Device and method for purifying beryllium metal by vacuum distillation enhanced by gradient magnetic field

Abstract

The present invention discloses a device for purifying beryllium metal by vacuum distillation with enhanced gradient magnetic field, belonging to the semiconductor material technology. It includes a vacuum chamber (15), in which a substrate pedestal (3), a collector (9) and a distillation furnace (6) are sequentially arranged from top to bottom. A crucible (8) is arranged in the distillation furnace (6). A permanent magnet (4) and a water-cooled shielding plate (5) are also arranged between the collector (9) and the crucible (8), and the water-cooled shielding plate (5) is located between the permanent magnet (4) and the crucible (8). Among them, the permanent magnet (4) has asymmetric magnetic poles. The present invention also discloses a method for purifying beryllium using the above device. By setting a gradient magnetic field, the present invention can reduce the content of Fe element in beryllium metal to below 5 ppm, the content of Mn element to below 3 ppm, and the content of Cr and Ni elements to below 0.5 ppm, greatly improving the purity of beryllium metal and reducing the purification cost of crude beryllium.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor materials, and in particular to a device and method for purifying metallic beryllium by vacuum distillation enhanced by a gradient magnetic field. Background Art

[0002] High-purity beryllium is an important semiconductor doping material, commonly used in the preparation of multi-purpose devices, including first-generation silicon devices, second-generation GaAs-based and lnP-based devices, third-generation GaN, SiC, and ZnO devices, as well as second-class superlattice devices and InSb devices in the infrared field. The advantages of beryllium in semiconductor doping are that it has a relatively small atomic weight, is easy to migrate and replace trivalent metals (Ga or In), has a high activation rate, and has various doping forms, including diffusion, molecular beam epitaxy, liquid phase vapor deposition, and ion implantation.

[0003] The physical and chemical properties of beryllium and its impurity spectrum determine that it is very difficult to purify. Relatively speaking, vacuum distillation is an effective method for purifying metallic beryllium. It can remove Al, Mg, Zn, Pb, K, and Na. It has the advantages of simple equipment, short operation process, and low pollution in a confined space. The structure of the existing vacuum distillation equipment for purifying beryllium is as follows: Figure 1 As shown, it includes a vacuum chamber 15, the left side of the vacuum chamber 15 is connected to a molecular pump 14, the molecular pump 14 is connected to a mechanical pump 11, a vacuum flange 2 and a glove box 10 are arranged on the right side of the vacuum chamber 15, and a substrate base 3, a collector 9 and a distillation furnace 6 are arranged in the vacuum chamber 15 from top to bottom, a crucible 8 is arranged in the distillation furnace 6, and a substrate lifting assembly 1 connected to the substrate base 3 is also arranged above the vacuum chamber 15. However, this method is difficult to completely remove the Fe element in beryllium because the vapor pressure of Be is close to that of Fe. In the experiment of vacuum distillation purification of beryllium, the Fe content of crude beryllium is 654 ppm, and the Fe content after vacuum distillation purification is 120 ppm. Although the Fe content can be reduced to a certain extent, it is difficult to completely remove it. Elements that are difficult to remove by existing vacuum distillation purification methods include Cr, Ni, and Mn.

[0004] In semiconductor applications, Fe is an active dopant and its content needs to be strictly controlled. However, Fe is the main impurity element in crude beryllium and is difficult to remove by other purification methods. Therefore, removing Fe impurities from beryllium is a key issue that needs to be solved urgently. Summary of the invention

[0005] One of the purposes of the present invention is to provide a device for purifying metallic beryllium by vacuum distillation enhanced by a gradient magnetic field to solve the above-mentioned problems.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A device for purifying beryllium metal by vacuum distillation with enhanced gradient magnetic field, comprising a vacuum chamber, a molecular pump is connected to the left side of the vacuum chamber, the molecular pump is connected to a mechanical pump, a vacuum flange and a glove box are arranged on the right side of the vacuum chamber, a substrate base, a collector and a distillation furnace are sequentially arranged in the vacuum chamber from top to bottom, a crucible is arranged in the distillation furnace, and it is characterized in that: A permanent magnet and a water-cooled shielding plate are further arranged between the collector and the crucible, and the water-cooled shielding plate is located between the permanent magnet and the crucible, wherein the permanent magnet has asymmetric magnetic poles.

