A method for preparing low-stress diamond film by synthesizing metal Ga buffer layer using ultrasonic cavitation technology

Abstract

The application provides a method for preparing a low-stress diamond film by synthesizing a metal Ga buffer layer by using an ultrasonic cavitation technology, and comprises the following steps: liquid metal gallium is added into ethanol, ultrasonic treatment is performed, then supernatant is taken after standing, and liquid metal gallium nanoparticle suspension is obtained; the obtained liquid metal gallium nanoparticle suspension is spin-coated on a substrate, and after drying, a Ga buffer layer is deposited on the substrate; a microwave plasma chemical vapor deposition (MPCVD) process is used to grow a diamond film on the Ga buffer layer, and a low-stress diamond film is obtained. The Ga buffer layer is first prepared on the substrate, and then the growth of the diamond film is performed; the method can effectively reduce the residual stress of the diamond film, prevent the problems such as warping and fracture of the diamond film caused by thermal stress, and explores a new method for the preparation of a buffer layer material.

Description

Technical Field

[0001] This invention relates to a method for preparing low-stress diamond films by synthesizing metallic Ga buffer layers using ultrasonic cavitation technology, belonging to the field of crystal synthesis technology. Background Technology

[0002] Diamond films possess exceptional mechanical, thermal, optical, electrical, and acoustic properties, leading to their widespread application across various fields. Microwave plasma chemical vapor deposition (MPCVD) for diamond preparation offers advantages such as simple operation, large sample size, and high sample quality. However, residual stress often exists during MPCVD diamond film preparation. High residual stress can cause warping or even fracture of the film, severely limiting its subsequent use. To achieve low-stress diamond film preparation, a common method is to prepare a buffer layer, and a suitable buffer layer material is crucial for reducing diamond film stress. Commonly used metal buffer layer materials in heterogeneous diamond growth include iridium (Ir), nickel (Ni), copper (Cu), platinum (Pt), tungsten (W), and molybdenum (Mo). While some metal buffer layers can alleviate the difference in lattice constants between the diamond film and the substrate, their effect on increasing the diamond nucleation rate is not significant. Furthermore, metal nitrides and carbides are also common buffer layer materials in diamond growth.

[0003] Low-melting-point metals / alloys refer to metals and their alloys with melting points below 300℃, typically between 30 and 200℃. Low-melting-point metals include bismuth, tin, lead, indium, gallium, rubidium, and cesium. Because of their low melting points, these metals readily transform into a fluid form upon heating, hence the term liquid metals. These liquid metals, due to their low melting points, high electrical conductivity, and high fluidity, have found widespread application in fields such as medicine and electronics. Liquid metals possess metallic properties and unique surface activity, fundamentally different from those encountered in other liquids. Among known liquid metals, Ga exhibits low toxicity and high chemical stability, thus its excellent thermal conductivity, electrical conductivity, tunable fluidity / rheology, controllable surface chemistry, and compatibility with various materials enhance functionality.

[0004] Therefore, exploring suitable buffer layer materials that match the lattice constant and thermal expansion coefficient of the substrate material is of great significance for the preparation of low-stress diamond films. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing low-stress diamond films by synthesizing a Ga buffer layer using ultrasonic cavitation technology. This invention first prepares a Ga buffer layer on a substrate, followed by diamond film growth. The method effectively reduces residual stress in the diamond film, preventing warping and breakage caused by thermal stress, and explores a new method for preparing buffer layer materials.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing low-stress diamond films by synthesizing metallic Ga buffer layers using ultrasonic cavitation technology includes the following steps:

[0008] (1) Add liquid gallium metal to ethanol, perform ultrasonic treatment, and then let it stand to take the supernatant to obtain a liquid gallium metal nanoparticle suspension; spin-coat the obtained liquid gallium metal nanoparticle suspension onto a substrate, and after drying, deposit a Ga buffer layer on the substrate.

[0009] (2) A diamond film was grown on a Ga buffer layer using microwave plasma chemical vapor deposition (MPCVD) to obtain a low-stress diamond film.

[0010] According to a preferred embodiment of the present invention, the mass ratio of liquid gallium metal to the volume of ethanol in step (1) is 1g:40-60mL.

[0011] According to a preferred embodiment of the present invention, the ultrasonic treatment time in step (1) is 20-30 min; the ultrasonic power is 80 W; and the settling time is 1-3 h.

[0012] According to a preferred embodiment of the present invention, the substrate in step (1) is a silicon substrate.

