Modified region forming method, through-hole forming method, condenser lens device, and method for manufacturing article having modified region

Abstract

To provide a modified region forming method capable of reducing a difference between the inner diameter of a through-hole on a surface and the inner diameter of a center in the depth direction of the through-hole when the through-hole is formed in an article.SOLUTION: This modified region forming method comprises a modified region forming step of forming a modified region 20 reaching a backside 10c from a surface 10a of an article 10 by irradiating the position for forming the modified region 20 of the article 10 with an ultrashort pulse laser beam via a condenser lens system 140. The condenser lens system 140 includes two axicon lenses 141 and 143 arranged along an optical axis 165 of the ultrashort pulse laser beam 161, and a convex lens 142 disposed between the two axicon lenses. The ultrashort pulse laser beam 161 passed through the condenser lens system 140 becomes an annular convergent Bessel beam 164. The annular convergent Bessel beam 164 is configured to be converged between the surface 10a and the backside 10c of the article 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a modified region forming method, a through-hole forming method, a condenser lens device, and a method for manufacturing an article having a modified region. [Background technology]

[0002] Interposers, which have through electrodes formed on the front and back surfaces of a plate-shaped 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 interposer materials include glass, epoxy resin, and silicon. Among these, glass is considered to be an excellent material for interposers 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. In addition, photolithography technology for forming wiring patterns has been established.

[0003] To create an interposer using glass, it is necessary to form a large number of fine through-holes (TGVs: Through Glass Vias) of, for example, 150 μm or less 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 portion).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 desired holes in the locations where the modified portions are formed is to apply a high voltage to a pair of electrodes, as in the hole formation method described in Patent Document 1. However, a method of etching with a hydrofluoric acid-based etching solution such as hydrofluoric acid or an acid containing hydrofluoric acid is generally adopted as 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, when a glass substrate having a modified region formed thereon for forming a through-hole is etched using a hydrofluoric acid-based etching solution, the etching rate is high in the modified region and etching proceeds in the thickness direction of the substrate, whereas the etching rate is low in the unmodified region and etching proceeds in the lateral direction of the substrate. In this case, there is a problem that the inner diameter of the through-hole near the center of the glass substrate may become smaller than the inner diameter of the through-hole near the surface due to the difference in etching rate between the modified region and the unmodified region.

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide a modified region forming method that can reduce the difference between the inner diameter of a through hole near the surface and the inner diameter of the through hole at the center in the depth direction when an article having a modified region formed thereon is etched with a hydrofluoric acid-based etching solution to form a through hole; to provide a through hole forming method; to provide a focusing lens device that can form a modified region; and to provide a method for manufacturing an article having a modified region. [Means for solving the problem]

[0009] [1] The modified region formation method of the present invention includes a modified region formation step of forming a modified region extending from the front surface to the back surface of an article as a workpiece by irradiating an ultrashort pulsed laser beam via a focusing lens system onto a position where the modified region is to be formed on the article, wherein the focusing lens system includes two axicon lenses arranged along the optical axis of the ultrashort pulsed laser beam and a convex lens arranged between the two axicon lenses, and the ultrashort pulsed laser beam that passes through the focusing lens system becomes a circular, convergent Bessel beam, which is configured to converge between the front surface and the back surface of the article.

[0010] [2] The modified region formation method of the present invention is the modified region formation method described above, and it is preferable that the light density at the position of the main peak in the light density distribution of the extremely short pulsed laser light at the center position between the front surface and the back surface in the optical axis direction of the article is greater than the light density at the position of the main peak in the light density distribution of the extremely short pulsed laser light on the front surface of the article.

[0011] [3] The modified region formation method of the present invention is the modified region formation method described above, wherein the optical density at the position of the main peak in the optical density distribution of the ultrashort pulsed laser light on the surface of the article is greater than the threshold at which the article is modified, and the optical density at the position of the first diffraction ring in the optical density distribution of the ultrashort pulsed laser light on the surface of the article is preferably less than the threshold at which the article is modified.

[0012] [4] The modified area formation method of the present invention is the modified area formation method described above, and it is preferable that the light density at the position of the first diffraction ring in the light density distribution of the ultrashort pulse laser light at the center position between the front surface and the back surface in the optical axis direction of the article is greater than the threshold value at which the article is modified.

[0013] [5] The modified region formation method of the present invention is the modified region formation method described above, and it is preferable that the optical density at the position of the main peak in the optical density distribution of the extremely short pulsed laser light at the center position between the front surface and the back surface in the optical axis direction of the article is greater than six times the optical density at the position of the main peak in the optical density distribution of the extremely short pulsed laser light on the front surface of the article.

[0014] [6] The modified region forming method of the present invention is the above-mentioned modified region forming method, wherein the convex lens is preferably an aspherical lens.

[0015] [7] The modified region forming method of the present invention is the above-mentioned modified region forming method, and preferably includes a concave lens between the two axicon lenses.

[0016] [8] The modified region forming method of the present invention is the above-mentioned modified region forming method, wherein the in-plane distribution of the light density of the ultrashort pulsed laser light incident on the focusing lens system is preferably a Gaussian distribution.

[0017] [9] The modified area formation method of the present invention is the modified area formation method described above, and preferably has a correction optical system that corrects the light density distribution of the laser light incident on the focusing lens system, and the correction optical system makes a correction to increase the light density in the central part.

[0018]

[10] The modified area formation method of the present invention is the modified area formation method described above, and it is preferable that the correction optical system has a first aspherical surface and a second aspherical surface, and is configured so that when the in-plane distribution of the light density of the ultrashort pulse laser light incident on the focusing lens system is a Gaussian distribution, the light density in the central part is greater.

[0019]

[11] A method for forming a through hole of the present invention includes any of the above-described methods for forming a modified region, and an etching step of etching the article having the modified region formed thereon to form a through hole.

[0020]

[12] The focusing lens device of the present invention is a focusing lens device that forms a modified region extending from the front surface to the back surface of an article as a workpiece by irradiating an ultrashort pulsed laser beam via a focusing lens system at a position where a modified region is to be formed on the article, wherein the focusing lens system comprises two axicon lenses arranged along the optical axis of the ultrashort pulsed laser beam and a convex lens arranged between the two axicon lenses, and the ultrashort pulsed laser beam that passes through the focusing lens system becomes a circular converging Bessel beam, and the circular converging Bessel beam is configured to converge between the front surface and the back surface of the article.

[0021]

[13] The method for manufacturing an article having a modified region of the present invention includes a modified region formation step of forming a modified region extending from the front surface to the back surface of the article by irradiating an ultrashort pulsed laser beam via a focusing lens system at a position on the article where the modified region is to be formed, wherein the focusing lens system includes two axicon lenses arranged along the optical axis of the ultrashort pulsed laser beam and a convex lens arranged between the two axicon lenses, and the ultrashort pulsed laser beam that passes through the focusing lens system becomes a circular converging Bessel beam, and the circular converging Bessel beam is configured to converge between the front surface and the back surface of the article.

[0022] According to the modified region forming method of the present invention, first, the first axicon lens, which is one of two axicon lenses and is located closer to the light source, converts an ultrashort pulse laser beam into an annular Bessel beam. Next, the convex lens located between the two axicon lenses converts the annular Bessel beam into a converging Bessel beam. Here, "converging" means that the beam is converging with respect to the annular shape of the annular Bessel beam formed by the first axicon lens, and specifically, refers to a change in the thickness of the annulus becoming thinner.

