Optical element inspection method, inspection device, and laser machining device

Abstract

To provide an optical element inspection method which enables appropriate detection of deterioration of an optical element.SOLUTION: An optical element inspection method for inspecting an optical element is provided, the method comprising a laser beam irradiation step of irradiating an optical element with a laser beam, a wavefront data acquisition step of acquiring wavefront data corresponding to a wavefront of the laser beam transmitted through or reflected by the optical element, and a determination step of determining the state of deterioration of the optical element based on the wavefront data.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical element inspection method and inspection device for inspecting an optical element, and a laser processing device for irradiating a workpiece with a laser beam. [Background technology]

[0002] In the device chip manufacturing process, a wafer is used in which devices are formed in multiple areas partitioned by multiple streets (planned division lines) arranged in a grid pattern. The wafer is divided along the streets to produce individual pieces, thereby manufacturing device chips equipped with devices. The device chips are incorporated into various electronic devices such as mobile phones and personal computers.

[0003] A cutting device that cuts the workpiece with an annular cutting blade is used to divide the wafer. In recent years, development has also been underway to divide the wafer by laser processing using a laser processing device. The laser processing device is equipped with a chuck table that holds the wafer and a laser beam irradiation unit that irradiates the wafer with a laser beam. The laser beam irradiation unit has a built-in optical system that is composed of various optical elements (mirrors, focusing lenses, etc.) and directs the laser beam to the workpiece.

[0004] For example, Patent Document 1 discloses a method of forming a modified layer along the streets inside the wafer by focusing a laser beam that is transparent to the wafer. The region of the wafer where the modified layer is formed becomes more fragile than other regions. Therefore, when an external force is applied to a wafer on which a modified layer is formed along the streets, the wafer breaks along the streets and is divided into multiple device chips.

[0005] Patent Document 2 also discloses a method of partially removing a low dielectric constant insulating film (Low-k film) formed on a wafer by irradiating it with a laser beam before cutting the wafer with a cutting blade. If the low dielectric constant insulating film is removed along the streets, it is possible to prevent the cutting blade rotating at high speed from coming into contact with the low dielectric constant insulating film when the cutting blade is subsequently cut into the wafer, and peeling of the low dielectric constant insulating film is prevented.

[0006] When performing the above-mentioned laser processing on a wafer, a high-power laser beam is often used. Therefore, if the optical system installed in the laser beam irradiation unit is used continuously for a long period of time, the optical elements included in the optical system may be deteriorated by irradiation with the laser beam. If wafer processing is continued in a state where the optical elements are deteriorated, the laser beam may not be irradiated on the wafer under the desired conditions, which may result in processing defects.

[0007] In view of this, a laser processing device has been proposed that is equipped with a function for monitoring the deterioration state of an optical element built into a laser beam irradiation unit. For example, Patent Document 3 discloses a laser processing device that determines whether or not damage has occurred to an optical element based on the output of a laser beam. In this way, by monitoring the state of the optical element, it becomes possible to quickly discover deterioration of the optical element and take measures to avoid the occurrence of processing defects. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2002-192370 A [Patent Document 2] JP 2003-320466 A [Patent Document 3] JP 2021-30283 A Summary of the Invention [Problem to be solved by the invention]

[0009] Inspection of optical elements mounted on laser processing equipment involves the use of a method for observing the appearance of the optical element with an optical microscope, a method for detecting damage to the optical element based on the output of the laser beam as described above, and the like. However, minute deterioration of the optical element, such as partial peeling of a thin film (such as a dielectric multilayer film functioning as an anti-reflection film) formed on the optical element or adhesion of foreign matter to the optical element, is often not fully reflected in the appearance of the optical element or the output of the laser beam. In this case, the deterioration of the optical element cannot be found even if the optical element is inspected, and laser processing using the optical element in a deteriorated state may continue, leading to the risk of processing defects being unavoidable.

[0010] The present invention has been made in view of the above problems, and has an object to provide an optical element inspection method, inspection device, and laser processing device that are capable of accurately detecting deterioration of optical elements. [Means for solving the problem]

[0011] According to one aspect of the present invention, there is provided an optical element inspection method for inspecting an optical element, the method comprising: a laser beam irradiation step of irradiating a laser beam onto the optical element; a wavefront data acquisition step of acquiring wavefront data corresponding to the wavefront of the laser beam that has passed through or been reflected by the optical element; and a determination step of determining a state of deterioration of the optical element based on the wavefront data.

[0012] Preferably, the optical element inspection method further comprises a reference wavefront data acquisition step of acquiring reference wavefront data corresponding to the wavefront of the laser beam not passing through the optical element, and the determination step of determining a deterioration state of the optical element based on a result of comparing the wavefront data with the reference wavefront data. Also, preferably, the determination step of identifying a deteriorated region of the optical element based on the wavefront data.

[0013] According to another aspect of the present invention, there is provided an inspection apparatus for inspecting an optical element, the inspection apparatus comprising: a laser beam irradiation unit that irradiates a laser beam onto the optical element; a wavefront data acquisition unit that acquires wavefront data corresponding to the wavefront of the laser beam that has passed through or been reflected by the optical element; and a judgment unit that judges a state of deterioration of the optical element based on the wavefront data.

[0014] Furthermore, according to another aspect of the present invention, there is provided a laser processing apparatus that irradiates a laser beam onto a workpiece, the laser processing apparatus comprising: a laser oscillator; an optical system having an optical element that guides the laser beam emitted from the laser oscillator to the workpiece; a wavefront data acquisition unit that acquires wavefront data corresponding to the wavefront of the laser beam that has passed through or been reflected by the optical element; and a judgment unit that judges the state of deterioration of the optical element based on the wavefront data. Effect of the Invention

[0015] In the optical element inspection method, inspection device, and laser processing device according to one aspect of the present invention, the deterioration state of the optical element is determined based on wavefront data of a laser beam transmitted through or reflected by the optical element, thereby making it possible to accurately detect the deterioration of the optical element. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram showing an inspection device. [Diagram 2] Figure 2(A) is a schematic diagram showing a laser beam irradiation unit that irradiates a laser beam onto a transmissive optical element, Figure 2(B) is a schematic diagram showing a laser beam irradiation unit that irradiates a laser beam onto a lens, and Figure 2(C) is a schematic diagram showing a laser beam irradiation unit that irradiates a laser beam onto a reflective optical element. [Diagram 3] 1 is a flowchart showing a method for inspecting an optical element. [Figure 4]FIG. 4(A) is an image showing the phase distribution of the wavefront of a laser beam, and FIG. 4(B) is an image showing the intensity distribution of the laser beam. [Diagram 5] FIG. 2 is a block diagram showing a determination unit. [Figure 6] FIG. 6(A) is an image showing the phase distribution of the wavefront of a laser beam that does not pass through an optical element, and FIG. 6(B) is an image showing the differential phase distribution. [Figure 7] FIG. 2 is a perspective view showing a laser processing device. [Figure 8] FIG. 2 is a schematic diagram showing a laser beam irradiation unit. [Figure 9] FIG. 2 is a schematic diagram showing a laser beam irradiation unit when acquiring wavefront data. [Figure 10] FIG. 4 is a schematic diagram showing a laser beam irradiation unit when acquiring reference wavefront data. [Figure 11] FIG. 13 is a schematic diagram showing a laser beam irradiation unit according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] (Embodiment 1) Hereinafter, an embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. First, a configuration example of an inspection device according to this embodiment will be described. FIG. 1 is a schematic diagram showing an inspection device 2 that inspects an optical element 4. The inspection device 2 inspects the optical element 4 by determining a deterioration state of the optical element 4. In other words, the optical element 4 corresponds to a test element that is an object to be inspected by the inspection device 2.

[0018] For example, the optical element 4 is composed of a single element or multiple elements, and is incorporated into an optical system for guiding a laser beam for laser processing to a workpiece. The irradiation conditions (travel direction, shape, focal point, output, etc.) of the laser beam for laser processing are adjusted by the optical element 4. For example, the optical element 4 is used as a component of an optical system mounted on a laser processing device 40 (see FIG. 7) described later.

[0019] Specifically, the optical element 4 corresponds to an optical component such as a lens, a mirror, a filter, a prism, an optical window, etc. In addition, the optical element 4 may be a polarizer such as a wave plate, a polarizing beam splitter (PBS), a diffractive optical element (DOE), or an LCOS-SLM (Liquid Crystal On Silicon - Spatial Light Modulator), or may be an optical component such as an optical attenuator or a beam expander.

[0020] The inspection device 2 includes a laser beam irradiation unit 8 that irradiates a laser beam 6. The laser beam 6 is irradiated from the laser beam irradiation unit 8 to the optical element 4, and the laser beam 6 passes through or is reflected by the optical element 4.

[0021] The inspection device 2 also includes a wavefront data acquisition unit 10 that acquires wavefront data corresponding to the wavefront of the laser beam 6. The wavefront data acquisition unit 10 is provided with a light receiving surface 10a that receives the laser beam 6. The wavefront data acquisition unit 10 detects the wavefront of the laser beam 6 based on the laser beam 6 received by the light receiving surface 10a, and generates wavefront data corresponding to the wavefront of the laser beam 6.

