Tungsten sputtering target

Abstract

To provide a tungsten sputtering target capable of forming a tungsten film with a low specific resistance when the tungsten film is formed using the tungsten sputtering target.SOLUTION: The present invention provides a tungsten sputtering target (excluding those doped with molybdenum (Mo)), where a purity of tungsten is 5 N (99.999 wt.%) or more, the impurities of carbon and oxygen contained in tungsten are 10 wtppm or less, respectively, and an average grain size of tungsten crystals is 347 μm or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a tungsten sputtering target used when forming a gate electrode or wiring material such as an IC or LSI by a sputtering method.

Background Art

[0002] In recent years, with the high integration of ultra-LSIs, studies have been conducted on using materials with lower electrical resistivity as electrode materials and wiring materials. Among these, high-purity tungsten, which has low resistivity and is thermally and chemically stable, is used as an electrode material and wiring material. These electrode materials and wiring materials for ultra-LSIs are generally manufactured by sputtering and CVD methods. However, the sputtering method is more widely used than the CVD method because the structure and operation of the apparatus are relatively simple, film formation can be easily achieved, and the cost is low.

[0003] For tungsten sputtering targets, high purity and high density are required. In recent years, for films formed by sputtering using tungsten sputtering targets for electrode materials and wiring materials for ultra-LSIs, materials with even lower electrical resistivity have been demanded.

[0004] On the other hand, Patent Document 1 discloses a tungsten sintered body sputtering target characterized in that the purity of tungsten is 5N (99.999 wt%) or more and the carbon content of impurities contained in tungsten is 5 wtppm or less. By forming a film using such a tungsten sintered body sputtering target, it has an excellent effect that it is possible to stably reduce the electrical resistivity in the tungsten film.

[0005] Thus, Patent Document 1 has succeeded in reducing the specific resistance of the tungsten film formed by sputtering by achieving high purity of the tungsten sputtering target.

[0006] However, the reduction of the resistance of the tungsten film due to purification is approaching its limit, and other measures need to be taken to further reduce the resistance.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, an object of the present invention is to provide a tungsten sputtering target capable of forming a tungsten film having a low specific resistance when forming a tungsten film using a tungsten sputtering target.

Means for Solving the Problems

[0009] When performing sputtering on a tungsten sputtering target, a film formation method can be considered in which a noble gas typified by Ar or Kr is collided at a high speed, and the ejected tungsten element is deposited on the surface of a substrate such as a silicon (Si) wafer to form a tungsten film having a predetermined thickness. However, during film formation, noble gases such as Ar may be fixed on the substrate surface together with the tungsten element, and as a result, a tungsten film incorporating Ar or the like may be generated. Such a tungsten film tends to have a higher specific resistance compared to a tungsten film in which Ar is not incorporated.

[0010] Therefore, in order to reduce the amount of noble gas atoms incorporated, a method of using Kr gas having a large atomic radius can be considered. However, since Kr gas is more expensive than Ar gas, it leads to an increase in production cost. Therefore, improvement of the tungsten sputtering target itself is strongly desired.

[0011] Based on the above findings, the present invention provides a tungsten sputtering target in which noble gases such as Ar and Kr are less likely to be incorporated into the tungsten film during film formation, enabling the formation of a tungsten film with a lower incorporation amount of Ar or the like compared to the case of forming a film using a conventional tungsten sputtering target, and enabling the formation of a tungsten film with a low resistivity.

[0012] And the inventors of the present invention have made it possible to form a tungsten film with a low resistivity by controlling the average particle size of the tungsten sputtering target to exceed 100 μm.

