Method of manufacturing a diamond substrate

Abstract

The present disclosure relates to a method of manufacturing a diamond substrate that comprises a {111}-plane surface. The method comprises: - fabricating a plurality of mesa structures on a main diamond substrate, wherein the main diamond substrate comprises a first surface that has a planar orientation that has a misorientation angle relative to the {111} surface; - growing diamond on the first surface of the main diamond substrate by applying a vapor-phase synthesis method on at least the first surface of the main diamond substrate; - cutting the main diamond substrate along the {111} plane such that a distance between the first surface and a second surface that is arranged opposite of the first surface is reduced; and - removing material from the second surface until the main diamond substrate is separated in a plurality of diamond substrates that correspond to the plurality of mesa structures.

Description

[0001] METHOD OF MANUFACTURING A DIAMOND SUBSTRATE

[0002] The present disclosure relates to a method of manufacturing a diamond substrate that comprises a { 111 } -plane surface. The disclosure further relates to a diamond substate obtained from the method, and a quantum system that comprises such a diamond substrate.

[0003] Spin defects in diamond, particularly Nitrogen- Vacancy (NV) colour centres, are suitable for solid-state quantum systems. They can function as quantum bits, also named qubits, even under ambient conditions. Individual NV colour centres can be manipulated using optically detected electron spin resonance (ESR) techniques, involving microwave pulses under a magnetic field, laser initialization, and spin state readout via photoluminescence intensity modulation.

[0004] For diamond,{ 111 } -oriented crystals offer optimal integration into on-chip electronics and photonics devices. This is attributed to the NV colour entre axis being perpendicular to the (111) plane, while the electric dipole of the NV colour centre aligns parallel to the (111) plane. Consequently, large equipment such as triaxial electromagnets is unnecessary; instead, compact devices with smaller coils or attached permanent magnets embedded in a chip can be utilized. Furthermore, achieving maximal resonant mode coupling with specific photonic structures and partially contributing to optimal Purcell enhancement become achievable. However, producing high-purity { 111 } crystals poses significant challenges compared to { 100} crystals, thereby impeding their industrial progress.

[0005] Considering the potential industrial constraints related to cost and crystallinity uniformity, chemical vapour deposition (CVD) thin films grown on { 111 } crystals offer advantages for industrial applications. Flat as-grown { 111 } CVD surfaces are preferred for integration into photonics and electronics. Post-growth planarization processes like mechanical polishing can compromise NV colour centre properties due to residual polishing damage. Notably, the (111) face, being the hardest, makes mechanical polishing impractical for planarization. Hence, there is a need for a method to fabricate parallel substrates with a flat as-grown surface on one side, especially for application-friendly { 111 } crystals tailored for on-chip quantum devices.

[0006] It is an object for the present disclosure to obviate or at least reduce the abovementioned problems. In particular, it may be an object of the present disclosure to provide a method that simplifies the fabrication of diamond substrates that comprise a { 111 } -plane surface.

[0007] This object is achieved by a method of manufacturing a diamond substrate that comprises a { 111 } -plane surface, comprising: fabricating a plurality of mesa structures on a main diamond substrate, wherein the main diamond substrate comprises a first surface that has a planar orientation that has a misorientation angle relative to the { 111 } surface; growing diamond on the first surface of the main diamond substrate by applying a vapor-phase synthesis method on at least the first surface of the main diamond substrate; cutting the main diamond substrate along the { 111 } plane such that a distance between the first surface and a second surface that is arranged opposite of the first surface is reduced; and removing material from the second surface until the main diamond substrate is separated in a plurality of diamond substrates that correspond to the plurality of mesa structures.

[0008] An advantage of the present disclosure is that the plurality of mesas can each be used as quantum device. Due to the creation of the plurality of mesas on the main diamond substrate which are later separated into the plurality of diamond substrates, the production of the quantum devices can be easily scaled. Particularly, by dividing the main number substrate in the plurality of mesas all individual mesas can simultaneously grow diamond on the first surface during the vapour-phase synthesis method step. In this way, with one growing step many quantum devices can be produced.