[0022] As the wavefront data acquisition unit 10, for example, a Shack-Hartmann wavefront sensor is used. In this case, the wavefront data acquisition unit 10 includes a microlens array and an imaging element such as a CCD (Charged-Coupled Devices) sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) sensor. When the laser beam 6 is irradiated onto the imaging element via the microlens array, a plurality of focused spots (Hartmann spots) are formed on the imaging surface (light receiving surface 10a) of the imaging element. Then, the wavefront data acquisition unit 10 identifies the wavefront of the laser beam 6 based on the position (displacement) of each focused spot, and generates and outputs a phase distribution (wavefront map) of the wavefront of the laser beam 6 as wavefront data.

[0023] However, there is no limitation on the type of the wavefront data acquisition unit 10. For example, a shearing interferometer, a wavefront curvature sensor, a pyramid wavefront sensor, or the like can be used as the wavefront data acquisition unit 10. In addition, the type of wavefront data acquired by the wavefront data acquisition unit 10 is also not limited as long as the shape of the wavefront of the laser beam 6 can be specified.

[0024] Note that the wavefront data acquisition unit 10 may acquire intensity data corresponding to the intensity of the laser beam 6, in addition to the wavefront data of the laser beam 6. For example, when a Shack-Hartmann wavefront sensor is used as the wavefront data acquisition unit 10, the intensity of the laser beam 6 at each focused spot is calculated, and the calculated intensity is mapped on the light receiving surface 10a to measure the intensity of the laser beam 6, thereby generating and outputting an intensity distribution (intensity map) of the laser beam 6 as intensity data. In this case, both the wavefront data and the intensity data can be acquired by one wavefront data acquisition unit 10.

[0025] 1, when the optical element 4 is a transmission type optical element that transmits the laser beam 6, the wavefront data acquisition unit 10 acquires wavefront data of the laser beam 6 that has passed through the optical element 4. On the other hand, when the optical element 4 is a reflection type optical element that reflects the laser beam 6, the wavefront data acquisition unit 10 acquires wavefront data of the laser beam 6 reflected by the optical element 4. In this case, the light receiving surface 10a of the wavefront data acquisition unit 10 is disposed on the optical path of the reflected light of the laser beam 6 irradiated to the optical element 4.

[0026] Furthermore, the inspection device 2 includes a judgment unit 12 that judges the deterioration state of the optical element 4 based on the wavefront data. The judgment unit 12 is configured by, for example, a computer, and includes a processor such as a CPU (Central Processing Unit) and memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory).

[0027] The inspection device 2 may include a controller (control unit, control unit, control device) that controls the inspection device 2. The controller controls the operation of each component (laser beam irradiation unit 8, wavefront data acquisition unit 10, etc.) that constitutes the inspection device 2 by outputting a control signal to the component. In this case, the controller may also function as the judgment unit 12, or the controller and the judgment unit 12 may be separately and independently mounted.

[0028] When the optical element 4 deteriorates, a change (distortion) occurs in the wavefront of the laser beam 6 irradiated to the optical element 4, and the change is reflected in the wavefront data. Therefore, the wavefront data acquired by the wavefront data acquisition unit 10 differs depending on whether the optical element 4 has deteriorated or not.

[0029] For example, when the optical element 4 has a thin film such as a dielectric multilayer film that functions as an anti-reflection film, the irradiation of the laser beam for laser processing may cause the thin film to partially peel off (float) or deteriorate, such as being damaged. In addition, the substrate (glass material, etc.) of the optical element 4 may be partially damaged together with the thin film by the irradiation of the laser beam. Furthermore, foreign matter such as impurities contained in the air may adhere to the optical element 4, and the impurities adhered to the optical element 4 may be burned by the laser beam for laser processing, causing the foreign matter to adhere to the optical element 4.

[0030] The above-mentioned deterioration of the optical element 4 often does not affect the appearance of the optical element 4 or the output of the laser beam 6, but is likely to be reflected in the wavefront of the laser beam 6. Therefore, the judgment unit 12 judges the state of deterioration of the optical element 4 based on the wavefront data acquired by the wavefront data acquisition unit 10. This makes it possible to accurately detect deterioration of the optical element 4 that is difficult to detect by conventional methods. A specific example of the judgment process by the judgment unit 12 will be described later (see FIG. 5).

[0031] The specific configuration of the laser beam irradiation unit 8 is appropriately set depending on the type of optical element 4. Figures 2(A) to 2(C) show laser beam irradiation units 8 (laser beam irradiation units 8A, 8B, and 8C) that irradiate laser beams 6 to three different types of optical elements 4 (optical elements 4A, 4B, and 4C).

[0032] 2(A) is a schematic diagram showing a laser beam irradiation unit 8A that irradiates an optical element 4A with a laser beam 6. The optical element 4A is a transmissive planar optical element that transmits the laser beam 6, and includes an irradiated surface 4a onto which the laser beam 6 is irradiated and an exit surface 4b from which the laser beam 6 exits. Examples of the transmissive optical element 4A include a filter, an optical window, a beam splitter, and a polarizer.

[0033] The laser beam irradiation unit 8A includes a laser oscillator 20 such as a YAG laser, a YVO4 laser, a YLF laser, or the like, and an optical system 22A that guides the laser beam 6 emitted from the laser oscillator 20 to the wavefront data acquisition unit 10 via the optical element 4A. For example, the optical system 22A includes an optical attenuator 24 that attenuates the laser beam 6 emitted from the laser oscillator 20, an expansion optical system 26 that expands the laser beam 6 emitted from the optical attenuator 24, and a reduction optical system 28 that reduces the laser beam 6 emitted from the expansion optical system 26 and transmitted through the optical element 4A.

[0034] The optical attenuator 24 is an optical element that attenuates the laser beam 6 so as to make it suitable for detection of the wavefront of the laser beam 6 by the wavefront data acquisition unit 10. For example, the optical attenuator 24 includes optical elements such as an optical filter and a wedge substrate.

[0035] The expansion optical system 26 is an optical element that expands the diameter of the laser beam 6 so that the laser beam 6 is incident on the optical element 4 with a predetermined diameter. On the other hand, the reduction optical system 28 is an optical element that reduces the diameter of the laser beam 6 so that the laser beam 6 emitted from the optical element 4 is irradiated on the light receiving surface 10a of the wavefront data acquisition unit 10 with a predetermined diameter. For example, the expansion optical system 26 and the reduction optical system 28 are configured by a pair of beam expanders arranged in opposite directions to each other.

[0036] When inspecting a transmission type optical element 4A, the laser oscillator 20, the optical attenuator 24, and the magnifying optical system 26 are arranged on the irradiated surface 4a side of the optical element 4A, and the reduction optical system 28 and the wavefront data acquisition unit 10 are arranged on the exit surface 4b side of the optical element 4A. The laser beam 6 emitted from the laser oscillator 20 is attenuated by the optical attenuator 24 and magnified by the magnifying optical system 26, and then irradiated onto the irradiated surface 4a side of the optical element 4A. The laser beam 6 irradiated onto the optical element 4A passes through the optical element 4A, exits from the exit surface 4b, and reaches the light receiving surface 10a of the wavefront data acquisition unit 10 after being reduced by the reduction optical system 28.

[0037] 2(B) is a schematic diagram showing a laser beam irradiation unit 8B that irradiates the laser beam 6 onto the optical element 4B. The optical element 4B is a lens (condenser lens) that can condense the laser beam 6, and is a type of transmissive optical element. For example, the optical element 4B is a convex lens, and is mounted on a condenser that condenses the laser beam for laser processing in a laser processing device 40 (see FIG. 7) described later.

[0038] The laser beam irradiation unit 8B includes a laser oscillator 20 and an optical system 22B that guides the laser beam 6 emitted from the laser oscillator 20 to the wavefront data acquisition unit 10 via an optical element 4B. Similarly to the optical system 22A (see FIG. 2(A)), the optical system 22B includes an optical attenuator 24 and a magnifying optical system 26.

[0039] The optical element 4B has a function of focusing the laser beam 6. Therefore, when inspecting the optical element 4B, the diameter of the laser beam 6 on the light receiving surface 10a can be adjusted by adjusting the position of the light receiving surface 10a of the wavefront data acquisition unit 10 according to the focusing position of the laser beam 6, without using the reduction optical system 28 (see FIG. 2(A)).

[0040] 2(C) is a schematic diagram showing a laser beam irradiation unit 8C that irradiates the laser beam 6 to the optical element 4C. The optical element 4C is a reflective optical element that reflects the laser beam 6, and has a reflective surface 4c that reflects the laser beam 6. Examples of the reflective optical element 4C include a mirror, a prism, and a polarizing beam splitter.

[0041] The laser beam irradiation unit 8C includes a laser oscillator 20 and an optical system 22C that guides the laser beam 6 emitted from the laser oscillator 20 to the wavefront data acquisition unit 10 via an optical element 4C. Similarly to the optical system 22A (see FIG. 2(A)), the optical system 22C includes an optical attenuator 24, a magnifying optical system 26, and a reducing optical system 28.

