High-purity cordierite materials for semiconductor applications

Abstract

To provide a cordierite material that: has a coefficient of thermal expansion (CTE) that is substantially zero across a temperature range of operation; has a Young's Modulus of substantially greater than 130 GPa; is essentially free of pores; provides high thermal conductivity; and can be polished to a low surface roughness, and to provide a method for producing the same.SOLUTION: A cordierite sintered body comprises 90 to 98 vol.% of a cordierite crystal phase as measured using X-ray diffraction, SEM and image processing methods. The cordierite sintered body has at least one surface comprising pores having a diameter of 0.1 to 5 μm as measured using SEM and image processing methods.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to low thermal expansion ceramics comprising substantially phase-pure cordierite sintered bodies. More specifically, the present disclosure relates to low thermal expansion cordierite sintered bodies suitable for use in semiconductor processing equipment, such as chucks having layers comprising the cordierite sintered bodies, stages for exposure apparatus, supports for optical elements in lithography apparatus, and photolithographic patterning reticles for semiconductor manufacturing. [Background technology]

[0002] As miniaturization in semiconductor manufacturing continues, materials with very low thermal expansion are required for sufficient positioning accuracy in the microlithography processes used for this purpose. Thus, wafer positioning requires an accuracy in the region of 0.1 nm, and therefore a thermal expansion coefficient of <0.5 ppm / K (i.e., <0.5 × 10) to avoid incorrect positioning due to small temperature fluctuations. -6 / K), preferably <0.05 ppm / K, preferably <0.005 ppm / K. Materials used in microlithography processes must also have a high Young's modulus to prevent vibration and ensure mechanical stability of the components, and a high thermal conductivity to dissipate heat and temperature fluctuations during processing.

[0003] Components used herein, such as substrate holders (known as wafer stages), reticles, and optical supports, today use either low-expansion glass-ceramics based on LiO2-Al2O3-SiO2 (LAS) glass ceramics (e.g., Zerodur®) or sintered ceramics, often based on cordierite. Glass-ceramics derived from the LAS system, in which a lithium-high quartz solid solution forms the primary crystalline phase, can be fabricated with particularly low thermal expansion coefficients of less than 0.02 ppm / K (in the temperature range of 0-50°C). An additional advantage is that, as a result of their fabrication method, they have no measurable porosity. However, their Young's moduli are typically in the range of only 90-95 GPa, which is too low for many applications. Furthermore, the thermal conductivity of these low-expansion glass-ceramics is low.

[0004] Cordierite-containing ceramics also have thermal expansion coefficients in the range of <0.1 ppm / K over a narrow temperature range of 20-25°C, as described, for example, in U.S. Patent Application Publication No. 2013 / 0225392. However, such ceramics are porous as a result of their manufacturing process and are characterized by a low Young's modulus of 70 GPa. This porosity leads to the formation of defects or holes during polishing, making the surface unsuitable for depositing reflective materials to form reflective reticles with very low surface roughness for use in lithography applications. In addition, they have poor thermal conductivity, which causes thermal fluctuations during semiconductor processing, and are too weak for some applications. Such ceramics also often contain additives, such as dopants and / or sintering aids, and other phases besides the cordierite crystalline phase. These additives and the presence of phases other than cordierite significantly change the coefficient of thermal expansion (CTE) with temperature and also reduce thermal conductivity, reducing exposure accuracy when used as a reflective reticle in lithography applications, and reducing corrosion and erosion resistance when used in semiconductor plasma processing chambers.

[0005] The electronics industry has recognized the beneficial thermal properties of cordierite material when used as a substrate and has compensated for its detrimental porosity. For example, U.S. Patent No. 8,736,810 discloses a reflective reticle that substantially reduces or eliminates pattern distortion resulting from absorption of EUV energy, in which the reticle has a layer of ultra-low expansion glass placed on the cordierite substrate to compensate for the porous surface. However, this adds additional material and process costs to the reflective reticle and its manufacture. Furthermore, the glass layer also reduces the thermal conductivity of the reticle, thereby increasing thermal gradients that can cause pattern distortion.

[0006] Thus, there is a need in the art for cordierite materials that can be used, for example, as wafer supports such as vacuum or electrostatic chucks, support and positioning members for optical elements, and substrates suitable for use as part of reflective reticles in semiconductor manufacturing equipment, that have a coefficient of thermal expansion (CTE) that is substantially zero over the operating temperature range, that have a Young's modulus that is substantially greater than 130 GPa, that are essentially pore-free, that provide high thermal conductivity, and that can be polished to a low surface roughness.

[0007] Summary of the Invention These and other needs are addressed by the various embodiments, aspects, and configurations disclosed herein.

[0008] In one embodiment, cordierite (MgAlSiO 18 ), and having at least one surface, the cordierite sintered body has a density of 2.55 to 2.63 g / cc.

[0009] In another aspect, a method for making a cordierite sintered body is disclosed, the method comprising: a) combining powders including silicon dioxide (SiO), magnesium oxide (MgO), and aluminum oxide (AlO) to form a powder mixture; b) firing the powder mixture by heating to raise the temperature of the powder mixture to a sintering temperature and maintaining the sintering temperature to form a sintered powder mixture; c) placing the sintered powder mixture within a volume defined by a sintering machine toolset to create a vacuum within the volume; and d) applying pressure to the sintered powder mixture while heating to the sintering temperature to sinter to form MgAlSiO. 18 and e) forming a cordierite sintered body containing the above compound; and e) reducing the temperature of the cordierite sintered body.

[0010] In another embodiment, MgAlSiO 18 and a photolithography reticle comprising at least one layer of a cordierite sintered body having at least one surface, the cordierite sintered body having a density of 2.55 to 2.63 g / cc.

[0011] In a further embodiment, Mg2Al4Si5O 18 and a support chuck including at least one layer of cordierite sintered body having at least one surface, the cordierite sintered body having a density of 2.55 to 2.63 g / cc.

[0012] In a still further aspect, MgAlSiO 18 and a support structure comprising at least one layer of cordierite sintered body having at least one surface, the cordierite sintered body having a density of 2.55 to 2.63 g / cc.

[0013] In yet another aspect, a cordierite sintered body is disclosed that is made by a method comprising: a) combining powders including silicon dioxide (SiO), magnesium oxide (MgO), and aluminum oxide (AlO) to form a powder mixture; b) firing the powder mixture by heating to raise the temperature of the powder mixture to a firing temperature and maintaining the firing temperature to produce a fired powder mixture; c) placing the fired powder mixture within a volume defined by a sintering apparatus toolset to create a vacuum within the volume; and d) applying pressure to the fired powder mixture while heating to the sintering temperature to sinter to produce MgAlSiO. 18 and e) forming a cordierite sintered body containing the above compound; and e) reducing the temperature of the cordierite sintered body.

[0014] Embodiment 1. A cordierite sintered body comprising 90 to 98 volume % cordierite crystalline phase as measured using X-ray diffraction, SEM, and image processing methods, wherein the cordierite sintered body has at least one surface comprising pores having diameters of 0.1 to 5 μm as measured using SEM and image processing methods.

[0015] Embodiment 2. The cordierite sintered body of claim 1, wherein the cordierite sintered body comprises cordierite crystalline phase in an amount of 90 vol% or more, preferably 95 vol% or more, preferably 90-97 vol%, preferably 93-98 vol%, preferably 95-98 vol%, preferably 90-95 vol%, preferably 93-97 vol%.

[0016] Embodiment 3. The cordierite sintered body according to embodiment 1 or 2, wherein at least one surface comprises pores having a diameter of 0.1 to 4 um, preferably 0.1 to 3 um, preferably 0.1 to 2 um, preferably 0.1 to 1 um.

[0017] Embodiment 4. The cordierite sintered body of any one of embodiments 1 to 3, having a density, measured according to ASTM B962-17, of 2.55 to 2.63 g / cc, preferably 2.58 to 2.63 g / cc, preferably 2.61 to 2.63 g / cc, preferably 2.62 to 2.63 g / cc.

[0018] Embodiment 5. The cordierite sintered body according to any one of embodiments 1 to 4, having a volume porosity of 0.1 to 4%, preferably 0.1 to 3%, preferably 0.1 to 2%, preferably 0.1 to 1%, preferably 0.1 to 0.5%, preferably 0.5 to 4%, preferably 0.5 to 3%, preferably 1 to 4%, preferably 1 to 3%, preferably 1 to 2%, preferably 1.5 to 3.5%, calculated from density measurements performed in accordance with ASTM B962-17.

[0019] Embodiment 6. The cordierite sintered body according to any one of embodiments 1 to 5, having a Young's modulus, measured according to ASTM E1876-15, of 125 to 180 GPa, preferably 125 to 160 GPa, preferably 125 to 140 GPa, preferably 130 to 180 GPa, preferably 130 to 160 GPa, preferably 130 to 150 GPa.

[0020] Embodiment 7. The cordierite sintered body of any one of embodiments 1 to 6, wherein the cordierite sintered body is substantially free of glassy phase as determined by x-ray diffraction.

[0021] Embodiment 8. The cordierite sintered body of any one of embodiments 1 to 7, wherein the cordierite sintered body is substantially crystalline as determined by x-ray diffraction.

[0022] Embodiment 9. The cordierite sintered body according to any one of embodiments 1 to 8, having an arithmetic mean height (Sa) on the surface of 75 nm or less, preferably 50 nm or less, preferably 25 nm or less, preferably 15 nm or less, preferably 10 nm or less, preferably 2 to 15 nm, preferably 2 to 10 nm, preferably 2 to 8 nm, preferably 2 to 5 nm, measured according to ISO Standard 25178-2-2012.

[0023] Embodiment 10. The cordierite sintered body according to any one of embodiments 1 to 9, having a maximum height (Sz) according to ISO Standard 25178-2-2012 of less than 5.5 μm, preferably less than 4.0 μm, preferably less than 3.0 μm, preferably less than 2.0 μm, preferably less than 1.5 μm, preferably less than 1 μm, preferably 0.3 to 3 μm, preferably 0.3 to 2 μm, preferably 0.3 to 1 μm.

[0024] Embodiment 11. The cordierite sintered body of any one of embodiments 1 to 10, wherein at least one surface of the cordierite sintered body has a porosity in an amount of less than 1%, preferably less than 0.9%, preferably less than 0.8%, preferably less than 0.6%, preferably less than 0.3%, preferably less than 0.1%, preferably about 0.05%, relative to the total area of ​​the at least one surface, as measured using SEM and ImageJ methods.

[0025] Embodiment 12. The cordierite sintered body according to any one of embodiments 1 to 11, wherein the cordierite sintered body does not contain a sintering aid.

[0026] Embodiment 13. The cordierite sintered body according to any one of embodiments 1 to 12, wherein the cordierite sintered body does not contain a dopant.

[0027] Embodiment 14. The cordierite sintered body according to any one of embodiments 1 to 13, having a purity of 99.9 to 99.995%, preferably 99.95 to 99.995%, relative to a 100% pure cordierite sintered body, as measured using an ICPMS method.

[0028] Embodiment 15. The cordierite sintered body of any one of embodiments 1 to 14, wherein the cordierite sintered body comprises a cordierite crystalline phase in an amount of about 95% to about 98% by volume and a sapphirine crystalline phase in an amount of about 2% to about 5% by volume, as measured using X-ray diffraction, SEM, and image processing methods.

[0029] Embodiment 16. A method for producing a cordierite sintered body, comprising the steps of: a) combining powders including silicon dioxide (SiO), magnesium oxide (MgO), and aluminum oxide (AlO) to form a powder mixture; b) calcining the powder mixture by applying heat until a calcination temperature is reached and maintained at the calcination temperature to form a calcined powder mixture; c) placing the fired powder mixture within a volume defined by a tool set of a sintering machine and creating a vacuum within the volume; d) sintering the fired powder mixture by applying pressure while heating to a sintering temperature to form a cordierite sintered body; e) reducing the temperature of the cordierite sintered body.

[0030] Embodiment 17. Further comprising the steps of: f. optionally, annealing the cordierite sintered body by applying heat to raise the temperature of the cordierite sintered body until an annealing temperature is reached; g. reducing the temperature of the annealed cordierite sintered body.

[0031] Embodiment 18. Further comprising the steps of: h. The method of embodiment 16 or 17, comprising machining the cordierite sintered body to produce a cordierite sintered component, such as a photolithography reticle, a support for an optical element, a vacuum chuck, an electrostatic chuck, a support chuck, a reticle chuck for use in a microlithography process, or the like.

[0032] Embodiment 19. The method of any one of embodiments 16 to 18, wherein the pressure is from 5 MPa to 100 MPa, preferably from 5 MPa to 60 MPa, preferably from 5 MPa to less than 50 MPa, preferably from 5 MPa to 40 MPa, preferably from 5 MPa to 20 MPa, preferably from 10 MPa to 60 MPa, preferably from 10 MPa to 50 MPa, preferably from 10 to 40 MPa, preferably from 10 to 30 MPa, preferably from 10 to 20 MPa, preferably from 15 to 45 MPa, preferably from 15 MPa to 30 MPa, preferably from 20 MPa to 40 MPa.

[0033] Embodiment 20. The method of any one of embodiments 16-19, wherein the sintering temperature is 800-1300°C, preferably 800-1250°C, preferably 900-1300°C, preferably 900-1250°C, preferably 900-1200°C, preferably 900-1100°C, preferably 1000-1300°C, preferably 1100-1300°C, preferably 1100-1250°C.

[0034] Embodiment 21. The method of any one of embodiments 16-20, wherein the calcined powder mixture has a purity greater than 99.95% as measured using ICPMS methods.

[0035] Embodiment 22. The calcined powder mixture has a surface area of ​​8 to 20 m as measured using BET surface area analysis as measured in accordance with ASTM C1274. 2 / g, preferably 10 to 20m 2 / g, preferably 12 to 20 m 2 / g, preferably 14 to 20 m 2 / g, preferably 16 to 20 m 2 / g, preferably 8 to 18 m 2 / g, preferably 8 to 16 m 2 / g, preferably 8 to 14 m 2 / g, preferably 10 to 20m 2 / g, preferably 14 to 20 m 2 / g, preferably 16 to 20 m 222. The method according to any one of embodiments 16 to 21, having a specific surface area of ​​1 / g.

[0036] Embodiment 23. A photolithography reticle comprising at least one layer of the cordierite sintered body of any one of embodiments 1-15.

[0037] Embodiment 24. A support structure comprising at least one layer of the cordierite sintered body of any one of embodiments 1-15.

[0038] Embodiment 25. A support chuck comprising at least one layer of the cordierite sintered body of any one of embodiments 1-15.

[0039] Embodiment 26. A cordierite sintered body made by the method of any one of embodiments 16-22, wherein the powder is free of naturally occurring materials including talc, kaolin, gibbsite, dolomite, sepiolite, forsterite, and other clays and clay-based compounds.

[0040] Embodiment 27. The cordierite sintered body of claim 26, wherein each of the powder, powder mixture, and calcined powder mixture is free of naturally occurring materials including talc, kaolin, gibbsite, dolomite, sepiolite, forsterite, and other clays and clay-based compounds.

[0041] Embodiment 28. The cordierite sintered body of embodiment 26 or 27, wherein the cordierite sintered body is free of naturally occurring materials including talc, kaolin, gibbsite, dolomite, sepiolite, forsterite, and other clays and clay-based compounds.

[0042] Embodiment 29. The cordierite sintered body of any one of embodiments 26-28, wherein the powder, powder mixture, and fired powder mixture are each substantially free of glass-forming ingredients including alkali metal elements including lithium (Li), sodium (Na), and potassium (K); alkaline earth metal elements including calcium (Ca), strontium (Sr), and barium (Ba); transition metals including chromium (Cr), nickel (Ni), iron (Fe), copper (Cu), zinc (Zn), lead (Pb), rubidium (Rb); metalloid elements including boron (B), germanium (Ge), arsenic (As), antimony (Sb), and bismuth (Bi).

