A low-oxygen high-density Ru sputtering target, a preparation method thereof and uses thereof

Abstract

The present invention discloses a low-oxygen high-density Ru sputtering target, a preparation method thereof and uses thereof. The oxygen content of the sputtering target is less than 50 ppm, the thickness of the surface coarse grain layer is less than 50 μm, the average grain size is 2-8 microns, the pores at the grain boundaries are nearly spherical with a diameter less than 1 μm, and the relative density of the target is greater than 99% of the theoretical density. The preparation method uses high-purity ruthenium powder with controllable morphology and particle size distribution as raw materials, and prepares a ruthenium target by vacuum hot pressing sintering; by controlling the vacuum degree and pressure sintering, a target blank is obtained, and finally a sputtering target with low oxygen, high density and good machining performance is obtained. By controlling the powder morphology, particle size distribution and vacuum hot pressing sintering process, the present invention improves the disadvantages of high oxygen content, thick surface coarse grain layer, low density and poor machining performance of ruthenium targets, obtains a sputtering target with low oxygen content, high density and good machining performance, and avoids the disadvantage of difficult machining of targets prepared by conventional hot pressing sintering processes.

Description

Technical Field

[0001] The present invention belongs to the technical field of precious and rare metal sputtering targets, and relates to a low-oxygen high-density Ru sputtering target, a preparation method and uses thereof. The sputtering target can be used for coating information storage or semiconductor integrated circuits, and has good machining performance. Background Art

[0002] A sputtering target is a raw material for physical vapor deposition (PVD) coating. Compared with other PVD coating methods such as arc ion plating or vacuum evaporation coating, the thin films prepared by sputtering have excellent properties, such as dense film structure, uniform film thickness, etc., and are one of the current mainstream coating methods. Ruthenium (Ru) is a precious metal element with a high melting point, and its crystal structure is hexagonal close-packed. Ruthenium thin films prepared by magnetron sputtering with ruthenium sputtering targets are widely used in fields such as information storage and semiconductor integrated circuits. For example, ruthenium thin films are applied to the lower underlying layer of disks in hard disk drives for grain refinement and reduction of lattice mismatch, and ruthenium thin films have great application prospects in the diffusion barrier layer of copper interconnects and the next-generation interconnects in semiconductor integrated circuits. To achieve these applications, it is first necessary to prepare sputtering targets with good surface quality and excellent use performance.

[0003] Due to the characteristics of ruthenium having a high melting point and being brittle, ruthenium sputtering targets are usually prepared by powder metallurgy methods, and the preparation methods include vacuum hot pressing sintering, hot isostatic pressing sintering, and spark plasma sintering, etc. For example, CN201810661515.4 discloses a method for preparing a ruthenium target by vacuum hot pressing sintering; JP-A-2007-113032 discloses a method for preparing a ruthenium target by discharge pressure sintering; US20090010792Al discloses a method for preparing ruthenium and ruthenium alloy targets; CN102485378 discloses a method for preparing a ruthenium target by direct heating and pressure sintering. Although the methods for preparing ruthenium targets in the above patents are different, and the obtained ruthenium target densities can all reach more than 98% of the theoretical density, the publicly available information on how to control the machining performance of ruthenium targets is very little. Some patents related to ruthenium targets, such as: CN102922231 A discloses a processing method for ruthenium and ruthenium alloy targets; CN104032270A discloses a large-size ruthenium-based alloy sputtering target and a preparation method thereof; CN11270210A discloses a ruthenium sputtering target with high grain orientation.

[0004] However, during the machining process of the target, phenomena such as edge chipping, cracking, and generation of microcracks still occur from time to time. Existing patents or other literatures on machining methods for ruthenium or other refractory metal sputtering targets often only involve using appropriate machining methods for blanks with specific structures to achieve the machining process. However, there is no literature on improving the machining performance by regulating the structure of ruthenium targets.

[0005] For example, due to characteristics such as small equipment investment and simple operation, vacuum hot pressing sintering is still a commonly used method for densifying ruthenium targets. However, a coarse grain layer is likely to form on the surface of ruthenium targets prepared by the vacuum hot pressing method. For instance, in the publicly published literature (Luo Junfeng et al., Research on the Sintering Process of Ruthenium Metal Sputtering Targets, Powder Metallurgy Industry, 2012, 22(1): 28-31), the thickness of the coarse grain layer on the surface of ruthenium billets prepared by vacuum hot pressing sintering at temperatures above 1400°C can reach about 1 mm. And the surface coarse grain layer is one of the important reasons for cracking and chipping during the machining process. At the same time, to improve the machining performance of ruthenium targets, higher requirements are also put forward for the structure and properties of the targets themselves, such as oxygen content, density, grain size and distribution, etc. At the same time, the applicant found that too high oxygen content and low density are also the reasons for machining defects such as microcracks.

[0006] Therefore, how to improve the machining performance of ruthenium targets by controlling the above-mentioned properties of the targets is the key in the development process of ruthenium targets. Summary of the Invention

[0007] The first object of the present invention is to provide a low-oxygen high-density Ru sputtering target with good machining performance, and another object of the present invention is to provide a preparation method for a low-oxygen high-density Ru sputtering target with good machining performance; a further object is to realize the application of the Ru sputtering target.

[0008] The first object of the present invention is achieved as follows: A low-oxygen high-density Ru sputtering target, the oxygen content of the Ru sputtering target is less than 50 ppm, the thickness of the surface coarse grain layer is less than 50 μm, the average grain size is 2-8 microns, the pores at the grain boundaries are spherical, the maximum pore diameter is less than 1 μm, and the density of the target is greater than 99% of the theoretical density.

