TWI675116B - Ti-Al alloy sputtering target - Google Patents

Abstract

A Ti-Al alloy sputtering target, which is a sintered body target containing 39.6-80.0 at% Al, and the remaining part is composed of Ti and unavoidable impurities, which is characterized by the area ratio of the Ti ₃ Al crystal phase in the target structure It is below 40%. The subject of this case is to provide a sputtering target which can prevent abnormal discharge during sputtering and has few particles.

Description

Ti-Al alloy sputtering target

The present invention relates to a Ti-Al alloy sputtering target capable of preventing abnormal discharge during sputtering and generating few particles.

The manufacturing of semiconductor devices has made great progress, and the design of G (byte) DRAM has been completed. Many thin films are formed in the manufacturing steps of such semiconductor devices, but the density of the films is increased due to the extremely small distance between the thin films, which results in the diffusion of the substances constituting the films or the impurities contained in the films to the adjacent films problem. Therefore, the balance between the film itself and the constituent materials of the adjacent film is broken, causing a problem that the function of the film that must be possessed is reduced. There are cases where the film is heated to several hundred degrees in the manufacturing steps of such a thin film, and the temperature may rise in the use of an electronic device in which a semiconductor device is assembled. Such a temperature rise will further increase the diffusion coefficient of the above-mentioned substances, and there are cases in which there is a major problem that the function of the electronic device is reduced due to diffusion.

For example, if a capacitor using barium-strontium-titanate (BST) is used, generally, a barrier layer (film) of TiAlN is formed between the silicide (TiSi ₂ ) layer and the BST layer in this structure. The reason is to prevent contamination due to diffusion of oxygen from the BST layer of the silicide layer. The barrier layer of TiAlN is a dense layer that hardly reacts with other substances under a slight heat. Therefore, in this case, it can also fully function as a barrier layer of about 3 ~ 5nm. Generally, the barrier layer of TiAlN is formed by sputtering. Sputtering is a method in which positive ions such as Ar ⁺ physically collide with a target provided on the cathode, and the metal atoms constituting the target are released by the impact energy. In the formation of the nitride, the following method can be used: : Using a TiAl alloy as a target and performing sputtering in a mixed gas environment of argon and nitrogen.

In the past, a TiAl alloy target has been used without much consideration, considering that such an extremely thin TiAlN barrier layer has sufficient functions. However, most of the barrier layers of TiAlN are extremely thin films that do not affect other functional films. Therefore, in the case where a dense film is not formed uniformly and well, the function as a barrier film is very high. . In addition, the particles generated during the formation of the barrier film significantly reduce the characteristics, and therefore it is required to reduce the particles as much as possible. In particular, as semiconductor devices have become more integrated and ultra-miniaturized, such requirements have been further increased. Because of this situation, the properties of the TiAl alloy target must be more closely watched and tightly controlled.

Regarding the TiAl alloy sputtering target, for example, Patent Document 1 discloses a target for reducing impurities such as alkali metals, radioactive elements, and transition metals. This technique is an excellent technique for suppressing a reduction in the function of the barrier film, but cannot sufficiently suppress particles generated during sputtering. In addition, Patent Document 2 also discloses that by reducing the content of oxygen, nitrogen, carbon, and the like, deterioration of element characteristics and abnormal discharge due to impurity gas components are suppressed. Reducing the content of impurities has a considerable effect on improving the quality of the membrane, but it is not possible to obtain a homogeneous membrane with few particles alone. It is also known that there are other technologies that try to reduce impurities in the target (Patent Documents 3 to 12).

[Patent Document 1] Japanese Patent Laid-Open No. 2000-273623

[Patent Document 2] Japanese Patent Laid-Open No. 2003-73815

[Patent Document 3] Japanese Patent Laid-Open No. 04-066214

[Patent Document 4] Japanese Patent Laid-Open No. 04-120225

[Patent Document 5] Japanese Patent Laid-Open No. 04-218649

[Patent Document 6] Japanese Patent Laid-Open No. 04-246137

[Patent Document 7] Japanese Patent Laid-Open No. 05-059466

[Patent Document 8] Japanese Patent Laid-Open No. 05-140669

[Patent Document 9] Japanese Unexamined Patent Publication No. 05-345936

[Patent Document 10] Japanese Patent No. 2890053

[Patent Document 11] Japanese Patent No. 2989060

[Patent Document 12] Japanese Patent No. 4820507

The object of the present invention is to provide a TiAl alloy sputtering target, which can prevent abnormal discharge during sputtering, and has fewer particles.