[0007] As a preferred technical solution: The shape and structure of the permanent magnet are: The N pole is arc-shaped (more preferably 1 / 4 arc), the S pole is triangular tip-shaped, a notch space is arranged between the N pole and the S pole as the gradient magnetic field region, magnetic induction lines start from the N pole and focus on the tip of the S pole, and its typical preferred three-dimensional structure is as Figure 5 , the top view is as Figure 6 , and the dimensions are as Figure 7 .

[0008] The second object of the present invention is to provide a method for purifying beryllium metal by vacuum distillation with enhanced gradient magnetic field using the above device, and the technical solution adopted is that its steps include: loading, first vacuum pumping, vacuum volatilization, first cooling and sampling, installing a high-purity collector, second vacuum pumping, vacuum distillation, second cooling and sampling.

[0009] As a preferred technical solution:

[0010] The method of the vacuum volatilization is: Turn on the cooling water of the distillation furnace, set the temperature curve, start heating, raise the temperature to 300°C ± 50°C, at a rate of 8°C / min ± 4°C / min, keep the temperature constant for 120 min ± 60 min, then raise the temperature to 800°C ± 50°C, at a rate of 8°C / min ± 4°C / min, keep the temperature constant for 120 min ± 60 min, and finally raise the temperature to 1000°C ± 200°C, at a rate of 8°C / min ± 4°C / min, keep the temperature constant for 240 min ± 120 min, and vacuum volatilize to remove Al, Mg, Zn, Pb, K, Na.

[0011] As a preferred technical solution:

[0012] The method of the vacuum distillation is: Turn on the cooling water of the distillation furnace, set the temperature curve, start heating, raise the temperature to 1200°C ± 150°C, at a rate of 8°C / min ± 4°C / min, keep the temperature constant for 240 min ± 120 min, the crude beryllium evaporates from the crucible, beryllium atoms travel perpendicular to the magnetic field direction, have no magnetic moment and are not affected by force, move in a straight line and deposit on the high-purity collector, while impurity atoms such as Fe, Cr, Ni, and Mn are deflected and removed by the action of the gradient magnetic field.

[0013] As a preferred technical solution: The high-purity collector is also cleaned before installation and use. The cleaning steps include: adding degreaser and ultrasonic cleaning, pickling with mixed acid, rinsing with pure water, and drying.

[0014] The inventor of the present application found through analysis that the electron configuration of Be atoms is 1s 2 2s 2 , and both 1s and 2s are filled shells. When electrons fill a certain shell, the orbital motions and spin orientations of each electron occupy all possible directions. In this way, the magnetic moments of the electrons themselves must cancel each other out. Therefore, for any shell filled with electrons, the total magnetic moment is zero. Thus, beryllium atoms have no magnetic moment. Among the impurity elements Fe, Cr, Ni, and Mn in beryllium, the atomic numbers are close, and they are all transition elements. The 3d electron shells are not filled, and they have inherent atomic magnetic moments.

[0015] The differences in atomic numbers, electron configurations, unfilled shells, and electron vacancies between Be atoms and impurity atoms including Fe, Cr, Ni, Mn, etc. are shown in Table 1.

[0016] Table 1 Comparison of electron configurations of various related atoms

[0017]

[0018] In view of the differences in atomic magnetic moments between Be and other impurity atoms such as Fe, the present invention provides an asymmetric magnetic pole (permanent magnet) to generate a non-uniform magnetic field (gradient magnetic field) to enhance the effect of vacuum distillation for purifying metallic beryllium. That is, during the flight of evaporated atoms, magnetic atoms are equivalent to a magnetic needle. For example Figure 4 , the magnitude of the force it receives is proportional to the gradient of the magnetic field. Therefore, an asymmetric magnetic pole as shown in Figure 5 is designed to increase the magnetic field gradient. Atoms such as Fe, Cr, Ni, and Mn are deflected by the force, while Be atoms are not affected by the force, so as to achieve the purpose of removing Fe, Cr, Ni, and Mn elements.

