A processing method for thinning a silicon carbide wafer using laser modification and a silicon carbide wafer thinning sheet
By employing a method of forming a modified layer on a silicon carbide wafer through two laser scans and combining it with a grinding wheel for thinning, the problems of low efficiency, high cost, and mechanical stress damage in existing technologies have been solved, achieving a high-efficiency and low-cost wafer thinning process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SICC SHANGHAI CO LTD
- Filing Date
- 2025-08-29
- Publication Date
- 2026-05-12
AI Technical Summary
Existing silicon carbide wafer thinning methods are inefficient, costly, and prone to introducing mechanical stress damage, leading to decreased wafer yield and warping problems.
The modified layer is formed by two laser scans. The modified layer is formed inside and at the edge of the silicon carbide wafer by a picosecond laser device. Combined with grinding wheel thinning, the modified layer method is optimized to reduce separation difficulty and warping. After laser modification, grinding wheel thinning is performed to reduce wear and cost.
It significantly reduces separation difficulty and warping issues, reduces grinding wheel wear by more than 20%, lowers overall cost by 30%, reduces wafer breakage rate to below 4%, and improves wafer yield.
Smart Images
Figure CN121156853B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of crystal laser processing technology, and more specifically, to a processing method for thinning silicon carbide wafers using laser modification and a silicon carbide wafer thinning sheet. Background Technology
[0002] Silicon carbide (SiC) is a high-performance semiconductor material widely used in high-power, high-frequency, and high-temperature electronic devices. With the development of SiC technology, its applications in power electronics, optoelectronic devices, and high-temperature devices are constantly expanding, especially in power management applications where MOSFET devices show great promise. MOSFETs are vertically mounted devices; the thinner the overall thickness, the lower the on-resistance and the lower the power consumption. Since the drain of the device is generally on the back side of the wafer, after the front-side wafer fabrication is completed, the SiC wafer thickness needs to be reduced to lower the on-resistance of the device. Current SiC wafer thinning methods have many shortcomings; low production efficiency and high production costs restrict the application and promotion of the process.
[0003] Existing SiC wafer thinning methods are mainly based on the "in-feed principle" of abrasive wheel thinning. The wafer is held on a vacuum stage, and thinning is achieved through the rotation of the stage and the longitudinal feed motion of the abrasive wheel. This process suffers from several drawbacks. First, due to the high hardness of silicon carbide, abrasive wheel thinning results in high wheel consumption and low efficiency. During thinning, the "hard-on-hard" grinding method, with direct contact between the abrasive grains and the wafer, introduces mechanical stress at the contact points, easily leading to defects such as cracks and edge chipping, thus affecting wafer yield. Second, the thinner the wafer, the greater the warpage, resulting in a larger total TV value (TTV) of the substrate after thinning, making precise thickness control more difficult and increasing the processing complexity.
[0004] To address the aforementioned issues, based on traditional abrasive wheel thinning, the "Taiko process" has been proposed. This process preserves the outer edge (approximately 3mm) of the wafer during back-side thinning, only thinning the inner part of the wafer. Introducing this technology reduces the handling risks of thin wafers and minimizes warpage. Furthermore, based on this, a thinning method targeting the inner regions of the wafer has been developed. This method uses laser separation of the inner wafer region followed by a circumferential cutting process at the wafer edges, further reducing processing costs while ensuring wafer warpage is minimized.
[0005] Existing silicon carbide wafer thinning methods mainly involve grinding wheel thinning. During the interaction between the grinding wheel and the wafer, diamond particles adhered to the grinding wheel create mechanical friction with the silicon carbide. The difference in hardness between diamond and silicon carbide allows for the removal of the silicon carbide wafer. Although diamond is the hardest material in nature, silicon carbide, with a Mohs hardness of 9.2–9.5, is the second hardest material in nature (10). This dictates that grinding wheel thinning is achieved through a "hard-on-hard" grinding process. This process is inefficient, consumes a significant amount of diamond grinding wheel material, and easily introduces mechanical stress during the process, affecting wafer yield. In summary, this process has drawbacks such as slow processing efficiency, high processing cost, and susceptibility to mechanical stress damage. Another approach is to use lasers or grinding wheels to process the inside of the wafer first, and then perform circumferential cutting on the outer edge. This process is technically complex, and the additional circumferential cutting steps introduce the risk of wafer breakage, reducing wafer yield and increasing production costs. Summary of the Invention
[0006] To address the aforementioned problems, the first aspect of this invention provides a method for processing silicon carbide wafers using laser-modified thinning technology, the method comprising the following steps:
[0007] S1: Perform a full-scale laser scan on the surface of the silicon carbide wafer to be thinned, forming a modified layer inside the silicon carbide wafer.
