Optical device and fine modified region forming method

Abstract

One aspect of the present invention is an optical device 100A that forms a fine modified region in a workpiece 9 using laser light (pulsed laser light 1), the optical device 100A comprising: an optical system 3 having a first axicon lens 21 and a second axicon lens 22 that are provided along the traveling direction of the laser light, and a mirror 4 that is provided between the first axicon lens 21 and the second axicon lens 22 and that reflects the laser light, the optical system 3 emitting a convergent beam 10 from the second axicon lens 22; and a control unit 5 having a function of scanning the convergent beam 10 on the workpiece along a predetermined beam scanning direction 15 by controlling the reciprocating movement of the mirror 4 and the second axicon lens 22.　According to the optical device 100A of one aspect of the present invention, the fine modified region can be formed at a higher speed than before.

Description

Optical device and method for forming finely modified region Cross Reference

[0001] The present application claims priority based on Japanese Patent Application No. 2025-027757 filed in Japan on February 25, 2025, and all contents described in said application are hereby incorporated herein by reference in their entirety.

[0002] One aspect of the present invention relates to an optical device and a method for forming a finely modified region.

[0003] In recent years, further higher integration of semiconductor packages has been demanded, and since further miniaturization of wiring in the so-called front-end process is not easy, interest in the so-called back-end process has been increasing. Among these is Chiplet technology. This is a technology in which small semiconductor chips each having functions assigned according to their roles are combined like blocks and housed in a single package. An interposer (intermediate substrate) is used for connection between semiconductor chips and the like. A glass substrate or the like is used for the interposer, and a large number of fine through holes (TGV: Through Glass Vias) are formed in the plane to achieve conduction between circuits on the front and back sides.

[0004] In order to form a large number of fine through holes in an interposer, a convergent pulsed laser beam is irradiated onto a workpiece while appropriately moving a stage on which the workpiece is mounted, so that fine modified regions (hereinafter referred to as "finely modified regions") are formed at a plurality of predetermined locations. Subsequently, wet etching of the workpiece is performed with a hydrofluoric acid-based etchant or the like to form a large number of fine through holes from the plurality of finely modified regions. In this case, if a convergent pulsed laser beam generated using, for example, an axicon lens is used as the convergent pulsed laser beam, a Bessel beam region having an extremely high aspect ratio can be generated. Therefore, a high-quality finely modified region having a more uniform diameter than conventional ones over the depth direction (thickness direction) of the workpiece, and consequently, a high-quality fine through hole having a more uniform diameter than conventional ones over the depth direction (thickness direction) of the interposer can be formed (see, for example, Patent Document 1).

[0005] Japanese Patent Publication No. 2023-136442

[0006] However, in the field of technology for forming micro-modified regions on workpieces, there is a challenge in forming these regions at a faster speed than conventional methods. This challenge is not limited to cases where focused pulsed laser light generated using an axicon lens is used. Therefore, the present invention aims to provide an optical device and a method for forming micro-modified regions that can form them at a faster speed than conventional methods.

[0007] [1] An optical device relating to one aspect of the present invention is an optical device for forming a micro-modified region on a workpiece using laser light, comprising: a first axicon lens and a second axicon lens provided along the direction of propagation of the laser light, and a mirror provided between the first axicon lens and the second axicon lens for reflecting the pulsed laser light, wherein the optical system emits a convergent beam from the second axicon lens; and a control unit having the function of scanning the convergent beam on the workpiece along a predetermined beam scanning direction by controlling the reciprocating motion of the mirror and the second axicon lens.

[0008]

[15] A method for forming a micro-modified region according to one aspect of the present invention is a method for forming a micro-modified region on a workpiece using an optical device comprising: "an optical system having a first axicon lens and a second axicon lens provided along the direction of propagation of pulsed laser light, and a mirror provided between the first axicon lens and the second axicon lens for reflecting the pulsed laser light"; "a stage configured to be movable along predetermined main scanning directions and sub-scanning directions that are mutually orthogonal in a plane parallel to the mounting surface, and to be rotatable with respect to a predetermined axis perpendicular to the mounting surface"; and "a control unit having the function of scanning a convergent beam on a workpiece along a predetermined beam scanning direction by controlling the reciprocating motion of the mirror and the second axicon lens," wherein, with the beam scanning direction and the sub-scanning direction tilted by a predetermined angle (α), the convergent beam is scanned along the beam scanning direction while the stage is moved along the main scanning direction, thereby forming a row of spots by the pulsed laser light on the workpiece along the sub-scanning direction.

[0009] According to the optical device relating to the first aspect described above, it is possible to form micro-modified regions at a faster speed than conventional methods. Furthermore, according to the optical device relating to the other aspect of the present application and the method for forming micro-modified regions described above, it is possible to form a large number of micro-modified regions at a faster speed than conventional methods.

[0010] A diagram illustrating the overview of the optical device 100A according to Embodiment 1. A diagram illustrating the structure of the optical device 100A according to Embodiment 1 (using a voice coil motor 7). A diagram illustrating the method of forming a spot row over the entire processing area 95. A diagram illustrating the method of forming a spot row along the sub-scanning direction in the "forward spot row formation area". A diagram illustrating the two-dimensional method of forming a spot row in the "forward spot row formation area". A diagram illustrating the two-dimensional method of forming a spot row in the "return spot row formation area". A diagram illustrating the method of forming a spot row along the sub-scanning direction in the "return spot row formation area". A diagram illustrating the method of forming a spot row along the sub-scanning direction in the "return spot row formation area". A diagram illustrating the beam shift amount of the converging beam 10 and the movement range of the mirror 4. A diagram illustrating the formation position of the Bessel beam area 11. A diagram illustrating the configuration of the mirror 4. A diagram illustrating the configuration of the second axicon lens 22. A diagram illustrating the overview of the optical device 100B according to Embodiment 2. A schematic plan view of the optical device 100B shown in Figure 13.

[0011] The following describes an optical device relating to one aspect of the present invention with reference to the figures. Each drawing is a schematic diagram and does not necessarily strictly reflect an actual optical device. Each embodiment does not limit the scope of the claims. Not all elements and combinations thereof described in each embodiment are essential to the present invention. For components that can be considered substantially equivalent, the same reference numerals are used across embodiments, and further explanation may be omitted (although some explanations may overlap).

