Variable multi-focal laser stealth cutting optical path, device and method

Abstract

The application discloses a variable multi-focus laser stealth cutting optical path, device and method, comprising a laser, a beam splitting and combining module, a focal point macro adjustment module, a focusing objective lens and a machining platform arranged in sequence along the optical path. The beam splitting and combining module divides the incident laser into at least two sub-beams, and each sub-beam is selectively provided with a focusing lens with different focal lengths; the focal point macro adjustment module comprises a lens driven by a voice coil motor, which quickly changes the characteristics of the light beam before entering the focusing objective lens; the focusing objective lens is installed on a piezoelectric displacement stage for micron-level precision focusing. The voice coil motor realizes large-range and rapid coarse adjustment of the focal point position, the piezoelectric displacement stage realizes micron-level fine adjustment and real-time compensation of the focal point position, and different lenses are configured in the beam splitting path to flexibly generate a single focal point, a static multi-focus point and a dynamic scanning multi-focus point, thereby significantly improving the machining efficiency of laser stealth cutting, improving the layer uniformity and adaptability to different materials and thicknesses.

Description

Technical Field

[0001] This invention relates to the field of laser precision machining technology, specifically to a variable multi-focus laser stealth cutting optical path, device, and method. Background Technology

[0002] Third-generation semiconductor materials, represented by wide-bandgap semiconductor materials such as silicon carbide, gallium nitride, and zinc oxide, are widely used in high-frequency and high-power devices, photovoltaics, new energy vehicles, and defense communications due to their wide bandgap, high electron mobility, and high thermal conductivity. Taking the manufacturing process of silicon carbide as an example, silicon carbide powder is first used to make silicon carbide ingots. The ingots are then sliced, ground, and polished to create silicon carbide substrates. After epitaxial growth, the substrates undergo photolithography, etching, ion implantation, and metal passivation to obtain silicon carbide wafers. These wafers are then diced to obtain dies, which are then packaged to obtain devices. In the semiconductor device manufacturing process, the quality of wafer dicing directly affects the wafer's size, thickness, and surface roughness. Because silicon carbide has a Mohs hardness of 9.5 and is relatively brittle, the dicing process has even higher requirements.

[0003] Compared to traditional diamond cutting and laser scribing technologies, laser stealth cutting technology focuses a laser beam through the surface of silicon carbide into the material, forming a modified layer at a specified depth. Then, external force is applied to peel off the wafer, resulting in lower thermal effects, less edge chipping, and higher cutting efficiency. Therefore, the distribution and formation of the modified layer are the core aspects of laser stealth cutting. Discontinuous fractures and crack path deviations in the modified layer can lead to burrs at the edges, reducing the final cutting quality. When cutting thicker wafers, a single laser focus is limited by the laser's depth of focus and often cannot cover the entire depth of the wafer. Existing solutions mainly fall into two categories: one uses a single focus to perform multiple layered scans along the thickness direction to form multiple modified layers, but this is inefficient, and multiple scans can easily lead to thermal stress accumulation, affecting material properties. Secondly, multi-focus parallel processing can be employed. Using multiple laser focal points to simultaneously dice within the wafer can shorten the laser focal point scanning time. For example, diffractive optical elements (DOEs) or spatial light modulators (SLMs) can be used to directly generate multiple focal point arrays. However, once a DOE is fabricated, the resulting focal pattern is fixed, making it difficult to flexibly control focal point changes. While SLMs can be flexibly programmed to modulate and generate multiple focal points and two-dimensional or three-dimensional light fields with specific energy distributions, they are complex and costly. Another approach is to use beam splitters or multi-beam interference to form multiple laser focal points. Although this method is less expensive, the generated laser focal points are in a single position, the beam expander moves slowly, limiting the ability to quickly adjust the focal point position, and the adjustment accuracy is difficult to guarantee.