[0023] Furthermore, of the two axicon lenses, the second axicon lens, which is positioned closer to the article, "converges" the annular converging Bessel beam onto the optical axis of the ultrashort pulsed laser light. The annular converging Bessel beam converged by the second axicon lens is focused between the front and back surfaces of the article.

[0024] This allows the optical density at the position where the modified region is formed on the article to be greater than the optical density at the position where the main peak of the optical density distribution at the center of the article in the direction of forming the modified region is located on the surface of the article, thereby allowing the modified region to be formed over a wider area at the center of the article in the direction of forming the modified region than at the surface of the article.

[0025] Furthermore, the inner diameter of the through hole at the center of the depth direction of the through hole after etching can be increased, and the difference between the inner diameter of the opening of the through hole and the inner diameter of the center of the depth direction of the through hole can be reduced.

[0026] Furthermore, since the inner diameter of the through-hole can be increased at the center in the depth direction of the through-hole, there is also the effect that the through-hole can be formed in a thicker substrate.

[0027] The focusing lens device of the present invention can make the light density at the position where the modified region of the article is formed at the center of the article in the direction of modified region formation greater than the light density at the position where the light density distribution of the article in the direction of modified region formation is main peak, thereby forming a modified region over a wider area at the center of the article in the direction of modified region formation than at the surface of the article.

[0028] As a result, the inner diameter of the through hole at the center of the depth direction of the through hole after etching can be increased, and the difference between the inner diameter of the opening of the through hole and the inner diameter of the center of the depth direction of the through hole can be reduced.

[0029] According to the method for manufacturing an article having a modified region of the present invention, the optical density at the position where the modified region is formed in the article, at the position of the main peak of the optical density distribution at the center of the article in the direction of forming the modified region, can be made higher than the optical density at the position of the main peak of the optical density distribution on the surface of the article, thereby making it possible to manufacture an article having a modified region over a wider area at the center of the article in the direction of forming the modified region than at the surface of the article.

[0030] As a result, the inner diameter of the through hole at the center of the depth direction of the through hole after etching can be increased, and the difference between the inner diameter of the opening of the through hole and the inner diameter of the center of the depth direction of the through hole can be reduced. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a diagram showing an example of a laser processing apparatus 100A that can be suitably used when forming a modified region on a glass substrate 10 using the modified region forming method according to the first embodiment. [Figure 2] 10 is a diagram showing the relationship between the focal length of a convex lens 142 and the light density distribution in the thickness direction of a glass substrate 10. FIG. [Figure 3] 10 is a diagram showing the position at which a circular convergent Bessel beam 164 emitted from a condenser lens system 140 converges when a convex lens with a different focal length is used as the convex lens 142. FIG. [Figure 4] 10 is a diagram showing the relationship between the apex angle of the second axicon lens 143 and the light density distribution in the thickness direction of the glass substrate 10. FIG. [Figure 5] 10 is a diagram showing the relationship between the light density distribution of laser light 161 incident on the condenser lens system 140 and the light density distribution in the thickness direction of the glass substrate. FIG. [Figure 6] 1 is a schematic diagram of a glass substrate 10 on which a modified region is formed by the modified region forming method according to the first embodiment and a through-hole is formed by the through-hole forming method. [Figure 7] 1 is a flowchart showing steps of a modified region forming method and a through-hole forming method according to the first embodiment. [Figure 8]FIG. 2 is a diagram for explaining a light beam when a glass substrate 10 is irradiated with a circular convergent Bessel beam 164. [Figure 9] FIG. 10 is a diagram showing the light density distribution when a glass substrate 10 is irradiated with a circular convergent Bessel beam 164. [Figure 10] FIG. 10 is a diagram showing an example of a correction optical system 150 according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, modes for carrying out the present invention (hereinafter referred to as "embodiments") will be described. The embodiments described below are preferred modes for carrying out the invention, and the present invention is not limited to the embodiments described below. Furthermore, if the explanations in each embodiment are repeated, they may be omitted.

[0033] 1. Embodiment 1 1-1. Laser processing equipment First, a laser processing device that can be suitably used in the modified region forming method and through-hole forming method of the first embodiment will be described.

[0034] Fig. 1 shows a laser processing apparatus 100A that can be suitably used when forming a modified region on a glass substrate 10 using the modified region forming method according to embodiment 1. Fig. 1 shows an x-axis, a y-axis, and a z-axis that are perpendicular to each other. In Fig. 1, the x-axis and y-axis directions correspond to the horizontal direction, and the z-axis direction corresponds to the vertical direction (the direction of gravity).

[0035] 1-1-1. Overview of laser processing equipment As shown in FIG. 1, the laser processing apparatus 100A includes a laser oscillator 120 that irradiates an extremely short pulse laser beam (hereinafter referred to as "laser beam") 161 onto a glass substrate 10, which is an article placed on a table (not shown), a light-guiding optical system 130 that guides the laser beam 161 irradiated from the laser oscillator 120 to an irradiation position on the glass substrate 10, and a focusing lens system 140 that converges an annular convergent Bessel beam between the front and back surfaces of the glass substrate.

[0036] The laser processing apparatus 100A may include a correction optical system 150 between the laser oscillator 120 and the condenser lens system 140, which corrects the density distribution of light incident on the condenser lens system 140.

[0037] The glass substrate 10 is flat and placed on a table (not shown). The glass substrate 10 placed on the table can be moved in an xy plane consisting of the x-axis and the y-axis, and up and down along the z-axis, by a table driving means (not shown). By controlling the movement of the table on the xy plane, the irradiation position of the laser light on the glass substrate 10 on the xy plane can be adjusted. Furthermore, by controlling the movement of the table in the z-axis direction, the position of the glass substrate 10 in the z-axis direction can be adjusted so that the annular convergent Bessel beam 164 converges between the substrate front surface 10a and the substrate back surface 10c of the glass substrate 10.

[0038] In addition, by adjusting the position of the focusing lens system 140 in the z-axis direction between the mirror 131 of the light-guiding optical system 130 and the glass substrate 10, it is also possible to converge the annular convergent Bessel beam 164 between the substrate front surface 10a and the substrate back surface 10c of the glass substrate 10.

[0039] The light-guiding optical system 130 has a mirror 131, and reflects the laser light 161 emitted from the laser oscillator 120 at an angle of 90 degrees by the mirror 131. The laser light 161 reflected at an angle of 90 degrees passes through the condenser lens system 140 and is set to be perpendicularly incident on the surface 10a of the glass substrate 10.

[0040] In the first embodiment, the laser oscillator 120, the light-guiding optical system 130, and the condenser lens system 140 are collectively referred to as a laser irradiation unit 160.

[0041] 1-1-2.Condenser lens system The focusing lens system 140 includes two axicon lenses, a first axicon lens 141 and a second axicon lens 143, arranged along the optical axis 165 of the laser beam 161, and a convex lens 142 arranged between the two axicon lenses.

[0042] Here, the condenser lens system 140 is configured so that the first axicon lens 141 can be replaced with an axicon lens having a different apex angle. Also, the convex lens 142 can be replaced with a convex lens having a different focal length. Furthermore, the second axicon lens 143 can be replaced with an axicon lens having a different apex angle.

