Patent Application
20080006204
As used herein, approximating language may be applied to modify any quantitative representation that may vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially,” may not to be limited to the precise value specified, in some cases.
As used herein, the term “substrate” and “wafer” may be used interchangeably; referring to the semiconductor wafer substrate being supported/heated by the apparatus of the invention. Also as used herein, the “treating apparatus” may be used interchangeably with “handling apparatus,” “heater,” “heating apparatus,” or “processing apparatus,” referring to an apparatus containing at least one heating element to heat the wafer supported thereon.
As used herein, the term “circuit” may be used interchangeably with “electrode,” and the term “resistance heating element” may be used interchangeably with “resistor,” or “heating resistor.” The term “circuit” may be used in either the single or plural form, denoting that at least one unit is present.
As used herein, a component (e.g., a layer or a part) having a closely matched coefficient of thermal expansion (CTE) means that the CTE of the component is between 0.75 to 1.25 of the CTE of the adjacent component (another layer, a substrate, or another part).
As used herein, the term “functional members” of a wafer processing apparatus include but are not limited to, holes, tabs on the edge of the heater, contacts to the electrode, or inserts in the substrate to meet other functional requirements of the wafer processing apparatus.
As used herein, the term “etch-resistant” may be used interchangeably with “corrosion resistant,” referring to a material that is etch-resistant, or having a low-etch rate in a harsh environment, i.e., an environment comprising halogens or when exposed to plasma etching, reactive ion etching, plasma cleaning, or gas cleaning at an operating temperature of at least 400° C. in one embodiment, 500° C. in a second embodiment, and 800° C. in a second embodiment.
In one embodiment, the etch-resistant rate is less than 1000 Angstroms per minute (Å/min) in a harsh environment operated in a temperature range of 25-600° C. In a second embodiment, the etch rate is less than 500 Angstroms per minute (Å/min) for a temperature range of 25-600° C. In a third embodiment, the rate is less than 100 Angstroms per minute (Å/min) for a temperature range of 25-600° C. In a fourth embodiment, the rate is less than 1000 Angstroms per minute (Å/min) in a temperature range of 200-600° C. In a fifth embodiment, the rate is less than 500 Angstroms per minute (Å/min) in a temperature range of 200-600° C.
In one aspect of the invention, the electrode comprises at least one of molybdenum, nickel, cobalt, iron, tungsten, ruthenium, and alloys thereof, and the protective coating layer comprises at least one of aluminum nitride, aluminum oxide, aluminum oxynitride or combinations thereof, having CTE ranging from 0.75 to 1.25 of the CTE of the base substrate.
Embodiments of the wafer processing apparatus of the invention are illustrated as follows, by way of a description of the materials being employed, the manufacturing process thereof and also with references to the figures.
General Embodiments of the Wafer Processing Apparatus: In one embodiment as illustrated in
With respect to the base substrate of the wafer processing apparatus of the invention, in one embodiment as illustrated in
With respect to the overcoat layer 19 of the electrically conducting disk 18, the layer 19 comprises at least one of an oxide, nitride, carbide, carbonitride or oxynitride of elements selected from a group consisting of B, Al, Si, Ga, Y, refractory hard metals, transition metals; oxide, oxynitride of aluminum; and combinations thereof. With respect to the optional tie-layer, the layer comprises at least one of: a nitride, carbide, carbonitride, boride, oxide, oxynitride of elements selected from Al, Si, refractory metals including Ta, W, Mo, transition metals including titanium, chromium, iron; and mixtures thereof. In one embodiment, the tie-layer comprises at least one of a TiC, TaC, SiC, MoC, and mixtures thereof.
In one embodiment as illustrated in
In one embodiment as illustrated in
In another embodiment as illustrated in
In one embodiment, the sheet resistance of the electrode is controlled within a range of 0.001 to 0.10 Ω/sq to meet the electrical resistance requirement for the electrode, while maintaining the optimal path width and space between the paths of the electrode pattern. In a second embodiment, the sheet resistance is controlled within a range of 0.005 to 0.05 Ω/sq. The sheet resistance is defined as the ratio of electrical resistivity to film thickness.
In the wafer processing apparatus of the invention, one or more electrodes can be employed. Depending on the application, the electrode may function as a resistive heating element, a plasma-generating electrode, an electrostatic chuck electrode, or an electron-beam electrode.
