A method for reducing warpage of a silicon carbide substrate wafer
By attaching a pad to the center of the recessed surface of the silicon carbide substrate and adjusting the adsorption method to achieve thinning, the problem of excessive warpage was solved, improving device manufacturing quality and yield, and reducing costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUZHOU TONY SEMICONDUCTOR TECHNOLOGY CO LTD
- Filing Date
- 2023-03-27
- Publication Date
- 2026-08-04
AI Technical Summary
Existing technologies are unable to effectively reduce the warpage of silicon carbide substrates, especially in thinning processes. Excessive warpage leads to poor device manufacturing quality, and photolithography processes are complex and costly.
Thinning is achieved by attaching a pad to the center of the concave surface of the silicon carbide substrate, keeping the convex surface raised. Double-sided thinning is performed by removing different amounts of material from different locations, and the thickness and warpage are adjusted by using a suction cup.
This significantly reduced the warpage of silicon carbide substrates, improved device manufacturing quality, reduced costs, and increased yield.
Smart Images
Figure CN116525426B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for reducing the warpage of silicon carbide substrates, belonging to the field of semiconductor materials technology. Background Technology
[0002] Silicon carbide (SiC) substrates are the cornerstone of gallium nitride (GaN) and silicon carbide (SiC) applications in third-generation semiconductor materials. Due to technological and process limitations, the large-scale application of GaN materials as substrates still faces challenges. Its main application involves using sapphire, silicon wafers, or semi-insulating SiC wafers as substrates to epitaxially grow GaN devices, primarily in macro base station communication radio frequency (RF) fields. Silicon carbide (SiC), on the other hand, is mainly used for epitaxial growth of SiC epitaxial layers on conductive SiC substrates, applied in various power devices. In recent years, with the maturity of technology and the decrease in manufacturing costs, its application in the new energy field has continued to penetrate. Silicon carbide will be a crucial foundation for future SiC and GaN devices in the new energy and 5G communication fields.
[0003] Silicon carbide substrates have a crucial characteristic called warpage, also known as bow value. Bow values can be positive or negative, representing the direction of warpage. A positive bow indicates an upward bulge, while a negative bow indicates a downward bulge. A higher bow value indicates greater warpage. The warpage of the wafer has a significant impact on device manufacturing quality.
[0004] Chinese invention patent application CN 2019113576197 discloses a method for improving the warpage of silicon carbide wafers, specifically by dry etching on the back side of the silicon carbide wafer. More specifically, it includes the following steps: S1, ion implantation on the front side of the silicon carbide wafer; S2, dry etching on the back side of the silicon carbide wafer obtained in step S1; S3, subsequent photolithography processing on the front side of the wafer obtained in step S2. This method relies on a photolithography machine, which is expensive, typically costing between $30 million and $500 million; furthermore, the photolithography process is complex, generally involving silicon wafer surface cleaning and drying, primer coating, spin-coating of photoresist, soft baking, alignment and exposure, post-baking, development, hard baking, and etching. Therefore, reducing the warpage of silicon carbide substrates remains a pressing problem in this field. Summary of the Invention
[0005] The present invention aims to solve the above-mentioned problems and thereby provides a method for reducing the warpage of silicon carbide substrates.
[0006] The technical solution of the present invention to solve the above problems is as follows:
[0007] A method for reducing the warpage of a silicon carbide substrate includes the following steps:
[0008] a. Provide a silicon carbide substrate with one side being raised and the other side being recessed;
[0009] b. Place a shim at the center of the recessed surface;
[0010] c. The silicon carbide substrate is attached to the suction cup of the thinning machine with the pad side facing the suction cup, so that the raised surface remains raised. Then the raised surface is thinned to produce different removal amounts at different parts of the raised surface of the silicon carbide substrate.
[0011] d. Then, the other side is thinned to adjust the overall thickness of the silicon carbide substrate.
[0012] Thinning is a standard process for silicon carbide materials. Specifically, the silicon carbide substrate is fixed to a chuck on the rotary table of a thinning machine. As the chuck rotates, the grinding wheel also rotates at high speed and feeds along the axial direction, achieving single-sided grinding. The other surface is then processed using the same method to produce a double-sided thinned silicon carbide substrate.
[0013] The most important purpose of the thinning process is to control the warpage of the product, with the ultimate goal of making the bow value close to 0. Therefore, a method that can precisely remove protrusions or depressions in the product is particularly necessary. However, the thickness of a standard silicon carbide substrate is around 480μm. If thinning is performed according to the normal processing flow, the carbon side thins from 480μm to 420μm, and the silicon side from 420μm to 360μm. The amount of material removed during thinning on both sides is equal, and the amount removed at each location on the processed surface is also the same. Therefore, the current thinning process cannot achieve the goal of improving the bow value. How to reduce the bow value of silicon carbide substrates with excessively high bow values is a problem that needs to be solved.
[0014] In the above-described technical solution of the present invention, by using a pad on the recessed surface, the silicon carbide substrate held by the suction cup remains convex on the raised surface, or even protrudes further. Thus, during the thinning process, the amount removed from the raised area will be greater than the amount removed from other areas, thereby improving the bow value.