[0013] According to a preferred embodiment of the present invention, the spin coating process conditions in step (1) are as follows: spin coating is performed at a speed of 100-500 rpm for 5-10 seconds using a spin coater, followed by spin coating at a speed of 1200 rpm for 10-30 seconds, so that liquid metal Ga nanoparticles are uniformly deposited on the substrate.

[0014] According to a preferred embodiment of the present invention, the drying in step (1) is natural drying at room temperature until the solvent has completely evaporated.

[0015] According to a preferred embodiment of the present invention, the diamond film growth process in step (2) is a prior art technique; preferably, the specific process is as follows:

[0016] The substrate with the deposited Ga buffer layer is placed on the substrate stage of the MPCVD system reaction chamber. The vacuum system is turned on, and after the vacuum level in the chamber reaches 10 mtorr, hydrogen gas is introduced. When the gas pressure in the reaction chamber reaches 100-150 torr and the temperature reaches 800-1000℃, CH4 and O2 are introduced to grow the diamond film. After the growth is completed, the introduction of CH4 and O2 is stopped, and the temperature is lowered. During the cooling process, H2 is continued to be introduced until the sample cools to room temperature.

[0017] More preferably, the microwave power during the growth of the diamond film is 3-4kW;

[0018] More preferably, the flow rate of the hydrogen gas is 400-500 sccm;

[0019] More preferably, the flow rate of CH4 is 2-6% of the hydrogen flow rate; the flow rate of oxygen is 0.5-1 sccm;

[0020] Further preferred, the growth time of the diamond film is 4-150 hours.

[0021] The technical features and beneficial effects of this invention are as follows:

[0022] 1. This invention successfully fabricated a Ga buffer layer on a substrate using ultrasonic and spin-coating techniques. Subsequently, a low-stress diamond film was prepared on the buffer layer using microwave plasma chemical vapor deposition (MPCVD). This invention provides an in-depth study of the morphology, composition, and stress of the diamond film cross-section. Diamond growth experiments show that the diamond film prepared using liquid gallium as a buffer layer exhibits even lower stress. The method of this invention is environmentally friendly; liquid gallium is non-toxic and low-cost. Combined with ultrasonic methods, it successfully prepares low-stress diamond films. The method is simple, rapid, reliable, environmentally friendly, interference-free, and low-cost.

[0023] 2. The method for preparing the liquid metal Ga buffer layer in this invention is low in cost and simple and fast, providing a new approach for the growth of low-stress diamond; this invention has high versatility and can be used for the synthesis of other liquid metals, and is suitable for the preparation of low-stress crystal materials. Attached Figure Description

[0024] Figure 1The images show SEM images and elemental distribution diagrams of the diamond films grown in Example 1 and Comparative Example 1, where (a) is a cross-sectional view of the diamond film of Comparative Example 1 grown on a silicon substrate, (b) is the C elemental distribution diagram of the diamond film of Comparative Example 1, (c) is the Si elemental distribution diagram of the diamond film of Comparative Example 1, (d) is the Ga elemental distribution diagram of the diamond film of Comparative Example 1, (e) is the O elemental distribution diagram of the diamond film of Comparative Example 1, (f) is a cross-sectional view of the diamond film of Example 1 grown on a silicon substrate, (g) is the C elemental distribution diagram of the diamond film of Example 1, (h) is the Si elemental distribution diagram of the diamond film of Example 1, (i) is the Ga elemental distribution diagram of the diamond film of Example 1, and (j) is the O elemental distribution diagram of the diamond film of Example 1.

[0025] Figure 2 Optical photographs and Raman peak diagrams of different regions of the diamond films grown in Example 1 and Comparative Example 1 are shown, where (a) is an optical photograph of the diamond film grown in Comparative Example 1, (b) is a Raman peak diagram of different regions of the diamond film grown in Comparative Example 1, (c) is an optical photograph of the diamond film grown in Example 1, and (d) is a Raman peak diagram of different regions of the diamond film grown in Example 1.

[0026] Figure 3 Optical photographs and Raman mapping images of the diamond films grown in Example 2 and Comparative Example 2 are shown, where (a) is an optical photograph of the cross-section of the diamond film in Comparative Example 2, and (b) is an optical photograph of the diamond film in Comparative Example 2 grown at 1332 cm⁻¹. -1 Raman mapping plots of peak intensity, (c) shows the diamond film of Comparative Example 2 at 520.3 cm⁻¹. -1 Raman mapping plots of peak intensity, (d) is the diamond film of Comparative Example 2 at 1580 cm⁻¹ -1 Raman mapping plots of peak intensity; (e) is an optical photograph of the cross-section of the diamond film of Example 2; (f) is an optical photograph of the diamond film of Example 2 at 1332 cm⁻¹. -1 Raman mapping plots of peak intensity, (g) is the diamond film of Example 2 at 520.3 cm⁻¹. -1 Raman mapping plotted with peak intensity, (h) is the diamond film of Example 2 at 1580 cm⁻¹ -1 Raman mapping plots of peak intensities, with the inset showing the Raman spectrum at R5.

