High frequency polishing of ceramics

Abstract

1. A method for polishing a surface of a polycrystalline sintered ceramic body, comprising the steps of: a) providing a sintered ceramic body comprising a polycrystalline material and having a density of about 99.5% to about 99.999% of the theoretical density of the polycrystalline material, the sintered ceramic body having at least one surface; b) grinding the at least one surface until the surface has (i) an average flatness of 25 microns or less measured over four quadrants of the at least one surface at angles of 0°, 90°, 180°, and 270° as measured with a spherometer, (ii) an Ra of less than 14 microinches, and (iii) an Rz of less than 160 microinches; and c) lapping the at least one surface with a lapping plate and lapping media slurry after the grinding step. and d) successively polishing the at least one surface in a series of polishing steps until, after lapping, the at least one surface exhibits an Ra value of ≦2 microinches, an Rz of ≦2 microinches, and an absolute value of flatness greater than 15 microns as measured by a spherometer, the polishing being performed in an apparatus comprising a plurality of elliptical oscillating orbital sanders, each of the plurality of orbital sanders comprising a polishing pad that contacts the at least one surface during polishing, the series of polishing steps including i) a first polishing step in which the polishing pad is used with a slurry of 4 micron to 10 micron grit particles, and ii) a second polishing step in which the polishing pad is used with a slurry of 1 micron to 3 micron grit particles.

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for polishing dense sintered ceramic bodies to a very high degree of surface smoothness suitable for use as corrosion-resistant components in semiconductor plasma processing chambers.

[0002] Semiconductor processing requires the use of halogen-based gases in combination with high electric and magnetic fields to create a plasma environment. This plasma environment is created in a vacuum chamber to etch or deposit materials on a semiconductor substrate. These vacuum chambers include components such as a disk or window, a liner, an injector, a ring, and a cylinder. During semiconductor plasma processing, the substrate is typically supported within the vacuum chamber by a substrate holder, as disclosed in U.S. Pat. Nos. 5,262,029 and 5,838,529. Process gases for creating the plasma processing environment can be supplied to the chamber by various gas delivery systems. Some processes involve the use of radio frequency (RF) fields, where the process gas is introduced into the processing chamber, while the RF field is applied to the process gas to generate a plasma of the process gas. The ceramic materials used to form these components, particularly for RF applications, have a 1×10 -3A dielectric loss tangent on the order of 0.1 Ω or less is required. Dielectric losses higher than this can cause overheating and hot spots within the components during use, leading to process variations and yield loss. The use of components made from high-purity starting powders and manufacturing processes that preserve initial purity provides sintered ceramics that meet these low-loss requirements. The harsh plasma processing environment necessitates the use of highly corrosion- and erosion-resistant materials for chamber components. These components are formed from materials that provide resistance to corrosion and erosion in plasma environments, as described, for example, in U.S. Pat. Nos. 5,798,016, 5,911,852, 6,123,791, and 6,352,611. Furthermore, plasma processing chambers are designed to include components such as disks, rings, and cylinders that confine the plasma over the wafer being processed. However, these components used in plasma processing chambers are continually attacked by the plasma, resulting in corrosion, erosion, or the accumulation of contaminants and polymer buildup. Plasma etching and deposition conditions cause erosion and roughening of the surfaces of chamber components exposed to the plasma. This erosion contributes to wafer-level contamination through the release of particles from component surfaces into the chamber, resulting in yield loss of semiconductor devices.

[0003] To address this, chamber components often have surface layers that resist corrosion and erosion when exposed to process gases. Surface layers can be formed on bases or substrates that may have excellent mechanical, electrical, or other desirable properties. For example, corrosion-resistant films or coatings of yttrium oxide or yttrium aluminum garnet (YAG) are known to be deposited on bases or substrates made of different materials that are cheaper and stronger than most corrosion-resistant materials. Such films or coatings have been fabricated by several methods. Vapor deposition has been used to deposit corrosion-resistant films on substrates, but deposition is limited to relatively thin layers due to internal film stresses, and small pores often exist in thin films. These internal film stresses cause poor interlayer adhesion, typically resulting in delamination at the interface between the corrosion-resistant film and the substrate, making these layers prone to cracking and peeling, thereby leading to undesirable particulate contamination. Corrosion-resistant coatings or films fabricated by aerosol or plasma spray techniques typically exhibit high levels of porosity, ranging from 3% to approximately 50%, and correspondingly low densities. Furthermore, these films produced by aerosol or spray methods exhibit poor interfacial adhesion between the substrate material and the corrosion resistant layer, resulting in spalling and flaking and subsequent chamber contamination. Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, there is a need to produce hard ceramic materials with highly polished surfaces having a surface roughness of less than about 2 microinches, uniformly for large-sized (greater than 100 mm, e.g., 100 mm to 625 mm) high-strength sintered ceramic bodies, to enable large-scale manufacturing of corrosion-resistant semiconductor devices.