[0043] Embodiment 30. The cordierite sintered body of any one of embodiments 26-29, wherein the cordierite sintered body is free of glass-forming ingredients including alkali metal elements including lithium (Li), sodium (Na), and potassium (K); alkaline earth metal elements including calcium (Ca), strontium (Sr), and barium (Ba); transition metal elements including chromium (Cr), nickel (Ni), iron (Fe), copper (Cu), zinc (Zn), lead (Pb), rubidium (Rb); metalloid elements including boron (B), germanium (Ge), arsenic (As), antimony (Sb), and bismuth (Bi). [Brief explanation of the drawings]

[0044] [Figure 1] 1 shows a reflective lithography apparatus;

[0045] [Figure 2] 1 illustrates a schematic representation of an exemplary reflective reticle embodiment for use in an EUV lithography apparatus.

[0046] [Figure 3] 1 illustrates an exemplary embodiment of a support structure disclosed herein.

[0047] [Figure 4] 1 shows the results of X-ray diffraction of the cordierite sintered body of Comparative Example 1.

[0048] [Figure 5] FIG. 4 shows a 5000x micrograph of the cordierite sintered body of Comparative Example 1.

[0049] [Figure 6] 1 shows X-ray diffraction results for a calcined powder mixture according to embodiments disclosed herein.

[0050] [Figure 7] 1 shows an X-ray diffraction result of a cordierite sintered body according to an embodiment disclosed herein.

[0051] [Figure 8] 1 shows an SEM micrograph at 1000x of a cordierite sintered body according to embodiments disclosed herein.

[0052] [Figure 9] 9 shows an SEM micrograph of the same surface area of ​​FIG. 8 taken using topography imaging mode at 1000x magnification of a cordierite sintered body according to embodiments disclosed herein.

[0053] [Figure 10] FIG. 1 is a cross-sectional view of an SPS sintering apparatus with a toolset positioned in a simplified arrangement within a vacuum chamber (not shown) used to sinter ceramic materials.

[0054] [Figure 11A] 11 shows the embodiment of FIG. 10 showing one foil layer.

[0055] [Figure 11B] 11 shows an alternative embodiment to FIG. 10 showing two foil layers.

[0056] [Figure 11C] 11 shows another alternative embodiment of FIG. 10 showing three foil layers.

[0057] [Figure 12A] FIG. 11 is a plan view of the SPS sintering apparatus of FIG. [Figure 12B] FIG. 11 is a plan view of the SPS sintering apparatus of FIG.

[0058] [Figure 13] 1 is a graph showing the radial dispersion of the average coefficient of thermal expansion (CTE) of graphite materials A and B at 1200° C.

[0059] [Figure 14A] The standard deviation of the thermal expansion coefficients of graphite materials A and B is shown in ppm. [Figure 14B] The radial deviation (absolute deviation) of the thermal expansion coefficient measured over the operating temperature range of 200 to 1200°C for graphite materials A and B is shown.

[0060] [Figure 15] 1 is a graph showing the thermal expansion coefficients of graphite materials A and B in the range of 400 to 1400°C. DETAILED DESCRIPTION OF THE INVENTION

[0061] Reference will now be made in detail to certain embodiments. Examples of certain embodiments are illustrated in the accompanying figures. While the present disclosure will be described in conjunction with these specific implementations, it will be understood that the present disclosure is not limited to such specific embodiments. On the contrary, the present disclosure is intended to cover alternatives, modifications, and equivalents that may be included within the spirit and scope of the present invention as defined by the appended claims. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. The present disclosure may be practiced without some or all of these specific details.

[0062] Embodiments are disclosed, including the best mode known to the inventors for carrying out the invention. Modifications of those embodiments will become apparent to those skilled in the art upon reading the following detailed description. The inventors contemplate the use of such modifications as appropriate by those skilled in the art, and the inventors contemplate the invention being practiced otherwise than as specifically described. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Furthermore, any combination of elements in all possible variations thereof disclosed above is encompassed by the invention unless the context indicates otherwise or is clearly contradicted. Furthermore, all features disclosed with respect to the method of making a cordierite sintered body also apply to the product, cordierite sintered body, and vice versa.

[0063] All references, including cited publications, patent applications, and patents, are herein incorporated by reference to the same extent as if each reference was individually and specifically indicated to be incorporated by reference and was set forth in its entirety. definition

[0064] The use of the terms "a," "an," and "the" and similar referents in the context of describing the present invention (particularly in the context of the claims below) should be construed to cover both the singular and the plural unless otherwise indicated herein or clearly contradicted by context. The terms "comprising," "having," "including," and "containing" should be construed as open-ended terms (i.e., meaning "including, but not limited to") unless otherwise indicated. The listing of ranges of values ​​is intended to serve as a shorthand method for referring individually to each separate value falling within the range, unless otherwise indicated, and each separate value is incorporated into the specification as if it were individually listed. All methods described can be performed in any suitable order unless otherwise indicated or clearly contradicted by context. The use of any and all examples or exemplary language (e.g., "such as") is intended merely to better clarify the invention and does not limit the scope of the invention unless specifically claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. Use of the term "comprising" in the specification and claims includes the narrower terms "consisting essentially of" and "consisting of."

[0065] As used herein, the term "EUV photolithography" refers to extreme ultraviolet lithography used in the manufacture of articles such as, for example, integrated circuits.

[0066] As used herein, the term "EUV photomask substrate" or "substrate" refers to a multilayer film stack. The films are typically deposited on a specialized 6" x 6" substrate with ULE / LTEM features. An EUV photomask is a patterned reflective mask used in EUV photolithography.

[0067] The terms "photomask" and "reticle" are used interchangeably.

[0068] 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.

[0069] As used herein, the term "cordierite sintered body" is synonymous with "sinter," "body," or "sintered body" and refers to a solid ceramic article comprising cordierite formed from a powder mixture disclosed herein that has been subjected to a pressing and heat treatment process to form a cordierite body from the powder mixture. In embodiments, the term "cordierite sintered body" refers to a one-piece body. "One-piece" means a single piece or member that is complete in itself, without additional pieces, i.e., the member is one monolithic piece formed as a unit with another member.

[0070] As used herein, the term "purity" refers to the absence of various contaminants and / or impurities, expressed as a percentage of the total mass, in a) the starting materials from which the powder mixture may be formed, b) the powder mixture after processing and firing, and c) the cordierite sintered body disclosed herein. Higher purity, approaching 100%, refers to a material essentially free of contaminants or impurities, containing only the intended material composition of Mg, Al, Si, and O, and optional dopants and / or sintering aids.

[0071] As used herein, the term "impurities" refers to compounds / contaminants, including impurities other than the starting materials themselves, including Mg, Al, Si, and O, and optional dopants and / or sintering aids, present in a) the starting materials that may form the powder mixture, b) the powder mixture after processing and / or the fired powder mixture, and c) the cordierite sintered body. Impurities may be present in the starting powder materials, powder mixture, and / or fired powder mixture after processing / combining or during sintering, and may be present in the cordierite sintered body, and are reported in ppm, with lower ppm levels indicating lower impurity content.

[0072] The conversion of purity in percent to impurities in ppm is known to those skilled in the art such that a 1% decrease in purity = 10,000 ppm impurities.

[0073] As used herein, the term "dopant" does not include the magnesium oxide, silicon dioxide, and aluminum oxide of the starting materials to the extent that they may remain in the cordierite sintered body. Impurities differ from dopants in that dopants, as defined herein, are compounds that are intentionally added to the starting powder or powder mixture to obtain particular electrical, mechanical, optical, or other properties, such as, for example, grain size modification and phase purity in the cordierite sintered body.

[0074] As used herein, the term "sintering aid" refers to an additive such as zirconia or calcia that improves densification during the sintering process, thereby reducing porosity.

[0075] As used herein, the term "tool set" may include a die and two punches, and optionally additional spacer elements.

[0076] As used herein, the term "phase" is understood to mean a crystalline region having a particular crystal structure.

[0077] As used herein, the term "stiffness" is synonymous with and consistent with the definition of Young's modulus as known to those skilled in the art.

[0078] The terms "calcining" or "calcining," when used in connection with a heat treatment process, are understood to mean a heat treatment step performed on a powder or powder mixture in air to, for example, remove moisture and / or surface impurities, increase crystallinity, and in some embodiments, modify the surface region of the powder and / or powder mixture.

[0079] As applied to ceramic heat treatment, the term "annealing" is understood herein to mean a heat treatment in which the disclosed cordierite sintered bodies are brought to a constant temperature in air and allowed to cool slowly to relieve stress and / or normalize stoichiometry.

[0080] The term "Sa" as known in the art relates to the arithmetic mean height of a surface and represents the absolute value of the arithmetic mean over the entire surface, commonly referred to as "surface roughness." The definition according to ISO 25178-2-2012 section 4.1.7 is the arithmetic mean of the absolute values ​​of the ordinate values ​​within a defined area (A) calculated according to the following formula:

number

[0081] The term "Sz", as known in the art, refers to the maximum height (of a scale-limited surface), or "peak to valley", and is defined as the sum of the maximum peak height value and the maximum valley depth value within a defined area (A) as defined in ISO 25178-2-2012 section 4.1.6.

[0082] As used herein, the terms "substantially," "approximately," and "about" are used in connection with numbers and therefore allow for a variance of plus or minus 10%.

[0083] In the following description, a given range includes a lower and upper threshold. Thus, a definition of a parameter A in the sense of "ranging from X to Y" or "ranging from X to Y" means that A is any value of X, Y, and any value from X to Y. A definition of a parameter A in the sense of "up to Y" or "at least X" therefore means that A is any value less than Y and Y, or A is any value greater than X and X, respectively.

[0084] Cordierite sintered body

[0085] The following detailed description assumes that the present disclosure is implemented in equipment such as a lithography apparatus, more specifically an EUV lithography apparatus (as shown in FIG. 1 ), to enable patterning of nanometer-scale features for etching and / or deposition processes required as part of semiconductor wafer fabrication. However, the present disclosure is not limited thereto. Workpieces may be of various shapes, sizes, and materials and combinations of materials. In addition to processing semiconductor wafers, other workpieces that can benefit from the present disclosure include any lithography process where very fine-scale resolution is desirable, wafer support structures such as mirrors, optical element supports, stages, or chucks, high-precision and cryogenic lens holders, ultra-low expansion substrates for positional control of various lenses and mirrors, micromechanical devices where precise positional control is required over a temperature range from ambient to, for example, ±100° C., and various other articles.

[0086] Lithography is widely recognized as a key process in the manufacture of integrated circuits (ICs) and other devices and / or structures. A lithography apparatus is a machine used during lithography (a reflective lithography apparatus is shown in FIG. 1 ) that applies a desired pattern onto a substrate semiconductor wafer, such as onto a target portion of the substrate wafer. During IC fabrication using a lithography apparatus, a patterning device (also called a mask, reticle, photomask, or reflective reticle) 100 generates the circuit pattern that will be formed on an individual layer in the IC. Examples of patterning devices 100 include reticles, masks, programmable mirror arrays, and programmable LCD panels. This pattern is transferred onto an area C (e.g., comprising part of one or several dies) on a substrate (e.g., a silicon wafer) 80. Transfer of the pattern is typically accomplished by imaging onto a layer of photosensitive material (e.g., resist) provided on the substrate. The term "patterning device" 100 should be interpreted broadly to refer to any device that can be used to impart a beam of radiation B having a pattern in its cross-section, such as to form a pattern in region C of wafer 80. The pattern imparted to beam of radiation B corresponds to a particular functional layer in a device being formed in region C, such as an integrated circuit. Generally, a single substrate contains a network of adjacent regions that are successively patterned. Fabrication of different layers of an IC often requires imaging different patterns on the different layers with different reticles. Therefore, it is necessary to change reticles during the lithography process.

[0087] 1 shows a reflective lithographic apparatus 98 including an illuminator (illumination system, "IL") configured to condition an illumination beam B (e.g., EUV illumination), a first support platform (e.g., reticle or mask support) 82 configured to support a patterning device (e.g., mask, reticle, photomask, photolithographic reticle, reflective reticle) 100 and connected to a first positioner 214 configured to position the patterning device 100 with high precision, and a second support platform (e.g., wafer table, wafer chuck, wafer support) 84 configured to hold a substrate (e.g., a photoresist-coated wafer) 80 and connected to a second positioner 216 configured to position the wafer 80 with high precision. The lithographic apparatus 98 also includes a projection system (Proj) configured to project a pattern imparted to the illumination beam B by the patterning device 100 onto the wafer 80. In the lithographic apparatus 98, the patterning device 100 and the projection system are reflective. As further shown in FIG. 1 , an illuminator (IL) receives an illumination beam B from an illumination source. The illumination beam B is incident on a patterning device (e.g., a mask, photomask, photolithographic reticle, reflective reticle) 100 held on a first support platform (e.g., a reticle support, mask support) 82 and is patterned by the patterning device 100. In the lithographic apparatus 98, the illumination beam B is reflected from the patterning device (e.g., a mask, reticle, photomask, photolithographic reticle, reflective reticle) 100. After reflecting from the patterning device (e.g., mask) 100, the illumination beam B passes through a projection system (Proj), which focuses the illumination beam B onto an area C of the wafer 80. With the aid of a second positioner 216 and a position sensor PS2 (e.g., an interferometric device, a linear encoder or a capacitive sensor), the second support platform 84 can be moved with high precision, for example to position a different region C in the path of the illumination beam B.Similarly, a first positioner 214 and another position sensor PS1 can be used to position a patterning device (eg, a mask, a reflective reticle, a photolithographic reticle) 100 with respect to the path of the illumination beam B with high precision.

[0088] Existing EUV lithography equipment typically incorporates reflective reticles having substrates formed from ultra-low expansion (ULE) glass, a glass-ceramic material that has a substantially zero coefficient of thermal expansion over a wide range of operating temperatures. The selection of ULE glass as a substrate is typically based on the thermal expansion coefficient of ULE glass and the ability to polish the surface of the ULE glass to the fine surface requirements necessary for EUV lithography applications (i.e., a surface that is substantially free of defects and exhibits very low roughness that is substantially flat).

[0089] Generally, existing reflective reticles for EUV lithography equipment typically exhibit a reflectivity of approximately 70%. Therefore, depending on the pattern to be printed, existing reflective reticles absorb approximately 30% to 100% of the energy of the incident EUV radiation beam. Such absorption can cause significant heating of the reticle, which, despite the relatively low thermal expansion coefficient of the ULE glass substrate, can distort or deform the reticle surface and cause errors in the projected image.

[0090] To form semiconductor devices with very fine feature sizes, such as node dimensions of 9 nm down to, for example, 5 nm, precision is required during exposure onto wafer 80. Factors such as thermal expansion and deformation of patterning device 90 due to heat generated from absorbing radiation, and vibration of first and second support platforms 82 and 84 during use, are problematic and reduce exposure precision when patterning semiconductor devices onto a wafer.

[0091] To address these factors, patterning device 100, first support platform 82, and second support platform 84 preferably comprise a cordierite sintered body as disclosed herein, which has high thermal conductivity, a low coefficient of thermal expansion (1 ppm / °C or less) over the temperature range of 0-50°C, and a high Young's modulus. In some embodiments, the cordierite sintered body has a unitary body. In other embodiments, the cordierite sintered body comprises two or more cordierite sintered bodies that are joined using the methods disclosed herein to form a cordierite composite.

[0092] Disclosed herein is a cordierite sintered body having 90-98 volume % cordierite crystalline phase as measured using X-ray diffraction, SEM, and image processing methods, the cordierite sintered body having at least one surface containing pores having diameters of 0.1-5 μm as measured using SEM and image processing methods. The cordierite sintered body is suitable for use as a material layer for reflective reticles, photolithography reticles, support members or structures or platforms, stages, wafer chucks, positioning elements, and electrostatic chucks for use in EUV lithography equipment, or as a substrate.