[0015] As a preferred embodiment of the above technical solution, step d specifically involves: removing the pad, adsorbing the silicon carbide substrate onto the suction cup of the thinning machine with the raised surface facing the suction cup, so that the silicon carbide substrate produces an annular protrusion in the outer region of the central area of the recessed surface, and then performing a thinning process on the recessed surface to produce different removal amounts of the silicon carbide substrate at different parts of the recessed surface.
[0016] In step d, the protruding surface with more removal in the central area is specifically attached to the suction cup of the thinning machine.
[0017] As a preferred embodiment of the above technical solution, the size of the gasket does not exceed the recessed area of the recessed surface.
[0018] As a preferred embodiment of the above technical solution, the protrusions on the raised surface are spherical protrusions; and the depressions on the recessed surface are spherical depressions.
[0019] As a preferred embodiment of the above technical solution, the gasket is a gasket made of a flexible material. More preferably, the gasket is made of plastic, elastomer, or paper material, such as nylon film, PP film, PE film, TPU film, rubber film, label paper, etc.
[0020] As a preferred embodiment of the above technical solution, in step c, the size of the planar area does not exceed half of the convex surface.
[0021] As a preferred embodiment of the above technical solution, in step d, the size of the second planar region does not exceed half of the concave surface.
[0022] As a preferred embodiment of the above technical solution, the raised surface is a carbon surface and the recessed surface is a silicon surface.
[0023] As a preferred embodiment of the above technical solution, the suction cup is a chuck suction cup.
[0024] As a preferred embodiment of the above technical solution, the thickness of the gasket is 2~10μm; more preferably, the thickness of the gasket is 3~8μm.
[0025] In summary, the present invention has the following beneficial effects:
[0026] 1. This invention uses a pad to attach to the recessed part of the concave surface of a silicon carbide substrate with a large bow value. This allows the original protruding part to remain protruding after being attracted by a suction cup, or even become more protruding. This makes it easier to thin the protruding part during the thinning process, so that the amount of removal of the protruding part is greater than that of other parts, thereby improving the bow value.
[0027] 2. After thinning the raised surface by removing different amounts of material from different parts, the present invention adsorbs the silicon carbide substrate onto the suction cup of the thinning machine with the raised surface of the recessed area facing the suction cup. This causes the silicon carbide substrate to generate annular protrusions in the outer region of the central area of the recessed surface. This not only adjusts the overall thickness of the silicon carbide substrate but also enables thinning by removing different amounts of material from different parts of the recessed surface, further improving the bow value. Attached Figure Description
[0028] Figure 1 This is a schematic diagram illustrating the principle of the present invention;
[0029] Figure 2This is a 3D topographic image of the silicon surface formed by FRT before thinning in Embodiment 1 of the present invention;
[0030] Figure 3 This is a 3D topographic image of the silicon surface formed by FRT after double-sided thinning of silicon and carbon in Embodiment 1 of the present invention;
[0031] In the figure, 1-protruding surface, 2-recessed surface, 3-shield, 11-recessed area, 20-protrusion, 21-second recessed area. Detailed Implementation
[0032] The present invention will be further explained and described below with reference to the accompanying drawings.
[0033] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. Any changes made by those skilled in the art after reading the specification of the present invention, as long as they are within the scope of the claims, will be protected by patent law. Example
[0034] A method for reducing the warpage of a silicon carbide substrate includes the following steps:
[0035] a. such as Figure 1 As shown in (a), a silicon carbide substrate is provided with one side being a raised surface 1 and the other side being a recessed surface 2; as Figure 2 As shown, the 3D morphology of the silicon surface of the substrate before thinning is shown. At this time, the bow value is -27, and it presents a shape with a central depression and a convex shape around the perimeter.
[0036] b, such as Figure 1 As shown in (b), a gasket 3 is attached to the center of the recessed surface 2;
[0037] c. For example Figure 1 (c) shows that the silicon carbide substrate is adsorbed onto the chuck of the thinning machine with the side with the pad 3 facing the chuck, so that the raised surface 1 remains raised. In this step, if the pad 3 is not attached, the raised surface 1 and the concave surface 2 cannot be maintained due to the vacuum suction on the concave surface. This is because the vacuum suction process will change the shape of the silicon carbide substrate, causing the entire substrate to be flat against the vacuum chuck, and the purpose of different removal amounts in different parts cannot be achieved in the future.
[0038] Then, the raised surface 1 is thinned to create a planar region in the central area of the silicon carbide substrate; for example... Figure 1 As shown in (d), after the silicon carbide substrate is removed from the chuck, the planar area automatically transforms into the recessed area 11, resulting in a silicon carbide substrate with a thinned carbon surface.
[0039] d. Remove the gasket 3, as follows: Figure 1As shown in (e), the silicon carbide substrate is adsorbed onto the chuck of the thinning machine with the raised surface 1, which forms the recessed area 11, facing the chuck. This creates an annular protrusion 20 on the outer periphery of the central region of the recessed surface 2. In this step, after removing the pad 3, the silicon carbide substrate is flipped over and adsorbed onto the chuck. At this time, due to the center being flat and the edges warped, after adsorbing the entire raised surface, a... Figure 1 (e) The annular protrusion; that is, an uneven surface appears on the concave surface. Therefore, a thinning machine can be used to remove different amounts of material from different parts of the original concave surface.
