WO2006041989A2

WO2006041989A2 - Sputtering target and method of its fabrication

Info

Publication number: WO2006041989A2
Application number: PCT/US2005/035940
Authority: WO
Inventors: Toshio Inase; Shunsuke Yatsumani; Eugene Y. Ivanov; Ronald G. Jordan
Original assignee: Tosoh Smd, Inc.; Tosoh Corporation
Priority date: 2004-10-05
Filing date: 2005-10-04
Publication date: 2006-04-20
Also published as: WO2006041989A3; TW200623242A

Abstract

Disclosed is a sputtering target that may be used to provide an electrode for FPD devices. The electrode for semiconductor devices is made of an aluminum-based alloy containing one or more alloying elements selected from rare earth alloying elements present in a total amount from 0.01 to 3 at %. The method of fabricating a target includes the steps of continuous casting with electromagnetic stirring, in which the elements mentioned above are dissolved in an A1 matrix, and precipitating part or all of the elements dissolved in the A1 matrix as intermetallic compounds during solidification. The target is made of an aluminum-based alloy containing the above elements by thermo mechanical fabrication, rolling or extrusion process.

Description

SPUTTERING TARGET FOR FORMING ELECTRODE FILM FOR SEMICONDUCTOR DEVICES AND METHOD OF ETS FABRICATION

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the priority benefit of U.S. Provisional Patent

Application Serial No. 60/616,016 filed October 5, 2004.

BACKGROUND OF THE INVENTION Field of Invention

[0002] The present invention relates to a sputtering target for forming an electrode for semiconductor devices, its fabrication method, and particularly to an aluminum-based alloy sputtering target and its fabrication method.

Description of Related Art

[0003] Liquid crystal displays (hereinafter, referred to as an "LCD") are thinner, lighter and more energy efficient when compared to conventional displays using a cathode-ray tube. To improve the image quality, LCDs use a thin film transistor (hereinafter, referred to as "TFT") as a switching element. Here, the TFT is composed of a semi-conducting film having an electrode made of a thin metal film, typically an aluminum based alloy. In the TFT, the interconnections and the electrode are electrically connected to each other. The aluminum-based alloy films are typically deposited on glass, silicon and silicon with Siθ2 layer substrates by DC magnetron sputtering.

[0004] Various properties are required for a semiconductor device electrodes that are used for the LCD mentioned above. First, decreasing the resistivity of the electrode is important for suppressing signal delay. For example, in large colored LCDs, the resistivity (electrical resistance) of the electrode for semiconductor devices should be lower than 20 μΩcm, preferably lower than 3.5 μ.Ωcm.

[0005] The electrode material for semiconductor devices having a low resistivity may include Ag, Au, Cu and Al. For example, Al thin-film metallization has been used for interconnection conductors in silicon integrated circuit (IC) microfabrication. However, Al is insufficient in thermal stability, and has a disadvantage in generating hillocks on the surface of an electrode film during a heating process in the TFT fabrication process, after deposition of the electrode film.

[0006] To reduce hillocks growth on an Al electrode film, some studies have indicated that an aluminum-based alloy film can be used instead of Al. An aluminum-based alloy film, especially containing one or more rare earth elements (hereinafter, referred to as "REM") has excellent thermal stability and therefore exhibits low hillock growth during heating after deposition to form an electrode film. As a result of the improved thermal stability, fewer hillocks are generated on the aluminum based alloy film during heating after deposition. For that reason, some studies have suggested that Al-REM alloy sputtering targets should be used to form the Al-REM alloy film. For example, such aluminum-based alloys typically have been produced by means of powder metallurgy processes of the Al-REM alloy. However, target materials formed by powder metallurgy processes have high levels of oxygen, for example greater than 1000 ppm, and this results in increasing the resistivity of the film formed by such targets. Another process of making Al-REM alloy is by the melting process. But Al-REM alloy targets formed by ordinary melting process usually do not have uniform microstructure. This causes unstable sputtering performance that, in tarn, results in non-uniform sputtering rates and film composition during the sputtering process. [0007] Accordingly, there is a need to provide a sputtering target for forming an electrode material for LSI semiconductor devices that inhibits the generation of hillocks in and reduces the resistivity (i.e., lower than 20 μΩcm) of the electrode.

