GB2609023A

GB2609023A - Growing of diamonds

Info

Publication number: GB2609023A
Application number: GB2110305.6A
Authority: GB
Inventors: Yayon Yosef; Shalev Tom; Bashari Reem; Yaacov Mizrahi Ohad; Mishuk Eran; Ofir Asher
Original assignee: Lusix Ltd
Current assignee: Lusix Ltd
Priority date: 2021-07-18
Filing date: 2021-07-18
Publication date: 2023-01-25
Also published as: GB202110305D0; WO2023002330A1

Abstract

Method of growing a single crystal diamond comprising providing a single crystal diamond substrate in the form of a polygonal disk having more than four sides and growing a rough single crystal diamond by chemical vapour deposition, the planes of the sides of the substrate are selected such that the growth of the single crystal diamond does not occur at the same rate on all sides, the resulting grown rough single crystal diamond having an outline shape different from that of the substrate. The substrate may be mirror symmetrical about two mutually orthogonal axes. The substrate maybe a hexagonal disk lying n the plane (1 0 0) with three opposed pairs of sides. The substrate may be an octagonal disk in the plane (1 0 0) with three opposed pairs of sides. Also claimed is a rough manufactured single crystal diamond having top and bottom faces lying substantially parallel to on another, the bottom face has a polygonal outline with ore than four sides that differs from the outline of the top face.

Description

GROWING OF DIAMONDS

FIELD

The present disclosure relates to the manufacture of diamonds by growing of single crystal diamond on seeds, also herein termed substrates.

BACKGROUND

Growing of a diamond by epitaxial deposition of carbon atoms on a single crystal substrate by means of chemical vapour deposition (CVD) is known. The present Applicant's earlier patent publication W02020/240459 describes in detail a CVD apparatus in which a plasma is generated by means of microwave energy. The CVD apparatus will be briefly described herein, but the afore-mentioned publication is incorporated herein by reference in its entirety for a fuller understanding of the CVD process.

Following CVD growth, high value gems are obtained by cutting and polishing the rough diamond, a craft which is very sensitive to the shape of the lab grown uncut product, also referred to as rough stone. To minimize material loss during the polishing process, some polished diamond cuts are preferred over others. For illustration, Figure la and Figure lb show an emerald cut diamond fitted, using a Scanox HD system by OGI Systems, respectively into a rectangular and a square shape rough diamond of the same weight and height.

Table 1

Rough shape Rough W x L x H (mm) Rough weight (et) Emerald weight (et) Emerald yield (/o) Emerald L/W Rectangular 7.38 x 10.43 x 4.33 5.45 2.76 50.6 1.58 Square 8.60 x 8.62 x 4.33 5.45 2.27 41.7 1.32 The table above summarizes the yield of material usage and the dimensions of the rough and polished diamonds as obtained from the Scanox fitting instillment comparing different shapes of rough stones having a same initial weight. It can be seen in Figure lb that the edges near the long dimension of the prospective emerald cut go to waste in the square diamond. Moreover, to increase the material usage, the aspect ratio between the length and width (LAY) should be as low as possible, making the emerald shape less ideal when the initial rough diamond is square shaped.

Therefore, to supply the demand for certain diamond cuts it is important to control the morphology of the grown single crystal diamond (SCD) rough stone.

During epitaxial growth, vertical and lateral expansion can take place resulting in enlargement of the substrate area and thickness [References 1-2[. Silva et.al. showed the evolution of SCD morphology based on the relative growth velocities of four low index planes: 11 0 01, {1 1 fl, {1 1 0), and { I 1 3), known as the a, f3, and 7 parameters ['ere' 31. By careful choice of the CVD process, these parameters can be tuned, and certain crystallographic planes evolve [Re at the expense of other planes ferences 4-7].

CVD processes used in the diamond manufacturing industry conventionally commence with a square shaped (1 0 0) oriented substrate. The side faces delineating the substrate are typically {1 00) or 11 1 01 planes. Regardless of the a, 13, andy parameters, a square shape (1 0 0) substrate would result in the SCD growing with a top surface having an at least fourfold rotational symmetry (such as a square or an octagon), which favours diamond cuts with an aspect ratio (L/W) close to 1:1.