In order to solve the above problems, the present inventors made diligent research and found that in the Ti-Al alloy target provided by the powder metallurgy method, the internal structure of the target can be controlled by closely adjusting the composition and mixing ratio of the raw material powder, The unevenness of the eroded surface can be reduced, thereby forming a film with few particles.

Based on this knowledge, the present inventors have provided the following inventions.

1) A Ti-Al alloy sputtering target, which is a sintered body target containing 39.6-80.0 at% Al, and the remaining part is composed of Ti and unavoidable impurities, which is characterized by the Ti ₃ Al crystal phase in the target structure The area ratio is 40% or less.

2) The Ti-Al alloy sputtering target according to 1) has a relative density of 98% or more.

3) The Ti-Al alloy sputtering target according to 1) or 2), whose oxygen content is 400 wtppm or less.

The Ti-Al alloy sputtering target of the present invention has the following excellent effects: By reducing the area of the Ti ₃ Al crystalline phase existing in the target structure, cracks in the target surface can be suppressed, and particles during sputtering can be reduced. .

FIG. 1 is a micrograph (magnification: 100 times) of a sputtering target of Example 1 obtained by using an optical microscope.

FIG. 2 is a micrograph (magnification: 100 times) of a sputtering target of Comparative Example 1 obtained by using an optical microscope.

The Ti-Al alloy sputtering target of the present invention is characterized in that it contains 39.6 to 80.0 at% Al, and the remaining portion is composed of Ti and unavoidable impurities. There are Ti ₃ Al crystal phases and TiAl crystals in the target structure. phase.

Generally, an alloy sputtering target is produced by a melt casting method. In the case of a Ti-Al alloy, if the Al composition is in the range of about 40 to 80 at%, it is difficult to perform plastic processing, so the powder metallurgy method is used. The present invention obtains the target of desired characteristics in the composition range using such powder metallurgy.

In addition, if the composition of Al is less than 39.6 at%, the crystal structure exhibits significant brittleness and cannot withstand the impact caused by pressure and cooling during sintering, and strain introduced by processing (strain introduction) and the like, crystal grains are generated on the surface and inside of the target, and the crystal grains have microstructures containing cracks. Therefore, the composition of Al is set to 39.6 at% or more.

It is important in the present invention that the area ratio of the Ti ₃ Al crystal phase in the sputtering target structure is 40% or less, preferably 30% or less, and further preferably 20% or less. In Ti-Al, not only the TiAl phase, but Ti ₃ Al is present on the low composition side of Al, and plural intermetallic compounds such as TiAl ₂ and TiAl ₃ are present on the high composition side of Al. When it contains Al 39.6 ~ 80.0 at%, it not only has a single phase, but also has such a plurality of mixed structures. Among them, because Ti ₃ Al is highly brittle, if the area ratio of the crystal phase becomes high, the number of particles increases when sputtering is performed. Therefore, it is desirable that the area ratio of the Ti ₃ Al crystal phase stays within the above-mentioned numerical range.

The calculation of the area ratio of the Ti ₃ Al crystal phase was performed as follows.

First, the surface of the sputtering target was etched with an acid (a mixture of water: nitric acid: hydrofluoric acid = 6: 3: 1) at room temperature for 20 seconds to expose the tissue. Then, the surface structure of the target was observed with an optical microscope (magnification: 100 times). Then, in the visual field (area: 900 μm × 700 μm), a ratio obtained by dividing the area of the Ti ₃ Al crystal phase by the entire area of the visual field was set as an area ratio (%).

Specifically, 9 equal divisions in the vertical direction and 7 equal divisions in the horizontal direction are divided at 100 μm intervals with respect to the visual field (total number of blocks: 63). Then, if a Ti ₃ Al structure exists in a part of each divided block, it is set to “0.5”, and if a Ti ₃ Al structure exists in the whole of each block, it is set to “1”, and The area ratio of the crystal phase of Ti ₃ Al was determined.

For example, in one part of the block there are several blocks of tissue of Ti ₃ Al 12, there is the case where the number of blocks 3 ₃ Al to Ti in the overall organization of the block, (12 × 0.5 + 3 × 1) /63×100=14.3(%) becomes the area ratio of the Ti ₃ Al crystal phase.

