Illumination optical system and laser processing apparatus

Abstract

To adjust a size in a different direction of a light flux of a laser beam independently.SOLUTION: An illumination optical system, which guides a laser beam to an irradiation surface, is provided with light quantity uniformizing parts for uniformizing the laser beam, and includes a first pair formed of two first cylindrical lens arrays in which the light quantity uniformizing part is arranged along a z axis, and a second pair formed of two second cylindrical lens arrays arranged along the z axis, wherein the z axis is an optical axis direction, a direction orthogonal to the z axis and a y axis is an x axis, and a direction orthogonal to the z axis and x axis is the y axis. The first cylindrical lens array has a lens function in an x-axis direction. The second cylindrical lens array has the lens function in the y-axis direction. At least one of a first interval of the first pair of the first cylindrical lens arrays and a second interval of the second pair of the second cylindrical lens arrays varies.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to an illumination optical system used for irradiating a linear laser beam onto a photomask, and a laser processing apparatus including the illumination optical system.

Background Art

[0002] It is known that a workpiece (workpiece, for example, a resin layer of a printed circuit board) made of a non-metallic material such as resin or silicon is subjected to ablation processing (ablation: removal processing by melting and evaporation) into the shape of a pattern (for example, via) of a photomask by scanning with laser light transmitted through the photomask. When precise processing is required, processing by ablation using an excimer laser (KrF laser, wavelength 248 nm) is performed.

[0003] As an example, the illumination optical system of such a processing apparatus forms a beam so that the irradiation area becomes linear, and homogenizes the laser light by, for example, a fly-eye lens so that the fluence of light in the irradiation area (photomask surface) becomes uniform. Note that the linear laser beam means a laser beam whose cross-sectional shape of the light beam in a plane orthogonal to the optical axis is linear. In a linear beam, non-isotropic fine adjustment such as adjusting only the length without changing the width of the line is required.

[0004] For example, Patent Document 1 describes an optical system for shaping line-shaped light, in which the divergence angle (irradiation range) of the laser light is finely adjusted by changing the lens interval L of the beam expander 40. Patent Document 2 describes that the integrator section (90) includes two fly-eye lenses (91, 92), and the fly-eye lens interval adjustment mechanism (95) changes the interval d in the optical axis direction between the two fly-eye lenses (91, 92) to correct the change in the average illuminance value on the exposure surface. When the interval d between the fly-eye lens 91 and the fly-eye lens 92 is short, illumination with a low NA and a large field of view is realized by shortening the focal length f. On the other hand, when the interval d between the fly-eye lens 91 and the fly-eye lens 92 is long, illumination with a high NA and a small field of view is realized by increasing the focal length f.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In Patent Document 1, the magnification adjustment of the laser beam is performed using a variable laser beam expander. However, in a variable laser beam expander, since the magnification adjustment is performed in an equal direction, it is not suitable for a line-shaped beam that requires non-equal-direction fine adjustment. Patent Document 2 changes the combined focal length of the pair of lens elements 93A and 93B by adjusting the interval between the fly-eye lenses to change the field of view. However, in this method, since the magnification adjustment is performed in an equal direction as in Patent Document 1, fine adjustment of the magnification in a non-equal direction cannot be performed.

[0007] Accordingly, an object of the present invention is to provide an illumination optical system and a laser processing apparatus capable of performing fine adjustment that is not isotropic with respect to the light beam of the laser light.

