JP2020038870A - Method of processing wafer - Google Patents

Abstract

To prevent a device from being damaged by cracks generated when trimming a chamfering portion of a wafer.SOLUTION: A method of processing a wafer is provided, the method comprising: a trimming step in which a blade 613 is caused to cut into a chamfering portion Wd from a surface Wa of a wafer W to a depth reaching a finished thickness L1 and is cut along the outer peripheral edge to remove the chamfering portion Wd; and after the performance of the trimming step, a grinding step of grinding the back surface Wb of the wafer to reduce the thickness to the finished thickness L1. Before the performance of the trimming step, the method further comprises a laser processing step in which an annular modified region M is formed extending from the wafer surface Wa to a cutting depth of the blade 613 by irradiating the wafer W with a laser beam of a wavelength having transmissivity along the outer peripheral edge, in an outer peripheral surplus area Wa2 and on the inside of the wafer from a position Y2 where the blade 613 is caused to cut into in the trimming step. Thereby, extension of cracks generated in the trimming step to a device region Wa1 is to be stopped by the annular modified region M.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a wafer processing method for grinding the back surface of a wafer to a finished thickness.

  A so-called sharp edge is formed at the chamfered portion of the outer peripheral edge of the wafer when the back surface of the wafer is ground and thinned, and in order to prevent the possibility of the chip being damaged at the sharp edge, the cutting blade is used before grinding. So-called edge trimming (see, for example, Patent Document 1) for removing a chamfered portion is widely adopted.

JP 2000-173961 A

  However, compared to a cutting blade with a width of about 20 μm used in ordinary dicing, for example, a thick blade with a width of about 1 mm is used in edge trimming. It takes a larger amount than the dicing of the wafer, and chipping or cracking called chipping is likely to occur at the edge of the cutting groove. When the generated crack reaches the device, the device is damaged, which is a problem.

  Therefore, in the processing method for grinding and thinning the back surface of the wafer, there is a problem in that the device is prevented from being damaged by cracks generated when trimming the chamfered portion on the outer peripheral edge of the wafer.

  The present invention for solving the above problems has a device region in which a plurality of devices are formed on the front surface and an outer peripheral surplus region surrounding the device region, and grinds the back surface of a wafer having a chamfer on the outer periphery. A method of processing a wafer to be thinned to a finished thickness by cutting a cutting blade from the surface of the wafer to the chamfered portion to a depth reaching the finished thickness and cutting along a peripheral edge. A trimming step of removing a chamfer portion, and a grinding step of grinding the back surface of the wafer to thin the finished thickness after performing the trimming step, and performing the trimming step before performing the trimming step. A laser beam having a wavelength that is transparent to the wafer inside the wafer in a peripheral surplus area and inside the wafer from a position where the cutting blade is cut in the trimming step. A laser processing step of irradiating along the outer peripheral edge to form an annular modified region from the surface of the wafer to the cutting depth of the cutting blade, wherein cracks generated in the trimming step are formed by the device. This is a method of processing a wafer, in which extension to a region is stopped by the annular modified region.

  According to another aspect of the present invention, there is provided a wafer having a device region in which a plurality of devices are formed on a surface thereof, a peripheral outer surplus region surrounding the device region, and a chamfered portion on the outer periphery. In a bonded wafer stuck on a carrier plate, a wafer processing method of grinding the back surface of the wafer to a thinner thickness, wherein a wafer is cut from the back surface of the wafer to the chamfered portion by a cutting blade. A trimming step of cutting the chamfered portion by cutting along the outer peripheral edge and cutting the chamfered portion, and after performing the trimming step, grinding the back surface of the wafer to finish the finished thickness. Before performing the trimming step, the cutting blade is cut in the outer peripheral surplus area and in the trimming step. A laser beam that irradiates a laser beam having a wavelength that is transmissive to the wafer inside the wafer from the position to be formed along the outer peripheral edge to form an annular modified region from the back surface of the wafer to the front surface of the wafer And a processing step, wherein the annular modified region stops the cracks generated in the trimming step from extending to the device region.

