EP1415022A1 - Systeme et procede de prodution de diamant synthetique - Google Patents

Systeme et procede de prodution de diamant synthetique

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Publication number
EP1415022A1
EP1415022A1 EP01959891A EP01959891A EP1415022A1 EP 1415022 A1 EP1415022 A1 EP 1415022A1 EP 01959891 A EP01959891 A EP 01959891A EP 01959891 A EP01959891 A EP 01959891A EP 1415022 A1 EP1415022 A1 EP 1415022A1
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EP
European Patent Office
Prior art keywords
diamond
substrate
single crystal
thermal conductivity
boron
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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EP01959891A
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German (de)
English (en)
Inventor
Robert C. Linares
Patrick J. Doering
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Apollo Diamond Inc
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Apollo Diamond Inc
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Filing date
Publication date
Application filed by Apollo Diamond Inc filed Critical Apollo Diamond Inc
Priority to EP10153726A priority Critical patent/EP2189555A2/fr
Publication of EP1415022A1 publication Critical patent/EP1415022A1/fr
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
    • C30B25/02—Epitaxial-layer growth
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • C30B29/04—Diamond

Definitions

  • the present invention relates to synthetic diamonds and to methods for preparing and using synthetic monocrystalline diamonds.
  • the invention relates to monocrystalline diamonds produced by the method of chemical vapor deposition, including the role of impurities such as nitrogen, phosphorous, sulfur, boron, and the isotope 13 C in such compositions.
  • Monocrystalline diamonds as found in nature, can be classified according to color, chemical purity and end use.
  • the majority of monocrystalline diamonds are colored, and contain nitrogen as an impurity, and are thereby used primarily for industrial purposes; these would be classified as type la and lb.
  • the majority of gem diamonds (which are all considered "monocrystalline" diamonds) are colorless or various light colors and contain little or no nitrogen impurities; and would be classified as type Ila.
  • Types la, lb and Ila are electrical insulators.
  • a rare form of monocrystalline diamond (classified as type Hb) contains boron as an impurity, is blue in color and is a semiconductor.
  • Monocrystalline diamond provides a wide and useful range of extreme properties, including hardness, coefficient of thermal expansion, chemical inertness and wear resistance, low friction, and high thermal conductivity.
  • monocrystalline diamond is also electrically insulating and optically transparent from the ultra-violet (UN) to the far infrared (IR), with the only absorption being carbon- carbon bands from about 2.5 ⁇ m to 6 ⁇ m.
  • UUN ultra-violet
  • IR far infrared
  • monocrystalline diamonds find use in many diverse applications including, as heat spreaders, abrasives, cutting tools, wire dies, optical windows, and as inserts and/or wear- resistant coatings for cutting tools.
  • the engineering and industrial uses of diamonds have been hampered only by the comparative scarcity of natural monocrystalline diamond. Hence there has been a long running quest for routes to synthesize monocrystalline diamond in the laboratory.
  • Synthetic monocrystalline diamonds for industrial use, can be produced by a variety of methods, including those relying on a "high pressure method” and those involving controlled vapor deposition (CND). Diamond produced by either the "high pressure method” or the CVD method can be produced as monocrystalline diamond or polycrystalline diamond. High pressure diamond is usually formed as micron sized crystals, which can be used as grit or loose abrasive, or set into metal or resin for cutting, grinding or other applications.
  • So called 'industrial diamond' has been synthesized commercially for over 30 years using high-pressure high-temperature (HPHT) techniques, in which monocrystalline diamond is crystallized from metal solvated carbon at pressures of about 50 tolOO kbar and temperatures of about 1800 to 2300K. hi the high pressure method the crystals grow in a three dimensional manner and the crystal is all of one impurity level, except for possible discontinuities arising from fluctuations in the growth cycle. See, for example, R.C. Burns and G. Davis, "Growth of Synthetic Diamond", pp. 396-422, The Properties of Natural and Synthetic Diamond, J.E. Field, editor, Academic Press (1992), US Patents 3,850,591 and 4,034,066.
  • HPHT high-pressure high-temperature
  • CVD diamond grows two dimensionally, layer by layer, and it is therefore possible to build up a bulk crystal (or plate or film) which can be of a single composition or composed of layers of many compositions (called a "structure").
  • CVD diamond grown in this manner can show mechanical, tribological, and even electronic properties comparable to those of natural diamond. See, for example, Y. Sato and M. Kamo, "Synthesis of Diamond From the Vapor Phase", pp.
  • Chemical vapor deposition involves a gas-phase chemical reaction occurring above a solid surface, which causes deposition onto that surface. All CVD techniques for producing diamond films require a means of activating gas- phase carbon-containing precursor molecules. This generally involves thermal (e.g., hot filament) or plasma (e.g., D.C., R.F., or microwave) activation, or the use of a combustion flame (oxyacetylene or plasma torches).
  • thermal e.g., hot filament
  • plasma e.g., D.C., R.F., or microwave
  • a combustion flame oxyacetylene or plasma torches.
  • Two of the more popular experimental methods include the use of a hot filament reactor, and the use of a microwave plasma enhanced reactor. While each method differs in detail, they all share features in common.
  • growth of diamond normally requires that the substrate be maintained at a temperature in the range of 1000-1400 K, and that the precursor gas be diluted in an excess of hydrogen (typical CH 4 mixing ratio ⁇ l-2vol%).
  • the resulting films are usually polycrystalline (unless a monocrystalline diamond seed is provided) with a morphology that is sensitive to the precise growth conditions. Growth rates for the various deposition processes vary considerably, and it is usually found that higher growth rates can be achieved only at the expense of a corresponding loss of film quality. Quality is generally taken to imply some measure of factors such as the ratio of sp3 (diamond) to sp2-bonded (graphite) carbon in the sample, the composition (e.g. C-C versus C-H bond content) and the crystallinity.
  • combustion methods deposit diamond at high rates (typically 100 ⁇ m/ hr to 250 ⁇ m/hr), but often only over very small, localized areas and with poor process control, thereby leading to poor quality films.
  • the hot filament and plasma methods tend to provide have much slower growth rates (0.1-10 ⁇ m/hr), but produce high quality films.
  • One of the great challenges facing researchers in CVD diamond technology is to increase the growth rates to economically viable rates (to the level of 100 + ⁇ m/h, or even one or more rnm/hr) without compromising film quality.
  • the typical power rating for a microwave reactor is ⁇ 5 kW, but the next generation of such reactors have power ratings up to 50-80 kW. This gives a much more realistic deposition rate for the diamond, but for a much greater cost, of course.
  • Thermodynamically, graphite, not diamond, is the stable form of solid carbon at ambient pressures and temperatures.
  • the fact that diamond films can be formed by CVD techniques is inextricably linked to the presence of hydrogen atoms, which are generated as a result of the gas being 'activated', either thermally or via electron bombardment.
  • These H atoms are believed to play a number of crucial roles in the CVD process: • They undergo H abstraction reactions with stable gas-phase hydrocarbon molecules, producing highly reactive carbon-containing radical species. This is important, since stable hydrocarbon molecules do not react to cause diamond growth.
  • the reactive radicals, especially methyl, CH can diffuse to the substrate surface and react, forming the C-C bond necessary to propagate the diamond lattice.
  • H-atoms terminate the 'dangling' carbon bonds on the growing diamond surface and prevent them from cross-linking, thereby reconstructing to a graphite-like surface.
