TWI898152B - Illumination optical system and laser processing equipment - Google Patents

Abstract

The purpose of the present invention is to be able to independently adjust the size of the laser beam in different directions. An illumination optical system guides laser light to an irradiation surface, comprising: a light intensity uniformizing unit for uniformizing the laser light, wherein the z-axis is the optical axis direction, the direction perpendicular to the z-axis and the y-axis is the x-axis, and the direction perpendicular to the z-axis and the x-axis is the y-axis. The light intensity uniformizing unit is composed of a first pair of two first cylindrical lens arrays arranged along the z-axis, and a first pair of two cylindrical lens arrays arranged along the z-axis. The second pair of two second cylindrical lens arrays is composed of two pieces arranged along the z-axis. The first cylindrical lens array has a lens function in the x-axis direction, and the second cylindrical lens array has a lens function in the y-axis direction. At least one of the first spacing of the first cylindrical lens array of the first pair and the second spacing of the second cylindrical lens array of the second pair is a variable structure.

Description

Illumination optical system and laser processing equipment

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

A widely known technique involves scanning a non-metallic workpiece (e.g., the resin layer of a printed circuit board) made of resin, silicone, or other materials with laser light through a mask, ablation-processing (ablation: removing by melting and evaporation) the workpiece into a pattern (e.g., vias) matching the mask's pattern. For precision machining, ablation using an excimer laser (KrF laser, 248nm wavelength) is often used.

For example, the illumination optical system of the aforementioned processing device generates a linear beam that illuminates the area. To even out the luminous flux across the illuminated area (mask surface), the laser light is homogenized using, for example, a fly-eye lens. Linear laser light refers to laser light whose cross-sectional shape on a plane perpendicular to the optical axis is linear. Linear beams require fine-tuning in non-uniform directions, adjusting only the length without changing the line width.

For example, Patent Document 1 describes an optical system for forming linear light, wherein the expansion angle (irradiation range) of the laser light is finely adjusted by changing the lens spacing L of the beam expander 40. Furthermore, Patent Document 2 describes an integrator (90) having two fly-eye lenses (91, 92), and a fly-eye lens spacing adjustment mechanism (95) that changes the spacing d between the two fly-eye lenses (91, 92) in the optical axis direction to correct changes in the average illumination value on the exposure surface. When the distance d between fly-eye lenses 91 and 92 is short, the focal distance f is shortened, achieving low NA and wide field of view illumination. On the other hand, when the distance d between fly-eye lenses 91 and 92 is long, the focal distance f is lengthened, achieving high NA and narrow field of view illumination.

[Prior Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Publication No. 2003-053578

Patent Document 2: WO-A1-2019/059315

Patent Document 1 uses a variable laser beam expander to adjust the magnification of the laser beam. However, a variable laser beam expander adjusts the magnification in all directions, making it unsuitable for linear beams that require fine adjustment in all directions. Patent Document 2 adjusts the distance between the fly-eye lenses to change the combined focal distance of a pair of lens elements 93A and 93B, thereby varying the field of view. However, this method, like Patent Document 1, adjusts the magnification in all directions, making it impossible to finely adjust the magnification in all directions.

Therefore, the object of the present invention is to provide an illumination optical system and a laser processing device that can perform non-isotropic fine adjustment of the laser light beam.

The present invention is an illumination optical system that guides laser light to an irradiation surface, including: a light intensity uniformizing unit that uniformizes the laser light, wherein the z-axis is the optical axis direction, the direction perpendicular to the z-axis and the y-axis is the x-axis, and the direction perpendicular to the z-axis and the x-axis is the y-axis. The light intensity uniformizing unit is composed of a first pair of two first cylindrical lens arrays arranged along the z-axis, and a first pair of two first cylindrical lens arrays arranged along the z-axis. The second pair of cylindrical lens arrays is composed of two second cylindrical lens arrays arranged along the z-axis, wherein 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. The present invention also provides a laser processing device comprising: a light source for emitting laser light; an illumination optical system for illuminating a photomask with the laser light having a linear cross-section, while simultaneously scanning the photomask with a scanning mechanism; a projection optical system for illuminating a workpiece with the laser light transmitted through the photomask; a workpiece placement table for placing the workpiece on the table while simultaneously moving the workpiece in the x-y direction; and a light intensity uniformization unit of the illumination optical system having the aforementioned structure.

