Optical device and modified region forming method

Abstract

To provide an optical device in which the inner diameter of a through-hole formed by wet-etching a modified region formed by condensing and irradiating a pulse laser beam can be made nearly uniform.SOLUTION: The optical device includes a first axicon lens 20 and a light collection optical system 40 that collects pulsed laser light, and a convergence position of a convergent beam B2 converged by the light collection optical system 40 is deviated from a plane 101 that is perpendicular to an optical axis A and includes a center of a Bessel beam region 100 formed by the first axicon lens 20 and a second axicon lens 40 when the light collection optical system 40 is replaced with an optical system having no light collection characteristics.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an optical device and a method for forming a modified region. [Background technology]

[0002] Interposers and glass core substrates (hereinafter referred to as "interposers, etc.") that have through electrodes formed on the front and back surfaces of a plate-like substrate to ensure electrical continuity of wiring patterns are widely used in electronic devices because they allow for high-density mounting of electronic components. Examples of materials for interposers, etc. include glass, epoxy resin, and silicon. Among these, glass is considered to be an excellent material for interposers, etc., because it has advantages such as excellent high-frequency characteristics, high flatness, little warping, the ability to process large areas, and the ability to mass-produce at low cost, as well as the established photolithography technology for forming wiring patterns.

[0003] To create an interposer or the like using glass, it is necessary to form a large number of fine through-holes (TGV: Through Glass Via) in a flat glass substrate. Laser light is generally used to form such through-holes, and various techniques have been proposed in the past (for example, Patent Document 1).

[0004] In the through-hole forming method described in Patent Document 1, pulsed laser light having a pulse width of picoseconds to nanoseconds is irradiated onto a glass substrate, causing localized destruction in the glass substrate and forming a filament-like channel (corresponding to the modified region).The filament-like channel is then sandwiched between a pair of electrodes, and a high voltage is applied to the pair of electrodes, thereby expanding the filament-like channel to the desired hole diameter.

[0005] One example of a method for forming the desired through-hole in the location where the modified region is formed is to apply a high voltage to a pair of electrodes, as in the through-hole formation method described in Patent Document 1. However, a more generally adopted method is wet etching using a hydrofluoric acid-based etchant, which is a simpler method that allows for mass production. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2013-534868 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the prior art, if the light intensity of the laser light irradiated onto the glass substrate near the center of the substrate in the direction in which the through holes are formed is not sufficiently greater than the light intensity at the surface of the substrate, when the glass substrate is irradiated with pulsed laser light and then wet etching is performed to form through holes, the inner diameter of the through holes near the center of the glass substrate in the direction in which the through holes are formed becomes smaller than the inner diameter of the through holes near the surface, making it difficult to form through holes with a uniform inner diameter.

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide an optical device in which the inner diameter of the through hole after wet etching can be made closer to uniform by appropriately arranging the optical system in the optical device.

[0009] In addition, the present invention has been made in consideration of the above circumstances, and aims to provide a method for forming a modified area that can make the inner diameter of a through hole after wet etching closer to uniform by appropriate means of irradiating an object with laser light. [Means for solving the problem]

[0010] (1) An optical device of this application example is an optical device that forms a modified region extending from the front surface to the back surface of an article as a workpiece by irradiating a pulsed laser beam with a focused beam at a position where a modified region is to be formed on the article, the optical device comprising: a first axicon lens arranged on the incident side in the optical axis direction of the pulsed laser beam; a second axicon lens arranged on the exit side in the optical axis direction; and a focusing optical system that converges the pulsed laser beam, wherein, when the focusing optical system is replaced with an optical system that does not have focusing properties, the convergence position of the convergent beam converged by the focusing optical system is perpendicular to the optical axis and deviated from a plane that includes the center of a Bessel beam region formed by the first axicon lens and the second axicon lens.

[0011] (2) In the optical device of this application example, it is preferable that the convergence position of the convergent beam be offset from a plane including the center of the Bessel beam region to a side opposite to a side on which the second axicon lens is disposed, in the optical axis direction.

[0012] (3) In the optical device of this application example, it is preferable that the convergence position of the convergent beam is biased to a position away from the rear surface of the article.

[0013] (4) In the optical device of this application example, it is preferable that the convergence position of the convergent beam be biased, in the optical axis direction, from a plane including the center of the Bessel beam region toward a side where the second axicon lens is disposed.

[0014] (5) In the optical device of this application example, it is preferable that the conical surface of the second axicon lens faces the incident side in the optical axis direction.

[0015] (6) In the optical device of this application example, it is preferable that the light intensity of the pulsed laser light at the surface of the article is smaller than the light intensity of the pulsed laser light at a center position between the surface and the back surface in the optical axis direction of the article, and is greater than a threshold light intensity that forms a modified region in the article.

[0016] (7) In the optical device of this application example, it is preferable that the focusing optical system includes one or more optical elements arranged on the optical axis of the pulsed laser beam, and a focusing position adjustment mechanism that adjusts the focusing position of the pulsed laser beam that has passed through the focusing optical system.

[0017] (8) In the optical device of this application example, it is preferable that the optical device further includes a beam shape correction mechanism that is arranged on the incident side of the first axicon lens and corrects the beam shape of the pulsed laser light.

[0018] (9) In the optical device of this application example, it is preferable that the beam shape correction mechanism is an ellipticity correction optical system that corrects the ellipticity of the beam of the pulsed laser light and has a rotation mechanism that rotates around the optical axis of the pulsed laser light.

[0019] (10) A modified region formation method of this application example is a method for forming a modified region extending from the front surface to the back surface of an article as a workpiece by irradiating a pulsed laser beam onto a position where a modified region is to be formed on the article, the method comprising the steps of: making the pulsed laser beam incident on a first axicon lens arranged on an incident side in the optical axis direction of the pulsed laser beam; making the pulsed laser beam incident on a focusing optical system arranged on an exit side of the first axicon lens in the optical axis direction; and making the pulsed laser beam incident on a second axicon lens arranged on the exit side of the focusing optical system in the optical axis direction, wherein, when the focusing optical system is replaced with an optical system without focusing properties, the convergence position of the convergent beam converged by the focusing optical system is perpendicular to the optical axis and deviated from a plane including the center of a Bessel beam region formed by the first axicon lens and the second axicon lens. [Effects of the Invention]

[0020] The optical device of the present invention includes a first axicon lens arranged on the incident side in the optical axis direction of pulsed laser beam, a second axicon lens arranged on the exit side in the optical axis direction, and a focusing optical system that focuses the pulsed laser beam, and when the focusing optical system is replaced with an optical system that does not have focusing properties, the focusing position of the convergent beam focused by the focusing optical system is deviated from a plane that is perpendicular to the optical axis and that includes the center of the Bessel beam region formed by the first axicon lens and the second axicon lens.

