Target, sintered body, and manufacturing method thereof

Abstract

Provided are: a target in which the shift of composition is suppressed and which comprises Mg and Ga; a sintered body; and methods respectively for producing the target and the sintered body.　The target has a composition represented by the formula: MgxGayO4 in which an y / x value, which is a compositional ratio between x and y, is 1.90 to 2.10, and has a relative density of 87% or more.

Description

[Technical Field]

[0001] The present invention relates to a target, a sintered body, and a method for producing the same, and more particularly to a target containing Mg and Ga as a composition, a sintered body, and a method for producing the same. [Background technology]

[0002] A magnetoresistive element is a magnetic sensor that measures the magnitude of a magnetic field based on the principle of the magnetoresistive effect. The magnetoresistive element is used in magnetic recording read heads, etc. The magnetoresistive element has a layered structure. The layered structure includes two magnetic layers, and a spacer layer or insulating layer between the two. This spacer layer or insulating layer functions as a tunnel barrier, contributing to the performance of the magnetoresistive element. Patent Documents 1 and 2 disclose MgGa2O4 as one of the materials for the spacer layer or insulating layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-027896 [Patent Document 2] Japanese Patent Application Publication No. 2019-012810 Summary of the Invention [Problem to be solved by the invention]

[0004] One method for forming the above-mentioned layer structure is a sputtering method. For example, the present inventors attempted to manufacture a new MgGa2O4 target for use in forming the above-mentioned spacer layer or insulating layer.

[0005] The composition of the target may be inherited by the composition of the compound in the spacer layer or insulating layer. Therefore, it is important to strictly control the composition of the target. If there is a deviation in the composition of the target, this deviation will be inherited when the spacer layer or insulating layer is formed by a sputtering method, and ultimately, this deviation may affect the performance of the spacer layer or insulating layer as a tunnel barrier.

[0006] In view of the above circumstances, an object of the present invention is to provide a target containing Mg and Ga in which deviation in composition is suppressed, a sintered body, and methods for producing the same. [Means for solving the problem]

[0007] The metallic element Ga that constitutes MgGa2O4 has the property of easily volatilizing at high temperatures. Therefore, if Ga volatilizes during the process of manufacturing an MgGa2O4 target, deviations in the composition of the final target product will occur. After extensive research, the inventors have discovered several important points in the target manufacturing process, particularly when producing a sintered body by hot pressing. The first point is that Ga is easily volatilized when sintered in a vacuum atmosphere. The second point is that there is an appropriate sintering temperature range that can prevent Ga volatilization. The third point is that there are appropriate pressing conditions that can prevent Ga volatilization.

[0008] The present invention was completed based on the above findings, and in one aspect includes the following inventions. (Invention 1) Mg x Ga y A target having a composition represented by O4, The value of y / x, which is the composition ratio of x to y, is 1.90 to 2.10, Targets with relative density of 87% or higher. (Invention 2) The target of Invention 1, wherein the value of x is 0.90 to 1.10. (Invention 3) 3. The target according to invention 1 or 2, having a purity of 4N or more. (Invention 4) 4. The target according to any one of Inventions 1 to 3, wherein the impurity concentration is less than 100 ppm by mass. (Invention 5) A method for producing a target according to any one of inventions 1 to 4, The method comprises: providing a raw material powder; hot pressing to produce a sintered body; Including, The hot pressing is carried out so as to satisfy all of the following conditions: Atmosphere: Inert gas atmosphere Sintering temperature: 1200~1300℃ Pressure: 250kgf / cm 2 End (Invention 6) 6. The method of claim 5, wherein the providing step includes synthesizing using raw material powder having a purity of 4N or higher. (Invention 7) Mg x Ga y A sintered body having a composition represented by O4, The value of y / x, which is the composition ratio of x to y, is 1.90 to 2.10, A sintered body having a relative density of 87% or more. (Invention 8) The sintered body of Invention 7, wherein the value of x is 0.90 to 1.10. (Invention 9) 9. The sintered body according to invention 7 or 8, having a purity of 4N or more. (Invention 10) 10. The sintered body according to any one of inventions 7 to 9, wherein the impurity concentration is less than 100 ppm by mass. [Effects of the Invention]

[0009] In one aspect, the value of y / x, which is the composition ratio of x to y, is 1.90 to 2.10. That is, deviation in composition is suppressed. Furthermore, it is possible to suppress the loss of the desired function when the film is formed, which would be caused by deviation in composition. DETAILED DESCRIPTION OF THE INVENTION

[0010] Specific embodiments for carrying out the present invention will be described below. The following description is intended to facilitate understanding of the present invention and is not intended to limit the scope of the present invention.

