Ultra-smooth metal film and preparation method thereof

Abstract

The invention discloses an ultra-smooth metal film and a preparation method thereof, and belongs to the technical field of metal films. The preparation method of the ultra-smooth metal film comprises the following steps: stripping a single-crystal two-dimensional material to expose a fresh surface layer, and then cleaning residual steps and burrs on the fresh surface layer of the single-crystal two-dimensional material to obtain a mask layer with a smooth and flat surface; depositing a metal film on the stripping surface of the mask layer by adopting a thermal evaporation mode; adhering a supporting layer to the surface of the metal film; stripping the mask layer from the metal film with the supporting layer until the complete metal surface of the metal film is exposed; and cleaning the stripped metal film, and removing the residual single crystal two-dimensional material on the metal surface of the metal film to obtain the ultra-smooth metal film. According to the preparation method, the surface roughness of the gold thin film can be remarkably reduced, and the stability and reliability of electric contact between the thin film and graphite can be improved while the performance of the film layer is kept.

Description

Technical Field

[0001] The invention belongs to the technical field of metal films, and in particular relates to an ultra-smooth metal film and a preparation method thereof. Background Art

[0002] Metal films play a vital role in a wide range of applications due to their excellent conductivity, chemical stability and unique optical properties. In particular, they are essential components in electronic and optoelectronic devices that achieve low contact resistance and high durability. Among them, the control and optimization of surface roughness are key factors in improving the performance and reliability of metal films, especially in a variety of technical applications such as electronic devices, sensors, electrode materials and catalysis. Smooth metal films can significantly improve their performance and long-term stability. Therefore, further research and optimization of the surface roughness of metal films will have a profound impact on their applications in multiple fields.

[0003] In order to reduce the surface roughness of metal films, many studies have proposed different technical methods. Among them, magnetron sputtering technology is currently the most widely used method for preparing metal films. Its preparation is simple and efficient, but it has some shortcomings in reducing the roughness and PV (peak-to-valley difference of the component surface) value, which are mainly manifested in the following aspects:

[0004] 1. Surface roughness is difficult to control: Although magnetron sputtering technology can control the thickness and uniformity of the film to a certain extent, its control over the surface roughness of the metal film is relatively limited. Under low pressure and low temperature conditions, magnetron sputtering may cause uneven deposition of metal atoms on the substrate surface, forming a relatively rough film surface, especially in larger deposition areas.

[0005] 2. Deposition rate has an impact on roughness: In the magnetron sputtering process, the deposition rate is closely related to the surface smoothness of the film. A higher deposition rate may cause more particles to accumulate on the film surface, thereby increasing the roughness and even producing irregular surface textures. Although some degree of optimization can be achieved by adjusting parameters such as sputtering power and gas flow, the control accuracy and range are still limited.

[0006] 3. It is difficult to reduce the PV value: Due to the complex collision angle and energy between metal atoms and the substrate surface during magnetron sputtering, there is often a certain peak-to-valley imbalance on the surface of the metal film, resulting in a higher PV value. Although some optimization methods (such as low-temperature deposition or the use of suitable substrate materials) can reduce the PV value to a certain extent, to achieve an extremely low PV value (such as less than a few nanometers), other post-processing technologies are usually required.

[0007] 4. Substrate effect: The surface quality of magnetron sputtered metal films is greatly affected by the substrate material. For example, when the substrate surface roughness is high, the surface quality of the metal film is difficult to be effectively improved, and may even magnify the unevenness of the substrate surface.

[0008] 5. Non-uniformity of film structure: Although magnetron sputtering can produce uniform thin films, the non-uniformity of the film structure may increase the surface roughness during the deposition of some thicker or complex metal films, especially during the deposition angle and film stacking process, making it difficult to further optimize the surface smoothness. In general, although magnetron sputtering metal mold film technology is an efficient and widely used method for preparing thin films, it still has certain limitations in achieving ultra-smooth surfaces, reducing roughness and PV values, and other post-processing technologies or improved preparation processes are needed to overcome these shortcomings.