  The method of processing a wafer according to the present invention, before performing the trimming step, a laser having a wavelength that is transparent to the wafer inside the wafer in a peripheral surplus area and at a position inside the wafer where the cutting blade is cut in the trimming step. A laser processing step that irradiates the beam along the outer periphery to form an annular modified area from the wafer surface to the cutting depth of the cutting blade extends cracks generated in the trimming step to the device area It is possible to dampen in the annular reforming region. That is, it is possible to prevent the device from being damaged by cracks generated when trimming the chamfered portion.

  Further, the wafer processing method according to the present invention, after performing the trimming step, grinding step to grind the back surface of the bonded wafer to a thinner thickness, and before performing the trimming step, the outer peripheral excess area At the trimming step, a laser beam having a wavelength that has transparency to the bonded wafer is applied along the outer peripheral edge of the bonded wafer inside the position where the cutting blade is cut in the trimming step, and bonded from the back surface of the bonded wafer. By performing the laser processing step of forming an annular modified region reaching the surface of the bonded wafer, it is possible to prevent the crack generated in the trimming step from extending to the device region by the annular modified region. That is, it is possible to prevent the device from being damaged by cracks generated when trimming the chamfered portion.

It is a perspective view showing an example of a wafer. It is sectional drawing which shows an example of a wafer. FIG. 4 is an explanatory diagram illustrating an example of a laser processing step. It is sectional drawing which expands and shows the state in which the cyclic | annular modified area | region was formed in the wafer. It is a top view showing an example of the wafer in which the annular modification field was formed. FIG. 9 is a cross-sectional view illustrating a state in which a laser beam is irradiated to the wafer a plurality of times while changing the focal point position in the thickness direction of the wafer to form an annular modified region. FIG. 3 is a plan view showing an example of a wafer in which an annular modified region including pores and a deteriorated region is formed. It is sectional drawing explaining the state which trimmed the chamfered part of a wafer. It is sectional drawing explaining the state which grinds the back surface of a wafer and thins it to finish thickness. It is a perspective view which shows an example of a bonded wafer. It is sectional drawing which shows an example of a bonded wafer. It is explanatory drawing explaining an example of the laser processing step performed to a bonded wafer. It is sectional drawing which expands and shows the state in which the modification layer and the crack were formed in the wafer of the bonded wafer. It is sectional drawing which expands and shows the state in which the cyclic | annular modified area | region was formed in the wafer. It is sectional drawing explaining the state which trimmed the chamfer part of a bonded wafer. It is sectional drawing explaining the state which grinds the back surface of the wafer of a bonded wafer and thins it to finish thickness.

(Embodiment 1)
Hereinafter, each step of the wafer processing method according to the present invention (hereinafter, referred to as the wafer processing method of the first embodiment) will be described.

(1-1) Example of Laser Processing Step The wafer W shown in FIGS. 1 and 2 is, for example, a semiconductor wafer having a circular outer shape made of silicon as a base material, and has a device region Wa1 and a device region on its surface Wa. An outer peripheral surplus area Wa2 surrounding Wa1 is provided. The device region Wa1 is partitioned in a lattice shape by a plurality of scheduled lines S that are orthogonally different from each other, and devices D such as ICs are formed in the respective regions partitioned in the lattice shape. The back surface Wb of the wafer W facing downward in FIG. 1 is a surface to be ground later. The outer periphery of the wafer W is chamfered, for example, to form a chamfered portion Wd having a substantially arc-shaped cross section.
The wafer W may be made of gallium arsenide, sapphire, gallium nitride, silicon carbide, or the like in addition to silicon.

  The wafer W is transferred to, for example, the laser processing apparatus 1 shown in FIG. The laser processing apparatus 1 includes at least a holding table 10 that suction-holds a wafer W, and a laser beam irradiation unit 11 that can irradiate the wafer W held on the holding table 10 with a laser beam having a transmissive wavelength. ing.

  The holding table 10 is rotatable around the axis in the Z-axis direction, and is reciprocally movable in the X-axis direction, which is the processing feed direction, and the Y-axis direction, which is the indexing feed direction, by moving means (not shown). The holding table 10 has, for example, a circular outer shape, and is provided with a flat holding surface 10a made of a porous member and holding the wafer W. The holding table 10 can suction-hold the wafer W on the holding surface 10a by transmitting the suction force generated by a suction source (not shown) communicating with the holding surface 10a to the holding surface 10a.