[0042] When inspecting a reflective optical element 4C, the laser oscillator 20, the optical attenuator 24, the magnifying optical system 26, the reducing optical system 28, and the wavefront data acquisition unit 10 are arranged on the reflecting surface 4c side of the optical element 4C. The laser beam 6 emitted from the laser oscillator 20 is attenuated by the optical attenuator 24 and expanded by the expanding optical system 26, and then irradiated onto the optical element 4C. The laser beam 6 irradiated onto the optical element 4C is reflected by the reflecting surface 4c, reduced by the reducing optical system 28, and then reaches the light receiving surface 10a of the wavefront data acquisition unit 10.

[0043] As described above, the laser beam irradiation unit 8 is configured according to the type of the optical element 4. Then, wavefront data indicating the wavefront of the laser beam 6 transmitted through or reflected by the optical element 4 is acquired by the wavefront data acquisition unit 10, and the optical element 4 is inspected based on the wavefront data.

[0044] Next, a specific example of an optical element inspection method for inspecting the optical element 4 using the inspection apparatus 2 will be described. Fig. 3 is a flowchart showing the optical element inspection method.

[0045] When inspecting the optical element 4, first, a laser beam 6 is irradiated onto the optical element 4 (laser beam irradiation step S1). In the laser beam irradiation step S1, the laser beam 6 is irradiated onto the optical element 4 from a laser beam irradiation unit 8 (see FIG. 1). As a result, the laser beam 6 that has passed through or been reflected by the optical element 4 is irradiated onto the light receiving surface 10a of the wavefront data acquisition unit 10.

[0046] Next, wavefront data corresponding to the wavefront of the laser beam 6 transmitted through or reflected by the optical element 4 is acquired (wavefront data acquisition step S2). In the wavefront data acquisition step S2, the wavefront data acquisition unit 10 is operated in a state in which the laser beam 6 is irradiated onto the light receiving surface 10a of the wavefront data acquisition unit 10. As a result, the wavefront data acquisition unit 10 detects the wavefront of the laser beam 6 received by the light receiving surface 10a, and generates wavefront data of the laser beam 6.

[0047] In the following, as an example, a case will be described in which the optical element 4 to be inspected is a condenser lens (see FIG. 2(B)) and the wavefront data acquisition unit 10 is a Shack-Hartmann wavefront sensor. In this case, the wavefront data acquisition unit 10 can acquire the phase distribution of the wavefront of the laser beam 6 that has passed through the optical element 4 (condenser lens) as wavefront data.

[0048] 4(A) is an image diagram showing a phase distribution 30 of the wavefront of the laser beam 6. When the laser beam 6 transmitted through the optical element 4 reaches the light receiving surface 10a of the wavefront data acquisition unit 10, the wavefront data acquisition unit 10 identifies the shape of the wavefront of the laser beam 6 based on the position of the focused spot (Hartmann spot) and calculates a phase distribution 30 indicating the shape of the wavefront. This phase distribution 30 corresponds to the wavefront data of the laser beam 6.

[0049] The phase distribution 30 is a phase map that two-dimensionally represents the wavefront of the laser beam 6. The X-axis and Y-axis of the phase distribution 30 indicate the position (coordinate) of the wavefront of the laser beam 6 in a plane (a plane parallel to the light receiving surface 10a) perpendicular to the traveling direction of the laser beam 6. A value proportional to the height of the wavefront of the laser beam 6 at each position (coordinate) is mapped as the phase distribution 30.

[0050] Note that the specific values ​​to be mapped in the phase distribution 30 can be appropriately selected. For example, the wavefront height [nm] may be directly mapped, or the wavefront height may be divided by the wavelength [nm] of the laser beam 6 to convert it into a dimensionless quantity and then mapped. Furthermore, the value converted into the dimensionless quantity may be multiplied by 2π to convert it into a phase value [rad] and then mapped. FIG. 4(A) shows, as an example, a phase distribution 30 in which the value obtained by dividing the wavefront height of the laser beam 6 by the wavelength of the laser beam 6 is displayed in shading. When the wavefront of the laser beam 6 is a plane that is approximately parallel to the light receiving surface 10a, the phase distribution 30 is displayed in approximately the same gradation.

[0051] Here, when the optical element 4 deteriorates, a change appears in the phase distribution 30. For example, when partial peeling (floating) occurs in a thin film (such as a dielectric multilayer film functioning as an anti-reflection film) on the surface of the optical element 4, the wavefront is locally deformed in region A on the phase distribution 30 corresponding to the region where deterioration of the optical element 4 has occurred, and the height of the wavefront fluctuates. Therefore, by checking the phase distribution 30, it is possible to determine whether the optical element 4 has deteriorated and to identify the region where the deterioration of the optical element 4 has occurred.

[0052] 4(B) is an image diagram showing the intensity distribution 32 of the laser beam 6. As described above, the wavefront data acquisition unit 10 may acquire intensity data corresponding to the intensity of the laser beam 6, in addition to the wavefront data of the laser beam 6. For example, the wavefront data acquisition unit 10 also functions as a beam profiler, and calculates the intensity distribution 32 of the laser beam 6 by measuring the power density of the laser beam 6 on the light receiving surface 10a. This intensity distribution 32 corresponds to the intensity data of the laser beam 6.

[0053] The intensity distribution 32 is an intensity map that two-dimensionally represents the intensity of the laser beam 6. The X-axis and Y-axis of the intensity distribution 32 represent the position (coordinates) of the laser beam 6 on a plane (a plane parallel to the light-receiving surface 10a) perpendicular to the traveling direction of the laser beam 6. The normalized intensity (power density) of the laser beam 6 on the light-receiving surface 10a is represented by shading in the intensity distribution 32.

[0054] When the optical element 4 deteriorates, a change also appears in the intensity distribution 32. For example, the intensity of the laser beam 6 changes locally in an area B on the intensity distribution 32 corresponding to an area where deterioration has occurred in the optical element 4. Therefore, depending on the type and degree of deterioration of the optical element 4, it is possible to determine whether or not the optical element 4 has deteriorated based on the intensity distribution 32, and to identify the area where deterioration has occurred in the optical element 4.

[0055] However, when the deterioration of the optical element 4 is due to partial peeling of a thin film or the like, region A (see FIG. 4(A)) shown in phase distribution 30 is wider than region B (see FIG. 4(B)) shown in intensity distribution 32. That is, even minute changes in the optical element 4 that do not appear in intensity distribution 32 are reflected in phase distribution 30. Therefore, by using phase distribution 30, it is possible to more accurately grasp the presence or absence and the extent of deterioration of the optical element 4.

[0056] In the above, a case has been described in which the phase distribution 30 and the intensity distribution 32 of the laser beam 6 are acquired by the wavefront data acquisition unit 10. However, if the intensity distribution 32 is not used in a later step, acquisition of the intensity distribution 32 may be omitted. In addition, in the above, an example has been described in which the phase distribution 30 is acquired as the wavefront data of the laser beam 6, but the type of wavefront data is not limited as long as the state of the wavefront of the laser beam 6 is reflected.

[0057] Next, the deterioration state of the optical element 4 is judged based on the wavefront data of the laser beam 6 (judgment step S3). When the wavefront data is acquired by the wavefront data acquisition unit 10, the wavefront data is output from the wavefront data acquisition unit 10 to the judgment unit 12 (see FIG. 1), and the judgment unit 12 judges the deterioration state of the optical element 4 based on the wavefront data.

[0058] 5 is a block diagram showing the functional configuration of the judgment unit 12. As described above, the judgment unit 12 is configured by a computer or the like, and includes an inspection unit 14 that executes inspection of the optical element 4, and a storage unit 16 that stores various information (data, programs, etc.) used in the inspection of the optical element 4.

[0059] The inspection unit 14 includes a data processing unit 14a that performs data processing on the wavefront data. When the phase distribution 30 (see FIG. 4(A)) is acquired by the wavefront data acquisition unit 10, the phase distribution 30 is input to the data processing unit 14a as wavefront data 34. Then, the data processing unit 14a performs a predetermined data processing on the wavefront data 34 to extract information required for determining the deterioration state of the optical element 4 from the wavefront data 34.

[0060] For example, when the wavefront data 34 is a phase distribution 30, a reference value (threshold value) that determines an allowable range of the wavefront height (shading in FIG. 4A) of the laser beam 6 is set in advance and stored in the storage unit 16. Then, the data processing unit 14a compares the wavefront height (value corresponding to shading) shown in the phase distribution 30 with the reference value to identify an area A (see FIG. 4A) in which the wavefront height of the laser beam 6 is outside the allowable range. Specifically, an area in which the wavefront height exceeds a reference value (upper limit value) or an area in which the wavefront height is less than a reference value (lower limit value) is set as the area A. Then, information on the area A identified by the data processing unit 14a (presence or absence of the area A, size, etc.) is stored in the storage unit 16 together with the phase distribution 30.

[0061] The inspection unit 14 also includes a determination unit 14b that determines the deterioration state of the optical element 4. The information of the region A acquired by the data processing unit 14a is input to the determination unit 14b. Then, the determination unit 14b executes a determination process to determine the deterioration state of the optical element 4 based on the information of the region A.