[0008] Optionally, a protective film can be applied to the un-laser-irradiated side of the silicon carbide wafer, such as... Figure 2 As shown, the protective film can be a common pyrolytic blue film or UV film used for thinning. The film can be applied manually or by machine. After the protective film is applied, excess film needs to be precisely trimmed along the circumference of the wafer surface. During operation, the silicon carbide wafer with the film applied to the un-laser-irradiated side is transferred to the stage of the laser scanning equipment, with the side of the silicon carbide wafer to be thinned (laser-irradiated side) facing upwards. (Refer to...) Figure 3 As shown, the laser generator is continuously moved within a certain interval to scan the surface of the wafer, thereby completing the modification treatment of the target thickness.
[0009] Optionally, silicon carbide wafers can be obtained by laser lift-off of silicon carbide ingots.
[0010] S2: Perform a second laser scan on the circumferential edge of the surface to be thinned after the first laser scan, so that the modified layer formed on the circumferential edge extends towards the surface to be thinned; wherein, the thickness of the modified layer after the second laser scan is greater than the thickness of the modified layer after the first laser scan.
[0011] The silicon carbide wafer is first subjected to a first laser scan on the entire surface to be thinned. After the entire surface is laser-modified, the focal length of the laser is increased upward (towards the laser irradiation surface) to the focal length of the silicon carbide wafer. A second laser scan is then performed only on the circumferential edge of the silicon carbide wafer to be thinned. This causes the modified layer formed on the circumferential edge to extend towards the surface to be thinned, resulting in an overall increase in the thickness of the modified layer formed on the circumferential edge compared to the first laser modification. The thickness of the modified layer after the second laser scan is greater than that after the first laser scan. In other words, the total thickness of the modified layer after the second laser scan is greater than that after the first laser scan.
[0012] S3: The silicon carbide wafer scanned by the second laser is sequentially separated and thinned using a grinding wheel to obtain a thinned silicon carbide wafer sheet. Refer to the flowchart for the laser-modified silicon carbide wafer thinning process. Figure 1 As shown.
[0013] Optionally, the thickness of the modified layer in the second laser scan is increased by 3-7 μm compared to the thickness of the modified layer in the first laser scan. Alternatively, the thickness of the modified layer in the second laser scan is increased by 3-5 μm compared to the thickness of the modified layer in the first laser scan. For example, the thickness of the modified layer in the second laser scan can be increased by 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, or any value and range between these values.
[0014] Optionally, with the center of the silicon carbide wafer as the center, the inner diameter of the circumferential edge portion is 0.6-0.8 times the total wafer radius. Further, refer to... Figure 4 As shown, Figure 4 An exemplary embodiment of a schematic diagram of the silicon carbide wafer position is shown. The silicon carbide wafer is divided into a circumferential edge portion and an internal portion, with the center of the silicon carbide wafer as the center. R2 is the radius of the silicon carbide wafer, and R1 is the inner diameter of the circumferential edge portion (or the radius of the internal portion of the wafer). The second laser scanning area is the region with a radius greater than R1.
[0015] Optionally, the laser-modified thinning thickness is >80μm. Compared with the traditional direct thinning process of grinding wheels, the laser-modified method of this invention can directly process according to the target thickness. The thicker the target thickness, the higher the time efficiency. Generally, when the thinning thickness is >80μm, the laser-modified time is much shorter than the traditional direct thinning time of grinding wheels, which can significantly reduce the overall processing time.
