Laser processing method, laser processing apparatus, and mask

Abstract

When forming cavities or other features using ablation processing, over-processing is suppressed. [Solution] A rectangular mask pattern MP1 (MP2) is formed on the mask M used in the laser processing apparatus 100. The mask pattern MP1 (MP2) is provided with light-shielding portions P1 (Q1) and transparent portions P2 (Q2) along the pattern edges corresponding to the sub-scanning direction (Y direction). Due to the complementary pattern shape (geometry) of the light-shielding portion P1 (Q1) and the transparent portion P2 (Q2), the light intensity distribution of the laser beam is averaged near the edge portion CR of the processing area AR of the substrate W, and over-processing of the processing area AR is suppressed.

Description

Technical Field

[0001] The present invention relates to a laser processing apparatus, and particularly to a mask pattern and a processing method.

Background Art

[0002] With the miniaturization and high-density mounting of electronic devices and the like, high-precision pattern formation is required for printed wiring boards and the like. For example, in a laminated substrate, it is necessary to form fine vias and grooves (trenches) on the order of μm.

[0003] As a method for performing microfabrication, ablation processing is performed. In this process, a laser beam with a high energy density is scanned over a mask and projected onto a workpiece such as a substrate. By instantaneously evaporating and removing the material surface in accordance with the mask pattern, vias, grooves for wiring, and the like can be formed on the substrate (see, for example, Patent Document 1).

[0004] When irradiating a substrate with a high-frequency laser beam to form a cavity (recess), problems occur such that the bottom surface of the corner portion is etched deeper than other surfaces due to wall reflection, impact due to gasification, and heating of the gas. To prevent this, the irradiation area and irradiation time of the laser beam are changed to form the corner portion in a stepped or rounded shape (see Patent Document 2). By increasing the mechanical strength of the corner portion, crack generation is suppressed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] When forming relatively large cavities on a substrate, ringing occurs, resulting in peak-like intensity changes at both ends of the light intensity distribution of the laser beam image irradiated onto the substrate. This causes a high-intensity laser beam to irradiate the area near the walls of the processing region. Consequently, over-processing occurs near the walls, where the bottom surface is cut deeper than necessary.

[0007] Therefore, when forming cavities or other structures by ablation, it is necessary to suppress over-processing. [Means for solving the problem]

[0008] One aspect of the present invention is a laser processing method in which a line-shaped laser beam is scanned over a mask on which a mask pattern has been formed, and the pattern beam that has passed through the mask is projected onto the workpiece using a projection optical system to perform ablation processing. The shape of the mask pattern varies depending on the processing pattern, and for example, a rectangular pattern that forms a cavity can be formed.

[0009] In the present invention, in the mask pattern, a transparent portion and a light-shielding portion are formed along the pattern edge corresponding to the main scanning direction, each having a pattern width smaller than the wavelength of the line-shaped laser beam and the resolution power according to the numerical aperture of the projection optical system, respectively, or a transparent portion and a light-shielding portion having a pattern size smaller than the resolution power, respectively.

[0010] A mask pattern having a transparent portion and a light-shielding portion, each having a pattern width smaller than the resolution, can be configured such that the light-shielding portion is a bar-shaped pattern extending along the pattern edge, and the transparent portion is formed between the light-shielding portion of the bar-shaped pattern and the pattern edge. For example, the mask pattern can be formed such that the width of the light-shielding portion corresponding to the main scanning direction is narrower than the width of the transparent portion corresponding to the main scanning direction.

[0011] A mask pattern having a transparent portion and a light-shielding portion, each having a pattern size smaller than the resolution, can be configured such that the light-shielding portion and the transparent portion are each rectangular patterns, arranged alternately along the pattern edge. For example, the light-shielding portion and the transparent portion can be formed so as to be in contact with the pattern edge. Furthermore, the mask pattern can be formed such that the pattern size of the light portion is smaller than the pattern size of the transparent portion.

[0012] Another embodiment of the present invention is a mask used in a laser processing apparatus that scans a line-shaped laser beam across the mask and projects the pattern beam that has passed through the mask onto a workpiece using a projection optical system to perform ablation processing, the mask having a mask pattern, wherein the mask pattern has a transparent portion and a light-shielding portion formed along the pattern edge of the mask pattern, each having a pattern width or pattern size smaller than the wavelength of the line-shaped laser beam and the resolution power according to the numerical aperture of the projection optical system, respectively.

