KR20240131594A - Electrode static chuck and fabrication method thereof - Google Patents

Abstract

Provided is an electrostatic chuck which comprises: an upper body on which a substrate can be mounted; and a lower body brazed to the upper body and including a flow path through which a fluid for cooling the substrate can flow, wherein the brazing is formed by forming respective metal layers on one side of the upper body and one side of the lower body and forming a brazing filler metal between the metal layers. The electrostatic chuck according to the present invention enables easy brazing of MMC, titanium, and titanium-aluminum alloys, which were difficult to join by conventional methods, through the selection of metal layers and brazing filler metals.

Description

Electrostatic chuck and fabrication method thereof {Electrode static chuck and fabrication method thereof}

The present invention relates to an electrostatic chuck and a method for manufacturing the same.

Electrostatic Chuck (ESC) is a key component that is placed inside the vacuum chamber of semiconductor and display manufacturing equipment to hold the substrate (silicon wafer) to the lower electrode using the power of static electricity.

The types of electrostatic chucks are classified according to the type of dielectric, and are broadly divided into three types: polyimide film, anodizing plate type, and ceramic type. Research on these various materials is continuously being conducted, and aluminum is generally used.

Semiconductor production processes can take place in extreme conditions, so there is a need to develop electrostatic chucks that can withstand extremely low (-100℃) and extremely high (+400℃) temperatures.

The coefficient of thermal expansion of aluminum is approximately 23.8 X 10 ⁶ /℃, which shows limitations in safely holding wafers in extreme environments due to thermal expansion. However, metal matrix composites (hereinafter referred to as 'MMC') materials have a low coefficient of thermal expansion of approximately 3 to 14 X 10 ⁶ /℃, and are attracting attention as a material that can replace aluminum.

MMC is a material that can obtain properties superior to those of individual constituent materials by artificially adding a second phase reinforcing agent to a metal matrix. It is widely applied not only in the semiconductor field but also in military equipment, electronic and electrical equipment, land transportation equipment, aerospace equipment, precision equipment, basic industries, and leisure products.

Currently, in the semiconductor component market, the limitations of the existing aluminum body electrostatic chuck are being felt, and development of an MMC body electrostatic chuck that can be used in extreme environments is in progress.

To manufacture an electrostatic chuck, a process of joining materials, such as joining aluminum to aluminum or MMC to MMC, is performed.

Joining techniques include brazing, including vacuum brazing, infrared welding using insert metal, friction welding, diffusion bonding, composite welding such as electron beam welding, and electric discharge welding.

The brazing process is mainly used for joining Al BODYs, and a welding agent is placed between a pair of Al BODYs, and they are fused at a temperature of around 600℃ in a vacuum chamber to produce a single parent material. This brazing joint has almost no restrictions on shape and size, allows for precise joining, and has the advantage of being able to simultaneously join multiple joints in one process at a relatively low joining temperature.

For brazing joints, a brazing filler metal (BFM) suitable for the base metal is selected and injected into the space between the base metals to be joined to form a welding joint.

There are many known technologies for joining processes between Al BODYs or for selecting brazing filler metals, making the joining process easy. However, for the joining process between MMC BODYs, there is no suitable brazing filler metal. Currently, joining technologies between MMC BODYs are hardly known, and applying the above-mentioned joining process between Al BODYs causes various problems.

For example, when applying the existing Al BODY bonding process and the brazing filler metal used at that time, the MMC BODY bonding is not easily formed because the brazing filler metal does not react even when the appropriate brazing bonding process is performed. In addition, the aluminum present in the MMC does not react at 660℃, which is the melting point of aluminum, but reacts at the melting point of the brazing filler metal, causing a problem in that the aluminum that has penetrated into the MMC base material is easily eluted out of the base material.

Due to these problems, the MMC BODY bonding process requires not only very delicate temperature control, but also the selection of an appropriate brazing filler metal. However, there is currently no suitable MMC bonding method, so research and development on this is urgently needed.

