A method for preparing a low-oxygen WTi target material for sputtering

Abstract

The application discloses a preparation method of a low-oxygen WTi target material for sputtering, and relates to the technical field of target material preparation, and comprises the following steps: firstly, Ti powder and W powder are added into a powder mixing barrel, then powder mixing balls are added into the powder mixing barrel, pure Ar gas is filled, and the WTi powder is obtained by being transferred into a ball mill for uniform mixing; the WTi powder is poured into a mold and flattened; the graphite mold is placed into a sintering furnace with an initial pressure of 0, then the pressure is increased to 6-10 MPa at a rate of 0.1-0.3 MPa / min, the pressure is kept for 10-15 min, then the pressure is released to -(0.5-0.8) MPa, the pressure is kept for 5-10 min again, then the pressure is increased to 6-10 MPa at a rate of 0 1-0.3 MPa / min after the pressure keeping is finished, the pressure is kept for 10-15 min, and then the pressure is released to 0 MPa; the sintering furnace is vacuumized to below 5 Pa, then the temperature is increased to 1250-1350 DEG C in a segmented mode, the temperature is kept for 30-60 min, the pressure is increased to 30-40 MPa at the same time, the temperature and pressure are kept for 90-150 min, then the temperature is decreased to 100-300 DEG C, and the WTi alloy target blank is obtained; the WTi alloy target blank obtained by the method has extremely low oxygen content, high density and purity, and the crystal is more fine and uniform, the compactness is stronger, and the conductivity and sputtering property are better.

Description

Technical Field

[0001] This invention relates to the field of target preparation technology, and specifically to a method for preparing a low-oxygen WTi target for sputtering. Background Technology

[0002] Microwave power devices are the core and key components of microelectronic devices. Their reliability directly affects the reliability and lifespan of electronic equipment or components. The quality of the metallized thin film of the device determines the reliability of the microwave power device. To improve or guarantee the reliability or lifespan of microwave power devices, multilayer refractory metal thin films must be used. WTi alloys, due to their low resistivity, good thermal stability, and oxidation resistance, are widely used as diffusion barrier layers in Al, Cu, and Ag wiring. WTi thin films are an essential metal layer that plays a diffusion barrier role, and their quality directly determines the reliability of the device. WTi thin films are prepared by sputtering deposition; therefore, high-quality WTi sputtering targets are a prerequisite for obtaining high-performance thin films. The semiconductor field has strict requirements on the density, purity, impurities, gas elements, and phase composition of WTi sputtering targets, making their preparation quite difficult.

[0003] In existing technologies, the preparation of WTi sputtering targets typically uses high-purity W and Ti as raw materials. W powder and Ti powder are mixed evenly, compacted in a mold, and finally sintered to obtain the WTi alloy target blank. During the preparation process, to obtain an alloy target with extremely low oxygen content, it is necessary to minimize oxygen interference. For example, Ar gas is introduced during mixing to remove oxygen, or vacuum sintering is used to avoid the influence of oxygen.

[0004] However, even with the above treatments, it is still difficult to avoid the subtle effects of oxygen throughout the process. For example, when using W powder and Ti powder, gaps will be generated in the powder cake, and these gaps contain a small amount of oxygen; therefore, it is difficult to obtain WTi sputtering targets with extremely low oxygen content. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a low-oxygen WTi sputtering target, thereby solving the following technical problems: How to reduce the oxygen content in WTi sputtering targets.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing a low-oxygen WTi sputtering target includes the following steps: (1) Mixing powder: Add Ti powder and W powder to the mixing tank, wherein the proportion of Ti powder is (9.5-11.5) wt% and the proportion of W is (88.5-90.5) wt%; then add mixing balls to the mixing tank, and after purging pure Ar gas for 15-30 minutes, transfer the material in the mixing tank to the ball mill and mix evenly to obtain WTi powder; (2) Molding: Pour WTi powder into the mold and spread it evenly; (3) Pre-pressurization: Place the graphite mold containing WTi powder into a sintering furnace with an initial pressure of 0, then increase the pressure to (6-10) MPa at a rate of (0.1-0.3) MPa / min, hold the pressure for 10-15 min, then release the pressure by 0.5-0.8 MPa, hold the pressure again for 5-10 min, and after the pressure holding is completed, increase the pressure to (6-10) MPa at a rate of (0.1-0.3) MPa / min, hold the pressure for 10-15 min, and then release the pressure to 0 MPa; (4) Hot pressing sintering: The sintering furnace is evacuated to below 5 Pa, and then the temperature is raised to 1250-1350℃ in stages, held for 30-60 min, and pressurized to (30-40) MPa. After holding for 90-150 min, the temperature is lowered to 100-300℃ to obtain the WTi alloy target billet. (5) Machining: The WTi alloy target blank is machined to the size of the target blank, and relevant defects and density tests are performed. After no abnormalities are found, the low oxygen WTi target material for sputtering is obtained.

