Vacuum chuck and method of manufacturing the same

Abstract

This invention relates to a method for preparing a vacuum chuck. The method involves isostatically pressing pressureless silicon carbide granules into a vacuum chuck green blank, processing the green blank, followed by high-temperature sintering, dimensional precision machining, and sandblasting and polishing to produce a texture-free vacuum chuck. Next, a metal catalyst film is sputtered onto the adsorption surface of the vacuum chuck, and a carbon nanotube coating is chemically deposited. Finally, the carbon layer surface of the vacuum chuck undergoes ultra-precision machining to produce a vacuum chuck with low reflectivity and high flatness accuracy. This dual approach of texture-free surface and low-reflection treatment effectively solves the problem in the semiconductor industry where optical systems cannot distinguish between wafer defects and the background of the vacuum chuck when inspecting compound transparent wafers.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor wafer inspection technology, specifically relating to a high-flatness vacuum chuck for transparent sheet inspection and its preparation method. Background Technology

[0002] In third-generation semiconductor compound wafers, gallium nitride (GaN), gallium oxide (Ga2O3), and magnesium aluminate (MgAlO4) are typically transparent. These transparent compound wafers have high light transmittance (typically >80% in the visible / near-infrared bands). However, the optical systems of wafer inspection equipment (such as bright-field illumination, dark-field illumination, and interferometry) need to detect surface and internal defects (scratches, particles, cracks, and uneven thickness) on the wafer. But transparent wafers cannot block the structural / reflection signals of the chuck, which are misjudged by the inspection system as "surface defects" or "morphological fluctuations" on the wafer.

[0003] Machining textures (such as milling marks, sandblasting textures), adsorption holes, positioning grooves, and surface contaminants on the surface of a vacuum chuck "penetrate" through the transparent wafer into the inspection lens. Light undergoes secondary reflection between "air → wafer lower surface → vacuum chuck surface," and the reflected light superimposes with the signal from the wafer's upper surface, causing the vacuum chuck's morphology to be "imprinted" in the inspection image. This leads to a surge in false positive rates, making it impossible to distinguish between defects in the wafer itself and the vacuum chuck background. Currently, traditional vacuum chuck adsorption surfaces are made of black microporous ceramic, which effectively avoids milling textures and adsorption holes. However, the flatness accuracy of microporous ceramic vacuum chucks adsorbing wafers is not high, typically between 5-10 micrometers. Furthermore, after a period of use, microporous ceramic particles are prone to shedding and clogging the micropores.

[0004] Therefore, in view of the problems that the vacuum chuck cannot accurately adsorb semiconductor transparent sheets and that the detection system cannot distinguish between defects in the transparent sheet itself and the chuck background, the technical problem to be solved by this invention is how to prepare a vacuum chuck with low reflection and no surface texture to reduce the morphological signal of the chuck itself, while taking into account the flatness accuracy of the adsorbed transparent sheet. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a vacuum chuck with high flatness accuracy for the inspection of transparent sheets. This vacuum chuck has low reflection and no surface texture, which reduces the morphological signal of the chuck itself, while taking into account the flatness accuracy of the adsorbed transparent sheet. It solves the problems of insufficient accuracy of existing vacuum chucks in adsorbing semiconductor transparent sheets and the inability of the detection system to distinguish between defects in the transparent wafer itself and the chuck background.

[0006] The present invention also provides a method for preparing the above-mentioned high-flatness vacuum chuck for transparent sheet inspection.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a high-precision vacuum chuck with low reflection and no surface texture includes the following steps: isostatic pressing, green blank processing, high-temperature vacuum sintering, dimensional finishing, sandblasting and polishing, sputtering of a metal catalytic film, chemical deposition of a carbon nanotube coating, and ultra-precision machining.

[0008] Furthermore, the isostatic pressing process specifically involves: designing the silicon carbide green blank forming size based on the shrinkage characteristics of the pressureless sintered silicon carbide granulated powder, and then obtaining a vacuum chuck green blank with a certain strength by dry pressing and isostatic pressing of the silicon carbide granulated powder; the dry pressing process parameters are: holding pressure at 80-120MPa for 5-30s; the cold isostatic pressing process is: holding pressure at 170-240MPa for 5-15min.

