Laser processing device, laser processing method, program, and manufacturing method of wafer

Abstract

To improve through-put of laser processing compared to conventional methods when laser processing is performed in a state that laser processing conditions may be adjusted according to an impurity concentration of each area of an exposed surface of a workpiece.SOLUTION: A laser processing device includes a holding unit, a laser beam radiation unit, a processing feeding unit, a first resistance measurement device having a first measurement head, and a controller. When a laser beam is radiated to a workpiece with the holding unit and a collector moved relative to each other in a processing feeding direction, the controller measures electric resistance or electric resistivity of an area to be measured (measurement area) of the workpiece with the first measurement head and maintains or changes, according to the electric resistance and the electric resistivity of the measurement area, processing conditions of the workpiece by the laser beam radiated to the measurement area.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laser processing device that processes a workpiece with a laser beam, a laser processing method that processes a workpiece with a laser beam, and a program for causing a computer installed in the laser processing device to execute a laser beam irradiation process. [Background technology]

[0002] A technique has been proposed in which a pulsed laser beam having a wavelength that can pass through a SiC (silicon carbide) ingot is used to form a separation layer with reduced mechanical strength at a predetermined depth from one side of the SiC ingot, and SiC wafers are separated from the SiC ingot using this separation layer as a starting point (see, for example, Patent Document 1).

[0003] Compound semiconductors such as SiC are sometimes doped with impurities to impart conductivity. For example, to make an SiC ingot n-type, the ingot is doped with donors such as nitrogen (N) or phosphorus (P), and to make an SiC ingot p-type, the ingot is doped with acceptors such as boron (B) or aluminum (Al).

[0004] Incidentally, there is variation in electrical resistivity among multiple SiC ingots. In n-type SiC ingots, the higher the nitrogen impurity concentration, the lower the electrical resistivity, and the higher the nitrogen impurity concentration, the higher the laser beam absorption rate.

[0005] Therefore, when the focal point of a laser beam passing through a SiC ingot is positioned within the SiC ingot and the above-mentioned separation layer is formed by multiphoton absorption occurring at the focal point, if the same laser processing conditions are always applied to each of multiple SiC ingots, the separation layer may not be formed properly.

[0006] Therefore, it has been proposed to measure the electrical resistivity of the SiC ingot in advance using a resistance measurement means before laser processing, and then apply laser processing conditions adjusted according to the electrical resistivity of the SiC ingot (see, for example, Patent Document 2). However, when the SiC ingot undergoes crystal growth, the distribution of impurity concentration within the SiC ingot is not necessarily uniform.

[0007] The SiC single crystal, for example, is mainly aligned along the c-axis (i.e., <0001> This is achieved by growing a crystal along the {0001} facet, but during crystal growth, the amount of nitrogen incorporated tends to be higher in the facet corresponding to {0001} than in other regions.

[0008] In this specification, a region where crystal growth has progressed on a facet corresponding to {0001} is referred to as a facet region, and a region of the SiC ingot other than the facet region is referred to as a non-facet region.

[0009] In a SiC ingot, the impurity concentration in the facet region is higher than the impurity concentration in other regions. In one example, the facet region with a relatively high impurity concentration is formed in the center of the SiC ingot, and the non-facet region with a relatively low impurity concentration is formed in the outer periphery of the SiC ingot so as to surround the facet region.

[0010] Since the facet region has a higher impurity concentration than the non-facet region, the facet region has a higher absorption rate of the laser beam than the non-facet region, which means that the facet region has a lower transmittance of the laser beam through the SiC ingot than the non-facet region.

[0011] Therefore, when laser processing is performed on both the facet region and the non-facet region under predetermined laser processing conditions, for example, good laser processing is achieved in the non-facet region, but in the facet region, there is a risk of processing defects occurring because the laser beam energy per unit area does not reach the processing threshold.

[0012] Incidentally, there is a negative correlation coefficient between the impurity concentration in a SiC ingot and the number of fluorescent photons emitted by the SiC ingot after absorbing irradiated excitation light. Specifically, the higher the impurity concentration, the lower the number of fluorescent photons. Therefore, it has been proposed to change the laser processing conditions based on the number of fluorescent photons in each of multiple regions on the exposed surface of a single SiC ingot (see, for example, Patent Document 3).

[0013] However, when a fluorescence detection process is performed before the laser processing process, in which excitation light is irradiated onto the entire exposed surface of the workpiece, such as a SiC ingot, to examine the distribution of fluorescence generation, there is a problem that the number of steps required for the fluorescence detection process increases and throughput decreases compared to normal laser processing that does not involve the fluorescence detection process.

[0014] Even when the resistance measurement process described above is performed using a resistance measurement means to measure the electrical resistivity of the entire exposed surface of the workpiece, the labor required for the resistance measurement process increases and throughput decreases compared to normal laser processing that does not involve the resistance measurement process. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-111143 [Patent Document 2] Patent Publication No. 2021-106186 [Patent Document 3] Japanese Patent Publication No. 2022-127088 Summary of the Invention [Problem to be solved by the invention]

[0016] The present invention has been made in consideration of the above problems, and aims to improve the throughput of laser processing compared to conventional methods when performing laser processing while making it possible to adjust the laser processing conditions according to the impurity concentration in each region of the exposed surface of the workpiece. [Means for solving the problem]

[0017] According to one aspect of the present invention, a laser processing apparatus for processing a workpiece with a laser beam includes a laser beam irradiation unit including a holding unit for holding the workpiece, a laser oscillator for emitting the laser beam, and a condenser having a condensing lens for condensing the laser beam emitted from the laser oscillator, a processing feed unit having a first motor for relatively moving the holding unit and the condenser along a processing feed direction, and a first measuring head whose position relative to the condenser is fixed and which can be moved together with the condenser relative to the holding unit along the processing feed direction by the processing feed unit, and a controller having a processor and a memory and controlling the laser beam irradiating unit and the processing feed unit, wherein the controller measures the electrical resistance or electrical resistivity of a measurement area of ​​the workpiece using the first measuring head when the laser beam is irradiated onto the workpiece while moving the holding unit and the condenser relatively along the processing feed direction, and maintains or changes the processing conditions of the workpiece using the laser beam irradiated onto the measurement area in accordance with the electrical resistance or electrical resistivity of the measurement area.

[0018] Preferably, the laser processing apparatus further includes a second resistance measuring device that has a second measuring head whose relative position to the collector and the first measuring head is fixed and which is movable together with the collector relative to the holding unit along the processing feed direction by the processing feed unit, and measures the electrical resistance or electrical resistivity of the workpiece via the second measuring head, and the first measuring head and the second measuring head are arranged to sandwich the collector in the processing feed direction.

[0019] Preferably, when the laser beam is irradiated onto the workpiece while the holding unit and the collector are moved relatively along the processing feed direction, the controller measures the electrical resistance or electrical resistivity using one of the first measuring head and the second measuring head which is ahead of the collector in the processing feed direction.

[0020] Preferably, the laser processing apparatus further includes an indexing feed unit having a second motor for moving the holding unit and the collector relatively along an indexing feed direction that intersects with the processing feed direction, and when processing the workpiece with the laser beam, the controller moves the holding unit and the collector relatively so as to sequentially repeat a first processing feed for moving the holding unit and the collector relatively so that the first measuring head leads the collector in the processing feed direction, a first indexing feed for moving the holding unit and the collector relatively in the indexing feed direction, a second processing feed for moving the holding unit and the collector relatively so that the second measuring head leads the collector in the processing feed direction, and a second indexing feed for moving the holding unit and the collector relatively in the indexing feed direction.

[0021] According to another aspect of the present invention, there is provided a laser processing method for processing a workpiece with a laser beam, comprising: a holding step of holding the workpiece with a holding unit; and a laser beam irradiation step of measuring the electrical resistance or electrical resistivity of a measurement area of ​​the workpiece using a first measuring head whose position relative to the condenser is fixed when irradiating the laser beam onto the workpiece while moving the holding unit and a condenser relatively along the processing feed direction, and maintaining or changing the processing conditions of the workpiece using the laser beam irradiated onto the measurement area in accordance with the electrical resistance or electrical resistivity of the measurement area.

[0022] According to yet another aspect of the present invention, there is provided a program for causing a computer mounted on a laser processing apparatus to execute a laser beam irradiation step in which, when a laser beam is irradiated onto a workpiece while a holding unit holding the workpiece and a condenser are moved relative to each other along the processing feed direction, the first measuring head has a fixed position relative to the condenser to measure the electrical resistance or electrical resistivity of a measurement area of ​​the workpiece, and the processing conditions of the workpiece using the laser beam irradiated onto the measurement area are maintained or changed depending on the electrical resistance or electrical resistivity of the measurement area.

