Illumination optical system and laser processing apparatus

Abstract

To prevent occurrence of loss of a laser beam by uniformizing the laser beam by a lens array in which thicknesses of lenses are not uniform.SOLUTION: An illumination optical system, which guides a laser beam to an irradiation surface, includes a first lens array and second lens array each of which has a plurality of lenses aligned along a z axis and aligned in at least one direction of an x axis and y axis, wherein the z axis is an optical axis direction, a direction orthogonal to the z axis and y axis is the x axis, and a direction orthogonal to the z axis and x axis is the y axis. Thicknesses of the lenses of one of the first and second lens arrays are not uniform in at least one direction.SELECTED DRAWING: Figure 7

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 made of a non-metallic material such as resin or silicon (for example, a resin layer of a printed circuit board) is ablated (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 shapes the beam so that the irradiation area is linear, and homogenizes the light, for example, by a fly-eye lens so that the fluence of the 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.

[0004] In this illumination optical system, since the light source is a laser beam with high coherence, if each wavelength split by the fly-eye lens does not interfere with each other, the illumination of the photomask surface is averaged and becomes uniform. Generally, the higher the number of divisions of the fly-eye lens (the narrower the pitch of the fly-eye), the higher the uniformity of illumination. However, since the wavelength of the excimer laser light source is narrow-band, the spatial coherence is high, and when the pitch of the fly-eye lens is narrowed, interference fringes of illumination occur on the photomask surface. These interference fringes can be avoided by providing a difference in the optical path length in the optical axis direction of the fly-eye lens.

[0005] For example, in Patent Document 1, in order to generate such an optical path difference, a glass plate with different thicknesses is provided in parallel with the fly-eye lens as a phase difference generation unit.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The configuration of Patent Document 1 requires adding an optical member as a phase difference generation unit to the illumination optical system, and energy loss of the laser light occurs in the optical member. Since the processing apparatus uses a high fluence laser, the loss caused by the optical path difference member becomes a non-negligible amount. Further, if there is an error in the positioning between the optical member and the fly-eye lens, it will further cause energy loss.

[0008] Therefore, an object of the present invention is to provide an illumination optical system and a laser processing apparatus that have a function of generating a phase difference in the fly-eye lens itself, have less energy loss, and do not require alignment of members.

Means for Solving the Problems

[0009] The present invention is an illumination optical system that guides laser light 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, including a first lens array and a second lens array each having a plurality of lenses arranged along the z-axis and arranged along at least one of the x-axis and the y-axis, In the direction in which the light beams emitted from the respective lenses of the second lens array interfere with each other, having lenses with mutually varying thicknesses alternately which is an illumination optical system. Further, the present invention is an illumination optical system that guides laser light to an irradiation surface, The z-axis is taken as the optical axis direction, the direction orthogonal to the z-axis and the y-axis is taken as the x-axis, and the direction orthogonal to the z-axis and the x-axis is taken as the y-axis. Along the z-axis, a beam shaping unit, a lens array unit, and a collimating lens unit are arranged in this order. The beam shaping unit and the collimating lens unit are composed of a first cylindrical lens having a lens action in the x-axis direction and a second cylindrical lens having a lens action in the y-axis direction. The lens array unit 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. The first cylindrical lens array or the second cylindrical lens array of the first pair or the second pair A plurality of cylindrical lenses that make up of Central thickness is an illumination optical system in which the above is not constant. Furthermore, the present invention includes a light source that emits laser light, an illumination optical system that converts the laser light into 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 the 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, and is a laser processing apparatus in which the illumination optical system has the above-described configuration.

Advantages of the Invention

[0010] According to at least one embodiment, the present invention can prevent the generation of energy loss of the laser light by preventing interference by varying the thickness of the lens array itself. Note that the effects described here 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

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

[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] Figure 1 is a schematic configuration diagram of an example of a processing apparatus to which the present invention is applicable, 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.

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

[0015] The photomask 13 has a mask pattern corresponding to a processing pattern formed by ablation on a workpiece (hereinafter appropriately referred to as a substrate W). That is, a pattern by a light-shielding film (for example, a Cr film) that blocks KrF excimer laser is drawn on a base material (for example, quartz glass) that transmits 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.

