Tantalum target material, method for producing the same, and use thereof

Abstract

The application belongs to the field of target material preparation, and particularly discloses a tantalum target material, a preparation method and application thereof. In the method, stress annealing, cold forging and heat treatment, two-stage rolling in different directions, intermediate static pressure treatment and recrystallization annealing are sequentially performed on a tantalum ingot, and each step is matched with each other, so that the tantalum target material has more uniform grain distribution, finer grains and a higher proportion of {111} grain orientation, thereby controlling the sputtering rate and sputtering stability, improving the uniformity of sputtering film and achieving the purpose of improving the film quality.

Description

Technical Field

[0001] This invention belongs to the field of target material preparation, specifically relating to a tantalum target material, its preparation method, and its application. Background Technology

[0002] In chip manufacturing, tantalum (Ta) thin films serve as diffusion barrier layers for Cu interconnects, preventing copper atoms from diffusing into the Si substrate and reducing current density and device performance. Tantalum sputtering targets, as the raw material for forming Ta thin films, have gradually become one of the key raw materials in the semiconductor industry. Tantalum targets form tantalum thin films through magnetron sputtering. This is achieved using physical vapor deposition (PVD) technology, where high-pressure accelerated gaseous Ar ions bombard the tantalum target, sputtering tantalum atoms or ion clusters from the target and depositing them as a thin film onto the silicon wafer. Tantalum is a body-centered cubic (BCC) metal, a high-level fault-energy metal. The internal structure, grain size, and crystal orientation of the tantalum target directly affect the quality of the film formed by magnetron sputtering. The following phenomena generally exist: (1) Regarding the influence of grain orientation on sputtering rate (S), S{110}>S{100}>S{111}; (2) As the grain size increases, the film deposition rate tends to decrease; (3) Within a suitable grain size range, the plasma impedance of the target material is low, the film deposition rate is high, and the film thickness uniformity is good. It can be seen that grain orientation and grain size are key factors affecting the sputtering rate, film uniformity, and overall quality of the target material. However, in the actual target material preparation process, the control technology of grain, crystal orientation, and sputtering rate is a difficult point in the industry, resulting in very poor uniformity of the sputtered film. Summary of the Invention

[0003] To address the problem of poor uniformity of tantalum thin films caused by the difficulty in controlling the sputtering rate of tantalum targets in the prior art, this invention will provide a tantalum target, its preparation method, and its application.

[0004] To achieve the above objectives, the following technical solutions are specifically included:

[0005] On one hand, the present invention provides a method for preparing a tantalum target, comprising the following steps:

[0006] (1) Anneal the tantalum ingot obtained by electron beam melting to obtain annealed tantalum ingot;

[0007] (2) The annealed tantalum ingot is subjected to cold forging and heat treatment in sequence to obtain the forged tantalum ingot;

[0008] The cold forging process includes sequential upsetting and drawing.

[0009] (3) the forged tantalum ingot is sequentially subjected to first-stage cross-rolling, static pressure treatment, second-stage cross-rolling, to obtain a rolled tantalum ingot; in the static pressure treatment, the tantalum ingot after the first-stage cross-rolling is deformed in the thickness direction; in the first-stage cross-rolling, the rolling directions of adjacent passes are different by 90°; in the second-stage cross-rolling, the rolling direction of the first pass in the second-stage cross-rolling is different from the rolling direction in the first stage by 45°-135°, and the rolling directions of adjacent passes are different by 90°;

[0010] (4) the rolled tantalum ingot is subjected to annealing treatment under vacuum, to obtain a tantalum target; the annealing treatment adopts a stepwise heating mode.

[0011] The tantalum ingot obtained by electron beam melting is subjected to annealing treatment, to remove stress in the tantalum ingot, reduce the risk of cracking in subsequent forging and pressing, and provide a basis for subsequent reduction of grain size and increase of {111} orientation ratio.

