Erbium aluminum perovskite compositions and related methods and articles

Abstract

Described are aluminate compositions that contain erbium aluminum oxide as a perovskite crystalline structure; methods of preparing aluminate compositions that contain erbium aluminum perovskite; articles that contain erbium aluminum perovskite, and methods of preparing and methods of using articles that contain erbium aluminum perovskite.

Description

[0001] ERBIUM ALUMINUM PEROVSKITE COMPOSITIONS AND RELATED METHODS AND ARTICLES

[0002] FIELD

[0003] [1] The description relates to compositions that contain erbium aluminum oxide as a perovskite crystalline structure (or “crystalline phase”); methods of preparing compositions that contain erbium aluminum perovskite; articles that contain erbium aluminum perovskite; sintered bodies that comprises erbium aluminum perovskite; and methods of preparing and methods of using compositions and articles that contain erbium aluminum perovskite.

[0004] BACKGROUND

[0005] [2] Ceramics, meaning room-temperature solid inorganic non-metallic materials, are known to exist as having different chemical compositions that may have a range of different crystalline and non-crystalline (amorphous) morphologies. Among known ceramic materials, one class that includes a large number of chemically-diverse varieties is aluminates, which are composed of aluminum, oxygen, and metal atoms. Aluminates encompass materials with a large range of chemical compositions, many of which are capable of existing in multiple different crystalline phases. Within aluminates that contain the same metal element, a slightly different stoichiometry or crystalline makeup can produce significantly different mechanical, optical, and chemical properties, allowing for different uses of slightly different versions of aluminates.

[0006] [3] As just one example out of many known aluminates, aluminates that contain yttrium can form ceramics that have a range of highly distinctive and specialized optical, chemical, and mechanical properties. Highly pure yttrium aluminum oxide in a cubic crystalline form, often referred to as a garnet (YAG), for example, has well-known chemical inertness and is used as a chemically-resistant material in the presence of plasma and halogens, e.g., as a coating within plasma chambers. YAG having the cubic crystalline structure can also be doped with another rare earth metal atoms for use in a solid-state laser such as Nd: YAG. Yttrium aluminum oxide exists in various different crystalline forms that include distorted cubic crystalline structure, such as an orthorhombic crystalline structure, a perovskite structure (YAP), and a monoclinic crystalline structure (YAM). [4] One type of ceramic that has not been the subject of study is erbium aluminate (“erbium aluminum oxide”). This aluminate may exhibit multiple different crystalline forms (or “phases”) depending on the composition including as the erbium aluminum garnet phase EnAlsO (“ErAG”), as the erbium aluminum monoclinic phase Er4ATO9 (“ErAM”), or as the erbium aluminum perovskite phase ErAlCh (“ErAP”).

[0007] [5] The unique chemistry of the rare earth (Lanthanide) aluminates gives them a high resistance to fluorine-based chemistry, particularly as a plasma, commonly used for semiconductor processing in etch chambers. In the semiconductor manufacturing industry, processing equipment such as plasma etching chambers and plasma deposition chambers (referred to collectively as “plasma chambers”) contain a highly pure environment that is as free as possible from particle contaminants. Interior surfaces and components of plasma chambers are made of inert materials that are resistant to chemical degradation because chemical degradation of those materials within a plasma chamber will produce particle contaminants in the chamber. Reducing the reaction of the chamber materials with the plasma environment through the use of ceramic components is an area of high interest to improve yield and up-time that are impacted be degrading chamber materials.

[0008] [6] US 2022 / 234959 Al describes nanoparticles having a thin film coating, whereby the thin film coating may be composed of different materials such as erbium aluminum oxide. However, the prior art reference neither discloses the structure of the erbium aluminum oxide nor that the material has a specific phase purity. A thin film coating is prepared by atomic layer deposition which may lead to specific crystalline forms.

[0009] US 10730798 B refers to a ceramic coating which may be formed on a substrate using slurry plasma spray deposition. Thereby, the coating may comprise ErA103.

[0010] SUMMARY

[0011] [7] While many ceramic materials have good resistance to chemical degradation and controlled erosion effects in the presence of reactive chemicals and plasmas, ongoing interest exists for still-better-performing materials, e.g., ceramic materials with still better chemical inertness that produce ever-lower amounts of particle contamination when used at an interior of a plasma chamber. Due to the complex nature of the semiconductor manufacturing process a wide range of plasma chemistries and process conditions are present requiring a range of material solutions to achieve the best performance.

[0012] [8] Described herein are a novel erbium aluminate composition that contain predominately erbium aluminum perovskite. A crystalline perovskite phase is considered to have a stoichiometry described by the formula ABX3, including where generally A is a positively- charged ion such as yttrium or in this case an erbium ion, B is a positively-charged ion such as aluminum ion, and X is a negatively-charged ion such as oxygen ion. The ideal cubic structure has the B cation in 6-fold coordination, surrounded by an octahedron of anions, and the A cation in 12-fold cuboctahedral coordination. Consistent with this definition, erbium aluminum perovskite has the chemical formula ErAlCh, meaning nominally having a stoichiometric ratio of 1 erbium atom to 1 aluminum atom to 3 oxygen atoms.

