Electrostatic chuck including an upper ceramic layer including a dielectric layer, and related methods and structures

Abstract

An electrostatic chuck apparatus useful for supporting a workpiece during processing of the workpiece, an upper ceramic layer component of an electrostatic chuck assembly having a dielectric layer, a relatively smooth surface, or both deposited thereon, and an associated method are described.

Description

[Technical Field]

[0001] The present disclosure relates to an electrostatic chuck apparatus useful for supporting a workpiece during processing of the workpiece, an upper ceramic layer component of an electrostatic chuck assembly having a dielectric layer, a relatively smooth surface, or both deposited thereon, and related methods. [Background technology]

[0002] Electrostatic chucks are used in semiconductor and microelectronic device processing to support a workpiece, such as a semiconductor wafer or microelectronic device substrate, for performing a process on the workpiece. The lower surface of the workpiece is supported on the upper surface of the chuck, while the chuck applies a downward force to the workpiece using electrostatic attraction between the workpiece and the chuck.

[0003] The chuck includes an upper layer made of a dielectric material, such as ceramic. Beneath the upper ceramic layer is an electrode layer on the lower surface of the upper ceramic layer. During operation, a voltage is applied to the electrodes of the electrode layer, which induces a charge in the supported workpiece. The induced charge in the workpiece has an opposite polarity to the voltage applied to the electrodes. The opposite charge between the electrode layer and the supported workpiece creates an electrostatic attraction force between the workpiece and the chuck. This electrostatic attraction exerts a downward force on the workpiece toward the upper surface of the chuck, maintaining the workpiece's position during machining.

[0004] Chucks include various structures, devices, and designs that enable them to perform. A typical electrostatic chuck assembly is a multi-component structure that includes a flat upper surface that supports a workpiece, electrical components such as electrodes, a conductive coating on the upper surface, a ground connection for removing electrostatic charge from the chuck or the supported workpiece, one or more cooling systems for controlling the temperature of the chuck or the supported workpiece, 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, a base layer for supporting the upper ceramic layer, and cooling and electrical connections for connecting the chuck to a tool interface.

[0005] As the workpiece is being machined, it is supported by the upper surface of the chuck and is pressed down against the upper surface by electrostatic charges induced in the workpiece. After the machining step is completed, the voltage to the electrode is turned off, the induced charges dissipate or preferably are removed, and the workpiece can be lifted from the chuck.

[0006] Ideally, the top ceramic layer of the electrostatic chuck is a perfect insulator that is unaffected by the voltage applied to the electrode below it during operation: the ceramic layer will not exhibit any charge caused by the voltage at the electrode, either by induction or conduction.

[0007] This is the ideal effect between an electrode and a perfectly insulating ceramic layer. However, in real-world systems, ceramic materials are not perfect insulators, and a charged electrode in contact with the surface of the ceramic layer will result in a non-zero flow of charge from the electrode to the ceramic layer. This effect is referred to as charge "injection" into the ceramic layer, and results in a "residual" charge that slowly builds up within the ceramic layer over the life of the electrostatic chuck.

[0008] If a significant level of residual charge accumulates within the ceramic layer of the chuck, the residual charge can cause difficulties during use of the chuck. The residual charge can cause a workpiece to "stick" to the top surface of the chuck, which is sometimes referred to as "wafer sticking." Wafer sticking refers to the undesirable electrostatic attraction of the chuck to the workpiece, especially after the step of removing the voltage from the electrostatic chuck's electrodes. Wafer sticking can make it difficult to lift the wafer from the chuck or cause the wafer to experience unpredictable movement during removal. Sticking can also contribute to wafer breakage. Summary of the Invention

[0009] This application describes a novel electrostatic chuck apparatus and component layers of the novel electrostatic chuck apparatus. Methods are also described for preparing the ceramic layers of the described electrostatic chucks and for preparing multi-component electrostatic chucks including the soon-to-be-described upper ceramic layer.

[0010] A need exists to reduce or prevent the buildup of electrostatic charge on the ceramic layer of an electrostatic chuck during use of the chuck. Charge buildup is believed to occur due to charge transfer from an electrode on the lower surface of the ceramic layer to the ceramic layer when a voltage is applied to the electrode.

