Molybdenum-containing powder and target

Abstract

This molybdenum-containing powder has an average grain diameter as determined by Fisher sub-sieve sizer (FSSS) of 0.1 μm to 10 μm, a molybdenum content of at least 99.99 mass%, and a compressive deformation strength that exceeds 0 MPa but does not exceed 200 MPa.

Description

[Technical Field]

[0001] The present disclosure relates to a molybdenum-containing powder and a target. This application claims priority based on Japanese Patent Application No. 2023-176717, filed on October 12, 2023. All contents described in said Japanese patent application are incorporated herein by reference. [Background Art]

[0002] Conventionally, molybdenum-containing powders are disclosed in, for example, Japanese Patent Laid-Open No. 2005-133197 (Patent Document 1), Japanese Patent Laid-Open No. 2005-133198 (Patent Document 2), International Publication No. 2011-004887 (Patent Document 3), International Publication No. 2019-176962 (Patent Document 4), Japanese Patent Laid-Open No. 2005-314714 (Patent Document 5), and Japanese Patent Laid-Open No. 2005-314715 (Patent Document 6). [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Laid-Open No. 2005-133197 [Patent Document 2] Japanese Patent Laid-Open No. 2005-133198 [Patent Document 3] International Publication No. 2011-004887 [Patent Document 4] International Publication No. 2019-176962 [Patent Document 5] Japanese Patent Laid-Open No. 2005-314714 [Patent Document 6] Japanese Patent Laid-Open No. 2005-314715 [Brief Summary of the Invention]

[0004] The molybdenum-containing powder of this disclosure has an average particle size of 0.1 μm or more and 10 μm or less according to the Fsss method, a molybdenum content of 99.99% by mass or more, and a compressive deformation strength greater than 0 MPa and 200 MPa or less. [Modes for carrying out the invention]

[0005] [Issues this disclosure aims to address] Conventional methods involve manufacturing sintered bodies from molybdenum-containing powder. However, these sintered bodies have a problem with low density.

[0006] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described.

[0007] (Previous challenges) Conventionally, an intermediate product is produced by filling a reduction boat with ADM (ammonium molybdate) or MoO3 (molybdenum trioxide) powder, inserting it into a reduction furnace in a hydrogen atmosphere, and reducing it at a constant temperature. This intermediate product is then further heated at a high temperature to produce a powder containing molybdenum.

[0008] Patent documents 1 and 2 disclose coarse-grained high-purity metal molybdenum powder suitable for use as a raw material powder in the manufacture of high-purity metal molybdenum sintering targets for sputtering.

[0009] Patent Document 3 discloses high-purity molybdenum powder and a method for producing it. The molybdenum has a purity of 99.99% or higher and a primary particle content of 50% or higher. In the production method, hydrogen reduction of ammonium molybdate salt powder is performed. An aqueous solution of ammonium molybdate is brought into contact with a cation exchange resin to prepare an aqueous solution containing a molybdenum compound, which is then dried with a spray dryer. The resulting molybdenum oxide powder can be reduced to obtain a powder containing high-purity molybdenum.

[0010] Patent Document 4 describes a material with a purity of 99.999% or higher, a relative density of 98% or higher, an average particle size of 45 μm or less, and a radiation dose of 0.03 cph / cm³. 2Particles can be reduced by the following: Molybdenum powder is manufactured using a hot press (HP).

[0011] In conventional techniques, if there are voids in the molybdenum target for sputtering, sputtering is not uniform, and micro-voids are generated during film formation. Therefore, it is necessary to provide a target with a low porosity and high density. There has been a need to provide a molybdenum sputtering target capable of forming a molybdenum film with a low defect rate.

[0012] Generally, the sintering temperature of molybdenum is around 1800°C to 2000°C, and high-temperature heat treatment is essential to obtain a dense sintered body.

[0013] In powders containing molybdenum with a W content of 90 ppm or more, the compressive deformation strength of the powder is high, resulting in high surface tension and a low driving force for sintering densification. Therefore, powders containing molybdenum have poor sinterability, leading to higher sintering costs.

[0014] A higher volume diffusion coefficient in molybdenum-containing powders improves the driving force for sintering densification. When the molybdenum content is less than 99.99% or the W content is high, the volume diffusion coefficient is lowered due to inhibition by impurities and W. In other words, grain coarsening is less likely to occur in powders containing low-purity molybdenum.

