Tungsten target and method for producing same

Abstract

The invention provides a tungsten target and a manufacturing method thereof, which can inhibit the generation of pores, which is the cause of the generation of particles, and can control the size and distribution of the tungsten target with high precision. The tungsten target is formed from a sintered body of a tungsten powder, and has a relative density of 99% or more, and in a 0.15 mm2 observation region, there are 20 or less pores having a size of 0.01 [mu] m2 or more and less than 0.2 [mu] m2, 5 or less pores having a size of 0.2 [mu] m2 or more and less than 1.8 [mu] m2, and 1 or less pores having a size of 1.8 [mu] m2 or more.

Description

Technical Field

[0001] The present invention relates to a tungsten target formed of a sintered body of tungsten powder and a method for producing the same. Background Art

[0002] In recent years, tungsten with heat resistance and low resistance properties has been widely used as a wiring material or electrode material in the field of semiconductor device manufacturing. Tungsten film is usually formed by sputtering. In the sputtering of tungsten film, argon ions generated by plasma discharge collide with a tungsten target, knocking out tungsten atoms from the target surface, and causing the tungsten atoms to accumulate on a substrate arranged opposite to the target. At this time, particles generated from the target surface adhere to the substrate and reduce the yield, which is known as a major problem in the process. Therefore, in the tungsten target, a tungsten target with very few particles, fine and uniform grains, and high relative density is also indispensable.

[0003] For example, Patent Document 1 describes a method for producing a tungsten target in which a small amount of molybdenum is added to tungsten powder to prevent particle generation. This method can produce a target having a relative density of 95% or more and an average particle size of 10 μm or more and 300 μm or less.

[0004] In addition, Patent Document 2 describes a method for manufacturing a sputtering target as follows: after filling a metal capsule with tungsten powder, the powder is pressurized by a room temperature press, then packaged in a vacuum, and then the capsule is subjected to a hot isostatic pressing (HIP) treatment. By this method, a tungsten target having an average particle size of 20 μm or more and 100 μm or less, a relative density of 99% or more, and an oxygen content of 10 mass ppm or more and 15 mass ppm or less can be obtained.

[0005] However, in the conventional method for manufacturing a tungsten target, the crystal grain size has a large variation and cannot be suppressed to a fine and uniform average grain size of several tens of μm or less. Therefore, the particle suppression effect during sputtering is insufficient, and the yield is reduced.

[0006] Therefore, as a method for manufacturing a tungsten target capable of suppressing the average particle size to less than tens of μm, the following method for manufacturing a tungsten target is proposed: it includes the steps of preparing a preliminary molded body of tungsten powder having a relative density of not less than 70% and not more than 90% and an oxygen content of not less than 100 mass ppm and not more than 500 mass ppm, and sintering the above-mentioned preliminary molded body by hot isostatic pressing at a temperature of not less than 1700°C and not more than 1850°C (see patent document 3).

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2001-295036

[0010] Patent Document 2: Japanese Patent Application Publication No. 2003-193225

[0011] Patent Document 3: WO2012 / 042791 Summary of the invention

[0012] Problems to be solved by the invention

[0013] However, as the miniaturization of wiring using tungsten is progressing, particles generated from tungsten targets will have a great impact on the yield, so it is expected that the generation of particles will be further suppressed. In addition, the hot isostatic pressing method using CAN is very complicated and has low productivity, so it is difficult to use in reality. In addition, if the crystal grain size becomes too fine, it may lead to a decrease in the film formation rate.

[0014] Therefore, the main cause of particles during sputtering film formation on a tungsten target was studied. It was found that, with the target manufactured using the above-mentioned manufacturing method, the relative density of the sintered body reached close to 100%, but pores existed anyway, and their size and distribution state were not controlled. Therefore, the generation of particles could not be suppressed, which became the reason for the reduction in yield.

[0015] Therefore, in order to improve the yield, a tungsten target with extremely little generation of particles is required, and a production method capable of obtaining the tungsten target is required.

[0016] In view of the above circumstances, an object of the present invention is to provide a tungsten target and a method for producing the same, which can suppress the generation of voids that cause the generation of particles and can control the size and distribution of the voids with high precision.

[0017] Means for solving problems

[0018] In order to achieve the above object, the first embodiment of the present invention is a tungsten target, which is formed by a sintered body of tungsten powder, wherein the relative density is 99% or more, and the surface of the sintered body is 0.15 mm 2 The size of the observation area is 0.01 μm 2 Above and less than 0.2μm 2 The number of pores is less than 20 and the size is 0.2 μm. 2 Above and less than 1.8μm 2 The number of pores is less than 5 and the size is 1.8 μm 2 The number of the above pores is 1 or less.

[0019] A second aspect of the present invention is the tungsten target according to the first aspect, wherein the Vickers hardness is 355 or more and 375 or less.

[0020] A third aspect of the present invention is that, in the tungsten target of the second aspect, a ratio of a standard deviation 3σ of the Vickers hardness to an average value of the Vickers hardness is 0.07 or less.

[0021] A fourth aspect of the present invention is that in the tungsten targets of the first to third aspects, an average grain size calculated as an equivalent circle diameter is 150 μm or less.

