WO2024237257A1 - Molybdenum target and method for producing same - Google Patents

Abstract

The present invention provides a molybdenum target and a method for producing the same, wherein the occurrence of particle-causing pores is suppressed, and the size and distribution of the pores are highly accurately controlled. Provided is a molybdenum target formed from a sintered body of molybdenum powder, the molybdenum target having a relative density of 99% or more, an oxygen content of 25 ppm or less, a carbon content of 30 ppm or less, a tungsten content of 10-100 ppm, and a molybdenum content excluding the oxygen content, the carbon content, and the tungsten content of 99.999 mass% or more. In an observation region measuring 0.15 mm², the number of pores having a size of 0.01 μm² or more and less than 0.2 μm² is 20 or less, the number of pores having a size of 0.2 μm² or more and less than 1.8 μm² is 5 or less, and the number of pores having a size of 1.8 μm² or more is 1 or less.

Description

Molybdenum target and method for producing same

The present invention relates to a molybdenum target formed from a sintered body of molybdenum powder and a method for manufacturing the same.

In recent years, in the field of semiconductor device manufacturing, tungsten, which has heat resistance and low resistance properties, has been widely used as a wiring material or electrode material. Tungsten films are generally formed by the sputtering method. In tungsten film sputtering, argon ions generated by plasma discharge are collided with a tungsten target, knocking out tungsten atoms from the target surface and depositing the tungsten atoms on a substrate placed opposite the target. At this time, it is known that a major problem in the process is that particles generated from the target surface adhere to the substrate and reduce the yield. For this reason, it is essential that the tungsten target has extremely low particle generation, fine and uniform crystal grains, and a high relative density.

However, even if a high-purity tungsten film can be formed, there is a concern that it may not be able to meet the future demand for even lower resistance. Therefore, it is necessary to find a promising material to replace tungsten.
In this regard, molybdenum films have attracted attention as they may be able to achieve sufficiently low electrical resistance values. However, they are also known to have a problem in that they generate a high rate of particles during sputtering, which reduces material yields.

Therefore, a molybdenum sputtering target capable of effectively reducing particles during sputtering has been proposed, which has a molybdenum content of 99.99% by mass or more, a relative density of 98% or more, and an average crystal grain size of 400 μm or less. The method for producing the sputtering target includes the steps of preparing molybdenum powder, hot pressing the molybdenum powder under a load at a temperature of 1350°C to 1500°C, and hot isostatic pressing the compact obtained by the hot pressing at a temperature of 1300°C to 1850°C (see Patent Document 1).

JP 2022-125041 A

However, it has been found that even the technique disclosed in Patent Document 1 cannot sufficiently reduce the generation of particles from the molybdenum target.
In particular, as wiring and the like using molybdenum becomes finer, particles generated from the molybdenum target have a significant effect on yield, and therefore there is a demand for further suppression of particle generation.

As a result of researching the causes of particles that occur when forming a film by sputtering a molybdenum target, it was discovered that targets manufactured using the above-mentioned manufacturing method have a relative density of sintered bodies that reaches just under 100%, but pores are inevitably present and the size and distribution of these pores are not controlled, making it impossible to suppress particle generation and resulting in reduced yields.

Therefore, to improve yields, a molybdenum target that generates as few particles as possible is required, and a manufacturing method that can obtain such a molybdenum target is required.

In light of these circumstances, the objective of the present invention is to provide a molybdenum target and a manufacturing method thereof that suppresses the generation of pores, which are the cause of particle generation, and controls the size and distribution with high precision.

In order to achieve the above object, a first aspect of the present invention is a molybdenum target formed of a sintered body of molybdenum powder, the molybdenum target having a relative density of 99% or more, an oxygen content of 25 ppm or less, a carbon content of 30 ppm or less, a tungsten content of 10 ppm to 100 ppm, a molybdenum content excluding the oxygen content, the carbon content, and the tungsten content of 99.999 mass% or more, and having, in an observation area of 0.15 ^mm2 , 20 or less pores having a size of 0.01 ^μm2 or ^more and less than ^{0.2 μm2} , 5 or less pores having a size of 0.2 μm2 or more and less than 1.8 μm2, and 1 or less pores having a size of 1.8 μm2 or ^more .

A second aspect of the present invention is the molybdenum target of the first aspect, in which the average grain size d _Ave calculated based on the equivalent circle diameter is 20 μm or more and 100 μm or less, and the ratio (3σ/d _Ave ) of the standard deviation 3σ of the grain size calculated based on the equivalent circle diameter to the average grain size d _Ave is 1.2 or less.

The third aspect of the present invention is a molybdenum target according to the second aspect, in which the average aspect ratio of the grain size is less than 1.2.

