Electrostatic chuck and related methods and structures

Abstract

Electrostatic chucks that are useful for supporting a workpiece during processing of the workpiece, and electrostatic chuck base components fabricated by additive manufacturing techniques, are described.

Description

[Technical Field]

[0001] The present disclosure relates to the field of electrostatic chuck base components useful for supporting a workpiece during workpiece processing steps, the base component ("base") being fabricated to include flow channels that have improved effectiveness in cooling the supported workpiece. [Background technology]

[0002] Electronic chucks (also simply referred to as "chucks") are used in semiconductor and microelectronic device processing. The chuck holds a workpiece, such as a semiconductor wafer or a microelectronic device substrate, in place to perform a process on the surface of the workpiece. Electrostatic chucks support and secure the workpiece on the upper surface of the chuck by creating an electrostatic attraction between the workpiece and the chuck. An electrostatic attraction between the workpiece and the chuck is created by applying a voltage to electrodes contained within the chuck to induce charges of opposite polarities on the workpiece and the chuck.

[0003] Chucks include various structures, devices, and designs that enable or improve the performance of the chuck. A typical electrostatic chuck assembly is a multi-part structure that includes a flat upper surface that supports a workpiece, electrical components such as electrodes, conductive coatings, and ground connections for controlling the electrostatic charge on the chuck and the supported workpiece, one or more cooling systems for controlling the temperature of the chuck, the supported workpiece, or both, various other components that may include measurement probes, sensors, and movable pins adapted to support or change the position of the workpiece relative to the chuck, and cooling and electrical connections for coupling the chuck to a tool interface.

[0004] A typical feature of an electrostatic chuck is a base that includes a cooling system made up of a pattern of internal channels or passages formed in the body of the chuck. The channels are used to pass a flow of cooling fluid (e.g., gas, water, or another liquid) through the interior of the chuck to remove heat from the chuck and control the temperature of the chuck and the workpiece supported by the chuck. Processing the workpiece can cause the temperature of the chuck to increase. By passing the cooling fluid through the chuck, heat is removed from the chuck and the temperature of the workpiece is controlled. The arrangement and distribution of the channels within the base will affect the location and uniformity of heat removal from the base and the supported substrate.

[0005] Desirably, the base can be designed to provide a uniform cooling effect over the area of the base to the greatest extent possible, however, the design of the cooling channels is limited by the materials previously used to form the base structure (e.g., hard metals and ceramic materials) and the current technology available for forming the base from current base materials.

[0006] The base of an electrostatic chuck assembly must be made from a high-hardness, high-strength solid material that can be machined to form structures with very precise features such as dimensions, flatness, surface roughness, cooling channels, and openings. Current materials used to manufacture the base of an electrostatic chuck include aluminum and other metals or ceramics that can be formed into precision base structures by machining techniques. Besides alumina, these materials can exhibit high hardness properties that make them difficult and expensive to manufacture using high-precision machining techniques.

[0007] Current methods form two opposing components by machining them into separate pieces (e.g., an upper and lower piece) to form a base containing internal cooling channels, and the two separately formed pieces are then joined together, typically by a vacuum brazing or electron beam welding process.

[0008] Vacuum brazing is a specialized process used in the aerospace industry that can be expensive and not readily available. Vacuum brazing involves forming a joint between two opposing surfaces by using a furnace to melt a "filler material" placed between the two surfaces and allowing the molten filler material to solidify to form a joint or vacuum brazed joint. The filler material may be a material that melts at a temperature lower than the melting temperature of the two parts being joined. The joint formed by the "filler" material is typically visible in the final vacuum brazed base structure. Overall, the formation of two separate parts, each through complex machining steps, combined with the subsequent vacuum brazing process, results in high material and processing costs and potentially very long manufacturing lead times.

[0009] An alternative process uses preformed tubes as cooling channels and then casts material over the tubes to form the base.

[0010] The cost and difficulty of fabricating the base may encourage the use of different, more desirable materials for use as the electrostatic chuck base. Desirable materials may include high hardness materials, such as ceramics and various metal alloys, such as titanium alloys. While these materials are desirable for use in the base because of their extreme hardness, they are also very difficult to process by machining. Other desirable materials may include materials with relatively low thermal expansion coefficients, such as those similar to that of the ceramic layers of the chuck assembly. Summary of the Invention

[0011] In one aspect, the present disclosure relates to an electrostatic chuck base. The base includes an upper base surface, a lower base surface, an inner portion between the upper base surface and the lower base surface, and a flow path within the inner portion. The flow path includes an inlet at the surface of the chuck base, an outlet at the surface of the chuck base, a length between the inlet and the outlet, and a cross-section along the configured length. The cross-section includes one of various cross-sectional areas along the length, various cross-sectional shapes along the length, or various distances from the upper surface, the lower surface, or both along the length.

[0012] In another aspect, the present disclosure relates to a method of fabricating an electrostatic chuck base as described by an additive manufacturing method. The method includes forming a first feedstock layer on a surface, the first feedstock layer including inorganic particles; forming solidified feedstock from the first feedstock layer; forming a second feedstock layer on the first feedstock layer, the second feedstock layer including inorganic particles; and forming second solidified feedstock from the second feedstock layer, wherein the solidified feedstock layers are part of a multi-layer composite electrostatic chuck base.

[0013] In another aspect, the present disclosure relates to a method of forming an electrostatic chuck base as described by an additive manufacturing method. The method includes forming a lower base portion including a bottom surface by additive manufacturing; forming an intermediate base portion including a flow path on the lower base portion by additive manufacturing; and forming an upper base portion including an upper surface on the intermediate base portion by additive manufacturing.

[0014] Refer to the drawings that form a part of the present disclosure and illustrate embodiments in which the materials and methods described herein are practicable.

Brief Description of the Drawings

[0015] [Figure 1] A side view of an electrostatic chuck assembly as described. [Figure 2A] A top view of the base as described. [Figure 2B] It is a side cutaway view of the base as described. [Figure 2C] It is a side cutaway view of the base as described. [Figure 3A] It is a side cutaway view of the base as described. [Figure 3B] It is a side cutaway view of the base as described. [Figure 4] It is a top cutaway view of the base as described. [Figure 5] It is a perspective cutaway view of the base as described. [Figure 6] It is a top cutaway view of the base as described. [Figure 7] It is a top cutaway view of the base as described. [Figure 8] It is a diagram showing the steps of the exemplary method as described. [Figure 9] It is a diagram showing the steps of the exemplary method as described.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The drawings are schematic and exemplary and not necessarily to scale.

[0017] The following description relates to a base structure useful in an electrostatic chuck. The base includes a pattern of flow channels distributed throughout the interior of the base, and this pattern can be used to control the temperature of the base by flowing a fluid through the flow channels during use.

[0018] The base includes an upper base surface, a lower base surface, and an interior portion between the upper and lower surfaces. The upper and lower surfaces are considered to extend over a region defined in the "x direction" and "y direction". The distance between the upper and lower surfaces is referred to as the thickness of the base in the "z direction".

[0019] The base includes a channel extending along a length through the interior of the base. The base includes an inlet to the channel at a surface of the base, an outlet for the channel at a surface of the base, a length of the channel between the inlet and outlet, and a cross-sectional shape and area everywhere along the length. The term "channel" refers to a single channel, or a portion or segment of a channel. The term "channel" may be used to refer to multiple channels, or different portions or segments of a single channel that span a substantial area of the base. In some examples, the length of the channel between the inlet and outlet may be referred to as a single channel.

[0020] According to a conventional base structure, the base includes a flow passage extending through the interior of the base through which a fluid can flow during use of the base as a component of an electrostatic chuck. The fluid can be any fluid, either a gas or a liquid, and can be flowed through the flow passage for any purpose. One purpose is to control the temperature of the base, the electrostatic chuck, and the workpiece supported by the chuck. Typically, the fluid flowing through the flow passage is a cooling fluid, such as water, and for this reason, the flow passage may be referred to as a "cooling flow passage." The cooling flow passage can be useful for flowing different types of fluids, such as a purge gas, which is effective for removing the cooling fluid from the flow passage and for drying the flow passage.

[0021] In conventional base designs, the flow channels in the base (sometimes referred to as "cooling channels") are designed to have a uniform cross-sectional configuration everywhere along the length of the channel, including a uniform cross-sectional shape and a uniform cross-sectional area. Also, according to conventional base construction, the cooling channels are located at a uniform position, e.g., depth, within the base (in the "z-direction" along the thickness of the base); that is, conventional channels are located at a distance from the upper surface that is a distance along the entire length of the channel (between the inlet and outlet) and a distance from the lower surface that is a distance along the entire length of the channel (between the inlet and outlet).