[0013] [9] In one aspect, the present disclosure relates to an erbium aluminum oxide composition comprising a phase purity of at least 90 weight percent erbium aluminum perovskite.

[0014]

[0010] In the sense of the present invention, phase purity means how much weight percent is defined by a single crystal species in the composition compared to the totality of species present.

[0015]

[0011] In an embodiment, the erbium aluminum oxide composition comprises impurities of no more than 1250 ppm.

[0016]

[0012] More preferably, the erbium aluminum oxide composition comprises impurities of no more than 250 ppm.

[0017]

[0013] In the sense of the present invention, the amount of impurities is defined as the amount of components other than erbium aluminum oxide being present in the composition according to the present invention. This is also known as chemical impurity.

[0018]

[0014] That said, the phase purity means all the crystalline parts of a material are of the same structure, such as a single type of crystal lattice. Overall purity is about the chemical makeup. It is a measure of how much of the material is the desired substance versus impurities, regardless of crystal structure. It is possible for a material to be phase-pure but still have chemical impurities, or be chemically pure but still have multiple crystal phases.

[0019]

[0015] A composition that contains (comprises, consists of, or consists essentially of) erbium aluminum perovskite may be in any useful form and prepared by any of various useful methods. Examples of erbium aluminum perovskite compositions include: particles (“erbium aluminum perovskite particles”); collections of erbium aluminum perovskite particles in the form of a powder composition (an “erbium aluminum perovskite powder”); a coating on substrate (e.g., an “erbium aluminum perovskite coating”); and solid materials such as a solid body that has a low porosity (e.g., an “erbium aluminum perovskite sintered body”). Example methods described herein for preparing these compositions produce a composition that has a non-zero porosity, i.e., a porosity that is measurably greater than zero, such as a porosity in a range from 0.01 up to 5 or 10 percent, for example below 1 percent.

[0020]

[0016] Materials that contain erbium aluminum perovskite have been created on a limited basis within the literature for development of phase diagrams that support the science of phaseequilibria, typically using melting techniques such as arc-melting that result in highly contaminated material samples with uncontrolled microstructure and porosity. These techniques are utilized to study the material systems phase relationships across a range of temperatures and compositions, however they are not viable for the production of monolithic components or feedstock for powders due to poor control over material properties and generally extreme contamination from the arc electrodes or water-cooled sample holder, in addition to the small sample weights typically used.

[0021]

[0017] Erbium aluminum perovskite particles and erbium aluminum perovskite powder that contains erbium aluminum perovskite particles may be more preferably prepared by solid state synthesis methods, also referred to herein as “heat treating” or “calcining.” By example methods, aluminum oxide (alumina) particles and erbium oxide (erbia) particles can be combined with equal stoichiometric amounts of erbium atoms and aluminum atoms (1 erbium atom: 1 aluminum atom) and the combination can be heated at a temperature that causes the aluminum oxide and the erbium oxide to react to form an erbium aluminum perovskite powder made of individual erbium aluminum perovskite crystalline particles. The particles formed by this method, and the powder that contains the particles, can each contain predominantly erbium aluminum perovskite. According to example powders prepared by these methods, erbium aluminum perovskite powders may contain at least 80, 90, 95, 98, or 99 weight percent erbium aluminum perovskite that is generally present as small crystals that are substantially free of porosity.

[0022]

[0018] An erbium aluminum perovskite powder may be used to form ErAP compositions, such as coatings and sintered bodies. By example methods, an erbium aluminum perovskite coating may be formed on a substrate by commonly utilized techniques known in the art such as plasma spray or more preferable an aerosol deposition coating method. An ErAP coating may also be formed by other coating methods, such as by deposition methods that include chemical vapor deposition (CVD) methods, atomic layer deposition (ALD) methods and physical vapor deposition (PVD) methods that are generally used to create very thin coatings that have low durability in plasma erosion or general handling of components with such a coating applied.

[0023]

[0019] An erbium aluminum perovskite sintered body may be formed by a sintering method such as conventional sintering or by reactive sintering. Conventional sintering routes typically start with a pre-formed ErAP powder system that is heated with or without an applied pressure to reduce surface area and create a dense ceramic body. By a reactive sintering method, a powder mixture that contains erbium oxide particles and aluminum oxide particles is heated to cause erbium oxide and aluminum oxide of the powder mixture to react to form erbium oxide perovskite, with the particles growing together, without melting, through a reduction of surface area in the powder to form the erbium aluminum perovskite sintered body. Sintered bodies can have a range of porosity levels depending on the starting materials and desired final form of the ceramic component.

[0024]

[0020] In one aspect, the disclosure relates to a method of preparing an erbium aluminum oxide composition that includes at least 90 weight percent erbium aluminum perovskite. The method includes: preparing a powder mixture comprising erbium oxide particles and aluminum oxide particles; and heating the powder mixture, without melting the particles, to cause the erbium oxide and aluminum oxide of the powder mixture to react to form erbium aluminum perovskite.