[0009] Furthermore, the green body processing specifically involves: processing the outer diameter and thickness of the isostatically pressed vacuum chuck green body according to the sintering shrinkage ratio and the size and structure of the vacuum chuck; milling several evenly distributed protrusions on the surface of the vacuum chuck green body using a diamond grinding head to ensure the smoothness of the protrusion processing surface, which helps to reduce the surface roughness of the ceramic after sintering.

[0010] Furthermore, the high-temperature vacuum sintering specifically involves placing the processed green blank into a vacuum atmosphere sintering furnace, introducing nitrogen or argon gas for protection, and holding the furnace at a temperature of 2000-2100℃ for 120-180 minutes.

[0011] Furthermore, the dimensional precision machining specifically involves machining the outer circle, thickness, etc. of the vacuum chuck blank after high-temperature vacuum sintering to the required dimensions, and then machining the parallelism and flatness to the required accuracy.

[0012] Furthermore, the sandblasting polishing specifically involves a combination of sandblasting jets and diamond rubber abrasive, divided into two steps: rough polishing and fine polishing. The surface of the vacuum chuck with protrusions is polished. During rough polishing, the sandblasting pressure is 0.5~0.8 MPa, the diamond rubber abrasive grit size is 500#-800#, and the roughness Ra reaches 0.4-0.6 micrometers. During fine polishing, the sandblasting pressure is 0.3~0.5 MPa, the diamond rubber abrasive grit size is 10000#-20000#, and the roughness Ra reaches 0.05-0.2 micrometers. The diamond surface is coated with rubber, which helps reduce the impact force of the diamond on the vacuum chuck during polishing, providing a certain buffering effect and reducing the occurrence of chipping.

[0013] Furthermore, the sputtered metal catalytic film is specifically produced as follows: a 1-4 nm thick Fe metal film is sputtered onto the polished surface of a vacuum chuck with raised dots in an atmosphere sintering furnace at a sputtering power of 100-150 W and an argon pressure of 0.5-1 Pa; subsequently, a mixture of H2 and Ar with a volume ratio of 1:1.5-2.5 is introduced, and the temperature is simultaneously raised to 750℃-850℃ and annealed at high temperature for 20-30 minutes, causing the Fe film to decompose into uniform Fe nanoparticles that adhere to the entire surface of the vacuum chuck with raised dots. The particle size range is 4-9 nm.

[0014] Furthermore, the chemically deposited carbon nanotube coating is specifically prepared using a metal Fe catalytic reduction chemical deposition method. A vacuum chuck after sputtering the metal catalyst film is placed in a high-temperature furnace under a vacuum atmosphere and heated to 800-830℃ (the optimal temperature range for the catalyst). Simultaneously, a gaseous carbon source (CH4) is introduced, with the total gas flow rate controlled at 130-170 sccm. The deposition time is 20-50 minutes, and the thickness of the carbon nanotube coating is controlled to be 20-25 micrometers. The carbon nanotube coating prepared by the metal catalytic reduction gas method is uniform, free of any impurities, and has excellent smoothness, making it a high-quality ultra-black material coating with an absorbance exceeding 99%.

[0015] Furthermore, the ultra-precision machining specifically involves: using a robotic polishing machine to perform ultra-precision polishing on the top surface of the vacuum chuck bumps, using diamond polishing fluid with a particle size of W0.3-W1, and polishing time of 20-30 minutes, so that the flatness accuracy of the top of all bumps is <1 micrometer.

[0016] The present invention also provides a vacuum chuck prepared by the above preparation method.

[0017] Furthermore, the vacuum chuck has a diameter greater than 300 mm, a thickness less than 15 mm, a bump diameter of 400-800 micrometers, and a bump height of 100-300 micrometers.

[0018] The key points and innovations of this invention are mainly as follows: 1) This invention is the first to employ a surface-polished, textureless design combined with a high-absorbency carbon nanomaterial coating to fabricate a high-flatness, high-precision vacuum chuck. This is a novel composite material combining silicon carbide ceramics and carbon nanomaterials. When light passes through a transparent wafer and shines onto the textureless, low-roughness, mirror-like surface of the vacuum chuck (see...),... Figure 4 On the surface, the light will reflect along a fixed direction, forming uniform reflected light instead of messy texture signals. This way, the wafer inspection system sees a uniform background, reducing false defects in topography at the source.

