Illumination optical system and laser processing device

Abstract

To prevent a high temperature of an optical element, and prevent elongation of an optical path length and an increase in a size of a device.SOLUTION: An illumination optical system guides a laser beam to an irradiation surface, and is provided with light quantity uniformizing parts for uniformizing the laser beam, and includes a first lens array 43a, second lens array 43b, and third lens array 43c in which the light quantity uniformizing parts are arrayed sequentially along an optical axis. The second lens array 43b is arranged in a position behind a focal point of the first lens array 43a. The illumination optical system is structured so that a light-condensing point does not exist on an optical path from the second lens array 43b to the irradiation surface. The first lens array 43a and third lens array 43c have positive power, and the second lens array 43b has negative power.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to an illumination optical system used for irradiating a photomask with a line-shaped laser beam, and a laser processing apparatus equipped with the illumination optical system. [Background technology]

[0002] It is known that a workpiece (e.g., a resin layer of a printed circuit board) made of non-metallic materials such as resin or silicon can be ablated (removal by melting or evaporation) into the shape of the pattern of the photomask (e.g., via) by scanning the workpiece with laser light that has passed through a photomask. When precision processing is required, ablation processing is performed using an excimer laser (KrF laser, wavelength 248 nm).

[0003] Ablation processing using an excimer laser requires irradiating the workpiece with extremely high energy light, and a high-fluence beam passes through an illumination optical system. This causes problems with the heat damaging the glass materials and coating films of optical elements such as lenses. In addition, if the optical elements are arranged so as not to create a focal point on the optical elements in order to prevent them from becoming too hot, the optical elements must be arranged to avoid the focal point, which increases the optical path length, i.e., increases the size of the device.

[0004] For example, the illumination optical system described in Patent Document 1 has a configuration in which a hologram element 12, a cylindrical lens array 13a, and a cylindrical lens array 13b are arranged in this order along the optical axis.

[0005] Patent Document 2 describes a beam homogenizer that can elongate and thin the irradiation area. In the configuration of Patent Document 2, cylinder arrays 1A, 2B, and 1B are arranged in order along the optical axis, and a light collecting section is located behind the cylinder array 1B. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2003-090959 A [Patent Document 2] Japanese Patent Application Publication No. 10-153746 Summary of the Invention [Problem to be solved by the invention]

[0007] In the illumination optical system of Patent Document 1, since a light collecting part exists near the lens surface of the cylindrical lens array 13b, there is a problem of heat generation of the cylindrical lens array 13b. Also, in the configuration of Patent Document 2, although there is no light collecting part on the optical element, there are restrictions on the arrangement of the optical element, which makes the optical path longer and the device larger.

[0008] SUMMARY OF THE PRESENT EMBODIMENTS It is therefore an object of the present invention to provide an illumination optical system and a laser processing apparatus in which the optical element does not have a light-collecting portion and the optical path can be prevented from becoming long. [Means for solving the problem]

[0009] The present invention provides an irradiation optical system for guiding laser light to an irradiation surface, comprising: A light quantity uniformizing unit that uniformizes the laser light is provided. The light amount uniformizing unit has a first lens array, a second lens array, and a third lens array that are arranged in order along an optical axis, a second lens array is disposed behind the focal point of the first lens array; The optical path from the second lens array to the irradiation surface is configured so that there is no focal point, The first lens array and the third lens array have positive power, and the second lens array is an illumination optical system having negative power. The present invention also provides an irradiation optical system for guiding laser light to an irradiation surface, comprising: A light quantity uniformizing unit that uniformizes the laser light is provided. The z-axis is the optical axis direction, the direction perpendicular to the z-axis and y-axis is the x-axis, and the direction perpendicular to the z-axis and x-axis is the y-axis. The light quantity uniformizing unit is configured such that a first lens array unit having a lens action in one of the x-axis direction and the y-axis direction, and a second lens array unit having a lens action in the other of the x-axis direction and the y-axis direction are sequentially arranged along the z-axis, the first lens array portion has a first cylindrical lens array, a second cylindrical lens array, and a third cylindrical lens array arranged in order along an optical axis; a second cylindrical lens array is disposed behind the focal point of the first cylindrical lens array; There is no light focusing point on the optical path from the second cylindrical lens array to the irradiation surface, The first cylindrical lens array and the third cylindrical lens array have positive power, and the second cylindrical lens array has negative power in the illumination optical system. Furthermore, the present invention provides a laser beam splitter comprising: an illumination optical system that converts the laser light into a line-shaped laser light cross section and irradiates the photomask with the laser light, and scans the photomask with a scanning mechanism; a projection optical system that irradiates a workpiece with a laser beam passing through a photomask; a workpiece placement table on which a workpiece is placed and which moves the workpiece in the x and y directions; The light amount uniformizing section of the illumination optical system is configured as described above in the laser processing apparatus. Effect of the Invention