[0062] For example, when the phase distribution 30 does not include the region A, the determination unit 14b determines that the optical element 4 is in a normal state without degradation, and outputs a signal (normal signal) indicating that to the outside. On the other hand, when the phase distribution 30 includes the region A, the determination unit 14b recognizes the region A as a degradation region corresponding to the degradation region of the optical element 4. This identifies the degradation region of the optical element 4. The determination unit 14b also determines that the optical element 4 is in a degradation state, and outputs a signal (degradation signal) indicating that to the outside.

[0063] As described above, the determination of the deterioration state of the optical element 4 and the identification of the deteriorated area are automatically executed by the data processing unit 14a. Note that the data processing unit 14a may output a signal indicating the degree of deterioration (deterioration level signal) according to the size of the area A, in addition to the normal signal or the deteriorated signal.

[0064] Furthermore, only when the size of region A is outside a predetermined allowable range, the determination unit 14b may recognize region A as a deteriorated region and determine that the optical element 4 is deteriorated. In this case, a reference value (threshold value) that determines the allowable range of the size of region A is set in advance and stored in the storage unit 16. Then, the determination unit 14b determines whether region A is a deteriorated region by comparing the size of region A with the reference value.

[0065] For example, the upper limit of the size of the region A can be set to a value corresponding to the size of the region of the optical element 4 that is irradiated with the laser beam 6 (beam diameter of the laser beam 6 irradiated to the optical element 4). This makes it possible to avoid the inherent aberration characteristics of the optical element 4 being erroneously recognized as deterioration of the optical element 4.

[0066] Furthermore, the lower limit of the size of region A can be set to a value equivalent to the minimum spot diameter based on the diffraction limit of laser beam 6. This minimum spot diameter corresponds to the theoretical minimum value of the size of the region of optical element 4 irradiated with laser beam 6. This makes it possible to prevent measurement noise of the wavefront, etc. from being erroneously recognized as deterioration of optical element 4.

[0067] As described above, in the determination step S3, the deterioration state of the optical element 4 is determined based on the presence or absence (and the size) of the region A in the phase distribution 30. However, the contents of the data processing by the data processing unit 14a and the determination processing by the determination unit 14b may be changed as appropriate within the range in which the deterioration state of the optical element 4 can be determined.

[0068] For example, after identifying region A, data processing unit 14a may calculate the gradient (amount of change) of the wavefront height in region A and output it to determination unit 14b. In this case, a reference value (upper limit value) that determines an allowable range of the gradient of the wavefront height is set in advance and stored in storage unit 16.

[0069] Then, the determination unit 14b compares the maximum value of the gradient of the wavefront height in the region A with a reference value. As a result, if the maximum value of the gradient is equal to or less than the reference value, the determination unit 14b determines that the optical element 4 is not deteriorated and is in a normal state, and outputs a normal signal. On the other hand, if the maximum value of the gradient exceeds the reference value, the determination unit 14b recognizes the region A as a deteriorated region, determines that the optical element 4 is deteriorated, and outputs a deterioration signal.

[0070] In this way, by calculating the gradient of the wavefront height of the laser beam 6, it becomes possible to determine that the optical element 4 is degraded only when the wavefront height changes suddenly in the region A. This makes it possible to avoid erroneously determining that the optical element 4 is degraded when, for example, the entire wavefront of the laser beam 6 is formed into a gently curved shape due to the characteristics of the optical element 4.

[0071] Furthermore, the intensity data may be used in addition to the wavefront data to determine the deterioration state of the optical element 4. For example, a phase distribution 30 (see FIG. 4(A)) and an intensity distribution 32 (see FIG. 4(B)) are acquired by the wavefront data acquisition unit 10, and the phase distribution 30 and the intensity distribution 32 are input as wavefront data and intensity data, respectively, to the data processing unit 14a. In this case, the data processing unit 14a identifies the region A (see FIG. 4(A)) based on the wavefront data 34, and identifies the intensity of the laser beam 6 in the region A based on the intensity distribution 32.

[0072] Then, when region A includes a region where the intensity of the laser beam 6 is outside a predetermined allowable range, the judgment unit 14b recognizes region A as a deteriorated region. For example, region A is recognized as a deteriorated region only when region A includes a region where the intensity of the laser beam 6 is locally low. This makes it possible to detect damage to the optical element 4 that prevents part of the laser beam 6 from reaching the light receiving surface 10a (see FIG. 1, etc.).

[0073] There is also no limitation on the method of identifying region A by the data processing unit 14a. For example, the data processing unit 14a performs edge detection processing on the phase distribution 30 (see FIG. 4(A)) using a first-order differential filter or a second-order differential filter to detect a region (edge) in the phase distribution 30 where the amount of phase change exceeds a predetermined reference value. Then, the data processing unit 14a determines that the extracted edge is the contour of region A, and recognizes the inside of the edge as region A. Note that the detection of the edge may be performed based on the amount of phase change between adjacent pixels, or based on the amount of phase change between pixels at a predetermined pitch.

[0074] Furthermore, the wavefront data may also reflect manufacturing errors of the optical element 4 and the laser beam irradiation unit 8, wavefront measurement errors caused by floor noise output by the image pickup element constituting the wavefront data acquisition unit 10, and the like, in addition to the shape of the wavefront caused by deterioration of the optical element 4. Therefore, in order to determine the deterioration state of the optical element 4 with high accuracy, it is desirable to remove these errors from the acquired wavefront data.

[0075] Therefore, the deterioration state of the optical element 4 may be determined after applying a spatial filter to the wavefront data. For example, a wavefront reflecting manufacturing errors of the optical element 4 or the laser beam irradiation unit 8 often exhibits a low spatial frequency. Therefore, a spatial filter that removes low frequency components is effective for removing the influence of the above-mentioned manufacturing errors from the wavefront data. On the other hand, a wavefront measurement error caused by floor noise output by the imaging element exhibits a high spatial frequency. Therefore, a spatial filter that removes high frequency components is effective for removing the influence of the above-mentioned floor noise from the wavefront data.

[0076] There is no limitation on the specific method of applying a spatial filter to wavefront data. For example, the acquired wavefront data may be decomposed using Zernike polynomials, and low-order components may be removed as low-frequency components, and high-order components may be removed as high-frequency components. In addition, when removing high-frequency components, a spatial moving average may be calculated.

[0077] As described above, in the inspection device 2 and the optical element inspection method according to this embodiment, the deterioration state of the optical element 4 is determined based on the wavefront data of the laser beam 6 transmitted through or reflected by the optical element 4. This makes it possible to accurately detect deterioration of the optical element 4 that is difficult to detect by conventional methods.

[0078] In this embodiment, the case has been described where the optical element 4 is inspected solely using the wavefront data of the laser beam 6 that has passed through or been reflected by the optical element 4. However, the deterioration state of the optical element 4 can also be determined based on the above wavefront data and wavefront data (reference wavefront data) corresponding to the wavefront of the laser beam 6 that has not passed through the optical element 4.

[0079] Specifically, first, at any timing before the execution of the determination step S3, reference wavefront data corresponding to the wavefront of the laser beam 6 that has not passed through the optical element 4 is acquired (reference wavefront data acquisition step). For example, in the reference wavefront data acquisition step, the optical element 4 is temporarily removed from the optical path of the laser beam 6 in the inspection device 2 (see FIG. 1), and the laser beam 6 is irradiated onto the light receiving surface 10a of the wavefront data acquisition unit 10 without passing through the optical element 4. By operating the wavefront data acquisition unit 10 in this state, wavefront data (reference wavefront data) of the laser beam 6 that has not passed through the optical element 4 is acquired.

[0080] 6(A) is an image diagram showing a phase distribution 36 of the wavefront of the laser beam 6 that has not passed through the optical element 4. For example, as reference wavefront data, the phase distribution 36 of the wavefront of the laser beam 6 that has not passed through the optical element 4 is acquired. Note that the characteristics of the optical element 4 are not reflected in the phase distribution 36.

[0081] Then, in a determination step S3 (see FIG. 5), based on a result of comparing the wavefront data with the reference wavefront data, the deterioration state of the optical element 4 is determined. For example, the data processing unit 14a (see FIG. 5) obtains a differential phase distribution equivalent to the difference between the phase distribution 30 and the phase distribution 36 by subtracting the phase distribution 36 (see FIG. 6(A)) from the phase distribution 30 (see FIG. 4(A)).

[0082] 6(B) is an image diagram showing the differential phase distribution 38. In the differential phase distribution 38, the influence of the characteristics of optical elements other than the optical element 4 is excluded, and only the characteristics of the optical element 4 are reflected. Then, when the differential phase distribution 38 is acquired, the above-mentioned data processing and determination processing are executed on the differential phase distribution 38. This makes it possible to determine the state of deterioration of the optical element 4 based on the wavefront data reflecting only the characteristics of the optical element 4, improving the determination accuracy.

[0083] In the judgment step S3, instead of generating the differential phase distribution 38, the wavefront data (phase distribution 30) and the reference wavefront data (phase distribution 36) may be subjected to data processing by the data processing unit 14a (see FIG. 5). In this case, deteriorated regions are extracted from the wavefront data and the reference wavefront data. Then, a deteriorated region that exists in the wavefront data but does not exist in the reference wavefront data is recognized as a deteriorated region that is to be subjected to judgment processing by the judgment unit 14b (see FIG. 5).

