Ultra-pure tin preparation method integrating high-temperature volatilization impurity removal and vacuum distillation grading purification

Abstract

The invention belongs to the field of ultrapure tin preparation, and provides a high-temperature volatilization impurity removal and vacuum distillation grading purification integrated ultrapure tin preparation method which comprises the steps of device building, high-temperature volatilization impurity removal, vacuum distillation purification and condensation collection and product collection. When the device is built, a crucible in a vacuum medium-frequency induction furnace is communicated with a crucible in a vacuum distillation furnace through a high-temperature-resistant pipe fitting, and in the technological process, molten tin subjected to high-temperature impurity removal is transferred into the vacuum distillation furnace through the high-temperature-resistant pipe fitting under the vacuum condition by utilizing the pressure difference in a furnace cavity of the vacuum medium-frequency induction furnace and a furnace cavity of the vacuum distillation furnace; according to the preparation method, the raw materials of the light source excitation material can be recycled, so that the problem of secondary pollution caused by the transfer of the materials among different devices is avoided, the preparation of an ultra-pure tin product with the purity being greater than or equal to 99.999995% and the oxygen content being less than or equal to 1 ppm is realized, the product quality can meet the requirements of an EUV photoetching machine on the purity and the oxygen content of the light source excitation material, and the requirement of the high-end electronic industry on the ultra-pure tin can be better met.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of ultra-pure tin preparation and relates to an ultra-pure tin preparation method integrating high-temperature volatile impurity removal and vacuum distillation fractional purification. BACKGROUND

[0002] As the core key equipment in the semiconductor industry, there are many research institutions independently developing extreme ultraviolet lithography machines (EUV lithography machines). The light source is a core component of the EUV lithography machine, and extreme ultraviolet light is generated by means of high-energy laser (carbon dioxide laser) bombardment of tin droplets. The purity of tin is required to reach 99.999995% (7N5 level), and the oxygen content of tin is strictly required to be less than 1 ppm. The development of low-oxygen ultra-pure tin becomes a key material in the development process of the EUV lithography machine.

[0003] In the prior art, the preparation methods of ultra-pure tin mainly include electrolytic refining, zone melting and vacuum distillation. However, the purity of the ultra-pure tin prepared by these methods is difficult to reach more than 99.9999% (6N level), which cannot meet the demand of the high-end electronic industry for ultra-pure tin, especially cannot meet the purity requirement of the light source excitation material of the EUV lithography machine. At the same time, the existing ultra-pure tin preparation method needs to use multiple devices for step-by-step processing. For example, the high-temperature volatile impurity removal process and the vacuum distillation purification process are carried out in different devices in steps. After the high-temperature volatile impurity removal is completed in the previous device, the ingot is formed, taken out and transferred to the next device for vacuum distillation purification. Not only is the process flow complex and the production efficiency low, but also the heating temperature in different devices is as high as 1000 ℃ or more, the energy consumption is very high, and the transfer process between different devices is easy to cause secondary pollution and impurity residue of the product, which leads to the difficulty in further improving the purity of the product, the high oxygen content and the poor consistency of the product. SUMMARY

[0004] In view of the problems that the purity and oxygen content of the ultra-pure tin product prepared by the traditional ultra-pure tin preparation method cannot meet the purity and oxygen content requirements of the light source excitation material tin of the EUV lithography machine, the production efficiency is low and the energy consumption is high, the application provides an ultra-pure tin preparation method integrating high-temperature volatile impurity removal and vacuum distillation fractional purification, so as to realize the preparation of 7N5 level ultra-pure tin with low oxygen content and improve the production efficiency and reduce the process energy consumption.

[0005] To achieve the above application purposes, the technical solutions adopted by the application are as follows:

[0006] The ultra-pure tin preparation method integrating high-temperature volatile impurity removal and vacuum distillation fractional purification comprises the following steps:

[0007] (1) Device construction: the vacuum medium frequency induction furnace and the vacuum distillation furnace are connected through high-temperature-resistant pipe fittings, the inlet end of the high-temperature-resistant pipe fittings is communicated with the crucible in the vacuum medium frequency induction furnace, the outlet end of the high-temperature-resistant pipe fittings is communicated with the crucible in the vacuum distillation furnace, and a control valve is arranged on the high-temperature-resistant pipe fittings;