[0093] A cordierite sintered body was prepared from a powder mixture containing about 22.2 mol% MgO, about 22.2 mol% Al2O3, and about 55.6 mol% SiO2, as disclosed herein, which was sintered as disclosed herein to form a body of the composition Mg2Al4SiO5 18The primary crystalline phase is formed, including the cordierite crystalline phase. In other words, the cordierite crystalline phase is the primary crystalline phase of the material. According to an embodiment, the cordierite crystalline phase fraction of the primary crystalline phase is 90% by volume or greater, preferably 93% by volume or greater, preferably 95% by volume or greater, preferably 98% by volume or greater, preferably 90-98% by volume, preferably 90-97% by volume, preferably 93-98% by volume, preferably 95-98% by volume, preferably 90-95% by volume, preferably 93-97% by volume, and most preferably 98% by volume. The identity and fraction of the crystalline phases are determined by X-ray diffraction measurements in the 2θ = 8°-85° range using a PANanlytical Aeris model XRD, which allows for crystalline phase differentiation to within ±5% by volume, combined with SEM imaging and ImageJ image processing. The combination of XRD, SEM, and image processing software allows for phase purity to be determined to within ±0.1% by volume. All SEM images were obtained using a Nano Science Instruments Phenom XL scanning electron microscope (SEM) equipped with a backscattered electron detector (BSD) that also has energy dispersive spectroscopy (EDS) and topography modes. Combining SEM images with ImageJ image processing software as disclosed herein allows for phase identification and feature measurement down to approximately ±0.1 volume percent of the cordierite sintered bodies disclosed herein. ImageJ, developed at the National Institutes of Health (NIH), is a Java-based, public domain image processing and analysis program for image processing of scientific multidimensional images. SEM images were taken at 1000x magnification using BSD and topography modes to identify crystalline phases and any porosity present.

[0094] To determine phase purity with greater accuracy, e.g., up to about 98%, SEM images were taken using backscatter detection (BSD) techniques known to those skilled in the art. Using BSD, the cordierite phase appears light gray, aluminum oxide and / or alumina-rich phases appear black or dark gray, and porosity, if present, also appears black. Images were taken at 1000x magnification using BSD techniques known to those skilled in the art to identify crystalline phases and any porosity present (for Sample 015), as shown in Figure 8 . To distinguish between black areas containing crystalline phases (other than cordierite) and black areas containing porosity, the BSD images were processed with black and white thresholds using ImageJ processing software to highlight dark or black areas that may contain either porosity or crystalline phases (other than cordierite). The total area of ​​the surface containing either porosity or crystalline phases (confirmed by XRD to contain sapphirine) was calculated.

[0095] Using the topography mode of the BSD detector, topographic images (as shown in FIG. 9 ) were obtained across the entire surface of the cordierite sintered body. To identify regions or areas containing porosity, the topographic images were processed with black and white thresholds using ImageJ processing software to highlight black regions within the image that may contain porosity or surface defects. The total area of ​​the surface containing porosity was calculated from the topographic imaging and subtracted from the total area of ​​the surface containing either porosity or crystalline phase to obtain both the percentage of the surface containing porosity and the percentage of the surface containing crystalline phase (other than cordierite). Using the disclosed topographical method, at least one surface of the cordierite sintered body contains porosity in an amount of less than about 1%, preferably less than about 0.9%, preferably less than about 0.8%, preferably less than about 0.6%, preferably less than about 0.3%, preferably less than about 0.1%, and preferably less than about 0.05% of the total area of ​​the at least one surface. As a result, using XRD, SEM, and ImageJ methods, the cordierite sintered body has a density of about 99% and contains about 2% by volume of sapphirine phase (and thereby about 98% by volume of cordierite crystalline phase).

[0096] The highly phase-purified cordierite sintered body disclosed herein exhibits minimal change in CTE (e.g., 0.1 × 10) over the temperature range of 0 to 500°C. -6 / °C or less). By appropriate selection of starting powders and careful control of the sintering process, cordierite sintered bodies containing a majority amount (up to 98% by volume) of the cordierite crystalline phase can be produced, as disclosed.

[0097] The X-ray diffraction results for the cordierite sintered body are shown in FIG. 7. The X-ray diffraction results confirmed a phase-purified sintered body containing cordierite and sapphirine- and alumina-rich phases. All peaks (except for the one designated "S" for sapphirine) corresponded to the cordierite crystalline phase. No peaks corresponding to the silica, alumina, or magnesia starting materials were detected. Using peak intensity ratio comparisons known to those skilled in the art, the cordierite sintered body shown in FIG. 7 contained cordierite crystalline phase in an amount of approximately 95% to 98% by volume of the sintered body and sapphirine crystalline phase in an amount of approximately 2% to 5% by volume.

[0098] Pore ​​size in the cordierite sintered body was evaluated using ImageJ analysis methods. The topographic image of Figure 9 was imported into ImageJ software and thresholded as previously disclosed. Pore size was measured within ImageJ software. As shown in Figure 9, a cordierite sintered body according to embodiments disclosed herein has at least one surface containing pores with a maximum diameter of about 5 μm or less, preferably 4 μm or less, preferably 3 μm or less, preferably 2 μm or less, and preferably 1 μm or less, as measured using ImageJ software. Feature dimensions can be measured to an accuracy of about ±0.1 μm using SEM images in combination with ImageJ software; therefore, the cordierite sintered body may contain pores with diameters of 0.1-5 μm, preferably 0.1-4 μm, preferably 0.1-3 μm, preferably 0.1-2 μm, and preferably 0.1-1 μm.

[0099] The surface of a cordierite sintered body having a porosity and pore size in the disclosed ranges provides a sintered body that can be polished to a very low surface roughness, Sa (e.g., about 25 nm or less), and peak-to-valley measurement, Sz (e.g., less than about 1 μm).

[0100] To achieve the precision required for exposure to form semiconductor devices with very fine feature sizes, such as node sizes of 10 nm and below, it is necessary to minimize distortions and changes in the dimensions of patterned features on a reflective reticle and changes in the position of lithography components due to temperature changes. These effects reduce the accuracy of exposure when patterning semiconductor devices onto a wafer. To maintain the overall exposure precision of a lithography apparatus, more specifically the dimensions of patterns on a reflective reticle, as well as the positioning of various components of the lithography apparatus, it is preferable to minimize the coefficient of linear expansion (CTE) of cordierite sintered bodies used as positioning members for, for example, reflective reticles, reticle chucks, and / or optical components according to embodiments. Specifically, the absolute value of the CTE should be 1 ppm / °C or less (i.e., ≦1×10) at temperatures between 0°C and 50°C, as measured according to ASTM E228. -6 / °C), and preferably the coefficient of linear expansion is about 0±0.020 ppm / °C at temperatures between 0 and 50°C. Those skilled in the art will appreciate that the units of the coefficient of linear expansion may alternatively be, for example, 1×10 according to ASTM E228. -6 It will be appreciated that the coefficient of linear expansion (CTE) may be written as cm / cm / °C. Measurements of the coefficient of linear expansion (CTE) were performed in accordance with ASTM E228 using a Linseis model number L75VD1600C. Accordingly, the cordierite sintered bodies disclosed herein have low coefficients of thermal expansion, high densities and correspondingly low porosities, and high Young's moduli, making them particularly suitable for use as positioning members for EUV reflective reticles, electrostatic chucks and / or reticle chuck components, and components of lithographic apparatus.

[0101] Particularly for use as a reflective reticle in a lithography apparatus, a cordierite body with very low porosity, particularly one with low porosity across at least one surface, is desirable to maximize the accuracy of the device pattern during exposure. Lower porosity corresponds to higher density. The higher the density of a cordierite body, the lower its porosity. The theoretical density value of cordierite has been reported as 2.66 g / cc (DRLide, CRC Handbook of Chemistry and Physics, CRC Press (2012)). Therefore, all relative density values ​​(or theoretical density %) are calculated using 2.66 g / cc as the theoretical density of cordierite. Cordierite bodies prepared according to the methods disclosed herein, and cordierite sintered components made from the bodies, have high density in preferred embodiments. Density measurements were performed using Archimedes' buoyancy method according to ASTM B962-17. Density measurements were performed using a liquid of known density, such as water, and by weighing the sample in air according to the following formula:

number

[0102] Where A = weight of sample in air, B = weight of sample in liquid, D a = density of air (0.0012 g / cc), D1 = density of the liquid. This calculation can be used to determine density with a high degree of accuracy, as disclosed herein. The density values ​​reported herein are the average of five measurements, and therefore the reported densities are to be interpreted as average densities.

[0103] Cordierite sintered bodies prepared according to the methods disclosed herein have densities (reported as percentages of theoretical density, or relative densities) of 96% or more, preferably 97% or more, preferably 98% or more, preferably 98.5% or more, and more preferably about 99% or more of the theoretical density for cordierite as reported herein. Thus, in other words, cordierite sintered bodies prepared according to the present disclosure have densities of 2.55 to 2.63 g / cc (96% to 99% of theoretical). In some embodiments, cordierite sintered bodies have densities of 2.58 to 2.63 g / cc (97% to 99% of theoretical), preferably 2.61 to 2.63 g / cc (98% to 99% of theoretical), and preferably 2.62 to 2.63 g / cc (98.5% to 99% of theoretical), as measured according to ASTM B962-17. As a percentage of theoretical density, the cordierite sintered body has 96% or more of the theoretical value, preferably 97% or more, preferably 98% or more, preferably 98.5% or more, more preferably 99% or more, preferably 96-99% of the theoretical value reported herein.

[0104] The relative density (RD) of a given material is defined as the ratio of the measured density of a sample to the reported theoretical density of the same material, as shown in the following equation: Volume porosity (Vp) is calculated from the density measurements as follows:

number

[0105] where ρ sample is the (Archimedean) density measured according to ASTM B962-17, ρ theoretical is the reported theoretical density disclosed herein, and RD is the relative (fractional) density. Using this calculation, volume porosity levels (or bulk porosity) of 0.1-4%, preferably 0.1-3%, preferably 0.1-2%, preferably 0.1-1%, and preferably 0.1-0.5% have been calculated from density measurements made according to ASTM B962-17 for the cordierite sintered bodies disclosed herein.

[0106] The cordierite sintered bodies disclosed herein have porosity on the surface (evident upon polishing) and throughout the body. Thus, in embodiments, the cordierite sintered body may comprise a monolithic body made according to the processes disclosed herein, which has porosity distributed throughout the body and measured as volume, or bulk porosity (calculated from density measurements disclosed herein). Thus, porosity measured on the surface represents porosity within the volume or bulk of the cordierite sintered body. Volume porosity is understood to be representative of porosity on the surface as measured, for example, using scanning electron microscopy. As used herein, volume porosity and bulk porosity are synonymous.

[0107] During use, a lithography system requires movement of the support platform holding the photomask (or reflective reticle) 100 and / or the substrate (i.e., semiconductor substrate) 80. This movement generates vibrations within the system during exposure and patterning, which in turn change the position of the support structure, wafer, and / or reflective reticle. This results in pattern distortion and reduced exposure accuracy. A cordierite sintered body with high stiffness, as measured by Young's modulus, is desirable to prevent and minimize vibrations in the lithography system during use. Measurements were performed according to ASTM E1876-15 using a GrindoSonic MK7 Impulse Excitation Technique (IET), which can measure over a frequency range of 10 to 100 kHz with a standard accuracy of better than 0.005%. Young's modulus is defined as the ratio of tensile or compressive stress to the corresponding strain below the proportional limit of the material. A cordierite sintered body having a Young's modulus of 125-180 GPa, preferably 125-160 GPa, preferably 125-140 GPa, preferably 130-180 GPa, preferably 130-160 GPa, and preferably about 130-150 GPa, as measured according to ASTM E1876-15, can provide sufficient rigidity and a high Young's modulus to maintain exposure accuracy during use in a lithography apparatus. If the cordierite sintered body has a rigidity or Young's modulus below the disclosed range, vibrations (of various components such as the wafer or reticle chuck, stage, and reflective reticle) will occur after movement has stopped, and vibrations will be present during exposure, reducing exposure accuracy. The presence of volume porosity significantly affects Young's modulus, with higher porosity decreasing Young's modulus. Cordierite sintered bodies made by the processes disclosed herein exhibit high Young's modulus values ​​due to low levels of volume porosity, providing mechanical stability and resistance to vibration during use in lithography equipment as disclosed herein, enabling the patterning of fine-scale, high-resolution circuits.

[0108] During use, such as in EUV applications, reflective reticles absorb approximately 30 to approximately 100% of the incident radiation, which can result in significant heating and thermal gradients across the reticle thickness. If the reticle's thermal conductivity is lower than the disclosed range, the heat resulting from EUV radiation is not uniformly distributed across the reticle thickness, resulting in localized heating and high thermal gradients. This localized heating causes thermally induced deformation of the substrate and the patterned reticle surface of the reflective layer, which in turn causes errors in the image projected onto the substrate. Therefore, thermal distortion of both the patterned image and the patterned surface is a limiting factor in imaging performance in existing EUV lithography systems. Therefore, the effects of localized reticle heating due to radiation absorption can be reduced by increasing the thermal conductivity of the substrate in reflective reticles. By increasing the thermal conductivity of the substrate, thereby decreasing its thermal resistance (at a given thickness), heating due to absorbed radiation can be more uniformly distributed throughout the thickness of the substrate and more effectively conducted from the substrate to surrounding support devices, including, but not limited to, a reticle chuck and / or a mask table. Cordierite is known to have high thermal conductivity. The cordierite sintered bodies disclosed herein can be very dense, substantially phase pure, and highly crystalline, resulting in sintered bodies with high thermal conductivity. Thus, in some embodiments, the cordierite sintered bodies disclosed herein can have a thermal conductivity of 3.5 W / mK or greater, preferably 3.5 to 5 W / mK, preferably 3.5 to 4 W / mK, and preferably 4 to 5 W / mK. Thermal conductivity can be calculated from thermal diffusivity measurements performed in accordance with ASTM E1461-13. Cordierite sintered bodies having thermal conductivities within the disclosed ranges provide reticle substrates that can substantially reduce or eliminate any induced distortion of the patterning surface and therefore any induced errors in the patterned image.

[0109] The cordierite sintered body disclosed has a melting point of 1×10 at temperatures of 0 to 50°C. -6 / °C or less, and has a coefficient of thermal expansion (CTE) of 2 to 3 ppm / °C at temperatures between 50 and 500°C.

[0110] The above-described phase purity, density (and corresponding lower porosity), porosity (by surface area), pore size, elastic modulus, and thermal expansion coefficient of embodiments of cordierite sintered bodies according to the present disclosure are higher than those achieved for cordierite or low CTE glasses in the prior art. For example, the following information listed in Table 1 is from Kyocera's website, and Table 2 lists the properties for Ferrotec: [Table 1] [Table 2]

[0111] Thus, the disclosed cordierite sintered bodies provide improved materials for use in semiconductor applications, such as reticles for transferring patterns to wafers, wafer chucks, reticle support structures, and optical device positioning structures. The high-density cordierite sintered bodies disclosed herein yield materials that can be polished to extremely smooth, flat surfaces that provide a fine surface finish for subsequent material deposition. These depositions can be either a ULE (ultra-low expansion) glass surface layer that provides a very smooth surface (very low surface roughness that is defect-free and virtually flat), and / or a reflective metal layer such as aluminum, gold, platinum, palladium, and / or other metals, or both, in any particular order, depending on the application and the performance at operating frequencies required by the layers for EUV lithography reticle applications. In certain embodiments, the low surface roughness (i.e., high smoothness) of the high-density cordierite sintered bodies disclosed herein can enable the reflective reticle 100 shown in FIG. 2A , which, in certain embodiments, may not include a ULE glass surface (when polished to a nanometer-scale surface finish). In some embodiments, the surface roughness (e.g., about 75 nm or less) of the high-density cordierite sintered bodies disclosed herein can provide structures with very thin layers of ULE glass surface layer (shown as feature 206 in FIG. 2B ), e.g., less than about 0.2 mm, preferably less than about 0.1 mm, preferably less than about 0.05 mm, and preferably less than about 0.025 mm thick. Essential requirements for EUV lithography applications require a cordierite sintered body surface that is substantially defect-free and substantially flat, exhibiting very low surface roughness (Sa) and very low maximum peak height (Sz, peak-to-valley). While illustrated and described above with reference to certain specific embodiments, reflective reticle 100 is not limited to the details shown. Rather, various modifications of reflective reticle 100 (e.g., additional glass and / or reflective layers, etc.) may be made within the scope of the following claims and their equivalents without departing from the spirit of the present disclosure.

