A method for processing micro-via of sapphire wafer array by ultrafast laser

Abstract

The application belongs to the technical field of ultrafast laser processing, and particularly discloses a sapphire wafer array micro-hole ultrafast laser processing method. In view of the problems that transparent hard and brittle materials such as sapphire are prone to edge collapse, cracks and hole matrix ablation in the process of ultrafast laser processing of high depth-diameter ratio and small-diameter array micro-holes, the method proposes to perform bidirectional processing on the transparent hard and brittle materials such as sapphire by using ultrafast laser. On the one hand, high damage rate of high pulse energy laser is used to remove materials quickly, so that the processing efficiency is improved and the internal stress of the material is controlled. On the other hand, various defects that occur when sapphire is processed by using high pulse energy laser are avoided through reasonable process design, so that the forming quality of the sapphire micro-hole is improved, and a new method for processing array micro-holes of thick sapphire wafers is provided.

Description

Technical Field

[0001] This invention relates to the field of ultrafast laser processing technology, specifically to an ultrafast laser processing method for sapphire wafer array micro-vias. Background Technology

[0002] 2.5D interconnect technology based on through-hole interconnects utilizes metal-filled through-holes (diameter: 50μm~100μm) within the interconnect to replace traditional wire bonding for vertical interconnection, reducing interconnect length, increasing signal transmission speed, and enabling low-power and high-speed communication between chips. In the era of high-frequency communication, next-generation interconnect materials such as sapphire and glass, due to their excellent insulation properties, ensure signal integrity while their higher mechanical strength and surface flatness allow for finer-pitch wiring, gradually becoming excellent alternatives to silicon-based interconnects.

[0003] However, the high hardness and brittleness of sapphire, along with its high reflectivity to lasers, make high-quality precision machining of sapphire a challenge. Rapid, high-quality forming technologies for sapphire micro-vias are rarely reported, severely restricting the development of sapphire devices. Commonly used sapphire through-hole machining technologies include abrasive jet machining, electrochemical discharge machining, rotary ultrasonic grinding, and focused ion beam machining. However, these technologies are often insufficient for the rapid machining of small-diameter micro-vias (50μm–100μm), and the machining quality is difficult to guarantee.

[0004] Ultrafast lasers, with their extremely high peak power and extremely short pulse width, can induce multiphoton absorption in materials, leading to physical processes such as avalanche ionization and Coulomb explosions. This allows them to damage almost any material, providing a new technological means for processing transparent, hard, and brittle materials such as sapphire. Simultaneously, the pulse width, shorter than the electron-phonon interaction time, gives ultrafast lasers a unique "cold processing" effect. Their energy deposition rate far exceeds the thermal diffusion rate, and the material is removed through vaporization, resulting in a minimal heat-affected zone and significant advantages in processing quality.

[0005] Although the unique nonlinear absorption effect enables ultrafast lasers to rapidly process transparent, hard, and brittle materials such as sapphire, the severe heat accumulation and intense stress wave impact generated by plasma expansion during the processing of high aspect ratio and small aperture micro-holes can still easily lead to problems such as microcracks, edge chipping, remelting layers, ablation particles, and molten material splashing, which seriously affect the forming quality of sapphire micro-holes. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing an ultrafast laser processing method for small-diameter array micro-vias on thick sapphire wafers. It primarily addresses the difficulties in processing small-diameter sapphire micro-vias and the problems of edge chipping, cracking, melt formation, and peri-hole substrate ablation during high-pulse-energy ultrafast laser processing of sapphire micro-vias. The method employs high-pulse-energy ultrafast laser processing to improve material removal rate while simultaneously proposing ultrafast laser bidirectional drilling to suppress various defects during high-pulse-energy ultrafast laser processing.

