Large-size single-crystal diamond wafer and method for manufacturing the same

Abstract

The application provides a preparation method of a large-size single-crystal diamond wafer, comprising the following steps: S1, growing a single-crystal epitaxial layer of iridium on a sapphire substrate in an A plane; S2, growing a single-crystal epitaxial layer of cubic boron nitride on the single-crystal epitaxial layer of iridium; and S3, growing a diamond film on the single-crystal epitaxial layer of cubic boron nitride. The preparation method reduces the lattice mismatch between the substrate and the diamond layer, and has low preparation cost.

Description

Technical Field

[0001] This invention relates to a large-size single-crystal diamond wafer and its preparation method, belonging to the field of large-size diamond wafer preparation technology. Background Technology

[0002] Diamond's excellent physicochemical properties make it widely used in many fields. Diamond is an indirect bandgap semiconductor material with a bandgap of approximately 5.2 eV, a thermal conductivity as high as 22 W / (cmK), and room-temperature electron and hole mobilities as high as 4500 cm⁻¹. 2 / (Vs) and 3380cm 2 Diamond's energy density (Vs) is significantly higher than that of third-generation semiconductor materials GaN and SiC. Therefore, diamond has broad application prospects in high-power power electronic devices operating at high temperatures and high-frequency high-power microwave devices. In addition, due to its large exciton binding energy (80 meV), diamond can achieve high-intensity free exciton emission (emission wavelength of about 235 nm) at room temperature, which has great potential in the fabrication of high-power deep ultraviolet light-emitting diodes. It also plays an important role in the development of extreme ultraviolet, deep ultraviolet, and high-energy particle detectors.

[0003] Meanwhile, breakthroughs in large-size, high-quality single-crystal diamond are a major bottleneck restricting its application. Regarding growth technology, with the development of large-size synthetic diamond material preparation technology, especially with the in-depth research on high-temperature high-pressure (HTHP) chemical vapor deposition (CVD), obtaining larger-size HTHP single-crystal diamonds places extremely stringent requirements on equipment, leading to a significant increase in equipment costs. Since CVD synthesis of diamond breaks the equipment's limitations on substrate size, providing conditions for large-area single-crystal diamond growth, CVD has become the preferred solution for high-purity, large-area production. Currently, commonly used CVD methods for synthesizing single-crystal diamond mainly include microwave plasma CVD (MPCVD). Microwave plasma chemical vapor deposition (MPCVD) single-crystal diamond growth technology generally uses metal as the cavity. Due to its advantages such as pollution-free microwave energy, pure gas raw materials, and the absence of catalysts and impurities, the quality of diamond is improved, making it stand out among many diamond preparation methods and becoming one of the most promising technologies for preparing large-size, high-quality single-crystal diamonds. This also greatly expands the application potential of diamond materials in high-tech fields.

[0004] However, these traditional methods for growing large-area single-crystal diamond wafers present several challenges. One major challenge is the mismatch in lattice constants between the substrate and the diamond layer, making it difficult to produce high-quality diamond wafers. Another problem with traditional methods is the need for improved microwave-enhanced chemical vapor deposition (MPCVD) chambers with DC bias, which increases production costs and complexity. Summary of the Invention

[0005] This invention provides a large-size single-crystal diamond wafer and its preparation method, which can effectively solve the above-mentioned problems.

[0006] This invention is implemented as follows:

[0007] A method for preparing a large-size single-crystal diamond wafer includes the following steps:

[0008] S1, Iridium single-crystal epitaxy is grown on sapphire in plane A;

[0009] S2, growing cubic boron nitride single-crystal epitaxy on iridium single-crystal epitaxy;

[0010] S3, diamond film is grown on a single crystal epitaxial layer of cubic boron nitride.

[0011] As a further improvement, the growth in step S1 is performed using an electron beam evaporation method or a sputtering method.

[0012] As a further improvement, the deposition conditions for the electron beam evaporation method are: substrate temperature of 800-1000℃ and vacuum degree <10. -9 Torr.

[0013] As a further improvement, the sputtering method involves sputtering iridium using a DC bias sputtering gun, with the following deposition conditions: vacuum degree <5mTorr, substrate temperature 800-1000℃, and a negative substrate bias voltage of 50-300V applied.