[0015] Considering these factors, a high-purity molybdenum-containing powder capable of densifying sintered bodies was required.

[0016] By using a molybdenum-containing powder that is highly pure, has low compressive deformation strength, and is easily sintered and densified, the following effects can be expected.

[0017] First, it becomes possible to provide a molybdenum target with low porosity and high density, which suppresses the generation of microvoids during film deposition.

[0018] Low-temperature sintering is enabled, which reduces sintering costs and also reduces energy consumption, thereby contributing to solving energy problems.

[0019] EUV mask blanks are coated with a Mo / Si multilayer film, and the presence of 1 nm irregularities in the film causes a phase shift of 50° or more for a wavelength of 13.5 nm, which can become a defect. Using the high-density molybdenum target produced from the high-purity molybdenum-containing powder of the present disclosure can contribute to reducing defects during molybdenum film formation.

[0020] (Description of the Present Disclosure) The molybdenum-containing powder of the present disclosure has an average particle diameter measured by the Fsss method of 0.1 µm or more and 10 µm or less, a molybdenum content of 99.99% by mass or more, and a compressive deformation strength of more than 0 MPa and 200 MPa or less.

[0021] In the molybdenum-containing powder configured as described above, since the molybdenum content is 99.99% by mass or more, the compressive deformation strength is easily lowered. When the compressive deformation strength exceeds 200 MPa, the molybdenum-containing powder is less likely to deform, and voids are easily generated during sintering.

[0022] Tungsten is treated as an impurity, and when the molybdenum content is 99.99% by mass or more, the powder does not contain tungsten.

[0023] If the average particle diameter measured by the Fsss method is less than 0.1 µm, the powder is prone to ignition and becomes difficult to handle. If the average particle diameter measured by the Fsss method exceeds 10 µm, the density of a sintered body produced from the molybdenum-containing powder tends to decrease. More preferably, the average particle diameter measured by the Fsss method is 1 µm or more and 9 µm or less. Within this range, the powder can be handled most safely, and the density of the sintered body can be improved.

[0024] Preferably, the tungsten content is 90 ppm or less. Within this tungsten content range, the compressive deformation strength of the molybdenum-containing powder can be reliably reduced. More preferably, the tungsten content is 0 ppm or more and 10 ppm or less.

[0025] Preferably, the molybdenum content is 99.999% by mass or more. Within this molybdenum content range, the compressive deformation strength of the molybdenum-containing powder can be reliably reduced.

[0026] Preferably, the compressive deformation strength is greater than 0 MPa and 135 MPa or less. In this case, the deformation strength is small, so voids during sintering can be reliably reduced.

[0027] Preferably, the powder contains molybdenum, and a target is manufactured from a sintered body of the molybdenum-containing powder, and the surface irregularities of the mask blanks manufactured from the target by sputtering are less than 1 nm.

[0028] Preferably, the target is made of the above-mentioned molybdenum-containing powder, and the number of particles in the sputtered molybdenum thin film is 1 mm. 2 There are 50 or fewer within that limit.

[0029] When conventional molybdenum-containing powder is subjected to a 50 MPa load using a hot press, the sintering density is 93% at 1800°C for 200 minutes. However, the disclosed product achieves a sintering density of 98% or higher. This makes it possible to provide a high-density target with low porosity.

[0030] Normally, when sintered at 1800°C, a relative density of 90% or more is achieved after 60 minutes of sintering. However, in this disclosed product, a relative density of 97.5% or more is achieved after 60 minutes of sintering at 1800°C. This reduces sintering costs.

[0031] (Manufacturing method explanation) (1) Refining Process 1 MoO3 powder is sublimated in a roasting furnace at a temperature of 500°C to 650°C to remove molybdenum. The sublimated material adheres to the molybdenum lid, and the powder is collected to obtain MoO3 powder with a low wtr concentration. The wtr content decreases as the sublimation and rapid cooling are repeated at the appropriate temperature.

[0032] (2) Reduction Process 2: Raw material sieving After refining, the MoO3 powder is passed through a sieve with a predetermined mesh size to remove coarse and fine particles. The mesh size of the sieve is adjusted as appropriate depending on the raw material and the target molybdenum powder particle size.

