A method for high-quality exfoliation of large-size diamond by double-laser composite modification

Abstract

This invention discloses a high-quality exfoliation method for large-size diamonds using dual-laser composite modification, comprising the following steps: placing and fixing the sample on a three-dimensional moving platform, with the upper surface of the sample being the (100) crystal plane; focusing a laser generated by an ultrafast laser generator through the upper surface of the sample into the sample interior, and then performing a first point scan on the sample using the laser generated by the ultrafast laser generator to form an independent dot matrix structure; performing a second point scan on the sample using the laser generated by the ultrafast laser generator to form a crack-interconnected dot matrix structure; performing a third line scan on the sample using a laser generated by a nanosecond laser generator; and finally, ultrasonically exfoliating the sample in a water bath. This invention, by employing a dual-laser composite modification process combined with a biomimetic "honeycomb" and "tortoise shell" crack structure design, effectively guides the cracks to propagate directionally along the (100) crystal plane, avoiding the oblique cracking problem of the previous exfoliation surface being the (111) crystal plane, and greatly improving the integrity and smoothness of the exfoliation surface.

Description

Technical Field

[0001] This invention relates to the field of diamond wafer processing, and specifically to a method for high-quality removal of large-size diamonds through dual-laser composite modification. Background Technology

[0002] Diamond, possessing superior semiconductor properties compared to Si, GaN, and SiC, such as ultra-high thermal conductivity, insulation, and wide bandgap, holds promise as the ultimate fourth-generation semiconductor material. However, diamond's extremely high hardness and high chemical inertness are a double-edged sword, serving as the foundation for its superior performance while also presenting unprecedented challenges to its processing. These characteristics make it difficult to achieve efficient and low-damage processing of diamond wafers using traditional methods such as wire sawing and ion implantation, further hindering its development in semiconductor substrates and ultra-thin heat dissipation substrates. Therefore, developing efficient and precise diamond processing technologies has become a key area of ​​research in materials science and engineering. Among these, laser processing has emerged due to its high precision, non-contact nature, and versatility. In particular, laser lift-off technology for semiconductor wafer slicing has become a revolutionary technology in recent years.

[0003] Recently, Chinese invention patent applications CN115555744A, CN119082879A, CN120055592A, and CN120095380A have all reported laser lift-off technology for diamond. However, in the prior art, the final lift-off surface of diamond is always the (111) crystal plane.

[0004] The Vickers hardness of single-crystal diamond is approximately 80–120 GPa, with differences in hardness values ​​between different crystal planes: (100) < (110) < (111). Due to its strong anisotropy, the (111) crystal plane has the largest interplanar spacing and the highest atomic density, the lowest covalent bond formation energy, and the lowest covalent bond density between (111) crystal planes. Therefore, single-crystal diamond is very prone to dissociation along the (111) crystal plane, which limits its machinability. At the same time, cracks also tend to extend along the (111) crystal plane, resulting in poor fracture toughness of diamond. This is also the objective reason why the exfoliation surfaces in the prior art are all (111) crystal planes.

[0005] Studies have found that during the growth and epitaxy process, the (111) crystal plane is more prone to defects such as twins and stacking faults when used as the growth surface, making it difficult to produce a smooth surface. Therefore, in actual samples, most single-crystal diamonds grown using the (100) crystal plane are grown with the (100) crystal plane as the top surface. If the technology in existing patents is used to process conventional macroscopic samples with the (100) crystal plane as the main surface, the resulting samples are all inclined surfaces separated along the cleavage plane (111). When diamond is used as a semiconductor substrate or heat dissipation substrate, the surface flatness requirement is high. Therefore, how to perform high-quality peeling on the conventional (100) crystal plane and suppress the cleavage of the (111) plane is particularly important. Summary of the Invention

[0006] To address the shortcomings of existing technologies, such as the inability to suppress cleavage of the (111) crystal plane and the inability to peel off the (100) crystal plane, this invention provides a high-quality peeling method for large-size single-crystal diamond (100) facet wafers using dual-laser composite modification. This method can suppress cleavage of the (111) plane in conventional (100) CVD single-crystal diamond ingots and peel off to obtain complete (100) facet wafers.

