Aluminum or aluminum alloy sputtering target and method for manufacturing the same

Abstract

The sputtering target is manufactured by adjusting the ratio of the gas flow volume (Nm3)/molten liquid flow mass (kg) to 5 Nm3/kg or more in the gas atomizing step of the spray forming method using an Al or Al alloy sputtering target material in which the maximum length of all the inclusions is 20 &mgr;m or less.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a sputtering target material comprising aluminum or an aluminum alloy (referred to an aluminum or aluminum alloy sputtering target hereinafter), and a method for manufacturing the same. The present invention especially relates to an aluminum or aluminum alloy sputtering target material for use in forming semiconductor electrode films and a method for manufacturing the same, relating among all to an aluminum or aluminum alloy sputtering target for forming semiconductor electrode films being advantageous as liquid crystal display electrodes (thin film wiring and the electrode itself) and a method for manufacturing the same.

[0003] 2. Description of the Related Art

[0004] Use of liquid crystal displays (abbreviated as LCD hereinafter) has been recently expanded since it can be made thin and lightweight besides consuming small amount of electric power while maintaining high resolution as compared with conventional cathode-ray tubes (CRT). The LCDs having a structure in which semiconductor devices such as thin film transistors (abbreviated as TFT hereinafter) are integrated as switching elements have been recently proposed and widely used in order to enhance image quality. The TFT as used herein refers to an active element produced by connecting semiconductor electrodes comprising a thin metal film to a semiconductor film formed on an insulation substrate made of, for example, a glass. The semiconductor electrode is defined as an electrode to be used as a part of the TFT including a thin film wiring and the electrode itself. Once the active element is formed into the TFT, the wiring and the electrode itself are put into electrical continuity with each other.

[0005] Among various characteristics required for the LCD as described above, making electrical resistivity small for preventing signal delay is being one of the most crucial characteristics in compliance with the trends toward large size or highly sophisticated LCDs.

[0006] The semiconductor electrode for use in the LCD is produced by a sputtering method in which a sputtering target is used for sputtering. The sputtering target serves as a sputtering source for forming the semiconductor electrode on a substrate by sputtering, usually comprising a circular or rectangular plate. Atoms constituting the sputtering target are emitted into the space and deposited on the confronting substrate by exchange of kinetic momentum when accelerated particles collide with the surface of the sputtering target during sputtering.

[0007] High melting point metals such as Ta, Mo, Cr, Ti, W, Zr and Nb have been used for sputtering target materials for forming these semiconductor electrodes for use in the LCD. However, since the high melting point metals such as Ta, Mo, Cr, Ti, W, Zr and Nb have so high specific resistivity when they are formed into thin films that their application for the foregoing object have became difficult, because currently used LSIs are so highly integrated that a wiring width of as fine as 1 &mgr;m is required for the circuit. In other words, resistivity of the semiconductor electrode manufactured by using the sputtering target material comprising the foregoing high melting point metals is so high that the material became hardly compatible with fine wiring width as described above. Accordingly, development of semiconductor electrode materials having low resistivity as substitutes of the foregoing high melting point metals is desired.

[0008] Examples of the semiconductor electrode materials with desirable low resistivity include Au, Cu and Al. However, Au does not exhibit suitable etching characteristic, besides it is expensive, required for forming into a desired pattern after depositing a sheet of electrode, or an electrode film (a wiring film). Cu has some problems in adhesive property and corrosion resistance while Al has so poor heat resistance that minute hills called hillocks appear on the surface during the heating step (at about 250 to 400° C.), an inevitable production process of the TFT, after forming the electrode film. Because the electrode film is formed at the lowermost layer in the TFT-LCD, other films can not be laminated thereon when these hillocks are generated.

[0009] An electrode film comprising an Al alloy containing the alloy components as disclosed in Japanese Unexamined Patent Publication No. 7-45555 which is hereby fully incorporated by reference, and an Al alloy sputtering target for forming such Al alloy electrode film are proposed as a means for avoiding the hillock problems in the Al electrode film.

[0010] However, there arise another problems that particles and splashes are appeared to generate when the semiconductor electrode is formed on the substrate by sputtering using the sputtering target materials comprising the Al or Al alloys as described above. Particles scattering from the target are turned into clusters that directly adhere to the thin film on the substrate, or adhered or deposited layers on the surrounding wall or components is peeled off to adhere to the thin film on the substrate (so-called particle problem). Otherwise, droplets of the target material are scattered and adhere to the thin film on the substrate (so-called splash problem).