[0011] Applicants have determined that this type of charge buildup in the ceramic layer can be reduced by providing the ceramic layer with a relatively smooth surface where it contacts the electrode, by disposing a dielectric layer between the ceramic layer and the electrode, by forming the electrode from an electrode material (metal, metal oxide, or other non-metallic material) that has a high work function, or by a combination of two or more of these features.

[0012] The described electrostatic chuck assemblies can include an upper ceramic layer having an upper surface and a lower surface, with a dielectric layer disposed between the lower surface and an electrode in contact with the lower surface of the ceramic layer. The dielectric layer acts as an insulating layer between the electrode and the ceramic layer that can reduce the amount of charge that flows from the electrode to the ceramic layer and that can cause residual charge buildup within the ceramic layer.

[0013] Additionally or alternatively, the lower surface of the ceramic layer in contact with the electrode can be relatively smooth, i.e., have a low surface roughness, such as a roughness of 0.6, 0.4, or 0.1 microns (Ra) or less. Applicant has determined that the surface roughness of the ceramic layer at the electrode location can affect charge transfer, i.e., electrical conduction, from the electrode to the ceramic layer. A relatively low surface roughness can reduce the amount of charge transferred from the electrode to the ceramic layer during use, compared to the amount of charge transferred to the ceramic layer when the surface has a higher roughness. Surface roughness can be measured using known equipment and methods, for example, by using a Bruker DekTak XT stylus profilometer with a stylus tip radius of 12.5 μm, a downforce of 10 mN, and a scan length of 2 mm for 60 seconds.

[0014] Additionally or alternatively, the electrodes of the electrostatic chuck may be made from one or more metallic materials that exhibit a high work function, for example, a work function of at least 4.5 or at least 5 electron volts.

[0015] In one aspect, the present disclosure relates to an electrostatic chuck that includes a ceramic layer having an upper surface and a lower surface, an electrode at the lower surface, and a dielectric layer between the ceramic layer and the electrode.

[0016] In another aspect, the present disclosure relates to an electrostatic chuck that includes a ceramic layer having an upper surface and a lower surface, and an electrode on the lower surface, the lower surface having a surface roughness (Ra) of 0.4 microns or less.

[0017] In yet another aspect, the present disclosure relates to a method of preparing an electrostatic chuck, the method including, for a ceramic layer having an upper surface and a lower surface, forming a dielectric layer on the lower surface and forming an electrode layer on the dielectric layer.

[0018] Yet another aspect of the present disclosure relates to a method of preparing an electrostatic chuck, the method including forming an electrode layer on a ceramic layer having an upper surface and a lower surface, the electrode layer having a surface roughness (Ra) of 0.4 microns or less. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a side view of an illustrated electrostatic chuck assembly. DETAILED DESCRIPTION OF THE INVENTION

[0020] The following description relates to a novel electrostatic chuck apparatus (sometimes referred to herein as an "electrostatic chuck assembly," "electrostatic chuck," or "chuck") and component layers of the novel electrostatic chuck apparatus. Also described are methods for preparing the top ceramic layer of the described electrostatic chuck, and for preparing a multi-component electrostatic chuck including the soon-to-be-described top ceramic layer.

[0021] An exemplary electrostatic chuck device includes an upper ceramic layer having an upper surface and a lower surface, with a dielectric layer deposited on the lower surface of the ceramic layer, where the dielectric layer acts as an insulating layer between the electrode and the ceramic layer. The insulating dielectric layer can act as an insulating, non-conductive barrier between the electrode and the ceramic layer that reduces the amount of charge that can flow from the electrode to the ceramic layer and cause residual charge buildup within the ceramic layer.

[0022] Additionally or alternatively, the lower surface of the ceramic layer in contact with the electrode may be relatively smooth and may have a low surface roughness, such as a roughness that is 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1 microns (Ra) or less. Unless otherwise specified, when referring to the roughness of the lower surface, this roughness refers to the roughness at the point on the lower surface of the ceramic layer where the electrode is located, prior to placement of the electrode, in the absence of the dielectric layer.

[0023] Additionally or alternatively, the electrodes of the electrostatic chuck may be made from one or more metallic materials that exhibit a high work function, for example, a work function of at least 4.5 or at least 5 electron volts.