SUMMARY OF THE INVENTION

[0008] One aspect of the present invention pertains to a sputtering target for an electrode for semiconductor devices with fewer tendencies to generate hillocks and having a resistivity lower than 20 μΩ cm. Another aspect of the present invention pertains to a method of fabricating the sputtering target that is used to form an electrode for semiconductor devices as mentioned above. Still another aspect of the present invention pertains to an aluminum-based alloy which is suitable to produce said sputtering target. [0009] Accordingly, one exemplary embodiment of the invention pertains to a sputtering target for producing an electrode for semiconductor devices and to fabrication methods for making the sputtering target and to the electrode that is formed via PVD from the target.

[0010] According to one embodiment of the invention, a sputtering target for an electrode for semiconductor devices is made of an aluminum-based alloy containing one or more alloying elements selected from the group of rare earth elements in total amount below 3 at% . When the contents of alloying elements of target are more than 3 at % , the resistivity of the resulting film increases to an undesirable level, The contents of alloying elements in the target are preferably from trace to less than 1 at% , more preferably less than 0.5 at% . [0011] According to one embodiment of the invention, a sputtering target for an electrode for semiconductor devices contains less than 100 ppm oxygen. When the oxygen content in the target is more than 100 ppm, the resistivity of the film increases to an undesirable level.

[0012] According to one embodiment of the invention, a sputtering target for an electrode for semiconductor devices has a microstructure comprising areas of aluminum grains and boundary areas of a coexistent state that includes an aluminum phase and an aluminum-additive phase. According to the present invention, said sputtering target has an aluminum grain size of greater than 10 micrometers and less than 500 micrometers. A sputtering target having a large grain size over 500 micrometers exhibits unstable sputtering performance, which results in an unstable sputtering rate and non-uniform composition of the film made during sputtering. Preferably, sputtering targets in accordance with the present invention have aluminum grain sizes of less than 200 micrometers. According to the present invention, the boundary areas composed at the coexistent state have widths of less than 30 micrometers, preferably less than 10 micrometers. When the width of boundary areas of coexistent state are over 30 micrometers, the microstructure of target does not have a uniform phase and the performance of the target during sputtering becomes unstable. [0013] According to another embodiment of the invention, an aluminum-based alloy for the target mentioned above contains one or more alloying elements selected from the group of rare earth elements present in total amount below 3 at%, preferably from trace to less than 1 at%, more preferably less than 0.5 at%. In the present invention, said aluminum-based alloy for the target contains less than 100 ppm oxygen. In one exemplary embodiment, the aluminum-based alloy for the target has an aluminum grain size of less than 500 micrometers, preferably less than 200 micrometers. In one embodiment, the aluminum-based alloy for the target has boundary areas of less than 30 micrometers in size, preferably less than 10 micrometers.

[0014] According to another embodiment of the invention, the aluminum based alloy mentioned above is made by a continuous casting method using electromagnetic stirring

(hereinafter, referred to as "EMS"). The aluminum-based alloy sputtering target in this aspect of the invention is made from the aluminum-based alloy that has been produced via the

EMS method.

[0015] According to another embodiment of the invention, a sputtering target for an electrode for semiconductor devices comprising aluminum and one or more alloying elements selected from the group of rare earth elements is provided, wherein the surface roughness

(Ra) of erosion area of said Al alloy sputtering target after initial discharge of 15 Wh/cm² is less than 1.5 micrometers.

[0016] According to another embodiment of the invention, an electrode for a TFT of an LCD exhibits lower hillock growth and has a resistivity of less than 20 μΩcm when produced by use of sputtering target in this invention.

[0017] These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above mentioned and other features of this invention will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0019] FIG. 1 shows a schematic diagram of a method of making an aluminum-based alloy film;

[0020] FIG. 2 shows the appearance and the microstructure of a cast Al-Nd ingot produced by electromagnetic stirring: (a) and (b) are the ingot cross sections (the length of the bar attached in the figure represents 12 mm), (c) is a magnified view of the microstructure of the ingot (the length of the bar attached in the figure represents 50 micrometers), (d) is a magnified SEM image of Nd rich area (i.e., a boundary area of the coexistent state) in (c) (the length of the bar attached in the figure represents 5 micrometers), (e) is another SEM image of the microstructure of the Al-Nd ingot (the length of the bar attached in the figure represents 10 micrometers), (f) is a magnified SEM image of Nd rich area (a boundary area of coexistent state) in (e) (the length of the bar attached in the figure represents 2 micrometers);