[0012] [Embodiment 1] In Embodiment 1, the optical device of the present invention will be described using an optical device that uses pulsed laser light as the laser light as an example. Figures 1 to 12 are diagrams illustrating the optical device according to Embodiment 1. Figure 1 is a diagram illustrating the outline of the optical device. Figure 2 is a diagram illustrating the structure of the optical device (using a voice coil motor 7). For the sake of ease of explanation, an XYZ coordinate system having X, Y, and Z axes is shown on the predetermined drawings (the X axis corresponds to the main scanning direction, and the Y axis corresponds to the sub-scanning direction. The main scanning direction and sub-scanning direction will be described later in the explanation of Figure 3, etc.).

[0013] [Optical Device] As shown in Figure 1, the optical device is an optical device that forms a modified region on a workpiece 9 using a convergent beam 10. The optical device comprises an optical system 2, a mirror 4, and a control unit 5. The optical system 2, which generates the convergent beam 10 from laser light (pulsed laser light 1), has a first axicon lens 21 and a second axicon lens 22 provided along the direction of propagation of the pulsed laser light 1. The mirror 4 is provided between the first axicon lens 21 and the second axicon lens 22 and reflects the pulsed laser light 1. The control unit 5 scans the convergent beam 10 along a predetermined beam scanning direction 15 on the workpiece by controlling a reciprocating motion that moves the mirror 4 and the second axicon lens 22 back and forth along the optical axis Ax of the pulsed laser light 1 from the first axicon lens 21 toward the mirror 4. In Figure 1, the beam scanning direction 15 at an intermediate position within the reciprocating movement range or effective movement range of the reciprocating motion is shown. The same applies to Figure 13, which will be described later. (The effective range of movement, etc., will be explained later using Figure 9(b)).

[0014] [Optical System 2] When the pulsed laser light 1 passes through the first axicon lens 21 that constitutes the optical system 2, it becomes a converging Bessel beam in which the outer diameter of the ring (a ring composed of the entire Bessel beam) gradually decreases, generating the first Bessel beam region 11a (parallel rays are inside the ring). This Bessel beam region 11a is generated at the location where the light (Bessel beam) emitted from the first axicon lens 21 overlaps. The first Bessel beam region 11a is a preliminary stage to the final Bessel beam region 11 that is emitted to the workpiece 9.

[0015] Subsequently, the beam diverges, and the outer diameter of the ring gradually increases. After being reflected by mirror 4 and changing direction, it passes through the second axicon lens 22 that constitutes the optical system 2, becoming a converging Bessel beam again, with the outer diameter of the ring gradually decreasing. This forms a Bessel beam region 11 at or near the point of convergence, and irradiates the workpiece 9 placed on the stage 6. The Bessel beam region 11 (including the initial Bessel beam region 11a) is a region with high optical energy formed in the direction of the optical axis. The diameter (beam waist diameter) of the Bessel beam region 11 is approximately the same.

[0016] The length, diameter, etc., of the Bessel beam region 11 can also be changed by changing the apex angle or apex angle (angle formed by the base and equilateral sides) of the second axicon lens 22, or the angle of incidence of the pulsed laser light 1 onto the workpiece 9.

[0017] When pulsed laser light 1 is irradiated onto the workpiece 9, the Bessel beam region 11 formed (in the length direction) along the thickness direction of the workpiece 9 makes it easy to uniformly form a modified region from the front to the back surface of the workpiece 9. Therefore, it becomes easy to form a through hole with a uniform inner diameter from the front to the back surface of the workpiece 9.

[0018] [Mirror 4] As shown in Figures 1 and 2, Mirror 4 is provided between the first axicon lens 21 and the second axicon lens 22, and reflects the pulsed laser light 1 coming from the first axicon lens 21 toward the second axicon lens 22. Mirror 4 may be, for example, a galvanometer mirror in which the rotating mirror and motor are integrated, with the rotating mirror fixed so that it does not rotate. Preferably, the reflective surface is flat.

[0019] [Control Unit 5] The control unit 5 controls the reciprocating motion of the mirror 4 and the second axicon lens 22 along the optical axis Ax of the pulsed laser light 1 that travels from the first axicon lens 21 toward the mirror 4. In Embodiment 1, the mirror 4 and the second axicon lens 22 are mounted on a housing 31, and the mirror 4 and the second axicon lens 22 are moved back and forth by moving the housing 31 back and forth.

[0020] The control unit 5 (specific circuit diagrams are not shown) is composed of, for example, logic circuits, a microcomputer, etc. The microcomputer is a computer mainly composed of a CPU (Central Processing Unit), ROM, RAM, input / output ports, interfaces, etc. It performs various controls (such as the reciprocating motion of the mirror 4 and the second axicon lens 22, the rotation of the stage 6, the movement of the stage 6 in the main scanning direction or sub-scanning direction, and the generation of pulsed laser light 1) according to instructions pre-stored in the ROM.

[0021] [Optical System 2] The optical system 2 comprises a first axicon lens 21, a housing 31 (to which a mirror 4 and a second axicon lens 22 are attached), and a voice coil motor 7, etc. In other words, these are mounted on the system. The housing 31 is configured to be able to reciprocate (move back and forth) within the optical system 2 by the drive of the voice coil motor 7. When the housing 31 moves back and forth, the pulsed laser light 1 (converging beam 10) that has passed through the second axicon lens 22 is irradiated onto the workpiece 9 through a window provided in the optical system (which is provided so as not to hinder the passage of the convergent beam 10 even when it moves back and forth).

[0022] When the control unit 5 drives the voice coil motor 7, the housing 31 reciprocates, and the converging beam 10 is scanned over the workpiece along a predetermined beam scanning direction 15 (the reciprocating direction of the housing 31). As a result, the vessel beam region 11 is formed over a wide area of ​​the workpiece 9, and a large number of fine modification regions can be formed on the workpiece 9.

[0023] Since a modified region is formed in the irradiated area of ​​the workpiece 9, a through hole is formed by utilizing the difference in etching speed between the modified region and the unmodified region during etching.

