A method for preparing ultra-high purity copper ingot

Abstract

The present application relates to a kind of preparation methods of ultra-high purity copper ingot, the preparation method includes the following steps: (1) with copper sheet as raw material, carry out vacuum medium frequency induction smelting, obtain copper liquid;The vacuum medium frequency induction smelting includes sequentially carried out first temperature rise, first holding, second temperature rise, second holding, third temperature rise and third holding;(2) the copper liquid obtained in step (1) is refined, to obtain the copper liquid after purification;(3) the copper liquid after purification obtained in step (2) is sequentially cast, cooled and machined, to obtain ultra-high purity copper ingot.The preparation method provided by the present application is not only simple operation, lower energy consumption, but also can avoid the introduction of carbon particles and other impurities in smelting, improve the purity of ingot, reduce the oxygen content of ingot, make the internal structure of ingot uniform, less defect.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a method for preparing ultra-high purity copper ingots. Background Technology

[0002] With the continuous development of large-scale integrated circuit manufacturing technology, chip sizes are gradually shrinking to submicron and nanometer levels. RC delay and electromigration phenomena in metal interconnects have become major factors affecting chip performance. Traditional aluminum and aluminum alloy interconnects can no longer meet the requirements of very large-scale integrated circuit manufacturing processes. Compared to aluminum, copper has higher resistance to electromigration and lower resistivity, especially ultra-high purity copper (purity ≥6N), which represents a significant breakthrough in reducing chip interconnect resistance and improving its operating speed.

[0003] Therefore, the demand for ultra-high purity copper sputtering targets is gradually increasing, and the quality requirements for these targets are also becoming more stringent. Currently, copper sputtering targets are generally required to possess properties such as high purity, low oxygen content, and uniform hardness. Existing processes typically employ methods such as vacuum arc melting, vacuum electromagnetic levitation melting, or vacuum electron beam melting to prepare ultra-high purity copper sputtering targets.

[0004] For example, CN102031394A discloses an apparatus and method for preparing high-purity copper. In this method, the cathode copper is first cleaned to remove the main impurity elements on the exposed surface; then, impurities are removed through electron beam melting, electromagnetic purification, and direct directional solidification; finally, a high-purity copper ingot with a uniform columnar solidification structure is obtained. However, the electron beam melting method consumes a lot of energy, and the equipment and operation are relatively complex.

[0005] In addition, existing processes generally use electrolytic copper as raw material, but gaseous impurities in electrolytic copper are difficult to remove, and the density of electrolytic copper differs greatly from the theoretical value, with many internal defects, resulting in a single product form. Impurities are easily introduced during smelting, ultimately leading to products that cannot meet the requirements of ultra-high purity copper sputtering materials.

[0006] Therefore, it is of great significance to provide a method for preparing ultra-high purity copper ingots with high purity and low oxygen content. Summary of the Invention

[0007] To address the above problems, the present invention aims to provide a method for preparing ultra-high purity copper ingots. Compared with the prior art, the preparation method provided by the present invention is not only simple to operate and has low energy consumption, but also avoids the introduction of impurities such as carbon particles during smelting, improves the purity of the ingot, reduces the oxygen content of the ingot, and makes the internal structure of the ingot uniform with fewer defects.

[0008] To achieve this objective, the present invention adopts the following technical solution: This invention provides a method for preparing ultra-high purity copper ingots, the method comprising the following steps: (1) Using copper sheets as raw material, vacuum medium frequency induction melting is carried out to obtain copper liquid; The vacuum intermediate frequency induction melting includes a first heating, a first holding, a second heating, a second holding, a third heating, and a third holding in sequence; (2) The copper liquid obtained in step (1) is refined to obtain purified copper liquid; (3) The purified copper liquid obtained in step (2) is sequentially cast, cooled and machined to obtain ultra-high purity copper ingots.

[0009] The preparation method provided by this invention is carried out in a vacuum medium-frequency induction furnace. The furnace body mainly includes an induction coil, a graphite crucible, and a furnace lining (made of high-purity graphite). When medium-frequency alternating current passes through the induction coil, an alternating magnetic field is generated. The metal in the crucible, located in the middle of the coil, cuts the alternating electromagnetic force, generating an alternating current (i.e., eddy current) inside. The eddy current causes the metal atoms to move at high speeds and randomly, and the collisions between the atoms generate heat, thus melting the metal. In the vacuum medium-frequency induction melting process, a first heating and a first holding are performed to dry the graphite crucible and furnace charge; then a second heating and a second holding are performed to fully volatilize the low-melting-point infusible materials; followed by a third heating and a third holding to fully melt the copper sheet. Preliminary degassing and slag removal are performed under high vacuum conditions to further improve the purity of the copper liquid. The preparation method provided by this invention can avoid introducing impurities such as carbon particles during melting, improve the purity of the ingot, reduce the oxygen content of the ingot, and make the internal structure of the ingot uniform with fewer defects.

