Laser processing apparatus and laser processing method

Abstract

To suppress accuracy in following displacement of a laser beam incident surface from deteriorating.SOLUTION: A laser processing device 1 executes trace processing, modified region formation processing and follow-up processing. In the tracing processing, displacement data and driving data are obtained, along a line 5, with a follow-up starting position TS0 set as a starting point. In the modified region formation processing, starting and stopping of radiation of processing laser light L1 for processing are controlled, so that a modified region 6 is formed along the line 5. In the follow-up processing, when the modified region 6 is formed, a light condensing part 14 is moved along an optical axis direction by an actuator 18 on the basis of the driving data. In the follow-up processing, early follow-up processing for driving the actuator 18 on the basis of the driving data can be executed, with a side closer to a front side by a correction distance than the follow-up starting position TS0 set as a starting point.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a laser processing apparatus and a laser processing method.

Background Art

[0002] There is known a laser processing apparatus that forms a modified region along a line on an object by moving the condensing point of a first laser beam along the line while irradiating the object with the first laser beam. In such a laser processing apparatus, while irradiating the object with the first laser beam through a condensing lens along the line, the condensing lens is moved along the optical axis direction by an actuator so that the condensing point of the first laser beam follows the displacement of the laser beam incident surface of the object (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the laser processing apparatus as described above, for example, when performing laser processing on an object in which the displacement of the laser beam incident surface changes steeply, overshoot (rapidly changing beyond the target value) occurs in the drive data for driving the actuator, and there is a possibility that a delay occurs in the drive with respect to the change in the displacement of the laser beam incident surface. As a result, the error between the displacement of the laser beam incident surface and the movement amount of the condensing lens in the optical axis direction increases, and there is a risk that the accuracy of following the displacement of the laser beam incident surface decreases.

[0005] Therefore, an object of the present invention is to provide a laser processing apparatus and a laser processing method capable of suppressing a decrease in the accuracy of following the displacement of the laser beam incident surface.

Means for Solving the Problems

[0006] The laser processing apparatus according to the present invention is a laser processing apparatus that forms a modified region along a line on an object by irradiating the object with a first laser beam and moving the focal point of the first laser beam along the line, comprising: a support unit for supporting the object; an irradiation unit for irradiating the object with a first laser beam via a focusing lens; a moving mechanism for moving the irradiation unit relative to the support unit along the line; an actuator for moving the focusing lens along the optical axis; a data acquisition unit for receiving a second laser beam reflected from the laser beam incident surface of the object to acquire displacement data related to the displacement of the laser beam incident surface, and for driving the actuator so that the focal point follows the displacement of the laser beam incident surface based on the displacement data; and a control unit for controlling the irradiation unit, the moving mechanism and the actuator, wherein the control unit moves the irradiation unit relative to the support unit along the line using the moving mechanism. While doing so, the system performs a first process in which the data acquisition unit acquires displacement data and drive data, starting from the point when the irradiation position of the second laser beam on the laser beam incident surface is located at the tracking start position; a second process in which, after the first process, the irradiation unit is moved relative to the line by the moving mechanism, and the start and stop of irradiation of the first laser beam by the irradiation unit is controlled to form a modified region on the target object; and a third process in which, when the modified region is formed along the line by the second process, the actuator moves the focusing lens along the optical axis direction based on the drive data acquired in the first process. In the third process, an early tracking process can be performed in which the actuator is driven based on the drive data acquired in the first process, starting from the point when the irradiation position of the second laser beam on the laser beam incident surface is located one correction distance in the relative movement direction of the irradiation unit relative to the tracking start position.

[0007] The laser processing method according to the present invention is a laser processing method that uses a laser processing apparatus to irradiate an object with a first laser beam and move the focal point of the first laser beam along a line to form a modified region on the object along a line, wherein the laser processing apparatus comprises a support part for supporting the object, an irradiation part for irradiating the object with a first laser beam via a focusing lens, a moving mechanism for moving the support part and / or the irradiation part along a line, an actuator for moving the focusing lens along the optical axis, and a data acquisition unit for receiving a second laser beam reflected from the laser beam incident surface of the object to acquire displacement data related to the displacement of the laser beam incident surface, and for driving the actuator so that the focal point follows the displacement of the laser beam incident surface based on the displacement data, wherein the support part and / or the irradiation part are moved along a line by the moving mechanism The process includes: a first step in which displacement data and drive data are acquired by a data acquisition unit, starting when the focusing point is located at the tracking start position while moving along the line; a second step in which, after the first step, the support unit and / or irradiation unit are moved along the line by the moving mechanism, and the irradiation unit irradiates the object with a first laser beam to form a modified region; and a third step in which, when forming a modified region along the line in the second step, the focusing lens is moved along the optical axis direction by an actuator based on the drive data acquired in the first step, wherein the third step includes an early tracking step in which the actuator is driven based on the drive data acquired in the first step, starting when the irradiation position of the second laser beam on the laser beam incident surface is located one correction distance in the relative movement direction of the irradiation unit forward of the tracking start position.

[0008] In such laser processing apparatuses and methods, when forming a modified region on an object along a line, the timing of reproducing the drive data can be advanced compared to the time of acquiring the drive data. Therefore, even if overshoot occurs in the drive data, the delay in actuator operation due to the overshoot can be reduced when forming the modified region, and the error between the displacement of the laser beam incident surface and the amount of movement of the focusing lens in the optical axis direction can be reduced. Consequently, it is possible to suppress a decrease in the accuracy of tracking the displacement of the laser beam incident surface.

[0009] In the laser processing apparatus according to the present invention, the control unit moves the irradiation unit relative to the line using a moving mechanism, and starting from the point when the irradiation position of the second laser beam on the laser beam incident surface is at the tracking start position, it drives the actuator based on the drive data acquired in the first process and performs a fourth process in which it detects movement amount data related to the amount of movement of the focusing lens in the optical axis direction using a sensor. Based on the displacement data or drive data acquired in the first process and the movement amount data detected in the fourth process, it calculates a correction distance and / or outputs information related to the correction distance via an output unit. In this case, it becomes possible to calculate and / or output the correction distance using the displacement data or drive data and the actual movement amount data of the focusing lens.

[0010] The laser processing apparatus according to the present invention includes an input unit that receives input from a user to perform a test of early tracking processing. When the control unit receives such input from the input unit, it may perform a first process and a fourth process, and calculate a correction distance based on the displacement data or drive data acquired in the first process and the movement amount data acquired in the fourth process. In this case, the correction distance can be automatically calculated by the user providing input to perform a test of early tracking processing via the input unit.

[0011] The laser processing apparatus according to the present invention includes an input unit that receives input from a user to perform a test of early tracking processing. When the control unit receives such input from the input unit, it performs the first and fourth processes. While relatively moving the irradiation unit along the line using a moving mechanism, the control unit starts from the point when the irradiation position of the second laser beam on the laser beam incident surface is located a correction candidate distance in the relative movement direction of the irradiation unit from the tracking start position. Based on the drive data acquired in the first process, it drives the actuator and performs a fifth process multiple times, changing the correction candidate distance, to acquire movement amount data related to the amount of movement of the focusing lens in the optical axis direction using a sensor. Based on the displacement data or drive data acquired in the first process and the multiple movement amount data acquired in the fourth process and multiple fifth processes, one of the multiple correction candidate distances may be calculated as the correction distance. In this case, the correction distance can be automatically calculated by the user providing input to perform a test of early tracking processing via the input unit.

[0012] In the laser processing apparatus according to the present invention, the object may have a through hole. When the second laser beam crosses the through hole, overshoot is likely to occur in the drive data. In this regard, the present invention makes it possible to reduce the delay in actuator drive caused by the overshoot when the second laser beam crosses the through hole by early tracking processing.

[0013] In the laser processing apparatus according to the present invention, in the third process, if the irradiation position of the second laser beam is within the range of the through hole, the position of the focusing lens along the optical axis direction may be maintained at a constant position. Normally, when the irradiation position of the second laser beam is within the range of the through hole, overshoot tends to occur in the drive data. In this regard, in the present invention, since the position of the focusing lens along the optical axis direction is maintained at a constant position when the irradiation position of the second laser beam is within the range of the through hole, it is possible to suppress such overshoot.

[0014] In the laser processing apparatus according to the present invention, the line includes a first line and a second line intersecting the first line. In the second process, along the first line, the irradiation unit is moved relative to the object by a moving mechanism, and the start and stop of irradiation of the first laser beam by the irradiation unit are controlled to form a modified region in the object and a crack reaching the laser beam incident surface. Then, along the second line, the irradiation unit is moved relative to the object by a moving mechanism, and the start and stop of irradiation of the first laser beam by the irradiation unit are controlled to form a modified region in the object. In the third process, when forming a modified region along the second line by the second process after forming a modified region along the first line, an early follow-up process may be performed. When forming a modified region along the second line after forming a modified region and a half-cut (crack reaching the laser beam incident surface) along the first line, the object is prone to warping due to the influence of functional elements (device multilayer films and bumps, etc.) and half-cuts provided on the surface side of the object, and overshoot is likely to occur in the drive data. In this regard, the present invention makes it possible to reduce the delay in actuator operation caused by overshoot when forming a modified region along the second line by performing an early follow-up process.