[0043] As a result, as will be explained in detail later, at the position where the modified region 20 of the glass substrate 10 is formed, the light density at the position of the main peak in the light density distribution in a plane perpendicular to the optical axis 165 of the laser light at the center position (substrate center) 10b (see Figure 6) between the substrate surface 10a and the substrate back surface 10c of the glass substrate 10 can be made larger than the light density at the position of the main peak in the light density distribution in a plane perpendicular to the optical axis 165 of the laser light on the substrate surface 10a, and the light density at the position of the main peak in the light density distribution in a plane perpendicular to the optical axis 165 of the laser light on the substrate back surface 10c.

[0044] This allows the modified region 20 to be formed in a wider area at the center position (substrate center) 10b between the substrate front surface 10a and the substrate back surface 10c of the glass substrate 10 than on the substrate front surface 10a and the substrate back surface 10c.

[0045] In the following description, "the central position 10b between the substrate front surface 10a and the substrate back surface 10c" will be referred to as "substrate center 10b," and "the optical axis 165 of the laser light 161" will be referred to as "optical axis 165." Furthermore, "the light density distribution in a plane perpendicular to the optical axis 165 of the substrate front surface 10a" will be referred to as "the light density distribution of the substrate front surface 10a," "the light density distribution in a plane perpendicular to the optical axis 165 of the substrate center 10b" will be referred to as "the light density distribution of the substrate center 10b," and "the light density distribution in a plane perpendicular to the optical axis 165 of the substrate back surface 10c" will be referred to as "the light density distribution of the substrate back surface 10c."

[0046] The first axicon lens 141, the convex lens 142, and the second axicon lens 143, which are components of the condenser lens system 140, will be described in detail below.

[0047] The first axicon lens 141 converts the laser light 161 emitted from the laser oscillator 120 into an annular Bessel beam 162 and makes it incident on the convex lens 142 .

[0048] The condenser lens system 140 is configured so that the first axicon lens 141 can be replaced with an axicon lens having a different apex angle.

[0049] The apex 141a of the cone of the first axicon lens 141 is preferably arranged facing the laser oscillator 120. By arranging the apex 141a of the cone of the first axicon lens 141 facing the laser oscillator 120, it is possible to prevent the laser beam 161 reflected by the first axicon lens 141 from returning to the laser oscillator 120 and damaging the laser oscillator 120.

[0050] The apex angle of the first axicon lens 141 is not particularly limited as long as it is larger than the apex angle of the second axicon lens 143, which will be described later, but is preferably in the range of 145° to 175°, and more preferably in the range of 150° to 170°.

[0051] By setting the apex angle of the first axicon lens 141 to an angle greater than the apex angle of the second axicon lens 143, the annular convergent Bessel beam 164 can be converged.

[0052] Furthermore, by setting the apex angle of the first axicon lens 141 to be equal to or less than the upper limit of the above-mentioned numerical range, it is possible to keep the overall length of the collecting lens system 140 at an appropriate length. On the other hand, by setting the apex angle of the first axicon lens 141 to be equal to or more than the lower limit of the above-mentioned numerical range, it is possible to prevent the distance from the collecting lens system 140 to the glass substrate 10, that is, the working distance, from becoming too short, and it is possible to ensure an appropriate working distance.

[0053] Furthermore, since the apex angle of the first axicon lens 141 is within the above range, the light density at the position of the main peak in the light density distribution at the substrate center 10b of the glass substrate 10 can be made even greater than the light density at the position of the main peak in the light density distribution at the substrate front surface 10a and the light density at the position of the main peak in the light density distribution at the substrate back surface 10c.

[0054] This allows the modified region 20 to be formed in a wider range at the substrate center 10b of the glass substrate 10 than at the substrate front surface 10a and the substrate back surface 10c (see FIG. 6).

[0055] The convex lens 142 is disposed between the first axicon lens 141 and the second axicon lens 143. The convex lens 142 converts the annular Bessel beam 162 emitted from the first axicon lens 141 into a converging annular Bessel beam 163 and makes it incident on the second axicon lens 143. "Converging" here means that the beam is converged with respect to the annular shape of the annular Bessel beam 162 formed by the first axicon lens.

[0056] The condenser lens system 140 is configured so that the convex lens 142 can be replaced with a convex lens having a different focal length.

[0057] The convex lens 142 can be any lens having a positive refractive power, and can be a biconvex lens, a convex-plano lens, a convex-concave lens, or the like.

[0058] Furthermore, in addition to a spherical lens whose convex surface forms part of a spherical surface, an aspherical lens can be used as the convex lens 142. By using an aspherical lens as the convex lens 142, spherical aberration can be kept small.

[0059] Furthermore, the convex lens 142 may be a combination of multiple optical elements to generate positive refractive power. For example, one or more convex lenses may be combined with one or more concave lenses to generate positive refractive power. By combining one or more convex lenses with one or more concave lenses, it is possible to minimize spherical aberration.

[0060] By minimizing the spherical aberration of the convex lens, the light density at the main peak position in the light density distribution at the substrate center 10b can be made even greater than the light density at the main peak position in the light density distribution at the substrate front surface 10a and the light density at the main peak position in the light density distribution at the substrate back surface 10c. Furthermore, by minimizing the spherical aberration of the convex lens, the uniformity of the light density distribution at the substrate front surface 10a and the light density distribution at the substrate back surface 10c can be improved.

[0061] The focal length of the convex lens is not particularly limited, but is preferably 100 mm to 200 mm, and more preferably 100 mm to 150 mm. When the focal length of the convex lens is within the above range, the light density at the main peak in the light density distribution at the substrate center 10b, at the position where the modified region 20 of the glass substrate 10 is formed, can be made much higher than the light density at the main peak in the light density distribution at the substrate front surface 10a and the light density at the main peak in the light density distribution at the substrate back surface 10c.

[0062] This allows the modified region 20 to be formed in a wider range at the substrate center 10b of the glass substrate 10 than at the substrate front surface 10a and the substrate back surface 10c (see FIG. 6).

[0063] 2 is a diagram showing the relationship between the focal length of the convex lens 142 and the light density distribution in the thickness direction of the glass substrate 10. The focal length of the convex lens 142 was changed to four levels: 100 mm, 150 mm, 200 mm, and 300 mm, and the light density at the position of the optical axis 165 on the substrate surface 10a, the substrate center 10b, and the substrate back surface 10c was simulated. The apex angle of the first axicon lens 141 was 160°, the apex angle of the second axicon lens 143 was 130°, and the thickness of the glass substrate 10 was 1 mm.

[0064] The horizontal axis represents the position in the thickness direction of the glass substrate 10. The origin is the substrate center 10b. The vertical axis represents the light density in Fig. 2(a), and represents the light density normalized by the light density at the origin (substrate center 10b) in Fig. 2(b).

[0065] From Figure 2, it can be seen that when the focal length of the convex lens 142 is 100 mm, 150 mm, or 200 mm, the light density at the center 10b of the substrate is six or more times the light density at the front surface 10a of the substrate and the light density at the back surface 10c of the substrate, and that the light density at the center 10b of the substrate is sufficiently higher than the light density at the front surface 10a of the substrate and the light density at the back surface 10c of the substrate.

[0066] When the focal length is 100 mm, the light density at the center 10b of the substrate is high, but at the same time, the light density at the front surface 10a of the substrate and the light density at the rear surface 10c of the substrate are low.

