Laser processing machine and method for forming a laser beam using the same

Abstract

A laser processing machine is disclosed that includes a light source configured to provide a laser beam, a beam expander including a birefringent material configured to birefringently form a first laser beam polarized in a first direction and a second laser beam polarized in a second direction perpendicular to the first direction, and a focusing lens configured to focus the first laser beam and the second laser beam on a workpiece, wherein the first laser beam and the second laser beam are focused at different depths from a surface of the workpiece.

Description

[Technical Field]

[0001] The present invention relates to a laser processing machine and a method for forming a laser beam using the same. [Background technology]

[0002] A laser processing machine is a device that uses a laser beam to groove, scribe, drill, dice, or cut wafers or other workpieces. Because the surface must be processed to a depth of 10-20 μm or more depending on the type of wafer, the greater the depth of focus of the laser processing machine, the more advantageous it is. This is because an insufficient depth of focus can prevent the wafer from being irradiated with a uniform beam size due to variations in the workpiece height and machine vibration, ultimately leading to a deterioration in processing quality.

[0003] Attempts have been made to increase the depth of focus by increasing the focal length of the focusing lens, but this has the drawback of increasing the diffraction limit and degrading the quality of the processing beam.

[0004] Therefore, there is a need for a technique that allows for increased depth of focus without degrading the quality of the processing beam. Summary of the Invention [Problem to be solved by the invention]

[0005] One technical problem to be solved by the present invention is to provide a laser processing machine that can increase the depth of focus without degrading the quality of the processing beam.

[0006] Another technical problem to be solved by the present invention is to provide a laser processing machine that can increase the processing speed by forming multiple focal points.

[0007] Another technical problem to be solved by the present invention is to provide a laser processing machine that can reduce the size of a laser beam while minimizing loss of the laser beam. [Means for solving the problem]

[0008] According to an embodiment of the present invention, there may be provided a laser processing machine comprising: a light source configured to supply a laser beam; a beam expander having a birefringent material configured to birefringence the laser beam to form a first laser beam polarized in a first direction and a second laser beam polarized in a second direction perpendicular to the first direction; and a focusing lens configured to focus the first laser beam and the second laser beam on a workpiece, wherein the first laser beam and the second laser beam are focused at different depths from the surface of the workpiece.

[0009] The beam expander may include a birefringent lens configured to receive the laser beam and form the first and second laser beams, a concave lens configured to refract the first and second laser beams, and a convex lens configured to refract the first and second laser beams that pass through the concave lens.

[0010] The birefringent lens may be a plano-convex lens having a planar and a convex surface, and the laser beam may be incident normal to the planar surface.

[0011] The distance between the first and second laser beams incident on the concave lens may be smaller than the distance between the first and second laser beams incident on the convex lens.

[0012] The beam expander may include a first lens configured to receive the laser beam and refract the received laser beam in a focusing direction, a birefringent plate configured to receive the laser beam that has passed through the first lens and form the first laser beam and the second laser beam, and a second lens configured to refract the first laser beam and the second laser beam.

[0013] The focal point of the laser beam may be formed between the first lens and the birefringent plate.

[0014] The first laser beam and the second laser beam may intersect inside the beam expander.

[0015] The laser processing machine may further include a diffractive optical element (DOE) positioned between the beam expander and the focusing lens and configured to convert the first laser beam and the second laser beam emitted from the beam expander into flat-top beams.

[0016] The laser processing machine may further comprise a wave plate configured to change the polarization direction of the laser beam so that the polarization direction of the laser beam forms a 45 degree angle with the optical axis of the birefringent material.

[0017] The difference in size between the first laser beam and the second laser beam focused on the workpiece may be within a predetermined range.

[0018] The distance between the first focal plane where the first laser beam is focused and the second focal plane where the second laser beam is focused can be 10 μm or more.

[0019] The birefringent material may have positive birefringence.

[0020] The first laser beam and the second laser beam imaged on the workpiece may have a rectangular beam shape with a major axis length at least nine times longer than the minor axis length.