[0010] According to at least one embodiment, the present invention can prevent the optical element from becoming too hot, and can prevent the optical path from becoming too long and the device from becoming too large. Note that the effects described herein are not necessarily limited to those described herein, and may be any of the effects described herein or effects different from those effects. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a laser processing device to which the present invention can be applied. [Diagram 2] FIG. 2 is a front view of one embodiment of the present invention. [Diagram 3] FIG. 3 is a plan view showing the relationship between a photomask and a line-shaped beam in one embodiment of the present invention. [Figure 4] FIG. 4 is an enlarged plan view of an example of a substrate used in one embodiment of the present invention. [Diagram 5] FIG. 5 is a block diagram showing an optical system in one embodiment of the present invention. [Figure 6] FIG. 6A is a side view of an example of the configuration of an illumination optical system, and FIG. 6B is a top view of the example of the configuration of the illumination optical system. [Figure 7] FIG. 7 is an enlarged side view of a configuration of a portion of one embodiment of the present invention. [Figure 8] FIG. 8 is a side view of a modified embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the embodiments described below are preferred specific examples of the present invention, and the content of the present invention is not limited to these embodiments.

[0013] 1 is a schematic diagram of an example of a processing apparatus, such as a laser processing apparatus, to which the present invention can be applied. The laser processing apparatus has a laser light source 11. The laser light source 11 is an excimer laser light source that irradiates a KrF excimer laser light having a wavelength of 248 nm in pulses. The laser light is supplied to a line-shaped laser scanning mechanism 12.

[0014] The line-shaped laser scanning mechanism 12 has an illumination optical system that shapes a laser beam into a rectangular shape (line shape), and a scanning mechanism (linear motion mechanism) for scanning the photomask 13 with the laser beam LB.

[0015] The photomask 13 has a mask pattern formed thereon that corresponds to a processing pattern to be formed by ablation on a workpiece (hereinafter referred to as a substrate W). That is, a pattern is drawn on a base material (e.g., quartz glass) that transmits the KrF excimer laser, using a light-shielding film (e.g., a Cr film) that blocks the KrF excimer laser. The processing pattern may be a through via, a non-through via, or a groove (trenches) for a wiring pattern. After the processing pattern is formed by ablation processing, a conductor such as copper is filled in.

[0016] The laser light LB that has passed through the photomask 13 is incident on the projection optical system 14. The laser light emitted from the projection optical system 14 is irradiated onto the surface of the substrate W. The projection optical system 14 has focal planes at the photomask surface and the surface of the substrate W. The substrate W is a resin substrate in which a copper wiring layer is formed on a substrate such as an epoxy resin, and an insulating layer is formed thereon.

[0017] The substrate W is provided with a plurality of pattern areas WA, and is fixed on a mounting table 15 for mounting the workpiece thereon. The mounting table 15 is displaced in two dimensions and rotated, so that each pattern area WA can be positioned relative to the photomask 13. In order to process the entire area to be processed on the substrate W, the mounting table 15 moves the substrate W stepwise in the scanning direction.

[0018] An embodiment of the laser processing device will be described with reference to Fig. 2. The laser processing device is attached to a base portion 21 and an upper frame 22 that constitute a support body. The upper frame 22 is fixed onto the base portion 21. The base portion 21 and the upper frame 22 are made of a material that has high rigidity and has vibration damping properties.

