Molybdenum sputtering target, method for producing same, and method for forming molybdenum film

Abstract

Disclosed is a molybdenum sputtering target in which the content of metal impurities is 100 ppm by mass or less, the tungsten content is 50 ppm by mass or less, and the oxygen concentration is 50 ppm by mass or less.

Description

Technical Field

[0001] The present invention relates to a molybdenum sputtering target, a method for manufacturing the same, and a method for forming a molybdenum film. Background Art

[0002] In recent years, as a means for forming an electronic circuit pattern of a semiconductor, EUV lithography using extreme ultraviolet (EUV) has attracted attention. A mask blank (EUV mask blank) used in EUV lithography is manufactured by alternately laminating a silicon thin film and a molybdenum thin film on a glass substrate by a sputtering method, and a molybdenum sputtering target can be used for forming the molybdenum thin film.

[0003] As a conventional molybdenum sputtering target, for example, a sputtering target having a molybdenum content of 99.99 mass% or more, a relative density of 98% or more, and an average grain size of 400 μ μm or less has been reported (Patent Document 1), and thus generation of particles during sputtering can be effectively reduced. In addition, a molybdenum sputtering target that can provide a thin film with low particles and excellent pattern formation processability has been disclosed, in which the total concentration of Cd, Cr, Fe, Mn, Ni, Ca, Co, Cu, Mg, Pb, Ti, Zn, Si, and Al in the sputtering target is 50 ppm or more and 1000 ppm or less, and the relative density is 99% or more (Patent Document 2).

[0004] Prior Art Documents Patent Documents Patent Document 1: WO 2019 / 176962 Patent Document 2: JP-A-2005-154814 Summary of the Invention Technical Problem to be Solved by the Invention In order to suppress generation of particles during sputtering, it is required that the molybdenum sputtering target used in the manufacture of EUV mask blanks has a further increased purity, that is, a molybdenum content rate, as compared with conventional molybdenum sputtering targets. However, from the viewpoints of particle improvement and yield improvement in the manufacture of EUV mask blanks, reduction of metal impurities in the molybdenum sputtering targets of Patent Document 1 and Patent Document 2 is not sufficient. In addition, Patent Document 1 discloses that tungsten is an inevitable impurity, that is, molybdenum contains tungsten and it is difficult to separate tungsten from molybdenum.

[0005] An object of the present invention is to provide at least one of a molybdenum sputtering target in which metal impurities, particularly tungsten, are further reduced as compared with conventional molybdenum sputtering targets, a method for manufacturing the same, and a method for forming a molybdenum film using the same.

[0006] Technical Solution for Solving the Technical Problem The inventors of the present invention and the like have studied the reduction of metal impurities in a molybdenum sputtering target, particularly the reduction of tungsten. As a result, the inventors of the present invention and the like have found a method for separating tungsten, which has been difficult to separate from molybdenum in the past, and thereby can reduce the tungsten in the molybdenum sputtering target.

[0007] That is, as shown in the claims of the present invention, in addition, the gist of the present invention is as follows.

[0008] (1) A molybdenum sputtering target, wherein the content of metal impurities is 100 mass ppm or less, the tungsten content is 50 mass ppm or less, and the oxygen concentration is 50 mass ppm or less.

[0009] (2) The molybdenum sputtering target according to (1) above, wherein the content of metal impurities is 70 mass ppm or less, the tungsten content is 45 mass ppm or less, and the oxygen concentration is 45 mass ppm or less.

[0010] (3) The molybdenum sputtering target according to (1) or (2) above, wherein the content of metal impurities is 10 mass ppm or more, the tungsten content is 5 mass ppm or more, and the oxygen concentration is 5 mass ppm or more.

[0011] (4) The molybdenum sputtering target according to any one of (1) to (3) above, wherein the ratio R of the tungsten content (mass ppm) to the content of metal impurities (mass ppm) W is 0.9 or less.

[0012] (5) The molybdenum sputtering target according to any one of (1) to (4) above, wherein the ratio R of the tungsten content (mass ppm) to the content of metal impurities (mass ppm) W is 0.1 or more.

[0013] (6) The molybdenum sputtering target according to any one of (1) to (5) above, wherein the metal impurities are Li, Be, B, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Th, U, and W.

