A method for preparing and recycling high-purity tungsten target material

Abstract

The application belongs to the technical field of magnetron sputtering target material manufacturing, and discloses a method for preparing and recycling high-purity tungsten target material. The method uses a used tungsten residual target as raw material, obtains primary tungsten powder after mechanical crushing and ball milling, and obtains low-purity tungsten hexafluoride with a purity of 2N-4N by reacting the crushed and milled tungsten powder with fluorine gas at high temperature. Then, the secondary tungsten powder with a purity of greater than or equal to 7N, an oxygen content of less than or equal to 300ppm, impurity elements Fe, Ni, Cr, K and Mo of less than or equal to 0.01ppm, and an average particle size of less than or equal to 3 microns is obtained by adopting the CVD deposition mode. The secondary tungsten powder can be used as raw material to prepare high-purity tungsten and tungsten alloy target material again.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of manufacturing of magnetron sputtering target material, and particularly relates to a method for preparing and recycling high-purity tungsten target material. BACKGROUND

[0002] Tungsten target material has the characteristics of high melting point (3410℃), high density (19.3g / cm 3 ), high thermal conductivity (165W / (m·K), high strength, low expansion coefficient (4.6×10 -6 mm -1 ), and high corrosion resistance, and is widely used in advanced memory manufacturing processes. In recent years, through research, tungsten is expected to replace copper as an interconnection material. High-purity tungsten target is a key material for memory device manufacturing, and the annual consumption is very large. However, after high-purity tungsten target is sputtered by physical vapor deposition (PVD) method, due to the uniformity of the magnetic field, sputtering tracks with different sputtering depths are generated. When the use depth of one of the sputtering tracks approaches the thickness of the target material, the target material cannot be used any more. At this time, the utilization rate of the target material is only less than 30%, and the remaining more than 70% of the high-purity tungsten residual target cannot be used any more.

[0003] Due to the high melting point of high-purity tungsten target, high-purity tungsten powder is used as the raw material for preparation by sintering. However, high-purity tungsten powder is usually obtained by calcination and reduction of high-purity ammonium paratungstate (APT) as raw material. The current high-purity tungsten powder prepared by chemical method is limited by the low purity of APT raw material. The high-quality and high-grade tungsten concentrate is becoming less and less, and the content of various impurities in the tungsten concentrate, especially molybdenum, potassium, iron and chromium, is relatively high, which cannot be removed in the process of preparing high-purity tungsten powder. The content of Fe, Ni, Cr, K and Mo impurity elements in the prepared high-purity tungsten powder is all ≥0.1ppm, and the content of Mo impurity element is more than 1ppm. If high-purity tungsten residual target block is used as raw material to prepare high-purity tungsten powder, Fe, Ni, Cr and other impurities are easily introduced in the process of crushing, and the purity of the finally prepared tungsten powder is ≤2N, which cannot meet the purity requirement of high-purity tungsten target.

[0004] Therefore, the current high-purity tungsten residual target can only be used as a low-purity industrial additive added to the steel liquid, and the utilization value is very low. How to recycle high-purity tungsten target material with high value is the current difficulty. SUMMARY

[0005] In view of the problems mentioned in the prior art, the present patent provides a method for preparing and recycling high-purity tungsten target material: The present application belongs to the technical field of magnetron sputtering target material manufacturing, and discloses a method for preparing and recycling high-purity tungsten target material. The preparation and recycling method uses a used high-purity tungsten residual target as raw material, obtains tungsten powder after mechanical crushing and ball milling, reacts the tungsten powder obtained after crushing and ball milling with fluorine gas at high temperature to obtain low-purity tungsten hexafluoride with a purity of 2N-4N, and then adopts a CVD deposition method to obtain high-purity tungsten powder with a purity of ≥7N, an O content of ≤300ppm, impurity elements Fe, Ni, Cr, K and Mo each being ≤0.01ppm, and an average particle size of ≤3μm. The high-purity tungsten powder can be used as raw material to prepare high-purity tungsten and tungsten alloy target material again.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A method for preparing high-purity tungsten target material by using a tungsten residual target, comprising the following steps:

[0008] 1) crushing to obtain primary tungsten powder (i.e. low-purity tungsten powder);

[0009] In the step 1), the particle size of the primary tungsten powder is 1-20μm;

[0010] 2) using a fixed bed reactor to react the primary tungsten powder with fluorine gas to obtain low-purity tungsten hexafluoride;

[0011] In the step 2), the purity of the low-purity tungsten hexafluoride is 2N-4N;

[0012] 3) using the low-purity tungsten hexafluoride obtained in the step 2) and hydrogen gas as raw material to perform deposition in a chemical vapor deposition (CVD) device, and finally obtaining secondary tungsten powder (i.e. high-purity tungsten powder);

[0013] 4) sintering the secondary tungsten powder obtained in the step 3) to prepare a finished tungsten target material;

[0014] In the step 4), the purity of the finished tungsten target material is ≥6N, preferably ≥7N, and more preferably ≥7N6.

[0015] In some preferred embodiments, in the step 3), the purity of the secondary tungsten powder is ≥7N, the O content is ≤300ppm, the impurity elements Fe, Ni, Cr, K and Mo are each ≤0.01ppm, and the average particle size is ≤3μm.

[0016] In some preferred embodiments, in the step 2), the temperature of the fixed bed reactor is 200-400℃; and / or

[0017] The pressure of the fixed bed reactor is 0.1-0.5MPa.

[0018] In some preferred embodiments, in step 2), the ratio of the amount of the primary tungsten powder to the fluorine gas is 1:3-1:5; and / or

[0019] The flow rate is 0.5-1.5 L / min.

[0020] In some preferred embodiments, in step 3), the temperature of the reactor in the chemical vapor deposition (CVD) equipment is 900-1000°C; and / or

[0021] The pressure of the reactor in the chemical vapor deposition (CVD) equipment is 0.5-1.5 atm.

[0022] In some preferred embodiments, in step 4), the flow rate of the secondary tungsten hexafluoride is 15-20 g / min; and / or

[0023] The flow rate of the hydrogen gas is 2-2.5 L / min.

[0024] In some preferred embodiments, in step 1), the crushed raw material is a tungsten residual target, preferably a recycled tungsten target material; more preferably a tungsten residual target with a purity of ≥5N.

[0025] In step 1), the crushing method uses any one or a combination of at least two of the following: cutting, mechanical crushing, and ball milling; preferably, the cutting uses any one or a combination of at least two of the following: wire cutting, water cutting, and laser cutting.

[0026] In some preferred embodiments, in step 1), the crushing method is as follows:

[0027] 1-1) Prepare a tungsten residual target with a purity of ≥5N, cut it into pieces with a size of ≤20*20 mm, preferably an area of ≤400 mm 2 , more preferably the length of each side of the pieces is ≤20 mm; then crush the pieces into small pieces with a size of ≤3*3 mm, preferably an area of ≤9 mm 2 , more preferably the length of each side of the small pieces is ≤3 mm; and

[0028] 1-2) Use ball milling to prepare the crushed tungsten pieces into primary tungsten powder with a particle size of 1-20 μm, the ball milling speed is 50-200 r / min, and the ball milling time is 2-10 h.

[0029] In some preferred embodiments, in step 3), the impurity elements are selected from any one or a combination of at least two of the following: Fe, Ni, Cr, K, Mo, and O; preferably Fe, Ni, Cr, and other impurities introduced during the crushing and ball milling of the tungsten residual target.

[0030] The application also provides the high-purity tungsten target prepared by the preparation method, which has a purity of 6N or more, preferably 7N or more.

[0031] More preferably, the impurity element content includes but is not limited to Fe, Ni, Cr, K and Mo, each of which is 0.01 ppm or less.

[0032] The O content is 300 ppm or less.

[0033] The application has at least the beneficial effect that the high-purity tungsten target can be recycled at high value: the technology uses used tungsten residual targets as raw materials, prepares high-purity tungsten powder (i.e. secondary tungsten powder) for secondary use to prepare high-purity tungsten targets again, and has high utilization value.

