Hafnium oxide target material and preparation method thereof

Abstract

The invention belongs to the technical field of target material preparation, and discloses a hafnium oxide target material preparation method, which comprises: loading hafnium oxide powder into a mold, placing into a vacuum hot pressing sintering furnace, pre-pressing, carrying out primary sintering, and cooling to obtain a target material blank; and putting the target material blank into a normal-pressure sintering furnace for secondary sintering, and cooling to obtain the hafnium oxide target material. Wherein the specific operation of the primary sintering is as follows: in a vacuum environment, raising the temperature to 500-700 DEG C at the speed of 2-10 DEG C / min, and then keeping the temperature for 5-10 minutes; then pressurizing is conducted, heating continues to be conducted after the pressure reaches 190 t within 70-90 min, the temperature is increased to 1000-1600 DEG C at the speed of 2-10 DEG C / min, and heat preservation and pressure maintaining are conducted for 70-120 min; the specific operation of secondary sintering is as follows: the temperature is raised to 1000-1600 DEG C at the speed of 1-5 DEG C / min, heat preservation is performed for 6-10 h, and the density of the hafnium oxide target material is improved through a two-time sintering process; in addition, the invention also discloses the hafnium oxide target material which is prepared by the preparation method of the hafnium oxide target material.

Description

Technical Field

[0001] This application relates to the technical field of target material preparation, and particularly relates to a hafnium oxide target and a preparation method thereof. Background Art

[0002] Hafnium oxide (HfO 2 ) materials have high melting points, good thermal stability and chemical stability, are transparent in the ultraviolet to infrared bands, have low light absorption and dispersion, high refractive index, high laser damage threshold, excellent thermal stability and transparency, etc., and are widely used in optoelectronic devices. HfO 2 thin films can also be applied to complementary metal oxide semiconductor devices, field effect transistors, memories, etc. In addition, it has a high dielectric constant and low electron tunneling effect, and is compatible with the CMOS process. HfO 2 has become an ideal material to replace SiO 2 dielectrics in gate oxides; using its high dielectric constant and wide bandgap characteristics, it can also be used in capacitors and electromagnetic devices, etc.

[0003] Chinese Patent Application No. 201010529363.6 discloses a single crystal high-K gate dielectric material and a preparation method thereof, which records that a pure hafnium oxide target is prepared by processes such as pressing, cold isostatic pressing, and sintering. However, because hafnium oxide is brittle and prone to cracking, during the sintering process, problems such as insufficient density and uneven shrinkage are likely to occur. To solve such problems, there is a preparation method of a hafnium oxide ceramic product disclosed in Chinese Patent Application No. 202111655442.6, which promotes the densification and high-temperature stability of the target by adding appropriate additives (such as lanthanum oxide, yttrium oxide, etc.) as strengthening components and bonding through a binder.

[0004] The problem to be solved by this solution: how to propose a preparation method of hafnium oxide target different from the prior art. Summary of the Invention

[0005] The purpose of this application is to propose a hafnium oxide target and a preparation method thereof. By optimizing the sintering process of the target, vacuum hot pressing sintering with segmented heating is used to better form the hafnium oxide target, and atmospheric pressure sintering is combined to improve the densification of the hafnium oxide target.

[0006] To achieve the above purpose, this application discloses a preparation method of a hafnium oxide target, and the preparation method includes the following steps:

[0007] Step 1: Load hafnium oxide powder into a mold, place it in a vacuum hot pressing sintering furnace for pre-pressing, primary sintering, and cooling to obtain a primary sintered target;

[0008] Step 2: Put the once-sintered target into an atmospheric-pressure sintering furnace for secondary sintering and cooling to obtain a hafnium oxide target;

[0009] The once-sintering process is as follows: In a vacuum environment, heat up at a rate of 2 - 10 °C / min to 500 - 700 °C, then hold for 5 - 10 min; then apply pressure, and when the pressure reaches 190 t within 70 - 90 min, continue to heat up at a rate of 2 - 10 °C / min to 1000 - 1600 °C, and hold for 70 - 120 min while maintaining pressure;

