Substrate holder for an electrostatic chuck

Abstract

The invention relates to a substrate holder (1) for an electrostatic chuck, comprising a ceramic plate (2) with a ceramic plate upper face (4) and a ceramic plate lower face (5), the ceramic plate upper face (4) being designed to hold a workpiece, and comprising a base (3) with a base upper face (6) and a base lower face (7), wherein the base upper face is provided at least partly as a support surface for connecting to the ceramic plate lower face, and the support surface is the plane which protrudes farthest in the direction of the ceramic plate. The substrate holder is characterized in that the base upper face (6) is connected, over the entire surface thereof, to the ceramic plate lower face (5) via a solder material (8) in the region of the support surface, and the base is produced from a refractory metal-based alloy.

Description

[0001] 1153 EP, 28.01.2026

[0002] Substrate holder for an electrostatic clamping device

[0003] The present invention relates to a substrate holder for an electrostatic clamping device, comprising a ceramic plate and a base plate, wherein the base plate is at least partially designed as a contact surface for connection with the ceramic plate 5, and the contact surface of the base plate is fully bonded to the ceramic plate via a solder material, and the base plate is made of a refractory metal-based alloy. The present invention further relates to the use of the substrate holder according to the invention for holding and processing semiconductor wafers, as well as to an electrostatic clamping device comprising the substrate holder according to the invention.

[0004] 10 An electrostatic chuck (also known as an electrostatic chuck or E-Chuck) uses the force of electrostatic attraction to securely hold, fix, position, and / or, if necessary, level workpieces, such as semiconductor wafers, on a ceramic surface during a high-precision manufacturing process, thus ensuring their stability. Such a chuck consists of several components, such as a dielectric layer (e.g., aluminum oxide) and an electrode layer (e.g., molybdenum, copper, or graphite), which together generate an electrostatic field to fix the workpiece on a ceramic surface without mechanical clamps or vacuum suction cups. E-Chucks are important components used in various industries, from semiconductor manufacturing to aerospace engineering, wherever precision manufacturing is required.

[0005] Patent application US 2021 / 0391153 describes a substrate processing device that also includes a platform for supporting a substrate / workpiece. The focus here is on the material selection of the platform's base (plate), which consists of two components. One component has a low coefficient of thermal expansion and high thermal conductivity, while the other component has a low density. The base (plate) thus consists, on the one hand, of a material with a density of 5.0 g / cm³. 3 or less (such as AI, Al alloy, titanium or titanium alloy) and on the other hand made of a material with a low coefficient of expansion of 5.0 *10 -6 1 / K or less (such as tungsten or molybdenum).

[0006] 30 Patent US 10,249,526 B2 describes an electrostatic clamping device consisting of a ceramic base body with a top and a bottom surface onto which a variety of objects can be attached by metallic bonding, soldering or other joining methods. Public1153 EP, 28.01.2026

[0007] 2

[0008] The component is attached to various points on the underside of the ceramic body. For example, an object (such as an adapter) can be made of molybdenum. A base plate on the underside of the ceramic body can be made of aluminum or steel. Preferably, a cooling plate or insulators are also present.

[0009] 5 Such multilayer structures can, for example, offer increased stability, improved dielectric properties or thermal resistance, but their manufacture is complex (which also leads to increased costs), maintenance and repair can be difficult, and thermal and / or mechanical stresses may occur between the materials.

[0010] 10 Although it is known to match the coefficients of thermal expansion between different materials, e.g., refractory metal(s) and ceramics, it remains difficult to provide substrate holders made of these materials that can be used at both low (e.g., temperatures of -50°C) and high process temperatures (e.g., temperatures above 400°C, max. 500°C), are resistant to thermal cycles with large temperature fluctuations (e.g., fluctuations between -100°C and +40°C), and exhibit low stresses in the ceramic or prevent cracking. Furthermore, the outgassing rate of the materials used should be low so that, in vacuum applications, purity, production quality, and process stability are not compromised, and thus the performance of the E-Chuck is not negatively affected.

