JPH1060632A - Sputtering target, its production, and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sputtering target excellent in resistances to oxidation, corrosion, electromigration and stress migration by providing a composition composed essentially of Cu and also limiting the content of O. SOLUTION: Cu of >=99.9999wt.% purity, from which gas components of O, N, C, and H are removed, is used as a basis metal, which is subjected, in an atmosphere of <=0.1vol.ppm O content, in inert gas or in vacuum, to melting, casting, cooling, and solidification. The resultant ingot is rolled, forged, subjected to machining such as cutting, annealed to undergo removal of working strain, and further subjected, if necessary, to external working and then subjected to cleaning with organic solvent and to etching with dilute nitric acid, by which the sputtering target, containing 0.001-0.03wt.ppm O, preferably 0.001-0.05ppm S, can be obtained. By carrying out sputtering by the use of this target and performing film formation of copper wiring, a semiconductor device minimal in the rate of discontinuity and improved in reliability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a sputtering target containing copper as a main component, and a semiconductor device having a wiring formed using the sputtering target containing copper as a main component.

[0002]

2. Description of the Related Art In recent years, the development of LSI manufacturing technology has been remarkable.
And ultra-large-scale integrated circuits (LSIs), and the wiring width is becoming finer for higher integration. Copper (Cu) is particularly promising as a wiring material for next-generation LSIs requiring fine processing with a line width of 0.3 μm or less, such as a DRAM of 64 megabits or more.

Conventionally, Al alloys having low electric resistance and high adhesion to Si have been widely used as wiring materials for VLSIs formed on silicon substrates. With miniaturization, there is a problem that the reliability of the device is reduced due to disconnection caused by electromigration or stress migration.

Copper is being studied as a wiring material in place of such an Al alloy, and copper has an electric resistance of 3 times that of Al.
Since the current density can be increased by a factor of 2 and the melting point is higher than 400 ° C., when a thin film used as an internal wiring for a VLSI is formed, the wiring material is resistant to electromigration and stress migration. In order to become, it is considered promising.

[0005] In the prior art, a sputtering target made of organometallic copper, electrolytic copper or oxygen-free copper has been used when forming copper wiring. However, since the purity of these sputtering targets was about 99.99% by weight, the purity of the obtained thin film was also about the same. In the case of using such a low-purity wiring material, the electromigration resistance and the stress migration property, which are the merits of copper, are lost. Therefore, low corrosion resistance is a problem, and it has not been possible to commercialize.

Japanese Patent Application Laid-Open No. Hei 5-31424 discloses that copper wiring is inferior in oxidation resistance to aluminum or aluminum alloy wire, and as a solution to this problem, copper, Ti, Z
It is described that n is added as a trace element. However, in this technique, it is necessary to uniformly disperse the added metal, and for this purpose, for example, a purity of 99.
In the case of producing a sputtering target in which Ti is added to 9999% by weight of copper, the ingot must be rapidly cooled to prevent precipitation of the added element. For this purpose, a continuous casting device capable of rapid cooling is required. Further, since the purity of Ti is as low as 99.99% by weight, unintended impurities are introduced, and there is a problem that it is difficult to control the characteristics of the thin film.

An extremely high purity is required for a copper wiring material used for a super LSI wiring. For example, JP-A-8-81
No. 719 discloses that when copper is used for wiring, the presence of an alkali metal such as sodium or potassium as an impurity changes the flat band voltage or the threshold voltage to cause instability of the MOS characteristics, resulting in deterioration of the oxide film breakdown voltage. There is a description of a technology that reduces impurities to the ppt level because it causes micro defects such as heavy metals such as iron and nickel, and there is a problem that oxidation causes wafer defects in places touched by stainless steel. is there.

In order to minimize the effects of such impurities,
Conventionally, a sputtering target using copper purified by an electrolytic refining method or a zone refining method has been studied as a film forming material. In these materials, the problematic impurities are mainly metal components, and studies have been made to reduce, for example, Ag, Fe, Bi, Sb, As, and Pb as much as possible to obtain high-purity copper. In the past, very few gas components were examined as impurities.

[0009]

A gas component present in a gaseous, molecular, or compound state in copper of a film-forming wiring,
That is, when a gas component element such as oxygen, hydrogen, or sulfur is present, the gas component causes corrosion due to reaction with moisture or the like that enters from outside the package portion of the LSI. In addition, a small amount of oxygen released during film formation oxidizes the film to increase the resistivity and causes corrosion due to oxidation.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems. In the case where a wiring is formed by a sputtering method using copper as a sputtering target, oxidation resistance, corrosion resistance, electromigration resistance, and stress migration resistance are provided. It is an object of the present invention to provide a sputtering target having excellent performance, a semiconductor device having a copper wiring wired by the sputtering target, and a method for manufacturing the same.