[0007] The first aspect of this invention provides a method for high-quality exfoliation of large-size diamonds through dual-laser composite modification, comprising the following steps:

[0008] (1) Place the diamond sample to be stripped on a three-dimensional moving platform. The upper surface of the sample is the (100) crystal plane.

[0009] (2) The laser generated by the ultrafast laser generator is focused through the upper surface of the sample to a certain depth inside the sample. Then, the laser generated by the ultrafast laser generator is used to perform the first point scan on the sample to form an independent point array structure.

[0010] (3) The sample is scanned a second time using a laser generated by an ultrafast laser generator to form a lattice structure with interconnected cracks;

[0011] (4) Line scanning of the sample is performed using a laser generated by a nanosecond laser generator;

[0012] (5) Water bath ultrasonic peeling of samples.

[0013] Compared with existing technologies, the greatest advantage of this invention lies in achieving high-quality peeling on large-size single-crystal diamond with a conventional (100) crystal plane, successfully suppressing the problem of diamond's natural tendency to cleave along the (111) crystal plane. By employing a dual-laser composite modification process, combined with a biomimetic "honeycomb" and "tortoise shell" crack structure design, the cracks are effectively guided to propagate directionally along the (100) crystal plane, avoiding the oblique cracking problem of the previous peeling surface being the (111) crystal plane, and greatly improving the integrity and smoothness of the peeling surface.

[0014] Furthermore, this invention utilizes the complementary pulse widths of picosecond and nanosecond lasers to precisely control internal modification and crack propagation, achieving stable formation of the release layer and efficient crack propagation. Combined with a water bath ultrasonic exfoliation process, this simplifies the exfoliation process and improves the exfoliation quality. The overall process combines the advantages of high quality, low damage, and wide applicability, meeting the urgent need for high-quality diamond wafer exfoliation in fields such as semiconductor substrates and high-end heat dissipation substrates.

[0015] Preferably, in step (1), the roughness Sa of the upper surface of the diamond sample to be peeled is <5nm, the surface flatness of the diamond sample to be peeled is <20μm, and the lower surface of the diamond sample to be peeled is pre-treated by sanding.

[0016] More preferably, in step (1), the surface flatness of the diamond sample to be peeled is <10μm. This is to ensure the consistency of the laser-modified plane inside the diamond. In order to meet the flatness requirements during the processing, a sample with a polished upper surface and a frosted lower surface can be selected, which can reduce the tilt angle error caused by double-sided polishing.

[0017] This invention does not limit the selection of diamond samples. The diamond can be natural diamond or synthetic diamond, such as diamond prepared by chemical vapor deposition (CVD) and high-temperature high-pressure (HPHT) methods; it can be single-crystal diamond or polycrystalline diamond. Single-crystal diamond has different crystal planes (100), (110), and (111), and there may be tilt angles at these crystal planes, but as long as the upper surface of the sample being processed is flat, this invention is applicable. Similarly, the shape of the object being processed is not limited to this; as long as the upper surface is flat, it can be a bulk diamond crystal, a diamond ingot, a disc-shaped diamond wafer, etc. In short, as long as the diamond is a transparent, flat sample, this invention can be applied to complete slices of any nature, shape, size, and crystal plane.

[0018] Preferably, in step (2), the depth D of the laser generated by the ultrafast laser generator focusing through the upper surface of the sample into the interior of the sample is 80-600 μm. The focusing depth D in this invention can be adjusted according to the required peeling thickness.

[0019] Preferably, in step (2), the number of pulses in the first point scan is 1-100, the scanning interval is 10-50μm, and the energy is 1.5-10μJ.

[0020] Preferably, the pulse width of the laser from the ultrafast laser generator is in the range of 290 fs to 15 ps.

[0021] Preferably, the wavelength of the nanosecond laser generator is 532 nm, and the pulse width is < 10 ns.

