Sintered lanthanum zirconium oxide, multilayer sintered ceramic bodies and related methods

Abstract

Sintered lanthanum zirconium oxide (LZO) materials, multilayer sintered ceramic bodies containing sintered lanthanum zirconium oxide and a support layer are described, as well as methods for preparing them using plasma discharge sintering technology.

Description

Technical Field

[0001] The following describes sintered lanthanum zirconium oxide (LZO), multilayer sintered ceramic bodies containing sintered lanthanum zirconium oxide and a support layer, and methods for preparing them using plasma discharge sintering technology. Background Technology

[0002] Semiconductor processing equipment, such as plasma etching chambers and plasma deposition chambers (collectively referred to as "plasma chambers"), requires a high-purity, contaminant-free plasma environment. To achieve this contaminant-free environment, the interiors of these chambers use chemically resistant surfaces to prevent particulate contamination that could be introduced into the plasma chamber.

[0003] Semiconductor and microelectronic device fabrication requires steps involving the processing of semiconductor and microelectronic device substrates in a plasma atmosphere, which is generated by exposing halogen-based gases to an electromagnetic field within a evacuated plasma chamber. The plasma atmosphere is used during the etching or deposition of materials on the semiconductor and microelectronic device substrates, and this atmosphere must be substantially free of particulate contamination.

[0004] Plasma atmospheres can degrade materials located within the plasma chamber. Contact with plasma can lead to chemical degradation, corrosion, and roughening of surfaces, resulting in the introduction of surface materials as contaminants (e.g., particulate contaminants) into the plasma chamber. Particulate contaminants can deposit on the substrate being processed within the chamber, causing defects and reduced semiconductor device yield if this occurs.

[0005] To reduce particulate contamination from plasma generation, the surfaces inside the plasma chamber can be made of materials resistant to both plasma and the halogen-based process gases used to generate the plasma (i.e., "plasma-resistant"). Materials such as yttrium oxide and yttrium aluminum garnet (YAG) have been used as thin-film coatings on the inner surfaces of plasma chambers and plasma chamber components. These films or coatings have been prepared using several methods, including vapor deposition and aerosol or plasma spraying. Such films and coatings can exhibit performance defects due to their relatively thinness, low density, and high porosity. Additionally, coatings applied to another material may readily delaminate at the interface between the coating and that material, potentially leading to cracking and peeling, as well as the release of particulate contaminants from the surface. Coatings applied via aerosol or plasma spraying typically exhibit porosity levels of 3% to 50%, correspondingly low density, and poor adhesion between the substrate and coating materials, resulting in peeling, flaking, and chamber contamination. Summary of the Invention

[0006] There is a persistent need for materials that exhibit high resistance to plasma and halogen-based gases, and therefore produce low levels of particulate contamination when used inside a plasma chamber. Materials for these applications offer high resistance to plasma and chlorine and fluorine-based process gases, low dielectric loss, high thermal conductivity, and can be machined to form solid bodies for use inside a plasma chamber. Related surface properties may include one or more of the following: high heat resistance; high purity; high density, such as low porosity, where any pores present have a small maximum size; small grain size; high mechanical strength and hardness; and a thickness that allows for extended surface life inside the plasma chamber.

[0007] For suitability for use in a plasma chamber, the body containing a plasma-resistant surface may preferably have dimensions suitable for use inside a plasma chamber, such as a flat body having a length, width, or diameter dimension greater than 100 mm (e.g., 100 mm to 625 mm) and a thickness that allows the body to provide plasma resistance over a fairly long service life.

[0008] In some applications, the plasma-resistant surface is a single layer of a multilayer ceramic body comprising a support layer and a plasma-resistant layer. For these multilayer ceramic bodies, the individual layers may preferably have sufficiently similar thermal expansion properties (e.g., as measured by the coefficient of thermal expansion) to allow the multilayer body to withstand heating and cooling without suffering physical damage such as cracking or delamination.

[0009] The following describes sintered lanthanum zirconium oxide materials (“sintered lanthanum zirconium oxide” or “sintered LZO”) that can be used as plasma-resistant materials in plasma chambers. Sintered lanthanum zirconium oxide materials can be produced using a spark plasma sintering process, which has been developed to produce sintered lanthanum zirconium oxides with physical properties including: plasma resistance, heat resistance, high purity, high density (including low porosity and small maximum pore size), and small grain size (including small average grain size and small maximum grain size). These processes also produce lanthanum zirconium oxide materials exhibiting good mechanical strength and hardness, as well as machinability. Sintered lanthanum zirconium oxide can be formed into circular forms with dimensions suitable for use in plasma chambers, including a diameter of at least 100 mm and a thickness allowing for a considerably long service life when used in a plasma chamber.

[0010] In some examples, lanthanum zirconium oxide materials can be formed as multilayer sintered ceramic bodies comprising sintered lanthanum zirconium oxide layers and a support layer, such as zirconium oxide toughened alumina (ZTA). The multilayer sintered ceramic body should exhibit good interlayer adhesion, and the different layers should be compatible in terms of processing during the sintering process, so that two layers of the sintered body are formed using a single sintering step; for example, the materials of the two layers should have similar coefficients of thermal expansion.

[0011] Previously, unsintered lanthanum zirconium oxide (“LZO”) materials have been used as plasma-sprayed LZO coatings in plasma chamber components. See U.S. Patent No. 10,388,492. These coated materials have high porosity and lack high density, which is useful for the surface inside the plasma chamber. Based on different prior applications, Chinese Patent Publication CN103803972 B describes a sintered LZO ceramic body prepared by hot-pressing sintering. This ceramic body is described as suitable for use as a thermal insulation material in high-temperature aerospace applications (such as under hypersonic flight conditions at super-angle of attack), but is not described as having particularly high purity or density (e.g., greater than 95% or 98% of theoretical density), low porosity or small pore size, or fine average or maximum grain size.

