An Ag-Cu-Al alloy thin film and a preparation method thereof

Abstract

The invention discloses an Ag-Cu-Al alloy thin film and a preparation method thereof. By atomic content percentage, Cu is 4-28%, Al is 3-18.3%, and the rest is Ag. The Ag-Cu-Al alloy thin film is prepared by magnetron sputtering co-sputtering. The obtained thin film has uniform composition and dense structure. In magnetron sputtering co-sputtering, the content of Cu and Al in the Ag-Cu-Al alloy thin film is adjusted by controlling the deposition power, so that the microstructure of the alloy thin film forms a nanocrystalline, ultrafine nanocrystalline or crystal-amorphous dual-phase nanostructure. The alloying of Cu and Al can effectively improve the mechanical properties of the Ag alloy thin film, and its strengthening effect increases with the increase of the content of Cu and Al.

Description

Technical Field

[0001] The present invention relates to the field of metallic structural materials, and particularly to an Ag-Cu-Al alloy thin film and a preparation method thereof. Background Art

[0002] In flexible electronic devices and microelectromechanical systems, metallic thin films are ideal interconnection structures due to their excellent mechanical and electrical properties. During service, metallic thin films are subjected to load and Joule heat. Therefore, performance requirements for strength, hardness, plasticity, wear resistance, thermal stability, and electrical conductivity are proposed for metallic thin films.

[0003] According to the application requirements of the interconnection structures in flexible electronic devices and microelectromechanical systems, Ag elements with a large number of slip systems, good deformation performance, high electrical conductivity, and no dense defects are often selected for metallic thin films. However, although Ag thin films exhibit excellent ductility and fatigue resistance, their mechanical strength and hardness are relatively low. Therefore, in practical applications, it may be necessary to further strengthen or improve Ag thin films to increase their hardness, enhance their wear resistance, and meet higher mechanical strength requirements. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides an Ag-Cu-Al alloy thin film and a preparation method thereof. The prepared silver-copper-aluminum alloy thin film has a uniform microstructure and excellent mechanical properties, and the alloying of copper and aluminum can effectively improve the service performance of the silver alloy thin film.

[0005] The present invention is realized by the following technical solutions:

[0006] An Ag-Cu-Al alloy thin film, by atomic content percentage, Cu is 4-28%, Al is 3-18.3%, and the rest is Ag;

[0007] The microstructure of the Ag-Cu-Al alloy thin film is nanocrystalline, ultrafine nanocrystalline, or crystalline-amorphous dual-phase nanostructure.

[0008] Preferably, by atomic content percentage, the Cu is 4-10.1%, the Al is 3-6.6%, and the microstructure of the alloy thin film is nanocrystalline;

[0009] The Cu is 10.2-21.2%, the Al is 6.7-13.4%, the microstructure of the alloy thin film is nanocrystalline, and the grain size of the nanocrystals is less than 5 nm;

[0010] The Cu is 21.3-28.3%, the Al is 13.5-18.3%, and the microstructure of the alloy thin film is crystalline-amorphous dual-phase nanostructure.

[0011] Preferably, the nano-indentation hardness of the Ag-Cu-Al alloy thin film is 2.21 to 5.05 GPa.

[0012] Preferably, the Ag-Cu-Al alloy thin film is 2.4 to 3.3 μm.

[0013] A method for preparing an Ag-Cu-Al alloy thin film includes the following steps:

[0014] Step 1, removing impurities from the substrate;

[0015] Step 2, in a vacuum environment, using a CuAl alloy target and an Ag target and combining a magnetron sputtering co-sputtering method to deposit an Ag-Cu-Al alloy thin film on the substrate;

[0016] Step 3, cooling the substrate obtained in Step 2 to room temperature to obtain an Ag-Cu-Al alloy thin film.