[0011]

According to a first aspect of the present invention, there is provided a sputtering target containing copper as a main component.
It is characterized by containing oxygen (O) in an amount of 001 ppm by weight or more and 0.03 ppm by weight or less.

According to a second aspect of the present invention, there is provided a sputtering target containing copper as a main component, wherein
As described above, it is characterized by containing 0.05 wt ppm or less of sulfur (S).

According to a third aspect of the present invention, there is provided a sputtering target having both of the features of the first and second aspects simultaneously.

According to a fourth aspect of the present invention, there is provided the sputtering target according to any one of the first to third aspects, wherein the copper material is melted in a vacuum or in an inert gas to process a cast ingot. It is characterized by the following.

According to a fifth aspect of the present invention, in the sputtering target of the fourth aspect, the copper material excludes oxygen (O), nitrogen (N), and gas components of carbon (C) and hydrogen (H). Of copper having a purity of 99.9999% by weight or more.

According to a sixth aspect of the present invention, there is provided a semiconductor device according to the first aspect.
A film is formed by using the sputtering target according to any one of the above-described items.

According to a seventh aspect of the present invention, there is provided a method of manufacturing a sputtering target containing copper as a main component, excluding oxygen (O), nitrogen (N), and gas components of carbon (C) and hydrogen (H). A melting step of dissolving the base metal in an atmosphere having an oxygen concentration of 0.1 ppm by volume or less using copper having a purity of 99.9999% by weight or more as a base metal;
A solidification step of solidifying the dissolved base metal in an atmosphere of 1 ppm by volume or less.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION According to studies by the inventors, 99.9999% by weight of purity excluding gas components (O, N, C, H).
Using the above copper as a base metal, the oxygen concentration is set to 0.01 volume pp.
By forming a sputtering target from an ingot melted and cast in an atmosphere of m or less, a gas component contained in the sputtering target can be reduced, and the gas component contains oxygen (O) of 0.001 wt ppm or more. 0.
03 wt ppm or less, sulfur (S) is 0.001 wt pp
It was found that the content was not less than m and not more than 0.05 ppm by weight, and the content of hydrogen was less than 1 ppm by weight. By using this sputtering target and the copper wiring formed by this sputtering target, a copper thin film wiring excellent in oxidation resistance, corrosion resistance, electromigration resistance and stress migration resistance could be obtained.

The sputtering target is prepared by the following method.

Copper having a purity of 99.9999% by weight or more excluding gas components (O, N, C, H) is used. The reason for this is that if a substance having a purity lower than this is used, a small amount of impurities will act and the predetermined effect will not be obtained. Also,
This is because those contained as trace impurities cannot be removed by the treatment after dissolution.

Regarding the above purity, the gas components (O, N, C,
Excluding H), five nines of normal purity, ie, 99.999% by weight or Six Nine 99.999%
For the purity expressed as 9% by weight, the gas components contained in the metal, for example, oxygen gas for O, O component of oxides, and carbide, gas, hydrocarbon, and S for C For example, if it is S sulfide, sulfurous acid peroxide, gas, or H, water, gas, ammonia gas, hydride, etc. may be mentioned, but these gas components are not usually analyzed, and the purity is indicated from the analysis result of the metal component. Therefore, the actual purity is unknown. Therefore, in this specification, the gas components (O, N, C, H)
Is expressed by the purity excluding.

For example, in the melting and casting of copper, a continuous casting method described in JP-A-5-31424 can be used. However, a batch method in which melting is performed independently and then casting is performed may be used. Any melting furnace or casting furnace that takes measures to prevent the contamination of impurities can be used.

The melting atmosphere is in an inert gas or in a vacuum. This means that some of the trace impurities present in copper can be volatilized and removed, and if dissolved in air,
This is because copper oxide is generated by reacting with oxygen or moisture in the atmosphere, or copper gas is contaminated by absorbing hydrogen gas.

During the casting, it is necessary to perform the casting in an inert gas atmosphere or vacuum for the same reason as the melting. This atmosphere is continued until the metal solidifies and cools, but the cooling may be either rapid cooling or slow cooling, but rapid cooling is preferred.