[0019] 2) This invention is the first to deposit a carbon nanotube coating on the surface of a vacuum chuck bump structure using metal-catalyzed reduction vapor deposition. This coating absorbs almost all incident visible light, with no significant wavelength blind spots, meeting the requirements for ultra-black materials and further reducing secondary light reflection. This dual approach of a texture-free surface and low-reflection treatment effectively solves the problem in the semiconductor industry where optical systems cannot distinguish between defects in the wafer itself and the vacuum chuck background when inspecting compound transparent wafers.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This invention is the first to employ a surface polishing process with a texture-free finish combined with a high-absorbency carbon nanomaterial coating to fabricate a high-flatness precision vacuum chuck. This is a novel composite material combining silicon carbide ceramics and carbon nanomaterials. The vacuum chuck has a diameter greater than 300 mm and a thickness less than 15 mm. It can adsorb 6 / 8 / 12mm transparent semiconductor sheets, with bump diameters of 400-800 micrometers, bump heights of 100-300 micrometers, a surface roughness Ra of 0.05-0.2 micrometers, a visible light absorption rate of over 99%, and a flatness precision of <1 micrometer.

[0021] 2) The vacuum chuck prepared by this invention, when light shines through a transparent wafer onto the textureless, low-roughness surface of the chuck, reflects along a fixed direction, forming uniform reflected light rather than chaotic texture signals. This ensures that the wafer inspection system sees a uniform background, fundamentally reducing false defects caused by topography. Secondly, the carbon nanotube coating deposited on the chuck surface absorbs almost all incident visible light, with no significant wavelength blind spots, meeting the requirements for ultra-black materials, thereby further reducing secondary light reflection. This combination of textureless surface and low-reflection treatment effectively solves the problem in the semiconductor industry where optical systems cannot distinguish between wafer defects and the vacuum chuck background when inspecting compound transparent wafers. Attached Figure Description

[0022] Figure 1 A 3D diagram of the overall structure of the vacuum chuck; Figure 2 A partial 3D view of the convex surface of the vacuum chuck; Figure 3 A cross-sectional schematic diagram of the vacuum chuck bumps and carbon nanotube coating; Figure 4 This is a photograph of the vacuum chuck product of the present invention. Detailed Implementation

[0023] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0024] In the following embodiments, all raw materials used are common commercially available products that can be directly purchased, or can be prepared using conventional techniques in the art. Processes or steps not described in detail can be performed using conventional techniques in the art, and since they are not the innovation of this application, they will not be elaborated upon here. Example 1

[0025] A method for fabricating a low-reflection, textureless, high-flatness precision vacuum chuck includes the following steps: Isostatic pressing: Based on the shrinkage characteristics of pressureless sintered silicon carbide granulation powder, a 12-inch silicon carbide green blank forming size was designed. Then, the silicon carbide granulation powder was subjected to dry pressing and isostatic pressing (dry pressing process parameters: holding pressure at 120MPa for 20s; cold isostatic pressing process: holding pressure at 200MPa for 5min) to obtain a vacuum chuck green blank with a bending strength of about 50MPa.

[0026] Green blank processing: Based on the sintering shrinkage ratio and the dimensions and structure of the vacuum chuck, the outer diameter and thickness of the isostatically pressed 12-inch vacuum chuck green blank (i.e., silicon carbide circular green blank) are machined. Several evenly distributed protrusions are milled onto the surface of the vacuum chuck green blank using a diamond grinding head (see...). Figure 1 and Figure 2 This ensures the smoothness of the surface of the convex surface, which helps to reduce the surface roughness of the ceramic after sintering.

[0027] High-temperature vacuum sintering: The processed green blank is placed in a vacuum atmosphere sintering furnace, protected by argon gas, and sintered at a temperature of 2050℃ for 150 minutes.

[0028] Dimensional precision machining: The outer circle and thickness of the vacuum chuck blank after high-temperature sintering are machined to the required dimensions, the parallelism is machined to 5 micrometers, and the flatness is machined to 1 micrometer.