[0005] Advantageously, the present disclosure provides a method for polishing the surface of a large sized sintered ceramic body to a uniform surface smoothness of about 2 microinches to about 1.5 microinches. Disclosed herein is a method for polishing the surface of a polycrystalline sintered ceramic body, the method comprising the steps of: a) providing a sintered ceramic body comprising a polycrystalline material and having a density of about 99.5% to about 99.999% of the theoretical density of the polycrystalline material, the sintered ceramic body having at least one surface; and b) polishing the surface to a flatness of (i) 25 microns or less on average, as measured with a spherometer, across four quadrants of the at least one surface at angles of 0°, 90°, 180°, and 270°, (ii) an Ra of less than 14 microinches, and (iii) a) grinding at least one surface until it has an Rz of less than 160 microinches; b) lapping the at least one surface with a lapping plate and lapping media slurry after the grinding step; c) lapping the at least one surface with a lapping plate and lapping media slurry after the lapping step; and d) successively polishing the at least one surface in a series of polishing steps until, after lapping, the at least one surface exhibits an Ra value of ≦2 microinches, an Rz of ≦2 microinches, and an absolute flatness value of greater than 15 microns as measured by a spherometer, wherein the polishing is performed in an apparatus comprising a plurality of elliptical oscillating orbital sanders (also referred to as orbit sanders), each of the plurality of orbital sanders comprising a polishing pad that contacts the at least one surface during polishing, the series of polishing steps comprising: i) a first polishing step in which the polishing pad is used with a slurry of 4 micron to 10 micron grit particles; and ii) a second polishing step in which the polishing pad is used with a slurry of 1 micron to 3 micron grit particles.

[0006] In another aspect, provided herein is a polycrystalline sintered ceramic body comprising at least 99.99% YAG and having at least one top surface having a surface area greater than 400 square inches, the surface having a spherometer measurement of greater than 15 microns absolute across the four quadrants of the disc, Ra and Rz of less than or equal to 2 microinches each across the surface area, and a porosity of less than 0.045% across the surface area, wherein the sintered ceramic disc has a thickness of at least 20 mm.

[0007] In yet another aspect, there is provided herein a polishing apparatus comprising a plate having a plurality of elliptically oscillating orbital sanders, each containing a polishing pad, and a rotatable table suitable for rotating a part to be polished, wherein the plate remains fixed during polishing while the part rotates on the table, and the orbital sanders are mounted on the plate such that the polishing pads face the rotatable table.

[0008] The embodiments of the present invention may be used alone or in combination with each other. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of an embodiment disclosed herein. [Figure 2] FIG. 2 is a perspective view of an exemplary mounting plate. [Figure 3] FIG. 3 is a diagram of an embodiment of a random orbital sander for use in the embodiments disclosed herein. [Figure 4] FIG. 4 is a perspective view of an embodiment of a housing for a random orbital sander for use in the embodiments disclosed herein. [Figure 5] FIG. 5 is a diagram of an embodiment of a random orbital sander ready to be mounted on a plate such as that of FIG. 2 in an embodiment disclosed herein. [Figure 6]FIG. 6 is an exemplary embodiment of a polishing apparatus for use in the disclosed method. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following detailed description provides preferred exemplary embodiments only and is not intended to limit the scope, applicability, or configuration of the present invention. Rather, the following detailed description of preferred exemplary embodiments provides an enabling description for those skilled in the art to practice preferred exemplary embodiments of the present invention. Various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the present invention, as set forth in the appended claims.

[0011] The term "about" means approximately or approximately, and in the context of numerical values ​​or ranges described herein, means, in one embodiment, ±20%, ±10%, ±5%, or ±3% of the recited or claimed numerical value or range.

[0012] As used in the context of describing the present disclosure (particularly in the context of the claims), the terms "a," "an," and "the" and similar referents should be construed to cover both the singular and the plural unless otherwise indicated herein or clearly contradicted by context. The recitation of ranges of values ​​herein is merely intended to serve as a shorthand method for referring individually to each separate value falling within the range. Unless otherwise indicated herein, each separate value is incorporated herein as if it were individually listed herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples or exemplary language (e.g., "etc.") provided herein is intended merely to better explain the disclosure and does not limit the scope of the claims. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the disclosure.

[0013] Unless expressly stated otherwise, the term "comprising" is used in the context of this document to indicate that further members may optionally be present in addition to the members of the list introduced by "comprising." However, for certain embodiments of the present disclosure, the term "comprising" is intended to encompass the possibility that no further members are present, i.e., for the purposes of this embodiment, "comprising" should be understood to have the meaning of "consisting of" or "consisting essentially of."

[0014] As used herein, the following terms are defined as follows: "alumina" is understood to be aluminum oxide, including Al2O3, "zirconia" is understood to be zirconium oxide, including ZrO2, and "yttria" is understood to be yttrium oxide, including Y2O3.

[0015] As used herein, the terms "semiconductor wafer," "wafer," "substrate," and "wafer substrate" are used interchangeably. Wafers or substrates used in the semiconductor device industry typically have diameters of 200 mm, or 300 mm, or 450 mm.