[0010] The secondary sintering temperature is 1000 - 1600 °C, and the sintering time is 6 - 10 h;

[0011] First, use the vacuum hot-pressing sintering method to form the hafnium oxide target blank. During the vacuum hot-pressing sintering process, under the action of high temperature and pressure, diffusion occurs inside, making it easier to obtain a uniform target blank, and enabling the target blank to reach densification in a shorter time. Moreover, by dividing the sintering temperature into two stages, the temperature field in the vacuum furnace can be made more uniform, reducing the risk of cracking of the target during the sintering process; then subject the formed target blank after hot-pressing sintering to atmospheric-pressure sintering, which enhances the atomic activity on the surface of the powder particles. Through surface diffusion and grain boundary diffusion, the pores are filled, promoting the bonding between particles. At the same time, during the grain growth process, the grain boundaries move and engulf the pores, reducing the defects inside the material, thereby improving the density of the target.

[0012] Preferably, the secondary sintering temperature is 1200 - 1400 °C, and the sintering time is 6 - 10 h.

[0013] Preferably, the pre-pressing operation in Step 1 is: Raise the pressure to 60 - 70 t at a rate of 2 - 5 t / min, then hold for 5 - 10 min, and after releasing the pressure to 0 t within 5 - 10 min, perform vacuum treatment;

[0014] After the pre-pressing is completed, a pressure-relieving process is also required. Through the process of pre-pressing → pressure-relieving, the hafnium oxide powders can be fully contacted with each other, and during the subsequent sintering process, diffusion between the powders is more likely to occur, improving the density after vacuum hot-pressing.

[0015] Preferably, the purity of the hafnium oxide powder in Step 1 is ≥4N.

[0016] Preferably, graphite paper is laid on the bottom and side of the mold in Step 1.

[0017] In addition, a hafnium oxide target obtained by the preparation method of the hafnium oxide target described above is also disclosed.

[0018] Preferably, the density of the hafnium oxide target is >95%.

[0019] The beneficial effects of this application are:

[0020] The present application provides a hafnium oxide target and a preparation method thereof. By optimizing the sintering process of the target, the hafnium oxide target is formed by vacuum hot pressing sintering with a segmented temperature rise, and combined with atmospheric pressure sintering, the density of the hafnium oxide target is improved. Detailed implementation manners

[0021] In the description of the present application, it should be noted that for those not specifying specific conditions in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For reagents or instruments not indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0022] Example 1

[0023] A hafnium oxide target is prepared by the following steps:

[0024] Step 1: Load 6 kg of hafnium oxide powder with a purity of 4N into a mold, place it in a vacuum hot pressing sintering furnace, raise the temperature to 65 t at a rate of 3 t / min, hold the pressure for 7 min to complete the pre-pressing operation, and after releasing the pressure to 0 t in 7 min, perform vacuum treatment. Then raise the temperature to 600 °C at a rate of 6 °C / min and keep it warm for 7 min; then increase the pressure to 190 t within 80 min and continue to raise the temperature, raise the temperature to 1300 °C at a rate of 6 °C / min, hold the temperature and pressure for 95 min, and cool to room temperature to obtain a green target;

[0025] Step 2: Place the green target in an atmospheric pressure sintering furnace, raise the temperature to 1300 °C at a rate of 3 °C / min, keep it warm for 8 h, and cool to room temperature to obtain the hafnium oxide target.

[0026] Example 2

[0027] Step 1: Load 6 kg of hafnium oxide powder with a purity of 4N into a mold, place it in a vacuum hot pressing sintering furnace, raise the temperature to 60 t at a rate of 2 t / min, hold the pressure for 10 min to complete the pre-pressing operation, and after releasing the pressure to 0 t in 5 min, perform vacuum treatment. Then raise the temperature to 600 °C at a rate of 6 °C / min and keep it warm for 7 min; then increase the pressure to 190 t within 80 min and continue to raise the temperature, raise the temperature to 1300 °C at a rate of 6 °C / min, hold the temperature and pressure for 95 min, and cool to room temperature to obtain a green target;

[0028] Step 2: Place the green target in an atmospheric pressure sintering furnace, raise the temperature to 1300 °C at a rate of 3 °C / min, keep it warm for 8 h, and cool to room temperature to obtain the hafnium oxide target.