[0012] The tantalum ingot is subjected to cold forging and pressing, which includes upsetting and elongation, this mode can break the coarse columnar crystals of the tantalum ingot, refine the grains, and control the orientation distribution in the grains through the two forging modes of upsetting and elongation and the deformation rate; heat treatment is adopted after cold forging and pressing, which is used to control the {111}, {110} and {100} orientation distribution and ratio, to intervene and optimize the crystal orientation control in subsequent rolling.

[0013] The two-stage cross-rolling in different directions and the static pressure treatment in the two-stage cross-rolling can further refine the grains and significantly increase the {111} orientation ratio.

[0014] The stepwise heating mode is adopted for the annealing treatment of the rolled tantalum target blank, to realize recrystallization, further increase the {111} orientation ratio and refine the grains.

[0015] In the method, the tantalum ingot is sequentially subjected to stress annealing, cold forging and pressing and heat treatment, two-stage rolling in different directions and intermediate static pressure treatment, and recrystallization annealing, the steps are mutually matched, the grain distribution of the tantalum target is more uniform, the grains are finer, and the {111} grain orientation ratio is higher; and by increasing the {111} grain orientation ratio, the sputtering rate is reduced to a certain extent, the sputtering stability is increased, the sputtering film uniformity is improved, and the film quality is improved.

[0016] Preferably, the purity of the tantalum ingot obtained by electron beam melting is ≥99.99wt%, and further preferably 99.99wt%-999.995wt%.

[0017] Preferably, in step (1), the temperature of the annealing treatment is 1000-1400℃, and the time of the annealing treatment is 1-3h.

[0018] The tantalum ingot obtained by electron beam melting is subjected to annealing treatment to remove stress in the tantalum ingot and reduce the risk of cracking in subsequent forging, and the effect of stress removal is more optimal at the above-mentioned annealing treatment temperature and time.

[0019] Preferably, in step (2), the number of times of sequentially performing the cold forging and the heat treatment is 1-4.

[0020] The number of times of the combination of cold forging and heat treatment can further refine the grains, so that the cold forging and the heat treatment cooperate with each other to improve the grains and their orientation as a whole.

[0021] Preferably, in step (2), in the cold forging, the number of times of sequentially performing upsetting and elongation is 1-4, the deformation rate of each upsetting is 20%-50%, and the deformation rate of each elongation is 30%-70%; the temperature of the heat treatment is 1000-1300℃, and the time of the heat treatment is 1-4h.

[0022] The cold forging includes a combination mode of 1-4 times of upsetting and elongation, and the deformation rate is controlled, so that the coarse grains can be further broken in all directions to achieve the purpose of refining the grains.

[0023] Preferably, in step (2), the cold forging further includes rounding, and rounding in the cold forging process can increase the utilization rate of the subsequent target material.

[0024] Preferably, in step (3), in the first-stage cross-rolling and the second-stage cross-rolling, the total deformation rate is 65%-90%, and the total pass is 15-40 passes.

[0025] Further preferably, in the first-stage cross-rolling, the total deformation rate is 40%-60%, and the total pass is 10-25 passes.

[0026] Further preferably, in the second-stage cross-rolling, the total deformation rate is 10%-40%, and the total pass is 10-20 passes.

[0027] In each stage, increasing the rolling pass can further refine the grains to a certain extent, but the process cycle is increased.

[0028] Preferably, in step (3), in the first-stage cross-rolling and the second-stage cross-rolling, the rolling rate is respectively selected from 10-50 m / min, and the rolling mill diameter is respectively selected to be more than 500 mm.

[0029] Preferably, in step (3), the total deformation rate of the target material in the thickness direction during the static pressure treatment is 10%-30%.

[0030] Preferably, in step (3), the pressure in the thickness direction during the static pressure treatment is 1000-3000 tons.

[0031] The static pressure treatment of the present application only applies pressure in the thickness direction, and the static pressure treatment deforms the tantalum ingot after the first stage cross-rolling in the thickness direction. With the above deformation rate controlled, the proportion of {111} grain orientation can be significantly improved on the basis of obtaining lower grains.

[0032] Preferably, in step (4), the temperature of the annealing treatment is 900-1200℃, the time of the annealing treatment is 2-4h, and the stepwise heating mode specifically includes the following steps: heating from room temperature to 300-500℃ within 1-3h and maintaining the temperature for 1-2h; and then continuously heating to 1000-1200℃ within 2-4h and maintaining the temperature for 2-4h.