[0016] As used herein, the term "sintered ceramic body" is synonymous with "multilayer sintered ceramic body," "multilayer corrosion-resistant ceramic," "corrosion-resistant body," "sintered ceramic," "multilayer monolithic body," and similar terms, and refers to a single, monolithic sintered ceramic article formed from co-compressing two or more powder mixtures by applying pressure and heat to create a single, dense, multilayer sintered ceramic body. The single multilayer sintered ceramic body can be machined into a single multilayer sintered ceramic component useful as a chamber component in plasma processing applications. Thus, such multilayer sintered ceramic bodies disclosed herein are not formed by laminating preformed layers together; i.e., the multilayer sintered ceramic bodies disclosed herein are not laminates.

[0017] As used herein, the term "layer" is understood to mean a thickness of material, typically one of several. The material may be, for example, a ceramic powder, a powder mixture, a fired powder mixture, or a sintered region or portion.

[0018] As used herein, "ambient temperature" refers to a temperature range of about 22°C to 25°C.

[0019] Semiconductor etch and deposition reactors require reactor components with surfaces that are highly resistant to corrosion and erosion by the halogen-containing plasmas required for processing. The surfaces preferably minimize particle shedding from the component surface into the chamber. In addition, chamber components must have sufficient mechanical strength for handling and use, especially at large (>100 mm diameter) component sizes. Sintered ceramic bodies may be machined into sintered components and therefore must be capable of being handled and machined at large sizes while providing corrosion resistance, low particle shedding, and high mechanical strength.

[0020] Disclosed herein is a method for polishing a surface of a polycrystalline sintered ceramic body, the method comprising the steps of: a) providing a sintered ceramic body comprising a polycrystalline material and having a density of about 99.5% to about 99.999% of the theoretical density of the polycrystalline material, the sintered ceramic body having at least one surface; b) grinding the at least one surface until the surface has (i) an average flatness of 25 microns or less measured across four quadrants of the at least one surface at angles of 0°, 90°, 180°, and 270° as measured with a spherometer; (ii) an Ra of less than 14 microinches; and (iii) an Rz of less than 160 microinches; and c) grinding the at least one surface with a lapping plate and lapping media slide after the grinding step. d) successively polishing the at least one surface in a series of polishing steps until, after lapping, the at least one surface exhibits an Ra value of ≦2 microinches, an Rz of ≦2 microinches, and an absolute flatness value of greater than 15 microns as measured by a spherometer, the polishing being performed in an apparatus comprising a plurality of elliptical oscillating orbital sanders, each of the plurality of orbital sanders comprising a polishing pad that contacts the at least one surface during polishing, the series of polishing steps comprising: i) a first polishing step in which the polishing pad is used with a slurry of 4 micron to 10 micron grit particles; and ii) a second polishing step in which the polishing pad is used with a slurry of 1 micron to 3 micron grit particles. Sintered ceramic body

[0021] The first step of the method includes providing a sintered ceramic body comprising a polycrystalline material and having a density of about 99.5% to about 99.999% of the theoretical density of the polycrystalline material, the sintered ceramic body having at least one surface. As used herein, the term "providing" refers to obtaining or beginning a process with a sintered ceramic body having the described properties.

[0022] Sintered ceramic bodies for polishing by the disclosed method have a maximum dimension greater than 100 mm, e.g., 100 mm to about 625 mm, preferably 100 mm to 622 mm, preferably 200 mm to about 625 mm, preferably 300 mm to about 625 mm, preferably 400 mm to about 625 mm, preferably 500 mm to about 625 mm, preferably 300 mm to 622 mm, preferably 400 mm to 622 mm, preferably 500 mm to 622 mm, etc. The sintered ceramic body has a surface area greater than 400 square inches, a thickness of at least 20 mm, and is preferably opaque, although it may be translucent.

[0023] In some embodiments, the sintered ceramic body comprising the polycrystalline material is a single-layer sintered ceramic body, while in other embodiments, the sintered ceramic body is a multi-layer sintered ceramic body. Suitable single-layer sintered ceramic bodies are disclosed, for example, in WO 2020 / 206389 (yttrium oxide), WO 2021 / 141676 (yttrium aluminum oxide), WO 2022 / 015688 (magnesium aluminate spinel), and International Application Nos. PCT / US2021 / 054947 (zirconia-toughened alumina) and PCT / US2021 / 052989 (yttrium oxide), the disclosures of which are incorporated herein by reference in their entireties. Suitable multilayer sintered ceramic bodies are disclosed, for example, in International Application No. PCT / US2021 / 054773, International Application No. PCT / US2021 / 063973, International Application No. PCT / US2021 / 052981 (Sintered Ceramic Body of Large Dimension and Method of Making), and International Publication No. WO 2021 / 141676 (Yttrium Aluminum Oxide), the disclosures of which are incorporated herein by reference in their entireties. In addition to the methods disclosed in the above-referenced patent applications, suitable apparatus and methods for producing high-density, large-size sintered ceramic bodies for polishing in accordance with the disclosed methods are disclosed in International Application No. PCT / US2021 / 052978 (Apparatus for Preparation of Sintered Ceramic Body of Large Dimension) and International Application No. PCT / US2021 / 052981 (Sintered Ceramic Body of Large Dimension and Method of Making), the disclosures of which are incorporated herein by reference in their entireties.

[0024] Preparation of the sintered ceramic bodies disclosed herein may also be achieved through the use of pressure-assisted sintering methods, such as uniaxial hot pressing, whereby a die configuration or tool set is heated by an externally applied heat source, such as induction heating.

