Sputtering target and method for manufacturing sputtering target

Abstract

A sputtering target that is 10–20 at% B, the remainder including Fe. As observed by SEM image, the average area of Fe-B phases of the sputtering target is no more than 20 μm2.

Description

Technical Field

[0001] This specification discloses a technology related to a sputtering target and a method for manufacturing the sputtering target.

Background Art

[0002] Among non-volatile memories that retain memory without power supply, there is a magnetic resistance memory (MRAM) that stores memory based on the magnetization state of a magnetic tunnel junction.

[0003] In a magnetic resistance memory, a material added with boron may be used for the perpendicular magnetization film of a tunnel magnetoresistance element as its component. Such a perpendicular magnetization film can be formed by a sputtering method using a sputtering target containing boron and at least one of iron and cobalt.

[0004] Examples of sputtering targets containing boron used for such magnetic resistance memories or other applications include those described in Patent Documents 1 to 4.

[0005] Patent Documents 1 and 2 describe "a magnetic material sputtering target made of a sintered body in which the content of B is 26 at% or more and 40 at% or less, and the remainder is one or more elements selected from Co or Fe, wherein there are a high-concentration phase of B and a low-concentration phase of B in the target, and the diameter of the largest inscribed circle that can be drawn in the high-concentration phase of B is 15 μm or more and there is one or less." Patent Documents 1 and 2 also describe "a method for manufacturing a magnetic material sputtering target, wherein a magnetic material target raw material powder in which the content of B is 26 at% or more and 40 at% or less, and the remainder is one or more elements selected from Co or Fe, is produced by a gas atomization method, this gas atomized raw material powder is sintered to form a target, the target has a structure in which a high-concentration phase of B and a low-concentration phase of B exist, and the high-concentration phase of B in which the diameter of the largest inscribed circle that can be drawn in the high-concentration phase of B is 15 μm or more is one or less."

[0006] Patent Documents 3 and 4 disclose a sputtering target material consisting of, in at.%, 10 to 50% of B, with the balance being at least one of Co and Fe and inevitable impurities, in which the intensity ratio [I((CoFe) 2 B(200))] of the X-ray diffraction intensity of B(200) to the X-ray diffraction intensity of (CoFe) 2 B and the intensity ratio [I((CoFe) 3 B(121))] of the X-ray diffraction intensity of B(121) to the X-ray diffraction intensity of (CoFe) 3 B, [I((CoFe) 3 B) / I((CoFe) 2 B)] is 1.50 or less, a CoFeB-based alloy sputtering target material is described.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] In the sputtering target containing boron as described above, particularly in the case of containing boron in a predetermined amount and further containing iron, a large number of particles are generated during sputtering, which causes a problem of reducing the product yield.

[0009] This specification discloses a sputtering target capable of effectively reducing particles and a method for manufacturing the sputtering target.

Means for Solving the Problems

[0010] The sputtering target disclosed in this specification contains B at 10 at% to 20 at%, with the balance being Fe, and the average area of the Fe-B phase by SEM image observation is 20 μm 2 as follows.

[0011] The method for manufacturing the sputtering target disclosed in this specification includes a sintering step of holding a raw material powder containing B at 10 at% to 20 at% and containing Fe at a temperature of 800°C or higher and lower than 900°C for 1 hour to 3 hours while applying pressure See, in the sintering process, the heating rate until reaching the temperature is set to 5 °C / min or more, and the cooling rate after reaching the temperature is set to 1 °C / min or more. is as follows.

Advantages of the Invention

[0012] According to the sputtering target described above, particles during sputtering can be effectively reduced.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0014] Hereinafter, the embodiments disclosed in this specification will be described in detail. The sputtering target of one embodiment contains B at 10 at% to 20 at%, with the balance being Fe, and the average area of the Fe-B phase by SEM image observation is 20 μm 2 as follows. This sputtering target is obtained, for example, as a sintered body of the raw material powder after a sintering step of holding a predetermined raw material powder at a temperature of 800°C or higher and lower than 900°C for 1 hour to 3 hours while applying pressure, as described later.