[0021] According to an embodiment of the present invention, there may be provided a method for forming a laser beam using a laser processing machine including a light source, a beam expander including a birefringent material, and a focusing lens. The method includes the steps of: directing a laser beam provided from the light source to be incident on the beam expander; birefringently forming a first laser beam polarized in a first direction and a second laser beam polarized in a second direction perpendicular to the first direction using the beam expander; and focusing the first laser beam and the second laser beam on a workpiece using the focusing lens, wherein the first laser beam and the second laser beam are focused at different depths from the surface of the workpiece.

[0022] The beam expander may further include a birefringent lens, a concave lens, and a convex lens. Forming the first and second laser beams may include receiving the laser beams using the birefringent lens to form the first and second laser beams, refracting the first and second laser beams using the concave lens, and refracting the first and second laser beams that have passed through the concave lens using the convex lens.

[0023] The beam expander may further include a first lens, a birefringent plate, and a second lens. The step of forming the first laser beam and the second laser beam may include the steps of receiving the laser beam using the first lens and refracting the received laser beam in a focusing direction, receiving the laser beam that has passed through the first lens using the birefringent plate to form the first laser beam and the second laser beam, and refracting the first laser beam and the second laser beam using the second lens. [Effects of the Invention]

[0024] The disclosed technology may have the following effects, however, this does not mean that a specific embodiment must include all or only the following effects, and therefore the scope of the disclosed technology should not be understood as being limited thereby.

[0025] According to an embodiment of the present invention, by forming multiple focal points using two laser beams with mutually perpendicular polarization directions, the depth of focus can be increased without loss of energy and degradation of processing beam quality.

[0026] According to the embodiment of the present invention, the processing amount per unit time and the processing speed can be improved by using multiple beams. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a schematic diagram of a laser processing machine (1) according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram of a laser processing machine (1) according to an embodiment of the present invention. [Figure 3] FIG. 1 is a schematic diagram of a laser processing machine (1) according to another embodiment of the present invention. [Figure 4] 1 is a table showing the transmission pattern of the birefringent plate (135) and the multifocal spacing as a function of the angle of incidence of the laser beam (L) according to an embodiment of the present invention. [Figure 5] 2A-2C are diagrams illustrating a method of forming a first laser beam (L1) and a second laser beam (L2) according to an embodiment of the present invention. [Figure 6] 1 illustrates a laser beam directed at a workpiece according to an embodiment of the present invention. [Figure 7a] 1 is experimental data for a laser beam according to an embodiment of the present invention. [Figure 7b] 1 is experimental data for a laser beam according to an embodiment of the present invention. [Figure 7c] 1 is experimental data for a laser beam according to an embodiment of the present invention. [Figure 8] 1 is experimental data for a laser beam according to an embodiment of the present invention. [Figure 9] This is experimental data showing the images of two laser beams depending on the relationship between the polarization directions of the two laser beams. DETAILED DESCRIPTION OF THE INVENTION

[0028] The above description of the present invention does not include a complete listing of all aspects of the present invention. It should be understood that the present invention includes all methods, apparatuses, and systems that can be implemented from all appropriate combinations of the various aspects disclosed in the above summary and the following detailed description and claims. Furthermore, effects that can be obtained or predicted from embodiments of the present invention are directly or implicitly disclosed in the detailed description of embodiments of the present invention. For example, various effects predicted by embodiments of the present invention are disclosed in the detailed description below.

[0029] Aspects, features and advantages of specific embodiments of the present invention will become apparent during the course of the following description, taken in conjunction with the accompanying drawings.

[0030] The terms used herein will be briefly explained and the invention will be described in detail.

[0031] The terms used in the embodiments of the present invention are selected from currently widely used and most general terms possible, taking into consideration the functions of the present invention. However, these terms may change depending on the objectives of those skilled in the art, precedents, or the emergence of new technologies. Furthermore, in specific examples, there are terms arbitrarily selected by the applicant, and in this case, their meanings are explained in detail in the corresponding descriptions of the present disclosure. Therefore, the terms used in the present invention should be defined based on the meaning and overall content of the terms in the present invention, rather than simply the name of the term.

[0032] The embodiments of the present invention may be subject to various modifications and have various embodiments, and specific embodiments are shown in the drawings and described in detail in the detailed description. However, this does not limit the scope of protection to the specific embodiments, but should be understood to include all modifications, equivalents, and alternatives within the spirit and technical scope of the disclosure. If it is determined that a detailed description of related well-known technology may obscure the gist of the embodiments, the detailed description will be omitted.