[0009] Another object of the present invention is achieved as follows. The preparation method is realized by the technological steps of raw material preparation, pressure sintering and machining, specifically:

[0010] (1) Raw material preparation: Using high-purity ruthenium powder with a purity of 4N or above as the raw material, the ruthenium powder is nearly spherical, the average particle size is 0.5-5 μm, and the oxygen content is less than 500 ppm;

[0011] (2) Pressure sintering: Loading the provided raw material powder into a graphite mold, spraying a BN coating with a thickness of about 0.1-0.5 mm on the surface of the mold and the spacer blocks, and realizing densification through vacuum hot pressing sintering; during vacuum hot pressing sintering, when the vacuum degree reaches 1×10 -2 -10 -3After reaching [Pa], start heating up. The heating and pressure increase are carried out simultaneously. First, heat up to 600°C - 800°C at a heating rate of 2 - 5°C / min and a pressure increase rate of 0.03 - 0.09 MPa / min until the pressure reaches 10 - 15 MPa. After reaching the temperature, keep the temperature and pressure constant for 0.5 hours. Secondly, heat up to 1100°C - 1200°C at a heating rate of 2 - 4°C / min while increasing the pressure at a pressure increase rate of 0.15 - 0.6 MPa / min until the pressure reaches 30 - 50 MPa. After reaching the temperature, keep the temperature and pressure constant for 1 - 2 hours. Start depressurizing 0.5 hours before the end of heat preservation. After depressurizing to below 5 MPa, start cooling down and take out the blank after cooling in the furnace to below 400°C;

[0012] (3) Machining: First, use grinding to remove the surface coarse grain layer at a rotational speed of 300 - 500 RPM and a feed rate of 0.01 - 0.2 mm / min, and control the total grinding amount within 0.5 mm. After grinding, perform turning. For turning, use carbide inserts or cubic boron nitride turning tools at a rotational speed of 500 - 1000 RPM and a feed rate of 0.02 - 0.3 mm / min, and control the total turning amount within 2 mm.

[0013] Advantages of the present invention:

[0014] The present invention utilizes the excellent properties of low-oxygen high-density ruthenium sputtering as a thin film material. Through the structural optimization and modification of Ru, the machining performance of ruthenium is improved, and it is expected to be used as a ruthenium sputtering target for information storage or semiconductor coating. The present invention overcomes the technical defect of the prior art that only simply focuses on the internal organizational structure of the target or simply optimizes the machining process of the ruthenium target by tool selection. According to the physical and chemical characteristics of ruthenium, a method for preparing a Ru sputtering target with excellent structural and machining properties is specifically developed. It is not only easy to operate but also has good stability. On the one hand, by controlling the powder raw materials, disadvantages such as uneven grain size and distribution are improved; on the other hand, by controlling the process parameters of the pressure sintering process, a sputtering target with a thin surface coarse grain layer, low oxygen content, and high density can be obtained after pressing, avoiding the disadvantages of the target prepared by the prior art vacuum hot pressing technology, such as a thick surface coarse grain layer, high oxygen content, low density, and poor machinability. At the same time, based on the above control of the target structure and performance, the final machining of the target is realized by grinding first and then turning, fully meeting the requirements of the information storage and semiconductor fields for ruthenium sputtering targets. Description of the drawings

[0015] Figure 1 SEM morphology diagram of the ruthenium powder used in Example 1 of the present invention;

[0016] Figure 2 SEM fracture diagram of the ruthenium sputtering target prepared by the method described in Example 1 of the present invention;

[0017] Figure 3 SEM micrograph of the fracture surface of the ruthenium sputtering target prepared by the method described in Comparative Example 1 of the present invention;

[0018] Figure 4 SEM micrograph of the coarse-grained layer of the fracture surface of the ruthenium sputtering target prepared by the method described in Comparative Example 2 of the present invention;

[0019] Figure 5 SEM micrograph of the fracture surface of the ruthenium sputtering target prepared by the method shown in Comparative Example 2 of the present invention;

[0020] Figure 6 SEM micrograph for measuring the holes on the fracture surface of the ruthenium sputtering target prepared by the method shown in Comparative Example 2 of the present invention;

[0021] Figure 7 SEM micrograph of the ruthenium raw material powder used in the method shown in Comparative Example 4 of the present invention;

[0022] Figure 8 SEM micrograph of the fracture surface of the ruthenium sputtering target prepared by the method shown in Comparative Example 4 of the present invention. Detailed implementation manners

[0023] The present invention will be further described below in conjunction with embodiments, but the present invention is not limited in any way. Any transformation or substitution based on the teachings of the present invention falls within the protection scope of the present invention.

[0024] The low-oxygen high-density Ru sputtering target with good machinability described in the present invention has an oxygen content of less than 50 ppm, a surface coarse-grained layer thickness of less than 50 μm, an average grain size of 2 - 8 μm, spherical holes at grain boundaries, a maximum hole diameter of less than 1 μm, and a target density greater than 99% of the theoretical density.

[0025] Preferably, the oxygen content of the target is less than 25 ppm. More preferably, the oxygen content of the target is less than 15 ppm.

[0026] Preferably, the thickness of the surface coarse-grained layer of the target is less than 25 μm.

[0027] Preferably, the maximum hole diameter at the grain boundaries of the target is less than 0.5 μm.

[0028] Preferably, the target density is greater than 99.5% of the theoretical density.

[0029] The method for preparing the low-oxygen high-density Ru sputtering target with good machinability described in the present invention includes:

[0030] (1) Using high-purity ruthenium powder with a purity of 4N or more as the raw material, the ruthenium powder is nearly spherical, with an average particle size of 0.5 - 5 μm and an oxygen content of less than 500 ppm;

[0031] (2) Load the provided raw material powder into a graphite mold. The surface of the mold and the spacer blocks are sprayed with a BN coating about 0.1 - 0.5 mm thick, and densification is achieved through vacuum hot pressing sintering; during vacuum hot pressing sintering, when the vacuum reaches 1×10 -2 -10 -3 Pa, start heating. The heating and pressure increase are carried out simultaneously. First, heat to 600°C - 800°C, with a heating rate of 2 - 5°C / min and a pressure increase rate of 0.03 - 0.09 MPa / min, and a pressure of 10 - 15 MPa. After reaching the temperature, hold the temperature and pressure for 0.5 hours; then heat to 1100°C - 1200°C, with a heating rate of 2 - 4°C / min. While heating, increase the pressure simultaneously, with a pressure increase rate of 0.15 - 0.6 MPa / min and a pressure of 30 - 50 MPa. After reaching the temperature, hold the temperature and pressure for 1 - 2 h. Start relieving the pressure 0.5 hours before the end of heat preservation. After relieving the pressure to below 5 MPa, start cooling and cool the furnace to below 400°C before taking out the blank;

[0032] (3) First, use grinding to remove the surface coarse grain layer, with a rotational speed of 300 - 500 RPM, a feed rate of 0.01 - 0.2 mm / min, and the total grinding amount controlled within 0.5 mm; after grinding, perform turning. For turning, use a cemented carbide blade or a cubic boron nitride turning tool, with a rotational speed of 500 - 1000 RPM, a feed rate of 0.02 - 0.3 mm / min, and the total turning amount controlled within 2 mm.