[0023] According to yet another aspect of the present invention, there is provided a laser processing apparatus for processing a workpiece with a laser beam, the apparatus comprising: a holding unit for holding the workpiece; a laser oscillator for emitting the laser beam; a laser beam irradiation unit including a condenser having a condenser lens for condensing the laser beam emitted from the laser oscillator; a processing feed unit having a first motor for relatively moving the holding unit and the condenser along a processing feed direction; a measuring head whose position relative to the condenser is fixed and which is movable together with the condenser relative to the holding unit along the processing feed direction by the processing feed unit; an excitation light source; and a controller having a processor and a memory, and controlling the laser beam irradiation unit and the processing feed unit, wherein the controller changes the processing conditions of the workpiece by the laser beam irradiated to the measurement area of ​​the workpiece in accordance with the number of photons of fluorescence from the measurement area of ​​the workpiece obtained using the measurement head when the laser beam is irradiated to the measurement area of ​​the workpiece while moving the holding unit and the condenser relatively along the processing feed direction. [Effects of the Invention]

[0024] In laser processing according to one embodiment of the present invention, when a laser beam is irradiated onto a workpiece, the electrical resistance or electrical resistivity of the measurement area of ​​the workpiece is measured using a first measuring head, and the processing conditions of the workpiece using the laser beam irradiated onto the measurement area are maintained or changed depending on the measured electrical resistance or electrical resistivity of the measurement area.

[0025] Therefore, measurement of the electrical resistance or electrical resistivity of the workpiece and laser processing of the workpiece according to the electrical resistance or electrical resistivity can be performed in parallel in time. In other words, in a single processing feed operation, it is possible to investigate the laser processing conditions and perform laser processing that reflects the investigation results.

[0026] Therefore, compared to starting laser processing after measuring the electrical resistance or electrical resistivity in the region corresponding to the movement locus of the focal point of the laser beam on the exposed surface of the workpiece, the number of steps can be reduced, which means that the throughput of laser processing can be improved.

[0027] In another aspect of the laser processing of the present invention, when a laser beam is irradiated onto a workpiece, the processing conditions of the workpiece using the laser beam irradiated onto the measurement area are maintained or changed depending on the number of photons of fluorescence from the measurement area of ​​the workpiece obtained using the measurement head.

[0028] Therefore, measurement of the number of photons of fluorescence from the workpiece and laser processing of the workpiece according to the number of photons of fluorescence can be performed in parallel in time. In other words, in a single processing feed operation, it is possible to investigate the laser processing conditions and perform laser processing that reflects the investigation results.

[0029] Therefore, compared to starting laser processing after measuring the number of photons of fluorescence in an area corresponding to the movement locus of the focal point on the exposed surface of the workpiece, the number of steps can be reduced, which means that the throughput of laser processing can be improved. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 2 is a perspective view of the laser processing device. [Figure 2] FIG. 2(A) is a side view of the ingot, and FIG. 2(B) is a plan view of the ingot. [Figure 3] FIG. 2 is a schematic diagram of a laser beam irradiation unit. [Figure 4] FIG. 2 is a block diagram of a main part of the laser processing device. [Figure 5] FIG. 1 is a flow diagram of a laser processing method. [Figure 6] FIG. 1 is a plan view of an ingot showing a first processing feed, a first indexing feed, a second processing feed, and a second indexing feed. [Figure 7] Figure 7(A) is a schematic diagram showing the measurement of electrical resistivity and laser processing at time t1, Figure 7(B) is a schematic diagram showing the measurement of electrical resistivity and laser processing at time t2, and Figure 7(C) is a schematic diagram showing the measurement of electrical resistivity and laser processing at time t3. [Figure 8] 1 is a graph showing the correspondence relationship between electrical resistivity and pulse energy. [Figure 9] FIG. 10 is a block diagram showing a main part of a laser processing device according to a first modified example. [Figure 10] FIG. 10 is a block diagram showing a main part of a laser processing device according to a second embodiment. [Figure 11] FIG. 10 is a partial cross-sectional side view showing a first measuring head in a second embodiment. [Figure 12] Figure 12(A) is a plan view showing the positional relationship between the collector, first measurement head, and second measurement head in the second modified example, Figure 12(B) is a diagram showing which of the first measurement head and the second measurement head is used for measurement results that the controller stores, and Figure 12(C) is a diagram showing the movement range of the first measurement head in the above embodiment in comparison with the second modified example. DETAILED DESCRIPTION OF THE INVENTION

[0031] (First embodiment) An embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a perspective view of a laser processing apparatus 2. In Fig. 1, some of the components of the laser processing apparatus 2 are shown in functional blocks.

[0032] 1 are perpendicular to one another. The +X and -X directions are parallel to the X axis but in opposite directions to one another. Similarly, the +Y and -Y directions are parallel to the Y axis but in opposite directions to one another, and the +Z and -Z directions are parallel to the Z axis but in opposite directions to one another.

[0033] In this specification, the +X direction and the -X direction may be collectively referred to as the X-axis direction. Similarly, the +Y direction and the -Y direction may be collectively referred to as the Y-axis direction, and the +Z direction and the -Z direction may be collectively referred to as the Z-axis direction.

[0034] The X-axis is parallel to the machining feed direction (i.e., the +X direction and the -X direction), the Y-axis is parallel to the indexing feed direction (i.e., the +Y direction and the -Y direction), and the Z-axis is parallel to the vertical direction (i.e., the up-down direction).

[0035] The laser processing device 2 includes a base 4 that supports each of the components. The base 4 includes a rectangular parallelepiped flat plate portion 6 and a wall portion 8 that extends upward from one end of the flat plate portion 6. A disk-shaped chuck table (holding unit) 10 is provided above the flat plate portion 6.

[0036] The chuck table 10 has a disk-shaped frame. A disk-shaped recess is provided in the radial center of the frame. A porous plate having an outer diameter approximately the same as that of the recess is fixed in this recess. The upper surface of the frame and the upper surface of the porous plate are approximately flush with each other, forming a substantially flat holding surface 10a. The holding surface 10a is disposed approximately parallel to the XY plane.

[0037] The laser processing device 2 is provided with a vacuum generating device (not shown) such as a vacuum pump or an ejector. Negative pressure is transmitted from the vacuum generating device to the porous plate via a predetermined flow path (not shown). This negative pressure causes the ingot (workpiece) 11 to be sucked and held on the holding surface 10a.

[0038] Fig. 2(A) is a side view of the ingot 11, and Fig. 2(B) is a plan view of the ingot 11. The ingot 11 of this embodiment is a cylindrical SiC ingot, and has a diameter of 8 inches (approximately 200 mm) and a thickness of approximately 20 mm.

[0039] However, the material of the ingot 11 is not limited to SiC, and may be other materials such as GaN (gallium nitride), GaO (gallium oxide), LiTaO (lithium tantalate), etc. Furthermore, the shape of the ingot 11 is not limited to a cylindrical shape, and may be other shapes such as a flat plate shape, a rectangular parallelepiped shape, etc.

[0040] The ingot 11 has one substantially flat surface 11a and another surface 11b. As shown in Fig. 2(A), in the ingot 11, the c-axis 11c of the single crystal SiC is slightly tilted with respect to a perpendicular line 11d that is perpendicular to the one surface 11a and the other surface 11b.

[0041] In Fig. 2(A), the c-axis 11c is indicated by a two-dot chain line, and the perpendicular line 11d is indicated by a one-dot chain line. The c-axis 11c is perpendicular to the c-plane 11e. For ease of explanation, Fig. 2(A) shows one specific c-plane 11e. The angle α between the c-axis 11c and the perpendicular line 11d (i.e., the off angle) is 1° or more and 6° or less (typically 4°).

[0042] The ingot 11 has, on its outer peripheral side surface, a primary orientation flat 13 and a secondary orientation flat 15. The primary orientation flat 13 is longer than the secondary orientation flat 15. However, the orientation flat is not essential, and a notch may be provided instead of the orientation flat.

[0043] In this embodiment, the ingot 11 is doped with a donor such as nitrogen. The ingot 11 includes the facet region 11f and the non-facet region 11g, which is a region other than the facet region 11f. The impurity concentration in the facet region 11f is higher than the impurity concentration in the non-facet region 11g.

[0044] The facet region 11f of this embodiment is a columnar region formed along the c-axis 11c from one surface 11a to the other surface 11b. The non-facet region 11g is formed so as to surround the facet region 11f.

