Laser processing method and laser processing apparatus

Abstract

To provide a laser processing method that can form holes with highly precise, planned shape accuracy even in metal materials that are difficult to process. [Solution] The laser processing method includes the step of forming a hole in the workpiece by rotating the polarization plane of a linearly polarized laser and scanning the laser around the surface of the workpiece.

Description

[[Technical Field]]

[0001] The present invention relates to a laser processing method and a laser processing apparatus. [[Background Art]]

[0002] Conventionally, laser processing has been used for microfabrication such as cutting and drilling of various workpieces. For example, Patent Document 1 discloses a method for manufacturing a sample stage for an electron microscope, in which after a diamond film is formed on a metal substrate by plasma CVD, the diamond film is processed into a desired shape using a laser processing method. [[Prior Art Documents]] [[Patent Documents]]

[0003] [[Patent Document 1]] Japanese Unexamined Patent Publication No. 9-115471 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0004] Incidentally, for example, when forming micron-sized holes accurately and precisely, so-called trepanning processing (hollowing processing), in which a hole is formed while circularly scanning a laser beam, is sometimes performed.

[0005] However, when a hole is formed by trepanning processing, subtle deviations and distortions occur in the opening shape of the hole, which may result in low shape accuracy. For example, when forming a hole having a circular opening, the opening shape of the hole may slightly deviate from a perfect circle. Such subtle deviations and distortions of the opening shape may be problematic particularly in members used for electronic devices, electromechanical machinery, and the like. This problem is even more of a concern particularly in difficult-to-process materials with high hardness and high melting points, such as nickel, molybdenum, and cobalt-chromium alloy. Therefore, if processing with high shape accuracy as planned can be performed with few subtle deviations and distortions of the opening shape, processing of various workpieces including difficult-to-process materials will be facilitated.

[0006] The object of the present invention is to provide a laser processing method and a laser processing apparatus that can form holes with highly precise, planned shape accuracy, even in materials that are difficult to process. [Means for solving the problem]

[0007] The present invention relates to the following laser processing method and laser processing apparatus. [1] A laser processing method comprising the step of forming a hole in a workpiece by rotating the polarization plane of a linearly polarized laser and scanning the laser around the surface of the workpiece. [2] The laser processing method according to [1], wherein in the step of forming the hole, the plane of polarization of the laser is rotated by one or more rotations. [3] The laser processing method according to [1] or [2], wherein the laser is a pulsed laser with a wavelength of 600 nm or less. [4] The laser processing method according to [3], wherein the pulse width of the pulsed laser is 10 picoseconds or less. [5] The laser processing method according to any one of [1] to [4], wherein the workpiece includes a metal material that is difficult to process. [6] The laser processing method according to [5], wherein the difficult-to-process metal material comprises molybdenum. [7] A laser processing apparatus comprising a stage for placing a workpiece on it, a laser emission unit for emitting a linearly polarized laser, and a light guide unit for guiding the laser emitted from the laser emission unit to a workpiece placed on the stage, wherein the light guide unit comprises a polarization direction adjustment member for adjusting the angle of the polarization direction of the laser, and a rotating unit for rotating the polarization direction adjustment member when the laser is irradiated onto the surface of the workpiece. [8] The laser processing apparatus according to [7], wherein the light guide unit further comprises a light scanning unit for scanning the laser in a circular motion. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a laser processing method and a laser processing apparatus that can form holes with highly precise, planned shape shapes even in materials that are difficult to process. [Brief explanation of the drawing]

[0009] [Figure 1] Figures 1A to 1C are schematic diagrams illustrating a laser processing method according to one embodiment of the present invention. [Figure 2] Figure 2 illustrates the roundness of the hole opening shape. [Figure 3] Figure 3 is a schematic diagram showing the configuration of a laser processing apparatus according to one embodiment of the present invention. [Figure 4] Figures 4A and 4B illustrate the mechanism of action. [Figure 5] Figure 5 is an SEM image showing the results of Example 1. [Figure 6] Figure 6 is a graph showing the results of Example 2. [Modes for carrying out the invention]

[0010] 1. Laser processing method Figures 1A to 1C are schematic diagrams illustrating a laser processing method according to one embodiment of the present invention. Of these, Figures 1A and 1B are cross-sectional views, and Figure 1C is a plan view. Figure 2 is a diagram illustrating the roundness of the hole opening shape.