[0009] In addition to magnetron sputtering technology, some heat treatment processes, polishing technology, deposition technology, helium ion beam lithography technology and other methods have emerged to reduce the surface roughness of metal films. Among them, the heat treatment process can reduce the surface roughness of 1μm 2 The roughness of the gold film surface is reduced to less than 1nm, and the peak-to-valley difference (PV) value can be controlled within 25nm. Chemical polishing technology can reduce the RMS roughness of the gold film surface to 0.26nm, while the maximum height is only 4.55nm. In addition, the combination of mechanical and chemical polishing methods has also achieved remarkable results, reducing the 1μm 2 The RMS roughness of the gold film was reduced from 1.15nm to 0.4nm, and the peak-to-valley difference reached 2.1±0.5nm. In terms of deposition technology, the use of mica substrate can promote the growth of ultra-smooth surface of the gold film, especially in <111> The crystal growth in the crystal direction makes the RMS roughness of these gold films reach 0.3nm, and the peak-to-valley difference is about 5nm. In addition, helium ion beam lithography technology also shows excellent flatness control, and can prepare single-crystal gold films with Ra of 0.267nm and maximum height of 12nm. However, although the above technologies reduce the roughness to a certain extent, the PV value of the metal film surface is still difficult to improve well.

[0010] In summary, how to reduce the peak-to-valley difference of the metal film while reducing the surface roughness of the metal film is still a difficult problem that needs to be solved urgently. Summary of the invention

[0011] The main purpose of the present invention is to provide an ultra-smooth metal film and a method for preparing the same, so as to solve the problem that the existing method for preparing the metal film is difficult to effectively reduce the surface roughness and peak-to-valley difference of the film at the same time.

[0012] In order to achieve the above object, the present invention provides a method for preparing an ultra-smooth metal film, comprising the following steps:

[0013] The single crystal two-dimensional material is peeled off to expose a fresh surface layer, and then the steps and burrs remaining on the fresh surface layer of the single crystal two-dimensional material are cleaned to obtain a mask layer with a smooth and flat surface;

[0014] Depositing a metal film on the stripping surface of the mask layer by thermal evaporation;

[0015] bonding a support layer to the surface of the metal film;

[0016] Peeling the mask layer off the metal film with the support layer until the complete metal surface of the metal film is exposed;

[0017] The metal film after peeling is cleaned to remove the residual single crystal two-dimensional material remaining on the metal surface of the metal film, so as to obtain the ultra-smooth metal film.

[0018] Furthermore, before bonding the support layer to the surface of the metal film, the method further includes: sputtering a metal transition layer onto the surface of the metal film.

[0019] Further, the mask layer is peeled off from the metal film with the support layer until the complete metal surface of the metal film is exposed, including:

[0020] First, the mask layer is completely peeled off from the metal film with the support layer, and then the mask layer remaining on the metal film is locally peeled off in fine detail, and the peeling is repeated for multiple times until the complete metal surface is exposed.

[0021] Furthermore, the single crystal two-dimensional material is selected from any one of highly oriented pyrolytic graphite, hexagonal boron nitride or molybdenum disulfide.

[0022] Furthermore, the material of the support layer is a silicon wafer and / or electroplated metal.

[0023] Furthermore, the metal transition layer is selected from one or more of chromium, titanium, nickel, silver or copper.

[0024] Furthermore, when the metal transition layer is chromium, the sputtering adopts magnetron sputtering, and the parameter conditions of the magnetron sputtering are: the deposition power is 140-160w, the cavity is passed with Ar gas as the atmosphere gas, the flow rate is 45-55 Sccm, and the pressure is 5.0×10 -6 Pa~6.0×10 -6 Pa, the deposition rate is The deposition cooling time is 150 to 200 seconds.

[0025] Furthermore, the metal film is selected from any one of gold, silver, copper, platinum or nickel.

[0026] Furthermore, when the metal film is a gold film, the current of the thermal evaporation is 0.12-0.15A, and the deposition rate is The pressure is 8×10 -6 Pa~9×10 -6 Pa, the deposition cooling time is 15 to 20 minutes.

[0027] Furthermore, the thickness of the metal film is 100-200 nm.

