Nanotwinned silver material and preparation method therefor

Abstract

Provided in the present invention are a nanotwinned silver material and a preparation method therefor. The preparation method comprises the following steps: step S1, cleaning a substrate, and drying same; and S2, selecting a silver target as a target material, placing the substrate and the target material into a magnetron sputtering device, vacuumizing same, and then applying a negative bias voltage to the substrate to perform direct-current magnetron sputtering deposition, wherein the bias voltage of the substrate ranges from -50 V to -200 V, the temperature of the substrate is 25-50ºC, the argon flow is 30-50 sccm, the vacuum degree of a sputtering chamber is 0.3-1.0 Pa, and the deposition time is 15-90 min. By means of the technical solution of the present invention, the prepared nanotwinned silver material contains high-density nano-twins, the proportion of twin boundaries is greater than 90%, and the hardness, electromigration resistance and thermal stability of the material are improved while the material has both high conductivity and high heat conductivity; and the obtained nanotwinned silver material has good comprehensive performance.

Description

A nano-twinned silver material and preparation method thereof Technical Field

[0001] The present invention belongs to the technical field of advanced preparation of metal materials, and in particular relates to a nano-twinned silver material and a preparation method thereof. Background Art

[0002] As packaging technology evolves toward higher density and higher reliability, interconnect materials are increasingly demanding superior properties, including high strength, excellent thermal and electrical conductivity, thermal stability, electromigration resistance, and high-temperature performance. Silver, a metal with excellent electrical and thermal conductivity and oxidation resistance, is a key material for achieving electrical interconnects in electronic circuit manufacturing. However, silver's inherent low strength and susceptibility to electromigration failure during service as an interconnect material severely limit its application in electronic packaging interconnects.

[0003] Summary of the Invention

[0004] In response to the above technical problems, the present invention discloses a nano-twinned silver material and a preparation method thereof. The obtained silver material has excellent properties such as high strength, anti-electromigration performance, high thermal stability, and high thermal and electrical conductivity.

[0005] To this end, the technical solution adopted in the present invention is:

[0006] A method for preparing a nano-twinned silver material comprises the following steps:

[0007] Step S1, cleaning and drying the substrate;

[0008] In step S2, a silver target is selected as the target material, and the substrate and the target material are placed in a magnetron sputtering device. After vacuuming, a negative bias voltage is applied to the substrate for DC magnetron sputtering deposition, wherein the substrate bias voltage is -50 to -200 V, the substrate temperature is 25 to 50°C, the argon flow rate is 30 to 50 sccm, the vacuum degree of the sputtering chamber is 0.3 to 1.0 Pa, and the deposition time is 15 to 90 min.

[0009] The nanotwinned silver material produced using this technical solution boasts high density and exhibits enhanced strength and excellent electromigration resistance while maintaining the inherent electrical and thermal conductivity of the silver material. Because the grain boundary energy of coherent nanotwin boundaries is low, only approximately 10% of that of high-angle grain boundaries, the nanotwins in the material also effectively improve the material's thermal stability at high temperatures. This high-density nanotwinned silver, as an interconnect material, is expected to address the issues of low shear strength and poor electromigration resistance in silver interconnect layers, improving the service temperature and reliability of interconnect solder joints.

[0010] As a further improvement of the present invention, in step S2, the power is 100-300W.

[0011] As a further improvement of the present invention, the target material is a 99.999% silver target.

[0012] As a further improvement of the present invention, in step S2, the distance between the substrate and the target is 10-20 cm.

[0013] As a further improvement of the present invention, the substrate is a silicon substrate or a copper substrate.

[0014] As a further improvement of the present invention, the thickness of the substrate is 200-500 μm.

[0015] As a further improvement of the present invention, step S1 includes cleaning the polished substrate with an acid solution, then cleaning with deionized water, drying the surface moisture, and then drying.

[0016] The present invention also discloses a nano-twinned silver material, which is prepared by using any of the above methods for preparing the nano-twinned silver material.