[0029] Sandblasting and polishing: A combination of sandblasting jet and diamond rubber abrasive is used, consisting of two steps: rough polishing and fine polishing, to polish the surface of the vacuum chuck with protrusions. During rough polishing, the sandblasting pressure is 0.8 MPa, the diamond rubber abrasive grit is 600#, and the surface roughness Ra reaches 0.4 micrometers. During fine polishing, the sandblasting pressure is 0.3 MPa, the diamond rubber abrasive grit is 10000#, and the surface roughness Ra reaches 0.1 micrometers.

[0030] Sputtering of a metal catalytic film: A 3 nm thick Fe metal film was sputtered onto the polished surface of a vacuum chuck with raised bumps in an atmosphere sintering furnace. The sputtering power was 120 W, and the argon pressure was 0.7 Pa. Subsequently, a mixture of H2 and Ar gas with a volume ratio of 1:2 was introduced, and the temperature was raised to 800 °C for high-temperature annealing for 20 minutes. This caused the Fe film to decompose into uniform Fe nanoparticles, which adhered to the entire surface of the vacuum chuck with raised bumps, with a particle size range of 5 nm.

[0031] Chemical deposition of carbon nanotube coating: A metal Fe catalytic reduction chemical deposition method was used. The vacuum chuck after sputtering the metal catalytic film was placed in a high-temperature furnace under a vacuum atmosphere and heated to 810°C. Simultaneously, a gaseous carbon source (CH4) was introduced, with the total gas flow rate controlled at 150 sccm. The deposition time was 30 minutes, and the thickness of the carbon nanotube coating was controlled to be 20 micrometers (see...). Figure 3 ).

[0032] Ultra-precision machining: The top surface of the vacuum chuck bumps is polished with a robotic polishing machine using diamond polishing fluid with a particle size of W0.3 for 20 minutes, resulting in a flatness accuracy of less than 1 micrometer on the top of all bumps.

[0033] Testing revealed that the vacuum chuck prepared above (see...) Figure 4 With a diameter of 305mm and a thickness of 14mm, it can stably adsorb 12 semiconductor transparent sheets. The bump diameter is 400 micrometers, the bump height is 130 micrometers, the adsorption surface roughness Ra is 0.05 micrometers, the visible light absorption rate is 99.1%, and the flatness accuracy is 0.852 micrometers.

[0034] Comparative Example 1 Compared to Example 1, the processes of sandblasting and polishing, sputtering of metal catalyst film, and chemical deposition of carbon nanotube coating are missing.

[0035] A method for preparing a vacuum chuck includes the following steps: Isostatic pressing: Based on the shrinkage characteristics of pressureless sintered silicon carbide granulation powder, the forming size of 12-inch silicon carbide green blank is designed. Then, the silicon carbide granulation powder is subjected to dry pressing and isostatic pressing (dry pressing process parameters: holding pressure at 100MPa for 15s; cold isostatic pressing process: holding pressure at 180MPa for 7min) to obtain vacuum chuck green blank.

[0036] High-temperature vacuum sintering: The processed green blank is placed in a vacuum atmosphere sintering furnace, protected by argon gas, and sintered at 2100℃ for 120 minutes.

[0037] Dimensional precision machining: The outer circle and thickness of the vacuum chuck blank after high-temperature sintering are machined to the required dimensions. Several evenly arranged protrusions are milled on the surface of the vacuum chuck blank using CNC equipment. The parallelism is machined to 5 micrometers and the flatness is machined to 3 micrometers.

[0038] Ultra-precision machining: The top surface of the vacuum chuck bumps is polished using a ring polisher with diamond polishing fluid of particle size W1 for 60 minutes, resulting in a flatness of 3 micrometers on the top of all bumps.

[0039] Testing revealed that the vacuum chuck prepared above has a diameter of 310 mm and a thickness of 15 mm. It can stably adsorb 12 semiconductor transparent sheets, with a bump diameter of 450 micrometers, a bump height of 100 micrometers, obvious bump processing texture, an adsorption surface roughness Ra of 1.6 micrometers, a visible light absorption rate of 52%, and a flatness accuracy of 3 micrometers. The overall performance of the product is far inferior to that of Example 1.

