JP7783597B2 - Modified region forming method, through-hole forming method, condenser lens device, and method for manufacturing article having modified region - Google Patents

Description

The present invention relates to a method for forming a modified region, a method for forming a through hole, a focusing lens device, and a method for manufacturing an article having a modified region.

Interposers, which have through electrodes formed on the front and back surfaces of a plate-shaped substrate to ensure electrical continuity for the 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. Of these, glass is considered an excellent material for interposers because of its excellent high-frequency characteristics, high flatness, minimal warping, ability to be processed over large areas, and low-cost mass production. In addition, photolithography technology for forming wiring patterns has been established, making it an excellent material for interposers.

To create an interposer using glass, it is necessary to form a large number of fine through-holes (TGVs: Through Glass Vias), each measuring 150 μm or less, in a flat glass substrate. Laser light is typically used to form these through-holes, and various techniques have been proposed (see, for example, Patent Document 1).

In the through-hole formation 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 filament-like channels (corresponding to modified areas). The filament-like channels are then sandwiched between a pair of electrodes, and a high voltage is applied to the pair of electrodes, expanding the filament-like channels to the desired hole diameter.

One example of a method for forming the desired holes in the modified areas is to apply a high voltage to a pair of electrodes, as in the hole formation method described in Patent Document 1. However, a more simple method that is suitable for mass production is generally etching using a hydrofluoric acid-based etching solution such as hydrofluoric acid or an acid containing hydrofluoric acid.

Special Publication No. 2013-534868

However, when a glass substrate with modified regions formed to form through-holes is etched using a hydrofluoric acid-based etching solution, the etching rate is fast in the modified regions, with etching proceeding in the thickness direction of the substrate, whereas the etching rate is slower in the unmodified regions, with etching proceeding in the lateral direction of the substrate. This poses a problem: due to the difference in etching rate between the modified and unmodified regions, the inner diameter of the through-holes near the center of the glass substrate can become smaller than the inner diameter of the through-holes near the surface.

The present invention was 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 at the center of the through hole 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.

[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 (workpiece) by irradiating the article with an ultrashort pulsed laser beam via a focusing lens system at a position 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, which is configured to converge between the front surface and the back surface of the article.

[2] The modified region formation method of the present invention is the modified region formation method described above, and preferably, the optical density at the main peak position in the optical density distribution of the ultrashort 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 main peak position in the optical density distribution of the ultrashort pulsed laser light on the surface of the article.

[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 preferably 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.

[4] The modified region formation method of the present invention is the modified region formation method described above, and preferably, the light density at the position of the first diffraction ring in the light density distribution of the ultrashort pulse laser light at a 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 formation method of the present invention is the modified region formation method described above, wherein the optical density at the main peak position in the optical density distribution of the ultrashort pulsed laser light at the center position between the front surface and the back surface in the optical axis direction of the article is preferably greater than six times the optical density at the main peak position in the optical density distribution of the ultrashort pulsed laser light on the surface of the article.

[6] The modified region formation method of the present invention is the modified region formation method described above, and it is preferable that the convex lens is an aspherical lens.

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

[8] The modified region formation method of the present invention is the modified region formation method described above, 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.

[9] The modified region formation method of the present invention is the modified region formation method described above, and preferably includes 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 performs a correction that increases the light density in the central portion.

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

[11] The through-hole forming method of the present invention comprises any of the modified region forming methods described above, and an etching step of etching the article in which the modified region has been formed to form a through-hole.

[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. 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. The ultrashort pulsed laser beam that passes through the focusing lens system becomes a circular converging Bessel beam, and this circular converging Bessel beam is configured to converge between the front surface and the back surface of the article.

[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, which is configured to converge between the front surface and the back surface of the article.

According to the modified region formation method of the present invention, first, the first axicon lens, which is positioned closer to the light source than the other of the two axicon lenses, converts the ultrashort pulse laser light into an annular Bessel beam. Next, the convex lens positioned between the two axicon lenses converts the annular Bessel beam into a converging Bessel beam. "Converging" here means that the beam is converging relative to the annular shape of the annular Bessel beam formed by the first axicon lens; specifically, it means that the thickness of the annulus becomes thinner.

Furthermore, of the two axicon lenses, the second axicon lens 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 converges between the front and back surfaces of the article.

This allows the light density at the position where the modified region of the article is formed to be greater than the light density at the position of the main peak of the light density distribution at the center of the article in the direction of modified region formation. As a result, a modified region can be formed over a wider area at the center of the article in the direction of modified region formation than at the surface of the article.