[0014] (7) A method for manufacturing a molybdenum sputtering target, which manufactures the molybdenum sputtering target according to any one of the above (1) to (6). The manufacturing method includes: a first ion exchange step, in which a first molybdenum solution is brought into contact with a first ion exchange resin one or more times to obtain a second molybdenum solution, and the first ion exchange resin is one type of ion exchange resin among cation exchange resins or anion exchange resins; a second ion exchange step, in which the second molybdenum solution is brought into contact with a second ion exchange resin one or more times to obtain a third molybdenum solution containing a solvent and a precipitate, and the second ion exchange resin is the other type of ion exchange resin different from the first ion exchange resin among cation exchange resins or anion exchange resins; an oxidation step, in which the precipitate after removing the solvent from the third molybdenum solution is subjected to an oxidation treatment to obtain molybdenum oxide powder; a reduction step, in which the molybdenum oxide powder is reduced to form molybdenum powder; and a sintering step, in which the molybdenum powder is sintered under pressure.

[0015] (8) According to the manufacturing method described in the above (7), wherein the oxidation treatment is a heat treatment performed in an air atmosphere at a temperature of 400 °C or higher.

[0016] (9) According to the manufacturing method described in the above (7) or (8), wherein the pressure sintering is at least one of hot pressing and hot isostatic pressing (HIP).

[0017] (10) A method for forming a molybdenum film, which includes: a step of manufacturing a molybdenum film by sputtering using the molybdenum sputtering target according to any one of the above (1) to (6).

[0018] Advantages of the Invention According to the present invention, it is possible to provide at least one of a molybdenum sputtering target in which metal impurities, particularly tungsten, are further reduced compared to conventional molybdenum sputtering targets, a manufacturing method thereof, and a method for forming a molybdenum film using the same.

[0019] Preferably, by using the molybdenum sputtering target of the present invention, the amount of particles generated during sputtering can be reduced compared to the prior art. Description of the Drawings

[0020] Figure 1 It is a cross-sectional view showing an embodiment of the molybdenum sputtering target of the present invention.

[0021] Figure 2 It is a cross-sectional view showing a substrate with a molybdenum film manufactured by an embodiment of the method for forming a molybdenum film of the present invention. Detailed Embodiments

[0022] Hereinafter, the present invention will be described in detail. However, the description of the constituent elements described below is an example of an embodiment of the present invention, and the present invention is not limited to these contents. In addition, in the present invention, any combination of the structures and parameters disclosed in this specification is included. Moreover, the range of any combination of the upper and lower limits of the values disclosed in this specification is also included in the present invention.

[0023] <Molybdenum Sputtering Target> This embodiment relates to a molybdenum sputtering target (hereinafter, also referred to as "Mo target"). In this embodiment, the Mo target refers to a target mainly composed of molybdenum and a target substantially composed of molybdenum. In particular, it is a target mainly composed of molybdenum and used for sputtering, especially a target with a molybdenum content of 99.9 mass% or more.

[0024] The content of metal impurities in the Mo target of this embodiment is 100 mass ppm or less. If the content of metal impurities exceeds 100 mass ppm, the amount of particles during sputtering increases. The content of metal impurities in the Mo target is preferably 80 mass ppm or less, 70 mass ppm or less, 65 mass ppm or less, 50 mass ppm or less, 45 mass ppm or less, 30 mass ppm or less, or 20 mass ppm or less.

[0025] The Mo target of this embodiment preferably does not contain metal impurities (that is, the total of metal impurities is 0 mass ppm), but the Mo target may also contain metal impurities. In this case, the total content of metal impurities in the Mo target of this embodiment can be exemplified as exceeding 0 mass ppm, 0.01 mass ppm or more, 0.1 mass ppm or more, 1 mass ppm or more, 5 mass ppm or more, 10 mass ppm or more, 15 mass ppm or more, or 18 mass ppm or more. The total content of metal impurities in the Mo target of this embodiment is preferably more than 0 mass ppm and 65 mass ppm or less, more preferably 0.01 mass ppm or more and 45 mass ppm or less, and further preferably 0.1 mass ppm or more and 20 mass ppm or less.

[0026] The "metal impurities" in this embodiment refer to metal elements other than molybdenum. Specifically, they are Li, Be, B, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Th, U, and W.

[0027] The tungsten content in the Mo target of the present embodiment is 50 mass ppm or less, preferably 45 mass ppm or less, 30 mass ppm or less, 25 mass ppm or less, 20 mass ppm or less, 15 mass ppm or less, or 10 mass ppm or less. Generally, tungsten is regarded as an inevitable impurity of molybdenum. Needless to say, the difference between the two, and their separation is very difficult. Therefore, in the purification of Mo targets to high purity, mainly the reduction of the amount of metal elements other than tungsten has been studied in the past. In contrast, in the present embodiment, attention is paid to the following situation: tungsten is the cause of an increase in particles, and if the W concentration exceeds 50 mass ppm, particles are likely to be generated during sputtering. The Mo target of the present embodiment preferably does not contain tungsten (that is, the total of tungsten is 0 mass ppm), but the Mo target may also contain tungsten. In this case, the total content of tungsten in the Mo target of the present embodiment can be exemplified as exceeding 0 mass ppm, 0.01 mass ppm or more, 0.1 mass ppm or more, 1 mass ppm or more, 5 mass ppm or more, or 10 mass ppm or more. The total content of tungsten in the Mo target of the present embodiment is preferably more than 0 mass ppm and 45 mass ppm or less, more preferably 0.01 mass ppm or more and 25 mass ppm or less, and further preferably 0.1 mass ppm or more and 10 mass ppm or less.