[0004] Therefore, there is a lack of simple and reliable technical means that can simultaneously achieve rapid, wide-range coarse adjustment and precise micron-level fine adjustment of the focal point during laser stealth cutting, while ensuring that the optical path is simple and easy to implement, so as to further improve the processing efficiency of laser stealth cutting. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a variable multi-focus laser stealth cutting optical path, device, and method. Its structure is relatively simple, cost is controllable, and it can flexibly, quickly, and accurately control the position and number of internal focal points during laser stealth cutting. A voice coil motor enables large-scale, rapid coarse adjustment of the laser focal point position, while a piezoelectric displacement stage enables micron-level fine adjustment and real-time compensation of the focal point position. Furthermore, by configuring different lenses in the beam-splitting sub-optical path, single-focus, static multi-focus, and dynamic scanning multi-focus modes can be flexibly generated. This significantly improves the processing efficiency of laser stealth cutting, the uniformity of the modified layer, and its adaptability to different materials and thicknesses.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a variable multi-focus laser stealth cutting optical path, comprising a laser emitting module, a beam splitting and combining module, a macro-focus adjustment module, and a micro-focus adjustment and focusing module arranged sequentially along the optical path;

[0008] The beam splitting and combining module includes a beam splitter, at least two parallel sub-optical paths, and a beam combiner. The beam splitter splits the laser beam emitted by the laser emission module into at least two sub-beams, which then enter the sub-optical paths respectively. The beam combiner combines the sub-beams modulated by the sub-optical paths and outputs them. Each sub-optical path may optionally be equipped with a first-type convex lens. By replacing the convex lenses with different focal lengths, the divergence angle of the beam entering the macroscopic adjustment module can be changed, thereby creating focal points at different depths within the material after final beam combining, forming a static multifocal path. The initial number and relative positions of the focal points can be set through the beam splitting and combining module and the optional lenses with different focal lengths.

[0009] The macroscopic focus adjustment module is set in the output optical path of the beam combiner, including a second type of convex lens that can move along the optical axis, a voice coil motor that drives the second type of convex lens to move, and a displacement detection component for detecting the displacement of the second type of convex lens; by driving the second type of convex lens to perform large stroke and high acceleration displacement through the voice coil motor, a fast and large-range scanning of the focus position is achieved;

[0010] The focus micro-adjustment and focusing module includes a focusing objective and a piezoelectric displacement stage that carries the focusing objective. The piezoelectric displacement stage is used to drive the focusing objective to move at the micrometer level along its optical axis. By driving the focusing objective to perform micrometer-level displacement through the piezoelectric displacement stage, fine adjustment of the focus position, thermal drift compensation, and surface undulation tracking can be achieved.

[0011] Piezoelectric displacement stages can achieve nanometer- to micrometer-level stepping within milliseconds, exhibiting extremely fast response speeds. They are primarily used to compensate for potential nonlinear errors during large-scale scanning by voice coil motors, focus drift caused by material thermal effects during processing, and microscopic undulations on the workpiece surface, ensuring that the laser focus always precisely falls at the target depth.

[0012] Furthermore, a beam shaping module is provided between the laser emitting module and the beam splitting and combining module. The beam shaping module includes a variable magnification beam expander, an adjustable aperture, and a first half-wave plate arranged sequentially along the optical path. The laser beam emitted by the laser emitting module is expanded by the variable magnification beam expander. After the expanded laser beam is incident on the adjustable aperture, it passes through the first half-wave plate. The beam splitter is a polarization beam splitter. The first half-wave plate cooperates with the polarization beam splitter to adjust the power of the laser beam in each sub-optical path.

[0013] The adjustable aperture, in combination with apertures at various locations in the subsequent optical path (such as apertures placed in front of beam splitters, beam combiners, and the fourth convex lens), is mainly used during debugging to facilitate rapid collimation and correction of the beam, adjusting the center of the beam before and after transmission to a consistent height and horizontal position.

[0014] Furthermore, each of the sub-optical paths is provided with a second half-wave plate for adjusting the polarization state of the beam, and the second half-wave plate is located in front of the first type of convex lens.

[0015] Furthermore, the displacement detection component includes a grating ruler and a reading head. The grating ruler moves synchronously with the second type of convex lens and cooperates with the fixed reading head to obtain the moving distance of the second type of convex lens along the optical axis.

[0016] Furthermore, it also includes a coaxial vision monitoring module, which includes a dichroic mirror and an imaging device (CCD camera). The dichroic mirror is disposed between the macro-focus adjustment module and the focusing objective lens, and is used to transmit visible light from the processing area to the imaging device to realize real-time observation of the processing process and provide visual feedback for closed-loop control.

