Illumination optical system and laser processing device

Abstract

Provided are an illumination optical system and a laser processing apparatus. The size of different directions of a laser beam can be adjusted independently. An illumination optical system that guides laser light toward an irradiation surface, in which a configuration is adopted in which the illumination optical system has a light quantity homogenizing section that homogenizes laser light, a z-axis is set as an optical axis direction, a direction perpendicular to the z-axis and a y-axis is set as an x-axis, a direction perpendicular to the z-axis and the x-axis is set as the y-axis, the light quantity homogenizing section is composed of a first pair and a second pair, the first pair is composed of two first cylindrical lens arrays arranged along the z-axis, the second pair is composed 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, and at least one of a first interval of the first cylindrical lens array of the first pair and a second interval of the second cylindrical lens array of the second pair is variable.

Description

Technical Field

[0001] The present invention relates to an illumination optical system for irradiating a photomask with a linear laser beam, and to a laser processing apparatus having an illumination optical system. Background Technology

[0002] A known technique involves scanning a workpiece (e.g., the resin layer of a printed circuit board) made of non-metallic materials such as resin or silicon using a laser that passes through a photomask, thereby ablating the workpiece into the shape of the photomask pattern (e.g., vias). For applications requiring precision machining, excimer lasers (KrF lasers, wavelength 248 nm) are used for ablation-based processing.

[0003] As an example, the illumination optics system of a processing apparatus shapes the laser beam into a linear irradiation area, homogenizing the laser beam using, for example, a fly-eye lens, to ensure uniform light flux within the irradiated area (photomask surface). Furthermore, a linear laser refers to a laser beam whose cross-sectional shape is linear in a plane perpendicular to the optical axis. In a linear beam, the aim is to achieve non-isotropic fine-tuning, adjusting only the length without changing the width of the line.

[0004] For example, Patent Document 1 describes an optical system that shapes linear light, by adjusting the beam spread angle (irradiation range) of the laser by changing the lens spacing L of the beam expander 40. Furthermore, Patent Document 2 describes an integrator unit (90) with two fly-eye lenses (91, 92), where a fly-eye lens spacing adjustment mechanism (95) changes the spacing d of the optical axes of the two fly-eye lenses (91, 92) to correct for changes in the average illuminance value on the exposure surface. When the spacing d between fly-eye lenses 91 and 92 is short, the focal length f is shorter, thereby achieving low NA and a wide field of view illumination. On the other hand, when the spacing d between fly-eye lenses 91 and 92 is long, the focal length f is longer, thereby achieving high NA and a narrow field of view illumination.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2003-053578

[0006] Patent Document 2: WO-A1-2019 / 059315

[0007] In Patent Document 1, the magnification of the laser beam is adjusted using a variable laser beam expander. However, the variable laser beam expander performs isotropic magnification adjustment, making it unsuitable for linear beams requiring anisotropic fine-tuning. Patent Document 2 changes the combined focal length of a pair of lens elements 93A and 93B by adjusting the spacing of the fly-eye lenses, thereby changing the field of view. However, this method, like Patent Document 1, performs isotropic magnification adjustment, thus preventing anisotropic fine-tuning of the magnification. Summary of the Invention

[0008] Therefore, the object of the present invention is to provide an illumination optical system and a laser processing apparatus capable of anisotropically fine-tuning a laser beam.

[0009] This invention relates to an illumination optical system that guides a laser beam toward an irradiated surface. The illumination optical system employs the following structure: It has a light homogenization section that homogenizes the laser beam. The z-axis is defined as the optical axis, the direction perpendicular to both the z-axis and y-axis is defined as the x-axis, and the direction perpendicular to both the z-axis and x-axis is defined as the y-axis. The light homogenization section consists of a first pair and a second pair. The first pair consists of two arrays of first cylindrical lenses arranged along the z-axis, and the second pair consists of two arrays of second cylindrical lenses arranged along the z-axis. The first cylindrical lens arrays function as lenses in the x-axis direction, and the second cylindrical lens arrays function as lenses in the y-axis direction. At least one of the first spacing of the first cylindrical lens arrays in the first pair and the second spacing of the second cylindrical lens arrays in the second pair is variable.