[0112] Surface roughness measurements were performed under Class 1 cleanroom environmental conditions using a Keyence 3D laser scanning confocal digital microscope, model VK-X250X. The microscope was placed on a TMC tabletop CSP benchtop passive vibration isolation table with a natural frequency of 2.8 Hz. This non-contact system uses a laser beam and optical sensor to analyze the surface via the intensity of the reflected light. The microscope acquires a total of 786,432 data points: 1,024 in the x-direction and 786 in the y-direction. After a given scan is completed, the objective lens moves by a set pitch in the z-direction, and the intensity is compared between scans to determine focus. This microscope complies with ISO 25178 Surface Texture (Areal Roughness Measurement), an international standard related to the analysis of surface roughness.

[0113] Detailed images of the sample were obtained by laser scanning the surface at 20x magnification using a confocal microscope. Roughness was obtained by profiling seven segmented blocks. The measurement sampling length, lambda chi (λ), was adjusted to limit line readings to measurements from five of the seven central blocks according to ISO Specification 4288: Geometrical Product Specifications (GPS) -- Surface Texture: Profile Methods -- Rules and Procedures for the Evaluation of Surface Texture.

[0114] Ra, as known to those skilled in the art, represents the arithmetic mean roughness of a 2D profile according to ISO 4287:1997 Geometric Product Specifications (GPS)--Surface Texture: Profile Method, which is based on a mechanical stylus contacting the surface to create a linear profile.

[0115] Sa represents the height difference across the 3D measurement surface using the laser method, while Ra represents the height difference across the 2D linear profile scan.

[0116] Ra is limited by the geometry of the stylus tip and can therefore lose fine feature detail and distort peaks and valleys, which is problematic when measuring fine sub-micron features and is a limitation in using Ra values ​​to compare with Sa values.

[0117] The measurement section was selected within a representative polished area of ​​the cordierite sintered body. The surface roughness characteristics Sa and Sz are parameters known in the underlying technical field and are described, for example, in ISO standard 25178-2-2012.

[0118] Cordierite sintered bodies having high densities (about 96% to about 99% of theoretical) disclosed herein can be polished to a very smooth surface that is substantially free of defects. Lower density sintered bodies have a higher degree of porosity, resulting in higher surface roughness and more defects. High density (and therefore low porosity) sintered bodies provide a surface that includes pores having diameters of 5 μm or less, and a surface area that has porosity in an amount of less than 0.8%, preferably less than 0.5%, preferably less than 0.3%, preferably less than 0.1%, and preferably about 0.05%, relative to the total area of ​​at least one surface. The disclosed cordierite sintered bodies and / or components made therefrom having a corrosion-resistant polished surface characterized by porosity as disclosed may have an arithmetic mean height (Sa) of 75 nm or less, preferably 50 nm or less, preferably 25 nm or less, preferably 15 nm or less, preferably 10 nm or less, preferably between 2 and 15 nm, preferably between 2 and 10 nm, preferably between 2 and 8 nm, preferably between 2 and 5 nm, and a maximum height / peak-to-valley (Sz) of less than 5.5 μm, preferably less than 4.0 μm, preferably less than 3.0 μm, preferably less than 2.0 μm, preferably less than 1.0 μm, preferably less than 0.75 μm, preferably between 0.3 and 3 μm, preferably between 0.3 and 2 μm, preferably between 0.3 and 1 μm, when the surface is measured according to ISO standard 25178-2-2012. Without being bound by any particular theory, if the surface roughness and peak-to-valley are reduced, in certain embodiments, the thickness of the ULE glass surface layer can be reduced to increase thermal conductivity and reduce thermal resistance, thus improving the pattern accuracy of the reflective reticle and reducing the manufacturing steps in assembly.

[0119] Method for producing cordierite sintered body Cordierite sintered bodies have been prepared using pressure-assisted sintering in combination with DC sintering and related techniques, which use direct current to heat an electrically conductive die configuration or tool set, thereby sintering the material. This heating regime allows for very high heating and cooling rates to be applied, enhancing densification mechanisms over diffusion mechanisms that promote grain growth, facilitating the preparation of cordierite sintered bodies with very fine grain sizes and very high densities (and therefore low porosity), and transferring the intrinsic properties of the original powder to their nearly or fully dense products. As used herein, DC sintering techniques involved non-pulsed DC current to promote powder consolidation and densification.

[0120] A cordierite sintered body may be prepared by a method comprising the steps of: a) combining powders including silicon dioxide (SiO), magnesium oxide (MgO), and aluminum oxide (AlO) to form a powder mixture; b) firing the powder mixture by applying heat to a firing temperature and maintaining the firing temperature to form a fired powder mixture; c) placing the fired powder mixture within a volume defined by a sintering machine toolset and creating a vacuum within the volume; d) applying pressure to the fired powder mixture while heating to the sintering temperature to form a cordierite sintered body; and e) reducing the temperature of the cordierite sintered body. The following additional steps are optional: f) annealing the cordierite sintered body by optionally applying heat to raise the temperature of the cordierite sintered body until the annealing temperature is reached; g) reducing the temperature of the annealed cordierite sintered body to ambient temperature by removing the heat source applied to the cordierite sintered body; and h) machining the cordierite sintered body to produce sintered cordierite components such as photolithography reticles, reflective reticles, support structures, wafer stages, substrates, composite substrates, vacuum chucks, support chucks, electrostatic chucks (ESCs), and wafer chucks for use in microlithography processes.

[0121] The above-described characteristics of the cordierite sintered body are achieved by, among other things, adjusting the purity of the oxides constituting the powder mixture, the mixing and firing conditions, the pressure applied to the fired powder mixture, the sintering temperature of the powder mixture, the sintering time of the powder mixture, the temperature of the cordierite sintered body during the optional annealing step, and the duration of the annealing step. The cordierite sintered body is particularly suitable for use as a substrate or layer of a reflective reticle for EUV lithography processes and devices. The cordierite sintered body is also suitable for use as a low-thermal-expansion positioning element for optical components in microlithography processes and as an electrostatic chuck for holding either or both a reflective reticle and / or a wafer substrate. The methods disclosed herein are suitable for producing cordierite sintered bodies, particularly those with large dimensions (100-620 mm diameter), using a scalable manufacturing process.

[0122] The methods disclosed herein allow for the preparation of cordierite sintered bodies and sintered parts preferably containing 90-99.9 volume % cordierite crystalline phase without the use of dopants and / or sintering aids.

[0123] In some embodiments, the aforementioned cordierite sintered bodies and sintered parts may be made with an optional dopant of a rare earth oxide selected from the group consisting of Y, Sc, La, Er, Ce, Cr, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu, and oxides and combinations thereof, in an amount of ≧0.0001 wt %, preferably ≧0.0005 wt %, preferably ≧0.0010 wt %, preferably ≧0.0025 wt %, each based on the total mass of the starting oxide powder, and the optional dopant can be added to the starting powder, the powder mixture, or the fired powder mixture. In other embodiments, the aforementioned cordierite sintered bodies and sintered parts may be made with the disclosed optional dopants in an amount of ≦0.05 wt. %, preferably ≦0.03 wt. %, preferably ≦0.01 wt. %, preferably ≦0.0075 wt. %, preferably ≦0.0050 wt. %, preferably ≦0.0025 wt. %, respectively, based on the total mass of the starting oxide powder, and the optional dopants can be added to the starting powder, powder mixture, or fired powder mixture.

[0124] In alternative embodiments disclosed herein, the cordierite sintered body may be prepared without at least one or all of the aforementioned dopants. In particular, for applications requiring high thermal conductivity and a controlled CTE, it may be preferable for the cordierite sintered body to be dopant-free. Thus, in certain embodiments, the cordierite sintered body is substantially free of, or free of, at least one or all of the aforementioned dopants.

[0125] Sintering aids can be used as needed in preparing the cordierite sintered bodies and sintered parts disclosed herein, but they are not required and are optional. In certain embodiments, the cordierite sintered bodies disclosed herein may include an optional sintering aid selected from the group consisting of zirconia and calcia, and combinations thereof. In some embodiments, these sintering aids can be added in an amount of ≥ 0.0002 wt%, preferably ≥ 0.0005 wt%, preferably ≥ 0.0010 wt%, and preferably ≥ 0.0025 wt%, each based on the total mass of the starting oxide powder. In other embodiments, the optional sintering aids can be present in an amount of ≤ 0.05 wt%, preferably ≤ 0.03 wt%, preferably ≤ 0.01 wt%, preferably ≤ 0.0075 wt%, preferably ≤ 0.0050 wt%, and preferably ≤ 0.0025 wt%, each based on the total mass of the starting oxide powder, and the optional sintering aids can be added to either the starting powder, the powder mixture, or the fired powder mixture. In certain applications requiring corrosion and erosion resistance, high thermal conductivity, and controlled CTE, it may be preferable for the cordierite body to be free of at least one, or all, of the sintering aids. Thus, in embodiments, the cordierite body is substantially free of, or free of, at least one, or all, of the aforementioned sintering aids.

[0126] Step a) of the method disclosed herein involves combining powders including silicon dioxide (SiO), magnesium oxide (MgO), and aluminum oxide (AlO) to form a powder mixture. The starting powders for forming cordierite sintered bodies and / or sintered parts are preferably commercially available powders of high purity. However, other oxide powders, such as those produced from chemical synthesis processes and related methods, may also be used. The starting powders are chemically refined powders including magnesia, silica, and alumina, which are combined to form a powder mixture in proportions to form cordierite (after sintering). This method differs from other cordierite production methods, which often use starting powders including naturally occurring raw mineral deposits containing naturally occurring materials such as talc, kaolin, gibbsite, dolomite, sepiolite, forsterite, and various clays and clay-based compounds. These mineral deposits often contain undesirable elements, particularly iron, as well as other impurities, resulting in cordierite sintered bodies of low purity and unsuitable for end-use applications. Thus, to form high purity cordierite sintered bodies, the starting powders, powder mixtures, and calcined powder mixtures disclosed herein are substantially free of or free of at least one, or all, of naturally occurring materials including talc, kaolin, gibbsite, dolomite, sepiolite, forsterite, and other clays and clay-based compounds.

[0127] More specifically, naturally occurring mineral deposits may contain compounds and impurities that contribute to the formation of a glassy phase in the cordierite sintered body. Glass-forming components present in mineral deposits may include alkali metal elements including lithium (Li), sodium (Na), and potassium (K); alkaline earth metals including calcium (Ca), strontium (Sr), and barium (Ba); transition metals including chromium (Cr), nickel (Ni), iron (Fe), copper (Cu), zinc (Zn), lead (Pb), and rubidium (Rb); and metalloid elements including boron (B), germanium (Ge), arsenic (As), antimony (Sb), and bismuth (Bi). Those skilled in the art know that these glass-forming components form a glassy phase. The formation of a glassy phase (as used herein, glassy phase means an amorphous, non-crystalline phase) within a cordierite body can increase the variability of the CTE (particularly over the temperature range of 0 to 500°C), decrease the thermal conductivity, and decrease the Young's modulus. A substantially crystalline cordierite body with high phase purity formed from the high-purity starting powders disclosed herein is desirable for achieving a low CTE, high thermal conductivity, and high Young's modulus. The XRD results in Figure 7 show a highly crystalline cordierite body. In comparison, the XRD results for the fired powder mixture in Figure 6 show a convex gradation in the pattern (also described as a "bump" or "hump") with a maximum around 22 degrees. This convex gradation may result from nanometer-scale silica particles that produce an XRD pattern similar to that of amorphous, glassy materials known to have very limited or no long-range order. (As used herein, long-range order is intended to mean a material in which atomic particles exhibit periodicity over many atomic diameters, with each atomic particle having a specific relationship within the material.) The XRD pattern in Figure 7 does not exhibit such a "hump," and therefore indicates a cordierite sintered body that is highly crystalline and substantially free of or free of glassy phase.

[0128] Powder characteristics such as specific surface area (SSA, or BET surface area) and particle size were measured for the starting powders. The specific surface area (SSA) of the starting powders, powder mixtures, and calcined powder mixtures was measured in the range of 0.01 to 2000 m. 2 The surface area was measured using a Horiba BET Surface Area Analyzer Model SA-9601, which is capable of measuring most samples with an accuracy of 10% or better across a specific surface area range of 100 / g. BET or SSA measurements were performed according to ASTM C1274. The particle sizes of the starting powders, powder mixtures, and calcined powder mixtures were measured using a Horiba Model LA-960 Laser Scattering Particle Size Analyzer, which is capable of measuring particle sizes from 10 nm to 5 mm. As disclosed below, the d50 particle size is defined as the median, representing the value above which half of the particle population lies and below which half lies. Similarly, 90% of the distribution lies below the d90 particle size, and 10% of the particle population lies below the d10 particle size.

[0129] The silicon dioxide (SiO) powder disclosed herein preferably includes pyrogenic (or fumed) silica powder. Pyrogenic silica powder is known to contain branched structures and aggregates or agglomerates, and therefore is non-spherical. The difficulty of measuring the particle size of non-spherical particles, and the inherently high uncertainty associated with this, are known to those skilled in the art. Measurements using the laser scattering particle size distribution analyzer disclosed herein are based on the assumption that the particle shape is substantially spherical. Due to its production method (e.g., by flame pyrolysis of silicon-containing compounds such as silicon tetrachloride or sand), pyrogenic silica powder contains substantially non-spherical aggregates or agglomerates with very high aspect ratios. Therefore, when measuring fumed silica powder, the results obtained using the laser scattering particle size distribution method disclosed herein may not provide sufficient accuracy. Therefore, the particle sizes reported for the fumed silica powder disclosed herein are those reported in the literature. Typically, the silica powder disclosed herein contains very small silica crystallites. The silica powder disclosed herein has a primary particle size of about 100 nm (primary particles include single particles or single crystallites) and a d50 of about 9 um.

[0130] The magnesium oxide (MgO) powder may comprise commercially available crystalline magnesia powder having a d10 particle size of preferably 0.03-0.3 μm, preferably 0.05-0.3 μm, preferably 0.075-0.3 μm, preferably 0.1-0.3 μm, preferably 0.03-0.25 μm, preferably 0.03-0.15 μm, preferably 0.03-0.075 μm, preferably 0.1-0.2 μm, a d50 particle size of 0.5-5 μm, preferably 0.5-3 μm, preferably 0.5-2 μm, preferably 1-5 μm, preferably 2-5 μm, preferably 3-5 μm, preferably 1-3 μm, and a d90 particle size of 6-30 μm, preferably 6-25 μm, preferably 6-20 μm, preferably 10-30 μm, preferably 15-30 μm, preferably 15-25 μm.

[0131] Aluminum oxide powders used as starting materials according to embodiments disclosed herein may include commercially available crystalline alumina having a d10 particle size of 0.05-2 μm, preferably 0.05-1 μm, preferably 0.05-0.75 μm, preferably 0.05-0.5 μm, preferably 0.08-2 μm, preferably 0.1-2 μm, preferably 0.2-2 μm, preferably 0.5-2 μm, preferably 0.2-2 μm, preferably 0.05-0.1 μm, more preferably 0.08-0.1 μm.

[0132] The d50 particle size of the aluminum oxide powder used as starting material is 0.15 to 5 μm, preferably 0.15 to 4 μm, preferably 0.15 to 3 μm, preferably 0.15 to 2 μm, preferably 0.15 to 1 μm, preferably 0.15 to 0.75 μm, preferably 0.15 to 0.5 μm, preferably 0.2 to 5 μm, preferably 0.5 to 3 μm, preferably 1 to 3 μm, more preferably 0.15 to 0.3 μm.

[0133] The d90 particle size of the aluminum oxide powder used as the starting material is 0.5 to 10 μm, preferably 0.75 to 10 μm, preferably 1 to 10 μm, preferably 3 to 10 μm, preferably 0.75 to 5 μm, preferably 0.5 to 3 μm, preferably 0.5 to 1 μm, more preferably 0.5 to 0.8 μm.

[0134] Silicon dioxide (SiO2) is 20-40m 2 / g, preferably 20 to 35 m 2 / g, preferably 20 to 30m 2 / g, preferably 25 to 40 m 2 / g, preferably 30 to 40m 2 / g, preferably about 30m 2 / g, more preferably 25 to 35m 2 / g specific surface area (SSA).

[0135] Magnesium oxide (MgO) is 2 to 10 m 2 / g, preferably 2 to 8 m 2 / g, preferably 2 to 6 m 2 / g, preferably 4 to 10 m 2 / g, preferably 4 to 8 m 2 / g, more preferably 4 to 6 m 2 / g specific surface area.

