Laser welding method and device for diamond and sapphire

Abstract

The invention relates to a diamond and sapphire laser welding method and device.The diamond and sapphire laser welding method comprises the steps that after being pretreated, a diamond piece and a sapphire piece are stacked and placed on a displacement table, the diamond piece and the sapphire piece make contact with each other to form a to-be-welded interface, and the sapphire piece is located above the diamond piece; a light beam of a femtosecond laser is controlled to be focused in the sapphire sheet, and the focus is located at the position 20 micrometers above the interface to be welded; the displacement table is driven to move relative to the laser focus, meanwhile, laser is output in a pulse string mode to conduct scanning welding, according to the pulse string mode, a single laser pulse string comprises a plurality of sub-pulses, the energy of the single sub-pulse is 12 microJ, the number of the sub-pulses is five, and the repetition frequency is 30 MHz. According to the laser welding method and device for the diamond and the sapphire, high-strength metallurgical bonding between the diamond and the sapphire can be achieved under the conditions that no welding flux is used and materials do not need to be in optical tight contact.

Description

Technical Field

[0001] This invention belongs to the field of laser welding technology, and particularly relates to a laser welding method and apparatus for diamond and sapphire. Background Technology

[0002] Against the backdrop of the rapid development of semiconductor technology towards high power and high integration, unprecedented demands are being placed on the performance of key materials and their integration processes. Diamond, as the material with the highest thermal conductivity (over 2000 W / (m*K)) and the greatest hardness (Mohs hardness 10) in nature, possesses outstanding physical, optical, and mechanical properties, making it an ideal candidate material for high-end heat dissipation and substrates. In comparison, sapphire (alumina single crystal, Al2O3) also performs exceptionally well, with a Mohs hardness of 9, a melting point exceeding 2054℃, and good thermal conductivity (approximately 25 W / (m*K)) and high-temperature stability, making it an indispensable packaging and window material in semiconductor devices. Combining the ultra-high thermal conductivity of diamond with the high-temperature resistance and high light transmittance of sapphire, and achieving reliable welding between the two, could potentially lead to new semiconductor device packaging structures with significantly improved heat dissipation performance and reliability, or provide higher-performance composite substrates for third-generation semiconductors, possessing significant industrial application value.

[0003] However, achieving high-strength, low-damage welding between diamond and sapphire faces a series of fundamental challenges. First, the extremely high thermal stability of both materials constitutes a technological hurdle: the sublimation temperature of diamond and the melting point of sapphire both far exceed the operating window of conventional brazing or fusion welding processes, making it difficult for traditional thermal processing methods to achieve effective material fusion at the interface. Second, although both materials have high thermal conductivity, the thermal behavior of the welding interface is extremely complex. When using continuous or long-pulse lasers for welding, the laser energy is rapidly conducted and diffused by the diamond, preventing the formation of sufficient heat accumulation in the welding area to melt or bond the materials, resulting in low interfacial bonding strength. Furthermore, increasing the laser energy to promote bonding can easily lead to irreversible damage such as diamond graphitization or sapphire cracking due to uncontrolled energy input.

[0004] Existing technologies have not yet provided a reliable welding solution that can overcome the energy loss problem caused by high thermal conductivity and precisely control heat input to avoid material damage without using solder or relying on close optical contact. Summary of the Invention

[0005] In view of this, the present invention provides a laser welding method and apparatus for diamond and sapphire, solving the problem of welding diamond and sapphire.

[0006] To achieve the above objectives, in a first aspect, the technical solution of the present invention to solve the technical problem is to provide a laser welding method for diamond and sapphire, comprising: pre-treating diamond and sapphire sheets, stacking them on a displacement stage, so that the two contact to form a welding interface, wherein the sapphire sheet is located above the diamond sheet; controlling the beam of a femtosecond laser to focus within the sapphire sheet, and setting the focal point to a position 20 μm above the welding interface; driving the displacement stage to move relative to the laser focal point, and simultaneously outputting laser in a pulse train mode for scanning welding, wherein the pulse train mode comprises multiple sub-pulses in a single laser pulse train, the energy of a single sub-pulse is 12 μJ, the number of sub-pulses is 5, the repetition frequency of the pulse train is 50 kHz, and the repetition frequency of the sub-pulses is 30 MHz.