[0017] Preferably, the method for removing impurities from the substrate in Step 1 is as follows:

[0018] Ultrasonically cleaning the polished substrate in acetone and absolute ethanol in sequence and then drying it;

[0019] Using an acid solution to erode the dried substrate to remove the silicon oxide layer to obtain a substrate with impurities removed.

[0020] Preferably, the vacuum degree of the vacuum environment in Step 2 is below 4.0×10-4 Pa, and the deposition of the Ag-Cu-Al alloy thin film is carried out under an argon atmosphere.

[0021] Preferably, in Step 2, the CuAl alloy target is sputtered using a DC power supply, and the Ag target is sputtered using an RF power supply.

[0022] Preferably, the sputtering power of the Ag target is 80 to 100 W, the sputtering power of the CuAl alloy target is 15 to 200 W, the deposition pressure is 0.5 Pa, and the deposition time is 4922 to 11850 s.

[0023] Preferably, the substrate is a silicon substrate.

[0024] Compared with the prior art, the present invention has the following beneficial technical effects:

[0025] The silver-copper-aluminum alloy thin film provided by the present invention has Ag as the main element, and Cu and Al as alloying elements. All three elements are metals with an FCC structure, having many slip systems, good deformation performance, and high electrical conductivity. Among them, Cu and Ag have a positive mixing enthalpy and are almost insoluble, so Cu is slightly solid-solved in the crystal grains while precipitating at the grain boundaries; Al and Ag have a negative mixing enthalpy and are mutually soluble in a large range, and they are also prone to form intermetallic compounds Ag2Al and Ag3Al; while the two alloying elements Cu and Al have a negative mixing enthalpy and are extremely prone to form the intermetallic compound Al2Cu. Therefore, this silver-copper-aluminum alloy thin film has rich alloying forms and can carry out composition design and microstructure regulation.

[0026] For this silver-copper-aluminum alloy thin film, by controlling the atomic content of Cu-Al, the microstructure of the alloy thin film forms three microstructural morphologies: nanocrystals, ultrafine nanocrystals, and crystal-amorphous dual-phase nanostructures. In terms of mechanical properties, as the content of (Cu-Al) increases, the nanoindentation hardness of the silver-copper-aluminum alloy thin film shows a gradually increasing trend, that is, the more the content of alloying elements in the silver-copper-aluminum alloy thin film of the present invention, the more obvious the strengthening effect.

[0027] A preparation method of an Ag-Cu-Al alloy thin film of the present invention is prepared by a method of magnetron sputtering with two targets co-sputtering. First, use acetone and absolute ethanol to clean the impurities on the surface of the Si substrate with a growth orientation of <111>, and then remove the oxide film on the surface of the Si substrate through the erosion of hydrofluoric acid aqueous solution and the rinsing with deionized water, and carry out sputtering deposition at room temperature after ion etching with Ar+ in a vacuum environment. To ensure a fixed ratio of the two alloying elements, a preparation method of co-sputtering with a pure Ag target and a Cu-Al alloy target is adopted, where the atomic ratio of the Cu-Al alloy target is 1:1, and the composition of the silver-copper-aluminum alloy thin film is adjusted by setting the power of the two targets. To ensure the stability of the microstructure and the uniformity of the composition of the silver-copper-aluminum alloy thin film, the substrate is rotated at a fixed speed during the deposition process to ensure that the metal atoms sputtered from the two targets are evenly distributed on the substrate. After the magnetron sputtering process is completed, the deposited substrate is taken out after being naturally cooled to room temperature in a high-vacuum coating chamber. Finally, the deposited silver-copper-aluminum alloy thin film has a flat surface, a uniform and dense microstructure, and few defects. Description of the Drawings

[0028] Figure 1 XRD pattern diagrams of Ag-Cu-Al alloy thin films with different compositions prepared by magnetron sputtering of the present invention;

[0029] Figure 2 TEM planar photographs of Ag-Cu-Al alloy thin films with different compositions prepared by magnetron sputtering of the present invention;

[0030] Figure 3The nano-indentation load-displacement curves of Ag-Cu-Al alloy films with different compositions prepared by magnetron sputtering according to the present invention;

[0031] Figure 4 The nano-indentation hardness results of Ag-Cu-Al alloy films with different compositions prepared by magnetron sputtering according to the present invention. Detailed implementation manners

[0032] The present invention will be further described in detail below with reference to the accompanying drawings. The following is an explanation of the present invention rather than a limitation.

