A microvia processing method based on picosecond-microsecond composite laser

Abstract

The application discloses a kind of microvia processing methods based on picosecond-microsecond composite laser, steps include: S1: processing substrate is washed and dried;S2: setting laser processing path;S3: first pulsed laser is generated and shaped;S4: after interval predetermined time, second pulsed laser is generated and primarily shaped;S5: first pulsed laser and second pulsed laser are integrated by beam combiner, and cooperate in predetermined position, form microvia;Again, microvia is sequentially processed along laser processing path in processing substrate, microvia array processed in processing substrate can be formed.The microvia processing method is through the synergistic mechanism of " picosecond pulse induced channel " and " microsecond pulse selective removal ", using its no diffraction, long focal depth characteristics, can be processed in hard and brittle transparent material once microvia with depth-diameter ratio more than 300:1, and single-hole processing time can be shortened to 20 μs, suitable for high depth-diameter ratio microvia high-density, mass production.

Description

Technical Field

[0001] This invention relates to the field of laser processing, and more particularly to a method for processing micro-through holes based on picosecond-microsecond composite lasers. Background Technology

[0002] High-density, high-aspect-ratio microvias are key structures in cutting-edge fields such as advanced packaging and microfluidic chips, and their processing quality directly affects device performance and integration density. Laser processing, as a precise and flexible micro / nano manufacturing method, plays an irreplaceable role in this field. Current laser processing technology faces challenges in processing high-performance microvias, including complex timing control, limited aspect ratios, and low processing efficiency. In particular, processing high aspect ratio microvias struggles to balance depth and diameter accuracy, becoming a bottleneck restricting technological development.

[0003] Although existing technologies employ Bessel beams for laser processing, utilizing the energy difference of dual pulses to clear blockages within holes, or using lasers with different pulse widths for step-by-step roughing and finishing, these methods still have significant shortcomings in terms of one-time forming of ultra-high aspect ratio micro-holes, synergistic improvement of processing efficiency and quality, and guarantee of process stability, thus restricting their widespread application in high-end precision manufacturing. Summary of the Invention

[0004] The purpose of this invention is to propose a micro-hole processing method based on picosecond-microsecond composite lasers, in order to solve the problems of the above-mentioned processing methods, which are difficult to balance processing efficiency and quality, have complex timing control, or are difficult to stably achieve one-time forming of ultra-high aspect ratio through holes.

[0005] To achieve this objective, the present invention adopts the following technical solution: This invention provides a method for fabricating micro-vias based on picosecond-microsecond composite lasers, comprising the following steps: S1: Clean and dry the substrate and fix it on the processing plane; S2: Set the laser processing path; S3: Generate and shape the first pulse laser; the first pulse laser is a microsecond-level Bessel beam; S4: After a predetermined interval, a second pulse laser is generated and initially shaped; the second pulse laser is a picosecond-level Bessel beam; S5: The first pulse laser and the second pulse laser are integrated through a beam combiner and acted synergistically at a predetermined position to form a micro-via; then, micro-vias are sequentially processed on the processing substrate along the laser processing path to form a micro-via array on the processing substrate.

[0006] In the micro-via fabrication method based on picosecond-microsecond composite laser, in step S1, the fabrication substrate includes one of BK7 glass, SLG glass, quartz glass, sapphire, and silicon carbide.

[0007] In the micro-via processing method based on picosecond-microsecond composite laser, the cleaning step in step S1 includes the following steps: immersing the processing substrate in acetone solution and ultrasonically cleaning for 8-11 minutes; then immersing the processing substrate in anhydrous ethanol solution and ultrasonically cleaning for 8-11 minutes; then immersing the processing substrate in deionized water and ultrasonically cleaning for 8-11 minutes.

[0008] In the micro-via fabrication method based on picosecond-microsecond composite laser, in step S3, the first pulse laser is generated by a microsecond-level pulse laser, the output power of the microsecond-level pulse laser is 95-110W, and the wavelength of the first pulse laser is 1065-1075nm.

[0009] In the micro-via fabrication method based on picosecond-microsecond composite laser, in step S4, the pulse energy of the second pulse laser is 245-260 μJ, and the laser wavelength is 1028-1032 nm.

[0010] In the micro-via fabrication method based on picosecond-microsecond composite laser, the pulse width of the second pulse laser is 4 to 6 ps.

