JP2023066564A - Illumination optical system and laser processing device - Google Patents

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

The present invention relates to an illumination optical system used for irradiating a photomask with linear laser light, and a laser processing apparatus equipped with the illumination optical system.

A workpiece (workpiece, for example, a resin layer of a printed circuit board), which is a non-metallic material such as resin or silicon, is scanned with a laser beam that has passed through a photo-photomask, thereby scanning the workpiece with a pattern of the photo-photomask. It is known to ablate shapes (eg vias). When precision processing is required, processing is performed by ablation using an excimer laser (KrF laser, wavelength 248 nm).

As an example, the illumination optical system of such a processing apparatus shapes the beam so that the irradiation area becomes linear, and the light is emitted by, for example, a fly-eye lens so that the fluence of light in the irradiation area (photomask surface) is uniform. It is homogenized. Note that the line-shaped laser beam means a laser beam having a line-shaped cross-sectional shape of the luminous flux on a plane perpendicular to the optical axis.

In this illumination optical system, since the light source is a highly coherent laser beam, the illumination of the photomask surface is averaged and uniform unless the wavelengths split by the fly-eye lens interfere with each other. In general, the greater 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 band of the excimer laser light source is narrowed, the spatial coherence is high, and when the pitch of the fly-eye lens is narrowed, interference fringes of illumination are generated on the photomask surface. This interference fringe can be avoided by providing a difference in optical path length in the optical axis direction of the fly's eye lens.

For example, in Patent Document 1, in order to generate such an optical path difference, a glass plate having a different thickness is provided parallel to the fly-eye lens as a phase difference generator.

JP 2016-38456 A

In the configuration of Patent Document 1, it is necessary to add an optical member as a phase difference generator to the illumination optical system, and energy loss of laser light occurs in the optical member. Since the processing apparatus uses a high fluence laser, the amount of loss due to the optical path difference member is not negligible. Moreover, if there is an error in the positioning of the optical member and the fly-eye lens, it causes further energy loss.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an illumination optical system and a laser processing apparatus in which the fly-eye lens itself has a function of generating a phase difference, thereby reducing energy loss and eliminating the need to align members. It is in.

The present invention provides an irradiation optical system for guiding a laser beam to an irradiation surface,
The z-axis is the optical axis direction, the direction perpendicular to the z-axis and the y-axis is the x-axis, the direction perpendicular to the z-axis and the x-axis is the y-axis,
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 illumination optical system, the thickness of one lens of the first lens array and the second lens array is not constant in at least one direction.
The present invention also provides an irradiation optical system for guiding a laser beam to an irradiation surface,
The z-axis is the optical axis direction, the direction perpendicular to the z-axis and the y-axis is the x-axis, the direction perpendicular to the z-axis and the x-axis is the y-axis,
A beam shaping section, a lens array section, and a collimating lens section are arranged in order along the z-axis,
The beam shaping section and the collimating lens section are composed of a first cylindrical lens having lens action in the x-axis direction and a second cylindrical lens having lens action in the y-axis direction,
A first pair of two first cylindrical lens arrays arranged along the z-axis, and two second cylindrical lens arrays arranged along the z-axis. and a second pair consisting of
The first cylindrical lens array has lens action in the x-axis direction, the second cylindrical lens array has lens action in the y-axis direction,
In the illumination optical system, the thickness of the first cylindrical lens array or the second cylindrical lens array of the first pair or the second pair is not constant in at least one direction.
Furthermore, the present invention provides a light source that emits laser light,
an illumination optical system for irradiating a photomask with laser light having a linear cross section and scanning the photomask by a scanning mechanism;
a projection optical system that irradiates a workpiece with a laser beam passed through a photomask;
a workpiece placement table on which the workpiece is placed and which moves the workpiece in the xy direction;
This is a laser processing apparatus in which the illumination optical system is configured as described above.

According to at least one embodiment, the present invention prevents interference by making the thickness of the lens array itself different, so that energy loss of laser light can be prevented. Note that the effects described herein are not necessarily limited, and may be any of the effects described herein or effects different from them.

FIG. 1 is a diagram showing a schematic configuration of a laser processing apparatus to which the present invention can be applied. FIG. 2 is a front view of one embodiment of the present invention. FIG. 3 is a plan view showing the relationship between a photomask and linear beams in one embodiment of the present invention. FIG. 4 is an enlarged plan view of an example substrate used in one embodiment of the present invention. FIG. 5 is a block diagram showing an optical system in one embodiment of the invention. 6A is a side view of the configuration of an example of the illumination optical system, FIG. 6B is a top view of the configuration of the example of the illumination optical system, and FIG. 6C is a configuration of the example of the illumination optical system with a part omitted. and FIG. 6D is a top view of an example of an illumination optical system with a part thereof omitted. FIG. 7 is an enlarged side view of a configuration of a portion of one embodiment of the present invention;

Hereinafter, embodiments of the present invention and the like will be described with reference to the drawings. The embodiments and the like described below are preferred specific examples of the present invention, and the content of the present invention is not limited to these embodiments and the like.