[0014] As a further improvement, the growth in step S2 is carried out by sputtering, and the deposition conditions are: the substrate temperature is fixed at 600-800℃, and a negative substrate bias voltage of 50-300V is applied.

[0015] As a further improvement, the growth in step S3 is performed using microwave plasma-enhanced chemical vapor deposition.

[0016] As a further improvement, the microwave plasma-enhanced chemical vapor deposition method is as follows: deposition is performed on a substrate preheated to 700°C in a mixed hydrogen methane atmosphere, followed by deposition at a deposition temperature of 800-1100°C, without applying a substrate bias voltage.

[0017] A large-size single-crystal diamond wafer prepared by the above method.

[0018] The beneficial effects of this invention are:

[0019] This invention utilizes cubic boron nitride (c-BN) as a buffer layer. The lattice constant of the c-BN layer is closer to that of diamond, reducing the lattice mismatch between the substrate and the diamond layer. This method provides a practical and effective way to produce large-area single-crystal diamond wafers with better quality and performance than conventional methods.

[0020] The method of the present invention does not require an improved microwave enhanced chemical vapor deposition (MPCVD) chamber with DC bias, thus reducing production costs and complexity. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure for growing large-size single-crystal diamond wafers according to an embodiment of the present invention.

[0023] Figure 2 This is the XRD pattern of the sample obtained in step S2 of the preparation method of large-size single-crystal diamond wafers provided in Embodiment 1 of the present invention.

[0024] Figure 3 This is an XRD pattern of a large-size single-crystal diamond wafer sample provided in Embodiment 1 of the present invention.

[0025] Figure 4 This is an optical photograph of a large-size single-crystal diamond wafer provided in Embodiment 1 of the present invention.

[0026] Figure 5 This is an AFM image of a large-size single-crystal diamond wafer provided in Embodiment 1 of the present invention.

[0027] Figure 6 This is an optical microscope image of a large-size single-crystal diamond wafer provided in Embodiment 1 of the present invention.

[0028] Figure 7 These are photographs and SEM images of the diamond wafer sample provided in Comparative Example 1 of this invention. In the images, A is a photograph and B is an SEM image. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] like Figure 1 As shown, this embodiment of the invention provides a method for preparing a large-size single-crystal diamond wafer, comprising the following steps:

[0031] S1, grow a single-crystal epitaxial layer of iridium (Ir) on the A-plane sapphire; S2, grow a single-crystal epitaxial layer of cubic boron nitride (c-BN) on the single-crystal epitaxial layer of iridium; S3, grow a diamond film on the single-crystal epitaxial layer of cubic boron nitride.

[0032] As a further improvement, the growth in step S1 is performed using electron beam evaporation or sputtering. The deposition conditions for the electron beam evaporation method are: substrate temperature 800-1000℃, vacuum degree <10. -9 Torr. The sputtering method involves sputtering iridium using a DC bias sputtering gun. The deposition conditions are: vacuum degree <5mTorr, substrate temperature 800-1000℃, and a negative substrate bias voltage of 50-300V applied during the deposition process, which helps to better form crystal nuclei on the sapphire substrate.

[0033] As a further improvement, the growth in step S2 is performed using sputtering. Since c-BN has a similar cubic crystal structure and lattice parameters, it can be grown on the iridium layer by sputtering deposition. A pure iridium target is used to grow c-BN, and a substrate bias voltage is applied. Applying a negative substrate bias voltage of 50-300V during deposition helps to form a cubic crystal structure, rather than hexagonal boron nitride. The substrate temperature is kept constant at 600-800°C during deposition.

[0034] As a further improvement, the growth in step S3 employs microwave plasma-enhanced chemical vapor deposition (MPCVD). MPCVD involves deposition on a substrate preheated to 700°C in a mixed hydrogen-methane atmosphere, followed by deposition at a temperature of 800-1100°C. This method eliminates the need for a DC bias voltage on the substrate, producing large-area single-crystal diamond wafers with superior quality and performance compared to traditional methods, thus reducing production costs and complexity.