[0008] (2) High-temperature volatile impurity removal: close the control valve, and under the protection of high-purity inert gas, the raw material tin ingot is loaded into the crucible of the vacuum medium frequency induction furnace, a layer of porous filler is arranged at the bottom of the crucible, the vacuum medium frequency induction furnace is vacuumized to a pressure less than 10 -3 Pa in the furnace cavity, the crucible is heated to 1100-1300 ℃ and fully heat-insulated to remove volatile impurities, and high-temperature impurity-removed molten tin is obtained;

[0009] In this step, the purity of the raw material tin ingot is 5N or 6N, and the pressure in the vacuum medium frequency induction furnace cavity is kept less than 10 -3 Pa during heating and heat-insulating;

[0010] (3) Vacuum distillation purification and condensation collection: the pressure in the vacuum medium frequency induction furnace cavity is controlled to keep at the level of step (2), the vacuum distillation furnace cavity is vacuumized to a pressure at least one order of magnitude lower than the pressure in the vacuum medium frequency induction furnace cavity, the control valve is opened, the high-temperature impurity-removed molten tin is guided into the crucible of the vacuum distillation furnace through the high-temperature-resistant pipe fittings by using the pressure difference between the vacuum medium frequency induction furnace cavity and the vacuum distillation furnace cavity, the control valve is closed, the pressure in the vacuum distillation furnace cavity is kept at least one order of magnitude lower than the pressure in the vacuum medium frequency induction furnace cavity, the crucible is heated to 1200-1400 ℃, and heat-insulated distillation is performed; during heat-insulated distillation, the vapor generated by distillation continuously enters the multi-stage condensation system of the vacuum distillation furnace, and different boiling point substances are separated and collected in the multi-stage condensation system, ultra-pure tin is collected in the low-temperature condensation zone with a temperature of 50-100 ℃, and the collected ultra-pure tin is cooled to room temperature in the vacuum distillation furnace to form;

[0011] (4) Product collection: the formed ultra-pure tin product is collected under the protection of high-purity inert gas, and the purity of the ultra-pure tin product is above 7N5 level and the oxygen content is ≤1 ppm.

[0012] In the above technical solution, in order to utilize the pressure difference between the vacuum medium frequency induction furnace cavity and the vacuum distillation furnace cavity, the high-temperature impurity-removed molten tin is smoothly transported from the vacuum medium frequency induction furnace to the vacuum distillation furnace through the high-temperature-resistant pipe fittings, the pressure in the vacuum distillation furnace cavity is controlled to be less than 10 -4 Pa in step (3), and further, the pressure in the vacuum distillation furnace cavity is preferably controlled to be less than 10 -5 Pa in step (3).

[0013] In the technical solution, in order to smoothly transport the high-temperature impurity-removed molten tin from the vacuum medium-frequency induction furnace to the vacuum distillation furnace through the high-temperature-resistant pipe, when the device is built in step (1), the position of the inlet end of the high-temperature-resistant pipe is preferably higher than the position of the outlet end, for example, the position of the vacuum medium-frequency induction furnace can be controlled to be higher than the position of the vacuum distillation furnace.

[0014] In the technical solution, in step (3), when the high-temperature impurity-removed molten tin is introduced into the crucible of the vacuum distillation furnace through the high-temperature-resistant pipe by using the pressure difference between the furnace cavities of the vacuum medium-frequency induction furnace and the vacuum distillation furnace, in order to avoid the porous filler being sucked into the crucible of the vacuum distillation furnace, in step (1), when the device is built, the inlet end of the high-temperature-resistant pipe is ensured to be located in the crucible and above the porous filler. Further, the inner diameter of the inlet end of the high-temperature-resistant pipe can be controlled to be smaller than the size of the porous filler.

[0015] In the technical solution, in order to facilitate the operation of the control valve, the control valve is located outside the vacuum medium-frequency induction furnace and the vacuum distillation furnace.

[0016] In the technical solution, in the process of transporting the high-temperature impurity-removed molten tin from the vacuum medium-frequency induction furnace to the vacuum distillation furnace through the high-temperature-resistant pipe, in order to avoid the high-temperature-resistant pipe causing secondary pollution of the product, the high-temperature-resistant pipe is preferably a high-purity quartz pipe.

[0017] In step (2) of the technical solution, the length of the holding time should ensure that volatile impurities can be sufficiently removed during the holding process. The volatile impurities mainly include low-boiling-point impurities such as Pb, Bi, and As. The composition of the volatile gas can be monitored by a mass spectrometer or a spectrometer during the holding period until the volatile impurities are sufficiently removed. Preferably, the holding time in step (2) is controlled to be 2-3 h.

