CVD single crystal diamond

Abstract

CVD single crystal diamond having a smallest linear dimension equal to or greater than 3.5 mm, a concentration of monosubstitutional nitrogen atoms in the neutral charge state (Ns0) between 20 and 250 ppb as measured by EPR, and a hue angle hab between 75 and 135°.

Description

[Technical Field]

[0001] The present invention relates to CVD single-crystal diamond and a method for producing CVD single-crystal diamond. [Background technology]

[0002] Interest in the chemical vapor deposition (CVD) synthesis of diamond began in the 1980s, and research by various groups around the world continues to this day. Much of the published research on single-crystal CVD diamond materials discloses the growth of thin layers (<1 mm) on single-crystal diamond substrates by homoepitaxial growth, primarily using microwave plasma CVD. The synthesis of thick, high-quality layers of single-crystal CVD diamond materials is successful only by stably maintaining physically extreme process conditions over many days, and typically requires highly specialized synthesis machinery and equipment. The synthesis parameters crucial for single-crystal CVD diamond growth include the substrate type (e.g., whether manufactured by CVD, under high pressure / high temperature, or natural geological synthesis), the method of preparing the substrate from the original matrix crystal, the substrate morphology (including crystal orientation of faces and / or edges), the substrate temperature during growth and thermal control of the growing crystal, and the vapor phase synthesis environment itself. The latter is influenced by the process gas composition (including impurities), the gas pressure within the process chamber, and the amount of microwave power supplied to the synthesis process, in addition to various mechanical factors such as the size of the process chamber, the process gas injection / exhaust morphology, and the process gas flow rate. Many of these parameters are interrelated so that if one parameter changes, others change accordingly, ensuring a suitable growth area. Failure to select and maintain suitable process conditions for the entire deposition area throughout the entire synthesis process can result in high levels of uncontrolled process variability, unusable products with unsuitable material properties, and even complete destruction of the crystal due to catastrophic cracking, twinning, or graphitization.

[0003] Diamond possesses high thermal conductivity, broad clarity, low dielectric loss, hardness, and other well-known properties. These properties, individually or in combination, are valuable in numerous scientific and technical applications. Synthetic diamond materials can be designed to have advantageous properties, and examples of suitable applications in specific forms are well known in the art. Technological advancements have improved the availability of synthetic diamonds, and they can now be found in several consumer applications as well as an increasing number of technical applications, including mechanical wear elements and optical elements. One prominent application in recent years is the use of synthetic diamond gemstones in jewelry. For polished products of a given quality, the market price is primarily determined by the size (mass) of the gemstone, and then the maximum mass obtainable in a given shape is determined by the minimum length dimension of the parent crystal. The minimum length dimension is usually the thickness (relative to the width or depth) for CVD crystals. For example, a round brilliant (RB) gemstone shape typically requires a minimum dimension of about 4 mm to produce a 1 carat (1 ct) portion, while a 2 ct RB requires about 5.5 mm. This assumes that there are no constraints on other dimensions. One appearance used to distinguish high and low quality diamond gemstones is the range of color "grades" sometimes given to diamonds before they are sold to consumers. Such grades relate to the amount of light absorption exhibited by a given gemstone. Industry standards such as the Gemological Institute of America (GIA) color grades D, E, and F constitute the "colorless" category, while grades G, H, I, and J are considered "near colorless." To date, the ability to reliably manufacture large-sized diamonds in the colorless and / or near-colorless tier has been a challenge. For specific optical applications, it is desirable to provide a material that has low light absorbance and can yield a "colorless" grade of D, E, or F when polished as a gemstone. Such a material can constitute a single-crystal CVD synthetic diamond material with a low impurity concentration. A higher impurity concentration increases the light absorbance of the material. Conversely, a material suitable for colorless gemstones may also have desirable properties for specific optical applications. Patent documents relating to the above-mentioned optical grade single-crystal CVD synthetic diamond materials and their applications include International Publication Nos. 2004 / 046427 and 2007 / 066215.

[0004] The color of a diamond gemstone is characterized not only by its intensity but also by its hue, such as yellow, brown, pink, and blue. Brown diamonds, or those with a significant brown component in their hue (e.g., brown-yellow), are generally undesirable for gemstones. Pink and blue diamonds with similar color intensity to yellow and / or brown diamonds in the near-colorless category are usually graded "fancy light" rather than near-colorless. Currently, the GIA does not offer letter grades for such samples. While it varies by individual preference, the most widely accepted hue in colorless to near-colorless diamonds is yellow. CVD-synthesized diamond materials typically exhibit a brownish hue during growth and can change to hues including pinkish-brown, pinkish-orange, pink, orange-pink, or yellow with any post-growth heat treatment. As described in International Publication No. 2004 / 022821, such heat treatment is preferably carried out at temperatures above 1400°C if the hue change should be achieved within a practical timeframe for the industrial process. It is further taught that at temperatures above 1600°C, as required to produce a specific hue, the rate of graphitization can be significant unless a diamond stabilization pressure of at least several gigapascals (GPa) is applied. When graphitization occurs, it unnecessarily reduces the mass of usable diamond, which in turn limits the size of gemstones that can be manufactured. Furthermore, there is a risk of graphitizing or otherwise damaging the diamond if inappropriate or poorly controlled high-pressure / high-temperature (HPHT) treatment is applied, making it potentially unusable.

[0005] A known property of CVD gemstones is photochromism, meaning they are prone to color changes, particularly in response to sunlight or other light sources that substantially emit ultraviolet (UV) wavelengths. This primary change in light absorption is usually caused by a reversible charge transfer process associated with specific defects, particularly silicon vacancy (SiV) centers, which are rare in natural or HPHT synthetic diamonds. In cases where clear color classification and / or letter grading are intended, photochromism in CVD diamond gemstones is usually undesirable, and gemstones without this undesirable feature may be preferred. Another aspect of diamond gemstone quality is clarity, meaning the absence of flaws visible to the naked eye. While various types of inclusions and cracks are the most typical characteristics and result in insufficient clarity, CVD-synthetic diamond gemstones found on the market sometimes exhibit what gemologists call "grain," which is localized variation in refractive index. The paper "The Impact of Internal Whitish and Reflective Graining on the Clarity Grading of D-to-Z Color Diamonods at the GIA Laboratory," published on page 206 onwards in Gems & Gemology volume 42, issue 4 (winter 2006), describes grain in detail, although it mainly relates to natural diamonds. It should be noted that this clarity characteristic is rarely found in natural diamonds and is not always listed in grading reports. Grain can interfere with the intended light propagation path of a polished gemstone, sometimes resulting in a loss of clarity and contrast.

[0006] Considering the above requirements for thickness and quality, which are not easy to achieve individually, let alone when combined, it is desirable to manufacture CVD-synthesized single-crystal diamond material as economically as possible, whether for gemstone or industrial applications. The technical requirements for low-cost, large-scale CVD single-crystal diamond manufacturing can generally be understood as maximizing the amount of polished carats produced per unit of input resources (e.g., manpower, consumables, energy, etc.). Input resources are closely related. For example, the key to minimizing labor requirements is automation, which depends on a reproducible large-batch manufacturing process. Large production batches also require many or large reactors, but the latter is preferred, as long as it is technically feasible, in order to minimize capital investment in replication equipment. Thus, the most important basic factors are the number of single-crystal diamonds that can be grown simultaneously in one reactor, and the growth rate that can be achieved in that case. While maintaining material quality and the overall level of process resources per carat produced, achieving a growth rate sufficient to justify producing only one single-crystal sample per reactor at a time may be challenging. However, growing a small number of crystals simultaneously and faster can produce diamonds at a volume fraction equivalent to growing many crystals slowly. For example, growing one crystal at 1 mm / h using 0.5 kW of electricity may be more difficult than producing 100 crystals each at a vertical growth rate of 0.01 mm / h in a single growth reactor using a total of 50 kW of power in a single synthesis run. The latter option can also save a great deal of time and effort that would be involved in starting and ending a single sample process; for example, if 100 crystals are needed, it could save more than 100 times the time and effort in the process of producing 100 crystals. The values ​​given in this example are merely hypothetical and depend on the specific reactor and process, but those skilled in the art will recognize the basic logic. Therefore, synthesizing multiple single-crystal CVD diamonds together in a single reactor may be commercially advantageous.

[0007] Heterogeneity can be present in multiple crystals in terms of morphology (including the presence of cracks), growth rate, or impurity content and dispersion. Even when the gas-phase chemistry and plasma environment are controlled to be substantially homogeneous, as described in International Publication 2013 / 087697, heterogeneous impurity incorporation can occur due to temperature fluctuations on the growth surface that affect the rate of impurity incorporation. Furthermore, since the growth rates of various crystal planes have different temperature dependencies, unintentional temperature fluctuations can make it difficult to control the crystal morphology. Such control is desirable, in particular, to avoid cracking. Temperature fluctuations can be perpendicular to the growth direction (i.e., spatial distribution) at a particular point within the deposition area, and / or parallel to the growth direction (temporal or altitude distribution) due to temperature fluctuations over the duration of the growth run (from the beginning to the end of the thickness). The proportion of grown diamond material suitable for a given application usually depends on the packing density of the reactor, and it is unlikely that a typical practitioner attempting to synthesize many crystals to be physically compatible will achieve good results in this way. Therefore, the optimal balance may lie between the volume of diamond grown per unit of input resources and the sensitivity of the process, product, and / or application to any non-uniformity that may occur simultaneously with attempting to increase this value.