  • the abrasion process is usually carried out by polishing the substrate with an abrasive grit, usually diamond powder of 0.1 ⁇ m to 10 ⁇ m particle size, either mechanically or by ultrasonic agitation.
  • an abrasive grit usually diamond powder of 0.1 ⁇ m to 10 ⁇ m particle size, either mechanically or by ultrasonic agitation.
  • the need to damage the surface in such a poorly defined manner, prior to deposition may severely inhibit the use of CVD diamond for applications in areas such as the electronics industry, where circuit geometries are frequently on a submicron scale. This concern has led to a search for more controllable methods of enhancing nucleation, such as ion bombardment.
  • Ion bombardment can be performed in a microwave deposition reactor, by simply adding a negative bias of a few hundred volts to the substrate and allowing the ions to (i) damage the surface, (ii) implant into the lattice, and (iii) form a carbide interlayer.
  • CVD chemical vapor deposition
  • a polished monocrystalline diamond is used as a seed crystal and the structure of that seed crystal is reproduced in the new monocrystalline diamond grown on the seed.
  • the resulting monocrystalline diamond has superior properties to polycrystalline diamond for most industrial, optical, electronic and consumer applications.
  • the temperature of the cutting tool increases to the point that it degrades by oxidation, corrosion, or fracturing and the tool becomes unusable. Furthermore, as the tool is degrading, the quality and precision of the part being fabricated degrades significantly.
  • a cutting tool is made of diamond, the high thermal conductivity of diamond, heat from the cutting tip or edge is rapidly removed from that tip or edge to the tool holder and the temperature of the cutting tip or edge runs significantly cooler than comparable tools made from other materials such as carbides, oxides, nitrides or borides. Therefore, diamond tools can generally run longer and provide higher quality manufactured parts over a longer period of time than alternative cutting materials.
  • wire dies are made of diamond because they have great resistance to wear and because the heat of drawing the wire can rapidly be dissipated from the wire. This results in a longer life for the wire die, and higher quality of wire for a longer length than can be obtained with alternative wire die materials.
  • thermal lensing occurs when light is partially absorbed by the lens material and the lens material heats causing a change in index of refraction of the lens material. Since the heat generated by the laser beam must be dissipated to the outer surfaces of the sense there will be a gradient in the index of refraction of the material and that will cause the laser beam to be distorted or to focus or defocus in an uncontrolled manner.
  • Diamond has also been suggested for use to cool three dimensional arrays of semiconductor devices or IC's to produce very high speed three dimensional computers where the stacks of chips are to be cooled by contact with diamond plates.
  • R. Eden Applications in Computers, Handbook of Industrial Diamonds and Diamond Fihns, pp 1073-1102, Editors, Mark Prelas, Galina Popovici and Louis Bigelow, Marcel Decker, NY, 1998.
  • the performance and lifetime is directly related to the temperature of the active part of the device and tool.
  • the operating temperature of the active part of the device/tool is directly related to the thennal conductivity of the diamond heat being used.
  • Polycrystalline diamond typically has the lowest thermal conductivity, nitrogen doped single crystal is higher, followed by pure diamond which has the highest.
  • the highest thermal conductivity natural diamond is type Ua which contains little to no nitrogen and has values of thermal conductivity of 2000 to 2500 watt/meter degree Kelvin (W/mK).
  • W/mK watt/meter degree Kelvin
  • any property of diamond which causes a variation in the mean free path of a phonon will cause a variation in thermal conductivity of the diamond.
  • Scattering of phonons reduces the mean free path and phonon scattering can be caused phonon-phonon interactions (ppi), grain boundaries (gb), dislocations (dis), vacancies (vac), impurities (imp), isotopes (iso) and other mechanisms including voids (othr).
  • thermal conductivity of diamond could be altered by changing the purity the diamond starting materials with respect to the carbon isotopes. For instance, when diamond crystals or polycrystalline diamond was produced which was 99.999% pure with respect to the 12 C isotope, the thermal conductivity at room temperature increased to 3300 W/mK. It was also concluded that this was indeed the highest thermal conductivity possible and that since this high thermal conductivity was also observed in polycrystalline diamond, crystalline properties such as grain boundaries were not a major loss of thermal conductivity. Theoretical analysis of the thermal conductivity of diamond was conducted (P. G. Klemens, Solid State Physics: Advances in Research and Applications, edited by R. Seitz and D. Turnbill
  • the ability to increase the thermal conductivity of single crystal diamond by over 50% from 2300 W/mK to 3300 W/mK or more would offer significant performance enhancements for diamond cutting tools, diamond wire dies, high power laser windows, high power semiconductor devices such as lasers, microwave devices and three dimensional computers or circuits.
  • the advantages of enhanced thermal conductivity diamond have, to date however, not been applicable to any commercial application because the cost of producing C enhanced precursor gasses (typically methane gas) is prohibitively high compared to the cost of natural isotope gasses.
  • the cost of 12 C enriched precursors, such as methane gas is $75 to $200 per gram, compared with the cost of unenriched methane at less than $0.01 per gram.
  • the present invention provides synthetic monocrystalline diamonds providing an improved combination of such properties as thermal conductivity, crystal perfection, coloration, strength, velocity of sound, fracture toughness, hardness, shape and the like.
  • the improved diamonds are prepared by a method of controlled vapor deposition (CVD) in which the amounts and/or types of impurities are modified and carefully controlled, within one or more layers of the diamond, in order to provide an overall improved product and/or improved process of preparing such a product.
  • impurities include, for instance, the affirmative addition of impurities such as boron within one or more layers of a multi-layered diamond, in order to achieve an improved combination of such properties as hardness, fracture toughness, electrical conductivity, optical properties, and crystal perfection.
  • the control of such impurities involves lowering nitrogen content in a thick, single-layered diamond, while maintaining C isotope levels at natural or near-natural levels, in order to achieve, among other things, improved thermal conductivity.
  • the present invention provides a synthetic monocrystalline diamond composition comprising one or more monocrystalline diamond layers formed by chemical vapor deposition, the layers including one or more layers having an increased concentration of one or more impurities (such as boron and/or isotopes of carbon), as compared to other layers or comparable layers without such impurities.
  • impurities such as boron and/or isotopes of carbon
  • the invention provides a method of preparing such a diamond, the method involving the steps of growing a layer of diamond with a designated impurity, growing an additional layer of monocrystalline diamond with different impurities and/or impurity levels, and repeating tins process with various layers of varied composition and thickness to achieve the desired structure.
  • the invention provides a system for use in performing such a method, and articles incorporating such a composition.
  • doped it is meant that at least one layer within a composition of this invention has been grown with an amount of one or more impurities, e.g., incorporated into the gas stream, in order to bring about an amount of an impurity, such as boron, sulfur, phosphorous, carbon isotopes, or lithium in the synthetic monocrystal layer, sufficient to produce a measurable change in the electrical, physical, optical, electronic or crystallographic properties.
  • impurity such as boron, sulfur, phosphorous, carbon isotopes, or lithium in the synthetic monocrystal layer
  • the invention involves a variety of structures that can be built from monocrystalline diamond of this invention, e.g., one composed of layers containing different concentrations of impurities, as well as methods that employ such structures.
  • the invention also describes new uses for semiconducting monocrystalline diamond made by the addition of impurity-doped layers, as well as methods for using and methods for producing monocrystalline diamond crystals with improved optical and electrical properties, and methods for using both undoped and doped monocrystalline diamond plates. All of these methods and compositions refer to monocrystalline diamond grown by the CVD method.