[0012] In addition, sintered ceramic bodies including polycrystalline yttrium aluminum garnet (YAG) layers have previously been prepared by plasma discharge sintering. See PCT Publication WO 2022 / 133180.

[0013] This paper describes sintered lanthanum zirconium oxide (LZO) materials prepared by reacting lanthanum oxide and zirconium oxide powders using a spark plasma sintering (SPS) process. Both lanthanum oxide and zirconium oxide powders possess very high purity, and the powder preparation and processing steps prior to and during the sintering step can be controlled to achieve the desired high purity of the sintered LZO body. For example, the two powder materials can be combined into a homogeneous powder mixture by grinding, and optionally calcined to reduce the impurity content of the powder mixture.

[0014] During the sintering step, a combination of process conditions can be controlled to produce sintered lanthanum oxide materials with desired density (including the presence and size of pores) and microstructure (e.g., grain size). These process conditions may include pressure applied to the powder mixture (“sintering pressure”), heating rate (temperature distribution), maximum temperature or temperature range (“sintering temperature”), current passing through the die, and the amount of time the powder mixture is held at the sintering temperature (“sintering time”).

[0015] An example method for sintering a powder mixture containing lanthanum oxide powder and zirconium oxide powder may be used with a sintering pressure not exceeding 100 MPa and a sintering temperature not exceeding 1625 degrees Celsius. The sintering time depends on the size of the mold used to contain the powder mixture, wherein the sintering time for a mold with a diameter of 100 mm to 150 mm is typically not more than 120 minutes, 90 minutes, or 60 minutes.

[0016] An exemplary sintered lanthanum zirconium oxide material prepared according to the method described herein may have one or a combination of the following: a purity of at least 99.999%, a density of at least 96% of the theoretical density, a porosity in the range of 0.0005% to 2%, pores with a maximum size of 10 micrometers or preferably 5 micrometers as measured on the surface of the sintered lanthanum zirconium oxide, an average grain size of less than 10 micrometers, and a maximum grain size of less than 10 micrometers.

[0017] In one respect, the following description refers to sintered lanthanum zirconium oxide having a purity of at least 99.999% and a certain density.

[0018] On the other hand, the following description relates to a multilayer sintered ceramic body comprising a sintered lanthanum zirconium oxide layer and a sintered zirconium oxide toughened alumina layer.

[0019] On the other hand, the following description relates to sintered lanthanum zirconium oxide and multilayer sintered ceramic bodies prepared by spark plasma sintering as described.

[0020] On the other hand, the following description relates to a method for preparing sintered lanthanum zirconium oxide. The method includes: preparing a powder mixture comprising lanthanum oxide particles and zirconium oxide particles; placing the powder mixture into a graphite mold; removing oxygen from the mold; and sintering the powder mixture in the mold by applying pressure to the powder mixture and passing an electric current through the mold to raise the temperature of the powder mixture and causing the lanthanum oxide to react with the zirconium oxide powder to form sintered lanthanum zirconium oxide.

[0021] In another aspect, this specification relates to a method for preparing a multilayer sintered ceramic body comprising a lanthanum zirconium oxide layer and a zirconium oxide-toughened alumina layer. The method includes: preparing a first powder mixture comprising lanthanum oxide particles and zirconium oxide particles; preparing a second powder mixture comprising zirconium oxide and alumina; forming a layer of the first powder mixture in a graphite mold; forming a layer of the second powder mixture in a graphite mold; and sintering the first and second powder mixtures by: applying pressure to the first and second powder mixtures in the mold and passing an electric current through the mold to raise the temperature of the first and second powder mixtures, thereby forming a lanthanum zirconium oxide layer in the first powder mixture and a zirconium oxide-toughened alumina layer in the second powder mixture. Attached Figure Description

[0022] Figure 1 This is a schematic cross-sectional view of an example apparatus for preparing sintered lanthanum zirconium oxide.

[0023] Figure 2 The coefficients of thermal expansion of lanthanum zirconium oxide and zirconium oxide-toughened alumina are shown.

[0024] Figure 3 This is a schematic cross-sectional view of an example apparatus for preparing a multilayer sintered ceramic body comprising sintered lanthanum zirconium oxide and a support layer.

[0025] Figure 4 This is a photograph of a multilayer sintered ceramic body prepared according to this instruction manual.

[0026] All accompanying drawings are schematic and not necessarily drawn to scale. Detailed Implementation

[0027] The following describes sintered lanthanum zirconium oxide materials prepared by a spark plasma sintering (“SPS”) process, wherein lanthanum oxide powder reacts with zirconium oxide powder during the formation of the sintered lanthanum zirconium oxide material. The sintered LZO (La₂Zr₂O₇) produced by the spark plasma sintering process has one or a combination of the following: high purity, high density, low porosity (low volumetric porosity and small maximum pore size), and fine grain size (in terms of average and maximum grain size). The example sintered LZO material prepared as described may have one or more of the following: a purity of at least 99.999% (e.g., at least 99.9999% or 99.99999%); a density of at least 96%, 97%, 98%, or 99% of the theoretical density; a porosity in the range of 0.0005% to 2%; a maximum pore size of 5 micrometers or 10 micrometers; an average grain size of less than 10 micrometers; and a maximum grain size not exceeding 10 micrometers.

