High-purity bismuth target material and preparation method thereof

Abstract

The invention provides a high-purity bismuth target material and a preparation method thereof, and the preparation method comprises the following steps: carrying out vacuum hot pressed sintering on high-purity bismuth powder to obtain a high-purity bismuth target blank; the heat preservation temperature of the vacuum hot pressing sintering is 180-200 DEG C, and the heat preservation time of the vacuum hot pressing sintering is 35-45 min; the heating rate of the vacuum hot pressing sintering is 5-8 DEG C / min. The preparation method provided by the invention can be used for preparing the bismuth target material with high purity, high relative density, good conductivity and no surface defect.

Description

Technical Field

[0001] The invention belongs to the technical field of target materials, and in particular relates to a high-purity bismuth target material and a preparation method thereof. Background Art

[0002] Target materials are basic consumables in the magnetron sputtering process. Not only are they used in large quantities, but the quality of the target materials also plays a crucial role in determining the performance of the film. Target materials have a wide range of applications, mainly including optical targets, targets for display films, targets for semiconductors, targets for recording media, superconducting targets, etc. Among them, targets for semiconductors, targets for displays, and targets for recording media are the three most widely used targets. In order to increase the rate of film preparation and ensure the growth quality of the film, sputtering targets must meet certain index requirements.

[0003] Bismuth targets have the characteristics of high purity and high density. They are mainly used in electron beam evaporation coating machines and can be used to prepare various metal films and alloy films. In addition, bismuth targets can also be used to prepare various optical films, such as anti-reflection films, reflective films and filters.

[0004] For bismuth targets, both the preparation method and raw materials will affect their performance. How to prepare bismuth targets with high purity, high relative density, good conductivity and no surface defects has become an important research topic. Summary of the invention

[0005] In response to the above technical problems, the present application provides a high-purity bismuth target and a preparation method thereof.

[0006] To achieve the above objectives, this application proposes the following technical solutions: In a first aspect, a method for preparing a high-purity bismuth target is provided, comprising: High-purity bismuth powder is used for vacuum hot pressing sintering to obtain a high-purity bismuth target blank; the vacuum hot pressing sintering temperature is 180-200°C, the vacuum hot pressing sintering insulation time is 35-45min; the vacuum hot pressing sintering heating rate is 5-8°C / min.

[0007] Furthermore, the vacuum hot pressing sintering pressure is 37~43Mpa.

[0008] Furthermore, the vacuum degree of the vacuum hot pressing sintering is ≤10Pa.

[0009] Furthermore, the method for preparing the high-purity bismuth powder comprises: Dissolve bismuth nitrate in dilute nitric acid to obtain solution A; Add urea solution to solution A until the pH value of solution A reaches 8-10, stir for a period of time, transfer to a reactor, perform hydrothermal reaction, and obtain precursor slurry; The precursor slurry is subjected to solid-liquid separation, washing and drying to obtain a precursor powder; the precursor powder is calcined to obtain bismuth oxide; Bismuth oxide is reduced to obtain high-purity bismuth powder.

[0010] Furthermore, in the solution A, the molar ratio of bismuth nitrate to nitric acid is 3:1.0-1.45.

[0011] Furthermore, the temperature of the hydrothermal reaction is 170-200° C.; the time of the hydrothermal reaction is 8-12 hours.

[0012] Furthermore, the calcination temperature is 350-450° C.; and the calcination time is 4-6 hours.

[0013] Furthermore, the reduction is hydrogen reduction; the temperature of the hydrogen reduction is 750-850°C.

[0014] Furthermore, it also includes a post-processing step of cutting and removing excess material on the surface of the high-purity target blank, and then performing milling. In a second aspect, a high-purity bismuth target is provided, which is prepared using the aforementioned preparation method.

[0015] Furthermore, the relative density of the high-purity bismuth target is above 99%, the electrical conductivity is above 900 S / m, the impurity content is below 100 ppm, and the surface of the high-purity bismuth target has no spots or color differences.

