Method of wafer generation

Abstract

The present application provides a wafer production method that reduces the likelihood of defects occurring in the peripheral region of a wafer in subsequent processes. A laser beam is irradiated on the central region of the workpiece excluding the peripheral region, which is the region from the outer edge of the workpiece to the inside of a prescribed distance, to form a separation layer. In this case, a separation layer is not formed in the peripheral region of the workpiece by the irradiation of the laser beam, and the formation of an ablation mark on the peripheral surface of the workpiece is prevented. As a result, the likelihood of defects occurring in the peripheral region of the wafer separated from the workpiece in subsequent processes is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to a wafer production method. BACKGROUND

[0002] A chip of a semiconductor device is generally produced using a wafer in a disc shape. The wafer is produced, for example, by cutting from a cylindrical semiconductor ingot using a wire saw and then polishing a front surface to finish it into a mirror surface (see, for example, Patent Literature 1).

[0003] Specifically, when a wafer is cut from an ingot using a wire saw, fine irregularities are formed on the front surface of the wafer, and the wafer as a whole is bent (warping occurs on the wafer). Therefore, for the wafer thus cut, in order to remove the irregularities, the front surface is polished.

[0004] However, when the wafer is polished, a part of the wafer on the polished surface side becomes a polishing slurry and is discarded, and the wafer is thinned. Based on this point, the wafer is generally cut from the ingot in a manner thicker than the wafer used in the production of a semiconductor device.

[0005] The ingot used in the production of a chip of a semiconductor device is expensive. Therefore, when a wafer is produced by a method requiring polishing, the production cost of a chip of a semiconductor device produced using the wafer also easily increases.

[0006] In addition, monocrystal SiC (silicon carbide), which is expected as a material for power devices, is high in hardness. Therefore, in the case where a wafer is cut from a monocrystal SiC ingot using a wire saw, the required time easily becomes long, and the wire saw easily wears.

[0007] As a result, the production cost of a monocrystal SiC wafer easily increases. In view of this, a method of peeling a wafer from an ingot using a laser beam without using a wire saw has been developed (see, for example, Patent Literature 2).

[0008] In this method, a laser beam of a wavelength that transmits through the ingot is irradiated to the ingot with a focal point of the laser beam positioned inside the ingot. Thereby, a peeling layer including a modified layer and a crack extending from the modified layer is formed inside the ingot. And the ingot is separated along the peeling layer, thereby peeling a wafer from the ingot.

[0009] Patent Literature 1: Japanese Patent Application Publication No. 2000-94221

[0010] Patent Literature 2: Japanese Patent Application Publication No. 2016-111143

[0011] In the above method, a chuck table holding the ingot is moved linearly in a manner that one end to the other end of the ingot passes right below the condenser (laser head), while the laser beam is irradiated by the laser beam irradiation unit toward right below the condenser.

[0012] Here, when the laser beam is irradiated near one end and near the other end (the outer peripheral region) of the ingot, the power at the focal point of the laser beam is sometimes unstable. This case will be described below with reference to Figure 10 (A) to Figure 10 (E) of FIG. 10. Also, Figure 10 (A) to Figure 10 (E) of FIG. 10 are diagrams showing a case where the laser beam 3 is irradiated near one end of the ingot 1 while moving the chuck table that holds the ingot 1.

[0013] When the laser beam 3 is irradiated near one end of the ingot 1, as shown in (A) of FIG. 11, the focal point of the laser beam 3 is positioned at a height corresponding to the inside of the ingot 1 in a state where the optical axis 5 of the laser beam 3 is sufficiently separated toward the outside with respect to the outer peripheral surface of the ingot 1. Figure 10

[0014] When the chuck table is moved so that the optical axis 5 is located slightly outside the outer peripheral surface of the ingot 1, as shown in (B) of FIG. 11, a part of the laser beam 3 passes through the upper surface of the ingot 1. Also, due to the difference in the refractive index of the ingot 1 and the atmosphere, the height of the focal point of the laser beam LB that passes through the inside of the ingot 1 is shifted from the height of the focal point of the laser beam LB that does not pass through the inside of the ingot 1. Figure 10

[0015] When the chuck table is moved so that the optical axis 5 is located at the outer peripheral surface of the ingot 1, as shown in (C) of FIG. 11, about half of the laser beam 3 on the side close to the ingot 1 passes through the upper surface of the ingot 1. Also, as described above, the height of the focal point of the laser beam that passes through the inside of the ingot 1 is shifted from the height of the focal point of the laser beam 3 that does not pass through the inside of the ingot 1. Figure 10

[0016] When the chuck table is moved so that the optical axis 5 is located slightly inside the outer peripheral surface of the ingot 1, as shown in (D) of FIG. 11, a part of the laser beam 3 passes through the focal point inside the ingot 1 via the outer peripheral surface of the ingot 1. At this time, an ablation mark based on multiphoton absorption is formed on the outer peripheral surface of the ingot 1. Also, as with the above, the height of the focal point of the laser beam 3 that passes through the outer peripheral surface of the ingot 1 is shifted from the height of the focal point of the laser beam 3 that passes through the upper surface of the ingot 1. Figure 10

