Preparation method of tetra (dimethylamino) hafnium

Abstract

The invention discloses a preparation method of tetra (dimethylamino) hafnium, and belongs to the technical field of preparation of IVB group metal organic compounds. The preparation method comprises the following steps: S1, carrying out primary rectification on a tetra (dimethylamino) hafnium crude product, and collecting a primary main fraction; s2, dissolving the primary main fraction, and recrystallizing to obtain a crystal; and S3, dissolving the crystal, carrying out secondary rectification, and collecting a secondary main fraction. The tetra (dimethylamino) hafnium crude product is derived from waste liquid in the production process of cyclopentadienyl tris (dimethylamino) hafnium, and the crude product contains less than or equal to 8.0 ppm of Fe and less than or equal to 1.0 ppm of Ti; according to the method, 6N-grade (99.9999% or above) ultra-high-purity recovery of the TDMAHf product in the CpHf synthesis waste liquid is achieved by optimizing key parameters such as rectification and recrystallization parameters, and the recovered product completely meets the strict requirements of high-end fields such as semiconductor film deposition on metal precursors; the preparation method is short in process period and high in treatment efficiency, does not introduce other impurities, and can realize industrial application.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of group IV B metal organic compounds, and particularly relates to a method for preparing tetrakis(dimethylamino)hafnium. Background Art

[0002] Tetrakis(dimethylamino)hafnium (TDMAHf), a high-purity hafnium-based precursor, has important applications in semiconductor manufacturing processes, particularly atomic layer deposition (ALD). Cyclopentadienyltris(dimethylamino)hafnium (CpHf) is often synthesized industrially through a ligand exchange reaction between TDMAHf and cyclopentadiene monomer or metal compounds containing cyclopentadienyl groups.

[0003] During the synthesis of CpHf, some TDMAHf fails to coordinate with the cyclopentadiene monomer, resulting in unreacted TDMAHf in the reaction wastewater after the reaction. Industrially, crude TDMAHf is typically separated and recovered from the reaction wastewater using vacuum distillation. However, due to trace metal impurities (such as Fe and Ti) inherent in the raw materials, and the potential introduction of additional impurities due to equipment corrosion during the high-temperature reaction and distillation processes, the resulting crude TDMAHf product can contain significantly excessive levels of Fe and Ti impurities, making it difficult to meet the stringent purity requirements for semiconductor-grade precursors. This presents significant obstacles to the recovery and reuse of the precursor from the wastewater.

[0004] Existing purification technologies (such as conventional distillation and molecular sieve adsorption) have limited effectiveness in removing metal impurities, mainly because the boiling points of Fe and Ti impurities are close to those of TDMAHf, making conventional distillation difficult to achieve effective separation. In addition, metal impurities may exist in the form of complexes or colloidal particles, and traditional adsorption methods have poor selectivity and insufficient capacity.

[0005] Therefore, developing a refining method that can efficiently and deeply remove impurity elements, especially Fe and Ti impurities, from crude TDMAHf is of great significance for achieving high-value recovery of TDMAHf, improving raw material utilization, and ensuring the security of the semiconductor precursor supply chain. Summary of the Invention

[0006] The present invention aims to provide a method for preparing tetrakis(dimethylamino)hafnium to address the problem of high impurity content and difficulty in removing tetrakis(dimethylamino)hafnium recovered from CpHf synthesis wastewater. By sequentially subjecting the tetrakis(dimethylamino)hafnium separated from the wastewater to distillation, recrystallization, and fractionation treatments, and further optimizing process parameters and other process conditions, the recovered tetrakis(dimethylamino)hafnium can achieve a purity of 6N or higher. This method is time-efficient and highly effective, suitable for large-scale industrial application.

