Sputtering target material

Abstract

A sputtering target material, wherein the strength of a sputtering target material can be enhanced without using pure Ta to prevent cracking during sputtering and generating particles and to suppress an irregular composition of a sputtered film, is provided. The present invention provides a sputtering target material containing, in at %, 35% to 50% of Ta with the balance being Ni and an inevitable impurity, wherein the sputtering target is composed only of a Ni.sub.2Ta compound phase and a NiTa compound phase, and a microstructure in each of the Ni.sub.2Ta compound phase and the NiTa compound phase has a maximum inscribed circle diameter of not more than 10 m.

Claims

1. A sputtering target material, comprising, in at %, 35% to 50% of Ta with the balance being Ni and an inevitable impurity, wherein the sputtering target material is composed only of a Ni.sub.2Ta compound phase and a NiTa compound phase, and wherein a microstructure in each of the Ni.sub.2Ta compound phase and the NiTa compound phase has a maximum inscribed circle diameter of not more than 10 m.

2. The sputtering target material according to claim 1, wherein the sputtering target material has a bending strength of not less than 450 MPa.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a micrograph, observed by an electron scanning microscope (SEM), of a microstructure of a sputtering target material according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(2) The present invention will be described in detail below.

(3) The sputtering target material according to the present invention contains, in at %, 35% to 50% of Ta with the balance being Ni and an inevitable impurity. On the other hand, when Ta is less than 35% or more than 50%, only either one of Ni.sub.2Ta and NiTa compounds is formed. In other words, the equilibrium diagram shows that a phase which is formed between 100% Ni and Ni-35Ta (exclusive) is Ni, Ni.sub.8Ta, Ni.sub.3Ta, and/or Ni.sub.2Ta, a phase which is formed between Ni-50Ta (exclusive) and 100% Ta is NiTa, NiTa.sub.2, and/or Ta, and Ni.sub.2Ta and NiTa can coexist only between Ni-35Ta and Ni-50Ta.

(4) FIG. 1 is a micrograph, observed by an electron scanning microscope (SEM), of a microstructure of a sputtering target material according to the present invention. In the FIGURE, Sign 1 represents a Ni.sub.2Ta compound phase (gray) and Sign 2 represents a NiTa compound phase (white), and it is seen that the microstructure of the sputtering target material is composed only of two phases, which are a Ni.sub.2Ta compound phase and a NiTa compound phase. In the present invention, formation of a fine phase such that a microstructure in each of the Ni.sub.2Ta compound phase and the NiTa compound phase has a maximum inscribed circle diameter of not more than 10 m is characteristic. By allowing a microstructure of the sputtering target material to have such phases, the strength of the sputtering target material can be enhanced to suppress generating particles during sputtering and to prevent an irregular composition of a sputtered film due to an irregular composition in the sputtering target material.

(5) Since an atomized powder is used for a component composition limited to the range of 35 to 50% of Ta with the balance being Ni as described above, the phase formed is composed of only Ni.sub.2Ta compound phase and NiTa compound phase. In the other words, both Ni.sub.2Ta compound phase and NiTa compound phase coexist, and therefore a phase other than the two phases does not exist. By allowing a microstructure of the sputtering target material to have such phases, the strength of the sputtering target material can be enhanced to suppress generating particles during sputtering and to prevent an irregular composition of a sputtered film due to an irregular composition in the sputtering target material.

(6) Moreover, by allowing a molding temperature to be 1000 C. to 1200 C. and a molding pressure to be 100 to 150 MPa, a fine structure is achieved. On the other hand, when the molding temperature is less than 1000 C. and the molding pressure is less than 100 MPa, an intended fine structure cannot be sufficiently achieved. In addition, when the molding temperature is higher than 1200 C. and the molding pressure is more than 150 MPa, the inscribed circle diameter of the microstructure in each of the Ni.sub.2Ta compound phase and the NiTa compound phase cannot be achieved to be not more than 10 m. Therefore, it is preferred that the molding temperature be 1000 C. to 1200 C. and the molding pressure be 100 to 150 MPa.

(7) As described above, in the present invention, it is possible to provide a sputtering target material such that the strength of the sputtering target material can be enhanced and also that cracking during sputtering, generating particles and an irregular composition of a sputtered film can be prevented, by such a way that only both Ni.sub.2Ta compound phase and the NiTa compound phase coexist as a constituent phase without using pure Ta and that the microstructure is allowed to be such a fine structure that the inscribed circle diameter of the microstructure in each of the Ni.sub.2Ta compound phase and the NiTa compound phase is not more than 10 m.

(8) As a rapid cooling solidification method applied for producing the sputtering target material according to the present invention, a gas atomization process in which less impurity is contaminated and a spherical powder suitable for sintering because of its high packing ratio can be obtained is preferred. As a pressure sintering method for the powder, methods such as hot press, hot isostatic pressing, electric pressure sintering and hot extrusion can be applied. Among these, hot isostatic pressing is especially preferred by reason that its pressing pressure is high and that a dense sintered compact is obtained even though coarsening of an intermetallic compound phase is suppressed restricting a maximum temperature to low.