In one embodiment of the invention as illustrated in
In one embodiment, the protective coating layer 25 comprises at least a nitride, carbide, carbonitride or oxynitride of elements selected from a group consisting of B, Al, Si, Ga, Y, refractory hard metals, transition metals, and combinations thereof, having a CTE ranging from 2.0×10−6/K to 10×10−6/K in a temperature range of 25 to 1000° C.
In one embodiment, the protective coating layer 25 comprises a high thermal stability zirconium phosphates, having the NZP structure. The term NZP refers to NaZr2 (PO4)3, as well as to related isostructural phosphates and silicophosphates having a similar crystal structure. These materials in one embodiment are prepared by heating a mixture of alkali metal phosphates or carbonates, ammonium dihydrogen phosphate (or diammonium phosphate) and tetravalent metal oxides.
In one embodiment, the NZP-type coating layer 25 has a general formula: (L,M1,M2,Zn,Ag,Ga,In,Ln,Y,Sc)1(Zr,V,Ta,Nb,Hf,Ti,Al,Cr,Ln)m(P,Si,VAl)n(O,C,N)12 wherein L=alkali, M1=alkaline earth, M2=transition metal, Ln=rare earth and the values of l, m, n are so chosen that a charge balance is maintained. In one embodiment, the NZP-type protective coating layer 25 includes at least one stabilizer selected from the group of alkaline earth oxides, rare earth oxides, and mixtures thereof. Examples include yttria (Y2O3) and calcia (CaO).
In a third embodiment, the protective coating layer 25 contains a glass-ceramic composition containing at least one element selected from the group consisting of elements of the group 2a, group 3a and group 4a of the periodic table of element. The group 2a as referred to herein means an alkaline earth metal element including Be, Mg, Ca, Sr and Ba. The group 3a as referred to herein means Sc, Y or a lanthanoid element. The group 4a as referred to herein means Ti, Zr or Hf Examples of suitable glass-ceramic compositions for use as the coating layer 25 include but are not limited to lanthanum aluminosilicate (LAS), magnesium aluminosilicate (MAS), calcium aluminosilicate (CAS), and yttrium aluminosilicate (YAS).
In one example, the protective coating layer 25 contains a mixture of SiO2 and a plasma-resistant material comprising an oxide of Y, Sc, La, Ce, Gd, Eu, Dy, or the like, or a fluoride of one of these metals, or yttrium-aluminum-garnet (YAG). Combinations of the oxides of such metals, and/or combinations of the metal oxides with aluminum oxide, may be used. In a third embodiment, the protective coating layer 25 comprises from 1 to 30 atomic % of the element of the group 2a, group 3a or group 4a and from 20 to 99 atomic % of the Si element in terms of an atomic ratio of metal atoms exclusive of oxygen. In one example, the layer 25 includes aluminosilicate glasses comprising from 20 to 98 atomic % of the Si element, from 1 to 30 atomic % of the Y, La or Ce element, and from 1 to 50 atomic % of the Al element, and zirconia silicate glasses comprising from 20 to 98 atomic % of the Si element, from 1 to 30 atomic % of the Y, La or Ce element, and from 1 to 50 atomic % of the Zr element.
In another embodiment, the protective coating layer 25 is based on Y2O3—Al2O3—SiO2(YAS), with the yttria content varying from 25 to 55 wt. % for a melting point of less than 1600° C. and a glass transition temperature (Tg) in a narrow range of 884 to 895° C., with optional dopants added to adjust the CTE to match that of the adjacent substrate. Examples of dopants include BaO, La2O3, or NiO to increase the CTE of the glass, and ZrO2 to decrease the CTE of the glass. In yet another embodiment, the protective coating layer 25 is based on BaO—Al2O3—B2O3—SiO2 glasses, wherein La2O3, ZrO2, or NiO is optionally added to adjust the CTE of the glass to appropriate match the CTE of the substrate. In one example, the coating layer 25 comprises 30-40 mol % BaO, 5-15 mole % Al2O3; 10-25 mole % B2O3, 25-40 mole % SiO2; 0-10 mole % of La2O3; 0-10 mole % ZrO2; 0-10 mole % NiO with a molar ratio B2O3/SiO2 ranging from 0.25 to 0.75.
The protective coating layer 25 can accommodate small concentrations of other non-metallic elements such as nitrogen, oxygen and/or hydrogen without any deleterious effects on corrosion resistance or etch resistance. In one embodiment, the coating layer contains up to about 20 atomic percent (atom %) of hydrogen and/or oxygen. In another embodiment, the protective coating 25 comprises hydrogen and/or oxygen up to about 10 atom %.
