TWI909410B - Sputtering target and process for producing the same - Google Patents

Abstract

This disclosure provides a sputtering target and a method for manufacturing the sputtering target, wherein the sputtering target contains 55% to 80% by weight of Ni, the balance of W and general impurities, and the sputtering target contains a W phase, a Ni (W) solid solution phase, and an intermetallic phase that does not contain a pure Ni phase and contains or does not contain an intermetallic phase with an average area of less than 5% as measured by the cross-section of the sputtering target.

Description

Splash targets and methods for manufacturing splash targets

This disclosure relates to a sputtering target and a method for manufacturing the sputtering target.

W-Ni alloy (tungsten-nickel alloy) is a high-melting-point, high-hardness, and high-corrosion-resistant alloy, widely used in machinery, electronics, medical devices, automotive parts, aerospace and military industries, daily hardware parts, industrial processing molds, etc.

Electrochromic layers composed of W-Ni mixed oxides have been known for many years. A particularly advantageous W/Ni atomic ratio of approximately 0.33 is found in W-alloyed NiO_{_x} (W-Ni mixed oxide). At this ratio, the charge transfer resistance is optimal, ensuring extremely fast optical conversion behavior of the electrochromic layer. Electrochromic layers fabricated in this manner are produced using sputtering targets, for example, composed of W-Ni alloys, which are formed by reactive magnetron sputtering followed by etching under oxygen to form the W-Ni mixed oxide layer. Oxide targets are also known from existing techniques.

Furthermore, W-Ni alloys can be used as barrier layers in copper/tin (Cu/Sn) bonding applications. Submicron Cu/Sn bonding with a transient Ni buffer layer at 225°C can overcome the physical limitations of 5-micron (μm) Cu/Sn, and 10-nanometer (nm) Ni layers suppress large Cu/Cn interdiffusion in steps prior to the main bonding process. When the temperature approaches the Sn melting point, the Ni layer dissolves, and the molten Sn forms submicron-scale Cu/Sn bonds. The excellent mechanical strength and electrical properties of this approach demonstrate great potential for high-density three-dimensional (3D) interconnects. Similarly, W-Ni alloys can also be used as bonding layers between thin-film transistors (TFTs) and light-emitting diode (LED) cells.

For sputtering targets composed of W-Ni alloys, conventional applications employ thermal powder coating processes. However, this process results in high chemical impurity content and low density. High chemical impurity content leads to inconsistent coating coverage and thus negatively impacts the homogeneity of the deposited layer. The low density of the sputtering target material also adversely affects the coating coverage. Furthermore, thermal spraying can only produce a limited material thickness, which restricts the target's material utilization and service life.

If a sputtering target composed of a W-Ni alloy, as currently used, is manufactured by thermal spraying, the result of using Ni and W powders as raw materials is that a pure nickel fraction exhibiting ferromagnetic properties is present in the sputtering target. These ferromagnetic regions are unfavorable for magnetron sputtering because they lead to varying coating ratios and thus negatively impact the homogeneity of the deposited layer.

Furthermore, thermal spraying can only adjust the material density to a limited extent. The low density of the sputtering target material also has a negative impact on the coating coverage. In addition, thermal spraying can only produce a limited material thickness, which limits the material utilization and service life of the target.

Another drawback is the presence of metallic impurities in the sprayed powder due to the manufacturing process (which are directly transported to the resulting sputtering target). Impurities in the sputtering coating can adversely affect the properties of the optical layer.

Additional non-metallic, especially oxidized or insulating inclusions or phases that may be embedded in the sputtering target during thermal spraying can increase the particle count during sputtering, which in turn can adversely affect the properties of the sputtered layer (adhesion, specific resistance, layer homogeneity) and the coating method (high arc rate).

To overcome the aforementioned defects of thermal spraying, WO2015089533A1 describes a sputtering target with low Ni content and high W content. Through the sintering process described therein, the oxygen content can be controlled below 100 micrograms per gram (μg/g), and the density can reach over 90% by weight. However, this process has the following drawbacks: because the low W phase acts as the second phase, the Ni content distribution on the surface of the sputtering target is uneven, the pure W phase content is too high, and the sputtering target may include the pure Ni phase, thereby reducing the material uniformity and affecting the sputtering effect.

The purpose of this disclosure is to at least partially overcome the shortcomings of the prior art and to provide an improved sputtering target and a method for manufacturing the sputtering target.

The first aspect of this disclosure relates to a sputtering target containing 55% to 80% by weight of Ni, the balance of W, and general impurities. The sputtering target contains a W phase, a Ni (W) solid solution phase, and an intermetallic phase that does not contain a pure Ni phase and has an average area of less than 5% as measured by the cross-section of the sputtering target.

Alternatively, the sputtering target contains 60% to 70% by weight of Ni.

Alternatively, the sputtering target contains 60% to 65% Ni by weight.

Alternatively, the oxygen content of the sputtering target is less than 50 μg/g.

Alternatively, the oxygen content of the sputtering target is less than 40 μg/g.

Alternatively, the hardness of the sputtering target is less than 500 HV10.

