Non-uniform multi-focal cell modification system and method for laser dicing of transparent materials

Abstract

The application discloses a non-uniform multi-focus unit modification system for transparent material laser slicing, which comprises an ultrashort pulse laser, a light beam regulation system, a light beam shaping system, a focusing objective, a visual positioning system and a high-precision three-dimensional motion platform; a transparent material sample to be sliced is placed on the high-precision three-dimensional motion platform; the ultrashort pulse laser provides a picosecond laser beam for the whole system; the laser beam generated by the ultrashort pulse laser is transmitted to the light beam shaping system through the light beam regulation system, a plurality of non-uniform laser beams are generated, and then the laser beams are focused and contracted through the focusing objective, so that a plurality of non-uniform focal points are obtained; the focal points are focused on the inside of the transparent material sample on the high-precision three-dimensional motion platform to perform slicing work; wherein the high-precision three-dimensional motion platform realizes the movement of the transparent material sample in x, y and z directions; and the visual positioning system is used for identifying and positioning the transparent material sample. The application can significantly improve the processing efficiency under the premise of ensuring the slicing quality.

Description

Technical Field

[0001] This invention relates to the field of laser processing technology for semiconductor materials, and specifically to a system and method for modifying non-uniform multifocal units in laser slicing of transparent materials. Background Technology

[0002] Transparent materials have been widely used in semiconductor and electronic device manufacturing due to their excellent mechanical strength, thermal stability, corrosion resistance, and photoelectric properties. However, transparent materials are hard and brittle, and traditional wire saw cutting techniques suffer from problems such as high material loss (up to 30%~50%), low cutting efficiency, severe surface damage, and easy warping and edge chipping, which seriously restrict the cost reduction and industrial application of transparent material substrates.

[0003] In recent years, ultrafast laser stealth slicing technology has become a research hotspot for slicing transparent materials due to its advantages such as non-contact operation, high precision, and low loss. This technology utilizes a laser that penetrates the material surface and focuses internally, forming a modified layer through nonlinear absorption effects. This disrupts molecular bonds and induces crack formation, significantly reducing material strength and enabling easy separation. Existing laser slicing technologies generally employ a single-focus, single-scan processing strategy. This involves using fixed laser parameters (such as pulse energy and repetition frequency) and a scanning path to perform a single scan of the material's interior to form the modified layer. This strategy cannot effectively reconcile the inherent contradiction between processing efficiency and material loss, is difficult to adapt to the inherent material inhomogeneities of transparent materials, and has weak control over the stress field within the modified layer. The direct consequence is a narrow process window; in pursuit of high yield, efficiency is often sacrificed or losses increased, leading to poor process stability and limited overall efficiency.

[0004] To improve efficiency, some methods have introduced multifocal shaping. However, multifocal energy distribution is uniform, ignoring the inherent properties of transparent materials, making targeted modification impossible, and easily leading to excessive damage or insufficient modification. For example, Zhang et al. [arXiv:2411.18093] used a spatial light modulator to generate a multifocal picosecond laser beam with uniform energy distribution to achieve vertical slicing of 4H-SiC ingots. However, this method ignored the local inhomogeneity of SiC crystals, resulting in insufficient crack connection and discontinuous crack propagation when the focal energy is too low, or excessive longitudinal damage and expansion of the heat-affected zone when the energy is too high, thus increasing the surface roughness of the slice. Both excessively high and low laser modification layer energy can lead to material damage, discontinuous cracks, or rough slice surface.

[0005] Therefore, there is an urgent need for a system and processing method that can achieve efficient and controllable modification layer formation through multi-focus non-uniform control, so as to significantly improve the efficiency and quality of laser slicing of transparent materials. Summary of the Invention

[0006] To overcome the shortcomings of the existing technology, this invention provides a non-uniform multifocal unit modification system and method for laser slicing of transparent materials. By using a spatial light modulator combined with a focusing objective lens, the laser focus is shaped into multiple focal points with different energies distributed in a one-dimensional planar array, forming a non-uniform multifocal light field. Through a specific scanning path, a stable and continuous unit modification layer is efficiently prepared inside the transparent material. The degree of modification can be locally controlled by utilizing the energy differences of each focal point, thereby significantly improving processing efficiency while ensuring the quality of the slice.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A non-uniform multifocal unit modification system for laser slicing of transparent materials includes an ultrashort pulse laser, a beam control system, a beam shaping system, a focusing objective, a vision positioning system, a three-dimensional motion platform, and a control computer; the transparent material sample to be sliced ​​is placed on the three-dimensional motion platform;

[0009] The ultrashort pulse laser provides a picosecond laser beam for the entire system. The laser beam generated by the ultrashort pulse laser is transmitted to the beam shaping system through the beam control system to generate multiple non-uniform laser beams (i.e., multiple laser beams with symmetrical concave energy distribution in a one-dimensional planar array). After being focused and condensed by the focusing objective, multiple non-uniform focal points are obtained. The focal points are focused on the interior of a transparent material sample on a high-precision three-dimensional motion platform for slicing.

[0010] The three-dimensional motion platform enables the transparent material sample to move in the x, y, and z directions; the visual positioning system is used to identify and locate the transparent material sample.

[0011] The ultrashort pulse laser, beam shaping system, visual positioning system, and three-dimensional motion platform are controlled by a control computer.

[0012] The three-dimensional motion platform, through its reciprocating motion, causes the laser focus to scan within the sample. Multiple focuses thus act in parallel on the OXY plane at the same Z-axis position inside the transparent material sample, forming a cavity array (each focus induces a micro-cavity, which generates micro-explosions or vaporization cavities due to nonlinear absorption effects). Simultaneously, between the cavities in the cavity array, the stress field gradient induced by the difference in focus energy promotes the continuous propagation and lateral connection of microcracks. The entire slicing process is observed through a visual positioning system.

[0013] The beam control system includes a half-wave plate, a GranTyl prism, a beam expander, and a first reflector arranged coaxially along the beam propagation direction. The half-wave plate and the GranTyl prism are placed in sequence, and the beam passes through the half-wave plate first and then through the GranTyl prism. The half-wave plate is used to adjust the polarization direction of the input laser beam, and the GranTyl prism filters out all s-component light.