[0011] 1. Targets and sintered bodies 1-1.Composition In one embodiment, the present invention relates to a target and a sintered body containing Mg and Ga. The composition of the Mg and Ga contained in the target and the sintered body is expressed as follows: Mg x Ga y O4 Here, the value of y / x, which is the composition ratio of x to y, is 1.90 to 2.10. Within this composition ratio range, the performance requirements for the film can be met when the film is formed. The value is preferably 1.95 to 2.05, and more preferably 2.00 or less (no volatilization of Ga occurs).

[0012] The value of x is preferably 0.90 to 1.10, more preferably 0.95 to 1.05. From the viewpoint of the theoretical value derived from Mg1Ga2O4, the Mg concentration (at %) is preferably 14.3%±1.4%, more preferably 14.3%±0.7%.

[0013] The value of y is preferably 1.80 to 2.20, more preferably 1.90 to 2.10. From the viewpoint of the theoretical value derived from Mg1Ga2O4, the Ga concentration (at %) is preferably 28.6%±2.8%, more preferably 28.6%±1.4%.

[0014] The purity (mass %) of the target and sintered body represented by the above composition may be 4N or more, preferably 99.995% or more, and more preferably 5N or more. The upper limit is not particularly limited, but may be, for example, 8N or less.

[0015] The total impurity concentration of the target and sintered body represented by the above composition may be less than 100 ppm by mass, preferably less than 50 ppm by mass, and more preferably less than 10 ppm by mass.

[0016] The impurity concentration refers to the total concentration of Al, Ca, Cu, Fe, Mn, Ni, Si, and Zn. Furthermore, the purity refers to a value calculated by converting the impurity concentration (ppm by mass) to mass% and subtracting the converted value from 100% by mass. The concentrations of elements contained in the compositions of the target and sintered body, and the concentrations of elements corresponding to impurities, can be measured by inductively coupled plasma optical emission spectroscopy (ICP).

[0017] The purity and impurity concentration described above can suppress defects (e.g., particles) during sputtering. Furthermore, when a magnetoresistive element is manufactured by film formation, deterioration in performance of the magnetoresistive element can be suppressed.

[0018] 1-2.Other In a further embodiment, the relative density of the target and sintered body of the present invention may be 87% or more, preferably 88% or more, and more preferably 90% or more. By having the above relative density, defects (e.g., particles) during sputtering can be suppressed.

[0019] The relative density referred to in this specification was calculated by (measured density / true density) × 100 (%). Here, the "measured density" was measured by the Archimedes method in accordance with JIS-R1634-1998. The "true density" was measured by converting Mg and Ga into oxides, MgO and Ga2O3, respectively, and determining their weight ratios. Here, the weight ratios of MgO and Ga2O3 thus determined are designated a (%) and b (%), respectively. Here, a and b can be determined from the raw material composition in the mixed powder used for molding when producing the oxide sintered body, i.e., the ratio of the amounts of each oxide powder charged. Next, the true density of each oxide was determined as follows: MgO: 3.585 g / cm 3 , Ga2O3: 5.941 g / cm 3 Using the above formula, the theoretical density A (g / cm 3 ) is calculated. A=(a+b) / ((a / 3.585)+(b / 5.941))

[0020] For example, when aiming to synthesize a composite oxide of MgGa2O4 (and ignoring the volatilization of Ga), the conversion is based on mixing MgO and Ga2O3 in a molar ratio of 1:1. Here, the molar masses of both are as follows: MgO: 40.3044 g / mol Ga2O3: 187.444 g / mol Therefore, when they are mixed in a 1:1 molar ratio, the weight ratio of the two is calculated as follows: a 100×40.3044 / (40.3044+187.444)=18% b 100×187.444 / (40.3044+187.444)=82% When the above a and b are applied to the formula for calculating the theoretical density A, the following calculation is obtained. A=(18+82) / ((18 / 3.585)+(82 / 5.941))=5.312(g / cm 3 )

[0021] The shapes of the target and the sintered body are not particularly limited, and may be cylindrical or flat (for example, rectangular, disc-shaped, etc.).