[0019] A line-shaped laser scanning mechanism consisting of the scanning mechanism 16 and the illumination optical system 17, a mask stage 18 (supporting part for the photomask) on which the photomask 13 is placed, and the projection optical system 14 are fixed to the upper frame 22. A mounting table 15 is fixed on the base part 21. That is, the scanning mechanism 16, the illumination optical system 17, the mask stage 18, the projection optical system 14, and the mounting table 15 are positioned so as to satisfy a predetermined optical relationship (a relationship in which the laser light is correctly incident on the illumination optical system 17), and after positioning, when the base part 21 and the upper frame 22 are swung due to vibrations caused by the scanning operation of the illumination optical system 17 and the displacement operation of the mounting table 15, they are displaced together. The incident position and incident angle of the laser light with respect to the illumination optical system 17 are corrected by the beam position correction part 27.

[0020] The laser light source 11 is housed in a housing 24 provided separately from the base unit 21 and the upper frame 22. The laser light source 11 irradiates a KrF excimer laser (referred to as laser light) L1 having a wavelength of 248 nm in pulses. The laser light L1 and a guide laser light (not shown) are incident on a beam position correction unit (referred to as a beam steering mechanism) 27.

[0021] The beam position correction unit 27 is a mechanism for performing positioning (position and incident angle) of the laser light L1 in real time. The beam position correction unit 27 adjusts the laser light L1 so that it is always incident on the illumination optical system 17 at the correct position and angle regardless of the inclination of the base unit 21 and the upper frame 22 of the laser processing apparatus. The wavelength of the guide laser light is, for example, 400 nm to 700 nm. The mirror included in the beam position correction unit 27 has two reflective films that reflect the laser light L1 and the guide laser light, which have different wavelengths. The beam position correction unit 27 is provided with a beam shaping unit for making each laser light incident on each reflective film.

[0022] The laser light L1 emitted from the beam position correction unit 27 is reflected by the mirror 28 and enters the illumination optical system 17. The illumination optical system 17 homogenizes the intensity distribution of the light emitted from the laser light source and shapes it into a line-shaped laser light for processing. The illumination optical system 17 has a lens array (also called a fly-eye lens array) for shaping the line-shaped laser light. The lens array is a lens array in which multiple convex lenses are arranged in the direction in which the laser light is expanded. The line-shaped laser light LB from the illumination optical system 17 irradiates the mask 13. A specific example of the illumination optical system 17 will be described later.

[0023] The scanning mechanism 16 is a part of the illumination optical system 17, and moves the entire illumination optical system 17. The scanning mechanism 16 moves the laser light LB relative to the photomask 13, and the photomask 13 and the substrate W, which are fixed to the mask stage 18 and the mounting table 15, respectively, are scanned with the laser light.

[0024] 3 shows the relationship between the size of the laser light LB and the photomask 13. For example, the length x width of the laser light LB is 100 x 0.1 (mm) or 35 x 0.3 (mm). The width direction perpendicular to the length direction of the laser light LB is the scanning direction.

[0025] The photomask 13 has a mask pattern drawn by forming a blocking film (such as a chromium film or an aluminum film) that blocks the KrF excimer laser light on a base material (such as quartz glass) that transmits the KrF excimer laser light. The photomask 13 may be drawn with a pattern that appears repeatedly on the substrate W, or may be drawn with a pattern that covers the entire substrate W.

[0026] The mask stage 18 has an xyθ stage capable of holding the photomask 13 and positioning the photomask. A camera (not shown) is provided for reading alignment marks provided on the photomask 13 and positioning the photomask 13.

[0027] The laser light that has passed through the photomask 13 is incident on the projection optical system 14. The projection optical system 14 is a projection optical system having focal points on the surface of the photomask 13 and the surface of the substrate W, and projects the light that has passed through the photomask 13 onto the substrate W. Here, the projection optical system 14 is configured as a reduced projection optical system (for example, 1 / 4 magnification).