[0022] A fifth aspect of the present invention is the tungsten target of the fourth aspect, wherein a ratio of a standard deviation 3σ of grain sizes calculated as equivalent circle diameters to an average grain size is 1.5 or less.

[0023] The sixth method of the present invention is a method for manufacturing a tungsten target, which uses tungsten powder with an average particle size of less than 3 μm and a median particle size D50 of less than 2.8 μm obtained by a laser diffraction scattering method, hot pressing at a temperature of more than 1400°C and less than 1500°C, and then sintering by hot isostatic pressing at a temperature of more than 1800°C and less than 1850°C.

[0024] A seventh aspect of the present invention is the method for producing a tungsten target according to the sixth aspect, wherein a ratio of an average particle size of the tungsten powder obtained by the laser diffraction scattering method to D90 is 2.5 or less.

[0025] An eighth aspect of the present invention is the method for producing a tungsten target according to the sixth or seventh aspect, wherein a ratio of an average particle size of the tungsten powder obtained by the laser diffraction scattering method to D95 is 3.0 or less. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 0.01 to 0.2 μm in the examples and comparative examples of the present invention 2 A graph showing the relationship between the number of pores and the number of particles.

[0027] Figure 2 The 0.2 to 1.8 μm values ​​of the examples and comparative examples of the present invention are shown. 2 A graph showing the relationship between the number of pores and the number of particles.

[0028] Figure 3 1.8 μm is shown in the examples and comparative examples of the present invention. 2 Above is a graph of the relationship between the number of pores and the number of particles. DETAILED DESCRIPTION

[0029] In the tungsten target of the present invention, the purity of tungsten is 5N (99.999 mass %) or higher, the carbon and oxygen impurities contained in tungsten are each 30 mass ppm or lower, and the average grain size is 150 μm or lower.

[0030] (purity)

[0031] In order to form a tungsten film with a low resistivity, it is necessary to suppress impurities contained in the tungsten film, and therefore it is essential to highly purify the tungsten target. Specifically, it is necessary to have a purity of 99.999 mass % (5N) or more.

[0032] (Gas composition)

[0033] The gas components such as carbon and oxygen contained in the tungsten target have an adverse effect on the resistivity of the tungsten film. These gas components are taken into the tungsten film during film formation, so as their content increases, the resistivity of the tungsten film tends to increase. Therefore, the carbon contained in the tungsten target is preferably 20 mass ppm or less, more preferably 10 mass ppm or less. In addition, oxygen is preferably 30 mass ppm or less, more preferably 20 mass ppm or less.

[0034] (Crystalline particle size)

[0035] In the tungsten target of the present invention, the average value of the crystal grain size calculated as the equivalent circle diameter is 10 μm or more and 150 μm or less, and more preferably 30 μm or more and 100 μm or less.

[0036] The reason for adopting such an average value of the crystal grain size (average grain size) is as follows.

[0037] The smaller the average grain size of the tungsten target, the smaller the difference in erosion amount caused by the orientation difference of each crystal grain existing on the target surface. Therefore, the number of abnormal discharges caused by unevenness decreases, and the generation of particles during film formation can be suppressed.

[0038] On the other hand, if the average particle size becomes too small, the film formation rate becomes too slow, and thus, the productivity decreases.

[0039] In addition, the ratio of three times the standard deviation (3σ) of the particle diameter calculated as the equivalent circle diameter to the average particle diameter is 1.5 or less. This ratio is obtained by dividing the standard deviation 3σ by the average particle diameter.

[0040] The reason why the ratio is preferably 1.5 or less is as follows.

[0041] The deviation of the crystal grain size is related to the number and size of pores. The smaller the deviation of the crystal grain size, the fewer the number of pores in the target and the smaller their size. Therefore, if it is within the above range, the generation of particles during film formation can be suppressed.

[0042] (Relative density)

[0043] The relative density of the tungsten target is preferably 99% or more. If the relative density of the target is 99% or more, the gas component contained in the target is small, so when the film is formed, the increase in the resistivity of the film can be suppressed. In addition, the higher the relative density of the target, the fewer the number of pores, so the number of abnormal discharges caused by the unevenness of the target surface decreases, which can suppress the generation of particles during film formation.

[0044] (Vickers hardness)

[0045] The average value of the Vickers hardness of the tungsten target is preferably 355 or more and 375 or less.

[0046] The reason why the average value of the Vickers hardness is preferably within the above range is as follows.

[0047] The average value of Vickers hardness is related to the number and size of pores in the target. The higher the average value of Vickers hardness is, the fewer the number of pores in the target is and the smaller the size of the pores is. Therefore, the generation of particles during film formation can be suppressed.

[0048] On the other hand, when the average hardness is very large, it is highly likely that the target internal strain has not been removed due to inappropriate heat treatment conditions, which may cause cracking due to thermal stress during target processing or film formation by sputtering.

[0049] The ratio of three times the standard deviation of Vickers hardness (3σ) to the average value of Vickers hardness is 0.07. The calculation method is to divide the standard deviation 3σ by the average value of Vickers hardness.

[0050] The reason why the ratio of three times the standard deviation of the Vickers hardness (3σ) to the average value of the Vickers hardness is preferably within the above range is as follows.

[0051] The variation in Vickers hardness is related to the number and size of pores. The smaller the variation in Vickers hardness is, the fewer the number of pores in the target is and the smaller the size of the pores is. Therefore, the generation of particles during film formation can be suppressed.

