Preparation method and application of polycrystalline diamond film

Abstract

The invention discloses a preparation method and application of a polycrystalline diamond film, and the preparation method comprises the following steps: S1, foamy copper is die-cast on a copper substrate to form a copper substrate; s2, pickling the copper substrate to remove an oxide layer; s3, the surface of the copper substrate is coated with a diamond powder suspension seed layer; and S4, the copper substrate 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 substrate is subjected to acid etching or laser cutting, and the polycrystalline diamond film is obtained. The polycrystalline diamond film prepared by the preparation method does not warp and fall off due to the difference of thermal expansion coefficients of copper and diamond in the growth process, so that the regular and firmly attached polycrystalline diamond film can be prepared, and the polycrystalline diamond film has wide application in the field of high-thermal-conductivity and wear-resistant electronic device heat dissipation materials.

Description

Technical Field

[0001] This invention belongs to the field of polycrystalline diamond film preparation technology, specifically relating to a method for preparing polycrystalline diamond films and their applications. Background Technology

[0002] Diamond, due to its extremely high thermal conductivity, hardness, and chemical stability, has irreplaceable application value in fields such as heat dissipation coatings, cutting tools, and semiconductor devices. Copper, as a metal material with high thermal conductivity, low cost, and excellent plasticity, is an ideal growth carrier for diamond. The lattice constant of copper (approximately 0.361 nm) is very similar to that of diamond (approximately 0.357 nm); at the same time, carbon has extremely low solid solubility in copper, preventing the formation of a carbide transition layer. Therefore, theoretically, direct deposition of diamond on a copper substrate can yield polycrystalline diamond films with high crystallinity and high growth rate. However, diamond has an extremely low coefficient of thermal expansion (approximately 0.86 × 10⁻⁶). -6 / K) and copper's high coefficient of thermal expansion (approximately 17 × 10) -6 The significant difference between the diamond film and copper substrate ( / K) results in substantial residual thermal stress at the film-substrate interface during deposition and subsequent cooling. This stress can easily lead to cracking, warping, and even large-area peeling of the diamond film from the copper substrate, posing a significant challenge to the direct fabrication of intact and firmly adhered diamond films on copper substrates.

[0003] Patent application CN102337514A discloses a method for growing strongly adhering diamond films on copper substrates using a diamond embedding method. This method involves uniformly mixing copper powder and diamond powder (volume ratio 1:1~5), followed by cold pressing to prepare a diamond / copper composite substrate. Pre-embedded diamond microparticles serve as mechanical anchors and nucleation centers, achieving strong mechanical bonding between the diamond film and the copper substrate during CVD deposition. This effectively solves the film peeling problem caused by thermal expansion coefficient mismatch, achieving an adhesion strength greater than 15 N / cm for the first time. 2 A complete copper-based diamond film. However, a significant limitation is the low tolerance for errors in the composite substrate ratio (adhesion drops sharply to 5 N / cm when diamond powder > 1:5). 2 The cold pressing process, if the substrate porosity and density are not controlled, will result in uneven film growth.

[0004] Patent application CN120006249A discloses a method for growing diamond films on copper substrates. This method employs a dual-size diamond particle embedding and a titanium transition layer design. First, micron-sized first diamond particles are embedded into the copper substrate through grinding / photolithography pits to form mechanical anchors. Then, a thermal expansion buffer layer is constructed by sputtering a titanium transition layer and high-temperature annealing. Subsequently, nano-sized second diamond particles are attached to increase the nucleation density. Finally, an adhesion of 5.1 N and a low coefficient of friction are achieved during CVD deposition, significantly addressing the challenges of adhesion and nucleation rate in copper-based diamond films. However, the core drawback of this method is that its high-temperature annealing temperature is very close to the melting point of copper, drastically increasing the risk of substrate deformation. Furthermore, the thickness of the titanium transition layer is highly sensitive, exhibiting discontinuity when greater than 100 nm and a surge in interfacial thermal resistance when greater than 300 nm. The actual thermal conductivity is not disclosed, raising concerns about its heat dissipation performance.