Furthermore, the inner diameter of the through-hole at the center of its depth direction after etching can be increased, thereby reducing the difference between the inner diameter of the opening of the through-hole and the inner diameter of the center of its depth direction.

In addition, the inner diameter of the through-hole can be widened in the center of the depth direction, which has the effect of allowing through-holes to be formed in thicker substrates.

The focusing lens device of the present invention makes it possible to make the light density at the position where the modified region of the article is formed, at the position of the main peak of the light density distribution at the center of the article in the direction of modified region formation, greater than the light density at the position of the main peak of the light density distribution on the surface of the article. This makes it possible to form 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.

As a result, the inner diameter of the through hole at the center of its depth direction 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 its depth direction can be reduced.

The method for manufacturing an article having a modified region of the present invention makes it possible to make the optical density at the position where the modified region of the article is formed, at the position of the main peak of the optical density distribution at the center of the article in the direction of the modified region formation, greater than the optical density at the position of the main peak of the optical density distribution on the surface of the article. This makes it possible to manufacture an article having a modified region over a wider area at the center of the article in the direction of the modified region formation than at the surface of the article.

As a result, the inner diameter of the through hole at the center of its depth direction 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 its depth direction can be reduced.

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. 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. 10 is a diagram showing the position at which a circular convergent Bessel beam 164 emitted from the condenser lens system 140 converges when a convex lens with a different focal length is used as the convex lens 142. FIG. 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. 10 is a diagram showing the relationship between the light density distribution of the laser light 161 incident on the condenser lens system 140 and the light density distribution in the thickness direction of the glass substrate. FIG. 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 Embodiment 1 and a through-hole is formed by the through-hole forming method. 1 is a flowchart showing steps of a modified region forming method and a through-hole forming method according to the first embodiment. 10 is a diagram for explaining a light beam when a glass substrate 10 is irradiated with a circular convergent Bessel beam 164. FIG. 10 is a diagram showing a light density distribution when a glass substrate 10 is irradiated with a circular convergent Bessel beam 164. FIG. FIG. 10 is a diagram showing an example of a correction optical system 150 according to a second embodiment.

The following describes modes for carrying out the present invention (hereinafter referred to as "embodiments"). The embodiments described below represent preferred modes for carrying out the invention, and the present invention is in no way limited to the embodiments described below. Furthermore, where explanations for each embodiment overlap, they may be omitted.

1. Embodiment 1
1-1. Laser Processing Apparatus First, a laser processing apparatus that can be suitably used for the modified region forming method and through-hole forming method of the first embodiment will be described.

Figure 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 formation method according to embodiment 1. Figure 1 shows the x-axis, y-axis, and z-axis, which are perpendicular to each other. In Figure 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).

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

The laser processing apparatus 100A may be provided with a correction optical system 150 between the laser oscillator 120 and the focusing lens system 140, which corrects the light density distribution incident on the focusing lens system 140.

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 the xy plane, which is made up of the x and y axes, and along the z axis (up and down), by a table driving means (not shown). By controlling the movement of the table in the xy plane, the irradiation position of the laser light on the glass substrate 10 in 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.

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 surface 10a and the substrate back surface 10c of the glass substrate 10.

The light-guiding optical system 130 has a mirror 131 that reflects the laser light 161 emitted from the laser oscillator 120 at a 90-degree angle. The laser light 161 reflected at a 90-degree angle is set to be incident perpendicularly on the surface 10a of the glass substrate 10 via the focusing lens system 140.

In embodiment 1, the laser oscillator 120, the light-guiding optical system 130, and the focusing lens system 140 are collectively referred to as the laser irradiation unit 160.

The condensing 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.

Here, 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. The convex lens 142 can be replaced with a convex lens having a different focal length. The second axicon lens 143 can be replaced with an axicon lens having a different apex angle.

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 front surface 10a and the substrate back surface 10c 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 in a plane perpendicular to the optical axis 165 of the laser light on the substrate front 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.

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

In the following specification, "the central position 10b between the substrate 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 surface 10a" will be referred to as "the light density distribution of the substrate 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."

The following provides a detailed description of the components of the focusing lens system 140: the first axicon lens 141, the convex lens 142, and the second axicon lens 143.

The first axicon lens 141 converts the laser light 161 emitted from the laser oscillator 120 into a circular Bessel beam 162 and makes it incident on the convex lens 142.

In the focusing lens system 140, the first axicon lens 141 is configured so that it can be replaced with an axicon lens having a different apex angle.

