Multilayer nano-copper film structure and its assisted sapphire substrate processing method

Abstract

This invention provides a multilayer copper film deposition-assisted sapphire substrate and its processing method, comprising a sapphire substrate, a first copper film, a second copper film, a third copper film, and a glass slide connected in sequence. The first copper film covers the surface of the sapphire substrate, the third copper film covers the surface of the glass slide, and the second copper film is located at the four corners of the first copper film and between the first and third copper films, thus forming an air gap between the first and third copper films. The multilayer nano-copper film structure of this invention can effectively suppress the generation of ablation cracks, and the resulting ablation pits exhibit a regular circular morphology, showing a certain improvement in the morphology of the ablation pits. Using nano-copper films instead of more expensive gold films reduces production costs to some extent.

Description

Technical Field

[0001] This invention relates to the field of laser nanofabrication, and more particularly to a multilayer copper nanofilm structure and its auxiliary sapphire substrate processing method. Background Technology

[0002] Sapphire (α-Al₂O₃), due to its high hardness, excellent chemical stability, and wide transmittance, is an ideal material for key components such as high-end optical windows and semiconductor substrates. Especially in the field of lasers, sapphire can be used to fabricate critical components such as laser diodes and laser cavities. However, these properties also make sapphire a typical difficult-to-machine material. Femtosecond lasers, due to their ultrafast pulse characteristics, can interact with materials through nonlinear effects, theoretically enabling "cold processing" of sapphire. This avoids damage such as the heat-affected zone (HAZ) and microcracks, and is one of the effective methods for achieving high-precision micro / nano processing of sapphire.

[0003] The high transparency of sapphire in the near-infrared band (e.g., 800 nm) results in extremely low direct absorption efficiency of femtosecond lasers. To overcome this obstacle, researchers have developed various auxiliary processing techniques. Among them, laser-induced back-side wet etching (LIBWE) utilizes the energy absorbed by the liquid on the back side of the substrate to process transparent materials, enabling the fabrication of complex three-dimensional structures. However, bubbles generated during the process can lead to geometric errors, and local overheating can easily induce microcracks. Another technique, laser-induced plasma-assisted ablation (LIPAA), effectively suppresses microcrack formation through ion bombardment. However, the mechanisms affecting key parameters of this technique (such as the distance between the target and the substrate) are still unclear, and pure plasma bombardment carries the risk of secondary damage such as graphitization. In contrast, laser-induced metal film-assisted ablation (LIMAA) enhances laser energy absorption by directly depositing a metal film (such as a gold film) on the sapphire substrate, resulting in a simpler process. Q. Wen et al. systematically studied the effect of nano-gold layers on the ablation performance of sapphire femtosecond lasers, finding that under conditions of 50 pulses and 150 μJ energy, the material removal rate was increased by 2.24 times, and the thermal crack density was lower. Nevertheless, the high cost of precious metal (such as gold) targets for LIMAA technology hinders large-scale applications; secondly, the uniformity of the metal film has a decisive impact on the ablation quality and consistency, placing stringent requirements on the deposition process.

[0004] There is an urgent need to develop a new, economical, efficient, and low-damage sapphire femtosecond laser micromachining method to address the problems of high cost, poor process stability, and inadequate thermodynamic damage control in existing auxiliary technologies. Summary of the Invention

[0005] This invention proposes a multilayer nano-copper film structure and an auxiliary sapphire substrate processing method to overcome or partially overcome the above-mentioned problems.

[0006] One aspect of the present invention provides a multilayer nano-copper film structure, comprising a sapphire substrate, a first copper film, a second copper film, a third copper film, and a glass slide connected in sequence. The first copper film covers the surface of the sapphire substrate, the third copper film covers the surface of the glass slide, and the second copper film is located at the four corners of the first copper film and between the first and third copper films, so that an air gap is formed between the first and third copper films.

[0007] Furthermore, the second copper film consists of four rectangular copper films located in the four corner regions of the first copper film.

[0008] Furthermore, the thickness of the first copper film is 10-50 nm, the thickness of the second copper film is 50-200 nm, and the thickness of the third copper film is 30-100 nm.

