Sputtering target and method for manufacturing sputtering target

Abstract

To provide a sputtering target that mainly includes molybdenum and can effectively reduce particles at the time of sputtering, and to provide a method for manufacturing a sputtering target.SOLUTION: A sputtering target includes 99.99 mass% or more molybdenum and has an average crystal grain size of 400 μm or less. When the sputtering target is subjected to pre-sputtering with 1.7 kWhr under the condition of input electrical power of 0.5 kW and an Ar gas pressure of 0.5 Pa, and a film with a 30nm film thickness is deposited on a silicon substrate with a 4-inch diameter, the number of particles having a particle size of 0.07 μm or more and adhering to the silicon substrate is less than 38.SELECTED DRAWING: None

Description

[Technical field]

[0001] This specification discloses techniques relating to sputtering targets and methods for producing sputtering targets. [Background technology]

[0002] In recent years, as LSIs become increasingly highly integrated, the use of materials with lower electrical resistivity as electrode and wiring materials has been considered. Under these circumstances, high-purity tungsten has come to be used as an electrode and wiring material because of its relatively low resistivity and good thermal and chemical stability.

[0003] In the meantime, when manufacturing electrode materials and wiring materials, it is common to form thin films by a sputtering method using a sputtering target. In the electrode materials and wiring materials containing the above-mentioned high-purity tungsten, there is a demand for sputtering targets made of high-purity and high-density tungsten.

[0004] As this type of technology, Patent Documents 1 and 2 propose "a tungsten sintered sputtering target, characterized in that the purity of tungsten is 5N (99.999%) or more and the carbon impurity contained in the tungsten is 3wtppm or less." This "tungsten sintered sputtering target" is said to "make it possible to stably reduce the electrical resistance value in the tungsten film."

[0005] Although not related to the above-mentioned tungsten sputtering target, Patent Document 3 describes a method for producing a high-purity molybdenum target for LSI electrodes having a purity of 99.999% or more, an alkali metal content of 100 ppb or less, and a radioactive element content of 10 ppb or less, the method comprising: dissolving metallic molybdenum or a molybdenum compound to produce a molybdenum-containing aqueous solution; purifying the aqueous solution and then crystallizing molybdenum-containing crystals; separating the crystals into solid and liquid, washing and drying the crystals, and then reducing them by heating to prepare high-purity molybdenum powder; pressure-molding and sintering the high-purity molybdenum powder, and then melting the high-purity molybdenum ingot with an electron beam; and then plastically working and machining the ingot. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5944482 [Patent Document 2] US Patent Application Publication No. 2015 / 0023837 [Patent Document 3] Japanese Patent Application Publication No. 4-218912 Summary of the Invention [Problem to be solved by the invention]

[0007] However, there is a concern that the high purity tungsten film mentioned above will not be able to meet the future demand for even lower resistance, so it is necessary to find a promising material to replace tungsten. In this regard, although a molybdenum film may be able to realize a sufficiently low electrical resistance value, the "high-purity molybdenum target for LSI electrodes" described in Patent Document 3 has a problem in that particles are generated at a high rate during sputtering, which reduces the material yield.

[0008] In order to solve the above-mentioned problems, this specification proposes a sputtering target that contains mainly molybdenum and can effectively reduce particles during sputtering, and a method for manufacturing the sputtering target. [Means for solving the problem]

[0009] The sputtering target disclosed in this specification has a molybdenum content of 99.99 mass % or more, a relative density of 98% or more, and an average crystal grain size of 400 μm or less. The present specification also discloses a method for producing a sputtering target, which includes the steps of preparing a molybdenum powder, hot pressing the molybdenum powder under a load at a temperature of 1350°C to 1500°C, and hot isostatically pressing a compact obtained by the hot pressing at a temperature of 1300°C to 1850°C. Effect of the Invention

[0010] According to the above-described sputtering target and method for producing a sputtering target, it is possible to effectively produce a sputtering target that contains mainly molybdenum and that can effectively reduce particles during sputtering. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the invention disclosed in this specification will be described. A sputtering target according to one embodiment of the present invention has a molybdenum content of 99.99 mass % or more, a relative density of 98% or more, and an average crystal grain size of 400 μm or less. 2 It is preferable that:

[0012] Until now, the sputtering method using a sputtering target made of high-purity tungsten has been used to manufacture electrode materials and wiring materials for highly integrated LSIs. However, the tungsten films formed in this way may not be able to meet the demand for lower resistance, which is expected to continue to grow in the future. In response to this, the inventors have investigated the film formation characteristics of high-melting point metals and have found that a thin film made of molybdenum, which is one of the high-melting point metals, may be able to achieve a lower resistance value than a thin film made of tungsten.