[0021] According to the present invention, an optical device can be provided in which the inner diameter of a through hole formed by wet etching a modified region formed by irradiating a focused pulsed laser beam can be made closer to uniform.

[0022] A modified region forming method of the present invention includes the steps of: making a pulsed laser beam incident on a first axicon lens arranged on the incident side in the optical axis direction of the pulsed laser beam; making the pulsed laser beam incident on a focusing optical system arranged on the exit side of the first axicon lens; and making the pulsed laser beam incident on a second axicon lens arranged on the exit side of the focusing optical system, wherein, when the focusing optical system is replaced with an optical system that does not have focusing properties, the convergence position of a convergent beam converged by the focusing optical system is perpendicular to the optical axis and deviated from a plane including the center of a Bessel beam region formed by the first axicon lens and the second axicon lens.

[0023] According to the present invention, a modified region forming method can be provided that can make the inner diameter of a through hole formed by wet etching a modified region formed by irradiating it with focused pulsed laser light closer to uniform. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram for explaining an optical device 1 according to the first embodiment. [Figure 2]FIG. 2 is a diagram for explaining the arrangement of the first axicon lens 20, the second axicon lens 30, and the focusing optical system 40 provided in the optical device 1 according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing a change in the spot diameter of the laser light L on the glass substrate 11 when the cone angle of the second axicon lens 30 is changed in the optical device 1 according to the first embodiment. [Figure 4] FIG. 4 is a diagram illustrating a state in which the convergence position of the convergent beam B2 converged by the focusing optical system 40 is biased. [Figure 5] FIG. 5 is a diagram showing the results of calculating the light intensity distribution in the through-hole formation direction (depth direction) of the glass substrate 11 in the optical device 1 according to the first embodiment. [Figure 6] FIG. 6 is a diagram for explaining the arrangement of the first axicon lens 20, the second axicon lens 30, and the focusing optical system 40 provided in the optical device 2 according to the second embodiment. [Figure 7] FIG. 7 is a diagram showing a change in the spot diameter of the laser light L on the glass substrate 11 when the cone angle of the second axicon lens 30 is changed in the optical device 2 according to the second embodiment. [Figure 8] FIG. 8 is a diagram showing the results of calculating the light intensity distribution in the through-hole formation direction (depth direction) of the glass substrate 11 in the optical device 2 according to the second embodiment. [Figure 9] FIG. 9 is a diagram showing the relationship between the focal length and the light intensity ratio in the light collecting optical system 40 provided in the optical device 2 according to the second embodiment. [Figure 10] FIG. 10 is a diagram showing the results of calculating the light intensity distribution in the through-hole formation direction (depth direction) of the glass substrate 11 in the optical device 2 according to the second embodiment. [Figure 11] FIG. 11 is a diagram for explaining the third axicon lens 32 that can be provided in the optical device 2 according to the second embodiment. [Figure 12] FIG. 12 is a diagram for explaining a light-collecting optical system 40 that can be provided in the optical device 2 according to the second embodiment. [Figure 13] FIG. 13 is a diagram for explaining the beam shape correction mechanism provided in the optical device 1 according to the first embodiment or the optical device 2 according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] The optical device and modified region forming method according to the present invention will be described below based on the embodiments shown in the drawings. Note that not all of the elements and their combinations described in the embodiments are necessarily essential to the solution of the present invention. Furthermore, the drawings are created for the purpose of explaining the invention, and do not accurately depict the components included in the invention.

[0026] [Embodiment 1] 1.Optical device 1 First, an optical device 1 according to embodiment 1 will be described. Fig. 1 is a diagram shown for explaining the optical device 1 according to embodiment 1. Fig. 2 is a diagram shown for explaining the arrangement of a first axicon lens 20, a second axicon lens 30, and a focusing optical system 40 provided in the optical device 1 according to embodiment 1.

[0027] As shown in Figures 1 and 2, the optical device 1 of embodiment 1 is an apparatus that forms a modified region extending from the front surface to the back surface of an article 10 as a workpiece by concentrating and irradiating pulsed laser light L (in the following description, "pulsed laser light L" may be simply referred to as "laser light L") at a position where a modified region is to be formed on the article 10.

[0028] Examples of the article 10 include a glass substrate, a silicon substrate, an epoxy resin substrate, etc. The shape and material of the article 10 are not important as long as the crystalline structure of the article 10 can be modified by laser light and through-holes can be formed. In the following description, the article 10 will be described as a glass substrate 11.

[0029] 1 and 2, the optical device 1 includes a first axicon lens 20, a second axicon lens 30, and a focusing optical system 40. The optical device 1 may include a laser light irradiation unit 60 that emits laser light L, a beam shape correction mechanism 70 that adjusts the beam shape of the laser light L, and a mirror 80 that reflects the laser light L emitted by the laser light irradiation unit 60 and guides it to the beam shape correction mechanism 70.

[0030] Each element constituting the optical device 1 will be described below.

[0031] The laser light irradiation unit 60 includes a laser oscillator (a femtosecond pulse laser oscillator or a picosecond pulse laser oscillator) that emits an ultrashort pulse laser light. Here, "ultrashort pulse laser light" refers to a pulse laser light having a pulse width of, for example, 10 psec or less. The laser oscillator outputs a pulse laser light having a wavelength of 500 nm to 2000 nm.

[0032] The first axicon lens 20 is disposed on the incident side in the direction of the optical axis A of the laser light L. There is no particular limitation on the size of the cone angle (apex angle) of the first axicon lens 20, but it is preferably, for example, between 150 degrees and 170 degrees. The cone angle of the first axicon lens 20 in the optical device 1 according to embodiment 1 is, for example, 160 degrees.

[0033] The laser light L incident on the first axicon lens 20 changes its traveling direction at the entrance surface and the exit surface of the first axicon lens 20. The laser light L emitted from the first axicon lens 20 enters the focusing optical system 40.

