Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C14/00—Glass compositions containing a non-glass component, e.g. compositions containing fibres, filaments, whiskers, platelets, or the like, dispersed in a glass matrix
  • C03C14/006—Glass compositions containing a non-glass component, e.g. compositions containing fibres, filaments, whiskers, platelets, or the like, dispersed in a glass matrix the non-glass component being in the form of microcrystallites, e.g. of optically or electrically active material
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C14/00—Glass compositions containing a non-glass component, e.g. compositions containing fibres, filaments, whiskers, platelets, or the like, dispersed in a glass matrix
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
  • C09K5/08—Materials not undergoing a change of physical state when used
  • C09K5/14—Solid materials, e.g. powdery or granular
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28B1/00—Producing shaped prefabricated articles from the material
  • B28B1/26—Producing shaped prefabricated articles from the material by slip-casting, i.e. by casting a suspension or dispersion of the material in a liquid-absorbent or porous mould, the liquid being allowed to soak into or pass through the walls of the mould; Moulds therefor ; specially for manufacturing articles starting from a ceramic slip; Moulds therefor
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B19/00—Other methods of shaping glass
  • C03B19/02—Other methods of shaping glass by casting molten glass, e.g. injection moulding
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B19/00—Other methods of shaping glass
  • C03B19/06—Other methods of shaping glass by sintering, e.g. by cold isostatic pressing of powders and subsequent sintering, by hot pressing of powders, by sintering slurries or dispersions not undergoing a liquid phase reaction
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B19/00—Other methods of shaping glass
  • C03B19/06—Other methods of shaping glass by sintering, e.g. by cold isostatic pressing of powders and subsequent sintering, by hot pressing of powders, by sintering slurries or dispersions not undergoing a liquid phase reaction
  • C03B19/066—Other methods of shaping glass by sintering, e.g. by cold isostatic pressing of powders and subsequent sintering, by hot pressing of powders, by sintering slurries or dispersions not undergoing a liquid phase reaction for the production of quartz or fused silica articles
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B20/00—Processes specially adapted for the production of quartz or fused silica articles, not otherwise provided for
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C14/00—Glass compositions containing a non-glass component, e.g. compositions containing fibres, filaments, whiskers, platelets, or the like, dispersed in a glass matrix
  • C03C14/004—Glass compositions containing a non-glass component, e.g. compositions containing fibres, filaments, whiskers, platelets, or the like, dispersed in a glass matrix the non-glass component being in the form of particles or flakes
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
  • C04B35/14—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on silica
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/64—Burning or sintering processes
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
  • F27B14/00—Crucible or pot furnaces
  • F27B14/08—Details specially adapted for crucible or pot furnaces
  • F27B14/10—Crucibles
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2214/00—Nature of the non-vitreous component
  • C03C2214/04—Particles; Flakes
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2214/00—Nature of the non-vitreous component
  • C03C2214/08—Metals
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2214/00—Nature of the non-vitreous component
  • C03C2214/16—Microcrystallites, e.g. of optically or electrically active material
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2214/00—Nature of the non-vitreous component
  • C03C2214/30—Methods of making the composites
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
  • F27B14/00—Crucible or pot furnaces
  • F27B14/08—Details specially adapted for crucible or pot furnaces
  • F27B2014/0843—Lining or casing
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/13—Hollow or container type article [e.g., tube, vase, etc.]
  • Y10T428/131—Glass, ceramic, or sintered, fused, fired, or calcined metal oxide or metal carbide containing [e.g., porcelain, brick, cement, etc.]

Definitions

• the invention relates to a composite material with a matrix of fused silica, in which regions of silicon-containing phase - "Si phase" - have been embedded.
• the invention further concerns a heat-absorbing component composed of the composite material, and also a method for producing it by forming a porous shaped body from a powder mixture comprising amorphous fused silica powder and a silicon-containing powder - "Si powder" - and/or from a mixed powder of amorphous fused silica interspersed with silicon-containing phase - "Si-SiO 2 powder” - and compacting the shaped body to give the composite material.
