Method for improving nucleation quality and density of monocrystal diamond based on special support structure

Abstract

The invention discloses a method for improving the nucleation quality and density of single crystal diamond based on a special support structure, and relates to the field of single crystal diamond heteroepitaxy, the method comprises the steps that a composite substrate is placed on the upper surface of a molybdenum support for bias enhanced nucleation, and the molybdenum support is of a circular truncated cone structure. By utilizing the circular-truncated-cone-shaped molybdenum support, on one hand, the distance from plasma glow to the Ir surface of the composite substrate is reduced, the effective contact area between the direct-current glow and the Ir surface is increased, and the nucleation quality and density are improved; and on the other hand, the circular-truncated-cone-shaped molybdenum support can restrain the direct-current glow on the upper surface of the circular-truncated-cone-shaped molybdenum support, underflow of the direct-current glow is effectively hindered, damage to the Ir film caused by stroboflash possibly occurring in the direct-current glow is avoided, and the nucleation stability is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of single crystal diamond heteroepitaxial growth, and in particular relates to a method for improving the quality and density of single crystal diamond nucleation based on a special support structure. Background Art

[0002] Compared to traditional silicon, wide-bandgap semiconductors are more suitable for the production of high-voltage, high-frequency, and high-power semiconductor devices and are considered key players in materials innovation in the post-Moore era. The exceptional performance of wide-bandgap semiconductors, particularly the large bandgap, high thermal conductivity, and high mobility of single-crystal diamond, combined with its far superior electrical performance and stability compared to polycrystalline diamond, makes them ideal for the development of next-generation high-power and high-frequency electronic devices. Although the small size and high cost of single-crystal diamond have limited its application, advances in heteroepitaxial growth technology have provided a new path for the production of high-quality, large-scale single-crystal diamond, revolutionizing the application of diamond in the electronics industry.

[0003] Heteroepitaxial growth, the epitaxial growth of single-crystal diamond on a non-diamond single-crystal substrate, requires the primary consideration of substrate selection. The chosen substrate must meet the following requirements: 1) high crystal quality; 2) large size; 3) high melting point; 4) minimal lattice mismatch with diamond; 5) low thermal expansion coefficient; and 6) stable properties. Researchers have discovered that the optimal solution to date is to grow rare and expensive Ir thin films on common oxide substrates (e.g., MgO, SrTiO3, Al2O3), and then heteroepitaxially grow single-crystal diamond films on the resulting composite substrates (e.g., Ir / MgO, Ir / SrTiO3, Ir / Al2O3, etc.).

[0004] Heteroepitaxial growth of single-crystal diamond on composite substrates typically involves two stages: first, forming uniformly oriented, aligned island-shaped diamond nuclei on the Ir surface through a bias-enhanced nucleation (BEN) process; then, rapid growth occurs to form a continuous single-crystal film. However, single-crystal diamond is prone to DC glow instability during the BEN nucleation process, which severely affects the quality and density of the nuclei formed, resulting in low nucleation efficiency. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a method for improving the quality and density of single crystal diamond nucleation based on a special support structure. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0006] The present invention provides a method for improving the quality and density of single-crystal diamond nucleation based on a special support structure, comprising: placing a composite substrate on the upper surface of a molybdenum support for bias-enhanced nucleation, wherein the molybdenum support is a truncated cone structure, the diameter of the upper surface of the molybdenum support is adapted to the size of the composite substrate, the diameter of the lower surface of the molybdenum support is 2 to 2.5 times the diameter of the upper surface, and during the nucleation process, the distance from the plasma glow to the upper surface of the composite substrate is 30 to 50 mm.

[0007] In one embodiment of the present invention, the composite substrate is Ir / MgO, Ir / SrTiO 3 or Ir / Al 2 O 3 .

[0008] In one embodiment of the present invention, the composite substrate is placed on the upper surface of a molybdenum support for bias-enhanced nucleation, and the process also includes: preparing an Ir metal film on an oxide substrate using a magnetron sputtering process to form the composite substrate.