[0007] To achieve the above process, the present invention provides an ultrafast laser processing method for sapphire wafer array microvias, comprising the following steps:

[0008] Step 1: Place the sapphire sample in an ethanol solution for ultrasonic cleaning. After cleaning, remove and wipe it. Use a fixture to fix the sapphire sample on the processing platform. During the processing, coaxially blow dry air or inert gas.

[0009] Step 2: Set the laser parameters and scanning path, process blind holes on the lower surface of the sample, and deepen the blind hole by removing material layer by layer by adjusting the focus position;

[0010] Step 3: Set the laser parameters and scanning path, process the blind hole structure on the surface of the sapphire, and then use a high pulse energy laser to quickly drill through the hole to complete the through hole processing;

[0011] Step 4: Immerse the processed sapphire sample in a hydrofluoric acid solution to etch the surface deposits and the molten material inside the holes.

[0012] Preferably, in step one, the thickness of the sapphire sample is 200μm to 500μm, and the processing area on the lower surface of the sapphire is not obstructed during the assembly process. The inert gas blown coaxially is one of nitrogen, helium, and argon, and the gas pressure is 10psi to 50psi.

[0013] Preferably, in steps two and three, the ultrafast laser generated by the laser has a wavelength of 1030 nm, a pulse width of 0.25 ps to 10 ps, ​​a repetition frequency of 1 kHz to 1 MHz, and a pulse energy of 0 μJ to 200 μJ.

[0014] Preferably, in step two, when processing the blind hole on the lower surface, the laser scanning path used for processing each layer has the same shape, which is one or a combination of two of the following: a circle, a concentric circle, an annular vortex, and a vortex. The number of scanning circles is 500 to 10,000, the outer diameter of the scanning path is 10 μm to 45 μm, and the inner diameter is 0 μm to 35 μm. The specific parameters are adjusted according to the target hole diameter.

[0015] Preferably, in step two, the initial defocusing amount of the laser processing of the lower surface blind hole is -900μm to -300μm, the initial pulse energy is 2μJ to 20μJ, the diameter of the processed lower surface blind hole is larger than the diameter of the inner hole formed in the perforation stage (here, the diameter of the lower surface blind hole is the size of the lower surface blind hole opening; if the diameter of the lower surface blind hole is smaller than or equal to the diameter of the hole in the subsequent perforation stage, severe back substrate ablation will occur), and the depth of the blind hole is between 10μm and 200μm, with the specific value determined according to the target hole diameter and the actual surface quality requirements.

[0016] Preferably, in step two, while moving the focus upward to scan layer by layer, the scanning diameter and laser pulse energy of each layer are gradually reduced, the scanning layer spacing is 1μm to 50μm, the scanning diameter between consecutive layers is reduced by 0μm to 5μm, and the laser pulse energy is reduced by 0μJ to 5μJ.

[0017] Preferably, in step three, the perforation process is divided into two steps: blind hole processing on the upper surface and high-pulse energy laser perforation. The laser pulse energy used in the blind hole processing is 30μJ to 100μJ, and the laser defocusing amount is -700μm to 0μm. The laser pulse energy used in the perforation process is 150μJ to 200μJ, and the laser defocusing amount is -1mm to 0mm.

[0018] Preferably, in step three, the laser scanning path shape used in the upper surface blind hole processing and perforation process is one or a combination of two of the following: circular, concentric circle, annular vortex, and vortex. The number of processing circles is 20 to 200, and the scanning diameter is 5 μm to 45 μm.

[0019] Preferably, in step four, the hydrofluoric acid used for etching has a mass concentration of 40%, ultrasonic waves are used to assist the etching process, and the etching time is 0.5h to 12h.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The ultrafast laser processing method for sapphire wafer array micro-vias provided by the present invention enables rapid processing of array micro-vias with a diameter as low as about 50 μm and a spacing of 100 μm to 500 μm on sapphire wafers with a thickness of 200 μm to 500 μm. The obtained micro-vias are free from defects such as cracks and chipping and have high surface quality.