  The laser beam irradiating means 11 is held by the holding table 10 by causing the laser beam oscillated from the laser beam oscillator 119 to enter the condenser lens 111a inside the condenser 111 via the transmission optical system. The laser beam can be focused on the wafer W and irradiated. The height position of the focal point of the laser beam can be adjusted in the Z-axis direction by a focal point position adjusting means (not shown).

  The laser processing apparatus 1 includes an alignment unit 14 that recognizes the coordinate position of the chamfered portion Wd of the wafer W and the coordinate position of the center of the wafer W. The alignment unit 14 includes a light irradiating unit (not shown), an optical system that captures reflected light from the wafer W, and an imaging device that photoelectrically converts a subject image formed by the optical system and outputs image information. 140.

  In the laser processing step, first, as shown in FIG. 3, the wafer W is placed on the holding surface 10a of the holding table 10 with the front surface Wa facing upward, and the wafer W is suction-held by the holding table 10. The center of rotation of the holding table 10 and the center of the wafer W are substantially aligned.

  For example, moving means (not shown) moves the holding table 10 below the alignment means 14 to perform edge alignment. That is, the holding table 10 rotates, and the camera 140 captures images of the outer periphery of the wafer W held at the holding table 10 at a plurality of locations. Then, for example, the coordinates of three points that are separated from each other on the outer peripheral edge are detected, and a more accurate center coordinate of the wafer W on the holding table 10 is obtained by a geometric calculation process based on the coordinates of the three points.

  Then, based on the information of the center coordinates of the wafer W and the information of the size of the wafer W which is recognized in advance, the holding table 10 is moved in the horizontal direction, and is moved to the outer peripheral surplus area Wa2 and a trimming step described later. The holding table 10 is positioned at a predetermined position such that a predetermined position Y1 inside the wafer W is located immediately below the light collector 111 from a position Y2 at which the cutting blade 613 shown in FIG.

Next, the focal point position of the laser beam focused by the condenser lens 111a is set to a predetermined height position inside the wafer W, that is, for example, a depth reaching the finished thickness L1 of the wafer W shown in FIG. It is positioned at a height position Z3 (a cutting depth position of the cutting blade 613) slightly lower than the height position Z2. The finished thickness L1 is a thickness from the height position Z1 on the upper surface of the device D to the height position Z2. Then, a laser beam having a transmissive wavelength is pulse-oscillated at a predetermined repetition frequency from the laser beam oscillator 119 to the wafer W, and the laser beam is focused and irradiated inside the wafer W held by the holding table 10. .
The output of the laser beam is set, for example, to a condition in which cracks occur vertically from the modified layer formed on the wafer W. However, the output is set to a condition in which cracks do not occur vertically from the modified layer by lowering the output. May be done. Also, the setting of the focal point position is not limited to the above example.

  The laser beam before reaching the focal point position has transparency to the wafer W, but the laser beam reaching the focal point position has a very high absorption characteristic locally to the wafer W. Is shown. Therefore, as shown in FIG. 4, the wafer W in the vicinity of the focal point position is modified by absorbing the laser beam so that the modified layer extends in the vertical direction (mainly upward) from the focal point position. It is formed. Further, fine cracks are simultaneously formed in the vertical direction from the modified layer. That is, the modified region M including the modified layer and the crack is formed on the wafer W. The upper end of the formed modified region M reaches the surface Wa of the wafer W.

  While irradiating the laser beam along the outer peripheral edge of the wafer W, the holding table 10 is rotated 360 degrees around the Z-axis at a predetermined rotation speed, so that the inside of the wafer W as shown in FIG. An annular modified region M extending from the outer peripheral surplus region Wa2 of the surface Wa to the cutting depth of the cutting blade 613 is formed. A region outside the two-dot chain line in the outer peripheral surplus region Wa2 of the wafer W shown in FIG. 5 is a region to be trimmed by the cutting blade 613.

  The formation of the annular modified region M is not limited to the above example. For example, when the finished thickness of the wafer W is large (when the cutting depth of the cutting blade 613 is increased) or the like, the holding table 10 is rotated at a predetermined rotation speed while irradiating the laser beam along the outer peripheral edge of the wafer W. The laser beam is irradiated onto the multi-pass wafer W while shifting the focal point position by a predetermined distance upward in the thickness direction of the wafer W (Z-axis direction) every time the wafer W is rotated 360 degrees around the axis in the Z-axis direction. Is also good.

