JP2002069626A - Sputtering target and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sputtering target capable of dissolving the non-uniformity of thickness by variation and the like of voltage in sputtering, when forming an electrode film by sputtering method. SOLUTION: Copper and aluminum are blended to form a mixture containing 2.5 wt.% copper and the balance aluminum, and it is charged into a crucible, melted and cast to produce an ingot. The obtained ingot is homogenized, and thereafter cooled, that is, this ingot is, after chamfering, cold-worked so that the ratio of cold-working, namely, the diminishing ratio of cross section by cold-working, is 60% or above. The obtained worked material is annealed, in a flow of argon, at the same temperature or a little higher temperature than it as the maximum arriving temperature of the target, when the maximum arriving temperature of the target is over 350 deg.C in sputtering, and at 350 deg.C or above when the maximum arriving temperature of the target is below 350 deg.C in sputtering, and thereafter is quickly cooled to produce the sputtering target.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sputtering target made of an aluminum alloy used for forming an electrode of an electronic component and a method of manufacturing the same.

[0002]

2. Description of the Related Art In an electronic component such as a surface acoustic wave device, an electrode is formed by evaporating aluminum on the element or by sputtering. The aluminum film formed in this way is lightweight and has good electric characteristics and is suitable as an electrode material, but has a drawback of causing a temporal change due to repeated stress. To eliminate this drawback,
An electrode was formed by forming a film obtained by adding 50% by weight or less of copper or the like to aluminum.

[0003]

In recent years, with the progress of miniaturization and higher precision of electronic components, electrodes used in these components are required to have higher processing accuracy. That is, in an electronic component such as a surface acoustic wave device, the resonance frequency is affected by the thickness of the electrode, and it is very important how to obtain an electrode film having a constant and uniform thickness. From this point, the sputtering method is recommended over the vapor deposition method,
Even with the sputtering method, it is not possible to sufficiently eliminate the non-uniformity of the thickness due to the fluctuation of the voltage or the like during the sputtering, and it cannot be said that sufficient film thickness control is always performed.

An object of the present invention is to provide a sputtering target which can solve the above-mentioned problems of the prior art when forming an electrode film by a sputtering method and which can control the film thickness with high accuracy.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an aluminum alloy target containing 2 to 5% by weight of Cu and the balance substantially consisting of aluminum. An aluminum alloy sputtering target having a crystal grain size of 100 μm or less.

In another embodiment of the present invention, copper and aluminum are mixed and put into a crucible so that copper is 2 to 5% by weight, and the balance is aluminum, melted and cast to obtain an ingot.
The obtained ingot is homogenized, then cooled and, if necessary, is beveled, and then cold-worked so that the cold-working rate, that is, the cross-sectional reduction rate by cold working, is 60% or more. If the maximum temperature attained by the target during sputtering exceeds 350 ° C. in an argon gas flow of the obtained work material, the target maximum temperature at the time of sputtering is equal to or slightly higher than the maximum temperature reached by the target. In the case where the temperature is lower than ℃, the method is a method of manufacturing an aluminum alloy sputtering target which is annealed at 350 ° C or more, quenched after annealing, and used as a sputtering target.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The purpose of the present invention is to use copper as an alloy component and to control the crystal diameter by using appropriate heat treatment and processing to obtain a good aluminum alloy target. Things. Therefore, the present invention does not refuse to add another element to aluminum for another purpose. The meaning of the present invention that “the remainder substantially consists of aluminum” means this point.

In the sputtering method, the emission angle of metal atoms emitted from crystal particles existing on the surface of a sputtering target (hereinafter simply referred to as “target”) varies depending on the orientation of the crystal. Therefore, when each crystal grain of the target is large, a relatively large anisotropy occurs in the average crystal orientation composed of each crystal grain,
The thickness of the obtained film will vary. Therefore, if the crystal grains constituting the target are sufficiently small, the anisotropy of the crystal orientation as an average becomes small, and the variation in the thickness of the obtained film becomes so small as to be negligible.

In general, a pure metal such as aluminum tends to have a large crystal grain. Even if copper or the like is added as in the related art, simply mixing, dissolving, casting, and rolling will result in a coarse target structure. Further, depending on the alloy composition and the manufacturing method, even when the initial crystal grain size is small, the crystal grains are coarsened by heating by sputtering, and the uniformity of the film thickness distribution is reduced.

[0010] In order to maintain a stable fine crystal structure even by heating during sputtering, it is necessary to keep the added amount of copper within a certain range. If the amount of copper added is less than 2% by weight with respect to the target, a fine crystal structure cannot be obtained regardless of the processing method. Even if you get it,
Crystals become coarse due to heating during sputtering. The crystal structure stabilizes as the amount of copper increases, but 5% by weight
If the addition exceeds the range, the compound of aluminum and copper is coarsely distributed, and the workability is reduced. Therefore, in the present invention, the amount of copper added to aluminum is set to 2 to 5% by weight based on the target.