• a heat-absorbing component composed of the composite material
• Fabrication processes for semiconductor components and optical displays use a host of equipment such as reactors, apparatuses, carrier trays, bells, crucibles, protective shields, or else more simple components such as tubes, rods, plates, flanges, rings or blocks. They are required to satisfy exacting requirements in respect of purity, chemical and thermal stability, and mechanical strength. They may consist, for example, of stainless steel, but are increasingly being made from fused silica. The reason is that, given high purity, the silicon dioxide material behaves inertly towards the usual semiconductor materials. Fused silica, moreover, is notable for high chemical stability with respect to numerous process media, and also for high stability with respect to fluctuating temperatures.
• An apparatus for the heat treatment of individual semiconductor wafers is known from DE 695 27 918 T2. It comprises a dome-shaped reactor vessel and a heater which is installed outside the reactor vessel, in the ceiling portion.
• the reactor vessel is produced as a one-part fused silica body without a welded portion, and in the heat-exposed ceiling portion is made from transparent fused silica, and otherwise from opaque fused silica.
• Fused silica is brittle and cannot be worked mechanically as easily as, for instance, metal.
• the mechanical working is improved according to
• US 6,486,084 B2 by a composite material of the generic type stated at the outset, in which a fused silica matrix is intercalated with a second phase comprising silicon, SiC, silicon nitride, titanium nitride or titanium carbide.
• the weight fraction of the fused silica phase is approximately 60% to 85%.
• the Si-SiO 2 composite material is produced by mixing silicon powder having an average particle size of 0.9 ⁇ and a purity of 99.99% with fused silica powder having an average particle size of 0.6 ⁇ , hot-pressing the powder mixture to form a shaped body, and then sintering this body under reduced pressure at 1400°C to give the composite material. It has an open porosity of 1 %.
• Si phase also referred to below as "Si phase” - makes up not more than 5% by weight, and is provided on the basis of silicon powder having a particle size of not more than 100 ⁇ .
• the composite material features high temperature resistance and dimensional stability even in a humid atmosphere.
• Composite materials comprising heat-absorbing black fused silica are also employed for applications in which rapid temperature changes occur, such as in the case of lamp-assisted RTP (Rapid Thermal Processing) systems, for instance.
• RTP Rapid Thermal Processing
• One particular challenge here is the reproducible establishment of a uniform temperature distribution on the semiconductor wafer to be treated.
• Nonuniformities in the treatment temperature can lead to nonuniform physical properties, such as, for example, in the particle size and in the concentration of dopants, which may destroy an electronic circuit and reduce the yield.
• porous SiO 2 material is treated with a reductive, carbon-containing medium, such as carbon monoxide for instance, at an elevated temperature of around 100 to 800°C, and is subsequently vitrified at a temperature of around 1300 to 1900°C.
• a reductive, carbon-containing medium such as carbon monoxide for instance
• a component of this kind When a component of this kind is used under oxidizing conditions, however, it is necessary to protect the carbon from oxidation, in the form, for example, of a protective layer of pure SiO 2 .
• a protective layer of this kind may intensify the reflection of the component.
• Fine-grained powders can easily cake together, and so one difficulty when producing the known composite material is to mix the finely divided fused silica powder uniformly with the finely divided metal or semimetal powder. The consequence is a heterogeneous distribution of the phases within the composite material, which in turn promotes the devitrification tendency of the fused silica phase.
• the component comprising the composite material may fail as a result of crystallization and cracking.
• the known composite material exhibits open porosity and is therefore not suitable for applications where high purity or imperviousness to gas are important factors. Over the course of the deployment, contaminants may collect in the open pores and reach the material to be treated. It is an object of the invention, therefore, to provide a composite material which is suitable for the production of components for use in high-temperature processes for heat treatment even when exacting requirements are imposed on
• a further object of the invention is to specify a method which permits reproducible production of a composite material of this kind.
