JP7475211B2 - Inspection method for laser processing equipment - Google Patents

Description

The present invention relates to a method for inspecting a laser processing device.

As a method for dividing a workpiece such as a semiconductor wafer into chip-sized pieces, a laser processing device that irradiates a laser beam along a planned division line set on the surface of the workpiece is known (see Patent Document 1). Laser processing devices are generally configured such that a laser beam emitted from a mounted laser oscillator is propagated through various optical components such as mirrors and lenses, and is focused by a concentrator to be irradiated onto the processing point of the workpiece.

In such laser processing equipment, if the position of each optical component changes due to vibration or other reasons, the state of the laser beam propagating through each optical component at the processing point changes, and appropriate processing results may not be obtained. Therefore, the position of the collector in the optical axis direction is changed while checking the processing state when processing is performed at each position, thereby confirming the appropriate focal position (see Patent Document 2).

JP 2007-275912 A JP 2013-078785 A

However, the above-mentioned confirmation work requires the preparation of wafers for the confirmation work, and there is a possibility of variation in the prepared wafers themselves, or errors due to the person measuring the processed wafers. Furthermore, if the processing conditions set in the laser processing device differ between the confirmation work and mass production, even if there are no problems during the confirmation work, there is a possibility that processing defects will occur during mass production.

The present invention was made in consideration of these problems, and its purpose is to provide an inspection method for a laser processing device that can reduce processing defects caused by variations in the workpiece and errors by the person making the measurement.

In order to solve the above-mentioned problems and achieve the object, the present invention provides an inspection method for a laser processing device comprising: a chuck table having a holding surface for holding a workpiece; a laser beam irradiation unit including a laser oscillator and a condenser for focusing a laser beam oscillated from the laser oscillator; a Z-axis movement unit for moving a focal point of the laser beam focused by the condenser in an optical axis direction perpendicular to the holding surface of the chuck table; an imaging unit capable of imaging plasma generated at the focal point of the laser beam; and a control unit for controlling each component, the inspection method comprising the steps of: moving a focal point of the laser beam focused by the condenser of the laser beam irradiation unit in air; an imaging step of imaging, after the focal point positioning step, plasma generated at the focal point at each output while changing the output of the laser beam, with the imaging unit; a measurement step of measuring plasma intensity at each output from the image captured in the imaging step; and a judgment step of calculating an approximation function of the relationship between each output and the plasma intensity measured in the measurement step, and judging that the laser processing apparatus is acceptable if the output of the laser beam at which the plasma intensity becomes zero in the approximation function is within a predetermined range, and judging that the laser processing apparatus is unacceptable if it is not within the predetermined range .
Another aspect of the inspection method for a laser processing apparatus of the present invention is an inspection method for a laser processing apparatus including a chuck table having a holding surface for holding a workpiece, a laser beam irradiation unit including a laser oscillator and a condenser for condensing a laser beam oscillated from the laser oscillator, a Z-axis direction moving unit for moving a focal point of the laser beam focused by the condenser in an optical axis direction perpendicular to the holding surface of the chuck table, an imaging unit capable of imaging plasma generated at the focal point of the laser beam, and a control unit for controlling each component, the inspection method including the steps of: positioning the focal point of the laser beam focused by the condenser of the laser beam irradiation unit in air; the laser processing apparatus is characterized by having a focal point positioning step in which a focal point is located at the focal point of the laser beam; an imaging step in which, after the focal point positioning step, an imaging unit is used to image the plasma generated at the focal point at each output while changing the output of the laser beam; a measurement step in which the plasma intensity at each output is measured from the image captured in the imaging step; and a judgment step in which, for the plasma intensity measured in the measurement step, an approximation function of the relationship between each output and the plasma intensity is calculated, and if the slope of the approximation function is within a predetermined range, the laser processing apparatus is judged to be acceptable, and if the slope is not within the predetermined range, the laser processing apparatus is judged to be unacceptable, and based thereon, the laser processing apparatus is judged to be unacceptable.

The laser beam irradiation unit may also include a spatial light modulator having a liquid crystal layer between the laser oscillator and the condenser for displaying a predetermined pattern, and in the measurement step, the plasma intensity of the laser beam emitted from the laser oscillator may be measured while the pattern to be displayed on the liquid crystal layer of the spatial light modulator when processing the workpiece is displayed.

The laser beam irradiation unit may also include a beam splitting unit between the laser oscillator and the collector that splits the laser beam, and in the measurement step, the plasma intensity of the laser beam split by the beam splitting unit and focused by the collector may be measured.