[0033] Preferably, during the raw material preparation process, its average particle size is 0.5 - 3 μm and the oxygen content is less than 300 ppm.

[0034] Preferably, the Ru sputtering target is used to prepare a medium for the information storage or semiconductor field.

[0035] The Ru sputtering target of the present invention is one of the important coating materials in the fields of information storage or semiconductors. Not only are high requirements imposed on the structure and performance of the target, but there are also drawbacks such as great difficulty in machining. For example, the ruthenium sputtering target used in current hard disk drives is required to have a purity of more than 4N5, an oxygen content of less than 50 ppm, a relative density greater than 99% of the theoretical density, and also requires fine and uniform grain size. At the same time, during the preparation of the target, failures such as chipping, cracking, and generation of microcracks during machining result in a significant reduction in the yield of the ruthenium sputtering target. Vacuum hot pressing sintering, as the current mainstream densification method for powder metallurgy targets, is widely used in the preparation of ruthenium targets. However, a coarse grain layer is likely to be generated on the surface of the ruthenium target sintered by vacuum hot pressing. At the same time, to achieve a high relative density, the process of vacuum hot pressing needs to be strictly controlled. In addition, even for a blank with a high relative density, if the oxygen content of the target blank is high and the internal grain size and distribution are uneven, the above-mentioned machining failures are also likely to occur during machining. The inventor of the present invention has found that by controlling the structure and performance such as the thickness of the coarse grain layer, oxygen content, relative density, and grain size of the Ru surface, the machining performance of the target can be effectively improved and the yield of the target can be increased. Ruthenium, as a precious metal element, has a high melting point and stable chemical properties. In order to achieve applications in the fields of semiconductors and magnetic recording, strict control needs to be carried out on the raw materials and preparation process of the ruthenium target.

[0036] To control the structure and performance of the ruthenium sputtering target, it is first necessary to control the raw materials used, specifically including the microscopic morphology, size distribution, and oxygen content of the raw materials. For the powder metallurgy process, even if raw material powders with different initial morphologies and size distributions are used and supplemented with a suitable sintering process, the final grain size of the blank may be relatively close. However, to achieve this possibility, a large number of experiments are required. In the experiments conducted by the inventor, when using raw material powders with different initial morphologies and size distributions, there are significant differences in the grain size and distribution of the target after vacuum hot pressing sintering. Through a series of experiments on ruthenium powders with different morphologies and oxygen contents in this experiment, it is found that when the ruthenium powder is near-spherical and the average particle size is 0.5 - 5 μm, the grain size and distribution of the target after vacuum hot pressing are more easily controlled. This is because the loose packing density of near-spherical powders is greater, and a higher green density can be obtained. When the average particle size is 0.5 - 5 μm, the pressure differences at different positions of the target blank caused by the friction and stress between the powder particles are smaller. Preferably, the average particle size of the powder is 0.5 - 3 μm. When the oxygen content in the powder is less than 500 ppm, the oxygen content after vacuum hot pressing is more easily achieved to be 50 ppm. Preferably, the oxygen content in the powder is less than 300 ppm. At the same time, in order to meet the needs of the information storage and semiconductor fields, the purity requirement of the ruthenium powder is greater than 4N.

[0037] After selecting the appropriate powder raw materials, during the vacuum hot pressing process, the thickness of the surface coarse grain layer can be effectively controlled by surface coating with BN and controlling the sintering process. On the one hand, the strictly controlled BN coating can effectively reduce the heat concentration at the contact between the pressing punch and the ruthenium blank during the pressing process, and reduce the grain growth caused by overburning due to abnormal local temperature rise. Through experiments, it is appropriate to spray a BN coating with a thickness of about 0.1 - 0.5 mm on both the die surface and the spacer block. Preferably, a BN coating with a thickness of about 0.2 - 0.4 mm is sprayed. On the other hand, in order to achieve densification, control the oxygen content, grain size and distribution of the target, it is necessary to strictly control the vacuum hot pressing sintering process. First, a certain degree of vacuum needs to be achieved, preferably 1×10 -2 -10 -3Pa. The next key steps are heating up and pressurizing. The common practice is to first heat up, and then increase the pressure after reaching a certain temperature. The heating rate is relatively fast, up to 10 - 20 °C / min. For example, in the literature (Luo Junfeng et al., Research on the Sintering Process of Ruthenium Metal Sputtering Targets, Powder Metallurgy Industry, 2012, 22(1): 28 - 31), the heating rate can reach 25 °C / min. In the disclosed experiments, at the beginning of heating, a heating rate of 2 - 5 °C / min is appropriate. At the same time, pressurization starts during heating, and the pressure is maintained to increase at a certain rate relative to the temperature. For example, when the temperature is below 600 °C - 800 °C, the pressurization rate is 0.03 - 0.09 MPa / min, and when the temperature is above 600 °C - 800 °C, the pressurization rate is 0.15 - 0.6 MPa / min. The reason for this is that in the initial stage of heating, the temperature is relatively low, and grain rearrangement and plastic flow are the main reasons for densification. At this time, the densification rate increases very fast, and only a relatively low pressure is needed to quickly increase the densification. At the same time, in order to quickly and fully volatilize the residual gas and moisture in the powder gaps, the heating rate should not be too fast. The preferred heating rate is 2 - 5 °C / min. At the same time, when the temperature reaches 600 - 800 °C, keep it warm for a period of time, preferably 0.5 h. This can adjust the rapid decrease in vacuum during the heating process and improve the densification effect. After the heat preservation ends, as the temperature rises, the main factors in the densification process become grain boundary migration and volume diffusion. At this time, the preferred heating rate is 2 - 4 °C / min, and the preferred pressurization rate is 0.15 - 0.6 MPa / min. In order to achieve densification, the highest temperature should reach 1100 - 1200 °C, and the final pressure is 30 - 50 MPa. Compared with the existing temperature, the final sintering temperature of the present invention is lower, which helps to reduce the unit energy consumption and control the grain size. Higher temperatures can also achieve densification, but it not only takes more time but also causes abnormal grain growth inside the target, affecting the use performance of the target. Subsequently, it is the process of cooling down and releasing pressure. To reduce stress, preferably, start releasing pressure 0.5 hours before the end of heat preservation. After releasing the pressure below 5 MPa, start cooling down, and take out the blank after cooling in the furnace to below 400 °C.