[0016] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: The preparation method provided in the present application can prepare a bismuth target material with high purity, high relative density, good conductivity and no surface defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 This is a picture of the high-purity bismuth planar target prepared in Example 1.

[0019] Figure 2 This is a picture of the high-purity bismuth planar target prepared in Comparative Example 3. DETAILED DESCRIPTION

[0020] The present invention provides a method for preparing a high-purity bismuth target, comprising: High-purity bismuth powder is used for vacuum hot pressing sintering to obtain a high-purity bismuth target blank; the insulation temperature of the vacuum hot pressing sintering is 180-200°C, and the insulation time of the vacuum hot pressing sintering is 35-45min (for example, 35min, 38min, 40min, 42min, 45min, etc.); the heating rate of the vacuum hot pressing sintering is 5-8°C / min (for example, 5°C / min, 6°C / min, 7°C / min and 8°C / min, etc.).

[0021] The preparation method uses high-purity bismuth powder as raw material for vacuum hot pressing sintering, and controls the process conditions of vacuum hot pressing sintering. The density and conductivity of the prepared target material are relatively high, and the appearance of the target material is also relatively good.

[0022] In some preferred embodiments, the pressure of the vacuum hot pressing sintering is 37-43 MPa, for example, 37 MPa, 38 MPa, 39 MPa, 40 MPa, 41 MPa, 42 MPa, 43 MPa, etc.

[0023] In some preferred embodiments, the vacuum degree of the vacuum hot pressing sintering is ≤10Pa.

[0024] In some preferred embodiments, the method for preparing the high-purity bismuth powder comprises: Dissolve bismuth nitrate in dilute nitric acid to obtain solution A; Add urea solution to solution A until the pH value of solution A reaches 8-10 (e.g., 8, 8.5, 9, 9.5, 10, etc.), stir for a period of time, transfer to a reactor, perform hydrothermal reaction, and obtain a precursor slurry; The precursor slurry is subjected to solid-liquid separation, washing and drying to obtain a precursor powder; the precursor powder is calcined to obtain bismuth oxide; Bismuth oxide is reduced to obtain high-purity bismuth powder.

[0025] Compared with bismuth powder prepared by grinding process, the high-purity bismuth powder prepared by hydrothermal precipitation-pyrolysis-reduction in the above preparation method has lower impurity content; compared with ordinary precipitation, the hydrothermal precipitation reaction of the above preparation method is more thorough and has higher yield, and even if the reactants contain insoluble substances, they can be dissolved and reacted; and compared with bismuth compounds prepared by other pH adjusters (such as ammonia water, NaOH solution) using urea solution as pH adjuster, the former has a slower and more uniform reaction process, the obtained product is more uniform, and the particle size is relatively small, so the former is roasted-reduced to obtain high-purity bismuth powder, and the high-purity bismuth powder is used as a raw material to prepare a target material, and the prepared target material has higher density and better conductivity.

[0026] In some preferred embodiments, in the solution A, the molar ratio of bismuth nitrate to nitric acid is 3:1.0-1.45, for example, 3:1, 3:1.1, 3:1.2, 3:1.3, 3:1.4, 3:1.45, etc. Studies have shown that the bismuth target prepared by using the raw materials of this ratio and then sintering the bismuth compound by roasting-reduction-vacuum hot pressing has higher density and conductivity.

[0027] In some preferred embodiments, the temperature of the hydrothermal reaction is 170-200°C, for example, 170°C, 180°C, 190°C, 200°C, etc.; the time of the hydrothermal reaction is 8-12h, for example, 8h, 9h, 10h, 11h, 12h, etc.

[0028] In some preferred embodiments, the calcination temperature is 350-450°C, for example, 350°C, 380°C, 400°C, 420°C, 450°C, etc.; the calcination time is 4-6h, for example, 4h, 4.5h, 5h, 5.5h, 6h, etc.