[0007] In order to achieve the above technical effects, the present invention is implemented by the following technical means:

[0008] First, the present application provides a method for preparing tetrakis(dimethylamino)hafnium, comprising the following steps: S1. Distill the crude tetrakis(dimethylamino)hafnium once at a temperature of 80-100°C and a pressure of 0.3-1.0 mbar, and collect the main fraction; S2, dissolving the primary main fraction in a solvent, and recrystallizing at -20-15°C to obtain crystals; S3, the crystals of dissolved S2 are subjected to secondary distillation at a distillation temperature of 80-100°C and a pressure of 0.4-1.2 mbar, and the secondary main fraction is collected.

[0009] Furthermore, the crude tetrakis(dimethylamino)hafnium product is derived from waste liquid from the production process of cyclopentadienyltris(dimethylamino)hafnium (i.e., CpHf). In one embodiment, the preparation steps of cyclopentadienyltris(dimethylamino)hafnium include: (1) reacting tetrakis(dimethylamino)hafnium with cyclopentadiene monomer to produce CpHf; (2) separating CpHf by distillation. Furthermore, the preparation of cyclopentadienyltris(dimethylamino)hafnium can be a one-pot process or a step-by-step process, which is not specifically stipulated in this application. Furthermore, the crude tetrakis(dimethylamino)hafnium product is derived from the waste liquid after distillation in step (3).

[0010] Furthermore, the crude tetrakis(dimethylamino)hafnium product contains ≤8.0 ppm of Fe and ≤1.0 ppm of Ti. In one embodiment, the crude tetrakis(dimethylamino)hafnium product contains 2.5-8.0 ppm of Fe and 0.1-1.0 ppm of Ti. In one embodiment, the crude tetrakis(dimethylamino)hafnium product contains 2.5-5.0 ppm of Fe and 0.1-0.5 ppm of Ti. In one embodiment, the crude tetrakis(dimethylamino)hafnium product contains 2.5-4.0 ppm of Fe and 0.1-0.3 ppm of Ti.

[0011] Furthermore, the distillation temperature in S1 is 85-95°C, exemplified but not limited to any one of 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C, and 95°C.

[0012] Furthermore, the distillation pressure in S1 is 0.6-1.0 mbar, such as, but not limited to, any one of 0.6 mbar, 0.65 mbar, 0.7 mbar, 0.75 mbar, 0.8 mbar, 0.85 mbar, 0.9 mbar, 0.95 mbar, and 1.0 mbar.

[0013] Furthermore, in S1, the front fraction accounts for 5-15% of the crude quality, the primary main fraction accounts for 60-90% of the crude quality; the remainder is the rear fraction and the still residue; preferably, the front fraction accounts for 7-12% of the crude quality, and the primary main fraction accounts for 70-85% of the crude quality.

[0014] Furthermore, the collection rate of the front fraction in S1 is 10-50 d / min, preferably 20-40 d / min, and exemplary but not limiting collection rates of the front fraction are any one of 10 d / min, 12 d / min, 15 d / min, 20 d / min, 23 d / min, 25 d / min, 28 d / min, 30 d / min, 32 d / min, 35 d / min, 37 d / min, 39 d / min, and 40 d / min.

[0015] Furthermore, the collection rate of the primary main fraction in S1 is 35-60 d / min, preferably 40-50 d / min. Exemplary but not limiting primary main fraction collection rates include any one of 35 d / min, 38 d / min, 40 d / min, 42 d / min, 44 d / min, 45 d / min, 46 d / min, 50 d / min, 52 d / min, 55 d / min, 57 d / min, 59 d / min, and 60 d / min. In this application, the unit "d / min" means "drops per minute," and each 20 drops weighs about 1 g.

[0016] Furthermore, the solvent is an alkane solvent, including but not limited to at least one of n-butane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, and n-dodecane. In a preferred embodiment, the solvent includes n-hexane.

[0017] Furthermore, the amount of solvent used is 1-3 times the mass of the primary main fraction.