  • Applicants have discovered the manner in which monocrystalline diamond can be prepared having a thermal conductivity significantly greater than has previously been known for comparable (i.e., non-isotopically enriched, CVD-grown) diamond.
  • Such diamond exhibits, for instance, thermal conductivity of at least about 2300 W/mK, preferably at least about 2500 W/mK, and more preferably at least about 2800 W/mK while retaining a 13 C isotope content within the normal range (e.g., greater than about 0.1% and more preferably greater than about 0.8%).
  • the method and composition of the present invention can take a variety of embodiments, including the following:
  • the use of diamond in this section refers to monocrystalline diamond. While not intending to be bound by theory, the method and composition of the present invention, in at least one embodiment, are based on the fact that nitrogen or boron atoms are larger than carbon atoms. Therefore when these elements are added to the diamond structure, the crystal lattice expands. When high levels of nitrogen or boron are incorporated in the diamond, the average distance between carbon atoms in the diamond becomes measurably larger than pure diamond. See, for example, A.R. Lang, "Diffraction and Imaging Studies of Diamond", pp. 215- 258, The Properties of Natural and Synthetic Diamond, J.E.
  • This equation, along with the equations which give the lattice constant change due to impurity addition, can be used to produce a layer or layers with a tailored strain energy.
  • Crystals of diamond usually contain dislocations that are discontinuities in the arrangement of the atoms from perfect order. These dislocations usually travel in straight lines and therefore extend from the substrate into the film or crystal grown on the substrate. It has been demonstrated on conventional semiconductors that when a dislocation intersects with a layer that is in compression or tension, that the dislocation will change direction and run at an angle different from its original direction. (See J.Y. Tsao, B.W. Dodson, S.T. Picraux and D.M. Cornelison, "Critical Stress for Si x - Ge (1-X) Strained-Layer Plasticity", 59 (21) Physical Review Letters, pp. 2455-2458, 23 November 1987).
  • the method of the present invention can be use to prepare low-dislocation or dislocation-free diamond crystals, substrates and structures.
  • the method can also be used to prepare strain free optical elements made from low or dislocation free diamond. Strain results in birefringence that degrades the performance of optical elements such as lenses and windows and gemstones.
  • the method further permits the production of low-dislocation or dislocation-free substrates for semiconductor devices. It is known in silicon, and has been reported in diamond, that impurities can accumulate on dislocations that leads to localized degradation of device performance.
  • the present invention therefore also includes higher performance devices using substrates with low dislocations and made by a method as described herein.
  • Diamond plates made entirely of alternating layers of doped and undoped diamond are also expected to provide increased strength and resistance to cracking. These would be useful in surgical blades, cutting tools, slicing tools, wire dies and other applications where stress will be applied.
  • Diamond plates can be fashioned into small sharp blades which are highly advantageous for certain types of surgery, including for instance, a surgical blade which is heavily doped with boron and blue in color. See US Patent No. 5,713,915 with regard to surgical blades generally. Such a blade provides a particular advantage since it is provides better visibility of the blade; as compared to conventional diamond blades, which are typically colorless or pale yellow and difficult to see.
  • the diamond blade surface can be placed in compression, thereby giving it added strength.
  • the boron doped diamond can be provided as the whole volume of the blade or as a coating on the outer layer or inner layer.
  • Diamond coloration can also be used to make diamonds which are more easily fabricated using laser cutting techniques.
  • the addition of boron results in an optical absorption in the near infrared which leads to higher absorption of YAG laser light and this reduces the power level required in fabricating articles by laser cutting.
  • diamond is often shaped by cutting with a YAG laser operating at 1.06 microns. Addition of boron increases the optical absorption at this wavelength, and this can significantly simplify the laser cutting process by allowing use of lower power, which in turn will reduce damage and cracking of the manufactured diamond part.
  • the change in absorption at 1.06 microns can be tailored by controlling the amount of boron which is introduced, and the position of the absorption in the diamond can be tailored by the position of the boron layer in a multilayer structure. Since the boron doped layer can be added at any time in the process, it will be possible to place the blue coloring inside a transparent sheath, providing the blue coloring while permitting polishing of the outer surface.
  • the blue internal or external diamond layer can be provided for any use where easy visual or optical detection of the diamond is required.
  • a surgical blade can be made of solid boron doped diamond. The color can be varied from light blue to black depending on the boron concentration.
  • a third family of applications is based on the fact that boron doping leads to electrical conductivity.
  • Applications include the following:
  • the method of the present invention can be used to coat a single crystal diamond tool with boron doped single crystal diamond, and measure the stress on the tool under operation and its temperature. This, in turn, can be used to provide an in situ sensor for monitoring and controlling a machining operation, permitting it to operate in an optimal manner. This feature can also be adapted for use in providing mechanically guided surgical blades for minimally evasive types of surgery.
  • Diamond can be used to slit materials such as plastic film, paper and the like or cut tissue thin sections in a microtome. A common problem with such process is the accumulation of static electricity that leads to catastrophic electrical discharge or accumulation of dust, dirt and cutting residue on the cut surface. Boron doped diamond surfaces on the tool can be used to prevent such static buildup, h some cases it might be desirable to use an entire tool of solid boron doped diamond rather than a film or multilayer structure.
  • Boron doped diamond is highly resistant to corrosion in acidic or basic aqueous solutions. Boron doped polycrystalline diamond has been used as electrodes for electrochemical synthesis of materials such as oxygen and chlorine. Polycrystalline diamond electrodes have a lifetime that is many times that of conventional electrode materials such as graphite or stainless steel. However, polycrystalline diamond undergoes catastrophic failure at many hours of operation. Polycrystalline diamond is composed of millions of tiny crystallites which connect to each other at grain boundaries. These grain boundaries tend to accumulate impurities which are slowly attacked leading to the failure. Applicant has produced electrodes made of single crystal boron doped diamond. These electrodes have no grain boundaries and have life times which are significantly longer than polycrystalline diamond and show uniform wear, but no catastrophic failure.
  • single crystal diamond electrodes can withstand several orders of magnitude higher current than polycrystalline diamond without catastrophic failure or measurable erosion.
  • a composition of this invention can provide unique and specific semiconducting properties useful, for example, in fabricating such things as tools, microtomes, cutting tools for detectors, and the like.
  • the doped layer(s) of the present invention can also include situations where the spacing between carbon atoms is decreased rather than increased. Carbon is found in several isotopes. C is the most common isotope while C is about 1% abundant. Diamond that consists of all 13 C atoms has a smaller spacing between the carbon atoms than normal diamond (which contains 99% 12 C and 1% 13 C).
  • This heterostructure can include alternating layers of undoped 12 C and 13 C diamond. Such a structure can end in either a 12 C or a 13 C layer and then be used to grow single crystal plates of either 12 C or 13 C diamond.
  • a pseudomorphic structure can be built in which layers are alternately in compression and tension and which any layer can be doped with boron or nitrogen (or some other element).
  • the electrical and device properties arise from the strain induced electrical discontinuity.
  • Phosphorous has recently been shown to be a n-type dopant in CVD diamond (see Koizumi, Diam Films 1997 (see S. Koizumi, et. al., "Growth and characterization of phosphorus doped n-type diamond thin films", Diamond and Related Materials 7, p. 540-544 (1998)).
