Laser processing equipment and laser processing methods

Abstract

This invention provides a laser processing apparatus and a laser processing method that can reduce cutting losses when cutting wafers from an ingot. The irradiation conditions of the laser beam for each of the plurality of regions included on the upper surface of the ingot are set according to the number of photons of fluorescence generated when each region is irradiated with excitation light. Here, the number of fluorescence photons depends on the concentration of impurities doped in the ingot. Therefore, even when the ingot contains regions with different impurity concentrations, a release layer can be formed at a uniform depth from the upper surface of the ingot. This reduces cutting losses when cutting wafers from the ingot.

Description

Technical Field

[0001] This invention relates to a laser processing apparatus and a laser processing method for forming a release layer in an ingot for cutting out wafers. Background Technology

[0002] Semiconductor device chips are typically manufactured using disk-shaped wafers. These wafers are produced, for example, by cutting them from cylindrical semiconductor ingots using a wire dicing machine. However, when wafers are manufactured in this way, there is a problem that a large portion of the ingot is lost as cutting wear (cutting amount), making it uneconomical.

[0003] Furthermore, SiC (silicon carbide) single crystals, used as materials for power devices, have high hardness. Therefore, when using a wire cutting machine to cut wafers from SiC single crystal ingots, the cutting process is time-consuming and has poor productivity.

[0004] In view of these aspects, a method for cutting wafers from a spindle using a laser beam instead of a wire cutting machine has been proposed (see, for example, Patent Document 1). In this method, a laser beam is irradiated onto the spindle in such a way that the focal point of the laser beam of wavelength that passes through the spindle is positioned inside the spindle.

[0005] Thus, a release layer containing a modified layer and cracks extending from the modified layer is formed inside the ingot. Then, when an external force is applied to the ingot with the release layer formed by ultrasonic vibration or the like, the ingot separates from the release layer, and the wafer is cut out.

[0006] In addition, SiC single crystal ingots are usually doped with impurities such as nitrogen to impart conductivity. However, sometimes such impurities are not uniformly doped in SiC single crystal ingots, resulting in multiple regions with different impurity concentrations.

[0007] For example, in the growth of SiC single crystals, the atomically flat regions known as facets have higher impurity concentrations than other regions (non-facet regions). Moreover, regions with high impurity concentrations, such as facets, have higher refractive indices and higher energy absorption rates compared to non-facet regions.

[0008] Therefore, when forming a release layer on a SiC single crystal ingot containing a small facet region using the above method, there are problems such as the release layer becoming uneven in position (height) and the cutting loss increasing.

[0009] In view of this, a laser processing apparatus has been proposed for determining the facet region and non-facet region of a SiC ingot and irradiating the two regions with laser beams according to different irradiation conditions (see, for example, Patent Document 2).

[0010] Patent Document 1: Japanese Patent Application Publication No. 2016-111143

[0011] Patent Document 2: Japanese Patent Application Publication No. 2020-77783

[0012] Sometimes the impurity concentration in the facet region is uneven, differing between the center and the periphery. In such cases, even if the laser beam is irradiated onto the facet region under different irradiation conditions than that on non-facet regions, the position (height) of the peeling layer formed in the facet region may still deviate.

[0013] Furthermore, non-facet regions sometimes contain areas with varying impurity concentrations. Therefore, even if laser beams are irradiated onto both facet and non-facet regions under different irradiation conditions, it may not be possible to sufficiently reduce cutting losses. Summary of the Invention

[0014] In view of this, the object of the present invention is to provide a laser processing apparatus and a laser processing method capable of reducing cutting losses when cutting wafers from a spindle.

[0015] The inventors discovered that the higher the concentration of impurities doped in the ingot, the fewer photons of fluorescence generated when excitation light is irradiated onto the ingot, thus completing this invention.

[0016] For example, according to one aspect of the invention, a laser processing apparatus is provided that forms a release layer in an ingot for cutting a wafer, wherein the laser processing apparatus comprises: a holding unit having a holding surface for holding the ingot; a fluorescence detection unit that irradiates the ingot with excitation light of a predetermined wavelength from above the ingot and detects fluorescence generated from the ingot; a laser beam irradiation unit that positions a focal point of a laser beam of a wavelength transmitted through the ingot at a depth from the upper surface of the ingot equivalent to the thickness of the wafer to be cut from the ingot for irradiation to form the release layer; and a horizontal movement mechanism that moves the holding unit and the laser beam irradiation unit... The device moves relative to the holding surface in a direction parallel to it; and a control unit, the control unit having: a storage unit that stores each of a plurality of coordinates on a coordinate plane parallel to the holding surface representing a plurality of regions contained in the upper surface of the ingot, in association with the number of photons of fluorescence detected by the fluorescence detection unit when each of the plurality of regions is irradiated with the excitation light; and an irradiation condition setting unit that sets the irradiation conditions of the laser beam for each of the plurality of regions represented by the plurality of coordinates based on the number of photons of fluorescence stored in association with each of the plurality of coordinates.

