BACKGROUND OF THE INVENTION
This application claims the benefit of U.S. Provisional Patent Application No. 60/506,336, entitled “HIGH-ALLOY METALS REINFORCED BY DIAMOND-LIKE FRAMEWORK AND METHOD OF MAKING THE SAME”, filed on Sep. 25, 2003
The present invention relates to metal alloys. Particularly the invention relates to amorphous metals or metal-metalloids alloyed with non-metallic elements.
Over the past few decades, amorphous alloys have been produced with various characteristics with regard to magnetic, mechanical, and chemical properties, electrical resistivity, and corrosion resistance, and also at a relatively low cost. For instance, various amorphous Fe group alloys, Pd-alloys, Cu alloys, Zr alloys, and Ti-alloys have been produced by rapidly cooling the molten alloy. These amorphous metals possess certain mechanical and chemical characteristics not achievable in crystalline materials. Rapid cooling technology, however, does not allow for adequate control of the fine structure of solidifying metals. A combined amorphous and nano-crystalline structure, such as in U.S. Pat. No. 5,873,958, may provide metals with improved mechanical properties, especially when nano-crystals possess some elongated forms. The combined structure is typically produced with multiple mechanical and thermal treatments of metals, e.g., involving a multi step structural transformation of solid metals.
Surface amorphisation or passivation may be used to improve corrosion resistance. U.S. Pat. No. 5,062,900, for example, describes a process for improving corrosion resistance of a metallic material by treating the surface with a low-temperature plasma, at a pressure of 1 to 103 Pa in an atmosphere of one or more specified gases to modify the surface's state.
Intermetallic and transition metal-metalloid amorphous alloys, such as silicides, have also been produced. Traditionally, such products are produced using ceramic technology. Conventional ceramic materials, however, have low fracture toughness, especially at high temperatures, low strength, and poor reliability. Ceramic nanocomposites with improved mechanical properties at high temperatures have been developed by uniformly dispersing submicrometer or nano-sized second phase particles within the matrix grains and at the grain boundaries. Incorporating submicron molybdenum metal or molybdenum-containing compounds into the ceramic improves mechanical properties such as strength, fracture toughness, and reliability.
U.S. Pat. No. 5,795,837, discusses a multi-step process that involves combining liquid-phase chemical reactions, spraying, and sintering to produce nanometer-sized, uniformly dispersed molybdenum, molybdenum silicide, or molybdenum carbide/ceramic sintered composites.
U.S. Pat. No. 5,865,909 discusses a boron-modified molybdenum silicide material having a composition of about 80 to 90 weight % Mo, about 10 to 20 weight % Si, and about 0.1 to 2 weight % B. A multiphase microstructure that includes a Mo5Si3 phase increases high temperature creep resistance. The boron modified molybdenum silicide material is fabricated into electrical components, such as resistors and interconnects, and other high temperature structural members. U.S. Pat. No. 6,099,978 discusses a molybdenum silicide-containing product that includes tungsten silicide having an emissivity about 0.7 for use as heaters in rapid solidification processing (RSP) and rapid thermal processing (RTP).
Titanium silicide is widely used in the microelectronics industry for self-aligned patterning due to an advantageous combination of its electrical, chemical and thermal properties. However, TiSi2 has two different crystalline phases. The higher resistivity C49 phase is formed first. In order to obtain the lower resistivity C54 phase, a second high-temperature temperature annealing step is required that can have detrimental effects on the silicide and other integrated circuit elements, such as peeling and cracking of dielectric elements and a change of electrical characteristics of conducting elements. In general, as line-widths and film thickness continue to be scaled down, it becomes important to eliminate extra annealing. On the other hand, if the phase transformation is not completed or is not uniform, very large scale integrated circuits experience accelerated degradation of structure and performance. In some very large scale integrated circuits these types of failures may reach 5-10 percent. Although various approaches were suggested to resolve this polymorphism problem, all of them suffer from similar deficiencies. In addition, the crystalline structure of silicide causes a principle problem in forming a transistor gate with length of less than 0.1 microns.
U.S. Pat. No. 5,646,070 discusses a method of forming electrically conductive contacts to a surface of silicon semiconductor material with three layers of different suicides, using various PVD and CVD processes for deposition followed by annealing. Such a complex technology is necessary because no one silicide alone can satisfy simultaneously the requirements of adhesion, electrical resistivity, and self-aligned formation of the contacts. On the other hand, the multi layer structure and CVD deposition result in problems with inter-layer and layer CVD gas media interaction.
U.S. Pat. No. 6,372,566 discusses amorphizing a top portion of a gate structure containing silicides of Mo, Co, W, Ta, Nb, Ru, Cr or a combination of refractory metals. The amorphizing is accomplished by introducing impurities of As, Ge, or their combination. However, such a partial amorphizing also introduces extra thermal steps in the VLIC technology, as well as additional substances, which may diffuse into the transistor structure and deteriorate its characteristics. Furthermore, any post-amorphizing of an already formed solid does not create a uniform structure and usually results in built-in stress. All these problems would become increasingly serious as the very large scale integrated circuit patterning advances into a sub-micron range.
U.S. Pat. No. 5,776,264 discusses a method of slow, low-temperature, controlled oxidation of metallic powders with the particle size less than ˜80 microns in an oxygen starved environment containing less than 3% oxygen and an inert gas. The amorphous metal oxide can then be reacted in a reducing environment, such as hydrogen, to form the amorphous elemental metal. This amorphous elemental metal can then be reacted with a carburizing gas to form the carbide, with ammonia gas to form the nitride, or with hexamethylsilane to form the silicide. However, this multi-step high-temperature process may be only applied for powder production.
