A method for preparing a polycrystalline diamond film and applications thereof

Abstract

The application discloses a preparation method of a polycrystalline diamond film and application of the polycrystalline diamond film. The preparation method comprises the following steps: S1, foamed copper is pressure-cast on a copper substrate to form a copper base; S2, the copper base is subjected to pickling to remove an oxide layer; S3, a diamond powder suspension seed layer is coated on the surface of the copper base; S4, the copper base coated with the diamond powder suspension seed layer is placed in a CVD reaction cavity, methane and hydrogen are introduced, the growth temperature is controlled, a polycrystalline diamond film is deposited, the copper base is subjected to acid etching or laser cutting, and the polycrystalline diamond film is obtained. The polycrystalline diamond film prepared through the preparation method will not be warped or dropped due to the difference in thermal expansion coefficients of copper and diamond in the growth process, and then a regular and firmly-attached polycrystalline diamond film can be prepared, and the polycrystalline diamond film has wide application in the fields of high-thermal-conductivity, wear-resistance and electronic device heat dissipation materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polycrystalline diamond film preparation, and particularly relates to a polycrystalline diamond film preparation method and application. BACKGROUND

[0002] Diamond has irreplaceable application value in the fields of heat dissipation coating, cutting tool, semiconductor device, etc. due to its extremely high thermal conductivity, hardness and chemical stability. Copper is an ideal diamond growth carrier as a metal material with high thermal conductivity, low cost and excellent plasticity. The lattice constant of copper (about 0.361 nm) is very similar to the lattice constant of diamond (about 0.357 nm); at the same time, the solid solubility of carbon in copper is extremely low, and no carbide transition layer is formed. Therefore, in theory, polycrystalline diamond film with high crystalline quality and high growth rate can be obtained by directly depositing diamond on a copper substrate. However, there is a huge difference between the extremely low thermal expansion coefficient (about 0.86×10 -6 / K) of diamond and the relatively high thermal expansion coefficient (about 17×10 -6 / K) of copper, which causes significant residual thermal stress at the film-substrate interface during the deposition process and subsequent cooling process. The stress is extremely easy to cause cracks, warping and even large-area peeling of the diamond film from the copper substrate, so that it is a great challenge to prepare an integrated and firmly adhered diamond film directly on the copper substrate.

[0003] The patent application with the publication number CN102337514A discloses a method for growing a strongly adhered diamond film on a copper substrate by diamond inlaying method. The method uniformly mixes copper powder and diamond powder (volume ratio 1:1~5), then cold-presses to prepare a diamond / copper composite substrate, uses the pre-embedded diamond micro powder as a mechanical anchor point and nucleation center, realizes strong mechanical combination of the diamond film and the copper substrate during CVD deposition, effectively solves the film peeling problem caused by the mismatch of thermal expansion coefficients, and first obtains an integrated copper-based diamond film with an adhesion greater than 15 N / cm 2 . However, the significant limitations are as follows: the fault tolerance of the composite substrate ratio is low (the adhesion drops to 5 N / cm 2 when the ratio of diamond powder is greater than 1:5); the cold-pressing process does not control the porosity and density of the substrate, which may cause uneven film growth.

[0004] The invention patent application with the publication number CN120006249A discloses a diamond film based on copper substrate growth and a preparation method thereof. The method is designed by double-grain diamond particle embedding and titanium transition layer. First, micron-sized first diamond particles are embedded into the copper substrate through grinding / lithographic pit to form mechanical anchor points. A titanium transition layer is sputtered and a thermal expansion buffer layer is constructed by high-temperature annealing. Then, nanoscale second diamond particles are attached to improve nucleation density. Finally, in the CVD deposition, the adhesion force is 5.1 N and the low friction coefficient is achieved, which significantly solves the copper-based diamond film bonding force and nucleation rate pain points. However, the core defect of this method is that the high-temperature annealing temperature is very close to the melting point of copper, the risk of substrate deformation increases dramatically, and the thickness of the titanium transition layer is very sensitive, which is discontinuous when greater than 100 nm, and the interface thermal resistance soars when greater than 300 nm. The actual thermal conductivity is not disclosed, and the heat dissipation performance is questionable.

[0005] Therefore, finding a preparation method that can prepare a complete and firmly adhered polycrystalline diamond film on a copper substrate is still one of the core difficulties in the field of polycrystalline diamond film preparation technology and an important direction for future material engineering design. SUMMARY

[0006] In view of the deficiencies of the prior art, the first aspect of the present application provides a preparation method of a polycrystalline diamond film, which can effectively alleviate the problem of easy breakage and cracking caused by the difference in thermal expansion coefficient between copper and diamond, and further prepare a complete and firmly adhered polycrystalline diamond film.

