Copper target and manufacturing method thereof

Abstract

A manufacturing method of a copper target includes the following steps. A copper ingot is subjected to a heating step to form a heated copper blank. The heated copper blank is subjected to a hot rolling step to form a hot rolled copper plate. The hot-rolled copper plate is subjected to an air cooling step to obtain the copper target. The copper target has a specific content of crystal grains with a specific crystal orientation and a specific grain size, so that the copper target has better sputtering efficiency during the sputtering process and can form a uniform thin film.

Description

[Technical Field]

[0001] This invention relates to a copper target and a method for manufacturing the same, and more particularly to a copper target with a specific content of crystal grains and a method for manufacturing the same. [Previous Technology]

[0002] With the miniaturization of electronic components and the increase in the number of wiring layers within chips, aluminum metal wires have encountered problems such as electromigration and high resistivity. Due to the characteristics of copper metal, such as low resistivity, high resistance to electromigration and high thermal conductivity, copper metal wires have gradually replaced aluminum metal wires for applications such as very large integrated circuits. [Summary of the Invention]

[0003] The manufacturing method of the copper target material of the present invention is simple and economical. Because the copper target material of the present invention has a specific content of crystallized grains with a specific orientation and a specific grain size, it exhibits better sputtering efficiency during the sputtering process and can form a uniform thin film.

[0004] At least one embodiment of the present invention provides a method for manufacturing a copper target, comprising the following steps: A heating step is performed on a copper ingot to form a heated copper billet. The heated copper billet is then hot-rolled to form a hot-rolled copper plate, wherein the final rolling temperature of the hot-rolling step is 350°C to 500°C. The hot-rolled copper plate is then air-cooled to obtain a copper target, wherein the cooling rate of the air-cooling step is 20°C / min to 50°C / min, and the proportion of grains in the (111) crystal orientation of the copper target is greater than 20%.

[0005] In at least one embodiment of the present invention, the purity of the copper ingot is at least 99.995 wt.%.

[0006] In at least one embodiment of the present invention, the heating temperature of the heating step is 400°C to 500°C, and the heating time of the heating step is 2 hours to 5 hours.

[0007] In at least one embodiment of the present invention, the hot rolling reduction in the hot rolling step is 75% to 85%.

[0008] In at least one embodiment of the present invention, the cooling rate of the air cooling step is 20°C / min to 25°C / min.

[0009] In at least one embodiment of the present invention, the ratio of the proportion of grains in the (111) crystal orientation to the proportion of grains in the (100) crystal orientation of the copper target is greater than 1.

[0010] In at least one embodiment of the present invention, the method for manufacturing copper targets excludes the hot forging step of heating copper billets, and the method for manufacturing copper targets excludes the cold rolling step and the heat treatment step of hot-rolled copper plates.

[0011] At least one embodiment of the present invention provides a copper target material manufactured by the above-described copper target material manufacturing method, wherein the average size of the copper target material grains is less than 45µm.

[0012] In at least one embodiment of the present invention, the thickness of the copper target is 15 mm to 30 mm.

[0013] In at least one embodiment of the present invention, the sputtering rate of the copper thin film formed by magnetron sputtering of the target material with a DC power of 500W is greater than 50 Å / s.

Implementation Method

[0014] The manufacture and use of embodiments of the present invention will be discussed in detail below. However, it will be understood that the embodiments provide many applicable inventive concepts that can be implemented in a wide variety of specific situations. The specific embodiments discussed are for illustrative purposes only and are not intended to limit the scope of the invention.

[0015] In this document, the range represented by "one value to another value" is a summary representation that avoids listing all the values ​​in the range in the specification. Therefore, the description of a particular value range covers any value within that value range as well as the smaller value range defined by any value within that value range, just as if the arbitrary value and the smaller value range were explicitly stated in the specification.

[0016] Copper metal wires in integrated circuits can first be formed into copper metal thin films using a pure copper target via magnetron sputtering, and then formed into copper metal wires using photolithography and etching processes. The purity, grain size, and crystal orientation of the copper target affect the sputtering effect and thin film properties. Specifically, the higher the purity of the target, the better the thin film performance. The sputtering rate of targets with smaller grain sizes is greater than that of targets with larger grain sizes. In addition, the crystal orientation of the target also affects the sputtering rate and the uniformity of the thin film thickness. The crystal structure of copper is face-centered cubic (FCC), and the sputtering rate of the crystal orientation from fastest to slowest is (111) > (100) > (110). Therefore, the higher the proportion of grains in the (111) crystal orientation, the faster the sputtering rate and the better the uniformity of the thin film thickness.