[0022] Compared to such conventional base structures, the cooling channels of the base structure herein have non-uniform physical characteristics, such as cross-sectional profile and positioning within the base thickness, which improves base cooling efficiency, base cooling uniformity, or both.

[0023] To improve the efficiency or uniformity with which the cooling channels function, the channels can be formed within the base to include physical features that vary along their length. The channels can exhibit one or a combination of varying (non-uniform) cross-sectional areas along their length, varying (non-uniform) cross-sectional shapes along their length, or varying (non-uniform) locations within the base along their length, i.e., varying distances from the upper or lower surface. In an exemplary base structure, the cooling channels can be formed as a pattern of channels designed to improve the efficiency and uniformity of heat transfer for a particular workpiece that may be supported by the base assembly and for the non-uniform characteristics of the particular workpiece. This feature, sometimes referred to as “conformal cooling,” allows for a pattern of channels within the base to be designed and formed in a specific design to match the specific heat removal requirements of a workpiece (e.g., a semiconductor or microelectronic device or wafer) that will be supported by the electrostatic chuck assembly during use.

[0024] Changing the size, shape, or location characteristics of the flow path openings within the base can enable improved control of the temperature across the base area. While used to cool a substrate supported by the chuck, various factors can result in non-uniform heat transfer on the upper surface of the chuck or non-uniform temperature in local regions of the upper surface of the chuck. As an example, the heat transfer effect is different at the edges of the chuck, e.g., at the outer periphery of the chuck, compared to non-edge portions of the chuck. By being able to escape heat energy laterally from the chuck at the edges, a temperature drop occurs on the surface of the chuck along the edges. To correct for the edge effect, i.e., to prevent the temperature drop on the upper surface of the chuck near the edges, the cooling flow paths near the edges (i.e., a portion of the flow paths close to the edges) can be located closer to the upper surface of the chuck (i.e., may be at a reduced depth) compared to the cooling flow paths at locations that are not the edges.

[0025] As a separate effect, the cooling flow paths define an enclosed "cooling loop" that starts at an inlet, extends along the entire length of the cooling flow paths within the chuck, and ends when the cooling fluid exits the chuck at an outlet. The cooling fluid enters the cooling loop having the lowest temperature that occurs at the inlet. As the fluid passes through the flow paths, the fluid becomes laden with heat energy, the temperature of the fluid rises, and the initial portion of the cooling loop is the colder portion having a lower cooling fluid temperature. In the later portion of the flow paths closer to the outlet (the warmer portion), the temperature of the fluid rises and the fluid has a reduced capacity to remove heat from the chuck. The higher temperature on the chuck surface will occur in the warmer portion of the cooling loop closer to the outlet because the cooling fluid has a higher temperature.

[0026] To prevent this type of temperature rise on the chuck surface and non-uniform temperature on the chuck surface, the cooling channels can be positioned in the z-direction at a location closer to the upper surface of the chuck in the (warmer) portion of the length of the channel compared to the initial (cooler) portion of the cooling loop. By arranging the channels and the cooling fluid closer to the upper surface, it becomes possible to improve the heat transfer from the surface of the warmer portion of the cooling loop, which has a higher temperature, to the fluid.

[0027] Generally speaking, the distance of the cooling channel from the upper surface of the chuck (i.e., the position of the channel in the z-direction, or "depth") can be selected to affect the desired heat transfer between the cooling fluid and a location on the chuck surface. This distance or depth can be measured in a direction perpendicular to the upper surface, between the upper surface of the base and the location of the channel closest to the upper surface. Generally speaking, to increase the amount of heat transfer between the cooling fluid and the base surface, the channel can be positioned relatively close to the upper base surface (in the z-direction with a reduced depth). To reduce the amount of heat transfer between the cooling fluid and a local area of the base surface, the channel can be positioned relatively far from the upper base surface (in the z-direction with a larger depth). The depth of the channel along the length of the channel can vary stepwise or non-stepwise at any rate along the length of the channel.

[0028] As a different way of affecting the rate or amount of heat transfer between the cooling fluid and the chuck surface, the cross-sectional area of the cooling fluid can be adapted to be arranged at locations on the chuck surface that require a larger volume of the cooling fluid for a larger amount of heat removal. Generally speaking, to increase the amount of heat transfer between the cooling fluid and a local area of the chuck surface, the cross-sectional area of the cooling channel can be increased. To reduce the amount of heat transfer between the cooling fluid and a local area of the chuck surface, the cross-sectional area of the cooling channel can be reduced. The change in the cross-sectional area of the channel can be brought about as a stepwise change, such as a stepwise increase in the diameter that tapers, or in the form of a relatively abrupt change, such as an orifice with a smaller diameter located between two portions of the channel having the same diameter.

[0029] In a different example of improving temperature non-uniformities in the upper surface of the base during use, the cooling channel system of the base may include a main channel (the "primary channel") and side channels (the "secondary" channel, the "supply" channel, and the "connecting" channel) that connect two other channel portions and allow cooling fluid to flow between the two channel portions. The secondary channels may be characterized as having a smaller cross-sectional area relative to the main channel and providing a relatively short length of channel connecting one main channel to the next. By way of example, different portions of the channel system within the base will contain cooling fluid at higher temperatures (warmer portions) and lower temperatures (cooler portions).

[0030] To improve temperature non-uniformity in different portions of the flow path system, a portion of the cooling fluid flow from a cooler portion of the flow path may be diverted from the cooler portion of the flow path to add to a portion of the cooling fluid flow in the warmer portion. The diverted flow may flow from a main flow path, which is a cooler portion having the cross-sectional area of the main flow path, to a different main flow path, which is a warmer portion also having the cross-sectional area of the main flow path. The diverted flow may pass from the cooler portion to the warmer portion through a side flow path connecting the two portions, where the side flow path has a reduced cross-sectional area relative to the two main flow paths (each having a larger cross-sectional area). The reduced cross-sectional area of the side flow path would be sized to provide a flow rate from the cooler flow path portion to the warmer flow path portion, thereby resulting in a desired reduction in the temperature of the cooling fluid flow in the warmer portion.

[0031] As yet another different design feature, a portion of the cooling flow path may pass across or under different portions of the cooling flow path, and the two flow paths are at different depths (in the z-direction) within the thickness of the base and are located at the same x and y locations relative to a region of the base surface. For some designs, crossing one flow path into a different flow path can be useful in creating a flow path pattern that improves the distribution of the cooler and warmer sections of the cooling loop.

[0032] For example, some flow path designs divide the base into a left and a right half, each half including a closed-loop flow path, and the two flow paths start at a single inlet and end at a single outlet. In this type of two-flow-path system, each flow path helps to cool approximately one-half of the base, and the cross-shaped flow path portion allows the cooling fluid on both sides (the two halves) of the base to flow through the flow path portion at the edge of the base before flowing through the flow path portion at the non-edge portion of the base. See the description of FIG. 7 below.

[0033] The electrostatic chuck as described is a multi-piece (or "multiple-component") structure that includes a plurality of separately fabricated or individually fabricated parts (components) assembled in layers to form an electrostatic chuck assembly. The assembly includes various structures and features that are specific to the electrostatic chuck assembly and that enable the electrostatic attraction to hold the workpiece in place on the upper surface of the chuck (referred to as the "workpiece contact surface") and allow the chuck to support the workpiece (e.g., a semiconductor substrate, a microelectronic device, a semiconductor wafer, a precursor thereof) during processing. Examples of workpieces used with electrostatic chucks include semiconductor wafers, flat screen displays, solar cells, reticles, and photomasks. The workpiece can have an area of a circular wafer with a diameter of 100 millimeters, 200 millimeters, 300 millimeters, or 450 millimeters or more.

[0034] The chuck includes an upper "workpiece contact surface" adapted to support a workpiece during processing. The upper surface typically has a circular surface area with a circular edge that defines the periphery of both the workpiece contact surface and the multilayer chuck. As used herein, the term "workpiece contact surface" refers to the upper exposed surface of the electrostatic chuck that contacts the workpiece during use and includes a "primary field" made of a ceramic material, typically with embossments on the upper surface, and an optional conductive coating that may cover at least a portion of the upper surface. The workpiece is held at the workpiece contact surface above the upper surface of the ceramic material, in contact with the embossed upper surface, and is held or "clamped" against the electrostatic chuck during use. Exemplary electrostatic chuck assemblies can be used in AC and DC Coulomb-type chucks and Johnsen-Rahbek-type chucks.

[0035] The chuck assembly (or simply "chuck") also includes several other layers, devices, structures, and features that are required or optional for the chuck to function. These may include an electrode layer that generates an electrostatic attraction between the chuck and the workpiece to hold the workpiece in place during processing, a grounding device such as a grounding layer and associated electrical connections, measurement devices for measuring pressure, temperature, or electrical properties during the processing process, gas flow conduits (cooling channels) as part of the temperature control function, a backside gas flow function for gas flow and pressure control between the workpiece contact surface and the workpiece, and a conductive surface coating.