• this object is achieved, starting from a composite material of the generic type specified at the outset, in accordance with the invention by a composite material which is impervious to gas, has a closed porosity of less than 0.5% and a specific density of at least 2.19 g/cm 3 , and at a temperature of 1000°C has a spectral emissivity of at least 0.7 for wavelengths between 2 and 8 ⁇ .
• the matrix of the composite material of the invention is either opaque but preferably translucent or transparent.
• the matrix is intercalated in very fine division with regions of a phase that comprises silicon (Si) in elemental form and is referred to here as "Si phase".
• the Si phase consists of an Si-based alloy, of doped silicon or of undoped silicon. At its most simple it is polycrystalline, though it can also be monocrystalline or amorphous.
• the finely divided regions of the Si phase act within the matrix firstly as optical defect sites, and give the composite material - according to layer thickness - a black or blackish-grey visual appearance at room temperature. Secondly, the defect sites also have consequences for the absorption of heat by the composite material overall. This is essentially attributable to the properties of the
• semiconducting elemental silicon whereby on the one hand the energy between valency band and conduction band (band-gap energy) decreases with the temperature, and on the other hand, given sufficiently high activation energy, electrons are promoted from the valency band into the conduction band, a process associated with a significant rise in the absorption coefficient.
• the thermally activated occupation of the conduction band means that semiconducting silicon (in the following also referred to as "elemental silicon”) is to a certain extent transparent for certain wavelengths (such as above about 1000 nm) at room temperature and is opaque at high temperatures. This effect is dependent on factors including structure (amorphous/crystalline) and doping of the silicon, is noticeable above about 600°C, and reaches saturation above about 1000°C.
• spectral absorptivity % and spectral emissivity ⁇ % of a real body in thermal equilibrium correspond to one another.
• the spectral emissivity ⁇ can be calculated as follows:
• the emissivity is at least 0.7, and preferably, indeed, more than 0.75.
• the reflectance for wavelengths between 2 and 8 ⁇ and at temperatures above 1000°C is therefore not more than 0.3.
• the composite material of the invention is predestined as a thermal radiation absorber and diffuser for service in heat treatments at high temperatures above 600°C, more particularly above 800°C and very preferably at 1000°C or more.
• the composite material of the invention exhibits high absorption capacity and emission capacity for thermal radiation between 2 ⁇ and 8 ⁇ , in other words in the wavelength range of infra-red radiation.
• the high absorption capacity for thermal radiation reduces the reflection thereof at the surfaces of the composite material. In this way, instances of local, non-reproducible heating as a result of reflected thermal radiation are avoided, and a uniform temperature distribution is obtained in the environment of the composite material.
• the "spectral emissivity” referred to here is the "normal spectral emissivity”. This quantity is determined on the basis of a measurement principle which is known under the designation "Black-Body Boundary Conditions” (BBC) and is published in "DETERMINING THE TRANSM ITTANCE AND EMITTANCE OF TRANSPARENT AND SEM TRANSPARENT MATERIALS AT ELEVATED TEMPERATURES”; J. Manara, M. Keller, D. Kraus, M. Arduini-Schuster; 5th European Thermal-Sciences Conference, The Netherlands (2008).
• the Si phase is very finely and homogeneously distributed within the fused silica matrix. Although it bears directly against the surface, there is no need for a coating to protect from oxidation. A coating would otherwise lead to additional unwanted reflections at the interface with the composite material.
• the composite material of the invention exhibits surprising structural properties. It is impervious to gas - that is, it has no open porosity - and the volume fraction of closed pores within the composite material - at less than 0.5% - is relatively low. This is also a reason for the surprisingly high density of at least 2.19 g/cm 3 .
• the specific densities of transparent, undoped fused silica and of elemental silicon are similar and are situated at approximately 2.2 g/cm 3 or at 2.33 g/cm 3 (silicon).
• the matrix preferably comprises small pores having a maximum pore dimension of less than 10 ⁇ .
• the pores are formed predominantly between sintered SiO 2 particles, and generally have a non-circular form.
