Method and equipment for stripping wafer by laser

Abstract

The invention provides a wafer laser stripping method and device, and belongs to the technical field of wafer manufacturing, and the method comprises the steps: 1, transmitting a pulse laser beam I through a nanosecond laser, focusing the pulse laser beam I to a first depth H1 in a to-be-processed wafer, and carrying out scanning processing to form a first modified layer; step 2, a pulse laser beam II is emitted through a nanosecond laser, the pulse laser beam II is focused at a second depth H2 of the wafer to be processed for scanning processing, a stripping layer is formed, the energy of the pulse laser beam II is smaller than that of the pulse laser beam I, and the second depth H2 is smaller than the first depth H1; and step 3, stripping the surface of the to-be-processed wafer in a vacuum adsorption mode to obtain a target wafer. According to the method, crack induction, crack propagation and target wafer stripping can be carried out by adopting one device, the required stripping force is small, and stripping of the target wafer can be realized by only needing the force of 40-60N.

Description

Technical Field

[0001] The present invention relates to the technical field of wafer manufacturing, and in particular to a method and equipment for laser wafer peeling. Background Art

[0002] Wafers are not only an important technology related to national defense security, but also a key technology that the global automotive and energy industries attach great importance to. Slicing the grown crystals into slices is the first step in processing single crystals into wafers. Slicing is prone to cracks on the surface and subsurface of the wafer, increasing the breakage rate and manufacturing cost of the wafer. Therefore, controlling the surface crack damage of the wafer is of great significance to promoting the development of silicon carbide device manufacturing technology.

[0003] The existing laser processing method for obtaining wafers is divided into three steps: the first step is to induce the formation of a modified layer by laser; the second step is to expand the cracks in the modified layer by another laser, or other methods including freezing, ultrasound, etc.; the third step is to peel off the wafer by freezing, ultrasound, chemical corrosion, mechanical pulling, etc.

[0004] For example, the invention patent application with publication number CN119282408A discloses a dual-laser synchronous coaxial modification and stripping device and a dual-laser synchronous coaxial modification and stripping method. The method uses a dual-laser synchronous coaxial modification and stripping device to determine the layer to be stripped in the part to be stripped; then an ultrashort pulse laser is emitted to the layer to be stripped to form an initial modified layer; and a continuous laser is emitted to the initial modified layer to heat the initial modified layer to form a cracked completely modified layer.

[0005] In addition, the Institute of Semiconductors of the Chinese Academy of Sciences also disclosed a dual-laser splitting method and device in an invention patent with announcement number CN114985990B. The method uses a dual-laser splitting device to split brittle materials. First, an ultrashort pulse laser beam is passed through a beam expander and then focused into the brittle material through a beam focuser; then the depth of the focus of the laser beam in the brittle material is adjusted, and the ultrashort pulse laser beam forms cracks inside the brittle material through nonlinear absorption; a short pulse or continuous laser emits a short pulse laser beam or a continuous laser beam after a preset interval time, and focuses on the brittle material; under the thermal characteristics of the short pulse laser beam or the continuous laser beam, the cracks spread evenly to the surrounding area; the position of the focus of the laser beam in the brittle material is adjusted in a certain path to etch the entire brittle material, so that the brittle material is split into a target wafer and remaining material.

[0006] However, the short pulse or continuous laser and ultrashort pulse laser used in the above methods have a pulse width of picoseconds, sub-picoseconds or femtoseconds, and they all repeatedly perform laser scanning to expand cracks. The peeling force required to finally peel off the peeling layer obtained by the expansion of the modified layer and microcracks is large, which makes it easy to damage the wafer during the peeling process and has low processing efficiency. Summary of the invention

[0007] The technical problem to be solved by the present invention is how to reduce the peeling force required for laser processing to obtain a wafer, so as to avoid wafer damage and improve processing efficiency.