U.S. Pat. No. 5,718,867 discusses an alloy based on a silicide containing: chromium 41-55%, molybdenum 13-35%, and silicon 25-35%; or chromium 35-55%, molybdenum 13-35%, silicon 13-35%, yttrium 0.001-0.3%, and/or tungsten 0.001-10%. This alloy is distinguished by a high oxidation resistance, and insofar as it still has mechanical strength at temperatures of over 1000 degrees, which beneficially may be used for structural material in gas turbines. The important advantage of these alloys is a lower density than the nickel-base superalloys normally used.
U.S. Pat. No. 5,585,313 discusses a SiC—MoSi2 infiltration material with high heat-resistant property, which can be used at 1500° C. at atmospheric pressure. This ceramic composite material having high heat-resistant properties can be obtained by infiltrating aluminum silicide with molybdenum in a porous preform of silicon carbide having porosity of 10 to 50% in volume ratio. This material is expressed by a formula of Mo (Alx Si1-x)2 (where 0.1<x<0.5).
U.S. Pat. No. 5,708,408 discusses an electrical resistance element consisting of combined molybdenum and tungsten silicide Mox W1-x Si2, where x is between 0.5 and 0.75, wherein from 10% to 40% of the total of the silicide material is replaced with at least one of the compounds molybdenum boride or tungsten boride; those compounds are present in the silicide material in particle form.
U.S. Pat. No. 6,106,957 discusses a metal-matrix diamond or cubic boron nitride composite. The metal-matrix/diamond composite includes grains of diamond uniformly distributed in a metal matrix. Alternatively, grains of cubic boron nitride may be used. Suitable metals for the metal matrix material may include nickel, cobalt, iron, and mixtures or alloys thereof. Other transition metals also may be used. The metal-matrix/diamond or metal matrix/cubic boron nitride composite has high fracture toughness due to its fine microstructure. Such a metal-matrix/diamond or metal-matrix/cubic boron nitride composite is suitable for use in blanks or cutting elements for cutting tools, drill bits, dressing tools, and wear parts.
It is understood from general knowledge and empirical experience that the finer the structure achieved, the better properties of the final product. However, to obtain finer structures, additional treatment steps are required. The structural resolution of such post-solidification technology is still very limited, and only certain specific shapes of metal products like wire are feasible. The thermal stability of produced structure is also not high enough for some applications.
- SUMMARY OF THE INVENTION
U.S. Pat. Nos. 5,352,493; 5,718,976; and 6,080,470 discuss two novel classes of metal-carbon composites based on diamond-like and synergetic graphite diamond stabilized amorphous carbon. These composites possess very low stress or no stress, long-term thermal stability at much higher temperatures than DLC (conventional diamond like carbon), may sustain during a short exposure, and may be grown up to thicknesses of a few hundred micrometers. Conventional DLC may not be grown over the thickness over ˜2 micrometers. Metal-carbon composites of atomic scale (meaning they are uniform in composition when viewed at the individual atom level) include interpenetrating diamond-like carbon and metallic atomic-scale frameworks consisting of random chains of atomic diameters. Some of these materials show exceptionally high thermal stability with regard to other known amorphous materials while preserving mechanical and tribological properties of diamond-like matter and allow controllable variation of electrical properties over a range of 18 orders of magnitude of conductivity which is not achievable for other known classes of materials. Still some properties, such as ductility, thermal stability, and high-temperature oxidation resistance are not sufficient for many applications. Additionally, the electrical conductivity of predominantly carbon materials is limited, while ferromagnetic properties and some other physical properties and metallic features are not achievable.
The nano-crystalline metal or metalloid alloys of the present invention, whether amorphous or otherwise, possess unique structural uniformity on an atomic scale, which are free of larger clusters or separate phases. The metal, e.g., films, are reinforced, stabilized, and hardened with a framework formed by predominantly sp3-bonded carbon, also known as diamond-like carbon. Optionally, other alloying nonmetallic elements selected from the group of Si, B, O, N may additionally be used to stabilize the entire structure.
In one aspect of the invention, a class of high-alloy metals is provided that includes a metallic matrix and a reinforcing framework that penetrates through the metallic matrix to reinforce the metallic matrix. The reinforcing framework includes a diamond-like sp3 bonded carbon component interspersed within the metallic matrix.
This new class of amorphous and nano-crystalline alloys overcomes many barriers of existing technologies, by, in certain instances, simultaneously increasing the thermal stability and corrosion resistance of the high alloy amorphous metals and preserving many mechanical and tribological properties of diamond-like matter. The new amorphous or nano-crystalline high-alloy metals, intermetallics, and transition metal-metalloids possess very high uniformity and superior structural stability. They may be deposited upon various substrates as uniform, multi-layer or functionally graded coatings with a pre-designed multi-layer profile in one continuous deposition process. The deposited layers generally have excellent adhesion to the various substrates, and the interfaces between the layers of different compositions are self-consistent, the layers possess the proper amorphous or required nano-crystalline structure, and they do not require post-deposition amorphizing. In one embodiment, the deposition temperature is low, and the built-in stress is absent or extremely low. In one embodiment, the deposited layers are free from pores exceeding the diameter of metallic atoms, and the specific gravity of deposited materials is essentially below that of the corresponding crystalline alloys. The resistivity of said alloys is controllably variable up to higher values than available in pure metals or refractory intermetallics. The emissivity of certain of metal-metalloid-based alloys exceeds 0.8.