[0007] In a further embodiment of the present invention: in step (1), the purity of the Ti powder is ≥99.95%, the O content is 200-250ppm, and the C content is 10-20ppm; the purity of the W powder is ≥99.999%, the O content is 1200-1400ppm, and the C content is 40-60ppm.

[0008] In a further embodiment of the present invention, the particle size of the Ti powder and W powder is 5-8 μm.

[0009] In a further embodiment of the present invention: in step (1), the ball-to-powder ratio is 1:2.

[0010] In a further embodiment of the present invention: in step (1), the ball mill is a drum ball mill, the rotation speed of the drum ball mill is set to 200-400 r / min, and the duration is 8-16 h.

[0011] In a further embodiment of the present invention: in step (2), the mold is a graphite mold. Before pouring WTi powder into the graphite mold, graphite paper of the corresponding size is first cut and laid on the bottom and inner side of the graphite mold; in step (5), the graphite paper is removed from the WTi alloy target blank before grinding.

[0012] In a further embodiment of the present invention: in step (4), the segmented heating is as follows: first, the temperature is increased to 600-800℃ at a rate of 15-20℃ / min; then, the temperature is increased to 900-1150℃ at a rate of 8-10℃ / min, held for 30-60min, and then increased to 1250-1350℃ at a rate of 4-8℃ / min.

[0013] In a further embodiment of the present invention: in step (5), the feed rate of the grinding machine is 2-10 μm, and the wire EDM feed rate is 2-5 mm / min.

[0014] The beneficial effects of this invention are: (1) In the pre-compression process of this invention, the pressure is increased to (6-10) MPa at a rate of (0.1-0.3) MPa / min, held for 10-15 min, then depressurized by 0.5-0.8 MPa, held for 5-10 min again, and after the pressure holding is completed, the pressure is increased to (6-10) MPa at a rate of (0.1-0.3) MPa / min, held for 10-15 min, and then depressurized to 0 MPa. During the first pressure increase and holding, the WTi powder is initially compacted, but there are still a small number of gaps inside. The air in the gaps contains O element. Therefore, a second pressure reduction and holding process is performed. Since the WTi powder particles are already regularly arranged during the first pressure increase and holding process, the pressure reduction will cause the WTi powder to expand slightly in a regular manner. At this time, the powder particles in the gaps in the WTi powder will automatically align themselves under the force of the regular powder particles, thus eliminating the gaps. Therefore, the WTi powder can be completely compacted during the third pressure increase and holding process, which greatly reduces the existence of gaps in the WTi powder and reduces the oxygen content. As a result, the final WTi alloy target blank has low oxygen content and high density and purity. (2) In the hot pressing sintering process of this invention, the temperature is first raised to 1250-1350℃ and held for 30-60 min, while the pressure is increased to (30-40) MPa. After holding for 90-150 min, the temperature is lowered to 100-300℃. In the segmented heating process, the second and third heating processes are followed by heat holding operations. On the one hand, this can make the temperature field uniform, so that the temperature inside and outside the WTi alloy target blank is consistent and the thermal force is more uniform. Therefore, it can improve the density of the WTi alloy target blank and make the crystal distribution inside the WTi alloy target blank more uniform. On the other hand, it can also avoid the rapid change of expansion stress caused by the direct temperature rise, which would lead to the formation of intergranular pores in the crystals inside the WTi alloy target blank under the action of thermal expansion stress and fracture stress, resulting in an increase in the oxygen content of the WTi alloy target blank. Attached Figure Description

[0015] The invention will now be further described with reference to the accompanying drawings.