FIG. 1 is a schematic configuration 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 device has a laser light source 11 . The laser light source 11 is, for example, an excimer laser light source that emits pulses of KrF excimer laser light with a wavelength of 248 nm. Laser light is supplied to the linear laser scanning mechanism 12 .

The linear 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 photomask 13 with the laser beam LB.

The photomask 13 is formed with 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 of a light-shielding film (eg, a Cr film) that blocks the KrF excimer laser is drawn on a base material (eg, quartz glass) that transmits the KrF excimer laser. Processing patterns include through vias, non-through vias, trenches for wiring patterns, and the like. After the pattern is formed by ablation, it is filled with a conductor such as copper.

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

The substrate W is provided with a plurality of pattern areas WA, and is fixed on a mounting table 15 for mounting a workpiece. The pattern area WA can be positioned with respect to the photomask 13 by displacing and rotating the mounting table 15 two-dimensionally. Further, in order to process the region to be processed over the entire substrate W, the mounting table 15 moves the substrate W stepwise in the scanning direction.

An embodiment of the laser processing apparatus will be described with reference to FIG. A laser processing device 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 vibration damping properties.

A linear laser scanning mechanism consisting of a scanning mechanism 16 and an illumination optical system 17, a mask stage 18 (photomask support) on which the photomask 13 is placed, and a projection optical system 14 are fixed to the upper frame 22. be done. A mounting table 15 is fixed on the base portion 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 satisfy a predetermined optical relationship (relationship in which laser light is correctly incident on the illumination optical system 17). After the positioning, when the base portion 21 and the upper frame 22 oscillate due to vibration 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 beam position corrector 27 corrects the incident position and incident angle of the laser beam with respect to the illumination optical system 17 .

The laser light source 11 is housed in a housing 24 provided separately from the base portion 21 and the upper frame 22 . A laser light source 11 emits pulses of a KrF excimer laser (called laser light) L1 having a wavelength of 248 nm. A laser beam L1 and a guide laser beam (not shown) are incident on a beam position corrector (called a beam steering mechanism) 27 .

The beam position corrector 27 is a mechanism for positioning (position and incident angle) of the laser beam L1 in real time. The beam position correction unit 27 adjusts the laser beam L1 so that it always enters the illumination optical system 17 at the correct position and angle regardless of the inclination of the base unit 21 and upper frame 22 of the laser processing apparatus. The wavelength of the guiding laser light is set to 400 nm to 700 nm, for example. The mirror included in the beam position correction unit 27 has two reflection films that reflect the wavelengths of 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 beam incident on each reflection film.

A laser beam 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 the light into a linear processing laser beam. The illumination optical system 17 has a lens array (also called a fly-eye lens array) for shaping linear laser light. The lens array is a lens array in which a plurality of convex lenses are arranged in a direction to magnify laser light. A 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.

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 with respect to the photomask 13 by the scanning mechanism 16, and the photomask 13 and the substrate W fixed to the mask stage 18 and the mounting table 15, respectively, are scanned with the laser beam.

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

In the photomask 13, a mask pattern is drawn by forming a blocking film (chromium film, aluminum film, etc.) for blocking KrF excimer laser light on a base material (for example, quartz glass) that transmits KrF excimer laser light. ing. On the photomask 13, a pattern that appears repeatedly on the substrate W may be drawn, or a pattern that covers the entire substrate W may be drawn.

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

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 focal points 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. FIG. Here, the projection optical system 14 is configured as a reduction projection optical system (for example, 1/4 magnification).

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 and rotating in the xy directions by a table moving mechanism. It is also step-movable along the scanning direction so that the entire substrate W can be ablated. An alignment camera (not shown) for capturing images of alignment marks provided on the substrate W is installed near the mounting table 15 . Furthermore, a z mechanism or the like for focus adjustment may be provided.

The substrate W (workpiece) is, for example, an organic substrate for a printed wiring board, and a layer to be processed by laser processing is formed on the surface thereof. The layer to be processed is, for example, a resin film or a metal foil, and is made of a material that can be subjected to processing such as via formation by laser light. A laser processing machine is used to form vias and wiring patterns, and in subsequent processes, the processed portions are filled with a conductor such as copper.

FIG. 4 shows an enlarged example of the substrate W. As shown in FIG. The substrate W is a multi-sided substrate, and pattern areas WA corresponding to the pattern of the photomask 13 are repeatedly provided in an (8×8) matrix on the substrate W. As shown in FIG. In FIG. 4, the horizontal direction is the secondary step direction, and the vertical direction is the main step direction. After one pattern area WA is scanned, the next pattern area is scanned. The illustrated scanning direction (arrow) is an example.