In another aspect of the invention, a method of forming high-alloy metals containing a metallic matrix reinforced by a diamond like framework that includes carbon atoms in an sp3 state is providing by depositing on a surface of a substrate a layer of the metal matrix, by directing toward the substrate a first deposition flux that includes least one constituent metal atomic species selected from the group consisting of metal ions, metal atoms, and metal clusters. A carbon constituent may then be deposited on the metal matrix by directing toward the matrix a second deposition flux that includes carbon. The temperature of the substrate during the depositions may be maintained to less than about 400 degrees C., and preferably between 10 degree C. and 150 degrees C.
BRIEF DESCRIPTION OF THE FIGURES
Additional aspects of the present invention will be apparent in view of the description which follows.
FIG. 1 is a schematic model representation of the atomic arrangement of a high alloy amorphous metal reinforced with a carbon diamond-like framework, in accordance with one embodiment of the present invention.
FIG. 2 is a schematic model representation of the atomic arrangement of a high alloy nano crystalline metal reinforced with a carbon diamond-like framework, in accordance with one embodiment of the present invention.
FIG. 3 is a graph showing the range of metal content in Atomic % vs. Radius of metallic elements, in accordance with one embodiment of the present invention.
FIG. 4 is a schematic view of vacuum deposition system for fabricating carbon reinforced high-alloy metals, in accordance with one embodiment of the present invention.
FIG. 5 is a schematic view of vacuum deposition system for fabricating carbon reinforced high-alloy metals, having molecular beam deposition and radiation surface heating capability, in accordance with one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 6 is a flow diagram showing the deposition process in accordance with one embodiment of the present invention.
The present invention provides a new class of high-alloy metals that include a metallic matrix and a reinforcing nonmetallic framework that penetrates through the metallic matrix to provide reinforcement thereto. The reinforcing nonmetallic atomic-scale framework generally includes a diamond-like sp3 bonded carbon component that is interspersed within the metallic matrix to provide reinforcement to the metallic matrix. In one embodiment of the invention, the integration of the metallic matrix and the reinforcing nonmetallic framework occurs on an atomic scale of individual atoms, unlike conventional alloy structures that exhibit a mixture of single crystal phases separated by grain boundaries. In this instance, the high metal alloys are unlike conventional metal alloys in that they are predominately amorphous in structure, and may have carbon contents that are above, e.g., far or substantially above, the soluble levels of carbon allowable in most alloys. The term “high-alloy” material generally refers to a material with a high degree of bonding and structural integration between the carbon and the metal on an atomic or nanometer scale. In one embodiment of the invention, unlike conventional process technology where the metal alloy is solidified from melts, the high-alloy metals described in the present invention are formed by deposition processes such as sputtering and chemical vapor deposition. Optionally, other nonmetallic elements in addition to carbon may be used to stabilize the diamond-like carbon framework and the metal structure, such as silicon, boron, oxygen, nitrogen, or their combination.
As used herein, the term “high-alloy metal” refers to a material that has a structure that includes a metallic matrix combined with a reinforcing, three dimensional, non-metallic framework of sp3 bonded carbon (with or without the addition of other elements), where the non-metallic framework is an intrinsic and inseparable component of the alloy structure down to the atomic level. The three dimensional non-metallic framework of sp3 bonded carbon is also referred to as “a carbon diamond-like framework”. The term “high-alloy amorphous metal” refers to a high-alloy metal where the metallic matrix is predominately amorphous in structure with little or no detectable crystallinity. The term “high-alloy nano-crystalline metal” refers to a high-alloy metal where there is detectable crystallinity in the metallic matrix, but the crystals are on the order of about 100 nanometers or below in size. As used in this specification, the terms “high-alloy metal” and “high-alloy metal reinforced with a carbon diamond-like framework”, “carbon reinforced high-alloy metal”, and “carbon reinforced alloys” are synonymous.
FIG. 1 is a schematic model representation of an atomic arrangement of the high-alloy amorphous metal reinforced with a carbon diamond-like framework, in accordance with one embodiment of the present invention. The smaller diameter spheres 1 represent carbon atoms and larger diameter spheres 2 represent metal atoms. In this schematic, a high-alloy metal, preferably an alloy based on one of transition metals or their combination, is reinforced with predominantly sp3-bonded carbon, also known as diamond-like carbon. The metallic matrix of the high-alloy metal shown is predominantly amorphous. A metal is predominately amorphous if there is little or essentially no detectable crystalline phases of the metal. The structure shown is therefore predominantly free from nano- or micro-crystals of metals, carbides, or free carbon. Typically, nano-crystals are crystals in the about 30 nm to about 100 nm size range. More specifically, a high metal alloy is predominately if the content of crystals of any size detectable by x-ray or electron diffraction techniques, or by STM (scanning tunneling microscopy) or AFM (atomic force microscopy) does not exceed about 10 weight % of the total, and more preferably does not exceed about 1.0 weight % of the total content of material.
FIG. 2 is a schematic model representation of atomic arrangement of the high-alloy nano-crystalline metal reinforced with a carbon diamond-like framework, in accordance with another embodiment of the present invention. In this embodiment, the structure of the metallic matrix is predominately nano-crystalline, exhibiting crystal sizes in the range of about 30 to about 100 nm in size. In FIG. 2, individual metal atoms 2 and individual carbon atoms 1 can be seen in clusters. Metal atom clusters 14 and 16 are examples of nano-crystals of discrete metal phases. Carbon atom clusters are shown in areas 10 and 12. A metal matrix is predominately nano-crystalline or crystalline if the content of nano-crystals or crystals of any size, respectively, detectable by x-ray or electron diffraction techniques, or by STM or AFM, for this state, exceeds about 10 weight % of the total.