According to at least one embodiment, the present invention can adjust the magnification of laser light in a desired direction by adjusting the spacing between two cylindrical lens arrays. Furthermore, the effects described here are not limiting and can be any of the effects described in this specification, or effects of a different nature.

11: Laser light source

12: Linear laser scanning mechanism

13: Mask

14: Projection Optical System

15: Load desktop

16: Scanning Agency

17: Illumination Optical System

18: Mask Platform

21: Base

22: Upper frame

24: Frame

27: Beam Position Correction Unit

28: Mirror

30,31: Beam shaping section

31a,31b: Cylindrical lens

32: Lens array

33: Collimating lens

33a,33b: Cylindrical lens

34: Pair 1

35: Pair 2

36a, 36b: First cylindrical lens array

37a, 37b: Second cylindrical lens array

L1: Laser light

LB: Laser light

W: Workpiece (substrate)

WA: Pattern Area

Figure 1 shows the schematic structure of a laser processing device that can use the present invention.

Figure 2 is a front view of an embodiment of the present invention.

Figure 3 is a plan view showing the relationship between the mask and the linear beam according to one embodiment of the present invention.

Figure 4 is an enlarged plan view of an example of a substrate used in one embodiment of the present invention.

FIG5 is a block diagram showing an optical system according to an embodiment of the present invention.

Figure 6 is a diagram illustrating an example of an illumination optical system.

Figure 6A is a side view of the structure of an example illumination optical system.

Figure 6B is a top view of the structure of an example illumination optical system.

Figure 6C is a side view of an example of an illumination optical system, with part of the structure omitted.

Figure 6D is a top view of an example of an illumination optical system, with a portion of the structure omitted.

The following describes embodiments of the present invention with reference to the drawings. 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.

Figure 1 is a schematic diagram showing an example of a processing device capable of using the present invention, such as a laser processing device. The laser processing device includes a laser light source 11. Laser light source 11 is, for example, an excimer laser light source that pulses KrF excimer laser light with a wavelength of 248 nm. The laser light is supplied to a line laser scanning mechanism 12.

The line laser scanning mechanism 12 includes an illumination optical system that shapes the laser beam into a rectangular shape (line), and a scanning mechanism (linear motion mechanism) for scanning the mask 13 with the laser beam LB.

The mask 13 has a mask pattern corresponding to the processing pattern formed by etching on the workpiece (hereinafter referred to as the substrate W). Specifically, the pattern is formed by drawing a light-shielding film (e.g., a Cr film) on a substrate (e.g., quartz glass) that blocks the KrF excimer laser. The processing pattern includes vias, non-vias, and trenches for wiring patterns. After the processing pattern is formed by etching, a conductor such as copper is filled in.

Laser light LB passes through mask 13 and enters projection optical system 14. Laser light emitted from projection optical system 14 is irradiated onto the surface of substrate W. Projection optical system 14 has focal planes on the mask surface and the surface of substrate W. Substrate W is a resin substrate such as an epoxy resin substrate with a copper wiring layer formed on top and an insulating layer formed thereon.

A substrate W is provided with multiple pattern areas WA and is fixed to a mounting table 15 for the workpiece. The mounting table 15 is movable in two dimensions, and the position of each pattern area WA relative to the photomask 13 can be determined by rotation. Furthermore, to allow processing of the entire workpiece area on the substrate W, the mounting table 15 steps the substrate W in the scanning direction.

One embodiment of a laser processing device will be described with reference to FIG2 . The laser processing device is mounted on a base 21 and an upper frame 22 that form a support. The upper frame 22 is fixed to the base 21. The base 21 and the upper frame 22 are made of a material with high rigidity and vibration damping properties.

The upper frame 22 secures the line laser scanning mechanism consisting of the scanning mechanism 16 and the illumination optical system 17, the mask stage 18 (mask support) on which the mask 13 is placed, and the projection optical system 14. The mounting table 15 is secured to the base 21. Specifically, the scanning mechanism 16, illumination optical system 17, mask stage 18, projection optical system 14, and mounting table 15 are positioned to satisfy a predetermined optical relationship (one in which laser light is accurately incident on the illumination optical system 17). Once positioned, vibrations caused by the scanning motion of the illumination optical system 17 and the positional movement of the mounting table 15 can cause the base 21 and upper frame 22 to shift in position as a whole if they are shaken. The incident position and angle of the laser light on the illumination optical system 17 are corrected by the beam position correction unit 27.