[0015] In the laser processing apparatus according to the present invention, in the third process, when a modified region is formed along the first line by the second process, a normal tracking process may be performed in which the actuator is driven based on the drive data acquired in the first process, starting from the tracking start position. In this case, a modified region can be formed along the first line under the execution of the normal tracking process.

[0016] The laser processing apparatus according to the present invention may include an input unit that receives input regarding the correction distance from the user, and a display unit that displays a setting screen for setting the correction distance according to the input from the input unit. In this case, the user can input the correction distance via the input unit and set the correction distance on the setting screen.

[0017] In the laser processing apparatus according to the present invention, in the third process, the position along the optical axis direction of the condenser lens may be maintained at a fixed position at the initial stage and / or the final stage of the second process. Usually, at the initial stage and / or the final stage of the second process, since the second laser beam straddles the edge portion of the object, overshoot is likely to occur in the drive data. In this regard, in the present invention, since the position along the optical axis direction of the condenser lens is maintained at a fixed position at the initial stage and / or the final stage of the second process, it is possible to suppress the overshoot.

Effect of the Invention

[0018] According to the present invention, it is possible to provide a laser processing apparatus and a laser processing method capable of suppressing a decrease in the accuracy of following with respect to the displacement of the laser light incident surface.

Brief Description of the Drawings

[0019] [Figure 1] FIG. 1 is a schematic plan view showing a laser processing apparatus according to an embodiment. [Figure 2] FIG. 2 is a perspective view showing an object according to an embodiment. [Figure 3] FIG. 3 is a configuration diagram showing a laser processing head according to an embodiment. [Figure 4] FIG. 4 is a cross-sectional view of an object for explaining a trace process according to an embodiment. [Figure 5] FIG. 5 is a cross-sectional view of an object for explaining a follow-up process according to an embodiment. [Figure 6] FIG. 6 is another cross-sectional view of an object for explaining a follow-up process according to an embodiment. [Figure 7] FIG. 7 is a graph showing the difference between drive data and lens movement amount. [Figure 8] FIG. 8 is a graph showing the difference between the displacement of the laser light incident surface and the lens movement amount. [Figure 9] FIG. 9 is a flowchart showing an example of processing when the follow-up test button of the GUI is operated. [Figure 10]FIG. 10 is a flowchart showing another processing example when the follow-up test button of the GUI is operated. [Figure 11] FIG. 11 is a flowchart showing another processing example when the follow-up test button of the GUI is operated. [Figure 12] FIG. 12(a) is a diagram showing an example of a setting screen displayed on the GUI. FIG. 12(b) is a diagram showing another example of the setting screen displayed on the GUI. FIG. 12(c) is a diagram showing another example of the setting screen displayed on the GUI. FIG. 12(d) is a diagram showing another example of the setting screen displayed on the GUI. [Figure 13] FIG. 13(a) is a graph showing an example of the displacement of the laser light incident surface, drive data, and lens movement amount. FIG. 13(b) is a graph showing another example of the displacement of the laser light incident surface, drive data, and lens movement amount. [Figure 14] FIG. 14 is a cross-sectional view of an object for explaining the follow-up process according to a modified example. [Figure 15] FIG. 15 is another cross-sectional view of an object for explaining the follow-up process according to a modified example.

BEST MODE FOR CARRYING OUT THE INVENTION

[0020] Hereinafter, embodiments will be described in detail with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0021] As shown in FIG. 1, the laser processing apparatus 1 is an apparatus for laser-processing an object 100. The laser processing apparatus 1 forms a modified region along a line on the object 100 by moving the condensing point (condensing position, at least a part of the condensing region) of the processing laser light along a line where formation of the modified region is planned while irradiating the object 100 with the processing laser light. The laser processing apparatus 1 includes a stage 7, a laser processing head 10A, a vertical axis rail 22, a horizontal axis rail 24, an imaging unit 25, a GUI 9, and a control unit 8.

[0022] As shown in Figure 2, line 5 is set on object 100. Line 5 is a virtual line for cutting object 100. Line 5 is not limited to a straight line; it may be curved, a three-dimensional shape combining both, or a line with specified coordinates. Line 5 is not limited to a virtual line; it may be a line actually drawn on the surface of object 100.

[0023] The modified regions may be formed continuously or intermittently. The modified regions may be in the form of rows or points; the important thing is that the modified regions are formed at least inside the object 100. Furthermore, cracks may be formed starting from the modified regions, and both the cracks and the modified regions may be exposed on the outer surface (front, back, or outer periphery) of the object 100. The laser beam incident surface when forming the modified regions may be the front surface 100a of the object 100 or the back surface 100b of the object 100.

[0024] A modified region is a region in which the density, refractive index, mechanical strength, or other physical properties differ from those of the surrounding area. Examples of modified regions include melted regions (meaning at least one of the following: regions that have melted and then resolidified, regions in a molten state, and regions in the process of resolidifying from melt), crack regions, dielectric breakdown regions, refractive index change regions, and regions where these are mixed. Modified regions in the material of object 100 include regions where the density of the modified region has changed compared to the density of the unmodified region, and regions where lattice defects have formed. If the material of object 100 is single-crystal silicon, the modified region can also be called a high dislocation density region.

[0025] Regions where the density of the molten region, refractive index change region, modified region changes compared to the density of the unmodified region, and regions where lattice defects are formed may further contain cracks (fractures, microcracks) within these regions or at the interface between the modified and unmodified regions. The contained cracks may extend across the entire modified region, or form in only a part or multiple parts. Object 100 includes a substrate made of a crystalline material having a crystalline structure.

[0026] For example, object 100 includes a substrate formed from at least one of gallium nitride (GaN), silicon (Si), silicon carbide (SiC), LiTaO3, and sapphire (Al2O3). In other words, object 100 includes, for example, a gallium nitride substrate, a silicon substrate, a SiC substrate, a LiTaO3 substrate, or a sapphire substrate. The crystalline material may be either anisotropic or isotropic. Furthermore, object 100 may include a substrate made of an amorphous material having an amorphous structure, for example, a glass substrate.

[0027] In this embodiment, the laser processing apparatus 1 can form a modified region by forming multiple modified spots (processing marks) along line 5. In this case, the modified region is formed by the convergence of multiple modified spots. A modified spot is a modified portion formed by one pulse of pulsed laser light (i.e., one pulse of laser irradiation: laser shot). Examples of modified spots include crack spots, melting spots, refractive index change spots, or a mixture of at least one of these. The size of the modified spots and the length of the cracks that are generated can be appropriately controlled considering the required cutting accuracy, the required flatness of the cut surface, the thickness and type of the object 100, the crystal orientation, etc. In this embodiment, modified spots can be formed as a modified region along line 5.

[0028] In one example shown in Figure 2, the object 100 is, for example, a substrate made of a semiconductor material such as silicon, on which multiple functional elements are formed in a matrix on the surface side. The functional elements are, for example, light-receiving elements such as photodiodes, light-emitting elements such as laser diodes, or circuit elements formed as circuits. When the object 100 is supported on the stage 7 (see Figure 1), for example, the surface 100a of the object 100 (the side with the multiple functional elements) is attached to the film 112 stretched over the annular frame 111.

[0029] Object 100 is provided with an orientation flat indicating the crystal orientation. Line 5 is set up in a grid pattern such that multiple lines 5a extending parallel to each other and multiple lines 5b extending perpendicular to line 5a and parallel to each other pass between adjacent functional elements (hereinafter also referred to as "streets"). Multiple through holes H0 penetrating from the surface 100a to the back surface 100b are formed in object 100 so as to be arranged at predetermined intervals in a plan view. Object 100 is, for example, a wafer with a thickness of 300 μm, and there are abrupt displacements on the outer surface other than the edge.

[0030] As shown in Figure 1, Stage 7 is a support for the object 100. Stage 7 is configured to rotate about an axis parallel to the vertical. The object 100 is placed on Stage 7. Stage 7 is rotationally driven by the driving force of a known drive device such as a motor. Stage 7 supports the object 100 by holding the frame 111 (see Figure 2) with a clamp and by adsorbing the film 112 (see Figure 2) with a vacuum chuck.

[0031] As shown in Figures 1 and 3, the laser processing head 10A irradiates the object 100 placed on the stage 7 with a processing laser beam L1, which is the first laser beam, via the focusing unit 14, thereby forming a modified region inside the object 100. The laser processing head 10A is movable linearly in the vertical direction along the vertical axis rail 22 by the driving force of a known drive device such as a motor. The laser processing head 10A is also movable linearly in the horizontal direction along the horizontal axis rail 24 by the driving force of a known drive device such as a motor. The laser processing head 10A constitutes the irradiation unit. The focusing unit 14 includes a focusing lens.