• the fused silica of the matrix over a large wavelength range, appears not very opaque, but instead more translucent or even transparent.
• thermal radiation is able to penetrate deeply into the material, and in this way reaches lower-lying absorption centres in the form of regions composed of Si phase. This therefore contributes to greater heat absorption.
• the spatial resolution of standard spectrometers does not allow the transmission of the matrix to be determined free of influence by the interspersed Si phase.
• the transparency or translucency of the matrix is evident, however, from the absence of visible bubbles under the microscope.
• bubble-free fused silica With bubble-free fused silica, the direct spectral transmission at a path length of 1 mm in the wavelength range from 600 nm to 2650 nm is at least 0.3.
• the composite material of the invention does not have any open porosity, a simple density measurement is possible in accordance with the principle of Archimedes.
• the porosity is determined from the density measurement, taking account of the specific composition of the composite material and of the specific densities of fused silica matrix and Si phase.
• the absorption of heat by the composite material is dependent on the proportion of the Si phase.
• the weight fraction of the Si phase ought therefore preferably to be at least 0.1 %.
• a high volume fraction of the Si phase may hinder the production of the composite material.
• the weight fraction of the Si phase is preferably not more than 5%.
• the matrix of the composite material of the invention consists preferably of fused silica having a hydroxyl group content of not more than 30 ppm by weight.
• hydroxyl groups are therefore unfavourable in respect of a high dimensional stability under thermal load.
• the hydroxyl group content of transparent fused silica is customarily determined from an infra-red transmission measurement. For the heat-absorbing composite material, however, this method of measurement is not readily suitable. For this reason, the hydroxyl group content of the composite material is determined on the basis of emission measurements in the range of the absorption wavelength of the hydroxyl groups in fused silica (at 2.72 ⁇ ), by comparison with a standard of known hydroxyl group content.
• the matrix consists of undoped or doped fused silica.
• Doped fused silica in the sense of the invention may comprise, apart from SiO 2 , other oxidic, nitridic or carbidic components, in an amount up to a maximum of 20% by weight.
• the Si phase, besides silicon, may also comprise other semimetals or metals, but not more than up to 50% by weight, more preferably not more than 20% by weight.
• provision is made for the Si phase to consist of silicon having a metallic purity of at least 99.99%, and for the matrix to have a chemical purity of at least 99.99% SiO 2 and a cristobalite content of not more than 1 %.
• the silicon in the Si phase may take up oxygen, nitrogen or carbon.
• metallic purity is meant the chemical purity solely of the metallic and/or semimetallic constituents of the phase, disregarding any non-metallic constituents, such as oxides, nitrides, carbides, oxynitrides and the like.
• a low cristobalite content in the matrix ensures a low devitrification tendency and hence a low risk of cracking in service.
• a particularly high emissivity can be achieved if the Si phase exhibits non- spherical morphology with maximum dimensions of on average less than 20 ⁇ , but preferably more than 3 ⁇ .
• the non-spherical morphology of the Si phase also contributes to a high mechanical strength and to a low tendency on the part of the composite material towards cracking.
• the "maximum dimension" relates to the longest extent of an isolated region with Si phase that can be seen in a ground section. The median value of all of the longest extents in a ground-section image forms the average value specified above.
• the object stated above is achieved in accordance with the invention by a component which has at least one surface formed of the composite material that consists of a matrix of fused silica, in which regions of silicon-containing phase - "Si phase" - have been embedded, that is impervious to gas, and that has a closed porosity of less than 0.5% and a specific density of at least 2.19 g/cm 3 , and, at a temperature of 1000°C, has a spectral emissivity of at least 0.7 for wavelengths between 2 and 8 ⁇ .
• the component of the invention consists wholly or partly of the composite material according to the invention. Where the component consists only partly of the composite material, said material forms at least part of the surface. On account of its chemical composition, a coating comprising the composite material is particularly suitable for application to fused silica, in other words for production of fused silica/composite material assemblies.