In the present invention, the relative density of the sputtering target is preferably set to 95% or more. It is preferably set to 98% or more. The powder metallurgy method has a reduced density compared to the case made by the dissolution casting method. However, by using an atomized raw material, a very dense target structure can be obtained. The atomized raw material is homogeneously temporarily melted by induction heating. Alloy composition. In addition, such a dense target has an excellent effect of suppressing abnormal discharge and reducing generation of particles during sputtering. The relative density can be calculated by the following formula.

Relative density (%) = Archimedes density / Theoretical density × 100

In the present invention, the oxygen content in the sputtering target is set to 400 wtppm or less, preferably 300 wtppm or less, and more preferably 250 wtppm or less. Oxygen contained in the target may form an oxide, and there are cases in which microarcing with the oxide as a starting point occurs during sputtering, and the generation of particles is increased. In particular, in order to obtain a homogeneous and dense target, it is necessary to miniaturize the raw material powder, but Ti, which is a raw material powder, has a property of having a high affinity for oxygen. In the present invention, as described below, a TiAl alloy is synthesized by induction heating and melting in advance, and this metal molten liquid is sprayed by a gas atomization method, thereby obtaining a fine and low-oxygen raw material powder for sintering. The oxygen content can be measured using an oxygen analyzer manufactured by LECO.

In addition, the present invention does not include gas components (C, O, H, N, P, S), and preferably has a purity of 4N (99.99%) or more. Since the sputtering target of the present invention is used to form a laminated film of a semiconductor device such as a diffusion barrier film, by removing metal impurities as much as possible, degradation of characteristics can be reduced, and the function as a diffusion barrier film can be effectively exerted. Such a high-purity sputtering target, as described below, inductively heats a high-purity Ti raw material and an Al raw material to synthesize a TiAl alloy in advance, and sprays this metal molten liquid through a gas atomization method, thereby obtaining a high-purity sputtering target. Raw powder for sintering. The above purity can be calculated from the content of impurities contained in the sintered body, and the content contained in the sintered body The content of some impurities is measured using GDMS (glow discharge mass spectrometry). However, since Sr has insufficient measurement accuracy, it is excluded from the calculation of the purity.

The sputtering target of the present invention can be produced, for example, as follows. First, a Ti bulk material having a purity of 4N or more and an Al bulk material having a purity of 4N or more are introduced into a water-cooled copper crucible at a specific ratio, and a Ti-Al alloy is produced by dissolution by induction heating. Then, the obtained alloy melt is sprayed by an atomization method, thereby obtaining a Ti-Al alloy powder with low oxygen. Then, the Ti-Al alloy powder having an average particle diameter of 350 μm or less as adjusted as described above is hot-pressed at a temperature of 1100 to 1400 ° C. and a pressure of 300 kgf / cm ² , thereby making it possible to produce a dense Ti-Al alloy with low oxygen content. Al alloy target. At this time, cold isostatic pressing (CIP treatment) or hot isostatic pressing (HIP treatment) is effective in view of increasing density in conjunction with hot pressing or replacing hot pressing. The thus-produced ingot was cut into the shape of a target, the surface was polished, and a Ti-Al alloy sputtering target was prepared.

For example, in the case of making a target of Ti-50 at% Al, the composition above and below (for example, Ti-48 at% Al or Ti-52 at% Al) is not a TiAl phase, and Ti exists on the low Al composition side. ₃ Al phase, there are many kinds of intermetallic compounds such as TiAl ₂ phase and TiAl ₃ on the high Al composition side. Therefore, when the atomized powder of a single composition of Ti-50 at% Al is to be produced, there is a problem that a homogeneous Ti-Al alloy cannot be obtained because the melting points of Ti and Al are different. Especially in the composition side where Al is higher than 50 at%, there is a wide range of crystalline phases of TiAl. In contrast, in the composition side where Al is lower than 50 at%, the crystalline phase rapidly changes to Ti ₃ Al, so directly When the composition of Ti-50 at% Al is used as a target to melt the raw materials, there are cases where the crystal phase is biased to one of Ti ₃ Al or TiAl, and the quality of the targets is not uniform.

Here, in the present invention, two types of raw material powders of the upper and lower compositions are prepared for the target composition, and the mixing ratio is calculated so as to become a target of a desired composition ratio, and these raw material powders are mixed at a specific ratio. By sintering it, the following target can be produced: in the target, the macroscopic field of view is homogeneous, the composition variation between targets is small, and the quality inconsistency between targets is suppressed. In addition, different crystalline phases have different sputtering speeds. Therefore, if the proportions of the respective crystalline phases are greatly different, it will be the case that local erosion is formed, and the unevenness increases the generation of particles. Therefore, it is desirable that the target composition is obtained by mixing equal amounts of two kinds of raw material powders having different compositions to obtain the target intermediate composition.