[0052] (Porosity)

[0053] The tungsten target of the present invention is 0.15mm 2 The size of the observation area is 0.01 μm 2 Above and less than 0.2μm 2 The number of pores is less than 20 and the size is 0.2 μm. 2 Above and less than 1.8μm 2 The number of pores is less than 5 and the size is 1.8 μm 2 The number of the above pores is 1 or less.

[0054] The reasons why the size and the number of existence in the present invention are set to the above ranges are as follows.

[0055] By controlling the size and number of pores, the electric field is concentrated on the pores, which can suppress particles generated by local dissolution and scattering, and improve the yield. In addition, since the number of particles generated is continuously reduced until the end of the target life, stable production can be achieved.

[0056] A tungsten target having very few coarse pores and in which localization of pores in the surface direction and thickness direction of the tungsten target is suppressed has not been realized so far, but it can be realized by having the above-mentioned relative density, hardness and crystal grain size characteristics. In addition, the tungsten target of the present invention having very few coarse pores and in which localization of pores in the surface direction and thickness direction of the tungsten target is suppressed can be realized by the manufacturing method described below.

[0057] The tungsten target of the present invention described above has small and few pores as described above. Therefore, by using this tungsten target, the amount of generated particles can be greatly reduced, and a high-quality tungsten film can be stably formed.

[0058] A method for producing a tungsten target according to one embodiment of the present invention will be described.

[0059] The tungsten target of the present invention can be manufactured as follows: using tungsten powder with an average particle size of less than 3 μm and D50 of less than 2.8 μm obtained by a laser diffraction scattering method, hot pressing (HP process) at a temperature of not less than 1400°C and not more than 1500°C, and then sintering by hot isostatic pressing (HIP process) at not less than 1800°C and not more than 1850°C.

[0060] The first essential point of the method for producing a sputtering target of the present invention is to use a tungsten powder having an average particle size of 3 μm or less, preferably 2.8 μm or less, and D50 of 2.8 μm or less, preferably 2.5 μm or less.

[0061] Since the oxygen content of the raw material powder affects the oxygen content of the tungsten target, the oxygen content of the raw material powder is, for example, 1000 mass ppm or less.

[0062] The second essential point of the method for producing a sputtering target of the present invention is to use a tungsten powder having a value obtained by dividing D90 obtained by a laser diffraction scattering method by an average particle size of 2.5 or less, preferably 2.3 or less.

[0063] The third essential point of the method for producing a sputtering target of the present invention is to use a tungsten powder having a value obtained by dividing D95 obtained by a laser diffraction scattering method by an average particle size of 3 or less, preferably 2.8 or less.

[0064] In this way, by using a tungsten powder with an extremely narrow particle size distribution range, that is, a small deviation of the particle size relative to the average particle size, a tungsten target with extremely small and few pores can be achieved. In the present invention, such a narrow particle size distribution feature is defined as a value obtained by dividing D90 obtained by a laser diffraction scattering method by the average particle size or a value obtained by dividing D95 obtained by a laser diffraction scattering method by the average particle size is less than a specified value. It should be noted that a powder with a wide particle size distribution that deviates from this range cannot achieve the effect of the present invention.

[0065] The sputtering target of the present invention can be produced by hot pressing the tungsten powder at a temperature of 1400° C. to 1500° C., and then sintering the tungsten powder by hot isostatic pressing at 1800° C. to 1850° C.

[0066] By vacuum hot pressing in a high vacuum area, degassing and sintering are promoted, and a high-density sintered body can be obtained while reducing the amount of oxygen contained in the tungsten target. When the oxygen content of the tungsten powder is high, the number of oxides in the tungsten target increases, and the frequency of particle generation increases. In addition, sintering is hindered by a thick surface oxide film, and a high-density sintered body cannot be obtained.

[0067] In addition, as described above, gas components such as carbon and oxygen contained in the tungsten target have an adverse effect on the resistivity of the tungsten film, so the carbon content in the tungsten target is preferably 20 mass ppm or less, more preferably 10 mass ppm or less. In addition, the oxygen content is preferably 30 mass ppm or less, more preferably 20 mass ppm or less.

[0068] As described above, the oxygen concentration can be achieved by vacuum hot pressing.

[0069] On the other hand, regarding carbon concentration, during hot pressing, carbon diffuses from the graphite components constituting the hot pressing device to the tungsten sintered body, which is the cause of the increase in carbon content. Therefore, the lower the hot pressing temperature, the better. As long as it is below 1500°C, it is possible to stably achieve a content of less than 20 mass ppm, preferably less than 10 mass ppm.

[0070] In the HP process, a sintered body with a relative density of 95% or more is produced. The HP temperature for producing a sintered body with such characteristics is preferably 1400°C or more and 1500°C or less. If the HP temperature is too low, the density cannot be increased to a level that allows HIP treatment. If it is too high, coarse pores are formed locally due to rapid grain growth, which is not preferred. If the pressure generated by the HP is too low, the density cannot be increased to a level that allows HIP treatment. If it is too high, the consumption of the HP device will increase. For example, the pressure during HP treatment is 39.2MPa (400kg / cm 2 ) and above 44.1MPa(450kg / cm 2 ) or less. The holding time of HP in this process is 600 minutes or more and 1200 minutes or less. If the holding time of HP is too short, the density cannot be increased to a density that can be subjected to HIP treatment, and if it is too long, productivity is reduced. In the present invention, it is important to control the powder particle size and particle size distribution so that the HP temperature is 1400°C or more and 1500°C or less and the holding time of HP is 600 minutes or more and 1200 minutes or less. In this way, the coarsening of pores in the sintered body can be suppressed, and fine pores can be uniformly dispersed in the sintered body.