[0007] The preparation method of a polycrystalline diamond film provided by the present application comprises:

[0008] S1, foaming copper is pressure cast on a copper substrate to form a copper base;

[0009] S2, the copper base is subjected to acid pickling to remove the oxide layer;

[0010] S3, a diamond powder suspension seed layer is coated on the surface of the copper base;

[0011] S4, the copper base coated with the diamond powder suspension seed layer is placed in a CVD reaction chamber, methane and hydrogen are introduced, the growth temperature is controlled, a polycrystalline diamond film is deposited, the copper base is etched with acid or cut with a laser, and a polycrystalline diamond film is obtained.

[0012] Compared with growing diamond directly on a copper substrate, the present application forms a copper base by die casting the foamed copper on the copper substrate, on one hand, the porous structure of the foamed copper in the lateral direction can be reserved, which can effectively absorb thermal stress caused by the difference in thermal expansion coefficient during the growth of the polycrystalline diamond film through elastic deformation, and play a buffering role, thereby significantly inhibiting the fragile and cracking problems of the polycrystalline diamond film, on the other hand, the foamed copper can be stably attached to the copper substrate, realizing the direct combination of diamond and copper, and the composite material can be directly applied to the field of heat dissipation.

[0013] Moreover, the present application further forms a seed layer of diamond powder suspension on the copper base by spraying, fixes the diamond powder through the longitudinal porous structure of the foamed copper, forms multiple bonding points at the growth interface, and enhances the interface bonding capacity in a mechanical interlocking manner, thereby effectively improving the adhesion and stability of the polycrystalline diamond film on the copper base.

[0014] In addition, the copper base formed by die casting the foamed copper on the copper substrate has excellent heat conduction performance, can quickly conduct heat, helps to maintain the uniformity of the temperature during the growth of the polycrystalline diamond film, and avoids excessive local temperature difference as much as possible, thereby improving the growth quality and efficiency, and the process can be expanded to the maximum size of the diamond allowed by the equipment growth.

[0015] Preferably, the thickness of the foamed copper is 1-3 mm, and the compression rate of the foamed copper after die casting is 50%-90%, and the compression rate is the ratio of the difference between the thickness of the foamed copper after die casting and the thickness of the foamed copper before die casting to the thickness of the foamed copper before die casting.

[0016] By controlling the thickness of the foamed copper and the compression rate of the foamed copper after die casting, the foamed copper can be die cast to a thickness of hundreds of microns, a more dense porous structure is obtained, and the foamed copper is stably attached to the copper substrate, thereby avoiding the foamed copper from being deformed greatly at high temperature when the thickness of the foamed copper after die casting is too thick, causing the polycrystalline diamond film to be warped and fall off on a large scale, and avoiding the elastic buffering capacity from being reduced due to insufficient porous structure when the foamed copper after die casting is too thin.

[0017] Preferably, the average pore size of the foamed copper is 10-30 μm.

[0018] By providing a suitable average pore size of the foamed copper, the foamed copper can have sufficient elastic deformation capacity in the lateral porous structure after die casting, effectively buffering thermal stress, and the longitudinal porous structure can effectively anchor the diamond powder suspension, thereby preparing a complete and firmly attached polycrystalline diamond film.

[0019] Preferably, the process parameters of the die casting are as follows: the temperature of the die casting is 800-1000℃, the pressure of the die casting is 8-12 MPa, and the time of the die casting is 1-3 h under vacuum environment.

[0020] The present application provides suitable process parameters of the die casting of the foamed copper, which is die cast to a thickness of hundreds of microns, on one hand, the transverse porous structure is retained to buffer thermal stress, on the other hand, the longitudinal structure is made more compact to enhance the substrate stability, so that the foamed copper is stably attached to the copper substrate, and the diamond powder suspension is anchored.

[0021] Further preferably, the process parameters of the die casting are as follows: the temperature of the die casting is 800-950℃, the pressure of the die casting is 9-11 MPa, and the time of the die casting is 1-2 h under vacuum environment.

[0022] Preferably, the copper substrate is a copper sheet.

[0023] Preferably, the thickness of the copper substrate is 1-3 mm.

[0024] Preferably, the specific step of the acid pickling is as follows: the copper substrate is immersed in dilute hydrochloric acid with a volume concentration of 3%-15% and is ultrasonically cleaned for 10-30 min, so that the copper oxide on the surface of the copper substrate is removed, thereby ensuring that the diamond powder suspension is firmly attached to the surface of the copper substrate.