[0036] One layer of a typical chuck assembly is a ceramic layer (also known as a dielectric layer) at the top of the assembly. The ceramic layer may be the topmost layer of the assembly and may include the upper surface of the chuck other than a conductive coating or an emboss that can be disposed on the upper surface of the ceramic layer. The conductive coating on the upper surface may be connected to electrical ground through a ground layer or a ground pin also included in the chuck assembly. The ceramic layer may be made of useful ceramic materials such as, among others, alumina, aluminum nitride, quartz, SiO2 (glass). The ceramic layer may be made of a single (integral) layer of material or, if necessary, may be made of two or more different materials, for example, multiple layers of different materials. The total thickness of the ceramic layer (having one or more layers of ceramic material) may be any effective thickness, for example, a thickness in the range of 1 to 10 millimeters, for example, 1 to 5 millimeters.

[0037] The ceramic layer is supported below by a base layer (abbreviated as "base") as described herein that can be made of metals such as, among others, aluminum, aluminum alloy, titanium, titanium alloy, stainless steel, metal matrix composites as described herein.

[0038] Typically, between the ceramic layer and the base, there is one or more of a bonding layer (e.g., a polymer adhesive), an electrode, a ground layer, an insulating layer that enables the electrodes and other layers to function electrically, or an additional circuit.

[0039] An example of a useful chuck assembly is shown in FIG. 1. The chuck assembly 10 includes a base 12, a ceramic layer (assembly) 14, and a bonding layer 16 that bonds the base 12 to the ceramic layer 14. The ceramic layer 14 includes subcomponents such as electrodes (not specifically shown). The upper surface of the ceramic layer 14 has a pattern of embossments 18. As shown, a wafer 20 is supported by the embossments. A space 22 exists between the lower surface of the wafer 20 and the top of the ceramic layer 14. The space 22 is created by the embossments 18 located on the upper surface of the ceramic layer 14, which support the wafer 20 a short distance above the upper surface of the ceramic layer 18. During use, a flow of cooling gas can pass through the space 22 between the wafer 20 and the ceramic layer 14 to control (e.g., reduce) the temperature of the wafer 20. The base 12 includes cooling channels, not specifically shown.

[0040] The chuck assembly herein includes a base structure including cooling channels. The base structure as described includes cooling channels having non-uniform characteristics, such as non-uniform location within the base in the z-direction, non-uniform cross-sectional area, or non-uniform cross-sectional shape. These characteristics can be effective to improve the cooling efficiency and cooling (temperature) uniformity of the base, chuck, and supported workpiece, regardless of how these features are produced as part of the base, i.e., regardless of what type of process is used to produce these features and the base structure as a whole. Therefore, the disclosure herein does not require any particular method of fabricating a base to include cooling channels with the described non-uniform characteristics to result in improved cooling efficiency and cooling uniformity.

[0041] Yet additive manufacturing can be particularly effective for producing non-uniform features of cooling channels having considerable complexity, such as channel systems having various shapes, cross sections, and depths, optional cross shapes, and optional combinations of connected channels. Therefore, this specification will primarily use terminology that refers to additive manufacturing, even though the base structure of this description need not be made by additive manufacturing.

[0042] Cooling channels formed by additive manufacturing techniques can be more accurate compared to channels formed using currently known machining techniques, can be formed in alternative cross-sectional shapes (which cannot be formed by machining), can be formed in more complex (serpentine three-dimensional) patterns, can be easily formed three-dimensionally within the base, can be easily formed in the base with a high channel density or with interconnected channels. Examples of cross-sectional shapes of the cooling channels include circular, triangular, hexagonal, dome-shaped (curved at one end and flat at the other end), and teardrop-shaped.

[0043] According to a preferred additive manufacturing method, the entire base structure including the internal cooling channels can be produced using additive manufacturing techniques. The cooling channel system can be formed in the base structure by an additive manufacturing method as a connected pattern or system of optionally interconnected open spaces (e.g., "empty" locations) that form a closed-loop channel extending into a region within the base. The channels are defined by the absence of the base material at various locations of the channels, and no other structure is required to form or define the structure of the channels within the base. The channels extend throughout the interior of the base layer and, for example, by an additive manufacturing method, do not require a structure or surface other than the space formed within the base structure during the formation of the base.

[0044] The channels are defined by the surface of the base material with no other material required on the surface. In particular, the cooling channels do not include or require additional structures other than the base structure, such as separate tubes, pipes, or conduits formed separately from the base structure and combined with or placed within the base structure. In use, the cooling fluid flows through the cooling channels in contact with the sidewalls made of the base material, and there is no other material present to form or define the inner surface of the channels.

[0045] The cooling channels function to circulate a cooling fluid (e.g., water or another cooling liquid) through an interior portion of the base to remove heat from and control the temperature of the base, chuck, and supported workpiece. The channels are formed within the base and extend two-dimensionally, vertically (e.g., from above, in a "top view") relative to the area of the base surface in the x and y directions, and optionally vertically along the thickness of the base (z direction). The cooling channels include at least one inlet in the base that allows the cooling fluid to enter the base and at least one outlet that allows the fluid to exit the base. Between the inlet and outlet is a closed loop of the channel or channel system.

[0046] 2A and 2B show a single general example of a base 100 herein including channels as described. Base 100 includes a perimeter 110, an upper surface 102, a lower surface 104 (each having an area extending in both the x- and y-directions), and a thickness (in the z-direction) between the two opposing surfaces. Cooling channels 106 (shown in FIG. 2B as having a circular cross-section) are present in a serpentine pattern in the interior portion of the base.

[0047] 2A does not show that different portions of the flow channels 106 may also have different cross-sectional shapes, different cross-sectional areas, or different depth locations within the thickness (z-direction) of the base 100. FIG. 2B shows that different portions of the flow channels 106 are located at different locations in the thickness direction.

[0048] FIG. 2C shows examples of cross-sectional shapes of cooling channels, including cross-sections that are triangular (i), hexagonal (ii), dome-shaped (curved at one end and flat at the opposite end) (iii), and teardrop-shaped (iv).

[0049] With these or other cross-sectional shapes, other non-uniform features of the cooling channels can also be incorporated into the base design. For example, the cooling channels can be formed to have a greater volume towards the upper surface of the base compared to the bottom surface of the base, the channels can be shaped such that a greater portion of the channel faces the upper surface, or different portions of the channel can be positioned at different distances from the upper and lower surfaces of the base. The channels can have portions located at different positions along the thickness of the base. Alternatively or additionally, the cross-sectional profile of the cooling channels can vary based on the location within the base, the cross-section of the channel can be sized to become smaller, or shaped differently in certain portions of the base near the center of the base, and can become larger or be shaped differently at the edges to enable more uniform heat transfer and improved temperature control on the upper base surface (or vice versa). In other design examples, two channels or channel portions (main channels) can be connected by smaller "lateral channels" having a smaller cross-sectional area than the main channels to allow the flow of cooling fluid from one portion of the channel to a different portion of the channel.

[0050] Referring now to FIGS. 3A and 3B, two opposing side cross-sectional views of a base as described herein are shown. Features corresponding to those of FIGS. 2A, 2B, and 2C are indicated by numbers, although the structural details may be different. In FIGS. 3A and 3B, left and right cross-sections of the base 100 are shown to illustrate the location of the channel 106. The base 100 includes an outer peripheral portion 110, an upper surface 102, a lower surface 104 (each having regions extending in both the x and y directions), and a thickness (in the z direction) between the two opposing surfaces. The cooling channel 106 extends within the solid base material 108.

[0051] In this example, the flow path 106 is made with a similar cross-sectional shape (circular) and cross-sectional size along the entire length of the flow path or flow path system. However, different portions of the base 100 include flow paths 106 that are located at different distances (depths) from the upper surface 102. Portion 110 is considered the colder portion of the flow path 106, is upstream from the warmer portion 112, and conveys fluid at a relatively low temperature. The cooling fluid flows into the flow path 106 at the inlet, first through the colder portion 110, and then through the warmer portion 112. The warmer portion, which is portion 112, contains the cooling fluid that will be slightly heated compared to the fluid contained upstream in the colder portion 110. The flow path 106 of the warmer portion 112 is positioned closer to the upper surface 102 compared to the flow path 106 of the colder portion 110 in order to adjust the temperature of the cooling fluid to increase as the fluid passes through the warmer portion 112.

