30 . In addition, the focusing point position of the laser light collected by the laser head 62 can be adjusted to a direction perpendicular to the holding surface 300 of the holding table 30 (Z axis direction).

An alignment means 64 for detecting the planned division line S of the workpiece W is disposed near the laser head 62 (for example, on the outer surface of the housing 60). The alignment means 64 includes an infrared irradiation means (not shown) that irradiates infrared rays, an infrared camera 640 composed of an optical system for capturing infrared rays, an imaging element (infrared ray CCD) that outputs an electrical signal corresponding to the infrared rays, and the like. From the image acquired by the infrared camera 640, the planned division line S on the surface Wa of the workpiece W is detected through image processing such as pattern matching.

(1) First modified layer formation step First, as shown in FIGS. 1 and 2 , the workpiece W is attracted and held by the holding table 30 with the back surface Wb facing upward. Next, the holding table 30 holding the workpiece W is sent to the -X direction (forward direction) as shown in FIG. 2 , and is captured by the infrared camera 640 from the back side Wb of the workpiece W. The alignment means 64 performs image processing such as pattern matching on the planned dividing line S of the surface Wa based on the image of the planned dividing line S captured by the infrared camera 640, and detects the planned dividing line that serves as a reference for irradiating laser light. S position.

As the position of the planned dividing line S is detected, the holding table 30 holding the workpiece W is indexed and fed in the Y-axis direction, and the planned dividing line S, which becomes the reference for irradiating the laser light, is aligned with the laser head 62 Alignment in the Y-axis direction. Next, as shown in FIG. 3 , the light collecting point position P1 of the laser light LB1 collected by the light collecting lens 62 a is positioned at a predetermined height position inside the workpiece W, that is, for example, a relatively high height position. The height position Z1 of the finished thickness H1 (for example, about 30 μm) of the wafer shown in FIG. 3 is slightly closer to the back surface Wb side (upper side). Then, the laser light LB1 with a wavelength that is transparent to the workpiece W is oscillated from the laser light oscillator 61 shown in FIG. 2 , and as shown in FIGS. 2 and 3 , the laser light LB1 is concentrated and irradiated to inside the workpiece W held by the holding table 30 .

The laser light output and repetition frequency of the laser light oscillator 61 are set to conditions such that cracks do not occur in the upper and lower parts of the first modified layer M1 (see FIG. 3 ) formed on the workpiece W. In particular, it is set so that the average output is low (0.5W or less). An example of the above conditions is as follows. Wavelength: 1342nm Repetition frequency: 90kHz Average output: 0.5W Processing feed speed: 700mm/second

While irradiating the workpiece W with the laser beam LB1 from the back surface Wb side along the planned division line S, the workpiece W is processed and fed in the -X direction at the above-mentioned processing feed speed, as shown in Figures 2 and 3 , forming the first modified layer M1 inside the workpiece W. The laser light LB1 before reaching the light collection point position P1 is transparent to the workpiece W, but the laser light LB1 reaching the light collection point position P1 shown in FIG. 3 is locally very transparent to the workpiece W. absorption properties. Therefore, the workpiece W near the light collection point position P1 absorbs the laser light LB1 and is modified, and the first modified layer M1 forming a predetermined length mainly faces upward (the back surface Wb side) from the light collection point position P1. extend.

Since the average output of the set laser light LB1 is reduced, although the first modified layer M1 is formed on the workpiece W as shown in FIG. 3 , no cracks (or cracks) will occur upward and downward from the first modified layer M1 Even if it occurs, it will be a very small crack that can be ignored). That is, the first modified layer M1 that does not generate cracks from the top to bottom and whose lower end is slightly closer to the back surface Wb side than the height position Z1 corresponding to the finished thickness H1 of the wafer will move from the -X direction as shown in Figure 3 In the +X direction, they are linearly arranged inside the workpiece W with slight intervals along the planned dividing line S in the X-axis direction. The first modified layer M1 is formed so that the lower end is located slightly closer to the back surface Wb than the height position Z1 corresponding to the finished thickness H1. However, since the average output of the set laser light LB1 is lowered, cracks are not formed, so there is no The laser light LB1 is scattered from the light collection point position P1 toward the surface Wa side via a crack. Therefore, there is no situation where the scattered laser light LB1 attacks the functional element D formed on the surface Wa and causes damage to the functional element D, even if the first modification is formed near the height position Z1 corresponding to the completed thickness H1 of the wafer. Plasma layer M1 also does not cause problems.

