A porous ceramic electrostatic chuck having a gradient porosity structure and a method of making the same

Abstract

This invention discloses a porous ceramic electrostatic chuck with a gradient porosity structure and its preparation method, belonging to the field of electrostatic chuck technology. The chuck substrate includes a surface dense dielectric layer, an intermediate gradient porosity control layer, and a bottom supporting ceramic layer. The intermediate gradient porosity control layer is disposed between the surface dense dielectric layer and the bottom supporting ceramic layer. The intermediate gradient porosity control layer has varying porosity along its thickness direction to form a thermal conductivity gradient and a dielectric constant gradient. An electrostatic adsorption electrode layer is disposed within the surface dense dielectric layer. This application, by setting the intermediate gradient porosity control layer structure, can simultaneously achieve both surface dielectric strength and internal thermal resistance adjustment capabilities; it can reduce the temperature difference within the wafer surface and improve the temperature compensation capability of the edge region.

Description

Technical Field

[0001] This invention relates to the field of electrostatic chuck technology, and in particular to a porous ceramic electrostatic chuck with a gradient pore structure and its preparation method. Background Technology

[0002] Electrostatic chucks are widely used in semiconductor etching, thin film deposition, ashing, and ion implantation processes to hold and hold wafers, and to control process temperature in conjunction with heating, cooling, and back gas heat conduction. Traditional electrostatic chucks typically use dense alumina, aluminum nitride, or other ceramic materials as the dielectric substrate.

[0003] While existing dense ceramic electrostatic chucks possess good insulation and mechanical stability, they still have shortcomings in heat conduction path adjustment, local thermal resistance design, edge temperature compensation, and thermal shock resistance. Directly replacing dense ceramics with ordinary porous ceramics can easily introduce problems such as decreased strength, increased discharge risk, and excessively high pore connectivity.

[0004] Therefore, a structural solution is needed that can utilize porous ceramics to adjust thermal properties while maintaining the dielectric properties, mechanical strength, and adsorption stability required by the electrostatic chuck. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a porous ceramic electrostatic chuck with a gradient pore structure and its preparation method, so as to overcome the shortcomings of existing electrostatic chucks in terms of temperature uniformity, adjustable thermal resistance, thermal shock resistance and structural reliability.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] This invention discloses a porous ceramic electrostatic chuck with a gradient porosity structure, comprising a chuck substrate, the chuck substrate comprising a surface dense dielectric layer, an intermediate gradient porosity control layer and a bottom supporting ceramic layer, the intermediate gradient porosity control layer being disposed between the surface dense dielectric layer and the bottom supporting ceramic layer, the intermediate gradient porosity control layer having varying porosity along the thickness direction to form a thermal conductivity gradient and a dielectric constant gradient, and an electrostatic adsorption electrode layer being disposed within the surface dense dielectric layer.

[0008] Preferably, the porosity of the intermediate gradient pore control layer gradually decreases from the side of the underlying supporting ceramic layer to the side of the surface dense dielectric layer.

[0009] Preferably, the porosity of the surface dense dielectric layer is 0.5% to 5%.

[0010] Preferably, the porosity of the intermediate gradient pore control layer is 5% to 30%, and its pore size is 0.5 to 50 μm.

[0011] Preferably, the closed-pore ratio of the intermediate gradient pore control layer is greater than 50%.

[0012] Preferably, the electrostatic adsorption electrode layer is a unipolar electrode or a bipolar electrode.

[0013] Another aspect of the present invention discloses a method for preparing the porous ceramic electrostatic chuck, comprising:

[0014] Prepare ceramic slurries with different pore-forming agent contents;

[0015] A layered green body is formed, consisting of a dense dielectric layer on the surface, a gradient porosity control layer in the middle, and a supporting ceramic layer at the bottom.

[0016] An electrostatic adsorption electrode layer is embedded or formed, and after degreasing and sintering, a chuck substrate with a gradient pore structure is formed.

[0017] Preferably, the pore-forming agent is any one or a mixture of two or more of graphite, PMMA, starch microspheres, and resin microspheres.

[0018] Preferably, the sintering temperature is 1400–1850°C.

[0019] The above technical solution has the following beneficial effects:

[0020] By setting an intermediate gradient porosity control layer structure, both surface dielectric strength and internal thermal resistance adjustment capabilities can be taken into account simultaneously; the temperature difference within the wafer surface can be reduced, and the temperature compensation capability of the edge region can be improved.

[0021] Porous structures can improve thermal shock resistance and reduce thermal stress concentration during rapid heating and cooling processes;

[0022] By controlling the closed-pore ratio and pore size distribution, the risk of discharge can be reduced and adsorption stability can be maintained.

[0023] Through layered design, thermal performance can be optimized without significantly sacrificing mechanical strength. Attached Figure Description

[0024] Figure 1 This is a cross-sectional view of the porous ceramic electrostatic chuck of the present invention.

[0025] Figure 2 This is a schematic diagram of the gradient porosity distribution along the thickness direction of the present invention.

