A method for mass production of ultraflat polycrystalline diamond films

Abstract

The application provides a method for mass production of super-flat polycrystalline diamond film, comprising the following steps: (1) growing a layer of polycrystalline diamond film on a growth substrate with diamond seeds on the surface by using chemical vapor deposition method; (2) cutting at least a part of the grown substrate to form a boundary line where the polycrystalline diamond film is connected with the growth substrate; (3) pasting a peeling tape; (4) peeling the polycrystalline diamond film from the surface of the growth substrate by pulling the peeling tape, so that the nucleation surface of the polycrystalline diamond film is exposed, wherein the roughness of the exposed nucleation surface is smaller than that of the growth surface. The application develops a novel and simple method for producing polycrystalline diamond film with reasonable price, mass production, super-flatness and transferability by turning over the nucleation surface of the grown polycrystalline diamond film, and the method has great potential in practical application.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of polycrystalline diamond film preparation process, and particularly relates to a method for large-scale manufacturing of polycrystalline diamond film with super-flat surface. BACKGROUND

[0002] High-quality synthetic diamond materials have been considered as ideal candidates for mechanical, electronic and optical applications due to their excellent physical and chemical properties. So far, people have successfully synthesized diamond materials, but it is still quite challenging to obtain large-scale, high-quality and ultra-thin diamond films.

[0003] Doped diamond can further expand its application in electronic devices, such as p-type semiconductor doped with boron and superconductor, and quantum photonics materials based on atomic defects doped with nitrogen, silicon, etc., especially those called next-generation diamond substrates, such as films, which are expected to play an important role in effective heat dissipation of circuits and high-power electronic devices, especially for emerging soft / flexible electronic devices.

[0004] Realizing the above-mentioned diamond-based functional elements necessarily involves standard nanofabrication and seamless integration, all of which put higher requirements on the surface roughness of diamond materials. In addition, the flat surface of the device is also a prerequisite for many testing / characterization methods, which are widely used in the corresponding field, such as thermal conductivity measurement and bonding in the semiconductor industry.

[0005] However, unlike other materials such as silicon, it is very difficult to planarize diamond materials, which requires a lot of time and energy through traditional methods such as polishing.

[0006] Diamond films are mainly prepared by homo- and hetero-growth through chemical vapor deposition (CVD) technology. Single-crystal diamond (SCD) films are mainly obtained by homo-growth on bulk diamond substrates, which represent the highest quality required for many applications. For example, it has high value for high mobility of electrons and holes, as well as excellent resistance to radiation, for detectors in nuclear and high-energy physics experiments. However, the expensive growth process, limited manufacturing scale and complex processing of CVD-grown SCD hinder its popularization and application.

[0007] Although the hetero-growth of SCD on iridium has been confirmed in a limited number of laboratories around the world, it is still difficult to control the quality of the obtained diamond, which tends to form polycrystalline diamond (PCD) films due to lattice mismatch. Therefore, it is still very challenging to construct large-area SCD films on any substrate.

[0008] In contrast, polycrystalline diamond (PCD) films can be easily obtained on a variety of common substrates, such as Si, SiC, TiC, Co, Pt, AI2O3, Ni and Re, etc., which are cheap and easy to grow. In particular, at a sufficiently high nucleation density, it can form a continuous film, and the quality of the film is closely related to the directionality of the nucleation. In order to optimize the PCD film, researchers have proposed the concept of nanocrystalline and ultra-nanocrystalline diamond film, which forms a continuous nucleus by depositing diamond seeds. However, the surface smoothness of the PCD film is not satisfactory, which is one of the biggest bottlenecks for promoting such an excellent platform.

[0009] In summary, the extremely strict growth conditions of single crystal diamond (SCD) greatly hinder the application of diamond materials in large-scale, cost-acceptable fields; and the poor surface morphology and high roughness caused by the uneven profile of polycrystalline diamond (PCD) seriously limit its further construction of high-precision photonic structures at the nanometer / micrometer scale. SUMMARY

[0010] Therefore, the purpose of the present application is to overcome the problems of poor surface morphology and high roughness of polycrystalline diamond (PCD) film, and to provide a simple method for preparing large-area, ultra-flat and transferable PCD film in a scalable and controllable manner.

[0011] The first aspect of the present application provides a method for scaling up the growth of ultra-flat polycrystalline diamond film, comprising:

[0012] (1) growing a polycrystalline diamond film on a growth substrate having diamond seeds on the surface at a temperature of 800-1000℃ by chemical vapor deposition, wherein the polycrystalline diamond film comprises a growth surface (or called "growth face") with a first roughness and a nucleation surface (or called "nucleation face") bonded to the growth substrate;

[0013] (2) cutting at least a part of the growth substrate on which the polycrystalline diamond film is grown, which cutting operation forms a boundary line where the polycrystalline diamond film is bonded to the growth substrate;

[0014] (3) pasting a release tape to the growth surface of the polycrystalline diamond film, wherein the release tape extends beyond the polycrystalline diamond film at least at the edge of the cutting part to form a release operation end;

[0015] (4) pulling the release operation end to peel the polycrystalline diamond film from the surface of the growth substrate to expose the nucleation surface of the polycrystalline diamond film, wherein the exposed nucleation surface has a second roughness, and the second roughness is smaller than the first roughness.