[0017] When the chuck table is moved so that the optical axis 5 is sufficiently separated toward the inside with respect to the outer peripheral surface of the ingot 1, as shown in (E) of FIG. 11, the laser beam 3 entirely passes through the upper surface of the ingot 1. At this time, the laser beam 3 entirely goes toward a single focal point inside the ingot 1. Therefore, from when the focal point of the laser beam 3 is located at the outer peripheral surface of the ingot 1 (refer to (C) of FIG. 11) to this time (refer to (E) of FIG. 11), the power at the focal point of the laser beam 3 is unstable. Figure 10 Figure 10 Figure 10 ​​​​​​of the laser beam 3 at the focal point inside the ingot 1 is the highest.

[0018] In addition, when the chuck table is moved in a manner that the laser beam 3 is irradiated to the other end of the ingot 1, an ablation mark based on multi-photon absorption is also formed on the outer peripheral surface of the ingot 1, and the power density of the laser beam 3 at the focal point inside the ingot 1 changes.

[0019] In the case where the laser beam 3 is thus irradiated to the vicinity of one end and the vicinity of the other end (outer peripheral region) of the ingot 1 to form the ablation mark on the outer peripheral surface of the ingot 1, there is a concern that a defect is generated in the outer peripheral region of the wafer in a subsequent process (grinding, chemical mechanical polishing (CMP), edge trimming or chamfering, or the like) performed on the wafer peeled from the ingot 1. SUMMARY

[0020] In view of this point, an object of the present application is to provide a wafer production method capable of reducing the possibility of generation of a defect in the outer peripheral region of the wafer in a subsequent process.

[0021] According to the present application, there is provided a wafer production method of producing a wafer from a workpiece which is a single crystal SiC ingot or a single crystal SiC wafer, the workpiece having a first surface and a second surface which is a back surface of the first surface, the wafer having a thickness smaller than an interval between the first surface and the second surface, wherein the wafer production method includes a peeling layer forming step of positioning a focal point of a laser beam of a wavelength which transmits through the workpiece inside the workpiece, and irradiating the laser beam while relatively moving the workpiece and the focal point along an intersection line which intersects the first surface parallel to a c-plane of the workpiece to form a peeling layer including a modified portion and a crack extending from the modified portion along the c-plane, and a wafer peeling step of separating the workpiece along the peeling layer to peel the wafer from the workpiece, in the peeling layer forming step, the laser beam is irradiated only in a state where the focal point is positioned at a central region of the workpiece other than an outer peripheral region, which is a region from an outer periphery of the workpiece to an inside of a prescribed distance.

[0022] It is preferable that the wafer production method include an outer periphery detecting step of detecting an outer periphery of the workpiece by imaging the first surface side of the workpiece by an imaging unit before the peeling layer forming step.

[0023] It is preferable that the wafer production method include a grinding step of grinding a peeling surface of the wafer exposed by peeling the wafer from the workpiece after the wafer peeling step.

[0024] Preferably, the wafer production method includes a chamfering step of chamfering the outer periphery of the wafer after the wafer peeling step.

[0025] In the present application, a laser beam is irradiated only to a central region of the workpiece other than a removed outer peripheral region of the workpiece, which is a region from the outer periphery of the workpiece to an inside of a prescribed distance. In this case, a peeling layer is not formed in the outer peripheral region of the workpiece by the irradiation of the laser beam, thereby preventing the formation of an ablation mark on the outer peripheral surface of the workpiece. As a result, the possibility of a defect in the outer peripheral region of the wafer peeled from the workpiece when a subsequent process is performed on the wafer can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 (A) is a perspective view schematically showing an example of a workpiece, Figure 1 (B) is a side view schematically showing an example of a workpiece.

[0027] Figure 2 is a view schematically showing a state in which a laser beam is irradiated near one end of a workpiece.

[0028] Figure 3 is a flowchart showing an example of a wafer production method.

[0029] Figure 4 is a perspective view schematically showing a laser irradiation apparatus for performing a peeling layer formation step and a workpiece.

[0030] Figure 5 (A) is a cross-sectional view schematically showing a central region of a workpiece after a peeling layer formation step, Figure 5 (B) is a view schematically showing a workpiece after a peeling layer formation step.

[0031] Figure 6 is a cross-sectional view schematically showing a separation apparatus for performing a wafer peeling step and a workpiece.

[0032] Figure 7 is a flowchart showing another example of a wafer production method.

[0033] Figure 8 is a perspective view schematically showing a grinding apparatus for performing a grinding step and a wafer peeled from a workpiece.

[0034] Figure 9 is a side view schematically showing a chamfering apparatus for performing a chamfering step and a wafer peeled from a workpiece.