  • phosphorous is a significantly larger atom than carbon, nitrogen or boron (covalent radius of P is 1.57 times larger than N and 1.25 times larger than B) (see K. W. Boer, Survey of Semiconductor Physics, p. 25, van Nostrand (1990).) and this places limitations on the amount of phosphorous which can be incorporated into the diamond and limits its potential electrical performance in a device.
  • Sulfur has recently been shown to be a n-type dopant in CVD diamond (see Koizumi, Diam Films 1997 (M.N. Gumo, et al. "Sulfur: A New Donor Dopant for N-TYPE DIAMOND SEMICONDUCTORS, Applied Diamond Conference/Frontier Carbon Technology Joint Conference (1999) pg. 54).
  • sulfur is a significantly larger atom than carbon, nitrogen or boron (atomic radius of S is 1.49 times larger than N and 1.09 times larger than B) (see CRC Materials Science and Engineering Handbook, pg. 18 (CDC Press (1994).) and this places limitations on the amount of sulfur which can be incorporated into the diamond and limits its potential electrical performance in the device.
  • the method of this invention can be used to grow a monocrystalline diamond from normal isotope carbon and intersperse layers of 13 C diamond for the purpose of providing a marker for identifying the origin of the diamond as being CVD monocrystalline diamond for use in specific articles such as gemstones, e.g., where it is desirable to prevent confusion between natural and CVD grown monocrystalline diamond.
  • the entire monocrystal can be grown with a small amount of
  • C carbon and also provide a method of detection.
  • a method of detection would be high resolution x-ray diffraction, Raman spectroscopy, and mass spectroscopy, each of which can be used to measure isotope content.
  • the Raman method for instance, will show small changes in the crystal structure caused by enlarging or decreasing the lattice spacing.
  • CVD diamond is substantially the same as natural or high pressure diamond.
  • the method and composition of the present invention permit single crystal diamond to be provided in the form of plates or other substrates that can be used as the beginning step for producing a large number of diamond manufactured articles.
  • the method can also be used to eliminate a substantial number of fabrication steps such as sawing and lapping and increased yield of useful product.
  • the quality of CVD single crystal diamond is equal to or higher than natural or high pressure synthetic diamond, the resulting article will be of high quality, have less breakage, higher optical transmission and so forth.
  • the present invention therefore includes the use of CVD single crystal diamond plates, as described herein, for gemstones, scalpels, wire dies, microtomes, heat spreaders, optical windows, knives, cutting tools, and substrates for monocrystalline diamond active devices.
  • the method can be used to provide diamond layers with a boron concentration ranging from about 0.005 parts per million (ppma) to about 10,000 ppma, and preferably between about 0.05 parts ppma to about 3000 ppma.
  • a boron concentration ranging from about 0.005 parts per million (ppma) to about 10,000 ppma, and preferably between about 0.05 parts ppma to about 3000 ppma.
  • Such layers can be grown using the CVD technique by incorporating boron in the precursor gas at concentrations ranging from about 100 ppma to about 300,000 ppma, and from about 1000 ppma to about 100,000 ppma, respectively (with respect to the carbon in the gas phase).
  • Diamond layers with one dopant such as boron
  • diamond layers with tailored strain can be created by growing layers with selected impurity levels which create the desired lattice mismatch.
  • Such a structure can consist of undoped layers and or layers containing boron, nitrogen, phosphorus, sulfur, and/or isotopic enhancement.
  • Whole diamonds or individual layers can be made to have a blue coloration which ranges from sky blue to very dark blue by adding boron to the precursor gas to yield boron concentrations ranging from about 0.05 ppma to about 3000 ppma in the diamond, respectively, hi such films, the optical absorption coefficient for wavelengths from 450 nm to 7 ⁇ m will increase as the doping level is increased and as the thickness is increased.
  • Single diamonds or individual layers can be made with room temperature electrical resistivity ranging from about 100,000 ⁇ -cm to about 0.01 ⁇ -cm, and preferably from about 5000 ⁇ -cm to about 0.02 ⁇ -cm, by adding boron to the precursor gas to yield boron concentrations ranging from about 0.005 ppma to about 10,000 ppma (and preferably from about 0.01 ppma to about 3000 ppma) in the diamond.
  • boron doped layers can also be grown in conjunction with isotopically enriched layers in order to create layer junctions which have band gap discontinuities.
  • a boron-doped 13 C enriched layer on a natural isotope undoped layer creates a doped layer with a wider band gap than the undoped layer.
  • Such a layer can be expected to yield enhanced electrical properties relative to a structure with no band gap discontinuity.
  • the inventors have discovered that the normal isotope single crystal diamonds which are grown by the CVD process described herein, have a thermal conductivity substantially in excess of 2200 W/mK at room temperature. Measurements of thermal conductivity were made by the application of a heat source to one side of the diamond sample and measuring the temperature on the opposite side of the sample. The equipment was calibrated by measuring aluminum, copper, and nitrogen doped diamond and found to give a thermal conductivity of 3200 W/mK at room temperature.
  • the single crystal diamond produced herein has been tested as wire dies and has resulted in a larger yield of high quality wire than dies made with natural or high pressure synthetic diamond crystals. These results confirm that the articles of this invention will give increased performance through higher tool life.
  • Single crystal synthetic diamond has been grown by the high pressure method (US Patent 5,127,983) and found to exhibit a maximum thermal conductivity of 2200- 2500 W/mK at room temperature.
  • High pressure diamond has been grown as free standing crystals in sizes of several millimeters on an edge. These large crystals are readily fabricated by polishing into slabs by which accurate measurements of thermal conductivity can be made.
  • Single crystal diamond is produced by the CVD method by growth on a single crystal seed which may originate from a natural diamond crystal, a high pressure grown diamond crystal or a CVD grown diamond crystal.
  • a CVD crystal may be removed from its seed crystal by a number of means.
  • the seed crystal may be removed by grinding away the seed crystal with diamond grit in a manner which is well known in the art (Gridinsky).
  • the seed crystal may be removed by sawing with a diamond impregnated diamond wheel as commonly used to cut industrial and gem diamonds (Field).
  • a sacrificial layer is produced on the diamond seed surface, the CVD diamond is grown on top of this sacrificial layer and the sacrificial layer is subsequently removed to yield a free standing diamond crystal plate.
  • Methods for producing such a sacrificial layer and removal thereof are: ion implantation to form non-diamond layer beneath the seed surface followed by a oxidative removal process consisting of electrolysis or heating in an oxidizing atmosphere (US Patent 5,587,210), building a porous structure through which diamond can grow and which said porous structure can be removed by a combination of acid leaching and oxidation (US Patent 5,443,032, 5,614,019); or depositing a layer of non diamond material which can be removed by oxidation or other treatment (US Patent 5,290,392).
  • claims have been made and granted for growing and removing thick single crystal diamond from natural and high pressure diamond seed crystals.
  • high thermal conductivity single crystal diamond is obtained by growing in the following manner: (1) a diamond crystal at least about 20 micrometers, preferably 50 micrometers, and more preferably at least about 75 or even 100 micrometers, thick is grown on single crystal seed which can be chosen from natural diamond crystals, synthetic high pressure diamond crystals or synthetic CVD diamond crystals.
  • the diamond crystal is grown from hydrocarbon gasses and hydrogen and may contain or not contain oxygen and is rich in atomic hydrogen
  • the CVD growth is carried out at growth rates in excess of 10 micrometers per hour; the CVD grown crystal is removed from the seed crystal by grinding, sawing, use of a sacrificial layer or other removal method as might be found useful;
  • the nitrogen content of the starting gas composition is low enough as to result in a final CVD diamond crystal which has less than 10 to 20 ppm nitrogen incorporated into the crystal into substitutional sites and/or into interstitial sites.