[0010] Furthermore, the present invention is a laser processing apparatus comprising: a light source that emits laser light; an illumination optical system that makes the laser light into a laser with a linear cross-section and irradiates a photomask, and scans the photomask by means of a scanning mechanism; a projection optical system that irradiates the workpiece with the laser light after passing through the photomask; and a workpiece loading stage that loads the workpiece and moves the workpiece in the xy direction, wherein the light intensity homogenization section of the illumination optical system has the above-described structure.

[0011] According to at least one embodiment, the present invention enables magnification adjustment of the desired direction of a laser by adjusting the spacing of the two cylindrical lens arrays. Furthermore, the effects described herein are not necessarily limited and may be any effects described herein or effects different from them. Attached Figure Description

[0012] Figure 1 This is a diagram showing a schematic structure of a laser processing apparatus to which the present invention can be applied.

[0013] Figure 2 This is a front view of one embodiment of the present invention.

[0014] Figure 3 This is a top view illustrating the relationship between a photomask and a linear beam of light according to one embodiment of the present invention.

[0015] Figure 4 This is an enlarged top view of an example of a substrate used in one embodiment of the present invention.

[0016] Figure 5 This is a block diagram illustrating an optical system according to one embodiment of the present invention.

[0017] Figure 6 A is a side view of an example structure of an illumination optical system. Figure 6 B is a top view of an example structure of an illumination optical system. Figure 6 C is a side view of an example structure that omits a portion of the illumination optics system. Figure 6 D is a top view of an example of an illumination optics system, omitting a portion of the structure.

[0018] Label Explanation

[0019] W: Workpiece (substrate); 11: Laser source; 12: Linear laser scanning mechanism; 13: Photomask; 14: Projection optical system; 15: Placement stage; 16: Scanning mechanism; 17: Illumination optical system; 18: Mask stage; 30, 31: Beam forming section; 32: Lens array section; 33: Collimating lens section. Detailed Implementation

[0020] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, the embodiments described below are preferred examples of the present invention, and the scope of the present invention is not limited to these embodiments.

[0021] Figure 1 This is a schematic structural 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 includes a laser source 11. The laser source 11 is, for example, an excimer laser source that irradiates a KrF excimer laser with a wavelength of 248 nm in the form of pulses. The laser is supplied to a linear laser scanning mechanism 12.

[0022] The linear laser scanning mechanism 12 has an illumination optical system that shapes the laser beam into a rectangular shape (linear) and a scanning mechanism (linear mechanism) for scanning the laser LB light mask 13.

[0023] A mask pattern corresponding to the processing pattern to be formed on the workpiece (hereinafter, appropriately referred to as substrate W) by ablation is formed on the photomask 13. That is, a pattern formed by a light-shielding film (e.g., Cr film) that blocks the KrF excimer laser is drawn on a substrate (e.g., quartz glass) through which the KrF excimer laser passes. The processing pattern includes through-holes, non-through-holes, and grooves for wiring patterns. After the processing pattern is formed by ablation, a conductor such as copper is filled in.

[0024] The laser LB, after passing through the photomask 13, is incident on the projection optical system 14. The laser emitted from the projection optical system 14 irradiates the surface of the substrate W. The projection optical system 14 has a focal plane on both the photomask surface and the surface of the substrate W. The substrate W is, for example, a resin substrate on which a copper wiring layer is formed and an insulating layer is formed on the copper wiring layer.

[0025] The substrate W has multiple patterned areas WA, and the substrate W is fixed on a mounting stage 15 for placing the workpiece. The patterned areas WA can be positioned relative to the photomask 13 by shifting and rotating the mounting stage 15 in a two-dimensional direction. In addition, in order to process the entire area to be processed on the substrate W, the mounting stage 15 moves the substrate W stepwise in the scanning direction.

[0026] Reference Figure 2 One embodiment of the laser processing apparatus will be described. The laser processing apparatus is mounted on a base portion 21 and an upper frame 22 that constitute a support body. The upper frame 22 is fixed to 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.

[0027] A linear laser scanning mechanism consisting of a scanning mechanism 16 and an illumination optical system 17, a mask stage 18 (support for the photomask) for mounting the photomask 13, and a projection optical system 14 are fixed to the upper frame 22. A mounting stage 15 is fixed to the base 21. That is, the scanning mechanism 16, the illumination optical system 17, the mask stage 18, the projection optical system 14, and the mounting stage 15 are positioned to satisfy a specified optical relationship (a relationship that allows the laser to accurately incident on the illumination optical system 17). After positioning, if the base 21 and the upper frame 22 swing due to vibrations caused by the scanning action of the illumination optical system 17 and the displacement action of the mounting stage 15, they will move together. The incident position and incident angle of the laser relative to the illumination optical system 17 are corrected by the beam position correction unit 27.