[0016] According to the method provided by the present application, the first roughness can be 10-200 nm, for example, 20-50 nm. In a preferred embodiment of the present application, the second roughness can be 0.5-5 nm, preferably 0.5-2 nm, more preferably 0.5-1 nm.

[0017] According to the method provided by the present application, the particle size of the diamond seed in step (1) can be 2-10 nm. In some embodiments of the present application, the growth substrate can be selected from one or more of Si, SiC, TiC, Co, Pt, Al2O3, Ni, Re, Ir, SiO2, and Mo. In a preferred embodiment of the present application, the surface roughness of the growth substrate is less than 2 nm, preferably less than 1 nm, more preferably less than 0.5 nm. Preferably, the growth of the polycrystalline diamond film in step (1) is carried out using a microwave plasma assisted chemical vapor deposition (MPCVD) device. In some embodiments of the present application, the thickness of the polycrystalline diamond film can be 200 nm-100 μm, preferably 200 nm-10 μm, more preferably 400 nm-5 μm.

[0018] According to the method provided by the present application, the deposition temperature of the chemical vapor deposition method in step (1) is preferably 850-950°C.

[0019] According to the method provided by the present application, the cutting operation in step (2) is preferably carried out perpendicular to the growth surface of the polycrystalline diamond film. The cutting operation can be carried out along a straight line, a curve, or an arc. In a preferred embodiment of the present application, the cutting operation is such that the length of the interface line formed by the polycrystalline diamond film and the growth substrate is at least 1% of the circumference of the growth surface of the polycrystalline diamond film, for example, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, preferably 5%-20%, preferably 10%-12%.

[0020] In a preferred embodiment of the present application, in order to facilitate mass production, the cutting operation in step (2) can be carried out along a straight line. When the growth substrate is circular, the length of the interface line formed by the polycrystalline diamond film and the growth substrate is preferably 20%-50% of the diameter of the substrate.

[0021] The inventors of the present application have found through extensive experimental research that, by the cutting operation in step (2), the adhesion force caused by the excessive coverage of the polycrystalline diamond film on the sidewall of the growth substrate can be reduced, and the polycrystalline diamond film can gradually separate from the growth substrate starting from the cutting position with the help of the release tape, thereby obtaining a complete polycrystalline diamond film, and the growth substrate after peeling can also be recycled.

[0022] According to the method provided by the present application, the peeling tape in step (3) can be a 3M tape, a PVC tape, a PE tape, etc. In the embodiment of the present application, the peeling tape completely covers the PCD film remaining after the cutting operation, and has a margin at least at the cutting edge to facilitate the subsequent peeling operation.

[0023] The inventors of the present application have found through a large number of experimental researches that although the peeling performance of PCD films with different thicknesses is related to their mechanical strength, different peeling operations (such as speed and peeling angle) also have an impact on them. Reasonable peeling operation within the range allowed by the mechanical strength is a prerequisite for obtaining large-area, complete and less-cracked films.

[0024] In the present application, the peeling angle refers to the angle between the peeling force for pulling the peeling operation end to separate the PCD film from the growth substrate and the growth surface of the PCD film (with the starting position of the peeling operation end of the peeling tape defined as 0°). The peeling angle range for obtaining complete and less-cracked PCD films is referred to as the safe peeling angle.

[0025] In the present application, the completeness refers to the percentage of the area of the PCD film obtained by peeling to the area of the growth substrate after peeling.

[0026] According to the method provided by the present application, the speed for pulling the peeling operation end to peel the PCD film from the growth substrate surface in step (4) can be 1-10 mm / s. In the preferred embodiment of the present application, the peeling angle of the peeling operation in step (4) can be 10-90°.

[0027] According to the method provided by the present application, the nucleation surface has a higher refractive index than the growth surface. Preferably, the nucleation surface has a lower extinction coefficient than the growth surface.

[0028] The levels of these optical parameters of the PCD film prepared by the method of the present application are comparable to those of SCD grown by the CVD method.

[0029] According to the method provided by the present application, compared with the position of the (111) crystal plane XRD diffraction peak of the growth surface, the position of the (111) crystal plane XRD diffraction peak of the nucleation surface is closer to the standard (111) crystal plane XRD diffraction peak of single crystal diamond; and the full width at half maximum (FWHM) of the Raman spectrum of the (111) crystal plane of the nucleation surface is smaller than that of the (111) crystal plane of the growth surface. The shift of the XRD diffraction peak indicates the improvement of the crystalline quality, and the narrowing of the full width at half maximum of the Raman spectrum means that the internal crystallization of the film is improved.

[0030] According to the method provided by the application, the method can further comprise reducing the adhesion of the release tape by using a solvent to release the polycrystalline diamond film; or a heat-releasing release tape can be used to release the polycrystalline diamond film from the release tape by heating.

[0031] The second aspect of the application also provides a method for regulating the energy band of a diamond film, which comprises attaching the polycrystalline diamond film prepared by the method to the surface of a flexible substrate, stretching and / or compressing the polycrystalline diamond film by bending the flexible substrate, and regulating the energy band structure of the polycrystalline diamond film by the strain generated in the polycrystalline diamond film during the stretching and / or compressing.

[0032] Although the growth surface of the polycrystalline diamond film has been reported in a large number of studies, the nucleation surface is rarely mentioned because it is difficult to expose to the public. The present application first proposes a novel and simple method to obtain the nucleation surface of polycrystalline diamond in situ without introducing any damage, and large-area, ultra-flat and transferable polycrystalline diamond films can be mass-produced and controlled by using this method. By characterizing the surface morphology and material properties of the nucleation surface in detail, the effectiveness of the method of the present application is verified.