[0035] Figure 10 (A) to Figure 10(A) of FIG. 1 is a view showing a case where a laser beam is irradiated near one end of an ingot.

[0036] BRIEF DESCRIPTION OF DRAWINGS

[0037] 1: ingot; 3: laser beam; 5: optical axis; 11: workpiece; 11a: front surface; 11b: back surface; 11c: c-axis; 11d: perpendicular line; 11e: c-plane; 13: primary orientation plane; 15: secondary orientation plane; 17a: outer peripheral region; 17b: central region; 19: modified portion; 21: crack; 23: peeling layer; 25: wafer; 25a: peeling surface; 2: laser irradiation device; 4: chuck table; 6: laser beam irradiation unit; 8: head; 10: connecting portion; 12: imaging unit; 14: separation device; 16: liquid; 18: liquid tank; 20: placement table; 22: ultrasonic wave irradiation unit; 24: grinding device; 26: chuck table; 28: grinding unit; 30: spindle; 32: grinding wheel mount; 34: bolt; 36: grinding wheel; 38: base; 40: grinding tool; 42: chamfering device; 44: chuck table; 46: spindle; 48: grinding tool; 48a: upper portion; 48b: lower portion; 48c: central portion; 48d: upper chamfered portion; 48e: lower chamfered portion; 50: spindle. DETAILED DESCRIPTION

[0038] An embodiment of the present application will be described with reference to the drawings. Figure 1 (A) of FIG. 1 is a view showing a case where a laser beam is irradiated near one end of an ingot. Figure 1 (B) of FIG. 1 is a side view schematically showing an example of the workpiece. Figure 1 (A) and Figure 1 The workpiece 11 shown in (A) and (B) of FIG. 1 is a cylindrical single-crystal SiC ingot having a front surface (first surface) 11a and a back surface (second surface) 11b which are substantially parallel.

[0039] The workpiece 11 is produced by epitaxial growth. Also, the workpiece 11 is produced so as to be slightly inclined with respect to the perpendicular line 11d of the front surface 11a and the back surface 11b of the c-axis 11c of the single-crystal SiC in order to reduce crystal lattice defects formed in the interior. For example, the angle (deviation angle) a formed by the c-axis 11c and the perpendicular line 11d is 1° to 6° (typically 4°).

[0040] Two flat portions, i.e., a primary orientation plane 13 and a secondary orientation plane 15, showing the crystal orientation of the single-crystal SiC are formed in the outer peripheral region of the workpiece 11. Also, the primary orientation plane 13 is longer than the secondary orientation plane 15. In addition, the secondary orientation plane 15 is formed so as to be parallel to an intersection line which is a line intersecting a plane parallel to the c-plane 11e of the single-crystal SiC and the front surface 11a or the back surface 11b.

[0041] In addition, the workpiece 11 is not limited to a single crystal SiC ingot, and can be a single crystal SiC wafer peeled from a single crystal SiC ingot. In addition, one or both of the primary orientation flat 13 and the secondary orientation flat 15 can not be provided on the side surface of the workpiece 11.

[0042] In addition, the workpiece 11 is divided into an outer peripheral region 17a inside a prescribed distance from the outer periphery of the workpiece 11 and a central region 17b inside the outer peripheral region 17a. In addition, in Figure 1 (A) and Figure 1 (B) of the present embodiment, the boundary line between the outer peripheral region 17a and the central region 17b is shown by a broken line, but this boundary line is an imaginary line and does not exist in the actual workpiece 11.

[0043] Specifically, the outer peripheral region 17a is a region in which formation of an intentional separation layer is not performed in the separation layer formation step described later. On the other hand, the central region 17b is a region in which formation of an intentional separation layer is performed in the separation layer formation step described later.

[0044] In other words, the outer peripheral region 17a is a region in which a focal point of a laser beam for forming a separation layer is not positioned in the separation layer formation step described later. On the other hand, the central region 17b is a region in which a focal point of a laser beam for forming a separation layer is positioned in the separation layer formation step described later.

[0045] In addition, the width of the outer peripheral region 17a, that is, the interval between the outer periphery of the workpiece 11 and the central region 17b, is preferably set to be equal to or greater than the minimum value of the interval between the focal point of the laser beam passing through the upper surface of the workpiece 11 and the outer peripheral surface of the workpiece 11. Thus, the width of the outer peripheral region 17a can be set in dependence on the numerical aperture NA or the like of a condenser lens that condenses the laser beam irradiated to the workpiece 11.

[0046] Referring to Figure 2 This point will be described. In addition, Figure 2 is a view schematically showing the state of the workpiece 11 in which a laser beam is irradiated near one end. The workpiece 11 shown in Figure 2 A laser beam L is irradiated near one end of the workpiece 11 shown in FIG. 8. This laser beam L is condensed at a focal point F located inside the workpiece 11 on an optical axis O.

