WO2021237071A1

WO2021237071A1 - Coating for heaters and crucibles

Info

Publication number: WO2021237071A1
Application number: PCT/US2021/033624
Authority: WO
Inventors: Sudarshan NATARAJAN; Anand Murugaiah
Original assignee: Momentive Performance Quartz Inc
Current assignee: Momentive Performance Quartz Inc
Priority date: 2020-05-22
Filing date: 2021-05-21
Publication date: 2021-11-25
Anticipated expiration: 2022-11-22

Abstract

Provided is a coating for a heater or crucible. The coating may comprise one or more of alumina, silica, or yttria. The coating may be dielectric. The coating may be applied to a heater or crucible comprising a ceramic composite material. The coating may be applied by thermal or plasma spray methods. The ceramic composite material may comprise (i) boron nitride (BN) and (ii) a conductive ceramic material conductive ceramic material that is a boride, carbide, aluminide, or silicide of a metal, such as titanium diboride (TiB2). The coating may apply to high temperature vacuum processes, high temperature metal evaporation, and other applications. In particular, the coating may be provided in aluminum metal evaporation applications as well as other evaporation or melting applications including electronics, solar cells, OLEDs, semiconductor and industrial processing and coating applications, coating applications with other metals (e.g. copper, zinc, silver, magnesium, and the like), etc. The coating, and heaters or crucibles thereof, may provide electoral isolation and shock resistance, corrosion resistance, as well as the ability to change or tune the mechanical strength, surface roughness, coefficient of friction, optical properties such as emissivity or emission wavelengths, and surface chemistry.

Description

TITLE

COATING FOR HEATERS AND CRUCIBLES

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application claims priority to and the benefit of U.S. Provisional

Application 63/028,991, titled “COATING FOR HEATERS AND CRUCIBLES,” filed on

May 22, 2020, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF INVENTION

[0002] The present disclosure relates generally to a coating for a heater or crucible and, more particularly, to a heater or crucible comprising (1) a ceramic composite material of (i) boron nitride (BN) and (ii) a conductive ceramic material, and (2) a ceramic coating disposed thereon. In embodiments, the ceramic coating comprises one or more of alumina, silica, or yttria.

BACKGROUND

[0003] High temperature vacuum processes are utilized in the industrial production of semiconductors, electronics, displays, sensors, solar cells, and the like. High temperature vacuum processes are also used in the chemical, metal, ceramic, and glass processing industry. Metal evaporation, for example, is a common application of high temperature vacuum processes, and can require temperatures upwards of 1200°C and pressures lower than 10² Torr in order to generally achieve a technically or economically viable process. [0004] Conventional heating element materials used to reach the high temperatures in these vacuum processes often exhibit poor resistance to corrosion by oxygen, nitrogen, hydrogen, moisture, and molten or vapor metal. Conventional heating element materials such as graphite, pyrolytic graphite, refractory metals such as tungsten, molybdenum, and tantalum, carbon fiber composites, and the like, cannot withstand oxygen, nitrogen, hydrogen, or moisture corrosion at temperatures exceeding 400°C. These heating element materials are also susceptible to corrosion through exposure to molten or vapor metals, such as aluminum, which is one of the most commonly used metals for metal evaporation using high temperature vacuum processes.

[0005] Due to the poor corrosion resistance to oxygen, nitrogen, hydrogen, moisture, and molten or vapor metal, heating elements incorporating these materials are limited in lifetime operation and operation flexibility. To combat these issues, the heating elements are often coated with ceramics, nitrides, carbides, and the like, and involve more complex engineering that cannot be easily machined. Refractory wires and foils, for example, require dielectric structural support. Even if the heating element materials, such as graphite, can be machined, the needed aspect ratio of the coil length to width or thickness to meet the electrical resistance per unit area specification is difficult to achieve. The protective coatings and designs result in additional costs to produce the heating elements. Further, while protective coatings may prevent corrosion of the heating element material, the protective coatings can also reduce the operating pressure and temperature of the system. Silicon carbide, for example, negatively impacts the system as the silicon evaporates from the coating in vacuum processes. Refractory wires and foils also suffer from brittleness by recrystallization and/or creep and/or warp affecting performance, i.e. temperature uniformity and reliability in a mechanical shock prone environment.

[0006] Another option is to use different heating element materials. For example, ceramic composites may be capable of machining and still be suitable for use in high temperature vacuum and high temperature metal evaporation processes, and other applications, without the need for a protective coating. Ceramic composites may be suitable for these processes due to their corrosion resistance. International App. No. PCT/US2019/067019, which is herein incorporated by reference in its entirety, describes intermetallic composites, such as composites of boron nitride (BN) and titanium diboride (T1B2), for use in heater applications. [0007] While bare heaters incorporating ceramic composites may be useful or beneficial in some applications, these heaters may not be suitable for certain other applications, such as heating electrically conductive metals and liquids, or use in combination with a crucible. For example, even though ceramic composites would theoretically provide similar advantages as described above, such as being molten metal resistant (particularly to aluminum), and would be a potential material for aluminum evaporation applications such as plastic packaging and OLED electrode applications, use of crucibles and heaters made of ceramic composites in these applications is generally not considered. This is because, for one, articles made of ceramic composites are electrically conductive as the ceramic composites themselves are electrically conductive. As a result, if the ceramic composites were to come into contact with a naked (i.e., uncoated) heater or fixture, such as tungsten or carbon-based heaters, the ceramic composite might electrically short the system. As a result, although high temperature vacuum and high temperature metal evaporation processes are often used in applications such as electronics, solar cells, OLEDs, semiconductor and industrial processing and coating applications, coating applications with other metals (e.g. copper, zinc, silver, magnesium, and the like), etc., conventional heating element materials such as refractory metals and graphite are still used in these applications.

[0008] To ahempt to avoid the shorting problem with ceramic based heaters, ceramic coatings and sleeves have been implemented. While ceramic sleeves made of hard ceramic may help to prevent electrical shorting, such ceramic sleeves are not a feasible solution due to costs, machining, manufacturing constraints, and the like. Hard ceramics, such as alumina, are also expensive due to machining costs and can further break easily during handling or from thermal shock during rapid thermal cycling to meet production targets. Alumina further has a poor thermal shock resistance. Ceramic sleeves of machinable ceramics, like boron nitride, need to be a sufficient thickness to prevent breakage, but such additional thickness can act as a thermal choke, which can increase heat up time or decrease the maximum temperature reached by the crucible or heater. Pyrolytic boron nitride is similarly a costly option.

SUMMARY

[0009] The following presents a summary of this disclosure to provide a basic understanding of some aspects. This summary is not intended to identify key or critical elements or define any limitations of embodiments or claims. Furthermore, this summary may provide a simplified overview of some aspects that may be described in greater detail in other portions of this disclosure.