[0013] Furthermore, as a result of extensive research into sputtering targets capable of depositing the above-mentioned molybdenum thin film, it was found that a specific sputtering target manufactured by a specific manufacturing method can achieve an even lower resistance value and can form a thin film that can be suitably used for semiconductor applications. It was also found that such a sputtering target can effectively reduce the rate of particle generation during sputtering, thereby reducing the possibility of malfunction of electronic devices composed of the formed thin film. Such a sputtering target and a method for producing the same are described in detail below.

[0014] (composition) The sputtering target of this embodiment contains 99.99% by mass or more of molybdenum and is made of high-purity molybdenum of 4N or more. When the purity of molybdenum is high, the particle generation rate is significantly reduced, while when the purity of molybdenum is low, particles tend to increase. Therefore, from the viewpoint of particle reduction, the higher the purity of molybdenum, the more desirable it is. From this viewpoint, the molybdenum content in the sputtering target is preferably 99.999% by mass or more (i.e., 5N or more).

[0015] The above-mentioned purity means the purity excluding the inseparable homologous elements. In other words, the inseparable homologous element is tungsten, and here, the purity is defined as the ratio of the molybdenum content to the content of all metal elements other than tungsten and elements below the detection limit. The molybdenum content is measured and calculated by glow discharge mass spectrometry (GDMS).

[0016] (Relative Density) In an embodiment of the present invention, the relative density of the sputtering target is 98% or more. The higher the relative density, the more particles are reduced, but a low relative density tends to lead to an increase in particles. From this viewpoint, the relative density is preferably 99% or more, and more preferably 99.5% or more.

[0017] The relative density of a sputtering target is expressed as relative density = (measured density / theoretical density) x 100 (%). Here, the measured density is the density of the sputtering target measured by the Archimedes method using pure water as a solvent, and the theoretical density is the theoretical density when the molybdenum content is 100%.

[0018] (crystal grain size) When the crystal grain size of molybdenum contained in the sputtering target is large, the number of particles tends to increase, and when the crystal grain size is small, the number of particles tends to decrease. Therefore, the average crystal grain size of the molybdenum in the sputtering target is set to 400 μm or less, and preferably 200 μm or less. Although there is no disadvantage due to the average crystal grain size of the molybdenum being too small, the average crystal grain size may be, for example, 15 μm or more, typically 40 μm or more.

[0019] The above average crystal grain size is determined by observing the target surface with an optical microscope, drawing a straight line on the resulting structure photograph until the number of grains N is equal to or greater than 200, and calculating L / N from the number of grains on that line (N ≥ 200) and the total length of the line (L). The method for measuring this average crystal grain size complies with the intercept method specified in JIS G0551.

[0020] (Radiation Dose) The radiation dose of the sputtering target is 0.03cph / cm 2 If the radiation dose is high, the possibility of malfunction of an electronic device having a molybdenum thin film formed using the sputtering target increases, while if the radiation dose is low, the possibility of malfunction of such an electronic device decreases. Therefore, the radiation dose of the sputtering target is 0.02 cph / cm or less. 2 It is preferable that the concentration is 0.01 cph / cm or less, and more preferably 0.01 cph / cm 2 It is even more preferred that:

[0021] The above radiation dose was measured using a LACS-4000M manufactured by Sumika Chemical Analysis Center Co., Ltd., with P-10 gas (Ar-CH4 10%), flow rate of 100 ml / min, measurement time of 99 kr, and measurement area of ​​203 cm. 3 , and the counting efficiency is measured at 80%.

[0022] (Manufacturing method) One example of a method for producing the above-mentioned sputtering target is to carry out a powder metallurgy process in which a specific molybdenum powder is subjected to a combination of hot pressing (HP) and hot isostatic pressing (HIP), as described below.

[0023] First, molybdenum powder is prepared as a raw material. The molybdenum powder preferably has a particle size in the range of 0.1 μm to 10 μm, an average particle size of 1 μm to 5 μm, and a purity of molybdenum of 4N or more. If the particle size of the molybdenum powder is too large, there is a concern that the density will be low. If the particle size is too small, the powder will be bulky, which may increase the difficulty of handling and impair productivity (i.e., the bulkiness makes it difficult to fill a mold such as a hot press with multiple sheets, which may reduce the number of productions per run). If the purity of the molybdenum powder is low, the molybdenum content of the sputtering target to be manufactured will decrease. Therefore, it is preferable to use molybdenum powder with a purity of molybdenum of 5N or more. In order to reduce the radiation dose of the sputtering target to be manufactured, it is preferable to use molybdenum powder with a purity of 5N or more as a raw material.

