JP2024071062A - Laser irradiation device - Google Patents

Abstract

To provide a laser irradiation device which suppresses processing failure caused by contamination of an optical component, reduces down time and can improve productivity.SOLUTION: A laser irradiation device 1 has: a laser beam irradiation unit 20 which has a laser oscillator 22, a first mirror 24 for reflecting a laser beam 21 emitted from the laser oscillator 22 and changing a travel direction of the laser beam 21, and a light detection unit 30 which is arranged at a position opposite to a surface reflecting the laser beam 21 of the first mirror 24 and receives scattering light 31 from particles attached to the first mirror 24, and irradiates an object held on a holding table 10 with the laser beam 21; and a control unit 90 which controls each of the components, and determines whether or not the first mirror 24 is in a normal state on the basis of the light receiving amount of the scattering light 31 received by the light detection unit 30.SELECTED DRAWING: Figure 3

Description

The present invention relates to a laser irradiation device.

To divide a workpiece such as a semiconductor wafer, a laser processing device is used that irradiates a laser beam along a planned dividing line set on the surface of the workpiece (see Patent Document 1). In such a laser processing device, the laser beam emitted from a laser oscillator is guided using multiple optical components to irradiate the workpiece. These optical components are configured to be arranged inside a housing isolated from the outside, since the adhesion and contamination of particles, etc., directly leads to a decrease in output at the processing point and distortion of the beam shape.

JP 2003-320466 A

Although malfunctions caused by particles generated by parts placed inside the housing or particles that enter the box through small gaps have been reduced by measures such as increasing the airtightness and eliminating contaminants, they cannot be completely prevented, and particle adhesion to optical components remains an issue that must be resolved. Furthermore, when a malfunction occurs due to contamination of optical components, it is necessary to investigate which optical component is causing the malfunction, which results in longer downtime and reduced productivity.

The present invention was made in consideration of these problems, and its purpose is to provide a laser irradiation device that can suppress processing defects caused by contamination of optical components, reduce downtime, and improve productivity.

In order to solve the above problems and achieve the object, the laser irradiation device of the present invention comprises a holding table for holding an object, a laser beam irradiation unit for irradiating a laser beam onto the object held on the holding table, a moving unit for relatively moving the object held on the holding table and the laser beam irradiation unit, and a control unit for controlling each component. The laser beam irradiation unit has a laser oscillator, a first mirror for reflecting the laser beam emitted from the laser oscillator and changing the direction of travel of the laser beam, and a light detection unit that is positioned opposite the surface of the first mirror that reflects the laser beam and receives scattered light from particles attached to the first mirror, and the control unit is characterized in that it determines whether the first mirror is in a normal state or not based on the amount of scattered light received by the light detection unit.

In the laser irradiation device of the present invention, the laser beam irradiation unit may further include a second mirror between the laser oscillator and the first mirror, which reflects the laser beam emitted from the laser oscillator and guides it to the first mirror, and the control unit may determine whether the first mirror and the second mirror are in a normal state based on the amount of scattered light received by the light detection unit.

In addition, in the laser irradiation device of the present invention, the control unit may determine that the first mirror is not in a normal state when the amount of scattered light received by the light detection unit exceeds a predetermined threshold, and may determine that the second mirror is not in a normal state when the amount of scattered light received by the light detection unit falls below a predetermined threshold.

In addition, in the laser irradiation device of the present invention, the control unit may calculate a Mahalanobis distance from the intensity of the scattered light received by the light detection unit, and determine whether the first mirror and the second mirror are normal or not based on the Mahalanobis distance.

The present invention can reduce processing defects caused by contamination of optical components, reduce downtime, and improve productivity.

FIG. 1 is a perspective view showing an example of the configuration of a laser irradiation device according to an embodiment. FIG. 2 is a schematic diagram showing a first example of the schematic configuration of the laser beam irradiation unit shown in FIG. FIG. 3 is a schematic diagram showing a second example of the schematic configuration of the laser beam irradiation unit shown in FIG. FIG. 4 is a schematic diagram showing the transition of the amount of light received by the light detection unit. FIG. 5 is a schematic diagram showing the transition of the Mahalanobis distance calculated from the amount of light received by the light detection unit.