[0009] In one embodiment of the present invention, placing the composite substrate on the upper surface of a molybdenum support for bias-enhanced nucleation includes:

[0010] Placing the molybdenum holder on a diamond deposition substrate in a chamber of an equipment, and placing the composite substrate on the molybdenum holder;

[0011] The chamber is evacuated, and hydrogen is introduced to control the gas pressure in the chamber and the microwave power to activate the plasma glow;

[0012] Etching and cleaning the surface of the Ir metal film of the composite substrate using hydrogen;

[0013] Methane and nitrogen gases are introduced into the chamber, and a DC bias is turned on to perform bias-enhanced nucleation.

[0014] In one embodiment of the present invention, the chamber is evacuated to a vacuum degree of 2×10 -2 ~7×10 - 2 torr.

[0015] In one embodiment of the present invention, etching and cleaning the surface of the Ir metal film of the composite substrate using hydrogen gas includes:

[0016] The pressure in the chamber is increased to 23-28 torr, the microwave power is increased to 1000-1400 W, the temperature of the composite substrate reaches 750-850° C., and the surface of the Ir metal film of the composite substrate is etched and cleaned with hydrogen for 20 minutes.

[0017] In one embodiment of the present invention, the volume fraction of methane is 4% to 5%, and the volume fraction of nitrogen is 0.003% to 0.005%.

[0018] In one embodiment of the present invention, the DC bias voltage ranges from 190V to 240V.

[0019] In one embodiment of the present invention, after placing the composite substrate on the upper surface of the molybdenum holder for bias-enhanced nucleation, the method further comprises: in-situ power-off growth of single crystal diamond.

[0020] In one embodiment of the present invention, in-situ power-off epitaxial growth of single crystal diamond comprises:

[0021] After the nucleation is completed, the DC bias is turned off, the content of the methane gas is reduced, the content of the nitrogen gas is increased, and the epitaxial growth of the single crystal diamond is started;

[0022] After the growth is completed, the methane and nitrogen gas filling valves are closed to reduce the gas pressure and microwave power in the chamber;

[0023] After the plasma glow is extinguished, the hydrogen filling valve is closed to evacuate the chamber;

[0024] Nitrogen is introduced into the chamber to atmospheric pressure to complete heteroepitaxial growth of single crystal diamond.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The method of the present invention for improving the quality and density of single crystal diamond nucleation based on a special support structure utilizes a truncated cone-shaped molybdenum support. On the one hand, the distance from the plasma glow to the Ir surface of the composite substrate is reduced, thereby increasing the effective contact area between the DC glow and the Ir surface and improving the quality and density of nucleation. On the other hand, the truncated cone-shaped molybdenum support can confine the DC glow to the upper surface of the truncated cone-shaped molybdenum support, effectively preventing the underflow of the DC glow, avoiding the possible stroboscopic damage of the DC glow to the Ir film, and improving the stability of nucleation.

[0027] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following preferred embodiments are specifically cited and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is an example diagram of a frustum-shaped molybdenum support provided by an embodiment of the present invention.

[0029] Figure 2 A comparison diagram of DC glow in the bias-enhanced nucleation process provided by an embodiment of the present invention.

[0030] Figure 3A comparison chart of the mass and density of single crystal diamond nuclei provided in an embodiment of the present invention with and without a truncated cone-shaped molybdenum support for nucleation. DETAILED DESCRIPTION

[0031] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the following is a detailed description of a method for improving the quality and density of single crystal diamond nucleation based on a special support structure proposed in accordance with the present invention, in combination with the accompanying drawings and specific embodiments.

[0032] The aforementioned and other technical contents, features, and effects of the present invention are clearly presented in the following detailed description of the specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a deeper and more specific understanding of the technical means and effects adopted by the present invention to achieve the intended purpose can be obtained. However, the accompanying drawings are provided for reference and illustration purposes only and are not intended to limit the technical solutions of the present invention.