[0025] The polycrystalline material of the sintered ceramic body is preferably at least one selected from the group consisting of YAG, yttria, alumina, magnesium aluminate spinel, and a combination of yttria and zirconia. In multi-layer embodiments, each subsequent layer may be selected from at least one of YAG, yttria, alumina, magnesium aluminate spinel, and a combination of yttria and zirconia.

[0026] In certain embodiments, the sintered ceramic bodies disclosed herein have the formula YAlO (with a composition comprising yttrium and alumina in a ratio of about 3:5) having a garnet structure. 12 The polishing method includes at least one first layer having at least one polycrystalline ceramic material including YAG (yttrium aluminum oxide or yttrium aluminate), spinel (magnesium aluminate spinel, MgAl2O4), yttria, and zirconia, where the zirconia is present in the yttria in an amount of 10 mole % or more ZrO2 and 25 mole % or less ZrO2. It is the at least one first layer that provides the surface that is polished according to the disclosed method.

[0027] In a preferred embodiment, the sintered ceramic body disclosed herein comprises at least one first layer having at least one polycrystalline ceramic material comprising YAG, and thus the surface to be polished comprises YAG.

[0028] Sintered ceramic bodies for use in the disclosed methods have a density of from about 99.5% to about 99.999%, such as from about 99.5% to about 99.99%, and such as from about 99.56% to about 99.78%, of the theoretical density of the polycrystalline material.

[0029] Density measurements of multilayer bodies have proven difficult due to differences in layer densities. Density measurements can be performed on multilayer sintered ceramic bodies by sectioning a sample cut from the full thickness of the body into its first and second layers and measuring the density of each individual layer. Here, we describe density measurements on a two-layer sintered ceramic body, prepared from Example 4 of International Application PCT / US2021 / 063973, which includes a thinner first layer of YAG and a thicker second layer of zirconia-toughened alumina. Density measurements were performed according to the Archimedes immersion method of ASTM B962-17, and densities of 4.55 g / cc to 4.57 g / cc, preferably about 4.56 g / cc, were measured for polycrystalline YAG in at least one first layer. The reported density values ​​are averages over five measurements, and the standard deviation in the measurements (using known standards) was determined to be about 0.002. Commercially available single crystal samples of bulk YAG were measured for density using the method disclosed herein. An Archimedes density of 4.56 g / cc was obtained over five measurements, and this value is designated as the theoretical density of YAG used herein. Therefore, the at least one first layer containing YAG in a multilayer sintered ceramic body according to one embodiment has a theoretical density of 99.5% to 99.999% of the theoretical density of YAG. The density of the at least one second layer containing approximately 16 volume percent stabilized zirconia and / or partially stabilized zirconia (and the remainder alumina) was measured according to the Archimedes immersion method of ASTM B962-17, and a density of approximately 4.32 g / cc was calculated. Using a volumetric rule of mixtures known in the art, a density of 4.31 g / cc to 4.33 g / cc, preferably approximately 4.32 g / cc, was measured and designated as the theoretical density of the at least one second layer 102 containing alumina and approximately 16 volume percent stabilized zirconia and / or partially stabilized zirconia. Thus, at least one second layer 102 of the multilayer sintered ceramic body (comprising approximately 16% by volume zirconia and the remainder alumina) has a percent theoretical density of 98% to 100% of theoretical density, preferably 99% to 100%, preferably 99.5% to 100%, preferably about 100% of theoretical density.The single multilayer sintered ceramic body disclosed according to this embodiment comprises at least one first and second layer, each having a percent theoretical density (also referred to as relative density, RD) that is greater than 98%, preferably between 98% and 100%, preferably between 99% and 100%, preferably between 99.5% and 99.999%, preferably about 100% of the theoretical density of the single multilayer sintered ceramic body.

[0030] The relative density (RD) of a given material is defined as the ratio of the measured density of the sample to the theoretical density of the same material, as shown in the following equation: Volume porosity (Vp) is calculated from the density measurements as follows:

number

[0031] The sintered ceramic bodies disclosed above have an average density of 99.5% to 99.999%, with a density variation of 5% or less, preferably 4% or less, preferably 3% or less, preferably 2% or less, preferably 1% or less across their greatest dimension, such that the greatest dimension may be, for example, about 625 mm or less, 622 mm or less, 610 mm or less, preferably 575 mm or less, preferably 525 mm or less, preferably 100 mm to 625 mm, preferably 100 mm to 622 mm, preferably 100 mm to 575 mm, preferably 200 mm to 625 mm, preferably 200 mm to 510 mm, preferably 400 mm to 625 mm, preferably 500 mm to 625 mm.