[0029] In some preferred embodiments, the reduction is hydrogen reduction; the temperature of the hydrogen reduction is 750-850° C., such as 750° C., 780° C., 800° C., 820° C., 850° C., etc. The reduction time can be conventionally determined according to the reduction needs.

[0030] Some preferred embodiments also include cutting away excess material on the surface of the high-purity target blank and then performing a post-processing step of milling the surface.

[0031] In some preferred embodiments, the relative density of the high-purity bismuth target is above 99%, the electrical conductivity is above 900 S / m, the impurity content is below 100 ppm, and the surface of the high-purity bismuth target has no spots or color differences.

[0032] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the specification, but the protection scope of the present invention is not limited to the following specific embodiments.

[0033] Example 1 (1) Weigh a solution according to the volume ratio of nitric acid (mass concentration 76%): deionized water = 1:3 to prepare a dilute nitric acid solution for later use; weigh a certain amount of 3.7 mol / L urea aqueous solution for later use, and weigh a certain amount of bismuth nitrate pentahydrate powder for later use.

[0034] (2) Dissolve the weighed bismuth nitrate pentahydrate in dilute nitric acid. The molar ratio of bismuth nitrate pentahydrate to dilute nitric acid is HNO3:Bi(NO3)3·5H2O=3:1.25. Stir continuously at 80°C using a magnetic stirrer until the bismuth nitrate pentahydrate is completely dissolved. The stirring time is 10-15 min. Continuously add urea aqueous solution to the stirred solution until the pH value of the solution reaches 10. Continue stirring for 30 min.

[0035] (3) The solution obtained in step (2) was added into a high-pressure reactor, which was sealed and placed in a muffle furnace and heated at 180° C. for 10 h. After the reactor was cooled to room temperature, the product was centrifuged, washed with deionized water, and dried in an oven for 10 h to obtain a precursor powder. The yield of the precursor powder was measured to be 85.22%.

[0036] (4) The precursor powder obtained in step (3) was calcined at 400° C. to obtain bismuth oxide powder. The Malvern test result of the powder was D90=0.447 μm.

[0037] (5) hydrogenating the bismuth oxide powder obtained in step (4) at 800° C. to obtain high-purity bismuth powder; (6) The bismuth powder obtained in step (5) is subjected to vacuum hot pressing and sintering at a heating rate of 5°C / min to 180°C, a pressure of 40 MPa, and a vacuum degree of ≤10 Pa, and then kept at this temperature for 40 min to obtain a high-purity bismuth target blank, which is then cooled in the furnace for 4 h to room temperature and the high-purity bismuth target is taken out.

[0038] (7) After the high-purity bismuth target blank is cooled, the excess material on the surface of the high-purity bismuth target blank is cut off by diamond wire cutting to obtain a high-purity bismuth target blank with a specific shape.

[0039] (8) The high-purity bismuth target blank is fixed on a CNC milling machine and milled with a 150-mesh resin diamond grinding wheel at a milling speed of 600 r / min. After the milling is completed, a high-purity bismuth flat target is obtained. The picture of the obtained high-purity bismuth flat target is shown in the figure. Figure 1 As shown, from Figure 1 It can be seen that the obtained target material has no color difference and spots. After testing, the target material density is 99.03%, the conductivity is 984S / m, and the total impurity content is 28ppm.

[0040] Example 2 (1) Weigh a solution according to the volume ratio of nitric acid: deionized water = 1:3 to prepare a dilute nitric acid solution for later use; weigh a certain amount of 3.7 mol / L urea aqueous solution for later use, and weigh a certain amount of bismuth nitrate pentahydrate powder for later use.