[0016] Figure 1 This is a schematic diagram of the microstructure of the WTi alloy target blank prepared in Example 1 of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1

[0019] Weigh 95g of Ti powder with a purity of 99.95%, an O content of 200ppm, a C content of 10ppm, and a particle size of 8µm, and add 905g of W powder with a purity of 99.999%, an O content of 1200ppm, a C content of 40ppm, and a particle size of 8µm into a mixing tank. Then add 500g of mixing balls into the mixing tank. After purging the mixing tank with pure Ar gas for 15min, transfer the material in the mixing tank to a drum ball mill with a speed set to 200r / min and mix for 16h to obtain WTi powder. Graphite paper is laid on the bottom and inner side of the graphite mold, and then WTi powder is spread evenly in the graphite mold to ensure that the powder is spread evenly. Then the graphite mold is placed in a sintering furnace with an initial pressure of 0 for pre-compression. The pre-compression process is as follows: first, the pressure is increased to 6MPa at a rate of 0.1MPa / min, held for 15min, then depressurized by 0.5MPa, held for 10min again, and after the pressure is held, the pressure is increased to 6MPa at a rate of 0.1MPa / min, held for 15min, and then depressurized to 0MPa to complete the pre-compression. The sintering furnace was then evacuated to 4 Pa, and a segmented heating process was initiated. The heating rate was as follows: first, the temperature was increased to 600℃ at 15℃ / min; then increased to 900℃ at 8℃ / min and held for 60 min; then increased to 1250℃ at 4℃ / min and held for 60 min, while simultaneously pressurizing to 30 MPa. This was followed by holding at that temperature and pressure for 150 min, and then cooling to 300℃, thus obtaining the WTi alloy target billet. Its microstructure is as follows: Figure 1 As shown.

[0020] Example 2

[0021] Weigh 105g of Ti powder with a purity of 99.95%, an O content of 230ppm, a C content of 15ppm, and a particle size of 7µm, and add 895g of W powder with a purity of 99.999%, an O content of 1300ppm, a C content of 50ppm, and a particle size of 7µm into a mixing tank. Then add 500g of mixing balls into the mixing tank. After purging the mixing tank with pure Ar gas for 25min, transfer the material in the mixing tank to a drum ball mill with a speed set to 300r / min and mix for 12h to obtain WTi powder. Graphite paper is laid on the bottom and inner side of the graphite mold, and then WTi powder is spread evenly in the graphite mold to ensure that the powder is spread evenly. Then the graphite mold is placed in a sintering furnace with an initial pressure of 0 for pre-compression. The pre-compression process is as follows: first, the pressure is increased to 8MPa at a rate of 0.2MPa / min, held for 12min, then the pressure is released to 0.7MPa, held for 8min again, and after the pressure is released, the pressure is increased to 8MPa at a rate of 0.2MPa / min, held for 12min, and then the pressure is released to 0MPa, which completes the pre-compression. The sintering furnace was then evacuated to 4 Pa, and the temperature was raised in stages. The heating process was as follows: first, the temperature was raised to 700℃ at a rate of 18℃ / min; then, it was raised to 1050℃ at a rate of 9℃ / min and held for 45 min; then, it was raised to 1300℃ at a rate of 6℃ / min and held for 45 min, while the pressure was increased to 35 MPa. After holding at this temperature and pressure for 120 min, the temperature was lowered to 200℃, thus obtaining the WTi alloy target billet.