[0028] As used herein, the term "spark plasma sintering" ("SPS") refers to a method of bonding individual particles of powder together to form a dense sintered material (also known as a "sintered body") by applying pressure to the particles while simultaneously heating the particles in a mold through an electric current passing through the mold; heating the particles in the mold to a temperature high enough that the individual particles bond together through atomic diffusion at the particle surface, but still below the melting point of the particles. This method uses the simultaneous application of uniaxial pressure and an electric current passing through the mold to raise the temperature of the powder particles in the mold. Spark plasma sintering differs from hot pressing sintering, which uses an external heat source (such as a furnace or resistance heating element) to heat the mold containing the powder to be sintered.

[0029] The spark plasma sintering process for preparing sintered lanthanum zirconium oxide is performed using a spark plasma sintering apparatus comprising a mold having a mold interior and a movable surface (e.g., the surface of a "punch") disposed within the mold interior, the movable surface being movable to apply pressure to powder contained within the mold interior. One or more layers of powder mixture can be placed within the mold interior, and then the one or more layers of powder mixture are compressed within the mold interior by applying pressure to the one or more layers of powder mixture using the surface of the movable punch. When the powder mixture is compressed within the mold interior, heat is generated within the mold by passing an electric current through the mold; the heat passing through the mold raises the temperature of the powder mixture and simultaneously applies pressure to the powder mixture within the mold interior. The powder mixture can be contained within the mold interior in a vacuum or another controlled atmosphere (e.g., argon or hydrogen) to prevent undesirable reactions (e.g., oxidation) in the powder mixture, thereby producing a sintered material with the desired high purity. The electric current can be pulsed or non-pulsated and can be alternating current ("AC") or direct current ("DC").

[0030] According to the process described above, the purity, preparation, and treatment of the powder mixture before and during the sintering step can be controlled to achieve the desired high purity of the sintered LZO body. In the example process, the powder mixture is formed from two powders, namely lanthanum oxide (La₂O₃) powder and zirconium oxide (ZrO₂) powder, in a ratio of two moles of zirconium oxide to one mole of lanthanum oxide. The zirconium oxide powder can be pure zirconium oxide (unstabilized) or it can be stable zirconium oxide powder containing zirconium oxide and a certain amount of yttrium oxide (Y₂O₃), for example, about 3 mol% of yttrium oxide (e.g., 3-YSZ) based on the total weight of zirconium oxide and yttrium oxide in the zirconium oxide powder.

[0031] The powder mixture may comprise, consist substantially of, or consist of lanthanum oxide powder and zirconium oxide powder (which may contain a certain amount of yttrium oxide). A powder mixture consisting substantially of lanthanum oxide powder and zirconium oxide powder refers to a powder mixture that contains lanthanum oxide powder and zirconium oxide powder, and no more than trace amounts of any other material (such as sintering aids, dopants, or impurities), for example, less than 5% by weight, 2% by weight, 1% by weight, 0.5% by weight, or 0.1% by weight of these or any other type of material other than lanthanum oxide powder and zirconium oxide powder.

[0032] The raw material particles are in powder form, that is, a collection of extremely fine, dry, solid, free-flowing granular particles. The powder contains particles of relatively uniform size, with the largest particle size being in the micrometer range, for example, less than 1,000 micrometers, 800 micrometers, or 500 micrometers. The powder can be prepared based on the largest particle size by methods such as passing the powder through a sieve with a nominal mesh size of less than 1,000 micrometers, 800 micrometers, or 500 micrometers (e.g., 18-mesh, 25-mesh, or 40-mesh sieves).

[0033] To produce sintered LZO with extremely high purity, a powder mixture can be formed from lanthanum oxide and zirconium oxide with extremely high purity. According to an example method, the lanthanum oxide powder can have a purity of at least 99.999%, 99.9999%, for example, at least 99.99999%. The zirconium oxide powder (with optional yttrium oxide) can have a purity of at least 99.99%, for example, at least 99.999%, as measured using inductively coupled plasma mass spectrometry (ICP-MS).

[0034] Lanthanum oxide powder and zirconium oxide powder are combined and mixed to form a homogeneous powder mixture. As an example, a ball mill and solid grinding media can be used to mix the powders. Preferred types of ball mills and grinding media are those that minimize the introduction of contaminants into the powder from the ball mill or grinding media during mixing. For example, a preferred ball mill may include an interior lined with a durable polymer material that does not degrade during grinding and resists the shedding of polymer material particles into the powder mixture. Example ball mills may be lined with a polyolefin coating, such as polyethylene or polypropylene. Similarly, preferred grinding media (grinding balls) are types that do not degrade during grinding and resist the shedding of grinding media material into the powder mixture. Examples of useful or preferred grinding media may be made of ceramic materials such as stabilized zirconium oxide, so that even if zirconium oxide grinding media detaches, the detachment only adds to the zirconium oxide particles already present in the mixed powder.

[0035] During the grinding process, the solvent can be added along with the powder. A useful solvent that does not react with the powder can be selected, such as ethanol.

[0036] Optionally, after grinding, the powder mixture can be processed by calcining to remove residual solvents and potential organic impurities that may be present in the powder mixture. The calcination step heats the powder mixture to a temperature that will not cause the powder particles to melt or react, thereby removing impurities or volatile materials from the powder mixture. The step of calcining the powder mixture containing lanthanum oxide powder and zirconium oxide powder can be heated to a temperature in the range of 600 to 850 degrees Celsius, while maintaining a sufficient amount of time available to remove impurities from the powder mixture.