[0028] The laser source 11 is housed within a frame 24, which is separate from the base 21 and the upper frame 22. The laser source 11 irradiates a KrF excimer laser (referred to as laser) L1 with a wavelength of 248 nm in the form of pulses. Laser L1 and a guiding laser (not shown) are incident on a beam position correction unit (referred to as beam steering mechanism) 27.

[0029] The beam position correction unit 27 is a mechanism for real-time positioning (position and incident angle) of the laser L1. Regardless of the tilt of the base 21 and upper frame 22 of the laser processing apparatus, the beam position correction unit 27 can adjust the laser L1 to always be incident on the illumination optical system 17 at an accurate position and angle. Furthermore, the wavelength of the guiding laser 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 wavelengths of the laser L1 and the guiding laser, respectively. A beam shaping unit is provided in the beam position correction unit 27 for directing each laser beam onto its respective reflective film.

[0030] The laser L1 emitted from the beam position correction unit 27 is reflected by the reflector 28 and incident on the illumination optical system 17. The illumination optical system 17 homogenizes the intensity distribution of the light emitted from the laser source and shapes it into a linear processing laser. The illumination optical system 17 has a lens array (also called a fly-eye lens array) for shaping the linear laser. The lens array is a lens array obtained by arranging multiple convex lenses in the direction of laser amplification. The linear laser LB from the illumination optical system 17 illuminates the mask 13. Specific examples of the illumination optical system 17 will be described later.

[0031] The scanning mechanism 16 is part of the illumination optical system 17, enabling the entire illumination optical system 17 to move. The laser LB is moved relative to the photomask 13 by means of the scanning mechanism 16, and the photomask 13 and the substrate W, which are respectively fixed to the mask stage 18 and the stage 15, are scanned by the laser.

[0032] Figure 3 The relationship between the size of the laser LB and the photomask 13 is shown. For example, the (length × width) of the laser LB is (100 × 0.1 (mm)) or (35 × 0.3 (mm)). The width direction perpendicular to the length direction of the laser LB is the scanning direction.

[0033] The mask pattern of photomask 13 is depicted by forming a blocking film (chromium film, aluminum film, etc.) on a substrate (e.g., quartz glass) that allows KrF excimer laser to pass through, thereby blocking the KrF excimer laser. The photomask 13 can depict a pattern that repeats on the substrate W, or it can depict a pattern that covers the entire substrate W.

[0034] The mask stage 18 has an xyθ stage for holding and positioning the photomask 13. A camera (not shown) is provided for reading alignment marks set on the photomask 13 and positioning the photomask 13.

[0035] 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 with a focal point on the surface of the photomask 13 and the surface of the substrate W, and projects the light passing through the photomask 13 onto the substrate W. Here, the projection optical system 14 is configured as a scaled-down projection optical system (e.g., 1 / 4).

[0036] The mounting stage 15 fixes the substrate W using vacuum adsorption or the like, and positions the substrate W relative to the photomask 13 by moving and rotating in the x and y directions using a stage moving mechanism. Furthermore, it can move in a stepping motion along the scanning direction, allowing sintering processing to be performed on the entire substrate W. An alignment camera (not shown) is provided next to the mounting stage 15 to capture images of alignment marks provided on the substrate W. A focusing mechanism, etc., may also be provided.

[0037] The substrate W (workpiece) is, for example, an organic substrate for printed wiring boards, on which a processing layer for laser processing is formed. The processing layer is, for example, a resin film or a metal foil, formed from a material capable of being processed by laser to form vias and the like. Vias and wiring patterns are formed using a laser processing machine, and in subsequent processes, conductors such as copper are filled into the processed areas.

[0038] Figure 4 An example of substrate W is shown under magnification. Substrate W is a panel substrate, on which patterned regions WA corresponding to the pattern of photomask 13 are repeatedly arranged in an (8×8) matrix. Figure 4 In the diagram, the horizontal direction is the secondary stepping direction, and the vertical direction is the primary stepping direction. After scanning a pattern area WA, the next pattern area is scanned. The scanning direction (arrow) shown in the illustration is an example.

[0039] In another embodiment of the invention, although not shown, a conveying mechanism is provided for loading and unloading the workpiece onto and from the worktable. For example, a SCARA robot can be used. Additionally, an air-conditioned room (not shown) is provided, consisting of a frame covering the processing equipment and the laser light source.