[0033] An Ag-Cu-Al alloy film, the atomic percentage of its chemical composition is that Cu is 4-28%, Al is 3-18.3%, and the rest is Ag; the alloy film is prepared by magnetron sputtering co-sputtering method, and the thickness of the alloy film is 2.4-3.3 μm.

[0034] In this alloy film, different atomic percentage contents of Cu and Al make the microstructure of the alloy film form three microstructures: nanocrystals, ultrafine nanocrystals, and crystal-amorphous dual-phase nanostructures.

[0035] When Cu is 4-10.1% and Al is 3-6.6%, the microstructure of the alloy film is nanocrystals;

[0036] When Cu is 10.2-21.2% and Al is 6.7-13.4%, the microstructure of the alloy film is nanocrystals, and the grain size of the nanocrystals is less than 5 nm;

[0037] When Cu is 21.3-28.3% and Al is 13.5-18.3%, the microstructure of the alloy film is crystal-amorphous dual-phase nanostructure.

[0038] Figure 1 The XRD pattern diagrams of Ag-Cu-Al alloy films with different compositions prepared by magnetron sputtering according to the present invention are shown, which illustrate the phase composition of the Ag-Cu-Al alloy films; Figure 2 The TEM plane photographs of Ag-Cu-Al alloy films with different compositions prepared by magnetron sputtering according to the present invention are shown, which illustrate that there are three microstructures in the Ag-Cu-Al alloy films: nanocrystals, ultrafine nanocrystals, and crystal-amorphous dual-phase nanostructures; Figure 3 The nano-indentation load-displacement curves and nano-indentation hardness results of Ag-Cu-Al alloy films with different compositions prepared by magnetron sputtering according to the present invention are shown, indicating that the hardness of the Ag alloy film is improved with the alloying of Cu and Al, and its nano-indentation hardness increases with the increase of the atomic contents of Cu and Al. When the atomic ratio composition is 53% Ag, 28% Cu, and 19% Al, the nano-indentation hardness value reaches the highest, which is 5.05 GPa.

[0039] The Ag-Cu-Al alloy thin film of the present invention has a uniform and dense surface, uniform distribution of alloy elements inside, and its microstructure presents a nano-crystal, ultra-fine nano-crystal, crystal-amorphous dual-phase nano-structure. The Ag-Cu-Al alloy thin film of the present invention has excellent mechanical properties and thermal stability.

[0040] The preparation method of the above-mentioned Ag-Cu-Al alloy thin film will be elaborated in detail below.

[0041] A preparation method of an Ag-Cu-Al alloy thin film includes the following steps:

[0042] Step 1, removing impurities from the substrate;

[0043] Specifically, take a single-crystal Si substrate with a <111> growth orientation and single-sided polishing, ultrasonically clean it in acetone and ethanol for 10 minutes each and then dry it. The surface roughness of the ultrasonically cleaned single-crystal silicon substrate is less than 0.8 nm, so as to remove the stains and dust attached to the surface of the Si substrate, which is beneficial to improving the bonding force between the thin film and the substrate. Then, etch the dried Si substrate with an aqueous hydrofluoric acid solution and rinse it thoroughly with deionized water to remove the silicon oxide layer on its surface to ensure the growth orientation of the crystal during the sputtering deposition process.

[0044] Step 2, etching the substrate in a vacuum environment.

[0045] Specifically, fix the single-crystal silicon substrate on the substrate plate, automatically send it into the magnetron sputtering vacuum coating chamber by mechanical means, and pump the vacuum to a background vacuum degree below 4.0×10-4 Pa. Etch it for 5 minutes in an argon atmosphere, and the etching power is 200 W.

