WO1999066099A1 - Target material for spattering - Google Patents

Abstract

A target for spattering comprising a noble metal, characterized in that it has a columnar crystal texture which grows in the normal direction to a spattering plane. The target is free from the occurrence of the problem that a fine block in a cluster form is missed from a target, which problem is likely to occur in a target for spattering obtained by using the dissolution casting method or the powder metallurgy method, and can be used for producing a thin film having good film properties, and further is a high purity noble metal target for spattering having little internal defect.

Description

 Specification

 Spaghetti Ring Evening Material Technical Field

 The present invention relates to a sputtering target material. In particular, it relates to sputtered evening gate materials made of precious metals. 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 precious metal thin films are mainly manufactured by a sputtering method, which is one of the physical vapor deposition methods. In the case of using this sputtering method, the purity of the sputtering material, the structure of the target material and the like greatly affect the characteristics of the formed thin film.

 That is, the characteristics such as specific resistance that are practically required for the thin film electrode can be determined simply by controlling the purity of the sputtering target material. In this regard, a sufficiently satisfactory spattering material manufactured by the conventional melting method or powder metallurgy method has been obtained.

 However, in the process of using the sputtering target manufactured by the melting method or the powder metallurgy method, fine cluster-like lumps were missing from the sputtering target, adhered to the thin film formation surface, and changed the electrical resistance. In some cases, the product quality was adversely affected, for example, resulting in a reduction in product yield.

In particular, in the case of a sputtering target material manufactured by powder metallurgy, hot forming is generally performed under hydrostatic pressure using the HIP method, but voids may remain between particles. May be trapped. Once this trapped gas flows out, it affects the degree of vacuum required during sputtering and deteriorates the film properties. There is.

 In addition, if the sputtering material having such gas trapped voids is heated during sputtering, the gas remaining in the sputtering material expands due to heating, causing damage such as blowholes to occur. It is conceivable to give it to the ring wood itself in the evening. Disclosure of the invention

Therefore, an object of the present invention is to solve the conventional problems as described above, so that fine cluster-like lumps are not lost, good thin film characteristics can be obtained, and internal defects are extremely small. An object of the present invention is to provide a high-purity noble metal sputtering target material for sputtering. The present inventors have thought that the metallographic structure of the sputtering target material must be considered in order to prevent the conventional problem of the loss of fine cluster-like lump, and completed the present invention. than it was led to the _c Therefore, in describing the present invention, the mechanism of loss of conventional dissolving铸造method or fine class evening one like mass of sputtered produced evening by powder metallurgy from Ge' preparative material How you think is very important.

 Therefore, it is first explained how the problem that had occurred in the conventional sputtering evening gate material was perceived, and based on this concept, the sputtering evening evening material according to the present invention was used. Then, the spattering material according to the present invention will be described by clarifying how the problem was solved.

 It is a matter of course that the sputtering target material manufactured by the conventional melting method or powder metallurgy is composed of countless crystals of constituent metals. FIG. 2 schematically shows a cross-sectional structure observed in a sputtering target material manufactured by a melting method.

Various crystal planes having different crystal orientations are irregularly distributed on the sputtering surface of the sputtering target material having the crystal structure shown in FIG. In other words, it has a sputtered surface as a polycrystal. W

You. This is supported by analyzing the spectrum detected by X-ray diffraction, which shows that the (100), (002), (110), and (111) planes are the spectrum of the standard sample. It is a fact that it can be observed at almost the same rate as torr.

 When sputtering is performed using a sputtering target material having a sputtered surface as a polycrystal and using oxygen, nitrogen, argon, etc. as sputter ions, the sputtering rate depends on the plane orientation of the crystal appearing on the surface and the sputter ion type. different. In other words, in the conventional sputtering target material having various crystal planes on the surface, the sputter rate differs for each crystal plane so that the existence of a preferential sputtering plane is affirmed. Crystals with a low sputter rate coexist.