• the component, or at least the surface of the component has the optical and structural properties elucidated above for the composite material of the invention, particularly with regard to the high emissivity of at least 0.7 - preferably at least 0.75 - and the low reflectance of not more than 0.3 at wavelengths between 2 and 10 ⁇ and at a temperature of 1000°C.
• the component possesses a fused silica matrix with a low pore content and with elemental Si phase incorporated therein in finely divided but encapsulated form. Even in the case of thin layers - above about 1 mm - the component is opaque in the visible wavelength range, but otherwise largely has the chemical and mechanical properties typical of fused silica.
• the component is especially suitable also for applications where high thermal and chemical stability and high resistance with respect to corrosive gases and liquids are important factors.
• Such requirements often exist for components in semiconductor fabrication, in optics, and in chemical engineering.
• the component is visually appealing, and so uses from an artistic or aesthetic aspect also come into consideration.
• the high emissivity of the composite material predestines the
• the component of the invention is designed for example as a reactor, fitting or wafer holder for use in an oxidizing or heat-treating operation, in epitaxy or in chemical vapour deposition.
• the component takes the form, for example, of a vessel, dish, enclosure, as a solid body, hollow body in expanded or curved form. In simple cases it is configured as a plate, ring, flange, dome, crucible or solid or hollow cylinder.
• the composite material may be present in the form of a solid body or a layer. In the latter case, for example, in the form of a fused silica/composite material assembly as a hollow cylinder having a hollow cylinder wall composed of a plurality of coaxial layers, of which one consists of the composite material.
• the object specified above starting from a method of the generic type specified at the outset, is achieved in accordance with the invention in that the forming of the shaped body comprises a slipcasting process in which a suspension is produced that comprises the powder mixture and/or the mixed powder in a liquid, the suspension is consolidated by removal of liquid to form a green body, and the shaped body is formed from the green body by drying.
• the shaped body is formed by hot pressing of a powder mixture.
• the method of the invention comprises a slipcasting process in which, ahead of the shaped body, an intermediate is produced in the form of a green body.
• Both the slipcasting process itself and the intermediate state in the green body allow measures for the setting and alteration of properties having consequences from the ultimate composite material.
• the processing of the initial powders in the suspension facilitates intimate mixing with one another and the establishment of a homogeneous distribution in the green body.
• the liquid also has the function of a binding agent or activating agent between the solid components. In the course of a long-lasting homogenizing operation, the liquid may alter the surfaces of the powder particles and give rise in particular to interactions between them, something which on subsequent sintering may contribute to a more impervious and more stable bond.
• the suspension may be based on an organic solvent, preferably on an alcoholic basis or more preferably on an aqueous basis.
• the polar nature of the aqueous phase may be beneficial to the aforementioned interactions of the fused silica particles with one another and with the Si powder particles, thereby facilitating the drying and sintering of the green body.
• the assembly of fused silica phase and Si phase is porous and can be modified via the gas phase, with particular mention being made of doping and reactive drying.
• the green body in general already has a shape which comes close to the final contour of the component that is to be produced.
• the shape in question is, for example, a solid body, a hollow body, or a layer on a base body.
• the green body can be obtained by casting the suspension into a mould.
• other processing methods for the suspension are also suitable, such as introduction into a mould under suction, or else dipping, spraying, brushing on, trowelling on, transfer, deposition, knifecoating and the like.
• the green body is dried and a largely water-free shaped body is obtained from it. As an inevitable result of its production, however, the green body contains a large amount of hydroxyl groups. It is sintered to form a gas-impervious, mechanically stable component comprising the composite material.
• the sintering temperature here is to be selected such that while the Si phase does not melt, the density achieved for the sintered composite material is as high as possible.
• sintering temperature sintering temperature, sintering time, atmosphere
• the SiO 2 content of the amorphous fused silica particles is preferably at least 99.99% by weight.
• the solids fraction of a suspension prepared using such particles consists of SiO 2 to an extent of at least 99.99% by weight. Binders or adjuvants of that kind are not provided.