[0017] A method for manufacturing a copper target is known, which involves hot forging and drawing a copper billet at high temperature, followed by multiple reciprocating cold rolling and annealing heat treatment to obtain the copper target. Another method for manufacturing a copper target involves hot forging and a first heat treatment of a copper billet, followed by cold forging, a second heat treatment, and static pressing to obtain the copper target, wherein the (110) crystal orientation grain ratio of the copper target is 30% to 50%. Yet another method for manufacturing a copper target involves hot forging, a first heat treatment, cold forging, a second heat treatment, and two static pressing steps on a copper billet to obtain the copper target, wherein the (110) crystal orientation grain ratio of the copper target is 50% to 70%. All of the above methods for manufacturing copper targets require hot forging, cold rolling, and heat treatment, making the manufacturing process complex and uneconomical.

[0018] A known method for manufacturing a copper sputtering target involves upsetting, drawing, and hot forging a copper billet into a rectangular copper billet, followed by annealing heat treatment, hot rolling, and a second heat treatment step to obtain the copper sputtering target, wherein the grain size of the copper sputtering target is less than 100µm. However, this method requires hot forging, hot rolling, and two heat treatment steps, making the manufacturing process complex and uneconomical. Furthermore, the excessively large grain size is detrimental to the sputtering rate of the copper thin film.

[0019] A method for manufacturing a copper target is known, which involves hot rolling a copper billet at high temperature followed by a rapid cooling step to obtain the copper target. However, the recrystallization amount of this copper target is insufficient, which is not conducive to the subsequent sputtering formation of a copper thin film.

[0020] The manufacturing method of the copper sputtering target in this invention does not require the above-mentioned hot forging step, cold rolling step, and heat treatment step, thus it is more economical. The copper sputtering target of this invention has specific grain content, orientation, and size, resulting in better sputtering efficiency during the sputtering process and the formation of a uniform copper thin film.

[0021] Please refer to Figure 1, which is a schematic flowchart of a method 100 for manufacturing a copper sputtering target according to some embodiments of the present invention. As shown in step 110 of Figure 1, a heating step is performed on the copper ingot to form a heated copper blank. In some embodiments, the purity of the copper ingot may selectively be at least 99.995 wt.%, but is not limited thereto. When the purity of the copper ingot is at least 99.995 wt.%, the impurity content of the copper film formed by the subsequent sputtering of the copper target is low, which is beneficial to the conductivity of the copper metal wire. The copper ingot contains other unavoidable impurities, such as Ag, Fe, Sn, As, Mn, O, S, etc. In some embodiments, the total weight of the above impurities does not exceed 50 ppm of the copper ingot.

[0022] In some embodiments, the heating temperature of the heating step may selectively be between 400°C and 500°C, but is not limited to this, for example, 420°C, 440°C, 460°C, 480°C, or 490°C. If the heating temperature is less than 400°C, the resulting copper target material will have more elongated grains and fewer equiaxed grains. Compared to elongated grains, the copper thin film formed by the copper target material with equiaxed grains has a faster sputtering rate. If the heating temperature is greater than 500°C, the average grain size of the resulting copper target material will be too large, which is not conducive to subsequent sputtering. In other words, when the heating temperature is within the above range, it is beneficial to form the copper target material with specific content of crystal orientation and specific grain size as described in this invention.

[0023] In some embodiments, the heating time of the heating step may selectively be 2 hours to 5 hours, but is not limited to this, for example, 3 hours or 4 hours. When the heating time is within the above range, the copper ingot can be heated sufficiently and uniformly.

[0024] Then, as shown in step 120 of FIG. 1, the heated copper billet is subjected to a hot rolling step to form a hot-rolled copper plate. In some embodiments, the finishing temperature of the hot rolling step is 350°C to 500°C, for example, 380°C, 420°C, 450°C, or 480°C. If the finishing temperature is less than 350°C, the recrystallization amount of the obtained copper target may be insufficient. If the finishing temperature is greater than 500°C, the average grain size of the subsequently obtained copper target is too large, which is not conducive to subsequent sputtering. In other words, when the finishing temperature is within the above range, it is beneficial to form the copper target with specific content of crystallization orientation and specific grain size as described in this invention.

[0025] In some embodiments, the hot rolling reduction in the hot rolling step may selectively be 75% to 85%, but is not limited to this, for example, 80%. If the hot rolling reduction is less than 75%, the rolling force is too small, resulting in insufficient driving force and an inability to form a sufficient amount of recrystallized structure. If the hot rolling reduction is greater than 85%, the thickness of the subsequently obtained copper sputtering target may be too thin. In other words, when the hot rolling reduction is within the above range, it is beneficial to form the copper sputtering target with the specific content and orientation of grains as described in this invention.