KR Publication Patent No. 10-2018-0017634 (2018.02.21) KR Publication Patent No. 10-2016-0126924 (2016.11.02)

The present invention can be applied to semiconductor manufacturing processes under extreme conditions, and research was conducted on bonding materials to enable the production of electrostatic chucks of all MMC BODY, all Al BODY, and all TiAl BODY.

Accordingly, by forming a metal layer on the joint surface where bonding is performed and performing brazing bonding by limiting the type of brazing filler metal, bonding of MMC, aluminum, and titanium-aluminum alloy materials that were difficult to bond in the past becomes possible.

The purpose of the present invention is to provide an electrostatic chuck and a method for manufacturing the same.

The present invention provides an electrostatic chuck including an upper body on which a substrate can be mounted; and a lower body brazed to the upper body and including a flow path through which a fluid for cooling the substrate can flow.

The above brazing joint is formed by forming a metal layer on each side of the upper body and the lower body, and forming a brazing filler metal between them to join them.

The base materials of the upper body and lower body are the same and are either metal matrix composites (MMC), titanium, or titanium-aluminum alloy.

The above metal layer is an aluminum deposition layer having a thickness of 1 ㎛ to 20 ㎛.

In addition, the present invention

Step of preparing the upper body and lower body;

A step of forming a metal layer on one side of the upper and lower bodies;

A step of arranging the upper and lower bodies on which the metal layers are formed so that the metal layers face each other and interposing a brazing filler metal between them; and

A method for manufacturing an electrostatic chuck is provided, including a step of brazing and joining the upper body and the lower body by performing a brazing joining process.

The electrostatic chuck according to the present invention can facilitate brazing joining of MMC, titanium, and titanium-aluminum alloy, which were difficult to join in the past, by selecting a metal layer and a brazing filler metal.

In particular, the above material can be applied to a semiconductor production process, can be applied in extreme conditions of extremely low or extremely high temperatures, and enables the production of electrostatic chucks of All MMC BODY, All Al BODY, and All TiAl BODY.

Figure 1 is a cross-sectional view for explaining the manufacture of the electrostatic chuck of the present invention.

The present invention discloses an electrostatic chuck and a method for manufacturing the same.

The electrostatic chuck comprises an upper body on which a substrate can be mounted; and a lower body brazed to the upper body and including a flow path through which a fluid for cooling the substrate can flow.

The substrate includes a substrate for forming a semiconductor or display product, and may include, for example, a silicon substrate or a glass substrate.

The manufacture of an electrostatic chuck according to the present invention follows the following steps.

Step a) preparing the upper body and lower body;

Step b) forming a metal layer on one side of the upper and lower bodies;

Step c) a step of arranging the upper and lower bodies on which the metal layers are formed so that the metal layers face each other and interposing a brazing filler metal between them; and

Step d) A step of brazing and joining the upper body and the lower body by performing a brazing joining process.

Each step is described below with reference to the drawings. Figure 1 is a cross-sectional view for explaining the manufacturing of the electrostatic chuck of the present invention.

(step a)

First, the method for manufacturing an electrostatic chuck according to the present invention prepares an upper body (10) and a lower body (20).

The upper body (10) has a flat substrate shape so that the substrate can be settled. In addition, the lower body can have a cooling path and a gas path built in through which a fluid for cooling the substrate can flow, and can further have a heat-conducting layer for heat conduction and a heater for controlling the substrate temperature. The electrostatic chuck having this structure can be square or circular when viewed from above, and can have various shapes as needed. The structure of the electrostatic chuck is not particularly limited in the present invention and can include a known structure.

The base material of the upper body (10) and the lower body (20) can be any of the metals, ceramics, and composite materials known to be used in electrostatic chucks. Among these, the present invention manufactures the upper body (10) and the lower body (20) using the same material.