[0014] After the beam passes through the half-wave plate, the p-component and s-component are separated by the Glan Taylor prism, and the s-component is completely filtered out, ensuring that the light incident on the liquid crystal spatial light modulator is all p-component light. At the same time, it can also achieve stepless adjustment of the beam energy. The beam expander is used to expand the incident beam to 4-5 times.

[0015] The ultrashort pulse laser is a picosecond laser, emitting a Gaussian beam. The half-wave plate is a true zero-order half-wave plate made of quartz, with a designed wavelength of 1030-1064 nm, consistent with the laser wavelength. The Glan Taylor prism has an aperture of 8-12 mm and an operating wavelength of 200 nm-3.0 μm. The beam expander is a 2-10x adjustable coaxial beam expander.

[0016] The beam shaping system includes a spatial light modulator, a first lens, an aperture stop, a second lens, and a second mirror arranged sequentially along the beam transmission direction.

[0017] The spatial light modulator is superimposed with a blazed grating to dynamically control the intensity distribution of the transverse laser field, shaping the ultrashort pulse laser beam transmitted from the beam control system into multiple laser beams distributed in a non-uniform planar one-dimensional array (i.e., multiple laser beams with symmetrical concave energy distribution in a planar one-dimensional array).

[0018] The spatial light modulator, the first lens, the aperture stop, the second lens, and the second reflector are placed sequentially on the same straight line, and the distance between each of the spatial light modulator, the first lens, the aperture stop, the second lens, and the second reflector is one focal length.

[0019] The focal length is the same as that of the first lens.

[0020] Both the first lens and the second lens are lenses with a focal length of 150-300 mm, and the diameter of the aperture stop is 1 mm to 12 mm.

[0021] The first lens and the second lens form a 4f system, which, together with a blazed grating and an aperture stop, is used to filter out zero-order diffraction light and adjust the optical path.

[0022] The spatial light modulator is based on the phase hologram of the superimposed blazed grating, and the generated non-uniform multi-beam laser beam field is located at the +1 diffraction order. By adjusting the spatial frequency of the blazed grating, the deflection angle of the +1 order diffracted beam is controlled, so that it is spatially separated from the zero order diffracted light on the Fourier surface of the first lens in the subsequent 4f system. The aperture stop is used to filter out interference components such as the zero order light, allowing only the useful +1 order multi-beam laser beam to pass through.

[0023] The control computer is connected to an ultrashort pulse laser, a spatial light modulator, a three-dimensional motion platform, and a CCD camera;

[0024] These devices are used to control the parameter settings of ultrashort pulse lasers, compile and load holograms on spatial light modulators, move transparent material crystal samples at a constant speed using a three-dimensional motion platform, and identify, locate, and observe the beam energy of transparent material samples.

[0025] The parameter settings of the ultrashort pulse laser specifically refer to adjusting the laser pulse width, repetition frequency, and single pulse energy; wherein the laser pulse width ranges from 100 fs. 2ps, with a repetition frequency range of 1kHz. 100kHz, single pulse energy range is 5μJ 20μJ;

[0026] The focusing objective has a focal length of 2-6 mm, a numerical aperture (NA) of 0.4-0.85, and a magnification of 20-100 times. It is used to focus non-uniform multiple laser beams to form non-uniform multifocal points (i.e., multiple laser focal points with symmetrical concave energy distribution in a planar one-dimensional array).

[0027] The focusing objective is placed at the coaxial position of the beam reflected by the second mirror.

[0028] The visual positioning system includes a long-pass dichroic mirror, a CCD camera, and a ring-shaped white light source.

[0029] The long-pass dichroic mirror is used to transmit 1064nm long-pass infrared laser light and reflect white light; the ring-shaped white light source is used to provide illumination for the CCD camera 18; the CCD camera is used to observe the transparent material sample at the coaxial position of the beam of white light emitted from the ring-shaped white light source after reflection by the long-pass dichroic mirror.

[0030] During the slicing process, the laser beam output by the ultrashort pulse laser passes sequentially through a half-wave plate, a Glan Taylor prism, a beam expander, a first reflecting mirror, a spatial light modulator with a superimposed blazed grating, a first lens, an aperture stop, a second lens, a second reflecting mirror, and a long-pass dichroic mirror before being focused by the focusing objective; the laser beam output by the focusing objective acts on the interior of the transparent material sample to perform slicing.

[0031] Meanwhile, this invention also provides a method for modifying non-uniform multifocal units in laser slices of transparent materials, comprising the following steps:

[0032] Step 1: Fix the transparent material sample on the three-dimensional motion platform, adjust the three-dimensional motion platform by controlling the computer so that the position of the transparent material sample is directly opposite the exit end of the focusing objective lens, and identify the position of the sample by the visual positioning system;

[0033] Step 2: Based on the required thickness of the transparent material sample to be cut, set the processing parameters of the ultrashort pulse laser through the control computer, and move the three-dimensional motion platform to position the laser focus at the preset slicing starting depth (Z-axis position) inside the sample.

[0034] Step 3: Turn on the laser to emit laser light, and then load a preset phase hologram onto the spatial light modulator through the control computer, superimpose a blazed grating, and shape the input Gaussian beam into multiple laser beams distributed in a non-uniform planar one-dimensional array, while ensuring that the zero-order light is filtered out by the aperture stop; the beam is transmitted from the beam shaping system and passes through the objective lens to obtain a non-uniform multifocal beam (multiple laser focal points with symmetrical concave energy distribution in a planar one-dimensional array), at which point the multifocal beam is focused on the preset slice initiation depth inside the sample.

[0035] The phase transfer function of a multifocal array with non-uniform energy distribution on a one-dimensional plane was calculated analytically. After being encoded into a phase hologram by a computer controller, it was loaded onto a spatial light modulator to generate a multifocal light field. The energy distribution of the multifocal array was then controlled and speckle suppression was optimized by an energy gradient optimization function and a random phase perturbation function, respectively. The complex amplitude transfer function was obtained by superimposing the two functions. The zero-order diffraction spot was then separated by a blazed grating and encoded into a hologram by a computer controller. This hologram was loaded onto a spatial light modulator to achieve complex amplitude modulation. Finally, a non-uniform multifocal array with the lowest energy at the center focus and the energy of the two side focus points increasing symmetrically was obtained.