[0016] The laser beam LB that has passed through the photomask 13 is incident on the projection optical system 14. The laser beam 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.

[0017] 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 two-dimensional directions and rotated to position the pattern regions WA with respect to the photomask 13, respectively. Further, in order to enable processing of the processing region over the entire substrate W, the mounting table 15 is configured to step-move the substrate W in the scanning direction.

[0018] 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. 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.

[0019] 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 to an upper frame 22. A mounting table 15 is fixed on a 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.

[0020] A 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.

[0021] 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 a 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 allowing each laser light to be incident on each reflection film is provided in the beam position correction unit 27.

[0022] 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.

[0023] 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 placement table 15, are scanned by the laser beam.

[0024] FIG. 3 shows the relationship between the laser beam LB and the size of 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.

[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 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 that covers the entire substrate W.

[0026] The mask stage 18 holds the photomask 13 and includes 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.

[0027] 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).

[0028] The placement table 15 fixes the substrate W by vacuum adsorption 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.

[0029] 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 capable of processing 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.

[0030] 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.

[0031] In one 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.

[0032] 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, each part of the drive unit, the alignment of the photomask and the substrate W, manages production information, manages recipes, and the like.

[0033] When the optical system in the above-described laser processing apparatus is represented as a block diagram, it is as shown in FIG. 5. Parts corresponding to FIG. 1 and FIG. 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 reflective films.

[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 equalization 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 equalizes the distribution of the laser beam and makes it 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.

[0035] 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 is incident on the projection optical system 14. The projection optical system 14 projects the light transmitted 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. 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, the 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 light is the x-axis direction, and the length direction of the line-shaped laser light is the y-axis direction.

[0037] 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. These elements having a lens action 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. These elements having a lens action are extracted and shown in FIG. 6D.

[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 the laser light from the light source is incident on the cylindrical lens 31a, laser light that spreads in the x-axis direction (width direction) is generated from the cylindrical lens 31a. Further, when the laser light is incident on the cylindrical lens 31b, laser light that spreads in the y-axis direction (length direction) is generated from the cylindrical lens 31b. The laser light from the cylindrical lens 31b is emitted from the beam shaping unit 31. The beam shaping unit 31 enlarges the laser light in accordance with the size of the incident surface of the cylindrical lens array of the lens array unit 32 and makes the laser light incident on the cylindrical lens array parallel. Note that the laser light 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 pair 34 of the source-side cylindrical lens arrays 36a 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 formed by arranging a plurality of small-diameter cylindrical lenses (convex lenses) in the x-axis direction. The incident-side lens surface of the cylindrical lens array 36a is convex, and the exit-side lens surface is flat. The incident-side lens surface of the cylindrical lens array 36b is flat, and the exit-side lens surface is convex. The cylindrical lens arrays 36a and 36b equalize the laser light.

[0040] The laser light emitted from the first pair 34 is incident on the first pair 35 of the source-side cylindrical lens arrays 37a 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 formed by arranging a plurality of small-diameter cylindrical lenses (convex lenses) in the y-axis direction. The cylindrical lens arrays 37a and 37b equalize the laser light.

[0041] The laser light emitted from the second pair 35 of the cylindrical lens arrays 37b 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 split laser light into parallel light and superimposes and equalizes it on the irradiation surface.

[0042] In one embodiment of the present invention, the thickness of one lens of the first cylindrical lens array and the second cylindrical lens array included in the first pair 34 and / or the second pair 35 of the lens array unit 32 is not constant in at least one direction. FIG. 7 shows an example in which the thickness of the lens of one cylindrical lens array 36b of the first pair 34 is not constant. The cylindrical lens arrays 36a and 36b are, for example, those in which five small-diameter cylindrical lens arrays are arranged in the x direction.

[0043] The thicknesses of the lenses of the cylindrical lens array 36b are alternately different such that the lens surface on the plane side has a step of ΔT when viewed from the side. ΔT is set to a value such that no light and dark interference fringes occur (for example, ΔT is about 1 (mm)). Such a cylindrical lens array 36b can generate an optical path length difference and prevent interference fringes from occurring on the output side of the cylindrical lens array 38b.