[0035] In this embodiment of the invention, the lattice constant difference between iridium and diamond is 7.03%, wherein the lattice constant of iridium is [missing value]. The lattice constant of diamond is Because c-BN has The lattice constant of the c-BN layer is closer to that of diamond. Therefore, adding a c-BN intercalation layer as a buffer between the iridium and diamond layers can gradually match the lattice constant, reducing the lattice mismatch between the substrate and the diamond layer. Furthermore, a key problem with using iridium as a substrate in conventional methods is its higher coefficient of thermal expansion (CTE) compared to diamond, which can lead to structural defects and degrade the quality of the diamond film over time. In this invention, the CTE of c-BN is more similar to that of iridium than that of diamond, ensuring that the diamond film maintains its integrity and quality over time. This method provides a practical and effective way to produce large-area single-crystal diamond wafers with better quality and performance than conventional methods.

[0036] This invention provides a large-size single-crystal diamond wafer prepared by the above-described method.

[0037] Example 1

[0038] This invention provides a method for preparing a large-size single-crystal diamond wafer, comprising the following steps:

[0039] S1, Iridium single-crystal epitaxy is grown on sapphire in plane A; the growth is performed by electron beam evaporation, and the deposition conditions are: substrate temperature 950℃, vacuum degree <10 -9 Torr.

[0040] S2, cubic boron nitride single-crystal epitaxy is grown on iridium single-crystal epitaxy; the growth is carried out by sputtering method, and the deposition conditions are: the substrate temperature is fixed at 700℃C and a negative substrate bias voltage of 180V is applied.

[0041] S3, diamond film is grown on a cubic boron nitride single-crystal epitaxial layer. Growth is performed using microwave plasma-enhanced chemical vapor deposition. Deposition is carried out in a mixed hydrogen-methane atmosphere on a substrate preheated to 700°C, followed by deposition at a further temperature of 1010°C, without applying a substrate bias voltage.

[0042] Comparative Example 1

[0043] The difference from Example 1 is that step S2 is omitted, and cubic boron nitride single-crystal epitaxy is not grown on the iridium single-crystal epitaxy.

[0044] The performance tests of the samples in Example 1 and Comparative Example 1 are as follows: Figures 2 to 7 As shown.

[0045] like Figure 2 As shown, the XRD pattern of the sample obtained in step S2 of the fabrication method of the large-size single-crystal diamond wafer in Example 1 shows two distinct peaks corresponding to the sapphire substrate (1120) and the iridium buffer layer (002) after iridium deposition on the sapphire substrate. The peak at a 2θ angle of approximately 37.5° corresponds to the (1120) plane of the sapphire substrate. The peak at a 2θ angle of approximately 47.5° corresponds to the (002) plane of the iridium buffer layer. These peaks confirm the successful growth of the iridium buffer layer on the A-side sapphire substrate.

[0046] like Figure 3 As shown, the X-ray diffraction (XRD) pattern of the large-area single-crystal diamond wafer of Example 1 reveals the crystallization peaks of the materials used to produce the large-area single-crystal diamond wafer, including sapphire (1120), Ir (002), c-BN (200), and Ir (111). The position, intensity, and shape of each peak provide important information about the crystal structure and orientation of each material, which is crucial for determining the optimal growth conditions for the diamond layer and ensuring good alignment of the crystal structure of the diamond layer with the underlying substrate and buffer layer. A peak for sapphire (1120) was observed at 37.5 degrees, a peak for Ir (002) at 47.5 degrees, a peak for c-BN (200) at 43 degrees, and a peak for Ir (111) at 41.6 degrees. The presence of distinct peaks for each material indicates that the crystal structure of each layer is well aligned with the underlying layer, suggesting that the c-BN / Ir / sapphire structure can be successfully grown and used as a substrate for producing large-area single-crystal diamond wafers.

[0047] In summary, the XRD data support the effectiveness of the method proposed in this invention, providing valuable information for optimizing the growth process and ensuring the quality and performance of the final diamond product.

