TANTALUM SPUTTERING TARGET, AND PRODUCTION METHOD THEREFOR

Abstract

Provided is a tantalum sputtering target, which includes an area ratio of crystal grains of which a {111} plane is oriented in a direction normal to a rolling surface (ND) is 35% or more when the ND, which is a cross section orthogonal to a sputtering surface of a target, is observed via Electron Backscatter Diffraction Pattern method. The object of the present invention is to provide a tantalum sputtering target in which a sputtered material can be uniformly deposited on a wafer surface under high-power sputtering conditions by increasing the straightness of the sputtered material. By using this kind of tantalum target for sputter-deposition, it is possible to improve the film thickness uniformity and the throughput of deposition even for fine wiring.

Claims

1. A tantalum sputtering target comprising, an area ratio of crystal grains of which a {111} plane is oriented in a direction normal to a rolling surface (ND) is 35% or more when the ND, which is a cross section orthogonal to a sputtering surface of a target, is observed via Electron Backscatter Diffraction Patterns.

2. The tantalum sputtering target according to claim 1, wherein a ratio {111}/{100} of an area ratio of crystal grains of which a {111} plane is oriented in a direction normal to a rolling surface (ND) and an area ratio of crystal grains of which a {100} plane is oriented in the ND is 2.0 or more when the ND, which is a cross section orthogonal to a sputtering surface of a target, is observed via Electron Backscatter Diffraction Patterns.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a diagram illustrating the positions where the structure of the sputtering target was observed.

[0014] FIG. 2 is a diagram illustrating the positions where the sheet resistance of the film formed on the wafer was measured.

[0015] FIG. 3 shows images of the crystal orientation distribution of the target of Example 1 observed via EBSPs.

DESCRIPTION OF THE EMBODIMENTS

[0016] The sputtering target according to the embodiments of the present invention is characterized in that an area ratio of crystal grains of which a {111} plane is oriented in a direction normal to a rolling surface (ND) is 35% or more when the ND, which is a cross section orthogonal to a sputtering surface of a target, is observed by a method using Electron Backscatter Diffraction Patterns (abbreviated EBSP(s) hereinafter). With regard to the area ratio, an EBSP device (JSM-7001 FTTLS-type field emission electron microscope/crystal orientation analyzing device OIM6.0-CCD/BS) is used to observe five positions shown in FIG. 1 (left) and obtain an average area ratio of crystal grains of which the {111} plane is oriented in the ND with regard to the structure of the cross section (width: 2 mm, height: 6.35 mm) orthogonal to the sputtering surface as shown in FIG. 1 (right).

[0017] With tantalum having a body-centered cubic structure, the atomic close-packed direction is <111>, and the relation of the sputtering surface and the close-packed direction is important in controlling the sputter direction of the sputtered material. When the {111} plane is oriented in the direction normal to the rolling surface (ND), since the close-packed direction coincides with the direction normal to the sputtering surface, the straightness of the sputtered material can be increased. Note that the crystal grains of which the {111} plane is oriented in the ND include the crystal grains of which the orientation deviation of the {111} plane relative to the direction normal to the rolling surface (ND) is within 15. While there is no particular limit in the upper limit value of the area ratio of the crystal grains having the {111} plane, in effect it is difficult to achieve an area ratio of 60% or higher.

[0018] According to the embodiment of the present invention, when a direction normal to a rolling surface (ND), which is a cross section orthogonal to a sputtering surface of a target, is observed via EBSPs, a ratio {111}/{100} of an area ratio of crystal grains of which a {111} plane is oriented in the ND and an area ratio of crystal grains of which a {100} plane is oriented in the ND is preferably 2.0 or more. When the {100} plane is oriented in the direction normal to the rolling surface (ND), since the angle of the close-packed direction relative to the direction normal to the sputtering surface will become large (wide), the straightness of sputter-deposition can be further improved by lowering the ratio of this plane. As the ratio of {111}/{100} is greater, the deposition rate can be increased. Further, deposition with film thickness uniformity is also consequently enabled for some reason. Note that the crystal grains of which the {100} plane is oriented in the ND include the crystal grains of which the orientation deviation of the {100} plane relative to the direction normal to the rolling surface (ND) is within 15. Furthermore, the area ratio of the crystal grains having the {100} plane is obtained in the same manner as the area ratio of the crystal grains having the {111} plane described above.

[0019] According to the embodiment of the present invention, a tantalum target having a purity of 99.99% or higher is preferably used. Since impurities in the target may cause the device characteristics in a semiconductor integrated circuit to deteriorate, a tantalum target having the highest purity is preferably used. In the present invention, the purity of 99.99% (4N) means that the total amount of Na, Al, Si, K, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Zr is less than 100 ppm when a Ta ingot is analyzed via glow discharge mass spectrometry (GDMS).

[0020] The method of producing the tantalum sputtering target of the present invention is as follows.