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]
First, the overall configuration of a laser irradiation 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 a laser irradiation device 1 according to an embodiment. 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 irradiation device 1 of the embodiment, the processing feed direction is the X-axis direction, the indexing feed direction is the Y-axis direction, and the focal point position adjustment direction is the Z-axis direction.

As shown in FIG. 1, the laser irradiation device 1 includes a holding table 10, a laser beam irradiation unit 20, a moving unit 60, an imaging unit 70, a display unit 80, and a control unit 90. The laser irradiation device 1 according to the embodiment is a device that processes the workpiece 100, which is an object to be processed, by irradiating the workpiece 100 with a laser beam 21. The processing of the workpiece 100 by the laser irradiation device 1 includes, for example, a modified layer forming process that forms a modified layer inside the workpiece 100 by stealth dicing, a groove processing that forms a groove on the surface of the workpiece 100, or a cutting process that cuts the workpiece 100 along a planned division line.

The workpiece 100 is, for example, a wafer such as a disk-shaped semiconductor device wafer or an optical device wafer, using silicon (Si), sapphire (Al ₂ O ₃ ), gallium arsenide (GaAs), silicon carbide (SiC), or lithium tantalate (LiTaO ₃ ) as a substrate. Note that the workpiece 100 is disk-shaped in the embodiment, but may not be disk-shaped in the present invention. The workpiece 100 is transported and processed in a state in which it is supported within an opening of the frame 110, with, for example, 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 holding table 10 holds the workpiece 100 (object) 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 holding table 10 holds the workpiece 100 placed on the holding surface 11 by suction. A plurality of clamps 12 are arranged around the holding table 10 to clamp an annular frame 110 that supports the workpiece 100.

The holding 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 an X-axis direction moving plate 14. The rotation unit 13 and holding table 10 are moved in the X-axis direction by an X-axis direction moving unit 61 (described later) via the X-axis direction moving plate 14. The rotation unit 13 and holding table 10 are moved in the Y-axis direction by a Y-axis direction moving unit 62 (described later) via the X-axis direction moving plate 14, the X-axis direction moving unit 61, and the Y-axis direction moving plate 15.

The laser beam irradiation unit 20 is a unit that irradiates a laser beam 21 onto a workpiece 100 (target object) held on the holding surface 11 of the holding table 10. Of the laser beam irradiation unit 20, at least the condenser 23 (see FIG. 2) is supported by a Z-axis direction moving unit 63 (described later) that is installed on a pillar 3 erected from the device body 2 of the laser irradiation device 1. A specific configuration example of the laser beam irradiation unit 20 will be described in detail later.

The moving unit 60 shown in FIG. 1 is a unit that moves the focal point of the laser beam 21 relative to the workpiece 100 held on the holding table 10. The moving unit 60 includes an X-axis moving unit 61, a Y-axis moving unit 62, and a Z-axis moving unit 63.

The X-axis direction moving unit 61 is a unit that moves the holding table 10 and the focal point of 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 61 moves the holding table 10 in the X-axis direction. In the embodiment, the X-axis direction moving unit 61 is installed on the device body 2 of the laser irradiation device 1. The X-axis direction moving unit 61 supports the X-axis direction moving plate 14 so that it can be moved freely in the X-axis direction.

The Y-axis direction moving unit 62 is a unit that moves the holding table 10 and the focal point of 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 62 moves the holding table 10 in the Y-axis direction. In the embodiment, the Y-axis direction moving unit 62 is installed on the device body 2 of the laser irradiation device 1. The Y-axis direction moving unit 62 supports the Y-axis direction moving plate 15 so that it can move freely in the Y-axis direction.

The Z-axis direction moving unit 63 is a unit that moves the holding table 10 and the focal point of 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 63 moves at least the condenser 23 of the laser beam irradiation unit 20 in the Z-axis direction. In the embodiment, the Z-axis direction moving unit 63 is installed on a pillar 3 that stands upright from the device body 2 of the laser irradiation device 1. The Z-axis direction moving unit 63 supports at least the condenser 23 of the laser beam irradiation unit 20 so that it can be moved freely in the Z-axis direction.