[0011] A laser processing method according to one embodiment of the present invention is a method of forming holes in the surface of a workpiece by irradiating it with a laser. The laser processing method includes a step of forming holes 10a in the workpiece 10 by rotating the polarization plane of a linearly polarized laser 20 and scanning the laser 20 in a circular motion (see Figures 1A to 1C).

[0012] The workpiece 10 is not particularly limited as long as it can be laser-processed. Examples of materials that are the main component of the workpiece 10 include semiconductors such as silicon, metals such as copper, iron, aluminum, molybdenum, and tungsten, and alloys such as stainless steel and Invar. The main component refers to a component that is preferably contained in an amount of 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, based on the total mass of the workpiece. Only one type of these materials may be contained, or two or more types may be contained. Among these, the workpiece 10 preferably contains a metal material, and more preferably contains a hard-to-process metal material.

[0013] That is, in recent industrial fields, various metals are used in accordance with their physical properties. Not only iron and aluminum, which are typical base metals, and various alloys based on these, but also rare metals, which are "metals that exist in rare quantities or are extremely economically or physically difficult to extract", such as titanium, nickel, cobalt, vanadium, and molybdenum, are used in various fields depending on the application. These metal materials are processed into various shapes and sizes according to their applications.

[0014] Among metal materials, most rare metals are hard-to-process metal materials. The term "hard-to-process metal material" refers to a metal material that has properties such as being hard and causing rapid wear of processing machines, being hard but brittle and cracking during processing, having high viscosity and easily generating burrs on cut and cut surfaces, and having poor thermal conductivity, easily accumulating heat, and causing welding of the processed surface. Since it is difficult for conventional machine tools to perform precise and fine processing on a workpiece containing such a hard-to-process metal material, it is particularly desirable that laser processing can be applied thereto.

[0015] Examples of the hard-to-process metal material include, as described above, rare metals such as nickel, cobalt, molybdenum, and tungsten, and alloys of two or more of these (e.g., cobalt-molybdenum alloys), with molybdenum being preferred. Molybdenum is extremely hard, has high electrical resistance as a metal, and has an extremely high melting point of 2620°C. Therefore, molybdenum is widely used as a material for semiconductor substrates and electric furnaces.

[0016] Among the above, crystalline difficult-to-process metal materials have an absorption coefficient for laser light that is more likely to depend on the polarization state of the laser than amorphous materials, so deviation or distortion tends to occur in the opening shape of the hole depending on the polarization state of the laser. According to the laser processing method of the present embodiment, even in a workpiece 10 including such a crystalline difficult-to-process metal material, a hole with little deviation or distortion in the opening shape can be formed.

[0017] The shape of the workpiece 10 is not particularly limited either, and is, for example, a plate shape. When the workpiece 10 is plate-shaped, the thickness of the workpiece 10 can be, for example, 1 µm or more and 1000 µm or less, preferably 1 µm or more and 100 µm or less.

[0018] The irradiated linearly polarized laser 20 may be a pulsed laser or a continuous wave oscillation laser, and is preferably a pulsed laser.

[0019] The wavelength and pulse width of the pulsed laser are not particularly limited as long as the intended processing can be performed on the workpiece 10. For example, the wavelength of the pulsed laser is preferably 600 nm or less, more preferably 200 nm or more and 600 nm or less. The pulse width of the pulsed laser is preferably 10 picoseconds or less, more preferably 0.1 picoseconds or more and 5 picoseconds or less. Thereby, even for a workpiece 10 including, for example, a difficult-to-process metal material, processing with high shape accuracy can be achieved.

[0020] As described above, a so-called trepanning process is performed, in which the laser 20 is irradiated onto the surface of the workpiece 10 while scanning it in a circular motion. Trepanning is a method of cutting out a shape by scanning the laser 20 around the surface of the workpiece 10, for example, in a circular motion (see Figure 3A). Trepanning is suitable, for example, when processing a hole with a diameter larger than the beam spot diameter. In trepanning, the processing time is longer compared to when the laser 20 is not scanned around the surface, but the processing quality tends to be better. This is because the processing is done slowly with a low-intensity laser beam. In Figure 1A, a hole 10a is formed on the surface of the workpiece 10 by irradiating it with the laser 20 while scanning it in a circular motion (see Figures 1A and 1B).