[0037] Plasma sintering can be used to sinter powder mixtures to prepare sintered lanthanum zirconium oxide. The powder mixture is placed inside a mold in a controlled atmosphere (e.g., in a vacuum or inert atmosphere to prevent combustion of the graphite mold) and compressed within the mold during sintering. The temperature of the powder mixture is increased by passing an electric current through the mold. During the sintering step, the pressure (“sintering pressure”), heating rate (temperature distribution), maximum temperature or temperature range (“sintering temperature”), type of current passing through the mold, and the amount of time the powder is held at the sintering temperature (“sintering time”) can be controlled to produce sintered lanthanum zirconium oxide materials with the desired density (including the presence and maximum pore size), microstructure (e.g., grain size), and purity.

[0038] The pressure applied to the powder mixture during the sintering step can be, in combination with a useful sintering temperature and sintering time, a pressure that will produce sintered lanthanum zirconium oxide material with high density, desired purity, and fine grain structure. Examples of useful sintering pressures can be up to about 100 MPa, up to 50 MPa, or up to 25 MPa, such as pressures in the range of 10 MPa to 50 MPa.

[0039] Sintering temperature effectively allows the lanthanum oxide in lanthanum oxide powder particles to react with the zirconium oxide in zirconium oxide particles to form lanthanum zirconium oxide. When the powder mixture is held at the sintering temperature for an effective amount of time (“sintering time”), the particles bond together to form a solid, high-density (low-porosity) sintered lanthanum zirconium oxide. Examples of useful sintering temperatures can be up to 1650 degrees Celsius, such as up to 1600 degrees Celsius or 1550 degrees Celsius, and useful sintering times can be less than 120 minutes, for example, less than 90 minutes or less than 60 minutes for molds with a diameter of 100 to 150 mm or smaller. Different mold sizes may require different sintering times.

[0040] The type of current passing through the mold can be pulsed, non-pulsed, alternating current (“AC”), or direct current (“DC”). The preferred current is non-pulsed direct current.

[0041] Figure 1 An example of a plasma sintering apparatus useful according to the method described herein is shown. Figure 1The components of a plasma sintering apparatus 100 are schematically illustrated, including a mold 102, a lower punch 110, and an upper punch 120. The mold 102 is an annular structure defining an interior 104 between an inner wall 106 of the mold 102, an upper surface 112 of the lower punch 110, and a lower surface 122 of the upper punch 120. The mold and punch arrangement is housed within a vacuum chamber (not shown) to control the atmosphere of the interior 104 during the sintering step. During sintering, oxygen can be removed from the chamber either directly by a vacuum pump or by displacement with a non-reactive gaseous substance (e.g., helium) or a reactive gaseous substance (e.g., hydrogen). The interior 104 has a volume suitable for receiving a powder mixture 130, which can be compressed under pressure applied between the surfaces of the upper punch 120 and the lower punch 110.

[0042] The upper punch 120 and the lower punch 110 are operatively coupled to components of the plasma sintering apparatus 100 in a manner that allows the upper punch 110 and the lower punch 120 to apply pressure to the powder mixture 130 at the interior 104. The inner diameter of the die 102 is slightly larger than the diameter of the upper punch 120 and the lower punch 110, wherein a small gap is provided between the inner surface 106 of the die 102 and the outer surface of the upper punch 120 and the lower punch 110 to allow the upper punch 120 and the lower punch 110 to move within the die 102.

[0043] The mold 102 is made of a conductive material (such as graphite) to allow an electric current to pass through the mold 102, thereby heating the mold 102 and the powder mixture 130 contained within the interior 104. The upper punch 120 and the lower punch 110 are also formed of a conductive material (such as conductive graphite material). The graphite material of the punches 110, 120, or the mold 102 can be any useful type of graphite, such as isotropic graphite, reinforced graphite (such as carbon-carbon composites), or graphite material containing fibers, particles, flakes, networks, or laminates of other conductive materials (such as carbon) in a matrix of isotropic graphite material.

[0044] The arrangement of the die 102 with the upper punch 120 and the lower punch 110 may also include additional components to facilitate the sintering process, such as spacers, gaskets, liner, and other tooling kit components. Typically, such additional structures may also be made of conductive materials such as graphite, but other materials may also be included.

[0045] According to as stated and as Figure 1 Some of the illustrated methods involve placing a liner between the surface of the powder mixture in the mold and the surface of the punch or the interior of the mold. The liner serves to prevent powder from sticking or adhering to the surface of the mold or punch and allows the sintered body to be removed from the mold and punch after the sintering process.

[0046] The pads can be made of high-purity conductive materials, such as graphite having a purity of at least 99.7%, 99.8%, or 99.9%, and can be in the form of films or sheets (“foils”), for example, having a thickness of less than one millimeter, such as a thickness in the range of 0.13 millimeters to 0.76 millimeters. These types of graphite foil materials are commercially available, for example, products sold by NeoGraf Solutions, LLC under the trade name GTA Flexible Graphite.

[0047] Additionally, to form high-purity sintered lanthanum zirconium oxide, the conductive pad (or "foil") may include an inert (non-reactive) coating on its surface that comes into contact with the powder mixture containing lanthanum oxide and zirconium oxide. This non-reactive coating can be prepared by coating a non-reactive material (e.g., boron nitride) or a suitably sized bulk metal sheet known to be generally non-reactive (e.g., molybdenum, niobium, tantalum, or tungsten) onto a conductive substrate (e.g., graphite foil). When the powder mixture contains zirconium oxide, the zirconium oxide can react with the carbon in the graphite pad during sintering to form zirconium carbide, which, if formed, reduces the purity of the sintered lanthanum zirconium oxide. The non-reactive coating prevents contact between the graphite of the pad and the zirconium oxide in the powder mixture, thereby preventing the formation of zirconium carbide during sintering.

