A method for repairing warpage of a silicon carbide wafer and a silicon carbide wafer

Abstract

The application discloses a silicon carbide wafer warping repairing method and a silicon carbide wafer, and comprises the following steps: S1. pretreatment: chamfering treatment is performed on a wafer with a wire cutting warping degree exceeding a standard; S2. film pasting: full-surface mapping measurement is performed on the wafer, a high point of wafer warping is positioned, and a positioning film is pasted on the back of the high point; S3. wax pasting: wax is pasted on the back of the wafer, and then the back of the wafer is pasted on a ceramic disc; S4. single polishing: the ceramic disc on which the wafer is placed is placed on a single polishing machine, single polishing processing is performed on the front surface of the wafer, processing time is 5-15 min, and pressure is 200-300 g / cm2; S5. wax removing: the positioning film and the wax on the wafer are removed, and the wafer is cleaned; S6. fine grinding: fine grinding processing is performed on the wafer, processing time is 100-200 min, processing pressure is 150-250 g / cm2, and the rotation speed of the lower disc is 15-25 rpm; S7. rough polishing: rough polishing processing is performed on the wafer, processing time is 100-150 min, processing pressure is 150-250 g / cm2, and the rotation speed of the lower disc is 15-25 rpm; and S8. fine polishing: fine polishing processing is performed on the wafer, processing time is 180-250 min, processing pressure is 300-400 g / cm2, and the rotation speed of the lower disc is 25-40 rpm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor wafer processing, and mainly relates to a silicon carbide wafer warping repair method and a silicon carbide wafer. BACKGROUND

[0002] The third-generation semiconductor silicon carbide (SiC) substrate is the core basic material for manufacturing high-performance power devices (such as MOSFETs and diodes) and radio frequency devices. Compared with traditional silicon (Si) substrates, SiC has significant advantages such as large band gap, high breakdown field strength, high thermal conductivity, and fast electron saturation drift speed, and is suitable for high-temperature, high-voltage, high-frequency, and high-power application scenarios (such as electric vehicles, photovoltaic inverters, and 5G base stations).

[0003] However, the preparation and processing of SiC substrates are extremely difficult, and are one of the links with the highest technical barriers and the largest cost proportion in the industry chain. At present, silicon carbide wafer processing technology is still in the stage of continuous optimization and improvement, and there are many technical bottlenecks in key process links such as wafer cutting, grinding, and polishing. For example, the high hardness and brittleness of SiC material lead to occasional large warping during cutting, and low warping (Warp) and bending (Bow) cannot be ensured after grinding and polishing, further increasing the difficulty of SiC processing. SUMMARY

[0004] One object of the present application is to provide a wafer warping repair method to solve the problem of wafer warping exceeding the tolerance during cutting and low yield during processing.

[0005] Another object of the present application is to improve the yield of wafer warping repair and reduce the waste of raw materials.

[0006] To achieve the above objects, the technical scheme adopted by the present application is as follows: a silicon carbide wafer warping repair method, comprising the following steps:

[0007] S1. Pretreatment: chamfering the wafer with line cutting warping exceeding the tolerance;

[0008] S2. Film sticking: performing full-surface mapping measurement on the wafer, positioning the high point of the wafer warping, and sticking a positioning film on the back of the high point;

[0009] S3. Wax sticking: sticking wax on the back of the wafer, and then sticking the back of the wafer on a ceramic disc;

[0010] S4. Single polishing: placing the ceramic disc with the wafer on a single polishing machine, and performing single polishing on the front surface of the wafer, with a processing time of 5-15 min and a pressure of 200-300 g / cm 2 ;

[0011] S5. Dewaxing: Remove the positioning film and wax from the wafer and clean the wafer.

[0012] S6. Fine Grinding: The wafer is finely ground on both sides for 100-200 minutes at a pressure of 150-250 g / cm. 2 The lower plate speed is 15-25 rpm;

[0013] S7. Rough Polishing: Double-sided rough polishing of the wafer, processing time 100-150 min, processing pressure 150-250 g / cm. 2 The lower plate speed is 15-25 rpm;

[0014] S8. Fine Polishing: Double-sided fine polishing of the wafer, processing time 180-250 min, processing pressure 300-400 g / cm. 2 The lower plate speed is 25-40 rpm.

[0015] As a preferred embodiment, the minimum distance between the edge of the positioning film and the edge of the high point is 2-3 mm, and the maximum distance is 5-7 mm.

[0016] As a preferred embodiment, the thickness of the positioning film covering the high point is 0.01mm-0.05mm.

[0017] As a preferred embodiment, in step S1, the pre-treated wafer has a cutting warpage > 35 μm and a wafer thickness of 440 μm-600 μm.