[0021] Foremost, tantalum is melted and cast to prepare an ingot, and the prepared ingot is thereafter forged. The ingot is subject to press forging to prepare a billet, and the billet is cut into an appropriate size and then subject to heat treatment. Furthermore, the billet is subject to first forging, first heat treatment, and second forging, divided into two, and then subject to second heat treatment, preferably at the temperature from 950 to 1100 C. The embodiments of the present invention are not particularly limited to the foregoing processes, and the number of times that forging is performed and the temperature of the heat treatment may be suitably selected upon performing the processes in order to adjust the forged structure.

[0022] Next, 1) the obtained material is rolled consecutively two or more times in one direction, and 2) rotated 90 degrees and then additionally rolled consecutively two or more times. These processes are repeated (1.fwdarw.2.fwdarw.1.fwdarw.2.fwdarw. . . . ) in two sets or more to subsequently obtain a predetermined plate thickness. The foregoing rolling processes are adjusted so that the structural orientation is controlled at a rolling reduction of 12% or more and the total rolling reduction is 85% or higher. The number of rolling passes contributes considerably to controlling the orientation and the {100} orientation ratio can be increased when the number of passes is greater. Meanwhile, since the rolling workload will increase when the number of passes is greater, it is important to appropriately adjust the conditions regarding the number of passes. While heat treatment may also be performed during the rolling process, it is recommended to perform the heat treatment after the final rolling as will be explained below, rather than during the rolling process. The condition of heat treatment is at 750 to 1000 C. and preferably for 4 hours or longer.

[0023] Next, the rolled material is subject to heat treatment preferably at 750 to 1000 C. for 1 hour or longer, and thereafter machined into an intended shape to obtain a target. It is thereby possible to effectively destroy the forged structure and obtain a uniform and fine structure based on the rolling process. With regard to the texture of the present invention formed via the rolling process and heat treatment, the intended structural orientation can be obtained by comprehending which plane is preferentially oriented based on the EBSP method, and feeding back the results to the rolling process and heat treatment conditions.

EXAMPLES

[0024] Now the embodiment of the present invention is explained in detail with reference to the examples. These examples are merely illustrative, and the present invention shall in no way be limited thereby. In other words, the embodiment of the present invention covers the other modes and modifications included in the technical concept of this invention.

[0025] The evaluation method adopted in the Examples and Comparative

[0026] Examples is as follows.

(Film Thickness Uniformity and Rate of Variability Thereof)

[0027] The film thickness uniformity and the rate of variability thereof are evaluated using the average value and the standard deviation of the rate of variability of the film thickness (standard deviation/average value100) of each target life (i.e. each wafer). The target life can be represented as the integration of the power during sputtering and the total sputtering time. For example, when sputtering is performed at a power of 15 kW for 100 hours, the target life will be 1500 kWh.

[0028] As a specific evaluation method, foremost, sputtering is performed for every 300 kWh (power of 300 kW for 1 hour), and a total of 7 wafers are deposited. Subsequently, the in-plane sheet resistance at 49 locations of each wafer is measured as shown in FIG. 2, the obtained values are converted into a film thickness (resistance value of tantalum is deemed 180 cm), and the standard deviation and the average value of the film thickness are thereby obtained. Subsequently, the in-plane rate of variability of film thickness (%) of each wafer=standard deviation/average value100 is calculated, and the average value of rate of variability of film thickness calculated for each wafer is used as the film thickness uniformity. As the rate of variability of the film thickness uniformity, standard deviation/average value (corresponding to film thickness uniformity)100 among wafers (relative to the target life) is calculated utilizing the rate of variability of film thickness of each wafer obtained above.

Example 1

[0029] A tantalum raw material having a purity of 99.997% was subject to electron beam melting and cast to prepare an ingot having a length of 1000 mm and a diameter of 195 mm. The ingot was subject to cold press forging to obtain a diameter of 150 mm, and thereafter cut to a required length to obtain a billet. Next, the billet was subject to heat treatment at a temperature of 1250 C., once again subject to cold first forging, subject to heat treatment at 1000 C., then subject to cold second forging, divided into two, and once again subject to heat treatment at 1000 C.

[0030] Subsequently, the forged billet was subject to cold rolling. The rolling process was performed by repeating continuous rolling passes at a rolling reduction of 12% or more a total of 10 times, and thereafter performing a rolling pass at a rolling reduction of less than 12%. After the rolling process, the rolled material was subject to heat treatment at 800 C. Next, finish machining was performed to the obtained target material having a thickness of 10 mm and a diameter of 500 mm to prepare a tantalum sputtering target having a thickness of 6.35 mm and a diameter of 450 mm.