[0007] In one specific embodiment, the pretreatment of the diamond sheet and sapphire sheet includes: cleaning the diamond sheet and sapphire sheet in anhydrous ethanol and then drying them, and polishing both sides of the diamond sheet and sapphire sheet.

[0008] In one specific embodiment, the diamond sheet has a thickness of 0.2 to 0.6 mm, the sapphire sheet has a thickness of 0.5 mm to 1 mm, and the two are naturally stacked with an interface gap width of 15 μm to 30 μm.

[0009] In one specific embodiment, the thickness of the diamond sheet is 0.5 mm, and the thickness of the sapphire sheet is 1 mm.

[0010] In one specific embodiment, the scanning welding trajectory consists of multiple parallel straight lines, the laser moving speed is 0.2 mm / s, and the spacing between adjacent straight lines is 0.1 mm.

[0011] In one specific embodiment, the femtosecond laser outputs a pulse width of 600 fs, an average power of 3 W, and an output repetition frequency of 50 kHz.

[0012] In one specific embodiment, the temperature of the interface area to be welded during the line sweep welding process is between 50°C and 60°C.

[0013] In one specific embodiment, positioning the focal point 20 μm above the interface to be welded includes: observing the stacked sapphire and diamond sheets using a microscope, and controlling the position of the focal point by adjusting the Z-axis of the displacement stage.

[0014] In one specific embodiment, after the scanning welding is completed, the shear force of the welding interface between the diamond and the sapphire is measured.

[0015] Secondly, the present invention provides a laser welding apparatus for diamond and sapphire, comprising: a sample carrying unit for carrying and fixing pre-treated stacked diamond and sapphire sheets, and bringing them into contact to form a welding interface, wherein the sapphire sheet is located above the diamond sheet; a positioning unit for controlling the beam of a femtosecond laser to focus within the sapphire sheet, and positioning the focal point at a position 20 μm above the welding interface; and a scanning unit for driving a displacement stage to move relative to the laser focal point, and simultaneously outputting laser in a pulse train mode for scanning welding, wherein the pulse train mode comprises multiple sub-pulses in a single laser pulse train, the energy of a single sub-pulse is 12 μJ, the number of sub-pulses is 5, the repetition frequency of the pulse train is 50 kHz, and the repetition frequency of the sub-pulses is 30 MHz.

[0016] Compared with the prior art, the laser welding method and apparatus for diamond and sapphire provided by the present invention have the following advantages: By employing femtosecond laser pulse train mode, coupled with precise spatial positioning and motion control, a high-strength metallurgical bond between diamond and sapphire was achieved without the use of any solder and without requiring optically tight contact between the materials. Specifically, by outputting a femtosecond laser in a pulse train mode with specific parameters—five 12μJ sub-pulses per pulse train at a frequency of 30MHz—and precisely focusing the focus on the interior of the sapphire at a distance of 20μm from the interface, a suitable amount of slag was generated on the sapphire side and sputtered onto the diamond surface below, thus forming a strong connection. This process strictly controls the temperature of the welding area within an extremely low range of 50-60℃, completely avoiding diamond graphitization, sapphire thermal cracking, and internal stress problems caused by thermal expansion coefficient mismatch, thus perfectly preserving the excellent intrinsic properties of the base materials. Ultimately, an interfacial shear strength of approximately 60MPa was achieved, providing a reliable, precise, and highly promising new micro-nano interconnect technology solution for the fabrication of high-performance semiconductor device packaging, composite substrates, and other products. Attached Figure Description

[0017] Figure 1 A schematic diagram illustrating the application environment of a laser welding method for diamond and sapphire provided in the first embodiment of the present invention; Figure 2 A schematic flowchart illustrating the steps of a laser welding method for diamond and sapphire provided in the first embodiment of the present invention; Figure 3 This is a timing diagram of a femtosecond laser pulse train mode; Figure 4 This is a schematic diagram of the weld side under a microscope. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0019] It should be noted that all directional indications in the embodiments of this application are only used to explain the relative positional relationship and movement of each component in a specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0020] Furthermore, the use of terms such as "first" and "second" in this application is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed in this application.

[0021] The first embodiment of this application provides a laser welding method for diamond and sapphire, applicable to, for example... Figure 1 In the application environment shown, the beam emitted by the femtosecond laser is amplified by the beam expander module and focused onto the sample by the focusing lens. The sample (i.e., the diamond and sapphire to be welded) is fixed on a three-axis displacement stage. The X and Y axes of the displacement stage are controlled by computer software programming, which can perform precise two-dimensional planar motion to form a set scanning path (such as a parallel straight line). The Z axis is used to manually fine adjust the position of the focus in the material depth direction.