The present invention can reduce machining defects caused by variations in the workpiece and errors made by the person making the measurements.

FIG. 1 is a perspective view showing an example of the configuration of a laser processing device according to an embodiment. FIG. 2 is a schematic diagram showing the configuration of a laser beam irradiation unit of the laser processing apparatus shown in FIG. FIG. 3 is a flowchart showing the flow of the inspection method for the laser processing device according to the embodiment. FIG. 4 is a schematic diagram showing an example of the light-focus point positioning step shown in FIG. FIG. 5 is a diagram showing an example of an image captured in the imaging step shown in FIG. FIG. 6 is a graph showing an example of the distribution of plasma intensity by the measurement step shown in FIG. FIG. 7 is a schematic diagram showing the configuration of a laser beam irradiation unit of a laser processing apparatus according to a first modified example. FIG. 8 is a schematic diagram showing the configuration of a laser beam irradiation unit of a laser processing apparatus according to a second modified example.

The following describes in detail the form (embodiment) for carrying out the present invention with reference to the drawings. The present invention is not limited to the contents described in the following embodiment. The components described below include those that a person skilled in the art can easily imagine and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. Various omissions, substitutions, or modifications of the configuration can be made without departing from the spirit of the present invention.

[Embodiment]
An inspection method for a laser processing device 1 according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing an example of the configuration of the laser processing device 1 according to the embodiment. FIG. 2 is a schematic diagram showing the configuration of the laser beam irradiation unit 20 of the laser processing device 1 shown in FIG. 1. In the following description, the X-axis direction is one direction in a horizontal plane. The Y-axis direction is a direction perpendicular to the X-axis direction in a horizontal plane. The Z-axis direction is a direction perpendicular to the X-axis direction and the Y-axis direction. In the laser processing device 1 of the embodiment, the processing feed direction is the X-axis direction, and the indexing feed direction is the Y-axis direction.

As shown in FIG. 1, the laser processing device 1 includes a chuck table 10, a laser beam irradiation unit 20, an output measurement unit 30, an X-axis direction moving unit 40, a Y-axis direction moving unit 50, a Z-axis direction moving unit 60, an imaging unit 70, a display unit 80, and a control unit 90.

The laser processing device 1 according to the embodiment processes the workpiece 100 by irradiating the workpiece 100 held on the chuck table 10 with a laser beam 21 by a laser beam irradiation unit 20. The processing of the workpiece 100 by the laser processing device 1 includes, for example, groove processing for forming grooves on the surface of the workpiece 100, modified layer forming processing for forming a modified layer inside the workpiece 100 by stealth dicing, and cutting processing for cutting the workpiece 100 along the planned division line.

In the embodiment, the workpiece 100 is a wafer such as a disk-shaped semiconductor wafer or an optical device wafer, whose substrate is silicon (Si), sapphire (Al ₂ O ₃ ), gallium arsenide (GaAs), silicon carbide (SiC), or the like, and is a wafer for mass production processing. Note that the workpiece 100 is not limited to the embodiment, and does not have to be disk-shaped in the present invention. For example, the workpiece 100 is supported in an opening of the annular frame 110 by having an annular frame 110 attached thereto and a tape 111 having a diameter larger than the outer diameter of the workpiece 100 attached to the back surface of the workpiece 100.

The chuck table 10 holds the workpiece 100 on the holding surface 11. The holding surface 11 is a disk shape formed from porous ceramics or the like. In the embodiment, the holding surface 11 is a plane parallel to the horizontal direction. The holding surface 11 is connected to a vacuum suction source, for example, via a vacuum suction path. The chuck table 10 suction-holds the workpiece 100 placed on the holding surface 11. A plurality of clamps 12 are arranged around the chuck table 10 to clamp an annular frame 110 that supports the workpiece 100.

The chuck table 10 is rotated around an axis parallel to the Z-axis direction by the rotation unit 13. The rotation unit 13 is supported by the X-axis direction moving plate 14. The rotation unit 13 and the chuck table 10 are moved in the X-axis direction by the X-axis direction moving unit 40 via the X-axis direction moving plate 14. The rotation unit 13 and the chuck table 10 are moved in the Y-axis direction by the Y-axis direction moving unit 50 via the X-axis direction moving plate 14, the X-axis direction moving unit 40, and the Y-axis direction moving plate 15.

The laser beam irradiation unit 20 is a unit that irradiates a pulsed laser beam 21 onto the workpiece 100 held on the chuck table 10. As shown in FIG. 2, the laser beam irradiation unit 20 includes a laser oscillator 22, a mirror 26, and a condenser 28. The arrow in FIG. 2 indicates the direction of movement of the chuck table 10 during processing feed.