[0018] In the technical solution, the holding and distillation time in step (2) is preferably controlled to be 1-2 h.

[0019] In step (3) of the technical solution, the collected ultra-pure tin is preferably cooled to room temperature at a cooling rate of 5-10 ℃ / min.

[0020] In the technical solution, the material of the crucible of the vacuum medium-frequency induction furnace is high-purity quartz or high-purity graphite, and the material of the porous filler is high-purity alumina, high-purity graphene, or high-purity quartz. The purity of the high-purity quartz, high-purity graphite, high-purity graphene, and high-purity alumina is all ≥99.9999%.

[0021] In the technical scheme, the porous filler is filled in the bottom of the crucible of the vacuum medium-frequency induction furnace, and is used to adsorb impurities in the molten tin in the crucible in step (2). Further, the porous filler is in a granular form, and the porous filler has a nano-scale or micro-scale pore structure.

[0022] In the technical scheme, the size of the porous filler can be about 10 mm, for example, 5-15 mm, and correspondingly, the inner diameter of the inlet end of the high-temperature-resistant pipe is 10%-20% smaller than the size of the porous filler. Further, the porous filler can be filled in the bottom of the crucible to form a layer, and the filling thickness of the porous filler in the bottom of the crucible can be 10-20 mm.

[0023] In the technical scheme, the high-purity quartz crucible, the high-purity quartz filler and the high-purity quartz tube need to be immersed in aqua regia, then washed with ultrapure water and dried before use; the high-purity graphite crucible, the high-purity graphene filler and the high-purity alumina filler need to be immersed in aqua regia, then washed with ultrapure water, and then impurities are removed by vacuum calcination at 1000-1100 ℃.

[0024] In the technical scheme, the purity of the high-purity inert gas is ≥99.999%, and the high-purity inert gas can be high-purity argon.

[0025] Compared with the prior art, the technical scheme provided by the present application has the following beneficial technical effects:

[0026] 1. The present application provides a method for preparing ultra-pure tin by integrating high-temperature volatilization and vacuum distillation, which comprises the following steps: (1) preparing high-purity tin by vacuum medium-frequency induction melting; (2) transferring the high-temperature volatilization and vacuum distillation of the molten tin in the vacuum medium-frequency induction furnace to the vacuum distillation furnace through the high-temperature-resistant pipe; (3) controlling the pressure in the vacuum medium-frequency induction furnace and the vacuum distillation furnace, and constructing a pressure difference; and (4) controlling the control valve on the high-temperature-resistant pipe to realize the transfer of the molten tin in the vacuum medium-frequency induction furnace to the vacuum distillation furnace. The material transfer process is carried out in a vacuum condition, avoiding secondary pollution caused by the transfer of the material between different devices, thereby reducing the purity of the ultra-pure tin product, increasing the impurity content and the oxidation, and realizing the preparation of an ultra-pure tin product with a purity of ≥99.999995% (7N5 level) and an oxygen content of ≤1 ppm. The product quality can meet the purity and oxygen content requirements of the EUV photoetching machine for light source excitation materials, and can better meet the demand of the high-end electronic industry for ultra-pure tin.

[0027] 2. The method of the present application realizes the transfer of liquid molten tin between the vacuum medium frequency induction furnace and the vacuum distillation furnace by connecting the crucible in the furnace cavity of the vacuum medium frequency induction furnace with the crucible in the furnace cavity of the vacuum distillation furnace through the high-temperature-resistant pipe and controlling the pressure in the furnace cavities of the vacuum medium frequency induction furnace and the vacuum distillation furnace in combination with the process. After the molten tin is transferred to the vacuum distillation furnace, it still remains in the molten state, so that the heating time in the vacuum distillation furnace can be greatly shortened. Compared with the prior art which needs to go through the process path of heating and melting-casting ingot-forming-cooling-reheating and evaporation by using multiple devices in a step-by-step manner, the method of the present application only needs to go through the process path of heating and melting-maintaining the molten tin state for evaporation, which not only can shorten the process flow and improve the production efficiency, but also can effectively reduce the energy consumption of the process. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a schematic diagram of the connection between the vacuum medium frequency induction furnace and the vacuum distillation furnace in the embodiment, and the reference signs are explained as follows: 1 is the vacuum medium frequency induction furnace, 2 is the vacuum distillation furnace, 3 is the high-temperature-resistant pipe, 4 is the crucible in the vacuum medium frequency induction furnace, 5 is the crucible in the vacuum distillation furnace, 6 is the control valve, and 7 is the porous filler. DETAILED DESCRIPTION

[0029] The method of preparing ultra-pure tin by integrating high-temperature volatile impurity removal and vacuum distillation fractional purification according to the present application will be further described below by means of embodiments. It is necessary to point out that the following embodiments are only used for further description of the present application and cannot be understood as limiting the protection scope of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the specific implementation of the present application according to the above description, which still belongs to the protection scope of the present application.

