Inspection apparatus and inspection method

Abstract

Provided are an inspection device and an inspection method capable of detecting isobars of a Gaussian distribution of laser light with high precision. The inspection device of a laser oscillator includes a light-reducing plate that reduces the intensity of laser light immediately after emission from a laser oscillator; a photographing unit that photographs the laser light reduced by the light-reducing plate using a plurality of pixels; a processing unit that processes an image photographed by the photographing unit; and a display unit that displays the image processed by the processing unit. The processing unit has two thresholds of at least an inner circle and an outer circle that divide the intensity of the laser light.

Description

Technical Field

[0001] The present invention relates to an inspection device and an inspection method for inspecting the accuracy of a laser oscillator that oscillates laser light. Background Art

[0002] A wafer having multiple devices such as ICs and LSIs formed on the front surface is divided by a plurality of intersecting predetermined dividing lines and is divided into individual device chips by a cutting device or a laser processing device. The divided device chips are used in electronic devices such as mobile phones and personal computers.

[0003] The laser processing device is roughly composed of a chuck worktable, a laser beam irradiation unit and a feeding mechanism. The chuck worktable holds the chip, the laser beam irradiation unit irradiates the laser beam to the chip held on the chuck worktable, and the feeding mechanism performs relative processing and feeding on the chuck worktable and the laser beam irradiation unit.

[0004] There are the following types of laser beam irradiation units: a type in which a workpiece is irradiated with laser beams of a wavelength that is absorbent to the workpiece to perform groove processing on the upper surface of the workpiece by ablation (for example, see patent document 1); a type in which a focal point of a laser beam of a wavelength that is transmissive to the workpiece is positioned inside the workpiece and the workpiece is irradiated with laser beams to form a modified layer inside the workpiece (for example, see patent document 2).

[0005] In such a laser processing apparatus, an M2 measuring instrument is used to confirm the contour lines (lines connecting a plurality of points of the same intensity) of the Gaussian distribution of the laser beam.

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 10-305420

[0007] Patent Document 2: Japanese Patent No. 3408805

[0008] However, M2 measurement is a measurement that observes the shape of the light spot focused by the condenser, but it cannot detect the contour lines of the Gaussian distribution of the laser light with sufficient resolution. In practice, when the workpiece is irradiated with laser light, subtle deformation of the light spot shape (deformation of the contour lines) is often observed based on the processing results. Therefore, M2 measurement lacks reliability in terms of reference accuracy. Summary of the Invention

[0009] Therefore, an object of the present invention is to provide an inspection device and an inspection method capable of detecting contour lines of a Gaussian distribution of laser light with high accuracy.

[0010] According to one aspect of the present invention, an inspection device is provided for inspecting the accuracy of a laser oscillator that oscillates laser light, wherein the inspection device comprises: a dimming plate that dims the laser light just after it is emitted from the laser oscillator; a photographing unit that uses a plurality of pixels to photograph the laser light dimmed by the dimming plate; a processing unit that processes the image photographed by the photographing unit; and a display unit that displays the image processed by the processing unit, the processing unit having at least two thresholds, an inner circle and an outer circle, for dividing the intensity of the laser light, and the display unit displays the inner circle and the outer circle.

[0011] Preferably, the processing unit has at least a middle circle threshold between the inner circle threshold and the outer circle threshold. Preferably, the processing unit calculates an offset between the center of the inner circle and the center of the outer circle or the center of the middle circle, and the display unit displays the offset.

[0012] According to another aspect of the present invention, an inspection method is provided, which is a method for inspecting a laser oscillator in a laser processing device, wherein the laser processing device includes: a laser oscillator that oscillates laser light; a condenser that focuses the laser light; an optical system that is arranged between the laser oscillator and the condenser and guides the laser light; and a chuck worktable that holds a workpiece processed by the laser light focused by the condenser, wherein the inspection method includes the following steps: a shooting unit positioning step of positioning the shooting unit between the laser oscillator of the laser processing device and the optical system; a shooting step of using the shooting unit to shoot the laser light just after it is emitted from the laser oscillator; a processing step of using the processing unit to process the image shot by the shooting unit; and an inspection step of causing a display unit to display the image processed by the processing unit, and inspecting the accuracy of the laser oscillator through the image displayed by the display unit.

[0013] According to the inspection apparatus of the present invention, it is possible to detect the contour lines of the Gaussian distribution of the laser beam with high accuracy.