[0018] Further, the recrystallization temperature is -15~10°C, preferably -10~8°C; exemplary but not limiting recrystallization temperatures include any one of -15°C, -14°C, -13°C, -12°C, -11°C, -10°C, -9°C, -8°C, -7°C, -6°C, -5°C, -4°C, -3°C, -2°C, -1°C, 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, and 8°C.

[0019] Furthermore, the recrystallization time is ≥24 h, preferably 24-60 h.

[0020] Furthermore, the Fe content in the tetrakis(dimethylamino)hafnium crystal obtained in S2 is less than 0.5 ppm, and the Ti content is ≤ 0.1 ppm.

[0021] Furthermore, the distillation pressure in S3 is 0.4-0.8 mbar.

[0022] Furthermore, in S3, the front fraction accounts for 5-15% of the feed mass, the secondary main fraction accounts for 70-90% of the feed mass; the remainder is the rear fraction and the kettle residue.

[0023] Furthermore, the collection rate of the front fraction in S3 is 20-40 d / min; the collection rate of the secondary main fraction is 40-50 d / min.

[0024] Furthermore, the same distillation device is used in S1 and S3, and the distillation column height is ≥1m, and exemplary but not limiting column heights include any one of 1m, 1.5m, 2m, 2.5m, 3m, 3.5m, 4m, etc.

[0025] Furthermore, the distillation column is loaded with fillers, which include glass spring fillers. In one embodiment, the glass spring fillers are filled to the top of the distillation column, and the filling length accounts for 1 / 20-1 / 5 of the height of the distillation column.

[0026] Furthermore, the packing includes at least one of stainless steel structured packing, stainless steel triangular spiral packing, and metal ball rings. In one embodiment, the packing includes glass spring packing filled at the top of the distillation column and stainless steel triangular spiral packing filled at the rest of the distillation column.

[0027] Furthermore, the secondary main fraction collected in S3 is used as electronic grade tetrakis(dimethylamino)hafnium, and the Fe content in the secondary main fraction is ≤0.1ppm, and the Ti content is ≤0.01ppm.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects:

[0029] (1) This application achieves, for the first time, the ultra-high purity recovery of TDMAHf products from CpHf synthetic wastewater, using an optimized three-stage purification process of "primary distillation-recrystallization-secondary distillation," to a level 6N (99.9999% or higher). The recovered products fully meet the stringent requirements for metal precursors in high-end fields such as semiconductor thin film deposition. The above treatment processes work together to solve the problem of difficult removal of impurities such as Fe and Ti in TDMAHf. The Fe impurity content in the recovered products is less than 0.1ppm, and the Ti impurity content is less than 0.01ppm.

[0030] (2) This application can further improve the product yield on the basis of improving the purity of TDMAHf product by optimizing key parameters such as distillation and recrystallization parameters, and has significant economic benefits.

[0031] (3) This application does not require a special reaction device, the preparation method has a short process cycle, high processing efficiency and will not introduce other impurities, and can be applied industrially. DETAILED DESCRIPTION

[0032] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0033] Unless otherwise specified, in the following examples and comparative examples, the crude tetrakis(dimethylamino)hafnium product is derived from the fore-distillate wastewater of the CpHf production process, wherein the Fe content is 2.825 ppm and the Ti content is 0.217 ppm. The collection rate unit d / min means drops per minute, and the weight of every 20 drops is approximately 1 g.

[0034] Example 1

[0035] This embodiment provides a method for preparing tetrakis(dimethylamino)hafnium, comprising the following steps:

[0036] S1. Set up the distillation apparatus and check for leaks. Pump 2.353 kg of tetrakis(dimethylamino)hafnium crude product into the distillation kettle under negative pressure. Evacuate the kettle to 0.8 mbar. Open -10°C condensate and heat the kettle until the kettle temperature is about 90°C and the tower top temperature rises to about 40°C. Collect the front fraction at a rate of 30 d / min, and the collected amount is 10% of the crude product quality. After the end, transfer the main fraction once. Under nitrogen protection, control the main fraction collection rate at 45 d / min, and the collected amount is 80% of the crude product quality (about 1.882 kg). Stop the distillation and turn off the heating when there is basically no reflux in the kettle. Change the product receiving bottle under nitrogen protection. After the temperature in the kettle basically drops to room temperature, the back fraction can be obtained.