[0028] The ratio R of the content of tungsten (mass ppm) to the content of metal impurities (mass ppm) W As long as it is 1 or less, there is no particular limitation, but from the viewpoint of suppressing the generation of particles during sputtering, the smaller the better. The ratio R W For example, it is preferably 0.9 or less, 0.8 or less, 0.7 or less, 0.65 or less, or 0.6 or less.

[0029] As the above ratio R W , for example, it can be exemplified as 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, or 0.5 or more. The ratio R W is preferably 0.1 or more and 0.7 or less, more preferably 0.2 or more and 0.65 or less, and further preferably 0.3 or more and 0.6 or less.

[0030] In the present embodiment, the content of metal impurities and the content of tungsten can be measured by glow discharge mass spectrometry (GDMS) using a common glow discharge mass spectrometer (for example, ELEMENT GD PLUS, manufactured by ThermoFisher Scientific). As the conditions for GDMS measurement, the following conditions can be cited.

[0031] (Measurement conditions) Discharge gas: High-purity Ar (purity: 99.9999 vol%) Discharge conditions: 12 mA, 0.8 kV Analysis area: A region with a diameter of 8 mm The oxygen concentration in the Mo target of the present embodiment is 50 mass ppm or less. If the oxygen concentration exceeds 50 mass ppm, the amount of particles generated during sputtering increases. Oxygen is the cause of particle generation, so the oxygen concentration is preferably low, for example, preferably 45 mass ppm or less, 40 mass ppm or less, 35 mass ppm or less, 30 mass ppm or less, 25 mass ppm or less, 20 mass ppm or less, 15 mass ppm or less, or 10 mass ppm or less. In addition, the oxygen concentration can be exemplified as 0.05 mass ppm or more, 0.5 mass ppm or more, 1 mass ppm or more, 5 mass ppm or more, or 10 mass ppm or more. The oxygen concentration is preferably 0.05 mass ppm or more and 45 mass ppm or less, more preferably 0.5 mass ppm or more and 30 mass ppm or less, and further preferably 1 mass ppm or more and 20 mass ppm or less.

[0032] In the present embodiment, for the "oxygen concentration", as long as it is based on JIS Z 2613, using an oxygen-nitrogen analyzer (for example, model: ON736, manufactured by LECO Corporation), when the measurement sample is heated to 3000 °C, measure CO and CO 2 mass, and based on the mass of CO and CO 2 mass, calculate the mass ratio [mass ppm] of oxygen per unit mass of the measurement sample.

[0033] Measurement method: Pulse furnace melting-infrared absorption method Mass of the measurement sample: 0.1 ± 0.05 g The relative density of the Mo target of the present embodiment is preferably 98% or more, 99% or more, 99.3% or more, 99.5% or more, or 99.8% or more. By making the relative density high, the amount of particles generated during sputtering is more easily reduced.

[0034] The "relative density" in the present embodiment is represented by the following formula.

[0035] Relative density = (measured density / true density) × 100 (%) Here, the measured density is a value that can be measured by the Archimedes method based on JIS R 1634, and the true density is the density of a target with a molybdenum content of 100 mass% (10.22 g / cm 3 )

[0036] The relative density is preferably high. The relative density can be 99.9% or less or 99.99% or less.

[0037] <Manufacturing method of Mo target> The Mo target of the present embodiment can be manufactured by the following manufacturing method, which includes: a first ion exchange step in which a molybdenum solution (first molybdenum solution) is brought into contact with one of a cation exchange resin and an anion exchange resin (first ion exchange resin) more than once to obtain a second molybdenum solution; a second ion exchange step in which the molybdenum solution after the first ion exchange step (the above-mentioned second molybdenum solution) is brought into contact with the other ion exchange resin (second ion exchange resin) different from the first ion exchange resin among the above-mentioned cation exchange resin and the above-mentioned anion exchange resin more than once to obtain a third molybdenum solution containing a solvent and a precipitate; an oxidation step in which the precipitate remaining after removing the solvent from the molybdenum solution (third molybdenum solution) after the second ion exchange step is oxidized to obtain molybdenum oxide powder; a reduction step in which the molybdenum oxide powder is reduced to obtain molybdenum powder; and a firing step in which the above-mentioned molybdenum powder is pressure-fired. Hereinafter, the first molybdenum solution, the second molybdenum solution, or the third molybdenum solution may also be referred to as "molybdenum solution" respectively.