[0084] In addition, the structure, method, and the like according to the present embodiment can be appropriately modified and implemented without departing from the scope of the object of the present invention. In addition, the present embodiment can be appropriately combined with other embodiments.

[0085] (Embodiment 2) In this embodiment, an example of the configuration of a laser processing apparatus capable of carrying out the optical element inspection method described in embodiment 1 will be described. That is, this embodiment relates to a laser processing apparatus equipped with an inspection device 2 (see FIG. 1).

[0086] Fig. 7 is a perspective view showing the laser processing device 40. In Fig. 7, the X-axis direction (processing feed direction, first horizontal direction, left-right direction) and the Y-axis direction (indexing feed direction, second horizontal direction, front-back direction) are perpendicular to each other. Also, the Z-axis direction (up-down direction, height direction, vertical direction) is perpendicular to the X-axis direction and the Y-axis direction.

[0087] The laser processing apparatus 40 performs laser processing on a workpiece 11. For example, the workpiece 11 is a disk-shaped wafer made of a semiconductor material such as single crystal silicon, and has a front surface (first surface) and a back surface (second surface) that are generally parallel to each other.

[0088] The workpiece 11 is divided into a plurality of rectangular regions by a plurality of streets (planned division lines) arranged in a lattice pattern so as to intersect with one another. Devices such as ICs (Integrated Circuits), LSIs (Large Scale Integrations), LEDs (Light Emitting Diodes), and MEMS (Micro Electro Mechanical Systems) devices are formed in each of the plurality of regions divided by the streets on the front side of the workpiece 11. By dividing the workpiece 11 along the streets, a plurality of chips (device chips) each including a device are manufactured.

[0089] However, there are no limitations on the type, material, shape, structure, size, etc. of the workpiece 11. For example, the workpiece 11 may be a substrate (wafer) made of a semiconductor other than silicon (GaAs, InP, GaN, SiC, etc.), sapphire, glass, ceramics, resin, metal, etc. In addition, there are no limitations on the type, number, shape, structure, size, arrangement, etc. of devices, and the workpiece 11 does not necessarily have to have devices formed thereon.

[0090] When processing the workpiece 11 with the laser processing device 40, the workpiece 11 is supported by an annular frame 13 for ease of handling (transporting, holding, etc.) the workpiece 11. The frame 13 is made of a metal such as SUS (stainless steel), and a circular opening is provided in the center of the frame 13, penetrating the frame 13 in the thickness direction. The diameter of the opening in the frame 13 is larger than the diameter of the workpiece 11.

[0091] A circular sheet 15 is fixed to the workpiece 11 and the frame 13. For example, a tape including a film-like substrate formed into a circular shape and an adhesive layer (glue layer) provided on the substrate is used as the sheet 15. The sheet 15 may also be a thermocompression sheet that does not include an adhesive layer and can be thermocompression bonded to the workpiece 11 and the frame 13.

[0092] With the workpiece 11 placed inside the opening of the frame 13, the center of the sheet 15 is attached to the workpiece 11, and the outer periphery of the sheet 15 is attached to the frame 13. In this way, the workpiece 11 is supported by the frame 13 via the sheet 15.

[0093] The laser processing apparatus 40 includes a base 42 that supports each of the components that make up the laser processing apparatus 40. The upper surface of the base 42 is a flat surface that is roughly parallel to the horizontal plane (XY plane), and a moving unit (moving mechanism) 44 is provided on the upper surface of the base 42. The moving unit 44 includes a Y-axis moving unit (Y-axis moving mechanism) 46 and an X-axis moving unit (X-axis moving mechanism) 56.

[0094] The Y-axis movement unit 46 includes a pair of Y-axis guide rails 48 disposed along the Y-axis direction on the upper surface of the base 42. A flat Y-axis movement table 50 is mounted on the pair of Y-axis guide rails 48 so as to be slidable along the Y-axis guide rails 48.

[0095] A nut portion (not shown) is provided on the back surface (lower surface) side of the Y-axis moving table 50. A Y-axis ball screw 52 disposed along the Y-axis direction between a pair of Y-axis guide rails 48 is screwed into this nut portion. In addition, a Y-axis pulse motor 54 is connected to an end of the Y-axis ball screw 52. When the Y-axis pulse motor 54 rotates the Y-axis ball screw 52, ​​the Y-axis moving table 50 moves in the Y-axis direction along the Y-axis guide rails 48.

[0096] The X-axis movement unit 56 includes a pair of X-axis guide rails 58 arranged along the X-axis direction on the front (upper) surface side of the Y-axis movement table 50. A flat X-axis movement table 60 is mounted on the pair of X-axis guide rails 58 so as to be slidable along the X-axis guide rails 58.

[0097] A nut portion (not shown) is provided on the rear surface (lower surface) side of the X-axis moving table 60. An X-axis ball screw 62 arranged along the X-axis direction between a pair of X-axis guide rails 58 is screwed into this nut portion. An X-axis pulse motor 64 is connected to an end of the X-axis ball screw 62. When the X-axis pulse motor 64 rotates the X-axis ball screw 62, the X-axis moving table 60 moves in the X-axis direction along the X-axis guide rails 58.

[0098] A chuck table (holding table) 66 that holds the workpiece 11, and a wavefront data acquisition unit 70 are provided on the X-axis moving table 60. That is, the chuck table and the wavefront data acquisition unit 70 are connected to the moving unit 44.

[0099] The upper surface of the chuck table 66 is a flat surface roughly parallel to the horizontal plane (XY plane) and constitutes a holding surface 66a that holds the workpiece 11. The holding surface 66a is connected to a suction source (not shown) such as an ejector via a flow path (not shown), a valve (not shown), and the like formed inside the chuck table 66. In addition, a plurality of clamps 68 that grip and fix the frame 13 are provided around the periphery of the chuck table 66.

[0100] The wavefront data acquiring unit 70 corresponds to the wavefront data acquiring unit 10 (see FIG. 1) of the inspection device 2, and acquires wavefront data of a laser beam irradiated from a laser beam irradiating unit 76 described later. Details of the wavefront data acquiring unit 70 will be described later (see FIGS. 8 to 10).

[0101] When the Y-axis moving table 50 is moved along the Y-axis direction, the chuck table 66 and the wavefront data acquisition unit 70 move along the Y-axis direction. When the X-axis moving table 60 is moved along the X-axis direction, the chuck table 66 and the wavefront data acquisition unit 70 move along the X-axis direction. That is, the moving unit 44 functions as a moving mechanism that moves the wavefront data acquisition unit 70 along the X-axis direction and the Y-axis direction. Furthermore, the chuck table 66 is connected to a rotation drive source (not shown) such as a motor that rotates the chuck table 66 around a rotation axis approximately parallel to the Z-axis direction.

[0102] A rectangular parallelepiped support structure 72 is provided at the rear end of the base 42 (rear of the moving unit 44). The support structure 72 is formed so as to protrude upward from the upper surface of the base 42, and the surface (front surface) of the support structure 72 is disposed along the XZ plane. A columnar support member 74 protruding forward from the surface of the support structure 72 is connected to the support structure 72.

[0103] The laser processing apparatus 40 also includes a laser beam irradiation unit 76 that irradiates a laser beam onto the workpiece 11. The laser beam irradiation unit 76 includes a laser processing head 78 provided at the tip of the support member 74. The laser processing head 78 irradiates a laser beam onto the workpiece 11 held by the chuck table 66, whereby laser processing is performed on the workpiece 11.

[0104] Further, an imaging unit 80 is provided at the tip of the support member 74. The imaging unit 80 includes an imaging element such as a CCD sensor or a CMOS sensor, and captures an image of the workpiece 11 held by the chuck table 66. There is no limitation on the type of imaging unit 80, and a visible light camera or an infrared camera can be used. For example, the workpiece 11 and the laser processing head 78 are aligned based on an image acquired by imaging the workpiece 11 with the imaging unit 80.

[0105] The support member 74 may be connected to the support structure 72 via a Z-axis moving unit (not shown) that moves the support member 74 along the Z-axis direction. For example, a ball screw type moving mechanism is installed as the Z-axis moving unit on the front side of the support structure 72. In this case, by moving (raising and lowering) the support member 74 along the Z-axis direction with the Z-axis moving unit, it is possible to adjust the height position of the focal point of the laser beam irradiated from the laser processing head 78 and adjust the focus of the imaging unit 80.

[0106] Moreover, the laser processing apparatus 40 includes a display unit (display section, display device) 82 and an alarm unit (alarm section, alarm device) 84. The display unit 82 displays information related to the laser processing apparatus 40. Moreover, the alarm unit 84 notifies the operator of the information related to the laser processing apparatus 40.

[0107] The display unit 82 can be configured with various displays. For example, a touch panel display is used as the display unit 82. In this case, an operation screen for inputting information to the laser processing apparatus 40 is displayed on the display unit 82, and the operator can input information to the laser processing apparatus 40 by touching the display unit 82. In other words, the display unit 82 also functions as an input unit (input section, input device) for inputting various information to the laser processing apparatus 40, and is used as a user interface. However, the input unit may be an electronic device such as a mouse, keyboard, receiver, etc. that is provided separately and independently from the display unit 82.