[0011] The object of the present invention is to provide a substrate holder for an electrostatic clamping device which does not exhibit cracking in the ceramic and can be used over a large temperature range (~150°C or less to +500°C). At the same time, the substrate holder according to the invention is resistant to thermal cycles with large temperature fluctuations. The substrate holder according to the invention features a simple, solid connection between the base plate and the ceramic plate via a solder material, without the ceramic plate exhibiting cracks after soldering to the base plate, under thermal stress over a large temperature range, or under alternating thermal stress. Furthermore, the

[0012] 30 substrate holders according to the invention exhibit a low outgassing rate.

[0013] Public1153 EP, 28.01.2026

[0014] 3

[0015] The technical problem of the present invention is solved by the subject matter of claim 1. Advantageous embodiments of the invention can be found in the dependent claims, which are freely combinable with one another.

[0016] According to the present invention, a substrate holder for an electrostatic

[0017] 5. Clamping device comprising a ceramic plate with a ceramic plate top and a ceramic plate bottom, wherein the ceramic plate top is designed to hold a workpiece, and a base plate with a base plate top and a base plate bottom. The base plate top is designed, at least partially, as a bearing surface for connection with the ceramic plate bottom. The bearing surface 10 is a plane that projects furthest towards the ceramic plate; i.e., if the base plate has several protrusions or depressions, the bearing surface is the protrusion that projects furthest upwards and thus establishes the connection to the ceramic plate. The substrate holder is characterized in that the base plate top is fully bonded to the ceramic plate bottom in the area of ​​its bearing surface via a solder material, and the base plate is made of a refractory metal-based alloy.Thus, a substrate holder is provided that is suitable for use in an electrostatic clamping device, has better thermal conductivity and a low outgassing rate, and shows no cracking in the ceramic over a large temperature range or over a large temperature span, i.e., both at low and high temperatures, or strong 20 cyclic temperature fluctuations, and thus has high temperature resistance.

[0018] A ceramic is understood to be a class of inorganic, non-metallic materials that typically offer high heat resistance, low outgassing, high mechanical strength, and uniform holding force. They are inherently brittle. In the substrate holder according to the invention, the ceramic acts as a dielectric component, thus serving as an electrical insulator and, in combination with other materials, contributing to the storage of electrical energy.

[0019] In a further development according to the invention, the ceramic plate is free of built-in elements, i.e., there are no additional components or parts in the ceramic plate.

[0020] 30 installed. Installed elements / components can be, for example, cooling elements, heating elements, electrode films, etc. As already stated above, the ceramic is inherently brittle. Public1153 EP, 28.01.2026

[0021] 4

[0022] and prone to fractures and cracks, so such installation requires a complex procedure. Furthermore, integrating such elements into the ceramic slab can be very expensive.

[0023] In a further embodiment, the substrate holder according to the invention is thereby

[0024] 5 is characterized by the fact that the ceramic plate's surface is exposed and not covered or protected by other materials or layers. This means the ceramic plate is in direct contact with the environment or the workpiece. This offers advantages such as improved heat dissipation and direct electrostatic adhesion.

[0025] The solder material serves to bond the upper surface of the base plate to the underside of the ceramic plate in the area of ​​its contact surface, creating a material bond that is inseparable and permanent. This results in a high bond strength, high force transmission, and a high degree of sealing.

[0026] In a preferred embodiment, the solder material is an active solder suitable for joining 15 non-metallic materials (such as ceramics) with metallic materials.

[0027] This allows for direct soldering of the ceramic without the need for additional metallization. Active solders are metallic solders whose alloy composition enables them to wet non-metallic materials. They are based, for example, on silver, copper, titanium, zirconium, or hafnium, which react with the ceramic plate.