The apex 141a of the cone of the first axicon lens 141 is preferably positioned facing the laser oscillator 120. By positioning the apex 141a of the cone of the first axicon lens 141 facing the laser oscillator 120, it is possible to prevent the laser light 161 reflected by the first axicon lens 141 from returning to the laser oscillator 120 and damaging the laser oscillator 120.

There are no particular restrictions on the apex angle of the first axicon lens 141, as long as it is larger than the apex angle of the second axicon lens 143 (described later), but it is preferably in the range of 145° to 175°, and more preferably in the range of 150° to 170°.

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.

Furthermore, by having the apex angle of the first axicon lens 141 be equal to or less than the upper limit of the above numerical range, the overall length of the focusing lens system 140 can be kept to an appropriate length. On the other hand, by having the apex angle of the first axicon lens 141 be equal to or greater than the lower limit of the above numerical range, the distance from the focusing lens system 140 to the glass substrate 10, the so-called working distance, does not become too short, and an appropriate working distance can be ensured.

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

This allows the modified region 20 to be formed over a wider area at the center 10b of the glass substrate 10 than on the front surface 10a and back surface 10c of the substrate (see Figure 6).

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 relative to the annular shape of the annular Bessel beam 162 formed by the first axicon lens.

In the focusing lens system 140, the convex lens 142 is configured so that it can be replaced with a convex lens having a different focal length.

The convex lens 142 can be any lens with positive refractive power, and can be a biconvex lens, a convex-plano lens, or a convex-concave lens.

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.

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.

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

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. By having the focal length of the convex lens within the above range, the light density at the main peak in the light density distribution at the center 10b of the substrate, at the position where the modified region 20 of the glass substrate 10 is formed, can be made much greater than the light density at the main peak in the light density distribution at the front surface 10a of the substrate and the light density at the main peak in the light density distribution at the back surface 10c of the substrate.

This allows the modified region 20 to be formed over a wider area at the center 10b of the glass substrate 10 than on the front surface 10a and back surface 10c of the substrate (see Figure 6).

Figure 2 shows 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, substrate center 10b, and 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.

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

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 more than six times the light density at the front surface 10a of the substrate and 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 back surface 10c of the substrate.

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 back surface 10c of the substrate are low.

Figure 3 shows 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. Figure 3 shows that when a convex lens 142 with a short focal length is used as the convex lens 142, the annular convergent Bessel beam 164 converges to 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 a convex lens 142 with a long focal length is used.

When a convex lens with a focal length of 100 mm is used as the convex lens 142, the annular convergent Bessel beam 164 is thought to have converged at a position close to the substrate center 10b between the substrate surface 10a and the substrate back surface 10c. As a result, the annular convergent Bessel beam 164 is thought to have not converged sufficiently on the substrate surface 10a and the substrate back surface 10c, resulting in a decrease in the light density on the substrate surface 10a and the substrate back surface 10c.

The power of the laser light 161 emitted from the laser oscillator 120 can be increased to increase the light density on the substrate surface 10a and the substrate back surface 10c to a level that can modify the glass substrate 10.

The second axicon lens 143 is arranged 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.

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. Furthermore, the apex 143a of the cone of the second axicon lens 143 may be oriented toward either the glass substrate 10 or the convex lens 142.

When the apex 143a of the cone of the second axicon lens 143 is positioned facing the glass substrate 10, the annular convergent Bessel beam 163 enters the flat surface 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 allows the performance of the coating applied to the second axicon lens 143 to be fully utilized, and the transmittance of the annular convergent Bessel beam 163 entering the second axicon lens 143 to be increased.

On the other hand, if the apex 143a of the cone of the second axicon lens 143 is positioned facing the convex lens 142, the apex 143a of the cone of the axicon lens 143, which is prone to breakage, can be placed facing inward of the lens barrel. This has the effect of making the device easier to handle.

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 it is preferably between 120° and 150°, and more preferably between 120° and 140°.

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.

Furthermore, by having the apex angle of the second axicon lens 142 be equal to or less than the upper limit of the above numerical range, the overall length of the focusing lens system 140 can be kept at an appropriate length. On the other hand, by having the apex angle of the second axicon lens 143 be equal to or greater than the lower limit of the above numerical range, the distance from the focusing lens system 140 to the glass substrate 10, the so-called working distance, does not become too short, and an appropriate working distance can be ensured.

Furthermore, by having the apex angle of the second axicon lens 143 within the above range, the light density at the main peak position 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 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.