 Microscopically, with the progress of sputtering, the erosion of crystal grains having crystal planes that are easily sputtered on the surface layer becomes severe, and the erosion of crystal grains having crystal planes that are hardly sputtered on the surface layer is observed. Since the surface of the sputtering target is moderate, an uneven shape is formed on the surface of the sputtering target material, and the surface of the sputtering target becomes rough. The degree of the roughening of the surface of the sputtering material varies depending on the type of the sputter ion, but appears as a remarkable phenomenon as the sputter rate increases. Therefore, this phenomenon is particularly likely to occur when argon, which is widely used industrially, is used because of the high sputter rate.

 When sputtering is further continued, the surface layer of the sputtering target material, which is sputtered, is hardened by the implantation of sputter ions, and the thinned grains that are eroded by the sputter ring become grain boundaries that are hardened by work hardening. Along the surface, and then fall off from the surface of the sputtering target material to the thin film formation surface. That is, it can be said that the above-mentioned fine cluster-like lump is one in which the crystal grain itself has peeled and dropped.

In particular, in a sputtering method in which a sputtering target is disposed above a substrate on which a thin film is formed, such as roof sputtering, there is a high risk that crystal grains will be peeled off and adhere to the substrate. The absence of fine-grained cluster-like clumps from the puttering gate material is an important quality of the sputtering bar material.

 In order to solve the problem of the sputtering target material manufactured by the conventional melting method or powder metallurgy method, the crystal structure of the noble metal target material for sputtering according to the present invention is changed to a columnar structure. The sputtering target material is a sputtering target material made of a noble metal and characterized by having a columnar crystal structure grown in the normal direction to the sputtering surface. .

 The sputtering target material having a columnar structure grown in the normal direction to the sputtering surface has a continuous crystal structure in the thickness direction, and the crystal structure schematically shown in Fig. 1. It is. Therefore, when the structure has a discontinuous structure in the thickness direction shown in FIG. 2, the problem of the conventional sputtering target material, that is, the falling off of fine crystal grains, is extremely unlikely to occur.

 In addition, the columnar structure can be said to be an organization that grew with a preferred 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 constituting the material. This makes it possible to align the crystal orientations of the surface of the sputtering target material and to minimize the consumption of the microscopically non-uniform sputtering target material.

 As described above, the noble metal sputtering target material according to the present invention is characterized by having a crystal structure including columnar crystals grown in the normal direction to the sputtering surface, thereby providing a fine cluster-like structure. It can be a noble metal thin film source having good characteristics without generating a lump.

By the way, as for the sputtering target material composed of columnar crystals as in the present invention, those for other metal species such as titanium are well known. <For the sputtering target material such as titanium, for example, By controlling the heat flow in the post-solidification process in one direction (unidirectional solidification) There is one configured using columnar crystals to be manufactured.

 However, no method has been devised for forming a noble metal target material from columnar crystals, and there has been no report on 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 the material by melting, and the crystal structure of such a high melting material is made into columnar crystals by the above-described unidirectional solidification. That is because it is impossible in practice. For this reason, it was not conceivable from the state of the art that noble metal target materials had a crystal structure composed of columnar crystals.

 Under these circumstances, the present inventors conducted further research in order to obtain a target material composed of columnar crystals of the noble metal, and as a result, they found that the crystal structure containing the columnar crystals contained the noble metal salt. It is a sputtering target material composed of columnar crystals electrolytically deposited from the contained solution.

 The columnar crystals electrolytically precipitated from the solution containing the noble metal salt can be precipitated at a relatively low temperature while having a slow deposition rate. The process management is simple and the production efficiency is good, so there is an advantage that it is inexpensive compared to conventional precious metal evening-get materials.

 In addition, columnar crystals formed by electrolytic deposition are high-purity crystals with a low impurity content, because they are produced by separation and deposition using a deposition potential difference peculiar to the electrolytic method. Therefore, the target material according to the present invention also has a feature of high purity with very few internal defects.

 Furthermore, in recent years, it has been necessary to increase the diameter of the target material in order to improve the productivity of the thin film element. However, in response to the demand for a larger diameter of the target material, the target material of the present invention is also required. Can be handled relatively easily by appropriately changing the electrolysis conditions and precipitation conditions of the columnar crystals, and consists of large-diameter and uniform columnar crystals that could not be solved even by conventional unidirectional solidification. It can be used as a getter material in the evening.