[0033] Compared with other methods of exposing the nucleation surface (such as the method of sacrificing the growth substrate described in the previous application 202310540694.7), the method of the present application reduces impurities caused by multiple operations (such as grinding and etching). Therefore, this peeling method can maintain the original state of the nucleation surface without causing any damage. By characterizing the roughness of the growth surface and the nucleation surface of polycrystalline diamond films of different thicknesses, it can be seen that the roughness of the nucleation surface of various thicknesses can be less than 1 nm, while the roughness of the growth surface increases with the thickness. Compared with the reported studies on optimizing the surface roughness of diamond films, the peeling method of the present application has obvious advantages in both the thickness range and the size of the film. Therefore, so far, the method of the present application can be considered as the best method to obtain polycrystalline diamond films with the largest size, the flattest surface and the largest thickness range. The novel, scalable and controllable strategy proposed by the present application paves the way for the development of high-quality and cost-effective polycrystalline diamond films, and makes polycrystalline diamond films expected to become the basic components of various high-performance structures and devices in different fields. BRIEF DESCRIPTION OF DRAWINGS

[0034] Hereinafter, the embodiments of the present application will be described in detail with reference to the accompanying drawings, in which:

[0035] Figure 1 A schematic diagram of the method for preparing a polycrystalline diamond film of the present application.

[0036] Figure 2 Figures (a), (b) and (c) are photographs of a 2-inch silicon wafer on which a polycrystalline diamond film was grown (a), a peeling process (b), and a polycrystalline diamond film after peeling and a silicon wafer after peeling (c) in Example 1, respectively.

[0037] Figure 3 Photographs of nucleation surfaces of polycrystalline diamond films having different thicknesses prepared in Examples 2-5.

[0038] Figure 4 Statistical graphs of cracks and integrity of polycrystalline diamond films having different thicknesses prepared in Examples 2-5.

[0039] Figure 5 SEM images of a growth surface (a), a nucleation surface (b), and a cross-section (c) of a polycrystalline diamond film having a thickness of 1000 nm prepared in Example 5.

[0040] Figure 6 SEM images of a growth surface (top) and a nucleation surface (bottom) of polycrystalline diamond films having different thicknesses prepared in Examples 2-5.

[0041] Figure 7 AFM images of a growth surface (a) and a nucleation surface (b) of a polycrystalline diamond film having a thickness of 1000 nm prepared in Example 5, and a nucleation surface (c) of a polycrystalline diamond film having a thickness of 1000 nm prepared in Example 6.

[0042] Figure 8 Roughness statistics (statistical area 20 μm x 20 μm) of growth surfaces and nucleation surfaces of PCD films having different thicknesses prepared in Examples 2-5 (a), comparison of the method of the present application with other reported methods in terms of film thickness and roughness (b), and comparison of the method of the present application with other methods in terms of film size and roughness (c).

[0043] Figure 9 Refractive index comparison of a growth surface (a) and a nucleation surface (b) of a polycrystalline diamond film prepared in Example 1.

[0044] Figure 10 XRD results of a growth surface (a) and a nucleation surface (b) of a polycrystalline diamond film prepared in Example 1.

[0045] Figure 11 Raman spectra of a growth surface (a) and a nucleation surface (b) of a polycrystalline diamond film prepared in Example 1.

[0046] Figure 12 Photographs of a 360-degree bending method (a) and a winding on a cylinder having different radii (b) of a 4-μm-thick polycrystalline diamond film prepared in Example 7.

[0047] Figure 13 Different bending modes (a) and corresponding strain distribution on the surface (b) of a 4 pm thick polycrystalline diamond film prepared in Example 7 on a flexible PDMS substrate.

[0048] Figure 14 Variation of electrical conductivity of a 4 pm thick polycrystalline diamond film prepared in Example 7 under different strains (a) and bending cycles (b).

[0049] Figure 15 Raman spectrum (a) and XPS measurement results (b and c) of a polycrystalline diamond film prepared in Example 5.

[0050] Figure 16 Contact angle experimental photos and data summary of growth surface and nucleation surface of PCD films of different thicknesses.

[0051] Figure 17 Friction coefficient of growth surface and nucleation surface (a) of a polycrystalline diamond film prepared in Example 5 and the relationship curve between external force acting on the growth surface and nucleation surface and the indentation depth formed (b).

[0052] Figure 18 Refractive index (a) and extinction coefficient (b) of growth surface and nucleation surface of a polycrystalline diamond film with a thickness of 500 nm; and refractive index (c) and extinction coefficient (d) of growth surface and nucleation surface of a polycrystalline diamond film with a thickness of 1000 nm.

[0053] Figure 19 Fatigue test results of polycrystalline diamond films of the present application, wherein (a) is a photo after >10,000 deformation cycles at 2% strain; (b) is a 5x magnification optical image corresponding to regions 1 and 2 in (a).

[0054] Figure 20 Comparison of experimental statistics of microcrack density on thin films of different thicknesses peeled off at different peeling angles (a) and simulation calculation of crack propagation probability on films of different thicknesses at different peeling angles (b) in Example 9 of the present application.

[0055] Figure 21 Photos before (a) and after (b) peeling and resistance change (c) before and after peeling of a 2-inch polycrystalline diamond film after making a chip array in Example 10 of the present application.