[0036] Step 4: Position the 3D motion platform at the bottom left corner of sample 13 (X=0, Y=0); move the platform at a constant speed along the positive scanning direction (Y-axis increases) to scan the length of the sample using a non-uniform multi-focus scanning method; after scanning, move the 3D motion platform vertically (X-axis increases by 3 μm); then scan back to the beginning from the end along the reverse scanning direction (Y-axis decreases); repeat the above positive and negative scanning process on the OXY plane at the same Z-axis position until the X-axis has moved a cumulative 30 μm, so that the discrete modified cavities generated by the multi-focus are tightly connected laterally. The purpose is to construct a modified cavity array with a definite width, continuous modification, and sufficient modification to guide crack initiation. Since the energy of each focus is distributed in a symmetrical concave shape with a low center and high sides during each reciprocating scan, the local stress field generated between the cavities has a favorable lateral gradient, which promotes the generation and continuous propagation of microcracks between adjacent cavities, ultimately forming a non-uniform unit modification layer with a width of 30 μm on the same Z-plane;

[0037] The effect of this design is that it not only ensures that cracks are effectively guided within the modified layer, preferentially and stably propagating laterally (X direction) and interconnecting with each other to form a smooth separation surface; but also significantly suppresses the excessive growth of harmful longitudinal cracks and subsurface damage that are easily caused by uniform or excessive energy, providing a continuous and controllable weakening channel for subsequent controlled external force-induced directional crack propagation and sheet peeling.

[0038] Step 5: Starting from the end position of the current unit modification layer, increase by 100 μm along the X-axis to locate the starting position of the next unit modification layer; repeat step 4 until the entire sample width is covered; during processing, the vision positioning system monitors the formation of the modification layer and crack propagation in real time; after completing all unit modification layers, remove the transparent material sample and turn off all equipment;

[0039] Step 6: Apply external force to the processed transparent material sample to induce crack propagation, causing the cracks to propagate directionally along the unit modified layer array and connect with each other, ultimately achieving complete peeling of the transparent material sheet to obtain the transparent material sheet.

[0040] In step 3, the phase transfer function of a non-uniform multi-beam laser array with the lowest energy at the central focal point and symmetrically increasing energy at the two side focal points on a one-dimensional plane was calculated using analytical methods. The phase transfer function is:

[0041] (1)

[0042] It is a phase function; A n ——No. n The relative amplitude of each focal point; u n , vn ——No. n Normalized spatial frequency of each focus; x , y —SLM plane coordinates / mm; N — Total number of focal points; λ — Wavelength / nm;

[0043] The phase transfer function was encoded into a phase hologram using a control computer and then loaded into a spatial light modulator to generate a multifocal light field. The energy gradient optimization function and the random phase perturbation function were then used to regulate the energy distribution and optimize speckle suppression of the multifocal array, respectively. The complex amplitude transfer function was obtained by superimposing the two functions. The energy gradient optimization function is as follows:

[0044] (2)

[0045] in, This is the energy gradient intensity coefficient; x 0 represents the array center position in mm; The gradient distribution range is shown in mm.

[0046] The random phase perturbation function is

[0047] (3)

[0048] in, β This is the phase perturbation intensity coefficient; R The effective perturbation region radius is given in mm; rand(- π , π Generate random numbers that are uniformly distributed in the range [-π, π].

[0049] Then, a composite phase hologram is obtained using a blazed grating, and the composite phase function is:

[0050] (4)

[0051] in, f x , f y The spatial frequency (line / mm) of the blazed grating;

[0052] The image is encoded into a hologram using a control computer and loaded onto a liquid crystal spatial light modulator to achieve complex amplitude modulation. Finally, a non-uniform multi-beam laser array is obtained, in which the energy distribution in the lateral direction is the lowest at the central focal point and the energy at the two side focal points increases symmetrically in sequence. This is more in line with the requirements for laser slicing of transparent materials.

[0053] In step 6, the method of applying external force to achieve complete peeling of the transparent material sheet is: applying tension or ultrasonic vibration.

[0054] The beneficial effects of this invention are:

[0055] This invention uses a spatial light modulator and objective lens to shape a single ultrafast laser beam into a planar one-dimensional non-uniform multifocal array (multiple laser focal points with symmetrical concave energy distribution in a planar one-dimensional array). A combined reciprocating scanning and lateral stepping approach is used to construct a unit modification layer array within a transparent material. The parallel multifocal scanning significantly improves the efficiency of material modification, while the non-uniform energy distribution of the focal points, in conjunction with the multiple scanning strategy, creates an optimized stress field within the unit modification layer. This ensures the directional and stable propagation of cracks, guaranteeing slicing success and surface quality, while effectively suppressing excessively deep longitudinal cracks and subsurface damage. Thus, while achieving high-efficiency processing, material loss is kept to a low level. Furthermore, the method exhibits strong adaptability, effectively compensating for the negative impacts of the inherent optical inhomogeneities of transparent materials. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of a non-uniform multifocal unit modification system for laser slicing of transparent materials, as described in this invention.

[0057] Figure 2 This is a schematic diagram of the fabrication of a unit modified layer array based on a planar one-dimensional non-uniform multifocal structure as described in this invention.

[0058] Figure 3 The images show the upper and lower surfaces of the sample after laser slicing and peeling of silicon carbide crystals using a non-uniform multi-focus processing unit modified layer array as described in this invention (the upper surface is on the left and the lower surface is on the right).

