Laser processing apparatus, laser processing method, and mask

Abstract

When forming cavities or other features using ablation processing, over-processing is suppressed. [Solution] In the laser processing apparatus 100, ablation processing is performed using a rectangular first mask pattern MP1. Then, ablation processing is performed using a rectangular second mask pattern MP2. The width B1 of the first mask pattern MP1 according to the sub-scanning direction (Y direction) and the width B1 of the second mask pattern MP2 according to the sub-scanning direction (Y direction) are different, and the width is narrower by the amount of ringing (parts of light intensity change) that occur at both ends of the line-shaped laser beam LB.

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 of performing microfabrication, ablation processing is performed. In this process, a laser beam with a high energy density is scanned on 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 engraved deeper than other surfaces due to wall reflection, impact due to gasification, and high temperature 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 across a mask, and the pattern beam that has passed through the mask is projected onto a workpiece to perform ablation processing. For example, ablation processing can be performed to form cavities in a substrate, which is a workpiece.

[0009] In the laser processing method of the present invention, multiple rectangular mask patterns with different widths corresponding to the sub-scanning direction are formed on a mask. Multiple rectangular mask patterns that are geometrically similar to each other are formed on a single mask, for example. Then, by repeatedly processing a predetermined processing area of ​​a workpiece using the multiple rectangular mask patterns, the bottom surface of the processing pattern formed in the processing area is flattened.

[0010] It is possible to form a first mask pattern and a second mask pattern on a mask, which is narrower than the first mask pattern in the sub-scanning direction, corresponding to the ringing of the line-shaped laser beam. For example, the first and second mask patterns can be formed on a single mask. Alternatively, multiple pairs of the first and second mask patterns can be regularly formed on a single mask.

[0011] When processing a processing area using the second mask pattern, the energy density of the linear laser beam can be reduced compared to when processing the processing area using the first mask pattern.

[0012] Furthermore, ablation can be performed on the processing area using a first mask pattern to reduce the depth to a level shallower than the target depth, and then ablation can be performed using a second mask pattern to reach the target depth. For example, ablation can be performed on the processing area using the first mask pattern to reach a depth of 80% or more of the target depth.

[0013] Another embodiment of the present invention is a mask which is rectangular in shape and has a first mask pattern and a second mask pattern which are aligned along a predetermined direction, the lengths of the first and second mask patterns along the predetermined direction are equal, the widths of the first and second mask patterns along the direction perpendicular to the predetermined direction are different, and the width of the second mask pattern along the direction perpendicular to the predetermined direction is narrower than that of the first mask pattern by an amount corresponding to the ringing of a line-shaped laser beam. When the mask is placed on the mask stage of a laser processing apparatus, the first and second mask patterns are formed such that the predetermined direction is aligned with the scanning direction.

[0014] Another embodiment of the present invention is a laser processing apparatus that performs ablation processing with a laser beam, comprising: a line beam forming unit that forms a line laser beam from a laser beam emitted from a light source; a mask stage capable of supporting a mask having a rectangular first mask pattern and a rectangular second mask pattern that is narrower in width in the sub-scanning direction than the first mask pattern by an amount corresponding to the ringing of the line laser beam, and capable of moving the mask in the scanning direction and the sub-scanning direction; a scanning mechanism for scanning the line laser beam; a projection optical system for projecting the pattern beam transmitted through the mask onto a workpiece; a processing stage capable of moving the workpiece in the scanning direction and the sub-scanning direction; and a control unit that controls the light source, scanning mechanism, mask stage and processing stage, wherein the control unit controls the light source, scanning mechanism, mask stage with the mask mounted on it and the processing stage so as to flatten the bottom surface of the processing pattern formed in the processing area, and performs repeated processing on the processing area using the first and second mask patterns.