[0030] In each of the following embodiments and comparative examples, the high-purity quartz crucible, the high-purity quartz filler and the high-purity quartz tube involved need to be first immersed in aqua regia and then washed with ultrapure water and dried before use; the high-purity graphite crucible, the high-purity graphene filler and the high-purity alumina filler involved need to be first immersed in aqua regia, then washed with ultrapure water, and then calcined at 1000-1100 ℃ in vacuum to remove impurities before use.

[0031] In each of the following embodiments, the vacuum medium frequency induction furnace and the vacuum distillation furnace used in the device building process are both devices already existing in the prior art. In order to connect the furnace cavities of the vacuum medium frequency induction furnace and the vacuum distillation furnace through the high-temperature-resistant pipe, a hole with a diameter matching the outer diameter of the high-temperature-resistant pipe is formed on the furnace body of the vacuum medium frequency induction furnace and the vacuum distillation furnace, and the high-temperature-resistant pipe is sealed after installation, in combination with a sealing element.

[0032] Embodiment 1

[0033] In this embodiment, a method for preparing ultrapure tin that integrates high-temperature volatilization for impurity removal and vacuum distillation for fractional purification is provided, and the steps are as follows:

[0034] (1) Device setup: such as Figure 1 As shown, a vacuum intermediate frequency induction furnace and a vacuum distillation furnace are connected by a high-temperature resistant pipe fitting with an inner diameter of 8 mm. The inlet end of the high-temperature resistant pipe fitting is connected to the crucible inside the vacuum intermediate frequency induction furnace. After the bottom of the crucible inside the vacuum intermediate frequency induction furnace is filled with porous packing, the inlet end of the high-temperature resistant pipe fitting is positioned above the porous packing, approximately 10 mm away from it. The outlet end of the high-temperature resistant pipe fitting is connected to the crucible inside the vacuum distillation furnace. By adjusting the placement or installation height of the vacuum intermediate frequency induction furnace and the vacuum distillation furnace, the inlet end of the high-temperature resistant pipe fitting is positioned higher than the outlet end. A control valve is installed on the high-temperature resistant pipe fitting, located outside the vacuum intermediate frequency induction furnace and the vacuum distillation furnace. The high-temperature resistant pipe fitting is a high-purity quartz tube.

[0035] (2) High-temperature volatilization and impurity removal: Close the control valve on the high-temperature resistant pipe fitting. Under the protection of high-purity argon, put 100 g of tin ingot (purity 99.9999%, 6N grade) into the high-purity quartz crucible of the vacuum intermediate frequency induction furnace. The quartz crucible is filled with a porous packing material with a thickness of about 10 mm. The porous packing material is high-purity alumina packing material. The porous packing material is granular with a particle size in the range of 5~10 mm. The porous packing material has a nanoscale pore structure. Evacuate the furnace cavity of the vacuum intermediate frequency induction furnace until the furnace pressure is less than 10. -3 Pa. Start the intermediate frequency induction system of the vacuum intermediate frequency induction furnace, heat the quartz crucible to 1300 ℃, and hold for 2 hours to remove volatile impurities (mainly Pb, Bi, and As), obtaining high-temperature purified molten tin. During this heating and holding process, maintain the pressure in the vacuum intermediate frequency induction furnace cavity below 10 Pa. -3 Pa.