Alternatively, the intermetallic phase may be selected from any one or more substances in the group consisting of: _Ni₄W , WNi, _W₂Ni .

Alternatively, the sputtering target has an average grain size of less than 40 μm for the W phase.

Alternatively, the sputtering target has a relative density of over 90%.

Alternatively, the sputtering target has a relative density of over 99.5%.

The second aspect of this disclosure relates to a method for manufacturing the sputtering target described in the first aspect of this disclosure, the method being carried out via a powder metallurgy approach and comprising the following steps: performing a compaction step, wherein a powder mixture of W powder and Ni powder is compacted by applying pressure, heat, or pressure and heat to obtain a compacted billet; and performing a cooling step, wherein the resulting compacted billet is cooled to a temperature range of 750°C to 1000°C at a cooling rate greater than 3 gelvin/min (K/min).

If the compaction step is achieved by sintering at a temperature of 1100°C to 1450°C, the sintering atmosphere is combined with a first gas and/or a vacuum. Preferably, the sintering atmosphere is changed from a vacuum to the first gas, that is, sintering is carried out successively under a vacuum and a first gas.

Alternatively, the process also includes thermomechanical treatment or heat treatment of the billet between the compaction and cooling steps. However, if such thermomechanical treatment or heat treatment is performed after the sintering step, the cooling rate in the cooling step is changed to be greater than 30 K/min in a temperature range of at least 750°C to 900°C.

Alternatively, the process also includes thermomechanical treatment or heat treatment at temperatures ranging from 970°C to 1450°C.

Alternatively, the thermomechanical treatment or heat treatment includes at least one forging step or rolling step.

The following is a detailed description of the sputtering target involved in the first aspect of this disclosure.

As shown in Figure 1 (see ASM Handbook Vol. III, Alloy Phase Diagrams 1992), the sputtering target contains a W phase, a Ni(W) solid solution phase, and a Ni-free phase, wherein the Ni(W) solid solution phase has a W-alloyed Ni mixed crystal, preferably a W-saturated Ni mixed crystal.

The sputtering target according to this disclosure preferably contains an intermetallic phase with an average area of less than 5% as measured at a cross section of the target material. Preferably, the sputtering target according to this disclosure contains a pure W phase with an average area of less than 5%.

To determine the proportion of intermetallic phases present in the sputtering target according to this disclosure, the average area proportion is analyzed at a cross-section. For this purpose, a metallographically polished cross-section is produced and examined by optical or electron microscopy. The metallographically polished cross-section is a two-dimensional cross-section of a three-dimensional sputtering target. Area analysis can be performed on the micrograph produced in this manner using commercially available image analysis software. This is done through image analysis to determine the proportion of each phase in the aforementioned microstructure, typically by comparing the phases to be distinguished. Phases that are difficult to distinguish can be further compared using a suitable etching method. In this case, the intermetallic phase can be distinguished from the Ni mixed crystals (Ni(W) phase, W-saturated Ni mixed crystals) by etching with a suitable etching solution (e.g., 85 ml of ammonia solution and 5 ml of 30% hydrogen peroxide solution), and the area ratio can be determined. However, depending on the state of the microstructure, alternative etching solutions and processes can also be considered. The average area ratio is calculated as the arithmetic mean of five area ratio measurements taken on five image regions of 100 μm × 100 μm on a metallographic polished section photographed at 1000x magnification. A uniform sputtering surface elemental distribution can be obtained with less than 5% intermetallic phase. The maximum deviation of Ni content in the manufactured sputtering target is much lower than that of the sputtering target produced by the method of WO2015089533A1, resulting in very high Ni uniformity at different locations on the sputtering target. As an alternative, the presence of intermetallic phases in the sputtering target can be easily confirmed or ruled out using relevant JCPDS cards via X-ray diffraction (XRD) (considering the corresponding X-ray detection limit).

The intermetallic phase can be selected from any of the following: _Ni₄W , WNi, _W₂Ni .

As can be seen from the phase diagram in Figure 1, when the Ni content in the sputtering target is greater than 55% by weight, the brittle _Ni₄W phase appears preferentially. When the nickel content is even higher, the ferromagnetic nickel phase can appear.

The sputtering target of this disclosure contains 55% to 80% by weight Ni, the balance W, and unavoidable impurities. The term "unavoidable impurities" refers to production-related contaminants, consisting of gaseous or associated elements, originating from the raw materials used. These impurities are preferably present in the sputtering target of this disclosure in proportions below 100 μg/g (corresponding to ppm) for gases (C, H, N, O) and below 500 μg/g for other elements. Suitable methods for elemental analysis depend on the element being analyzed. The sputtering target of this disclosure is characterized by a high Ni content and a low W content. In the Ni-W layer produced by a protected sputtering target, Ni acts as a buffer layer to dissolve molten Sn, successfully achieving submicron-level Cu/Sn bonding, thereby obtaining excellent mechanical strength and electrical properties. The Ni-W layer produced by this sputtering target can be used for TFT electrode bonding and semiconductor 3D integration, effectively solving the technical problems of reduced material uniformity and impaired sputtering effects caused by existing sputtering targets, exhibiting high purity, high density, and good application performance. The sputtering target disclosed herein is further preferably composed of 60% to 70% Ni, and even more preferably 60% to 65% Ni, which further achieves better material uniformity and application performance.