[0022] Example 3

[0023] Weigh 115g of Ti powder with a purity of 99.95%, an O content of 250ppm, a C content of 20ppm, and a particle size of 5µm, and add 885g of W powder with a purity of 99.999%, an O content of 1400ppm, a C content of 60ppm, and a particle size of 5µm into a mixing tank. Then add 500g of mixing balls into the mixing tank. After purging the mixing tank with pure Ar gas for 15min, transfer the material in the mixing tank to a drum ball mill with a speed set to 400r / min and mix for 8h to obtain WTi powder. Graphite paper is laid on the bottom and inner side of the graphite mold, and then WTi powder is spread evenly in the graphite mold to ensure that the powder is spread evenly. Then the graphite mold is placed in a sintering furnace with an initial pressure of 0 for pre-compression. The pre-compression process is as follows: first, the pressure is increased to 10MPa at a rate of 0.3MPa / min, held for 10min, then depressurized to 0.8MPa, held for 5min again, and after the pressure is held, the pressure is increased to 10MPa at a rate of 0.3MPa / min, held for 10min, and then depressurized to 0MPa to complete the pre-compression. The sintering furnace was then evacuated to 4 Pa, and the temperature was raised in stages. The heating process was as follows: first, the temperature was raised to 800℃ at a rate of 20℃ / min; then, it was raised to 1150℃ at a rate of 10℃ / min and held for 30 min; then, it was raised to 1350℃ at a rate of 8℃ / min and held for 30 min, while the pressure was increased to 40 MPa. After holding the temperature and pressure for 90 min, the temperature was lowered to 100℃, thus obtaining the WTi alloy target billet.

[0024] Comparative Example 1

[0025] Compared with Example 1, the only difference is that the pre-compression process is as follows: first, the pressure is increased to 6 MPa at a rate of 0.1 MPa / min, and after holding the pressure for 15 minutes, the pressure is released directly to 0 MPa, thus completing the pre-compression.

[0026] Comparative Example 2

[0027] Compared with Example 1, the only difference is that the pre-compression process is as follows: first, the pressure is increased to 6 MPa at a rate of 0.1 MPa / min, held for 15 minutes, then depressurized by 0.4 MPa, held for 10 minutes again, and after the pressure holding is completed, the pressure is increased to 6 MPa at a rate of 0.1 MPa / min, held for 15 minutes, and then depressurized to 0 MPa, thus completing the pre-compression.

[0028] Comparative Example 3

[0029] Compared with Example 1, the only difference is that the pre-compression process is as follows: first, the pressure is increased to 6 MPa at a rate of 0.1 MPa / min, held for 15 minutes, then depressurized to 0.9 MPa, held for 10 minutes again, and after the pressure holding is completed, the pressure is increased to 6 MPa at a rate of 0.1 MPa / min, held for 15 minutes, and then depressurized to 0 MPa, thus completing the pre-compression.

[0030] Comparative Example 4

[0031] Compared with Example 1, the only difference is that the heating process is as follows: first, the temperature is increased to 600°C at a rate of 15°C / min; then, it is increased to 900°C at a rate of 8°C / min; then, it is increased to 1250°C at a rate of 4°C / min; at the same time, the pressure is increased to 30MPa; after holding the temperature and pressure for 150min, the temperature is reduced to 300°C to obtain the WTi alloy target billet.

[0032] Comparative Example 5

[0033] Compared with Example 1, the only difference is that the heating process is as follows: first, the temperature is increased to 600°C at a rate of 15°C / min; then, it is increased to 900°C at a rate of 8°C / min; then, it is increased to 1250°C at a rate of 4°C / min; the temperature is held for 60 min while the pressure is increased to 30 MPa; then, the temperature and pressure are held for 150 min before the temperature is reduced to 300°C, thus obtaining the WTi alloy target billet.

[0034] Comparative Example 6

[0035] Compared with Example 1, the only difference is that the heating process is as follows: first, the temperature is raised to 600°C at a rate of 15°C / min; then, it is raised to 900°C at a rate of 8°C / min, held for 60 min, and then raised to 1250°C at a rate of 4°C / min; at the same time, the pressure is increased to 30 MPa, and then the temperature and pressure are held for 150 min before being cooled to 300°C, thus obtaining the WTi alloy target billet.