[0024] Therefore, in the optical apparatus 100A according to Embodiment 1, since the convergent beam 10 that has passed through the second axicon lens 22 is a convergent beam generated using an axicon lens, a Bessel beam region 11 with an extremely high aspect ratio is formed near the workpiece 9. For this reason, the optical apparatus 100A according to Embodiment 1 can form a high-quality micro-modification region with a more uniform diameter than conventional methods over the depth direction (thickness direction) of the workpiece.

[0025] Furthermore, in the optical device 100A according to Embodiment 1, the converging beam 10 is scanned on the workpiece 9 along a predetermined beam scanning direction by the reciprocating motion of the mirror 4 and the second axicon lens 22, which are capable of high-speed reciprocating motion. Therefore, with the optical device 100A according to Embodiment 1, a large number of fine modification regions can be formed on the workpiece at a faster speed than in the conventional method.

[0026] The pulsed laser light 1 reflected by the mirror 4 passes through the second axicon lens to become a focused beam 10 and is incident on the workpiece 9. However, since the mirror 4 and the second axicon lens 22 reciprocate together, the angle of incidence of the focused beam on the workpiece 9 is the same regardless of the reciprocating position. Therefore, the Bessel beam region 11 can be formed in the same direction (lengthwise) regardless of the reciprocating position (for example, it can be formed perpendicular to the workpiece 9, or in the Z-axis direction).

[0027] Next, we will explain the components of the optical device and the terminology used in the explanation. [Location where the pulsed laser light 1 is reflected or passed through] As shown in Figures 1 and 2, the pulsed laser light 1 (annular Bessel beam) is reflected in the region enclosed by the dotted line of the mirror 4. When viewed from the optical axis direction (Y-axis direction) in which the pulsed laser light 1 is incident on the mirror 4, this is an annular region centered on the optical axis Ax (annular means ring-shaped, and includes circular annular shapes such as ellipses, ovals, short circles, and perfect circles). Also, the pulsed laser light 1 (annular Bessel beam) passes through the region enclosed by the dotted line of the second axicon lens 22. When viewed from the optical axis direction (Z-axis direction) in which the pulsed laser light 1 is moving from the mirror 4 towards the second axicon lens 22, this is an annular region centered on the optical axis Ax.

[0028] [Optical axis Ax] The optical axis Ax, indicated by the dashed line, is the optical axis through which light actually passes until it enters the first axicon lens 21. However, after passing through the first axicon lens 21, it is an optical axis through which light may not actually pass (a virtual optical axis). As described above, the pulsed laser light 1 does not reflect at the optical axis Ax in the mirror 4 (it reflects in the annular reflection region), and does not pass at the optical axis Ax in the second axicon lens 22 (it passes through the annular region).

[0029] [Pulsed laser light 1] "Pulsed laser light 1" refers to pulsed laser light with pulse widths such as nanoseconds, picoseconds, and femtoseconds.

[0030] [Converging Beam 10] In Embodiment 1, the pulsed laser light 1 after passing through the second axicon lens 22 becomes a convergent beam 10 as the outer diameter of the beam decreases along the direction of propagation. The convergent beam forms a Bessel beam region 11 near the workpiece 9.

[0031] [Axicon Lens] An "axicon lens" is a cone-shaped lens. However, the second axicon lens 22 does not need to be entirely cone-shaped. It is sufficient that the region through which the pulsed laser light 1 passes is part of a cone; for example, it may be a cone with the top part of the cone cut off. The cone of the first axicon lens 21 of the optical device 100A may be on either the output side or the input side of the pulsed laser light 1.

[0032] [Workpiece 9] For workpiece 9, for example, a sapphire substrate, a glass substrate (plate), etc. is used. Preferably, it is a transparent substrate. It does not have to be completely transparent. It is sufficient if it has transparency that does not significantly hinder the formation of a modified region by the focused beam 10. Using a glass substrate as workpiece 9 is advantageous in terms of the availability of the material, etc.

[0033] [Mounting of mirror 4, etc. to housing 31] As shown in Figures 1 and 2, the mirror 4 and the second axicon lens 22 are mounted on housing 31, which is subjected to one-dimensional reciprocating motion (for example, linear reciprocating motion) by a voice coil motor 7.

[0034] [Holding Member 32] In the optical device 100A, the mirror 4 and the second axicon lens 22 are attached to the housing 31 via a holding member 32. In the example shown in Figure 2, the mirror 4 is attached to the housing 31 via a holding member 32 provided on its back surface, and the second axicon lens 22 is attached to the housing 31 via a holding member 32 provided on the outside of the annular region (outside the conical base) on the output side. The holding member 32 of the mirror 4 and the holding member 32 of the second axicon lens 22 may be connected to each other. The holding member 32 is made of, for example, an aluminum plate, a resin plate, a resin layer, a glass plate, a wooden board, etc. It is preferable that the holding member 32 is made of a non-magnetic material. The housing 31 is connected to the bobbin 72 (movable part) of the voice coil motor 7, and performs one-dimensional reciprocating motion.

[0035] In this way, when the mirror 4 and the second axicon lens 22 are attached to the housing 31, it becomes possible to move back and forth while maintaining the optical positional relationship between the mirror 4 and the second axicon lens 22.

[0036] The structure of the voice coil motor 7 and the materials of the housing 31 will be described. The voice coil motor 7 has a yoke 71 (iron), a bobbin 72 (non-magnetic), a permanent magnet 73 mounted on the yoke 71, and a coil 74 wound around the bobbin 72. The bobbin 72 is attached to the housing 31. The permanent magnet 73 and the part of the bobbin 72 where the coil 74 is wound are located opposite each other with a space in between. For example, an Nd-Fe-B magnet is used as the permanent magnet 73.

[0037] When current is passed through the coil 74, the bobbin 72 (movable part) expands and contracts (one-dimensional reciprocating motion) relative to the yoke 71 (fixed part) due to a force acting according to Fleming's left-hand rule (the voice coil motor 7 can be considered a type of linear motor). As the bobbin 72 expands and contracts (reciprocating motion), the mirror 4 and the second axicon lens 22 attached to the housing 31 also reciprocate together with the housing 31. The control unit 5 controls the timing of the current flowing through the coil 74, etc.