[0045] In addition, in Figure 2(B), for the sake of convenience of explanation, the boundary between the facet region 11f and the non-facet region 11g is shown, but in the actual ingot 11, such a boundary may not be visible with visible light.

[0046] Returning to Fig. 1, we will now explain other components of the laser processing apparatus 2. An indexing feed unit 12 that moves the chuck table 10 along the Y axis is provided below the chuck table 10. The indexing feed unit 12 has a pair of guide rails 14.

[0047] The pair of guide rails 14 are fixed to the upper surface of the flat plate portion 6 and are arranged substantially parallel to the Y axis. A moving table 16 is slidably attached to the pair of guide rails 14. A nut portion (not shown) is provided on the underside of the moving table 16.

[0048] A screw shaft 18, which is disposed substantially parallel to the Y-axis, is rotatably coupled to this nut portion via a plurality of balls (not shown). One end of the screw shaft 18 is connected to a motor (second motor) 20, such as a servo motor or a stepping motor.

[0049] When the screw shaft 18 is rotated by the motor 20, the moving table 16 moves along the Y axis. A processing feed unit 22 is provided on the upper surface of the moving table 16. The processing feed unit 22 has a pair of guide rails 24.

[0050] The pair of guide rails 24 are fixed to the upper surface of the moving table 16 and are arranged substantially parallel to the X-axis. A moving table 26 is slidably attached to the pair of guide rails 24. A nut portion (not shown) is provided on the lower surface of the moving table 26.

[0051] A screw shaft 28, which is disposed substantially parallel to the X-axis, is rotatably coupled to this nut portion via a plurality of balls (not shown). One end of the screw shaft 28 is connected to a motor (first motor) 30, such as a servo motor or a stepping motor.

[0052] When the screw shaft 28 is rotated by the motor 30, the moving table 26 moves along the X-axis. By adjusting the moving speed of the moving table 26, it is possible to adjust the interval between adjacent pulses (i.e., pulse pitch) in the X-axis direction when a pulsed laser beam L (see FIG. 3), which will be described later, is irradiated onto the ingot 11.

[0053] A cylindrical support base 32 is provided on the upper surface of the moving table 26. The above-mentioned chuck table 10 is provided on the top of the support base 32. A rotation drive source (not shown), such as a motor, is provided inside the support base 32.

[0054] The rotation axis of the chuck table 10 corresponds to or is connected to the output shaft of the rotary drive source. The longitudinal direction of the rotation axis of the chuck table 10 is disposed approximately parallel to the Z axis, and when the rotary drive source is operated, the chuck table 10 rotates around the rotation axis.

[0055] A beam-shaped support arm 8a is provided above the chuck table 10. A condenser 36 of a laser beam irradiation unit 34 is provided at the tip of the support arm 8a. The laser beam irradiation unit 34 has a laser oscillator 38 (see FIG. 3) fixed to the base 4.

[0056] Fig. 3 is a schematic diagram of the laser beam irradiation unit 34. Note that Fig. 3 shows some of the components of the laser beam irradiation unit 34 in functional blocks. The laser oscillator 38 has a laser medium. The laser medium is, for example, a crystal such as Nd:YAG.

[0057] By irradiating the laser medium with excitation light from a light source such as a flash lamp or a laser diode, the laser oscillator 38 emits a pulsed laser beam L having a wavelength that is transmitted through the ingot 11 (for example, 1064 nm).

[0058] The laser beam L emitted from the laser oscillator 38 is incident on the optical modulator 40. The optical modulator 40 can adjust the power (i.e., average output, peak power, etc.) of the laser beam L in accordance with an electrical signal input to the optical modulator 40, and also controls whether or not the laser beam L is irradiated onto the condenser 36.

[0059] The optical modulator 40 is, for example, an Acousto-Optic Modulator (AOM), an Electro-Optic Modulator (EOM), or a Liquid Crystal on Silicon-Spatial Light Modulator (LCOS-SLM).

[0060] The AOM, EOM, LCOS-SLM, etc. are controlled by electrical signals from the controller 60 described later, and therefore can operate with a higher response speed than an attenuator that has a half-wave plate and a polarizing beam splitter and physically rotates the half-wave plate relative to the polarizing beam splitter.

[0061] The repetition frequency of the laser beam L can also be controlled by controlling the operation of the AOM and EOM with the controller 60. By adjusting the repetition frequency of the laser beam L, the pulse pitch of the laser beam L in the X-axis direction can be adjusted when the moving table 26 is moved at a constant speed along the X-axis.

[0062] The pulse pitch of the laser beam L in the X-axis direction may be adjusted by adjusting either or both of the moving speed of the moving table 26 along the X-axis direction and the repetition frequency of the laser beam L.

[0063] The laser beam L that has passed through the optical modulator 40 proceeds to the condenser 36. A mirror 36a and a condenser lens 36b are provided inside the condenser 36. The laser beam L that has been reflected by the mirror 36a is condensed by the condenser lens 36b and then irradiated toward the holding surface 10a.

[0064] The condenser lens 36b is configured to be movable along the Z axis by a piezo actuator (not shown) having a piezo element. By moving the condenser lens 36b along the Z axis, the position of the focal point P (see FIG. 7(A)) of the laser beam L can be moved along the Z axis.

[0065] By moving the position of the focal point P along the Z axis, the power of the laser beam L irradiated onto the ingot 11 can be adjusted when forming a separation layer 11i (see Figure 7(A), etc.) at a predetermined depth within the ingot 11.

[0066] 1 again, a description will be given of other components of the laser processing apparatus 2. A first measuring head 44 constituting a first resistance measuring device 42 is fixed to the tip of the support arm 8a at a position adjacent to the condenser 36 in the −X direction.

[0067] That is, the spatial position of the first measuring head 44 is fixed relative to the condenser 36. However, the first measuring head 44 is configured to be movable relative to the chuck table 10 along the processing feed direction.

[0068] Specifically, when the processing feed unit 22 is used to move the chuck table 10 and the condenser 36 relative to each other along the processing feed direction, the first measuring head 44 moves relative to the chuck table 10 along the processing feed direction together with the condenser 36.

[0069] Furthermore, when the indexing feed unit 12 is used to move the chuck table 10 and the collector 36 relative to each other along the indexing feed direction, the first measuring head 44 moves relative to the chuck table 10 along the indexing feed direction together with the collector 36.

[0070] A second measurement head 54 constituting a second resistance measuring device 52 is fixed to the tip of the support arm 8a at a position adjacent to the condenser 36 in the +X direction. The spatial position of the second measurement head 54 relative to the condenser 36 is also fixed.

[0071] The first measurement head 44 and the second measurement head 54 are arranged in the processing feed direction so as to sandwich the condenser 36. When the processing feed direction (i.e., the movement direction of the focal point P of the laser beam L) is the -X direction, the first measurement head 44 precedes the condenser 36 in the processing feed direction, and when the processing feed direction is the +X direction, the second measurement head 54 precedes the condenser 36 in the processing feed direction.

[0072] The second measuring head 54 is also configured to be movable relative to the chuck table 10 in the processing feed direction. Specifically, when the processing feed unit 22 is used to move the chuck table 10 and the condenser 36 relative to each other in the processing feed direction, the second measuring head 54, like the first measuring head 44, also moves relative to the chuck table 10 together with the condenser 36 in the processing feed direction.

[0073] Furthermore, when the indexing feed unit 12 is used to move the chuck table 10 and the condenser 36 relatively along the indexing feed direction, the second measuring head 54 also moves together with the condenser 36 relatively to the chuck table 10 along the indexing feed direction, similar to the first measuring head 44. The indexing feed direction is, for example, the -Y direction, but may also be the +Y direction.

[0074] The first resistance measuring device 42 and the second resistance measuring device 52 utilize eddy currents generated in a localized region of one surface 11a (for example, a circular region with a diameter of approximately 5.0 mm to 10 mm) to measure the electrical resistance or electrical resistivity in the localized region of one surface 11a (corresponding to the measurement region 11h (see Figure 6) described later).

[0075] As the first resistance measuring device 42 and the second resistance measuring device 52, for example, the EC-80P, which is a non-contact resistance measuring device manufactured and sold by Napson Corporation, can be used.

[0076] 4 is a block diagram of the main parts of the laser processing apparatus 2. First, an overview of the first resistance measuring device 42 will be described. The first measuring head 44 has a magnetic core (not shown) made of a material such as Mn-Zn ferrite. An excitation coil 44a is wound around the magnetic core.