OBJECT

The present disclosure is concerned with growing uncut diamonds of which the shape is optimised for the manufacture inter alia of polished gemstones having an aspect ratio between their length and width (L/W) greater than 1:1, such as the emerald-cut diamonds shown in Figure I a and Figure 1 b.

SUMMARY

There is herein disclosed a method of growing a single crystal diamond which comprises providing a single crystal diamond substrate in the form of a polygonal disk having more than four sides, and growing a rough single crystal diamond on the substrate by chemical vapour deposition, wherein the planes of the sides of the substrate are selected such that the growth of single crystal diamond does not occur at the same rate on all sides, whereby the upper surface of the grown rough single crystal diamond has an outline shape different from that of the substrate To produce rough diamonds of generally rectangular shape, the substrate should be minor symmetrical about two mutually orthogonal axes In one embodiment, the substrate may be a hexagonal disk lying in the plane (1 0 0) with three opposed pairs of sides, a first pair lying in the planes (0 1 1) and (0 il), a second pair lying in the planes (0 1 0) and (0 1 0), and a third pair lying in the planes (0 01) and (0 0 1), the separation between the sides of the first pair being less that the separation between the sides of the second arid third pair.

The substrate of the latter embodiment may be produced by commencing with a square substrate having sides coinciding with the second and third pairs of sides and cutting off two opposite corners of the square to form the first pair of sides of the hexagon In an alternative embodiment, the substrate may be an octagonal disk in the plane (1 0 0) with four opposed pairs of sides, a first pair lying in the planes (0 1 1) and (0 II), a second pair lying in the planes (0 1 0) and (0 I_ 0), a third pair lying in the planes (0 01) and (0 0 1), and a fourth pair lying in the planes (0 1 1) and (0 1 i), the separation between the sides of the first pair being less that the separation between the sides of the second and third pair, arid the separation between the sides of the fourth pair being greater that the separation between the sides of the second and third pair.

The substrate of the latter embodiment may be produced by commencing with a square substrate having sides coinciding with the second and third pairs of sides and cutting off all four corners of the square to form the first and fourth pairs of sides of the octagon.

In one embodiment, the plane (1 0 0) of the substrate grows upwardly at a rate substantially similar to the lateral growth rate of the second pair of sides lying in the planes (0 1 0) and (0 I 0). This is expected if growth conditions (e.g., temperature, plasma components and the like) adjacent each of said faces are essentially similar. The present disclosure further provides manufactured rough diamonds produced by the above method and set out in the appended claims 7 to 10. Namely, there is provided a rough manufactured single crystal diamond having top and bottom faces lying substantially parallel to one another, wherein the bottom face has a polygonal outline with more than four sides, the bottom face (previously attached to a similarly shaped seed) differing from the outline of the top face. The top face typically has a 2-fold rotational symmetry. Such rough diamonds favour the extraction of cut diamond having an aspect ratio (L/W) greater than 1:1.

The disclosure is predicated on the principle that by careful choice of the substrate shape, and the CVD process parameters such that expansion of the substrate area would be favoured, a rough single crystal diamond may be obtained with a surface shape that favours diamond cuts with an aspect ratio higher than one (e.g., emerald, oval, pear, marquise, and baguette).

While the present invention is mainly described with respect to gemstones, this should not be construed as limiting and the present method, and rough diamonds that may be obtained therefrom, can serve for the manufacturing of cut diamonds adapted to additional uses, such as optical devices, electronic devices, cutting tools, and like known industrial uses of diamonds.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be described by reference to the accompanying drawings, in which: Figures la and lb as previously described, are diagrams that demonstrate the wastage that results when producing an emerald-cut polished diamond from rough diamond grown on a to square substrate, Figure 2 shows a hexagonal substrate from which a rectangular, rough diamond can be grown; Figure 3 shows an octagonal substrate from which a rectangular, rough diamond can be grown; Figures 4 and 5 are top and bottom views respectively, of a rough diamond grown from a hexagonal substrate; Figure 6 is a schematic representation of a CVD apparatus; Figure 7 is a perspective view showing how a polished oval diamond may be obtained from a rough diamond grown on a rectangular substrate; and Figure 8 is a view similar to that of Figure 7, showing how a polished oval diamond may be obtained from a rough diamond grown on a hexagonal substrate, according to the present teachings

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 6, which is derived from W02020/240459, shows schematically a plasma enhanced chemical vapour deposition (PECVD) apparatus 800, which may be used in implementing the method of the present disclosure. The apparatus comprises a microwave generator 810 configured to generate microwaves at a desired power and frequency, and a plasma chamber 820, into which the microwaves so generated are introduced. Plasma chamber 820 comprises a base 822, a top plate 824, and a side wall 826 extending from the base to the top plate defining a resonance cavity for supporting a microwave resonance mode between the base and the top plate. A plasma cloud that can be generated in operation of the apparatus is schematically depicted by a dotted hemisphere hovering over the surface of a holder 850.