In another embodiment of the present invention, the nano-crystalline content is between the embodiments described in FIG. 1 and FIG. 2 above. That is, where the structure of the high-alloy metal exhibits crystal sizes in the range of about 30 to about 100 nm in size, and the content of crystals of any size detectable by x-ray or electron diffraction techniques, or by STM or AFM, is between about 1 weight % and about 10 weight % of the total. Thus, it is possible to alter the structure of the present invention in a controlled and continuous manner from a totally amorphous state as is shown in FIG. 1 to a nano-crystalline state as shown in FIG. 2.
In yet another embodiment, according to the present invention, the predominantly amorphous high-alloy metal contains an atomic-scale framework or nano-wires of selected metallic elements. It can be seen in FIG. 1 that in a number of areas the metal atoms 2 are touching each other in long strings. By extending this structure over longer atomic distances, the metal atoms can be described as forming a nanowire backbone structure within the amorphous carbon phases. The carbon phases can also form intertwined backbone structures as well, giving the composite metal-carbon structure unique and desirable physical properties. Due to the “single dimensionality” of long strings of atoms, the observed crystal structure is still amorphous, even though there is a backbone structure in the material.
The pure amorphous structure of high-alloy metals shown in FIG. 1
may be distinguished from the nano-crystalline structure shown in FIG. 2
by a number of methods, which can be used singly or in combination:
- 1. High-resolution x-ray diffraction, especially synchrotron beam light source diffraction. This method allows examining the entire volume of relatively thick materials, although it possesses a limited sensitivity to the trace percentage of nano-crystals.
- 2. Electron diffraction. This method possesses a high resolution sensitive to the trace levels of nano-crystals, although it only allows examination of the thin sub-surface layer in the nanometer depth range.
- 3. Non-linear optical response, especially second harmonic generation under intensive laser irradiation. This method is very sensitive to metallic nano-crystals and allows examining the thin sub-surface layer in the nanometer depth range. It is less sensitive to the state of the surface than electron diffraction.
In the aforementioned embodiments, the metallic component of the high-alloy metal may be selected from among the following: Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Co, Ni, Pd, Ir, Pt, Rh, Ru, Os, Ag and Cu or alloys or combinations thereof. High-alloy metals, where the metallic component is Cr, for example, may find use in products such as high-precision variable resistors in radio-electronics, position transducers, surface heaters, and non-electrochemical chromium coatings for virtually any substrate. These alloys have high thermal stability, good oxidation resistance, high micro-hardness, high wear resistance, and high thermal shock resistance. The addition of Fe and Ni to the Cr improves the chemical corrosion resistance and biocompatibility, potentially replacing the silver on plated electrodes used in electrocardiographs, electroencephalographs and other bio-electronic monitoring functions. The improved corrosion resistance may be further utilized in coatings applied to lower cost substrates such as carbon steel, where the cost of the total product can be reduced compared to the manufacture utilizing solid stainless steel. The aforementioned alloys can also be used as a substitute for Cr electroplated coatings, replacing a toxic and environmentally unfriendly process.
High-alloy metals that include Co, Fe, and Ni may be utilized in applications requiring good magnetic, electrical resistivity, and thermal characteristics. High-alloy metals containing Mo, W, and Hf have utility in cold emission cathodes, where they exhibit a higher stability and reduced work function compared to the pure component counterparts. The addition of Cr to the Mo, W, and Hf produces an alloy useful in thermal resistors widely used in ink jet printing heads and office copy machines. High-alloy metals comprising W, Hf, Ti, Cr, Ta, and Nb, in various combinations, may be utilized as surface coatings for cutting tools, due to the combined properties of hardness and low friction. Metals of the platinum group such as Pt, Pd, Rh, Ru, Ir, Os, and Re, as well as Ni, Cu, Mo, V, and Ag have found widespread utility as catalysts for numerous applications. High-alloy metals containing these elements have a significant potential for catalytic applications, since the nano-crystalline structure of the catalytic metal matrix produces a high effective dispersion and subsequent high catalytic activity. Deposition of very thin films on high surface area substrates further enhances total catalytic activity while minimizing total catalyst metal consumption.
In a one embodiment of the present invention, silicon and oxygen may be added to the high metal alloy carbon reinforced structures, in either the predominately amorphous structure shown in FIG. 1 or the nano-crystalline structure shown in FIG. 2. In this instance, the high metal alloy carbon reinforced structure is stabilized by amorphous silicon, and the amorphous silicon is stabilized by oxygen.
In the fully amorphous form, the carbon-carbon bonds, metals-carbon bonds, metal-silicon bonds, silicon and metal oxide bonds, and the silicon-carbon bonds are randomly and uniformly distributed through the entire high-alloy structure. The structure is predominantly free from nano- or micro-crystals of metals, carbides, silicides, oxides, or free carbon. In this embodiment, the observed crystallinity is similar to that observed for the structure of FIG. 1. Specifically, the content of crystals (between about 30 and about 100 nanometer) of any size detectable by x-ray or electron diffraction techniques, or by STM or AFM does not exceed about 10 weight % of the total, and more preferably does not exceed about 1.0 weight % of the total content of material.
In the nano-crystalline structure, the addition of silicon and oxygen produce a nano-crystalline high-alloy metal comprising nano-crystals of metals and/or metal-metalloid compounds, such as carbides or silicides. In this case, the content of crystals (between about 30 and about 100 nanometer) of any size detectable by x-ray or electron diffraction techniques, or by STM or AFM exceeds about 10 weight % of the total content of material. The transition between the fully amorphous structures and the nano-crystalline structures are continuously controllable, allowing the production of intermediate levels (between about 1% and about 10%) of nano-crystallinity.