[0077] When a high-frequency voltage of about 0.4 MHz to 10 MHz is applied to the excitation coil 44a with the lower end of the magnetic core positioned close to the surface 11a, a time-varying magnetic field is generated in the magnetic core, generating eddy currents on the surface 11a of the ingot 11. This causes a change in the current flowing through the excitation coil 44a.

[0078] Changes in the current flowing through the excitation coil 44a are detected by a first current detector 46. The first current detector 46 may be a resistance detection type having a shunt resistor through which a current flows, or may be a magnetic field detection type that measures changes in current using a magnetic field.

[0079] The first current detector 46 further includes a computer including a processor represented by a CPU (Central Processing Unit), a main storage device such as a DRAM (Dynamic Random Access Memory), and an auxiliary storage device such as a flash memory.

[0080] The auxiliary storage device stores software including a predetermined program. The function of the first current detector 46 is realized by operating a processor or the like in accordance with this software. Note that instead of a processor, a field-programmable gate array (FPGA), an application-specific integrated circuit (ASIC), or the like may also be used.

[0081] The first current detector 46 converts the change in the current flowing through the excitation coil 44a into the electrical resistance (i.e., volume resistance (Ω) or sheet resistance (Ω / □)) or electrical resistivity (Ω·cm) of the circular area on one surface 11a according to a predetermined formula. Whether to use electrical resistance or electrical resistivity can be determined appropriately depending on the object to be measured.

[0082] The first current detector 46 is configured to be able to communicate, via wired or wireless communication, with a controller 60 that controls the entire laser processing apparatus 2. The first current detector 46 notifies the controller 60 of information such as the calculated electrical resistivity, thereby enabling the controller 60 to grasp the electrical resistance or electrical resistivity of the ingot 11 measured via the first measuring head 44.

[0083] The second resistance measuring device 52 also has a magnetic core, an exciting coil 54a, a second current detector 56, etc. The configuration of the second resistance measuring device 52 is similar to that of the first resistance measuring device 42, so details will be omitted.

[0084] The second current detector 56 notifies the controller 60 of information such as the calculated electrical resistivity, so that the controller 60 can grasp the electrical resistance or electrical resistivity of the ingot 11 measured via the second measuring head 54.

[0085] In addition, instead of the resistance measurement method using eddy currents generated in the ingot 11 by applying a high-frequency voltage as in this embodiment, a resistance measurement method of the ingot 11 using corona discharge, a resistance measurement method using electrostatic coupling between the measurement cable and the ingot 11, a resistance measurement method using eddy currents generated by applying a pulse voltage to the ingot 11, etc. may also be used.

[0086] The various methods described above are advantageous in that the electrical resistivity and the like of a local region of the ingot 11 can be measured without the first measuring head 44 and the second measuring head 54 coming into contact with the ingot 11, and therefore scratches and the like are not formed on the ingot 11 (particularly on the surface 11a). However, the method for measuring the electrical resistivity and the like is not limited to such a non-contact method.

[0087] Instead of the non-contact method, a contact method may be applied, such as a two-terminal method in which two measuring terminals (not shown) are brought into contact with one surface 11a of the ingot 11 to measure the electrical resistivity, etc. of a local area of ​​the ingot 11, or a four-terminal method in which four measuring terminals (not shown) are brought into contact with one surface 11a of the ingot 11 to measure the electrical resistivity, etc. of a local area of ​​the ingot 11.

[0088] However, in the contact method, in order to minimize scratches and the like formed on one surface 11a of the ingot 11, it is preferable to control the measurement conditions, such as the height position of the lower end of the measurement terminal in the Z-axis direction and the processing feed speed, more precisely than in the non-contact method.

[0089] 1, a description will be given of other components of the laser processing apparatus 2. The support arm 8a is also provided with a head portion of a microscope camera unit (not shown). The microscope camera unit includes an objective lens, a light source, and a solid-state imaging element.

[0090] The microscope camera unit captures an image of the surface 11a using, for example, visible light. Based on the image of the surface 11a, the rotation drive source in the support base 32 is operated to adjust the orientation of the chuck table 10 so that a predetermined direction (e.g., primary orientation flat 13) of the ingot 11 held by suction on the holding surface 10a becomes approximately parallel to the X-axis (see FIG. 6).

[0091] 1, a cover (not shown) that covers the above-mentioned components is provided on the base 4. A touch panel 64 is provided on the side of the cover that is located at the end in the +Y direction. The touch panel 64 is, for example, a liquid crystal display that includes a capacitive touch sensor.

[0092] The touch panel 64 functions as an input device for the operator to input instructions to the laser processing device 2, a GUI (Graphical User Interface) for inputting instructions, and a display device for displaying images obtained via the microscope camera unit, etc.

[0093] Note that a display device that does not have the function of an input device may be provided in the laser processing device 2 instead of the touch panel 64. In this case, however, an input device (keyboard, mouse, trackball, touchpad, digitizer, etc.) for the operator to input instructions to the controller 60 is provided separately.

[0094] The laser processing device 2 is provided with a controller 60 that controls the operation of the chuck table 10, the indexing feed unit 12, the processing feed unit 22, the rotation drive source within the support base 32, the laser beam irradiation unit 34, the microscope camera unit, the touch panel 64, etc.

[0095] The controller 60 also controls the operation of the first resistance measuring device 42 and the second resistance measuring device 52 so as to operate one of the first measuring head 44 and the second measuring head 54 that precedes the collector 36 in the processing feed direction.

[0096] The controller 60 is configured by a computer having a processor 60a, such as a CPU (Central Processing Unit), and a memory 60b. The memory 60b includes a main storage device such as a DRAM (Dynamic Random Access Memory) and an auxiliary storage device such as a flash memory.

[0097] The auxiliary storage device stores software including a predetermined program. The functions of the controller 60 are realized by operating the processor 60a and other components in accordance with this software.

[0098] The predetermined program includes a program for causing the controller 60 to execute the laser beam irradiation step S20 described below, and this program is stored in the auxiliary storage device of the controller 60.

[0099] However, this program may alternatively be stored in an external storage device 62 such as a USB (Universal Serial Bus) memory, an optical disk, an SD memory card, or an HDD (hard disk drive), and may be executed by inputting the program read via a reading device into the processor 60a.

[0100] The external storage device 62 may be interpreted as a non-transitory tangible recording medium on which a program is recorded. Next, a laser processing method for forming a separation layer 11i inside the ingot 11 by laser processing the ingot 11 with a laser beam L will be described.

[0101] 5 is a flow diagram of a laser processing method for performing laser processing on an ingot 11 using the laser processing device 2. In this embodiment, a holding step S10 and a laser beam irradiation step S20 are performed in this order.

[0102] In the holding step S10, the ingot 11 transferred to the holding surface 10a is suction-held on the holding surface 10a by negative pressure. Next, in this example, the primary orientation flat 13 is positioned approximately parallel to the X-axis using the above-mentioned microscope camera unit or the like.

[0103] The subsequent laser beam irradiation step S20 includes a first processing feed S21, a determination of whether indexing feed is necessary S22, a first indexing feed S23, a second processing feed S24, a determination of whether indexing feed is necessary S25, and a second indexing feed S26.

[0104] 6 is a plan view of the ingot 11 showing the first processing feed S21, the first indexing feed S23, the second processing feed S24, and the second indexing feed S26. In FIG. 6, the movement locus of the focal point P of the laser beam L during the processing feed and the movement locus of the focal point P of the laser beam L during the indexing feed are indicated by dashed lines.

[0105] 6, some of the multiple measurement areas 11h where the electrical resistance or electrical resistivity is measured are shown by dashed lines as an example. Either the electrical resistance or the electrical resistivity may be measured in the measurement areas 11h, but in the laser beam irradiation step S20, either one of them is consistently measured.

[0106] The measurement area 11h is, for example, a circular area with a diameter of about 5.0 mm to 10 mm. The center-to-center distance between the measurement areas 11h in the X-axis direction is, for example, 10 mm, but the center-to-center distance between the measurement areas 11h is not limited to this example.

[0107] When processing the ingot 11 with the laser beam L, first, the chuck table 10 and the condenser 36 are moved relative to each other so that the first measuring head 44 leads the condenser 36 in the processing feed direction (-X direction) (first processing feed S21).

[0108] At this time, the controller 60 uses the first measuring head 44 to measure the electrical resistance or electrical resistivity of the measurement area 11h of the ingot 11, and maintains or changes in real time the laser processing conditions of the ingot 11 using the laser beam L irradiated onto the measurement area 11h in accordance with the electrical resistance or electrical resistivity of the measurement area 11h.