[0022] Preferably, in step (2), the dot matrix structure is a structure of interconnected regular hexagons or a structure of interconnected rectangles.

[0023] Preferably, in step (3), the second dot scanning position is the center of each regular hexagon of the interconnected regular hexagons or the center of each rectangle of the interconnected rectangle structure.

[0024] In step (4), the line scanning can adopt a "Z"-shaped line scanning, and the frequency, energy magnitude, scanning speed, and scanning pitch are adjusted in real time according to the peeling thickness. In addition, in order to obtain wafers with different peeling effects, other scanning methods such as cross scanning and "return" shape can also be adopted, which are not particularly limited in the present invention.

[0025] Preferably, in step (5), the parameters of the water bath ultrasonic wave are: power is 150 - 250 W, water temperature is 50 - 70 °C, and the frequency is in a frequency sweeping mode.

[0026] The second aspect of the present invention provides a system used for the method of realizing high-quality peeling of large-size diamond by dual-laser composite modification, including: an ultrafast laser processing system, a nanosecond laser processing system, a three-dimensional displacement platform, and a control system; the ultrafast laser processing system includes an ultrafast laser generator, a first reflecting mirror, a first half-wave plate, a first beam splitting polarizer, a first beam expander, a second reflecting mirror, a first spatial light modulator, a first 4f system lens, a second 4f system lens, a third reflecting mirror, a first beam splitter, a first CCD camera, and a first objective lens; the nanosecond laser processing system includes a nanosecond laser generator, a fourth reflecting mirror, a second beam expander, a second half-wave plate, a second beam splitting polarizer, a fifth reflecting mirror, a second spatial light modulator, a third 4f system lens, a fourth 4f system lens, a second beam splitter, a second CCD camera, and a second objective lens.

[0027] In the present invention, optical control devices such as 4f systems and spatial light modulators are integrated in both laser systems. Through multi-focus parallel processing and dynamic spot shaping, not only the dot matrix modification efficiency is significantly improved, but also the crack propagation direction and scanning coverage uniformity are optimized, providing guarantee for large-area rapid processing. By spherical aberration correction, the influence caused by a large refractive index inside the material is reduced, the consistency of the modified plane is ensured, and the roughness of the peeling surface is reduced.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] (1) The multi-pulse-width laser cooperation strategy of dual-laser composite modification

[0030] This invention employs a composite refining method combining picosecond and nanosecond lasers, which complement each other in terms of pulse width, energy, and functional division. The picosecond laser is used to achieve high-precision internal refining structures, while the nanosecond laser is used for macroscopic crack propagation based on thermal stress. The combination of the two effectively achieves high-quality peeling of large-size single-crystal diamond (100) wafers.

[0031] (2) Biomimetic structural design to control crack path and suppress cleavage tendency

[0032] This invention introduces for the first time biomimetic crack structures of "honeycomb" and "tortoise shell" shapes. By constructing multi-level modified regions through double picosecond laser dot matrix scanning, it effectively suppresses the tendency of diamond to naturally cleave along the (111) crystal plane, realizes the directional and stable propagation of cracks in the (100) crystal plane, and improves the integrity and surface quality of the peeled wafer.

[0033] (3) Stress difference-driven large crack propagation mechanism

[0034] This invention utilizes the stress difference between the material phase transition structure induced by picosecond lasers and the thermal excitation by nanosecond lasers to trigger large-area crack propagation within a predetermined (100) plane. This method avoids the uncontrollability of random crack propagation, ensures the consistency of the peeling interface, and controls the final wafer thickness.

[0035] (4) Non-destructive and efficient water bath ultrasonic ablation process

[0036] Unlike traditional adhesive pull-out or mechanical impact peeling methods, this invention uses variable frequency ultrasonic technology in a temperature-controlled water bath environment to achieve spontaneous peeling of diamond wafers, avoiding surface contamination and mechanical damage, and obtaining high-quality (100)-faceted wafers with a roughness better than 2μm.