[0052] Similarly, the edge portion 114 absorbs more heat from the atmosphere compared to either the colder portion 110 or the warmer portion 112 due to the exposed surface of the base 100 at the outer peripheral portion 110. This increased amount of heat added to the edge portion 114 causes the temperature of the edge portion 114 and of the cooling fluid passing through the flow path 106 at or near the edge portion 114 to increase. To adjust for the loss of cooling capacity of the water flowing through the edge portion 114, the flow path 106 may also be positioned closer to the upper surface 102 at the edge portion 114, for example, compared to the flow path 106 of the colder portion 110.

[0053] FIG. 4 is a top cross-sectional view of a base as described herein. Features corresponding to those of FIGS. 2A, 2B, and 2C are indicated by numbers, but the structural details may be different. In FIG. 4, a cross-section of the base 100 is shown, and in particular, it is shown that the flow paths 106 extend through the solid base material 108 in the x and y directions. Three flow paths 106 are shown, each of which has a cross-sectional shape that is circular and a cross-sectional size (area) that is substantially uniform along the length of the flow path 106.

[0054] A flow channel 106 passing through a surface (not shown) of the base 100 is connected to an inlet 118. During use of the base 106, cooling fluid enters the flow channel 106 through the inlet 118 and flows in two directions, as a first flow F1 and a second flow F2. Near the inlet 118, the flow channel 106 includes a reduced diameter portion or orifice 120, which affects the relative amounts of flows F1 and F2 as the cooling fluid enters the flow channel 106 from the inlet 118. The orifice 120 is a compression orifice, which allows for a reduction in the flow rate through the flow channel 106 at the location of the orifice 120. As a result, the constriction effect of the orifice 120 results in a higher flow rate (amount of fluid per time) for flow F2 and a lower flow rate for flow F1.

[0055] Figure 5 is a cross-sectional perspective view of a base as described herein. Features corresponding to those of Figures 2A, 2B, and 2C are indicated by numerals, although details of construction may differ. In Figure 5, a cross-section of the base 100 is shown, specifically showing the main channels 106(a, b) and smaller (in length and cross-sectional area) lateral channels 122 extending through the solid base material 108 in the x and y directions.

[0056] The flow path system of Figure 5 includes main flow paths ("main" flow paths) 106(a, b) connected by a side flow path ("connecting" flow path) 122. The side flow path 122 has a smaller cross-sectional area relative to the main flow path 106 and a relatively short length extending between the two main flow paths to connect the flows of the two main flow paths. In this example, the main flow path 106a contains a flow of cooling fluid having a lower temperature than the cooling fluid flowing through flow path 106b. The main flow path 106a is closer to the inlet upstream than the main flow path 106b, i.e., "upstream" from flow path 106b.

[0057] To improve temperature uniformity within the base 100, the flow of cooler fluid in the channel 106a is diverted from the cooler portion of the channel 106a to each of the two warmer channels 106b. The diverted fluid flows from the cooler channel 106a to the warmer channel 106b through each of the side channels 122 (see arrows indicating the direction of flow). Each side channel 122 has a reduced cross-sectional area relative to the larger cross-sectional areas of the main channels 106a and 106b. The reduced cross-sectional area of the side channels 122 results in a flow rate from the cooler channel portion 106a to the warmer channel portion 106b such that the temperature of the cooling fluid in the warmer channel portion 106b is reduced as desired.

[0058] Figure 6 is a top cross-sectional view of a base as described herein. Features corresponding to those in Figures 2A, 2B, and 2C are indicated by numerals, but the details of construction are different. In Figure 6, a cross-section of base 100 is shown, specifically showing channels 106a and 106b extending as closed loops through solid base material 108 in the x and y directions, respectively. Cooling fluid enters base 100 at inlet 130, and the flow splits into two directions as indicated by the flow arrows.

[0059] Flow path 106a includes a closed loop between inlet 130 and outlet 132 that covers approximately half of the surface area of base 100. Flow path 106b includes a closed loop between inlet 130 and outlet 132 that covers approximately half of the surface area of base 100. In a first flow direction (to the left as shown), cooling fluid flows through flow path 106a, which has a relatively large cross-sectional area relative to the area of the bottom half (as shown) of base 100. At the end of flow path 106a, the flow path tapers to a reduced diameter 136. After passing through the taper, the fluid exits flow path 106a through outlet 132.

[0060] In a second flow direction (right as shown) from inlet 130, the cooling fluid flows into flow path 106b and tapered section 134 and then into a portion of flow path 106b in the upper half of base 100 (as shown). Flow path 106b has a relatively small cross-sectional area compared to flow path 106a. At the end of flow path 106b with such a reduced diameter there is an outlet 132.

[0061] According to the present specification, in accordance with the exemplary base 100 of FIG. 6, all of the different features of the base's flow paths have individual effects, but combinations of two or more features can be used together to achieve desired temperature control in different regions of the base. In a specific example, flow paths having different combinations of depth, cross-sectional area, and cross-sectional shape may be designed within the base to control local temperature variations of an electrostatic chuck that may occur during use of the chuck to support a workpiece. With respect to the base 100 of FIG. 6, flow path 106a and flow path 106b have different cross-sectional areas and, although not specifically shown, may be at different cross-sectional depths in the z direction of base 100. Generally, the base's flow paths may include locations of different depths and portions of flow paths representing different combinations of cross-sectional area or shape. A useful effect of a flow path design that includes combinations of these features can be effective heat removal and temperature uniformity of the base during use.

[0062] FIG. 7 is a top cross-sectional perspective view of the base as described. Features corresponding to those of FIGS. 2A, 2B, and 2C are indicated by numbers, but the structural details are different.

[0063] In FIG. 7, a cross-section of base 100 is shown, and it is shown that flow path 106 extends as a closed loop through solid base material 108 in the x and y directions. Flow path 106a includes a closed loop that covers approximately half of the surface area of base 100 (lower left half as shown) between inlet 130 and outlet 132. Flow path 106b includes a closed loop that covers approximately half of the surface area of base 100 (upper right half) between inlet 130 and outlet 132.

[0064] The cooling fluid enters the flow path 106 at the inlet 130, and this flow is split into two directions as indicated by the flow arrows. In the first flow direction (upper left as shown), the cooling flow path 106a extends directly to the outer region of the base 100 and passes near the base edge at the outer peripheral portion 110. In the second flow direction (right as shown), the cooling flow path 106 extends directly to a different outer region of the base 100 opposite, and passes near the edge of the base 100 at the outer peripheral portion 110. By first entering the flow paths 106a and 106b at the inlet 130 and extending to these edge portions of the base 100, the cooling fluid is at the original (minimum) temperature when passing through the edge portions of the flow paths 106a and 106b in the edge region of the base 100. Each of the two flow paths extends through the entire different half of the base 100 (upper right for flow path 106b, lower left for flow path 106a). After passing through the closed loop in each half of the base 100, each flow exits the flow paths 106a and 106b by passing through the outlet 132.

[0065] At the intersection 134, the flow path 106a passes below (in the z - direction) the flow path 106 at the unconnected intersection 134. At the intersection 134, since the two flow paths are at different z - direction depths within the thickness of the base 100, the two flow paths are located at the same x - location and y - location of the base 100, but the flows in the two flow paths are not connected. Advantageously, the unconnected intersection 134 allows the two different flows (the right - hand flow and the left - hand flow) at the inlet 130 to each first proceed to the edge portion of the base 100.

[0066] The following description relates to a method for creating a substantially non - porous three - dimensional base structure of a solid that may be useful as a component of an electrostatic chuck assembly having cooling flow paths as described, by an additive manufacturing method. These include methods commonly referred to as "3D printing" techniques.

[0067] Various types of additive manufacturing techniques are known. Additive manufacturing methods generally include a series of individual layer forming steps of continuously forming a plurality of layers of a solidified feedstock composite taken from layers of a feedstock. Using a series of additive manufacturing steps, where each step forms a single layer of the structure, a plurality of layers of solidified feedstock are continuously formed into a structure herein referred to as a multi-layer composite (or "composite").

[0068] As used herein, the term "composite" (or "multi-layer composite") refers to a structure formed by additive manufacturing by continuously forming a series of a plurality of individual, separately formed layers of solidified feedstock. The composite includes each of an upper portion (having an upper surface), a bottom portion (having a bottom surface), and an inner portion (including, for example, cooling channels), and all three portions are formed and held together solely by the layer forming steps of the additive manufacturing method (e.g., without using a vacuum brazing process or any other type of joining process to join two separately fabricated parts together), taking the form of a base of an electrostatic chuck (the "base"), and may be referred to herein as a "continuous" base or a "continuous layer" of the base.