[0018] As a preferred option, the polishing cloth used in the S4 step single-polishing process is made of polyurethane with a hardness of 85-98A; the agglomerated diamond liquid has a particle size of D50 of 6-9 μm, a viscosity of 10-20 Pa·s, and a flow rate of 20-50 ml / min; the polishing head speed is 25-30 rpm; the lower plate speed is 20-28 rpm; and the high point removal amount of the wafer after single polishing is 10-30 μm.

[0019] As a preferred option, the polishing cloth used in the S6 step fine grinding process is made of non-woven fabric with a hardness of 80-95A; the agglomerated diamond liquid has a particle size of D50 of 6-9 μm, a viscosity of 10-20 Pa·s, and a flow rate of 20-50 ml / min; the thickness removal of the wafer after fine grinding is 15-30 μm; and the TTV is <4 μm.

[0020] As a preferred option, the polishing cloth used in the S7 step rough polishing process is made of non-woven fabric with a hardness of 80-95A; the particle size of the polishing liquid is D50: 0.1-0.25um; and the thickness removal of the wafer after fine polishing is 8-12μm, with TTV < 3um.

[0021] As a preferred option, the S8 step fine polishing process also includes: a polishing head rotation speed of 25-40 rpm, a polishing slurry particle size of D50 of 60-120 nm, a pH of 8-11, and a wafer thickness removal of 0.5-1 μm after fine polishing, with TTV < 3 μm and LTV < 1 μm.

[0022] As a preferred embodiment, the positioning film may be a UV film, a blue film, or an epoxy functional film.

[0023] As a preferred embodiment, a silicon carbide wafer obtained by the silicon carbide wafer warpage repair method described above has a warpage value of <20µm.

[0024] Compared with the prior art, the beneficial effects of this application are as follows:

[0025] (1) This application targets wafers with abnormal cutting values. Based on the surface data of the full map mapping (MAP), a positioning film is applied only to the high warp area. In subsequent single polishing, fine grinding and other processes, the positioning film is equivalent to "lifting" the high warp of the wafer, which makes it easier for the equipment to "minimally" correct the warped position of the wafer.

[0026] (2) The warpage repair method provided in this application can repair the high warpage points of the wafer, ensuring the accuracy of wafer warpage repair, greatly reducing the phenomenon of excessive wafer warpage value after polishing, improving wafer production yield and reducing wafer material waste. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process for repairing silicon carbide wafer warping according to this application.

[0028] Figure 2 This is a full-surface mapping distribution of silicon carbide wafer warpage (Bow-Warp mode) in one embodiment of this application.

[0029] Figure 3 This is a full-surface mapping distribution of warpage of a repaired silicon carbide wafer (Bow-Warp mode) in one embodiment of this application.

[0030] Figure 4 This is a top view of the positioning film area on the back side of the wafer in one embodiment of this application.

[0031] Figure 5 This is a top view of the positioning film area on the back side of the wafer in another embodiment of this application.

[0032] In the diagram: 10, wafer; 20, high point; 21, edge of high point; 30, positioning film; 31, edge of positioning film. Detailed Implementation

[0033] The present application will be further described below with reference to specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0034] In the description of this application, it should be noted that the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., which indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and should not be construed as limiting the specific protection scope of this application.

[0035] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0036] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0037] like Figure 1 This application provides a method for repairing the warpage of a silicon carbide wafer 10, which reduces the warpage value of the silicon carbide wafer 10 to within 20 μm. The method mainly includes the following steps:

[0038] S1. Pre-processing: Chamfering is performed on wafers with excessive wire-cut warpage;

[0039] It is understandable that chamfering can eliminate tiny edge cracks and stress concentration points caused by wafer dicing. Grinding sharp edges into smooth arcs can not only prevent wafer breakage during subsequent operations, but also release local stress, providing a more stable and safer base for high-precision shaping and polishing.

[0040] In some embodiments, for silicon carbide wafers 10 that warp due to wire cutting, in step S1, it is preferable to perform chamfering and warp repair treatment on wafers 10 with a warp value > 35 μm and a thickness of 440-600 μm. It should be understood that the silicon carbide wafer 10 warp repair method provided in this application needs to be applied to wafers 10 with high warp to improve resource utilization efficiency. When the warp value > 35 μm, the wafer 10 has repair significance. A wafer 10 thickness of 440-600 μm provides the necessary mechanical strength and stability, ensuring sufficient substrate thickness to withstand mechanical stresses during subsequent high-pressure single-sided polishing processes, preventing cracking or new damage during processing.

[0041] S2. Film application: Perform full-surface mapping measurement on wafer 10, locate the high point 20 of the warped wafer 10, and apply the positioning film 30 to the back of the high point 20.