The carbon content of either the nano-crystalline or amorphous embodiments described above may be in the range of about 10 volume % to about 50 volume %. Preferably, the carbon content should be within the range of about 25 to about 33 volume %. The minimum preferable volume fraction of about 25% is determined by the structural percolation threshold defining the combined content of stabilizing elements sufficient to form a continuous stress free network penetrating throughout of high-alloy reinforced metal. Carbon content below about 25 volume % is not sufficient to form a continuous diamond-like framework, if so desired. If carbon content is less than about 25 volume %, but higher than about 10 volume %, separate and randomly distributed carbon fragments are formed within the structure. These carbon fragments may still provide a stabilizing and reinforcing effect on the high-alloy amorphous or nano-crystalline metal structure, however, the reinforcing and stabilizing effects are not as large in magnitude as in the preferable range of carbon content. Carbon contents above 50 volume % may not desirable because carbon would begin replacing the metallic matrix for a carbon-based one. A metal content exceeding about 50 volume %, but less than about 90 volume %, may therefore be desired.
In the embodiments containing silicon and oxygen, metal contents exceeding about 50 volume % and carbon contents exceeding about 25 volume % may be desired in this respect. Therefore the combined silicon and oxygen volume percentage should be below about 25 volume %. The total silicon and oxygen content may range from about 5 to about 50 atomic % (not volume %) of the carbon content, but preferably should be below about 35 atomic %. The atomic ratio of silicon:oxygen should be below or less than 1:2, and preferably below 1:1.
FIG. 3 is a graph showing the range of metal content 30 in Atomic % vs. Radius of metallic elements 32, as a function of the metal content in volume %. Note that the ordinate is in units of atomic % (as opposed to volume %). Three curves are plotted in FIG. 3; curve 34 representing a fixed limitation of 50 volume % metal, curve 36 representing a fixed limitation of 75 volume % metal, and dashed curve 38 representing a fixed limitation of 90 volume % metal. Curves 34 and 38 represent the minimum and maximum recommended limits of metal content, respectively. In each case, the metal content, in atomic %, decreases with increasing atomic radius of the metal, since, at a fixed total volume of metal, increasing atomic radius would decrease the total number of atoms thus decreasing the atomic percentage.
FIG. 4 is a schematic view of vacuum deposition system for fabricating carbon reinforced alloys, in accordance with one embodiment of the present invention. In this embodiment, contained within vacuum deposition chamber 50 is a substrate holder 40 supporting deposition substrates 42. Holder 40 may rotate via drive 48, and a planetary drive may also rotate the individual substrates 42 within holder 40. Holder 40 may also be equipped with a heater (not shown) to heat substrates 42 prior to and during deposition. Power to heater and drive motors would be supplied by connections 46 if so equipped. Substrate holder 40 may also be coupled to a high voltage power supply (not shown) via connection 52. In one embodiment, piping 54 couples the deposition chamber 50 to mechanical and/or diffusion pumps (not shown) for creating and maintaining a vacuum during deposition. Plasmatron 44 and magnetrons 60 are disposed, e.g., within a wall, opposing the sample holder 40. Connections 56 and 58 couple the plasmatron 44 and magnetrons 60 to power supplies (not shown).
In at least one embodiment, the deposition flux directed to the samples 42 on holder 40 is uniform across the entire diameter or area of holder 40. Rotation of the holder 40 combined with the rotation of individual substrates 42 may be used to maintain uniform deposition within the substrates. Precursor flow (that supplies carbon, silicon, and/or oxygen species) is coupled to or fed into the plasmatron 44 to supply the non-metallic species and a metal sputtering target (not shown) coupled to or fed into magnetron 60 supplies the metal species. Fluxes from the plasmatron 44 and the magnetron 60 may be started and stopped by toggling electrical power to the plasmatron and magnetron. Preferably, the fluxes are prevented from reaching the substrates by movable shutters (not shown) placed between the magnetron and plasmatron sources and the substrate. Since deposition under these conditions is primarily line of sight, shutters are effective in stopping the deposition process without having to deal with long delays in powering up and down the magnetron 60 and plasmatron 44 sources. Instead, they can be left running at steady state.
FIG. 5 is a schematic view of vacuum deposition system for fabricating carbon reinforced alloys, having molecular beam deposition and radiation surface heating capability, in accordance with one embodiment of the present invention. Vacuum chamber 50 contains substrate holder 62, which differs from holder 40. Holder 62 does not contain a planetary substrate rotation system (or the system can be turned off or disabled). Holder 62 may or may not contain a substrate heating system. Holder 62 is rotated by drive 48. Pulse radiation heaters 70 and 80, molecular beam sources 72 and 78, and plasmatrons 74 and 76 are disposed, e.g., within a wall, opposing the sample holder 62. Molecular beam sources 72 and 78 allow lower energy deposition than that obtained with magnetron sputtering of the embodiment shown in FIG. 4. Under some conditions, this may reduce the tendency to form carbides and suicides in the deposited films.