[0024] Applicant has determined that the surface roughness of a ceramic layer at the point of contact with an electrode can affect charge transfer, i.e., electrical conduction, from the electrode to the ceramic layer. The degree of surface roughness of a ceramic layer has been found to affect the transfer and accumulation of residual charge within the ceramic layer. Without being bound by any particular theory, it is hypothesized that localized (e.g., minute or microscopic) peaks on the surface of a ceramic layer may increase the tendency to accept charge from an adjacent electrode. A ceramic surface containing higher peaks, measured as a higher roughness (Ra), can allow for greater charge transfer from the electrode to the ceramic layer compared to a ceramic surface containing lower peaks, measured as a lower roughness (Ra).

[0025] The described electrostatic chuck is a multi-piece ("multilayer" or "multi-component") structure that includes multiple separately or individually prepared components assembled together as layers to form an electrostatic chuck assembly. The assembly includes various structures and features that are typical of an electrostatic chuck assembly, allowing the chuck to support a workpiece (e.g., a semiconductor substrate, a microelectronic device, a semiconductor wafer, or a precursor thereof) during processing while simultaneously generating an electrostatic attraction between the workpiece and the chuck that holds the workpiece in place at the chuck's upper surface. Exemplary workpieces used with electrostatic chucks include semiconductor wafers, flat screen displays, solar cells, reticles, and photomasks. The workpiece may have an area greater than that of a 100-millimeter diameter circular wafer, a 200-millimeter diameter wafer, a 300-millimeter diameter wafer, or a 450-millimeter diameter wafer.

[0026] 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 multi-layer chuck. As used herein, the term "workpiece contact surface" refers to the upper exposed surface of the electrostatic chuck, which contacts the workpiece during use and includes a "main region," which is made of a ceramic material and has a top surface, typically with embossments on the top surface, with an optional conductive coating that may cover at least a portion of the top surface. The workpiece is held at the workpiece contact surface with the bottom surface of the workpiece supported by and in contact with the embossments on the top surface, such that the workpiece is supported a small distance above the top surface of the ceramic layer.

[0027] The chuck includes an electrode used to apply a downward force to the workpiece to hold it firmly in place against the workpiece contact surface. The electrode is positioned below the upper ceramic layer. When a voltage is applied to the electrode, an electrostatic attraction is generated between the chuck and the workpiece. A voltage of one polarity induces charges of the opposite polarity in the supported workpiece. The opposing charges present in the workpiece (of one polarity) and the electrode (of the opposite polarity) generate an electrostatic attraction between the electrode and the supported workpiece. Exemplary electrostatic chuck assemblies can be used with AC and DC Coulomb force chucks as well as Johnsen-Rahbek chucks.

[0028] The chuck assembly may also include any number of other layers, devices, structures, or features necessary or useful for the functioning of the chuck. Examples include grounding devices such as a grounding layer and associated electrical connections, measurement devices for measuring pressure, temperature, or electrical properties while the chuck is in use, conduits (cooling channels) in a layer (e.g., base) of the chuck useful as part of the temperature control function, backside gas flow features for gas flow and pressure control between the workpiece contact surface and the workpiece, conductive surface coatings, and others.

[0029] One layer of the chuck assembly is an upper ceramic layer (or "ceramic layer" for short) at the top of the assembly. The ceramic layer may be the top layer of the assembly, excluding any conductive coatings or embossings, etc., that may be disposed on the top surface of the ceramic layer. The ceramic layer may be made of any useful ceramic dielectric material. Exemplary materials include alumina (Al2O3), aluminum nitride, quartz, and SiO2 (glass), among others. The ceramic layer may be made of a single (unitary) layer of material, or alternatively, may be made of two or more different materials, e.g., multiple layers of different materials, as desired. The thickness of the ceramic layer may be any effective thickness, e.g., a thickness ranging from 50 microns to 1 millimeter.

[0030] The ceramic layer can comprise, consist essentially of, or consist of a dielectric material, e.g., a ceramic material. The ceramic layer is made of a material that provides dielectric properties along with desired mechanical properties, such as stiffness. The ceramic layer can contain at least 90, 95, or 99 weight percent of one or more different ceramic materials.