[0009] Furthermore, the thickness of the first copper film is 20 nm, the thickness of the second copper film is 100 nm, and the thickness of the third copper film is 60 nm.

[0010] In another aspect, the present invention provides a method for processing a sapphire substrate assisted by the multilayer nano-copper film structure described above, the method comprising: Assemble the multilayer nano-copper film structure by placing the sapphire substrate with the front side facing up and the side with the first copper film deposited facing down, so that the glass slide is located at the bottom of the entire structure, ensuring that the relative positions of the first copper film, the second copper film, the third copper film and the central air gap are fixed. A femtosecond laser source is used, and the femtosecond laser is incident in a direction perpendicular to the sapphire substrate. The laser is focused onto the third copper film on the upper surface of the transparent glass slide through a microscope objective. The femtosecond laser energy is absorbed by the third copper film, inducing the third copper film to evaporate and ionize, generating high-temperature and high-pressure plasma that is ejected upwards. Part of the plasma passes through the central air gap formed by the second copper film support and bombards the first copper film upwards, while another part transfers heat to the first copper film through the thermal conduction of the second copper film; thus, through the synergistic effect of the plasma and the multilayer copper film, low-damage ablation processing of the sapphire substrate is achieved.

[0011] Furthermore, the method also includes: Electron beam evaporation technology is used to deposit a first copper film on the lower surface of a sapphire substrate and a third copper film on the upper surface of a glass slide. The first copper film completely covers the lower surface of the sapphire substrate, and the third copper film completely covers the upper surface of the transparent glass slide. A second copper film is deposited at the four corners of the first copper film using mask positioning technology; The side of the sapphire substrate with the second copper film deposited is bonded to the side of the transparent glass slide with the third copper film deposited, and fixed with high-temperature adhesive to ensure a tight bond and a preset air gap between the first and third copper films.

[0012] Furthermore, the high-temperature, high-pressure plasma induced by the femtosecond laser undergoes inverse bremsstrahlung absorption when passing through the air gap, thereby increasing the internal energy of the plasma; and the high thermal conductivity of the first, second, and third copper films forms a synergistic energy coupling with the inverse bremsstrahlung absorption, resulting in a mixed absorption rate at the interface between the sapphire substrate and the first copper film that is greater than the absorption rate of conventional laser-induced metal film-assisted ablation.

[0013] Furthermore, the mixing absorption rate at the interface between the femtosecond laser and the first copper film... A mixed Compared with traditional laser-induced metal film-assisted ablation absorption rate A LIMAA The following relationship must be satisfied: , In the above formula, ΔA plasma The increase in absorptivity contributed by the inverse bremsstrahlung absorption effect. ΔA Cu The increase in absorption rate is the contribution of thermal conduction from the first copper film, the second copper film, and the third copper film.

[0014] The thickness design of the first, second, and third copper films is based on the following thermal resistance calculation model: , In the above formula, R For thermal resistivity, Δ d For copper film thickness, k Thermal conductivity, A The area of ​​the copper film; The first copper film has a thickness of 10-50 nm to ensure energy absorption; the second copper film has a thickness of 50-200 nm to ensure air gap stability and achieve thermal coupling; and the third copper film has a thickness of 30-100 nm to absorb laser light and generate plasma.

[0015] This invention provides a multilayer nano-copper film structure and its auxiliary sapphire substrate processing method. The multilayer nano-copper film structure includes a sapphire substrate, a first copper film, a second copper film, a third copper film, and a glass slide arranged sequentially. The first copper film covers the surface of the sapphire substrate, the third copper film covers the surface of the glass slide, and the second copper film is located at the four corners of the first copper film and between the first and third copper films, thus forming an air gap between the first and third copper films. The multilayer nano-copper film structure of this invention can effectively suppress the generation of ablation cracks, and the resulting ablation pits exhibit a regular circular morphology, showing a certain improvement in the morphology of the ablation pits. Using nano-copper films instead of more expensive gold films reduces production costs to some extent.