[0013] Another aspect of the present invention is a laser processing apparatus comprising: a mask stage capable of supporting the mask such that the pattern edge of the mask pattern is aligned with the main scanning direction; a line beam forming unit that forms a line beam based on a laser beam emitted from a light source; a scanning mechanism that scans the line beam with respect to the mask; a projection optical system that projects the line beam onto a workpiece; and a processing stage capable of supporting a workpiece. [Effects of the Invention]

[0014] According to the present invention, when forming cavities or the like by ablation processing, over-processing can be suppressed. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram of the laser processing apparatus according to this embodiment. [Figure 2] This is a schematic block diagram of a laser processing device. [Figure 3]It is a figure showing a mask pattern. [Figure 4] It is a figure showing the cross-sectional intensity distribution of an optical image and a processed cross-sectional view of a substrate when irradiating a linear laser beam onto the substrate. [Figure 5] It is a figure showing the light intensity distribution by simulation.

Mode for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0017] FIG. 1 is a schematic configuration diagram of the laser processing apparatus according to the present embodiment. FIG. 2 is a schematic block diagram of the laser processing apparatus.

[0018] The laser processing apparatus 100 is a processing apparatus capable of forming a pattern on a substrate W by ablation processing, and includes a line beam forming unit 20, a projection optical system 30, a mask stage 40, and a processing stage 50. The line beam forming unit 20, the mask stage 40, and the processing stage 50 are equipped in a device body not shown and are movable with respect to the device body. The mask M and the substrate W are mounted on the mask stage 40 and the processing stage 50, respectively. The substrate W is constituted by a resin substrate such as a printed substrate here.

[0019] The laser 10 installed beside the device body oscillates a laser beam with a high energy density. Here, an excimer laser that pulse-irradiates KrF excimer laser light with a wavelength of 248 nm is applied. The laser beam oscillated from the laser 10 is guided to the line beam forming unit 20 via a correction optical system for optical axis adjustment not shown. The laser 10 may be configured as a part of the laser processing apparatus 100, or may be configured as a separate device.

[0020] The line beam forming unit 20 includes an optical system such as a lens array 24, a line beam forming optical system 25 including a laser light cylindrical lens, and an angle switching mirror 26. The lens array 24 adjusts the intensity distribution of the incident laser light. The line beam forming optical system 25 shapes the beam light beam of the incident laser light into a line-shaped laser beam LB.

[0021] The line beam forming unit 20 houses an optical system such as the line beam forming optical system 25 in its casing 20K, and the casing 20K is supported by a scanning mechanism 60. The scanning mechanism 60 can move the line beam forming unit 20 at a speed determined along the main scanning direction (X direction), and can relatively move the line-shaped laser beam LB in the main scanning direction (X direction), which is the scanning direction, with respect to the mask M.

[0022] The angle switching mirror 21 provided in the line beam forming unit 20 can shift the irradiation position of the line-shaped laser beam LB on the mask M along the sub-scanning direction (Y direction) by switching its angle (position), that is, can switch the scanning area. Here, the angle switching mirror 21 is provided at a conjugate position between the lens array 24 and the line beam forming optical system 25.

[0023] The mask stage 40 supports the mask M and can move and rotate it in the main scanning direction (X direction) and the sub-scanning direction (Y direction), which is the scanning width direction of the line-shaped laser beam LB. The mask stage moving mechanism 70 drives the mask stage 40 based on a signal output from a position detection encoder (not shown).

[0024] The projection optical system 30 is an imaging optical system that focuses on the surface of the mask M and the surface of the substrate W, and projects light (pattern light) that has passed through the mask pattern formed on the mask M onto the substrate W. Here, the projection magnification is set to 1.0x, but it is also possible to set the projection magnification to, for example, 0.5x by configuring a reduction projection optical system. The projection optical system 30 is provided with a focus adjustment mechanism, which allows the amount of defocusing to be adjusted.

[0025] The processing stage 50 fixes the substrate W by vacuum suction or the like, and can move and rotate the substrate W in the main scanning direction (X direction) and the sub-scanning direction (Y direction). The processing stage movement mechanism 80 drives the processing stage 50 based on signals output from a position detection encoder (not shown). An alignment camera (not shown) is installed next to the processing stage 50 to capture alignment marks provided on the substrate W.

[0026] The substrate W, which is a resin substrate, has a copper wiring layer formed on a base material such as epoxy resin, and an insulating layer formed on top of that. By irradiating the substrate W with high-energy-density excimer laser light from the excimer laser 10, ablation occurs on the substrate W, and a pattern (hereinafter referred to as the processed pattern) WA is formed according to the mask pattern formed on the mask M. The processed pattern WA can be formed as through vias, non-through vias, or grooves (trenches) and cavities for wiring patterns.