[0025] Preferably, after the acid pickling step, the copper substrate is sequentially immersed in acetone and alcohol and is ultrasonically cleaned for 10-30 min, so that the organic contaminants such as grease on the surface of the copper substrate are removed.

[0026] Preferably, the particle size of the diamond powder suspension is 0.5-10 μm. Since the average pore size of the foamed copper provided by the present application is 10-30 μm, the diamond powder suspension with a smaller particle size can better penetrate into the pore size, thereby effectively improving the nucleation density and the adhesion.

[0027] Preferably, in step S4, the flow rate of the hydrogen is 200-600 sccm, the flow rate of the methane is 1%-10% of the flow rate of the hydrogen, the growth temperature is 800-1100℃, the deposition pressure of the deposited polycrystalline diamond film is 8-15 kPa, and the deposition power of the deposited polycrystalline diamond film is 2500-6000 W.

[0028] The present application provides suitable process parameters of the deposition and growth of the polycrystalline diamond film, which can effectively exert the effect of the copper substrate on the relief of thermal stress and provide good growth conditions for the preparation of a regular polycrystalline diamond film.

[0029] In a second aspect, the application also provides a polycrystalline diamond film prepared by the method for preparing a polycrystalline diamond film and application of the polycrystalline diamond film in the field of high-thermal-conductivity, wear-resistant and electronic device heat dissipation materials.

[0030] The polycrystalline diamond film prepared by the method for preparing a polycrystalline diamond film on the copper substrate based on the chemical vapor deposition method has great significance for realizing portability and higher heat dissipation efficiency of electronic devices and has wide application in the field of high-thermal-conductivity, wear-resistant and electronic device heat dissipation materials.

[0031] Compared with the prior art, the application has the following beneficial effects:

[0032] The polycrystalline diamond film prepared by the method for preparing a polycrystalline diamond film on the copper substrate based on the chemical vapor deposition method has great significance for realizing portability and higher heat dissipation efficiency of electronic devices and has wide application in the field of high-thermal-conductivity, wear-resistant and electronic device heat dissipation materials.

[0033] Moreover, the application also sprays a diamond powder suspension on the copper substrate, anchors the diamond powder by using the longitudinal porous structure of the foam copper, forms a plurality of bonding points at the growth interface, further enhances the interface bonding capacity through mechanical interlocking, and effectively improves the adhesion and overall stability of the polycrystalline diamond film on the copper substrate.

[0034] In addition, the copper substrate has excellent heat conduction performance, can effectively ensure the uniformity of the temperature in the growth process, and can prepare a polycrystalline diamond film with better growth quality and efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The XRD graph of the polycrystalline diamond film prepared in Example 1 of the application.

[0036] Figure 2 The Raman graph of the polycrystalline diamond film prepared in Example 1 of the application.

[0037] Figure 3 The SEM graph of the polycrystalline diamond film prepared in Example 1 of the application.

[0038] Figure 4 The actual object graph of the polycrystalline diamond film prepared in Example 1 of the application.

[0039] Figure 5 The SEM graph of the growth interface of the polycrystalline diamond film prepared in Example 1 of the application and the copper substrate.

[0040] Figure 6XRD pattern of the polycrystalline diamond film prepared for Example 2 of the present application.

[0041] Figure 7 Raman pattern of the polycrystalline diamond film prepared for Example 2 of the present application.

[0042] Figure 8 SEM pattern of the polycrystalline diamond film prepared for Example 2 of the present application.

[0043] Figure 9 Actual pattern of the polycrystalline diamond film prepared for Comparative Example 1 of the present application.

[0044] Figure 10 Actual pattern of the polycrystalline diamond film prepared for Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without any creative work, fall within the protection scope of the present application.

[0046] Example 1

[0047] A 2 mm thick foam copper with an average pore size of 30 μm was placed on a copper sheet with the same size, and pushed into a vacuum hot-pressing furnace, with a temperature of 800℃, a pressure of 9 MPa, and a maintaining time of 1 hour. After the press-casting, the thickness of the foam copper was 500 μm, and the foam copper was press-cast on the copper sheet as a copper substrate. Then the copper substrate was immersed in dilute hydrochloric acid with a volume concentration of 10%, and the container containing the copper substrate and the dilute hydrochloric acid was put into an ultrasonic cleaning machine, with an ultrasonic cleaning time of 10 minutes. The ultrasonic cleaning program was started to remove the copper oxide on the surface of the copper substrate, and then the copper substrate was sequentially immersed in acetone and alcohol for ultrasonic cleaning for 10 minutes. Then a diamond powder suspension with a particle size of 1 μm was sprayed on the surface of the copper substrate using a spraying device, so as to form a uniform diamond powder seed layer on the surface of the substrate.