[0016] Optionally, both the first and second laser scans utilize picosecond laser equipment; further, the laser wavelength is 532-1064 nm, and the pulse width is 45-500 ps. Optionally, the laser power for both the first and second laser scans is 2-22 W, and the scanning rate is 300-800 mm / s. Optionally, the scanning paths for the first and second laser scans move laterally along the <11-20> crystal plane at certain intervals, forming several single scanning paths, with the interval between adjacent single scanning paths being 120-350 μm. Further, this invention relates to a silicon carbide modification and thinning method based on picosecond laser equipment. Since wavelength determines the laser's penetration depth—the longer the wavelength, the deeper the penetration—and pulse width determines the number of laser interactions in a localized area—the shorter the pulse width, the better the localized processing. By introducing a picosecond laser device, a laser beam of a specific wavelength and pulse width is focused near a silicon carbide crystal, forming a processing focal zone with extremely high power density. In this region, crystal molecules absorb photon energy and release free electrons. The micro-explosion effect generated by Coulomb repulsion breaks the molecular bonds of silicon carbide, altering its crystal structure. Simultaneously, single-crystal structures above and below the laser focal point develop cracks due to nonlinear stress. A modified layer is formed at the target thickness inside the silicon carbide wafer. Subsequently, by applying appropriate external forces in different directions, complete wafer separation can be achieved without being affected by wafer warping. However, the laser implementation method of this invention is not limited to this; those skilled in the art can achieve the same effect using different types of lasers, such as femtosecond lasers, or different scanning methods.
[0017] After two laser scans, the total thickness of the modified layer in the second laser scan is greater than that in the first laser scan. By applying appropriate external forces in different directions, complete wafer separation can be achieved without being affected by wafer warping. The separated wafer has essentially reached the desired target thickness, but the surface still retains a layer of crack damage caused by laser modification, requiring further thinning with a grinding wheel. At this point, the crystal phase structure of the silicon carbide wafer surface has changed due to the laser modification method. Simultaneously, due to the presence of local microcracks, the resistance during grinding is lower. Using a grinding wheel with appropriate hardness and mesh size can further reduce wear, achieving wafer thickness and surface condition consistent with traditional thinning methods while reducing production costs. Because the edge thickness is higher than the internal thickness, the internal stress of the crystal remains essentially balanced, reducing the cracking rate and surface warping during the grinding wheel thinning process.
[0018] Optionally, step S3 may further include the following steps:
[0019] S31: The silicon carbide wafer to be thinned in the second laser scan is first coated with a film and fixed on the bonding ring. The film is then adsorbed onto the bonding ring using a ring-mounted adsorption fixture. By applying tension, the silicon carbide wafer is separated along the modified layer to obtain a silicon carbide sub-wafer.
[0020] Furthermore, a protective film is first applied to the thinning surface (laser irradiation surface) of the silicon carbide wafer after the second laser scan, referring to... Figure 5 The diagram shown illustrates a silicon carbide wafer lamination process. Figure 5 The left side is a 3D view, and the right side is a side view. For example, a blue film or UV film can be applied to provide an adsorption plane for the subsequent ring-shaped adsorption fixture, preventing breakage or bending after separation and affecting the silicon carbide wafer. The film (blue film or UV film) is fixed to the mounting ring, and the ring-shaped adsorption fixture adsorbs the mounting ring. The un-laser-irradiated surface of the silicon carbide wafer can be fixed by a vacuum suction cup during separation. For example, the ring-shaped adsorption fixture includes suction nozzles and connecting rods arranged in a ring at certain intervals. The upper end of the suction nozzles is opened to connect to a vacuum generator, and one end of the connecting rod is connected to the suction nozzles. A pressure sensor is connected to the connecting rod. Optionally, there are no fewer than 6 suction nozzles. For example, there are 8 suction nozzles. The suction nozzles are evenly distributed on the adsorption fixture at certain intervals. During separation, each suction nozzle is adsorbed onto the mounting ring by the action of the vacuum generator. See the wafer separation schematic diagram for reference. Figure 6 As shown, a uniform pulling force is gradually applied from the Notch port to the opposite direction of the Notch. Pressure sensors continuously detect and record the pulling force values in each direction (ensuring a linear relationship between the pulling force and time at each point). The surface wafer will gradually separate until the pulling force reaches zero. If separation fails the first time, the initial pulling force can be increased for another attempt. The pulling force is 8-16N, generally not exceeding 16N. Furthermore, the laser refining process in this application involves two treatments. The separated silicon carbide sub-wafers have a greater thickness at their overall circumferential edge than their internal thickness, and their separation direction is uniform (the Notch port of the wafer must be in a fixed direction for each loading). This ensures that the force is transmitted along the <11-20> direction during wafer separation, greatly reducing the difficulty of separation and the likelihood of wafer breakage.