[0037] (5) Wide range of applicable sample types and morphological conditions

[0038] This invention is applicable to diamond materials from various sources, including CVD, HPHT, and natural single-crystal diamonds. It is not limited by sample size (up to wafer-level diamond slices; due to the difficulty and slowness of diamond growth, sizes above 7*7mm are generally considered large; considering cost-effectiveness, the maximum slice size demonstrated in this embodiment is 10*10mm), shape (block or sheet), or crystal angle. As long as the sample surface has a certain degree of flatness, this invention can be implemented. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the process for achieving high-quality exfoliation of large-size diamonds through dual-laser composite modification according to the present invention.

[0040] Figure 2 This is a schematic diagram of the optical path for dual-laser composite material modification.

[0041] Figure 3 This is a schematic diagram of the diamond crystal structure;

[0042] Figure 4 This is a schematic diagram of a laser beam focused inside a sample.

[0043] Figure 5 This is a schematic diagram of the scanning process during the first application of the picosecond laser in Example 1;

[0044] Figure 6 This is a schematic diagram of the scanning process during the second action of the picosecond laser in Example 1;

[0045] Figure 7 This is a schematic diagram of the scanning process during nanosecond laser action in Example 1;

[0046] Figure 8 This is a schematic diagram of water bath ultrasonic ablation.

[0047] Figure 9 Photographs of the sample's peeled surface and laser confocal microscope images;

[0048] Figure 10 This is a schematic diagram of laser scanning in Example 2.

[0049] Appendix Figure 2 Middle Marker:

[0050] 1-Ultrafast laser generator, 2-First reflecting mirror, 3-First half-wave plate, 4-First beam splitter polarizer, 5-First beam expander, 6-Second reflecting mirror, 7-First spatial light modulator (SLM), 8-First 4f system lens, 9-Second 4f system lens, 10-Third reflecting mirror, 11-First beam splitter, 12-First CCD camera, 13-First objective lens, 14-Three-dimensional displacement platform, 15-Sample, 16-Control system, 17-Nanosecond laser generator, 18-Fourth reflecting mirror, 19-Second beam expander, 20-Second half-wave plate, 21-Second beam splitter polarizer, 22-Fifth reflecting mirror, 23-Second spatial light modulator (SLM), 24-Third 4f system lens, 25-Fourth 4f system lens, 26-Second beam splitter, 27-Second CCD camera, 28-Second objective lens. Detailed Implementation

[0051] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0052] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0053] The process flow diagram of the method for high-quality exfoliation of large-size diamonds using dual-laser composite modification according to the present invention is attached. Figure 1 As shown, it includes the following three parts:

[0054] (1) Preparations before laser processing, including sample selection and placement, laser selection and focusing;

[0055] (2) Modification process and crack propagation during laser processing, including picosecond laser first processing, picosecond laser second processing, and nanosecond laser processing;

[0056] (3) After laser processing, an ideal wafer is obtained, and a high-quality wafer with (100) face is obtained by water bath ultrasonic peeling.

[0057] Appendix Figure 2 This is a schematic diagram of the optical path for dual-laser composite refining in this invention. The optical path is mainly divided into two parts: one is the ultrafast laser processing system (attached). Figure 2 One is a serial number 1-13), and the other is a nanosecond laser processing system (attached). Figure 2 (Sections 17-28). In the ultrafast laser processing system, the ultrafast laser generator 1 has two selectable wavelengths of 1030 / 515nm and an adjustable pulse width of 290fs-15ps. The ultrafast laser is generated from the ultrafast laser generator 1, passes through a series of optical components 2-11, and is finally focused on the sample to be processed by the 50x first objective lens 13. The image is then fed back to the control system 16 in real time through the first CCD camera 12. In the nanosecond laser processing system, the nanosecond laser generator 17 has a wavelength of 532nm and a pulse width of <10ns. The nanosecond laser is generated from the nanosecond laser generator 17, passes through a series of optical components 18-26, and is finally focused on the sample to be processed by the second objective lens 28. The image is then fed back to the control system 16 in real time through the second CCD camera 27. The nanosecond laser optical path also incorporates a spatial light modulator 23 and a 4f system 24-25. Besides the aforementioned focus modulation (parallel multifocal and spherical aberration correction), this group of optical elements can also be used to shape the beam, for example, transforming a conventional circular spot into an ellipsoidal or linear spot. After beam shaping, the crack propagation effect can be enhanced during processing, thereby increasing the scanning interval and further improving processing efficiency.