[0008] For gemstone applications, where materials containing considerable concentrations of impurities may have little to no visible color (as described, for example, in International Publication No. 2006 / 136929) and are therefore desirable as gemstones, high-purity diamond material is conventionally superior when specific defects are not required. However, the relatively low growth rate of high-purity CVD diamond material presents a striking contrast, as it is time-consuming and expensive to produce thick layers. Therefore, in this and other commercial applications requiring relatively large fragments of CVD diamond, there may be a need for specific optimizations of the synthesis process for growth rate and morphology, even at the expense of potentially lower purity. One method for controlling growth rate and morphology is to intentionally add dopant-like defects. Since nitrogen has been found to increase the growth rate of the material and influence the formation of structural crystal defects such as dislocations, nitrogen is one of the most important dopants in CVD diamond synthesis, potentially making the diamond less fragile than nitrogen-free diamonds (and thus easier to grow as a thick layer without cracking). Therefore, nitrogen-doped single-crystal CVD-synthesized diamond materials have been widely studied and reported in the literature. The results of nitrogen doping can vary significantly depending on the amount of nitrogen incorporated into the diamond. As described in International Publication 2004 / 046427, low levels of nitrogen doping have little effect on light absorption or, in fact, the growth rate, and may be beneficial in reducing strain within the CVD crystal. On the other hand, high nitrogen addition promotes the growth of the material, as disclosed in International Publication 2003 / 052177, and its growth rate allows for relatively rapid thick layer formation. This, however, can be noticeably brown in color. In extreme cases, excessive nitrogen concentrations in CVD process gases can rapidly and uncontrollably grow materials containing low-quality diamonds (e.g., improperly shaped or cracked) or significant non-diamond (e.g., graphite) portions, significantly limiting the value of the product in any application requiring diamond. Returning to International Publication No. 2004 / 022821, it is taught that not only can the hue change with heat treatment, but a reduction in the overall level of light absorption may also occur, allowing for the consideration of growing CVD single-crystal diamonds that have unacceptable absorption for a given application in their initial state but become suitable after treatment. Such a strategy may be advantageous when the treatment process is relatively economical compared to longer growth periods, in which case the usual practitioner may employ nitrogen doping (or other methods) to reduce the synthesis time of the diamond material rather than being constrained by the light absorption requirements of the final product. Such optimization can be seen as distinct from post-growth heat treatment, as it is applied to improve the acceptability of diamonds produced by difficult-to-control synthesis processes, as it usually requires a high degree of predictability of synthesis and treatment results, provided there is confidence that both product specifications and cost targets will be met.

[0009] There is very little prior art describing either the growth of multiple CVD single-crystal diamonds or the distribution of properties (hardness, etc.) that occur between these diamonds. The conditions necessary for growing multiple single-crystal diamonds with properties desirable for specific applications in high yield are still largely unknown. While studies on the uniformity of certain regions are publicly known from the perspective of polycrystalline diamond wafers or thin films, what has been disclosed in this regard is unrelated to the requirements for growing a relatively large number of substantially separated single-crystal diamonds. [Overview of the project]

[0010] It is desirable to provide a method for continuously and on a large scale to produce high-quality single-crystal CVD-synthesized diamond layers having a specific minimum thickness. Much is already known about single-crystal diamond synthesis and the heat treatment of the resulting single-crystal diamond materials to achieve specific properties desired for specific applications. However, single-crystal CVD diamond with the advantageous properties achieved in embodiments of the present invention has not been previously disclosed. Furthermore, no process suitable for economically producing CVD diamond with reproducible properties, such as size and color grade, on a large scale in a single run has been previously disclosed.

[0011] According to the first aspect, the following: The minimum length dimension (e.g., length, width, or depth) is 3.5 mm or more; As measured by EPR, a single substituted nitrogen atom (N) in a neutral charge state s 0 The concentration of ) is between 20 and 250 ppb; hue angle h ab The angle is between 75 and 135 degrees. A CVD single-crystal diamond with specific properties is provided. International Publication No. 2011 / 076643 discloses CVD single-crystal diamond, which is at least partially N s 0 Absorption causes a temperature greater than approximately 80° ab It has. However, such samples have N greater than about 0.5 ppm (500 ppb). s 0 It is constrained to have a concentration. This is twice the maximum value of the present invention and does not correspond to color grades of J or less in gemstones of about 1 carat or more. Furthermore, International Publication 2011 / 076643 teaches that instead of HPHT annealing as a means of achieving such a hue angle, which is described as an expensive process that can result in poor yields due to cracking, oxygen is instead added to the synthesis process gas to reduce browning of the material in the as-grown state. In further comparison, in Examples 4 and 5 of WO 2004 / 022821, HPHT annealed CVD single crystal diamonds with h ab of about 100° and about 115° are disclosed. These diamonds have minimum length dimensions of 2 and 3 mm, respectively, and in each case correspond to the growth thickness. Although described as near colorless in actual size, they contain 1.1 and 2.2 ppm of N s 0 and thus if similar materials were available in sizes sufficient for gems of about 1 ct or more, the gems would not be near colorless. In contrast, materials according to some embodiments of the present invention can easily grow to a thickness of at least 3.5 mm, and in the examples at least 6 mm in actuality, and the resulting 1 to 2 ct gems are at least near colorless grade after annealing. The N s 0 concentration reduced to 50 ppb is claimed in WO 2004 / 022821, and the hue angle corresponding to such a value is defined as being less than 65°.

[0012] CVD single crystal diamonds optionally have a total concentration of neutral and negatively charged nitrogen vacancy centers (NV 0 and NV - ) that is less than 0.1 times the N s 0 concentration, or less than 10 ppb, whichever is greater. CVD single crystal diamonds optionally have a hue angle h ab selected from any of 85 to 125°, 90 to 120°, and 95 to 115°. These features are due to a more precisely optimized heat treatment process and approximate the desired "cape" yellow hue. CVD single crystal diamonds optionally use an excitation wavelength of 660 nm and are quantified by the ratio of the total peak area of the SiV - zero phonon line to the peak area of the diamond's primary Raman signal in a photoluminescence measurement performed at a temperature of 77 K, and are selected from less than 0.5; less than 0.1; less than 0.05; and less than 0.01 of SiV -It exhibits luminescence. Such values ​​indicate a diamond material with very few silicon impurities, which consequently does not exhibit significant photochromism. CVD single-crystal diamond exhibits low optical birefringence with low strain at an arbitrary temperature of 20°C. When measuring an area of ​​at least 3 mm × 3 mm, the third quartile of the refractive index difference of light polarized parallel to the slow and fast phase axes is averaged over the sample thickness, resulting in a value of 1 × 10⁻⁶. -4 and 5×10 -5 The values ​​must not exceed one of the following ranges. These low birefringence values ​​indicate suitable samples for producing single-crystal CVD diamonds without "grain," otherwise their perceived clarity may be affected.

[0013] CVD single-crystal diamonds are optionally at least 60 mm 3 , at least 80mm 3 and at least 100 mm 3 It has a total volume selected from one of the following. For example, these volumes apply when creating a round brilliant gemstone with a mass ranging from approximately 1 carat to over 1.75 carats. CVD single-crystal diamond may be gem-like in appearance, and its chrominance C is selected from less than 8, less than 6, and less than 4. * ab It possesses such a value. Such a value can be measured, for example, for gemstones that are at least near colorless. CVD single-crystal diamond may be gem-like in nature, and according to the Gemological Institute of America (GIA) scale and methods, N s 0 When the concentration is between 20 and 100 ppb, one of D, E, or F is selected, and N s 0 When the concentration is between 80 and 250 ppb, the color grade is selected from G, H, I, and J. Such ranges and values ​​were not known together prior to the present invention, and in some embodiments, they can be selected separately, for example, to meet the requirements of different market segments. CVD single-crystal diamonds may be in the shape of polished samples and may include gemstones having clarity grades selected from VS2, VS1, VVS2, VVS1, IF, and FL according to the Gemological Institute of America (GIA) scale and methods. These clarity grades correspond to samples that are free from clarity defects or have such defects. However, such defects are only observable under magnification and not visible to the naked eye. Some embodiments of the present invention provide single-crystal diamonds that would typically be suitable for one of these grades, and gemstones formed therefrom can be sold as commercial or high-quality commodities, but are not limited to these.