[0028] The mounting table 15 fixes the substrate W by vacuum suction or the like, and positions the substrate W with respect to the photomask 13 by moving it in the x and y directions and rotating it using a table movement mechanism. The mounting table 15 can also move in steps along the scanning direction so that ablation processing can be performed over the entire substrate W. An alignment camera (not shown) is installed beside the mounting table 15 to capture an image of an alignment mark provided on the substrate W. Furthermore, a z mechanism for focus adjustment or the like may be provided.

[0029] The substrate W (workpiece) is, for example, an organic substrate for a printed wiring board, and has a layer to be processed by laser on its surface. The layer to be processed is, for example, a resin film or metal foil, and is made of a material that can be processed by laser light, such as via formation. Vias and wiring patterns are formed by a laser processing machine, and in a subsequent process, the processed portion is filled with a conductor such as copper.

[0030] FIG. 4 shows an enlarged view of an example of a substrate W. The substrate W is a multiple substrate, and pattern areas WA corresponding to the patterns of the photomask 13 are repeatedly provided in an (8×8) matrix on the substrate W. In FIG. 4, the horizontal direction is the sub-step direction, and the vertical direction is the main step direction. After a certain pattern area WA is scanned, the next pattern area is scanned. Note that the scanning direction (arrow) shown in the figure is just an example.

[0031] In one embodiment of the present invention, a transport mechanism (not shown) is provided, and the transport mechanism places and removes the workpiece on the placement table. For example, a SCARA robot or the like can be used. Also, an air-conditioned chamber (not shown) is provided to cover the housing of the processing device and the laser light source.

[0032] In one embodiment of the present invention described above, a vibration control device (not shown) is provided for controlling the entire apparatus. The control device controls the laser light source 11, controls each part of the drive unit, aligns the photomask and the substrate W, manages production information, manages recipes, and so on.

[0033] Fig. 5 shows a block diagram of the optical system in the above-mentioned laser processing apparatus. Parts in Fig. 5 corresponding to those in Figs. 1 and 2 are denoted by the same reference symbols. Laser light from the laser light source 11 is supplied to a beam shaping unit 30. Laser light from the beam shaping unit 30 is supplied to a beam position correction unit 27. The beam position correction unit 27 adjusts the laser light so that the laser light is always incident on the illumination optical system 17 at the correct position and angle. As described above, the beam shaping unit 30 shapes the laser light so that the laser light from the laser light source 11 and the guide laser light are incident on a reflective film other than the mirror.

[0034] The illumination optical system 17 has a configuration in which a beam shaping unit 31, a lens array unit 32 as a light amount uniformizing unit, and a collimating lens unit 33 are arranged in order along the optical axis. The beam shaping unit 31 forms a rectangular laser beam having a predetermined length and width, and the lens array unit 32 uniformly distributes the laser beam and converts it into a line-shaped laser beam. The lens array unit 32 is composed of an x-direction lens array unit 34 consisting of three first cylindrical lens arrays (referred to as SLA in FIG. 5) 36a, a second cylindrical lens array 36b, and a third cylindrical lens array 36c arranged along the optical axis direction, and a y-direction lens array unit 35 consisting of two cylindrical lens arrays 37a and 37b arranged along the optical axis direction.

[0035] The laser light from the lens array unit 32 is converted into a substantially parallel light by the collimating lens unit 33. The laser light from the collimating lens unit 33 of the illumination optical system 17 is irradiated onto the photomask 13. The laser light that has passed through the photomask 13 is incident on the projection optical system 14. The projection optical system 14 projects the light that has passed through the photomask 13 onto the substrate W.

[0036] An example of the illumination optical system 17 will be described with reference to FIG. 6. The direction parallel to the optical axis of the illumination optical system 17 is the z-axis, the direction perpendicular to the z-axis and y-axis is the x-axis, and the direction perpendicular to the z-axis and x-axis is the y-axis. That is, the x-axis and y-axis are perpendicular to the z-axis and perpendicular to each other. FIG. 6A is a side view of the illumination optical system 17, and FIG. 6B is a top view of the illumination optical system 17. Furthermore, the width direction of the line-shaped laser light is the x-axis direction, and the length direction of the line-shaped laser light is the y-axis direction. FIG. 17 is an enlarged side view of the x-direction lens array unit 34.