[0071] Hot isostatic pressing (HIP) is applied to the HP-treated sintered body in order to reduce the pores in the sintered body and increase the density.

[0072] The HIP temperature is 1800°C or higher and 1850°C or lower. When the HIP temperature is lower than 1800°C, it is difficult to obtain a high relative density of 99% or higher within a processing time suitable for mass production due to the low processing temperature. In addition, if the HIP temperature exceeds 1850°C, the high processing temperature will cause a rapid coarsening of the grains and the formation of coarse pores locally, which is not preferred. The pressure is not particularly limited, for example, it is set to be 100 to 200 MPa or lower, and in this embodiment, it is 176.4 MPa (1800 kg / cm 2 ).

[0073] According to the above manufacturing method, a tungsten target having the characteristics of the present invention can be obtained. In particular, the number of pores in the tungsten target can be reduced, the size of the pores can be reduced, and the localization of the pores can be suppressed. Therefore, by using the sputtering target of this embodiment, the generation of particles during film formation can be reduced, and a high-quality tungsten film can be stably formed.

[0074] The existence of pores in the sputtering target is highly correlated with the size of the raw material powder and its particle size distribution, the relative density of the sintered body, the size and distribution of the target's crystal grain size, and the size and distribution of the hardness. The finer the size of the raw material powder, the narrower the range of its particle size distribution, the higher the relative density of the sintered body, the smaller the deviation of the crystal grain size and the deviation of the hardness, then the less pores are generated and their size becomes very small.

[0075] On the other hand, even if the crystal grain size is fine, if the deviation is large, the generation of coarse pores cannot be suppressed. The present invention improves the relative density of the sintered body and suppresses the deviation of the crystal grain size and the deviation of the hardness by optimizing the size and particle size distribution of the raw material powder, hot pressing conditions, and hot isostatic pressing conditions. As a result, it is found that the tungsten target of the present invention can be manufactured with very few coarse pores and almost no localization of pores.

[0076] That is, in the method for producing a tungsten target of the present embodiment, the raw material powder is hot pressed at a temperature of 1400° C. to 1500° C., and then sintered by hot isostatic pressing at 1800° C. to 1850° C.

[0077] According to the above-mentioned method for manufacturing a tungsten target, a sputtering target with small and few pores can be obtained. For example, according to the above-mentioned method, the following tungsten targets can be stably manufactured: 2 The size of the observation area is 0.01 μm 2 Above and less than 0.2μm 2The number of pores is less than 20 and the size is 0.2 μm. 2 Above and less than 1.8μm 2 The number of pores is less than 5 and the size is 1.8 μm 2 The number of the above pores is 1 or less.

[0078] In the manufacturing method of the tungsten target of the present invention, the following tungsten targets can be manufactured efficiently and stably: the relative density is greater than 99%, the Vickers hardness is greater than 355 and less than 375, the ratio of the standard deviation 3σ of the Vickers hardness to the average value of the Vickers hardness is less than 0.07, the average particle size is less than 150μm, and the ratio of the standard deviation 3σ of the average particle size to the average particle size is less than 1.5.

[0079] Thus, a tungsten target having small and few pores can be manufactured, and by using this tungsten target, the amount of generated particles can be greatly reduced, and a high-quality tungsten film can be stably formed.

[0080] The sintered body produced as described above is processed into a predetermined target shape in the processing step. The processing method is not particularly limited, and typically a mechanical processing method such as grinding and cutting is applied. The processing size and shape are determined according to the specifications of the target, for example, it is processed into a circle or a rectangle. The processed sintered body is bonded to a backing plate to form a sputtering cathode.

[0081] Example

[0082] Hereinafter, the present invention will be described with reference to Examples and Comparative Examples.

[0083] The average particle size and particle size distribution of the tungsten powder were determined using a particle size distribution measuring apparatus "LS13320" manufactured by Microchip Bayer.

[0084] (Examples 1-5)

[0085] As shown in Table 1, at a temperature shown in Table 1, 1400° C. to 1500° C. or less, a tungsten powder having a purity of 5N, an average particle size of 3 μm or less obtained by a laser diffraction scattering method, a median particle size D50 of 2.8 μm or less, a value obtained by dividing D90 by the average particle size of 2.5 or less, and a value obtained by dividing D95 by the average particle size of 3 or less was hot pressed, and then HIP was performed at a temperature of 1800° C. to 1850° C. or less as shown in Table 1, thereby obtaining a tungsten sintered body. The obtained tungsten sintered body was finished into a predetermined target shape (diameter 440 mm, thickness 6 mm) by grinding using a lathe.