The protective coatings layer 25 may be deposited on substrates by processes known in the art, including thermal/flame spray, plasma discharge spray, expanding thermal plasma (ETP), ion plating, chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), metal organic chemical vapor deposition (MOCVD) (also called Organometallic Chemical Vapor Deposition (OMCVD)), metal organic vapor phase epitaxy (MOVPE), physical vapor deposition processes such as sputtering, reactive electron beam (e-beam) deposition, ion plasma deposition, and plasma spray. Exemplary processes are thermal spray, ETP, CVD, and ion plating.
The thickness of the protective coating layer 25 varies depending upon the application and the process used, e.g., CVD, ion plating, ETP, etc, varying from 1 μm to a few hundred μm, depending on the application. Longer life cycles are generally expected when thicker protective layers are used.
Corrosion Resistant Connectors and Configurations: In a typical wafer processing environment with the use of corrosive gases, atomic entry of the fluorine based gases can rapidly attack components of the wafer processing apparatus through the contact areas or functional members with mechanical components such as electrical connections, inserts including but not limited to gas feed-through channels, recessed areas, raised areas, MESA, through-holes such as lift-pin holes, threaded bolt holes, blind holes, and the like. Example of functional members include but are not limited electrical leads, tabs, inserts, and through-holes, etc, which penetrates through the contact areas, thus creating a gap for corrosive gases to attack the base components such as the substrate.
In one embodiment of the invention, the leads to the electrode, mechanical components and fasteners for attaching function members are coated with an electrically conductive etch resistant material having sufficient ductility property to conform the thermal expansion of the base material. In another embodiment, the electrode itself is coated with the electrically conductive etch-resistant material. Examples of suitable etch-resistant materials include but are not limited to nickel, chromium, superalloys, or other conductive materials that have a ductility of >5% when applied as a coating layer.
In one embodiment of the invention, customized connectors are used providing etch resistant protection to the connection. In a second embodiment, etch resistant electrically conductive materials are used to protect exposed electrical connectors from the corrosive environment.
In yet another embodiment, etch resistant compositions are used as fillers, adhesives, glues, or sealants to further provide protection to the contact connections from atomic entry of corrosive gases.
Embodiments of the corrosion resistant connections of the invention are further illustrated as follows with references to the figures.
A conector nut 220 is used to fasten a threaded connector rod 210 into place. In one embodiment, the threaded connector rod 210 and connector nut 220 are made from the same refractory metal material with a CTE that closely matches the CTE of the substrate 100 and the over-coating layer 300. An example is molybdenum with a CTE that closely matches the CTE of the AlNlayer. In a second embodiment, they are of different materials with closely matched CTEs. In one embodiment, the rod 210 and/or nut 220 are additionally plated with Nickel or other conductive etch resistant materials (not shown). As illustrated, the rod 210 is threaded into a threaded hole in the substrate 100. In one embodiment (not shown), the rod 210 is press-fit into a blind hole in the substrate, or glued into a hole in the substrate 100.
As it is sometimes difficult to provide adequate coating in sharp corners or crevices in the deposition process, i.e., called “partial shadowing,” which could possibly result in a thinner over-coating limiting the life of the wafer handling apparatus,
In yet another embodiment of the wafer handling apparatus 10 as illustrated in
In
It should be noted that the corrosion resistant configurations of the invention are not limited to the illustrated embodiments, features of the embodiments may be combined and or modified, allowing variations from the embodiments without departing from the concept of a wafer processing with corrosion resistant connections.
Corrosion Resistant Filler/Adhesive/Protective Sealant: As illustrated in the Figures of various embodiments of the invention with corrosion resistant connections, a corrosion resistant filler 230 is used in a number of embodiments.
As used herein, the term “filler” may be used interchangeably with “sealant,” “glue,” “adhesive,” or “protective sealant,” referring to a material that can further protect components in wafer processing apparatuses such as electrodes, connectors, rods, fasteners such as nuts, rivets, etc. from microscopic attacks in the wafer processing chamber. The filler can comprise any ceramic, glass, or glass-ceramic material that exhibits resistance to elevated temperature and is thermally compatible with the substrate and other components, e.g., the graphite heater element, metal fasteners, etc. The filler is also chemically compatible with the semiconductor processing environment.