(9) Note that both melting casting method and powder sintering method can be applied for the sputtering target material according to the present invention as long as a microstructure thereof can be controlled. Note that it is desirable that a solidification rate be faster than that of general castings in which, for example, molten alloy is cast into a mold cooled by water cooling or the like in order to control the maximum inscribed circle diameter of the microstructure in each of the Ni.sub.2Ta compound phase and the NiTa compound phase to be not more than 10 m in the microstructure when a melting casting method is applied.

(10) It is preferred that the sputtering target material according to the present invention have a bending strength of not less than 450 MPa. The bending strength of the sputtering target material according to the present invention is, for example, not less than 500 MPa and not more than 750 MPa. Note that the bending strength is measured as follows: A specimen of 4 mm wide, 3 mm high and 25 mm long which is cut away from a sintered alloy by a wire is evaluated by three-point bending test, and the obtained result is defined as a three-point bending strength. A three-point bending test is carried out in such a way that a rolling reduction is applied with a distance between support points of 20 mm and a stress (N) at the time is then measured and a three-point bending strength is calculated according to the following formula:
A three-point bending strength (MPa)=(3stress (N)a distance between support points (mm)/(2a specimen width (mm)(a specimen thickness (mm).sup.2)

EXAMPLES

(11) The present invention will be described more specifically with examples below.

(12) NiTa alloy powders were produced from respective component composition shown in Table 1 by a gas atomization process. The obtained powders were classified to not more than 500 m, and used as raw material powders for HIP molding (hot isostatic pressing). A billet for HIP molding was produced by such a way that a raw material powder is filled into a carbon steel can of 50 mm long with 250 mm in diameter, then degassed in vacuum and mounted. This powder billet was HIP-molded in a condition of molding pressure, molding temperature and retention time shown in Table 1. Thereafter, a sputtering target material of 7 mm thick with 180 mm in diameter was produced from the compact.

(13) For the evaluation, a microstructure of a sputtering target material was evaluated for the maximum inscribed circle being able to be drawn in the compound by taking a specimen for an electron scanning microscope (SEM) from the sputtering target material listing, polishing the cross section of the specimen and taking a backscattered electron image. The specimen was analyzed along a line of 1 mm long at five measurement positions using an Electron Probe Micro Analyzer, and the difference of the maximum and minimum values of Ni atomic weight was then evaluated. When the maximum and minimum values of Ni atomic weight are not more than 20 at %, it shall be OK as a sputtering target material having good homogeneity. When the difference of the maximum and minimum values of Ni atomic weight are not less than 20 at %, it shall be NG.

(14) For evaluating for particles, the sputtering target material sample was deposited on an aluminum substrate of 1.75 mm thick with 95 mm in diameter under Ar gas pressure of 0.9 Pa using a DC magnetron sputter, and the amount of particles was then evaluated using Optical Surface Analyzer.

(15) For evaluating for an irregular composition of sputtered film, the sputtered substrate was analyzed along a line of 1 mm long at five measurement positions using an Electron Probe Micro Analyzer, and the difference of the maximum and minimum values of Ni atomic weight was then evaluated. When the maximum and minimum values of Ni atomic weight are not more than 20 at %, it shall be OK as a film having good homogeneity. When the maximum and minimum values of Ni atomic weight are not less than 20 at %, it shall be NG.

(16) For evaluating the strength of the sputtering target material, a specimen of 4 mm wide, 3 mm high and 25 mm long was cut away from TP by a wire, and then evaluated by three-point bending test. A three-point bending test is carried out in a condition that a rolling reduction is applied with a distance between support points of 20 mm and a stress (N) at the time is then measured and a three-point bending strength is calculated according to the following formula:
A three-point bending strength (MPa)=(3stress (N)a distance between support points (mm)/2a specimen width (mm)(a specimen thickness (mm).sup.2)

