Bonded diamond structures

Abstract

Bonded diamond structures and methods for fabricating bonded diamond structures are described wherein a bonded diamond structure may comprise an inorganic oxide layer provided on a base substrate; and, a (100) oriented diamond substrate directly bonded to the oxide layer, the surface of the diamond substrate having an average surface roughness between 2 and 10 nm and the bonding being characterized by a shear strength equal to or larger than 2 MPa.

Description

[0001] Bonded diamond structures

[0002] Technical field

[0003] The disclosure relates to bonded diamond structures, and in particular, though not exclusively, to bonded diamond on insulator structures on insulator structures, devices comprising such bonded structures and methods for fabricating such bonded structures.

[0004] Diamond plays an important rol in state-of-the-art optical devices for telecommunications and quantum computing. For example, a modular quantum computer chip based on spin qubits in diamond enabkes an increased connectivity, a high fidelity, and a low error-rate when the number of qubits increases. High-quality diamond substrates however have a limited size (currently in the order of mm2) preventing use of advanced semiconductor manufacturing line. One way of addressing large-scale integration of optical devices and qubits is bonding diamond substrates to an oxide covered base substrate to form a bonded diamond on insulator structure. Both (111) and (100) oriented diamond layers are used however (100) oriented diamond is preferential due to better electronic properties, easier to polish and less expensive to produce.

[0005] Direct bonding of crystalline diamond substrates to a termal or native oxide layer over a silicon substrate is a promising approach for realizing such structures. In the article by Matsumae, T., et al. Hydrophilic low-temperature direct bonding of diamond and Si substrates under atmospheric conditions, Scripta Materialia, 175, 24-28 (2020) describe a process of direct bonding of (111) oriented diamond on a thermally oxidezed surface of a silicon substrate. A further article by Matsumae, T., et al., Low-temperature direct bonding of diamond (100) substrate on Si wafer under atmospheric conditions, Scripta Materialia, 191, 52-55 (2021) the authors describe the bonding of (100)-oriented diamond to a thin (native or thermal) silicon oxide layer over a silicon substrate and with a pressure applied during the annealing. The shear strength however was very weak.

[0006] EP4160670A1 describes direct bonding of (100) and (111) oriented diamond substrates to a thermally or native oxidized surface of a silicon substrate. Low bonding strengths for (100) oriented diamond strucutres and moderate to high bonding strengths for (111) oriented diamond substrates were found using an ammonia I hydrogen peroxide OH surface passivation step. These known diamond bonding processes provide acceptable bonding strengths for bonding a (111) oriented diamond substrate to a thermal or native oxide laye. However, when bonding a (100) diamond substrate to an oxide layer or bonding a (100) or (111 ) diamond substrate to a relatively thick deposited oxide layer only low bonding strengths can be achieved. Low bonding strengths are problematic because in order to manufacture structures for optical devices, the bondend diamond structures require further processing including process steps for thinning and polishing the relatively thick diamond substrate. Additionally, the ability to bond to deposited oxide layers is important because typically to fabricate optical devices based on a bonded diamond structures a relatively thick high-quality oxide layer (with low density of electronic defects) are needed.

[0007] Hence, from the above it follows that there is a need in the art for bonded diamond structures wherein a diamon substrate is bonded to oxide layers with elevated bonding strengths, in particular bonding strengths which are higher than the bonding strengths achieved in the prior art.

[0008] Summary

[0009] The embodiments in this disclosure generally relate to bonded diamond structures, wherein a diamond substrate is directly bonded to an oxide layer that is provided over a base substrate.

[0010] In an aspect, the embodiments relate to a bonded diamond structure comprising: an inorganic oxide layer provided on a base substrate; and, a (100) oriented diamond substrate directly bonded to the oxide layer, the bonding being characterized by a shear strength equal to or larger than 2 MPa, preferably equal to or larger than 3 MPa, more preferably equal to or larger than 4 MPa.

[0011] Inventors discovered that when using a diamond substrate with a relatively rough surface between 2 and 10 nm (rms) in a direct bonding scheme based on OH passivation of the diamond surface, a strong direct bonding can be established between a surface of the diamond substrate and the oxide layer on the base substrate. Here, the term direct bonding refers to a bonding process where the two sufaces that need to be bonded are brought in direct contact with each other so that a bonding between atoms at the surface of the diamond substrate and atoms at the surface of the oxide layer. This way bonded diamond structures can be realized wherein the bonding strength is substantially higher than those known from the prior art.