Figure 4 shows 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 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.

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 Figure 4(a), and the light density normalized by the light density at the origin (substrate center 10b) in Figure 4(b).

From Figure 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 center 10b of the substrate is more than six times the light density at the front surface 10a of the substrate and 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 back surface 10c of the substrate.

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 back surface 10c of the substrate are low.

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 light density on the substrate front surface 10a and the substrate back surface 10c.

The power of the laser light 161 emitted from the laser oscillator 120 can be increased to increase the light density on the substrate surface 10a and the substrate back surface 10c to a level that can modify the glass substrate 10.

As described above, in the focusing lens system 140, the first axicon lens 141 is configured to be replaceable with an axicon lens having a different apex angle. The convex lens 142 is also configured to be replaceable with a convex lens having a different focal length. Furthermore, the second axicon lens 143 is configured to be replaceable with an axicon lens having a different apex angle.

This allows the focusing lens system 140 to adjust the position at which the annular convergent Bessel beam 164 is focused. In other words, the focusing lens system 140 can focus the annular convergent Bessel beam 164 between the substrate front surface 10a and the substrate back surface 10c of the glass substrate 10.

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 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.

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

Next, we will explain the laser oscillator 120 that can be used in the laser processing device of embodiment 1.

The laser oscillator 120 is a laser oscillator (femtosecond pulse laser oscillator or picosecond pulse laser oscillator) that emits ultrashort pulse laser light and outputs laser light 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.

In embodiment 1, pulsed laser light with a pulse width of 10 psec or less is used, with a wavelength of 1030 nm, a beam diameter of 3 mm to 6 mm, and an average output of 50 W.

The light density distribution of the laser light 161 emitted by the laser oscillator 120 is preferably a Gaussian distribution. Because 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 main peak position 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 greater than the light density at the main peak position in the light density distribution on the substrate front surface 10a and the light density at the main peak position in the light density distribution on the substrate back surface 10c.

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

Figure 5 shows the relationship between the light density distribution of the 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 the laser light 161 incident on the condenser lens system 140 was changed to a Gaussian distribution or a flat distribution, and the light density at the position of the optical axis 165 on the substrate surface 10a, substrate center 10b, and 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°, the focal length of the convex lens 142 was 200 mm, and the thickness of the glass substrate 10 was 1 mm.

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 Figure 5(a), and the light density normalized by the light density at the origin (substrate center 10b) in Figure 5(b).

From Figure 5, it can be seen that the light density at the center 10b of the substrate is greater when the light density distribution of the laser light 151 is a Gaussian distribution. In other words, in the modified region formation method of embodiment 1, it can be confirmed that laser light 161 incident on the focusing lens system 140 is preferably laser light whose light density distribution is centered on the optical axis 165, for example, laser light having a Gaussian distribution.

1-2. Modified Region Forming Method and Through-Hole Forming Method Next, the modified region forming method and 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. Fig. 7 is a flowchart showing the steps of the modified region forming method and through-hole forming method according to embodiment 1.

The modified region forming method according to embodiment 1 includes a modified region forming step (step ST1) in which a modified region 20 is formed in a glass substrate 10 as an article. The through-hole forming method also includes the modified region forming step (step ST1) described above and an etching step (step ST2) in which the glass substrate 10 on which the modified region 20 has been formed is etched to form a through-hole.

1, the modified region forming step according to the first embodiment is a step of irradiating a laser beam 161 through a condenser lens system 140 onto a position where the modified region 20 is to be formed on a glass substrate 10, which is an article serving as a workpiece, using the laser processing apparatus 100A shown in FIG. 1 to form the modified region 20 extending from the front surface 10a to the back surface 10c of the glass substrate 10 (step ST1). The condenser lens system 140 includes a first axicon lens 141, a convex lens 142, and a second axicon lens 143.

The first axicon lens 141 converts the laser light 161 into a circular Bessel beam 162 and makes it incident on the convex lens 142.

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, which is then incident on the second axicon lens 143.

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

Here, 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. The convex lens 142 can be replaced with a convex lens having a different focal length. The second axicon lens 143 can be replaced with an axicon lens having a different apex angle.

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 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.

The following explains the mechanism by which the optical density of the annular convergent Bessel beam 164 at the main peak in the optical density distribution at the substrate center 10b of the glass substrate 10 can be made greater than the optical density at the main peak in the optical density distribution at the substrate surface 10a and the optical density at the main peak in the optical density distribution at the substrate back surface 10c.