[0014] CVD single crystal diamond can be optionally H3(NVN) 0 ) Centers are included. When heat treatment is performed at a sufficient temperature for a sufficient time to achieve the desired yellow hue, H3 centers are typically formed within the disclosed material. If detectable, photoluminescence from H3 centers can be compared to photoluminescence from other defects to help establish annealing conditions within the optimal range. CVD single-crystal diamond exhibits a photoluminescence measurement of less than 30 (NV) when using an excitation wavelength of 455 to 459 nm and performing the measurement at a temperature of 77 K. 0 +NV - ) / H3 ratio is shown. NV 0 NV - Each of the H3 defects is quantified by the ratio of the peak area of ​​the zero-phonon line to the primary Raman signal of the diamond. The value of this ratio is arbitrarily selected from less than 20, less than 15, less than 10, less than 5, and less than 2. Such observational records indicate sufficient annealing conditions to achieve as-grown to yellow hue change as much and as completely as possible in a given sample. CVD single-crystal diamond exhibits an N3 / H3 ratio of less than 0.1 in photoluminescence measurements performed at a temperature of 77 K, using optionally excitation wavelengths of 323 to 327 nm for N3 and 455 to 459 nm for H3. Each defect is quantified by the ratio of the peak area of ​​the zero-phonon line to the primary Raman signal of the diamond. The value of this ratio is optionally selected from less than 0.05, less than 0.02, and less than 0.01. This level of value corresponds to a heat treatment process that is less stringent than necessary to achieve the desired range of hue angles within the scope of the present invention.

[0015] Therefore, the desired qualities of the disclosed material are designed as colorless or near-colorless and are considered to be at least many, and in some embodiments substantially all, qualities necessary to produce high-quality CVD synthetic diamond gemstones of broad interest. Furthermore, CVD synthetic diamond materials can be manufactured reproducibly, economically, and on a large scale using currently available technologies. The applications of diamond are not limited to gemstones. As an option, CVD single-crystal diamond can be formed into mechanical elements. Such elements typically have a wear surface that undergoes sliding or moving contact with another surface. Non-limiting examples of such mechanical elements include wire drawing dies, graphic tools, engraving tools (stichels), and high-pressure fluid jet nozzles such as high-pressure water jet nozzles. Alternatively, CVD single-crystal diamond can be formed into optical elements. Exemplary optical elements include intracavity optical elements, high-power transmission optical elements, Raman laser optical elements, etalons, and total internal reflection (ATR) optical elements.

[0016] According to the second aspect, a method for producing the CVD single-crystal diamond described above in the first aspect is also provided. This method is Placing multiple single-crystal diamond substrates on a substrate carrier in a chemical vapor deposition reactor; The process gas, containing hydrogen-containing gas, carbon-containing gas, and nitrogen-containing gas, is supplied to the reactor such that the relative amounts of these gases are stoichiometrically equal to a C2H2 / H2 ratio of 1% to 5% and an N2 / C2H2 ratio of 4 ppm to 60 ppm; Growing multiple single-crystal CVD diamonds on at least a portion of the surface of multiple single-crystal diamond substrates at a temperature of 750°C to 1100°C; This includes annealing at least a portion of the resulting single-crystal CVD diamonds at a temperature of 1700°C to 2200°C. The method optionally includes carrying out growth on a substrate as a single CVD synthesis cycle or "run" without interruption. Such an uninterrupted process is advantageous over a "stop-start" or layer-by-layer process, for example, in improving equipment utilization efficiency, avoiding the need to prepare multiple growth crystals, and preventing any adverse effects of interfaces formed between grown layers in the manufactured material by continuous growth cycles. In our preferred embodiment, as detailed in the examples, growth to the full thickness is carried out substantially always without interruption. This method optionally allows CVD synthesis to take at least 10 mm. 3 / h, at least 20mm 3 / h, at least 30mm 3 / h, at least 40mm 3 / h and at least 50mm 3 This includes providing a volume growth rate for single-crystal diamond material selected from either / h. This method optionally includes performing annealing under diamond-stabilized pressure. This allows for the use of high temperatures and / or long annealing times without causing any loss or damage to the CVD single-crystal material due to graphitization. This method optionally applies when the total volume of single-crystal diamonds treated in a single annealing operation is at least 500 mm³. 3 , at least 1000mm 3 , at least 1500mm 3and at least 2000mm 3 This includes being selected from any of the following.

[0017] This method optionally includes providing carbon-containing and hydrogen-containing process gases in amounts stoichiometrically equivalent to C2H2 / H2 ratios within a range selected from either 2% to 4% or 2.5% to 3.5%. These ranges are chosen to strike a balance between growth rate and material quality. The method optionally includes providing nitrogen-containing and carbon-containing process gases in amounts stoichiometrically equivalent to N2 / C2H2 ratios in ranges selected from 5 ppm to 20 ppm; 10 ppm to 50 ppm; 7 ppm to 15 ppm; and 15 ppm to 35 ppm. These ranges have been found suitable for providing CVD single-crystal diamond materials suitable for colorless to near-colorless synthetic gemstones after HPHT annealing. More specifically, in certain embodiments, the selection of these ranges allows for the selective production of either colorless or near-colorless gemstones. This method optionally involves growing multiple CVD single-crystal diamonds at temperatures selected from 800°C to 1050°C; 800°C to 950°C; and 825°C to 925°C. By maintaining all growing samples within these narrow ranges, in certain embodiments, it is possible to achieve more uniform nitrogen doping and a narrower color grade distribution among the diamonds to be completed as gemstones. This method optionally includes performing annealing at a temperature selected from 1750°C to 2100°C; 1800°C to 2000°C; and 1850°C to 1950°C. These narrow temperature ranges strike a balance between the effectiveness and speed of the annealing process, which are difficult to achieve using common equipment, materials, and processes. This method optionally includes cutting and polishing at least one of a plurality of single-crystal diamonds to form a gemstone. Furthermore, it optionally provides that the gemstone includes at least a portion of a single-crystal diamond substrate.

[0018] The present invention will be described in more detail below with reference to the attached figures, based on the examples. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 is a flowchart illustrating an exemplary process for producing CVD single-crystal diamond. [Modes for carrying out the invention]

[0020] While CVD single-crystal diamonds, such as those used in gemstones, are widely available on the market, a rough study of currently available products indicates a range of varying qualities and sizes. Clarity, color, and size are inconsistently combined, and sometimes even within the same manufacturer, no two samples are exactly alike. This suggests that a method for reproducibly mass-producing relatively large single-crystal CVD diamond pieces of superior quality remains unknown. The inventors have developed high-quality, continuously mass-producible CVD-synthesized diamonds. Here, “mass-producible” means not only that many dozens of single-crystal diamond materials can be produced at once in a single reactor, but also that the yield prospects, given the predicted production costs and specified production periods, allow for the planning and scheduling of production runs consisting of numerous synthesis cycles across numerous CVD reactors necessary to meet large-scale requirements. In some embodiments of the present invention, those skilled in the art can select a GIA color category or grade to apply to the finished product, cut and polished as a gemstone, in a manner that does not significantly impact production costs during synthesis.

[0021] The conditions described herein provide CVD single-crystal diamond materials with relatively small internal strain, thereby minimizing yield reduction due to cracking and avoiding significant stress-induced birefringence and / or visible grain in the finished product. Essentially, according to some embodiments, no cracks that limit yield occur in the synthesis run. This is partly due to the use of a single-crystal substrate (seed) with few structural defects, such as non-diamond inclusions, twinning, polishing damage, or dislocations crossing the surface. A preferred method for achieving the required high structural quality is to use a vertically cut CVD substrate, as described in International Publication No. 2004 / 027123, the contents of which are incorporated herein by reference. The disclosure describes a method for manufacturing a single-crystal diamond plate, comprising the steps of: providing a diamond substrate having a surface substantially free of structural defects; growing diamond homoepitaxially on the surface by CVD; and cutting the resulting grown crystal transversely, usually perpendicular (i.e., at 90° or nearly 90°) to the surface of the substrate on which the diamond growth occurs, to manufacture a single-crystal CVD diamond plate. This plate, or more typically a number of such plates obtained from each crystal, are used as substrates for further growth. Since expanding defects (dislocations and their aggregates) tend to propagate in the direction of growth, thinly cutting the diamond perpendicular to the direction of growth minimizes the possibility of defects intersecting new maximum faces, resulting in a low tendency for nucleation or dislocation increase. It is advantageous to use synthesis conditions for growing the substrate that are sufficiently similar to those used for the final diamond product, minimizing the difference in color between the substrate and the remaining crystals. This eliminates the need to remove the substrate before completing the gemstone, and the total usable thickness afterward is the sum of the substrate thickness and the subsequently grown thickness.

[0022] A CVD single-crystal diamond according to a specific embodiment of the present invention, when completed into a round brilliant gemstone shape with a mass of 1 to 2 ct and a GIA cut grade of very good or excellent, is classified as a near-colorless category (GIA grade G, H, I, or J) if it contains a single substituted nitrogen (N) with a neutral charge. s 0 ) If we consider it to be 100 to 250 ppb, or colorless (grade D, E, or F), then N s 0 It is known that it should contain 20 to 80 ppb. In all examples, these concentrations are measured by electron paramagnetic resonance (EPR) spectroscopy after deep UV illumination, which preferably ensures that any charge transfer effects are avoided. The color grades form a continuous scale, and therefore N s 0 If the concentration is in the intermediate range of 80 to 100 ppb, the gemstone is located almost on the border between the colorless and near-colorless categories. However, this category classification is unclear, given that color grades according to the GIA method can generally vary from one unit to another among different gemological laboratories. N of colorless CVD single crystal diamond gemstones s 0 While concentrations below 20 ppb would not further improve the color grade (D-grade diamond gemstones do not need to be completely colorless), the combination of low growth rate and strain-increasing tendency, known from International Publication No. 2004 / 046427, makes synthesis more difficult and time-consuming.