[0028] Another aspect of the present invention provides an ultra-smooth metal film, which is prepared by the above-mentioned method for preparing the ultra-smooth metal film.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention uses a single crystal two-dimensional material as a mask to prepare a metal film with an ultra-smooth surface. This is based on the excellent property that the surface of the single crystal two-dimensional material has uniform atomic-level smoothness. By contacting the target metal surface of the metal film with the smooth surface mask of the single crystal two-dimensional material, the surface smoothness of the single crystal two-dimensional material is mapped on the surface of the metal film, and the metal film can achieve near-atomic smoothness in the micrometer scale region. At the same time, the present invention also sets a metal transition layer between the metal film and the support layer to provide structural support for the metal film during the mask layer peeling and subsequent cleaning process, maintain structural stability, and avoid wrinkles in the metal film. The preparation method of the present invention overcomes the limitations of traditional preparation processes in fine surface smoothness, while having both low surface roughness and low peak-to-valley difference.

[0031] In addition, compared with conventional magnetron sputtering technology, the preparation method of the present invention can not only significantly reduce the surface roughness of the gold film, but also improve the stability and reliability of the electrical contact between the film and graphite while maintaining the performance of the film layer. In addition, the present invention verifies the advantages of this ultra-smooth metal film in terms of device life through friction and wear tests, demonstrating the potential of this technology in extending the service life of metal films and improving the overall performance of equipment. Compared with existing processes, this method has obvious advantages, especially in high-end technology applications that require surface flatness and long-term stability, such as microelectronic devices, sensors, and energy equipment.

[0032] In summary, the method for preparing the ultra-smooth metal film of the present invention innovatively combines single-crystalline two-dimensional materials and metal transition layers, improves the surface quality and electrical contact performance of the metal film, and provides a solution with broad application prospects for related fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic flow chart of a method for preparing an ultra-smooth gold film according to Example 1 of the present invention is shown;

[0034] Figure 2 The atomic force microscope morphology image and morphology analysis result (20 micrometers square) of the ultra-smooth gold film of Example 1 of the present invention are shown;

[0035] Figure 3 The atomic force microscope morphology image and morphology analysis result (20 micrometers square) of the gold film of comparative example 1 of the present invention are shown;

[0036] Figure 4 The atomic force microscope morphology image and morphology analysis result (20 micrometers square) of the ultra-smooth gold film of Example 2 of the present invention are shown;

[0037] Figure 5 The atomic force microscope morphology image and morphology analysis result (3 micrometers square) of the ultra-smooth gold film of Example 2 of the present invention are shown;

[0038] Figure 6 The atomic force microscope morphology image and morphology analysis result (3 micrometers square) of the gold film of comparative example 1 of the present invention are shown. DETAILED DESCRIPTION

[0039] It should be noted that, in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper limit and the lower limit of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or the intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope. The present invention will be described in detail below in conjunction with the embodiments.

[0040] In order to achieve the above object, a first aspect of an embodiment of the present invention provides a method for preparing an ultra-smooth metal film, comprising the following steps:

[0041] Step S1, peeling off the single crystal two-dimensional material to expose a fresh surface layer, and then cleaning the steps and burrs remaining on the fresh surface layer of the single crystal two-dimensional material to obtain a mask layer with a smooth and flat surface;

[0042] Step S2, depositing a metal film on the peeling surface of the mask layer by thermal evaporation;

[0043] Step S3, bonding a support layer to the surface of the metal film;

[0044] Step S4, peeling the mask layer from the metal film with the support layer until the complete metal surface of the metal film is exposed;

[0045] Step S5, cleaning the peeled metal film to remove the residual single crystal two-dimensional material remaining on the metal surface of the metal film, thereby obtaining the ultra-smooth metal film.

[0046] In order to ensure a smooth surface during the deposition of the metal film and minimize defects such as burrs and steps, the present invention performs a stripping and cleaning process on the single crystal two-dimensional material. A smooth, high-quality mask layer is obtained through the above-mentioned treatment, which promotes a more uniform and accurate deposition of the metal film. The present invention uses thermal evaporation to deposit the metal film on the stripping surface of the mask layer. This thermal evaporation deposition method can ensure that the interface between the metal film and the mask layer has a relatively weak bonding force, which is crucial for facilitating the subsequent removal of the mask layer from the surface of the metal film. Controlling the bonding strength of the interface minimizes potential damage to the metal film. At the same time, the present invention also bonds a support layer on the other side of the metal film to ensure stable support of the metal film and reduce the impact of the metal film's mask layer stripping process on the morphology of the metal film.