Molecular beam sources may also enable the deposition of carefully controlled molecular clusters useful in constructing nano-crystalline structures. The molecular beam sources can be focused to cover a single substrate 42, a group of substrates, or a limited area on a single substrate. If different materials are deposited by each molecular beam source, selective layering of single monolayers of the different materials can be accomplished. The molecular beam sources can be “shuttered” or turned on and off in synch with the substrates rotating on the holder 62. To complement the selective deposition afforded by the molecular beam sources, pulse radiation heaters 70, 80 may also be employed. The radiation heaters may be infrared lasers or other focused radiation heating sources. The heating provided by the pulse radiation heaters 70, 80 is generally localized to particular areas of the substrate surface, and can be synchronized with the deposition process of the molecular beam sources. Since the heating is limited to the substrate surface, heat dissipates quickly, allowing hotter or colder local deposition temperatures to be produced, e.g., in sequence as the substrates rotate to new locations. This allows optimum thermal environments to be provided for each localized molecular beam deposition. Molecular beam sources 72 and 78 are coupled to power supplies (not shown) by connections 84 and 88, respectively. Pulsed radiation sources 70 and 80 are coupled to power supplies (not shown) by connections 82 and 90, respectively. Plasmatron 74 is coupled to power supplies (not shown) via connections 86.
A number of parameters impact the deposition of the films in the present invention, and should be taken into account in the design of the process deposition chambers of FIGS. 4 and 5
, such as:
- 1. the energy of the carbon-containing deposition flux,
- 2. the energy of the metal-containing deposition flux,
- 3. the mean free path of the carbon-containing deposition flux compared to the distance within the deposition chamber 50 between the source of the flux and the deposition surface 42,
- 4. the mean free path of the metal-containing deposition flux compared to the distance within the deposition chamber 50 between the source of the flux and the deposition surface 42,
- 5. the temperature of the substrate surface during deposition.
With respect to the energy criteria of item 1 above, in one embodiment of the invention, at least about 50% of the atomic species in the carbon, silicon, and oxygen containing deposition flux possess energies of at least about 10 eV, but preferably energies in the range of about 20 to about 100 eV. With respect to the energy criteria 2 above, in one embodiment of the invention, at least about 50% of the atomic species (including molecular clusters) in the metal containing deposition flux possess energies do not exceed about 20 eV, but preferably about 90% of the metal containing deposition flux possess energies below about 10 eV. With respect to the mean free path criteria of items 3 and 4 above, in one embodiment of the invention, the mean free path of both the carbon, silicon, oxygen deposition fluxes and the metal deposition fluxes must exceed the distance within the deposition chamber 50 between the source of the flux and the deposition surface 42. With respect to the temperature criteria, in one embodiment of the invention, the substrate 42 surface temperature should not exceed about 400° C., but preferably does not exceed about 150° C., and more preferably does not exceed about 100° C.
The energy of the incident carbon-containing flux in the above-indicated range is sufficient to overcome the activation barrier for sp3 carbon bonds formation. Higher energy levels would activate the metallic atoms in the deposited layer and produce an excess of carbon-metal bonds instead of diamond-like carbon-carbon bonds. Similar undesired effect would result from the excessive energy of the metal-containing particles. Additionally, it is important to prevent vapor phase reactions between the carbon containing and metal containing fluxes and the subsequent deposition of the reaction products on the substrate. These reaction products will interfere with the proper formation of the desired amorphous high-alloy metal. For the construction of a pure amorphous high-alloy metal, the carbon containing flux should include atoms and/or low-molecular weight clusters. The metal containing flux should include only individual atoms. For the construction of a nano-crystalline high-alloy metal, the incident metal-containing flux may contain multi-atom clusters not exceeding the required size of nano-crystals in the final material.
In order to minimize flux unwanted flux interactions, the deposition may be realized by alternating the predominantly carbon containing flux and metal containing flux. Preferably, the total amount of deposited material including both metallic and non-metallic components should not exceed one mono-layer during any one period of alternation. This may be accomplished in the apparatus of FIG. 5 by alternating the time of deposition of the two different fluxes, since the deposition of each component is uniformly distributed over the entire surface of holder 40 during deposition. In the apparatus of FIG. 6, the deposition fluxes can be localized to a particular zone immediately above the holder 62. Interaction of the fluxes is avoided by localized placement, and the alternation effect is obtained by rotation of the holder at the appropriate rotation rate though the deposition zones.
FIG. 6 is a process flow diagram showing the deposition process steps for the chamber 50 in FIG. 4 in accordance with one embodiment of the present invention. The process generally starts by loaded a substrate(s) onto the holder 40 at step 100. Surface dust and debris may be removed by blowing with a jet of Ar or N2 at step 102. The chamber is then closed in step 104 and rough pumped down to a pressure, e.g., of less than about 8×10−4 torr, at step 106. The chamber may then be pumped to a lower pressure, e.g., of less than about 5×10−7 torr, at step 108, such as with a diffusion pump. The chamber may then be back filled with Ar to a pressure, e.g., of about 5×10−5 torr, at step 110. At step 112, the rotation drive 48 may be turned on and the substrate heaters in holder 40 may be activated if necessary.
Following step 112, the high voltage supply connected at 52 may be turned on to, e.g., a 1500 volt, 13.56 MHz bias voltage, at step 114. At step 118, the precursor flow rate and the plasmatron 44 are turned on, and at step, 120, a layer or monolayer of carbon and/or carbon/silicon/oxygen are deposited on the substrate. At step 122, the carbon containing flux is terminated, either by powering down the plasmatron or by shuttering the flux stream as disclosed previously. At step 124, the metal containing flux may then be started by powering up the magnetron, or opening the shutter blocking the magnetron, and at step 126, a monolayer of amorphous metal or metal nano-crystals is deposited on the substrate over the previous deposition. At step 128, the sputtering metal flux is terminated, either by powering down the magnetron of by shuttering the metal atom flux, and the completeness of the deposition is determined at step 130. If the process is not complete, the NO branch leaving step 130 leads back to step 118 and the deposition steps are repeated. If the process is complete, the YES branch leads to step 132 where the diffusion pump is valved off from the chamber and the chamber is back filled with N2 or Ar and the substrates are cooled at step 134. The substrates may then be removed from the chamber at step 136.