[0067] Fig. 3 is a diagram showing the position at which the annular convergent Bessel beam 164 emitted from the condensing lens system 140 converges when a convex lens with a different focal length is used as the convex lens 142. Fig. 3 shows that when the convex lens 142 with a short focal length is used as the convex lens 142, the annular convergent Bessel beam 164 converges at a position closer to the condensing lens system 140 and in a narrower range in the direction in which the optical axis 165 extends than when the convex lens 142 with a long focal length is used.

[0068] When a convex lens with a focal length of 100 mm was used as the convex lens 142, it is believed that the annular convergent Bessel beam 164 converged at a position close to the substrate center 10b between the substrate front surface 10a and the substrate back surface 10c. As a result, it is believed that the annular convergent Bessel beam 164 was not sufficiently converged on the substrate front surface 10a and the substrate back surface 10c, and the light density on the substrate front surface 10a and the substrate back surface 10c decreased.

[0069] In order to increase the light density on the substrate front surface 10a and the light density on the substrate back surface 10c to a level at which the glass substrate 10 can be modified, the power of the laser light 161 emitted from the laser oscillator 120 can be increased.

[0070] The second axicon lens 143 is disposed along the optical axis 165 and converges the annular convergent Bessel beam 163 toward the optical axis 165. The annular convergent Bessel beam 164 converged by the second axicon lens 143 converges between the substrate front surface 10a and the substrate back surface 10c of the glass substrate 10.

[0071] The focusing lens system 140 is configured so that the second axicon lens 143 can be replaced with an axicon lens 143 having a different apex angle. The orientation of the apex 143a of the cone of the second axicon lens 143 may be either toward the glass substrate 10 or toward the convex lens 142.

[0072] When the apex 143a of the cone of the second axicon lens 143 is arranged facing the glass substrate 10, the annular convergent Bessel beam 163 is incident on the flat surface side of the second axicon lens 143, and the angle of incidence of the convergent Bessel beam 163 with respect to the second axicon lens 143 becomes close to perpendicular. This makes it possible to make full use of the performance of the coating applied to the second axicon lens 143 and to increase the transmittance of the annular convergent Bessel beam 163 incident on the second axicon lens 143.

[0073] On the other hand, when the apex 143a of the cone of the second axicon lens 143 is arranged facing the convex lens 142, the apex 143a of the cone of the axicon lens 143, which is easily damaged, can be placed facing inward of the lens barrel. This has the effect of making the device easier to handle.

[0074] The apex angle of the second axicon lens 143 is not particularly limited as long as it is smaller than the apex angle of the first axicon lens 141, but is preferably 120° to 150°, and more preferably 120° to 140°.

[0075] By setting the apex angle of the second axicon lens 143 to an angle smaller than the apex angle of the first axicon lens 141, the annular convergent Bessel beam 164 can be converged.

[0076] Furthermore, by setting the apex angle of the second axicon lens 142 to be equal to or less than the upper limit of the above-mentioned range of numerical values, it is possible to keep the overall length of the condensing lens system 140 at an appropriate length. On the other hand, by setting the apex angle of the second axicon lens 143 to be equal to or more than the lower limit of the above-mentioned range of numerical values, it is possible to prevent the distance from the condensing lens system 140 to the glass substrate 10, that is, the working distance, from becoming too short, and to ensure an appropriate working distance.

[0077] Furthermore, since the apex angle of the second axicon lens 143 is within the above range, the light density at the position of the main peak in the light density distribution at the substrate center 10b of the glass substrate 10 can be made even greater than the light density at the position of the main peak in the light density distribution on the substrate front surface 10a and the light density at the position of the main peak in the light density distribution on the substrate back surface 10c.

[0078] 4 is a diagram showing the relationship between the apex angle of the second axicon lens 143 and the light density distribution in the thickness direction of the glass substrate 10. The apex angle of the second axicon lens 143 was changed to four levels: 120°, 130°, 140°, and 150°, and the light density at the position of the optical axis 165 on the substrate front surface 10a, substrate center 10b, and substrate back surface 10c was simulated. The apex angle of the first axicon lens 141 was 160°, the focal length of the convex lens 142 was 200 mm, and the thickness of the glass substrate 10 was 1 mm.

[0079] The horizontal axis represents the position in the thickness direction of the glass substrate 10. The origin is the substrate center 10b. The vertical axis represents the light density in Fig. 4(a), and represents the light density normalized by the light density at the origin (substrate center 10b) in Fig. 4(b).

[0080] From FIG. 4, it can be seen that when the apex angle of the second axicon lens 143 is 120° or 130°, the light density at the substrate center 10b is six or more times the light density at the substrate front surface 10a and the light density at the substrate back surface 10c, and that the light density at the substrate center 10b is sufficiently higher than the light density at the substrate front surface 10a and the light density at the substrate back surface 10c.

[0081] When the apex angle of the second axicon lens 143 is 120°, the light density at the center 10b of the substrate is high, but at the same time, the light density at the front surface 10a of the substrate and the light density at the rear surface 10c of the substrate are low.

[0082] This is thought to be because, when the second axicon lens 143 with a small apex angle is used, the annular convergent Bessel beam 164 converges at a position close to the substrate center 10b. As a result, the annular convergent Bessel beam 164 does not converge sufficiently on the substrate front surface 10a and the substrate back surface 10c, which is thought to result in a decrease in the light density on the substrate front surface 10a and the substrate back surface 10c.

[0083] In order to increase the light density on the substrate front surface 10a and the light density on the substrate back surface 10c to a level at which the glass substrate 10 can be modified, the power of the laser light 161 emitted from the laser oscillator 120 can be increased.

[0084] As described above, the focusing lens system 140 is configured so that the first axicon lens 141 can be replaced with an axicon lens having a different apex angle. Also, the convex lens 142 can be replaced with a convex lens having a different focal length. Furthermore, the second axicon lens 143 can be replaced with an axicon lens having a different apex angle.

[0085] This allows the condensing lens system 140 to adjust the position at which the annular convergent Bessel beam 164 is converged. That is, the condensing lens system 140 can converge the annular convergent Bessel beam 164 between the substrate front surface 10a and the substrate back surface 10c of the glass substrate 10.

[0086] Furthermore, the light density at the position of the main peak in the light density distribution at the center 10b of the substrate can be made larger than the light density at the position of the main peak in the light density distribution on the front surface 10a of the substrate and the light density at the position of the main peak in the light density distribution on the back surface 10c of the substrate.

[0087] This allows the modified region 20 to be formed in a wider range at the substrate center 10b of the glass substrate 10 than at the substrate front surface 10a and the substrate back surface 10c.

[0088] Next, the laser oscillator 120 that can be used in the laser processing apparatus of the first embodiment will be described.

[0089] The laser oscillator 120 is a laser oscillator (femtosecond pulse laser oscillator or picosecond pulse laser oscillator) that emits an ultrashort pulse laser beam, and outputs laser beam 161 with a wavelength of 800 nm to 2000 nm. For example, an R-series oscillator manufactured by RAYDIANCE (wavelength 1553 nm, output power 10 W to 15 W, pulse width 500 fsec to 800 fsec), a Monaco-series oscillator manufactured by COHERENT (wavelength 1035 nm, output power 20 W to 40 W, pulse width 400 fsec to 10 psec), or a TruMicro-series oscillator manufactured by TRUMPF (wavelength 1030 nm, output power 10 W to 50 W, pulse width 400 fsec to 20 psec) can be used.

[0090] In the first embodiment, a pulsed laser beam having a pulse width of 10 psec or less is used, and the pulsed laser beam has a wavelength of 1030 nm, a beam diameter of 3 mm to 6 mm, and an average output of 50 W.

