JP2020009864A - Grinding method of workpiece - Google Patents

Abstract

To provide a grinding method of workpiece capable of restraining elongation of crack toward the center of a workpiece while grinding.SOLUTION: A grinding method of workpiece includes a trimming step ST1 of forming a flat surface on which laser light can impinge, by cutting the outer peripheral end of a workpiece by means of a cutting blade while turning a chuck table holding the workpiece in such a state as the cutting blade is cutting in the outer peripheral end by a prescribed thickness from the back side of the workpiece, a modified layer formation step ST2 for forming an annular modified layer along the outer peripheral edge in the workpiece, by irradiating the flat surface of the workpiece formed in the trimming step ST1 with laser light of such a wavelength as having transparency to the workpiece from the back side of the workpiece, and a grinding step ST3 of forming the workpiece with a prescribed finish thickness, by grinding the workpiece from the back side after execution of the modified layer formation step ST2.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for grinding a workpiece.

  When a hard-to-cut workpiece such as a sapphire wafer is ground, the workpiece may crack from the outer periphery. In order to solve this kind of problem, a processing method is used in which edge trimming is performed from the front side of the workpiece and then the workpiece is ground from the back side.

  However, the above-mentioned processing method has a problem in that when chipping occurs on the device surface during edge trimming and grinding is performed, cracks extending toward the center from the chipping generated during edge trimming are formed on the workpiece. Was. In addition, the above-mentioned processing method involves performing edge trimming from the front surface side and then grinding the workpiece from the back surface side, so that a man-hour for attaching a protective tape or the like to the front surface side of the workpiece after edge trimming is used. There was a problem that required.

  Therefore, in order to solve the above-described problem, the applicant of the present invention has proposed a wavelength having a transmittance to the workpiece from one surface of the workpiece along the outer peripheral edge of the workpiece before grinding. A processing method of irradiating a laser beam or the like to form an annular modified layer or the like inside a workpiece and removing an outer peripheral end of the workpiece has been proposed (for example, see Patent Document 1). The modified layer or the like formed by the processing method disclosed in Patent Literature 1 stops cracks generated from the outer periphery during grinding by the modified layer, and suppresses progression toward the center side from the modified layer.

JP 2006-108532 A

  In the processing method disclosed in Patent Literature 1, an object to be processed is a GaN (Gallium Nitride: gallium nitride) which becomes a light emitting element such as an LED (Light Emitting Diode) grown on a sapphire wafer. In the case of a wafer on which a metal pattern is formed, even if a workpiece is irradiated with a laser beam having a wavelength having transparency, ablation occurs on the front surface. However, in the case of the above-described wafer, the back surface is often a matte surface with irregularities, and in the case of the matte surface, a laser beam is scattered, so that a modified layer is stably formed from the back surface. Is difficult.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a method of grinding a workpiece which can suppress a crack from extending toward the center of the workpiece during grinding. That is.

  In order to solve the above-mentioned problems and achieve the object, a method for grinding a workpiece according to the present invention is a method for grinding a workpiece, wherein the workpiece is cut from a rear surface side to an outer peripheral end portion. A trimming step of cutting the outer peripheral end of the workpiece with a cutting blade while rotating the chuck table holding the workpiece with the blade cut into a predetermined thickness, and forming a flat surface through which a laser beam can be incident; and The flat surface formed in the trimming step from the back side of the workpiece is irradiated with a laser beam having a wavelength that is transparent to the workpiece, and a circular ring is formed inside the workpiece along the outer peripheral edge. A modified layer forming step of forming a modified layer, and a grinding step of grinding the workpiece from the back side to form a predetermined finished thickness after performing the modified layer forming step. And

  In the method for grinding a workpiece, the modified layer may be formed on a back surface side of the finished thickness.

  The present invention has an effect that a crack can be suppressed from extending toward the center of a workpiece during grinding.

FIG. 1 is a perspective view of a workpiece to be processed by the workpiece grinding method according to the first embodiment. FIG. 2 is a side view of a main part of the workpiece shown in FIG. FIG. 3 is a flowchart illustrating a flow of the method of grinding a workpiece according to the first embodiment. FIG. 4 is a side view partially showing a trimming step of the method of grinding a workpiece shown in FIG. FIG. 5 is a side view partially showing a modified layer forming step of the method for grinding a workpiece shown in FIG. FIG. 6 is a side view partially showing a grinding step of the method of grinding a workpiece shown in FIG.