[0040] In one embodiment of the present invention described above, a control device (not shown) is provided for controlling the entire apparatus. The control device performs control of the laser light source 11, control of each part of the drive unit, alignment of the photomask and substrate W, management of production information, and formula management, etc.

[0041] If the optical system of the aforementioned laser processing device is represented as a block diagram, such asFigure 5 As shown. For Figure 5 In and Figure 1 and Figure 2 The corresponding parts are labeled with the same reference numerals. The laser from the laser source 11 is provided to the beam shaping unit 30. The laser from the beam shaping unit 30 is provided to the beam position correction unit 27. The beam position correction unit 27 adjusts the laser so that it always incident on the illumination optical system 17 at an accurate position and angle. As described above, the beam shaping unit 30 shapes the laser so that the laser from the laser source 11 and the guiding laser are incident on a reflective film different from that of the reflector.

[0042] The illumination optical system 17 has a structure in which a beam shaping section 31, a lens array section 32 serving as a light intensity homogenizing section, and a collimating lens section 33 are arranged sequentially along the optical axis. The beam shaping section 31 forms a rectangular laser beam with a predetermined length and width, and the lens array section 32 ensures that the laser beam is uniformly distributed and becomes a linear laser beam. The lens array section 32 consists of a first pair 34 and a second pair 35. The first pair 34 consists of an array of two first cylindrical lenses arranged along the optical axis (in... Figure 5 The second pair of 35 consists of two second cylindrical lens arrays 37a and 37b arranged along the optical axis.

[0043] The collimating lens 33 makes the laser light from the lens array 32 approximately parallel. The laser light from the collimating lens 33 of the illumination optical system 17 illuminates the photomask 13. The laser light after passing through the photomask 13 is incident on the projection optical system 14. The projection optical system 14 projects the light after passing through the photomask 13 onto the substrate W.

[0044] Reference Figure 6 An example of the illumination optical system 17 will be described. The direction parallel to the optical axis of the illumination optical system 17 is defined as the z-axis, the direction perpendicular to both the z-axis and y-axis is defined as the x-axis, and the direction perpendicular to both the z-axis and x-axis is defined as the y-axis. That is, the axes perpendicular to the z-axis and mutually perpendicular are defined as the x-axis and y-axis. Figure 6 A is a side view of the illumination optics system 17. Figure 6 B is a top view of the illumination optical system 17. Furthermore, the width direction of the linear laser is the x-axis direction, and the length direction of the linear laser is the y-axis direction.

[0045] exist Figure 6 In the side view of A, the cylindrical lens 31a, cylindrical lens arrays 36a and 36b, and cylindrical lens 33a, shown in thick lines, are elements that function as lenses in the x-axis direction. These elements with lens functions are extracted and... Figure 6 It is shown in C. Additionally, in Figure 6In the side view of B, the cylindrical lens 31b, cylindrical lens arrays 37a, 37b, and cylindrical lens 33b, shown in thick lines, are elements that function as lenses in the y-axis direction. These elements that function as lenses are extracted and... Figure 6 It is shown in D.

[0046] The beam shaping section 31 has the following structure: cylindrical lenses 31a, which act as lenses in the x-axis direction (in other words, have optical power in the x-axis direction), and cylindrical lenses 31b, which act as lenses in the y-axis direction (in other words, have optical power in the y-axis direction), are arranged sequentially in the z-axis direction. When laser light from a light source is incident on the cylindrical lens 31a, laser light that extends in the x-axis direction (width direction) is generated from the cylindrical lens 31a. Furthermore, when laser light is incident on the cylindrical lens 31b, laser light that extends 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 section 31. The beam shaping section 31 amplifies the laser light according to the size of the incident surface of the cylindrical lens array of the lens array section 32, and causes the laser light to be incident parallel to the cylindrical lens array. In addition, the laser light incident on the fly-eye lens has an intensity deviation such as a Gaussian curve.

[0047] The laser emitted from the beam shaping section 31 is incident on the source side of the first pair of cylindrical lens arrays 36a of the lens array section 32. A cylindrical lens array 36b is arranged parallel to the cylindrical lens array 36a along the z-axis. Multiple small-diameter cylindrical lenses (convex lenses) are arranged in the cylindrical lens arrays 36a and 36b along the x-axis. The incident lens surface of the cylindrical lens array 36a is convex, and the exit lens surface is flat. The incident lens surface of the cylindrical lens array 36b is flat, and the exit lens surface is convex. Laser homogenization is achieved through the cylindrical lens arrays 36a and 36b.