In the embodiment, each of the X-axis direction moving unit 61, the Y-axis direction moving unit 62, and the Z-axis direction moving unit 63 includes a well-known ball screw, a well-known pulse motor, and a well-known guide rail. The ball screw is provided so as to be rotatable about its axis. The pulse motor rotates the ball screw about its axis. The guide rail of the X-axis direction moving unit 61 supports the X-axis direction moving plate 14 so as to be movable in the X-axis direction. The guide rail of the X-axis direction moving unit 61 is provided fixedly to the Y-axis direction moving plate 15. The guide rail of the Y-axis direction moving unit 62 supports the Y-axis direction moving plate 15 so as to be movable in the Y-axis direction. The guide rail of the Y-axis direction moving unit 62 is provided so as to be fixed to the device body 2. The guide rail of the Z-axis direction moving unit 63 supports at least the condenser 23 of the laser beam irradiation unit 20 so as to be movable in the Z-axis direction. The guide rail of the Z-axis direction moving unit 63 is provided so as to be fixed to the pillar 3.

The imaging unit 70 captures an image of the workpiece 100 held on the holding table 10. The imaging unit 70 includes a CCD (Charge Coupled Device) camera or an infrared camera. The imaging unit 70 is fixed, for example, adjacent to the condenser 23 (see FIG. 2) of the laser beam irradiation unit 20. The imaging unit 70 captures an image of the workpiece 100 to obtain an image for performing alignment between the workpiece 100 and the laser beam irradiation unit 20, and outputs the obtained image.

The display unit 80 is a display section configured with a liquid crystal display device or the like. The display unit 80 displays, for example, a setting screen for processing conditions, the state of the workpiece 100 imaged by the imaging unit 70, the state of the processing operation, etc. on the display surface. If the display surface of the display unit 80 includes a touch panel, the display unit 80 may also 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 information and images displayed on the display surface of the display unit 80 can be switched by operations from the input section or the like.

The control unit 90 is a computer including a processing unit as a calculation means, a storage device as a storage means, and an input/output interface device as a communication means. The processing unit includes, for example, a microprocessor such as a CPU (Central Processing Unit). The storage device has a memory such as a HDD (Hard Disk Drive), a ROM (Read Only Memory), or a RAM (Random Access Memory). The processing unit performs various calculations based on a predetermined program stored in the storage device. The processing unit outputs various control signals to each of the above-mentioned components via the input/output interface device according to the calculation results.

Next, the specific configuration of the laser beam irradiation unit 20 will be described. FIG. 2 is a schematic diagram showing a first example of the general configuration of the laser beam irradiation unit 20 shown in FIG. 1. As shown in FIG. 2, the laser beam irradiation unit 20 has a laser oscillator 22, a condenser 23, a first mirror 24, a light detection unit 30, and a housing 40.

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

The condenser 23 includes a focusing lens and focuses the laser beam 21 emitted from the laser oscillator 22 at a predetermined position. The condenser 23 focuses the laser beam 21 on the workpiece 100 held on the holding surface 11 of the holding table 10, and irradiates the workpiece 100. The laser beam 21 focused by the condenser 23 passes through the emission port 41 of the housing 40 and is emitted to the outside of the housing 40.

The first mirror 24 reflects the laser beam 21 emitted from the laser oscillator 22 to change the direction of travel of the laser beam 21. In the embodiment, the first mirror 24 reflects the laser beam 21 so as to guide it toward the condenser 23. If particles are attached to the surface 241 of the first mirror 24, part of the laser beam 21 will strike the particle without being reflected toward the condenser 23, generating scattered light 31.