[0032] As shown in Figure 3, the laser processing head 10A comprises a housing 11, an incident unit 12, an adjustment unit 13, and a focusing unit 14. The incident unit 12 causes processing laser light L1 output from a light source (not shown) to enter the housing 11. The light source outputs processing laser light L1 that is penetrating to the object 100, for example, by a pulse oscillation method. The adjustment unit 13 is located inside the housing 11. The adjustment unit 13 adjusts the processing laser light L1 incident from the incident unit 12. Each component of the adjustment unit 13 is attached to an optical base 29 provided inside the housing 11. The optical base 29 is integrated with the housing 11.

[0033] The adjustment unit 13 includes an attenuator 31, a beam expander 32, a mirror 33, a reflective spatial light modulator 34, and an imaging optical system 35. The attenuator 31 adjusts the output of the processing laser beam L1 incident from the incident unit 12. The beam expander 32 expands the diameter of the processing laser beam L1 whose output has been adjusted by the attenuator 31. The mirror 33 reflects the processing laser beam L1 whose diameter has been expanded by the beam expander 32.

[0034] The reflective spatial light modulator 34 modulates the processing laser light L1 reflected by the mirror 33. The reflective spatial light modulator 34 is, for example, a reflective liquid crystal on silicon (LCOS) spatial light modulator (SLM). The imaging optical system 35 constitutes a bilateral telecentric optical system in which the reflective surface 34a of the reflective spatial light modulator 34 and the entrance pupil surface 14a of the light-gathering unit 14 are in an imaging relationship. The imaging optical system 35 is composed of three or more lenses.

[0035] The light-gathering unit 14 is positioned to pass through a hole 26a formed in the lower wall of the housing 11. The light-gathering unit 14 focuses the processing laser beam L1, which has been adjusted by the adjustment unit 13, and emits it out of the housing 11. In such a laser processing head 10A, the processing laser beam L1 enters the housing 11 from the incident unit 12, travels through it, is sequentially reflected by the mirror 33 and the reflective spatial light modulator 34, and then is emitted out of the housing 11 from the light-gathering unit 14.

[0036] The laser processing head 10A further comprises a dichroic mirror 15, a distance measuring sensor 16, an observation unit 17, an actuator 18, and a circuit unit 19. The dichroic mirror 15 is positioned between the imaging optical system 35 and the light-gathering unit 14. The dichroic mirror 15 transmits the processing laser light L1. From the viewpoint of suppressing astigmatism, the dichroic mirror 15 is preferably, for example, cube-shaped or two plate-shaped mirrors arranged in a twisted relationship.

[0037] The distance measuring sensor 16 irradiates the laser beam incident surface of the object 100 with a second laser beam, the distance measuring laser beam L2, and receives the reflected light of the distance measuring laser beam L2 reflected from the laser beam incident surface. The distance measuring sensor 16 acquires information about the received reflected light as displacement data relating to the displacement (including unevenness and inclination, etc.) of the laser beam incident surface of the object 100. The displacement data is, for example, a voltage value corresponding to the received reflected light.

[0038] As the distance measuring sensor 16 is a sensor coaxial with the processing laser beam L1, sensors such as astigmatism sensors can be used. If the sensor is on a different axis from the processing laser beam L1, sensors such as triangulation sensors, laser confocal sensors, white light confocal sensors, spectral interferometry sensors, and astigmatism sensors can be used as the distance measuring sensor 16. The type of distance measuring sensor 16 is not particularly limited, and various sensors can be used. As the distance measuring sensor 16 coaxial with the processing laser beam L1, a triangulation sensor that utilizes the eccentricity of the distance measuring laser beam L2 and its reflected light in the focusing unit 14 can be used. The distance measuring sensor 16 constitutes the data acquisition unit.

[0039] The observation unit 17 outputs observation light L20 for observing the laser beam incident surface of the object 100, and detects the observation light L20 reflected from the laser beam incident surface. In other words, the observation light L20 output from the observation unit 17 is irradiated onto the laser beam incident surface via the focusing unit 14, and the observation light L20 reflected from the laser beam incident surface is detected by the observation unit 17 via the focusing unit 14. The wavelengths of the processing laser light L1, the distance measuring laser light L2, and the observation light L20 are all different from each other (at least their central wavelengths are offset from each other).

[0040] The actuator 18 is mounted on the optical base 29. The actuator 18 moves the light-gathering unit 14 along its optical axis (hereinafter also simply referred to as "optical axis direction") by means of a driving force, for example, a piezoelectric element. The circuit unit 19 is, for example, a plurality of circuit boards. The circuit unit 19 processes the signal output from the distance sensor 16 and the signal input to the reflective spatial light modulator 34. The circuit unit 19 controls the actuator 18 based on the signal output from the distance sensor 16. The circuit unit 19 is electrically connected to the control unit 8 (see Figure 1).

[0041] The circuit unit 19 acquires drive data to drive the actuator 18 so that the focal point (focusing unit 14) of the processing laser beam L1 follows the laser beam incident surface, based on the displacement data acquired by the distance measuring sensor 16. For example, the circuit unit 19 calculates a drive voltage value (control command value) as drive data to drive the actuator 18 so that the voltage value as displacement data becomes a target voltage value. The circuit unit 19 drives the actuator 18 based on the drive data to make the focal point of the processing laser beam L1 follow the displacement of the laser beam incident surface. The drive data may also be waveform data with the horizontal axis of the drive voltage value as position (coordinate or distance) and the vertical axis as the drive voltage value. The circuit unit 19 stores the drive data.

[0042] The target voltage value is a reference (target) voltage value for driving the focusing unit 14 to follow the laser beam incident surface, and is a value based on the voltage value acquired by the distance measuring sensor 16 during height setting, as described later. The control that drives the actuator 18 to follow the laser beam incident surface will hereafter also be called AF (autofocus) tracking control. In AF tracking control, the focusing unit 14 moves along the optical axis direction based on the displacement data so that the distance between the laser beam incident surface of the object 100 and the focusing position of the processing laser beam L1 is kept constant. The function of executing AF tracking control and the function of storing the drive data may be provided by the control unit 8 or other circuit units. The circuit unit 19 constitutes the data acquisition unit.

[0043] Returning to Figure 1, the vertical axis rail 22 is a rail that extends vertically. The vertical axis rail 22 is attached to the laser processing head 10A via the mounting portion 21. The vertical axis rail 22 moves the laser processing head 10A vertically so that the focal point of the processing laser beam L1 moves vertically. The horizontal axis rail 24 is a rail that extends horizontally. The horizontal axis rail 24 is attached to the vertical axis rail 22 via the mounting portion 23. The horizontal axis rail 24 moves the laser processing head 10A relative to the stage 7 along line 5 so that the focal point of the processing laser beam L1 moves along line 5. The horizontal axis rail 24 constitutes a moving mechanism.

[0044] The imaging unit 25 images the object 100 from a direction along the incident direction of the processing laser beam L1. The imaging unit 25 includes an alignment camera AC and an imaging unit IR. The alignment camera AC and the imaging unit IR are mounted together with the laser processing head 10A on the mounting unit 21. The alignment camera AC, for example, uses light transmitted through the object 100 to image a device pattern, etc. The image obtained is used for aligning the irradiation position of the processing laser beam L1 with respect to the object 100. The imaging unit IR images the object 100 using light transmitted through the object 100. For example, if the object 100 is a wafer containing silicon, the imaging unit IR uses light in the near-infrared region. In the laser processing apparatus 1, the processing state of laser processing can be confirmed non-destructively using the imaging unit IR.

[0045] The control unit 8 is configured as a computer device including a processor, memory, storage, and communication devices. In the control unit 8, software (programs) loaded into memory, etc., are executed by the processor, and the reading and writing of data in memory and storage, as well as communication by communication devices, are controlled by the processor. The control unit 8 controls each part of the laser processing apparatus 1 and realizes various functions.

[0046] The control unit 8 controls at least the operation of the stage 7, the operation of the laser processing head 10A, the movement of the laser processing head 10A along the vertical axis rail 22 and the horizontal axis rail 24, and the operation of the actuator 18. The control unit 8 moves the laser processing head 10A relative to the stage 7 along the line 5, and while positioning the focal point of the processing laser beam L1 on the line 5 in the object 100, controls the start and stop of irradiation of the processing laser beam L1 from the laser processing head 10A under AF tracking control, thereby forming a modified region along the line 5.