[0041] (2) Dissolve the weighed bismuth nitrate pentahydrate metal salts in dilute nitric acid, with the molar ratio of bismuth nitrate pentahydrate to dilute nitric acid being HNO3:Bi(NO3)3·5H2O=3:1.25, and stir continuously at 80°C using a magnetic stirrer until the bismuth nitrate pentahydrate is completely dissolved, with the stirring time being 10-15 minutes; continue to add urea aqueous solution to the stirred solution until the pH value of the solution reaches 10. Continue stirring for 30 minutes.

[0042] (3) The solution obtained in step (2) is added into a high-pressure reactor, which is sealed and placed in a muffle furnace, and heated at 180° C. for 10 h. After the reactor is cooled to room temperature, the product is centrifuged, washed with deionized water, and dried in an oven for 10 h to obtain a precursor powder.

[0043] (4) The obtained precursor powder is calcined at 400° C. to obtain bismuth oxide powder.

[0044] (5) hydrogenating the bismuth powder obtained in step (4) at 800° C. to obtain high-purity bismuth powder; (6) The bismuth powder obtained in step (5) is subjected to vacuum hot pressing and sintering at a heating rate of 5°C / min to 190°C, a pressure of 40 MPa, and a vacuum degree of ≤10 Pa, and then kept at this temperature for 40 min, cooled in the furnace for 4 h to room temperature, and the high-purity bismuth target blank is taken out.

[0045] (7) After cooling, the high-purity bismuth target blank is cut off with diamond wire cutting to obtain a high-purity bismuth target blank with a specific shape. The high-purity bismuth target blank is fixed on a CNC milling machine and milled with a 150-mesh resin diamond grinding wheel at a milling speed of 600 r / min. After milling, a high-purity bismuth flat target is obtained. The obtained target material has no color difference and spots, and the target material density is detected to be 99.28%, the conductivity is 998S / m, and the total impurity content is 30ppm.

[0046] Example 3 (1) Weigh a solution according to the volume ratio of nitric acid: deionized water = 1:3 to prepare a dilute nitric acid solution for later use; weigh a certain amount of 3.7 mol / L urea aqueous solution for later use, and weigh a certain amount of bismuth nitrate pentahydrate powder for later use.

[0047] (2) Dissolve the weighed bismuth nitrate pentahydrate metal salts in dilute nitric acid, with the molar ratio of bismuth nitrate pentahydrate to dilute nitric acid being HNO3:Bi(NO3)3·5H2O=3:1.25, and stir continuously at 80°C using a magnetic stirrer until the bismuth nitrate pentahydrate is completely dissolved, with the stirring time being 10-15 min; continuously add urea aqueous solution to the stirred solution until the pH value of the solution reaches 10, and continue stirring for 30 min.

[0048] (3) The solution obtained in step (2) is added into a high-pressure reactor, which is sealed and placed in a muffle furnace, and heated at 180° C. for 10 h. After the reactor is cooled to room temperature, the product is centrifuged, washed with deionized water, and dried in an oven for 10 h to obtain a precursor powder.

[0049] (4) The obtained precursor powder is calcined at 400° C. to obtain bismuth oxide powder.

[0050] (5) hydrogenating the bismuth powder obtained in step (4) at 800° C. to obtain high-purity bismuth powder; (6) The bismuth powder obtained in step (5) is subjected to vacuum hot pressing and sintering at a heating rate of 5°C / min to 200°C, a pressure of 40 MPa, and a vacuum degree of ≤10 Pa, and then kept at this temperature for 40 min, cooled in the furnace for 4 h to room temperature, and the high-purity bismuth target blank is taken out.

[0051] (7) After cooling, the high-purity bismuth target blank is cut off with diamond wire cutting to obtain a high-purity bismuth target blank with a specific shape. The obtained high-purity bismuth target blank is fixed on a CNC milling machine and milled with a 150-mesh resin diamond grinding wheel at a milling speed of 600 r / min. After the milling is completed, a high-purity bismuth flat target is obtained.

[0052] The obtained target material has no color difference and spots, and the target material density is detected to be 99.65%, the conductivity is 1038S / m, and the total impurity content is 27ppm.