[0033] Terms such as first and second may be used to describe various components, but the components should not be limited by these terms. These terms are used only to distinguish one component from another.

[0034] In this application, the terms "comprises" or "consists of" and the like specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described herein, and are not to be understood as excluding the possible presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0035] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily implement them with reference to the accompanying drawings. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein. In the drawings, parts not related to the description are omitted to simplify the description of the present invention, and like parts are designated by like reference numerals throughout this specification.

[0036] FIG. 1 is a schematic diagram of a laser processing machine according to an embodiment of the present invention.

[0037] Referring to Figure 1, the laser processing machine (1) may include a light source (110), a wave plate (120), a beam expander (130), a beam shaping unit (140), and an imaging unit (150). The laser processing machine (1) may process a workpiece (10) using laser beams (L1, L2). For example, the laser processing machine (1) may groove or scribe the workpiece (10) using the laser beams (L1, L2). The workpiece (10) may be a wafer or an ABF (Ajinomoto Build-up Film) substrate.

[0038] The light source (110) may generate a laser beam (L). The laser beam (L) may be a Gaussian beam. Alternatively, the laser beam (L) may be a flat-top beam. The light source (110) may output the laser beam (L). The light source (110) may transmit the laser beam (L) through a wave plate (120).

[0039] The wave plate (120) can change the polarization direction of the laser beam (L). The wave plate (120) can adjust the polarization direction of the laser beam (L) so that the polarization direction of the laser beam (L) forms a predetermined angle (e.g., 45 degrees) with the optical axis of the birefringent material included in the beam expander (130). The wave plate (120) can be a half-wave plate (HWP).

[0040] The beam expander (130) may receive the laser beam (L) that has passed through the wave plate (120). The beam expander (130) may form a first laser beam (L1) and a second laser beam (L2) from the laser beam (L). The beam expander (130) may birefringently form the first laser beam (L1) and the second laser beam (L2). The laser beam (L) that has entered the beam expander (130) may be birefringent while passing through the beam expander (130) and may be split into the first laser beam (L1) and the second laser beam (L2). The first laser beam (L1) may be an ordinary ray (o-ray), and the second laser beam (L2) may be an extraordinary ray (e-ray). Conversely, the first laser beam (L1) may be an extraordinary ray, and the second laser beam (L2) may be an ordinary ray.

[0041] The polarization direction of the first laser beam (L1) may be a first direction. The polarization direction of the second laser beam (L2) may be a second direction perpendicular to the first direction. Therefore, the first laser beam (L1) and the second laser beam (L2) will not interfere with each other. In other words, there may be no coherence between the first laser beam (L1) and the second laser beam (L2). No energy loss will occur due to interference between the first laser beam (L1) and the second laser beam (L2). The first direction and the second direction may form a 45-degree angle with the polarization direction of the laser beam (L).

[0042] The beam expander (130) may include a birefringent material, a concave lens, and a convex lens. The birefringent material may be a birefringent lens or a birefringent plate. The birefringent material may have positive or negative birefringence. The beam expander (130) may be implemented as a BET (Beam Expanding Telescope). The birefringent lens may be a plano-convex lens having a plano and a convex surface. The birefringent plate may have a plano surface. In one embodiment, the beam expander (130) may be comprised of a birefringent material, a concave lens, and a convex lens. In another embodiment, the beam expander (130) may be comprised of a birefringent material and two convex lenses. In yet another embodiment, the beam expander (130) may be comprised of a birefringent material, multiple concave lenses, and multiple concave lenses.

[0043] The beam shaping unit (140) may shape or form the shapes of the first laser beam (L1) and the second laser beam (L2). The beam shaping unit (140) may convert the first laser beam (L1) and the second laser beam (L2) into flat-top beams. The first laser beam (L1) and the second laser beam (L2) may be converted from Gaussian beams into flat-top beams by the beam shaping unit (140). The beam shaping unit (140) may include a diffractive optical element (DOE). The beam shaping unit (140) may include an aspherical lens.