That is, the annular modified region M (the first stage from the −Z direction) including the modified layer Ma and the crack C shown in FIG. 6 formed by rotating the holding table 10 holding the wafer W by one 360 ° rotation. Above the quality region M), a second-stage annular modified region M including the modified layer Ma and the crack C may be further formed. Further, a third-stage modified layer and cracks and a fourth-stage modified layer and cracks (not shown in FIG. 6) are formed up to the surface Wa. In this case, for example, a crack C extending above the first-stage modified layer Ma and a crack C extending below the second-stage modified layer Ma are connected. The cracks C in the other stages are also connected. Then, an annular modified region M is formed inside the wafer W from the outer peripheral surplus region Wa2 of the front surface Wa to the height position Z3 where the cutting depth of the cutting blade 613 is set.
Note that the reformed region M may be formed by connecting the modified layer Ma itself in each step in the thickness direction of the wafer W instead of the crack C in each step, but a path in which the cracks C in each step are less likely to be connected. With the laser beam irradiation, the annular modified region M extending from the outer peripheral surplus region Wa2 of the front surface Wa to the cutting depth of the cutting blade 613 can be formed inside the wafer W, which is efficient.

  Further, in the formation of the annular reformed region M, each time the holding table 10 is rotated by 360 degrees around the axis in the Z-axis direction, the light-condensing point position is shifted upward by a predetermined distance in the thickness direction (Z-axis direction). Instead of irradiating the laser beam with a plurality of passes, a laser beam oscillated from a laser beam oscillator 119 shown in FIG. The light spot is located at a different position in the thickness direction of the wafer W. Then, by rotating the holding table 10 around the axis in the Z-axis direction at a predetermined rotation speed by one 360 °, the inside of the wafer W is simultaneously reformed at a plurality of condensing points, and the surface of the wafer W is An annular modified region M extending from the outer peripheral surplus region Wa2 to the cutting depth of the cutting blade 613 may be formed.

(1-2) Another Example of Laser Processing Step Another example of the laser processing step will be described below.
The edge alignment is performed in the same manner as the example of the laser processing step (1-1) described above, and is performed in the outer peripheral surplus area Wa2 and at a position Y2 at which the cutting blade 613 shown in FIG. The holding table 10 shown in FIG. 3 is positioned such that the predetermined position Y1 inside the wafer W is located immediately below the condenser 111.

For example, a pulse laser may be provided by further disposing a separate lens above or below the condenser lens 111a shown in FIG. 3, or by using the condenser lens 111a shown in FIG. 3 as a condenser lens having, for example, spherical aberration. The focus point of the beam can be positioned so as to extend in the thickness direction of the wafer W.
Then, in a state where the focal point is linearly extended in the thickness direction of the wafer W, a laser beam having a wavelength that is transparent to the wafer W is pulse-oscillated from the laser beam oscillator 119 at a predetermined repetition frequency. The beam is focused on the inside of the wafer W and irradiated.
It is sufficient that the laser beam can be irradiated to the wafer W in a state where the aberration occurs in the optical axis direction. Therefore, a pulse laser beam having a predetermined divergence angle is oscillated from the laser beam oscillator 119 and collected by the condenser lens 111a. You may make it light.

Due to the irradiation of the laser beam, the inside of the wafer W shown in FIG. 7 has pores Mc or cracks (not shown) extending in the thickness direction (Z-axis direction) of the wafer W and the wafers W surrounding the pores Mc or cracks. An altered region Md extending in the thickness direction is formed. That is, from the surface Wa of the wafer W to the cutting depth of the cutting blade 613, a modified region Mg (a so-called shield tunnel) composed of the pore Mc or the crack and the altered region Md is formed on the wafer W.
Then, while irradiating the laser beam along the outer peripheral edge of the wafer W, the holding table 10 is rotated 360 degrees around the axis in the Z-axis direction at a predetermined rotation speed, so that the wafer W as shown in FIG. The modified region Mg is formed in a ring shape inside. In this example, the altered regions Md adjacent to each other are formed so as to partially overlap each other, but the altered regions Md do not have to overlap, and may be processed under the condition that cracks are formed between the altered regions Md. Good.
A region outside the two-dot chain line in the outer peripheral surplus region Wa2 of the wafer W shown in FIG. 7 is a region to be trimmed by the cutting blade 613.