Figure 8 is a diagram illustrating the light flux when a glass substrate 10 is irradiated with a circular convergent Bessel beam 164. Figure 9 is a diagram illustrating the light density distribution when a glass substrate 10 is irradiated with a circular convergent Bessel beam 164. Figure 9(a) shows the light density distribution at position A-A on the substrate surface 10a, Figure 9(b) shows the light density distribution at position B-B on the substrate center 10b, and Figure 9(c) shows the light density distribution at position C-C on the substrate back surface 10c.

Note that, although Figure 8 shows that the light flux of the annular convergent Bessel beam 164 is not present at the position of the optical axis 165 on the substrate front surface 10a and the substrate back surface 10c, the light density distribution on the substrate front surface 10a in Figure 9(a) and the light density distribution on the substrate back surface 10c in Figure 9(c) show that main light density peaks 61a and 61c are present at the position of the optical axis 165. This is because the annular convergent Bessel beam 164 is converged and therefore close to each other on the substrate front surface 10a and the substrate back surface 10c, and this interacts with each other to cause the main peak to appear at the position of the optical axis 165.

In Figures 9(a) to (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.

First, we will explain the light density distribution at the center 10b of the substrate in Figure 9(b). At the center 10b of the substrate, a main peak 61b where the light density is maximum can be seen at the position of the optical axis 165, i.e., the origin of the horizontal axis of the graph.

Furthermore, a first diffraction ring 62b and a second diffraction ring 63b are observed on either side of the main peak 61b. The light density at the position of the main peak 61b is approximately 6 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.

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

The light density distribution at the substrate center 10b is compared with 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 threshold value 65. In other words, at the substrate center 10b of the glass substrate 10, modification has occurred 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 threshold value 65. No modification has occurred in this region.

Next, we will explain the light density distribution on the substrate surface 10a in Figure 9(a). 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.

In addition, a first diffraction ring 62a is present 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 at the substrate center 10b.

When comparing the light density distribution on the substrate surface 10a 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.

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 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 main peak 61b in the light density distribution at the center 10b of the substrate.

A first diffraction ring 62c exists outside the main peak. The light density at the first ring 62c in the light density distribution on the back surface 10c of the substrate is also lower than the light density at the position of the first ring 61c in the light density distribution at the center 10b of the substrate.

When comparing the light density distribution on the back surface 10c of the substrate 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 less than the threshold.

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

Here, the modified region 20 where the glass substrate 10 is modified is the region where the light density 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 modification occurs is also wide.

In other words, the region Rb belonging to the main peak 61b in the light density distribution at the substrate center 10b, where the threshold value 65 is exceeded and modification occurs, is wider than the region Ra belonging to the main peak 61a in the light density distribution at the substrate front surface 10a, where the threshold value 65 is exceeded and modification occurs, and the region Rc belonging to the main peak 61c in the light density distribution at the substrate back surface 10c, where the threshold value 65 is exceeded and modification occurs.

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

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 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 on the substrate 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 on the substrate back surface 10c.

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 on the front surface 10a of the substrate 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.

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

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 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 are greater than the threshold value 65 at which modification occurs.

As a result, the glass substrate 10 is modified at the position of the main peak 61a on the substrate surface 10a and the position of the main peak 61c on the substrate back surface 10c, forming modified regions 20.

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

As a result, when the modified glass substrate 10 is etched to form through-holes 30, perfectly circular through-holes 30 corresponding to the shapes of the main peaks 61a, 61c can be formed on the front surface 10a and back surface 10c of the glass substrate 10.

Furthermore, in the modified region formation method of embodiment 1, 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.

This allows the modified regions 20a, 20b to be formed over a wider area in the center 10b of the substrate than on the front surface 10a and back surface 10c of the substrate.

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 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.

Between the main peak 61b and the first diffraction ring 62b, there is an unmodified region where the optical density of the irradiated laser light 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 center 10b of the substrate.

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 substrate center 10b 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 of the light density distribution on the substrate front surface 10a and the light density at the position of the main peak 61c of the light density distribution on the substrate back surface 10c.

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

1-2-2. Etching Step 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 rear 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 rear surface 10e of the glass substrate 10 are formed. At the same time as the etching to thin the glass substrate 10, the etching solution permeates the modified region 20, etching the modified region 20 and forming pilot holes 30a (see FIG. 6).

When the modified region 20 is eroded by the etching solution and the pilot hole 30a is formed, 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).