[0038] [Housing 31] In the optical device of Embodiment 1, the mirror 4 and the second axicon lens 22 are mounted on the housing 31, and the housing 31 is reciprocated by a voice coil motor 7. The voice coil motor 7 operates using magnetic force. For this reason, it is preferable that the housing 31 be made of a non-magnetic material. A "non-magnetic material" refers to a material that does not possess magnetism. Examples include copper, aluminum, resin (plastic), wood, glass, etc. However, even if a material has magnetism, it is acceptable if the magnetism is weak and does not significantly affect the magnetic field (does not hinder movement).

[0039] If the housing 31 is made of a non-magnetic material, the magnetic field used to drive the voice coil motor 7 is less likely to be disturbed, and the reciprocating motion of the mirror 4 and the second axicon lens 22 can be performed accurately.

[0040] [Method for forming a spot row by scanning a convergent beam 10] The method for forming a spot row by scanning a convergent beam 10 in the optical device 100A will be explained using Figures 3 to 5. Figure 3 is a diagram to explain the method for forming a spot row over the entire processing area 95. Figure 4 is a diagram to explain the method for forming a spot row along the sub-scanning direction in the "forward path spot row formation area". Figure 5 is a diagram to explain the two-dimensional method for forming a spot row in the "forward path spot row formation area". In Figures 3 to 5, the X-axis is an axis along the main scanning direction, the Y-axis is an axis along the sub-scanning direction, and the Z-axis is an axis perpendicular to the X-axis and Y-axis.

[0041] As described above, the optical apparatus 100A according to Embodiment 1 further comprises a stage 6 for placing the workpiece 9 (see Figures 1 and 2). The stage 6 is configured to be movable along predetermined mutually orthogonal main scanning direction (X-axis direction) and sub-scanning direction (Y-axis direction) in a plane parallel to the mounting surface (XY plane) (see Figures 3 to 5).

[0042] Before explaining the method for forming a spot row over the entire processing area 95 (see Figure 3), we will first explain the method for forming a spot row along the sub-scanning direction with reference to Figure 4, and then explain the method for forming a spot row in two dimensions with reference to Figure 5.

[0043] In the optical apparatus 100A according to Embodiment 1, the control unit 5 rotates the stage 6, or the mirror 4 and second axicon lens 22 (the term "housing 31" may be used instead of "mirror 4 and second axicon lens 22"), so that the beam scanning direction 15 and the sub-scanning direction (Y-axis direction) are tilted by a predetermined angle (α) (see Figure 4(a)), and while gradually moving the stage 6 along the main scanning direction (X-axis direction), it scans the converging beam 10 along the beam scanning direction 15 (see Figures 4(b) to 4(d)), thereby forming a row of spots (P01, P02, P03, ...) on the workpiece 9 along the sub-scanning direction (Y-axis direction). Specifically, the step of forming a row of spots along the sub-scanning direction is carried out as follows.

[0044] [Method for Forming Spot Row Along Sub-Scanning Direction] First, the control unit 5 moves the stage 6 to the initial position and rotates the housing 31 to the maximum movement position on the +Y side (see FIG. 10(b) described later), and starts controlling the movement operation of the stage 6 along the main scanning direction and the reciprocating operation of the housing 31 (see FIG. 4(a)). At this time, the control unit 5 synchronizes the movement operation of the stage 6 and the reciprocating operation of the housing 31 using a rotational position detection encoder (not shown).

[0045] Thereafter, after time t0 passes and time t1 comes, the stage 6 moves leftward from the position at time t0, and the housing 31 moves a predetermined distance in the -Y direction (forward movement operation). As a result, the convergent beam 10 is irradiated to a predetermined position on the workpiece 9, and a spot P01 is formed at that position (see FIG. 4(b)). The forward movement position of the housing 31 at time t1 is the maximum effective movement position (+Y side).

[0046] Thereafter, when time t2 comes, the stage 6 moves leftward from the position at time t1, and the housing 31 moves a predetermined distance in the -Y direction (forward movement operation). As a result, the convergent beam 10 is irradiated to a predetermined position on the workpiece 9 (a position where spot P01 and spot P02 are aligned in a line along the sub-scanning direction), and a spot P02 is formed at that position (see FIG. 4(c)).

[0047] Thereafter, when time t3 comes, the stage 6 moves leftward from the position at time t2, and the housing 31 moves a predetermined distance in the -Y direction (forward movement operation). As a result, the convergent beam 10 is irradiated to a predetermined position on the workpiece 9 (a position where spots P01 to P03 are aligned in a line along the sub-scanning direction), and a spot P03 is formed at that position (see FIG. 4(d)).

[0048] In this way, by repeating spot formation along the sub-scanning direction, a spot row (P01, P02, P03, ...) extending in the direction along the sub-scanning direction is formed on the workpiece 9.

[0049] [Two-dimensional method of forming spot rows in the "forward path spot row formation area"] Next, with reference to Figure 5, the two-dimensional method of forming spot rows in the "forward path spot row formation area" will be explained. First, the first spot row (the leftmost spot row in Figure 5, hereinafter referred to as the first spot row) is formed along the sub-scanning direction. Next, once the formation of the first spot row is complete, the housing 31 performs a recovery operation (movement in the +Y direction) to return to the maximum movement position (+Y side) for forming the next spot row (hereinafter referred to as the next spot row) along the sub-scanning direction, and then forms the next spot row in the same manner as above. The stage 6 is always moving at a constant speed along the main scanning direction (in this case, from right to left), and by repeating the above spot row formation, a large number of spot rows are formed bidimensionally within the "forward path spot row formation area" (see Figures 3 and 5).

[0050] Thus, by providing a stage 6, and with the beam scanning direction 15 and the sub-scanning direction tilted by a predetermined angle (α), and moving the stage 6 along the main scanning direction while scanning the convergent beam 10 along the beam scanning direction 15, a spot row of pulsed laser light 1 is formed on the workpiece along the sub-scanning direction, making it possible to form spots on the entire workpiece at high speed (and to form the corresponding modified regions at high speed).

[0051] In the optical apparatus 100A according to Embodiment 1, the control unit 5 tilts the beam scanning direction 15 and the sub-scanning direction by a predetermined angle (α), and then moves the stage 6 along the main scanning direction while repeatedly forming a spot row with pulsed laser light 1 along the sub-scanning direction, thereby forming a two-dimensional spot row within the processing area 95 of the workpiece 9. At this time, the control unit 5 synchronizes the movement of the stage 6 along the main scanning direction with the reciprocating movement of the housing 31.