[0010] Provided is a coating for a heater or crucible formed from a ceramic composite. Also provided is a heater or crucible formed from a ceramic composite where the heater or crucible comprises a coating on a surface thereof. The coated heaters and crucibles, may be used in high temperature vacuum processes, high temperature metal evaporation, and other applications, without electrically shorting the system. The coated heaters and crucibles may further provide additional benefits including one or more of corrosion resistance by oxygen, nitrogen, hydrogen, other gases or gas radicals such as chlorine, fluorine, moisture, and molten or vapor metal, abrasion resistance, as well as the ability to change or tune the mechanical strength, surface roughness, coefficient of friction, optical properties such as emissivity or emission wavelengths, and surface chemistry.

[0011] In one embodiment, the coating may comprise one or more of alumina, silica, or yttria. The coating may be dielectric. The coating may be applied to a heater or crucible comprising a ceramic composite material. The coating may be applied by thermal or plasma spray methods. The ceramic composite material may comprise (i) boron nitride (BN) and (ii) a conductive ceramic material conductive ceramic material that is a boride, carbide, aluminide, or silicide of a metal, such as, for example, titanium diboride (T1B2).

[0012] The coating may apply to high temperature vacuum processes, high temperature metal evaporation, and other applications. In particular, the coating may be provided in aluminum metal evaporation applications as well as other evaporation or melting applications including electronics, solar cells, OLEDs, semiconductor and industrial processing and coating applications, coating applications with other metals (e.g. copper, zinc, silver, magnesium, and the like), etc. The coating, and heaters or crucibles thereof, may provide electoral isolation and shock resistance, corrosion resistance, as well as the ability to change or tune the mechanical strength, surface roughness, coefficient of friction, optical properties such as emissivity or emission wavelengths, and surface chemistry.

[0013] In one aspect, provided is an article comprising an intermetallic composite substrate coated with a ceramic coating, the intermetallic composite substrate comprising boron nitride and a ceramic material, and the ceramic coating comprising alumina, yttria, silica, or a combination of two or more thereof.

[0014] In one embodiment, the intermetallic composite has a first coefficient of thermal expansion, and the ceramic coating has a second coefficient of thermal expansion, and the first coefficient of thermal expansion is within about 30% of the second coefficient of thermal expansion.

[0015] In one embodiment, wherein the first coefficient of thermal expansion is within about 10% of the second coefficient of thermal expansion.

[0016] In one embodiment in accordance with any of the previous embodiments, the intermetallic composite is a porous material having a porosity of from about 5% to about 25% based on the volume of the intermetallic composite.

[0017] In one embodiment in accordance with any of the previous embodiments, the intermetallic composite has an oxygen content of from about 1% to about 10% by weight of the substrate.

[0018] In one embodiment in accordance with any of the previous embodiments, the ceramic material of the intermetallic composite is selected from a boride, a carbide, an aluminide, or a silicide of a metal. In one embodiment, the metal is selected from Ti, Cu, Ni, Mg, Ta, Fe, Zr, Nb, Hf, V, W, Mo, and Cr.

[0019] In one embodiment in accordance with any of the previous embodiments, the ceramic material of the intermetallic composite is selected from TiAl, TiAb, CU2AI, NiAl, Ni Al, TaAb, TaAl, FeAl, Fe₃Al, Al₃Mg₂, TiB₂, TiB, ZrB_2, NbB₂, TaB₂, HfB₂, VB₂, TaB, VB, TiC, TaC, WC, HfC, VC, MoC, TaC, Cr?C₃. or a combination of two or more thereof. [0020] In one embodiment in accordance with any of the previous embodiments, the ceramic material of the intermetallic composite is a titanium boride.

[0021] In one embodiment in accordance with any of the previous embodiments, the ceramic material of the intermetallic composite is selected from a titanium boride and silica carbide.

[0022] In one embodiment, the silica carbide is present in an amount of from about

5% to about 35% by weight of the ceramic material.

[0023] In one embodiment in accordance with any of the previous embodiments, the intermetallic composite has a weight ratio of boron nitride to ceramic material of from 10:90 to about 90:10. In one embodiment, the weight ratio of boron nitride to ceramic material is from about 40:60 to about 60:40.

[0024] In one embodiment in accordance with any of the previous embodiments, the coating comprises a mixture of yttria and aluminua.

[0025] In one embodiment in accordance with any of the previous embodiments, the coating comprises a mixture of yttria, alumina, and silica.

[0026] In one embodiment in accordance with any of the previous embodiments, the coating has a thickness of from about 0.001 inches to about 0.01 inches. In one embodiment, the coating has a thickness of from about 0.003 inches to about 0.007 inches. In one embodiment, the coating has a thickness of about 0.005 inches.

[0027] In one embodiment in accordance with any of the previous embodiments, the article is selected from a heater or a crucible.

[0028] In one aspect, provide is a method of heating an object comprising placing the object adjacent to or in contact with the heater or crucible of any of the previous embodiments, and heating the heater or crucible to a temperature of up to about 1200 °C. [0029] In another aspect, provided is a method of making an article of any of the previous embodiments comprising: providing an intermetallic substrate and applying a coating comprising alumina, yttria, silica, or a combination of two or more thereof to a surface of the intermetallic substrate.

[0030] In one embodiment, the method comprises treating the surface of the intermetallic substrate prior to applying the coating, wherein the surface is treated by roughening the surface of the substrate, sintering the substrate, outgassing the substrate, surface oxygenation, or a combination of two or more thereof.

[0031] Further aspects and embodiments of the technology are further described and understood with reference to the drawings and detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0032] Other objects and advantages of the present invention can be understood from the following description when read in conjunction with the accompanying drawings in which:

[0033] FIG. 1 shows an embodiment of a heater;

[0034] FIG. 2 shows a heater, in which FIG. 2(a) is a partial plan view thereof and

FIG. 2(b) is an enlarged cross-section taken along B-B in FIG. 2(a);

[0035] FIG. 3 is a plan view of a heater;

[0036] FIG. 4 is an enlarged cross-section taken along A-A in FIG. 35;

[0037] FIG. 5 is a plan view of a heater embodying a spiral shape;

[0038] FIG. 6 is a plan view of a heater embodying a rectangular shape;

[0039] FIG. 7 is a plan view of other embodiments of a heater;

[0040] FIG. 8 is an enlarged cross-sectional view of the heater of FIG. 7 along line 7-

7;

[0041] FIG. 9 is a plan view of other embodiments of a heater;

[0042] FIG. 10 is an enlarged cross-sectional view of the heater of FIG. 9 along line

9-9;

[0043] FIG. 11 is a perspective view of a heater;

[0044] FIG. 12 is a top plan view of the heater of FIG. 11 ;

[0045] FIG. 13 is a front plan view of the heater of FIG. 11 ;

[0046] FIG. 14 is a side plan view of the heater of FIG. 11 ;

[0047] FIG. 15 is a perspective view of a heater;

[0048] FIG. 16 shows an embodiment of a ceramic composite substrate, wherein the ceramic composite substrate is coated with alumina;

[0049] FIG. 17 shows an embodiment of a ceramic composite substrate, wherein the ceramic composite substrate is coated with yttria;

[0050] The drawings are not to scale unless otherwise noted. The drawings are for the purpose of illustrating aspects and embodiments of the present invention and are not intended to limit the invention to those aspects illustrated therein. Aspects and embodiments of the present invention can be further understood with reference to the following detailed description.