[0009] The plurality of mesa structures can be separated into the plurality of diamond substrates by removing material from the second surface of the main diamond substrate. The material is removed from the second surface until the trenches or grooves which separate the plurality of mesa structures are reached. In this way the plurality of mesa structures are effectively transformed into separate diamond substrates which can form quantum devices.

[0010] A further advantage of cutting the main diamond substrate along { 111 } plane is that the first surface on which the diamond has been grown and the second surface are substantially parallel to each other. This has the consequence that the first and second surfaces are parallel or perpendicular to the quantization axis direction and electric people direction of colour centre, which ensures optimal device performance with efficient initialization and reading of the spins states when the diamond substrate is integrated into a quantum device. An even further advantage is that large equipment such as triaxial electromagnets is unnecessary for manipulating the colour centre. Instead, compact devices with smaller coils or attached permanent magnets embedded in a chip can be utilized. Furthermore, achieving maximal resonant mode coupling with specific photonic structures and partially contributing to optimal Purcell enhancement become achievable.

[0011] An even further advantage is that by growing diamond by applying a vapor-phase synthesis method the concentration of 13C and / or 12C atoms in the diamond can be controlled. This is particularly important for quantum applications that require high purity crystals with reduced 13C nuclear spins. An even further advantage of the method is that a large area of a first surface can be obtained. Furthermore, the waste of diamond during the production of the diamond substrate is reduced compared to laser cutting the first surface there is no kerf loss from laser cutting.

[0012] In an embodiment fabricating the plurality of mesa structures comprises creating at least one groove or trench that separates the individual mesa structures from each other, wherein the groove or trench extends from the first surface towards the second surface.

[0013] The groove or trench separates adjacent mesa structures. The groove or trench extends from the first surface towards the second surface. An advantage of the groove or trench is that the mesa structures can effectively be separated from each other to later form diamond substrates.

[0014] In an embodiment removing material from the second surface comprises removing material until the at least one groove or trench is connected to the second surface.

[0015] By connecting the at least one groove or trench to the second surface each of the plurality of mesa structures are separated, thereby forming the plurality of diamond substrates.

[0016] In an embodiment after cutting the main diamond substrate along the (111) plane the second surface is substantially parallel to the first surface. An advantage of the first surface and the second surface being substantially parallel is that large equipment such as triaxial electromagnets is unnecessary for manipulating the colour centre. Instead, compact devices with smaller coils or attached permanent magnets embedded in a chip can be utilized.

[0017] In other words, after cutting the main diamond substrate along the (111) plane the second surface is the (111) plane of the crystal lattice of the main diamond substrate. In this way, if the second surface is arranged on the chip of the quantum device, the magnetic field of the quantum device can effectively be positioned parallel to the NV-axis. In other embodiments, the first surface may be the (111) plane and is arranged on the chip of the quantum device.

[0018] In an embodiment the misorientation angle is in the range of 0.5-10 degrees, preferably in the range of 1-5 degrees, and most preferably in the range of 2-4 degrees.

[0019] Experiments have shown that the abovementioned ranges of the misorientation angle provide a fast growth of the diamond during the step of vapor-phase synthesis while realising a flat as grown diamond surface that is parallel to the { 111 } plane of the diamond lattice.

[0020] In an embodiment fabricating the plurality of mesa structures on the main diamond substrate comprises fabricating the plurality of mesa structures in a grid-like structure, preferably a rectangular grid-like structure.

[0021] The rectangular grid-like structure has the advantage that the amount of diamond substrates obtained from the main diamond substrate is maximized. This saves material and thereby reduces the cost of obtaining the diamond substrates.

[0022] In an embodiment growing the diamond comprises step-flow growth of the diamond. In an embodiment the vapor-phase synthesis method comprises chemical vapour deposition.

[0023] The growth conditions during the chemical vapor deposition are in one example embodiment 880-940 degrees Celsius, with a gas pressure of 0.13-0.16 bar. The C atoms are provided by methane being present in the gas used, wherein the methane concentration was below 0.1%. The flow rate of the gas was less than 3500 standard cubic centimeters per minute (seem).

