Optical device and method for forming fine modified region

Abstract

To provide an optical device capable of forming a fine modified region at a higher speed than conventional devices. [Solution] The optical device 100A forms a fine modified region on a workpiece 9 using laser light (pulsed laser light 1), and includes an optical system 3 having a first axicon lens 21 and a second axicon lens 22 arranged along the traveling direction of the laser light, and a mirror 4 arranged between the first axicon lens 21 and the second axicon lens 22 for reflecting the laser light, and emits 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 motion of the mirror 4 and the second axicon lens 22.

Description

[Technical Field]

[0001] One aspect of the present invention relates to an optical device and a method for forming a fine modified region. [Background technology]

[0002] In recent years, there has been a demand for even higher integration of semiconductor packages, and because it is not easy to further miniaturize wiring in the so-called front-end process, interest in so-called back-end processes is growing. One such technology is chiplet. This is a technology in which small semiconductor chips, each with its own assigned function, are combined like blocks and placed in a single package. An interposer (intermediate substrate) is used to connect semiconductor chips together. The interposer uses a glass substrate or similar, and has many fine through-glass vias (TGVs) formed within its surface to ensure electrical continuity between the circuits on the front and back.

[0003] To form a large number of fine through-holes in an interposer, a stage on which the workpiece is mounted is moved appropriately while irradiating the workpiece with a converging pulsed laser beam to form fine modified regions (hereinafter referred to as "fine modified regions") at a large number of predetermined locations, and then wet-etching the workpiece with a hydrofluoric acid-based etching solution or the like to form a large number of fine through-holes from the fine modified regions. In this case, if a converging pulsed laser beam generated using, for example, an axicon lens is used as the converging pulsed laser beam, a Bessel beam region with an extremely high aspect ratio can be generated, thereby forming high-quality fine modified regions with a more uniform diameter than conventional ones across the depth direction (thickness direction) of the workpiece, and ultimately high-quality fine through-holes with a more uniform diameter than conventional ones across the depth direction (thickness direction) of the interposer (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-136442 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the technical field of forming fine modified regions in workpieces, there is a challenge of wanting to form fine modified regions faster than ever before, and this challenge does not exist only when using convergent pulsed laser light generated using an axicon lens. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical device and a method for forming a fine modified region that are capable of forming a fine modified region at a higher speed than conventional methods. [Means for solving the problem]

[0006] [1] An optical device according to one aspect of the present application, An optical device for forming a fine modified region on a workpiece using laser light, an optical system including a first axicon lens and a second axicon lens provided along a traveling direction of the laser beam, and a mirror provided between the first axicon lens and the second axicon lens for reflecting the pulsed laser beam, wherein the optical system outputs a convergent beam from the second axicon lens; and a control unit having a 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.

[0007]

[15] A method for forming a fine modified region according to one aspect of the present application includes: A method for forming a fine modified region on a workpiece using an optical device comprising: "an optical system including a first axicon lens and a second axicon lens arranged along the traveling direction of a pulsed laser beam, and a mirror arranged between the first axicon lens and the second axicon lens to reflect the pulsed laser beam," "a stage configured to be movable along predetermined main scanning and sub-scanning directions that are orthogonal to each other in a plane parallel to a mounting surface, and to be rotatable about a predetermined axis that is orthogonal to the mounting surface," and "a control unit having a function of scanning a convergent beam on the workpiece along a predetermined beam scanning direction by controlling the reciprocating motion of the mirror and the second axicon lens," With the beam scanning direction and the sub-scanning direction tilted by a predetermined angle (α), the stage is moved along the main scanning direction while the convergent beam is scanned along the beam scanning direction, thereby forming a spot train of the pulsed laser light on the workpiece along the sub-scanning direction.

[0008] According to the optical device of the above aspect, it is possible to form fine modified regions at a higher speed than conventional methods. Also, according to the optical device and the fine modified region forming method of another aspect of the present application, it is possible to form a large number of fine modified regions at a higher speed than conventional methods. [Brief explanation of the drawings]

[0009] [Figure 1] 1A and 1B are diagrams illustrating an overview of an optical device 100A according to a first embodiment. [Figure 2] 1 is a diagram illustrating the structure of an optical device 100A according to a first embodiment (using a voice coil motor 7). FIG. [Figure 3] 10A and 10B are diagrams illustrating a method of forming a spot train over the entire processing target area 95. [Figure 4] 10A and 10B are diagrams for explaining a method of forming a spot train along the sub-scanning direction in an "outgoing spot train formation region." [Figure 5]10A and 10B are diagrams for explaining a two-dimensional spot train formation method in the "outbound spot train formation region." [Figure 6] 10A and 10B are diagrams for explaining a two-dimensional spot train formation method in the "returning spot train formation region." [Figure 7] 10A and 10B are diagrams for explaining a method of forming spot trains along the sub-scanning direction in a "returning spot train forming region." [Figure 8] 10A and 10B are diagrams for explaining a method of forming spot trains along the sub-scanning direction in a "returning spot train forming region." [Figure 9] 3 is a diagram for explaining the beam shift amount of a convergent beam 10 and the movement range of a mirror 4. FIG. [Figure 10] FIG. 2 is a diagram illustrating the position where the Bessel beam region 11 is formed. [Figure 11] FIG. 2 is a diagram illustrating the configuration of a mirror 4. [Figure 12] FIG. 2 is a diagram illustrating the configuration of a second axicon lens 22. [Figure 13] FIG. 10 is a diagram illustrating an overview of an optical device 100B according to a second embodiment. [Figure 14] FIG. 14 is a schematic plan view of the optical device 100B shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] An optical device according to one aspect of the present invention will be described below with reference to the drawings. Each drawing is a schematic diagram and does not necessarily accurately reflect an actual optical device. Each embodiment does not limit the scope of the claims. Not all of the elements and combinations thereof described in each embodiment are essential to the present invention. The same reference numerals are used across embodiments for components that can be considered substantially equivalent, and repeated explanations may be omitted (some explanations may be duplicated).