(2) Trimming Step Hereinafter, a trimming step for the wafer W on which the modified regions M shown in FIGS. Note that even if the wafer W is the wafer W on which the modified region Mg shown in FIG. 7 is formed, the trimming step is performed in the same manner as the procedure described below.
The wafer W on which the modified region M has been formed is transferred to the holding table 65 of the cutting device 6 shown in FIG. 8, and is suction-held on the holding surface 65a of the holding table 65 with the front surface Wa facing upward. The holding table 65 is rotatable around the axis in the Z-axis direction and is reciprocally movable in the X-axis direction.
The cutting means 61 for trimming the wafer W included in the cutting device 6 includes a spindle 610 whose axis is in the Y-axis direction, a motor (not shown) for rotating the spindle 610, and a cutting blade 613 mounted on the tip of the spindle 610. The cutting blade 613 rotates as the motor drives the spindle 610 to rotate.
The cutting blade 613 is a cutting blade for edge trimming having a larger blade thickness (for example, a blade thickness of 1 mm) than a normal cutting blade for dicing.

  In the trimming step, for example, information on the coordinate position of the center of the wafer W and the coordinate position of the outer peripheral edge on the holding table 65 is recognized by an alignment unit (not shown) (edge alignment is performed). Then, the cutting means 61 is moved in the Y-axis direction based on the information, and positions the cutting blade 613 at a position Y2 radially inward from the outer peripheral edge in the outer peripheral surplus area Wa2 by a predetermined distance. That is, for example, the cutting blade 613 is positioned such that about ／ of the lower end surface of the cutting blade 613 contacts the outer peripheral surplus area Wa2 of the wafer W including the chamfered portion Wd of the wafer W.

  Next, a motor (not shown) rotates the spindle 610 counterclockwise as viewed from the + Y direction, thereby rotating the cutting blade 613 fixed to the spindle 610 in the same direction at a high speed. Further, the cutting means is arranged such that the lowermost end of the cutting blade 613 is located at a height position Z3 (a height position slightly lower than the height position Z2), which is a depth from the surface Wa of the wafer W to the finished thickness L1. 61 is sent in the -Z direction. The cutting means 61 may be lowered until the lowermost end of the cutting blade 613 reaches the height position Z2.

  Then, after the rotating cutting blade 613 is cut from the surface Wa of the wafer W to the chamfered portion Wd to a depth that reaches the finished thickness L1, the holding table 65 is moved in the + Z direction while the cutting blade 613 is continuously rotated at a high speed. When rotated 360 degrees in the counterclockwise direction as viewed from above, cutting (downcut trimming) is performed along the outer peripheral edge of the wafer W, and the chamfered portion Wd of the entire circumference of the wafer W is removed.

  Cracks generated on the outer peripheral edge of the wafer W by the trimming of the chamfered portion Wd by the cutting blade 613 are blocked by the annular modified region M extending from the outer peripheral surplus region Wa2 of the surface Wa to the cutting depth of the cutting blade 613, This prevents the device D from being damaged.

(3) Grinding Step Next, the surface protection tape T shown in FIG. 9 having substantially the same diameter as that of the wafer W is attached to the surface Wa by a roller or the like that rolls on a tape mounter (not shown) to protect the surface Wa. It will be in the state that was done.

The wafer W to which the surface protection tape T is adhered is transported to the chuck table 75 of the grinding device 7 shown in FIG. 9 and is suction-held on the holding surface 75a of the chuck table 75 with the back surface Wb facing upward.
A grinding unit 71 for grinding a wafer W of the grinding apparatus 7 shown in FIG. 9 includes a rotating shaft 710 whose axis is in the Z-axis direction, a disk-shaped mount 713 connected to the lower end of the rotating shaft 710, and a mount 713. And a grinding wheel 714 removably connected to the lower surface of the grinding wheel. The grinding wheel 714 includes a wheel base 714b, and a plurality of substantially rectangular parallelepiped grinding wheels 714a disposed annularly on the bottom surface of the wheel base 714b.