[0048] The laser emitted from the first pair 34 is incident on the source side of the second pair 35 cylindrical lens array 37a 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. Multiple small-diameter cylindrical lenses (convex lenses) are arranged in the cylindrical lens arrays 37a and 37b along the y-axis direction. Laser homogenization is achieved through the cylindrical lens arrays 37a and 37b.

[0049] The laser emitted from the second pair of cylindrical lens arrays 37b of the lens array section 32 is incident on the first cylindrical lens 33a of the collimating lens section 33. The cylindrical lens 33a acts as a lens in the x-axis direction. A second cylindrical lens 33b is arranged parallel to the cylindrical lens 33a. The cylindrical lens 33b acts as a lens in the y-axis direction. The collimating lens section 33 makes the segmented laser light parallel and makes them overlap and homogenize on the illumination surface.

[0050] In one embodiment of the present invention, such as Figure 6 A and Figure 6 As shown in B, at least one of the first interval of the first cylindrical lens arrays 36a and 36b of the first pair 34 and the second interval of the second cylindrical lens arrays 37a and 37b of the second pair 35 is variable. In one embodiment, both the first interval and the second interval are variable.

[0051] In one embodiment of the present invention described above, the spacing of the cylindrical lens array is made variable, thereby enabling adjustment of the magnification in the desired direction.

[0052] The above describes one embodiment of the present invention in detail, but the present invention is not limited to the above embodiment and various modifications can be made according to the technical concept of the present invention. For example, a lens array obtained by arranging lenses along both the x-axis and y-axis directions can also be used. Furthermore, the present invention is not limited to a structure with two pairs of lenses, and can be applied to a structure with a pair of lenses. Moreover, the order of the x-direction lens array section 34 and the y-direction lens array section 35 can also be the reverse of the order of the above embodiment. In addition, the structures, methods, processes, shapes, materials, and values ​​listed in the above embodiments are merely examples, and different structures, methods, processes, shapes, materials, and values ​​can be used as needed.

Claims

1. An illumination optical system that guides a laser beam with a divergence angle emitted from a point source toward an irradiated surface, wherein, The illumination optical system adopts the following structure: The illumination optical system has a light intensity homogenization section that homogenizes the laser beam. Set the z-axis as the optical axis, the direction perpendicular to both the z-axis and y-axis as the x-axis, and the direction perpendicular to both the z-axis and x-axis as the y-axis. The light homogenization section consists of a first pair and a second pair. The first pair consists of an array of two first cylindrical lenses arranged along the z-axis, and the second pair consists of an array of two second cylindrical lenses arranged along the z-axis. The first cylindrical lens array functions as a lens in the x-axis direction, and the second cylindrical lens array functions as a lens in the y-axis direction. At least one of the first spacing of the first cylindrical lens array in the first pair and the second spacing of the second cylindrical lens array in the second pair is variable. A beam shaping section, a light intensity homogenizing section, and a collimating lens section are arranged sequentially along the z-axis, making the laser beam a linear laser beam that extends in the x-axis direction. The beam shaping section amplifies the laser beam based on the size of the incident surface of the cylindrical lens array closest to the beam shaping section in the first and second cylindrical lens arrays of the light intensity homogenizing section, and directs the laser beam parallel to the cylindrical lens array of the light intensity homogenizing section. The collimating lens section makes the laser beam parallel.

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

3. The illumination optical system according to claim 1, wherein, The light intensity homogenization section has the first pair disposed on the side where the laser is incident from the beam shaping section, and the second pair disposed on the side where the laser is emitted toward the collimating lens section.

4. The illumination optical system according to claim 1, wherein, The light intensity homogenization section has the second pair disposed on the side where the laser is incident from the beam shaping section, and the first pair disposed on the side where the laser is emitted toward the collimating lens section.

5. A laser processing apparatus, comprising: A light source that emits laser light; An illumination optical system that directs the laser beam as a linear laser beam onto a photomask and scans the photomask using a scanning mechanism; A projection optical system that projects a laser beam, after passing through the photomask, onto the workpiece; and A workpiece is placed on a worktable, which allows the workpiece to move in the xy directions. The illumination optical system is the structure described in claim 1.

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