Method for correcting warpage of silicon carbide epitaxial wafer

Abstract

The application discloses a method for correcting warping degree of silicon carbide epitaxial wafer, which comprises the following steps: firstly, one side of the protective film of the epitaxial wafer is attached to the porous ceramic adsorption table of a thinning machine, the epitaxial wafer is adsorbed in vacuum, and the carbon surface of the epitaxial wafer is thinned by using a diamond grinding wheel with 8000-30000 meshes; then, the thinned epitaxial wafer is attached to a chemical mechanical polishing device, the carbon surface of the epitaxial wafer is polished under the pressure of 100g-300g / cm 2 for 5-60min by using 0.1-1μm polycrystalline diamond abrasive liquid according to the warping degree of the thinned epitaxial wafer; and finally, the polished epitaxial wafer is washed on both sides. The method can correct the warping degree of the silicon carbide epitaxial wafer, and the thinning amount of the epitaxial wafer is small, so that the property of the epitaxial wafer is not affected.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide epitaxial technology, and in particular to a method for correcting the warpage of silicon carbide epitaxial wafers. Background Technology

[0002] If the warpage exceeds the standard after homoepitaxial growth on a silicon carbide substrate, specific methods are required to correct it and restore the curvature and warpage to the product specification range without changing the product properties.

[0003] The existing method for correcting the warpage of silicon carbide epitaxial wafers is back-side thinning, which is generally used to thin the carbon layer of the epitaxial wafer, i.e., reduce the substrate thickness. This reduces device resistance and improves the success rate of device bonding. In practice, the circuit surface is first protected with a film, and then the carbon surface is thinned under vacuum adsorption. After thinning, the wafer is diced into multiple devices according to the size of the die. However, existing methods for correcting the warpage of silicon carbide epitaxial wafers are limited by the processing precision of the thinning machine. Therefore, they typically thin the back side of the wafer by tens to hundreds of micrometers to reduce resistance or other effects, resulting in a large thinning amount that affects the properties of the epitaxial product.

[0004] Therefore, it is necessary to provide a method for correcting the warpage of silicon carbide epitaxial wafers with a smaller thinning amount that does not affect the properties of the epitaxial product, in order to solve the above-mentioned problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for correcting the warpage of silicon carbide epitaxial wafers with a small amount of thinning that does not affect the properties of the epitaxial product.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: a method for correcting the warpage of a silicon carbide epitaxial wafer, comprising the following steps:

[0007] (1) Provide an epitaxial wafer with unacceptable warpage, and attach a protective film to the silicon surface of the epitaxial wafer, wherein the edge of the protective film is flush with the edge of the epitaxial wafer;

[0008] (2) The protective film side of the epitaxial wafer is attached to the porous ceramic adsorption stage of the thinning machine, the epitaxial wafer is vacuum adsorbed, and the carbon surface of the epitaxial wafer is thinned by an 8000~30000 mesh diamond grinding wheel.

[0009] (3) The thinned epitaxial wafer is attached to a chemical mechanical polishing (CMP) device, and polished with 0.1~1μm polycrystalline diamond powder slurry at a concentration of 100g~300g / cm², depending on the warpage of the thinned epitaxial wafer. 2 The carbon surface of the epitaxial wafer is polished under pressure for 5-60 minutes;

[0010] (4) Place the polished epitaxial wafer into a fully automatic double-sided brushing machine, and use a nylon brush and two fluids to repeatedly brush both sides of the epitaxial wafer. After brushing, spin dry the epitaxial wafer.

[0011] (5) Irradiate the epitaxial wafer with the specified protective film energy, and then peel off the protective film of the epitaxial wafer.

[0012] Preferably, in the method for correcting the warpage of silicon carbide epitaxial wafers of the present invention, in step (2), the diamond grinding wheel rotates at high speed to rapidly cut the carbon surface of the epitaxial wafer to reduce its thickness by 2~5μm.