[0056] Figure 22 Scanning electron microscope images of micro / nano fabrication respectively performed on growth surface and nucleation surface of a polycrystalline diamond film in Example 11 of the present application.

[0057] Figure 23Fluorescence spectrum of NV centers in the polycrystalline diamond film prepared in Example 12 of the present application (a); and the results of optical detection magnetic resonance (ODMR) test of the polycrystalline diamond film with NV centers (b). DETAILED DESCRIPTION

[0058] The present application will be further described in conjunction with the specific embodiments, and the examples given are only for the purpose of illustrating the present application, but not for limiting the scope of the present application.

[0059] Figure 1 is a schematic diagram of the polycrystalline diamond film preparation method of the present application, and the preparation process includes:

[0060] I. CVD growth of polycrystalline diamond film;

[0061] II. Cutting the grown substrate and polycrystalline diamond film to the next part to form a new boundary;

[0062] III. Paste the adhesive tape for mechanical peeling to separate the polycrystalline diamond film from the substrate.

[0063] Example 1

[0064] Manufacture of polycrystalline diamond film

[0065] (1) Growth of polycrystalline diamond film on silicon substrate

[0066] Diamond heteroepitaxial growth on silicon substrate includes three steps: pretreatment of the substrate, deposition of diamond seed crystal and CVD growth of polycrystalline diamond film.

[0067] Pretreatment of the substrate: pretreat the silicon surface with hydrogen plasma, place a 2-inch silicon wafer in a microwave plasma assisted chemical vapor deposition (MPCVD) device under the conditions of 1300W power, 35Torr chamber pressure and 300sccm H2gas flow for 10 minutes.

[0068] Deposition of diamond seed crystal: mix diamond seed crystal (purchased from Tokyo Chemical Industry Co., Ltd.) with a size of less than 10 nm, dimethyl sulfoxide (DMSO), anhydrous ethanol and acetone in a mass ratio of 1:5000:250:250. Ultrasonically disperse the mixture for 12 hours, then centrifuge at 1000r / min for 20 minutes to separate the impurities. Spin the suspension on the silicon wafer, deposition parameters: 500r / min, add 3 drops within 15s, then increase the speed to 4500r / min for 110s. Repeat three times.

[0069] CVD growth of diamond film: A silicon wafer with diamond seeds deposited thereon was placed in an MPCVD apparatus (Seki 6350) to grow a diamond film, the main growth parameters including: 3400W microwave power, 900°C temperature, 15sccm methane flow rate, and 40 minutes of growth time, to grow a PCD film of about 447 thick on the silicon substrate.

[0070] (2) Dicing of polycrystalline diamond film and growth substrate

[0071] A 2-inch silicon wafer with a polycrystalline diamond film grown on the surface was diced with a silicon wafer dicer or a diamond cutter to form a new boundary along a straight line at a distance of 2-5 mm from the edge of the back surface of the growth substrate, so that a clear demarcation line of the polycrystalline diamond film and the growth substrate was formed at the dicing position.

[0072] (3) Adhesion of release tape

[0073] A release tape with a size of 10 cm x 6 cm was adhered to the growth surface of the polycrystalline diamond film, so as to completely cover the growth surface of the polycrystalline diamond film and extend beyond the edge of the polycrystalline diamond film at the dicing position to form a release operation end (release pull handle).

[0074] (4) Release of polycrystalline diamond film

[0075] The release operation end reserved in step (3) was pulled at a release angle of 40-60 degrees and a speed of 5 mm / s to release the polycrystalline diamond film from the surface of the silicon wafer, so as to expose the nucleation surface of the polycrystalline diamond film.

[0076] Figure 2 are photos taken during the operation process of the present embodiment. Among them, Figure 2 The photos of (a), (b) and (c) of FIG. 1 are, in order, photos of a 2-inch silicon wafer with a polycrystalline diamond film grown on the surface, a release process, a polycrystalline diamond film after release, and a silicon wafer after release.

[0077] Examples 2-5

[0078] Manufacture of polycrystalline diamond films with different thicknesses

[0079] Polycrystalline diamond films with thicknesses of 200 nm, 400 nm, 800 nm and 1000 nm were respectively manufactured in a manner similar to that of Example 1. Figure 3 are photos of the nucleation surfaces of polycrystalline diamond films with different thicknesses after release. It can be seen from the photos that polycrystalline diamond films with different thicknesses can be completely released from the substrate, which proves the effectiveness of the release method of the present application.

[0080] To effectively evaluate their performance, the number of micro-cracks (generated during exfoliation) and the integrity (proportion of the grown substrate size) of these PCD films were statistically analyzed. Figure 4 The crack and integrity statistics of the PCD films of different thicknesses prepared in Example 2-5 are shown. The right-hand side images are 50x optical images of the PCD films with thicknesses of 200 nm (upper) and 1000 nm (lower), respectively. As can be seen from the images, the crack density of the 200 nm thin film is significantly higher than that of the 1000 nm thin film. From these results, it can be seen that the number of cracks is increasing as the thickness decreases, which indicates that the PCD film has exfoliation properties similar to two-dimensional materials when the thickness is thinned to 200 nm. At the same time, the integrity of the exfoliated film decreases from 100% to 99.43% as the thickness is thinned to 200 nm, which is mainly related to the different adhesion of the grown substrate.