A fourth aspect of the present invention is the molybdenum target according to any one of the first to third aspects, wherein the average Vickers hardness is 180 or less, and the ratio of the standard deviation 3σ of the Vickers hardness to the average Vickers hardness H _Ave (3σ/H _Ave ) is 0.07 or less.

A fifth aspect of the present invention is a method for producing a molybdenum target, comprising the steps of: using a molybdenum powder having an average particle size D _Ave of 2.5 to 4.0 μm, a median diameter D50 of 2.0 to 3.5, a ratio of the median diameter D90 to the average particle size D _Ave (D90/D _Ave ) of 1.7 or less, and a ratio of the median diameter D95 to the average particle size D _Ave (D95/D _Ave ) of 2.0 or less, as determined by a laser diffraction/scattering method; hot pressing the molybdenum powder at a temperature of 1400° C. to 1500° C.; and then sintering the molybdenum powder by hot isostatic pressing at a temperature of 1500° C. to 1600° C.

The sixth aspect of the present invention is the method for producing a molybdenum target according to the fifth aspect, in which the molybdenum powder has a tungsten content of 10 ppm to 100 ppm, and a molybdenum content excluding the oxygen content, carbon content, and tungsten content is 99.999 mass% or more.

The seventh aspect of the present invention is the method for producing a molybdenum target according to the fifth or sixth aspect, in which the hot pressing is performed under high vacuum at a holding temperature of 1400 to 1500°C for a holding time of 360 to 600 minutes.

The present invention makes it possible to realize a molybdenum target and a manufacturing method thereof that suppresses the generation of pores, which are the cause of particle generation, and controls the size and distribution of the pores with high precision.

FIG. 1 is a graph showing the relationship between the number of pores of 0.01 to 0.2 ^μm2 and the number of particles in the examples of the present invention and the comparative examples. FIG. ¹ is a graph showing the relationship between the number of pores of 0.2 to 1.8 μm2 and the number of particles in the examples and comparative examples of the present invention. FIG. 1 is a diagram showing the relationship between the number of pores having a size of 1.8 μm ² or more and the number of particles in an embodiment of the present invention and a comparative example.

The molybdenum target of the present invention has a molybdenum purity (content) of 5N (99.999% by mass) or more, a relative density of 99% or more, an oxygen content of 25 ppm or less, a carbon content of 30 ppm or less, a tungsten content of 10 ppm to 100 ppm, and in an observation area of 0.15 ^mm2 , there ^are 20 or less pores having a size of 0.01 ^μm2 or ^more and less than 0.2 ^μm2 , 5 or less pores having a size of 0.2 μm2 or more and less than 1.8 μm2, and 1 or ^less pores having a size of 1.8 μm2 or more. The 5N purity of molybdenum means that the molybdenum content excluding the oxygen content, carbon content, and tungsten content is 99.999% by mass or more.

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

(Gas components)
Gas components such as carbon and oxygen contained in the molybdenum target adversely affect the resistivity of the molybdenum film. These gas components are incorporated into the molybdenum film during film formation, and the resistivity of the molybdenum film tends to increase as the content of these gas components increases. Therefore, the carbon content of the molybdenum target is preferably 30 mass ppm or less, and the oxygen content is preferably 25 mass ppm or less.

(Tungsten content)
The molybdenum target of the present invention has a tungsten content of 10 ppm to 100 ppm, preferably 20 ppm to 50 ppm.

The reason for setting the tungsten content in this range is as follows.
Normally, the tungsten content is reduced to an unavoidable level, but in the present invention, the tungsten content is set within a predetermined range. If the tungsten content is too low, grain growth is likely to occur during sintering, the crystal grain size becomes large, and large pores are likely to be formed. On the other hand, if the tungsten content is too high, sinterability becomes poor, and it tends to be difficult to achieve high density.

(Crystal Grain Size)
In the molybdenum target of the present invention, the average crystal grain size d _Ave calculated based on the circle-equivalent diameter is 20 μm or more and 100 μm or less.

The reason for setting such an average value of the crystal grain size (average grain size) is as follows.
The smaller the average grain size of the molybdenum target, the smaller the difference in the amount of erosion caused by the orientation difference of each crystal grain on the target surface can be, so that the number of abnormal discharges caused by unevenness is reduced and the generation of particles during film formation can be suppressed.

On the other hand, if the average particle size is too small, the film formation rate becomes too slow, resulting in reduced productivity.

The ratio (3σ/d _Ave ) of the standard deviation 3σ of the particle diameter calculated based on the equivalent circle diameter to the average particle diameter d _Ave is 1.2 or less. This ratio is calculated by dividing the standard deviation 3σ by the average particle diameter.
The aspect ratio of the particle size is less than 1.2. This aspect ratio is the value obtained by dividing the major axis of the particle image by the minor axis to determine the "particle size calculated based on the circle equivalent diameter," and was determined using the image analysis software "Image-j."