[0136] Aluminum oxide powder is typically 5-18m 2 / g, preferably 5 to 16 m 2 / g, preferably 5 to 14 m 2 / g, preferably 5 to 12 m 2 / g, preferably 5 to 10 m 2 / g, preferably 7 to 18 m 2 / g, preferably 9 to 18 m 2 / g, preferably 12 to 18 m 2 / g, preferably 15 to 18 m 2 / g specific surface area.

[0137] The purity of the silicon dioxide (SiO2) and aluminum oxide (Al2O3) powders used as starting materials is preferably 99.99% or more, more preferably 99.999% or more, and most preferably about 99.9999%, compared to 100% pure silica and alumina.

[0138] The purity of the magnesium oxide (MgO) powder is preferably 99.9% or more, preferably 99.95% or more, and more preferably 99.99% or more.

[0139] The magnesia and alumina starting powders are preferably crystalline, thereby having long-range crystallographic order. Each or all of the magnesia, silica, and alumina starting powders may be sieved, tumbled, blended, crushed, or jet-milled according to methods known to those skilled in the art. In some embodiments, the magnesia, silica, and alumina starting powders may optionally be calcined according to methods known to those skilled in the art to achieve the powder characteristics disclosed herein.

[0140] Comparative cordierite sintered bodies disclosed herein were made with silica grains having a d50 of 200-250 μm and a sintered powder mixture formed therefrom having a d50 of approximately 13 μm and a d90 of approximately 90 μm. These d50 and d90 values ​​indicate powder agglomeration, which may result in the formation of larger crystallites and residual phases present in the microstructure upon sintering. This particle size distribution resulted in microcracks upon sintering (as shown in FIG. 5) due to the CTE mismatch between the silica-rich aggregates and other phases in the cordierite sintered body, and residual silica-rich phases such as tridymite or cristobalite, as shown in the XRD pattern of Comparative Example 1 in FIG. 4. Using starting powders and powder mixtures with d50 and d90 particle sizes smaller than those of the comparative examples, preferably within the disclosed ranges, combined with the disclosed high-energy mixing process, can result in a more uniform and smaller particle size distribution. This combination of the disclosed starting powders to form the powder mixture, the fired powder mixture having the characteristics disclosed herein, and the disclosed reactivity to form cordierite in an in situ process allows for the formation of a cordierite sintered body having the preferred properties disclosed herein.

[0141] In one embodiment, the powder mixture is composed of a molar ratio of about 22.2 mol% MgO, about 22.2 mol% Al2O3, and about 55.6 mol% SiO2 as the starting powder mixture. Representative properties of the starting powder are listed in Table 4. [Table 3]

[0142] The preparation of powder mixtures combining the aforementioned powders, including silicon dioxide (SiO), magnesium oxide (MgO), and aluminum oxide (AlO), can be accomplished using the following powder preparation techniques: ball milling (axial rotation), tumbling (end-over-end or vertical) mixing, jet milling, and combinations thereof.

[0143] The ball milling or end-over-end / tumbling mixing process is preferably carried out under wet conditions. Using wet mixing conditions, starting powders weighed in relative amounts to form the cordierite crystalline phase may be ball milled or end-over-end / tumbling mixed using high-purity (≥99.99%) alumina media to preserve the purity of the starting powders during mixing. In other embodiments, zirconia media may be used to break down hard agglomerates. All purity measurements disclosed herein were measured above the reporting limit for the specific element and were performed using an Agilent 7900 ICP-MS Model G8403. High-purity alumina media was tested using the ICPMS method disclosed herein and found to have a purity of about 99.99% or greater. The media used to carry out the combining process has a diameter of, for example, 5 to 20 mm, preferably 10 to 20 mm, more preferably about 20 mm, and is added in a loading amount of about 75 to about 200 wt %, preferably about 100 to about 200 wt %, more preferably about 125 to about 175 wt %, based on the weight of the powder.

[0144] Starting powders of silica, magnesia, and alumina can be suspended in various solvents, such as ethanol, methanol, and other alcohols, to form slurries. The slurries formed (either for ball milling or tumbling mixing processes) can contain ethanol in an amount of 100-300% by weight, preferably 150-300% by weight, preferably 200-300% by weight, preferably 250-300% by weight, and preferably 150-250% by weight, based on the total powder weight. The amount of ethanol can be adjusted as needed to ensure sufficient mobility of the medium in the slurry to thoroughly mix the powders.

[0145] The use of ball milling and tumbling mixing is a high-energy process that breaks down fine particles and agglomerates, resulting in a homogeneous powder mixture prior to calcination. The term "homogeneous" means that the powder or powder mixture has substantially the same overall properties and is uniform and free of irregularities. Thus, a "homogeneous powder mixture" refers to a powder or powder mixture that has spatially uniform particle size distribution (PSD) and specific surface area (SSA) and no significant gradients in specific surface area or particle size distribution, i.e., a substantially uniform powder or powder mixture. Wet mixing improves powder dispersion through increased mobility, providing a fine-scale homogeneous mixture prior to heat treatment or calcination. Wet ball milling or tumbling mixing can be performed for a duration of 8 to 48 hours, preferably 12 to 48 hours, preferably 16 to 48 hours, preferably 8 to 36 hours, preferably 8 to 24 hours, preferably 16 to 24 hours, preferably 12 to 24 hours. Ball milling may be performed in a vessel approximately 200 mm in diameter, using an RPM (revolutions per minute) of 50-250 RPM, preferably 75-200 RPM, preferably 75-150 RPM, and preferably 100-125 RPM. The RPM may vary depending on the size of the vessel selected for use; for example, a vessel larger than 200 mm in diameter may have a correspondingly lower RPM, as known to those skilled in the art. Wet end-over-end / tumbling (or vertical) mixing may be performed at 10-30 RPM, preferably about 20 RPM. The powder slurry is dried according to known methods. After wet ball milling and / or wet end-over-end / tumbling mixing and drying, the powder mixture may optionally be sieved and blended using any number of meshes, e.g., having openings of 45-400 μm, in any number of repetitions or in any order.

[0146] Jet milling processes, as known to those skilled in the art, can also be used to modify the particle size distribution of the starting powder and / or thoroughly mix the powder to form a powder mixture or calcined powder mixture with a narrow particle size distribution. Jet milling uses high-velocity jets of either inert gas or air to collide powder particles without the use of grinding or mixing media, thereby maintaining the initial purity of the milled powder. The chamber can be designed to preferentially reduce the size of larger particles, narrowing the powder particle size distribution. Once the desired particle size, determined by the machine settings prior to processing, is reached, the powder exits the jet milling chamber. The starting powder, powder mixture, and / or calcined powder mixture disclosed herein may be subjected to jet milling at a pressure of approximately 100 psi, as disclosed herein, separately, in any combination, or all of the disclosed powder milling / mixing processes. After jet milling, the powder or powder mixture may optionally be sieved and blended using any number of meshes, e.g., with openings between 45 and 400 μm, in any number of repetitions or in any order.

[0147] As disclosed herein, the aforementioned mixing and milling methods, either media-free or using high-purity alumina media, maintain the purity of the starting powders during the combining process, such that the cordierite bodies formed therefrom have very high purity. Cordierite bodies having purities of greater than 99.99%, preferably greater than 99.995%, and preferably about 99.999% (relative to a 100% pure cordierite body) are disclosed, and the purity of the starting powders is maintained in the fired powder mixtures disclosed herein and throughout the methods disclosed herein.

[0148] The aforementioned powder preparation techniques can be used alone, or in any combination thereof, or for mixtures of two or more powders that are then combined and sintered into the final cordierite body.

[0149] Step b) of the method disclosed herein includes calcining the powder mixture by applying heat until the calcination temperature is reached and maintaining the calcination temperature to produce a calcined powder mixture. This step can be performed to remove moisture and ensure uniform surface conditions of the cordierite powder before sintering. In some embodiments, the calcination can reduce the surface area of ​​the starting powder and / or powder mixture, while in other embodiments, the calcination does not reduce the surface area of ​​the powder. Higher calcination temperatures can also reduce the specific surface area and can be adjusted within the disclosed range. The calcination following the heat treatment step can be performed at temperatures of about 600°C to about 1000°C, preferably about 700°C to about 1000°C, preferably about 800°C to about 1000°C, preferably about 600°C to about 900°C, preferably about 600°C to about 800°C, and preferably about 700°C to about 900°C. Calcination can be carried out in an oxygen-containing environment for a duration of 4 to 12 hours, preferably 4 to 10 hours, preferably 4 to 8 hours, preferably 6 to 12 hours, preferably 5 to 7 hours. The powder mixture may optionally be sieved, before or after calcination, using a mesh with openings of 45 to 400 μm, for example, repeatedly and in any order, and may be tumbling and / or mixing and / or blending, and combinations thereof, according to known methods. Tumbling and / or blending and / or mixing of the powder mixture and / or calcined powder mixture can be carried out without a medium or using a high-purity (>99.9%) alumina medium or zirconia medium, as disclosed herein, according to known methods.

[0150] In embodiments, depending on the temperature and duration of the firing conditions, firing can result in a fired powder mixture containing magnesium oxide, silica, and aluminum oxide present from the starting powder, as shown in Figure 6A for a firing condition of 600°C for 6 hours. In other embodiments, higher firing conditions can result in a fired powder mixture containing a powder having a cordierite crystalline phase and a crystalline phase corresponding to the starting powder, as shown in Figure 6B for firing conditions of 900°C and 1000°C for 6 hours.

[0151] After calcination, the specific surface area and particle size of the calcined powder mixture were measured using the methods disclosed herein.

[0152] The fired powder mixture, combined in a powder ratio to form cordierite crystalline phase upon sintering, may have a d10 particle size of 0.05-3 μm, 0.05-2 μm, 0.05-1 μm, preferably 0.1-3 μm, preferably 0.1-2 μm, preferably 0.25-3 μm, preferably 0.25-1 μm, preferably 0.05-0.5 μm, preferably 0.1-0.3 μm.

[0153] The calcined powder mixture may have a d50 particle size of 0.2 to 5 μm, preferably 0.2 to 4 μm, preferably 0.2 to 3 μm, preferably 0.2 to 2 μm, preferably 0.2 to 1 μm, preferably 0.2 to 0.5 μm.

[0154] The calcined powder mixture may have a d90 particle size of 10-75 μm, preferably 10-70 μm, preferably 10-60 μm, preferably 10-50 μm, preferably 10-40 μm, preferably 20-75 μm, preferably 40-75 μm, preferably 50-75 μm, preferably 50-70 μm, preferably a d90 particle size of 75 μm or less and 20 μm or more.

[0155] The specific surface area of ​​the calcined powder mixture is 8 to 20 m 2 / g, preferably 10 to 20m 2 / g, preferably 12 to 20 m2 / g, preferably 14 to 20 m 2 / g, preferably 16 to 20 m 2 / g, preferably 8 to 18 m 2 / g, preferably 8 to 16 m 2 / g, preferably 8 to 14 m 2 / g, preferably 10 to 20m 2 / g, preferably 14 to 20 m 2 / g, preferably 16 to 20 m 2 / g.

[0156] Before and / or after firing, the cordierite powder may be sieved and / or tumbled according to known methods. 2 If the surface area of ​​the sintered powder mixture is greater than 8 m / g, it becomes difficult to handle the powder during loading into the sintering equipment tool set, especially if the particle size is large. 2 If the sintered cordierite phase is less than 0.015 / g, the driving force for the formation of the cordierite crystalline phase during the in situ reactive sintering process may be reduced, resulting in a lower density sintered cordierite body. In some embodiments, a powder mixture after firing may be preferable, and Figure 6 shows XRD results for a fired powder mixture disclosed herein. Figure 6A shows an exemplary fired powder mixture disclosed herein that was fired in air at 600°C for 6 hours, and Figure 6B shows an overlay of two exemplary fired powder mixtures disclosed herein, one powder fired in air at 900°C for 6 hours and the other fired in air at 1000°C for 6 hours. The formation of the cordierite crystalline phase is indicated by a "C" in the XRD pattern in Figure 6B. Cordierite sintered bodies disclosed herein typically have a hexagonal crystal structure. Table 4 lists the ranges of properties for the fired powder mixtures disclosed herein. [Table 4]

[0157] Step c) of the method disclosed herein involves placing the calcined powder mixture in a volume defined by a toolset of a sintering machine and creating a vacuum within the volume. The sintering machine used in the process according to one embodiment includes a toolset including at least one graphite die, typically a cylindrical graphite die having a volume and first and second openings, and further including a first and second punch. The first punch is moved into the first opening of the die, the calcined powder mixture is placed in the second opening of the die, and the second punch is moved into the second opening of the die, thereby placing the calcined powder mixture within the volume defined by the toolset of the sintering machine. The calcined powder mixture (which will combine to form the cordierite phase upon sintering) is placed within the toolset. A vacuum, known to those skilled in the art, is established within the volume created by the toolset. Typical vacuum conditions include 10 -2 ~10 -3 Pressures of up to 1000 Torr are used. A vacuum is applied primarily to remove air and protect the graphite from burning, and to remove most of the air from the powder.

[0158] The disclosed methods utilize commercially available high purity silica, magnesia, and alumina powders (and / or those prepared from chemical synthesis techniques) and do not require sintering aids, dopants, cold pressing, forming, or machining of the white body prior to sintering. The starting powders for forming the calcined powder mixture are preferably free of naturally occurring raw materials such as those disclosed herein, which are often high in undesirable impurities; thus, disclosed herein are calcined powder mixtures that are substantially free or free of naturally occurring materials, including talc, kaolin, gibbsite, dolomite, sepiolite, forsterite, and various clays and clay-based compounds.

[0159] Step d) of the method disclosed herein includes applying pressure to the sintered powder mixture while heating it to a sintering temperature to form a cordierite sintered body, and step e) reduces the temperature of the cordierite sintered body by removing the heat source of the sintering apparatus and cooling the cordierite sintered body. The pressure applied to the sintered powder mixture contained within the volume defined by the tool set is in the range of 5 MPa to 100 MPa, preferably 5 MPa to 60 MPa, preferably 5 MPa to 45 MPa, preferably 5 MPa to 20 MPa, preferably 10 MPa to 60 MPa, preferably 10 MPa to 45 MPa, preferably 10 MPa to 40 MPa, preferably 10 MPa to 30 MPa, preferably 10 MPa to 20 MPa, preferably 15 MPa to 45 MPa, preferably 15 MPa to 30 MPa, preferably 20 MPa to 40 MPa. The pressure is applied axially on the material contained within the die.

[0160] In a preferred embodiment, the powder mixture is heated directly by the punch and die of the sintering apparatus. The die is constructed of a conductive material such as graphite to promote resistive / Joule heating. Sintering apparatus and procedures are disclosed in U.S. Patent Application Publication No. 2010 / 0156008(A1), which is incorporated herein by reference.

[0161] The temperatures of a sintering apparatus according to the present disclosure are typically measured within the graphite die of the apparatus, and therefore, it is preferred that the temperatures be measured as close as possible to the cordierite powder being processed so that the temperatures indicated are actually realized in the powder being sintered.

[0162] Heat is applied to the powder mixture placed in the die to facilitate a sintering temperature of 900-1300°C, preferably 900-1250°C, preferably 900-1200°C, preferably 900-1150°C, preferably 900-1100°C, preferably 1000-1300°C, preferably 1050-1300°C, preferably 1100-1300°C, preferably 1150-1300°C, preferably 1200-1300°C, preferably 1150-1250°C.

[0163] Sintering can typically be carried out over an isothermal time of 0.5 to 180 minutes, preferably 0.5 to 120 minutes, preferably 0.5 to 100 minutes, preferably 0.5 to 80 minutes, preferably 0.5 to 60 minutes, preferably 0.5 to 40 minutes, preferably 0.5 to 20 minutes, preferably 5 to 120 minutes, preferably 10 to 120 minutes, preferably 20 to 120 minutes, preferably 40 to 120 minutes, preferably 60 to 120 minutes, preferably 80 to 100 minutes, preferably 85 to 95 minutes, preferably 10 to 60 minutes, preferably 10 to 45 minutes, or preferably 10 to 30 minutes. In certain embodiments, sintering can be carried out without an isothermal time, and cooling begins at a rate disclosed herein after the sintering temperature is reached. In step e) of the process, the cordierite sintered body is passively cooled by removal of the heat source. Natural convection is allowed to occur until the cordierite sintered body reaches a temperature at which it can be easily handled and optionally the annealing and / or machining process can begin.

