Inspection unit

Abstract

To provide an inspection unit which can know in advance that an optical system of laser beam irradiation means has a stain, a damage or an abnormality causing a trouble in laser processing.SOLUTION: An inspection unit 9 is used in a laser processing device 1 configured by including an oscillator 72 for oscillating a laser beam and an optical system having a light collector 71 for guiding and collecting the laser beam oscillated by the oscillator 72. The inspection unit 9 has a camera 90 for capturing a spot of the laser beam and processing means 92 for generating light intensity by two-dimensional coordinates of an X-coordinate and a Y-coordinate corresponding to a two-dimensional image captured by the camera 90. The processing means 92 has determination means 94 which generates a three-dimensional approximate curve or approximate curved surface using light intensity corresponding to the two-dimensional coordinates as a Z-coordinate and determines that the optical system on an optical path on the oscillator 72 side of a point where the spot is captured has a stain, a damage or an abnormality when a difference between light intensity Z1 of the Z-coordinate corresponding to the two-dimensional coordinates and light intensity Z1 indicated by the approximate curve or the approximate curved surface exceeds an allowable value.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an inspection unit used in a laser processing apparatus.

Background Art

[0002] A wafer on which a plurality of devices such as ICs and LSIs are partitioned by a dicing line and formed on the surface is divided into individual device chips by a dicing apparatus or a laser processing apparatus, and is used in electric devices such as mobile phones and personal computers.

[0003] A dicing apparatus includes a holding means for holding a wafer, a cutting means rotatably mounted with a cutting blade for cutting the wafer held by the holding means, and a feeding means for relatively feeding the holding means and the cutting means, and can divide the wafer into individual device chips with high precision (see, for example, Patent Document 1).

[0004] In addition, a laser processing apparatus includes a holding means for holding a wafer, a laser beam irradiation means for irradiating a laser beam onto the wafer held by the holding means, and a feeding means for relatively feeding the holding means and the laser beam irradiation means, and can divide the wafer into individual device chips with high precision or form a starting point when dividing the wafer into individual device chips (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the laser beam irradiation means of the above-described laser processing apparatus includes an optical system (reflective mirrors, lenses, beam splitters, diffraction gratings, cover glasses, spatial light modulators, masks, etc.) including an oscillator that oscillates a laser beam and a condenser that guides and condenses the laser beam oscillated by the oscillator. If there is dirt, scratches, or abnormalities in the optical system or the condenser, there is a problem that the shape of the spot of the laser beam is distorted and high-precision processing becomes impossible. The abnormalities in the optical system include, for example, distortion caused by expansion of the lens constituting the optical system, displacement from the position where the lens should be disposed, and malfunction of the spatial light modulator.

[0007] The present invention has been made in view of the above facts, and its main technical problem is to provide an inspection unit that can previously detect dirt, scratches, or abnormalities in the optical system of the laser beam irradiation means that hinder laser processing.

Means for Solving the Problem

[0008] In order to solve the above main technical problem, according to the present invention, there is provided an inspection unit used in a laser processing apparatus including an oscillator that oscillates a laser beam and an optical system including a condenser that guides and condenses the laser beam oscillated by the oscillator. The inspection unit includes a camera that images a spot of the laser beam, and processing means that generates light intensity in two-dimensional coordinates of X coordinates and Y coordinates corresponding to a two-dimensional image imaged by the camera. The processing means generates a three-dimensional approximate curve or approximate surface using the light intensity corresponding to the two-dimensional coordinates as the Z coordinate, and when the difference between the light intensity of the Z coordinate corresponding to the two-dimensional coordinates and the light intensity indicated by the approximate curve or the approximate surface exceeds an allowable value, determination means is provided that determines that there is dirt, scratches, or abnormalities in the optical system on the optical path on the oscillator side from the point where the spot was imaged.

[0009] A display means for displaying the two-dimensional image processed by the processing means is provided, and it is preferable to display the approximate curve or the approximate surface two-dimensionally on the display means. Further, it is preferable to rotate the two-dimensional coordinates to display the approximate curve or the approximate surface two-dimensionally.