[0038] The manufacturing method of the present embodiment includes a first ion exchange step and a second ion exchange step (hereinafter, the first ion exchange step and the second ion exchange step are collectively referred to as "ion exchange steps"), in which the first ion exchange step brings the first molybdenum solution into contact with one of a cation exchange resin and an anion exchange resin (first ion exchange resin) more than once; the second ion exchange step brings the molybdenum solution after the first ion exchange step (second molybdenum solution) into contact with the other ion exchange resin (second ion exchange resin) different from the first ion exchange resin among the cation exchange resin and the anion exchange resin more than once. Thereby, the contents of metal impurities and tungsten in the Mo target can be reduced.

[0039] The number of times the molybdenum solution in the ion exchange step is brought into contact with the cation exchange resin or the anion exchange resin is more than once respectively, and it is more preferably more than twice. Among them, the number of times of contact can also be 5 times or less respectively. There is no particular limitation on which of the contact of the molybdenum solution with the cation exchange resin or the contact of the molybdenum solution with the anion exchange resin is carried out first. For example, the first molybdenum solution can be brought into contact with the cation exchange resin in the first ion exchange step, and then the second molybdenum solution can be brought into contact with the anion exchange resin in the second ion exchange step, or the first molybdenum solution can be brought into contact with the anion exchange resin in the first ion exchange step, and then the second molybdenum solution can be brought into contact with the cation exchange resin in the second ion exchange step. It is preferred that the first molybdenum solution is brought into contact with the cation exchange resin in the first ion exchange step, and then the second molybdenum solution is brought into contact with the anion exchange resin in the second ion exchange step.

[0040] By contacting a molybdenum solution with a cation exchange resin, metal cations dissolved as cations in the molybdenum solution are adsorbed and removed. The metal cations adsorbed on the cation exchange resin can be exemplified by one or more selected from chromium, iron, nickel, calcium, cobalt, copper, magnesium, and aluminum.

[0041] The cation exchange resin supplied to the ion exchange process is not particularly limited as long as it is a resin having the ability to exchange metal cations. For example, strongly acidic cation exchange resins having strongly acidic sulfo groups as exchange groups can be mentioned. As specific cation exchange resins, one or more selected from DIAION SK1B, DIAION SK110, AMBERLITE IR120B, and DOWEX50WX8 can be mentioned.

[0042] The contact between the molybdenum solution and the anion exchange resin is carried out for the purpose of removing tungsten dissolved as a metal anion in the molybdenum solution. In order to reduce the tungsten content, the contact between the molybdenum solution and the anion exchange resin is preferably carried out 2 or more times. On the other hand, when the tungsten concentration in the molybdenum solution reaches equilibrium, even if the contact between the molybdenum solution and the anion exchange resin is increased, no tungsten reduction effect is obtained. Therefore, the contact between the molybdenum solution and the anion exchange resin may be 4 or less times.

[0043] The anion exchange resin supplied to the ion exchange process is not particularly limited as long as it is a resin that exchanges metal anions. Styrene-based macroporous weakly basic anion exchange resins can be mentioned. As specific anion exchange resins, one or more selected from DIAION WA10, DIAION WA20, DIAION WA30, AMBERLITE IRA96SB, AMBERLITE IRA98, DOWEX66, and DOWEX77 can be mentioned.

[0044] The contact between the molybdenum solution and the ion exchange resin can be carried out by any contact method, and at least one of stirring and mixing and passing the solution can be mentioned. Preferably, the molybdenum solution is passed through the ion exchange resin.

[0045] The space velocity SV (Space Velocity) during passing the solution is not particularly limited. For example, it is 2 h -1 or more and 20 h -1 or less. If the space velocity SV is within the above range, impurities can be reduced without impairing productivity. In addition, the space velocity SV is preferably 3 h -1 or more or 4 h -1 or more, and preferably 15 h -1 or less or 10 h -1 or less.

[0046] The molybdenum solution used in the ion exchange process may be an acid solution containing at least one of metallic molybdenum and molybdenum compounds, preferably an acid solution containing metallic molybdenum. Examples of the acid contained in the acid solution include one or more selected from peroxyacid, hydrochloric acid, and sulfuric acid, and preferably at least one of peroxyacid and hydrochloric acid. The molybdenum concentration in the molybdenum solution is preferably 50 g / L or more and 300 g / L or less. If the molybdenum concentration is within the above range, a decrease in productivity and the precipitation of molybdic acid when passing through the ion exchange resin can be suppressed. The molybdenum concentration is more preferably 100 g / L or more and 200 g / L or less.