[0047] The formation and cessation of the modified region can be switched as follows. For example, in the laser processing head 10A, the formation and cessation of the formation of the modified region can be switched by switching the start and stop (ON / OFF) of the irradiation (output) of the processing laser light L1. Specifically, if the laser oscillator is composed of a solid-state laser, the start and stop of the irradiation of the processing laser light L1 can be switched at high speed by switching the ON / OFF of a Q switch (AOM (acousto-optic modulator), EOM (electro-optic modulator), etc.) provided in the resonator. If the laser oscillator is composed of a fiber laser, the start and stop of the irradiation of the processing laser light L1 can be switched at high speed by switching the ON / OFF of the output of the semiconductor lasers constituting the seed laser and amplifier (excitation) laser. If the laser oscillator uses an external modulation element, the ON / OFF of the irradiation of the processing laser light L1 can be switched at high speed by switching the ON / OFF of an external modulation element (AOM, EOM, etc.) provided outside the resonator.

[0048] Alternatively, the formation and cessation of the modified region may be achieved in the following ways: For example, the optical path of the processing laser beam L1 may be opened and closed by controlling a mechanical mechanism such as a shutter, thereby switching between the formation and cessation of the modified region. The formation of the modified region may be stopped by switching the processing laser beam L1 to CW light (continuous wave). The formation of the modified region may be stopped by displaying a pattern (for example, a textured pattern that causes laser scattering) on ​​the liquid crystal layer of the reflective spatial light modulator 34 that prevents the focusing state of the processing laser beam L1 from being modified. The formation of the modified region may be stopped by controlling an output adjustment unit such as an attenuator to reduce the output of the processing laser beam L1 to a level that prevents the formation of the modified region. The formation of the modified region may be stopped by switching the polarization direction. The formation of the modified region may be stopped by scattering (skipping) the processing laser beam L1 in a direction other than the optical axis and cutting it off.

[0049] The control unit 8 can, in cooperation with the circuit unit 19, perform a trace processing process in which a distance measuring laser beam L2 is scanned along line 5 and then a processing laser beam L1 is scanned under AF tracking control to form a modified region, and a real-time processing process in which a distance measuring laser beam L2 is scanned along line 5 while a processing laser beam L1 is scanned under AF tracking control to form a modified region.

[0050] The tracing process includes tracing (first process), modification region formation process (second process), and tracking process (third process). In the tracing process, a distance measuring laser beam L2 is scanned along line 5 by a distance measuring sensor 16, and displacement data and drive data are acquired by the circuit unit 19. In the modification region formation process, after the tracing process, a processing laser beam L1 is scanned along line 5 by a laser processing head 10A to form a modification region on the object 100. In the tracking process, AF tracking control is performed when forming the modification region. In the tracking process, early tracking processing is possible, in which AF tracking control is performed by advancing the start point of drive data playback by the correction distance, and normal tracking processing is possible, in which AF tracking control is performed without advancing the start point of drive data playback.

[0051] In the real-time machining process, the distance measuring laser beam L2 is scanned along line 5 by the distance measuring sensor 16, and displacement data and drive data are acquired by the circuit unit 19. Based on the drive data, the machining laser beam L1 is scanned by the laser machining head 10A to form a modified region on the target object 100 under AF tracking control. In the real-time machining process, each process of the trace machining process (tracing process, modified region formation process, and tracking process) is executed simultaneously and in parallel. Details of each process executed by the control unit 8 and the circuit unit 19 will be described later.

[0052] In the tracing process of this embodiment, as shown in Figure 4, the laser processing head 10A is moved relative to the horizontal axis rail 24 along line 5, and displacement data and drive data are acquired and recorded by the distance measuring sensor 16 and the circuit unit 19, with the starting point being when the irradiation position of the distance measuring laser beam L2 on the laser beam incident surface is at the tracking start position TS0 and the ending point being the tracking end position TE0. The section from the tracking start position TS0 to the tracking end position TE0 is the tracking section in which AF tracking control is performed.

[0053] In the laser processing apparatus 1 of this embodiment, the tracking section can be set arbitrarily. That is, in the laser processing apparatus 1, the tracking start position TS0 and the tracking end position TE0 can be set arbitrarily. The tracking start position TS0 and the tracking end position TE0 may be set based on light intensity, or based on coordinates, or they may be set by intentionally shifting them by a predetermined amount from the position based on light intensity or coordinates. Light intensity reference is a method of determining the reference for the tracking start position TS0 by detecting the edge of the object 100 based on the detection value of the distance measuring sensor 16. Coordinate reference is a method of determining the reference for the tracking start position TS0 based on the set coordinates. The tracking start position TS0 and the tracking end position TE0 may be set and stored in the control unit 8. The tracking section may correspond to the effective area portion inside the edge (periphery) of the object 100. The drive data here may be waveform data in a graph where the horizontal axis is the position along line 5 and the vertical axis is the drive voltage value of actuator 18.

[0054] In the modification region formation process of this embodiment, after the tracing process, as shown in Figure 5, the laser processing head 10A is moved relative to the line 5 by the horizontal axis rail 24 from one end to the other, while the start and stop of irradiation of the processing laser light L1 by the laser processing head 10A are controlled. This moves the focal point of the processing laser light L1 from one end to the other of the line 5, and a modification region 6 is formed inside the object 100 along the line 5 from one end to the other. In addition, in the modification region formation process, after the tracing process, as shown in Figure 6, the laser processing head 10A is moved relative to the line 5 by the horizontal axis rail 24 from the other end to the one end of the line 5, while the processing laser light L1 is irradiated by the laser processing head 10A. This causes the processing laser beam L1 to be focused into the object 100, and the focusing point to be moved from the other end of the line 5 to the one end, thereby forming a modified region 6 inside the object 100.

[0055] In the tracking process of this embodiment, when a modified region is formed along the line 5 by the modified region formation process, AF tracking control is performed by moving the focusing unit 14 along the optical axis direction using the actuator 18 based on the drive data acquired in the tracing process. Here, in the early tracking process performed in the tracking process, as shown in Figure 5, when the laser processing head 10A is moved relative to the line 5 from one end to the other, the actuator 18 is driven based on the drive data (i.e., the drive data is reproduced by the actuator 18) starting from the point when the irradiation position of the distance measuring laser beam L2 on the laser beam incident surface is located one correction distance forward from the tracking start position TS0 in the relative movement direction of the laser processing head 10A.

[0056] Furthermore, in the early tracking process performed during the tracking process, as shown in Figure 6, when the laser processing head 10A is moved relative to the other end of line 5 from the other end to the one end, the actuator 18 is driven based on the drive data (i.e., the drive data is played back in reverse by the actuator 18) starting from the point when the irradiation position of the distance measuring laser beam L2 on the laser beam incident surface is located one correction distance closer to the laser processing head 10A in the relative movement direction than the tracking start position TS0.

[0057] In the early tracking process, the timing at which the actuator 18 is started to be driven by the drive data is such that the optical axis of the light-gathering unit 14 is shifted by a correction distance from the tracking start position TS0 toward the edge of the object 100. When the drive data is played back or reversed in the early tracking process, the coordinates associated with the drive data are shifted by a correction distance toward the rear in the relative movement direction of the laser processing head 10A compared to the coordinates associated with the drive data during the tracing process.

[0058] In the normal tracking process performed during tracking, the actuator 18 is driven based on the drive data, starting from the point when the irradiation position of the distance measuring laser beam L2 on the laser beam incident surface is at the tracking start position TS0.

[0059] In the tracking process of this embodiment, AF fixing (hereinafter also simply referred to as "AF fixing") is performed at the beginning and end of the modification region formation process to maintain the position of the focusing unit 14 along the optical axis direction at a constant position. In AF fixing, the drive data input to the actuator 18 is fixed (for example, the drive voltage value of the actuator 18 is kept from fluctuating from the voltage value immediately preceding it) to maintain the position of the focusing unit 14 along the optical axis direction. In this tracking process, AF fixing is performed in the section from the tracking start position TS0 to a position located a distance away from the laser processing head 10A by the AF fixing distance in the relative movement direction. Also, in the tracking process, AF fixing is performed in the section from the tracking end position TE0 to a position located a distance away from the laser processing head 10A by the AF fixing distance in the relative movement direction. In this AF fixing, the position of the focusing unit 14 along the optical axis direction is substantially fixed. "Approximately fixed" includes not only a state in which the light-gathering unit 14 does not move from a certain position, but also a state in which the light-gathering unit 14 moves in such a way that its movement is sufficiently smaller than that of the actuator 18 in normal operation (when AF fixing is not performed). In other words, in AD fixed mode, the light-gathering unit 14 may move slowly.

[0060] The control unit 8 moves the laser processing head 10A relative to the horizontal axis rail 24 along the line 5, and starting when the irradiation position of the distance measuring laser beam L2 on the laser beam incident surface is at the tracking start position TS0, it drives the actuator 18 based on the drive data acquired in the tracing process and executes a lens movement amount detection process (fourth process) in which it detects movement amount data related to the amount of movement of the focusing unit 14 in the optical axis direction using a sensor. The lens movement amount detection process may be executed simultaneously or in parallel with the tracing process, or it may be executed separately from the tracing process. The sensor is a known sensor, such as a strain gauge provided on the actuator 18. The movement amount data corresponds to the current position data of the movable part of the actuator 18. The movement amount data of the focusing unit 14 is also referred to as the "lens movement amount".