DETAILED DESCRIPTION

[0051] Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. It is to be understood that other embodiments may be utilized and structural and functional changes may be made without departing from the respective scope of the invention. Moreover, features of the various embodiments may be combined or altered without departing from the scope of the invention. As such, the following description is presented by way of illustration only and should not limit in any way the various alternatives and modifications that may be made to the illustrated embodiments and still be within the spirit and scope of the invention. [0052] Disclosed is a dielectric coating. In an embodiment, the coating may be applied by thermal or plasma spray methods. In an embodiment, the coating may be produced or applied as sol-gel. The coating may comprise one or more of alumina (AI₂O₃), silica (S1O2), or yttria (Y). The coating may be applied to a ceramic composite. The ceramic composite may include (i) boron nitride (BN), and (ii) a conductive ceramic material wherein the conductive ceramic material is selected from a boride, carbide, aluminide, or silicide of a metal or silicon.

[0053] The thickness, composition, and morphologies of the coating may be chosen as desired for a particular purpose or intended application. In one aspect, the coating composition can be selected to achieve certain properties. For example, the coating may be chosen and applied to provide one or more of: electrical isolation, shock resistance, corrosion resistance, as well as to tune the mechanical strength, surface roughness, coefficient of friction, optical properties such as emissivity or emission wavelengths, and surface chemistry. Similarly, the ceramic composite may be chosen and applied to provide one or more of the above properties. The coating may provide similar corrosion resistance to that of the ceramic composite, including corrosion resistance by oxygen, nitrogen, hydrogen, other gases or gas radicals such as chlorine, fluorine, moisture, and molten or vapor metal. The coating may also provide corrosion resistance to materials that the ceramic composite is not by itself normally resistance against, including strong acids or other molten metals.

[0054] Additionally, the coating may avoid contamination from the underlying layer flaking off. For example, ceramic composites comprising BN can shed BN particulates during handling and use due to the softness of the material. Since ceramic composite heaters and crucibles typically require high aspect ratio serpentine machined patterns, the coating may also provide increased strength to the heater or crucible and remedy any brittleness that may be evident due to machining. The thickness, composition, and morphologies of the coating may enable enhanced adhesion of the coating to the underlying layer. Substrate dimensions such as, for example, radius of comers and edges may be increased to reduce the stress and improve the adhesion of coating.

[0055] The thickness of the coating may be selected as desired for a particular purpose or intended application. In one embodiment, the thickness of coating may range from 0.001 inches (0.025 mm) to 0.010 inches (0.25 mm), from 0.003 inches (0.075 mm) to 0.007 mm (0.18 mm), or from 0.004 inches (0.10 mm) to 0.005 inches (0.125 mm).

[0056] In an embodiment, coating morphology and adherence can be modified by post-thermal processing of the coated heater or crucible. For example, for a coating that comprises a mixture of yttria and alumina, post-thermal processing may be used to enable formation of a stable yttrium aluminum garnet (YAG) phase. For a coating that comprises a mixture of yttria, alumina, and silica (YAS), post-thermal processing may be used to form, chemically wet, spread, or adhere to YAS glass on the heater or crucible. Post-thermal processing may be used in conjunction with oxygenation of the substrate surface to facilitate and enable reactive wetting during post-thermal processing.

[0057] The thickness, composition, and morphologies of the coating may also be tuned by changing the process of application. For example, the thickness, composition, and morphologies of the coating may be tuned by changing the thermal or plasma spray process conditions such as gas ratios, flows, power, distance from substrate, substrate temperature, coating temperature, feed rates of powders, and the like. The coating may be applied after machining or forming of the heater or crucible or the coating may be applied prior.

[0058] The thickness, composition, and morphologies of the coating may be chosen to enhance the adhesion to the substrate (e.g. the ceramic composite). In one embodiment, adhesion of the coating to the substrate can be enhanced by providing a coating with a CTE that matches or substantially matches the CTE of the substrate. CTE of the coating can be chosen or tuned by selecting the properties of the coating such as, for example, porosity, particle size, thickness, composition of the coating, etc., or a combination of two or more of those properties. So these properties can be selected as desired to provide a CTE suitable to enhance adhesion with the substrate. The composite materials may further include an oxide sintering aid or one or more of the composite materials may be oxygenated. In addition to such pre-processing steps, post-thermal processing of the coated heater or crucible may be implemented in order to form various stable phases of the coating component materials or to enable reactive wetting.

[0059] In one embodiment, the substrate has a first CTE, and the coating has a second CTE, and the first CTE is within 30% of the second CTE, within 25% of the second CTE, within 20% of the second CTE, within 15% of the second CTE, within 10% of the second CTE, within 5% of the second CTE, even within 1% of the second CTE. It will be appreciated that “within X percent of the second CTE” means that the first CTE differs from the second CTE by plus or minus the stated percent of the second CTE. In one embodiment, the first CTE is from about 0.1% to about 30% of the second CTE, from about 1% to about 25% of the second CTE, from about 5% to about 20% of the second CTE, or from about 10% to about 15% of the second CTE, Generally, the difference between the CTE of the substrate and the CTE of the coating can be greater (if desired) as the thickness of the coating decreases.

[0060] In turn, the underlying layer or substrate may be selected as desired to match the properties of the coating and vice versa for an intended application or use of the heater or crucible. Properties and parameters of the coating and substrate material that can be considered for coating a particular substrate include, for example, material composition, particle size, thickness, coefficient of thermal expansion (CTE), surface roughness, and porosity. The composite materials employed to form the heater or crucible may further include an oxide sintering aid or one or more of the composite materials may be oxygenated. After the coating layer is applied, a surface oxygenation process may be carried out. The surface of the substrate layer may also be cleaned prior to adding the coating.

[0061] For example, in one embodiment the composition of the coating may be selected or modified to more closely match the CTE and/or particle size of the ceramic composite (and vice versa where the composition of the ceramic composite may be modified to the CTE and particle size of the coating). Using an intermetallic composite of BN and T1B2 as an example, BN has a comparatively low CTE and larger particle size and T1B2 has a comparatively high CTE and fine particle size (e.g. D50 < 3). Depending on the ratio of the BN to T1B2 in the composite employed to form the heater or crucible, the composition of the coating used to coat the heater or crucible may be configured to match the properties of the intermetallic composite. Since alumina has a comparatively low CTE and yttria has a comparatively high CTE, the composition of the coating and ratio of components such as alumina and yttria in the coating can be selected to match with the low CTE of BN and high CTE of T1B2, respectively. Similarly, silica has a comparatively low CTE to that of the higher CTE of yttria and alumina has a comparative CTE in between that of yttria and silica. As a result, the ratios of these components may be selected and modified to match the CTE of the components of the intermetallic composite (and vice versa where the ratios of the components of the intermetallic composite may be modified to match the CTE of the coating).