The ratio of the standard deviation 3σ of the grain size to the average grain size d _Ave (3σ/d _Ave ) is preferably 1.2 or less for the following reasons.
There is a correlation between the variation in crystal grain size and the number and size of pores. The smaller the variation in crystal grain size, the fewer the number of pores in the target and the smaller their size. Therefore, within the above range, the generation of particles during film formation can be suppressed.
The aspect ratio of the grain size is preferably less than 1.2 because it provides a stable deposition rate that does not adversely affect production, and the deposition rate is unlikely to change even when the target is replaced.

(Relative Density)
The relative density of the molybdenum target is preferably 99% or more. If the relative density of the target is 99% or more, the amount of gas components contained in the target is small, so that when a 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 that the number of abnormal discharges caused by the unevenness of the target surface is reduced, and the generation of particles during film formation can be suppressed.

(Vickers hardness)
The average Vickers hardness of the molybdenum target is preferably 160 or more and 180 or less, and more preferably 165-175.

The reason why the average value of the Vickers hardness is preferably within the above range is as follows.
There is a correlation between the average Vickers hardness and the number and size of pores in a target. The higher the average Vickers hardness, the fewer the number and smaller the size of pores in the target, making it possible to suppress particle generation during film formation.

On the other hand, if the average Vickers hardness is very high, it is highly likely that the appropriate heat treatment conditions were not applied and that internal strain in the molybdenum has not been removed. This internal strain can become the starting point for cracks caused by thermal stress during target processing or deposition by sputtering.

The ratio (3σ/H _Ave ) of the standard deviation 3σ of the Vickers hardness to the average value H _Ave of the Vickers hardness is preferably 0.07 or less. The calculation method was to divide the standard deviation 3σ by the average value of the Vickers hardness.

The reason why the above-mentioned range of the ratio of three times the standard deviation of Vickers hardness (3σ) to the average value of Vickers hardness is preferable is as follows.

There is a correlation between the variation in Vickers hardness and the number and size of pores. The smaller the variation in Vickers hardness, the fewer the number of pores in the target and the smaller their size, which makes it possible to suppress particle generation during film formation.

(Poa)
The molybdenum target of the present invention has, in an observation area of 0.15 ^mm2 , 20 or less pores having a size of 0.01 ^μm2 or ^more and less than 0.2 ^μm2 , 5 or ^less pores having a size of 0.2 μm2 or more and less than 1.8 μm2, and 1 or less pores having a size of 1.8 μm2 or ^more .

The reasons for setting the size and number of the particles in the above-mentioned ranges in the present invention are as follows.
By controlling the size and number of pores, the electric field is concentrated in the pores, which suppresses the generation of particles due to localized dissolution and scattering, improving yield. In addition, the number of particles generated remains low until the end of the target's life, realizing stable production.

　A molybdenum target with extremely few coarse pores and suppressed pore localization in the surface and thickness directions of the molybdenum target has not been realized until now, but it can be realized by having the relative density, hardness, and crystal grain size characteristics described above. In addition, the molybdenum target of the present invention with extremely few coarse pores and suppressed pore localization in the surface and thickness directions of the molybdenum target can be realized by the manufacturing method described below.

As described above, the molybdenum target of the present invention has small and few pores, so by using this molybdenum target, the amount of particles generated can be significantly reduced, making it possible to stably form a high-quality molybdenum film.

This section describes a method for manufacturing a molybdenum target according to one embodiment of the present invention.

The molybdenum target of the present invention can be produced by using molybdenum powder having an average particle size D _Ave of 2.5 to 4.0 μm and a median diameter D50 of 2.0 to 3.5, which are obtained by a laser diffraction/scattering method, hot pressing at a temperature of 1400° C. to 1500° C. (HP process), and then sintering by hot isostatic pressing at a temperature of 1500° C. to 1600° C. (HIP process).

The first point of the method for producing a sputtering target of the present invention is to use a molybdenum powder having an average particle size D _Ave of 2.5 to 4.0 μm, preferably 2.8 to 3.7 μm, and a median diameter D50 of 2.0 to 3.5, preferably 2.2 to 3.3 μm, as measured by a laser diffraction/scattering method.

A second key point of the method for producing a sputtering target of the present invention is to use molybdenum powder having a ratio of median diameter D90 to average particle diameter D _Ave (D90/D _Ave ) of 1.7 or less, preferably 1.5 or less.

The third point of the method for producing a sputtering target of the present invention is to use tungsten powder having a ratio (D95/D _Ave ) of the median diameter D95 to the average particle diameter D _Ave of 2.0 or less, preferably 1.8 or less.