[0011] In the micro-via fabrication method based on picosecond-microsecond composite laser, the predetermined time in step S4 is 9-12 μs.

[0012] In the micro-via processing method based on picosecond-microsecond composite laser, in step S2, the distance between two adjacent micro-vias is 40-60 μm, and the laser processing path is zigzag.

[0013] One of the technical solutions in this invention can have the following beneficial effects: The described micro-via fabrication method utilizes a synergistic mechanism of "picosecond pulse induction channel" and "microsecond pulse selective removal," employing a Bessel beam instead of a Gaussian beam. Leveraging Bessel's non-diffraction and long focal depth characteristics, it can fabricate micro-vias with aspect ratios exceeding 300:1 in a single operation on hard and brittle transparent materials. Furthermore, the processing time for a single hole can be reduced to 20 μs, making it suitable for high-density, mass production of high aspect ratio micro-vias. Attached Figure Description

[0014] Figure 1 This is a processing optical path diagram of one embodiment of the present invention; In the attached diagram: 1. Processing substrate; 2. First pulsed laser; 3. First axial pyramid; 4. First lens; 5. Second pulsed laser; 6. Second axial pyramid; 7. Second lens; 8. Beam combiner; 9. Beam splitter; 10. Charge-coupled device. Detailed Implementation

[0015] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0016] This invention provides a method for fabricating micro-vias based on picosecond-microsecond composite lasers, comprising the following steps: S1: Clean and dry the substrate and fix it on the processing plane; S2: Set the laser processing path; S3: Generate and shape the first pulse laser; the first pulse laser is a microsecond-level Bessel beam; S4: After a predetermined interval, a second pulse laser is generated and initially shaped; the second pulse laser is a picosecond-level Bessel beam; S5: The first pulse laser and the second pulse laser are integrated through a beam combiner and acted synergistically at a predetermined position to form a micro-via; then, micro-vias are sequentially processed on the processing substrate along the laser processing path to form a micro-via array on the processing substrate.

[0017] The described picosecond-microsecond composite laser-based micro-via fabrication method combines microsecond-level and picosecond-level Bessel beams to achieve a synergistic effect of "picosecond pulse-induced transient plasma filament channel" and "microsecond pulse selective absorption ablation." The picosecond-level Bessel beam, due to its extremely short pulse width and extremely high peak power, induces a long-range, transient plasma filament in the substrate's processing area through nonlinear effects when propagating in a transparent medium. The material within this filament channel undergoes a dramatic increase in its optical absorption coefficient due to ionization. The energy of the microsecond-level Bessel beam is then highly selectively and efficiently absorbed within this pre-formed filament channel, thereby achieving precise and efficient material removal.

[0018] By employing the above processing method, the energy of the microsecond-level Bessel beam is precisely localized within the extremely small range of the optical filament channel. This not only achieves extremely high energy utilization but also effectively suppresses heat diffusion at the source, reduces the heat-affected zone, and forms micro-through holes with smooth walls, no recast layer, and no microcracks on the processing substrate. This enables high-quality processing of micro-through holes with low thermal damage.

[0019] When ultra-intense, ultra-short laser pulses propagate in transparent media such as air, water, and glass, nonlinear optical effects such as self-focusing and self-phase modulation achieve a dynamic balance with the plasma defocusing effect, forming a self-sustaining, high-energy-density, long-range propagation bright plasma channel, called a plasma filament. In step S5, the picosecond-level Bessel beam first induces the generation of a long-range plasma filament inside the processing substrate, significantly improving the light absorption coefficient of the channel. This ensures that the energy of the microsecond-level Bessel beam is absorbed only by the filament channel, preventing energy diffusion to the hole walls. Moreover, the plasma filament defines the area where material is removed, ensuring smooth hole walls and uniform hole diameter. Furthermore, due to the long-range characteristics of the plasma filament, combined with the long focal depth characteristics of the Bessel beam, it supports high aspect ratio processing. Because the energy of the microsecond-level Bessel beam is highly selectively and efficiently absorbed within the filament channel, precise material removal is possible.

[0020] The microsecond-level Bessel beam is initiated first, but due to its very long pulse width (microsecond-level), it continues to output power even when the picosecond-level Bessel beam is emitted at a certain moment. Therefore, at the instant the picosecond-level Bessel beam is activated, the microsecond-level Bessel beam already exists and is in a stable power state.