[0062] It is noted that the coating may be formed as individual layers of its components, such as one or more of alumina, silica, and yttria, or the coating may be formed by a mixture, such as a mixture that is substantially homogenous, of one or more of alumina, silica, and yttria. In one embodiment, the composition of the coating can be graded along the thickness of the coating layer. As an example of providing a graded coating, a first deposited layer of the coating may differ from the one or more of the subsequent layers employed to form the coating. In one embodiment, the first deposited layer differs from the last deposited layer of the coating. In such a gradient coating layer, at least two of the layers differ from one another with respect to their compositions. Compositionally graded coatings can be employed to tune two competing attributes such as adhesion and corrosion resistance or emissivity or coefficient of friction or surface chemistry. For example, a silica rich layer may be used in the first deposited coating to enhance bonding and the subsequent layers may have lower concentrations of silica and higher concentrations of, for example, alumina and/or yttria to enhance corrosion resistance. [0063] In addition, or alternatively, to selecting a coating composition based on the substrate being employed, the substrate can be modified to enhance the adhesion of coating. There are a number of different methods that can be employed to modify the substrate to match one or more properties of the coating.

[0064] In an embodiment, the substrate may be roughened. The substrate may be roughened by any suitable method including, but not limited to, sand blasting, sawing or grinding as well as electrical discharge or spark machining, laser, or water-jet, techniques. In an embodiment, the roughening of the substrate may remove material from the surface of the substrate. This rough or uneven surface of the substrate may enhance the adhesion of the applied coating.

[0065] In an embodiment, the substrate may be sintered or outgassed. The sintering and outgassing may occur and high temperatures and may alter the porosity and CTE of the substrate. For example, the substrate may be sintered or outgassed at a temperature greater than 1800°C. The sintering may comprise vacuum sintering. The sintering and outgassing may reduce outgassing and resistance changes during operation of the heater or crucible and may also enhance the adhesion of the applied coating.

[0066] In an embodiment, the substrate base material composition may be altered to match the porosity and CTE of the coating and to enhance the adhesion of the applied coating. For example, the ceramic composite may include mixtures or combinations of different conductive ceramic components as desired for a particular purpose or intended application. This may include a combination of different types of conductive ceramics, e.g., a boride and a carbide. This may also include different materials within a given class of conductive ceramic, e.g., two or more different types of borides, carbides, silicides, aluminides, etc.

[0067] In one embodiment, the substrate has a porosity such that the pores comprise from about 5% to about 25% of the total volume of the substrate. The pore size is not particularly limited. Pore volume can be measured by any suitable method including, but not limited to via a helium pycnometer, or visually using scanning electron microscopy. In embodiments, the pores can have a pore size of from about 1 pm to about 50 pm; from about 5 pm to about 40 pm; from about 10 pm to about 30 pm; or from about 15 pm to about 25 pm. Pore size can be evaluated using scanning electron microscopy.

[0068] In an embodiment, the substrate base material particle size may be altered to enhance the adhesion of the applied coating. Using a BN/T1B2 intermetallic composite as an example, the D50 particle size for BN may be about 2-20 microns and the D50 particle size for T1B2 may be about 2-30 microns. In one embodiment, the D50 particle size for BN may be about 7 microns and the D50 particle size for T1B2 may be about 14 microns. Particle size can be determined by any suitable method. In one embodiment, particle size is determined by laser diffraction of suspended particles in deionized water.

[0069] In an embodiment, the substrate may be oxygenated. For example, in a

BN/T1B2 intermetallic composite, the BN, T1B2, or one or more other components in the ceramic composite may be oxygenated or an oxide sintering agent may be incorporated into the substrate in order to enhance the adhesion of the coating. The sintering agent, aid, or binder may include calcium oxide, other metal oxides chosen from alkaline earth metals, aluminum and its associated compounds such as aluminum nitride, silicon and its associated compounds including silicon carbide or silicon nitride, carbon, metals or metals compounds of transition metals selected from tungsten, titanium, nickel, cobalt, iron, chromium, and the like, and a combination of two or more thereof. In an example, the total oxygen content of the substrate may be between 1% and 10% by weight, between 2.5% and 7.5% by weight, or between 3% and 5% by weight of the substrate.

[0070] In an embodiment, the substrate may be prepared by a surface oxygenation process to enhance the adhesion of the coating. The surface oxygenation process, unlike oxygenating a component of the substrate or adding in a sintering aid, may only affect the exterior surface of the substrate and not the full layer of the substrate. The surface oxygenation process may include propane torch, oxygen plasma, ozone treatment, thermal oxidation, and the like. Such oxygenation of the surface of the substrate may occur before or after machining of the heater or crucible.

[0071] In an embodiment, the substrate surface may be cleaned. The substrate surface may be cleaned in an ultrasonic bath or other particle removal methods. The cleaning of the substrate surface may remove loose particles and enhance adhesion of the coating. One or more of the other modification steps of the substrate as described herein such as roughening the surface, sintering or outgassing, changing the composition or the particle size of the substrate components, oxygenating the substrate components or adding a sintering aid, and oxygenating the surface of the substrate may be carried out prior to this cleaning step. In other words, the cleaning step may help to remove particles that were dislodged based on the roughening, sintering, or oxygenation steps, and the like. Cleaning of the substrate surface may be the last modification step prior to coating.

[0072] The conductive ceramic material of the ceramic composite may be selected from a boride, carbide, aluminide, and/or silicide of a metal. In one embodiment, the metal in the conductive ceramic material can be selected from Ti, Cu, Ni, Mg, Ta, Fe, Zr, Nb, Hf, V, W, Mo, Cr, etc. Examples of suitable aluminides include, but are not limited to, aluminides of Ti, Cu, Ni, Mg, Ta, Fe, etc. In one embodiment, the aluminide is chosen from TiAl, Ti AT,. CU₂AI, NiAl, N1₃AI, TaAT. TaAl, FeAl, Fe₃Al, AFMg^. etc. The conductive ceramic can also be a transition metal boride, carbide, or silicide. Examples of suitable borides, carbides, or silicides include borides, carbides, or silicides of Ti, Zr, Nb, Ta, Hf, V, W, Mo, Cr, etc. Examples of suitable borides include, but are not limited to, T1B₂, TiB, ZrB_2, NbB₂, TaB₂, HfB2, VB2, TaB, VB, etc. Examples of suitable carbides include, but are not limited to, TiC, TaC, WC, HfC, VC, MoC, TaC, CT7C3. etc. It will be appreciated that the conductive ceramic material can include various ratios of the respective atoms as may be suitable to match the coating and promote its adhesion.

[0073] The ratio of boron nitride to conductive ceramic material can be selected as desired, such as to match the coating and promote its adhesion. In one embodiment, the (weight) ratio of boron nitride to conductive ceramic is selected from 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, etc. In an embodiment, the composite material includes a titanium boron material. The titanium-boron material may include any ratio of titanium to boron as may be suitable to match the coating and promote its adhesion. This includes T1B₂ as well as other ratios including, but not limited to T1B_1.5 to T1B_3.5, including ratios in between those values (e.g., T1B_2.3-3.5). Titanium-boron materials include combinations of titanium and boron in various ratios. The most prevalent form is T1B2. Titanium-boron materials as used herein also include other ratios including, but not limited TiBi_.5-3_.5.