[0015] (Composition) The sputtering target shall contain at least B (boron) and Fe (iron). The content of B shall be 10 at% to 20 at%, preferably 14 at% to 20 at%, more preferably 16 at% to 20 at%. If the content of B is too low, it is considered that the film formed with the sputtering target cannot exhibit the desired characteristics. On the other hand, if the content of B is too high, the sinterability of the powder deteriorates, and particles are generated at a level that cannot be solved only by optimizing the sintering conditions.

[0016] The content of Fe is, for example, 5 at% to 80 at%, typically 20 at% to 65 at%.

[0017] The sputtering target may further contain Co. In this case, the content of Co is preferably 5 at% to 80 at%, and more preferably 20 at% to 65 at%.

[0018] The purity, which is the total content of B, Fe and Co, is preferably 3N (99.9 mass%) or more. When Co is not included, the content of Co is 0 (zero) mass%. This is because if the purity is less than 3N, impurities may cause particle generation. The purity is more preferably 3N5 (99.95 mass%) or more. This purity can be determined by GDMS analysis.

[0019] In addition, the sputtering target may contain impurities such as Si and / or Ni, etc. in a total amount of 100 mass ppm or less in addition to the above-described elements. Impurities contained in such an amount are acceptable.

[0020] (Fe-B phase) In the sputtering target having the composition as described above, an Fe-B phase exists. The Fe-B phase in the sputtering target is observed by an SEM (scanning electron microscope) image for a cross section orthogonal to the sputtering surface used for sputtering, and its average area is 20 μm 2 or less. Thereby, the surface roughness of the post-use sputtering surface described later after subjecting the sputtering surface to predetermined sputtering is improved. As a result, the generation of particles during use by sputtering can be effectively reduced.

[0021] From this viewpoint, the average area of the Fe-B phase in the sputtering target is preferably 15 μm 2 or less, and more preferably 10 μm 2 or less. The average area may be, for example, 2 μm 2 or more, typically 5 μm 2 or more.

[0022] The above-mentioned average area of the Fe-B phase is obtained by calculating the total area and the number of Fe-B phases within the field of view of the SEM image of the cross-section orthogonal to the sputtering surface through image analysis, and dividing the total area by the number. In SEM images, usually when two or more phases exist, a contrast between two or more phases occurs such that relatively light elements such as B appear black, while relatively heavy elements appear white (see, for example, FIGS. 1 and 2). Among the Fe-B phases that appear black in the SEM image, those that are adjacent and connected to each other are counted as one Fe-B phase as a whole. Also, when a Fe-B phase existing at the outer edge of the SEM image only partially enters the field of view of the SEM image, only the area of the part that enters the field of view is considered, and that part is regarded as one Fe-B phase and counted. FIG. 3 shows the result of performing image analysis on the SEM image of FIG. 2 and identifying the Fe-B phases that appear black in the SEM image. By performing image analysis on the SEM image in this way, it is possible to calculate the total area and the number of Fe-B phases. When calculating the average area of the Fe-B phase, it is sufficient to analyze a single SEM image of the above-mentioned cross-section.

[0023] (Surface roughness of the sputtering surface after use) In the above-mentioned sputtering target, it is desirable that the surface roughness Ra of the sputtering surface after use that appears after performing predetermined sputtering using it is small. Specifically, when the sputtering target is set in a sputtering apparatus and used up to 60 kWh at an output of 600 W, the surface roughness Ra of the sputtering surface after use of the sputtering target is preferably 2.0 μm or less. As this sputtering apparatus, the model number C-7100GT manufactured by Canon Anelva can be used.

[0024] As a result, the grain boundaries between the Fe-B phase and other phases with different sputtering rates become less prominent, the occurrence of arcing and the like can be suppressed, and particles can be further reduced. In other words, in the sputtering target where the surface roughness Ra of the sputtered surface after use exceeds 2.0 μm, there is a risk of particle generation due to arcing or the like.

[0025] The surface roughness Ra of the sputtered surface after use is more preferably 1.5 μm or less. On the other hand, the surface roughness Ra of the sputtered surface after use may be, for example, 0.4 μm or more.