(17) TABLE-US-00001 TABLE 1 Inscribed Inscribed circle circle drawn drawn Bending Component in Ni.sub.2Ta in NiTa strength Uniformity composition Molding Molding Retention compound compound Uniformity of Number of (at %) temperature pressure time phase phase of target of sputtered No Ta Ni ( C.) (MPa) (Hr) (m) (m) target (MPa) particles film Note 1 35.4 Balance 1100 100 3 4 3 OK 730 2 OK Inventive 2 37.5 Balance 1170 150 5 3 2 OK 700 1 OK Example 3 40.0 Balance 1150 130 2 3 3 OK 720 1 OK 4 45.0 Balance 1000 110 5 3 4 OK 500 2 OK 5 48.9 Balance 1200 100 8 3 4 OK 600 1 OK 6 35.0 Balance 1000 130 3 7 2 OK 650 1 OK 7 36.0 Balance 1140 130 3 4 3 OK 630 0 OK 8 38.0 Balance 1130 150 5 3 3 OK 720 2 OK 9 42.0 Balance 1120 150 5 4 3 OK 730 2 OK 10 43.0 Balance 1180 150 5 4 4 OK 680 2 OK 11 47.0 Balance 1170 140 5 3 5 OK 690 1 OK 12 50.0 Balance 1190 140 5 3 7 OK 700 1 OK 13 52.0 Balance 1340 160 10 Ni.sub.2Tadoes Wholly OK 200 23 OK Comparative notexist NiTa Example compound phase 14 37.5 Balance 1340 160 10 16 8 OK 200 19 OK 15 34.0 Balance 1340 130 10 WhollyNi.sub.2Ta NiTa OK 200 19 OK compound doesnot phase exist 16 35.4 Balance 1150 150 3 15 15 NG 430 5 NG 17 41.7 Balance 1150 130 3 5 13 NG 380 5 NG 18 37.5 Balance 1150 100 3 13 10 NG 400 3 NG Note 1) Underline means not being within the present invention. Note 2) Each Comparative Example 16, 17 and 18 is a target component composition composed of a mixture of a pure Ta powder, Ni37.5Ta atomized powder and pure Ni atomized powder obtained by changing a mixing weight ratio.

(18) As shown in Table 1, No. 1 to 12 are Inventive Examples and No. 13 to 18 are Comparative Examples.

(19) In Comparative Example No. 13, Ta component composition is high and uniformly NiTa compound phase. In the other words, Ni.sub.2Ta is not present, and stiffness is therefore very low because the component composition is wholly NiTa compound phase. A lot of particles are generated because of low stiffness. In Comparative Example No. 14, the maximum inscribed circle diameter of the microstructure of the Ni.sub.2Ta compound phase is coarsened to be 16 m, and the stiffness is therefore low. A lot of particles are therefore generated. In Comparative Example No. 15, Ta component composition is low and uniformly Ni.sub.2Ta compound phase. In the other words, NiTa compound phase is not present, and stiffness is therefore very low because the component composition is wholly Ni.sub.2Ta compound phase. A lot of particles are therefore generated.

(20) Comparative Example No. 16 was produced by such a way that pure Ta powder, Ni-37.5Ta atomized powder and pure Ni atomized powder were mixed with mixing ratio of 41.33:33.1:25.57 for 30 minutes using a V-type mixer, filled into a carbon steel can of 50 mm long with 250 mm in diameter, then degassed in vacuum and mounted. This powder billet was HIP-molded in a condition of molding pressure, molding temperature and retention time shown in Table 1. Thereafter, a sputtering target material of 7 mm thick with 180 mm in diameter was produced from the compact. The maximum inscribed circle diameter of the microstructure of the NiTa compound phase is coarsened to be 15, and also Ta phase, Ni.sub.3Ta phase and Ni phase exist other than Ni.sub.2Ta compound phase and NiTa compound phase, and the stiffness is therefore low. A lot of particles are therefore generated.

(21) Comparative Example No. 17 was produced by such a way that pure Ta powder and Ni-37.5Ta atomized powder were mixed with mixing ratio of 11.09:88.91 for 30 minutes using a V-type mixer in the same manner as No. 16, filled into a carbon steel can of 50 mm long with 250 mm in diameter, then degassed in vacuum and mounted. This powder billet was HIP-molded in a condition of molding pressure, molding temperature and retention time shown in Table 1. Thereafter, a sputtering target material of 7 mm thick with 180 mm in diameter was produced from the compact. The maximum inscribed circle diameter of the microstructure of the NiTa compound phase of the target material is coarsened to be 13 m, and also Ta phase exist other than Ni.sub.2Ta compound phase and NiTa compound phase, the stiffness is therefore low though it is improved better than Comparative Example 16, and the particles are therefore generated. In addition, it contains pure Ta, and its composition is ununiform as a sputtering target material, and the sputtered film has an irregular composition.

(22) Comparative Example No. 18 was produced by such a way that pure Ta powder and pure Ni atomized powder were mixed with mixing ratio of 64.91:35.09 for 30 minutes using a V-type mixer in the same manner as No. 16, filled into a carbon steel can of 50 mm long with 250 mm in diameter, then degassed in vacuum and mounted. This powder billet was HIP-molded in a condition of molding pressure, molding temperature and retention time shown in Table 1. Thereafter, a sputtering target material of 7 mm thick with 180 mm in diameter was produced from the compact. The maximum inscribed circle diameter of the microstructure of the Ni.sub.2Ta compound phase of the target material is coarsened to be 13 m, and also Ta phase, Ni.sub.3Ta phase and Ni phase exist other than Ni.sub.2Ta compound phase and NiTa compound phase, the stiffness is therefore low though it is improved better than Comparative Example 16, and the particles are therefore generated. In addition, it contains pure Ta and Ni.sub.3Ta phases, and its composition is ununiform as a sputtering target material, and the sputtered film has an irregular composition.