[0059] The attached figures are labeled as follows:

[0060] 1. Ultrashort pulse laser; 2. Half-wave plate; 3. Glan Taylor prism; 4. Beam expander; 5. First reflecting mirror; 6. Spatial light modulator with superimposed blazed gratings; 7. First lens; 8. Aperture stop; 9. Second lens; 10. Second reflecting mirror; 11. Long-pass dichroic mirror; 12. Objective lens; 13. Transparent material sample; 14. Three-dimensional motion platform; 15. CCD camera; 16. Control computer; 17. Ring white light source. Detailed Implementation

[0061] The present invention will now be described in further detail with reference to the accompanying drawings.

[0062] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a non-uniform multifocal unit modification system and method for laser slicing of transparent materials. This system uses a spatial light modulator combined with a focusing objective to shape the laser focus into multiple focal points with different energies distributed in a planar one-dimensional array, forming a non-uniform multifocal light field. Through a specific scanning path, a stable and continuous unit modification layer is efficiently prepared within the transparent material. The degree of modification is locally controlled by utilizing the energy differences of each focal point, thereby significantly improving processing efficiency while ensuring slice quality.

[0063] Please see Figure 1 The present invention provides a non-uniform multifocal unit modification system for laser slicing of transparent materials, comprising an ultrashort pulse laser 1, a beam control system, a beam shaping system, a focusing objective lens 12, a visual positioning system, a three-dimensional motion platform 14, and a control computer 16;

[0064] The three-dimensional motion platform 14 enables the transparent material sample 13 to move in the x, y, and z directions; the visual positioning system is used to identify and position the transparent material sample 13; the visual positioning system includes a long-pass dichroic mirror 11, a CCD camera 15, and a ring-shaped white light source 17; the focusing objective lens 12 is used to focus non-uniform multiple laser beams to output non-uniform multifocal points (i.e., multiple laser focal points with symmetrical concave energy distribution in a one-dimensional planar array), and the output laser beam acts on the interior of the transparent material sample 13 on the three-dimensional motion platform 14 to slice it.

[0065] The ultrashort pulse laser 1 provides a picosecond laser beam for the entire system. The laser beam is transmitted to the beam shaping system via the beam control system to generate multiple non-uniform laser beams (i.e., multiple laser beams with symmetrical concave energy distribution in a one-dimensional planar array). After being focused and contracted by the focusing objective lens 12, multiple non-uniform focal points are obtained. Then, the beam is applied to the interior of the transparent material sample 13 on the three-dimensional motion platform 14 to perform slicing. A cavity array is formed on the OXY plane at the same Z-axis position within the transparent material sample 13, and microcracks are continuously extended between the cavities in the cavity array. The entire slicing process is observed by a visual positioning system.

[0066] The ultrashort pulse laser 1 is a picosecond laser, and the emitted laser beam is a Gaussian beam.

[0067] The beam control system includes a half-wave plate 2, a Glan Taylor prism 3, a beam expander 4, and a first reflector 5 arranged sequentially along the beam propagation direction. The half-wave plate 2 and the Glan Taylor prism 3 are placed sequentially, and the beam first passes through the half-wave plate 2 and then through the Glan Taylor prism 3, which is used to control the polarization direction of the input laser beam and filter out all s-component light. After the beam passes through the half-wave plate 2, the p-component light and the s-component light are separated by the Glan Taylor prism 3, and all s-component light is filtered out, ensuring that the light incident on the liquid crystal spatial light modulator is all p-component light. At the same time, it can also achieve stepless adjustment of the beam energy. The beam expander 4 is used to expand the incident beam to 4-5 times.

[0068] The half-wave plate 2 is a quartz true zero-order half-wave plate with a designed wavelength of 1064nm, which is consistent with the laser wavelength. The Glan Taylor prism 3 has a light-transmitting aperture of 10 mm and an operating wavelength of 200 nm-3.0 μm. The beam expander 4 is a 2-10x adjustable coaxial beam expander.

[0069] The beam shaping system consists of a spatial light modulator 6, a first lens 7, an aperture stop 8, a second lens 9, and a second reflecting mirror 10 arranged sequentially; wherein

[0070] The spatial light modulator 6, with its superimposed blazed grating, is used to dynamically control the laser light field distribution. It shapes the ultrashort pulse laser beam transmitted from the beam control system into a non-uniform multi-beam laser array with a one-dimensional plane energy distribution exhibiting the lowest energy at the central focal point and symmetrically increasing energy at the two side focal points. The principle is as follows: the phase transfer function of this non-uniform multi-beam laser array with the lowest energy at the central focal point and symmetrically increasing energy at the two side focal points is calculated analytically. The phase transfer function is...

[0071] (1)

[0072] It is a phase function; A n ——No. n The relative amplitude of each focal point; u n , v n ——No. n Normalized spatial frequency of each focus; x , y —SLM plane coordinates / mm; N — Total number of focal points; λ — Wavelength / nm;

[0073] The phase transfer function is encoded into a phase hologram using the control computer 16 and then loaded into the spatial light modulator 6 to generate a multifocal light field. The energy gradient optimization function and the random phase perturbation function are then used to regulate the energy distribution and optimize speckle suppression of the multifocal array, respectively. The complex amplitude transfer function is obtained by superimposing the two functions. The energy gradient optimization function is...

[0074] (2)

[0075] in, This represents the energy gradient intensity coefficient. x 0 represents the array center position in mm; The gradient distribution range is given by (mm); the random phase perturbation function is given by (mm).

[0076] (3)

[0077] in, β This is the phase perturbation intensity coefficient; R The effective perturbation region radius is given in mm; rand(- π , π Generate random numbers that are uniformly distributed in the range [-π, π].

[0078] Then, a composite phase hologram is obtained using a blazed grating, and the composite phase function is:

[0079] (4)

[0080] in, f x , f y The spatial frequency (line / mm) of the blazed grating;

[0081] The image is encoded into a hologram by the control computer 16 and loaded onto the liquid crystal spatial light modulator 6 to achieve complex amplitude modulation. Finally, a non-uniform multi-beam laser array with a horizontal energy distribution that is the lowest at the center focus and symmetrically increases at the two side focus points is obtained, which is more in line with the requirements of laser slicing of transparent materials.

[0082] The spatial light modulator 6 is a Hamamatsu X15213-03BL reflective pure phase liquid crystal spatial light modulator. It has 1272×1024 pixels, a pixel size of 12.5μm, and an effective liquid crystal panel area of ​​15.9×12.8 mm. 2 .