[0027] Figure 4The results of Raman spectroscopy tests are obtained by taking four points R1, R2, R3, and R4 along the thickness direction from near the interface on the diamond films grown in Example 2 and Comparative Example 2. Among them, (a) is the Raman spectroscopy test result of point R1, (b) is the Raman spectroscopy test result of point R2, (c) is the Raman spectroscopy test result of point R3, and (d) is the Raman spectroscopy test result of point R4. Detailed Implementation

[0028] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings, but is not limited thereto.

[0029] Example 1

[0030] A method for preparing low-stress diamond films by synthesizing metallic Ga buffer layers using ultrasonic cavitation technology includes the following steps:

[0031] (1) Add 0.2g of liquid gallium metal to 10mL of ethanol and sonicate for 20min at a power of 80W. After standing for 2h, take the supernatant to obtain a liquid gallium metal nanoparticle suspension. Spin coat the obtained liquid gallium metal nanoparticle suspension onto a Si(100) substrate. Use a spin coater to spin coat at 500rpm for 10s, then spin coat at 1200rpm for 20s. Allow the solvent to evaporate naturally at room temperature and uniformly deposit a Ga buffer layer on the Si(100) substrate.

[0032] (2) A low-stress diamond film was grown on a Ga buffer layer using microwave plasma chemical vapor deposition (MPCVD). The specific steps for growing the diamond film are as follows: The Si(100) substrate with the Ga buffer layer was placed on the substrate stage of the MPCVD system reaction chamber. The vacuum system was turned on. After the vacuum degree in the chamber reached 10 mtorr, hydrogen gas was introduced at a flow rate of 500 sccm. After the gas pressure in the reaction chamber reached 120 torr and the temperature reached 830℃, CH4 and O2 were introduced. The flow rate of CH4 was 4% of the hydrogen flow rate and the flow rate of oxygen was 0.5 sccm. The diamond film was grown under a microwave power of 3.5 kW. After 60 h of growth, the introduction of CH4 and O2 was stopped and the temperature was lowered. During the cooling process, H2 was introduced until the sample cooled to room temperature, and a low-stress diamond film was obtained.

[0033] Example 2

[0034] A method for preparing a low-stress diamond film by synthesizing a metal Ga buffer layer using ultrasonic cavitation technology is described in Example 1, except that the growth time in step (2) is 4 hours.

[0035] Comparative Example 1

[0036] A method for preparing a diamond film is described in Example 1, except that in step (1), liquid gallium metal is replaced with nano-diamond powder (particle size of 50 nm).

[0037] Comparative Example 2

[0038] A method for preparing a diamond film is described in Example 1, except that: in step (1), liquid gallium metal is replaced with nano-diamond powder (particle size of 50 nm); and in step (2), the growth time is 4 h.

[0039] The comprehensive analysis is as follows:

[0040] The cross-sectional morphology and elemental distribution of the diamond film without a Ga buffer layer prepared in Comparative Example 1 and the diamond film with a Ga buffer layer prepared in Example 1 were characterized using SEM. In Comparative Example 1 without a Ga buffer layer, the diamond film was grown directly on the surface of the silicon substrate, such as... Figure 1 As shown in (a), mapping tests were performed on the cross-section of the diamond film without the Ga buffer layer. The distributions of elements C, Si, Ga, and O are as follows: Figure 1 As shown in (b)-(e), no Ga element was found in the cross-sectional view at this time. A small amount of O element was uniformly distributed in the diamond film. This is because a small amount of O2 was introduced during the growth of the diamond film to improve its quality. When a Ga buffer layer was added in Example 1, a new layer appeared between the diamond film and the silicon substrate. Figure 1 (f) Mapping tests were performed on the distribution of C, Si, Ga, and O elements in the cross-section of the sample. Figure 1 (g)-(j)) When the Ga buffer layer is present on the silicon substrate, liquid metal Ga can catalyze the decomposition of methane and the formation of graphite. At the same time, due to the penetration of C at high temperature, a Ga / C composite layer with a thickness of about 2 μm will first be generated on the surface of the silicon substrate, followed by a graphite layer with a thickness of 2 μm. Finally, a diamond film is prepared on this composite buffer layer. Similarly, when the Ga buffer layer is covered, a small amount of O element can still be observed to be uniformly distributed in the diamond film. During diamond growth in MPCVD, due to the etching effect of hydrogen during the heating process, no Ga oxide was found in the cross-section.