Advantages of the Invention

[0010] The inspection unit of the present invention is an inspection unit used in a laser processing apparatus including an optical system including an oscillator that oscillates a laser beam and a condenser that guides and condenses the laser beam oscillated by the oscillator. The inspection unit includes a camera that images a spot of the laser beam, and processing means that generates light intensity in two-dimensional coordinates of an X coordinate and a Y coordinate corresponding to a two-dimensional image imaged by the camera. The processing means generates a three-dimensional approximate curve or approximate surface using the light intensity corresponding to the two-dimensional coordinates as a Z coordinate. When the difference between the light intensity of the Z coordinate corresponding to the two-dimensional coordinates and the light intensity indicated by the approximate curve or the approximate surface exceeds an allowable value, the inspection unit includes determination means for determining that there is dirt, damage, or an abnormality in the optical system on the optical path on the oscillator side from the point where the spot was imaged. Therefore, it is possible to know in advance that there is dirt, damage, or an abnormality in the optical system (condenser, optical system, reflection mirror, etc.) on the optical path on the oscillator side from the point where the spot was imaged, which may hinder laser processing, and prompt maintenance such as cleaning, repair, or replacement, so that high-precision processing can be maintained.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of an inspection unit configured based on the present invention will be described in detail with reference to the accompanying drawings.

[0013] FIG. 1 shows an overall perspective view of a laser processing apparatus 1 in which an inspection unit 90 (see FIG. 2) of the present embodiment to be described later is disposed. The illustrated laser processing apparatus 1 includes at least a laser beam irradiation means 7 that irradiates a workpiece held by a holding means 3 with a laser beam.

[0014] As shown in FIG. 2, the laser beam irradiation means 7 includes an oscillator 72 that oscillates a laser beam, a condenser lens 71 that condenses the laser beam oscillated by the oscillator 72 and irradiates a workpiece (a silicon wafer 10 in the present embodiment) held by the holding means 3, an optical system 73 disposed between the oscillator 72 and the condenser lens 71, and a reflection mirror 74 that reflects the laser beam LB0 oscillated by the oscillator 72 and irradiated through the optical system 73 and irradiates a laser beam LB1 toward the condenser lens 71. Although the details of the illustrated optical system 73 are omitted, for example, it can include a reflection mirror, a lens, a beam splitter, a diffraction grating, a cover glass, a spatial phase modulation element, a mask, etc. The configuration of the optical system 73 is appropriately selected according to the processing conditions when processing the workpiece by the laser beam irradiation means 7 and the material of the workpiece. In addition, the "optical system" in the present invention includes the condenser lens 71 and the reflection mirror 74 in addition to the illustrated optical system 73. Further, the wafer 10 processed in the present embodiment includes a device region in which a plurality of devices are formed at the center of the surface and an outer peripheral surplus region surrounding the device region, and is integrated with an annular frame F via an adhesive tape T as shown in the figure.

[0015] Returning to FIG. 1 and continuing the description, the laser processing apparatus 1 of the present embodiment is configured on a base 2. In addition to the above configuration, an alignment unit 6 that images a workpiece held by the holding unit 3 and performs alignment, a moving unit 4 that moves the holding unit 3, a frame body 5 including a vertical wall portion 5a erected on the side of the moving unit 4 and a horizontal wall portion 5b extending horizontally from the upper end portion of the vertical wall portion 5a, a display unit 8, and a control unit 100 are provided.

[0016] The holding unit 3 is a unit that holds the wafer 10 as a workpiece. More specifically, as shown in FIG. 1, a rectangular X-axis direction movable plate 31 mounted on the base 2 so as to be movable in the X-axis direction, a rectangular Y-axis direction movable plate 32 mounted on the X-axis direction movable plate 31 so as to be movable in the Y-axis direction, a cylindrical support column 33 fixed to the upper surface of the Y-axis direction movable plate 32, a rectangular cover plate 34 fixed to the upper end of the support column 33, and a chuck table 35 extending upward through a long hole formed in the cover plate 34 are provided. The chuck table 35 is configured to be rotatable by a rotation driving unit (not shown) housed in the support column 33. On the upper surface of the chuck table 35, a circular suction chuck 36 that forms a holding surface by a breathable member is disposed. The suction chuck 36 is connected to a suction unit (not shown) by a flow path passing through the support column 33. Around the suction chuck 36, four clamps 37 that grip a frame F that supports the wafer 10 when holding the wafer 10 on the chuck table 35 are arranged at equal intervals. By operating the suction unit, a negative pressure is generated on the upper surface of the suction chuck 36 to suck the wafer 10, and at the same time, the frame F can be gripped by the clamps 37 to fix the wafer 10 to the chuck table 35.