[0016] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0017] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. In the drawings: Figure 1 This is a schematic diagram of a multilayer copper nanofilm structure. Figure 2 A flowchart of a fabrication method for sapphire substrates assisted by a multilayer nano-copper film structure; Figure 3 This is a schematic diagram showing the relative positions of the multilayer copper nanofilm structure and the focusing objective of the femtosecond laser.

[0018] Figure 4 This is a schematic diagram of a multilayer copper nanofilm structure placed on a 3D displacement platform.

[0019] Figure 5 Simulation of the temperature field of a sapphire substrate assisted by a multilayer copper nanofilm structure under different power femtosecond laser ablation.

[0020] Figure 6 The images show the ablation morphology of the multilayer copper nanofilm structure, including: Figure 6 (a)-(c) show the morphology of ablation on bare sapphire. Figure 6 (d)-(f) show the morphology of ablation assisted by multilayer nano-copper films.

[0021] Figure 7 shows the comparative test results of the ablation morphology of the multilayer copper nanofilm structure with different laser pulse numbers as a function of power, where: Figure 7(a) shows the test results for a pulse count of 10. Figure 7(b) shows the test results for a pulse count of 20. Figure 7(c) shows the test results for a pulse count of 40. Figure 7(d) shows the test results for a pulse count of 60.

[0022] Figure 8 shows a comparative test of the ablation morphology with the number of pulses under different laser powers, where: Figure 8(a) shows the test results of the multilayer copper nanofilm structure. Figure 8(b) shows the test results for bare sapphire. Detailed Implementation

[0023] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0024] Reference Figure 1 The multilayer nano-copper film structure provided in this embodiment of the invention comprises, from top to bottom, a sapphire substrate 1, a first copper film 2, a second copper film 3, a third copper film 4, and a transparent glass slide 5. The first copper film 2 completely covers the lower surface of the sapphire substrate 1 (i.e., the surface layer that mates with the copper film), and the third copper film 4 completely covers the upper surface of the transparent glass slide 5 (i.e., the surface layer that mates with the copper film). The second copper film 3 is fixedly disposed between the first copper film 2 and the third copper film 4, precisely positioned at the four corners of the first copper film 2. Through the supporting effect of the second copper film 3, a stable central air gap is formed between the first copper film 2 and the third copper film 4. This air gap provides the necessary space for the subsequent transmission and energy coupling of femtosecond laser-induced plasma.

[0025] In this embodiment of the invention, a thin first copper film 2 is deposited on the surface of a sapphire substrate 1 to completely cover the substrate surface, forming a base layer; in a designated area on the base layer, four thicker second copper films 3 are deposited a second time using masking technology to form a locally thickened reinforcement layer structure.

[0026] In this embodiment of the invention, the second copper film 3 set at the four corners not only supports the first copper film 2 and forms an air gap, but also realizes local heat conduction between the first copper film 2 and the third copper film 4, laying a structural foundation for the synergistic energy coupling of plasma and multilayer copper films, and effectively solving the technical problems of energy dispersion and excessive heat-affected zone in traditional single-layer copper film assisted processing.

[0027] Furthermore, in a specific embodiment of the present invention, the second copper film 3 adopts four independent rectangular copper film structures, which correspond to the four corner regions of the first copper film 2 respectively. This structural design can minimize the use of copper film material and reduce production costs while ensuring support stability, and at the same time avoid excessive copper film coverage from affecting plasma transmission efficiency.

[0028] Furthermore, in this embodiment of the invention, the thickness of the first copper film 2 is set to 10-50 nm, preferably 20 nm. This thickness can ensure effective absorption of laser energy while avoiding heat accumulation caused by excessive thickness. The thickness of the second copper film 3 is set to 50-200 nm, preferably 100 nm, to ensure that it has sufficient support strength and heat conduction efficiency, so as to achieve stable support and heat transfer between the first copper film 2 and the third copper film 4. The thickness of the third copper film 4 is set to 30-100 nm, preferably 60 nm, to meet the energy absorption requirements of femtosecond laser back ablation and to quickly induce the generation of high-temperature and high-pressure plasma.