[0091] The light density distribution of the laser light 161 emitted by the laser oscillator 120 is preferably a Gaussian distribution. When the light density distribution of the laser light 161 is a Gaussian distribution, when the annular convergent Bessel beam 164 converges between the substrate front surface 10a and the substrate back surface 10c of the glass substrate 10, the light density at the position of the main peak in the light density distribution at the substrate center 10b can be made larger than the light density at the position of the main peak in the light density distribution on the substrate front surface 10a and the light density at the position of the main peak in the light density distribution on the substrate back surface 10c at the position where the modified region 20 of the glass substrate 10 is formed.

[0092] This allows the modified region 20 to be formed in a wider area at the substrate center 10b of the glass substrate 10 than at the substrate front surface 10a and the substrate back surface 10c.

[0093] 5 is a diagram showing the relationship between the light density distribution of laser light 161 incident on the condenser lens system 140 and the light density distribution in the thickness direction of the glass substrate. The light density distribution of laser light 161 incident on the condenser lens system 140 was changed to a Gaussian distribution or a flat distribution, and the light densities at the positions of the optical axis 165 on the substrate surface 10a, the substrate center 10b, and the substrate back surface 10c were simulated. The apex angle of the first axicon lens 141 was 160°, the apex angle of the second axicon lens 143 was 130°, the focal length of the convex lens 142 was 200 mm, and the thickness of the glass substrate 10 was 1 mm.

[0094] The horizontal axis represents the position in the thickness direction of the glass substrate 10. The origin is the substrate center 10b. The vertical axis represents the light density in Fig. 5(a), and represents the light density normalized by the light density at the origin (substrate center 10b) in Fig. 5(b).

[0095] 5, it can be seen that the light density at the substrate center 10b is higher when the light density distribution of the laser beam 151 is a Gaussian distribution. That is, it can be confirmed that in the modified region formation method of the first embodiment, the laser beam 161 to be incident on the condenser lens system 140 is preferably a laser beam whose light density distribution is centered on the optical axis 165, for example, a laser beam having a Gaussian distribution.

[0096] 1-2. Method for forming modified region and method for forming through-hole Next, a modified region forming method and a through-hole forming method according to embodiment 1 will be described. Fig. 6 is a schematic diagram of a glass substrate 10 on which a modified region has been formed by the modified region forming method according to embodiment 1 and a through-hole has been formed by the through-hole forming method according to embodiment 1. Fig. 7 is a flowchart showing the steps of the modified region forming method and the through-hole forming method according to embodiment 1.

[0097] The modified region forming method according to the first embodiment includes a modified region forming step (step ST1) of forming a modified region 20 in a glass substrate 10 as an article. The through-hole forming method includes the modified region forming step (step ST1) described above, and an etching step (step ST2) of etching the glass substrate 10 on which the modified region 20 has been formed to form a through-hole.

[0098] 1-2-1. Modified area formation process The modified region forming step according to the first embodiment is a step of irradiating a laser beam 161 via a condenser lens system 140 onto a position where a modified region 20 is to be formed on a glass substrate 10, which is an article serving as a workpiece, using, for example, a laser processing apparatus 100A shown in Fig. 1, to form a modified region 20 that extends from the front surface 10a to the back surface 10c of the glass substrate 10 (step ST1). The condenser lens system 140 has a first axicon lens 141, a convex lens 142, and a second axicon lens 143.

[0099] The first axicon lens 141 converts the laser light 161 into an annular Bessel beam 162 and makes it incident on the convex lens 142 .

[0100] The convex lens 142 is disposed between the first axicon lens 141 and the second axicon lens 143. The convex lens 142 converts the annular Bessel beam 162 emitted from the first axicon lens 141 into an annular converging Bessel beam 163 and makes the beam incident on the second axicon lens 143.

[0101] The second axicon lens 143 irradiates the glass substrate 10 with a circular, convergent Bessel beam 164 .

[0102] Here, the condenser lens system 140 is configured so that the first axicon lens 141 can be replaced with an axicon lens having a different apex angle. Also, the convex lens 142 can be replaced with a convex lens having a different focal length. Furthermore, the second axicon lens 143 can be replaced with an axicon lens having a different apex angle.

[0103] As a result, at the position where the modified region 20 of the glass substrate 10 is formed, the light density at the position of the main peak in the light density distribution at the center 10b of the substrate can be made larger than the light density at the position of the main peak in the light density distribution on the surface 10a of the substrate and the light density at the position of the main peak in the light density distribution on the back surface 10c of the substrate.

[0104] The mechanism by which the optical density of the annular convergent Bessel beam 164 at the position of the main peak in the optical density distribution at the substrate center 10b of the glass substrate 10 can be made larger than the optical density at the main peak in the optical density distribution on the substrate front surface 10a and the optical density at the main peak in the optical density distribution on the substrate back surface 10c will be described below.

[0105] Fig. 8 is a diagram for explaining a light flux when a glass substrate 10 is irradiated with a circular convergent Bessel beam 164. Fig. 9 is a diagram showing a light density distribution when a glass substrate 10 is irradiated with a circular convergent Bessel beam 164. Fig. 9(a) shows the light density distribution at a position AA on the substrate front surface 10a, Fig. 9(b) shows the light density distribution at a position BB on the substrate center 10b, and Fig. 9(c) shows the light density distribution at a position CC on the substrate back surface 10c.

[0106] 8, no light flux of the annular convergent Bessel beam 164 exists at the position of the optical axis 165 on the substrate front surface 10a and the substrate back surface 10c. However, the light density distribution on the substrate front surface 10a in FIG. 9(a) and the light density distribution on the substrate back surface 10c in FIG. 9(c) show that main peaks 61a and 61c of light density exist at the position of the optical axis 165. This is because, on the substrate front surface 10a and the substrate back surface 10c, the annular convergent Bessel beam 164 converges and is close to each other, and therefore interacts with each other, causing the main peak to appear at the position of the optical axis 165.

[0107] 9(a) to 9(c), the horizontal axis represents the distance from the optical axis 165, and the vertical axis represents the optical density. The scales of the vertical and horizontal axes of each graph are the same for ease of comparison.

[0108] First, the light density distribution at the substrate center 10b in Fig. 9(b) will be described. At the substrate center 10b, a main peak 61b where the light density is maximum is observed at the position of the optical axis 165, that is, the position of the origin of the horizontal axis of the graph.

[0109] A first diffraction ring 62b and a second diffraction ring 63b are also observed on both sides of the main peak 61b. The light density at the position of the main peak 61b is approximately six times the light density at the position of the first diffraction ring 62b and approximately 13 times the light density at the position of the second diffraction ring.

[0110] The graph shows the threshold 65, which is the light density at which the glass substrate 10 is modified. Here, the threshold 65 is the light density at which the crystalline structure of the glass is destroyed and modification occurs when the glass substrate 10 is irradiated with laser light.

[0111] The light density distribution at the substrate center 10b is compared with a threshold value 65. The light density at the position of the main peak 61b and the light density at the position of the first diffraction ring 62b exceed the threshold value 65. That is, at the substrate center 10b of the glass substrate 10, modification occurs at the position of the main peak 61b and the position of the first diffraction ring 62b. On the other hand, there is a region between the position of the main peak 61b and the position of the first diffraction ring 62b where the light density does not reach the threshold value 65. No modification occurs in this region.