[0033] An embodiment of the present invention provides a method for improving the quality and density of single-crystal diamond nucleation based on a special support structure, comprising: placing a composite substrate on the upper surface of a molybdenum support for bias-enhanced nucleation, wherein the molybdenum support is a truncated cone structure, the upper surface diameter of the molybdenum support is adapted to the size of the composite substrate, and the lower surface diameter of the molybdenum support is 2 to 2.5 times the upper surface diameter. During the nucleation process, the distance from the plasma glow to the upper surface of the composite substrate is 30 to 50 mm.

[0034] It's understandable that the size of the top surface of the truncated cone-shaped tray is determined by the dimensions of the composite substrate. It serves to support the composite substrate while confining the DC glow to the composite substrate's surface as much as possible. The larger diameter of the bottom surface of the truncated cone-shaped tray increases the contact area between the tray and the deposition substrate, effectively enhancing heat dissipation. The height of the truncated cone-shaped tray adapts to the equipment cavity, minimizing the distance the plasma glow needs to reach the sample surface and enhancing stability. During the nucleation process, the tall tray brings the composite substrate closer to the top plate, increasing the contact area between the DC glow and the sample while confining the plasma glow, preventing it from underflowing and ensuring DC glow stability.

[0035] See Figure 1 , Figure 1 An example diagram of a truncated cone type molybdenum support provided by an embodiment of the present invention is shown in FIG. Figure 1 The upper surface diameter of the truncated cone-shaped molybdenum support is 20 mm, the height is 20 mm, and the lower surface diameter is 50 mm.

[0036] Optionally, the composite substrate is Ir / MgO, Ir / SrTiO3 or Ir / Al2O3.

[0037] In this embodiment, a frustoconical molybdenum holder was chosen for nucleation because molybdenum is a perfect material that is simultaneously fire-resistant, clean, conductive, and deformation-resistant. It protects the sample without disrupting experimental conditions in extremely high temperatures and complex electromagnetic environments, making it an ideal choice for diamond growth equipment. Furthermore, the slope of the frustoconical holder, compared to the vertical slope of a cylindrical holder, helps rebound the accelerated plasma within the chamber back to the center, rather than colliding with the vertical side of the cylindrical holder and sliding directly downward. Furthermore, the sloped surface forces particles attempting to escape downward to undergo repeated collisions and rebounds, each collision consuming energy and ultimately confining the particles to the top region. The frustoconical holder also alters the gas flow within a small area of ​​the chamber, creating a small upward airflow at the slope. This airflow lifts some of the glow particles and prevents them from settling downward.

[0038] In this embodiment, the composite substrate is placed on the upper surface of a molybdenum support for bias-enhanced nucleation, and the process previously includes: preparing an Ir metal film on an oxide substrate using a magnetron sputtering process to form the composite substrate.

[0039] Alternatively, the oxide substrate may be MgO, SrTiO 3 or Al 2 O 3 .

[0040] Specifically, an Ir target with a mass purity greater than 99.99% was selected as the sputtering target, and the magnetron sputtering conditions were set as follows: substrate temperature was 780°C, vacuum degree was 1×10 -5 ~1.5×10 -5 The sputtering power was 115W, the gas pressure was 12 mtorr, and the sputtering time was 2 hours. The pressure in the chamber was controlled by introducing argon gas with a purity of 99.9999% by mass and a flow rate of 50 sccm.

[0041] In this embodiment, placing the composite substrate on the upper surface of the molybdenum support for bias-enhanced nucleation may include the following steps:

[0042] Step 1: Place a molybdenum holder on the diamond deposition substrate in the equipment chamber, and place the composite substrate on the molybdenum holder.

[0043] In this embodiment, the device used is a modified dish-type chamber MPCVD device, in which the upper plate in the chamber of the MPCVD device is connected to a DC voltage source, and the diamond deposition substrate is grounded.

[0044] Step 2: Evacuate the chamber and introduce hydrogen to control the gas pressure and microwave power in the chamber to activate the plasma glow.