[0026] Next, as shown in steps 130 and 140 of FIG. 1, the hot-rolled copper sheet is subjected to an air-cooling step to obtain a copper target. It is understood that the term "air-cooling step" as used herein refers to cooling the hot-rolled copper sheet in the atmosphere. In some embodiments, the cooling rate of the air-cooling step is 20°C / min to 50°C / min, for example, 25°C / min, 30°C / min, or 40°C / min. In other embodiments, the cooling rate of the air-cooling step is 20°C / min to 25°C / min. If the cooling rate is less than 20°C / min, the process time will increase, and the average grain size will be too large. If the cooling rate is greater than 50°C / min, the recrystallization amount of the obtained copper target may be insufficient, and the grain content in each crystal orientation may be insufficient. In other words, when the cooling rate is within the above range, it is beneficial to form the copper target with a specific content of grains in the crystal orientation described in this invention.

[0027] It is worth noting that in the copper target manufacturing method 100, a hot rolling step (i.e., step 120) and an air cooling step (i.e., step 130) are directly performed on the heated copper billet. In some embodiments, the copper target manufacturing method 100 excludes a hot forging step on the copper ingot. In some embodiments, the copper target manufacturing method 100 excludes a cold rolling step and a heat treatment step on the hot-rolled copper plate. Therefore, compared to copper target manufacturing methods that include hot forging, cold rolling, and / or heat treatment steps, the copper target manufacturing method 100 of this invention is economically efficient, and the obtained copper target is beneficial for forming conductive thin films for semiconductor integrated circuits.

[0028] In some embodiments, the grain percentage of the copper target at the (111) crystal orientation is greater than 20%, for example, greater than 22% or greater than 25%. In some embodiments, the grain percentage of the copper target at the (111) crystal orientation is less than 40%. In some embodiments, the ratio of the grain percentage at the (111) crystal orientation to the grain percentage at the (100) crystal orientation is greater than 1, for example, greater than 1.1 or greater than 1.5. In some embodiments, the grain percentage of the copper target at the (100) crystal orientation is 13% to 20%, for example, 15% or 18%. In some embodiments, the grains of the copper target are equiaxed. Copper films formed from copper targets with equiaxed grains have a faster sputtering rate.

[0029] In some embodiments, the average grain size of the copper target is less than 45µm. In other embodiments, the average grain size of the copper target is 35µm to 45µm. The smaller the average grain size, the higher the sputtering rate of the target, which can save process time and costs. When the average grain size is less than 45µm, it is beneficial to improve the sputtering rate of the copper thin film. In some embodiments, the thickness of the copper target is 15mm to 30mm, for example 20mm or 25mm.

[0030] In some embodiments, the sputtering rate of the copper thin film formed by magnetron sputtering of the target material with a DC (direct current) power of 500W is greater than 50 Å / s. In some specific embodiments, the chamber pressure before sputtering is 2 × 10⁻⁶ torr. In some specific embodiments, the vacuum level during sputtering is 1 × 10⁻³ torr to 5 × 10⁻³ torr. In some specific embodiments, the argon gas release rate is 5 sccm to 30 sccm.

[0031] The following experimental examples illustrate the application of the present invention, but they are not intended to limit the present invention. Anyone skilled in the art can make various modifications and refinements without departing from the spirit and scope of the present invention.

[0032] Experimental Examples 1 and 2, and Comparative Examples 1 to 3

[0033] In Experimental Example 1, a 100mm copper ingot was hot-rolled into a 20mm copper target at different heating temperatures. First, the copper ingot was heated to form a heated copper billet, wherein the purity of the copper ingot was at least 99.995 wt.%, and the heating temperature was 400°C to 500°C. Then, the heated copper billet was hot-rolled to form a hot-rolled copper plate, wherein the hot-rolling temperature was 400°C, and the final rolling temperature was 391°C. Afterward, the hot-rolled copper plate was air-cooled to obtain the copper target of Experimental Example 1, wherein the cooling rate was 20°C / min. The recrystallization rate of the copper target was measured using backscattered electron diffraction (EBSD) to determine the grain proportion at each crystal orientation. The process conditions and evaluation results of Experimental Example 1 are shown in Table 1 below.