[0086] (Comparative Example 1)

[0087] As shown in Table 1, at the temperature shown in Table 1, 1750° C., a tungsten powder having a purity of 5N, an average particle size of 3 μm or more obtained by a laser diffraction scattering method, a median particle size D50 of 2.8 μm or more, a value obtained by dividing D90 by the average particle size of 2.5 or more, and a value obtained by dividing D95 by the average particle size of 3 or more was hot pressed, and then HIP was performed at a temperature of 1750° C. shown in Table 1 to obtain a tungsten sintered body. The obtained tungsten sintered body was finished into a specified target shape (diameter 440 mm, thickness 6 mm) by grinding using a lathe.

[0088] (Comparative Example 2)

[0089] As shown in Table 1, at a temperature of 1750°C shown in Table 1, a tungsten powder having a purity of 5N, an average particle size of 3 μm or more obtained by a laser diffraction scattering method, a median particle size D50 of 2.8 μm or more, a value obtained by dividing D90 by the average particle size of 2.5 or more, and a value obtained by dividing D95 by the average particle size of 3 or more was hot pressed, and then HIP was performed at a temperature of 1850°C shown in Table 1 to obtain a tungsten sintered body. The obtained tungsten sintered body was finished into a specified target shape (diameter 440 mm, thickness 6 mm) by grinding using a lathe.

[0090] (Comparative Example 3)

[0091] As shown in Table 1, at a temperature of 1650°C shown in Table 1, a tungsten powder having a purity of 5N, an average particle size of 3 μm or more obtained by a laser diffraction scattering method, a median particle size D50 of 2.8 μm or more, a value obtained by dividing D90 by the average particle size of 2.5 or more, and a value obtained by dividing D95 by the average particle size of 3 or more was hot pressed, and then HIP was performed at a temperature of 1900°C shown in Table 1 to obtain a tungsten sintered body. The obtained tungsten sintered body was finished into a specified target shape (diameter 440 mm, thickness 6 mm) by grinding using a lathe.

[0092] (Comparative Example 4)

[0093] As shown in Table 1, at the temperature shown in Table 1, 1500° C., a tungsten powder having a purity of 5N, an average particle size of 3 μm or more obtained by a laser diffraction scattering method, a median particle size D50 of 2.8 μm or more, a value obtained by dividing D90 by the average particle size of 2.5 or more, and a value obtained by dividing D95 by the average particle size of 3 or more was hot pressed, and then HIP was performed at a temperature of 1850° C. shown in Table 1 to obtain a tungsten sintered body. The obtained tungsten sintered body was finished into a specified target shape (diameter 440 mm, thickness 6 mm) by grinding using a lathe.

[0094] (Comparative Example 5)

[0095] As shown in Table 1, at the temperature shown in Table 1, 1500° C., a tungsten powder having a purity of 5N, an average particle size of 3 μm or more obtained by a laser diffraction scattering method, a median particle size D50 of 2.8 μm or more, a value obtained by dividing D90 by the average particle size of 2.5 or less, and a value obtained by dividing D95 by the average particle size of 3 or more was hot pressed, and then HIP was performed at a temperature of 1850° C. shown in Table 1 to obtain a tungsten sintered body. The obtained tungsten sintered body was finished into a specified target shape (diameter 440 mm, thickness 6 mm) by grinding using a lathe.

[0096] (Comparative Example 6)

[0097] As shown in Table 1, a tungsten powder having a purity of 5N, an average particle size of 3 μm or more obtained by a laser diffraction scattering method, a median particle size D50 of 2.8 μm or less, a value obtained by dividing D90 by the average particle size of 2.5 or less, and a value obtained by dividing D95 by the average particle size of 3 or more was hot pressed at a temperature of 1650° C. shown in Table 1, and then HIP was performed at a temperature of 1850° C. shown in Table 1 to obtain a tungsten sintered body. The obtained tungsten sintered body was finished into a predetermined target shape (diameter 440 mm, thickness 6 mm) by grinding using a lathe.

[0098] (Comparative Example 7)

[0099] As shown in Table 1, a tungsten powder having a purity of 5N, an average particle size of 3 μm or more obtained by a laser diffraction scattering method, a median particle size D50 of 2.8 μm or less, a value obtained by dividing D90 by the average particle size of 2.5 or less, and a value obtained by dividing D95 by the average particle size of 3 or more was hot pressed at a temperature of 1450° C. shown in Table 1, and then HIP was performed at a temperature of 1850° C. shown in Table 1 to obtain a tungsten sintered body. The obtained tungsten sintered body was finished into a predetermined target shape (diameter 440 mm, thickness 6 mm) by grinding using a lathe.

[0100] (Comparative Example 8)

[0101] As shown in Table 1, a tungsten powder having a purity of 5N, an average particle size of 3 μm or more obtained by a laser diffraction scattering method, a median particle size D50 of 2.8 μm or less, a value obtained by dividing D90 by the average particle size of 2.5 or less, and a value obtained by dividing D95 by the average particle size of 3 or less was hot pressed at a temperature of 1650° C. shown in Table 1, and then HIP was performed at a temperature of 1850° C. shown in Table 1 to obtain a tungsten sintered body. The obtained tungsten sintered body was finished into a specified target shape (diameter 440 mm, thickness 6 mm) by grinding using a lathe.