[0033] The stepwise heating mode with the above conditions is more optimal in terms of grain refinement.

[0034] Preferably, in step (4), the vacuum degree of the vacuum condition is less than or equal to 5x10 -3 Pa.

[0035] In another aspect, the present application provides a tantalum target prepared by the preparation method of the tantalum target.

[0036] Preferably, the average grain size of the tantalum target is 60-80μm, and the average area of the grains with {111} plane oriented along the normal direction is 25%-40% when the microstructure of the tantalum target in the cross section perpendicular to the sputtering surface is observed by electron backscatter diffraction.

[0037] The present inventors have found that when the average grain size of the tantalum target is 60-80μm and the average area of the grains with {111} plane oriented along the normal direction is 25%-40%, the sputtering rate can be reduced to a certain extent, the sputtering stability can be improved, the uniformity and quality of the sputtering film can be improved.

[0038] In addition, the present application also provides a use of the tantalum target in the preparation of integrated circuits.

[0039] The tantalum target of the present application has uniform grain distribution, appropriate average grain size, and appropriate proportion of {111} grain orientation. In the case of high-power sputtering, the deposition rate of the sputtering film is appropriate, the stability of the film formation is high, the uniformity of the sputtering film is high, and the requirements of high-quality semiconductor sputtering film are met.

[0040] Compared with the prior art, the present application has the following beneficial effects: in the method, the tantalum ingot is sequentially subjected to stress annealing, cold forging and heat treatment, two-stage rolling in different directions, intermediate static pressure treatment and recrystallization annealing, and each step is matched with each other, so that the tantalum target material has more uniform grain distribution, finer grains and higher {111} grain orientation ratio, thereby controlling the sputtering rate and sputtering stability, improving the uniformity of sputtering film deposition and achieving the purpose of improving film quality. DETAILED DESCRIPTION

[0041] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below through specific examples. Unless otherwise specified, the test methods used in the examples and / or comparative examples are conventional methods; and the materials, reagents, etc. used are commercially available unless otherwise specified.

[0042] The tantalum ingot obtained by electron beam melting used below has a purity of 99.995wt%, and the contents of W, Mo and Nb are <10ppm. In the process of preparing the tantalum ingot by electron beam melting, the main high voltage is 35-50KV, the auxiliary high voltage is 1-3KV, the emission current is 2-5A, the temperature is 2800-3200℃, and the time is 3-6h. The same kind of tantalum ingot is used in each example and comparative example.

[0043] Example 1

[0044] A preparation method of a tantalum target material, comprising the following steps:

[0045] (1) annealing a tantalum ingot obtained by electron beam melting at 1300℃ and keeping the temperature for 2h to obtain an annealed tantalum ingot;

[0046] (2) sequentially subjecting the annealed tantalum ingot to a combined treatment of 2 times of cold forging and heat treatment to obtain a forged tantalum ingot; comprising the following specific steps:

[0047] (2-1) upsetting the annealed tantalum ingot for the first time, the upsetting deformation rate being 50%; elongating the tantalum ingot for the first time, the elongation deformation rate being 70%; upsetting the tantalum ingot for the second time, the upsetting deformation rate being 50%; elongating the tantalum ingot for the second time, the elongation deformation rate being 70%; upsetting the tantalum ingot for the third time, the upsetting deformation rate being 50%; elongating the tantalum ingot for the third time, the elongation deformation rate being 70%;

[0048] (2-2) heat treating at 1150℃ for 2h;

[0049] (2-3) The annealed tantalum ingot is subjected to the following processes: first upsetting with a deformation rate of 50%; first drawing with a deformation rate of 70%; second upsetting with a deformation rate of 50%; second drawing with a deformation rate of 70%; third upsetting with a deformation rate of 50%; and third drawing with a deformation rate of 70%.