[0028] In a preferred embodiment, the solder material is a silver-, copper-, titanium-, or zirconium-based active solder. In particular, active solders made of titanium / silver, indium / copper / silver, silver / copper / indium / titanium, or titanium / copper / silver are used. Soldering is carried out, for example, under a protective gas atmosphere (e.g., argon, nitrogen, or mixtures thereof), under a hydrogen atmosphere, or in a vacuum.

[0029] The active solder can be applied to the base plate and / or the ceramic plate at room temperature as a foil, paste, or powder, particularly via cold gas spraying (CGS). If a solder foil is used, this foil can have a thickness between 10 and 300 µm.

[0030] Public1153 EP, 28.01.2026

[0031] 5

[0032] In a preferred embodiment, the active solder is applied to a uniform, smooth surface or contact area of ​​the base plate, which has been previously ground to a standard standard. This means that small depressions and / or peaks may still be present on the surface or contact area of ​​the base plate.

[0033] 5 A plumb line gap forms between the top of the base plate and the bottom of the ceramic plate.

[0034] In a preferred embodiment, this solder gap can be between 30 and 200 pm, preferably between 40 and 100 pm. Within this thickness range, the quality and durability of the solder joint are improved.

[0035] The bearing surface of the base plate's upper surface is the specific area on which the ceramic plate rests with its underside. This bearing surface is a plane that projects furthest towards the ceramic plate or its underside. For example, if the base plate has recesses or holes on its upper surface, the bearing surface may only comprise 50% of the base plate's total surface area. The bearing surface is preferably at least 70%, and more preferably at least 90%, of the

[0036] 15 Total surface area of ​​the base plate. A larger contact area ensures better stability.

[0037] In a preferred embodiment, the entire or nearly the entire upper surface of the base plate is designed as a bearing surface, i.e., the bearing surface comprises at least 99% of the total surface area of ​​the base plate. The base plate has no raised areas or depressions, but may have small holes.

[0038] 20 The term “fully bonded” means that the upper surface of the base plate is continuously bonded to the underside of the ceramic plate via the solder material in the area of ​​its contact surface, and in particular without interruptions or gaps in the solder material. Furthermore, the solder material is applied evenly and completely across the contact surface. The solder layer is preferably at least 92%, more preferably 95%, and particularly preferably 100% bonded in the area of ​​the contact / bonding surface (which connects the underside of the ceramic plate and the upper surface of the base plate). This can be verified, for example, by an ultrasound examination (C-scan). This ensures a virtually complete or complete, material-bonded, and uniform bond in the area of ​​the contact surface, which provides both mechanical stability and

[0039] 30 ensures thermal and electrical conductivity. Furthermore, the stress on the ceramic (at high temperatures or thermal cycles) is distributed evenly across the entire surface. Public1153 EP, 28.01.2026

[0040] 6

[0041] The contact area is distributed, which is particularly important to minimize material fatigue and thus extend the service life.

[0042] The base plate of the substrate holder is made of a refractory metal-based alloy. Refractory metal-based alloys are defined as alloys containing > 50 wt.%, preferably > 65 wt.%, of a refractory metal selected from groups 4, 5, and 6 of the periodic table. Molybdenum (Mo) and tungsten (W) are particularly commonly used. For example, a molybdenum-based alloy is defined as having a Mo content of > 50 wt.% Mo, particularly > 65 wt.% Mo. The same applies to a tungsten-based alloy. In another embodiment, the refractory metal-based alloy can also contain > 80 wt.% of the respective refractory metal. Preferably, the refractory metal-based alloy has a refractory metal content between > 50 wt.% and < 99.7 wt.% of the respective refractory metal.

[0043] In a preferred embodiment, the refractory metal-based alloy molybdenum alloy is a Mo-titanium (Ti) alloy with 25-38 wt.%, preferably 32-35 wt.% Ti, 15% balance molybdenum and unavoidable impurities.

[0044] The base plate preferably has a density of more than 97% of the relative density.