[0047] Further, when the interval between the optical axis O and the outer peripheral surface of the work 11 is r or more, the laser beam L passes through the upper surface of the work 11 entirely without passing through the outer peripheral surface of the work 11. In other words, here, the minimum value of the interval between the focal point of the laser beam L that passes through the upper surface of the work 11 entirely and the outer peripheral surface of the work 11 is made r. Therefore, in order to make the laser beam L not pass through the outer peripheral surface of the work 11, it is necessary to set the width of the outer peripheral region 17a to be r or more.

[0048] Here, when the angle formed by the imaginary line where the laser beam L does not refract and proceeds straight when being incident to the work 11 and the optical axis O is made θ, and the interval between the intersection (imaginary focal point F0) of the imaginary line and the optical axis O and the upper surface of the work 11 is made z, r can be expressed by the following numerical formula 1.

[0049] [Formula 1]

[0050] r = z x tan θ · · · (Formula 1)

[0051] Further, when the refractive index of the atmosphere is made n, the numerical aperture NA of the condensing lens that converges the laser beam L can be expressed by the following numerical formula 2, and the angle θ formed by the imaginary line and the optical axis O can be expressed by the following numerical formula 3 using the numerical aperture NA.

[0052] [Formula 2]

[0053] NA = n x sin θ · · · (Formula 2)

[0054] [Formula 3]

[0055]

[0056] When formula 3 is substituted into formula 1, r can be expressed by the following numerical formula 4.

[0057] [Formula 4]

[0058]

[0059] The numerical aperture NA and the refractive index n of the atmosphere, which are included in the parameters on the right side of formula 4, can be grasped before the laser beam L is irradiated to the work 11. Further, the interval z between the upper surface of the work 11 and the imaginary focal point F0 can be set when the laser beam L is irradiated to the work 11.

[0060] Therefore, as for the width r of the outer peripheral region 17a that is necessary in order to make the laser beam L not pass through the outer peripheral surface of the work 11, it can be calculated before the laser beam L is actually irradiated to the work 11. Further, it is preferable that the width of the outer peripheral region 17a be set to be r or more as thus calculated.

[0061] However, in a case where the power density of the laser beam irradiated in order to form the separation layer on the work 11 is not high (for example, in a case where an ablation mark is not formed even if the laser beam is irradiated to the outer peripheral surface of the work 11), the width of the outer peripheral region 17a can be made smaller than r.

[0062] On the other hand, the outer peripheral region 17a is a region in which a crack is intended to propagate from the boundary between the outer peripheral region 17a and the central region 17b to the outer peripheral surface of the work 11 in a wafer separation step described later. Therefore, it is preferable that the width of the outer peripheral region 17a is not made too large.

[0063] For example, the width of the outer peripheral region 17a is preferably 4 times or less, more preferably 3 times or less, and most preferably 2 times or less, of r.

[0064] Figure 3 is a flowchart showing an example of a method of producing a wafer of the present embodiment. In this method, first, a laser beam is irradiated to the work 11 to form a separation layer (separation layer forming step: S1).

[0065] Figure 4 is a perspective view schematically showing a laser irradiation apparatus for performing the separation layer forming step (S1) and the work 11. In addition, the X-axis direction and the Y-axis direction shown in the drawing are directions perpendicular to each other on a horizontal plane, and the Z-axis direction is a direction (plumb direction) perpendicular to the X-axis direction and the Y-axis direction. Figure 4

[0066] Figure 4 The laser irradiation apparatus 2 shown in the drawing has a chuck table 4 having a circular holding surface substantially parallel to a horizontal plane, and is capable of holding the work 11 with the holding surface. The chuck table 4 is connected to a suction mechanism (not shown).

[0067] The suction mechanism has a suction pump or the like, and is capable of generating a negative pressure on the holding surface of the chuck table 4. Also, when the suction mechanism is operated in a state where the work 11 is placed on the holding surface, the work 11 is held by suction on the chuck table 4.

[0068] In addition, the chuck table 4 is connected to an X-axis direction moving mechanism (not shown) and a Y-axis direction moving mechanism (not shown). The X-axis direction moving mechanism and the Y-axis direction moving mechanism each have, for example, a ball screw and a motor or the like. Also, when the X-axis direction moving mechanism and / or the Y-axis direction moving mechanism is operated, the chuck table 4 moves in the X-axis direction and / or the Y-axis direction.

[0069] ​Further, the chuck table 4 is coupled with a rotation mechanism (not shown). The rotation mechanism has, for example, a spindle and a motor. Also, when the rotation mechanism is operated, the chuck table 4 rotates with a straight line through the center of the holding surface in the Z-axis direction as a rotation axis.

[0070] A head 8 of the laser beam irradiation unit 6 is provided above the chuck table 4. The head 8 is provided at a front end (one end) portion of a coupling portion 10 extending in the Y-axis direction. Further, the head 8 houses an optical system such as a condenser lens and a mirror, and the coupling portion 10 houses an optical system such as a mirror and / or a lens.