[0026] Figure 3 This is a comparison diagram of the temperature difference control between the present invention and a traditional dense ceramic electrostatic chuck. Detailed Implementation

[0027] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] refer to Figure 1 A porous ceramic electrostatic chuck with a gradient pore structure includes a chuck substrate, wherein the chuck substrate includes a surface dense dielectric layer 3, an intermediate gradient pore control layer 2 and a bottom supporting ceramic layer 1. The intermediate gradient pore control layer 2 is disposed between the surface dense dielectric layer 3 and the bottom supporting ceramic layer 1. The intermediate gradient pore control layer 2 has a varying porosity along the thickness direction to form a thermal conductivity gradient and a dielectric constant gradient. An electrostatic adsorption electrode layer 4 is disposed in the surface dense dielectric layer.

[0029] Specifically, the chuck substrate includes a surface dense dielectric layer 3, an intermediate gradient porosity control layer 2, and a bottom support ceramic layer 1, which are arranged sequentially from top to bottom. The intermediate gradient porosity control layer 2 is located between the two layers. The intermediate gradient porosity control layer 2 has a varying porosity along the thickness direction. Specifically, the porosity of the intermediate gradient porosity control layer 2 gradually decreases from one side of the bottom support ceramic layer 1 to the side of the surface dense dielectric layer 3, so as to form a gradient of thermal conductivity and a gradient of dielectric constant. By setting a gradient porosity structure through the intermediate gradient porosity control layer 2, the area near the surface can have both high dielectric strength and low discharge risk, while the area near the bottom layer has adjustable thermal resistance and strong thermal buffering capacity.

[0030] The intermediate gradient pore control layer is used to adjust the equivalent thermal conductivity, which satisfies the following:

[0031]

[0032] Where, k eff k is the equivalent thermal conductivity of the intermediate gradient pore control layer. s φ is the intrinsic thermal conductivity of the matrix solid material, φ is the porosity, and β is the pore structure correction factor.

[0033] Since the porosity varies along the thickness direction, the equivalent thermal resistance of the suction cup substrate is:

[0034]

[0035] Among them, R th Let L be the equivalent thermal resistance of the chuck substrate, L be the thickness of the chuck substrate, A be the effective heat transfer area perpendicular to the heat conduction direction, and k be the effective thermal resistance of the chuck substrate. eff (x) represents the gradient porosity equivalent thermal conductivity at position x along the thickness direction;

[0036] In some embodiments, the porosity of the surface dense dielectric 3 is 0.5% to 5%. Specifically, the porosity of the surface dense dielectric layer 3 is 0.5% or 5%, or it can be 1.5%. In addition, the porosity of the surface dense dielectric layer 3 can also gradually decrease from the side near the intermediate gradient porosity control layer 2 upwards. For example, the porosity can be gradually reduced from 5% near the intermediate gradient porosity control layer to 0.5%, or the porosity can be gradually reduced from 4.5% to 1%.

[0037] In some embodiments, the porosity of the intermediate gradient porosity control layer 2 is 5% to 30%, and its pore size is 0.5 to 50 μm. Specifically, the porosity of the intermediate gradient porosity control layer 2 is in the range of 5% to 30%, and can also be 6% to 22%. It varies in a gradient along the thickness direction. For example, it can be a gradual decrease from 30% porosity on the side near the bottom supporting ceramic layer 1 to 5% porosity on the side of the surface dense dielectric layer 3, or a gradual decrease from 25% porosity on the side near the bottom supporting ceramic layer 1 to 10% porosity on the side of the surface dense dielectric layer 3.

[0038] refer to Figure 2 In the figure, the upper part is the upper part of the intermediate gradient porosity control layer 2, which is the side close to the surface dense dielectric layer 3, the lower part is the lower part of the intermediate gradient porosity control layer 2, which is the side close to the bottom supporting ceramic layer 1, and the middle part is the middle part of the intermediate gradient porosity control layer 2. The thickness range between the upper part and the surface layer is the porosity distribution of the surface dense dielectric layer 3 from the bottom to the upper surface. It can be a fixed porosity or it can be made into a porosity that gradually decreases from bottom to top as shown in the figure.

[0039] In some embodiments, the closed-pore ratio of the intermediate gradient pore control layer 2 is greater than 50%, specifically 55% or 65%, and the maximum closed-pore ratio can be 80%.

[0040] In some embodiments, an electrostatic adsorption electrode layer 4 is provided within the surface dense dielectric layer 3 to generate electrostatic adsorption force, allowing the electrostatic chuck to adsorb the wafer. The electrostatic adsorption electrode layer 4 is a unipolar electrode or a bipolar electrode.

[0041] A method for preparing the above-mentioned porous ceramic electrostatic chuck specifically includes the following steps:

[0042] Step 1: Prepare ceramic powder, sintering aid, pore-forming agent, and organic binder to form multiple sets of ceramic slurries or granulated powders with different porosities. Specifically, the ceramic powder can be any one or a mixture of two or more of alumina powder, aluminum nitride powder, silicon nitride powder, and mullite, or a composite material thereof. The pore-forming agent can be any one or a mixture of two or more of graphite, PMMA (polymethyl methacrylate), starch microspheres, and resin microspheres. The sintering aid can be MgO or CaO, and the organic binder can be polyvinyl butyral (PVB).