[0052] Therefore, in the optical device 100A according to Embodiment 1, while the stage 6 is moved once in the main scanning direction, spots are formed bidirectionally within the "forward path spot row formation region" (see Figure 5). As a result, the optical device 100A according to Embodiment 1 can form a large number of micro-modification regions on the workpiece at a faster speed than conventional methods.

[0053] [Method for forming spot rows across the entire processing area 95] Referring again to Figures 3 and 5, the method for forming spot rows across the entire processing area 95 will be explained. First, a spot row is formed two-dimensionally in a certain "forward spot row formation area" (for example, the forward spot row formation area R1 in Figure 3) by forming a spot row from left to right using the method shown in Figures 3 and 5. Once the formation of the spot row in that area is complete, the control unit 5 (temporarily interrupts the formation of the spot row) moves the stage 6 along the sub-scanning direction to the next processing area, the "return spot row formation area" (for example, the return spot row formation area R2 in Figure 3), and then forms a spot row two-dimensionally in that area by forming a spot row from right to left. At this time, as shown in Figure 4 and Figure 7 which will be described later, the spot row is formed two-dimensionally in the "return spot row formation area" under the condition that the angle α between the beam scanning direction 15 and the sub-scanning direction (Y-axis direction) is the opposite of the forward spot row formation area.

[0054] Once the formation of the spot rows in the "return spot row formation region" is complete, the control unit 5 (temporarily interrupts spot formation) moves the stage 6 along the sub-scanning direction to the next processing region, the "next forward spot row formation region" (for example, the forward spot row formation region R3 in Figure 3), and then forms the spot rows in that region from left to right, thereby forming the spot rows two-dimensionally. At this time, the formation of the spot rows along the sub-scanning direction is performed under the condition that the angle between the beam scanning direction 15 and the sub-scanning direction (Y-axis direction) is the opposite of that in the "return spot row formation region," and the spot rows are formed two-dimensionally in the "forward spot row formation region." By repeating these steps, a large number of spot rows are formed over the entire processing area 95 of the workpiece 9.

[0055] As described above, in the optical device 100A according to Embodiment 1, the operation of forming a two-dimensional row of spots on the workpiece is repeated while intermittently moving the stage 6 along the sub-scanning direction and while reciprocating the stage 6 along the main scanning direction. As a result, with the optical device 100A according to Embodiment 1, a row of spots can be formed over the entire area 95 of the workpiece 9.

[0056] Figure 6 is a diagram illustrating a two-dimensional method for forming spot rows in the "return path spot row formation region". Figure 7 is a diagram illustrating a method for forming spot rows along the sub-scanning direction in the "return path spot row formation region". In the optical device 100A according to Embodiment 1, if spot rows are formed in the "return path spot row formation region" using the same method as in the "forward path spot row formation region", the stage 6 is moving in the reverse direction (from left to right), making it impossible to form spot rows along the sub-scanning direction (Y-axis direction). Therefore, in the optical device 100A according to Embodiment 1, as shown in Figures 6 and 7, spot rows (P11, P12, P13...) are formed two-dimensionally in the "return path spot row formation region" under the condition that the angle between the beam scanning direction 15 and the sub-scanning direction (Y-axis direction) is the opposite of that in the "forward path spot row formation region".

[0057] Thus, in the optical device 100A according to Embodiment 1, the angle between the beam scanning direction 15 and the sub-scanning direction (Y-axis direction) is reversed between the "forward spot row formation region" and the "return spot row formation region" when forming the spot row. Therefore, according to the optical device 100A according to Embodiment 1, the spot row can be correctly formed along the sub-scanning direction in both the "forward spot row formation region" and the "return spot row formation region".

[0058] Figure 8 is a diagram illustrating a method for forming other spot rows along the sub-scanning direction in the "return path spot row formation region". In the optical device 100A according to Embodiment 1, in the "forward path spot row formation region", spot rows (P01, P02, P03...) may be formed in the forward direction along the sub-scanning direction as shown in Figure 4, and in the "return path spot row formation region", spot rows (P11, P12, P13...) may be formed in the reverse direction along the sub-scanning direction as shown in Figure 8. Even in this way, spot rows can be correctly formed along the sub-scanning direction in both the "forward path spot row formation region" and the "return path spot row formation region".

[0059] Here, using Figure 9, we will explain the movement range of the mirror 4 and the second axicon lens 22 (housing 31), and the beam shift amount of the focusing beam 10. Starting with Figure 9(b), which shows the movement range of the mirror 4, the mirror 4 and the second axicon lens 22 (housing 31) reciprocate within a reciprocating movement range between the maximum movement position (+Y side) and the maximum movement position (-Y side). In the reciprocating movement's turning point range, a spot P is not formed considering acceleration and deceleration, and the range in which the reciprocating movement is at a substantially constant speed is considered the effective movement range, within which the spot P is formed. Figure 9(a) is a diagram for explaining the beam shift amount of the focusing beam 10. Since the spot P is formed within the effective movement range of the housing 31 shown in Figure 9(b), this range becomes the effective scanning range of the focusing beam 10, and this range becomes the maximum beam shift amount. Dividing the beam in the middle of the maximum beam shift positions on the +Y side and the -Y side, the maximum beam shift amount (1 / 2) is as shown in the figure.

[0060] The convergent beam 10 may be emitted when the reciprocating speed is constant, under the control of the control unit 5. For example, under the control of the control unit 5, the mirror 4 (mirror 4 and second axicon lens 22, housing 31) reciprocates within the reciprocating movement range shown in Figure 9(b).

[0061] Let's explain using the example of a case where a converging beam 10 is emitted during the forward movement and a spot P is formed. The mirror 4 moves from the maximum movement position (-Y side) to (+Y side) by the return movement, then turns around and moves from (+Y side) to (-Y side) (forward movement). The mirror 4's operating speed (movement speed) is zero at the turning position, but when it enters the forward movement, it accelerates until it reaches a predetermined speed (turning range). Once it reaches the predetermined speed, the operating speed is maintained constant (effective movement range). As it approaches the maximum movement position (-Y side), it decelerates and turns around (turning range). Then it enters the return movement.