[0023] The above N, which had not been disclosed previously s 0 Assuming that the grade matches, another problem to be addressed in this invention is given N s 0The question is how the concentration, and therefore the specific color category or grade, can actually be achieved. The solution herein is to recognize that the ratio of nitrogen to carbon available in the CVD process gas is reflected in the ratio of hard diamond, and therefore to appropriately select this ratio for the desired intensity of yellow color in the product, as further detailed in the following examples. Furthermore, the ratio of carbon to available hydrogen is selected to achieve the target growth rate. Those skilled in the art will recognize that such selections are reactor and process-dependent, and therefore examples are provided herein. This is partly because the main factors influencing the diamond growth rate and material properties are the C1 radical species (e.g., C atoms, CH, CH2, and CH3), nitrogen radical species (e.g., N atoms, NH, and CN), and the flow of H atoms accompanying the growing diamond surface. However, these are difficult to measure and are usually unknown to the average practitioner, and are determined only indirectly by the process and reactor design. Apart from the hydrogen / methane / nitrogen mixture, which is usually considered the most practical and economical raw material for industrial processes, there are other viable chemical reactions. For example, among many other possibilities, the use of acetylene or propane instead of methane, and ammonia or nitrous oxide instead of molecular nitrogen can be considered. It may also be necessary to consider the reactions between the feedstocks. For example, it is known that some molecular oxygen is added to the hydrogen / methane process mixture. If this is done, the carbon atoms from methane must be reduced by the number of oxygen atoms added by the overall formation of CO. CO does not decompose effectively into C1 radicals in the chemical environment of the plasma CVD process and therefore does not contribute to diamond growth. Simple and useful calculations for a wide range of process chemistry, e.g., those with little or no molecular hydrogen and based on carbon dioxide and methane, should assume that the feedstocks react with each other to form a mixture of stoichiometric amounts of molecular nitrogen (N2), acetylene (C2H2), molecular hydrogen (H2), and carbon monoxide (CO), with the remainder being a gas that does not contain N, C, H, or O atoms, such as an inert gas.Although not commonly used, halogen-containing processes can be adapted by treating any halogen as hydrogen. Therefore, in the following examples, methane is used as the carbon source instead of acetylene, but the synthesis environment is also specified in terms of equivalent (calculated) ratios of N2 / C2H2 and C2H2 / H2, further facilitating comparison with other process chemistry.

[0024] When synthesizing diamond crystals, heat treatment is performed to convert the hue from the original brownish color to the desired yellow. In a preferred embodiment, the heat treatment is carried out at a temperature above 1600°C and under diamond stabilization pressure, as described in International Publication 2004 / 022821, the details of which are incorporated herein by reference. This is known as high-pressure high-temperature (HPHT) annealing. To achieve such pressure, HPHT requires considerable mechanical force to be applied to the material being treated, which can cause microscopic cracks (if present) to expand to an extent undesirable for the final application. Typically, such cracks are associated with polycrystalline material that forms as a byproduct on the surface of the CVD single crystal. To avoid compromising clarity, it is advantageous to prepare the CVD single-crystal diamond for HPHT annealing by removing any polycrystalline material that potentially contains cracks, preferably so that this "skin" portion is not included in the finished CVD single-crystal diamond gemstone. This avoids further loss due to cracking. Even more advantageously, the crystal may be partially or completely finished as a gemstone before annealing. In this case, since some of the gemstone is removed by cutting and / or polishing, the finished product will inevitably be smaller than the as-grown crystal, allowing more gemstones to be processed in each HPHT annealing operation. As with CVD synthesis, the process parameters required for HPHT annealing are determined in detail by the equipment, materials, and methods used, and these can vary by a typical practitioner for incidental reasons such as relative cost, without affecting the ability to achieve given conditions, as will be recognized by those skilled in the art. Therefore, again, specific examples are given for advice, not as limiting examples. As described herein, a common method is to irreversibly convert optically active point defects formed in diamond during CVD synthesis at relatively low temperatures into a thermodynamically stable form by reacting them together at relatively high temperatures. Typically, the main optically active point defects incorporated during CVD synthesis, which is carried out at temperatures between 700 and 1200°C, are N s 0 These are vacancy complexes (e.g., clusters and chains that contribute to the brown color). HPHT annealing at temperatures above approximately 1600°C can dissociate the vacancy complexes. This allows for later removal, so minimizing the as-grown brown state is not necessary for all applications. The resulting free vacancies migrate within the crystal until they encounter other defects and take on a form that is stable at higher temperatures. Generally, these combine with substituted nitrogen atoms to form NV defects, resulting in pinkish colors ranging from orange-pink to reddish-pink and then purplish-pink.

[0025] Free vacancies, if present, can bond with substituted silicon atoms, forming silicon vacancy (SiV) defects. While planned silicon doping using silicon-containing gases is known, silicon is widely accepted as an impurity in CVD-synthesized diamond materials, generally originating from CVD reactor components such as quartz glass dielectric barriers. Silicon is primarily composed of substituted atoms (Si). s It is incorporated into CVD diamonds as Si. s Because it is not optically active, it is difficult to detect in materials at low concentrations. On the other hand, SiV defects form preferentially to NV defects during annealing and can be easily observed in both neutral and negatively charged states. At room temperature, SiV 0It shows an absorption line at 946 nm (1.31 eV) and related phonon sidebands, while SiV - It shows an absorption line at 737 nm (1.68 eV), and similarly related bands. In particular, SiV 0 The sidebands extend into the visible spectrum, and samples containing this defect at sufficient concentrations may appear gray or grayish-blue. In particular, SiV is a strong electron acceptor, so when N is present in a diamond sample... s When present together, charge transfer between them usually results in the primary charge state being N s + and SiV - Neither contributes significantly to the perceived color of the sample. It contains a relatively high concentration of substituted nitrogen, but silicon doping allows for N s 0 A CVD single-crystal diamond with virtually no light absorption is disclosed in International Publication No. 2006 / 136929. A significant drawback of this method is that the resulting CVD single-crystal diamond exhibits strong photochromism. As described in “Optical properties of the neutral silicon split-vacancy center in diamond,” published as document number 245208 in Physical Review B volume 84 (December 2011), when such a sample is irradiated with UV light, the ionization process N s + +SiV - →N s 0 +SiV 0 This was triggered, and the yellow N s 0 and gray-blue SiV 0The combination of light absorption imparts a grayish color. Neither the photochromism itself nor the resulting color is particularly desirable in colorless and near-colorless gemstone applications and certain industrial applications. To avoid such color, the usual practitioner needs to limit the concentration of SiV defects to tens of ppb or less, preferably less. For annealed samples, satisfying this requirement usually involves minimizing the total silicon concentration in the CVD single-crystal diamond material, because otherwise, the formation of SiVs in the presence of free vacancies is essentially unavoidable.

[0026] At a processing temperature of approximately 1700°C, NV defects can move as a single unit within the crystal, encountering other defects or each other, and recombining to form new defects that are stable at that temperature. Such defects are H3 centers, consisting of two substituted nitrogen atoms (NVNs) separated by vacancies in an overall neutral charge state. 0 It consists of H3. H3 shows an absorption line at 503.2 nm (2.463 eV) and related bands, exhibiting a yellow color. Notably, the coupling of two NV defects, which is a key pathway in forming the H3 center, releases a free vacancy. That is, NV + NV → NVN(H3) + V. This vacancy is N s Because it can combine with and reform NV, there is no clear temperature threshold for the remaining NV defects that are removed by conversion to H3. Rather, the degree of conversion (the degree of color change from pinkish to yellow) depends on the duration of annealing and the reaction NV+N s →Excess N that promotes NVN sIt also depends on the usefulness (or vice versa) of the process. When processing materials with an unknown defect concentration, one method to ensure a final yellow hue is simply to increase the temperature to further dissociate NVs. However, this may require very high temperatures, e.g., above 2200°C, thus increasing the risk of graphitization and fracture of the material that should have been improved by the process. Such graphitization at high temperatures can be inhibited by applying higher pressure, e.g., above 8 GPa, but this requires either a large and powerful pressure generator or a reduction in volume that allows for high pressure. Due to practical limitations, the latter is the more common solution, but this inevitably reduces the amount of CVD single-crystal diamond material that can be processed in each annealing operation without proportionally reducing the processing time required per HPHT cycle, or the amount of labor or consumables. Therefore, generally, the annealing process is not economical when excessively high temperatures and pressures are used. This is clearly undesirable if one of the reasons for performing the annealing is to minimize the total cost of manufacturing the diamond material. When processing the disclosed CVD single-crystal material, it has been found that a pale yellow color, which is the desired photostability and free from brown or pink nuances, can be produced by annealing within a relatively narrow, predictable temperature range, considerably lower than the temperature at which diamond is converted to graphite, under typical pressures achievable by a normal HPHT operator. By finding and subsequently reproducing process conditions that provide this temperature range, those skilled in the art can process the disclosed material quantitatively and reliably without causing any graphitization or significant surface damage, even when fully finished as cut and polished parts such as gemstones. However, the optimal temperature for achieving hue conversion without graphitization is determined, at least to some extent, by the applied pressure and duration of annealing, and in any case, accurately measuring the temperature and / or pressure achieved in many types of HPHT equipment is not easy. Therefore, a measurement method is further disclosed that allows those skilled in the art to determine this simply by testing the processed material. Details of the actual measurement are shown in the examples.