[0013] Preferably, in the method for correcting the warpage of silicon carbide epitaxial wafers of the present invention, step (3) includes:

[0014] (31) The adsorption pad is attached to the ceramic disk of the chemical mechanical polishing equipment, and the carbon side of the epitaxial wafer is attached to the adsorption pad with the carbon side facing out.

[0015] (32) The polycrystalline diamond powder grinding slurry is dropped onto the polishing pad of the chemical mechanical polishing equipment at a rate of 20~100ml / min;

[0016] (33) The cylinder of the chemical mechanical polishing equipment is pressurized to 100g~300g / cm. 2 The carbon surface of the epitaxial wafer is then polished for 5-60 minutes.

[0017] Preferably, in the method for correcting the warpage of silicon carbide epitaxial wafers of the present invention, step (4) includes:

[0018] (41) The polished epitaxial wafer is placed in a fully automatic double-sided brushing machine. The fully automatic double-sided brushing machine rotates the epitaxial wafer at 500 rpm and the nylon brush at 2000 rpm. The two fluids are used to repeatedly brush one side of the epitaxial wafer from the edge to the center 2 to 5 times. The diameter of the nylon brush is 0.04 to 0.1 mm and the bristle length is 10 to 20 mm.

[0019] (42) Turn the epitaxial wafer over and repeat the brushing step in step (41);

[0020] (43) Spin dry the epitaxial wafer.

[0021] Preferably, in the method for correcting the warpage of silicon carbide epitaxial wafers of the present invention, the two fluids are formed by pure water and nitrogen.

[0022] Preferably, in the method for correcting the warpage of silicon carbide epitaxial wafers of the present invention, step (5) specifically comprises:

[0023] According to the recommended energy of the protective film, select the appropriate energy to irradiate the protective film for a certain period of time, and then use film-removing tape to peel off the protective film.

[0024] Preferably, in the method for correcting the warpage of silicon carbide epitaxial wafers of the present invention, the protective film is a UV film.

[0025] Compared with the prior art, the method for correcting the warpage of silicon carbide epitaxial wafers in this invention first uses an 8000-30000 grit diamond grinding wheel to thin the carbon surface of the epitaxial wafer, and then, based on the degree of warpage of the thinned epitaxial wafer, uses a 0.1-1 μm polycrystalline diamond powder polishing slurry at a concentration of 100g-300g / cm³. 2 The carbon surface of the epitaxial wafer is polished under pressure for 5-60 minutes. By combining the aforementioned thinning and polishing processes, the amount of thinning can be adjusted according to the warpage of the epitaxial wafer. Compared with the existing wave-building method, this invention only thins the epitaxial wafer by a few micrometers to achieve the effect of correcting warpage. The amount of thinning of the epitaxial wafer is small, and the purpose is only to correct the warpage of the epitaxial wafer, without affecting the properties of the epitaxial wafer. Attached Figure Description

[0026] Figure 1 This is a flowchart of the method for correcting the warpage of silicon carbide epitaxial wafers according to the present invention.

[0027] Figure 2 yes Figure 1 The sub-flowchart of step S03.

[0028] Figure 3 yes Figure 1 The sub-flowchart of step S04.

[0029] Figure 4 This is a partial structural schematic diagram of the biaxial thinning machine used in this invention.

[0030] Figure 5 This is a partial structural schematic diagram of the chemical mechanical polishing equipment used in this invention.

[0031] Figure 6 yes Figure 5 A structural diagram from another angle.

[0032] Figure 7 This is a schematic diagram of the warpage detection results of the epitaxial wafer before correction in this invention.

[0033] Figure 8 This is a schematic diagram of the warpage detection results of the epitaxial wafer after correction by the method of this invention. Detailed Implementation

[0034] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which similar element reference numerals represent similar elements. It should be noted that the directional descriptions involved in the present invention, such as up, down, left, right, front, and rear, indicating directions or positional relationships, are based on the directions or positional relationships shown in the drawings and are only for the convenience of describing the technical solutions of this application or / 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 therefore should not be construed as a limitation of this application. The terms "first," "second," etc., described are only used to distinguish technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the sequential relationship of the indicated technical features.