[0044] The imaging unit (150) can image the first laser beam (L1) and the second laser beam (L2) onto the workpiece (10). The imaging unit (150) can image the first laser beam (L1) onto a first imaging plane (P1). The focal point of the first laser beam (L1) can be formed at the first imaging plane (P1). The first imaging plane (P1) can be the surface of the workpiece (10). The imaging unit (150) can image the second laser beam (L2) onto a second imaging plane (P2). The focal point of the second laser beam (L2) can be formed at the second imaging plane (P2). The distance (d) between the first imaging plane (P1) and the second imaging plane (P2) can be 10 μm or more. That is, the distance between the focal point of the first laser beam (L1) and the focal point of the second laser beam (L2) can be 10 μm or more. The imaging unit (150) can include at least one lens. The imaging unit (150) can include a focusing lens.

[0045] The laser processing machine (1) can generate multiple beams (L1, L2) from a single laser beam (L). The laser processing machine (1) can increase the depth of focus (DOF) of the laser beam (L) by multi-focusing the multiple beams (L1, L2) onto two imaging planes (P1, P2). When the distance (d) between the first imaging plane (P1) and the second imaging plane (P2) is 10 μm or more, the depth of focus (DOF) can be increased by 10 μm or more. Because the first laser beam (L1) and the second laser beam (L2) do not interfere with each other, independent imaging quality can be maintained.

[0046] FIG. 2 is a schematic diagram of a laser processing machine (1) according to an embodiment of the present invention.

[0047] Referring to Figure 2, the laser processing machine (1) may include a beam expander (130), a beam shaping unit (140), and an imaging unit (150). The beam expander (130) may include a birefringent lens (131), a concave lens (132), and a convex lens (133). The beam shaping unit (140) may be a diffractive optical element (DOE). The imaging unit (150) may be a focusing lens.

[0048] The beam expander 130 can receive a laser beam L. The laser beam L can be output from the light source 110, pass through the wave plate 120, and enter the beam expander 130. The laser beam L can be incident perpendicularly on the plane of the birefringent lens 131.

[0049] The beam expander (130) may generate and output a first laser beam (L1) and a second laser beam (L2) from the laser beam (L). The beam expander (130) may form the first laser beam (L1) and the second laser beam (L2) using a birefringent lens (131). Due to the birefringence properties of the birefringent lens (131), the laser beam (L) passing through the birefringent lens (131) may be split into the first laser beam (L1) and the second laser beam (L2). For example, the first laser beam (L1) may be an ordinary ray, and the second laser beam (L2) may be an extraordinary ray.

[0050] The polarization direction of the first laser beam (L1) and the polarization direction of the second laser beam (L2) may be perpendicular. For example, the polarization direction of the laser beam (L) may be at an angle of 45 degrees to the optical axis of the birefringent lens (131), and the polarization direction of the first laser beam (L1) and the polarization direction of the second laser beam (L2) may be perpendicular. When the polarization direction of the first laser beam (L1) and the polarization direction of the second laser beam (L2) are perpendicular, interference between the first laser beam (L1) and the second laser beam (L2) does not occur. Therefore, energy loss due to interference between the first laser beam (L1) and the second laser beam (L2) can be prevented.

[0051] The distance between the two beams (L1, L2) output by the beam expander (130) can determine the distance between the focal points of the two beams (L1, L2) (i.e., the depth of focus). The distance between the two beams (L1, L2) can be determined based on the birefringent lens (131), the concave lens (132), and the convex lens (133). The distance between the two beams (L1, L2) can be adjusted according to the sizes or refractive indices of the birefringent lens (131), the concave lens (132), and the convex lens (133). For example, the distance between the two beams (L1, L2) within the beam expander (130) can increase along the propagation direction of the two beams (L1, L2). The concave lens (132) and the convex lens (133) can increase the depth of focus by increasing the distance between the two beams (L1, L2).

[0052] The beam shaping unit (140) may shape the two beams (L1, L2) to have a predetermined size or shape. The beam shaping unit (140) may shape the two beams (L1, L2) to be flat-top beams. The beam shaping unit (140) may shape the two beams (L1, L2) to have a rectangular shape with different lengths in the horizontal and vertical directions. For example, at the imaging plane, the two beams (L1, L2) may have a major axis length of 50 μm and a minor axis length of 5 μm. At the imaging plane, the two beams (L1, L2) may have a rectangular beam shape with the major axis length at least 9 times longer than the minor axis length.