[0045] A density greater than 98% of the relative density is particularly advantageous. For example, if the base plate is made of a Mo-Ti alloy, it will have a density greater than 7 g / cm³. 3 preferably more than 7.24 g / cm³ 3 (i.e., >99% of the relative density).

[0046] 20. The relative density can be determined, for example, from a micrograph of the base plate. This involves analyzing the microstructure of the compound, with the relative density indicating the ratio of the measured density to the density of an ideal, pore-free material.

[0047] According to further training, the refractory metal-based alloy has a linear coefficient of thermal expansion (CTE) of over 5.5*10 -6 1 / K at room temperature. The maximum CTE is 9*10 -6 1 / K. The linear coefficient of thermal expansion is material-specific and temperature-dependent. It indicates how the refractory metal alloy changes its dimensions at specific temperatures. To achieve crack-free bonding between the base plate and the ceramic plate, it is important that the CTE value of both materials is identical or only slightly different over a wide temperature range. This means that the linear

[0048] Public1153 EP, 28.01.2026

[0049] 7

[0050] The coefficient of thermal expansion (CTE) of the ceramic plate in this embodiment has a similar value. This helps to avoid thermal stresses and potential cracks.

[0051] In a preferred embodiment, the ceramic is an oxide or nitride ceramic 5 or a carbide ceramic. For example, Al₂O₃ (aluminum oxide), ZrCh (zirconia), YSZ (yttrium-stabilized zirconia), SisN₄ (silicon nitride), AIN (aluminum nitride), or SiC (silicon carbide) can be used. Ceramic composites (consisting of a ceramic matrix reinforced with ceramic fibers or particles) are also suitable. In ceramic composites, the mechanical and thermal properties can be optimized.

[0052] 10 properties of the material have been improved, making it more resistant and versatile than conventional ceramics.

[0053] In the present invention, the workpiece, for example a semiconductor wafer, is placed on the top side of the ceramic plate.

[0054] In a preferred embodiment, the base plate is composed of at least two plates, both of which are made of a refractory metal-based alloy. However, the base plate can also have three, four, or more plates. Each individual plate in this assembly can be made of different or identical refractory metal-based alloys. The plates are joined by diffusion welding. If two plates are made of identical refractory metal-based alloys, the joining zone 20 or connection zone of the welded base plates has the same physical and mechanical properties as the base plate. In a preferred embodiment, at least two plates of the base plate are made of the same refractory metal-based alloy. Diffusion welding is a welding technique that allows the joining of the two refractory metal-based plates without the use of filler materials.

[0055] This allows, for example, the creation of internal structures (geometries) on the base plate. If plates are made of the same material type, the entire base plate will have the same properties. For instance, internal cooling channels can be easily created in the base plate. To achieve this, at least one plate is provided with depressions / protrusions before diffusion welding, so that internal channels are formed when it is joined to the second plate. However, it is also possible for both plates to have depressions and / or protrusions. In this case,

[0056] Public1153 EP, 28.01.2026

[0057] 8

[0058] Internal structures are also used during the welding of the plates. These internal structures can, for example, enable temperature control across the entire surface of the substrate holder. Furthermore, one or more plates may have bores that can serve, for example, as positioning pins for diffusion welding. These positioning pins keep the plates in the correct position while they are diffusion-welded under pressure and high temperature. In addition, such bores can also be used, for example, as gas or liquid conduits. Which of the aforementioned plates, which may have bores and / or recesses and / or protrusions, is subsequently soldered to the ceramic plate is

[0059] 10 application-dependent.

[0060] In another embodiment, one plate has recesses and a second plate has bores positioned above the recesses. This makes it possible, for example, for cooling channels to border directly on the top surface of the base plate, enabling effective cooling of the ceramic after the top surface of the base plate and the underside of the ceramic plate have been soldered together.