[0058] A schematic diagram of the single-crystal diamond crystal structure in an embodiment of the present invention is shown below. Figure 3Single-crystal diamond belongs to the cubic crystal system, and its three-dimensional structure contains numerous equivalent crystal planes. Within a crystal, crystal planes with identical interplanar spacing and atomic distribution, differing only in spatial orientation, can be grouped into the same family of crystal planes. For example, in the diamond crystal structure, (100), (010), (001), The crystal planes all belong to the {100} crystal plane family and together form a regular hexahedron, with its six crystal planes being equivalent; similarly, its (110), (101), (011), The crystal planes all belong to the {110} crystal plane family and together form a dodecahedron; its (111), They belong to the {111} crystal facet family and form an octahedron. Since the (111) crystal facet is a cleavage plane, this is why natural diamonds usually appear as octahedrons. It should be noted that the (100), (110), and (111) crystal facets mentioned in this invention usually refer to the {100}, {110}, and {111} crystal facet families.

[0059] Example 1

[0060] This embodiment provides a method for high-quality exfoliation of large-size diamonds using dual-laser composite modification. The dual-laser composite modification method for high-quality exfoliation of large-size diamonds in this embodiment is as shown in the attached figure. Figure 2 The schematic diagram of the dual-laser composite refining optical path shown includes the following steps:

[0061] S1: The object to be processed is CVD block single crystal diamond (3*4*1mm, 7*7*1mm, 10*10*3mm). In this embodiment, the size is 10*10*3mm. The (100) surface with an offset angle of 0° on the main surface is placed and fixed on the three-dimensional displacement platform 14.

[0062] S2: The upper surface of the sample is a smooth, polished surface. The first CCD camera 12 focuses on the sample surface and captures an image, which is then displayed on the computer screen. The computer control system moves the three-dimensional displacement platform upwards a certain distance, allowing the laser beam to penetrate the sample's upper surface and focus at a preset depth within the sample. For example... Figure 4The diagram shows a laser beam focused at a certain depth inside the sample in an embodiment of the present invention. The laser beam passes through the (100) crystal plane 15a on the upper surface of the sample and is focused onto the (100) crystal plane 15b at a certain depth inside the sample. The focusing depth D can be adjusted according to the required peeling thickness (80-600μm). In addition, in order to better allow the laser to pass through the upper surface and reduce energy loss during the energy transfer process, the diamond upper surface 15a is selected as a smooth surface after polishing, Sa<5nm. Furthermore, in order to ensure the consistency of the laser-modified plane inside the diamond, the surface flatness of the processed sample should be less than 20μm (within 10μm for best results). To meet the flatness requirements during the processing, a sample with one side polished (upper surface 15a) and the other side ground (lower surface 15c) can be selected, which can reduce the tilt angle error caused by double-sided polishing.

[0063] S3: The aforementioned bulk single-crystal diamond was subjected to the first laser processing modification using a picosecond laser (290 fs - 15 ps). A schematic diagram of the scanning process during the first picosecond laser treatment is attached. Figure 5 As shown, after the laser is focused to a certain depth inside the sample, the three-dimensional moving platform 14 is controlled by the control system 16 to scan point by point in the two-dimensional plane (y, z). The number of pulses, scanning interval and energy are adjusted according to the thickness of the strip. The ranges are the number of pulses (1-100), scanning interval (10-50μm) and energy (1.5-10μJ). These laser-modified particles are periodically distributed on the same (100) plane inside the sample, like a hexagonal "honeycomb". Since the spacing between the modified particles is inconsistent at this time, the influence between them is small. Therefore, no cracks will appear along the (111) slope on the entire modified surface. At this time, the honeycomb plane is like a macroscopic "bamboo joint", which firmly controls the subsequent crack changes within the same (100) plane.