[0034] The prepared high-purity tungsten powder (i.e. secondary tungsten powder) has higher purity: the high-purity tungsten powder prepared by the patent using tungsten residual targets as raw materials has a purity of 7N (i.e. 99.99999%) or more, and the purity of the finished target material can be as high as 7N6 (i.e. 99.999996%) or more.

[0035] Impurities introduced during the crushing process can be removed, and the prepared high-purity tungsten powder has lower impurity elements: the patent uses CVD to prepare high-purity tungsten powder, which can remove such impurities by using the difference in vapor pressure between tungsten and impurity elements during the preparation of tungsten hexafluoride and CVD deposition, and the final impurity elements Fe, Ni, Cr, K and Mo have a content of 0.01 ppm or less.

[0036] High-purity tungsten hexafluoride is not required for deposition: the application only needs to obtain low-purity tungsten hexafluoride when preparing tungsten hexafluoride, and does not need to further purify the high-purity tungsten hexafluoride with a purity of 6N or more for later CVD deposition. When the tungsten powder is deposited later, the Fe, Ni, Cr and other impurities introduced during the ball milling process are removed again through high-temperature reaction, so as to achieve the same effect as the high-purity W powder deposited by high-purity tungsten hexafluoride.

[0037] The application adjusts the relationship between the CVD deposition temperature and the gas flow rate and pressure to ensure the yield of the deposition process, and the yield can be 80-90% or more. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The flowchart for recycling the high-purity tungsten target. DETAILED DESCRIPTION

[0039] The application will be further described below with reference to the accompanying drawings Figure 1 and the detailed description, but it does not mean to limit the scope of protection of the application.

[0040] The inventive mechanism of the present application is that: using the used high-purity tungsten residual target (purity ≥ 5N) as raw material, tungsten powder is obtained after mechanical crushing and ball milling. The primary tungsten powder obtained after crushing and ball milling is reacted with fluorine gas at high temperature, and low-purity tungsten hexafluoride is obtained after reaction with fluorine gas. Then, the secondary tungsten powder with purity ≥ 7N, O content ≤ 300ppm, impurity elements Fe, Ni, Cr, K, Mo ≤ 0.01ppm, and average particle size ≤ 3μm is obtained by CVD deposition. The secondary tungsten powder can be used as raw material to prepare high-purity tungsten and tungsten alloy finished target material again. In order to better explain the present application and facilitate understanding, the present application is described in detail below through specific implementation examples and comparative examples.

[0041] Example 1~16, residual target cutting: prepare high-purity tungsten residual target with purity ≥ 5N, cut into size 10*10mm fragments by wire cutting, water cutting or laser cutting, and then crush into size 2*2mm small fragments by mechanical crushing.

[0042] Ball milling: use ball milling to prepare the crushed tungsten fragments into primary tungsten powder (i.e. low-purity tungsten powder) with particle size of 3μm, ball milling speed is 100 r / min, and ball milling time is 5 h.

[0043] Preparation of low-purity tungsten hexafluoride: using the obtained primary tungsten powder as raw material, the primary tungsten powder is reacted with fluorine gas using a fixed bed reactor, and low-purity tungsten hexafluoride with purity of 2N-4N is obtained. The temperature of the fixed bed reactor is 200-400℃, and the pressure is 0.1-0.5MPa.

[0044] Chemical vapor deposition (CVD deposition): using the obtained low-purity tungsten hexafluoride and hydrogen as raw materials, deposition is carried out in a CVD device, and finally high-purity tungsten powder (i.e. secondary tungsten powder) with purity ≥ 7N, O content ≤ 300ppm, impurity elements Fe, Ni, Cr, K, Mo ≤ 0.01ppm, and average particle size ≤ 3μm is obtained. The temperature of the CVD reactor is 900-1000℃, the pressure is 0.5-1.5atm, the flow rate of high-purity tungsten hexafluoride is 15-20g / min, and the flow rate of hydrogen is 2-2.5L / min.