[0038] The thickness of the coarse-grained layer on the surface of the target prepared by this process is small, usually less than 50 μm, the oxygen content is low, usually less than 50 ppm, and the average grain size is 2-8 μm. Preferably, the thickness of the coarse-grained layer on the surface of the target is less than 25 μm. Preferably, the oxygen content of the target is less than 25 ppm. Preferably, the oxygen content of the target is less than 15 ppm. At the same time, for the target prepared by the above method, during the densification process, the increase in density is in dynamic equilibrium with the reduction in porosity and the decrease in gas content. The original pores at the grain boundaries gradually shrink and gradually become spherical. The size and shape of the pores are closely related to the density of the target. The inventors found that when densification is completed, there are fewer pores or the pores are spherical at the grain boundaries, the maximum pore diameter is less than 1 μm, and the density of the target can be greater than 99% of the theoretical density. Preferably, the maximum pore diameter at the grain boundaries of the target is less than 0.5 μm. Preferably, the density of the target is greater than 99.5% of the theoretical density.

[0039] Subsequently, machining of the target blank is also required. In order to further reduce machining failures such as cracking and microcrack generation, the surface coarse-grained layer is first removed by grinding. This is because during grinding, the movement direction of the grinding wheel is parallel or tangent to the machining surface, and compared with machining methods such as turning, the stress it receives is smaller. And the stress difference between the surface and the core of the target at the beginning of machining is one of the inducements for machining failure. Preferably, an alumina grinding wheel is used during grinding, the rotational speed is 300-500 RPM, the feed rate is 0.01-0.2 mm / min, and it is appropriate to control the total grinding amount within 0.5 mm; after grinding is completed, turning can be carried out. On the one hand, after the surface coarse-grained layer and the stress layer are machined, machining failures are less likely to occur during subsequent machining. On the other hand, turning can effectively improve the machining efficiency. Preferably, cemented carbide inserts or cubic boron nitride turning tools are used for turning, the rotational speed is 500-1000 RPM, the feed rate is 0.02-0.3 mm / min, and the total turning amount is controlled within 2 mm;

[0040] Example 1

[0041] Using 4N5 (purity 99.995%) Ru as the raw material, the SEM morphology of the ruthenium powder is as Figure 1 shown. The powder particles are nearly spherical, with uniform size distribution. The size of a single particle is about 0.5-3 μm, and the oxygen content is about 500 ppm. Weigh 177 grams of ruthenium powder, fill the provided raw material powder into a graphite mold, and spray a BN coating about 0.5 mm thick on the surface of the mold and the spacer blocks. Densification is achieved by vacuum hot pressing sintering; during vacuum hot pressing sintering, when the vacuum degree reaches 1×10 -2After reaching [Pa], heating and pressure increase are carried out simultaneously. First, heat up to 600 °C at a heating rate of 2 °C / min and a pressure increase rate of 0.033 MPa / min until the pressure reaches 10 MPa. After reaching the temperature, hold the temperature and pressure for 0.5 hours. Secondly, heat up to 1100 °C at a heating rate of 2.5 °C / min and a pressure increase rate of 0.15 MPa / min, and the final pressure is 30 MPa. After reaching the temperature, hold the temperature for 1 h. Start pressure relief 0.5 hours before the end of heat preservation. After the pressure is relieved to below 5 MPa, start cooling and cool in the furnace until the billet is taken out below 400 °C; then machine the target billet. First, use grinding to remove the surface coarse grain layer. Use an alumina grinding wheel with a rotation speed of 300 RPM and a feed rate of 0.2 mm / min. The total grinding amount is controlled within 0.5 mm; after grinding, perform turning. Use a carbide insert turning tool for turning with a rotation speed of 1000 RPM and a feed rate of 0.3 mm / min. The total turning amount is controlled within 0.8 mm. Thus, a Ru target with a diameter of Ф50×6 mm is obtained.

[0042] Example 2

[0043] Using 5N (purity 99.999%) Ru as the raw material, the SEM morphology of the ruthenium powder is as Figure 1 shown. The powder particles are nearly spherical with uniform size distribution. The size of a single particle is about 0.5 - 5 μm, and the oxygen content is about 200 ppm. Weigh 583 grams of ruthenium powder and load the provided raw material powder into a graphite mold. Spray a BN coating about 0.4 mm thick on the surface of the mold and the spacer blocks, and achieve densification through vacuum hot pressing sintering; during vacuum hot pressing sintering, when the vacuum reaches 1×10 -2 -10 -3 Pa, heating and pressure increase are carried out simultaneously. First, heat up to 800 °C at a heating rate of 4 °C / min and a pressure increase rate of 0.055 MPa / min until the pressure first reaches 11 MPa. After reaching the temperature, hold the temperature and pressure for 0.5 hours. Secondly, heat up to 1200 °C at a heating rate of 2.5 °C / min and a pressure increase rate of 0.22 MPa / min, and the pressure finally reaches 35 MPa. After reaching the temperature, hold the temperature for 2 h. Start pressure relief 0.5 hours before the end of heat preservation. After the pressure is relieved to below 5 MPa, start cooling and cool in the furnace until the billet is taken out below 400 °C; then machine the target billet. First, use grinding to remove the surface coarse grain layer with a rotation speed of 400 RPM and a feed rate of 0.1 mm / min. The total grinding amount is controlled within 0.4 mm; after grinding, perform turning. Use a carbide insert or cubic boron nitride turning tool for turning with a rotation speed of 600 RPM and a feed rate of 0.2 mm / min. The total turning amount is controlled within 0.6 mm. Thus, a Ru target with a diameter of Ф100×5 mm is obtained.