Next, a method for manufacturing the target of the present invention, in particular, a method for controlling the crystal grain size will be described. First, a predetermined amount of copper and aluminum or an aluminum alloy is weighed in a crucible, melted, and cast to obtain an ingot. As a melting method, general high frequency melting or the like can be used. Vacuum melting may be applied to prevent oxidation. The mold material is not particularly limited as long as it does not react with aluminum or copper, and usually a crucible made of iron or graphite is used.

When melted and cast as described above, the structure of the resulting ingot is composed of coarse crystal grains and the distribution of the added copper is not uniform. It is desirable to make the copper distribution uniform by performing cold rolling or the like. If the distribution of copper is non-uniform, the crystal grain size of the target will be non-uniform due to the difference in concentration. The subsequent cooling is preferably performed at a cooling rate as fast as possible, but ordinary shower cooling or the like is sufficient.

Thereafter, the ingot is worked into a shape close to the target by cold rolling, cold forging, or the like. The crystal grain size of the target changes depending on the degree of processing at this time. When the cold working ratio, that is, the cross-sectional reduction ratio of the workpiece is less than 60%, the target particle size becomes coarse. Since the grain size of the target becomes smaller as the cold working ratio becomes higher, the thickness of the ingot can be calculated from the final target thickness and the required working ratio.

[0014] In order to obtain a good target, it is desirable to remove as much as possible the processed structure generated by the cold working. For this reason, the cold-worked material is heated and annealed. At this time, recrystallization occurs depending on the annealing temperature and the annealing time, and a target with less distortion can be obtained, but the grain size also changes. When 2 to 5% by weight of Cu is added as in the present invention, 350 ° C. is required to obtain a uniform recrystallized structure.
Annealing at the above temperature is necessary. If the temperature is lower than this, the processed structure remains, resulting in a structure having an uneven crystal orientation. Further, the remaining strain is recovered by heating during sputtering, which causes a change in the target structure and warpage of the target. When annealing at a temperature of 350 ° C. or more,
A uniform recrystallization structure is obtained, and the crystal orientation is also random.

[0015] When the annealing temperature is further increased, the crystal grains become coarse and have an orientation biased to a specific orientation called a rolling texture. Since the crystal grains increase as the annealing temperature increases, it is desirable that the annealing temperature be as low as possible within a range where a recrystallized structure can be obtained.

However, if the annealing temperature is lower than the maximum temperature attained by the target at the time of sputtering, grain growth occurs during sputtering, causing a change in the film forming characteristics with time during sputtering. Annealing at a temperature equal to or higher than the maximum temperature attained by the target during sputtering during annealing stabilizes the target structure and enables stable sputtering characteristics to be obtained. The target maximum temperature during sputtering is 350
Naturally, the annealing temperature is lower than 350 ° C., but by annealing at 350 ° C. or higher, a change in film forming characteristics during sputtering can be reduced.

However, even in the case of high-temperature annealing, if the annealing is performed for a short time as in continuous annealing, a uniform target structure with relatively small crystal grains can be obtained.

If the annealing temperature is not lower than the melting point, the target partially dissolves and has no effect.

[0019]

EXAMPLES The above-described target of the present invention and the method for producing the same will be described in more detail with reference to examples.

Using high purity aluminum and electrolytic copper having a purity of 99.99% or more as raw materials, 10 kg of each alloy having the composition shown in Table 1 was melted by a vacuum melting method, poured into a stainless steel mold, and the ingot was cast. Produced. The obtained ingot was kept in an argon stream at 500 ° C. for 24 hours to perform a homogenization treatment, and then the ingot was shower-cooled. The ingot was chamfered to obtain a plate having a thickness of 100 mm. Next, this plate material was cut out and cold rolled to obtain a plate thickness of 50 to 20 mm, and then annealed at 500 ° C. for 2 hours in an argon stream, followed by shower cooling to obtain a starting material.

(Examples 1 to 6, Comparative Examples 1 to 6) These sheet materials having a thickness of 20 to 100 mm were cold-rolled to a thickness of 10 mm. The cold working rates are 50, 60, 80 and 90%, respectively. After annealing these plate materials at respective temperatures of 300 ° C. to 500 ° C., they were cut out into 150 mm disks and surface ground to prepare targets. The cut-out remainder was polished and etched, the structure was observed using an optical microscope, and the crystal grain size of about 200 crystal grains was measured by a cutting method to obtain an average value.

Using the produced target, an aluminum alloy electrode was formed on a piezoelectric ceramic substrate by DC sputtering. After pre-sputtering for 30 minutes, sputtering was performed for 3 minutes to form an electrode having a thickness of about 50 nm. The resonance frequency of the obtained piezoelectric element was measured, and an accurate film thickness was calculated. For some of the targets, after continuous sputtering was performed for 24 hours, a film was formed again on the ceramic substrate.

After the test, these sputtering targets were cut and the crystal grain size was measured again. The target temperature during sputtering was measured at 370 ° C. using a thermocouple. Table 1 summarizes the ratio of copper, the working ratio, the annealing temperature, the annealing time, and the crystal grain size.