[0026] (Density ratio) The density ratio of the sputtering target is preferably greater than 99%. This is because when the density ratio is greater than 99%, internal defects of the target that cause particle generation can be reduced. In this regard, the density ratio is more preferably 99.9% or more. The density ratio of the sputtering target is measured by the Archimedes method.

[0027] The density ratio of the sputtering target is calculated from the theoretical density calculated by calculation and the measured density measured by the Archimedes method using the formula: density ratio = (measured density measured by the Archimedes method) ÷ (theoretical density) × 100 (%). Here, the theoretical density is the density when it is assumed that the constituent components of the sputtering target are mixed without diffusing or reacting with each other, and is calculated by the formula: theoretical density = Σ (molecular weight of constituent components × molar ratio of constituent components) / Σ (molecular weight of constituent components × molar ratio of constituent components / literature value density of constituent components). However, in reality, since each element of FeCoB exists in a reactive state, the true value of the target sputtering target may be higher than the above theoretical density. Therefore, the density ratio calculated using the above theoretical density may exceed 100%.

[0028] (Manufacturing method) The sputtering target described above can be manufactured, for example, as follows.

[0029] First, a raw material preparation step is performed to prepare a raw material powder containing B at 10 at% to 30 at% and containing Fe. The raw material powder shall have the content of each element adjusted so as to obtain the composition of the predetermined sputtering target as described above. Therefore, the raw material powder may further contain Co as required. When the raw material powder contains Co, the content of Co can be 5 at% to 80 at%.

[0030] When producing the raw material powder, it is preferable to use the gas atomization method from the viewpoint of reducing the oxygen content of the raw material powder. In the gas atomization method, for example, under an inert gas atmosphere, high-pressure gas is sprayed onto a molten metal in which B, Fe, Co, etc. are dissolved to make it powdery. Also, for example, by sieving the gas atomized powder, etc., it is preferable to make the average particle size D50 of the raw material powder 50 μm to 300 μm. Thereby, the sintering of the raw material powder in the subsequent sintering step becomes easy, and it becomes possible to obtain a sputtering target with a high density.

[0031] Next, the above raw material powder can be subjected to a sintering step of being pressurized and held at a predetermined temperature for a predetermined time. Thereby, a predetermined sintered body is obtained. For this sintering, a vacuum hot press method or other hot press methods, a plasma discharge sintering method, or a hot isostatic pressing method, etc. can be used.

[0032] Here, it is important that the temperature during pressurization is 800 °C or higher and less than 900 °C, and this temperature is held for 1 hour to 3 hours. By making the temperature during pressurization relatively low and the holding time relatively short in this way, grain growth is suppressed, and the above-mentioned average area of the sputtering target can be reduced. Also, thereby, the structure becomes finer, so the surface roughness Ra of the sputtering surface after use described above also becomes smaller.

[0033] More specifically, if this temperature is less than 800°C, the density will not increase sufficiently. On the other hand, if the temperature is 900°C or higher, it will cause an increase in the average area and surface roughness Ra, and as a result, the particles will increase during sputtering. When the holding time is less than 1 hour, the density will not increase sufficiently. Also, when the holding time is longer than 3 hours, the average area and surface roughness Ra will increase due to grain growth over time.

[0034] From such a perspective, the temperature during pressurization is preferably 800°C or higher and less than 900°C, and more preferably 850°C or higher and less than 900°C. Also, the holding time is 1 hour to 3 hours, more preferably 1 hour to 2 hours.

[0035] Also, the heating rate until reaching the above temperature is preferably 5°C / min or higher, and more preferably 5°C / min to 10°C / min. Further, in the cooling after reaching the above temperature, the cooling rate is preferably 1°C / min or higher. By increasing the heating rate and cooling rate, the heating time can be made shorter, further suppressing grain growth and achieving a significant reduction in the average area and surface roughness Ra. To achieve a predetermined cooling rate, forced cooling such as air cooling may be employed.

[0036] In the sintering process, the pressure, atmosphere, etc. can be appropriately determined according to various conditions. For example, the pressure can be 15 MPa to 30 MPa, and the atmosphere can be a vacuum atmosphere, etc.