[0053] The imaging unit (150) can image the two beams (L1, L2) respectively onto the workpiece (10). The imaging unit (150) can image the first laser beam (L1) onto a first imaging plane (P1). The focal point of the first laser beam (L1) can be formed at the first imaging plane (P1). The first imaging plane (P1) can be inside the workpiece (10). The imaging unit (150) can image the second laser beam (L2) onto a second imaging plane (P2). The focal point of the second laser beam (L2) can be formed at the second imaging plane (P2). The second imaging plane (P2) can be on the surface of the workpiece (10). The distance between the focal point of the first laser beam (L1) and the focal point of the second laser beam (L2) can be 10 μm or more. That is, the focal depth of the laser beam (L) can be increased by 10 μm or more. Therefore, even if the depth of the workpiece (10) changes, a beam with uniform characteristics (e.g., energy, size, shape, etc.) can be irradiated onto the workpiece (10). Furthermore, the processing speed can also be improved.

[0054] The central axes of the birefringent lens (131), the concave lens (132), and the convex lens (133) may be positioned on the same axis (C). This allows for a compact design of the beam expander (130). The central axes of the beam shaping section (140) and the imaging section (150) may be positioned on the same axis (C) as the central axes of the birefringent lens (131), the concave lens (132), and the convex lens (133). However, this is not limited to the above, and it should be noted that in other embodiments, the central axes of at least some of the birefringent lens (131), the concave lens (132), the convex lens (133), the beam shaping section (140), and the imaging section (150) may be positioned on different axes.

[0055] FIG. 3 is a schematic diagram of a laser processing machine (1) according to another embodiment of the present invention.

[0056] Referring to Figure 3, the beam expander (130) may include a first lens (134), a birefringent plate (135), and a second lens (136). The first lens (134) may receive the laser beam (L) and refract it in a focusing direction. For example, the first lens (134) may refract the laser beam (L) incident parallel to the optical axis of the first lens (134) by 45 degrees. The focal point of the laser beam (L) may be formed between the first lens (134) and the birefringent plate (135). The first lens (134) may be a convex lens.

[0057] The birefringent plate (135) can receive the laser beam (L) that has passed through the first lens (134). The laser beam (L) can be incident on the birefringent plate (135) at an incident angle within a predetermined range. For example, the predetermined range can be from 0 degrees to 90 degrees.

[0058] The birefringent plate (135) can form a first laser beam (L1) and a second laser beam (L2) from the laser beam (L). Due to the birefringence properties of the birefringent plate (135), the laser beam (L) can be split into the first laser beam (L1) and the second laser beam (L2) while passing through the birefringent plate (135). For example, the first laser beam (L1) can be an ordinary ray, and the second laser beam (L2) can be an extraordinary ray.

[0059] The polarization direction of the first laser beam (L1) and the polarization direction of the second laser beam (L2) may be perpendicular. For example, if the polarization direction of the laser beam (L) is at a 45-degree angle with the optical axis of the birefringent plate (135), the polarization direction of the first laser beam (L1) and the polarization direction of the second laser beam (L2) may be perpendicular. If the polarization direction of the first laser beam (L1) and the polarization direction of the second laser beam (L2) are perpendicular, interference between the first laser beam (L1) and the second laser beam (L2) will not occur. Therefore, energy loss due to interference between the first laser beam (L1) and the second laser beam (L2) can be prevented.

[0060] The distance between the focal points of the two beams (L1, L2) can be determined based on the thickness (1351) of the birefringent plate (135). For example, as the thickness (1351) of the birefringent plate (135) increases, the distance between the focal points of the two beams (L1, L2) can increase.

[0061] The second lens (136) may refract the first laser beam (L1) and the second laser beam (L2). The second lens (136) may converge the first laser beam (L1) and the second laser beam (L2) so that they do not diverge beyond a certain range. This may allow the first laser beam (L1) and the second laser beam (L2) that have passed through the second lens (136) to intersect. For example, the first laser beam (L1) and the second laser beam (L2) may intersect inside the beam expander (130).

[0062] The beam shaping unit (140) has been described above with reference to FIG. 2 and will not be described again.

