JP3436763B2 - Sputtering target material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sputtering target material. In particular, it relates to a sputtering target material made of a noble metal.

BACKGROUND ART Noble metal thin films such as ruthenium and iridium have been widely used in recent years as thin film electrodes on semiconductor device wafers.

These noble metal thin films are mainly manufactured by a sputtering method which is one of physical vapor deposition methods. When this sputtering method is used, the properties of the thin film to be formed largely depend on the purity of the sputtering target material, the texture shape, and the like.

That is, the characteristics such as the specific resistance required for the thin film electrode in practical use can be determined by simply controlling the purity of the sputtering target material. With respect to this point, even a sputtering target material manufactured by the conventionally used melting casting method or powder metallurgy method has been sufficiently satisfactory.

However, in the process of using the sputtering target manufactured by the melting casting method or the powder metallurgy method, fine cluster-shaped lumps are missing from the sputtering target and adhere to the thin film forming surface, which adversely affects the product quality such as changing the electric resistance. In some cases, which may be a factor to reduce the product yield.

Further, particularly in the case of a sputtering target material manufactured by the powder metallurgy method, it is generally hot-formed under hydrostatic pressure using the HIP method, but voids may remain between particles, and gas is trapped in this void. It may be done. Once the trapped gas flows out, it may affect the stability of the degree of vacuum required at the time of sputtering and deteriorate the film characteristics.

Moreover, when a sputtering target material having a void that traps such a gas is heated during sputtering, the gas remaining in the sputtering target material expands due to heat, and damage such as blowholes is given to the sputtering target material itself. Can be considered.

DISCLOSURE OF THE INVENTION Therefore, an object of the present invention is to solve the conventional problems as described above, and it is possible to obtain good thin film characteristics without the loss of fine cluster-like lumps.
An object of the present invention is to provide a high-purity precious metal sputtering target material for sputtering, which has extremely few internal defects.

In order to prevent the loss of fine cluster-like lumps, which is a conventional problem, the inventors have considered that the metal structure of the sputtering target material must be taken into consideration, and the present invention has been completed. It was. Therefore,
In explaining the present invention, it is very important how to consider the mechanism of the loss of fine cluster-like lumps from the sputtering target material manufactured by the conventional melt casting method or powder metallurgy method.

Therefore, it was first explained how to grasp the problem that occurred in the conventional sputtering target material, and based on this idea, it was clarified how the problem was solved by using the sputtering target material according to the present invention. The sputtering target material according to the present invention will be described below.

As a matter of course, the sputtering target material manufactured by the conventional melt casting method or powder metallurgy method is composed of innumerable crystals of constituent metals. FIG. 2 schematically shows the cross-sectional structure found in the sputtering target material manufactured by the melt casting method.

Various crystal planes having different crystal orientations are irregularly distributed on the sputtering surface of the sputtering target material having the crystal structure as shown in FIG. In other words, it has a sputtering surface as a polycrystalline body. This is supported by the fact that when the spectrum detected by X-ray diffraction is analyzed, the (100), (002), (110), and (112) planes can be observed at almost the same rate as the spectrum of the standard sample. is there.

When a sputtering target material having a sputtering surface as a polycrystalline body is sputtered using oxygen, nitrogen, argon, or the like, the sputter rate varies depending on the plane orientation of the crystal appearing on the surface and the sputter ion species. In other words, in the conventional sputtering target material in which various crystal planes appear on the surface, the sputter rate is different for each crystal plane so that the existence of the preferential sputtering surface is affirmed. Low crystals coexist.

Microscopically, as the sputtering progresses, the erosion of the crystal grains in which the crystal planes that are easily sputtered on the surface layer appear more intense, and the erosion of the crystal grains in which the crystal planes that are hard to sputter on the surface layer appear are gradual. Therefore, an uneven shape is formed on the surface of the sputtering target material, and the surface of the sputtering target material becomes rough. The phenomenon in which the surface of the sputtering target material is roughened varies depending on the sputter ion species, but a phenomenon with a higher sputter rate appears as a remarkable phenomenon. Therefore, this phenomenon is particularly likely to occur when argon is used widely industrially because of its high sputter rate.