[0164] During sintering, volume reduction typically occurs, so that the cordierite sintered body may have a volume that is about one-third the volume of the starting powder when placed in the sintering machine tool set.

[0165] In one embodiment, the order of application of pressure and temperature may be varied in accordance with the present disclosure, meaning that the indicated pressure may be applied first, followed by application of heat to reach the desired temperature. Additionally, in other embodiments, the indicated heat may also be applied first to reach the desired temperature, followed by application of the indicated pressure. In a third embodiment according to the present disclosure, temperature and pressure may be applied simultaneously to the cordierite powder to be sintered, ramping up to the indicated values.

[0166] Induction or radiant heating methods can also be used to heat the sintering apparatus and indirectly heat the cordierite powder in the tool set.

[0167] In contrast to other sintering techniques, sample preparation before sintering, i.e., by cold pressing or molding on a white surface, is not required, and the cordierite powder is directly filled into the mold. This reduction in processing steps results in higher purity of the final cordierite sintered body.

[0168] In further contrast to other sintering techniques, sintering aids are not required. Also, high purity starting powders are desirable for forming cordierite sintered bodies with a high (greater than about 80% by volume) cordierite phase content in the sintered body, thereby achieving a sintering temperature of preferably 1×10 over the temperature range of 0 to 50°C. -6 A low CTE of 99.9 ppm / °C or less can be achieved. The presence of other phases, whether amorphous or crystalline, affects the CTE value and the CTE distribution over a particular temperature range. Therefore, it is preferable to obtain a phase-pure cordierite sintered body. The use of high-purity starting materials that are free of sintering aids and dopants and have a purity of 99.9% to 99.995% or greater relative to the powder containing 100% of their respective oxides (i.e., containing only the respective oxides, without impurities, sintering aids, or dopants) allows for the production of high-purity cordierite sintered bodies having a purity of 99.9 to 99.995%, preferably 99.95 to 99.995%, and preferably 99.99 to 99.995%, relative to the purity of the 100% pure cordierite sintered body.

[0169] In further contrast to other sintering techniques, cordierite sintered bodies containing greater than 90 volume % cordierite phase are formed by in situ reactive sintering during the sintering process due to the combination of particle size distribution, purity, specific surface area characteristics of the disclosed fired powder mixture, and sintering conditions of pressure, temperature, and time.

[0170] In one embodiment, process step d) may further comprise a pre-sintering step with a specific heating ramp of 0.1°C / min to 100°C / min, preferably 1°C / min to 50°C / min, more preferably 2 to 25°C / min, until a specific pre-sintering time is reached.

[0171] The cordierite sintered bodies disclosed herein have an overall purity of greater than 99.9%, preferably greater than 99.99%, preferably greater than 99.995%, and preferably about 99.999%, based on 100% pure cordierite.

[0172] In another embodiment, process step d) may further comprise a pre-sintering step using the specific heating gradient described above and the specific pressure gradient described above.

[0173] In one embodiment, at the end of process step d), the method may further comprise step e): cooling the cordierite sintered body by natural cooling (unforced cooling) of the process chamber under vacuum conditions, as known to those skilled in the art. In a further embodiment according to process step e), the cordierite sintered body may be cooled under convection of an inert gas, for example, argon or nitrogen at 1 bar. Other gas pressures above or below 1 bar may also be used. In a further embodiment, the cordierite sintered body is cooled under forced convection conditions in an oxygen environment. At the end of sintering step d), the power applied to the sintering apparatus is removed, and the pressure applied to the cordierite sintered body is removed, followed by cooling according to step e).

[0174] The formation of high density, phase-pure cordierite sintered bodies disclosed herein is achieved by a reactive sintering process, whereby cordierite is formed in situ from starting powders of silica, magnesia, and alumina, without the use of naturally occurring raw materials.

[0175] The properties of the cordierite sintered bodies are listed in Table 5. Comparative samples 3 and 18 are included due to their high density characteristics. [Table 5]

[0176] Step f) of the method disclosed herein is optionally a step of annealing the cordierite sintered body by applying heat to raise the temperature of the cordierite sintered body to an annealing temperature, and step g) is a step of lowering the temperature of the annealed ceramic sintered body. In optional step f), the cordierite sintered body or component obtained in step d) or h), respectively, can be subjected to an annealing procedure. In other examples, annealing of the cordierite sintered body or component may not be performed. Under other circumstances, annealing may be performed in a furnace outside the sintering apparatus or within the sintering apparatus itself without removing it from the apparatus.

[0177] For the purposes of annealing according to the present disclosure, the cordierite sintered body may be removed from the sintering apparatus after cooling according to process step e) and the annealing process step may be carried out in a separate apparatus such as a furnace.

[0178] In some embodiments, for purposes of annealing according to the present disclosure, the cordierite sintered body in step d) may be annealed sequentially in the sintering apparatus without the need to remove it from the sintering apparatus between sintering step d) and the optional annealing step.

[0179] This annealing can improve the chemical and physical properties of the sintered body. The annealing process can be carried out by conventional methods used for annealing glasses, ceramics, and metals, and the degree of improvement can be selected by selecting the annealing temperature and the duration for which the annealing is continued.

[0180] Typically, the optional step f) of annealing the cordierite sintered body is carried out at a temperature of about 800 to about 1200°C, preferably about 900 to about 1200°C, preferably about 1000 to about 1200°C, more preferably about 900 to about 1100°C.

[0181] The optional annealing step f) is intended to correct the oxygen vacancies in the crystal structure back to the stoichiometric ratio. Annealing cordierite typically requires a period of 1 to 24 hours, preferably 1 to 20 hours, preferably 1 to 16 hours, more preferably 4 to 8 hours in an oxygen-containing environment.

[0182] Typically, the optional process step f) of annealing the ceramic sintered body is carried out in an oxidizing atmosphere, whereby the annealing process increases the albedo, reduces stress, improves mechanical handling, and reduces porosity. The optional annealing step may also be carried out in air.

[0183] After optional process step f) of annealing the cordierite body, the temperature of the sintered, and in some cases annealed, cordierite body is reduced to ambient temperature according to process step g), and the sintered, and optionally annealed, cordierite body is removed from the furnace if the annealing step is performed outside the sintering apparatus, or from the tool set if annealing step f) is performed within the sintering apparatus.

[0184] The cordierite body can then be machined, cut, and / or polished into a final body, such as a reticle substrate for use in an EUV lithography process. Machining of the cordierite body to produce a cordierite component can be performed according to methods known to those skilled in the art. For example, the cordierite body, in embodiments, is formed in the shape of a disk having a diameter ranging from 10 mm up to 550 mm with a thickness ranging from 4 mm to 100 mm. The body can also be machined into various shapes and / or component shapes as needed for the application. The high density achieved according to the methods disclosed herein allows the surface of the cordierite body to be polished to a fine surface finish. Surface roughness Sa, as defined herein, is a measure of the arithmetic mean height of a surface as known according to ISO 25178 Surface Texture (Areal Roughness Measurement), a collection of international standards related to the analysis of surface roughness. The disclosed cordierite sintered bodies may have a surface roughness Sa value of less than 18 nm, preferably less than 15 nm, preferably less than 10 nm, more preferably less than 8 nm, more preferably less than 5 nm, and more preferably less than 2 nm.

[0185] The methods disclosed herein provide improved control over maximum pore size, higher density, improved mechanical strength, and thereby improved handleability of cordierite sintered bodies / components, particularly those cordierite bodies having maximum dimensions of, for example, 200-550 mm or greater, and reduced oxygen vacancies within the lattice of corrosion-resistant cordierite sintered components.

[0186] Thus, in one embodiment disclosed herein is a cordierite sintered body made by a method comprising: a) combining powders including silicon dioxide (SiO), magnesium oxide (MgO), and aluminum oxide (AlO) to form a powder mixture; b) firing the powder mixture by heating to raise the temperature of the powder mixture to a firing temperature and maintaining the firing temperature to produce a fired powder mixture; c) placing the fired powder mixture within a volume defined by a sintering apparatus toolset to create a vacuum within the volume; and d) applying pressure to the fired powder mixture while heating to the sintering temperature to sinter to produce MgAlSiO. 18 and e) forming a cordierite sintered body containing the above compound; and e) reducing the temperature of the cordierite sintered body.

[0187] All features disclosed with respect to the method of making a cordierite sintered body also apply to the product, the cordierite sintered body, and vice versa.

[0188] Use as a photolithography reticle In this specification, Mg2Al4Si5O 18 and a photolithography reticle comprising at least one layer of a cordierite sintered body having at least one surface, the cordierite sintered body having a density of 2.55 to 2.63 g / cc.

[0189] One exemplary use of the disclosed cordierite sintered bodies is as a reflective reticle for use in EUV lithography applications, which substantially reduces or eliminates pattern distortion due to absorption of EUV radiation while maintaining a reticle thickness that meets industry standards.

[0190] 2A and 2B schematically illustrate an embodiment of an EUV reflective reticle 100 including a substrate 102 and a reflective layer 104, with FIG. 2B further including a layer of ULE glass 206. The photolithographic reticle embodiment of FIGS. 2A and 2B includes a substrate 102 having one or more layers of highly reflective material deposited thereon to form the reflective layer 104. A pattern (not shown) can be formed on the reflective surface of layer 104 by chemical etching of a patterned layer of resist, or additionally or alternatively by any other technique apparent to one skilled in the art. The reflective layer 104 can be formed from aluminum or other highly reflective metals selected for their application-specific properties at a selected frequency of use.

[0191] The substrate 102 comprises a cordierite sintered body made by the methods disclosed herein, which has a substantially zero coefficient of thermal expansion over the range of temperatures to which the photolithographic reticle 100 is subjected. The physical and chemical properties of the cordierite sintered body disclosed herein (e.g., very high density, low surface smoothness, and absence of defects) make the cordierite sintered body suitable for use as a reticle substrate by providing a low-porosity upper surface 106 that supports polishing and the application of a reflective film, which is free of subsequent pores or porosity, has a low surface roughness (Sa), and has a low peak-to-valley (Sz) value, where the surface properties are measured as a "peak-to-valley" (Sz) value and a surface roughness (Sa). Without being bound by any particular theory, if the top surface 106 of the substrate has sufficiently low surface roughness and peak-to-valley measurements (e.g., Sz of about 14 nm or less and Sa of about 10 nm or less), in certain embodiments, the reticle 100 does not have an additional layer of ULE glass disposed between the top surface of the substrate and the at least one reflective layer 104, or a ULE glass layer above the reflective layer. Sintered cordierite bodies that can be polished to peak-to-valley features within the ranges disclosed herein can provide reflective reticles with reduced thermal resistance, thereby reducing pattern distortion upon heating. In embodiments, this layer can have a minimal thickness, such as less than 0.025 mm, to maintain a relatively low thermal resistance. For example, U.S. Pat. No. 8,736,810 discloses that microstructural defects (voids) make cordierite unsuitable for use as a substrate in reflective reticles, requiring an additional layer of material between the reflective layer and the substrate. The additional material layer can be a metal layer, such as, but not limited to, aluminum, a non-metallic conductive material such as graphite, or any combination thereof. In contrast, an EUV reflective reticle according to the present disclosure comprises a substrate including the cordierite body disclosed herein and at least one layer of highly reflective material that forms a reflective layer. Substrates including the cordierite body disclosed herein do not suffer from the drawbacks associated with pattern distortion resulting from localized heating due to absorbed radiation, and they exhibit surface properties that allow highly reflective materials to be placed directly on the surface of the substrate.

[0192] The cordierite sintered body substrate 102 has a substantially zero coefficient of thermal expansion over the ambient temperature range (approximately 22°C to 25°C) and a thermal conductivity that is approximately three times greater than the thermal conductivity of the optical layers (e.g., cordierite has a thermal conductivity of approximately 3.8 to approximately 5 W / (m-°C) at 25°C, while ULE glass has a thermal conductivity of approximately 1.31 W / (m-°C) at 25°C). In one embodiment, the thickness of the substrate 102 may be approximately 5.00 mm or greater.

[0193] To maintain high exposure accuracy, patterning device 100 and / or wafer 80 are supported by first and second support platforms 82 and 84. First support platform 82 (as shown in FIG. 1) may include either a fixed or movable frame, structure, or support. Embodiments of the support chuck and support structures 82 and 84 are shown in FIGS. 3A and 3B.

[0194] Use as a support structure

[0195] Another exemplary use of the disclosed cordierite sintered body is as a support chuck or support structure (shown in FIGS. 3A and B, respectively) for use in EUV lithography applications that substantially reduces or eliminates pattern distortion and positional variations due to absorption of EUV radiation. The support structure and / or support chuck may be made of MgAlSiO 18 The cordierite sintered body may include at least one layer having at least one surface comprising:

[0196] FIG. 3A shows an exemplary cross-sectional view of a support chuck 300, which in some embodiments may comprise an electrostatic chuck configured to support a component 302 (which may include, but is not limited to, a patterning device 100 or a wafer 80 mounted thereon). According to certain illustrative examples, the support chuck 300 includes a chuck substrate 304, and in certain embodiments in which the support chuck 300 has electrostatic clamping functionality, the chuck substrate 304 may further include a built-in charge plate 306 operable to be charged to apply an electrostatic force to the component 302. In some embodiments, the support chuck 300 may be mounted to the first or second support platforms 82 and 84. The support chuck 300 further includes a number of support pins 308 designed to support the component 302, leaving a space between the component 302 and the chuck substrate 304 (and, if applicable, the charge plate 306) to allow gas to flow therebetween to reduce the clamping effect. The receptacle 60 is mounted to the first and second support structures ( 82 and 84 , respectively) so that its upper surface is flush with the upper surface of the component 302 .

[0197] FIG. 3B shows an exemplary cross-sectional view of support structure 400. According to a specific illustrative example, support structure 400 supports component 302 mounted thereon (which in some embodiments may include, but is not limited to, patterning device 100 or wafer 80) and further includes composite substrates 404a-d. Support structure 400 includes a first lower component 404a bonded (e.g., by soldering, diffusion bonding, and similar methods known to those skilled in the art) to a second lower component 404b, together forming the base body ("bulk") of support structure 400. Support structure 400 may include multiple channels 406 for removing heat that is more intensely generated as a result of absorption of radiation by composite substrates 404a-d at the high beam intensities of microlithography. Support structure 400 further includes upper support structures (404c and 404d) for supporting component 302. These structures each include a first upper structure 404c and a second upper structure 404d. The upper support structure provides increased precision during exposure through controlled positional change during EUV exposure.

[0198] It will be appreciated that additional channels 406, for example for receiving built-in components or heating elements, may also be provided in the support structure 400 (or alternatively in the chuck substrate 304 of the support chuck 300), which may also be provided in a mesh or honeycomb structure, for example as described above, to achieve further weight reduction while maintaining high rigidity.

[0199] The support chuck 300 and support structure 400 thus formed can withstand the high beam intensities of microlithography, thereby providing a lightweight construction due to the types of components selected, while ensuring good heat transfer and low thermal expansion, and a high Young's modulus for high mechanical stability and positional accuracy. The support chuck 300 and / or support structure 400 can be formed either as a composite structure (such as a honeycomb or mesh pattern) or as a monolithic block of cordierite.

[0200] Chuck substrate 304 and composite substrates 404a-d preferably comprise the cordierite sintered body disclosed herein.

[0201] Equipment / Spark Plasma Sintering Tools Disclosed herein is a spark discharge plasma sintering (SPS) tool that includes a die with a sidewall having an inner wall and an outer wall, the inner wall having a diameter that defines an interior volume capable of receiving at least one ceramic powder; and an upper punch and a lower punch operatively coupled to the die, each of the upper punch and the lower punch having an outer wall that defines a diameter that is smaller than the diameter of the inner wall of the die, thereby forming a gap between each of the upper punch and the lower punch and the inner wall of the die when at least one of the upper punch and the lower punch moves within the interior volume of the die, the gap having a width of 10 μm to 100 μm, and the at least one ceramic powder having a specific surface area (SSA) of 1 to 18 m / g, as measured in accordance with ASTM C1274.