[0036] (3) Vacuum distillation purification and condensation collection: The pressure inside the vacuum medium-frequency induction furnace is controlled to maintain the level in step (2), and the furnace cavity of the vacuum distillation furnace is evacuated until the pressure inside the furnace is less than 10. -5 Pa, and control the vacuum distillation furnace cavity to be evacuated until the pressure inside the cavity is at least one order of magnitude lower than the pressure inside the vacuum induction furnace cavity. Open the control valve on the high-temperature resistant pipe, and use the pressure difference between the vacuum induction furnace cavity and the vacuum distillation furnace cavity to guide the high-temperature purified molten tin through the high-temperature resistant pipe into the crucible of the vacuum distillation furnace. Close the control valve on the high-temperature resistant pipe; maintain the vacuum distillation furnace cavity evacuated until the furnace pressure is less than 10 Pa. -5Pa, the crucible is heated to 1300 ℃, and the vacuum distillation furnace is kept for 1.5 h. During the keeping, the vapor generated by distillation continuously enters the multi-stage condensation system of the vacuum distillation furnace, and sequentially passes through the high-temperature condensation zone (600-800 ℃), the medium-temperature condensation zone (400-600 ℃) and the low-temperature condensation zone (50-100 ℃) of the multi-stage condensation system, so as to realize separation and collection of different substances with different boiling points. The ultra-pure tin is collected in the low-temperature condensation zone, and the collected ultra-pure tin is cooled to room temperature at a cooling rate of 8 ℃ / min in the vacuum distillation furnace to form a shape.

[0037] (4) Product collection: collect the shaped ultra-pure tin product under the protection of high-purity argon.

[0038] (5) Repeat the operations of steps (2)-(4) for 2 times, and totally prepare 3 batches of ultra-pure tin products.

[0039] The three batches of ultra-pure tin products collected in this embodiment are detected for the content of total element impurities, and the results show that:

[0040] The first batch of products: the product purity is 99.999995% (7N5 level), and the contents of impurity elements S, Se, Zn, Fe, Pb, Bi and Cd are all ≤0.007 ppm, and the oxygen content is ≤0.92 ppm;

[0041] The second batch of products: the product purity is 99.999995%, and the contents of impurity elements S, Se, Zn, Fe, Pb, Bi and Cd are all ≤0.007 ppm, and the oxygen content is ≤0.9 ppm;

[0042] The third batch of products: the product purity is 99.999995%, and the contents of impurity elements S, Se, Zn, Fe, Pb, Bi and Cd are all ≤0.007 ppm, and the oxygen content is ≤0.86 ppm.

[0043] The qualities of the three batches of products can all meet the requirements of the purity and oxygen content of the light source excitation material of the EUV photoetching machine, which indicates that the quality of the ultra-pure tin product produced by the method has high consistency.

[0044] Comparative Example 1

[0045] This comparative example is used for comparison with Example 1, and provides a high-temperature volatilization impurity removal-vacuum distillation fractional purification step-by-step ultra-pure tin preparation method, and the steps are as follows:

[0046] (1) High-temperature volatilization impurity removal: 100 g of tin ingot (purity 99.9999%, 6N level) is loaded into a high-purity quartz crucible of a vacuum medium-frequency induction furnace, high-purity quartz filler is loaded into the quartz crucible, and then the furnace cavity of the vacuum medium-frequency induction furnace is vacuumized to a pressure less than 10-3 Pa. Start the intermediate frequency induction system of the vacuum intermediate frequency induction furnace, heat the quartz crucible to 1300 ℃, and keep it for 2 h to remove volatile impurities (mainly Pb, Bi, and As) to obtain high-temperature impurity-removed molten tin. During the heating and keeping process, the pressure in the furnace cavity of the vacuum intermediate frequency induction furnace is kept less than 10 -3 Pa.

[0047] (2) Ingot casting: under the protection of high-purity argon, the high-temperature impurity-removed molten tin in step (1) is cast into ingots to obtain ingot-cast tin.

[0048] (3) Vacuum distillation and condensation collection: under the protection of high-purity argon, the ingot-cast tin in step (2) is added to the crucible in the distillation chamber of the vacuum distillation furnace, the furnace cavity of the vacuum distillation furnace is vacuumized to a pressure less than 10 -5 Pa, then the crucible is heated to 1300 ℃, and kept for 1.5 h for distillation; during the keeping and distillation process, the vapor generated by distillation continuously enters the multi-stage condensation system of the vacuum distillation furnace, and sequentially passes through the high-temperature condensation zone (600-800 ℃), the medium-temperature condensation zone (400-600 ℃), and the low-temperature condensation zone (50-100 ℃) of the multi-stage condensation system to realize the separation and collection of different substances with different boiling points, and the ultra-pure tin is collected in the low-temperature condensation zone, and the collected ultra-pure tin is cooled to room temperature in the vacuum distillation furnace at a cooling rate of 8 ℃ / min to form. During the heating, keeping and distillation, and condensation process, the pressure in the furnace cavity of the vacuum distillation furnace is kept less than 10 -5 Pa.