Table 1 Example Cu working rate Annealing temperature Annealing time Crystal grain size (% by weight) (%) (° C) (min) (μm) 1 2.2 80 390 120 85 2 2.2 90 380 120 67 3 3.9 80 390 120 83 4 3.9 90 420 420 120 62 5 4.8 80 380 120 72 6 4.8 90 90 450 10 55 Comparative example 1 1.2 80 330 120 120 Working structure 2 1.2 80 390 120 400 3 5.8 90 390 120 Work structure Rolling crack 4 5.8 80 420 120 30 Rolling crack 5 3.9 50 390 120 145 6 2.2 80 350 120 52

In Examples 1 to 7 of the present invention, copper is contained in an amount of 2.2 to 4.8% by weight, a cold working rate of 70 to 90% is performed, and annealing is performed at 350 to 450 ° C. ~
A relatively uniform crystal grain size of 85 μm is obtained. On the other hand, in Comparative Example 1 where the amount of copper was small, the processed structure remained even after annealing at 330 ° C., and in Comparative Example 2 where the amount of copper was the same and the annealing temperature was 360 ° C., a coarse crystal structure of 400 μm was obtained. As a result, a fine and uniform target structure cannot be obtained regardless of the annealing conditions. In Comparative Examples 3 and 4 having a large amount of copper, the processed structure remains after annealing at 390 ° C., whereas fine crystals of about 30 μm are obtained at 420 ° C. However, these samples are cracked by cold rolling of 50% or more, and a good target cannot be obtained.

In Comparative Example 5 in which the amount of copper was 3.9% and the rolling reduction was 50%, the crystal grain size after annealing was as large as 145 μm. Comparative Example 6 is an example in which the annealing temperature is lower than the maximum attainable temperature of the target at the time of sputtering. Next, a target was produced using these plates except for Comparative Examples 3 and 4 in which cracks occurred during rolling, and a long-term sputtering test was performed. In Table 2, the film thickness of the electrodes formed on 20 substrates is measured, the difference between the maximum film thickness and the minimum film thickness between the electrodes is taken, and the value obtained by dividing by the average film thickness is expressed as a film thickness variation in percentage. Indicated.
The results obtained when the same film formation was performed after continuous sputtering for 24 hours are also shown.

[0027]

In Examples 1 to 6 of the present invention, the film thickness variation is small, and the film thickness variation hardly changes even after continuous sputtering for 24 hours. On the other hand, in Comparative Example 1 in which the processed structure remains, the variation in the film thickness is large. Similarly, Comparative Examples 2 and 5 having a large crystal grain size also have large variations in film thickness. In Comparative Example 6, which was annealed at 350 ° C. and had crystal grains of 52 μm, the initial characteristics were excellent, but the film thickness variation was large after continuous sputtering for 24 hours.

When the target was cut after the test and the erosion portion was observed, in Comparative Example 6, the crystal grain size was coarsened to 93 μm. This is considered to be due to the influence of sputter heating. In contrast, in Examples 1 to 6, 24
No significant change in crystal grain size was observed even after continuous sputtering.

Next, the distance between the target and the substrate during sputtering is increased, and the maximum temperature of the target is set to 340 ° C.
After the same target as in Comparative Example 6 was continuously sputtered for 24 hours, the film thickness of the electrode was measured in the same manner. As a result, the variation in the film thickness was reduced to 1.4%. This result indicates that in order to stabilize the target structure, it is effective to determine the annealing conditions based on the use conditions of the target. In spattering, there is a serious problem that the film thickness varies during sputtering as well as the variation depending on the position in one sputtering. According to the target of the present invention, a film having a stable thickness can be obtained not only due to a variation in position due to the crystal structure but also for a long time use.

As described above, by using the sputtering target of the present invention, an electrode film having a small variation in film thickness can be formed, which has a great effect on controlling the characteristics of electronic components.

[0032]

As described above, the present invention provides a stable aluminum alloy sputter target having a crystal grain size of 100 μm or less which is excellent in film thickness controllability and which does not cause the crystal grains to become coarse even by heating during sputtering. Therefore, high film thickness controllability can be maintained for a long time from the start of sputtering. Although the present invention is particularly effective for electrodes such as surface acoustic wave devices, it can also contribute to improving the quality of other electronic components.

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Claims (2)

[Claims] 1. An aluminum alloy sputtering target containing 2 to 5% by weight of Cu and the balance substantially consisting of aluminum, wherein the crystal constituting the target has a grain size of 100 μm or less. Alloy sputtering target. 2. An ingot is prepared by mixing and melting copper and aluminum so that the content of copper is 2 to 5% by weight, and the balance is substantially aluminum, and the resulting ingot is homogenized. After the treatment, it is cooled and, if necessary, is chamfered, and then cold-worked so that the cold-working rate, that is, the cross-sectional reduction rate due to the cold-working, becomes 60% or more. A method of manufacturing an aluminum alloy sputtering target in which annealing is performed at any one of the following temperatures, followed by rapid cooling after annealing. (1) If the maximum temperature at which the target reaches the target during sputtering exceeds 350 ° C., the annealing temperature is equal to or higher than the target maximum temperature and equal to or lower than the melting point. (2) If the maximum target temperature during sputtering is lower than 350 ° C., the annealing temperature is 350 ° C. or higher and the melting point or lower.