Preparation method of bimodal grain structure alumina ceramics and alumina ceramics

Abstract

This invention discloses a method for preparing bimodal grain-structured alumina ceramics and the alumina ceramics themselves. The method involves mixing at least three different particle sizes of alumina powder to obtain a main material, which is then mixed with a sintering aid containing at least one rare earth oxide. After molding and sintering, the alumina ceramics are obtained. The sintered alumina ceramics exhibit a morphology where large grains are filled with smaller grains. Because the gaps between the large grains are filled by the smaller grains, the intergranular spaces in the ceramic are reduced, thereby maximizing the packing density. Compared to traditional alumina ceramics sintered with a single particle size, the three-particle-size gradation of this invention achieves a relative density of over 93% after sintering, significantly improving the density and mechanical strength of the ceramics while correspondingly reducing dielectric loss.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic materials technology, specifically to a method for preparing bimodal grain structure alumina ceramics and the alumina ceramics themselves. Background Technology

[0002] With the continuous development of semiconductor technology, especially in the field of wafer manufacturing, the performance requirements for wafer chucks are becoming increasingly stringent. As a crucial component in the semiconductor production process, wafer chucks are widely used in wafer handling, fixing, and positioning, and their performance directly affects production efficiency and product quality.

[0003] Alumina ceramics are considered an ideal material for manufacturing wafer chucks due to their excellent high-temperature resistance, chemical stability, and mechanical strength. However, existing alumina ceramic chucks typically use alumina raw materials with a single particle size during production, resulting in pores or voids within the ceramic body and a low density (usually 85%-90%). This low density not only affects the thermal conductivity and mechanical strength of the alumina ceramic but also makes it difficult to meet high-precision surface flatness requirements, thus impacting the alignment accuracy and adsorption uniformity during wafer processing.

[0004] Furthermore, the presence of pores significantly deteriorates the dielectric properties of alumina ceramics. When a large number of pores exist within the alumina ceramic, the difference in dielectric constant between the pores and the ceramic matrix leads to uneven electric field distribution, resulting in a significant increase in overall dielectric loss. Higher dielectric loss causes abnormal heating of the chuck body, which severely interferes with the temperature uniformity of the wafer surface, thereby affecting the stability of wafer manufacturing processes (such as etching and deposition), and ultimately reducing the yield of wafer production. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to provide a method for preparing alumina ceramics with both high density and low dielectric loss.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for preparing bimodal grain structure alumina ceramics is characterized by: mixing at least three alumina powders of different particle sizes to obtain a main material, and then molding and sintering it to obtain alumina ceramics.

[0008] As an optimization, the at least three different particle sizes include a first particle size, a second particle size, and a third particle size, wherein the first particle size is 200nm-500nm, the second particle size is 500nm-2000nm, and the third particle size is 90μm-110μm, and the first particle size is smaller than the second particle size.

[0009] As an optimization, the mass ratio of the alumina powder with the first particle size, the second particle size, and the third particle size is 1:1:1.

[0010] As an optimization, it also includes mixing a sintering aid containing at least one rare earth oxide with the main material.

[0011] As an optimization, the rare earth oxide includes at least one of europium oxide, cerium oxide, and neodymium oxide.

[0012] As an optimization, the sintering aid is cerium oxide.

[0013] As an optimization, based on the total mass of raw materials, the proportion of the main material is 98.5%-99.5%, and the proportion of the sintering aid is 0.5%-1.5%.

[0014] As an optimization, it also includes adding a binder to mix with the main material and sintering aid, wherein the binder is polyvinyl alcohol.

[0015] The present invention also discloses an alumina ceramic, which is prepared by the above-described method for preparing bimodal grain structure alumina ceramic.

[0016] As an optimization, the alumina ceramic is used as an electrostatic chuck in the wafer manufacturing process.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) Alumina powder with at least three different particle sizes is used for gradation, and after sintering, a morphology is formed in which large grains are filled with small grains. Since the gaps between large grains are filled by small grains, the gaps between ceramic grains are smaller, thereby maximizing the packing density. Compared with alumina ceramics fired with a single particle size in the traditional method, the relative density of the three-particle-size gradation of the present invention can reach more than 93% after sintering, which significantly improves the density and mechanical strength of the ceramic.

[0019] (2) The reduction in porosity results in a dielectric loss that is significantly lower than that of traditional comparative samples, thereby effectively suppressing the abnormal heating of the electrostatic chuck during operation and ensuring the temperature uniformity of the wafer surface.