[0025]

[0021] In another aspect, the disclosure relates to methods of forming a coating on a substrate surface, the coating comprising at least 90 weight percent erbium aluminum perovskite. The method includes: providing a powder comprising particles that comprise at least 90 weight percent aluminum perovskite; forming an aerosol that contains the particles; and under vacuum conditions, directing the aerosol toward a surface of a substrate such that the particles contact the surface and remain at the surface as a coating that comprises at least 90 weight percent erbium aluminum perovskite.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027]

[0022] Figure 1 shows measured erosion data for sample ceramics, including a sample of erbium aluminum perovskite as described. DETAILED DESCRIPTION

[0028]

[0023] The following describes compositions that contain erbium aluminum oxide as a perovskite crystalline structure (or “crystalline phase”), this crystalline form of erbium aluminum oxide being referred to herein as “erbium aluminum perovskite” or ErAP. Also described are methods of preparing compositions that contain erbium aluminum perovskite, articles that contain erbium aluminum perovskite, e.g., a substrate that has a coating that contains erbium aluminum perovskite, methods of using articles that include erbium aluminum perovskite, and sintered bodies that contain erbium aluminum perovskite.

[0029]

[0024] Erbium aluminum oxide may exist in multiple different crystalline forms (or “phases”) including as the erbium aluminum garnet phase (“ErAG”), as the erbium aluminum monoclinic phase (“ErAM”), or as the erbium aluminum perovskite phase (“ErAP”).

[0030]

[0025] Example compositions as described (e.g., an erbium aluminum perovskite powder composition, an erbium aluminum perovskite coating, or an erbium aluminum perovskite sintered body) can comprise, consists of, or consists essentially of polycrystalline erbium aluminum oxide in the perovskite phase, e.g., may contain at least 80, 85, 90, 95, 97, 98, 99, or 99.975 weight percent erbium aluminum oxide in the perovskite form (“erbium aluminum perovskite”), as opposed to other crystalline forms an oxide of erbium. Example compositions may contain other forms of erbium aluminum oxide such as erbium aluminum garnet, or related materials (e.g., erbium oxide, E C or aluminum oxide, AI2O3), in lesser amounts, e.g., may contain less than 5, 3, 2, or 1 weight percent of such other materials. Amounts of erbium aluminum perovskite in a composition can be measured using known techniques and equipment, including inductively coupled plasma mass spectrometry (ICP-MS). Equipment for measuring the amounts of a substance in a composition, include for example, an Agilent 7900 ICP-MS (Model G8403), commercially available from Agilent Technologies, Inc. (USA).

[0031]

[0026] As used herein, an erbium aluminum perovskite composition (e.g., a particle, a combination or collection of particles (i.e. , a “powder”), a coating, or a sintered body, that “consists essentially of” erbium aluminum perovskite is a composition that contains erbium aluminum perovskite and not more than a minor amount of chemically different materials, e.g., not more than 5, 3, 2, or 1 weight percent of any other material, e.g., erbium aluminum oxide in the garnet form, erbium oxide (E Ch), aluminum oxide (AI2O3), or a combination of these or other materials.

[0032]

[0027] Stated differently, a composition as described can comprise, consist of, or consist essentially of erbium aluminum oxide having the chemical formula ErAlOs, meaning nominally having a stoichiometric ratio of 1 erbium atom to 1 aluminum atom to 3 oxygen atoms. Example compositions can have these atomic ratios, with the stoichiometric value of each individual atom in the composition falling within a range approximately equal to the stoichiometric value (e.g., within 1 percent of the stoichiometric value) as will be understood by one of skill in the chemical and materials arts. Such a composition that comprises or consists essentially of erbium aluminum perovskite of the chemical formula ErAlCh can contain erbium, aluminum, and oxygen atoms in a stoichiometric ratio of one erbium atom to one aluminum atom to three oxygen atoms, with not more than a one percent deviation of the stoichiometric value for each atom, individually. Example compositions may contain a ratio of erbium atoms to aluminum atoms to oxygen atoms in ratios of from 0.99 to 1.01 erbium atoms to from 0.99 to 1.01 aluminum atoms to from 2.97 to 3.03 oxygen atoms; or ratios of from 0.999 to 1.001 erbium atoms, from 0.999 to 1.001 aluminum atoms, and from 2.997 to 3.003 oxygen atoms.

[0033]

[0028] An amount in weight percent of erbium aluminum perovskite phase in a composition can be measured by surface analysis of the composition by determining an amount, in percent, of an area of a surface of the material that is erbium aluminum perovskite. The amount in percent of the area that is erbium aluminum perovskite is considered to be the same as the amount in percent of erbium aluminum perovskite in the composition by weight. An amount of erbium aluminum perovskite in a composition or at a surface of a composition can be determined by known methods such as scanning electron microscopy, x-ray diffraction, or atomic force microscopy (AFM).

[0034]

[0029] A composition that contains erbium aluminum perovskite may be in any useful form. Examples include: an “erbium aluminum perovskite particle,” a collection of erbium aluminum perovskite particles in the form of a “powder composition” (e.g., an “erbium aluminum perovskite powder”); a coating on substrate (e.g., an “erbium aluminum perovskite coating”); or a solid material such as a sintered body (e.g., an “erbium aluminum perovskite sintered body”) formed by a sintering method, e.g., a reactive sintering method.