[0069] The term "continuous" in this context means that the base or layer structure is formed as a composite structure of a single piece from a plurality of continuously formed layers. The term "continuous" does not refer to a structure made by forming two individual parts separately and then joining the two separately formed parts together, for example, by a vacuum brazing technique or a different type of joining technique. A continuous base structure does not include seams or boundaries resulting from a joining process, particularly seams or boundaries made of a joining material or filler material having a composition different from that of the base material.

[0070] One specific example of an additive manufacturing technology is a technique commonly referred to as "selective laser melting." Selective laser melting (SLM), also known as direct metal laser melting (DMLM) or laser powder bed fusion (LPBF), is a three-dimensional printing method that uses a high-power density laser to melt solid particles of a feedstock material, allowing the molten (liquid) material of the particles to flow and form a continuous layer of molten material, which can then be cooled and solidified to form a solidified feedstock. According to one particular exemplary method, the particles of the feedstock can be completely melted to form a liquid (i.e., liquefied), and the liquid material can be allowed to flow to form a substantially continuous, substantially non-porous film (e.g., greater than 80, 85, or 90% porosity) that can then be cooled and hardened as a solidified feedstock layer of a multilayer composite.

[0071] Selective laser melting includes similar features to another additive manufacturing technique known as selective laser sintering ("SLS"). Selective laser sintering uses laser energy to cause particles of a feedstock material to sinter, i.e., to melt the particles without melting them. This results in a structure formed by the heated particles of material having spaces between the particles, meaning that the structure is porous. In contrast, selective laser melting can be used to cause particles to completely melt to form a solid (substantially non-porous) three-dimensional structure.

[0072] Additive manufacturing techniques can be useful for forming base structures made from a wide range of materials, including metallic materials (including alloys) and metal matrix composites. The range of metals, alloys, and metal matrix composites potentially usable to form bases using additive manufacturing techniques, including selective laser melting, can advantageously include materials that are not easily formed into useful base structures by prior techniques, such as machining techniques. The range of materials available for additive manufacturing includes metals and metal alloys that can be melted by laser energy, such as aluminum alloys, titanium alloys, and various metal matrix composites, some of which are not easily processed by machining. Exemplary materials may exhibit high hardness such that they may be difficult to process using machining techniques to form precise structures for electrostatic chuck bases, including precise dimensions and complex cooling channels. Using additive manufacturing techniques, such materials can be processed to form base structures containing complex, enclosed (“embedded”) cooling channels, even from materials that would similarly be difficult to form using standard machining techniques.

[0073] The material used to fabricate the base can be any material useful for fabricating the base of an electrostatic chuck assembly, for example, inorganic materials including various metals (including alloys) and metal matrix composites. The term "metal" is used herein to refer to any metallic or semi-metallic chemical element or an alloy of two or more of these elements, consistent with the meaning of the term "metal" within metallurgical, chemical, and additive manufacturing technologies.

[0074] The term "metal matrix composite" ("MMC") refers to a composite material made to include at least two components or two phases, where one phase is a metal or metal alloy and the other phase is a different metal or another non-metallic material such as fibers, particles, or whiskers dispersed in the metal matrix. The non-metallic material may be carbon-based, inorganic, ceramic, etc. Some exemplary metal matrix composites are made from combinations of aluminum alloys with alumina particles, aluminum alloys with carbon, aluminum alloys with silicon, aluminum alloys containing silicon carbide (SiC), titanium alloys with TiB2, titanium alloys with silicon, and titanium alloys with silicon carbide (SiC).

[0075] Metals and metal alloys that may be useful according to the methods herein include metals and metal alloys that have been conventionally used to fabricate the base structure for an electrostatic chuck assembly, as well as other materials that have not been used. Useful or preferred materials include metals such as iron alloys (e.g., stainless steel and other types of steel), titanium and titanium alloys, aluminum and aluminum alloys, and various metal matrix composites.

[0076] According to this method, the base can be fabricated from a greater variety of materials than those that could be used to fabricate the base from prior methods (e.g., machining methods). With a greater variety of materials available, the base material may be selected to provide physical properties that are particularly useful or desirable in the base of an electrostatic chuck assembly and that take into account the materials used in other components of the assembly such as adjacent ceramic layers.

[0077] The coefficient of thermal expansion (「CTE」) is a known physical property of metals, metal matrix composites, and ceramic materials. The materials of the base layer herein may generally have a coefficient of thermal expansion comparable to that of various metals and ceramic materials that have been previously used to form components of the base assembly of an electrostatic chuck. Some exemplary materials that may be useful as the base or ceramic layer of the base assembly as described and their approximate CTE values are, as follows, alumina (8.1×10 -6 m / (m K)), aluminum (21~24×10 -6 m / (m K)), aluminum alloy (AlSi7Mg) (21~22×10 -6 m / (m K)), aluminum nitride (5.3×10 -6 m / (m K)), stainless steel 440C (10.2×10 -6 m / (m K)), stainless steel 17-4PH (10.8×10 -6 m / (m K)), steel M2 (tool) (11×10 -6 m / (m K)), titanium (8.6×10 -6 m / (m K)), titanium alloy Ti-6Al-4v (TC4) (8.7~9.1×10 -6 m / (m K)).

[0078] By way of example, useful or preferred coefficients of thermal expansion of metals or metal matrix composites used to fabricate the base as described may be in the range of 4×10 -6 m / (m K) to 30×10 -6 m / (m K), for example, in the range of 5×10 -6 m / (m K) to 25×10 -6 m / (m K).

[0079] In certain preferred base structures and electrostatic chuck assemblies, the material of the base may preferably have a coefficient of thermal expansion that matches or is similar to that of the adjacent layers of the assembly. In many cases, as part of the electrostatic chuck assembly, the base layer is positioned near, adjacent to, or in other cases sufficiently close to the ceramic layer of the assembly such that the base layer and the ceramic layer are subject to similar temperature conditions and the thermal expansion of one is affected (e.g., restricted) by the other. In such cases, useful combinations of the base layer and the ceramic layer of the assembly can be made from materials having approximately equal coefficients of thermal expansion. A preferred base for the electrostatic chuck assembly can have a coefficient of thermal expansion on the order of that of the ceramic layer that is part of the same chuck assembly. The coefficient of thermal expansion of the base can be within 25, 20, 15, 10, or 5% of the coefficient of thermal expansion of the ceramic layer (m / (m - kelvin)). The layer-by-layer approach of additive manufacturing techniques as described can enable the formation of complex and precise intricate shapes that are very effective when included in the electrostatic chuck base. Compared to machining techniques, the additive manufacturing techniques as described are very complex, cover most of the surface area of the base, occupy a large volume of the base structure relative to the overall volume of the base structure, or can be more efficient in creating a pattern of cooling channels structured in a specially designed (specialized) pattern that enables the cooling of a particular workpiece having specific features supported by the electrostatic chuck during use.

[0080] Channels formed by additive manufacturing techniques may have different or diverse shapes (cross-sections), patterns (relative to the surface of the base assembly), and sizes (e.g., the width or diameter of the channel), and may have surface features that enable the fluid flowing through the channel to flow smoothly and efficiently. For example, in machining processes, typically channels with (square) cross-sections are produced, but additive manufacturing techniques can be useful for producing channels with (circular) cross-sections, so that compared to the turbulent flow when passing through a channel with a square cross-section, it may be possible to improve the flow (laminar flow) when passing through this channel. As another example, the channel can be formed to exhibit an asymmetric cross-section, which can enable the design of a channel with improved heat transfer efficiency through the surface of the base.

[0081] By additive manufacturing methods, a complete (or substantially complete) and functional base layer of an electrostatic chuck can be fabricated using a single manufacturing process (a single additive manufacturing "step"), thereby resulting in high manufacturing efficiency (high manufacturing throughput) with a reduced amount of time per unit. A base layer with substantially all of the required structures (including the bottom portion, inner portion, and upper portion) can be fabricated by a single series of additive manufacturing steps. For example, what can be referred to as a "one-step" additive manufacturing process for forming the base structure can form many, most, or all of the required structures of the base (including the bottom portion, inner portion, and upper portion) as a single continuous layer, as a multi-layer composite as described. The one-step additive manufacturing process avoids the need to perform additional steps of individually forming a plurality of separate parts in separate steps and then joining the plurality of separately formed parts together to form a functional base structure.

[0082] Furthermore, additive manufacturing techniques can be used to form a base with high-precision dimensions including very precise flatness and low surface roughness.

[0083] According to the exemplary method, the base can be fabricated to exhibit a high flatness, e.g., a "super flat" surface, and by measuring the flatness at the upper surface of the metal matrix composite layer of the assembly, the high flatness of the base can improve the flatness of the electrostatic chuck assembly.