[0046] Step 3, in a vacuum environment, deposit an Ag-Cu-Al alloy thin film on the substrate by using a CuAl alloy target and an Ag target in combination with the magnetron sputtering co-sputtering method;

[0047] Among them, the Ag target (purity 99.995 wt%) uses a radio frequency power supply with a power of 80-100 W, the CuAl alloy target (purity 99.99 wt%) uses a direct current power supply, the atomic ratio of Cu and Al in the CuAl alloy target is 1:1, the power is 15-200 W, the deposition gas pressure is set at 0.5 Pa, the deposition temperature is room temperature, the substrate plate rotation speed is 15 r / min. At the same time, turn on the direct current power supply and the radio frequency power supply to start co-sputtering deposition. The deposition time is 4922-11850 s, and the thickness of the obtained Ag-Cu-Al alloy thin film is 2.4-3.3 μm.

[0048] Step 4, cooling the substrate obtained in Step 3 to room temperature to obtain the Ag-Cu-Al alloy thin film.

[0049] Due to the long - time bombardment of the substrate by sputtered atoms during the deposition process, the Ag - Cu - Al alloy film has a certain temperature rise when the process is completed. Therefore, after the deposition, the substrate should be allowed to cool down to room temperature in the high - vacuum coating chamber along with the furnace before being taken out.

[0050] The Ag - Cu - Al alloy film is deposited on the surface of a single - crystal Si wafer by magnetron co - sputtering. The principle is as follows: Ar+ ions are generated by the ionization of Ar gas and are accelerated to bombard the surface of the cathode target under the attraction of the cathode potential, causing the target to sputter, ejecting target atoms and secondary electrons. Under the action of the electric and magnetic fields, the target atoms are deposited on the anode substrate. The secondary electrons move in a cycloid trajectory in the plasma region near the target surface, increasing the collision probability with Ar molecules and ionizing more Ar+ to achieve a high deposition rate. Compared with other preparation techniques, the prominent advantages of this technique are high ionization rate, fast deposition rate, low working temperature, the composition of the alloy film can be independently adjusted, and it is not easy to cause non - uniform microstructure due to the agglomeration and back - sputtering of target atoms. After the sputtering deposition process is completed, to prevent debonding, cracking, generation of large internal stresses caused by the difference in thermal expansion coefficients between the film material and the substrate, and oxidation of the sample when it contacts air at high temperature, it is naturally cooled to room temperature in the high - vacuum coating chamber, and finally the deposited atoms fully diffuse to form an Ag - Cu - Al alloy film with different compositions.

[0051] Example 1

[0052] Step 1: The single - side polished single - crystal silicon substrate is ultrasonically cleaned in analytical - grade acetone and absolute ethanol for 10 min in sequence, and then immediately dried with warm air.

[0053] Step 2: The single - crystal silicon substrate is fixed on the substrate plate with polyimide tape, mechanically and automatically sent into the magnetron sputtering vacuum coating chamber, evacuated to a background vacuum of less than 4.0×10 - 4 Pa, and etched in an argon atmosphere for 5 min with an etching power of 200 W.

[0054] Step 3: Deposit the Ag - Cu - Al alloy film on the single - crystal silicon substrate by magnetron sputtering using a dual - target of DC and RF power supplies.

[0055] Among them, the Ag target (purity 99.995 wt%) uses an RF power supply with a power of 100 W, the CuAl alloy target (purity 99.99 wt%) uses a DC power supply with a power of 15 W, the deposition pressure is set at 0.5 Pa, the deposition temperature is room temperature, the substrate plate rotation speed is 15 r / min, and the DC power supply and the RF power supply are turned on simultaneously for co - sputtering deposition for 5553 s.