[0022] 2. The ultrafast laser processing method for micro-vias on sapphire wafer arrays provided by this invention introduces edge constraints by processing blind holes on the lower surface, thus avoiding large-area edge chipping on the back of the sapphire due to the crystal orientation effect caused by the fracture of single-crystal hard and brittle materials during subsequent high-pulse energy processing.

[0023] 3. The ultrafast laser processing method for sapphire wafer array micro-vias provided by this invention increases the depth of blind holes on the lower surface of the sapphire wafer while avoiding damage to the already formed micro-via profile during subsequent laser scanning by employing a dynamic modulation strategy of simultaneously shifting the focal spot upwards and reducing pulse energy and scanning diameter. Utilizing the shielding effect of the sidewalls of the blind holes on the lower surface and the internal molten material on the refracted beam, the ablation of the sapphire substrate around the holes caused by the absorption of refracted beam energy by the sapphire substrate around the holes is significantly suppressed.

[0024] 4. The sapphire wafer array micro-via ultrafast laser processing method provided by this invention utilizes high-pulse-energy ultrafast lasers for rapid perforation, improving processing efficiency. The upper surface perforation process is performed through a two-step laser scanning process. First, a blind hole is processed on the upper surface using a laser. The blind hole structure limits molten material splashing during the subsequent high-pulse-energy laser perforation process, preventing molten material from overflowing onto the hole opening surface.

[0025] 5. The ultrafast laser processing method for sapphire wafer array micro-vias provided by this invention effectively controls the internal stress of the sapphire wafer during the hole-making process, enabling high-density array hole processing without the appearance of obvious cracks.

[0026] 6. The ultrafast laser processing method for sapphire wafer array micro-vias provided by this invention has a simple process, high processing efficiency, and is conducive to large-scale group hole processing and practical industrial applications. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the tooling used in the method of the present invention.

[0028] Figure 2 This is a process flow diagram of the method of the present invention.

[0029] Figure 3 This is a schematic diagram of bidirectional drilling using the method of the present invention.

[0030] Figure 4 This is a step-by-step schematic diagram of the bidirectional drilling process of the present invention.

[0031] Figure 5 This is a schematic diagram of the negative defocusing position in the method of the present invention.

[0032] Figure 6 This is a schematic diagram of the scanning path of the method of the present invention.

[0033] Figure 7 The images show the top and bottom surfaces and cross-sectional morphology of the sapphire micro-hole obtained in Example 1.

[0034] Figure 8 The images show the top and bottom surfaces and cross-sectional morphology of the sapphire micro-hole obtained in Example 2.

[0035] Figure 9 This is a topographic image of the lower surface of the sapphire micro-hole obtained after processing using the comparative method.

[0036] In the figure: 1-Ultrafast laser beam, 2-Sapphire, 3-Fixing fixture, 4-Concave groove sample fixing platform, 5-Ultrafast laser beam for drilling the lower surface, 6-Beam movement direction during drilling the lower surface, 7-Laser scanning path for drilling the lower surface, 8-Scanning layer spacing, 9-Difference decrease in scanning diameter, 10-Blind hole on the lower surface, 11-Ultrafast laser beam for drilling the upper surface, 12-Laser scanning path for drilling the upper surface, 13-Blind hole on the upper surface, 14-Through hole, 15-Circular scanning path, 16-Concentric circular scanning path, 17-Annular vortex scanning path, 18-Vortex scanning path. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments are merely illustrative and not intended to limit the scope of the invention in any way. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0038] The ultrafast laser processing method for sapphire wafer array microvias proposed in this invention utilizes high-pulse-energy ultrafast lasers to process sapphire wafers, thereby improving the microvia forming speed. Simultaneously, a bidirectional drilling process is proposed: "blind holes are processed layer by layer on the lower surface, and blind holes are processed first on the upper surface before punching." This avoids problems such as cracking, molten material overflow, and peri-hole substrate ablation that occur during high-pulse-energy ultrafast laser processing of sapphire microvias. Thus, rapid and high-quality processing of microvias on high-hardness and brittle wafer materials is achieved. The overall process flow of this method is as follows: Figure 2 As shown, the machining diagram of the bidirectional drilling process is as follows. Figure 3 and 4 As shown.