[0008] To solve the above problems, the present invention provides a method for laser stripping a wafer, comprising the following steps: Step 1: A pulsed laser beam I is emitted by a nanosecond laser and focused to a first depth H1 inside the wafer to be processed for scanning processing to form a plurality of initial modified lines and initial cracks; Step 2, emitting a pulsed laser beam II through a nanosecond laser, focusing on the second depth H2 of the wafer to be processed for scanning processing, the scanning path of the pulsed laser beam II overlaps with the scanning path of the pulsed laser beam I, forming a plurality of secondary modified lines and secondary cracks, and extending the initial crack to form an extended crack, the secondary modified line is connected to the initial modified line through the extended crack to form a peeling layer, the energy of the pulsed laser beam II is less than the energy of the pulsed laser beam I, the second depth H2 is less than the first depth H1, and H1-H2=tanα×D±R / 2, wherein α is the inclination angle between the {0001} crystal plane of the wafer to be processed and the cross section of the wafer, D is the scanning spacing of the pulsed laser beam I, and R is the longitudinal width of the initial modified line; Step three, using vacuum adsorption to peel off the peeling layer from the surface of the wafer to be processed to obtain a target wafer.

[0009] Compared with the prior art, the wafer stripping method of the present invention uses two laser scans combined with vacuum adsorption stripping to perform crack induction and crack extension, and target wafer stripping. The required stripping force is small, and only 40~60N of force is needed to achieve the stripping of the target wafer from the wafer to be stripped.

[0010] In a possible implementation, the energy of the pulsed laser beam I in step one is 1.5 to 2 times the energy of the pulsed laser beam II in step two.

[0011] By properly controlling the energy of the pulsed laser beam, the effect of modification and crack expansion of the modified layer can be achieved. The energy of the pulsed laser beam I and the energy of the pulsed laser beam II should be controlled within a reasonable ratio range, because the first scan is to form the initial modified line and the initial crack, and the second scan is to allow the initial modified line to absorb the laser energy again and grow longitudinally to form a secondary modified line. The high-energy pulsed laser beam I can make the temperature of the processing position inside the wafer rise more easily, causing the processing area to melt quickly, and then after cooling, an amorphous amorphous area can be formed at a preset depth of the wafer, and initial cracks and initial modified lines are generated in and around the amorphous area. The laser scanning again uses a low-energy pulsed laser beam II to repeat the path of the first scan, so that the initial modified line absorbs the energy of the pulsed laser beam II and then grows, and expands to expand the initial crack into an extended crack, and then the initial modified line and the secondary modified line are connected by the extended crack to form a peeling layer. Because there is an initial crack as a basis, the energy required for crack expansion is not very large, so the energy of the second pulsed laser beam II only needs to be 1 / 2~2 / 3 of the energy of the first pulsed laser beam I. However, the low-energy pulsed laser beam II of the present invention can still use the same nanolaser as the first pulsed laser beam I, because the second scan only raises the beam focus by H1-H2, and does not change the type of light source, so that the actual energy value of the low-energy pulsed laser beam II is much larger than the beam energy of the picosecond laser and femtosecond laser in the prior art, and also improves the scanning efficiency. Wherein H1-H2=tanα×D±R / 2 is calculated by determining the α angle according to the type of wafer to be processed, then determining the D value according to the scanning spacing, and determining R according to the longitudinal width of the initial modified line, that is, the depth range of influence of the beam spot.

[0012] In a possible implementation, the energy of the pulse laser beam I is 15 μJ-30 μJ, and the energy of the pulse laser beam II is 10 μJ-15 μJ.

[0013] The above energy range is the optimal energy range for silicon carbide wafer peeling.

[0014] In a possible implementation, the laser beam emitted by the laser has a wavelength of 492 nm to 577 nm, a pulse width of 1 ns to 20 ns, and a repetition frequency of 10 kHz to 1000 kHz.

[0015] Considering that the chemical bond energy of the wafer material itself guides the energy required to form the initial crack, for silicon carbide wafers, a laser beam at the green light wavelength is the best choice that meets the requirements. A wavelength that is too short will have a bit of excess energy, and a wavelength that is too long will not be able to efficiently form the initial crack.

[0016] In a possible implementation manner, the spot overlap rate of the pulsed laser beam I is 60% to 85%; And / or, the spot overlap rate of the pulse laser beam II is 20% to 60%.

[0017] In the above scheme, a higher overlap rate is selected for pulse laser beam I, so that the spot energy is larger and more uniform, which meets the requirements for forming an initial crack. Correspondingly, the energy required to expand the crack is low, so the spot overlap rate of pulse laser beam II can be smaller, and the area scanned at one time is larger, so the work efficiency will be higher.

[0018] In a possible implementation, the scanning interval D width of the pulse laser beam I is 40 μm to 200 μm.