[0021] Therefore, although the microsecond-level Bessel beam is emitted first, the induction of long-range plasma filaments inside the material must be accomplished by an ultra-high power density picosecond-level Bessel beam. Only the extremely short pulse width and high peak power of the picosecond-level Bessel beam can instantaneously break through a narrow plasma channel inside the transparent material through a nonlinear ionization process.

[0022] The moment the picosecond-level Bessel beam induces the filament, the energy of the pre-existing and continuously irradiating microsecond-level Bessel beam will be strongly absorbed by this newly formed plasma filament with an extremely high absorption coefficient, thereby rapidly heating and removing the material inside the filament.

[0023] The described micro-via fabrication method utilizes a synergistic mechanism of "picosecond pulse induction channel" and "microsecond pulse selective removal," employing a Bessel beam instead of a Gaussian beam. Leveraging Bessel's non-diffraction and long focal depth characteristics, it can fabricate micro-vias with aspect ratios exceeding 300:1 in a single operation on hard and brittle transparent materials. Furthermore, the processing time for a single hole can be reduced to 20 μs, making it suitable for high-density, mass production of high aspect ratio micro-vias.

[0024] Specifically, in step S1, the processing substrate includes one of BK7 glass, SLG glass, quartz glass, sapphire, and silicon carbide.

[0025] Sapphire and silicon carbide are materials with extremely high hardness and strong chemical inertness. Sapphire has high thermal conductivity, while silicon carbide is a wide-bandgap semiconductor. Under the action of ultrafast lasers, sapphire and silicon carbide undergo direct bond breakage and nonlinear absorption. The aforementioned micro-via fabrication method can ensure both processing efficiency and the quality of the micro-via walls.

[0026] Specifically, in step S1, the cleaning step includes the following steps: immersing the processing substrate in acetone solution and ultrasonically cleaning for 8-11 minutes; then immersing the processing substrate in anhydrous ethanol solution and ultrasonically cleaning for 8-11 minutes; then immersing the processing substrate in deionized water and ultrasonically cleaning for 8-11 minutes.

[0027] When immersing the substrate in acetone solution, anhydrous ethanol solution, or deionized water, the substrate must be completely submerged. Acetone solution is used to remove organic matter such as grease from the silicon wafer surface, while anhydrous ethanol solution is used to remove any remaining acetone, and deionized water is used to remove any remaining anhydrous ethanol.

[0028] By employing the above cleaning steps, through gradient cleaning with acetone, anhydrous ethanol, and deionized water, combined with the physical vibration of ultrasound, organic contaminants and polar residues on the surface of the substrate can be removed sequentially, preventing impurities on the substrate from affecting subsequent micro-via processing.

[0029] Specifically, in step S3, the first pulsed laser is generated by a microsecond-level pulsed laser with an output power of 95-110W and a wavelength of 1065-1075nm.

[0030] By employing the aforementioned output power, it is ensured that the first pulse laser can continuously and fully heat, melt, and even vaporize or ionize the material within the channel, thereby achieving efficient material removal within the micro-hole.

[0031] Specifically, in step S4, the pulse energy of the second pulsed laser is 245–260 μJ, and the laser wavelength is 1028–1032 nm.

[0032] Adjustments are made within the aforementioned pulse energy range based on the actual substrate thickness and type to ensure that the second pulse laser has an extremely short duration and extremely high peak power.

[0033] In a specific embodiment of the present invention, two independent lasers are used to generate microsecond-level long pulses and picosecond-level ultrashort pulses, respectively, with different wavelengths. The two pulses are closely coordinated in time, acting on the same position of the workpiece within the same processing cycle, forming a real-time, mechanism-integrated synergistic effect.

[0034] Specifically, the pulse width of the second pulse laser is 4 to 6 ps.

[0035] When performing step S5, the pulse width of the second pulse laser can be extended, thereby expanding the effective area of ​​the optical filament and achieving the purpose of increasing the diameter of the micro-hole.

[0036] Specifically, in step S4, the predetermined time is 9 to 12 μs.