[0081] Example 6

[0082] Optimization of the fabrication of PCD films

[0083] In a similar manner to Example 1, a PCD film with a thickness of 1000 nm was fabricated, except that before the substrate was pretreated, the surface of the silicon wafer was polished to reduce the roughness from 1 nm to 0.5 nm.

[0084] Morphology and performance characterization of polycrystalline diamond films

[0085] 1. The growth surface, nucleation surface and cross-section of the PCD films of different thicknesses prepared in Example 2-6 were characterized by SEM.

[0086] Figure 5 The typical SEM images of the growth surface, nucleation surface and cross-section of the 1000 nm thick PCD film prepared in Example 5 are shown. Figure 6 The SEM images of the growth surface (upper) and nucleation surface (lower) of the PCD films of different thicknesses prepared in Example 2-5 are shown. As can be seen from the images, Figure 5 It can be seen that there are various large grains (hundreds of nanometers) on the growth surface, but the nucleation surface shows a flat morphology without any visible grains; from the cross-section, the gradient change in the size of the grains can also be seen. In addition, Figure 6The SEM images also show that the grains on the growth surface are increasing in size as the thickness increases, in sharp contrast to the nucleation surface where the surface morphology remains unchanged. This apparent difference in growth surface morphology is mainly related to the growth mode of the PCD film. Specifically, diamond particles with a size no greater than 10 nm are deposited as seeds on the silicon substrate prior to CVD growth; during the subsequent growth, the diamond particles can only grow randomly in the upward and horizontal directions because the silicon substrate hinders the growth of the diamond in the downward direction. In particular, the morphology of the nucleation surface depends on the surface of the growth substrate, the size of the seeds, and the nucleation density.

[0087] 2. Atomic force microscopy (AFM) was used to characterize the growth surface and the nucleation surface of the PCD films of different thicknesses prepared in Examples 2-6.

[0088] Figure 7 AFM images of the growth surface (a) and the nucleation surface (b) of the 1000 nm thick PCD film prepared in Example 5, and the nucleation surface (c) of the 1000 nm thick PCD film prepared in Example 6 are shown.

[0089] By Figure 7 As can be seen from the AFM images, the surface roughness (Ra) of the PCD film of Example 5 decreases from 36.2 nm (growth surface) to 0.952 nm (nucleation surface), and when a smoother growth substrate is used in Example 6, the surface roughness continues to decrease to 0.612 nm. This ultra-smooth surface is comparable to that of a polished single-crystal diamond and meets the requirements of high-precision nanomachining. In addition, compared to other strategies for exposing the nucleation surface, such as sacrificial growth substrates, the method of the present application avoids impurities caused by multiple operations. Therefore, this peeling method can maintain the original state of the nucleation surface without causing any damage.

[0090] Figure 8The figures are as follows: (a) Statistical analysis of the roughness of the growth and nucleation surfaces of PCD films of different thicknesses obtained in Examples 2-5 (statistical area 20 μm × 20 μm); (b) Comparison of the method of the present invention with other reported methods in terms of film thickness and roughness; and (c) Comparison of the method of the present invention with other methods in terms of film size and roughness. By comparing the roughness of the growth and nucleation surfaces of PCD films of different thicknesses, it can be seen that the roughness of the nucleation surface is less than 1 nm for both thicknesses, while the roughness of the growth surface increases progressively. Compared with previously reported studies on optimizing the surface roughness of diamond films, the peeling method of the present invention has significant advantages in both thickness range and PCD film size. Therefore, it can be considered the best method to date for obtaining PCD films with the largest size, smoothest surface, and largest thickness range. Furthermore, if the growth time is extended and a larger growth substrate is used, even thicker and larger PCD films can be obtained.

[0091] 3. The refractive index of the growth surface and nucleation surface of the polycrystalline diamond film in Example 1 was measured using an optical ellipsometer, such as... Figure 9 As shown in the figure, n represents the refractive index, and k represents the extinction coefficient. From Figure 9 The measurement results show that the nucleation surface has a higher refractive index and a lower extinction coefficient than the growth surface, and it was found that the levels of these optical parameters of the nucleation surface are comparable to those of SCD grown by CVD.

[0092] 4. The crystallization characteristics of the polycrystalline diamond film prepared in Example 1 were characterized using X-ray diffraction (XRD) technology, such as... Figure 10 As shown, distinct diffraction peaks were obtained at 43.96°, 75.14°, and 91.52°, corresponding to the (111), (220), and (311) crystal planes, respectively, confirming the diamond-like properties of the nucleation surface. The strong diffraction peak of the (111) crystal plane indicates its dominance, consistent with other reports. Furthermore, the full width at half maximum (FWHM) of the (111) crystal plane diffraction peak on the nucleation surface is 0.64° narrower than that on the growth surface. In addition to the change in FWHM, the position of the diffraction peak of the (111) crystal plane shows a significant shift. Figure 10 (Illustration) The diffraction peak shifts from 44.36° (growth surface) to 43.96° (nucleation surface), which is close to the position (43.95°) of a standard (111) oriented SCD. The shift in diffraction peak indicates an improvement in crystal quality, which may be related to the release of internal stress. Typically, residual stress is introduced into the film due to the lattice mismatch between diamond and the heterogeneous substrate, which further induces lattice distortion, leading to an anomalous shift in diffraction peaks. By employing the manufacturing method of this invention, residual stress has the opportunity to be released after the growth substrate is removed.