[0045] Preparation of tungsten target material: the obtained high-purity tungsten powder is sintered to prepare high-purity tungsten target (i.e. finished target material) with purity ≥ 6N.

[0046] The target material parameters and performance prepared in Examples 1~16 are shown in Table 1.

[0047] Comparative Example 1, residual target cutting: prepare high-purity tungsten residual target with purity ≥ 5N, cut into size 10*10mm fragments by wire cutting, water cutting or laser cutting, and then crush into size 2*2mm small fragments by mechanical crushing.

[0048] Ball milling: the broken tungsten pieces were prepared into tungsten powder with a particle size of 3 μm by using a ball milling method, the prepared ball milling speed was 100 r / min, and the ball milling time was 5 h. The prepared tungsten powder had a purity of 2N, an O content of 800 ppm, impurity elements Fe, Ni, Cr≥100 ppm, K≥0.1 ppm, and Mo≥5 ppm.

[0049] Preparation of tungsten target: the obtained tungsten powder was sintered to obtain a high-purity tungsten target with a purity of 1N8, an oxygen content of 460 ppm, an average grain size of 34 μm, a relative density of 99.9%, impurity elements Fe, Ni, Cr≥100 ppm, K≥0.1 ppm, and Mo≥5 ppm.

[0050] Result analysis: by comparing Example 1 with the comparative example, it can be seen that the comparative example adopts a conventional method for recycling the existing high-purity tungsten target, and the tungsten powder with low purity can be obtained by crushing and ball milling, and the target purity is only 1N8 after sintering again, which cannot meet the requirement of high-purity target (purity≥7N). The Example can prepare high-purity tungsten powder from high-purity tungsten residual target, and then prepare high-purity tungsten target again, which has high utilization value.

[0051] Comparative Example 2, 1. Classification pretreatment: high-purity ammonium paratungstate APT was used as raw material, and air flow classification pretreatment was performed, and the classification wheel frequency was 6 HZ.

[0052] 2. Calcination: calcination was performed at 480℃ for 2 h and at 850℃ for 1.5 h, and after sieving, high-purity WO3 was prepared. 3。

[0053] 3. Preparation of high-purity tungsten powder: the prepared high-purity WO3 was used as raw material, high-purity hydrogen was introduced at 950℃ for reduction for 6 h, and after sieving, high-purity tungsten powder with a purity of 5N, an O content of 700 ppm, impurity elements Fe, Ni, Cr, K≥0.1 ppm, and Mo impurity content of 1.7 ppm, and an average particle size of 1.8 μm was prepared.

[0054] 4. Preparation of tungsten target: the obtained tungsten powder was sintered to obtain a high-purity tungsten target with a purity of 4N9, an oxygen content of 320 ppm, an average grain size of 12 μm, a relative density of 99.9%, impurity elements Fe, Ni, Cr, K≥0.1 ppm, and Mo impurity content of 1.7 ppm.

[0055] Result analysis: By comparing Example with Comparative Example 2, it can be seen that Comparative Example 2 is a conventional chemical method for preparing high-purity tungsten powder on the market, and only high-purity tungsten powder with a purity of <5N can be obtained, and the oxygen content and the content of impurity elements such as Fe, Ni, Cr, K and Mo are high, which is more than 10 times of Example; and the oxygen content is about 4 times of Example 1, and the effect is significantly different. The purity of high-purity tungsten powder prepared by Example by CVD method can reach more than 7N, and the difference in vapor pressure between tungsten and impurity elements can be utilized in the preparation of tungsten hexafluoride, rectification and CVD deposition process to remove such impurities, and the content of impurity elements Fe, Ni, Cr, K and Mo is ≤0.01 ppm.

[0056] Comparative Example 3, 1. Preparation of raw materials: low-purity tungsten hexafluoride (purity 4N) was prepared as raw material.

[0057] 2. Preparation of high-purity tungsten target material: deposition was carried out in a CVD device, and the base material was copper, and finally a tungsten target material with a purity of 5N7, an oxygen content of 12 ppm, an average grain size of 150 μm, a relative density of 99.9%, and impurity elements Fe, Ni, Cr, K and Mo≥0.1 ppm was obtained. The temperature of the CVD reactor was 550°C, the pressure was 1 atm, the flow rate of high-purity tungsten hexafluoride was 0.5 g / min, and the flow rate of hydrogen was 1 L / min.