[0021] The light intensity per unit area at the irradiation spot of the laser 20 is not particularly limited, but it is preferable to lower it from the viewpoint of suppressing the generation of minute droplet-shaped deposits (droplet-like deposits). In other words, according to the inventors' studies, when trepanning is performed by scanning the surface of a workpiece 10 such as a molybdenum plate with a laser, droplet-like deposits may form near the opening edge of the hole 10a on the laser emission side. In contrast, by reducing the intensity of the irradiating laser, it is possible to make it more difficult for droplet-like deposits to form.

[0022] Specifically, the light intensity per unit area at the laser 20 irradiation spot is 0.1 J / cm². 2 More than 1J / cm 2 Preferably, it is 0.2 J / cm². 2 More than 0.4J / cm 2 The following is more preferable: In the case of a pulsed laser, the light intensity per unit area at the irradiation spot can be adjusted by the laser pulse energy and the irradiation spot diameter.

[0023] In the hole-forming process, as described above, the laser 20 is scanned around the surface of the workpiece 10 while rotating the polarization plane of the laser 20. The method of rotating the polarization plane of the laser 20 is not particularly limited. For example, holes 10a can be formed by rotating a λ / 2 wave plate and scanning the laser 20 that has passed through the λ / 2 wave plate around the surface of the workpiece 10 (see Figure 3 below).

[0024] While the laser 20 is scanning in a circular motion, the polarization plane of the laser 20 may be rotated continuously or intermittently. In this embodiment, the rotation direction of the polarization plane of the laser 20 is the same as the direction of the circular scanning motion.

[0025] The number of rotations of the polarization plane of the laser 20 during one circular scan (number of rotations of the polarization plane of the laser 20 per circular scan) can be arbitrarily set according to the required shape accuracy of the hole 10a and the number of circular scans. The number of rotations of the polarization plane of the laser 20 per circular scan may be one or more, or less than one.

[0026] Similarly, the total number of rotations of the polarization plane of the laser 20 while forming one hole 10a (total number of rotations of the polarization plane of the laser 20 while forming one hole 10a) can also be arbitrarily set. The total number of rotations of the polarization plane of the laser 20 while forming one hole 10a may be the same as or greater than the number of circular scans, or it may be less. In this embodiment, it is preferable to rotate the polarization plane of the laser 20 a total of one or more times while forming one hole 10a, and more preferably three to 100 times. This allows the aperture shape to be made closer to a perfect circle, for example, when forming a hole with a circular aperture shape. It should be noted that the total number of rotations of the polarization plane of the laser 20 is preferably less than the number of circular scans, because beyond a certain number of rotations the shape accuracy of the hole aperture hardly changes any further.

[0027] The circumferential scanning of the laser 20 is usually repeated until a hole 10a is formed. The number of circumferential scans depends on the thickness of the workpiece 10 and the light intensity per unit area at the laser 20 irradiation spot, but can be, for example, 10 to 100,000 times, preferably 100 to 10,000 times. The diameter of the circumferential scan may be constant.

[0028] In this way, by rotating the polarization plane of the laser 20 and scanning the laser 20 in a circular motion, for example, when forming a hole with a circular aperture shape, the aperture shape can be made closer to a perfect circle. When the aperture shape of hole 10a is circular, the roundness of the aperture shape is preferably less than 5%, more preferably 2.5% or less, and even more preferably 1% or less. The lower limit of the roundness is preferably as small as possible, for example, 0% or more.

[0029] If the opening shape of hole 10a is circular as shown in Figure 2, the roundness of the opening shape is defined by the following formula. Here, Y is the maximum diameter of the opening and X is the minimum diameter, and Y > X. Roundness (%) = {(YX) / X} × 100 The smaller this value, the closer the opening shape of hole 10a will be to a perfect circle, that is, a perfect circle.

[0030] Hole 10a may be a straight hole or a tapered hole. In Figure 1B, hole 10a is a tapered hole. When hole 10a is a tapered hole, the taper angle θ of the tapered hole is not particularly limited, but is preferably 10° or more and 70° or less, and more preferably 20° or more and 50° or less (see Figure 1B).