[0021] FIG. 3 shows the microstructure of a rolled aluminum-based alloy target:

(a) is a SEM image of the alloy target of transverse view with respect to the sputtering surface (the length of the bar attached in the figure represents 10 micrometers), (b) is a SEM image of the alloy target of normal view with respect to the sputtering surface (the length of the bar attached in the figure represents 10 micrometers), (c) is another SEM image of the alloy target material (the length of the bar attached in the figure represents 50 micrometers), (d) is a magnified SEM image of Nd rich area (a boundary area of coexistent state) in (c) (the length of the bar attached in the figure represents 2 micrometers);

[0022] FIG. 4 shows the appearance and the microstructure of Al-Nd ingot produced by ordinary melting process; (a) and (b) are the ingot cross sections (the length of the bar attached in the figures represents 12 mm), (c) is a magnified view of the microstructure (the length of the bar attached in the figure represents 200 micrometers), (d) is another SEM image of the microstructure of the Al-Nd ingot (the length of the bar attached in the figure represents 200 micrometers).

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS [0023] The invention will now be described in the following detailed description with reference to the drawings, wherein preferred embodiments are described in detail to enable practice of the invention. Although the invention is described with reference to these specific preferred embodiments, it will be understood that the invention is not limited to these preferred embodiments. But to the contrary, the invention includes numerous alternatives, modifications and equivalents as will become apparent from consideration of the following detailed description.

[0024] FIG. 1 schematically illustrates a process of making an aluminum-based alloy sputtering target and a process of making an electrode firm by sputtering an aluminum-based alloy target. According to one embodiment of the invention, an aluminum-based master alloy, indicated at 12, containing aluminum 14 and at least one rare earth metal (REM) indicated at 16 is produced using a continuous casting process. The aluminum-based alloy is described below as an Al-Nd alloy, but it is to be understood that other REM and combinations of REMs may be used in the aluminum-based alloy without departing from the scope of the invention. For example, the alloy may contain one, two, or more additives selected from the group of rare earth elements. As used in this application, REM is intended to include yttrium (Y), as well as the lanthanoid elements. The lanthanoid elements contain elements from La, of atomic number 57, to Lu, of atomic number 71, in the periodic table. The casting process can be a true continuous casting method or a semi-continuous method without departing from the scope of the invention. While REMs are preferred additives, it also should be understood that additional elements, such as Cu, Si, Ni, Zn, can also be used to improve alloy film properties such as contact resistance and electrochemical properties of the alloy and film made of such an alloy.

[0025] Referring to the schematic diagram of the process in FIG. 1, the master alloy

12 is produced by melting high purity Al 14 in high vacuum. Nd 16 is then systematically added to obtain a master Al-Nd alloy ingot 12 having a composition between about 5 and about 50 wt% Nd. This alloy 12 serves as a master alloy for continuous casting. Additional pure aluminum 18 is melted in the furnace under Ar at between about 700-730⁰C. Then, master Al-Nd ingots are added to achieve the desired final alloy composition indicated at 20. The final aluminum-based alloy 20 suitably contains Nd less than 3 at%, more preferably less than 1.0 at%, and even more desirably less than 0.5 at%. It is desirable that the atmosphere be controlled as would be understood by one skilled in the casting art. Desirably, the material is again rotary fluxed with Ar to degas the material and is continuously degassed within the Ar atmosphere during the casting process. The aluminum-based alloy 20 suitably has an oxygen content of less than 100 ppm oxygen.

[0026] As illustrated in the embodiment illustrated in FIG. 1, the alloy 20 is cast using a direct-chill (DC) casting method 22. A suitable electromagnetic stirring (EMS) machine 24 is used during the solidification phase of casting. The casting is enhanced by single-phase electromagnetic vibrations just prior to casting ring containing sufficient amount of turns per coil. Suitable electromagnetic stirring current is between about 100 and 600 A. Casting conditions and tooling design are adjusted to promote favorable stirring by strategic placement of the mushy zone within the highest magnetic field area. [0027] The microstructure of the metal is controlled by the magnetic field intensity and oscillation pattern of the EMS. Desired properties of the microstructure of the ingot will be set forth in more detail below. Example 1 and FIG. 2 explained below more fully describe the microstructure of the ingot, which is composed of the areas of aluminum grain (areas which contains undetectable or trace of additives by EPMA (Electron Probe Micro Analysis)) and the boundary areas of coexistent state comprising aluminum phase and aluminum-additive phase as shown in FIG. 2 (c) and (e). The microstructure of the preferred aluminum-based alloy ingot shows that the size of the aluminum grains is less Irian 500 micrometers, more preferably less than 200 micrometers. In the aluminum based alloy of this invention, the width of the surrounding boundary areas of coexistent state is less than 30 micrometers, more preferably less than 10 micrometers.