[0011] While the problems of particle and splash generation has been solved by decreasing the content of inclusion in the sputtering target materials as small as possible, it was pointed out in Japanese Unexamined Patent Publication No. 9-25564 which is hereby fully incorporated by reference that the utmost number of the inclusions having a mean particle size of 10 &mgr;m or more in the target should be reduced to less than 40 particles/cm2. However, the countermeasure as described above was proved to be insufficient for solving the problems of particle and splash generation.

[0012] Among the problems of particle and splash generation, the crucial problem that is urgently to be solved is that generation of splash provides serious obstacle on the performance of the thin film on the substrate or of the semiconductor electrode formed thereon. Splashes tend to be formed especially when an Al alloy sputtering target is used in order to prevent hillocks from appearing on the Al electrode film.

[0013] Splashes are generated not only in forming the foregoing semiconductor electrode for use in LCDs, but also in forming wiring of semiconductor integrated circuits and reflection layers of magnetic recording and photomagnetic recording media by sputtering as well.

SUMMARY OF THE INVENTION

[0014] Accordingly, the object of the present invention is to provide an aluminum or aluminum alloy sputtering target material hardly generating splashes when used for sputtering, and a method for manufacturing the same.

[0015] In a first aspect, the present invention provides an aluminum or aluminum alloy sputtering target comprising aluminum or an aluminum alloy containing inclusions having a maximum length of 20 &mgr;m or less.

[0016] The sputtering target material as described above allows splashes to be suppressed from generating during sputtering. The maximum length of the inclusions is limited to 20 &mgr;m or less because the inclusions with a maximum length of more than 20 &mgr;m makes the splashes to be readily generated owing to these inclusions, insufficiently suppressing generation of the splashes.

[0017] It is advantageous that all the inclusions have a maximum length of 10 &mgr;m or less.

[0018] The sputtering target material with the maximum length of the inclusions as described above allows the splashes to be hardly generated, more securely suppressing splash generation.

[0019] In a preferred embodiment, the present invention provides a method for fabricating an Al or Al alloy sputtering target material by a spray forming method, wherein the ratio of the gas flow volume (Nm3)/molten liquid flow mass (kg) in a gas atomizing step of the spray forming method is adjusted to 5 Nm3/kg or more.

[0020] In the method described above, the molten liquid of the Al or Al alloy is atomized to be dispersed into molten or semi-molten small particles as well as crashing the inclusion into small pieces in the atomizing step of the spray forming method. These small particles of semi-molten Al or Al alloy are successively deposited by spraying onto a bottom floor or in a mold, thereby forming the Al or Al alloy sputtering target material. When the ratio of the gas flow volume (Nm3)/molten liquid flow mass (kg) in the gas atomizing step of the spray forming method is adjusted to 5 Nm3/kg or more, the size (the maximum length) of all the inclusions after crushing becomes 20 &mgr;m or less, making it possible to obtain the Al or Al alloy sputtering target material in which the size of all the inclusions is 20 &mgr;m or less.

[0021] It is also advantageous to adjust the ratio of the gas flow volume (Nm3)/molten liquid flow mass (kg) to 10 Nm3/kg or more.

[0022] When the ratio of the gas flow volume (Nm3)/molten liquid flow mass (kg) is adjusted to 10 Nm3/kg or more, an Al or Al alloy sputtering target material in which the size (the maximum length) of all the inclusions is 10 &mgr;m or less.

[0023] It is also advantageous to use nitrogen gas for the atomizing gas in the gas atomizing step along with adjusting the ratio of the gas flow volume (Nm3)/molten liquid flow mass (kg) to 10 Nm3/kg or more.