[0027] As the scanning mechanism 60 moves the line beam forming unit 20 in the main scanning direction (X direction), a line-shaped laser beam LB perpendicular to the main scanning direction (X direction) and parallel to the sub-scanning direction (Y direction) moves relative to the mask M (mask stage 40), the projection optical system 30, and the substrate W (processing stage 50). As a result, the mask M and substrate W mounted on the mask stage 40 and processing stage 50, respectively, are scanned.

[0028] The mask pattern formed on the mask M has an area size that exceeds the longitudinal width of the linear laser beam LB, depending on the processing area AR where the processing pattern WA is formed and the projection magnification of the projection optical system 30. By repeatedly scanning along the main scanning direction (X direction) while switching the irradiation position of the linear laser beam LB with the angle switching mirror 26, the processing pattern WA is formed over the entire processing area AR.

[0029] The processing stage 50 moves in steps along the main scanning direction (X direction) and the sub-scanning direction (Y direction) each time a processing pattern WA is formed in the processing area, and ablation processing is performed over the entire substrate W. After the processing pattern is formed on the substrate W by ablation processing, a conductor such as copper is filled in. Alternatively, a mask pattern for drawing the pattern over the entire substrate W may be formed on the mask M.

[0030] The controller 90 controls the angle switching mirror 26, scanning mechanism 60, mask stage moving mechanism 70, and processing stage moving mechanism 80 of the line beam forming unit 20, and performs control during the ablation processing, namely, positioning of the mask M, positioning of the substrate W, movement of the line-shaped laser beam LB in the main scanning direction (X direction), and switching of the irradiation position along the sub-scanning direction (Y direction).

[0031] The controller 90 shown in Figure 2 controls the operation of the processing apparatus 100. When an operator performs an input operation for ablation processing, the controller 90 drives the laser 10 and drives and controls the scanning mechanism 60 to scan a line of light in the X direction. The controller 90 also controls the movement of the mask stage 40 and the processing stage 50, adjusts the optical axis misalignment based on the output signal from the detection unit (not shown), and performs alignment processing by the alignment camera 91 and controls the opening and closing of the shutter mechanism 93.

[0032] In this embodiment, repeated ablation processing is performed on a predetermined processing area using two mask patterns with different widths along the sub-scanning direction (Y direction). This will be described in detail below.

[0033] Figure 3 shows the mask pattern. Here, a mask pattern is formed that creates a rectangular cavity as the processing pattern WA.

[0034] The mask M has a rectangular mask pattern MP1, as shown in Figure 3(A). The mask M is positioned on the mask stage 40 such that the short edge E of the mask pattern MP1 is aligned with the main scanning direction (X direction).

[0035] The mask pattern MP1 is configured as a pattern in which a bar-shaped light-shielding portion P1 is partially provided on a rectangular transparent portion P. The bar-shaped light-shielding portion P1 is formed at predetermined intervals from the pattern edge E along a direction corresponding to the sub-scanning direction (Y direction). A transparent portion P2 of the bar-shaped pattern is partitioned between the light-shielding portion P1 and the pattern edge E.

[0036] Figure 4 shows the cross-sectional intensity distribution of the optical image and the processed cross-sectional view of the substrate W when a linear laser beam LB is irradiated onto the substrate W.

[0037] The laser light emitted from the light source 10 is high-energy-density pulsed light, and the line beam forming unit 20 forms a line-shaped laser beam LB with a uniform light intensity distribution. The width LW of the line-shaped laser beam LB incident on the mask M in the sub-scanning direction (Y direction) is greater than the width W1 (Figure 3) of the mask pattern MP1 corresponding to the sub-scanning direction (Y direction), and a portion of the line-shaped laser beam LB that has passed through the mask pattern MP1 irradiates the processing area AR. Here, the width CW of the processing area AR in the sub-scanning direction (Y direction) is equal to the width W1 of the mask pattern MP1 in the sub-scanning direction (Y direction).

[0038] The light intensity distribution of a linear laser beam LB after it passes through the mask pattern MP1 is prone to ringing at its edges. Figure 4 shows the light intensity distribution of the pattern beam reaching the processing area AR of the substrate W, indicated by the symbol LD. Due to ringing, the light intensity distribution LD shows changes in light intensity that have localized peaks.