- EXAMPLE 1
The present invention is described in the following Examples, which are set forth to aid in the understanding of the invention, and should not be construed to limit in any way the scope of the invention as defined in the claims which follow thereafter.
Five micron films that include 52 to 80 atomic % Cr, 36 to 15 atomic % carbon, 7 to 3 atomic % silicon, and 5 to 2 atomic % oxygen, were deposited in accordance with at least one embodiment of the present invention, at a substrate temperature of about 150 degrees Celsius. Polymethylphenyldisiloxane, (CH3)3SiO[CH3C6H5SiO]3Si(CH3)—, was used as for the precursor, introduced at a flow rate of 1.1 to 1.5 cm3/hr, to achieve a growth rate of 5 microns/hr.
- EXAMPLE 2
Table 1 shows the electrical resistivity and structure as a function of chromium content. All films in Table 1 demonstrate thermal stability exceeding 1100° C. in the absence of oxygen, and sustain a 30-minute exposure in air up to a temperature of 950° C. After the aforementioned high temperature exposure, minor changes in the mechanical properties occur, accompanied by an increase in the percentage of nano-crystallinity. The films posses a micro-hardness of 12 to 15 GPa, high wear resistance, high thermal shock resistance, and good adhesion to a variety of surfaces. These films may be used as high-precision variable resistors in electronics, in position transducers, as surface heaters, and as non-electrochemical chromium coatings for many types of substrates.
| ||TABLE 1 |
| || |
| || |
| ||Cr Content, ||Resistivity, || |
| ||atomic % ||Ohm-cm ||Structure |
| || |
| ||52% ||4 × 10−4 ||amorphous |
| ||60% ||3 × 10−4 ||amorphous |
| ||70% ||2.5 × 10−4 ||predominately amorphous |
| ||75% ||2 × 10−4 ||predominately amorphous |
| ||80% ||1 × 10−4 ||nano-crystalline |
| || |
Five micron films that include 50 to 80 atomic % Fe0.72Cr0.18Ni0.10 metal alloy, 37.5 to 15 atomic % carbon, 9.5 to 3.8 atomic % silicon, and 3 to 1.2 atomic % oxygen, were deposited in accordance with the preferred embodiments of the present invention. As in Example 1, substrate temperature was 150° C., and the polymethylphenyldisiloxane precursor was introduced at a flow rate of 1.1 to 1.5 cm3/hr to achieve a growth rate was 5 microns/hr.
Table 2 shows the electrical resistivity and structure as a function of metal alloy content. All films in Table 2 demonstrate thermal stability up to at least 900° C. in the absence of oxygen, and sustain a 30 minute exposure in air up to a temperature of 900° C. These films possess a micro hardness in the range of 11 to 13 GPa, high wear resistance, very high thermal shock resistance, low friction, and uniform structure.
- EXAMPLE 3
The alloy films in Table 2 have a wide range of applications, particularly as protective coatings, where in many cases they can replace chromium and other electroplated coatings. These materials can be deposited upon a variety of substrates including metals, ceramics, composites, glasses, and plastics including Teflon®.
| ||TABLE 2 |
| || |
| || |
| ||Alloy Content, ||Resistivity, || |
| ||atomic % ||Ohm-cm ||Structure |
| || |
| ||50% ||5 × 10−4 ||amorphous |
| ||60% ||4 × 10−4 ||amorphous |
| ||70% ||2.5 × 10−4 ||predominately amorphous |
| ||80% ||1.5 × 10−4 ||nano-crystalline |
| || |
- EXAMPLE 4
A series of 1 micron thick films of amorphous and nano-crystalline hafnium reinforced by a carbon diamond-like framework and stabilized by silicon and oxygen were deposited on silicon wafers in accordance with at least one embodiment of the present invention and under similar deposition conditions described in example 1. The chemical composition of the films was 40 atomic % hafnium, 45 atomic % carbon, 9 atomic % silicon, and 6 atomic % oxygen. These films have electrical conductivity in the range of 3×10−3 to 5×10−4 Ohm-cm., and demonstrated high thermal shock resistance and high chemical corrosion resistance in aggressive environments at temperatures exceeding 500° C.
- EXAMPLE 5
Samples of 1 micron thick films of amorphous tungsten, molybdenum and tantalum reinforced by a carbon diamond-like framework and stabilized by silicon and oxygen were deposited on dielectric substrates utilized in the electronics industry according to at least one embodiment of the present invention and under similar deposition conditions as in example 1. The chemical composition of the films was 50 atomic % of corresponding metals, 38 atomic % carbon, 7 atomic % silicon, and 56 atomic % oxygen. Films exhibited an electrical conductivity of approximately 10−3 Ohm-cm and demonstrated high thermal stability up to at least 900° C. When a DC voltage in the range of about 10 V to 50 V is applied via electrodes to localized areas of the film, current filaments form between electrodes, heating the film along the filaments up to estimated temperature of about 500° C. to 600° C. This phenomena was also observed in a membrane produced based on these films. The hot current filaments emit infrared light with emissivity greater than 0.7. The emission may be switched off with a characteristic time of response not exceeding 0.01 second.