[0024] The Al or Al alloy sputtering target material in which the size (the maximum length) of all the inclusions is 10 &mgr;m or less, along with containing 0.1 mass % or less of nitrogen, can be obtained to allow splashes to be hardly generated during sputtering, thereby enabling to form an Al or Al alloy thin film with small specific resistivity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 denotes a table indicating the sputtering conditions described in the Examples;

[0026] FIG. 2 denotes a table indicating the manufacturing conditions of the sputtering target material according to Examples 1 to 4, and the results of investigations on the size of the inclusion, the number of the splash having a size of 10 &mgr;m or more, and the oxygen content;

[0027] FIG. 3 denotes a table indicating the manufacturing conditions of the sputtering target according to Examples 5 to 9, and the results of investigations on the size of the inclusion, the number of the splash having a size of 10 &mgr;m or more, and the oxygen content;

[0028] FIG. 4 denotes a table indicating the sputtering conditions of the sputtering target material according to Example 10;

[0029] FIG. 5 denotes a table showing the relation between the maximum length of the inclusion and the number of the splash having a size of 10 &mgr;m or more with respect to the Al or Al alloy sputtering target material according to Example 4;

[0030] FIG. 6 denotes a graph showing the relation between the maximum length of the inclusion and the number of the splash having a size of 10 &mgr;m or more with respect to the Al or Al alloy sputtering target material according to Example 4; and

[0031] FIG. 7 denotes a graph showing the relation between the nitrogen content and electrical resistivity of the thin film obtained with respect to the sputtering target material according to Example 10.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0032] The Al or Al alloy sputtering target material according to the preferred embodiment of the present invention and the method for fabricating the same will be described hereinafter.

[0033] The present invention was completed based on the results obtained through intensive studies for developing the Al or Al alloy sputtering target material that hardly generates splashes.

[0034] The inventors of the present invention have manufactured the Al sputtering target material and Al alloy sputtering target material having various size of inclusion. The behavior of these sputtering target materials during sputtering has been fully investigated using these materials as sputtering targets.

[0035] The results indicated that the splash is generated when cooling of the target material is partially inhibited around the inclusion, especially at just above the inclusion, in the sputtering target material. In other words, it was found that the site around the inclusion is melted by plasma heating during sputtering and the splash is generated by allowing the molten layer to scatter by electromagnetic force forming droplets, that the splash is largely correlated with the size of the inclusion rather than the amount of the inclusion as described in Japanese Unexamined Patent Publication No. 9-25564, and that generation of the splash can be suppressed when the size (the maximum length, or the length of the portion having the maximum length) of the inclusion is 20 &mgr;m or less, or little splashes are generated when the size of the inclusion is 10 &mgr;m or less.

[0036] The size of the portion where cooling is inhibited by the inclusion during sputtering becomes small in the Al sputtering target material and Al alloy sputtering target material having the inclusion with a size (the maximum length) of 20 &mgr;m or less and the molten layer is hardly formed. Accordingly, the scattering frequency of the molten layer as droplets, or the frequency of splash generation, is so markedly decreased to sufficiently suppress generation of the splash. Especially, when the size of all the inclusion is 10 &mgr;m or less, the splash is substantially not generated.

[0037] In the first step of the method for manufacturing the Al or Al alloy sputtering target material according to the present invention, a ingot is produced by a spray forming method using a molten liquid. The molten liquid of Al or an Al alloy is deposited by gas atomizing to obtain a ingot. The ratio of the gas flow volume (Nm3)/molten liquid flow mass (kg) in the gas atomizing step of the spray forming method is adjusted to 5 Nm3/kg or more, thereby enabling to obtain the Al or Al alloy sputtering target material according to the present embodiment, or the sputtering target material comprising the Al or Al alloy having the maximum length of all the inclusions of 20 &mgr;m or less. The ratio of the gas flow volume (Nm3)/molten liquid flow mass (kg) in the gas atomizing step of the spray forming method is adjusted to 5 Nm3/kg or more because, when the ratio is less than 5 Nm3/kg, a substantial number of inclusions having the maximum length of more than 20 &mgr;m are included in the Al or Al alloy sputtering target material, the inclusion serving as trigger points for generating the splashes during sputtering in the sputtering target material as described above.

[0038] The Al or Al alloy sputtering target material obtained by the spray forming method as described above contains a higher concentration of oxygen in the material than the Al or Al alloy sputtering target material obtained by the vacuum melting method. However, the splashes are hardly generated in the former material as compared with the latter material during sputtering, in spite of the fact that the former contains larger amount of the inclusions in the material than the latter. This is because the former contains smaller size of inclusions than the latter. In other words, the large number of the inclusions have little influence when the size of the inclusion is small as in the former case, hardly generating the splashes. In the melting methods in vacuum or in the air, so many inclusions having a size of more than 20 &mgr;m are formed that they serve as trigger points of splash generation.