[0112] Next, the light density distribution on the substrate surface 10a in Figure 9(a) will be described. On the substrate surface 10a, a main peak 61a where the light density distribution is maximum is observed at the position of the optical axis 165. The light density at the position of the main peak 61a in the light density distribution on the substrate surface 10a is lower than the light density at the position of the main peak 61b in the light density distribution at the substrate center 10b.

[0113] In addition, a first diffraction ring 62a exists outside the main peak. The light density at the position of the first ring 62a in the light density distribution on the substrate surface 10a is also smaller than the light density at the position of the first ring 62b in the light density distribution on the substrate center 10b.

[0114] When the light density distribution on the substrate surface 10a is compared with the threshold 65 at which modification occurs, the light density at the position of the main peak 61a exceeds the threshold 65, but the light density at the position of the first diffraction ring 62a is lower than the threshold 65.

[0115] The light density distribution on the rear surface 10c of the substrate in Figure 9(c) will be described. The light density distribution on the rear surface 10c of the substrate is similar to the light density distribution on the front surface 10a of the substrate. A main peak 61c, where the light density distribution is maximum, is observed at the position of the optical axis 165. The light density at the position of the main peak 61c in the light density distribution on the rear surface 10c of the substrate is lower than the light density at the position of the main peak 61b in the light density distribution at the center 10b of the substrate.

[0116] The first diffraction ring 62c is located outside the main peak. The light density at the first ring 62c in the light density distribution on the rear surface 10c of the substrate is also smaller than the light density at the position of the first ring 61c in the light density distribution at the center 10b of the substrate.

[0117] When the light density distribution on the rear surface 10c of the substrate is compared with the threshold 65 at which modification occurs, the light density at the position of the main peak 61c exceeds the threshold 65, but the light density at the position of the first diffraction ring 62c is lower than the threshold.

[0118] The light density distributions on the substrate front surface 10a, the substrate center 10b, and the substrate back surface 10c have been described above. As already explained, the light density at the position of the main peak 61b in the light density distribution at the substrate center 10b is greater than the light density at the position of the main peak 61a in the light density distribution on the substrate front surface 10a and the light density at the position of the main peak 61c in the light density distribution on the substrate back surface 10c.

[0119] Here, the modified region 20 where the glass substrate 10 is modified is a region where the light density in that region exceeds the threshold value 65. The position of the main peak 61b in the light density distribution at the substrate center 10b exceeds the threshold value 65 because the light density value is large, and the region Rb where the modification occurs is also wide.

[0120] That is, among the regions belonging to the main peak 61b in the light density distribution at the center 10b of the substrate, the region Rb where the threshold value 65 is exceeded and modification occurs is wider than the region Ra among the regions belonging to the main peak 61a in the light density distribution at the front surface 10a of the substrate where the threshold value 65 is exceeded and modification occurs, and the region Rc among the regions belonging to the main peak 61c in the light density distribution at the back surface 10c of the substrate where the threshold value 65 is exceeded and modification occurs.

[0121] This allows the modified region 20 to be formed in a wider area at the substrate center 10b of the glass substrate 10 than at the substrate front surface 10a and the substrate back surface 10c.

[0122] Furthermore, when the glass substrate 10 with the modified region 20 formed therein is etched to form the through-hole 30, the modified region 20 is formed over a wide area, so that the inner diameter d2 of the through-hole at the substrate center 10b can be widened. This makes it possible to reduce the difference between the inner diameter d2 of the through-hole at the substrate center and the inner diameter d1 of the through-hole at the substrate front surface 10a, and the difference between the inner diameter of the through-hole d2 at the substrate center 10b and the inner diameter d3 of the through-hole at the substrate back surface 10c.

[0123] It is preferable that the light density at the position of the main peak 61b in the light density distribution at the center 10b of the substrate is greater than the light density at the position of the main peak 61a in the light density distribution at the front surface 10a of the substrate and the light density at the position of the main peak 61c in the light density distribution at the rear surface 10c of the substrate.

[0124] This allows the modified region 20 to be formed in a wider range at the substrate center 10b of the glass substrate 10 than at the substrate front surface 10a and the substrate back surface 10c.

[0125] Furthermore, in the modified region formation method of embodiment 1, it is preferable that the light density at the position of the main peak 61a in the light density distribution on the substrate surface 10a and the light density at the position of the main peak 61c in the light density distribution on the substrate back surface 10c are greater than the threshold value 65 at which modification occurs.

[0126] As a result, the glass substrate 10 is modified at the position of the main peak 61a on the substrate front surface 10a and the position of the main peak 61c on the substrate back surface 10c, and modified regions 20 are formed.

[0127] On the other hand, the light density at the position of the first diffraction ring 62a in the light density distribution on the substrate front surface 10a and the light density at the position of the first diffraction ring 62c in the light density distribution on the substrate back surface 10c are preferably smaller than the modification threshold 65. That is, it is preferable that the glass substrate 10 is not modified at the position of the first diffraction ring 62a on the substrate front surface 10a and the position of the first diffraction ring 62c on the substrate back surface 10c.

[0128] As a result, when the modified glass substrate 10 is etched to form the through holes 30, the through holes 30 can be formed in perfect circles corresponding to the shapes of the main peaks 61a, 61c on the substrate front surface 10a and the substrate back surface 10c of the glass substrate 10.

[0129] Furthermore, in the modified region forming method of the first embodiment, it is preferable that the light density at the position of the first diffraction ring 62b in the light density distribution at the substrate center 10b is greater than the threshold value 65 at which the glass is modified.

[0130] This allows the modified regions 20a, 20b to be formed in a wider range at the substrate center 10b than at the substrate front surface 10a and substrate back surface 10c.

[0131] Furthermore, when the modified glass substrate 10 is etched to form the through-hole 30, the inner diameter d2 of the through-hole at the substrate center 10b can be made even larger. Also, the difference between the inner diameter d2 of the through-hole at the substrate center 10b and the inner diameter d1 of the through-hole 30 on the substrate front surface 10a, and the difference between the inner diameter d2 of the through-hole at the substrate center 10b and the inner diameter d3 of the through-hole 30 on the substrate back surface 10c can be made smaller.

[0132] Between the main peak 61b and the first diffraction ring 62b, there is an unmodified region where the light density of the irradiated laser beam 151 does not reach the threshold value 65. However, if the unmodified region is removed by "slow" etching, the etching solution can reach the modified region 20b. Once the etching solution reaches the modified region 20b, it can remove the modified region 20b by "fast" etching, thereby increasing the inner diameter d2 of the through-hole 30 at the substrate center 10b.

[0133] Furthermore, in the modified region formation method of embodiment 1, the light density at the position of the main peak 61b of the light density distribution at the center 10b of the substrate is preferably at least six times, more preferably at least eight times, and even more preferably at least ten times the light density at the position of the main peak 61a in the light density distribution on the substrate surface 10a and the light density at the position of the main peak 61c in the light density distribution on the back surface 10c of the substrate.

[0134] Since the optical density at the position of the main peak 61b in the optical density distribution at the substrate center 10b is within the above range relative to the optical density at the position of the main peak 61a in the optical density distribution on the substrate surface 10a or the optical density at the position of the main peak 61c in the optical density distribution on the substrate back surface 10c, at the position where the modified region 20 of the glass substrate 10 is formed, the optical density at the position of the main peak in the optical density distribution at the substrate center 10b of the glass substrate 10 can be made even greater than the optical density at the position of the main peak in the optical density distribution on the substrate surface 10a and the optical density at the position of the main peak in the optical density distribution on the substrate back surface 10c.