[0017] The moving means 4 includes an X-axis moving means 4a for moving the holding means 3 in the X-axis direction and a Y-axis moving means 4b for moving the holding means 3 in the Y-axis direction orthogonal to the X-axis direction. The X-axis moving means 4a converts the rotational motion of the motor 42a into linear motion via a ball screw 42b and transmits it to the X-axis movable plate 31, and moves the X-axis movable plate 31 in the X-axis direction along a pair of guide rails 2A, 2A arranged along the X-axis direction on the base 2. The Y-axis moving means 4b converts the rotational motion of the motor 44a into linear motion via a ball screw 44b, transmits it to the Y-axis movable plate 32, and moves the Y-axis movable plate 32 in the Y-axis direction along a pair of guide rails 31a, 31a arranged along the Y-axis direction on the X-axis movable plate 31.

[0018] In addition to the optical system constituting the laser beam irradiation means 7 described with reference to FIG. 2, the inspection unit 9 of the present embodiment is housed in the horizontal wall portion 5b of the frame body 5. On the lower surface side of the tip of the horizontal wall portion 5b, a condenser 71 is arranged which constitutes a part of the laser beam irradiation means 7 and condenses the laser beam to irradiate the chuck table 35. Alignment means 6 is arranged at a position adjacent to the condenser 71 in the X-axis direction on the lower surface side of the tip of the horizontal wall portion 5b. The alignment means 6 is an imaging means for imaging the wafer 10 held by the holding means 3 and detecting the position and orientation of the wafer 10, the processing position to which the laser beam should be irradiated, and the like.

[0019] The control means 100 is constituted by a computer and includes a central processing unit (CPU) that performs arithmetic processing according to a control program, a read-only memory (ROM) that stores the control program and the like, a readable and writable random access memory (RAM) for temporarily storing the detected detection values, arithmetic results, etc., an input interface, and an output interface (illustrations of details are omitted). The alignment means 6, the display means 8, the moving means 4 including the X-axis moving means 4a and the Y-axis moving means 4b, etc. described above are connected to the control means 100, and the information of the image data imaged by the alignment means 6 is stored in an appropriate memory and displayed on the display means 8.

[0020] In the laser beam irradiation means 7 of the laser processing apparatus 1 of the present embodiment, as shown in FIG. 2, an inspection unit 9 configured based on the present invention is attached.

[0021] The inspection unit 9 includes a camera 90 and a processing means 92 that generates light intensity in two-dimensional coordinates of the X coordinate and the Y coordinate corresponding to the two-dimensional image captured by the camera 90. The laser beam LB0 oscillated by the oscillator 72 of the laser beam irradiation means 7 described above hits the reflection mirror 74 via the optical system 73 and is irradiated as the processing laser beam LB1 toward the condenser 71. At the same time, a part of it passes through the reflection mirror 74 and becomes the laser beam LB2. The camera 90 images the spot (beam) of the laser beam LB2 that has passed through the reflection mirror 74. The laser beam LB2 is so-called leakage light and is a laser beam weakened to a power density that does not damage the light receiving element of the camera 90.

[0022] The processing means 92 of the present embodiment is configured as a control means 100 that controls each operating part of the laser processing apparatus 1, and generates light intensity in two-dimensional coordinates of the X coordinate and the Y coordinate corresponding to the two-dimensional image showing the shape of the spot imaged by the camera 90. Further, the processing means 92 generates a three-dimensional approximate curve or approximate surface with the light intensity generated corresponding to the two-dimensional coordinates as the Z coordinate, and determines whether the difference (|Z1 - Z2|) between the light intensity Z1 of the Z coordinate of the measured value corresponding to the two-dimensional coordinates and the light intensity Z2 indicated by the approximate curve or the approximate surface generated by the processing means 92 exceeds an allowable value. When it is determined that the difference exceeds the allowable value, it includes a determination means 94 that determines that there is dirt, damage, or abnormality in the optical system on the optical path on the oscillator 72 side from the point where the spot was imaged (details will be described later).

[0023] The laser processing apparatus 1 of the present embodiment generally has the configuration described above. According to the inspection unit 9 described above, the inspection of the laser beam irradiation means 7 of the laser processing apparatus 1 can be carried out in the following form, for example.