[0039] Nitrogen concentration in the Al or Al alloy sputtering target material becomes high when nitrogen gas is used for the atomizing gas in the atomizing step of the spray forming method in manufacturing the Al or Al alloy sputtering target material by the spray forming method. The Al or Al alloy thin film for the Al electrode, manufactured by sputtering using the sputtering target material containing a high concentration of nitrogen as described above, naturally contains a high concentration of nitrogen, showing high specific resistivity by being influenced by included nitrogen. When the Al alloy thin film is formed using a sputtering target material comprising an Al—Ti alloy (Al alloy containing Ti) for example, electrical resistivity of the Al thin film becomes higher as the nitrogen concentration in the sputtering target obtained is higher as shown in FIG. 7. Accordingly, a lower nitrogen concentration in the Al or Al alloy sputtering target material is preferable from the view point of specific resistivity of the Al or Al alloy sputtering target material, a content of 0.1 mass % or less being desirable.

[0040] The upper limit of the nitrogen concentration was set to 0.1 mass % or less because a material having resistivity comparable to that of the material containing 0% of nitrogen is urgently desired from the view point of suppressing increase of specific resistivity due to increase of the nitrogen concentration.

[0041] Accordingly, the inventors of the present invention have carried out intensive studies for developing the technology by which the nitrogen concentration of the Al or Al alloy sputtering target material obtained can be reduced especially to 0.1 mass % or less when nitrogen gas is used for the atomizing gas in the gas atomizing step of the spray forming method. It was found from the results of the investigation that, when the ratio of the gas flow volume (Nm3)/molten liquid flow mass (kg), or the ratio of nitrogen gas flow volume Nm3)/molten liquid flow mass (kg), is adjusted to 10 Nm3/kg or more, an Al or Al alloy sputtering target material containing 0.1 mass % or less of nitrogen can be obtained.

[0042] The size (the maximum length) of all the inclusions is 10 &mgr;m or less in the Al or Al alloy sputtering target material obtained by the method as hitherto described, hardly generating the splashes during sputtering since the material was obtained by the manufacturing method having basically the same construction as that of the manufacturing method according to the present invention.

[0043] Accordingly, the Al or Al alloy sputtering target material in which the size (the maximum length) of all the inclusions is 10 &mgr;m or less along with containing 0.1 mass % or less of nitrogen can be obtained when nitrogen gas is used for the atomizing gas in the gas atomizing step of the spray forming method for producing the Al or Al alloy sputtering target material, wherein the ratio of the gas flow volume (Nm3)/molten liquid mass (kg) is adjusted to 10 Nm3/kg or more. The splashes are hardly generated during sputtering in the Al or Al alloy sputtering target material obtained by the method as described above, making it possible to form the Al or Al alloy thin film having low specific resistivity.

[0044] When the ratio of the gas flow volume (Nm3)/molten liquid flow mass (kg), or the nitrogen gas flow volume (Nm3)/molten liquid flow mass (kg), in the gas atomizing step is adjusted to 10 Nm3/kg or more, the Al or Al alloy sputtering target material containing 0.1 mass % or less of nitrogen can be obtained by using nitrogen gas for the atomizing gas in the gas atomizing step of the spray forming method as hitherto described. This is because, after allowing droplets (molten or semi-molten small particles) to deposit on the bottom floor or in the mold, the droplets are quickly solidified by nitrogen gas, hardly inducing a reaction between Al and N to reduce the amount of nitride formed.

[0045] When the ratio of the nitrogen gas flow volume (Nm3)/molten liquid flow mass (kg) described above is less than 10 Nm3/kg, cooling of the droplets deposited on the bottom floor or in the mold, especially at the center of the deposit (deposited layer of the droplets) becomes insufficient, making the reaction of Al with N relatively easy to form a lot of nitride by the reaction, thereby increasing the nitrogen concentration in the Al or Al alloy sputtering target material obtained to more than 0.1 mass %.

[0046] The maximum length of the inclusion refers to the length of the largest part in the inclusion in the present invention. For example, the maximum length corresponds to the diameter when the inclusion assumes a spherical shape or to the maximum side length when the inclusion assumes a nearly rectangular shape. The term that the maximum length of all the inclusions is 20 &mgr;m or less means that all the inclusions in the material have a maximum length of 20 &mgr;m or less.