[0039] Example 1

[0040] In this implementation, the experimental material was a C-face double-polished sapphire wafer with a sample thickness of 400 μm. The ultrafast laser generated a laser wavelength of 1030 nm and a pulse width of 500 fs, with a focused spot diameter of 20 μm and a galvanometer scanning speed of 500 mm / s. This implementation utilizes the proposed ultrafast laser processing method for sapphire wafer array microvias to achieve the processing of crack-free sapphire microvias with a diameter of 60 μm and a taper of less than 6°. Specifically, the process includes the following steps:

[0041] Step 1: Take a sapphire wafer sample measuring 10mm × 10mm × 0.4mm and immerse it in an ethanol solution for ultrasonic cleaning for 3 minutes. After cleaning, wipe it with lens paper to ensure the sample surface is clean and free of stains. Place the cleaned sapphire sample on the concave groove sample fixing platform, ensuring that the lower surface of the sample's processing area is not obstructed. Place two fixing clamps on the upper two sides of the sample, so that the sample is not easily moved during the sample stage movement due to pressure on both sides (e.g., ...). Figure 1 As shown in the figure, argon is used as a protective gas during the processing, and the gas flow pressure is set to 20 psi.

[0042] Step 2: Adjust the laser defocus to -900μm to -300μm (see diagram of negative defocus position). Figure 5 (As shown), repetition frequency 200kHz, pulse energy 2μJ~20μJ. The laser scanning path is set to "annular vortex line + circle" (e.g., Figure 6 As shown, the scanning circle count is 500-2000 circles for the annular vortex and 1000-5000 circles for the circular scan. The inner diameter of the annular vortex is 15μm and the outer diameter is 33μm, while the diameter of the circular scan path is 33μm. After a single layer is scanned, the laser pulse energy is adjusted to 10μJ-20μJ, the repetition frequency is 50kHz, and the defocusing amount is -500μm--400μm. The scanning diameter of each layer is reduced by 0μm-2μm, and the laser focus is controlled to move upward. The interlayer spacing is 20μm. During the upward focus movement, the pulse energy is reduced by 0μJ-5μJ, and scanning stops when the focus position reaches -300μm.

[0043] Step 3: Adjust the laser defocus to -700μm~0μm, and use an ultrafast laser with a pulse energy of 30μJ~100μJ in a vortex scanning path (e.g., Figure 6 As shown, blind holes are machined on the surface of sapphire with a scanning number of 20 to 200 revolutions and a scanning diameter of 23 μm. After the blind holes are machined, the laser pulse energy is changed to 150 μJ to 200 μJ, the defocusing amount is -1 mm to 0 mm, and the holes are rapidly drilled using a vortex line scanning method with a scanning number of 20 to 200 revolutions and a scanning diameter of 23 μm.

[0044] Step 4: Place the processed sample in a 40% hydrofluoric acid solution and ultrasonically immerse it for 1 hour to etch the surface deposited particles and the molten material inside the pores.

[0045] See Figure 7 As shown, this embodiment utilizes the method described in this invention to achieve the machining of crack-free sapphire micro-holes with a diameter of 60 μm, a depth-to-diameter ratio as high as 1:6.67, and a taper of less than 6°. This embodiment did not encounter problems such as edge chipping, cracking, melt formation, or ablation of the surrounding substrate during high-pulse-energy ultrafast laser processing, ensuring the machining quality of the micro-holes.