[0109] Therefore, the controller 60 can perform, in parallel in time, the measurement of the electrical resistance or electrical resistivity of each of the multiple measurement areas 11h that are discretely arranged along the movement trajectory of the focal point P of the laser beam L, and the laser processing of the ingot 11 according to the electrical resistance or electrical resistivity.

[0110] In other words, it is possible to investigate the laser processing conditions and perform laser processing that reflects the investigation results in a single processing feed operation. Therefore, the number of steps can be reduced compared to when laser processing is started after measuring the electrical resistance or electrical resistivity in the region corresponding to the movement locus of the focal point P of the laser beam L on one surface 11a (i.e., the exposed surface) of the ingot 11. In other words, it is possible to improve the throughput of laser processing.

[0111] In the first processing feed S21 shown in Figure 6, the electrical resistance or electrical resistivity of each measurement area 11h is measured, but since the laser beam L is always irradiated onto the non-facet area 11g, the laser processing conditions are maintained unchanged.

[0112] This forms a separation layer 11i inside the ingot 11. The separation layer 11i is a region having reduced mechanical strength compared to a region not irradiated with the laser beam L, and includes a modified region (not shown) in which the crystallinity has changed from single crystal to amorphous, polycrystalline, or the like due to multiphoton absorption, and cracks (not shown) extending from the modified region.

[0113] At the end of the first processing feed S21, the focal point P has not yet reached the end of the indexing feed direction (-Y direction) (YES in S22), so the chuck table 10 and the collector 36 are then moved a predetermined distance relative to each other in the indexing feed direction (first indexing feed S23).

[0114] When the focal point P reaches the end in the indexing feed direction (for example, a position less than 100 μm from the outer periphery in the −Y direction) (NO in S22 (S25)), the laser processing is terminated.

[0115] After the first indexing feed S23, the chuck table 10 and the collector 36 are moved relative to each other so that the second measuring head 54 leads the collector 36 in the processing feed direction (+X direction) (second processing feed S24).

[0116] At this time, the controller 60 uses the second measuring head 54 to measure the electrical resistance or electrical resistivity of the measurement area 11h of the ingot 11, and maintains or changes in real time the laser processing conditions of the ingot 11 using the laser beam L irradiated onto the measurement area 11h in accordance with the electrical resistance or electrical resistivity of the measurement area 11h.

[0117] 6, the electrical resistance or electrical resistivity of each measurement region 11h is measured, but the laser beam L is always irradiated onto the non-facet region 11g, so the laser processing conditions are maintained unchanged. This forms a separation layer 11i inside the ingot 11.

[0118] At the end of the second processing feed S24, the focal point P has not yet reached the end of the indexing feed direction (YES in S25), so the chuck table 10 and the condenser 36 are then moved relatively a predetermined distance in the indexing feed direction (second indexing feed S26). On the other hand, if the focal point P has reached the end of the indexing feed direction (NO in S26), the laser processing is terminated.

[0119] 6, after the second indexing feed S26, the first processing feed S21 is performed again. In this manner, the controller 60 moves the chuck table 10 and the condenser 36 relatively to each other so as to sequentially repeat the first processing feed S21, the first indexing feed S23, the second processing feed S24, and the second indexing feed S26.

[0120] In the second first processing feed S21 shown in Figure 6, measurement and laser processing are performed on a straight line where non-faceted areas 11g and faceted areas 11f are mixed, so the laser processing conditions are changed depending on the electrical resistivity, etc. of each measured area 11h.

[0121] The second first processing feed S21 is shown schematically in Figures 7(A) to 7(C). For ease of explanation, the facet region 11f and the non-facet region 11g are hatched differently in Figures 7(A) to 7(C).

[0122] Furthermore, as the chuck table 10 and the ingot 11 move in the +X direction (see the left arrows in FIG. 7(A) and other figures), the condenser 36, the first measuring head 44, and the second measuring head 54 move in the -X direction. In this case, the processing feed direction is the -X direction.

[0123] 7A is a schematic diagram showing measurement of electrical resistivity and laser processing at time t1. At time t1, the first measurement head 44 measures the electrical resistivity of the non-faceted region 11g, and the condenser 36 irradiates the laser beam L onto the non-faceted region 11g located further in the +X direction than the first measurement head 44.

[0124] The laser processing conditions for the non-facet region 11g at time t1 are maintained unchanged from the predetermined laser processing conditions in accordance with the electrical resistivity of the non-facet region 11g measured immediately beforehand via the first measurement head 44.

[0125] 7B is a schematic diagram showing measurement of electrical resistivity and laser processing at time t2 after time t1. At time t2, the first measuring head 44 measures the measurement area 11h in the facet area 11f. X1 The condenser 36 irradiates the laser beam L onto a non-facet region 11g located in the +X direction from the first measuring head 44.

[0126] The laser processing conditions for the non-faceted region 11g at time t2 are also maintained unchanged from the predetermined laser processing conditions in accordance with the electrical resistivity of the non-faceted region 11g measured immediately beforehand via the first measurement head 44.

[0127] 7C is a schematic diagram showing measurement of electrical resistivity and laser processing at time t3 after time t2. At time t3, the first measuring head 44 measures a measurement area 11h in the facet area 11f that is different from the measurement area 11h at time t2. X2The collector 36 measures the electrical resistivity of the measurement area 11h in the facet area 11f. X1 A laser beam L is irradiated onto the target.

[0128] The laser processing conditions in the facet region 11f at time t3 are the same as those in the measurement region 11h in the facet region 11f measured immediately before by the first measurement head 44. X1 The predetermined laser processing conditions are changed depending on the electrical resistivity of the material.

[0129] In the facet region 11f, which has a relatively high impurity concentration, the absorption rate of the laser beam L in the ingot 11 is higher than in the non-facet region 11g, which has a relatively low impurity concentration. Therefore, when laser processing the facet region 11f, the controller 60 changes one or more of the following (a) to (d):

[0130] (a) Power of laser beam L (b) Amount of defocus (i.e., the height position of the focal point P in the Z-axis direction) (c) Repetition frequency of the laser beam L and / or relative processing feed rate between the focal point P and the ingot 11 (d) The number of times the laser beam L is moved along the same path of the focal point P (i.e., the number of passes)

[0131] For example, in the facet region 11f, compared to the non-facet region 11g, (a) the power of the laser beam L can be increased to increase the energy density of the laser beam L at the depth position where the separation layer 11i is formed. This allows the separation layer 11i to be formed at approximately the same depth position from the one surface 11a.

[0132] Furthermore, for example, in the facet region 11f, as compared with the non-facet region 11g, the height position of the focal point P in the (b) Z-axis direction can be set higher than the one surface 11a and closer to the one surface 11a, thereby increasing the energy density of the laser beam L at the depth position where the separation layer 11i is formed and the overlapping area (i.e., overlap rate) between the focal points. This allows the separation layer 11i to be formed at approximately the same depth position from the one surface 11a in the facet region 11f and the non-facet region 11g.

[0133] Furthermore, for example, in the facet region 11f, the pitch of the focal points P can be narrowed by increasing the repetition frequency of the laser beam L (c) compared to the non-facet region 11g. This allows the energy density, overlap rate, etc. of the laser beam L to be increased.

[0134] Therefore, the separation layer 11i can be formed at approximately the same depth from the surface 11a in the facet region 11f and the non-facet region 11g. The repetition frequency can be increased by, for example, stopping the thinning out of one or more pulses performed by the optical modulator 40.

[0135] Furthermore, for example, in the facet region 11f, the pitch of the focal points P can be narrowed by lowering the processing feed rate (c) compared to the non-facet region 11g. This allows the overlap rate of the laser beam L to be increased.

[0136] Therefore, the separation layer 11i can be formed at approximately the same depth from the one surface 11a in the facet region 11f and the non-facet region 11g. The processing feed speed can be changed by changing the output of the motor 30 and changing the movement speed of the moving table 26 by the processing feed unit 22.

[0137] Furthermore, for example, in the facet region 11f, the number of passes (d) can be increased compared to the non-facet region 11g, thereby allowing the facet region 11f to be laser processed multiple times. As a result, the separation layer 11i can be formed at approximately the same depth from the one surface 11a.

[0138] After the facet region 11f is laser processed, the laser processing conditions are returned to the original when laser processing is performed on the non-facet region 11g. In the second processing feed S24 after the first processing feed S21, laser processing is similarly performed using the condenser 36 and the second measurement head 54, which precedes the condenser 36 in the processing feed direction.