[0041] Raman spectroscopy was performed on the large-size diamond films obtained in Example 1 and Comparative Example 1. Figure 2(a) and (c) are optical photographs of diamond films grown on Si substrates without and with a Ga buffer layer, respectively. The diameter of the diamond film is 50 mm, and the sample surface is relatively uniform. To verify the effect of the buffer layer on the diamond growth quality, five regions were uniformly selected from the center to the edge of the sample, and Raman mapping tests were performed. The results were averaged, and a Raman peak position diagram was plotted. The Raman peak positions of different regions in the diamond film without the Ga buffer layer are shown below. Figure 2 As shown in (b), the characteristic Raman peak positions of the diamond film in different regions show very little variation, remaining at approximately 1333.5 cm⁻¹. -1 The Raman peak positions of the diamond film covered with the Ga buffer layer are as follows: Figure 2 As shown in (d), the characteristic Raman peaks of the diamond film vary very little in different regions, with the characteristic Raman peak of diamond located at ~1332.7 cm⁻¹. -1 Compared with diamond films without Ga buffer layers, the diamond Raman characteristic peaks are shifted to the left less and the stress is reduced. This ultimately enabled the fabrication of a low-stress diamond film with a diameter of 50 mm and a thickness of 300 μm, laying the foundation for the development of diamond power semiconductor devices.

[0042] The cross-sections of the diamond films prepared in Comparative Example 2 without a Ga buffer layer and the diamond films prepared in Example 2 with a Ga buffer layer were characterized by morphology and Raman mapping. First, it was observed that in Comparative Example 2 without a Ga buffer layer, the diamond directly bonded to the silicon substrate, as shown in the optical photographs below. Figure 3 As shown in (a), Raman mapping tests were performed on the cross-sectional region of the silicon-based diamond sample, and the results were obtained at 1332 cm⁻¹. -1 520.3cm -1 1580cm -1 Plot a mapping diagram of the Raman peak intensity at the location, as shown below. Figure 3 As shown in ((b)-(d)), no other components besides silicon and diamond were observed in the Raman spectra. Figure 3 (e) is a cross-sectional optical photograph of the diamond film with a Ga buffer layer prepared in Example 2, showing a 4 μm thick buffer layer between the diamond film and the Si substrate. Raman spectroscopy was performed on the cross-sectional area at 1332 cm⁻¹. -1 520.3cm -1 and 1580cm -1 Plot a mapping diagram of the Raman peak intensity at the location, as shown below. Figure 3 As shown in (f)-(h), Raman spectroscopy revealed that a 4 μm thick buffer layer containing graphite was observed at the interface between the diamond film and the Si substrate. The Raman spectrum of this layer is shown in the inset of 3(h), which corresponds to the SEM results.

[0043] Raman spectroscopy was performed on the diamond films prepared in Example 2 and Comparative Example 2. In Comparative Example 2, without the Ga buffer layer, four points (R1, R2, R3, and R4) were taken along the thickness direction from near the interface on the diamond film for Raman spectroscopy testing. The specific locations are shown in Figure (3(b)). The characteristic Raman peaks of the diamond film shifted to higher wavenumbers by 0.94, 1.14, 0.69, and 0.54 cm⁻¹, respectively. -1 The diamond film is subjected to compressive stress. The overall stress of the diamond film first increases and then decreases with the thickness. The increase in stress at R2 may be due to the change in growth stress. According to formula (1) and the actual measured Raman peak shift, when the Ga buffer layer is not covered, the stress values ​​at positions R1, R2, R3 and R4 are -0.328, -0.397, -0.240 and -0.188 GPa, respectively. In Example 2, when the Ga buffer layer is covered, four points R1, R2, R3 and R4 are selected on the diamond film for Raman testing. The specific sampling points are shown in Figure (3(f)). It is observed that the residual stress of the diamond film first increases and then decreases with the increase of thickness. The characteristic Raman peaks of the diamond are shifted to higher wavenumbers by 0.67, 0.71, 0.47 and 0.41 cm, respectively. -1 Stress measurement in Raman spectroscopy is primarily achieved through Raman shift. The difference between the Raman scattered light frequency and the Rayleigh scattered light frequency is called the Raman shift, and changes in molecular vibrational energy levels are often the decisive factor affecting the Raman shift. In Raman spectroscopy measurements, different chemical bonds or ground states exhibit different vibrational modes, which can serve as the theoretical basis for Raman spectroscopy analysis of molecular structure.

