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EP-3818199-B1 - METHOD OF MANUFACTURE OF SINGLE CRYSTAL SYNTHETIC DIAMOND MATERIAL

EP3818199B1EP 3818199 B1EP3818199 B1EP 3818199B1EP-3818199-B1

Inventors

  • FRIEL, IAN
  • ATKINSON, Katharine Louise
  • TWITCHEN, DANIEL JAMES

Dates

Publication Date
20260506
Application Date
20190705

Claims (8)

  1. A method of manufacturing synthetic single crystal diamond material using a chemical vapour deposition process, the method comprising: providing a freestanding synthetic single crystal diamond substrate wafer having a dislocation density of at least 10 7 cm -2 , by the steps of (i) locating a non-diamond substrate over a substrate holder within a further reactor, the substrate comprising a surface on which the synthetic single crystal diamond substrate wafer is to be grown heteroepitaxially; (ii) feeding process gases into the further reactor; and (iii) growing the synthetic single crystal diamond substrate wafer on the surface of the non-diamond substrate; the method further comprising: locating the synthetic single crystal diamond substrate wafer over a substrate holder within a chemical vapour deposition reactor; feeding process gases into the reactor, the process gases including a gas comprising carbon; growing synthetic diamond material on a surface of the single crystal diamond substrate wafer at a growth temperature of at least 900°C to a thickness of at least 0.5 mm and with lateral dimensions of at least 4 mm by 4 mm such that the grown synthetic diamond material is crack free.
  2. The method according to claim 1, wherein the process gases comprise hydrogen and not more than 5% oxygen.
  3. The method according to claim 1 or 2, wherein the non-diamond substrate comprises any of iridium, silicon and silicon carbide.
  4. The method according to any one of claims 1 to 3, further comprising removing the non-diamond substrate from the synthetic single crystal diamond substrate wafer prior to locating the synthetic single crystal diamond substrate wafer over the substrate holder.
  5. The method according to any one of claims 1 to 4, wherein the grown synthetic diamond material is oriented at substantially {100} relative to the synthetic single crystal diamond substrate wafer.
  6. The method according to any one of claims 1 to 5, wherein the reactor is operated at a power density in the range 150 to 600 Wcm -2 of the surface of the substrate.
  7. The method according to any one of claims 1 to 6, comprising growing the synthetic diamond material having an area from 16 mm 2 to 18000 mm 2 .
  8. The method according to any one of claims 1 to 7, wherein the growth temperature is selected from any of at least 925°C, at least 950°C, at least 1000°C and at least 1050°C.

Description

Field The invention relates to the field of manufacturing single crystal synthetic diamond material, in particular single crystal synthetic diamond material manufactured using a Chemical Vapour Deposition (CVD) method. 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 wafe