[0139] In this way, the controller 60 of this embodiment measures the electrical resistance or electrical resistivity of the measurement area 11h using one of the first measuring head 44 and the second measuring head 54 that precedes the condenser 36 in the processing feed direction during laser processing, and maintains or changes the laser processing conditions of the ingot 11 using the laser beam L irradiated onto the measurement area 11h depending on the electrical resistance or electrical resistivity of the measurement area 11h.

[0140] Therefore, the number of steps can be reduced compared to when laser processing is started after measurement of the electrical resistance or electrical resistivity is completed in the region corresponding to the movement locus of the focal point P of the laser beam L on the one surface 11a of the ingot 11. In other words, the throughput of the laser processing can be improved.

[0141] In this embodiment, when the power and / or repetition frequency among the laser processing conditions is changed, the laser processing conditions can be changed using the optical modulator 40, which allows for a higher response speed than an attenuator that physically rotates a half-wave plate. Therefore, changes in the laser processing conditions can be made to sufficiently follow the processing feed speed.

[0142] The laser processing conditions (when the power of the laser beam L is changed) for the first processing feed S21 and the second processing feed S24 are shown below. Note that since the average output is equal to the product of the pulse energy and the repetition frequency, the pulse energy under the following laser processing conditions corresponds to 20 μJ or more and 180 μJ or less.

[0143] Wavelength: 1064nm Average output: 0.6W to 5.4W Repetition frequency: 30kHz Pulse width: 3ns Processing feed rate: 165mm / s Defocus amount: 188 μm (distance in the +Z direction based on surface 11a) Depth of separation layer: 500 μm (distance in the −Z direction based on one surface 11a)

[0144] 8 is a graph showing the electrical resistivity of the ingot 11 and the pulse energy of the laser beam L adjusted depending on the electrical resistivity. In the facet region 11f and the non-facet region 11g, the electrical resistivity varies within a range of, for example, 16 mΩ cm or more and 22 mΩ cm or less.

[0145] Furthermore, in the facet region 11f, the electrical resistivity is lower than that in the non-facet region 11g, but the electrical resistivity can vary within a range of 16 mΩ·cm to 22 mΩ·cm.

[0146] Therefore, the controller 60 stores the correspondence between the electrical resistivity (mΩ·cm) and the pulse energy (μJ) shown in FIG. 8 in an auxiliary storage device, and maintains or changes the pulse energy (i.e., average output) according to the electrical resistivity obtained via the first measuring head 44 or the second measuring head 54.

[0147] Of course, instead of the pulse energy (i.e., average output), as described above, (b) the amount of defocus, (c) the repetition frequency and / or processing feed rate of the laser beam L, and (d) the number of passes may be changed.

[0148] It should be noted that (a) power, (b) defocus amount, and (c) repetition frequency and / or processing feed rate are not limited to being changed in a binary manner between the facet region 11f and the non-facet region 11g.

[0149] In each of the facet region 11f and the non-facet region 11g, at least one of (a) power, (b) defocus amount, and (c) repetition frequency and / or processing feed rate may be changed linearly or stepwise.

[0150] The laser processing conditions may be left unchanged in the non-facet region 11g, and at least one of (a) power, (b) defocus amount, and (c) repetition frequency and / or processing feed rate may be changed linearly or stepwise only in the facet region 11f.

[0151] (First Modification) Next, a first modification of the first embodiment will be described with reference to Fig. 9. Fig. 9 is a block diagram showing the main parts of a laser processing apparatus 72 in the first modification. In the first modification, the first current detector 46 and the second current detector 56 are configured integrally with the controller 60.

[0152] For example, the processor 60a and memory 60b constituting the controller 60, the first current detector 46 and the second current detector 56 are housed in the same housing (not shown) or fixed to the same motherboard.

[0153] Second Embodiment Next, a laser processing apparatus 82 according to a second embodiment will be described with reference to Figures 10 to 12. Note that the same components as those in the laser processing apparatus 2 according to the first embodiment will be described using the same reference numerals.

[0154] A laser processing apparatus 82 of the second embodiment has a first fluorescence measurement apparatus 92 and a second fluorescence measurement apparatus 102 instead of the first resistance measurement apparatus 42 and the second resistance measurement apparatus 52. Fig. 10 is a block diagram showing the main parts of the laser processing apparatus 82 of the second embodiment.

[0155] The first fluorescence measurement device 92 has a first measurement head 94 at the tip of the support arm 8a, at a position adjacent to the condenser 36 in the −X direction. In other words, the spatial position of the first measurement head 94 relative to the condenser 36 is fixed.

[0156] However, the first measuring head 94 is configured to be movable relative to the chuck table 10 in the processing feed direction. In other words, when the processing feed unit 22 is used to move the chuck table 10 and the condenser 36 relative to each other in the processing feed direction, the first measuring head 94 moves together with the condenser 36 relative to the chuck table 10 in the processing feed direction.

[0157] Furthermore, the first measuring head 94 is configured to be movable relative to the chuck table 10 along the indexing feed direction. In other words, when the indexing feed unit 12 is used to move the chuck table 10 and the condenser 36 relative to each other along the indexing feed direction, the first measuring head 94 moves together with the condenser 36 relative to the chuck table 10 along the indexing feed direction.

[0158] A second measuring head 104 constituting a second fluorescence measuring device 102 is fixed to the tip of the support arm 8a at a position adjacent to the condenser 36 in the +X direction. In other words, the spatial position of the second measuring head 104 relative to the condenser 36 is also fixed, and the first measuring head 94 and the second measuring head 104 are arranged so as to sandwich the condenser 36 in the processing feed direction.

[0159] However, the second measuring head 104 is configured to be movable relative to the chuck table 10 in the processing feed direction. In other words, when the processing feed unit 22 is used to move the chuck table 10 and the condenser 36 relative to each other in the processing feed direction, the second measuring head 104 also moves relative to the chuck table 10 along the processing feed direction together with the condenser 36, similar to the first measuring head 94.

[0160] The second measuring head 104 is configured to be movable relative to the chuck table 10 along the indexing feed direction. In other words, when the indexing feed unit 12 is used to move the chuck table 10 and the condenser 36 relative to each other along the indexing feed direction, the second measuring head 104 moves together with the condenser 36 relative to the chuck table 10 along the indexing feed direction.

[0161] The first fluorescence measuring device 92 has a first measuring head 94, and the second fluorescence measuring device 102 has a second measuring head 104. The first measuring head 94 and the second measuring head 104 irradiate a localized region (e.g., a circular region with a diameter of approximately 200 μm to 500 μm) of one surface 11a with excitation light A (see FIG. 11) having ultraviolet light (e.g., 365 nm) that is absorbed by the ingot 11.

[0162] Fig. 11 is a partial cross-sectional side view showing a first measuring head 94 in the second embodiment. In Fig. 11, some of the components of the first measuring head 94 are shown as functional blocks.

[0163] The first measurement head 94 has an excitation light source 84. The excitation light source 84 has, for example, a GaN-based LED (Light Emitting Diode). The excitation light source 84 emits excitation light A having a predetermined power.

[0164] A prism mirror 84a is provided on the side of the excitation light source 84. The excitation light A emitted from the excitation light source 84 is reflected downward by the prism mirror 84a. A condenser lens 84b is provided below the prism mirror 84a.

[0165] The excitation light A reflected by the prism mirror 84a is focused to a predetermined point by the condenser lens 84b. In this embodiment, the predetermined point corresponds to a point on one surface 11a of the ingot 11. An elliptical mirror 86 is provided below the prism mirror 84a and the condenser lens 84b so as to surround the irradiation area of ​​the excitation light A on the one surface 11a in a plan view.

[0166] The elliptical mirror 86 has a reflecting surface 86a on its inner surface. The reflecting surface 86a corresponds to a part of the outer surface 86b of the spheroid. The major axis of the spheroid is aligned along the Z axis, and the minor axis of the spheroid is aligned along the XY plane. The elliptical mirror 86 has two focal points F1 and F2. The position of the focal point of the condenser lens 84b substantially coincides with the position of the focal point F1.

[0167] When excitation light A is focused at focal point F1, fluorescence B is generated from one surface 11a of ingot 11 that has absorbed excitation light A. Fluorescence B emitted from one surface 11a is reflected by reflecting surface 86a of elliptical mirror 86 and then focused at focal point F2 via filter 88.