[0048] The prepared copper substrate with the diamond seed layer is placed in a suitable position within the reaction chamber, ensuring it is firmly fixed and preventing movement. Next, the reaction chamber is closed, and the vacuum pump is started to evacuate the chamber. After evacuation, the microwave power supply is turned on to initiate the ignition process. After ignition, the growth gas pressure and power are gradually increased alternately to raise the temperature inside the reaction chamber to approximately 900°C. Once the temperature reaches the desired range, methane and hydrogen are introduced according to the set gas conditions: methane flow rate is 6% of the hydrogen flow rate, and hydrogen flow rate is 400 sccm. Simultaneously, the deposition gas pressure is controlled at 11 kPa, and the deposition power at 3000 W.

[0049] Once the diamond has grown to the predetermined time, the growth process is stopped. First, all gases except hydrogen are shut off. Then, the gas pressure and power are gradually and alternately reduced, causing the temperature inside the reaction chamber to gradually decrease. When the gas pressure drops to 1 kPa and the power drops to 500 W, the stop button on the device is pressed to officially stop the growth process. After the sample has completely cooled, the reaction chamber is opened, and the copper substrate is removed, thus completing the preparation of the polycrystalline diamond film. Acid etching is then performed using 70% nitric acid until the copper substrate is completely dissolved, completing the peeling process.

[0050] The XRD pattern of the polycrystalline diamond film prepared in Example 1 of this invention is as follows: Figure 1 As shown, Figure 1 The horizontal axis 2θ represents the diffraction angle, which is twice the angle between the X-ray beam and the incident X-ray beam when the X-ray beam reaches the detector after diffraction on the sample surface. It can be seen that the diamond content is relatively high, and the (111) crystal plane has good crystallinity and prominent orientation. The crystal structure of the foamed copper is still preserved after diamond growth, and the basic characteristics of the substrate are not completely destroyed. The growth of diamond on the copper substrate is relatively ideal, and the crystallinity, content and purity of the diamond phase are all good.

[0051] The Raman image of the polycrystalline diamond film prepared in Example 1 of this invention is as follows: Figure 2 As shown, the polycrystalline diamond film sample contains a diamond phase, and the Raman signal of the diamond phase is relatively significant.

[0052] SEM image of the polycrystalline diamond film prepared in Example 1 of this invention, as shown below. Figure 3 As shown, relatively regular crystal faces with certain angles can be observed. These crystal faces overlap to form the crystal shape, reflecting the good crystallinity of diamond. It conforms to the growth morphology related to the (111) crystal orientation, indicating that the diamond growth quality is good and the crystal development is relatively complete.

[0053] A physical image of the polycrystalline diamond film prepared in Example 1 of this invention is shown below. Figure 4As shown in the figure, a relatively regular polycrystalline diamond film can be observed, and the thickness thereof is measured as 311 μm.

[0054] Example 2

[0055] The difference between Example 2 and Example 1 is that, in Example 2, the parameters for pressure casting of the 2 mm-thick foam copper on the copper substrate are as follows: the temperature is 1000 ℃, the pressure is 12 MPa, and the pressure casting time is 3 hours, and the thickness of the foam copper after pressure casting is 300 μm, and the average pore size of the foam copper is 15 μm.

[0056] The XRD pattern of the polycrystalline diamond film prepared in Example 2 is shown in the figure. Figure 6 As shown in the figure, it is indicated that the content of diamond is relatively high, and the crystallinity of the (111) crystal face is good and the orientation is relatively prominent, and the crystal structure of the foam copper is still retained after the growth of diamond, and the basic characteristics of the substrate are not completely destroyed, Figure 6 The 2θ in the abscissa has the same meaning as Figure 1 The 2θ in the abscissa has the same meaning as

[0057] The Raman pattern of the polycrystalline diamond film prepared in Example 2 is shown in the figure. Figure 7 As shown in the figure, it is indicated that the diamond phase exists in the prepared polycrystalline diamond film sample, and the Raman signal of the diamond phase is relatively significant.

[0058] The SEM pattern of the polycrystalline diamond film prepared in Example 2 is shown in the figure. Figure 8 As shown in the figure, although there are a small amount of broken crystal particles, it can still be seen that the diamond presents a large number of crystal structures with obvious geometric shapes, and the crystals are mostly in the form of pyramids, and the crystals are interwoven and stacked with each other.