[0037] S2. Use n-hexane to completely dissolve the primary main fraction. The amount of n-hexane used is twice the total mass of the primary main fraction. Store the mixture in a sealed container at 2°C for 48 hours for recrystallization. Then, remove the crystals and rinse the crystal surface with n-hexane to rinse away the remaining mother liquor. After rinsing, vacuum remove the n-hexane on the crystal surface to obtain tetrakis(dimethylamino)hafnium crystals (about 1.712 kg).

[0038] S3. Set up the distillation device and check for leaks. After the crystals obtained in S2 are completely melted, they are pumped into the distillation kettle with negative pressure. The kettle is evacuated to 0.8 mbar. -10℃ condensate is turned on and the kettle is heated until the temperature in the distillation kettle is about 95℃ and the temperature at the top of the tower is raised to about 40℃. The secondary front distillate is collected at a rate of 30 d / min, and the collection amount is 10% of the feed mass. After the end, the main distillate is transferred. Under nitrogen protection, the collection speed of the secondary main distillate is controlled at 40 d / min, and the collection amount is 85% of the feed mass (about 1.456 kg). When there is basically no reflux in the kettle, the distillation is stopped and the heating is turned off. The product receiving bottle is replaced under nitrogen protection. The temperature in the kettle is basically reduced to room temperature.

[0039] The same distillation device is used in S1 and S3. The height of the distillation column is 1.5m. The distillation column packing includes glass spring packing and stainless steel triangular spiral packing. The glass spring packing is located at the top of the distillation column, and the filling volume at the top is 1 / 10 of the height of the distillation column.

[0040] The tetrakis(dimethylamino)hafnium crystals of S2 and the secondary main fraction of S3 were taken for ICP-MS purity detection. The results showed that the Fe content in the crystals was 0.412ppm and the Ti content was 0.005ppm; the Fe content in the secondary main fraction was 0.065ppm and the Ti content was 0.002ppm. The above preparation method obtained 6N grade tetrakis(dimethylamino)hafnium, and the qualified product yield was 61.88%.

[0041] No Zr or Nb elements were detected in the qualified products, and the contents of other element impurities were also within the industry control range, meeting the requirements of electronic-grade chemicals.

[0042] Example 2

[0043] This embodiment provides a method for preparing tetrakis(dimethylamino)hafnium, comprising the following steps:

[0044] S1. Set up the distillation apparatus and check for leaks. Pump 2.550 kg of tetrakis(dimethylamino)hafnium crude product into the distillation kettle under negative pressure. Evacuate the kettle to 0.9 mbar. Turn on -10°C condensate and heat the kettle until the temperature in the distillation kettle is about 100°C and the temperature at the top of the tower rises to about 40°C. Collect the front fraction at a rate of 40 d / min, and the collected amount is 7% of the crude product quality. After the end, transfer the main fraction once. Under nitrogen protection, control the main fraction collection rate at 50 d / min, and the collected amount is 75% of the crude product quality (about 1.913 kg). Stop the distillation and turn off the heating when there is basically no reflux in the kettle. Change the product receiving bottle under nitrogen protection. After the temperature in the kettle basically drops to room temperature, the back fraction can be obtained.

[0045] S2. Use n-hexane to completely dissolve the primary main fraction. The amount of n-hexane used is 1.5 times the mass of the primary main fraction. Store it in a sealed container at 5°C for 24 hours for recrystallization. Then take out the crystals and rinse the crystal surface with n-hexane to rinse away the remaining mother liquor. After rinsing, use vacuum to remove the n-hexane on the crystal surface to obtain tetrakis(dimethylamino)hafnium crystals (1.588 kg).