[0048] like Figure 4As shown in the photographs of the large-size single-crystal diamond wafer of Example 1, a cBN / Ir / sapphire sample was used as a substrate for the growth of high-quality, large-area single-crystal diamond wafers. The sample is displayed on a 2-inch a-facet sapphire wafer, with a clearly visible cBN / Ir buffer layer on top of the sapphire substrate. An iridium layer is also visible between the cBN layer and the sapphire substrate. The surface of the buffer layer appears smooth and uniform, without any visible cracks or defects that could potentially affect the growth of the diamond layer. This indicates that the growth process was stable and consistent, resulting in a high-quality buffer layer highly suitable for diamond growth. Overall, the photographs provide visual evidence of the successful growth of the cBN / Ir / sapphire structure and demonstrate the potential of using this method to produce large-area single-crystal diamond wafers.

[0049] like Figure 5 As shown, atomic force microscopy (AFM) data from the large-area single-crystal diamond wafer of Example 1 provides important information about the surface morphology and roughness of the cBN / Ir / sapphire structure used as a substrate for producing large-area single-crystal diamond wafers. The AFM data shows well-defined step flows on the surface of the cBN / Ir / sapphire structure, following a 7-degree cut of the A-plane sapphire substrate. Furthermore, the average surface roughness measured by AFM is 0.815 nm. These characteristics are important parameters for producing large-area single-crystal diamond wafers because they affect the quality and performance of the diamond layers. A smooth and uniform substrate surface is ideal because it minimizes defects and dislocations in the diamond layers, resulting in higher quality and more reliable final products. The AFM data, including step flow and surface roughness measurements, supports the effectiveness of the method proposed in this invention and provides valuable information for optimizing the growth process and ensuring the quality and performance of the final diamond product.

[0050] like Figure 6 As shown, optical microscopic images of a large-size single-crystal diamond wafer from Example 1 reveal the surface of the diamond layer grown on the cBN / Ir / sapphire sample. The surface appears smooth and uniform, with noticeable signs of step flow after a 7-degree cut on the A-side sapphire substrate. The step flow visible in the optical microscopic images is consistent with the results obtained from AFM analysis of the sample. The average roughness obtained from the AFM data is 0.815 nm, indicating a highly uniform and smooth surface with minimal roughness. Overall, the optical microscopic images provide further evidence of the high quality of the diamond layer grown on the cBN / Ir / sapphire sample using the method proposed in this invention. The smooth and uniform surface observed in the images indicates that the diamond layer is well-bonded to the cBN / Ir / sapphire structure, and that this method can be used to produce high-quality diamond layers on a variety of substrate sizes.

[0051] like Figure 7 As shown, a photograph of the sample in Comparative Example 1 ( Figure 7 A) shows an attempt at diamond growth on Ir / a-planar sapphire for comparison with diamond growth on cBN / Ir / a planar sapphire.

[0052] The semi-solid diamonds grown in this study were produced under growth conditions of CH4: 20 sccm and H2: 500 sccm without substrate bias. The substrate used was Ir / sapphire, and SEM images were taken. Figure 7 B) To confirm the presence of semi-diamond diamond. Due to the lack of substrate bias, semi-diamond was generated during the growth process. Since the substrate was not biased during growth, nucleation on the substrate was unfavorable, and secondary nucleation (in the form of semi-solid diamond) occurred instead. Therefore, attempts to grow single-crystal diamond using the same growth conditions were unsuccessful.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for preparing a large-size single-crystal diamond wafer, characterized in that, Includes the following steps: S1, Iridium single-crystal epitaxy is grown on sapphire in plane A; the growth is performed using electron beam evaporation, and the deposition conditions for electron beam evaporation are: substrate temperature 800-1000℃, vacuum degree <1×10⁻⁶. -9 Torr; S2, a cubic boron nitride single crystal epitaxial layer is grown on an iridium single crystal epitaxial layer; the growth is carried out by sputtering, and the deposition conditions are: the substrate temperature is fixed at 600-800 ℃, and a negative substrate bias voltage of 50-300 V is applied. S3, a diamond film is grown on a cubic boron nitride single crystal epitaxial layer; the growth is performed using microwave plasma-enhanced chemical vapor deposition; the microwave plasma-enhanced chemical vapor deposition is performed as follows: deposition is carried out on a substrate preheated to 700 °C in a mixed hydrogen methane atmosphere, and then deposition is carried out at a deposition temperature of 800-1100 °C without applying a substrate bias voltage.

2. A large-size single-crystal diamond wafer prepared by the method of claim 1.

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