GB2638116A

GB2638116A - CVD single crystal diamond material

Info

Publication number: GB2638116A
Application number: GB2316754.7A
Authority: GB
Inventors: Trefor Williams Gruffudd; William Hardeman David
Original assignee: Element Six Technologies Ltd
Current assignee: Element Six Technologies Ltd
Priority date: 2023-11-01
Filing date: 2023-11-01
Publication date: 2025-08-20
Also published as: WO2025093434A1; GB202316754D0; GB202403847D0; GB2635248A

Abstract

A method of manufacturing CVD single crystal diamond material comprises providing a first single crystal diamond material having a largest linear dimension of at least 50 mm and a surface dislocation density of at least 107 cm-2, disposing a first buffer layer configured to limit the propagation of dislocations on a surface of the first single crystal diamond material, in a chemical vapour deposition reactor homoepitaxially growing diamond material on the first buffer layer, disposing a further buffer layer configured to limit the propagation of dislocations on a surface of the homoepitaxially grown diamond material, homoepitaxially growing further diamond material on the further buffer layer, and repeating the steps of disposing a further buffer layer and growing further diamond material until the homoepitaxially grown diamond material has a surface dislocation density of less than 105 cm-2. At least one of the buffer layers may comprise a mask with openings, a diamond layer containing metal impurities having a larger atomic radium than that of carbon, or a layer of surface depressions or protrusions.

Description

CVD SINGLE CRYSTAL DIAMOND MATERIAL

Field

The invention relates to the field of CVD single crystal diamond material and methods of manufacturing CVD single crystal diamond material.

Background

Diamond materials may be categorized into three main types: natural diamond materials; HPHT (high pressure high temperature) synthetic diamond materials, and CVD (chemical vapour deposited) synthetic diamond materials. These categories reflect the way in which the diamond materials are formed. Furthermore, these categories reflect the structural and functional characteristics of the materials. This is because while natural, HPHT synthetic, and CVD synthetic diamond materials are all based on a theoretically perfect diamond lattice the defects in these material are not the same. For example, CVD synthetic diamond contains many defects unique to the process of CVD, and whilst some defects are found in other diamond forms, their relative concentration and contribution is very different. As such, CVD synthetic diamond materials are different to both natural and HPHT synthetic diamond materials.

Diamond materials may also be categorized according to their physical form. In this regard, diamond materials may be categorized into three main types: single crystal diamond materials; polycrystalline diamond materials; and composite diamond materials. Single crystal diamond materials are in the form of individual single crystals of various sizes ranging from small "grit' particles used in abrasive applications through to large single crystals suitable for use in a variety of technical applications as well for gemstones in jewellery applications. Polycrystalline diamond materials are in the form of a plurality of small diamond crystals bonded together by diamond-to-diamond bonding to form a polycrystalline body of diamond material such as a polycrystalline diamond wafer. Such polycrystalline diamond materials can be useful in various applications including thermal management substrates, optical windows, and mechanical applications. Composite diamond materials are generally in the form of a plurality of small diamond crystals bonded together by diamond-to-diamond or a non-diamond matrix to form a body of composite material. Various diamond composites are known including diamond containing metal matrix composites, particularly cobalt metal matrix composites known as polycrystalline diamond (PCD), and skeleton cemented diamond (ScD) which is a composite comprising silicon, silicon carbide, and diamond particles.

It should also be appreciated that within each of the aforementioned categories there is much scope for engineering diamond materials to have particular concentrations and distributions of defects in order to tailor diamond materials to have particular desirable properties for particular applications. The present disclosure is concerned with CVD single crystal synthetic diamond materials.

CVD processes for synthesis of diamond material are well known. Being in the region where diamond is metastable compared to graphite, synthesis of diamond under CVD conditions is driven by surface kinetics and not bulk thermodynamics. Diamond synthesis by CVD is normally performed using a small fraction of carbon (typically <5%), typically in the form of methane although other carbon containing gases may be utilized, in an excess of molecular hydrogen. If molecular hydrogen is heated to temperatures in excess of 2000 K, there is a significant dissociation to atomic hydrogen. In the presence of a suitable substrate material, CVD synthetic diamond material can be deposited. Polycrystalline CVD diamond material may be formed on a non-diamond substrate such as a refractory metal or silicon substrate. Single crystal CVD synthetic diamond material may be formed by homoepitaxial growth on a single crystal diamond substrate.