[0084] Flatness is a typical characteristic of an electrostatic chuck or a base component of the chuck and can be measured by known techniques such as using a coordinate measuring machine. Generally, flatness is measured and reported as the height difference (in the z-direction) between the peaks (highest measured points) and valleys (lowest measured points) of the measured surface, and is expressed in units of distance, e.g., microns. A base with a diameter of 300 millimeters formed by machining alone may be formed to exhibit a flatness as low as 30 microns. On the surface of an equivalent base (300 millimeter diameter) as described herein, after forming the base by an additive manufacturing process and further machining the base surface by a machining process, the flatness of the base can be improved compared to a base formed by machining alone. The flatness of the base surface after additive manufacturing may be below 45 or 50 microns, e.g., as low as 40 microns. The surface may be further machined by a machining process to result in an even lower flatness, e.g., less than 30 microns, e.g., less than 20 microns, or about 15 microns.

[0085] In certain advanced applications of electrostatic chuck assemblies (e.g., Cryo, low angle implantation), the useful chuck assembly should exhibit ultra-high flatness measured at the upper surface of the assembly (e.g., the top of the ceramic layer). The preferred flatness value for a particular application of the chuck assembly may be less than 10 microns when measured at the upper ceramic surface for a 300 millimeter chuck. It is also important to maintain this ultra-high flatness characteristic over a wide range of operating temperatures. The flatness of the chuck assembly over a temperature range can be improved by precisely matching the coefficient of thermal expansion values of the different layers (ceramic layer and base layer) of the chuck assembly, and also by improving heat dissipation from the assembly for heat extraction (heat removal by fluid flow through the base), and further by improving the flatness of the surfaces of these layers at the joints between the layers. The materials used to form the base of the chuck assembly, such as titanium, titanium alloys, and metal matrix composites, can result in an improvement in CTE matching and an improvement in flatness compared to previous materials commonly used to form chuck bases, such as aluminum, which are less rigid than these materials.

[0086] Furthermore, additive manufacturing methods can be used to fabricate the base to exhibit a relatively low roughness. Roughness is a typical characteristic of the base of an electrostatic chuck and can be measured by known analytical techniques, including, for example, that represented by the arithmetic mean of the surface roughness profile (denoted as "Ra") using a 3D laser microscope or a stylus profilometer. Ra is calculated as the average roughness of the measured microscopic peaks and valleys of the surface. After fabrication by the additive manufacturing method as described, an exemplary surface of the base, which has had its roughness reduced by a machining process, can have a surface roughness (Ra) as low as less than 1 micron, for example less than 0.5 micron, or about 0.1 micron. The roughness (Ra) can be determined by one of various standard methods such as ISO 4287-1:1984 or ASTM F 1048.

[0087] The improved accuracy of forming the base allows for greater accuracy in forming multilayer chuck assemblies including ceramic layers attached to the base, including improved flatness measured at the top of the ceramic layers. A typical base fabricated by a machining method having a diameter of 300 millimeters may be combined with a ceramic layer to form an assembly exhibiting a flatness as low as 30 microns measured at the upper ceramic surface. In exemplary embodiments, the base layer herein may be combined with a comparable ceramic layer to form an assembly having a diameter of 300 millimeters exhibiting a flatness as low as 30 microns, e.g., less than 25 microns, e.g., less than 20 microns, or as low as about 15 or 10 microns, measured at the upper ceramic surface. To achieve this low flatness of the metal matrix composite layer of the base assembly, the base layer may be formed by additive manufacturing, and the surface of the base assembly (which will contact the metal matrix composite layer) may be machined to improve the flatness of the surface produced by the additive manufacturing process.

[0088] The methods herein use additive manufacturing techniques to form a base structure (e.g., a continuous base layer, or a portion of a base layer) by sequentially forming multiple layers of a composite. The composite is formed from multiple layers, each of which individually can have any useful thickness, and from one or more materials that can be melted and flowed to form a dense, inorganic (e.g., metal or metal matrix composite) solid that is useful as the substantially non-porous material of the base structure.

[0089] In general, the base can be considered to have the form of a flat, thin, typically circular structure (viewed from the top and bottom), such as a flat disk including two opposing, flat, circular surfaces of a certain thickness. The two opposing surfaces act as the top and bottom of the base layer. An interior portion of the base resides between the two opposing surfaces. The interior portion can include an enclosed system of channels (cooling channels) that extend through the interior portion in a meandering, undulating, twisting, circuitous, or serpentine path.

[0090] The flow path can accommodate a flow of fluid (e.g., water or another liquid or gaseous coolant) that can be used to control the temperature of the base during operation of the base. Vertical holes ("openings") extending between the thickness and between two opposing surfaces of the base (from top to bottom and throughout the thickness), or other structures such as flow paths or grooves in one or both of the top and bottom surfaces, may also be formed on the surface of the base.

[0091] The functional base layer of the chuck assembly can be considered to include at least three different parts, namely, a lower part including the bottom surface, an upper part including the upper surface opposite the bottom surface, and an intermediate ("inner") part disposed between the upper part and the lower part and which may include cooling flow paths. Preferably, according to the preferred method as described, all three parts and all their layers can be manufactured by an additive manufacturing method, whereby a single (preferably continuous) series of layer forming steps is used and, optionally, preferably all the layer forming steps are performed on a single additive manufacturing apparatus to form all the layers of the functional base layer as a continuous, seam-free layer of inorganic material without any seams or internal boundaries such as seams that can be formed by a joining process (e.g., vacuum brazing). "Continuous" means that each layer forming step in a series of additive manufacturing steps is performed in sequence without performing any different type of step (e.g., any type of non-layer forming step) between any two of the layer forming steps and without performing a joining step (different from the additive manufacturing step) that joins two parts of the base layer together using a filling material, brazing material, or adhesive, etc.

[0092] Such a method may include, as an example of the methods described herein, forming the lower part of the base including the bottom surface by additive manufacturing, forming the intermediate part of the base including the cooling flow path on the lower part by additive manufacturing, and forming the upper part of the base including the upper surface on the intermediate part by additive manufacturing.

[0093] Each layer of the composite material can be formed from a desired material with a desired thickness as desired, resulting in a base structure in the form of a multi-layer composite material having desired properties. By an exemplary additive manufacturing method, each layer is generally made from an aggregate of particles (referred to as "feedstock") in the form of powder. The feedstock can include small particles composed of one or various different inorganic materials that can be melted by a high-energy laser to form a continuous layer of molten material, which then cools and solidifies to form a layer of the multi-layer composite material.

[0094] Useful particles according to the present specification can be any particles that can be processed to form a useful multi-layer composite material as described. The particles can be included in, composed of, or substantially composed of a feedstock in the form of powder that contains inorganic particles that can be melted using energy from a high-energy laser to form a layer of the multi-layer composite material.

[0095] Examples of useful particles include, as described, inorganic particles that can be melted or liquefied by laser energy to form a layer of the base structure. Examples of such particles include inorganic particles made of metals (including alloys) and metal matrix composites. Some useful examples generally include metals and metal alloys such as aluminum, titanium, and their alloys, as well as metal matrix composites. One specific example of a useful aluminum alloy is AlSiMg. One specific example of a useful titanium alloy is Ti6Al4V.

[0096] The useful particles of the feedstock can be of any size (e.g., average particle diameter) or size range that is effective, including small or relatively small particles on the micron scale (e.g., having an average size of less than 500 microns, less than 100 microns, less than 50 microns, less than 10 microns, or less than 5 microns).

[0097] The particles are selected to achieve the effectiveness of the described processing, are included in the feedstock, are formed in the feedstock layer, can be melted and flow to form a continuous layer, and the continuous layer can be cooled and solidified to form the feedstock as a layer of the multi-layer composite. The size, shape, and chemical composition of the particles can be any that are effective for these purposes.

[0098] The particles can be in the form of a feedstock composite that can be used in the additive manufacturing process described herein. By way of example, the feedstock useful in the additive manufacturing process may include particles that can be melted to form a continuous substantially non-porous layer of the multi-layer composite. The feedstock material need not contain any other materials, but may optionally contain a small amount of other materials at will. The exemplary feedstock composite may contain at least 80, 90, or 95, 98, or 99% inorganic particles by weight, based on the total weight of the feedstock composite. Optionally, one or more other raw materials such as a flow aid, surfactant, lubricant, or leveling agent may be present in a small amount.

[0099] Each layer of the multi-layer composite may be formed to have any useful thickness. The thickness of the layer of the multi-layer composite is what is measured after the layer of the composite is formed by melting the particles of the feedstock layer and solidifying the continuously melted composite. Exemplary thicknesses of the layer of the composite may range from 30 microns to 100 microns, 200 microns, or more, for example, from 30 to 50, 60, 70, 80 microns to 90, 100, 150, 200, 300, 400, or 500 microns. In an exemplary composite structure, all layers of the composite may have the same thickness or substantially the same thickness. In other exemplary composite structures, not all layers may have the same thickness, and different layers of the composite may have different thicknesses respectively.

