Electrostatic chuck and method of manufacturing the same

Abstract

This invention relates to an electrostatic chuck and its manufacturing method. It solves the problem of reduced wafer yield caused by partial damage due to thermal expansion of the electrostatic chuck, and increases wafer lifespan by making the thermal expansion coefficient of the lower plate of the electrostatic chuck similar to that of the upper plate.

Description

Technical Field

[0001] The present invention relates to an electrostatic chuck and a method for manufacturing the same. The electrostatic chuck is made of a sintered material composed of aluminum and other materials. The sintered material is used as a base or chuck material for placing wafers in a furnace or chamber in a semiconductor manufacturing process. Prior Art

[0002] The manufacturing process for integrated circuits (ICs) on semiconductor wafers is typically a multi-step process, involving at least dozens to hundreds of steps. The semiconductor manufacturing process is essentially carried out in a high-temperature, high-pressure chamber for each wafer. Finished products are gradually produced by repeating finishing processes in various chambers and under various environments. Typical process steps include deposition, exposure, etching, and ion implantation. By repeating these processes under various conditions, active components such as transistors and diodes are formed within the silicon substrate, and various types of conductive layers connecting the active components or insulating layers are repeatedly formed on the silicon substrate. As mentioned above, this process is essentially carried out in semiconductor manufacturing equipment or chambers within such equipment while the wafer is in the wafer state. This is called pre-processing. A furnace, processing equipment, reaction chamber, or processing chamber can be used instead of the chamber.

[0003] After various temperature and pressure settings are applied for the pre-processing steps, various types of gases are introduced into the chamber via a showerhead to induce the desired chemical reactions on the wafer. Plasma is sometimes generated using these gases. The wafer within the chamber needs to be positioned and secured so that it does not move during the processing. The structure used to position and secure the wafer is a chuck. The chuck can have various forms or shapes, as needed. Recently, electrostatic chucks (ESCs) have become increasingly popular. ESCs are a type of chuck in which a wafer can be secured to the chuck by applying an electrostatic voltage to the chuck, generating electrostatic force. These ESCs are primarily used to horizontally secure and position semiconductor wafers, and are also used to horizontally secure large-scale LCD glass substrates.

[0004] After a semiconductor wafer is loaded into the chamber and placed in the ESC, power is supplied to the ESC via electrodes embedded therein, generating static electricity on the ESC surface. This triggers a clamping operation, in which the wafer is securely secured to the ESC. This involves a pre-treatment step at high temperature and high pressure. After one step of the process is completed, power to the ESC is shut off, followed by a unclamping operation, in which the wafer is detached from the ESC. This allows the wafer to be released from the ESC.

[0005] Typically, manufacturing processes performed in a chamber involve introducing chemical materials into the chamber, generating chemical reactions at high temperatures and high pressures. Sometimes, the manufacturing process can be performed in a plasma state. This process can be repeated countless times, requiring only maintenance and repair periods. Therefore, ESCs must also possess high durability, corrosion resistance, and high insulation properties. Essentially, the coefficient of thermal expansion and thermal conductivity must be adjusted to within normal standards.

[0006] FIG1 shows a conventional electrostatic chuck (ESC) 100 comprising an upper plate 120, a lower plate 130, and adhesive 150. The upper plate 120 holds the wafer 20 in direct contact with the wafer 20, the lower plate 130 is bonded to the upper plate 120, and the adhesive 150 is used to bond the plates together. The upper plate 120 is made of a thin ceramic, approximately 1 to 5 mm thick, to facilitate heat transfer to the wafer 20. Adhesive 150 is made of a material such as epoxy resin. Materials containing metal components are often used for the lower plate 130, which transfers heat to the ESC 100. However, the upper and lower plates 120, 130 have different thermal expansion coefficients due to their different materials. In a chamber environment subject to drastic temperature fluctuations, the upper and lower plates 120, 130 may separate to the point where the adhesive tears or the upper plate may crack. This can lead to additional maintenance, repair, and yield issues.

[0007] For example, a ceramic upper plate has a coefficient of thermal expansion (CTE) of approximately 0.4-13.5 [µm / °C], while an aluminum lower plate has a CTE of 20-30 [µm / °C]. Therefore, the greater the difference between the temperature at which the upper and lower plates are bonded and combined and the ambient temperature of the process performed within the chamber, the more likely the bond between the upper and lower plates will break, or the ceramic upper plate will break. This is because the ceramic upper plate is harder than the aluminum lower plate, and softer than the aluminum lower plate. Even with a simple calculation based on thermal expansion, if the temperature difference is 100°C, the difference in dimensional change between the upper and lower plates can exceed 1000µm. This presents a significant problem.