[0102] (Comparative Example 9)

[0103] As shown in Table 1, a tungsten powder having a purity of 5N, an average particle size of 3 μm or more obtained by a laser diffraction scattering method, a median particle size D50 of 2.8 μm or less, a value obtained by dividing D90 by the average particle size of 2.5 or less, and a value obtained by dividing D95 by the average particle size of 3 or less was hot pressed at a temperature of 1450° C. shown in Table 1, and then HIP was performed at a temperature of 1850° C. shown in Table 1 to obtain a tungsten sintered body. The obtained tungsten sintered body was finished into a specified target shape (diameter 440 mm, thickness 6 mm) by grinding using a lathe.

[0104] (Comparative Example 10)

[0105] As shown in Table 1, at the temperature shown in Table 1, 1650° C., a tungsten powder having a purity of 5N, an average particle size of 3 μm or less obtained by a laser diffraction scattering method, a median particle size D50 of 2.8 μm or less, a value obtained by dividing D90 by the average particle size of 2.5 or less, and a value obtained by dividing D95 by the average particle size of 3 or less was hot pressed, and then HIP was performed at a temperature of 1850° C. shown in Table 1 to obtain a tungsten sintered body. The obtained tungsten sintered body was finished into a specified target shape (diameter 440 mm, thickness 6 mm) by grinding using a lathe.

[0106] (Comparative Example 11)

[0107] As shown in Table 1, a tungsten powder having a purity of 5N, an average particle size of 3 μm or less obtained by a laser diffraction scattering method, a median particle size D50 of 2.8 μm or less, a value obtained by dividing D90 by the average particle size of 2.5 or less, and a value obtained by dividing D95 by the average particle size of 3 or less was hot pressed at a temperature of 1450° C. shown in Table 1, and then HIP was performed at a temperature of 1750° C. shown in Table 1 to obtain a tungsten sintered body. The obtained tungsten sintered body was finished into a predetermined target shape (diameter 440 mm, thickness 6 mm) by grinding using a lathe.

[0108] The relative density, Vickers hardness, crystal grain size, oxygen content, carbon content, and porosity of the obtained target were measured in the following order. The results are shown in Tables 2 and 3.

[0109] (Relative density)

[0110] Samples of 10×10×6 mm2 were collected from the center, end, and half of the straight line connecting the center and end of the obtained tungsten target. The cross section of each sample was polished and etched, and the specific gravity was calculated using the Archimedean method. The theoretical density of tungsten (19.3 g / cm 3The relative density of each sample was calculated by adding the relative density of each sample and dividing the sum by the number of samples, which was used as the relative density of the tungsten target of the present invention.

[0111] (Vickers hardness)

[0112] Samples of 10×10×6 mm2 were collected from the center, end, and half of the straight line connecting the center and end of the obtained tungsten target. After grinding the cross section of each sample, the hardness was measured three times at intervals of 1 mm in the depth direction of the target using a Vickers hardness tester "HM-200" manufactured by Mitutoyo Co., Ltd. with a load of 1 kg and a load time of 15 seconds. The average value of the obtained values ​​was calculated. The value obtained by adding the average values ​​calculated for each sample and dividing it by the number of samples is used as the hardness of the tungsten target of the present invention. In addition, the standard deviation of the tungsten target is the value obtained by adding the standard deviations calculated from each sample and dividing it by the number of samples as the standard deviation of the present invention.

[0113] (Crystalline particle size)

[0114] Samples of 10×10×6 mm2 were collected from the center, end, and half of the straight line connecting the center and end of the obtained tungsten target. For each sample, the cross section was ground and etched. The images taken at 1 mm intervals in the depth direction of the target were taken using an optical microscope "Digital Microscope VHX-6000" manufactured by Keyence Corporation. The equivalent circle diameter was calculated using the image analysis software "Image-j" and the average value was calculated. The average values ​​calculated for each test piece were added and divided by the number of samples as the average particle size of the tungsten target of the present invention. In addition, the standard deviation of the tungsten target is the value obtained by adding the standard deviations calculated from each sample and dividing it by the number of samples as the standard deviation of the present invention.

[0115] (oxygen content)

[0116] When the tungsten sintered body was processed into a target shape, an analysis sample was collected and the oxygen content of the molded body was measured. The oxygen content was analyzed using an analysis device "TC-600" manufactured by LECO Corporation.

[0117] (Carbon content)

[0118] When the tungsten sintered body is processed into a target shape, an analysis sample is collected and the carbon content of the molded body is measured. The carbon content is analyzed using an analysis device "EMIA-320V" manufactured by Horiba, Ltd.

[0119] (Porosity)

[0120] Samples of 10×10×6 mm2 were collected from the center, end, and half of the straight line connecting the center and end of the obtained sputtering target. After grinding the cross section of each sample, two SEM images were taken at intervals of 1 mm in the depth direction of the target using an electron microscope "TM4000Plus" manufactured by Hitachi High-Technologies Corporation. For the captured SEM images, the area of ​​the pores was calculated using the image analysis software "Image-j", and the size and number of the pores in each sample were calculated. The value obtained by adding the size and number of the pores obtained for each sample and dividing it by the number of samples is used as the size and number of the pores of the tungsten target of the present invention.

[0121] Furthermore, using the obtained targets of Examples and Comparative Examples, films were formed as follows, the resistivity of the films was measured as follows, and particles were evaluated as follows.