[0032] The high density of sintered ceramic bodies polished according to the disclosed method leads to high surface hardness values ​​that may provide resistance to the erosive effects of ion bombardment used during typical plasma processes. Erosion or spalling can result from ion bombardment of component or layer surfaces due to the use of inert plasma gases such as Ar. These materials with high hardness values ​​may be preferred for use as materials for components due to their improved hardness values ​​providing greater resistance to ion bombardment and resulting erosion. Accordingly, the sintered ceramic bodies exhibit high Vickers hardness. For example, hardness measurements were performed on an exemplary sintered ceramic body including a YAG layer providing the polished surface according to ASTM Standard C1327, "Standard Test Method for Vickers Indentation Hardness of Advanced Ceramics." The test equipment used for all hardness measurements was a Wilson Micro Hardness Tester Model VH1202. Hardness values ​​of the YAG surfaces have been measured to be at least 1200 HV, preferably at least 1400 HV, preferably at least 1800 HV, preferably at least 2000 HV, 1300 HV to 1600 HV, 1300 HV to 1500 HV, 1300 HV to 1450 HV, 1300 HV to 1400 HV, 1400 HV to 1600 HV, 1450 HV to 1600 HV, and 1450 HV to 1550 HV. Measurements were made using the Vickers hardness method known in the art and converted to SI units of GPa. Hardness values ​​of 12.75 GPa to 15.69 GPa, 12.75 GPa to 14.71 GPa, 12.75 GPa to 14.22 GPa, 12.75 GPa to 13.73 GPa, 13.73 GPa to 15.69 GPa, and 14.22 GPa to 15.69 GPa, preferably 14.22 GPa to 15.20 GPa, have been measured. These high hardness values ​​can contribute to improved resistance to ion bombardment during semiconductor etching processes and reduced erosion during use, providing extended component life when the multilayer sintered ceramic body is machined into sintered ceramic components having fine-scale features.

[0033] In one embodiment, the sintered ceramic body has an average hardness of 13.0 GPa to 16.0 GPa calculated from eight test replicates using an applied load of 0.2 kgf as measured according to ASTM Standard C1327. In another embodiment, the sintered ceramic body has an average hardness of about 13.5 GPa to 15 GPa calculated from eight test replicates using an applied load of 0.2 kgf as measured according to ASTM Standard C1327. In yet another embodiment, the sintered ceramic body may have an average hardness of about 13.8 GPa to 15.8 GPa calculated from eight test replicates using an applied load of 0.025 kgf.

[0034] Sintered ceramic bodies polished according to the methods disclosed herein are translucent and not optical grade. In embodiments, the sintered ceramic bodies transmit less than 60% of light.

[0035] Sintered ceramic bodies polished according to the methods disclosed herein typically have a thickness of at least 10 mm, preferably between 10 mm and 30 mm, and more preferably between 25 mm and 28 mm. Grinding process

[0036] The disclosed method includes grinding at least one surface performed to modify the surface of the sintered ceramic body to (i) an average flatness of 25 microns or less measured across four quadrants of at least one surface at angles of 0°, 90°, 180°, and 270° as measured with a spherometer, (ii) an Ra of less than 14 microinches, and (iii) an Rz of less than 160 microinches.

[0037] The function of the grinding process is to flatten the surface of the sintered ceramic body to be polished. Surface flatness can be measured with a spherometer, such as a Mahr gauge, model Millimess 1003 spherometer, available from the Mahr Group of Mahr GmbH (Goettingen, Germany). Flatness is preferably measured with the spherometer across the entire surface, or in some embodiments, across four quadrants of the surface at angles of 0, 90, 180, and 270 degrees, using a flat fixture with the aforementioned Mahr gauge calibrated to a master flat, such as a surface plate available from Standridge Granite Corp. (Santa Fe Springs, California).

[0038] Ra and Rz are different parameters of roughness. Ra is the average roughness of a surface. Rz is the difference between the highest "peak" and the deepest "valley" on a surface.

[0039] Ra is the integer average of all absolute roughness profile deviations from the centerline within the measurement length. Rz is the absolute peak-to-valley average of five consecutive sample lengths within the measurement length. Ra compares all dimensions and has no significant value in separating bad from good cylinders.

[0040] The average roughness value Ra (DIN 4768) is the arithmetic mean of all the values ​​of the roughness profile R within the measurement distance lm. It therefore specifies the average deviation of this surface profile from the mean line.

[0041] The mean roughness depth Rz (DIN 4768) is the average value of five individual roughness depths measured over successive distances. In other words, the calculation is made from five Rt values. The deviation from the mean line is focused on, especially the highest peaks and valleys.

[0042] In one embodiment, the disclosed process includes grinding the surface of the sintered ceramic body using a Blanchard machine until the ceramic surface has a flatness of 25 microns or less measured across the four quadrants of the surface at angles of 0, 90, 180, and 270 degrees. In addition, Ra must be less than 14 microinches and Rz must be less than 160 microinches, more preferably less than 150 microinches.

[0043] Ra and Rz can be measured with a digital microscope, such as the Keyence VK-X200 series available from Keyence Corporation of America (Itasca, Illinois, USA). wrapping

[0044] The methods disclosed herein include lapping at least one surface with a lapping plate and a lapping media slurry. Lapping is a process well known in the art and involves contacting at least one surface of a sintered ceramic body with the surface of a lapping plate while rotating at least one of the ceramic body and the plate to remove material from the surface of the sintered ceramic body and provide a flatter and / or smoother surface than before the lapping step. This includes at least partial removal of scratches in the surface, if present. Abrasive media (e.g., diamond grit or alumina) can be used to help remove material from the surface and provide a smoother surface. The abrasive material can be fixed to the lapping plate and / or distributed on the surface of the lapping plate (e.g., as an abrasive slurry) during lapping.