Once the workpiece W travels in the −X direction to a predetermined position in the X-axis direction where the irradiation of laser light LB1 is completed along one row of planned division lines S, the irradiation of laser light LB1 is stopped, and the workpiece W The processing feed in the -X direction will be stopped.

(2) Second modified layer formation step Next, a laser light having a wavelength that is transparent to the workpiece W is irradiated from the back surface Wb side of the workpiece W along the planned division line S, and the first modified layer formed in the first modified layer forming step is The quality layer M1 is further toward the back surface Wb side (upper side) and forms a second modified layer in which cracks occur at the upper and lower sides. For example, the laser light output and repetition frequency of the laser light oscillator 61 are set to conditions that cause cracks to occur from the upper and lower sides of the second modified layer M2 (see FIG. 4 ) formed on the workpiece W. In particular, the average output is set to be higher (0.8W or more) than when the first modified layer M1 is formed. An example of the above conditions is as follows. Wavelength: 1342nm Repetition frequency: 90kHz Average output: 0.8W Processing feed speed: 700mm/second

As shown in FIG. 4 , the light collecting point position P2 of the laser light LB2 collected by the light collecting lens 62 a (see FIG. 5 ) is positioned at a distance from the formed light beam by a light collecting point position adjustment means (not shown). The height position Z2 of the first modified layer M1 is at a predetermined distance above the light collecting point position P1 and is close to the back surface Wb side of the workpiece W. In addition, the distance between the light-concentrating point position P1 and the light-concentrating point position P2 is set so as to extend from the formed second modified layer M2 to the crack below as shown in FIG. 4 in this embodiment. Ma does not reach the first modified layer M1, but it may be set so that the crack Ma extending downward from the second modified layer M2 reaches the first modified layer M1.

Then, the laser light LB2 having a wavelength that is transparent to the workpiece W is oscillated from the laser light oscillator 61 shown in FIG. 5 , and the laser light LB2 is focused on the target as shown in FIGS. 4 and 5 . The inside of the workpiece W held by the holding table 30.

The object W is processed and fed at a processing feed speed of 700 mm/second while the laser beam LB2 is irradiated from the back surface Wb side to the object W along the planned division line S where the first modified layer M1 is first formed. In the +X direction (composite direction), as shown in FIGS. 4 and 5 , the second modified layer M2 is formed inside the workpiece W. That is, as shown in FIG. 4 , the workpiece W near the light collection point position P2 absorbs the laser light LB2 and is modified, and is formed to extend mainly upward (the back surface Wb side) from the light collection point position P2 by a predetermined amount. The length of the second modified layer M2. Furthermore, fine cracks Mb and Ma are simultaneously formed in the up and down directions from the second modified layer M2. In this embodiment, the crack Ma extending from the second modified layer M2 to the lower surface does not reach the first modified layer M1, but the crack Ma may reach the first modified layer M1.

Cracks Mb are generated on the back Wb side (upper side) of the first modified layer M1, and the second modified layer M2 above and below will move from the +X direction to the -X direction as shown in Figures 4 and 5. They are linearly arranged inside the workpiece W with fine intervals along the planned division line S in the X-axis direction. Then, once the workpiece W travels in the +X direction to a predetermined position in the X-axis direction where the irradiation of the laser light LB2 ends along one row of planned division lines S, the irradiation of the laser light LB2 is stopped and the workpiece W is processed. The processing feed of object W in the +X direction will be stopped.