[0034] The apex of the cone of the first axicon lens 20 is preferably arranged to face the laser light irradiation unit 60. This makes it possible to prevent the laser light L reflected by the incident surface of the first axicon lens 20 from returning to the laser light irradiation unit 60 and damaging the laser oscillator.

[0035] The laser light L emitted from the first axicon lens 20 is incident on the focusing optical system 40 as an annular beam B1 (see FIG. 1). The focusing optical system 40 is disposed between the first axicon lens 20 and the second axicon lens 30 in the direction of the optical axis A. The focusing optical system 40 is configured with, for example, a convex lens. The focusing optical system 40 converts the incident annular beam B1 into a convergent beam B2 (see FIG. 1) and emits the beam. The focusing optical system 40 will be described in detail later.

[0036] The second axicon lens 30 is disposed on the exit side in the direction of the optical axis A of the laser light L. The convergent beam B2 incident on the second axicon lens 30 changes its traveling direction at the entrance surface and the exit surface of the second axicon lens 30. The convergent beam B2 emerging from the second axicon lens 30 then converges.

[0037] By appropriately selecting the cone angle of the second axicon lens 30, it is possible to determine the spot diameter of the laser light L on the glass substrate 11. That is, by increasing the cone angle of the second axicon lens 30, the spot diameter of the laser light L on the glass substrate 11 becomes larger, and by decreasing the cone angle of the second axicon lens 30, the spot diameter of the laser light L on the glass substrate 11 becomes smaller.

[0038] 3 is a diagram showing changes in the spot diameter of the laser light L on the glass substrate 11 when the cone angle of the second axicon lens 30 is changed in the optical device 1 according to embodiment 1. It can be seen that by setting the cone angle of the second axicon lens 30 to 95 degrees or less, the spot diameter of the laser light L on the glass substrate 11 can be made 2.0 μm or less. This makes it possible to form a fine through-hole in the glass substrate 11.

[0039] Next, the light collecting optical system 40 will be described.

[0040] As described above, the focusing optical system 40 converts the annular beam B1 incident on the focusing optical system 40 into a convergent beam B2 and emits the beam. The focusing optical system 40 includes one or more optical elements. Examples of the optical element include a convex lens and a concave lens. The optical element may also be a diffractive element.

[0041] The convex lens can be any lens having a positive refractive index, and various types of convex lenses such as a biconvex lens, a plano-convex lens, or a convex-concave lens can be used.

[0042] In addition to a spherical lens whose convex surface forms part of a spherical surface, an aspherical lens can also be used as the convex lens. By using an aspherical lens as the convex lens, spherical aberration can be reduced.

[0043] Furthermore, the focusing optical system 40 may be configured by combining a convex lens with other optical elements to produce a positive refractive index. For example, one or more convex lenses may be combined with one or more concave lenses to produce a positive refractive index. By combining one or more convex lenses with one or more concave lenses, the focal length of the focusing optical system 40 can be adjusted. In addition, spherical aberration can be minimized.

[0044] When the focusing optical system 40 is replaced with an optical system that does not have focusing properties, the focusing position of the convergent beam B2 focused by the focusing optical system 40 is deviated from a plane 101 (see FIG. 4 ) that is perpendicular to the optical axis A and includes the center of the Bessel beam region 100 formed by the first axicon lens 20 and the second axicon lens 30.

[0045] Here, "optical system without focusing properties" refers to an optical system made of the same material as the optical elements that make up the focusing optical system 40, or an optical system made of a material with the same refractive index and thickness. For example, if the focusing optical system 40 is a lens, it refers to a flat plate that has the same thickness as the optical axis of the lens and is made of the same material (e.g., glass) as the lens. Also, if the focusing optical system 40 is a diffractive element, it refers to a substrate on which no diffractive element is formed.

[0046] Using FIG. 4, we will explain the Bessel beam region 100 formed by the first axicon lens 20 and the second axicon lens 30 when the focusing optical system 40 is replaced with an optical system that does not have focusing properties, and the plane 101 that is perpendicular to the optical axis A and includes the center of the Bessel beam region 100.

[0047] In the following description, "when the focusing optical system 40 is replaced with an optical system without focusing properties, the plane 101 that is perpendicular to the optical axis A and includes the center of the Bessel beam region 100 formed by the first axicon lens 20 and the second axicon lens 30" may be referred to as "the plane 101 including the center of the Bessel beam region 100", and "when the focusing optical system 40 is replaced with an optical system without focusing properties, the plane is deviated from the plane 101 that is perpendicular to the optical axis A and includes the center of the Bessel beam region 100 formed by the first axicon lens 20 and the second axicon lens 30" may be simply referred to as "the convergence position of the convergent beam B2 is deviated".

[0048] FIG. 4 is a diagram illustrating a state in which the convergence position of the convergent beam B2 converged by the focusing optical system 40 is biased.

[0049] FIG. 4(a) is a diagram illustrating the Bessel beam region 100 formed by the first axicon lens 20 and the second axicon lens 30, and the position where "a plane 101 that is perpendicular to the optical axis A and includes the center of the Bessel beam region 100" is formed when the focusing optical system 40 is replaced with an optical system that does not have focusing properties.

[0050] When the focusing optical system 40 is replaced with an optical system without focusing properties, the laser light L remains as annular beam B1 even after passing through the first axicon lens 20 and the second axicon lens 30 and reaches the glass substrate 11, forming a Bessel beam region 100. As shown in FIG. 4(a), the Bessel beam region 100 is formed in the region where the annular beams B1 overlap. A plane 101 that is perpendicular to the optical axis A and includes the center of the Bessel beam region 100 is the plane indicated by the reference numeral 101 in FIG. 4(a).

[0051] 4(b) is a diagram showing a case where the convergent beam B2 converged by the focusing optical system 40 is focused on a plane 101 including the center of the Bessel beam region 100. In the following description, the "convergent beam B2 converged by the focusing optical system 40" may be simply referred to as the "convergent beam B2."

[0052] 4(b), the focal position of the focusing optical system 40 is adjusted so that the convergent beam B2 converges on a plane 101 including the center of the Bessel beam region 100. Examples of a method for adjusting the focal position of the focusing optical system 40 include a method for adjusting the focal length of the optical system in the focusing optical system 40, specifically, a method for changing the focal length of the lens when the focusing optical system 40 is a lens, a method for adjusting the position where the focusing optical system 40 is disposed, and the like.