[0033] Step 3: One-step reduction (MoO3 → MoO2) The MoO3 powder produced in step 1 is sieved. Then, the sieved powder is filled into a molybdenum boat (molybdenum content of 99.99% by mass or more). The optimal reduction conditions (temperature, hydrogen flow rate, raw material input amount, equipment used, etc.) are appropriately selected to achieve the target powder particle size. This completes the first stage of reduction.

[0034] Process 4: Intermediate sieving The MoO2 powder is sieved. The mesh size of the sieve is adjusted as appropriate depending on the raw material and the target molybdenum powder particle size.

[0035] Step 5: Two-stage reduction (MoO2 → Mo) The MoO2 powder after intermediate sieving is packed into a molybdenum boat (molybdenum content of 99.99% by mass or higher). The reduction conditions are adjusted according to the target Fsss particle size. The powder is reduced until it contains metallic molybdenum, and then removed from the boat.

[0036] Process 6: Final sieving The resulting molybdenum-containing powder is sieved. The mesh size of the sieve is adjusted as appropriate depending on the raw materials and the target particle size of the molybdenum-containing powder.

[0037] [Details of the embodiments of this disclosure] <Examples> In Example 1 of Sample No. 1 below, the following steps are performed: Step 1: Refining, Step 2: Raw material sieving, Step 3: Single-stage reduction, Step 4: Intermediate sieving, Step 5: Double-stage reduction, Step 6: Final sieving, Step 7: Sintering, Step 8: Sputtering, and Thin film evaluation.

[0038] <Process Details> Step 1: Refining MoO3 powder with a low wt concentration is obtained by heating and sublimating the MoO3 powder and then rapidly cooling it.

[0039] The sublimation temperature is preferably between 500°C and 800°C. Below 500℃, sublimation of MoO3 powder is slow. Above 650℃, WO3 powder sublimation increases, making it difficult to obtain MoO3 powder with a low W content.

[0040] By repeating the sublimation and rapid cooling process multiple times, a MoO3 powder with a low wtr content can be obtained.

[0041] Process 2: Raw material sieving The MoO3 powder refined in step 1 is sieved.

[0042] Step 3: One-step reduction (MoO3 → MoO2) The MoO3 sieved in step 2 is packed into a molybdenum boat to a thickness of 35 mm. A pusher-type reduction furnace is used with a hydrogen flow rate of 5 m³. 3 MoO2 is obtained by performing a reduction treatment under the conditions of / h and a reduction temperature of 500°C.

[0043] The preferred thickness of MoO3 when filling the board is between 20mm and 50mm. Exceeding this thickness may hinder the reduction of the raw materials within the board. Below this thickness, it is not industrially viable (in terms of cost and efficiency).

[0044] The hydrogen flow rate is 3m 3 / h or more is preferable. 3m 3 If the rate is less than / h, there is a risk that the reduction of raw materials inside the boat will not proceed properly.

[0045] The reduction temperature is preferably between 450°C and 650°C. Above 650°C, the temperature approaches the melting point, potentially causing the raw materials to melt. Below 450°C, the reduction of the raw materials in the boat may not proceed properly.

[0046] Process 4: Intermediate sieving The MoO2 obtained in step 3 is sieved with a mesh size of 1 mm. The coarse particles are removed and the sieved portion is collected. A mesh size of 1 mm or less is preferable. If it exceeds 1 mm, the agglomerated powder may not be removed, and the reduction of the remaining agglomerated powder may not proceed.

[0047] Step 5: Two-stage reduction (reduction of MoO2) The MoO2 remaining after intermediate sieving is packed into a molybdenum boat to a thickness of 20 mm. A pusher-type reduction furnace is used with a hydrogen flow rate of 10 m³. 3 The reduction process is carried out at a reduction temperature in the range of approximately 600-1260°C, depending on the target Fsss particle size. The powder containing metallic molybdenum is reduced and then extracted.

[0048] A thickness of 20mm to 50mm is preferable. If it exceeds 50mm, the reduction of raw materials inside the boat may not proceed properly. A thickness of less than 20mm is not industrially viable (in terms of cost and efficiency).

[0049] The hydrogen flow rate is 5m 3 / h or more is preferable. 5m 3 If the rate is less than / h, there is a risk that the reduction of raw materials inside the boat will not proceed properly.

[0050] A reduction temperature of 600°C or higher is preferable. Below 600°C, the reduction of the raw materials inside the boat may not proceed properly.