Here, as the solution containing a noble metal, only an aqueous solution containing a noble metal salt is used. However, it also includes a mixed salt in a molten state in which a noble metal salt is mixed. In particular, a sunset material comprising columnar crystals precipitated from the mixed molten salt is preferable from the viewpoint of purity and directivity of the crystal plane. This is because the use of molten salt electrolysis among electrolysis makes it easy to adjust the composition of the molten salt used as the electrolytic solution, and also makes it possible to more effectively use the difference in deposition potential with impurities. It can be separated and precipitated. In addition, the molten salt electrolysis can directly obtain a precious metal sunset material having a desired shape in a relatively short time as compared with the case of precipitating a noble metal from a noble metal aqueous solution, and by appropriately changing the electrolysis conditions, The structure of precipitates can be controlled, and it can be used as a sputtering target material with a developed columnar structure.

 Here, iridium, ruthenium, platinum, gold, palladium, rhodium, osmium, and rhenium are considered as the noble metal used in the sputtering target material of the present invention. Among them, platinum, ruthenium, and iridium are significantly inferior in physical workability to gold, which is the same noble metal, and cannot be rolled or forged in practice. Considering manufacturing methods other than metallurgical methods is accompanied by significant restrictions. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a schematic diagram of a cross-sectional crystal structure of a sputtering target material having a columnar crystal structure, and FIG. 2 is a schematic diagram of a cross-sectional crystal structure of a sputtering target material obtained by a melting method. is there.

 FIG. 3 is a schematic structural diagram of a molten salt electrolysis apparatus. FIG. 4 is a cross-sectional crystal structure of a ruthenium target material for sputtering according to the present invention, which is a crystal grain structure observed by an optical microscope. FIG. 5 is a graph showing a grain structure of a sputtering target material according to the present invention. This is the grain structure of the crystals observed under an optical microscope as a cross-sectional crystal structure.

FIG. 6 shows a ruthenium substrate for sputtering according to the present invention. This is the surface particle structure visually observed on the spattered surface after the spattering of the wood material. Figure 7 shows the surface particle structure of the sputtering target of the sputtering target manufactured by the melting method, which was visually observed after the sputtering.

 Further, FIG. 8 (a) shows the surface crystal structure of the ruthenium sputtering target material for sputtering according to the present invention by SEM observation of the sputtering ring surface after the completion of the sputtering, and FIG. 8 (b) This is the profile of the surface roughness of the sputtering surface after the end of sputtering. Fig. 9 (a) shows the surface crystallographic structure of the sputtered surface of the ruthenium target material for sputtering obtained by the melt-casting method after SPM, which was observed by SEM. This is a profile of the surface roughness of the sputtering surface after completion. BEST MODE FOR CARRYING OUT THE INVENTION

 First Embodiment: In order to explain the noble metal target material for sputtering according to the present invention in more detail, as an embodiment, first, a noble metal target material was manufactured by electrolyzing an aqueous solution containing platinum.

 An aqueous solution having the following composition was used as a platinum solution serving as an electrolytic bath.

白金を析出させる力ソードには、 銅円板 （直径： 1 3 Omm) を用い た。 この力ソードは、 電解脱脂、 酸活性処理、 白金ストライクめっきを 施した後、 上記水溶液中に浸漬し電解を行った。

A copper disc (diameter: 13 Omm) was used as the force sword for depositing platinum. The force sword was subjected to electrolytic degreasing, acid activation treatment, platinum strike plating, and then immersed in the above aqueous solution for electrolysis.

The electrolysis was performed with a bath temperature of 95 :, a power source current density of 3 AZdm ² , and an electrolysis time of 125 hours. And the molten salt electrolysis As a result, platinum having a thickness of 3 mm was obtained. The cathode to which the electrolytic platinum had adhered was used as a platinum-plated material for sputtering, which was a disc-shaped platinum plate, by dissolving the underlying copper plate. X-ray diffraction analysis of the crystal structure of the platinum target material showed that the integrated intensity of the (200) plane was particularly stronger than that of the other crystal planes. Then, the integrated intensity ratio between the (200) plane and the other crystal plane is higher than that in the case of analyzing a ruthenium sample in a powder state, and the target material according to the present embodiment is (200) The structure was found to be strongly oriented on the surface. Second Embodiment: Next, a mixed molten salt was used as a precious metal solution to be precipitated, and a molten salt electrolysis apparatus 1 was used to produce a evening target material.