[0059] Comparative Example 1

[0060] The difference between Comparative Example 1 and Example 1 is that, in Comparative Example 1, pure copper is used as the copper substrate, and no foam copper is pressure cast on the copper substrate.

[0061] The physical map of the polycrystalline diamond film prepared in the present application Comparative Example 1 is shown in the figure. Figure 9 As shown in the figure, it can be seen that the crystalline quality of the polycrystalline diamond film directly grown on the pure copper is poor, and the phenomenon of cracking occurs.

[0062] Comparative Example 2

[0063] The difference between Comparative Example 2 and Example 1 is that, in Comparative Example 2, the 2 mm-thick foam copper is directly placed on the pure copper substrate without the pressure casting step.

[0064] The physical map of the polycrystalline diamond film prepared in the present application Comparative Example 2 is shown in the figure.Figure 10 As shown, it indicates that the un-pressing foamed copper will have a large elastic deformation in the high temperature process of growing the polycrystalline diamond film, and still cause the polycrystalline diamond film to warp and fall off.

[0065] As shown, it indicates that the un-pressing foamed copper will have a large elastic deformation in the high temperature process of growing the polycrystalline diamond film, and still cause the polycrystalline diamond film to warp and fall off. Figure 5 As shown, it indicates that the un-pressing foamed copper will have a large elastic deformation in the high temperature process of growing the polycrystalline diamond film, and still cause the polycrystalline diamond film to warp and fall off. As shown, it indicates that the un-pressing foamed copper will have a large elastic deformation in the high temperature process of growing the polycrystalline diamond film, and still cause the polycrystalline diamond film to warp and fall off. As shown, it indicates that the un-pressing foamed copper will have a large elastic deformation in the high temperature process of growing the polycrystalline diamond film, and still cause the polycrystalline diamond film to warp and fall off. As shown, it indicates that the un-pressing foamed copper will have a large elastic deformation in the high temperature process of growing the polycrystalline diamond film, and still cause the polycrystalline diamond film to warp and fall off.

Claims

1. A method for preparing a polycrystalline diamond film, characterized in that, Includes the following steps: S1. Copper foam is die-cast onto a copper substrate to form a copper base; S2. Pickling the copper substrate to remove the oxide layer; S3. Coat the copper substrate surface with a diamond powder suspension seed layer; S4. Place the copper substrate coated with a diamond powder suspension seed layer in the CVD reaction chamber, introduce methane and hydrogen, control the growth temperature, deposit a polycrystalline diamond film, and then acid-etch or laser-cut the copper substrate to obtain a polycrystalline diamond film.

2. The method for preparing a polycrystalline diamond film according to claim 1, characterized in that, The thickness of the foamed copper is 1~3 mm, and the compression rate of the foamed copper after die casting is 50%~90%.

3. The method for preparing a polycrystalline diamond film according to claim 1, characterized in that, The average pore size of the copper foam is 10~30 μm.

4. The method for preparing a polycrystalline diamond film according to claim 1, characterized in that, The die-casting process parameters are as follows: under vacuum conditions, the die-casting temperature is 800~1000℃, the die-casting pressure is 8~12 MPa, and the die-casting time is 1~3h.

5. The method for preparing a polycrystalline diamond film according to claim 1, characterized in that, The copper substrate is a copper sheet.

6. The method for preparing a polycrystalline diamond film according to claim 1, characterized in that, The thickness of the copper substrate is 1~3 mm.

7. The method for preparing a polycrystalline diamond film according to claim 1, characterized in that, The specific steps of the pickling are as follows: immerse the copper substrate in dilute hydrochloric acid with a volume concentration of 3% to 15% and ultrasonically clean it for 10 to 30 minutes.

8. The method for preparing a polycrystalline diamond film according to claim 1, characterized in that, The particle size of the diamond powder suspension is 0.5~10 μm.

9. The method for preparing a polycrystalline diamond film according to claim 1, characterized in that, In step S4, the flow rate of hydrogen is 200~600 sccm, the flow rate of methane is 1%~10% of the hydrogen flow rate, the growth temperature is 800~1100℃, the deposition pressure of the polycrystalline diamond film is 8~15 kPa, and the deposition power of the polycrystalline diamond film is 2500~6000 W.

10. An application of a polycrystalline diamond film in the fields of high thermal conductivity, wear resistance, and heat dissipation materials for electronic devices, characterized in that, The polycrystalline diamond film is prepared by the method according to any one of claims 1 to 9.

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