[0015] Another aspect of the present invention is a laser processing method in which a line-shaped laser beam is scanned across a mask, the pattern beam transmitted through the mask is projected onto a workpiece, and ablation processing is performed. The method involves forming multiple mask patterns on the mask, each having different widths for the pattern edges that intersect in a direction corresponding to the sub-scanning direction and being similar to each other, and repeatedly processing a predetermined processing area of ​​the workpiece using the multiple rectangular mask patterns to flatten the bottom surface of the processing pattern formed in the processing area. [Effects of the Invention]

[0016] According to the present invention, when forming cavities or the like by ablation processing, over-processing can be suppressed. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic diagram of the laser processing apparatus according to this embodiment. [Figure 2]It is a schematic block diagram of a laser processing apparatus. [Figure 3] It is a diagram showing a mask pattern. [Figure 4] It is a diagram showing a cross section of a substrate during laser processing of the substrate. [Figure 5] It is a diagram showing the cross-sectional intensity distribution of an optical image when a linear laser beam is irradiated onto a substrate. [Figure 6] It is a diagram showing the flow of ablation processing.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0019] FIG. 1 is a schematic configuration diagram of a laser processing apparatus according to the present embodiment. FIG. 2 is a schematic block diagram of the laser processing apparatus.

[0020] 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 mounted on a device main body (not shown) and are movable with respect to the device main body. The mask M and the substrate W are respectively mounted on the mask stage 40 and the processing stage 50. The substrate W is here constituted by a resin substrate such as a printed circuit board.

[0021] The laser 10 installed beside the device main body oscillates laser light 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 light 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.

[0022] The line beam forming unit 20 includes a line beam forming optical system 25, which includes a lens array 24 and a laser light cylindrical lens, as well as optical systems such as angle switching mirrors 26 and 27. The lens array 24 adjusts the intensity distribution of the incident laser light. The line beam forming optical system 25 shapes the beam of the incident laser light into a line-shaped laser beam LB. For example, it is possible to shape the line-shaped laser beam LB into a rectangular beam of light with a longitudinal direction of 26 mm and a width direction of 0.1 mm on the mask surface.

[0023] The line beam forming unit 20 houses optical systems 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 predetermined speed along the scanning direction (X direction), and can move the line-shaped laser beam LB relative to the mask M in the scanning direction (X direction).

[0024] The angle-switching mirror 21 provided in the line beam forming section 20 can switch its angle (position) to shift the irradiation position of the line-shaped laser beam LB on the mask M along the sub-scanning direction (Y direction), that is, to 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.

[0025] The mask stage 40 supports the mask M and can be moved and rotated in the 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).

[0026] 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.

[0027] The processing stage 50 fixes the substrate W by vacuum suction or the like, and can move and rotate the substrate W in the scanning direction (X direction) and 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.

[0028] 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.

[0029] As the scanning mechanism 60 moves the line beam forming unit 20 in the scanning direction (X direction), a line-shaped laser beam LB perpendicular to the 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.

[0030] 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 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.

[0031] Each time a processing pattern WA is formed in the processing area, the processing stage 50 moves in steps along the scanning direction (X direction) and the sub-scanning direction (Y direction), performing ablation processing 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.

[0032] 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 scanning direction (X direction), and switching of the irradiation position along the sub-scanning direction (Y direction).

[0033] 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 optical axis detection unit (not shown), and performs alignment processing by the alignment camera (not shown) and controls the opening and closing of the shutter mechanism 93.

[0034] 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.

[0035] Figure 3 shows the mask pattern. Here, a mask pattern is formed that creates a rectangular cavity as the processing pattern WA.

[0036] The mask M has multiple regularly arranged mask patterns formed on it. Specifically, a pair of rectangular mask patterns, a first mask pattern MP1 and a second mask pattern MP2, are arranged parallel to each other, and these mask patterns MP are regularly arranged at predetermined intervals along the edges of the mask M. The mask M is mounted on the mask stage 40 so that the first and second mask patterns MP1 and MP2, as shown in Figure 3, are aligned along the X and Y directions.

[0037] The widths of the first and second mask patterns MP1 and MP2, corresponding to their scanning direction (X direction), are greater than the width of the linear laser beam LB in its scanning direction (X direction). The linear laser beam LB is scanned across the mask M, and the laser beam, which forms the pattern light, is irradiated over the entire processing area AR.