[0035] Please refer to the following first. Figure 1 As shown, the method for correcting the warpage of silicon carbide epitaxial wafers provided by the present invention includes the following steps:

[0036] S01. Provide an epitaxial wafer with unacceptable warpage, and attach a protective film to the silicon surface of the epitaxial wafer, wherein the edge of the protective film is flush with the edge of the epitaxial wafer;

[0037] In one specific embodiment of the present invention, the protective film is a UV film, which is used to protect the epitaxial wafer. Of course, the protective film is not limited to a UV film; any other protective film that can be used on the epitaxial wafer and can protect its silicon surface is acceptable.

[0038] S02. The protective film side of the epitaxial wafer is attached to the porous ceramic adsorption stage of the thinning machine, the epitaxial wafer is vacuum adsorbed, and the carbon surface of the epitaxial wafer is thinned using an 8000~30000 mesh diamond grinding wheel.

[0039] See Figure 4 As shown, the thinning technology specifically uses a thinning machine 10 to fix the epitaxial wafer 30 onto the porous ceramic adsorption stage 12 of the thinning machine 10 via vacuum adsorption. A diamond grinding wheel 11 is then used to rapidly cut the carbon surface of the epitaxial wafer 30 under high-speed rotation, resulting in high efficiency and precision. The structure and working principle of other parts of the thinning machine 10 are conventional methods well-known to those skilled in the art and will not be described in detail further.

[0040] In one specific embodiment of the present invention, the diamond grinding wheel is controlled to rotate at high speed to rapidly cut and thin the carbon surface of the epitaxial wafer by 2-5 μm. It is understood that the thinning thickness is not limited to 2-5 μm, and can be adjusted according to different types of epitaxial wafers and their resulting warpage.

[0041] S03. The thinned epitaxial wafer is attached to a chemical mechanical polishing (CMP) device. Depending on the warpage of the thinned epitaxial wafer, a 0.1~1μm polycrystalline diamond powder polishing slurry is used at a polishing rate of 100g~300g / cm². 2 The carbon surface of the epitaxial wafer is polished under pressure for 5-60 minutes;

[0042] See Figure 5-6 As shown, in this invention, a chemical mechanical polishing (CMP) device 20 is used to polish the thinned epitaxial wafer. Specifically, the epitaxial wafer 30 is attached to the ceramic disk 22 of the CMP device 20, and then, under the pressure of the cylinder 21, the epitaxial wafer 30 interacts with the polycrystalline diamond powder polishing slurry and the polishing pad 23, which can remove the damaged layer on the carbon surface of the epitaxial wafer 30 and reduce the surface roughness.

[0043] In this invention, multiple thinned epitaxial wafers are attached to a ceramic disk 22, and multiple epitaxial wafers 30 are chemically and mechanically polished at one time, which greatly improves the efficiency of chemically and mechanically polishing.

[0044] The structure and working principle of the other parts of the chemical mechanical polishing equipment 20 involved in this invention are conventional methods well known to those skilled in the art, and will not be described in detail here.

[0045] S04. Place the polished epitaxial wafer into a fully automatic double-sided brushing machine, and use a nylon brush and two fluids to repeatedly brush both sides of the epitaxial wafer. After brushing, spin dry the epitaxial wafer.

[0046] In one embodiment of the present invention, a fully automatic double-sided brushing machine uses nylon brushes with a diameter of 0.04~0.1mm and a bristle length of 10~20mm, and uses pure water and nitrogen to form a two-fluid mixture to repeatedly rinse the epitaxial wafer. Of course, the diameter and bristle length of the nylon brush are not limited to the aforementioned data, and other types of nylon brushes can be used as needed.

[0047] S05. Irradiate the protective film with the specified protective film energy, and then peel off the protective film of the epitaxial wafer.