[0083] The spatial light modulator 6, the first lens 7, the aperture stop 8, the second lens 9, and the second reflector 10 are placed sequentially on the same straight line. The first lens 7 is placed one focal length apart from the spatial light modulator 6, the aperture stop 8 is placed one focal length apart from the spatial light modulator 6, the first lens 7 is placed one focal length apart from the aperture stop 8, the second lens 7 is placed one focal length apart from the aperture stop 8, and the second reflector 10 is placed one focal length apart from the aperture stop 8. The focal length of each of these is the same as that of the first lens 7.

[0084] The first lens 7 and the second lens 9 are both lenses with a focal length of 200mm, and the diameter of the aperture stop 8 is 1mm to 10mm.

[0085] The first lens 7 and the second lens 9 form a 4f system, which, together with the blazed grating and the aperture stop 8, is used to filter out zero-order diffraction light and adjust the optical path.

[0086] When a phase hologram of a blazed grating is superimposed on the spatial light modulator 6, the spatial frequency of the blazed grating is adjusted so that all the non-uniform laser beams obtained by shaping enter the +1 diffraction order. After being focused by the first lens 7 in the 4f system, the non-uniform laser beams and the zero-order diffracted light are separated by a certain distance radially on the focal plane of the first lens 7. Then, the physical blocking of the aperture stop 8 is used to filter out the interference light such as the zero-order diffracted light.

[0087] The control computer 16 is connected to the ultrashort pulse laser 1, the spatial light modulator 6, the three-dimensional motion platform 14, and the CCD camera 15.

[0088] These are respectively used to control the parameter setting of the ultrashort pulse laser 1, the compilation and loading of the hologram on the spatial light modulator 6, the uniform movement of the transparent material sample 13 driven by the three-dimensional motion platform 14, and the identification, positioning and beam energy observation of the transparent material sample 13.

[0089] The visual positioning system includes a long-wavelength dichroic mirror 11, a CCD camera 15, and a ring-shaped white light source 17.

[0090] The focusing objective 12 has a focal length of 4 mm, a numerical aperture (NA) of 0.65, and a magnification of 50x. It is used to focus non-uniform multiple laser beams to output non-uniform multi-focal points (i.e., multiple laser focal points with symmetrical concave energy distribution in a planar one-dimensional array).

[0091] The focusing objective lens 12 is positioned coaxially with the beam reflected by the second reflecting mirror 10.

[0092] The long-pass dichroic mirror 11 is used to transmit 1064nm long-pass infrared laser light and reflect white light.

[0093] The ring-shaped white light source 17 is used to provide illumination for the CCD camera 18;

[0094] The long-pass dichroic mirror 11, objective lens 12, and ring white light source 17 are placed sequentially on the same horizontal line; the CCD camera 15 is placed on the bypass of the long-pass dichroic mirror 11 on the same horizontal line.

[0095] During the slicing process, the laser beam output by the ultrashort pulse laser 1 passes sequentially through a half-wave plate 2, a Glan Taylor prism 3, a beam expander 4, a first reflecting mirror 5, a spatial light modulator 6 with a superimposed blazed grating 6, a first lens 7, an aperture stop 8, a second lens 9, a second reflecting mirror 10, and a long-pass dichroic mirror 11 before being focused by the focusing objective lens 12; the laser beam output by the focusing objective lens 12 acts on the interior of the transparent material sample 13 to perform slicing.

[0096] The three-dimensional motion platform 14 has a travel of 60mm in the x and y directions and a travel of 30mm in the z direction, with an accuracy of 0.001mm.

[0097] This invention provides a method for modifying non-uniform multifocal units in laser slices of transparent materials, comprising the following steps:

[0098] Step 1: Fix the transparent material sample 13 on the three-dimensional motion platform 14, adjust the position of the transparent material sample 13 to face the exit end of the focusing objective lens through the control computer 16, and identify the position of the sample through the visual positioning system;

[0099] Step 2: Based on the required thickness of the transparent material sample 13 to be cut, the processing parameters of the ultrashort pulse laser 1 are set by the control computer 16, and the three-dimensional motion platform 14 is moved to position the laser focus at the preset slicing starting depth (Z-axis position) inside the sample.

[0100] Step 3: Turn on the laser to emit laser light, and then load a preset phase hologram onto the spatial light modulator 6 through the control computer 16, and superimpose a blazed grating to shape the input Gaussian beam into multiple laser beams distributed in a non-uniform planar one-dimensional array, while ensuring that the zero-order light is filtered out by the aperture stop 8; the beam is transmitted from the beam shaping system and is focused by the objective lens 12 to obtain a non-uniform multifocal beam (multiple laser focal points with symmetrical concave energy distribution in a planar one-dimensional array). At this time, the multifocal beam is focused on the preset slice initiation depth inside the sample.

[0101] The phase transfer function of a multifocal array with non-uniform energy distribution on a one-dimensional plane was calculated analytically. After being encoded into a phase hologram by a computer controller 16, it was loaded onto a spatial light modulator 6 to generate a multifocal light field. The energy distribution of the multifocal array was then controlled and speckle suppression was optimized by an energy gradient optimization function and a random phase perturbation function, respectively. The complex amplitude transfer function was obtained by superimposing the two functions. The zero-order diffraction spot was then separated by a blazed grating and encoded into a hologram by the computer controller 16. This hologram was loaded onto the spatial light modulator 6 to achieve complex amplitude modulation. Finally, a non-uniform multifocal array with the lowest energy at the center focus and the energy of the two side focus points increasing symmetrically was obtained.

[0102] Step 4: Position the 3D motion platform 14 at the lower left corner of the sample 13 (X=0, Y=0); move the platform at a constant speed along the positive scanning direction (Y-axis increases) to scan the length of the sample using a non-uniform multi-focus scanning method; after the scan is completed, move the 3D motion platform 14 along the vertical direction (X-axis increases by 3 μm); then scan back to the beginning from the end along the reverse scanning direction (Y-axis decreases); repeat the above positive and negative scanning process on the OXY plane at the same Z-axis position until the X-axis has moved a cumulative 30 μm, generating a cavity array, and continuously expanding microcracks are generated between the cavities in the cavity array, ultimately forming a non-uniform unit modification layer with a width of 30 μm (due to different focus energies, the degree of modification is symmetrically concavely distributed, promoting the lateral propagation of cracks).