The sputtering target disclosed herein preferably has an oxygen content of less than 50 μg/g, and more particularly less than 40 μg/g.

Oxygen content can be determined in a simple way using an inductively coupled plasma emission spectrometer (ICP-OES).

The sputtering target disclosed herein has a preferred HV10 hardness (Vickers hardness) of less than 500 HV10.

It has been found that satisfactory toughness of the sputtering target can be optimally ensured when the HV10 hardness is less than 500 HV10. This simplifies handling during manufacturing, such as in optional mechanical forming steps. During use, especially as a single-piece tubular target in one embodiment, a hardness less than 500 HV10 significantly simplifies handling.

For the purposes of this invention, the HV10 hardness (Vickers hardness) is the arithmetic mean of five hardness measurements.

The sputtering target disclosed herein preferably has a relative density exceeding 90%, more preferably exceeding 92%, and most preferably exceeding 99.5%. Higher target density results in more favorable properties. Targets with low relative density have a relatively high proportion of porosity, which can be a source of actual leakage and/or impurities and particles during sputtering. Furthermore, sputtering targets with low density readily absorb water or other impurities, leading to difficult-to-control process parameters. Additionally, during sputtering, materials with only a low degree of densification exhibit lower ablation rates than materials with higher relative densities.

As is well known, relative density can be easily determined using Archimedes' principle and the method of buoyancy.

Because of the different geometric requirements imposed on the sputtering target according to this disclosure in different coating equipment and in order to coat substrates with different geometric structures, such a target may be in the form of a planar target (e.g., in the form of a plate or disc), a rod, a tubular target, or a main body with other complex shapes.

The sputtering target according to the present invention preferably has an average grain size of less than 40 μm, more preferably less than 20 μm of the W phase.

The average grain size of the W phase is less than 40 μm, more preferably less than 20 μm, resulting in exceptionally uniform sputtering behavior and thus the deposition of exceptionally uniform layers with exceptionally uniform thickness. Furthermore, the notch effect of the W phase is kept low in this manner, resulting in optimally ensuring satisfactory toughness of the sputtering target.

The diameter of aggregates of multiple W phase grains can exceed 40 μm, but in the sputtering target disclosed herein, these aggregates cannot be considered as single grains of the W phase.

The average grain size of the W phase can be easily determined by performing a line section measurement on the metallographic polished section.

As described above, the sputtering target according to the first aspect of this disclosure effectively solves the technical problem of reducing material uniformity and affecting sputtering effect, and has high density and good application performance.

The sputtering target disclosed herein can be applied in the following areas: - As a bonding solution in display applications, such as LED chips on a TFT backplane; - As a thin layer in electrochromic devices or reflective heat-insulating coating stacks; - As a protective cover layer for underlying metal lines, such as copper or aluminum substrates, preventing environmental exposure and oxidation; - As a buffer layer, controlling elemental diffusion between different layers by applying a specific thickness (t), such as 5 nm < t < 50 nm; - As a nickel source for packaging and welding applications; - Deposition of oxides or nitrides using reactive sputtering processes. - As a barrier layer in thin film stacking, it prevents cross-diffusion of elements, for example, in the metallization of thin-film transistors, where it enters the semiconductor material and copper wires, which would degrade electrical performance.

The manufacturing method of the sputtering target of the second aspect of this disclosure will be described below.

The second aspect of this disclosure describes a method for manufacturing the sputtering target described in the first aspect of this disclosure via a powder metallurgy approach, characterized in that it comprises at least the following steps: Performing a compaction step, wherein a powder mixture of W powder and Ni powder is compacted by applying pressure, heat, or pressure and heat to obtain a compacted billet; and Performing a cooling step, wherein the resulting compacted billet is cooled to a temperature range of 750°C to 1000°C at a cooling rate greater than 3 K/min.

The compaction step, as part of the method for manufacturing a W-Ni sputtering target according to the present invention, results in the compaction and densification of a suitable powder mixture by applying pressure, heat, or both to form a blank. This can be carried out by various process steps, such as by pressing and sintering, cold isostatic pressing, hot isostatic pressing, hot pressing, or discharge plasma sintering (SPS), or a combination of these methods, or other methods of compacting the powder mixture.

The production of powder mixtures according to the method of this disclosure is preferably achieved by weighing appropriate amounts of W powder and Ni powder and placing them in a suitable mixing apparatus until a homogeneous distribution of the components in the powder mixture is ensured. For the purposes of this disclosure, the powder mixture may comprise pre-alloyed or partially alloyed powders containing the components W, Ni, and X.

The powder mixture produced in this way is preferably filled into a mold for compaction. Suitable molds are those for cold isostatic pressing or flexible tubes, hot presses or discharge plasma sintering equipment, or, in the case of hot isostatic pressing, cans.