[0017] As a further improvement of the present invention, the internal microstructure of the nano-twin silver material is composed of columnar crystals with a width of 200 to 1000 nm that grow along the deposition direction, and the nano-twin layer perpendicular to the deposition direction is located inside the columnar crystals, and the average thickness of the nano-twin layer is 10-100 nm.

[0018] As a further improvement of the present invention, the columnar crystal surface has a (111) preferred orientation.

[0019] As a further improvement of the present invention, the thickness of the nano-twinned silver material is 2-50 μm.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] First, by adopting the technical solution of the present invention, the nano-twinned silver material prepared has a high density of nano-twins, and the proportion of twin boundaries is greater than 90%. Under the conditions of high electrical conductivity and high thermal conductivity, the hardness, anti-electromigration performance and thermal stability of the material are greatly improved; the obtained nano-twinned silver material has excellent comprehensive performance, which can solve the current problems of low strength and poor anti-electromigration performance of silver materials, and can be used as an interconnect layer in power device packaging, advanced packaging, electromechanical system (MEMS) packaging and other fields.

[0022] Second, the technical solution of the present invention uses magnetron sputtering technology to prepare nano-twinned silver materials with the advantages of easy control of thickness and uniform structure, and strong adhesion; at the same time, the physical vapor deposition technology is compatible with microelectronics manufacturing processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a focused ion beam (FIB) imaging picture of the cross section of the nano-twinned silver material deposited on the silicon substrate according to Example 1 of the present invention.

[0024] FIG2 is a transmission electron microscope image of the nano-twinned silver material deposited on the silicon substrate according to Example 1 of the present invention, showing a high-density nano-twinned layer perpendicular to the deposition direction, and the arrow indicates the deposition direction of the material.

[0025] FIG3 is a focused ion beam (FIB) imaging picture of the cross section of the silver material deposited on the silicon substrate in Comparative Example 1 of the present invention.

[0026] FIG4 is a FIB imaging picture of the nano-twinned silver material deposited on the silicon substrate according to Example 3 of the present invention.

[0027] FIG5 is a FIB imaging picture of the nano-twinned silver material deposited on the silicon substrate according to Example 4 of the present invention. DETAILED DESCRIPTION

[0028] The preferred embodiments of the present invention are described in further detail below.

[0029] Example 1

[0030] A high-density nanocrystalline silver material is prepared on a <111> single-crystal silicon substrate using biased DC magnetron sputtering technology. The method for preparing nano-twinned silver material using magnetron sputtering technology described in this embodiment includes the following steps:

[0031] S1. Cleaning a 2-inch <100> single crystal silicon substrate after chemical mechanical polishing with a solution of hydrofluoric acid: water at a mass ratio of 1:50 to remove the natural oxide layer; then, cleaning with deionized water; and drying the surface with a spin dryer for later use;

[0032] S2. Place the silicon substrate with the surface oxide film removed and the 99.999% silver target on the magnetron sputtering workbench, and adjust the distance between the substrate and the target to 15 cm;

[0033] S3. After evacuation, the process parameters for sputtering deposition are set as follows: -100 V bias voltage is applied to the deposition substrate, power: 250 W, substrate temperature: 25° C., argon gas flow rate: 40 sccm, sputtering chamber vacuum: 0.5 Pa, and then sputtering deposition is performed on the substrate;

[0034] S4. Keep step S3 for 20 minutes to obtain a high-density nano-twinned silver material with a thickness of about 3 μm.

[0035] Figure 1 shows a focused ion beam (FIB) image of a cross-section of a nanotwinned silver material deposited on a silicon substrate according to Example 1 of the present invention. The image shows that nearly all of the columnar grains in the material contain a high density of nanotwins, with approximately 100% of the grains containing these twins. Figure 2 shows a transmission electron microscopy (TEM) image of the nanotwinned silver material deposited on a silicon substrate, in which the nanotwins are clearly visible.