[0020] (3) It exhibits a bimodal grain structure in microscopic display, with small grains uniformly filling the spaces between large grains and clean grain boundaries free of impurities;

[0021] (4) The alumina ceramics prepared are particularly suitable for electrostatic chucks in wafer manufacturing processes, providing uniform adsorption force, excellent thermal conductivity and low dielectric loss, which significantly improves the yield of wafer processing. Attached Figure Description

[0022] Figure 1This is a SEM grain size distribution diagram of the alumina ceramic prepared in Example 1 of the present invention;

[0023] Figure 2 This is a SEM cross-sectional morphology image of the alumina ceramic prepared in Example 1 of the present invention;

[0024] Figure 3 The energy spectrum of the alumina ceramic prepared in Example 1 of this invention;

[0025] Figure 4 The image shows the XRD pattern of the alumina ceramic prepared in Example 1 of this invention.

[0026] Figure 5 This is a SEM grain size distribution diagram of the alumina ceramic prepared in Example 2 of the present invention;

[0027] Figure 6 This is a SEM cross-sectional morphology image of the alumina ceramic prepared in Example 2 of the present invention;

[0028] Figure 7 The energy spectrum of the alumina ceramic prepared in Example 2 of this invention;

[0029] Figure 8 The image shows the XRD pattern of the alumina ceramic prepared in Example 2 of this invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0031] Definitions: In this specification, "%" refers to mass percentage (wt%); "total mass of raw materials" refers to the sum of the mass of the main material (i.e., alumina powders of three different particle sizes) and the sintering aid, excluding subsequently added binders, dispersants, or solvents; the amount of binder (polyvinyl alcohol) is calculated separately based on the mass of the main material, but the specific amount can be adjusted according to actual needs and does not constitute a limitation of the present invention. "Dielectric loss" is the dielectric loss tangent (tanδ) measured at a frequency of 1MHz.

[0032] Example 1

[0033] Preparation of main ingredients: Weigh 10g of alumina powder with a first particle size D50 of 300nm, 10g of alumina powder with a second particle size D50 of 1000nm, and 10g of alumina powder with a third particle size D50 of 100μm (mass ratio 1:1:1), mix and grind them in an agate mortar for 30 minutes to obtain the main ingredients.

[0034] Preparation of sintering aids: Weigh cerium oxide ( ) Powder, based on the total mass of the main material and sintering aid, weigh 1 wt% of cerium oxide (i.e., 30g of main material corresponds to 0.303g of cerium oxide).

[0035] Mixing and ball milling: Mix the above main materials with sintering aids, use zirconia balls as grinding balls and deionized water as the medium, and ball mill for 4 hours.

[0036] Pre-calcination and granulation: The ball-milled slurry is dried at 100℃ for 6 hours. The dried lumps are then ground into powder using a mortar and passed through a 120-mesh sieve. The powder is then poured into a mortar and a certain amount of 5% polyvinyl alcohol solution is gradually added while grinding. The powder is then passed through a 60-mesh sieve to obtain granulated powder.

[0037] Molding and debinding: Pour the granulated powder into the tableting mold and press it into a green blank with a pressure of 5T for 2 minutes. Then, heat it to 600℃ at a heating rate of 2℃ / min and hold it for 2 hours. Cool it in the furnace to obtain alumina debinding sheets.

[0038] Sintering: The green body after debinding is heated to 1600℃ at a heating rate of 5℃ / min and held for 3 hours for solid-state sintering. It is then cooled to room temperature in the furnace to obtain alumina ceramic.

[0039] Product Performance

[0040] The relative density of the alumina ceramic prepared in this embodiment was 96% according to the water displacement method test. The cross-sectional morphology and grain size distribution were observed using scanning electron microscopy (SEM). Figure 1 and Figure 2 As shown, its microstructure is uniform and dense, with tightly bonded grains. It also exhibits two types of grains with significantly different sizes, representing a non-uniform microstructure where coarse and fine grains coexist. For example... Figure 3 As shown, the distribution of Ce elements is very uniform, which results in their high density. For example... Figure 4 As shown, X-ray diffraction (XRD) analysis revealed that the alumina ceramic had good crystallinity, almost no extra impurities, and the peak positions were almost entirely consistent with the standard card, indicating that the Al2O3 main phase was not destroyed.