[0005] Therefore, finding a method to prepare complete and firmly attached polycrystalline diamond films on copper substrates remains one of the core challenges in the field of polycrystalline diamond film preparation technology, and is also an important direction for future materials engineering design. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the first aspect of this invention provides a method for preparing a polycrystalline diamond film. This method can effectively alleviate the problem of fragility and cracking caused by the difference in thermal expansion coefficients between copper and diamond, thereby obtaining a complete and firmly adhered polycrystalline diamond film.

[0007] This invention provides a method for preparing a polycrystalline diamond film, comprising: 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.

[0008] Compared to growing diamond directly on a copper substrate, this invention uses copper foam to die-cast onto a copper substrate to form a copper base. On the one hand, it retains the lateral porous structure of the copper foam. This structure can effectively absorb thermal stress caused by the difference in thermal expansion coefficients through elastic deformation during the growth of the polycrystalline diamond film, thus playing a buffering role and significantly suppressing the fragility and cracking problems of the polycrystalline diamond film. On the other hand, the copper foam can be stably attached to the copper substrate, realizing the direct bonding between diamond and copper. This composite material can be directly applied to the field of heat dissipation.

[0009] Furthermore, the present invention also improves the adhesion and stability of polycrystalline diamond film on copper substrate by spraying a diamond powder suspension seed layer onto the copper substrate, using the longitudinal porous structure of foamed copper to fix diamond micro powder, and forming multiple bonding points at the growth interface to enhance the interface bonding ability in a mechanical interlocking manner.

[0010] Furthermore, the copper substrate formed by die-casting foamed copper onto a copper substrate in this invention has excellent thermal conductivity and can quickly conduct heat, which helps to maintain temperature uniformity during the growth of polycrystalline diamond films, minimizes excessive local temperature differences, and thus improves growth quality and efficiency. This process can be extended to the maximum diamond size allowed by the equipment.

[0011] 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%, wherein 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.

[0012] This invention controls the thickness of the copper foam and the compression ratio of the copper foam after die casting, enabling the copper foam to be die-cast to a thickness of hundreds of micrometers, resulting in a denser porous structure that can stably adhere to a copper substrate. This avoids the large deformation that occurs at high temperatures when the die-cast copper foam is too thick, which could lead to warping and large-scale detachment of the grown polycrystalline diamond film. It also avoids the reduced elastic buffering capacity caused by insufficient porous structure when the die-cast copper foam is too thin.

[0013] Preferably, the average pore size of the copper foam is 10~30 μm.

[0014] By providing a suitable average pore size for the foamed copper, the present invention can ensure that the transverse porous structure of the foamed copper has sufficient elastic deformation capacity after die casting, effectively buffering thermal stress; while the longitudinal porous structure can effectively anchor the diamond powder suspension, thereby preparing a complete and firmly attached polycrystalline diamond film.

[0015] Preferably, 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 1~3 h.

[0016] This invention provides suitable foamed copper die-casting process parameters to die-cast the foamed copper to a thickness of hundreds of micrometers. On the one hand, it retains its transverse porous structure to buffer thermal stress, and on the other hand, it makes the longitudinal structure more compact to enhance the stability of the substrate, allowing the foamed copper to adhere stably to the copper substrate, while anchoring the diamond powder suspension.

[0017] More preferably, the die-casting process parameters are as follows: in a vacuum environment, the die-casting temperature is 800~950℃, the die-casting pressure is 9~11 MPa, and the die-casting time is 1~2 h.

[0018] Preferably, the copper substrate is a copper sheet.

[0019] Preferably, the thickness of the copper substrate is 1 to 3 mm.

[0020] Preferably, the specific steps of the pickling are as follows: immersing the copper substrate in dilute hydrochloric acid with a volume concentration of 3% to 15% and ultrasonically cleaning for 10 to 30 minutes, which can remove the copper oxide on the surface of the copper substrate, thereby ensuring that the diamond powder suspension is firmly attached to the surface of the copper substrate.