[0049] (4) Product collection: under the protection of high-purity argon, the formed ultra-pure tin product is collected.

[0050] (5) Repeat the operations of steps (1)-(4) for 2 times, and totally prepare 3 batches of ultra-pure tin products.

[0051] The three batches of ultra-pure tin products collected in the present comparative example are detected for the content of total element impurities, and the results show that:

[0052] The first batch of product: the product purity is 99.999991% (7N1 level), and the contents of impurity elements S, Se, Zn, Fe, Pb, Bi, and Cd are all ≤0.016 ppm, and the oxygen content is ≤4.5 ppm;

[0053] The second batch of product: the product purity is 99.999993% (7N3 level), and the contents of impurity elements S, Se, Zn, Fe, Pb, Bi, and Cd are all ≤0.02 ppm, and the oxygen content is ≤4.8 ppm;

[0054] The product of the third batch: the product purity is 99.999992% (7N2 level), and the content of impurity elements S, Se, Zn, Fe, Pb, Bi and Cd is all ≤0.014 ppm, and the oxygen content is ≤4.9 ppm.

[0055] Compared with Example 1, the content of impurity elements in the ultra-pure tin product of Comparative Example 1 is higher, especially the oxygen content is significantly increased, and the quality of the product prepared by Comparative Example 1 cannot meet the purity and oxygen content requirements of the light source excitation material of the EUV photoetching machine.

[0056] Example 2

[0057] In this embodiment, an ultra-pure tin preparation method integrating high-temperature volatilization impurity removal and vacuum distillation fractional purification is provided, and the steps are as follows:

[0058] (1) Device construction: same as Example 1.

[0059] (2) High-temperature volatilization impurity removal: close the control valve on the high-temperature resistant pipe, and under the protection of high-purity argon, 100 g of tin ingot (purity 99.9999%, 6N level) is loaded into the high-purity graphite crucible of the vacuum medium-frequency induction furnace, and high-purity quartz filler is loaded in the graphite crucible, and then the furnace cavity of the vacuum medium-frequency induction furnace is vacuumized to a pressure less than 5×10 -4 Pa. Start the medium-frequency induction system of the vacuum medium-frequency induction furnace, heat the graphite crucible to 1300 ℃, and keep the temperature for 2.5 h to obtain high-temperature impurity removal molten tin. During the heating and keeping process, the pressure in the furnace cavity of the vacuum medium-frequency induction furnace is kept less than 5×10 -4 Pa.

[0060] (3) Vacuum distillation purification and condensation collection: control the pressure in the furnace cavity of the vacuum medium-frequency induction furnace to keep the level of step (2), vacuumize the furnace cavity of the vacuum distillation furnace to a pressure less than 5×10 -5 Pa, and control the vacuumization of the furnace cavity of the vacuum distillation furnace to be at least one order of magnitude lower than the pressure in the furnace cavity of the vacuum medium-frequency induction furnace, open the control valve on the high-temperature resistant pipe, and use the pressure difference between the furnace cavities of the vacuum medium-frequency induction furnace and the vacuum distillation furnace to guide the high-temperature impurity removal molten tin into the crucible of the vacuum distillation furnace through the high-temperature resistant pipe, and close the control valve on the high-temperature resistant pipe; keep the furnace cavity of the vacuum distillation furnace vacuumized to a pressure less than 5×10 -5Pa, the crucible is heated to 1400 ℃, and the vacuum distillation furnace is kept for 2 h. During the keeping, the vapor generated by distillation continuously enters the multi-stage condensation system of the vacuum distillation furnace, and sequentially passes through the high-temperature condensation zone (600-800 ℃), the medium-temperature condensation zone (400-600 ℃), and the low-temperature condensation zone (50-100 ℃) of the multi-stage condensation system, so as to realize separation and collection of different substances with different boiling points. The ultra-pure tin is collected in the low-temperature condensation zone, and the collected ultra-pure tin is cooled to room temperature in the vacuum distillation furnace at a cooling rate of 5 ℃ / min to form a shape.

[0061] (4) Product collection: The ultra-pure tin product cooled and formed is collected under the protection of high-purity argon.

[0062] The ultra-pure tin product collected in this embodiment is detected for the content of all element impurities, and the results show that the purity of the product is 99.999996% (7N6 level), the contents of impurity elements S, Se, Zn, Fe, Pb, Bi, and Cd are all ≤0.005 ppm, the oxygen content is ≤0.6 ppm, and the product quality can meet the purity and oxygen content requirements of the EUV photoetching machine on the light source excitation material.