The laser oscillator 22 oscillates a laser beam 21 having a predetermined wavelength for processing the workpiece 100. The laser beam 21 irradiated by the laser beam irradiation unit 20 has a wavelength that is transparent or absorbent to the workpiece 100.

The mirror 26 reflects the laser beam 21 toward the workpiece 100 held on the holding surface 11 of the chuck table 10. In the embodiment, the mirror 26 reflects the laser beam 21 oscillated by the laser oscillator 22 toward the collector 28.

In the embodiment, the condenser 28 is a biconvex single lens. The condenser 28 focuses the laser beam 21 emitted from the laser oscillator 22 at a focusing point 29. The focusing point 29 is located, for example, in the air (see, for example, FIG. 4). The focusing point 29 is located, for example, on the surface or inside of the workpiece 100 held on the holding surface 11 of the chuck table 10. In the embodiment, the condenser 28 focuses the laser beam 21 reflected by the mirror 26 at the focusing point 29. Of the laser beam irradiation unit 20, at least the condenser 28 is supported by a Z-axis direction moving unit 60 installed on a pillar 3 erected from the device body 2 of the laser processing device 1 (see FIG. 1).

The output measuring unit 30 includes a light receiving surface 31. The light receiving surface 31 measures the output value of the laser beam 21 that has passed through the condenser 28. The output measuring unit 30 includes, for example, a laser power meter. The laser power meter includes a sensor that outputs a signal corresponding to the intensity of the laser beam 21 that has entered the light receiving surface 31 to the control unit 90 of the laser processing device 1. When the laser beam 21 is irradiated onto the light receiving surface 31, a signal corresponding to the output value of the laser beam 21 is output to the control unit, and the output value of the laser beam 21 that has passed through the condenser 28 can be measured.

In the embodiment, the output measuring unit 30 is installed near the chuck table 10, but may be installed anywhere as long as the output value of the laser beam 21 transmitted through the condenser 28 can be measured. The output measuring unit 30 may be installed so as to be freely movable together with the chuck table 10, or may be installed independently of the chuck table 10. In the embodiment, the planar shape of the light receiving surface 31 is circular, but the position and shape of the light receiving surface 31 are not particularly limited and may be set appropriately within a range in which the output value of the laser beam 21 can be measured.

As shown in FIG. 1, the X-axis direction moving unit 40 is a unit that moves the chuck table 10 and the laser beam irradiation unit 20 relatively in the X-axis direction, which is the processing feed direction. In the embodiment, the X-axis direction moving unit 40 moves the chuck table 10 in the X-axis direction. In the embodiment, the X-axis direction moving unit 40 is installed on the device body 2 of the laser processing device 1.

The X-axis direction moving unit 40 supports the X-axis direction moving plate 14 so that it can move in the X-axis direction. The X-axis direction moving unit 40 includes a well-known ball screw 41, a well-known pulse motor 42, and a well-known guide rail 43. The ball screw 41 is provided so that it can rotate around its axis. The pulse motor 42 rotates the ball screw 41 around its axis. The guide rail 43 supports the X-axis direction moving plate 14 so that it can move in the X-axis direction. The guide rail 43 is provided and fixed to the Y-axis direction moving plate 15.

The Y-axis direction moving unit 50 is a unit that moves the chuck table 10 and the laser beam irradiation unit 20 relatively in the Y-axis direction, which is the indexing feed direction. In the embodiment, the Y-axis direction moving unit 50 moves the chuck table 10 in the Y-axis direction. In the embodiment, the Y-axis direction moving unit 50 is installed on the device body 2 of the laser processing device 1.

The Y-axis direction moving unit 50 supports the Y-axis direction moving plate 15 so that it can move in the Y-axis direction. The Y-axis direction moving unit 50 includes a well-known ball screw 51, a well-known pulse motor 52, and a well-known guide rail 53. The ball screw 51 is provided so that it can rotate around its axis. The pulse motor 52 rotates the ball screw 51 around its axis. The guide rail 53 supports the Y-axis direction moving plate 15 so that it can move in the Y-axis direction. The guide rail 53 is provided and fixed to the device main body 2.

The Z-axis direction moving unit 60 is a unit that moves the focal point 29 of the laser beam 21 focused by the focusing device 28 in the optical axis direction perpendicular to the holding surface 11 of the chuck table 10. More specifically, the Z-axis direction moving unit 60 moves the chuck table 10 and the laser beam irradiation unit 20 relatively in the Z-axis direction, which is the focal point position adjustment direction. In the embodiment, the Z-axis direction moving unit 60 moves the laser beam irradiation unit 20 in the Z-axis direction. In the embodiment, the Z-axis direction moving unit 60 is installed on a pillar 3 erected from the device body 2 of the laser processing device 1.