[0028] In rolled or extruded targets, the size of aluminum grains is less than 500 micrometers, more preferably less than 200 micrometers and the width of boundary areas of coexistent state is less than 30 micrometers, more preferably less than 10 micrometers. [0029] A target for use in DC magnetron sputtering is then formed from the aluminum-based alloy billet using a thermomechanical process 26 such as pressing or rolling processes or both. The thermomechanical treatment may also include an appropriate anneal step. In one embodiment, the target is formed by a method of rolling in a roll press starting from an ingot of the aliirninum-based alloy. Other suitable severe deformation mechanical processes such as extrusion may be used without departing from the scope of the invention. The rolling process 26 can be accomplished using methods known to one skilled in the art. Accordingly, specific rolling details will not be provided herein.

[0030] The aluminum-based alloy is then deposited by sputtering at 28 to form an electrode for semiconductor devices. Sputtering can be accomplished using methods known to one skilled in the art. Accordingly, specific sputtering details will not be provided herein. Such an aluminum-based alloy target has an advantage in stabilizing the composition of the deposited aluminum-based alloy film or reducing the oxygen amount compared with typical composite targets. At this time, all or part of the alloying elements in the aluminum-based alloy are in the solid-solution state in the deposited film. The film is then heated or annealed, as shown schematically at 30 in FIG. 1, for about 30 min. to about 1 hour. The annealing temperature is desirably between 150° to 400⁰C. As a result of the heating or annealing process, part or all of the REM dissolved in the Al matrix is precipitated as intermetallic compounds, so that the total volume of the elements in solid-solution, which causes an increase in resistivity, is reduced. Therefore, the aluminum-based alloy film containing RBM can satisfy the requirements of a high thermal stability (high hillock resistance) and a low resistivity before and after the annealing, after deposition. Desirably, the resistivity is reduced to lower than 20 μΩcm. In particular, by utilizing the annealing step as the heat treatment for positively precipitating intermetallic compounds, and adjusting the total volume of the elements dissolved in the Al matrix after the heat-treatment through adjustment of the annealing temperature, the aluminum-based alloy film can satisfy each requirement by selecting the most suitable alloy composition and heating condition.

[0031] Changing the composition of target also changes the composition of the deposited film. It was discovered that hillock resistance was dependent on the concentration of REM and oxygen. The decreasing REM content in the film was accomplished by reducing oxygen in the target, since oxygen in the film lessens the effect of REM in suppressing hillocks.

[0032] Al-REM alloy targets produced by ordinary melting processes usually have a microstructure of large grains and inhomogenity, which result in unstable sputtering performance. This results in non-uniform sputtering rates and film composition during sputtering. Additionally, such targets tend to cause an anomalous discharge resulting in the generation of undesirable particles on the films.

[0033] The aluminum based alloy of this invention which is produced by using electromagnetic stirring has a microstructure of homogeneous and fine grains and has less oxygen, therefore a more stable discharge can be attained during sputtering of targets from the EMS methods and thin films of low resistivity and high hillock resistance can be made. These properties are desirable for electrodes for semiconductor devices. [0034] The present invention will be more clearly understood by way of the following examples which are included for illustrative purposes. Example 1

[0035] A binary aluminum-based alloy was produced by a continuous casting process using electromagnetic stirring. First, pure Al was melted in high vacuum at a temperature greater than 1000⁰C. Then, pure Nd was systematically added to obtain an Al-Nd alloy with a composition ranging between 5 and 50 wt% Nd. This Al-Nd alloy served as a master alloy for continuous casting.