[0031] The ceramic layer is supported below by a base layer ("base" for short) which may be made of a metal such as aluminum, an aluminum alloy, titanium, a titanium alloy, stainless steel, or a metal matrix composite, among others.

[0032] Typically, between the ceramic layer and the base there is one or more of a bonding layer (e.g., a polymer adhesive), an electrode layer containing one or more electrodes that contact the lower (bottom) surface of the ceramic layer, a ground layer, an insulating layer that enables the electrodes and other layers to function electrically, or additional circuitry.

[0033] An example of a useful chuck assembly is shown in FIG. 1. Chuck assembly 10 includes a base 12, a ceramic layer ("assembly") 14, and a bonding layer 16 that bonds the top surface of base 12 to the bottom or lower surface of ceramic layer 14. Ceramic layer 14 also includes an electrode (not specifically shown) disposed on the bottom surface. The top surface of ceramic layer 14 has a pattern of embossments 18. As shown, a workpiece (shown as a wafer 20) is supported by the embossments. A space 22 exists between the bottom surface of wafer 20 and the top of ceramic layer 14. The space 22 is created by embossments 18 located on the top surface of ceramic layer 14, which support wafer 20 a small distance above the top surface of ceramic layer 14.

[0034] In accordance with the ceramic layer and electrostatic chuck assembly herein, the ceramic layer of the chuck includes one or both of the following features: i) a low surface roughness on the bottom surface of the ceramic layer where it contacts the electrode; and ii) a dielectric layer on the bottom surface between the bottom surface of the ceramic layer and the electrode.

[0035] The ceramic layer includes a top surface, a bottom surface, and a bulk ceramic layer ("ceramic body") formed as a ceramic body having a thickness (typically in the range of 1 to 10 millimeters). The ceramic body can be formed by any useful process, an exemplary method of which includes one or more steps that can include molding or pressing a ceramic material (e.g., ceramic powder) to form a green body or compact (sometimes referred to as a "green body"), followed by a high-temperature sintering step to bond the ceramic particles of the compact or compact to form the ceramic body. The sintered ceramic body is a hard ceramic body having top and bottom surfaces. The ceramic body can have a uniform composition and a dense morphology as measured by low porosity, e.g., porosity (pore volume per volume of the bulk ceramic body) of less than 10 percent, 5 percent, or 2 or 1 percent.

[0036] For use in an electrostatic chuck, the upper and lower surfaces are very flat and are processed to have a desired surface roughness. Typically, the upper surface of the ceramic layer can be formed and processed to have a surface roughness (Ra) of 0.5 to about 1 micron.

[0037] In the case of the ceramic layer of previous electrostatic chuck assemblies, the lower surface of the ceramic layer facing the electrode and adhesive (bonding) layer is typically processed to have a surface roughness (Ra) of at least 0.6 microns, or even 1.0 microns or greater. This level of surface roughness has been used because it is effective in generating good adhesion between the ceramic surface and the adhesive of the bonding layer, and between the ceramic surface and the electrode that contacts it.

[0038] According to the present disclosure, the bottom surface of the ceramic layer (i.e., the surface of the ceramic layer that contacts the bonding layer and the electrode) can be formed and processed to be smoother than the bottom surface of the previous ceramic layer of the electrostatic chuck assembly. Applicant has determined that the level of roughness of the bottom surface of the ceramic layer in the area of ​​contact between the bottom surface of the ceramic layer and the electrode can affect the amount of electrostatic charge transferred from the electrode to the ceramic layer.

[0039] The roughness of a ceramic layer is a measure of the peak-to-valley microtopography of a surface. A surface with a larger difference between the peaks and valleys, a larger number of peaks and valleys, or both, may allow a larger amount of electrostatic charge to be transferred from an electrode to the surface compared to the amount of charge that would be transferred to a surface with a smaller difference between the peaks and valleys or a smaller number of peaks and valleys. A ceramic layer with a higher roughness in contact with a charged electrode may allow an increased amount of charge to be transferred to the ceramic layer from an electrode in contact with the ceramic layer and carrying a high-voltage charge. A relatively smooth surface of a ceramic layer with a reduced level of peak-to-valley microtopography and fewer peaks and valleys may reduce the presence or strength of magnetic fields generated at the peaks when a voltage is applied to an electrode in contact with the ceramic surface. Reducing the strength of the magnetic field at the ceramic surface may reduce the amount of charge that is released from the electrode to the ceramic layer at microscopic peaks and becomes an accumulated electrostatic charge within the ceramic layer.