The Z-axis direction moving unit 60 supports at least the condenser 28 (see FIG. 2) of the laser beam irradiation unit 20 so that it can move freely in the Z-axis direction. The Z-axis direction moving unit 60 includes a well-known ball screw 61, a well-known pulse motor 62, and a well-known guide rail 63. The ball screw 61 is provided so that it can rotate freely around its axis. The pulse motor 62 rotates the ball screw 61 around its axis. The guide rail 63 supports the laser beam irradiation unit 20 so that it can move freely in the Z-axis direction. The guide rail 63 is provided and fixed to the pillar 3.

As shown in FIG. 2, the imaging unit 70 is arranged to image, for example, the area directly above and below the condenser 28 of the laser beam irradiation unit 20. The imaging unit 70 images the plasma generated at the focal point 29 of the laser beam 21 focused by the condenser 28 of the laser beam irradiation unit 20. The imaging unit 70 includes a coaxial camera, a CCD (Charge Coupled Device) camera, or an infrared camera. The imaging unit 70 may be the same as or different from the camera that images the workpiece 100 held on the chuck table 10 to obtain an image for performing alignment to align the workpiece 100 with the laser beam irradiation unit 20.

As shown in FIG. 1, the display unit 80 is a display section configured by a liquid crystal display device or the like. The display unit 80 includes a display surface that displays an image captured by the imaging unit 70, a setting screen for processing conditions, a processing operation status, and the like. If the display surface includes a touch panel, the display unit 80 may include an input section. The input section can accept various operations such as an operator registering processing content information. The input section may be an external input device such as a keyboard. The display unit 80 switches information and images displayed on the display surface by operations from the input section or the like. The display unit 80 may include an alarm section. The alarm section emits at least one of sound and light to notify the operator of the laser processing device 1 of predetermined alarm information. The alarm section may be an external alarm device such as a speaker or a light-emitting device. The display unit 80 is connected to the control unit 90.

The control unit 90 controls each of the above-mentioned components of the laser processing device 1, and causes the laser processing device 1 to execute a processing operation on the workpiece 100. The control unit 90 controls the laser beam irradiation unit 20, the X-axis direction moving unit 40, the Y-axis direction moving unit 50, the Z-axis direction moving unit 60, the imaging unit 70, and the display unit 80. The control unit 90 is a computer including an arithmetic processing device as a calculation means, a storage device as a storage means, and an input/output interface device as a communication means. The arithmetic processing device includes, for example, a microprocessor such as a CPU (Central Processing Unit). The storage device has a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory). The arithmetic processing device performs various calculations based on a predetermined program stored in the storage device. The arithmetic processing device outputs various control signals to each of the above-mentioned components via the input/output interface device according to the calculation results, and controls the laser processing device 1.

The control unit 90, for example, drives the Z-axis direction moving unit 60 to move the collector 28 of the laser beam irradiation unit 20, thereby positioning the focal point 29 at a predetermined position. The control unit 90, for example, causes the imaging unit 70 to capture an image of the focal point 29 at each output while outputting the laser beam 21. The control unit 90, for example, measures the plasma intensity at each output of the laser beam 21 from the image of the plasma generated at the focal point 29 captured by the imaging unit 70.

Next, an inspection method using the laser processing device 1 will be described. FIG. 3 is a flowchart showing the flow of the inspection method of the laser processing device 1 according to the embodiment. The inspection method of the laser processing device 1 includes a focal point positioning step 201, an imaging step 202, a measurement step 203, and a judgment step 204.

(Light Focus Positioning Step 201)
Fig. 4 is a schematic diagram showing an example of the focal point positioning step 201 shown in Fig. 3. The focal point positioning step 201 is a step of positioning the focal point 29 of the laser beam 21, which is focused by the condenser 28 of the laser beam irradiation unit 20, in the air.

In the focal point positioning step 201, the X-axis direction moving unit 40, the Y-axis direction moving unit 50, and the Z-axis direction moving unit 60 are driven to move the focal point 29 focused by the laser beam irradiation unit 20 to a predetermined position. Specifically, the Z-axis direction moving unit 60 moves the condenser 28 in the Z-axis direction, which is the optical axis direction, so that the focal point 29 of the laser beam 21 focused by the condenser 28 is positioned in the air.