[0093] 5. Raman spectroscopy was used to further characterize the crystallinity of the polycrystalline diamond film prepared in Example 1. Figure 11 From the Raman spectrum, at 1332.8 cm⁻¹ -1 A distinct diamond scattering peak was observed at [location], further confirming the state of the film. Furthermore, from [location]... Figure 11 From the illustration, the FWHM (7.43 cm) on the nucleation surface... -1 The FWHM (7.67 cm) of the growth surface was greater than that of the growth surface. -1 The narrower diameter indicates improved internal crystallization of the film as measured from the nucleation surface.

[0094] As can be seen, in addition to the reduced roughness of the nucleation surface, the crystal quality is also optimized compared to the grown surface, based on Raman shift and X-ray diffraction performance. Furthermore, in terms of optical properties, the refractive index of the nucleation surface is lower than that of the grown surface, comparable to that of a single crystal.

[0095] Table 1 summarizes the comparison of polycrystalline diamond films prepared by the method of the present invention with previously reported polycrystalline diamond films in terms of surface roughness, thickness range, and size (film area).

[0096] Table 1

[0097]

[0098] As can be seen from the data in Table 1, the polycrystalline diamond film obtained by the method of the present invention has a very low surface roughness, which is close to the level of polished single-crystal diamond bulk. In addition, the obtained film is superior to the previously reported work in terms of size and thickness.

[0099] Example 7

[0100] Fabrication and characterization of a 4 μm thick polycrystalline diamond film

[0101] Following a method similar to that in Example 1, a polycrystalline diamond film with a thickness of 4 μm was fabricated, and then the polycrystalline diamond film was directly attached to a flexible PDMS substrate for bending performance and conductivity testing.

[0102] Flexural properties of polycrystalline diamond films

[0103] The polycrystalline diamond film peeled by the method of the present invention can be arbitrarily deformed without being limited by a rigid growth substrate. Figure 12 Photographs (A) showing a 4 μm thick PCD film bent at 360 degrees and (B) showing it wound around cylinders of different radii.

[0104] like Figure 12As shown, for the ~4 pm thick film prepared in Example 7, it can support 360° bending mode and its tolerable curvature radius can be reduced to 2 mm. And the film remains stable after more than 2500 bending cycles.

[0105] Fatigue test of polycrystalline diamond film

[0106] A polycrystalline diamond film with a thickness of 4 pm, which was prepared according to the method of Example 1, was attached to a flexible PDMS substrate and subjected to 2% deformation cycles. Figure 19 The (a) figure is a photo after >10000 deformation cycles at 2% strain; the (b) figure is a 5x magnification optical image corresponding to region 1 and region 2 in the (a) figure. As can be seen, the polycrystalline diamond film of the present application can withstand >10000 deformation cycles at 2% strain without any damage.

[0107] These incredible diamond bending and fatigue properties are first observed at the macro scale, compared to the maximum strain of previously reported polycrystalline diamond films occurring on micro scale samples. According to the theoretical prediction of single crystal diamond nanopillars in the past, the band gap will gradually decrease with the increase of strain. However, due to the complex crystal structure inside the diamond, this principle is rarely confirmed in theory and experiment. Fortunately, the present application can observe the dynamic properties of independent polycrystalline diamond films through a simple exfoliation strategy.

[0108] Conductivity of polycrystalline diamond film and its band gap regulation

[0109] In order to investigate the conductivity of polycrystalline diamond film under different bending degrees, the inventors adhered a polycrystalline diamond film with a thickness of 4 pm prepared in Example 7 to a flexible PDMS (polydimethylsiloxane) substrate with a thickness of 1 mm, and then successively adhered a soft conductive tape. By controlling the deformation of the PDMS substrate, the bending operation of the polycrystalline diamond film can be realized. In addition, by bending the PDMS substrate in different directions, the deformation of the polycrystalline diamond film under tensile and compressive strain can be observed respectively. According to the calculation results shown in the table, it can be seen that the strain distribution is uneven, and the maximum deformation occurs at the center position, whether it is the top surface or the bottom surface of the PDMS. Figure 13

[0110] Figure 14 The change of the electrical conductivity of the 4 pm thick polycrystalline diamond film prepared in Example 7 under different strains (a) and bending cycles (b). By measuring the resistance under dynamic strain, it is observed that the film has a huge piezoresistive property. In both bending modes, the resistance gradually decreases with the increase of strain, but the change amplitude of the resistance in the downward bending mode is greater than that in the upward bending mode. In addition, the resistance can be completely restored during the loading-unloading cycle. ​

[0111] The above results show that the energy band structure of the polycrystalline diamond film can be regulated by strain, and as the degree of strain increases, the energy band of the diamond gradually decreases, and thus the conductivity increases. Generally, the regulation of the energy band of the diamond is mainly achieved by element doping, but the diamond doping has high requirements on the process, and it is difficult to complete in an ordinary laboratory. The method for regulating the energy band of the diamond by strain greatly reduces the preparation difficulty and production cost, and provides convenience for the development of flexible diamond semiconductor devices and diamond-based sensor devices.

[0112] Example 8

[0113] Material properties of the polycrystalline diamond film

[0114] Figure 15 Raman spectrum (a) and XPS measurement results (b) and (c) of the polycrystalline diamond film prepared in the above embodiment 5.

[0115] Figure 16 Contact angle experimental photos and data summary of the growth surface and nucleation surface of the PCD film with different thicknesses.