[0056] Step 4: After the deposition is completed, the substrate is naturally cooled in the high-vacuum deposition chamber for 3 h to room temperature and then taken out to obtain an Ag-Cu-Al alloy film with a composition of 93.0 at% Ag - 4.0 at% Cu - 3.0 at% Al and a thickness of 2.4 μm.

[0057] The prepared Ag-Cu-Al alloy film is characterized by its microstructure and tested for its mechanical properties. Its microstructure is a nanocrystalline structure, and its nanoindentation hardness is measured to be 2.21 ± 0.29 GPa under a 1000 μN load by nanoindentation.

[0058] Example 2

[0059] Step 1: The single-sided polished single-crystalline silicon substrate is ultrasonically cleaned in analytical pure acetone and absolute ethanol for 10 min in sequence, and then immediately dried with warm air.

[0060] Step 2: The single-crystalline silicon substrate is fixed on the substrate holder with polyimide tape, mechanically and automatically fed into the magnetron sputtering vacuum coating chamber, evacuated to a background vacuum of less than 4.0×10-4 Pa, and etched in an argon atmosphere for 5 min with an etching power of 200 W.

[0061] Step 3: An Ag-Cu-Al alloy film is deposited on the single-crystalline silicon substrate by co-sputtering with a dual-target of DC and RF power supplies in magnetron sputtering;

[0062] Among them, the Ag target (purity 99.995 wt%) uses an RF power supply with a power of 100 W, the CuAl alloy target (purity 99.99 wt%) uses a DC power supply with a power of 40 W, the deposition gas pressure is set at 0.5 Pa, the deposition temperature is room temperature, the substrate holder rotation speed is 15 r / min, and the DC power supply and RF power supply are turned on simultaneously for co-sputtering deposition for 5400 s.

[0063] Step 4: After the deposition is completed, the substrate is naturally cooled in the high-vacuum deposition chamber for 3 h to room temperature and then taken out to obtain an Ag-Cu-Al alloy film with a composition of 83.1 at% Ag - 10.2 at% Cu - 6.7 at% Al and a thickness of 2.5 μm.

[0064] The prepared Ag-Cu-Al alloy film is characterized by its microstructure and tested for its mechanical properties. Its microstructure is an ultrafine nanocrystalline structure, and its nanoindentation hardness is measured to be 3.32 ± 0.27 GPa under a 1000 μN load by nanoindentation.

[0065] Example 3

[0066] Step 1: The single-sided polished single-crystalline silicon substrate is ultrasonically cleaned in analytical pure acetone and absolute ethanol for 10 min in sequence, and then immediately dried with warm air.

[0067] Step 2: Fix the single-crystalline silicon substrate on the base plate with polyimide tape, and mechanically and automatically send it into the magnetron sputtering vacuum coating chamber. Evacuate to a background vacuum of less than 4.0×10-4 Pa, and etch for 5 min in an argon atmosphere with an etching power of 200 W.

[0068] Step 3: Deposit an Ag-Cu-Al alloy film on the single-crystalline silicon substrate by co-sputtering with a dual target of DC and RF power supplies in magnetron sputtering;

[0069] Among them, the Ag target (purity 99.995 wt%) uses an RF power supply with a power of 100 W, and the CuAl alloy target (purity 99.99 wt%) uses a DC power supply with a power of 82 W. The deposition gas pressure is set at 0.5 Pa, the deposition temperature is room temperature, the base plate rotation speed is 15 r / min, and the DC and RF power supplies are turned on simultaneously for co-sputtering deposition for 5230 s.

[0070] Step 4: After the deposition is completed, naturally cool the substrate in the high-vacuum deposition chamber for 3 h to room temperature and then take it out to obtain an Ag-Cu-Al alloy film with a composition of 72.6 at% Ag - 16.9 at% Cu - 10.5 at% Al and a thickness of 2.9 μm.

[0071] Perform microstructure characterization and mechanical property testing on the prepared Ag-Cu-Al alloy film. Its microstructure is an ultrafine nanocrystalline structure, and its nanoindentation hardness measured by nanoindentation under a load of 1000 μN is 4.26 ± 0.07 GPa.