First, the chuck table 75 moves in the + Y direction, the center of rotation of the grinding wheel 714a is shifted in the horizontal direction by a predetermined distance from the center of rotation of the wafer W, and the rotation locus of the grinding wheel 714a passes through the center of rotation of the wafer W. Thus, the chuck table 75 is positioned. Next, as the rotating shaft 710 rotates, the grinding wheel 714 rotates around the axis in the Z-axis direction. Further, the grinding means 71 is sent in the −Z direction, and the grinding process is performed by the grinding wheel 714 a contacting the back surface Wb of the wafer W. During the grinding, the wafer W also rotates as the chuck table 75 rotates, so that the grinding wheel 714a performs the grinding of the entire back surface Wb of the wafer W. In addition, grinding water is supplied to a contact point between the grinding wheel 714a and the back surface Wb of the wafer W, and the contact point is cooled by the grinding water and the grinding debris is washed and removed.
Then, after grinding the wafer W to the finished thickness L1, the grinding means 71 is moved in the + Z direction and separated from the wafer W. Even if the modified region M remains on the wafer W after the grinding, no problem occurs because the position where the modified region M is formed is the outer peripheral surplus region Wa2.

(Embodiment 2)
Hereinafter, each step of the wafer processing method according to the present invention (hereinafter, referred to as a wafer processing method of Embodiment 2) will be described.

(1) Laser Processing Step The wafer W shown in FIGS. 10 and 11 is the same as the wafer described in the first embodiment. As shown in FIGS. 10 and 11, the wafer W is bonded on a carrier plate WP with an adhesive member J such as resin (not shown in FIG. 10) so as to be easily transported and held in each step of the wafer processing method of the second embodiment. , Ie, the bonded wafer WT. The centers of the wafer W and the carrier plate WP are substantially aligned.

The carrier plate WP shown in FIGS. 10 and 11 has, for example, a high rigidity and flat circular outer shape using silicon as a base material. In the illustrated example, the circular carrier plate WP has a diameter substantially the same as the diameter of the wafer W. However, the diameter may be larger than the diameter of the wafer W, or sapphire, glass, or the like may be used as a base material. May be used.
In FIG. 10, the constituent material of the bonding member J bonding the surface Wa of the wafer W facing downward and the surface WPa facing upward of the carrier plate WP is, for example, UV that cures when irradiated with ultraviolet light. A curable resin or a heat-curable resin that cures when heated is used.

  The bonded wafer WT is transferred to, for example, the laser processing apparatus 1 illustrated in FIG. 12 described in the first embodiment. Then, the bonded wafer WT is placed on the holding surface 10 a of the holding table 10 with the back surface Wb of the wafer W facing upward, and is suction-held by the holding table 10. The center of rotation of the holding table 10 and the center of the bonded wafer WT are substantially aligned.

  Edge alignment is performed by the alignment means 14, and the accurate center coordinates of the wafer W on the holding table 10 are obtained. Then, based on the information of the center coordinates of the wafer W and the information of the size of the wafer W which is recognized in advance, the holding table 10 is moved in the horizontal direction, and is moved to the outer peripheral surplus area Wa2 and a trimming step described later. The holding table 10 is positioned at a predetermined position such that a predetermined position Y4 inside the wafer W is located immediately below the light collector 111 than a position Y5 at which the cutting blade 613 shown in FIG.

Next, the focal point position of the laser beam condensed by the condenser lens 111a is set to, for example, a height position slightly lower than the height position Z4 which is a depth reaching the finished thickness L4 of the wafer W shown in FIG. Position. The finished thickness L4 is a thickness from the height position Z5 on the upper surface of the device D to the height position Z4. Then, a laser beam having a wavelength having transparency to the inside of the wafer W is pulse-oscillated from the laser beam oscillator 119 at a predetermined repetition frequency, and the laser beam is focused and irradiated inside the wafer W.
The setting of the focal point position is not limited to the above example.

  As shown in FIG. 13, the modified layer Ma is formed so as to extend in the vertical direction (mainly upward) from the position of the condensing point. Further, fine cracks C are simultaneously formed in the vertical direction from the modified layer Ma. By rotating the holding table 10 by 360 degrees around the axis in the Z-axis direction at a predetermined rotation speed while irradiating the laser beam along the outer peripheral edge of the wafer W, the plurality of modified layers Ma inside the wafer W A crack C extending vertically from the modified layer Ma is formed in an annular shape along the outer peripheral edge of the wafer W. The annular reformed region M including the reformed layer Ma and the crack C is defined as a first-stage reformed region M.