  • the single crystal diamond produced will have a thermal conductivity of greater than 2200 W/mK and the material will be of the size and quality required for use as tools, wire dies, optical windows and heat spreaders.
  • Thermal Conductivity Methods to measure diamonds thermal conductivity have been reviewed in the literature (see J.E. Graebner, "Thermal Measurement Techniques", p. 193-226, Handbook of Industrial Diamond and Diamond Films. M.A. Prelas, G. Popovici, and L.K. Bigelow, Editors, Marcel Dekker, Inc. (1998)).
  • the measurement techniques include the use of steady state heating wherein heat is applied to one part of the sample, and the temperature distribution on the rest of the sample is measured.
  • the thermal conductivity of diamond can also be measured using periodic heating to generate thermal waves, and the thermal diffusivity is measured.
  • a periodic heat source is applied to the sample via pulsed heating of a direct contact heater or by pulsed operation of a light source (such as a laser) which heats a region of the sample.
  • the thermal wave diffusion is measured using thermocouples or infrared temperature sensors, and this allows detemiination of the thermal diffusivity.
  • Nitrogen Content There are a number of methods used to measure the nitrogen content in diamond, with the most appropriate technique being determined by the type of nitrogen center found in the diamond being measured. Nitrogen can be present in a number of configurations in diamond, and the most common configurations are (see CD. Clark, A.T. Collins, and G.S. Woods, "Absorption and Luminescence Spectroscopy", The Properties of Natural and Synthetic Diamond, Edited by J.E.
  • single substitutional form a isolated nitrogen atom replaces one carbon atom in the lattice, the A-center; a pair of adjacent substitutional nitrogen atoms, and the B-center; attributed to four substitutional nitrogen atoms clustered around a lattice vacancy.
  • the nitrogen content in diamond can be determined using mass spectroscopy, optical absorption, and electron spin resonance (esr). Mass spectroscopy (such as secondary ion mass spectroscopy
  • SLMS SLMS
  • the ssf form (which is paramagnetic) can also be measured using esr by comparing the microwave absorption to the absorption of a standard with known spin concentration.
  • nitrogen has been found to incorporate almost exclusively n the ssf and so the nitrogen concentration is determined using either the infrared absorption (with the ssf calibration factor), esr, and/or mass spectroscopy.
  • the boron content in diamond can also be determined using mass spectroscopy, and using optical absorption, as well as through electrical measurements.
  • Boron concentration can also be determined by analyzing the electrical carrier concentration as a function of temperature using well established equations of electrical neutrality (see J.S. Blakemore, Semiconductor Statistics, Dover Publications (1987)).
  • the isotope content of diamond can be determined using mass spectroscopy, x-ray diffraction, and Raman spectrosopy .
  • the most accurate way to determine the isotopic content of a diamond is by using mass spectrometry techniques such as SIMS or analysis of the combustion products made by burning the diamond.
  • mass spectrometry techniques such as SIMS or analysis of the combustion products made by burning the diamond.
  • SIMS mass spectrometry techniques
  • Such techniques allow determination of the isotope content with a demonstrated resolution on the level of 0.01% (see T.R. Anthony, et. ah, "Thermal diffusivity of isotopically enriched 12C diamond" Physical Review B42, p. 1105 (1990).), while SIMS measurements are known to be capable of parts per billion resolution if appropriate measurement techniques are used and standard samples are available (see J.M.
  • High resolution x-ray diffraction can be used to measure the lattice constant, and the measured lattice constant can be used to determine the isotope content of the diamond using the equation given previously. Note that in order to determine the isotope content at atomic percent levels using x-ray analysis, the lattice constant must be determined with a resolution of 0.00005 angstroms. This requires use of high resolution x-ray diffraction equipment such as a double crystal diffractometer with a highly perfect monoclirometer crystal and including sample rotation. Such a measurement approach has been described by Bartels (see W. J. Bartels, Journal of Vacuum Science and Technology, Bl, p. 338 (1983).).
  • the isotope content can also be determined by measuring peak position of the first order one-phonon Raman band, with the isotopic dependence described by K.C. Hass, et. al. (see K.C. Hass, et. al., "Lattice dynamics and Raman spectra of isotopically mixed diamond", Physical Review B45, pp. 7171-7182 (1992).). Note that the position of the Raman band shifts from 1332 cm “1 to 1281 cm "1 for a isotope change from 100 % 12C to 100% 13C, with the position change being almost linear with isotope content.
  • the Raman line position in order to use Raman spectroscopy to measure 1% changes in isotope content, the Raman line position must be measured with a certainty which is ⁇ 0.5 cm "1 . This requires that measurements be performed using a high resolution Raman spectrometer, and requires that the diamond quality to be high enough to yield Raman line widths which are ⁇ 0.5 cm "1 . To measure isotope contents with a resolution less than 1% requires further increases in measurement accuracy.
  • a natural type LA diamond single crystal is sliced on a diamond impregnated saw to yield a substrate of (100) orientation.
  • the substrate is polished with diamond grit suspended in olive oil and impregnated into a cast iron plate to achieve a surface which is free of grooves, scratches or digs.
  • This substrate is then cleaned with hot detergent in an ultrasonic cleaner, rinsed in acetone and dried.
  • the substrate is placed in a hot filament chemical vapor deposition reactor (HFCVD) having a substrate heater consisting of a tungsten filament held within a molybdenum holder and having a rhenium filament approximately 10 mm from the substrate.
  • HFCVD hot filament chemical vapor deposition reactor
  • the reactor is evacuated to a pressure of less than 10 millitorr and then backfilled to a pressure of 40 torr with hydrogen having a purity of 99.999% and at a rate of 100 seem.
  • Power is applied to the rhenium filament to achieve a temperature of 2100°C, whereupon power is applied to the substrate heater until the substrate reaches a temperature of 950°C as measured by a disappearing filament optical pyrometer.
  • methane gas is added to the gas stream so that the final mixture is 99% hydrogen and 1% methane while maintaining the total gas flow at 100 seem.
  • Part of the hydrogen is converted to atomic hydrogen on the surface of the filament and the methane decomposes in the presence of the atomic hydrogen on the substrate surface to form an epitaxial layer of diamond. Growth is maintained for 24 hours at a rate of 1 micrometer per hour to form a single crystal deposit of 24 micrometers thick.
  • the methane flow is terminated, the filament power and substrate power are terminated and the substrate with film is cooled to room temperature.
  • the reactor is evacuated to remove all hydrogen and then filled with room air to atmospheric pressure.
  • the single crystal diamond substrate with the attached diamond film is removed and cleaned in a mixture of chromic acid and sulfuric acid at temperature of 250°C to remove residual non diamond carbon from the diamond surface, leaving a single crystal diamond film attached to a single crystal seed.
  • An undoped single crystal diamond plate having a (100) orientation is obtained having a thickness of approximately 24 ⁇ m.
  • a natural type UA diamond single crystal is sliced on diamond impregnated saw to yield a substrate of (100) orientation.
  • the substrate is polished with diamond grit suspended in olive oil and impregnated into a cast iron plate to achieve a surface which is flat and free of grooves, scratches or digs.
  • the substrate is then cleaned with hot detergent in an ultrasonic cleaner, rinsed in acetone and dried.