[0017] Furthermore, in the laser processing apparatus of the present invention, it is preferable that the storage unit pre-stores the irradiation conditions of the laser beam set for each region of the plurality of regions represented by the plurality of coordinates based on the number of photons of the fluorescence detected by the fluorescence detection unit, and the irradiation condition setting unit sets the irradiation conditions of the laser beam for each region of the plurality of regions represented by the plurality of coordinates with reference to the irradiation conditions of the laser beam corresponding to the number of photons of the fluorescence stored in the storage unit.

[0018] Furthermore, in the laser processing apparatus of the present invention, it is preferable that the irradiation condition setting unit sets the irradiation conditions of the laser beam according to the number of photons of the fluorescence stored in association with each of the plurality of coordinates, by changing at least one of the output of the laser beam, the height of the focusing lens that converges the laser beam, and the overlap rate of the laser beam.

[0019] According to another aspect of the present invention, a laser processing method is provided for forming a release layer in an ingot for cutting a wafer, wherein the laser processing method includes the following steps: a holding step for holding the ingot; a fluorescence detection step for irradiating the ingot with excitation light of a predetermined wavelength from above the ingot and detecting fluorescence generated from the ingot after the holding step; a storage step for storing each of a plurality of coordinates representing a plurality of regions included on the upper surface of the ingot in association with the number of photons of fluorescence detected when each of the plurality of regions was irradiated with the excitation light of the predetermined wavelength in the fluorescence detection step; and a laser beam irradiation step for forming a release layer in the ingot by moving the focal point of a laser beam of a wavelength that transmits through the ingot relative to the ingot, wherein the laser beam irradiation step is performed by changing the irradiation conditions of the laser beam on each of the plurality of regions represented by the plurality of coordinates according to the number of photons of fluorescence stored in association with each of the plurality of coordinates in the storage step.

[0020] Furthermore, in the laser processing method of the present invention, it is preferable that the laser processing method further includes an irradiation condition storage step: pre-storing irradiation conditions of the laser beam for each of the plurality of regions represented by the plurality of coordinates, based on the number of photons of the fluorescence generated from the ingot by irradiating the ingot with excitation light of the predetermined wavelength; and in the laser beam irradiation step, referring to the irradiation conditions of the laser beam corresponding to the number of photons of the fluorescence stored in the irradiation condition storage step, setting the irradiation conditions of the laser beam for each of the plurality of regions represented by the plurality of coordinates.

[0021] Furthermore, in the laser processing method of the present invention, it is preferable that, as the irradiation conditions of the laser beam, at least one of the following is set: the output of the laser beam, the height of the focusing lens that converges the laser beam, and the overlap rate of the laser beam.

[0022] In this invention, the irradiation conditions of the laser beam for each of the multiple regions is set based on the number of photons of fluorescence generated when excitation light is irradiated onto each of the multiple regions contained in the upper surface of the ingot. Here, the number of photons of fluorescence depends on the concentration of impurities doped in the ingot.

[0023] Therefore, in this invention, even when the ingot contains regions with varying impurity concentrations, a release layer can be formed at a uniform depth from the upper surface of the ingot. This reduces cutting losses when dicing wafers from the ingot. Attached Figure Description

[0024] Figure 1 (A) is a schematic front view showing an example of an ingot. Figure 1 (B) is a top view schematically showing an example of an ingot.

[0025] Figure 2 This is a perspective view schematically illustrating an example of a laser processing apparatus.

[0026] Figure 3 This is a schematic diagram illustrating the movement of a laser beam inside a laser processing device.

[0027] Figure 4 This is a schematic diagram illustrating an example of a fluorescence detection unit.

[0028] Figure 5 This is a functional block diagram that schematically illustrates an example of a control unit.

[0029] Figure 6 This is a diagram that schematically illustrates an example of multiple coordinates stored in the storage unit.

[0030] Figure 7 (A) and Figure 7 (B) are graphs that schematically illustrate the correspondence between the number of photons of fluorescence stored in the storage unit and the output of the laser beam. Figure 7 (C) and Figure 7 (D) are graphs that schematically illustrate the relationship between the number of photons of fluorescence stored in the storage unit and the height of the condenser lens. Figure 7 (E) and Figure 7 (F) are graphs that schematically show the correspondence between the number of photons of fluorescence stored in the storage unit and the overlap rate of the laser beam.

[0031] Figure 8 This is a flowchart illustrating an example of a laser processing method.

[0032] Figure 9 This is a perspective view schematically illustrating an example of a fluorescence detection procedure.

[0033] Figure 10 This is a perspective view schematically illustrating an example of a laser beam irradiation process.

[0034] Figure 11 This is a flowchart that schematically illustrates a variation of the laser processing method.