In the embodiment, in the focal point positioning step 201, the focal point 29 is positioned directly above the light receiving surface 31 of the output measurement unit 30. Specifically, the output measurement unit 30 is moved in the X-axis direction and the Y-axis direction by the X-axis direction moving unit 40 and the Y-axis direction moving unit 50 so that the focal point 29 is positioned directly above the light receiving surface 31 of the output measurement unit 30. In the present invention, the focal point 29 does not necessarily have to be positioned directly above the output measurement unit 30, but by positioning the focal point 29 directly above the output measurement unit 30 as in the embodiment, it is possible to simultaneously measure the output of the laser beam 21.

(Image capture step 202)
Fig. 5 is a diagram showing an example of an image captured in the imaging step 202 shown in Fig. 3. The imaging step 202 is a step in which, while changing the output of the laser beam 21, the imaging unit 70 images the plasma generated at the focal point 29 at each output. The imaging step 202 is performed after the focal point positioning step 201.

In the imaging step 202, first, with the focal point 29 positioned in the air, the imaging unit 70 images the plasma generated at the focal point 29 of the laser beam 21 oscillated from the laser oscillator 22. Next, the output of the laser beam 21 is changed, and the imaging unit 70 images the plasma generated at the focal point 29 of the laser beam 21 with the changed output. Similarly, while changing the output of the laser beam 21, the imaging unit 70 images the plasma generated at the focal point 29 at the output of each laser beam 21. The control unit 90 acquires each image captured by the imaging unit 70.

As shown in FIG. 5, the captured image shows the distribution of plasma in the XY plane with the focal point 29 as the reference point. In the example shown in FIG. 5, higher brightness indicates higher plasma intensity. Also, in the example shown in FIG. 5, a Gaussian distribution of brightness in the X-axis direction passing through the reference point, and a Gaussian distribution of brightness in the Y-axis direction passing through the reference point can be obtained.

(Measurement Step 203)
Fig. 6 is a graph showing an example of the distribution of the plasma intensity 91 by the measuring step 203 shown in Fig. 3. The measuring step 203 is a step of measuring the plasma intensity 91 at each output from the image captured in the imaging step 202.

In the measurement step 203, the plasma intensity 91 generated at the focal point 29 at the output of each laser beam 21 is measured based on each image captured in the imaging step 202. For example, the plasma intensity 91 is measured based on the Gaussian distribution of the brightness of the images acquired in the imaging step 202.

(Decision Step 204)
The judgment step 204 is a step for judging the pass/fail of the laser processing device 1 based on the plasma intensity 91 measured in the measurement step 203 .

In the judgment step 204, first, as shown in FIG. 6, for the plasma intensity 91 measured in the measurement step 203, an approximation function 92 of the relationship between the output of each laser beam 21 and the plasma intensity 91 generated at the focal point 29 is calculated. Next, in the approximation function 92, it is determined whether the intercept at which the plasma generation threshold 93 is reached, i.e., the output of the laser beam 21 at which the plasma intensity is 0, is within a predetermined range. In the judgment step 204, if it is determined that the plasma generation threshold 93 is within the predetermined range, it is determined that the laser processing device 1 is acceptable. In the judgment step 204, if it is determined that the plasma generation threshold 93 is not within the predetermined range, it is determined that the laser processing device 1 is unacceptable.

The criteria in the judgment step 204 are not limited to the above, and for example, it may be judged whether or not the slope of the approximation function 92 is within a predetermined range. In addition, the judgment results may be stored sequentially to detect changes over time in the state of the laser processing device 1.

As described above, the inspection method for the laser processing device 1 according to the embodiment focuses the laser beam 21 in the air, measures the plasma intensity 91 at the focusing point 29 in the air while changing the output, and judges whether the laser processing device 1 passes or fails based on the plasma intensity 91 for each output. The criteria for judging whether the laser processing device 1 passes or fails are based on, for example, the plasma generation threshold 93 or the slope of the approximation function 92 of the relationship between the plasma intensity 91 and the output.

The inspection method of the embodiment observes the plasma generated when the light is focused in air, so there is no need to process the workpiece 100 for confirmation and to check the processing state, and processing defects caused by errors made by the person measuring the processing state during confirmation can be suppressed. Since there is no need to process the workpiece 100 for confirmation, for example, it is possible to suppress the adhesion of debris generated from the workpiece 100 during processing for confirmation to optical components such as lenses that constitute the laser beam irradiation unit 20. In addition, since there is no need for the workpiece 100 for confirmation, it is possible to suppress changes in the processing state caused by the effects of variations in the material, thickness, doping amount, etc. for each workpiece 100.