[0013] Therefore, some aspects of the present invention are specified as follows. (1) A tungsten sputtering target (excluding those added with molybdenum (Mo)), wherein the purity of tungsten is 5N (99.999 wt%) or more, the carbon and oxygen of the impurities contained in tungsten are each 10 wtppm or less, and the average particle size of tungsten crystals is 347 μm or more. A tungsten sputtering target characterized by the above. (2) A tungsten sputtering target composed of tungsten and impurities, wherein the purity of tungsten is 5N (99.999 wt%) or more, the carbon and oxygen of the impurities contained in tungsten are each 10 wtppm or less, and the average particle size of tungsten crystals is 347 μm or more. A tungsten sputtering target characterized by the above. (3) The sputtering target according to (1) or (2), characterized in that the relative density is 99.3% or more.

Advantages of the Invention

[0014] According to the present invention, it is possible to provide a tungsten sputtering target capable of forming a tungsten film with a low resistivity when forming a tungsten film using the tungsten sputtering target.

Brief Description of the Drawings

[0015]

Figure 1

Embodiments for Carrying Out the Invention

[0016] The tungsten sputtering target of the present invention has a tungsten purity of 5N (99.999 wt%) or more, the impurities carbon and oxygen contained in tungsten are each 20 wtppm or less, and the average grain size of the tungsten crystals exceeds 100 μm.

[0017] (Purity) In order to form a tungsten film with low resistivity, it is necessary to suppress the impurities contained in the tungsten film. Therefore, it is essential to increase the purity of the tungsten sputtering target. Specifically, it is necessary to have a purity of 99.999 wt% (5N) or more.

[0018] (Impurities) In addition, impurities such as carbon and oxygen contained in the target are incorporated into the tungsten film during film formation. Therefore, as the amount of carbon increases, the resistivity of the tungsten film after sputtering film formation tends to increase. Therefore, it is necessary that the carbon and oxygen of the impurities contained in tungsten are each 50 wtppm or less. From the same point of view, it is preferable that the carbon and oxygen of the impurities contained in tungsten are each 30 wtppm or less, and more preferably 20 wtppm or less. And if the carbon and oxygen are each 10 wtppm or less, the influence on the resistivity of the tungsten film is almost eliminated. In order to reduce carbon, when filling tungsten powder into a graphite die and hot pressing, it is good to isolate it so as not to have direct contact with the graphite die.

[0019] (Average Grain Size of Tungsten Crystals) The tungsten sputtering target of the present invention has an average grain size of tungsten crystals exceeding 100 μm. Conventionally, it has been known that the average grain size of tungsten crystals is related to the density of the tungsten sputtering target, but no attention has been paid to the relationship between the average grain size of tungsten crystals and the amount of Ar atoms incorporated into the tungsten film during film formation. In the present invention, since the average grain size of tungsten crystals exceeds 100 μm, it becomes difficult for Ar atoms to be incorporated into the tungsten film during film formation, and as a result, a tungsten film with a small amount of Ar incorporation can be obtained. That is, even if the purity, density, etc. of the tungsten sputtering target are the same, a tungsten film with a lower specific resistance can be obtained when the average grain size of tungsten crystals exceeds 100 μm than when it is 100 μm or less. Therefore, the average grain size of tungsten crystals in the present invention is preferably 120 μm or more, more preferably 150 μm or more, and even more preferably 200 μm or more.

[0020] The average grain size of tungsten crystals can be determined by a value equivalent to the average line segment length per grain of the evaluation test line crossing the grain interior evaluated by the cutting method of JIS G 0551:2013. Specifically, microstructure observation is carried out using an optical microscope. In the observed and preserved microstructure photograph, draw a straight line on the photograph until the number of particles N = 200, and use the number of particles (N≥200) existing on the straight line and the total length of the straight line (L) to calculate the average grain size of the observed site by L / N.

[0021] (Relative density) The relative density of the tungsten sputtering target is preferably 99.3% or more. If the relative density of the target is 99.5% or more, since the gas components contained in the target are few, the specific resistance of the film can be suppressed when the film is formed. Also, the generation of dust due to abnormal discharge is suppressed. From the above viewpoints, the relative density of the target is more preferably 99.7% or more, and even more preferably 99.9% or more.