[0031] The surface of the tantalum sputtering target obtained based on the foregoing processes was polished with an abrasive paper (corresponds to #2000), additionally buffed with a Polipla solution and subject to mirror finishing, and thereafter treated with a mixed liquid of hydrofluoric acid, nitric acid, and hydrochloric acid. An EBSP device (JSM-7001 FTTLS-type field emission electron microscope/crystal orientation analyzing device OIM6.0-CCD/BS) was used to observe five positions of the obtained polished surface with regard to the structure of the cross section (width: 2 mm, height: 6.35 mm) orthogonal to the sputtering surface as shown in FIG. 1. Moreover, FIG. 3 shows the crystal orientation distribution. Consequently, the area ratio of the crystal grains having the {111} plane was 50.5%. The area ratio of the crystal grains of which the {100} plane is oriented in the ND was 7.5%. And the ratio {111}/{100} of the foregoing area ratios was 6.73. As a result of sputtering this target, the film thickness uniformity was 2.2 and the rate of variability of the film thickness uniformity was 0.15, both of which showed effectiveness. And, the deposition rate was 6.9 A/second, which was the intended sputter rate. The results are shown in Table 1.

Examples 2-5

[0032] A forged billet was prepared in the same manner as Example 1. Next, the forged billet was subject to cold rolling. The rolling process was performed by adjusting the number of sets of continuous rolling passes at a rolling reduction of 12% or more as shown in Table 1, and thereafter performing a rolling pass at a rolling reduction of 6% or more so that the total rolling reduction will be 85% or more. After the rolling process, the rolled material was subject to heat treatment at 800 C. Next, finish machining was performed to the obtained target material having a thickness of 10 mm and a diameter of 500 mm to prepare a tantalum sputtering target having a thickness of 6.35 mm and a diameter of 450 mm.

[0033] With regard to the sputtering target obtained based on the foregoing processes, the structure of the cross section orthogonal to the sputtering surface of the target was observed in the same manner as Example 1. Consequently, the area ratio of the crystal grains of which the {111} plane is oriented in the ND was 35% or more in all cases. And the ratio {111}/{100} of the foregoing area ratios was 2.0 or more in all cases. As a result of sputtering this target, the film thickness uniformity and the rate of variability of the film thickness uniformity in all cases showed effectiveness. And the deposition rate was the intended sputter rate. The results are similarly shown in Table 1.

Comparative Examples 1-5

[0034] A forged billet was prepared in the same manner as Example 1. Next, the forged billet was subject to cold rolling. The rolling process was performed by adjusting the number of sets of continuous rolling passes at a rolling reduction of 12% or more as shown in Table 1, and thereafter performing a rolling pass at a rolling reduction of 6% or more so that the total rolling reduction will be 85% or more. After the rolling process, the rolled material was subject to heat treatment at 800 C. Next, finish machining was performed to the obtained target material having a thickness of 10 mm and a diameter of 350 mm to prepare a tantalum sputtering target having a thickness of 6.35 mm and a diameter of 320 mm.

[0035] With regard to the sputtering target obtained based on the foregoing processes, the structure of the cross section orthogonal to the sputtering surface of the target was observed in the same manner as Example 1. As a result, the area ratio of the crystal grains of which the {111} plane is oriented in the ND was less than 35% in all cases. And the ratio {111}/{100} of the foregoing area ratios was more than 2.0 in all cases. As a result of sputtering this target, the film thickness uniformity and/or the rate of variability of the film thickness uniformity deteriorated in all cases. Moreover, the sputter rate was high. The results are similarly shown in Table 1.

TABLE-US-00001 TABLE 1 Number of continuous roll Film Deposition passes of 12% (111) (100) thickness rate: or more area ratio area ratio (111)/(100) uniformity (/second) Evaluation Example 1 10 50.5 7.5 6.73 2.2 6.9 Example 2 9 48.5 8.6 5.64 2.3 6.7 Example 3 8 44.1 12.9 3.42 2.4 6.4 Example 4 7 36.9 13.6 2.71 2.4 6.5 Example 5 6 36.7 18.3 2.01 2.6 6.4 Comparative 5 34.9 23.1 1.51 2.7 6.2 Example 1 Comparative 4 32.4 27.7 1.17 2.7 6.2 Example 2 Comparative 3 30.8 22.7 1.36 2.8 6.1 Example 3 x Comparative 2 27.2 27.4 0.99 2.7 6.3 Example 4 Comparative 1 24.3 29.5 0.82 2.9 6 Example 5 x Criteria .fwdarw. Deposition rate: 6.6 or more .fwdarw. Deposition rate: 6.2 to less than 6.4 Film thickness uniformity: Less than 2.4 Film thickness uniformity: 2.6 to less than 2.8 .fwdarw. Deposition rate: 6.4 to less than 6.6 x.fwdarw. Deposition rate: Less than 6.2 Film thickness uniformity: 2.4 to less than 2.6 Film thickness uniformity: 2.8 to less than 3.0

INDUSTRIAL APPLICABILITY

[0036] According to the embodiment of the present invention, by causing the structural orientation of a tantalum sputtering target to be a predetermined state, the straightness of the sputtered material can be increased and the sputtered material can be uniformly deposited on the wafer surface even under high-power sputtering conditions. The increase in the straightness of the sputtered material can eventually achieve both uniform film thickness and the throughput of deposition. Embodiments of the present invention provide a tantalum sputtering target that is useful in forming a thin film of an element wiring of a semiconductor integrated circuit.