[0061] The control unit 8 can calculate the correction distance based on the displacement data or drive data acquired in the tracing process and the movement data detected in the lens movement detection process. Figure 7 is a graph showing the drive data and lens movement, and Figure 8 is a graph showing the displacement of the laser beam incident surface and the lens movement. In the graph of Figure 7, the horizontal axis represents the position along line 5, and the vertical axis represents the values ​​corresponding to the drive data and lens movement. In the graph of Figure 8, the horizontal axis represents the position along line 5, and the vertical axis represents the values ​​corresponding to the displacement of the laser beam incident surface and the lens movement. For example, as shown in Figure 7, the control unit 8 calculates the peak position where the drive data is at its peak, and also calculates the peak position where the lens movement is at its peak. The control unit 8 calculates the difference ΔD1 between these peak positions as the value corresponding to the correction distance.

[0062] For example, as shown in Figure 8, the control unit 8 calculates the peak position where the displacement of the laser beam incident surface, obtained from the displacement data, reaches its peak, and also calculates the peak position where the lens movement amount reaches its peak. The control unit 8 calculates the difference ΔD2 between these peak positions as a value corresponding to the correction distance. The control unit 8 can output information regarding the calculated correction distance via the GUI 9. The correction distance can also be obtained by acquiring the waveform of each data with an oscilloscope and converting the time difference between the peaks of each data into a distance using the scan speed.

[0063] The control unit 8 may calculate the correction distance from the difference ΔD1 only, from the difference ΔD2 only, or from the differences ΔD1 and ΔD2. If there are multiple peaks in the displacement data, drive data, and movement amount data, multiple candidate correction distances may be calculated and one of them may be selected as the correction distance.

[0064] The correction distance may be calculated based on the higher peak among multiple peaks (when a large overshoot occurs). The correction distance may also be calculated based on the larger of the multiple differences ΔD1 and ΔD2. The method may also incorporate masking, such as prioritizing the number of peak occurrences and excluding peaks with low occurrence frequency from the candidates. A limit may be set on the correction distance, and at least one of the multiple correction distance candidates that exceeds this limit may be excluded from the candidates. Trace processing and lens movement detection processing may be performed along multiple different lines 5 to obtain multiple correction distance candidates, and the average value of these may be used as the correction distance. Multiple correction distance candidates may be used as different correction distances for each of the multiple lines 5.

[0065] As shown in Figure 1, GUI9 displays various information. GUI9 includes, for example, a touch panel display. GUI9 accepts various inputs through user operations such as touch. GUI9 accepts input from the user regarding the correction distance for early tracking processing. GUI9 displays information regarding the correction distance for early tracking processing. GUI9 displays a settings screen for setting the correction distance for early tracking processing according to the received input. GUI9 accepts input from the user to run a test of early tracking processing. GUI9 consists of an input unit, a display unit, and an output unit.

[0066] For example, GUI9 receives input from the user to perform an early tracking test (for example, by touching the tracking test button 94 described later) when the object 100 is placed on the stage 7 and attracted, various processing conditions for laser processing have been input, and initial settings have been completed. When this input is received, the control unit 8 performs the following processing.

[0067] Specifically, as shown in Figure 9, a tracing process is performed first. In particular, the distance measuring laser beam L2 is scanned along line 5 based on the set processing speed and other conditions (step S1). In step S1, the irradiation of the processing laser beam L1 is stopped. In step S1, displacement data of the laser beam incident surface along line 5 within the tracking range is acquired, and drive data is generated and acquired from this displacement data (step S2).

[0068] Next, lens movement detection processing is performed. Specifically, the actuator 18 is driven along line 5 within the tracking range based on drive data (step S3). In step S3, movement data of the light-gathering unit 14, which moves in the optical axis direction due to the drive of the actuator 18 within the tracking range, is acquired (step S4). Then, a difference ΔD1 or difference ΔD2 is calculated based on the displacement data or drive data acquired in step S1 and the movement data acquired in step S4, and the correction distance is automatically calculated from the difference ΔD1 or difference ΔD2 (step S5).

[0069] Alternatively, instead of the process shown in Figure 9, the control unit 8 may execute the process shown in Figure 10. In the process shown in Figure 10, after steps S11 to S14 similar to steps S1 to S4 above, the acquired displacement data, drive data, and travel amount data are displayed on the GUI 9 as tracking results (step S15). This allows the user to manually calculate the correction distance by referring to the display on the GUI 9.

[0070] Alternatively, instead of the process shown in Figure 9, the control unit 8 may execute the process shown in Figure 11. In the process shown in Figure 11, after steps S21 to S24 similar to steps S1 to S4 above, the correction candidate distance is set to an initial value and the counter k is set to 1 (steps S25, S26).

[0071] Next, starting from the point when the irradiation position of the distance-measuring laser beam L2 on the laser beam incident surface is located one correction candidate distance in the relative movement direction of the laser processing head 10A relative to the tracking start position TS0, the actuator 18 is driven based on the drive data acquired in step S21 (step S27). In step S27, the amount of movement data of the focusing unit 14 is acquired by the sensor (step S28). It is determined whether the counter k is N, that is, whether steps S27 and S28 have been repeated N times (step S29). If the result in step S29 is NO, the correction candidate distance is varied (for example, +1 mm) and the counter k is counted up (steps S30, S31). After that, the process returns to step S27.

[0072] On the other hand, if the answer in step S29 is YES, then one of the multiple correction candidate distances obtained by varying the distance in step S30 is calculated as the correction distance based on the displacement data or drive data obtained in step S1 and the multiple movement data obtained in steps S24 and S28 (step S30). For example, in step S30, the correction candidate distance at which the difference ΔD1 of the peak position is smallest, as shown in Figure 7, may be calculated as the correction distance. Alternatively, in step S30, the correction candidate distance at which the difference ΔD2 of the peak position is smallest, as shown in Figure 8, may be calculated as the correction distance.

[0073] Figures 12(a), 12(b), 12(c), and 12(d) show examples of setting screens displayed in GUI9. In the figures, the playback correction distance corresponds to the correction distance, and the edge AF fixed distance corresponds to the AF fixed distance when AF fixing is performed. As shown in Figures 12(a), 12(b), 12(c), and 12(d), the user can switch the mode between "Trace" and "Real-time" in the input field 91 of GUI9. When "Trace" is selected in GUI9, the control unit 8 can perform the trace processing. When "Real-time" is selected in GUI9, the control unit 8 can perform the real-time processing.

[0074] In GUI9, the user can input a correction distance value in input field 92. The control unit 8 may set the correction distance based on the value entered in input field 92. Note that in GUI9, if "Real-time" is selected in input field 91, input of a correction distance value is disabled (see Figure 12(c)). In GUI9, the user can input a fixed AF distance value in input field 93. The control unit 8 sets the fixed AF distance based on the value entered in input field 93. In GUI9, the user can touch the tracking test button 94. The tracking test button 94 is a button for inputting the execution of a test of the early tracking process. When the tracking test button 94 is touched, the control unit 8 starts a series of processes shown in Figure 9, Figure 10, or Figure 11, and calculates the correction distance. The calculated correction distance may be automatically entered and displayed in input field 92.

[0075] Next, an example of a laser processing method using the laser processing device 1 will be described.

[0076] The following describes an example in which a modified region 6 is formed on the object 100 along line 5 by irradiating the object 100 with processing laser light L1 and moving the focal point of the processing laser light L1 along line 5. In this example, the mode is selected as "Trace" on the GUI9 settings screen, the correction distance is set by input or automatic calculation, and the distance of the edge to which AF is fixed is entered.

[0077] First, the object 100 is placed on the stage 7 with its back surface 100b facing the laser beam incidence surface and then adsorbed. For example, based on the image of the laser beam incidence surface of the object 100 acquired by the imaging unit 25, the control unit 8 moves the laser processing head 10A vertically and moves the focusing unit 14 vertically so that the focal point of the processing laser beam L1 is positioned on the laser beam incidence surface (height setting). At this time, the voltage value acquired by the distance sensor 16 is stored as the target voltage value.

[0078] Next, a trace process is performed along line 5 to acquire and store displacement data and drive data for the tracking section from the tracking start position TS0 to the tracking end position TE0 (first step). In the trace process, without irradiating the laser processing head 10A with processing laser light L1, the laser processing head 10A is moved relative to line 5 while the distance measuring laser light L2 is irradiated from the distance measuring sensor 16, and voltage values ​​are acquired as displacement data. In the trace process, the distance measuring laser light L2 may be irradiated continuously, or it may be irradiated only on the laser light incident surface of the tracking section. In the trace process, drive data is acquired to drive the actuator 18 so that the voltage value as displacement data acquired by the distance measuring sensor 16 becomes the target voltage value.