[0035] Label Explanation

[0036] 11: Ingot (11a: Upper surface (front), 11b: Lower surface (back), 11c: C-axis) (11d: Perpendicular line, 11e: C-plane) (11f: Small facet area, 11g: Non-small facet area); 13: Primary orientation plane; 15: Secondary orientation plane; 2: Laser processing device; 4: Base; 6: Horizontal moving mechanism; 8: Y-axis guide rail; 10: Y-axis moving plate; 12: Lead screw shaft; 14: Motor; 16: X-axis guide rail; 18: X-axis moving plate; 20: Lead screw shaft; 22: Motor; 24: Worktable base; 26: Chuck worktable (holding unit) (26a: Holding surface); 30: Support structure; 32: Lead Vertical moving mechanism; 34: Z-axis guide rail; 36: Z-axis moving plate; 38: motor; 40: support member; 42: laser beam irradiation unit; 44: laser oscillator; 46: housing (46a, 46b: reflectors); 48: irradiation head (48a: reflector, 48b: condenser lens); 50: fluorescence detection unit; 52: excitation light source; 54: reflector; 56: condenser lens; 58: elliptical mirror (58a: reflecting surface, 58b: ellipse); 60: light receiving part (60a: light receiving surface); 62: filter; 64: touch panel; 66: control unit; 68: processing unit; 70: storage unit; 72: irradiation condition setting unit. Detailed Implementation

[0037] The embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 (A) is a schematic front view illustrating an example of an ingot being cut into wafers using a laser processing apparatus. Figure 1 (B) is a top view of the ingot.

[0038] Figure 1 (A) and Figure 1The ingot 11 shown in (B) is, for example, composed of a cylindrical SiC single crystal, having a generally parallel upper surface (front) 11a and lower surface (back) 11b. The ingot 11 is generated by epitaxial growth with the c-axis 11c of the SiC single crystal slightly inclined relative to the perpendicular line 11d of the front surface 11a and the back surface 11b.

[0039] For example, the angle (offset angle) α between the c-axis 11c and the perpendicular 11d is 1° to 6° (representatively 4°). In addition, two planar portions showing the crystal orientation of the SiC single crystal are formed on the side of the ingot 11, namely the primary orientation plane 13 and the secondary orientation plane 15.

[0040] The primary orientation plane 13 is longer than the secondary orientation plane 15. In addition, the secondary orientation plane 15 is formed to be parallel to the intersection line that intersects the face parallel to the c-plane 11e of the SiC single crystal and the front face 11a or the back face 11b.

[0041] Furthermore, ingot 11 is doped with impurities such as nitrogen to impart conductivity. In addition, ingot 11 contains a flat region at the atomic level, namely facet region 11f, and a region other than facet region 11f, namely non-facet region 11g.

[0042] Furthermore, the impurity concentration in the small facet region 11f is higher than the impurity concentration in the non-small facet region 11g. Additionally, in Figure 1 In (B), the boundary between the facet region 11f and the non-facet region 11g is shown by a dashed line, but this boundary line is an imaginary line and does not exist in the actual ingot 11.

[0043] Furthermore, the material of ingot 11 is not limited to SiC, but can also be LiTaO3 (lithium tantalate: LT) or GaN (gallium nitride). Additionally, one or both of the primary orientation plane 13 and the secondary orientation plane 15 may not be provided on the side of ingot 11.

[0044] Figure 2 This is a perspective view schematically illustrating an example of a laser processing apparatus. Additionally, Figure 2 The X-axis and Y-axis directions shown are perpendicular to each other on the horizontal plane. In addition, the Z-axis direction is perpendicular to the X-axis and Y-axis directions (vertical direction).

[0045] Figure 2 The laser processing apparatus 2 shown has a base 4 that supports all its components. A horizontal moving mechanism 6 is disposed on the upper surface of the base 4. The horizontal moving mechanism 6 has a pair of Y-axis guide rails 8 that are fixed to the upper surface of the base 4 and extend along the Y-axis direction.

[0046] A Y-axis moving plate 10 is connected to the upper part of a pair of Y-axis guide rails 8 in a manner that allows it to slide along the pair of Y-axis guide rails 8. In addition, a lead screw 12 extending along the Y-axis direction is arranged between the pair of Y-axis guide rails 8. A motor 14 for rotating the lead screw 12 is connected to one end of the lead screw 12.

[0047] A ball screw is formed by providing a nut portion (not shown) on the surface of the lead screw shaft 12 with a helical groove. The nut portion houses the balls that roll on the surface of the rotating lead screw shaft 12. That is, when the lead screw shaft 12 rotates, the balls circulate in the nut portion, and the nut portion moves along the Y-axis direction.

[0048] Furthermore, the nut is fixed to the lower surface of the Y-axis moving plate 10. Therefore, if the lead screw 12 is rotated by the motor 14, the Y-axis moving plate 10 and the nut move together along the Y-axis.

[0049] A pair of X-axis guide rails 16 extending along the X-axis direction are fixed on the upper surface of the Y-axis moving plate 10. An X-axis moving plate 18 is connected to the upper part of the pair of X-axis guide rails 16 in a manner that allows it to slide along the pair of X-axis guide rails 16.

[0050] Additionally, a lead screw 20 extending along the X-axis direction is disposed between a pair of X-axis guide rails 16. A motor 22 for rotating the lead screw 20 is connected to one end of the lead screw 20.

[0051] A ball screw is formed by providing a nut portion (not shown) on the surface of the lead screw shaft 20 with a helical groove. The nut portion houses the balls that roll on the surface of the rotating lead screw shaft 20. That is, when the lead screw shaft 20 rotates, the balls circulate within the nut portion, and the nut portion moves along the X-axis.