[0010] In this invention, "ultra-high purity" refers to a purity ≥ 6N.

[0011] Preferably, the purity of the copper sheet in step (1) is ≥6N, for example, it can be 99.9999%, 99.99991%, 99.99992%, 99.99993%, 99.99994% or 99.99995%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0012] Preferably, the copper sheet is circular in shape.

[0013] Preferably, the copper sheet comprises an electrolytic copper sheet.

[0014] In this invention, it is preferred to use circular copper sheets for vacuum medium-frequency induction melting, which can avoid the edges of the copper raw material scratching the crucible, avoid introducing carbon particles contained in the crucible into the copper liquid, and make full use of the crucible space.

[0015] Preferably, the vacuum degree of the vacuum intermediate frequency induction melting is ≤3.6×10⁻⁶. -1Pa, for example, could be 3.6 × 10 - 1 Pa, 3.4 × 10 -1 Pa, 3.2 × 10 -1 Pa, 3×10 -1 Pa, 2.8 × 10 -1 Pa, 2.6 × 10 -1 Pa, 2.4 × 10 -1 Pa, 2.2×10 -1 Pa or 2×10 -1 Pa, but not limited to the listed values, applies to other unlisted values ​​within the range as well.

[0016] Preferably, the power supply for the vacuum intermediate frequency induction melting is 40-45kW, for example, it can be 40kW, 41kW, 42kW, 43kW, 44kW or 45kW, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0017] Preferably, the endpoint temperature of the first heating in step (1) is 400-450℃, for example, it can be 400℃, 405℃, 410℃, 415℃, 420℃, 425℃, 430℃, 435℃, 440℃, 445℃ or 450℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Preferably, the first heat preservation time is 50-60 minutes, for example, it can be 50 minutes, 52 minutes, 54 minutes, 56 minutes, 58 minutes or 60 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, the endpoint temperature of the second heating in step (1) is 700-750℃, for example, it can be 700℃, 705℃, 710℃, 715℃, 720℃, 725℃, 730℃, 735℃, 740℃, 745℃ or 750℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] In this invention, it is preferable to control the final temperature of the second heating within a specific range, which can further remove low-melting-point infusible impurities.

[0021] Preferably, the second heat preservation time is 50-60 minutes, for example, it can be 50 minutes, 52 minutes, 54 minutes, 56 minutes, 58 minutes or 60 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] Preferably, the endpoint temperature of the third heating step (1) is 1050-1100℃, for example, it can be 1050℃, 1060℃, 1070℃, 1080℃, 1090℃ or 1100℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] In this invention, it is preferable to control the final temperature of the third heating step within a specific range, which can further degas and remove slag.

[0024] Preferably, the third heat preservation time is 50-60 minutes, for example, it can be 50 minutes, 52 minutes, 54 minutes, 56 minutes, 58 minutes or 60 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the refining temperature in step (2) is 1500-1550℃, for example, it can be 1500℃, 1510℃, 1520℃, 1530℃, 1540℃ or 1550℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] In this invention, it is preferable to control the refining temperature within a specific range, which allows the molten copper to fully volatilize and release gas until no more bubbles are generated on the surface of the molten copper, thereby further reducing gaseous impurities in the ingot.

[0027] Preferably, the refining time is 30-40 minutes, for example, 30 minutes, 32 minutes, 34 minutes, 36 minutes, 38 minutes or 40 minutes, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the casting rate in step (3) is 50-60 mm / min, for example, it can be 50 mm / min, 52 mm / min, 54 mm / min, 56 mm / min, 58 mm / min or 60 mm / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the casting method includes hot-top continuous casting.

[0030] In this invention, the hot-top continuous casting method, compared with the traditional cooling water continuous casting method, can avoid the cooling water directly contacting the ingot surface, thereby avoiding ingot oxidation and significantly reducing the oxygen content of the ingot.