[0040] Thus, the bottom surface of the ceramic layer herein has a relatively smooth surface compared to those used in previous electrostatic chucks, particularly in the region of the surface that contacts the electrode. A smoother surface can have the effect of reducing peak-to-valley roughness and reducing the amount of charge transferred to the ceramic layer from the high-voltage electrode that contacts the ceramic layer. Over the use time of an electrostatic chuck containing a smoother ceramic layer, the amount of residual charge that builds up within the ceramic layer will be reduced. Examples of useful or preferred roughness levels for the bottom surface of the ceramic layer can be 0.6 microns, 0.5 microns, 0.4 microns, 0.3 microns, 0.2 microns, 0.1 microns, or 0.05 microns or less.

[0041] Additionally or alternatively, the ceramic layer may include a dielectric layer applied to the lower surface in contact with the electrode. As used herein, a "dielectric layer" is a layer or coating that has been fabricated to include a dielectric material added (e.g., deposited) onto the surface of the ceramic layer by a deposition method such as atomic layer deposition, chemical vapor deposition, physical vapor deposition, etc. A "dielectric layer" may be an initially deposited layer or coating, or a modification or derivative thereof, such as a deposited layer that is subsequently chemically modified, or treated, or further processed.

[0042] The dielectric layer is an electrically insulating layer that provides electrical insulation and resistance to electrical flow between the ceramic layer and the electrode in contact with the ceramic layer. The dielectric layer has a high dielectric strength, e.g., a high resistivity (ρ ohm-m), e.g., at least as high as the resistivity of the ceramic layer, and preferably a higher resistivity, e.g., at least 1×10 14 It may have a resistivity of ρ ohm-m.

[0043] Examples of dielectric materials include alumina (Al2O3), silicon-based ceramic materials (e.g., SiO2, SiN), metal oxides such as zirconium oxide or hafnium oxide, or combinations thereof. If necessary, for example, based on performance and manufacturing considerations, the dielectric layer applied to the surface of the ceramic layer can be made of the same type of dielectric material as the ceramic layer. According to a specific example, the ceramic layer can be made of alumina, and the dielectric layer applied to the ceramic layer can also be made of alumina. According to another example, the dielectric layer can be made of a dielectric material different from the material of the ceramic layer.

[0044] The dielectric layer can comprise, consist essentially of, or consist of a dielectric material applied or deposited on the lower surface of the ceramic layer. The dielectric layer is made of one or more materials that have high dielectric strength and can be applied to the lower surface of the ceramic layer to form a continuous, electrically insulating layer. The dielectric layer can contain at least 90, 95, or 99 weight percent of one or more different dielectric materials.

[0045] The dielectric layer can exhibit any useful thickness, such as a thickness in the nanometer or micron range. Useful or preferred dielectric layers can be deposited on the ceramic layer surface with a thickness and technique that allows the dielectric layer to conform to the microstructure present on the ceramic layer surface. That is, the dielectric layer is conformal and does not affect the roughness of the ceramic layer surface by significantly increasing or decreasing the measured surface roughness, e.g., by changing the measured surface roughness by more than 2, 5, or 10 percent. The measured roughness of the ceramic layer after the dielectric layer is applied thereto can be within the ranges described for the ceramic layer before the dielectric layer is applied thereto; for example, the ceramic layer including the dielectric layer applied thereto can exhibit a roughness level of 0.6 microns, 0.5 microns, 0.4 microns, 0.3 microns, 0.2 microns, 0.1 microns, or 0.05 microns or less.

[0046] Useful thicknesses of dielectric layers applied by deposition techniques, such as atomic layer deposition, can be less than 200 nanometers, for example, from a few nanometers (e.g., 5 or 10 nanometers) to 400 nanometers (nm), or from 50 or 100 nanometers to 200 nanometers. The dielectric layer can be continuous over the entire surface of the ceramic layer, or at least over the portion of the ceramic layer surface that contacts the electrode.