[0044] Example 3

[0045] Using Ru with a purity of 99.998% (4N8) as the raw material, the SEM morphology of the ruthenium powder is as Figure 1 shown. The powder particles are nearly spherical, with a uniform size distribution. The size of a single particle is about 0.5 - 3 μm, and the oxygen content is about 300 ppm. Weigh 2194 grams of ruthenium powder, and load the provided raw material powder into a graphite mold. Both the mold surface and the spacer are sprayed with a BN coating about 0.1 mm thick, and densification is achieved through vacuum hot pressing sintering. During vacuum hot pressing sintering, after the vacuum reaches 1×10 -2 Pa, heating and pressure increase are carried out simultaneously. First, heat up to 700 °C at a heating rate of 5 °C / min and a pressure increase rate of 0.086 MPa / min. The pressure is first increased to 12 MPa, and after reaching the temperature, hold for 0.5 hours while maintaining temperature and pressure. Then, heat up to 1150 °C at a heating rate of 3 °C / min and a pressure increase rate of 0.27 MPa / min. The pressure is finally increased to 35 MPa, and after reaching the temperature, hold for 2 h. Start pressure relief 0.5 hours before the end of heat preservation. After the pressure is relieved below 5 MPa, start cooling and cool in the furnace to below 400 °C and then take out the blank. Subsequently, machine the target blank. First, use grinding to remove the surface coarse grain layer at a rotational speed of 400 RPM and a feed rate of 0.05 mm / min. The total grinding amount is controlled within 0.5 mm. After grinding, perform turning. Use a cubic boron nitride turning tool for turning at a rotational speed of 800 RPM and a feed rate of 0.1 mm / min. The total turning amount is controlled within 1.8 mm. Thus, a Ru target with a size of Ф165×6 mm is obtained.

[0046] Example 4

[0047] Using Ru with a purity of 99.995% (4N5) as the raw material, the SEM morphology of the ruthenium powder is as Figure 1 shown. The powder particles are nearly spherical, with a uniform size distribution. The size of a single particle is about 0.5 - 3 μm, and the oxygen content is about 400 ppm. Weigh 2059 grams of ruthenium powder, and load the provided raw material powder into a graphite mold. Both the mold surface and the spacer are sprayed with a BN coating about 0.5 mm thick, and densification is achieved through vacuum hot pressing sintering. During vacuum hot pressing sintering, after the vacuum reaches 1×10 -3After reaching 3×10

[0048] Example 5

[0049] Using Ru with a purity of 99.999% as the raw material, the SEM morphology of the ruthenium powder is as Figure 1 shown. The powder particles are nearly spherical, with a uniform size distribution. The size of a single particle is about 0.5 - 5 μm, and the oxygen content is about 500 ppm. Weigh 2488 grams of ruthenium powder, and load the provided raw material powder into a graphite mold. The surface of the mold and the spacer blocks are sprayed with a BN coating about 0.2 mm thick, and densification is achieved through vacuum hot pressing sintering. During vacuum hot pressing sintering, after the vacuum reaches 3×10 -3 Pa, heating and pressure increase are carried out simultaneously. First, heat up to 600 °C at a heating rate of 2 °C / min and a pressure increase rate of 0.050 MPa / min. The pressure first rises to 15 MPa. After reaching the temperature, hold the temperature and pressure for 0.5 hours. Secondly, heat up to 1200 °C at a heating rate of 4 °C / min and a pressure increase rate of 0.33 MPa / min. The final pressure is 50 MPa. After reaching the temperature, hold the temperature and pressure for 1 h. Start pressure relief 0.5 hours before the end of heat preservation. After the pressure is relieved to below 5 MPa, start cooling, and cool in the furnace until the blank is taken out below 400 °C. Subsequently, machine the target blank. First, use grinding to remove the surface coarse grain layer at a rotational speed of 300 RPM and a feed rate of 0.01 mm / min. The total grinding amount is controlled within 0.4 mm. After grinding, perform turning using a cemented carbide insert turning tool at a rotational speed of 500 RPM and a feed rate of 0.05 mm / min. The total turning amount is controlled within 0.7 mm. Finally, obtain a Ru target with a size of Ф250×3 mm.

[0050] Example 6

[0051] Using Ru with a purity of 99.995% (4N5) as the raw material, the SEM morphology of the ruthenium powder is as follows Figure 1 shown. The powder particles are nearly spherical, with a uniform size distribution. The size of a single particle is about 0.5 - 3 μm, and the oxygen content is about 200 ppm. Weigh 3845 grams of ruthenium powder, and load the provided raw material powder into a graphite mold. The surface of the mold and the spacer blocks are both sprayed with a BN coating about 0.3 mm thick, and densification is achieved through vacuum hot pressing sintering. During vacuum hot pressing sintering, after the vacuum reaches 1×10 -2 Pa, heating and pressure increase are carried out simultaneously. First, heat up to 800 °C at a heating rate of 4 °C / min and a pressure increase rate of 0.07 MPa / min. The pressure is first increased to 14 MPa, and after reaching the temperature, hold the temperature and pressure for 0.5 hours. Then, heat up to 1150 °C at a heating rate of 2 °C / min and a pressure increase rate of 0.23 MPa / min. The final pressure is 40 MPa. After reaching the temperature, hold the temperature for 2 h. Start pressure relief 0.5 hours before the end of heat preservation. After the pressure is relieved to below 5 MPa, start cooling and cool the furnace to below 400 °C and then take out the blank. Subsequently, machining is carried out on the target blank. First, use grinding to remove the surface coarse grain layer at a rotational speed of 350 RPM and a feed rate of 0.02 mm / min. The total grinding amount is controlled within 0.5 mm. After grinding, turning is carried out. The turning uses a carbide insert turning tool at a rotational speed of 1000 RPM and a feed rate of 0.25 mm / min. The total turning amount is controlled within 0.9 mm. Thus, a Ru target with a size of Ф300×3 mm is obtained