When sputtering is further continued, the surface layer of the sputtering target material to be sputtered is work-hardened by the implantation of sputter ions, and the crystal grains eroded and thinned by sputtering peel off along the grain boundaries that have become work-hardened and become brittle. In addition, the sputtering target material may fall off from the surface to the thin film formation surface. That is, it can be said that the above-mentioned fine cluster-shaped lumps are those in which the crystal grains themselves have peeled off.

Among them, in a sputtering method in which a sputtering target is placed above a substrate on which a thin film is formed, such as roof sputtering, there is a high risk that crystal grains will peel off and adhere to the substrate, and the sputtering target material will be fine. The absence of large cluster-shaped lumps is an important quality of sputtering target material.

In order to solve the problem of the sputtering target material produced by the above-mentioned conventional melt casting method or powder metallurgy method, it is effective to make the crystal structure of the noble metal target material for sputtering according to the present invention into a columnar structure. Therefore, the sputtering target material made of a noble metal is characterized by having a columnar crystal structure grown in a direction normal to the sputtering surface.

The sputtering target material having a columnar structure grown in the direction normal to the sputtering surface has a continuous crystal structure in the thickness direction, which is the crystal structure schematically shown in FIG. Therefore, in the case of having a discontinuous structure in the thickness direction shown in FIG. 2, the problem that the conventional sputtering target material has, that is, the fine crystal particles fall off, is extremely unlikely to occur.

Further, it can be said that the columnar structure is a structure that has grown in a preferential orientation in the growth process. Therefore, by making the crystal structure of the material a columnar structure, it is possible to give a certain level of directivity to the crystal orientation of each crystal forming the material. This makes it possible to align the crystal orientations on the surface of the sputtering target material and reduce microscopically non-uniform consumption of the sputtering target material.

As described above, the noble metal sputtering target material according to the present invention is characterized by being composed of a crystal structure including columnar crystals grown in the direction normal to the sputtering surface, whereby fine cluster-like lumps are generated. It can be a source of a noble metal thin film having good characteristics without causing any deterioration.

By the way, as the sputtering target material composed of columnar crystals as in the present invention, those for other metal species such as titanium are well known. Some of the sputtering target materials such as titanium are formed by using columnar crystals produced by controlling the heat flow in the solidification process after melting in one direction (unidirectional solidification).

However, it has not been contrived in the past to construct a noble metal target material from columnar crystals, and there has been no report of the existence of such a material.
This is because the noble metal is a material having an extremely high melting point, and as described above, it is difficult to produce it by melt casting, and it is difficult to make the crystal structure of the high melting point material into a columnar crystal by the above-mentioned directional solidification. Because it is impossible in practice. Therefore, it has not been possible to conceive from the state of the art so far that the crystal structure of the noble metal target material is composed of columnar crystals.

Under such circumstances, the present inventors have conducted further research to obtain a target material composed of columnar crystals of a noble metal, and as a result, have found that the crystal structure containing the columnar crystals contains a noble metal salt. A sputtering target material composed of columnar crystals electrolytically deposited from a solution.

The columnar crystals electrolytically deposited from the solution containing this noble metal salt can be deposited at a relatively low temperature even though the deposition rate is slow. Since it is simple and has good manufacturing efficiency, it has an advantage of being cheaper than the conventional noble metal target material.

Further, the columnar crystal formed by electrolytic deposition is a high-purity crystal with a small amount of impurities, since it is produced by separate precipitation utilizing the difference in deposition potential peculiar to the electrolytic method. Therefore, the target material according to the present invention is also characterized by high purity with very few internal defects.

Further, in recent years, it is necessary to increase the diameter of the target material in order to improve the productivity of the thin film element, and the target material of the present invention has a columnar crystal structure even in response to the demand for increasing the diameter of the target material. It is possible to deal with it relatively easily by appropriately changing the electrolysis conditions and precipitation conditions, and to use a target material consisting of large diameter and uniform columnar crystals that could not be solved by conventional unidirectional solidification. You can

Here, the solution containing the noble metal includes not only an aqueous solution containing the noble metal salt but also a mixed salt in a molten state in which the noble metal salt is mixed.