[0047] In the oxidation process, the precipitate remaining after removing the solvent from the third molybdenum solution after the second ion exchange process is oxidized to obtain molybdenum oxide powder.

[0048] The method for removing the solvent from the third molybdenum solution is arbitrary as long as the molybdenum solution (third molybdenum solution) obtained by the second ion exchange process is dried. The drying method is not particularly limited as long as it can remove the solvent. For example, it can be mentioned that the third molybdenum solution is dried in an air atmosphere at a temperature of 60°C or more and 100°C or less for a time of 48 hours or more and 96 hours or less (evaporation drying method).

[0049] The oxidation treatment may be any method that can oxidize the precipitate remaining after removing the solvent from the third molybdenum solution, and the precipitate may be heated (e.g., fired) in an air atmosphere at a temperature of 400°C or more. The upper limit of the firing temperature (heating temperature) can be exemplified as 600°C.

[0050] In the reduction process, the molybdenum oxide powder is reduced to obtain molybdenum powder. The reduction atmosphere is not particularly limited, and examples include one or more selected from a hydrogen-containing atmosphere, a carbon monoxide-containing atmosphere, and an ammonia-containing atmosphere, and preferably a hydrogen-containing atmosphere. In the reduction in a hydrogen-containing atmosphere, the molybdenum oxide is fired in a furnace in a hydrogen atmosphere. The treatment temperature is not particularly limited, and preferably 900°C or more and 1200°C or less. By setting the treatment temperature within the above temperature range, the reduction reaction from molybdenum oxide to molybdenum is carried out, and molybdenum powder with a low oxygen content can be easily obtained. More preferably, the above treatment temperature is 950°C or more and 1150°C or less.

[0051] In the firing process, the above molybdenum powder is subjected to pressure firing. The firing method may be pressure sintering (also referred to as "pressure firing"), and examples of this pressure sintering include at least one of hot pressing and hot isostatic pressing (HIP).

[0052] In addition, in the firing process, as the molybdenum powder, its non-formed body (non-compacted powder) can be supplied, or its formed body (compacted powder) can be supplied instead of the non-formed body. The method of forming the molybdenum powder is not particularly limited, and for example, at least one of pressing and cold isostatic pressing (CIP) treatment can be cited. A formed body (CIP formed body) is obtained by subjecting the primary formed body obtained by pressing to CIP treatment. The pressure as a condition of pressing can be exemplified as 5 MPa or more and 50 MPa or less, and in addition, the pressure as a condition of CIP treatment can be exemplified as 100 MPa or more and 500 MPa or less.

[0053] The shape of the formed body of molybdenum powder (molybdenum formed body) only needs to be any shape that can be used for pressure sintering, and one or more selected from a disc shape, a column shape, and a polyhedron shape can be exemplified.

[0054] In order to increase the density of the sintered body and make it easy to reduce the oxygen concentration contained in the sintered body, pressure sintering is preferably hot pressing and hot isostatic pressing (HIP).

[0055] The hot pressing temperature is preferably 1300 °C or more and 1500 °C or less. By setting the hot pressing temperature within the above temperature range, the oxygen contained in the sintered body can be sufficiently reduced. The hot pressing temperature is more preferably 1350 °C or more and 1450 °C or less. The hot pressing pressure is preferably 1 MPa or more and 100 MPa or less, and further preferably 10 MPa or more and 70 MPa or less. The heating rate until reaching the hot pressing temperature is arbitrary, and can be exemplified as 100 °C / hour or more and 800 °C / hour or less, preferably 300 °C / hour or more and 700 °C / hour or less.

[0056] The atmosphere for hot pressing only needs to be a vacuum atmosphere.

[0057] The holding time at the hot pressing temperature is not particularly limited, and can be set to any time according to the amount of molybdenum supplied to the firing process, the firing method, the characteristics of the firing furnace used, etc., and can be appropriately determined in such a way as to reduce the oxygen concentration of the sintered body after hot pressing. As the holding time at the hot pressing temperature, for example, 1 hour or more and 15 hours or less can be cited.

[0058] In order to achieve an increase in the density of the sintered body after hot pressing and a decrease in the oxygen content, vacuum firing can be performed on the sintered body after hot pressing and before HIP treatment. The conditions for vacuum firing are not particularly limited, and for example, firing can be performed in a vacuum atmosphere at 1600 °C or more and 1800 °C or less.