[0047] Many methods are known and commercially useful and effective for depositing layers of dielectric materials on ceramic surfaces. Common examples include atomic layer deposition (ALD), chemical vapor deposition (CVD), and physical vapor deposition (PVD) (e.g., sputtering), as well as modifications of these methods, such as plasma-enhanced chemical vapor deposition (PECVD). Dielectric layers prepared by a particular type of deposition method may be referred to by their deposition method. For example, a dielectric layer applied by a chemical vapor deposition method may be referred to as a "CVD dielectric layer," a dielectric layer applied to a ceramic layer by an atomic layer deposition method may be referred to as an "ALD dielectric layer," and a dielectric layer applied to a ceramic layer by a physical vapor deposition method may be referred to as a "PVD dielectric layer."

[0048] While the ceramic layer and chuck assemblies described herein are not limited to any particular method of forming or applying a dielectric layer to a ceramic surface or to any particular form of the dielectric layer, dielectric layers exhibiting certain properties may be particularly useful. For example, a dielectric layer applied to a ceramic layer to provide an electrical insulating (dielectric) effect, such as high resistivity, should exist across the ceramic layer surface as a continuous, substantially defect-free layer. Additionally, it is potentially preferable that the dielectric layer be relatively densely applied and conformal to the surface of the ceramic layer.

[0049] Thus, useful or preferred dielectric layers include ALD dielectric layers, which refers to dielectric layers applied by atomic layer deposition onto the surface of a ceramic layer. Atomic layer deposition techniques are effective in generating deposited layers of dielectric materials that are relatively dense (compared to layers applied by other deposition techniques), have very low levels of defects, are fairly conformal, and exhibit good dielectric properties.

[0050] Atomic layer deposition is a method for depositing very thin layers of material (here, a dielectric material) on a substrate material (here, the surface of a ceramic layer). The dielectric layer may be made of a single type of deposition material, or may be made of multiple (e.g., two or more) different materials deposited as alternating layers (sublayers) within the dielectric layer. According to an exemplary ALD dielectric layer, the ALD layer may be made of a single type of dielectric material, such as ZrO, HfO, or alumina. According to another exemplary ALD dielectric layer, the deposited ALD dielectric layer may be made of multiple sublayers of different (e.g., alternating) dielectric materials; for example, the dielectric layer may be made of alternatingly deposited sublayers of ZrO and HfO.

[0051] Advantages that can be achieved with dielectric layers prepared by atomic layer deposition include excellent conformality of the dielectric layer to the substrate microstructure (e.g., an applied ALD dielectric layer does not significantly affect measured surface roughness values), precise control of the dielectric layer thickness, high uniformity of the dielectric layer thickness across the area of ​​the layer, the ability to apply two or more different deposited dielectric materials as different sublayers of the dielectric layer, and preparing coatings with very low levels of defects such as pinholes, cracks, fissures, and grain boundaries.

[0052] The electrode layer can include one or many separate electrode elements positioned across a portion of the lower surface of the ceramic layer, typically as a pattern of one or many electrodes. The electrodes can be formed or applied to the ceramic layer, or to a dielectric layer previously disposed on the ceramic layer, by any of a variety of methods, including by deposition methods. One or more electrodes of the electrode layer can be applied or deposited on the ceramic layer surface in a pattern applied to only a portion of the surface. According to another method, electrodes can be formed on the ceramic layer surface by first applying a continuous layer of conductive (e.g., metallic) electrode material across the entire surface of the ceramic layer, followed by etching to remove portions of the continuous layer and leave the desired pattern.

[0053] Various methods are known for depositing layers of electrode materials onto ceramic surfaces, common examples being atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD) (e.g., sputtering), as well as many modifications of these methods, such as plasma-enhanced chemical vapor deposition (PECVD).

[0054] The electrode can be made of any metal or nonmetal (including metal alloys) that can be effective as an electrode and that can be processed to form an electrode structure as part of an electrostatic chuck, for example, by depositing the electrode on the surface of a ceramic layer. Exemplary electrode materials include metals, metal alloys, and the conductive nonmetals titanium nitride, zirconium nitride, chromium nitride, and indium tin oxide, among others.