[0052] Furthermore, the nut is fixed to the lower surface of the X-axis moving plate 18. Therefore, if the lead screw 20 is rotated by the motor 22, the X-axis moving plate 18 and the nut move together along the X-axis direction.

[0053] A cylindrical worktable base 24 is disposed on the upper surface of the X-axis moving plate 18. In addition, a chuck worktable (holding unit) 26 for holding the spindle 11 is disposed on the upper part of the worktable base 24.

[0054] A rotary drive source, such as an electric motor (not shown), is connected to the lower part of the worktable base 24. The chuck worktable 26 rotates about a rotation axis that is approximately parallel to the Z-axis direction by the force generated from this rotary drive source.

[0055] Furthermore, the worktable base 24 and the chuck worktable 26 move in the X-axis and Y-axis directions via the aforementioned horizontal moving mechanism 6. A portion of the upper surface of the chuck worktable 26 is formed, for example, from a porous material, and functions as a holding surface 26a for holding the spindle 11.

[0056] The holding surface 26a is approximately parallel to the X-axis and Y-axis directions. Furthermore, the holding surface 26a is connected to a suction source (not shown) such as a vacuum pump via a flow path (not shown) provided inside the chuck stage 26. When this suction source operates, a negative pressure is generated on the holding surface 26a. This allows, for example, the spindle 11 placed on the holding surface 26a on the back side 11b to be suctioned and held.

[0057] A support structure 30 with a side surface approximately parallel to the Y-axis direction is provided on one side of the base 4. A vertical moving mechanism 32 is arranged on the side surface of the support structure 30. The vertical moving mechanism 32 has a pair of Z-axis guide rails 34 fixed to the side surface of the support structure 30 and extending along the Z-axis direction.

[0058] A Z-axis moving plate 36 is connected to the side of a pair of Z-axis guide rails 34 away from the support structure 30 in a manner that allows it to slide along the pair of Z-axis guide rails 34. Additionally, a lead screw (not shown) extending along the Z-axis direction is disposed between the pair of Z-axis guide rails 34. A motor 38 for rotating the lead screw is connected to one end of this lead screw.

[0059] A ball screw is formed by providing a nut portion (not shown) on the surface of the lead screw shaft with helical grooves. The nut portion houses the balls that roll on the surface of the rotating lead screw shaft. That is, when the lead screw shaft rotates, the balls circulate within the nut portion, and the nut portion moves along the Z-axis.

[0060] Furthermore, the nut is fixed to the side of the Z-axis moving plate 36 near the support structure 30. Therefore, if the lead screw shaft is rotated by the motor 38, the Z-axis moving plate 36 and the nut move together along the Z-axis direction.

[0061] A support member 40 is fixed to the side of the Z-axis moving plate 36 away from the support structure 30. The support member 40 supports a portion of the laser beam irradiation unit 42. Figure 3 This diagram schematically illustrates the travel of the laser beam L inside the laser processing apparatus 2. Additionally, in Figure 3 In the diagram, a portion of the constituent elements of the laser beam irradiation unit 42 are shown in a functional block diagram.

[0062] like Figure 2 and Figure 3As shown, the laser beam irradiation unit 42 includes, for example, a laser oscillator 44 fixed to the base 4; a cylindrical housing 46 supported on the support member 40 and longer in the Y-axis direction; and an irradiation head 48 disposed at one end of the housing 46 (the other end in the Y-axis direction).

[0063] The laser oscillator 44 has a laser medium such as Nd:YAG suitable for laser oscillation, and generates a laser beam L with a wavelength (e.g., 1064 nm) that passes through the ingot 11 and is emitted toward the housing 46. In addition, the laser oscillation performed in the laser oscillator 44 can be either continuous wave (CW) oscillation or pulsed oscillation.

[0064] The housing 46 will form part of the optical system constituting the laser beam irradiation unit 42, for example... Figure 3 The reflectors 46a and 46b shown are used to house the laser beam L emitted from the laser oscillator 44 and guide it toward the irradiation head 48.

[0065] The irradiation head 48 houses another part of the optical system constituting the laser beam irradiation unit 42, such as a reflector 48a and a focusing lens 48b. Furthermore, the laser beam L guided from the housing 46 has its path changed downward by the reflector 48a, and is focused at a predetermined height on the chuck table 26 side by the focusing lens 48b.

[0066] like Figure 2 As shown, a fluorescence detection unit 50 is arranged adjacent to the irradiation head 48 in the X-axis direction. Figure 4 This is a schematic diagram illustrating one example of the fluorescence detection unit 50. Additionally, in Figure 4 In the diagram, a portion of the constituent elements of the fluorescence detection unit 50 are shown in a functional block diagram.

[0067] The fluorescence detection unit 50 has an excitation light source 52. The excitation light source 52 has, for example, a GaN-based light-emitting element, and illuminates an excitation light A of a wavelength (e.g., 365 nm) that is absorbed by the ingot 11 through a side-facing reflector 54. Furthermore, the excitation light A reflected by the reflector 54 is focused by a lower condenser lens 56.