[0036] Prior to continuous casting, the furnace was prepared by melting additional pure Al under Ar, at between 700-730⁰C. Then, the Al-Nd ingots were added to achieve the desired final alloy composition. The material was again rotary fluxed with Ar for degassing, and continuously degassed within the Ar atmosphere during casting. The casting was done by a direct-chill method, enhanced by single-phase electromagnetic vibrations just prior to casting ring.

[0037] As an example, the microstructure of the resulting Al-Nd alloy ingot of Nd content of 0.6 at% is shown in FIG. 2 with photos of different magnifications. FIG. 2 (a) and FIG. 2 (b) show ingot cross sections. FIG. 2 (c) shows the microstructure of typical ingot areas. Darker areas in FIG. 2 (c) represent the boundary areas of coexistent state comprising Al phase and Al-additive phase, while the light gray areas are the areas of Al grains. As shown in FIG. 2 (c), the areas of Al grains are surrounded by the boundary areas of coexistent state, and said boundary areas exist as layers surrounding said areas of Al grains and separating said areas of Al grains from each other. The microstructure of the Al-alloy ingot shows that the size of the Al grains that are surrounded by the boundary areas of the coexistent state is less than 500 micrometers, and the width of the boundary areas is less than 10 micrometers. FIG. 2 (d) shows the magnified SEM image of Nd rich area (a boundary area of coexistent state) in FIG. 2 (c). Black dots in FIG. 2 (d) are Al-Nd phase such as an intermetallic compound, and light gray areas are the Al phase. As shown in FIG. 2 (c), the aluminum-based alloy manufactured by continuous casting with electromagnetic stirring has a microstructure of small and homogeneous grains.

[0038] FIG. 2 (e) is another SEM image of the microstructure of the Al-Nd ingot, and FIG. 2 (f) is a magnified SEM image of Nd rich area (a boundary area of coexistent state) in FIG. 2 (e). Black areas in FIG. 2 (e) are the areas of Al grains and light gray areas are the boundary areas of the coexistent state. Light gray areas in FIG. 2 (f) are the areas of Al-additive phase and darker gray areas are the areas of Al phase.

Example 2

[0039] An Al alloy sputtering target was formed by the method of rolling in a roll press starting from the ingot described in Example 1. As an example, the microstructure of the rolled aluminum-based alloy target of Nd content of 0.6 at% is shown in FIG. 3. The microstructure of the Al alloy sputtering target comprises areas of Al grains and boundary areas of the coexistent state comprising Al phase and Al-additive phase. FIG. 3 (a) shows the magnified SEM image of the Al alloy target of transverse view with respect to the sputtering surface, and FIG 3 (b) shows the magnified SEM image of normal view with respect to the sputtering surface. Dark gray areas in FIG. 3 (a) and FIG. 3 (b) represent the boundary areas of the coexistent state, and light gray areas represent areas of Al grains. FIG. 3 (c) is another SEM image of the microstructure of the Al alloy target, and FIG. 3 (d) is a magnified SEM image of Nd rich area (a boundary area of coexistent state) in FIG. 3 (c). Black areas in FIG. 3 (c) are the areas of Al grains, and light gray areas are the boundary areas of coexistent state. The size of aluminum grains of the sputtering target was greater than 10 micrometers and less than 500 micrometers, and the width of the boundary areas of the coexistent state was less than 30 micrometers. Black areas in FIG. 3 (d) are the areas of Al phase, and light gray areas are the areas of Al-additive phase.

Example 3 Comparative Example 1

[0040] Al alloy sputtering targets of Al-Nd alloy with several compositions were made in the same way as Example 2 (using EMS and rolling). The resulted Al-Nd alloy contained less than 100 ppm oxygen. Sputtering target of Al-Nd alloy with several compositions were also made using atomized Al-Nd alloy powder and hot isostatic press for comparison. The resulted Al-Nd alloy contained about 1000 ppm oxygen (Comparative Example 1). Then Al-Nd alloy films with 200 nm thickness were deposited on glass substrate by DC magnetron sputtering using these targets. [0041] The films were then annealed at 35O⁰C for 1 hour in nitrogen atmosphere.

Then resistivity and hillock density were measured. Resistivity was measured by conventional 4 point probe method. Hillock density was measured as follows :

(1) Taking a picture of the surface of annealed sample using a polarized optical microscope (magnification: X 500).