[0030] An erbium aluminum perovskite powder composition as described may comprise, consist of, or consist essentially of erbium aluminum perovskite particles, i.e., particles that comprise, consist of, or consist essentially of erbium aluminum perovskite. The erbium aluminum perovskite powder composition can be prepared from a powder mixture that contains aluminum oxide particles (e.g., “aluminum oxide powder”) and erbium oxide particles (e.g., “erbium oxide powder”) by heating the powder mixture to form the erbium aluminum perovskite powder. Example methods include those referred to as “solid phase synthesis” or “solid state reaction” methods, which may also be referred to as “heat treating” or “calcining.”

[0035]

[0031] An erbium oxide powder is a powder that contains (comprises, consists of, or consists essentially of) a collection of erbium oxide particles, with each erbium oxide particle containing (comprising, consisting of, or consisting essentially of) erbium oxide; e.g., individual erbium oxide particles can contain at least 95, 98, 99, or 99.9 weight percent erbium oxide based on total particle weight. An erbium oxide particle that consists essentially of erbium oxide is a particle that contains erbium oxide and not more than 3, 2, 1, or 0.5 weight percent of any other material. The erbium oxide powder can contain (comprise, consist of, or consist essentially of) the erbium oxide particles, and may contain at least 95, 98, 99, or 99.9 weight percent erbium oxide, based on total weight erbium oxide powder. An erbium oxide powder that consists essentially of erbium oxide is a powder that contains erbium oxide and not more than 3, 2, 1, or 0.1 weight percent of other materials.

[0036]

[0032] An aluminum oxide powder is a powder that contains (comprises, consists of, or consists essentially of) a collection of aluminum oxide particles, with each aluminum oxide particle containing (comprising, consisting of, or consisting essentially of) aluminum oxide, e.g., individual aluminum oxide particles can contain at least 99, 99.9, 99.99, or 99.999 weight percent aluminum oxide based on total particle weight. An aluminum oxide particle that consists essentially of aluminum oxide is a particle that contains aluminum oxide and not more than 1 , 0.1, 0.01, or 0.001 weigh percent of any other material. The aluminum oxide powder can contain (comprise, consist of, or consist essentially of) the aluminum oxide particles, and may contain at least 99, 99.9, 99.99 or 99.999 or higher weight percent aluminum oxide, based on total weight aluminum oxide powder. An aluminum oxide powder that consists essentially of aluminum oxide is a powder that contains aluminum oxide and not more than 1, 0.1, 0.01, or 0.001 weight percent of other materials.

[0033] According to one example, an erbium aluminum perovskite powder can be prepared by a solid state synthesis method. Example solid state synthesis methods include a step of combining erbium oxide powder and aluminum oxide powder to form a powder mixture that contains (comprises, consists of, or consists essentially of) erbium oxide particles and aluminum oxide particles, and heating the powder mixture, without melting the particles of the powder mixture, to cause the aluminum oxide and the erbium oxide to react to form “erbium aluminum perovskite particles” that contain a high weight percent of erbium aluminum perovskite.

[0037]

[0034] The powder mixture can be prepared by combining erbium oxide powder and aluminum oxide powder in stoichiometrically equal amounts of aluminum and erbium, meaning equal or approximately equal amounts (atomic) of erbium and aluminum. The powder mixture can be processed to adjust the size and size distribution of particles of the powder to produce a powder mixture that is highly homogeneous (thoroughly mixed) and that contains erbium oxide particles and aluminum oxide particles that have particle sizes and particle size distributions that allow the powder mixture to be efficiently heated to react and form erbium aluminum perovskite particles. A useful powder mixture can contain erbium oxide particles and aluminum oxide particles that are of relatively small (fine) particle sizes, with the particle sizes and the particles size distributions of the erbium oxide particles and the aluminum oxide particles being similar. Heating erbium oxide and aluminum oxide particles having similar particle sizes and similar particle size distributions facilitates the reaction of erbium oxide with aluminum oxide at elevated temperature to form erbium aluminum perovskite. To effectively react the erbium oxide and the aluminum oxide of a powder mixture to form a high amount of erbium aluminum perovskite, particles of relatively uniform size allow for close packing and a high degree of contact between the particles during heating.

[0038]

[0035] Desired particle sizes and particle size distributions of the particles of the powder mixture, and a homogeneous mixture, can be achieved by useful mixing and particle size control methods, such as ball milling, particle separation (e.g., by sieving), or both. Ball milling the powder mixture may be performed by combining the powder mixture with a liquid (e.g., organic solvent such as ethanol) to form a slurry, and wet milling the slurry with a ceramic or metal media (e.g., alumina). Jet milling may be a useful alternative mixing technique to wet milling.