[0008] In particular, as the aspect ratios of vertically formed structures in semiconductor integrated circuits have recently reached tens to hundreds, etching processes or plasma processes at temperatures below room temperature have become increasingly important. Consequently, the temperature adaptability issue in ESCs (where wafer temperature is directly regulated) has become more severe.

[0009] For reference, the thermal expansion coefficients of ceramics magnesium oxide (MgO), aluminum oxide (Al 2O 3), soda-lime glass, and silicon dioxide (SiO 2) are known to be approximately 13.5, 7.6, 9.0, and 0.4 [µm / °C], respectively, with some errors depending on the measurement environment and the degree of impurities contained.

[0010] Even in sub-zero environments, where the temperature gradually decreases from room temperature in the operating environment, the problems caused by differences in CTE are the same. CTE refers to the value that increases with each 1°C increase in temperature. When the temperature decreases by 1°C, thermal contraction occurs, and the CTE becomes negative (-). Summary of the Invention

[0011] Various embodiments relate to a configuration and method of manufacturing the same configuration so that the coefficient of thermal expansion of a lower plate of an electrostatic chuck is equal to or at least similar to the coefficient of thermal expansion of an upper plate of the electrostatic chuck.

[0012] Furthermore, various embodiments provide for users to reduce the cost and time spent on maintenance and repair by further extending the life of the electrostatic chuck.

[0013] Furthermore, various embodiments are directed to preventing a reduction in wafer yield due to a partial damage phenomenon caused by thermal expansion of an electrostatic chuck.

[0014] In one embodiment, an electrostatic chuck is provided, comprising an upper plate made of ceramic and having a wafer positioned therein, a lower plate bonded to the upper plate, and an adhesive for bonding the upper and lower plates together. The lower plate can be sintered and molded at high temperature under vacuum and pressure conditions by mixing a first powder comprising at least one of aluminum, stainless steel (SUS), titanium, and magnesium, and a second powder comprising at least one of silicon carbide (SiC), silicon nitride (Si3N4), silicon, diamond, carbon nanotubes, and graphene. The mixing ratio of the first powder to the second powder can be 4:6 to 6:4.

[0015] In one embodiment, a method for manufacturing an electrostatic chuck is provided. The chuck includes an upper plate made of ceramic and having a wafer mounted therein, a lower plate bonded to the upper plate, and an adhesive for bonding the upper and lower plates together. The lower plate can be manufactured by the following steps: a first step of preparing a first powder comprising at least one of aluminum, stainless steel, titanium, and magnesium; a second step of preparing a second powder comprising at least one of silicon carbide (SiC), silicon nitride (Si3N4), silicon, diamond, carbon nanotubes, and graphene; a third step of mixing the first and second powders; and a fourth step of sintering and molding the mixed powder at high temperature under vacuum and pressure conditions to form a molded body of the lower plate. The ratio of the first and second powders mixed in the third step can be between 4:6 and 6:4.

[0016] The present invention has the following effects: users can reduce the cost and time for maintenance and repair by further extending the life of the ESC.

[0017] The present invention has the following effects: it can prevent the problem of reduced wafer yield due to partial damage caused by thermal expansion of an electrostatic chuck, and can improve productivity in a semiconductor mass production process. Simple diagram description

[0018] FIG. 1 is a diagram schematically illustrating a conventional ESC according to the related art.

[0019] FIG. 2 is a diagram schematically illustrating an ESC according to an embodiment of the present invention.

[0020] FIG. 3 is a schematic diagram illustrating a process of forming the lower plate of the ESC in FIG. 2 .

[0021] FIG. 4 is a diagram illustrating thermal expansion coefficients according to composition ratios of lower plate compositions of an ESC according to an embodiment of the present invention.

[0022] FIG5 is a schematic diagram illustrating a flow of a method of manufacturing an ESC according to an embodiment of the present invention.

[0023] FIG. 6 is a schematic diagram for describing a process for forming the lower plate according to an embodiment of the present invention, wherein electrodes have been buried in the ESC. Implementation Method

[0024] Hereinafter, the embodiment of the present invention is described in detail with reference to the drawings so that those skilled in the art to which the present invention pertains can easily practice the embodiment. In the element symbols appearing in the drawings, the same element symbols indicate the same parts.

[0025] In describing the present invention, when it is determined that a detailed description of related known technologies may make the subject matter of the present invention unclear, the detailed description will be omitted.

[0026] Terms such as first and second can be used to describe various components, but the components are not limited by the terms. The terms are only used to distinguish one component from another.