[0048] In one specific embodiment of the present invention, step S05 specifically involves: selecting an appropriate energy to irradiate the UV film for a certain duration according to the recommended energy of the UV film, and then peeling off the UV film using film-removing tape.

[0049] The following is combined Figures 1-2 As shown, in a specific embodiment of the method for correcting the warpage of silicon carbide epitaxial wafers according to the present invention, step S03 specifically includes the following steps:

[0050] S31. The adsorption pad is attached to the ceramic disk of the chemical mechanical polishing equipment, and then the multiple thinned epitaxial sheets are attached to the adsorption pad with the carbon side facing out.

[0051] See details Figure 5-6 As shown, in this invention, a ceramic disc 22 is disposed below the cylinder 21 of the chemical mechanical polishing device 20, and a polishing pad 23 is disposed below the ceramic disc 22, as shown. Figure 5 As shown. Before polishing, the adsorption pad 24 is first attached to the ceramic disk 22. Multiple thinned epitaxial wafers 30 are then attached to the adsorption pad 24 with their carbon surfaces facing outwards. That is, the carbon surface of each epitaxial wafer 30 is positioned away from the adsorption pad 24, thus facing the polishing pad 23. Figure 5-6 As shown.

[0052] In this embodiment, performing chemical mechanical polishing on multiple epitaxial wafers 30 simultaneously can improve the efficiency of chemical mechanical polishing.

[0053] S32. Add 0.1~1μm polycrystalline diamond powder polishing slurry to the polishing pad of the chemical mechanical polishing equipment at a rate of 20~100ml / min;

[0054] S33, the cylinder of the chemical mechanical polishing equipment is pressurized to 100g~300g / cm. 2 The carbon surface of the epitaxial wafer is then polished for 5-60 minutes.

[0055] See Figure 5-6 As shown, in step S33 above, the cylinder is pressurized by 100g~300g / cm. 2 Then, the epitaxial wafer 30 interacts with the polycrystalline diamond powder polishing slurry and polishing pad 23 to remove the damaged layer on the carbon surface of the epitaxial wafer 30 and reduce the surface roughness.

[0056] The following is combined Figure 1 , Figure 3 As shown, in a specific embodiment of the method for correcting the warpage of silicon carbide epitaxial wafers according to the present invention, step S04 specifically includes the following steps:

[0057] S41. Place the polished epitaxial wafer into a fully automatic double-sided brushing machine, with the epitaxial wafer rotating at 500 rpm and the nylon brush rotating at 2000 rpm. Use two fluids to repeatedly brush one side of the epitaxial wafer from the edge to the center 2 to 5 times. The diameter of the nylon brush is 0.04 to 0.1 mm and the bristle length is 10 to 20 mm.

[0058] Understandably, the diameter and bristle length of the nylon brush are not limited to those in this embodiment, and other specifications of nylon brushes can be selected as needed.

[0059] S42. Flip the epitaxial wafer over and repeat the brushing step in step S41.

[0060] S43. Spin dry the epitaxial wafer.

[0061] The following is combined Figures 1-8 As shown, a specific embodiment of the method for correcting the warpage of silicon carbide epitaxial wafers according to the present invention will be described.

[0062] S11. Provide an epitaxial wafer with unacceptable warpage, and use a fully automatic film applicator to attach a UV film to the silicon surface of the epitaxial wafer, with the edge of the UV film flush with the edge of the epitaxial wafer;

[0063] See Table 1 below and Figure 7 As shown, in this specific embodiment, the total thickness (Thickness) of the epitaxial wafer before film application is 353.994 μm, the flatness (TTV) is 5.269 μm, the local flatness (LTV) is 1.4542 μm, the warp value of the epitaxial wafer is 44.536 μm, and the bow value is 42.662 μm. A UV film is then applied to protect the epitaxial wafer.