[0047] The flow mass of the molten liquid in the gas atomizing step of the spray forming method refers to a mass of the molten liquid per unit time flowing out of the molten liquid exit of the vessel containing the molten liquid. The gas flow volume in the step refers to the volume per unit time flowing out of the gas exit of the atomizing gas source for gas atomizing the flowing molten liquid.

[0048] The ratio of the gas flow volume (Nm3)/molten liquid flow mass (kg) in the gas atomizing step of the spray foing method refers to the ratio between the gas flow volume and molten liquid flow mass when the molten liquid flow mass is expressed by kg/unit time and the gas flow volume is expressed by Nm3/unit time, or the ratio of the gas flow volume (Nm3/unit time)/molten liquid flow mass (kg/unit time). The definition of the unit time should be the same in the expression of the molten liquid flow mass and gas flow volume. The gas flow volume (Nm3)/molten liquid flow mass (kg) described above is also referred to the gas/metal ratio.

[0049] For example, when the gas flow volume is 40 Nm3/min and the molten liquid flow mass is 4 kg/min, the ratio of the gas flow volume (Nm3)/molten liquid flow mass (kg) is expressed by 40 (Nm3/min)/4 (kg/min) or 40 (Nm3)/4 (kg), or 10 Nm3/min.

EXAMPLES

Example 1 to 3

[0050] An Al—Nd alloy containing 2 at % (atomic percentage) of Nd (Al—Nd (2 at %) alloy) was melted and a ingot was made using the alloy by the spray forming method. The molten liquid of the Al—Nd (2 at %) alloy was subjected to gas atomization to deposit in the mold, thereby obtaining a ingot of the Al—Nd (2 at %) alloy. Nitrogen gas was used as the atomizing gas in the gas atomizing step of the spray forming method. The ratios of the nitrogen gas flow volume (Nm3)/molten liquid mass (kg) were adjusted to 6 Nm3/kg, 10 Nm3/kg or 15 Nm3/kg, respectively, in the gas atomizing step of the spray forming method. The method for making the ingot of the Al—Nd (2 at %) alloy (the sputtering target material) described above corresponds to the production method in the present embodiment.

[0051] After forging and rolling of the ingot, a disk of the sputtering target material of the Al—Nd (2 at %) alloy with a diameter of 4 inches was manufactured by machining.

[0052] The size (the maximum diameter) of the inclusion and oxygen content, as well as the frequency of generation of the splashes, were investigated with respect to the sputtering target material of the Al—Nd (2 at %) alloy fabricated as described above.

[0053] Samples for microscopic measurement of the size of the inclusions were taken from the sputtering target material and, after polishing the samples, were observed under an optical microscope to measure the size of the inclusion. Oxygen content was determined by gas analysis of the sample taken from the sputtering target material.

[0054] For the purpose of investigating the frequency of splash generation, the sputtering target material was subjected to sputtering for 1 hour under the sputtering conditions listed in FIG. 1. After forming a thin film of the Al—Nd (2 at %) alloy on the substrate, the surface of this thin film was observed under an optical microscope to count the number of the splashes having a size (the maximum length) of 10 &mgr;m or more, since the splash having a size of 10 &mgr;m or more causes a severe problem on the performance of the thin film.

[0055] The results of measurements with respect to the size of the inclusion, oxygen content and the number of splashes having a size of 10 &mgr;m or more are listed in FIG. 2.

[0056] It was shown in FIG. 2 that all the sizes of the inclusions were 20 &mgr;m or less in Examples 1 to 3. The maximum length of the inclusion in the Al—Nd (2 at %) sputtering target material, obtained by adjusting the ratio of the nitrogen gas flow volume (Nm3)/molten liquid mass (kg) to 6 Nm3/kg, was 16 &mgr;m, the maximum length of the inclusion in the Al—Nd (2 at %) sputtering target material, obtained by adjusting the ratio of the nitrogen gas flow volume (Nm3)/molten liquid mass (kg) to 10 Nm3/kg, was 8 &mgr;m, and the maximum length of the inclusion in the Al—Nd (2 at %) sputtering target material, obtained by adjusting the ratio of the nitrogen gas flow volume (Nm3)/molten liquid mass (kg) to 15 Nm3/kg, was 4 &mgr;m. These Al—Nd (2 at %) sputtering target materials refer to the sputtering target material according to Example 1, the sputtering target material according to Example 2 and the sputtering target material according to Example 3, respectively, in the order of the above description hereinafter.