[0039] When ablation processing is performed using a laser beam with such an optical intensity distribution LD, the high-energy-density laser beam continuously irradiates the edge portion CR along the main scanning direction (X direction) of the processing area AR throughout the scanning process. As a result, the bottom surface CB of the processing pattern WA, which is the cavity, is over-machined as the edge portion CR is deeply removed, creating a groove.

[0040] On the other hand, with respect to the edge portion in the sub-scanning direction (Y direction), since the linear laser beam LB propagates in the main scanning direction (X direction), the light intensity of the pattern beam reaching the processing area AR does not remain consistently high. When the linear laser beam LB begins to pass through the mask pattern MP1, a low-intensity pattern beam is incident on the processing area AR without imaging. As the linear laser beam LB propagates, the intensity of the pattern beam increases, and then decreases again just before passing through. Therefore, over-processing due to ringing as described above does not occur in the edge portion along the sub-scanning direction (Y direction).

[0041] In this embodiment, the light-shielding portion P1 and the light-transmitting portion P2 are both configured as bar-shaped patterns with unresolved pattern widths B1 and B2. Here, the resolution of the laser processing apparatus 100 is determined by the following formula. Here, R is the resolving power (resolution), λ (nm) is the wavelength of the laser beam emitted from the laser 10, and NA represents the numerical aperture of the projection optical system 30. The constant K is determined according to the illumination conditions, exposure conditions, etc. R = K·λ / NA ····(1)

[0042] Because the mask pattern MP1 includes a light-shielding section P1, the light intensity distribution LD decreases in accordance with the position of the light-shielding section P1. Furthermore, since both the light-shielding section P1 and the transparent section P2 have pattern widths B1 and B2 that are not resolved in the processing area AR, the energy density (fluence) of the laser beam that reaches near the edge portion CR of the processing area AR is averaged.

[0043] Here, the unresolved pattern widths B1 and B2 (collectively referred to as Bx) in the mask pattern MP1 represent the resolution R divided by the projection magnification Ms, and their dimensions can be expressed by the following formula. Bx <R / Ms ····(2)

[0044] As a result, in the edge portion CR of the processed pattern WA formed after ablation, the bottom surface CB is flattened, and the formation of grooves in the edge portion CR can be suppressed. The width B1 of the light-shielding portion P1 and the width B2 of the light-transmitting portion P2 can be set to various values ​​within the range that satisfies equation (1) above. For example, the width B1 of the light-shielding portion P1 can be set to be smaller than the width B2 of the light-transmitting portion P2. Also, the width B2 of the light-transmitting portion P2 can be set to be smaller than twice the width B1 of the light-shielding portion P1.

[0045] The constant K is a value that depends on the illumination conditions and exposure conditions of the laser processing apparatus 100, and is set to, for example, 0.25. Depending on the conditions, it may be set to a value in the range of 0.25 to 0.60.

[0046] On the other hand, it is also possible to apply mask pattern MP2, shown in Figure 3(B), instead of mask pattern MP1.

[0047] In the mask pattern MP1, rectangular light-shielding sections Q1 are arranged at predetermined intervals along the pattern edge E. Between the light-shielding sections Q1, rectangular transparent sections Q2 are formed. The complementary light-shielding sections Q1 and Q2 are arranged in contact with the pattern edge E.

[0048] The light-shielding portion Q1 and the light-transmitting portion Q2 have a pattern size (vertical × horizontal) smaller than the resolution according to equation (1) above. The vertical length H of the light-shielding portion Q1 and the light-transmitting portion Q2 is the same length H along the main scanning direction (X direction), while the horizontal width H1 of the light-shielding portion Q1 along the sub-scanning direction (Y direction) is shorter than the width H2 of the light-transmitting portion Q2 along the sub-scanning direction (Y direction).

[0049] By forming a rectangular pattern consisting of a light-shielding portion Q1 and a light-transmitting portion Q2 at the pattern edge E, changes in light intensity occur near the pattern edge E of the light intensity distribution while scanning the line-shaped laser beam LB. Furthermore, because the pattern size of the light-shielding portion Q1 and the light-transmitting portion Q2 is smaller than the resolution, the energy accumulated at the edge portion CR of the processed pattern WA during scanning is averaged out. As a result, over-processing at the edge portion CR of the processed pattern WA is suppressed.

[0050] As described above, the mask M used in the laser processing apparatus 100 of this embodiment has a rectangular mask pattern MP1 (MP2) formed on it. The mask pattern MP1 (MP2) is provided with light-shielding portions P1 (Q1) and transparent portions P2 (Q2) along the pattern edges corresponding to the sub-scanning direction (Y direction). Due to the complementary pattern shape (geometry) of the light-shielding portions P1 (Q1) and transparent portions P2 (Q2), the light intensity distribution of the laser beam is averaged near the edge portion CR of the processing area AR of the substrate W, and over-processing of the processing area AR is suppressed.