[0011] [Embodiment 1] In the first embodiment, the optical device of the present invention will be described using an example of an optical device that uses pulsed laser light as the laser light. FIGS. 1 to 12 are diagrams shown to explain the optical device according to the first embodiment. FIG. 1 is a diagram shown to explain the outline of the optical device. FIG. 2 is a diagram shown to explain the structure of the optical device (using a voice coil motor 7). For ease of explanation, an XYZ coordinate system having X, Y, and Z axes is depicted on certain 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 the sub-scanning direction will be described later in the explanation of FIG. 3, etc.).

[0012] [Optical device] As shown in FIG. 1, the optical device forms a modified region on a workpiece 9 using a convergent beam 10. The optical device includes 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 arranged along the traveling direction of the pulsed laser light 1. The mirror 4 is arranged between the first axicon lens 21 and the second axicon lens 22 and reflects the pulsed laser light 1. 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 from the first axicon lens 21 toward the mirror 4, thereby scanning the convergent beam 10 on the workpiece along a predetermined beam scanning direction 15. 1 shows the beam scanning direction 15 at the intermediate position of the reciprocating movement range or the effective movement range of the reciprocating motion. The same applies to FIG. 13, which will be described later. (The effective movement range and the like will be described later with reference to FIG. 9(b)).

[0013] [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 convergent Bessel beam whose outer diameter of the ring (the ring made up of the entire Bessel beam) gradually decreases, generating the first Bessel beam region 11a (parallel rays inside the ring). This Bessel beam region 11a is generated where the light (Bessel beam) emitted from the first axicon lens 21 overlaps. The first Bessel beam region 11a is a precursor to the final Bessel beam region 11 that is emitted to the workpiece 9.

[0014] After that, it diverges, and the outer diameter of the ring gradually increases. After being reflected by mirror 4, it changes its direction of travel and passes through second axicon lens 22 constituting optical system 2, whereupon it becomes a converging Bessel beam whose outer diameter gradually decreases again, forming a Bessel beam region 11 at or near the point of convergence, and is irradiated onto workpiece 9 placed on stage 6. The Bessel beam region 11 (including the first Bessel beam region 11a) is a region formed in the optical axis direction where the optical energy is large. The diameters (beam waist diameters) of the Bessel beam regions 11 are almost the same.

[0015] The length, diameter, etc. of the Bessel beam region 11 can also be changed by changing the apex angle or base angle (the angle formed by the base and an equal side) of the second axicon lens 22, or the angle of incidence of the pulsed laser beam 1 onto the workpiece 9.

[0016] When the workpiece 9 is irradiated with the pulsed laser beam 1, a Bessel beam region 11 (whose length direction is) is formed in the thickness direction of the workpiece 9, which makes it easy to form a modified region uniformly from the front surface to the back surface of the workpiece 9. This makes it easy to form a through hole with a uniform inner diameter from the front surface to the back surface of the workpiece 9.

[0017] [Mirror 4] As shown in FIGS. 1 and 2, the 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. The mirror 4 may be, for example, a galvanometer mirror in which a rotating mirror and a motor are integrated, but the rotating mirror is fixed so as not to rotate. Preferably, the reflecting surface is flat.

[0018] [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 beam 1 traveling from the first axicon lens 21 toward the mirror 4. In the first embodiment, the mirror 4 and the second axicon lens 22 are attached to a housing 31, and the mirror 4 and the second axicon lens 22 are reciprocated by reciprocating the housing 31.

[0019] The control unit 5 (specific circuits and the like are not shown) is composed of, for example, a logic circuit, a microcomputer, etc. The microcomputer is a computer that mainly comprises a CPU (Central Processing Unit) and is composed of ROM, RAM, input / output ports, interfaces, etc. 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 the pulsed laser light 1) are performed by instructions pre-stored in the ROM.

[0020] [Optical system 2] The optical system 2 includes a first axicon lens 21, a housing 31 (to which a mirror 4 and a second axicon lens 22 are attached), a voice coil motor 7, and the like. In other words, these are mounted on the housing 31. The housing 31 is configured to be able to move back and forth (to move back and forth) within the optical system 2 by being driven by the voice coil motor 7. When the housing 31 moves back and forth, the pulsed laser light 1 (convergent beam 10) that has passed through the second axicon lens 22 passes through a window provided in the optical system (provided so that the passage of the convergent beam 10 is not hindered even when the housing 31 moves back and forth), and is irradiated onto the workpiece 9.

[0021] When the voice coil motor 7 is driven by the control unit 5, the housing 31 is reciprocated, and the convergent beam 10 scans the workpiece along a predetermined beam scanning direction 15 (the direction of reciprocating movement of the housing 31). Furthermore, since the Bessel beam region 11 is formed in a wide region of the workpiece 9, a large number of fine modified regions can be formed in the workpiece 9.

[0022] A modified region is formed at the irradiated portion of the workpiece 9, and a through hole is formed by utilizing the difference in etching speed between the modified region and the non-modified region during etching.