  • HFCVD hot filament chemical vapor deposition reactor
  • the reactor is evacuated to a pressure of less than 10 millitorr and the backfilled to a pressure of 40 torr with hydrogen having a purity of 99.999% and at a rate of 100 seem.
  • Power is applied to the rhenium filament to achieve a temperature of 2100°C whereupon power is applied to the substrate heater until the substrate reaches a temperature of 950°C as measured by a disappearing filament optical pyrometer.
  • methane gas which has been enriched with respect to 13 C is added to the gas stream so that the final mixture is 99% hydrogen and 1% 13 C methane while maintaining the total gas flow at 100 seem.
  • Part of the hydrogen is converted to atomic hydrogen on the surface of the filament and the methane decomposes in the presence of the atomic hydrogen on the substrate surface to form an epitaxial layer of diamond.
  • An undoped single crystal diamond plate having a (100) orientation is obtained having a thickness of approximately 24 ⁇ m.
  • a high pressure synthetic type lb diamond single crystal is ground and polished to yield a substrate with a (100) orientation.
  • the substrate is then cleaned with hot detergent in an ultrasonic cleaner, rinsed in acetone and dried.
  • the substrate is placed in a hot filament chemical vapor deposition reactor (HFCVD) having a substrate heater consisting of a tungsten filament held within a molybdenum holder and having a rhenium filament approximately 10 mm from the substrate.
  • HFCVD hot filament chemical vapor deposition reactor
  • the reactor is evacuated to a pressure of less than 10 millitorr and then backfilled to a pressure of 40 torr with hydrogen having a purity of 99.999% and at a rate of 100 seem.
  • Power is applied to the rhenium filament to achieve a temperature of 2100°C whereupon power is applied to the substrate heater until the substrate reaches a temperature of 1000°C as measured by a disappearing filament optical pyrometer.
  • acetone vapor is added to the gas stream so that the final mixture is 99%> hydrogen and 1% acetone while maintaining the total gas flow at 100 seem.
  • Part of the hydrogen is converted to atomic hydrogen on the surface of the filament and the acetone decomposes in the presence of the atomic hydrogen on the substrate surface to form an epitaxial layer of diamond. Growth is maintained for 48 hours at a rate of 1 micrometer per hour to form a single crystal deposit of 48 micrometers thick.
  • the acetone flow is terminated, the filament power and substrate power are terminated and the substrate with film is cooled to room temperature.
  • the reactor is evacuated to remove all hydrogen and then filled with room air to atmospheric pressure.
  • the single crystal diamond substrate with the attached diamond film is removed and cleaned in a mixture of chromic acid and sulfuric acid at temperature of 250°C to remove residual non diamond carbon from the diamond surface. After cleaning the substrate and diamond are mounted in a saw having a copper blade impregnated with diamond grit, and sawing through the seed diamond to detach the single crystal diamond film from the single crystal seed. An undoped single crystal diamond plate having a (100) orientation is obtained having a thickness of approximately 48 ⁇ m.
  • a high pressure synthetic type lb diamond single crystal is ground and polished to yield a substrate with a (100) orientation.
  • the substrate is then cleaned with hot detergent in an ultrasonic cleaner, rinsed in acetone and dried.
  • the substrate is placed in a hot filament chemical vapor deposition reactor (HFCVD) having a substrate heater consisting of a tungsten filament held within a molybdenum holder and having a rhenium filament approximately 10 mm from the substrate.
  • HFCVD hot filament chemical vapor deposition reactor
  • the reactor is evacuated to a pressure of less than 10 millitorr and then backfilled to a pressure of 40 torr with hydrogen having a purity of 99.999% and at a rate of 100 seem.
  • Power is applied to the rhenium filament to achieve a temperature of 2100°C whereupon power is applied to the substrate heater until the substrate reaches a temperature of 1000°C as measured by a disappearing filament optical pyrometer.
  • acetone vapor is added to the gas stream so that the final mixture is 99% hydrogen and 1% acetone containing 1000 parts per million of methyl borate while maintaining the total gas flow at 100 seem.
  • Part of the hydrogen is converted to atomic hydrogen on the surface of the filament and the acetone decomposes in the presence of the atomic hydrogen on the substrate surface to form an epitaxial layer of diamond. Growth is maintained for 12 minutes at a rate of 1 micrometer per hour to form a boron doped single crystal deposit of 0.2 micrometers thick.
  • the acetone flow is terminated, the filament power and substrate power are terminated and the substrate with film is cooled to room temperature.
  • the reactor is evacuated to remove all hydrogen and then filled with room air to atmospheric pressure.
  • the single crystal diamond substrate with the attached diamond film is removed and cleaned in a mixture of chromic acid and sulfuric acid at temperature of 250°C to remove residual non diamond carbon from the diamond surface. After cleaning the substrate with the attached single crystal boron doped film diamond are mounted in a van der Pauw test system to measure the resistivity and mobility.
  • a boron doped single crystal film of diamond having a (100) is grown having a thickness of approximately 0.2 ⁇ m and is attached to a single crystal diamond substrate.
  • a polished CVD grown diamond single crystal having a (100) orientation is cleaned with hot detergent in an ultrasonic cleaner, rinsed in acetone and dried.
  • the substrate is placed in a hot filament chemical vapor deposition reactor (HCFVD) having a substrate heater consisting of a tungsten filament held within a molybdenum holder and having a rhenium filament approximately 10 mm from the substrate.
  • HCFVD hot filament chemical vapor deposition reactor
  • the reactor is evacuated to a pressure of less than 10 millitorr and then backfilled to a pressure of 40 torr with hydrogen having a purity of 99.999%) and at a rate of 100 seem.
  • Power is applied to the rhenium filament to achieve a temperature of 2100°C whereupon power is applied to the substrate heater until the substrate reaches a temperature of 950°C as measured by a disappearing filament optical pyrometer.
  • methane gas which has been enriched with respect to C is added to the gas stream so that the final mixture is 99% hydrogen and 1% 13 C methane while maintaining the total gas flow at 100 seem.
  • Part of the hydrogen is converted to atomic hydrogen on the surface of the filament and the methane decomposes in the presence of the atomic hydrogen on the substrate surface to form an epitaxial layer of diamond.
  • the single crystal diamond substrate with the attached diamond film is removed and cleaned in a mixture of chromic acid and sulfuric acid at temperature of 250°C to remove residual non diamond carbon from the diamond surface, leaving a single crystal 13 C diamond film attached to normal isotope diamond seed.
  • a polished CVD grown diamond single crystal having a (100) orientation is cleaned with hot detergent in an ultrasonic cleaner, rinsed in acetone and dried.
  • HCFVD hot filament chemical vapor deposition reactor
  • substrate heater consisting of a tungsten filament held within a molybdenum holder and having a rhenium filament approximately 10 mm from the substrate.
  • the reactor is evacuated to a pressure of less than 10 millitorr and then backfilled to a pressure of 40 torr with hydrogen having a purity of 99.999% and at a rate of 100 seem.
  • Power is applied to the rhenium filament to achieve a temperature of 2100°C whereupon power is applied to the substrate heater until the substrate reaches a temperature of 950°C as measured by a disappearing filament optical pyrometer.
  • methane gas which has been enriched with respect to 13 C and diborane is added to the gas stream so that the final mixture is 99% hydrogen and 1% 13 C methane containing 100 ppm of diborane while maintaining the total gas flow at 100 seem.