[0061] In diffusion welding, it is crucial that the surfaces to be welded are as flat and smooth as possible to ensure close contact between the surfaces to be welded, so that the contact allows the diffusion of atoms across the joining zone or connection zone.

[0062] 20 The base plate, or at least the two base plate plates of the present invention, are preferably manufactured by powder metallurgy via pressing, sintering, and / or hot isostatic pressing. This can be easily determined from the microstructure of the base plate, since the microstructure is fine-grained immediately after sintering. Powder metallurgy allows for the production of complex geometries with minimal material loss, resulting in a homogeneous composition as well as controlled porosity and density.

[0063] In particular, the substrate holder according to the invention is used for holding and processing a semiconductor wafer. A semiconductor wafer is a thin slice of a semiconductor material, such as silicon, which serves as the basis for the fabrication of integrated circuits.

[0064] 30 circuits and other microelectronic components. The semiconductor wafers are also used for solar cells or sensors. The use of the substrate holder according to the invention Public1153 EP, 28.01.2026

[0065] 9

[0066] enables safe transport between different process stations (without damaging the wafer), stable and precise positioning of the wafer during processing (which improves the accuracy and quality of the manufactured wafers), and efficient process control.

[0067] 5 The present invention further relates to an electrostatic clamping device comprising the substrate holder according to the invention, electrode(s), a voltage source and a control unit.

[0068] The electrode(s) is / are attached to or near the ceramic plate in such a way that an electric field is generated when an electric voltage is applied. This electric field causes an electrostatic attraction between the substrate holder and the workpiece placed on it.

[0069] The voltage source applies an electrical voltage to the electrodes, ensuring that the electric field remains stable and uniform.

[0070] The control unit regulates the applied voltage and thus the strength of the electrostatic attraction. This makes it possible to precisely control the clamping force.

[0071] In a preferred embodiment of the clamping device, the base plate incorporates a cooling system. This allows the temperature within the clamping device to be controlled and prevents overheating of the individual components. Effective heat dissipation, for example, enables a homogeneous temperature distribution across the entire substrate holder. A well-functioning cooling system allows the clamping device to operate under constant conditions, improving the precision and stability of the machining process. Furthermore, effective cooling extends the service life of the clamping device by reducing the thermal stress on the individual components.

[0072] Further advantages and expediencies of the invention will become apparent from the following description of an embodiment according to the invention and an embodiment not according to the invention, with reference to the accompanying figures.

[0073] The figures show

[0074] Fig. 1: schematic cross-section of a substrate holder according to the present invention;

[0075] Public1153 EP, 28.01.2026

[0076] 10

[0077] Fig. 2: Top side(s) of the ceramic plate(s) in the examples according to the invention;

[0078] Fig. 3 Diagram representation of the relative length change AL / Lo of a base plate (MoTi) and a ceramic plate (Al2O3) at different temperatures;

[0079] Fig. 4 Top side(s) of the ceramic plate(s) in the comparison examples;

[0080] Fig. 5 schematic cross-section of a substrate holder according to a further embodiment of the present invention;

[0081] Fig. 6 Microstructure of a diffusion-welded base plate (MoTi-MoTi) according to the invention in a light microscopic image at 100x magnification.

[0082] Fig. 7 shows a cross-section of a substrate holder according to the present invention in a light microscopic image at a magnification of 500x.

[0083] The invention is explained in more detail below by means of production examples and the accompanying figures:

[0084] 15

[0085] Examples (according to the invention):