In particular, the electrostatic chuck of the present invention can be applied to a semiconductor manufacturing process that can withstand extremely low temperature (-100℃) and extremely high temperature (+400℃) environments, and thus an electrostatic chuck of All MMC BODY, All Al BODY, and All TiAl BODY is manufactured using a material that can be applied even in such extreme environments, preferably one of MMC, titanium (Ti), or titanium aluminum (TiAl) alloy.

In this specification, 'All MMC BODY' means that the base material of the upper body (10) and the lower body (20) is made of MMC, 'All Al BODY' means that the base material of the upper body (10) and the lower body (20) is made of aluminum (Al), and 'All TiAl BODY' means that the base material of the upper body (10) and the lower body (20) is made of titanium aluminum (TiAl).

MMC refers to a matrix in which a reinforcing agent is dispersed and reinforced in the form of particles, whiskers, or fibers. The matrix and reinforcing agent are composed of a combination of metal and ceramic, and are a metal composite material in which a matrix such as Al, Ti, M, or Si is reinforced with at least one reinforcing agent selected from SiC, alumina, TiB ₂ , graphite, and boron (B) dispersed and reinforced in the form of particles, whiskers, or fibers. Among these, a composite material in which SiC is dispersed as a reinforcing agent in the matrix of Al has excellent low thermal expansion, high thermal conductivity, and heat dissipation properties along with the light weight of alumina.

According to one embodiment, the MMC is a cast type containing 30 to 40 vol% SiC and 60 to 70 vol% Al, and an infiltrated type containing 70 to 75 vol% SiC and 25 to 30 vol% Al, and for example, products such as SA301, SA401, SA701, and SA001 can be used.

SA301 SA401 SA701 SA001 Ceramic types SiC 30 vol% SiC 40 vol% SiC 70 vol% Si 75 vol% Type of metal Al 70 vol% Al 60 vol% Al 30 vol% Al 25 vol% Density (g/cm ³ ) 2.8 2.9 3.0 2.4 Flexural strength (MPa) - - 340 150 Young's modulus (GPa) 125 150 260 120 Poissonby(-) 0.29 0.29 0.20 0.29 Fracture toughness (MPa·m ^1/2 ) 15 14 8 3 Coefficient of thermal expansion (x10 ⁶ ) 14 13 7 9 Thermal Conductivity (W/m K) 150 155 160 120 Specific heat (J/g K) 0.8 0.9 0.6 0.9 Volume resistivity (Ω cm) - - 1 x 10 ^-5 4 x 10 ^-5 hardness HRB 90 HRB 93 HRB110

SA301 contains 30% SiC in 70% aluminum by volume, and SA401 contains 40% SiC in 60% aluminum by volume. These materials have a Young's modulus higher than cast iron at the same weight as aluminum, and enable the production of complex shapes in both small and large sizes. SA701 is a composite material infiltrated with 30% aluminum by volume into a SiC porous body (70% by volume). It has a Young's modulus 1.3 times that of stainless steel at the same weight as aluminum, and has excellent thermal properties. It is easier to manufacture than ceramics, and it increases fracture toughness by infiltrating metal, so it does not break, making it suitable as a body for an electrostatic chuck that can be used in extreme environments.

SA001 is a composite material that impregnates (fills together) 25 volume% aluminum into a Si porous body (75 volume%). It is lighter than aluminum, has rigidity equivalent to cast iron, and has low thermal expansion properties similar to ceramic materials.

Among them, the present invention may be SA701 in which 70 volume% of SiC is infiltrated into 30 volume% of Al.

According to another embodiment, the parent material of the upper body (10) and the lower body (20) may be titanium or a titanium-aluminum alloy material. These materials have less thermal deformation at low and high temperatures than aluminum, and have the advantage of being applicable in extreme environments.

The upper body (10) and the lower body (20) of the present invention are joined through brazing.

A typical brazing joint is formed by forming a brazing filler metal between an upper body (10) and a lower body (20) and then pressing at high temperature under vacuum conditions. This method can be performed smoothly when the bodies are made of aluminum, but in the case of materials such as MMC, titanium or titanium aluminum of the present invention, the joint itself is not performed, or aluminum is dissolved or the body, i.e., the base material, is deformed during the joining process.