[0053] 4(c) is a diagram showing an example in which the convergence position of the convergent beam B2 converged by the focusing optical system 400 is deviated from the plane 101 including the center of the Bessel beam region 100. Specifically, the convergence position of the convergent beam B2 is deviated in the direction of the optical axis A to the side opposite to the side where the first axicon lens 20 is disposed (to the right of the glass substrate 11 in FIG. 4(c)).

[0054] In the case shown in FIG. 4(c), the focusing position of the focusing optical system 40 is adjusted so that the convergent beam B2 is converged on a surface 102 located on the opposite side to the side on which the second axicon lens 30 is disposed, with respect to a surface 101 including the center of the Bessel beam region 100.

[0055] 4(d) is a diagram showing another example in which the convergence position of the convergent beam B2 converged by the focusing optical system 400 is deviated from the plane 101 including the center of the Bessel beam region 100. Specifically, the convergence position of the convergent beam B2 is deviated in the direction of the optical axis A to the side where the second axicon lens 30 is disposed (to the left of the glass substrate 11 in FIG. 4(d)).

[0056] In this case, the focal position of the focusing optical system 40 is adjusted so that the convergent beam B2 converges onto a surface 103 located on the side where the second axicon lens 30 is disposed in the direction of the optical axis A, with respect to a surface 101 including the center of the Bessel beam region 100.

[0057] FIG. 5 is a diagram showing the results of calculating the light intensity distribution in the through-hole formation direction (depth direction) of the glass substrate 11 for the optical device 1 according to the first embodiment.

[0058] 5(a) shows the results of calculating the light intensity distribution in the direction in which the through-holes are formed in the glass substrate 11 for an optical device according to the prior art. The horizontal axis represents the position in the depth direction of the glass substrate 11. The thickness of the glass substrate 11 is set to 1.0 mm, with 0.0 mm corresponding to the position on the front surface 12 of the glass substrate 11 and 1.0 mm corresponding to the position on the back surface 13 of the glass substrate 11. The vertical axis represents the light intensity.

[0059] The calculation conditions are as follows: Cone angle of the second axicon lens 30: 92 deg Condensing optical system 40: convex lens (f=300mm) L2 (distance from the focusing optical system 40 to the second axicon lens 30): 144.8 mm WD (distance from the second axicon lens 30 to the glass substrate 11): 11 mm

[0060] 5(a), the light intensity distribution of the laser light L in the optical device according to the conventional technology is concentrated in a narrow range of 0.2 mm to 0.3 mm near the center 14 in the thickness direction of the glass substrate 11. On the other hand, the light intensity on the front surface 12 and the back surface 13 of the glass substrate 11 is weak.

[0061] This is because the optical device 1 according to the conventional technology is designed so that the convergent beam B2 converged by the focusing optical system 40 is focused at a surface 101 including the center of the Bessel beam region 100, i.e., near the center 14 in the thickness direction of the glass substrate 11 (see FIG. 4(b)). Therefore, the light intensity distribution of the laser light L is concentrated at the center 14 in the thickness direction of the glass substrate 11, and the light intensity on the front surface 12 and the back surface 13 is weak.

[0062] 5(b) and 5(c) show the results of calculating the light intensity distribution in the through-hole formation direction (depth direction) of the glass substrate 11 in the optical device 1 according to embodiment 1. Fig. 5(b) shows the calculation results when a convex lens with a focal length f = 500 mm is used as the focusing optical system 40, and Fig. 5(c) shows the calculation results when a convex lens with a focal length f = 600 mm is used as the focusing optical system 40.

[0063] Here, by using a convex lens with a long focal length as the focusing optical system 40, the focal position of the focusing optical system 40 can be shifted in the direction of the optical axis A from the plane 101 including the center of the Bessel beam region 100 to the opposite side to the side where the second axicon lens 30 is disposed (to the right side of the glass substrate 11 in FIG. 4(c)).

[0064] By using a convex lens with f=500 mm or a convex lens with f=600 mm as the focusing optical system 40, it is possible to distribute a light intensity equal to or greater than a predetermined value over the entire 1 mm thick glass substrate 11 in the through-hole formation direction (see Figures 5(b) and 5(c)). Note that "a light intensity equal to or greater than a predetermined value" here means a light intensity greater than the threshold value for forming a modified region in the glass substrate 11.

[0065] In the optical device 1, the convergence position of the convergent beam B2 converged by the focusing optical system 40 is offset from the plane 101 including the center of the Bessel beam region 100, thereby making it possible to reduce the light intensity at the peak position in the light intensity distribution of the laser light L. Also, the light intensity can be increased at positions around the peak position, i.e., positions closer to and farther from the position where the peak is formed in the light intensity distribution, in the through-hole formation direction. As a result, the light intensity distribution in the through-hole formation direction of the article 10 (glass substrate 11), which is the workpiece, can be made closer to uniform.

[0066] According to the optical device 1, the convergence position of the convergent beam B2 converged by the focusing optical system 40 is deviated from the plane 101 including the center of the Bessel beam region 100, so that the light intensity distribution of the laser light L can be made closer to a desired light intensity distribution.

[0067] By forming a desired light intensity distribution in the through-hole formation direction, a region where the light intensity is equal to or greater than a predetermined light intensity can be formed from the front surface 12 to the back surface 13 of the glass substrate 11. As a result, when through-holes are formed in the glass substrate 11 by wet etching, the through-holes can have a uniform inner diameter.

[0068] 4(c), it is preferable that the convergent position of the convergent beam B2 is offset from the surface 101 including the center of the Bessel beam region 100 to the side opposite to the side where the second axicon lens 30 is disposed, in the direction of the optical axis A. In other words, the focal position of the focusing optical system 40 is adjusted so that the convergent beam B2 is converged on the surface 102 that is opposite to the side where the second axicon lens 30 is disposed, in the direction of the optical axis A, from the surface 101 including the center of the Bessel beam region 100.

[0069] The convergent position of the convergent beam B2 is offset from the surface 101 including the center of the Bessel beam region 100 to the side opposite to the side where the second axicon lens 30 is disposed. This makes it possible to obtain the effect of focusing the convergent beam B2 on the surface 102 that is farther away from the surface 101 including the center of the Bessel beam region 100, in addition to the effect obtained when the convergent position of the convergent beam B2 is offset as described above.