[0051] Process 6: Final sieving The obtained molybdenum-containing powder is then sieved using a sieve with a mesh size of 500 μm or less to remove coarse aggregates that tend to clog the sieve. This allows the powder below the sieve to be recovered.

[0052] Step 7: Sintering Using the powders obtained in steps 1-6, molybdenum sintered bodies were manufactured at a pressure of 50 MPa and a heating temperature of 1800°C for 60 to 200 minutes. Furthermore, high-purity metallic molybdenum sintered targets were manufactured by removing surface oxides through machining.

[0053] Step 8: Spattering Of the targets manufactured in step 7, those with a low wattage content and a relative density of 99% or higher (sample numbers 4, 7, 11, and 15) were brazed onto a pure copper backing plate. This was then mounted in a DC magnetron sputtering apparatus.

[0054] Sputtering was performed using Ar as the sputtering gas and a sputtering power of 300W. A high-purity metallic molybdenum thin film with a thickness of 0.3μm was formed on the entire surface of a Si wafer with a diameter D of 100mm.

[0055] Sample numbers 1 to 29 and sample numbers 101 to 104 The number of sublimation and cooling cycles was changed based on sample number 1. This resulted in the production of samples 2 through 29. The results are shown in Tables 1 and 2.

[0056] [Table 1]

[0057] [Table 2]

[0058] Sample number 101 was manufactured according to Patent Document 1 (Japanese Patent Publication No. 2005-133197). Sample number 102 was manufactured according to Patent Document 3 (International Publication No. 2011-004887).

[0059] In Tables 1 and 2, "Mo" indicates the molybdenum content (mass%) in the molybdenum-containing powder.

[0060] The molybdenum content is analyzed using a flat-cell glow discharge mass (GD-MS) spectroscopy. Under an Ar atmosphere, a glow discharge is performed with the sample as the negative electrode. The Ar gas collides with the sample, causing the constituent elements to sputter. The elements released by sputtering are ionized in the Ar plasma. The ionized atoms are measured using a dual-focusing mass spectrometer to determine the element's qualitative properties and concentration.

[0061] The molybdenum content was calculated based on the formula: Content = 100% - 14 elements [Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Si, Sn, Na, K, W]. Tungsten (W) is treated as an impurity.

[0062] "Compressive strength" refers to the strength measured by a microcompression test (single or particle crushing strength). The unit is "MPa". The equipment used is a Shimadzu Corporation microcompression tester MCT-510. A small amount of particles is scattered on the sample stage. A load is applied to a single particle placed between the upper flat indenter and the lower sample stage at a constant increasing rate. The crushing strength of the particle is measured as the compressive deformation strength from the deformation behavior of the sample at this time. The test force and compressive displacement during the deformation process of the sample are measured and recorded.

[0063] "Fsss" refers to the average particle size measured by the Fsss method. The unit is "μm". Fsss is measured using the Fisher method. The instrument used for measurement is the Fisher Scientific Fisher Sub-Sieve Sizer Model 95. A sample of true density is filled into a sample tube, the porosity is determined from the sample height, air at a pressure of 1 MPa is passed through it, and the manometer water level is read as a value on the calculator chart. This value is expressed in μm as the average particle size. Fsss represents the average particle size of the powder, and a lower value indicates a smaller average particle size.

[0064] "W" indicates the tungsten content (ppm mass%) in the molybdenum-containing powder. Similar to the measurement of the molybdenum content described above, the tungsten content is analyzed using a flat-cell glow discharge mass (GD-MS) analysis. When a glow discharge is performed with the sample as the negative electrode in an Ar atmosphere, the Ar gas collides with the sample, sputtering the constituent elements of the sample. The elements released by sputtering are ionized in the Ar plasma. The ionized tungsten atoms are measured using a double-focusing mass spectrometer to calculate the tungsten content.

[0065] "Sublimation temperature" refers to the sublimation temperature in step 1. The unit is "°C". The number of sublimation-cooling cycles is the number of sublimation and cooling cycles in step 1. If this number is 1, it indicates that sublimation and cooling occurred once.

[0066] "Relative density 200Min" is the relative density of the sintered body after sintering for 200 minutes in step 7. "Relative density 60Min" is the relative density of the sintered body after sintering for 60 minutes in step 7. The density of the sintered body is measured using the Archimedes method.

[0067] These results indicate that the compressive strength of the molybdenum-containing powder is low in samples 1 through 29. Consequently, the relative density of the sintered body produced from this powder is high.