[0046] S3. Set up the distillation device and check for leaks. After the crystals obtained in S2 are completely melted, they are pumped into the distillation kettle with negative pressure. The kettle is evacuated to 0.6 mbar. -10℃ condensate is turned on and the kettle is heated until the temperature in the distillation kettle is about 90℃ and the temperature at the top of the tower is raised to about 42℃. The secondary front distillate is collected at a rate of 40 d / min, and the collection amount is 5% of the feed mass. After the end, the secondary main distillate is transferred. Under nitrogen protection, the collection speed of the secondary main distillate is controlled at 45 d / min, and the collection amount is 90% of the feed mass (about 1.429 kg). When there is basically no reflux in the kettle, the distillation is stopped and the heating is turned off. The product receiving bottle is replaced under nitrogen protection. The temperature in the kettle is basically reduced to room temperature.

[0047] The same distillation device is used in S1 and S3. The height of the distillation column is 2m. The distillation column packing includes glass spring packing and stainless steel triangular spiral packing. The glass spring packing is located at the top of the distillation column, and the filling volume at the top is 1 / 8 of the height of the distillation column.

[0048] ICP-MS purity analysis revealed 0.615 ppm Fe and 0.042 ppm Ti in the crystals. The secondary main fraction contained 0.095 ppm Fe and 0.013 ppm Ti. The above preparation method yielded 6N-grade tetrakis(dimethylamino)hafnium with a yield of 56.04%.

[0049] Example 3

[0050] This embodiment provides a method for preparing tetrakis(dimethylamino)hafnium, comprising the following steps:

[0051] S1. Set up the distillation apparatus and check for leaks. Pump 1.860 kg of tetrakis(dimethylamino)hafnium crude product into the distillation kettle under negative pressure. Evacuate the kettle to 0.6 mbar. Open -10°C condensate and heat the kettle until the temperature in the distillation kettle is about 85°C and the temperature at the top of the tower rises to about 40°C. Collect the front fraction at a rate of 20 d / min, and the collected amount is 5% of the crude product quality. After the end, transfer the main fraction once. Under nitrogen protection, control the main fraction collection rate at 40 d / min, and the collected amount is 85% of the crude product quality (about 1.581 kg). Stop the distillation and turn off the heating when there is basically no reflux in the kettle. Change the product receiving bottle under nitrogen protection. After the temperature in the kettle basically drops to room temperature, the back fraction can be obtained.

[0052] S2. Use n-hexane (1 times the mass of the first main fraction) to completely dissolve the first main fraction. Store in a sealed container at -4°C for 60 h for recrystallization. Then take out the crystals and rinse the crystal surface with n-hexane to rinse away the remaining mother liquor. After rinsing, use vacuum to remove the n-hexane on the crystal surface to obtain tetrakis(dimethylamino)hafnium crystals (1.455 kg).

[0053] S3. Set up the distillation device and check for leaks. After the crystals obtained in S2 are completely melted, they are pumped into the distillation kettle with negative pressure. The kettle is evacuated to 0.7 mbar. -10℃ condensate is turned on and the kettle is heated until the temperature in the distillation kettle is about 95℃ and the temperature at the top of the tower is raised to about 40℃. The secondary front distillate is collected at a rate of 20 d / min, and the collection amount is 15% of the feed mass. After the end, the secondary main distillate is transferred. Under nitrogen protection, the collection speed of the secondary main distillate is controlled to 50 d / min, and the collection amount is 80% of the feed mass (about 1.164 kg). When there is basically no reflux in the kettle, the distillation is stopped and the heating is turned off. The product receiving bottle is replaced under nitrogen protection. The temperature in the kettle is basically reduced to room temperature.