[0059] After hot pressing, in order to obtain a sintered body with high density, it is preferable to perform hot isostatic pressing (HIP) treatment. The temperature of the HIP treatment is preferably 1600 °C or higher and 1900 °C or lower. By setting it within the above temperature range, the density of the sintered body can be increased. The heating rate until reaching the temperature of the HIP treatment is arbitrary, and examples thereof include 100 °C / hour or higher and 800 °C / hour or lower, and preferably 300 °C / hour or higher and 700 °C / hour or lower. The atmosphere for the HIP treatment only needs to be a non-oxidizing atmosphere, preferably an inert atmosphere or a reducing atmosphere, and more preferably an argon atmosphere. The pressure of the HIP treatment is preferably 50 MPa or higher and 200 MPa or lower. By setting the pressure of the HIP treatment within the above pressure range, the density of the sintered body can be increased. The treatment time is not particularly limited and can be appropriately determined according to the characteristics of the HIP treatment furnace used in such a way that the relative density becomes a sufficient value. As the firing time, for example, 1 hour or more and 15 hours or less can be cited.

[0060] The sintered body obtained by the above pressure sintering can be directly used as a Mo target, and alternatively, it can be used as a Mo target by processing it into a desired size. In addition, a Mo target product including a bonded body of a Mo target and a back plate can be manufactured by bonding a Mo target including the above HIP sintered body or its processed body to the back plate.

[0061] <Method for forming molybdenum film> The method for forming a molybdenum film according to the present embodiment includes a step of manufacturing a molybdenum film by sputtering using the Mo target of the present embodiment. Specifically, by using Figure 1 the Mo target 1 shown, it is possible to manufacture Figure 2 the molybdenum film 20 shown.

[0062] As Figure 2 shown, the substrate 100 with a molybdenum film includes a substrate 10 and a molybdenum film 20 formed on the substrate 10. By using the Mo target 1 for sputtering, it is possible to provide a molybdenum film 20 in which generation of particles is suppressed during film formation.

[0063] The substrate 10 is not particularly limited, and examples thereof include a glass substrate and a quartz substrate.

[0064] The temperature of the substrate 10 (film formation temperature) is not particularly limited, and for example, it can be room temperature (25 °C).

[0065] The process gas during film formation is not particularly limited as long as it is a gas type that generates sputtering by discharge, and for example, it can be argon.

[0066] The discharge power during film formation is not particularly limited, and for example, it can be 2.5 W / cm 2 or more and 50 W / cm 2 or less.

[0067] The film formation time is not particularly limited. For example, it can be 10 minutes or more and 60 minutes or less.

[0068] Sputtering can be carried out using a common sputtering device. The conditions for sputtering are not particularly limited. Sputtering can be carried out, for example, under the following conditions.

[0069] Discharge method: Ion beam sputtering Target size: 4 inches Target tilt angle: 45° Introduced gas: Argon Microwave power supply: 100 W Substrate: 4-inch silicon wafer Substrate plane orientation: (001) plane Acceleration voltage: 2 kW Film formation temperature: 25 °C Film formation time: 10 min Vacuum degree: 7×10 -4 Pa The evaluation of the number of particles in the molybdenum film 20 of this embodiment can be carried out, for example, using an atomic force microscope (SPM-9600: manufactured by Shimadzu Corporation).

[0070] Specifically, the evaluation of the number of particles can be carried out in the following manner.

[0071] From a circular plate-shaped silicon wafer with a molybdenum film of radius R, a total of 5 parts including 1 point at the center of the wafer, 2 points at a position 0.5R away from the center of the wafer, and 2 points at the outer peripheral part (the part at a position R away from the center of the wafer), cut out a part with a size of 15 mm×15 mm, perform ultrasonic cleaning for 120 seconds using acetone of electronic industry grade, and then dry it using compressed nitrogen to make a measurement sample. Then, for the surface of the molybdenum film of the measurement sample in the area of 2 μ m×2 μ m, observe 5 fields of view for each measurement sample, a total of 25 fields of view, and calculate by converting the number of detected particles into the number per 1 cm×1 cm area.

[0072] The analysis can be carried out using open-source software Gwyddion. Based on the maximum height (TOP) and minimum height (BTM) of the AFM image, which is the image observed by the atomic force microscope (AFM), set the height threshold at the position of the height that is 30% away from the minimum height based on the value of TOP - BTM (100%), and further define the island-shaped part with a circle conversion diameter of 15 nm or more above the height threshold as a particle.

[0073] Examples Hereinafter, the present invention will be described by way of examples, but the present invention is not limited to the following examples.