[0041] The specific D50 values ​​(300nm, 1000nm, 100μm) given in this embodiment are for illustrative purposes only. Those skilled in the art will understand that as long as the particle size distribution range of the selected alumina powder falls within the range defined in claim 2 (first particle size 200-500nm, second particle size 500-2000nm, third particle size 90-110μm), and the mass ratio is 1:1:1, high-density, low-dielectric-loss alumina ceramics can be obtained through the preparation method of this invention. The mass ratio of 1:1:1 mentioned in the claims of this invention refers to an ideal ratio. In actual operation, due to the accuracy limitations of weighing equipment and batch differences in raw materials, conventional measurement errors are allowed in the mass ratio of each component; for example, the deviation of each component relative to 1 should not exceed ±5% to ±10%. A ratio within this error range (e.g., (0.9~1.1):(0.9~1.1):(0.9~1.1)) can achieve the technical effects of this invention and should be considered equivalent to 1:1:1. Examples 2 and 3 below used different particle size values, and both verified the above conclusions.

[0042] Example 2

[0043] This embodiment is basically the same as Embodiment 1, except that the sintering aid is europium oxide (weighed at 0.5 wt%, i.e., 0.15 g for 30 g of main material) and the particle size is different. The remaining steps and parameters are the same as in Embodiment 1. Figure 5 and Figure 6 As shown, its microstructure is uniform and dense, with tight bonding between grains. Coarse grains are filled with fine grains, and the resulting alumina ceramic has a relative density of 95%. The microstructure also exhibits a bimodal grain structure with two different grain distributions. For example... Figure 7 As shown, the distribution of Eu elements is very uniform, which also contributes to their high density. Figure 8 As shown, X-ray diffraction (XRD) analysis revealed that the alumina ceramic had good crystallinity, almost no extra impurities, and the peak positions were almost entirely consistent with the standard card, indicating that the Al2O3 main phase was not destroyed.

[0044] Example 3

[0045] This embodiment is basically the same as Example 1, except that the sintering aid is neodymium oxide (weighed at 1.5wt%, i.e., 0.456g for 30g of main material) and the particle size is different. The remaining steps and parameters are the same as in Example 1. The alumina ceramic obtained has a relative density of 93%, and the microstructure also shows a bimodal grain structure with two grain distributions.

[0046] The alumina ceramic preparation method provided by this invention is simple, reproducible, and requires no expensive equipment or complex operations, making it suitable for industrial production. The resulting alumina ceramic has high density (relative density ≥93%) and a unique bimodal grain structure, making it particularly suitable for electrostatic chucks in semiconductor wafer manufacturing processes. It can significantly reduce chuck body heating, improve wafer temperature uniformity, and increase process yield.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing alumina ceramic with a bimodal grain structure, characterized in that: At least three different alumina powders of different particle sizes are mixed to obtain the main material, which is then shaped and sintered to obtain alumina ceramics.

2. The method for preparing bimodal grain structure alumina ceramics according to claim 1, characterized in that: The at least three different particle sizes include a first particle size, a second particle size, and a third particle size, wherein the first particle size is 200nm-500nm, the second particle size is 500nm-2000nm, and the third particle size is 90μm-110μm, and the first particle size is smaller than the second particle size.

3. The method for preparing bimodal grain structure alumina ceramics according to claim 2, characterized in that: The mass ratio of the alumina powder with the first particle size, the second particle size, and the third particle size is 1:1:

1.

4. The method for preparing bimodal grain structure alumina ceramics according to claim 1, characterized in that: It also includes mixing a sintering aid containing at least one rare earth oxide with the main material.

5. The method for preparing bimodal grain structure alumina ceramics according to claim 4, characterized in that: The rare earth oxides include at least one of europium oxide, cerium oxide, and neodymium oxide.

6. The method for preparing bimodal grain structure alumina ceramics according to claim 4, characterized in that: The sintering aid is cerium oxide.

7. The method for preparing bimodal grain structure alumina ceramic according to claim 4, characterized in that: Based on the total mass of raw materials, the main material accounts for 98.5%-99.5%, and the sintering aid accounts for 0.5%-1.5%.

8. The method for preparing bimodal grain structure alumina ceramic according to claim 4, characterized in that: It also includes mixing a binder with the main material and sintering aid, wherein the binder is polyvinyl alcohol.

9. An alumina ceramic, characterized in that: It is prepared by the method for preparing bimodal grain structure alumina ceramics according to any one of claims 1 to 8.

10. The alumina ceramic according to claim 9, characterized in that: The alumina ceramic is used as an electrostatic chuck in the wafer manufacturing process.

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