[0048] The non-reactive coating can be prepared using any material that can separate the powder mixture from the conductive material (e.g., graphite) of the conductive pad and prevent the material of the conductive pad from reacting with the powder mixture. The non-reactive coating can be applied to the conductive (e.g., graphite) pad by any useful method. As a specific example, the non-reactive coating can be made of high-purity (at least 97% purity) boron nitride and can be applied to the conductive pad (e.g., graphite pad) by spraying in the form of an aerosol.

[0049] For example, such as Figure 1 As shown, a boron nitride-coated graphite foil 142 is located between the upper punch 120 and the powder mixture 130, and a second boron nitride-coated graphite foil 142 is located between the lower punch 110 and the powder mixture 130. The foil 142 located between the lower punch 110 and the powder mixture 130 is arranged such that the boron nitride side 144 faces the lower surface of the powder mixture 130, while the graphite side faces the upper surface of the lower punch 110. Similarly, the foil 142 located between the upper punch 120 and the powder mixture 130 is arranged such that the boron nitride side 144 faces the upper surface of the powder mixture 130, while the graphite side faces the lower surface of the upper punch 120. In this arrangement, the boron nitride side of each foil 142 contacts the upper or lower surface of the powder mixture 130 and prevents the graphite of the foil 142 from contacting the powder mixture 130, thereby preventing a reaction between the graphite of the foil 142 and the powder of the powder mixture 130, for example, preventing the carbon of the graphite from reacting with zirconium oxide to form zirconium carbide.

[0050] The method described above can be performed using selected process characteristics (such as sintering pressure, sintering temperature, and sintering time) to form sintered lanthanum zirconium oxide with a very useful combination of physical properties, including high purity, high density (low porosity), and desired morphology as measured by grain size. Sintered lanthanum zirconium oxide materials with high purity, high density (including low porosity), small maximum pore size, and small grain size are particularly useful as thermally stable, plasma-resistant internal surfaces within plasma processing apparatuses, especially for types of processes involving plasma deposition or plasma etching that employ halogen-based process gases introduced into the plasma processing chamber while an RF field is applied to the process gases to generate plasma.

[0051] In these applications, to prevent localized hot spots and overheating during use, the plasma-resistant inner surface preferably has low dielectric loss. The dielectric loss of the plasma-resistant surface can be affected by material properties including grain size and the presence of impurities. The presence of impurities in the plasma-resistant surface can lead to higher dielectric loss. Using high-purity powders from powder mixtures and employing processing and treatment methods as described herein to maintain their purity, sintered lanthanum oxide materials with extremely high purity can be produced. Therefore, by the methods described herein, sintered lanthanum zirconium oxide materials can have a purity of at least 99.999%, such as at least 99.9999% or 99.9999%, as measured using ICPMS methods.

[0052] Grain size also affects the properties of sintered lanthanum oxides, including dielectric loss and mechanical properties such as hardness and strength. The method described herein can be used to prepare sintered lanthanum zirconium oxides with fine grains (e.g., small grain size and small maximum grain size). A smaller maximum grain size may be preferred because larger grains within a material with smaller grains can become critical defect sites that reduce the material's strength.

[0053] Examples of sintered lanthanum oxide materials prepared as described may have an average grain size of less than 10 micrometers, such as less than 8 micrometers, including average grain sizes from 0.4 micrometers to 6.5 micrometers or from 0.4 micrometers to 5 micrometers. These sintered lanthanum oxide materials may also have a maximum grain size of less than 10 micrometers, such as less than 8 micrometers, less than 6 micrometers, or 5 micrometers. The grain size of the sintered lanthanum zirconium oxide can be measured using known techniques, including linear intercept grain size measurements using the Heyn linear intercept procedure as described in ASTM Standard El 12-2010, “Standard Test Method for Determining Average Grain Size.”

[0054] The sintered lanthanum zirconium oxide material prepared as described can also have high density and high relative density, i.e., density close to the theoretical density. High density can be achieved by forming lanthanum zirconium oxide containing a small number of pores within the solid (preferably any pores being small in size). The theoretical density of lanthanum zirconium oxide is the maximum achievable density assuming no internal pores or contaminants, and has been calculated to be 6.050 g / cm³. Example sintered lanthanum oxide materials prepared as described can have a density of at least 5.90 g / cm³, for example at least 5.964 g / cm³ (“Archimedean density”), measured according to ASTM B962-17, and a relative density of at least 98, 99, or 99.5, i.e., at least 98%, 99%, or 99.5% of the theoretical density of lanthanum zirconium oxide.

[0055] Due to their high density, sintered lanthanum zirconium oxides may have low porosity, meaning a low amount of vacant space within or on the surface of the material. During use in a plasma chamber, the pores at the surface of the lanthanum zirconium oxide material allow reactive gases or plasma to enter the surface and cause undercutting or corrosion, potentially leading to particle shedding that becomes a contaminant within the chamber. As used herein, the “porosity” of a porous body (also known as “volume porosity” or “void fraction”) is a measure of the amount of void (i.e., “empty”) space in the body, expressed as a percentage of the total volume of the body, and calculated as the fraction of the void volume to the total volume of the body. A body with 0% porosity is completely solid. A certain amount of pores is typically present in sintered lanthanum oxide materials, and any pores present are preferably small in size and have a small maximum pore diameter.

[0056] The example sintered lanthanum zirconium oxide materials prepared as described may have a porosity (measured as a percentage of the material's surface area) in the range of 0.0005% to 2%, for example 0.001% to 1.5%, or 0.01% to 0.5%, as measured using SEM. These sintered lanthanum zirconium oxide materials may have a maximum pore size of no more than 10 micrometers, for example 1 to 5 micrometers. The porosity and pore size of the sintered lanthanum zirconium oxide can be measured using known techniques, including preparing images of the sintered lanthanum zirconium oxide surface using a scanning electron microscope (e.g., at 5000x magnification) and analyzing the images using ImageJ software (ImageJ was developed by the National Institutes of Health (NIH) and is a Java-based public domain image processing and analysis program for image processing of scientific multidimensional images).