[0022] In one embodiment, such as Figures 2 to 4 As shown, a laser welding method for diamond and sapphire includes: S100: After pre-processing, diamond sheets and sapphire sheets are stacked on a displacement stage so that they come into contact to form a welding interface, with the sapphire sheet located above the diamond sheet. Specifically, the diamond and sapphire sheets are cleaned with anhydrous ethanol and then dried in an ultra-clean environment. The sapphire sheet is then placed on top of the diamond sheet, allowing gravity to bring them into natural contact and form the interface to be soldered. At this point, a gap exists between the two sheets, primarily determined by the surface roughness of the diamond, requiring no additional pressure or solder.

[0023] S200 controls the femtosecond laser beam to be focused into the sapphire wafer and positions the focal point 20μm above the interface to be welded. Specifically, by adjusting the Z-axis of the displacement stage, the femtosecond laser beam is focused inside the sapphire wafer, with the focal point located approximately 20 μm above the interface to be welded. This focal point position is a critical parameter for successful welding; if the focal point deviates from this position by more than 10 μm, it will significantly reduce the welding strength or even lead to welding failure. Therefore, accurate positioning must be achieved through microscopic observation and fine adjustment of the displacement stage.

[0024] S300 drives the displacement stage to move relative to the laser focus, and simultaneously outputs laser in pulse train mode for scanning welding. In pulse train mode, a single laser pulse train includes multiple sub-pulses, the energy of a single sub-pulse is 12μJ, the number of sub-pulses is 5, the repetition frequency of the pulse train is 50kHz, and the repetition frequency of the sub-pulses is 30MHz. Specifically, the displacement stage moves the sample according to a preset pattern, while a femtosecond laser outputs in pulse train mode. Each pulse train contains 5 sub-pulses with an energy of 12 μJ and a repetition frequency of 30 MHz. Under these parameters, the laser induces nonlinear absorption and ionization within the sapphire, generating a suitable amount of slag that flows to the diamond surface, achieving reliable welding between the two. The final interfacial shear strength can reach approximately 60 MPa.

[0025] In one embodiment, preprocessing the diamond sheet and sapphire sheet includes: After cleaning the diamond and sapphire sheets in anhydrous ethanol and drying them, both sides of the diamond and sapphire sheets were polished.

[0026] Understandably, cleaning with anhydrous ethanol effectively removes organic contaminants and particles adhering to the material surface, preventing them from carbonizing or generating impurities during subsequent laser treatment and contaminating the welding interface, thus ensuring the purity and reliability of the interface bonding. Double-sided polishing of the diamond and sapphire significantly reduces their surface roughness. This allows for the formation of more uniform and controllable micro-gaps (e.g., 15-30 μm) during natural stacking, providing consistent spatial conditions for subsequent slag flow and filling. Furthermore, the smooth surface reduces laser scattering, allowing energy to be more concentrated on the pre-defined focal area, improving process controllability and repeatability. This simple cleaning and polishing step lays a solid interface foundation for subsequent high-precision laser welding.

[0027] In one embodiment, the diamond sheet has a thickness of 0.2 to 0.6 mm, the sapphire sheet has a thickness of 0.5 mm to 1 mm, and the two are naturally stacked with an interface gap width of 15 μm to 30 μm.

[0028] Understandably, the thickness range of the diamond and sapphire wafers is common in commercial products, making this method highly feasible and cost-effective, eliminating the need for custom-sized materials. Secondly, this thickness combination ensures sufficient mechanical strength for stable operation while avoiding excessive laser energy attenuation or complex heat accumulation caused by excessive material thickness, thus facilitating welding process control. The gap width between the sapphire and diamond is approximately 15-30 μm, which allows the sapphire slag generated in subsequent steps to be fully sputtered onto the diamond surface, achieving a good welding effect—crucial for achieving high-strength interface bonding. The natural stacking method also avoids material damage or additional stress that may result from applied external forces, simplifying the clamping process and improving process reliability and consistency.

[0029] In one embodiment, the thickness of the diamond sheet is 0.5 mm and the thickness of the sapphire sheet is 1 mm.