[0012] In an embodiment, the shear strength between the diamond substrate and the oxide covered substrate is between 1 ,5 and 14 MPa, preferably between 2 and 12 MPa. In an embodiment, the bonding may be characerizd by atomic bonding between oxygen atoms at the surface of the oxide layer and carbon atoms at the surface of the diamond substrate.

[0013] In an embodiment, the oxide layer may be a deposited oxide layer.

[0014] In an embodiment, the deposited oxide layer may be a non-stochiometric oxide layer.

[0015] In an embedment, the thickness of the oxide layer may be between 50 nm and 500 micrometer.

[0016] In an embodiment, the base substrate may be of a metal or a semiconductor.

[0017] In an embodiment, the inorganic oxide layer may be a metal oxide layer or a semiconductor oxide layer.

[0018] In an embodiment, the metal oxide layer or the semiconductor oxide layer may be an oxide that is different from the oxide of the metal or semiconductor of the base substrate.

[0019] In an embodiment, the oxide layer may be a thermal oxide layer or native oxide layer, the thermal oxide layer or native oxide layer being formed in the surface of the base substrate.

[0020] Here, thermal oxidation refers to an oxidation process (wet or dry) wherein an oxidizing agent is diffused into an oxidizable material at elevated termperaturs and reacts with it. Depending the thermal oxidation process, a thermal oxide layer between 5 nm and 10 micron can be formed. Typically, thicker thermal oxide layers (in the range of micrometers) require high temperatures, which may affect the base substrate. A native oxide layer is formed by exposing the surface of the substrate to an oxidizing agent, e.g. oxygen or ambient air. This way, a thin oxide layer with the thickness between 0.5 and 5 nm may be form over the substrate.

[0021] In an embodiment, the oxide layer may be a deposited oxide layer, i.e. an oxide layer deposted on the substrate using a thin-film deposition technique, preferably a low temperature thin film deposition technique. Here, low temperature deposition may refer to deposition techniques for substrate temperatures lower than 400 °C, preferably lower than 300 °C, more preferably lower than 250 °C.

[0022] In an embodiment, the thin-film deposition technique may be a thermal deposition method, for example vacuum evaporation, laser deposition, molecular beam epitaxy MBE, ion plating, activated reactive evaporation (ARE) or ionized cluster beam deposition (ICBC).

[0023] In another embodiment, the thin-film deposition technique may be a chemical deposition method, for example plasma, laser or thermal chemical vapour deposition CVDs or a chemical solvent deposition. In an embodiment, the deposited oxide layer may have thickness that is larger than oxides that can be achieved using thermal oxidation. In that case, the layer thickness may be largr than 10 micron, preferably larger than 50 micron, more preferably larger than 100 micron.

[0024] In a further aspect, the embodients may relate to a bonded diamond structure comprising: an inorganic oxide layer deposited on a base substrate, preferably the deposited inorganic oxide layer being a non-stochiometric oxide layer oxide layer; and, a diamond substrate directly bonded to the oxide layer, wherein the bonding is characerizd by atomic bonding between oxygen atoms at the surface of the oxide layer and carbon atoms at the surface of the diamond layer.

[0025] In an embodiment, the diamond substrate may be an (100) oriented diamond substrate or a (111) oriented diamond substrate.

[0026] In an embodiment, the thickness of the deposited oxide layer may be between 50 nm and 500 micrometer, preferably between 50 nm and 500 nm.

[0027] In an embodiment, the deposited oxide layer may have a thickness that is larger than the thickness of an oxide layer that is realized using thermal oxidation. Typically, due to the nature of the thermal oxidation process, the thickness of oxide layers realized with thermal oxidation is limited to layer thicknesses of about 10 micron, especially at low temperatures. Hence, the thickness of the deposited oxide layer may be larger than 10 micron, preferably larger than 50 micron, more preferably larger than 100 micron.

[0028] In an embodiment, the inorganic oxide layer may be a metal oxide layer or a semiconductor oxide layer.

[0029] In an embodiment, the thickness of the diamond substrate may be less than 10 micron, preferably less than 1 micron, more preferably less than 500 nm.

[0030] In an embodiment, a pattern is etched into the diamond substrate to form a patterned diamond substrate.