[0054] The same distillation device is used in S1 and S3. The height of the distillation column is 1.5m. The distillation column packing includes glass spring packing and stainless steel triangular spiral packing. The glass spring packing is located at the top of the distillation column, and the filling volume at the top is 1 / 10 of the height of the distillation column.

[0055] ICP-MS purity analysis revealed 0.485 ppm Fe and 0.022 ppm Ti in the crystals. The secondary main fraction contained 0.088 ppm Fe and 0.019 ppm Ti. The above preparation method yielded 6N-grade tetrakis(dimethylamino)hafnium with a yield of 62.58%.

[0056] Comparative Example 1

[0057] This comparative example provides a preparation method of tetrakis(dimethylamino)hafnium, which is basically the same as Example 1, except that the stainless steel metal spiral packing in the distillation column is replaced with metal θ-ring packing.

[0058] The ICP-MS purity test results showed that the Fe content in the crystals was 0.825ppm and the Ti content was 0.127ppm; in the secondary main distillation, the Fe content was 0.213ppm and the Ti content was 0.109ppm, and no qualified 6N grade tetrakis(dimethylamino)hafnium was obtained.

[0059] Comparative Example 2

[0060] This comparative example provides a preparation method of tetrakis(dimethylamino)hafnium, which is basically the same as that of Example 1, except that the distillation columns used in S1 and S3 are fully loaded with triangular spiral packing.

[0061] ICP-MS purity analysis revealed 0.735 ppm Fe and 0.011 ppm Ti in the crystals. The secondary main distillate contained 0.153 ppm Fe and 0.007 ppm Ti. No qualified 6N-grade hafnium tetrakis(dimethylamino) was obtained.

[0062] Comparative Example 3

[0063] This comparative example provides a preparation method of tetrakis(dimethylamino)hafnium, which is basically the same as Example 1, except that the vacuum degree in the reactor in S1 is 1.2 mbar and the temperature in the distillation reactor is 115°C.

[0064] ICP-MS purity analysis revealed an Fe content of 0.335 ppm and a Ti content of 0.012 ppm in the crystals. The secondary main fraction contained 0.095 ppm Fe and 0.007 ppm Ti. The above preparation method yielded 0.303 kg of 6N-grade tetrakis(dimethylamino)hafnium, with a qualified yield of 13.76%. While qualified product was produced, the yield was too low.

[0065] Comparative Example 4

[0066] This comparative example provides a preparation method of tetrakis(dimethylamino)hafnium, which is basically the same as Example 1, except that the amount of the front fraction collected in S1 is 1% of the crude quality, and the amount of the primary main fraction collected is 90% of the crude quality.

[0067] ICP-MS purity test results showed that the Fe content in the crystals was 1.446 ppm and the Ti content was 0.153 ppm; in the secondary main fraction, the Fe content was 0.912 ppm and the Ti content was 0.125 ppm. The above preparation method did not produce qualified 6N grade tetrakis(dimethylamino)hafnium.

[0068] Comparative Example 5

[0069] This comparative example provides a preparation method of tetrakis(dimethylamino)hafnium, which is basically the same as Example 1, except that: in S1 and S3, the collection speed of the primary main fraction and the secondary main fraction is 70 d / min.

[0070] The ICP-MS purity test results showed that the Fe content in the crystals was 0.405 ppm and the Ti content was 0.009 ppm; in the secondary main distillation, the Fe content was 0.208 ppm and the Ti content was 0.004 ppm, and no qualified 6N grade tetrakis(dimethylamino)hafnium was obtained.

[0071] Comparative Example 6

[0072] This comparative example provides a preparation method of tetrakis(dimethylamino)hafnium, which is basically the same as that of Example 1, except that: in S2, diethyl ether is used to dissolve the primary main fraction for recrystallization.