[0023] Therefore, in the optical device 100A according to the first embodiment, the convergent beam 10 that has passed through the second axicon lens 22 is a convergent beam generated using an axicon lens, and therefore a Bessel beam region 11 having an extremely high aspect ratio is formed in the vicinity of the workpiece 9. Therefore, the optical device 100A according to the first embodiment can form a high-quality fine modified region having a more uniform diameter across the depth direction (thickness direction) of the workpiece than conventionally.

[0024] Furthermore, in the optical device 100A according to the first embodiment, the convergent 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, the optical device 100A according to the first embodiment can form a large number of fine modified regions on the workpiece at a higher speed than conventional methods.

[0025] The pulsed laser light 1 reflected by the mirror 4 passes through the second axicon lens to become a convergent beam 10, which 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 convergent 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 direction) regardless of the reciprocating position (for example, it can be formed in a direction perpendicular to the workpiece 9 or in the Z-axis direction).

[0026] Next, each component of the optical device and the terms used in the description will be explained. [Location where pulsed laser light 1 is reflected or passes through] As shown in Figures 1 and 2, the pulsed laser beam 1 (annular Bessel beam) is reflected by the area surrounded by the dotted line on the mirror 4. When viewed from the optical axis direction (Y-axis direction) in which the pulsed laser beam 1 is incident on the mirror 4, this is an annular area centered on the optical axis Ax (annular means ring-shaped, and includes an ellipse, an oval, an oblong, a perfect circle, etc.). Moreover, the pulsed laser beam 1 (annular Bessel beam) passes through a region surrounded by a dotted line in the second axicon lens 22. When viewed from the optical axis direction (Z-axis direction) in which the pulsed laser beam 1 travels from the mirror 4 to the second axicon lens 22, this is a ring-shaped region centered on the optical axis Ax.

[0027] [Optical axis Ax] The optical axis Ax indicated by the dashed dotted line is the optical axis along which light actually passes until it enters the first axicon lens 21, but is an optical axis (virtual optical axis) along which light may not actually pass after passing through the first axicon lens 21. As described above, the pulsed laser beam 1 is not reflected at the optical axis Ax on the mirror 4 (it is reflected at an annular reflection region), and does not pass through the optical axis Ax on the second axicon lens 22 (it passes through an annular region).

[0028] [Pulse laser light 1] The "pulse laser light 1" refers to pulsed laser light having a pulse width of, for example, nanoseconds, picoseconds, or femtoseconds.

[0029] [Convergent beam 10] In the first embodiment, the pulsed laser beam 1 after passing through the second axicon lens 22 becomes a convergent beam 10, with the outer diameter of the beam decreasing along the traveling direction. The convergent beam forms a Bessel beam region 11 in the vicinity of the workpiece 9.

[0030] [Axicon Lens] An "axicon lens" is a conical lens. The second axicon lens 22 does not need to be entirely conical. It is sufficient that the area through which the pulsed laser beam 1 passes is a part of a cone, and for example, the cone may be a cone with its apex cut off. The cone of the first axicon lens 21 of the optical device 100A may be located on either the exit side or the entrance side of the pulsed laser beam 1.

[0031] [Workpiece 9] The workpiece 9 may be, for example, a sapphire substrate or a glass substrate (plate). A transparent substrate is preferable. It does not have to be completely transparent. It only needs to have a degree of transparency that does not significantly impede the formation of a modified region by the convergent beam 10. Using a glass substrate as the workpiece 9 is advantageous in terms of material availability, etc.

[0032] [Attaching the mirror 4, etc. to the housing 31] As shown in FIGS. 1 and 2, the mirror 4 and the second axicon lens 22 are attached to a housing 31 in which a one-dimensional reciprocating motion (for example, a linear reciprocating motion) is performed by a voice coil motor 7.

[0033] [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 FIG. 2, the mirror 4 is attached to the housing 31 via a holding member 32 provided on the back surface, and the second axicon lens 22 is attached to the housing 31 via a holding member 32 provided outside the annular region (outside the conical bottom surface) on the output side. The holding member 32 for the mirror 4 and the holding member 32 for 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 plate, or the like. The holding member 32 is preferably made of a non-magnetic material. The housing 31 is connected to a bobbin 72 (moving part) of the voice coil motor 7, and performs a one-dimensional reciprocating motion.

[0034] In this way, when the mirror 4 and the second axicon lens 22 are attached to the housing 31, the mirror 4 and the second axicon lens 22 can move back and forth while maintaining the optical positional relationship between them.

[0035] The structure of the voice coil motor 7 and the material 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 portion of the bobbin 72 around which the coil 74 is wound are disposed opposite each other across a space. The permanent magnet 73 is, for example, an Nd—Fe—B magnet.

[0036] When a current is passed through the coil 74, a force acting according to Fleming's left-hand rule causes the bobbin 72 (movable part) to perform an expansion / contraction motion (one-dimensional reciprocating motion) relative to the yoke 71 (fixed part) (the voice coil motor 7 can also be considered a type of linear motor). When the bobbin 72 performs an expansion / contraction motion (reciprocating motion), the mirror 4 and the second axicon lens 22 attached to the housing 31 also perform a reciprocating motion together with the housing 31. The control unit 5 controls the timing of the current passed through the coil 74, etc.