[0079] Next, a modification region formation process is performed along multiple lines 5 to form modification regions 6 along multiple lines 5 inside the object 100 (second step). In the modification region formation process, the processing laser light L1 is turned ON in the tracking section and OFF in the other sections. When forming the modification regions 6 by the modification region formation process, a tracking process is performed to execute AF tracking control, which is feedback control that moves the focusing unit 14 vertically to follow the displacement of the laser light incident surface (third step). In the tracking process of this embodiment, the starting point of the playback of the drive data is advanced by the correction distance to perform AF tracking control (early tracking step). Note that the ON / OFF timing of the processing laser light L1 is not advanced. After that, the dicing tape attached to the object 100 is expanded. As a result, the object 100 is cut along each line 5 and made into chips, obtaining multiple chips.

[0080] As described above, in the laser processing apparatus 1 and laser processing method of this embodiment, when forming a modified region 6 on the object 100 along the line 5, the timing of reproducing the drive data can be advanced compared to the time of acquiring the drive data. Therefore, even if an overshoot occurs in the drive data, when forming the modified region 6, the delay in driving the actuator 18 (the delay in the movement of the focusing unit 14 in the optical axis direction) due to the overshoot can be reduced, and the error between the displacement of the laser beam incident surface and the amount of movement of the focusing unit 14 in the optical axis direction can be reduced.

[0081] Therefore, according to this embodiment, it is possible to suppress the decrease in accuracy of tracking the displacement of the laser beam incident surface. Not only at the edge of the object 100, but also in the effective area inside the edge of the object 100, it is possible to suppress the delay in driving the actuator 18 due to steep displacement (occurrence of overshoot). In other words, in this embodiment, for an object 100 with a large displacement of the laser beam incident surface, the displacement data and driving data are measured in advance, and then laser processing is performed with the processing laser beam L1 while operating the actuator 18 with an accelerated playback timing of the driving data (with control of direction in terms of distance or time), thereby improving the positional accuracy of the modified region 6. It is also possible to suppress the delay in driving the actuator 18, which is difficult to address with AF fixed.

[0082] In the laser processing apparatus 1, the control unit 8 performs lens movement detection processing. In the lens movement detection processing, while the laser processing head 10A is moved relative to the line 5, starting from the point when the irradiation position of the distance measuring laser beam L2 on the laser beam incident surface is at the tracking start position TS0, the actuator 18 is driven based on the drive data acquired in the tracing process, and movement data related to the movement of the focusing unit 14 in the optical axis direction is detected by a sensor. The control unit 8 then calculates the correction distance and outputs it via the GUI 9 based on the displacement data or drive data acquired in the tracing process and the movement data detected in the lens movement detection processing. In this case, it is possible to calculate and output the correction distance using the displacement data or drive data and the actual movement data of the focusing unit 14.

[0083] In the laser processing apparatus 1, when the user touches the tracking test button 94 on the GUI 9 and the GUI 9 receives input to execute the early tracking process test, the control unit 8 executes steps S1 and S2 related to the tracing process and steps S3 and S4 related to the lens movement amount detection process. Then, the control unit 8 calculates the correction distance based on the displacement data or drive data acquired in step S1 and the movement amount data acquired in step S4. In this way, the laser processing apparatus 1 can automatically calculate the correction distance by having the user input to execute the early tracking process test via the GUI 9.

[0084] As described above, in the laser processing apparatus 1, if the user touches the follow test button 94 of the GUI 9 and the GUI 9 receives input to execute a test of the early follow processing, the control unit 8 may execute the above steps S21 and S22 related to the trace processing and the above steps S23 and S24 related to the lens movement amount detection processing. The control unit 8 may move the laser processing head 10A relative to the line 5 using the movement mechanism, and starting from the point when the irradiation position of the distance measuring laser beam L2 on the laser beam incident surface is located one correction candidate distance closer to the laser processing head 10A in the relative movement direction than the follow start position, the control unit 8 may execute the above steps S25 to S31, which are performed multiple times by changing the correction candidate distance, while driving the actuator 18 based on the drive data acquired in the trace processing, to acquire movement amount data (fifth processing) related to the amount of movement of the focusing unit 14 in the optical axis direction using a sensor. The control unit 8 may then execute step S32, which calculates one of the multiple candidate correction distances as the correction distance based on the displacement data or drive data acquired in step S21, the amount of movement data acquired in step S24, and the multiple amount of movement data acquired in steps S25 to S31. In this way, the laser processing apparatus 1 can automatically calculate the correction distance by having the user input a test of the early tracking process via the GUI 9.

[0085] In the laser processing apparatus 1, the object 100 has a through hole H0. When the distance measuring laser beam L2 crosses the through hole H0, an overshoot due to a sudden step, which is not seen in mirror wafers, is likely to occur in the drive data. In this regard, the laser processing apparatus 1 can reduce the delay in driving the actuator 18 caused by this overshoot when the distance measuring laser beam L2 crosses the through hole H0 by performing early tracking processing. It is also conceivable to perform AF locking when the distance measuring laser beam L2 crosses the through hole H0, but AF locking is not sufficient and is not effective.

[0086] In the laser processing apparatus 1, the GUI9 accepts input regarding the correction distance from the user and displays a settings screen for setting the correction distance according to that input. In this case, the user can input the correction distance via the GUI9 and set the correction distance on the settings screen.

[0087] In the tracking process, the laser processing apparatus 1 maintains the position of the focusing unit 14 along the optical axis direction at a constant position during the initial and final stages of the modified region formation process. Normally, during the initial and final stages of the modified region formation process, the distance-measuring laser beam L2 crosses the edge of the object 100, making it easy for overshoot to occur in the drive data. In this regard, the laser processing apparatus 1 maintains the position of the focusing unit 14 along the optical axis direction at a constant position during the initial and final stages of the modified region formation process, thereby suppressing this overshoot. This makes it possible to further suppress the decrease in tracking accuracy with respect to the displacement of the laser beam incident surface.

[0088] In the laser processing device 1, the correction distance can be set in the GUI 9. Furthermore, by operating the tracking test button 94 in the GUI 9, it is possible to check in advance whether correction is necessary, or to automatically calculate or suggest the optimal correction distance. As a result, it can handle the processing of various objects 100. The GUI 9 may also include a function to set whether or not to perform early tracking processing.

[0089] Figures 13(a) and 13(b) are graphs showing examples of the displacement of the laser beam incident surface, drive data, and lens movement. In Figures 13(a) and 13(b), the horizontal axis represents the position along line 5. The results in Figures 13(a) and 13(b) are examples of laser processing performed on the same object 100. Figure 13(a) shows an example of tracing processing performed with normal tracking processing as the tracking process. Figure 13(b) shows an example of tracing processing performed with early tracking processing as the tracking process.

[0090] In the example shown in Figure 13(a), when the tracing process related to normal tracking is performed, there is a delay in the driving of the actuator 18 in response to changes in the displacement of the laser beam incident surface, and the error between the displacement of the laser beam incident surface and the amount of movement of the focusing unit 14 becomes large. In this case, as shown in Figure 13(b), by performing the tracing process related to early tracking, the delay in the driving of the actuator 18 in response to changes in the displacement of the laser beam incident surface is reduced, the error between the displacement of the laser beam incident surface and the amount of movement of the focusing unit 14 is reduced, and the accuracy of tracking the displacement of the laser beam incident surface is improved. It should be noted that while the tracking error is greatly reduced in areas where rapid displacement occurs, there is a concern that the tracking error may worsen in areas where the displacement is gradual. However, overall, the object 100 can be said to have been stabilized with reduced tracking error.

[0091] In this embodiment, when processing an object with a thickness of 50 μm (a so-called ultra-thin wafer), the margin for processing conditions is small, so normal tracking processing is more effective than early tracking processing, and therefore normal tracking processing may be performed.

[0092] As described above, one aspect of the present invention is not limited to the embodiments described above.

[0093] In the tracking process of the above embodiment, if the irradiation position of the distance measuring laser beam L2 is within the range of the through hole H0, AF fixing may be performed to maintain the position of the focusing unit 14 along the optical axis direction at a constant position. When the irradiation position of the distance measuring laser beam L2 is within the range of the through hole H0, overshoot is likely to occur in the drive data. In this regard, if the irradiation position of the distance measuring laser beam L2 is within the range of the through hole H0, the position of the focusing unit 14 along the optical axis direction at a constant position can be suppressed. This makes it possible to further suppress the decrease in tracking accuracy with respect to the displacement of the laser beam incident surface.