[0014] According to the inspection method of the laser oscillator of the present invention, the contour lines of the Gaussian distribution of the laser beam can be detected with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a block diagram of an inspection device according to an embodiment of the present invention.

[0016] Figure 2 (a) is a schematic diagram of a cross-sectional image of laser light with the centers of the inner circle, middle circle, and outer circle aligned. Figure 2 (b) is a schematic diagram of a cross-sectional image of the laser beam with the centers of the inner circle, the middle circle, and the outer circle shifted.

[0017] Figure 3This is a perspective view of a laser processing device that can be inspected using the inspection method of the present invention.

[0018] Figure 4 yes Figure 3 The block diagram of the main parts of the laser processing device is shown.

[0019] Description of labels

[0020] 2: Inspection device; 4: Laser oscillator; 6: Light-reduction plate; 8: Shooting unit; 10: Processing unit; 12: Display unit; 14: Inner ring; 16: Middle ring; 18: Outer ring; 20: Laser processing device; 22: Laser oscillator; 24: Condenser; 26: Optical system; 28: Holding unit; LB: Laser beam. DETAILED DESCRIPTION

[0021] Hereinafter, preferred embodiments of the inspection device and the inspection method according to the present invention will be described with reference to the accompanying drawings.

[0022] Reference Figure 1 For explanation, the inspection device 2 includes: a dimming plate 6, which dims the laser light LB just emitted from the laser oscillator 4; a shooting unit 8, which uses multiple pixels to shoot the laser light LB dimmed by the dimming plate 6; a processing unit 10, which processes the image captured by the shooting unit 8; and a display unit 12, which displays the image processed by the processing unit 10.

[0023] As the dimming plate 6, an appropriate dimming member such as an ND filter can be used. The dimming plate 6 is, for example, positioned immediately after the laser oscillator 4, which emits laser light LB (so-called seed light) with a repetition frequency of approximately tens of MHz and an output of approximately several mW. Specifically, the laser light LB emitted from the laser oscillator 4 is dimmed by the dimming plate 6 before being converted in frequency by a repetition frequency conversion member (not shown) and amplified and output by an output amplifier (not shown), and then captured by the imaging unit 8.

[0024] The imaging unit 8 may be, for example, a CCD camera, and uses a plurality of pixels to image a cross section (a cross section perpendicular to the optical axis) of the laser beam LB reduced in intensity by the neutral density plate 6 .

[0025] The processing unit 10 can be configured as a computer. It includes a central processing unit (CPU) that performs computations according to a control program, a read-only memory (ROM) that stores the control program, and a readable and writable random access memory (RAM) that stores computation results. The processing unit 10 is electrically connected to the imaging unit 8, and the cross-sectional image perpendicular to the optical axis of the laser beam LB captured by the imaging unit 8 is transmitted to the processing unit 10.

[0026] The processing unit 10 has at least two thresholds, an inner and outer threshold, for classifying the intensity of the laser beam LB. The processing unit 10 of this embodiment further has a middle threshold between the inner and outer thresholds. The inner threshold is greater than both the middle and outer thresholds, and the middle threshold is greater than the outer threshold (inner threshold > middle threshold > outer threshold). Alternatively, the processing unit 10 may have three or more thresholds.

[0027] The processing unit 10 performs a four-valued processing on the cross-sectional image of the laser light LB based on the three thresholds of the inner circle, the outer circle and the middle circle, and divides the cross-sectional image of the laser light LB according to the intensity of the laser light LB. Figure 2 As understood, the processing unit 10 divides the cross-sectional image of the laser light LB into a circular first area R1 (black area) where the intensity of the laser light LB is greater than the threshold of the inner circle, an annular second area R2 (light gray area) where the intensity of the laser light LB is less than the threshold of the inner circle and greater than the threshold of the middle circle, an annular third area R3 (dark gray area) where the intensity of the laser light LB is less than the threshold of the middle circle and greater than the threshold of the outer circle, and a fourth area R4 (white area) where the intensity of the laser light LB is less than the threshold of the outer circle.

[0028] The processing unit 10 calculates the area of ​​the first region R1 based on the cross-sectional image of the laser beam LB subjected to the quaternization process, calculates the diameter of a circle having the same area as the calculated area of ​​the first region R1, and calculates the center of gravity of the first region R1. Figure 2 As shown, the processing unit 10 performs the following processing: using the calculated center of gravity of the first region R1 as the center C1, and drawing the inner circle 14 in the cross-sectional image of the laser light LB subjected to the four-valued processing according to the calculated diameter of the circle (equivalent to the circle of the first region R1).