[0019] Compared with the prior art, the advantages of the present invention are as follows: By setting a gradient magnetic field, the present invention can reduce the content of Fe element in metallic beryllium to less than 5 ppm, reduce the content of Mn element by less than 3 ppm, and can reduce the content of Cr and Ni elements to less than 0.5 ppm, greatly improving the purity of metallic beryllium and reducing the purification cost of crude beryllium. Description of the Drawings

[0020] Figure 1 It is a structural diagram of a vacuum distillation device for purifying metallic beryllium in the prior art;

[0021] Figure 2 It is a structural diagram of a gradient magnetic field enhanced vacuum distillation device for purifying metallic beryllium of the present invention;

[0022] Figure 3 It is the design diagram of the gradient magnetic field of the present invention;

[0023] Figure 4 It is the force on the magnetic atoms in the gradient magnetic field;

[0024] Figure 5 It is the three-dimensional structure diagram of the permanent magnet in Embodiment 1;

[0025] Figure 6 It is the top view of the permanent magnet in Embodiment 1;

[0026] Figure 7 It is the size of the permanent magnet in Embodiment 1.

[0027] In the figure: 1. Substrate lifting assembly; 2. Vacuum flange; 3. Substrate base; 4. Permanent magnet; 5. Water-cooled shielding plate; 51. Central hole; 6. Distillation furnace; 7. Gas release valve; 8. Crucible; 9. Collector; 10. Glove box; 11. Mechanical pump; 12. Bellows; 13. Stop valve; 14. Molecular pump; 15. Vacuum chamber; 16. Atomic beam; 17. Cooling water interface; a. Crude beryllium raw material. Specific implementation manners

[0028] The present invention will be further described below in conjunction with the drawings.

[0029] A device for vacuum distillation and purification of beryllium metal with enhanced gradient magnetic field, the structure of which is as Figure 2 shown, including a vacuum chamber 15,

[0030] The left side of the vacuum chamber 15 is connected to a molecular pump 14, the molecular pump 14 is connected to a mechanical pump 11, the molecular pump 14 and the mechanical pump 11 are connected by a bellows 12, and a stop valve 13 is provided at one end of the bellows 12 close to the molecular pump 14;

[0031] The right side of the vacuum chamber 15 is provided with a vacuum flange 2 and a glove box 10, the vacuum chamber 15 is communicated with the glove box 10 through a pipeline, and a gas release valve 7 is provided on the pipeline;

[0032] Inside the vacuum chamber 15, a substrate base 3, a collector 9, a permanent magnet 4, a water-cooled shielding plate 5 and a distillation furnace 6 are arranged in sequence from top to bottom. A crucible 8 for placing the crude beryllium raw material a is arranged inside the distillation furnace 6. Between the collector 9 and the crucible 8, a permanent magnet 4 and a water-cooled shielding plate 5 are also arranged. Cooling water interfaces 17 are provided at both ends of the water-cooled shielding plate 5. Above the vacuum chamber 15, a substrate lifting assembly 1 connected to the substrate base 3 is also provided;

[0033] In order to enhance the effect of the force and deflection of impurity atoms such as Fe in the z direction, the present invention designs a permanent magnet with asymmetric magnetic poles, and its magnetic field design is as Figure 3 shown, the three-dimensional structure of the permanent magnet 4 in this embodiment is asFigure 5 , and its top view is as Figure 6 , and its dimensions are as Figure 7 ;

[0034] The principle of gradient magnetic field enhancement is as follows: Magnetic atoms are equivalent to a magnetic needle, and the force acting on it in the z direction is as Figure 4 , and the magnitude of the force is proportional to the gradient of the magnetic field. In order to increase the gradient of the magnetic field, a permanent magnet as Figure 5 is designed; under high vacuum conditions, crude beryllium evaporates from crucible 8. After the evaporated atoms pass through the central hole 51 of the water-cooled shield 5, they enter the gradient magnetic field region and travel in the direction perpendicular to the magnetic field. Fe, Cr, Ni, and Mn in the crude beryllium are deflected by the force perpendicular to the traveling direction, and beryllium atoms have no magnetic moment and are not affected by the force. The formed atomic beam 16 flies straight to the collector 9 for deposition, obtaining high-purity beryllium, thereby achieving the purpose of removing impurity elements such as Fe.