[0029] The reasonable limitation of the thickness of each copper film layer is based on the overall design of synergistic energy coupling: First, if the copper film thickness is too small, film discontinuity and insufficient light energy absorption will easily occur, while if the thickness is too large, heat diffusion will be aggravated and the heat-affected zone will be expanded; second, within the above-mentioned thickness range, the copper film can simultaneously satisfy the dual functions of spatial support and heat conduction; third, within the preferred thickness range, the copper film can efficiently absorb laser energy, ensuring stable plasma excitation. Under the limited thickness and preferred size matching, the overall structure can obtain the optimal mixed absorption rate, thereby forming a well-formed ablation microstructure and effectively suppressing the generation of sapphire microcracks.

[0030] Furthermore, this embodiment of the invention also provides a method for processing a sapphire substrate 1 assisted by a multilayer nano-copper film structure. This method specifically includes a deposition method for the multilayer nano-copper film structure and a femtosecond laser processing method for the sapphire substrate 1 based on this structure. The deposition method for the multilayer nano-copper film structure sequentially includes a pretreatment stage, a deposition stage, and a post-treatment stage. The specific operations of each stage are as follows: Furthermore, in the pretreatment stage, the sapphire substrate 1 is cleaned to remove contaminants from its surface to ensure the adhesion and deposition quality of the subsequent copper film deposition. The specific operations include: placing the sapphire substrate 1 in a solution of propanol and isopropanol for ultrasonic cleaning to remove surface oil, impurities and other contaminants; then rinsing the sapphire substrate 1 with ultrapure water to remove residual cleaning solution; and finally drying the surface of the sapphire substrate 1 with high-purity nitrogen to avoid water residue affecting the deposition effect.

[0031] In a specific embodiment of the present invention, the pretreatment stage is carried out as follows: a single-crystal sapphire substrate with a size of 5 mm × 5 mm, a thickness of 0.3 mm, and an Al2O3 purity of 99.997% is selected as the processing substrate. It is placed in a propanol solution and an isopropanol solution in sequence and ultrasonically cleaned for 20 minutes at room temperature to thoroughly remove contaminants from the substrate surface. Subsequently, the sapphire substrate is repeatedly rinsed with ultrapure water with a resistivity ≥18.2 MΩ·cm to remove residual propanol and isopropanol solutions from the surface. Finally, the surface of the sapphire substrate is dried with high-purity nitrogen gas with a purity of 99.999% in a uniform airflow to obtain a clean and dry sapphire substrate for later use.

[0032] Furthermore, in the deposition stage, high-vacuum electron beam evaporation technology is used to deposit multilayer copper films. The specific operation is as follows: the pretreated, cleaned, and dried sapphire substrate is fixed on the rotatable sample holder of the electron beam evaporation system, and the system parameters are adjusted to ensure that the vacuum degree of the electron beam evaporation system is better than 5.0 × 10⁻⁶. -4 Pa, the heating temperature is set to 300℃, an electron gun with a power of 10 kW is used, and a high-purity copper target is used as the evaporation source to ensure the purity and uniformity of the copper film deposition.

[0033] Further, the specific deposition steps of the multilayer copper nanofilm are as follows: First, an electron beam evaporation technique is used to deposit a first copper film 2 on a designated surface layer of the sapphire substrate 1 (i.e., the surface that will subsequently cooperate with the second copper film 3), and simultaneously a third copper film 4 is deposited on a designated surface layer of the transparent glass slide 5 (i.e., the surface that will subsequently cooperate with the second copper film 3). The first copper film 2 completely covers the corresponding surface layer of the sapphire substrate 1, and the third copper film 4 completely covers the corresponding surface layer of the transparent glass slide 5. Subsequently, a mask technique is used to precisely deposit the second copper film 3 at the four corners of the first copper film 2. Finally, the side of the sapphire substrate 1 with the second copper film 3 deposited is bonded to the side of the transparent glass slide 5 with the third copper film 4 deposited, and fixed with high-temperature adhesive to ensure that the two are tightly bonded and precisely positioned, while ensuring that a stable air gap is formed between the first copper film 2 and the third copper film 4.