[0029] Example 3

[0030] Step 1: Load 6 kg of hafnium oxide powder with a purity of 4N into a mold, place it in a vacuum hot-pressing sintering furnace, raise the pressure to 70 t at a rate of 5 t / min and hold the pressure for 5 min to complete the pre-pressing operation. After releasing the pressure to 0 t in 10 min, perform vacuum treatment. Then, raise the temperature to 600 °C at a rate of 6 °C / min and hold the temperature for 7 min. Then, increase the pressure to 190 t within 80 min and continue to raise the temperature. Raise the temperature to 1300 °C at a rate of 6 °C / min, hold the temperature and pressure for 95 min, and cool to room temperature to obtain a green body of the target.

[0031] Step 2: Place the green body of the target in an atmospheric-pressure sintering furnace, raise the temperature to 1300 °C at a rate of 3 °C / min, hold the temperature for 8 h, and cool to room temperature to obtain a hafnium oxide target.

[0032] Example 4

[0033] A hafnium oxide target is prepared by the following steps:

[0034] Step 1: Load 6 kg of hafnium oxide powder with a purity of 4N into a mold, place it in a vacuum hot-pressing sintering furnace, raise the pressure to 65 t at a rate of 3 t / min and hold the pressure for 7 min to complete the pre-pressing operation. After releasing the pressure to 0 t in 3 min, perform vacuum treatment. Then, raise the temperature to 600 °C at a rate of 6 °C / min and hold the temperature for 7 min. Then, increase the pressure to 190 t within 80 min and continue to raise the temperature. Raise the temperature to 1300 °C at a rate of 6 °C / min, hold the temperature and pressure for 95 min, and cool to room temperature to obtain a green body of the target.

[0035] Step 2: Place the green body of the target in an atmospheric-pressure sintering furnace, raise the temperature to 1300 °C at a rate of 3 °C / min, hold the temperature for 8 h, and cool to room temperature to obtain a hafnium oxide target.

[0036] Example 5

[0037] A hafnium oxide target is prepared by the following steps:

[0038] Step 1: Load 6 kg of hafnium oxide powder with a purity of 4N into a mold, place it in a vacuum hot-pressing sintering furnace, raise the pressure to 65 t at a rate of 3 t / min and hold the pressure for 7 min to complete the pre-pressing operation. After releasing the pressure to 0 t in 12 min, perform vacuum treatment. Then, raise the temperature to 600 °C at a rate of 6 °C / min and hold the temperature for 7 min. Then, increase the pressure to 190 t within 80 min and continue to raise the temperature. Raise the temperature to 1300 °C at a rate of 6 °C / min, hold the temperature and pressure for 95 min, and cool to room temperature to obtain a green body of the target.

[0039] Step 2: Place the green body of the target in an atmospheric-pressure sintering furnace, raise the temperature to 1300 °C at a rate of 3 °C / min, hold the temperature for 8 h, and cool to room temperature to obtain a hafnium oxide target.

[0040] Example 6

[0041] Basically the same as Example 1, except that the specific process of the first sintering in Step 1 is as follows: heat up to 500 °C at a rate of 2 °C / min and then hold for 10 min; then increase the pressure to 190 t within 90 min and continue heating, heat up to 1000 °C at a rate of 2 °C / min, and hold under pressure for 120 min.

[0042] Example 7

[0043] Basically the same as Example 1, except that the specific process of the first sintering in Step 1 is as follows: heat up to 700 °C at a rate of 10 °C / min and then hold for 5 min; then increase the pressure to 190 t within 70 min and continue heating, heat up to 1600 °C at a rate of 10 °C / min, and hold under pressure for 70 min.