[0037] [Case 31] In the optical device of the first embodiment, the mirror 4 and the second axicon lens 22 are attached to a housing 31, and the housing 31 is reciprocated by a voice coil motor 7. The voice coil motor 7 operates using magnetic force. Therefore, it is preferable that the housing 31 be made of a non-magnetic material. "Non-magnetic materials" refer to materials that do not have magnetism. Examples include copper, aluminum, resin (plastic), wood, glass, etc. However, even if a material has magnetism, it is permissible as long as it has a weak magnetism that does not significantly affect the magnetic field (does not impede movement).

[0038] 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.

[0039] [Method of forming a spot train by scanning with a convergent beam 10] A method for forming a spot train by scanning the convergent beam 10 in the optical device 100A will be described using Figures 3 to 5. Figure 3 is a diagram shown to explain a method for forming a spot train over the entire processing target area 95. Figure 4 is a diagram shown to explain a method for forming a spot train along the sub-scanning direction in the "outgoing spot train formation area". Figure 5 is a diagram shown to explain a method for two-dimensionally forming a spot train in the "outgoing spot train 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 and Y axes.

[0040] As described above, the optical device 100A according to the first embodiment further includes the stage 6 on which the workpiece 9 is placed (see FIGS. 1 and 2). The stage 6 is configured to be movable along predetermined mutually orthogonal main scanning directions (X-axis direction) and sub-scanning directions (Y-axis direction) within a plane parallel to the placement surface (within the XY plane) (see FIGS. 3 to 5).

[0041] Before explaining the method for forming a spot row over the entire processing target area 95 (see Figure 3), we will explain the method for forming a spot row along the sub-scanning direction with reference to Figure 4, and then we will explain the method for forming a spot row two-dimensionally with reference to Figure 5.

[0042] In the optical device 100A according to the first embodiment, the control unit 5 rotates the stage 6 or the mirror 4 and the 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 at a predetermined angle (α) as shown in FIG. 4(a) (see FIG. 4(a)), and scans the convergent beam 10 along the beam scanning direction 15 while gradually moving the stage 6 along the main scanning direction (X-axis direction) (see FIGS. 4(b) to 4(d)), thereby forming a train of spots (P01, P02, P03, . . . ) on the workpiece 9 along the sub-scanning direction (Y-axis direction). The step of forming the train of spots along the sub-scanning direction is specifically performed as follows.

[0043] [Method of forming a spot row along the sub-scanning direction] First, the control unit 5 moves the stage 6 to its initial position and rotates the housing 31 to the maximum movement position on the +Y side (see FIG. 10(b) described later), and then starts controlling the movement of the stage 6 along the main scanning direction and the reciprocating movement of the housing 31 (see FIG. 4(a)). At this time, the control unit 5 synchronizes the movement of the stage 6 with the reciprocating movement of the housing 31 using a rotational position detection encoder (not shown).

[0044] After that, at time t1 after passing time t0, stage 6 moves leftward from its position at time t0, and housing 31 moves a predetermined distance in the -Y direction (forward movement). As a result, convergent beam 10 is irradiated onto a predetermined position on workpiece 9, and spot P01 is formed at that position (see FIG. 4(b)). The forward movement position of housing 31 at time t1 becomes the maximum effective movement position (+Y side).

[0045] After that, at time t2, stage 6 moves leftward from its position at time t1, and housing 31 moves a predetermined distance in the -Y direction (forward movement). As a result, convergent beam 10 is irradiated onto a predetermined position on workpiece 9 (a position where spots P01 and P02 are aligned in the sub-scanning direction), and spot P02 is formed at that position (see FIG. 4(c)).

[0046] After that, at time t3, stage 6 moves leftward from its position at time t2, and housing 31 moves a predetermined distance in the -Y direction (forward movement). As a result, convergent beam 10 is irradiated onto a predetermined position on workpiece 9 (a position where spots P01 to P03 are aligned in the sub-scanning direction), and spot P03 is formed at that position (see FIG. 4(d)).

[0047] In this way, by repeating the formation of spots along the sub-scanning direction, a row of spots (P01, P02, P03, . . . ) extending in the sub-scanning direction is formed on the workpiece 9.

[0048] [Method for two-dimensionally forming a spot train in the "outbound spot train forming region"] Next, a method for two-dimensionally forming a spot train in the "outgoing spot train forming region" will be described with reference to FIG. First, the first spot train is formed along the sub-scanning direction (the leftmost spot train in Figure 5, hereinafter referred to as the first spot train). Next, when the formation of the first spot train is completed, the housing 31 performs a return movement (movement in the +Y direction) to return to the maximum movement position (+Y side) for forming the next spot train along the sub-scanning direction (hereinafter referred to as the next spot train), and then forms the next spot train in the same manner as above. Note that the stage 6 always moves at a constant speed along the main scanning direction (from right to left in this case), and by repeating the above spot train formation, many spot trains are formed in a dual manner within the "outgoing spot train formation area" (see Figures 3 and 5).

[0049] In this way, by providing a stage 6 and scanning the convergent beam 10 along the beam scanning direction 15 while moving the stage 6 along the main scanning direction with the beam scanning direction 15 tilted at a predetermined angle (α) relative to the sub-scanning direction, and by having the function of forming a row of spots on the workpiece with the pulsed laser light 1 along the sub-scanning direction, it becomes possible to form spots at high speed over the entire workpiece (and to form corresponding modified regions at high speed as well).

[0050] In this way, in the optical device 100A according to the first embodiment, 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 repeating the operation of forming a spot train with the pulsed laser light 1 along the sub-scanning direction, thereby forming a spot train two-dimensionally within the processing target region 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.