Atomic hydrogen present in the process selectively etches off non-diamond carbon from the substrate such that diamond growth can occur. Various methods are available for heating carbon containing gas species and molecular hydrogen in order to generate the reactive carbon containing radicals and atomic hydrogen required for CVD synthetic diamond growth including arc-jet, hot filament, DC arc, oxy-acetylene flame, and microwave plasma.

A problem with prior art methodologies is how to achieve large area single crystal CVD synthetic diamond material. It has been found that large area single crystal diamond can be grown by a process known as "heteroepitaxial growth". This is where diamond nucleates and grows epitaxially on a non -diamond substrate. Iridium has been found to be a suitable substrate to allow diamond nucleation and growth, but other substrates such as silicon, silicon carbide, copper, nickel, rhenium and titanium carbide have been investigated. US 7,396,408 describes such a process. In this case, diamond is grown in a CVD process using a silicon carbide or silicon single crystal wafer that has a layer of iridium deposited on its surface. This is used as a substrate on which to heteroepitaxially deposit and grow diamond. During the growth process, diamond crystallites nucleate on the iridium film. These crystallites grow and merge to form a single crystal layer, which is continued until a single crystal diamond wafer of the desired thickness is formed. Typically the dislocation density reduces via dislocation interactions (fusion and annihilation) as growth proceeds, leading to a single crystal diamond wafer that has a higher dislocation density adjacent to the original nucleation face compared to the growth face.

A problem with large area single crystal diamond growth using a heteroepitaxial growth method is that the crystal lattice parameter mismatch between the iridium (or other substrate) and the grown diamond causes a high dislocation density in the resultant diamond wafer which, even after the annihilation and fusion of dislocations in the early stages of growth, can still be of an order typically observed in natural type Ila diamonds (around 107 cm-2 and greater). Such a high density of dislocations can be detrimental for certain industrial applications of CVD diamond, such as low birefringence optical windows, ruling out the direct use of heteroepitaxially grown CVD diamond for such applications.

A further problem is that the substrate materials used for heteroepitaxial growth can lead to an undesirable incorporation of impurities into the grown diamond lattice, such as silicon.

It may further be the case that the growth conditions required to grow high quality grades of CVD diamond (such as a high microwave power density), are incompatible with the substrate materials used for heteroepitaxial growth. For example, the use of a silicon substrate, with its relatively low thermal conductivity (compared to that of diamond), can set a practical limit on the CVD process power density, since higher power densities lead to higher heat fluxes. These can in turn generate thermal gradients within the silicon wafer, which lead to its mechanical failure.

Summary

For certain applications of CVD diamond requiring large area single crystals, it is desirable to provide a process for growing on a heteroepitaxially grown single crystal CVD diamond wafer previously detached from its non-diamond substrate.

However, it is known from prior art that CVD diamond growth on single crystal substrates with a high density of dislocations, such as those manufactured from type Ila natural diamond, or from heteroepitaxially grown CVD diamond, can lead to undesirable crack formation, and/or an undesirable transition from single crystal to polycrystalline diamond (see for example, Schermer et. al., Diamond and Related Materials, Volume 3, Issues 4-6, April 1994, Pages 408-416). Such undesirable effects can occur even for CVD diamond layers grown relatively thinly (around 0.5 mm). It is therefore desirable to provide a process for growing relatively thick, crack-free single crystal CVD diamond on single crystal diamond substrates with a high density of dislocations, such as heteroepitaxially grown CVD diamond substrates.

It is an object of the present invention to provide CVD single crystal diamond material with a large area and a low surface dislocation density, and to provide methods for making such CVD single crystal diamond material.

According to a first aspect, there is provided a method of manufacturing CVD single crystal diamond material using a chemical vapour deposition process. The method comprises: providing a first single crystal diamond material having a largest linear dimension of at least 50 mm and a surface dislocation density of at least 107 cm-2; disposing a first buffer layer on a surface of the first single crystal diamond material, the buffer layer configured to limit the propagation of dislocations; in a chemical vapour deposition reactor, homoepitaxially growing diamond material on the first buffer layer on the first single crystal diamond material; a) disposing a further buffer layer on a surface of the homoepitaxially grown diamond material, the further buffer layer configured to limit the propagation of dislocations; b) in a chemical vapour deposition reactor, homoepitaxially growing further diamond material on the further buffer layer; and repeating steps a) and b) until the homoepitaxially grown diamond material has a surface dislocation density of less than 105 cm-2.