[0071] The other end portion of the coupling portion 10 is coupled with a Z-axis direction moving mechanism (not shown). The Z-axis direction moving mechanism has, for example, a ball screw and a motor. Also, when the Z-axis direction moving mechanism is operated, the head 8 and the coupling portion 10 move in the Z-axis direction.

[0072] Further, the laser beam irradiation unit 6 has a laser oscillator (not shown) that generates a laser beam of a wavelength (for example, 1064 nm) that transmits the workpiece 11. The laser oscillator has, for example, a laser medium such as Nd:YAG. Also, when the laser beam is generated by the laser oscillator, the laser beam is irradiated to the holding surface side of the chuck table 4 via the optical system housed in the coupling portion 10 and the head 8.

[0073] Further, a photographing unit 12 that can photograph the holding surface side of the chuck table 4 is provided at a side portion of the coupling portion 10. The photographing unit 12 has, for example, a light source such as an LED (Light Emitting Diode), an objective lens, and a photographing element such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor. Also, the objective lens of the photographing unit 12 is provided at a position separated in the X-axis direction from the condenser lens housed in the head 8.

[0074] The peeling layer formation step (S1) using the laser irradiation device 2 is performed, for example, in the following order. First, the workpiece 11 is placed on the holding surface of the chuck table 4 with the front surface 11a upward. Next, the suction mechanism is operated so that the workpiece 11 is suction-held on the chuck table 4.

[0075] Next, the rotation mechanism rotates the chuck table 4 so that the secondary orientation plane 15 becomes parallel to the X-axis direction, based on the image of the front surface 11a of the workpiece 11 formed by the imaging by the imaging unit 12, and the like. Next, the X-axis direction moving mechanism and / or the Y-axis direction moving mechanism moves the chuck table 4 so as to position the head 8 directly above the central region 17b near the boundary between the outer peripheral region 17a and the central region 17b of the workpiece 11.

[0076] Next, the optical system of the head 8 and / or the connecting portion 10 is set in a manner that the focal point of the laser beam irradiated from the laser beam irradiation unit 6 is positioned inside the workpiece 11. For example, the Z-axis direction moving mechanism moves the head 8 and the connecting portion 10 so that the interval between the condensing lens housed in the head 8 and the front surface 11a of the workpiece 11 becomes a prescribed distance.

[0077] In addition, the setting of the optical system can be performed at any timing as long as it is before the laser beam is irradiated to the workpiece 11. For example, the setting of the optical system can be performed before the rotation and movement of the chuck table 4 described above. In addition, the setting of the optical system is performed in a manner that the interval between the focal point of the laser beam and the front surface 11a of the workpiece 11 is slightly larger than the thickness of a wafer used in the manufacture of a chip of a semiconductor device.

[0078] Next, the laser beam irradiation unit 6 irradiates the laser beam of the wavelength that transmits the workpiece 11 while moving the chuck table 4 by the X-axis direction moving mechanism in a manner that the focal point of the laser beam does not exceed the central region 17b. That is, the workpiece 11 and the focal point of the laser beam are relatively moved along the intersection line that intersects the c-plane 11e of the workpiece 11 (single crystal SiC) and the front surface 11a, and the laser beam is irradiated to the central region 17b by the laser beam irradiation unit 6.

[0079] Next, the same irradiation of the laser beam is repeatedly performed. Specifically, the laser beam is irradiated to the portion along the X-axis direction that is separated by a prescribed distance in the Y-axis direction from the portion along the X-axis direction of the central region 17b to which the laser beam is irradiated. Thereby, a plurality of columns of the modified portion 19 along the X-axis direction are formed in the entire inside of the central region 17b.

[0080] Figure 5 (A) is a cross-sectional view schematically showing the central region 17b of the workpiece 11 after the separation layer formation step (S1), Figure 5 (B) is a view schematically showing the workpiece 11 after the separation layer formation step (S1).

[0081] As Figure 5 (A) and Figure 5of the modification 19, the crack 21 advances along the c-plane lie from the modification 19. Thus, the peeling layer 23 having the modification 19 and the crack 21 is formed in the central region 17b, and the peeling layer 23 is separated upward and downward by applying an external force to the work 11.

[0082] In Figure 3 the method shown in FIG. 8, after the peeling layer forming step (SI), the work 11 is separated along the peeling layer 23 to peel the wafer from the work 11 (wafer peeling step: S2). Figure 6 is a cross-sectional view schematically showing a separation device for performing the wafer peeling step (S2) and the work 11.

[0083] Figure 6 The separation device 14 shown in FIG. 9 has a liquid tank 18 that houses a liquid 16 inside. A placement table 20 on which the work 11 is placed is provided at the bottom of the liquid tank 18, and the work 11 is placed on the placement table 20 in a state of being immersed in the liquid tank 18.