[0017] Furthermore, the first type of convex lens in each of the sub-optical paths is a plano-convex lens with different focal lengths. By replacing the first type of convex lens with different focal lengths, and coordinating with the displacement of the second type of convex lens driven by the voice coil motor, a single or multiple laser-modified layer with adjustable position and spacing can be generated inside the workpiece to be processed.

[0018] The present invention also provides a variable multi-focus laser stealth cutting device, including the above-mentioned laser stealth cutting optical path and a processing platform for carrying the workpiece to be processed.

[0019] The present invention also provides a laser stealth cutting method using the above-mentioned device, comprising the following steps:

[0020] S1: Based on the material of the workpiece to be processed and the target cutting depth, determine whether to install a first type of convex lens in each of the sub-optical paths in the beam splitting and combining module, and select the focal length of the first type of convex lens, so as to set the initial number and spacing of focal points;

[0021] S2: Start the laser emission module and drive the second type of convex lens to move along the optical axis by controlling the voice coil motor, so that the laser focus can perform a large-scale scan in the thickness direction of the workpiece to be processed, forming a macroscopic modification area;

[0022] S3: With the assistance of the coaxial vision monitoring module, based on real-time processing feedback, the piezoelectric displacement stage drives the focusing objective to perform micron-level displacement adjustment, thereby fine-tuning and compensating for the laser focus position.

[0023] S4: Repeat steps S2 and S3 until a complete and uniform modified layer is formed in the current processing area;

[0024] S5: Move the processing platform or the optical path to cut the next processing area.

[0025] Furthermore, in step S2, the voice coil motor is controlled by a preset program to drive the second type of lens to perform periodic reciprocating motion, so that the laser focus performs real-time dynamic scanning inside the workpiece to be processed, forming a continuous or quasi-continuous modified layer.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) In the present invention, replaceable lenses with different focal lengths are introduced as basic configuration units in each sub-optical path of the beam splitting and beam combining module. This design makes the system no longer dependent on expensive and fixed customized optical components (such as DOE) or complex programming devices (such as SLM) to generate multi-focals. Operators only need to physically replace or select lenses in the sub-optical paths to switch between basic processing modes such as single-focal (all sub-optical path lenses have the same focal length or are empty), dual-focal (only one sub-optical path uses a lens or two sub-optical paths use lenses with different focal lengths), and even multi-focal (expanding the number of sub-optical paths and configuring different lenses), adapting to the process window with different material, thickness and cutting quality requirements.

[0028] (2) Based on the beam splitting and beam combining optical path structure, this invention achieves a wide range of laser focus movement by rapidly displacing the lens through a voice coil motor, and can generate a variety of efficient processing modes. For example, in the "static dual-focus" mode, by stepping the second type of convex lens, the two modified layers can be translated synchronously to efficiently fill the cutting section; in the "dynamic scanning dual-focus" mode, by the high-frequency reciprocating motion of the lens, the two focal points can be rapidly scanned near their respective depths to form a more uniform and continuous modified surface, effectively suppressing cracks and thermal damage.

[0029] (3) This invention creatively combines two actuators with different performance characteristics, namely a voice coil motor (used to drive a second type of convex lens) and a piezoelectric displacement stage (used to drive a focusing objective), to construct a "macro-micro" dual drive system. The voice coil motor enables large-scale and rapid coarse adjustment of the laser focus position, while the piezoelectric objective displacement stage provides micron-level focus position compensation. This reduces the number of laser scans and avoids excessive energy concentration, which helps to ensure the uniformity of the modified layer and improve the cutting quality.

[0030] (4) Compared with the SLM solution, the present invention uses conventional optical components and electromechanical modules, which has a simpler structure, lower cost, and is more suitable for the high power and long-term stable operation requirements of industrial sites.