The light detection unit 30 detects the received light. The light detection unit 30 is positioned opposite the surface 241 of the first mirror 24 that reflects the laser beam 21. The light detection unit 30 receives a portion of the scattered light 31 from particles attached to the first mirror 24. The light detection unit 30 outputs information on the amount of received light to the control unit 90 (see FIG. 1). The light detection unit 30 is, for example, a PIN photodiode, and generates a current of a magnitude according to the amount of received light by receiving light. The PIN photodiode detects the amount of received light by detecting the current.

The housing 40 houses various optical components of the laser beam irradiation unit 20. The housing 40 houses at least the optical path of the laser beam 21 emitted from the laser oscillator 22 until it is focused by the condenser 23, various optical components including the first mirror 24 arranged on the optical path, and the light detection unit 30 in a continuous storage space, and seals it from the outside. The laser beam 21 focused by the condenser 23 is emitted from an exit 41 formed in the housing 40 and is irradiated toward the workpiece 100 held on the holding table 10. The exit 41 may be a window made of transparent glass or the like, or may be the focusing lens of the condenser 23 itself.

In the laser irradiation device 1 configured as described above, the control unit 90 judges whether the first mirror 24 is in a normal state or not based on the amount of scattered light 31 received by the light detection unit 30. The control unit 90 pre-stores a predetermined threshold value that determines the amount of light received as normal, for example, based on the amount of light received by the light detection unit 30 when no particles are attached to the first mirror 24 and the laser beam 21 is propagating normally along the optical path.

For example, if a particle is attached to the surface 241 of the first mirror 24, part of the laser beam 21 will hit the particle without being reflected toward the collector 23, generating scattered light 31. At this time, the amount of light received by the light detection unit 30 increases by the amount of scattered light 31 received, compared to the amount of light received under normal circumstances. For example, if the amount of light received by the light detection unit 30 exceeds a predetermined threshold, the control unit 90 determines that the first mirror 24 is not in a normal state, and outputs the determination result to the display unit 80, etc.

Next, another configuration example of the laser beam irradiation unit 20 will be described. FIG. 3 is a schematic diagram showing a second example of the schematic configuration of the laser beam irradiation unit 20 shown in FIG. 1. The second example of the laser beam irradiation unit 20-1 shown in FIG. 3 differs from the first example of the laser beam irradiation unit 20 shown in FIG. 2 in that it has a second mirror 25 and a third mirror 26. In the following description, the same components as those of the first example of the laser beam irradiation unit 20 are given the same reference numerals and will not be described.

The second mirror 25 is disposed on the optical path between the laser oscillator 22 and the first mirror 24. The second mirror 25 reflects the laser beam 21 emitted from the laser oscillator 22 to change the traveling direction of the laser beam 21. The second mirror 25 reflects the laser beam 21 so as to guide it toward the first mirror 24. If particles are attached to the surface 251 of the second mirror 25 that reflects the laser beam 21, part of the laser beam 21 will hit the particle without being reflected toward the first mirror 24, causing scattered light.

The third mirror 26 reflects the laser beam 21 reflected by the first mirror 24 to change the direction of travel of the laser beam 21. The third mirror 26 reflects the laser beam 21 so as to guide it toward the collector 23.

In the laser irradiation device 1 configured as described above, the control unit 90 not only determines whether the first mirror 24 is in a normal state, but also determines whether the second mirror 25 is in a normal state, based on the amount of scattered light received by the light detection unit 30. The control unit 90 pre-stores, for example, the amount of light received by the light detection unit 30 when no particles are attached to either the first mirror 24 or the second mirror 25 and the laser beam 21 is propagating normally along the optical path, as a reference value 91 (see FIG. 4). The control unit 90 also pre-stores a predetermined range 92 (see FIG. 4) that defines the amount of light received as normal, based on the reference value 91. The range 92 includes an upper threshold and a lower threshold.

For example, if a particle is attached to the surface 241 of the first mirror 24, part of the laser beam 21 will hit the particle without being reflected toward the third mirror 26, generating scattered light 31. At this time, the amount of light received by the light detection unit 30 increases by the amount of scattered light 31 received, compared to the amount of light received under normal circumstances. For example, if the amount of light received by the light detection unit 30 exceeds a predetermined threshold, the control unit 90 determines that the first mirror 24 is not in a normal state, and outputs the determination result to the display unit 80, etc.