[0040] Then, the annular protrusion 20 is thinned to create a second planar region in the corresponding area; such as Figure 1 As shown in (f), after the silicon carbide substrate is removed from the chuck, the second planar region automatically transforms into the second recessed region 21;
[0041] While thinning the annular protrusion 20, the thickness of the entire silicon carbide substrate is also adjusted.
[0042] like Figure 3 The figure shows the FRT diagram of the silicon carbide substrate after double-sided silicon-carbon thinning in this embodiment. As can be seen from the figure, the bow value changed from -27 to -14 after double-sided thinning, which reduced the absolute value of substrate curvature and thus achieved the purpose of reducing warpage.
[0043] In this embodiment, the raised surface 1 is a carbon surface, and the recessed surface 1 is a silicon surface; both the carbon and silicon surfaces are spherical. The gasket 3 is a PP film with a thickness of 5 μm. Figure 1 It can be seen that its size is adapted to the concave area of the concave surface 2. From Figure 1 It can also be seen that the area of the annular protrusion 20 does not exceed half of the concave surface 2.
[0044] More specifically, the applicant processed 35 defective wafers with excessive BOW values according to the above method, and the data is summarized below.
[0045] Film number BOW value before processing BOW value after processing Boow value difference 3623-17 -34 -23 11 3623-19 -27 -14 13 3623-13 -30 -17 13 3623-15 -32 -22 10 3623-18 -25 -6 19 1706-11 -27 -17 10 1706-12 -26 -17 9 1706-14 -25 -10 15 1706-15 -25 -12 13 1706-16 -27 -20 7 3624-17* -31 -5 26 3624-18* -26 -3 23 3624-19* -26 9 35 1813-17 -25 -16 9 2208-06 -25 -19 6 2208-07 -27 -20 7 2208-08 -29 -22 7 2208-09 -29 -6 23 0312-05 -27 1.4 28 0312-08 -31 -4 27 0614-12 -28 -10 18 0718-10 -26 -19 7 0718-12 -27 -19 8 0718-14 -25 -20 5 0718-15 -27 -20 7 0913-10 -27 -8 19 1212-05 -30 -22 8 1414-07 -25 -12 13 2306-07 -26 -19 7 2306-11 -26 -20 6 2306-15 -29 -22 7 2701-9 -30 -7 23 2702-13 -26 -6 20 2702-15 -26 -11 15 1706-04* -25 -14 11
[0046] Small batch data summary
[0047] project BOW value BOW value after processing Difference average value -27 -13 14 Minimum value -25 9 5 Maximum value -34 -23 35
[0048] As can be seen from the table above:
[0049] 1. All 35 BOW wafers were qualified after over-processing, with an overall warpage reduction of 14μm. Four wafers (3624-17, 3624-18, 3624-19, and 1706-04) were defective and entered into the warehouse due to thickness exceeding the lower limit; the overall yield rate was 88.5%.
[0050] 2. Based on a yield rate of 90%, the yield rate can be increased by 8.85% through the processing of this invention.
Claims
1. A method for reducing the warpage of a silicon carbide substrate, comprising the following steps: a. Provide a silicon carbide substrate with one side being a raised surface (1) and the other side being a recessed surface (2); b. Place a gasket (3) at the center of the concave surface (2); c. The silicon carbide substrate is attached to the suction cup of the thinning machine with the side with the pad (3) facing the suction cup, so that the raised surface (1) remains raised. Then the raised surface (1) is thinned so that a flat area appears in the center area of the raised surface (1) of the silicon carbide substrate. d. Remove the pad (3), and attach the silicon carbide substrate to the suction cup of the thinning machine with the raised surface (1) facing the suction cup. This will cause the silicon carbide substrate to generate an annular protrusion (20) in the outer region of the central area of the recessed surface. Then, the recessed surface (2) will be thinned to produce different removal amounts at different parts of the recessed surface (2), thereby adjusting the overall thickness of the silicon carbide substrate. In step c, the size of the planar area does not exceed half of the protruding surface (1); In step d, the concave surface (2) is thinned, specifically the annular protrusion (20) is thinned to create a second planar area in the corresponding region; the size of the second planar area does not exceed half of the concave surface (2).
2. The method of claim 1 wherein: The size of the gasket does not exceed the recessed area of the recessed surface (2).
3. The method of claim 1, wherein: The raised surface (1) has a spherical raised surface; the concave surface (2) has a spherical concave surface.
4. The method of claim 1 wherein: The gasket (3) is a gasket made of flexible material.
5. The method of claim 1 wherein: The raised surface (1) is a carbon surface, and the recessed surface (2) is a silicon surface.
6. The method for reducing the warpage of a silicon carbide substrate according to claim 1, characterized in that: The thickness of the gasket (3) is 2~10μm.