[0042] Specifically, the surface of wafer 10 is scanned point by point using high-precision inspection equipment (such as a laser interferometer, optical profilometer, or white light interferometer) to obtain the warpage value of each tiny region, and referenced. Figure 2 As shown, this is a visualization graphic that quantitatively characterizes the spatial distribution of warpage on the surface of wafer 10. The "red" area represents the high warpage point 20, which exceeds the standard; the "yellow" and "green" areas represent the low warpage points; and the "blue" area represents the normal points. Through the "red" area on the visualization graphic, it is possible to clearly identify the location where the positioning film 30 needs to be attached to the back of wafer 10, avoiding "insufficient protection" or "over-coverage" caused by blindly attaching the film. Moreover, it is possible to accurately repair the high warpage point 20 of wafer 10, minimizing damage to the healthy areas of wafer 10 on the one hand, and maximizing the warpage correction efficiency of wafer 10 on the other hand.

[0043] S3. Apply wax: Apply wax to the back of wafer 10, and then attach the back of wafer 10 to the ceramic disk;

[0044] Specifically, prepare a ceramic disk with a diameter of 485mm. Preheat the ceramic disk to 100-130℃. Place the wafer 10 with the positioning film 30 attached into the ceramic disk (each disk holds 3-6 wafers 10). Then, place the entire ceramic disk into a fully automatic waxing machine. Drip wax to fill the gap between the back film layer of the wafer 10 and the ceramic disk. Bake and cure at 200-230℃ to ensure that the wax is completely melted and fully fills the gap, making the wafer 10, positioning film 30, and ceramic disk a unified whole, preventing displacement during polishing. It can be understood that preheating the ceramic disk reduces the viscosity of the wax, promoting rapid and uniform spread of the wax liquid, avoiding "local accumulation" or "residual air bubbles" of the wax layer caused by a cold ceramic disk. Filling the microscopic gap between the back film layer of the wafer 10 and the ceramic disk with the wax layer can eliminate interface stress concentration, preventing film layer cracking or wafer 10 warping recurrence during polishing.

[0045] S4. Single-sided polishing: Place the ceramic disk containing wafer 10 on a single-sided polishing machine and perform single-sided polishing on the front side of wafer 10. Processing time: 5-15 minutes; pressure: 200-300 g / cm². 2 ;

[0046] Specifically, a 50B single-sided polishing machine is provided. The machine is equipped with a PP (polishing) head and a lower polishing disc, both with independent speed control. A ceramic disc (Ф485mm) holding 3-6 wafers is fed into the polishing machine and placed in the center of the lower disc. The ceramic disc is fixed to the lower disc by vacuum adsorption to ensure no slippage during rotation. A polyurethane polishing cloth (hardness 85-98A) is used, and agglomerated diamond liquid (particle size D50 = 6-9μm, viscosity 10-20 Pa·s, flow rate 20-50 mL / min) is added. The PP head speed is set to 25-30 rpm, the lower disc speed to 20-28 rpm, and the pressure to 200-300 g / cm³. 2 Contact the front side of the wafer 10, processing time 5-15 minutes, precisely remove 10-30μm high spots 20.

[0047] It should be understandable that when the PP head is pressed down, the set pressure (200-300g / cm) is applied. 2 When contacting the front side of wafer 10, since the high point 20 of wafer 10 is attached to the back side with positioning film 30, the warped part of the high point 20 of wafer 10 is preferentially ground off, so as to achieve the effect of accurately removing the high point 20.

[0048] S5. Dewaxing: Remove the positioning film 30 and wax from wafer 10 and clean wafer 10.

[0049] Specifically, after single-use cleaning, manually remove the positioning film 30 and wax from the back of wafer 10, clean wafer 10 thoroughly, and ensure that there is no residual wax or film fragments on the surface of wafer 10.

[0050] S6. Fine Grinding: Double-sided fine grinding of wafer 10, processing time 100-200 min, processing pressure 150-250 g / cm. 2 The lower plate speed is 15-25 rpm;

[0051] Specifically, a double-sided precision grinding machine is provided, equipped with upper and lower grinding discs, driven by a planetary gear, to achieve simultaneous double-sided grinding of wafer 10. A planetary gear (with 6-14 wafer 10 slots, corresponding to 6-14 wafers being processed) made of blued steel and 0.3-0.4mm thick is mounted on the spindle. Cleaned and dried wafer 10 are sequentially placed into the planetary gear slots. Non-woven polishing cloth (hardness 80-95A) is installed on both the upper and lower discs; the processing pressure is set to 150-250g / cm. 2The lower plate rotates at 15-25 rpm, and agglomerated diamond liquid (particle size D50=6-9μm, viscosity 10-20Pa·s, flow rate 20-50mL / min) is added dropwise. The processing time is 100-200min, and the wafer thickness 10 is removed simultaneously on both sides by 15-30μm. The TTV (total thickness deviation of wafer 10) is controlled to be <4μm.