[0031] The method for forming tapered holes is not particularly limited. For example, if the laser 20 is repeatedly scanned in a circular motion at a constant diameter, either straight holes or tapered holes may be formed depending on the material of the workpiece 10. For example, in the case of a workpiece 10 containing molybdenum, tapered holes can be formed even if the diameter of the circular scan is constant.

[0032] The plan view shape of the opening of hole 10a is not particularly limited and may be circular, elliptical, or polygonal, such as a quadrilateral. In Figures 1A to 1C, the plan view shape of the opening of hole 10a is circular. The diameter of the opening of hole 10a when viewed from above is not particularly limited. For example, the diameter of the opening of hole 10a on the laser emission side is preferably larger than the diameter of the irradiation spot of the laser 20, and can be, for example, 1 μm or more and 1,000 μm or less.

[0033] 2. Laser processing equipment Next, a preferred embodiment of the laser processing apparatus used in the above-described laser processing method will be explained.

[0034] Figure 3 is a schematic diagram showing the configuration of a laser processing apparatus 100 according to one embodiment of the present invention.

[0035] As shown in Figure 3, the laser processing apparatus 100 includes a stage 110, a laser emission unit 120, a light guide unit 130, an imaging unit 140, and a control unit 150.

[0036] Stage 110 is a stage for placing the workpiece 10. Stage 110 may be fixed in position or may be configured to be movable in the XYZ directions. If Stage 110 is configured to be movable in the XYZ directions, Stage 110 may be configured to be movable under the control of Control Unit 150.

[0037] The laser emission unit 120 emits a linearly polarized laser. In Figure 3, the laser emission unit 120 is a light source that emits a linearly polarized laser. The light source can be any light source that continuously or pulses the linearly polarized laser described above, and it is preferable that it is a light source that emits a pulsed laser of linear polarization with the wavelength and pulse width described above. The laser emission unit 120 may be configured to allow adjustment of its output and repetition frequency under the control of the control unit 160.

[0038] The laser emission unit 120 may also have a light source for emitting an unpolarized laser and a polarizer for converting the unpolarized laser into a linearly polarized laser, instead of a light source for emitting a linearly polarized laser. Thus, the laser emission unit 120 may be configured to emit a linearly polarized laser.

[0039] The light guide unit 130 guides the laser emitted from the laser emission unit 120 to the workpiece 10 placed on the stage 110. The light guide unit 130 includes a polarization direction rotation unit 131, a beam size changing unit 132, an optical scanning unit 133, an fθ lens 134, and two mirrors 135a and 135b.

[0040] The polarization direction rotation unit 131 continuously or intermittently rotates the polarization direction of the laser when the emitted laser is irradiated onto the surface of the workpiece 10. Here, continuously or intermittently rotating the polarization direction means changing the rotation angle of the polarization direction over time. The polarization direction rotation unit 131 has a polarization direction adjustment member 131a and a rotation unit 131b.

[0041] The polarization direction adjustment member 131a adjusts the polarization direction (or the angle of the polarization plane) of the laser emitted from the laser emission unit 120. The polarization direction adjustment member 131a is not particularly limited as long as it has the above function. In Figure 3, the polarization direction adjustment member 131a is a λ / 2 wave plate. The λ / 2 wave plate is positioned so that the incident surface of the laser 20 is perpendicular to the optical axis of the laser beam.

[0042] A λ / 2 waveplate is an optical element made of a transparent material with birefringence. A λ / 2 waveplate has a specific optical axis, and when linearly polarized light with polarization components parallel to this optical axis passes through the waveplate, the polarization direction remains unchanged. On the other hand, if the polarization direction is incident at an angle θ with respect to the optical axis of the waveplate, the vibration direction of the emitted linearly polarized light is emitted at an angle θ opposite to the polarization direction of the incident light with respect to the optical axis of the waveplate. In other words, when linearly polarized light is incident at an angle θ with respect to the optical axis of the λ / 2 waveplate, it is emitted as linearly polarized light with its vibration direction rotated by 2θ. Due to this effect, a λ / 2 waveplate can rotate the polarization direction of linearly polarized light.

[0043] Note that the polarization direction adjustment member 131a is not limited to a λ / 2 wave plate. For example, instead of using a λ / 2 wave plate, a liquid crystal polarization rotator or a Faraday rotator utilizing the magnetic Faraday effect may be used.