The laser light source 11 is housed in a housing 24, which is separate from the base 21 and upper frame 22. The laser light source 11 pulses a 248nm wavelength KrF excimer laser (referred to as laser light) L1. Laser light L1 and the guide laser light (not shown) enter the beam position correction unit (also referred to as the beam steering mechanism) 27.

The beam position correction unit 27 is a mechanism for real-time positioning (position and incident angle) of the laser light L1. The beam position correction unit 27 ensures that the laser light L1 is always incident on the illumination optical system 17 at the correct position and angle, regardless of the tilt of the base 21 and upper frame 22 of the laser processing device. The wavelength of the guiding laser light is, for example, between 400 nm and 700 nm. The mirror included in the beam position correction unit 27 has two reflective coatings that reflect the laser light L1 and the guiding laser light of different wavelengths, respectively. A beam shaping unit is provided within the beam position correction unit 27 to ensure that each laser light is incident on each reflective coating.

Laser light L1 emitted from beam position correction unit 27 is reflected by mirror 28 and enters illumination optical system 17. Illumination optical system 17 uniformizes the intensity distribution of light emitted by the laser light source, forming a linear processing laser beam. Illumination optical system 17 includes a lens array (also called a fly's eye lens array) for forming the linear laser beam. The lens array is composed of a plurality of convex lenses arranged in a direction that amplifies the laser beam. Linear laser light LB emitted from illumination optical system 17 illuminates mask 13. A specific example of illumination optical system 17 will be described later.

Scanning mechanism 16 is part of illumination optical system 17 and moves the entire illumination optical system 17. Scanning mechanism 16 moves laser beam LB relative to photomask 13, scanning photomask 13 and substrate W, which are fixed to photomask stage 18 and mounting table 15, respectively.

Figure 3 shows the relationship between the size of the laser beam LB and the mask 13. For example, the (length x width) of the laser beam LB is (100 x 0.1 mm), (35 x 0.3 mm), etc. The length direction and the perpendicular width direction of the laser beam LB are the scanning directions.

The mask 13 is formed by forming a blocking film (chromium film, aluminum film, etc.) on a substrate (such as quartz glass) through which the KrF excimer laser light passes. This shields the KrF excimer laser light, thereby creating a mask pattern. The mask 13 can depict a pattern that repeats on the substrate W or a pattern that covers the entire substrate W.

The mask stage 18 has an xyθ platform that holds the mask 13 and can position the mask. It also has a camera (not shown) that reads the alignment marks on the mask 13 to position the mask 13.

Laser light passing through the mask 13 enters the projection optical system 14. The projection optical system 14 has focal points on the surface of the mask 13 and the surface of the substrate W, and projects the light transmitted through the mask 13 onto the substrate W. Here, the projection optical system 14 is configured as a reduced projection optical system (e.g., 1/4 magnification).

The mounting table 15 secures the substrate W by vacuum suction or other means, and is positioned relative to the photomask 13 by x-y movement and rotation via a table movement mechanism. Furthermore, it can be moved in steps along the scanning direction, enabling ablation processing over the entire substrate W. An alignment camera (not shown) is installed next to the mounting table 15 to capture alignment marks on the substrate W. A z-mechanism for focus adjustment may also be provided.

A substrate W (workpiece), such as an organic substrate for a printed wiring board, has a surface on which a layer to be laser-processed is formed. This layer, such as a resin film or metal foil, is made of a material that can be processed by laser light to form vias, etc. The vias or wiring pattern are formed using a laser, and the processed portion is subsequently filled with a conductor such as copper.

Figure 4 shows an example of an enlarged view of a substrate W. This substrate W has multiple chamfers, and pattern areas WA corresponding to the pattern on the mask 13 are arranged repeatedly in an (8×8) matrix. In Figure 4, the horizontal direction represents the sub-stepping direction, and the vertical direction represents the main stepping direction. Once one pattern area WA is scanned, the next pattern area is scanned immediately. The illustrated scanning directions (arrows) are examples only.