[0021] S32: The separation surface of the silicon carbide sub-wafer is thinned by grinding wheel to obtain a thinned silicon carbide wafer.
[0022] Optionally, the separation surface of the silicon carbide sub-wafer can be thinned using a grinding wheel. During the thinning process, refer to... Figure 7 As shown, the stage and the grinding wheel rotate relative to each other, and the grinding wheel is gradually fed from top to bottom. During this process, the influence area of the modified layer gradually weakens from the surface to the interior. By controlling the feed amount and feed speed, different grinding wheel wear can be obtained.
[0023] Optionally, the first feed rate is 15-25 μm with a feed speed of 0.5-0.6 μm / s; the second feed rate is 8-12 μm with a feed speed of 0.3-0.4 μm / s; and the third feed rate is 8-12 μm with a feed speed of 0.2-0.25 μm / s. By gradually increasing the feed rate and decreasing the feed speed, and reducing the feed speed to half its initial value when the feed rate is 80% of the target thickness, the grinding wheel wear can be minimized.
[0024] Furthermore, after separation, the silicon carbide sub-wafers have a higher edge thickness than the internal thickness, resulting in a near-equilibrium state of internal stress. Therefore, a single grinding wheel (an 8000# grinding wheel for SiC substrates) can be used for thinning. Compared to the "coarse + fine" dual-grinding wheel approach, single-wheel processing avoids the introduction of additional localized stress due to the direction of force and the single-pass processing, preventing disruption of the wafer's internal stress balance. This reduces the likelihood of abnormal warping in the center ("I-shaped" surface). Under the same TTV level, this translates to better flatness in the central region, which is more beneficial for subsequent processing. Simultaneously, the application of a single grinding wheel can reduce grinding wheel usage costs by at least 30% (related to the thinning thickness).
[0025] The second aspect of the present invention provides a silicon carbide wafer thinning wafer, wherein the silicon carbide wafer thinning wafer TTV is not higher than 1.2 μm and the cleavage rate is not higher than 4%.
[0026] Optionally, the TTV of the silicon carbide wafer thinning is not higher than 0.8μm, and the cleavage rate is not higher than 3%.
[0027] Optionally, the silicon carbide wafer thinning wafer can be any size from 4 to 12 inches.
[0028] Optionally, the silicon carbide wafer thinning sheet can be N-type or H-type.
[0029] Compared with the prior art, the present invention achieves at least one of the following beneficial effects:
[0030] (1) The present invention uses a laser-modified silicon carbide wafer thinning processing method. By performing two laser scans, the modification method is optimized, which can significantly reduce the separation difficulty and the warping problem after wafer thinning.