[0034] As shown in Table 1, the copper target material of Experimental Example 1 has equiaxed grains with an average grain size of approximately 37.7 µm. The proportion of grains in the (111) crystal orientation of the copper target material is approximately 25.3%, and the proportion of grains in the (100) crystal orientation is approximately 14.2%, with the ratio of the proportion of grains in the (111) crystal orientation to that in the (100) crystal orientation being approximately 1.7. The sputtering rate of the copper thin film formed by magnetron sputtering of the target material with a DC power of 500 W is greater than 52.5 Å / s, wherein the cavity pressure before sputtering is 2 μ10⁻⁶ torr, the vacuum degree during sputtering is 1 μ10⁻³ to 5 μ10⁻³ torr, and the argon gas release rate is 5 sccm to 30 sccm.

[0035] Table 1 Experimental Example 1 Experiment Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Hot forging temperature X X 700°C 700°C X Rolling temperature 400°C 500°C room temperature 300°C 600°C Rolling temperature 391°C 484°C room temperature 296°C 570°C Cooling rate 20°C / min 25°C / min X 20°C / min 30°C / min Annealing temperature X X 500°C X X Grain types Equiaxed crystal Equiaxed crystal Equiaxed crystal elongated crystal Equiaxed crystal Grain size 37.7µm 41.3µm 72.6µm 82.1µm 52.8µm (111) 25.3% 22.8% 24.7% 27.1% 15.7% (100) 14.2% 18.3% 16.7% 12.5% 24.1% (111) / (100) 1.7 1.2 1.5 2.2 0.7 sputtering rate 52.5 Å / s 50.1 Å / s 41.2 Å / s 38.6 Å / s 43.7 Å / s

[0036] In Experimental Example 2, a manufacturing method similar to that of Experimental Example 1 was used, with the difference being the change in hot rolling temperature, finishing rolling temperature, and cooling rate. The process conditions and evaluation results of Experimental Example 2 are shown in Table 1 above.

[0037] In Comparative Example 1, a 180mm copper ingot was processed through different steps to form a 20mm copper target. First, the copper ingot was heated to form a heated copper billet, wherein the purity of the copper ingot was at least 99.995 wt.%, and the heating temperature was 700°C. Then, the heated copper billet was subjected to a unidirectional vertical hot forging step to form a 70mm hot-forged copper billet. Afterward, the hot-forged copper billet was cold-rolled at room temperature to form a 20mm cold-rolled copper sheet. The cold-rolled copper sheet was then annealed at an annealing temperature of 500°C to obtain the copper target of Comparative Example 1. The process conditions and evaluation results of Comparative Example 1 are shown in Table 1 above.

[0038] The results in Table 1 show that although the proportion of grains in the (111) crystal orientation of the copper target of Comparative Example 1 exceeds 20%, and the ratio of the proportion of grains in the (111) crystal orientation to the proportion of grains in the (100) crystal orientation is >1, the sputtering rate of the copper thin film formed by magnetron sputtering of the target with a DC power of 500W is low (approximately 41.2 Å / s) because the average size of the grains is >50µm.

[0039] In Comparative Example 2, a 180mm copper ingot was hot-rolled into a 20mm copper target at different heating temperatures. First, the copper ingot was heated to form a heated copper billet, wherein the purity of the copper ingot was at least 99.995 wt.%, and the heating temperature was 700°C. Then, the heated copper billet was subjected to a unidirectional vertical hot forging step to form a 70mm hot-forged copper billet. Afterward, the heated copper billet was hot-rolled at a lower temperature to form a hot-rolled copper sheet with a thickness of approximately 20mm, wherein the hot-rolling temperature was 300°C, and the final rolling temperature was 296°C. Afterward, the hot-rolled copper sheet was air-cooled to obtain the copper target of Comparative Example 2, wherein the cooling rate was 20°C / min. The process conditions and evaluation results of Comparative Example 2 are shown in Table 1 above.

[0040] The results in Table 1 show that, due to the lower hot rolling temperature of Comparative Example 2, the copper target did not undergo recrystallization, resulting in mainly rolled elongated grains and thus a larger average grain size (approximately 82.1 µm). Although the proportion of grains in the (111) crystal orientation of the copper target in Comparative Example 2 exceeded 20%, and the ratio of the proportion of grains in the (111) crystal orientation to the proportion of grains in the (100) crystal orientation was greater than 1, the average grain size was greater than 50 µm. Therefore, the sputtering rate (approximately 38.6 Å / s) of the copper thin film formed by magnetron sputtering of the target with a DC power of 500 W was relatively low.