[0027] The most direct quantitative indicator of the minimum sufficient conditions is the measured CIELAB h-angle, as defined by the International Commission on Illumination in CIE015:2004: "Technical Report, Colorimetry, 3rd Edition". ab This is important to the purpose of this application. For other equivalent materials, this value is determined almost entirely by the processing conditions and is actually independent of the size and shape of the sample (therefore, for example, if gemstones are the intended final product, the measurement does not require a fully finished gemstone). From the light absorption spectrum h ab The procedure for calculating h is detailed in CIE015:2004, and such spectra can be measured, for example, by transmission through a sample with polished parallel surfaces, or by using an integrating sphere for irregular shapes including gemstones. Other measurement methods are also possible, one of which is used in the examples. In the CIELAB color model, h ab =0° represents red, h ab =90° is yellow. The intermediate value representing the brown-orange hue is typical of untreated or very lightly treated CVD materials. As the treatment temperature increases, the hue angle initially does not change while no reaction occurs, and then tends to decrease toward the lowest value due to the formation of NV defects as the conditions approach the optimal range. At the lower limit of the optimal region h ab The hue angle begins to rise again, at a temperature slightly above the minimum hue angle (approximately 50°C or higher). However, processing at the lowest optimal temperature (hereinafter referred to as the threshold temperature, approximately 1700°C) requires a long time to achieve the desired hue conversion because the hue angle slowly rises towards yellow. If graphitization occurs at or below the threshold temperature, the pressure needs to be increased to widen the process window. The higher the mobility of the NV defects, the faster the hue angle change becomes as the temperature rises, and the processing time required at approximately 1750°C is usually reduced to less than one hour. Further increasing the temperature to shorten the required annealing time is usually a matter of the executor's judgment and may be determined by economic considerations based on the choice of equipment, materials, and process. Complete hue conversion is 90 <h abIt shows <120°, i.e., a slightly greenish-yellow hue from yellow. The exact hue angle at the end point is determined by the balance between the concentrations of N s 0 and H3 in the annealed material. This is mainly the effect of the brown in the as-grown state. The more brown the material is, the more pores it contains, and as a result, more H3 is produced by its treatment.

[0028] An excellent indicator of conditions that exceed the point of impairing recovery when treating CVD single-crystal diamond materials and are thus unnecessarily close to the graphitization threshold is the formation of a significant concentration of N3 defects. The N3 center consists of three substitutional nitrogen atoms surrounding a vacancy (3N + V) and shows an absorption line at 415.2 nm (2.985 eV) and related vibronic bands. Due to the absorption at the blue end of this visible spectrum, it is unlikely to achieve a concentration in CVD materials that would significantly affect the normally observed color, but it also exhibits a yellow hue. Importantly, N3 is thermodynamically more stable than H3 and is thus preferentially formed especially at 2200 °C or above 2200 °C. By sensitively detecting N3 (e.g., by photoluminescence spectroscopy) and maintaining a concentration below a specific level for other related defects such as H3 in the disclosed material, an ordinary practitioner can define the upper limit of the optimal range without the need for direct knowledge of temperature and pressure.

Example

[0029] As described in International Publication No. WO 2004 / 027123, a plurality of CVD single-crystal diamond substrates were fabricated as plates cut transversely. The plates had a (100) orientation plane and edges and were finished with dimensions of 4.5 × 4.5 × 0.3 mm required for making a 1 ct round brilliant gemstone product, or 5.5 × 5.5 × 0.3 mm for a similar 2 ct product. The substrates were attached to a suitably prepared substrate carrier and placed in a CVD reactor according to International Publication No. WO 2005 / 010245 and International Publication No. WO 2017 / 050620. The design and structure of the CVD reactor minimized the silicon impurity source in the diamond material. For example, as described in International Publication No. WO 2012 / 084660, the quartz glass dielectric barrier constituted only a small portion of the surface area exposed to the reactor process, was well cooled, and was positioned away from the deposition area. The reactor could provide a process purity sufficient to produce the electronic grade single crystal CVD diamond disclosed in International Publication Nos. WO 01 / 096633 and WO 01 / 096634. A process gas containing molecular hydrogen, a carbon-containing gas (methane in this example), and a nitrogen-containing gas (molecular nitrogen here) was supplied to the CVD reactor. The CVD reactors used by various practitioners widely differed in terms of performance characteristics, and the synthetic processes utilized were also, for example, accidental depending on the growth temperature but could still be significantly different. Adaptation to these differences is known in the art. Using the apparatus according to the present invention, as required for near-colorless CVD single crystal diamond gems, materials containing N s 0 from 100 to 250 ppb were found to be derived from a synthetic process utilizing a gas-phase concentration equivalent to 18 to 34 ppm of N2 / C2H2 by the above calculation method. This was shown by 9 to 17 ppm of N2 / CH4 in the process chemistry of the present applicants. N s 0 with 20 to 80 ppb, and thus similar gems of colorless grade require an equivalent of 7 to 15 ppm of N2 / C2H2, or 3.5 to 7.5 ppm of N2 / CH4 in the examples of the present applicants. Importantly, the N s 0The concentration was almost linearly proportional to the N2 / C2H2 equivalent ratio during synthesis, meaning that a small number of experiments were needed to establish the necessary relationship. This near linearity, along with the high consistency of the synthesized material and processing results, facilitated the selection of intended products not only by category but also by specific color grades. Therefore, for this embodiment, the applicants selected N2 / C2H2 equivalent ratios of 28 and 12 ppm, respectively, so that the gemstones would have color grades close to the intermediate grade within their category. These were H / I and E, respectively. Thus, the C2H2 / H2 equivalent ratio was selected so that the growth rate was within the optimal range, taking into account material quality, uniformity, and process input resources such as the total volume of gas and total power required during the synthesis process. The optimal growth rate range was achieved using a C2H2 / H2 equivalent ratio of 2.5 to 3.5% (CH4 / H2 ratio of 5.5 to 7.5%). The relationship between the C2H2 / H2 equivalent ratio and the growth rate is known to vary depending on the reactor design, but can be easily determined by a typical practitioner. The applicants found that the reactor they developed was nearly linear.

[0030] Microwave energy was supplied at a frequency of 896 or 915 MHz to form a process gas plasma in the reactor. The required operating frequency is determined primarily by the dimensions of the reactor, and a typical operator may choose to use a smaller reactor than that in this embodiment and utilize a microwave frequency of 2450 MHz, without substantially deviating from any other details shown herein. Single-crystal CVD diamond material was grown without interruption on the surface of each of several single-crystal diamond substrates to a thickness of approximately 4 mm to approximately 6 mm. The crystal temperature during growth is affected by the amount of nitrogen incorporated in the process gas to match a given N2 / C2H2 equivalent ratio. Here, the temperature was measured on the polycrystalline diamond region between adjacent single crystals using an optical pyrometer operating at a wavelength of 2.2 μm, which was shown through an 8 mm thick IR-grade quartz glass observation window. One-color measurements were performed assuming no transmission loss and an emissivity of 0.9 for the polycrystalline diamond. This shows a consistent and reproducible reading within a true thermodynamic temperature of approximately 10°C, as measured using (e.g.) a two-color pyrometer. The temperatures measured in this way ranged from 825 to 925°C throughout the growth period. In this embodiment, the amount of CVD single-crystal diamond material available for the final product is approximately 45 to 60 mm per reactor, depending on the precise process parameters used. 3 The diamonds were grown at a volume fraction of / h. These values ​​correspond to approximately 0.8 to 1.1 carats of high-quality single-crystal diamonds grown per reactor hour.

[0031] After growth, the CVD single-crystal diamond crystal was detached from the substrate carrier. The substrate carrier grew around the crystal and separated from the arbitrary polycrystalline diamond, characterized by the intensity of its brown color. Color measurements were performed by photographing the as-grown sample under uniform white backlight transmission (through thickness, i.e., from substrate to top surface) in another dark environment. Calibrated CIELAB color coordinates were obtained by referring to a standard ANSI IT8.7 / 1-1993 transmission test subject photographed under the same conditions. Thus, the saturation C was obtained relative to the white point from the surrounding backlight area. * ab(As per CIE015:2004) and hue angle h ab The temperature was measured for each crystal. CVD single-crystal diamond crystals intended for colorless gemstones were measured at approximately 55° to 65° h. ab While those grown for near-colorless gemstones and with high nitrogen content exhibited a slightly larger hue angle of approximately 60° to 70° on average, the saturation value is related to the perceived intensity of the color, C * ab =0 corresponds to neutral colors or colorless, i.e., white, gray, or black, while higher values ​​correlate with high saturation of any non-neutral hue. When measured at a total thickness of 5.5 to 6.5 mm (i.e., including the substrate), most CVD single-crystal diamond crystals for colorless gemstones have a C value of 3.5 to 5.5. * ab It has a large value, while near-colorless gemstones tend to have a larger value, ranging from about 4 to 12 C * ab That was the case.