[0024] Next, in the hot pressing step, the molybdenum powder is filled into a mold or other predetermined shape, which is heated and maintained at a predetermined temperature while a predetermined load is applied. Here, the load is applied while maintaining the maximum temperature of the raw material at 1350°C to 1500°C. If the temperature is low, the relative density of the sputtering target cannot be sufficiently increased, while if the temperature is high, there is a concern that the grain size will become large and the number of particles will increase. Therefore, the temperature during hot pressing is set to 1350°C to 1500°C.

[0025] The time for maintaining the temperature as described above is preferably 60 to 300 minutes. If the maintaining time is too short, there is a concern that the density will be low, and if it is too long, there is a possibility that the particle size will become coarse. The load applied at this time is 150kg / cm 2 ~300kg / cm 2 It is particularly preferable to set the density to 200 kg / cm 2 ~300kg / cm 2If the load is too small, there is a possibility that the density will be low. However, if the load is too large, there is no particular problem. If the equipment such as the die can withstand it, increasing the load will lead to higher density. However, generally, a load of 300 kg / cm is recommended. 2 This is often the upper limit.

[0026] In addition, in order to reduce the difference between the set temperature and the actual temperature when heating in the hot press, for example, when the temperature reaches a temperature range of 800°C to 1200°C during heating, it is preferable to hold the temperature range for 30 minutes.

[0027] The compact obtained in the hot pressing step is then subjected to hot isostatic pressing, which increases the density of the resulting sputtering target. In the hot isostatic pressing process, the temperature is typically 1300°C to 1850°C and the pressure is 1300 kg / cm 2 ~2000kg / cm 2 The load is applied for 60 to 300 minutes. If these conditions of temperature, load and time are not met, the density will be low. Therefore, in the case of hot isostatic pressing, the temperature is set to 1400°C to 1850°C and the load is set to 1500 kg / cm. 2 ~1900kg / cm 2 and the time period is more preferably 60 to 300 minutes. The sintered body obtained by hot isostatic pressing can be subjected to grinding or other shaping processes as necessary to produce a sputtering target having a desired size and shape.

[0028] The sputtering target manufactured in this manner has a low particle generation rate during sputtering, and due to the low radiation dose, there is a low possibility that electronic devices having a thin film of molybdenum formed therewith will malfunction.

[0029] The present invention is not limited to the above-described embodiments, and each component of the embodiments can be modified without departing from the scope of the present invention. For example, various aspects can be configured by appropriately combining multiple components of each embodiment. It is also possible to delete some components from all the components of the embodiments. EXAMPLES

[0030] Next, a sputtering target as described above was actually produced as a prototype, and its effects were confirmed, which will be described below. However, the description here is merely for illustrative purposes and is not intended to be limiting.

[0031] Molybdenum powder with an average particle size of 5μm and a specified purity is filled into a carbon die and heated at a specified temperature with a pressure of 300kgf / cm 2 The resulting compact was subjected to a load of 1800 kgf / cm at a specified temperature. 2 A sintered body was obtained by hot isostatic pressing under a load of 164 mm. The sintered body was then shaped to produce a sputtering target with a diameter of 164 mm and a thickness of 5 mm.

[0032] In Examples 1 to 7 and Comparative Examples 1 and 2, sputtering targets were manufactured in the same manner, except that the maximum temperature reached by hot pressing (HP) and the maximum temperature reached by hot isostatic pressing (HIP) were changed as shown in Table 1. In Comparative Examples 3 and 4, sputtering targets were manufactured by forming with hot pressing and then hot rolling instead of the above-mentioned hot pressing and hot isostatic pressing. In this hot rolling, the target was passed between rolls five times at a temperature of 1200°C in Comparative Example 3, and six times at a temperature of 1200°C in Comparative Example 4, to roll it to a thickness of 10 mm, and then finished to the above dimensions by shaping.

[0033] For each sputtering target manufactured as described above, the purity, average crystal grain size (grain size), relative density (density), and radiation dose were measured according to the measurement methods described above. The results are shown in Table 1. Regarding the measurement of purity, the molybdenum content was measured by glow discharge mass spectrometry (GDMS) using ELEMENT GD manufactured by Thermo Fisher, the carbon concentration was measured by a carbon analyzer (CSLS600) manufactured by LECO, and the oxygen concentration was measured by an oxygen / nitrogen simultaneous analyzer (TC-600) manufactured by LECO, each measured by an inert gas fusion method. The purity shown in Table 1 means the purity (mass%) of molybdenum in the sputtering target. The purity of the sputtering target was almost the same as the purity of the raw material molybdenum powder.