In this way, in the present invention, a molybdenum target with extremely small pores and few pores can be realized by using a molybdenum powder having a particle size in a predetermined range and a very narrow particle size distribution range, i.e., a small variation in particle size from the average particle size. In the present invention, the characteristic of such a narrow particle size distribution is defined as a value obtained by dividing the median diameter D90 by the average particle size D _Ave obtained by the laser diffraction/scattering method or a value obtained by dividing the median diameter D95 by the average particle size D _Ave obtained by the laser diffraction/scattering method being equal to or less than a predetermined value. Note that a powder having a wide particle size distribution outside this range cannot achieve the effects of the present invention.

Also, if the average particle size of the powder is too large, a sintered body with the specified density cannot be obtained, and if it is too small, the density will rise sharply during hot pressing (HP) and oxides will be trapped, so it is necessary to keep it within a specified range.

The molybdenum powder used in the present invention has a tungsten content of 10 ppm to 100 ppm, and a molybdenum content excluding the oxygen content, carbon content, and tungsten content of 99.999 mass% or more.

The oxygen content affects the oxygen content of the molybdenum target, so it is preferable to set the oxygen content of the raw material powder to, for example, 3000 mass ppm or less. This increases the amount of oxide sublimation, which may damage the hot press equipment.

The sputtering target of the present invention can be manufactured by hot pressing the above-mentioned molybdenum powder at a temperature of 1400°C or higher and 1500°C or lower, and then sintering it by hot isostatic pressing at a temperature of 1500°C or higher and 1600°C or lower.

Vacuum hot pressing in a high vacuum region promotes degassing and sintering, and allows for a high-density sintered body to be obtained while reducing the amount of oxygen contained in the molybdenum target. If the oxygen content of the molybdenum powder is high, the number of oxides in the molybdenum target increases, and the frequency of particle generation increases. In addition, sintering is inhibited by a thick surface oxide film, making it impossible to obtain a high-density sintered body.

Here, high vacuum refers to 1×10 ⁻² Pa or less, preferably 1×10 ⁻³ Pa or less, and more preferably 1×10 ⁻⁴ Pa or less.

As mentioned above, gas components such as carbon and oxygen contained in the molybdenum target adversely affect the resistivity of the molybdenum film, so the carbon content in the molybdenum target is preferably 30 ppm by mass or less, and the oxygen content is preferably 25 ppm by mass or less.

As mentioned above, oxygen concentration can be achieved by vacuum hot pressing.

On the other hand, with regard to carbon concentration, during hot pressing, carbon diffuses from the graphite components that make up the hot pressing device into the molybdenum sintered body, causing an increase in the carbon content. Therefore, the lower the hot pressing temperature, the better, and at 1500°C or less, a stable carbon concentration of 30 ppm by mass or less, and preferably 20 ppm by mass or less, can be achieved.

In the HP process, a sintered body having a relative density of 95% or more is produced. The HP temperature for producing a sintered body having such characteristics is preferably 1400°C or more and 1500°C or less. If the HP temperature is too low, the density does not rise to a level at which HIP treatment is possible, and if it is too high, coarse pores are formed locally due to rapid grain growth, which is not preferable. If the HP pressure is too low, the density does not rise to a level at which HIP treatment is possible. If it is too high, the HP device will wear out rapidly. For example, the pressure during HP treatment is 39.2 MPa (400 kg/ ^cm2 ) or more and 44.1 MPa (450 kg/ ^cm2 ) or less. The HP holding time in this process is 360 minutes or more and 600 minutes or less. If the HP holding time is too short, the density does not rise to a level at which HIP treatment is possible, and if it is too long, productivity will decrease. In the present invention, it is essential to control the powder particle size and particle size distribution, set the HP temperature to 1400° C. or higher and 1500° C. or lower, and set the HP holding time to 360 minutes or higher and 600 minutes or lower. This makes it possible to prevent the pores in the sintered body from becoming coarse and to uniformly disperse fine pores in the sintered body.

Hot isostatic pressing (HIP) is applied to the sintered body that has been subjected to HP treatment to reduce the pores in the sintered body and increase its density.

The HIP temperature is 1500°C or more and 1600°C or less. When the HIP temperature is less than 1500°C, the processing temperature is low, so it is difficult to obtain a high relative density of 99% or more within a processing time suitable for mass production. In particular, in the present invention, since a molybdenum powder with a tungsten content in a predetermined range is used, a sintered body with a relative density of 99% or more cannot be obtained at a temperature lower than 1500°C. In addition, when the HIP temperature exceeds 1600°C, the high processing temperature leads to rapid coarsening of the crystal grains, and coarse pores are formed locally, which is not preferable. The pressure is not particularly limited, and is, for example, 100 to 200 MPa, and is 176.4 MPa (1800 kg/ ^cm2 ) in this embodiment.

The above manufacturing method makes it possible to obtain a molybdenum target having the characteristics of the present invention. In particular, it is possible to reduce the number of pores in the molybdenum target, reduce their size, and suppress their localization. Therefore, by using the sputtering target of this embodiment, it is possible to reduce particle generation during film formation, and it is possible to stably form a high-quality molybdenum film.