[0072] Example 4

[0073] Step 1: Ultrasonically clean the single-crystalline silicon substrate with one side polished in analytical pure acetone and absolute ethanol for 10 min respectively, and then immediately dry it with warm air.

[0074] Step 2: Fix the single-crystalline silicon substrate on the base plate with polyimide tape, and mechanically and automatically send it into the magnetron sputtering vacuum coating chamber. Evacuate to a background vacuum of less than 4.0×10-4 Pa, and etch for 5 min in an argon atmosphere with an etching power of 200 W.

[0075] Step 3: Deposit an Ag-Cu-Al alloy film on the single-crystalline silicon substrate by co-sputtering with a dual target of DC and RF power supplies in magnetron sputtering;

[0076] Among them, the Ag target (purity 99.995 wt%) uses an RF power supply with a power of 92 W, and the CuAl alloy target (purity 99.99 wt%) uses a DC power supply with a power of 116 W. The deposition gas pressure is set at 0.5 Pa, the deposition temperature is room temperature, the base plate rotation speed is 15 r / min, and the DC and RF power supplies are turned on simultaneously for co-sputtering deposition for 4922 s.

[0077] Step 4: After the deposition is completed, the substrate is naturally cooled in the high-vacuum deposition chamber for 3 h to room temperature and then taken out to obtain an Ag-Cu-Al alloy film with a composition of 65.4 at% Ag - 21.2 at% Cu - 13.4 at% Al and a thickness of 3.3 μm.

[0078] The prepared Ag-Cu-Al alloy film is characterized for its microstructure and mechanical properties tested. Its microstructure is an ultrafine nanocrystalline structure, and its nanoindentation hardness is measured to be 4.67 ± 0.06 GPa under a 1000 μN load by nanoindentation.

[0079] Example 5

[0080] Step 1: The single-sided polished single-crystalline silicon substrate is ultrasonically cleaned in analytical pure acetone and absolute ethanol for 10 min in sequence, and then immediately dried with warm air.

[0081] Step 2: The single-crystalline silicon substrate is fixed on the substrate holder with polyimide tape, mechanically and automatically fed into the magnetron sputtering vacuum coating chamber, evacuated to a background vacuum of less than 4.0×10-4 Pa, and etched in an argon atmosphere for 5 min with an etching power of 200 W.

[0082] Step 3: The Ag-Cu-Al alloy film is deposited on the single-crystalline silicon substrate by co-sputtering with a dual-target of DC and RF power supplies of magnetron sputtering;

[0083] Among them, the Ag target (purity 99.995 wt%) uses the RF power supply with a power of 80 W, the CuAl alloy target (purity 99.99 wt%) uses the DC power supply with a power of 200 W, the deposition pressure is set at 0.5 Pa, the deposition temperature is room temperature, the substrate holder rotation speed is 15 r / min, and the DC power supply and the RF power supply are simultaneously turned on for co-sputtering deposition for 5000 s.

[0084] Step 4: After the deposition is completed, the substrate is naturally cooled in the high-vacuum deposition chamber for 3 h to room temperature and then taken out to obtain an Ag-Cu-Al alloy film with a composition of 53.4 at% Ag - 28.3 at% Cu - 18.3 at% Al and a thickness of 3.3 μm.

[0085] The prepared Ag-Cu-Al alloy film is characterized for its microstructure and mechanical properties tested. Its microstructure is a crystal-amorphous dual-phase nanostructure, and its nanoindentation hardness is measured to be 5.05 ± 0.11 GPa under a 1000 μN load by nanoindentation.