[0116] Figure 17 Friction coefficient (a) of the growth surface and nucleation surface of the polycrystalline diamond film prepared in embodiment 5, and the relationship curve between the external force acting on the growth surface and nucleation surface and the indentation depth formed (b).

[0117] Figure 18 Refractive index (A) and extinction coefficient (B) of the growth surface and nucleation surface of the polycrystalline diamond film with a thickness of 500 nm, and refractive index (C) and extinction coefficient (D) of the growth surface and nucleation surface of the polycrystalline diamond film with a thickness of 1000 nm.

[0118] The above results show that, compared with the growth surface, the nucleation surface has a higher refractive index and a lower extinction coefficient. The refractive index of the nucleation surface is comparable to that of the monocrystalline bulk diamond. Moreover, as the thickness increases, the refractive index of the growth surface and the nucleation surface decreases, and the extinction coefficient increases. Such a diamond film with high refractive index and low absorption coefficient provides a possibility for the development of diamond-based micro-nano optical devices, such as optical superlenses, optical modulators, etc.

[0119] Example 9

[0120] Influence of different peeling angles

[0121] In a similar way as in Example 1, polycrystalline diamond films of different thicknesses were manufactured and exfoliated at a constant rate (10 mm / min) and different exfoliation angles (20°-90°). In addition, possible crack propagation was simulated by a phase field method. For a detailed description of the phase field method, see the following two references:

[0122] Miehe, C., Hofacker, M. & Welschinger, F. A phase field model for rate- independent crack propagation: Robust algorithmic implementation based on operator splits. Computer Methods in Applied Mechanics and Engineering 199, 2765-2778 (2010).

[0123] Spatschek, R., Brener, E. & Karma, A. Phase field modeling of crack propagation. Philosophical Magazine 91, 75-95 (2011).

[0124] By calculating the crack density on the exfoliated films, it was found that the exfoliation quality depends on the exfoliation angle and the thickness match of the film. For thicker films (800 nm and 1000 nm), a large range of exfoliation angles (20°-90°) can be used to obtain crack-free films; when the film thickness is 600 nm, the exfoliation angle range for the least cracks is reduced to 40°-70°. When the film continues to thin, the operating window continues to shrink.

[0125] Phase-field simulations were performed on a 600 nm thick polycrystalline diamond film subjected to peeling at different peeling angles of 30°, 60°, and 90°. The initial crack sizes were set to 56 nm (upper surface) and 1.2 nm (lower surface), with 95% of the cracks smaller than these dimensions for the corresponding surfaces. The simulation results show that at a small peeling angle of 30°, the separated film undergoes slight bending deformation, with both the upper and lower surfaces under tensile stress, ultimately leading to large crack propagation starting from the upper surface. In contrast, at a larger peeling angle (90°), the upper surface (concave) of the film is compressed, preventing potential crack growth. However, on the highly deformed lower surface (convex) side of the film, increased tensile stress triggers the propagation of small initial cracks. Therefore, at a moderate peeling angle (60°), no crack propagation occurs within the 600 nm thick film.

[0126] For thicker films (700 nm to 1000 nm), simulations show that a peel angle between approximately 30° and 90° can prevent crack propagation. These results agree well with the observed crack densities of different peeled films. Therefore, they can be used to guide the large-scale production of crack-free films.

[0127] Example 10

[0128] Integrity and quality evaluation of polycrystalline diamond films

[0129] The initial resistance of the polycrystalline diamond film grown in Example 1 was measured to be approximately 104 Ω.

[0130] Since the resistance of a diamond film is determined by its integrity and quality, in order to evaluate the potential impact of the peeling process on the film quality, a chip array was fabricated on a 2-inch diamond film, each containing a pair of gold electrodes, and the change in resistance before and after peeling was measured. Figure 21 Photographs of the chip array fabricated on a 2-inch polycrystalline diamond film before (a) and after (b) peeling, and the resistance change before and after peeling (c).

[0131] from Figure 21 Figure (c) shows a relatively uniform resistance distribution, indicating that the film of the present invention is consistent throughout the entire 2-inch diamond film, and the resistance remains almost uniform at each location after peeling (the overall resistance decreases, possibly related to the removal from the silicon substrate). This result demonstrates that the polycrystalline diamond film of the present invention has good integrity and high quality.

[0132] Example 11

[0133] Micro / nano fabrication on polycrystalline diamond films

[0134] The micro / nano structures were prepared on the growth surface and nucleation surface of the polycrystalline diamond film prepared in Example 1 by electron beam lithography (EBL) and plasma etching technology, and the results are shown in Figure 22 .

[0135] By comparing the micro / nano structures prepared on the growth surface and nucleation surface, it can be seen that the residual on the nucleation surface is significantly less, and the structure accuracy is higher.

[0136] Example 12

[0137] Application of polycrystalline diamond film as quantum platform

[0138] According to the similar method of Example 1, the polycrystalline diamond film was prepared, except that nitrogen was introduced during the CVD growth process to produce special atomic defects on the film, which are called nitrogen vacancy (NV) color centers.

[0139] The diamond film was excited by a 532 nm laser (Changchun Xin Industrial Company, MGL-FN-5321W), and the laser was focused on the diamond film through a 40x air objective. The excited NV fluorescence was filtered by a 605 nm long pass filter and imaged on an EMCCD (Teledyne Photometrics, Evolve 512 Delta), as shown in Figure 23 (a) of the figure. The inset in the fluorescence image shows the bright spot corresponding to the emission of the NV color center. The peak at about 640 nm represents the zero phonon line of NV-.