  An embodiment (embodiment) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. The components described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Further, the configurations described below can be appropriately combined. Further, various omissions, substitutions, or changes in the configuration can be made without departing from the spirit of the present invention.

[Embodiment 1]
A method for grinding a workpiece according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a workpiece to be processed by the workpiece grinding method according to the first embodiment. FIG. 2 is a side view of a main part of the workpiece shown in FIG. FIG. 3 is a flowchart illustrating a flow of the method of grinding a workpiece according to the first embodiment.

  The method for grinding the workpiece according to the first embodiment is the method for grinding the workpiece 1 shown in FIG. A workpiece 1 shown in FIG. 1 which is a processing target of the workpiece grinding method according to the first embodiment is a disc-shaped optical device wafer having sapphire as a substrate 2. In the first embodiment, the workpiece 1 has a film 4 formed on a front surface 3 of a substrate 2 and a back surface 5 of the substrate 2 formed on a matte surface. In the first embodiment, the film 4 is a film epitaxially grown on the surface 3 of the substrate 2 and is made of, for example, GaN (Gallium Nitride: gallium nitride) that becomes a light emitting element such as an LED (Light Emitting Diode). . Further, in the present invention, the film 4 causes ablation on the surface of the film 4 even when the substrate 2 is irradiated with a laser beam 22 (shown in FIG. 5) having a wavelength having transparency.

  In the present invention, the modified layer 9 (shown in FIG. 5) is formed inside the substrate 2 by scattering the laser beam 22 even when the substrate 2 is irradiated with the laser beam 22 having a wavelength having transparency. This is a surface on which fine irregularities are formed on the back surface 5 to such an extent that it is difficult to perform the process. That is, the surface roughness of the matte surface is a value that makes it difficult to scatter the laser beam 22 and form the modified layer 9 inside the substrate 2 even when the substrate 2 irradiates the laser beam 22 having a wavelength having transparency. It is.

  In the first embodiment, the workpiece 1 is an optical device wafer using sapphire as the substrate 2. In the present invention, a disc-shaped semiconductor wafer or silicon carbide (SiC) using silicon as the substrate 2 is used. A wafer such as an optical device wafer serving as the substrate 2 may be used. Further, in the present invention, the workpiece 1 may be a wafer in which devices are formed in a plurality of regions divided into grid-like planned dividing lines on the surface 3 of the substrate 2. A metal pattern made of a metal such as TEG (Test Element Group) may be formed on the line. In the present invention, the metal pattern causes ablation on the surface of the metal pattern even when the substrate 2 is irradiated with the laser beam 22 having a wavelength having transparency.

  In short, the workpiece 1 referred to in the present invention is such that the substrate 2 has a film 4 or a metal pattern or the like that causes ablation of the transparent laser beam 22 on the surface 3 of the substrate 2, and the substrate 2 has a transparent laser beam. A pear surface that scatters 22 is formed on the back surface 5 of the substrate 2. Further, as shown in FIG. 2, the workpiece 1 has a chamfered portion 7 having an arc-shaped cross section from the front surface 3 to the back surface 5 at the outer peripheral end 6.

  The method of grinding a workpiece according to the first embodiment is a method of thinning the workpiece 1 to a finished thickness of 100. As shown in FIG. 3, the method of grinding a workpiece includes a trimming step ST1, a modified layer forming step ST2, and a grinding step ST3.

(Trimming step)
FIG. 4 is a side view partially showing a trimming step of the method of grinding a workpiece shown in FIG. The trimming step ST1 is a chuck that holds the workpiece 1 in a state where the cutting blade 12 of the cutting device 10 shown in FIG. In this step, the outer peripheral end 6 of the workpiece 1 is cut by the cutting blade 12 while rotating the table 11 about the axis, thereby forming the flat surface 8 on which the laser beam 22 can be incident.