  Further, each time the holding table 10 is rotated 360 degrees around the axis in the Z-axis direction at a predetermined rotation speed, the laser beam is shifted upward by a predetermined distance in the thickness direction of the wafer W (Z-axis direction). By irradiating the beam to the multi-pass wafer W, the annular modified region M including the second-stage modified layer Ma and the crack C shown in FIG. An annular modified region M is formed, and an annular modified region M including a fourth-stage modified layer Ma and a crack C is formed. As a result, the annular modified region M including the four-stage modified layer Ma and the crack C forms an annular modified region M extending from the back surface Wb to the front surface Wa along the outer peripheral edge of the wafer W. Note that, in the annular modified region M extending from the back surface Wb to the front surface Wa, the modified layer Ma of each stage may be connected instead of the crack C, or the modified layer Ma may be attached to the front surface Wa or the back surface Wb of the wafer W. It may be exposed. Alternatively, the modified layer Ma and the cracks C may be formed one step at a time from the back surface Wb side of the wafer W downward to form an annular modified region M from the back surface Wb to the front surface Wa.

The laser processing step is not limited to the above example. For example, the laser beam oscillated from the laser beam oscillator 119 shown in FIG. 12 is branched into laser beams on a plurality of optical paths, and the focal points of the laser beams on each optical path are located at different positions in the thickness direction of the wafer W. Then, the inside of the wafer W is simultaneously reformed at a plurality of focal points by rotating the holding table 10 at a predetermined rotation speed around the axis in the Z-axis direction by 360 degrees, and the inside of the wafer W is An annular modified region M extending from Wb to the surface Wa may be formed.
Alternatively, an annular modified region Mg called a shield tunnel composed of the pore Mc or the crack and the altered region Md described in another example of the (1-2) laser processing step in the first embodiment is provided inside the wafer W on the back surface. It may be formed to extend from Wb to the surface Wa.

(2) Trimming Step The bonded wafer WT in which the modified region M is formed on the wafer W is transported to the holding table 65 of the cutting device 6 shown in FIG. Is held by suction on the holding surface 65a. In the trimming step, for example, information on the coordinate position of the center of the wafer W and the coordinate position of the outer peripheral edge on the holding table 65 is recognized by an alignment unit (not shown). Then, the cutting means 61 is moved in the Y-axis direction based on the information, and the cutting blade 613 is positioned at a position Y5 radially inward from the outer peripheral edge of the wafer W in the outer peripheral surplus area Wa2 by a predetermined distance. That is, for example, the cutting blade 613 is positioned such that about ／ of the end surface of the cutting blade 613 contacts the back surface Wb of the wafer W including the chamfered portion Wd of the wafer W.

  Next, the cutting blade 613 is rotated, for example, clockwise as viewed from the + Y direction side. Further, the cutting is performed such that the lowermost end of the cutting blade 613 is located at a height position (a position slightly lower than the height position of the outer peripheral surplus region Wa2) where the lower end of the wafer W reaches the finished thickness L4 from the back surface Wb. The means 61 is sent in the -Z direction. Then, after the rotating cutting blade 613 is cut from the back surface Wb of the wafer W to the chamfered portion Wd to a depth reaching the finished thickness L4, the holding table 65 is kept rotating at a high speed, and the holding table 65 is moved in the + Z direction. When rotated 360 degrees in the counterclockwise direction as viewed from above, cutting (upcut trimming) is performed along the outer peripheral edge of the wafer W, and the chamfered portion Wd of the entire circumference of the wafer W is removed. The reason for performing the trimming by the up-cut is that in the trimming by the down-cut, generated cutting chips may scatter to the carrier plate WP and damage the carrier plate WP.

  Cracks generated on the outer peripheral edge of the wafer W by the trimming of the chamfered portion Wd by the cutting blade 613 are stopped by the annular modified region M from the back surface Wb of the wafer W to the front surface Wa of the wafer W, so that the device D is damaged. Is prevented.

(3) Grinding Step The bonded wafer WT subjected to the edge trimming is transferred to the chuck table 75 of the grinding device 7 shown in FIG. 16, and is suction-held on the holding surface 75a of the chuck table 75 with the back surface Wb facing upward. Is done.