[0034] In addition, using each of the above-mentioned sputtering targets, sputtering was performed on a silicon substrate in an atmosphere filled with Ar gas to form a molybdenum film. Specifically, the sputtering target was attached to a magnetron sputtering device (Canon Anelva C-3010 sputtering system) and sputtering was performed. The sputtering conditions were an input power of 0.5 kW and an Ar gas pressure of 0.5 Pa, and after performing pre-sputtering at 1.7 kWhr, a film was formed on a 4-inch silicon substrate with a thickness of 30 nm. The number of particles with a particle diameter of 0.07 μm or more that adhered to the substrate was measured using a surface foreign matter inspection device (Candela CS920, KLA-Tencor). The results are also shown in Table 1.

[0035] [Table 1]

[0036] In Examples 1 to 7, sputtering targets having high purity, high relative density, and small average crystal grain size were obtained by manufacturing the targets by hot pressing and hot isostatic pressing under predetermined conditions, and thus particles during sputtering could be effectively reduced.

[0037] On the other hand, in Comparative Example 1, the relative density was low due to the low hot pressing temperature. In Comparative Example 2, the purity of the sputtering target was low due to the low purity of the raw molybdenum powder. In Comparative Example 3, the purity was low and the target was manufactured by rolling instead of hot isostatic pressing, resulting in a large average crystal grain size. Note that in Comparative Examples 2 and 3, the radiation dose was high due to the influence of the raw molybdenum powder.

[0038] In Comparative Example 4, the average crystal grain size was large because the alloy was produced by rolling instead of hot isostatic pressing. As a result, in all of Comparative Examples 1 to 4, the amount of particles increased.

[0039] The present invention also includes the following inventions. [1] A sputtering target having a molybdenum content of 99.999% by mass or more, a relative density of 98% or more, an average crystal grain size of 45 μm or less, and a radiation dose of 0.03 cph / cm 2 A sputtering target that is: [2] Radiation level is 0.02cph / cm 2 The sputtering target according to [1] below. [3] The sputtering target according to [1] or [2], having a relative density of 99% or more. [4] A method for producing a sputtering target according to any one of [1] to [3], A method for producing a sputtering target, comprising 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. [5] In the hot pressing step, the load applied to the molybdenum powder is 200 kg / cm 2~300kg / cm 2 The method for producing a sputtering target according to [4], [6] The method for producing a sputtering target according to [4] or [5], wherein the hot pressing is carried out for 60 minutes to 300 minutes. [7] In the step of hot isostatic pressing, the load applied to the compact is 1300 kg / cm 2 ~2000kg / cm 2 The method for producing a sputtering target according to any one of [4] to [6], [8] The method for producing a sputtering target according to any one of [4] to [7], wherein the hot isostatic pressing is carried out for 60 minutes to 300 minutes. [9] The method for producing a sputtering target according to any one of [4] to [8], wherein in the step of preparing molybdenum powder, a molybdenum powder having a purity of 5N or more and an average particle size of 1 μm to 5 μm is prepared.

Claims

1. A sputtering target having a molybdenum content of 99.99 mass% or more, a relative density of 98% or more, and an average crystal grain size of 400 μm or less, A plate-shaped sputtering target having a diameter of 164 mm is placed in a magnetron sputtering device, a Canon Anelva C-3010 sputtering system, and pre-sputtering is performed at 1.7 kWhr under conditions of an input power of 0.5 kW and an Ar gas pressure of 0.5 Pa. Then, a film having a thickness of 30 nm is formed on a 4-inch silicon substrate. This sputtering target has fewer than 38 particles having a particle diameter of 0.07 μm or more adhering to the silicon substrate.

2. The sputtering target according to claim 1 , wherein the number of particles is 33 or less.

3. 3. The sputtering target according to claim 1, wherein the molybdenum content is 99.999 mass % or more.

4. Radiation dose is 0.03 cph / cm 2 The sputtering target according to any one of claims 1 to 3, wherein:

5. Radiation dose is 0.02 cph / cm 2 The sputtering target according to any one of claims 1 to 3, wherein:

6. The sputtering target according to any one of claims 1 to 5, wherein the average crystal grain size is 200 µm or less.

7. The sputtering target according to any one of claims 1 to 6, wherein the average crystal grain size is determined by observing the target surface with an optical microscope, drawing a straight line on the obtained microstructure photograph until the number of grains reaches N≧200, and calculating L / N from the number of grains present on the straight line (N≧200) and the total length of the line (L), and the method for measuring the average crystal grain size is in accordance with the cutting method specified in JIS G0551.

Images