Repeated use of a buffer layer to filter or restrict propagation of dislocations from one layer to a subsequently grown layer of diamond allows single crystal diamond with much reduced concentrations of dislocations to be achieved. As an option, the iterative process may be repeated until a surface dislocation density selected from any of less than 5 x 104 cm-2, less than 104 cm-2, less than 5 x 103 cm-2 and less than 103 cm-2 is achieved.

Various types of buffer layer may be used, and the same type of buffer layer need not be used each time.

As an option, at least one of the first buffer layer and the further buffer layer comprises a mask with openings, the mask arranged to only allow dislocation growth through the openings.

As an option, at least one of the first buffer layer and the further buffer layer comprises a diamond buffer layer, the diamond buffer layer containing metal impurities having a larger atomic radius than the atomic radius of carbon.

As an option, at least one of the first buffer layer and the further buffer layer comprises a layer of surface depressions, such as trenches, voids or apertures.

As an option, at least one of the first buffer layer and the further buffer layer comprises a layer of surface protrusions, such as nano-pillars.

The first single crystal diamond material optionally has a largest linear dimension selected from any of at least 75 mm and at least 100 mm. The resultant CVD single crystal diamond material will have a similar largest linear dimension. Any suitable shape may be used. For example, the largest linear dimension may be a radius of a disc, or a side of a square.

The homoepitaxially grown diamond material or further diamond material is optionally grown to a thickness selected from any of at least 10 pm, at least 50 pm, at least 100 pm.

As a further option, the method comprises growing any of the homoepitaxially grown diamond material and further diamond material to a thickness selected from any of no more than 500 pm, no more than 400 pm, no more than 300 pm and no more than 200 pm.

As an option, the first single crystal diamond material is removed from the homoepitaxially grown diamond.

The method using a power density sufficient to achieve a homoepitaxially grown diamond material growth rate selected from any of at least 4 pm per hour, at least 5 pm per hour, at least 10 pm per hour and at least 15 pm per hour.

The method optionally comprises processing a surface of the homoepitaxially grown diamond material or further diamond material to reduce surface damage. This processing may be, for example, any of polishing, chemical mechanical polishing, etching, and laser processing.

As an option, the homoepitaxially grown diamond material is oriented at substantially {100}.

As an option, the homoepitaxially grown diamond material is oriented at substantially {111}.

As an option, the first single crystal diamond material is grown heteroepitaxially. This type of material typically has a high dislocation density, but the technique makes the production of large area single crystal CVD diamond achievable.

According to a second aspect, there is provided a CVD single crystal diamond material manufactured as described above in the first aspect.

According to a third aspect, there is provided CVD single crystal diamond material having a largest linear dimension of at least 50 mm and a surface dislocation density of no more than 105 cm-3.

As an option, the largest linear dimension selected from any of at least 75 mm and at least 100 mm.

As an option, the surface dislocation density is selected from any of less than 5 x 104 cm-3, less than 104 cm-3. less than 5 x 103 cm-3 and less than 103 cm-3.

The CVD single crystal diamond material optionally further comprises a single substitutional nitrogen concentration as measured by electron paramagnetic resonance (EPR) of at least 1x1013 atoms cm-3 and no more than 5x1013cm-3.

As a further option, the single substitutional nitrogen concentration as measured by electron paramagnetic resonance (EPR) is at least 3x1015 atoms cm-3 and no more than 5x1017cm-3.

As an option, a largest growth surface of the material is oriented substantially on a {100} plane. As an alternative option, a largest growth surface of the material is oriented substantially on a {111} plane.

The CVD single crystal diamond optionally has a surface roughness Ra selected from any of less than 1 nm, less than 0.5 nm, less than 0.3 nm and less than 0.2 nm.