Means for Solving the Problems

[0008] The present invention is having a divergence angle an irradiation optical system that guides laser light to an irradiation surface and z with the axis in the optical axis direction, the direction orthogonal to the z-axis and the y-axis as the x-axis, and the direction orthogonal to the z-axis and the x-axis as the y-axis, along the z-axis, a beam shaping unit, a light quantity equalization unit for equalizing the laser light, and a collimating lens unit are arranged in this order composed of a first pair consisting of two first cylindrical lens arrays arranged along the z-axis and a second pair consisting of two second cylindrical lens arrays arranged along the z-axis, the first cylindrical lens array has a lens action in the x-axis direction, the second cylindrical lens array has a lens action in the y-axis direction, configured such that at least one of the first interval of the first cylindrical lens array of the first pair and the second interval of the second cylindrical lens array of the second pair is variable, to obtain a line-shaped laser beam with the laser light extended in the x-axis direction is an illumination optical system. Further, the present invention includes a light source that emits laser light, an illumination optical system that forms the laser light into a laser light with a line-shaped cross section and irradiates a photomask, and scans the photomask by a scanning mechanism, a projection optical system that irradiates a workpiece with the laser light that has passed through the photomask, a workpiece mounting table on which the workpiece is placed and that moves the workpiece in the x-y direction, illumination optical the system is is a laser processing apparatus configured as described above.

Effects of the Invention

[0009] According to at least one embodiment, the present invention can adjust the magnification in a desired direction of the laser light by adjusting the distance between two cylindrical lens arrays. Note that the effects described herein are not necessarily limited, and may be any of the effects described in this specification or effects different from them.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0011] 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.

[0012] FIG. 1 is a schematic configuration diagram of an example of a processing apparatus to which the present invention can be applied, for example, a laser processing apparatus. The laser processing apparatus has a laser light source 11. The laser light source 11 is, for example, an excimer laser light source that pulse-irradiates KrF excimer laser light having a wavelength of 248 nm. The laser light is supplied to a line-shaped laser scanning mechanism 12.

[0013] 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 light LB.

[0014] On the photomask 13, a mask pattern corresponding to a processing pattern formed by ablation on a workpiece (hereinafter appropriately referred to as the substrate W) is formed. That is, a pattern by a light-shielding film (for example, a Cr film) that blocks the KrF excimer laser is drawn on a base material (for example, quartz glass) that transmits the KrF excimer laser. Examples of the processing pattern include through vias, blind vias, and grooves (trenches) for wiring patterns. After the processing pattern is formed by ablation processing, a conductor such as copper is filled.

[0015] 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 irradiates the surface of the substrate W. The projection optical system 14 has focal planes on 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.

[0016] The substrate W is provided with a plurality of pattern regions WA and is fixed on a mounting table 15 for mounting the workpiece. The mounting table 15 can be displaced in a two-dimensional direction and rotated to position the pattern regions WA with respect to the photomask 13, respectively. Further, in order to enable processing of the entire processed region of the substrate W, the mounting table 15 is configured to step-move the substrate W in the scanning direction.

[0017] An embodiment of the laser processing apparatus will be described with reference to FIG. 2. The laser processing apparatus is attached to a base portion 21 and an upper frame 22 that constitute a support body. The upper frame 22 is fixed on the base portion 21. The base portion 21 and the upper frame 22 are made of a material with high rigidity and characteristics of attenuating vibration.

[0018] For the upper frame 22, a line laser scanning mechanism composed of a scanning mechanism 16 and an illumination optical system 17, a mask stage 18 (a support part for a photomask) on which a photomask 13 is placed, and a projection optical system 14 are fixed. A mounting table 15 is fixed on the base part 21. That is, these scanning mechanism 16, illumination optical system 17, mask stage 18, projection optical system 14, and mounting table 15 are positioned so as to satisfy a predetermined optical relationship (a relationship in which laser light is correctly incident on the illumination optical system 17). After positioning, when the base part 21 and the upper frame 22 swing 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 integrally. The incident position and incident angle of the laser light with respect to the illumination optical system 17 are corrected by a beam position correction unit 27.

[0019] The laser light source 11 is housed in a housing 24 provided separately from the base part 21 and the upper frame 22. The laser light source 11 pulse-irradiates a KrF excimer laser (referred to as laser light) L1 having a wavelength of 248 nm. The laser light L1 and guide laser light (not shown) are incident on a beam position correction unit (referred to as a beam steering mechanism) 27.