[0058] Result analysis: Comparative Example 3 uses the commonly used method in the prior art to deposit on the base material copper by CVD, and Comparative Example 3 uses the same low-purity tungsten hexafluoride (purity 2N-4N) as Example. By comparing Example with Comparative Example 3, it can be seen that the tungsten target material obtained by directly CVD depositing low-purity tungsten hexafluoride as raw material in Comparative Example 3 has a purity of 5N7, an oxygen content of 12 ppm, and impurity elements Fe, Ni, Cr, K and Mo≥0.1 ppm, and an average grain size of 150 μm. While Example uses the used high-purity tungsten target material as raw material after recovery to obtain low-purity tungsten hexafluoride (purity 2N-4N). High-purity tungsten powder is obtained by CVD deposition using low-purity tungsten hexafluoride, and high-purity tungsten target material is obtained by sintering using high-purity tungsten powder, and the purity of high-purity tungsten target material obtained by Example can reach more than 7N, and the oxygen content, Fe, Ni, Cr, K and Mo impurity element content is far lower than that of Comparative Example 3, and the average grain size of high-purity tungsten target material obtained by Example is 11-34 μm, which is also far smaller than that of Comparative Example 3.

[0059] Comparative Example 4, 1. Preparation of raw materials: low-purity tungsten hexafluoride (purity 4N) was prepared as raw material.

[0060] 2. Preparation of high purity tungsten: deposition in a CVD device, substrate material is copper, finally obtain purity 5N7, oxygen content is 12 ppm, average grain size 150 μm, relative density 99.9%, impurity elements Fe, Ni, Cr, K, Mo≥0.1 ppm of tungsten target material. Among them, the temperature of the CVD reactor is 550℃, the pressure is 1 atm, the flow rate of high purity tungsten hexafluoride is 0.5 g / min, and the flow rate of hydrogen is 1 L / min.

[0061] 3. Rolling: the tungsten blank obtained by CVD deposition is rolled, the rolling heating temperature is 1500℃, the holding time is 30 min, and the rolling pass is 3 times, and the deformation amount of each pass is 10%.

[0062] 4. Heat treatment: the rolled slab is subjected to recrystallization heat treatment under vacuum, the heat treatment temperature is 1200℃, the holding time is 2h, and finally the high purity tungsten target material with purity 5N7, oxygen content 12ppm, average grain size 90μm, relative density 99.9%, impurity elements Fe, Ni, Cr, K, Mo≥0.1ppm is obtained.

[0063] Result analysis: compared with Comparative Example 3, the rolling and heat treatment steps are added, and the average grain size of the target material obtained is reduced from 150μm to 90μm, and the average grain size of the target material obtained in the example is 11-34μm, the average grain size of the target material of Comparative Example 4 is still more than 3 times compared with the example, and the difference is significant.

[0064] Example 17, residual target cutting: prepare high purity tungsten residual target with purity≥5N, cut into size 10*10mm fragments by wire cutting or water cutting or laser cutting, and then break into size 2*2mm small fragments by mechanical breaking.

[0065] Ball milling: the broken tungsten fragments are prepared into tungsten powder with a particle size of 3μm by ball milling, the ball milling speed is 100 r / min, and the ball milling time is 5h.

[0066] Preparation of tungsten hexafluoride: using the obtained tungsten powder as raw material, using a fixed bed reactor to react tungsten powder with fluorine gas to obtain low purity tungsten hexafluoride, wherein the temperature of the fixed bed reactor is 200℃, and the pressure is 0.1MPa.

[0067] Chemical vapor deposition (CVD deposition): the obtained low-purity tungsten hexafluoride and hydrogen are used as raw materials to carry out deposition in a CVD device, and finally high-purity tungsten powder with purity 5N9, O content 400 ppm, impurity elements Fe, Ni, Cr, K, Mo content ≥0.1 ppm, and average particle size 2.1 μm is obtained. The temperature of the CVD reactor is 850°C, the pressure is 0.5 atm, the flow rate of tungsten hexafluoride is 15 g / min, and the flow rate of hydrogen is 2.5 L / min.