[0086] In a first step, a molybdenum (Mo) powder with a particle size of approximately 4.5–5 pm (measured using a Fisher sub-sieve sizer) is mixed with a titanium (Ti) powder with an average particle size of <160 pm in a ratio of 31 wt.% Ti, 69 wt.% Mo until a homogeneous mixing degree of 20 is achieved. The powder mixture is then filled into a tube mold and cold isostatically pressed at a pressure of approximately 160 MPa. The resulting disc-shaped green body is then hot isostatically pressed (HIP) at 1000°C and a pressure of 100 MPa to form a base plate (sheet) with a diameter of approximately 380 mm. After this step, the base plate has a relative density of > 97%. Finally, in a first example, the base plate is soldered to an approximately 4 mm thick AbOs ceramic with a purity of 96%. In another example, the base plate is coated with approximately...4 mm thick AbOs ceramic with a purity of 99.99%. The solder used in both examples is an Ag-based active solder (for example, Ticusil® or Incusil® from Morgan Advanced Materials). In both cases, the solder is applied as a solder foil with a thickness of 100 µm. Soldering was carried out across the entire surface at a temperature between 750 and 950°C and a holding time between 15 and 30 minutes. Fig. 1.

[0087] Public1153 EP, 28.01.2026

[0088] 11

[0089] Figure 1 schematically shows the cross-section of the substrate holder (1) according to the invention. The ceramic plate (2) has a ceramic plate top (4) and a ceramic plate bottom (5), wherein the ceramic plate top (4) is designed as a holding surface for a workpiece (e.g., silicon wafer). The base plate (3) has a base plate top (6) and a

[0090] 5 Base plate underside (7). The base plate topside (6) is fully bonded to the ceramic plate underside (5) via a solder material (8) to obtain the substrate holder according to the invention.

[0091] Figures 2A and 2B show the respective ceramic plate top surface of the substrate holders according to the invention directly after soldering. Fig. 2A: substrate holder according to the invention after dye penetrant testing, wherein the ceramic has a purity of 96%; Fig. 2B: substrate holder according to the invention after dye penetrant testing, in which the ceramic has a purity of 99.99%. To better visualize any irregularities, e.g., cracks or defects, in the ceramic plate, a dye penetrant test (also called a dye test or dye penetration test) was performed. In this test, a liquid dye penetrant is applied to the surface of the substrate holder 15 (i.e., to the ceramic plate) and left to act for a certain period of time. The excess dye penetrant is then removed, and a developer is applied, which makes the cracks or defects visible. The images in Figures 2A and 2B were taken under UV light.

[0092] Figure 2C shows the bond quality, i.e., the connection of the ceramic plate to the base plate, for a ceramic with 96% purity, and Figure 2D shows the bond quality for a ceramic with 99.99% purity. Both figures were obtained via a C-scan or contour scan (ultrasonic testing), without having to destroy the substrate holder for this test. In this ultrasonic test, imaging is achieved by sending and receiving ultrasonic pulses, whereby reflected echoes are analyzed and converted into an image (here, the connection between the ceramic plate and the base plate). This allows conclusions to be drawn about the quality and integrity of the solder joint. If no signal (0%) or a very low signal is reflected, this indicates a good bond. Figures 2C and 2D show the results of this test. No defects in the bond between the ceramic plate and the base plate could be detected in either sample.There is a full-surface and homogeneous 30 connection between the ceramic plate and the base plate.

[0093] Public1153 EP, 28.01.2026

[0094] 12

[0095] In summary, the substrate holders according to the invention exhibit a crack-free ceramic surface after soldering. The bond between the ceramic and the base plate after soldering is homogeneous and defect-free when tested ultrasonically. The substrate holders according to the invention exhibit both the required gas tightness and good thermal conductivity. Simultaneously, they demonstrate good resistance to thermal cycling and high process temperatures.

[0096] Figure 3 shows, as an example, the relative change in length dL / Lo of an unsoldered MoTi plate (gray line) and an unsoldered AhOs plate (black line) at different temperatures. Here, Lo is the original length and dL is the change in length of the material due to the temperature change. The diagram shows that the relative change in length of the two materials is largely identical between room temperature and a temperature of 1000°C.