[0063] Example 3

[0064] The operation of this embodiment is basically the same as that of Example 2, except that the tin ingot with a purity of 99.9999% (6N level) in Example 2 is replaced by a tin ingot with a purity of 99.999% (5N level).

[0065] The ultra-pure tin product collected in this embodiment is detected for the content of all element impurities, and the results show that the purity of the product is 99.999995% (7N5 level), the contents of impurity elements S, Se, Zn, Fe, Pb, Bi, and Cd are all ≤0.008 ppm, the oxygen content is ≤0.98 ppm, and the product quality can meet the purity and oxygen content requirements of the EUV photoetching machine on the light source excitation material.

[0066] Example 4

[0067] In this embodiment, a method for preparing ultra-pure tin integrating high-temperature volatilization impurity removal and vacuum distillation fractional purification is provided, and the steps are as follows:

[0068] (1) Device building: same as Example 1.

[0069] (2) High-temperature volatilization impurity removal: close the control valve on the high-temperature resistant pipe fitting, and put 100 g of tin ingot (purity 99.9999%, 6N level) into the high-purity quartz crucible of the vacuum medium-frequency induction furnace under the protection of high-purity argon. The high-purity quartz filler is filled in the quartz crucible, and then the furnace cavity of the vacuum medium-frequency induction furnace is vacuumized to a pressure less than 10 -4Pa. Start the intermediate frequency induction system of the vacuum intermediate frequency induction furnace, heat the quartz crucible to 1100 ℃, and keep the temperature for 3 h to obtain high-temperature impurity-removed molten tin. During the heating and keeping process, the pressure in the furnace cavity of the vacuum intermediate frequency induction furnace is kept less than 10 -4 Pa.

[0070] (3) Vacuum distillation purification and condensation collection: control the pressure in the furnace cavity of the vacuum intermediate frequency induction furnace to keep the level of step (2), vacuumize the furnace cavity of the vacuum distillation furnace to a pressure less than 10 -5 Pa in the furnace, control the vacuumization of the furnace cavity of the vacuum distillation furnace to a pressure at least one order of magnitude lower than the pressure in the furnace cavity of the vacuum intermediate frequency induction furnace, open the control valve on the high-temperature resistant pipe, use the pressure difference between the furnace cavities of the vacuum intermediate frequency induction furnace and the vacuum distillation furnace to guide the high-temperature impurity-removed molten tin into the crucible of the vacuum distillation furnace through the high-temperature resistant pipe, and close the control valve on the high-temperature resistant pipe; keep the vacuumization of the furnace cavity of the vacuum distillation furnace to a pressure less than 10 -5 Pa, heat the crucible to 1200 ℃, and keep distillation for 1 h. During the keeping distillation, the vapor produced by distillation continuously enters the multi-stage condensation system of the vacuum distillation furnace, and successively passes through the high-temperature condensation zone (600-800 ℃), the medium-temperature condensation zone (400-600 ℃), and the low-temperature condensation zone (50-100 ℃) of the multi-stage condensation system to realize the separation and collection of different substances with different boiling points. The ultra-pure tin is collected in the low-temperature condensation zone, and the collected ultra-pure tin is cooled to room temperature in the vacuum distillation furnace at a cooling rate of 10 ℃ / min to form.

[0071] (4) Product collection: collect the cooled and formed ultra-pure tin product under the protection of high-purity argon.

[0072] The ultra-pure tin product collected in the embodiment is detected for the content of total element impurities, and the result shows that the purity of the product is 99.999995% (7N5 level), the content of impurity elements S, Se, Zn, Fe, Pb, Bi, and Cd is all ≤0.007 ppm, the oxygen content is ≤0.86 ppm, and the quality of the product can meet the purity and oxygen content requirements of the EUV photoetching machine for light source excitation materials.