[0037] In the side view of Fig. 6A, the cylindrical lens 31a, the cylindrical lens arrays 36a, 36b, and 36c, and the cylindrical lens 33a shown in thick lines are elements having a lens effect in the x-axis direction. Also, in the side view of Fig. 6B, the cylindrical lens 31b, the cylindrical lens arrays 37a and 37b, and the cylindrical lens 33b shown in thick lines are elements having a lens effect in the y-axis direction.

[0038] The beam shaping unit 31 has a configuration in which a cylindrical lens 31a having a lens action in the x-axis direction (in other words, having power in the x-axis direction) and a cylindrical lens 31b having a lens action in the y-axis direction (in other words, having power in the y-axis direction) are arranged in order in the z-axis direction. When a laser beam from a light source is incident on the cylindrical lens 31a, a laser beam having a spread in the x-axis direction (width direction) is generated from the cylindrical lens 31a. Furthermore, when the laser beam is incident on the cylindrical lens 31b, a laser beam having a spread in the y-axis direction (length direction) is generated from the cylindrical lens 31b. The laser beam from the cylindrical lens 31b is emitted from the beam shaping unit 31. The beam shaping unit 31 expands the laser beam in accordance with the size of the entrance surface of the cylindrical lens array of the lens array unit 32, and the laser beam is made to be incident on the lens array unit 32 in parallel. The laser beam incident on the fly-eye lens has an intensity bias such as a Gaussian curve.

[0039] The laser light emitted from the beam shaping unit 31 is incident on the first cylindrical lens array 36a on the light source side of the x-direction lens array unit 34 (an enlarged side view is shown in FIG. 7) of the lens array unit 32. A second cylindrical lens array 36b and a third cylindrical lens array 36c are arranged parallel to the cylindrical lens array 36a along the z-axis direction. The cylindrical lens arrays 36a and 36c are each formed by arranging a plurality of small-diameter cylindrical lenses (convex lenses) in the x-axis direction. Therefore, the cylindrical lens arrays 36a and 36c have positive lens power. The lens surface on the entrance side of the cylindrical lens array 36a is convex, and the lens surface on the exit side is flat. The lens surface on the entrance side of the cylindrical lens array 36c is flat, and the lens surface on the exit side is convex. The cylindrical lens array 36b is an array of multiple small diameter cylindrical lenses (concave lenses) in the x-axis direction. Therefore, the cylindrical lens array 36b has a negative lens power. The cylindrical lens arrays 36a, 36b, and 36c homogenize the laser light.

[0040] The laser light emitted from the x-direction lens array section 34 is incident on the cylindrical lens array 37a on the light source side of the y-direction lens array section 35 of the lens array section 32. A cylindrical lens array 37b is arranged parallel to the cylindrical lens array 37a along the z-axis direction. The cylindrical lens arrays 37a and 37b are each formed by arranging a plurality of small-diameter cylindrical lenses (convex lenses) in the y-axis direction. The cylindrical lens arrays 37a and 37b homogenize the laser light.

[0041] The laser light emitted from the cylindrical lens array 37b of the y-direction lens array section 35 of the lens array section 32 is incident on the first cylindrical lens 33a of the collimating lens section 33. The cylindrical lens 33a has a lens effect in the x-axis direction. The second cylindrical lens 33b is arranged in parallel to the cylindrical lens 33a. The cylindrical lens 33b has a lens effect in the y-axis direction. The collimating lens section 33 collimates the split laser light and superimposes it on the irradiation surface to make it uniform.

[0042] In one embodiment of the present invention, as shown in FIG. 6A and FIG. 7, the x-direction lens array on the light source side A second cylindrical lens array 36b is disposed at a position behind the focal point of the first cylindrical lens array 36a of the unit 34, so that there is no focal point on the optical path from the second cylindrical lens array 36b to the irradiation surface.

[0043] In the embodiment described above, the lens array section 32 is composed of the x-direction lens array section 33 and the y-direction lens array section 34, but it may be configured to have only one of the lens array sections. Also, it may be configured such that one lens array section has a lens action in both the x-direction and the y-direction.