[0094] The above embodiments and modifications describe an example of performing laser processing on an object 100 in which a through-hole H0 has been formed, but the invention is not limited thereto. One aspect of the present invention is also applicable to an object 100 in which no through-hole H0 has been formed. In this case, as shown in Figure 14, in the modified region formation process, the laser processing head 10A is moved relative to the object 100 by a horizontal axis rail 24 along a line (first line) 5a, and the start and stop of irradiation of the processing laser light L1 by the laser processing head 10A is controlled to form a modified region 6 in the object 100, and a half-cut (not shown), which is a crack that reaches the laser light incident surface, is formed from the modified region 6. Subsequently, as shown in Figure 15, the laser processing head 10A is moved relative to the object 100 by a horizontal axis rail 24 along a line (second line) 5b perpendicular to line 5a, and the start and stop of irradiation of the processing laser light L1 by the laser processing head 10A is controlled to form a modified region 6 in the object 100.

[0095] In this case, during the tracking process, early tracking processing may be performed when forming the modified region 6 along line 5b. Early tracking processing can reduce the delay in driving the actuator 18 due to overshoot when forming the modified region 6 along line 5b. The above effect of suppressing the decrease in tracking accuracy with respect to the displacement of the laser beam incident surface is particularly effective. This is because when forming the modified region 6 along line 5b after forming the modified region 6 and half-cut along line 5a, the object 100 warps due to the influence of functional elements (device multilayer films and bumps, etc.) and half-cut, causing steep irregularities to occur, for example, at the front and rear positions in the direction spanning line 5a, which makes it easy for overshoot to occur in the driving data. Also, in the tracking process, as shown in Figure 14, normal tracking processing may be performed when forming the modified region 6 along line 5a. In this case, the modified region 6 can be formed along line 5a under the execution of normal tracking processing.

[0096] Note that line 5b does not need to be perpendicular to line 5a; it is sufficient if it intersects with it. When forming the modified region 6 along line 5a, a normal follow-up process is performed, but instead, an early follow-up process may be performed.

[0097] In the embodiments and modifications described above, the calculated correction information was displayed and output to GUI9, but it is not necessary to output it to GUI9. The output of GUI9 may also be output using audio or the like. The information output to GUI9 is ​​not limited to numerical values ​​of the correction distance, but can be any information related to the correction distance. For example, a signal that allows tracking error to be grasped (displacement data, etc.) may be displayed on GUI9, in which case the user can determine the correction distance while looking at the signal. In this case, the user can also determine the correction distance that best reduces the tracking error by looking at the parts of the signal where the tracking error is severe (parts where there is overshoot).

[0098] In the above embodiments and modifications, the voltage value corresponding to the reflected light received by the distance measuring sensor 16 is used as displacement data. However, the displacement data is not particularly limited as long as it relates to the displacement of the laser beam incident surface, and such displacement data can be obtained by various known techniques. The displacement data may also be a voltage value obtained by a distance measuring sensor provided on a different axis from the optical axis of the processing laser beam L1. In this case, the obtained voltage value can be treated in the same way as the voltage value of the distance measuring sensor 16 described above. The displacement data may also be data relating to the position of the movable part of the actuator 18. If a sensor capable of measuring the surface shape of the laser beam incident surface of the object 100 is used separately, the data relating to the detection result of that sensor may be used as displacement data. The displacement data may also be the absolute position of the light-gathering unit 14 in the vertical direction. The displacement data may also be the relative position of the light-gathering unit 14 with respect to its height-set position in the vertical direction.

[0099] In the embodiments and modifications described above, an AF difference signal may be acquired in place of or in addition to at least one of the differences ΔD1 and ΔD2. The AF difference signal is the difference between the target voltage value and the post-feedback voltage value, which is the voltage value as potential data acquired by the distance measuring sensor 16 as a result of AF tracking control. The AF difference signal represents how much the focusing unit 14 and the laser beam incident surface are deviating from the target distance. The post-feedback voltage value is the target voltage value when the tracking of the focusing position by AF tracking control is accurately achieved (in this case, the AF difference signal = 0). On the other hand, if the tracking of the focusing position by AF tracking control is not accurately achieved for some reason, the post-feedback voltage value will be a value that is deviating from the target voltage value (in this case, the AF difference signal ≠ 0). As an example, in step S28 above, an AF difference signal may be acquired instead of the movement amount data, and in step S32 above, one candidate correction coefficient when the AF difference signal is smallest may be calculated as the correction distance.

[0100] In the embodiments and modifications described above, the back surface 100b of the object 100 was used as the laser light incident surface, but any other surface of the object 100 may be used as the laser light incident surface. In the embodiments and modifications described above, the modified region 6 may be, for example, a crystalline region, a recrystallized region, or a gettering region formed inside the object 100. The crystalline region is a region that maintains the structure of the object 100 before processing. The recrystallized region is a region that solidifies as a single crystal or polycrystalline material after evaporation, plasmaification, or melting. The gettering region is a region that exhibits a gettering effect, collecting and capturing impurities such as heavy metals, and may be formed continuously or intermittently. Furthermore, for example, the laser processing apparatus 1 may be applied to processing such as ablation.

[0101] In the embodiments and modifications described above, AF fixing was achieved by fixing the drive data of the actuator 18, but instead, AF fixing may be achieved by fixing the voltage value as displacement data. In the embodiments and modifications described above, the moving mechanism only needs to be configured to move at least one of the stage 7 and the laser processing head 10A. In the embodiments and modifications described above, some of the functions of the control unit 8 may be performed by the circuit unit 19. In the embodiments and modifications described above, while drive data is acquired by performing trace processing, the actuator 18 may be driven with the said drive data to acquire movement amount data and / or AF difference signals. In the embodiments and modifications described above, distance differences ΔD1 and ΔD2 were calculated, but instead, time differences may be calculated.

[0102] The components in the embodiments and modifications described above are not limited to the materials and shapes described above, and various materials and shapes can be applied to them. Furthermore, the components in the embodiments and modifications described above can be arbitrarily applied to the components in other embodiments or modifications.

[0103] The constituent elements of one embodiment of the present invention are described below. <Invention 1> A laser processing apparatus that forms a modified region along a line on an object by irradiating the object with a first laser beam and moving the focal point of the first laser beam along the line, A support part that supports the aforementioned object, An irradiation unit that irradiates the object with the first laser light through a focusing lens, A moving mechanism for moving the irradiation unit relative to the support unit along the line, An actuator that moves the aforementioned focusing lens along the optical axis, A data acquisition unit receives a second laser beam reflected from the laser beam incident surface of the object, thereby acquiring displacement data relating to the displacement of the laser beam incident surface, and acquires drive data to drive the actuator so that the focusing point follows the displacement of the laser beam incident surface based on the displacement data. The system comprises the irradiation unit, the moving mechanism, and a control unit that controls the actuator, The control unit, A first process in which, while moving the irradiation unit relative to the line by the moving mechanism, the data acquisition unit acquires the displacement data and the drive data, starting from the point when the irradiation position of the second laser beam on the laser beam incident surface is at the tracking start position, After the first process, a second process is performed in which the irradiation unit is moved relative to the object by the moving mechanism along the line, and the start and stop of irradiation of the first laser beam by the irradiation unit is controlled to form the modified region on the object. When forming the modified region along the line by the second process, a third process is performed in which the actuator moves the focusing lens along the optical axis direction based on the drive data acquired in the first process, In the third process described above, A laser processing apparatus capable of performing an early tracking process that drives the actuator based on the drive data acquired in the first process, starting from the point when the irradiation position of the second laser beam on the laser beam incident surface is located forward by a correction distance in the relative movement direction of the irradiation part from the tracking start position. <Invention 2> The control unit, While moving the irradiation unit relative to the line using the movement mechanism, a fourth process is performed in which, starting from the point when the irradiation position of the second laser beam on the laser beam incident surface is at the tracking start position, the actuator is driven based on the drive data acquired in the first process, and movement amount data related to the amount of movement of the focusing lens in the optical axis direction is detected by a sensor. A laser processing apparatus according to Invention 1, which calculates the correction distance and / or outputs information regarding the correction distance via an output unit, based on the displacement data or drive data acquired in the first process and the movement amount data detected in the fourth process. <Invention 3> It includes an input unit that receives input from the user to perform a test of the aforementioned early tracking process, When the control unit receives the input from the input unit, The first and fourth processes are executed, A laser processing apparatus according to Invention 2, which calculates the correction distance based on the displacement data or drive data acquired in the first process and the movement amount data acquired in the fourth process. <Invention 4> It includes an input unit that receives input from the user to perform a test of the aforementioned early tracking process, When the control unit receives the input from the input unit, The first and fourth processes are executed, While moving the irradiation unit relative to the line using the movement mechanism, a fifth process is performed multiple times, changing the correction candidate distance, starting from the point when the irradiation position of the second laser beam on the laser beam incident surface is located one correction candidate distance forward of the tracking start position in the relative movement direction of the irradiation unit, while driving the actuator based on the drive data acquired in the first process, and acquiring movement amount data related to the amount of movement of the focusing lens in the optical axis direction using a sensor. A laser processing apparatus according to Invention 2, which calculates one of the multiple correction candidate distances as the correction distance based on the displacement data or drive data acquired in the first process and the multiple movement amount data acquired in the fourth process and the multiple fifth processes. <Invention 5> The aforementioned object is a laser processing apparatus according to any one of inventions 1 to 4, having a through hole. <Invention 6> In the third process, if the irradiation position of the second laser beam is within the range of the through hole, the laser processing apparatus according to Invention 5 maintains the position of the focusing lens along the optical axis direction at a constant position. <Invention 7> The aforementioned line includes a first line and a second line that intersects the first line. In the second process described above, While moving the irradiation unit relative to the object along the first line using the moving mechanism, the start and stop of irradiation by the irradiation unit with the first laser light are controlled to form the modified region in the object and to form a crack that reaches the laser light incident surface, Along the second line, the irradiation unit is moved relative to the object by the moving mechanism, and the start and stop of irradiation of the first laser beam by the irradiation unit are controlled to form the modified region on the object. In the third process described above, A laser processing apparatus according to any one of inventions 1 to 6, wherein the early follow-up process is performed when forming the modified region along the second line by the second process after the formation of the modified region along the first line. <Invention 8> In the third process described above, The laser processing apparatus according to Invention 7, wherein when forming the modified region along the first line by the second process, a normal tracking process is performed in which the actuator is driven based on the drive data acquired in the first process, starting from the tracking start position. <Invention 9> An input unit that receives input from the user regarding the correction distance, A laser processing apparatus according to any one of claims 1 to 8 of the invention, comprising: a display unit that displays a setting screen for setting the correction distance in accordance with the input of the input unit. <Invention 10> The laser processing apparatus according to any one of claims 1 to 9 of the invention, wherein the third process maintains the position of the focusing lens along the optical axis direction at a constant position during the initial and / or final stages of the second process. [Explanation of Symbols]