[0038] At this stage, laser processing using only the first mask pattern MP1 is performed as the first stage of processing. Then, laser processing using only the second mask pattern MP2 is performed as the second stage of processing. The mask M and substrate W are moved stepwise along the X and Y directions, and the processing is repeated (multiple) while performing the processing.

[0039] For example, ablation is performed using four first mask patterns MP1 arranged in the scanning direction (X direction) in sequence, the mask M is moved in the sub-scanning direction (Y direction), and ablation is performed using four first mask patterns MP1 arranged in the next row in sequence. After that, ablation is performed using eight second mask patterns MP2.

[0040] Figure 4 shows a cross-section of the substrate W during laser processing. Figure 5 shows the cross-sectional intensity distribution of the optical image when a line-shaped laser beam LB is irradiated onto the substrate W.

[0041] 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 is greater than the width B1 corresponding to the sub-scanning direction (Y direction) of the mask pattern MP1, and the laser beam LB that has passed through the mask pattern MP1 irradiates the processing area AR as a pattern beam. Here, the width CW of the processing area AR in the sub-scanning direction (Y direction) is equal to the width B2 of the mask pattern MP1 in the sub-scanning direction (Y direction).

[0042] However, the light intensity distribution after a linear laser beam LB 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 with localized peaks.

[0043] 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 scanning direction (X direction) of the processing area AR throughout the scanning process. As a result, the edge portion CR is cut deeper than the rest of the processing area G, resulting in over-machining and the creation of grooves.

[0044] 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 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).

[0045] In this embodiment, the widths w of the first and second mask patterns MP1 and MP2 along the scanning direction are equal, while the width B2 of the second mask pattern MP2 corresponding to the sub-scanning direction (Y direction) is narrower than the width B1 of the first mask pattern MP2 corresponding to the sub-scanning direction (Y direction) (see Figure 4). Since the central positions of the first mask pattern MP1 and the second mask pattern MP2 along the sub-scanning direction (Y direction) are equal, the width of both edge portions CR of the processing area AR is narrower by ΔB each (2ΔB overall).

[0046] When ablation is performed on the machining area AR using the second mask pattern MP2, the ablation is performed on the machining area G excluding the edge portion CR, by the amount by which the width B2 corresponding to the sub-scanning direction (Y direction) of the second mask pattern MP2 is narrower. As a result, the bottom surface B of the machining pattern WA (cavity) formed in the machining area AR is flattened (see Figure 4).

[0047] Figure 6 shows the flow of the ablation process.

[0048] In the ablation process using the first mask pattern MP1, if the final target depth of the processed pattern WA (cavity) is HT, the ablation process using the first mask pattern MP1 is performed so that the material is ultimately removed to a depth H1 of a predetermined percentage (%) (S101). Here, the ablation process is performed to reach 80% of the target depth HT.

[0049] In the ablation process using the second mask pattern MP2, the remaining 20% ​​is removed. At this time, the energy density of the laser beam LB is reduced compared to the ablation process using the first mask pattern MP2 (S102, S103). The accumulated energy density (fluence) in the edge portion CR is lower than in other processed areas G, resulting in flattening of the bottom surface B.

[0050] Furthermore, when performing ablation using the second mask pattern MP2, some over-processing due to ringing occurs, but it is not as pronounced as with the first mask pattern MP1, and the bottom surface B is flattened. In addition, since a line-shaped beam LB with reduced energy density is formed, no over-processing occurs.

[0051] The above description explains a process that uses all of the mask patterns MP formed on the mask M, but the mask patterns formed on the mask M may be selected as appropriate and the ablation process may be performed. For example, the process may be to use multiple first mask patterns MP1 and then use one second mask pattern MP2 to perform the process only once. Alternatively, it is also possible to use the first mask pattern MP1 and the second mask pattern MP2 once each.

[0052] The mask pattern is not limited to a rectangular mask pattern that forms a cavity. Mask patterns for forming processing patterns such as trapezoids, polygons, or elongated holes (slits), or mask patterns for forming processing patterns with curves with radii or free curves as contour lines may be formed.