[0084] In addition, the separation device 14 has an ultrasonic wave irradiation unit 22 capable of irradiating ultrasonic waves. The ultrasonic wave irradiation unit 22 is movable, for example, between a retreat position away from the liquid 16 and a driving position in contact with the liquid 16 on the bottom surface.

[0085] The wafer peeling step (S2) using the separation device 14 is performed, for example, in the following order. First, after positioning the ultrasonic wave irradiation unit 22 at the retreat position, the work 11 is placed on the placement table 20 in a manner that the front surface lie faces upward.

[0086] Next, after positioning the ultrasonic wave irradiation unit 22 at the driving position, ultrasonic waves are irradiated from the bottom surface of the ultrasonic wave irradiation unit 22. The ultrasonic waves propagate in the liquid 16 to be irradiated to the work 11.

[0087] Thus, the work 11 is given ultrasonic wave vibration (external force) to further advance the crack 21 formed by the peeling layer forming step (SI). Also, the crack 21 advances not only to the central region 17b but also to the outer peripheral region 17a. As a result, the work 11 is separated along the peeling layer 23 to peel the wafer from the work 11.

[0088] In addition, in the Figure 6 embodiment, the entire work 11 placed on the placement table 20 is immersed in the liquid 16, but in the wafer peeling step (S2), the entire work 11 can not be immersed in the liquid 16.

[0089] For example, in the separation device 14, a nozzle for supplying liquid toward the workpiece 11 can be provided near the ultrasonic irradiation unit 22. Furthermore, in the wafer stripping step (S2), liquid can be supplied to the workpiece 11 from the nozzle while ultrasonic waves are irradiated by the ultrasonic irradiation unit 22, thereby imparting ultrasonic vibration (external force) to the workpiece 11.

[0090] exist Figure 3 In the wafer fabrication method shown, a release layer 23 is formed by irradiating a laser beam only on the central region 17b of the workpiece 11, excluding the outer peripheral region 17a. The outer peripheral region 17a is the region extending from the outer periphery of the workpiece 11 to the inside of a predetermined distance.

[0091] In this case, a release layer 23 is formed in the outer peripheral region 17a of the workpiece 11 without laser beam irradiation, thereby preventing the formation of ablation marks on the outer peripheral surface of the workpiece 11. As a result, the possibility of defects occurring in the outer peripheral region of the wafer during subsequent processes (grinding, chemical mechanical polishing, edge trimming, or chamfering, etc.) after the wafer is removed from the workpiece 11 can be reduced.

[0092] in addition, Figure 3 The wafer fabrication method shown is one aspect of the present invention, and wafer fabrication methods having different features are also included within the scope of the present invention. Figure 7 This is a flowchart illustrating another example of a wafer fabrication method falling within the technical scope of the present invention. Specifically, Figure 7 It is shown in Figure 3 The flowchart illustrates a wafer fabrication method that includes other steps based on the stripping layer formation step (S1) and the wafer stripping step (S2).

[0093] exist Figure 7 In the wafer fabrication method shown, before the lift-off layer formation step (S1), the outer periphery of the workpiece 11 is inspected (outer periphery inspection step: S3). For example, in the process of... Figure 4 After the chuck stage 4 of the laser irradiation device 2 shown attracts and holds the workpiece 11, the front side 11a of the workpiece 11 is photographed by the imaging unit 12 to form an image, and the outer perimeter detection step (S3) is performed based on the image.

[0094] When performing the peripheral inspection step (S3), the peripheral region 17a extending from the outer periphery of the workpiece 11 to within a specified distance can be accurately determined. Therefore, the formation of a release layer 23 in the peripheral region 17a of the workpiece 11 due to laser beam irradiation is reliably prevented. As a result, the possibility of defects occurring in the peripheral region of the wafer during subsequent processes on the wafer stripped from the workpiece 11 can be further reduced.

[0095] In addition, in Figure 7 In the wafer generation method shown in FIG. 1, after the wafer peeling step (S2), the peeling surface of the wafer peeled from the workpiece 11 (the surface of the wafer exposed due to peeling of the wafer from the workpiece 11) is ground (grinding step: S4). Figure 8 FIG. 2 is a perspective view schematically showing a grinding device for performing the grinding step (S4) and the wafer peeled from the workpiece 11.

[0096] Figure 8 The grinding device 24 shown in FIG. 2 has a chuck table 26 having a holding surface corresponding to a conical side surface shape with a center slightly protruding than an outer edge, and is capable of holding the wafer 25 with the holding surface. The chuck table 26 is coupled to a suction mechanism (not shown).

[0097] The suction mechanism has an air ejector or the like, and is capable of generating a negative pressure on the holding surface of the chuck table 26. Also, when the suction mechanism is operated in a state where the wafer 25 is placed on the holding surface, the wafer 25 is suction-held on the chuck table 26.