For example, if particles are attached to the surface 251 of the second mirror 25, part of the laser beam 21 will not be reflected toward the first mirror 24 but will strike the particle, causing scattered light. At this time, the amount of light received by the light detection unit 30 will be reduced by the amount of the laser beam 21 propagating to the first mirror 24 compared to the amount of light received under normal conditions. The control unit 90 determines that the second mirror 25 is not in a normal state when, for example, the amount of light received by the light detection unit 30 falls below a predetermined threshold, and outputs the determination result to the display unit 80, etc.

Here, we will explain the cases where the amount of light received by the light detection unit 30 indicates a normal value and an abnormal value, using some data. Figure 4 is a schematic diagram showing the progress of the amount of light received by the light detection unit 30. More specifically, Figure 4 is a graph showing the time progress of three pieces of data 93, 94, and 95 indicating the amount of light received by the light detection unit 30.

In the graph shown in FIG. 4, when the upper and lower limits of the amount of received light are within range 92, it can be inferred that this indicates that the amount of received light is not increasing due to the first mirror 24, or decreasing due to the second mirror 25. In this case, the control unit 90 determines that the first mirror 24 and the second mirror 25 are in a normal state.

Data 93 shows the change in the amount of light received by the light detection unit 30 when the first mirror 24 is dirty. As shown in FIG. 4, data 93 exceeds the upper limit of range 92, which is the normal amount of received light. In other words, data 93 can be inferred to indicate that scattered light 31 is generated in the first mirror 24, and the amount of received light has increased by the amount of scattered light 31. Therefore, when the amount of received light obtained from the light detection unit 30 indicates that it exceeds the upper limit of range 92, as in data 93, the control unit 90 determines that the first mirror 24 is not in a normal state.

Data 94 shows the change in the amount of light received by the light detection unit 30 when the second mirror 25 is dirty. As shown in FIG. 4, data 94 is below the lower limit of range 92 for the normal amount of received light. In other words, data 94 can be inferred to indicate that scattered light occurs in the second mirror 25, and the amount of laser beam 21 propagating to the first mirror 24 is reduced, resulting in a decrease in the amount of received light. Therefore, when the amount of received light obtained from the light detection unit 30 indicates that it is below the lower limit of range 92, as in data 94, the control unit 90 determines that the second mirror 25 is not in a normal state.

Data 95 shows the change in the amount of light received by the light detection unit 30 when the first mirror 24 and the second mirror 25 are dirty. As shown in FIG. 5, data 95 is above the upper limit of range 92, which is the normal amount of received light. In other words, data 95 indicates that scattered light 31 occurs at the first mirror 24, and the amount of received light increases by the amount of scattered light 31. On the other hand, data 95 indicates a lower value compared to data 93. In other words, data 95 indicates that scattered light occurs at the second mirror 25, and the amount of laser beam 21 propagating to the first mirror 24 decreases, and the amount of received light decreases by the amount of scattered light 31.

The control unit 90, for example, constantly monitors and records the transition of the amount of light received by the light detection unit 30, and by tracing back the data of the fluctuation in the amount of light received, it is possible to determine that there is an abnormality in the second mirror 25 as well as the first mirror 24. For example, if the data shows that the amount of light received exceeds the upper limit value from the range 92 of the normal amount of light received, remains at a nearly constant value for a while, and then decreases, it can be determined that an abnormality occurred first in the first mirror 24, and then an abnormality occurred in the second mirror 25 as well.

The control unit 90 may calculate the Mahalanobis distance from the amount of light received by the light detection unit 30, and may determine whether the first mirror 24 and the second mirror 25 are in a normal state based on the calculated Mahalanobis distance. FIG. 5 is a schematic diagram showing the progress of the Mahalanobis distance calculated from the amount of light received by the light detection unit 30. More specifically, FIG. 5 is a graph showing the threshold value 92-1 obtained by converting the upper limit value of the range 92 shown in FIG. 4 into the Mahalanobis distance from the reference value 91, and the time progress of the calculated values 93-1 and 95-1 obtained by converting the data 93 and 95 into the Mahalanobis distance from the reference value 91.