[0057] The numbers of splashes having a size (the maximum length) of 10 &mgr;m or more were 10, 5 and 3 in the sputtering target materials according to Example 1, Example 2 and Example 3, respectively. The frequencies of slush generation with a size of 10 &mgr;m or more that adversely affect the performance of the thin film were very small in Examples 1 to 3. When the number of the splashes having a size of 10 &mgr;m or more is adjusted to 10 or less, a significant technical achievement that allows the problem of making the wiring width very fine to be solved would be attained.

Comparative Example 1

[0058] A disk shaped Al—Nd (2 at %) sputtering target material (referred to the sputtering target material according to Comparative Example 1 hereinafter) with a diameter of 4 inches was manufactured by machining after melting the Al—Nd (2 at %) alloy in the air followed by casting and rolling.

[0059] The maximum length of the inclusion and other characteristics in the sputtering target material according to Comparative Example 1 were investigated by the same method as in Examples 1 to 3. The results are listed in FIG. 2. It is evident from FIG. 2 that the maximum length of the inclusion in the sputtering target material according to Comparative Example 1 was 60 &mgr;m, along with showing the number of the splashes with a size of 10 &mgr;m or more of as large as 54.

Comparative Example 2

[0060] A disk shaped Al—Nd (2 at %) sputtering target material (referred to the sputtering target material according to Comparative Example 2 hereinafter) with a diameter of 4 inches was manufactured by machining after melting the Al—Nd (2 at %) alloy in vacuum followed by casting and rolling.

[0061] The maximum length of the inclusion and other characteristics in the sputtering target material according to Comparative Example 2 were investigated by the same method as in Examples 1 to 3. The results are listed in FIG. 2. It is evident from FIG. 2 that the maximum length of the inclusion in the sputtering target material according to Comparative Example 2 was 30 &mgr;m, along with showing the number of the splashes with a size of 10 &mgr;m or more of as large as 25.

[0062] The results in Comparative examples 1 and 2 clearly shows that the size of all the inclusions can not be adjusted to 20 &mgr;m or less when the alloy is melted in the air or in vacuum.

Comparative Example 3

[0063] A disk shaped (4 inches in diameter) Al—Nd (2 at %) alloy sputtering target material (referred to the sputtering target material according to Comparative Example 3 hereinafter) was manufactured by the same method in Examples 1 to 3, except that the ratio of the nitrogen gas flow volume (Nm3)/molten liquid flow mass (kg) in the gas atomizing step of the spray forming method was adjusted to 4 Nm3/kg as shown in FIG. 2.

[0064] The maximum length of the inclusion and other characteristics in the sputtering target material according to Comparative Example 3 were investigated by the same method as in Examples 1 to 3. The results are listed in FIG. 2. It is evident from FIG. 2 that the maximum length of the inclusion in the sputtering target material according to Comparative Example 3 was 25 &mgr;m, along with showing the number of the splashes with a size of 10 &mgr;m or more of as large as 20.

Example 4

[0065] An Al—Nd (2 at %) alloy sputtering target material was manufactured by the same method as in Examples 1 to 3. The ratio of the nitrogen gas flow volume (Nm3)/molten liquid flow mass (kg) in the gas atomizing step of the spray forming method was used as variable parameters in order to allow the maximum length of the inclusion in the sputtering target material to change.

[0066] The maximum length of the inclusion and the number of splashes having a size of 10 &mgr;m or more generated during sputtering in the sputtering target material described above were investigated by the same method as in Examples 1 to 3. The relation between the maximum length of the inclusion and the number of splashes with a size of 10 &mgr;m or more, obtained based on the investigations above, is shown in FIG. 6.

[0067] It can be seen from FIG. 6 that, while the number of splashes with a size of 10 &mgr;m or more rapidly increases as the maximum length of the inclusion is increased in the region where the maximum length of the inclusion is more than 20 &mgr;m, little number of splashes with a size of 10 &mgr;m or more are found in the region where the maximum length of the inclusion is 20 &mgr;m or less, indicating that splashes are hardly generated.