In addition, inspection can be performed under the focused light conditions that will be used during actual mass production, rather than under processing conditions for confirmation. Specifically, the beam diameter and energy density of the laser beam 21 can be confirmed under the same conditions as during mass production. This has the effect of providing more accurate inspection results. If the inspection fails, it is sufficient to carry out tasks such as checking whether the output of the laser oscillator 22 itself has decreased or re-adjusting the optical axis.

Note that the present invention is not limited to the above embodiment. In other words, various modifications can be made without departing from the gist of the present invention. For example, in the focal point positioning step 201, the focal point 29 is positioned directly above the light receiving surface 31 of the output measurement unit 30 in the embodiment, but the present invention is not limited to this, and the focal point may be positioned directly above the chuck table 10, etc. Also, in the imaging step 202, the plasma is imaged from directly above the focal point 29, which is an extension of the optical axis, in the embodiment shown in FIG. 4, but in the present invention, the image may be imaged from directly below the focal point 29, which is an extension of the optical axis. Also, a separate optical path for imaging the plasma may be provided. In other words, the position at which the imaging unit 70 images the plasma is not limited to directly above or directly below.

The inspection method of the present invention is useful for laser processing in which plasma is generated at the focal point 29. That is, the inspection method of the present invention is applicable to a laser processing device 1 equipped with a sub-picosecond laser oscillator 22 in which plasma is generated at the focal point 29. The inspection method of the present invention is also applicable to ablation processing, but is more useful in stealth dicing processing, which has a high numerical aperture, since plasma is more likely to be generated in this processing. For example, the inspection method of the present invention is also applicable to a laser processing device equipped with a spatial light modulator 24 shown in the first modified example described below, and a laser processing device equipped with a beam branching unit 27 shown in the second modified example.

[First Modification]
The inspection method of the laser processing device 1 according to the first modification will be described with reference to the drawings. Fig. 7 is a schematic diagram showing the configuration of the laser beam irradiation unit 120 of the laser processing device 1 according to the first modification. In the laser beam irradiation unit 120 of the first modification shown in Fig. 7, the same components as those of the laser beam irradiation unit 20 of the embodiment shown in Fig. 2 are given the same reference numerals and will not be described. As shown in Fig. 7, the laser beam irradiation unit 120 of the first modification is different from the laser beam irradiation unit 20 of the embodiment in that it further includes a polarizing plate 23, a spatial light modulator 24, and a lens group 25.

In the first modification, the polarizing plate 23 is provided between the laser oscillator 22 and the spatial light modulator 24. The polarizing plate 23 polarizes the laser beam 21 emitted from the laser oscillator 22 into light in a specific direction.

The spatial light modulator 24 is provided between the laser oscillator 22 and the condenser 28. The spatial light modulator 24 performs phase modulation of the incident laser beam 21. The spatial light modulator 24 electrically controls the spatial distribution of the amplitude, phase, polarization, etc. of the laser beam 21 oscillated from the laser oscillator 22, thereby modulating the phase of the laser beam 21.
do.

The spatial light modulator 24 of the embodiment has a liquid crystal layer 241. The liquid crystal layer 241 displays a predetermined pattern. The pattern is a mapping of the voltage applied to the spatial light modulator 24. The pattern adjusts, for example, the optical characteristics of the laser beam 21 at the focal point 29. Adjustments to the optical characteristics include, for example, changing the shape of the laser beam 21 and attenuating the intensity.

The spatial light modulator 24 shapes the laser beam 21 into a desired beam shape by applying a voltage corresponding to the pattern displayed on the liquid crystal layer 241. In other words, the laser processing device 1 can adjust the output and spot shape at the focal point 29 by changing the voltage applied to the spatial light modulator 24.

In the embodiment, the spatial light modulator 24 reflects and outputs the laser beam 21, but in the present invention, the laser beam 21 may be transmitted and output. The laser beam irradiation unit 120 may also include a deformable mirror instead of the spatial light modulator 24. When a voltage according to a pattern is applied to the deformable mirror, the mirror film is deformed according to the pattern. While the spatial light modulator 24 uses green and IR (infrared) wavelengths of 405 nm or more, the deformable mirror can also be used with wavelengths of 355 nm, so it can also be used for ablation processing using UV (ultraviolet).