[0135] 1-2-2. Etching process After the modified region forming step (ST1), an etching step (ST2) is performed in which the glass substrate is etched with a hydrofluoric acid-based etching solution to form through-holes 30. In the etching step (ST2), the front surface 10a and the back surface 10c of the glass substrate 10 are etched, and the glass substrate 10 is thinned. As a result of the thinning, new front surface 10d and back surface 10e of the glass substrate 10 are formed. Simultaneously with the etching to thin the glass substrate 10, the etchant seeps into the modified region 20, etching the modified region 20 and forming pilot holes 30a (see FIG. 6).

[0136] When the modified region 20 is eroded by the etching solution to form the pilot hole 30a, etching of the modified region 20 proceeds in the thickness direction (z direction) of the glass substrate 10, and etching of the unmodified region proceeds simultaneously, with the etching solution that has entered the pilot hole 30a etching the inner wall of the pilot hole 30a in the lateral direction (direction along the xy plane).

[0137] At this time, the etching of the modified region 20 proceeds in the thickness direction (z direction) of the glass substrate 10, and is faster than the etching of the unmodified region proceeds in the lateral direction (direction along the xy plane) of the glass substrate 10. In the prior art, due to the difference in the etching rate between the modified region 20 and the unmodified region, the inner diameter of the through hole at the substrate center 10b tends to be smaller than the inner diameter of the through hole at the substrate front surface 10a and the inner diameter of the through hole at the substrate back surface 10c.

[0138] However, in the through-hole forming method of embodiment 1, in the modified region forming step (step ST1), the light density at the position of the main peak in the light density distribution at the substrate center 10b is greater than the light density at the peak position in the light density distribution on the substrate front surface 10a and the light density at the peak position in the light density distribution on the substrate back surface 10c. As a result, the range Rb of the modified region 20a formed by the main peak at the substrate center 10b is greater than the range Ra of the modified region 20a formed by the main peak on the substrate front surface 10a and the range Rc of the modified region 20a formed by the main peak on the substrate back surface 30c (see FIG. 8).

[0139] As a result, when the glass substrate 10 is etched to form the through hole 30, the difference between the inner diameter d1 of the through hole 30 at the substrate surface 10a, the inner diameter d3 of the through hole 30 at the substrate back surface 10c, and the inner diameter d2 of the through hole 30 at the substrate center 10b can be reduced (see Figure 6).

[0140] 2. Embodiment 2 Fig. 10 is a diagram showing an example of a correction optical system 150 in embodiment 2. Fig. 10(a) is a diagram showing how the light flux of laser light incident on the condenser lens system is corrected, and Fig. 10(b) is a diagram comparing the light density distribution 171 of the laser light before correction with the light density distribution 172 after correction.

[0141] Correction optical system 150 makes a correction to increase the light density in the central portion of the light density distribution of laser beam 161 that is made incident on condenser lens system 140. Any correction optical system can be suitably used as long as it makes a correction to increase the light density in the central portion of the light density distribution of incident laser beam 161. Optical element 151 has entrance surface 151a onto which laser beam 161 is incident and exit surface 151b from which the laser beam exits.

[0142] The incident surface 151a is formed as an aspherical surface with a convex center, with the curvature gradually decreasing toward the center. Of the laser beams 161 incident on the optical element 151, those that are incident on the peripheral portion of the incident surface 161a away from the center are incident on the optical element 151 at an angle nearly parallel to the optical axis 165. On the other hand, the light that is incident near the central annular zone has its traveling direction changed at the incident surface 161a so that it approaches the optical axis 165.

[0143] Exit surface 151b has an aspherical surface with a concave center, whose curvature gradually decreases toward the center. Of the laser beams 161 incident on optical element 151, those that are incident on the peripheral portion away from optical axis 165 of entrance surface 161a also exit optical element 151 at an angle close to perpendicular emission from exit surface 151b. On the other hand, light that is incident near the central annular zone of entrance surface 151a of optical element 151 and has its traveling direction changed so that it approaches optical axis 165 is returned to parallel rays at exit surface 151b.

[0144] 10(a) can correct the laser beam 161 incident on the condenser lens system 140 to increase the optical density in the central portion. For example, when laser beam having an optical density of Gaussian distribution 171 in FIG. 10(b) is incident on the optical element 151, it can emit laser beam having an optical density distribution 172 in which the optical density in the central portion is even greater.

[0145] The laser beam 172 having such a light density distribution is incident on the condenser lens system 140, and the circular converging Bessel beam 164 emitted from the condenser lens system is converged between the substrate surface 10a of the glass substrate 10 and the glass substrate 10c, thereby achieving the following effects.

[0146] That is, the light density at the position of the main peak in the light density distribution at the substrate center 10b of the glass substrate 10 can be made greater than the light density at the position of the main peak in the light density distribution at the substrate surface 10a and the light density at the position of the main peak in the light density distribution at the substrate back surface 10c.

[0147] As a result, the modified region 20 can be formed in a wider range at the substrate center 10b of the glass substrate 10 than at the substrate front surface 10a and the substrate back surface 10c.

[0148] Furthermore, when the modified glass substrate 10 is etched to form a through hole 30, the inner diameter d1 of the through hole at the substrate center 10b can be increased, and the difference between the inner diameter d1 of the through hole at the substrate surface 10a and the inner diameter of the through hole d2 at the substrate center 10b, and the difference between the inner diameter d3 of the through hole at the substrate back surface 10c and the inner diameter of the through hole d2 at the substrate center 10b can be reduced.

[0149] 3. Embodiment 3 The focusing lens device of embodiment 3 is a focusing lens device that forms a modified region 20 extending from the substrate surface 10a of the glass substrate 10 to the substrate back surface 10c by irradiating laser light 151 through a focusing lens system 140 at a position where a modified region 20 is to be formed on the glass substrate 10, which is an article serving as a workpiece.

[0150] A condensing lens device according to the third embodiment will be described below with reference to Fig. 1. Note that the description of parts that overlap with the above-described embodiments may be omitted as appropriate.

[0151] The condensing lens system 140 includes two axicon lenses, a first axicon lens 141 and a second axicon lens 143, arranged along an optical axis 165, and a convex lens 142 arranged between the two axicon lenses. The laser light 151 that passes through the condensing lens system 140 becomes a circular convergent Bessel beam 164, which is configured to converge between the substrate front surface 10a and the substrate back surface 10c.

[0152] This allows the light density at the position of the main peak in the light density distribution at the substrate center 10b of the glass substrate 10 to be greater than the position of the main peak in the light density distribution on the substrate surface 10a and the position of the main peak in the light density distribution on the substrate back surface 10c.

[0153] As a result, the modified region 20 can be formed in a wider range at the substrate center 10b of the glass substrate 10 than at the substrate front surface 10a and the substrate back surface 10c.

[0154] Furthermore, when the modified glass substrate 10 is etched to form a through hole 30, the inner diameter d1 of the through hole at the substrate center 10b can be increased, and the difference between the inner diameter d1 of the through hole at the substrate surface 10a and the inner diameter of the through hole d2 at the substrate center 10b, and the difference between the inner diameter d3 of the through hole at the substrate back surface 10c and the inner diameter of the through hole d2 at the substrate center 10b can be reduced.