[0108] The notification unit 84 is configured, for example, by an indicator light (warning light), and when an abnormality occurs in the laser processing device 40, it lights up or flashes to notify the operator of the abnormality. However, there is no limit to the type of the notification unit 84. For example, the notification unit 84 may be a speaker that notifies the operator of information by sound or voice, or may be a transmitter that transmits predetermined information to the outside via wire or wirelessly.

[0109] Furthermore, the laser processing apparatus 40 includes a controller (control unit, control section, control device) 86 that controls the laser processing apparatus 40. The controller 86 is connected to each component constituting the laser processing apparatus 40 (the moving unit 44, the chuck table 66, the wavefront data acquisition unit 70, the laser beam irradiation unit 76, the imaging unit 80, the display unit 82, the notification unit 84, etc.). The controller 86 outputs a control signal to each component of the laser processing apparatus 40, thereby controlling the operation of each component and operating the laser processing apparatus 40.

[0110] For example, the controller 86 is configured by a computer. Specifically, the controller 86 includes a processing unit that executes processes such as calculations necessary for the operation of the laser processing device 40, and a storage unit that stores various information (data, programs, etc.) used for the operation of the laser processing device 40. The processing unit is configured to include a processor such as a CPU, and the storage unit is configured to include memories such as a ROM and a RAM.

[0111] The wavefront data acquisition unit 70, the laser beam projection unit 76, and the controller 86 respectively have the functions of the wavefront data acquisition unit 10, the laser beam projection unit 8, and the judgment unit 12 of the inspection device 2 (see FIG. 1). That is, the laser processing device 40 is equipped with the functions of the inspection device 2. However, the laser processing device 40 may also be provided with the judgment unit 12 (see FIG. 1) separately and independently from the controller 86.

[0112] Fig. 8 is a schematic diagram showing the laser beam irradiation unit 76. The laser beam irradiation unit 76 performs laser processing on the workpiece 11 (see Fig. 7) held on the holding surface 66a of the chuck table 66 by irradiating the workpiece 11 with a laser beam 100. A specific configuration example of the laser beam irradiation unit 76 will be described below.

[0113] The laser beam irradiation unit 76 includes a laser oscillator 102 such as a YAG laser, a YVO4 laser, a YLF laser, or the like, an optical system 104 that guides a pulsed laser beam 100 emitted from the laser oscillator 102 to the workpiece 11 (see FIG. 7) held by the chuck table 66, and an optical system 120 that guides the laser beam 100 to the wavefront data acquisition unit 70.

[0114] The optical system 104 is composed of a plurality of optical elements. For example, the optical system 104 includes an output adjuster 106 such as an attenuator that adjusts the output of the laser beam 100, a polarizer 108 such as a wavelength plate that controls the polarization of the laser beam 100, an expansion optical system 110 such as a beam expander that expands the laser beam 100, and a condenser 112 that condenses the laser beam 100. The output of the laser beam 100 emitted from the laser oscillator 102 is adjusted by the output adjuster 106, and then enters the condenser 112 via the polarizer 108 and the expansion optical system 110.

[0115] The condenser 112 includes a condenser lens 114 such as a convex lens. The laser beam 100 incident on the condenser 112 passes through the condenser lens 114 and is condensed at a predetermined position. The condenser 112 is also connected to a moving mechanism 116 such as an actuator that moves (lifts and lowers) the condenser lens 114 along the Z-axis direction. By raising and lowering the condenser lens 114 with the moving mechanism 116, the height position of the focal point of the laser beam 100 can be adjusted. However, instead of the moving mechanism 116, a moving mechanism that moves (lifts and lowers) the entire optical system 104 along the Z-axis direction may be used.

[0116] The laser beam 100 focused by the condenser 112 is irradiated onto the workpiece 11 (see FIG. 7) held by the holding surface 66a of the chuck table 66. In this way, the workpiece 11 is subjected to a predetermined laser processing.

[0117] For example, the workpiece 11 is subjected to ablation processing by irradiating the workpiece 11 with a laser beam 100 that is absorbent for the workpiece 11. By forming grooves along the streets that extend from the front surface to the back surface of the workpiece 11 by the ablation processing, the workpiece 11 is divided along the streets.

[0118] It is also possible to divide the workpiece 11 by forming a modified layer in the workpiece 11. Specifically, a laser beam 100 that is transparent to the workpiece 11 is focused inside the workpiece 11, and the inside of the workpiece 11 is modified by multiphoton absorption. As a result, a modified layer is formed inside the workpiece 11 along the streets.

[0119] The area of ​​the workpiece 11 where the modified layer is formed becomes more fragile than other areas of the workpiece 11. Therefore, when an external force is applied to the workpiece 11 where the modified layer is formed along the streets, the modified layer functions as a splitting starting point (a trigger for splitting), and the workpiece 11 is split along the streets.

[0120] The optical system 120 includes a plurality of beam splitters 122 (beam splitters 122A, 122B, 122C) that split the laser beam 100. Each of the plurality of beam splitters 122 is provided between the optical elements included in the optical system 104, and splits the laser beam 100 into a laser beam for laser processing and a laser beam for inspecting the optical elements. Specifically, the beam splitter 122A is provided between the output adjuster 106 and the polarizer 108, the beam splitter 122B is provided between the polarizer 108 and the magnifying optical system 110, and the beam splitter 122C is provided between the magnifying optical system 110 and the condenser 112.

[0121] For example, the beam splitter 122 is made of a wedge substrate with a reflectance of about 3% on one side, and includes an irradiated surface 122a onto which the laser beam 100 is irradiated, and an exit surface 122b from which the laser beam 100 is emitted. The laser beam 100 irradiated to the beam splitter 122 is split into a laser beam that passes through the beam splitter 122 and travels straight, a laser beam that is reflected by the irradiated surface 122a of the beam splitter 122, and a laser beam that is reflected by the exit surface 122b of the beam splitter 122.

[0122] Light-shielding elements 124 are provided near the beam splitters 122. The light-shielding elements 124 are formed of a light-shielding plate, a beam damper, or the like, and block the laser beam 100 reflected by the exit surface 122b of the beam splitter 122. This makes it possible to prevent the laser beam 100 reflected by the exit surface 122b of the beam splitter 122 from adversely affecting laser processing or inspection of optical elements.

[0123] The beam splitter 122 is not limited to a wedge substrate, and may be, for example, a glass substrate whose irradiated surface and exit surface are generally parallel to each other. In this case, it is preferable to provide an anti-reflection film on the exit surface side of the glass substrate.

[0124] Moreover, the optical system 120 includes a mirror 126 that reflects the laser beam 100, movable optical elements 128A and 128B, and a movable light blocking element 134 that blocks the laser beam 100. The laser beam 100 reflected by the irradiated surfaces 122a of the beam splitters 122A, 122B, and 122C is irradiated onto the mirror 126 and the movable optical elements 128A and 128B, respectively.

[0125] The mirror 126 reflects the laser beam 100 reflected by the irradiated surface 122a of the beam splitter 122A toward the wavefront data acquisition unit 70. The laser beam 100 reflected by the mirror 126 travels along an optical path 136 from the mirror 126 toward the wavefront data acquisition unit 70.

[0126] The movable optical element 128A includes a mirror 130A that reflects the laser beam 100 reflected by the irradiated surface 122a of the beam splitter 122B, and a light blocking element 132A that blocks the laser beam 100 reflected by the mirror 126. The laser beam 100 reflected by the mirror 130A travels in a direction parallel to the optical path 136.

[0127] The movable optical element 128B includes a mirror 130B that reflects the laser beam 100 reflected by the irradiated surface 122a of the beam splitter 122C, and a light blocking element 132B that blocks the laser beam 100 reflected by the mirror 130A of the movable optical element 128A. The laser beam 100 reflected by the mirror 130B travels in a direction parallel to the optical path 136.

[0128] The movable optical elements 128A and 128B are configured to be movable along a direction intersecting the optical path 136. For example, a moving mechanism (not shown) such as an actuator that moves the movable optical elements 128A and 128B along a direction perpendicular to the optical path 136 is connected to each of the movable optical elements 128A and 128B.

[0129] The movable optical element 128A is positioned at a position where the mirror 130A and the light blocking element 132A are arranged out of the optical path 136 (retracted position, see FIG. 8), or at a position where the mirror 130A and the light blocking element 132A are arranged on the optical path 136 (light blocking position, see FIGS. 9 and 10). When the movable optical element 128A is positioned at the light blocking position, the laser beam 100 reflected by the mirror 130A travels along the optical path 136. In addition, the laser beam 100 reflected by the mirror 126 is blocked by the light blocking element 132A.

[0130] The movable optical element 128B is positioned at a position where the mirror 130B and the light blocking element 132B are arranged out of the optical path 136 (retracted position, see FIG. 8), or at a position where the mirror 130B and the light blocking element 132B are arranged on the optical path 136 (light blocking position, see FIGS. 9 and 10). When the movable optical element 128B is positioned at the light blocking position, the laser beam 100 reflected by the mirror 130B travels along the optical path 136. In addition, the laser beam 100 reflected by the mirror 130A of the movable optical element 128A positioned at the light blocking position is blocked by the light blocking element 132B.