[0037] Considering filament induction efficiency, energy coupling stability, and processing quality, the optimal lead time between the microsecond-level laser pulse and the picosecond-level laser pulse is 10 μs. If the predetermined delay is too short, the energy packet of the microsecond pulse will not generate significant thermal accumulation on the substrate before the picosecond pulse triggers; if the predetermined delay is too long, the thermal excitation and free electrons induced by the microsecond laser will gradually relax, weakening the absorption enhancement effect of the material and thus reducing the stability of the picosecond laser-induced filament, consequently affecting processing efficiency and aperture consistency.

[0038] Using the aforementioned predetermined time, microsecond-level laser pulses and picosecond-level laser pulses synergistically act on the same area of ​​the processing substrate within the duration window of the picosecond-level laser pulse, completing energy coupling within the window period of the optical filament. The energy field of the microsecond pulse induces the generation of a plasma optical filament in the picosecond pulse, achieving instantaneous synchronization and relaxing the core pulse synergistic delay control requirements to the microsecond level. Furthermore, the microsecond-level delay can be stably and cost-effectively achieved through the electrical trigger signal of the laser itself, thus completely eliminating the reliance on precision optical delay lines, greatly simplifying the complexity of system timing control, and improving the reliability of the process and the feasibility of industrial applications. Specifically, in step S2, the distance between two adjacent micro-holes is 40-60 μm, and the laser processing path is zigzag.

[0039] Example 1 A method for fabricating micro-vias based on picosecond-microsecond composite lasers includes the following steps: S1: Take a 5cm x 5cm square processing substrate 1 with a thickness of 0.5mm. The material of processing substrate 1 is BK7 glass. Clean processing substrate 1 by immersing it in acetone solution and ultrasonically cleaning for 10 minutes; then immerse processing substrate 1 in anhydrous ethanol solution and ultrasonically clean for 10 minutes; then immerse processing substrate 1 in deionized water and ultrasonically clean for 10 minutes; subsequently, place it in a drying oven to dry, and then fix it on the processing plane; please refer to the processing system. Figure 1The processing system includes a processing substrate 1, a first pulsed laser 2, a first axial pyramid 3, a first lens 4, a second pulsed laser 5, a second axial pyramid 6, a second lens 7, a beam combiner 8, a beam splitter 9, and a charge-coupled device 10. The beam splitter 9 is used to reflect part of the picosecond-microsecond composite laser to the charge-coupled device 10. The charge-coupled device 10 is used to acquire image information of the processing area in real time and to monitor the laser focus position and the processing area online, thereby assisting in achieving precise alignment of the processing position. S2: Set the laser processing path: Set the distance between two adjacent micro-vias to 40μm, and the processing path to be zigzag; adjust the laser focus to be inside the processing substrate 1; S3: Generate and shape the first pulse laser: make the first pulse laser emitted by the first pulse laser 2 at the microsecond level, and make the first pulse laser pass through the first axial pyramid 3 and the first lens 4 to reach the beam combiner 8; wherein, the first pulse laser is a microsecond-level Bessel beam with a wavelength of 1070nm and a power of 100W. S4: After a predetermined interval, the second pulse laser is generated and initially shaped: 10 μs after the first pulse laser 2 emits a microsecond-level pulse laser, the second pulse laser 5 emits a picosecond-level second pulse laser, and the second pulse laser passes through the second axial pyramid 6 and the second lens 7 to reach the beam combiner 8; wherein, the second pulse laser is a picosecond-level Bessel beam with a laser wavelength of 1030 nm, a single pulse energy of 250 μJ, and a pulse width of 5 ps; S5: The first pulse laser and the second pulse laser are integrated through the beam combiner 8 and formed into a dual-color Bessel beam through the optical path. The beams work together at a predetermined position on the processing substrate 1. The picosecond Bessel beam first induces a long-lifetime, high-absorption transient plasma filament channel inside the processing substrate 1. The energy of the microsecond Bessel beam is selectively absorbed into the filament channel, and the material in the filament channel is efficiently ionized and removed to form a micro-via. Then, the micro-vias are sequentially processed along the laser processing path on the processing substrate 1 to form a micro-via array on the processing substrate 1.