In the cooling step, the billet is cooled to a temperature range of 750°C to 1000°C at a cooling rate greater than 3 K/min. This cooling step, as part of the method for manufacturing a W-Ni sputtering target according to this disclosure, avoids the appearance of undesirable intermetallic phases. In a preferred embodiment, the billet is held in this temperature range for 15 minutes to 3 hours, more preferably 45 minutes to 2 hours, and even more preferably 45 minutes to 90 minutes. An excessively high proportion of intermetallic phases in the W-Ni sputtering target manufactured by the method of this disclosure can initially lead to a different sputtering rate than the remaining target, and thus cause non-uniform etching on the sputtering target, resulting in fluctuations in the deposition layer thickness. Furthermore, the brittle intermetallic phases in the microstructure of the sputtering target can lead to arcing or increased particle formation. On the other hand, the low toughness of the intermetallic phases makes it even more difficult to manipulate such sputtering targets.

As described above, if thermomechanical treatment or heat treatment is performed after the compaction step, such as a sintering step, the cooling rate is changed to a temperature range greater than 30 K/min to 750°C to 900°C. More preferably, in this cooling step of the resulting billet, the resulting billet is cooled to a temperature range of 750°C to 900°C at a cooling rate greater than 50 K/min, because this allows the material properties and microstructure of the target to be set in a particularly optimal manner. This type of cooling step can be achieved, for example, by cooling in air, water, or oil. This type of cooling step ensures that the formation of intermetallic phases is optimally avoided, and that the sputtering target manufactured by this method has the best possible combination of microstructure and mechanical properties.

Preferably, the compaction step is performed by sintering at a temperature of 1100°C to 1450°C, wherein the sintering atmosphere is combined with a first gas and/or a vacuum. In a preferred embodiment, both the first gas and a vacuum are used in the sintering process. It has been found that performing the compaction step by sintering at a temperature of 1100°C to 1450°C is particularly advantageous in the method for manufacturing W-Ni sputtering targets according to this disclosure. Here, sintering is a sintering method referred to as pressureless sintering at a pressure of less than 2 MPa, preferably at a pressure below atmospheric pressure.

Compaction at these temperatures optimally ensures solid-state sintering to a very high relative density within the existing powder mixture. Compaction below 1100°C may yield too low a density, while temperatures above 1450°C may result in reduced mechanical stability of the sputtering target. Compaction within the indicated temperature range ensures an optimal combination of high density and superior mechanical properties. Due to the high Ni content in the produced sputtering targets, conventional processes struggle to control the O content at low levels and achieve the density required for closed-cell conditions. Sintering at temperatures between 1100°C and 1450°C, with the sintering atmosphere combined with a first gas and/or vacuum, can significantly reduce the oxygen content. The first gas is preferably a mixture of gases with hydrogen as the main component. The mixture may also include argon, but is not limited to this, and may also include other suitable gases.

In the method for manufacturing a W-Ni sputtering target according to this disclosure, the thermomechanical treatment or heat treatment of the resulting billet is preferably performed between the compaction step and the cooling step. Such thermomechanical treatment or heat treatment can produce advantageous properties, such as a further increase in density and/or further homogenization of the microstructure.

Preferably, by means of such thermomechanical treatment or heat treatment, any small proportions of intermetallic phases that may remain can be homogeneously distributed in the microstructure of the sputtering target, thus minimizing the side effects of these phases. This fine distribution ensures uniform peeling without the formation of bumps during sputtering.

In the method of manufacturing W/Ni sputtering targets, it is preferable to carry out the thermomechanical treatment or heat treatment at a temperature in the range of 970°C to 1450°C.

Thermomechanical treatment or heat treatment is performed within the indicated temperature range in the two-phase region W(Ni)+Ni(W), and preferably, this prevents or substantially prevents the formation of other undesirable brittle intermetallic phases. Ideally, any intermetallic phases that may exist after compaction can be largely dissolved by such thermomechanical treatment or heat treatment.

By avoiding such undesirable brittle intermetallic phases as much as possible, W-Ni sputtering targets manufactured by the method disclosed herein are particularly well shaped. This also simplifies the manufacture of larger sputtering targets (and especially longer and preferably one-piece tubular targets), and has a favorable effect on the closeness to the achievable final geometry.

Preferably, the thermomechanical treatment or heat treatment includes at least one forging step or rolling step.

Within the scope of this disclosure, thermomechanical treatment or heat treatment can be performed in a single-stage or multi-stage manner. Combinations of various suitable methods are also possible. Therefore, thermomechanical treatment or heat treatment may contain one or more sub-steps that do not include or substantially do not include a sputtering target.

In the method of manufacturing a W-Ni sputtering target according to this disclosure, thermomechanical treatment or heat treatment including at least one rolling step or forging step is particularly advantageous.

The defined deformation can be introduced into the sputtering target in a particularly targeted manner by thermomechanical treatment or heat treatment containing at least one rolling or forging step. In this way, for example, excessive strengthening can be avoided, and thus, the deformation force can be prevented from exceeding the limit that can be applied.

The fabric can be purposefully placed in the sputtering target by means of thermomechanical treatment or heat treatment containing at least one rolling or forging step, which in turn can positively influence both the mechanical and sputtering properties of the sputtering target.

In addition, one or more rolling or forging steps can make it possible to change the thickness of the material along its length and set the thickness in a targeted manner.