[0103] Step 5: Increase the position of the current unit modification layer by 100 μm along the X-axis to locate the starting position of the next unit modification layer; repeat step 4 until the entire sample width is covered; during the processing, the vision positioning system monitors the formation of the modification layer and crack propagation in real time; after all unit modification layers are completed, remove the transparent material sample 13 and turn off all equipment;

[0104] Step 6: Apply external force to the processed transparent material sample 13 to induce crack propagation, so that the cracks propagate directionally along the unit modified layer array and connect with each other, and finally achieve complete peeling of the transparent material sheet to obtain the transparent material sheet;

[0105] Furthermore, in step 1, the transparent material sample 13 can be a transparent material such as silicon carbide, silicon, gallium nitride, diamond, sapphire, and zirconium oxide;

[0106] Furthermore, in step 2, setting the processing parameters of the ultrashort pulse laser 1 specifically refers to setting the pulse width, repetition frequency, and single pulse energy of the laser emitted by the laser.

[0107] The laser pulse width ranges from 100 fs. 2ps, with a repetition frequency range of 1kHz. 100kHz, single pulse energy range is 5μJ 20μJ.

[0108] Further, in step 3, the non-uniform multifocal focus (multiple laser focal points with symmetrical concave energy distribution in a planar one-dimensional array) specifically refers to multiple laser focal points with symmetrical concave energy distribution in a planar one-dimensional array, with a distance of 3 μm between the focal points, and the focal point array distribution direction is perpendicular to the scanning direction. Its energy distribution satisfies the following functional relationship: along the array direction (X-axis), the energy of the central focal point is the lowest, and it increases symmetrically by 1 μJ to both sides.

[0109] Furthermore, in step 4, the speed at which the transparent material sample 13 moves along the X and Y axes is controlled to be 2-1000 mm / s;

[0110] Furthermore, in step 6, the method of applying external force to achieve complete peeling of the transparent material sheet is to apply tension or ultrasonic vibration.

[0111] To address the limitations of current single-focus laser slicing techniques in adapting to the inherent material inhomogeneities of transparent materials and their weak ability to control the internal stress field of the modified layer, this invention provides a non-uniform multi-focus unit modification system and method for laser slicing of transparent materials. This system uses a spatial light modulator combined with a focusing objective to shape the laser focus into multiple focal points with different energies distributed in a one-dimensional planar array, forming a non-uniform multi-focus light field. Through a specific scanning path, a stable and continuous unit modified layer is efficiently prepared within the transparent material sheet. The degree of modification is locally controlled by utilizing the energy differences of each focal point, thereby significantly improving processing efficiency while ensuring slice quality.

[0112] Example

[0113] Taking laser slicing of silicon carbide crystals as an example, the main steps are as follows:

[0114] Step 1: Fix the silicon carbide crystal sample on a high-precision three-dimensional motion platform, adjust the position of the silicon carbide crystal sample to face the exit end of the focusing objective lens through the control computer, and identify the position of the sample through the visual positioning system;

[0115] Step 2: Based on the required thickness of the silicon carbide crystal sample to be cut, the processing parameters of the ultrashort pulse laser are set by the control computer, and the high-precision three-dimensional motion platform is moved to position the laser focus at the preset slicing starting depth (Z-axis position) inside the sample.

[0116] Step 3: Turn on the laser to emit laser light, and then load a preset phase hologram onto the spatial light modulator through the control computer, superimpose a blazed grating, and shape the input Gaussian beam into multiple laser beams distributed in a non-uniform planar one-dimensional array, while ensuring that the zero-order light is filtered out by the aperture stop; the beam is transmitted from the beam shaping system and passes through the objective lens to obtain a non-uniform multifocal beam (multiple laser focal points with symmetrical concave energy distribution in a planar one-dimensional array), at which point the multifocal beam is focused on the preset slice initiation depth inside the sample.

[0117] Step 4: Position the high-precision three-dimensional motion platform at the bottom left corner of the sample (X=0, Y=0); move the platform at a constant speed along the positive scanning direction (Y-axis increases) to scan the length of the sample using a non-uniform multi-focal scanning method; after the scan is completed, move the three-dimensional motion platform 14 along the vertical direction (X-axis increases by 3 μm); then scan back to the beginning from the end along the reverse scanning direction (Y-axis decreases); repeat the above positive and negative scanning process on the OXY plane at the same Z-axis position until the X-axis moves a cumulative 30 μm, generating a cavity array, and continuously expanding microcracks are generated between the cavities in the cavity array, ultimately forming a non-uniform unit modification layer with a width of 30 μm (due to different focal energy, the degree of modification is symmetrically concavely distributed, promoting the lateral propagation of cracks). Figure 2 This is a schematic diagram of the fabrication of a unit modified layer array based on a planar one-dimensional non-uniform multifocal focus;

[0118] Step 5: Increase the position of the current unit modification layer by 100 μm along the X-axis to locate the starting position of the next unit modification layer; repeat step 4 until the entire sample width is covered; during the processing, the vision positioning system monitors the formation of the modification layer and crack propagation in real time; after completing all unit modification layers, remove the silicon carbide crystal sample and turn off all equipment;

[0119] Step 6: Apply external force to the processed silicon carbide crystal sample to induce crack propagation, causing the cracks to propagate directionally along the unit modified layer array and connect with each other, ultimately achieving complete peeling of the silicon carbide wafer to obtain a silicon carbide crystal sheet. An image of the silicon carbide sample after laser slicing is shown below. Figure 3 As shown.