(2) Counting hillocks (small protrusions on the film) in an area (for example an area of 50 micrometers x 50 micrometers).

(3) Hillock density is calculated from the number of hillocks observed in the area. [0042] Resistivities and hillock densities of the films of Example 3 and Comparative Example 1 are listed in Table 1. It is shown that both resistivities and hillock densities of the films deposited by the targets of Example 3 were lower than those of the films deposited by the targets of Comparative Example 1 which contain more oxygen than those of Example 3. And hillock densities decreased significantly by adding even 0.1 at% Nd.

[0043] Therefore Al-Nd film with sufficiently low resistivity and low hillock density can be obtained by using the Al alloy sputtering target containing oxygen of less than 100 ppm and Nd of less than 0.5 at% .

Table 1

Example 4: Comparative Example 2, Comparative Example 3

[0044] An Al alloy sputtering target was produced using Al-0.6at% Nd-alloy

(3wt%Nd) made by the same manner as Example 2 (using EMS and rolling). The content of oxygen in the Al-Nd alloy target was less than 100 ppm.

[0045] For comparison, a sputtering target of Al-Nd alloy of Nd content of 2.0 at% was produced by an ordinary melting method, where electromagnetic stirring was not applied in the process (Comparative Example 2). The content of oxygen in this target was also less than 100 ppm.

[0046] The microstructure of this target produced by an ordinary melting method is shown in HG. 4. Light gray areas in FIG. 4 (c) represent the areas of Al grains, dark gray areas represent the areas containing Al-additive phase. HG. 4 (d) shows another SEM image of the microstructure of the ingot, where dark areas represent the areas of Al grains, light gray areas represent the areas containing Al-additive phase. The bars attached in FIG.

4 (c) and (d) both represent 200 micrometers shows that the areas of Al grains are much larger than 500 micrometers.

[0047] For further comparison, another sputtering target of Al-Nd alloy of Nd content of 1.8 at% (9 wt%Nd) was produced by means of powder metallurgy, using atomization process of Al-Nd alloy and consolidating atomized Al-Nd alloy powder by means of hot isostatic press (Comparative Example 3). The content of oxygen in this target was about 1000 ppm.

[0048] These three targets were then sputtered and binary aluminum-based alloy films with 200 nm thicknesses were deposited on silicon with SiCh layer substrates with 0.5 mm thickness by DC magnetron sputtering.

[0049] Particles greater than 0.5 micrometers on the deposited Al-Nd alloy films were counted using the laser scanning particle counter. The results are summarized in Table

4.

[0050] When the sputtering target produced by not using EMS is used, the number of the particles on the Al-Nd alloy films was much larger than that of the Example 4 where the sputtering target was manufactured by using electromagnetic stirring. [0051] Furthermore, Table 4 shows that the sputtering target with low oxygen content generates less particles on the Al alloy films, compared to the sputtering target with high oxygen content.

Table 4

Example 5: Comparative Example 4

[0052] Sputtering target of Al-0.2at%Nd-alloy was made by the same manner as

Example 2 (using EMS and rolling). For comparison, another sputtering target of Al-0.2at%Nd-alloy was also made by an ordinary melting method, in which electromagnetic stirring was not applied (Comparative Example 4). Then Al-Nd alloy films with 200 nm thickness were deposited on silicon substrates with 200 mm diameter and 0.5 mm thickness by DC magnetron sputtering using these targets. Prior to the film formation, pre-sputtering of 3 hours (15 Wh/cm²) was performed as an initial discharge for the targets, then the surface roughness of erosion area of the targets was measured.

[0053] After film formation of 200 nm thickness, particles greater than 0.5 micrometers on the deposited film were counted using a laser scanning particle counter. [0054] Results are shown in Table 5. The target produced by using EMS has smoother surface after initial discharge of 3 hours (15 Wh/cm²) and generates fewer particles in the deposition of Al-Nd alloy film compared with the target of Comparative Example 4 produced by an ordinary melting method, in which electromagnetic stirring was not applied. [0055] Large surface roughness (Ra) results in an anomalous discharge because electric field focuses at protrusion on the target .surface. An anomalous discharge during sputtering often causes molten metallic droplets to be ejected from the surface of the sputtering target. Such molten droplets produce particulate defects on the film. Accordingly, the target that has large surface roughness causes particle defects on an LCD panel due to the anomalous discharge.