[0034] In a specific embodiment of the present invention, the deposition process of the multilayer nano-copper film is further refined as follows: First, a continuous base copper film (i.e., the first copper film 2) with a thickness of 20 nm is deposited on the lower surface of the sapphire substrate, which completely covers the entire lower surface of the sapphire substrate; then, through mask positioning technology, secondary electron beam evaporation deposition is performed in the four corner regions of the first copper film 2 to form a square reinforced copper film structure with a local thickness of 100 nm (i.e., the second copper film 3). After deposition, the surface flatness of the nano-copper film is characterized by a profilometer. The results show that the surface undulation of the 20 nm thick first copper film 2 is controlled within 3 nm, and the surface undulation of the 100 nm thick second copper film 3 is controlled within 7 nm, which fully meets the high-quality requirements of subsequent femtosecond laser processing.

[0035] Furthermore, after deposition, the sapphire substrate 1 and glass slide 5 are cooled and then stored in a drying cabinet at a temperature controlled at 25°C. The deposited sapphire substrate 1 is then fixed onto the cover glass slide using high-temperature adhesive.

[0036] Furthermore, such as Figures 2-4 As shown, in this embodiment of the invention, the femtosecond laser processing of the sapphire substrate 1 requires first fixing the prepared multilayer nano-copper film structure onto a precision electric 3D displacement platform 7 to ensure the sample is firmly fixed and accurately positioned. Then, a femtosecond laser 6 is used to vertically irradiate it to achieve low-damage ablation of the sapphire substrate 1. The specific operation steps are as follows: S1. Assemble the multilayer nano-copper film structure by placing the sapphire substrate 1 with its front side facing up and the side with the first copper film 2 deposited facing down, so that the glass slide 5 is located at the bottom of the entire structure, ensuring that the relative positions of the first copper film 2, the second copper film 3, the third copper film 4 and the middle air gap are fixed. S2. A femtosecond laser source is used to make the femtosecond laser incident in a direction perpendicular to the sapphire substrate 1, and the laser is focused onto the third copper film 4 on the upper surface of the transparent glass slide 5 through a microscope objective. S3. The femtosecond laser energy is absorbed by the third copper film 4, inducing the third copper film 4 to evaporate and ionize, generating high-temperature and high-pressure plasma that is ejected upward. S4. Part of the plasma passes through the central air gap formed by the second copper film 3 and bombards the first copper film 2 upwards. Another part transfers heat to the first copper film 2 through the thermal conduction of the second copper film 3. This achieves low-damage ablation processing of the sapphire substrate 1 through the synergistic effect of plasma and multilayer copper films.

[0037] Specifically, in this embodiment of the invention, the plasma induced by the femtosecond laser exhibits a reverse bremsstrahlung absorption effect, which can efficiently absorb laser energy and reduce laser energy loss; simultaneously, the multilayer copper nanofilm possesses extremely high thermal conductivity (398 W·m). -1 ·K -1 The absorbed laser energy can be quickly conducted to the interface between the sapphire substrate 1 and the copper film. The inverse bremsstrahlung absorption effect of the plasma and the high thermal conductivity of the nano-copper film form a synergistic energy coupling effect, which significantly enhances the absorption efficiency of laser energy on the surface of the sapphire substrate 1, effectively reduces the ablation threshold of the sapphire, and thus realizes low-damage, high aspect ratio micromachining of the sapphire substrate 1, avoiding problems such as excessive heat-affected zone and edge cracks that occur in traditional processing methods.

[0038] Furthermore, in this embodiment of the invention, the high-temperature and high-pressure plasma induced by the femtosecond laser undergoes inverse bremsstrahlung absorption when passing through the air gap, thereby increasing the internal energy of the plasma; and the high thermal conductivity of the first copper film 2, the second copper film 3, and the third copper film 4 forms a synergistic energy coupling with the inverse bremsstrahlung absorption, resulting in a mixed absorption rate at the interface between the sapphire substrate 1 and the first copper film 2 that is greater than the absorption rate of conventional laser-induced metal film-assisted ablation.