[0120] Although this specification uses terms such as ultrashort pulse laser, beam control system, beam shaping system, visual positioning system, spatial light modulator, half-wave plate, Glan Taylor prism, beam expander, high-precision three-dimensional motion platform, control computer, long-pass dichroic mirror, focusing objective, transparent material sample, lens, aperture stop, CCD camera, ring white light source, and reflector extensively, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing the essence of the invention, and interpreting them as any additional limitation would be contrary to the spirit of the invention.

[0121] It should be understood that any parts not described in detail in this specification belong to the prior art.

[0122] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A non-uniform multifocal unit modification system for laser slicing of transparent materials, characterized in that, Includes an ultrashort pulse laser (1), a beam control system, a beam shaping system, a focusing objective (12), a visual positioning system, and a three-dimensional motion platform (14); the transparent material sample (13) to be sliced ​​is placed on the three-dimensional motion platform (14); The ultrashort pulse laser (1) provides a picosecond laser beam for the entire system. The laser beam generated by the ultrashort pulse laser (1) is transmitted to the beam shaping system through the beam control system to generate multiple non-uniform laser beams. After being focused and condensed by the focusing objective (12), multiple non-uniform focal points are obtained. Multiple non-uniform focal points refer to multiple laser focal points in which the energy is symmetrically concave in a one-dimensional planar array. The focus is on the interior of the transparent material sample (13) on the three-dimensional motion platform (14) for slicing. The three-dimensional motion platform (14) enables the transparent material sample (13) to move in the x, y, and z directions; the visual positioning system is used to identify and position the transparent material sample (13). The three-dimensional motion platform (14) uses its reciprocating motion to make the laser focus scan inside the sample. Multiple focal points thus act in parallel on the OXY plane at the same Z-axis position inside the transparent material sample (13), forming a cavity array. The beam shaping system includes a spatial light modulator (6), a first lens (7), an aperture stop (8), a second lens (9), and a second reflector (10) arranged sequentially along the beam transmission direction. The spatial light modulator (6) is superimposed with a blazed grating, which is used to dynamically control the intensity distribution of the transverse light field of the laser, and to shape the ultrashort pulse laser beam transmitted from the beam control system into multiple laser beams distributed in a non-uniform planar one-dimensional array. The non-uniform planar one-dimensional array of multiple laser beams is a non-uniform multi-beam laser beam array in which the energy distribution on the one-dimensional plane is the lowest at the central focal point and the energy at the two side focal points increases symmetrically.

2. The non-uniform multifocal unit modification system for laser slicing of transparent materials according to claim 1, characterized in that, Between the cavities in the cavity array, the stress field gradient induced by the difference in focal energy promotes the continuous propagation and lateral connection of microcracks, and the entire slicing process is observed by a visual positioning system.

3. The non-uniform multifocal unit modification system for laser slicing of transparent materials according to claim 1, characterized in that, The beam control system includes a half-wave plate (2), a GranTaylor prism (3), a beam expander (4), and a first reflector (5) arranged coaxially along the beam propagation direction. The half-wave plate (2) and the GranTaylor prism (3) are placed in sequence. The beam passes through the half-wave plate (2) first and then through the GranTaylor prism (3). The half-wave plate (2) is used to adjust the polarization direction of the input laser beam, and the GranTaylor prism (3) filters out all s-component light. After the beam passes through the half-wave plate (2), the p-component light and the s-component light are separated by the GranTeller prism (3), and the s-component light is completely filtered out. At the same time, the beam energy is infinitely adjustable. The beam expander (4) is used to expand the incident beam to 4-5 times. The ultrashort pulse laser (1) is a picosecond laser that emits a Gaussian beam. The half-wave plate (2) is a quartz true zero-order half-wave plate with a designed wavelength of 1030-1064 nm, which is consistent with the laser wavelength. The Glan Taylor prism (3) has an aperture of 8-12 mm and a working wavelength of 200 nm-3.0 μm. The beam expander (4) is a 2-10 times adjustable coaxial beam expander.

4. The non-uniform multifocal unit modification system for laser slicing of transparent materials according to claim 1, characterized in that, The spatial light modulator (6), the first lens (7), the aperture stop (8), the second lens (9) and the second reflector (10) are placed sequentially on the same straight line, and the distance between each of the spatial light modulator (6), the first lens (7), the aperture stop (8), the second lens (9) and the second reflector (10) is one focal length. The focal length is the same as that of the first lens (7); The first lens (7) and the second lens (9) are both lenses with a focal length of 150-300 mm, and the diameter of the aperture stop (8) is 1 mm to 12 mm. The first lens (7) and the second lens (9) form a 4f system, which, together with the blazed grating and the aperture stop (8), is used to filter out zero-order diffraction light and adjust the optical path. The spatial light modulator (6) generates a non-uniform multi-beam laser beam field based on the phase hologram of the loaded superimposed blazed grating, which is located at the +1 diffraction order. By adjusting the spatial frequency of the blazed grating, the deflection angle of the +1 order diffracted beam is controlled, so that it is spatially separated from the zero order diffracted light on the Fourier surface of the first lens (7) in the subsequent 4f system. The aperture stop (8) is used to filter out interference components such as the zero order light, allowing only the useful +1 order multi-beam laser beam to pass through.

5. The non-uniform multifocal unit modification system for laser slicing of transparent materials according to claim 1, characterized in that, The modification system also includes a control computer (16) connected to an ultrashort pulse laser (1), a spatial light modulator (6), a three-dimensional motion platform (14), and a CCD camera (15). They are respectively used to control the parameter setting of the ultrashort pulse laser (1), the compilation and loading of the hologram on the spatial light modulator (6), the uniform movement of the transparent material crystal sample (13) driven by the three-dimensional motion platform (14), and the identification, positioning and beam energy observation of the transparent material sample (13); The parameter settings of the ultrashort pulse laser (1) specifically refer to adjusting the laser pulse width, repetition frequency and single pulse energy emitted by the laser; wherein, the laser pulse width ranges from 100fs to 2ps, the repetition frequency ranges from 1kHz to 100kHz, and the single pulse energy ranges from 5μJ to 20μJ. The focusing objective (12) has a focal length of 2-6 mm, a numerical aperture (NA) of 0.4-0.85, and a magnification of 20-100 times. It is used to focus non-uniform multiple laser beams to form non-uniform multifocal points. The focusing objective (12) is placed at the coaxial position of the beam reflected by the second mirror (10).