[0055] A useful or preferred electrode material may be a metal having a "work function" that reduces the flow of electrons away from the electrode's structure, allowing them to escape from the electrode, cross into the dielectric layer, and remain there as a stored charge. The "work function" of a metallic material is a known property defined as the minimum energy required for an electron to escape from the metal surface. Preferred electrode materials can be metals having a work function of at least 4.5, 5 electron volts (eV). Examples of such metals include Ni, Co, W, Pb, Pt, Ir, and Au.

[0056] The electrode can comprise, consist essentially of, or consist of a metal having a work function of at least 4.5 or at least 5 electron volts. Useful electrode materials can be highly conductive and can be applied to the surface of the ceramic layer of the electrostatic chuck by, for example, deposition techniques, to function as an electrode. The electrode layer can contain at least 90, 95, or 99 weight percent of one or more different metal materials, for example, at least 90, 95, or 99 weight percent of one or more different metal materials having a work function of at least 4.5 or at least 5 electron volts.

[0057] The ceramic layer of the chuck assembly may be prepared by using a variety of useful processing and manufacturing techniques, such as known techniques for forming a ceramic layer body, known techniques for processing the surface of the ceramic layer to a desired surface roughness, and deposition techniques for applying an electrode layer, a dielectric layer, or both, to the surface of the ceramic layer.

[0058] According to one example, a method for preparing the described ceramic layer or electrostatic chuck can include forming an electrode layer on a surface of the described ceramic layer, which can include a dielectric layer, exhibit low surface roughness (e.g., 0.6 microns or less), or both.

[0059] The electrode layer and the optional dielectric layer may each be formed in a pattern.

[0060] Alternatively, the electrode layer, the method may include steps including depositing a dielectric layer on the lower surface as an unpatterned dielectric layer, depositing an electrode layer on the lower surface over the dielectric layer as an unpatterned electrode layer, and removing portions of the electrode layer by etching to form a patterned electrode layer.

[0061] In a first aspect, an electrostatic chuck comprises a ceramic layer having an upper surface and a lower surface, an electrode at the lower surface, and a dielectric layer between the ceramic layer and the electrode.

[0062] In a second aspect related to the first aspect, the dielectric layer is a CVD, ALD, or PECVD dielectric layer deposited on the lower surface.

[0063] In a third aspect of any of the previous aspects, the dielectric layer has a thickness of less than 200 nanometers.

[0064] In a fourth aspect of any of the previous aspects, the dielectric layer comprises a dielectric material different from the ceramic material of the ceramic layer.

[0065] In a fifth aspect according to any of the previous aspects, the dielectric layer comprises a metal oxide such as alumina (Al2O3), a silicon-based ceramic material (e.g., SiO, SiN), zirconium oxide, or hafnium oxide.

[0066] In a sixth aspect according to any of the previous aspects, the ceramic layer comprises alumina and the dielectric layer comprises alumina.

[0067] In a seventh aspect according to any of the previous aspects, the electrode comprises a metal having a work function of at least 4.5 electron volts.

[0068] In an eighth aspect related to the seventh aspect, the electrode comprises a metal selected from Ni, Co, W, Pb, Pt, Ir and Au.

[0069] In a ninth aspect according to any of the previous aspects, the lower surface has a surface roughness (Ra) of 0.4 microns or less.

[0070] In a tenth aspect according to any of the previous aspects, the lower surface has a surface roughness (Ra) of 0.1 microns or less.

[0071] In an eleventh aspect, in accordance with any of the previous aspects, the ceramic layer comprises alumina.

[0072] In a twelfth aspect, in accordance with any of the previous aspects, the dielectric layer is an alumina ALD dielectric layer.

[0073] In a thirteenth embodiment, an electrostatic chuck comprises a ceramic layer having an upper surface and a lower surface, and an electrode on the lower surface, the lower surface having a surface roughness (Ra) of 0.4 microns or less.

[0074] In a fourteenth aspect relating to the thirteenth aspect, the lower surface has a surface roughness (Ra) of 0.1 microns or less.

[0075] In a fifteenth aspect related to the thirteenth or fourteenth aspect, the electrode comprises a metal having a work function of at least 4.5 electron volts.