[0155] 4. Method for manufacturing an article having a modified region The method for manufacturing an article having a modified region according to embodiment 4 includes a modified region formation step of forming a modified region 20 extending from the front surface 10a to the back surface 10c of a glass substrate 10, which is an article serving as a workpiece, by irradiating laser light 151 via a focusing lens system 140 onto a position where the modified region 20 is to be formed on the glass substrate 10.

[0156] The condensing lens system 140 includes two axicon lenses, namely, a first axicon lens 141 and a second axicon lens 143, arranged along an optical axis 165, and a convex lens 142. The ultrashort pulsed laser light that has passed through the condensing lens system 140 becomes a circular convergent Bessel beam 164, which is configured to converge between the substrate front surface 10a and the substrate back surface 10c of the glass substrate 10.

[0157] A method for manufacturing an article having a modified region according to embodiment 4 will be described below with reference to Fig. 1 and Fig. 6 to Fig. 7. Note that explanations of parts that overlap with the explanations of the above-mentioned embodiments may be omitted as appropriate.

[0158] The glass substrate 10 is placed on a table (not shown) of the laser processing apparatus shown in Fig. 1. Laser light 151 emitted from the laser oscillator 120 is converted by the condenser lens system 140 into a circular, convergent Bessel beam 164, which is then irradiated onto the glass substrate 10.

[0159] This makes it possible to make the light density at the position of the main peak in the light density distribution at the center 10b of the substrate in the thickness direction of the substrate greater than the light density at the position of the main peak in the light density distribution on the front surface 10a of the substrate and the light density at the position of the main peak in the light density distribution on the back surface 10c of the substrate.

[0160] As a result, the modified region 20 can be formed in a wider range at the substrate center 10b of the glass substrate 10 than at the substrate front surface 10a and the substrate back surface 10c.

[0161] Furthermore, when the modified glass substrate 10 is etched to form a through hole 30, the inner diameter d1 of the through hole at the substrate center 10b can be increased, and the difference between the inner diameter d1 of the through hole at the substrate surface 10a and the inner diameter of the through hole d2 at the substrate center 10b, and the difference between the inner diameter d3 of the through hole at the substrate back surface 10c and the inner diameter of the through hole d2 at the substrate center 10b can be reduced. [Explanation of symbols]

[0162] 10...glass substrate, 10a...substrate surface, 10b...center position between the substrate surface and the substrate back surface (center of substrate), 10c...substrate back surface, 10d...substrate surface after etching, 10e...substrate back surface after etching, 20...modified region, 20a...modified region (modified region at the position of the main peak), 20b...modified region (modified region at the position of the first ring), 30...through hole, 30a...through hole (pilot hole), 30b...through hole, 61a, 61b, 61c...main peak, 62a, 62b, 62c...first ring, 63b...second ring, 65...threshold, 100A...laser Processing device, 120... laser oscillator, 130... optical optical system, 131... mirror, 140... focusing lens system, 141... first axicon lens, 141a... apex of cone, 142... convex lens, 143... second axicon lens, 143a... apex of cone, 150... correction optical system, 151... optical element, 151a... incident surface, 151b... exit surface, 160... laser irradiation unit, 161... ultrashort pulse laser light (laser light), 162... annular Bessel beam, 163, 164... annular convergent Bessel beam, 165... optical axis of laser light

Claims

1. 1. A modified region forming method comprising: a modified region forming step of forming a modified region extending from a front surface to a back surface of an article as a workpiece by irradiating an ultrashort pulsed laser beam via a condenser lens system at a position where a modified region is to be formed on the article, the modified region comprising: the focusing lens system comprises two axicon lenses arranged along an optical axis of the extremely short pulsed laser beam and a convex lens arranged between the two axicon lenses, the extremely short pulsed laser beam passing through the focusing lens system becomes a circular converging Bessel beam, and the circular converging Bessel beam is configured to converge between the front surface and the back surface of the article.

2. 2. The modified region forming method according to claim 1, A modified region forming method, characterized in that the optical density at the position of the main peak in the optical density distribution of the extremely short pulsed laser light at the center position between the front surface and the back surface in the optical axis direction of the article is greater than the optical density at the position of the main peak in the optical density distribution of the extremely short pulsed laser light on the surface of the article.

3. 3. The modified region forming method according to claim 1 or 2, the light density at the position of the main peak in the light density distribution of the ultrashort pulsed laser light on the surface of the article is greater than a threshold value at which the article is modified; A modified region forming method, characterized in that the light density at the position of the first diffraction ring in the light density distribution of the ultrashort pulse laser light on the surface of the article is smaller than a threshold value at which the article is modified.

4. The modified region forming method according to any one of claims 1 to 3, A modified area forming method, characterized in that the light density at the position of the first diffraction ring in the light density distribution of the ultrashort pulse laser light at the center position between the front surface and the back surface in the optical axis direction of the article is greater than the threshold value at which the article is modified.

5. The modified region forming method according to any one of claims 1 to 4, A modified region forming method, characterized in that the optical density at the main peak position in the optical density distribution of the extremely short pulsed laser light at the center position between the front surface and the back surface in the optical axis direction of the article is greater than six times the optical density at the main peak position in the optical density distribution of the extremely short pulsed laser light on the surface of the article.

6. The modified region forming method according to any one of claims 1 to 5, The modified region forming method is characterized in that the convex lens is an aspherical lens.

7. 7. The modified region forming method according to claim 6, A modified region forming method, characterized in that a concave lens is provided between the two axicon lenses.

8. The modified region forming method according to any one of claims 1 to 7, The modified region forming method is characterized in that the in-plane distribution of the light density of the ultrashort pulse laser light incident on the focusing lens system is a Gaussian distribution.

9. The modified region forming method according to any one of claims 1 to 8, a correction optical system that corrects the light density distribution of the laser light incident on the condenser lens system; The modified region forming method is characterized in that the correction optical system performs correction to increase the light density in the central portion.

10. 10. The modified region forming method according to claim 9, A modified region forming method characterized in that the correction optical system has a first aspherical surface and a second aspherical surface, and is configured so that when the in-plane distribution of the light density of the extremely short pulse laser light incident on the focusing lens system is a Gaussian distribution, the light density in the central portion is greater.

11. A modified region forming method according to any one of claims 1 to 10; and an etching step of etching the article on which the modified region has been formed to form a through hole.

12. A condenser lens device for forming a modified region extending from a front surface to a back surface of an article as a workpiece by irradiating an ultrashort pulsed laser beam via a condenser lens system at a position where a modified region is to be formed on the article, the device comprising: the focusing lens system includes two axicon lenses arranged along an optical axis of the ultrashort pulsed laser beam, and a convex lens arranged between the two axicon lenses, the ultrashort pulsed laser light that has passed through the focusing lens system becomes a circular converging Bessel beam, and the circular converging Bessel beam is configured to converge between the front surface and the back surface of the article.

13. A method for manufacturing an article having a modified region, comprising a modified region forming step of forming a modified region extending from a front surface to a back surface of the article by irradiating an ultrashort pulsed laser beam via a focusing lens system at a position where a modified region is to be formed on the article, the focusing lens system includes two axicon lenses arranged along an optical axis of the ultrashort pulsed laser beam, and a convex lens arranged between the two axicon lenses, the ultrashort pulsed laser light that has passed through the focusing lens system becomes a circular converging Bessel beam, and the circular converging Bessel beam is configured to converge between the front surface and the back surface of the article.

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