[0063] The imaging unit (150) can image the two beams (L1, L2) respectively onto the workpiece (10). The imaging unit (150) can image the first laser beam (L1) onto a first imaging plane (P1). The focal point of the first laser beam (L1) can be formed at the first imaging plane (P1). The first imaging plane (P1) can be the surface of the workpiece (10). The imaging unit (150) can image the second laser beam (L2) onto a second imaging plane (P2). The focal point of the second laser beam (L2) can be formed at the second imaging plane (P2). The second imaging plane (P2) can be inside the workpiece (10). The distance between the focal point of the first laser beam (L1) and the focal point of the second laser beam (L2) can be 10 μm or more. That is, the focal depth of the laser beam (L) can be increased by 10 μm or more. Therefore, even if the depth of the workpiece (10) changes, a beam with uniform characteristics (e.g., energy, size, shape, etc.) can be irradiated onto the workpiece (10). Furthermore, the processing speed can be improved compared to when a single beam is used. Since the two beams (L1, L2) do not interfere with each other, energy loss can also be prevented.

[0064] The central axes of the first lens (134), the birefringent plate (135), and the second lens (136) may be positioned on the same axis (C). This allows for a compact design of the beam expander (130). The central axes of the beam shaping section (140) and the imaging section (150) may be positioned on the same axis (C) as the central axes of the first lens (134), the birefringent plate (135), and the second lens (136). However, this is not limited to the above, and it should be noted that in other embodiments, the central axes of at least some of the first lens (134), the birefringent plate (135), the second lens (136), the beam shaping section (140), and the imaging section (150) may be positioned on different axes.

[0065] FIG. 4 is a table showing the transmission pattern of the birefringent plate (135) and the multifocal spacing as a function of the angle of incidence of the laser beam (L) according to an embodiment of the present invention.

[0066] 4, the angle of incidence (θ) of the laser beam (L) incident on the birefringent plate (135) can be related to the multifocal distance, which can refer to the distance (d) between the first image plane (P1) and the second image plane (P2), i.e., the depth of focus.

[0067] For example, when the incident angle (θ) is a first angle (θ1), the multifocal spacing can be a first distance (d1). When the incident angle (θ) is a second angle (θ2), the multifocal spacing can be a second distance (d2). The first angle (θ1) can be less than the second angle (θ2), and the first distance (d1) can be less than the second distance (d2). That is, as the incident angle (θ) increases, the distance between the first laser beam (L1) and the second laser beam (L2) transmitted through the birefringent plate (135) increases, and the multifocal spacing increases accordingly. Therefore, the incident angle (θ) can be determined based on the multifocal spacing. For example, if the multifocal spacing needs to be increased for a specific purpose, the incident angle (θ) can be increased. Conversely, if the multifocal spacing needs to be decreased, the incident angle (θ) can be decreased.

[0068] FIG. 5 is a diagram illustrating a method for forming a first laser beam (L1) and a second laser beam (L2) according to an embodiment of the present invention.

[0069] Referring to Figure 5, the laser beam (L) emitted from the light source (110) may pass through a polarizing plate (120). As it passes through the polarizing plate (120), the polarization direction of the laser beam (L) may be changed. For example, the polarization direction of the laser beam (L) passing through the polarizing plate (120) may be at a 45-degree angle with the optical axis (X) of the birefringent material (137). The polarizing plate (120) may be a half-wave plate.

[0070] The birefringent material (137) can birefringently polarize the laser beam (L) to form a first laser beam (L1) and a second laser beam (L2). The birefringent material (137) can be a birefringent lens (131) or a birefringent plate (135). When the polarization direction of the laser beam (L) is at 45 degrees to the optical axis (X) of the birefringent material (137), the polarization direction (P_L1) of the first laser beam (L1) and the polarization direction (P_L2) of the second laser beam (L2) can be perpendicular.

[0071] 6A and 6B show laser beams irradiated onto a workpiece according to an embodiment of the present invention, where Fig. 6A shows a first laser beam (L1) and Fig. 6B shows a second laser beam (L2).