[0022] (Manufacturing method) The tungsten sputtering target of the present invention is not particularly limited in its manufacturing method as long as it has each of the above-described characteristics. However, as a means of obtaining a tungsten sputtering target having such characteristics, a powder metallurgy method combining a hot press method (HP) and a hot isostatic pressing method (HIP) can be used. By controlling the appropriate conditions of HIP after HP as follows, the characteristics of the tungsten sputtering target of the present invention described above can be obtained. Further, in addition to the powder metallurgy method combining the HP method and the HIP method, the characteristics of the tungsten sputtering target of the present invention described above can also be obtained by performing a rolling process under appropriate conditions after the HP method.

[0023] First, in the HP process, tungsten powder as a raw material is filled into a predetermined mold, and a load is applied thereto for heat treatment. The tungsten powder used here preferably has a particle size of 5 μm or less. In the HP process, while raising the temperature at an appropriate heating rate, an appropriate load is applied for each temperature region to raise the temperature to the HP temperature, and the temperature is held at the HP temperature for a predetermined time. At this time, the heating rate is preferably about 2 to 10 ° C. / min. In this HP process, it is preferable to appropriately adjust and change the load applied in the temperature region of 600 to 1200 ° C. and the temperature region of 1200 ° C. or higher. Since degassing occurs at the initial stage of heating in the HP process, if a high load is applied during this process, sintering will proceed without sufficient degassing, the sintered body will not be densified, and it will contain a large amount of residual gas components such as oxygen inside. Therefore, in the HP process, by applying a low load in the low temperature region and a higher load in the high temperature region, the sintered body can be densified to obtain a sintered body with a low oxygen residue amount. Specifically, the load pressure in the temperature region of 600 to 1200 ° C. is 80 to 150 kg / cm 2 or so, and the load pressure in the temperature region of 1200 ° C. or higher is 200 to 350 kg / cm 2It is preferably set to such a degree. Also, during the heating process, introducing the step of maintaining at a constant temperature for a certain time several times is effective for obtaining a sintered body with high density and random orientation. The HP temperature at this time is preferably about 1600 to 1900 °C. If the HP temperature is too low, the density will not increase sufficiently, and if it is too high, the formation of the carbonized layer on the tungsten surface will progress, which is not preferable. If the heating rate is too fast, degassing in HP will not proceed sufficiently, which is not preferable. It is obvious that if the heating rate is too slow, it will lead to a decrease in productivity, which is not preferable. The holding time of this process is about 30 to 240 minutes and can be appropriately adjusted in consideration of conditions such as temperature. The holding time at the HP temperature can also be set and adjusted similarly.

[0024] For the HP-treated compact, in order to increase the average grain size of tungsten crystals and densify the compact, it is effective to subject the HP compact to HIP treatment. In the present invention, it is crucial that the temperature during HIP treatment is 1800 °C or higher and the treatment time is 5.5 hours or longer. By setting the HIP treatment conditions as the above conditions, a tungsten sputtering target with an average grain size of tungsten crystals exceeding 100 μm can be obtained. The pressure of HIP treatment can be adjusted with 1600 to 1900 kg / cm 2 as a reference. There is no particular limitation on the upper limit of the temperature during HIP treatment, but it is preferably 2200 °C or lower from the perspective of cost. There is no particular limitation on the upper limit of the time of HIP treatment, but it is preferably 8 hours or shorter from the perspective of cost.

[0025] Regarding the HP-treated compact, plastic working can also be performed by rolling instead of HIP. By adjusting the conditions of this hot rolling, the average grain size of tungsten crystals in the tungsten sputtering target of the present invention can be controlled. Specifically, the rolling temperature needs to be 1200°C or higher and 1700°C or lower, and it is important that the total reduction ratio is about 15 to 25%. Here, the total reduction ratio in the present invention is a numerical value obtained by multiplying the reduction ratio per pass by the number of passes in the rolling process. The reduction ratio per pass is represented by the following formula. The reduction ratio in one rolling is preferably about 3 to 12%. The number of passes is desirably 4 to 6 times. Reduction ratio per pass=(h n-1 -h n ) / h0 In the formula, h0 is the initial compact thickness, h n-1 is the compact thickness before rolling in the relevant pass, and h n is the compact thickness after rolling in the relevant pass.