[0031] Preferably, the purity of the ultra-high purity copper ingot in step (3) is ≥6N, for example, it can be 99.9999%, 99.99991%, 99.99992%, 99.99993%, 99.99994% or 99.99995%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the oxygen content of the ultra-high purity copper ingot is <1ppm, for example, it can be 0.9ppm, 0.8ppm, 0.7ppm, 0.6ppm or 0.5ppm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the number of particles ≥20μm in each gram of the ultra-high purity copper ingot is <250, for example, 240, 230, 220, 210 or 200, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] As a preferred embodiment of the present invention, the preparation method includes the following steps: (1) Using round copper sheets with a purity ≥ 6N as raw materials, place them in a graphite crucible and first perform vacuum treatment until the vacuum degree is ≤ 3.6 × 10⁻⁶. -1 Pa, and then vacuum medium-frequency induction melting is carried out under the power supply of 40-45kW to obtain copper liquid; The vacuum intermediate frequency induction melting includes: first heating to 400-450℃ and holding for 50-60 minutes, then heating to 700-750℃ and holding for 50-60 minutes, and then heating to 1050-1100℃ and holding for 50-60 minutes. (2) The copper liquid obtained in step (1) is refined at a temperature of 1500-1550℃ for 30-40 minutes to obtain purified copper liquid; (3) The purified copper liquid obtained in step (2) is cast at a speed of 50-60 mm / min, and then cooled and machined in sequence to obtain ultra-high purity copper ingots; The purity of the ultra-high purity copper ingot is ≥6N, the oxygen content of the ultra-high purity copper ingot is <1ppm, and the number of particles ≥20μm per gram of the ultra-high purity copper ingot is <250.

[0035] Compared with the prior art, the present invention has the following beneficial effects: The preparation method provided by this invention is not only simple to operate and has low energy consumption, but also avoids the introduction of impurities such as carbon particles during smelting, thereby improving the purity of the ingot and reducing its oxygen content. Under optimal conditions, the purity of the obtained ultra-high purity copper ingot reaches more than 99.99991%, the oxygen content reaches less than 0.8 ppm, and the number of particles per gram of ultra-high purity copper ingot reaches less than 54, resulting in a uniform internal structure and fewer defects in the ingot. Detailed Implementation

[0036] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0037] Example 1 This embodiment provides a method for preparing ultra-high purity copper ingots, the method comprising the following steps: (1) Using a round copper sheet with a purity of 6N as raw material, place it in a cylindrical graphite crucible and first perform a vacuum treatment to a vacuum degree of 3.6×10. -1 Pa, and then vacuum medium-frequency induction melting was carried out under a power supply of 42kW to obtain copper liquid; The vacuum intermediate frequency induction melting includes: first heating to 420°C and holding for 55 minutes, then heating to 720°C and holding for 55 minutes, and then heating to 1070°C and holding for 55 minutes. (2) The copper liquid obtained in step (1) is refined at a temperature of 1520℃ for 35 minutes to obtain purified copper liquid; (3) The purified copper liquid obtained in step (2) is hot-top continuous casting at a speed of 55 mm / min, and then cooled and machined in sequence to obtain ultra-high purity copper ingots.

[0038] Example 2 This embodiment provides a method for preparing ultra-high purity copper ingots, the method comprising the following steps: (1) Using a round copper sheet with a purity of 6N as raw material, place it in a cylindrical graphite crucible and first perform a vacuum treatment to a vacuum degree of 3.2×10. -1 Pa, and then vacuum medium-frequency induction melting was carried out under a power supply of 45kW to obtain copper liquid; The vacuum intermediate frequency induction melting includes: first heating to 400°C and holding for 60 minutes, then heating to 700°C and holding for 60 minutes, and then heating to 1050°C and holding for 60 minutes. (2) The copper liquid obtained in step (1) is refined at a temperature of 1500℃ for 40 minutes to obtain purified copper liquid; (3) The purified copper liquid obtained in step (2) is hot-top continuous casting at a speed of 50 mm / min, and then cooled and machined in sequence to obtain ultra-high purity copper ingots.

[0039] Example 3 This embodiment provides a method for preparing ultra-high purity copper ingots, the method comprising the following steps: (1) Using a round copper sheet with a purity of 6N as raw material, place it in a cylindrical graphite crucible and first perform a vacuum treatment to a vacuum degree of 3×10. -1 Pa, and then vacuum medium-frequency induction melting was carried out under a power supply of 40kW to obtain copper liquid; The vacuum intermediate frequency induction melting includes: first heating to 450°C and holding for 50 minutes, then heating to 750°C and holding for 50 minutes, and then heating to 1100°C and holding for 50 minutes. (2) The copper liquid obtained in step (1) is refined at a temperature of 1550℃ for 30 minutes to obtain purified copper liquid; (3) The purified copper liquid obtained in step (2) is hot-top continuous casting at a speed of 60 mm / min, and then cooled and machined in sequence to obtain ultra-high purity copper ingots.