[0039] Furthermore, the absorption coefficient of the reverse bremsstrahlung absorption effect α IB The following relationship must be satisfied: (1) In the above formula, n e and n i These are the electron and ion number densities, respectively. Z The average ion charge number. λ The wavelength of the laser. T e The absorption coefficient represents the electron temperature. This absorption coefficient is used to quantitatively characterize the plasma's ability to absorb femtosecond laser energy, thus providing theoretical support for the synergistic energy coupling between the plasma and the multilayer copper film.

[0040] Furthermore, the mixing absorption rate at the interface between the femtosecond laser and the first copper film 2 A mixed Compared with traditional laser-induced metal film-assisted ablation absorption rate A LIMAA The following relationship must be satisfied: (2) in, ΔA plasma The increase in absorptivity contributed by the inverse bremsstrahlung absorption effect. ΔA Cu The increase in absorption rate is contributed by the thermal conduction of the first copper film 2, the second copper film 3, and the third copper film 4, and satisfies... A mixed / A LIMAA >> 1. This ratio clearly demonstrates the advantages of the synergistic energy coupling between plasma and multilayer copper film in this invention, which can significantly improve the absorption efficiency of laser energy by the sapphire substrate 1, thereby reducing the ablation threshold and minimizing processing damage.

[0041] Furthermore, in this embodiment of the invention, the thermal conduction and thermal resistance of the first copper film, the second copper film, and the third copper film are defined by the following relationship: Fourier heat conduction formula: (3) In the above formula, Q represents heat flux. k Thermal conductivity, A Let Δ be the area of ​​the copper film. T For temperature difference, Δ d This represents the thickness of the copper film.

[0042] Furthermore, the thermal resistance calculation model obtained from the copper Fourier heat conduction formula is as follows: (4) In the above formula, P represents thermal power, and P = Q.

[0043] The thickness of the copper film determines the increment Δ of the thermal conductivity contribution absorptivity by adjusting the thermal resistance, effective heat transfer area, and light absorption capacity. A Cu If the film layer is too thin, the discontinuity of the film will reduce the heat transfer and absorption capacity; if the film layer is too thick, it will easily cause lateral heat diffusion. This invention optimizes Δ by limiting the reasonable thickness of each copper film layer, balancing thermal resistance and energy conduction. A Cu This enables localized energy concentration and low-damage ablation.

[0044] Furthermore, the ablation-completed sapphire substrate 1 needs to undergo post-treatment with acetone, isopropanol, and BOE solution, and the ablation morphology and ablation depth are obtained by scanning electron microscopy and profilometry.

[0045] Furthermore, this invention uses Comsol software to simulate laser ablation of a multilayer copper film structure. In a two-dimensional mode, the length of the sapphire substrate 1 is set to 150 μm and the height to 30 μm. The temperature distribution on the sapphire substrate 1 under femtosecond laser conditions of 5, 10, 15, and 20 μW using direct ablation and multilayer nano-copper film-assisted ablation methods is compared as follows: Figure 5 As shown, where Figure 5 (a) shows the simulation results of direct ablation. Figure 5 (b) shows the simulation results of multilayer copper film-assisted ablation. Analyzing the ablation temperature fields of both methods, under the same power of 20 μW, the high-temperature region in the temperature field of the multilayer copper nanofilm-assisted method appears more spatially concentrated, while that of direct ablation is relatively more dispersed. This observation suggests that the multilayer copper nanofilm-assisted method may more effectively concentrate energy at the target location, thereby potentially reducing heat diffusion to the surrounding material.

[0046] Furthermore, the femtosecond laser ablation test of sapphire in this embodiment of the invention is performed through the following steps: Step 1: Start-up and parameter settings of the femtosecond laser 6, using a Ti:sapphire ultrafast laser amplifier (Coherent Astrella), center wavelength 800 nm, pulse width 35 nm. f The laser energy was adjusted by rotating a half-wave plate and a thin-film polarizer, with the average power range set to 1–25 μW and monitored in real time by a power meter.

[0047] Step Two: Sample Fixation and Optical Focusing. The laser beam is vertically focused onto the sample surface through a 40x microscope objective (numerical aperture NA=0.75, ZEISS EC Plan-NEOFLUAR), as shown below. Figure 3 As shown. The copper-plated surface is used as the lower surface of the sapphire substrate 1 and is fixed to the precision electric 3D displacement platform 7 with high-temperature adhesive, as shown. Figure 4 As shown. The number of laser pulses (20–100 pulses) is controlled by an electronic shutter, and the scanning speed is set to 80 μm / s.