[0045] The lapping process disclosed herein may include one or more lapping steps to achieve a desired flatness and / or smoothness. In one embodiment, the lapping process includes (i) a first lapping step in which the lapping medium is alumina having an average particle size of 30 microns to 50 microns, (ii) a second lapping step in which the lapping medium is alumina having an average particle size of 10 microns to 20 microns, and (iii) a third lapping step in which the lapping medium is alumina having an average particle size of 5 microns to 10 microns. In another embodiment, the lapping medium in the first lapping step has a particle size of 40 microns, (ii) the lapping medium in the second lapping step has a particle size of 12 microns, and (iii) the lapping medium in the third lapping step has a particle size of 6 microns.

[0046] Lapping is performed by mounting a sintered ceramic body on a support (platen) with the ceramic surface to be polished facing up. While the ceramic surface rotates, a lapping plate is pressed against the ceramic surface and oscillated back and forth across it. The lapping can also rotate, and the lapping plate and support can rotate in the same or opposite directions. For a given grit size and fluid viscosity, varying the lapping pressure results in higher or lower material removal rates, thicker or thinner films, and coarser or finer surface finishes. Therefore, in practice, pressure is typically light at the beginning of the process, increasing as the work progresses, and decreasing toward the end. This results in optimal material removal rate, surface finish, and flatness, ensuring the overall surface finish quality is fully achieved. Waviness (also known as peaks and valleys) is a calculation of surface irregularities with spacing greater than the surface roughness. These are typically caused by warping, vibration, or deflection during the machining process.

[0047] Preferably, the surface smoothness after the lapping step is about 6 microinches. vibration polishing

[0048] The disclosed method includes successively polishing at least one surface in a series of polishing steps until, after lapping, the at least one surface exhibits an Ra value of ≦2 microinches, an Rz of ≦2 microinches, and an absolute flatness value of greater than 15 microns as measured by a spherometer, the polishing being performed in an apparatus comprising a plurality of elliptical oscillating orbital sanders, each including a polishing pad that contacts at least one surface during polishing, the series of polishing steps including: i) a first polishing step in which the polishing pad is used with an abrasive slurry containing grit particles of 4 microns to 10 microns; and ii) a second polishing step in which the polishing pad is used with an abrasive slurry containing grit particles of 1 micron to 3 microns.

[0049] Sanding according to the disclosed method is accomplished using an apparatus comprising a plurality of elliptically oscillating orbital sanders, each comprising an abrasive pad that contacts at least one surface during sanding. Referring to FIG. 1, an apparatus 10 is shown comprising a plate 2 comprising a plurality of elliptically oscillating orbital sanders 4 (also referred to herein as "orbital sanders"), each comprising an abrasive pad 8. Each of the plurality of orbital sanders 4 is attached to the plate 2 by a screw / bolt assembly 6. Orbital sanders are known in the art and may be powered either electrically or pneumatically. Non-limiting examples of orbital sanders 4 suitable for use in the disclosed polishing method include the random orbital sanders described in U.S. Pat. Nos. 5,934,985, 5,595,531, 5,580,302, 5,411,386, 5,392,568, and 5,384,984, all of which are incorporated herein by reference in their entireties, and / or commercially available orbital sanders, such as those available from Dynabrade in Clarence, NY, USA.

[0050] 2 shows plate 2 with holes 5 for receiving screw / bolt assemblies 6 for mounting each of a plurality of orbital sanders 4, and mounting portions 7 for mounting plate 2 on equipment for sanding operations. Plate 2 can be made from any durable material known in the art and suitable for withstanding sanding pressures, including steel. In the illustrated embodiment, plate 2 is circular, but can have any shape as long as it is rotatable.

[0051] 3-5 show the orbital sander 4, the housing 9, and the assembled orbital sander 4 ready for attachment to the plate 2, respectively. Referring to FIG. 3, the pneumatic orbital sander is shown having a pneumatic opening assembly 12 that includes an air inlet and an air outlet for supplying air and evacuating air as needed. In the exemplary embodiment, compressed air at approximately 100 psi is used to power the orbital sander. Not shown are the connections and hoses leading to a pressurized air source.

[0052] The polishing pad 8 includes a platen that may or may not include abrasive particles, also referred to herein as "grit particles," for polishing at least one surface of the sintered ceramic body. In embodiments where the platen does not include abrasive particles incorporated therein, an abrasive-containing slurry is applied between the sintered ceramic body and the platen for polishing. In either case, the phrase "the polishing pad includes X microns of grit particles" is intended to include particles provided by a liquid slurry. The platen is secured to a bearing via a plurality of threaded screws extending through openings in the platen. The bearing is eccentrically positioned relative to the motor's drive spindle, thus imparting orbital motion to the platen when the platen is rotated by the motor. The platen can be any size required, for example, from 80 mm to 300 mm in diameter. In one embodiment, the platen is 6 inches (152.4 mm).