[0031] (5) The present invention obtains the lens movement position through feedback devices such as grating ruler in motor module and adjusts the lens position in a timely manner within millisecond range by changing the drive current. The coaxial vision camera module detects the processing screen in real time. At the same time, the piezoelectric ceramic positioner drives the objective lens to achieve micron-level displacement within milliseconds. It can quickly compensate for laser focus drift caused by surface undulations or thermal effects of the processed material, forming a closed-loop control. It has the characteristics of fast adjustment speed, timely adjustment of processing parameters, and accurate compensation of laser focus position. Attached Figure Description

[0032] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0033] Figure 1 This is a schematic diagram of the variable multi-focus laser stealth cutting optical path in this invention;

[0034] Figure 2 This is a diagram of the main device of the variable multi-focus laser stealth cutting optical path in this invention;

[0035] Figure 3 This is a simulation diagram of the optical path before entering the focusing objective lens in this invention;

[0036] Figure 4 This is a flowchart illustrating the main processing steps of the variable multi-focus laser stealth cutting optical path in this invention.

[0037] Figure 5 The following are various hidden cutting modes in this invention: (a) schematic diagram of single-focus laser hidden cutting, (b) schematic diagram of dual-focus laser hidden cutting, and (c) schematic diagram of real-time changing dual-focus laser hidden cutting.

[0038] The specific reference numerals in the attached figures are as follows:

[0039] Laser 1, Variable magnification beam expander 2, Aperture 3, First half-wave plate 4, First reflecting mirror 5, Beam splitter and combiner module 6, Polarizing beam splitter 61, Second half-wave plate 62, Second reflecting mirror 63, First convex lens 64, Third reflecting mirror 65, Third half-wave plate 66, Second convex lens 67, Polarizing beam combiner 68, Fourth reflecting mirror 7, Macro-focus adjustment module 8, Third convex lens 81, Moving platform 82, Linear guide rail 83, Slider 84, Coil 85, Magnet 86, Fourth convex lens 9, CCD camera 10, Dichroic mirror 11, Piezoelectric objective lens positioner 12, Focusing objective lens 13, Workpiece 14, Workpiece platform 15. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1

[0042] This embodiment provides a variable multi-focus laser stealth cutting optical path, such as... Figure 1 As shown, it includes a laser 1, a laser beam expanding and shaping module, a beam splitting and combining module 6, a macroscopic focus adjustment module 8, and a microscopic focus adjustment and focusing module arranged sequentially along the optical path;

[0043] The laser beam expanding and shaping module includes a variable magnification beam expander 2, an adjustable aperture 3, a first half-wave plate 4, and a first reflector 5 for expanding the beam emitted by the laser.

[0044] The beam splitting and combining module 6 includes a polarization beam splitter 61, a second half-wave plate 62, a second reflector 63, a first convex lens 64, a third reflector 65, a third half-wave plate 66, a second convex lens 67, and a polarization beam combiner 68.

[0045] The macroscopic focus adjustment module 8 includes a third convex lens 81, a lens frame, a voice coil motor, a magnet 86, a coil 85, a linear guide rail 83, a grating ruler, a grating ruler reading head, and a fourth convex lens 9.

[0046] The focus micro-adjustment and focusing module includes a dichroic mirror 11, a CCD camera 10, a piezoelectric objective lens positioner 12, a focusing objective lens 13, a workpiece 14, and a workpiece platform 15.

[0047] Laser 1 outputs a picosecond pulsed laser with a wavelength of 1064nm and a beam diameter of approximately 3mm. After passing through a variable magnification beam expander 2 with a beam expansion ratio set to 2, the beam diameter is approximately 6mm. The expanded laser beam is incident on the aperture 3, passes through the first half-wave plate 4, and is then reflected by the first reflector 5 tilted at 45° to the beam splitting and combining module 6. The combination of the first half-wave plate 4 and the polarization beam splitter 61 in the beam splitting and combining module 6 allows for adjustment of the laser power in the optical path by rotating the polarization direction and selecting the transmitted polarization direction. After the laser beam enters the beam splitting and combining module 6, the beam first passes through the polarization beam splitter 61 and is split into two beams: one beam passes through the second half-wave plate 62 and is incident on the second reflector 63 tilted at 45°, and then passes through the first convex lens 64 before entering the polarization beam combiner 68. Another beam of light, also incident on the 45° tilted third reflecting mirror 65, is reflected to the third half-wave plate 66, then passes through the second convex lens 67 and is transmitted to the polarization combiner 68. The beams after passing through the first convex lens 64 and the second convex lens 67 are then combined into a single beam upon entering the polarization combiner 68. In the optical path, the second half-wave plate 62 and the third half-wave plate 66 are used to adjust the laser polarization state in the two optical paths. The first convex lens 64 and the second convex lens 67, as first-type convex lenses, are both plano-convex lenses with large focal lengths, far exceeding the distances between the first convex lens 64 and the macro-focus adjustment module 8, and between the second convex lens 67 and the macro-focus adjustment module 8.