[0040] Example 2 A method for fabricating micro-vias based on picosecond-microsecond composite lasers includes the following steps: S1: Take a 5cm × 5cm square processing substrate 1 with a thickness of 0.2mm. The material of processing substrate 1 is c-plane single crystal sapphire. Clean processing substrate 1 by immersing it in acetone solution and ultrasonically cleaning for 10 minutes; then immerse processing substrate 1 in anhydrous ethanol solution and ultrasonically clean for 10 minutes; then immerse processing substrate 1 in deionized water and ultrasonically clean for 10 minutes; subsequently, place it in a drying oven to dry, and then fix it on the processing plane; please refer to the processing system. Figure 1 ; S2: Set the laser processing path: Set the distance between two adjacent micro-vias to 60μm, and the processing path to be zigzag; adjust the laser focus to be inside the processing substrate 1; S3: Generate and shape the first pulse laser: make the first pulse laser emitted by the first pulse laser 2 at the microsecond level, and make the first pulse laser pass through the first axial pyramid 3 and the first lens 4 to reach the beam combiner 8; wherein, the first pulse laser is a microsecond-level Bessel beam with a wavelength of 1070nm and a power of 95W. S4: After a predetermined interval, the second pulse laser is generated and initially shaped: 10 μs after the first pulse laser 2 emits a microsecond-level pulse laser, the second pulse laser 5 emits a picosecond-level second pulse laser, and the second pulse laser passes through the second axial pyramid 6 and the second lens 7 to reach the beam combiner 8; wherein, the second pulse laser is a picosecond-level Bessel beam with a laser wavelength of 1030 nm, a single pulse energy of 245 μJ, and a pulse width of 5 ps; S5: The first pulse laser and the second pulse laser are integrated through the beam combiner 8 and formed into a dual-color Bessel beam through the optical path. The beams work together at a predetermined position on the processing substrate 1. The picosecond Bessel beam first induces a long-lifetime, high-absorption transient plasma filament channel inside the processing substrate 1. The energy of the microsecond Bessel beam is selectively absorbed into the filament channel, and the material in the filament channel is efficiently ionized and removed to form a micro-via. Then, the micro-vias are sequentially processed along the laser processing path on the processing substrate 1 to form a micro-via array on the processing substrate 1.

[0041] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these equivalent variations or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A method for fabricating micro-vias based on picosecond-microsecond composite lasers, characterized in that, Includes the following steps: S1: Clean and dry the substrate and fix it on the processing plane; S2: Set the laser processing path; S3: Generate and shape the first pulse laser; the first pulse laser is a microsecond-level Bessel beam; S4: After a predetermined interval, a second pulse laser is generated and initially shaped; the second pulse laser is a picosecond-level Bessel beam; S5: The first pulse laser and the second pulse laser are integrated through a beam combiner and acted synergistically at a predetermined position to form a micro-via; then, micro-vias are sequentially processed on the processing substrate along the laser processing path to form a micro-via array on the processing substrate.

2. The micro-via fabrication method based on picosecond-microsecond composite laser according to claim 1, characterized in that, In step S1, the processing substrate includes one of BK7 glass, SLG glass, quartz glass, sapphire, and silicon carbide.

3. The micro-via fabrication method based on picosecond-microsecond composite laser according to claim 1, characterized in that, In step S1, the cleaning process includes the following steps: immersing the substrate in acetone solution and ultrasonically cleaning for 8-11 minutes; then immersing the substrate in anhydrous ethanol solution and ultrasonically cleaning for 8-11 minutes; then immersing the substrate in deionized water and ultrasonically cleaning for 8-11 minutes.

4. The method for fabricating micro-vias based on picosecond-microsecond composite lasers according to claim 1, characterized in that, In step S3, the first pulsed laser is generated by a microsecond-level pulsed laser with an output power of 95-110W and a wavelength of 1065-1075nm.

5. The method for fabricating micro-vias based on picosecond-microsecond composite lasers according to claim 1, characterized in that, In step S4, the pulse energy of the second pulsed laser is 245–260 μJ, and the laser wavelength is 1028–1032 nm.

6. The method for fabricating micro-vias based on picosecond-microsecond composite lasers according to claim 5, characterized in that, The pulse width of the second pulse laser is 4 to 6 ps.

7. The method for fabricating micro-vias based on picosecond-microsecond composite lasers according to claim 1, characterized in that, In step S4, the predetermined time is 9 to 12 μs.

8. The method for fabricating micro-vias based on picosecond-microsecond composite lasers according to claim 1, characterized in that, In step S2, the distance between two adjacent micro-holes is 40-60 μm, and the laser processing path is zigzag.

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