[Example]

Next, examples and comparative examples will be described. Furthermore, these examples and comparative examples are intended to make the invention of this case easy to understand, and it should be understood that the content of the invention is not limited by these.

(Example 1)

The Ti bulk material with a purity of 4N or more and the Al bulk material with a purity of 4N or more were melted by induction heating using a water-cooled copper crucible. This alloy melt was sprayed by an atomization method to produce an average particle size of 300 μm, Ti-Al alloy atomized powder containing 53.0 at% Al. A Ti-Al alloy powder (atomized powder) containing Al 47.0 at% was produced by the same method. Next, these powders were weighed so that Ti: Al = 50: 50 (at%), mixed, and then hot-pressed at a temperature of 1300 ° C and a pressure of 300 Kgf / cm ² for 3 hours to produce a sintered body.

The relative density of the obtained sintered body was 99.98%. After the surface of this sintered body was exposed to the structure with fluoric nitric acid, the structure was observed with an optical microscope (magnification: 100 times) (FIG. 1). As a result, the area ratio of Ti ₃ Al was 4.0%. As a result of analysis of impurities in the sintered product, the purity was 99.99%, and the oxygen content was 250 ppm. Next, this sintered body was subjected to machining such as cutting and grinding to produce a Ti-Al alloy sputtering target. After the target produced as described above was connected to the back plate, sputtering was performed in the chamber, and the amount of particles during sputtering was investigated. The sputtering conditions were set to power: DC, input power: 15kW, ultimate vacuum: 5 × 10 ^-8 Torr, ambient gas: Ar, sputtering pressure: 5 × 10 ^-3 Torr, and sputtering time: 15 seconds. As a result, the number was 25, which was less than the comparative example described later.

(Examples 2 to 3)

The Ti bulk material with a purity of 4N or more and the Al bulk material with a purity of 4N or more were melted by induction heating using a water-cooled copper crucible. This alloy melt was sprayed by an atomization method to produce an average particle size of 300 μm, Ti-Al alloy atomized powder containing Al 38.0 at%. A Ti-Al alloy powder (atomized powder) containing Al 47.0 at% was produced by the same method. Then, in Example 2, Ti: Al = 55: 45 (at%) was used, and in Example 3, Ti: Al = 60: 40 (at%) was used to measure and mix these powders. A sintered body was produced by performing a hot-pressing treatment at a temperature of 1300 ° C and a pressure of 300 Kgf / cm ² for 3 hours.

The relative densities of the obtained sintered bodies were all 99.99%. After exposing the surface of the sintered body with fluoric nitric acid, the structure was observed with an optical microscope (magnification: 100 times). As a result, the area ratios of Ti ₃ Al were 10.2% (Example 2) and 21.8% (implementation Example 3). In addition, as a result of analyzing impurities of the sintered product, the purity was 99.99%, and the oxygen contents were 270 ppm (Example 2) and 360 ppm (Example 3). Next, this sintered body was subjected to machining such as cutting and grinding to produce a Ti-Al alloy sputtering target. After the target produced as described above was connected to the back plate, sputtering was performed in the chamber under the same conditions as in Example 1, and the amount of particles during sputtering was investigated. As a result, there were 12 (Example 2) and 16 (Example 3), which were fewer than the comparative examples described later.

(Example 4)

The Ti bulk material with a purity of 4N or more and the Al bulk material with a purity of 4N or more were melted by induction heating using a water-cooled copper crucible. This alloy melt was sprayed by an atomization method to produce an average particle size of 300 μm, Ti-Al alloy atomized powder containing Al 47.0 at%. Also, a Ti-Al alloy powder (atomized powder) containing Al 58.0 at% was produced by the same method. Next, these powders were weighed so that Ti: Al = 50: 50 (at%), mixed, and then hot-pressed at a temperature of 900 ° C and a pressure of 100 Kgf / cm ² for 2 hours to produce a sintered body.

As a result of measuring the relative density of the obtained sintered body, it was reduced to 92.34%. After the surface of this sintered body was exposed to tissue with fluorinated nitric acid, the structure was observed with an optical microscope (magnification: 100 times). As a result, the area ratio of Ti ₃ Al was 8.9%. As a result of analyzing the impurities of the sintered product, the purity was 99.99%, and the oxygen content was 290 ppm. Next, this sintered body was subjected to machining such as cutting and grinding to produce a Ti-Al alloy sputtering target. After the target produced as described above was connected to the back plate, sputtering was performed in the chamber under the same conditions as in Example 1, and the amount of particles during sputtering was investigated. As a result, in Example 4 having a density of 92.34%, there was a slight increase to 76.