[0052] S7. Rough Polishing: Double-sided rough polishing of wafer 10, processing time 100-150 min, processing pressure 150-250 g / cm. 2 The lower plate speed is 15-25 rpm;

[0053] Specifically, a stainless steel planetary wheel (0.3-0.4mm thick, with 6-14 wafer 10 slots) is installed on the main shaft of the rough polishing machine. Stainless steel offers better corrosion resistance than blued steel (suitable for the weakly alkaline environment of CMP polishing fluid), and its thin structure reduces pressure on the wafer 10 edges. The finely ground wafer 10 is then placed into the planetary wheel slots, with non-woven polishing cloth (hardness 80-95A) installed on both the upper and lower disks; the processing pressure is set to 150-250 g / cm². 2 Set the lower plate speed to 15-25 rpm, add polishing slurry (particle size D50=0.1-0.25μm, pH=7-10, purplish-red liquid), and set the processing pressure to 150-250 g / cm. 2 The processing time is 100-150 minutes, and the thickness of wafer 10 is removed simultaneously on both sides by 8-12 μm, controlling the TTV of wafer 10 to be <3 μm. It should be understood that rough polishing (CMP, chemical mechanical polishing) is a key process after fine grinding. Its goal is to remove the microscopic damage layer remaining after fine grinding, adjust the thickness to the target range, and achieve an ultra-flat surface of wafer 10 through the synergistic effect of chemical and mechanical processes.

[0054] S8. Fine Polishing: Fine polishing of wafers up to 10mm in size, processing time 180-250 minutes, processing pressure 300-400 g / cm. 2 The lower plate speed is 25-40 rpm.

[0055] Specifically, the rough-polished wafer 10 is placed into a fine polishing machine for further processing, using a Ф485mm ceramic disk (approximately 485mm in diameter). The ceramic disk holds 3-6 wafer 10s, reducing the number of wafers compared to rough polishing and improving the uniformity of pressure per wafer. The PP head and lower disk rotate at 25-40 rpm. Polishing slurry (particle size D50=60-120nm, pH=8-11) is added, and the processing pressure is set to 300-400g / cm. 2 The processing time is 180-250 min, removing 0.5-1 μm of residual defects from rough polishing, and controlling TTV (total thickness deviation of wafer 10) < 3 μm and LTV (local thickness deviation of wafer 10) < 1 μm.

[0056] It is worth mentioning that existing processing techniques cannot repair the warpage of wafers with excessive warpage values. This application addresses the surface shape of wafers with excessive warpage values ​​by performing a positioning film application process on the high warpage point 20 of wafer 10, which can effectively repair the warpage value. After fine polishing, the warpage value is reduced to less than 20um, solving the problem of excessive warpage value and low yield in the processing.

[0057] In some embodiments, the positioning film 30 on the back side of wafer 10 may be a UV film, a blue film, or an epoxy functional film, preferably a UV film. The UV film is a thin film formed by coating a substrate (such as PET) with a UV-curable adhesive, which can be rapidly cured by ultraviolet irradiation. The volume shrinkage rate of the UV adhesive during curing is about 0.5-1%, which can generate a weak reverse stress in the high-point area 20. This stress works synergistically with the mechanical removal of single polishing to accelerate warpage correction and reduce the amount of polishing required.

[0058] In some embodiments, the positioning film 30 covers the high point 20 with a thickness of 0.01mm-0.05mm, a width w of 20mm-60mm, and a length L that covers either the area of ​​the high point 20 or the entire wafer 10. Figure 4 and Figure 5 As shown, specifically, a positioning film 30 is attached to the back of wafer 10. The length of the positioning film 30 refers to the dimension extending along the 'vertical diameter direction' of the circle, covering both sides of the cross-section of wafer 10; the width refers to the arc span dimension along the 'horizontal direction' (perpendicular to the length direction) of the circle, and the width does not necessarily cover both sides of the cross-section of wafer 10; the positioning film 30 is 20-60mm wide, precisely defining the "fixed area" and the "buffer zone" to avoid over-covering the healthy area of ​​wafer 10; the length covers the high point 20 area or the entire wafer 10, which can eliminate the stress difference along the length of wafer 10 and prevent damage to wafer 10 due to large local stress.

[0059] It is understandable that thick films, due to their high rigidity, are difficult to adhere to minute curves, easily leading to the formation of air bubbles or gaps under the film. This results in uneven pressure transmission, causing over-polishing of high-point areas or under-polishing of healthy areas. A thickness of 0.01mm-0.05mm allows the film layer to adapt to warped surfaces, and the pressure is evenly distributed to the back side of wafer 10 through the film layer, keeping the pressure deviation within a small range and ensuring precise removal of high-point areas.

[0060] In addition, when the film is peeled off after polishing, excessively thick films are prone to leaving adhesive residue due to "cohesion", while thin films of 10-50μm have lower cohesion and the adhesive layer is easier to separate from the wafer during peeling.