[0098] In addition, the chuck table 26 is coupled to a horizontal direction moving mechanism (not shown). The horizontal direction moving mechanism has, for example, a ball screw and a motor or the like. Also, when the horizontal direction moving mechanism is operated, the chuck table 26 moves in the horizontal direction.

[0099] In addition, the chuck table 26 is coupled to a rotation mechanism (not shown). The rotation mechanism has, for example, a spindle and a motor or the like. Also, when the rotation mechanism is operated, the chuck table 26 rotates in the direction of the arrow a shown in FIG. 2 with a straight line passing through the center of the holding surface in the vertical direction as a rotation axis. Figure 8

[0100] A grinding unit 28 is provided above the chuck table 26. The grinding unit 28 has a spindle 30 coupled to a motor at an upper end portion. A disc-shaped grinding wheel mounting seat 32 is fixed to a lower end portion of the spindle 30.

[0101] A plurality of openings (not shown) passing through the grinding wheel mounting seat 32 in the vertical direction are provided in the grinding wheel mounting seat 32. The plurality of openings are arranged in a ring shape with a gap in the circumferential direction of the grinding wheel mounting seat 32.

[0102] A grinding wheel 36 is mounted to a lower portion of the grinding wheel mounting seat 32. The grinding wheel 36 has a ring-shaped base 38. A plurality of internal thread portions (not shown) are provided in an upper portion of the base 38, and lower end portions of bolts 34 are screwed into the internal thread portions.

[0103] ​In addition, a plurality of grinding stones 40 are fixed to the lower end of the base 38 in a ring shape at intervals in the circumferential direction of the base 38. The lower surfaces of the plurality of grinding stones 40 are arranged at substantially the same height, and these lower surfaces serve as the grinding surface of the grinding unit 28.

[0104] In addition, the main shaft 30 is connected to a vertical direction moving mechanism (not shown). The vertical direction moving mechanism has, for example, a ball screw and a motor. When the vertical direction moving mechanism is operated, the main shaft 30, the grinding wheel mount 32, and the grinding wheel 36 move in the vertical direction.

[0105] The grinding step (S4) using the grinding device 24 is performed, for example, in the following order. First, the wafer 25 is placed on the chuck table 26 in a state in which the chuck table 26 and the grinding unit 28 are separated in both the horizontal direction and the vertical direction, with the separation surface (a surface exposed by the separation of the workpiece 11 along the separation layer 23) 25a of the wafer 25 facing upward.

[0106] Next, the suction mechanism is operated so that the wafer 25 is held in a sucked state on the chuck table 26. Next, the chuck table 26 is moved by the horizontal direction moving mechanism so that the rotation axis of the chuck table 26 overlaps the annular region in which the plurality of grinding stones 40 are arranged.

[0107] Next, the chuck table 26 is rotated by the rotation mechanism, and the motor connected to the upper end of the main shaft 30 rotates the main shaft 30, the grinding wheel mount 32, and the grinding wheel 36.

[0108] Next, the main shaft 30, the grinding wheel mount 32, and the grinding wheel 36 are lowered by the vertical direction moving mechanism so that the separation surface 25a of the wafer 25 contacts the lower surfaces of the plurality of grinding stones 40. Thus, the separation surface 25a of the wafer 25 is ground.

[0109] Here, the wafer 25 is separated from the workpiece 11 with the crack 21 that advances along the c-plane 11e that is slightly inclined with respect to the front surface 11a and the back surface 11b as a boundary. Therefore, fine irregularities are often formed on the separation surface 25a of the wafer 25.

[0110] In this regard, the grinding step (S4) described above can remove the fine irregularities formed on the separation surface 25a of the wafer 25. Therefore, it is a preferred embodiment of the present application that the grinding step (S4) is performed after the wafer forming step (S2).

[0111] In addition, in the wafer forming method shown in FIG. 1, the outer periphery of the wafer 25 is chamfered after the grinding step (S4) (chamfering step: S5). Figure 7 Figure 9 ​is a side view schematically showing a chamfering device for performing the chamfering step (S5) and the wafer 25.

[0112] Figure 9 The chamfering device 42 shown has a chuck table 44 having a generally parallel circular holding surface with which the wafer 25 can be held. In addition, the holding surface is smaller in size (diameter) than the wafer 25. Therefore, the outer periphery of the wafer 25 is not directly supported by the chuck table 44.

[0113] The upper end of a spindle 46 is fixed to the lower end of the chuck table 44. In addition, a motor (not shown) is connected to the lower end of the spindle 46. When the motor is operated, the chuck table 44 and the spindle 46 rotate about a straight line along the vertical direction passing through the center of the horizontal cross section of the chuck table 44 in the direction of the arrow c shown. Figure 9

[0114] In addition, the chuck table 44 is connected to a suction mechanism (not shown) via the spindle 46. The suction mechanism has a suction pump or the like and can generate a negative pressure on the holding surface of the chuck table 44. When the suction mechanism is operated in a state in which the wafer 25 is placed on the holding surface, the wafer 25 is held by suction to the chuck table 44.