[0047] In a preferred embodiment of the present invention, before bonding the support layer to the surface of the metal film, it also includes: sputtering a metal transition layer onto the surface of the metal film. In order to further ensure the structural stability of the metal film during the subsequent peeling of the mask layer and the subsequent cleaning process, the present invention sets a metal transition layer between the metal film and the support layer. The metal transition layer has a high hardness and can achieve a small flexibility to avoid wrinkles of the metal film after the mask layer is peeled off. In addition, the present invention deposits the metal transition layer on the surface of the metal film by sputtering. The sputtering method can achieve a strong bonding force between the metal film and the metal transition layer, thereby more effectively providing structural support for the metal film.

[0048] Furthermore, the metal transition layer can be selected from one or more of chromium, titanium, nickel, silver or copper. When the metal transition layer is chromium, in some optional embodiments of the present invention, the sputtering adopts magnetron sputtering, and the parameter conditions of the magnetron sputtering are: the deposition power is 140-160w, the cavity is passed through Ar gas as the atmosphere gas, the flow rate is 45-55Sccm, and the pressure is 5.0×10 -6 Pa~6.0×10 -6 Pa, the deposition rate is The deposition cooling time is 150 to 200 seconds.

[0049] In a specific embodiment of the present invention, the mask layer is peeled off from the metal film with the support layer in the following manner: first, the mask layer is peeled off as a whole from the metal film with the support layer, and then the mask layer remaining on the metal film is locally and finely peeled off, and the peeling is repeated multiple times until the complete metal surface is exposed.

[0050] In order to further improve the smoothness of the metal film surface, in some optional embodiments of the present invention, the single crystal two-dimensional material can be selected from any one of highly oriented pyrolytic graphite, hexagonal boron nitride or molybdenum disulfide.

[0051] In order to further improve the structural stability of the metal film, in some optional embodiments of the present invention, the material of the support layer can be selected from, for example, silicon wafers and / or electroplated metals, and some other materials with higher hardness can also be used.

[0052] In some optional embodiments of the present invention, the metal film is selected from any one of gold, silver, copper, platinum or nickel. When the metal film is a gold film, in some optional embodiments of the present invention, the current of the thermal evaporation is 0.12-0.15A, and the deposition rate is The pressure is 8×10 -6 Pa~9×10 -6 Pa, the deposition cooling time is 15 to 20 minutes. In the specific implementation process, the deposition cooling time cannot be too short, otherwise it will easily cause pores in the gold film and cause morphological defects.

[0053] In some optional embodiments of the present invention, the thickness of the metal film is 100-200 nm, for example, the thickness may be 100 nm, 120 nm, 140 nm, 150 nm, 160 nm, 180 nm, or 200 nm.

[0054] In a second aspect of an embodiment of the present invention, an ultra-smooth metal film is provided, which is prepared by the above-mentioned method for preparing the ultra-smooth metal film.

[0055] Based on the above reasons, the ultra-smooth metal film surface of the present invention has both ultra-low surface roughness and PV value, and the stability of electrical contact with graphite is also very high, which is particularly suitable for high-end technology applications such as microelectronic devices, sensors and energy equipment.

[0056] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0057] Example 1

[0058] A method for preparing an ultra-smooth gold film, such as Figure 1 As shown, the following steps are included:

[0059] Step a: The highly oriented pyrolytic graphite (HOPG) is peeled off, that is, the HOPG is split into two halves to expose a fresh surface layer, and then the steps and burrs remaining on the surface are cleaned with tape to obtain a mask layer with a smooth and flat surface.

[0060] Step b: Deposit a 200nm thick gold film on the peeled surface of the cut HOPG by thermal evaporation. The specific parameters of thermal evaporation are: evaporation current 0.12-0.15A, deposition rate First at 8.08×10 -6 Pa pressure, the gold film was deposited. As the thickness increased, the pressure gradually decreased to 2.18×10 -6 Pa, and the cooling time after deposition is 15 minutes.

[0061] Step c: After the gold film is deposited, a 100 nm chromium layer is magnetron sputtered on the surface of the gold film as a metal transition layer. The specific parameters of the magnetron sputtering are: deposition power 150 W, Ar gas as the atmosphere gas in the cavity, flow rate 50 Sccm, at 5.4×10 -6 Pa pressure 100 nm of chromium was deposited at a deposition rate of , and cooling was performed for 180 seconds after the deposition was completed.