[0045] In this embodiment, the chamber is evacuated to a vacuum degree of 2×10 -2 ~7×10 -2 torr.

[0046] Step 3: Etch and clean the surface of the Ir metal film on the composite substrate using hydrogen.

[0047] Optionally, the pressure in the chamber is increased to 23-28 torr, the microwave power is increased to 1000-1400 W, the temperature of the composite substrate reaches 750-850° C., and the surface of the Ir metal film of the composite substrate is etched and cleaned with hydrogen for 20 minutes.

[0048] Step 4: Introduce methane and nitrogen gases into the chamber and turn on the DC bias to perform bias-enhanced nucleation.

[0049] Optionally, the volume fraction of the introduced methane is 4% to 5%, and the volume fraction of the introduced nitrogen is 0.003% to 0.005%.

[0050] It is understandable that after the methane and nitrogen gases are introduced, wait for 3 to 5 minutes until the hydrogen, methane and nitrogen in the chamber are fully mixed before turning on the DC bias to perform bias-enhanced nucleation.

[0051] In this embodiment, after the three gases in the chamber are evenly mixed, the DC bias is turned on and the voltage is gradually increased to 190-240V so that the initial current reaches 0.12A to perform bias-enhanced nucleation.

[0052] In this embodiment, the duration of the bias enhanced nucleation process is 45 minutes.

[0053] Furthermore, after placing the composite substrate on the upper surface of the molybdenum support for bias-enhanced nucleation, the method further includes: in-situ power-off growth of single crystal diamond.

[0054] In this embodiment, the modified dish-shaped MPCVD equipment is continued to be used for in-situ power-off growth, and the in-situ power-off growth time is 30 minutes. Specifically, the following steps may be included:

[0055] Step 1: After nucleation is completed, turn off the DC bias, reduce the methane gas content, increase the nitrogen content, and start the epitaxial growth of single crystal diamond.

[0056] In this embodiment, the volume fraction of methane gas is reduced to 1%, and the volume fraction of nitrogen gas is increased to 0.005%.

[0057] Step 2: After the growth is completed, close the methane and nitrogen gas filling valves to reduce the air pressure and microwave power in the chamber.

[0058] Step 3: After the plasma glow is extinguished, close the hydrogen filling valve to evacuate the chamber;

[0059] Step 4: Nitrogen is introduced into the chamber to atmospheric pressure to complete the heteroepitaxial growth of single crystal diamond.

[0060] The method of this embodiment for improving the quality and density of single crystal diamond nucleation based on a special support structure utilizes a truncated cone-shaped molybdenum support. On the one hand, this reduces the distance between the plasma glow and the Ir surface of the composite substrate, thereby increasing the effective contact area between the DC glow and the Ir surface and improving the quality and density of nucleation. On the other hand, the truncated cone-shaped molybdenum support can confine the DC glow to the upper surface of the truncated cone-shaped molybdenum support, effectively preventing the underflow of the DC glow, avoiding the possible stroboscopic damage of the DC glow to the Ir film, and improving the stability of nucleation.

[0061] See Figure 2 , Figure 2 This is a comparison diagram of DC glow in the bias-enhanced nucleation process provided by an embodiment of the present invention. Figure 2 As shown, the left picture is a stable DC glow image after using a frustum-type molybdenum support structure in the bias-enhanced nucleation process. It can be seen from the picture that the plasma glow is completely concentrated on the substrate surface; the right picture is a DC glow image using a cylindrical high molybdenum support structure. It can be seen from the picture that part of the plasma glow overflows, weakening the effect of the DC glow.

[0062] See Figure 3 , Figure 3 The present invention provides an embodiment of the present invention providing a comparison of the quality and density of single crystal diamond nuclei after nucleation using a truncated cone-shaped molybdenum support and without. Figure (a) shows a sample image after nucleation without a truncated cone-shaped molybdenum support; Figure (b) shows a sample image after nucleation without a truncated cone-shaped molybdenum support. The square protrusions framed in the figure are typical single crystal diamond nuclei with successful nucleation. It can be clearly seen from the figure that the nucleation density in Figure (b) is much higher than that in Figure (a).