Examples

[0026] Hereinafter, the present invention will be specifically described based on examples and comparative examples. The descriptions of the following examples and comparative examples are merely specific examples for facilitating the understanding of the technical content of the present invention, and the technical scope of the present invention is not limited by these specific examples.

[0027] (Examples 1 to 3) Tungsten powder with a purity of 5N (99.999 wt%) and an average particle size of 1 μm was filled in a carbon die, and HP was performed in a vacuum chamber under the condition of a maximum temperature of 1600°C. The HP load applied at that time was 240 kgf / cm 2 . Regarding the HP compact thus obtained, HIP treatment was further performed under the conditions shown in Table 1. Shape processing was performed on the sintered body subjected to HIP treatment to obtain a sputtering target with a diameter of 400 mm and a thickness of 6 mm.

[0028] (Example 4) The carbon die was filled with tungsten powder having a purity of 5N (99.999 wt%) and an average particle size of 1 μm, and HP was performed in a vacuum chamber under the condition of a maximum temperature of 1600 °C. The HP load applied at that time was 240 kgf / cm 2 was used. Regarding the HP compact obtained in this way, further rolling treatment was performed at 1400 °C with 6 passes of rolling, a reduction ratio of 4.2% per pass of rolling, and a total reduction ratio of 25%.

[0029] (Example 5) The carbon die was filled with tungsten powder having a purity of 5N (99.999 wt%) and an average particle size of 1 μm, and HP was performed in a vacuum chamber under the condition of a maximum temperature of 1600 °C. The HP load applied at that time was 240 kgf / cm 2 was used. Regarding the HP compact obtained in this way, further rolling treatment was performed at 1400 °C with 5 passes of rolling, a reduction ratio of 5.0% per pass of rolling, and a total reduction ratio of 25%.

[0030] (Example 6) The carbon die was filled with tungsten powder having a purity of 5N (99.999 wt%) and an average particle size of 1 μm, and HP was performed in a vacuum chamber under the condition of a maximum temperature of 1600 °C. The HP load applied at that time was 240 kgf / cm 2 was used. Regarding the HP compact obtained in this way, further rolling treatment was performed at 1700 °C with 4 passes of rolling, a reduction ratio of 3.8% per pass of rolling, and a total reduction ratio of 15%.

[0031] (Comparative Examples 1 to 3) The carbon die was filled with tungsten powder having a purity of 5N (99.999 wt%) and an average particle size of 1 μm, and HP was performed in a vacuum chamber under the maximum temperature conditions shown in Table 1. The HP load applied at that time was 240 kgf / cm 2 was used. Regarding the HP compact obtained in this way, HIP treatment was further performed under the conditions shown in Table 1. Shape processing was performed on the sintered body subjected to HIP treatment to obtain a sputtering target having a diameter of 400 mm and a thickness of 6 mm.

[0032] (Comparative Example 4) The carbon dies were filled with tungsten powder having a purity of 5N (99.999 wt%) and an average particle size of 1 μm, and HP was performed in a vacuum chamber under the condition of a maximum temperature of 1200°C. The HP load applied at that time was 240 kgf / cm 2 This was used as the standard. For the HP compact obtained in this way, further rolling treatment was performed at 1400°C with 8 passes of rolling, a reduction ratio of 11.3% per pass of rolling, and a total reduction ratio of 90%.