[0062] Step d: Adhere the silicon wafer to the surface of the metal transition layer with epoxy resin to form a support layer.

[0063] Step e: Mechanically strip the HOPG mask layer on the surface of the metal film with the metal transition layer and the support layer. Utilizing the layered structure of HOPG, use Scotch tape (high-performance fiber-reinforced tape) to completely strip the HOPG on the surface of the gold film. Then use the edge of the tape to perform local miniaturized stripping. Repeat the stripping process several times until the complete gold surface is exposed.

[0064] Step f: Clean the peeled gold film to remove the residual HOPG remaining on the surface of the gold film, thereby obtaining an ultra-smooth metal film.

[0065] Example 2

[0066] A method for preparing an ultra-smooth gold film is different from Example 1 only in that the treatment of step c is not performed during the film preparation process, that is, a metal transition layer is not sputtered on the surface of the gold film.

[0067] Comparative Example 1

[0068] A gold-plated silicon wafer is purchased from Beijing Tebowande Technology Co., Ltd. The gold-plated silicon wafer is made by adopting the existing conventional magnetron sputtering method.

[0069] Performance Testing

[0070] (1) Morphological characterization:

[0071] The gold films of Examples 1 to 2 and Comparative Example 1 were characterized by atomic force microscopy. The morphology characterization diagrams and results are shown in FIG. Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6 The right dialog box in the figure shows the parameters of the surface morphology. The "Adev[Ra]" line is the Ra roughness value of the area. The "Max" and "Min" lines are the maximum height and maximum depth in the scan area, respectively. The PV value is the sum of the absolute values ​​of these two maximum values.

[0072] The gold film of Example 1 of the present invention achieves a roughness of Ra=0.15nm in a 20 micrometer square area, and a PV value of 2.56nm (see Figure 2 ); while the roughness of the gold film in the 20 micron square area of ​​Comparative Example 1 is Ra = 0.68nm, and the PV value is 7.26nm (see Figure 3 ). It can be seen that the roughness and PV value of the gold film of Example 1 of the present invention in a 20 micron square area are much lower than those of the gold film of Comparative Example 1.

[0073] from Figure 2 and Figure 4 From the morphological comparison, it can be found that Example 2 has more steps and wrinkles in the 20-micron square area than Example 1. This is because the gold film of Example 1 of the present invention is sputtered with a metal transition layer during the preparation process, while the gold film in Example 2 is not prepared using a metal transition layer. Since Example 1 with a sputtered metal transition layer has structural support from the metal transition layer during the subsequent mask layer stripping and subsequent cleaning processes, the overall flatness of the gold film is improved.

[0074] The present invention further characterized the performance of the wrinkle-free area (3 microns square) of the gold film of Example 2, and found that the roughness of the wrinkle-free area (3 microns square) can still reach Ra = 0.12nm, and the PV value of the surface is 1.38nm (see Figure 5 ), while the surface roughness of the gold film of Comparative Example 1 in the same size 3 micron square area is Ra = 0.75nm, and the PV value is 7.82nm (see Figure 6 ). For the flat area without wrinkles, the gold film of Example 2 still maintains surface morphology parameters similar to those of Example 1, and the surface morphology parameters are greatly improved compared with those of Comparative Example 1.

[0075] In summary, the surface roughness of the gold film prepared by the method of the present invention is reduced by more than 75% compared with the gold film prepared by magnetron sputtering (Comparative Example 1) which is already below 1nm, and the PV value is also reduced by more than 60%. This means that the surface roughness and peak deviation of the gold film prepared by the method of the present invention are greatly reduced, and it is expected to provide better performance in the electrical properties and friction properties of the gold film.

[0076] (2) Contact resistance test:

[0077] The smooth surface of the gold film of Example 1 and Comparative Example 1 was brought into contact with a graphite square block with a side length of 6 μm, and the contact resistance between the interfaces was tested. After testing, the contact resistance test result of the interface between the gold film of Example 1 prepared by the method of the present invention and the graphite was 3.91Ω, while the contact resistance of the interface between the gold film prepared by magnetron sputtering in Comparative Example 1 and the graphite was 10.45Ω. It can be seen that the gold film prepared by the present invention has better electrical contact performance.