[0063] For example, a strontium titanate (SrTiO3) single crystal, namely STO <100> The substrate is used as the substrate, and the method of improving the quality and density of single crystal diamond nucleation based on the special support structure of this embodiment is described.

[0064] Step i: Using magnetron sputtering process to prepare Ir metal thin film on SrTiO3 substrate to form Ir / SrTiO3 composite substrate, wherein Ir target with mass purity greater than 99.99% is selected as sputtering target, and magnetron sputtering conditions are set as follows: substrate temperature 780℃, vacuum degree 1.2×10 -5 torr, the sputtering power is 115W, and the pressure in the cavity is controlled by introducing argon gas, wherein the purity of argon gas by mass is 99.9999%, the argon gas flow rate is 50sccm, and the gas pressure in the cavity is controlled at 18mtorr before magnetron sputtering. When sputtering starts, the gas pressure is reduced to 12mtorr, and the sputtering time is 2 hours.

[0065] Step ii: Place the molybdenum holder on the diamond deposition substrate in the modified dish-shaped MPCVD chamber, place the composite substrate on the molybdenum holder, close the chamber cover and evacuate the chamber to 4×10 -2 torr.

[0066] Step iii: Introduce hydrogen into the chamber, control the gas pressure and microwave power in the equipment cavity, activate the plasma glow, increase the gas pressure in the cavity to 25 torr, increase the microwave power to 1400W, so that the temperature of the composite substrate reaches 750°C, and use hydrogen to etch and clean the surface of the Ir metal film on the composite substrate for 20 minutes.

[0067] Step iv: 5% by volume of methane and 0.004% by volume of nitrogen are introduced into the chamber, and the gases in the chamber are allowed to mix thoroughly for 3 to 5 minutes.

[0068] Step v: Turn on the DC bias and gradually increase it to 220 V, so that the current reaches 0.12 A, and start the bias-enhanced nucleation process for 45 minutes;

[0069] Step vi: After nucleation is completed, the DC bias is turned off, the volume fraction of methane gas is reduced to 1%, the volume fraction of nitrogen gas is increased to 0.005%, and single crystal diamond epitaxial growth is started for 30 minutes.

[0070] Step vii: After the growth is completed, the methane and nitrogen gas filling valves are closed, and the air pressure and microwave power in the chamber are reduced to lower the temperature of the composite substrate. After the plasma glow is extinguished, the hydrogen gas filling valve is closed to evacuate the chamber, and nitrogen is introduced into the chamber to atmospheric pressure. The equipment chamber cover is opened to obtain high-quality, high-density single-crystal diamond nuclei on the Ir / SrTiO3 composite substrate.

[0071] For example, the preparation process of the Ir / MgO composite substrate is consistent with the preparation process of the Ir / SrTiO3 composite substrate. The difference between using the Ir / MgO composite substrate for diamond heteroepitaxy and using the Ir / SrTiO3 composite substrate for diamond heteroepitaxy is that when the surface of the Ir metal film of the composite substrate is etched and cleaned with hydrogen, the gas pressure in the chamber is increased to 25 torr, the microwave power is 1400 W, and the substrate temperature is 850°C.

[0072] It should be noted that, in this document, relational terms such as first and second are used solely to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. Furthermore, the terms "comprise," "include," or any other variations thereof are intended to encompass non-exclusive inclusion, such that an article or device comprising a list of elements includes not only those elements but also other elements not explicitly listed. Without further limitation, an element defined by the phrase "comprising a..." does not preclude the presence of additional identical elements in the article or device comprising the element. Terms such as "connected" or "connected" are not limited to physical or mechanical connections but may include electrical connections, whether direct or indirect. References to orientations or positional relationships, such as "upper," "lower," "left," and "right," are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate description and simplify the description of the present invention. They do not indicate or imply that the device or element referred to must have, be constructed, or operate in a specific orientation, and are therefore not to be construed as limiting the present invention.