The PECVD apparatus includes a waveguide 830 for introducing the microwaves from the microwave generator 810 into the plasma chamber 820. A gas flow system 840 for feeding process gases into the plasma chamber and removing exhaust gases therefrom is schematically represented by ingoing and outgoing arrows 842 and 844, respectively. The substrate holder 850 comprising an outer surface 852 and at least one supporting surface 854 for supporting a substrate of single crystal diamond to serve as a seed (e.g., 856), the seed supporting surface 854 being recessed with respect to the outer surface 852 of the holder. The apparatus also has a pressure regulator 860 for regulating the pressure within the plasma chamber 820 and a cooling system 870 for regulating the temperature of the substrate holder 850. While the pressure regulator 860 is, for simplicity and clarity of the drawing, represented as an arrow pointing to the plasma chamber, such a regulator is typically positioned at the exhaust 844 of the process gases.

Box 880 represents a control system for setting the relative rate of growth of the SCD on the seed substrate and of PCD on the surface of the holder. For instance, the controller 880 may control at least one of the microwave power, the cooling of the substrate holder and the chemical composition of the process gases, such that a single crystal diamond is grown on the substrate so as to protrude above the surface of the holder 850.

W02020/240459 describes how the growth of the SCD above the surface of the holder 850 may be constrained to reduce in cross sectional area, or at least not to increase in cross sectional area, with increased distance from the surface of the holder by the simultaneous growth of a polycrystalline diamond (PCD) layer on the surface of the holder. Such constraint of the growth of the SCD diamond is not required in the present disclosure, and instead the area of the SCD diamond expands both within and outside the recessed pocket. Indeed, the holder may not require recessed pockets, but they are preferred as they tend to reduce the growth of PCD on the SCD surfaces.

In the present method, the extent of growth both sideway (in directions substantially parallel to the plane of the holder) and upwardly (in a direction essentially perpendicular to the surface of the holder) depends on the respective growth rates of each of the side and top faces of the growing SCD, which in turn is governed by their individual crystallographic orientation The side faces having the slowest growth rate are expected to constitute the side faces of the final rough diamond, whereas the increased growth rates of the other faces will lead them to adopt a relatively new shape.

Experimental data An SCD substrate having a thickness of 300pm, with top surface oriented along the (1 0 0) direction and delineated by f 1 0 0) and {1 1 0) planes, as shown in Figure 2 was placed in a PECVD reactor apparatus as shown in Figure 6. The holder 850 had multiple recessed pockets Process conditions were set to favour lateral growth of the seed surface. Due to differences between the growth velocity in the 11 0 01 and the 11 1 01 planes (indicated by the dashed arrows of different magnitude in Figure 2), the shape of the resulting SCD surface was a rough rectangle as shown in Figures 4 and 5 The height of the grown diamond is approximately 5mm, this being about 60% of its short lateral dimension.

The substrate from which the diamond was grown has been cut away in Figure 5 and its shape (outlined in the drawing) can clearly be seen in Figure 5 to be hexagonal, while the outline of the top surface of the resulting rough diamond is substantially rectangular, as can be seen in Figure 4. It is common in practice, to cut away the substrate from the grown diamond so that it may be recycled.

It can be seen in Figure 5 that the hexagonal bottom face is bounded by first, second and third pairs of sides, the sides of each pair being parallel to one another. The second and third pairs of sides lie at right angles to one another and meet at two opposed uppermost and lowermost apices of the hexagon, as viewed in the drawing. The sides of the first pair, which are the vertical sides in Figures 4 and 5, are longer than the sides of the second and third pairs and lie parallel to an imaginary line extending between the opposed apices of the hexagon.