In this embodiment, high-purity argon is used as the inert gas. This high purity argon has
U grade (6N = 99.99999) manufactured by Taiyo Toyo Oki Co., Ltd.
%, Impurities 0.1 ppm or less). The concentrations of O, N, C and H in argon are as follows.

O = <0.1 ppm N = <1 ppm C = <0.1 ppm H = <0.1 ppm Dissolve in an atmosphere having an oxygen concentration of 0.01 vol ppm or less,
Process using the cast ingot.

[0027] The solidified ingot obtained by casting is subjected to mechanical processing such as rolling, forging and cutting as necessary to obtain a sputtering target.

Using the sputtering target, a thin film forming process is performed.

The analysis of gas components was performed by the following method usually used for high-purity copper metal. That is, carbon (C) and oxygen (O) were measured by charged particle activation analysis using a cyclotron CYPRIS370 manufactured by Sumitomo Heavy Industries, Ltd. For nitrogen (N), RH manufactured by LECO
-1E and hydrogen (H) for TC-43 manufactured by LECO
6 using the combustion thermal conductivity method. Sulfur (S) was measured by glow discharge mass spectrometry using VG9000 manufactured by VG.

Hereinafter, examples and comparative examples according to the present invention will be described in detail with reference to the drawings.

(Embodiment 1) In this embodiment, gas components (O,
This shows an example in which a sputtering target is prepared from copper having a purity of 99.9999% by weight excluding (N, C, H) using a batch-type casting furnace.

FIG. 1 is a flowchart showing a processing flow of a method for manufacturing a sputtering target according to this embodiment.

FIG. 2 is a schematic sectional view of a batch type casting furnace used in the present embodiment. The following description is made with reference to the schematic sectional view of FIG.

In a high-purity carbon crucible 21 shown in FIG. 2, copper 99.9999% by weight excluding gas components was added.
2 was charged to about 10 kg. In addition, the crucible 21 used was one that had been pre-baked in an ultra-high purity argon atmosphere at 1500 ° C. for 5 hours.

The evacuation of the melting chamber and the replacement of high-purity argon gas were repeated several times, and the oxygen concentration in the melting chamber was 0.1 volume p.
After confirming that the temperature became pm or less, heating and melting were started. Then, after the raw material copper 22 was completely dissolved, it was gradually cooled from the bottom of the crucible 21 and solidified. The obtained ingot had a cylindrical shape with a diameter of 10 cm and a thickness of 14 cm. The ingot had no casting defects, and the ingot was close to a single crystal. Using this as a raw material, it was processed to a thickness of 3 cm by forging. By this forging, the structure of the ingot became finer, and it became a fine polycrystal suitable for a sputtering target.

Next, after removing the contaminated layer on the surface of the ingot with nitric acid, annealing was performed at 135 ° C. for 30 minutes in a high-purity argon atmosphere to remove working strain. The crystal grain size of the ingot after annealing was 1 mm or less.

Next, cross rolling was performed to form a plate having a thickness of 7 mm. The obtained rolled plate was subjected to surface grinding and outer shape processing to form a disk having a diameter of 6 inches and a thickness of 5 mm. Next, after the disk was washed with an organic solvent, the disk was etched using dilute nitric acid to obtain a sputtering target.

The impurity analysis of the sputtering target was performed by glow discharge mass spectrometry. As a result, the impurity metal component was the same as the analysis value of the raw material, and the analysis result is shown in the table of FIG. The analysis results of gas impurities at this time are also shown in the table of FIG.

Using the sputtering target obtained as described above, a 0.3 μm-wide
A copper wiring having a thickness of 0.8 μm was formed. At this time, the film was deposited on the Si substrate at an argon gas pressure of 3 × 10 ⁻³ Torr and a discharge power of 500 W.

Next, a protective film having a thickness of 0.
An 8 μm SiN film was deposited. The current density of this sample was 1 × 10 ⁶ A / cm ² and the ambient temperature was 200 ° C.
A 2,000 hour acceleration test was performed to measure the disconnection defect rate. As a result, the disconnection failure rate of the sample was 1.0%, and the results are also shown in the table of FIG.

(Embodiment 2) In this embodiment, the gas components (O,
This shows an example in which a sputtering target is prepared from copper having a purity of 99.99999% by weight excluding (N, C, H) using a batch-type casting furnace.

The procedure was as described in Example 1, except that copper having a purity of 99.99999% by weight was used. The method for forming the sputtering target is the same as that in Example 1, and will not be described.