[0035] The method for vacuum distillation and purification of metallic beryllium with gradient magnetic field enhancement using the above device includes loading, primary vacuum pumping, vacuum volatilization, primary cooling and sampling, installing a high-purity collector, secondary vacuum pumping, vacuum distillation, and secondary cooling and sampling. The specific step process is as follows:

[0036] (1) Loading: Take the crude beryllium raw material a, weigh it, load it into the beryllium oxide crucible 8, then load the beryllium oxide crucible 8 into the distillation furnace 6, and then load the impurity collector 9 onto the substrate base 3, and close the vacuum flange 2;

[0037] (2) Primary vacuum pumping: Close the gas release valve 7, start the mechanical pump 11, open the stop valve 13, and when the vacuum reaches 10 Pa, start the molecular pump 14 and the molecular pump cooling water for vacuum pumping;

[0038] (3) Vacuum volatilization: When the vacuum degree reaches 2.0×10 -4 Pa, set the heating curve of the distillation furnace 6, start the cooling water, start heating, and remove Al, Mg, Zn, Pb, K, and Na by vacuum volatilization;

[0039] (4) Primary cooling and sampling: When the vacuum distillation furnace body cools down to room temperature, open the gas release valve 7, fill the vacuum chamber 15 with high-purity argon gas. When it is in balance with the external air pressure, open the vacuum flange 2 and take out the impurity collector;

[0040] (5) Installing the high-purity collector 9: Before installing and using the high-purity collector, remove the surface oil and metal impurities by degreasing ultrasonic cleaning and pickling with a mixed acid, then ultrasonically wash and rinse with pure water, dry it after completion, and then install it on the substrate base 3 and close the vacuum flange 2;

[0041] (6) Secondary vacuum pumping: Operate as in step (2);

[0042] (7) Vacuum distillation: Set the heating curve of the vacuum distillation furnace 6, start the cooling water, start heating, maintain a high temperature for constant temperature. The crude beryllium evaporates from the beryllium oxide crucible 8, travels perpendicular to the magnetic field direction, is not affected by force, and moves linearly to deposit on the high-purity collector 9, while impurity atoms such as Fe are deflected and removed by the action of the gradient magnetic field.

[0043] (8) Secondary cooling and sampling: Operate as in step (4), take out the high-purity collector 9, strip the high-purity beryllium sheet, and perform purity detection using ICPMS.

[0044] The following are examples of specific implementation using the above method: Example

[0045] A method for purifying metallic beryllium by vacuum distillation enhanced by a gradient magnetic field, comprising the following steps:

[0046] Weigh 5 g of crude beryllium chips with impurity content as shown in Table 2, put them into the beryllium oxide crucible 8, and then install the oxidation crucible 8 into the vacuum distillation furnace 6; install the impurity collector 9 into the substrate base 3, close the vacuum flange 2, close the air release valve 7, evacuate to 2.0×10 -4 Pa, start heating, heat the distillation furnace 6 to 300 °C at a heating rate of 8 °C / min, maintain a constant temperature for 120 min, then heat to 800 °C at a heating rate of 8 °C / min, maintain a constant temperature for 120 min, and finally heat to 900 °C at a heating rate of 8 °C / min, maintain a constant temperature for 240 min. Al, Mg, Zn, Pb, K, and Na are preferentially volatilized and removed. After this high-temperature constant-temperature section, cool down to 700 °C at a rate of -8 °C / min, the temperature program ends, and it is naturally cooled to room temperature. Then open the air release valve, fill with high-purity argon gas. After the air pressure is balanced with the outside, open the vacuum flange 2 and take out the impurity collector. Replace it with a high-purity collector. Before its installation and use, remove the surface oil and metal impurities by degreasing ultrasonic cleaning and pickling with a mixed acid, then rinse with pure water, dry after completion, and then install it into the substrate base 3, close the vacuum flange 2, close the air release valve 7, evacuate to 2.0×10 -4 Pa, start heating, heat the distillation furnace to 1230 °C at a heating rate of 8 °C / min, maintain a constant temperature for 360 min. The beryllium is deposited on the high-purity collector by vacuum distillation, and Fe, Cr, Ni, and Mn are deflected and removed by the action of the gradient magnetic field. After the high-temperature constant-temperature section, cool down to 700 °C at a rate of -8 °C / min, then the temperature program ends, and it is naturally cooled to room temperature. Open the air release valve, fill with high-purity argon gas. After the air pressure is balanced with the outside, open the vacuum flange and take out the high-purity collector, strip the high-purity beryllium, and perform ICPMS detection;

[0047] The impurity element contents before and after the treatment in this example are shown in Table 2.