[0068] Additionally, the fluorescence detection unit 50 has an annular elliptical mirror 58, which has a reflective surface 58a on its inner side. Furthermore, in Figure 4 The cross-section of the elliptical mirror 58 is shown in the figure. The reflecting surface 58a is equivalent to a part of the surface of an ellipse obtained by rotating an ellipse 58b, which has a major axis extending in the vertical direction and a minor axis extending in the horizontal direction, about the major axis.

[0069] The elliptical mirror 58 has two focal points F1 and F2, which converge light generated from one of them (e.g., focal point F1) to the other (e.g., focal point F2). Additionally, the condenser lens 56 is designed such that its focal point is approximately the same as focal point F1. That is, the excitation light A converges at focal point F1.

[0070] Furthermore, the fluorescence detection unit 50 includes a light-receiving section 60. The light-receiving section 60 may be, for example, a photomultiplier tube that outputs an electrical signal indicating the number of photons in light received at wavelengths of 900 nm or less. Alternatively, the light-receiving section 60 may be a photomultiplier tube that outputs an electrical signal indicating the number of photons in light received at wavelengths of 1200 nm or 1500 nm or less. Additionally, the light-receiving section 60 is designed such that the center of the light-receiving surface 60a coincides with the focal point F2 of the elliptical mirror 58.

[0071] Furthermore, in the fluorescence detection unit 50, the light generated at focal point F1 and reflected by the elliptical mirror 58 passes through the filter 62 and is directed toward focal point F2. That is, the filter 62 is disposed in the optical path between focal points F1 and F2 of the elliptical mirror 58. The filter 62 is, for example, an IR filter that allows light with wavelengths of 750 nm or higher to pass through while blocking light with wavelengths less than 750 nm.

[0072] In addition, the fluorescence detection unit 50 is fixed to the housing 46 of the laser beam irradiation unit 42. Therefore, when the vertical movement mechanism 32 is activated, the housing 46 of the laser beam irradiation unit 42, the irradiation head 48, and the fluorescence detection unit 50 move in the Z-axis direction.

[0073] Additionally, the upper part of base 4 is covered by a cover (not shown) that houses the various components. On one side of this cover... Figure 2 The configuration shown includes a touch panel 64. The touch panel 64 is composed of an input device such as a capacitive touch sensor or a resistive film touch sensor, and a display device such as a liquid crystal display or an organic EL (Electroluminescence) display.

[0074] The operation of each component of the laser processing device 2 described above is controlled by a control unit built into the laser processing device 2. Figure 5 This is a functional block diagram that schematically illustrates an example of such a control unit. Figure 5 The control unit 66 shown includes, for example, a processing unit 68 that generates various signals to cause the constituent elements to operate; and a storage unit 70 that stores various information (data and programs, etc.) used in the processing unit.

[0075] The functions of the processing unit 68 are specifically implemented by a CPU (Central Processing Unit) or the like, which reads and executes programs stored in the storage unit 70. Furthermore, the functions of the storage unit 70 are specifically implemented by at least one of semiconductor memories such as DRAM (Dynamic Random Access Memory), SRAM (Static Random Access Memory), and NAND flash memory, as well as magnetic storage devices such as HDD (Hard Disk Drive).

[0076] The processing unit 68 includes an irradiation condition setting unit 72, which sets the irradiation conditions for the laser beam L irradiated from the laser beam irradiation unit 42 for the ingot 11, which is attracted and held on the holding surface 26a of the chuck stage 26 on the back side 11b side. For example, the irradiation condition setting unit 72 irradiates the excitation light A from the excitation light source 52 when the focal point F1 coincides with any one of the multiple coordinates of multiple regions included on the coordinate plane parallel to the holding surface 26a.

[0077] At this time, the light-receiving part 60 of the fluorescence detection unit 50 receives the fluorescence B generated at the focal point F1 and generates an electrical signal indicating the number of photons of the fluorescence B. Furthermore, the irradiation condition setting unit 72 associates the coordinates consistent with the focal point F1 with the number of photons of the fluorescence B detected by the fluorescence detection unit 50 when the excitation light A is irradiated onto the area of ​​the front surface 11a of the ingot 11 represented by the coordinates, and stores it in the storage unit 70.

[0078] Similarly, the irradiation condition setting unit 72 irradiates the excitation light A from the excitation light source 52 with the focus F1 aligned with the remaining coordinates among the plurality of coordinates. As a result, an electrical signal indicating the number of photons of fluorescence B is generated in the same number as the remaining number of coordinates. Furthermore, the irradiation condition setting unit 72 associates the remaining coordinates among the plurality of coordinates with the number of photons of fluorescence B detected by the fluorescence detection unit 50 when the excitation light A is irradiated to the remaining regions among the plurality of regions of the front surface 11a of the ingot 11 represented by the plurality of coordinates, and stores this association in the storage unit 70.

[0079] Figure 6 This diagram schematically illustrates an example of multiple coordinates stored in the storage unit 70. Additionally, Table 1 schematically illustrates an example of the number of photons (count per second: counts per second) of fluorescence B detected by the fluorescence detection unit 50 when excitation light A is irradiated onto multiple regions of the front surface 11a of the ingot 11 represented by these multiple coordinates.