[0072] Referring to FIG. 6, the first laser beam (L1) and the second laser beam (L2) may have rectangular beam shapes. The first laser beam (L1) and the second laser beam (L2) may have beam spots of the same size. The polarization direction of the first laser beam (L1) may be perpendicular to the polarization direction of the second laser beam (L2). For example, the polarization direction of the first laser beam (L1) may be in the y-axis direction, and the polarization direction of the second laser beam (L2) may be in the x-axis direction. Meanwhile, in other embodiments, the polarization direction of the first laser beam (L1) may be in the x-axis direction, and the polarization direction of the second laser beam (L2) may be in the y-axis direction.

[0073] The length of the first laser beam (L1) in the major axis direction may be at least 9 times longer than the length of the minor axis direction. The length of the second laser beam (L2) in the major axis direction may be at least 9 times longer than the length of the minor axis direction. The difference in size between the first laser beam (L1) and the second laser beam (L2) irradiated onto the workpiece (10) may be within a predetermined range.

[0074] Figures 7a, 7b, and 7c show experimental data for laser beams according to an embodiment of the present invention. Figure 7a shows experimental data when a first laser beam polarized in the x-axis direction is irradiated onto a workpiece. Figure 7b shows experimental data when a second laser beam polarized in the y-axis direction is irradiated onto a workpiece. Figure 7c shows experimental data when both the first and second laser beams are irradiated onto a workpiece. In Figures 7a, 7b, and 7c, z represents the relative distance from the focusing lens included in the imaging unit (150) in the direction toward the workpiece.

[0075] Figure 7a shows the image, waveform, and size of the first laser beam as a function of the relative distance (z). Observing the image and size of the first laser beam, the focus of the first laser beam was maintained at a relative distance (z) of 49.885 μm to 49.895 μm. The focal depth of the first laser beam was measured to be 10 μm.

[0076] Figure 7b shows the image, waveform, and size of the second laser beam as a function of the relative distance (z). Observing the image and size of the second laser beam, the focus of the second laser beam was maintained at a relative distance (z) of 49.875 μm to 49.885 μm. The depth of focus of the second laser beam was measured to be 10 μm.

[0077] 7c shows the image, waveform, and size of the combined beam from the first and second laser beams as a function of the relative distance (z). The combination of the first and second laser beams can be achieved by irradiating the workpiece with both the first and second laser beams.

[0078] Referring to Figure 7c, the focus of the combined beam was maintained at a relative distance (z) of 49.875 μm to 49.895 μm. The depth of focus of the combined beam was measured to be 20 μm. That is, when both the first and second laser beams were used, the depth of focus was twice as large as when only the first or second laser beam was used. Increasing the depth of focus of the laser beam means that the depth range that can be irradiated with a uniformly sized beam increases. For example, in grooving, the depth of a groove in a wafer can be gradually increased by the laser beam. In this case, the more consistent the groove width is depending on the groove depth, the better the processing quality. Increasing the depth of focus allows a uniformly sized beam to be irradiated on the wafer surface even when the groove depth changes, which is advantageous for processing quality.

[0079] FIG. 8 shows experimental data for a laser beam according to an embodiment of the present invention.

[0080] The x-axis of the graph (80) in FIG. 8 represents the depth direction of the workpiece, and the y-axis represents the lateral position. Referring to the graph (80), it can be seen that the focal points of the two laser beams are formed at different depths. The laser processing machine (1) can groove or scribe the workpiece (10) based on a multi-focus method. Alternatively, it can perform drilling or dicing. Because the laser processing machine (1) uses multiple beams, it has the advantageous effects of a higher processing volume per unit time and a higher processing speed compared to conventional processing machines that use a single beam. However, it should be noted that the units shown in FIG. 8 are merely one embodiment, and the present invention is not limited to these specific values.

[0081] Figure 9 shows experimental data showing the images of two laser beams depending on the polarization direction of the two laser beams. Specifically, Figure 9 shows the images when each laser beam is irradiated independently onto the workpiece, and when both laser beams are irradiated together.

[0082] Referring to FIG. 9, it can be seen that interference fringes appear when multiple focal points are formed by a first laser beam and a second laser beam having the same polarization direction. On the other hand, when the polarization direction of the first laser beam is perpendicular to the polarization direction of the second laser beam, interference fringes do not appear even when multiple focal points are formed. The laser processing machine (1) according to the present invention can use two beams (L1, L2) whose polarization directions are perpendicular to each other. Therefore, interference between the two beams (L1, L2) does not occur, and no energy loss due to interference occurs. As a result, no degradation in processing quality is observed.