[0068] Although the results as hitherto described in Examples 1 to 4 and in Comparative Example 3 are obtained by using nitrogen gas as the atomizing gas in the gas atomizing step of the spray forming method, the same results can be obtained when other atomizing gases such as argon gas are used instead of nitrogen gas.

Examples 5 to 7

[0069] An Al—Ti alloy (Al alloy containing Ti) was melted to make a ingot by the spray forming method. Nitrogen gas was used as the atomizing gas in the gas atomizing step of the spray forming method. The ratios of the nitrogen gas flow volume (Nm3)/molten liquid flow mass (kg) in this gas atomizing step were changed to 14.3 Nm3/kg, 12.9 Nm3/kg and 10.0 Nm3/kg as shown in FIG. 3.

[0070] The content of nitrogen (nitrogen concentration) in the ingot above was measured by nitrogen gas analysis of the samples taken from the ingot for the nitrogen gas analysis sample. After forging and rolling of the ingot, a disk of the sputtering target material of the Al—Ti alloy with a diameter of 4 inches was manufactured by machining. Next, a thin film of the Al—Ti alloy was formed on the substrate by sputtering under the sputtering condition shown in FIG. 4 using the sputtering target material described above. After a conventional heat treatment, the electric resistivity of this thin film was measured. The thin film was processed by photolithography as a resistivity measuring pattern with a dimension of 100 &mgr;m in width and 10 &mgr;m in length and specific resistivity was measured by a four point probe method. The results of measurements are shown in FIG. 3. The nitrogen contents were as low as 0.015, 0.018 and 0.027 mass %, respectively, all being 0.1 mass % or less, allowing the increase of the electrical resistivity ascribed to respective nitrogen contents (0.1 mass % or less) to be suppressed below 0.11 &mgr;&OHgr;.cm, 0.13 &mgr;&OHgr;.cm and 0.20 &mgr;&OHgr;.cm.

Examples 8 and 9

[0071] An Al—Ti alloy was melted to make an ingot by the spray forming method. Nitrogen gas was used as the atomizing gas in the gas atomizing step of the spray forming method. The ratios of the nitrogen gas flow volume (Nm3)/molten liquid flow mass (kg) in this gas atomizing step were changed to 14.3 Nm3/kg and 10.0 Nm3/kg as shown in FIG. 3.

[0072] The content of nitrogen in the ingot in Examples 8 and 9 was measured by the same method as in Examples 5 to 7. The results of measurements are shown in FIG. 3. The nitrogen contents were as low as 0.012 and 0.020 mass %.

[0073] While a smaller nitrogen content is preferable for reducing electrical resistivity, the nitrogen content will be discussed in Reference examples 1 to 4 below.

Reference Examples 1 and 2

[0074] Al—Ti alloy ingot were made by the same method as in Examples 5 to 7, except that the ratios of the nitrogen gas flow volume (Nm3)/molten liquid flow mass (kg) were adjusted to 8.88 and 8.93 Nm3/kg as shown in FIG. 3.

[0075] Nitrogen contents of the ingot in Reference Example 1 and 2 were measured by the same method as in Examples 5 to 7. The results of the measurements are shown in FIG. 3. The nitrogen contents in respective samples are 0.13 and 0.41 mass %, all exceeding 0.1 mass %.

Reference Examples 3 and 4

[0076] Al—Ti alloy ingots were made by the same method as in Examples 8 and 9, except that the ratios of the nitrogen gas flow volume (Nm3)/molten liquid flow mass (kg) were adjusted to 9.0 and 8.9 Nm3/kg as shown in FIG. 3.

[0077] Nitrogen contents of the ingots in Reference Example 3 and 4 were measured by the same method as in Examples 5 to 7. The results of the measurements are shown in FIG. 3. The nitrogen contents in respective samples are 0.11 and 0.33 mass %, all exceeding 0.1 mass %.

Example 10

[0078] An Al alloy sputtering target material was manufactured by the same method as in Examples 1 to 3 by using an Al—Ti alloy instead of the Al—Nd alloy as the Al alloy. The ratio of the nitrogen gas flow volume (Nm3)/molten liquid flow mass (kg) in the gas atomizing step of the spray forming method was used as variable parameters in order to allow the nitrogen content in the sputtering target material to change.