[0070] That is, the focusing optical system 40 deflects the convergent beam B2 from a surface 101 including the center of the Bessel beam region 100 onto a surface 102 opposite to the side where the second axicon lens 30 is disposed. In this case, a convex lens with a long focal length can be used for the focusing optical system 40. A convex lens with a long focal length has smaller aberration than a convex lens with a short focal length. Therefore, the optical device 1 can suppress spherical aberration in the focusing optical system 40. As a result, it is possible to provide an optical device 1 that can more uniformly form the inner diameter of a through hole formed by wet etching a modified region formed by irradiating the laser light L.

[0071] Furthermore, by setting the surface 102 where the convergent beam B2 converges in the focusing optical system 40 at a position farther away from the surface 101 including the center of the Bessel beam region 100, the length of the region where the convergent beam B2 overlaps becomes longer. In other words, the range of the region where the desired light intensity distribution of the laser light L can be formed also becomes longer. This makes it possible to form through holes even in the article 10 (thick glass substrate 11) that is long in the through-hole formation direction.

[0072] The convergent position of the convergent beam B2 is preferably biased to a position away from the rear surface 13 of the article 10 (glass substrate 11).

[0073] The convergent position of the convergent beam B2 is offset from the plane 101 including the center of the Bessel beam region 100 and further offset to a position away from the rear surface 13 of the article 10 (glass substrate 11), thereby making it possible to form a desired light intensity distribution of the laser light L at the position where the article 10 (glass substrate 11) is placed in the through-hole formation direction. As a result, when through-holes are formed in the glass substrate 11 by wet etching, it is possible to form through-holes with a uniform inner diameter.

[0074] Furthermore, as shown in FIG. 4(d), the convergence position of the convergent beam B2 may be shifted in the optical axis direction from the plane 101 including the center of the Bessel beam region 100 to the side where the second axicon lens 30 is disposed.

[0075] The effect of the present invention, that is, a desired light intensity distribution of the laser light L in the through-hole formation direction, can be achieved by biasing the convergent beam B2 toward the side where the second axicon lens 30 is disposed relative to the plane 101 including the center of the Bessel beam region 100. As a result, when through-holes are formed in the glass substrate 11 by wet etching, the through-holes can have a uniform inner diameter.

[0076] When the convergent beam B2 is biased toward the side where the second axicon lens 30 is disposed relative to the plane 101 including the center of the Bessel beam region 100, the length of the overlapping region of the convergent beam B2 tends to be short. However, when the thickness of the article 10 (glass substrate 11) that is the workpiece is relatively thin, even if the length of the overlapping region of the convergent beam B2 is short, it can cover the length of the article 10 (glass substrate 11) in the through-hole formation direction. Therefore, this embodiment can be suitably applied when the thickness of the article 10 (glass substrate 11) that is the workpiece is relatively thin.

[0077] Furthermore, in the optical device 1, the light intensity of the laser light L on the front surface 12 of the glass substrate 11 is smaller than the light intensity of the laser light L at a position midway between the front surface 12 and the back surface 13 in the direction of the optical axis A of the glass substrate 11, and is greater than the threshold value for forming a modified region in the glass substrate 11. This makes it possible to prevent the through hole from becoming thinner or being blocked at the center 14 of the glass substrate 11 when the through hole is formed in the glass substrate 11 by wet etching. That is, this has the effect of making the inner diameter of the through hole after wet etching closer to uniform.

[0078] [Embodiment 2] 2.Optical device 2 Next, an optical device 2 according to embodiment 2 will be described. Fig. 6 is a diagram showing the arrangement of the first axicon lens 20, the second axicon lens 30, and the focusing optical system 40 provided in the optical device 2 according to embodiment 2.

[0079] The optical device 2 differs from the optical device 1 according to embodiment 1 in the orientation in which the second axicon lens 30 is disposed and the size of the cone angle of the second axicon lens 30. The other configurations are the same as those of the optical device 1. Therefore, the description of the optical device 2 according to embodiment 2 will focus on the differences from the optical device 1 according to embodiment 1, and a description of the same points as the optical device 1 will be omitted.

[0080] As shown in FIG. 6, the optical device 2 includes a first axicon lens 20, a second axicon lens 30, and a focusing optical system 40.

[0081] In the optical device 2, the conical surface of the second axicon lens 30 is disposed facing the incident side (the side where the focusing optical system 40 is disposed) in the direction of the optical axis A. By employing such a configuration, the optical device 2 can reduce the coat angle (the angle of incidence on the axicon surface) of the incident light entering the second axicon lens 30.

[0082] Specifically, when an axicon lens with a cone angle of 160 degrees is used as the first axicon lens 10 and an axicon lens with a cone angle of 90 degrees is used as the second axicon lens 30, the coating angle of the second axicon lens 30 (the angle of incidence to the second axicon lens 30) can be set to 49.5 degrees.

[0083] This is a sufficiently small number compared to the coat angle of the second axicon lens 30 (the exit angle from the second axicon lens 30) of 75.6 deg when an axicon lens with the same cone angle of 90 deg is used as the second axicon lens 30 in the optical device 1 of embodiment 1.

[0084] That is, by arranging the second axicon lens 30 so that the conical surface faces the incident side, the coating angle can be made smaller than when the conical surface faces the exit side. This makes it possible to improve the coating characteristics on the conical surface. That is, it is possible to suppress reflection of the laser light L on the conical surface.

[0085] Furthermore, by arranging the conical surface of the second axicon lens 30 facing the incident side in the direction of the optical axis A, the distance WD from the second axicon lens 30 to the article 10 (glass substrate 11) can be made large. This makes it possible to prevent sublimates generated when the article 10 is processed with laser light from adhering to the second axicon lens 30.

[0086] 7 is a diagram showing changes in the spot diameter of the laser light L on the glass substrate 11 when the cone angle of the second axicon lens 30 is changed in the optical device 2 according to embodiment 2. It can be seen that by setting the cone angle of the second axicon lens 30 to 77 degrees or less, the spot diameter of the laser light L on the glass substrate 11 can be made 2.0 μm or less. In other words, it is possible to form a fine through-hole in the glass substrate 11.