[0168] Filter 88 is an optical filter that blocks light with wavelengths less than 750 nm and transmits light with wavelengths equal to or greater than 750 nm. A photocathode 90a of a photomultiplier tube (i.e., optical sensor) 90 is disposed at focal point F2. Photomultiplier tube 90 further includes an entrance window, multiple dynodes, an anode (none of which are shown), etc.

[0169] A first predetermined circuit 96 including a divider circuit and the like is electrically connected to the photomultiplier tube 90. When the photomultiplier tube 90 receives light having a wavelength of 1500 nm or less, an electrical signal indicating the number of photons of the received light is transmitted to the controller 60 via the first predetermined circuit 96.

[0170] This allows the controller 60 to grasp the number of photons of the fluorescence B measured via the first measuring head 94 without coming into contact with (i.e., in a non-contact manner with) the ingot 11. The configuration of the second measuring head 104 is also approximately the same as that of the first measuring head 94.

[0171] The second fluorescence measuring device 102 has a second measuring head 104 and a second predetermined circuit 106 corresponding to the first predetermined circuit 96 (see FIG. 10). By using the second measuring head 104, the controller 60 can also grasp the number of photons of the fluorescence B.

[0172] The number of photons of fluorescence B is negatively correlated with the impurity concentration in ingot 11. Specifically, the higher the impurity concentration, the lower the number of photons of fluorescence B. In one example, the number of photons measured in facet region 11f is 1000 cps (counts per second) or more and 4000 cps or less, and the number of photons measured in non-facet region 11g is 5000 cps or more.

[0173] It is also possible to omit the elliptical mirror 86 and provide a dichroic mirror (not shown) instead of the prism mirror 84a. The dichroic mirror has the function of reflecting the excitation light A in the ultraviolet band but transmitting the fluorescence B in the infrared band.

[0174] If the elliptical mirror 86 is omitted and a dichroic mirror is provided instead of the prism mirror 84a, the excitation light A from the excitation light source 84 is first reflected by the dichroic mirror and then focused onto one surface 11a of the ingot 11 via the focusing lens 84b.

[0175] When the ingot 11 absorbs the excitation light A, fluorescence B is emitted from one surface 11a, and passes through the condenser lens 84b, dichroic mirror, and filter 88 in this order, before reaching the photomultiplier tube 90. In this manner, the controller 60 can also grasp the number of photons of fluorescence B measured via the first measurement head 94.

[0176] In the second embodiment, when the laser beam L is irradiated onto the ingot 11, the number of photons of the fluorescence B from the measurement region 11h is measured using one of the first measurement head 94 and the second measurement head 104 that is ahead of the condenser 36 in the processing feed direction.

[0177] Then, the laser processing conditions of the ingot 11 using the laser beam L irradiated onto the measurement area 11h are maintained or changed according to the number of photons of the fluorescence B from the measurement area 11h. In other words, measurement of the number of photons of the fluorescence B in the ingot 11 and laser processing of the ingot 11 according to the number of photons of the fluorescence B can be performed in parallel in terms of time.

[0178] That is, in one processing feed operation, it is possible to investigate the laser processing conditions and perform laser processing that reflects the investigation results. Therefore, compared to starting laser processing after completing measurement of the number of photons of fluorescence B in the area corresponding to the movement locus of focal point P on one surface 11a (i.e., exposed surface) of ingot 11, the number of steps can be reduced. In other words, it is possible to improve the throughput of laser processing.

[0179] In the second embodiment, the laser processing conditions may also be changed by changing at least one of (a) power, (b) defocus amount, (c) repetition frequency and / or processing feed rate, and (d) number of passes.

[0180] The laser processing conditions may be changed binary in the facet region 11f and the non-facet region 11g, or the laser processing conditions may be changed linearly or stepwise in both the facet region 11f and the non-facet region 11g, or the laser processing conditions may be changed linearly or stepwise only in the facet region 11f without changing the laser processing conditions at all in the non-facet region 11g.

[0181] When the above-described laser processing method is performed using the laser processing device 82, the steps are also performed in the order of the holding step S10 and the laser beam application step S20. The laser beam application step S20 includes a first processing feed S21, a determination of whether indexing feed is necessary S22, a first indexing feed S23, a second processing feed S24, a determination of whether indexing feed is necessary S25, and a second indexing feed S26.

[0182] Before laser processing, when first measuring the distribution of the number of photons of fluorescence B within one surface 11a, the focal point of excitation light A is usually moved spirally on one surface 11a (so-called helical scanning) in order to measure a wide area quickly (see Patent Document 3 mentioned above).

[0183] In contrast, in this embodiment, the movement path of the focal point of the excitation light A is substantially the same linear path as the movement path of the focal point P of the laser beam L, so helical scanning is not performed as long as the ingot 11 is laser processed with the laser beam L by the first processing feed S21 and the second processing feed S24.

[0184] The predetermined program stored in the auxiliary storage device of the controller 60 includes a program for causing the controller 60 to execute the laser beam irradiation step S20. Alternatively, however, this program may be stored in the external storage device 62 and executed by reading the program via a reading device and inputting it into the processor 60a.

[0185] (Second Modification) Next, a second modification of the first and second embodiments will be described with reference to Figures 12(A) to 12(C). As shown in Figure 12(A), in the second modification, the first measuring head 44 and the second measuring head 54 are moved by a predetermined distance Δ y It is positioned so that only the

[0186] Of course, the first measuring head 94 and the second measuring head 104 are positioned at a predetermined distance Δ y Therefore, in the second modified example, the first measuring head 44 (94) and the second measuring head 54 (104) are referred to as a first measuring head 44 (94) and a second measuring head 54 (104).

[0187] In Figures 12(A) to 12(C), for convenience, parentheses are not placed around the symbols corresponding to the measurement heads, but a combination of a collector 36, a first measurement head 44, and a second measurement head 54 may be used, or a combination of a collector 36, a first measurement head 94, and a second measurement head 104 may be used.

[0188] 12A is a plan view showing the positional relationship between the condenser 36, the first measuring head 44 (94), and the second measuring head 54 (104) in the second modified example. y is equal to a natural number multiple of the index feed amount in the laser beam irradiation step S20, and the predetermined distance Δ y is, for example, 1.0 mm.

[0189] In the laser beam irradiation step S20 of the second modified example, similarly to the above-described embodiment, the first processing feed S21, the first indexing feed S23, the second processing feed S24, and the second indexing feed S26 are sequentially repeated. However, in the initial first processing feed S21, laser processing is not performed, and only the electrical resistance or electrical resistivity (or the number of photons of fluorescence B) of the measurement region 11h (see FIG. 6) is measured.

[0190] Then, in the first second processing feed S24, laser processing is performed while maintaining or changing the laser processing conditions for irradiating the measurement area 11h according to the electrical resistance or electrical resistivity (or the number of photons of fluorescence B) measured in the first first processing feed S21, and the electrical resistance or electrical resistivity (or the number of photons of fluorescence B) of a measurement area 11h different from the first first processing feed S21 is measured.

[0191] In this way, in the second modified example, measurements are made using the first measuring head 44 (94) and the second measuring head 54 (104) on the line to be processed that precedes in the indexing feed direction, and laser processing is performed on the line to be processed that follows in the indexing feed direction under laser processing conditions that reflect the most recent measurement results by the first measuring head 44 (94) and the second measuring head 54 (104) simultaneously.

[0192] 12(A), area C1 indicates the movement range of the first measuring head 44 (94) in the initial second processing feed S24. Similarly, area C2 indicates the movement range of the second measuring head 54 (104) in the initial second processing feed S24. Furthermore, area C3 indicates the range through which both the first measuring head 44 (94) and the second measuring head 54 (104) pass in the initial second processing feed S24.

[0193] In the second variant, electrical resistance or electrical resistivity (or the number of photons of fluorescence B) is measured using both the first measuring head 44 (94) and the second measuring head 54 (104), rather than using either the first measuring head 44 (94) or the second measuring head 54 (104) that precedes in the processing feed direction.

[0194] 12(B) is a diagram showing which of the first measuring head 44 (94) and the second measuring head 54 (104) is used to store the measurement results that are used by the controller 60. The controller 60 stores the measurement results obtained using the first measuring head 44 (94) for the left half region D1 of the surface 11a, and stores the measurement results obtained using the second measuring head 54 (104) for the right half region D2 of the surface 11a.

[0195] Figure 12(C) is a diagram showing the movement range of the first measurement head 44 (94) in the above-described embodiment in comparison with the second modification, and shows the advantages of the second modification compared to the above-described embodiment. The area C1 shown in Figure 12(C) is the same as the area C1 shown in Figure 12(A).