[0029] Furthermore, the processing unit 10 calculates the total area of ​​the first and second regions R1 and R2 based on the cross-sectional image of the laser beam LB subjected to the quaternization process, calculates the diameter of a circle having the same area as the calculated total area of ​​the first and second regions R1 and R2, and calculates the center of gravity of the second region R2. Figure 2 As shown, the processing unit 10 performs the following processing: taking the calculated center of gravity of the second region R2 as the center C2, and based on the diameter of the calculated circle (equivalent to the circles of the first and second regions R1 and R2), the middle circle 16 is depicted in the cross-sectional image of the laser light LB that has been four-valued.

[0030] Furthermore, the processing unit 10 calculates the total area of ​​the first, second, and third regions R1, R2, and R3 based on the cross-sectional image of the laser beam LB subjected to the quaternization process, calculates the diameter of a circle having the same area as the total area of ​​the first, second, and third regions R1, R2, and R3, and calculates the center of gravity of the third region R3. Figure 2 As shown, the processing unit 10 performs the following processing: using the calculated center of gravity of the third region R3 as the center C3, based on the calculated diameters of the circles (corresponding to the first, second, and third regions R1, R2, and R3), an outer circle 18 is drawn in the cross-sectional image of the laser beam LB that has been subjected to the four-valued processing. In this way, the processing unit 10 performs the processing of drawing three circles, namely the inner circle 14, the middle circle 16, and the outer circle 18, as the contour lines of the laser beam LB in the cross-sectional image of the laser beam LB.

[0031] The processing unit 10 of this embodiment calculates the offset between the center C1 of the inner ring 14 (the center of gravity of the first region R1) and the center C3 of the outer ring 18 (the center of gravity of the third region R3) or the center C2 of the middle ring 16 (the center of gravity of the second region R2). The processing unit 10 can make a judgment as follows: when the offset between the center C1 of the inner ring 14 and the center C2 of the middle ring 16 or the center C3 of the outer ring 18 is less than a specified value (for example, less than 5% of the diameter of the outer ring 18), the use of the laser oscillator 4 is allowed; when the offset exceeds the specified value, the use of the laser oscillator 4 is not allowed. In addition, in Figure 2 In (a), a schematic diagram of a cross-sectional image of the laser beam LB is shown with the centers C1, C2, and C3 of the inner ring 14, the middle ring 16, and the outer ring 18 aligned. Figure 2 (b) shows a schematic diagram of a cross-sectional image of the laser light LB when the centers C1, C2, and C3 of the inner ring 14, the middle ring 16, and the outer ring 18 are offset and the offset between the center C1 of the inner ring 14 and the center C3 of the outer ring 18 exceeds the above-specified value.

[0032] The display unit 12 may be composed of a display device having a liquid crystal screen or the like. Figure 1 As shown, the display unit 12 is electrically connected to the processing unit 10 , and the cross-sectional image of the laser beam LB processed by the processing unit 10 is sent to the display unit 12 .

[0033] The display unit 12 displays at least the inner ring 14 and the outer ring 18 together with the cross-sectional image of the laser beam LB processed by the processing unit 10. Figure 2 As shown, the display unit 12 of this embodiment further displays the middle circle 16 , and displays the centers C1 , C2 , and C3 of the inner circle 14 , the middle circle 16 , and the outer circle 18 , respectively.

[0034] The display unit 12 may also display the offset amount calculated by the processing unit 10, the result of the processing unit 10's determination regarding whether to permit use of the laser oscillator 4, and the like. The offset amount displayed on the display unit 12 may be the offset between the center C1 of the inner ring 14 and the center C3 of the outer ring 18, or the offset between the center C1 of the inner ring 14 and the center C2 of the middle ring 16.

[0035] Next, an inspection method using the inspection apparatus 2 described above will be described.

[0036] Figure 3 A laser processing device 20 is shown that can implement the inspection method using the inspection device 2. Figure 4 FIG shows a block diagram of a laser processing device 20. The laser processing device 20 includes a laser oscillator 22 (see FIG. Figure 4 ), which emits laser light LB; the condenser 24 (refer to Figure 3 and Figure 4 ), which focuses the laser beam LB; optical system 26 (refer to Figure 4 ), which is disposed between the laser oscillator 22 and the condenser 24 and guides the laser beam LB; and a holding unit 28 (refer to Figure 3 and Figure 4 ) which holds the workpiece W processed by the laser beam LB focused by the condenser 24.