[0048] The beam of light passing through polarization combiner 68 is incident on the 45° tilted fourth reflecting mirror 7 and reflected to the third convex lens 81 in the macro-focus adjustment module 8. The third convex lens 81 serves as a second type of convex lens. After passing through the third convex lens 81, the beam is incident on the fourth convex lens 9. The distance between the two lenses is close to the sum of their respective focal lengths, so this combination is similar to a Keplerian beam expander. The slight change in the distance between them is the key to changing the divergence angle of the beam entering the objective lens, thereby achieving a macro-level change in the vertical position of the focal point. The selection of different focal lengths for the first convex lens 64 and the second convex lens 67 corresponds to the degree of increase in the distance between the vertical positions of the final focal point. Next, the beam is incident on the 45° tilted dichroic mirror 11. The reflected beam is then incident perpendicularly on the focusing objective lens 13 fixed by the piezoelectric objective lens positioner 12, converging into a beam with a spot diameter in the micrometer range, and acting on the interior of the workpiece 14. The workpiece 14 is fixed on the processing platform 15 for processing. The piezoelectric objective lens positioner 12 is controlled by a piezoelectric controller. By adjusting the voltage change of the piezoelectric ceramic in the piezoelectric objective lens positioner 12, the focusing objective lens 13 is driven to achieve a minute positional movement. Visible light within a certain range on the processing platform 15 passes through the optical path of the focusing objective lens 13 and is incident on the dichroic mirror 11, and then transmitted to the lens of the coaxially set CCD camera 10 for real-time coaxial monitoring of the processing scene.

[0049] like Figure 2 As shown, in the macroscopic focus adjustment module 8, the third convex lens 81 is fixed on the moving platform 82 of the voice coil motor. The moving platform 82 is placed on the linear guide rail 83. Slider 84 is installed on both sides of the linear guide rail 83. A grating ruler and a reading head are installed below the moving platform. As the grating ruler moves with the moving platform 82, it will pass by the reading head fixed below. After the reading head reads the moving distance of the grating ruler, it obtains the relative distance of the displacement of the moving platform 82, thereby providing timely feedback on the current position information. Limit switches are set below the two farthest distance positions of the moving platform 82 to prevent the moving platform 82 from moving beyond the limit position, thereby damaging the mechanical device.

[0050] When the macro-focus adjustment module 8 is running, it sends the target position command for the third convex lens 81 to the driver of the voice coil motor. The driver then obtains the current position information of the moving platform 82 through a grating ruler and a reading head. After comparing the target position, the driver generates a working current applied to the voice coil motor. Since the coil is in the magnetic field of the magnet 86, when the coil 85 of the voice coil motor is energized, it is affected by the Lorentz force, causing the coil 85 and the connected moving platform 82 to move on the linear guide rail 83, driving the third convex lens 81 to the designated position. The focal position inside the wafer changes accordingly at different positions of the third convex lens 81. Therefore, after the moving platform 82 moves through multiple positions, the sequence of relationships between the position of the third convex lens 81 and the focal position inside the wafer can be established.

[0051] In this embodiment, the voice coil motor has a stroke of 20 mm, a continuous thrust of approximately 10 N, a peak thrust of approximately 58 N, and an achievable maximum speed of 1.2 m / s. Therefore, it can carry the frame and the third convex lens 81, weighing approximately 10 g in total, forward a maximum distance of approximately 12 mm within 0.02 s.