[0019] In the above scheme, the scanning interval is reasonably arranged according to the energy of the nanosecond laser.

[0020] In a possible implementation, the wafer (5) to be processed is selected from one of a silicon carbide ingot, a silicon carbide wafer, and a single crystal silicon wafer.

[0021] The energy of the laser beam corresponds to the chemical bond energy of the wafer. The chemical bond energies of the three types of wafers mentioned above are equivalent, so all of them are applicable.

[0022] In a possible implementation manner, in step 1, the wafer to be processed is fixed on a movable platform having an X-axis and a Y-axis so that the crystal orientation of the wafer to be processed is Orthogonal to the X-axis, crystal direction Orthogonal to the Y axis.

[0023] Both silicon carbide and single crystal silicon have diamond structures. Orthogonal, the second orientation plane X direction and the crystal direction Orthogonal, which is the preferred orientation method, facilitates the formation of initial cracks, consumes less time and is highly efficient.

[0024] The present invention also provides a device for laser wafer peeling, comprising: A pulsed laser system for emitting a laser beam; an optical system for focusing the laser beam; A mobile platform for fixing the wafer to be processed; A vacuum adsorption system is used to adsorb and separate the target wafer from the wafer to be processed; and a control system for controlling the pulse laser system, the optical system, the mobile platform and the vacuum adsorption system; the pulse laser system, the optical system and the mobile platform are all fixed on a base, and the vacuum adsorption system is fixed on the mobile platform.

[0025] In a possible implementation, the pulse laser system comprises a pulse laser, wherein the pulse laser (1) is a nanosecond laser, and the nanosecond laser is fixed on a base; And / or, the optical system comprises a reflector and a focusing lens arranged in the optical path, the reflector is fixed on a base, and the focusing lens is fixed on a movable platform; And / or, the mobile platform includes an X-axis electric-controlled platform, a Y-axis electric-controlled platform and a Z-axis electric-controlled platform fixed on a base, and the focusing objective lens is fixed on the Z-axis electric-controlled platform; And / or, the vacuum adsorption system includes a vacuum adsorption platform fixed on the X-axis electric control platform and a vacuum suction cup independent of the base.

[0026] In a possible implementation, the NA value of the focusing objective lens is 0.5-0.95, and the working distance is 1 mm-10 mm.

[0027] In the above scheme, these parameters are the preferred values ​​according to the wafer type and laser beam type of the present invention. Within this range, the focused beam has the highest working efficiency and better effect.

[0028] The beneficial effects of the present invention are: The wafer stripping method of the present invention does not require ultrasonic crack induction after modification. It only needs to raise the height value of the focus point and use the same nanosecond laser to achieve crack expansion. The crack growth direction is easy to control, the time consumption is short, and the efficiency is high. The use of green light can make the absorption efficiency inside the silicon carbide higher, and it is easier to produce a modified layer. For the second scanning process, the prior art usually uses a processing method of repeatedly scanning the same position, that is, the processing method remains basically unchanged, but the processing method of the present invention is to lift the Z axis, which is more conducive to expanding the connection of the crack. The stripping force processed by this method will be much smaller than the stripping force of direct repeated processing, so it can be directly stripped by means of a vacuum suction cup. The suction cup stripping steps are simple, and there is no need for gluing and degumming processes. The stripping efficiency is high, and the loss is small, there is no chemical pollution, and it is environmentally friendly.

[0029] The wafer stripping method of the present invention can use the same equipment, that is, a laser combined with a mobile platform and a vacuum adsorption platform, and all actions can be completed on this one device, instead of using 2 to 3 lasers for stripping in the past, which improves the utilization rate of the equipment and reduces costs. The formation of the modified layer, crack propagation and wafer stripping are completed in synchronous and continuous processing, rather than separate asynchronous processing, and there is no need for a debonding process, so the work efficiency is high.

[0030] The wafer stripping method of the present invention does not have a chemical corrosion step and is environmentally friendly.

[0031] Because the wafer to be processed is fixed in a reasonable orientation, the focusing point of the laser beam is consistent during scanning, the amorphous area formed is also relatively consistent, the suction cup peeling force is small, and the surface roughness of the final peeled product is small and the quality is high.