[0030] Understandably, this combination, within the provided general thickness range, has been experimentally verified to achieve the aforementioned welding method with exceptional stability and efficiency. On one hand, the 1mm thick sapphire sheet provides sufficient operating space for safe laser focusing within its interior (e.g., 20μm from the interface), effectively avoiding the problems of low laser transmission or focus positioning tolerance caused by excessively thin materials. On the other hand, the 0.5mm thick diamond sheet, while possessing good mechanical support, has heat capacity and thermal diffusion characteristics that match those of the 1mm sapphire sheet, facilitating the formation of a relatively stable and controllable local thermal environment during welding, promoting uniform slag sputtering within the interface gap (15-30μm). This preferred thickness combination has been proven to reliably achieve an interfacial shear strength of approximately 60MPa, representing a concrete and effective implementation scheme balancing process feasibility, cost, and final weld performance.

[0031] In one embodiment, the scanning welding trajectory consists of multiple parallel straight lines, the laser moving speed is 0.2 mm / s, and the spacing between adjacent straight lines is 0.1 mm.

[0032] Understandably, setting the scanning path as multiple parallel straight lines provides a systematic and comprehensive energy input method for the welding area, ensuring that the entire interface to be welded can be processed uniformly and continuously. A laser movement speed of 0.2 mm / s is an optimized parameter that allows the laser to act long enough at each point to ensure that each pulse train fully excites nonlinear absorption in the material and generates sufficient slag, while avoiding excessive energy accumulation and potential thermal damage due to slow movement. The 0.1 mm spacing between adjacent trajectories is an experimentally verified optimal value; increasing this spacing significantly reduces weld strength. This is because this spacing ensures that the slag areas generated by adjacent welding trajectories can fully overlap and connect, thereby forming a continuous, dense, and complete metallurgical bonding layer at the interface. These parameters work synergistically to achieve uniform, sufficient, and efficient energy coverage and material modification of the entire welding interface, directly guaranteeing a shear strength of approximately 60 MPa.

[0033] In one embodiment, the femtosecond laser outputs a pulse width of 600 fs, an average power of 3 W, and an output repetition frequency of 50 kHz.

[0034] Understandably, a pulse width of 600 fs is typical for femtosecond lasers, generating extremely high peak power. This ensures that laser energy is primarily absorbed by the sapphire material through nonlinear processes such as multiphoton absorption and avalanche ionization, forming highly localized plasma at the focal point and inducing a material phase transition. This is crucial for achieving precise micro-area melting within materials with extremely high thermal conductivity. The average power of 3 W and the repetition frequency of 50 kHz together determine a single-pulse energy of 60 μJ. This energy level is optimized to drive the aforementioned nonlinear processes and generate sufficient slag, while avoiding irreversible damage such as material cracking or diamond graphitization caused by excessive energy injection in a single operation. These three parameters work synergistically to provide ideal input conditions for subsequently finely splitting the energy into five 12 μJ sub-pulses (sub-pulse frequency 30 MHz) in Burst mode, forming the initial link of a complete, controllable, and efficient energy transfer chain from laser output to the welding point.

[0035] In one embodiment, the temperature of the interface area to be welded during the scanning welding process is between 50°C and 60°C.

[0036] Understandably, this temperature is far below the initial graphitization temperature of diamond (approximately 700°C) and the melting point of sapphire (2054°C), and even below the melting temperature of many conventional solders. This means that the entire soldering process is completed in a near-room temperature environment with minimal thermal impact on the base material.

[0037] The achievement of this low-temperature characteristic fundamentally stems from the ultrashort pulse action of femtosecond lasers and the energy-time distribution strategy of the burst mode. The femtosecond pulse, through nonlinear absorption, almost instantaneously deposits energy within an extremely small volume, transforming it into a plasma or molten state of the material, rather than heating the entire material through traditional heat conduction. The burst mode further subdivides the energy of a single action into multiple high-repetition-rate sub-pulses, avoiding the severe thermal shock that a single giant pulse might cause. The combination of these two approaches ensures that heat is strictly confined to the focal micro-region and rapidly dissipated.

[0038] Therefore, maintaining the interface at a low temperature of 50-60°C minimized all adverse effects introduced by high heat. This included completely preventing graphitization of diamond due to high temperatures, which would degrade its exceptional thermal conductivity; preventing microcracks in sapphire due to thermal stress; and eliminating the risk of significant internal stress arising after cooling due to differences in thermal expansion coefficients between dissimilar materials. Ultimately, while achieving a high-strength interfacial bond (approximately 60 MPa shear force), the original superior properties of both the welded diamond and sapphire bulk materials were well preserved, achieving a balance between bond strength and material functionality.