The lens group 25 is provided between the spatial light modulator 24 and the condenser 28. The lens group 25 is a 4f optical system consisting of two lenses, a lens 251 and a lens 252. The 4f optical system is an optical system in which the rear focal plane of the lens 251 and the front focal plane of the lens 252 coincide with each other, and an image on the front focal plane of the lens 251 is formed on the rear focal plane of the lens 252. The lens group 25 expands or reduces the beam diameter of the laser beam 21 output from the spatial light modulator 24. In the first modified example, the laser beam 21 that has passed through the lens group 25 is reflected by the mirror 26 to the condenser 28.

In the inspection method for a laser processing device equipped with a laser beam irradiation unit 120 of the first modified example, in the focal point positioning step 201, the focal point 29 of the laser beam 21 is positioned in the air while a pattern is displayed on the liquid crystal layer 241 of the spatial light modulator 24. The pattern displayed on the liquid crystal layer 241 at this time is the pattern to be displayed on the liquid crystal layer 241 of the spatial light modulator 24 when processing the workpiece 100. The method for positioning the focal point 29 of the laser beam 21 is the same as in the embodiment, so a description thereof will be omitted.

In the imaging step 202 of the first modified example, while a pattern is displayed on the liquid crystal layer 241 of the spatial light modulator 24, an image of plasma generated at the focal point 29 of the laser beam 21 oscillated from the laser oscillator 22 is captured. In the imaging step 202 of the first modified example, as in the embodiment, while changing the output of the laser beam 21, an image of plasma generated at the focal point 29 at the output of each laser beam 21 is captured by the imaging unit 70.

In the measurement step 203 of the first modified example, similar to the embodiment, the plasma intensity generated at the focal point 29 at the output of each laser beam 21 is measured based on each image captured in the imaging step 202. That is, with a pattern displayed on the liquid crystal layer 241 of the spatial light modulator 24, the plasma intensity of the plasma generated at the focal point 29 of the laser beam 21 oscillated from the laser oscillator 22 is measured.

In the judgment step 204 of the first modified example, the pass/fail of the laser processing device equipped with the spatial light modulator 24 is judged based on the plasma intensity measured in the measurement step 203. The method of judging the pass/fail of the laser processing device is the same as in the embodiment, so the explanation is omitted.

[Second Modification]
Next, an inspection method for the laser processing device 1 according to the second modification will be described with reference to the drawings. Fig. 8 is a schematic diagram showing the configuration of the laser beam irradiation unit 220 of the laser processing device 1 according to the second modification. In the laser beam irradiation unit 220 of the second modification shown in Fig. 7, the same components as those of the laser beam irradiation unit 20 of the embodiment shown in Fig. 2 are given the same reference numerals, and the description thereof will be omitted. As shown in Fig. 8, the laser beam irradiation unit 220 of the second modification is different from the laser beam irradiation unit 20 of the embodiment in that it further includes a beam branching unit 27.

The beam splitting unit 27 is provided between the laser oscillator 22 and the condenser 28. In the second modified example, the laser beam 21 oscillated from the laser oscillator 22 and reflected by the mirror 26 is incident on the beam splitting unit 27. The beam splitting unit 27 splits the incident laser beam 21 into at least two or more beams and transmits them to the condenser 28. In the second modified example, the direction in which the laser beam 21 splits is the X-axis direction (the processing feed direction).

The beam splitting unit 27 is, for example, a diffractive optical element. A diffractive optical element has a function of splitting the incident laser beam 21 into multiple laser beams by utilizing the diffraction phenomenon. The beam splitting unit 27 may be, for example, a Wollaston prism. A Wollaston prism is a polarizing prism that utilizes birefringence and has a function of splitting the incident laser beam 21 into two orthogonal linearly polarized laser beams.

The multiple laser beams 21 split by the beam splitting unit 27 are focused at respective focusing points 29. In the second modified example, the focusing points 29 are arranged linearly and at equal intervals in the X-axis direction.

In the inspection method for a laser processing device equipped with a laser beam irradiation unit 220 of the second modified example, in the focal point positioning step 201, the focal point 29 of the laser beam 21 that is split by the beam splitting unit 27 and focused by the focusing device 28 is positioned in the air. The method for positioning the focal point 29 of the laser beam 21 is the same as in the embodiment, so a description thereof will be omitted.

In the imaging step 202 of the second modified example, the plasma generated at each focal point 29 of the laser beam 21 that is branched by the beam branching unit 27 and focused by the focusing device 28 is imaged. In the imaging step 202 of the second modified example, as in the embodiment, the plasma generated at each focal point 29 at the output of each laser beam 21 is imaged by the imaging unit 70 while changing the output of the laser beam 21.