The presence of pores in a sputtering target is strongly 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 hardness. The finer the raw material powder is and the narrower the range of its particle size distribution, the higher the relative density of the sintered body is, and the smaller the variation in crystal grain size and hardness is, the more significantly the occurrence of pores is reduced and their size becomes extremely small.

On the other hand, even if the crystal grain size is fine, if there is a large variation, the formation of coarse pores cannot be suppressed. The present invention has found that by optimizing the size and particle size distribution of the raw material powder, the hot pressing conditions, and the hot isostatic pressing conditions, it is possible to increase the relative density of the sintered body and suppress the variation in crystal grain size and hardness, thereby manufacturing a molybdenum target of the present invention with very few coarse pores and almost no localization of pores.

In other words, in the method for manufacturing a molybdenum target of this embodiment, the raw material powder is hot pressed at a temperature of 1400°C or higher and 1500°C or lower, and then sintered by hot isostatic pressing at a temperature of 1500°C or higher and 1600°C or lower.

According to the above-mentioned method for producing a molybdenum target, it is possible to obtain a sputtering target having small and few pores. For example, according to the above-mentioned method, it is possible to stably produce a molybdenum target having 20 or ^less pores having a size of 0.01 μm2 ^{or more} and less than 0.2 ^μm2 , 5 or ^less pores having a size of 0.2 μm2 or more and less than 1.8 μm2, and 1 or less pores having a size of 1.8 μm2 or more in an observation area of 0.15 ^mm2 .

The method for manufacturing a molybdenum target of the present invention can efficiently and stably manufacture a molybdenum target having a relative density of 99% or more, a Vickers hardness of 180 or less, a ratio of the standard deviation 3σ of Vickers hardness to the average Vickers hardness H _Ave (3σ/H _Ave ) of 0.07 or less, an average grain size of 20 μm or more and 100 μm or less, and a ratio of the standard deviation 3σ of the average grain size to the average grain size H _Ave (3σ/H _Ave ) of 1.2 or less.

This makes it possible to manufacture a molybdenum target with small and few pores. By using this molybdenum target, the amount of particles generated can be significantly reduced, making it possible to stably form a high-quality molybdenum film.

The sintered body produced as described above is processed into a predetermined target shape in the processing step. There are no particular limitations on the processing method, but typically mechanical processing methods such as grinding and cutting are applied. The processed size and shape are determined according to the target specifications, and the target is processed into a circular or rectangular shape, for example. The processed sintered body is bonded to a backing plate to form a sputtering cathode.

The present invention will be described below with reference to examples and comparative examples.
The average particle size and particle size distribution of the molybdenum powder were determined using a particle size distribution measuring device "LS13320" manufactured by Microtrackbell.

(Examples 1 to 4)
As shown in Table 1, a molybdenum powder having a tungsten content of 10 ppm to 100 ppm, a molybdenum content excluding tungsten and gas contents of 99.999 mass% or more (purity 5N), an average particle size D _Ave obtained by a laser diffraction/scattering method of 2.5 to 4.0 μm, a median diameter D50 of 2.0 to 3.5, a ratio of the median diameter D90 to the average particle size D _Ave (D90/D _Ave ) of 1.7 or less, and a ratio of the median diameter D95 to the average particle size D _Ave (D95/D _Ave ) of 2.0 or less was used, and the powder was hot pressed at a temperature shown in Table 1, that is, a temperature of 1400° C. or more and 1500° C. or less, and then HIPed at a temperature shown in Table 1 of 1500° C. or more and 1600° C. or less to obtain a molybdenum sintered body. The obtained molybdenum sintered body was finished into a predetermined target shape (diameter 440 mm, thickness 6 mm) by grinding using a lathe.

(Comparative Example 1)
As shown in Table 1, molybdenum powder having an average particle size D _Ave smaller than 2.5 μm, a median diameter D50 smaller than 2.0 μm, a ratio of the median diameter D90 to the average particle size D _Ave (D90/D _Ave ) of 1.7 or less, and a ratio of the median diameter D95 to the average particle size D _Ave (D95/D _Ave ) of 2.0 or less, obtained by laser diffraction/scattering method, was used and hot pressed at the temperature shown in Table 1 to obtain a molybdenum sintered body. Perhaps because the particle size of the molybdenum powder was too small, the density rose sharply and a large amount of oxide was trapped.