[0074] In one embodiment, the ceramic material comprises two or more ceramic materials. In one embodiment, the ceramic material is selected from a titanium boride and a silicon carbide. The silicon carbide can be present in an amount of from about 5% to about 35% by weight, from about 10% to about 20% by weight, or from about 15% to about 20% by weight based on the weight of the ceramic material in the composite.

[0075] The ceramic composite and coating thereof may be used in both heater and crucible applications. The heaters may be 2-D or 3-D configurations. The coating may be applied after machining into either a heater or a crucible.

[0076] In an embodiment, a heater may include a body. The body may have a first surface and a second surface. The body may have a configuration defining a predetermined path defining a plurality of heating rungs. The body may include at least one heating surface, the heating surface being generally smooth and generally flat, a recess formed in the body, at least a portion of the body having a cross-sectional shape selected from the group consisting of: generally T-shape, generally C-shape, generally U-shape, generally I-shape, and generally H-shape, and where the cross-sectional shape extends along at least a portion of the body. In an embodiment, a heater may comprise an upper surface and a lower surface, and a plurality of heating rungs, where the heating rungs may comprise a major portion oriented horizontal to a plane defined by the upper surface. In an embodiment, a heater may comprise a first surface and a second surface, and a plurality of heating rungs, where the heating rungs may comprise a major portion oriented vertically to a plane defined by the first surface.

[0077] In an embodiment, a body of a heater may further comprise at least two zones or electrode paths. The multi-zone heater may have a different power flux density at different locations. Manipulating the aspect ratio of coil length to width or thickness in order to change the resistance per unit area would result in different power flux densities. In an embodiment, the body may comprise two halves connected in series, where each half has a configuration defining a predetermined path defining a plurality of heating rungs. In an embodiment, the body may comprise a plurality of heating rungs oriented adjacent to one another along their lengths. Each heating rung may have substantially the same width. In another embodiment, the width of at least one heating rung may be narrower than the width of at least one other heating rung. The width of an uppermost heating rung at a top of an upper surface of the body may be narrower than at least one other heating rung. In another embodiment, the width of the uppermost heating rung at the top of the upper surface of the body is less than or equal to half the width of at least one other heating rung.

[0078] In an embodiment, a crucible may include a body. The body may include a bottom wall and a sidewall extending up from the bottom wall and defining a cavity. In an embodiment, the cavity may be configured to hold a molten material. The crucible may be formed monolithically of a single component or the crucible may include multiple components and configurations. In an embodiment, the crucible may be split into a top and a bottom section, wherein the top and bottom sections are of approximately the same circumferences and positioned abut each other around the circumference. The sections may have a predetermined substantially uniform circumference along the vertical axis. The cavity and crucible may generally comprise the same circumference along the length of its body or the cavity and crucible may have a varying circumference along the length of its body.

[0079] The coated heater or crucible may be corrosion resistant against oxygen, nitrogen, hydrogen, ammonia, other gases or gas radicals such as chlorine, fluorine, and moisture up to, for example, a temperature of 900°C, and may offer increased corrosion resistance against molten or vapor metal, including aluminum, copper, and tin. The coated heater or crucible may be sufficiently rigid and may not require additional dielectric structural support. The coated heater or crucible may be sufficiently fracture resistant to enable machining of intricate and complex patterns and designs with a high aspect ratio of the coil length to width or thickness within a unit area. For instance, the aspect ratio per unit area may be as high as 100 within a square inch of heater surface, up to 60 within a square inch of heater surface, or up to 50 within a square inch of heater surface. In some embodiments, the aspect ratio may range from 5-100 within a square inch, or about 6.5 cm², of heater surface. [0080] The width or thickness of the resulting heating element comprising the ceramic composite and coating can be as low as 1 mm and the coil length within a square inch can be as high as lOOx the width or thickness. The ceramic composite and coating can hold up against thermal and mechanical shock during installation and cleaning even at these smaller thicknesses. The width and thickness of the resulting heating element comprising the ceramic composite and coating may also be greater than 1 mm, including 5 mm, 10 mm, 15 mm, 20 mm, etc. For example, the width and thickness of the heating elements may range from 0.5 mm to 50 mm.

[0081] In addition to high temperature vacuum processes, the ceramic composite and coating may also be used to replace atmospheric heating element alloy materials, such as molybdenum-silicide, nickel-chromium, and iron-chromium-aluminum, which are typically used in atmospheric conditions such as material processing and fuel cells as well as consumer electrical and electronic products such as e-cigarettes, medical equipment, home heating, automotive interior and engine applications, and the like.

[0082] The heater or crucible can be machined by any machining process. In an embodiment, a method of manufacturing includes Computer Numerical Control (CNC) machining (cutting, lathing, milling, drilling) with diamond tooling. For example, with respect to a heater, the ceramic composite enables realization of high aspect ratio serpentine features as thin as 1 mm by CNC machining with diamond tooling. Other material removal techniques such as electrical discharge or spark machining, laser, water-jet, sand blasting, sawing, grinding and the like may also be used to machine heaters and crucibles comprising the ceramic composite. In an embodiment, a method of manufacturing the ceramic composite includes hot pressing a blend of BN and the conductive ceramic, as in one embodiment, titanium-boride (e.g., TiB2), with a sintering aid or binder. The sintering aid or binder may include calcium oxide, other metal oxides chosen from alkaline earth metals, aluminum and its associated compounds such as aluminum nitride, silicon and its associated compounds including silicon carbide or silicon nitride, carbon, metals or metals compounds of transition metals selected from tungsten, titanium, nickel, cobalt, iron, chromium, and the like, and a combination of two or more thereof.

[0083] The resistance per unit area of the heater or crucible may be tuned and manipulated by changing the aspect ratio per unit area and thickness. The ceramic composite may have a high thermal conductivity and low Coefficient of Thermal Expansion (CTE), and a superior thermal shock resistance, for example, greater than 200°C/s or greater than 1000°C/min. The ceramic composite may enable realization of high power flux density, such as greater than 10 W/cm², greater than 25 W/cm², or greater than 50 W/cm². After machining to a final shape of the heater or crucible or before, the heater or crucible comprising the ceramic composite may be outgassed or vacuum sintered at a temperature greater than 1800°C to reduce outgassing and resistance changes during operation of the heater. As a result, the ceramic composite further enables a resistance per unit area to achieve a power density as high as 60 W/cm² with current under 40 amps at the operation temperature of about 1500°C.

[0084] In addition to vacuum outgassing, the heater or crucible including unreacted sintering aids and volatile compounds may be cleaned off by chemical leaching using inorganic or organic acids, bases, or solvents. Suitable acids include HF, acetic acid, and HC1; suitable bases include dilute NaOH and NH₄OH; and suitable solvents include hot methanol or water, or combination of two more of any of the foregoing. Chemical leaching may be used to reduce outgassing, and to tune or stabilize the resistivity of the material.