[0097] Examples for comparison:

[0098] In the comparative example, the base plate was manufactured from a pure refractory metal, in this case, a molybdenum (Mo) powder with a particle size of approximately 4.5–5 pm (measured using a Fisher sub-sieve sizer). The Mo powder has a Mo content of 99.97 wt.%, the remainder being unavoidable impurities. The powder is filled into a tube mold and cold isostatically pressed at a pressure of approximately 160 MPa. The resulting cuboid green body is then sintered at 2000°C and subsequently rolled into a sheet. A round base plate with a diameter of approximately 380 mm is then cut from the rolled sheet. After this step, the 20-gauge base plate has a relative density of > 99.9%. In a further comparative example, the base plate is then brazed to an approximately 4 mm thick Al₂O₃ ceramic with a purity of 96%. In another comparative example, the base plate is coated with an approximately...The components are bonded to 4 mm thick AhOs ceramic with a purity of 99.6%. The solder used is an Ag-based active solder (for example, Ticusil® or Incusil® from Morgan Advanced Materials). In both cases, the solder is applied as a 100 µm thick foil. Soldering was performed across the entire surface.

[0099] Figures 4A and 4B show the surface of the ceramic plate of the substrate holders, which are not according to the invention, directly after soldering. Fig. 4A: substrate holder not according to the invention after dye penetrant testing, wherein the ceramic has a purity of 96%; Fig. 4B: substrate holder not according to the invention after dye penetrant testing, in which the ceramic has a purity of 99.6%. To better visualize any irregularities, e.g. cracks or Public1153 EP, 28.01.2026

[0100] 13

[0101] Defects in the ceramic plate were detected using a dye penetrant test (also called dye penetration test). In this test, a liquid dye penetrant is applied to the surface (ceramic plate) of the substrate holder and left to act for a certain period of time. Afterwards, the excess dye penetrant is removed, and a developer is applied, which makes the cracks or defects visible. The two images above were taken under UV light.

[0102] Figure 4C shows the bond quality, i.e., the adhesion of the ceramic plate to the base plate, for a ceramic with 96% purity. As mentioned above (in the example according to the invention), a C-scan (ultrasonic testing) was performed. Figure 4C shows that most of the bonding surface is reflected at approximately 40-50% (see 10 light gray areas), and some portions of the bonding surface are even reflected at 100% (see dark areas). This corresponds to an average bond with some areas already exhibiting poor adhesion. Figure 4D shows the bond quality for a ceramic with 99.6% purity. In the C-scan, most of the bonding surface is reflected at 100% (see dark areas). Only a small portion of the bonding surface is reflected at approximately 40-50% (see light gray areas). This corresponds to a rather poor bond to the ceramic plate.4C and 4D cause the cracks to scatter the ultrasonic pulses, and consequently the bonding in the area of ​​the cracks cannot be assessed.

[0103] In Figures 4A and 4B, cracks are clearly visible in the surface of the ceramic after soldering. The bond between the ceramic and the base plate after the full-surface soldering 20 is moderate to poor.

[0104] It is evident here that the base material is a crucial component of the substrate holder according to the invention.

[0105] Fig. 5 schematically shows a further embodiment of the substrate holder according to the invention in cross-section. In this embodiment, the substrate holder (1) according to the invention comprises a ceramic plate (2) with a top surface (4) and a bottom surface (5), wherein the top surface (4) is designed as a holding surface for a workpiece (e.g., silicon wafer). The base plate (3) is made up of two refractory metal-based plates (3A, 3B) which are joined by diffusion welding (the joining zone is indicated by the dashed black line in the figure (10)). One of the refractory metal-based plates (3A) 30 has recesses so that, when welded to the second refractory metal-based plate (3B), internal structures (9), e.g., channels, are formed between the refractory metal-based plates.