In this way, for example, the first modified layer forming step is performed together with the processing feed of the workpiece W in the -X direction (forward direction), and the first modified layer forming step is performed together with the processing feed of the workpiece W in the + ), the second modified layer forming step performed together with the processing feed is set as one set, and the workpiece W is laser processed along one row of planned dividing lines S. In addition, in the second modified layer forming step, the same row of planned division lines S may be irradiated with laser in multiple paths from the back surface Wb side while shifting the position of the light collection point to the upper side in the forward and backward directions. The light LB2 reaches the workpiece W, and along the planned division line S, a second modified layer of the second stage is formed above the previously formed second modified layer M2 (the second modified layer M2 as the first stage). Layer M2, the second modified layer M2 of the third stage, etc. In this case, for example, the crack Mb extending on the upper side of the second modified layer M2 of the first stage and the crack Ma extending on the lower side of the second modified layer M2 of the second stage are connected.

For example, for one row of planned division lines S, after a set of the first modified layer forming step and the second modified layer forming step is performed, the holding table 30 shown in FIGS. 1 and 5 is indexed and fed in the Y-axis direction. , aligning the planned dividing line S located on the partition wall where the planned dividing line S of the first modified layer M1 and the second modified layer M2 is formed, and the laser head 62 in the Y-axis direction. After being aligned, the first modified layer forming step and the second modified layer forming step are performed as a set for the new column of planned division lines S to form the first modified layer M1 and the second modified layer M2. A set of the same first modified layer forming step and second modified layer forming step is performed sequentially along each planned dividing line S, thereby forming the first modified layer along all planned dividing lines S extending in the X-axis direction. Modified layer M1 and second modified layer M2.

Furthermore, once the holding table 30 is rotated 90 degrees and the workpiece W is irradiated with the same laser light, the first modified layer M1 can be formed inside the workpiece W along all the planned division lines S vertically and horizontally. and the second modified layer M2. In addition, for example, the first modified layer forming step may be performed along all the planned division lines S vertically and horizontally to form the first modified layer M1 vertically and horizontally inside the workpiece W, and then, the first modified layer M1 may be formed along all the vertical and horizontal division lines S. The second modified layer forming step is performed by dividing the planned line S to form the second modified layer M2 vertically and horizontally inside the workpiece W.

(3)Backside grinding steps Next, the workpiece W on which the first modified layer M1 and the second modified layer M2 are formed is transported to the grinding device 2 shown in FIG. 6 , for example. The grinding device 2 shown in FIG. 6 is a device that grinds the workpiece W held on the holding table 20 by the grinding means 21.

The holding base 20 that holds the workpiece W has a circular outer shape and is provided with a holding surface 200 made of a porous member or the like that attracts and holds the workpiece W. The holding surface 200 communicates with an attraction source (not shown). The holding base 20 is rotatable around an axis in the vertical direction (Z-axis direction) by the rotation means 23 connected to the bottom side, and is reciprocally movable in the X-axis direction.

The grinding means 21 includes a spindle 210 whose axis direction is the Z-axis direction, a motor (not shown) that drives the spindle 210 to rotate, a mount 211 connected to the lower end side of the spindle 210, and a removable The grinding wheel 212 is installed below the fixed part 211. The grinding wheel 212 includes an annular wheel base 212b and a plurality of substantially rectangular parallelepiped-shaped grinding stones 212a annularly arranged on the lower surface of the wheel base 212b. The grinding stone 212a is formed by, for example, using an appropriate adhesive to fix and adhere diamond grains or the like.

For example, a flow path (not shown) is formed inside the spindle 210 and is connected to a grinding water supply source to become a passage for grinding water. The flow path is formed in the axial direction of the spindle 210 . The flow path is opened on the bottom surface of the grinding wheel 212 so as to be able to face the grinding wheel 212 . The grinding whetstone 212a sprays grinding water.

First, the center of the holding table 20 and the center of the workpiece W are approximately aligned, and the workpiece W is loaded onto the holding surface 200 with the back side Wb facing upward. Then, the attraction force generated by the attraction source (not shown) is transmitted to the holding surface 200 , whereby the holding table 20 attracts and holds the workpiece W.

Next, the holding table 20 holding the workpiece W moves in the −X direction under the grinding means 21 to align the grinding wheel 212 of the grinding means 21 with the workpiece W. For example, as shown in FIGS. 6 and 7 , the rotation center of the grinding wheel 212 deviates from the horizontal direction only by a predetermined distance relative to the rotation center of the workpiece W, so that the rotation track of the grinding stone 212 a passes through the workpiece W. of the rotation center.