[0024] In an example embodiment, the temperature during the chemical vapour deposition is in the range of 500-1500 degrees Celsius, preferably in the range of 750-1250 degrees Celsius, and most preferably in the range of 800-1000 degrees Celsius. The gas pressure is in the of 0.05-0.5 bar, preferably in the range of 0.1 -0.2 bar, and most preferably in the range of 0.13-0.16 bar. The methane concentration of the gas no more than 1%, preferably no more than 0.5 %, and most preferably not more than 0.1%. The flow rate of the gas is in the range of 100-10,000 standard cubic centimeters per minute (seem), preferably in the range of 200-5000 seem, most preferably in the range of 3000-4000 seem.

[0025] In an embodiment fabricating a plurality of mesa structures comprises etching, preferably dry-etching such as reactive ion etching, the main diamond substrate.

[0026] The dry etching may comprise arranging, on the first surface of the main diamond substrate, a mask comprising at least one opening. The at least one opening is configured to be positioned on the desired locations of the trenches or grooves. The mask may be a quartz mask.

[0027] In an embodiment removing material from the second surface comprises etching, preferably dry-etching, the second surface.

[0028] In an embodiment cutting the main diamond substrate comprises laser cutting.

[0029] Preferably, the laser cutting is performed at a predetermined distance from the plurality of mesa structures. Afterwards, the second surface may be etched. By laser cutting at a predetermined distance, damage from the laser cutting cannot impact the mesa structures.

[0030] In an embodiment the method further comprises introducing a colour centre in the plurality of mesa structures or in the plurality of diamond substrates.

[0031] By introducing, or implanting, a colour centre in the plurality of mesa structures or in the plurality of diamond substrates the diamond substrate can be used in quantum applications.

[0032] In an embodiment the method further comprises the step of annealing the diamond substrate for activating the colour centres.

[0033] In an embodiment the method further comprises: providing a main diamond substrate that comprises the first surface that is provided with the misorientation angle with respect to the { 111 } surface. The disclosure further relates to a diamond substrate obtained by the method according to any one of the foregoing embodiments, wherein the diamond substrate optionally corresponds to one of the plurality of mesa structures.

[0034] The diamond substrate provides similar effects and advantages as disclosed for the method. All features that are disclosed in relation to the method can also be applied to the diamond substrate.

[0035] The disclosure further relates to a quantum system comprising a diamond substrate according to the present disclosure.

[0036] The quantum system provides similar effects and advantages as disclosed for the method and the diamond substrate. All features that are disclosed in relation to the method and the diamond substrate can also be applied to the quantum system.

[0037] The quantum system may be a quantum optical network comprising a plurality of nodes, each node comprising a diamond substrate hosting a qubit.

[0038] Further advantages, features and details are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, wherein: figure 1A, a side view of a first example of a main diamond substrate; figure IB, a top view of a first example of a main diamond substrate; figure 2A, a side view of a second example of a main diamond substrate; figure 2B, a top view of a second example of a main diamond substrate; figure 3A, a side view of a third example of a main diamond substrate; figure 3B, a top view of a third example of a main diamond substrate; figure 4, a side view of a fourth example of a main diamond substrate; figure 5, a schematic example of separating the main diamond substrate into a plurality of diamond substrates; figure 6, a side view of a mesa structures with the diamond lattice; and figure 7, an example embodiment of a method.

[0039] Main diamond substrate 2 (figure 1A-B) comprises first surface 4 and oppositely arranged second surface 6. Second surface 6 is substantially parallel with respect to first surface 4. Main diamond substrate 2 is substantially made of diamond wherein the diamond is arranged in its crystal structure. First surface 4 has a planar orientation that has a misorientation angle relative to the (111) surface. Line Ai indicates the direction of the (111) plane of the crystal lattice of main diamond substrate 2. The misorientation angle 0 between first surface 4 and line Ai is in the illustrated embodiment 3 degrees.

[0040] First surface 4 comprises a plurality of steps 8. Each step 8 comprises long side 10 and short side 12. Long side 10 is oriented parallel to the (111) plane of the crystal lattice of main diamond substrate 2. It is noted that each of the plurality of steps 8 are atomic steps, and that the length of long side 10 and short side 12 have been amplified for illustrator purposes.