[0073] In the description of this specification, the reference terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" mean that the specific features or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described can be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0074] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for improving the quality and density of single crystal diamond nucleation based on a special support structure, characterized in that: include: The composite substrate is placed on the upper surface of a molybdenum support for bias-enhanced nucleation, wherein the molybdenum support is a truncated cone structure, the upper surface diameter of the molybdenum support is adapted to the size of the composite substrate, and the lower surface diameter of the molybdenum support is 2 to 2.5 times the upper surface diameter. During the nucleation process, the distance from the plasma glow to the upper surface of the composite substrate is 30 to 50 mm.

2. The method for improving the quality and density of single crystal diamond nucleation based on a special support structure according to claim 1, characterized in that: The composite substrate is Ir / MgO, Ir / SrTiO3 or Ir / Al2O3.

3. The method for improving the quality and density of single crystal diamond nucleation based on a special support structure according to claim 1, characterized in that: The composite substrate is placed on the upper surface of the molybdenum support for bias-enhanced nucleation, which also includes: preparing an Ir metal film on an oxide substrate using a magnetron sputtering process to form the composite substrate.

4. The method for improving the quality and density of single crystal diamond nucleation based on a special support structure according to claim 1, characterized in that: The composite substrate is placed on the upper surface of the molybdenum support for bias-enhanced nucleation, including: Placing the molybdenum holder on a diamond deposition substrate in a chamber of an equipment, and placing the composite substrate on the molybdenum holder; The chamber is evacuated, and hydrogen is introduced to control the gas pressure in the chamber and the microwave power to activate the plasma glow; Etching and cleaning the surface of the Ir metal film of the composite substrate using hydrogen; Methane and nitrogen gases are introduced into the chamber, and a DC bias is turned on to perform bias-enhanced nucleation.

5. The method for improving the quality and density of single crystal diamond nucleation based on a special support structure according to claim 4, characterized in that: The chamber was evacuated to a vacuum degree of 2×10 -2 ~7×10 -2 torr.

6. The method for improving the quality and density of single crystal diamond nucleation based on a special support structure according to claim 4, characterized in that: Etching and cleaning the surface of the Ir metal film of the composite substrate using hydrogen gas, comprising: The pressure in the chamber is increased to 23-28 torr, the microwave power is increased to 1000-1400 W, the temperature of the composite substrate reaches 750-850° C., and the surface of the Ir metal film of the composite substrate is etched and cleaned with hydrogen for 20 minutes.

7. The method for improving the quality and density of single crystal diamond nucleation based on a special support structure according to claim 4, characterized in that: The volume fraction of the methane is 4% to 5%, and the volume fraction of the nitrogen is 0.003% to 0.005%.

8. The method for improving the quality and density of single crystal diamond nucleation based on a special support structure according to claim 4, characterized in that: The DC bias voltage ranges from 190V to 240V.

9. The method for improving the quality and density of single crystal diamond nucleation based on a special support structure according to claim 4, characterized in that: After placing the composite substrate on the upper surface of the molybdenum support for bias-enhanced nucleation, the method further includes: in-situ power-off growth of single crystal diamond.

10. The method for improving the quality and density of single crystal diamond nucleation based on a special support structure according to claim 9, characterized in that: In-situ power-off epitaxial growth of single crystal diamond, including: After the nucleation is completed, the DC bias is turned off, the content of the methane gas is reduced, the content of the nitrogen gas is increased, and the epitaxial growth of the single crystal diamond is started; After the growth is completed, the methane and nitrogen gas filling valves are closed to reduce the gas pressure and microwave power in the chamber; After the plasma glow is extinguished, the hydrogen filling valve is closed to evacuate the chamber; Nitrogen is introduced into the chamber to atmospheric pressure to complete heteroepitaxial growth of single crystal diamond.

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