[0037] like Figure 3 As shown, the laser processing device 20 includes a base 30 and a housing 32 that extends upward from the upper surface of the base 30 and then extends substantially horizontally. The laser oscillator 22 and the optical system 26 are disposed within the housing 32, and the condenser 24 is disposed on the front lower surface of the housing 32. Furthermore, a camera 34 is mounted on the front lower surface of the housing 32. This camera 34 is used to image the workpiece W held by the holding unit 28 and detect an area to be laser processed.

[0038] The laser oscillator 22 emits, for example, a laser beam LB (so-called seed light) having a repetition frequency of about tens of MHz and an output of about several mW. The optical system 26 has: a repetition frequency conversion unit (not shown), which converts the repetition frequency of the laser beam LB emitted from the laser oscillator 22 into an appropriate repetition frequency (for example, about several hundred kHz); an output amplifier (not shown), which amplifies the output of the laser beam LB emitted from the laser oscillator 22 into an appropriate output (for example, about tens of W); an output adjustment unit (not shown), which adjusts the output of the laser beam LB amplified by the output amplifier into an appropriate output; and a wavelength conversion unit (not shown), which converts the wavelength of the laser beam LB emitted from the laser oscillator 22 into an appropriate wavelength. Then, as Figure 4As shown, the laser beam LB emitted from the laser oscillator 22 is converted to an appropriate frequency, output, and wavelength by the optical system 26 , and then reflected by the reflective mirror 36 and guided to the condenser 24 , where it is condensed and irradiated onto the workpiece W.

[0039] Reference Figure 3 To explain, the holding unit 28 includes: an X-axis movable plate 38 mounted on the base 30 so as to be movable in the X-axis direction indicated by arrow X; a Y-axis movable plate 40 mounted on the X-axis movable plate 38 so as to be movable in the Y-axis direction (direction indicated by arrow Y) perpendicular to the X-axis direction; a support column 42 fixed to the upper surface of the Y-axis movable plate 40; and a cover plate 44 fixed to the upper end of the support column 42. The XY plane defined by the X-axis and Y-axis directions is substantially horizontal.

[0040] The cover plate 44 is provided with a long hole 44a extending in the Y-axis direction. A chuck table 46 extending upward through the long hole 44a is rotatably mounted on the upper end of the support column 42. The chuck table 46 is rotated by a rotation unit (not shown) built into the support column 42. A porous circular adsorption chuck 48 connected to a suction unit (not shown) is arranged at the upper end of the chuck table 46. The suction unit generates a suction force on the upper surface of the adsorption chuck 48 in the chuck table 46, thereby adsorbing and holding the workpiece W placed on the upper surface of the adsorption chuck 48. In addition, a plurality of clamps 50 are arranged at intervals along the circumferential direction around the periphery of the chuck table 46.

[0041] The holding unit 28 is fed for machining in the X-axis direction along the guide rail 30a on the base 30 by an X-axis feed mechanism 56. The X-axis feed mechanism 56 includes a ball screw 52 connected to the X-axis movable plate 38 and extending in the X-axis direction, and a motor 54 for rotating the ball screw 52. Furthermore, the holding unit 28 is indexed and fed in the Y-axis direction along the guide rail 38a on the X-axis movable plate 38 by a Y-axis feed mechanism 62. The Y-axis feed mechanism 62 includes a ball screw 58 connected to the Y-axis movable plate 40 and extending in the Y-axis direction, and a motor 60 for rotating the ball screw 58.

[0042] When the inspection device 2 is used to inspect the accuracy of the laser oscillator 22 of the laser processing device 20 , the following imaging unit positioning step is first performed: the dimming plate 6 and imaging unit 8 of the inspection device 2 are positioned between the laser oscillator 22 and the optical system 26 of the laser processing device 20 .

[0043] After the imaging unit positioning step is performed, the imaging step is performed in which imaging unit 8 captures the laser beam LB immediately after it is emitted from laser oscillator 22 of laser processing device 20. The laser beam LB captured by imaging unit 8 in the imaging step is the laser beam LB attenuated by light reduction plate 6. Furthermore, the cross-sectional diameter of the laser beam LB captured by imaging unit 8 is, for example, approximately 5 mm to 6 mm.

[0044] After the photographing step is performed, the following processing step is performed: the image photographed by the photographing unit 8 is processed by the processing unit 10 .