[0053] Comparative Example 1 The difference between this comparative example and Example 3 is that 3.7 mol / L of dilute ammonia water is prepared in step (1), and dilute ammonia water is used instead of urea aqueous solution as the pH regulator in step (2).

[0054] The Malvern measurement of the obtained bismuth powder is D90=1.134μm; the obtained target material has no color difference and spots. The target material density is 96.13%, the conductivity is 320S / m, and the total impurity content is 28ppm.

[0055] By comparing Example 3 with Comparative Example 1, it can be seen that after using dilute ammonia water instead of urea aqueous solution as the pH regulator, the particle size of the powder prepared by the hydrothermal reaction is significantly increased, and the density and conductivity of the target material finally prepared are significantly reduced. After analysis, this may be because compared with the ammonia aqueous solution, the precipitation reaction of the urea aqueous solution with the cation is slower, the prepared precipitate is more likely to be a single oxide with uniform composition, and the particle size of the obtained product is smaller, so that the target material prepared by the obtained product has a higher density and a higher conductivity.

[0056] Example 4 The only difference between this embodiment and embodiment 3 is that the heating rate in step (6) is different. The heating rate in this embodiment is 8° C. / min.

[0057] The obtained target material has no color difference and spots, and the target material density is detected to be 99.53%, the conductivity is 1031S / m, and the total impurity content is 28ppm.

[0058] Example 5 The only difference between this embodiment and embodiment 3 is that the insulation time in step (6) is different. In this embodiment, the insulation time is 35 minutes.

[0059] The obtained target material has no color difference and spots, and the target material density is detected to be 99.60%, the conductivity is 1034S / m, and the total impurity content is 27ppm.

[0060] Example 6 The only difference between this embodiment and embodiment 3 is that the insulation time in step (6) is different. In this embodiment, the insulation time is 45 minutes.

[0061] The obtained target material has no color difference and spots, and the target material density is detected to be 99.58%, the conductivity is 1035S / m, and the total impurity content is 28ppm.

[0062] Example 7 The only difference between this embodiment and embodiment 3 is that the molar ratio of bismuth nitrate pentahydrate to dilute nitric acid HNO3:Bi(NO3)3·5H2O in step (2) is different. In this embodiment, the molar ratio is 3:1.45.

[0063] The obtained target material has no color difference and spots, and the target material density is detected to be 99.46%, the conductivity is 1016S / m, and the total impurity content is 29ppm.

[0064] Example 8 The only difference between this embodiment and embodiment 3 is that the molar ratio of bismuth nitrate pentahydrate to dilute nitric acid HNO3:Bi(NO3)3·5H2O in step (2) is different. In this embodiment, the molar ratio is 3:1.70.

[0065] The obtained target material has no color difference and spots, and the target material density is detected to be 97.42%, the conductivity is 650S / m, and the total impurity content is 28ppm.

[0066] By comparing the bismuth targets obtained in Example 1, Example 7 and Example 8, it is found that the molar ratio of bismuth nitrate pentahydrate to dilute nitric acid in the raw material will also affect the density and conductivity of the target.

[0067] Comparative Example 2 The difference between this comparative example and Example 1 is that the heating rate in step (6) is different. The heating rate in this comparative example is 10° C. / min.

[0068] The obtained target material has no color difference and spots. The density of the obtained target material is measured to be 98.12%, the conductivity is 810S / m, and the total impurity content is 32ppm.

[0069] Comparative Example 3 The difference between this comparative example and Example 1 is that the hot pressing and heat preservation temperature in step (6) is different. The hot pressing and heat preservation temperature in this comparative example is 170°C.

[0070] The obtained target material has no color difference and spots. The density of the obtained target material is measured to be 98.56%, the conductivity is 685S / m, and the total impurity content is 30ppm.