[0052] In this embodiment, Zemax simulation was used to simulate the change in the laser focal position generated by the optical path containing the first convex lens 64; the same simulation was applied to the optical path containing the second convex lens. Figure 3 In the optical path, the sub-optical path where the second convex lens is located is blocked. The first convex lens 64 is a plano-convex lens with a focal length of 2000mm, a radius of curvature of 1033.6mm, and a center thickness of 2.1mm. The third convex lens 81 is a biconvex lens with a focal length of 100mm, a radius of curvature of 102.4mm, and a center thickness of 3.6mm. The fourth convex lens 9 is a plano-convex lens with a focal length of 75mm, a radius of curvature of 34.39mm, and a center thickness of 2.4mm. The straight-line distance between the center of the first convex lens 64 and the polarization combiner 68 is ( d 1) The straight-line distance between the second convex lens 67 and the polarization combiner 68 is 60mm. d 2) The straight-line distance between the polarization combiner 68 and the fourth reflecting mirror 7 is 60mm. d 3) The initial straight-line distance between the fourth reflecting mirror 7 and the third convex lens 81 in the macro-focus adjustment module 8 is 70mm. d 4) The initial straight-line distance between the third convex lens 81 and the fourth convex lens 9 is 30mm. d 6) The straight-line distance between the fourth convex lens 9 and the focusing objective lens 13 is 175mm. d 7) The focal length is 240mm. Focusing objective 13 is a high-power objective with a magnification of 50X and a NA of 0.65. d 8 represents the distance between the last mirror surface of the focusing objective 13 and the laser focal point.

[0053] As can be seen from Table 1, the focal point of the laser after passing through the focusing objective lens 13 is denoted as... d 8, d 8 is 2.318mm. When the voice coil motor in the macroscopic adjustment module 8 of the drive focus moves 2mm, d The distance of 6 increases to 177mm, corresponding to a focal position of 2.311mm. d The distance of 6 increases to 179mm, corresponding to a focal point of 2.304mm. d The distance of 6 increases to 181mm, corresponding to a focal position of 2.295mm. d The distance of 6 increases to 183mm, and the corresponding focal position is 2.284mm. d The distance of 6 is increased to 185mm, and the corresponding focal position is 2.270mm. d The distance of lens 6 increases to 187mm, corresponding to a focal point position of 2.253mm. That is, after the third convex lens 81 moves by about 12mm, the maximum distance the focal point can move is 65.1μm.

[0054] Table 1

[0055]

[0056] Example 2

[0057] This embodiment provides a variable multi-focus laser stealth cutting optical path, which differs from Embodiment 1 in that: the first convex lens 64 is a plano-convex lens with a focal length of 1000mm, a radius of curvature of 515.1mm, and a center thickness of 2.2mm. As can be seen from Table 1, the initial straight-line distance ( d 6) When the focal length is 175mm, the focal point of the laser after passing through the focusing objective lens 13 is recorded as: d 8, d 8 is 2.297mm. d When the distance of lens 6 is increased to 177mm, 179mm, 181mm, 183mm, 185mm, and 187mm respectively, the corresponding focal positions are 2.286mm, 2.273mm, 2.257mm, 2.237mm, 2.209mm, and 2.171mm respectively. That is, after the third convex lens 81 moves by about 12mm, the maximum distance the focal point can move is 126.2μm.

[0058] The first convex lens 64 is replaced with a plano-convex lens with a focal length of 750 mm, a radius of curvature of 386.3 mm, and a center thickness of 2.2 mm. After the third convex lens 81 moves by approximately 12 mm, the maximum distance the focal point can move is 240.6 μm.

[0059] When no lens is placed at the position of the first convex lens 64, after the third convex lens 81 moves by about 12 mm, the maximum distance that the focal point can move is 40.9 μm.