Brief Description of Drawings

Non-limiting embodiments will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a flow diagram showing exemplary steps to produce CVD single crystal diamond material with a low dislocation density; and Figure 2 illustrates schematically exemplary steps to produce CVD single crystal diamond with a low dislocation density starting from heteroepitaxially grown diamond.

Detailed description

Large area substrates are required in order to grow large area single crystal CVD synthetic diamond. As discussed above, large area single crystal diamond can be grown using techniques such as heteroepitaxial growth. Heteroepitaxially grown diamond typically has a high density of dislocations. For example, type lb single crystals typically have between 104 and 106 dislocations per cm2. In contrast, figures of greater than 10' dislocations per cm2 have been reported for heteroepitaxially grown diamond in Shreck et. al., Appl. Phys. Lett. 78, 192 (2001).

For certain applications, for example electronic applications, it is desirable to significantly reduce the concentration of dislocations in the diamond. It is known to use heteroepitaxially grown diamond as a substrate on which to grow single crystal diamond homogeneously (e.g. W02020/008044). However, surface defects in the heterogeneously grown diamond substrate propagate into the homogeneously grown diamond and so the resultant homogeneously grown diamond will typically have a similar surface dislocation density to the heterogeneously grown diamond substrate.

Some techniques are available to limit the propagation of dislocations from a diamond substrate into subsequently grown diamond. This means that the resultant subsequently grown diamond material has a reduced dislocation density compared to the substrate on which it was grown.

Ohmagari et. al., Phys. Status Solidi A 2019, 216, 1900498 describes a technique in which the propagation of dislocations from a single crystal diamond substrate into a subsequently grown diamond material is suppressed using a technique referred to as metal-assisted termination. In this technique, a layer of metal impurities that possess larger covalent radii than that of the carbon atoms in the diamond lattice is randomly incorporated during epitaxial growth by CVD. The presence of these larger metal impurities suppresses the propagation of dislocations into the subsequently grown diamond material.

Tang et. al., Appl. Phys. Lett. 108, 052101 (2016) describes a technique in which a gold masking layer having openings is deposited on the surface of the substrate prior to subsequent growth of diamond material. Dislocations in the substrate below the gold layer cannot propagate into the subsequently grown diamond material, and lateral overgrowth above the gold layer ensures that the subsequently grown diamond material is continuous without gaps.

Techniques such as these can be used to reduce the concentration of dislocations in subsequently grown diamond material, but for some applications the reduction in dislocation concentration is insufficient. Furthermore, these techniques have not been demonstrated on large area single crystal diamond (with a largest linear dimension of at least 50 mm). This introduces additional challenges owing to variations in dislocation densities.

Figure 1 is a flow diagram showing exemplary steps to produce CVD single crystal synthetic diamond material with a low dislocation density. The following numbering corresponds to that of Figure 1: S1. A first single crystal diamond material having a largest linear dimension of at least 50 mm is provided as a substrate. This material typically has a dislocation density measured at the surface of more than 10' cm'. The dislocation density is measured by counting etch pits in a given surface area after applying an oxygen plasma etch. In some cases, it is advantageous to process a surface of the substrate wafer to reduce surface damage. Examples of processing include polishing, chemical mechanical polishing, etching, and laser processing. Processing may also include removing any non-diamond material from the heteroepitaxially grown diamond material. Single crystal diamond material with such a large area can be obtained by heteroepitaxial growth, or other techniques such as mosaicking smaller single crystal diamonds together.

S2. A first buffer layer is disposed on a surface of the first single crystal diamond material. The buffer layer is provided to limit the propagation of dislocations.

As described above, different types of buffer layer can be used to limit the propagation of dislocations. In one example, the first buffer layer comprises a mask (e.g. a gold mask) with openings. In another example, the first buffer layer is a layer containing metal impurities that have a larger atomic radius than the atomic radius of carbon. In a further example, the first buffer layer comprises a layer of surface depressions.

These may take the forms of voids, apertures, trenches or other depressions in the surface of the first single crystal diamond material. In a further example, the first buffer layer comprises a layer of surface protrusions. These may take the firm of nanopillars created by selective etching or processing of the first single crystal diamond material. The buffer layer may, as in the first example, be a physical layer disposed on the surface of the first single crystal diamond material, or it may be a structured or altered surface.