[0071] Comparative Example 4 The difference between this comparative example and Example 1 is that the hot pressing and heat preservation temperature in step (6) is different. The hot pressing and heat preservation temperature in this comparative example is 210°C.

[0072] The pictures of the obtained target are as follows Figure 2 As shown, from Figure 2 It can be seen that there are spots and color differences on the surface of the target material. The density of the target material is 99.76%, the conductivity is 1125S / m, and the total impurity content is 30ppm.

[0073] Comparative Example 5 The only difference between this comparative example and Example 3 is that the temperature is raised to 200° C. at a heating rate of 5° C. / min and then kept at this temperature for 60 min.

[0074] The obtained target material has no color difference and spots. The target material density is measured to be 98.12%, the electrical conductivity is 680S / m, and the total impurity content is 29ppm.

[0075] Comparative Example 6 The only difference between this comparative example and Example 3 is that the temperature is raised to 200° C. at a heating rate of 5° C. / min and then kept at this temperature for 20 min.

[0076] The obtained target material has no color difference and spots. The target material density is measured to be 98.72%, the electrical conductivity is 496S / m, and the total impurity content is 29ppm.

[0077] By comparing the target materials obtained in the above embodiments and the comparative examples, it is found that by strictly controlling the hot pressing temperature range, the heating rate range and the holding time range, a bismuth target material with high relative density, high electrical conductivity and no color difference and spots on the surface can be prepared; when the hot pressing temperature, the holding time and the heating rate are not properly controlled, the prepared target material may have a lower relative density, lower electrical conductivity, or have defects such as color difference and spots on the surface.

[0078] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a high-purity bismuth target, characterized in that: include: High-purity bismuth powder is used for vacuum hot pressing sintering to obtain a high-purity bismuth target blank; the insulation temperature of the vacuum hot pressing sintering is 180-200°C, the insulation time of the vacuum hot pressing sintering is 35-45min; the heating rate of the vacuum hot pressing sintering is 5-8°C / min.

2. The method for preparing a high-purity bismuth target according to claim 1, characterized in that: The pressure of the vacuum hot pressing sintering is 37-43Mpa; the vacuum degree of the vacuum hot pressing sintering is ≤10Pa.

3. The method for preparing a high-purity bismuth target according to claim 1, characterized in that: The preparation method of the high-purity bismuth powder comprises: Dissolve bismuth nitrate in dilute nitric acid to obtain solution A; Add urea solution to solution A until the pH value of solution A reaches 8-10, stir for a period of time, transfer to a reactor, perform hydrothermal reaction, and obtain precursor slurry; The precursor slurry is subjected to solid-liquid separation, washing and drying to obtain a precursor powder; the precursor powder is calcined to obtain bismuth oxide; Bismuth oxide is reduced to obtain high-purity bismuth powder.

4. The method for preparing a high-purity bismuth target according to claim 3, characterized in that: In the solution A, the molar ratio of bismuth nitrate to nitric acid is 3:1.0-1.

45.

5. The method for preparing a high-purity bismuth target according to claim 3, characterized in that: The temperature of the hydrothermal reaction is 170-200° C.; the time of the hydrothermal reaction is 8-12 hours.

6. The method for preparing a high-purity bismuth target according to claim 3, characterized in that: The calcination temperature is 350-450° C.; the calcination time is 4-6 hours.

7. The method for preparing a high-purity bismuth target according to claim 3, characterized in that: The reduction is hydrogen reduction; the temperature of the hydrogen reduction is 750-850°C.

8. The method for preparing a high-purity bismuth target according to claim 3, characterized in that: The method also includes a post-processing step of cutting and removing excess material on the surface of the high-purity target blank, and then performing a milling surface.

9. High purity bismuth target, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. The high purity bismuth target material according to claim 9, characterized in that: The high-purity bismuth target has a relative density of more than 99%, an electrical conductivity of more than 900 S / m, an impurity content of less than 100 ppm, and a surface of the high-purity bismuth target without spots or color differences.

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