[0140] The 532 nm laser was kept constant during the entire measurement process, and the optical detection magnetic resonance (ODMR) measurement was carried out. By external pulse triggering, the MW (microwave) frequency was linearly scanned from 2800 to 2940 MHz. Figure 23 The ODMR spectrum results shown in (b) of the figure show that under the action of an external magnetic field, the spin state (±1) of the NV color center can be effectively separated. Therefore, the polycrystalline diamond film provided by the present application has great application potential in quantum technology.

Claims

1. A method for large-scale manufacturing of ultra-flat polycrystalline diamond films, the method comprising: (1) A polycrystalline diamond film is grown on a growth substrate with diamond seed crystals on its surface by chemical vapor deposition, wherein the polycrystalline diamond film comprises: a growth surface having a first roughness and a nucleation surface bonded to the growth substrate. (2) Cut off at least a portion of the growth substrate on which a polycrystalline diamond film has been grown, such that a boundary line is formed at the cut point where the polycrystalline diamond film and the growth substrate are bonded. (3) Adhere the release tape to the growth surface of the polycrystalline diamond film, wherein the release tape extends beyond the polycrystalline diamond film at least at the edge of the cut to form a release operation end; (4) Pull the peeling operation end to peel the polycrystalline diamond film off the growth substrate surface so as to expose the nucleation surface of the polycrystalline diamond film, wherein the exposed nucleation surface has a second roughness and the second roughness is less than the first roughness.

2. The method according to claim 1, wherein, The first roughness is 10-200 nm; the second roughness is 0.5-5 nm.

3. The method according to claim 2, wherein, The first roughness is 20-50 nm; the second roughness is 0.5-2 nm.

4. The method according to claim 3, wherein, The second roughness is 0.5-1 nm.

5. The method according to claim 1, wherein, The diamond seed crystals mentioned in step (1) have a particle size of 2-10 nm.

6. The method according to claim 1, wherein, In step (1), a microwave plasma-assisted chemical vapor deposition apparatus is used to grow polycrystalline diamond films.

7. The method according to claim 1, wherein, The growth substrate is selected from one or more of Si, SiC, TiC, Co, Pt, Al2O3, Ni, Re, Ir, SiO2 and Mo.

8. The method according to claim 1, wherein, The surface roughness of the growth substrate is less than 2 nm.

9. The method according to claim 8, wherein, The surface roughness of the growth substrate is less than 1 nm.

10. The method according to claim 9, wherein, The surface roughness of the growth substrate is less than 0.5 nm.

11. The method according to claim 1, wherein, The thickness of the polycrystalline diamond film is 200nm-100μm.

12. The method according to claim 11, wherein, The thickness of the polycrystalline diamond film is 200nm-10μm.

13. The method according to claim 12, wherein, The thickness of the polycrystalline diamond film is 400nm-5μm.

14. The method according to any one of claims 1 to 13, wherein, The cutting operation described in step (2) is to cut perpendicular to the growth surface of the polycrystalline diamond film.

15. The method according to any one of claims 1 to 13, wherein, The cutting operation described in step (2) ensures that the length of the boundary line between the formed polycrystalline diamond film and the growth substrate is at least 1% of the perimeter of the growth surface of the polycrystalline diamond film.

16. The method according to claim 15, wherein, The cutting operation results in the length of the boundary line between the formed polycrystalline diamond film and the growth substrate being 5%-20% of the perimeter of the growth surface of the polycrystalline diamond film.

17. The method according to claim 16, wherein, The cutting operation results in the length of the boundary line between the formed polycrystalline diamond film and the growth substrate being 10%-12% of the perimeter of the growth surface of the polycrystalline diamond film.

18. The method according to claim 1, wherein, The growth substrate is circular, and the length of the boundary line between the polycrystalline diamond film cut in step (2) and the growth substrate is 20%-50% of the diameter of the growth substrate.

19. The method according to any one of claims 1 to 13, wherein, In step (4), the speed at which the polycrystalline diamond film is peeled off the growth substrate surface by pulling the peeling operation end is 1-10 mm / s.

20. The method according to any one of claims 1 to 13, wherein, The peeling angle in step (4) is 10-90 degrees.

21. The method according to any one of claims 1 to 13, wherein, The nucleation surface has a higher refractive index than the growth surface.

22. The method according to any one of claims 1 to 13, wherein, The nucleation surface has a lower extinction coefficient than the growth surface.

23. The method according to any one of claims 1 to 13, wherein, Compared to the position of the (111) crystal plane XRD diffraction peak of the growth surface, the position of the (111) crystal plane XRD diffraction peak of the nucleation surface is closer to the standard (111) crystal plane XRD diffraction peak of single-crystal diamond; and the full width at half maximum (FWHM) of the (111) crystal plane XRD diffraction peak of the nucleation surface is smaller than that of the (111) crystal plane XRD diffraction peak of the growth surface.

24. A method for controlling the band structure of a diamond film, the method comprising attaching a polycrystalline diamond film manufactured by the method of any one of claims 1 to 23 to a surface of a flexible substrate, stretching and / or compressing the polycrystalline diamond film by bending the flexible substrate, and controlling the band structure of the polycrystalline diamond film by the strain generated by the polycrystalline diamond film during the stretching and / or compression process.

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