[0057] The method described above can also be used to prepare multilayer ceramic bodies comprising a combination of a sintered lanthanum zirconium oxide layer (including having the properties described above) and a support layer. The support layer can be made of ceramic materials, such as materials comprising a combination of alumina and zirconium oxide, for example, zirconium oxide toughened alumina (ZTA). The support layer can be formed by sintering the support layer using plasma discharge sintering technology, wherein the sintered lanthanum zirconium oxide layer and the support layer are sintered simultaneously to form a multilayer sintered ceramic body. The process for forming a multilayer sintered ceramic body by sintering must be effective to ensure that the resulting multilayer sintered ceramic body exhibits useful structural and mechanical properties, such as strength and hardness, good adhesion at the interlayer interfaces, no cracking, no unwanted materials or impurities formed due to material reactions between different layers during sintering, and the high purity, density, and fine grain size of the sintered lanthanum zirconium oxide layer.

[0058] Example support layers comprising zirconia-toughened alumina may contain alumina and zirconia, wherein the zirconia is stable or partially stable. Useful examples of zirconia-toughened alumina may contain 10 wt% to 40 wt% zirconia, such as 20 wt% to 25 wt% zirconia, with the balance being alumina and no more than 1 wt% impurities.

[0059] Preferably, the coefficient of thermal expansion (CTE) of the support layer (such as ZTA) is approximately the same as that of lanthanum zirconium oxide to allow the two layers of the multilayer sintered ceramic body to be processed through sintering and cooling without subjecting the two layers to physical stress or damage during cooling, such as fracture, cracking, or delamination due to different thermal shrinkage rates during cooling. The coefficient of thermal expansion of lanthanum zirconium oxide is approximately 7.5 × 10⁻⁶ in the temperature range of 25°C to 1200°C. -6 / °K (or parts per million, ppm) to 10×10 -6 Between 6°K and 1200°C, the coefficient of thermal expansion of zirconia-toughened alumina is 6 × 10⁻⁶. -6 / °K (or parts per million, ppm) to 10×10 -6 Between / °K. Figure 2 A comparison of the CTE of LZO and ZTA containing 22% wt% zirconium oxide is shown. The CTE values ​​were measured using a vertical dilatometer (L75 Platinum series model) from Linseis.

[0060] The example multilayer sintered ceramic body described may include a sintered lanthanum zirconium oxide layer and a zirconium oxide-toughened alumina layer, which have a strength not exceeding 1 × 10⁻⁶ as measured according to ASTM E228-17 in a temperature range of 25°C to 1200°C. -6 / degrees Celsius (ppm), 2×10 -6 / degrees Celsius or 3×10-6 The maximum CTE difference per degree Celsius (i.e., the CTE difference between two materials measured at the same temperature). Figure 2 It is shown that (at a temperature of approximately 375 K) for a ZTA containing 22% by weight of zirconium oxide, the maximum CTE difference between LZO and ZTA within this temperature range is less than 2 ppm but greater than 1 ppm. In a preferred example of a multilayer sintered body as described, the ZTA may have a CTE that more closely matches the CTE of the LZO to prevent cracking or other physical damage that may occur during cooling of the multilayer sintered body after sintering. Zirconia-toughened alumina with a maximum CTE difference of less than 1 ppm from the CTE of LZO within this temperature range may contain more than 22% by weight of zirconium oxide, for example, up to or greater than 30%, 35%, 38%, or 40% zirconium oxide.

[0061] Figure 3 A plasma sintering apparatus is shown that can be used to form a multilayer sintered ceramic body according to the method described above, the multilayer sintered ceramic body comprising a sintered lanthanum zirconium oxide layer and a ceramic support layer, such as a zirconium oxide toughened alumina layer. Figure 3 The illustration shows, for example Figure 1 The components of a plasma sintering apparatus 100, which is adapted to form a multilayer sintered ceramic body including a lanthanum zirconium oxide layer and a support layer. Figure 3 The plasma sintering apparatus 100 contains powder mixture 1 and powder mixture 2, powder mixture 1 containing a combination of lanthanum oxide and zirconium oxide, and powder mixture 2 containing a combination of zirconium oxide and alumina. During a sintering step using the conditions described, heat and pressure are simultaneously applied to powder mixture 1 and powder mixture 2 contained in a mold 102. Pressure is applied to the powder mixtures to sinter them together, wherein the two powder mixtures are bonded together to form a multilayer sintered ceramic body comprising a sintered lanthanum zirconium oxide layer (from powder mixture 1) and a support layer, such as zirconium oxide toughened alumina from powder mixture 2. Boron nitride-coated graphite foil 142 is located between an upper punch 120 and powder mixture 130, wherein the boron nitride side 144 faces the upper surface of powder mixture 130, while the graphite side faces the lower surface of the upper punch 120. Uncoated graphite foil 146 is located between the upper surface of a lower punch 110 and the lower surface of powder mixture 130.