In one embodiment of the present invention, a transport mechanism (not shown) is provided, and the workpiece is placed on and removed from the placement table by the transport mechanism. For example, a SCARA robot or the like can be used. It also has an air-conditioning chamber (not shown) that covers the processing device and the housing of the laser light source.

In one embodiment of the invention described above, a controller (not shown) is provided for controlling the entire apparatus. The control device controls the laser light source 11, controls each part of the driving section, aligns the photomask and the substrate W, manages production information, manages recipes, and the like.

FIG. 5 is a block diagram showing the optical system in the laser processing apparatus described above. Parts in FIG. 5 corresponding to those in FIGS. 1 and 2 are denoted by the same reference numerals. Laser light from the laser light source 11 is supplied to the beam shaping section 30 . A laser beam from the beam shaping section 30 is supplied to the beam position correcting section 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 section 30 shapes laser light so that the laser light from the laser light source 11 and the guide laser light are incident on a reflecting film different from the mirror.

The illumination optical system 17 has a configuration in which a beam shaping section 31, a lens array section 32 as a light amount homogenizing section, and a collimator lens section 33 are arranged in order along the optical axis. The beam shaping section 31 forms a rectangular laser beam having a predetermined length and width, and the lens array section 32 makes the distribution of the laser light uniform and linear laser light. The lens array section 32 includes a first pair 34 consisting of 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 consisting of two second cylindrical lens arrays 37a and 37b arranged along the .

The laser light from the lens array section 32 is made into substantially parallel light by the collimating lens section 33 . The photomask 13 is irradiated with laser light from the collimating lens portion 33 of the illumination optical system 17 . Laser light passing 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. FIG.

An example of the illumination optical system 17 will be described with reference to FIG. The direction parallel to the optical axis of the illumination optical system 17 is the z-axis, the direction orthogonal to the z-axis and the y-axis is the x-axis, and the direction orthogonal to the z-axis and the x-axis is the y-axis. That is, the x-axis and the y-axis are perpendicular to the z-axis and perpendicular to each other. 6A is a side view of the illumination optical system 17, and FIG. 6B is a top view of the illumination optical system 17. FIG. Furthermore, 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.

In the side view of FIG. 6A, a cylindrical lens 31a, cylindrical lens arrays 36a and 36b, and a cylindrical lens 33a indicated by thick lines are elements having a lens action in the x-axis direction. These lens elements 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 effect in the y-axis direction. These lens elements are extracted and shown in FIG. 6D.

The beam shaping unit 31 includes 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 lens in the y-axis direction (in other words, having power in the y-axis direction). It has a structure in which cylindrical lenses 31b having an action 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 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, the laser beam is generated from the cylindrical lens 31b with a spread in the y-axis direction (longitudinal direction). A laser beam from the cylindrical lens 31 b is emitted from the beam shaping section 31 . The beam shaping section 31 expands the laser light according to the size of the incident surface of the cylindrical lens array of the lens array section 32, and makes the laser light incident on the cylindrical lens array in parallel. be. Note that the laser light incident on the fly-eye lens has an intensity bias such as a Gaussian curve.

The laser light emitted from the beam shaping section 31 is incident on the cylindrical lens array 36 a of the first pair 34 of the lens array section 32 on the light source side. A cylindrical lens array 36b is arranged parallel to 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 lens surface on the incident side of the cylindrical lens array 36a is convex, and the lens surface on the exit side is planar. The incident-side lens surface of the cylindrical lens array 36b is flat, and the exit-side lens surface is convex. Laser light is homogenized by cylindrical lens arrays 36a and 36b.

The laser light emitted from the first pair 34 is incident on the cylindrical lens array 37 a of the second pair 35 of the lens array section 32 on the light source side. 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 formed by arranging a plurality of small-diameter cylindrical lenses (convex lenses) in the y-axis direction. The laser light is made uniform by the cylindrical lens arrays 37a and 37b.

The laser light emitted from the cylindrical lens array 37 b of the second pair 35 of the lens array section 32 is incident on the first cylindrical lens 33 a of the collimating lens section 33 . The cylindrical lens 33a has a lens action in the x-axis direction. A 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 collimator lens unit 33 converts the split laser beams into parallel beams and makes them uniform by superimposing them on the irradiation surface.

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

The thicknesses of the lenses are alternately varied so that the lens surface on the plane side of the cylindrical lens array 36b has a step of ΔT when viewed from the side. ΔT is set to a value that does not cause bright and dark interference fringes (for example, ΔT is about 1 (mm)). Such a cylindrical lens array 36b can prevent interference fringes from occurring on the output side of the cylindrical lens array 38b due to an optical path length difference.