[0062] The convergent beam 10 is not emitted during the time period within the return range. The convergent beam 10 is emitted during the time period within the effective movement range. The same applies when the convergent beam 10 is emitted during the return operation and spot P is formed.

[0063] If the focusing beam 10 is configured to be emitted when the reciprocating speed is constant, controlled by the control unit 5, it becomes easier to equalize the irradiation time for each spot P when forming a large number of spots P, and to uniformly form a large number of fine modification regions. Alternatively, since the focusing beam 10 is emitted when the reciprocating speed is constant, the irradiation position accuracy of the spots P is improved, making it easier to form a large number of fine modification regions with high positional accuracy.

[0064] As a supplement to Figure 3, when the stage 6 moves back and forth in the main scanning direction, it repeats the operation of ...stop (reversal position) - [forward path] - acceleration - constant speed - deceleration - stop (reversal position) - [return path] - acceleration - constant speed - deceleration - stop (reversal position) - [forward path] - acceleration - constant speed - deceleration - stop (reversal position)... (see Figure 3). Preferably, the control unit 5 controls the emission of pulsed laser light 1, the reciprocating movement of the housing 31, etc., so as to form a spot P during the constant speed. If the reversal position is outside the workpiece 9, the processing area 95 (spot formation area) where the constant speed is maintained can be widened.

[0065] [Bessel beam region 11] Next, the Bessel beam region 11 will be described. After the pulsed laser light 1 passes through the second axicon lens 22, it becomes a focused beam 10 and is irradiated onto the workpiece 9. A Bessel beam region 11 is generated at the point where the focused beam 10 intersects, forming a fine modification region on the workpiece 9.

[0066] Figure 10 is a diagram illustrating the formation position of the vessel beam region 11. The workpiece 9 is a glass substrate of a predetermined thickness. The position of the vessel beam region 11 (position relative to the thickness direction of the workpiece 9) may change depending on the reciprocating movement position of the mirror 4. Note that in Figures 10(a) to (c), "the mirror" has the same meaning as "the mirror 4 and the second axicon lens 22" or "the housing 31".

[0067] As shown in Figure 10(a), when the mirror 4 is at its maximum effective movement position on the +Y side, the vessel beam region 11 is formed downward with respect to the thickness direction of the workpiece 9, but the vessel beam region 11 covers the thickness region of the workpiece 9. As shown in Figure 10(c), when the mirror 4 is at its maximum effective movement position on the -Y side, the vessel beam region 11 is formed upward with respect to the thickness direction of the workpiece 9, but the vessel beam region 11 covers the thickness region of the workpiece 9. As shown in Figure 10(b), when the mirror 4 is in the central position, the vessel beam region 11 is formed at an intermediate position between Figures 10(a) and 10(c), but the vessel beam region 11 covers the thickness region of the workpiece 9.

[0068] In the example shown in Figure 10, the workpiece 9 is a glass substrate, and the length of the vessel beam region 11 formed near the workpiece 9 is greater than the thickness of the glass substrate. At any moment during the reciprocating motion of the mirror 4 and the second axicon lens 22, the vessel beam region 11 (formed by the vessel beam 10 emitted from the second axicon lens 22) covers the thickness of the glass substrate.

[0069] In this way, regardless of the reciprocating position of the mirror 4, the vessel beam region 11 covers the thickness region of the glass substrate, making it possible to form a good modified region from the front to the back surface of the workpiece 9 (glass substrate).

[0070] The following description of the method for forming a micro-modified region is made possible by the above description of the optical device 100A. The method for forming a micro-modified region on a workpiece 9 using an optical device 100A comprising: "an optical system 2 having a first axicon lens 21 and a second axicon lens 22 provided along the direction of propagation of pulsed laser light 1, and a mirror 4 provided between the first axicon lens 21 and the second axicon lens 22 for reflecting the pulsed laser light 1"; "a stage 6 configured to be movable along predetermined main scanning directions and sub-scanning directions that are mutually orthogonal in a plane parallel to the mounting surface, and to be rotatable with respect to a predetermined axis perpendicular to the mounting surface"; and "a control unit 5 having the function of scanning the converging beam 10 on the workpiece 9 along a predetermined beam scanning direction 15 by controlling the reciprocating motion of the mirror 4 and the second axicon lens 22, A method for forming a fine modification region, wherein the beam scanning direction 15 and the sub-scanning direction are tilted by a predetermined angle (α), and the stage 6 is moved along the main scanning direction while scanning the converging beam 10 along the beam scanning direction 15, thereby forming a row of spots by the pulsed laser light 1 on the workpiece 9 along the sub-scanning direction.

[0071] This method allows for the formation of micro-modified regions at a faster speed than conventional methods, for the same reasons as described for optical device 100A.

[0072] [Example of Mirror 4 Configuration] Figure 11 is a diagram illustrating the configuration of the mirror 4. The mirror 4 may have a full mirror surface, as shown in Figure 11(a), in which the area inside 45 of the annular reflective region 44 is also a mirror surface; or, as shown in Figure 11(b), it may have an annular mirror surface in which the entire area inside 45 of the annular reflective region 44 is absent (or deleted); or, as shown in Figures 11(c) and 11(d), it may have a structure in which a part of the inside 45 of the annular reflective region 44 is absent. Note that Figure 11(c) has a structure in which a reinforcing support 47 is provided inside 45 of the annular reflective region 44, and Figure 11(d) has a structure in which a number of holes 48 (or cavities) are provided inside 45 of the annular reflective region 44. Note that reference numeral 46 in Figures 11(a) and (b) indicates a handling member.

[0073] As shown in Figure 11(a), the mirror surface of the mirror 4 is oval-shaped because the region that reflects the focusing beam 10 during use has an oval shape when viewed along a direction perpendicular to the mirror surface. This reduces the area and weight compared to a mirror with a circular surface. Alternatively, as shown in Figures 11(b) to 11(d), the mirror 4 may have a structure in which all or part of the inside of the region that reflects the focusing beam 10 during use (annular reflection region 44) is absent. This further reduces the weight of the mirror 4 (especially the mirror surface). As a result, the reciprocating motion of the mirror 4 can be increased in speed, which in turn increases the spot formation speed and the formation speed of the fine modification region.