A filler is regarded herein as thermally compatible if the coefficient of thermal expansion (CTE) of the filler matrix closely matches the CTE of the adjacent substrate, thus the differential thermal expansion of materials during thermal cycling does not result in delamination or peeling of the filler. In one embodiment, the filler comprises a material having a CTE having a value in-between that of the ceramic substrate and the metallic interconnect/fastener. Borosilicate glass, aluminosilicate glass and high silica glass as well as mixtures of glass are examples of suitable fillers.
A filler regarded herein as chemically compatible for use in a semiconductor processing environment means a filler that is low in the reactivity with a corrosive gas or its plasma; even if a reaction with fluorine in the corrosive gas occurs, the formed substances are a high-boiling compound; and it is effective for suppressing corrosion caused by the plasma or corrosive gas.
In one embodiment, the filler composition contains at least one element selected from the group consisting of elements of the group 2a, group 3a and group 4a of the periodic table of element. The group 2a as referred to herein means an alkaline earth metal element including Be, Mg, Ca, Sr and Ba. The group 3a as referred to herein means Sc, Y or a lanthanoid element. The group 4a as referred to herein means Ti, Zr or Hf.
Examples of suitable compositions for use as fillers include but are not limited to lanthanum aluminosilicate (LAS), magnesium aluminosilicate (MAS), calcium aluminosilicate (CAS), and yttrium aluminosilicate (YAS). The choice of a particular matrix material is based on the anticipated demands of the intended application. In one embodiment, the matrix material is selected to match a heater application with AlNcoating layer with a theoretical average CTE of 4.9×10−6/K, a graphite heater element having a theoretical CTE of 5.3×10−6/K In another embodiment, a filler is selected for a CTE value in-between the CTE of the AlNcoating layer of 4.9×10−6/K and the CTE of the refractory metal fasteners, comprising a material such as tungsten W, molybdenum Mo, tantalum Ta, or alloys such as copper tungsten (CuW), copper molybdenum (CuMo with a CTE of 6.9 ppm/C for 85/15 MoCu), molybdenum manganese (MoMn) etc.
In one embodiment, the filler is a composition based on BaO—Al2O3—B2O3—SiO2 glasses, wherein La2O3, ZrO2, and NiO is optionally added to adjust the CTE of the glass to appropriate match the CTE of the substrate. In one embodiment, the composition comprises 30-40 mol % BaO, 5-15 mole % Al2O3; 10-25 mole % B2O3, 25-40 mole SiO2; 0-10 mole % of La2O3; 0-10 mole % ZrO2; 0-10 mole % NiO with a molar ratio B2O3/SiO2 ranging from 0.25 to 0.75. In another embodiment, La2O3, ZrO2, or NiO is added in an amount sufficient for the filler to have a CTE matching that of AlN as a coating layer and graphite as a base layer, with the addition of La2O3 and NiO increasing the CTE of the glasses and the addition of ZrO2 decreases the CTE of the glasses.
In another embodiment, the filler is a composition based barium lanthanum silicate (BLS) glass, with general compositions ranging from 30-35 mole % BaO, 10-15 mole % La2O3, and 50-60 mole % SiO2, for glasses having CTE of 10-12 ppm and softening temperature in the range of 750° C. to 850° C.
In yet another embodiment, the filler is a composition based on Y2O3—Al2O3—SiO2 (YAS) glasses, with the yttria content varying from 25 to 55 wt. % for a melting point of less than 1600° C. and a glass transition temperature (Tg) in a narrow range of 884 to 895° C., and wherein the CTE generally increases with increasing Y2O3 and decrease with increasing SiO2. In one embodiment, the YAS filler composition comprises 25-55 wt. % Y2O3, 13 to 35 wt. % Al2O3, and 25 to 55 wt. % SiO2 for a CTE ranging from 31 to 70 10−7/K. In a second embodiment, the YAS composition comprises 17 Y2O3-19 Al2O3-64 SiO2 all in mol. % for excellent chemically durable properties.
In one embodiment, dopants are added to YAS glass composition in an amount sufficient to optimize the CTE to match that of the adjacent substrate. Examples of dopants include BaO, La2O3, ZrO2, or NiO, with most components to increase the CTE of the glass, with the exception of ZrO2 which decreases the CTE of the glass.