[0085] The conductive ceramic, e.g., T1B2_, provides electrical conductivity. BN provides structure in the ceramic composite that enables the ceramic composite to be machined. BN aids in the machinability of the ceramic composite because of its softness, aids in the thermal shock resistance of the ceramic composite because of its high thermal conductivity, has the ability to achieve high electrical resistance per unit area due to its high resistivity even at high temperatures of 1500°C and superior chemical resistance complementing and/or supplementing chemical resistance of the conductive ceramic, e.g.,

T1B2. [0086] BN can be used to increase or tune the resistivity. T1B2 can be used to increase or tune the resistivity. Resistivity can also be tuned up or down by decreasing or increasing T1B2 or by the addition of a boride, silicide, aluminide, or carbide of metals from subgroup 3, 4, 5, 6, etc. of the periodic table. Conductive oxide ceramics and glass may also be used for tuning resistivity. Non-conductive ceramics such as aluminum oxide and sintering aids and binders may also be used to tune the resistivity. Resistivity of the composite can be varied from 300 MOC (micro ohm cm) to 10000 MOC. Resistance per unit area can be tuned by machining high aspect ratio features as detailed above and/or changing the resistivity of the base stock with the goal of achieving the desired power flux density at a desired current. [0087] For example, the demonstration heaters shown in FIG. 1 were manufactured from AC6043 grade boron nitride composites commercially sold by Momentive Quartz and Ceramics, USA. Typical properties are as follows: density is about 2.78 gm/cm³, coefficient of thermal expansion (25-1500°C) is about 7ppm/C, modulus of elasticity is about 107 GPa, Flexural strength at 25°C is about 89.6 Mpa and at 1500°C is about 16.5 Mpa, thermal conductivity at 25°C is about 70W/mK and at 1500C is about 43 W/mK, Rockwell Hardness is about 123, and volume resistivity at 25°C is in the range of about 400 to 1,600 MOC (micro-ohm-cm). As disclosed herein, the resistivity and other mechanical properties such as machinability can be tuned to ranges greater than above mentioned values by adjusting the ratio of T1B2 and BN. Since the resistivity of hot pressed T1B2 is very low, typically below 30 MOC at 25°C, even though materials made with greater than 95% T1B2 may be electrically conductive, it may be difficult to achieve the resistance per unit area to deliver a power density as high as 60 W/cm² with current under 40A. Further, materials with 95% or greater % of T1B2 would be brittle to handle and difficult to machine even with a diamond tool as they tend to form cracks. In some embodiments, volume resistivity of from about 400 to about 10,000, or 400 to about 5,000 MOC may be achieved. These materials would also not be able withstand thermal shock. As a result, additional composite materials, such as BN, in order to tune the resistivity and other mechanical properties of the heater.

[0088] FIG. 1 depicts a heating element 400 comprising a plurality of heating rungs in a 2-D orientation. The heating rungs may include upward heating rungs 410, 440, horizontal heating rungs 420, 450, and downward heating rungs 430, 460. As with all the described heater configurations, the heater comprises a ceramic composite including boron nitride (BN) and titanium diboride (TiB2). There are terminal connecting holes 470, 472 at respective end portions 480, 482 of the heating element 400. The connecting holes 470, 472 are the points of attachment of an electrical power source which provides the electric current to the heating element 400.

[0089] FIG. 2A depicts a heater comprising a rectangular heater body including a terminal end portion with a connecting hole, with a cross-section taken at position B-B shown in FIG. 2B. The terminal end portions have a widened and expanded shape at the end portion to decrease electric resistance.

[0090] FIG. 3 depicts a heater 1 comprising a C-shaped heater body 2. There are terminal connecting holes 3a, 3b at respective end portions of the C-shaped heater body 2, the opposing exterior end surfaces 7a and 7b being spaced apart so as to define a gap G therebetween. The connecting holes 3a and 3b are the points of attachment of an electrical power source which provides the electric current to the heater 1.

[0091] FIG. 4 is an enlarged cross-section taken along A-A in FIG. 4 where the heater body 2 has an upper horizontal wall 8 having a smooth and flat top heating surface 4 onto which an object to be heated, such as a wafer, is mounted directly or indirectly via a susceptor, etc. A center portion of the underside of the heater body 2 is recessed to form an elongated groove or recess 5 between a pair of opposite vertical side walls or ribs 6a, 6b, said side walls having inner surfaces 9a and 9b which at least partially define the recess 5. The recess 5 and side walls 6a, 6b extend in an arcuate linear direction of the C-shaped heater body 2 so as to provide an inverted U-shaped cross section along a middle portion 7c of the heater, but not at the end portions of the heater body. In particular, the recess 5 terminates at end surfaces 5 a and 5b, the portion of the body between recess end surfaces 5 a and 5b and the respective exterior end surfaces la and lb defining the respective end portions of the body. The body 2 has the same width W along its entire length, including both end portions and the middle portion 7c therebetween. The full thickness of the body 2 at the end portions maintains a relatively cooler temperature at the end portions but the uniform width of the body improves control of the heat distribution pattern. The middle portion 7c of the body has a reduced cross sectional area available for electrical conduction thereby increasing, and improving heater resistance.

[0092] The heater body can be designed into a spiral heat pattern, such as heater V shown in FIG. 5, and as shown in Japanese patent publication No. 2005-86117(A). In some applications, the heater body is formed into a square or rectangular pattern, such as heater 1” shown in FIG. 6. These and other heater shapes are also within the scope of the present invention, such as a serpentine or helical pattern.

[0093] FIGs. 7 and 8 show an embodiment of a heater. Heater 41 may include a generally a C-shaped heater body 42. The heater body 42 may include terminal connecting holes 43a, 43b, which may be located at respective end portions of the C-shaped heater body 42. The opposing exterior end surfaces 47a and 47b may be generally spaced apart so as to define a gap G2 between such. The connecting holes 43a and 43b may be the points of attachment of an electrical power source (not shown) that may provide the electric current to the heater 41. By way of a non-limiting example, in these embodiments the heater body 42 may have a cross-sectional shape such as shown in FIG. 8. As shown in FIG. 8 the heater body 42 may have a generally horizontally symmetrical cross-sectional shape, such as by way of a non-limiting example, a generally H-shaped cross-sectional shape. In these embodiments, the heater body 42 may include a generally centrally positioned and generally horizontal wall 48.

[0094] In these embodiments, a top and bottom central portion 51, 53 of the heater body 42 may be recessed to form a pair of elongated grooves or recesses 45a, 45b between a pair of opposite vertical side walls or ribs 46a, 46b. The recesses 45a, 45b may be positioned on both the top and bottom portion of the heater body 42. The side walls 46a, 46b may each include inner surfaces 49a, 49b, 49c and 49d, which may at least partially define the recesses 45a, 45b. The recesses 45a, 45b and side walls 46a, 46b may extend in an arcuate linear direction of the generally C-shaped heater body 42. This may provide a generally H-shaped cross sectional shape along at least a middle portion 47c of the heater 41. The vertical side walls 46a, 46b may each possess a generally smooth and flat heating surface 44a, 44b, respectively onto which an object to be heated, such as a wafer, may be mounted directly or indirectly via a susceptor, etc.