[0024] First, an unprocessed wafer 10 supported by a frame F via an adhesive tape T is conveyed to the above-described laser processing apparatus 1. The wafer 10 is placed on the chuck table 35 of the holding means 3, the suction means is operated to generate a negative pressure in the suction chuck 36 for suction, and the frame F is gripped by the clamp 37 to fix the wafer 10 to the chuck table 35.

[0025] The above-described moving means 4 is operated to move the chuck table 35 directly below the alignment means 6, image the wafer 10 fixed to the chuck table 35, detect the processing position, and adjust the rotational position of the chuck table 35. Next, the moving means 4 is operated to position the chuck table 35 directly below the condenser 71 of the laser beam irradiation means 7. Here, directly below the condenser 71, an outer peripheral surplus region where no device is formed on the surface of the wafer 10 is positioned. Next, the laser beam irradiation means 7 is operated to oscillate a laser beam LB0 by the oscillator 72. As described with reference to FIG. 2, a part of the laser beam LB0 oscillated by the oscillator 72 of the laser beam irradiation means 7 passes through the reflection mirror 74 and becomes a laser beam LB2 with a reduced power density, and the spot thereof is imaged by the camera 90.

[0026] The above-described processing means 92 generates light intensities corresponding to the coordinate positions of the X coordinate and the Y coordinate of the two-dimensional image from the two-dimensional image of the laser beam LB2 imaged by the camera 90. The X coordinate and the Y coordinate of this two-dimensional image are the coordinates provided by the camera 90 when imaging the spot of the laser beam LB2.

[0027] The processing means 92 generates three-dimensional information with the light intensity as the Z coordinate based on the light intensity at each coordinate position in the X coordinate and Y coordinate corresponding to the two-dimensional image showing the shape of the spot imaged by the camera 90. As shown in FIG. 3, a display means 8 is connected to the control means 100 provided with the processing means 92, and the two-dimensional image S1 based on the three-dimensional information generated by the processing means 92 is displayed in the first display area 8A of the display means 8. In the first display area 8A of the display means 8, a straight line X1 indicating the horizontal direction passing through the center of the first display area 8A and a straight line Y1 orthogonal to the straight line X1 at the center of the first display area 8A are displayed (both are shown by two-dot chain lines). The image S1 displays a state where the intersection of the straight line X1 and the straight line Y1 coincides with the optical axis of the laser beam LB2. In the initial state, the X axis and Y axis for specifying the image S1 showing the shape of the spot imaged by the camera 90 are displayed so as to coincide with the straight line X1 and the straight line Y1 shown on the display means 8.

[0028] The image S1 displayed in the first display area 8A shown in FIG. 3 shows contour lines connecting Z coordinate positions with the same light intensity for convenience of explanation, but in reality, based on the three-dimensional information with the light intensity of the X coordinate and Y coordinate in the image S1 as the Z coordinate value, the light intensity can be distinguished by the change in color. In the illustrated image S1, the contour lines of the convex region are shown by solid lines, but if there is a region where the value of the light intensity is concave, the contour lines are shown by broken lines (see FIG. 4).

[0029] Also, in the present embodiment, in the first display area 8A, a two-dimensional image S2 showing the light intensity value of the image S1 passing through the straight line X1 indicating the horizontal direction as the Z coordinate is shown in the second display area 8B set on the lower side of the first display area 8A. The two-dimensional image S2 shown in this second display area 8B can be said to be a so-called cross-sectional view of the image S1 shown in the first display area 8A formed based on the three-dimensional information, cut by the straight line X1.

[0030] As described above, the processing means 92 generates a three-dimensional approximation curve or approximation surface based on the three-dimensional information indicating the value of the light intensity corresponding to the two-dimensional coordinates of the image S1 with the Z coordinate. In the present embodiment, corresponding to the two-dimensional image S2 shown in the second display area 8B of the display means 8 in FIG. 3, a two-dimensional approximation curve P1 generated based on the above three-dimensional approximation curve or approximation surface is generated and displayed in the second display area 8B together with the above-described two-dimensional image S2. The approximation curve P1 is preferably a curve approximated by a smooth normal distribution curve.

[0031] The processing means 92 includes a determination means 94 that calculates the difference (|Z1 - Z2|) between the light intensity Z1 of the two-dimensional image S2 based on the measured values shown in the second display area 8B and the light intensity Z2 in the above-described approximation curve P1, and determines whether or not the difference exceeds an allowable value. Here, the allowable value is set based on the fact that the light intensity Z1 based on the measured values at each coordinate position deviates greatly from the light intensity Z2 of the approximation curve P1, and is a value set to detect dirt, scratches, or abnormalities in the optical system on the optical path on the oscillator 72 side rather than the point where the spot is imaged by the camera 90. It is a value appropriately set by experiments or the like carried out in advance.