[0202] 10 shows an SPS tool 1 with a simplified die / punch arrangement used to sinter ceramic powders to make large sintered ceramic bodies as disclosed herein. The terms "apparatus" and "tool" are used interchangeably with respect to a spark discharge plasma sintering apparatus.

[0203] Typically, the die / punch arrangement is within a vacuum chamber (not shown), as will be appreciated by those skilled in the art. Referring to Figure 10, a spark discharge plasma sintering tool 1 comprises a die system 2 having a sidewall including an inner wall 8 having a diameter that defines an interior volume capable of receiving at least one ceramic powder 5.

[0204] 10 , the spark discharge plasma sintering tool 1 includes an upper punch 4 and a lower punch 4′ operably coupled to the die system 2, each of the upper punch 4 and the lower punch 4′ having an outer wall 11 defining a diameter smaller than the diameter of the inner wall 8 of the die system 2, thereby forming a gap between each of the upper punch 4 and the lower punch 4′ and the inner wall 8 of the die system 2 when at least one of the upper punch 4 and the lower punch 4′ moves into the interior volume of the die system 2.

[0205] The die system 2 and the upper and lower punches 4, 4' may comprise at least one graphite. In certain embodiments, the graphite materials disclosed herein may comprise at least one isotropic graphite material. In other embodiments, the graphite materials disclosed herein may comprise graphite materials including at least one reinforced graphite material, such as, for example, a carbon-carbon composite, and fibers, particles, or sheets or meshes, or laminates of other conductive materials, such as carbon, in a matrix of isotropic graphite material. In other embodiments, the die and upper and lower punches comprise a combination of these isotropic and reinforced graphite materials.

[0206] For example, the graphite material used in some or all of the tool components, such as die 6 and punches 4 and 4', may comprise a porous graphite material that exhibits a porosity of about 5% to about 20%, about 5% to about 17%, about 5% to about 13%, about 5% to about 10%, about 5% to about 8%, about 8% to about 20%, about 12% to about 20%, about 15% to about 20%, about 11% to about 20%, about 5% to 15%, 6% to about 13%, and preferably about 7% to about 12%.

[0207] Preferably, the graphite material has an average pore size (pore diameter) of 0.4 to 5.0 μm, preferably 1.0 to 4.0 μm, and contains pores with a surface pore size of at most 30 μm, preferably at most 20 μm, preferably at most 10 μm. More preferably, pores with a surface pore size of 10 to 30 μm may be present.

[0208] The graphite material used in the tools disclosed herein may have an average particle size of <0.05mm, preferably <0.04mm, preferably <0.03mm, preferably <0.028mm, preferably <0.025mm, preferably <0.02mm, preferably <0.018mm, preferably <0.015mm, preferably <0.010mm.

[0209] The graphite material used in the tools disclosed herein may have an average particle size of >0.001 mm, preferably >0.003 mm, preferably >0.006 mm, preferably >0.008 mm, preferably >0.010 mm, preferably >0.012 mm, preferably >0.014 mm, preferably >0.020 mm, preferably >0.025 mm, preferably >0.030 mm.

[0210] The graphite material used in the tools disclosed herein has a tensile strength of ≥ 1.45 g / cm 3 , preferably ≥ 1.50 g / cm 3 , preferably ≥ 1.55 g / cm 3 , preferably ≥ 1.60 g / cm 3 , preferably ≥ 1.65 g / cm 3 , preferably ≥ 1.70 g / cm 3 , preferably ≥ 1.75 g / cm 3 The density may be

[0211] The graphite material used in the tools disclosed herein has a modulus of ≦1.90 g / cm 3 , preferably ≦1.85 g / cm 3 , and preferably ≦1.80 g / cm 3 The density may be

[0212] In an embodiment, the graphite material has a surface roughness of ≥ 3.3 x 10 -6 / ℃, ≥ 3.5 × 10 -6 / ℃, ≥3.7×10 -6 / ℃, ≥ 4.0 × 10 -6 / ℃, ≥ 4.2 × 10 -6 / ℃, ≥ 4.4 × 10 -6 / ℃, ≥ 4.6 × 10 -6 / ℃, ≥ 4.8 × 10 -6 / °C over the temperature range of about 400 to about 1400°C.

[0213] In an embodiment, the graphite material has a surface roughness of ≦7.0×10 -6 / °C, preferably ≦6.0×10 -6 / °C, preferably ≦5.0×10 -6 / °C, preferably ≦4.8×10 -6 / °C, preferably ≦4.6×10 -6 / °C over a temperature range of about 400 to 1400°C.

[0214] Table 6 lists the properties of exemplary graphite materials disclosed herein. [Table 6]

[0215] 11A-11C, die system 2 includes die 6 and, optionally, but preferably, at least one conductive foil 7 located on the interior wall of the die. There is no limit to the number of conductive foils on the interior wall of the die, and 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 conductive foils may be provided as circumferential liners between die 6 and each of upper punch 4 and lower punch 4', such that interior wall 8 of die system 2 (including at least one conductive foil, if present) and outer wall 11 of each of the upper and lower punches define gap 3. At least one conductive foil 7 includes graphite, niobium, nickel, molybdenum, platinum, and other ductile, conductive materials, and combinations thereof, that are stable within the temperature ranges according to the methods disclosed herein.

[0216] In certain embodiments, the conductive foil may comprise a flexible and compressible graphite foil as disclosed herein, having the following properties: a carbon content of more than 99 wt%, preferably more than 99.2 wt%, more preferably more than 99.4 wt%, more preferably more than 99.6 wt%, more preferably more than 99.8 wt%, more preferably more than 99.9 wt%, more preferably more than 99.99 wt%, more preferably more than 99.999 wt%, impurities less than 500 ppm, preferably less than 400 ppm, more preferably less than 300 ppm, more preferably less than 200 ppm, more preferably less than 100 ppm, more preferably less than 50 ppm, more preferably less than 10 ppm, more preferably less than 5 ppm, more preferably less than 3 ppm; a tensile strength of the graphite foil in the range of 0.4.0 to 6.0 MPa, preferably 4.2 to 5.8 MPa, more preferably 4.4 or 5.6 MPa, and / or The bulk density of the graphite foil is preferably in the range of 1.0 to 1.2 g / cc, preferably 1.02 to 1.18 g / cc, more preferably 1.04 to 1.16 g / cc, more preferably 1.06 to 1.16 g / cc.

[0217] In embodiments, the at least one foil typically comprises graphite. In certain embodiments, the at least one foil as part of the die system may include a circumferential liner between the surface of the die and each of the upper and lower punches.

[0218] The graphite foil can improve the temperature distribution throughout the powder during sintering. [Table 7]

[0219] Referring now to FIGS. 11A, 11B, and 11C, an SPS tool set having an embodiment of a graphite foil arrangement is shown. Ceramic powder 5 is placed between at least one of an upper punch 4 and a lower punch 4', with a gap 3 shown between the outer wall 11 of each of the upper and lower punches and the inner wall 8 of the die system 2. FIGS. 11A, 11B, and 11C each show one to three layers of conductive foil 7 and a die 6 as part of the die system 2. Thus, the gap extends from the inner wall 8 of the die system 2 to the outer wall 11 of each of the upper and lower punches. The gap spacing is arranged to allow for degassing of the powder before and / or during heating and sintering, while also maintaining ohmic contact between the punch and die to improve temperature distribution throughout the ceramic powder during heating and sintering.

[0220] The graphite foil may have a thickness of, for example, 0.025 to 0.260 mm, preferably 0.025 to 0.200 mm, preferably 0.025 to 0.175 mm, preferably 0.025 to 0.150 mm, preferably 0.025 to 0.125 mm, preferably 0.035 to 0.200 mm, preferably 0.045 to 0.200 mm, preferably 0.055 to 0.200 mm.

[0221] The distance of the gap 3 is measured from the inward surface of the foil 7 closest to the upper punch 4 and the lower punch 4' to the outer wall of the outer wall 11 of each of the upper and lower punches. A preferred range for the distance of the gap 3 is preferably 10 to 100 μm, preferably 10 to 80 μm, preferably 10 to 70 μm, preferably 10 to 60 μm, preferably 10 to 50 μm, preferably 30 to 70 μm, preferably 20 to 60 μm, preferably 30 to 60 μm.

[0222] Furthermore, the width of the gap 3 between the inner wall 8 of the die system 2 and the outer wall 11 of each of the upper and lower punches 4 and 4′ can be determined by one skilled in the art to sufficiently facilitate degassing of the powder during the preheating, heating, and sintering processes, on the one hand, and to provide sufficient electrical contact for Joule or resistive heating to effect sintering, on the other hand. If the gap 3 is spaced less than 10 μm apart, the force required to move at least one of the upper and lower punches within the internal volume of the die system and thereby assemble the tool set may cause damage to the tool set. Furthermore, a gap 3 less than 10 μm may not allow gases, organic matter, moisture, etc. adsorbed within the ceramic powder 5 to escape, thereby extending the process time during production and reducing the density of the cordierite sintered body by leaving porosity. In certain embodiments, if the width of the gap 3 is greater than about 70 μm, localized overheating may occur when sintering insulating materials, such as the powder mixtures and / or calcined powder mixtures disclosed herein, resulting in thermal gradients within the tool set during sintering. These thermal gradients (high resistivity of the oxide powder mixture, e.g., about 1 × 10 +10The density variations across the cordierite sintered body can be due to the resistivity (resulting from resistivities of Ω-cm or greater). A gap of 10 to 70 μm is preferred for forming large-sized cordierite sintered bodies from the powder mixtures and fired powder mixtures disclosed herein. Thus, in some embodiments, when sintering ceramic powders, including mixtures of oxide powders, the gap 3 between the inner wall 8 of the die system 2 and the outer wall 11 of each of the upper and lower punches is preferably 10 to 70 μm, preferably 10 to 60 μm, preferably 10 to 50 μm, preferably 10 to 40 μm, preferably 20 to 70 μm, preferably 30 to 70 μm, preferably 40 to 70 μm, preferably 50 to 70 μm, or preferably 30 to 60 μm. While not intending to be bound by any particular theory, it is believed that the gap spacing between the inner wall 8 of the die system 2 and the outer wall 11 of each of the upper and lower punches during sintering functions to facilitate degassing of the powder of organic matter, moisture, adsorbed molecules, etc. during the pre-sintering and sintering processes. This results in large-sized cordierite sintered bodies having high density, low volume porosity, low density variation, and improved mechanical properties such that the body can be easily handled without fracture. Sintered ceramic bodies comprising cordierite prepared as disclosed herein have dimensions ranging from 100 mm to 622 mm or greater, with respect to the maximum dimension of the cordierite sintered body.

[0223] In practice, the upper punch 4 and the lower punch 4' are not always perfectly aligned about the central axis. Figures 12A and 12B are plan views of the tool set 1, showing the arrangement of the upper punch 4 and the lower punch 4', the gap 3, the number of conductive foils 7, and the die system 2 about the central axis 9. In the embodiment shown in Figure 12A, the gap can be axisymmetric about the central axis 9. In another embodiment shown in Figure 12B, the gap can be asymmetric about the central axis 9. In both the illustrated axisymmetric and asymmetric embodiments, the gap 3 can extend between 10 um and 70 um when sintering the oxide ceramics disclosed herein.

[0224] The asymmetric performance of the gap can be measured by performing an analysis of the absolute radial deviation of the CTE over a range of temperatures. For example, Figure 13 shows the radial deviation from the average CTE at 1200°C for two isotropic graphite materials (A and B) used as punches and dies in the apparatus disclosed herein. Figure 13 shows that for materials that can successfully maintain the desired gap over a large temperature range, e.g., from room temperature to 2000°C, the radial deviation is at most >0.3 x 10 in the xy plane. -6 This indicates that the CTE cannot vary in ppm / °C. Material B exhibits an unacceptable CTE spread in the xy plane, while material A exhibits an acceptable CTE spread throughout the entire temperature range. The standard deviation of the CTE in ppm / °C for graphite materials A and B over a temperature range across the xy plane for both materials in Figure 13 is shown in Figure 14A), and the absolute radial variation (delta) of CTE (from lowest to highest) is shown in Figure 14B. Figure 15 shows the dispersion of the thermal expansion coefficients of graphite materials A and B from 400 to 1400°C.

[0225] Sintering equipment and procedures are disclosed in US Provisional Patent Application No. 63 / 124,547, which is incorporated herein by reference.

[0226] The advantages of the particular toolset design used in accordance with one embodiment may result in the overall technical effect of obtaining large ceramic bodies of very high purity (without the need for dopants and / or sintering aids) with high and uniform density and low volumetric porosity, thereby reducing the tendency for fracture in sintering processes according to the present disclosure, particularly SPS processes. Accordingly, all features disclosed with respect to the toolset also apply to the production of cordierite sintered bodies with dimensions greater than 100 mm, preferably between 100 mm and about 622 mm.

[0227] Use of the toolset disclosed herein makes it possible to achieve a more homogeneous temperature distribution in the powder being sintered, allowing for the production of cordierite sintered bodies, particularly those with larger dimensions, e.g., greater than 100 mm and / or 200 mm in their largest dimension, having very high (>96% of the theoretical density of cordierite as disclosed herein) and uniform density (<4% variation across their largest dimension), thereby reducing their tendency to fracture.

[0228] The disclosed toolsets may further include spacer elements, shims, liners, and other toolset components, typically fabricated from at least one of the graphite materials having the properties disclosed herein.

[0229] The cordierite sintered bodies disclosed herein, having the combined properties of crystalline phase purity, high (chemical) purity, low volume porosity (and corresponding high density), and high thermal conductivity, when used as components in lithography equipment, particularly EUV lithography, as disclosed herein, provide the synergistic effects of a controlled coefficient of thermal expansion, a high modulus of elasticity, high thermal conductivity, and a substantially smooth, non-porous polished surface. Using the spark discharge plasma sintering apparatus disclosed herein, these beneficial characteristics can be obtained in cordierite sintered bodies of large dimensions, particularly diameters of 100 mm to over 600 mm.

[0230] The features and advantages are more fully illustrated by the exemplary embodiments discussed below. [Example]

[0231] The general nature of the present disclosure will be more clearly illustrated in the following examples, which are intended to illustrate but not limit the disclosure.

[0232] All particle size measurements were performed using a Horiba Model LA-960 laser scattering particle size distribution analyzer, which is capable of measuring particle sizes from 10 nm to 5 mm. All specific surface area (SSA) measurements for the starting powders, powder blends, and calcined powder blends ranged from 0.01 to 2000 m for most samples. 2 Purity and impurities were measured using ICP-MS on an Agilent 7900 ICP-MS model G8403.