[0041] The orientations of the crystal lattice are also shown in figure 1A. Vector A2 indicates the vector perpendicular to the (112) plane, which is parallel to line Ai which is parallel to the (111) plane. Vector B is parallel to the misoriented (111) plane, which can be defined as the (111) plane which is rotated by misorientation angle 0. Vector C is the

[0111] vector which his perpendicular to the (111) plane of the crystal lattice of main diamond membrane 2. Vector D, which is directed towards the reader, is the

[0110] vector which is perpendicular to the (110) plane of the crystal lattice of main diamond membrane 2.

[0042] Figure IB illustrates figure 1A from direction N, and thus is a top view of main diamond membrane 2. Figure IB shows first surface 4. Top surface 4 comprises ridges 14 which extend in the direction of vector D, i.e. in the

[0110] direction. Ridges 14 in figure IB only show long side 10.

[0043] Main diamond substrate 2 (figure 2A-2B) has been divided in a plurality of mesa structures 16. Plurality of mesa structures 16 are separated by trench 18. Trench 18 is in the illustrated embodiment fabricated by etching first surface 4 of main diamond membrane 2. Mesa structure 16a and mesa structure 16b can both individually be manufactured into separate quantum devices. Main diamond substrate 2 has thickness Ti. The depth of trench 18 between mesa structure 16a and mesa structure 16b is in this illustrated embodiment Di. Depth Di of trench 18 is in the illustrated embodiment nearly half of thickness Ti of main diamond substrate 2. In the illustrated embodiment thickness TI is approximately 500 micrometres and depth Di is approximately 130 micrometres.

[0044] Plurality of mesa structures 16 (figure 2B, which shows a top view from direction N of figure 2A) comprises first mesa structure 16a, second mesa structure 16b, third mesa structure 16c, and fourth mesa structure 16d. First trench 18a and second trench 18b cross each other perpendicularly. First trench 18a separates first mesa structure 16a from second mesa structure 16b and third mesa structure 16c from fourth mesa structure 16d. Second trench 18b separates first mesa structure 16a from fourth mesa structure 16d and second mesa structure 16b from third mesa structure 16c. In figure 2B four mesa structures 16a, 16b, 16c, and 16d are illustrated. It is clear for the skilled person that by creating more trenches on first surface 4, for example on lines 18c, 18d, 18e and 18f the number of mesa structures can be increased.

[0045] Main diamond substrate 2 (figures 3A, 3B) comprises grown diamond 22 which is grown on first surface 4 of mesa structures 16a and 16b. Grown diamond 22 was grown on first surface 4 by chemical vapor deposition. Grown diamond 22 was grown from short sides 12 of steps 8 and was grown into grow direction G. In this way multiple layers 24 have been grown simultaneously from short side 12 into grow direction G. First mesa structure 16a comprises first top surface 20a, and second mesa structure 16b comprises second top surface 20b. First top surface 20a and second top surface 20b are positioned parallel to the (111) plane of the crystal lattice of main diamond substrate 2. As can be seen in figure 3B, each mesa structure 16a, 16b, 16c, 16d now respectively comprises a top surface 20a, 20b, 20c, 20d that is parallel to the (111) plane of the crystal lattice of diamond substrate 2. In trenches 18 diamond is also grown during chemical vapor deposition, which is indicated by residual grown diamond 23.

[0046] Grown diamond 22 can be divided into two parts, first grown diamond 25a (darker color) and second grown diamond 25b (lighter color). In case of CVD growth, first first grown diamond 25a is grown with step-flow growth. If then CVD growth is continued, also second grown diamond 25b will be grown. By also growing second grown diamond 25b, flat surface 20a, 20b is obtained.

[0047] Depth D2 is the depth of trenches 18 after CVD growth. Depth D2 is smaller than depth Di, as there is also diamond growth in trenches 18. Thickness T3 is the thickness of the CVD film grown on mesas 16a, 16b. After CVD growth, trench 18 should have depth D2 when maximum thickness T3 of grown diamond film 22 is reached. In other words, residual grown diamond 23 should not be more than thickness Di.

[0048] Second surface 6 (figure 4) of main diamond substrate 2 can now be cut. Main diamond substrate 2 is cut such that the cutting plane is along the (111) plane of the diamond lattice of main diamond substrate 2. Cutting second surface 2 is in the illustrated embodiment performed by lasercutting. Laser cutting plane P is shown in figure 4 as a dashed line.