A rough diamond grown from a substrate as shown in Figure 3 would, of course have an octagonal, rather than a hexagonal base. The octagonal base is bounded by first, second, third and fourth pairs of sides, the sides of each pair being parallel to one another. As with the hexagonal base, the second and third pairs of sides lie at right angles to one another. Furthermore, the first and fourth pairs of sides also lie at right angles to one another. The sides of the first pair and fourth pairs are respectively longer and shorter than the sides of the first and second pairs.

During growth of an SCD starting from a seed having a hexagonal contour as shown in Figure 2, the top surface evolves with time to form a shape similar in contour (and crystallographic orientation of its faces) to the octagonal seed of Figure 3 Stones grown from hexagonal or octagonal substrates, as proposed herein, have been found to have different contour of bottom and top faces, their overall shape being somewhat "inflated", "swelled-or "bulging". Some of the side faces of the resulting rough stone are more outwardly "curved" than a conventional rectangle stone grown on a rectangle seed having relatively flatter side faces The end-result of this shape not being a perfect rectangular box (nor a perfect truncated pyramid having a rectangular base and apex) is sufficiently "imperfect" with respect to the 3D-shape to provide an improved yield. The yield is improved if greater by at least 5% relative to the yield of a perfect rectangular box having optimal dimensions for the extraction of a polished diamond having a desirable weight, with minimal waste. The perfect rectangular box to which rough stone according to the present invention is compared typically has a face (e.g., a largest face) essentially similar to a less than ideal rectangular shape that would constitute a top surface of a rough diamond as herein taught. The comparison can be made starting from rough stones having essentially a same weight, or conversely from cut and polished diamonds having essentially a same shape and weight.

In some embodiments, the yield that can be obtained cutting rough diamonds prepared by the present method can be greater by at least 10%, or by at least 15% of the theoretical yield in a perfectly rectangular box. Understandingly, the absolute improvement in yield, as measured with respect to each rough diamond, would depend on the shape of the diamond to be cut and polished therefrom. Thus, for illustration, while a conventionally prepared rectangular box could be cut to an emerald shape with a yield of 50%, a "rectangular" stone prepared according to the present disclosure could be cut with a significantly greater yield, of at least 55% (i.e. at least 10% relatively greater) or even up to 60% (i.e. at least 20% relatively greater).

As can be seen from Figures 7 and 8, the invention also achieves less wastage of single crystal diamond when producing polished oval diamond, instead of emerald shaped ones. In these figures, it is assumed that the growth rate in the {110} direction is three times the growth rate in the {110} direction. In both cases, a 2 ct polished oval diamond can be obtained.

However, the polish yield when growing the rough diamond on a hexagonal substrate (Figure 8) is 39.6% as compared with only 33,1% when the rough diamond is grown on a rectangular substrate (Figure 7).

While Table 1 presented the optimal yield of material usage (i.e. minimal waste of rough material) comparing stones having a same initial weight but different shapes, their cutting and polishing resulting in cut diamonds having a different weight, Table 2 presents similar comparative information assuming the cut diamonds are identical. The minimal dimensions of the rough diamonds capable of producing a same cut, depending on their initial shapes were obtained from simulation. Since the shape of a rough diamond obtained by the present method, denominated "Present.' in the table, is not a perfect geometrical form, its dimensions are omitted.

Table 2

Rough shape Rough W x L x H (mm) Rough weight (ct) Emerald weight (ct) Emerald yield (%) Emerald L/VV Present NR 5.15 2.85 55.3 1.41 Rectangular 7.4 x 10.5 x 4.33 6.00 2.85 47.5 1.41 Square 10.5 x 10.5 x 4.33 8.60 2.85 33.1 1.41 References [1] Tallaire, Alexandre, et al. "Reduction of dislocations in single crystal diamond by lateral growth over a macroscopic hole." Advanced Materials 29.16 (2017): 1604823.

[2] Ren, Ze-Yang, et al. "Growth and Characterization of the Laterally Enlarged Single Crystal Diamond Grown by Microwave Plasma Chemical Vapor Deposition." Chinese Physics Letters 35.7 (2018): 078101.

[3] Silva, F., et al. "Geometric modeling of homoepitaxial CVD diamond growth: I. The {1 0 0){1 1 1){1 1 0) {1 1 3) system." Journal of crystal Growth 310.1 (2008): 187-203.