[0022] The final target may include a target body (i.e., the portion to be sputtered), a backing plate, and, in addition, a bonding layer.

[0023] 2. Manufacturing method In one embodiment, the present invention relates to a method for producing a target and a sintered body having the above composition, the method comprising at least the following steps: · Raw material powder supply process A process of hot pressing to produce a sintered body

[0024] Here, the hot pressing is carried out so as to satisfy all of the following conditions. Atmosphere: Inert gas atmosphere Sintering temperature: 1200~1300℃ Pressure: 250kgf / cm 2 End

[0025] Each step will be described in detail below.

[0026] 2-1. Provision of raw powder The raw materials for MgGaO may be, for example, powder of an oxide of Mg (e.g., MgO) and powder of an oxide of Ga (e.g., GaO). Preferably, the purity (mass%) of the powder of the oxide of Mg and the powder of the oxide of Ga is 99.99% or more (4N or more), more preferably 99.999% or more. This makes it possible to achieve the above-mentioned purity and impurity concentration.

[0027] Next, these raw material powders are mixed. At this time, the blending amounts are appropriately adjusted so that MgGa2O4 or a composition close to it is obtained. After mixing, the mixture is calcined, thereby synthesizing MgGa2O4. Calcination is performed in an air atmosphere at a temperature of 1000 to 1600°C (preferably 1200 to 1400°C) for 5 to 20 hours (preferably 10 to 15 hours). At temperatures above 1600°C, sintering proceeds, increasing the particle size, which requires high energy for pulverization (described later), increasing the cost of obtaining a fine powder.

[0028] After calcination, the powder is pulverized and mixed. The pulverization and mixing processes can be performed by a dry method or a wet method. Generally, a wet method has superior pulverization and mixing capabilities compared to a dry method. Therefore, it is preferable to perform pulverization and mixing using a wet method. Furthermore, it is preferable to use nylon balls, nylon pots, etc. to prevent impurities from being mixed in during pulverization and mixing.

[0029] The particle size after pulverization is not particularly limited, but the smaller the particle size, the higher the relative density can be, which is desirable. For example, the particle size after pulverization may be 0.1 to 10 μm, and preferably 0.5 to 5 μm.

[0030] 2-2.Hot press The powder obtained above was filled into a mold and subjected to a pressure of 250 kgf / cm 2 Then, hot pressing is performed. Here, the pressure is 250 kgf / cm 2 If the pressure is less than 300 kgf / cm, a sufficient relative density cannot be obtained, and the amount of Ga evaporated increases. This may lead to a decrease in the relative density due to the amount of Ga evaporated. Preferably, the pressure is 300 kgf / cm. 2 The upper limit of the pressure is not particularly limited, but is typically 500 kgf / cm 2 The following is the result.

[0031] The atmosphere is an inert gas atmosphere. In a vacuum, the amount of Ga that volatilizes increases, but by including an inert gas, the volatilization of Ga can be suppressed. Examples of inert gases include nitrogen and rare gases. Examples of rare gases include Ar.

[0032] The temperature for sintering by hot pressing is in the range of 1200 to 1300°C. If the temperature is lower than 1200°C, a sufficient relative density cannot be obtained. If the temperature is higher than 1300°C, Ga volatilizes excessively, which makes it impossible to obtain a sufficient relative density. The sintering time is not particularly limited, but may be 1 to 5 hours, and preferably 2 to 4 hours.