[0083] On the other hand, it should be noted that the laser processing machine (1) according to the present invention can be used not only for drilling but also for other processing using a laser beam, such as cutting or etching.

[0084] Although preferred embodiments of the present invention have been shown and described above, the present invention is not limited to the specific embodiments described above, and various modifications can be made by those skilled in the art to which the present invention pertains without departing from the gist of the present invention as claimed in the claims, and these modifications should not be understood separately from the technical spirit or possibilities of the present invention.

Claims

1. a light source configured to provide a laser beam; a beam expander comprising a birefringent material configured to birefringently expand the laser beam to form a first laser beam polarized in a first direction and a second laser beam polarized in a second direction perpendicular to the first direction; a focusing lens configured to focus the first laser beam and the second laser beam on a workpiece; Equipped with A laser processing machine, wherein the first laser beam and the second laser beam are focused at different depths from the surface of the workpiece.

2. The beam expander is a birefringent lens configured to receive the laser beam and form the first laser beam and the second laser beam; a concave lens configured to refract the first laser beam and the second laser beam; a convex lens configured to refract the first laser beam and the second laser beam that pass through the concave lens; The laser processing machine according to claim 1 , comprising:

3. the birefringent lens is a plano-convex lens having a planar surface and a convex surface; The laser processing machine according to claim 2 , wherein the laser beam is incident perpendicularly to the plane.

4. 3. The laser processing machine according to claim 2, wherein a distance between the first laser beam and the second laser beam incident on the concave lens is smaller than a distance between the first laser beam and the second laser beam incident on the convex lens.

5. The beam expander is a first lens configured to receive the laser beam and refract the received laser beam in a focusing direction; a birefringent plate configured to receive the laser beam that has passed through the first lens and form the first laser beam and the second laser beam; a second lens configured to refract the first laser beam and the second laser beam; The laser processing machine according to claim 1 , comprising:

6. 6. The laser processing machine according to claim 5, wherein the focal point of the laser beam is formed between the first lens and the birefringent plate.

7. 6. The laser processing machine according to claim 5, wherein the first laser beam and the second laser beam intersect inside the beam expander.

8. 2. The laser processing machine according to claim 1, further comprising a diffractive optical element (DOE) positioned between the beam expander and the focusing lens and configured to convert the first laser beam and the second laser beam emitted from the beam expander into flat-top beams.

9. 2. The laser processing machine according to claim 1, further comprising a wave plate configured to change the polarization direction of the laser beam so that the polarization direction of the laser beam forms a 45 degree angle with the optical axis of the birefringent material.

10. 2. The laser processing machine according to claim 1, wherein a difference in size between the first laser beam and the second laser beam focused on the workpiece is within a predetermined range.

11. 2. The laser processing machine according to claim 1, wherein a distance between a first focal plane on which the first laser beam is focused and a second focal plane on which the second laser beam is focused is 10 μm or more.

12. The laser processing machine according to claim 1 , wherein the birefringent material has a positive birefringence.

13. 2. The laser processing machine according to claim 1, wherein the first laser beam and the second laser beam formed on the workpiece have a rectangular beam shape with a major axis length at least nine times longer than the minor axis length.

14. 1. A method for forming a laser beam using a laser processing machine including a light source, a beam expander having a birefringent material, and a focusing lens, comprising: directing a laser beam provided by the light source so that it is incident on the beam expander; forming, by using the beam expander, a first laser beam polarized in a first direction and a second laser beam polarized in a second direction perpendicular to the first direction; using the focusing lens to focus the first laser beam and the second laser beam on a workpiece; Equipped with The method, wherein the first laser beam and the second laser beam are focused at different depths from the surface of the workpiece.

15. the beam expander further comprises a birefringent lens, a concave lens, and a convex lens; The step of forming the first laser beam and the second laser beam includes: receiving the laser beam using the birefringent lens to form the first laser beam and the second laser beam; refracting the first laser beam and the second laser beam using the concave lens; refracting the first laser beam and the second laser beam that have passed through the concave lens using the convex lens; The method of claim 14, comprising:

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