[0064] The purpose of this step is to limit the cleavage of the (111) plane. Inspired by the biomimetic structural design ideas of bamboo joints separating crack paths and honeycomb in nature, a special laser dot matrix process is adopted. These laser-modified particles are periodically and alternately distributed on the same (100) plane inside the sample, like a hexagonal "honeycomb". Since the spacing between the modified particles is inconsistent at this time, the influence between them is small. Therefore, no cracks will appear along the (111) slope on the entire modified surface. At this time, the honeycomb plane is like a macroscopic "bamboo joint", which firmly controls the subsequent crack changes within the same (100) plane. Due to the different lasers or sample selections, the degree of phase transition is different. The structural morphology and composition of modified particles, lines and surfaces can be diverse, and can be roughly divided into metastable diamond structures, amorphous carbon, mixed structures of sp3 diamond and sp2 graphite intertwined, and individual sp2 graphite structures, etc.

[0065] S4: The above sample was subjected to a second laser processing using an ultrafast picosecond laser (290 fs - 15 ps). A schematic diagram of the scanning process during the second picosecond laser treatment is attached. Figure 6 As shown. This process is based on step S3. At this point, the laser modification starting points are offset by L3 and L2 in the y and z directions, respectively. The side length of the hexagonal "honeycomb" is L1. Through geometric relationships, the offset spacing of the second pass can be calculated as L2 and L3 (i.e., L3:L2:L1 = 1:√3:2). This ensures that the laser modification points are precisely filled in the center of the hexagonal modification matrix from the previous process. Then, a method using... Figure 5 Laser point-by-point scanning was performed using the same process parameters. The beneficial effect of this step is that by filling the central modified point, the originally independent modified points are connected by micro-level cracks. At this time, the micro-cracks grow along the (100) plane and eventually cover the entire modified plane, forming a cracked morphology like a "tortoise shell".

[0066] The purpose of this step is to form interconnected microcracks on the (100) plane. Inspired by the crack morphology of the tortoise shell surface, a special laser dot matrix process is used again. At this time, the laser-modified particles need to be precisely filled in the center of the hexagonal modification matrix of the previous process, thereby forming an interconnected (100) plane of microcracks. This process can not only connect the microcracks on the plane to form a complete (100) modified surface, but also further suppress the crack growth on the (111) cleavage surface.

[0067] S5: The sample is subjected to a third laser processing using a nanosecond laser generator 17. A schematic diagram of the scanning process during nanosecond laser operation is attached. Figure 7 As shown. This process is one of the core steps and is crucial in determining the subsequent peeling process. Unlike the previous two point-by-point scanning methods, this scanning method is a line scan. The control system 16 controls the three-dimensional moving platform 14 to perform a "Z"-shaped line scan in the two-dimensional plane (y, z). The frequency, energy level, scanning speed, and scanning spacing L4 are adjusted in real time according to the peeling thickness. It should be noted that the nanosecond laser system and the ultrafast laser system of this invention are two independent systems; ensuring the consistency of the action positions between the different systems is particularly important. This embodiment... Figure 2The second spatial light modulator 23, the third 4f system lens 24, and the fourth 4f system lens 25 can not only adjust the beam shape, thereby increasing the scanning interval and improving efficiency, but also further correct the spherical aberration of the focal point, thereby ensuring the consistency of the modified surface and reducing deviation. In addition, in order to obtain wafers with different peeling effects, other scanning methods such as cross scanning and "U"-shaped scanning can also be adopted. The beneficial effects of this step are: after the first two precise lattice processes, the crack growth of the (111) cleavage plane is successfully suppressed, and at this time, the (100) modified surface with interconnected microcracks has been formed inside the diamond sample. Further irradiating the modified surface with a nanosecond laser with a longer pulse width can promote the full propagation of microcracks and form large cracks in the (100) plane.