[0048] Example 2

[0049] A method for purifying beryllium metal by vacuum distillation enhanced by a gradient magnetic field, comprising the following steps:

[0050] Weigh 5 g of coarse beryllium chips with impurity content as shown in Table 2, put them into the beryllium oxide crucible 8, and then install the oxidation crucible 8 into the vacuum distillation furnace 6; install the impurity collector 9 onto the substrate base 3, close the vacuum flange 2, close the gas release valve 7, evacuate to 2.0×10 -4 Pa, start heating, heat the distillation furnace 6 to 300 °C at a heating rate of 8 °C / min, keep it at a constant temperature for 120 min, then heat it to 800 °C at a heating rate of 8 °C / min, keep it at a constant temperature for 120 min, and finally heat it to 950 °C at a heating rate of 8 °C / min, keep it at a constant temperature for 240 min. Preferentially volatilize and remove Al, Mg, Zn, Pb, K, and Na. After the high-temperature constant-temperature section, cool it down to 700 °C at a rate of -8 °C / min. The temperature program ends, and it is naturally cooled to room temperature. Then open the gas release valve, fill it with high-purity argon gas. After the air pressure is balanced with the outside, open the vacuum flange 2 and take out the impurity collector. Replace it with a high-purity collector. Before its installation and use, remove the surface oil and metal impurities by degreasing ultrasonic cleaning and pickling with a mixed acid, then rinse it with pure water, dry it after completion, and then install it onto the substrate base 3, close the vacuum flange 2, close the gas release valve 7, evacuate to 2.0×10 -4 Pa, start heating, heat the distillation furnace to 1180 °C at a heating rate of 5 °C / min, keep it at a constant temperature for 330 min. Beryllium is deposited on the high-purity collector by vacuum distillation. Fe, Cr, Ni, and Mn are deflected and removed by the action of the gradient magnetic field. After the high-temperature constant-temperature section, cool it down to 700 °C at a rate of -8 °C / min, then the temperature program ends, and it is naturally cooled to room temperature. Open the gas release valve, fill it with high-purity argon gas. After the air pressure is balanced with the outside, open the vacuum flange and take out the high-purity collector, strip the high-purity beryllium, and perform ICPMS detection;

[0051] The impurity element contents before and after the treatment in this example are shown in Table 2.

[0052] Example 3

[0053] A method for purifying beryllium metal by vacuum distillation enhanced by a gradient magnetic field, comprising the following steps:

[0054] Weigh 5 g of coarse beryllium chips with impurity content as shown in Table 2, put them into the beryllium oxide crucible 8, and then install the oxidation crucible 8 into the vacuum distillation furnace 6; install the impurity collector 9 onto the substrate base 3, close the vacuum flange 2, close the gas release valve 7, evacuate to 2.0×10 -4Pa, start heating. The distillation furnace 6 is heated up to 300 °C at a heating rate of 8 °C / min, held at a constant temperature for 120 min, then heated up to 800 °C at a heating rate of 8 °C / min, held at a constant temperature for 120 min, and finally heated up to 1000 °C at a heating rate of 8 °C / min, held at a constant temperature for 330 min. Al, Mg, Zn, Pb, K, and Na are preferentially volatilized and removed. After the high-temperature constant-temperature stage ends, it is cooled down to 700 °C at a rate of -8 °C / min, the temperature program ends, and it is naturally cooled to room temperature. Then, the air release valve is opened, high-purity argon is filled, and after the air pressure is balanced with the outside, the vacuum flange 2 is opened, and the impurity collector is taken out. Replace it with a high-purity collector. Before its installation and use, ultrasonic degreasing and pickling with a mixed acid are used to remove surface oil stains and metal impurities, then it is rinsed with pure water, dried after completion, and then it is installed in the substrate base 3. The vacuum flange 2 is closed, the air release valve 7 is closed, and the vacuum is pumped to 2.0×10 -4 Pa, start heating. The distillation furnace is heated up to 1280 °C at a heating rate of 8 °C / min, held at a constant temperature for 240 min. Beryllium is deposited on the high-purity collector by vacuum distillation, and Fe, Cr, Ni, and Mn are deflected and removed by the action of the gradient magnetic field. After the high-temperature constant-temperature stage ends, it is cooled down to 700 °C at a rate of -8 °C / min, then the temperature program ends, and it is naturally cooled to room temperature. The air release valve is opened, high-purity argon is filled, and after the air pressure is balanced with the outside, the vacuum flange is opened, the high-purity collector is taken out, the high-purity beryllium is peeled off, and ICPMS detection is carried out;