[0031] In an embodiment, the material of the base susbstrate supporting the oxide layer may be one of: Si, SiC, SiN, SiGe, Ge, GasAs, GaN, InP, Cu, CuO, Al, AIN, Ti, TiN, TiO2, AI2O3, GaOx, MgO, Y3AI5O12, LiNbO3, LiTa3, ZnO.

[0032] In yet a further aspect, the embodiments may relate to a bonded diamond structure according to any of the above embodiments, wherein the base substrate comprises integrated circuits.

[0033] In yet another aspect, the emboidments may relate to a device, e.g. an optical device or an opto-electronic device that is manufactured based on a bonded diamond structure as defined with reference to the embodiments in this application.

[0034] In a further aspect, the embodiments relate to a method of fabricating a bonded diamond structure comprising: exposing a surface of a crystalline diamond substrate to a mixture of sulfuric acid and hydrogen peroxide to form an OH passivated surface, the surface of the diamond substrate having an average surface roughness between 2 and 10 nm; exposing a surface of an inorganic oxide layer provided on a substrate to an oxygen plasma to form an OH passivated surface; bringing the passivated surfaces in direct contact with each other to form a bonded diamond structure; and, applying a low temperature annealing step to the bonded diamond structure.

[0035] Brief Description of the drawings

[0036] Fig. 1A-1E depict a known method of bonding diamond to a thermally grown oxide layer;

[0037] Fig. 2 depicts a flow chart of the direct bonding process according to an embodiment.;

[0038] Fig. 3A-3B depict AFM pictures of surfaces of diamond substrates of different surface roughness;

[0039] Fig. 4 depicts a graph of the shear strength of the bonding as a function of the treatment

[0040] Fig. 5 depicts a plot of the surface roughness of a diamond substrate after treatment as a function of the treatment time.

[0041] Fig. 6A-6C depict XPS analysis for analyzing the elemental composition on the diamond surface during the piranha cleaning.

[0042] Fig. 7 illustrates OH passivantion of a diamond surface according to an embodiment;

[0043] Fig. 8 illustrates OH passivantion of a diamond surface using a known passivation scheme;

[0044] Fig. 9 depicts the formation of a thin-film diamond on insulator structure according to an embodiment.

[0045] Fig. 10 depicts the formation of part of a device based on a diamond on insulator structure according to an embodiments.

[0046] Description of the embodiments

[0047] The embodiments in this disclosure relate to bonding a diamond substrate to an oxide layer onto a substate. Some embodiments relate to bonding a (100) oriented diamond substrate to an oxide layer provided over a substrate. The (100) oriented diamond substrate may be bonded to the oxide layer with a bonding strength that is equal to or higher than 2 MPa or higher. Other embodiments relate to bonding a (100) or (111) oriented diamond substrate to an oxide layer which is deposited on a substrate. Here, the term deposited oxide layer refers to an oxide layer that is deposited using a thin-film deposition technique. Any suitable deposition technique may be used including but not limited to physical deposition techniques such as thermal deposition methods (e.g. vacuum evaporation, laser deposition, molecular beam epitaxy MBE, ion plating, activated reactive evaporation ARE, ionized cluster beam deposition ICBC) and chemical deposition methods (e.g. plasma, laser or thermal chemical vapour deposition CVDs, chemical solvent deposition). These thin-film deposition techniques, which have in common that a material is deposited onto a substate, should be demarcated from thermally grown thin-films wherein a top part of a substrate is chemically transformed into an oxide layer. These techniques typically need an activation energy in the form of an elevated temperature to trigger the chemical process.

[0048] Bonding of diamond, in partucular a diamond substrate, to a base substrate having a thin thermally grown oxide layer, e.g. a SiO2 layer, is known in the art. An example of the bonding process is schematically shown in Fig. 1A-1E. Fig. 1A shows the surface preparation of a substate having a very thin (e.g. 1-3 nm) thermally grown oxide layer and a diamond substrate to have OH-terminated surfaces. The hydroxyl groups OH groups may be introduced on the surface on the diamond surface using a hydroxylation step, e.g. by treating the surface with a mixture of sulfuric acid and hydrogen peroxide also known as a Piranha solution. Wetted OH-passivated surfaces may be brought in close contact with each other (Fig. 1B and 1C) and subjected to a low-temperature anneal to trigger a dehydration step (Fig. 1D) resulting in the formation of bonds between oxygen atoms at the surface of the oxide layer and carbon atoms at the surface of the diamond substrate (Fig. 1E).