[0068] The purpose of this step is to further expand the large cracks based on the interconnection of microcracks on the (100) plane, so as to facilitate subsequent peeling. Compared with the picosecond pulse of the ultrafast laser, the narrow nanosecond pulse with a slightly larger pulse width is chosen for further action, which is essentially to utilize its thermal effect without causing excessive thermal damage. Because the picosecond laser causes changes in the composition and structure between the modified layer and the original layer, their coefficients of thermal expansion differ. The further action of the narrow nanosecond laser will create a significant stress difference between the modified layer and the original layer. The stress will be released along the (100) plane of the microcracks modified in the previous process, thereby realizing the expansion of large cracks in the internal interface layer.

[0069] S6: The final sample is placed at the bottom of a glass beaker containing deionized water, and then subjected to ultrasonic treatment in a water bath to obtain a high-quality wafer with the (100) facet. A schematic diagram of ultrasonic peeling in a water bath is attached. Figure 8 As shown, the sample was placed at the bottom of a glass beaker, filled with about 2 / 3 volume of deionized water, and water bath ultrasound was started. The ultrasound parameters were set as follows: power 200W (100%), water temperature 60℃, and frequency in sweep mode, that is, periodically changing within a fixed frequency range (e.g., 40kHz→120kHz→40kHz) to avoid standing wave formation and make the sound field distribution more uniform. After about five minutes of ultrasound, the sample can spontaneously peel off the (100) surface. This ultrasonic peeling method is simple and efficient. Compared with other existing technologies that use adhesive and pull to peel it off, its peeling surface quality is higher and no adhesive removal is required. Compared with existing technologies that use tungsten needles for positioning and external force to peel it off, its action is simple and causes almost no damage to the sample.

[0070] Images of the exfoliated surfaces and laser confocal microscope images of the diamond samples prepared in the examples are shown below. Figure 9As shown, it can be seen from the figure that the peeling size of the sample reaches 10*10 mm, and the peeled sample is complete with a delicate surface and no damage. The morphology and roughness of the peeling surface were characterized by a laser confocal microscope, and the surface roughness Sa values were: b1 = 1.794 μm, b2 = 1.576 μm, b3 = 2.057 μm, c1 = 2.136 μm, c2 = 2.480 μm, c3 = 2.084. The average surface roughness was calculated to be 2.021 μm, indicating that the quality of the peeling surface is relatively high.

[0071] Example 2

[0072] In Example 1, the laser dot scanning method is a regular hexagon structure. This Example 2 mainly describes the second dot scanning method (rectangular structure). Without special instructions, the other method steps are the same as those in Example 1, so they will not be elaborated in this example.

[0073] As Figure 10 shown, it is the laser scanning schematic diagram of Example 2. The processing object is CVD bulk single crystal diamond (3*4*1 mm). Figure 10 (b) is the scanning process schematic diagram when the picosecond laser acts for the first time. The "return" shaped scanning method is adopted to form a rectangular modified structure. In this dot matrix process, the point spacing L5 in the y direction and the point spacing L6 in the z direction are consistent (i.e., L5 = L6), and the other specific laser parameter settings are the same as those in Example 1. Figure 10 (c) is the scanning process schematic diagram when the picosecond laser acts for the second time. This process is carried out on the basis of the Figure 10 (b) process. At this time, the laser modification starting points are offset from the origin by a distance of half of the origin spacing L7 and L8 in the y and z directions respectively (i.e., L8 = L7 = 1 / 2L6 = 1 / 2L5), ensuring that the laser modified points are accurately filled in the center of the square modified matrix of the previous process, and then the laser is scanned point by point in a "return" shape with the same process parameters as Figure 10 (b). Figure 10 (d) is the scanning process schematic diagram when the nanosecond laser acts, and its scanning spacing L4 and other process parameter settings can be referred to Example 1.

[0074] The beneficial effect of this example is that by adopting this "return" shaped dot matrix scanning method from the outside to the inside, in addition to being able to inhibit the cleavage of the (111) crystal plane like Example 1, it can also ensure the consistency of the modification degree from the edge to the center part, thereby further ensuring the success of subsequent water bath ultrasonic peeling and reducing the roughness of the peeling surface.