[0051] Therefore, in the optical device 100A according to the first embodiment, spots are formed dually in the "outgoing spot train formation region" while the stage 6 is moved once in the main scanning direction (see FIG. 5). As a result, the optical device 100A according to the first embodiment can form a large number of fine modified regions on the workpiece at higher speeds than conventional methods.

[0052] [Method of forming a spot array over the entire processing target area 95] 3 and 5, a method for forming a spot train over the entire processing target area 95 will be described. First, by using the method shown in FIGS. 3 and 5, a spot train is formed two-dimensionally by forming a spot train from left to right in a certain "outbound spot train formation region" (e.g., outbound spot train formation region R1 in FIG. 3). Then, when the formation of the spot train in that region is completed, the control unit 5 (temporarily suspends the formation of the spot train) moves the stage 6 along the sub-scanning direction to the next processing region, the "returning spot train formation region" (e.g., returning spot train formation region R2 in FIG. 3), and then forms a spot train two-dimensionally in that region by forming a spot train from right to left. At this time, as shown in FIG. 4 and FIG. 7 (described later), a spot train is formed two-dimensionally in the "returning spot train formation region" under the condition that the angle α between the beam scanning direction 15 and the sub-scanning direction (Y-axis direction) is opposite to that in the "outbound spot train formation region."

[0053] After completing the formation of the spot train in the "returning spot train formation region," the control unit 5 (temporarily suspends spot formation) moves the stage 6 along the sub-scanning direction to the next processing region, the "next outgoing spot train formation region" (e.g., outgoing spot train formation region R3 in FIG. 3), and then forms a spot train from left to right in that region, thereby forming a two-dimensional spot train. At this time, the spot train along the sub-scanning direction is formed two-dimensionally in the "outgoing spot train formation region" under the condition that the angle between the beam scanning direction 15 and the sub-scanning direction (Y-axis direction) is opposite to that in the "returning spot train formation region." By repeating these steps, multiple spot trains are formed throughout the entire processing target region 95 of the workpiece 9.

[0054] In this way, in the optical device 100A according to the first embodiment, the operation of forming a train of spots two-dimensionally on the workpiece is repeated while intermittently moving the stage 6 in the sub-scanning direction and while reciprocating the stage 6 in the main scanning direction. As a result, the optical device 100A according to the first embodiment can form a train of spots over the entire processing target region 95 on the workpiece 9.

[0055] Fig. 6 is a diagram shown to explain a method for two-dimensionally forming spot trains in the "returning spot train formation region." Fig. 7 is a diagram shown to explain a method for forming spot trains along the sub-scanning direction in the "returning spot train formation region." In optical device 100A according to embodiment 1, if a spot train is formed in the "returning spot train formation region" in the same way as in the "outgoing spot train formation region," it is not possible to form a spot train along the sub-scanning direction (Y-axis direction) because stage 6 moves in the opposite direction (from left to right). Therefore, in optical device 100A according to embodiment 1, a spot train (P11, P12, P13, ...) is formed two-dimensionally in the "returning spot train formation region" under the condition that the angle between beam scanning direction 15 and the sub-scanning direction (Y-axis direction) is opposite to that in the "outgoing spot train formation region," as shown in Figures 6 and 7.

[0056] In this way, 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 in the "outbound spot train formation area" and the "returning spot train formation area", and therefore, according to the optical device 100A according to embodiment 1, the spot train can be correctly formed along the sub-scanning direction in both the "outbound spot train formation area" and the "returning spot train formation area".

[0057] FIG. 8 is a diagram shown to explain another method of forming spot trains along the sub-scanning direction in the "returning spot train forming region." In optical device 100A according to embodiment 1, in the "outgoing spot train formation region," spot trains (P01, P02, P03,...) may be formed in the forward direction along the sub-scanning direction as shown in Fig. 4, and in the "returning spot train formation region," spot trains (P11, P12, P13,...) may be formed in the reverse direction along the sub-scanning direction as shown in Fig. 8. Even in this case, spot trains can be correctly formed along the sub-scanning direction in both the "outgoing spot train formation region" and the "returning spot train formation region."

[0058] Here, the movement ranges of the mirror 4 and the second axicon lens 22 (housing 31) and the beam shift amount of the convergent beam 10 will be summarized and explained using FIG. 9. Starting with FIG. 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). Taking into account acceleration and deceleration, the spot P is not formed within the return range of the reciprocating movement. The range in which the reciprocating movement moves at a substantially constant speed is set as the effective movement range, and the spot P is formed within this range. FIG. 9(a) is a diagram for explaining the beam shift amount of the convergent beam 10. Since the spot P is formed within the effective movement range of the housing 31 shown in FIG. 9(b), this range becomes the effective scanning range of the convergent beam 10, and this range is the maximum beam shift amount. If the area is divided midway between 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.

[0059] The convergent beam 10 may be emitted under the control of the control unit 5 when the speed of the reciprocating motion is constant. For example, under the control of the control unit 5, the mirror 4 (the mirror 4, the second axicon lens 22, and the housing 31) moves back and forth within the range of reciprocal movement shown in FIG. 9(b).

[0060] An example in which a convergent beam 10 is emitted during forward movement to form a spot P will be described. In its return motion, mirror 4 moves from the maximum movement position (-Y side) to (+Y side), then turns around and moves from (+Y side) to (-Y side) (forward motion). The operating speed (movement speed) of mirror 4 is zero at the turning position, but when it begins its forward motion, 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). When it approaches the maximum movement position (-Y side), it decelerates and turns around (turning range). It then begins its return motion.