[0027] Fig. 2 is a diagram schematically illustrating an electrostatic chuck (ESC) according to an embodiment of the present invention. Fig. 3 is a diagram illustrating a process of forming a lower plate of the ESC in Fig. 2 .

[0028] 2 , an ESC 200 according to an embodiment of the present invention includes an upper plate 210, a lower plate 220, and an adhesive 230. The upper plate 210 has the wafer 20 positioned therein by direct contact with the wafer 20, the lower plate 220 is bonded to the upper plate 210, and the adhesive 230 is used to bond the upper plate 210 and the lower plate 220 together.

[0029] The upper plate 210 is made of ceramic with a thin thickness of about 1 mm to 5 mm to facilitate heat transfer to the wafer 20. A material such as epoxy resin is used as the adhesive 230. A material containing a large amount of metal components is used as the lower plate 220 for transferring heat to the ESC 200.

[0030] The ESC 200 according to an embodiment of the present invention can solve the problem of adhesive tearing or upper plate cracking by making the thermal expansion coefficient of the lower plate 220 the same as the thermal expansion coefficient of the upper plate 210 or minimizing the difference between the thermal expansion coefficients of the lower plate 220 and the upper plate 210.

[0031] In an ESC 200 according to an embodiment of the present invention, a first powder comprising at least one of aluminum, stainless steel, titanium, and magnesium is mixed with a second powder comprising at least one of silicon carbide (SiC), silicon nitride (Si3N4), silicon, diamond, carbon nanotubes, and graphene. The mixture is then sintered and molded at high temperature under vacuum and pressure conditions. In this case, a preferred mixing ratio of the first powder to the second powder is 4:6 to 6:4.

[0032] In order to make the thermal expansion coefficient of the lower plate 220 the same as that of the upper plate 210 or minimize the difference between the thermal expansion coefficients of the lower plate 220 and the upper plate 210, in addition to the mixing ratio of the first powder and the second powder, it is also very important to adjust the particle size ratio of the first powder and the second powder.

[0033] In the ESC 200 according to the embodiment of the present invention, preferably, the ratio of the particle sizes of the first powder and the second powder of the lower plate 220 is adjusted to a range of 1:0.05 to 1:0.4.

[0034] Preferably, the lower plate 220 is sintered and molded at a temperature of 300° C. to 700° C. and a pressure of 10 MPa to 300 MPa for 30 minutes to 2 hours.

[0035] FIG. 4 is a diagram illustrating thermal expansion coefficients according to a composition ratio of components of a lower plate of an ESC according to an embodiment of the present invention.

[0036] FIG4 illustrates an embodiment in which AL6061 (i.e., aluminum alloy) is used as the first powder and silicon carbide (SiC) is used as the second powder, but the first powder and the second powder are not limited to this embodiment.

[0037] 4 , it can be seen that if the ratio of silicon carbide (SiC) (i.e., the second powder) to the mixture of aluminum alloy (AL6061) and silicon carbide (SiC) is in the range of 40 to 60 volume %, and if the particle size ratio of silicon carbide (SiC) (i.e., the second powder) to the aluminum alloy (AL6061) (i.e., the first powder) is in the range of 1:0.05 to 1:0.4, the thermal expansion coefficient of the composition is in the range of 10.79 (µm / m·°C) to 15.21 (µm / m·°C).

[0038] The results of FIG. 4 are shown in the following table.

[0039] Table 1 SiC to Al particle size ratio 1:0.05 1:0.1 1:0.2 1:0.4 Volume ratio of SiC (%) 40 15.21 13.28 13.72 13.81 50 11.45 13.01 13.17 13.03 60 11.05 11.05 11.79 10.79

[0040] If the particle size ratio of silicon carbide (SiC) (i.e., the second powder) to aluminum alloy (AL6061) (i.e., the first powder) is adjusted to a range of 1:0.05 to 1:0.4, and the ratio of silicon carbide (SiC) (i.e., the second powder) is adjusted to a range of 40-60 volume %, a lower plate having a thermal expansion coefficient within a preferred range can be obtained.

[0041] In this case, if the particle size ratio of silicon carbide (SiC) (i.e., the second powder) to aluminum alloy (AL6061) (i.e., the first powder) is less than 1:0.05, there is a problem of a sudden decrease in the heat transfer coefficient due to poor density and dispersibility of the powder, and a decrease in density after sintering. Furthermore, if the particle size ratio of silicon carbide (SiC) (i.e., the second powder) to aluminum alloy (AL6061) (i.e., the first powder) is greater than 1:0.4, there is a problem of a decrease in the thermal expansion coefficient due to a decrease in the bonding force between the particles.