Accordingly, the present invention solves the above problem by forming a metal layer on the joint surface (joint section, joint section, joint surface, etc.) where brazing is performed.

(step b)

According to one embodiment, the metal layer (11, 22) may be a layer made of aluminum. In a typical brazing joint, the joining is performed through melting of the base material and diffusion of the base material and brazing filler metal elements by the reaction between the brazing filler metal and the base material. At this time, an intermetallic compound may be generated between the base material and the brazing filler metal, which may reduce the joining strength. Accordingly, when the metal layers (11, 22) are formed, the direct reaction between the base material of the upper and lower bodies (10, 20) and the brazing filler metal (30) is suppressed, and the tensile and shear strengths at the joining surface are greatly improved due to the easy bonding between the metal layers (11, 22) and the brazing filler metal (30), and the joining strength is further improved.

According to one embodiment, the metal layer (11, 22) is formed to have a thickness of 1 ㎛ to 20 ㎛. If the thickness of the metal layer (11, 22) is less than the above range, the above problem cannot be solved, and if the thickness exceeds the above range, a problem of dissolution at the joint surface or a problem of reacting with the brazing filler metal (30) at the joint surface to generate an intermetallic compound, thereby lowering the joint strength, occurs. In addition, if a metal other than aluminum, such as Ti or Cu, is used as the material of the metal layer (11, 22), problems such as aluminum dissolution in the case of MMC and deformation of the base material due to high temperature in the case of titanium or titanium aluminum cannot be solved.

The formation of the metal layer (11, 22) can be accomplished by various methods, such as spraying, physical vapor deposition (PVD), chemical vapor deposition (CVD), and atomic layer chemical vapor deposition (ALD), but the physical vapor deposition method is used to form a uniform coating layer.

Physical vapor deposition is a method of deposition using vapor, and includes thermal deposition, electron beam deposition, E-beam deposition, laser deposition, arc ion plating, and sputtering processes. Among these, the sputtering process is used because it can obtain a high thin film density and a smooth, uniform coating layer.

The formation of the metal layer (11, 22) using the sputtering process is as follows: in the case of the Al metal layer, a base material having a purity of Al of 99.9% or higher is attached to the target in a DC magnetron configuration, and then the initial vacuum of the vacuum chamber is pumped to 10 ^-7 torr or higher, and then Ar gas is injected to form plasma. At this time, the Ar+ ions dissociated by the plasma are accelerated and collide with the Al target, and the Al particles that fall off are deposited on the base material. The thickness of the metal layer can be easily controlled through thin film monitoring during the sputtering process.

(step c)

The method for manufacturing an electrostatic chuck according to the present invention, as shown in Fig. 1, performs a step of arranging upper and lower bodies (10, 20) on which the metal layers (11, 22) are formed so that the metal layers (11, 22) face each other, and interposing a brazing filler metal (30) between them.

The formation area of the metal layer (11, 22) is formed over the entire surface of the joint surface joining the upper body (10) and the lower body (20). At this time, the form of the brazing joint formed on the joint surface includes a butt joint, a lap joint, a butt-lap or modification joint, etc.

By forming the above metal layers (11, 22), the selection of the brazing filler metal (30) is relatively more free because the metal layers (11, 22) are made of aluminum, and various types of applications are possible. However, since it must be usable in harsh environments such as extremely low or extremely high temperatures, the selection of the brazing filler metal (30) is also very important. In addition, the brazing filler metal (30) causes a change in the chemical composition at the joint surface, which lowers the joint strength of the joint and also adversely affects the strength and corrosion resistance of the base material.

Brazing filler metal (30) must be used for high-temperature brazing bonding for joining MMC, titanium or titanium-aluminum base materials. However, high-temperature brazing bonding has problems such as aluminum dissolution or deformation of the base material, so it is preferable to use an aluminum-based brazing filler metal (30) having a relatively lower melting point than SiC.