[0061] In some embodiments, the positioning film 30 completely covers the high point 20, meaning the area of ​​the positioning film 30 is larger than the area of ​​the high point 20. The minimum distance between the edge 31 of the positioning film and the edge 21 of the high point is 2-3 mm, and the maximum distance is 5-7 mm. On the one hand, this avoids the positioning film 30 area being too small, resulting in insufficient buffer space and the possibility of simultaneous removal of healthy areas or film edge displacement. On the other hand, it avoids the positioning film 30 covering too much of the healthy area of ​​the wafer 10, which would require additional energy to remove trace materials from non-target areas during polishing, prolonging the polishing time and reducing the efficiency of removing warpage from the high point 20 of the wafer 10. In other words, the 2-3 mm distance ensures both pressure buffering and film stability while controlling the additional polishing amount within a range that has no substantial impact on the healthy area, achieving an optimal balance between "precise repair" and "process efficiency."

[0062] In some embodiments, such as Figure 4 and Figure 5 As shown, the positioning film 30 can be a long strip shape that covers the high point 20 and extends to the edge of the wafer 10, or it can be a shape that adapts to the pattern of the high point 20. The long strip shape does not need to customize the outline according to the specific distribution of the high point 20. In mass production, the mold preparation, cutting or coating process is simpler. The shape that adapts to the pattern of the high point 20 can accurately position the area of ​​the high point 20. In the actual production process, the shape of the positioning film 30 can be set as needed. This application does not make specific limitations on this.

[0063] In some embodiments, the positioning film 30 at least covers the central region of the high point 20, and the width of the positioning film 30 covering the central region of the high point 20 is at least greater than 20 mm. It should be understood that... Figure 2 As shown in the red area, the central region of the high point 20 is the main location of warping, with the greatest deformation. After the positioning film 30 covers the main region, it can provide support for the central region of the high point 20 during the single polishing step. Thus, when the polishing machine applies pressure, the pressure is concentrated and transmitted to the center of the high point 20 through the positioning film 30, allowing this central region to be ground preferentially. This minimizes interference with the healthy areas of the wafer 10 and prevents non-warped areas from being mistakenly ground.

[0064] In some embodiments, the positioning film 30 covers at least the central region of the high point 20. The width of the positioning film 30 covering the central region of the high point 20 is preferably 20mm-60mm to avoid the positioning film 30 being too wide (>60mm) and covering too much healthy area, which would cause the polishing pressure in the single polishing step to be dispersed and unable to be concentrated on the central region of the high point 20, resulting in a decrease in the removal amount of the high point 20.

[0065] It is worth mentioning that, in order to ensure that the positioning film 30 is accurately attached to the back of the high point 20, in step S2, methods such as template making based on the full surface mapping distribution map, optical projection comparison, or fixture making can be used to achieve accurate attachment of the positioning film 30 to the back of the wafer 10.

[0066] In some embodiments, the method for applying a film to create a template based on a full-surface mapping distribution map includes:

[0067] (1) High point 20 boundary extraction: Import the full surface mapping measurement data into the computer-aided analysis software; set the warping threshold (e.g., the area ≥35μm is defined as high point 20), the software automatically identifies and extracts the boundary contour of high point 20; the system automatically generates a two-dimensional projection map of high point 20 and marks the coordinate points of the edge 21 of high point 20.

[0068] (2) Calculation of the size of the positioning film 30: Based on the coordinates of the high point edge 21, the software automatically extends outward by 2-3mm (preferably 2.5mm) to generate the outer contour of the positioning film 30; for the width direction, the system automatically calculates the width of the positioning film 30 (within the range of 20-60mm) according to the lateral span of the high point 20; for the length direction, the length of the positioning film 30 is set to cover the entire diameter of the wafer 10 or only cover the area of ​​the high point 20 plus the extension amount (2-3mm).

[0069] (3) Film template making: The calculated positioning film 30 contour data is transmitted to a laser cutting machine or CNC engraving machine; a hollow area that is completely consistent with the contour of the positioning film 30 is laser etched on a transparent PET film (thickness 0.1-0.2mm) to form a film positioning template; the positioning reference of wafer 10 is marked on the template (such as the position of the crystal orientation mark NOTCH (notch, notch) and the center mark of wafer 10).

[0070] (4) Film application: Place the film application positioning template on the back of wafer 10 and align it precisely with wafer 10 through the NOTCH groove or center positioning hole (alignment accuracy ≤ 0.1mm); through the cutout area of ​​the template, use an automatic film application device or manual tools to precisely apply the UV film to the corresponding position on the back of the high point 20; during the film application process, the edge of the UV film naturally coincides with the cutout boundary of the template, automatically achieving the requirement that "the distance between the edge of the positioning film 31 and the edge of the high point 21 is 2-3mm"; after the film application is completed, remove the positioning template and retain the positioning film 30 on the back of wafer 10.