[0046] Example 2

[0047] In this implementation, the experimental material was a C-face double-polished sapphire wafer with a sample thickness of 400 μm. The ultrafast laser generated a laser wavelength of 1030 nm and a pulse width of 500 fs, with a focused spot diameter of 20 μm and a galvanometer scanning speed of 500 mm / s. This implementation utilizes the proposed ultrafast laser processing method for sapphire wafer array microvias to achieve the processing of crack-free sapphire microvias with a diameter of 50 μm and a taper of less than 7°. Specifically, the process includes the following steps:

[0048] Step 1: Take a sapphire wafer sample measuring 10mm × 10mm × 0.4mm and immerse it in an ethanol solution for ultrasonic cleaning for 3 minutes. After cleaning, wipe it with lens paper to ensure the sample surface is clean and free of stains. Place the cleaned sapphire sample on the concave groove sample fixing platform, ensuring that the lower surface of the sample's processing area is not obstructed. Place two fixing clamps on the upper two sides of the sample, so that the sample is not easily moved during the sample stage movement due to pressure on both sides (e.g., ...). Figure 1 As shown in the figure, argon is used as a protective gas during the processing, and the gas flow pressure is set to 40 psi.

[0049] Step 2: Adjust the laser defocus to -600μm to -400μm, repetition frequency to 200kHz, and pulse energy to 2μJ to 10μJ. Set the laser scanning path to a vortex line (e.g., ...). Figure 6 As shown, the number of scans is 2000 to 5000, and the vortex diameter is 33 μm. After a single layer is scanned, the laser pulse energy is adjusted to 10 μJ to 20 μJ, the repetition frequency to 50 kHz, and the defocusing amount to -600 μm to -400 μm. The scanning diameter of each layer is reduced by 0 μm to 2 μm, and the laser focus is moved upwards. The interlayer spacing is 30 μm. During the upward focus movement, the pulse energy is reduced by 0 μJ to 5 μJ, and scanning is stopped when the focus position reaches -300 μm.

[0050] Step 3: Adjust the laser defocus to -400μm to -100μm, and use an ultrafast laser with a pulse energy of 30μJ to 100μJ in a vortex scanning path (e.g., Figure 6 (As shown) Blind holes are machined on the surface of sapphire with 20 to 200 scans and a scanning diameter of 15 μm. After the blind holes are machined, the laser pulse energy is changed to 150 μJ to 200 μJ, the defocusing amount is -1 mm to 0 mm, and rapid drilling is performed using a vortex line scanning method with 20 to 200 scans and a scanning diameter of 15 μm.

[0051] Step 4: Place the processed sample in a 40% hydrofluoric acid solution and ultrasonically immerse it for 0.5 hours to etch the surface deposited particles and the molten material inside the pores.

[0052] See Figure 8 As shown, this embodiment uses the method described in this invention to achieve the machining of crack-free sapphire micro-holes with a diameter of 50 μm, a depth-to-diameter ratio as high as 1:8, and a taper of less than 7°. This embodiment did not encounter problems such as edge chipping, cracking, melt formation, or ablation of the surrounding substrate during high-pulse-energy ultrafast laser processing, ensuring the machining quality of the micro-holes.

[0053] Comparative Example

[0054] Based on the parameters of Example 1, the following two processing methods were tested in this comparative example: 1. No bidirectional drilling was performed, that is, no blind hole processing was performed on the lower surface (step two was not performed); 2. Bidirectional drilling was performed, but the diameter of the blind hole on the lower surface was smaller than the diameter of the inner hole formed in the perforation stage (the laser scanning path settings in step two were adjusted, the scanning path was still "annular vortex line + circle", the inner diameter of the annular vortex line was adjusted to 10 μm and the outer diameter to 23 μm, and the diameter of the circular scanning path was 23 μm).

[0055] See Figure 9 As shown, processing sapphire micro-through holes using only high-pulse energy without bidirectional drilling results in large-area chipping on the lower surface of the sapphire and ablation of the surrounding substrate. Furthermore, the smaller diameter of the blind holes on the lower surface compared to the inner hole diameter formed during the drilling stage leads to severe ablation defects in the substrate around the hole openings on the lower surface of the sapphire. This comparative example demonstrates the excellent suppression effect of the bidirectional drilling process proposed in this invention on defects such as chipping, cracking, and ablation of the surrounding substrate that occur during the processing of sapphire micro-through holes.