[0044] Example 8

[0045] Basically the same as Example 1, except that the specific process of the second sintering in Step 2 is as follows: heat up to 1000 °C at a rate of 1 °C / min and hold for 10 h.

[0046] Example 9

[0047] Basically the same as Example 1, except that the specific process of the second sintering in Step 2 is as follows: heat up to 1600 °C at a rate of 5 °C / min and hold for 6 h.

[0048] Example 10

[0049] Basically the same as Example 1, except that the specific process of the second sintering in Step 2 is as follows: heat up to 1200 °C at a rate of 3 °C / min and hold for 6 h.

[0050] Example 11

[0051] Basically the same as Example 1, except that the specific process of the second sintering in Step 2 is as follows: heat up to 1400 °C at a rate of 3 °C / min and hold for 10 h.

[0052] Comparative Example 1

[0053] Basically the same as Example 1, except that the specific process of the first sintering in Step 1 is as follows: increase the pressure to 190 t within 70 min, then heat up to 950 °C at a rate of 10 °C / min, and hold under pressure for 102 min.

[0054] Comparative Example 2

[0055] A hafnium oxide target is prepared by the following steps:

[0056] Step 1: Load 6 kg of hafnium oxide powder with a purity of 4N into a mold, place it in a vacuum hot pressing sintering furnace, raise the pressure to 65 t at a rate of 3 t / min, hold the pressure for 7 min to complete the pre-pressing operation, release the pressure to 0 t after 7 min, then perform vacuum treatment, and then raise the temperature to 600 °C at a rate of 6 °C / min and hold the temperature for 7 min; then increase the pressure to 190 t within 80 min and continue to raise the temperature, raise the temperature to 1300 °C at a rate of 6 °C / min, hold the temperature and pressure for 9.5 h, and cool to room temperature to obtain a hafnium oxide target.

[0057] Comparative Example 3

[0058] A hafnium oxide target is prepared by the following steps:

[0059] Step 1: Load 6 kg of hafnium oxide powder with a purity of 4N into a mold, place it in a vacuum hot pressing sintering furnace, raise the pressure to 65 t at a rate of 3 t / min, hold the pressure for 7 min to complete the pre-pressing operation, and release the pressure to 0 t after 7 min to obtain a green target.

[0060] Step 2: Place the green target in an atmospheric pressure sintering furnace, raise the temperature to 1300 °C at a rate of 3 °C / min, hold the temperature for 10 h, and cool to room temperature to obtain a hafnium oxide target.

[0061] Comparative Example 4

[0062] It is basically the same as Example 1, except that the specific process of the first sintering in Step 1 is: raise the temperature to 800 °C at a rate of 6 °C / min and hold the temperature for 10 min; then increase the pressure to 190 t within 90 min and continue to raise the temperature, raise the temperature to 1000 °C at a rate of 2 °C / min, hold the temperature and pressure for 120 min.

[0063] Comparative Example 5

[0064] It is basically the same as Example 1, except that the specific process of the first sintering in Step 1 is: raise the temperature to 900 °C at a rate of 6 °C / min and hold the temperature for 10 min; then increase the pressure to 190 t within 90 min and continue to raise the temperature, raise the temperature to 1000 °C at a rate of 2 °C / min, hold the temperature and pressure for 120 min.

[0065] Performance test:

[0066] Target density: Measured by the Archimedes drainage method;

[0067] The test results are shown in Table 1:

[0068] Table 1

[0069] Group Target density (%) Example 1 98.8 Example 2 98.3 Example 3 98.2 Example 4 93.6 Example 5 93.8 Example 6 96.4 Example 7 96.5 Example 8 96.1 Example 9 96.0 Example 10 96.7 Example 11 96.9 Comparative Example 1 Target cracking Comparative Example 2 74.5 Comparative Example 3 78.5 Comparative Example 4 89.1 Comparative Example 5 88.8

[0070] Conclusion analysis:

[0071] 1. It can be seen from Examples 1 - 3 that when the process parameters in the preparation process of hafnium oxide target are changed, it will also have different effects on the density of the target.