[0048] Step 3: Sample characterization and post-ablation treatment. After femtosecond laser ablation, the sample needs to be ultrasonically cleaned in propanol and isopropanol solutions at room temperature for 1 hour to remove surface contaminants. Then, it is placed in a polytetrafluoroethylene cup containing a portion of HF solution (49%) and ultrasonically cleaned for 1 hour. After that, it is washed with ultrapure water and dried.

[0049] Furthermore, Figure 6 The results of comparative tests on the ablation morphology of sapphire surfaces are shown. Sapphire was ablated using a multilayer copper nanofilm synergistic structure and a metal-free film deposition structure at a laser power of 10 μW. The ablation morphologies were recorded at ablation times of 2 s, 4 s, and 6 s, and characterized using scanning electron microscopy. Figure 6 (a)-(c) show the morphology of ablation on bare sapphire, and (c)-(f) show the morphology of ablation using a multilayer copper nanofilm synergistic method. Table 1 shows the ablation results obtained by repeating the experiment three times, with the best morphology recorded, and the diameter of the ablation pits also recorded.

[0050] Table 1 Comparison of ablation pit diameters Ablation time (t / s) Naked sapphire (d / μm) Synergistic ablation of multilayer nanocopper films (d / μm) t = 2s 10.15 17.57 t = 4s 11.35 19.87 t = 6s 13.17 22.24 The above experiments show that the average increase in diameter compared to direct ablation is 15% at different times, and no macroscopic cracks are generated in the ablation morphology of the multilayer copper film assisted method.

[0051] Furthermore, this invention also includes a comparative test of the ablation morphology with power variation under different laser pulse counts, as shown in Figure 7. Under conditions of 10 (Figure 7(a)), 20 (Figure 7(b)), 40 (Figure 7(c)), and 60 (Figure 7(d)) ​​laser pulse counts, the average laser power was gradually increased from 2 μW to 20 μW in 2 μW increments. Experimental data show that, at the same power, as the pulse count increases to 20, 40, and 60, the ablation diameter of the method of this invention increases by 1.53 μm, 1.67 μm, and 1.43 μm respectively compared to direct ablation at a power of 14 μW.

[0052] Furthermore, Figure 8 shows the comparative test results of ablation morphology with varying pulse counts under different laser powers. Based on the above tests, the difference between the two ablation morphologies is more pronounced at a laser power of 14 μW. Laser powers of 12, 14, and 16 μW were used, and the diameter of the ablation pits was recorded at pulse counts of 10, 20, 40, 60, and 80, as shown in Figures 8(a) and (b). The test results indicate that the multilayer copper nanofilm-assisted method achieves good ablation morphology results regardless of variations in ablation power and pulse count.

[0053] The mode field matching graded-gradient structure design for coupling sapphire fiber and single-mode fiber provided in this invention has two core design advantages: First, by fully bonding the input end of the mode field matching graded-gradient structure to the single-mode fiber and coaxially bonding the output end to the end face of the sapphire fiber, precise mode field matching is achieved among the mode field matching graded-gradient structure, single-mode fiber, and sapphire fiber, effectively reducing insertion loss and mode disturbance during optical signal transmission. Second, through the independent nonlinear graded-gradient profile design of the graded cladding and graded core, the total length of the transition region of the mode field matching graded-gradient structure is significantly shortened while strictly meeting the requirements of adiabatic mode conversion of optical signals. This makes the entire device structure more compact, mechanically stronger, and adaptable to the application requirements of high-temperature extreme environments.

[0054] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art and should not be interpreted in an idealized or overly formal sense unless specifically defined.

[0055] For the sake of simplicity, the method embodiments are described as a series of actions. However, those skilled in the art should understand that the embodiments of the present invention are not limited to the described order of actions, because according to the embodiments of the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions involved are not necessarily essential to the embodiments of the present invention.