(Comparative Example 2)
As shown in Table 1, a molybdenum powder having an average particle size D _Ave of 2.5 to 4.0 μm, a median diameter D50 of 2.0 to 3.5, a ratio of the median diameter D90 to the average particle size D _Ave (D90/D _Ave ) of 1.7 or less, and a ratio of the median diameter D95 to the average particle size D _Ave (D95/D _Ave ) of 2.0 or less, obtained by a laser diffraction/scattering method, was used and hot pressed at the temperature shown in Table 1 to obtain a molybdenum sintered body. Since HIP was not performed, a sintered body with sufficient density was not obtained.

(Comparative Example 3-8)
As shown in Table 1, a molybdenum powder having an average particle size D _Ave smaller than 2.5 μm, a median diameter D50 smaller than 2.0 μm, a ratio of the median diameter D90 to the average particle size D _Ave (D90/D _Ave ) of 1.7 or less, and a ratio of the median diameter D95 to the average particle size D _Ave (D95/D _Ave ) of 2.0 or less, was used and hot pressed at the temperature shown in Table 1, followed by HIP to obtain a molybdenum sintered body. The obtained molybdenum sintered body was finished into a predetermined target shape (diameter 440 mm, thickness 6 mm) by grinding with a lathe.

(Comparative Example 9)
As shown in Table 1, a molybdenum powder having an average particle size D _Ave of 2.5 to 4.0 μm, a median diameter D50 of 2.0 to 3.5 μm, a ratio of the median diameter D90 to the average particle size D _Ave (D90/D _Ave ) of 1.7 or more, and a ratio of the median diameter D95 to the average particle size D _Ave (D95/D _Ave ) of 2.0 or more obtained by a laser diffraction/scattering method was used, hot pressed at the temperature shown in Table 1, and then subjected to HIP to obtain a molybdenum sintered body. The obtained molybdenum sintered body was finished into a predetermined target shape (diameter 440 mm, thickness 6 mm) by grinding with a lathe.

(Comparative Example 10)
As shown in Table 1, a molybdenum powder having an average particle size D _Ave obtained by a laser diffraction/scattering method greater than 4.0 μm, a median diameter D50 of 2.0 to 3.5 μm, a ratio of the median diameter D90 to the average particle size D _Ave (D90/D _Ave ) of 1.7 or less, and a ratio of the median diameter D95 to the average particle size D _Ave (D95/D _Ave ) of 2.0 or more was used, hot pressed at the temperature shown in Table 1, and then subjected to HIP to obtain a molybdenum sintered body. The obtained molybdenum sintered body was ground on a lathe to a predetermined target shape (diameter 440 mm, thickness 6 mm).

(Comparative Examples 11 to 13)
As shown in Table 1, a molybdenum powder having an average particle size D _Ave of more than 4.0 μm, a median diameter D50 of more than 3.5 μm, a ratio of the median diameter D90 to the average particle size D _Ave (D90/D _Ave ) of 1.7 or more, and a ratio of the median diameter D95 to the average particle size D _Ave (D95/D _Ave ) of 2.0 or more obtained by a laser diffraction/scattering method was used, hot pressed at the temperature shown in Table 1, and then subjected to HIP to obtain a molybdenum sintered body. The obtained molybdenum sintered body was finished into a predetermined target shape (diameter 440 mm, thickness 6 mm) by grinding with a lathe.

(Examples and Comparative Examples)
The relative density, Vickers hardness, crystal grain size, tungsten content, oxygen content, carbon content, and pores of the obtained targets were measured according to the following procedures. The results are shown in Tables 2 and 3.

(Relative Density)
Samples of 10 × 10 × 6 mmt were taken from the center, end, and halfway along the line connecting the center and end of the obtained molybdenum target, and the cross section of each sample was polished and etched, after which the specific gravity was calculated using the Archimedes method and the theoretical density of molybdenum (10.23 g/ ^cm3 ). The relative densities of each sample were added together and divided by the number of samples to obtain a value that was determined as the relative density of the molybdenum target according to the present invention.

(Vickers hardness)
Samples of 10 x 10 x 6 mmt were taken from the center, end, and halfway along the line connecting the center and end of the obtained molybdenum target, and the cross section of each sample was polished, and then hardness measurements were performed three times at 1 mm intervals in the depth direction of the target using a Mitutoyo Vickers hardness tester "HM-200" under a load of 1 kg and a load time of 15 seconds, using a Mitutoyo Vickers hardness tester "HM-200". The average value of the obtained values was calculated by adding up the average values calculated for each sample and dividing the result by the number of samples, which was taken as the hardness of the molybdenum target according to the present invention. Furthermore, the standard deviation of the molybdenum target was calculated by adding up the standard deviations calculated from each sample and dividing the result by the number of samples, which was taken as the standard deviation according to the present invention.