In one embodiment, the filler composition comprises from 1 to 30 atomic % of the element of the group 2a, group 3a or group 4a and from 20 to 99 atomic % of the Si element in terms of an atomic ratio of metal atoms exclusive of oxygen. In one embodiment of an aluminosilicate glass, the composition comprises from 20 to 98 atomic % of the Si element, from 1 to 30 atomic % of the Y, La or Ce element, and from 1 to 50 atomic % of the Al element. In yet another embodiment, the aluminosilicate glass has a composition such that the atomic ratio of the respective metal elements (Si:Al:group 3a) falls within the range connecting respective points of (70:20:10), (50:20:30), (30:40:30), (30:50:20), (45:50:5) and (70:25:5). In one embodiment of a zirconia silicate glass filler, the composition comprises from 20 to 98 atomic % of the Si element, from 1 to 30 atomic % of the Y, La or Ce element, and from 1 to 50 atomic % of the Zr element. In one example, the zirconia silicate glass has a composition such that the atomic ratio of the respective metal elements (Si:Zr:group 3a) falls within the range connecting respective points of (70:25:5), (70:10:20), (50:20:30), (30:40:30), (30:50:20) and (45:50:5). In another embodiment of a zirconia silicate glass filler, the atomic ratio of the respective metal elements (Si:Zr:group 3a) falls within the range connecting respective points of (70:25:5), (70:10:20), (50:22:28), (30:42:28), (30:50:20) and (45:50:5). In the case of a group 2a-containing zirconia silicate glass, the zirconia silicate glass has a composition such that the atomic ratio of the respective metal elements (Si:Zr:group 2a) falls within the range connecting respective points of (70:25:5), (45:25:30), (30:40:30), (30:50:20) and (50:45:5).
In one embodiment, the filler composition is a mixture of SiO2 and a plasma-resistant material comprising an oxide of Y, Sc, La, Ce, Gd, Eu, Dy, or the like, or a fluoride of one of these metals, or yttrium-aluminum-garnet (YAG). Combinations of the oxides of such metals, and/or combinations of the metal oxides with aluminum oxide, may be used. For example, Y2O3 can be used in combination with a minority percentage of Al2O3 (typically, less than about 20% by volume) to match the CTE of the glass filler composition with the underlying substrate of the heater.
Method for Forming & Applications of the Filler Composition: In one embodiment, the filler composition is in the form of a paste or paint, to be applied as a “filler” around the contact elements of the wafer processing device of the invention. In one embodiment, the composition is applied as a paste, spreading around the contact elements or fasteners forming a “bead.” In a second embodiment, the composition is applied as a paint, being sprayed or brushed onto the contact elements or fasteners forming a protective coating layer of at least 0.1 mil, protecting the connections from chlorine or fluorine species in a semiconductor processing environment. In a third embodiment, a protective coating layer of at least 0.5 mil is applied.
In yet another embodiment, the filler composition is applied broadly onto the heater assembly using a process known in the art for applying glass-ceramics, including thermal/flame spray, plasma discharge spray, sputtering, and chemical vapor deposition, for a coating/sealant layer of at least 0.5 mil to seal openings, cracks, etc. between the contact elements and the adjacent parts, as well as providing a protective coating layer onto the heater. In one embodiment, the protective sealant coating layer has a thickness of 0.5 to about 4 mils. In yet another embodiment, the surface of the substrate to be sealed is first heated to at least of 150-200° C. prior to being coated with a layer of the glass ceramic composition.
In applications as an adhesive/coating layer or a sealant for heaters or wafer holder device, the composition provides protection at >400° C. in both oxidizing and reducing atmospheres over an extended period of time (10 hrs.) in a semi-conductor processing environment. Additionally, the filler composition accommodates stresses generated due to potential CTE mismatches between the various heater components through hundreds of thermal cycles. In one embodiment for a paste application, the filler composition is first milled, forming “glass frit” with an average particle size of less than 100 mesh. In one embodiment, the glass frit has an average particle size of <80 mesh. In a second embodiment, of less than 60 mesh. In a third embodiment, of less than 40 mesh.
In one embodiment, the glass frit is first mixed with a metal oxide powder (in solution) in a ratio of 80:20 to 95:5 glass frit to metal oxide. Examples of metal oxide include but not limited to aluminum oxide, magnesium oxide, calcium oxide, yttrium oxide, and zinc oxide. In one embodiment, the metal oxide is Al2O3 having an average particle size of about 0.05 μm. In a third embodiment, the glass frit is mixed with a metal oxide in a solution form, e.g., colloidal silica, colloidal alumina, colloidal yttria, colloidal zirconia, and mixtures thereof
In one embodiment, the mixture is blended in equipment known the art, e.g., a ball mill, with a carrier solution forming a slurry or paste in a ratio of 10-25 wt. % carrier solution to 75-90 wt. % of glass frit/metal oxide mixture. In one embodiment, the carrier solution is a mixture of distilled water with less than 1 wt. % nitric acid. In a second embodiment, the carrier solution is a mixture of ethanol and distilled water. In a third embodiment, the carrier solution is LiOH.