[0131] The movable light-shielding element 134 is configured to be movable along a direction intersecting the optical path 136. For example, a moving mechanism (not shown) such as an actuator that moves the movable light-shielding element 134 along a direction perpendicular to the optical path 136 is connected to the movable light-shielding element 134. The movable light-shielding element 134 is positioned at a position off the optical path 136 (retracted position, see FIGS. 8 and 10) or at a position on the optical path 136 (light-shielding position, see FIG. 9). When the movable light-shielding element 134 is positioned at the light-shielding position, the laser beam 100 traveling along the optical path 136 is blocked by the movable light-shielding element 134.

[0132] There are no limitations on the configuration of the light blocking elements 132A, 132B and the movable light blocking element 134 as long as they can block the laser beam 100. For example, the light blocking elements 132A, 132B and the movable light blocking element 134 are configured by light blocking plates, beam dampers, or the like.

[0133] The optical system 120 guides the laser beam 100, which has passed through at least one of the optical elements (output adjuster 106, polarizer 108, magnifying optical system 110, condenser 112, etc.) included in the optical system 104, to the wavefront data acquisition unit 70. Then, the wavefront data acquisition unit 70 receives the laser beam 100 at a light receiving surface 70a and acquires wavefront data corresponding to the wavefront of the laser beam 100. Thereafter, the wavefront data acquisition unit 70 outputs the wavefront data to the controller 86, and the controller 86 determines the deterioration state of the optical elements based on the wavefront data.

[0134] The configuration and function of the wavefront data acquisition unit 70 are similar to those of the wavefront data acquisition unit 10 (see FIG. 1). For example, a Shack-Hartmann wavefront sensor is used as the wavefront data acquisition unit 70. The configuration and function of the controller 86 are similar to those of the judgment unit 12 (see FIG. 5), and the controller 86 judges the deterioration state of the optical element by executing data processing and judgment processing similar to those of the judgment unit 12.

[0135] The chuck table 66 may include a light shielding portion 66b that blocks the laser beam 100 emitted from the condenser 112 when the laser beam 100 is irradiated onto the wavefront data acquisition unit 70. For example, the light shielding portion 66b is configured by a light shielding plate, a beam damper, or the like.

[0136] The wavefront data acquisition unit 70 may also include a light amount adjuster 140 that adjusts the amount of light of the laser beam 100. For example, an ND (Neutral Density) filter is used as the light amount adjuster 140. The light amount adjuster 140 adjusts the amount of light of the laser beam 100 that reaches the light receiving surface 70a so that it is suitable for detecting the wavefront.

[0137] The wavefront data acquisition unit 70 and the laser beam irradiation unit 76 inspect any optical element included in the optical system 104. As an example, a case in which a deterioration state of the condenser lens 114 included in the condenser 112 is determined will be described below.

[0138] 9 is a schematic diagram showing the laser beam irradiation unit 76 when acquiring wavefront data. When inspecting the condenser lens 114, the condenser lens 114 is irradiated with a laser beam 100 (laser beam irradiation step S1), and wavefront data of the laser beam 100 transmitted through the condenser lens 114 is acquired (wavefront data acquisition step S2).

[0139] Specifically, first, the movable optical elements 128A and 128B and the movable light blocking element 134 are positioned at light blocking positions on the optical path 136. In addition, the position of the wavefront data acquisition unit 70 in the X-axis direction and the Y-axis direction is adjusted by the moving unit 44 (see FIG. 7 ) so that the laser beam 100 emitted from the light collector 112 is irradiated onto the light receiving surface 70a of the wavefront data acquisition unit 70.

[0140] Next, the laser oscillator 102 is operated. As a result, the laser beam 100 emitted from the laser oscillator 102 passes through the output adjuster 106, the beam splitter 122A, the polarizer 108, the beam splitter 122B, the magnifying optical system 110, and the beam splitter 122C in this order, and enters the condenser 112. Then, the laser beam 100 transmitted through the condenser lens 114 is irradiated onto the wavefront data acquisition unit 70 via the light amount adjuster 140 (laser beam irradiation step S1).

[0141] The laser beam 100 reflected by the irradiated surfaces 122a of the beam splitters 122A, 122B, and 122C is irradiated onto the mirrors 126, 130A, and 130B, respectively. The laser beam 100 reflected by the mirror 126 is blocked by the light-shielding element 132A, the laser beam 100 reflected by the mirror 130A is blocked by the light-shielding element 132B, and the laser beam 100 reflected by the mirror 130B is blocked by the movable light-shielding element 134. This makes it possible to prevent the laser beam 100 from being irradiated onto unintended locations other than the wavefront data acquisition unit 70.

[0142] Next, the wavefront data acquiring unit 70 is operated while the laser beam 100 is being irradiated onto the wavefront data acquiring unit 70. As a result, wavefront data of the laser beam 100 transmitted through the condenser lens 114 is acquired by the wavefront data acquiring unit 70 (wavefront data acquiring step S2).

[0143] For example, a phase distribution 30 (see FIG. 4(A)) of the wavefront of the laser beam 100 is acquired as the wavefront data. The wavefront data acquisition unit 70 also acquires intensity data of the laser beam 100 transmitted through the condenser lens 114, as necessary. For example, an intensity distribution 32 (see FIG. 4(B)) of the laser beam 100 is acquired as the intensity data.

[0144] The wavefront data (and intensity data) acquired by the wavefront data acquisition unit 70 is output to the controller 86. Then, the controller 86 determines the deterioration state of the condenser lens 114 based on the wavefront data (and intensity data) (determination step S3).

[0145] The contents of the process by the controller 86 when determining the deterioration state of the condenser lens 114 are similar to those of the determination unit 12 (see FIG. 5) in the first embodiment. Then, the controller 86 causes the display unit 82 (see FIG. 7) to display the result of the determination. At this time, the display unit 82 may display an image of the phase distribution 30 (see FIG. 4(A)), a figure or symbol indicating the area A (see FIG. 4(A)) of the phase distribution 30, a numerical value indicating the size of the area A, an image of the intensity distribution 32 (see FIG. 4(B)), and the like together with the result of the determination. Furthermore, when it is determined that the condenser lens 114 is deteriorated, the controller 86 causes the notification unit 84 (see FIG. 7) to notify an error.

[0146] As described above, the laser beam 100 irradiated to the wavefront data acquisition unit 70 passes through the condenser lens 114 as well as the output adjuster 106, the polarizer 108, and the magnifying optical system 110. Therefore, the wavefront data acquired by the wavefront data acquisition unit 70 may reflect not only the characteristics of the condenser lens 114 but also the characteristics of the output adjuster 106, the polarizer 108, and the magnifying optical system 110. Therefore, wavefront data (reference wavefront data) of the laser beam 100 that does not pass through the condenser lens 114 may be acquired (reference wavefront data acquisition step), and the deterioration state of the condenser lens 114 may be determined based on the result of comparing the wavefront data with the reference wavefront data.

[0147] 10 is a schematic diagram showing the laser beam irradiation unit 76 when acquiring reference wavefront data. In the reference wavefront data acquiring step, first, the movable optical elements 128A and 128B are positioned at light blocking positions on the optical path 136, and the movable light blocking element 134 is positioned at a retracted position off the optical path 136. In addition, the position of the wavefront data acquiring unit 70 in the X-axis direction and the Y-axis direction is adjusted by the moving unit 44 (see FIG. 7) so that the light receiving surface 70a of the wavefront data acquiring unit 70 is positioned on an extension line of the optical path 136.

[0148] Next, the laser oscillator 102 is operated. As a result, the laser beam 100 emitted from the laser oscillator 102 passes through the output adjuster 106, the beam splitter 122A, the polarizer 108, the beam splitter 122B, and the magnifying optical system 110 in this order, and is then irradiated onto the beam splitter 122C. The laser beam 100 is then reflected by the irradiated surface 122a of the beam splitter 122C, and is then reflected by the mirror 130B, and is irradiated onto the wavefront data acquisition unit 70 via the light amount adjuster 140.

[0149] The laser beam 100 transmitted through the beam splitter 122C is blocked by a light-shielding portion 66b provided on the chuck table 66. The laser beam 100 reflected by the irradiated surfaces 122a of the beam splitters 122A and 122B is irradiated onto the mirrors 126 and 130A, respectively. The laser beam 100 reflected by the mirror 126 is blocked by the light-shielding element 132A, and the laser beam 100 reflected by the mirror 130A is blocked by the light-shielding element 132B.

[0150] Next, while the wavefront data acquisition unit 70 is irradiated with the laser beam 100, the wavefront data acquisition unit 70 is operated. As a result, wavefront data of the laser beam 100 that has passed through the output regulator 106, the polarizer 108, and the magnifying optical system 110 but has not passed through the condenser lens 114 is acquired as reference wavefront data. As the reference wavefront data, for example, the phase distribution 36 of the wavefront of the laser beam 100 (see FIG. 6(A)) is acquired.