• the level of impurities is preferably less than 1 ppm by weight. This starting material does not pose any risk of
• the shaped body In order to avoid melting of the Si phase during sintering of the shaped body, the shaped body is heated to a sintering temperature below the melting temperature of the semimetal.
• the shaped body here is held at the sintering temperature for a period of at least 30 minutes.
• Figure 1 shows a flow diagram to illustrate the production of one embodiment of the fused silica component of the invention for use in semiconductor fabrication, on the basis of one procedure according to the invention
• Figure 2 shows a diagram with the normal emissivity as a function of the
• Figure 3 shows a diagram of the normal emissivity as a function of the
• Figure 4 shows a diagram of the normal emissivity as a function of the
• Figure 5 shows a diagram of the normal emissivity as a function of the
• the method of the invention is elucidated by way of example hereinafter, using the production of a heat insulation ring made of fused silica for an RTP reactor for the treatment of a wafer, with reference to Figure 1 .
• Sample 1 For a batch of 10 kg of base slip 1 (SiO 2 /water slip), in a drum mill having a fused silica lining and a capacity of approximately 20 litres, 8.2 kg of amorphous granular fused silica 2, obtained by fusing natural raw silica material and having particle sizes in the range between 250 ⁇ and 650 ⁇ , are mixed with 1 .8 kg of deionized water 3 having a conductivity of less than 3 S.
• the granular fused silica 2 has been purified beforehand in a hot chlorinating process; it is ensured that the cristobalite content is below 1 % by weight.
• This mixture is ground on a roller bed at 23 rpm, using fused silica grinding balls, for a period of 3 days until the base slip 1 is homogeneous and has a solids content of 78%.
• the grinding balls are subsequently removed from the resultant base slip 1 , and an admixture is made, in the form of silicon powder 4 having a metallic purity of 99.99%, in an amount such as to give a solids content of 83% by weight.
• the silicon powder 4 consists of substantially non-spherical powder particles with a narrow particle size distribution, whose D 97 is approximately 10 ⁇ and whose fine fraction, with particle sizes of less than 2 ⁇ , has been removed beforehand.
• the silicon powder 4 is dispersed uniformly in the base slip 1 by continuous mixing.
• the slip filled with the silicon powder 4 is homogenized for a further 12 hours.
• the homogeneous slip 5 obtained in this way has a solids content of 83%.
• the weight fraction of the silicon powder as a proportion of the overall solids content is 5%, and the volume fraction, owing to the similar specific densities of SiO 2 and Si, is likewise almost 5% - more precisely, 4.88%.
• the SiO 2 particles 2 in the fully homogenized slip 5 exhibit a particle size distribution characterized by a D 50 of about 8 ⁇ and by a D 90 of about 40 ⁇ .
• the slip 5 is cast into a pressure casting mould in a commercial pressure casting machine and dewatered via a porous polymeric membrane, to form a porous green body 6.
• the green body 6 has the shape of a ring for an RTP reactor for the treatment of wafers.
• the green body 6 is dried in a ventilated oven at about 90°C for five days and, after cooling, the resulting porous blank 7 is worked mechanically almost to the final dimensions of the fused silica ring 8 to be produced.
• the blank 7 For the sintering of the blank 7, it is heated in a sintering oven, under air, to a heating temperature of 1390°C over the course of an hour, and is held at this temperature for 5 h. Cooling takes place with a cooling ramp of 1 °C/min to an oven temperature of 1000°C, and thereafter without regulation, with the oven closed.
• the resulting fused silica ring 8 is superficially abraded to give an average surface roughness Ra of approximately 1 ⁇ . It consists of a gas-impervious composite material having a density of 2.1958 g/cm 3 , in which non-spherical regions of elemental Si phase, separated from one another in a matrix of opaque fused silica, are distributed homogeneously, the size and morphology of these Si phase regions corresponding largely to those of the Si powder employed. The maximum dimensions are on average (median value) in the range from about 1 to 10 ⁇ .
• the composite material is stable in air to a temperature of up to about 1200°C.