[0074] [Example of the configuration of the second axicon lens 22] Figure 12 is a diagram shown to illustrate the structure of the second axicon lens 22. The second axicon lens 22 may be conical in shape as a general axicon lens, but as shown in Figures 12(a) and (b), it may consist of a lens having a structure in which all or part of the inner 25 of the annular region 24 through which the pulsed laser light 1 passes is absent (or deleted or hollowed out). Reference numeral 26 indicates a handling member. Figure 12(a) is an example in which the cone portion is removed and the other part (base portion) is left, and Figure 12(b) is an example in which the entire inner 25 of the annular region 24, including the base portion, is removed.

[0075] Figure 12(c) shows an example where the cone portion is removed and the base portion is left, and part of the base portion is also removed and a reinforcing support 27 is provided. Figure 12(d) shows an example where the cone portion is removed and the base portion is left, and a number of holes 48 (or cavities) are provided in the base portion. The second axicon lens 22 can also be described as a conical lens without a cone portion.

[0076] By configuring the second axicon lens 22 in this way, for the same reasons as explained for the mirror 4, it becomes possible to lighten the second axicon lens 22, increase the speed of its reciprocating motion, increase the speed of spot formation, and increase the speed of formation of the fine modification region.

[0077] Furthermore, if the shape does not include a cone, the pulsed laser light 1 going from the first axicon lens 21 to the mirror 4 will not be obstructed by the cone.

[0078] As described above, the optical device 100A according to Embodiment 1 makes it possible to form a large number of fine modification regions at a faster speed than in the conventional method.

[0079] [Embodiment 2] Figures 13 to 14 are diagrams illustrating the optical apparatus according to Embodiment 2. The optical apparatus according to Embodiment 2 is basically the same as the optical apparatus according to Embodiment 1, but differs in that it has a lens system 29 and uses a linear motor 8 instead of a voice coil motor 7.

[0080] Figure 13 is a diagram illustrating the overview of the optical device 100B. As shown in Figure 13, in the optical device 100B, when the pulsed laser light 1 passes through the first axicon lens 21, it becomes a converging pre-Bessel beam in which the outer diameter of the ring (a ring composed of the entire Bessel beam) gradually decreases, generating the first Bessel beam region 11a (parallel rays within the ring).

[0081] Subsequently, the beam diverges, and the outer diameter of the ring gradually increases. However, the lens system 29 (convex lens system) located where the initial Bessel beam region 11a is sank causes the ring to become a converging beam 10 with a gradually decreasing thickness, which is then incident on the mirror 4 and reflected. After passing through the second axicon lens 22, the outer diameter of the ring gradually decreases, and the ring becomes a converging beam 10 with a gradually decreasing thickness, forming a Bessel beam region 11, which is then irradiated onto the workpiece 9.

[0082] [Lens system 29] In addition to the first axicon lens 21 and the second axicon lens 22, the optical system 2 further includes a lens system 29 that adjusts the length of the Bessel beam region 11 at the beam waist position near the workpiece of the converging beam 10.

[0083] When a lens system 29 (convex lens system) is provided, the converging beam 10 becomes one in which the thickness of the ring gradually decreases. As a result, the diameter of the converging beam 10 irradiated onto the workpiece 9 (outer diameter of the ring) becomes smaller, and consequently, the length of the bessel beam region 11 at the beam waist position increases (the diameter decreases). The length of the bessel beam region 11 can be changed by changing the magnification of the lens.

[0084] The lens system 29 is not limited to a convex lens system; a concave lens system may also be used. When a concave lens system is provided, the thickness of the ring gradually increases, so the diameter of the focusing beam 10 irradiated onto the workpiece 9 (the outer diameter of the ring) becomes larger, and consequently the length of the bessel beam region 11 at the beam waist position becomes shorter (the diameter becomes larger).

[0085] Thus, if the optical system 2 further includes a lens system 29 that adjusts the length of the Bessel beam at the beam waist position near the workpiece of the converging beam 10, it becomes easier to form a higher quality modified region with a Bessel beam of an appropriate length corresponding to the thickness of the workpiece 9.

[0086] In the optical device 100B, a linear motor 8 is used instead of a voice coil motor 7. This point will be explained. In the optical device 100B shown in Figure 13, the second axicon lens 22 is attached to the mirror 4 by a holding member 32, and the mirror 4 is attached to the housing 31. In this way, the mirror 4 and the second axicon lens 22 are attached to the housing 31, which is subjected to one-dimensional reciprocating motion by the linear motor 8. Note that the method of attachment is not limited to the above method. For example, the mirror 4 and the second axicon lens 22 may be attached separately to the housing 31 by the holding member 32.

[0087] Figure 14 is a schematic plan view of the optical device 100B (a schematic view of the optical device 100B in Figure 13 from above). As shown in Figures 13 and 14, the optical system 2 includes a first axicon lens 21, a housing 31 (to which the mirror 4 and the second axicon lens 22 are mounted), and a linear motor 8, etc. In other words, these are mounted together. The housing 31 reciprocates (in the beam scanning direction 15) driven by the linear motor 8. The convergent beam 10 emitted from the second axicon lens 22 is irradiated onto the workpiece 9 through a window 341 provided in the optical system 2.

[0088] The linear motor 8 has a fixed part 81 (fixed side) and a movable part 82 (movable side) that moves relative to the fixed part 81. The fixed part 81 is fixedly attached to the optical system 2, and the movable part 82 is attached to the housing 31. The fixed part 81 and the movable part 82, which have alternating S and N poles of magnets, are arranged to face each other. One of the fixed part 81 and the movable part 82 has a permanent magnet 73, and the other has an electromagnet that becomes an N or S pole when current is passed through a coil (not shown). By passing current through the coil, an alternating magnetic field is generated on the side with the electromagnet, and the magnetic attractive and repulsive forces between it and the side with the permanent magnet 73 generate a driving force in the straight-line direction. When the movable part 82 moves back and forth, the housing 31 attached to the movable part 82 also moves back and forth.

[0089] With this configuration, it becomes possible to perform a reciprocating motion while maintaining the optical positional relationship between the mirror 4 and the second axicon lens 22.