[0106] 14

[0107] Plates (3A, 3B) are formed. After diffusion welding, the base plate has a top surface (6) and a bottom surface (7). The top surface (6) of the base plate is fully bonded to the bottom surface (5) of the ceramic plate via a solder material (8). The channels (9) can, for example, be used as coolant channels. Advantageously, the two refractory metal-based plates (3A, 3B) of the base plate are thus joined without additive materials (such as adhesion promoters). The embodiment described here is only exemplary and is in no way intended to restrict the number or shape of the coolant channels.

[0108] Fig. 6 shows a light microscopic image of the base plate in the area of ​​the

[0109] 10. Diffusion welding. In this example, both refractory metal-based plates that form the base plate are made of the same material. The bonding zone between the two plates is indicated by the lateral arrows. No transition zone is visible. Thus, a metallurgical bond is present after diffusion welding; that is, the base plate exhibits the same physical and mechanical properties as the two refractory metal-based plates.

[0110] Fig. 7 shows a cross-section of the substrate holder according to the invention in a light microscopic image at 500x magnification. The ceramic plate is Al₂O₃ with a purity of 99.99%, the solder layer is Ticusil®, and the base plate is a molybdenum-based alloy. The ceramic plate (A) is fully bonded to the base plate (B) via the solder material 20 (C).

[0111] Public

Claims

1153 EP, 28.01.2026 15 REQUIREMENTS 1. A substrate holder (1) for an electrostatic clamping device comprising a ceramic plate (2) with a ceramic plate top (4) and a ceramic plate bottom (5), wherein the ceramic plate top (4) is designed to hold a workpiece, and a base plate (3) with a base plate top (6) and a base plate bottom (7), wherein the base plate top is formed at least partially as a bearing surface for connection with the ceramic plate bottom, and the bearing surface is a plane that projects furthest towards the ceramic plate, characterized in that the base plate top (6) is fully connected to the ceramic plate bottom (5) in the area of ​​its bearing surface via a solder material (8), and the base plate is made of a refractory metal-based alloy.

2. Substrate holder according to claim 1, characterized in that the entire upper surface of the base plate is designed as a bearing surface.

3. Substrate holder according to claim 1 or claim 2, characterized in that the ceramic plate (2) is free of built-in elements.

4. Substrate holder according to one of the preceding claims, characterized in that the ceramic plate top surface (4) is exposed.

5. Substrate holder according to any one of the preceding claims, characterized in that the solder material (8) is a silver-, copper-, titanium- or zirconium-based active solder.

6. Substrate holder according to any one of the preceding claims, characterized in that the refractory metal-based alloy is a tungsten-based or a molybdenum-based alloy.

7. Substrate holder according to one of the preceding claims, characterized in that the refractory metal-based alloy has a linear coefficient of thermal expansion of over 5.5*10-6 1 / K at room temperature.

8. Substrate holder according to one of the preceding claims, characterized in that the Mo-based alloy is a molybdenum-titanium alloy. 1153 EP, 28.01.2026 16 9. Substrate holder according to one of the preceding claims, characterized in that the ceramic plate is made of an inorganic, non-metallic material selected from the group consisting of oxide ceramics, nitride ceramics, carbide ceramics or ceramic fiber composites.

10. Substrate holder according to one of the preceding claims, characterized in that the base plate is constructed from at least two diffusion-welded refractory metal-based plates.

11. Substrate holder according to claim 10, characterized in that at least two plates of the base plate are made of the same refractory metal-based alloy.

12. Substrate holder according to one of the preceding claims, characterized in that the base plate has an internal structure.

13. Substrate holder according to one of the preceding claims, characterized in that the base plate or the at least two plates of the base plate are manufactured by powder metallurgy via pressing, sintering and / or hot isostatic pressing.

14. Use of the substrate holder according to any one of claims 1 to 13 in an electrostatic clamping device for holding and processing a semiconductor wafer.

15. Electrostatic clamping device, comprising: a substrate holder according to any one of claims 1 to 13, Electrode(s) for generating an electrostatic field, a voltage source to apply an electrical voltage to the electrode(s), a control unit to monitor and regulate the voltage.

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