In one embodiment of the present invention, a transport mechanism (not shown) is provided to place workpieces on and off the loading table. For example, a SCARA robot can be used. Furthermore, an air-conditioned room (not shown) is provided, which includes a housing that houses the processing device and laser light source.

In one embodiment of the present invention described above, a control device (not shown) is provided for controlling the entire device. The control device controls the laser light source 11, various components of the drive unit, aligns the mask with the substrate W, manages production information, and manages inventory.

Figure 5 shows a block diagram of the optical system in the laser processing apparatus described above. Components in Figure 5 corresponding to those in Figures 1 and 2 are denoted by the same reference symbols. 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 it 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 are incident on a reflective film other than the mirror surface.

The illumination optical system 17 has a structure in which a beam shaping unit 31, a lens array unit 32 serving as a light intensity equalizer, and a collimating lens unit 33 are arranged in this order along the optical axis. The beam shaping unit 31 forms a rectangular laser beam with a predetermined length and width. The lens array unit 32 uniformizes the distribution of the laser beam into a linear laser beam. The lens array unit 32 comprises a first pair 34 and a second pair 35. The first pair 34 comprises two first cylindrical lens arrays (labeled "SLA" in Figure 5) 36a and 36b arranged along the optical axis. The second pair 35 comprises two second cylindrical lens arrays 37a and 37b, also arranged along the optical axis.

The laser light from the lens array section 33 is converted into nearly parallel light by the collimating lens section 33. The laser light from the collimating lens section 33 of the illumination optical system 17 irradiates the mask 13. The laser light that passes through the mask 13 enters the projection optical system 14. The projection optical system 14 projects the light that has passed through the mask 13 onto the substrate W.

An example of an illumination optical system 17 is described with reference to Figure 6 . The direction parallel to the optical axis of the illumination optical system 17 is the z-axis, the direction perpendicular to the z-axis and y-axis is the x-axis, and the direction perpendicular to the z-axis and x-axis is the y-axis. In other words, the axes perpendicular to the z-axis and orthogonal to each other are the x-axis and y-axis. Figure 6A is a side view of the illumination optical system 17, and Figure 6B is a top view of the illumination optical system 17. The width direction of the laser line beam is the x-axis, and the length direction of the laser line beam is the y-axis.

In the side view of Figure 6A, cylindrical lens 31a, cylindrical lens arrays 36a and 36b, and cylindrical lens 33a, shown in bold, function as lenses in the x-axis direction. These lens-functioning elements are extracted and shown in Figure 6C. Furthermore, in the side view of Figure 6B, cylindrical lens 31b, cylindrical lens arrays 37a and 37b, and cylindrical lens 33b, shown in bold, function as lenses in the y-axis direction. These lens-functioning elements are extracted and shown in Figure 6D.

The beam shaping unit 31 has a structure in which a cylindrical lens 31a, which functions as a lens in the x-axis direction (in other words, has refractive power in the x-axis direction), and a cylindrical lens 31b, which functions as a lens in the y-axis direction (in other words, has refractive power in the y-axis direction), are arranged in sequence along the z-axis. When laser light from a light source enters cylindrical lens 31a, laser light is generated, which expands from cylindrical lens 31a in the x-axis direction (width direction). Furthermore, when laser light enters cylindrical lens 31b, laser light is generated, which expands from cylindrical lens 31b in the y-axis direction (length direction). The laser light from cylindrical lens 31b is emitted from the beam shaping unit 31. The beam shaping unit 31 expands the laser light according to the size of the incident surface of the cylindrical lens array of the lens array unit 32, and causes the laser light to enter the cylindrical lens array in parallel. Furthermore, the laser light entering the fly-eye lens has an intensity distribution similar to a Gaussian curve.

The laser light emitted from the beam shaping unit 31 enters the cylindrical lens array 36a on the light source side of the first pair 34 of lens arrays 32. Cylindrical lens array 36b is arranged parallel to cylindrical lens array 36a along the z-axis. Cylindrical lens arrays 36a and 36b consist of multiple small-diameter cylindrical lenses (convex lenses) arranged along the x-axis. The lens surface on the incident side of cylindrical lens array 36a is convex, while the lens surface on the emission side is flat. The lens surface on the incident side of cylindrical lens array 36b is flat, while the lens surface on the emission side is convex. Cylindrical lens arrays 36a and 36b homogenize the laser light.