[0045] In the processing step, the cross-sectional image of the laser beam LB is first quadratured based on three thresholds: the inner circle 14, the middle circle 16, and the outer circle 18. The processing unit 10 then divides the cross-sectional image of the laser beam LB into four regions, R1, R2, R3, and R4, based on the intensity of the laser beam LB. The processing unit 10 then depicts the inner circle 14, the middle circle 16, and the outer circle 18 in the quadratured cross-sectional image of the laser beam LB. The processing unit 10 then calculates the offset between the center C1 of the inner circle 14 and the center C3 of the outer circle 18 or the center C2 of the middle circle 16.

[0046] After the processing step is performed, an inspection step is performed in which the image processed by the processing unit 10 is displayed on the display unit 12 , and the accuracy of the laser oscillator 22 of the laser processing device 20 is inspected using the image displayed on the display unit 12 .

[0047] During the inspection process, the offset between the center C1 of the inner ring 14 and the center C3 of the outer ring 18 or the center C2 of the middle ring 16 is displayed on the display unit 12 along with a cross-sectional image of the laser beam LB processed by the processing unit 10. By checking the image displayed on the display unit 12, it is determined whether the use of the laser oscillator 22 is permitted. The determination of whether the use of the laser oscillator 22 is permitted can be made as follows: if the offset is below a specified value (e.g., less than 5% of the diameter of the outer ring 18), the use of the laser oscillator 22 is permitted; if the offset exceeds the specified value, the use of the laser oscillator 22 is not permitted. If the use of the laser oscillator 22 is not permitted, in addition to replacing the laser oscillator 22, the frequency conversion unit, output amplifier, or wavelength conversion unit may be replaced, deleted, or added.

[0048] As described above, in this embodiment, the inner circle 14, the middle circle 16 and the outer circle 18 are displayed on the display unit 12 as the contour lines of the laser light LB, and the offset between the center C1 of the inner circle 14 and the center C3 of the outer circle 18 or the center C2 of the middle circle 16 is displayed on the display unit 12. Therefore, the contour lines of the Gaussian distribution of the laser light LB can be detected with high precision, and the accuracy of the laser oscillator 22 can be checked.

Claims

1. An inspection device for inspecting the accuracy of a laser oscillator that oscillates laser light, wherein: The inspection device has: a dimming plate for dimming the laser light immediately after it is emitted from the laser oscillator; a photographing unit, which uses a plurality of pixels to photograph the laser light dimmed by the light-dimming plate; a processing unit configured to process the image captured by the capturing unit; and a display unit that displays the image processed by the processing unit, The processing unit has at least two thresholds, an inner circle and an outer circle, for dividing the intensity of the laser light, and the display unit displays the inner circle and the outer circle. The processing unit has at least a middle circle threshold value between the inner circle threshold value and the outer circle threshold value. The processing unit calculates an offset between the center of the inner circle and the center of the outer circle or the center of the middle circle, and the display unit displays the offset.

2. An inspection method for a laser oscillator in a laser processing device, the inspection method being performed using the inspection device. The laser processing device comprises: a laser oscillator that oscillates laser light; a condenser that focuses the laser light; an optical system disposed between the laser oscillator and the condenser and guiding the laser light; and A chuck table holds a workpiece to be processed by the laser beam focused by the condenser. And the inspection device has: a dimming plate for dimming the laser light immediately after it is emitted from the laser oscillator; a photographing unit, which uses a plurality of pixels to photograph the laser light dimmed by the light-dimming plate; a processing unit configured to process the image captured by the capturing unit; and a display unit that displays the image processed by the processing unit, The processing unit has at least two thresholds, an inner circle and an outer circle, for dividing the intensity of the laser light, and the display unit displays the inner circle and the outer circle. The processing unit has at least a middle circle threshold value between the inner circle threshold value and the outer circle threshold value. The processing unit calculates the offset between the center of the inner circle and the center of the outer circle or the center of the middle circle, and the display unit displays the offset. in, The inspection method includes the following steps: a photographing unit positioning step of positioning the inspection device including the photographing unit and the dimming plate between the laser oscillator and the optical system of the laser processing device so that the laser light is directly transmitted from the laser oscillator to the dimming plate without passing through a lens or other optical element that changes the cross section of the laser light, and then directly transmitting the laser light from the dimming plate to the photographing unit; a photographing step of photographing the laser beam immediately after being emitted from the laser oscillator using the photographing unit; a processing step, using a processing unit to process the image captured by the capturing unit; and In the inspection step, a display unit displays the image processed by the processing unit, and the accuracy of the laser oscillator is inspected through the image displayed by the display unit.

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