[0039] In one embodiment, positioning the focal point 20 μm above the interface to be welded includes: observing the stacked sapphire and diamond sheets using a microscope, and controlling the position of the focal point by adjusting the Z-axis of the displacement stage.

[0040] Understandably, adjusting the Z-axis of the stage to control the focal spot position aims to achieve precise control. If the focal spot deviates from the preset 20μm above the interface position by more than 10μm, it will significantly weaken the welding strength or even lead to failure. Therefore, fine-tuning the Z-axis is a reliable control strategy that achieves optimal feel and real-time feedback to meet this extreme precision requirement. It allows the operator to fine-tune the focal spot to the target depth with extremely high sensitivity based on real-time microscopic observations.

[0041] Using a microscope provides a reliable visual benchmark and basis for judgment for this fine adjustment. Through the microscope, the operator can clearly observe the sample surface, determine the relative position of the laser focal spot, and ultimately confirm that the focal point has precisely fallen into the designated area inside the sapphire wafer, approximately 20 μm from the interface.

[0042] Through a combination of observation and adjustment, a closed-loop, high-precision positioning system is formed. This ensures that every welding experiment or production operation can repeatedly place the starting point of energy input (laser focus) at the theoretically optimal position, thus providing a foundation for subsequent pulse train energy to excite the molten slag and achieve an interface strength of approximately 60 MPa.

[0043] In one embodiment, after the scanning welding is completed, the shear force of the welding interface between the diamond and the sapphire is measured.

[0044] Understandably, measuring the shear force at the weld interface is a core verification step for objectively and quantitatively evaluating the final effect and reliability of the welding method. This measurement directly verifies the performance of the welded joint under actual mechanical loads.

[0045] Shear force measurements verify whether the interface bonding formed by this method can meet the basic mechanical strength requirements for high-reliability device packaging or composite substrate applications. Simultaneously, the measurement results provide direct experimental evidence and support for the optimized combination of a complete set of process parameters (such as pulse energy of 12 μJ, sub-pulse number of 5, spacing of 0.1 mm, and speed of 0.2 mm / s), confirming the ultimate effectiveness of the synergistic effect of these parameters and providing a complete and verifiable causal chain for this method.

[0046] A second embodiment of the present invention provides a laser welding apparatus for diamond and sapphire, comprising: The sample support unit is used to support and fix the pre-treated stacked diamond sheet and sapphire sheet, and to make them contact each other to form a welding interface, wherein the sapphire sheet is located above the diamond sheet; The positioning unit is used to control the focus of the femtosecond laser beam onto the sapphire wafer and to position the focal point 20μm above the interface to be welded. The scanning unit is used to drive the displacement stage to move relative to the laser focus, and at the same time output laser in pulse train mode for scanning welding. In pulse train mode, a single laser pulse train includes multiple sub-pulses, the energy of a single sub-pulse is 12μJ, the number of sub-pulses is 5, the repetition frequency of the pulse train is 50kHz, and the repetition frequency of the sub-pulses is 30MHz.

[0047] In this embodiment, the sample carrier unit can be a displacement stage, and the positioning unit includes a femtosecond laser and a beam shaping and focusing assembly. The femtosecond laser generates femtosecond laser pulses, and the beam shaping and focusing assembly focuses the femtosecond laser pulses onto the sapphire wafer, positioning the focal point 20 μm above the interface to be welded. The scanning unit is connected to the femtosecond laser and the sample carrier unit, driving the sample carrier unit to move relative to the laser focal point while simultaneously controlling the femtosecond laser to output laser light in a pulse train mode for scanning and welding.