[0056] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, any of the claimed embodiments can be used in any combination.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multilayer nanocopper film structure, characterized in that, The sapphire substrate, a first copper film, a second copper film, a third copper film, and a glass slide are arranged in sequence. The first copper film covers the surface of the sapphire substrate, the third copper film covers the surface of the glass slide, and the second copper film is located at the four corners of the first copper film and between the first and third copper films, so that an air gap is formed between the first and third copper films.

2. The multilayer copper nanofilm structure according to claim 1, characterized in that, The second copper film consists of four rectangular copper films located in the four corner regions of the first copper film.

3. The multilayer copper nanofilm structure according to claim 1 or 2, characterized in that, The thickness of the first copper film is 10-50 nm, the thickness of the second copper film is 50-200 nm, and the thickness of the third copper film is 30-100 nm.

4. The multilayer copper nanofilm structure according to claim 3, characterized in that, The thickness of the first copper film is 20nm, the thickness of the second copper film is 100nm, and the thickness of the third copper film is 60nm.

5. A method for processing a sapphire substrate assisted by a multilayer nano-copper film structure as described in any one of claims 1-4, characterized in that, The method includes: Assemble the multilayer nano-copper film structure by placing the sapphire substrate with the front side facing up and the side with the first copper film deposited facing down, so that the glass slide is located at the bottom of the entire structure, ensuring that the relative positions of the first copper film, the second copper film, the third copper film and the central air gap are fixed. A femtosecond laser source is used, and the femtosecond laser is incident in a direction perpendicular to the sapphire substrate. The laser is focused onto the third copper film on the upper surface of the transparent glass slide through a microscope objective. The femtosecond laser energy is absorbed by the third copper film, inducing the third copper film to evaporate and ionize, generating high-temperature and high-pressure plasma that is ejected upwards. Part of the plasma passes through the central air gap formed by the second copper film support and bombards the first copper film upwards, while another part transfers heat to the first copper film through the thermal conduction of the second copper film; thus, through the synergistic effect of the plasma and the multilayer copper film, low-damage ablation processing of the sapphire substrate is achieved.

6. The method according to claim 5, characterized in that, The method further includes: Electron beam evaporation technology is used to deposit a first copper film on the lower surface of a sapphire substrate and a third copper film on the upper surface of a glass slide. The first copper film completely covers the lower surface of the sapphire substrate, and the third copper film completely covers the upper surface of the transparent glass slide. A second copper film is deposited at the four corners of the first copper film using mask positioning technology; The side of the sapphire substrate with the second copper film deposited is bonded to the side of the transparent glass slide with the third copper film deposited, and fixed with high-temperature adhesive to ensure a tight bond and a preset air gap between the first and third copper films.

7. The method according to claim 5, characterized in that, The high-temperature, high-pressure plasma induced by the femtosecond laser undergoes inverse bremsstrahlung absorption as it passes through the air gap, increasing the internal energy of the plasma. Furthermore, the high thermal conductivity of the first, second, and third copper films forms a synergistic energy coupling with the inverse bremsstrahlung absorption, resulting in a mixed absorption rate at the interface between the sapphire substrate and the first copper film that is greater than the absorption rate of conventional laser-induced metal film-assisted ablation.

8. The method as described in claim 7, characterized in that, Mixed absorption rate at the interface between the femtosecond laser and the first copper film A mixed Compared with traditional laser-induced metal film-assisted ablation absorption rate A LIMAA The following relationship must be satisfied: ， In the above formula, ΔA plasma The increase in absorptivity contributed by the inverse bremsstrahlung absorption effect. ΔA Cu The increase in absorption rate is the contribution of thermal conduction from the first copper film, the second copper film, and the third copper film.

9. The method according to claim 8, characterized in that, The thickness design of the first, second, and third copper films is based on the following thermal resistance calculation model: , In the above formula, R For thermal resistivity, Δ d For copper film thickness, k Thermal conductivity, A The area of ​​the copper film; The first copper film has a thickness of 10-50 nm to ensure energy absorption; the second copper film has a thickness of 50-200 nm to ensure air gap stability and achieve thermal coupling; and the third copper film has a thickness of 30-100 nm to absorb laser light and generate plasma.

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