(Crystal Grain Size)
Samples of 10 x 10 x 6 mmt were taken from the center, end, and half of the line connecting the center and end of the obtained molybdenum target, and the cross section of each sample was polished and etched. Images were taken at 1 mm intervals in the depth direction of the target using an optical microscope "Digital Microscope VHX-6000" manufactured by Keyence Corporation, and the circle equivalent diameter was determined using image analysis software "Image-j" to calculate the average value. The average values calculated for each test piece were added together and divided by the number of samples to obtain the average grain size of the molybdenum target according to the present invention. Furthermore, the standard deviation of the molybdenum target was determined by adding the standard deviations obtained from each sample and dividing the result by the number of samples to obtain the standard deviation according to the present invention.

(Oxygen Content)
When the molybdenum sintered body was processed into a target shape, an analysis sample was taken and the oxygen content of the compact was measured. The oxygen content was analyzed using an analyzer "TC-600" manufactured by LECO Corporation.

(Carbon Content)
When the molybdenum sintered body was processed into a target shape, an analysis sample was taken and the carbon content of the compact was measured. The carbon content was analyzed using an analyzer "EMIA-320V" manufactured by Horiba, Ltd.

(Poa)
Samples of 10 x 10 x 6 mmt were taken from the center, end, and halfway along the line connecting the center and end of the obtained sputtering target, and after polishing the cross section of each sample, two SEM images were taken at 1 mm intervals in the depth direction of the target using an electron microscope "TM4000Plus" manufactured by Hitachi High-Technologies Corporation. The pore area of the taken SEM images was determined using image analysis software "Image-j", and the size and number of pores in each sample were calculated. The size and number of pores determined for each sample were added together and divided by the number of samples to determine the size and number of pores of the molybdenum target according to the present invention.

Furthermore, using the obtained targets of the examples and comparative examples, films were formed as follows, the resistivity of the films was measured as follows, and particles were evaluated as follows.

The results of Examples 1 to 4 and Comparative Examples 1 to 13 are shown in Table 3, and the relationship between the number of pores of a given size and the number of particles is shown in Figures 1 to 3. Note that resistivity of 11 μΩ cm or less was marked as O, and that exceeding 11 μΩ cm was marked as X. If the resistivity is 11 μΩ cm or less, low-resistance LSI wiring can be formed, making it possible to realize a device with low power consumption.
The film thickness distribution was evaluated as 0 if it was 2% or less, and 0 if it was more than 2%. If the film thickness distribution is 2% or less, devices with little variation in performance and quality can be produced stably.

(Resistivity measurement)
The obtained molybdenum target was bonded to an aluminum alloy backing plate with an In-based brazing material to form a sputtering cathode. The sputtering cathode was assembled in an ULVAC sputtering device "ENTRON (registered trademark)" to form a molybdenum thin film with a thickness of 10 nm on a semiconductor wafer with a diameter of 300 mm. The sputtering conditions were as follows: ultimate pressure: 1×10 ⁻⁵ Pa, discharge method: DC, power: 4 kW, gas source: Ar, gas flow rate: 150 sccm, film formation temperature: 200° C., sputtering time: 5 seconds, and distance between the target and the wafer: 60 mm.

The film thickness was measured at nine points on the molybdenum thin film on the wafer using a TECHNORAYS S-MAT2300, and the sheet resistance was measured using a KLATencor OmniMap RS100 to calculate the resistivity (μΩ·cm) of the thin film, and the average value was used as the resistivity of the molybdenum thin film.

(Particle measurement)
For the 10 nm thick molybdenum thin film used for resistivity measurement, the surface of the molybdenum 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, and the number of particles with a size of 0.065 μm or more was measured. The number of particles was the number per 70,685 ^mm2 , and it was determined that 20 or less was preferable, and 15 or less was more preferable.

(Measurement of film thickness distribution)
The film thickness of the molybdenum thin film on the wafer was measured at 49 points using a TECHNORAYS S-MAT2300, and the film thickness was calculated using the following formula.
Film thickness distribution (%) = (maximum value - minimum value) / (maximum value + minimum value) x 100

As shown in Examples 1 to 4, a molybdenum powder having a tungsten content of 10 ppm to 100 ppm, a molybdenum content excluding tungsten and gas content of 99.999 mass% or more (purity 5N), an average particle size D _Ave obtained by a laser diffraction/scattering method of 2.5 to 4.0 μm, a median diameter D50 of 2.0 to 3.5, a ratio of the median diameter D90 to the average particle size D _Ave (D90/D _Ave ) of 1.7 or less, and a ratio of the median diameter D95 to the average particle size D _Ave (D95/D _Ave ) of 2.0 or less was used, and the powder was hot pressed at a temperature of 1400° C. to 1500° C., and then HIPed at a temperature of 1500° C. to 1600° C., thereby obtaining a molybdenum sintered body. The obtained molybdenum sintered body has a relative density of 99% or more, and a molybdenum target can be obtained in which, in an observation area of ^{0.15 mm2} , there are 20 or less pores with a size of 0.01 ^{μm2 or} more and less than 0.2 ^μm2 , 5 or less pores with a size of 0.2 μm2 ^or more and less than 1.8 μm2, and 1 or less pores with a size of 1.8 μm2 or more. By using such a molybdenum target, it is possible to suppress the generation of particles, and it becomes possible to stably form a high-quality molybdenum thin film.