[0062] Example

[0063] Example 1

[0064] Two powder components, lanthanum oxide (La₂O₃) and zirconium oxide (ZrO₂), were ball-milled in ethanol for approximately 22 hours. The mixture was then rotary evaporated to remove the ethanol. The powder mixture was subsequently pressed into a graphite mold by spark plasma sintering (SPS). Both 40mm and 4-inch molds were used to produce sintered lanthanum zirconium oxide (La₂Zr₂O₇). Boron nitride-coated graphite foil was placed next to the powder mixture, with the boron nitride coating facing the mixture, to prevent zirconium oxide from reacting with the graphite foil to form zirconium carbide. XRD phase analysis confirmed that the resulting sintered lanthanum zirconium oxide material formed using both the 40mm and 4-inch molds was 100% La₂Zr₂O₇, and the density of the sintered lanthanum zirconium oxide exceeded the theoretical density by 99.5%.

[0065] Example 2

[0066] (A) Two separate layers of two different powder mixtures were placed in a mold for plasma discharge sintering. One powder mixture was a combination of lanthanum oxide powder and zirconium oxide powder to react and form sintered lanthanum zirconium oxide, and the second powder mixture was a combination of alumina and zirconium oxide to form zirconium oxide-toughened alumina. The two powder mixtures were placed as two separate layers in a 40 mm mold and sintered at a sintering temperature of 1625 °C using a sintering pressure of 25 MPa. A boron nitride-coated graphite foil was placed between the lanthanum oxide and zirconium oxide powder mixture and the mold, with the boron nitride side of the foil facing the powder mixture. A graphite foil was placed between the alumina and zirconium oxide powder mixture and the mold. At this temperature and pressure, the LZO powder mixture reacted with the ZTA powder mixture, and the materials melted due to the excessively high sintering temperature.

[0067] (B) In a similar process using the same mold and the same two powder mixtures, a sintering temperature of 1550°C was used. The powder mixture was held at this sintering temperature for 30 minutes under a sintering pressure of 25 MPa. At this sintering temperature, the powder mixtures did not react together, and the process successfully produced a two-layer sintered ceramic body comprising a sintered lanthanum zirconium oxide layer and a zirconium oxide-toughened alumina layer.

[0068] (C) Using a relatively large-diameter mold (4 inches in diameter or approximately 100 mm), a first powder layer of a 202 g powder mixture of lanthanum oxide and zirconium oxide was placed in the mold, and a second powder layer of a 404 g powder mixture of zirconium oxide and alumina was placed on top of the first powder layer. The second powder contained approximately 22% by weight of zirconium oxide, with the balance being alumina and trace impurities. A boron nitride-coated graphite foil was placed between the lanthanum oxide and zirconium oxide powder mixture and the mold, with the boron nitride side of the foil facing the powder mixture. A graphite foil was placed between the alumina and zirconium oxide powder mixture and the mold. The two powder layers were sintered at a sintering pressure of 15 MPa and a sintering temperature of 1500 °C for 45 minutes. This process successfully produced two sintered ceramic bodies having a sintered lanthanum zirconium oxide layer with a relative density of 96.3% determined by dimensional analysis and a zirconium oxide-toughened alumina layer with a relative density of 94.6%. Figure 4 The image shows a photograph of the resulting 4-inch multilayer sintered ceramic body 150, which has a sintered lanthanum zirconium oxide layer 152 bonded to a zirconium oxide toughened alumina layer 154. Figure 4 The body 150 shown includes cracks on the upper surface of the sintered lanthanum zirconium oxide layer 152.

[0069] Example 3 (Indicative)

[0070] The sintered multilayer body of Example 2 (C) was formed using ZTA containing 22% by weight of zirconium oxide, and the formed multilayer sintered body contained cracks due to the different CTE of ZTA and LZO.

[0071] Although the following has not yet been experimentally confirmed, the applicant anticipates that a ZTA with a high zirconium oxide content (e.g., up to or greater than 30%, 35%, 38%, or 40% zirconium oxide) can be used to perform a process similar to Example 2(C). This ZTA will have a CTE that more closely matches that of LZO, for example, with a maximum difference of no more than 1 ppm from the CTE of LZO over a temperature range of 25°C to 1200°C. The applicant anticipates that the process of Example 2(C) will be used to prepare multilayer sintered bodies with a diameter of 100 mm, having both ZTA and LZO layers and being free of cracks.

[0072] More specifically, using a relatively large-diameter mold (4 inches in diameter or approximately 100 mm), a first powder layer of a mixture of 202 g of lanthanum oxide and zirconium oxide powders is placed in the mold, and a second powder layer of a mixture of 404 g of zirconium oxide and alumina powders is placed on top of the first powder layer. The powder mixture of the second powder layer will contain approximately 30% to 40% zirconium oxide, with the balance being alumina and trace impurities. The amount of zirconium oxide within this range will be selected to avoid cracking of the multilayer sintered body during cooling after the sintering step.

[0073] A boron nitride-coated graphite foil will be placed between a mixture of lanthanum oxide and zirconium oxide powders and a mold, with the boron nitride side of the foil facing the powder mixture. A graphite foil will also be placed between a mixture of alumina and zirconium oxide powders and the mold. The two powder layers will be sintered under conditions that produce a multilayer sintered ceramic body, such as a sintering pressure of 15 MPa at a sintering temperature of 1500°C for 45 minutes. This process is expected to produce a bilayer sintered ceramic body having a sintered lanthanum zirconium oxide layer with a relative density of at least 96% and a zirconium oxide-toughened alumina layer with a relative density of at least 94%. The process is expected to produce a 100 mm diameter multilayer sintered body free from cracks that may form during the cooling of the body after sintering.

Claims

1. A sintered lanthanum zirconium oxide having a purity of at least 99.999% as measured by ICPMS and a density of at least 96% of the theoretical density, wherein the pores have a maximum size of 5 micrometers as measured on the surface of the lanthanum zirconium oxide.