[0060] Example 3

[0061] This embodiment provides a main processing flow for a variable multi-focus laser stealth cutting optical path, such as... Figure 4 As shown, firstly, the wafer processing area is selected, and laser parameters such as power, pulse width, and repetition rate are set, along with the focal length selection of the first convex lens 64 and the second convex lens 67. Table 1 only lists the changes in the focal spot radius and focal position corresponding to each 2mm movement of the third convex lens 81 when the focal lengths of the first convex lens 64 or the second convex lens 67 are 750mm, 1000mm, 2000mm, and without any lenses, thus establishing the relationship between the movement distance of the third convex lens 81 and the focal spot movement distance. Since the distances d1+d3+d4 and d2+d3+d4 are much smaller than the focal lengths of the first convex lens 64 and the second convex lens 67, the beam incident on the third convex lens 81 is nearly parallel, with a small divergence angle. The back-and-forth movement of the third convex lens 81 causes a change in d3+d4, which in turn changes the divergence angle of the beam incident on the third convex lens 81 and the divergence angle of the beam exiting from the fourth convex lens 9, thus affecting the change in the spot and position of the laser focal point. When selecting the focal lengths of the first convex lens 64 and the second convex lens 67, it is necessary to consider the requirements of the wafer processing technology, such as the material type, thickness, and processing efficiency of the wafer, as well as the required thickness, spacing, and quantity of the modified layers inside the wafer. For example, after determining the thickness and quantity of the modified layers inside the wafer based on process requirements, according to Table 1, the first convex lens 64 or the second convex lens 67 corresponding to a maximum focal point movement distance greater than the total thickness range of the modified layers is selected. During processing, as the position of the third convex lens 81 moves stepwise, different modified layers are successively formed at the corresponding laser focal point positions. Based on the different numbers of modified layers, the movement distance of the third convex lens 81 is calculated through simulation and process effects.

[0062] After the stealth dicing process begins, based on the correspondence between the third convex lens 81 mounted on the motor platform and the laser focal point behind the focusing objective 13, the voice coil motor is controlled to drive the third convex lens 81 to move rapidly, achieving a large-scale modification layer inside the wafer. Based on the images monitored by the coaxial camera and the quality of the modification layer inside the wafer being detected, the piezoelectric ceramic-driven focusing objective 13 is adjusted vertically at the micrometer level to compensate for the positional shift of the focal point inside the wafer. The next process step is selected based on the uniformity of the modification layer inside the wafer. If the quality of the modification layer does not meet the requirements, the process loops back to the first step, resetting the movement positions of the third convex lens 81 and the focusing objective 13. If the wafer modification quality is good, the next area is processed, and the processing flow is repeated.

[0063] like Figure 5 As shown, by changing the selection of the first convex lens 64 and the second convex lens 67, and by using two laser focus tuning methods with the voice coil motor and the piezoelectric ceramic positioner, a variety of hidden cutting methods can be achieved. Figure 5 (a) is a schematic diagram of single-focus laser lithography. In this case, no convex lenses are placed in either of the two optical paths after beam splitting, and only one type of modified layer is formed inside the workpiece during processing. Changing the position of the modified layer is achieved by moving the focusing objective 13 via piezoelectric ceramic drive, or by changing the position of the third convex lens 81. d A distance of 6. Figure 5 (b) is a schematic diagram of dual-focal laser slicing, which involves two types of modification layers, each with three layers. This can be achieved by placing a convex lens in one optical path after beam splitting or by placing convex lenses in both optical paths. An example is given here where convex lenses are placed in both optical paths. The first convex lens 64 is a plano-convex lens with a focal length of 2000mm, and the second convex lens 67 is a plano-convex lens with a focal length of 750mm. During processing, two modification layers can be generated inside the wafer, and then the position of the third convex lens 81 can be changed. d By advancing 2mm in 6 steps, both modified layers can be moved up or down a certain distance. Repeating this process can achieve multi-layer modified layers. Figure 5 (c) is a schematic diagram of real-time changing dual-focus laser hidden cutting. Convex lenses with different focal lengths are placed in the two optical paths after beam splitting. During the processing, the voice coil motor is driven to quickly reciprocate and change the position of the third convex lens 81, so that the focal position generated by the two lasers changes synchronously. In addition, depending on the processing effect, the position of the objective lens fixed by the piezoelectric ceramic positioner can be adjusted before or during processing to achieve real-time compensation of the focal position.

[0064] To simplify the process, the simulations in the above embodiments do not consider the influence of wafer internal thickness and material refractive index. Only the focal positions of the third convex lens 81 with a step distance of 2mm and a travel distance of 12mm are listed. The same applies to other lens step distances. Based on the above embodiments, in actual processing, the position of the third convex lens 81 can be flexibly adjusted using a voice coil motor according to different processing thickness requirements to obtain different laser focal positions, thereby realizing a variable multi-focal laser slicing device.