In addition, in Examples 1 to 4, the hot pressing temperature is low at 1500°C or less, so the carbon content of the target is sufficiently low, making it possible to form a thin film with a sufficiently low resistivity of 11 μΩ·cm or less.

In Comparative Example 1, the powder was too fine and contained a large amount of oxygen, so that the density rose sharply during HP and oxides were trapped, while in Comparative Example 2, the density was insufficient because HIP was not performed.
In Comparative Examples 3 and 4, the tungsten content and oxygen content were high, resulting in high resistivity. In addition, the raw powder was too fine, resulting in a sudden increase in density during HP, and the HP temperature was low, resulting in oxides remaining without sublimation. In Comparative Example 3, abnormal grain growth occurred due to the high HIP temperature, and in Comparative Example 4, the density was low due to the low HIP temperature.
In Comparative Examples 5 and 6, the tungsten content and oxygen content were high, resulting in high resistivity. In addition, the powder was too fine and the oxygen content was high, resulting in a sudden increase in density during HP, leading to oxide trapping. In addition, the density was low due to the low HIP temperature.
In Comparative Example 7, the oxygen content was high, resulting in a high resistivity, and the raw material powder was too fine, resulting in a sudden increase in density during HP, causing some oxides to remain.
In Comparative Example 8, the oxygen content was high, so the resistivity was high, and the raw powder was too fine, so the density rose sharply during HP, leaving some oxides behind. Also, the HIP temperature was high, so abnormal grain growth occurred, and the aspect ratio became large.
In Comparative Examples 9 to 11, the raw material powder was coarse, resulting in insufficient density. In Comparative Example 11, the particle size was insufficient, resulting in uneven particle size and a large aspect ratio, resulting in insufficient density.
In Comparative Example 12, the high HIP temperature caused abnormal grain growth, resulting in a large aspect ratio, and the raw material powder was coarse, resulting in insufficient density.
In Comparative Example 13, the amount of carbon diffusion was large due to the high HP temperature. Also, due to insufficient adjustment of the raw material particle size distribution, the particle size was uneven, the aspect ratio was large, and the powder was coarse, resulting in insufficient density.

Claims (7)

A molybdenum target formed of a sintered body of molybdenum powder,
The relative density is 99% or more,
The oxygen content is 25 ppm or less, and the carbon content is 30 ppm or less,
The tungsten content is 10 ppm to 100 ppm;
The molybdenum content excluding the oxygen content, the carbon content, and the tungsten content is 99.999% by mass or more,
A molybdenum target having, in an observation area of 0.15 ^mm2 , 20 or less pores having a size of 0.01 ^{μm2 or} more and less than 0.2 ^μm2 , 5 or less pores having a size of 0.2 μm2 or more and less than 1.8 ^μm2 , and 1 or less pores having a size of 1.8 μm2 or ^more . The average particle diameter d _Ave calculated based on the circle equivalent diameter is 20 μm or more and 100 μm or less,
2. The molybdenum target according to claim 1, wherein the ratio (3σ/d _Ave ) of the standard deviation 3σ of grain size calculated based on the equivalent circle diameter to the average grain size d _Ave is 1.2 or less. The molybdenum target according to claim 2, in which the aspect ratio of the grain size d is less than 1.2. The average Vickers hardness is 180 or less,
4. The molybdenum target according to claim 1, wherein the ratio (3σ/H _Ave ) of the standard deviation 3σ of Vickers hardness to the average value H _Ave of Vickers hardness is 0.07 or less. a molybdenum powder having an average particle size D _Ave of 2.5 to 4.0 μm, a median diameter D50 of 2.0 to 3.5, a ratio of the median diameter D90 to the average particle size D _Ave (D90/D _Ave ) of 1.7 or less, and a ratio of the median diameter D95 to the average particle size D _Ave (D95/D _Ave ) of 2.0 or less, as measured by a laser diffraction/scattering method;
A method for manufacturing a molybdenum target, comprising hot pressing at a temperature of 1400° C. to 1500° C., and then sintering by hot isostatic pressing at a temperature of 1500° C. to 1600° C. The molybdenum powder has a tungsten content of 10 ppm to 100 ppm;
The method for producing a molybdenum target according to claim 5, wherein the molybdenum content excluding the oxygen content, the carbon content and the tungsten content is 99.999 mass % or more. 7. The method for producing a molybdenum target according to claim 5, wherein the hot pressing is carried out under high vacuum at a holding temperature of 1400 to 1500° C. for a holding time of 360 to 600 minutes.