In particular, the target material composed of columnar crystals precipitated from this mixed molten salt is preferable from the viewpoint of purity and crystal plane directivity. This is because, among the electrolysis, by using the molten salt electrolysis, it is easy to adjust the composition of the molten salt to be the electrolytic solution, and moreover the precipitation potential difference with the impurities can be more effectively utilized, so that the precious metal can be highly purified. Because it can be separated and precipitated. And molten salt electrolysis is
Compared with the case of depositing a noble metal from a noble metal aqueous solution, a noble metal target material having a desired shape can be directly obtained in a relatively short time, and by appropriately changing the electrolysis conditions,
The structure of the precipitate can be controlled, and a sputtering target material having a developed columnar structure can be obtained.

Here, as the noble metal used in the sputtering target material of the present invention, iridium, ruthenium, platinum,
Considering gold, palladium, rhodium, osmium and rhenium. Among them, platinum, ruthenium and iridium are significantly inferior in physical workability to gold, which is the same precious metal, and in reality, it is impossible to perform rolling, forging, etc. When considering a manufacturing method other than the method, there will be great restrictions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a cross-section crystal structure of a sputtering target material having a columnar crystal structure, and FIG. 2 is a schematic view of a cross-section crystal structure of a sputtering target material obtained by a melt casting method. is there.

Further, FIG. 3 is a schematic structural view of the molten salt electrolysis device.
FIG. 4 is a grain structure of crystals observed by an optical microscope as a cross-section crystal structure of the ruthenium target material for sputtering according to the present invention, and FIG. 5 is an optical structure as a cross-section crystal structure of the iridium target material for sputtering according to the present invention. It is the grain structure of crystals observed under a microscope.

And, FIG. 6 is a surface grain structure of the sputtering surface of the ruthenium target material for sputtering according to the present invention visually observed after the completion of sputtering. Figure 7
It is the surface grain structure of the sputtering surface of the ruthenium target material for sputtering produced by the melting and casting method after the completion of sputtering.

Further, FIG. 8 (a) shows the surface crystal structure of the sputtering surface of the ruthenium target material for sputtering according to the present invention after the completion of sputtering by SEM observation, and FIG. 8 (b) shows the surface roughness of the sputtering surface after the completion of sputtering. It is a profile of Sa. And FIG.9 (a) shows the surface crystal structure by SEM observation of the sputtering surface of the ruthenium target material for sputtering obtained by the melt-casting method after completion of sputtering, and FIG.9 (a) shows the surface of the sputtering surface after completion of sputtering. It is a profile of roughness.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment: In order to explain the precious metal target material for sputtering according to the present invention in more detail, as an embodiment, first, a precious metal target is prepared by electrolyzing an aqueous solution containing platinum. The wood was manufactured.

An aqueous solution having the following composition was used as the platinum solution to be the electrolytic bath.

A copper disk (diameter: 130 m
m) was used. This cathode was subjected to electrolytic degreasing, acid activation treatment, and platinum strike plating, and then immersed in the above aqueous solution for electrolysis.

The electrolysis conditions were a bath temperature of 95 ° C and a cathode current density of 3 A / d.
Electrolysis was performed at m ² and an electrolysis time of 125 hours. Then, as a result of performing molten salt electrolysis under these conditions, platinum having a thickness of 3 mm was obtained. As for the cathode to which this electrolytic platinum adhered, a copper plate as a base was melted to obtain a platinum target material for sputtering which is a disk-shaped platinum plate. When the crystal structure of the platinum target material was analyzed by X-ray diffraction,
The integrated intensity of the (200) plane was especially stronger than that of other crystal planes. The integrated intensity ratio between this (200) plane and another crystal plane is higher than that when a ruthenium sample in the powder state is analyzed, and the target material according to the present embodiment has a texture strongly oriented in the (200) plane. It turned out that

Second Embodiment: Next, a mixed molten salt was used as a noble metal solution to be deposited, and a target material was manufactured using the molten salt electrolysis apparatus 1.

As shown in FIG. 3, the molten salt electrolysis apparatus 1 includes a cylindrical container 2 having an open upper surface, a flange 3 provided with an electrolytic insertion port serving as a lid of the cylindrical container, a graphite electrolytic tank 4, and an object to be plated. It is provided with a preliminary exhaust chamber 5 for loading or unloading and the rotating means 6 of the object to be plated.