[0021] Preferably, after the pickling step, the copper substrate is sequentially immersed in acetone and alcohol for ultrasonic cleaning for 10-30 minutes each, in order to remove organic contaminants such as grease from the surface of the copper substrate.

[0022] 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 invention is 10~30 μm, by selecting a diamond powder suspension with a smaller particle size, it can better penetrate into the pores, thereby effectively improving its nucleation density and adhesion.

[0023] Preferably, 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.

[0024] This invention provides suitable process parameters for the deposition and growth of polycrystalline diamond films, which can effectively leverage the thermal stress mitigation effect of the copper substrate and provide favorable growth conditions for preparing well-formed polycrystalline diamond films.

[0025] Secondly, the present invention also provides an application of the polycrystalline diamond film prepared by the method of the polycrystalline diamond film in the fields of high thermal conductivity, wear resistance and heat dissipation materials for electronic devices.

[0026] This invention relates to a polycrystalline diamond film grown on a copper substrate using a chemical vapor deposition method. This film is of great significance for achieving lightweight and higher heat dissipation efficiency in electronic devices and has wide applications in the fields of high thermal conductivity, wear resistance, and heat dissipation materials for electronic devices.

[0027] Compared with the prior art, the present invention has the following beneficial effects: This invention forms a copper substrate by die-casting copper foam onto a copper substrate, and then uses the copper substrate to prepare a polycrystalline diamond film. On the one hand, it can retain the lateral porous structure of the copper foam and utilize its elastic deformation capability to effectively alleviate the thermal stress caused by the mismatch in the expansion coefficients between the copper substrate and the diamond, thereby avoiding the problem of brittleness or cracking of the polycrystalline diamond film. On the other hand, the copper foam can be stably attached to the copper substrate by the die-casting step, further preventing large-scale detachment of the polycrystalline diamond film.

[0028] Furthermore, the present invention also uses the longitudinal porous structure of copper foam to anchor the diamond powder by spraying a diamond powder suspension onto the copper substrate and forming multiple bonding points at the growth interface. Through mechanical interlocking, the interfacial bonding ability is further enhanced, effectively improving the adhesion and overall stability of the polycrystalline diamond film on the copper substrate.

[0029] Furthermore, the copper substrate described in this invention has excellent thermal conductivity, which can effectively ensure temperature uniformity during the growth process, resulting in polycrystalline diamond films with better growth quality and efficiency. Attached Figure Description

[0030] Figure 1 The image shows the XRD pattern of the polycrystalline diamond film prepared in Example 1 of this invention.

[0031] Figure 2 This is a Raman image of the polycrystalline diamond film prepared in Example 1 of the present invention.

[0032] Figure 3 This is a SEM image of the polycrystalline diamond film prepared in Example 1 of the present invention.

[0033] Figure 4 This is a physical image of the polycrystalline diamond film prepared in Example 1 of the present invention.

[0034] Figure 5 This is a SEM image of the growth interface between the polycrystalline diamond film and the copper substrate during the preparation of the polycrystalline diamond film in Example 1 of this invention.

[0035] Figure 6 The image shows the XRD pattern of the polycrystalline diamond film prepared in Example 2 of this invention.

[0036] Figure 7 This is a Raman image of the polycrystalline diamond film prepared in Example 2 of the present invention.

[0037] Figure 8 This is a SEM image of the polycrystalline diamond film prepared in Example 2 of the present invention.

[0038] Figure 9 This is a physical image of the polycrystalline diamond film prepared in Comparative Example 1 of the present invention.

[0039] Figure 10This is a physical image of the polycrystalline diamond film prepared in Comparative Example 2 of the present invention. Detailed Implementation