 As shown in FIG. 3, the molten salt electrolysis apparatus 1 includes a cylindrical container 2 having an open top, a flange 3 having an electrode inlet serving as a lid of the cylindrical container, a graphite electrolytic cell 4, It is provided with a preliminary exhaust chamber 5 for loading or unloading a plating object, and a rotating means 6 for the plating object.

 In the molten salt electrolysis apparatus 1 of FIG. 3, a ruthenium plate was used for the anode 7 located inside the electrolytic cell 4 made of graphite. The anode 7 is laid so as to be in contact with the bottom of the graphite electrolytic cell 4, and current is supplied through the graphite electrolytic cell 4. Electrolysis was performed. The composition of the mixed molten salt used here was as shown in Table 2. Table 2

 Constituent Component Direct / g

 Sodium chloride 1 577.9

 Potassium chloride 1 241.3

 Cesium chloride 689.4

Potassium ruthenate chloride 765.1 The electrolysis conditions were a bath temperature of 520 ° C., a power source current density of 2 AZ dm ² , and an electrolysis time of 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 washed with hydrochloric acid or sulfuric acid or the like and peeled off from the graphite electrode to obtain a disc-shaped ruthenium plate, a ruthenium sputtering target material for sputtering.

 Finally, the ruthenium sputtering target material for sputtering was bonded to a 3 mm-thick copper plate to obtain a ruthenium sputtering target for sputtering. When the crystal structure of the ruthenium sunset material was observed at a magnification of 100 with an optical metallurgical microscope, a columnar crystal structure as shown in FIG. 4 was obtained. When analyzed by X-ray diffraction, the integrated intensity of the (1 1 2) plane was particularly stronger than that of the other crystal planes. The integrated intensity ratio between the (111) plane and the other crystal plane is higher than that obtained when analyzing a ruthenium sample in a powder state, and the sunset material according to the present embodiment is (111). 2) It was found that the texture was strongly oriented on the surface. The presence or absence of internal defects was examined by an X-ray transmission test, but no internal defects were detected.

Third Embodiment: In the present embodiment, a ruthenium target was manufactured by changing the electrolysis conditions using the mixed molten salt shown in Table 2 and the apparatus shown in FIG. 1 used in the second embodiment. Therefore, since the basic embodiment is the same as the first embodiment, the duplicate description is omitted and only the electrolysis conditions are described.

The electrolysis conditions here were a bath temperature of 560 ° C., a power source current density of 3 AZ dm ² , and an electrolysis time of 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 the ruthenium target material is analyzed by X-ray diffraction, in the case of the ruthenium target material according to the present embodiment, the (001) plane shows the same tendency as in the first embodiment. The microstructure was found to be strongly oriented on the (001) plane. The presence or absence of internal defects was examined by an X-ray transmission test, but no internal defects were detected. The ruthenium targets manufactured in the first and second embodiments described above. Sputtering was actually performed using a pit. At this time, the sputter ring adopted a roof sputter ring type, and the ruthenium target was placed above the thin film forming substrate. A test with N = 100 was performed, but none of the crystal grains itself peeled off and affected the thin film performance.

 Fourth Embodiment: In the present embodiment, an iridium target material is 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. Table 3

電解条件は、 浴温 5 2 0 °C、 力ソード電流密度 2 A Z d m²、 電解時間 1 5 0時間とした。 この条件により溶融塩電解を行った結果、 厚さ 3 m mの電解イリジウムを得た。 電解イリジウムは、 塩酸又は硫酸等で酸洗 いして、 グラフアイ ト電極から剥離させ、 円盤状のイリジウム板である スパッタリング用イリジウムターゲッ ト材とした。

The electrolysis conditions were a bath temperature of 520 ° C., a power source current density of 2 AZ dm ² , and an electrolysis time of 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 or sulfuric acid or the like, and peeled off from the graphite electrode to obtain an iridium target material for sputtering, which is a disk-shaped iridium plate.