[0040] In summary, the present invention effectively solves the problem in the semiconductor industry where optical systems cannot distinguish between defects in the wafer itself and the background of the vacuum chuck by combining a texture-free surface and low-reflection treatment on the vacuum chuck.

Claims

1. A method for preparing a vacuum chuck, characterized in that, The process includes the following steps: isostatic pressing, green body processing, high-temperature vacuum sintering, dimensional precision machining, sandblasting and polishing, sputtering of metal catalytic films, chemical deposition of carbon nanotube coatings, and ultra-precision machining.

2. The method for preparing the vacuum chuck as described in claim 1, characterized in that, The isostatic pressing process specifically involves: designing the dimensions of the silicon carbide green blank, and then dry pressing and isostatic pressing the silicon carbide granulated powder to obtain a vacuum chuck green blank with a certain strength; the dry pressing process parameters are: holding pressure at 80-120MPa for 5-30 seconds; the cold isostatic pressing process is: holding pressure at 170-240MPa for 5-15 minutes.

3. The method for preparing the vacuum chuck as described in claim 1, characterized in that, The green blank processing specifically involves: machining the outer diameter and thickness of the isostatically pressed vacuum chuck green blank, and milling several evenly arranged protrusions on the surface of the vacuum chuck green blank using a diamond grinding head.

4. The method for preparing the vacuum chuck as described in claim 1, characterized in that, The high-temperature vacuum sintering process specifically involves placing the processed green blank into a vacuum atmosphere sintering furnace, introducing nitrogen or argon gas for protection, and sintering at a temperature of 2000-2100℃ for 120-180 minutes.

5. The method for preparing the vacuum chuck as described in claim 1, characterized in that, The sandblasting and polishing process specifically involves a combination of sandblasting jets and diamond rubber abrasive, divided into two steps: rough polishing and fine polishing. The surface of the vacuum chuck with protrusions is polished. During rough polishing, the sandblasting pressure is 0.5~0.8MPa, and the grit size of the diamond rubber abrasive is 500#-800#. During fine polishing, the sandblasting pressure is 0.3~0.5MPa, and the grit size of the diamond rubber abrasive is 10000#-20000#.

6. The method for preparing the vacuum chuck as described in claim 1, characterized in that, The sputtering of the metal catalytic film specifically involves sputtering a 1-4 nm thick Fe film onto the polished surface of a vacuum chuck with raised dots in an atmosphere sintering furnace. The sputtering power is 100-150 W, and the argon pressure is 0.5-1 Pa. Subsequently, a mixture of H2 and Ar with a volume ratio of 1:1.5-2.5 is introduced, and the temperature is raised to 750℃-850℃ and annealed at high temperature for 20-30 minutes to decompose the Fe film into uniform Fe nanoparticles.

7. The method for preparing the vacuum chuck as described in claim 1, characterized in that, The chemically deposited carbon nanotube coating is specifically prepared by using a metal Fe catalytic reduction chemical deposition method. The vacuum chuck after sputtering the metal catalytic film is placed in a high-temperature furnace under a vacuum atmosphere and heated to 800-830°C. At the same time, a gaseous carbon source CH4 is introduced, with the total gas flow rate controlled at 130-170 sccm. The deposition time is 20-50 minutes, and the thickness of the carbon nanotube coating is controlled at 20-25 micrometers.

8. The method for preparing the vacuum chuck as described in claim 1, characterized in that, The ultra-precision machining specifically involves using a polishing machine to perform ultra-precision polishing on the top surface of the vacuum chuck bumps, using diamond polishing fluid with a particle size of W0.3-W1, and polishing time of 20-30 minutes, so that the flatness accuracy of the top of all bumps is <1 micrometer.

9. A vacuum chuck prepared by any one of the preparation methods described in claims 1 to 8.

10. The vacuum chuck as described in claim 9, characterized in that, The vacuum chuck has a diameter greater than 300 mm, a thickness less than 15 mm, a bump diameter of 400-800 micrometers, and a bump height of 100-300 micrometers.

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