[0074] (Example 1) 150 g of commercially available molybdenum powder (purity: 99.95%, particle size: 3 - 7 μ m, product name: PD - 8002, manufactured by Starck) and 750 g of pure water were put into a polyethylene container to obtain a slurry. After placing the polyethylene container in a constant temperature bath at 25°C, the slurry was stirred while being cooled, and 544 g of hydrogen peroxide (special grade reagent, purity: 99.99%, manufactured by Fujifilm Wako Pure Chemical Corporation) was slowly added to the slurry so that the temperature rise caused by the heat of reaction did not exceed 65°C. After adding hydrogen peroxide, it was cooled to room temperature, and then the dissolved residue was removed by filtration to obtain an acid solution. After calculating the amount of molybdenum in the acid solution from the amount of molybdenum in the dissolved residue, pure water was added to the acid solution so that the molybdenum concentration became 120 g / L, thereby obtaining a molybdenum solution.

[0075] The molybdenum solution was passed through a cation exchange resin (product name: AMBERLITE IR120B, manufactured by Organo) once, and then passed through an anion exchange resin (product name: AMBERLITE IRA96SB, manufactured by Organo) once. The flow rate through both the cation exchange resin and the anion exchange resin was set to SV = 6 h -1 . After drying the molybdenum solution passed through the ion exchange resin in an air atmosphere at 80°C for 72 hours to remove the solvent, the remaining precipitate was calcined in an air atmosphere at 500°C for 2 hours to obtain molybdenum oxide powder. The molybdenum oxide powder was calcined under the following calcination conditions to perform hydrogen reduction, obtaining 125 g of molybdenum powder.

[0076] (Calcination conditions) Heating rate: 600°C / hour Calcination atmosphere: Hydrogen Calcination temperature: 1100°C Calcination time: 5 hours A total of 6 times of dissolution to calcination of molybdenum powder were carried out to obtain 750 g of molybdenum powder. The obtained molybdenum powder was filled into a mold with a diameter of 150 mm × height of 50 mm, and after being compression - molded at a pressure of 20 MPa, it was CIP - molded at a pressure of 300 MPa to obtain a CIP - formed body in the shape of a circular plate with a diameter of 122 mm × thickness of 9 mm. The CIP - formed body was subjected to hot - pressing treatment under the following conditions to obtain a hot - pressed sintered body.

[0077] (Treatment conditions) Heating rate: 600°C / hour Atmosphere: Vacuum Holding temperature: 1350 °C Pressure: 50 MPa Holding time: 10 hours Next, HIP treatment was performed on the hot press sintered body under the following conditions. The relative density of the HIP sintered body obtained by HIP treatment was 99.0%.

[0078] (Processing conditions) Heating rate: 600 °C / hour Atmosphere: argon Holding temperature: 1800 °C Pressure: 100 MPa Holding time: 10 hours The obtained HIP sintered body was cut and ground into a diameter of 101.6 mm × thickness of 6 mm to fabricate the Mo target of this example.

[0079] (Example 2) The number of liquid passages in the anion exchange resin was set to 2 times and the pressure of hot pressing was set to 80 MPa. Except for this, the Mo target of this example was fabricated by the same method as in Example 1.

[0080] (Example 3) The liquid passage rates in the cation exchange resin and the anion exchange resin were set to SV = 4 h -1 , after passing the liquid 3 times in the cation exchange resin and then passing the liquid 3 times in the anion exchange resin, the firing temperature and firing time as the hydrogen reduction treatment conditions were set to 1200 °C and 5 hours respectively, the holding temperature, holding time and pressure as the hot pressing treatment conditions were set to 1400 °C, 5 hours and 100 MPa respectively, and the holding temperature, holding time and pressure as the HIP treatment conditions were set to 1850 °C, 5 hours and 200 MPa respectively. Except for this, the Mo target was fabricated by the same method as in Example 1.

[0081] (Comparative Example 1) No liquid passage was performed in the cation exchange resin and the anion exchange resin. Except for this, the Mo target was fabricated by the same method as in Example 1.

[0082] (Comparative Example 2) No liquid passage was performed in the anion exchange resin. Except for this, the Mo target was fabricated by the same method as in Example 1.

[0083] Table 1 shows the manufacturing conditions of the Mo target, and Table 2 shows the relative density and impurity analysis results (impurity content) of the Mo target.

[0084] [Table 1] [Table 2] (Film formation of Mo film) The Mo targets obtained in Example 1 and Comparative Example 1 were machined respectively, and then joined to a backplane made of oxygen-free copper to fabricate Mo target products each including a joined body of the Mo target and the backplane. Then, under the following conditions, sputtering was carried out using the Mo target of the Mo target product to form a Mo film on a substrate.