6. The non-uniform multifocal unit modification system for laser slicing of transparent materials according to claim 1, characterized in that, The visual positioning system includes a long-pass dichroic mirror (11), a CCD camera (15), and a ring-shaped white light source (17). The long-pass dichroic mirror (11) is used to transmit 1064nm long-pass infrared laser light and reflect white light; the ring white light source (17) is used to provide illumination for the CCD camera (18); the CCD camera (18) is used to observe the transparent material sample (13) at the coaxial position of the beam of white light emitted from the ring white light source (17) after being reflected by the reflective surface of the long-pass dichroic mirror (14).

7. A modification method based on the non-uniform multifocal unit modification system for laser slices of transparent materials according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Fix the transparent material sample (13) on the three-dimensional motion platform (14), adjust the three-dimensional motion platform (14) by controlling the computer (16) so that the transparent material sample (13) is positioned directly opposite the exit end of the focusing objective (12), and identify the position of the sample by the visual positioning system; Step 2: The processing parameters of the ultrashort pulse laser (1) are set by the control computer (16) according to the thickness of the transparent material sample (13) to be cut, and the three-dimensional motion platform (14) is moved to position the laser focus at the preset slicing starting depth inside the sample. Step 3: Turn on the laser to emit laser light, and then load the preset phase hologram on the spatial light modulator (6) through the control computer (16), and superimpose the blazed grating to shape the input Gaussian beam into multiple laser beams distributed in a non-uniform one-dimensional array in a plane, while ensuring that the zero-order light is filtered out through the aperture stop (8); the beam is transmitted from the beam shaping system and is obtained by beam shrinking and focusing by the objective lens (12) to obtain a non-uniform multifocal beam. At this time, the multifocal beam is focused on the preset slice starting depth inside the sample. The phase transfer function of a multifocal array with non-uniform energy distribution on a one-dimensional plane was calculated using analytical methods. After being encoded into a phase hologram by a computer controller (16), it was loaded onto a spatial light modulator (6) to generate a multifocal light field. The energy distribution of the multifocal array was then controlled and speckle suppression was optimized by the energy gradient optimization function and the random phase perturbation function, respectively. The complex amplitude transfer function was obtained by superimposing the two functions. The zero-order diffraction spot was then separated by a blazed grating and encoded into a hologram by a computer controller (16). The hologram was loaded onto the spatial light modulator (6) to achieve complex amplitude modulation. Finally, a non-uniform multifocal array with the lowest energy in the middle focus and the symmetrically increasing energy of the two side focuses was obtained. Step 4: Position the three-dimensional motion platform (14) at the lower left corner of the transparent material sample (13); move the platform at a constant speed along the scanning direction to scan the length of the sample using a non-uniform multi-focus scanning method; after the scan is completed, move the three-dimensional motion platform (14) along the vertical direction; then scan back to the beginning from the end along the scanning reverse direction; repeat the above forward and reverse scanning process on the OXY plane at the same Z-axis position until the X-axis moves a cumulative 30 μm, so that the discrete modified cavities generated by the multi-focus are tightly connected in the transverse direction. In each reciprocating scan, the energy of each focus is arranged in a symmetrical concave distribution with a low center and high sides. The local stress field generated between the cavities has a favorable transverse gradient, which promotes the generation and continuous expansion of microcracks between adjacent cavities, and finally forms a non-uniform unit modification layer with a width of 30 μm on the same Z-plane. Step 5: Increase the position of the current unit modified layer by 100 μm along the X-axis to locate the starting position of the next unit modified layer; repeat step 4 until the entire sample width is covered; during the processing, the vision positioning system monitors the formation of the modified layer and crack propagation in real time; after all unit modified layers are completed, remove the transparent material sample (13) and turn off all equipment; Step 6: Apply external force to the processed transparent material sample (13) to induce crack propagation, so that the cracks propagate in a directional manner along the unit modified layer array and connect with each other, and finally achieve complete peeling of the transparent material sheet to obtain the transparent material sheet.

8. The method for modifying non-uniform multifocal units in laser slices of transparent materials according to claim 7, characterized in that, In step 3, the phase transfer function of a non-uniform multi-beam laser array with the lowest energy at the central focal point and symmetrically increasing energy at the two side focal points on a one-dimensional plane was calculated using analytical methods. The phase transfer function is: (1) It is a phase function; A n ——No. n The relative amplitude of each focal point; u n , v n ——No. n Normalized spatial frequency of each focus; x , y —SLM plane coordinates / mm; N —Total number of focal points; λ — Wavelength / nm; After the phase transfer function is encoded into a phase hologram using a control computer (16), it is loaded into a spatial light modulator (6) to generate a multifocal light field. Then, the energy gradient optimization function and the random phase perturbation function are used to regulate the energy distribution and optimize speckle suppression of the multifocal array, respectively. The complex amplitude transfer function is obtained by superimposing the two functions. The energy gradient optimization function is: (2) in, This is the energy gradient intensity coefficient; x 0 represents the array center position in mm; The gradient distribution range is shown in mm. The random phase perturbation function is (3) in, β This is the phase perturbation intensity coefficient; R The effective perturbation region radius is given in mm; rand(- π , π Generate random numbers that are uniformly distributed in the range [-π, π]. Then, a composite phase hologram is obtained using a blazed grating, and the composite phase function is: (4) in, f x , f y The spatial frequency of the blazed grating; The image is encoded into a hologram by a control computer (16) and loaded onto a liquid crystal spatial light modulator (6) to achieve complex amplitude modulation. Finally, a non-uniform multi-beam laser array is obtained, in which the energy distribution of the transverse energy distribution is the lowest at the center focus and the energy of the two side focuses increases symmetrically.

9. The method for modifying non-uniform multifocal units in laser-cut transparent materials according to claim 7, characterized in that, In step 6, the method of applying external force to achieve complete peeling of the transparent material sheet is: applying tension or ultrasonic vibration.

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