As shown in FIG. 5, it can be seen that the calculated values 93-1 and 95-1 exceed the threshold value 92-1, similar to the received light amount data 93 and 95 shown in FIG. 4. Therefore, it can be inferred that the calculated values 93-1 and 95-1 both indicate that at least one of the first mirror 24 and the second mirror 25 is not in a normal state.

Furthermore, when the raw data of the current value generated based on the amount of light received by the light detection unit 30 is on the order of μA, the Mahalanobis' distance calculated from the raw data is on the order of ¹⁰ to ^10. Therefore, by using the Mahalanobis' distance, it is possible to determine anomalies with high sensitivity.

In FIG. 4, the amount of light received is compared, but the current value output from the PIN photodiode may also be compared. Also, in the above explanation, the Mahalanobis distance is calculated from the amount of light received, but it may also be calculated from the current value.

As described above, in the laser irradiation device 1 according to the embodiment, the present invention places the light detection unit 30 at a position opposite the first mirror 24 that reflects the laser beam 21, and detects the amount of light 31 scattered by particles, making it possible to quickly detect which optical components are contaminated.

Furthermore, based on the amount (intensity) of scattered light 31 received by the optical detection unit 30, it is possible to simultaneously detect contamination of the first mirror 24 positioned opposite the optical detection unit 30 and contamination of the second mirror 25 positioned upstream of the first mirror 24, and distinguish which is contaminated. This allows the number of optical detection units 30 to be placed to be reduced, contributing to reduced equipment costs.

The Mahalanobis distance can also be calculated from the amount of light received (output current value), and whether or not the condition is normal can be determined based on the Mahalanobis distance. This has the effect of preventing processing defects, as even small drops in output that would fall within the margin of error in conventional power meter measurements can be clearly detected.

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, the optical detection unit 30 is not limited to detecting an abnormality in the second mirror 25 adjacent to the upstream side of the first mirror 24 opposite to it, but may also detect an abnormality in a mirror located further upstream.

REFERENCE SIGNS LIST 1 laser irradiation device 10 holding table 20, 20-1 laser beam irradiation unit 21 laser beam 22 laser oscillator 23 condenser 24 first mirror 25 second mirror 26 third mirror 30 light detection unit 31 scattered light 40 housing 60 moving unit 90 control unit 100 workpiece (object)

Claims (4)

A laser irradiation device,
A holding table for holding an object;
a laser beam irradiation unit that irradiates a laser beam onto the object held on the holding table;
a moving unit that moves the object held on the holding table and the laser beam irradiation unit relatively;
A control unit for controlling each of the components,
The laser beam irradiation unit includes:
A laser oscillator;
a first mirror for reflecting the laser beam emitted from the laser oscillator to change the direction of travel of the laser beam;
a light detection unit disposed at a position opposite to a surface of the first mirror that reflects the laser beam, the light detection unit receiving scattered light from particles adhering to the first mirror;
The control unit
a light detection unit that detects the amount of scattered light received by the first mirror and determines whether the first mirror is in a normal state or not based on the amount of scattered light received by the light detection unit. The laser beam irradiation unit includes:
a second mirror is provided between the laser oscillator and the first mirror for reflecting the laser beam emitted from the laser oscillator and directing it to the first mirror;
The control unit
2. The laser irradiation device according to claim 1, wherein it is determined whether or not the first mirror and the second mirror are in a normal state based on the amount of scattered light received by the light detection unit. The control unit
When the amount of scattered light received by the light detection unit exceeds a predetermined threshold, it is determined that the first mirror is not in a normal state;
3. The laser irradiation device according to claim 2, wherein the second mirror is determined to be abnormal when the amount of scattered light received by the light detection unit falls below a predetermined threshold value. The control unit
4. The laser irradiation device according to claim 3, wherein the light detection unit calculates a Mahalanobis distance from the intensity of the scattered light received, and determines whether the first mirror and the second mirror are normal or not based on the Mahalanobis distance.

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