[0085] (Sputtering conditions) Discharge method: Ion beam sputtering Target size: 4 inches Target tilt angle: 45° Introduced gas: Argon Microwave power supply: 100 W Substrate: 4-inch silicon wafer Substrate plane orientation: (001) plane Acceleration voltage: 2 kV Film formation temperature: 25°C Film formation time: 10 min Vacuum degree: 7×10 -4 Pa (Calculation of the number of particles) For the Mo film obtained by the above method, the number of particles was calculated. The number of particles was determined using an atomic force microscope (SPM-9600, manufactured by Shimadzu Corporation). Specifically, from a total of 5 parts including 1 part at the center of the silicon wafer with the Mo film, 2 parts at positions 0.5R away from the center of the wafer, and 2 parts in the peripheral part (the part at a position R away from the center of the wafer), parts with a size of 15 mm×15 mm were cut out. For this part, after ultrasonic cleaning with acetone at the electronic industry level for 120 seconds, it was dried using compressed nitrogen to prepare a measurement sample. Then, for a 2 μ m×2 μ m area on the surface of the Mo film of the measurement sample, observations were made for a total of 25 fields of view with 5 fields of view for each measurement sample. The number of detected particles was converted to the number per 1 cm×1 cm area for calculation. The analysis was performed using open-source software Gwyddion. Based on the maximum height (TOP) and minimum height (BTM) of the AFM image, which is the image observed by the atomic force microscope (AFM), the height threshold was set at the position of the height that is 30% of the minimum height based on the value of TOP - BTM (100%). Furthermore, the island-shaped parts with a converted diameter of 15 nm or more and above the height threshold were defined as particles. Table 3 shows the calculation results of the number of particles during film formation using the Mo target.

[0086] [Table 3] It should be noted that this application is based on the Japanese patent application filed on November 30, 2022 (Japanese Patent Application No. 2022-191776), the whole of which is incorporated by reference. In addition, all references cited herein are incorporated as a whole.

[0087] Description of Reference Numerals 1…Mo target (molybdenum sputtering target), 20…molybdenum film.

Claims

1. A molybdenum sputtering target, characterized in that, the content of metallic impurities is 100 mass ppm or less, the tungsten content is 50 mass ppm or less, and the oxygen concentration is 50 mass ppm or less.

2. The molybdenum sputtering target according to claim 1, wherein, the content of metallic impurities is 70 mass ppm or less, the tungsten content is 45 mass ppm or less, and the oxygen concentration is 45 mass ppm or less.

3. The molybdenum sputtering target according to claim 1 or 2, wherein, the content of metallic impurities is 10 mass ppm or more, the tungsten content is 5 mass ppm or more, and the oxygen concentration is 5 mass ppm or more.

4. The molybdenum sputtering target according to any one of claims 1 to 3, wherein, The ratio R of the content of tungsten in the content of metallic impurities W is 0.9 or less, and the unit of the content is mass ppm.

5. The molybdenum sputtering target according to any one of claims 1 to 4, wherein, The ratio R of the content of tungsten in the content of metallic impurities W is 0.1 or more, and the unit of the content is mass ppm.

6. The molybdenum sputtering target according to any one of claims 1 to 5, wherein, the metallic impurities are Li, Be, B, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Th, U, and W.

7. A method for manufacturing a molybdenum sputtering target according to any one of claims 1 to 6, characterized in that, it has: a first ion exchange step, in which a first molybdenum solution is brought into contact with a first ion exchange resin one or more times to obtain a second molybdenum solution, and the first ion exchange resin is one of a cation exchange resin and an anion exchange resin; a second ion exchange step, in which the second molybdenum solution is brought into contact with a second ion exchange resin one or more times to obtain a third molybdenum solution containing a solvent and a precipitate, and the second ion exchange resin is the other ion exchange resin different from the first ion exchange resin among a cation exchange resin and an anion exchange resin; an oxidation step, in which the precipitate remaining after removing the solvent from the third molybdenum solution is oxidized to obtain molybdenum oxide powder; a reduction step, in which the molybdenum oxide powder is reduced to produce molybdenum powder; and a firing step, in which the molybdenum powder is pressure-fired.

8. The manufacturing method according to claim 7, wherein, the oxidation treatment is heat treatment performed in an air atmosphere at a temperature of 400 °C or higher.

9. The manufacturing method according to claim 7 or 8, wherein, the pressure firing is at least one of hot pressing and hot isostatic pressing (HIP).

10. A method for forming a molybdenum film, characterized in that, it includes: a step of manufacturing a molybdenum film by sputtering using the molybdenum sputtering target according to any one of claims 1 to 6.

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