Finally, the iridium target material for sputtering and a 3 mm-thick copper plate were bonded to form a sputtering iridium target. When the crystal structure of the iridium sunset material was observed at a magnification of 100 with an optical metallographic microscope, a columnar crystal structure as shown in FIG. 5 was obtained. When analyzed by X-ray diffraction, it was found that the (220) plane had the same inclination as in the first embodiment, indicating that the structure was strongly oriented to the (2200) plane. The presence or absence of internal defects was examined by an X-ray transmission test, but no internal defects were detected. Further, sputtering was actually performed using this iridium target. At this time, the sputtering was of the roof sputtering type, and the iridium target was disposed above the thin film forming substrate.

An N-100 test was performed, but none of the crystal grains peeled off and had no effect on the thin film performance.

 Further, for comparison with the sputtering target material according to the present invention, a ruthenium target material was formed into a thin film by roof sputtering using a ruthenium target material for sputtering manufactured by a melting method. A comparative test was performed with the substrate placed above the substrate. As a result of the N2100 test, there were two points that seemed to have caused the crystal grains themselves to peel off and affect the thin film performance. Although not a very serious defect, there was a change in the electrical resistance.

 However, even at this level of fluctuation, in the semiconductor industry that performs quality control on the order of pbb, it can cause a very serious decrease in yield and reduce the reliability of product quality.

 After the sputtering by argon was completed, the sputtering surfaces of the ruthenium target material of the first embodiment and the ruthenium target material manufactured by the above-described melting 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 can be more easily compared with the ruthenium target material of the first embodiment shown in FIG. It can be seen that the erosion is uniform and the surface roughness is small compared to the material.

Furthermore, the results of observing this surface by SEM are shown in FIGS. 8 (a) and 9 (a), and the profiles obtained by the surface roughness meter are shown in FIGS. 8 (b) and 9 (b). Based on these results, the sputtered surface of the ruthenium target material of the first embodiment shown in FIG. 7 has a uniform unevenness with less unevenness than the sputtered surface of the ruthenium target material manufactured by the melting method shown in FIG. It will be qualitatively clear that it will be a ring surface. Therefore, the sputtering target material having columnar crystal grains obtained by the molten salt electrolysis method plays a very effective role in enabling stable operation. You. Industrial applicability

 The precious metal evening gate 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 film having excellent properties can be produced without crystal particles falling off in the sputtering process. By using the sputtering target material according to the present invention, it is possible to improve the yield and the reliability of product quality in the semiconductor industry.

Claims

The scope of the claims 1. A sputtering target material made of a noble metal, and having a crystal structure including columnar crystals grown in a direction normal to the sputtering surface.  2. The sputtering target material according to claim 1, wherein the crystal structure including columnar crystals is electrolytically precipitated from a solution containing a noble metal salt. 3. The sputtering target material according to claim 2, wherein the solution containing a noble metal salt is a molten salt mixed with a noble metal salt.  4. The sputtering target material according to claim 1, wherein the noble metal is one of platinum, ruthenium, and iridium.  5. The noble metal is platinum, and the ratio of the integrated intensity of the (200) plane measured by the X-ray diffraction method to the integrated intensity of other crystal planes is the (200) plane of platinum in a powder state. 4. The sputtering target material according to claim 1, wherein the ratio is higher than the ratio of the integrated intensity of the other crystal plane to the integrated intensity of the other crystal plane.  6. The noble metal is ruthenium, and the ratio of the integrated intensity of the (111) plane measured by the X-ray diffraction method to the integrated intensity of the other crystal plane is (111) of the ruthenium in powder state. 4. The sputtering target material according to claim 1, wherein the ratio is higher than the ratio of the integrated intensity of the plane to that of another crystal plane.  7. The noble metal is ruthenium, and the ratio of the integrated intensity of the (001) plane measured by X-ray diffraction to the integrated intensity of the other crystal planes is the (01) of the ruthenium in powder state. 4. The sputtering target material according to claim 1, wherein the ratio is higher than the ratio of the integrated intensity of the plane to that of another crystal plane. 8. The noble metal is iridium, and the ratio of the integrated intensity of the (2 0 0) plane measured by the X-ray diffraction method to the integrated intensity of the other crystal planes is iridium in a powder state. 4. The sputtering target material according to claim 1, wherein the ratio is higher than the ratio of the integrated intensity of the (220) plane of the system to that of another crystal plane. .