[0042] Table 2 mixture Thermal expansion coefficient (10 -6 / K) AL-1% SiC (particle size ratio 1:0.2) 22.29 AL-5% SiC (particle size ratio 1:0.2) 23.46 AL-10% SiC (particle size ratio 1:0.2) 22.56 AL-20% SiC (particle size ratio 1:0.2) 21.12 AL-30% SiC (particle size ratio 1:0.2) 19.98 AL-40% SiC (particle size ratio 1:0.2) 13.72 AL-50% SiC (particle size ratio 1:0.2) 13.17 AL-60% SiC (particle size ratio 1:0.2) 11.79 AL-70% SiC (particle size ratio 1:0.2) 10.12 AL-80% SiC (particle size ratio 1:0.2) 10.01

[0043] Table 2 shows experimental results of changes in properties according to the ratio of silicon carbide (SiC) to the mixture of aluminum alloy (AL6061) (ie, the first powder) and silicon carbide (SiC) (ie, the second powder).

[0044] As can be seen from Table 2, when the ratio of silicon carbide (SiC) to the mixture of aluminum alloy (AL6061) and silicon carbide (SiC) is 40% or less, the desired thermal expansion coefficient cannot be obtained, and when the ratio of silicon carbide (SiC) to the mixture of aluminum alloy (AL6061) and silicon carbide (SiC) is greater than 40%, the thermal expansion coefficient suddenly increases.

[0045] When the ratio of silicon carbide (SiC) to the mixture of aluminum alloy (AL6061) and silicon carbide (SiC) is greater than 60%, the distribution of powder properties deteriorates due to the decrease in dispersibility of the powder (i.e., the process of non-uniform mixing of the powder).

[0046] FIG5 is a schematic diagram illustrating a flow of a method of manufacturing an ESC according to an embodiment of the present invention.

[0047] 5 , the method for manufacturing an ESC according to an embodiment of the present invention includes a first powder preparation step S100, a second powder preparation step S200, a powder mixing step S300, and a sintering molding step S400.

[0048] In the first powder preparation step ( S100 ), a first powder 310 is prepared, namely, a molding powder comprising at least one of aluminum, stainless steel, titanium, and magnesium. Considering ease of molding processing, it is preferred that the prepared first powder contain aluminum as the primary component of the material. For reference, pure aluminum has a thermal expansion coefficient of 23.8 [µm / °C], aluminum oxide (Al 2 O 3) has a thermal expansion coefficient of 6.7 to 7.7 [µm / °C], and aluminum nitride (AlN) has a thermal expansion coefficient of 4.5 to 5.0 [µm / °C]. Hereinafter, the unit of thermal expansion coefficient is [µm / °C].

[0049] In the second powder preparation step S200, a second powder 320 is prepared, that is, an additive powder including at least one of silicon carbide (SiC), silicon nitride (Si3N4), silicon, diamond, carbon nanotubes and graphene.

[0050] In the second powder 320 (i.e., additive powder), silicon carbide (SiC) has a thermal expansion coefficient of 4.5 to 6.6, silicon nitride (Si3N4) has a thermal expansion coefficient of 2.6, stainless steel (SUS) has a thermal expansion coefficient of 10 to 18 according to its standard, diamond has a thermal expansion coefficient of approximately 1.1, and carbon nanotubes have a thermal expansion coefficient of 4 to 6 depending on their direction and the content of fine carbon.

[0051] In the powder mixing step S300, a first powder 310 (molding powder) and a second powder 320 (additive powder) are mixed. As an example, AL6061 (aluminum alloy) can be used as the first powder 310, and silicon carbide (SiC) can be used as the second powder 320. In this case, the particle size ratio of the first powder to the second powder is preferably 1:0.05 to 1:0.4.

[0052] In this case, the volume of second powder 320 (i.e., the additive powder) can be appropriately adjusted if necessary. For example, if silicon carbide (SiC) is used as second powder 320, the volume of the SiC can be increased or decreased within 40% to 60% of the total mixed powder 330. If AL6061 (i.e., an aluminum alloy) is used as first powder 310, the thermal expansion coefficient of the mixed powder gradually decreases from that of aluminum, depending on the mixing ratio. Since the second powder used as an additive is expected to be mixed with the first powder, it is preferable to use a material as the second powder that is advantageously pressurized and molded at high temperatures and that facilitates adjustment and prediction of the material's thermal expansion coefficient.

[0053] In the sintering molding step ( S400 ), the mixed powder is pressurized and molded as a sintering material to complete the lower plate 220 . The conditions for this sintering molding, namely, pressure, temperature, and time, vary depending on the desired state of the finished sintered material. Preferably, the sintering molding is performed at a pressure of 10 MPa to 300 MPa and a temperature of 300°C to 700°C for 30 minutes to 2 hours. The sintering molding step ( S400 ) can be performed using either cold pressing or high-pressure injection molding.