[0043] Step 2: Using casting, lamination, molding, dry pressing or slip casting to form a green body structure consisting of a dense surface dielectric layer, an intermediate gradient porosity control layer and a bottom supporting ceramic layer.

[0044] Step 3: Embed or print an electrostatic adsorption electrode layer and a heating layer into the green structure. The electrostatic adsorption electrode layer is used to generate electrostatic adsorption force, and the heating layer is used to heat the electrostatic chuck device.

[0045] Step 4: Degrease and step-sinter the layered green structure to decompose the pore-forming agent and form a gradient pore structure. The sintering temperature is in the range of 1400 to 1850℃.

[0046] Step 5: Perform surface finishing, metal lead connection, and insulating encapsulation on the sintered ceramic to obtain the finished porous ceramic electrostatic chuck.

[0047] Example 1

[0048] The electrostatic chuck in this embodiment is used in a 300mm wafer etching equipment. The total thickness of the chuck substrate is 8mm, including a surface dense dielectric layer 3, an intermediate gradient porosity control layer 2, and a bottom support ceramic layer 1.

[0049] The thickness and porosity of each layer are shown in Table 1 below:

[0050]

[0051] The ceramic material is an alumina-alumina nitride composite ceramic, and the electrostatic adsorption electrode layer is a bipolar electrode, buried at a depth of 0.35 mm from the surface of the dense dielectric layer.

[0052] Example 2

[0053] Preparation process of porous ceramic electrostatic chuck:

[0054] The slurry for preparing the surface dense dielectric layer 3 contains a pore-forming agent with a mass fraction of 1 wt%. The slurry for the intermediate gradient pore control layer 2 includes slurries with various porosities, and the pore-forming agents added to the slurries contain mass fractions of 5 wt%, 9 wt%, 13 wt%, and 16 wt%, respectively, to prepare green structures with different porosities. After the green structures with different porosities are stacked, they form the green structure of the intermediate gradient pore control layer. The slurry for preparing the bottom supporting ceramic layer 1 contains a pore-forming agent with a mass fraction of 3 wt%. After being cast and stacked, the layers are degreased at 600℃ and sintered at 1680℃ for 4 hours to complete the sintering.

[0055] The porous ceramic electrostatic chuck was tested after sintering, and the test results are shown in the table below:

[0056]

[0057] Experimental data:

[0058] The sample of this invention was compared with a traditional dense alumina electrostatic chuck under the following test conditions: target temperature 80 degrees Celsius, wafer size 300 mm, back gas of He, and process load of etching equivalent heat flux. Specific test data are shown in the table below:

[0059]

[0060] The results show that the present invention significantly improves temperature uniformity and thermal cycling stability while maintaining high insulation performance.

[0061] refer to Figure 3 As shown in the figure, the temperature difference gradually increases from the center to the edge, and the temperature difference of this application is smaller than that of traditional dense ceramic electrostatic chucks.

[0062] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A porous ceramic electrostatic chuck with a gradient pore structure, characterized in that, The chuck substrate includes a surface dense dielectric layer, an intermediate gradient porosity control layer, and a bottom support ceramic layer. The intermediate gradient porosity control layer is disposed between the surface dense dielectric layer and the bottom support ceramic layer. The intermediate gradient porosity control layer has a varying porosity along the thickness direction to form a thermal conductivity gradient and a dielectric constant gradient. An electrostatic adsorption electrode layer is disposed within the surface dense dielectric layer.

2. The porous ceramic electrostatic chuck according to claim 1, characterized in that, The porosity of the intermediate gradient pore control layer gradually decreases from the side of the bottom supporting ceramic layer to the side of the surface dense dielectric layer.

3. The porous ceramic electrostatic chuck according to claim 1, characterized in that, The porosity of the dense dielectric layer on the surface is 0.5% to 5%.

4. The porous ceramic electrostatic chuck according to claim 1, characterized in that, The porosity of the intermediate gradient pore control layer is 5% to 30%, and its pore size is 0.5 to 50 μm.

5. The porous ceramic electrostatic chuck according to claim 1 or 4, characterized in that, The closed-pore ratio of the intermediate gradient pore control layer is greater than 50%.

6. The porous ceramic electrostatic chuck according to claim 1, characterized in that, The electrostatic adsorption electrode layer is a unipolar electrode or a bipolar electrode.

7. A method for preparing a porous ceramic electrostatic chuck as described in any one of claims 1-6, characterized in that, include: Prepare ceramic slurries with different pore-forming agent contents; A layered green body is formed, consisting of a dense dielectric layer on the surface, a gradient porosity control layer in the middle, and a supporting ceramic layer at the bottom. An electrostatic adsorption electrode layer is embedded or formed, and after degreasing and sintering, a chuck substrate with a gradient pore structure is formed.

8. The preparation method according to claim 7, characterized in that, The pore-forming agent is any one or a mixture of two or more of graphite, PMMA, starch microspheres, and resin microspheres.

9. The preparation method according to claim 7, characterized in that, The sintering temperature is 1400–1850℃.

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