After the grinding wheel 212 and the workpiece W are aligned, the grinding wheel 212 will rotate as the spindle 210 is driven to rotate. Furthermore, the grinding means 21 is sent in the -Z direction, and the grinding stone 212a of the rotating grinding wheel 212 comes into contact with the back surface Wb of the workpiece W to perform grinding processing. During grinding, as the holding table 20 rotates, the workpiece W held on the holding surface 200 also rotates. Therefore, the grinding stone 212a performs a complete grinding process on the back surface Wb of the workpiece W. During the grinding process, grinding water is supplied to the contact area between the grinding stone 212a and the workpiece W to cool and clean the contact area. In addition, a grinding water nozzle (not shown) may be disposed so as to face the inner surface of the grinding stone 212a beyond the workpiece W, so that the grinding water sprayed from the grinding water nozzle flows from the inside of the rotating grinding wheel 212. The side surface is supplied to the contact portion between the grinding stone 212a and the workpiece W.

During the grinding process, grinding pressure in the -Z direction is applied to the workpiece W from the grinding stone 212a. Then, once the back surface Wb is ground, grinding stress relative to the grinding pressure is generated along the second modified layer M2 shown in FIG. 8 , starting from the second modified layer M2 with cracks Mb and Ma. The processed product W is divided into individual wafers. That is, the cracks Mb and Ma respectively extend toward the back surface Wb and the surface Wa of the workpiece W to form cutting grooves (gaps) Md. Then, the cutting groove Md reaches the surface Wa in one go through the first modified layer M1, so the workpiece W is divided into individual wafers C.

Here, the first modified layer M1 is formed with a fine-width cutting groove Me having a narrower groove width than the cutting groove Md formed in a portion of the workpiece W where the first modified layer M1 is not formed. This is considered to be because the first modified layer M1 is amorphous and has a state in which atoms or molecules exist irregularly. Furthermore, the first modified layer M1 is formed so that its lower end is located slightly closer to the back surface Wb than the height position Z1 corresponding to the completed thickness H1 of the wafer C. Therefore, even if the grinding water including grinding chips penetrates into the cutting groove (gap) Md Therefore, the first modified layer M1 fulfills the task of preventing the intrusion of grinding chips after the wafer is divided, and suppresses the adhesion of grinding chips to the side surface Cd of the wafer C.

As the grinding progresses, the second modified layer M2 will be removed from the workpiece W through grinding. The workpiece W is close to the completed thickness H1. Since the first modified layer M1 still exists, the grinding chips Cd on the side of the wafer adhere. will be suppressed. Furthermore, once the first modified layer M1 is removed from the workpiece W by grinding and the workpiece W reaches the completed thickness H1, the grinding means 21 will rise to the +Z direction, and the grinding stone 212a will move away from the workpiece W. , further, the supply of grinding water will be stopped, and grinding will be completed. The first modified layer M1 and the second modified layer M2 are removed by grinding until the workpiece W reaches the finished thickness H1, so there will be no reduction in the strength of the wafer C caused by the remaining modified layer.

In addition, the processing method of the workpiece of the present invention is not limited to the above-mentioned examples, and the components of the laser processing device 1 and the grinding device 2 shown in the drawings are not limited to these. The present invention can be exerted in any way. Change appropriately within the scope of the effect.

W‧‧‧Processed object Wa‧‧‧Surface of the workpiece Wb‧‧‧The back side of the workpiece S‧‧‧Scheduled dividing line D‧‧‧Functional components T‧‧‧Protective Tape 1‧‧‧Laser processing device 30‧‧‧holding table 300‧‧‧holding surface 6‧‧‧Laser light irradiation method 60‧‧‧Shell 61‧‧‧Laser light oscillator 62‧‧‧Laser head 62a‧‧‧Concentrating lens 64‧‧‧Alignment means 640‧‧‧Infrared Camera M1‧‧‧1st modified layer M2‧‧‧2nd modified layer Mb、Ma‧‧‧Crack 2‧‧‧Grinding device 20‧‧‧Retaining platform 200‧‧‧holding surface 21‧‧‧Grinding methods 210‧‧‧Spindle 211‧‧‧Fixing parts 212‧‧‧Grinding wheel 212b‧‧‧Wheel abutment 212a‧‧‧Grinding grinding stone 23‧‧‧Rotation means Md‧‧‧cutting ditch Me‧‧‧The thin and wide cutting groove of the first modified layer C‧‧‧Chip