[0044] 8, the beam shaping lens 41, the lens array section 42, and the collimator lens 43 may be arranged in order from the light source to the irradiation surface, and the lens array section 42 may be configured such that the lens array 43a, the lens array 43b, and the lens array 43c are arranged in order. The lens arrays 43a and 43c are convex lens arrays, and the lens array 43b is a concave lens array, and the lens array 43b is installed at a position behind the focal point of the lens array 43a, so that no focusing point exists on the optical path from the lens array 43b to the irradiation surface.

[0045] The embodiment of the present invention described above is arranged so as not to create a focal point on the optical element, thereby making it possible to prevent the optical element from becoming hot and to prevent the optical path length from becoming long and the device from becoming large.

[0046] Although one embodiment of the present technology has been specifically described above, the present invention is not limited to the above-mentioned embodiment, and various modifications based on the technical idea of ​​the present invention are possible. For example, the order of the x-direction lens array unit 34 and the y-direction lens array unit 35 may be reversed from that of the above-mentioned embodiment. In addition, the configurations, methods, steps, shapes, materials, and values ​​given in the above-mentioned embodiment are merely examples, and configurations, methods, steps, shapes, materials, and values ​​different from these may be used as necessary. [Explanation of symbols]

[0047] W...workpiece (substrate), 11...laser light source, 12...line-shaped laser scanning mechanism, 13...photomask, 14...projection optical system, 15...mounting table, 16...scanning mechanism, 17...illumination optical system, 18...mask stage, 30, 31...beam shaping section, 32...lens array section, 33...collimating lens section, 36a, 36b, 36c...cylindrical lens array

Claims

1. An irradiation optical system that guides laser light to an irradiation surface, A light quantity uniformizing unit that uniformizes the laser light is provided. the light amount uniformizing unit has a first lens array, a second lens array, and a third lens array that are arranged in order along an optical axis, the second lens array is disposed at a position behind the focal point of the first lens array; A light path from the second lens array to the irradiation surface is configured so that there is no light focusing point, The illumination optical system, wherein the first lens array and the third lens array have positive power, and the second lens array has negative power.

2. 2. The illumination optical system according to claim 1, wherein the first and third lens arrays are a collection of convex lenses, and the second lens array is a collection of concave lenses.

3. An irradiation optical system that guides laser light to an irradiation surface, A light quantity uniformizing unit that uniformizes the laser light is provided. The z-axis is the optical axis direction, the direction perpendicular to the z-axis and the y-axis is the x-axis, and the direction perpendicular to the z-axis and the x-axis is the y-axis. the light amount uniformizing unit is configured such that a first lens array unit having a lens action in one of the x-axis direction and the y-axis direction, and a second lens array unit having a lens action in the other of the x-axis direction and the y-axis direction are sequentially arranged along the z-axis, the first lens array portion includes a first cylindrical lens array, a second cylindrical lens array, and a third cylindrical lens array, which are arranged in order along an optical axis; The second cylindrical lens array is disposed at a position behind the focal point of the first cylindrical lens array; A light path from the second cylindrical lens array to the irradiation surface is configured so that there is no light focusing point, The illumination optical system, wherein the first cylindrical lens array and the third cylindrical lens array have positive power, and the second cylindrical lens array has negative power.

4. 4. The illumination optical system according to claim 3, wherein the first and third cylindrical lens arrays are a collection of cylindrical convex lenses, and the second cylindrical lens array is a collection of cylindrical concave lenses.

5. 4. The illumination optical system according to claim 3, wherein the beam shaping section, the light amount uniformizing section, and the collimating lens section are arranged in order along the z-axis.

6. A light source that emits laser light; an illumination optical system that converts the laser light into a laser light having a line-shaped cross section and irradiates a photomask with the laser light, and scans the photomask with a scanning mechanism; a projection optical system that irradiates a workpiece with the laser light passing through the photomask; a workpiece placement table on which the workpiece is placed and which moves the workpiece in an x-y direction; 4. The laser processing apparatus according to claim 3, wherein the light amount uniformizing section of the illumination optical system is configured as described above.

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