[0036] Example 2

[0037] A high-density nanocrystalline silver material is prepared on a polycrystalline copper substrate using bias DC magnetron sputtering technology. The method for preparing the nano-twinned silver material using magnetron sputtering technology described in this embodiment includes the following steps:

[0038] S1. Clean the polycrystalline copper substrate after mechanical polishing with a 5% (mass percentage) citric acid aqueous solution and then with deionized water; and then dry the surface with a spin dryer and dry it for later use;

[0039] S2. Place the polycrystalline copper substrate with the surface oxide film removed and the 99.999% silver target on the magnetron sputtering workbench, and adjust the distance between the substrate and the target to 20 cm;

[0040] S3. After evacuation, the process parameters for sputtering deposition are set as follows: -100 V bias voltage is applied to the deposition substrate, power: 300 W, substrate temperature: 25° C., argon gas flow rate: 50 sccm, sputtering chamber vacuum: 0.5 Pa, and then sputtering deposition is performed on the substrate;

[0041] S4. Keep step S3 for 30 minutes to obtain a high-density nano-twinned silver material with a thickness of about 10 μm.

[0042] Comparative Example 1

[0043] This comparative example comprises the following steps:

[0044] S1. Cleaning a 2-inch <100> single crystal silicon substrate after chemical mechanical polishing with a solution of hydrofluoric acid: water <1:50 to remove the natural oxide layer; then, cleaning with deionized water; and drying the surface with a spin dryer for later use;

[0045] S2. Place the silicon substrate with the surface oxide film removed and the 99.999% silver target on the magnetron sputtering workbench, and adjust the distance between the substrate and the target to 15 cm;

[0046] S3. After evacuation, the process parameters for sputtering deposition are set as follows: no bias is applied to the deposition substrate, power: 250 W, substrate temperature: 25° C., argon flow rate: 40 sccm, sputtering chamber vacuum: 0.5 Pa, and then sputtering deposition is performed on the substrate;

[0047] S4. Keep step S3 for 20 minutes to obtain a nanosilver material with a thickness of about 3 μm.

[0048] Figure 3 is a focused ion beam (FIB) imaging picture of the cross-section of the nanotwinned silver material deposited on the silicon substrate in Comparative Example 3. From the microstructure, it can be found that when no negative bias is applied, the bottom of the deposited material is an equiaxed crystal transition layer, and nanotwins exist in only a few grains, and no high-density nanotwinned material is obtained.

[0049] Example 3

[0050] A high-density nanocrystalline silver material is prepared on a <111> single-crystal silicon substrate using biased DC magnetron sputtering technology. The method for preparing nano-twinned silver material using magnetron sputtering technology described in this embodiment includes the following steps:

[0051] S1. Cleaning a 2-inch <100> single crystal silicon substrate after chemical mechanical polishing with a solution of hydrofluoric acid: water at a mass ratio of 1:50 to remove the natural oxide layer; then, cleaning with deionized water; and drying the surface with a spin dryer for later use;

[0052] S2. Place the silicon substrate with the surface oxide film removed and the 99.999% silver target on the magnetron sputtering workbench, and adjust the distance between the substrate and the target to 15 cm;

[0053] S3. After evacuation, the process parameters for sputtering deposition are set as follows: -50 V bias voltage is applied to the deposition substrate, power: 250 W, substrate temperature: 25° C., argon gas flow rate: 40 sccm, sputtering chamber vacuum: 0.5 Pa, and then sputtering deposition is performed on the substrate;

[0054] S4. Keep step S3 for 20 minutes to obtain a high-density nano-twinned silver material with a thickness of about 3 μm.

[0055] Figure 4 is a FIB imaging picture of the nano-twinned silver material deposited on the silicon substrate in Example 4 under the condition of a substrate bias voltage of -50 V. It can be seen from the figure that there is an equiaxed crystal transition layer at the bottom of the material obtained under this condition, and the volume fraction of the grains with high-density nano-twins is about 50%.