In addition, by means of rolling or forging, it is possible to ensure a favorable and uniform surface quality, high straightness and good roundness for further mechanical or thermomechanical or heat treatment of the sputtering target.

Preferably, a sputtering target containing 55% to 80% by weight of Ni, the balance W, and general impurities is manufactured using the method for manufacturing a W-Ni sputtering target according to this disclosure. In this case, the method of this disclosure ensures that the resulting W-Ni sputtering target contains a W phase, a Ni (W) solid solution phase, a Ni-free phase, and an intermetallic phase that contains or does not contain, with an average area ratio of less than 5% as measured by the cross-section of the sputtering target. Here, the area ratio is understood as the average area ratio, which is calculated as the arithmetic mean of five area ratio measurements taken on five image portions having a metallographic polishing cross-section of 100 μm × 100 μm, recorded at a magnification of 1000x.

The method for manufacturing W-Ni sputtering targets according to this disclosure ensures that the relative density of the W-Ni sputtering targets manufactured by this method exceeds 90%, more preferably exceeds 92%, and most preferably exceeds 99.5%. The method for manufacturing W-Ni sputtering targets according to this disclosure also optimizes the purity and mechanical properties of the resulting sputtering targets.

Therefore, the method of this disclosure produces extremely low levels of impurities in the sputtering target, for example, preferably less than 50 μg/g, and particularly preferably less than 40 μg/g. The substantial avoidance of the formation of brittle intermetallic phases also preferably leads to optimized hardness of the W-Ni sputtering target produced by the method of this disclosure.

Preferably, a hardness of less than 500 HV10 is achieved by means of the method disclosed herein.

In this case, the average grain size of the W phase achieved by the method according to the present disclosure is less than 40 μm, preferably less than 20 μm.

The following examples illustrate this disclosure.

Example

Example 1:

W metal powder with a particle size of 4 μm as determined by Fisher's method and Ni metal powder with a particle size of 4.2 μm as determined by Fisher's method were used as raw materials. 40 wt% of tungsten powder and 60 wt% of nickel powder were mixed in a mixer at a speed of 12 revolutions per minute (rpm) for 1 hour.

The powder mixture is introduced into rubber, which is then sealed at its open end by a rubber cap. The sealed rubber is positioned in an isostatic press and pressed at 200 MPa for 1 minute to provide a green compact with a relative density of 67%, a thickness of 23 mm, a width of 158 mm, and a length of 748 mm.

The green billet was first sintered in a vacuum at a heating rate of 3℃/min to 1350℃, held at 1350℃ for 1 hour, then the sintering atmosphere was changed to the first gas and held for another 3 hours. It was then cooled to 980℃ at a rate of 8℃/min, and the sintering atmosphere was changed to _H₂ atmosphere and held for 1 hour, before being cooled to room temperature at a rate of 10℃/min. After sintering, the sintered billet had a thickness of 20 mm, a width of 144 mm, a length of 665 mm, a relative density of 90.6%, and an oxygen content of 23.6 μg/g.

After sintering, the green blank is machined to provide dimensions of 15 mm thickness, 128 mm width, and 620 mm length. In Example 1, the sputtering target after sintering exhibits very high uniformity, with the maximum deviation of the Ni content percentage at different length locations on the sputtering target being only 0.1% to 0.3%.

The percentage of Ni content at different length positions of the sintered sputtering target (1/4 length, 1/2 length, and 3/4 length) was measured by X-ray fluorescence spectroscopy (XRF), and the maximum deviation was calculated. A sputtering target (Comparative Example 5) manufactured by the method of WO2015089533A1, with 40 wt% W and 60 wt% Ni, was also measured at the same positions for comparison. The results were then validated. Location 1/4 length 1/2 length 3/4 length maximum deviation Example 1 60.28% 60.10% 60.22% 0.28% Comparative Example 5 59.10% 62.14% 62.18% 2.18%

It is evident that the maximum deviation of Ni content in the sputtering target fabricated in Example 1 is much lower than that in the control group, with a very low maximum deviation of only 0.28%, resulting in very high uniformity of Ni at different locations. Furthermore, XRD measurements were performed on both Example 1 and Comparative Example 5. No pure Ni phase was found in the sputtering target fabricated in Example 1, while localized pure Ni phases were found in the sputtering target fabricated in the control group.

Figures 2A and 2B show the microstructure in the optical microscope image and SEM (scanning electron microscope) image of Example 1, respectively. Under the optical microscope, the Ni(W) solid solution phase appears light gray. The pure W phase appears as a patterned dark gray. Pores (generated by powder metallurgy production methods) and/or other artifacts (generated during preparation) appear black. In the SEM image, the light gray indicates the Ni(W) solid solution phase, while the pores and/or artifacts appear black, and the pure W phase appears white.

Comparative Example 5 (an example prepared by the method of WO2015089533A1, see also Table 1 and Example 4 of WO2015089533A1):

Tungsten (W) metal powder with a particle size of 4 μm as determined by the Fisher method and Ni metal powder sieved to a particle size of less than 160 μm were used as raw materials. 43 wt% tungsten powder and 57 wt% nickel powder were mixed in a mixer. Cold isostatic pressing was performed at 200 MPa to obtain a green compact with a diameter of 25 mm and a thickness of 13.5 mm. The green compact was then sintered by heating to 1350 °C over 2 hours, holding at that temperature for 4 hours, and then cooling over 2 hours. The relative density of the sintered compact was 73.7%, and the oxygen content was 268 μg/g. Intermetallic phases were detected by XRD.