  • Part of the hydrogen is converted to atomic hydrogen on the surface of the filament and the methane decomposes in the presence of the atomic hydrogen on the substrate surface to form an epitaxial layer of diamond.
  • the single crystal diamond substrate with the attached diamond film is removed and cleaned in a mixture of chromic acid and sulfuric acid at temperature of 250°C to remove residual non diamond carbon from the diamond surface, leaving a boron doped single crystal 13 C diamond film attached to a normal isotope single crystal diamond seed.
  • a boron and 13 C doped single crystal diamond film is grown (having reduced strain) attached to a CVD single crystal diamond substrate wherein the film has a
  • a polished CVD grown diamond single crystal having a (100) orientation is cleaned with hot detergent in an ultrasonic cleaner, rinsed in acetone and dried.
  • the substrate is placed in a hot filament chemical vapor deposition reactor (HCFVD) having a substrate heater consisting of a tungsten filament held within a molybdenum holder and having a rhenium filament approximately 10 mm from the substrate.
  • HCFVD hot filament chemical vapor deposition reactor
  • the reactor is evacuated to a pressure of less than 10 millitorr and then backfilled to a pressure of 40 torr with hydrogen having a purity of 99.999% and at a rate of 100 seem.
  • the single crystal diamond substrate with the attached diamond film is removed and cleaned in a mixture of chromic acid and sulfuric acid at temperature of 250°C to remove residual non diamond carbon from the diamond surface, leaving a phosphorous doped single crystal C diamond film attached to a normal isotope single crystal diamond seed.
  • a phosphorous and 13 C co doped single crystal diamond film (having reduced stress) is formed on a CVD single crystal diamond substrate having a (100) orientation, wherein the film is also (100) orientation and has a thickness of approximately 0.17 ⁇ m.
  • a polished CVD grown diamond single crystal having a (100) orientation and a thickness of 75 micrometers is cleaned with hot detergent in an ultrasonic cleaner, rinsed in acetone and dried.
  • the substrate is placed in a hot filament chemical vapor deposition reactor (HCFVD) having a substrate heater consisting of a tungsten filament held within a molybdenum holder and having a rhenium filament approximately 10 mm from the substrate.
  • HCFVD hot filament chemical vapor deposition reactor
  • the reactor is evacuated to a pressure of less than 10 millitorr and then backfilled to a pressure of 40 torr with hydrogen having a purity of 99.999%) and at a rate of 100 seem.
  • Power is applied to the rhenium filament to achieve a temperature of 2100°C whereupon power is applied to the substrate heater until the substrate reaches a temperature of 950°C as measured by a disappearing filament optical pyrometer.
  • methane gas and diborane is added to the gas stream so that the final mixture is 99% hydrogen and 1% methane containing 1000 ppm of diborane while maintaining the total gas flow at 100 seem.
  • Part of the hydrogen is converted to atomic hydrogen on the surface of the filament and the methane decomposes in the presence of the atomic hydrogen on the substrate surface to form an epitaxial layer of diamond. Growth is maintained for 15 minutes at a rate of 1 micrometer per hour to form a single crystal deposit of 0.25 micrometers thick.
  • the diborane flow is terminated, and the methane flow continued for an additional 75 hours.
  • the methane flow is terminated, the filament power and substrate power are terminated and the substrate with film is cooled to room temperature.
  • the reactor is evacuated to remove all hydrogen and then filled with room air to atmospheric pressure.
  • the single crystal diamond substrate with the attached diamond film is removed and cleaned in a mixture of chromic acid and sulfuric acid at temperature of 250°C to remove residual non diamond carbon from the diamond surface, leaving a boron doped single crystal diamond layer imbedded in a 150 micrometer thick diamond crystal.
  • a (100) oriented single crystal diamond structure is formed having a 75 ⁇ m thick undoped CVD diamond followed by a 0.25 ⁇ m thick boron doped single crystal diamond layer, followed by a 75 ⁇ m thick CVD single crystal diamond layer.
  • a polished CVD grown diamond single crystal having a (100) orientation and a thickness of 75 micrometers is cleaned with hot detergent in an ultrasonic cleaner, rinsed in acetone and dried.
  • the substrate is placed in a hot filament chemical vapor deposition reactor (HCFVD) having a substrate heater consisting of a tungsten filament held within a molybdenum holder and having a rhenium filament approximately 10 mm from the substrate.
  • HCFVD hot filament chemical vapor deposition reactor
  • the reactor is evacuated to a pressure of less than 10 millitorr and then backfilled to a pressure of 40 torr with hydrogen having a purity of 99.999% and at a rate of 100 seem.
  • Power is applied to the rhenium filament to achieve a temperature of 2100°C whereupon power is applied to the substrate heater until the substrate reaches a temperature of 950°C as measured by a disappearing filament optical pyrometer.
  • methane gas and diborane is added to the gas stream so that the final mixture is 99% hydrogen and 1% methane containing 1000 ppm of diborane while maintaining the total gas flow at 100 seem.
  • Part of the hydrogen is converted to atomic hydrogen on the surface of the filament and the methane decomposes in the presence of the atomic hydrogen on the substrate surface to form an epitaxial layer of diamond.
  • the single crystal diamond substrate with the attached diamond film is removed and cleaned in a mixture of chromic acid and sulfuric acid at temperature of 250°C to remove residual non diamond carbon from the diamond surface, leaving a heterostructure of alternating boron doped and undoped single crystal diamond layers.
  • a single crystal diamond structure is formed consisting often alternating layers of boron doped and undoped diamond of which are individually 0.02 ⁇ m thick, to total thickness being 0.2 ⁇ m thick, the structure being the upper layer of a 75 ⁇ m thick CVD single crystal diamond, all having a (100) orientation.
  • Example 10 Growth Of (100) Oriented Boron Doped Single Crystal Diamond On A CVD Grown Single Crystal Synthetic Diamond Using The Microwave Plasma Method.
  • a polished CVD grown diamond single crystal having a (100) orientation and a thickness of 75 micrometers is cleaned with hot detergent in an ultrasonic cleaner, rinsed in acetone and dried. Following cleaning the substrate is placed in a microwave plasma reactor (MWCVD) having a molybdenum substrate holder. The reactor is evacuated to a pressure of less than 10 millitorr and then backfilled to a pressure of 40 torr with hydrogen having a purity of 99.999% and at a rate of 100 seem.
  • MWCVD microwave plasma reactor
  • Power is applied to the microwave generator to achieve a plasma ball and a substrate temperature of 900°C as measured by a disappearing filament optical pyrometer.
  • methane gas and diborane is added to the gas stream so that the final mixture is 99% hydrogen and 1% methane containing 1000 ppm of diborane while maintaining the total gas flow at 100 seem.
  • Part of the hydrogen is converted to atomic hydrogen in the plasma and the methane decomposes in the presence of the atomic hydrogen on the substrate surface to form an epitaxial layer of diamond.
  • the single crystal diamond substrate with the attached diamond film is removed and cleaned in a mixture of chromic acid and sulfuric acid at temperature of 250°C to remove residual non diamond carbon from the diamond surface, leaving a boron doped single crystal diamond layer of 250 micrometer thick diamond crystal attached to an undoped single crystal diamond seed.
  • a boron doped single crystal diamond plate having a (100) orientation is obtained having a thickness of approximately 250 ⁇ m.