The chuck table 75 is positioned such that the chuck table 75 moves in the + Y direction and the rotation locus of the grinding wheel 714a passes through the center of rotation of the wafer W. Next, the grinding wheel 714 rotates around the axis in the Z-axis direction. Further, the grinding means 71 is sent in the −Z direction, and the grinding process is performed by the grinding wheel 714 a contacting the back surface Wb of the wafer W. During the grinding, the chuck table 75 rotates and the bonded wafer WT also rotates, so that the grinding wheel 714a performs the entire surface grinding of the back surface Wb of the wafer W. Further, grinding water is supplied to a contact point between the grinding wheel 714a and the back surface Wb of the wafer W, and cooling and cleaning removal of grinding dust are performed.
Then, after grinding the wafer W to the finished thickness L4, the grinding means 71 is moved in the + Z direction and separated from the wafer W. Even if the modified region M remains on the wafer W after the grinding, no problem occurs because the position where the modified region M is formed is the outer peripheral surplus region Wa2.

  The wafer processing method according to the present invention is not limited to the first and second embodiments described above, and it goes without saying that the method may be implemented in various forms within the scope of the technical idea. Further, the respective configurations of the laser processing device 1, the cutting device 6, and the grinding device 7 illustrated in the accompanying drawings are not limited thereto, and can be appropriately changed as long as the effects of the present invention can be exhibited.

W: Wafer Wa: Wafer surface Wa1: Device region Wa2: Outer peripheral surplus region Wb: Wafer back surface Wd: Chamfering unit 1: Laser processing device 10: Holding table 10a: Holding surface 11: Laser beam irradiation unit 111: Condenser 111a: condenser lens 119: laser beam oscillator 14: alignment means 140: camera M: modified area Ma: modified layer C: crack Mg: modified area Mc: pore Md: altered area 6: cutting device 65: holding Table 65a: Holding surface 61: Cutting means 610: Spindle 613: Cutting blade T: Surface protection tape 7: Grinding device 75: Chuck table 75a: Holding surface 71: Grinding means 710: Rotating shaft 713: Mount 714: Grinding wheel WP: Carrier plate J: Adhesive member WT: Bonded wafer

Claims (2)

Wafer processing that has a device region in which a plurality of devices are formed on the front surface and an outer peripheral surplus region surrounding the device region, and grinds the back surface of the wafer having a chamfered portion on the outer periphery to thin the wafer to a finished thickness. The method
A trimming step of cutting a cutting blade from the surface of the wafer to the chamfered portion to a depth to the finished thickness and cutting along the outer peripheral edge to remove the chamfered portion;
After performing the trimming step, grinding the back surface of the wafer to thin the finish thickness, comprising:
Prior to performing the trimming step, a laser beam having a wavelength that is transparent to the wafer inside the wafer in the outer peripheral surplus area and at a position inside the wafer where the cutting blade is cut in the trimming step is applied to the outer peripheral edge. A laser processing step of irradiating the wafer along the surface to form an annular modified region from the surface of the wafer to the cutting depth of the cutting blade,
A wafer processing method, wherein a crack generated in the trimming step is prevented from extending to the device region by the annular modified region. A bonded wafer in which a plurality of devices are formed on the surface and an outer peripheral surplus region surrounding the device region, and the surface of a wafer having a chamfer on the outer surface is bonded on a carrier plate. A method of processing a wafer in which the back surface of the wafer is ground to be thinned to a finished thickness,
A trimming step of cutting the cutting blade from the back surface of the wafer to the chamfered portion to a depth reaching the front surface of the wafer and cutting along the outer peripheral edge to remove the chamfered portion,
After performing the trimming step, a grinding step of grinding the back surface of the wafer to thin the finished thickness,
Prior to performing the trimming step, a laser beam having a wavelength that is transparent to the wafer inside the wafer in the outer peripheral surplus area and at a position inside the wafer where the cutting blade is cut in the trimming step is applied to the outer peripheral edge. Laser processing step of irradiating along to form an annular modified region from the back surface of the wafer to the front surface of the wafer,
A wafer processing method, wherein a crack generated in the trimming step is prevented from extending to the device region by the annular modified region.