[0071] In some embodiments, the film application method based on optical projection contrast includes:

[0072] (1) Projection system settings: Import the full surface mapping data of wafer 10 into the film application workbench equipped with an optical projection system; the system displays a visual graphic of “high point 20 area + 2-3mm outer extension area” on the projection screen according to the coordinates of the high point edge 21 (e.g., the red area represents the high point 20, and the yellow border represents the outer boundary of the positioning film 30).

[0073] (2) Wafer 10 alignment: Place wafer 10 on a transparent worktable and adjust the position of wafer 10 so that its NOTCH groove is aligned with the projection reference line; the projected image is superimposed on the back of wafer 10 in real time, and the operator can directly see the position of high point 20 and the precise area where the positioning film 30 should be attached.

[0074] (3) Film application: Apply pre-cut UV film (20-60mm wide, length covering the projected yellow border area) according to the yellow border area shown in the projection. When applying the film, ensure that the edge of the UV film coincides with the projected yellow border, with a tolerance of ±0.5mm. The system automatically detects the film application position. If the deviation is >0.5mm, an alarm will be issued, and readjustment is required. This method is suitable for production lines with a high degree of automation. The projection accuracy can reach ±0.1mm, ensuring that the distance between the edge of the positioning film 31 and the edge of the high point 21 is precisely controlled within 2-3mm.

[0075] In some embodiments, the fixture-based manufacturing method includes:

[0076] (1) Customized fixture manufacturing: Based on the full surface mapping data of wafer 10, a special film-applying fixture is designed; the fixture includes: ① wafer 10 positioning base (with NOTCH groove and center positioning post); ② adjustable positioning baffle (can be moved radially and circumferentially according to the position of high point 20); ③ UV film pressing roller (width 20-60mm adjustable).

[0077] (2) Fixture calibration: Adjust the positioning baffle to a position 2-3mm away from the edge 21 of the high point (measured precisely with a digital vernier caliper); lock the baffle position to form the physical boundary of the "high point 20+2-3mm buffer zone".

[0078] (3) Batch film application: Place wafer 10 into the fixture, and the NOTCH slot automatically engages with the positioning slot; apply the UV film roll to the back of wafer 10 using pressing rollers, the roller width limiting the UV film coverage area; the positioning baffle ensures that the edge of the UV film does not exceed the range of "high point edge 21+2-3mm"; after film application, automatically trim excess film. This method is suitable for wafers 10 in the same batch where the high point 20 positions are close, and can achieve semi-automatic batch film application.

[0079] Compared to existing technologies that eliminate warpage by grinding the entire wafer, insufficient grinding results in incomplete removal of warpage, rendering rework ineffective. Excessive grinding removes healthy areas of the wafer, causing previously flat areas to become concave, leading to "old warpage not eliminated, new concavity generated," and a worse overall surface appearance. In step S2 of this application, before rework, wafer 10 undergoes full surface mapping measurement (full MAP inspection) to obtain detailed three-dimensional topographic data of wafer 10, accurately locate the high points 20 of the warpage on wafer 10, and then attach a positioning film 30 to the back of wafer 10 based on the specific location of the high points 20 to achieve the effect of localized removal of wafer 10 warpage. It is understandable that during the subsequent step S4 single polishing of wafer 10, when the polishing machine applies pressure to wafer 10, the high point 20 of wafer 10 is higher than other areas on the back without the positioning film 30 because the positioning film 30 is attached to the back of the high point 20. As a result, the high point 20 on the front of wafer 10 is preferentially ground away by the polishing machine, which can accurately remove the warped points of wafer 10. This avoids the problem of insufficient or excessive grinding of wafer 10 as a whole, reduces the scrap rate of wafer 10 caused by over-processing, and reduces the rework cost of wafer 10.

[0080] Furthermore, two groups of wafers 10 with similar Warp values ​​were used to perform repair operations on the wafers 10 using the process of this application and the conventional process, respectively. After the repair was completed, 10 wafers 10 from each group were sampled to measure the average warpage change. The conventional process does not include steps S2 and S4 of the process of this application.

[0081]

Example 1

[0082] (1) Pre-processing: Provide a wire-cut wafer 10 to be processed. The wafer 10 is 6 inches in size and 440 μm thick. Select a wafer 10 with a warp value of 40-45 μm and perform chamfering on the wafer 10.

[0083] (2) Film application: Full surface mapping measurement is performed on the above wafer 10 to obtain the following results: Figure 2 The warpage distribution map of silicon carbide wafer 10 shown is a full-surface mapping map (Bow-Warp mode). The high point 20 of the warpage of wafer 10 is located. Based on the full-surface mapping map, a template is made by attaching a positioning film 30 with a width w of 35 mm and adapted to the shape of the high point 20. The distance between the edge 31 of the positioning film and the edge 21 of the high point is 2.5 mm. The positioning film 30 is selected as a UV film.