[0055] The contents of impurity elements before and after the treatment in this embodiment are shown in Table 2.

[0056] Experimental effect

[0057] Table 2 Purity of crude beryllium before and after purification by gradient magnetic field enhanced vacuum distillation Unit: ppm

[0058]

[0059] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An apparatus for purifying beryllium metal by vacuum distillation enhanced by a gradient magnetic field, comprising a vacuum chamber (15), a molecular pump (14) is connected to the left side of the vacuum chamber (15), the molecular pump (14) is connected to a mechanical pump (11), a vacuum flange (2) and a glove box (10) are arranged on the right side of the vacuum chamber (15), a substrate base (3), a collector (9) and a distillation furnace (6) are sequentially arranged in the vacuum chamber (15) from top to bottom, and a crucible (8) is arranged in the distillation furnace (6). Characterized in that: A permanent magnet (4) and a water-cooled shielding plate (5) are further arranged between the collector (9) and the crucible (8), the water-cooled shielding plate (5) is located between the permanent magnet (4) and the crucible (8), wherein the permanent magnet (4) has asymmetric magnetic poles; The shape and structure of the permanent magnet (4) are: the N pole is arc-shaped, the S pole is triangular tip-shaped, a notch space is arranged between the N pole and the S pole as a gradient magnetic field region, and magnetic induction lines start from the N pole and focus on the tip of the S pole.

2. A method for purifying beryllium metal by vacuum distillation enhanced by a gradient magnetic field using the apparatus according to claim 1, Characterized in that, Its steps include: loading, primary vacuum pumping, vacuum volatilization, primary cooling and sampling, installing a high-purity collector, secondary vacuum pumping, vacuum distillation, secondary cooling and sampling.

3. According to the method described in claim 2, Characterized in that: The method of vacuum volatilization is: turn on the cooling water of the distillation furnace (6), set the temperature curve, start heating, raise the temperature to 300 °C ± 50 °C at a rate of 8 °C / min ± 4 °C / min, keep the temperature constant for 120 min ± 60 min, then raise the temperature to 800 °C ± 50 °C at a rate of 8 °C / min ± 4 °C / min, keep the temperature constant for 120 min ± 60 min, and finally raise the temperature to 1000 °C ± 200 °C at a rate of 8 °C / min ± 4 °C / min, keep the temperature constant for 240 min ± 120 min, and remove Al, Mg, Zn, Pb, K, Na by vacuum volatilization.

4. According to the method described in claim 2, Characterized in that: The method of vacuum distillation is: turn on the cooling water of the distillation furnace (6), set the temperature curve, start heating, raise the temperature to 1200 °C ± 150 °C at a rate of 8 °C / min ± 4 °C / min, keep the temperature constant for 240 min ± 120 min, crude beryllium evaporates from the crucible (8), beryllium atoms travel perpendicular to the magnetic field direction, have no magnetic moment and are not affected by force, move linearly to deposit on the high-purity collector (9), while impurity atoms such as Fe, Cr, Ni, and Mn are deflected and removed by the action of the gradient magnetic field.

5. According to the method described in claim 2, Characterized in that: The high-purity collector is also cleaned before installation and use, and the cleaning steps include: adding a degreasing agent for ultrasonic treatment, pickling with a mixed acid, rinsing with pure water, and drying.

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