[0078] (3) Friction and wear performance test:

[0079] The friction and wear performance of the gold film of Example 1 and Comparative Example 1 was tested by sliding using a DLC (diamond-like carbon-based material) ball probe on an atomic mechanics microscope. The single sliding stroke was 5 microns, and 20,000 sliding cycles were performed under each positive pressure. The positive stress varied between 130 MPa and 320 MPa. As the positive stress increased, the maximum scratch depth of the sputtered gold film gradually increased from 4.79 nm to 32.82 nm, while the maximum scratch depth of the gold film prepared by the present invention fluctuated below 5 nm. Even under a positive stress of 316.8 MPa, the maximum scratch depth was still only 2.66 nm, which was reduced by an order of magnitude compared to 32.82 nm of the sputtered gold film under 310 MPa. In summary, the surface of the gold film prepared by the present invention has a better surface quality and better friction and wear performance.

[0080] The above-described embodiments only represent the embodiments of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. The present invention can also be implemented in other specific ways or other specific forms without departing from the gist or essential features of the present invention. Therefore, the described embodiments should be regarded as illustrative rather than restrictive in any respect. The scope of the present invention should be described by the attached claims, and any changes equivalent to the intention and scope of the claims should also be included in the scope of the present invention.

Claims

1. A method for preparing an ultra-smooth metal film, characterized in that: The following steps are involved: The single crystal two-dimensional material is peeled off to expose a fresh surface layer, and then the steps and burrs remaining on the fresh surface layer of the single crystal two-dimensional material are cleaned to obtain a mask layer with a smooth and flat surface; Depositing a metal film on the stripping surface of the mask layer by thermal evaporation; bonding a support layer to the surface of the metal film; Peeling the mask layer off the metal film with the support layer until the complete metal surface of the metal film is exposed; The metal film after peeling is cleaned to remove the residual single crystal two-dimensional material remaining on the metal surface of the metal film, so as to obtain the ultra-smooth metal film.

2. The method for preparing an ultra-smooth metal film according to claim 1, characterized in that: Before bonding the support layer to the surface of the metal film, the method further includes: sputtering a metal transition layer to the surface of the metal film.

3. The method for preparing an ultra-smooth metal film according to claim 1, characterized in that: The mask layer is peeled off from the metal film with the support layer until the complete metal surface of the metal film is exposed, including: First, the mask layer is completely peeled off from the metal film with the support layer, and then the mask layer remaining on the metal film is locally peeled off in fine detail, and the peeling is repeated for multiple times until the complete metal surface is exposed.

4. The method for preparing an ultra-smooth metal film according to claim 1, characterized in that: The single crystal two-dimensional material is selected from any one of highly oriented pyrolytic graphite, hexagonal boron nitride or molybdenum disulfide.

5. The method for preparing an ultra-smooth metal film according to claim 1, characterized in that: The material of the support layer is one or more of silicon wafer, electroplated metal, conductive tape or conductive silver paste.

6. The method for preparing an ultra-smooth metal film according to claim 2, characterized in that: The metal transition layer is selected from one or more of chromium, titanium, nickel, silver or copper.

7. The method for preparing an ultra-smooth metal film according to claim 6, wherein when the metal transition layer is chromium, the sputtering is performed by magnetron sputtering, and the parameters of the magnetron sputtering are as follows: the deposition power is 140-160W, the cavity is passed through Ar gas as the atmosphere gas, the flow rate is 45-55 Sccm, and the pressure is 5.0×10 -6 Pa~6.0×10 -6 Pa, the deposition rate is The deposition cooling time is 150 to 200 seconds.

8. The method for preparing an ultra-smooth metal film according to claim 1, characterized in that: The metal film is selected from any one of gold, silver, copper, platinum or nickel.

9. The method for preparing an ultra-smooth metal film according to claim 8, characterized in that: When the metal film is a gold film, the current of the thermal evaporation is 0.12-0.15A, and the deposition rate is The pressure is 8×10 -6 Pa~9×10 -6 Pa, the deposition cooling time is 15 to 20 minutes.

10. The method for preparing an ultra-smooth metal film according to any one of claims 1 to 9, characterized in that: The thickness of the metal film is 100-200 nm.

11. An ultra-smooth metal film, characterized in that: The ultra-smooth metal film is prepared by the method for preparing the ultra-smooth metal film according to any one of claims 1 to 10.

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