[0115] In addition, the chuck table 44 is connected to a horizontal direction moving mechanism (not shown) via the spindle 46. The horizontal direction moving mechanism has, for example, a ball screw and a motor or the like. When the horizontal direction moving mechanism is operated, the chuck table 44 moves in the horizontal direction.

[0116] A grinding tool 48 is provided to the side of the chuck table 44. The grinding tool 48 has a circular disk-shaped upper portion 48a and a lower portion 48b which are substantially equal in diameter, a circular disk-shaped central portion 48c which is smaller in diameter than the upper portion 48a and the lower portion 48b, a circular truncated cone-shaped upper chamfering portion 48d which is provided between the upper portion 48a and the central portion 48c in a manner connecting the upper portion 48a and the central portion 48c, and a circular truncated cone-shaped lower chamfering portion 48e which is provided between the lower portion 48b and the central portion 48c in a manner connecting the lower portion 48b and the central portion 48c.

[0117] The upper end of a spindle 50 is fixed to the lower end of the lower portion 48b. In addition, a motor (not shown) is connected to the lower end of the spindle 50. When the motor is operated, the grinding tool 48 and the spindle 50 rotate about a straight line along the vertical direction passing through the center of the horizontal cross section of the grinding tool 48 in the direction of the arrow d shown. Figure 9

[0118] ​​Further, the main shaft 50 is coupled to a vertical direction moving mechanism (not shown). The vertical direction moving mechanism has, for example, a ball screw and a motor. Also, when the vertical direction moving mechanism operates, the grinding tool 48 and the main shaft 50 move in the vertical direction.

[0119] The chamfering step (S5) using the chamfering device 42 is performed, for example, in the following order. First, in a state where the chuck table 44 and the grinding tool 48 are separated in the horizontal direction, the wafer 25 is placed on the chuck table 44.

[0120] Next, the suction mechanism is operated in a manner that the wafer 25 is suction-held to the chuck table 44. Next, the grinding tool 48 and the main shaft 50 are moved by the vertical direction moving mechanism in a manner that the height of the vertical direction center of the central portion 48c of the grinding tool 48 coincides with the height of the vertical direction center of the wafer 25.

[0121] Next, the motor coupled to the lower end portion of the main shaft 46 rotates the chuck table 44 and the main shaft 46, and the motor coupled to the lower end portion of the main shaft 50 rotates the grinding tool 48 and the main shaft 50.

[0122] Next, the chuck table 44 and the main shaft 46 are moved by the horizontal direction moving mechanism in a manner that the outer periphery of the wafer 25 contacts the upper chamfering portion 48d and the lower chamfering portion 48e of the grinding tool 48. Thus, the outer periphery of the wafer 25 is chamfered.

[0123] Here, the wafer 25 is peeled from the work 11, and the peeling layer 23 including the modified portion 19 and the crack 21 is not formed in the outer peripheral region 17a of the work 11. Therefore, the possibility that the modified portion 19 and the crack 21 exist in the vicinity of the outer periphery of the wafer 25 is low. Thus, the wafer 25 is a preferable wafer as a wafer whose outer periphery is chamfered.

[0124] Further, in the wafer production method shown in FIG. 1, the outer periphery detection step (S3), the grinding step (S4), and the chamfering step (S5) can be omitted. Figure 7 In the wafer production method shown in FIG. 1, the outer periphery detection step (S3), the grinding step (S4), and the chamfering step (S5) can be omitted.

[0125] In addition to the above, the configuration and the method of the above-described embodiments and the modified examples can be appropriately changed and implemented as long as the purpose of the present application is not deviated.

Claims

1. A wafer production method of producing a wafer from a work having a first face and a second face as a back face of the first face, the wafer having a thickness smaller than an interval between the first face and the second face, the wafer production method characterized by comprising steps of: a separation layer forming step of positioning a focal point of a laser beam of a wavelength that transmits the work inside the work, and irradiating the laser beam while relatively moving the work and the focal point along an intersection line that intersects the first face parallel to a c-face of the work, to form a separation layer including a modified portion and a crack extending from the modified portion along the c-face; and a wafer separation step of separating the work along the separation layer to separate the wafer from the work.

2. The wafer production method according to claim 1, wherein the wafer production method comprises an outer periphery detecting step of detecting an outer periphery of the work by photographing the first face side of the work by a photographing unit before the separation layer forming step.

3. The wafer production method according to claim 1, wherein the wafer production method comprises a grinding step of grinding a separation face of the wafer exposed by separating the wafer from the work after the wafer separation step.

4. The wafer production method according to claim 2, wherein the wafer production method comprises a grinding step of grinding a separation face of the wafer exposed by separating the wafer from the work after the wafer separation step.

5. The wafer production method according to any one of claims 1 to 4, wherein the wafer production method comprises a chamfering step of chamfering an outer periphery of the wafer after the wafer separation step. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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