S3. The first single crystal diamond material with the first buffer layer is used as a substrate for homoepitaxial growth. It is located in a CVD reactor, and homoepitaxially grown diamond is grown on the first buffer layer.

In order to grow the homoepitaxially grown diamond, process gases are fed into the CVD reactor. Such process gases typically include a carbon-containing gas such as methane, and hydrogen. A plasma is formed from the gases and the homoepitaxially grown diamond grows on the buffer layer.

CVD synthesis conditions are typically controlled such that the first single crystal diamond material is held at a desired temperature (typically between 800°C and 1200°C). If the temperature is too low, then growth rates are low. An upper limit to the growth temperature of 1200°C is generally required to avoid detrimental defect formation in the homoepitaxially grown diamond material such as twins. Furthermore, the temperature, in combination with other parameters such as carbon containing gas concentration, affects the morphology of the homoepitaxially grown diamond material and thus can be selected and controlled to achieve a desired morphology.

CVD synthesis conditions are typically controlled such that a CVD synthesis atmosphere comprises a carbon containing gas (e.g. methane) at a concentration by volume in a range 3 to 8%, more preferably in a range 4 to 6%. If the carbon containing gas concentration is too low, then growth rates are too low. If the carbon containing gas concentration is too high, then cracking may occur and/or the material may have a poor optical quality. Furthermore, as previously stated, carbon containing gas concentration, in combination with other parameters such as the first single crystal diamond material temperature, affects the morphology of homoepitaxially grown diamond material and thus is selected and controlled to achieve the desired morphology close to net shape of the final processed product.

CVD synthesis conditions are further controlled to provide a high power density across the substrate of at least 150 W/cm2, 180 W/cm2, 200 W/cm2, 230 W/cm2, 250 W/cm2, 270 W/cm2, 290 W/cm2, 310 W/cm2, or 330 W/cm2. The power density will generally be less than 600 W/cm2, 500 W/cm2, or 400 W/cm2. In the context of this specification, power density is defined as the total microwave input power divided by the area of the substrate, or the substrate holder, whichever has the greater area.

CVD synthesis conditions are further controlled to achieve a homoepitaxially grown diamond material growth rate selected from any of at least 4 pm per hour, at least 5 pm per hour, at least 10 pm per hour and at least 15 pm per hour.

The homoepitaxially grown diamond material is grown to a desired thickness. Typically, this may be at least 10 pm, at least 50 pm, or at least 100 pm.

If required, a surface processing operation is performed on the homoepitaxially grown diamond material to reduce surface damage. Examples of processing techniques include one or more of cutting, cleaving, lapping, polishing, scaife polishing and/or etching. This may reduce any surface roughness that arises during the growth process.

It has surprisingly been found that in most case, choosing not to process the surface prior to further growth can be beneficial. Processing such as polishing can introduce additional surface damage, which in turn can act as a nucleation point for new dislocations in subsequent diamond growth. However, a trade-off is that the thicker a diamond layer is grown, the more likely it is to have textured surface features such as steps which can introduce surface roughness. To minimise the chance of this, each homoepitaxial diamond layer is preferably grown to a thickness selected from any of no more than 500 pm, no more than 400 pm, no more than 300 pm and no more than 200 pm.

Furthermore, by not processing the surface before further growth, the need to etch the surface to clean it is removed. This is beneficial because etching can damage or remove the buffer layer, whether the layer is a discrete layer such as a gold mask, or a structured surface such as trenches or nano-pillars. In most circumstances it is preferred to avoid processing the surface prior to subsequent growth by careful control of the layer thickness.

S4. Once the homoepitaxially grown diamond material has been grown to the desired thickness, a further buffer layer is applied to the surface of the homoepitaxially grown diamond material. This further buffer layer is as described above in step S2. Note that the further buffer layer may be of the same type as the first buffer layer or may be of a different type.

S5. Further diamond material is homoepitaxially grown on the further buffer layer in a CVD reactor. This growth takes place as described in step S3 above.

S6. Once the further diamond material has been homoepitaxially grown on the further buffer layer, the surface of the diamond is assessed to measure the dislocation density of the surface, as described above. If a desired surface dislocation density has not been achieved, then steps S4 and S5 are repeated, with a still further buffer layer being applied to the surface of the most recently grown diamond material.