Laser light emitted from the first pair 34 enters cylindrical lens array 37a on the light source side of the second pair 35 of lens array section 32. Cylindrical lens array 37b is arranged parallel to cylindrical lens array 37a along the z-axis. Cylindrical lens arrays 37a and 37b consist of multiple small-diameter cylindrical lenses (convex lenses) arranged along the y-axis. Cylindrical lens arrays 37a and 37b homogenize the laser light.

Laser light emitted from the second pair 35 of cylindrical lens arrays 37b of the lens array unit 32 enters the first cylindrical lens 33a of the collimating lens unit 33. Cylindrical lens 33a functions as a lens in the x-axis direction. The second cylindrical lens 33b is arranged parallel to cylindrical lens 33a and functions as a lens in the y-axis direction. The collimating lens unit 33 converts the split laser light into parallel beams, superimposing and homogenizing them on the irradiation surface.

In one embodiment of the present invention, as shown in Figures 6A and 6B , at least one of the first spacing between the first cylindrical lens arrays 36a and 36b of the first pair 34 and the second spacing between the second cylindrical lens arrays 37a and 37b of the second pair 35 is variable. In another embodiment, both the first spacing and the second spacing are variable.

In one embodiment of the present invention described above, the intervals between the cylindrical lens arrays are made variable, so the magnification in a desired direction can be adjusted.

While one embodiment of the present technology has been specifically described above, the present invention is not limited to this embodiment and can be modified in various ways based on the technical principles of the present invention. For example, a lens array can be used in which lenses are arranged in both the x-axis and y-axis directions. Furthermore, the present invention is not limited to a configuration with two pairs of lenses; a configuration with a single lens array pair can also be used. Furthermore, the order of the x-axis lens array section 34 and the y-axis lens array section 35 can be reversed from that in the above embodiment. Furthermore, the structures, methods, steps, shapes, materials, and numerical values described in the above embodiments are merely examples, and structures, methods, steps, shapes, materials, and numerical values different from those described above may be used as needed.

31a,31b: Cylindrical lens

33a,33b: Cylindrical lens

34: Pair 1

35: Pair 2

36a, 36b: First cylindrical lens array

37a, 37b: Second cylindrical lens array

LB: Laser light

Claims (5)

An illumination optical system guides laser light with a divergence angle emitted from a point light source to an irradiation surface, comprising: a z-axis as an optical axis direction, an x-axis perpendicular to the z-axis and the y-axis, and a y-axis perpendicular to the z-axis and the x-axis. Along the z-axis, a beam shaping unit, a light uniformizing unit for uniformizing the laser light, and a collimating lens unit are sequentially arranged. The light uniformizing unit is a first cylindrical lens array composed of two pieces arranged along the z-axis. The laser beam is formed by a pair of cylindrical lens arrays and a second pair of cylindrical lens arrays formed of two second cylindrical lens arrays arranged along the z-axis. The first cylindrical lens array has a lens function in the x-axis direction, and the second cylindrical lens array has a lens function in the y-axis direction. At least one of the first spacing of the first cylindrical lens arrays of the first pair and the second spacing of the second cylindrical lens arrays of the second pair is variable, so that the laser beam becomes a linear laser beam extending in the x-axis direction. An illumination optical system as claimed in claim 1, wherein: the first interval and the second interval are made variable. The illumination optical system of claim 1, wherein: in the light uniformization section, the first pair is configured to the incident side of the laser light from the beam shaping section, and the second pair is configured to the exit side of the laser light toward the collimating lens section. The illumination optical system of claim 1, wherein: in the light uniformization section, the second pair is configured to the incident side of the laser light from the beam shaping section, and the first pair is configured to the exit side of the laser light toward the collimating lens section. A laser processing device includes: a light source for emitting laser light; an illumination optical system for illuminating a photomask with a linear cross-section with the laser light; a scanning mechanism for scanning the photomask with the laser light; a projection optical system for illuminating a workpiece with the laser light passing through the photomask; the workpiece being placed on a tabletop; and the workpiece being moved in the x-y direction while being placed on the tabletop. The illumination optical system includes a light intensity uniformization unit as described in claim 1.