[0031] (2) The present invention uses a laser-modified silicon carbide wafer thinning process. During the final thinning process, the presence of the modification layer on the wafer surface reduces the wear of the grinding wheel and the risk of wafer cracking. Currently, it has been measured that the wear can be reduced by more than 20% for the same thinning thickness. After integrating the grinding wheel, the overall cost is reduced by about 30%, and the cracking rate is less than 4%. At the same time, the final thickness that the grinding wheel needs to thin after laser modification (generally <80um) is much lower than the target thickness of traditional grinding wheel thinning (~250um), which can further reduce the processing cost while ensuring wafer warpage. Attached Figure Description
[0032] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:
[0033] Figure 1 An exemplary embodiment of the present invention is shown in the process flow diagram of laser-modified thinning of silicon carbide wafers;
[0034] Figure 2 An exemplary embodiment of a schematic diagram showing the application of a protective film to the un-laser-irradiated surface of a silicon carbide wafer is shown;
[0035] Figure 3 An exemplary embodiment of a schematic diagram of laser modification of silicon carbide wafers is shown;
[0036] Figure 4 An exemplary embodiment is shown, illustrating a schematic diagram of the location of the second laser scanning region on a silicon carbide wafer;
[0037] Figure 5 An exemplary embodiment of applying a protective film to the laser-irradiated surface of a silicon carbide wafer after a second laser scan is shown;
[0038] Figure 6 An exemplary embodiment of a schematic diagram of a silicon carbide wafer separation operation is shown;
[0039] Figure 7 An exemplary embodiment of a silicon carbide wafer thinning schematic diagram is shown;
[0040] Figure 8 An exemplary embodiment is shown, illustrating a surface profile of a silicon carbide wafer thinned according to Example 1;
[0041] Figure 9 An exemplary embodiment is shown, illustrating the surface profile of a silicon carbide wafer thinned in Comparative Example 2;
[0042] Figure 10 An exemplary embodiment is shown, which is a side view of the internal modification layer of a silicon carbide wafer after the second laser scan in Example 1.
[0043] Figure 11 An exemplary embodiment is shown, which is a side view of the internal modification layer of a silicon carbide wafer after a single laser scan of Comparative Example 1.
[0044] Figure 12 An exemplary embodiment is shown in Table 3, illustrating the locations for silicon carbide sub-wafer thickness testing.
[0045] Explanation of reference numerals in the attached figures:
[0046] 1-Silicon carbide wafer; 2-Protective film; 3-Laser generator; 4-Carrier stage; 5-Patch ring; 6-Nozzle; 7-Connecting rod; 8-Opening; 9-Ring-mounted adsorption fixture; 10-Vacuum chuck; 11-Grinding wheel. Detailed Implementation
[0047] To more clearly illustrate the overall concept of the present invention, a detailed description will be provided below with reference to the accompanying drawings and examples.
[0048] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.
[0049] Example 1
[0050] In an exemplary embodiment of the present invention, the processing method for thinning silicon carbide wafers using laser modification includes the following steps;
[0051] S1: Apply a blue film to the un-laser-irradiated side of the silicon carbide wafer. Precisely trim excess blue film along the wafer's circumference. Transfer the silicon carbide wafer with the film-protected un-laser-irradiated side to the stage of the laser scanning equipment, with the side to be thinned facing upwards. The laser generator emits a picosecond laser with a wavelength of 532nm and a pulse width of 500ps. Control the laser focal length X at a certain depth inside the wafer (target wafer thickness). By controlling the local laser output power to 10W and the movement speed to 400m / s, a processing focal zone with extremely high power density can be formed locally. In this region, the crystal molecules absorb photon energy and excite free electrons. The micro-explosion effect generated by Coulomb repulsion breaks the molecular bonds of silicon carbide, changing the crystal phase structure. At the same time, the single crystal structure above and below the laser focal point cracks due to nonlinear stress. The laser scanning path moves laterally along the <11-20> crystal plane. After a single path scan is completed, the second path scan is performed at a certain interval. The interval between the two adjacent moving paths is 120μm. After the entire surface is scanned, a modified layer will be formed along the 0001 plane in a certain depth area inside the ingot, accompanied by the generation of local microcracks.
[0052] S2: With the center of the silicon carbide wafer as the center, the inner diameter of the circumferential edge portion is 0.7 times the radius of the entire wafer. A second laser scan is performed on the area outside the inner diameter of the circumferential edge portion of the surface to be thinned after the first laser scan. The conditions for the second laser scan are the same as those for the first laser scan. The focal length of the laser acting on the silicon carbide wafer is reduced, so that the modified layer formed in the area outside the inner diameter of the circumferential edge portion extends towards the laser irradiation surface. The total thickness of the modified layer in the second laser scan is 5 μm thicker than that in the first laser scan.