[0104] 1...Laser processing device, 5...Line, 5a...Line (1st line), 5b...Line (2nd line), 6...Modification area, 7...Stage (support unit), 8...Control unit, 9...GUI (output unit, input unit, display unit), 10A...Laser processing head (irradiation unit), 14...Concentrating unit (concentrating lens), 16...Distance sensor (data acquisition unit), 18...Actuator, 19...Circuit unit (data acquisition unit, control unit), 24...Horizontal axis rail (movement mechanism), 100...Object, H0...Through hole, L1...Processing laser beam (1st laser beam), L2...Distance measuring laser beam (2nd laser beam), TS0...Tracking start position, ΔD1, ΔD2...Difference.

Claims

1. A laser processing apparatus that forms a modified region along a line on an object by irradiating the object with a first laser beam and moving the focal point of the first laser beam along the line, A support part that supports the aforementioned object, An irradiation unit that irradiates the object with the first laser light through a focusing lens, A moving mechanism for moving the irradiation unit relative to the support unit along the line, An actuator that moves the aforementioned focusing lens along the optical axis, A data acquisition unit receives a second laser beam reflected from the laser beam incident surface of the object, thereby acquiring displacement data relating to the displacement of the laser beam incident surface, and acquires drive data to drive the actuator so that the focusing point follows the displacement of the laser beam incident surface based on the displacement data. The system comprises the irradiation unit, the moving mechanism, and a control unit that controls the actuator, The control unit, A first process in which, while moving the irradiation unit relative to the line using the moving mechanism, the data acquisition unit acquires the displacement data and the drive data, starting from the point when the irradiation position of the second laser beam on the laser beam incident surface is at the tracking start position, After the first process, a second process is performed in which the irradiation unit is moved relative to the object by the moving mechanism along the line, and the start and stop of irradiation of the first laser beam by the irradiation unit is controlled to form the modified region on the object. When forming the modified region along the line by the second process, a third process is performed in which the actuator moves the focusing lens along the optical axis direction based on the drive data acquired in the first process, In the third process described above, A laser processing apparatus capable of performing an early tracking process that drives the actuator based on the drive data acquired in the first process, starting from the point when the irradiation position of the second laser beam on the laser beam incident surface is located one correction distance forward from the tracking start position in the relative movement direction of the irradiation part.

2. The control unit, While moving the irradiation unit relative to the line using the movement mechanism, a fourth process is performed in which, starting from the point when the irradiation position of the second laser beam on the laser beam incident surface is at the tracking start position, the actuator is driven based on the drive data acquired in the first process, and movement amount data related to the amount of movement of the focusing lens in the optical axis direction is detected by a sensor. The laser processing apparatus according to claim 1, wherein the apparatus calculates the correction distance and / or outputs information regarding the correction distance via an output unit, based on the displacement data or drive data acquired in the first processing and the amount of movement data detected in the fourth processing.

3. It includes an input unit that receives input from the user to perform a test of the aforementioned early tracking process, When the control unit receives the input from the input unit, The first process and the fourth process are executed, The laser processing apparatus according to claim 2, wherein the correction distance is calculated based on the displacement data or drive data acquired in the first processing and the movement amount data acquired in the fourth processing.

4. It includes an input unit that receives input from the user to perform a test of the aforementioned early tracking process, When the control unit receives the input from the input unit, The first process and the fourth process are executed, While moving the irradiation unit relative to the line using the movement mechanism, a fifth process is performed multiple times, changing the correction candidate distance, starting from the point when the irradiation position of the second laser beam on the laser beam incident surface is located one correction candidate distance forward of the tracking start position in the relative movement direction of the irradiation unit, while driving the actuator based on the drive data acquired in the first process, and acquiring movement amount data related to the amount of movement of the focusing lens in the optical axis direction using a sensor. The laser processing apparatus according to claim 2, wherein one of the plurality of correction candidate distances is calculated as the correction distance based on the displacement data or drive data obtained in the first process and the plurality of movement amount data obtained in the fourth process and the plurality of fifth processes.

5. The laser processing apparatus according to claim 1 or 2, wherein the object has a through hole.

6. The laser processing apparatus according to claim 5, wherein in the third process, when the irradiation position of the second laser beam is within the range of the through hole, the position of the focusing lens along the optical axis direction is maintained at a constant position.

7. The aforementioned line includes a first line and a second line intersecting the first line. In the second process described above, While moving the irradiation unit relative to the object along the first line using the movement mechanism, the start and stop of irradiation by the irradiation unit with the first laser light are controlled to form the modified region in the object and to form a crack that reaches the laser light incident surface, While moving the irradiation unit relative to the object along the second line using the moving mechanism, the start and stop of irradiation of the first laser beam by the irradiation unit are controlled to form the modified region on the object. In the third process described above, The laser processing apparatus according to claim 1 or 2, wherein the early follow-up process is performed when the modified region is formed along the second line by the second process after the modified region is formed along the first line.

8. In the third process described above, The laser processing apparatus according to claim 7, wherein when forming the modified region along the first line by the second processing, a normal tracking process is performed in which the actuator is driven based on the drive data acquired in the first processing, starting from the tracking start position.

9. An input unit that receives input from the user regarding the correction distance, A laser processing apparatus according to claim 1 or 2, comprising: a display unit that displays a setting screen for setting the correction distance in accordance with the input of the input unit.

10. The laser processing apparatus according to claim 1 or 2, wherein the third process maintains the position of the focusing lens along the optical axis direction at a constant position during the initial and / or final stages of the second process.

11. A laser processing method comprising using a laser processing apparatus to irradiate an object with a first laser beam and moving the focal point of the first laser beam along a line, thereby forming a modified region along the line on the object, The aforementioned laser processing apparatus is A support part that supports the aforementioned object, An irradiation unit that irradiates the object with the first laser light through a focusing lens, A moving mechanism for moving the support portion and / or the irradiation portion along the line, An actuator that moves the aforementioned focusing lens along the optical axis, The system includes a data acquisition unit that receives a second laser beam reflected from the laser beam incident surface of the object, thereby acquiring displacement data relating to the displacement of the laser beam incident surface, and acquires drive data to drive the actuator so that the focusing point follows the displacement of the laser beam incident surface based on the displacement data, The first step involves moving the support unit and / or the irradiation unit along the line using the moving mechanism, and acquiring the displacement data and the drive data using the data acquisition unit, starting from the point when the focusing point is located at the tracking start position. A second step is to move the support unit and / or the irradiation unit along the line using the moving mechanism, and irradiate the object with the first laser beam to form the modified region. The process includes, in the second step of forming the modified region along the line, a third step of moving the focusing lens along the optical axis direction by the actuator based on the drive data acquired in the first step, The previous third step is, A laser processing method comprising an early tracking step in which the actuator is driven based on the drive data acquired in the first step, starting from the point when the irradiation position of the second laser beam on the laser beam incident surface is located forward by a correction distance in the relative movement direction of the irradiation part compared to the tracking start position.

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