- EXAMPLE 6
Samples of 1 micron thick films of amorphous molybdenum disilicide (MoSi2) reinforced by a carbon diamond-like framework and stabilized by silicon and oxygen and consisting of these elements in an approximate range of about 60 atomic % MoSi2, 35 atomic % carbon, and 5% oxygen were deposited and tested in a manner similar to example 4. The hot current filaments in the films containing MoSi2 emit infrared light with evaluated emissivity at least 0.8.
Samples of Co—Ni amorphous and nano-crystalline alloys reinforced by a carbon diamond like framework and stabilized by silicon and oxygen were deposited on nano-crystalline ceramic substrates in accordance with the present invention and similar to deposition conditions described in example 1 with combined content of metallic elements within the range of 40 atomic % to 80 atomic %. All samples containing at least 50 atomic % of the metallic elements demonstrate ferromagnetic properties while maintaining the mechanical, thermal, and chemical stability previously described for alloys reinforced by a carbon diamond-like framework.
The precursor used in the aforementioned examples was polymethylphenyldisiloxane. However, a number of other compounds may also be used to the same effect. A selection of these compounds is shown in Table 3.
|TABLE 3 |
| || ||Boiling point, |
|Name ||Formula ||° C. |
|Propanol 3-trymethylsilyl ||C6H16OSi ||141 |
|Silacyclohexane ||C17H2OSi ||193 |
|Diethyldiethoxysilane ||C6H16O2Si ||114 |
|Diphenyldiethoxysilane ||C6H20O2Si ||167 |
|Diethoxymethylphenylsilane ||C11H18O2Si ||218 |
|Allydiethoxymethylsilane ||C6H18O2Si ||155 |
|Diemethoxydimethylsilane ||C4H12O2Si ||82 |
|Diemethoxydiphenylsilane ||C14H18O2Si ||161 |
|Diphenoxydimethylsilane ||C14H18O2Si ||130 |
|Ethenyldiethoxymethylsilane ||C7H16O2Si ||133 |
|Ethenylethoxydimethylsilane ||C6H14OSi ||99 |
|Ethenyltriethoxysilane ||C8H18O3Si || 68 or 148 |
|Ethoxytriethylsilane ||C8H20OSi ||154 |
|Ethoxytrimethylsilane ||C5H14OSi ||76 |
|Ethoxytriphenylsilane ||C20H20OSi ||344 |
|Ethyltrimethoxysilane ||C5H14O3Si ||124 |
|Methyltriphenoxysilane ||C19H18O3Si ||269 or 210 |
|1,3-phenylenebis(oxy) ||C12H22O2Si2 ||240 |
|Phenytripropylsilane ||C15H26Si ||146 |
|Tetravinylsilane ||C8H12Si2 ||130.2 |
|Tetraethylsilane ||C6H20Si ||154.7 |
|Tetramethylsilane ||C4H12Si ||26.6 |
|Tetraphenylsilane ||C24H20Si ||228 |
|Tributylsilane ||C12H28Si ||221 |
|Tributylphenylsilane ||C18H32Si ||140 |
|Triethoxysilane ||C6H16O3Si ||123.5 |
|Triethoxyethylsilane ||C8H20O3Si ||158.5 |
|Triethoxymethylsilane ||C7H18O3Si ||142 |
|Triethoxypenthylsilane ||C11H26O3Si ||95 |
|Triethoxyphenylsilane ||C9H20O3Si ||112 |
|Triethoxy-2-propenylsilane ||C9H20O3Si ||100 |
|Triethylsilane ||C6H16Si ||109 |
|Triethylfluorosilane ||C6H15FSi ||110 |
|Triethylphenylsilane ||C12H20Si ||236 |
|Trifluorophenylsilane ||C6H5F3Si ||101.5 |
|Trimethoxymethylsilane ||C4H12O3Si ||102.5 |
|Trimethoxyphenylsilane ||C9H14O3Si ||130 |
|Trimethylsilane ||C3H10Si ||6.7 |
|Trimethyl-4-methylphenylsilane ||C10H16Si ||192 |
|Trimethyl-2-methypropylsilane ||C7H18Si ||108.5 |
|Trimethylphenoxylsilane ||C9H14OSi ||119 |
|Trimethylphenylsilane ||C9H14Si ||169.5 |
|Trimethylphenylmetthylsilane ||C10H16Si ||190.5 |
|Trimethyl-2-propenylsilane ||C6H14Si ||86 |
|Trimethylpropylsilane ||C6H16Si ||89 |
|Trimethyl-4-trimethylsilyloxyphenylsilane ||C12H22OSi2 ||132 |
|Silanetriol, ethenyl, triacetate ||C8H12O6Si ||115 |
|Silanetriol, methyl, triacetate ||C7H12O6Si ||110 |
|Tripropylsilane ||C9H22Si ||172 |
|Dimethyl ethyl silanol ||C4H12OSi ||120 |
|Methyldiphenyl silanol ||C13H14OSi ||184 |
|Triethylsilanol ||C6H16OSi ||154 |
|Triephenylsilanol ||C18H16OSi |
Whereas the present invention may be embodied in many forms, details of the preferred embodiments are shown with the understanding that the present disclosure is not intended to limit the invention to the embodiments illustrated. Other high-alloy metal films stabilized by diamond-like carbon in addition to those specifically listed can be used in preparing the compositions in accordance with the present invention. While the invention has been particularly shown and described with reference to certain embodiments, it will be understood by those skilled in the art that various alterations and modifications in form and detail may be made therein. Accordingly, it is intended that the following claims cover all such alterations and modifications as fall within the true spirit and scope of the invention.