[0122] The results of Examples 1 to 5 and Comparative Examples 1 to 11 are shown in Table 3. In addition, the relationship between the number of pores of a predetermined size and the number of particles is shown in Table 3. Figure 1 to Figure 3 It should be noted that a resistivity of 11 μΩ·cm or less was marked as ○, and a resistivity exceeding 11 μΩ·cm was marked as ×. If the resistivity is 11 μΩ·cm or less, a low-resistance LSI wiring can be formed, and thus a device with low power consumption can be realized.

[0123] (Resistivity measurement)

[0124] The obtained tungsten target was bonded to an aluminum alloy backing plate using an In-based brazing material to form a sputtering cathode. The sputtering cathode was assembled into a sputtering device "ENTRON (registered trademark)" manufactured by ULVAC to form a 40nm thick tungsten film on a semiconductor wafer with a diameter of 300mm. The sputtering conditions were: the ultimate pressure: 1×10 -5 Pa, discharge mode: DC, power: 4kW, gas raw material: Ar, gas flow rate: 150sccm, film forming temperature: 200℃, sputtering time: 17 seconds, distance between target and wafer: 60mm.

[0125] The film thickness of the tungsten thin film at 9 points on the wafer was measured using "S-MAT2300" manufactured by TECHNORAYS, and the sheet resistance was measured using "OmniMap RS100" manufactured by KLA Tencor. The resistivity (μΩ·cm) of the thin film was calculated, and the average value was taken as the resistivity of the tungsten thin film.

[0126] (Determination of Particles)

[0127] The surface of the 40 nm thick tungsten thin film on a semiconductor wafer with a diameter of 300 mm was inspected using a surface inspection device "WM-10" manufactured by TOPCON Corporation for resistivity measurement, and the number of particles with a size of 0.1 μm or more was measured.

[0128] [Table 1]

[0129]

[0130]

[0131] [Table 2]

[0132]

[0133] [Table 3]

[0134]

[0135] As shown in Examples 1 to 5, tungsten powder having an average particle size of 3 μm or less, a median particle size D50 of 2.8 μm or less, a value obtained by dividing D90 by the average particle size of 2.5 or less, and a value obtained by dividing D95 by the average particle size of 3 or less is hot pressed at a temperature of 1400° C. to 1500° C., and then HIP is performed at a temperature of 1800° C. to 1850° C. as shown in Table 1, thereby obtaining a tungsten target having a relative density of 99% or more and a particle size of 0.15 mm 2 The size of the observation area is 0.01 μm 2 Above and less than 0.2μm 2 The number of pores is less than 20 and the size is 0.2 μm. 2 Above and less than 1.8μm 2 The number of pores is less than 5 and the size is 1.8 μm 2 The number of the above pores is 1 or less. By using such a tungsten target, the generation of particles can be suppressed, and a high-quality tungsten thin film can be stably produced.

[0136] In Examples 1 to 5, since the hot pressing temperature was as low as 1500° C. or less, a thin film having a sufficiently low carbon content in the target and a sufficiently low resistivity of 11 μΩ·cm or less could be formed.

[0137] In Comparative Example 1, compared with the Example, the particle size of the tungsten powder is larger, the particle size distribution is wider, the HP temperature is higher, and the HIP temperature is lower. Therefore, 0.01 μm 2 Above and less than 0.2μm 2 The number of pores is large, 0.2μm 2 Above and less than 1.8μm 2Therefore, it was confirmed that the frequency of particle generation was high and it was difficult to achieve stable production.

[0138] In addition, since the hot pressing temperature was high, the carbon content of the target could not be sufficiently reduced, and a thin film having a resistivity of 11 μΩ·cm or less could not be formed.

[0139] In Comparative Example 2, the particle size of the tungsten powder is larger, the particle size distribution is wider, and the HP temperature is higher than that of the embodiment. 2 Above and less than 0.2μm 2 The number of pores is large, 0.2μm 2 Above and less than 1.8μm 2 Therefore, it was confirmed that the frequency of particle generation was high and it was difficult to achieve stable production.

[0140] In addition, since the hot pressing temperature was high, the carbon content of the target could not be sufficiently reduced, and a thin film having a resistivity of 11 μΩ·cm or less could not be formed.

[0141] In Comparative Example 3, compared with the Example, the particle size of the tungsten powder is larger, the particle size distribution is wider, the HP temperature is higher, and the HIP temperature is higher. Therefore, 0.2 μm 2 Above and less than 1.8μm 2 Therefore, it was confirmed that the frequency of particle generation was high and it was difficult to achieve stable production.

[0142] In addition, since the hot pressing temperature was high, the carbon content of the target could not be sufficiently reduced, and a thin film having a resistivity of 11 μΩ·cm or less could not be formed.

[0143] In Comparative Example 4, the particle size of the tungsten powder is larger and the particle size distribution is wider than that of the embodiment. 2 Above and less than 0.2μm 2 The number of pores is large, 0.2μm 2 Above and less than 1.8μm 2 Therefore, it was confirmed that the frequency of particle generation was high and it was difficult to achieve stable production.

[0144] Note that, since the hot pressing temperature is as low as 1500° C. or lower, a thin film having a low carbon content in the target and a resistivity sufficiently low as 11 μΩ·cm or lower can be formed.