[0032] Before annealing, any non-diamond polycrystalline material, along with any surface defects, was removed from the grown CVD single-crystal diamond crystals, partially or completely completing the grown crystals as gemstones. Surface defects can increase the risk of failure during annealing due to crack initiation or propagation. Subsequently, a large portion of these crystals were collected to form a diamond-based molded body, which was embedded in a pressure-transmitting salt matrix and placed in an HPHT apparatus. In this example, the total size was approximately 1500 mm². 3 From 2500mm 3The molded bodies could contain single-crystal diamonds (approximately 30 to 40 ct), and all individual samples were treated to mutually consistent results. The conditions used for the HPHT treatment were indirectly estimated as 1900°C and a pressure of 7 GPa (70 kbar), with an annealing time of approximately 10 minutes. At this pressure, the treatment time could be appropriately adjusted, and comparable results were possible at any temperature from 1700 to approximately 2100°C, although higher temperatures required higher pressures. Practically, the temperature was selected to roughly fall within the optimal range of 7 GPa. After annealing, the molded bodies were dissolved in water to recover the diamonds and salts. No diamond cracking or graphitization was observed, and fully completed samples maintained their polish grade throughout the treatment.

[0033] After processing N s Electron paramagnetic resonance (EPR; also known as electron spin resonance ESR) spectroscopy was used to quantify the concentrations of NV. This experimental technique was chosen for its high sensitivity, quantitative accuracy, and ability to be used on samples of any shape, including gemstones, (especially compared to other common methods such as infrared or UV / visible absorption spectroscopy). However, N s + and NV 0 These cannot be detected by EPR, and if you want to perform a representative measurement, you should use (detectable and quantifiable) N s 0 and NV - It is important to mention that you must select and minimize N. s 0 Regarding deep UV irradiation, NV - The required charge state before measurement was prepared by heating the sample to 550°C in the dark. The colorless CVD single-crystal diamond sample had approximately 65 ppb of N s 0 (Average of three nominally identical samples) and undetectable amounts of NV - It was found to contain approximately 190 ppb of N in the near-colorless sample. s 0(The average of two nominally identical samples, one of which was also submitted to an external laboratory that provided the same results as the applicants within a few percent error in each measurement) and similarly undetectable NV - It contained NV by other EPR schemes. - Further measurements were performed to attempt detection, but these could not be detected due to their low concentrations. After demonstrating the method on different samples (not of the present invention) containing detectable amounts of NV, the true values ​​appear to be less than 5 ppb in near-colorless samples and less than 2 ppb in colorless samples, but the detection limit for NV is less than 10 ppb. - It became clear that the concentration of NV remaining after annealing is N s It couldn't have been more than about one-tenth of that, and the probability was even smaller in all cases.

[0034] Photoluminescence (PL) spectra of treated CVD single-crystal diamond samples were measured to compare the contributions of NV, H3, and N3. While PL is a highly sensitive technique, the intensity ratio of each signal is proportional to, but not equal to, the corresponding concentration, as the defect emission intensity depends on the excitation and detection efficiency and concentration of a given defect. The excitation efficiency of each defect is determined by the overlap between its absorption spectrum and excitation wavelength, and the detection efficiency is determined by the fluorescence quantum yield. These effects are determined by the physical properties of the defect, the selected excitation and detection wavelengths, and the temperature at which the measurement is performed. Our measurements were performed using a liquid nitrogen cryostat at a temperature of 77 K, with excitation wavelengths of 325 nm (helium-cadmium laser) and 457 nm (argon ion laser). Both the neutral and negatively charged states of NV defects, as well as H3, could be excited at 457 nm, and these were detected by zero-phonon emission lines (ZPL). 0 575.1nm (2.156eV), NV - H3 is located at 637.5 nm (1.945 eV), and H3 is located at 503.2 nm (2.463 eV). The measured ZPL intensities are measured against the primary Raman line R1 of diamond. 457It was divided by the intensity measured simultaneously. Therefore, for example, NV 0 457 =I(575.1nm) / I(R1 457 ) and I(·) represents the peak area. This excludes the overall coupling efficiency. This efficiency is equipment-dependent and can also be affected by (directionally dependent) reflections from, for example, the polished sample surface. Subsequently, the applicants calculated the ratio (NV) for colorless and near-colorless samples. 0 457 +NV - 457 ) / H3 457 Subsequently, NV / H3 was tested. NV / H3 will be minimized under optimal annealing conditions, but the minimum value is N s And after NV is formed from the free void, this NV moves and N s 0 Alternatively, it is determined by reaction kinetics that regulate the stepwise formation of H3 by reaction with another NV. In samples containing little nitrogen or (especially) vacancies, the subsequent process occurs with a small probability within a limited annealing time, resulting in a larger NV / H3 ratio than elsewhere. The sample has a pinkish hue after annealing, but rather the concentrations of both NV and H3 are very low, which is the main cause of the (yellow) hue. s 0 This should not be interpreted as suggesting that... Near colorless and colorless samples synthesized at similar growth rates (and therefore containing similar concentrations of vacancies) both had an NV / H3 PL of approximately 1.5 after annealing. Colorless samples synthesized at low growth rates showed large, variable NV / H3 values, roughly from 3 to 7, reflecting that H3 formation is more inhibited in such samples. If D-grade samples are produced instead of E-grade samples, even larger values ​​are expected for the same reason.

[0035] When N3 is excited at 457 nm, its ZPL (415.2 nm, 2.985 eV) is at a shorter wavelength than the excitation wavelength, resulting in very low excitation efficiency. Therefore, N3 was excited using a 325 nm laser. As expected for annealing conditions that do not exceed the maximum optimal temperature, N3 could not be detected in any of the samples treated at 1900 °C, nor would it be detected in samples treated at 2000 °C for 4 hours. While these latter conditions exceed the range required to achieve hue conversion, they are still within the optimal range as there is little risk of graphitization when performed at a moderate pressure of 7 GPa. At our high-temperature limit, further samples were annealed at 2200 °C for 1 hour to quantify the expected amount of N3 PL. This, however, required increasing the pressure to 8 GPa to avoid damage. It was difficult to infer a direct ratio to H3 because the spectra excited at 325 nm contain several unassigned lines that overlap with the ZPL of H3. Therefore, the applicants of N3 325 / H3 457 That is, the tests were performed after showing the ratio to the respective first-order Raman peak area as described above. While combining measurements using different excitations may seem inconvenient, in practice these excitation wavelengths (and associated gas lasers) are the most commonly used, and a limited selection is available for other wavelengths in this spectral range. N3 325 / H3 457 The values ​​were found to be between 0.01 and 0.02 after treatment at 2200°C. Slightly larger values ​​are expected under the same conditions as samples that are extremely brown in the as-grown state due to nitrogen aggregation using vacancies.

[0036] Quantitative measurement of the finished gemstone color is more difficult than measuring as-grown crystals due to specularity, numerous internal reflections, and dispersion within the polished material. Localized highlights and apparent color flashes, mainly depending on lighting conditions, must be disregarded when evaluating the gemstone's true body color. To perform this measurement, a photographic approach described in International Publication 2016 / 203210 was used. This technique is fast and a more reliable alternative to the use of a spectrophotometer and integrating sphere, and is therefore particularly useful when measuring many polished gemstones. Measuring the hue angle after annealing, it was found to be 105° for most colorless gemstones. <h ab <115°, 95° for most near-colorless gemstones. <h ab It is within the range of <105°. This indicates that all samples are yellow, and no brown, pink, or orange colors remain. Considering that none of the CVD single-crystal diamond samples showed any measurable photochromism, excitation was performed using a 660 nm diode laser and SiV at 77 K. - PL measurements were performed. Because low-temperature PL is the most sensitive, even samples with SiV orders of magnitude lower than those detectable by absorption can be quantified. - The signal is almost always observed in measurements of CVD-synthesized diamond materials. As with other PL measurements, SiV is observed at low temperatures. - Aside from showing two ZPLs at 736.5 and 736.8 nm respectively, the recorded values ​​are SiV relative to the primary Raman line of diamond. - This is the area ratio of the PL features, and therefore SiV - 660 =I(736.5nm) / I(R1 660 ) + I(736.8nm) / I(R1 660 ) In these samples, SiV - 660 The SiV is typically between 0.001 and 0.01, which is exceptionally small by commercial standards for CVD synthetic gemstones. Compared to gemstones from third-party manufacturers that do not utilize post-growth treatment, SiV is typically low. - 660The values ​​ranged from 0.5 to 1.5. However, there was considerable variation among suppliers, with third-party gemstones that had undergone HPHT annealing measuring values ​​from approximately 50 to 100.