[0053] S31: A blue film is first applied to the thinned surface (laser irradiation surface) of the silicon carbide wafer after the second laser scan. The blue film is fixed onto the mounting ring, and a ring-shaped adsorption fixture is used to adsorb the mounting ring. The ring-shaped adsorption fixture includes eight suction nozzles arranged in a ring at certain intervals and eight connecting rods. The upper end of each suction nozzle is opened and connected to a vacuum generator. One end of each connecting rod is connected to a suction nozzle, and the other end is connected to a pressure sensor. During the separation process, each suction nozzle is adsorbed onto the mounting ring by the action of the vacuum generator. (See the wafer separation diagram for reference.) Figure 6 As shown. A uniform pulling force is gradually applied from the notch port towards the opposite side of the notch. Pressure sensors continuously monitor and record the pulling force values in each direction. During this process, the surface wafer will gradually separate until the pulling force reaches zero. If separation fails on the first attempt, the initial pulling force can be increased and the attempt repeated. The pulling force should be 8-16N, with a maximum generally not exceeding 16N.
[0054] S32: The separation surface of the silicon carbide sub-wafer is thinned using a grinding wheel. The stage and the grinding wheel rotate relative to each other, and the grinding wheel is gradually fed from top to bottom. After the grinding wheel thinning is completed, the blue film on the un-laser-irradiated surface of the silicon carbide wafer is removed to obtain a thinned silicon carbide wafer sheet. The grinding wheel thinning processing parameters are shown in Table 1.
[0055] Table 1 Grinding wheel thinning parameters
[0056]
[0057] Example 2
[0058] In an exemplary embodiment of the present invention, the processing method for thinning silicon carbide wafers using laser modification includes the following steps;
[0059] S1: Apply a blue film to the un-laser-irradiated side of the silicon carbide wafer. Precisely trim excess blue film from the wafer surface along its circumference. Transfer the silicon carbide wafer with the film-protected un-laser-irradiated side to the stage of the laser scanning equipment, with the side to be thinned facing upwards. The laser generator emits a picosecond laser with a wavelength of 1064nm and a pulse width of 400ps. Control the laser focal length X at a certain depth inside the wafer (target wafer thickness). By controlling the local laser output power to 20W and the movement speed to 800mm / s, a processing focal zone with extremely high power density can be formed locally. In this region, the crystal molecules absorb photon energy and excite free electrons. The micro-explosion effect generated by Coulomb repulsion breaks the molecular bonds of silicon carbide, changing the crystal phase structure. At the same time, the single crystal structure above and below the laser focal point cracks due to nonlinear stress. The laser scanning path moves laterally along the <11-20> crystal plane. After a single path scan is completed, a second path scan is performed at a certain interval. The interval between the two adjacent moving paths is 200μm. After the entire surface is scanned, a modified layer will be formed along the 0001 plane in a certain depth area inside the ingot, accompanied by the generation of local microcracks.
[0060] S2: With the center of the silicon carbide wafer as the center, the inner diameter of the circumferential edge portion is 0.7 times the radius of the entire wafer. A second laser scan is performed on the area of the circumferential edge portion that is larger than the inner diameter of the surface to be thinned after the first laser scan. The conditions for the second laser scan are the same as those for the first laser scan. The focal length of the laser acting on the silicon carbide wafer is reduced, so that the modified layer formed in the area outside the inner diameter of the circumferential edge portion extends towards the laser irradiation surface. The total thickness of the modified layer in the second laser scan is 5μm higher than the position of the modified layer in the first laser scan.
[0061] S31: A blue film is first applied to the thinned surface (laser irradiation surface) of the silicon carbide wafer after the second laser scan. The blue film is fixed onto the mounting ring, and a ring-shaped adsorption fixture is used to adsorb the mounting ring. The ring-shaped adsorption fixture includes eight suction nozzles arranged in a ring at certain intervals and eight connecting rods. The upper end of each suction nozzle is opened and connected to a vacuum generator. One end of each connecting rod is connected to a suction nozzle, and the other end is connected to a pressure sensor. During the separation process, each suction nozzle is adsorbed onto the mounting ring by the action of the vacuum generator. (See the wafer separation diagram for reference.) Figure 6 As shown. A uniform pulling force is gradually applied from the notch port towards the opposite side of the notch. Pressure sensors continuously monitor and record the pulling force values in each direction. During this process, the surface wafer will gradually separate until the pulling force reaches zero. If separation fails on the first attempt, the initial pulling force can be increased and the attempt repeated. The pulling force should be 8-16N, with a maximum generally not exceeding 16N.