[0061] The convergent beam 10 is not emitted during the time period of the return range, and is emitted during the time period of the effective movement range. The same applies when the convergent beam 10 is emitted during the return operation to form the spot P.

[0062] If the convergent beam 10 is configured to be emitted when the operating speed of the reciprocating motion is constant under the control of the control unit 5, it is easier to equalize the irradiation time for forming each spot P when forming multiple spots P, making it easier to form multiple fine modified regions uniformly. Alternatively, because the convergent beam 10 is emitted when the operating speed of the reciprocating motion is constant, the accuracy of the irradiation position of the spots P is improved, making it easier to form multiple fine modified regions with high positional accuracy.

[0063] 3, when the stage 6 moves back and forth in the main scanning direction, the following operation is repeated (see FIG. 3): stop (turning position) - [forward path] - acceleration - constant speed - deceleration - stop (turning position) - [return path] - acceleration - constant speed - deceleration - stop (turning position) - [forward path] - acceleration - constant speed - deceleration - stop (turning position). Preferably, the control unit 5 controls the emission of the pulsed laser beam 1, the reciprocating movement of the housing 31, etc., so that the spot P is formed at the constant speed. If the turning position is located outside the workpiece 9, the processing target area 95 (spot formation area) where the speed is constant can be widened.

[0064] [Bessel beam region 11] Next, we will explain the Bessel beam region 11. After passing through the second axicon lens 22, the pulsed laser light 1 becomes a convergent beam 10 and is irradiated onto the workpiece 9. The Bessel beam region 11 is generated at the point where the convergent beams 10 intersect, forming a fine modified region in the workpiece 9.

[0065] FIG. 10 is a diagram for explaining the position where the Bessel beam region 11 is formed. The workpiece 9 is a glass substrate with a predetermined thickness. The position of the Bessel beam region 11 (the position in the thickness direction of the workpiece 9) may change depending on the reciprocating position of the mirror 4. Note that "the mirror" in FIGS. 10(a) to 10(c) has the same meaning as "the mirror 4 and the second axicon lens 22" or "the housing 31."

[0066] As shown in FIG. 10(a), when the mirror 4 is at the maximum effective movement position on the +Y side, the Bessel beam region 11 is formed downward in the thickness direction of the workpiece 9, but the Bessel beam region 11 covers the thickness region of the workpiece 9. As shown in Figure 10(c), when the mirror 4 is at the maximum effective movement position on the -Y side, the Bessel beam region 11 is formed upward in the thickness direction of the workpiece 9, but the Bessel beam region 11 covers the thickness region of the workpiece 9. As shown in FIG. 10(b), when the mirror 4 is in the central position, the Bessel beam region 11 is formed at the intermediate position between FIG. 10(a) and FIG. 10(c), but the Bessel beam region 11 covers the thickness region of the workpiece 9.

[0067] In the example described in FIG. 10 , the workpiece 9 is a glass substrate, and the length dimension of the Bessel beam region 11 of the convergent beam 10 formed in the vicinity of the workpiece 9 is greater than the thickness dimension of the glass substrate, so that at any moment during the reciprocating motion of the mirror 4 and the second axicon lens 22, the Bessel beam region 11 (formed by the convergent beam 10 emitted from the second axicon lens 22) covers the thickness region of the glass substrate.

[0068] In this way, the Bessel beam area 11 covers the thickness area of ​​the glass substrate regardless of the reciprocating movement position of the mirror 4, making it possible to form a good modified area from the front surface to the back surface of the workpiece 9 (glass substrate).

[0069] The following method for forming a fine modified region also applies to the above description of the optical device 100A. a control unit (5) having a function of scanning the convergent beam (10) along a predetermined beam scanning direction (15) on the workpiece (9) by controlling the reciprocating motion of the mirror (4) and the second axicon lens (22); A method for forming a fine modified region, in which 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 the convergent beam 10 is scanned 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.

[0070] According to this method, for the same reasons as those described for the optical device 100A, it is possible to provide a fine modified region forming method that can form the fine modified region at a higher speed than conventional methods.

[0071] [Mirror 4 configuration example] FIG. 11 is a diagram for explaining the configuration of the mirror 4. As shown in FIG. The mirror 4 may have an entire mirror surface, in which the inner region 45 of the annular reflective region 44 is also a mirror surface, as shown in Figure 11(a), or may have an annular mirror surface in which the entire inner region 45 of the annular reflective region 44 is missing (or removed), as shown in Figure 11(b), or may have a structure in which part of the inner region 45 of the annular reflective region 44 is missing, as shown in Figures 11(c) and 11(d). Note that Figure 11(c) has a structure in which a reinforcing support 47 is provided on the inner region 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 on the inner region 45 of the annular reflective region 44. Note that the reference numeral 46 in Figures 11(a) and (b) denotes a handling member.

[0072] The mirror 4 has an elliptical mirror surface as shown in FIG. 11(a) because the area that reflects the convergent beam 10 during use has an elliptical shape when viewed perpendicularly to the mirror surface. This reduces the area and weight compared to a circular mirror surface. Alternatively, the mirror 4 may have a structure in which all or part of the inside of the area that reflects the convergent beam 10 during use (annular reflection area 44) is removed, as shown in FIGS. 11(b) to 11(d). This further reduces the weight of the mirror 4 (particularly the mirror surface). This allows for faster reciprocating motion of the mirror 4, which in turn increases the speed at which spots are formed and the speed at which fine modified areas are formed.