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1 A 2 mm thick foamed copper sheet with an average pore size of 30 μm was placed on a copper sheet of the same size. This foamed copper was then pushed into a vacuum hot press furnace at a temperature of 800℃ and a pressure of 9 MPa for 1 hour. After die-casting, the foamed copper had a thickness of 500 μm. This foamed copper was then die-cast onto the copper sheet to serve as a copper substrate. The copper substrate was then immersed in a 10% (v / v) dilute hydrochloric acid solution. The container containing the copper substrate and the dilute hydrochloric acid was then placed in an ultrasonic cleaner. The ultrasonic cleaning time was set to 10 minutes, and the ultrasonic cleaning program was started to remove copper oxide from the surface of the copper substrate. The substrate was then sequentially immersed in acetone and alcohol for 10 minutes each for ultrasonic cleaning. Finally, a diamond powder suspension with a particle size of 1 μm was evenly sprayed onto the surface of the copper substrate using a spray device, thereby forming a uniform diamond powder seed layer on the substrate surface.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] A physical image of the polycrystalline diamond film prepared in Example 1 of this invention is shown below. Figure 4 As shown, a relatively well-formed polycrystalline diamond film can be observed, and its thickness is measured to be 311 μm.

[0048] Example 2 The only difference from Example 1 is that the parameters for die-casting 2 mm thick foamed copper on a copper substrate in Example 2 are: temperature 1000 ℃, pressure 12 MPa, die-casting time 3 hours, the thickness of the foamed copper after die-casting is 300 μm, and the average pore size of the foamed copper is 15 μm.

[0049] The XRD pattern of the polycrystalline diamond film prepared in Example 2 of this invention is shown below. Figure 6 As shown, 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. Figure 6 2θ in the x-axis and Figure 1 The meaning of 2θ on the x-axis is consistent. The growth of diamond on copper foam is relatively ideal, with good crystallinity, content, and purity of the diamond phase.

[0050] The Raman image of the polycrystalline diamond film prepared in Example 2 of this invention is as follows: Figure 7As shown, the polycrystalline diamond film sample contains a diamond phase, and the Raman signal of this diamond phase is quite significant.

[0051] SEM image of the polycrystalline diamond film prepared in Example 2 of this invention, as shown. Figure 8 As shown, although there are a few broken crystal particles, it can still be seen that diamond exhibits a large number of crystal structures with obvious geometric shapes. The crystals are mostly pyramid-shaped, and they are intertwined and stacked together.

[0052] Comparative Example 1 The only difference from Example 1 is that this Comparative Example 1 uses pure copper as the copper substrate and does not die-cast foamed copper on the copper substrate.

[0053] A physical image of the polycrystalline diamond film prepared in Comparative Example 1 of this invention is shown below. Figure 9 As shown, the polycrystalline diamond film grown directly on pure copper has poor crystal quality and exhibits cracking.

[0054] Comparative Example 2 The only difference from Example 1 is that in Comparative Example 2, a 2 mm thick foamed copper is placed directly on a pure copper substrate without a die-casting step.

[0055] A physical image of the polycrystalline diamond film prepared in Comparative Example 2 of this invention is shown below. Figure 10 As shown, during the high-temperature process of growing polycrystalline diamond films, the uncast copper foam undergoes significant elastic deformation, still causing the polycrystalline diamond film to warp and detach.

[0056] In summary, as shown in Comparative Examples 1 and 2 provided by this invention, directly using pure copper as a substrate, or placing excessively thick, uncast foamed copper on a pure copper substrate to grow a polycrystalline diamond film, both result in breakage and detachment. However, using the polycrystalline diamond film preparation method provided by this invention, where foamed copper is cast onto a copper substrate to form a copper base, as shown in Examples 1 and 2, the elastic deformation capability of the transverse porous structure of the foamed copper can absorb thermal stress. Furthermore, the cast foamed copper can be stably fixed on the copper substrate without excessive deformation. Additionally, by spraying a diamond powder suspension onto the copper substrate, the longitudinal porous structure can be used to fix the diamond micropowder, forming multiple bonding points at the growth interface. Figure 5 As shown, the interfacial bonding ability can be enhanced through mechanical interlocking, thereby significantly improving the adhesion and overall stability of the polycrystalline diamond film on the copper substrate. Moreover, compared with Example 2, Example 1 has a more suitable compression ratio of foamed copper under the die-casting process, which allows the polycrystalline diamond film to adhere more stably to the copper substrate, resulting in better growth quality and thus preparing a more regular polycrystalline diamond film.

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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