[0020] The beam position correction unit 27 is a mechanism for performing real-time positioning (position and incident angle) of the laser light L1. By the beam position correction unit 27, regardless of the inclination of the base part 21 and the upper frame 22 of the laser processing apparatus, the laser light L1 is adjusted to always enter the illumination optical system 17 at the correct position and angle. 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 reflection films that reflect the laser light L1 and the guide laser light having different wavelengths, respectively. A beam shaping unit for causing each laser light to be incident on each reflection film is provided in the beam position correction unit 27.

[0021] The laser beam L1 emitted from the beam position correction unit 27 is reflected by the mirror 28 and incident on the illumination optical system 17. The illumination optical system 17 equalizes the intensity distribution of the light emitted from the laser light source and shapes it into a linear processing laser beam. The illumination optical system 17 has a lens array (also referred to as a fly-eye lens array) for shaping the linear laser beam. The lens array is a lens array in which a plurality of convex lenses are arranged in a direction to expand the laser beam. The linear laser beam LB from the illumination optical system 17 irradiates the mask 13. A specific example of the illumination optical system 17 will be described later.

[0022] The scanning mechanism 16 is a part of the illumination optical system 17 and moves the entire illumination optical system 17. The laser beam LB is moved relative to the photomask 13 by the scanning mechanism 16, and the photomask 13 and the substrate W, which are respectively fixed to the mask stage 18 and the mounting table 15, are scanned by the laser beam.

[0023] FIG. 3 shows the relationship between the size of the laser beam LB and the photomask 13. For example, the laser beam LB has a size of (length × width) such as (100 × 0.1 (mm)), (35 × 0.3 (mm)). The width direction orthogonal to the length direction of the laser beam LB is the scanning direction.

[0024] The photomask 13 has a mask pattern drawn by forming a blocking film (such as a chromium film or an aluminum film) that blocks KrF excimer laser light on a substrate (such as quartz glass) that transmits KrF excimer laser light. The photomask 13 may draw a pattern that repeatedly appears on the substrate W, or may draw a pattern over the entire substrate W.

[0025] The mask stage 18 holds the photomask 13 and is equipped with an xyθ stage capable of positioning the photomask. A camera (not shown) for reading the alignment marks provided on the photomask 13 to position the photomask 13 is provided.

[0026] The laser light passing through the photomask 13 is incident on the projection optical system 14. The projection optical system 14 is a projection optical system having a focus on the surface of the photomask 13 and the surface of the substrate W, and projects the light transmitted through the photomask 13 onto the substrate W. Here, the projection optical system 14 is configured as a reduction projection optical system (for example, 1 / 4 times).

[0027] The placement 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 and rotating in the x-y directions by a table moving mechanism. Further, it is stepwise movable along the scanning direction so that application processing can be performed over the entire substrate W. An alignment camera (not shown) for imaging alignment marks provided on the substrate W is installed beside the placement table 15. Furthermore, a z mechanism for focus adjustment or the like may be provided.

[0028] The substrate W (workpiece) is, for example, an organic substrate for a printed wiring board, and a processed layer to be laser-processed is formed on the surface. The processed layer is, for example, a resin film or a metal foil, and is formed of a material that can be processed such as via formation by laser light. Vias and wiring patterns are formed by a laser processing machine, and conductors such as copper are filled in the processed portions in subsequent processes.

[0029] FIG. 4 shows an enlarged example of the substrate W. The substrate W is a multi chamfered substrate, and pattern regions WA corresponding to the pattern of the photomask 13 are repeatedly provided in a (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. When a certain pattern region WA is scanned, the next pattern region is scanned. Note that the illustrated scanning direction (arrow) is an example.

[0030] In an embodiment of the present invention, although not shown, a transfer mechanism is provided, and the transfer mechanism places and removes the workpiece on and from the placement table. For example, a scalar robot or the like can be used. Further, an air conditioning chamber (not shown) that covers the processing apparatus and the housing of the laser light source is provided.