[0068] In contrast, the molybdenum-containing powder in comparative samples 101 to 104 exhibits high compressive strength. As a result, the relative density of the sintered body produced from this powder is lower.

[0069] Next, according to step 7, molybdenum targets were manufactured from the sintered bodies of samples 4, 7, 11, 15, 101, 103, and 104. Sputtering was performed using these targets to form a molybdenum thin film on a wafer. The number of particles with a maximum diameter of 0.1 μm or larger within a 1 mm square (1 mm × 1 mm) area of ​​this molybdenum thin film was measured using a scanning electron microscope JSM-6460LA (manufactured by JEOL Ltd.). This measurement was performed at five locations on a single wafer, and the average value from these five locations was calculated. The results are shown in Table 3.

[0070] [Table 3]

[0071] Table 3 shows that the molybdenum thin films produced by sputtering targets manufactured from sample numbers 4, 7, 11, and 15 had a low particle count and yielded good results. In contrast, the comparative examples, sample numbers 101, 103, and 104, had a high particle count and showed a decrease in target quality.

[0072] Furthermore, multilayer mask blanks composed of molybdenum and silicon laminates were fabricated by sputtering targets manufactured from sample numbers 4, 7, 11, and 15. The surface roughness of these mask blanks was confirmed to be less than 1 nm. The surface roughness of the mask blanks was measured using an atomic force microscope (AFM). By bringing a nanometer-sized probe close to the sample and detecting the interatomic force acting between the needle tip and the sample, the surface roughness of the mask blanks was detected.

[0073] Note 1 A molybdenum-containing powder having an average particle size of 0.1 μm or more and 10 μm or less according to the Fsss method, a molybdenum content of 99.99% by mass or more, and a compressive deformation strength greater than 0 MPa and 200 MPa or less.

[0074] Note 2 A powder containing molybdenum as described in Appendix 1, with a tungsten content of 90 ppm or less.

[0075] Note 3 A powder containing molybdenum as described in Appendix 1 or 2, wherein the molybdenum content is 99.999% by mass or more.

[0076] Note 4 A powder containing molybdenum as described in any one of the appendices 1 to 3, wherein the compressive deformation strength is greater than 0 MPa and less than or equal to 135 MPa.

[0077] Note 5 A molybdenum-containing powder as described in any one of the appendices 1 to 4, wherein a target is manufactured from a sintered body of the molybdenum-containing powder, and the surface irregularities of a mask blank manufactured from the target by sputtering are less than 1 nm.

[0078] Note 6 A target comprising a sintered body of molybdenum-containing powder as described in any one of Appendix 1 to 5, wherein the number of particles with a maximum diameter of 0.1 μm or more on a 1 mm² area of ​​a molybdenum thin film sputtered using the target is 50 or less.

[0079] The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included.

Claims

1. A molybdenum-containing powder having an average particle size of 0.1 μm or more and 10 μm or less according to the Fsss method, a molybdenum content of 99.99% by mass or more, a tungsten content of 90 ppm or less, a compressive deformation strength greater than 0 MPa and 200 MPa or less, a molybdenum content calculated based on the formula 100% - 14 elements [Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Si, Sn, Na, K, W], and tungsten (W) treated as an impurity.

2. A powder containing molybdenum according to claim 1, wherein the molybdenum content is 99.999% by mass or more.

3. The molybdenum-containing powder according to claim 1 or 2, wherein the compressive deformation strength is greater than 0 MPa and less than or equal to 135 MPa.

4. A molybdenum-containing powder according to claim 1 or 2, wherein a target is manufactured from a sintered body of the molybdenum-containing powder, and the surface irregularities of a mask blank manufactured from the target by sputtering are less than 1 nm in height.

5. A target comprising a sintered body of molybdenum-containing powder according to claim 1 or 2, wherein a 1 mm molybdenum thin film is sputtered using the target. ２ A target having 50 or fewer particles with a maximum diameter of 0.1 μm or larger on its surface area.

6. A powder containing molybdenum according to claim 1 or 2, wherein the molybdenum content is 99.9991% by mass or less.

7. A powder containing molybdenum according to claim 1 or 2, wherein the compressive deformation strength is 100 MPa or more and 160 MPa or less.

8. A powder containing molybdenum according to claim 1 or 2, wherein the tungsten content is 0.1 ppm or more and 90 ppm or less.

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