[0073] The ICP-MS purity test results showed that the Fe content in the crystals was 1.253 ppm and the Ti content was 0.115 ppm; in the secondary main fraction, the Fe content was 0.807 ppm and the Ti content was 0.094 ppm, and no qualified 6N grade tetrakis(dimethylamino)hafnium was obtained.

[0074] The ICP-MS test results of the above embodiments and comparative examples are summarized in Table 1.

[0075] Table 1

[0076] From the above results, it can be seen that the protection scheme of the present application can obtain the optimal product purity and product yield, and can be used for industrial treatment of CpHf synthesis waste liquid to recover TDMAHf, with high economic benefits.

[0077] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0078] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing tetrakis(dimethylamino)hafnium, characterized in that: The following steps are involved: S1. Distill the crude tetrakis(dimethylamino)hafnium once at a temperature of 80-100°C and a pressure of 0.3-1.0 mbar, and collect the main fraction; S2, dissolving the primary main fraction in a solvent, and recrystallizing at -20 to 15°C to obtain crystals; S3, dissolve the crystals of S2 and perform secondary distillation at a distillation temperature of 80-100°C and a pressure of 0.4-1.2 mbar, and collect the secondary main fraction; The crude tetrakis(dimethylamino)hafnium product contains ≤8.0 ppm of Fe and ≤1.0 ppm of Ti.

2. The preparation method according to claim 1, characterized in that The crude tetrakis(dimethylamino)hafnium product is derived from waste liquid in the production process of cyclopentadienyltris(dimethylamino)hafnium; and / or the crude tetrakis(dimethylamino)hafnium product contains 2.5-8.0 ppm of Fe and 0.1-1.0 ppm of Ti.

3. The preparation method according to claim 1, characterized in that The distillation temperature in S1 is 85-95° C.; and / or, the distillation pressure in S1 is 0.6-1.0 mbar; and / or, the front fraction in S1 accounts for 5-15% of the crude product quality, and the primary main fraction accounts for 60-90% of the crude product quality; and / or, the collection rate of the front fraction in S1 is 10-50 d / min; and / or, the collection rate of the primary main fraction is 35-60 d / min.

4. The preparation method according to claim 1, characterized in that In S1, the front fraction accounts for 7-12% of the crude quality, and the primary main fraction accounts for 70-85% of the crude quality; and / or, the collection rate of the front fraction is 20-40 d / min; and / or, the collection rate of the primary main fraction is 40-50 d / min.

5. The preparation method according to claim 1, characterized in that The solvent is an alkane solvent, including at least one of n-butane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, and n-dodecane; and / or the amount of the solvent is 1-3 times the mass of the primary main fraction; and / or the recrystallization temperature is -15~10°C; and / or the recrystallization time is ≥24h.

6. The preparation method according to claim 1, characterized in that The recrystallization temperature is -10-8°C; and / or the recrystallization time is 24-60h; and / or the Fe content of the tetrakis(dimethylamino)hafnium crystal obtained in S2 is less than 0.5ppm, and the Ti content is ≤0.1ppm.

7. The preparation method according to claim 1, characterized in that The distillation pressure in S3 is 0.4-0.8 mbar; and / or, the front fraction accounts for 5-15% of the feed mass, and the secondary main fraction accounts for 70-90% of the feed mass; and / or, the collection rate of the front fraction in S3 is 20-40 d / min; and / or, the collection rate of the secondary main fraction is 40-50 d / min.

8. The preparation method according to claim 1, characterized in that The distillation column is loaded with fillers, which include glass spring fillers; and / or the glass spring fillers are filled to the top of the distillation column, and the filling length accounts for 1 / 20-1 / 5 of the height of the distillation column.

9. The preparation method according to claim 8, characterized in that The packing also includes at least one of stainless steel structured packing, stainless steel triangular spiral packing, and metal ball ring.

10. The preparation method according to claim 1, characterized in that The Fe content in the secondary main fraction is ≤0.1ppm, and the Ti content is ≤0.01ppm.

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