FIG. 1 is a perspective view illustrating a state in which laser light of a wavelength that is transparent to a workpiece is irradiated from the back side along a planned division line. Figure 2 is a diagram illustrating that when laser light of a wavelength that is transparent to the workpiece is irradiated from the back side along the line to be divided, cracks will not be formed from the upper and lower sides and the lower end will be located higher than the height corresponding to the completed thickness of the wafer. A cross-sectional view showing the state of the first modified layer slightly on the back side. FIG. 3 is an enlarged cross-sectional view illustrating the first modified layer. 4 is an enlarged illustration of irradiation of laser light with a wavelength that is transparent to the workpiece from the back side of the workpiece along the planned division line, and is formed on the first modified layer formed in the first modified layer forming step. Cross-sectional view of the second modified layer where the modified layer is further to the back side and cracks occur on the upper and lower sides. 5 is a cross-sectional view illustrating a state in which a second modified layer with upper and lower cracks formed is formed on the back side of the first modified layer formed in the first modified layer forming step. FIG. 6 is an illustration of grinding the back surface of a workpiece on which the first modified layer and the second modified layer are formed. The workpiece is formed into a wafer to its completed thickness, and the second modified layer with cracks is used as a starting point. A perspective view of the workpiece divided into individual wafers. FIG. 7 illustrates grinding the back surface of a workpiece on which the first modified layer and the second modified layer are formed. The workpiece is formed into a wafer to its completed thickness, and the second modified layer with cracks is used as a starting point. A cross-sectional view showing a state in which the workpiece is divided into individual wafers. 8 is an enlarged cross-sectional view illustrating the gaps (severing grooves) between the wafers formed by dividing the workpiece by grinding.

212a‧‧‧Grinding grinding stone

C‧‧‧Chip

Cd‧‧‧Side

D‧‧‧Functional components

H1‧‧‧Thickness

T‧‧‧Protective Tape

M1‧‧‧1st modified layer

M2‧‧‧2nd modified layer

Md‧‧‧cutting ditch

Me‧‧‧The thin and wide cutting groove of the first modified layer

W‧‧‧Processed object

Wa‧‧‧Surface of the workpiece

Wb‧‧‧The back side of the workpiece

S‧‧‧Scheduled dividing line

Z1‧‧‧height position

Claims (2)

A method for processing a workpiece in which a workpiece having functional elements formed in each area divided by a plurality of planned division lines formed on a surface in a grid-like manner is divided into individual parts along a planned division line. A method for processing a workpiece of a wafer, characterized by comprising: a first modified layer forming step of irradiating a wavelength that is transparent to the workpiece from the rear side of the workpiece along the planned division line The laser beam forms a first modified layer that does not generate cracks at the top and bottom and whose lower end is located slightly closer to the back side than a height corresponding to the completed thickness of the wafer; the second modified layer formation step starts from this The back side of the workpiece is irradiated with a laser light having a wavelength that is transparent to the workpiece along the planned division line, and the first modified layer formed in the first modified layer forming step is further The formation of cracks on the back side will occur in the upper and lower second modified layers; and the back surface grinding step is to grind the back surface of the workpiece on which the first modified layer and the second modified layer are formed to be processed. The completed thickness of the wafer is formed by the object, and the second modified layer with cracks is used as the starting point to divide the workpiece into individual wafers. In the back grinding step, even if the workpiece is processed using the second modified layer as the starting point, After the starting point is divided into wafers, there is also a first modified layer with a thin and wide cutting groove. The first modified layer prevents grinding water containing grinding chips from penetrating into the side of the wafer, thereby suppressing grinding of the side of the wafer. The attachment of debris. For example, the processing method of the workpiece in claim 1, wherein in the back surface grinding step, cracks are formed in the second modified layer forming step due to the grinding stress generated in the workpiece. The workpiece is broken by the above-mentioned second modified layer above and below.