Example 2:

W metal powder with a particle size of 4 μm as determined by Fisher's method and Ni metal powder with a particle size of 4.2 μm as determined by Fisher's method were used as raw materials. 35 wt% tungsten powder and 65 wt% nickel powder were mixed in a mixer at 12 rpm for 1 hour.

The powder mixture is introduced into rubber, which is then sealed at its open end by a rubber cap. The sealed rubber is positioned in an isostatic press and pressed at 200 MPa for 1 minute to provide a green compact with a relative density of 66%, a thickness of 25 mm, a width of 160 mm, and a length of 750 mm.

The green compact was first sintered in a vacuum at a heating rate of 3 °C/min to 1350 °C, held at 1350 °C for 1 hour, then the sintering atmosphere was changed to the first gas and held for another 3 hours. It was then cooled to 980 °C at a rate of 8 °C/min, and the sintering atmosphere was changed to _H₂ atmosphere and held for 1 hour, before being cooled to room temperature at a rate of 10 °C/min. After sintering, the sintered compact had a thickness of 22 mm, a width of 142 mm, a length of 667 mm, a relative density of 90.8%, and an oxygen content of 29.8 μg/g. In Example 2, the sputtering target exhibited very high uniformity after sintering, with the maximum deviation in the percentage of Ni content at different length positions on the sputtering target being only 0.1% to 0.3%.

The percentage of Ni content at different length positions of the sintered sputtering target (1/4 length, 1/2 length, and 3/4 length) was measured by X-ray fluorescence spectroscopy (XRF), and the maximum deviation was calculated. A sputtering target (Comparative Example 6) manufactured by the method of WO2015089533A1, with 35 wt% W and 65 wt% Ni, was also measured at the same positions for comparison. The results were then validated. Location 1/4 length 1/2 length 3/4 length maximum deviation Example 2 65.10% 65.15% 64.92% 0.15% Comparative Example 6 67.35% 63.76% 66.22% 2.35%

As can be seen, the maximum deviation of Ni content in the sputtering target fabricated in Example 2 is much lower than that in the control group, with a very low maximum deviation of only 0.15%, resulting in very high uniformity of Ni at different locations. Furthermore, XRD measurements were performed on both Example 2 and Comparative Example 6. No pure Ni phase was found in the sputtering target fabricated in Example 2, while localized pure Ni phases were found in the sputtering target fabricated in the control group. In Example 2, no intermetallic phases or pure W were detected by XRD measurements.

Figures 2C and 2D show the microstructure in the optical microscope image and scanning electron microscope (SEM) image of Example 2, respectively. Under the optical microscope, the Ni(W) solid solution phase appears light gray. Pores (generated by powder metallurgy production methods) and/or other artifacts (generated during preparation) appear black. Pure W phase is not shown in this image. In the SEM image, the light gray indicates the Ni(W) solid solution phase, while pores and/or artifacts appear black. Although a white pure W phase is shown in this image, the W phase was not detected in the XRD of this example, i.e., the W phase is below the detection limit.

Comparative Example 6 (an example prepared by the method of WO2015089533A1):

W metal powder with a particle size of 4 μm as determined by the Fisher method and Ni metal powder sieved to a particle size of less than 160 μm were used as raw materials. 35 wt% tungsten powder and 65 wt% nickel powder were mixed in a mixer. Cold isostatic pressing was performed at 200 MPa to obtain a green compact with a diameter of 25 mm and a thickness of 14.1 mm. The green compact was then sintered by heating to 1350 °C over 2 hours, holding at that temperature for 4 hours, and then cooling over 2 hours. The relative density of the sintered compact was 85.2%, and the oxygen content was 82 μg/g.

Example 3:

W metal powder with a particle size of 4 μm as determined by Fisher's method and Ni metal powder with a particle size of 4.2 μm as determined by Fisher's method were used as raw materials. 30 wt% tungsten powder and 70 wt% nickel powder were mixed in a mixer at 12 rpm for 1 hour.

The powder mixture is introduced into a flexible rubber tube, which is sealed at its open end by a rubber cap. The sealed rubber is positioned in an isostatic press and pressed at 200 MPa for 1 minute to provide a green compact with a relative density of 67% and dimensions of Ø 15 mm x 50 mm.

The green compact was first sintered in a vacuum at a heating rate of 3°C/min to 1350°C, held at 1350°C for 1 hour, then the sintering atmosphere was changed to the first gas and held for another 3 hours. It was then cooled to 980°C at a rate of 8°C/min, and the sintering atmosphere was changed to _H₂ atmosphere and held for 1 hour, before being cooled to room temperature at a rate of 10°C/min. The sintered green compact had dimensions of Ø 13 mm x 44 mm, a relative density of 92%, and an oxygen content of 32 μg/g. In Example 3, the sputtering target exhibited very high uniformity after sintering, with the maximum deviation in the percentage of Ni content at different lengths of the target being only 0.1% to 0.3%.