• the matrix is translucent to transparent. When viewed under a microscope, it exhibits no open pores, and at most closed pores with maximum dimensions of on average less than 10 ⁇ ; the porosity as calculated on the basis of the density is 0.37%, assuming a theoretical matrix density of 2.2 g/cm 3 and a theoretical Si phase density of 2.33 g/cm 3 .
• the incorporated Si phase contributes to the opacity and also has consequences for the thermal properties of the composite material overall.
• This composite material exhibits high absorption of thermal radiation at high temperature. This is shown by the diagram of Figure 2, with the spectral profile of the emissivity of this material. The emissivity at room temperature is measured in a customary way, using an Ulbricht sphere. This allows measurement of the directional hemispherical spectral reflectance R d h and of the directional hemispherical spectral
• T dh transmittance T dh , from which the normal spectral emissivity is calculated.
• the measurement at elevated temperature in the wavelength range from 2 to 18 ⁇ takes place by means of an FTIR spectrometer (Bruker IFS 66v Fourier Transform Infra-red (FTIR)), to which a BBC sample chamber is coupled via an additional optical system, on the basis of the aforementioned BBC measurement principle.
• FTIR FTIR spectrometer
• This sample chamber in the half-spaces in front of and behind the sample mount, has temperature-conditionable black-body surrounds and a beam exit opening with detector. The sample is heated to a predetermined temperature in a separate oven, and for measurement is moved into the beam path of the sample chamber, with the black-body surrounds set to the predetermined temperature.
• the intensity captured by the detector is composed of an emission component, a reflection component and a transmission component - that is, of intensity emitted by the sample itself, intensity impinging on the sample from the front half-space and reflected by said sample, and intensity which impinges on the sample from the rear half-space and is transmitted by said sample.
• Three measurements must be carried out in order to determine the individual parameters of emissivity, reflectance and transmittance.
• Figure 2 shows that the emissivity of sample 1 with 5% by weight Si phase in the wavelength range from 2 to about 4 ⁇ is heavily dependent on the temperature of the sample body. The greater the heating of the sample body, the higher the emission in this wavelength range, with no substantial difference being evident any longer between 1000°C and 1200°C. In the case of the samples heated to 1000°C and 1200°C, the normal emissivity in the whole of the wavelength range between 2 and 8 ⁇ is above 0.75; at the wavelength of 3 ⁇ it is 0.79.
• the emissivity increases essentially with the wavelength, but exhibits a pronounced minimum at approximately for measurement radiation of around 9 ⁇ .
• the minimum can be attributed to reflection by the fused silica of the matrix.
• the ring of composite material produced in this way surrounds a wafer that is to be treated.
• the internal diameter of this ring corresponds to the outer diameter of the wafer.
• the heating element of the RTP apparatus is generally configured as an array of IR emitters which are located in a plane above and/or below the combination of wafer and ring.
• the ring of composite material diminishes the effect of excessively rapid cooling at the wafer edge, and so contributes to uniform temperature distribution over the entire wafer surface.
• the composite material is predestined for applications where high heat absorption and low heat reflection, or a particularly homogeneous temperature distribution, are important factors. It may take a wide diversity of geometric forms, such as the form of a reactor, apparatus, carrier tray, bell, crucible or protective shield, or else the form of more simple components such as tubes, rods, plates, flanges, rings or blocks. Other examples include the following:
• Example 1 It has a density of about 2.16 g/cm 3 and a closed porosity of 2.5% and it acts primarily as a diffuse reflector, this being evident from the fact that it possesses a virtually constant direct spectral transmission of less than 10% in the wavelength range from 190 to 2650 nm with a path length of just 1 mm.
• the diagram of Figure 5 shows the spectral emissivity of this material (from two measurement runs) in the wavelength range between 0.25 ⁇ and 18 m at room temperature. In the visible wavelength range to approximately 2 ⁇ , the emissivity is less than 10%, a fact which can be attributed primarily to the high reflectivity of the opaque fused silica.

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