Further, in the molten salt electrolysis apparatus 1 of FIG. 3, a ruthenium plate was used as the anode 7 located inside the graphite electrolytic cell 4. The anode 7 was laid so as to come into contact with the bottom of the graphite electrolytic cell 4, and electric current was supplied through the graphite electrolytic cell 4. Molten salt electrolysis was performed using cylindrical graphite for the cathode 8. The composition of the mixed molten salt used here was as shown in Table 2.

Electrolysis conditions are bath temperature 520 ℃, cathode current density 2A / dm ² ,
The electrolysis time was 150 hours. As a result of performing molten salt electrolysis under these conditions, electrolytic ruthenium having a thickness of 3 mm was obtained. The electrolytic ruthenium was pickled with hydrochloric acid, sulfuric acid or the like and peeled off from the graphite electrode to obtain a ruthenium target material for sputtering which is a disc-shaped ruthenium plate.

Finally, the ruthenium target material for sputtering was adhered to a copper plate having a thickness of 3 mm to obtain a ruthenium target for sputtering. When the crystal structure of this ruthenium target material was observed with an optical metallographic microscope at 100 times, a columnar crystal structure as shown in FIG. 4 was obtained. When analyzed by X-ray diffraction, the integrated intensity of the (112) plane was particularly stronger than the integrated intensity of the other crystal planes. The integrated intensity ratio between the (112) plane and other crystal planes is higher than that when a ruthenium sample in the powder state is analyzed, and the target material according to the present embodiment has a structure in which the (112) plane is strongly oriented. It turned out that In addition, the presence or absence of internal defects was examined by an X-ray transmission test, but no internal defects were detected.

Third Embodiment: In this embodiment, a ruthenium target was manufactured by changing the electrolysis conditions using the mixed molten salt of Table 2 used in the second embodiment and the apparatus of FIG. Therefore,
Since the basic embodiment is the same as the first embodiment, duplicate description is omitted and only the electrolysis conditions are described.

The electrolysis conditions here are a bath temperature of 560 ° C and a cathode current density of 3
A / dm ² and electrolysis time were 100 hours. As a result of performing molten salt electrolysis under these conditions, electrolytic ruthenium having a thickness of 3 mm was obtained.

When the crystal structure of this ruthenium target material is analyzed by X-ray diffraction, in the case of the ruthenium target material according to the present embodiment, the same tendency as in the first embodiment is observed for the (001) plane, and the (001) plane is strongly oriented. It turned out that the organization In addition, the presence or absence of internal defects was examined by an X-ray transmission test, but no internal defects were detected.

Sputtering was actually performed using the ruthenium target manufactured in the first and second embodiments described above. At this time, a sputtering method of roof sputtering was adopted, and the ruthenium target was placed above the thin film formation substrate. The test was conducted with N = 100, but none of the crystal grains themselves exfoliated and fell off and affected the thin film performance.

Fourth Embodiment: In this embodiment, an iridium target material was manufactured using the molten salt electrolysis apparatus 1 shown in FIG. 3 similar to the first and second embodiments. The composition of the mixed molten salt used here was as shown in Table 3.

Electrolysis conditions are bath temperature 520 ℃, cathode current density 2A / dm ² ,
The electrolysis time was 150 hours. As a result of performing molten salt electrolysis under these conditions, electrolytic iridium having a thickness of 3 mm was obtained. The electrolytic iridium was pickled with hydrochloric acid, sulfuric acid or the like, and peeled from the graphite electrode to obtain an iridium target material for sputtering which is a disk-shaped iridium plate.

Finally, this iridium target material for sputtering was adhered to a copper plate having a thickness of 3 mm to obtain an iridium target for sputtering. When the crystal structure of this iridium target material was observed with an optical metallographic microscope at 100 times, a columnar crystal structure as shown in FIG. 5 was obtained. When analyzed by X-ray diffraction, the same tendency as in the first embodiment was observed on the (220) plane, and it was found that the texture was strongly oriented on the (220) plane. In addition, the presence or absence of internal defects was examined by an X-ray transmission test, but no internal defects were detected.

Furthermore, actual sputtering was performed using this iridium target. At this time, a sputtering method of roof sputtering was adopted, and the iridium target was placed above the thin film formation substrate. N = 100
Was conducted, but none of the crystal grains themselves peeled off and had an effect on the thin film performance.