[0072] 2. It can be seen from Example 1 and Examples 4 - 5 that after the pre - pressing of the target powder is completed, during the pressure relief process, the hafnium oxide powders can be fully contacted with each other. During the subsequent sintering process, it is easier for the powders to diffuse, improving the density after vacuum hot pressing. However, if the pressure relief is too fast or too slow, the density of the target becomes poor. It is speculated that this may be because the contact state between the powders is too tight or too loose, resulting in changes in the growth of grains during the sintering process, and thus affecting the density of the target.

[0073] 3. It can be seen from Example 1 and Examples 6 - 11 that when other process conditions remain unchanged and the process parameters of the first - stage sintering or the second - stage sintering are changed, it will have a certain impact on the density of the target. Among them, the process parameters of the first - stage sintering and the second - stage sintering in Example 1 are the best.

[0074] 4. It can be seen from Example 1 and Comparative Example 1 that during the first - stage sintering process, directly completing the first - stage sintering at a temperature of 950 °C without performing temperature - segmented sintering, the temperature field in the sintering furnace is uneven at this time, resulting in cracking of the target.

[0075] Further observing Comparative Examples 2 - 3, it can be seen that when only vacuum hot - press sintering or atmospheric - pressure sintering is used, since the above - mentioned two sintering methods can both improve the density of the target well, when only one of them is used for sintering, the density of the target will be relatively low.

[0076] 5. It can be seen from Example 1 and Comparative Examples 4 - 5 that during the first - stage sintering process, when the temperature of the first - stage of vacuum sintering is greater than 700 °C and less than 1000 °C, due to the longer heating - up time, the time for the target to be in an unstable temperature field increases, resulting in uneven growth of crystals, and thus the density of the target decreases.

[0077] The above - mentioned embodiments are the preferred embodiments of the present application. However, the embodiments of the present application are not limited by the above - mentioned embodiments. Any changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present application shall be equivalent replacement methods and are all included in the protection scope of the present application.

Claims

1. A method for preparing a hafnium oxide target, characterized in that: The preparation method comprises the following steps: Step 1: Put hafnium oxide powder into a mold, put it into a vacuum hot pressing sintering furnace for pre-pressing, primary sintering, and cooling to obtain a target material blank; Step 2: placing the target material blank into a normal pressure sintering furnace for secondary sintering and cooling to obtain a hafnium oxide target material; The specific operation of the first sintering is: in a vacuum environment, heat up to 500-700°C at 2-10°C / min and keep warm for 5-10 minutes; then pressurize, and continue to heat up after the pressure reaches 190t within 70-90 minutes, heat up to 1000-1600°C at 2-10°C / min, and keep warm and pressurized for 70-120 minutes; The specific operation of the secondary sintering is: heating to 1000-1600°C at 1-5°C / min and keeping the temperature for 6-10 hours.

2. The preparation method according to claim 1, characterized in that: The secondary sintering temperature is 1200-1400° C., and the sintering time is 6-10 hours.

3. The preparation method according to claim 1, characterized in that: The pre-pressing operation in step 1 is: increasing the pressure to 60-70t at 2-5t / min, maintaining the pressure for 5-10min, releasing the pressure to 0t in 5-10min, and then vacuuming.

4. The preparation method according to claim 1, characterized in that: The purity of the hafnium oxide powder in step 1 is ≥4N.

5. The preparation method according to claim 1, characterized in that: In the step 1, graphite paper is laid on the bottom and sides of the mold.

6. A hafnium oxide target, characterized in that: The target is prepared by the method for preparing the hafnium oxide target according to any one of claims 1 to 5.

7. The hafnium oxide target according to claim 6, characterized in that: The density of the hafnium oxide target material is greater than 95%.