[0044] The rotating unit 131b rotates the polarization direction adjustment member 131a (λ / 2 wave plate in Figure 3) when the laser is irradiated onto the surface of the workpiece 10. The rotating unit 131b is not particularly limited as long as it has the above function. In Figure 3, the rotating unit 131b is a rotating stage that supports the polarization direction adjustment member 131a and rotates around its axis (rotates in the plane direction). The rotating unit 131b can change the angle θ described above by rotating the polarization direction adjustment member 131a while maintaining that the incident surface of the polarization direction adjustment member 131a is perpendicular to the optical axis of the laser. Therefore, the angle of the polarization plane of the emitted laser can be freely controlled continuously or intermittently. The rotating unit 131b may be configured to adjust the rotation speed of the polarization direction adjustment member 131a (total number of rotations R during the processing to form the hole 10a) under the control of the control unit 150.

[0045] The beam size changing unit 132 adjusts the beam size of the laser. In Figure 3, the beam size changing unit 132 is a beam expander (lens pair).

[0046] The optical scanning unit 133 adjusts the laser irradiation position and scanning pattern, causing the laser to scan in a circular motion. In Figure 3, the optical scanning unit 133 is a galvanometer scanner. The optical scanning unit 133 may be configured to adjust the laser irradiation position and scanning pattern under the control of the control unit 150. This allows the laser to be irradiated onto the surface of the workpiece 10 in any shape while scanning.

[0047] The fθ lens 134 adjusts the focal position of the laser. The fθ lens 134 may be configured to allow adjustment of the focal position under the control of the control unit 150.

[0048] Mirrors 135a and 135b adjust the optical path of the laser. In Figure 3, mirror 135a adjusts the optical path so that the laser emitted from the laser emission unit 120 is incident on the polarization direction rotation unit 131. Mirror 135b adjusts the optical path so that the laser, after passing through the beam size changing unit 132, is incident on the optical scanning unit 133.

[0049] The imaging unit 140 captures images of the surface of the workpiece 10. The imaging unit 140 only needs to be capable of capturing images of the focal position, the processing process, and the surface condition of the workpiece 10. Such an imaging unit 140 can be a general-purpose camera, such as a CCD camera. The image information captured by the imaging unit 140 is output to the control unit 150.

[0050] The control unit 150 is a computer or the like, connected to the stage 110, laser emission unit 120, light guide unit 130, and imaging unit 140, etc. The control unit 150 can adjust the laser output and repetition frequency, for example, by controlling the laser emission unit 120. Furthermore, the control unit 150 can adjust the rotation speed and direction of the polarization plane of the laser by, for example, controlling the polarization direction rotation unit 131 of the light guide unit 130. The control unit 150 can also adjust the laser irradiation position or scanning pattern by, for example, controlling at least one of the optical scanning unit 133 of the light guide unit 130 and the stage 110. Additionally, the control unit 150 can adjust the laser's focal position by controlling the fθ lens 134. The control unit 150 may also perform these controls based on image information captured by, for example, the imaging unit 140.

[0051] (operation) The operation of the laser processing device 100 will be explained below with reference to Figure 3. The explanation will use an example where a pulsed laser is used.

[0052] The laser processing apparatus 100 first performs startup and adjustment operations on each part under the control of the control unit 150. Some of these operations may be performed manually. By adjusting the rotating part 131b of the light guide unit 130, the rotation speed and direction of the polarization plane of the laser are adjusted. In addition, by adjusting the optical scanning unit 133 and the fθ lens 134, the scanning pattern and focal position of the pulsed laser are adjusted. Furthermore, by adjusting the laser emission unit 120 and the fθ lens 134, the light intensity per unit area at the irradiation spot is adjusted.

[0053] Next, the laser processing apparatus 100 performs the hole formation process described above. Specifically, a pulsed laser is emitted from the laser light source 120. The emitted pulsed laser is incident on the polarization direction rotation unit 131. In the polarization direction rotation unit 131, the rotation unit 131b rotates the polarization direction adjustment member 131a under the control of the control unit 150. This causes the polarization plane of the pulsed laser incident on the polarization direction rotation unit 131 to rotate continuously or intermittently. The pulsed laser that has passed through the polarization direction rotation unit 131 has its beam diameter adjusted by the beam size changing unit 132, and then enters the optical scanning unit 133. The optical scanning unit 133 scans the surface of the workpiece 10 with a pulsed laser in a predetermined pattern, and the fθ lens 134 adjusts the focal position. This causes the pulsed laser to repeatedly scan the surface of the workpiece 10 while rotating its polarization plane. As a result, tiny holes 10a are formed.