[0053] In this case, multiple mask patterns can be formed in which the widths of the pattern edges intersecting the sub-scanning direction (Y direction) differ from each other, and which are geometrically similar to each other. When performing repeated machining, over-machining can be suppressed by positioning the mask M so that machining starts at the same position (reference position) in the machining area and scanning. [Explanation of Symbols]

[0054] 10 lasers 20 Linear beam forming section 40 Mask Stage 50 Processing Stages 60 Scanning mechanism 90 Controllers 100 Laser Processing Equipment AR processing area M Mask MP Mask Pattern MP1 First Mask Pattern MP2 Second Mask Pattern W board

Claims

1. A line-shaped laser beam is scanned across the mask. A processing method for performing ablation processing by projecting a pattern beam that has passed through the aforementioned mask onto a workpiece, Multiple rectangular mask patterns with different widths corresponding to the sub-scanning direction are formed on the aforementioned mask. A laser processing method characterized by flattening the bottom surface of a processing pattern formed in a predetermined processing area of ​​a workpiece by repeatedly processing the workpiece using the plurality of rectangular mask patterns.

2. The laser processing method according to claim 1, characterized in that a first mask pattern and a second mask pattern, which is narrower than the first mask pattern by an amount corresponding to the ringing of the line-shaped laser beam, are formed on the mask.

3. The laser processing method according to claim 2, characterized in that when processing the processing area using the second mask pattern, the energy density of the line-shaped laser beam is reduced compared to when processing the processing area using the first mask pattern.

4. The laser processing method according to claim 2, characterized in that ablation processing is performed on the processing area using the first mask pattern to make it shallower than the target depth, and then ablation processing is performed using the second mask pattern to reach the target depth.

5. The laser processing method according to claim 4, characterized in that ablation processing is performed on the processing area using the first mask pattern to reach a depth of 80% or more of the target depth.

6. The laser processing method according to claim 2, characterized in that the first and second mask patterns are formed on a single mask.

7. The laser processing method according to claim 6, characterized in that a plurality of pairs of the first and second mask patterns are regularly formed on the single mask.

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

9. Each has a rectangular shape and comprises a first mask pattern and a second mask pattern arranged along a predetermined direction. The lengths of the first and second mask patterns along a predetermined direction are equal, The widths of the first and second mask patterns along the direction perpendicular to the predetermined direction are different. A mask characterized in that the width of the second mask pattern along a direction perpendicular to a predetermined direction is narrower than that of the first mask pattern by an amount corresponding to the ringing of the line-shaped laser beam.

10. A processing apparatus that performs ablation processing using a laser beam, A line-shaped beam forming unit that forms a line-shaped laser beam from a laser beam emitted from a light source, A mask stage capable of supporting a mask having a rectangular first mask pattern and a rectangular second mask pattern that is narrower in width than the first mask pattern in the sub-scanning direction by an amount corresponding to the ringing of the line-shaped laser beam, and capable of moving the mask in the scanning direction and the sub-scanning direction, A scanning mechanism for scanning the aforementioned line-shaped laser beam, A projection optical system that projects the pattern beam transmitted through the mask onto a workpiece, A processing stage capable of moving the workpiece in the scanning direction and the sub-scanning direction, The system comprises the light source, the scanning mechanism, the mask stage, and the processing stage, and a control unit for controlling them. A laser processing apparatus characterized in that the control unit controls the light source, the scanning mechanism, the mask stage on which the mask is mounted, and the processing stage to flatten the bottom surface of the processing pattern formed in the processing area, thereby performing repeated processing on the processing area using the first and second mask patterns.

11. A line-shaped laser beam is scanned across the mask. A processing method for performing ablation processing by projecting a pattern beam that has passed through the aforementioned mask onto a workpiece, With respect to the aforementioned mask, multiple mask patterns are formed in which the widths of the pattern edges intersecting in a direction corresponding to the sub-scanning direction differ from each other and are similar to each other. A laser processing method characterized by flattening the bottom surface of a processing pattern formed in a predetermined processing area of ​​a workpiece by repeatedly processing the area using the plurality of mask patterns.

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