[0049] The direct diamond bonding process works well for bonding (111) oriented diamond to a native or thermaly oxidized silicon substrate. However, it does not provide sufficiently high bonding strengths for directly bonding a (111) or (100) oriented diamond substrate to an oxide layer that is deposed on a silicon substate. Nor does it provide sufficiently high bonding strengths for bonding a (100) oriented diamond substrate to a thermal or native oxide on a substrate.

[0050] These are substantial disadvantages as diamond-on-insulator structures for optical devices in telecom or quantum computing preferably are based on a (100) oriented diamond substrate that is bonded with substantial bonding strength to a high-quality oxide layer that is formed on a base substrate using a low temperature deposition technique. Such structures can be post-processed in order to from high-quality diamond structures for telecommunications and quantum computing. For example, MEMS type photonic devices or a qubit inside a photonic cavity based on free-standing diamond structures require diamond-on-insulator structures with an supporting oxide layer between a handling substrate and the diamond substrate of one or more micrometers thickness. Inventors discovered that when using diamond substrate with a relatively rough surface between 1 ,5 and 10 nm bondings with substantial shear strengths between 2 and 10 MPa can be established between the surface of the diamond substrate and the oxide layer that is deposed on the substrate.

[0051] Fig. 2 depicts a flow chart of the direct bonding process according to an embodiment. The method may start with exposing a surface of a crystalline diamond substrate to a mixture of sulfuric acid and hydrogen peroxide to form an OH passivated diamond surface (step 202). The surface of the diamond substrate may be selected or prepared, e.g. cleaved and / or mechanically polished, to have an average surface roughness between 2 and 10 nm. Further, in some embodiments, the diamond substrate may be a (100) oriented diamond substrate. In other embodiment, the diamond substrate may be a (111) oriented substrate.

[0052] The method may further comprise a step of exposing a surface of an inorganic oxide layer on a substrate to an oxygen plasma to form OH passivated surface (step 204). In an embodiment, the oxide layer may be a metal oxide. In another embodiment, the oxide layer may be semiconductor oxide layer. In some embodiments, the oxide layer may be a deposited oxide layer using a deposition technique. In other embodiments, the oxide layer may be a thermal oxide or a native oxide. The passivated surfaces may be brought in direct contact with each other to form a bonded diamond substrate structure (step 206). A low temperature annealing step is then applied to the bonded diamond substrate structure (step 208) to provide a bonding between the substrates. The resulting structure may form a diamond substrate that is directly bonded to the oxide layer that is deposited on the substrate. Here, the term low temperature annealing refers to temperature treatments wherein the structure is heated between 100 and 250 °C.

[0053] Different substrates and materials may be used when performing the steps of Fig. 2. For example, different diamond stubstrates may be used, e.g. a (100) oriented crystalline diamond substrate or a (111) oriented crystalinne diamond substrate. Further, the base susbstrate supporting the oxide layer may be Si, SiC, SiN, SiGe, Ge, GasAs, GaN, InP, Cu, CuO, Al, AIN, Ti, TiN, TiO2, AI2O3, GaOx, MgO, Y3AI5O12, LiNbO3, LiTa3, ZnO, or any other suitable material. The oxide layer may be made of a metal oxide or semiconductor oxide. In another embodiment, the oxide layer may comprise one or more oxides of the following elements Si, Ge, As, Se, SB, Te, Bi, or Al. When using a deposited oxide layer, the thickness of the oxide layer may be selected between 5 nm and 500 micrometer depending on the particular application.

[0054] The inventors discovered that the roughness of the surface of the diamond substrate has an impact on the bonding strength between the two subsrates. Based on this insight a (100) oriented diamond substrate may be bonded to an oxide layer on a support substrate with a bonding strength of 2 MPa or higher. Further, a diamond substatre (100) or (111) oriented diamond substrate may be bonded to an oxide layer that is deposited on a support substrate. Thus, the bonding method of Fig. 2 may be used to realize diamond on insulator structures.