[0056] Sputtering targets having low surface roughness (i.e., less than about 1.5 micrometers) in the erosion area after discharge can be obtained by using electromagnetic stirring, by which the aluminum-based alloy having a microstructure with homogeneous and fine grains is attained.

Table 5

[0057] As mentioned above, Al alloy sputtering targets consisting of aluminum-based alloy produced by using electromagnetic stirring in this invention have a microstructure of homogeneous and fine grains and have less oxygen, therefore stable discharge can be attained and thin films of low resistivity and high hillock resistance which are necessary for electrodes for semiconductor devices can be obtained. The microstructure of homogeneous and fine grains and less oxygen content also result in the smooth surface of the erosion area of the sputtering target during the deposition process, which suppress the anomalous discharge and reduce the generation of particles in the film deposition.

[0058] While this invention has been described in conjunction with the specific embodiments described above, it is evident that many alternatives, combinations, modifications and variations are apparent to those skilled in the art. Accordingly, the preferred embodiments of this invention, as set forth above are intended to be illustrative only, and not in a limiting sense. Various changes can be made without departing from the spirit and scope of this invention. [0059] What is claimed is :

Claims

1. An Al alloy sputtering target comprising aluminum and one or more alloying elements selected from the group of rare earth elements, wherein said Al alloy sputtering target has a microstructure comprising areas of aluminum grains and boundary areas of a coexistent state comprising aluminum phase and aluminum-additive phase.

2. The Al alloy sputtering target according to claim 1, wherein the total amount of alloying elements in said Al alloy sputtering target is less than 3 at% .

3. The Al alloy sputtering target according to claim 1, wherein said Al alloy sputtering target contains less than 100 ppm oxygen.

4. The Al alloy sputtering target according to claim 1 , wherein the size of said aluminum grains is greater than 10 micrometers and less than 500 micrometers.

5. The Al alloy sputtering target according to claim 1, wherein the width of said boundary areas is less than 30 micrometers.

6. The Al alloy sputtering target according to claim 1, wherein said Al alloy sputtering target is produced by using electromagnetic stirring.

7. An Al alloy sputtering target comprising aluminum and one or more alloying elements selected from the group of rare earth elements, wherein the surface roughness (Ra) of erosion area of said Al alloy sputtering target after initial discharge of 15 Wh/cm² is less than 1.5 micrometers.

8. The Al alloy sputtering target according to claim 7, wherein the total amount of alloying elements in said Al alloy sputtering target is less than 3 at% .

9. The Al alloy sputtering target according to claim 7, wherein said Al alloy sputtering target contains less than 100 ppm oxygen.

10. Aluminum based alloy for producing sputtering targets, wherein said aluminum based alloy contains one or more alloying elements selected from the group of rare earth elements, and said aluminum based alloy has a microstructure comprising areas of aluminum grains and boundary areas of a coexistent state comprising aluminum phase and aluminum-additive phase.

11. The aluminum based alloy according to claim 10, wherein the total amount of alloying elements in said aluminum based alloy is less than 3 at% .

12. The aluminum based alloy according to claim 10, wherein said aluminum based alloy contains less than 100 ppm oxygen.

13. The aluminum based alloy according to claim 10, wherein said aluminum grains in said aluminum based alloy have a size greater than 10 micrometers and less than 500 micrometers.

14. The aluminum based alloy according to claim 10, wherein the width of said boundary areas in said aluminum based alloy is less than 30 micrometers.

15. The aluminum based alloy according to claim 10, wherein said aluminum based alloy is produced by using electromagnetic stirring.

16. An electrode for semiconductor devices produced by sputtering of an Al alloy sputtering target comprising aluminum and one or more alloying elements selected from the group of rare earth elements, wherein said Al alloy sputtering target has a microstructure comprising areas of aluminum grains and boundary areas of a coexistent state comprising aluminum phase and aluminum-additive phase.

17. The electrode for semiconductor devices according to claim 16, wherein said semiconductor devices are thin film transistors used in flat panel displays.

18. The electrode for semiconductor devices according to claim 16, wherein total amount of alloying elements in said Al alloy sputtering target is less than 3 at% .

19. The electrode for semiconductor devices according to claim 16, wherein said Al alloy sputtering target contains less than 100 ppm oxygen.