[0084] (3) Applying wax: Prepare a ceramic disk with a diameter of 485mm. Preheat the ceramic disk to 120℃. Place the wafer 10 with the positioning film 30 applied into the ceramic disk (each disk carries 6 wafers 10). Then, place the entire ceramic disk into the fully automatic waxing machine. Drip wax to fill the gap between the film layer on the back of the wafer 10 and the ceramic disk. Bake and cure at 220℃ to ensure that the wax is completely melted and fully fills the gap, so that the wafer 10, the positioning film 30 and the ceramic disk form a whole, preventing displacement during subsequent polishing.

[0085] (4) Single-sided polishing: A 50B single-sided polishing machine is provided. The polishing machine is equipped with a PP head and a lower polishing disc, both of which have independent speed control. A ceramic disc (Ф485mm) with 6 wafers fixed on it is fed into the polishing machine and placed in the center of the lower disc. The ceramic disc and the lower disc are fixed by vacuum adsorption. Polyurethane polishing cloth (hardness 90A) is used, and agglomerated diamond liquid (D50=8μm, viscosity 15Pa·s, flow rate 20mL / min) is added dropwise. The PP head speed is set to 28rpm, the lower disc speed to 24rpm, and the pressure to 250g / cm. 2 Contact the front side of wafer 10, processing time 10 minutes.

[0086] (5) Dewaxing: Manually peel off the UV film and wax on the back of wafer 10 and clean wafer 10.

[0087] (6) Fine grinding: Install a blue steel planetary wheel (with 14 wafer 10 slots, corresponding to 14 wafers to be processed) on the spindle. Place the cleaned and dried wafers 10 into the planetary wheel slots one by one. Install non-woven polishing cloth (hardness 90A) on both the upper and lower disks; set the processing pressure to 250g / cm. 2 The lower plate rotates at 25 rpm, and agglomerated diamond liquid (particle size D50=8μm, viscosity 15Pa·s, flow rate 20mL / min) is added dropwise for 150 min.

[0088] (7) Rough polishing: A stainless steel planetary wheel (0.35mm thick, with 14 wafer 10 slots) is installed on the main shaft of the rough polishing machine. The finely ground wafer 10 is placed into the planetary wheel slots in sequence, and non-woven polishing cloth (hardness 90A) is installed on both the upper and lower disks; the processing pressure is set to 250g / cm. 2 The lower plate rotates at 25 rpm, and polishing slurry (particle size D50=0.15μm, pH=8, purple-red liquid) is added dropwise. The processing pressure is set to 250 g / cm. 2 Processing time: 120 minutes.

[0089] (8) Fine polishing: Place the rough-polished wafer 10 into the fine polishing equipment for processing. Use a Ф485mm ceramic disk to support 6 wafers 10, which reduces the number of wafers compared to rough polishing and improves the uniformity of pressure per wafer; PP head speed is 30 rpm, lower disk speed is 28 rpm; add polishing fluid (particle size D50=80nm, pH=9), and set the processing pressure to 300g / cm 2 Processing time: 200 minutes.

[0090] Example 2

[0091] The difference between Example 2 and Example 1 is as follows:

[0092] In the preprocessing step, wafer 10 with a warp value of 35-40μm was selected, and the remaining steps were the same as in Example 1.

[0093] Example 3

[0094] The difference between Example 3 and Example 1 is that in the preprocessing step, wafer 10 with a warp value of 30-35μm is selected, and the other steps are the same as in Example 1.

[0095] Example 4

[0096] The difference between Example 4 and Example 1 is that in the film application step, a positioning film 30 with a width w of 50mm is applied to the back of the high point 20, and the other steps are the same as in Example 1.

[0097] Example 4

[0098] The difference between Example 5 and Example 1 is that in the film application step, a positioning film 30 with a width w of 120mm is applied to the back of the high point 20, and the other steps are the same as in Example 1.

[0099] Comparative Example 1

[0100] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not include steps S2 and S4, while the remaining steps are the same as in Example 1.

[0101] Comparative Example 2

[0102] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not include steps S2 and S4; in the pretreatment step, wafer 10 with a warp value of 35-40 μm is selected, and the remaining steps are the same as in Example 1.

[0103] Comparative Example 3

[0104] The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 does not include steps S2 and S4; in the pretreatment step, wafer 10 with a warp value of 30-35μm is selected, and the remaining steps are the same as in Example 1.

[0105] The average Warp change of 10 tested wafers was extracted, and the specific data results are shown in the table below.

[0106]

[0107] Based on the comparison results of the warped wafers 10 (high / medium / low) of different severity in the data table after repair by the process of this application and the conventional process, compared with the conventional repair process, the average warp value of the wafer 10 repaired by this application can be reduced to less than 20μm, which significantly improves the wafer 10 repair yield and reduces the waste of wafer 10 material.