[0052] Example 7

[0053] Using Ru with a purity of 99.999% (5N) as the raw material, the SEM morphology of the ruthenium powder is as follows Figure 1 shown. The powder particles are nearly spherical, with a uniform size distribution. The size of a single particle is about 0.5 - 5 μm, and the oxygen content is about 200 ppm. Weigh 4996 grams of ruthenium powder, and load the provided raw material powder into a graphite mold. The surface of the mold and the spacer blocks are both sprayed with a BN coating about 0.4 mm thick, and densification is achieved through vacuum hot pressing sintering. During vacuum hot pressing sintering, after the vacuum reaches 5×10 -3After reaching 1 Pa, heating and pressure increase are carried out simultaneously. First, heat up to 700 °C at a heating rate of 5 °C / min and a pressure increase rate of 0.086 MPa / min. The pressure is first increased to 12 MPa. After reaching the temperature, hold the temperature and pressure for 0.5 hours. Secondly, heat up to 1100 °C at a heating rate of 3 °C / min and a pressure increase rate of 0.26 MPa / min. The final pressure is 35 MPa. After reaching the temperature, hold the temperature for 2 h. Start to relieve pressure 0.5 hours before the end of heat preservation. After relieving the pressure to below 5 MPa, start to cool down and cool the furnace to below 400 °C and then take out the blank; Subsequently, machine the target blank. First, use grinding to remove the surface coarse grain layer at a rotational speed of 500 RPM and a feed rate of 0.2 mm / min. The total grinding amount is controlled within 0.3 mm; After grinding, perform turning. Use a cubic boron nitride turning tool for turning at a rotational speed of 500 RPM and a feed rate of 0.15 mm / min. The total turning amount is controlled within 0.9 mm. Finally, obtain a Ru target with a size of Ф350×3 mm.

[0054] Example 8

[0055] Using 5N (purity 99.999%) Ru as the raw material, the SEM morphology of the ruthenium powder is as Figure 1 shown. The powder particles are nearly spherical, with a uniform size distribution. The size of a single particle is about 0.5 - 3 μm, and the oxygen content is about 200 ppm. Weigh 8272 grams of ruthenium powder. Load the provided raw material powder into a graphite mold. Spray a BN coating about 0.5 mm thick on the surface of the mold and the spacer blocks. Achieve densification through vacuum hot pressing sintering; During vacuum hot pressing sintering, when the vacuum degree reaches 1×10 -3 Pa, heating and pressure increase are carried out simultaneously. First, heat up to 800 °C at a heating rate of 2 °C / min and a pressure increase rate of 0.04 MPa / min. The pressure is first increased to 10 MPa. After reaching the temperature, hold the temperature and pressure for 0.5 hours. Secondly, heat up to 1200 °C at a heating rate of 4 °C / min and a pressure increase rate of 0.27 MPa / min. The final pressure is 30 MPa. After reaching the temperature, hold the temperature for 2 h. Start to relieve pressure 0.5 hours before the end of heat preservation. After relieving the pressure to below 5 MPa, start to cool down and cool the furnace to below 400 °C and then take out the blank; Subsequently, machine the target blank. First, use grinding to remove the surface coarse grain layer at a rotational speed of 300 RPM and a feed rate of 0.2 mm / min. The total grinding amount is controlled within 0.5 mm; After grinding, perform turning. Use a cubic boron nitride turning tool for turning at a rotational speed of 500 - 1000 RPM and a feed rate of 0.2 mm / min. The total turning amount is controlled within 0.9 mm. Finally, obtain a Ru target with a size of Ф440×3 mm.

[0056] Comparative Example 1

[0057] Using 4N5 (purity 99.995%) Ru as the raw material, the SEM morphology of the ruthenium powder is asFigure 1 As shown, the powder particles are nearly spherical with a uniform size distribution. The size of a single particle is about 0.05 - 3 μm, and the oxygen content is about 1000 ppm. Weigh 2488 grams of ruthenium powder. Load the provided raw material powder into a graphite mold. Both the mold surface and the spacer are sprayed with a BN coating about 0.5 mm thick, and densification is achieved through vacuum hot pressing sintering. During vacuum hot pressing sintering, after the vacuum reaches 1×10 -3 Pa, heating and pressure increase are carried out simultaneously. First, heat up to 800 °C at a heating rate of 20 °C / min. After reaching the temperature, hold the temperature and pressure for 0.5 hours. Secondly, heat up to 1500 °C at a heating rate of 10 °C / min. After reaching the temperature, hold the temperature for 2 h. After the heat preservation ends, start cooling and pressure relief, and cool the furnace to below 400 °C and then take out the blank. Subsequently, machine the target blank. Subsequently, turning is carried out at a speed of 600 RPM. Cubic boron nitride turning tools are used for turning, and the feed rate is 0.2 mm / min. Cracking occurs during the machining process, and the machining is terminated.