[0062] S32: The separation surface of the silicon carbide sub-wafer is thinned using a grinding wheel. The stage and the grinding wheel rotate relative to each other, and the grinding wheel is gradually fed from top to bottom. After the grinding wheel thinning is completed, the blue film on the un-laser-irradiated surface of the silicon carbide wafer is removed to obtain a thinned silicon carbide wafer sheet. The grinding wheel thinning processing parameters are shown in Table 1.
[0063] Example 3
[0064] The main difference from Example 1 is that the total thickness of the modified layer in the second laser scan is increased by 3 μm compared to the thickness in the first laser scan. All other steps are the same as in Example 1.
[0065] Example 4
[0066] Based on Example 1, the main difference is that the inner diameter of the circumferential edge portion is 0.8 times the radius of the entire wafer, with the center of the silicon carbide wafer as the center. The other steps are the same as in Example 1.
[0067] Example 5
[0068] The main difference from Example 1 is that the total thickness of the modified layer in the second laser scan is increased by 7 μm compared to the thickness in the first laser scan. All other steps are the same as in Example 1.
[0069] Comparative Example 1
[0070] Based on Example 1, the main difference is that step S2 is not involved in performing a second laser scan on the area outside the inner diameter of the circumferential edge portion. Instead, the silicon carbide wafer after the first laser scan is directly separated and subsequently thinned.
[0071] Comparative Example 2
[0072] Silicon carbide wafers are directly thinned using a grinding wheel.
[0073] Test case
[0074] The 8-inch, 200μm thick silicon carbide wafers prepared in the above examples and comparative examples were tested, as shown in Table 2.
[0075] Table 2
[0076]
[0077] Referring to Table 2, the silicon carbide wafers thinned using the laser-modified silicon carbide wafer thinning method of this application have a TTV (thinning volume) of no more than 1.2 μm and a cleavage rate of no more than 4%. It can be seen that the processing method of this application significantly reduces the problem of cleavage during cutting, improves wafer yield, and reduces production costs.
[0078] Table 3
[0079]
[0080] Referring to Table 3, the thickness variation of the silicon carbide sub-wafer obtained by the second laser refining separation in Example 1 and the thickness variation of the silicon carbide sub-wafer obtained by only one laser refining separation in Comparative Example 1 were tested. The test methods are as follows: Figure 12 As shown, with the center of the silicon carbide wafer as point (0,0), four points were symmetrically selected, and the thickness of the silicon carbide sub-wafer was measured at distances of 70mm and 80mm from the center. Referring to Table 3, it can be seen that the silicon carbide sub-wafer obtained after only one laser processing in Comparative Example 1 has a relatively uniform thickness across the entire surface. In Example 1, a second laser processing was performed on the circumferential edge portion based on the first laser processing. The edge thickness of the silicon carbide sub-wafer obtained after peeling was higher than the internal height, indicating that during the second laser processing of the circumferential edge portion, the modified layer formed in the circumferential edge portion extends towards the surface to be thinned (or the laser irradiation direction), and the thickness of the modified layer increases.
[0081] refer to Figure 8 As shown, Figure 8 An exemplary embodiment of the silicon carbide wafer thinning diagram of Example 1 is shown. After separation, the wafer edge has undergone two layers of laser processing. On the one hand, the separation difficulty is reduced because the separation force at the edge is less than that inside. On the other hand, the thickness of the target wafer edge is higher than that at the center after separation. At this time, the internal stress of the crystal is basically in equilibrium (the sum of the tensile and compressive stresses at the edge and the center of the wafer is zero). At this time, a single grinding wheel (e.g., 8000#) can be used for thinning. Since the direction of the grinding wheel force is edge-center-edge, the thinning can be completed in one step, avoiding the additional introduction of local stress of the grinding wheel and avoiding breaking the balance of internal stress of the wafer. This makes the wafer less prone to abnormal warping at the center (a "straight" surface). This is reflected in the image as better flatness in the central area.