[0036] Comparative Example 7

[0037] The only difference compared to Example 1 is: 1. The pre-compression process is as follows: First, increase the pressure to 6MPa at a rate of 0.1MPa / min, hold the pressure for 15min, and then release the pressure directly to 0MPa to complete the pre-compression. 2. The heating process is as follows: first, heat to 600℃ at a rate of 15℃ / min; then heat to 900℃ at a rate of 8℃ / min; then heat to 1250℃ at a rate of 4℃ / min; at the same time, pressurize to 30MPa, then hold at the temperature and pressure for 150min and then cool down to 300℃ to obtain the WTi alloy target billet.

[0038] Test case

[0039] The WTi alloy target blanks prepared in Examples 1-3 and Comparative Examples 1-7 were subjected to performance tests, and the test items are as follows: 1. The density of the WTi alloy target billet was tested using the Archimedes displacement method; 2. Take 15 15 A 15mm WTi alloy target blank was ground, polished, and then etched. The grain size of the WTi alloy target blank, including the average grain size of W and Ti, was observed by backscattering mode under SEM. 3. Take milling debris from the WTi alloy target billet and test the Ti content of the WTi alloy target billet by ICP-MS; 4. Take the debris from the milling of the WTi alloy target billet and analyze the C / O / N content of the alloy target billet using a carbon-sulfur analyzer and an oxygen-nitrogen-hydrogen analyzer. 5. Take 20 20 The purity of a 6mm WTi alloy target blank was tested using GDMS.

[0040] The test results are listed in Table 1, as follows: Table 1

[0041] Analysis of the data in Table 1 shows that the WTi alloy target blanks prepared in Examples 1-3 all have a density of 100%, an O content in the gaseous element content of 380-390 ppm, and a purity of over 99.99%. This indicates that the WTi alloy target blanks prepared by the method of the present invention have stronger compactness, lower oxygen content, and higher purity.

[0042] Compared with Example 1, Comparative Examples 1-3 showed a decrease in density, no significant change in grain size, a significant increase in O content, and a decrease in purity. This is because, in Examples 1-3, the pre-compression process was divided into three steps: pressure increase and holding, pressure decrease and holding, and pressure increase and holding. During the first pressure increase and holding, the WTi powder was initially compacted, but a small number of gaps still existed inside. The air in the gaps contained O elements. Therefore, a second pressure decrease and holding was performed. Since the WTi powder particles were already regularly arranged during the first pressure increase and holding, the pressure decrease would cause the WTi powder to expand slightly in a regular manner. At this time, the powder particles in the gaps of the WTi powder would automatically align themselves under the force of the regular powder particles, thus eliminating the gaps. Therefore, during the third pressure increase and holding, the WTi powder could be completely compacted, greatly reducing the existence of gaps in the WTi powder and thus reducing its oxygen content. In Comparative Example 1, only one pressure increase and holding was performed during pre-compression. After the WTi powder was compacted, a small number of gaps still existed inside, and the oxygen elements contained in the gaps were not treated. In Comparative Examples 2-3, although two pressure increases were performed during pre-compression, the pressure reduction range during the two pressure increases exceeded 0.5-0.8 MPa. When the pressure reduction was too low, the force exerted on the powder in the gaps by the regular powder was reduced, making it difficult to eliminate the gaps. When the pressure reduction was too high, the force exerted on the powder in the gaps by the regular powder was too great. Although the gaps could be destroyed, the powder distribution in the gaps became more disordered, making it impossible to eliminate the gaps and even creating more small gaps. The oxygen elements in these gaps were retained in the WTi alloy target blank during subsequent sintering, so the oxygen content increased slightly, and its density and purity also decreased.

[0043] Compared with Example 1, Comparative Examples 4-6 showed a decrease in density, a slight increase in crystal size, an increase in O content, and a decrease in purity. This is because in Examples 1-3, a holding operation was performed after the second and third heating in the segmented heating process. Since the final sintering temperature reached over 1000℃, the overall heating range was very large. Holding the temperature during the segmented heating process served two purposes: firstly, it helped to uniformize the temperature field, ensuring consistent temperatures inside and outside the WTi alloy target blank, resulting in more uniform thermal forces and thus improving the density of the WTi alloy target blank and making the crystal distribution inside the WTi alloy target blank more uniform; secondly, it also helped to avoid… The direct, gradual temperature increase causes excessively rapid changes in expansion stress in the WTi alloy target billet, leading to intergranular porosity under the combined effects of thermal expansion and fracture stress, thus increasing the oxygen content of the WTi alloy target billet. In Comparative Example 4, the holding operation after the second heating in the segmented heating process was omitted; in Comparative Example 5, the holding operation after the third heating in the heating process was omitted; and in Comparative Example 6, the holding operations after the second and third heating in the segmented heating process were omitted. Therefore, the density of the WTi alloy target billets prepared in Comparative Examples 4-6 decreased, the crystal size increased slightly, the O content increased, and the purity decreased.