[0037] After that, generally, the above sintered body is machined into a predetermined shape such as a disc by a lathe or surface grinding, etc., and its surface is polished. Thereby, a sputtering target can be manufactured.

Examples

[0038] Next, a sputtering target as described above was prototyped and its performance was confirmed, which will be described below. However, the description here is for illustrative purposes only and is not intended to be limiting.

[0039] Raw material powder prepared by the gas atomization method and adjusted to contain B, Co, and Fe with the composition shown in Table 1 was prepared. This raw material powder was pressurized under a vacuum atmosphere under the conditions of temperature, holding temperature, and heating rate shown in Table 1 to obtain a sintered body. The pressure was 29.42 MPa. The obtained sintered body was subjected to predetermined machining and polishing to fabricate a sputtering target.

[0040] For each sputtering target fabricated under different sintering conditions as shown in Table 1, the average area of the Fe-B phase, the surface roughness of the sputtering surface after use, and the density ratio were measured by the method described above. The results are also shown in Table 1. In addition, SEM images of the cross-sections orthogonal to the sputtering surfaces of the sputtering targets of Comparative Example 1 and Example 1 are shown in FIGS. 1 and 2, respectively.

[0041] In addition, using each sputtering target, sputtering was performed under the conditions of a power of 600 W, an Ar flow rate of 30 sccm, and a target film thickness of 20 nm using a C-7100GT manufactured by Canon Anelva. As a result, the number of particles shown in Table 1 was obtained.

[0042]

Table 1

[0043] As can be understood from Table 1, in Examples 1 to 8 held at a temperature of 800 °C or higher and lower than 900 °C for 1 to 3 hours during sintering, the average area became smaller. As a result, Examples 1 to 8 had a small number of particles during sputtering.

[0044] In Comparative Example 1, due to the high temperature during sintering, the average area increased and the number of particles increased. In contrast, in Comparative Example 2, due to the low temperature during sintering, there were many pores and the average area could not be measured. In this Comparative Example 2, the number of particles was large. In Comparative Example 3, due to the long temperature holding time during sintering, the average area increased and the number of particles was large. In Comparative Examples 4 and 5, the B content was high, the average area could not be measured due to pores, and the number of particles increased.

[0045] Therefore, it can be said that in Examples 1 to 8, the particles during sputtering were effectively reduced.

Claims

1. A sputtering target containing B in an amount of 10 at% to 20 at%, with the balance being Fe, and having an average area of the Fe-B phase by SEM image observation of 20 μm 2 or less.

2. The average area of the Fe—B phase is 15 μm 2 The sputtering target according to claim 1, wherein the above is 15 μm or less.

3. The average area of the Fe—B phase is 10 μm 2 The sputtering target according to claim 2, wherein the average area is 10 μm or less.

4. The sputtering target according to any one of claims 1 to 3, wherein when used at an output of 600 W up to 60 kWh using a sputtering apparatus, the surface roughness Ra of the sputtering surface after the use is 2.0 μm or less.

5. The sputtering target according to any one of claims 1 to 4, having a density ratio greater than 99%.

6. The sputtering target according to any one of claims 1 to 5, having a purity of 3N or more.

7. The sputtering target according to any one of claims 1 to 6, further containing Co and having a Co content of 5 at% to 80 at%.

8. A method for manufacturing a sputtering target, comprising: a sintering step of holding a raw material powder containing B at 10 at% to 20 at% and containing Fe at a temperature of 800°C or higher and lower than 900°C for 1 hour to 3 hours while applying pressure; The method for manufacturing a sputtering target, wherein in the sintering step, the heating rate until reaching the temperature is 5°C / min or more, and the cooling rate after reaching the temperature is 1°C / min or more.

9. The method for manufacturing a sputtering target according to claim 8, wherein in the sintering step, the temperature is 850°C or higher and lower than 900°C.

10. The method for manufacturing a sputtering target according to claim 8 or 9, wherein the raw material powder further contains Co at 5 at% to 80 at%.

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