[0037] Treated CVD single-crystal diamond gemstones always showed a higher C content compared to the same measurements performed before annealing. * ab The value was low. This indicates an overall decrease in color depth. As is the established practice for grading gemstones by color, colorless CVD single-crystal diamond gemstones, for round brilliant shapes, are measured when viewed through a pavilion with the table facets facing downwards, with a value of C. * ab The C20 range was 1.5 to 3.5 (many samples fell within the narrow range of 1.8 to 2.8). The color intensity observed for this shape and orientation was only slightly dependent on gemstone size (mass), and when produced from CVD crystals synthesized and processed under the same conditions, 1ct and 2ct round brilliants would be nearly the same C20. * ab This is measured. Near colorless CVD single crystal diamond gemstones generally have a large C value of 3.5 to 6.5. * ab The values ​​are distinguished by their relative values, with many falling in the middle of the range, namely between 4.2 and 5.2. These values ​​summarize the testing of hundreds of gemstones synthesized and processed at different times and in different factories using numerous sets of equipment, and are roughly the same as the distribution that occurs in large-scale production before any quality control standards are imposed on the final product.

[0038] The applicants measured C * ab Based on the values, a color grade equivalent to that of GIA is evaluated, C * abCalibration was performed using a series of natural diamond samples whose color grades were both publicly known. The color grades of the reference samples were given according to the method widely taught by the GIA and described in the paper 'Color grading “D-to-Z” diamonds at the GIA laboratory' on page 296 onwards in Gems & Gemology, volume 44, number 4 (winter 2008). Based on this, the boundary between grades F and G, i.e., the colorless and near-colorless categories, is C * ab It was determined that = 3.5, and approximately C * ab =7 is considered the upper limit of the near-colorless range; anything above this is considered slightly colored (K grade or higher). More specifically, 1.8 was measured in most colorless samples. <C * ab <2.8 is roughly equivalent to an E grade, and 4.2 <C * ab Near colorless samples falling within the <5.2 range are graded H. The applicants estimate that Grade I corresponds to 5.2. <C * ab This results in <6.2. Therefore, considering reasonable margins of error in grade estimation, as well as the possibility of discrepancies between grading laboratories, all measured gemstones were found to fall within the color category intended during the manufacturing planning stage. Some of the completed CVD single-crystal diamond gemstones were submitted to the GIA laboratory in New York, which assigned grades to almost all examples within the applicant's single grade. Specifically, the GIA grade was generally E for colorless gemstones and generally I for near-colorless gemstones. Furthermore, different samples within each color category were almost always assigned the same grade by the GIA, with only one exception. If the GIA grade differed systematically from the estimate, the N2 / CH4 ratio (in other words, the calculated N2 / C2H2 ratio) could be adjusted during the synthesis process to incorporate more or less nitrogen into the diamond, thereby increasing or decreasing the final grade as needed. The CH4 ratio (calculated C2H2 / H2 ratio) was then adjusted to maintain an economically optimal growth rate. No changes to the HPHT annealing process were necessary.

[0039] Birefringence measurements were performed on CVD single-crystal diamond material. The grown diamond material was formed into a cube. The cube had {110} oriented sides with edge lengths equal to the diagonals of the substrate, thus limiting the area of ​​the original substrate, as well as the {100} oriented top and bottom surfaces. After annealing the cube as described above, it was horizontally cut into a 0.7 mm thick plate, and both main surfaces were polished. Using a commercially available instrument (Sawlab LCC7201), the birefringence of the plate (defined as the difference in refractive index of light polarized parallel to the slow and fast axes, averaged over the thickness of the sample) was measured at a wavelength of 590 nm, and for most of its area, it was found to be well within the range of International Publication No. 2004 / 046427, which describes materials suitable for optical applications such as etalons. -5 The values ​​were on the order of 10. The exception was the region directly above the substrate edge. Dislocations tended to be concentrated at the boundaries between transverse and longitudinal growth regions, with local maximum birefringence of 10. -4The order was as follows. While these more birefringent inclusions in the crystal may be undesirable for all technical applications, considering they occupy only a tiny fraction of the total volume, they have been found to have no detriment to the visual clarity of CVD single-crystal diamond, and in any given example, the maximum birefringence is 4.3 × 10⁻¹⁶, as cited in "Synthetic moissanite: a new diamond substitute", Gems and Gemology volume 33, issue 4, winter 1997. -2 It is less than 1% of the total.

[0040] Figure 1 is a flowchart illustrating an example of the process for producing CVD single-crystal diamond. The following numbering corresponds to Figure 1. S1. Multiple single-crystal diamond substrates are placed on a substrate carrier in a CVD reactor. S2. Process gases are supplied to the reactor. The process gases include hydrogen-containing gases, carbon-containing gases, and nitrogen-containing gases. The relative amounts of these gases are stoichiometrically equivalent to a C2H2 / H2 ratio of 1% to 5% and an N2 / C2H2 ratio of 4 ppm to 60 ppm. A plasma is generated from the gases using microwaves. S3. Single-crystal CVD diamond is grown on the surface of multiple single-crystal diamond substrates at a temperature of 750°C to 1100°C. Growth is preferably carried out as a single, continuous, uninterrupted CVD synthesis cycle or "run". S4. The resulting single-crystal CVD diamonds are annealed at a temperature of 1700°C to 2200°C. Annealing is preferably carried out under diamond stabilization pressure. The grown single-crystal diamond can be cut and polished to form a gemstone, which may include at least a portion of the single-crystal diamond substrate. Cutting and polishing may be performed before or after annealing.

[0041] While the present invention has been specifically illustrated and described with reference to embodiments, it will be understood by those skilled in the art that various modifications can be made in form and detail without departing from the scope of the invention as defined in the appended claims. For example, those skilled in the art will recognize that the single-crystal diamond materials disclosed herein, as described in the appended claims, combine low and controllable light absorption, low birefringence, high purity with intentionally introduced nitrogen removed, low fluorescence, relatively large size, and the ability to be manufactured quantitatively and economically, thus possessing diverse potential applications. These may not necessarily be for consumer use and may include use in optical, thermal, or mechanical elements, or other technical products. For example, diamonds may be used in mechanical applications such as wire drawing dies, graphic tools, engraving tools, and high-pressure fluid jet nozzles such as high-pressure water jet nozzles. Alternatively, diamond can be formed into optical elements. Exemplary optical elements include cavity optical elements, high-power transmission optical elements, Raman laser optical elements, etalons, and total internal reflection (ATR) optical elements. These can benefit from the low absorption and low birefringence exhibited by the diamonds described herein. Due to diamond's high thermal conductivity, this material is particularly useful in applications requiring thermal diffusion. Another aspect of the present invention may be as follows: [1] The following, The minimum length dimension is 3.5 mm or more; As measured by EPR, a single substituted nitrogen atom (N) in a neutral charge state s 0 The concentration is between 20 and 250 ppb; hue angle h ab The angle is between 75 and 135 degrees; CVD single-crystal diamond with specific properties. [2] Nitrogen vacancy centers (NV) in neutral and negatively charged states 0 and NV - The total concentration of ) is the N s 0 A CVD single-crystal diamond as described in [1] above, wherein the concentration is less than 0.1 times the concentration or 10 ppb, whichever is greater. [3] A hue angle selected from 85 to 125°, 90 to 120°, and 95 to 115° ab A CVD single crystal diamond according to [1] or [2] above, having the above characteristics. [4] SiV as a function of the peak area of ​​the primary Raman signal of diamond in a photoluminescence measurement performed at a temperature of 77K using an excitation wavelength of 660nm.- Quantified by the ratio of the total peak area of ​​zero phonon lines, selected from <0.5; <0.1; <0.05; and <0.01 SiV - A CVD single-crystal diamond exhibiting luminescence, as described in any of [1] to [3] above. [5] When measuring an area of ​​at least 3 mm × 3 mm that has low optical birefringence exhibiting low strain at a temperature of 20°C, the third quartile value of the refractive index difference of light polarized parallel to the slow and fast phase axes is averaged over the thickness of the sample, resulting in 1 × 10⁻⁶ -4 and 5×10 -5 A CVD single-crystal diamond according to any one of [1] to [4] above, which does not exceed a value selected from any of the above. [6] The total volume of the single-crystal CVD diamond material is at least 60 mm 3 , at least 80mm 3 and at least 100 mm 3 A CVD single crystal diamond according to any of [1] to [5] above, selected from any of the above. [7] Gem-like, with a saturation of C selected from less than 8, less than 6, and less than 4. * ab A CVD single crystal diamond according to any one of [1] to [6] above, having the following characteristics. [8] Gem-like, according to the Gemological Institute of America (GIA) scale and method, the N s 0 When the concentration is between 20 and 100 ppb, one of D, E, and F is selected, and the N s 0 A CVD single-crystal diamond according to any one of [1] to [7], having a color grade selected from G, H, I, and J when the concentration is 80 to 250 ppb. [9] Gem-like, VS according to the Gemological Institute of America (GIA) scale and method. 2 , VS 1 VVS 2 VVS 1 CVD single crystal diamond according to any one of [1] to [8], having a clarity grade selected from either IF or FL.

[10] H3(NVN 0 ) A CVD single crystal diamond according to any one of [1] to [9], further comprising a center.