[0039]

[0036] After processing the powder mixture to provide desired particle size and particle size distribution, the powder mixture can be processed by a solid state synthesis method (heat treatment or “calcining”) that causes the erbium oxide and the aluminum oxide to react to form erbium aluminum perovskite powder. According to example methods, the powder mixture may be heated at atmospheric pressure and in an air atmosphere to form erbium aluminum oxide particles having the perovskite phase as the dominant form. By example methods, the powder mixture may be heated at ambient pressure, in air, and held at a temperature that is below a melting point of the composition and is effective to form erbium aluminum oxide that is predominantly in the perovskite phase as opposed to erbium aluminum garnet. Examples of useful temperatures may be in a range from 1400 to 1700 degrees Celsius, e.g., from 1450 to 1650 degrees Celsius. A temperature that is too high tends to favor the formation of the erbium aluminum garnet phase (ErAG). The powder mixture may be held at this temperature for an amount of time in a range of 2 to 6 hours.

[0040]

[0037] Another example of an ErAP system is a coating that is formed on a substrate (referred to as an “erbium aluminum perovskite coating” or “ErAP coating”) by utilizing a powder system. An ErAP coating may be formed on a substrate by any useful method, such as an aerosol coating method, plasma spray techniques, or any other useful coating deposition method chosen to achieve the desired coating thickness for morphology.

[0041]

[0038] The aerosol coating method utilizes an aerosol that contains ErAP particles dispersed in a flow of gas that may be optionally heating of the aerosol. The aerosol is typically directed into a vacuum chamber at low pressure and towards the surface of a substrate at a high velocity that is sufficient to cause the ErAP particles to impact the surface, resulting in ErAP particles adhering to the surface that can be built up over successive coating passes to form an ErAP coating. Examples of potential coating techniques include those referred to as aerosol deposition, thermal or plasma spraying, as well as similar known particulate spray methods. Example aerosol coating techniques can produce a coating on a substrate with the coating having a thickness in a range from 0.005 to 0.5 millimeters. With optimization of the process coatings densities can exceed 99% theoretical density also defined as less than 1% porosity.

[0042]

[0039] For use as an inert coating of a plasma chamber interior, the ErAP coating should have sufficient thickness that allows for the erosion of the ErAP coating during a period of use, typically referred to as the useful lifetime, before replacement. An aerosol coating method may be optimized to produce an ErAP coating that has an adequate useful thickness for this purpose, and a thickness that is greater than a coating prepared by certain deposition coating methods (CVD, ALD, PVD, etc.). In applications for which a plasma resistant coating having a greater thickness is preferred or required, the ErAP coating may be prepared by an aerosol coating method.

[0043]

[0040] A coating layer may also be formed by a deposition method such as chemical vapor deposition (CVD) methods, atomic layer deposition (ALD) methods, physical vapor deposition (PVD) methods, and other known physical, chemical, or atomic deposition-type coating methods. According to example deposition methods, a source of aluminum perovskite can be dispersed in a vacuum to form a molecular vapor. The vapor can be deposited onto a substrate surface as an ErAP coating.

[0044]

[0041] Another example of an ErAP composition is a sintered body formed by a sintering method, utilizing pre-reacted ErAP powders, or by a reactive sintering method starting from the appropriate oxide systems. By a reactive sintering method, a powder mixture that contains (comprises, consists of, or consists essentially of) erbium oxide particles and aluminum oxide particles is heated, optionally with pressure being applied to the powder mixtures, to cause erbium oxide and aluminum oxide of the powder mixture to react to form ErAP, with the particles growing together, without melting, to form a solid, dense, low porosity erbium aluminum perovskite sintered body. To achieve stable performance in a corrosive plasma environment a ceramic should be highly dense (>99% theoretical) with a uniform distribution of pores and grain size distribution through the entire sintered body. Such a uniform ceramic body cannot be achieved through melting and cooling as is commonly done with metals as the cooling and crystallization rate will not be uniform through the entire body, particularly with larger components. A non-uniform distribution of grain sizes and porosity can result in localized attack of the ceramic material which can cause rapid degradation of the ceramic material typically resulting in particle generation that impacts the quality of the product being processed in the plasma chamber system.

[0045]

[0042] According to example reactive sintering processes, the powder mixture is formed from aluminum oxide powder and erbium oxide powder in a ratio of one mole aluminum oxide to one mole erbium oxide. The aluminum oxide powder and the erbium oxide powder can be of high purity, e.g., at least 99% or most preferred up to 99.999% weight percent aluminum oxide or erbium oxide, respectively. The powder mixture can comprise, consist essentially of, or consist of the erbium oxide powder and aluminum oxide powder.

[0043] Examples of useful reactive sintering methods include spark plasma sintering and hot press sintering. As used herein the term “spark plasma sintering” (“SPS”) refers to a method of bonding together individual particles of a powder to form a dense (low porosity) sintered material (a.k.a. “sintered body”) by applying pressure to the particles while the particles are heated in a die by electric current that passes through a graphite punch and die assembly. SPS is also known as field-assisted sintering technology (“FAST”) or direct current sintering (“DCS”). The particles are heated to a temperature that is below the melting point of the particles but also sufficiently high to cause erbium oxide and aluminum oxide of the powder mixture to react to form erbium aluminum perovskite, while the individual particles become bonded together by atomic diffusion at the particle surfaces. A spark plasma sintering method uses contemporaneous application of uniaxial pressure and heat generated by electric current passing through the die to increase the temperature of the particles in the die. Spark plasma sintering differs from hot press sintering, which uses an external heat source such as radiant heating elements, a furnace, or resistive heating elements to heat a die that contains powder for sintering. SPS allows for higher heating rates than hot press, however when the different methods are operated in a similar manner the resulting product is substantially similar.