[0073] [Configuration example of second axicon lens 22] FIG. 12 is a diagram illustrating the structure of the second axicon lens 22. The second axicon lens 22 may have a conical shape as a whole, like a general axicon lens, but may also be made of a lens having a structure in which all or part of the inner surface 25 of the annular region 24 through which the pulsed laser light 1 passes is missing (or removed or hollowed out), as shown in Figures 12(a) and 12(b). Reference numeral 26 denotes a handling member. Figure 12(a) shows an example in which the cone portion is removed and the remaining portion (base portion) remains, while Figure 12(b) shows an example in which the entire inner surface 25 of the annular region 24, including the base portion, is removed.

[0074] Figure 12(c) shows an example in which the cone portion is removed, leaving the base portion, and the base portion is also partially removed and provided with a reinforcing support 27. Figure 12(d) shows an example in which the cone portion is removed, leaving the base portion, and multiple holes 48 (or cavities) are provided in the base portion. The second axicon lens 22 can also be described as a conical lens with no cone portion.

[0075] By configuring the second axicon lens 22 in this manner, for the same reasons as those explained for the mirror 4, it becomes possible to reduce the weight of the second axicon lens 22, increase the speed of its reciprocating motion, increase the speed at which the spot is formed, and increase the speed at which the fine modified region is formed.

[0076] If the shape is such that there is no cone portion, the pulsed laser light 1 going from the first axicon lens 21 to the mirror 4 will not be blocked by the cone portion.

[0077] As described above, the optical device 100A according to the first embodiment makes it possible to form a large number of fine modified regions at a higher speed than conventionally possible.

[0078] [Embodiment 2] 13 and 14 are diagrams shown to explain an optical device according to embodiment 2. The optical device according to embodiment 2 is basically the same as the optical device according to embodiment 1, but differs in that it includes a lens system 29 and uses a linear motor 8 instead of a voice coil motor 7.

[0079] FIG. 13 is a diagram illustrating an overview of the optical device 100B. As shown in FIG. 13, in the optical device 100B, when the pulsed laser light 1 passes through the first axicon lens 21, it becomes a convergent pre-Bessel beam in which the outer diameter of the ring (the ring formed by the entire Bessel beam) gradually decreases, and generates the first Bessel beam region 11a (parallel rays inside the ring).

[0080] Then, the light diverges, and the outer diameter of the ring gradually increases, but is converted into a convergent beam 10 whose ring thickness gradually decreases by a lens system 29 (convex lens system) provided at the location where the first Bessel beam region 11a is formed, and is then incident on and reflected by the mirror 4. After passing through the second axicon lens 22, the outer diameter of the ring gradually decreases, and the light diverges into a convergent beam 10 whose ring thickness gradually decreases, forming a Bessel beam region 11, which is then irradiated onto the workpiece 9.

[0081] [Lens System 29] Thus, the optical system 2 includes, in addition to the first axicon lens 21 and the second axicon lens 22, a lens system 29 that adjusts the length of the Bessel beam region 11 at the beam waist position of the convergent beam 10 near the workpiece.

[0082] When the lens system 29 (convex lens system) is provided, the thickness of the ring of the convergent beam 10 gradually decreases, so the diameter (outer diameter of the ring) of the convergent beam 10 irradiated onto the workpiece 9 decreases, and accordingly 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.

[0083] The lens system 29 is not limited to a convex lens system, but may be a concave lens system. If a concave lens system is provided, the beam will have a ring whose thickness gradually increases, so the diameter (outer diameter of the ring) of the convergent beam 10 irradiated onto the workpiece 9 will increase, and accordingly the length of the Bessel beam region 11 at the beam waist position will decrease (the diameter will increase).

[0084] In this way, if the optical system 2 further includes a lens system 29 that adjusts the length of the Bessel beam at the beam waist position of the convergent beam 10 near the workpiece, it becomes easier to form a modified region of higher quality by using a Bessel beam of an appropriate length corresponding to the thickness of the workpiece 9.

[0085] In the optical device 100B, a linear motor 8 is used instead of the voice coil motor 7. This point will be explained. 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 reciprocated one-dimensionally by the linear motor 8. The mounting method is not limited to the above. For example, the mirror 4 and the second axicon lens 22 may be mounted separately to the housing 31 by the holding member 32.

[0086] FIG. 14 is a schematic plan view of the optical device 100B (a schematic view of the optical device 100B of FIG. 13 as seen from above). As shown in Figures 13 and 14, the optical system 2 includes a first axicon lens 21, a housing 31 (to which a mirror 4 and a second axicon lens 22 are attached), a linear motor 8, and the like. In other words, these components are mounted on the housing 31. The housing 31 is driven by the linear motor 8 to reciprocate (in the beam scanning direction 15). The convergent beam 10 emitted from the second axicon lens 22 passes through a window 341 provided in the optical system 2 and is irradiated onto the workpiece 9.

[0087] The linear motor 8 has a fixed part 81 (fixed side) and a movable part 82 (movable side) that is movable 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. Fixed part 81 and movable part 82, with magnetic south and north poles arranged alternately, are arranged facing each other. One of fixed part 81 and movable part 82 uses a permanent magnet 73, and the other uses an electromagnet that becomes a north or south pole when a current is passed through a coil (not shown). Passing a current through the coil generates an alternating magnetic field on the side with the electromagnet, and the magnetic attraction and repulsion forces between the side with permanent magnet 73 generate a driving force in a straight line. When the movable part 82 reciprocates, the housing 31 attached to the movable part 82 also reciprocates.