[11] In photoluminescence measurements performed at a temperature of 77K using excitation wavelengths of 455 to 459 nm, the (NV) is less than 30. 0 +NV - A CVD single crystal diamond according to

[10] above, exhibiting a ) / H3 ratio, wherein the NV 0 NV - A CVD single-crystal diamond in which each of the H3 defects is quantified by the ratio of the peak area of ​​the zero-phonon line to the primary Raman signal of the diamond.

[12] A CVD single crystal diamond according to

[10] or

[11] , which exhibits an N3 / H3 ratio of less than 0.1 in a photoluminescence measurement performed at a temperature of 77K using an excitation wavelength of 323 to 327 nm in the case of N3 and an excitation wavelength of 455 to 459 nm in the case of H3, wherein each of the defects is quantified by the peak area ratio of the zero phonon line to the primary Raman signal of the diamond.

[13] A CVD single crystal diamond according to any one of [1] to

[12] , formed on a mechanical element.

[14] A CVD single crystal diamond according to any one of [1] to

[12] , formed on an optical element.

[15] The CVD single crystal diamond according to

[14] , wherein the optical element is selected from a cavity optical element, a high-power transmission optical element, a Raman laser optical element, an etalon, and an ATR optical element.

[16] A method for producing a plurality of single-crystal CVD diamonds according to any one of [1] to

[12] above, Placing multiple single-crystal diamond substrates on a substrate carrier in a chemical vapor deposition reactor; The process gas, which includes hydrogen-containing gas, carbon-containing gas, and nitrogen-containing gas, is supplied to the reactor, wherein the relative amounts of these gases are 1% to 5% C 2 H 2 / H 2 Ratio, and N from 4 ppm to 60 ppm 2 / C 2 H 2 The ratio and the stoichiometrically equivalent of supplying; The process involves growing the multiple single-crystal CVD diamonds on at least a portion of the surface of the multiple single-crystal diamond substrates at a temperature of 750°C to 1100°C; Annealing at least a portion of the resulting single-crystal CVD diamonds at a temperature of 1700°C to 2200°C, A method that includes this.

[17] The method according to

[16] , wherein the growth on the substrate is carried out without interruption as a single CVD synthesis cycle.

[18] The CVD synthesis is performed at least 10 mm 3 / h, at least 20mm 3 / h, at least 30mm 3 / h, at least 40mm 3 / h and at least 50mm 3 The method according to

[16] or

[17] , which provides a volume growth rate for a single-crystal diamond material grown in a single reactor selected from either / h.

[19] The method according to any one of

[16] to

[18] , wherein the annealing is performed under diamond stabilization pressure.

[20] The total volume of single-crystal diamonds processed in a single annealing operation is at least 500 mm³ 3 , at least 1000mm 3 , at least 1500mm 3 and at least 2000mm 3 A method according to any of the above

[16] to

[19] , selected from any of the above.

[21] The carbon-containing and hydrogen-containing process gases are in a range selected from 2% to 4% and 2.5% to 3.5%. 2 H 2 / H 2 The method according to

[19] or

[20] , provided in an amount that is stoichiometrically equivalent to the ratio.

[22] The nitrogen-containing and carbon-containing process gases are N in a range selected from 5 ppm to 20 ppm; 10 ppm to 50 ppm; 7 ppm to 15 ppm; and 15 ppm to 35 ppm. 2 / C 2 H 2 The method according to any one of

[16] to

[21] , provided in an amount that is stoichiometrically equivalent to a ratio.

[23] The method according to any one of

[16] to

[22] , wherein the plurality of CVD single-crystal diamonds are grown at a temperature selected from 800°C to 1500°C; 800°C to 950°C; and 825°C to 925°C.

[24] The method according to any one of

[16] to

[23] , wherein the annealing is carried out at a temperature selected from 1750°C to 2100°C; 1800°C to 2000°C; and 1850°C to 1950°C.

[25] The method according to any one of

[16] to

[24] , further comprising cutting and polishing at least one of the plurality of single-crystal diamonds to form a gemstone.

Claims

1. below, The minimum length dimension is 3.5 mm or more; EPR measures the single substituted nitrogen atom (N) in a neutral charge state. s 0 The concentration is between 20 and 250 ppb; Hue angle h ab The angle is between 75 and 135 degrees; Possessing characteristics, H3 (NVN 0 CVD single-crystal diamond, further containing the center.

2. Nitrogen vacancy centers (NV) in neutral and negatively charged states 0 and NV - The total concentration of the above N s 0 The CVD single-crystal diamond according to claim 1, wherein the concentration is less than 0.1 times the concentration or 10 ppb, whichever is greater.

3. A hue angle h selected from any one of 85 to 125°, 90 to 120°, and 95 to 115° ab The CVD single crystal diamond according to claim 1, having the same.

4. SiV as a function of the peak area of ​​the primary Raman signal of diamond in a photoluminescence measurement performed at a temperature of 77 K using an excitation wavelength of 660 nm. - Quantified by the ratio of the total peak area of ​​zero phonon lines, selected from <0.5; <0.1; <0.05; and <0.01 SiV - A CVD single-crystal diamond according to claim 1, exhibiting luminescence.

5. The total volume of the single-crystal CVD diamond material is at least 60 mm². 3 , at least 80 mm 3 and at least 100 mm 3 A CVD single-crystal diamond according to claim 1, selected from any of the following.

6. Gem-like, according to the Gemological Institute of America (GIA) scale and method, the N s 0 When the concentration is between 20 and 100 ppb, one of D, E, and F is selected, and the N s 0 The CVD single-crystal diamond according to claim 1, having a color grade selected from G, H, I, and J when the concentration is 80 to 250 ppb.

7. Gem-like, according to the Gemological Institute of America (GIA) scale and method, VS 2 , VS 1 VVS 2 VVS 1 CVD single-crystal diamond according to claim 1, having a clarity grade selected from either IF or FL.

8. In photoluminescence measurements performed at a temperature of 77 K using excitation wavelengths of 455 to 459 nm, values ​​less than 30 (NV) 0 +NV - CVD single crystal diamond according to claim 1, which shows the NV / H3 ratio 0 NV - A CVD single-crystal diamond in which each of the H3 defects is quantified by the ratio of the peak area of ​​the zero-phonon line to the primary Raman signal of the diamond.

9. A CVD single-crystal diamond according to claim 1, which exhibits an N3 / H3 ratio of less than 0.1 in a photoluminescence measurement performed at a temperature of 77 K using an excitation wavelength of 323 to 327 nm for N3 and an excitation wavelength of 455 to 459 nm for H3, wherein each of the N3 and H3 defects is quantified by the peak area ratio of zero phonon lines to the primary Raman signal of the diamond.

10. A CVD single-crystal diamond according to claim 1, formed on a mechanical element.

11. A CVD single-crystal diamond according to claim 1, formed on an optical element.

12. The CVD single-crystal diamond according to claim 11, wherein the optical element is selected from any of a cavity optical element, a high-power transmission optical element, a Raman laser optical element, an etalon, and an ATR optical element.

13. A method for producing a plurality of single-crystal CVD diamonds according to claim 1, Placing multiple single-crystal diamond substrates on a substrate carrier in a chemical vapor deposition reactor; The process gas, which includes hydrogen-containing gas, carbon-containing gas, and nitrogen-containing gas, is supplied to the reactor, wherein the relative amounts of these gases are 1% to 5% C 2 H 2 / H 2 Ratio, and N from 4 ppm to 60 ppm 2 / C 2 H 2 The ratio and the stoichiometrically equivalent of supplying; Growing the plurality of single-crystal CVD diamonds on at least a portion of the surface of the plurality of single-crystal diamond substrates at a temperature of 750°C to 1100°C; Annealing at least a portion of the resulting single-crystal CVD diamonds at a temperature of 1700°C to 2200°C, A method that includes this.

14. The above method, at least 10 mm 3 / h, at least 20 mm 3 / h, at least 30mm 3 / h, at least 40mm 3 / h and at least 50 mm 3 The method according to claim 13, which provides a volume growth rate for a single-crystal diamond material grown in a single reactor selected from any of the following: / h.

15. The method according to claim 13, wherein the annealing is performed under diamond stabilization pressure.

16. The total volume of single-crystal diamonds processed in a single annealing operation is at least 500 mm³. 3 , at least 1000 mm 3 , at least 1500 mm 3 and at least 2000 mm 3 The method according to claim 13, selected from any of the following.

17. The carbon-containing and hydrogen-containing process gases are in a range selected from either 2% to 4% and 2.5% to 3.5%. 2 H 2 / H 2 The method according to claim 13, provided in an amount that is stoichiometrically equivalent to a ratio.

18. The nitrogen-containing and carbon-containing process gases are N in a range selected from 5 ppm to 20 ppm; 10 ppm to 50 ppm; 7 ppm to 15 ppm; and 15 ppm to 35 ppm. 2 / C 2 H 2 The method according to claim 13, provided in an amount that is stoichiometrically equivalent to a ratio.

19. The method according to claim 13, wherein the plurality of CVD single-crystal diamonds are grown at a temperature selected from 800°C to 1050°C; 800°C to 950°C; and 825°C to 925°C.

20. The method according to claim 13, wherein the annealing is carried out at a temperature selected from 1750°C to 2100°C; 1800°C to 2000°C; and 1850°C to 1950°C.

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