[0095] The general H-shaped cross-sectional shape, however, may not extend to the end portions 47a, 47b of the heater body 42. By way of a non-limiting example, the recesses 45a, 45b may generally terminate at end surfaces 55a and 55b, the portion of the body 42 between recess end surfaces 55a and 55b and the respective exterior end surfaces 47a and 47b may define the respective end portions 57a, 57b of the body 42. As indicated above, the body 42 may have width W along its entire length, including both end portions and the middle portion 47c therebetween. The width W may be generally consistent along an entire length of the body 42.

[0096] Embodiments of a heater are shown in FIGs. 9 and 10. Heater 61 may include a generally a C-shaped heater body 62. The heater body 62 may include terminal connecting holes 63a, 63b, which may be located at respective end portions of the C-shaped heater body 62. The opposing exterior end surfaces 67a and 67b may be generally spaced apart so as to define a gap G3 between such. The connecting holes 63a and 63b may be the points of atachment of an electrical power source (not shown) that may provide the electric current to the heater 61. By way of a non-limiting example, in these embodiments the heater body 62 may have a cross-sectional shape such as shown in FIG. 10.

[0097] As shown in FIG. 10 the heater body 62 may have a generally symmetrical cross-sectional shape, such as by way of a non-limiting example, a generally I-shaped cross- sectional shape. Still further, the heater body 62 may have a generally horizontally symmetrical cross-sectional shape. In these embodiments, the heater body 62 may include a pair of generally horizontal walls 68a and 68b. The first wall 68a may be on the top portion of the body 62 and the second wall 68b may be on the botom portion of the body 62. Either or both of the horizontal walls 68a and 68b may possess a generally smooth and flat heating surface 64 onto which an object to be heated, such as a wafer, may be mounted directly or indirectly via a susceptor, etc.

[0098] In these embodiments, a pair of side walls 66a, 66b of the heater body 62 may be recessed to form a pair of elongated grooves or recesses 65a, 65b. By way of a non- limiting example, the recesses 65a, 65b may be formed in the pair of opposite vertical side walls 66a, 66b in any appropriate manner. Once the recesses 65a, 65b may be formed in the vertical side walls 66a, 66b, a generally central wall 72 may be formed in the heater body 62. This may define the generally I-shaped cross-sectional heater body 42. Side walls 73a, 73b of the central wall 72 may define the recesses 65a, 65b.

[0099] The recesses 65a, 65b and side walls 73a, 73b may extend in an arcuate linear direction of the generally C-shaped heater body 62 so as to provide a generally I-shaped cross sectional shape along at least a middle portion 67c of the heater 61. The generally I-shaped cross-sectional shape, however, may not extend to the end portions 75a, 75b of the heater body 62. By way of a non-limiting example, the recess 65a, 65b may terminate at end surfaces 75a and 75b. The portion of the body 62 between recess end surfaces 75a and 75b and the respective exterior end surfaces 67a and 67b may define the respective end portions 77a, 77b of the body 62.

[00100] As indicated above, the body 62 may have width W along its entire length, including both end portions 77a, 77b and the middle portion 67c therebetween. The width W may be generally consistent along an entire length of the body 62. While the exemplary dimensions are described above, the present teachings are not limited to these specific dimensions. The dimensions are merely exemplary and may be altered as required.

[00101] The heater may also be provided with a 3-D structure, for example to provide heating in a radial direction. In an embodiment, the heater comprises a body having a configuration defining a predetermined path defining a plurality of heating rungs. The heater can be an integral body where the path can be a continuous path comprising a plurality of heating rungs. In one embodiment, the heater comprises a body comprising two halves connected in series, where each half comprises a plurality of heating rungs in a predetermined configuration.

[00102] In accordance with aspects of the invention, the heater body comprises an upper surface, a lower surface, and the body has a configuration defining a predetermined path defining a plurality of heating rungs, where the heating rungs have a major portion that is oriented substantially parallel to the upper surface of the body. In one embodiment, the body comprises two halves connected in series, where each half has a configuration defining a predetermined path defining a plurality of heating rungs, where the heating rungs have a major portion oriented substantially parallel to the upper surface of the body.

[00103] By providing a configuration with the major portion of the heating rungs oriented substantially parallel to the upper surface of the body, the heater body has a larger cross-sectional area that allows the thermal expansion to be spread over the entire length of the heating rungs, which has been found to reduce the stress concentration over the heater body.

[00104] FIGs. 11-14 illustrate an embodiment in accordance with aspects of the present technology. The heater 100 comprises a first half 110 and a second half 120. The first half extends from a terminal 130, and the second half extends from a terminal 140. The terminals 130 and 140 include terminal connecting holes 132 and 142, respectively, which are points of attachment for an electrical power source to provide electrical current to the heater.

[00105] The heater 100 is illustrated as a cylindrical body comprising an upper surface 102. Each half, 110 and 120, defines a bottom surface 112 and 122, respectively. Each half of the heater body 100 is machined into a predetermined path defining a plurality of heater rungs 150 and 160. In FIGs. 11-14, the paths are provided in a serpentine arrangement with a major portion of the heating rung 150, 160 (or path) being oriented parallel with the upper surface of the heater, and a minor portion defining the turn in the path. As illustrated in FIGs. 11, 12, and 14, the respective serpentine pattern extends linearly and vertically from each terminal and then turns to form the major portions oriented horizontal and parallel to the plane of the upper surface of the heater. As shown in FIG. 15, a major portion of the rungs may also be oriented vertically.

[00106] It will be appreciated that the electrical flow path of the body may form any appropriate pattern, including, but not limited to, a spiral pattern, a serpentine pattern, a helical pattern, a zigzag pattern, a continuous labyrinthine pattern, a spirally coiled pattern, a swirled pattern or a randomly convoluted pattern. Additionally, the heater body can be provided in any suitable shape as desired for a particular purpose or intended application. [00107] In the embodiment of FIG. 14, the width 300 of the uppermost heating rung at the top of the upper surface of the body is narrower than the width 310 of the other heating rungs. In one embodiment, the width 300 is less than or equal to half the width 310.

[00108] As illustrated, there is a gap or space 170, 180 between successive heating rungs. In one embodiment, the gap can be uniform between successive heating rungs including at the turn. In another embodiment, the gap defined near the turn of the serpentine path can be provided such that it is sized to have one or more dimensions larger than a dimension of the gap between the major portions of the heating rungs. For example, the height or width of the gap near the turn can be larger than the gap between the major portions of the heating rungs. As shown in FIGs. 11, 13, and 14, the gap 172 near the turn of the path can be provided with a geometric shape including, but not limited to, a rectangle, a square, a circle, a triangle, a pentagon, a hexagon, a heptagon, etc. The larger gaps 172 can taper or lead to the gap between the heating rungs. As illustrated in FIGs. 11, 13, and 14, the gap 172 near the turn of the serpentine path is circular to provide a “keyhole” gap. The present design with the relatively large cross sectional area provided by arranging the heating rungs with the major portion oriented horizontally to the plane of the upper surface of the heater allows for the inclusion of the larger gap near the turn of the serpentine path. The larger gaps near the turns can further reduce the thermal stress of the heater.