[0087] 8 is a diagram showing the results of calculating the light intensity distribution in the through-hole formation direction (depth direction) of the glass substrate 11 in the optical device 2 according to embodiment 2. The horizontal axis represents the position in the depth direction of the glass substrate 11. The thickness of the glass substrate 11 is 1.0 mm, with 0.0 mm corresponding to the position on the front surface 12 of the glass substrate 11 and 1.0 mm corresponding to the position on the back surface 13 of the glass substrate 11. The vertical axis represents the light intensity.

[0088] The calculation conditions are as follows: Cone angle of the second axicon lens 30: 75 deg Converging optical system 40: convex lens (f=220 mm / used when the convergence position of the convergent beam B2 is offset) L2: 154.5 mm WD:25mm

[0089] 8, in the optical device 2 according to the second embodiment, the convergent beam B2 is also focused from the surface 101 including the center of the Bessel beam region 100, and therefore, in the light intensity distribution along the optical axis A of the laser light L, a light intensity equal to or greater than a predetermined value is distributed from the front surface 12 to the back surface 13 of the glass substrate 11. In other words, it can be seen that a processing depth of 1.0 mm can be ensured. Note that the "light intensity equal to or greater than a predetermined value" here means a light intensity greater than the threshold for forming a modified region in the glass substrate 11.

[0090] As described above, also in the optical device 2 according to the second embodiment in which the conical surface of the second axicon lens 30 is disposed facing the incident side in the direction of the optical axis A, the convergence position of the convergent beam B2 converged by the focusing optical system 40 is deviated from the plane 101 including the center of the Bessel beam region 100, and therefore the light intensity distribution of the laser light L can be made to be a desired light intensity distribution.

[0091] This allows the region where the light intensity is equal to or greater than a predetermined light intensity in the light intensity distribution of the laser light L in the through-hole formation direction to be expanded from the front surface 12 to the back surface 13 of the glass substrate 11. As a result, it is possible to provide an optical device 2 that can make the inner diameters of the through-holes formed by wet etching the modified regions formed by irradiating the laser light L with concentrated light closer to uniform.

[0092] 3. Method for determining the convergence position of a convergent beam converged by a focusing optical system In the above-described optical device 1 and optical device 2, the convergence position of the convergent beam B2 converged by the focusing optical system 40 is deviated from the plane 101 including the center of the Bessel beam region 100. Here, a method for determining the position at which the convergent beam B2 is converged in the optical device 1 and optical device 2 will be described.

[0093] The convergence position where the convergent beam B2 is converged by the focusing optical system 40 can be determined as follows. Here, the optical device 2 of the second embodiment, which uses a convex lens as an optical element of the focusing optical system 40, will be described as an example.

[0094] Using the radius of curvature R (focal length) of the convex lens as a parameter, the light intensity distribution of the laser light L in the direction in which the through-hole is formed in the glass substrate 11 is calculated under the condition that the distance L2 from the focusing optical system 40 to the second axicon lens 30 and the distance WD from the second axicon lens 30 to the glass substrate 11 are constant, and the intensity ratio is found.

[0095] The "intensity ratio" of the laser light L on the glass substrate 11 referred to here refers to the intensity ratio obtained by dividing the "light intensity at the center 14 of the glass substrate 11" calculated by the following formula (1) by the "average of the light intensity on the front surface 12 of the glass substrate 11 and the light intensity on the back surface 13 of the glass substrate 11." TIFF2026022898000002.tif22170

[0096] Fig. 9 is a diagram showing the relationship between the focal length and the light intensity ratio in the focusing optical system 40 included in the optical device 2 according to embodiment 2. In Fig. 9, the horizontal axis represents the focal length, and the vertical axis represents the intensity ratio.

[0097] Here, it is known that the preferable intensity ratio is in the range of 3 to 14. When the focal length of the focusing optical system 40 corresponding to the intensity ratio range of 3 to 14 is read from Fig. 9, it is found that the preferable range of the focal length is 200 mm to 213 mm.

[0098] 10 is a diagram showing the results of calculating the light intensity distribution in the through-hole formation direction (depth direction) of the glass substrate 11 in the optical device 2 according to embodiment 2. The horizontal axis represents the position in the depth direction of the glass substrate 11, and the vertical axis represents the light intensity.

[0099] When the focal length of the focusing optical system 40 is in the range of 200 mm or more and 213 mm or less, the light intensity is above a certain level throughout the entire thickness direction of the glass substrate 11, i.e., the light intensity is greater than the threshold value that causes a modified region to form in the glass substrate 11, and the light intensity at the center 14 of the glass substrate 11 is greater than the light intensity at the front surface 12 or the back surface 13 of the glass substrate 11, resulting in a light intensity distribution.

[0100] That is, in the optical device 2, the light intensity of the laser light L on the front surface 12 or the back surface 13 of the glass substrate 11 is smaller than the light intensity of the laser light L at the center 14 between the front surface 12 and the back surface 13 in the direction of the optical axis A of the glass substrate 11, and is greater than the threshold value for forming a modified region on the glass substrate 11.

[0101] As described above, the light intensity distribution formed is preferably such that the light intensity of the laser light L on the front surface 12 of the article 10 is smaller than the light intensity of the laser light L at the center 14 between the front surface 12 and the back surface 13 in the direction of the optical axis A, and is greater than the threshold value for forming a modified region in the article 10, but is not limited thereto. The light intensity distribution may be any light intensity distribution as long as it corresponds to the shape of the through-hole formed by wet etching in the through-hole formation direction. For example, the light intensity distribution may be substantially flat in the glass depth direction, as shown at f:250 in FIG. 10 .

[0102] According to the optical device 2, the convergent beam B2 passing through the inside of the glass substrate 11 can make the light intensity distribution of the laser light L in the through-hole formation direction in the glass substrate 11 closer to a desired light intensity distribution over a wide range in the through-hole formation direction in the glass substrate 11. According to the optical device 2, it is possible to provide a modified region forming method that can make the inner diameter of the through-hole formed by wet-etching the modified region formed by irradiating it with the laser light L closer to uniform.