[0032] The laser wafer stripping device of the present invention is assembled by purchasing a nano laser and a working platform already available on the market, has a simple structure, and can realize the whole process of wafer stripping by one device. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a flow chart of the laser wafer lift-off method in Example 1; Figure 2 is the transmittance of each wavelength to conductive silicon carbide; Figure 3 It is a schematic diagram of the equipment for laser wafer lift-off in the present invention; Figure 4 It is a schematic diagram of placing the wafer to be peeled off on the vacuum adsorption platform in the present invention; Figure 5 Schematic diagram of the initial focusing of the pulsed laser beam I to a preset depth in the present invention; Figure 6 A schematic diagram of the position where the pulsed laser beam I scans to the end of the present invention; Figure 7 A top view of the internal structure of the wafer to be peeled off after the pulse laser beam I in the present invention has finished scanning; Figure 8 for Figure 7 AA cross-sectional view, i.e., a front view of the internal structure of the wafer to be peeled off after the pulse laser beam I scans; Fig. 9 A schematic diagram of the initial focusing of the pulsed laser beam II at a preset depth in the present invention; Fig.10 A schematic diagram of the position where the pulse laser beam II scans to the end of the present invention; Fig.11 A top view of the internal structure of the wafer to be peeled off after the pulse laser beam II scans the wafer in the present invention; Fig.12 for Fig.11 BB cross-sectional view, i.e., a front view of the internal structure of the wafer to be peeled off after the pulse laser beam II scans; Fig.13 A schematic diagram of the process of peeling a wafer to be peeled off by a vacuum chuck in the present invention; Fig.14 This is a real picture of the target wafer after peeling in the present invention.

[0034] Description of reference numerals: 1. Pulse laser; 2. Reflector; 3. Z-axis electric control platform; 4. Focusing objective lens; 5. Wafer to be processed; 6. Vacuum adsorption platform; 7. X-axis electric control platform; 8. Y-axis electric control platform; 9. Base; 10. First orientation plane; 11. Second orientation plane; 12. Pulse laser beam I; 13. Initial modified point; 14. Initial modified line; 15. Initial crack; 16. Pulse laser beam II; 17. Second modified point; 18. Second modified line; 19. Second crack; 20. Extended crack; 21. Computer; 22. Remaining wafer; 23. Target wafer; 24. Vacuum suction cup. DETAILED DESCRIPTION

[0035] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation method and typical parameters of the present invention, and are not used to limit the parameter range described in the present invention. Reasonable changes derived therefrom are still within the scope of protection of the claims of the present invention.

[0036] It should be noted that the endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this article.

[0037] Unless otherwise defined, all terms, symbols and other scientific terms used herein are intended to have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. In some cases, terms with conventionally understood meanings are defined herein for the purpose of clarification or ease of reference, and such definitions herein should not be construed as indicating significant differences from conventional understandings in the art. The technical methods described or cited herein are generally well understood by those skilled in the art and are adopted by conventional methods. Unless otherwise stated, the use of commercially available instruments is carried out in accordance with the protocols and parameters given by the manufacturer.

[0038] Example 1

[0039] See also Figure 1The flow chart of the present invention shows that the wafer stripping method includes three main steps: step 1, the pulse laser 1 emits a first laser beam to generate an initial modified line 14 and an initial crack 15; step 2, the pulse laser 1 emits a second laser beam to generate a secondary modified line 18 and a secondary crack 19, the initial crack 15 is expanded into an extended crack 20, and the initial modified line 14 and the secondary modified line 18 are connected by the extended crack 20; step 3, the vacuum suction cup 24 on the vacuum adsorption platform 6 is used to strip the wafer, and the target wafer 23 is separated from the remaining wafer 22.

[0040] Taking the peeling of silicon carbide wafer as an example, the wafer 5 to be processed in the present invention can also be selected from silicon carbide ingots or single crystal silicon wafers. In order to make the wafer 5 to be processed form the modified line and crack extension more uniformly, and to reduce the equipment cost, the present invention has designed a laser peeling device for wafers. The device includes a pulse laser system for emitting a laser beam; an optical system for focusing the laser beam on the wafer 5 to be processed; a mobile platform for adjusting the position of the wafer 5 to be processed so that the laser beam can be focused to a preset depth of the part to be peeled off; a vacuum adsorption system for adsorbing and separating the target wafer 23 from the wafer 5 to be processed; and a control system for controlling the above-mentioned pulse laser system, optical system, mobile platform and vacuum adsorption system.