[0055] Fig. 3A-3B depict AFM pictures of surfaces of diamond substrates of different surface roughness. These two types of substrates have been used in the comparative experiments as described with reference to the embodiments in this disclosure. Fig. 3A shows the surface topology of a (100) oriented surface that has a relatively rough surface roughness between 3.51 - 4.48 nm (rms). Fig. 3B depicts the surface topology of a (100) oriented diamond surface having a relatively smooth surface roughness (rms) between 0.57 - 1.31 nm. The roughness of the sample may be measured using different techniques such a contact-type roughness meter which traces a probe across the surface of the target or a laser-based non-contact roughness meter which emits a laser beam onto the target and detects the reflected light to measure the roughness. The rougness referred to in this disclosure is referred to as the arithmetical mean roughness (Ra). This roughness is computed as the arithmetical mean value for a randomly sampled area, which is well-known in the field.

[0056] A diamond bonding experiment may include treating a (100) CVD diamond substrate (3.79 x 5.1 mm in size) of a predetermined surface rougness (in this example 4.48 nm) in a Piranha solution at a certain temperature and for a certain time period (in this example 75 °C for 10 minutes). A SiC>2 layer of a predetermined thickness (in this example 300 nm) may be deposited using a deposition process, such as a PECVD process, on a (100) silicon wafer. The surface of the SiC>2 layer may be subjected to a surface activation process by an oxygen plasma for 1 hour. The two substrates were contacted in an ambient environment without applying pressure and this structure was cooled for three days. The bonded structure is subsequently annealed at a temperature of 200 °C for 24 hours. No pressure was applied during the annealing.

[0057] Fig. 4 depicts a graph of the shear strength of the bonding between a (100) diamond substrate and a deposited SiC>2 layer (in this example a PECVD deposited as a function of the treatment time of the diamond surface in the Piranha solution for different initial surface roughnesses of the diamond surface. Here, the shear strength of the bonding may be measured using a standard measurement setup as described above with reference to Fig. 3. Two different types of diamond substrates were used namely a relatively thick (500 micron) diamond substrate (3.7 mm x 4 mm x 0.5 mm) denoted by the triangular and diamond shaped points in the graph and a relatively thin (50 micron) diamond substrate (3.7 mm x 4 mm x 0.05 mm) denoted by the circular dot in the graph. As shown in the figure by the diamond shaped points, when using a diamond substrate with a low surface roughness of 1.31 nm, no boding was possible irrespective of the treatment time. In contrast, when using a diamond surface with a rough surface of 3 nm - 4.5 nm, for the 500 micron thick diamond substrate a shear strength of approximately 4.8 MPa using a 10 min treatment time and 9.6 MPa at a 30 min treatment time was find. Similarly, for the 50 micron thick diamond substrate a bonding strength of approximately 2. MPa was found. This figure shows bonded structures can be obtained wherein the shear strength between the diamond substrate and the oxide covered substrate is between 1 ,5 and 12 Mpa.

[0058] Fig. 5 depicts a plot of the surface roughness of a diamond substrate after treatment as a function of the treatment time. This plot shows that starting with with an initial surface roughness of 3.5-5.5 nm (triangular dots) the roughness after treatment decreases from 3.5 nm after 10 min to approximately 1 nm after 30 min, which is close to the initial roughness of the smooth substrate. In the prior art it has been reported that the surface roughness of an initially very smooth surface (0.3 nm) increases with the surface treatment using the same Piranha solution and temperature, which is opposite to the trend of decreasing surface roughness when starting with a diamond surface that as initially rough surface sample as shown in Fig. 5.

[0059] Fig. 6A-6C depict XPS analysis results for analyzing the elemental composition on the diamond surface during the Piranha solution treatment. Here, Fig. 6A depics the carbon 1s peak, Fig. 65B depicts the oxygen 1s peak en Fig. 6C depicts the S2p3 peak. These graphs shown that for a treatement time of 10 min, when increasing the temperature from 65 °C to 75 °C, the intensity of S2p3 increased significantly, while the other peaks show no significant change. This would suggest residual sulfuric acid or sulfur atoms on the diamond surface after the cleaning. When increasing the treatment time up to 30 min, however, the intensity of sulfur decreased and, the intensity of carbon 1s and oxygen 1 s peaks increase. This suggests that the residual sulfur atoms become negligible and hydroxyl groups have been effectively attached on the diamond surface.