According to one embodiment, the brazing filler metal (30) of the present invention uses 4047 aluminum, or 4147 aluminum, which is one of the 4000 series aluminum alloys. The 4047 aluminum is represented as 4047 (BAISi-4) and is an aluminum alloy containing aluminum as the remainder, 11 to 13 wt% of silicon, 0.8 wt% or less of iron, 0.3 wt% or less of copper, 0.05 wt% or less of manganese, 0.05 wt% or less of magnesium, 0.1 wt% or less of zinc, 0.01 wt% or less of cadmium, 0.1 wt% or less of mercury, and 0.1 wt% or less of lead. The brazing filler metal has a melting point of 577°C to 582°C.

4147 Aluminum, denoted as 4047 (BAISi-9), is an aluminum alloy containing aluminum as the remainder, 11 to 13 wt% silicon, 0.8 wt% or less iron, 0.1 to 0.5 wt% magnesium, 0.25 wt% or less copper, 0.2 wt% or less zinc, 0.0003 wt% or less beryllium, and residual metals. The brazing filler metal has a melting point of 580°C to 600°C.

The brazing filler metal (30) of the present invention is easy to apply to the brazing joining process because it has a high silicon content, a low melting point, excellent melt fluidity, and the final product does not break, and has the characteristics of high wear resistance and heat resistance. The high silicon content improves fluidity with a smooth finish and reduced shrinkage during the welding process, enabling work in the harsh environment mentioned in the present invention.

In the case of the existing MMC, instead of reacting at 660℃, which is the melting point of aluminum, when heated to a temperature at the melting point level of the brazing filler metal (30), the aluminum manufactured by the infiltration method in the MMC is not only eluted out of the base metal, but also bonding between the MMC base metals does not occur. Accordingly, temperature control must be performed very delicately for MMC bonding, but even if temperature control is performed, bonding between the base metals does not occur. This can be resolved by selecting the brazing filler metal (30) along with the formation of the metal layers (11, 22) mentioned above.

In addition, since brazing can be performed at a lower temperature by selecting the metal layers (11, 22) and the brazing filler metal (30), the brazing temperature can be lowered from a high temperature of about 1000°C when the parent material is titanium or titanium aluminum. At this time, process stability can be secured by utilizing the vacuum degree and temperature rise curve.

The brazing filler metal (30) can be formed by applying the metal after preparing the molten solution, manufacturing it in the form of a brazing sheet, or forming the brazing filler metal by deposition and positioning it between the metal layers. At this time, the thickness of the application through the molten solution and the thickness of the brazing sheet can be 1 ㎛ to 100 ㎛. If the thickness is less than the above range, the bonding effect by the brazing filler metal cannot be expected, and if it is too thick, it can be dissolved from the base material during the bonding process.

(step d)

The manufacturing method of the present invention performs a step of brazing and joining the upper body (10) and the lower body (20) by performing a brazing joining process.

The brazing joint of the present invention uses a vacuum brazing joint process that brazes in a high vacuum atmosphere. The vacuum brazing has the advantages of having fewer defects in the joint, not requiring cleaning treatment to remove residues inside the joint, an attractive surface for the brazed product, and less deformation compared to other brazing methods.

Preferably, the brazing temperature is 570°C to 630°C for 5 to 20 minutes, considering the melting point of the brazing filler metal (30), and the pressure is in the range of 1.0Х10 ^-5 Torr to 5.0Х10 ^-5 Torr. The above brazing conditions are for obtaining the maximum shear strength at the joint, and if the temperature, time, and pressure are outside the above range, the joining of the upper body (10) and the lower body (20) may be difficult.

The upper body (10) and the lower body (20) are pressurized by a jig so that the brazing filler metal (30) is uniformly distributed on the metal layers (11, 22) while preventing them from leaking outward, thereby forming a strong joint.

Hereinafter, the present invention will be described in more detail by way of examples.

The embodiments according to this specification can be modified in many different forms, and the scope of this specification is not construed as being limited to the embodiments described below. The embodiments of this specification are provided to more completely explain this specification to a person having average knowledge in the art.