[0103] The optical device 2 may include a third axicon lens 32 instead of the second axicon lens 30. FIG. 11 is a diagram for explaining the third axicon lens 32 that the optical device 2 according to the second embodiment can include. In the optical device 2, when the incident position of the convergent beam B2 on the second axicon lens 30 is almost the same, the conical portion of the second axicon lens 30 does not need to be formed as a complete conical surface continuing from the bottom to the apex. In other words, it is sufficient that the position where the convergent beam B2 is incident is formed as a conical surface.

[0104] The third axicon lens 32 has a truncated conical shape as shown in Fig. 11. The third axicon lens 32 has a conical surface in a necessary and sufficient area for the convergent beam B2 emitted from the focusing optical system 40 to be incident thereon, and has a shape lacking an apex portion 32a.

[0105] By providing the third axicon lens 32 with the above-described configuration, the cost of manufacturing the second axicon lens 30 can be reduced while maintaining the function of the second axicon lens 30.

[0106] Fig. 12 is a diagram illustrating a focusing optical system 40 that can be included in the optical device 2 according to embodiment 2. Fig. 12(a) is a diagram illustrating the configuration of optical elements included in the focusing optical system 40. Fig. 12(b) is a diagram illustrating the distance between the lens surfaces of the lenses included in the focusing optical system 40 and the focal length.

[0107] The focusing optical system 40 includes one or more optical elements arranged on the optical axis A of the laser light L, and a focusing position adjustment mechanism (not shown) that adjusts the position where the convergent beam B2 converges. Specifically, the focusing optical system 40 includes a convex lens 42, a concave lens 43, and a focusing position adjustment mechanism that adjusts the distance between the convex lens 42 and the concave lens 43.

[0108] The focusing optical system 40 can adjust the focal position by adjusting the inter-surface distance L0 (see FIG. 12(a)) between the convex lens 42 and the concave lens 43 using the focusing position adjustment mechanism. In other words, the position where the convergent beam B2 emitted from the focusing optical system 40 converges can be adjusted.

[0109] Figure 12(b) shows the relationship between the inter-surface distance L0 between the convex lens 42 and the concave lens 43 and the focal length f, calculated when a plano-convex lens with a focal length of 100 mm is selected as the convex lens 42 and a plano-concave lens with a focal length of -150 mm is selected as the concave lens 43.

[0110] 12(b) shows that in the optical device 2, the focal length of the focusing optical system 40 can be changed in the range of 205 mm to 225 mm by changing the inter-surface distance L0 between the convex lens 42 and the concave lens 43 in the range of 16 mm to 23 mm. Because the focusing optical system 40 is made up of multiple optical elements and has a configuration that allows the focal length to be changed, it is not necessary to replace the focusing optical system 40 each time through holes are formed in multiple articles 10 that have different lengths in the through-hole formation direction or different refractive indices. As a result, there is an effect of improving work efficiency.

[0111] The optical device 1 according to the embodiment 1 and / or the optical device 2 according to the embodiment 2 can include a beam shape correction mechanism 70 (see FIG. 1). The beam shape correction mechanism 70 is disposed on the incident side of the first axicon lens 20, and corrects the beam shape of the laser light L. By including the beam shape correction mechanism 70, the beam shape of the laser light L can be shaped, and the laser light L having a shape closer to a perfect circle can be incident on the first axicon lens 20.

[0112] The beam shape correction mechanism 70 is an ellipticity correction optical system and preferably includes a rotation mechanism (not shown). Fig. 13 is a diagram for explaining the beam shape correction mechanism 70 included in the optical device 1 according to embodiment 1 or the optical device 2 according to embodiment 2. Here, the ellipticity correction function is a function of shrinking the beam shape in the long axis direction or expanding it in the short axis direction when the beam shape of the laser light L is assumed to be elliptical, as shown in Fig. 13(a).

[0113] The beam shape correction mechanism 70 can shrink the beam shape of the laser light L in the long axis direction or expand it in the short axis direction, thereby making the beam shape of the laser light L closer to a perfect circle. Making the beam shape closer to a perfect circle can prevent cracks from occurring in the article 10 (glass substrate 11) when the modified region is formed. As a result, when the modified region is etched by wet etching to form a through hole, a through hole that is close to a perfect circle can be formed.

[0114] By providing the beam shape correction mechanism 70 with a rotation mechanism, when the beam shape of the laser light L emitted from the laser light irradiation unit 60 is elliptical, the long and short axis directions of the laser light L can be made to coincide with the long and short axis directions of the ellipticity correction optical system. This makes it possible to make the beam shape of the laser light L closer to a perfect circle (see FIG. 13(b)).

[0115] 3. Modified region formation method Next, a modified region forming method according to an embodiment will be described.

[0116] The modified area formation method of the embodiment is a modified area formation method in which laser light L is irradiated onto a position where a modified area is to be formed on an article 10 as a workpiece, such as a glass substrate 11, thereby forming a modified area that extends from the front surface 12 to the back surface 13 of the glass substrate 11.

[0117] The method includes the steps of: making the laser light L incident on a first axicon lens 20 arranged on the incident side in the direction of the optical axis A of the laser light L; making the laser light L incident on a focusing optical system 40 arranged on the exit side of the first axicon lens 20 in the direction of the optical axis A; and making the laser light L incident on a second axicon lens 30 arranged on the exit side of the focusing optical system 40 in the direction of the optical axis A.

[0118] When the focusing optical system 40 is replaced with an optical system without focusing properties, the convergent beam B2 focused by the focusing optical system 40 is deviated from the plane 101 that is perpendicular to the optical axis A and includes the center of the Bessel beam region 100 formed by the first axicon lens 20 and the second axicon lens 30 (see Figures 4(c) and 4(d)).

[0119] The modified region forming method according to the embodiment can be implemented in the optical device 1 according to the first embodiment, the optical device 2 according to the second embodiment, and optical devices having equivalent functions to these.

[0120] The modified region forming method according to the embodiment includes the steps of: making laser light L incident on a first axicon lens 20 arranged on the incident side in the direction of the optical axis A of the laser light L; making laser light L incident on a focusing optical system 40 arranged on the exit side of the first axicon lens 20; and making laser light L incident on a second axicon lens 30 arranged on the exit side of the focusing optical system 40. When the focusing optical system 40 is replaced with an optical system that does not have focusing properties, the convergence position of a convergent beam B2 converged by the focusing optical system 40 is perpendicular to the optical axis A and deviated from a plane 101 including the center of a Bessel beam region 100 formed by the first axicon lens 20 and the second axicon lens 30.