[0060] Fig. 7 illustrates OH passivantion of a diamond surface according to an embodiment. In particular, this figure illustrates a surface passivation scheme associated with experimental results as described with reference to Fig. 4-6. In particular, the figure illustrates an OH passivation process of a surface for a diamond substrate surface of a predetermined roughness (step 702), in particular a roughness between 2 and 10 nm. When exposed to the mixture of sulfuric acid and hydrogen peroxide, the surface of the diamond subsrate will be etched aggressively. During the process, the relatively rough surface provides a relatively large effective surface for the sulfuric elements to adhere to the diamond surface (step 704). Then, during the etching process residual SO4 groups will be slowly replaced by hydroxyl groups. This process is realtivey slow and preferably requires a surface treatment of 10 minutes or more. Hence, the relatively rough surface supports the formation of Si-OH bonds as shown in steps 704 and 706. The end result of the process may be a relatively smooth (roughness in the order of one nanometer) OH passivated diamond surface (step 708). The large amount of OH groups, will provide a strong bonding of diamond to the oxide layer. This mechanism is supported by the experimental date of Fig. 6.

[0061] In contrast, when using a diamond substrate with an initially smooth surface the amount of OH bonds that can adhere to the diamond surface will be limited. This is schematically illustrated in Fig. 8 which shows the steps of OH passivation of a diamond surface using an OH passivation scheme known from the prior art. When starting the passivatioin process with an initially smooth surface (step 802) (e.g. a roughness of the order of 1 nm) the interaction (reaction) of the mixture of sulfuric acid and hydrogen peroxide with the diamond surface will be small so that during the passivation process only a small amount of SO4 groups adhere to the diamond surface and hence only a small amount of OH groups can be formed that can provide bonding with the oxide surface (steps 804-806). When using such OH passivated diamond surface, the bonding strength will be weaker than that of the initially rough diamond surfaces as shown in Fig. 8.

[0062] The embodiments in the application enable bonding of (100) type diamond substrates to an oxide layer that is deposited on a base layer to produce high-quality diamond on insulator structures. Fig. 9 depicts the formation of a thin-film diamond on insulator structure according to an embodiment. Fig. 9A depicts the process of direct bonding of a base substrate 902 which is covered by an oxide layer 904 to a substrate 906 according to the embodiments as described above with reference to Fig. 2-7, resulting in a bonded diamond structure - a diamond on silicon structure - as depicted in Fig. 9B, wherein bondings with substantial shear strengths between 4 and 10 MPa can be established between the surface of a (100) type diamond substrate and the oxide layer that is deposed on the substrate. Typically, the thickness of the diamond substrate may be between 1 and 500 micron, preferably between 10 and 500 micron, more preferably between 20-500 micron. Then, in some embodiments, a substrate thinning method may be used to reduce the thickness of the bonded diamond substrate to a thickness between that is suitable for manufacturing optical devices based on a thinned diamond-on-insulator structor for example a thickness between 10 and 600 nm, preferably between 20 and 400 nm.

[0063] To that end, a well-known substrate separation method based on ion implantation 908 may be used so separate the bonded diamond substrate into two diamond substrates. For example, a layer of hydrogen ions or a combination of helium and hydrogen ions may be implanted in the the diamond substrate at a particular height above the oxide layer, wherein the implanted layer is parallel to the surface of the diamond substrate. The implanted hydrogen layer will create a weak link in the diamond substrate so that when annealing the bonded structure comprising the diamond substrate with the hydrogen implanted layer, the diamond substrate will split in two at the height of the implanted hydrogen layer, leaving a thin diamond layer 906i bonded to the oxide layer 904. This way, bonded diamond-on-insulator structures can be realized wherein the bonded diamond layer is a thin film layer with a thickness of less than 1 micron, preferably less than 500 nm, more preferably less than 300 nm that is bonded to a deposited oxide layer.

[0064] The bonded thin-film diamond-on-insulator structure that is obtained by the bonding and separation process as described with reference to Fig. 9 may be further processed so that a structure and / or device can be formed. An example of such process steps are illustrated in Fig. 10, which may start with a polishing step (Fig. 9A) in which a polishing technique 1008, such as chemical-mechanical polising (CMP), is used to planarize the diamond surface to a flatness resulting in a bonded diamond structure including a substrate with an oxide layer and thin-film diamond layer bonded to the oxide layer.