[0196] In the above embodiment, the movement range of the first measuring head 44 (94) is an area C1' which is wider than the area C1. In the above embodiment, the first measuring head 44 (94) precedes the condenser 36 in the initial first processing feed S21, but the second measuring head 54 (104) precedes the condenser 36 in the subsequent initial second processing feed S24.

[0197] Therefore, in the above-described embodiment, in the first processing feed S21, the processing feed must be performed until the second measuring head 54 (104) is positioned outside in the X-axis direction beyond the starting position of the second processing feed S24 that immediately follows the first processing feed S21.

[0198] In contrast, in the second variant, both the first measuring head 44 (94) and the second measuring head 54 (104) are used, so even if the processing feed amount is shortened, it is possible to measure the electrical resistance or electrical resistivity (or the number of photons of fluorescence B) for the entire processed line where the first second processing feed S24 is performed.

[0199] As a result, the movement range of the first measuring head 44 (94) is shortened by the difference ΔC1 (=C1'-C1). Reducing the movement range is synonymous with reducing the processing feed amount, and reducing the processing feed amount reduces the time required for laser processing, thereby increasing the production efficiency of laser processing.

[0200] In addition, the structures, methods, etc. according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. The conductivity type of the ingot 11 is not particularly limited. The ingot 11 may be either n-type or p-type.

[0201] Furthermore, the ingot 11 is not limited to SiC, and the above-described laser processing method that takes into account non-uniformity of impurity concentration can be applied when forming the separation layer 11i on a workpiece such as a silicon (Si) ingot.

[0202] In any of the embodiments, after the laser beam irradiation step S20, a wafer (not shown) is peeled off from the ingot 11 at the separation layer 11i. After the peeling, the surface of the ingot 11 to be peeled is ground, polished, or the like, and then the holding step S10 and the laser beam irradiation step S20 are performed again, thereby manufacturing another wafer from the ingot 11. [Explanation of symbols]

[0203] 2: Laser processing equipment 4: base, 6: flat plate portion, 8: wall portion, 8a: support arm 10: chuck table (holding unit), 10a: holding surface 11: Ingot (workpiece) 11a: One side, 11b: Other side, 11c: c axis, 11d: Perpendicular line, 11e: c side 11f: faceted area, 11g: non-faceted area 11am, 11am X1 ,11h X2 :Measurement area, 11i: Separation layer 12: Indexing feed unit, 14: Guide rail 13: Primary orientation flat, 15: Secondary orientation flat 16: moving table, 18: screw shaft, 20: motor (second motor) 22: Processing feed unit, 24: Guide rail 26: moving table, 28: screw shaft, 30: motor (first motor) 32: Support stand 34: Laser beam irradiation unit 36: condenser, 36a: mirror, 36b: condenser lens 38: Laser oscillator, 40: Optical modulator 42: First resistance measuring device, 44: First measuring head, 44a: Excitation coil 46: First current detector 52: Second resistance measuring device, 54: Second measuring head, 54a: Excitation coil 56: Second current detector 60: Controller, 60a: Processor, 60b: Memory, 62: External storage device 64: Touch panel 72,82:Laser processing equipment 84: excitation light source, 84a: prism mirror, 84b: condenser lens 86: elliptical mirror, 86a: reflecting surface, 86b: outer surface, 88: filter 90: photomultiplier tube (optical sensor), 90a: photocathode 92: First fluorescence measuring device, 94: First measuring head, 96: First predetermined circuit 102: second fluorescence measuring device, 104: second measuring head, 106: second predetermined circuit A: Excitation light, B: Fluorescence, C1, C2, C3, C1´: Area Δ y :Predetermined distance, D1: Left half area, D2: Right half area, F1, F2: Focus L: laser beam, P: focal point S10: Holding step, S20: Laser beam irradiation step S21: 1st processing feed S22: Determine whether index feed is necessary, S23: First index feed S24: Second processing feed S25: Determine whether index feed is necessary, S26: Second index feed

Claims

1. A laser processing device that processes a workpiece with a laser beam, a holding unit for holding the workpiece; a laser beam irradiation unit including a laser oscillator that emits the laser beam and a condenser having a condensing lens that condenses the laser beam emitted from the laser oscillator; a processing feed unit having a first motor for relatively moving the holding unit and the condenser along a processing feed direction; a first resistance measuring device having a first measuring head whose position relative to the condenser is fixed and which is movable together with the condenser relative to the holding unit along the processing feed direction by the processing feed unit, the first resistance measuring device measuring the electrical resistance or electrical resistivity of the workpiece via the first measuring head; a controller having a processor and a memory and controlling the laser beam irradiation unit and the processing feed unit; Equipped with The controller measures the electrical resistance or electrical resistivity of the measurement area of ​​the workpiece using the first measuring head when irradiating the laser beam onto the workpiece while moving the holding unit and the condenser relatively along the processing feed direction, and maintains or changes the processing conditions of the workpiece using the laser beam irradiated onto the measurement area in accordance with the electrical resistance or electrical resistivity of the measurement area.

2. a second resistance measuring device having a second measuring head whose relative position with respect to the condenser and the first measuring head is fixed and which is movable together with the condenser relative to the holding unit along the processing feed direction by the processing feed unit, and which measures the electrical resistance or electrical resistivity of the workpiece via the second measuring head; 2. The laser processing device according to claim 1, wherein the first measuring head and the second measuring head are arranged to sandwich the condenser in the processing feed direction.

3. The laser processing apparatus according to claim 2, characterized in that when the laser beam is irradiated onto the workpiece while the holding unit and the condenser are moved relatively along the processing feed direction, the controller measures the electrical resistance or electrical resistivity using one of the first measuring head and the second measuring head which is ahead of the condenser in the processing feed direction.

4. an indexing feed unit having a second motor for relatively moving the holding unit and the light collector along an indexing feed direction intersecting the processing feed direction; When the workpiece is processed with the laser beam, a first processing feed that moves the holding unit and the condenser relatively so that the first measuring head precedes the condenser in the processing feed direction; a first indexing feed that moves the holding unit and the light collector relatively in the indexing feed direction; a second processing feed that relatively moves the holding unit and the condenser so that the second measuring head precedes the condenser in the processing feed direction; a second indexing step for relatively moving the holding unit and the light collector in the indexing direction; 4. The laser processing apparatus according to claim 2, wherein the controller moves the holding unit and the condenser relatively to each other so as to sequentially repeat the above.

5. A laser processing method for processing a workpiece with a laser beam, comprising: a holding step of holding the workpiece with a holding unit; a laser beam irradiation step in which, when the laser beam is irradiated onto the workpiece while the holding unit and the condenser are moved relatively along the processing feed direction, the electrical resistance or electrical resistivity of the measurement area of ​​the workpiece is measured using a first measuring head whose relative position with respect to the condenser is fixed, and the processing conditions of the workpiece using the laser beam irradiated onto the measurement area are maintained or changed depending on the electrical resistance or electrical resistivity of the measurement area; A laser processing method comprising:

6. The computer installed in the laser processing equipment A program for executing a laser beam irradiation process in which, when a laser beam is irradiated onto a workpiece while a holding unit holding the workpiece and a condenser are moved relatively in a processing feed direction, the program measures the electrical resistance or electrical resistivity of a measurement area of ​​the workpiece using a first measuring head whose relative position with respect to the condenser is fixed, and maintains or changes the processing conditions of the workpiece using the laser beam irradiated onto the measurement area in accordance with the electrical resistance or electrical resistivity of the measurement area.

7. A laser processing device that processes a workpiece with a laser beam, a holding unit for holding the workpiece; a laser beam irradiation unit including a laser oscillator that emits the laser beam and a condenser having a condensing lens that condenses the laser beam emitted from the laser oscillator; a processing feed unit having a first motor for relatively moving the holding unit and the condenser along a processing feed direction; a fluorescence measuring device having a measurement head whose position relative to the condenser is fixed and which is movable together with the condenser relative to the holding unit along the processing feed direction by the processing feed unit, the measurement head including an excitation light source, a condensing lens that condenses excitation light from the excitation light source onto the workpiece, and an optical sensor that receives fluorescence emitted from the workpiece by absorbing the excitation light; a controller having a processor and a memory and controlling the laser beam irradiation unit and the processing feed unit; Equipped with The controller changes the processing conditions of the workpiece by the laser beam irradiated onto the measurement area in accordance with the number of photons of fluorescence from the measurement area of ​​the workpiece obtained using the measurement head when irradiating the laser beam onto the workpiece while moving the holding unit and the condenser relatively along the processing feed direction.

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