[0058] Comparative Example 2

[0059] Using 5N (purity 99.999%) Ru as the raw material, the SEM morphology of the ruthenium powder is as Figure 1 shown. The powder particles are nearly spherical with a uniform size distribution. The size of a single particle is about 0.5 - 3 μm, and the oxygen content is about 200 ppm. Weigh 2488 grams of ruthenium powder. Load the provided raw material powder into a graphite mold. Both the mold surface and the spacer are sprayed with a BN coating about 0.5 mm thick, and densification is achieved through vacuum hot pressing sintering. During vacuum hot pressing sintering, after the vacuum reaches 1×10 -3 Pa, then heat up directly to 1600 °C at a heating rate of 25 °C / min. Start pressurizing after the temperature reaches 1200 °C, and the final pressure is 40 MPa. After reaching the temperature, hold the temperature and pressure for 2 h. After the heat preservation is completed, relieve the pressure, and the pressure is relieved within 0.5 hours. Cool the furnace to below 400 °C and then take out the blank. Subsequently, machine the target blank. First, use grinding to remove the surface coarse grain layer at a speed of 300 RPM and a feed rate of 0.2 mm / min. The total grinding amount is controlled within 0.5 mm. After grinding, turning is carried out. Cubic boron nitride turning tools are used for turning, with a speed of 500 RPM and a feed rate of 0.2 mm / min. The total turning amount is controlled within 0.9 mm. Cracking occurs during the turning process, and the machining is terminated.

[0060] Comparative Example 3

[0061] Using 5N (purity 99.999%) Ru as the raw material, the SEM morphology of the ruthenium powder is as Figure 1As shown, the powder particles are nearly spherical with a uniform size distribution. The size of a single particle is about 0.5 - 3 μm, and the oxygen content is about 1000 ppm. Weigh 2488 grams of ruthenium powder, load the provided raw material powder into a graphite mold, and spray a BN coating about 0.5 mm thick on both the mold surface and the spacer blocks. Densification is achieved through vacuum hot pressing sintering. During vacuum hot pressing sintering, after the vacuum reaches 1×10 -3 Pa, then start heating up directly to 1400 °C at a heating rate of 15 °C / min. Start applying pressure after the temperature reaches 1100 °C, with a final pressure of 45 MPa. Keep the temperature and pressure constant for 2 h after reaching the temperature, then start cooling down and reducing the pressure, and unload the pressure within 0.5 h. Cool the furnace to below 400 °C and take out the blank. Subsequently, machine the target blank. First, use grinding to remove the surface coarse grain layer at a rotational speed of 300 RPM and a feed rate of 0.2 mm / min, and control the total grinding amount within 0.5 mm. After grinding, perform turning using a cubic boron nitride turning tool at a rotational speed of 500 - 1000 RPM and a feed rate of 0.2 mm / min, and control the total turning amount within 0.9 mm. Cracking occurred during the machining process, and the machining was terminated.

[0062] Comparative Example 4

[0063] Using 5N (purity 99.999%) Ru as the raw material, the SEM morphology of the ruthenium powder is as Figure 7 shown. The powder particles are nearly spherical with a uniform size distribution. The size of a single particle is about 0.5 - 3 μm, and the oxygen content is about 500 ppm. Weigh 2488 grams of ruthenium powder, load the provided raw material powder into a graphite mold, and spray a BN coating about 0.5 mm thick on both the mold surface and the spacer blocks. Densification is achieved through vacuum hot pressing sintering. During vacuum hot pressing sintering, after the vacuum reaches 1×10 -3 Pa, then start heating up directly to 1300 °C at a heating rate of 10 °C / min. Start applying pressure after the temperature reaches 1000 °C, with a final pressure of 35 MPa. Keep the temperature and pressure constant for 2 h after reaching the temperature, then start cooling down and reducing the pressure, and unload the pressure within 0.5 h. Cool the furnace to below 400 °C and take out the blank; subsequently, machine the target blank. First, use grinding to remove the surface coarse grain layer at a rotational speed of 300 RPM and a feed rate of 0.2 mm / min, and control the total grinding amount within 0.5 mm. After grinding, perform turning using a cubic boron nitride turning tool at a rotational speed of 500 - 1000 RPM and a feed rate of 0.2 mm / min, and control the total turning amount within 0.9 mm. Finally, a Ru target with Ф250×3 mm can be obtained, but microcracks occurred during the turning process and still exist after the machining is completed.

[0064] Comparative Example 5

[0065] Using Ru with a purity of 99.995% as the raw material, the SEM morphology of the ruthenium powder is as Figure 1 shown. The powder particles are nearly spherical, with a uniform size distribution. The size of a single particle is about 0.5 - 3 μm, and the oxygen content is about 500 ppm. Weigh 177 grams of ruthenium powder, and load the provided raw material powder into a graphite mold. The surface of the mold and the pads are both sprayed with a BN coating about 0.5 mm thick, and densification is achieved through vacuum hot pressing sintering. During vacuum hot pressing sintering, after the vacuum reaches 1×10 -2 Pa, start heating and pressurizing. First, heat up to 600 °C at a heating rate of 2 °C / min and a pressure increase rate of 1 MPa / min until the pressure reaches 10 MPa. After reaching the temperature, hold the temperature and pressure for 0.5 hours. Then, heat up to 1100 °C at a heating rate of 2.5 °C / min and a pressure increase rate of 1.5 MPa / min. The final pressure is 30 MPa. After reaching the pressure, start holding the pressure. After reaching the temperature, hold the temperature for 1 h. Start relieving the pressure 0.5 hours before the end of the heat preservation. After relieving the pressure below 5 MPa, start cooling and cool the furnace to below 400 °C and then take out the blank. Subsequently, machine the target blank. First, use grinding to remove the surface coarse grain layer. Use an alumina grinding wheel with a rotational speed of 300 RPM and a feed rate of 0.2 mm / min. The total grinding amount is controlled within 0.5 mm. After grinding, perform turning. Use a carbide turning tool with a rotational speed of 1000 RPM and a feed rate of 0.3 mm / min. The total turning amount is controlled within 0.8 mm. Microcracks appear on the surface of the finally processed target material. Use SEM to observe the morphology and particle size of the powder, the thickness of the coarse grain layer on the fracture surface of the target material, the grain size, and the morphology and size of the pores at the grain boundaries. Use an oxygen and nitrogen analyzer to detect the oxygen content of the sample. Use the Archimedes drainage method to measure the actual density of the sample blank, and calculate the relative density according to the formula: relative density = ρactual / ρtheoretical × 100%.