[0056] Example 4

[0057] A high-density nanocrystalline silver material is prepared on a <111> single-crystal silicon substrate using biased DC magnetron sputtering technology. The method for preparing nano-twinned silver material using magnetron sputtering technology described in this embodiment includes the following steps:

[0058] S1. Cleaning a 2-inch <100> single crystal silicon substrate after chemical mechanical polishing with a solution of hydrofluoric acid: water at a mass ratio of 1:50 to remove the natural oxide layer; then, cleaning with deionized water; and drying the surface with a spin dryer for later use;

[0059] S2. Place the silicon substrate with the surface oxide film removed and the 99.999% silver target on the magnetron sputtering workbench, and adjust the distance between the substrate and the target to 15 cm;

[0060] S3. After evacuation, the process parameters for sputtering deposition are set as follows: -200 V bias voltage is applied to the deposition substrate, power: 250 W, substrate temperature: 25° C., argon gas flow rate: 40 sccm, sputtering chamber vacuum: 0.5 Pa, and then sputtering deposition is performed on the substrate;

[0061] S4. Keep step S3 for 20 minutes to obtain a high-density nano-twinned silver material with a thickness of about 3 μm.

[0062] FIG5 is a FIB imaging picture of the nano-twinned silver material deposited on the silicon substrate under the substrate bias voltage of -200 V in Example 5. It can be seen from the figure that high-density nano-twinned silver material can also be obtained under this condition.

[0063] The hardness of the magnetron sputtered Ag materials of Examples 1-4 and Comparative Example 1 was tested using a nanohardness tester. The results are shown in Table 1. As can be seen, the hardness of the Ag material of Comparative Example 1, which has a lower twin density, is 0.88 GPa, while the hardness of Example 1, which has a high twin density (90%-Nt), is 1.95 GPa, which is 2.21 times that of Comparative Example 1.

[0064] Table 1. Nanohardness test results of Examples and Comparative Examples

[0065] The thermal stability of the magnetron sputtered Ag materials in Examples 1-4 and Comparative Example 1 was tested by holding them at different temperatures for one hour. The critical temperature at which detwinning and grain growth begin was determined to evaluate the thermal stability of the materials. The critical detwinning temperatures are shown in Table 2. Compared to 200°C for Comparative Example 1, the instability temperature of the high-density twinned Ag materials in the Examples was increased to 350°C.

[0066] Table 2 Thermal stability test results of Examples and Comparative Examples

[0067] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing a nano twinned silver material, characterized in that: The steps include: Step S1, cleaning and drying the substrate; Step S2, a silver target is selected as the target material, and the substrate and the target material are placed in a magnetron sputtering device. After vacuuming, a negative bias voltage is applied to the substrate for DC magnetron sputtering deposition, wherein the substrate bias voltage is -50 to -200 V, the substrate temperature is 25 to 50°C, the argon gas flow rate is 30 to 50 sccm, the vacuum degree of the sputtering chamber is 0.3 to 1.0 Pa, and the deposition time is 15 to 90 min.

2. The method for preparing the nano twinned silver material according to claim 1, characterized in that: In step S2, the power is 100-300W.

3. The method for preparing the nano twinned silver material according to claim 2, characterized in that: The target material is a 99.999% silver target.

4. The method for preparing the nano twinned silver material according to claim 3, characterized in that: In step S2, the distance between the substrate and the target is 10-20 cm.

5. The method for preparing the nano twinned silver material according to claim 1, characterized in that: The substrate is a silicon substrate or a copper substrate.

6. The method for preparing the nano twinned silver material according to claim 5, characterized in that: The thickness of the substrate is 200-500 μm.

7. The method for preparing the nano twinned silver material according to claim 1, characterized in that: Step S1 includes cleaning the polished substrate with an acid solution, then cleaning with deionized water, drying after drying the surface moisture.

8. A nano twinned silver material, characterized in that: The nano twinned silver material is prepared by the method for preparing the nano twinned silver material according to any one of claims 1 to 7.

9. The nano twinned silver material according to claim 8, characterized in that: The internal microstructure of the nano-twin silver material is composed of columnar crystals with a width of 200-1000nm that grow along the deposition direction, the nano-twin lamellae perpendicular to the deposition direction are located inside the columnar crystals, and the average thickness of the nano-twin lamellae is 10-100nm.

10. The nano twinned silver material according to claim 8, characterized in that: The columnar crystal surface has a (111) preferred orientation, and the thickness of the nano-twinned silver material is 2-50 μm.

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