[0048] Compared with existing technologies, the laser welding method and apparatus for diamond and sapphire provided by this invention achieves a high-strength metallurgical bond between diamond and sapphire through femtosecond laser pulse train mode, coordinated with precise spatial positioning and motion control, without using any solder and without requiring optically close contact between the materials. Specifically, by outputting a femtosecond laser in a pulse train mode with specific parameters: each pulse train contains five 12μJ sub-pulses at a frequency of 30MHz, and the focus is precisely focused on the interior of the sapphire at a distance of 20μm from the interface, a suitable amount of slag is generated on the sapphire side, and its flow wets the surface of the underlying diamond, thereby forming a strong connection. This process strictly controls the temperature of the welding area within an extremely low range of 50-60℃, completely avoiding diamond graphitization, sapphire thermal cracking, and internal stress problems caused by thermal expansion coefficient mismatch, thus perfectly preserving the excellent intrinsic properties of the base material. Ultimately, a stable interfacial shear strength of approximately 60 MPa can be achieved, providing a reliable, precise, and highly promising novel micro-nano interconnect technology solution for the fabrication of high-performance semiconductor device packaging, composite substrates, and other products.

[0049] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method of laser welding of diamond and sapphire, characterized by, The method comprises the following steps: After pretreatment of the diamond sheet and the sapphire sheet, the two are stacked on a displacement table to make contact and form a welding interface, wherein the sapphire sheet is above the diamond sheet; The focus of the beam of the femtosecond laser is controlled to be in the sapphire sheet, and the focus is located 20 μm above the welding interface; The displacement table is driven to move relative to the laser focus, and the laser is output in a pulse train mode for scanning welding, wherein the pulse train mode includes multiple sub-pulses in a single laser pulse train, the energy of a single sub-pulse is 12 μJ, the number of sub-pulses is 5, the repetition frequency of the pulse train is 50 kHz, and the repetition frequency of the sub-pulse is 30 kHz.

2. A method of laser welding of diamond and sapphire as claimed in claim 1, wherein, The pretreatment of the diamond sheet and the sapphire sheet comprises the following steps: The diamond sheet and the sapphire sheet are washed in anhydrous ethanol and then dried, and the diamond sheet and the sapphire sheet are polished on both sides.

3. The laser welding method of diamond and sapphire according to claim 1, wherein: The thickness of the diamond sheet is 0.2-0.6 mm, and the thickness of the sapphire sheet is 0.5-1 mm, and the two are naturally stacked, and the interface gap width is 15-30 μm.

4. The laser welding method of diamond and sapphire according to claim 3, wherein: The thickness of the diamond sheet is 0.5 mm, and the thickness of the sapphire sheet is 1 mm.

5. The laser welding method of diamond and sapphire according to claim 1, wherein: The scanning welding track is a plurality of parallel straight lines, the laser moving speed is 0.2 mm / s, and the spacing between adjacent straight line tracks is 0.1 mm.

6. The laser welding method of diamond and sapphire according to claim 1, wherein: The pulse width of the output of the femtosecond laser is 600 fs, and the average power is 3 W.

7. The laser welding method of diamond and sapphire according to claim 1, wherein: During the line scanning welding process, the temperature of the welding interface region is between 50-60 °C.

8. A method of laser welding of diamond and sapphire as claimed in claim 1, wherein, The focus is located 20 μm above the welding interface comprises the following steps: The stacked sapphire sheet and diamond sheet are observed using a microscope, and the position of the focus is controlled by adjusting the Z-axis of the displacement table.

9. The laser welding method of diamond and sapphire according to claim 1, wherein: After the scanning welding is completed, the shear force of the welding interface between the diamond and the sapphire is measured.

10. A laser welding apparatus of diamond and sapphire, characterized by, The method comprises the following steps: A sample carrying unit is used to carry and fix the pretreated and stacked diamond sheet and sapphire sheet to make contact and form a welding interface, wherein the sapphire sheet is above the diamond sheet; A positioning unit is used to control the focus of the beam of the femtosecond laser in the sapphire sheet, and the focus is located 20 μm above the welding interface; A displacement table is used to drive the diamond sheet and the sapphire sheet to move relative to the laser focus, and the laser is output in a pulse train mode for scanning welding, wherein the pulse train mode includes multiple sub-pulses in a single laser pulse train, the energy of a single sub-pulse is 12 μJ, the number of sub-pulses is 5, the repetition frequency of the pulse train is 50 kHz, and the repetition frequency of the sub-pulse is 30 kHz. The scanning unit is used for driving the displacement table to move relative to the laser focus point, and simultaneously outputs laser in a pulse train mode for scanning welding, wherein the pulse train mode comprises a plurality of sub-pulses in a single laser pulse train, the energy of a single sub-pulse is 12 muJ, the number of sub-pulses is 5, the repetition frequency of the pulse train is 50 kHz, and the repetition frequency of the sub-pulse is 30 MHz.

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