[0046]

[0044] According to example spark plasma sintering methods, the powder mixture can be placed within an interior of a graphite die in a controlled, oxygen-free atmosphere such as a vacuum or inert atmosphere. The oxygen-free atmosphere is effective to prevent the graphite die from reacting or combusting. The pressure (“sintering pressure”), rate of temperature increase (temperature profile), maximum temperature or temperature range (“sintering temperature”), type of electric current passing through the die, and amount of time that the powder mixture is held at a sintering temperature (“sintering time”), are factors of the sintering process that can be controlled to produce a sintered erbium aluminum oxide body that contains erbium aluminum oxide predominantly in the form of erbium aluminum perovskite.

[0047]

[0045] Examples of useful sintering pressures can be up to about 140 megapascals (MPa). Pressures greater than 140 MPa will typically damage a graphite die. The sintering pressure is usually no more than 100 MPa, preferably up to 25 or 50 MPa, and more preferably in a range from 10 to 50 MPa.

[0048]

[0046] Examples of useful sintering temperatures may be up to 1700 degrees Celsius, e.g., from 1400 to 1700 such as from 1450 to 1650 degrees Celsius. A temperature that is too high may cause formation of the erbium aluminum garnet phase. A useful sintering time may be up to 180 or 120 minutes, c.g., up to 90 minutes or up to 60 minutes for dies of 100 mm to 150 mm diameter or less. Differently sized dies may require different sintering times, specifically very large systems.

[0049]

[0047] According to example spark plasma sintering methods, an erbium aluminum perovskite sintered body can contain predominantly erbium aluminum oxide in the perovskite form, e.g., at least 80, 90, 95, 96, 97, 98, or 99 weight percent erbium aluminum perovskite. For erosion resistance in a plasma chamber, low porosity is desirable, preferably 1% porosity or less (99% relative density or greater). Pores on a sintered body permit entrance of reactive gas or chemicals into the sintered body and increase the attack surface and promote undercutting of the sintered body, causing particle generation.

[0050]

[0048] An erbium aluminum perovskite composition in the form of an erbium aluminum perovskite coating on a substrate, or in the form of an erbium aluminum perovskite sintered body, may be useful as a corrosion resistant surface that is resistant to degradation in the presence of reactive chemicals or plasma. Example erbium aluminum perovskite coatings and erbium aluminum perovskite sintered bodies can have a high content of erbium aluminum perovskite, high purity, and a relatively high density (including low pore content). These compositions may be particularly useful as a thermally stable, plasma-resistant interior surface within a plasma chamber, particularly of a type that performs a plasma deposition or plasma etching process involving the use of halogen-based process gases introduced into a plasma processing chamber while an RF field is applied to the process gases to generate plasma.

[0051]

[0049] Example erbium aluminum oxide coatings and sintered bodies may be formed as an inert (chemically resistant) surface of an interior component of a plasma chamber, such as a plasma chamber used in semiconductor manufacturing. Example such components include windows (RF windows or lids), nozzles, gas injectors, diffusers (e.g., shower head diffusers), chamber liners, electronic wafer chucks, faceplates, spacers, isolator mixing manifolds, wafer supports, electronic wafer chucks, pinnacle, a plasma source adapter, a gas inlet adapter, and various rings such as focus rings and protective rings, among other components. The erbium aluminum perovskite surface can exhibit useful physical properties for these applications, including a low loss of RF transmission, for example as needed in a dielectric or RF window.

[0050] For use as an inert surface at an interior of a plasma chamber, an erbium aluminum perovskite sintered body or an erbium aluminum perovskite coating may exhibit useful or advantageous inertness in the presence of reactive chemicals such as a plasma, reactive halogen, or combinations of these. Example erbium aluminum perovskite sintered bodies and erbium aluminum perovskite coatings can exhibit a measured erosion (etching) rate that is less than an erosion (etching) rate of other ceramics, such as yttrium aluminum garnet (YAG), which is a ceramic material known to have high inertness to reactive chemicals and plasmas.

[0052] EXAMPLE 1 - Erosion Resistance of Ceramic Materials

[0053]

[0051] Figure 1 shows measured erosion depths of samples of ceramics that include: 1.) yttrium aluminum garnet (YAG), 2.) erbium aluminum garnet (ErAG), and 3.) erbium aluminum perovskite (ErAP).