In addition, the cross-sectional shape of the excimer laser beam is generally rectangular with an aspect ratio of 1:2, 1:5, etc., and the spatial coherence is not isotropic. It is higher in the hand direction. Therefore, interference fringes tend to occur in the lateral direction of the beam cross section. Thus, when the spatial coherence of laser light is not isotropic, the thickness of the lens is not constant in the direction of high spatial coherence.

Also, when the brightness of the interference fringes occurs in the x-axis direction on the irradiation surface when the lens thickness is the same, the lens thickness is changed in the x-axis direction of the cylindrical lens array 36b as in the example of FIG. Let When the thickness of the lens is the same and the brightness of the interference fringes occurs in the y-axis direction on the irradiation surface, the thickness of the lens in the y-axis direction of the cylindrical lens array 37b is not constant. Furthermore, when the thickness of the lens is the same and the brightness and darkness of the interference fringes occur in both the x-axis and y-axis directions on the irradiation surface, the x-axis direction of the cylindrical lens array 36b and the y-axis direction of the cylindrical lens array 37b Let the thickness of the lens be non-constant in both axial directions.

In the embodiment of the present invention described above, the thickness of the cylindrical lens array itself is made different, so the energy loss of the laser light can be reduced compared to a configuration in which separate optical members are provided.

In one embodiment of the present invention described above, the thickness of the lenses of the lens array is changed by alternately changing the thickness of the lenses so that the lens surfaces have steps when viewed from the side. . The present invention is not limited to this form. For example, the thickness may change stepwise in one direction when viewed from the side, or lenses with different thicknesses may be randomly arranged. good too. It is sufficient that each lens constituting the lens array has a thickness different from that of adjacent lenses in at least one direction.

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., given in the above-described embodiments are merely examples, and if necessary, different configurations, methods, processes, shapes, materials, numerical values, etc. may be used. good too.

W Workpiece (substrate) 11 Laser light source 12 Linear laser scanning mechanism 13 Photomask 14 Projection optical system 15 Placement table , 16... Scanning mechanism, 17... Illumination optical system, 18... Mask stage, 30, 31... Beam shaping section, 32... Lens array section, 33... Collimating lens section

Claims (7)

An irradiation optical system for guiding a laser beam to an irradiation surface,
The z-axis is the optical axis direction, the direction perpendicular to the z-axis and the y-axis is the x-axis, the direction perpendicular to the z-axis and the x-axis is the y-axis,
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;
An illumination optical system in which the thickness of one of the lenses of the first lens array and the second lens array is not constant in at least one direction. 2. The illumination optical system according to claim 1, wherein when the spatial coherence of laser light incident on the first lens array is not isotropic, the thickness of the lens is changed in the direction in which the spatial coherence is high. . When the thickness of the lens is the same and the brightness of the interference fringes occurs in the x-axis direction on the irradiation surface, the thickness of the lens is not constant in the x-axis direction, and the brightness of the interference fringes occurs in the y-axis direction. In this case, the thickness of the lens is not constant in the y-axis direction, and if light and dark interference fringes occur in both the x-axis and y-axis directions, the lens thickness is constant in both the x-axis and y-axis directions. 3. The illumination optical system according to claim 1 or 2, wherein 4. The illumination optical system according to any one of claims 1 to 3, wherein said lenses having different thicknesses are alternately provided in directions in which light beams emitted from respective lenses of said second lens array interfere with each other. 5. An illumination optical system according to claim 1, wherein said first and second lens arrays are cylindrical lens arrays. An irradiation optical system for guiding a laser beam to an irradiation surface,
The z-axis is the optical axis direction, the direction perpendicular to the z-axis and the y-axis is the x-axis, the direction perpendicular to the z-axis and the x-axis is the y-axis,
A beam shaping unit, a lens array unit, and a collimator lens unit are arranged in order along the z-axis,
The beam shaping section and the collimating lens section are composed of a first cylindrical lens having lens action in the x-axis direction and a second cylindrical lens having lens action in the y-axis direction,
A first pair of two first cylindrical lens arrays in which the lens array section is arranged along the z-axis, and two second cylinders arranged along the z-axis. a second pair of cull lens arrays;
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,
An illumination optical system, wherein the thickness of the first cylindrical lens array or the second cylindrical lens array of the first pair or the second pair is not constant in at least one direction. a light source that emits laser light;
an illumination optical system that irradiates the photomask with the laser beam having a linear cross section and scans the photomask with a scanning mechanism;
a projection optical system for irradiating an object to be processed with laser light passed through the photomask;
a workpiece placement table on which the workpiece is placed and which moves the workpiece in xy directions;
A laser processing apparatus, wherein the illumination optical system has the configuration according to claim 1 .

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