[0033] The obtained tungsten sputtering target was measured as follows. (Impurity Concentration) The carbon concentration was measured by the inert gas fusion method using a carbon analyzer [CSLS600 manufactured by LECO Corporation] after pulverizing each tungsten sputtering target. The oxygen concentration was measured by the inert gas fusion method using an oxygen / nitrogen simultaneous analyzer [TC-600 manufactured by LECO Corporation] for the above sample. (Average Particle Size of Tungsten Crystals) Microstructure observation was carried out using an optical microscope. In the observed and preserved tissue photographs, a straight line was drawn on the photograph until the number of particles N = 200, and the average particle size of the observed site was calculated using the number of particles (N ≥ 200) existing on the straight line and the total length of the straight line (L) as L / N. (Relative Density) The relative density referred to in this specification refers to the ratio of the measured density to the theoretical density. The measured density refers to the value measured by the Archimedes method using pure water as a solvent. For the theoretical density, the theoretical density when the tungsten content is 100% is used.

[0034] Furthermore, using the tungsten sintered body targets prepared in Examples 1 to 6 and Comparative Examples 1 to 4, a tungsten film was formed by sputtering using Ar gas on a silicon substrate, and the carbon concentration, oxygen concentration, Ar concentration, and specific resistance of the film were measured as follows. (Carbon Concentration, Oxygen Concentration, Ar Concentration) It was measured by secondary ion mass spectrometry (SIMS). The measuring device used was PHI ADEPT1010 manufactured by ULVAC-PHI, Inc. Note that "undetectable" in Table 1 means that it is less than the detection limit of the SIMS method. (Method for Measuring Specific Resistance) Using OMNIMAP RS75 manufactured by KLA-Tencor, the sheet resistance at 7 points on the wafer was measured, and the measured film thickness by XRR (X-ray reflectivity measurement) was multiplied, and the average value was taken as the specific resistance of the film.

[0035]

Table 1

[0036] In Examples 1 to 6, since the average particle diameter of the tungsten crystals exceeded 100 μm, few Ar atoms were incorporated into the film during film formation, and the specific resistance of the film was low. On the other hand, since the average particle diameter of the tungsten crystals in Comparative Examples 1 to 4 was 100 μm or less, many Ar atoms were incorporated into the film during film formation, and the specific resistance of the film was high.

[0037] In addition, some other forms of the present invention are specified as follows. (1) A tungsten sputtering target, wherein the purity of tungsten is 5N (99.999 wt%) or more, the impurities carbon and oxygen contained in tungsten are each 50 wtppm or less, and the average particle diameter of the tungsten crystals exceeds 100 μm. (2) The sputtering target according to (1), wherein the relative density is 99.3% or more. (3) The sputtering target according to (1) or (2), wherein the carbon and oxygen are each 10 wtppm or less. (4) A method for manufacturing a tungsten sputtering target, comprising forming tungsten powder by a hot pressing method (HP) and then densifying it by a hot isostatic pressing method (HIP). A method for manufacturing a tungsten sputtering target, characterized in that the temperature in the hot isostatic pressing method is 1800 °C or higher and the sintering time is 5.5 hours or longer. (5) A method for manufacturing a tungsten sputtering target, which comprises forming tungsten powder by a hot pressing method (HP) and then densifying it by a rolling method. A method for manufacturing a tungsten sputtering target, characterized in that the temperature in the rolling method is 1200 °C or higher and 1700 °C or lower, and the total reduction ratio is 15% or higher and 25% or lower. (6) The method for manufacturing a tungsten sputtering target according to (5), characterized in that the reduction ratio in each rolling in the rolling method is 3 to 12%.

Claims

1. A tungsten sputtering target (excluding those with added molybdenum (Mo)), characterized in that the purity of the tungsten is 5N (99.999 wt%) or more, the impurities of carbon and oxygen contained in the tungsten are each 10 wtppm or less, and the average grain size of the tungsten crystals is 347 μm or more.

2. A tungsten sputtering target comprising tungsten and impurities, the purity of the tungsten being 5N (99.999 wt%) or more, the impurities of carbon and oxygen contained in the tungsten being each 10 wtppm or less, and the average grain size of the tungsten crystals being 347 μm or more.

3. 3. The tungsten sputtering target according to claim 1, wherein the relative density is 99.3% or more.

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