[0041] See also Figure 2 For silicon carbide wafers, referring to the transmittance of conductive silicon carbide at various wavelengths in the figure, it can be seen that the laser beam in the green light band can meet the requirements of laser lift-off.

[0042] For details, see Figure 3 The pulse laser system includes a pulse laser 1. In this embodiment, the pulse laser 1 uses a 532nm green wavelength nanosecond laser with a transmittance that is superior to the common wavelengths of 1030nm, 1064nm, 355nm, etc. on the market. The laser model is Huari Laser-Cypress2-532-70. The laser transmittance is shown in Figure 2 See Figure 3 The mobile platform includes an X-axis electronically controlled platform 7, a Y-axis electronically controlled platform 8 and a Z-axis electronically controlled platform 3, which are used to adjust the position of the wafer 5 to be processed from three directions of X, Y and Z. The X-, Y- and Z-axis electronically controlled platforms are devices produced by AISTEC, and the model is LDCF-X250Y400Z150-GC2.

[0043] The optical system includes a reflector 2 and a focusing lens arranged in the optical path, the reflector 2 is fixed on the equipment base 9, the focusing lens 4 is fixed on the Z-axis electric control platform 3 on the mobile platform, and the Z-axis electric control platform 3 is fixed on the equipment base 9; the reflector 2 can reflect the light beam emitted by the pulse laser 1 to the focusing lens 4, so that the light beam is focused and irradiated on the wafer 5 to be processed. The NA value of the focusing lens 4 is 0.5~0.95, and the working distance is 1mm~10mm.

[0044] The vacuum adsorption system includes a vacuum adsorption platform 6 and a vacuum suction cup 24 fixed on the X-axis electric control platform 7. In this embodiment, the vacuum suction cup 24 is preferably set independently of the equipment base 9, and is set separately and is handheld; the vacuum adsorption platform 6 is fixed on the X-axis electric control platform for placing the sample of the wafer 5 to be processed, and the vacuum suction cup 24 is used as a manipulator to adsorb the target wafer 23 to separate it from the wafer 5 to be processed; the vacuum adsorption platform 6 is a device produced by AISTEC, model DD170-50. The control system includes a computer 21.

[0045] correspond Figure 4-Figure 7 The schematic diagram and detailed description of the silicon carbide wafer peeling method in this embodiment are as follows: Step 1: First, pre-treat the silicon carbide wafer with a size of 10mm×10mm. Polish the sample first, and then use an ultrasonic cleaner to clean the surface impurities.

[0046] Step 2: adjust the position of the wafer 5 to be processed on the equipment base 9 so that the first orientation plane 10 is consistent with the Y direction, and the second orientation plane 11 is consistent with the X direction, that is, the crystal orientation of the wafer 5 to be processed is Orthogonal to the X-axis, crystal direction Orthogonal to the Y axis, such as Figure 4 shown.

[0047] Step 3, set the pulse energy of the pulse laser 1 to 15μJ~30μJ, the pulse width to 2ns, the repetition frequency to 60kHz, and the pulse laser wavelength to 532nm, fix the silicon carbide wafer 5 to be processed on the vacuum adsorption platform 6 on the X-axis electric control platform 7 and the Y-axis electric control platform 8, the accuracy of the X-axis electric control platform 7 and the Y-axis electric control platform 8 reaches the μm level, control the computer 21 to control the pulse laser 1 to emit a laser beam as a pulse laser beam I12, the pulse laser beam I12 is reflected once by the reflector 2 and enters the focusing objective lens 4 fixed on the Z-axis electric control platform 3 for focusing, the spot diameter R after focusing is 10μm, and control the focus of the pulse laser beam I12 to be preset at a depth H1 of 300μm inside the silicon carbide wafer, such as Figure 5As shown. Theoretically, the height H1-H2 = tanα×D±R / 2, the angle α is determined according to the type of wafer to be processed, the D value is determined according to the scanning spacing, and the R value is determined according to the longitudinal width of the initial modified line, that is, the influence depth range of the beam spot. In step 3, the pulse energy of the pulse laser 1 can be adjusted between 15μJ and 30μJ, which can be 15μJ, 16μJ, 17μJ, 18μJ, 19μJ, 20μJ, 21μJ, 22μJ, 23μJ, 24μJ, 25μJ, 26μJ, 27μJ, 28μJ, 29μJ, 30μJ, etc.