[0033] 2-3. Other processes After the sintered body is obtained by hot pressing, other processing steps may be carried out as appropriate. For example, HIP treatment may be carried out to further improve the relative density. Furthermore, the sintered body may be subjected to machining such as grinding and / or cutting as appropriate to finish it into the shape of a product for shipping. The sintered body may then be bonded to a backing plate to form a final product. The conditions for these other steps are not particularly limited, and conditions known in the art may be used as appropriate. [Example]

[0034] MgO powder (purity 99.99%) and Ga2O3 powder (purity 99.99%) were prepared. The amounts of these powders were adjusted. Specifically, the amounts were adjusted so that the composite oxide Mg1Ga2O4 would be obtained if there was no loss due to volatilization or the like. These powders were mixed and calcined at 1300°C for 10 hours. The calcined powder was mixed and pulverized in a ball mill using nylon balls. The pulverized powder was filled into a mold and hot pressed under the conditions listed in Table 1. [Table 1]

[0035] The concentrations of Ga, Mg, and impurities in the obtained sintered body were measured by inductively coupled plasma atomic emission spectroscopy. Based on the measured concentrations, the ratio of Ga to Mg (Ga / Mg, unit: atomic %) was calculated. Furthermore, the relative density of the obtained sintered body was measured. The results are shown in Tables 2 and 3.

[0036] [Table 2] [Table 3]

[0037] The sintered bodies of Examples 1 to 3 all had sufficiently high relative densities, and Ga / Mg was in the range of 1.90 to 2.10. That is, the Ga / Mg was close to the theoretical value (theoretical value: Ga / Mg = 2.00). The Ga concentration itself was also close to the theoretical value (theoretical value: approximately 28.6%). Therefore, the deviation of the composition was sufficiently suppressed in the sintered bodies of Examples 1 to 3.

[0038] In Comparative Example 1, the sintering temperature was too low, so the relative density was low.

[0039] In Comparative Example 2, the sintering temperature was too high, which resulted in volatilization of Ga and a low Ga / Mg value. Also, in Comparative Example 2, the relative density was low due to the volatilization of Ga.

[0040] In Comparative Example 3, the atmosphere was a vacuum, so Ga volatilized, resulting in a low Ga / Mg value. Also, in Comparative Example 3, the relative density was low because Ga volatilized.

[0041] In Comparative Example 4, the pressure was too low, which resulted in the evaporation of Ga, resulting in a low Ga / Mg value. In addition, in Comparative Example 4, the pressure was too low and the evaporation of Ga caused a low relative density.

[0042] Furthermore, in the sintered bodies of Examples 1 to 3, the impurity concentrations were suppressed to less than 100 wtppm.

[0043] Specific embodiments of the present invention have been described above. The above embodiments are merely specific examples of the present invention, and the present invention is not limited to these embodiments. For example, technical features disclosed in one of the above embodiments may be applied to other embodiments. Furthermore, unless otherwise specified, for a particular method, the order of some steps may be interchanged, and additional steps may be added between two specific steps. The scope of the present invention is defined by the claims.

Claims

1. Mg composite oxide x Ga y O 4 A sputtering target consisting of a composition represented by the formula: the value of y / x, which is the composition ratio of x to y, is 1.90 to 2.10; A sputtering target having a relative density of 87% or more.

2. 2. The sputtering target of claim 1, wherein the value of x is 0.90 to 1.

10.

3. 3. The sputtering target according to claim 1, wherein the sputtering target has a purity of 4N or higher.

4. 4. The sputtering target according to claim 1, wherein the sputtering target has an impurity concentration of less than 100 ppm by mass.

5. A method for producing the sputtering target according to any one of claims 1 to 4, The method comprises: providing a raw material powder, wherein the raw material powder comprises an Mg oxide powder and a Ga oxide powder; a step of mixing and calcining the raw material powders to synthesize a powder having the composition described in claim 1; hot pressing to produce a sintered body; Including, The hot pressing is carried out so as to satisfy all of the following conditions: Atmosphere: Inert gas atmosphere Sintering temperature: 1200 to 1300°C Pressure: 250 kgf / cm 2 End

6. 6. The method of claim 5, wherein the providing step includes synthesizing using raw material powders having a purity of 4N or higher.

7. Mg composite oxide x Ga y O 4 A sintered body having a composition represented by the value of y / x, which is the composition ratio of x to y, is 1.90 to 2.10; A sintered body having a relative density of 87% or more, A sintered body having a purity of 4N or higher.

8. A sintered body having a composition represented by the composite oxide Mg x Ga y O 4 , the value of y / x, which is the composition ratio of x to y, is 1.90 to 2.10; A sintered body having a relative density of 87% or more, A sintered body having an impurity concentration of less than 100 ppm by mass.

9. 9. The sintered body according to claim 7 or 8, wherein the value of x is 0.90 to 1.10.

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