[0100] According to certain exemplary methods and base structures of this specification, the base may be fabricated by an additive manufacturing process by forming layers of composite material such that the base has different thicknesses at different portions of the base. Examples of these methods and structures include forming one or more layers (referred to as "fine layers") having a thinner thickness, for example, at the upper and bottom portions of the base, and forming a layer (a "coarse layer") having a thicker thickness, for example, at the inner portion of the base between the upper and bottom portions.

[0101] The position of one or more fine layers as part of a multi-layer composite material (for example, in the form of a base layer) may be at any useful position relative to the coarse layer. Various locations of the coarse and fine layers of the composite material, as well as various formation orders of the coarse layer relative to the fine layers, may be effective. However, according to certain embodiments of the base structure and related methods as described, one or more fine layers may preferably be present on one or more surfaces of the base, and the coarse layer may be present in the inner portion of the same base. Since the fine layer may exhibit more desirable physical properties compared to the coarse layer (see below), it may be desirable for the fine layer to be located on one or more surfaces. Layers in the inner portion of the base where higher quality is not as critical may be fabricated from the coarse layer to increase manufacturing efficiency (see below).

[0102] Forming layers of the base with different thicknesses can provide benefits in terms of processing efficiency and the physical properties of the base (or portions of the base). Forming one or more thicker "coarse" layers can have the beneficial effect of increasing the production rate and efficiency of the base. While thicker coarse layers may be of lower quality compared to thinner (fine) layers (see below), forming relatively thick layers can increase the production rate (requires less time) of the base, and increasing the thickness of the thicker (coarse) layers can reduce the total number of layers that must be formed and the number of layer formation steps required to produce a base with a particular thickness. The thickness of the coarse layers can be within the typical range of layers formed by additive manufacturing processes, for example, from 70, 80, 90, or 100 microns to 500 microns. Increasing the thickness of the coarse layers can reduce the number of steps and time required to form a finished multilayer composite of a given total thickness.

[0103] The thickness of a layer formed by additive manufacturing techniques can affect the physical properties (quality) of the layer when using the same feedstock and the same laser in the layer formation process. For example, a thinner layer may be formed that contains fewer internal open spaces, or "pores," compared to a thicker layer formed using the same feedstock and the same laser. The presence of pores in a layer can be measured and expressed in terms of the apparent density of the layer. Generally, when using an additive manufacturing process that applies the same laser and the same laser power to the feedstock layer for the same time, the apparent density of a thicker (coarse) layer will be lower than the apparent density of a similar (e.g., fine) layer of a thinner thickness but made from the same feedstock.

[0104] Apparent density refers to the measured density of the composite layer relative to the actual (or theoretical) density of the material used to form a layer in the form of a 100% solid non-porous (porosity 0) form. Since the composite layer is formed by a process that melts the particles of the feedstock, flows the melted particles, and enables the formation of a continuous layer (e.g., a "film") from the liquefied particle material, it typically results in a continuous solid material. However, typically, the continuous solid material formed is not 100% solid and contains a small amount of voids or pores that are not removed during the layer formation process. Pores can cause a decrease in the performance of the base, especially when the base is used in a process under vacuum, as the cooling fluid (water) may leak out of the cooling channels through the porous material of the base to the outside of the base.

[0105] In many cases, pores in a layer or composite can be optically visible on the surface or inside of the composite, with or without magnification. Alternatively, these voids can be detected as a decrease in the density (apparent density) of the composite layer or a portion of the composite. A layer formed without voids (a 100% solid inorganic material with 0% pores) would have a density equal to the density of the pore-free inorganic material used to make the layer. A mass of inorganic material containing pores would have a density (apparent density) slightly lower than the density of the inorganic material.

[0106] The density of the layer (apparent density when including the pore volume in the layer) is measured as the mass of the layer divided by the volume of the layer (including the pore volume), divided by the actual (theoretical) density value of the material used to form a layer with zero pore volume, and reported as a percentage of the actual density. The apparent density value of a layer or a portion (or base layer) of a composite as described is typically relatively high and may exceed, for example, 80, 90, 92, 96, 98, or 99% of the actual density of the material used to form the layer.

[0107] When forming a layer of a composite material from inorganic particles, energy from a high-power laser is used to melt the inorganic particles formed as a feedstock layer. The melted particles flow to form a continuous layer (e.g., a "film") that solidifies as a layer of the composite material. Ideally (theoretically), the laser energy would completely melt all of the particles of the feedstock composite material used to create the layer, and the flow of the liquefied particle material would form a liquid layer without voids, and that liquid layer would solidify to form a solid without voids. However, in practice, layers formed in this way generally may contain defects, voids, or partially unmelted particles, and the amount of these defects increases with the thickness of the layer formed (for the same feedstock, using the same laser, and applying the laser to a region of the feedstock layer for an equal amount of time).

[0108] The step of forming a thick layer of the composite material will involve forming a feedstock layer having a greater thickness and melting the particles of the feedstock. Using the same amount of laser output that can be used to melt the particles of a fine layer (having fewer particles) for the thick layer (having more particles), and applying the laser to a region of the feedstock for an equal amount of time, the amount of laser power available to melt the number of particles of the thicker feedstock layer (where there are more particles) is less per particle. The lower laser energy received per particle of the feedstock layer (where there are more particles in the thick feedstock layer) means that the thick layer may have a higher proportion of defects compared to the fine layer.

[0109] An increase in the amount of defects can correlate with a decrease in apparent density. The apparent density of the coarse layer is typically lower than that of the fine layer when using the same feedstock, the same laser, and the same exposure time of the laser to a region of the feedstock layer. In the exemplary method and base structure, the apparent density of any layer of the base may preferably be at least 98 or 99%. More specifically, the apparent density of the coarse layer of the base may preferably be at least 99.0%, for example, at least 99.2 or 99.4%. The apparent density of the fine layer of the base may preferably be greater than the apparent density of the coarse layer of the same base and may be at least 99.4%, for example, at least 99.6%.

[0110] Forming one or more "fine" layers with reduced layer thickness can be useful for improving the physical quality of the base structure. It has been found that finer layers of composites made by additive manufacturing methods exhibit useful or favorable physical properties such as higher density and a relatively low amount of defects such as pores formed in the layers.

[0111] On the other hand, forming a plurality of fine layers with reduced thickness during the additive manufacturing process will reduce the production rate of the multi-layer composite, i.e., the number of steps and time required to produce a multi-layer composite with a specific thickness will increase because more fine (thinner) layers have to be formed, which means that more additive manufacturing steps are required to make a multi-layer composite of a given thickness.

[0112] The thickness of the fine layer is within the typical range of the thickness of the layers formed by the additive manufacturing method, and in particular, can be the lower end thickness of a range such as a thickness in the range of 30 microns to 100 microns, for example, 30 - 50, 60, 70, 80, or 90 microns.

[0113] The base as described can be fabricated by additive manufacturing, which uses a series of individual layer-by-layer processes to form a dense metal or metal matrix composite multilayer composite structure. As one example, a technique called selective laser melting (SLM) is a version of additive manufacturing that can be used to form multilayer composites layer by layer. Selective laser melting uses high-power laser energy to selectively melt and flow metal or metal matrix composite particles in a feedstock layer, forming a substantially continuous, solidified feedstock layer.

[0114] More specifically, multilayer composites can be made by a sequential process that results in many thin cross sections (herein "solidified feedstock" of "layers") of a larger three-dimensional structure (the composite). A layer of feedstock is formed, and the layer includes many particles of a metal or metal matrix composite. Laser energy is selectively applied to the feedstock layer over a portion of the feedstock layer. The portion of the feedstock layer that receives the laser energy becomes a channel-free portion of a layer of the multilayer composite base, and the portion of the feedstock layer that does not receive the laser energy becomes a channel in the multilayer composite base.

[0115] The laser energy melts particles in the portion of the feedstock exposed to the laser energy. The molten particles liquefy and flow into successive layers of molten particle material, which then cool and solidify into a layer of solidified feedstock. After the initial layer of solidified feedstock is formed, an additional thin layer of feedstock is deposited on top of the completed layer containing the solidified feedstock. This process is repeated to form multiple layers of solidified feedstock, each layer formed on top of and adhering to the top surface of the previous layer. Multiple layers are deposited one after the other on each completed layer to form a multilayer composite, which is a composite of each layer of solidified feedstock. The multiple layers may be of the same composition and thickness, or may be of different compositions and layer thicknesses.