[0054]

[0052] The ceramic samples were tested for erosion resistance by exposing the samples to an inductively coupled plasma (ICP). Argon, oxygen (O2) and carbon tetrafluoride (CF4) were employed as plasma gases and fed at a rate of 5.0, 0.5 and 1.0 seem, respectively, (seem - standard cubic centimeters per minute). The ICP power was 600 W, the process pressure 0.01 mbar, the bias voltage 250 V and the exposure time 120 min. . Before plasma exposure, half of each sample was masked with plasma-resistant Kapton tape, to induce a defined etch step at the transition from etched to protected surface. The height of this etch step was measured with laser scanning microscopy and the results are displayed in Fig. 1.

[0055]

[0053] The compositions of the different ceramic samples were as follows:

[0056] YAG — high purity single phase yttrium aluminum garnet formed by spark plasma sintering.

[0057] ErAG — High purity dual phase erbium aluminum oxide with a major amount (>90%) of the garnet form and a minor amount (< 10%) of the perovskite phase, formed by spark plasma sintering. (Result of Rietveld refinement: 93% ErAG and 7% ErAP).

[0058] ErAP — high purity ( > 95 weight percent) single phase erbium aluminum perovskite formed by spark plasma by sintering.

[0059]

[0054] The data at figure 1 show that YAG, which is a ceramic commonly used as an inert material at interiors of plasma chambers, has better resistance to erosion than ErAG, and that high purity ErAP has improved resistance to erosion compared to YAG. This is a surprising result as garnets, especially YAG, are favored as the material having the best erosion resistance to the harsh environment of a plasma chamber.

[0060] EXAMPLE 2 — Erbium Aluminum Perovskite Sintered Body Produced by Spark Plasma Sintering Erbia and Alumina

[0061]

[0055] A powder mixture of alumina powder and erbia powder having equal stoichiometric amounts of erbia and alumina was processed by spark plasma sintering to form sintered erbium aluminum perovskite bodies in the form of disks measuring 40 mm in diameter.

[0062]

[0056] The powder mixture was formed by mixing 42.1 g of alumina with 157.9 g of erbia. The powder mixture was ball milled in the presence of 200 g of alumina milling media in 400 ml of EtOH (ethyl alcohol) at 125 revolutions per minute (rpms) for 21 hours. After rotary evaporating (also known as rotovapping) the slurry to remove the ethyl alcohol, and subsequent sieving, the resulting powder mixture was used in a spark plasma sintering process to produce erbium aluminum perovskite (“ErAP”) disks of approximately 40 millimeters in diameter. The spark plasma sintering was performed under vacuum at 25 MPa in a graphite die lined with graphite foil, as follows:

[0063]

[0057] Sample (i). The temperature of the powder mixture was increased from room temperature, at a heating rate of 50 degrees Celsius per minute, to 1600°C; the temperature of the powder mixture was then held at 1600°C for five minutes. The sintered body formed in the shape of a disk was assessed as probably not achieving full density (failed example).

[0064]

[0058] Sample (ii). The temperature of the powder mixture was increased from room temperature, at a heating rate of 10°C per minute, to 1625° C; the temperature of the powder mixture was then held at 1625 °C for five minutes. The sintered body formed in the shape of a disk was assessed as having been sintered successfully.

[0065]

[0059] While XRD (X-ray diffraction) analysis was not performed, based on the softness of the resulting sintered body during removal of adhered graphite foil, it is estimated that the sintered body was at least 90% ErAP, more likely around 95% ErAP. In comparison, ErAG is a harder phase and adhered graphite foil can be removed by sandblasting without damaging the sintered body. With the sintered body of this example, sandblasting produced many pits in the surface of the sintered body, indicative of the softer ErAP phase.

[0060] Sample (iii). The temperature of the powder mixture was increased from room temperature, at a heating rate of 25°C per minute, to 1000° C and from 1000°C to 1450°C at a heating rate of 10°C per minute; the temperature of the powder mixture was then held at 1450°C for 30 minutes. The sintered body formed in the shape of a disk was assessed as having been sintered successfully. These parameters were used to press the ErAP coupon in Fig. 1.

[0066] According to XRD analysis, the sintered body was 99 weight percent ErAP and 1 weight percent Er2O3.

[0067] EXAMPLE 3

[0068]

[0061] Powder mixtures of alumina powder and erbia powder having equal stoichiometric amounts of erbia and alumina were processed by a solid-state synthesis method using a heating (i.e., calcining) step to form an erbium aluminum perovskite powder (“ErAP powder”) by reaction of the erbia and alumina.

[0069]

[0062] In a first process, a mixture of 157.9g E Ch powder and 42.1g alumina powder was milled with 200g of AI2O3 media in 400 ml EtOH at 125 rpm for 22 hours. After rotary evaporating and sieving, this milled powder mixture was calcined in air at 3° / min to 1500° C then held at 1500° C for four hours. According to XRD analysis this produced a powder of 54 weight percent ErAP (ErAlCh), 25 weight percent ErAG (EnAlsOn) and 20 weight percent Erbia (EnOa). The first process is not according to the present invention.