[0086] The present invention discloses an Ag-Cu-Al alloy thin film and a preparation method thereof. The atomic percentage of (Cu-Al) is 7% to 47%, and the rest is Ag. The present invention is prepared by a method of magnetron sputtering double-target co-sputtering, wherein the Ag target uses a radio frequency power supply, and the CuAl alloy target uses a direct current power supply; the present invention adjusts the content of (Cu-Al) in the Ag-Cu-Al alloy thin film by controlling the deposition power. The obtained thin film has uniform composition and dense structure, and its microstructure presents a nanocrystalline, ultrafine nanocrystalline, crystal-amorphous dual-phase nanostructure. The alloying of (Cu-Al) can effectively improve the mechanical properties of the Ag alloy thin film, and its strengthening effect increases with the increase of the content of (Cu-Al); the present invention is strengthened by alloying, and alloying can change the microstructure of the material from multiple angles. By introducing alloying elements, the microstructure can be regulated in terms of grain size, twinning and stacking faults, texture orientation, element distribution, solid solution and precipitation, phase transformation and amorphization, etc., thereby directly affecting a series of properties such as the strength and plasticity of the metal thin film to optimize the service performance of the material.

[0087] The above content is only to illustrate the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. An Ag-Cu-Al alloy thin film, characterized in that, By atomic content percentage, Cu is 4 - 28.3%, Al is 3 - 18.3%, and the rest is Ag; The Ag-Cu-Al alloy thin film has a microstructure of nanocrystalline, ultrafine nanocrystalline, or crystalline-amorphous dual-phase nanostructure; Cu is 4 - 10.1%, Al is 3 - 6.6%, and the microstructure of this alloy thin film is nanocrystalline; Cu is 10.2 - 21.2%, Al is 6.7 - 13.4%, and the microstructure of this alloy thin film is ultrafine nanocrystalline, with the grain size of the ultrafine nanocrystals being less than 5 nm; Cu is 21.3 - 28.3%, Al is 13.5 - 18.3%, and the microstructure of this alloy thin film is crystalline-amorphous dual-phase nanostructure.

2. The Ag-Cu-Al alloy thin film according to claim 1, characterized in that, The nanoindentation hardness of the Ag-Cu-Al alloy thin film is 2.21 - 5.05 GPa.

3. An Ag-Cu-Al alloy thin film according to claim 1, characterized in that, The thickness of the Ag-Cu-Al alloy thin film is 2.4 - 3.3 μm.

4. A method for preparing an Ag-Cu-Al alloy thin film according to any one of claims 1-3, characterized in that, It includes the following steps: Step 1, remove the impurities of the substrate; Step 2, in a vacuum environment, use a CuAl alloy target and an Ag target and combine the magnetron sputtering co-sputtering method to deposit an Ag-Cu-Al alloy thin film on the substrate; Step 3, cool the substrate obtained in Step 2 to room temperature to obtain the Ag-Cu-Al alloy thin film.

5. The preparation method of an Ag-Cu-Al alloy thin film according to claim 4, characterized in that, The method for removing the substrate impurities in Step 1 is as follows: Ultrasonically clean the polished substrate in acetone and absolute ethanol in sequence and then dry it; Use an acid solution to erode the dried substrate to remove the silicon oxide layer to obtain a substrate with impurities removed.

6. The preparation method of an Ag-Cu-Al alloy thin film according to claim 4, characterized in that, The degree of vacuum of the vacuum environment described in Step 2 is 4.0×10 -4 Pa or less, and the Ag-Cu-Al alloy thin film is deposited under an argon atmosphere.

7. The preparation method of an Ag-Cu-Al alloy thin film according to claim 4, wherein In Step 2, the CuAl alloy target is sputtered using a DC power supply, and the Ag target is sputtered using an RF power supply.

8. The preparation method of an Ag-Cu-Al alloy thin film according to claim 4, characterized in that, The sputtering power of the Ag target is 80 - 100 W, the sputtering power of the CuAl alloy target is 15 - 200 W, the deposition pressure is 0.5 Pa, and the deposition time is 4922 - 11850 s.

9. The preparation method of an Ag-Cu-Al alloy thin film according to claim 5, characterized in that, The substrate is a silicon substrate.

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