[0049] After cutting second surface 6 (figure 5), material can be further removed from second surface 6. In the illustrated embodiment, the removal of material from the second surface is performed by reactive ion etching. Ions 26 are shot towards second surface 6 thereby removing material. It is clear for the skilled person that other methods that remove material from second surface 6 can also be performed and are comprised in the present disclosure.

[0050] Diamond is removed from second surface 6 until trench 18 is reached. When trench 18 is reached, no material is present between first mesa structure 16a and second mesa structure 16b. As no material is present, first mesa structure 16a and second mesa structure 16b are separated. In this way, two separate diamond substrates 28a and 28b are obtained. At this stage, the diamond substrate 28a (or mesa structure 16a), which due to laser cut line P is thicker than diamond substrate 28b, is still connected to diamond substrate 28d (mesa structure 16d). Diamond substrate 28d (mesa structure 16d) is not shown in figure 5 as it is located directly behind diamond substrate 28a (or mesa structure 16a). Therefore, by continuing the etching process further, it is possible to eventually separate diamond substrate 28a (or mesa structure 16a) with diamond substrate 28d (or mesa structure 16d), thus separating all the mesa structures.

[0051] First diamond substrate 28a and second diamond substrate 28b can individually be used to manufacture a quantum device. An advantage of first diamond substrate 28a and second diamond substrate 28b is that top surfaces 20a, 20b and bottom surfaces 30a, 30b are substantially parallel and are in the (111) plane of the diamond lattice of diamond membrane 2. This ensures that if an Nitron- Vacancy (NV) colour centre is introduced in first diamond substrate 28a or second diamond substrate 28b, the the electric dipole of the [11 l]-oriented colour centre aligns parallel to the (111) plane, and thus parallel to top surfaces 20a, 20b and bottom surfaces 30a, 30b. An advantage thereof is that large equipment such as triaxial electromagnets is unnecessary. Instead, compact devices with smaller coils or attached permanent magnets embedded in a chip can be utilized. Thus, achieving maximal resonant mode coupling with specific photonic structures fabricated near the top surfaces 20a and 20b becomes feasible. Additionally, the [l l l]-oriented NV is perpendicular to the bottom surfaces 30a and 30b. An advantage of this is that large equipment, such as triaxial electromagnets, to align a magnetic field parallel to the NV axis is unnecessary. Instead, by attaching the bottom surfaces 30a and 30b to a chip, compact devices with smaller coils or embedded permanent magnets within the chip can be utilized.

[0052] Figure 6 shows multiple layer 24a-24i that are grown on steps 8 of diamond membrane 2. Steps 8 comprise long side 10 and short side 12. Layers 24a-24i are grown from each short side 12 of each individual step 8. Layers 24a-24i are grown in direction G. Further displayed in diamond membrane 2 is crystal lattice 32. Thickness T2 of layers 24a-24i is in the illustrated embodiment approximately 0.2 nanometres.

[0053] Figure 7 illustrates an embodiment of the present disclosure. In first step 140 main diamond substrate 2 is fabricated with misorientation angle 0 from the (111) plane of diamond lattice 32. First surface 4 which is provided with misorientation angle 0 may be obtained through mechanical polishing of first surface 4. It is clear for the skilled person that fabrication step 140 is not essential to the present disclosure. Main diamond substrate 2 provided with first surface 4 that has misorientation angle 0 could for example also be provided by a supplier. First step 140 could also be omitted.

[0054] In step 142 mesa structures 16 are fabricated. Mesa structures 16 are fabricated by creating trenches 18 in first surface 4 of main diamond substrate 2. Trenches 18 may be fabricated by physical or chemical etching. Alternatively or additionally, trenches 18 are created by laser cutting. In a preferred embodiment, trenches 18 are created by reactive ion etching, preferably inductively coupled plasma reactive ion etching.