[0088] With this configuration, the mirror 4 and the second axicon lens 22 can move back and forth while maintaining the optical positional relationship between them.

[0089] Although the present invention has been described above based on the above embodiment, the present invention is not limited to the above embodiment. The present invention can be embodied in various forms without departing from the spirit of the present invention. For example, the following modifications are also possible.

[0090] (1) In the above-described embodiment, a pulsed laser beam is used as the laser beam, but the present invention is not limited to this. A CW laser beam may also be used as the laser beam. In this case, a linear fine modified region in plan view can be formed instead of a spot-shaped fine modified region in plan view.

[0091] (2) In the first embodiment, the spot train is formed in a direction parallel to the sub-scanning direction (a direction perpendicular to the main scanning direction), but it may be formed in an oblique direction that is not parallel to the sub-scanning direction.

[0092] (3) In embodiment 1, once scanning on the outbound 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 not be performed, and the stage 6 or optical system 2 may move to the return path where the spot P to be formed is located (the stage 6 or optical system 2 moves relatively) and scanning on the return path may be performed.

[0093] (4) The "workpiece 9" in the first and second embodiments may be read as a "virtual workpiece 9" if the workpiece 9 exists. [Explanation of symbols]

[0094] 1...pulse laser light, 10...convergent beam, 11...final 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 member, 27...support part, 28...hole, 29...lens system, 31...housing, 32...holding member, 341...window, 4...mirror, 44...annular reflective region, 45...inside, 46...handling member, 47...support part, 48...hole, 5...controller, 6...stage, 7...voice coil motor, 71...yoke, 72...bobbin, 73...permanent magnet, 74...coil, 8...linear motor, 81...fixed part, 82...moving part, 9...workpiece, 95...region to be processed, 100A, 100B...optical device, Ax...optical axis, P...spot

Claims

1. An optical device for forming a fine modified region on a workpiece using laser light, an optical system including a first axicon lens and a second axicon lens provided along a traveling direction of the laser beam, and a mirror provided between the first axicon lens and the second axicon lens for reflecting the laser beam, wherein the optical system emits a convergent beam from the second axicon lens; a control unit having a function of scanning the convergent beam on the workpiece along a predetermined beam scanning direction by controlling reciprocating movements of the mirror and the second axicon lens.

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

3. 2. The optical device according to claim 1, The optical system further includes a lens system that adjusts the length of a Bessel beam region formed by the convergent beam emitted from the second axicon lens.

4. 2. The optical device according to claim 1, An optical device, wherein the mirror and the second axicon lens are attached to a housing that is reciprocated one-dimensionally by a voice coil motor or a linear motor.

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

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

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

8. 3. The optical device according to claim 2, the workpiece is a glass substrate, a length dimension of a Bessel beam region formed in the vicinity of the workpiece of the pulsed laser beam is greater than a thickness dimension of the glass substrate, and at any moment during the reciprocating movements of the mirror and the second axicon lens, a Bessel beam region formed by the convergent beam output from the second axicon lens covers a thickness region of the glass substrate.

9. 3. The optical device according to claim 2, a stage for placing the workpiece thereon, the stage being configured to be movable along a predetermined main scanning direction and a sub-scanning direction which are orthogonal to each other in a plane parallel to the placement surface, and to be rotatable about a predetermined axis which is orthogonal to the placement surface; the control unit has a function of forming a train of spots by the 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 in a state in which the stage is rotated so that the beam scanning direction and the sub-scanning direction are tilted at a predetermined angle (α).

10. 10. The optical device according to claim 9, the control unit has a function of forming the spot train two-dimensionally on the workpiece by repeating the operation of forming the spot train by the pulsed laser light on the workpiece along the sub-scanning direction while moving the stage along the main scanning direction.

11. 11. The optical device according to claim 10, the control unit repeats the operation of forming the spot train 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, thereby forming the spot train over the entire surface of the area to be processed on the workpiece.

12. 12. The optical device according to claim 11, the control unit has a function of forming the spot sequence on the workpiece along the sub-scanning direction while the angle between the beam scanning direction and the sub-scanning direction is reversed on the outbound and return paths of the reciprocating movement.

13. 12. The optical device according to claim 11, The control unit has a function of forming the spot train in a forward direction along the sub-scanning direction on the workpiece during the outbound path of the reciprocating movement, and forming the spot train in a reverse direction along the sub-scanning direction on the workpiece during the return path of the reciprocating movement.

14. 2. The optical device according to claim 1, The optical device, wherein the convergent beam is emitted when the reciprocating motion speed is constant under the control of the control unit.

15. A method for forming a fine modified region on a workpiece using an optical device comprising: "an optical system including a first axicon lens and a second axicon lens provided along the traveling direction of a pulsed laser beam, and a mirror provided between the first axicon lens and the second axicon lens for reflecting the pulsed laser beam," "a stage configured to be movable along predetermined main scanning and sub-scanning directions that are orthogonal to each other in a plane parallel to a mounting surface, and to be rotatable about a predetermined axis that is orthogonal to the mounting surface," and "a control unit having a function of scanning a convergent beam on the workpiece along a predetermined beam scanning direction by controlling the reciprocating motion of the mirror and the second axicon lens," A method for forming a fine modified region, in which 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 the convergent beam is scanned along the beam scanning direction, thereby forming a series of spots by the pulsed laser light on the workpiece along the sub-scanning direction.

Images