[0108] Based on the data results from Examples 1, 4, and 5, attaching a positioning film 30 with a width w of 120 mm to the back of the high point 20 significantly increased the average Warp value of the wafer 10 after repair, even approaching the average Warp value of the control group without film application. This shows that a wider positioning film 30 is not necessarily better. An excessively wide positioning film 30 can easily cause the non-film-attached area to be ground away during single polishing, resulting in a decrease in the removal amount of the high point 20 and a decrease in the repair effect of the Warp value after the wafer 10 is repaired.

[0109] It is worth mentioning that, according to full-surface mapping measurements, the wafer 10 after final repair in Embodiments 1, 2, 3, and 4 of this application all exhibit the following characteristics: Figure 3 The warpage distribution map of wafer 10 shown (Bow-Warp mode) shows that the red area has disappeared, indicating that the warpage of the original high point 20 has been reduced to below the process standard.

[0110] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. A method for repairing warped silicon carbide wafers, characterized in that, Includes the following steps: S1. Pre-processing: Chamfering wafers with excessive wire-cut warpage; S2. Film application: Perform full-surface mapping measurement on the wafer to locate the high points of the wafer warping, and apply a positioning film to the back of the high points; S3. Applying wax: Apply wax to the back of the wafer, and then attach the back of the wafer to the ceramic disk; S4. Single polishing: Place the ceramic disk on which the wafer is placed on a single-sided polishing machine to perform single polishing on the front side of the wafer. Processing time: 5-15 minutes. Pressure: 200-300 g / cm²; S5. Dewaxing: Remove the positioning film and wax from the wafer and clean the wafer. S6. Fine grinding: The wafer is finely ground on both sides for 100-200 min, with a processing pressure of 150-250 g / cm² and a lower plate rotation speed of 15-25 rpm. S7. Rough polishing: The wafer is rough polished on both sides for 100-150 min, with a processing pressure of 150-250 g / cm² and a lower plate rotation speed of 15-25 rpm. S8. Fine polishing: Double-sided fine polishing of the wafer, processing time 180-250min, processing pressure 300-400g / cm², and lower plate rotation speed 25-40rpm.

2. The method for repairing silicon carbide wafer warping according to claim 1, characterized in that, The minimum distance between the edge of the positioning film and the edge of the high point is 2-3mm, and the maximum distance is 5-7mm.

3. The method for repairing silicon carbide wafer warping according to claim 2, characterized in that, The thickness of the positioning film covering the high point is 0.01mm-0.05mm.

4. The method for repairing silicon carbide wafer warping according to claim 1, characterized in that, In step S1, the pre-processed wafer has a cutting warpage > 35 μm and a wafer thickness of 440 μm-600 μm.

5. The method for repairing silicon carbide wafer warping according to claim 1, characterized in that, The polishing cloth used in the S4 step single-polishing process is made of polyurethane with a hardness of 85-98A; the aggregated diamond liquid has a particle size of D50 of 6-9 μm, a viscosity of 10-20 Pa·s, and a flow rate of 20-50 ml / min; the polishing head speed is 25-30 rpm; the lower plate speed is 20-28 rpm; and the high point removal of the wafer after single polishing is 10-30 μm.

6. The method for repairing silicon carbide wafer warping according to claim 1, characterized in that, The polishing cloth used in the S6 step fine grinding process is made of non-woven fabric with a hardness of 80-95A; the agglomerated diamond liquid has a particle size of D50 of 6-9 μm, a viscosity of 10-20 Pa·s, and a flow rate of 20-50 ml / min; the thickness removal of the wafer after fine grinding is 15-30 μm; TTV < 4 μm, where TTV is the total thickness deviation of the wafer.

7. The method for repairing silicon carbide wafer warpage according to claim 1, characterized in that, The polishing cloth used in the rough polishing process of step S7 is made of non-woven fabric with a hardness of 80-95A; the particle size of the polishing liquid is D50: 0.1-0.25um; after fine polishing, the thickness removal of the wafer is 8-12μm, and the TTV is <3um, where TTV is the total thickness deviation of the wafer.

8. The method for repairing silicon carbide wafer warping according to claim 1, characterized in that, The S8 step of the fine polishing process also includes: a polishing head rotation speed of 25-40 rpm, a polishing slurry particle size of D50 of 60-120 nm, a pH of 8-11, and a wafer thickness removal of 0.5-1 μm after fine polishing, with TTV < 3 μm and LTV < 1 μm. TTV is the total thickness deviation of the wafer, and LTV is the local thickness deviation of the wafer.

9. The method for repairing silicon carbide wafer warping according to claim 2, characterized in that, The positioning film can be selected as a UV film, a blue film, or an epoxy functional film.

10. A silicon carbide wafer, characterized in that, The wafer warpage value obtained by the method for repairing silicon carbide wafer warpage as described in any one of claims 1-9 is <20µm.

Images