[0055] In step 144 diamond is grown on top surfaces 20 of mesa structures 16. The diamond may be grown via chemical vapor deposition. The diamond may be grown by step-flow growth, wherein the diamond is grown on short sides 12 of steps 8 in direction G such that multiple layers 24 are created, wherein each layer 24 is associated with a step 8. As the layers are flat, post-growth flattening processes are not necessary. The growth conditions during the chemical vapor deposition are in one example embodiment 880-940 degrees Celsius, with a gas pressure of 0.13-0.16 bar. The C atoms are provided by methane being present in the gas used, wherein the methane concentration was below 0.1%. The flow rate of the gas was less than 3500 standard cubic centimeters per minute (seem).

[0056] In step 146, NV centers are introduced into the mesa structure by methods such as electron irradiation followed by annealing, ion implantation followed by annealing, or nitrogen delta- doping during CVD growth. It is clear for the skilled person that step 146 is optional, and the introduction of the NV centres could also take place after the separation of mesa structures 16 to from diamond substrates 28.

[0057] In step 148 second surface 6 is cut along the (111) crystal plane. In this way first surface 4 and second surface 6 are parallel to each other, and both are directed along the (111) crystal plane. In step 150 second surface 6 is etched, either by physical or chemical etching. In a preferred embodiment, trenches 18 are created by reactive ion etching, preferably inductively coupled plasma reactive ion etching. By etching diamond material away from second surface 6, the diamond material holding mesa structures 16 together is removed. If trenches 18 are reached, mesa structures 16 are separated into diamond substrates 28. The present disclosure is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following clauses within the scope of which many modifications can be envisaged.

Claims

CLAIMS1. Method of manufacturing a diamond substrate that comprises a { 111 } -plane surface, comprising: fabricating a plurality of mesa structures on a main diamond substrate, wherein the main diamond substrate comprises a first surface that has a planar orientation that has a misorientation angle relative to the { 111 } surface; growing diamond on the first surface of the main diamond substrate by applying a vapor-phase synthesis method on at least the first surface of the main diamond substrate; cutting the main diamond substrate along the { 111 } plane such that a distance between the first surface and a second surface that is arranged opposite of the first surface is reduced; and removing material from the second surface until the main diamond substrate is separated in a plurality of diamond substrates that correspond to the plurality of mesa structures.

2. Method according to any one of the foregoing claims, wherein fabricating the plurality of mesa structures comprises creating at least one groove or trench that separates the individual mesa structures from each other, wherein the groove or trench extends from the first surface towards the second surface.

3. Method according to claim 2. wherein removing material from the second surface comprises removing material until the at least one groove or trench is connected to the second surface.

4. Method according to any one of the foregoing claims, wherein after cutting the main diamond substrate along the (111) plane the second surface is substantially parallel to the first surface.

5. Method according to any one of the foregoing claims, wherein the misorientation angle is in the range of 0.5-10 degrees, preferably in the range of 1-5 degrees, and most preferably in the range of 2-4 degrees.

6. Method according to any one of the foregoing claims, wherein fabricating the plurality of mesa structures on the main diamond substrate comprises fabricating the plurality of mesa structures in a grid-like structure, preferably a rectangular grid-like structure.

7. Method according to any one of the foregoing claims, wherein growing the diamond comprises step-flow growth of the diamond.

8. Method according to any one of the foregoing claims, wherein the vapor-phase synthesis method comprises chemical vapour deposition.

9. Method according to any one of the foregoing claims, wherein fabricating a plurality of mesa structures comprises etching, preferably dry-etching such as reactive ion etching, the main diamond substrate.

10. Method according to any one of the foregoing claims, wherein removing material from the second surface comprises etching, preferably dry-etching, the second surface.

11. Method according to any one of the foregoing claims, wherein cutting the main diamond substrate comprises laser cutting.

12. Method according to any one of the foregoing claims, further comprising introducing a colour centre in the plurality of mesa structures or in the plurality of diamond substrates.

13. Method according to claim 12, further comprising the step of annealing the colour centres for activating the colour centres.

14. Method according to any one of the foregoing claims, further comprising: providing a main diamond substrate that comprises the first surface that is provided with the misorientation angle with respect to the { 111 } surface.

15. Diamond substrate obtained by the method according to any one of the foregoing claims, wherein the diamond substrate corresponds to one of the plurality of mesa structures.

16. Quantum system comprising a diamond substrate according to claim 15.

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