Examples of a desired surface dislocation density include less than 105 cm-2, less than 5 x 104 cm-2, less than 104 cm-2, less than 5 x 103 cm-2 and less than 103 cm-2. Different applications of the diamond material will have different requirements for the dislocation density.

Steps S4 to S6 are iteratively repeated until the desired surface dislocation density has been achieved.

At any point in the process described above, previous layers may be removed. This may be done using known techniques, such as grinding, a lift-off process using ion implantation and electrochemical etching, thin cutting and so on. For large area samples, lift off and grinding processes may be more suitable.

Note that the crystal orientation of the resultant CVD single crystal diamond material is determined by the crystal orientation of the first single crystal diamond material. Typical orientations for most applications include {100} and {111}. The precise crystallographic orientation may vary slightly from the desired crystallographic orientation.

Turning now to Figure 2, exemplary steps are shown to produce CVD single crystal diamond with a low dislocation density starting from heteroepitaxially grown diamond.

Heteroepitaxially grown single crystal synthetic diamond was grown on an Ir/A1203 substrate and had a dislocation density on a surface over 107 cm-2. The substrate was removed and the heteroepitaxially grown diamond was used as a first single crystal diamond material. The dislocation density was measured by applying an oxygen-containing plasma to the surface of the heteroepitaxially grown diamond. This forms etch pits that reveal the presence of dislocations. The number of etch pits in a predetermined area was counted to determine the dislocation density.

A gold first buffer layer was applied with a pattern of 8 pm apertures to allow selective overgrowth through the apertures.

The composite heteroepitaxially grown diamond and first buffer layer was placed in a 2.45 GHz microwave plasma CVD diamond reactor and diamond was grown on a surface of the freestanding synthetic single crystal diamond substrate wafer using a feed gas of methane and hydrogen, a power in a range of 3 to 60 kW, a pressure in a range of 90 to 400 torr and a growth temperature in a range of 900°C to 1050°C. The feed gas contained 0.6 ppm N2. Homoepitaxial diamond was grown on the first buffer layer to a thickness of 50 pm.

The dislocation density at the surface of the homoepitaxially grown diamond was measured as described above and found to be above the target of 105 cm 2, and so a further gold buffer layer was applied to the homoepitaxially grown diamond and the process repeated to grow further diamond material. This process was iterated until a single crystal diamond was achieved with a surface dislocation density of below 105 cm2. The final layer of further diamond material was separated from the rest of the diamond material by grinding away the rest of the diamond material to leave a CVD single crystal diamond material having a largest linear dimension of at least 50 mm and a surface dislocation density of no more than 104 cm2.

The single substitutional nitrogen content [NO] of the grown single crystal diamond was measured using UV-Visible absorption spectroscopy (described in WO 03/052177), and found to be 150 ppb. The single substitutional nitrogen content [Ns''] can also be measured by electron paramagnetic resonance (EPR).

Birefringence was measured using a technique similar to that described in W02004/046427 using a pixel size area in a range of 1 x 1 pm2 to 20 x 20 pm2. A maximum 'sin 51 was found to be around 0.8 for light having a wavelength of 550 nm using a sample of 3 x 3 x 0.5 mm. The An[average], the average value of the difference between the refractive index for light polarised parallel to the slow and fast axes averaged over the sample thickness, was found to be 1.6 x 10* A surface roughness Ra across the surface was measured to be around 0.5 nm.

While this invention has been particularly shown and described with reference to embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims. For example, while the examples describe a heteroepitaxially grown diamond substrate, other single crystal diamond material substrates could be used.