At this time, the etching of the modified region 20, which progresses in the thickness direction (z direction) of the glass substrate 10, is faster than the etching of the unmodified region, which progresses laterally (along the xy plane) of the glass substrate 10. In conventional technology, 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 center 10b of the substrate tends to be smaller than the inner diameter of the through hole at the front surface 10a of the substrate and the inner diameter of the through hole at the back surface 10c of the substrate.

However, in the through-hole formation method of embodiment 1, in the modified region formation process (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 Figure 8).

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 on the substrate surface 10a, the inner diameter d3 of the through hole 30 on 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).

2. Embodiment 2
Fig. 10 is a diagram showing an example of the correction optical system 150 in embodiment 2. Fig. 10(a) is a diagram showing how the light flux of the 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 of the laser light after correction.

The correction optical system 150 corrects the optical density distribution of the laser beam 161 incident on the focusing lens system 140 by increasing the optical density in the central portion. Any correction optical system 150 can be used as long as it corrects the optical density distribution of the incident laser beam 161 by increasing the optical density in the central portion. The optical element 151 has an entrance surface 151a onto which the laser beam 161 enters and an exit surface 151b from which the laser beam exits.

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 light 161 incident on the optical element 151, the laser light 161 that enters the peripheral portion away from the center of the incident surface 161a enters the optical element 151 at an angle close to parallel to the optical axis 165. On the other hand, the light that enters near the central annular zone has its direction of travel changed at the incident surface 161a so that it approaches the optical axis 165.

Emission surface 151b is formed with an aspherical surface that is concave at the center and whose curvature gradually decreases toward the center. Of the laser light 161 incident on optical element 151, laser light 161 that enters the peripheral portion of incidence surface 161a away from optical axis 165 also exits optical element 151 at an angle close to perpendicular emission at emission surface 151b. On the other hand, light that enters near the central annular zone of incidence surface 151a of optical element 151 and has its direction of travel changed so that it approaches optical axis 165 is returned to parallel rays at emission surface 151b.

The optical element 151 in Figure 10(a) can correct the laser light 161 incident on the focusing lens system 140 to increase the light density in the central portion. For example, when laser light with the light density of the Gaussian distribution 171 in Figure 10(b) is incident on the optical element 151, it can emit laser light with a light density distribution 172 in which the light density in the central portion is even greater.

By making laser light 172 having such a light density distribution incident on the focusing lens system 140 and converging the circular converging Bessel beam 164 emitted from the focusing lens system between the substrate surface 10a of the glass substrate 10 and the glass substrate 10c, the following effects can be achieved.

In other words, the light density at the main peak position 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 main peak position in the light density distribution at the substrate surface 10a and the light density at the main peak position in the light density distribution at the substrate back surface 10c.

As a result, the modified region 20 can be formed over a wider area at the center 10b of the glass substrate 10 than on the front surface 10a and back surface 10c of the substrate.

Furthermore, when the modified glass substrate 10 is etched to form the 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.

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.

The focusing lens device according to embodiment 3 will be described below with reference to Figure 1. Note that explanations of parts that overlap with the explanations of the above-mentioned embodiments may be omitted as appropriate.

The focusing 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 focusing lens system 140 becomes a circular converging Bessel beam 164, which is configured to converge between the substrate front surface 10a and the substrate back surface 10c.

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

As a result, the modified region 20 can be formed over a wider area at the center 10b of the glass substrate 10 than on the front surface 10a and back surface 10c of the substrate.

Furthermore, when the modified glass substrate 10 is etched to form the 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.

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 10 a to the back surface 10 c of the glass substrate 10 by irradiating the glass substrate 10, which is the article serving as the workpiece, with laser light 151 via a condenser lens system 140 at a position where the modified region 20 is to be formed.

The focusing 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. The ultrashort pulse laser light that passes through the focusing lens system 140 becomes a circular converging 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.

The method for manufacturing an article having a modified region according to embodiment 4 will be described below with reference to Figures 1, 6, and 7. Note that explanations of portions that overlap with those of the above-described embodiments may be omitted as appropriate.

The glass substrate 10 is placed on a table (not shown) of the laser processing device shown in Figure 1. The 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.

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.

As a result, the modified region 20 can be formed over a wider area at the center 10b of the glass substrate 10 than on the front surface 10a and back surface 10c of the substrate.

Furthermore, when the modified glass substrate 10 is etched to form the 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.

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 system, 131...mirror, 140...condensing lens system, 141...first axicon lens, 141a...apex of the cone, 142...convex lens, 143...second axicon lens, 143a...apex of the 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 (13)

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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.