[0116] An example (200) of a selective laser melting additive manufacturing technique useful for making a multi-layer composite material as described is shown in FIG. 7. This process can be carried out using commercially available selective laser melting additive manufacturing equipment and particles forming the feedstock. The feedstock 202 is a powder containing an aggregate of inorganic particles. According to the exemplary steps shown in FIG. 7, the powder feedstock (202) contained in the selective laser melting additive manufacturing apparatus is formed as a uniform layer on the build plate of the apparatus (204, 206). In the next step (208), an electromagnetic radiation source (e.g., a high-power laser) selectively irradiates a portion of the first layer of this feedstock by emitting radiation of a wavelength and energy that will melt the particles. The melted particles flow into a continuous film and then solidify by cooling. The layer of the feedstock may be a fine layer or a coarse layer and may have any useful thickness. The solidified material of the melted particles forms the feedstock solidified at the irradiated portion. The portion of the feedstock layer not formed in the solidified feedstock remains as the original liquid feedstock.

[0117] The build plate moves down (210), and a second layer (either a fine layer or a coarse layer) of the powder feedstock is formed as a second uniform layer on top of the first feedstock layer and on the solidified feedstock of the first feedstock layer (212). Then, the electromagnetic radiation source selectively irradiates a portion of the second layer (214) and melts the particles in this portion. The melted portion then cools to form the feedstock solidified in a portion of the second layer. The portion of the second layer not formed in the solidified feedstock remains as the original powder feedstock. Steps 212, 214, and 216 are repeated (218) to form a completed multi-layer solidified feedstock composite material surrounded by the original liquid feedstock (202).

[0118] The multi-layer solidified feedstock composite material is the main part containing the solidified feedstock of each formed layer and is composed of a plurality of continuous layers made from the material of the melted particles of the feedstock. The original feedstock (202) can be removed and is separable from the multi-layer composite material (218).

[0119] Referring to Figure 9, an exemplary process can be carried out using a commercially available selective laser melting additive manufacturing apparatus (230) and using a powder feedstock (232) according to the present disclosure. According to exemplary steps of the method, the feedstock (232) is formed as a uniform feedstock layer (234) on a build plate (238) of the apparatus (230). A laser (236) applies electromagnetic radiation (233) to a portion of the first layer (234), causing the feedstock particles to melt and flow into successive layers that can then be cooled to form a first solidified feedstock (240) in the portion. The portion (234) of the feedstock layer that is not formed into a solidified feedstock (240) remains as the original feedstock (232). The build plate (238) moves downward (214), and a second or subsequent feedstock layer (242) is formed on the first layer (234) and the first solidified feedstock (240). A laser (236) then selectively applies electromagnetic radiation (233) to portions of the second layer (242), causing the feedstock particles to melt and flow to form a continuous layer that can be cooled to form a solidified feedstock from the second layer. Portions of the second layer that are not formed into a solidified feedstock remain as the original powder feedstock. This sequence is repeated (250) to form a completed multi-layer solidified feedstock composite (252) surrounded by the original feedstock (232). The multi-layer solidified feedstock composite (252) is composed of the material of the molten particles of the feedstock, with the major portion including the solidified feedstock of each formed layer. The original feedstock (232) can be removed and separated from the multi-layer composite (252).

[0120] In a first aspect, the present disclosure provides an electrostatic chuck base comprising: an upper base surface; a lower base surface; an interior portion between the upper and lower base surfaces; and a flow path within the interior portion, the flow path including an inlet at a surface of the chuck base; an outlet at a surface of the chuck base; a length between the inlet and the outlet; and a cross-section along the length that includes a varying cross-sectional area along the length, a varying cross-sectional shape along the length, or a varying distance from an upper surface along the length.

[0121] The flow path is a second aspect according to the first aspect, including various distances from the upper surface along the length.

[0122] The flow path is a third aspect according to the first or second aspect, including various cross-sectional areas along the length.

[0123] The flow path is a fourth aspect according to the first aspect or the second aspect, including various cross-sectional shapes along the length.

[0124] The inlet passes through the lower surface, and a portion of the length having a smaller cross-sectional area is closer to the upper surface compared to a portion of the length having a larger cross-sectional area, which is a fifth aspect according to any of the preceding aspects.

[0125] A sixth aspect according to the first aspect, further including two unconnected intersecting flow path portions passing through one location between the upper base surface and the lower base surface.

[0126] A seventh aspect according to the first aspect, further including a flow path portion showing a tapered cross-sectional area.

[0127] The flow path includes an edge portion adjacent to the edge at the outer periphery of the base and an inner portion between the edge portion and the center of the base. The edge portion is closer to the upper surface compared to the inner portion, which is an eighth aspect according to the first aspect.

[0128] A ninth aspect according to the first aspect, where the flow path includes a portion that branches off from a single flow path to form two flow path portions.

[0129] A tenth aspect according to the first aspect, where the inlet is connected to a flow path extending in two directions from the inlet, and the outlet is connected to a flow path extending in two directions from the outlet.

[0130] A eleventh aspect according to the first aspect, where the flow path includes a first flow path portion, a second flow path portion, and a connecting flow path that connects the first flow path portion to the second flow path portion and enables fluid to flow from the first flow path portion into the second flow path portion.

[0131] A twelfth embodiment according to any of the preceding embodiments, further comprising a multilayer composite extending from the upper base surface to the lower base surface.

[0132] A thirteenth aspect according to the twelfth aspect, wherein the composite material does not include a metal seam.

[0133] A fourteenth aspect according to the thirteenth aspect, wherein the multilayer composite includes an aluminum alloy.

[0134] A fifteenth aspect according to the fourteenth aspect, wherein the aluminum alloy is AlSiMg.

[0135] The sixteenth aspect according to the thirteenth aspect, wherein the multilayer composite includes a titanium alloy.

[0136] A seventeenth aspect according to the sixteenth aspect, wherein the titanium alloy is Ti6Al4V.

[0137] An eighteenth aspect discloses a method of fabricating the electrostatic chuck base of any of the preceding aspects by additive manufacturing, the method including: forming a first feedstock layer on a surface, the feedstock layer comprising inorganic particles; forming a solidified feedstock from the first feedstock layer; forming a second feedstock layer on the first feedstock layer, the second feedstock layer comprising inorganic particles; and forming a second solidified feedstock from the second feedstock layer, wherein the solidified feedstock layer and the second feedstock layer are part of a multi-layer composite electrostatic chuck base.

[0138] A nineteenth embodiment according to the eighteenth embodiment, further comprising forming the solidified feedstock by melting the inorganic particles using a laser.

[0139] A twentieth aspect discloses a method of forming an electrostatic chuck base of any of the first to seventeenth aspects by additive manufacturing, the method including: additively manufacturing a lower base portion including a bottom surface; additively manufacturing a middle base portion on the lower base portion including a flow channel; and additively manufacturing a upper base portion on the middle base portion including an upper surface.

[0140] A 21st aspect according to the 20th aspect, further comprising: forming a lower base portion by an additive manufacturing process including forming a fine layer having a fine layer thickness; forming an intermediate base portion by an additive manufacturing process including forming a plurality of coarse layers, each coarse layer having a coarse layer thickness greater than the fine layer thickness; and forming an upper base portion by an additive manufacturing process including forming a fine layer having a fine layer thickness.

Claims

1. An electrostatic chuck base, comprising: an upper base surface; a lower base surface; an inner portion between the upper base surface and the lower base surface; and a flow path within the inner portion, wherein the flow path includes: an inlet on the surface of the chuck base; an outlet on the surface of the chuck base; a length between the inlet and the outlet; a cross-section along the length, wherein the cross-section along the length includes various cross-sectional areas along the length, various cross-sectional shapes along the length, or various distances from the upper base surface along the length, and the flow path includes a first flow path and a second flow path, wherein the first flow path covers half of the surface area of the chuck base and includes a closed loop between the inlet and the outlet, and the second flow path covers the other half of the surface area of the chuck base and includes another closed loop between the inlet and the outlet. An electrostatic chuck base.

2. The electrostatic chuck base according to claim 1, further comprising two unconnected intersecting flow path portions that pass through at one location between the upper base surface and the lower base surface.

3. The electrostatic chuck base according to claim 1, further comprising a flow path portion having a tapered cross-sectional area.

4. The electrostatic chuck base according to claim 1, further comprising a multilayer composite material that extends from the upper base surface to the lower base surface and does not include a metal seam.

5. A method of manufacturing the electrostatic chuck base according to claim 1 by additive manufacturing, comprising: forming a first supply material layer on a surface, the supply material layer including inorganic particles; forming a solidified supply material from the first supply material layer; forming a second supply material layer on the first supply material layer, the second supply material layer including inorganic particles; and forming a second solidified supply material from the second supply material layer, wherein the second solidified supply material layer and the second supply material layer are part of a multilayer composite electrostatic chuck base.

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