[0075] In summary, inspired by biomimetic structural design principles found in nature, such as the propagation of microcracks in tortoise shells and the separation of crack paths in bamboo joints, this invention employs a dual-pulse laser composite modification process. This process has successfully achieved high-quality peeling of diamonds of various sizes (3*4*1mm, 7*7*1mm, and 10*10*3mm) with a peeling surface roughness of only 2μm. This invention provides a high-quality and stable solution for the high-end diamond processing field.

[0076] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for high-quality exfoliation of large-size diamonds through dual-laser composite modification, characterized in that, Includes the following steps: (1) Place the diamond sample to be stripped on a three-dimensional moving platform. The upper surface of the sample is the (100) crystal plane. (2) The laser generated by the ultrafast laser generator is focused into the sample to a certain depth through the upper surface of the sample, and then the laser generated by the ultrafast laser generator is used to perform the first point scan on the sample to form an independent point array structure. (3) The sample is scanned a second time using a laser generated by an ultrafast laser generator to form a lattice structure with interconnected cracks; (4) A third line scan of the sample is performed using a laser generated by a nanosecond laser generator; (5) Water bath ultrasonic peeling of samples; In step (2), the lattice structure is an interconnected regular hexagon or an interconnected rectangular structure; In step (3), the second point scan position is the center of each of the interconnected regular hexagons, or the center of each of the interconnected rectangular structures; The first and second point scans use picosecond lasers; the third line scan uses nanosecond lasers.

2. The method for high-quality exfoliation of large-size diamonds using dual-laser composite modification according to claim 1, characterized in that, In step (1), the roughness Sa of the upper surface of the diamond sample to be peeled is <5 nm, the surface flatness of the diamond sample to be peeled is <20 μm, and the lower surface of the diamond sample to be peeled is pre-treated by sanding.

3. The method for high-quality exfoliation of large-size diamonds using dual-laser composite modification according to claim 1, characterized in that, In step (2), the laser generated by the ultrafast laser generator penetrates the upper surface of the sample and is focused into the interior of the sample to a depth D of 80-600 μm.

4. The method for high-quality exfoliation of large-size diamonds using dual-laser composite modification according to claim 1, characterized in that, In step (2), the number of pulses in the first point scan is 1-100, the scanning interval is 10-50 μm, and the energy is 1.5-10 μJ.

5. The method for high-quality exfoliation of large-size diamonds using dual-laser composite modification according to claim 1, characterized in that, The pulse width range of the laser from the ultrafast laser generator is 290 fs to 15 ps.

6. The method for high-quality exfoliation of large-size diamonds using dual-laser composite modification according to claim 1, characterized in that, The nanosecond laser generator has a wavelength of 532 nm and a pulse width of <10 ns.

7. The method for high-quality exfoliation of large-size diamonds using dual-laser composite modification according to claim 1, characterized in that, In step (5), the parameters of the water bath ultrasound are: power of 150-250 W, water temperature of 50-70 ℃, and frequency in sweep mode.

8. The system used in the method for high-quality exfoliation of large-size diamonds by dual-laser composite modification as described in any one of claims 1-7, characterized in that, include: The system comprises an ultrafast laser processing system, a nanosecond laser processing system, a three-dimensional displacement platform, and a control system. The ultrafast laser processing system includes an ultrafast laser generator, a first reflecting mirror, a first half-wave plate, a first beam-splitting polarizer, a first beam expander, a second reflecting mirror, a first spatial light modulator, a first 4f system lens, a second 4f system lens, a third reflecting mirror, a first beam splitter, a first CCD camera, and a first objective lens. The nanosecond laser processing system includes a nanosecond laser generator, a fourth reflecting mirror, a second beam expander, a second half-wave plate, a second beam-splitting polarizer, a fifth reflecting mirror, a second spatial light modulator, a third 4f system lens, a fourth 4f system lens, a second beam splitter, a second CCD camera, and a second objective lens.

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