[0065] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A variable multi-focus laser stealth cutting optical path, characterized in that, It includes a laser emission module, a beam splitting and combining module, a macroscopic focus adjustment module, and a microscopic focus adjustment and focusing module arranged sequentially along the optical path; The beam splitting and combining module includes a beam splitter, at least two parallel sub-optical paths, and a beam combiner. The beam splitter splits the laser beam emitted by the laser emission module into at least two sub-beams, which then enter the sub-optical paths respectively. The beam combiner combines the sub-beams modulated by the sub-optical paths and outputs them. Each sub-optical path may or may not have a first type of convex lens, which, in conjunction with the macro-focus adjustment module, is used to change the divergence angle of the corresponding sub-beam. The first type of convex lens in each sub-optical path is a plano-convex lens with the same or different focal lengths. The displacement of the first type of convex lens and the second type of convex lens driven by the voice coil motor are coordinated to generate a single or multiple laser-modified layer with adjustable position and spacing inside the workpiece to be processed. The focus macroscopic adjustment module is disposed on the output optical path of the beam combiner, and includes a second type of convex lens that can move along the optical axis, a voice coil motor that drives the second type of convex lens to move, and a displacement detection component for detecting the displacement of the second type of convex lens. The focus micro-adjustment and focusing module includes a focusing objective and a piezoelectric displacement stage that carries the focusing objective. The piezoelectric displacement stage is used to drive the focusing objective to move at the micrometer level along its optical axis.

2. The laser stealth cutting optical path according to claim 1, characterized in that, A beam shaping module is also provided between the laser emitting module and the beam splitting and combining module. The beam shaping module includes a variable magnification beam expander, an adjustable aperture, and a first half-wave plate arranged sequentially along the optical path. The laser beam emitted by the laser emitting module is expanded by the variable magnification beam expander. After the expanded laser beam is incident on the adjustable aperture, it passes through the first half-wave plate. The beam splitter is a polarization beam splitter. The first half-wave plate cooperates with the polarization beam splitter to adjust the power of the laser beam in each sub-optical path.

3. The laser stealth cutting optical path according to claim 2, characterized in that, Each of the sub-optical paths is provided with a second half-wave plate for adjusting the polarization state of the beam, and the second half-wave plate is located in front of the first type of convex lens.

4. The laser stealth cutting optical path according to claim 1, characterized in that, The displacement detection component includes a grating ruler and a reading head. The grating ruler moves synchronously with the second type of convex lens and cooperates with the fixed reading head to obtain the movement distance of the second type of convex lens along the optical axis.

5. The laser stealth cutting optical path according to claim 1, characterized in that, It also includes a coaxial vision monitoring module, which includes a dichroic mirror and an imaging device. The dichroic mirror is disposed between the focus macro-adjustment module and the focusing objective lens, and is used to transmit visible light from the processing area to the imaging device.

6. A variable multi-focus laser stealth cutting device, characterized in that, It includes the laser stealth cutting optical path as described in any one of claims 1-5, and the processing platform that carries the workpiece to be processed.

7. A laser stealth cutting method using the apparatus as described in claim 6, characterized in that, Includes the following steps: S1: Based on the material of the workpiece to be processed and the target cutting depth, determine whether to install a first type of convex lens in each of the sub-optical paths in the beam splitting and combining module, and select the focal length of the first type of convex lens, so as to set the initial number and spacing of focal points; S2: Start the laser emission module and drive the second type of convex lens to move along the optical axis by controlling the voice coil motor, so that the laser focus can perform a large-scale scan in the thickness direction of the workpiece to be processed, forming a macroscopic modification area; S3: With the assistance of the coaxial vision monitoring module, based on real-time processing feedback, the piezoelectric displacement stage drives the focusing objective to perform micron-level displacement adjustment, thereby fine-tuning and compensating for the laser focus position. S4: Repeat steps S2 and S3 until a complete and uniform modified layer is formed in the current processing area; S5: Move the processing platform or the optical path to cut the next processing area.

8. The laser stealth cutting method according to claim 7, characterized in that, In step S2, the voice coil motor is controlled by a preset program to drive the second type of convex lens to perform periodic reciprocating motion, so that the laser focus performs real-time dynamic scanning inside the workpiece to be processed, forming a continuous or quasi-continuous modified layer.

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