The percentage of Ni content at different length positions of the sintered sputtering target (1/4 length, 1/2 length, and 3/4 length) was measured by X-ray fluorescence spectroscopy (XRF), and the maximum deviation was calculated. A sputtering target (Comparative Example 7) manufactured by the method of WO2015089533A1, with 30 wt% W and 70 wt% Ni, was also measured at the same positions for comparison. The results were then validated. Location 1/4 length 1/2 length 3/4 length maximum deviation Example 3 70.10% 70.15% 69.92% 0.15% Comparative Example 7 72.35% 71.76% 68.22% 2.35%

As can be seen, the maximum deviation of Ni content in the sputtering target fabricated in Example 3 is much lower than that in the control group, with a very low maximum deviation of only 0.15%, resulting in very high uniformity of Ni at different locations. Furthermore, XRD measurements were performed on both Example 3 and Comparative Example 7. No pure Ni phase was found in the sputtering target fabricated in Example 3, while localized pure Ni phases were found in the sputtering target fabricated in the control group. In Example 3, no intermetallic phases or pure W were detected by XRD measurements.

Figures 2E and 2F show the microstructure in the optical microscope image and scanning electron microscope (SEM) image of Example 3, respectively. Under the optical microscope, the Ni(W) solid solution phase appears light gray. Pores (generated by the powder metallurgy production method) and/or other artifacts (generated during preparation) appear black. Pure W phase was not detected in this image. In the SEM image, the light gray indicates that the Ni(W) solid solution phase, pores, and/or artifacts appear black. Although a small white pure W phase is shown in this image, the W phase was not detected in the XRD of this example, i.e., the W phase is below the detection limit.

Comparative Example 7 (an example prepared by the method of WO2015089533A1):

W metal powder with a particle size of 4 μm as determined by the Fisher method and Ni metal powder sieved to a particle size of less than 160 μm were used as raw materials. 30 wt% tungsten powder and 70 wt% nickel powder were mixed in a mixer. Cold isostatic pressing was performed at 200 MPa to obtain a green compact with a diameter of 25 mm and a thickness of 14.6 mm. The green compact was then sintered by heating to 1350 °C over 2 hours, holding at that temperature for 4 hours, and then cooling over 2 hours. The relative density of the sintered compact was 85.7%, and the oxygen content was 120 μg/g.

Example 4

W metal powder with a particle size of 4 μm as determined by Fisher's method and Ni metal powder with a particle size of 4.2 μm as determined by Fisher's method were used as raw materials. 35 wt% tungsten powder and 65 wt% nickel powder were mixed in a mixer at 12 rpm for 1 hour.

The powder mixture is introduced into rubber, which is then sealed at its open end with a rubber cap. The sealed rubber is positioned in an isostatic press and pressed at 200 MPa for 1 minute to provide a green compact with a thickness of 22 mm. The green compact is first sintered in a vacuum at a heating rate of 3 °C/min to 1350 °C, held at 1350 °C for 1 hour, then the sintering atmosphere is changed to a first gas and held for another 3 hours, then cooled to 980 °C at a rate of 8 °C/min, then the sintering atmosphere is changed to _H₂ atmosphere and held for 1 hour, and finally cooled to room temperature at a rate of 10 °C/min. After sintering, the sintered billet has a thickness of 22 mm, a width of 142 mm, and a length of 667 mm. It is then subjected to two rolling passes to obtain a thickness of 15 mm. The rolled block is then annealed at 1300°C for half an hour and subjected to two more rolling passes to obtain a thickness of 10 mm. It is then machined using a leveling machine and finally annealed at 1200°C for half an hour. After annealing, a cooling rate of at least 34 K/min is achieved within a temperature range of 900 to 750°C. The green billet after this process has a relative density of 99.8% and an oxygen content of 15.9 μg/g.

The method for manufacturing a sputtering target according to the second aspect of this disclosure effectively solves the technical problem of reducing material uniformity and affecting sputtering effect, resulting in high density and good application performance.

Figure 3A shows the microstructure of the optical microscope image of Example 4, which shows the grain orientation and the high density of the material.

Figures 3B and 3C show the microstructure in the optical microscope image and scanning electron microscope (SEM) image of Example 4, respectively. Under the optical microscope, the Ni(W) solid solution phase appears light gray. Due to the high density of this material, almost no porosity is visible in this image. No pure W phase was detected in this image. The SEM image shows the grain orientation in the longitudinal direction. A single pure W grain can still be found in this image, but this is below the detection level of XRD.

Similarly, in Example 4, no pure Ni, no pure W, and no intermetallic phases were detected.

Pure Ni, due to its ferromagnetic properties, can affect the normal operation of magnetron sputtering. Therefore, the technical solution described in WO2015089533A1 uses a WNi ratio with a lower Ni content. Furthermore, it is generally believed in this field that to increase the uniformity of material element distribution, the content of the required alloying elements needs to be reduced; that is, to increase the uniformity of Ni distribution, the Ni content needs to be further reduced.