[0040] Example 4 This embodiment provides a method for preparing ultra-high purity copper ingots, which differs from Example 1 only in that the casting speed is 40 mm / min.

[0041] In this embodiment, the product surface cracks were severe due to the slow casting rate, resulting in the product being scrapped.

[0042] Example 5 This embodiment provides a method for preparing ultra-high purity copper ingots, which differs from Embodiment 1 only in that the casting speed is 70 mm / min.

[0043] In this embodiment, the product was scrapped due to excessively fast casting speed, which caused leakage.

[0044] Example 6 This embodiment provides a method for preparing ultra-high purity copper ingots, which differs from Example 1 only in that the final temperature of the second heating is 680°C.

[0045] Example 7 This embodiment provides a method for preparing ultra-high purity copper ingots, which differs from Example 1 only in that the final temperature of the second heating is 800°C.

[0046] Example 8 This embodiment provides a method for preparing ultra-high purity copper ingots. The only difference from Embodiment 1 is that the final temperature of the third heating step is 1000℃.

[0047] Example 9 This embodiment provides a method for preparing ultra-high purity copper ingots. The only difference between this embodiment and Example 1 is that the final temperature of the third heating step is 1200°C.

[0048] Comparative Example 1 This comparative example provides a method for preparing ultra-high purity copper ingots, which differs from Example 1 only in that the first heat preservation is not performed.

[0049] Comparative Example 2 This comparative example provides a method for preparing ultra-high purity copper ingots, which differs from Example 1 only in that a second heat preservation is not performed.

[0050] Comparative Example 3 This comparative example provides a method for preparing ultra-high purity copper ingots, which differs from Example 1 only in that a third heat preservation is not performed.

[0051] The purity of the ultra-high purity copper ingots prepared in Examples 1-3, 6-9 and Comparative Examples 1-3 was determined by GDMS (glow discharge mass spectrometry), and the results are shown in Table 1.

[0052] The oxygen content of the ultra-high purity copper ingots prepared in Examples 1-3, 6-9 and Comparative Examples 1-3 was determined by LECO (Lico gas content detection), and the results are shown in Table 1.

[0053] The number of particulate matter per gram of ultra-high purity copper ingots prepared in Examples 1-3, 6-9 and Comparative Examples 1-3 was determined by LPC (low particulate matter concentration detection), and the results are shown in Table 1.

[0054] Table 1 The following points can be observed from the data in Table 1: (1) As can be seen from the data of Examples 1-3, the purity of the ultra-high purity copper ingots obtained by the preparation method provided by the present invention reaches more than 99.99991%, the oxygen content reaches less than 0.8 ppm, and the number of particles per gram of ingot reaches less than 54.

[0055] (2) A comprehensive comparison of the data from Example 1 and Example 6-7 shows that the only difference between Example 6-7 and Example 1 is that the endpoint temperature of the second heating is not within the preferred range of the present invention. The purity of the ingot in Example 6-7 is significantly lower than that in Example 1, and the number of particles is significantly higher than that in Example 1. This is because when the endpoint temperature of the second heating is too low, the low melting point impurities are not fully melted and decomposed, resulting in a decrease in the purity of the ingot and an increase in the number of particles. When the endpoint temperature of the second heating is too high, the low melting point impurities are prone to chemical reaction with copper, which also leads to a decrease in the purity of the ingot and an increase in the number of particles. Therefore, it can be seen that the present invention preferably controls the endpoint temperature of the second heating within a specific range, which can further improve the purity of ultra-high purity copper ingots.

[0056] (3) A comprehensive comparison of the data from Examples 1 and 8-9 shows that the only difference between Examples 8-9 and Example 1 is that the final temperature of the third heating is not within the preferred range of the present invention. The purity of the ingots in Examples 8-9 is significantly lower than that in Example 1, and the number of particles is significantly higher than that in Example 1. The oxygen content in Example 8 is significantly higher than that in Example 1. This is because when the final temperature of the third heating is too low, the melting point of copper is not reached, which prevents the copper sheets from melting normally and prevents the initial degassing and slag removal, resulting in a decrease in the purity of the ingots and an increase in oxygen content and particulate matter. When the final temperature of the third heating is too high, the melting rate is too fast, and the stacked copper sheets are easy to tip over and scratch the crucible, resulting in an increase in carbon particles. Therefore, it can be seen that the present invention preferably controls the final temperature of the third heating within a specific range, which can further improve the purity of ultra-high purity copper ingots.