  In the trimming step ST1, the cutting device 10 suction-holds the front surface 3 of the workpiece 1 on the holding surface 13 of the chuck table 11. In the first embodiment, the surface protection tape 200 is attached to the film 4 on the front surface 3 side of the workpiece 1, and the cutting device 10 suctions the workpiece 1 to the holding surface 13 via the surface protection tape 200. Hold.

  In the trimming step ST1, as shown in FIG. 4, the cutting apparatus 10 rotates the chuck table 11 around an axis parallel to the vertical direction while rotating the cutting blade 12 by the spindle 15 of the cutting unit 14 to form the workpiece. A flat surface 8 is formed by cutting the chamfered portion 7 of the outer peripheral end portion 6 from the front surface 3 side by a predetermined thickness 101. The flat surface 8 is formed by cutting the cutting blade 12 rotated by the spindle 15 of the cutting unit 14 into the outer peripheral end 6, so that the laser beam 22 is focused inside the workpiece 1 without scattering. It is formed to a degree of surface roughness. The method of grinding the workpiece proceeds to the modified layer forming step ST2 after the trimming step ST1.

(Modified layer forming step)
FIG. 5 is a side view partially showing a modified layer forming step of the method for grinding a workpiece shown in FIG. The modified layer forming step ST2 irradiates the flat surface 8 formed in the trimming step ST1 from the back surface 5 side of the workpiece 1 with a laser beam 22 having a wavelength that is transparent to the workpiece 1, This is a step of forming an annular modified layer 9 inside the object 1 along the outer peripheral edge at a position inside the outer peripheral edge by a predetermined amount.

  The modified layer 9 refers to a region in which the density, refractive index, mechanical strength, and other physical properties are different from those of the surrounding base material. For example, the modified layer 9 includes a melt processing region, a crack region, and a dielectric breakdown region. , A refractive index change region, and a region in which these regions are mixed. In the first embodiment, the mechanical strength of the modified layer 9 is lower than the surrounding mechanical strength.

  In the modified layer forming step ST2, the laser processing device 20 suction-holds the front surface 3 side of the workpiece 1 on the holding surface 23 of the chuck table 21. In the first embodiment, the laser processing device 20 suction-holds the workpiece 1 on the holding surface 23 via the surface protection tape 200.

  In the modified layer forming step ST2, the laser processing apparatus 20 causes the laser beam irradiation unit 24 for irradiating the laser beam 22 to face the flat surface 8 in the vertical direction as shown in FIG. A point is set inside the workpiece 1, and the workpiece 1 is irradiated with the laser beam 22 from the laser beam irradiation unit 24 while rotating the chuck table 21 about an axis parallel to the vertical direction. In the modified layer forming step ST2, the laser processing apparatus 20 forms the modified layer 9 over the entire circumference on the surface 3 side of the flat surface 8 inside the workpiece 1. In the first embodiment, in the modified layer forming step ST2, the laser processing device 20 sets the focal point of the laser beam 22 from the film 4 closer to the back surface 5 than the finished thickness 100, and the modified layer 9 The film 20 is formed on the back surface 5 side of the film 4 from the finished thickness 100. The method of grinding the workpiece proceeds to the grinding step ST3 after the modified layer forming step ST2.

(Grinding step)
FIG. 6 is a side view partially showing a grinding step of the method of grinding a workpiece shown in FIG. The grinding step ST3 is a step of grinding the workpiece 1 from the back surface 5 side to form a predetermined finished thickness 100 after the modified layer forming step ST2 is performed.

  In the grinding step ST3, as shown in FIG. 6, the grinding device 30 suction-holds the front surface 3 of the workpiece 1 on the holding surface 33 of the chuck table 31 via the surface protection tape 200, and moves the chuck table 31 to the axial center. The back surface 5 is ground by rotating the grinding wheel 34 of the grinding unit 32 around the axis while rotating the grinding unit 32 around the axis to make contact with the back surface 5 of the workpiece 1. In the grinding step ST3, the grinding device 30 grinds and thins the workpiece 1 to a finished thickness of 100.