Claims

1. A method for preparing ultrapure tin that integrates high-temperature volatilization for impurity removal and vacuum distillation for fractional purification, characterized in that, Includes the following steps: (1) Setup of the apparatus: Connect the vacuum intermediate frequency induction furnace and the vacuum distillation furnace through a high-temperature resistant pipe. The inlet end of the high-temperature resistant pipe is connected to the crucible inside the vacuum intermediate frequency induction furnace, and the outlet end of the high-temperature resistant pipe is connected to the crucible inside the vacuum distillation furnace. A control valve is installed on the high-temperature resistant pipe. (2) High-temperature volatilization and impurity removal: Close the control valve, and under the protection of high-purity inert gas, load the raw tin ingots into the crucible of the vacuum intermediate frequency induction furnace. The bottom of the crucible is filled with porous packing. Evacuate the vacuum intermediate frequency induction furnace until the pressure inside the furnace cavity is less than 10. -3 Pa; The crucible is heated to 1100~1300 ℃ and held at that temperature for a sufficient period of time to remove volatile impurities, thus obtaining high-temperature purified molten tin; In this step, the purity of the raw tin ingot is 5N or 6N. During the heating and heat preservation process, the pressure inside the vacuum medium-frequency induction furnace cavity is maintained below 10. -3 Pa; (3) Vacuum distillation purification and condensation collection: The pressure in the vacuum medium-frequency induction furnace is controlled to be maintained at the level in step (2). The vacuum distillation furnace cavity is evacuated until the pressure in the furnace cavity is at least one order of magnitude lower than the pressure in the vacuum medium-frequency induction furnace cavity. The control valve is opened, and the molten tin with high temperature impurity removal is introduced into the crucible of the vacuum distillation furnace through the high temperature resistant pipe by utilizing the pressure difference between the vacuum medium-frequency induction furnace cavity and the vacuum distillation furnace cavity. The control valve is closed, and the pressure in the vacuum distillation furnace cavity is kept at least one order of magnitude lower than the pressure in the vacuum medium-frequency induction furnace cavity. The crucible is heated to 1200~1400 ℃ and kept warm for distillation. During the kept warm distillation process, the vapor generated by distillation continuously enters the multi-stage condensation system of the vacuum distillation furnace. The separation and collection of substances with different boiling points are realized in the multi-stage condensation system. Ultra-pure tin is collected in the low temperature condensation zone at 50~100 ℃, and the collected ultra-pure tin is cooled to room temperature in the vacuum distillation furnace for molding. (4) Product collection: The ultrapure tin product is collected under the protection of high-purity inert gas. The purity of the ultrapure tin product is ≥99.999995% and the oxygen content is ≤1 ppm.

2. The method for preparing ultrapure tin integrating high-temperature volatilization and vacuum distillation for fractional purification according to claim 1, characterized in that, In step (3), the pressure inside the vacuum distillation furnace cavity is controlled to be less than 10. -4 Pa.

3. The method for preparing ultrapure tin integrating high-temperature volatilization and vacuum distillation for fractional purification according to claim 1, characterized in that, In step (1), the inlet end of the high-temperature resistant pipe is controlled to be located inside the crucible and above the porous packing, and the position of the inlet end of the high-temperature resistant pipe is controlled to be higher than the position of the outlet end.

4. The method for preparing ultrapure tin integrating high-temperature volatilization and impurity removal with vacuum distillation and fractional purification according to claim 1, characterized in that, The control valve is located outside the vacuum intermediate frequency induction furnace and the vacuum distillation furnace.

5. The method for preparing ultrapure tin integrating high-temperature volatilization and impurity removal with vacuum distillation and fractional purification according to any one of claims 1 to 4, characterized in that, The heat preservation time in step (2) is 2~3 h.

6. The method for preparing ultrapure tin integrating high-temperature volatilization and vacuum distillation for fractional purification according to any one of claims 1 to 4, characterized in that, The time for heat preservation and distillation in step (3) is 1~2 h.

7. The method for preparing ultrapure tin integrating high-temperature volatilization and vacuum distillation for fractional purification according to any one of claims 1 to 4, characterized in that, In step (3), the collected ultrapure tin is cooled to room temperature and shaped at a cooling rate of 5~10 ℃ / min.

8. The method for preparing ultrapure tin integrating high-temperature volatilization and vacuum distillation for fractional purification according to any one of claims 1 to 4, characterized in that, The crucible of the vacuum intermediate frequency induction furnace is made of high-purity quartz or high-purity graphite, and the porous filler is made of high-purity alumina, high-purity graphene, or high-purity quartz.

9. The method for preparing ultrapure tin integrating high-temperature volatilization and vacuum distillation for fractional purification according to claim 8, characterized in that, The porous filler is granular and has a nanoscale or microscale pore structure.

10. The method for preparing ultrapure tin integrating high-temperature volatilization and vacuum distillation for fractional purification according to any one of claims 1 to 4, characterized in that, The high-purity inert gas includes high-purity argon.

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