[0070]

[0063] In a second process of producing ErAP powder, a mixture of 157.9g EnOa and 42.1g alumina was milled with 200g of AI2O3 media in 400 ml EtOH at 125 rpm for approximately 144 hours. After rotovapping, the mixture was calcined in air at 37min to 1500° C and held at 1500° C for four hours. According to XRD analysis, this resulted in 89.3 percent by weight ErAP, 3.7 percent by weight ErAG, and 7 percent by weight erbia. The second process is not according to the present invention.

[0071]

[0064] In a third process of producing ErAP powder, 355.3 grams Er2O3 powder was combined with 94.7 grams of alumina powder and attrition milled with 1446.6g of 3 mm alumina milling media in 400 ml EtOH for 2 hours. After rotovapping and sieving, the milled powder mixture was calcined at l°C / min to 1500 °C and held at 1500° C for 4 hours. According to XRD analysis, this resulted in a phase purity of 95.9 percent by weight ErAP, 3.6 percent by weight ErAG and 0.5 percent by weight erbia. The powder mixture after calcining was also analyzed for its overall purity using TCP-MS. An Agilent 7900 ICP-MS (Model G8403), commercially available from Agilent Technologies, Inc. (USA) was used to perform ICP-MS on the powder mixture after calcining. According to the analysis by ICP-MS, the powder had an overall purity of 99.975%. That is, the amount of impurities in the composition by weight was 0.025% or 250 ppm. The third process is according to the present invention.

[0072]

[0065] Regarding the above-described first to third processes, the following must be observed: The difference between the third process and the other processes that achieved the high phase purity is the mixing and milling procedure. In the first process, mixing was performed for 22 hours, which resulted in low phase purity, only 54 wt% ErAP. In the second process, mixing was performed for 144 hours, and phase purity increased to 89.3 wt% ErAP. However, 144 hours is a long mixing time. Therefore, in the third process, attrition milling was used, which imparts much more energy and required only 2 hours of milling to achieve a phase purity of 99.975 weight percent.

[0073]

[0066] The first and second processes used end-over-end bucket tumbling, while the third process used attrition milling. To achieve high phase purity and get all of the erbia to react with alumina, thorough mixing is required. In the present embodiments, it can either be used bucket tumbling for long periods of time or attrition milling to achieve the same result in a much shorter period of time for the mixing step. As alternatives to attrition milling, other high energy methods known in the ait, such as high shear mixing, high energy ball milling, planetary ball milling, or ultrasonic dispersion methods may be deployed to achieve thorough mixing and to reduce the period of time required for the mixing step, for example, high shear mixing, high energy ball milling, planetary ball milling or dispersion methods.

[0074]

[0067] The foregoing description has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limiting to the precise form or example disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from experimentation. Embodiments and examples were chosen and described in order to explain the principles and practical application in various embodiments and with various modifications as are suited to particular uses. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.

Claims

Claims:

1. An erbium aluminum oxide composition comprising a phase purity of at least 90 weight percent erbium aluminum perovskite.

2. The composition of claim 1, in the form of a sintered body.

3. The composition of claim 2, where the sintered body has a porosity in a range from 0.01 to 10 percent.

4. The composition of claim 1, where the composition comprises impurities of no more than 250 ppm.

5. The composition of claim 1 in the form of a powder that comprises particles that comprise at least 90 weight percent erbium aluminum perovskite.

6. The composition of claim 1 in the form of a coating.

7. The composition of claim 1, having a resistance to plasma etching that is greater than a resistance to plasma etching of yttrium aluminum garnet.

8. A plasma chamber comprising an interior and a composition of claim 7 within the interior as a plasma-facing surface.

9. A method of preparing an erbium aluminum oxide composition comprising at least 90 weight percent erbium aluminum perovskite, the method comprising: preparing a powder mixture comprising erbium oxide particles and aluminum oxide particles, and heating the powder mixture, without melting the particles, to cause the erbium oxide and aluminum oxide of the powder mixture to react to form erbium aluminum perovskite.

10. The method of claim 9, wherein the powder mixture is prepared by attrition milling the powder mixture for at least 2 hours.

11. The method of claim 10, comprising heating the powder mixture at approximately atmospheric pressure or below to form a powder comprising particles that comprise a phase purity at least 90 weight percent erbium aluminum perovskite.

12. The method of claim 10, comprising: placing the powder mixture in a die interior, removing gaseous oxygen from the die interior, applying unilateral pressure to the powder mixture in the die, and increasing a temperature of the powder mixture to cause erbium oxide and aluminum oxide of the powder mixture to react to form erbium aluminum perovskite, and to cause the particles to fuse together without melting to form a sintered body that comprises at least 90 weight percent erbium aluminum perovskite.

13. The method of claim 12, wherein the pressure does not exceed 50 MPa, and the temperature does not exceed 1700 degrees Celsius.

14. A method of forming a coating on a substrate surface, the coating comprising at least 90 weight percent erbium aluminum perovskite, the method comprising: providing a powder comprising particles that comprise a phase purity of at least 90 weight percent aluminum perovskite, forming an aerosol that contains the particles, and under vacuum conditions, directing the aerosol toward a surface of a substrate such that the particles contact the surface and remain at the surface as a coating that comprises at least 90 weight percent erbium aluminum perovskite.

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