[4] Clausing, R. E, et al. "Textures and morphologies of chemical vapor deposited (CVD) diamond." Diamond and Related Materials 1.5-6(1992): 411-415.

[5] Issaoui, R., et al. "Influence of oxygen addition on the crystal shape of CVD boron doped diamond." physica status solidi (a) 208.9 (2011): 2023-2027.

[6] Achard, J., et al. "High quality ATPACVD diamond single crystal growth: high microwave power density regime." Journal of Physics D: Applied Physics 40.20 (2007): 6175.

[7] Zhang, Li Zhu, Fu Zhong Wang, and Guang Tian. "Geometric Model of CVD Mono-Crystalline Diamond Growth." Applied Mechanics and Materials. Vol. 730. Trans Tech Publications Ltd, 2015.

Claims

CLAIMS1. A method of growing a single crystal diamond which comprises providing a single crystal diamond substrate in the form of a polygonal disk having more than four sides, and growing a rough single crystal diamond on the substrate by chemical vapour deposition, wherein the planes of the sides of the substrate are selected such that the growth of single crystal diamond does not occur at the same rate on all sides, whereby the upper surface of the grown rough single crystal diamond has an outline shape different from that of the substrate.
2 A method as claimed in claim 1, wherein, in order to produce rough diamonds having a generally rectangular shape, the substrate is mirror symmetrical about two mutually orthogonal axes
3 A method as claimed in claim 2, wherein the substrate is a hexagonal disk lying in the plane (1 0 0) with three opposed pairs of sides, a first pair lying in the planes (0 1 1) and (011), a second pair lying in the planes (01 0) and (0 0), and a third pair lying in the planes (0 01) and (0 0 I), the separation between the sides of the first pair being less that the separation between the sides of the second and third pair.
4. A method as claimed in claim 3, wherein the hexagonal substrate is formed by cutting off two opposite corners of a square seed having sides coinciding with the second and third pairs of sides and the hexagonal substrate, the cut corners forming the first pair of sides of the hexagonal substrate.
5. A method as claimed in claim 2, wherein the substrate is an octagonal disk in the plane (10 0) with three opposed pairs of sides, a first pair lying in the planes (0 1 1) and (0 11), a second pair lying in the planes (0 1 0) and (0 I 0), a third pair lying in the planes (0 01) and (0 0 I), and a fourth pair lying in the planes (0 1 1) and (0 1 1), the separation between the sides of the first pair being less that the separation between the sides of the second and third pair, and the separation between the sides of the fourth pair being greater that the separation between the sides of the second and third pair.
6. A method as claimed in claim 5, wherein the octagonal substrate is formed by cutting off all four corners of a square seed having sides coinciding with the second and third pairs of sides and the hexagonal substrate, the cut corners forming the first and fourth pairs of sides of the octagonal substrate.
7. A rough manufactured single crystal diamond having top and bottom faces lying substantially parallel to one another, wherein the bottom face has a polygonal outline with more than four sides that differs from the outline of the top face.
8. A rough diamond as claimed in claim 7, wherein the top face is generally rectangular, and the outline of bottom face is mirror symmetrical about two mutually orthogonal axes
9. A rough diamond as claimed in claimed in 8, wherein the bottom face is hexagonal and bounded by first, second and third pairs of sides, the sides of each pair being parallel to one another, wherein the second and third pairs of sides lie at right angles to one another and meet at two opposed apices of the hexagon, and the sides of the first pair are longer than the sides of the second and third pairs and lie parallel to an imaginary line extending between the latter opposed apices of the hexagon.
10. A rough diamond as claimed in claimed in 8, wherein the bottom face is octagonal, being bounded by first, second, third and fourth pairs of sides, the sides of each pair being parallel to one another, wherein the second and third pairs of sides lie at right angles to one another, the first and fourth pairs of sides lie at right angles to one another, and the sides of the first pair and fourth pairs are respectively longer and shorter than the sides of the first and second pairs.
11. A rough diamond as claimed in any one of claim 7 to claim 10, having a polishing efficiency for polishing any cut diamond shape out of the rough diamond greater by at least 5%, at least 10%, at least 15%, or at least 20% relative to a polishing efficiency for polishing a same cut diamond shape out of a rectangular box providing a minimal waste for the cut diamond shape.II