[0051] The mask pattern is not limited to a rectangular mask pattern that forms a cavity. Mask patterns for forming processing patterns such as triangles, trapezoids or polygons, rectangular patterns with rounded corners, oval patterns (slits), and mask patterns for forming processing patterns with curves or free curves as outlines may also be formed. [Examples]

[0052] The following describes an example using Figure 5. In this example, the light intensity distribution of the light (optical image) projected onto the substrate when a line-shaped laser beam is scanned using a laser processing apparatus with the mask pattern MP2 (Figure 3(B)) of the above embodiment was determined by simulation.

[0053] In the example, the analysis was performed with a laser beam wavelength of 248 nm, a projection optical system numerical aperture (NA) of 0.2, and a constant K of 0.25. However, the magnification of the projection optical system was set to 1 / 4 (i.e., 4x reduction projection), the pattern size of the mask pattern was 30 (μm) × 13.8 (μm), the pattern size of the light-shielding area was 1 (μm) × 0.6 (μm), and the pattern size of the transmission area was 1 (μm) × 1 (μm). Furthermore, the width of the line-shaped laser beam along the main scanning direction (X direction) in the mask was set to 0.1 (mm), and the width along the sub-scanning direction (Y direction) was set to 26 (mm).

[0054] Figure 5 shows the light intensity distribution where the depth direction is the main scanning direction (X direction). As shown in Figure 5, it can be seen that ringing is suppressed in the light intensity distribution near the edge of the pattern. Similarly, it was confirmed that ringing is suppressed in the light intensity distribution near the edge of the pattern with mask pattern MP1 (Figure 3(A)). [Explanation of Symbols]

[0055] 10 lasers 20 Linear beam forming section 40 Mask Stage 50 Processing Stages 60 Scanning mechanism 80 Controllers 100 Laser Processing Equipment AR processing area M Mask MP Mask Pattern MP1 Mask Pattern MP2 Mask Pattern W board

Claims

1. A line-shaped laser beam is scanned over the mask on which the mask pattern has been formed. A processing method for performing ablation by projecting a pattern beam that has passed through the mask onto a workpiece using a projection optical system, A laser processing method characterized in that, in the mask pattern, a transparent portion and a light-shielding portion, each having a pattern width or pattern size smaller than the wavelength of the line-shaped laser beam and the numerical aperture of the projection optical system, are formed along the pattern edge corresponding to the main scanning direction.

2. The light-shielding portion is a bar-shaped pattern extending along the edge of the pattern, The laser processing method according to claim 1, characterized in that the transparent portion is formed between the light-shielding portion of the bar-shaped pattern and the edge of the pattern.

3. The laser processing method according to claim 2, characterized in that the width of the light-shielding portion according to the main scanning direction is narrower than the width of the light-transmitting portion according to the main scanning direction.

4. The laser processing method according to claim 1, characterized in that the light-shielding portion and the light-transmitting portion each have a rectangular pattern and are arranged alternately along the edge of the pattern.

5. The laser processing method according to claim 3, characterized in that the light-shielding portion and the light-transmitting portion are in contact with the edge of the pattern.

6. The laser processing method according to claim 3, characterized in that the pattern size of the light-shielding portion is smaller than the pattern size of the light-transmitting portion.

7. The laser processing method according to any one of claims 1 to 6, characterized in that ablation processing is performed on the substrate, which is the workpiece, to form a cavity.

8. A mask used in a laser processing apparatus that scans a line-shaped laser beam across the mask and projects the pattern beam that has passed through the mask onto a workpiece using a projection optical system to perform ablation processing, Having a mask pattern, The mask is characterized in that, in the mask pattern, a transparent portion and a light-shielding portion are formed along the pattern edge of the mask pattern, each having a pattern width or pattern size smaller than the wavelength of the line-shaped laser beam and the resolution power according to the numerical aperture of the projection optical system.

9. A mask stage capable of supporting a mask having a mask pattern as described in claim 8, such that the pattern edge of the mask pattern is aligned with the main scanning direction, A line beam forming unit that forms a line beam based on a laser beam emitted from a light source, A scanning mechanism for scanning the line-shaped beam with respect to the mask, A projection optical system that projects the aforementioned line-shaped beam onto a workpiece, A processing stage capable of supporting the workpiece and A laser processing apparatus characterized by being equipped with the following features.

Images