[0080] Table 1

[0081] coordinate Number of photons (cps) x1, y1 5000 x2, y1 5000 x3, y1 4000 x4, y1 2500 x5, y1 1000 x6, y1 3000

[0082] That is, in the storage unit 70, for example, six coordinates (x1, y1), (x2, y1), (x3, y1), (x4, y1), (x5, y1), (x6, y1) are associated with six photon counts (5000cps), (5000cps), (4000cps), (2500cps), (1000cps), and (3000cps) respectively and stored.

[0083] Furthermore, the storage unit 70 pre-stores laser beam irradiation conditions for multiple regions of the front surface 11a of the ingot 11, represented by multiple coordinates, based on the number of photons of fluorescence B detected by the fluorescence detection unit 50. The irradiation condition setting unit 72 sets the laser beam L irradiation conditions for each region of the multiple regions of the front surface 11a of the ingot 11, represented by multiple coordinates, based on the irradiation conditions of the laser beam L corresponding to the number of photons of fluorescence B as specified in the storage unit 70.

[0084] Here, the irradiation conditions of the laser beam L, which are set for multiple regions of the front surface 11a of the ingot 11 represented by multiple coordinates, based on the number of photons of fluorescence B stored in the storage unit 70, will be explained. First, regarding the number of photons of fluorescence B generated by irradiating the ingot 11 with excitation light A, the higher the concentration of impurities (such as nitrogen) doped in the ingot 11, the fewer the number of photons of fluorescence B. Furthermore, the higher the impurity concentration in the ingot 11, the higher the refractive index and the higher the energy absorption rate.

[0085] Therefore, when a laser beam L of the wavelength transmitted through the ingot 11 is irradiated from the front side 11a onto an ingot 11 in regions with different impurity concentrations under the same irradiation conditions, the region with higher impurity concentration forms a stripping layer deeper than the front side 11a. In other words, the region with higher impurity concentration has a deeper focal point of the laser beam L than the front side 11a.

[0086] Therefore, in order to form a peeling layer with a uniform depth from the front face 11a in the ingot 11 where there are regions with different impurity concentrations, it is necessary to set the irradiation conditions of the laser beam L according to the impurity concentration.

[0087] Examples of the illumination conditions for such a laser beam L include the output of the laser beam L and the height of the focusing lens 48b that converges the laser beam L. Furthermore, when the laser beam L is a pulsed laser beam (where the laser oscillator 44 performs pulsed oscillations), the overlap rate of the laser beam L can also be included in the illumination conditions for the laser beam L.

[0088] For example, the irradiation condition setting unit 72 states that the more photons of fluorescence B, the more linear the output of laser beam L becomes (see reference). Figure 7(A) or stepwise (refer to) Figure 7 The irradiation conditions of the laser beam L are set by reducing (B)). Additionally, Figure 7 (A) and Figure 7 (B) are graphs schematically showing the correspondence between the number of photons of fluorescence B stored in the storage unit 70 and the output of the laser beam L. In this case, it is possible to reduce the deviation of the depth of the peeling layer formed in the ingot 11 in regions with different impurity concentrations from the front surface 11a.

[0089] Additionally, the irradiation condition setting unit 72 can also adjust the position (height) of the focusing lens 48b of the focusing laser beam L to be more linear as the number of photons of fluorescence B detected by the fluorescence detection unit 50 increases (see reference). Figure 7 (C) or stepwise (refer to) Figure 7 The irradiation conditions of the laser beam L are set by increasing (D). Additionally, Figure 7 (C) and Figure 7 (D) are graphs schematically showing the correspondence between the number of photons of fluorescence B stored in the storage unit 70 and the height of the condenser lens 48b. In this case, the deviation of the depth of the peeling layer formed in the ingot 11 in areas with different impurity concentrations from the front surface 11a can be reduced.

[0090] Furthermore, the irradiation condition setting unit 72 can also be configured such that the more photons of fluorescence B detected by the fluorescence detection unit 50, the more linear the overlap rate of the laser beam L, which serves as the pulsed laser beam, becomes (see reference). Figure 7 (E) or stepwise (refer to) Figure 7 The irradiation conditions of the laser beam L are set by reducing (F). Additionally, Figure 7 (E) and Figure 7 (F) are graphs schematically showing the correspondence between the number of photons of fluorescence B stored in the storage unit 70 and the overlap rate of the laser beam L. In this case, it is possible to reduce the deviation of the depth of the peeling layer formed in the ingot 11 in regions with different impurity concentrations from the front surface 11a.

[0091] In the laser processing apparatus 2, the irradiation conditions of the laser beam L for each of the multiple regions can be set according to the number of photons of fluorescence B generated when the excitation light A is irradiated on the multiple regions included in the upper surface (front) 11a of the ingot 11. Here, the number of photons of fluorescence B depends on the concentration of impurities doped in the ingot 11.

[0092] Therefore, in the laser processing apparatus 2, even when the ingot 11 contains regions with different impurity concentrations, a release layer can be formed at a uniform depth from the upper surface (front side) 11a of the ingot 11. This reduces cutting losses when cutting wafers from the ingot 11.