[0066] Analyze the target materials prepared in Examples 1 - 8 and Comparative Examples 1 - 4. Their corresponding oxygen content, surface coarse grain layer thickness, density, and machining performance are shown in Table 1.

[0067] Table 1 Partial properties of the target materials of different examples and comparative examples

[0068]

[0069] From Figure 1 it can be seen that the raw materials used for the ruthenium target material prepared in Example 1 are nearly spherical, and the particle size is between 0.5 - 5 μm.

[0070] From Figure 2 it can be seen that the target material prepared in Example 1 has a uniform microstructure.

[0071] As can be seen from Table 1, in Examples 1-8 of the present invention, the prepared target has a low oxygen content, with values all below 50 ppm, and a relatively thin surface coarse grain layer, below 100 μm; the relative density of the target prepared by the method provided by the present invention is generally high, with a relative density above 99.5%, and at the same time, the grain size is distributed between 2-5 μm, and the maximum pore size is less than 1 μm, having good machining performance.

[0072] In the comparative examples, due to the relatively fast heating and / or pressure increasing rate, the oxygen content is generally high, the relative density is low, and the grain distribution is uneven or abnormal grain growth occurs. For example, in Comparative Example 1, the grain size of the target is between 2-25 μm, and abnormal grain growth occurs in some grains, as Figure 3 shown. The relative density of the target prepared in Comparative Example 2 is only about 96% of the theoretical density. It can be seen from Figure 4 that the surface coarse grain layer reaches 438 μm; it can be seen from Figure 5 and Figure 6 that due to the fast heating rate and high sintering temperature, the grain size is generally above 10 μm, and some reach about 30 μm. At the same time, a large number of non-spherical pores appear at the grain boundaries, and the maximum pore size reaches about 4 μm. Therefore, the target cracks during processing. In Comparative Example 4, there is a large size difference in the particle size of the raw materials used, with nano-sized and micron-sized flaky particles, as Figure 7 shown. For the target sample prepared with this powder, the grain size also shows a particularly uneven phenomenon, with the grain size ranging from 0.5-6 microns, as Figure 8 shown. At the same time, a large number of surface microcracks appear during machining. In Comparative Example 5, the raw material powder and parameters such as the heating rate are the same as those in Example 1, except that the pressure increasing rate is relatively fast during the pressure sintering process. The obtained ruthenium target not only has a high oxygen content, a thick surface coarse grain layer, a low density, but also has poor machining performance.

[0073] In summary, in Examples 1-8, the method provided by the present invention is adopted to control the powder morphology, particle size distribution and vacuum hot pressing sintering process, improving the disadvantages of high oxygen content, thick surface coarse grain layer, low density and poor machining performance of the ruthenium target. At the same time, the targets prepared by the processes in Examples 1-8 have good properties such as grain size and distribution, oxygen content, and density, and are expected to be applicable to the preparation of thin films for information storage and semiconductor materials.

Claims

1. A preparation method of a low-oxygen high-density Ru sputtering target, characterized in that, it includes the following steps: Step (1), raw material preparation, including: using ruthenium powder with a purity of more than 4N as the raw material, the ruthenium powder is nearly spherical, with an average particle size of 0.5 - 5 μm and an oxygen content of less than 500 ppm; Step (2), pressure sintering, including: filling the high-purity ruthenium powder into a graphite mold and achieving densification through vacuum hot pressing sintering; During vacuum hot pressing sintering, when the vacuum degree reaches 1×10 -2 -1×10 -3 Pa, start heating up. The heating up and pressure increasing are carried out synchronously. First, heat up to 600°C - 800°C at a heating rate of 2 - 5°C / min and a pressure increasing rate of 0.03 - 0.09 MPa / min, with a pressure of 10 - 15 MPa. After reaching the temperature, keep the temperature and pressure for 0.5 hours. Secondly, heat up to 1100°C - 1200°C at a heating rate of 2 - 4°C / min. While heating up, increase the pressure simultaneously at a pressure increasing rate of 0.15 - 0.6 MPa / min, with a pressure of 30 - 50 MPa. After reaching the temperature, keep the temperature and pressure for 1 - 2 h. Start relieving the pressure 0.5 hours before the end of heat preservation. After relieving the pressure to below 5 MPa, start cooling down and take out the blank after cooling in the furnace to below 400°C; Step (3), machining, including: firstly, using grinding to remove the surface coarse grain layer; after grinding, turning is carried out to obtain the low-oxygen high-density Ru sputtering target; the oxygen content of the Ru sputtering target is less than 50 ppm, the thickness of the surface coarse grain layer is less than 50 μm, the average grain size is 2 - 8 μm, the pores at the grain boundaries are spherical, the maximum pore diameter is less than 1 μm, and the density of the target is greater than 99% of the theoretical density.

2. The preparation method according to claim 1, characterized in that: during grinding, the rotational speed is 300 - 500 RPM, the feed rate is 0.01 - 0.2 mm / min, and the total grinding amount is controlled within 0.5 mm; during turning, a cemented carbide blade or a cubic boron nitride turning tool is used for turning, the rotational speed is 500 - 1000 RPM, the feed rate is 0.02 - 0.3 mm / min, and the total turning amount is controlled within 2 mm.

3. The preparation method according to claim 1, characterized in that, in the said step (1), the average particle size is 0.5 - 3 μm and the oxygen content is less than 300 ppm.

4. The preparation method according to claim 1, characterized in that, the thickness of the surface coarse grain layer of the target is less than 25 μm.

5. The preparation method according to claim 1, characterized in that, the maximum pore diameter at the grain boundaries of the target is less than 0.5 μm.

6. The preparation method according to claim 1, characterized in that, the density of the target is greater than 99.5% of the theoretical density.

7. The preparation method according to any one of claims 1 - 6, characterized in that, the oxygen content of the target is less than 25 ppm.

8. The preparation method according to any one of claims 1 - 6, characterized in that, the oxygen content of the target is less than 15 ppm.

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