[0044] Compared with Comparative Example 1, Comparative Example 7 eliminated both the secondary pre-pressing operation and the heat preservation operation. As a result, the density of the WTi alloy billet decreased significantly, the crystal size increased significantly, the O content increased significantly, and the purity decreased significantly.

[0045] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for preparing a low-oxygen WTi sputtering target, characterized in that, Includes the following steps: (1) Mixing powder: Add Ti powder and W powder to the mixing tank, wherein the proportion of Ti powder is (9.5-11.5) wt% and the proportion of W is (88.5-90.5) wt%; then add mixing balls to the mixing tank, and after purging pure Ar gas for 15-30 minutes, transfer the material in the mixing tank to the ball mill and mix evenly to obtain WTi powder; (2) Molding: Pour WTi powder into the graphite mold and spread it evenly; (3) Pre-pressurization: Place the graphite mold containing WTi powder into a sintering furnace with an initial pressure of 0, then increase the pressure to (6-10) MPa at a rate of (0.1-0.3) MPa / min, hold the pressure for 10-15 min, then release the pressure by 0.5-0.8 MPa, hold the pressure again for 5-10 min, and after the pressure holding is completed, increase the pressure to (6-10) MPa at a rate of (0.1-0.3) MPa / min, hold the pressure for 10-15 min, and then release the pressure to 0 MPa; (4) Hot pressing sintering: The sintering furnace is evacuated to below 5 Pa, and then the temperature is raised to 1250-1350℃ in stages, held for 30-60 min, and pressurized to (30-40) MPa. After holding for 90-150 min, the temperature is lowered to 100-300℃ to obtain the WTi alloy target billet. (5) Machining: The WTi alloy target blank is machined to the size of the target blank, and relevant defects and density tests are performed. After no abnormalities are found, the low oxygen WTi target material for sputtering is obtained. In step (4), the segmented heating is as follows: first, the temperature is increased to 600-800℃ at a rate of 15-20℃ / min; then, the temperature is increased to 900-1150℃ at a rate of 8-10℃ / min, held for 30-60min, and then increased to 1250-1350℃ at a rate of 4-8℃ / min.

2. The method for preparing a low-oxygen WTi sputtering target according to claim 1, characterized in that, In step (1), the purity of the Ti powder is ≥99.95%, the O content is 200-250ppm, and the C content is 10-20ppm; the purity of the W powder is ≥99.999%, the O content is 1200-1400ppm, and the C content is 40-60ppm.

3. The method for preparing a low-oxygen WTi sputtering target according to claim 2, characterized in that, The particle size of the Ti powder and W powder is 5-8 μm.

4. The method for preparing a low-oxygen WTi sputtering target according to claim 1, characterized in that, In step (1), the ball-to-powder ratio is 1:

2.

5. The method for preparing a low-oxygen WTi sputtering target according to claim 1, characterized in that, In step (1), the ball mill is a drum ball mill, and the rotation speed of the drum ball mill is set to 200-400 r / min, and the duration is 8-16 h.

6. The method for preparing a low-oxygen WTi sputtering target according to claim 1, characterized in that, In step (2), before pouring WTi powder into the graphite mold, graphite paper of the corresponding size is first cut and laid on the bottom and inner side of the graphite mold; in step (5), the graphite paper is removed from the WTi alloy target blank before grinding.

7. The method for preparing a low-oxygen WTi sputtering target according to claim 1, characterized in that, In step (5), the grinding machine feed rate is 2-10 μm per pass, and the wire EDM feed rate is 2-5 mm / min.

Images