[0044] Also, the cross-sectional shape of the beam of the excimer laser light generally forms a rectangle with an aspect ratio of 1:2, 1:5, etc., and the spatial coherence is not isotropic, and is particularly higher in the short side direction than in the long side direction of the beam cross-section. For this reason, interference fringes are likely to occur in the short side direction of the beam cross-section. Thus, when the spatial coherence of the laser light is not isotropic, the thickness of the lens is made non-constant in the direction where the spatial coherence is high.

[0045] Also, when light and dark interference fringes occur in the x-axis direction on the irradiation surface when the lens thicknesses are the same, the lens thickness is changed in the x-axis direction of the cylindrical lens array 36b as in the example of FIG. 7. Also, when light and dark interference fringes occur in the y-axis direction on the irradiation surface when the lens thicknesses are the same, the thickness of the lens in the y-axis direction of the cylindrical lens array 37b is made non-constant. Further, when light and dark interference fringes occur in both the x-axis and y-axis directions on the irradiation surface when the lens thicknesses are the same, the thicknesses of the lenses are made non-constant in both the x-axis direction of the cylindrical lens array 36b and the y-axis direction of the cylindrical lens array 37b.

[0046] In one embodiment of the present invention described above, since the thickness of the cylinder lens array itself is made different, the energy loss of the laser light can be reduced as compared with the configuration in which another optical member is provided.

[0047] In one embodiment of the present invention described above, an arrangement in which the thicknesses of the lenses of the lens array are alternately different so that the lens surfaces have steps when viewed from the side is shown in order to change the thickness of the lenses of the lens array. The present invention is not limited to this form. For example, the thickness may be changed step by step in one direction when viewed from the side by a predetermined amount, or lenses having different thicknesses may be arranged randomly. It is sufficient that each lens constituting the lens array has a thickness different from that of another adjacent lens in at least one direction.

[0048] Although one embodiment of the present technology has been specifically described above, 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 is applicable not only to the configuration in which two pairs are provided but also to the configuration in which one pair of lens arrays is provided. In addition, the configurations, methods, processes, shapes, materials, numerical values, etc. described in the above embodiments are merely examples, and different configurations, methods, processes, shapes, materials, numerical values, etc. may be used as necessary.

Explanation of Reference Numerals

[0049] 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 irradiation optical system for guiding a laser beam 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, comprising a first lens array and a second lens array each having a plurality of lenses arranged along the z-axis and arranged along at least one of the x-axis and the y-axis, and an illumination optical system having lenses with mutually varying thicknesses alternately in the direction in which the light beams emitted from the respective lenses of the second lens array interfere.

2. When light and dark interference fringes occur in the x-axis direction on the irradiation surface when the thicknesses of the lenses are the same, the illumination optical system according to claim 1, which alternately has the lenses whose thicknesses vary with each other in the x-axis direction; when light and dark interference fringes occur in the y-axis direction, the illumination optical system alternately has the lenses whose thicknesses vary with each other in the y-axis direction; and when light and dark interference fringes occur in both the x-axis and the y-axis directions, the illumination optical system alternately has the lenses whose thicknesses vary with each other in both the x-axis and the y-axis directions.

3. The illumination optical system according to claim 1 or claim 2, wherein the first and second lens arrays are cylindrical lens arrays.

4. An irradiation optical system for guiding a laser beam 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 lens array section, and a collimating lens section are arranged in sequence, the beam shaping section and the collimating lens section are constituted by a first cylindrical lens having a lens action in the x-axis direction and a second cylindrical lens having a lens action in the y-axis direction, the lens array section is constituted by 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 in which the center thicknesses of a plurality of cylindrical lenses constituting the first cylindrical lens array or the second cylindrical lens array of the first pair or the second pair are not constant.

5. A light source that emits laser light, An illumination optical system that converts the laser light into laser light having a line-shaped cross section and irradiates a photomask with the laser light, 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, A laser processing apparatus in which the illumination optical system has the configuration according to claim 1.

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