[0076] In a sixteenth aspect relating to the fifteenth aspect, the electrode comprises Ni, Co, W, Pb, Pt, Ir, or Au.

[0077] In a seventeenth aspect, a method of using the electrostatic chuck of any of the previous aspects includes supporting a semiconductor wafer on an upper surface, applying a voltage to an electrode to induce a reverse voltage in the semiconductor wafer, processing the semiconductor wafer, removing the voltage from the electrode, and lifting the wafer from the upper surface.

[0078] In an eighteenth aspect relating to the seventeenth aspect, the voltage is a DC voltage.

[0079] In a nineteenth aspect, a method of preparing an electrostatic chuck includes, for a ceramic layer having an upper surface and a lower surface, forming a dielectric layer on the lower surface, and forming an electrode layer on the dielectric layer.

[0080] A twentieth aspect according to the nineteenth aspect, further comprising forming the dielectric layer by a method selected from chemical vapor deposition, plasma-enhanced chemical vapor deposition, and atomic layer deposition.

[0081] A twenty-first aspect according to the nineteenth aspect, further comprising forming the dielectric layer by atomic layer deposition.

[0082] A 22nd aspect according to any of the 19th to 21st aspects, further comprising depositing the electrode layer by a method selected from chemical vapor deposition, plasma-enhanced chemical vapor deposition, and atomic layer deposition.

[0083] In a 23rd aspect relating to any of the 19th to 22nd aspects, the dielectric layer contains a metal oxide such as alumina (Al2O3), a silicon-based ceramic material (for example, SiO, SiN), zirconium oxide, or hafnium oxide.

[0084] In a 24th aspect relating to any of the 19th to 23rd aspects, the dielectric layer has a thickness of less than 200 nanometers.

[0085] In a 25th aspect relating to any of the 19th to 24th aspects, the electrode comprises a metal having a work function of at least 4.5 electron volts.

[0086] In a twenty-sixth aspect relating to the twenty-fifth aspect, the electrode comprises Ni, Co, W, Pb, Pt, Ir, or Au.

[0087] In a 27th aspect relating to any of the 19th to 26th aspects, the lower surface has a surface roughness (Ra) of 0.4 microns or less.

[0088] In a twenty-eighth embodiment, a method of preparing an electrostatic chuck includes forming an electrode layer on a ceramic layer having an upper surface and a lower surface, the electrode layer having a surface roughness (Ra) of less than 0.4 microns.

[0089] In a twenty-ninth aspect relating to the twenty-eighth aspect, the electrode comprises a metal having a work function of at least 4.5 electron volts.

[0090] In a 30th aspect relating to the 28th aspect or the 29th aspect, the electrode comprises Ni, Co, W, Pb, Pt, Ir, or Au.

Claims

1. a ceramic layer including an upper surface and a lower surface; an electrode on the lower surface; a dielectric layer between the ceramic layer and the electrode; Equipped with 1. An electrostatic chuck wherein the lower surface has a surface roughness (Ra) of 0.4 microns or less.

2. A ceramic layer having an upper surface and a lower surface; an electrode on the lower surface; a dielectric layer between the ceramic layer and the electrode; Equipped with The electrostatic chuck, wherein the dielectric layer has a thickness of less than 200 nanometers.

3. 10. The electrostatic chuck of claim 1, wherein the dielectric layer comprises a dielectric material different from a ceramic material of the ceramic layer.

4. The dielectric layer is made of alumina (Al ２ O ３ ), a silicon-based ceramic material (e.g., SiO, SiN), a metal oxide such as zirconium oxide or hafnium oxide.

5. 10. The electrostatic chuck of claim 1, wherein the ceramic layer comprises alumina and the dielectric layer comprises alumina.

6. 10. The electrostatic chuck of claim 1, wherein the electrode comprises a metal having a work function of at least 4.5 electron volts.

7. 1. A method of preparing an electrostatic chuck, comprising: forming an electrode layer on a ceramic layer having an upper surface and a lower surface, the electrode layer having a surface roughness (Ra) of less than 0.4 microns.

8. The method of claim 7 , wherein the electrode layer comprises a metal having a work function of at least 4.5 electron volts.

9. The method of claim 7 , wherein the electrode layer comprises Ni, Co, W, Pb, Pt, Ir, or Au.

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