[0041] In Comparative Example 3, a 100mm copper ingot was processed through different steps to form a 20mm copper target. First, the copper ingot was heated to form a heated copper billet, wherein the purity of the copper ingot was at least 99.995 wt.%, and the heating temperature was 600°C. Then, the heated copper billet was hot-rolled to form a hot-rolled copper sheet, wherein the hot-rolling temperature was 600°C, and the final rolling temperature was 570°C. Afterward, the hot-rolled copper sheet was air-cooled to obtain the copper target of Comparative Example 3, wherein the cooling rate was 30°C / min. The process conditions and evaluation results of Comparative Example 3 are shown in Table 1 above.

[0042] Due to the higher hot rolling temperature of Comparative Example 3, the average size of the copper target grains (approximately 52.8 µm) is larger, the proportion of grains in the (111) crystal orientation is only 15.7%, the ratio of the proportion of grains in the (111) crystal orientation to the proportion of grains in the (100) crystal orientation is <1, and the sputtering rate of the copper thin film formed by magnetron sputtering of the target with a DC power of 500 W (approximately 43.7 Å / s) is lower.

[0043] As can be seen from the results in Table 1, compared with Comparative Example 1 which has a hot forging step and a cold rolling step, Comparative Example 2 which has a hot forging step and a lower hot rolling temperature, and Comparative Example 3 which has a higher hot rolling temperature, the sputtering rate of Experimental Example 1 and Experimental Example 2 is faster, thus saving process time costs.

[0044] As described above, the manufacturing method of the copper target material of the present invention eliminates the hot forging step, cold rolling step, and heat treatment step (e.g., annealing step) of the copper ingot, thereby obtaining a pure copper target material that meets the application requirements of the semiconductor industry, so that the coating performance meets the industry requirements (i.e., fast sputtering rate and good uniformity of film thickness). Therefore, the manufacturing method of the copper target material of the present invention has a simple process and is economical. The copper target material of this invention can be applied to conductive films of semiconductor integrated circuits, but is not limited thereto.

[0045] It is understood that although the present invention is illustrated by specific manufacturing methods and specific evaluation methods, the copper target material and manufacturing method of the present invention are not limited thereto, as any person with ordinary knowledge in the art to which the present invention pertains will know. Other manufacturing methods or other evaluation methods may also be used without departing from the spirit and scope of the present invention.

[0046] Although the present invention has been disclosed above by way of embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field to which the present invention pertains may make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims. [Simplified Explanation of the Diagram]

[0047] To make the above and other objects, features, advantages and embodiments of the present invention more apparent and understandable, the detailed description of the accompanying drawings is as follows. Figure 1 is a schematic flowchart of a method for manufacturing a copper target according to some embodiments of the present invention. [Biomaterial Storage]

[0049] Domestic storage information (please note in order of storage institution, date, and number): None. International storage information (please note in order of storage country, institution, date, and number): None.

Claims

1. A method for manufacturing a copper target, comprising: performing a heating step on a copper ingot to form a heated copper billet, wherein a heating temperature of the heating step is 400°C to 500°C; performing a hot rolling step on the heated copper billet after the heating step to form a hot-rolled copper plate, wherein a finishing rolling temperature of the hot rolling step is 350°C to 500°C and a hot rolling reduction of 75% to 85%; and performing an air cooling step on the hot-rolled copper plate to obtain the copper target, wherein a cooling rate of the air cooling step is 20°C / min to 50°C / min and the proportion of grains in the (111) crystal orientation of the copper target is greater than 20%.

2. The method for manufacturing a copper target as described in claim 1, wherein the purity of the copper ingot is at least 99.995 wt.%.

3. The method for manufacturing a copper target as described in claim 1, wherein the heating time of the heating step is 2 to 5 hours.

4. The method for manufacturing a copper target as claimed in claim 1, wherein the cooling rate of the air cooling step is 20°C / min to 25°C / min.

5. The method for manufacturing a copper target as described in claim 1, wherein the ratio of the proportion of grains in the (111) crystal orientation to the proportion of grains in the (100) crystal orientation of the copper target is greater than 1.

6. The method for manufacturing a copper target as claimed in claim 1, wherein the method excludes a hot forging step of the heated copper billet, and excludes a cold rolling step and a heat treatment step of the hot-rolled copper plate.

7. A copper target material manufactured by a method for manufacturing a copper target material as described in any one of claims 1 to 6, wherein the average grain size of the copper target material is less than 45 µm.

8. The copper target as described in claim 7, wherein the thickness of the copper target is 15 mm to 30 mm.

9. The copper target as claimed in claim 7, wherein one of the copper thin films formed by magnetron sputtering of the target at a DC power of 500W has a sputtering rate greater than 50 Å / s.

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