In the example, a glass was prepared from a homogeneous powder mixture from reagent grade raw materials in the amount of 45 wt % yttrium oxide, 20 wt % aluminum oxide, and 35 wt % silicon dioxide. The powder mixture was melted in a platinum crucible at 1400° C. for 1 hr. The glass melt was poured into a steel mold and annealed from 680° C. to room temperature in 12 h. Each glass was crushed and milled in propanol using a mill with Al2O3 elements, forming a glass grit composition having an average particle size of 100 μm.
In the next step, the glass grit was added to a colloidal alumina solution in an amount of 75 wt. % glass grit and 25 wt. % colloidal alumina, forming a glass-ceramic adhesive paint/adhesive. The colloidal alumina solution is commercially available as Nyacol® AL20DW from Nycaol Nano Technologies, containing 20-25 wt. Al2O3, <1 wt. % nitric acid in 75-79 wt. % distilled water. In applications, the paste is heated >1000° C. to form an etch resistant layer protecting the underlying components. The high temperature allows the paste to form a seal on contact surfaces including but not limited to functional members, lead, fasteners such as nuts, bolts, rivets, etc.
An electrically conductive heating element (molybdenum manganese) was deposited onto a ceramic substrate (AlN). The substrate contained through-holes to allow for installation of electrical contacts. In the next step, Ni-plated molybdenum posts were installed using molybdenum fasteners. The adhesive of Example 1 was painted around the contact points between the Ni-plated molybdenum posts, the molybdenum fasteners, heating element on the AlN substrate, and the AlN substrate. Next, the entire heater assembly including the contact was coated with AlN through a CVD process.
In a test simulating conditions of a heater with AlN substrate in a semiconductor processing environment, corrosion testing of the heater and contact was conducted after 100 thermal cycles between 400 and 500° C. at a ramp rate of 45° C./min. In another test, a heater with graphite core was cycled 100 times between 400 and 600° C. with a ramp rate of 60° C./min. The tests were to determine whether the glass ceramic adhesive would perform sufficiently under thermal stresses. After 100 thermal cycles, visual inspection showed that the heater coatings had no signs of failure due to thermal stresses, indicating that the CTE of the components was sufficiently matched, including that of the glass ceramic adhesive to protect the heater coatings.
Additionally, the heaters were installed in a vacuum chamber and brought to a pressure of approximately 1 millitorr. Power was then applied to the heater until the heater achieved 400° C. Once at 400° C., the heater was exposed to a fluorine/argon plasma for 10 hours. The plasma was generated using 400 sccm (standard cubic centimeters) of NF3 gas and 1200 sccm of Ar gas. The chamber pressure during testing was 2.8 torr.
There was not significant electrical resistance change (<0.4%) observed on both of the heaters during the 10-hour etching process. The heaters were removed from the chamber and visually observed after 10 hrs. There was no failure of the AlN coating around the contact fasteners. There was no failure of the contact points between and within the electrical contact assembly and the heater. The glass ceramic adhesive functioned as an excellent sealant material for the heater of the invention.
A filler composition comprising a powder mixture from reagent grade raw materials in the amount of 45 wt % yttrium oxide, 20 wt % aluminum oxide, 35 wt % silicon dioxide was compared with other materials known in the art, including alumina, molybdenum, TaC, AlN, graphite, and nickel. In the test, a) dimensions and mass of the sample was measured prior to testing; b) parts were placed in a vacuum chamber, which is then pumped down to a pressure of approximately 1 millitorr; c) the parts were heated to the desired testing temperature; d) a fluorine/argon plasma was generated above parts for the desired time period; e) after testing, the parts were removed from the chamber and the mass after exposure was recorded. The corrosion rate is calculated as follows:
corrosion rate=mass loss/density/exposed surface area/time;
wherein a negative corrosion rates indicate mass gain after exposure, which translates to excellent corrosion resistance.
The results of the experiments comparing YAS filler composition with other materials are as follows. Mo data is generally available from scientific references.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. All citations referred herein are expressly incorporated herein by reference.
This application claims the benefits of U.S. 60/806648 filed Jul. 6, 2006, which patent application is fully incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60806648 | Jul 2006 | US |