[0064] S12. The epitaxial wafer with the UV film attached is attached to the porous ceramic adsorption stage of the thinning machine, and the epitaxial wafer is vacuum adsorbed. Then, an 8000-mesh diamond grinding wheel made of diamond powder and resin is used to quickly cut the carbon surface of the epitaxial wafer under high speed.

[0065] In this specific embodiment, the diamond grinding wheel cuts the epitaxial wafer to a thickness of 3 μm, but this thickness is not limited to this. The specific cutting thickness can be flexibly adjusted according to the different values ​​of the warp of the epitaxial wafer. After thinning, the total thickness (Thickness) of the thinned epitaxial wafer is 351.116 μm, the flatness (TTV) is 11.426 μm, the local flatness (LTV) is 2.9514 μm, and the warp (Warp) of the thinned epitaxial wafer is 118.895 μm and the bow (Bow) is -87.698 μm, as shown in Table 1 below.

[0066] S13. Attach the adsorption pad to the ceramic disk of the chemical mechanical polishing (CMP) equipment. Then, attach the thinned epitaxial wafers, carbon side out, to the adsorption pad. Next, drop polycrystalline diamond polishing slurry onto the polishing pad of the CMP equipment at a rate of 50 ml / min, and pressurize the cylinder of the CMP equipment to 100 g / cm³. 2 And polish the carbon surface of the epitaxial wafer for 30 minutes;

[0067] See details Figure 5-6 As shown, in this invention, a ceramic disc 22 is disposed below the cylinder 21 of the chemical mechanical polishing device 20, and a polishing pad 23 is disposed below the ceramic disc 22, as shown. Figure 5 As shown. Before polishing, the adsorption pad 24 is first attached to the ceramic disk 22. Multiple thinned epitaxial wafers 30 are then attached to the adsorption pad 24 with their carbon surfaces facing outwards. That is, the carbon surface of each epitaxial wafer 30 is positioned away from the adsorption pad 24, thus facing the polishing pad 23. Figure 5-6 As shown. Then, a 0.1~1μm polycrystalline diamond powder polishing slurry is dropped onto the polishing pad 23 at a rate of 50ml / min, and then the cylinder 21 is pressurized to 100g~300g / cm. 2 The carbon surface of the epitaxial wafer 30 is polished for 5-60 minutes. Polishing reduces the roughness and damage layer of the carbon surface of the epitaxial wafer 30. Furthermore, performing chemical mechanical polishing on multiple epitaxial wafers 30 simultaneously improves the efficiency of chemical mechanical polishing.

[0068] S14. Place the polished epitaxial wafer in a fully automatic double-sided brushing machine, and set the rotation speed of the epitaxial wafer to 500 rpm and the rotation speed of the nylon brush to 2000 rpm. Use pure water and the two fluids formed by pure water and nitrogen to repeatedly brush one side of the epitaxial wafer from the edge to the center 2 to 5 times. Then turn the epitaxial wafer over and brush the other side from the edge to the center 2 to 5 times. After brushing, spin dry the epitaxial wafer.

[0069] In this embodiment, the diameter of the nylon brush of the fully automatic double-sided brushing machine is preferably 0.04-0.1 mm and the bristle length is preferably 10-20 mm, but it is not limited thereto.

[0070] S15. After irradiating the UV film with the recommended energy for 20 seconds, peel off the UV film using film-removing tape.

[0071] S16. Test results;

[0072] In this embodiment, after correction, the epitaxial wafer provided in step S111 has a total thickness of 350.139 μm, a flatness TTV of 9.687 μm, a local flatness LTV of 3.2991 μm, a warp of 12.067 μm, and a bow of -8.539 μm. See Table 1 below for details. Figure 8 As shown, it basically meets the product requirements.