  In the grinding step ST3, since the modified layer 9 is formed inside the outer peripheral end portion 6 of the workpiece 1, the workpiece 1 has a crack extending from the modified layer 9 toward the front surface 3 and the back surface 5. 9-1 is formed and broken at the modified layer 9 and the crack 9-1. For this reason, in the grinding step ST3, the crack generated at the outer edge of the workpiece 1 extends toward the center of the workpiece 1 and reaches the modified layer 9 and the crack 9-1. Since the fracture is caused by the modified layer 9 and the crack 9-1, the extension to the center side of the workpiece 1 beyond the modified layer 9 and the crack 9-1 is suppressed. In the grinding step ST3, the work piece 1 has the modified layer 9 formed on the back surface 5 side from the film 4 to the finished thickness 100 more than the finished thickness 100. Will be removed. The method of grinding the workpiece ends when the workpiece 1 is thinned to a finished thickness of 100.

  In the method of grinding a workpiece according to the first embodiment, a trimming step ST1 of cutting the outer peripheral end portion 6 from the back surface 5 side to form a flat surface 8 is performed, and the flat surface has a surface roughness that does not scatter the laser beam 22. 8 is formed. For this reason, the grinding method of the workpiece can form the modified layer 9 inside the workpiece 1 even when the laser beam 22 is irradiated on the back surface 5 side, which is the matte surface, and the grinding step ST3 It is possible to suppress the crack generated at the outer edge of the workpiece 1 from extending toward the center beyond the modified layer 9 and the crack 9-1. As a result, the method of grinding the workpiece can suppress the crack from extending toward the center of the workpiece 1 during grinding.

  In the method of grinding the workpiece, the modified layer 9 is formed on the back surface 5 side of the film 4 from the finish thickness 100, so that the modified layer 9 can be removed in the grinding step ST3. As a result, the method of grinding a workpiece can suppress a reduction in bending strength of a device chip obtained by dividing the workpiece 1.

  Further, in the processing method of the workpiece, the outer peripheral edge 6 is cut from the back surface 5 side in the trimming step ST1 to form the flat surface 8, and the laser beam 22 is irradiated from the back surface 5 side in the modified layer forming step ST2. In the grinding step ST3, the workpiece 1 is ground from the back surface 5 side. For this reason, in the method of processing the workpiece, it is not necessary to peel off the surface protection tape 200 adhered to the front surface 3 side before the trimming step ST1 and replace it with another tape or the like. As a result, the method for processing the workpiece can suppress an increase in required man-hours for processing.

  Note that the present invention is not limited to the above embodiment. That is, various modifications can be made without departing from the gist of the present invention. In the first embodiment, the cutting device 10, the laser processing device 20, and the grinding device 30 are suction-held on the holding surfaces 13, 23, and 33 of the chuck tables 11, 21, and 31 via the surface protection tape 200. However, in the present invention, the cutting device 10, the laser processing device 20, and the grinding device 30 are configured to separate the holding surface 13, 23, 33 from the surface 3 of the workpiece 1, on which the surface protection tape 200 is not adhered. The workpiece 1 may be suction-held on the holding surfaces 13, 23, 33 of the chuck tables 11, 21, 31 through a porous sheet (not shown).

DESCRIPTION OF SYMBOLS 1 Workpiece 5 Back surface 6 Outer edge 8 Flat surface 9 Modified layer 11 Chuck table 12 Cutting blade 22 Laser beam 100 Finished thickness ST1 Trimming step ST2 Modified layer forming step ST3 Grinding step

Claims (2)

A grinding method for a workpiece,
Cutting the outer peripheral edge of the workpiece with the cutting blade while rotating the chuck table holding the workpiece in a state where the cutting blade is cut into the outer peripheral edge by a predetermined thickness from the back side of the workpiece. A trimming step of forming a flat surface through which a laser beam can be incident;
The flat surface formed in the trimming step is irradiated from the back side of the workpiece with a laser beam having a wavelength having transparency to the workpiece, and a circular ring is formed inside the workpiece along an outer peripheral edge. A modified layer forming step of forming a modified layer of
After performing the modified layer forming step, a grinding step of grinding the workpiece from the back side to form a predetermined finished thickness,
A method of grinding a workpiece.   The method for grinding a workpiece according to claim 1, wherein the modified layer is formed on a back surface side of the finished thickness.

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