However, the inventors of this disclosure have discovered through research that, according to current understanding, further reducing the Ni content would cause the following problems: due to the scarcity of Ni phase regions, the W-Ni phase, as the second phase, would result in uneven distribution of Ni content in different parts of the sputtering target.

This disclosure adopts a technical solution opposite to WO2015089533A1, using a higher Ni content. However, this also leads to the following problems: 1) High Ni content may cause the formation of a pure Ni phase in the material, resulting in magnetism, which is not conducive to magnetron sputtering; 2) Due to the strong oxygen affinity of Ni, the oxygen content of the material may increase. In other words, it is difficult for high Ni-content WNi sputtering targets to achieve the result of materials without a pure Ni phase. How to control the formation of the pure Ni phase has become a technical challenge that needs to be overcome. The inventors of this disclosure have overcome the above-mentioned technical challenges through the improved technology described in the first and second embodiments above, thus effectively solving the technical problem of reducing material uniformity and affecting sputtering effect, resulting in high density and good application performance.

According to the sputtering target and the method for manufacturing the sputtering target disclosed herein, the technical problems of reducing material uniformity and affecting sputtering effect are effectively solved, and a sputtering target with high density and good application performance is obtained.

Although this disclosure has been illustrated and described with reference to certain preferred embodiments thereof, it should be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of this disclosure.

without

Figure 1 shows a phase diagram of the Ni-W system, with the composition range of the sputtering target according to the first aspect of this disclosure marked. Figures 2A and 2B show micrographs of a sputtering target (WNi 40/60) manufactured in Example 1 of the method for manufacturing a sputtering target according to the second aspect of this disclosure; Figures 2C and 2D show micrographs of a sputtering target (WNi 35/65) manufactured in Example 2 of the method for manufacturing a sputtering target according to the second aspect of this disclosure; and Figures 2E and 2F show micrographs of a sputtering target (WNi 30/70) manufactured in Example 3 of the method for manufacturing a sputtering target according to the second aspect of this disclosure. Figure 3A shows a micrograph of a sputtering target manufactured in Example 4 of the method for manufacturing a sputtering target according to the second aspect of this disclosure. Figures 3B and 3C show, respectively, light optical microscope and SEM images of the sputtering target (WNi 35/65 rolled) manufactured in Example 4 of the sputtering target manufacturing method of the second aspect of this disclosure.

without

Claims (14)

A sputtering target containing 60% to 70% by weight Ni, the balance being W and general impurities, wherein: the sputtering target contains a pure W phase, a Ni(W) solid solution phase, and an intermetallic phase that does not contain a pure Ni phase and has an average area ratio of less than 5% as measured by the cross-section of the sputtering target, and the sputtering target contains an oxygen content of less than 50 μg/g. The sputtering target as described in claim 1, wherein the sputtering target contains 60% to 65% by weight of Ni. The sputtering target as described in claim 1, wherein the sputtering target contains less than 40 μg/g of oxygen. The sputtering target as described in claim 1, wherein the sputtering target has a hardness of less than 500 HV10. The sputtering target as claimed in claim 1, wherein the intermetallic phase is selected from one or more of the group consisting of: _Ni₄W , WNi, _W₂Ni . The sputtering target as claimed in claim 1, wherein the sputtering target has an average grain size of less than 40 μm for the W phase. The sputtering target as described in claim 1, wherein the sputtering target has a relative density of more than 90%. The sputtering target as described in claim 7, wherein the sputtering target has a relative density of more than 99.5%. A method for manufacturing a sputtering target as described in any one of claims 1 to 8, the method being via a powder metallurgy approach, comprising the steps of: performing a compaction step, wherein a powder mixture of W powder and Ni powder is compacted by applying pressure, heat, or pressure and heat to obtain a compacted billet; and performing a cooling step, wherein the resulting compacted billet is cooled to a temperature range of 750 °C to 1000 °C at a cooling rate greater than 3 K/min. The method for manufacturing a sputtering target as described in claim 9, wherein the compaction step is achieved by sintering at a temperature of 1100°C to 1450°C, and the sintering atmosphere is combined with a first gas and/or a vacuum. A method for manufacturing a sputtering target as described in any one of claims 1 to 8, the method being via a powder metallurgy approach, comprising the following steps: performing a compaction step, wherein a powder mixture of W powder and Ni powder is compacted by applying pressure, heat, or pressure and heat to obtain a compacted billet; after the compaction step, performing thermomechanical treatment or heat treatment on the compacted billet; and performing a cooling step, wherein the compacted billet is cooled to a temperature range of at least 750°C to 900°C at a cooling rate greater than 30 K/min. The method for manufacturing a sputtering target as described in claim 11, wherein the compaction step is achieved by sintering at a temperature of 1100°C to 1450°C, and the sintering atmosphere is combined with a first gas and/or a vacuum. The method of manufacturing a sputtering target as described in claim 11 or 12, wherein the method further comprises: the thermomechanical treatment or the heat treatment being performed in a temperature range of 970°C to 1450°C. The method for manufacturing a sputtering target as described in claim 12, wherein the thermomechanical treatment or the heat treatment includes at least one forging step or a rolling step.