[0054] The control unit 150 may acquire the focal position and processing status through the imaging unit 140, and adjust the laser's focal position and scanning position by controlling the fθ lens 134 and the optical scanning unit 133 based on the acquired information.

[0055] Furthermore, in this embodiment, the control unit 150 adjusts the laser scanning pattern and focal position by adjusting the optical scanning unit 133 and the fθ lens 134, but is not limited to this. For example, the control unit 150 may adjust the laser scanning pattern, etc. by adjusting the position of the stage 110. Alternatively, the control unit 150 may adjust the laser scanning pattern, etc. by adjusting both the light guide unit 130 and the stage 110.

[0056] Furthermore, in this embodiment, the control unit 150 adjusts the light intensity per unit area of ​​the irradiation spot by adjusting the laser emission unit 120 and the fθ lens 134, but is not limited to this. For example, the control unit 150 may adjust the light intensity using only the fθ lens 134, or it may adjust the light intensity by placing a light-reducing member such as an ND filter in the optical path, or it may adjust the light intensity by moving the stage 110 in the Z-axis direction.

[0057] (effect) As described above, according to the laser processing method and laser processing apparatus of one embodiment of the present invention, a hole is formed in a workpiece by rotating the polarization plane of a linearly polarized laser and scanning the laser around the surface of the workpiece. As a result, for example, when forming a hole with a circular opening, the shape of the opening of the hole can be made to approach a perfect circle. In this way, it is possible to form a hole with a highly accurate opening shape that is as intended, with less deviation and distortion of the opening shape.

[0058] In particular, when processing workpieces containing crystalline, difficult-to-process metal materials, or when the laser undergoes a large number of circulating scans, anisotropy in the degree of light absorption of the workpiece is likely to occur depending on the polarization state of the laser, making it more prone to shape deviation and distortion. Even in such cases, it is possible to form holes with minimal deviation and distortion of the aperture shape, and with high precision in the desired shape.

[0059] (mechanism) It is presumed that deviations and distortions in the opening shape can be reduced by the following mechanism. However, the mechanism is not limited to this.

[0060] Figure 4A is an explanatory diagram showing the case where the plane of polarization of the laser is not rotated, and Figure 4B is an explanatory diagram showing the case where the plane of polarization of the laser is rotated once during one full rotation of the laser.

[0061] For example, if the plane of polarization of the laser is not rotated, the relative relationship between the contour of the hole opening and the direction of the plane of polarization of the laser (polarization vector) differs at points a, b, and c, as shown in Figure 4A. Therefore, the processing efficiency at each point differs, and the processed shape is also slightly different.

[0062] On the other hand, if the plane of polarization of the laser is rotated once during one circular scan, the relative relationship between the contour of the hole opening and the direction of the plane of polarization of the laser (polarization vector) becomes the same at points a, b, and c, as shown in Figure 4B. As a result, the processing efficiency at each point becomes equivalent, making it easier to achieve a uniform processed shape, and the shape of the hole opening is expected to become closer to a perfect circle.

[0063] Note that in Figure 4B, for the sake of clarity, an example was shown where the plane of polarization of the laser rotates once during one circular scan of the laser. However, the same principle applies even when the plane of polarization rotates only slightly or more than once during one circular scan. In these cases, the total processing efficiency (processing history) becomes uniform at points a, b, and c during the repeated circular scans of the laser until a hole is drilled. As a result, it is possible to form a hole with a highly accurate aperture shape, with minimal shape deviation and distortion. [Examples]

[0064] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0065] [Example 1] A molybdenum plate (crystalline, 10 μm thick) was processed using the laser processing apparatus shown in Figure 3. Specifically, a molybdenum plate was placed on the stage of the laser processing apparatus described above. Then, using a galvanoscanner and an fθ lens, the following pulsed laser was scanned around the surface of the molybdenum plate in a circular motion, drawing a circle of a predetermined diameter, under the following irradiation conditions. This formed a tapered hole (diameter 30 μm on the laser incidence side, diameter 20 μm on the laser emission side, taper angle 26 degrees). The focal point of the pulsed laser was set on the surface of the molybdenum plate. Furthermore, the scan diameter and center position of the pulsed laser were kept constant during its orbit.