[0031] In one embodiment of the present invention described above, a control device (not shown) for controlling the entire apparatus is provided. 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 and recipe management, and the like.

[0032] When the optical system in the above-described laser processing apparatus is represented as a block diagram, it is as shown in FIG. 5. The parts corresponding to FIGS. 1 and 2 in FIG. 5 are denoted by the same reference numerals. The laser light from the laser light source 11 is supplied to the beam shaping unit 30. The laser light from the beam shaping unit 30 is supplied to the beam position correction unit 27. The beam position correction unit 27 adjusts the laser light so that the laser light always enters 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 enter mirrors with different reflection films.

[0033] The illumination optical system 17 has a configuration in which a beam shaping unit 31, a lens array unit 32 as a light amount uniformization 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 makes the distribution of the laser beam uniform and forms a linear laser beam. The lens array unit 32 is composed of a first pair 34 including two first cylindrical lens arrays (denoted as SLA in FIG. 5) 36a and 36b arranged along the optical axis direction, and a second pair 35 including two second cylindrical lens arrays 37a and 37b arranged along the optical axis direction.

[0034] The laser light from the lens array unit 32 is made into 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 enters the projection optical system 14. The projection optical system 14 projects the light transmitted through the photomask 13 onto the substrate W.

[0035] An example of the illumination optical system 17 will be described with reference to FIG. 6. A direction parallel to the optical axis direction of the illumination optical system 17 is defined as the z-axis, a direction orthogonal to the z-axis and the y-axis is defined as the x-axis, and a direction orthogonal to the z-axis and the x-axis is defined as the y-axis. That is, axes perpendicular to the z-axis and orthogonal to each other are defined as the x-axis and the y-axis. 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. Further, the width direction of the line-shaped laser beam is the x-axis direction, and the length direction of the line-shaped laser beam is the y-axis direction.

[0036] In the side view of FIG. 6A, the cylindrical lens 31a, the cylindrical lens arrays 36a and 36b, and the cylindrical lens 33a indicated by thick lines are elements having a lens action in the x-axis direction. The elements having these lens actions are extracted and shown in FIG. 6C. In the side view of FIG. 6B, the cylindrical lens 31b, the cylindrical lens arrays 37a and 37b, and the cylindrical lens 33b indicated by thick lines are elements having a lens action in the y-axis direction. The elements having these lens actions are extracted and shown in FIG. 6D.

[0037] 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 the laser beam from the light source is incident on the cylindrical lens 31a, a laser beam that spreads in the x-axis direction (width direction) is generated from the cylindrical lens 31a. Further, when the laser beam is incident on the cylindrical lens 31b, a laser beam that spreads 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 incident surface of the cylindrical lens array of the lens array unit 32 and makes the laser beam incident on the cylindrical lens array parallel. Note that the laser beam incident on the fly-eye lens has an intensity bias such as a Gaussian curve.

[0038] The laser light emitted from the beam shaping unit 31 is incident on the cylindrical lens array 36a on the light source side of the first pair 34 of the lens array unit 32. The cylindrical lens array 36b is arranged in parallel with the cylindrical lens array 36a along the z-axis direction. The cylindrical lens arrays 36a and 35b are those in which a plurality of small-diameter cylindrical lenses (convex lenses) are arranged in the x-axis direction. The lens surface on the incident side of the cylindrical lens array 36a is convex, and the lens surface on the exit side is flat. The lens surface on the incident side of the cylindrical lens array 36b is flat, and the lens surface on the exit side is convex. The laser light is homogenized by the cylindrical lens arrays 36a and 36b.

[0039] The laser light emitted from the first pair 34 is incident on the cylindrical lens array 37a on the light source side of the second pair 35 of the lens array unit 32. The cylindrical lens array 37b is arranged in parallel with the cylindrical lens array 37a along the z-axis direction. The cylindrical lens arrays 37a and 37b are those in which a plurality of small-diameter cylindrical lenses (convex lenses) are arranged in the y-axis direction. The laser light is homogenized by the cylindrical lens arrays 37a and 37b.