[0093] Figure 8 This is a flowchart schematically illustrating an example of a laser processing method for forming a release layer in ingot 11 in order to cut out a wafer. In this method, ingot 11 is first held (holding step: S1).

[0094] For example, the spindle 11 is placed on the holding surface 26a of the chuck table 26 with its front side 11a facing upwards. Then, the attraction source connected to the holding surface 26a is activated. This attracts and holds the spindle 11, which is placed on the holding surface 26a with its back side 11b facing upwards.

[0095] Next, an excitation light A of a specified wavelength (e.g., 365 nm) is irradiated from above the ingot 11, and the fluorescence B generated from the ingot 11 is detected (fluorescence detection step: S2). Figure 9 This is a perspective view schematically illustrating an example of the fluorescence detection step (S2).

[0096] In the fluorescence detection step (S2), the excitation light A is irradiated onto the ingot 11 with the focal point F1 of the elliptical mirror 58 of the fluorescence detection unit 50, i.e., the height of the focusing point of the excitation light A, focused on the front surface 11a of the ingot 11. At this time, the focusing point of the excitation light A and the ingot 11 are moved relative to each other in the horizontal direction in such a way that the excitation light A is irradiated onto multiple regions of the front surface 11a of the ingot 11, represented by multiple coordinates on a coordinate plane parallel to the holding surface 26a.

[0097] For example, firstly, excitation light A is irradiated onto the area near the outer periphery of the front surface 11a of the spindle 11. Then, while irradiating the spindle 11 with excitation light A, the rotary drive source is operated in such a way that the chuck table 26 is rotated, and the motor 14 connected to the lead screw shaft 12 extending along the Y-axis is operated in such a way that the center of the holding surface 26a is slowly moved closer to the focal point of the excitation light A.

[0098] Therefore, according to Figure 9 The spiral trajectory shown by the dashed line irradiates the spindle 11 with excitation light A from the fluorescence detection unit 50. Furthermore, the light-receiving part 60 of the fluorescence detection unit 50 detects the fluorescence B generated from multiple regions included in the front surface 11a of the spindle 11. Additionally, the irradiation with excitation light A can be performed while rotating the rotary drive source to rotate the chuck table 26 and operating the motor 22 connected to the lead screw 20 extending along the X-axis.

[0099] Next, the multiple coordinates and the number of photons of fluorescence B are associated and stored (storage step: S3). Specifically, the storage unit 70 of the control unit 66 associates each of the multiple coordinates representing the multiple regions included in the front surface 11a of the ingot 11 with the number of photons of fluorescence B detected when the excitation light A is irradiated to the multiple regions respectively in the fluorescence detection step (S2) and stores them.

[0100] Next, while changing the irradiation conditions of the laser beam L on multiple regions of the front side 11a of the ingot 11 represented by multiple coordinates according to the photon number of fluorescence B, the ingot 11 is irradiated with the laser beam L to form a peeling layer (laser beam irradiation step: S4). Figure 10 This is a perspective view schematically illustrating an example of the laser beam irradiation step (S4).

[0101] In the laser beam irradiation step (S4), the focal point of the laser beam L with a wavelength (e.g., 1064 nm) that passes through the ingot 11 is positioned at a depth equivalent to the thickness of the wafer to be cut from the front surface 11a of the ingot 11 and then irradiated.

[0102] For example, firstly, a laser beam L is irradiated at one end of the front face 11a of the spindle 11 in the X-axis direction. While irradiating the spindle 11 with the laser beam L, the chuck table 26 is moved along the X-axis direction, and the motor 22 included in the horizontal moving mechanism 6 is activated until the focusing point of the laser beam L reaches the other end of the front face 11a of the spindle 11 in the X-axis direction.

[0103] Furthermore, the motor 14 included in the horizontal moving mechanism 6 is activated in a manner that moves the chuck table 26 along the Y-axis, and then the same operation is repeated. Thus, according to Figure 10 The dashed lines indicate multiple straight-line trajectories from the irradiation head 48 irradiating the ingot 11 with a laser beam L. As a result, a stripping layer is formed in the ingot 11.

[0104] Here, the irradiation of the laser beam L is performed on multiple regions of the front surface 11a of the ingot 11, represented by multiple coordinates stored in the storage unit 70 during the fluorescence detection step (S2). Furthermore, the irradiation conditions of the laser beam L for each of these multiple regions are set according to the number of photons of fluorescence B stored in association with each of the multiple coordinates. That is, the irradiation of the laser beam L is performed while changing the conditions according to the number of photons of fluorescence B stored in association with each of the multiple coordinates during the storage step (S3).

[0105] exist Figure 8In the laser processing method shown, the irradiation conditions of the laser beam L for each of the multiple regions are set based on the number of photons of fluorescence B generated when the excitation light A is irradiated onto the multiple regions included on the upper surface (front) 11a of the ingot 11. Here, the number of photons of fluorescence B depends on the concentration of impurities doped in the ingot 11.

[0106] Therefore, in this method, even when the ingot 11 contains regions with different impurity concentrations, a release layer can be formed at a uniform depth from the upper surface (front side) 11a of the ingot 11. This reduces cutting losses when dicing wafers from the ingot 11.