[0151] The reference wavefront data acquired by the wavefront data acquisition unit 70 is output to the controller 86. Then, the controller 86 judges the deterioration state of the condenser lens 114 based on the result of comparing the wavefront data with the reference wavefront data (judging step S3). This makes it possible to judge the deterioration state of the condenser lens 114 while excluding the influence of the characteristics of other optical elements. The contents of the process by the controller 86 when judging the deterioration state of the condenser lens 114 using the wavefront data and the reference wavefront data are similar to those of the judgment unit 12 in the first embodiment (see FIG. 5).

[0152] The optical elements through which the laser beam 100 irradiated to the wavefront data acquisition unit 70 passes can be freely selected by changing the positions of the movable optical elements 128A and 128B and the movable light blocking element 134. This allows any optical element included in the optical system 104 to be inspected.

[0153] Specifically, by positioning the movable optical elements 128A, 128B and the movable light blocking element 134 at the retracted positions, wavefront data of the laser beam 100 that has passed through the output adjuster 106 and has not passed through the polarizer 108, the magnifying optical system 110, and the condenser 112 is acquired. Also, by positioning the movable optical element 128A at the light blocking position and positioning the movable optical element 128B and the movable light blocking element 134 at the retracted positions, wavefront data of the laser beam 100 that has passed through the output adjuster 106 and the polarizer 108 and has not passed through the magnifying optical system 110 and the condenser 112 is acquired. In this manner, by changing the positions of the movable optical elements 128A, 128B and the movable light blocking element 134, a plurality of types of wavefront data can be acquired by the wavefront data acquisition unit 70.

[0154] Furthermore, the configuration of the laser beam irradiation unit 76 can be appropriately changed as long as it is possible to acquire wavefront data of the laser beam 100. For example, the optical system 104 may include an expanding optical system such as a beam expander that expands the laser beam 100 only when the wavefront data is acquired.

[0155] The magnifying optical system is provided, for example, between the laser oscillator 102 and the output adjuster 106, and magnifies the laser beam 100 so that the laser beam 100 is irradiated to the wavefront data acquisition unit 70 with a predetermined beam diameter. When performing laser processing on the workpiece 11, the magnifying optical system is retracted from the optical path of the laser beam 100. As a result, the laser beam 100 that has not passed through the magnifying optical system is irradiated to the workpiece 11.

[0156] Furthermore, the laser beam irradiation unit 76 may include a plurality of laser oscillators. In this case, a laser beam emitted from one laser oscillator is used for laser processing of the workpiece 11, and a laser beam emitted from another laser oscillator is used for acquiring wavefront data.

[0157] As described above, in the laser processing apparatus 40 according to this embodiment, the deterioration state of the optical element included in the optical system 104 that guides the laser beam 100 to the workpiece 11 is judged based on the wavefront data of the laser beam 100. This allows the deterioration of the optical element 4 to be accurately detected, and the occurrence of processing defects is suppressed.

[0158] In the present embodiment, the laser beam irradiation unit 76 is described as being capable of acquiring a plurality of types of wavefront data by one wavefront data acquisition unit 70. However, the laser processing apparatus 40 may acquire a plurality of types of wavefront data by using a plurality of wavefront data acquisition units.

[0159] 11 is a schematic diagram showing a laser beam irradiation unit 76A corresponding to a modified example of the laser beam irradiation unit 76. The laser beam irradiation unit 76A includes a plurality of wavefront data acquisition units 150 (wavefront data acquisition units 150A, 150B, 150C) instead of the mirror 126, the movable optical elements 128A and 128B, and the movable light blocking element 134 shown in FIG.

[0160] The configurations and functions of the plurality of wavefront data acquisition units 150 are similar to those of the wavefront data acquisition unit 70. For example, each of the plurality of wavefront data acquisition units 150 is configured by a Shack-Hartmann wavefront sensor.

[0161] The wavefront data acquiring units 150 are provided in the same number as the beam splitters 122. Specifically, the wavefront data acquiring units 150A, 150B, and 150C are installed on the optical path of the laser beam 100 reflected by the irradiated surfaces 122a of the beam splitters 122A, 122B, and 122C, respectively.

[0162] When the laser oscillator 102 is operated, the laser beam 100 reflected by the irradiated surfaces 122a of the beam splitters 122A, 122B, and 122C is irradiated to the wavefront data acquisition units 150A, 150B, and 150C, respectively. Then, the wavefront data of the laser beam 100 passing through the output adjuster 106 is acquired by the wavefront data acquisition unit 150A. In addition, the wavefront data of the laser beam 100 passing through the output adjuster 106 and the polarizer 108 is acquired by the wavefront data acquisition unit 150B. In addition, the wavefront data of the laser beam 100 passing through the output adjuster 106, the polarizer 108, and the magnifying optical system 110 is acquired by the wavefront data acquisition unit 150C.

[0163] Meanwhile, wavefront data of the laser beam 100 passing through the output adjuster 106, the polarizer 108, the magnifying optical system 110, and the condenser 112 is acquired by the wavefront data acquiring unit 70. Then, the wavefront data acquired by the wavefront data acquiring units 70, 150A, 150B, and 150C is output to the controller 86, which determines the deterioration state of the output adjuster 106, the polarizer 108, the magnifying optical system 110, or the condenser 112 based on the wavefront data.

[0164] As described above, a plurality of types of wavefront data can be simultaneously acquired by mounting a plurality of wavefront data acquisition units 70, 150A, 150B, and 150C on the laser processing apparatus 40. This eliminates the need to change the arrangement of optical elements according to the type of wavefront data (see FIGS. 9 and 10), and simplifies the process of acquiring wavefront data.

[0165] In addition, the structure, method, and the like according to the present embodiment can be appropriately modified and implemented without departing from the scope of the object of the present invention. In addition, the present embodiment can be appropriately combined with other embodiments. [Explanation of symbols]

[0166] 2. Inspection equipment 4,4A,4B,4C Optical elements 4a Irradiated surface 4b Output surface 4c reflective surface 6. Laser Beam 8,8A,8B,8C Laser beam irradiation unit 10 Wavefront Data Acquisition Unit 10a Photosensitive surface 12 Judgment Unit 14 Inspection Department 14a Data processing section 14b Judgment part 16 Memory section 20 Laser Oscillator 22A,22B,22C optical system 24 Optical attenuator 26 Magnification Optical System 28 Reduction optical system 30 Phase distribution 32 Intensity distribution 34 Wavefront Data 36 Phase distribution 38 Differential phase distribution 11 Workpiece 13 Frame 15 sheets 40 Laser processing equipment 42 Foundation 44 Mobile unit (mobile mechanism) 46 Y-axis movement unit (Y-axis movement mechanism) 48 Y-axis guide rail 50 Y-axis moving table 52 Y-axis ball screw 54 Y-axis pulse motor 56 X-axis movement unit (X-axis movement mechanism) 58 X-axis guide rail 60 X-axis moving table 62 X-axis ball screw 64 X-axis pulse motor 66 Chuck table (holding table) 66a Holding surface 66b Light shielding part 68 Clamp 70 Wavefront Data Acquisition Unit 70a Photosensitive surface 72 Support structure 74 Support member 76,76A Laser beam irradiation unit 78 Laser processing head 80 Imaging unit 82 Display unit (display unit, display device) 84 Notification unit (notification section, notification device) 86 Controller (control unit, control section, control device) 100 Laser Beam 102 Laser Oscillator 104 Optical system 106 Output regulator 108 Polarizer 110 Magnifying Optical System 112 Concentrator 114 Condenser Lens 116 Moving mechanism 120 Optical system 122, 122A, 122B, 122C Beam splitter 122a Irradiated surface 122b Output surface 124 Light-shielding element 126 Mirror 128A, 128B Movable optical element 130A, 130B Mirror 132A, 132B Light shielding element 134 Movable light blocking element 136 Light path 140 Light intensity adjuster 150, 150A, 150B, 150C Wavefront Data Acquisition Unit

Claims

1. 1. An optical element inspection method for inspecting an optical element, comprising: a laser beam irradiation step of irradiating the optical element with a laser beam; a wavefront data acquisition step of acquiring wavefront data corresponding to a wavefront of the laser beam transmitted through or reflected by the optical element; and a determination step of determining a state of deterioration of the optical element based on the wavefront data.

2. a reference wavefront data acquisition step of acquiring reference wavefront data corresponding to a wavefront of the laser beam not passing through the optical element, 2. The method for inspecting an optical element according to claim 1, wherein in the determining step, a deterioration state of the optical element is determined based on a result of comparing the wavefront data with the reference wavefront data.

3. 3. The optical element inspection method according to claim 1, wherein the determining step includes identifying a deteriorated area of ​​the optical element based on the wavefront data.

4. An inspection apparatus for inspecting an optical element, comprising: a laser beam irradiation unit that irradiates the optical element with a laser beam; a wavefront data acquisition unit for acquiring wavefront data corresponding to a wavefront of the laser beam transmitted through or reflected by the optical element; and a determination unit that determines a state of deterioration of the optical element based on the wavefront data.

5. A laser processing device that irradiates a workpiece with a laser beam, A laser oscillator; an optical system including an optical element for directing the laser beam emitted from the laser oscillator to the workpiece; a wavefront data acquisition unit for acquiring wavefront data corresponding to a wavefront of the laser beam transmitted through or reflected by the optical element; and a determination unit that determines a deterioration state of the optical element based on the wavefront data.

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