[0040] The laser light emitted from the cylindrical lens array 37b of the second pair 35 of the lens array unit 32 is incident on the first cylindrical lens 33a of the collimating lens unit 33. The cylindrical lens 33a has a lens action in the x-axis direction. The second cylindrical lens 33b is arranged in parallel with the cylindrical lens 33a. The cylindrical lens 33b has a lens action in the y-axis direction. The collimating lens unit 33 makes the divided laser light into parallel light and superimposes and homogenizes it on the irradiation surface.

[0041] In one embodiment of the present invention, as shown in FIGS. 6A and 6B, at least one of the first intervals of the first cylindrical lens arrays 36a and 36b of the first pair 34 and the second intervals of the second cylindrical lens arrays 37a and 37b of the second pair 35 is made variable. In one embodiment, both the first interval and the second interval are made variable.

[0042] In one embodiment of the present invention described above, since the intervals of the cylindrical lens arrays are variable, the magnification in a desired direction can be adjusted.

[0043] As described above, one embodiment of the present technology has been specifically described. However, the present invention is not limited to the above-described one embodiment, and various modifications based on the technical idea of the present invention are possible. For example, a lens array in which lenses are arranged in both the x-axis direction and the y-axis direction may be used. Furthermore, the present invention can be applied not only to a configuration in which two pairs are provided, but also to a configuration in which a pair of one lens array is provided. Furthermore, the order of the x-direction lens array unit 34 and the y-direction lens array unit 35 may be the reverse order of the above-described one embodiment. Also, the configurations, methods, steps, shapes, materials, and numerical values cited in the above-described embodiments are merely examples, and different configurations, methods, steps, shapes, materials, and numerical values may be used as necessary.

Explanation of Reference Numerals

[0044] W ··· Workpiece (substrate), 11 ··· Laser light source, 12 ··· Linear 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 unit, 32 ··· Lens array unit, 33 ··· Collimating lens unit

Claims

1. An illumination optical system for guiding a laser beam having a divergence angle to an irradiation surface, with the z-axis as the optical axis direction, the direction orthogonal to the z-axis and the y-axis as the x-axis, and the direction orthogonal to the z-axis and the x-axis as the y-axis, along the z-axis, a beam shaping section, a light quantity homogenizing section for homogenizing the laser beam, and a collimating lens section are arranged in sequence, the light quantity homogenizing section is composed of a first pair consisting of two first cylindrical lens arrays arranged along the z-axis and a second pair consisting of two second cylindrical lens arrays arranged along the z-axis, the first cylindrical lens array has a lens action in the x-axis direction, and the second cylindrical lens array has a lens action in the y-axis direction, an illumination optical system configured such that at least one of a first interval between the first cylindrical lens arrays of the first pair and a second interval between the second cylindrical lens arrays of the second pair is variable, and the laser beam is a linear laser beam extended in the x-axis direction.

2. The illumination optical system according to claim 1, wherein the first interval and the second interval are variable.

3. In the illumination optical system according to claim 2, the first pair of the light quantity homogenizing section is arranged on the side where the laser beam is incident from the beam shaping section, and the second pair is arranged on the side where the laser beam exits to the collimating lens section.

4. In the illumination optical system according to claim 2, the second pair of the light quantity homogenizing section is arranged on the side where the laser beam is incident from the beam shaping section, and the first pair is arranged on the side where the laser beam exits to the collimating lens section.

5. A light source that emits a laser beam, an illumination optical system that forms the laser beam into a linear laser beam in cross-section and irradiates a photomask, and scans the photomask by a scanning mechanism, a projection optical system that irradiates a workpiece with the laser beam passing through the photomask A workpiece mounting table on which the workpiece is placed and which moves the workpiece in the x-y direction. A laser processing apparatus in which the illumination optical system has the configuration according to claim 1.

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