[0066] (Pulsed laser) Wavelength: 355nm Pulse width: 3.0 picoseconds Oscillation repetition frequency: 1.0kHz Output (Power): 0.84mW Pulse energy: 0.84 J

[0067] (Irradiation conditions for pulsed laser) Diameter of the irradiation spot on the surface of the molybdenum plate: 17 μm Light intensity per unit area at the illumination spot: 0.39 J / cm² 2 Laser scanning speed: 3 mm / second Laser spot spacing: 3 μm Laser spot overlap rate: 77.1% Laser scanning diameter (circular scanning): 30 μm Number of laser orbital scans: 590

[0068] The drilling process under the above conditions was performed by continuously rotating a λ / 2 wave plate, thereby continuously rotating the plane of polarization of the laser. The rotation direction of the laser's polarization plane was the same as the scanning direction. The roundness of the hole opening shape was measured by varying the total number of rotations R (R = 0, 1, 2, 3 times) of the λ / 2 wave plate during the drilling of one tapered hole. The roundness was calculated based on the formula described above.

[0069] Figure 5 shows the dependence of the roundness of the machined hole opening shape on the rotational speed R.

[0070] As shown in Figure 5, it can be seen that as the total rotational speed R of the λ / 2 wave plate increases, the roundness of the hole opening shape becomes smaller and improves.

[0071] [Example 2] The tapered hole drilling process was performed under the same conditions as in Example 1, except that the total number of rotations R of the λ / 2 wave plate during the process of drilling one tapered hole was increased to 144 times. This allowed for a more detailed examination of the relationship between the total number of rotations R of the λ / 2 wave plate and the roundness of the opening shape of the drilled hole. Then, the roundness of the hole opening shape was measured and plotted for each rotational speed R. Figure 6 shows the results of plotting the roundness against rotational speed R.

[0072] As shown in Figure 6, the roundness of the aperture shape decreased sharply from 0 rotations R (when the λ / 2 wave plate is not rotated) to 3 rotations, and improved to less than 1%. Furthermore, when the rotation speed R exceeded 3 rotations, the roundness of the aperture shape remained almost constant at 0.6-0.8%. This effect was confirmed by investigating up to 144 rotations R. [Industrial applicability]

[0073] The laser processing method and laser processing apparatus according to the present invention are useful for manufacturing electronic device components, such as support plates for electron microscopes. [Explanation of Symbols]

[0074] 10. Object to be processed 10a hole 20 lasers 100 Laser Processing Equipment 110 stages 120 Laser Emission Unit 130 Light guide section 131 Polarization direction rotation part 131a Polarization direction adjustment member 131b Rotating part 132 Beam size change section 133 Galvanometer Scanner 134 fθ lens 135a, 135b Miller 140 Imaging Unit 150 Control Unit

Claims

1. The process involves rotating the polarization plane of a linearly polarized laser and scanning the laser around the surface of the workpiece to form a hole in the workpiece. Laser processing method.

2. In the step of forming the hole, the polarization plane of the laser is rotated by one or more rotations. The laser processing method according to claim 1.

3. The laser is a pulsed laser with a wavelength of 600 nm or less. The laser processing method according to claim 1.

4. The pulse width of the pulsed laser is 10 picoseconds or less. The laser processing method according to claim 3.

5. The workpiece includes a difficult-to-process metal material. The laser processing method according to claim 1.

6. The aforementioned difficult-to-process metallic material contains molybdenum, The laser processing method according to claim 5.

7. A stage for placing the workpiece, A laser emission unit for emitting a linearly polarized laser, A light guide unit for guiding the laser emitted from the laser emission unit to the workpiece placed on the stage, It has, The light guide section is A polarization direction adjusting member for adjusting the angle of the polarization direction of the laser, When the laser is irradiated onto the surface of the workpiece, a rotating part for rotating the polarization direction adjustment member and Having Laser processing equipment.

8. The light guide unit further includes a light scanning unit for scanning the laser in a circular motion. The laser processing apparatus according to claim 7.

Images