2. The lanthanum zirconium oxide according to claim 1, wherein the lanthanum zirconium oxide has an average grain size of less than 10 micrometers or a maximum grain size of less than 10 micrometers.

3. The lanthanum zirconium oxide according to any one of claims 1 or 2, wherein the lanthanum zirconium oxide has a density of at least 5.964 g / cm³ as measured according to ASTM B962-17, or has a density of 7.5 × 10⁻⁶ g / cm³ in a temperature range of 25°C to 1200°C. -6 Up to 10×10 -6 The coefficient of thermal expansion within the range of / degrees Celsius.

4. A multilayer sintered ceramic body comprising a sintered lanthanum zirconium oxide layer according to any one of claims 1 to 3 and a zirconium oxide-toughened alumina layer, wherein the zirconium oxide-toughened alumina layer comprises 20% to 25% zirconium oxide and no more than 1% impurities, wherein, as measured according to ASTM E228-17, the difference in the coefficient of thermal expansion between one layer and another does not exceed 3 × 10⁻⁶ in a temperature range of 25°C to 1200°C. -6 / degrees Celsius.

5. A method for preparing sintered lanthanum zirconium oxide according to any one of claims 1 to 3, the method comprising: A powder mixture comprising lanthanum oxide particles and zirconium oxide particles was prepared. The powder mixture is placed into a graphite mold. Eliminate oxygen in the mold. The powder mixture in the mold is sintered by applying pressure to the powder mixture and passing an electric current through the mold to raise the temperature of the powder mixture, thereby causing the lanthanum oxide to react with the zirconium oxide powder to form sintered lanthanum zirconium oxide. The method includes placing boron nitride-coated graphite between the surface of the graphite mold and the powder mixture, wherein the boron nitride coating contacts the powder mixture.

6. The method of claim 5, wherein the powder mixture comprises: Lanthanum oxide particles with a purity of at least 99.99999%, and Zirconium oxide particles with a purity of at least 99.99%, As measured using ICPMS, and the preparation of the powder mixture includes: The solvent is combined with the powder mixture, and The powder mixture is ground inside a cylindrical ball mill container, which has a polymer liner and uses stabilized zirconia grinding media.

7. The method according to claim 5 or 6, wherein the method comprises at least one of the following steps: The solvent is removed from the powder mixture by evaporation; After removing the solvent by evaporation, the first powder mixture is calcined, wherein... The temperature of the powder mixture during calcination shall not exceed 850 degrees Celsius.

8. The method according to any one of claims 5 to 7, wherein the current is a non-pulsed DC current.

9. The method according to any one of claims 5 to 8, the method comprising: The powder mixture is sintered at a sintering pressure not exceeding 100 MPa, and The powder mixture is sintered at a sintering temperature not exceeding 1625 degrees Celsius; The method preferably includes sintering the powder mixture for a sintering time of less than 90 minutes, preferably includes sintering the powder mixture at a sintering pressure not exceeding 50 MPa, and preferably includes sintering the powder mixture at a sintering temperature not exceeding 1550 degrees Celsius.

10. The method according to any one of claims 5 to 9, wherein the lanthanum zirconium oxide has one or more of the following: It has a hole with a maximum size of 5 micrometers measured on the surface of the lanthanum zirconium oxide. Average grain size less than 10 micrometers, and Maximum grain size less than 10 micrometers.

11. A method for preparing a multilayer sintered ceramic body, the multilayer sintered ceramic body comprising a lanthanum zirconium oxide layer and a zirconium oxide-toughened alumina layer, the method comprising: A first powder mixture comprising lanthanum oxide particles and zirconium oxide particles was prepared. Prepare a second powder mixture comprising zirconium oxide and alumina. A layer of the first powder mixture is formed in a graphite mold. A layer of the second powder mixture is formed in the graphite mold. The first powder mixture and the second powder mixture are sintered by: applying pressure to the first powder mixture and the second powder mixture in the mold and passing an electric current through the mold to raise the temperature of the first powder mixture and the second powder mixture, and causing the first powder mixture to form a lanthanum zirconium oxide layer and the second powder mixture to form a zirconium oxide toughened alumina layer, wherein preferably, the first powder mixture comprises: Lanthanum oxide particles with a purity of at least 99.9999%, and Zirconium oxide particles with a purity of at least 99.99%, If measured using ICPMS.

12. The method of claim 11, wherein the second powder mixture comprises 20% to 25% zirconium oxide, the balance being alumina and no more than 1% impurities, or wherein preparing the first powder mixture comprises: Combine the solvent with the first powder mixture, and The powder mixture is ground inside a cylindrical ball mill container, which has a polymer liner and uses stabilized zirconia grinding media.

13. The method according to claim 12, wherein the method comprises: After the solvent is removed by evaporation, the first powder mixture is calcined, wherein the temperature of the first powder mixture during calcination does not exceed 850 degrees Celsius. or A boron nitride-coated graphite is placed between the surface of the graphite mold and the first powder mixture, wherein the boron nitride coating contacts the first powder mixture; or The method includes sintering the powder mixture at a sintering pressure not exceeding 100 MPa and sintering the powder mixture at a sintering temperature not exceeding 1625 degrees Celsius; or The powder mixture is sintered for a sintering time of less than 60 minutes; or The powder mixture is sintered at a sintering pressure not exceeding 50 MPa; or The powder mixture is sintered at a sintering temperature not exceeding 1550 degrees Celsius.

14. The method according to any one of claims 11 to 13, wherein the lanthanum zirconium oxide has one or more of the following: It has a hole with a maximum size of 5 micrometers measured on the surface of the lanthanum zirconium oxide. Average grain size less than 10 micrometers, and Maximum grain size less than 10 micrometers.

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