[0048] Step 4, such as Figure 5-Figure 8 As shown, around the focus of the pulsed laser beam I 12, the single crystal silicon carbide is decomposed into amorphous silicon and amorphous carbon, and an initial modified point 13 with a certain thickness is formed. The X-axis electric control platform 7 is controlled to move toward the X direction relative to the focus of the pulsed laser beam I 12 at a speed of 105 mm / s, so that the focused spots of the pulsed laser beam I 12 overlap with each other, and the spot overlap rate is 60% to 85%, preferably 83%. The calculation formula of the spot overlap rate is: Because the spot overlap rate is high, the next scanning point is actually to irradiate the initial modified point 13 that has been decomposed into amorphous silicon and amorphous carbon with the pulse laser beam I 12 again. In this way, the pulse laser beam I 12 is absorbed by the amorphous carbon, which heats up and expands, and generates an initial crack 15 (the initial crack has a deflection angle α), and at the same time generates a second modified point. In this way, countless modified points are scanned to form an initial modified line 14. Figure 8 In the figure, the crystal plane corresponding to the initial crack 15 is the {0001} crystal plane. Since the peeling resistance of the {0001} crystal plane is the smallest, the initial crack 15 first appears on the {0001} crystal plane. The cross section of the wafer 5 to be processed corresponds to Figure 8 The horizontal line intersecting with the initial crack 15 in the middle, the inclination angle of the initial crack 15 relative to the horizontal line is the angle α.

[0049] Step 5, in the step of forming the initial peeling layer, the scanning pitch of the modified line processing is repeated, that is, the sub-interval D is 120 μm, and in the sub-interval D, the Y-axis electric control platform 8 is controlled to move in the Y direction (parallel to the direction of the first orientation plane) relative to the focus of the pulsed laser beam I 12. After the movement is completed, step 4 is repeated to form a plurality of initial modified lines 14.

[0050] Step 6, repeating steps 5 and 4 to form an initial peeling layer consisting of a plurality of initial modified lines 14 and initial cracks 15.

[0051] Step 7, such as Figure 9-12As shown, after the initial peeling layer is formed, the energy of the pulse laser 1 is adjusted to 10μJ~15μJ, the pulse width is 2ns, the repetition frequency is 60kHz, and the pulse laser wavelength is 532nm. The computer 21 controls the pulse laser 1 to emit a pulse laser beam II 16. The pulse laser beam II 16 is reflected once by the reflector 2 and enters the focusing objective lens 4 fixed on the Z-axis electric control platform 3 for focusing. The spot diameter after focusing is 10μm. The focus of the pulse laser beam II 16 is controlled to be 290μm at a preset depth H2 inside the wafer 5 to be processed, that is, the preset depth of the pulse laser beam II 16 focused on the wafer 5 to be processed is 10μm above the preset depth of the pulse laser beam I 12 scanning, so that the initial modified line 14 in the initial peeling layer absorbs the energy of the pulse laser beam II 16 to achieve longitudinal growth and become a secondary modified point 17. The scanning speed of the pulse laser beam II 16 is 360 mm / s, and the spot overlap rate is 20%~60%, preferably 60%. Scan again to form a secondary modified line 18 and a secondary crack 19, and make the amorphous carbon in the initial modified line 14 absorb the energy of the pulse laser beam II 16 and heat up, so that the initial crack 15 expands into an extended crack 20 (extending along the direction of the deflection angle α). Under the action of stress, the extended crack 20 will penetrate the secondary crack 19, so that the initial modified line 14 and the secondary modified line 18 are connected to each other by the extended crack 20. After step 7 is completed, all the initial modified lines 14 are connected to the secondary modified lines 18 after longitudinal growth by the extended crack 20 to form the final peeling layer.

[0052] Step 8, such as Fig.13 As shown, the vacuum chuck 24 is adsorbed on the wafer 5 to be processed which forms the final peeling layer, and a pulling force F perpendicular to the wafer plane is provided. Since the peeling layer is formed by the modified layer connected by the cracks, the bonding force is relatively weak, so the upward pulling force F in this embodiment is applied to 40-60N to peel it off. The target wafer 23 and the remaining wafer 22 are obtained.

[0053] The final peeled sample photo is as follows Fig.14 As shown, the left picture is a surface view of the upper target wafer, and the right picture is a surface view of the remaining wafer. It can be seen from the figures that the surface roughness of the wafer sample peeled off by the method of this embodiment is good.