[0056] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for ultrafast laser processing of microvia arrays on sapphire wafers, characterized in that, Includes the following steps: Step 1: Place the sapphire sample in an ethanol solution for ultrasonic cleaning. After cleaning, remove and wipe it. Use a fixture to fix the sapphire sample on the processing platform. During the processing, coaxially blow dry air or inert gas. Step 2: Set the laser parameters and scanning path, process blind holes on the lower surface of the sample, and deepen the blind hole depth by removing material layer by layer by adjusting the laser focus position; the initial defocus amount of the laser processing of the blind hole on the lower surface is -900 μm ~ -300 μm, the initial pulse energy is 2μJ ~ 20μJ, the diameter of the processed blind hole on the lower surface is larger than the diameter of the inner hole formed in the perforation stage, and the depth of the blind hole is between 10 μm and 200 μm; while moving the focus upward to scan layer by layer, gradually reduce the scanning diameter and laser pulse energy of each layer, the scanning layer spacing is 1 μm ~ 50 μm, the reduction in scanning diameter between consecutive layers is 0 μm ~ 5 μm, and the reduction in laser pulse energy is 0 μJ ~ 5 μJ; Step 3: Set the laser parameters and scanning path, process the blind hole structure on the surface of the sapphire, and then use a high pulse energy laser to quickly drill through the hole to complete the through hole processing; Step 4: Immerse the processed sapphire sample in a hydrofluoric acid solution to etch the surface deposits and the molten material inside the holes.

2. The ultrafast laser processing method for sapphire wafer array microvias according to claim 1, characterized in that, In step one, the thickness of the sapphire sample is 200 μm to 500 μm. During the assembly process, it is ensured that the processing area on the lower surface of the sapphire is not obstructed. The coaxially blown inert gas is one of nitrogen, helium, or argon, and the gas pressure is 10 psi to 50 psi.

3. The ultrafast laser processing method for sapphire wafer array microvias according to claim 1, characterized in that, In steps two and three, the ultrafast laser generated by the laser has a wavelength of 1030 nm, a pulse width of 0.25 ps to 10 ps, ​​a repetition frequency of 1 kHz to 1 MHz, and a pulse energy of 0 μJ to 200 μJ.

4. The ultrafast laser processing method for sapphire wafer array microvias according to claim 1, characterized in that, In step two, when processing the blind holes on the lower surface, the laser scanning path used for processing each layer has the same shape, which is one or a combination of two of the following: a circle, a concentric circle, or a vortex. The number of scanning circles is 500 to 10,000, the outer diameter of the scanning path is 10 μm to 45 μm, and the inner diameter is 0 μm to 35 μm.

5. The ultrafast laser processing method for sapphire wafer array microvias according to claim 1, characterized in that, In step three, the perforation process is divided into two steps: blind hole processing on the upper surface and high-pulse energy laser perforation. The laser pulse energy used in the blind hole processing is 30μJ~100μJ, and the laser defocus is -700μm~0μm. The laser pulse energy used in the perforation process is 150μJ~200μJ, and the laser defocus is -1mm~0mm.

6. The ultrafast laser processing method for sapphire wafer array microvias according to claim 1, characterized in that, In step three, the laser scanning path shape used in the blind hole processing and perforation process on the upper surface is one or a combination of two of the following: circular, concentric circles, and vortex lines. The number of processing circles is 20 to 200, and the scanning diameter is 5 μm to 45 μm.

7. The ultrafast laser processing method for sapphire wafer array microvias according to claim 1, characterized in that, In step four, the hydrofluoric acid used for etching has a mass concentration of 40%, and ultrasonic waves are used to assist in the etching process. The etching time is 0.5h to 12h.

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