[0233] Comparative Example 1: Sample 003 ball milling A powder mixture was prepared containing alumina, magnesia, and silica powders combined in relative amounts that sintered to form a phase pure cordierite crystalline phase. The alumina powder was approximately 24 m 2 The magnesia powder had a specific surface area (SSA) of about 4 m / g, a particle size distribution of d10 about 0.12 um, d50 about 0.67 um, d90 about 2.89 um, and a purity of 99.9985% relative to 100% pure alumina powder. 2 The silica powder had a specific surface area of ​​100% pure magnesia (µm / g), a particle size distribution of d10 of about 0.14 µm, d50 of about 3.3 µm, and d90 of about 6.5 µm, and a purity of 99.7966% relative to 100% pure magnesia. The silica powder included pyrogenic silica particles, which may be formed by spray-drying pyrogenic silica powder to agglomerate primary particles into larger aggregates or crystallites to produce silica particles. Silica particles may include both spherical and non-spherical particles. Measurements using the laser scattering particle size distribution analyzer disclosed herein are based on the assumption that the particles are substantially spherical. Therefore, results using the laser scattering particle size distribution method disclosed herein may not provide sufficient accuracy for measuring silica particles. Therefore, the particle sizes reported for the silica particles disclosed herein are those reported in the literature. The silica particles disclosed herein are generally in the range of 20-40 µm. 2The cordierite sintered body may have a specific surface area of ​​0.03-0.3 μm, a particle size distribution with a d50 of 200-250 μm, and a purity of greater than 99.999% relative to 100% pure silica. Cordierite sintered bodies made with silica particles according to this example having a particle size distribution as disclosed exhibit powder agglomeration, resulting in a large d50 particle size. This d50 particle size resulted in localized microcracking during sintering due to CTE mismatch between phases in the sintered ceramic. The use of less agglomerated starting powders with smaller d50 particle sizes combined with sufficient energy milling can result in the more uniform and smaller particle size distributions disclosed herein, ameliorating such microcracking. Particle size distributions with a d10 of 0.03-0.3 μm, a d50 of 0.2-5 μm, and a d90 of 40-120 μm, and a d90 of 20-40 μm, can be achieved. 2 Silica powders with an SSA of 0.1g / g are preferred. The powders were weighed and combined in a molar ratio that would form a cordierite phase upon sintering to form a powder mixture. The powder mixture was then transferred to a ball milling container. Ethanol was added to the powder mixture in an amount of 120% by powder weight to form a slurry, and a mixing medium was added in an amount of 100% by powder weight to facilitate mixing between the powders comprising the powder mixture. After mixing for 24 hours, the slurry containing the powder mixture was removed from the mixer, and the ethanol was removed from the slurry using a rotary evaporator. The powder mixture was then calcined at 600°C for 8 hours. Calcination reduces the moisture content, increases crystallinity, and may potentially reduce the surface area. The calcined powder mixture may optionally be sieved, tumbled, blended, or the like according to known methods after calcination. The calcined powder mixture had a mass of 23-27m. 2The powder mixture had a surface area of ​​1 / g, a particle size distribution of d10 about 2 μm, d50 about 10 μm, and d90 about 87 μm, and a purity of 99.986%. The powder mixture may optionally be sieved, blended, crushed, etc., either before or after firing. The fired powder mixture was then sintered under vacuum at a temperature of 1200°C and a pressure of 30 MPa for 30 minutes according to the method disclosed herein. The average density of five measurements, measured using the Archimedes method, was 2.62 g / cc, or 98.5% of theoretical density. The standard deviation was 0.002 g / cc. Accordingly, a volume or bulk porosity of 1.5% is calculated from the density measurements. Figure 5 shows an SEM micrograph of a cordierite sintered body according to this example. Silica-rich regions in the microstructure (e.g., containing silica-rich quartz phases such as cristobalite and / or tridymite) resulted in localized coefficient of thermal expansion (CTE) dispersion and subsequent microcracking during sintering, as well as residual quartz silica-rich phases such as tridymite or cristobalite, as shown in the XRD patterns (circled) in Figure 4. Therefore, to reduce or eliminate the silica-rich regions in the sintered body and prevent microcracking, it is recommended to use a silica starting powder with a primary particle size of about 100 nm and a d50 of about 9 μm or less, and further refine the powder to have a d90 particle size as small as possible, such as 10-75 μm, preferably less than 70 μm, and a d90 particle size of 8-20 μm. 2 It is preferred to carry out a mixing / milling process that results in a calcined powder mixture having an SSA of 1 / g.

[0234] Comparative Example 2: Sample 018 ball milling and planetary milling A powder mixture containing alumina, magnesia, and silica powders was prepared. The alumina powder was 22–26 m 2 The magnesia powder had a surface area of ​​about 4 m / g, a particle size distribution of d10 about 0.12 um, d50 about 0.67 um, d90 about 2.89 um, and a purity of 99.9985% relative to 100% pure alumina powder. 2The silica powder had a surface area of ​​1000 nm / g, a particle size distribution of d10 of about 0.14 μm, d50 of about 3.33 μm, and d90 of about 6.49 μm, and a purity of 99.7966% relative to 100% pure magnesia. The silica powder included pyrogenic silica particles that may be formed by spray-drying pyrogenic silica powder to agglomerate primary particles into larger aggregates or crystallites to produce pyrogenic silica particles. The silica particles include particles that may include both spherical and non-spherical particles in varying amounts. Measurements using the laser scattering particle size distribution analyzer disclosed herein are based on the assumption that the particles are substantially spherical. Therefore, results using the laser scattering particle size distribution method disclosed herein may not provide sufficient accuracy for measuring silica particles. Therefore, the particle sizes reported for the silica particles disclosed herein are those reported in the literature. The silica particles disclosed herein are generally in the range of 20-40 μm. 2 The powder mixture may have a specific surface area of ​​0.1 μm / g, a particle size distribution with a d50 of 200-250 μm, and a purity of greater than 99.999% relative to 100% pure silica. The powders were weighed and combined in a molar ratio that would form a cordierite phase upon sintering to create a powder mixture. The powder mixture was then transferred to a ball milling container. Ethanol was added to the powder mixture in an amount of 120% by powder weight to form a slurry, and a mixing medium was added in an amount of 100% by powder weight to promote mixing between the powders comprising the powder mixture. The slurry was ball milled for 16 hours, and the ethanol was removed from the slurry using rotary evaporation, as known to those skilled in the art. After drying, the powder mixture was subjected to a planetary milling process, as known to those skilled in the art, for a duration of 30 minutes. The powder mixture was then calcined at 600°C for 8 hours. Calcination reduces the moisture content, increases crystallinity, and may potentially reduce the surface area. The powder mixture may optionally be sieved, blended, crushed, etc., either before or after calcination. The calcined powder mixture was 23-27 m 2The calcined powder mixture had a surface area of ​​about 1 / g, a particle size distribution of d10 of about 1.5 μm, d50 of about 13 μm, and d90 of about 85 μm, and a purity of 99.7365%. The calcined powder mixture was then sintered under vacuum at 1180°C and 30 MPa for 30 minutes, according to the method disclosed herein. The average density of five measurements, measured using the Archimedes method, was 2.62 g / cc, or 98.5% of theoretical density. The apparent silica-containing regions in the microstructure caused a dispersion in the thermal expansion coefficient and subsequent microcracking, similar to that shown in Figure 5. Therefore, to reduce or eliminate the silica-rich regions in the sintered body and prevent microcracking, a silica starting powder with a primary particle size of about 100 nm and a d50 of about 9 μm or less was used, with the smallest possible d90 particle size, such as 10-75 μm, preferably less than 70 μm, and a d50 of 8-20 μm. 2 It may be preferable to perform a mixing / milling process that results in a calcined powder mixture having an SSA of 1 / g.

[0235] Example: Sample 015 Cordierite sintered body

[0236] A powder mixture was prepared containing alumina, magnesia, and silica powders combined in relative amounts to form a sintered body containing phase-pure crystalline cordierite. The alumina powder was approximately 6.5-8.5 m 2 The magnesia powder had a specific surface area (SSA) of about 5.5 to about 6.5 μm / g, a particle size distribution of about 0.07 to 0.09 μm in d10 particle size, about 0.15 to 0.25 μm in d50 particle size, and about 0.5 to 1 μm in d90 particle size, and a purity of 99.999% relative to 100% pure alumina powder. 2The silica had a specific surface area of ​​1000 nm / g, a particle size distribution with a d10 of about 0.09 to about 0.2 μm, a d50 of about 1.0 to 2.5 μm, and a d90 of about 18 to 28 μm, and a purity of 99.99% relative to 100% pure magnesia. The silica preferably comprises pyrogenic silica powder. Due to its method of manufacture (e.g., by flame pyrolysis of silicon-containing compounds such as silicon tetrachloride or sand), pyrogenic silica powder (or fumed silica powder) contains substantially non-spherical aggregates or aggregates with very high aspect ratios. Therefore, when measuring fumed silica powder, results using the laser scattering particle size distribution method disclosed herein may not provide sufficient accuracy. Therefore, the particle sizes reported for the fumed silica powders disclosed herein are those reported in the literature. The silica powders disclosed herein have a primary particle size of about 100 nm (primary particles include single particles or single crystallites), a d50 of about 9 μm, and a pore size of about 28 to 32 μm. 2 The powders may have a specific surface area of ​​100% / g and a purity of greater than 99.999% relative to 100% pure silica. Powders were weighed and combined in a molar ratio that would form a cordierite phase upon sintering to create a powder mixture. The powder mixture was then transferred to a container for tumbling (vertical or end-over-end) grinding. Approximately 250% ethanol based on the powder weight was added to the powder mixture to form a slurry, and approximately 150% high-purity (approximately 99.99% as measured using ICPMS) media based on the powder weight was added to facilitate mixing of the powder mixture. After mixing at approximately 20 RPM for 20 hours, the slurry containing the powder mixture was removed from the mixer, and the ethanol was removed from the slurry using rotary evaporation methods known to those skilled in the art. The mixture was then calcined at 600°C for 8 hours. The calcined powder mixture may optionally be sieved, tumbled, blended, or the like, according to known methods after calcination. The powder mixture has a surface area of ​​18-20 m (measured according to BET surface area measurement in accordance with ASTM C1274). 2 / g, a particle size distribution (measured using a Horiba Model LA-960 Laser Particle Size Distribution Analyzer as disclosed herein) of d10=0.10-0.25 um, d50=0.25-0.35 um, and d90=65-75 um, and a purity of 99.9993 (measured using an Agilent 7900 ICP-MS Model G8403 ICP-MS). The calcined powder mixture was then sintered under vacuum at a temperature of 1200°C and a pressure of 15 MPa for 30 minutes according to the method disclosed herein. The average density of five measurements (using the Archimedes method according to ASTM B962-17) was 2.573 g / cc or 96.73% of the theoretical density of cordierite, which is reported to be 2.66 g / cc (DRLide, CRC Handbook of Chemistry and Physics, CRC press (2012)). Accordingly, a volume or bulk porosity of 3.27% is calculated from the density measurements. The combined X-ray diffraction, SEM, and image analysis (using ImageJ analysis software) methods disclosed herein were performed on Sample 015.

[0237] X-ray diffraction revealed that the sintered body contained approximately 95% by volume of cordierite, as determined by comparison of peak intensity ratios known to those skilled in the art, and approximately 5% by volume of an alumina-rich sapphirine crystalline phase ((Mg,Al)(Al,Si)O, denoted by "S"), as shown in FIG. 20 ) was confirmed to be included.

[0238] To determine the phase purity with greater precision, for example, up to about 98%, SEM images were taken using backscattering detection (BSD) techniques known to those skilled in the art. Using BSD, the cordierite phase appears light gray, aluminum oxide and / or alumina-rich phases appear black or dark gray, and porosity, if present, also appears black. To identify the crystalline phases and any porosity present (for sample 015), as shown in Figure 8, images were taken at 1000x magnification using BSD techniques known to those skilled in the art. To distinguish between black regions containing sapphirine crystalline phase and those containing porosity, the BSD images were processed with black and white thresholds using ImageJ processing software to highlight dark or black regions that may contain either porosity or sapphirine crystalline phase. The total area of ​​the surface containing either porosity or sapphirine crystalline phase was calculated.

[0239] Using the topography mode of the BSD detector, topography images (as shown in FIG. 9 ) were acquired across the entire surface of the cordierite sintered body. To identify regions or areas containing porosity, the topography images were processed with black and white thresholds using ImageJ processing software to highlight black regions within the image that may contain porosity or surface defects. The total area of ​​the surface containing porosity was calculated from the topography images and subtracted from the total area of ​​the surface containing either porosity or the sapphirine crystalline phase to obtain both the percentage of the surface containing porosity and the percentage of the surface containing sapphirine. Using the disclosed topography method, at least one surface of the cordierite sintered body may contain porosity in an amount of less than about 1%, preferably less than about 0.9%, preferably less than about 0.8%, preferably less than about 0.6%, preferably less than about 0.3%, preferably less than about 0.1%, and preferably less than about 0.05%, relative to the total area of ​​the at least one surface.

[0240] Image analysis measurements were performed on the cordierite sintered body according to the example using the topography image of FIG. 9. The measurements showed that the cordierite sintered body had pores with a maximum pore diameter of 5 μm or less throughout the entire surface (as shown by feature 1 in FIG. 9). Features 2, 3, and 4 in FIG. 9 had pore diameters of 2 μm, 2 μm, and 3 μm, respectively. Using SEM and ImageJ processing, a minimum pore diameter of approximately ±0.1 μm can be measured. Therefore, the cordierite sintered body according to this example has a surface containing pores with diameters of 0.1 μm to 5 μm, preferably 0.1 μm to 4 μm, 0.1 μm to 3 μm, 0.1 μm to 2 μm, or 0.1 μm to 1 μm, as measured using SEM images and ImageJ processing.

[0241] The surface of the cordierite sintered body contains about 2% to about 5% sapphirine phase as measured using XRD, SEM, and ImageJ methods, and thus a cordierite sintered body containing about 95 to 98% cordierite phase and about 2 to 5% sapphirine phase is disclosed herein.

[0242] A number of embodiments are disclosed herein. Nevertheless, 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. A method for producing a cordierite sintered body, comprising the following steps: a) Silicon dioxide (SiO ２ ), magnesium oxide (MgO), and aluminum oxide (Al ２ O ３ ) to form a powder mixture; b) calcining the powder mixture by heating to raise the temperature of the powder mixture to a calcination temperature and maintaining the calcination temperature to form a calcined powder mixture; c) placing the sintered powder mixture in a volume defined by a tool set of a spark discharge plasma sintering apparatus and creating a vacuum within the volume; d) applying pressure to the fired powder mixture while heating to a sintering temperature to form a cordierite sintered body; e) a step of lowering the temperature of the cordierite sintered body.

2. Furthermore, the following steps: f) optionally annealing the cordierite sintered body by applying heat to raise the temperature of the cordierite sintered body until the annealing temperature is reached; and The method of claim 1 , further comprising: g) reducing the temperature of the annealed cordierite sintered body.

3. 3. The method of claim 1 or 2, further comprising the step of: h) machining the cordierite sintered body to produce cordierite sintered components such as photolithography reticles, supports for optical elements, vacuum chucks, electrostatic chucks, support chucks, reticle chucks for use in microlithography processes, and the like.

4. 3. The method according to claim 1, wherein the pressure is from 5 MPa to 100 MPa.

5. The method according to claim 1 or 2, wherein the sintering temperature is 800 to 1300°C.

6. 3. The method of claim 1 or 2, wherein the calcined powder mixture has a purity of 99.95% or greater as measured using ICPMS techniques.

7. The calcined powder mixture has a surface area of ​​8 to 20 m as measured using BET surface area analysis, measured in accordance with ASTM C1274. ２ 3. The method according to claim 1 or 2, wherein the specific surface area is 0.15 to 0.25 μm / g.

8. 10. The method of claim 1, wherein the powder is free of naturally occurring materials including talc, kaolin, gibbsite, dolomite, sepiolite, forsterite, and other clays and clay-based compounds.

9. 10. The method of claim 8, wherein the powder, powder mixture, and calcined powder mixture are each free of naturally occurring materials including talc, kaolin, gibbsite, dolomite, sepiolite, forsterite, and other clays and clay-based compounds.

10. 10. The method of claim 8 or 9, wherein the cordierite sintered body is free of naturally occurring materials including talc, kaolin, gibbsite, dolomite, sepiolite, forsterite, and other clays and clay-based compounds.

11. 10. The method of claim 8 or 9, wherein each of the powder, powder mixture, and fired powder mixture is substantially free of glass-forming ingredients, including alkali metal elements including lithium (Li), sodium (Na), and potassium (K); alkaline earth metal elements including calcium (Ca), strontium (Sr), and barium (Ba); transition metal elements including chromium (Cr), nickel (Ni), iron (Fe), copper (Cu), zinc (Zn), lead (Pb), rubidium (Rb); metalloid elements including boron (B), germanium (Ge), arsenic (As), antimony (Sb), and bismuth (Bi).

12. 10. The method of claim 8 or 9, wherein the cordierite sintered body is free of glass-forming ingredients, including alkali metal elements including lithium (Li), sodium (Na), and potassium (K); alkaline earth metal elements including calcium (Ca), strontium (Sr), and barium (Ba); transition metal elements including chromium (Cr), nickel (Ni), iron (Fe), copper (Cu), zinc (Zn), lead (Pb), rubidium (Rb); and metalloid elements including boron (B), germanium (Ge), arsenic (As), antimony (Sb), and bismuth (Bi).

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