[0054] The wavelength of the nanosecond laser given in this embodiment is a green wavelength of 532nm, because this is limited by the wavelength of green wave nanosecond lasers available on the market, but under the concept of the present invention, laser beams with wavelengths of 492~577nm can meet the requirements, and their processing is basically the same as that of laser beams with a wavelength of 532nm. The above method is also applicable to the peeling of silicon carbide ingots or single crystal silicon wafers.

[0055] Comparative Example 1 Different from the first embodiment, the pulse laser beam II 16 does not raise the Z-axis height, and the wafer peeling is performed by scanning the pulse laser beam I 12 and the pulse laser beam II 16 on the same plane: Step 1, first pre-process the silicon carbide wafer 5 to be processed with a size of 10mm×10mm, first polish the sample, and then use an ultrasonic cleaner to clean the surface impurities.

[0056] Step 2, Figure 3 The position of the wafer 5 to be processed is adjusted on the middle base 9 so that the first orientation plane 10 is consistent with the Y direction, and the second orientation plane 11 is consistent with the X direction, that is, the Y axis is aligned with the crystal direction. Orthogonal, X-axis and crystal direction Orthogonal, such as Figure 4 shown.

[0057] Step 3, set the pulse energy of the pulse laser 1 to 25 μJ, the pulse width to 2 ns, the repetition frequency to 60 kHz, and the pulse laser wavelength to 532 nm, fix the silicon carbide wafer 5 to be processed on the vacuum adsorption platform 6 on the X-axis electric control platform 7 and the Y-axis electric control platform 8, the accuracy of the X-axis electric control platform 7 and the Y-axis electric control platform 8 reaches the μm level, control the computer 21 to control the pulse laser 1 to emit a laser beam as a pulse laser beam I 12, the pulse laser beam I 12 is reflected once by the reflector 2 and enters the focusing objective lens 4 fixed on the Z-axis electric control platform 3 for focusing, the spot diameter after focusing is 10 μm, and control the focus of the pulse laser beam I 12 to be at a preset depth of 300 μm inside the wafer 5 to be processed, as shown in FIG. Figure 5 shown.

[0058] Step 4, such as Figures 5 to 8 As shown, around the focus of the pulsed laser beam I 12, the single crystal silicon carbide is decomposed into amorphous silicon and amorphous carbon, and an initial modified point 13 with a certain thickness is formed. The X-axis electric control platform 7 is controlled to move toward the X direction relative to the focus of the pulsed laser beam I 12 at a speed of 105 mm / s, so that the focused spots of the pulsed laser beam I 12 overlap each other, and the spot overlap rate is 83%. Because the spot overlap rate is high, the process of scanning to the second modified point is equivalent to scanning the initial modified point 13 that has been decomposed into amorphous silicon and amorphous carbon again. In this way, the pulsed laser beam I 12 is absorbed by the amorphous carbon, thereby heating and expanding, and generating an initial crack 15 (the initial crack 15 has a deflection angle α) and a second modified point at the same time. In this way, countless modified points are scanned to form an initial modified line 14.

[0059] Step 5, in the initial peeling step, the scanning pitch of the modified line processing is repeated, that is, the sub-interval D is 120 μm. In the sub-interval D, the Y-axis electric control platform 8 is controlled to move in the Y direction (parallel to the first orientation plane) relative to the focus of the pulsed laser beam I. After the movement is completed, step 4 is repeated to form a second modified line.

[0060] Step 6, repeating steps 5 and 4 to form an initial peeling layer formed by a plurality of initial modified lines 14 and initial cracks 15.

[0061] Step 7: Since most of the cracks are not completely connected to each other, the peeling force required for peeling is much greater than that in Example 1, and it cannot be peeled by the vacuum suction cup 24. The peeling force measured by the subsequent peeling by glue coating is 220N~230N.

[0062] By comparison, it can be seen that the peeling force of Example 1 (40-60N) is much smaller than the peeling force of Comparative Example 1 (220-230N). Therefore, the wafer peeling method of the present invention can reduce the peeling force required for laser processing to obtain the wafer, thereby avoiding wafer damage and improving processing efficiency.