[0050] (2-4) Heat treatment at 1150℃ for 2 hours;

[0051] (3) The forged tantalum ingot is subjected to a first-stage cross rolling, static pressing, and a second-stage cross rolling in sequence to obtain a rolled tantalum ingot.

[0052] The rolling mill uses rolls with a diameter of 500mm or more, the rolling speed is 25m / min, and the rolling is carried out without heating at a temperature of 0-30℃, so it is classified as cold rolling; the specific process is as follows:

[0053] (3-1) In the first stage of cross rolling, the first pass is rolled in the 0° direction (the amount of pressure each time is 1-10mm, the same below), the second pass is rolled in the 90° direction, the third pass is rolled in the 0° direction, the fourth pass is rolled in the 90° direction, and so on. The rolling directions of two adjacent passes are 90° apart, and a total of 20 passes are rolled. The total deformation rate in this stage is 50%.

[0054] (3-2) For the tantalum ingot after the first stage of cross rolling, apply 1500 tons of static pressure only in the thickness direction to achieve a 15% deformation rate in the thickness direction of the tantalum ingot.

[0055] (3-3) In the second stage of cross rolling, the first pass is rolled in the 135° direction (or in the direction that forms an angle of 135° with the 90° direction), the second pass is rolled in the 225° direction (forming an angle of 90° with the previous pass), the third pass is rolled in the 135° direction, the fourth pass is rolled in the 225° direction, and so on. The rolling directions of two adjacent passes differ by 90°, and a total of 12 passes are rolled. The total deformation rate in this stage is 25%.

[0056] (4) The rolled tantalum ingot is subjected to vacuum conditions (vacuum degree ≤ 5*E) -3 The tantalum sputtering material was obtained by annealing at 1050℃ (Pa) and 1050℃.

[0057] The annealing process uses a stepped heating method and includes the following steps:

[0058] The temperature was raised from room temperature (20℃) to 350℃ in 2 hours and held for 1 hour; then the temperature was raised to 1050℃ in 3 hours and held for 3 hours.

[0059] Example 2

[0060] The difference between this example and Example 1 is that the annealing temperature in step (1) of this example is 1000°C, and the rest of the process is the same.

[0061] Example 3

[0062] The difference between this example and Example 1 is that the annealing temperature in step (1) of this example is 1400°C, and the rest of the process is the same.

[0063] Example 4

[0064] The difference between this example and Example 1 is that in step (3-2) of this example, the tantalum ingot is deformed by 10% in the thickness direction, and the rest of the process is the same.

[0065] Example 5

[0066] The difference between this example and Example 1 is that in step (3-2) of this example, the tantalum ingot is deformed by 30% in the thickness direction, and the rest of the process is the same.

[0067] Comparative Example 1

[0068] The difference between this comparative example and Example 1 is that this comparative example lacks the annealing treatment in step (1), and the rest of the process is the same.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 1 is that in step (2) of this comparative example, the static pressure treatment process in step (3-2) is not performed, and the rest of the process is the same.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 1 is that in step (3-3) of this comparative example, the direction of the second-stage cross-rolling is the same as that of the first-stage cross-rolling, both of which are sequentially combined in the 0° and 90° directions, and the rest of the process is the same.

[0073] Test of the tantalum target:

[0074] (1) (1) Grain size: the average grain size is measured using a metallographic microscope and analysis software;

[0075] (2) {111} orientation ratio: tested using SEM and EBSD (electron backscatter diffraction) devices, the microstructure data graph of the rolling face normal (ND) direction of the section perpendicular to the sputtering surface of the target is obtained, and the {100} orientation analysis is performed using analysis software and the report is provided; wherein, the {111} surface along the ND oriented grains include the grains with the orientation deviation of the {111} surface relative to the rolling face normal direction (ND) within 15°.

[0076] Table 1

[0077]

[0078] From the above examples, the average size of the tantalum target grains prepared by the present application is 60-80 μm, and the average area of the grains with {111} plane oriented along the normal direction is > 25% (25%-40%). The present application increases the proportion of {111} grain orientation, which to some extent reduces the sputtering rate and increases the sputtering stability, and improves the uniformity of sputtering film.