[0082] refer to Figure 9 As shown, Figure 9 An exemplary embodiment of the surface profile of a silicon carbide wafer thinned in Comparative Example 2 is shown, the surface profile being M-shaped, with abnormal warping occurring at the center of the wafer.
[0083] refer to Figure 10 As shown, Figure 10 An exemplary embodiment is shown in the side view of the internal modification layer of the silicon carbide wafer after the second laser scan in Example 1. Figure 11 An exemplary embodiment is shown as a side view of the formation of a modified layer inside a silicon carbide wafer after a single laser scan, as illustrated in Comparative Example 1. The applicant... Figure 10 , 11The modified layer is represented by circles, and it can be seen that the overall modified layer thickens after the second laser scan.
[0084] The laser thinning thickness of this application is >80μm, but the final thickness that needs to be thinned by the grinding wheel after laser modification is <80μm. Compared with Comparative Example 2, the grinding wheel wear can be reduced by more than 20% at the same thinning thickness. When Comparative Example 2 uses traditional grinding wheel thinning, the thickness that needs to be thinned by the grinding wheel is >200μm. This further proves that the processing method of this application can further reduce processing costs and shorten the thinning time while ensuring wafer warpage.
[0085] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.
Claims
1. A processing method for thinning silicon carbide wafers using laser modification, characterized in that, The processing method includes the following steps: S1: Perform a full-scale laser scan on the surface of the silicon carbide wafer to be thinned to form a modified layer inside the silicon carbide wafer; S2: Perform a second laser scan on the circumferential edge of the surface to be thinned after the first laser scan, so that the modified layer formed on the circumferential edge extends towards the surface to be thinned. S3: Separate the silicon carbide wafers from the second laser scan sequentially and thin them with a grinding wheel to obtain thinned silicon carbide wafer sheets; The thickness of the modified layer after the second laser scan is greater than that after the first laser scan. The thickness of the modified layer in the second laser scan was 3-7 µm greater than that in the first laser scan.
2. The processing method according to claim 1, characterized in that, The thickness of the modified layer in the second laser scan was 3-5 µm greater than that in the first laser scan.
3. The processing method according to claim 1, characterized in that, With the center of the silicon carbide wafer as the center, the inner diameter of the circumferential edge portion accounts for 0.6-0.8 times the radius of the entire wafer.
4. The processing method according to claim 1, characterized in that, Laser-modified material can reduce thickness to >80µm.
5. The processing method according to claim 1, characterized in that, Both the first and second laser scans used picosecond laser equipment; furthermore, the laser wavelength was 532-1064nm and the pulse width was 45-500ps.
6. The processing method according to claim 1, characterized in that, The laser power for both the first and second laser scans is 2-22W, and the scanning rate is 300-800mm / s.
7. The processing method according to claim 1, characterized in that, The scanning paths of the first and second laser scans move laterally along the <11-20> crystal plane within a certain interval, forming several single scanning paths with an interval of 120-350um between adjacent single scanning paths.
8. The processing method according to claim 5, characterized in that, Step S3 also includes the following steps: S31: The silicon carbide wafer to be thinned in the second laser scan is first coated with a film and fixed on the bonding ring. The film is then adsorbed onto the bonding ring using a ring-mounted adsorption fixture. By applying tension, the silicon carbide wafer is separated along the modified layer to obtain a silicon carbide sub-wafer. S32: The separation surface of the silicon carbide sub-wafer is thinned by grinding wheel to obtain a thinned silicon carbide wafer.
9. The processing method according to claim 8, characterized in that, The ring-shaped adsorption fixture includes suction nozzles and connecting rods arranged in a ring at certain intervals. The upper end of the suction nozzle is opened to connect to a vacuum generator, one end of the connecting rod is connected to the suction nozzle, and the other end of the connecting rod is connected to a pressure sensor.