[0053] In some embodiments, the polishing pad 8 is an unfilled microcellular foam elastomer pad, such as a polyurethane pad commercially available from Universal Photonics Incorporated (Central Islip, NY, USA) (https: / / www.universalphotonics.com / UPIProducts / Consumables / tabid / 102 / prtype / 1105 / prid / 490 / Default.aspx).

[0054] The slurry suitable for use in the polishing step of the disclosed method comprises abrasive particles of desired size and a liquid delivery vehicle, such as water. The slurry may also comprise other components typically found in such slurries, such as lubricants. The abrasive (grit) particles must be harder than the surface to be polished, and can be selected from, for example, polycrystalline diamond particles and aluminum oxide particles. Preferably, the abrasive particles for the polishing step are polycrystalline diamond particles in aqueous suspension.

[0055] Referring to Figure 4, housing 9 has openings 11 for receiving an air supply hose if a pneumatic motor is used, or an electrical connection if an electric motor is used. Figure 5 shows the assembled orbital sander with the screw / bolt assemblies ready to be mounted onto plate 2. The orbital sander 4 can be mounted onto plate 2 in any suitable configuration.

[0056] The orbital sander 4 typically exhibits a speed of 5,000 RPM to 15,000 RPM. In some embodiments, the orbital sander exhibits a speed of 10,000 RPM to 15,000 RPM, and in preferred embodiments, a speed of 12,000 RPM (maximum). Such speeds can provide high shear rates for polishing. In some embodiments, if a slurry is used, the shear rate of the slurry relative to the sintered ceramic body is about 1 m / s to about 10 m / s, preferably about 6 m / s.

[0057] FIG. 6 shows an exemplary polishing apparatus 20 for use in the polishing step of the disclosed method. The plate 2 is fixed, and the rotatable table 22 is adapted to rotate a part 24 having a surface 26 to be polished by a slurry supplied by a slurry supply device 28. In the illustrated embodiment, there are four orbital sanders 4, although in other embodiments, there may be two, three, or five orbital sanders. The orbital sanders 4 are mounted on the plate 2 so that the polishing pad faces the rotatable table and, therefore, the sintered ceramic body fixed on the table. In the illustrated embodiment, during the polishing step, at least one surface of the sintered ceramic body is rotated, and the orbital sander is stationary. An example of a polishing apparatus is shown in FIG. 6.

[0058] The polishing step is preferably carried out in several successive substeps, each substep using grit of decreasing particle size relative to the previous step. In one embodiment, the series of polishing steps includes: i) a first polishing step in which the polishing pad contains 4-10 micron grit particles; and ii) a second polishing step in which the polishing pad contains 1-3 micron grit particles. In one embodiment, a 6 micron grit slurry is used in the first polishing step, and a 2 micron grit slurry is used in the second polishing step. In another embodiment, a 6 micron grit slurry is used in the first polishing step, and a 1 micron grit slurry is used in the second polishing step. Typically, the pressure on the surface of the sintered ceramic body during the polishing step is 0.2 psi to 2 psi, more preferably 0.3 psi to 1 psi, and the RPM of the rotary table is preferably 100 RPM to 200 RPM, more preferably 130-160 RPM, and even more preferably 140 RPM to 150 RPM.

[0059] After performing the methods disclosed herein, the porosity of the polished surface is preferably less than 0.045% across the polished surface area, as measured from SEM images using ImageJ software. Typically, measurements are made across seven SEM images. In some embodiments, the porosity in percent of total area, as measured from SEM images using ImageJ software, is shown in amounts between 0.0005% and 0.045%. Thus, for example, across an image with an area of ​​approximately 54 μm × 54 μm, the polished surface of a sintered ceramic body disclosed herein contains very low (<0.045% by total area) percentage porosity, thus providing a corrosion- and erosion-resistant surface for use in plasma processing chambers.

[0060] The disclosed method produces a polycrystalline sintered ceramic body having at least one top surface with a surface area greater than 400 square inches, the surface having a spherometer measurement of greater than 15 microns absolute across the four quadrants of the disc, Ra and Rz of less than or equal to 2 microinches each across the surface area, and a porosity of less than 0.045% across the surface area, and the sintered ceramic disc has a thickness of at least 20 mm.

[0061] In one embodiment in which the sintered ceramic body comprises YAG, the disclosed method produces a polycrystalline sintered ceramic body comprising at least 99.99% YAG and having at least one top surface with a surface area greater than 400 square inches, the surface having a spherometer measurement of greater than 15 microns absolute across the four quadrants of the disc, Ra and Rz of less than or equal to 2 microinches each across the surface area, and a porosity of less than 0.045% across the surface area, and the sintered ceramic disc has a thickness of at least 20 mm.

[0062] One advantage of the disclosed method is that it prevents grain pullout, which displaces grains on the surface, creating pits and therefore significant deviations in surface smoothness that can be easily attacked by plasma etching gases. [Example]

[0063] A 24-inch disk having a 99.99% YAG surface with an average YAG density of at least 99.5% of the maximum theoretical density of YAG was obtained. When lapped and polished as described herein, this 24-inch disk produced the average final Ra, Rz, and RSm values ​​shown in the table below. [Table 1]

[0064] For comparison, an exemplary 22-inch diameter disk was prepared that was 99.99% YAG, but had an average density of only about 97% of the maximum theoretical density of YAG. This exemplary disk was lapped and polished as described above, resulting in the average final Ra, Rz, and RSm values ​​shown in the table below. [Table 2]

[0065] As can be seen by comparing the values ​​in the two tables above, the comparative 22-inch diameter exemplary disk had a significantly rougher surface. Since the lapping and polishing processes were the same for both disks, this is believed to be due to differences in the average density of the YAG surface polished on the disks. In particular, the disk with the lower density surface resulted in greater surface roughness compared to the disk with the higher density.