[0079] From Example 1 and Comparative Examples 1-3, it can be seen that the tantalum ingot obtained by electron beam melting is subjected to annealing treatment to remove the stress in the tantalum ingot, reduce the risk of cracking in subsequent forging and pressing, and provide a basis for subsequent reduction of grain size and increase of {111} orientation proportion. The cross-rolling in different directions is carried out in two stages, and the static pressure treatment is carried out in the two-stage cross-rolling, which can further refine the grains and improve the {111} orientation distribution.

[0080] From Examples 1-3, it can be seen that the annealing temperature also has a certain influence on the grain size and {111} orientation proportion. The present application can select 1000-1400℃ for annealing. Within this range, the grain size is relatively small, and the {111} orientation proportion is relatively high.

[0081] From Examples 1-3, it can be seen that the deformation rate in the static pressure treatment process has a certain influence on the grain size and {111} orientation proportion. The present application can select the static pressure treatment to make the deformation rate of the tantalum ingot in the thickness direction reach 15%-30%. Within this range, the grain size is relatively small, and the {111} orientation proportion is relatively high. If the static pressure treatment makes the deformation rate of the tantalum ingot in the thickness direction too small, the degree of improving the {111} orientation proportion is not great. If the deformation rate is too large, the degree of improving the {111} orientation proportion is not great, and the required pressure is larger or the time is too long, resulting in low efficiency.

[0082] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A method for preparing a tantalum target, characterized in that, Includes the following steps: (1) Anneal the tantalum ingot obtained by electron beam melting to obtain annealed tantalum ingot; (2) The annealed tantalum ingot is subjected to cold forging and heat treatment in sequence to obtain the forged tantalum ingot; The cold forging process includes sequential upsetting and drawing. (3) The forged tantalum ingot is subjected to a first-stage cross rolling, a static pressing treatment, and a second-stage cross rolling in sequence to obtain a rolled tantalum ingot; in the static pressing treatment, the tantalum ingot after the first-stage cross rolling is deformed in the thickness direction, and the total deformation rate in the thickness direction of the target material is 10%-30%; in the first-stage cross rolling, the rolling directions of two adjacent passes differ by 90°; in the second-stage cross rolling, the rolling direction of the first pass in the second-stage cross rolling differs from the rolling direction in the first stage by 45°~135°, and the rolling directions of two adjacent passes differ by 90°; in the first-stage cross rolling and the second-stage cross rolling, the total deformation rate is 65%-90%, and the total number of passes is 15-40; (4) The rolled tantalum ingot is annealed under vacuum to obtain a tantalum target; the annealing process is carried out by step heating.

2. The method for preparing the tantalum target material as described in claim 1, characterized in that, In step (1), the annealing temperature is 1000-1400℃ and the annealing time is 1-3h.

3. The method for preparing the tantalum target material as described in claim 1, characterized in that, In step (2), the cold forging and heat treatment are performed 1-4 times in sequence.

4. The method for preparing the tantalum target material as described in claim 1, characterized in that, In step (2), the cold forging process involves upsetting and drawing 1-4 times in sequence, with a deformation rate of 20%-50% for each upsetting and a deformation rate of 30%-70% for each drawing; the heat treatment temperature is 1000-1300℃ and the heat treatment time is 1-4h.

5. The method for preparing the tantalum target material as described in claim 1, characterized in that, In step (4), the annealing temperature is 900-1200℃, the annealing time is 2-4h, and the step heating method specifically includes the following steps: heating from room temperature to 300-500℃ within 1-3h and holding for 1-2h; then heating to 1000-1200℃ for 2-4h and holding for 2-4h.

6. A tantalum target material prepared by the method of any one of claims 1-5.

7. The tantalum sputtering target as described in claim 6, characterized in that, The average grain size of the tantalum target is 60-80 μm. When the microstructure of the tantalum target on a cross section perpendicular to the sputtering surface is observed using electron backscatter diffraction, the average area of ​​the grains oriented along the normal direction of the {111} plane is 25%-40%.

8. The use of the tantalum sputtering material as described in claim 6 or 7 in the fabrication of integrated circuit boards.

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