[0073]

[0074] Table 1

[0075] In summary, the method for correcting the warpage of silicon carbide epitaxial wafers in this invention first involves thinning the carbon surface of the epitaxial wafer using an 8000-30000 grit diamond grinding wheel, and then, based on the degree of warpage of the thinned epitaxial wafer, using a 0.1-1 μm polycrystalline diamond powder polishing slurry at a concentration of 100 g-300 g / cm³. 2 The carbon surface of the epitaxial wafer is polished for 5-60 minutes under pressure. By combining the aforementioned thinning and polishing processes, the amount of thinning can be adjusted according to the warpage of the epitaxial wafer. Compared with existing thinning methods, this invention only thins the epitaxial wafer by a few micrometers to achieve the effect of correcting warpage. The amount of thinning of the epitaxial wafer is small, and the purpose is only to correct the warpage of the epitaxial wafer without affecting the properties of the epitaxial wafer.

[0076] The devices and equipment involved in the method of this invention are all conventional devices in the art and are conventional working methods well known to those skilled in the art, and will not be described in detail here.

[0077] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for correcting the warpage of silicon carbide epitaxial wafers, characterized in that, Includes the following steps: (1) Provide an epitaxial wafer with unacceptable warpage, and attach a protective film to the silicon surface of the epitaxial wafer, wherein the edge of the protective film is flush with the edge of the epitaxial wafer; (2) The protective film side of the epitaxial wafer is attached to the porous ceramic adsorption stage of the thinning machine, the epitaxial wafer is vacuum adsorbed, and the carbon surface of the epitaxial wafer is thinned by an 8000~30000 mesh diamond grinding wheel. The diamond grinding wheel rotates at high speed to quickly cut the carbon surface of the epitaxial wafer to reduce it by 2~5μm. (3) The thinned epitaxial wafer is attached to a chemical mechanical polishing (CMP) device, and polished with 0.1~1μm polycrystalline diamond powder slurry at a concentration of 100g~300g / cm², depending on the warpage of the thinned epitaxial wafer. 2 The carbon surface of the epitaxial wafer is polished under pressure for 5-60 minutes; (4) Place the polished epitaxial wafer into a fully automatic double-sided brushing machine, and use a nylon brush and two fluids to repeatedly brush both sides of the epitaxial wafer. After brushing, spin dry the epitaxial wafer. (5) Irradiate the epitaxial wafer with the specified protective film energy, and then peel off the protective film of the epitaxial wafer; Step (3) includes: (31) The adsorption pad is attached to the ceramic disk of the chemical mechanical polishing equipment, and the carbon side of the epitaxial wafer is attached to the adsorption pad with the carbon side facing out. (32) Add 0.1~1μm polycrystalline diamond powder polishing slurry to the polishing pad of the chemical mechanical polishing equipment at a rate of 20~100ml / min; (33) The cylinder of the chemical mechanical polishing equipment is pressurized to 100g~300g / cm. 2 The carbon surface of the epitaxial wafer is then polished for 5-60 minutes.

2. The method for correcting the warpage of silicon carbide epitaxial wafers as described in claim 1, characterized in that, Step (4) includes: (41) Place the polished epitaxial wafer in a fully automatic double-sided brushing machine, with the rotation speed of the epitaxial wafer at 500 rpm and the rotation speed of the nylon brush at 2000 rpm. Use two fluids to repeatedly brush one side of the epitaxial wafer from the edge to the center 2 to 5 times. The diameter of the nylon brush is 0.04 to 0.1 mm and the bristle length is 10 to 20 mm. (42) Turn the epitaxial wafer over and repeat the brushing step in step (41); (43) Spin dry the epitaxial wafer.

3. The method for correcting the warpage of silicon carbide epitaxial wafers as described in claim 2, characterized in that, The two fluids are formed by pure water and nitrogen.

4. The method for correcting the warpage of a silicon carbide epitaxial wafer as described in claim 1, characterized in that, Step (5) specifically involves: According to the recommended energy of the protective film, select the appropriate energy to irradiate the protective film for a certain period of time, and then use film-removing tape to peel off the protective film.

5. The method for correcting the warpage of a silicon carbide epitaxial wafer as described in any one of claims 1-4, characterized in that, The protective film is a UV film.

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