[0057] (4) A comprehensive comparison of the data from Example 1 and Comparative Examples 1-3 shows that the only difference between Comparative Examples 1-3 and Example 1 is that the first heat preservation, the second heat preservation, and the third heat preservation are not performed respectively. The purity of the ingot in Example 1 is significantly higher than that in Comparative Examples 1-3. The oxygen content and particle number in Example 1 are significantly lower than those in Comparative Examples 1-3. This is because when the first heat preservation is not performed, the crucible and metal charge are not dried, resulting in a significant increase in oxygen content. When the second heat preservation is not performed, low-melting-point impurities cannot be effectively removed, resulting in a decrease in the purity of the ingot and an increase in oxygen content and particle number. When the third heat preservation is not performed, the initial degassing and slag removal cannot be carried out after the copper sheet melts, resulting in an increase in oxygen content and particle number. It can be seen that the preparation method provided by the present invention can avoid the introduction of impurities such as carbon particles during smelting, improve the purity of the ingot, and reduce the oxygen content of the ingot.

[0058] In summary, the preparation method provided by this invention is not only simple to operate and has low energy consumption, but also avoids the introduction of impurities such as carbon particles during smelting, improves the purity of the ingot, reduces the oxygen content of the ingot, and makes the internal structure of the ingot uniform with fewer defects.

[0059] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing ultra-high purity copper ingots, characterized in that, The preparation method includes the following steps: (1) Using copper sheets as raw material, vacuum medium frequency induction melting is carried out to obtain copper liquid; The vacuum intermediate frequency induction melting includes a first heating, a first holding, a second heating, a second holding, a third heating, and a third holding in sequence; The copper sheet is an electrolytic copper sheet, and the copper sheet is circular in shape; (2) The copper liquid obtained in step (1) is refined to obtain purified copper liquid; (3) The purified copper liquid obtained in step (2) is sequentially cast, cooled and machined to obtain ultra-high purity copper ingots; the casting method is hot top continuous casting; Step (1) The final temperature of the first heating is 400-450℃; Step (1) The final temperature of the second heating is 705-750℃; The final temperature of the third heating step (1) is 1060-1100℃; Step (1) The first heating and the first heat preservation are used to dry the graphite crucible and the furnace charge; Step (1) The second heating and the second heat preservation allow the low-melting-point inmeltable material to fully evaporate; The third heating and third heat preservation in step (1) allow the copper sheet to melt completely; The oxygen content of the ultra-high purity copper ingot is <1ppm, the purity is ≥6N, and the number of particles ≥20μm in each gram of the ultra-high purity copper ingot is <54. The casting rate in step (3) is 50-60 mm / min.

2. The preparation method according to claim 1, characterized in that, The purity of the copper sheet in step (1) is ≥6N.

3. The preparation method according to claim 1, characterized in that, The vacuum degree of the vacuum intermediate frequency induction melting in step (1) is ≤3.6×10 -1 Pa.

4. The preparation method according to claim 1, characterized in that, The power supply for the vacuum intermediate frequency induction melting is 40-45kW.

5. The preparation method according to claim 1, characterized in that, The first heat preservation time is 50-60 minutes.

6. The preparation method according to claim 1, characterized in that, The second heat preservation time is 50-60 minutes.

7. The preparation method according to claim 1, characterized in that, The third heat preservation time is 50-60 minutes.

8. The preparation method according to claim 1, characterized in that, The refining temperature in step (2) is 1500-1550℃.

9. The preparation method according to claim 1, characterized in that, The refining time is 30-40 minutes.

10. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Using round copper sheets with a purity ≥ 6N as raw materials, place them in a graphite crucible and first perform vacuum treatment until the vacuum degree is ≤ 3.6 × 10⁻⁶. -1 Pa, and then vacuum medium-frequency induction melting is carried out under the power supply of 40-45kW to obtain copper liquid; The vacuum intermediate frequency induction melting includes: first heating to 400-450℃ and holding for 50-60 minutes, then heating to 705-750℃ and holding for 50-60 minutes, and then heating to 1060-1100℃ and holding for 50-60 minutes. (2) The copper liquid obtained in step (1) is refined at a temperature of 1500-1550℃ for 30-40 minutes to obtain purified copper liquid; (3) The purified copper liquid obtained in step (2) is cast at a speed of 50-60 mm / min, and then cooled and machined in sequence to obtain ultra-high purity copper ingots; The purity of the ultra-high purity copper ingot is ≥6N, the oxygen content of the ultra-high purity copper ingot is <1ppm, and the number of particles ≥20μm per gram of the ultra-high purity copper ingot is <54.

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