[0068] Preparation of tungsten target: the obtained high-purity tungsten powder can be used to prepare high-purity tungsten target with purity 5N, oxygen content 50 ppm, average grain size 16 μm, relative density 99.9%, and impurity elements Fe, Ni, Cr, K, Mo content all ≥0.1 ppm after sintering.

[0069] Result analysis: in the preparation of tungsten hexafluoride, both example 7 and example 17 only obtained low-purity tungsten hexafluoride, and did not carry out rectification and purification to obtain tungsten hexafluoride with purity 6N or above for later CVD deposition. In the later CVD deposition of tungsten powder, example 7 removed the impurities such as Fe, Ni, and Cr introduced in the ball milling process again through high-temperature reaction, thereby obtaining high-purity tungsten powder with purity 7N8 and oxygen content 180 ppm. Example 17 used low temperature (lower than 900°C) for CVD deposition, and could not completely remove the impurities such as Fe, Ni, and Cr introduced in the ball milling process, and finally obtained tungsten powder with Fe, Ni, Cr, K, Mo content ≥0.1 ppm, purity 5N9, and oxygen content 350 ppm. The Fe, Ni, Cr, K, Mo impurity content is more than 10 times of that of example 7, and the oxygen content is 2 times of that of example 7, and the effect difference is significant.

[0070] The main manufacturing processes and performance results in examples 1-16 are shown in Table 1.

[0071]

Claims

1. A method for preparing high-purity tungsten target material, comprising the following steps: 1) preparing tungsten target material or tungsten residual target with purity ≥ 5N, cutting into pieces with size ≤ 20*20 mm by cutting, and then crushing into small pieces with size ≤ 3*3 mm by mechanical crushing; preparing the crushed tungsten pieces into primary tungsten powder with particle size of 1-20 μm by ball milling at a ball milling speed of 50-200 r / min for 2-10 h; 2) reacting the primary tungsten powder with fluorine gas in a fixed bed reactor to obtain low-purity tungsten hexafluoride; in the step 2), the purity of the low-purity tungsten hexafluoride is 2N-4N; 3) depositing the low-purity tungsten hexafluoride obtained in the step 2) and hydrogen gas as raw materials in a chemical vapor deposition (CVD) device to obtain secondary tungsten powder; in the step 3), the temperature of the reactor in the CVD device is 900-1000 ℃, and the pressure of the reactor in the CVD device is 0.5-1.5 atm; 4) sintering the secondary tungsten powder obtained in the step 3) to prepare finished tungsten target material; in the step 4), the purity of the finished tungsten target material is ≥ 6N.

2. The method for preparing a high-purity tungsten target material according to claim 1, wherein, in the step 4), the purity of the secondary tungsten powder is ≥ 7N, the O content is ≤ 300 ppm, the impurity elements Fe, Ni, Cr, K and Mo are all ≤ 0.01 ppm, and the average particle size is ≤ 3 μm.

3. The method for preparing a high-purity tungsten target material according to claim 1, wherein, in the step 2), the temperature of the fixed bed reactor is 200-400 ℃; and / or the pressure of the fixed bed reactor is 0.1-0.5 MPa.

4. The method of producing a high purity tungsten target material according to claim 1 or 3, wherein in the step 2), the amount ratio of the primary tungsten powder to the fluorine gas is 1:3-1:5; and / or the flow rate of the fluorine gas is 0.5-1.5 L / min.

5. The method for preparing a high-purity tungsten target material according to claim 1, wherein, in the step 3), the flow rate of the low-purity tungsten hexafluoride is 15-20 g / min; and / or the flow rate of the hydrogen gas is 2-2.5 L / min.

6. The method for preparing a high-purity tungsten target material according to claim 1, wherein, the cutting uses any one or a combination of at least two of the following: wire cutting, water cutting and laser cutting.

Images