[0079] A thin film of the Al—Ti alloy was formed on the substrate by sputtering under the sputtering condition shown in FIG. 4 using the sputtering target material described above. After a conventional heat treatment, the electric resistivity of this thin film was measured. The thin film was processed by photolithography as a resistivity measuring pattern with a dimension of 100 &mgr;m in width and 10 &mgr;m in length and specific resistivity was measured by a four point probe method.

[0080] The nitrogen content in the sputtering target material according to Example 10 was measured by the same method as in Examples 5 to 7.

[0081] The relation between the nitrogen content in the sputtering target material and electrical resistivity of the thin film obtained was determined based on the results of measurements described above. The results are shown in FIG. 7. FIG. 7 shows that the electrical resistivity of the Al alloy thin film formed becomes smaller as the nitrogen content in the sputtering target material is lower.

[0082] While the results as hitherto described are obtained by using the Al—Nd alloy and Al—Ti alloy as the Al alloy in Examples 1 to 10, Comparative examples 1 to 3 and Reference Examples 1 to 4, the same tendency may be obtained using Al—Ta, Al—Fe, Al—Co, Al—Ni and Al—REM (rare earth metal) alloys instead of these Al alloys.

[0083] While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and the scope thereof.

[0084] The entire disclosure of Japanese Patent Application No. 10-40520 filed on Feb. 23, 1998 including specification, claims, drawings and summary are incorporated herein by reference in its entirety.

Claims

1. A method for manufacturing an aluminum or aluminum alloy sputtering target material comprising aluminum or aluminum alloy containing inclusions having a maximum length of 20 &mgr;m, wherein the ratio of the gas volume (Nm3)/the liquid mass (kg) is 5 Nm3/kg or more in a spray forming method including the step of obtaining an aluminum or aluminum alloy ingot by a gas atomizing step of a molten liquid having aluminum or aluminum alloy.

2. A method for manufacturing an aluminum or aluminum alloy sputtering target material according to

claim 1, wherein the ratio of the gas volume (Nm3)/the liquid mass (kg) is adjusted to be 10 Nm3/kg or more.

3. A method for manufacturing an aluminum or aluminum alloy sputtering target material according to

claim 2, wherein nitrogen gas is used for atomizing gas in the gas atomizing step.

4. A method for manufacturing an aluminum or aluminum alloy sputtering target material comprising aluminum or aluminum alloy containing inclusions having a maximum length of 20 &mgr;m comprises:

melting an material having aluminum or aluminum alloy ingot into a liquid flow;

atomizing a gas flow;

spraying the liquid flow onto a surface by means of said gas flow, wherein the ratio of the gas flow volume (Nm3)/the liquid flow mass (kg) is 5 Nm3/kg or more; and

depositing on said surface an aluminum or aluminum alloy sputtering target material comprising aluminum or aluminum alloy containing inclusions having a maximum length of 20 &mgr;m.

5. A method for manufacturing an aluminum or aluminum alloy sputtering target material according to

claim 4, wherein the ratio of the gas flow volume (Nm3)/the liquid flow mass (kg) is adjusted to be 10 Nm3/kg or more.

6. A method for manufacturing an aluminum or aluminum alloy sputtering target material according to

claim 5, wherein nitrogen gas is used for the gas flow.

7. A method for manufacturing an aluminum or aluminum alloy sputtering target material comprising aluminum or aluminum alloy containing inclusions having a maximum length of 10 &mgr;m comprises:

melting an material having aluminum or aluminum alloy ingot into a liquid flow;

atomizing a gas flow;

spraying the liquid flow onto a surface by means of said gas flow, wherein the ratio of the gas flow volume (Nm3)/the liquid flow mass (kg) is 5 Nm3/kg or more; and

depositing on said surface an aluminum or aluminum alloy sputtering target material comprising aluminum or aluminum alloy containing inclusions having a maximum length of 10 &mgr;m.

8. A method for manufacturing an aluminum or aluminum alloy sputtering target material according to

claim 7, wherein the ratio of the gas flow volume (Nm3)/the liquid flow mass (kg) is adjusted to be 10 Nm3/kg or more.

9. A method for manufacturing an aluminum or aluminum alloy sputtering target material according to

claim 8, wherein nitrogen gas is used for the gas flow.