[0066] Several embodiments have been described as disclosed herein. However, it will be understood that various modifications can be made without departing from the spirit and scope of the embodiments disclosed herein. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. 1. A method for polishing a surface of a polycrystalline sintered ceramic body, comprising: a. providing a sintered ceramic body comprising a polycrystalline material and having a density between 99.5% and 99.999% of the theoretical density of the polycrystalline material, the sintered ceramic body having at least one surface; grinding said at least one surface until said surface has (i) an average flatness of 25 microns or less measured across four quadrants of said at least one surface at angles of 0°, 90°, 180°, and 270° as measured with a spherometer, (ii) an Ra of less than 0.3556 μm (14 microinches), and (iii) an Rz of less than 4.064 μm (160 microinches), whereby Ra means the average roughness of a surface as the integer average of all absolute roughness profile deviations from a centerline within a measurement length, and Rz means the difference between the highest peak and deepest valley of said surface as an absolute peak-to-valley average of five consecutive sampling lengths within said measurement length; c) lapping the at least one surface with a slurry of lapping plate and lapping media after the grinding step; d. After lapping, successively polishing said at least one surface in a series of polishing steps until said at least one surface exhibits an Ra value of ≦0.0508 μm (2 microinches), an Rz of ≦0.0508 μm (2 microinches), and an absolute flatness value of greater than 15 microns as measured by a spherometer, said polishing being performed in an apparatus comprising a plurality of elliptical oscillating orbital sanders, each of said plurality of orbital sanders comprising an abrasive pad that contacts said at least one surface during polishing; The series of polishing steps includes: i. a first polishing step in which the polishing pad is used with a slurry of 4 micron to 10 micron grit particles; ii. a second polishing step in which the polishing pad is used with a slurry of 1 micron to 3 micron grit particles.

2. 2. The method of claim 1, wherein the lapping steps include: (i) a first lapping step in which the lapping media is alumina having an average particle size of 30 microns to 50 microns; (ii) a second lapping step in which the lapping media is alumina having an average particle size of 10 microns to 20 microns; and (iii) a third lapping step in which the lapping media is alumina having an average particle size of 5 microns to 10 microns.

3. 3. The method of claim 2, wherein (i) the lapping medium in the first lapping step has a particle size of 40 microns, (ii) the lapping medium in the second lapping step has a particle size of 12 microns, and (iii) the lapping medium in the third lapping step has a particle size of 6 microns.

4. 2. The method of claim 1, wherein the polycrystalline material is selected from the group consisting of YAG, yttria, alumina, magnesium aluminate spinel, and a combination of yttria and zirconia.

5. 10. The method of claim 1, wherein the grit particles in the first polishing step are 6 microns and the grit particles in the second polishing step are 2 microns.

6. 10. The method of claim 1, wherein the grit particles in the first polishing step are 6 microns and the grit particles in the second polishing step are 1 micron.

7. 10. The method of claim 1, wherein the Ra after the first and second polishing steps is less than 1.5 microinches.

8. 10. The method of claim 1, wherein the at least one surface rotates and the orbital sander remains stationary during the first and second sanding steps.

9. The method of claim 1 , wherein the polycrystalline material is YAG.

10. 10. The method of claim 9, wherein the density of the sintered ceramic body is 99.56% to 99.78% of the theoretical density of YAG.

11. The method of claim 1 , wherein the polycrystalline sintered ceramic body has a diameter of about 100 mm to about 625 mm.

12. 10. The method of claim 1, wherein the sanding pad rotates in an elliptical orbit at a speed of up to 12,000 RPM, resulting in an overwhelming velocity of 0.5 m / s to 5.0 m / s on said at least one surface.

13. The method of claim 1 , wherein the plurality of orbital sanders is selected from three and four.

14. The method of claim 13, wherein the plurality of orbital sanders is three.

15. The method of claim 13, wherein the plurality of orbital sanders is four.

16. 10. The method of claim 1, wherein the sintered ceramic body comprises a polycrystalline material having an average hardness of 13.0 GPa to 16.0 GPa calculated from eight test replicates using an applied load of 0.2 kgf measured according to ASTM standard C1327.

17. A method for producing a polycrystalline sintered ceramic body using the method of claim 1, comprising: The polycrystalline sintered ceramic body comprises at least 99.99% YAG and has a thickness of 0.2580 mm. ２ (400 square inches), said upper surface having a spherometer measurement of greater than 15 microns absolute across the four quadrants of the disk, Ra and Rz of less than or equal to 2 microinches each across said surface area, and a porosity of less than 0.045% across said surface area, wherein the sintered ceramic disk has a thickness of at least 20 mm.

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