[0121] As a result, the convergent beam B2 passing through the inside of the article can bring the light intensity distribution of the laser light L closer to a desired light intensity distribution in the direction of forming the through hole in the article 10, for example, the glass substrate 11. According to the modified region forming method of the embodiment, it is possible to provide a modified region forming method that can make the inner diameter of the through hole formed by wet etching the modified region formed by irradiating it with the laser light L closer to a uniform diameter.

[0122] The effects of the optical device and modified region forming method according to the embodiment will be described below.

[0123] The optical device according to the embodiment includes a first axicon lens 20 disposed on the incident side in the direction of an optical axis A of a laser beam L, a second axicon lens 30 disposed on the exit side in the direction of the optical axis A, and a focusing optical system 40 disposed between the first axicon lens 20 and the second axicon lens 30 and configured to focus the laser beam L. When the focusing optical system 40 is replaced with an optical system that does not have focusing properties, the focusing position of a convergent beam B2 focused by the focusing optical system 40 is perpendicular to the optical axis A and deviated from a plane 101 including the center of a Bessel beam region 100 formed by the first axicon lens 20 and the second axicon lens 30.

[0124] According to the optical device of the embodiment, an optical device 1 can be provided that can make the inner diameter of the through hole formed by wet etching the modified region formed by irradiating it with laser light L closer to uniform.

[0125] The modified region forming method according to the embodiment includes the steps of: making laser light L incident on a first axicon lens 20 arranged on the incident side in the direction of the optical axis A of the laser light L; making laser light L incident on a focusing optical system 40 arranged on the exit side of the first axicon lens 20; and making laser light L incident on a second axicon lens 30 arranged on the exit side of the focusing optical system 40. When the focusing optical system 40 is replaced with an optical system that does not have focusing properties, the convergence position of a convergent beam B2 converged by the focusing optical system 40 is perpendicular to the optical axis A and deviated from a plane 101 including the center of a Bessel beam region 100 formed by the first axicon lens 20 and the second axicon lens 30.

[0126] According to the modified area formation method of the embodiment, a modified area formation method can be provided that can make the inner diameter of the through hole formed by wet etching the modified area formed by irradiating laser light L closer to uniformity.

[0127] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0128] For example, the focusing optical system 40 may be disposed between the beam shape correction mechanism 70 and the first axicon lens 20, rather than between the first axicon lens 20 and the second axicon lens 30. Alternatively, the focusing optical system 40 may be disposed between the laser beam irradiation unit 60 and the beam shape correction mechanism 70. The above-described effects of the present invention can be achieved in an optical device in which the focusing optical system 40 is disposed between the beam shape correction mechanism 70 and the first axicon lens 20, and in an optical device in which the focusing optical system 40 is installed between the laser beam irradiation unit 60 and the beam shape correction mechanism 70. [Explanation of symbols]

[0129] 1...electronic module, 10...article, 11...glass substrate, 20...first axicon lens, 30...second axicon lens, 32...third axicon lens, 40...focusing optical system, 60...laser light irradiation unit, 70...beam shape correction mechanism, 80...mirror, L...laser light, A...optical axis of laser light, B1...annular beam, B2...converging beam

Claims

1. An optical device for forming a modified region extending from a front surface to a back surface of an article as a workpiece by irradiating a pulsed laser beam at a position where a modified region is to be formed on the article, the optical device comprising: a first axicon lens arranged on an incident side of the pulsed laser beam in the optical axis direction; a second axicon lens arranged on an exit side in the optical axis direction; and a focusing optical system that converges the pulsed laser beam, wherein, when the focusing optical system is replaced with an optical system not having focusing properties, a focusing position of a convergent beam focused by the focusing optical system is perpendicular to the optical axis and deviated from a plane including a center of a Bessel beam region formed by the first axicon lens and the second axicon lens.

2. 2. The optical device according to claim 1, a convergence position of the convergent beam is offset, in the optical axis direction, from a plane including a center of the Bessel beam region to a side opposite to a side on which the second axicon lens is disposed.

3. 3. The optical device according to claim 2, An optical device characterized in that the convergence position of the convergent beam is biased to a position away from the back surface of the article.

4. 2. The optical device according to claim 1, a convergence position of the convergent beam is biased, in the optical axis direction, from a plane including a center of the Bessel beam region toward a side where the second axicon lens is disposed.

5. 2. The optical device according to claim 1, an optical device, wherein the conical surface of the second axicon lens faces an incident side in the optical axis direction.

6. 2. The optical device according to claim 1, an optical device characterized in that the light intensity of the pulsed laser light at the surface of the article is smaller than the light intensity of the pulsed laser light at a center position between the surface and the back surface in the optical axis direction of the article, and is greater than a threshold light intensity that forms a modified region in the article.

7. 2. The optical device according to claim 1, The focusing optical system includes: one or more optical elements arranged on the optical axis of the pulsed laser beam; and a focusing position adjusting mechanism for adjusting a focusing position of the pulsed laser beam that has passed through the focusing optical system.

8. 2. The optical device according to claim 1, an optical device further comprising: a beam shape correction mechanism disposed on an incident side of the first axicon lens, the beam shape correction mechanism correcting a beam shape of the pulsed laser beam.

9. 9. The optical device according to claim 8, The optical device is characterized in that the beam shape correction mechanism is an ellipticity correction optical system that corrects the ellipticity of the beam of the pulsed laser light, and has a rotation mechanism that rotates around the optical axis of the pulsed laser light.

10. 1. A modified region forming method for forming a modified region extending from a front surface to a back surface of an article as a workpiece by irradiating a pulsed laser beam to a position where a modified region is to be formed on the article, the method comprising: making the pulsed laser beam incident on a first axicon lens arranged on an incident side in an optical axis direction of the pulsed laser beam; making the pulsed laser beam incident on a focusing optical system arranged on an exit side of the first axicon lens in the optical axis direction; causing the pulsed laser beam to be incident on a second axicon lens arranged on an exit side of the focusing optical system in the optical axis direction, a focusing position of a convergent beam focused by the focusing optical system is perpendicular to the optical axis and deviated from a plane including a center of a Bessel beam region formed by the first axicon lens and the second axicon lens when the focusing optical system is replaced with an optical system that does not have focusing properties.

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