[0145] In Comparative Example 5, the particle size of the tungsten powder is larger and the particle size distribution is wider than that of the embodiment. 2 Above and less than 1.8μm 2 Therefore, it was confirmed that the frequency of particle generation was high and stable production was difficult to achieve.

[0146] Note that, since the hot pressing temperature is as low as 1500° C. or lower, a thin film having a low carbon content in the target and a resistivity sufficiently low as 11 μΩ·cm or lower can be formed.

[0147] In Comparative Example 6, compared with the Example, the particle size of the tungsten powder is larger, the particle size distribution is wider, and the HP temperature is higher. Therefore, 0.01 μm 2 Above and less than 0.2μm 2 The number of pores is large, 0.2μm 2 Above and less than 1.8μm 2 The number of pores is large, 1.8μm 2 The number of pores is large. Therefore, it was confirmed that the frequency of particle generation was high and it was difficult to achieve stable production.

[0148] In addition, since the hot pressing temperature was high, the carbon content of the target could not be sufficiently reduced, and a thin film having a resistivity of 11 μΩ·cm or less could not be formed.

[0149] In Comparative Example 7, the particle size of the tungsten powder is larger and the particle size distribution is wider than that of the embodiment. 2 Above and less than 0.2μm 2 The number of pores is large, 0.2μm 2 Above and less than 1.8μm 2 Therefore, it was confirmed that the frequency of particle generation was high and stable production was difficult to achieve.

[0150] Note that, since the hot pressing temperature is as low as 1500° C. or lower, a thin film having a low carbon content in the target and a resistivity sufficiently low as 11 μΩ·cm or lower can be formed.

[0151] In Comparative Example 8, the particle size of the tungsten powder is larger than that of the embodiment, and the HP temperature is higher. Therefore, the particle size of the tungsten powder is larger than that of the embodiment, and the HP temperature is higher. 2 Above and less than 0.2μm 2 Therefore, it was confirmed that the frequency of particle generation was high and stable production was difficult to achieve.

[0152] It should be noted that, due to the high hot pressing temperature, the carbon content of the target could not be sufficiently reduced, and a thin film having a resistivity of 11 μΩ·cm or less could not be formed.

[0153] In Comparative Example 9, the particle size of the tungsten powder is larger than that of the Example, so that 0.01 μm 2 Above and less than 0.2μm 2 Therefore, it was confirmed that the frequency of particle generation was high and stable production was difficult to achieve.

[0154] Note that, since the hot pressing temperature is as low as 1500° C. or lower, a thin film having a low carbon content in the target and a resistivity sufficiently low as 11 μΩ·cm or lower can be formed.

[0155] In Comparative Example 10, the HP temperature is higher than that in the Example, so the 1.8 μm 2 The number of pores is large. Therefore, it was confirmed that the frequency of particle generation was high and it was difficult to achieve stable production.

[0156] In addition, since the hot pressing temperature was high, the carbon content of the target could not be sufficiently reduced, and a thin film having a resistivity of 11 μΩ·cm or less could not be formed.

[0157] In Comparative Example 11, the HIP temperature is lower than that in the Example, so the 0.01 μm 2 Above and less than 0.2μm 2 The number of pores is large, 1.8μm 2 The number of pores is large. Therefore, it was confirmed that the frequency of particle generation was high and it was difficult to achieve stable production.

[0158] Note that, since the hot pressing temperature is as low as 1500° C. or lower, a thin film having a low carbon content in the target and a resistivity sufficiently low as 11 μΩ·cm or lower can be formed.

Claims

1. A tungsten target, formed by a sintered body of tungsten powder, wherein: The relative density is more than 99%. At 0.15mm 2 The size of the observation area is 0.01 μm 2 Above and less than 0.2μm 2 The number of pores is less than 20 and the size is 0.2 μm. 2 Above and less than 1.8μm 2 The number of pores is less than 5 and the size is 1.8 μm 2 The number of the above pores is 1 or less.

2. The tungsten target according to claim 1, wherein: The Vickers hardness is 355 or more and 375 or less.

3. The tungsten target according to claim 2, wherein: The ratio of the standard deviation 3σ of the Vickers hardness to the average value of the Vickers hardness is 0.07 or less.

4. The tungsten target according to any one of claims 1 to 3, wherein The average particle size calculated as an equivalent circle diameter is 150 μm or less.

5. The tungsten target according to claim 4, wherein: The ratio of the standard deviation 3σ of the particle diameter calculated as the equivalent circle diameter to the average particle diameter is 1.5 or less.

6. A method for manufacturing a tungsten target, wherein: Using tungsten powder having an average particle size of 3 μm or less and a median particle size D50 of 2.8 μm or less obtained by a laser diffraction scattering method, hot pressing is performed at a temperature of 1400° C. to 1500° C., Thereafter, sintering is performed by hot isostatic pressing at 1800° C. or higher and 1850° C. or lower.

7. The method for producing a tungsten target according to claim 6, wherein: The ratio of the average particle size of the tungsten powder obtained by the laser diffraction scattering method to D90 is 2.5 or less.

8. The method for producing a tungsten target according to claim 6 or 7, wherein: The ratio of the average particle size of the tungsten powder obtained by the laser diffraction scattering method to D95 is 3.0 or less.

Images