(Example 5)

The Ti bulk material with a purity of 4N or more and the Al bulk material with a purity of 4N or more were melted by induction heating using a water-cooled copper crucible. This alloy melt was sprayed by an atomization method to produce an average particle size of 50μm, Ti-Al alloy atomized powder containing 47.0 at% Al. Also, a Ti-Al alloy powder (atomized powder) containing Al 58.0 at% was produced by the same method. Next, these powders were weighed so that Ti: Al = 50: 50 (at%), mixed, and then hot-pressed at a temperature of 1300 ° C and a pressure of 300 Kgf / cm ² for 3 hours to produce a sintered body.

The relative density of the obtained sintered body was 99.99%. After the surface of this sintered body was exposed to tissue with fluorinated nitric acid, the structure was observed with an optical microscope (magnification: 100 times). As a result, the area ratio of Ti ₃ Al was 6.3%. As a result of analysis of impurities in the sintered product, the purity was 99.99%, and the oxygen content was 570 ppm. Next, this sintered body was subjected to machining such as cutting and grinding to produce a Ti-Al alloy sputtering target. After the target produced as described above was connected to the back plate, sputtering was performed in the chamber under the same conditions as in Example 1, and the amount of particles during sputtering was investigated. As a result, in Example 5 having an oxygen value of 570 ppm, there was a slight increase to 53.

(Comparative Examples 1 to 3)

The Ti bulk material with a purity of 4N or more and the Al bulk material with a purity of 4N or more were melted by induction heating using a water-cooled copper crucible. This alloy melt was sprayed by an atomization method to produce an average particle size of 300 μm, Ti-Al alloy atomized powder containing Al 35.0 at%. A Ti-Al alloy powder (atomized powder) containing 55.0 at% of Al was produced by the same method. Then, in Comparative Example 1, it becomes Ti: Al = 50: 50 (at%), in Comparative Example 2 it becomes Ti: Al = 55: 45 (at%), and in Comparative Example 3, it becomes Ti: These powders were weighed in a manner of Al = 60: 40 (at%), mixed, and then hot-pressed at a temperature of 1300 ° C and a pressure of 300 Kgf / cm ² for 3 hours to produce a sintered body.

The relative densities of the obtained sintered bodies were all 99.99% or more. After the surface of this sintered body was exposed to tissue with fluorinated nitric acid, the structure was observed with an optical microscope (magnification: 100 times). A photograph of the structure of Comparative Example 1 is shown in FIG. 2 as a reference. The area ratios of Ti ₃ Al were 93.7% (Comparative Example 1), 72.1% (Comparative Example 2), and 69.6% (Comparative Example 3). In addition, as a result of analyzing impurities of the sintered product, the purity was 99.99%, and the oxygen content was 400 wtppm or less. Next, this sintered body was subjected to machining such as cutting and grinding to produce a Ti-Al alloy sputtering target. After the target produced as described above was connected to the back plate, sputtering was performed in the chamber under the same conditions as in Example 1, and the amount of particles during sputtering was investigated. The results were 129 (Comparative Example 1), 201 (Comparative Example 2), and 153 (Comparative Example 3).

In particular, the present invention has an excellent effect that, when performing sputtering that constitutes a laminated film, it is possible to prevent abnormal discharge and suppress generation of particles. These effects are particularly useful in semiconductor devices in which the bulk density becomes extremely high.

Claims (5)

A Ti-Al alloy sputtering target is a sintered body target containing 39.6 to 80.0 at% Al, and the remaining portion is composed of Ti and unavoidable impurities. It is characterized in that the target is only composed of TiAl intermetallic compounds. In the target structure, the area ratio of the Ti ₃ Al crystal phase is 40% or less (but excluding 0%). For example, the Ti-Al alloy sputtering target of the first patent application scope, wherein the area ratio of the Ti ₃ Al crystal phase in the target structure is 21.8% or less (but not including 0%). For example, the relative density of the Ti-Al alloy sputtering target of item 1 or 2 of the patent application range is above 98%. For example, the Ti-Al alloy sputtering target in the first or second patent application scope has an oxygen content of 400wtppm or less. For example, the Ti-Al alloy sputtering target in the third patent application scope has an oxygen content of 400 wtppm or less.