[0054] In some cases, in order to adjust the temperature of the lower plate, it is necessary to bury the electrode in the lower plate. In this case, after the mold of the lower plate is separated into two halves and the two molds are manufactured separately, the electrode needs to be buried between the two molds.

[0055] FIG. 6 is a schematic diagram for describing a process for forming a lower plate according to an embodiment of the present invention, wherein electrodes have been buried in an ESC.

[0056] In other words, as shown in FIG6 , after the lower plate 220 is divided into two halves (i.e., an upper portion 225 and a lower portion 221), the upper portion 225 and the lower portion 221 are formed separately using a method including a first powder preparation step S100, a second powder preparation step S200, a powder mixing step S300, and a sintering and molding step S400. Electrode 223 is printed or coated on lower portion 221, or provided on lower portion 221 using another method. Electrode 223 is then covered with upper portion 225, and then pressurized and sintered or compressed, thereby completing lower plate 220. If desired, before burying electrode 223 in lower portion 221, lower portion 221 and upper portion 225 of lower plate 220 can be selectively molded. This allows the electrode 223 to be buried in lower portion 221 by simple compression, instead of sintering and molding at high temperature, and then sintering and molding can be performed.

[0057] In embodiments of the present invention, in addition to the aforementioned powder metallurgy method of pressurizing and molding a mixed powder, the sintering and molding step can be replaced by another method. For example, the first powder can be sintered first, and then a casting method can be used in which the first powder is melted to form appropriate bubbles within the first powder. Subsequently, a method can be used in which the first powder is melted under pressure and the bubbles are filled with the melted product. Alternatively, a method can be used in which another first powder is melted first and then the second powder is added.

[0058] 20: Wafer 100:Electrostatic chuck (ESC) 120:On the board 130: Lower board 150: Adhesive 200:Electrostatic chuck (ESC) 210:On the board 220: Lower board 221: Lower part 223: Electrode 225: Upper part 230: Adhesive 310: First powder 320: Second powder 330: Mixed powder S100, S200, S300, S400: Steps

Claims

1. An electrostatic chuck comprising an upper plate; a lower plate; and an adhesive, the upper plate being made of ceramic and having a wafer disposed therein, the lower plate being bonded to the upper plate, the adhesive being used to bond the upper plate and the lower plate together, wherein the lower plate is sintered and molded under vacuum and pressure at high temperature by mixing a first powder comprising at least one of aluminum, stainless steel (SUS), titanium and magnesium and a second powder comprising at least one of silicon carbide (SiC), silicon nitride (Si3N4), silicon, diamond, carbon nanotubes and graphene, wherein the mixing ratio of the first powder and the second powder is 4:6 to 6:4, and the particle size ratio of the first powder and the second powder is 1:0.05 to 1:0.

4.

2. The electrostatic chuck as described in claim 1, wherein, The lower plate is sintered and molded at a temperature of 300°C to 700°C.

3. The electrostatic chuck as described in claim 1, wherein, The lower plate is sintered and molded under pressures ranging from 10 MPa to 300 MPa.

4. The electrostatic chuck as described in claim 1, wherein, The lower plate is sintered and molded for 30 minutes to 2 hours.

5. A method for manufacturing an electrostatic chuck, the electrostatic chuck comprising an upper plate, a lower plate, and an adhesive, the upper plate being made of ceramic and having a wafer disposed therein, the lower plate being bonded to the upper plate, the adhesive being used to bond the upper plate and the lower plate together, wherein... The lower plate is manufactured by the following steps: First step, preparing a first powder comprising at least one of aluminum, stainless steel, titanium and magnesium; Second step, preparing a second powder comprising at least one of silicon carbide (SiC), silicon nitride (Si3N4), silicon, diamond, carbon nanotubes and graphene; Third step, mixing the first powder and the second powder. The fourth step involves manufacturing the molded body of the lower plate by sintering and molding the mixed powder under vacuum and pressure at high temperature. The ratio of the first powder to the second powder mixed in the third step is 4:6 to 6:4, and the particle size ratio of the first powder to the second powder mixed in the third step is 1:0.05 to 1:0.

4.

6. The method as described in claim 5, wherein, The fourth step is carried out at a temperature of 300°C to 700°C.

7. The method as described in claim 5, wherein, The fourth step is carried out under pressures ranging from 10 MPa to 300 MPa.

8. The method as described in claim 5, wherein, The fourth step takes between 30 minutes and 2 hours.

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