[0090] Although the present invention has been described above based on the above embodiments, the present invention is not limited to the above embodiments. It can be implemented in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0091] (1) In the embodiments described above, pulsed laser light was used as the laser light, but the present invention is not limited thereto. CW laser light can also be used as the laser light. In this case, instead of a spot-shaped micro-modification region in a plan view, a linear micro-modification region in a plan view can be formed.

[0092] (2) In Embodiment 1, the spot rows were formed in a direction parallel to the sub-scanning direction (a direction perpendicular to the main scanning direction), but they may also be formed in an oblique direction that is not parallel to the sub-scanning direction.

[0093] (3) In Embodiment 1, when scanning on the forward path is completed, scanning is performed on the adjacent return path (see Figure 3, etc.). However, if there is no spot P to be formed on the adjacent return path, scanning on that return path may be omitted, and the system may move to a return path where there is a spot P to be formed (the stage 6 or optical system 2 moves relatively) to perform scanning on the return path.

[0094] (4) The “workpiece 9” in Embodiments 1 and 2 may be read as “virtual workpiece 9” which is assumed to be a workpiece 9.

[0095] 1...Pulsed laser light, 10...Converging beam, 11...Last Bessel beam region, 11a...First Bessel beam region, 15...Beam scanning direction, 2...Optical system, 21...First axicon lens, 22...Second axicon lens, 24...Annular region, 25...Inside, 26...Handling component, 27...Support part, 28...Hole, 29...Lens system, 31...Housing, 32...Holding component, 341...Window, 4...Mirror, 44...Annular reflection region, 45...Inside, 46...Handling component, 47...Support part, 48...Hole, 5...Control unit, 6...Stage, 7...Voice coil motor, 71...Yoke, 72...Bobbin, 73...Permanent magnet, 74...Coil, 8...Linear motor, 81...Fixed part, 82...Movable part, 9...Workpiece, 95...Processing target region, 100A, 100B...Optical device, Ax...Optical axis, P...Spot

Claims

1. An optical apparatus for forming a micro-modified region on a workpiece using laser light, comprising: an optical system having a first axicon lens and a second axicon lens provided along the direction of propagation of the laser light, and a mirror provided between the first axicon lens and the second axicon lens for reflecting the laser light, wherein a focusing beam is emitted from the second axicon lens; and a control unit having the function of scanning the focusing beam on the workpiece along a predetermined beam scanning direction by controlling the reciprocating motion of the mirror and the second axicon lens.

2. An optical device according to claim 1, wherein the laser light is pulsed laser light.

3. The optical apparatus according to claim 1, wherein the optical system further comprises a lens system for adjusting the length of the Bessel beam region formed by the focusing beam emitted from the second axicon lens.

4. An optical device according to claim 1, wherein the mirror and the second axicon lens are mounted on a housing that performs one-dimensional reciprocating motion by a voice coil motor or a linear motor.

5. An optical device according to claim 4, wherein the housing is made of a non-magnetic material.

6. The optical device according to claim 1, wherein the mirror has a structure in which all or part of the inside of the annular reflection region that reflects the laser light is missing.

7. The optical apparatus according to claim 1, wherein the second axicon lens is a lens having a structure in which all or part of the inside of the annular region through which the laser light passes is absent.

8. The optical apparatus according to claim 2, wherein the workpiece is a glass substrate, the pulsed laser light has a Bessel beam region formed near the workpiece whose length is greater than the thickness of the glass substrate, and at any moment during the reciprocating motion of the mirror and the second axicon lens, the Bessel beam region formed by the focusing beam emitted from the second axicon lens covers the thickness of the glass substrate.

9. The optical apparatus according to claim 2, further comprising a stage for placing the workpiece, the stage being movable along predetermined main scanning directions and sub-scanning directions that are mutually orthogonal in a plane parallel to the placement surface, and being rotatable about a predetermined axis perpendicular to the placement surface, wherein the control unit has the function of forming a spot row of pulsed laser light on the workpiece along the sub-scanning direction by scanning the convergent beam along the beam scanning direction while moving the stage along the main scanning direction, with the stage rotated such that the beam scanning direction and the sub-scanning direction are tilted by a predetermined angle (α).

10. An optical apparatus according to claim 9, wherein the control unit has the function of forming a two-dimensional spot row on a workpiece by repeatedly performing an operation to form the spot row on the workpiece along the sub-scanning direction with the pulsed laser light while moving the stage along the main scanning direction.

11. An optical apparatus according to claim 10, wherein the control unit has the function of forming the spot rows on the entire area to be processed on the workpiece by repeating the operation of forming the spot rows two-dimensionally on the workpiece while intermittently moving the stage along the sub-scanning direction and while reciprocating the stage along the main scanning direction.

12. An optical apparatus according to claim 11, wherein the control unit has the function of forming the spot row on the workpiece along the sub-scanning direction, with the angle between the beam scanning direction and the sub-scanning direction being opposite in forward and reverse directions during the forward and return movements of the reciprocating motion.

13. An optical apparatus according to claim 11, wherein the control unit has the function of forming the spot row in the forward direction along the sub-scanning direction on the workpiece during the forward movement of the reciprocating motion, and forming the spot row in the reverse direction along the sub-scanning direction on the workpiece during the return movement of the reciprocating motion.

14. An optical device according to claim 1, wherein the focusing beam is emitted when the operating speed of the reciprocating motion is constant, under the control of the control unit.

15. A method for forming a micro-modified region on a workpiece using an optical device comprising: "an optical system having a first axicon lens and a second axicon lens provided along the direction of propagation of pulsed laser light, and a mirror provided between the first axicon lens and the second axicon lens for reflecting the pulsed laser light"; "a stage configured to be movable along predetermined main scanning directions and sub-scanning directions that are mutually orthogonal in a plane parallel to the mounting surface, and to be rotatable about a predetermined axis perpendicular to the mounting surface"; and "a control unit having the function of scanning a convergent beam on a workpiece along a predetermined beam scanning direction by controlling the reciprocating motion of the mirror and the second axicon lens," wherein the beam scanning direction and the sub-scanning direction are tilted by a predetermined angle (α), and the stage is moved along the main scanning direction while scanning the convergent beam along the beam scanning direction, thereby forming a row of spots by the pulsed laser light on the workpiece along the sub-scanning direction.

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