In the measurement step 203 of the second modified example, similarly to the embodiment, the plasma intensity generated at each focal point 29 at the output of each laser beam 21 is measured based on each image captured in the imaging step 202. That is, the plasma intensity of the plasma generated at each focal point 29 of the laser beam 21 split by the beam splitting unit 27 and focused by the collector 28 is measured.

In the judgment step 204 of the second modified example, the pass/fail of the laser processing device equipped with the beam splitting unit 27 is judged based on the plasma intensity measured in the measurement step 203. The method of judging the pass/fail of the laser processing device is the same as in the embodiment, so the explanation is omitted.

As shown in the first and second modified examples, the inspection method of the present invention can be applied even when the focusing state is changed by the spatial light modulator 24 or when the laser beam 21 is branched to have multiple focusing points 29. That is, as in the first modified example, the pass/fail of the laser processing device can be determined by observing the plasma generated at the focusing point 29 where the focusing state is changed by the spatial light modulator 24. Also, as in the second modified example, the pass/fail of the laser processing device can be determined by observing the plasma generated at each focusing point 29 where the laser beam 21 is branched.

REFERENCE SIGNS LIST 1 laser processing device 10 chuck table 20, 120, 220 laser beam irradiation unit 21 laser beam 22 laser oscillator 23 polarizing plate 24 spatial light modulator 241 liquid crystal layer 25 lens group 251, 252 lens 26 mirror 27 branching unit 28 condenser 29 focusing point 30 output measuring unit 31 light receiving surface 60 Z-axis direction moving unit 70 imaging unit 90 control unit 91 plasma intensity 92 approximation function 93 plasma generation threshold 100 workpiece

Claims (4)

a chuck table having a holding surface for holding a workpiece;
a laser beam irradiation unit including a laser oscillator and a condenser for condensing a laser beam oscillated from the laser oscillator;
a Z-axis movement unit that moves a focal point of the laser beam focused by the focusing device in an optical axis direction perpendicular to a holding surface of the chuck table;
an imaging unit capable of imaging plasma generated at a focal point of the laser beam;
A control unit for controlling each of the components;
A method for inspecting a laser processing apparatus comprising:
a focusing point positioning step of positioning a focusing point of the laser beam focused by a focusing device of the laser beam irradiation unit in air;
an imaging step of imaging, by the imaging unit, plasma generated at the focal point at each output while changing the output of the laser beam after the focal point positioning step;
a measuring step of measuring plasma intensity at each output from the image captured in the imaging step;
a judgment step of calculating an approximation function of the relationship between each output and the plasma intensity measured in the measurement step, and judging that the laser processing device is acceptable if the output of the laser beam at which the plasma intensity becomes 0 in the approximation function is within a predetermined range, and judging that the laser processing device is unacceptable if the output is not within the predetermined range ;
A method for inspecting a laser processing device, comprising: a chuck table having a holding surface for holding a workpiece;
a laser beam irradiation unit including a laser oscillator and a condenser for condensing a laser beam oscillated from the laser oscillator;
a Z-axis movement unit that moves a focal point of the laser beam focused by the focusing device in an optical axis direction perpendicular to a holding surface of the chuck table;
an imaging unit capable of imaging plasma generated at a focal point of the laser beam;
A control unit for controlling each of the components;
A method for inspecting a laser processing apparatus comprising:
a focusing point positioning step of positioning a focusing point of the laser beam focused by a focusing device of the laser beam irradiation unit in air;
an imaging step of imaging, by the imaging unit, plasma generated at the focal point at each output while changing the output of the laser beam after the focal point positioning step;
a measuring step of measuring plasma intensity at each output from the image captured in the imaging step;
a judgment step of calculating an approximation function of the relationship between each output and the plasma intensity measured in the measurement step, judging that the laser processing device is acceptable if the slope of the approximation function is within a predetermined range, and judging that the laser processing device is unacceptable if the slope of the approximation function is not within the predetermined range;
A method for inspecting a laser processing device, comprising: the laser beam irradiation unit includes a spatial light modulator having a liquid crystal layer between the laser oscillator and the condenser for displaying a predetermined pattern;
In the measuring step, a plasma intensity of the laser beam oscillated from the laser oscillator is measured in a state where a pattern to be displayed on the liquid crystal layer of the spatial light modulator when processing the workpiece is displayed.
3. The method for inspecting a laser processing device according to claim 1 or 2 . the laser beam irradiation unit includes a beam splitting unit between the laser oscillator and the condenser for splitting the laser beam;
In the measuring step, a plasma intensity of a laser beam branched by the beam branching unit and collected by the collector is measured.
3. The method for inspecting a laser processing device according to claim 1 or 2 .

Images