[00109] The width of the heating rung is not particularly limited. In one embodiment each heating rung may have substantially the same width. In another embodiment, the width of two or more heating rungs can be different or varied from one another. For example, the width of at least one heating rung may be narrower than the width of at least one other heating rung. In one embodiment, the uppermost heating rung at the top of the upper surface of the body may be narrower than at least one other heating rung. For example, the width of the uppermost heating rung may be narrower than the width of the heating rung directly below it. The width of the uppermost rung may be narrower than each of the other rungs, and each of the other rungs may have the same or different widths. In one embodiment, the width of each heating rung is different and decreases from the lowest rung to the uppermost rung. In another embodiment, the width of the uppermost heating rung may be less than or equal to half the width of at least one other heating rung. For example, the width of the uppermost heating rung may be less than or equal to half the width of the heating rung directly below. [00110] In one embodiment one rung has a width that is about 0.5 times the width of another rung; about 0.4 times the width; about 0.3 times the width; about 0.2 times the width; even about 0.1 times the width of another rung. In another embodiment, one rung has a width that is about 0.05 to about 0.5 times the width of another rung; about 0.1 to about 0.4 times the width; even about 0.15 times to about 0.3 times the width of another rung.

[00111] Varying the width of the heating rungs has been found to impact the power density. For example, decreasing the width of the uppermost heating rung relative to the width of the other heating rungs increases the power density at the top of the heater. When the width of the uppermost heating rung is less than or equal to half the width of the heating rung directly below it, there is an increase in the power density at the top of the heater. Generally, it has been found that the change in power density can be calculated using the below formula: width ratio = 1/ 2- power density ratio

[00112] Thus, a width ratio of about 0.466 results in a power density ratio of 1.15, which means that the power density is increased by about 15%. Thus, varying the width of the heating rungs allows for controlling the power density of the heater.

EXAMPLES

[00113] Turning to FIGs. 16-17, shown is a substrate with the described coatings 500, 600, respectively. The substrate comprised a ceramic composite 510, 610 (gray color). FIG. 17 also shows part of the uncovered substrate 620 and a terminal connecting hole 630. The substrates of FIG. 16 and FIG. 17 each comprised about 55% weight percent BN, about 44% weight percent T1B2, and about 1% weight percent calcium oxide as a sintering aid. The total oxygen content of the mix for the substrate was about 2.5% by weight. The D50 particle size for BN was about 7 microns and the D50 particle size for T1B2 was about 14 microns. It is noted that these properties are not limiting and that the weight percent, oxygen content, and D50 particle size may be modified as described herein. The top surface of the substrate of FIG. 16 was coated with alumina, and the top surface of the substrate of FIG. 17 was coated with yttria. The coatings and substrates were put through several tests including heat. The coatings in FIG. 16 and FIG. 17 survived sonification through several heat cycles with >200 C s ramp up to 1200 °C. As a result, the coatings showed good survivability in high heat conditions.

[00114] Although the embodiments of the present invention have been illustrated in the accompanying drawings and described in the foregoing detailed description, it is to be understood that the present invention is not to be limited to just the embodiments disclosed, but that the invention described herein is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the claims hereafter. The claims as follows are intended to include all modifications and alterations insofar as they come within the scope of the claims or the equivalent thereof.

Claims

CLAIMS What is claimed is:

1. An article comprising an intermetallic composite substrate coated with a ceramic coating, the intermetallic composite substrate comprising boron nitride and a ceramic material, and the ceramic coating comprising alumina, yttria, silica, or a combination of two or more thereof.

2. The article of claim 1 wherein the intermetallic composite has a first coefficient of thermal expansion, and the ceramic coating has a second coefficient of thermal expansion, and the first coefficient of thermal expansion is within about 30% of the second coefficient of thermal expansion.

3. The article of claim 2, wherein the first coefficient of thermal expansion is within about 10% of the second coefficient of thermal expansion.

4. The article of any of claims 1-3, wherein the intermetallic composite is a porous material having a porosity of from about 5% to about 25% based on the volume of the intermetallic composite.

5. The article of any of claims 1-4, wherein the intermetallic composite has an oxygen content of from about 1% to about 10% by weight of the substrate.

6. The article of any of claims 1-5, wherein the ceramic material of the intermetallic composite is selected from a boride, a carbide, a aluminide, or a silicide of a metal.

7. The article of claim 6, wherein the metal is selected from Ti, Cu, Ni, Mg, Ta, Fe, Zr, Nb, Hf, V, W, Mo, and Cr.

8. The article of any of clams 1-7, wherein the ceramic material of the intermetallic composite is selected from TiAl, TiAb, C Al, NiAl, NbAl, TaAb, TaAl, FeAl, Fe₃Al, Al Mg2, TiB₂, TiB, ZrB_2,NbB₂, TaB₂, HfB₂, VB₂, TaB, VB, TiC, TaC, WC, HfC, VC, MoC, TaC, Cr?C₃. or a combination of two or more thereof.

9. The article of any of claims 1-7, wherein the ceramic material of the intermetallic composite is a titanium boride.

10. The article of any of claims 1-7, wherein the ceramic material of the intermetallic composite is selected from a titanium boride and silica carbide.

11. The article of claim 10, wherein the silica carbide is present in an amount of from about 5% to about 35% by weight of the ceramic material.

12. The article of any of claims 1-11, wherein the intermetallic composite has a weight ratio of boron nitride to ceramic material of from 10:90 to about 90:10.

13. The article of claim 12, wherein the weight ratio of boron nitride to ceramic material is from about 40:60 to about 60:40.

14. The article of any of claims 1-13, wherein the coating comprises a mixture of yttria and aluminua.

15. The article of any of claims 1-13, wherein the coating comprises a mixture of yttria, alumina, and silica.

16. The article of any of claims 1-15, wherein the coating has a thickness of from about 0.001 inches to about 0.01 inches.

17. The article of claim 16, wherein the coating has a thickness of from about 0.003 inches to about 0.007 inches.

18. The article of claim 16, wherein the coating has a thickness of about 0.005 inches.

19. The article of any of claims 1-18, wherein the article is selected from a heater or a crucible.

20. A method of heating an object comprising placing the object adjacent to or in contact with the heater or crucible of claim 19, and heating the heater or crucible to a temperature of up to about 1200 °C.

21. A method of making an article of any of claims 1-19 comprising: providing an intermetallic substrate and applying a coating comprising alumina, yttria, silica, or a combination of two or more thereof to a surface of the intermetallic substrate.

22. The method of claim 21 comprising treating the surface of the intermetallic substrate prior to applying the coating, wherein the surface is treated by roughening the surface of the substrate, sintering the substrate, outgassing the substrate, surface oxygenation, or a combination of two or more thereof.