Claims

Claims: 1. A method of manufacturing CVD single crystal diamond material using a chemical vapour deposition process, the method comprising: providing a first single crystal diamond material having a largest linear dimension of at least 50 mm and a surface dislocation density of at least 10' cm-2; disposing a first buffer layer on a surface of the first single crystal diamond material, the buffer layer configured to limit the propagation of dislocations; in a chemical vapour deposition reactor, homoepitaxially growing diamond material on the first buffer layer on the first single crystal diamond material; a) disposing a further buffer layer on a surface of the homoepitaxially grown diamond material, the further buffer layer configured to limit the propagation of dislocations; b) in a chemical vapour deposition reactor, homoepitaxially growing further diamond material on the further buffer layer; and repeating steps a) and b) until the homoepitaxially grown diamond material has a surface dislocation density of less than 105 cm-2.
2. The method according to claim 1, further comprising repeating steps b) and d) until the homoepitaxially grown diamond material has a surface dislocation density selected from any of less than 5 x 104 cm-2, less than 104 cm-2, less than 5 x 102 cm-2 and less than 102 cm-2.
3. The method according to any one of claims 1 or 2, wherein at least one of the first buffer layer and the further buffer layer comprises a mask with openings, the mask arranged to only allow dislocation growth through the openings.
4. The method according to any one of claims 1, 2, or 3, wherein at least one of the first buffer layer and the further buffer layer comprises a diamond buffer layer, the diamond buffer layer containing metal impurities having a larger atomic radius than the atomic radius of carbon.
5. The method according to any one of claims 1 to 4, wherein at least one of the first buffer layer and the further buffer layer comprises a layer of surface depressions.
6. The method according to any one of claims 1 to 5, wherein at least one of the first buffer layer and the further buffer layer comprises a layer of surface protrusions.
7. The method according to any one of claims 1 to 6, wherein the first single crystal diamond material has a largest linear dimension selected from any of at least mm and at least 100 mm.
8. The method according to any one of claims 1 to 7, further comprising growing any of the homoepitaxially grown diamond material and further diamond material to a thickness selected from any of at least 10 pm, at least 50 pm, at least 100 pm.
9. The method according to claim 8, further comprising growing any of the homoepitaxially grown diamond material and further diamond material to a thickness selected from any of no more than 500 pm, no more than 400 pm, no more than 300 15 pm and no more than 200 pm.
10. The method according to any one of claims 1 to 9, further comprising removing the first single crystal diamond material from the homoepitaxially grown diamond.
11. The method according to any one of claims 1 to 10, further comprising using a power density sufficient to achieve a homoepitaxially grown diamond material growth rate selected from any of at least 4 pm per hour, at least 5 pm per hour, at least 10 pm per hour and at least 15 pm per hour.
12. The method according to any one of claims 1 to 11, further comprising, prior to repeating steps a) and b), processing a surface of the homoepitaxially grown diamond material or further diamond material to reduce surface damage.
13. The method according to claim 12, wherein the processing comprises any of polishing, chemical mechanical polishing, etching, and laser processing.
14. The method according to any one of claims 1 to 13, wherein the homoepitaxially grown diamond material is oriented at substantially {100}.
15. The method according to any one of claims 1 to 13, wherein the homoepitaxially grown diamond material is oriented at substantially {111}.
16. The method according to any one of claims 1 to 15, wherein the first single crystal diamond material is grown heteroepitaxially.
17. CVD single crystal diamond material manufactured according to any one of claims 1 to 16.
18. A CVD single crystal diamond material having a largest linear dimension of at least 50 mm and a surface dislocation density of no more than 105 cm-2.
19. The CVD single crystal diamond material according to claim 18, wherein the largest linear dimension is selected from any of at least 75 mm and at least 100 mm.
20. The CVD single crystal diamond material according to claim 18 or claim 19, wherein the surface dislocation density selected from any of less than 5 x 104 cm-2, less than 104 cm-2. less than 5 x 103 cm-2and less than 103 cm-2.
21. The CVD single crystal diamond material according to any one of claims 18 to 20, further comprising a single substitutional nitrogen concentration as measured by electron paramagnetic resonance (EPR) of at least 1x1013 atoms cm-3 and no more than 5x1013cm-3.
22. The CVD single crystal diamond material according to claim 21, wherein the single substitutional nitrogen concentration as measured by electron paramagnetic resonance (EPR) of at least 3x1015 atoms cm-3 and no more than 5x1012cm-3.
23. The CVD single crystal diamond material according to any one of claims 18 to 22, wherein a largest growth surface of the material is oriented substantially on a {100} plane.
24. The CVD single crystal diamond material according to any one of claims 18 to 23, wherein a largest growth surface of the material is oriented substantially on a {111} 35 plane.
25. The CVD single crystal diamond material according to any one of claims 18 to 24, having a surface roughness Ra selected from any of less than 1 nm, less than 0.5 nm, less than 0.3 nm and less than 0.2 nm.