Furthermore, in order to compare with the sputtering target material according to the present invention, by using a ruthenium target material for sputtering produced by a melting and casting method, by roof sputtering, a ruthenium target material is placed above the thin film forming substrate for a comparative test. Carried out. As a result of conducting the test of N = 100, there were two points in which the crystal grains themselves were exfoliated and dropped, which seemed to affect the thin film performance. Although it was not a very serious defect, the electric resistance value changed.

However, even in this level of fluctuation, in the semiconductor industry in which quality control is performed on the order of ppb, it may cause a very serious decrease in yield and reduce the reliability of product quality.

After the sputtering with argon was finished, the sputtering surfaces of the ruthenium target material of the first embodiment and the ruthenium target material manufactured by the above-mentioned melting and casting method were observed. As can be seen from FIGS. 6 and 7, the ruthenium target material produced by the molten salt electrolysis shown in FIG. 6 is more uniformly eroded than the ruthenium target material of the first embodiment shown in FIG. It can be seen that the surface roughness is small.

Furthermore, the result of observing this surface by SEM is shown in FIG.
FIGS. 8A and 9A show profiles obtained by the surface roughness meter, and FIGS. 8B and 9B show the profiles. From this result,
Qualitatively, the sputtering surface of the ruthenium target material of the first embodiment shown in FIG. 7 is a uniform sputtering surface with less unevenness than the sputtering surface of the ruthenium target material manufactured by the melt casting method shown in FIG. Will also be clear. From this, the sputtering target material having columnar crystal grains obtained by the molten salt electrolysis method plays a very effective role in enabling stable operation.

INDUSTRIAL APPLICABILITY The noble metal target material for sputtering according to the present invention has a feature that the crystal structure is a columnar structure and the crystal orientation of the material surface is substantially constant. Due to this feature,
There is an effect that a crystal particle does not fall off in the sputtering process and a film having excellent properties can be produced. By using the sputtering target material according to the present invention, it is possible to improve yield and reliability of product quality in the semiconductor industry.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ritsuya Matsuzaka 26 Suzukawa, Isehara City, Kanagawa Prefecture Tanaka Kikin Industry Co., Ltd. Isehara Factory (56) Reference JP-A-11-158612 (JP, A) (58) ) Fields surveyed (Int.Cl. ⁷ , DB name) C23C 14/00-14/58 H01L 21 / 203,21 / 285 C25C 1 / 20,3 / 34 C25D 1 / 00,3 / 46-3/66

Claims (7)

(57) [Claims] 1. A sputtering target material composed of a noble metal having a crystal structure containing columnar crystals grown in a direction normal to a sputtering surface, wherein the crystal structure containing columnar crystals is formed from a solution containing a noble metal salt. The sputtering target material that has been analyzed. 2. The sputtering target material according to claim 1, wherein the solution containing the noble metal salt is a molten salt mixed with the noble metal salt. 3. The noble metal is any one of platinum, ruthenium, and iridium.
The sputtering target material according to the item. 4. The noble metal is platinum, and the ratio of the integrated intensity of the (200) plane measured by X-ray diffractometry to the integrated intensity of other crystal planes is that of platinum in the powder state (200) plane. The sputtering target material according to claim 1 or claim 2, which has a ratio higher than an integrated intensity and an integrated intensity of another crystal plane. 5. The noble metal is ruthenium, and the ratio of the integrated intensity of the (112) plane measured by X-ray diffractometry to the integrated intensity of other crystal planes is that of the ruthenium in the powder state (112) plane. The sputtering target material according to claim 1 or claim 2, which has a ratio higher than an integrated intensity and an integrated intensity of another crystal plane. 6. The noble metal is ruthenium, and the ratio of the integrated intensity of the (001) plane measured by X-ray diffractometry to the integrated intensity of other crystal planes is that of the (001) plane of powdery ruthenium. The sputtering target material according to claim 1 or claim 2, which is higher than the ratio of the integrated intensity and the integrated intensity of other crystal planes. 7. The noble metal is iridium, and the ratio of the integrated intensity of the (220) plane measured by X-ray diffractometry to the integrated intensity of other crystal planes is that of the (220) plane of iridium in the powder state. The sputtering target material according to claim 1 or claim 2, which is higher than the ratio of the integrated intensity and the integrated intensity of other crystal planes.