  • a polished CVD grown diamond single crystal having a (100) orientation and a thickness of 75 micrometers is cleaned with hot detergent in an ultrasonic cleaner, , rinsed in acetone and dried. Following cleaning the substrate is placed in an arc jet microwave plasma reactor (MPCVD) having a molybdenum substrate holder. The reactor is evacuated to a pressure of less than 10 millitorr and then backfilled to a pressure of 100 torr with hydrogen having a purity of 99.999% and at a rate of 5000 seem.
  • MPCVD arc jet microwave plasma reactor
  • Power is applied to produce an arc in the hydrogen stream and a substrate temperature of 900°C as measured by a disappearing filament optical pyrometer.
  • methane gas is added to the chamber so that the final mixture is 99% hydrogen and 1% methane while maintaining the total gas flow at 5000 seem.
  • Part of the hydrogen is converted to atomic hydrogen in the gas stream and the methane decomposes in the presence of the atomic hydrogen on the substrate surface to form an epitaxial layer of diamond.
  • the single crystal diamond substrate with the attached diamond film is removed and cleaned in a mixture of chromic acid and sulfuric acid at temperature of
  • An undoped single crystal diamond plate having a (100) orientation is obtained having a thickness of approximately 250 ⁇ m.
  • a polished CVD grown diamond single crystal having a (100) orientation and a thickness of 75 micrometers is cleaned with hot detergent in an ultrasonic cleaner, rinsed in acetone and dried. Following cleaning the substrate is placed in an combustion flame reactor (CFCVD) having a water cooled molybdenum substrate holder and operating at atmospheric pressure.
  • CFCVD combustion flame reactor
  • a gas mixture of acetylene and oxygen is utilized to heat the substrate to 1000°C as measured by a disappearing filament optical pyrometer. After stabilizing the flame and substrate temperature for five minutes, the acetylene concentration is raised so that the composition is carbon rich and so that diamond growth begins.
  • Part of the hydrogen is converted to atomic hydrogen in the flame and the acetylene and other hydrocarbons decomposes in the presence of the atomic hydrogen on the substrate surface to form an epitaxial layer of diamond. Growth is maintained for 25 hours at a rate of 20 micrometer per hour to form a single crystal undoped diamond of 500 micrometers thick. At the end of this time period the acetylene and oxygen flow are terminated and the substrate with film is cooled to room temperature. The single crystal diamond substrate with the attached diamond film is removed and cleaned in a mixture of chromic acid and sulfuric acid at temperature of 250°C to remove residual non diamond carbon from the diamond surface, leaving an undoped single crystal diamond layer of 500 micrometer thick diamond crystal attached to an undoped single crystal diamond seed. An undoped single crystal diamond plate having a (100) orientation is obtained having a thickness of approximately 500 ⁇ m.
  • a natural type LA diamond single crystal is sliced on a diamond impregnated saw to yield a substrate of (110) orientation.
  • the substrate is polished with diamond grit suspended in olive oil and impregnated into a cast iron plate to achieve a surface which is free of grooves, scratches or digs.
  • the substrate is then cleaned with hot detergent in an ultrasonic cleaner, rinsed in acetone and dried.
  • HFCVD hot filament chemical vapor deposition reactor
  • the reactor is evacuated to a pressure of less than 10 millitorr and then backfilled to a pressure of 40 torr with hydrogen having a purity of 99.999% and at a rate of 100 seem.
  • Power is applied to the rhenium filament to achieve a temperature of 2100°C whereupon power is applied to the substrate heater until the substrate reaches a temperature of 950°C as measured by a disappearing filament optical pyrometer.
  • methane gas is added to the temperature of the filament and substrate for five minutes methane gas is added to the gas stream so that the final mixture is 99% hydrogen and 1% methane while maintaining the total gas flow at 100 seem.
  • Part of the hydrogen is converted to atomic hydrogen on the surface of the filament and the methane decomposes in the presence of the atomic hydrogen on the substrate surface to form an epitaxial layer of diamond. Growth is maintained for 24 hours at a rate of 1 micrometer per hour to form a single crystal deposit of 24 micrometers thick. At the end of this time period the methane flow is terminated, the filament power and substrate power are terminated and the substrate with film is cooled to room temperature. At this point the reactor is evacuated to remove all hydrogen and then filled with room air to atmospheric pressure.
  • the single crystal diamond substrate with the attached diamond film is removed and cleaned in a mixture of chromic acid and sulfuric acid at temperature of 250°C to remove residual non diamond carbon from the diamond surface, leaving a single crystal diamond film attached to a single crystal seed.
  • An undoped single crystal diamond plate having a (110) orientation is obtained having a thickness of approximately 24 ⁇ m.
  • a natural type LA diamond single crystal is cleaved along the (111) plane to yield a substrate of (100) orientation.
  • the substrate is polished with diamond grit suspended in olive oil and impregnated into a cast iron plate to achieve a surface which is free of grooves, scratches or digs.
  • This substrate is then cleaned with hot detergent in an ultrasonic cleaner, rinsed in acetone and dried.
  • the substrate is placed in a hot filament chemical vapor deposition reactor (HFCVD) having a substrate heater consisting of a tungsten filament held within a molybdenum holder and having a rhenium filament approximately 10 mm from the substrate.
  • HFCVD hot filament chemical vapor deposition reactor
  • the reactor is evacuated to a pressure of less than 10 millitorr and then backfilled to a pressure of 40 torr with hydrogen having a purity of 99.999% and at a rate of 100 seem.
  • Power is applied to the rhenium filament to achieve a temperature of 2100°C whereupon power is applied to the substrate heater until the substrate reaches a temperature of 950°C as measured by a disappearing filament optical pyrometer.
  • methane gas is added to the temperature of the filament and substrate for five minutes methane gas is added to the gas stream so that the final mixture is 99% hydrogen and 1% methane while maintaining the total gas flow at 100 seem.
  • Part of the hydrogen is converted to atomic hydrogen on the surface of the filament and the methane decomposes in the presence of the atomic hydrogen on the substrate surface to form an epitaxial layer of diamond. Growth is maintained for 24 hours at a rate of 1 micrometer per hour to form a single crystal deposit of 24 micrometers thick.
  • the methane flow is terminated, the filament power and substrate power are terminated and the substrate with film is cooled to room temperature.
  • the reactor is evacuated to remove all hydrogen and then filled with room air to atmospheric pressure.
  • the single crystal diamond substrate with the attached diamond film is removed and cleaned in a mixture of chromic acid and sulfuric acid at temperature of 250°C to remove residual non diamond carbon from the diamond surface, leaving a single crystal diamond film attached to a single crystal seed.
  • An undoped single crystal diamond plate having a (111) orientation is obtained having a thickness of approximately 24 um.

Abstract

L'invention concerne des compositions de diamant monocristallin synthétique comportant une ou plusieurs couche(s) de diamant monocristallin formée(s) par dépôt chimique en phase vapeur. Ces couches comprennent une ou plusieurs couche(s) présentant une concentration accrue en une ou plusieurs impureté(s) (telle(s) que du bore et/ou des isotopes de carbone) comparativement à d'autres couches ou couches comparables dépourvues de telles impuretés. Ces compositions combinent de manière améliorée des propriétés parmi lesquelles figurent la couleur, la résistance, la vitesse du son, la conductivité électrique et la régulation des défauts. L'invention se rapporte en outre à un procédé correspondant de préparation desdites compositions, à un système permettant d'appliquer ce procédé, ainsi qu'à des articles comportant une telle composition.
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GB2511156A (en) * 2012-11-21 2014-08-27 Element Six Ltd Synthetic diamond heat spreaders
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