[0032] Here, the calculation of the difference by the determination means 94 is repeatedly performed while rotating the two-dimensional coordinates of the image S1 displayed in the first display area 8A of the display means 8 in FIG. 3 at a predetermined angular interval in the direction indicated by the arrow R1. Then, it is detected whether there is an area where the difference calculated at each rotation angle exceeds the allowable value. By rotating the two-dimensional coordinates of the image S1 displayed in the first display area 8A by 360° in the direction indicated by the arrow R1, the entire area of the spot imaged by the camera 90 can be inspected.

[0033] In the inspection performed by the processing means 92 shown in FIG. 3, at any angle, no difference exceeding the tolerance value is detected. Therefore, it is determined that there is no dirt, scratch, or abnormality in any of the optical systems on the optical path on the oscillator 72 side from the point where the spot was imaged by the camera 90, and it is determined that the laser processing using the laser beam LB1 is performed well. The result of this determination is stored in an appropriate memory means of the processing means 92 and is displayed at any position of the display means 8 as necessary.

[0034] FIG. 4 shows the results when the inspection by the above-described processing means 92 is performed when there is dirt, scratch, or abnormality in the optical system of the laser beam irradiation means 7 described above.

[0035] In the first display area 8A of the display means 8 shown in FIG. 4, an image S3 showing the shape and light intensity of the spot imaged by the camera 90 is shown at the position shown in FIG. 2. Further, in the second display area 8B, together with a two-dimensional image S4 showing the light intensity corresponding to the X coordinate and Y coordinate of the image S3 that coincides with the straight line X1 of the first display area 8A as the Z coordinate, an approximation curve P2 generated based on a three-dimensional approximation curve or approximation surface generated by three-dimensional information showing the value of the light intensity corresponding to the two-dimensional coordinates of the image S3 as the Z coordinate is displayed. This approximation curve P2 is also preferably a curve approximated by a smooth normal distribution curve, similar to the above-described approximation curve P1, and is displayed superimposed on the image S4.

[0036] Then, the difference (|Z1 - Z2|) between the light intensity Z1 shown by the above-described two-dimensional image S4 and the light intensity Z2 shown by the two-dimensional approximation curve P2 is calculated by the determination means 94, and it is determined whether it is larger than the tolerance value. In the inspection shown in FIG. 4, as understood from the image S3 displayed in the first display area 8A of the display means 8, a plurality of concave portions indicating regions with weak light intensity are shown by broken-line contour lines. For example, in the region of the concave portion H1 that coincides with the straight line X1, it is determined that the difference (|Z1 - Z2|) is larger than the tolerance value. The result is transmitted to the processing means 92 and stored in an appropriate memory.

[0037] Also in the inspection shown in FIG. 4, while rotating the two-dimensional coordinates of the image S3 displayed in the first display area 8A 360° in the direction indicated by the arrow R2, the determination means 94 calculates the difference between the light intensity Z1 indicated by the two-dimensional image S4 and the light intensity Z2 indicated by the above-described approximate curve P2 over the entire range of the X coordinate and Y coordinate forming the image S3. When it is determined that the difference is greater than the allowable value, it is transmitted to the processing means 92 each time, and is stored in an appropriate memory together with the X coordinate and Y coordinate of the area where it is determined that the difference is greater than the allowable value. In this way, the inspection is completed over the entire range of the X coordinate and Y coordinate forming the image S3. As described above, when there is an area where it is determined that the difference is greater than the allowable value, it is determined that there is dirt, damage, or abnormality in the optical system on the optical path closer to the oscillator 72 than the point where the spot was imaged by the determination means 94. As a result, it is transmitted to the control means 100 that there is a risk that the processing by the laser beam LB2 may not be performed normally, and a warning is issued to the operator as necessary. The warning can be implemented by display on the display means 8, operation of a warning buzzer, flashing of a red lamp, etc., and can prompt maintenance of the optical system disposed on the optical path closer to the oscillator 72 than the point where the spot was imaged. Further, when it is determined that the difference is greater than the allowable value in a plurality of areas, it is preferable to display information regarding the number of areas where it is determined that the difference is greater than the allowable value, the area of the areas where it is determined that the difference is greater than the allowable value, or the ratio of the area at the time of the warning.