[0044] σ=k·Δν (1)

[0045] Where k is a proportionality coefficient, closely related to the substrate material and selection method, and Δν is the Raman shift, thus the stress in the diamond film can be calculated by the shift of the Raman peak position. When the Raman peak position shifts towards higher wavenumbers, the diamond film is subjected to compressive stress; when the Raman peak position shifts towards lower wavenumbers, the diamond film is subjected to tensile stress. According to the formula and measured Raman peak shifts, the stress values ​​at positions R1, R2, R3, and R4 of the diamond film covered with a Ga buffer layer are -0.233, -0.247, -0.164, and -0.143 GPa, respectively. However, the increase in residual stress at R2 may be caused by changes in growth stress. By comparing the Raman spectra of diamond films without a Ga buffer layer and diamond films covered with a Ga buffer layer, it was found that the diamond film prepared with the Ga buffer layer has lower stress. This may be due to the unique properties of Ga. Ga has a melting point of 29.8°C and is liquid at room temperature. Therefore, Ga presents a fluid interface during the growth of diamond films. At the same time, Ga can catalyze the production of graphitic carbon. In other words, the presence of the Ga buffer layer reduces the difference in thermal expansion coefficients between the diamond film and the silicon substrate. Therefore, when covered with a Ga buffer layer, the grown diamond film has lower stress.

Claims

1. A method for preparing a low-stress diamond film by synthesizing a metallic Ga buffer layer using ultrasonic cavitation technology, comprising the following steps: (1) Add liquid gallium metal to ethanol, perform ultrasonic treatment, and then let it stand to collect the supernatant to obtain a liquid gallium metal nanoparticle suspension; spin-coat the obtained liquid gallium metal nanoparticle suspension onto a substrate, and after drying, deposit a Ga buffer layer on the substrate; the mass ratio of the liquid gallium metal to the volume of ethanol is 1g:40-60mL; the ultrasonic treatment time is 20-30min; the ultrasonic power is 80W; the substrate is a silicon substrate; the spin-coating process conditions are: spin-coating at a speed of 100-500rpm for 5-10s using a spin coater, and then spin-coating at a speed of 1200rpm for 10-30s; (2) A diamond film was grown on a Ga buffer layer by using microwave plasma chemical vapor deposition process to obtain a low-stress diamond film.

2. The method for preparing low-stress diamond films by synthesizing metallic Ga buffer layers using ultrasonic cavitation technology according to claim 1, characterized in that, The settling time mentioned in step (1) is 1-3 hours.

3. The method for preparing low-stress diamond films by synthesizing metallic Ga buffer layers using ultrasonic cavitation technology according to claim 1, characterized in that, The drying process described in step (1) involves natural drying at room temperature until the solvent has completely evaporated.

4. The method for preparing low-stress diamond films by synthesizing metallic Ga buffer layers using ultrasonic cavitation technology according to claim 1, characterized in that, The diamond film growth process in step (2) is as follows: The substrate with the deposited Ga buffer layer is placed on the substrate stage of the MPCVD system reaction chamber. The vacuum system is turned on, and after the vacuum level in the chamber reaches 10 mtorr, hydrogen gas is introduced. When the gas pressure in the reaction chamber reaches 100-150 torr and the temperature reaches 800-1000℃, CH4 and O2 are introduced to grow the diamond film. After the growth is completed, the introduction of CH4 and O2 is stopped, and the temperature is lowered. During the cooling process, H2 is continued to be introduced until the sample cools to room temperature.

5. The method for preparing low-stress diamond films by synthesizing metallic Ga buffer layers using ultrasonic cavitation technology according to claim 4, characterized in that, The microwave power during the growth of diamond films is 3-4 kW.

6. The method for preparing low-stress diamond films by synthesizing metallic Ga buffer layers using ultrasonic cavitation technology according to claim 4, characterized in that, The flow rate of hydrogen is 400-500 sccm; the flow rate of CH4 is 2-6% of the hydrogen flow rate; and the flow rate of oxygen is 0.5-1 sccm.

7. The method for preparing low-stress diamond films by synthesizing metallic Ga buffer layers using ultrasonic cavitation technology according to claim 4, characterized in that, The growth time of the diamond film is 4-150 hours.

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