[0107] in addition, Figure 8 The laser processing method shown is one aspect of the present invention, and the laser processing method of the present invention is not limited to this. Figure 8 The method shown. For example, in the laser processing method of the present invention, the irradiation conditions of the laser beam L, which are set for multiple regions of the front surface 11a of the ingot 11 represented by multiple coordinates according to the number of photons of the fluorescence B, can be pre-stored in the storage unit 70 (see reference 1) before the holding step (S1). Figure 11 ).

[0108] In other words, the laser processing method of the present invention may further include an irradiation condition storage step (S5), in which irradiation conditions of the laser beam L are pre-stored for multiple regions of the front surface 11a of the ingot 11 represented by multiple coordinates, based on the number of photons of fluorescence B. In this case, in the laser beam irradiation step (S4), the irradiation conditions of the laser beam L for each region of the multiple regions of the front surface 11a of the ingot 11 represented by multiple coordinates are set with reference to the irradiation conditions of the laser beam L corresponding to the number of photons of fluorescence B stored in the irradiation condition storage step (S5).

[0109] In addition, the structure and method of the above-described embodiments can be appropriately modified and implemented as long as they do not depart from the scope of the present invention.

Claims

1. A laser processing apparatus for forming a release layer in a spindle for cutting out wafers, characterized in that, The laser processing device includes: A holding unit having a holding surface for holding the ingot; A fluorescence detection unit irradiates the ingot with excitation light of a specified wavelength from above and detects the fluorescence generated from the ingot; The laser beam irradiation unit focuses a laser beam of wavelength that passes through the ingot at a depth from the upper surface of the ingot equivalent to the thickness of the wafer to be cut from the ingot, thereby forming a release layer. A horizontal moving mechanism that moves the holding unit and the laser beam irradiation unit relative to each other in a direction parallel to the holding surface; and Control unit The control unit has: The storage unit stores each of the multiple coordinates representing multiple regions contained on the upper surface of the ingot on a coordinate plane parallel to the holding surface, in association with the number of photons of fluorescence detected by the fluorescence detection unit when each of the multiple regions is irradiated with the excitation light. as well as The irradiation condition setting unit sets the irradiation conditions of the laser beam for each region in the plurality of regions represented by the plurality of coordinates based on the number of photons of the fluorescence stored in association with each of the plurality of coordinates.

2. The laser processing apparatus according to claim 1, characterized in that, The storage unit pre-stores the irradiation conditions of the laser beam for each region in the plurality of regions represented by the plurality of coordinates, based on the number of photons of the fluorescence detected by the fluorescence detection unit. The irradiation condition setting unit sets the irradiation conditions of the laser beam for each of the multiple regions represented by the multiple coordinates by referring to the irradiation conditions of the laser beam corresponding to the number of photons of the fluorescence stored in the storage unit.

3. The laser processing apparatus according to claim 1 or 2, characterized in that, The irradiation condition setting unit sets the irradiation conditions of the laser beam by changing at least one of the following methods: the number of photons of the fluorescence stored in association with each of the plurality of coordinates; the output of the laser beam; the height of the focusing lens that converges the laser beam; and the overlap rate of the laser beam, based on the number of photons of the fluorescence stored in association with each of the plurality of coordinates.

4. A laser processing method for forming a release layer in an ingot for cutting out wafers, characterized in that, This laser processing method includes the following steps: The holding step involves holding the ingot in place; The fluorescence detection step involves irradiating the ingot with excitation light of a specified wavelength from above and detecting the fluorescence generated from the ingot after the holding step. The storage step involves associating each coordinate among multiple coordinates representing multiple regions encompassed by the upper surface of the ingot with the number of photons of fluorescence detected when each of these regions is irradiated with excitation light of the specified wavelength in the fluorescence detection step; and storing the data. In the laser beam irradiation step, with the focal point of a laser beam of wavelength that transmits through the ingot positioned at a depth equivalent to the thickness of the wafer to be cut from the ingot at the upper surface of the ingot, a release layer is formed in the ingot by moving the focal point relative to the ingot. In this laser beam irradiation step, The release layer is formed in the ingot by varying the irradiation conditions of the laser beam in each of the plurality of regions represented by the plurality of coordinates, based on the number of photons of the fluorescence stored in association with each of the plurality of coordinates during the storage step.

5. The laser processing method according to claim 4, characterized in that, The laser processing method further includes the following irradiation condition storage step: pre-storing the irradiation conditions of the laser beam for each of the multiple regions represented by multiple coordinates, based on the number of photons of the fluorescence generated from the ingot by irradiating it with excitation light of the specified wavelength. In the laser beam irradiation step, the irradiation conditions of the laser beam corresponding to the number of photons of the fluorescence are set by referring to the irradiation conditions of the laser beam stored in the irradiation condition storage step.

6. The laser processing method according to claim 4 or 5, characterized in that, As the irradiation conditions for the laser beam, at least one of the following is set: the output of the laser beam, the height of the focusing lens that converges the laser beam, and the overlap rate of the laser beam, based on the number of photons of the fluorescence stored in association with each of the plurality of coordinates.

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