[0038] In the above-described embodiment, the camera 90 of the inspection unit 9 images the spot of the laser beam LB2 that has passed through the reflection mirror 74, and the above inspection is performed. However, the present invention is not limited to this. For example, on the optical path of the laser beam LB1 irradiated from the condenser 71 to the wafer 10, the above inspection unit 90 is disposed together with branching means (not shown) for branching a part of the laser beam LB1, and the spot of the laser beam branched by the branching means and having a reduced power density is imaged, and the inspection may be performed in the same procedure as the above-described inspection. In that case, the condenser 71 can be positioned on the optical path on the oscillator 72 side rather than the point where the spot is imaged, and the condenser 71 can be included in the inspection target by the inspection unit 90.

[0039] According to the above-described embodiment, in the laser beam irradiation means 7, it is possible to know in advance that there is dirt, scratches, or abnormalities that may interfere with laser processing in the optical system (condenser 71, optical system 72, reflection mirror 74, etc.) on the optical path on the oscillator 72 side rather than the point where the spot is imaged, and it is possible to promote maintenance such as cleaning, repairing, or replacing the optical system, and maintain high-precision processing.

[0040] Note that if the inspection unit 90 configured based on the present invention is used, it is possible to perform the inspection even while the laser processing on the wafer 10 is being performed by the above-described laser beam irradiation means 7.

[0041] In the above-described embodiment, a display unit 8 for displaying a two-dimensional image processed by a processing unit 92 is provided. An approximate curve is displayed two-dimensionally in a second display area 8B of the display unit 8, and the two-dimensional coordinates of the image displayed in the first display area 8A are rotated 360°, and it is determined whether or not the difference between the light intensity Z1 of the Z coordinate corresponding to the two-dimensional coordinates and the light intensity Z2 indicated by the approximate curve exceeds an allowable value over the entire range of the X and Y coordinates forming the image. However, the present invention is not limited to this. For example, the processing unit 92 generates an approximate surface corresponding to an image generated based on three-dimensional information in which the light intensity at each coordinate position is the value of the Z coordinate, and calculates at once the difference between the light intensity over the entire area of the two-dimensional image displayed in the first display area 8A and the light intensity over the entire area of the approximate surface generated based on the light intensity at each coordinate position of the two-dimensional image. At each coordinate position, it may be determined whether or not the difference between the light intensity Z1 of the Z coordinate corresponding to each two-dimensional coordinate and the light intensity Z2 indicated by the approximate curve exceeds an allowable value.

Explanation of Signs

[0042] 1: Laser processing apparatus 2: Base 3: Holding means 35: Chuck table 36: Suction chuck 37: Clamp 4: Moving means 4a: X-axis moving means 4b: Y-axis moving means 5: Frame 6: Alignment means 7: Laser beam irradiation means 71: Condenser 72: Oscillator 73: Optical system 74: Reflecting mirror 8: Display means 8A: First display area 8B: Second display area 9: Inspection unit 90: Camera 92: Processing means 94: Judgment means 100: Control means F: Frame T: Adhesive tape

Claims

Claim 1 An inspection unit used in a laser processing apparatus including an oscillator that oscillates a laser beam and an optical system including a condenser that guides and condenses the laser beam oscillated by the oscillator, the inspection unit includes a camera that images a spot of the laser beam and processing means that generates light intensity in two-dimensional coordinates of an X coordinate and a Y coordinate corresponding to a two-dimensional image imaged by the camera, the processing means generates a three-dimensional approximate curve or approximate surface with the light intensity corresponding to the two-dimensional coordinates as the Z coordinate, and when the difference between the light intensity of the Z coordinate corresponding to the two-dimensional coordinates and the light intensity indicated by the approximate curve or the approximate surface exceeds an allowable value, the inspection unit includes determination means for determining that there is dirt, damage, or an abnormality in the optical system on the optical path on the oscillator side from the point where the spot was imaged. Claim 2 The inspection unit according to claim 1, further comprising display means for displaying the two-dimensional image processed by the processing means, and displaying the approximate curve or the approximate surface in two dimensions on the display means. Claim 3 The inspection unit according to claim 2, wherein the two-dimensional coordinates are rotated to display the approximate curve or the approximate surface in two dimensions.

Images