[0063] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for laser stripping a wafer, characterized in that: The following steps are involved: Step 1: emitting a pulsed laser beam I (12) through a nanosecond laser, focusing it to a first depth H1 inside the wafer to be processed (5) for scanning processing, thereby forming a plurality of initial modified lines (14) and initial cracks (15); Step 2, emitting a pulsed laser beam II (16) through a nanosecond laser, focusing on a second depth H2 of the wafer to be processed (5) for scanning processing, wherein the scanning path of the pulsed laser beam II (16) overlaps with the scanning path of the pulsed laser beam I (12), forming a plurality of secondary modified lines (18) and secondary cracks (19), and expanding the initial crack (15) to form an extended crack (20), wherein the secondary modified line (18) is connected to the initial modified line (14) through the extended crack (20) to form a peeling layer, wherein the energy of the pulsed laser beam II (16) is less than the energy of the pulsed laser beam I (12), the second depth H2 is less than the first depth H1, and H1-H2=tanα×D±R / 2, wherein α is the inclination angle between the {0001} crystal plane of the wafer to be processed (5) and the wafer cross section, D is the scanning spacing of the pulsed laser beam I (12), and R is the longitudinal width of the initial modified line (14); Step three, using vacuum adsorption to peel off the peeling layer from the surface of the wafer to be processed (5) to obtain a target wafer.

2. The method for laser wafer lift-off according to claim 1, characterized in that: The energy of the pulsed laser beam I (12) is 1.5 to 2 times the energy of the pulsed laser beam II (16).

3. The method for laser wafer lift-off according to claim 2, characterized in that: The energy of the pulsed laser beam I (12) is 15 μJ to 30 μJ, and the energy of the pulsed laser beam II (16) is 10 μJ to 15 μJ.

4. The method for laser wafer lift-off according to claim 1, characterized in that: The laser beam emitted by the nanosecond laser has a wavelength of 492nm-577nm, a pulse width of 1ns-20ns, and a repetition frequency of 10kHz-1000kHz.

5. The method for laser wafer lift-off according to claim 1, characterized in that: The spot overlap rate of the pulsed laser beam I (12) is 60% to 85%; And / or, the spot overlap rate of the pulsed laser beam II (16) is 20% to 60%.

6. The method for laser wafer lift-off according to claim 1, characterized in that: The scanning interval D of the pulse laser beam I (12) is 40 μm to 200 μm.

7. The method for laser wafer lift-off according to claim 1, characterized in that: The wafer to be processed (5) is selected from one of a silicon carbide ingot, a silicon carbide wafer, and a single crystal silicon wafer.

8. The method for laser wafer lift-off according to claim 7, characterized in that: In the step 1, the wafer to be processed (5) is fixed on a movable platform having an X-axis and a Y-axis, so that the crystal orientation of the wafer to be processed (5) is Orthogonal to the X-axis, crystal direction Orthogonal to the Y axis.

9. A device for implementing the method for laser wafer lift-off according to any one of claims 1 to 8, characterized in that: include: A pulse laser system for emitting a laser beam; an optical system for focusing the laser beam; A mobile platform for fixing the wafer to be processed (5); A vacuum adsorption system, used for adsorbing and separating a target wafer (23) from a wafer to be processed (5); and a control system for controlling the pulse laser system, the optical system, the mobile platform and the vacuum adsorption system; The pulse laser system, the optical system and the mobile platform are all fixed on a base (9), and the vacuum adsorption system is fixed on the mobile platform.

10. The device according to claim 9, characterized in that The pulse laser system comprises a pulse laser (1), wherein the pulse laser (1) is a nanosecond laser, and the nanosecond laser is fixed on a base (9); And / or, the optical system comprises a reflector (2) and a focusing lens (4) arranged in the optical path, the reflector (2) is fixed on a base (9), and the focusing lens (4) is fixed on a movable platform; And / or, the mobile platform comprises an X-axis electric-controlled platform (7), a Y-axis electric-controlled platform (8) and a Z-axis electric-controlled platform (3) fixed on a base (9), and the focusing objective lens (4) is fixed on the Z-axis electric-controlled platform (3); And / or, the vacuum adsorption system comprises a vacuum adsorption platform (6) fixed on the X-axis electric control platform (7) and a vacuum suction cup (24) independent of the base (9).

11. The device according to claim 10, characterized in that The NA value of the focusing objective lens (4) is 0.5 to 0.95, and the working distance is 1 mm to 10 mm.

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