[0065] This structure may be used to manufacture (part of) a device, wherein the manufacturing method may include steps of structuring the diamond layer. For example, a resist layer may be deposited over the diamond layer (Fig. 10B), which may be structured using well-known semiconductor lithography techniques (Fig. 10C). As shown in Fig. 10D, a structured resist layer may be used to transfer a patterned structure 1018 into the diamond layer using a first dry etch step 1016 , using gases, e.g. oxygen and subsequently argon and chlorine or the like, resulting in a patterned diamond thin film layer 1020. Then, a second (isotropic) etch step 1022 may be used to etch part of the oxide layer under the patterned diamond layer away thus forming a free-standing diamond structure 1022 on a support substrate 1004. Such free-standing diamond structure may be used in a spin qubit inside a photonic cavity of diamond.

[0066] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0067] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments

Claims

CLAIMS1. A bonded diamond structure comprising: an inorganic oxide layer provided on a base substrate; and, a (100) oriented diamond substrate directly bonded to the oxide layer, the bonding being characterized by a shear strength equal to or larger than 2 MPa.

2. A bonded diamond structure according to claim 1 wherein the bonding is further characterized by atomic bonding between oxygen atoms at the surface of the oxide layer and carbon atoms at the surface of the diamond substrate.

3. A bonded diamond structure according to claims 1 or 2 wherein the oxide layer is a deposited oxide layer, preferably the deposited oxide layer being a non- stochiometric oxide layer.

4. A bonded diamond structure according to claim 3 wherien the thickness of the oxide layer is between 50 nm and 500 micrometer.

5. A bonded diamond structure according to any of claims 1-4 wherein the base substrate is of a metal or a semiconductor and / or wherein the inorganic oxide layer is a metal oxide layer or a semiconductor oxide layer, preferably the metal oxide layer or the semiconductor oxide layer being an oxide that is different from the oxide of the metal or semiconductor of the base substrate.

6. A bonded diamond structure according to claims 1 or 2 wherein the oxide layer is a thermal oxide layer or native oxide layer, the thermal oxide layer or native oxide layer being formed in the surface of the base substrate.

7. A bonded diamond structure comprising: an inorganic oxide layer deposited on a base substrate, the deposited inorganic oxide layer being a non-stochiometric oxide layer; and, a diamond substrate directly bonded to the oxide layer, the bonding being characerized by atomic bonding between oxygen atoms at the surface of the oxide layer and carbon atoms at the surface of the diamond layer and the bonding being characterized by a shear strength equal to or larger than 2 MPa.

8. A bonded diamond structure according to claim 7, wherein the diamond substrate is an (100) oriented diamond substrate or a (111) oriented diamond substrate.

9. A bonded diamond structure according to any of claims 1-8 wherein the thickness of the oxide layer is between 50 nm and 500 micrometer, preferably between 50 nm and 500 nm.

10. A bonded diamond structure according any of claims 1-9 wherein the inorganic oxide layer is a metal oxide layer or a semiconductor oxide layer.

11. A bonded diamond structure according to any of claims 1-10 wherein the thickness of the diamond substrate is less than 10 micron, preferably less than 1 micron, more preferably less than 500 nm, even more preferably less than 200 nm..

12. A bonded diamond structure according to claim 11 wherein a pattern is etched into the diamond substrate to form a patterned diamond substrate bonded to the base substrate.

13. A bonded diamond structure according any of claims 1-12 wherein material of the base susbstrate supporting the oxide layer is one of: Si, SiC, Si N , SiGe, Ge, GasAs, GaN, InP, Cu, CuO, Al, AIN, Ti, TiN, TiO2, AI2O3, GaOx, MgO, Y3AI5O12, LiNbO3, LiTa3, ZnO.

14. A bonded diamond structure according to any of claims 1-13 wherein the base substrate comprises integrated circuits.

15. Method of fabricating a bonded diamond structure comprising: exposing a surface of a crystalline diamond substrate to a mixture of sulfuric acid and hydrogen peroxide to form an OH passivated surface, the surface of the diamond substrate having an average surface roughness between 1.5 and 10 nm, preferably between 2 and 10 nm; exposing a surface of an inorganic oxide layer provided on a substrate to an oxygen plasma to form OH passivated surface bringing the passivated surfaces in direct contact with each other to form a bonded diamond structure; and,applying a low temperature annealing step to the bonded diamond structure.

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