[Example]

The substrate made of MMC (SA701) material was processed into an upper part of 36 mm (width) X 40 mm (height) X 12 mm (thickness) and a lower part of 40 mm (width) X 40 mm (height) X 16 mm (thickness), and then milling was performed on the surface to have a consistent roughness. Then, the joint of the bonding material was degreased and pickled to ensure a clean state.

The upper and lower substrates were transferred to the deposition chamber, and a base material having a purity of 999% or higher was attached to the target. After pumping the initial vacuum of the vacuum chamber to 10 ^-7 torr or higher, Ar gas was injected to form an aluminum metal layer using the DC-magnetron sputtering method.

The upper and lower substrates were placed so that their metal layers faced each other, a brazing filler metal sheet was inserted therein, and then placed in a vacuum furnace (vacuum level 2X10 ^-5 torr or less) to perform a brazing bonding process at 600°C for 5 minutes.

[Test Example 1] Whether brazing is used

The bonding was evaluated by changing the materials of the upper substrate and lower substrate, metal layer, and brazing filler, and the results are shown in the table below. At this time, the thickness of the metal layer was 15 ㎛, and the thickness of the brazing filler metal layer was approximately 5 ㎛.

Substrate material Metal layer Brazing filler metal Whether or not it is joined MMC Al 4047 Aluminum O Ti 4047 Aluminum X - 4047 Aluminum X, eruption Al Aluminum (99% purity) X, eruption Titanium Al 4047 Aluminum O Ti 4047 Aluminum X - 4047 Aluminum X Ti Titanium X Titanium Aluminum Alloy Al 4047 Aluminum O Ti 4047 Aluminum X - 4047 Aluminum X Ti Titanium X

As can be seen from the table above, bonding is achieved or not achieved depending on the material of the metal layer. In the case of the MMC substrate, aluminum was dissolved from the MMC. In addition, it can be seen that bonding is not achieved even when the metal layer is formed with the same material, such as a titanium substrate-titanium metal layer.

[Test Example 2] Evaluation of bonding strength according to metal layer thickness

In order to evaluate the tensile properties of the joint, a 10 mm diameter round bar was processed using the wire cutting method, and the round bar was then processed into a tensile specimen according to the ASTM E8 standard, and a tensile test was performed using an Instron tensile tester.

Substrate material Metal layer thickness (㎛) Tensile strength (MPa) Yield strength (MPa) MMC 0.5 245 184 1.0 415 335 5.0 427 374 15.0 458 386 20.0 446 365 25.0 348 312

As can be seen from the table above, there are differences in tensile strength and yield strength depending on the thickness of the metal layer, and the tensile strength and yield strength show high values within a certain range, indicating that the bonding strength is excellent when the metal layer is formed within a certain thickness range. This trend was also shown in titanium and titanium-aluminum alloy as substrate materials.

10: Upper body 20: Lower body
11, 20: Metal layer 30: Brazing filler metal

Claims (4)

An upper body on which a substrate can be mounted; and
A lower body is brazed to the upper body and includes a flow path through which a fluid for cooling the substrate can flow;
The above brazing joint is an electrostatic chuck in which each metal layer is formed on one side of the upper body and the lower body, and a brazing filler metal is formed between them to form a bond. In the first paragraph,
The base material of the upper body and lower body is the same, and is one of metal matrix composites (MMC), titanium, or titanium-aluminum alloy. In the first paragraph,
An electrostatic chuck wherein the metal layer is an aluminum deposition layer having a thickness of 1 ㎛ to 20 ㎛. Step of preparing the upper body and lower body;
A step of forming a metal layer on one side of the upper and lower bodies;
A step of arranging the upper and lower bodies on which the metal layers are formed so that the metal layers face each other and interposing a brazing filler metal between them; and
A method for manufacturing an electrostatic chuck, comprising: a step of performing a brazing joining process to braze the upper body and the lower body.