The impurity analysis of the sputtering target was performed by glow discharge mass spectrometry. As a result, the impurity metal component was the same as the analysis value of the raw material, and the analysis result is also shown in the table of FIG. The analysis results of gas impurities at this time are also shown in the table of FIG.

Using the sputtering target obtained as described above, a width of 0.3 μm was obtained by RF sputtering.
A copper wiring having a thickness of 0.8 μm was formed. At this time, the film was deposited on the Si substrate at an argon gas pressure of 3 × 10 ⁻³ Torr and a discharge power of 500 W.

Next, a protective film having a thickness of 0.
An 8 μm SiN film was deposited. The current density of this sample was 1 × 10 ⁶ A / cm ² and the ambient temperature was 200 ° C.
A 2,000 hour acceleration test was performed to measure the disconnection defect rate. As a result, the disconnection defect rate of the sample was 0.5%, and the results are shown in the table of FIG.

(Comparative Example 1) In this example, the gas components (O,
This shows an example in which a sputtering target is prepared from copper having a purity of 99.99% by weight excluding (N, C, H) using a batch-type casting furnace.

The method for producing an ingot using the batch-type casting furnace shown in FIG. 2 is the same as that in Example 1 except for the purity of the raw material copper, and therefore the description thereof is omitted.

The processing after obtaining the ingot will be described below.

The obtained ingot was processed to a thickness of 3 cm by forging. Next, after removing the contaminated layer on the surface of the ingot with nitric acid, annealing was performed at 350 ° C. for 30 minutes in a high-purity argon atmosphere to remove working strain. The grain size of the ingot after annealing is 1
mm or less. (Subsequently, it was cross-rolled and processed into a plate having a thickness of 7 mm.) The obtained rolled plate was subjected to surface grinding and outer shape processing to form a disk having a diameter of 6 inches and a thickness of 5 mm. Next, after the disk was washed with an organic solvent, the disk was etched using dilute nitric acid to obtain a sputtering target.

The impurity analysis of the sputtering target was performed by glow discharge mass spectrometry. The analysis results of the impurity metals and gas impurities at this time are also shown in the table of FIG.

Using the sputtering target obtained as described above, a 0.3 μm
A copper wiring having a thickness of 0.8 μm was formed. The film forming conditions at this time were the same as those in Example 1, and the argon gas pressure was 3 × 1.
It was deposited on a Si substrate at 0 ^-3 Torr and a discharge power of 500 W.

Next, a protective film having a thickness of 0.
An 8 μm SiN film was deposited. This sample was subjected to an acceleration test at a current density of 1 × 10 ⁶ A / cm ² and an ambient temperature of 200 ° C. for 2,000 hours to measure a disconnection defect rate.
As a result, the disconnection defect rate of the sample was 3.0%, and the results are also shown in the table of FIG.

(Other Embodiments) The present invention is not limited to the above embodiment, but allows various modifications.

In the above embodiment, two kinds of copper having a purity of 99.9999% by weight and 99.9999% by weight, excluding gas components, are used. However, copper of other purity may be used. .

Further, in the above-described embodiment, the case where a high-purity argon gas is used as the inert gas has been described. However, the present invention can be similarly carried out using another inert gas.

[0056]

As described above, according to the present invention, copper having a purity of 99.9999% by weight or more excluding gas components is used as a base metal in an atmosphere having an oxygen concentration of 0.1 ppm by volume or less. By melting and casting, it is possible to obtain a sputtering target excellent in oxidation resistance, corrosion resistance, electromigration resistance, and stress migration resistance, and a semiconductor element having copper wiring wired by the sputtering target.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a batch type casting furnace according to an embodiment.

FIG. 2 is a flowchart showing a processing flow of a method for manufacturing a sputtering target according to an embodiment.

FIG. 3 is a table showing analysis values of impurity elements of a sputtering target and a disconnection failure rate of copper wiring according to the embodiment;

Claims (7)

[Claims] 1. A sputtering target containing copper as a main component, wherein the sputtering target contains oxygen (O) in an amount of 0.001 to 0.03 ppm by weight. 2. A sputtering target containing copper as a main component, wherein the sputtering target contains 0.001 to 0.05 ppm by weight of sulfur (S). 3. A sputtering target having both the features of claim 1 and 2 at the same time. 4. The sputtering target according to claim 1, wherein the sputtering target is manufactured by processing an ingot cast by melting a copper material in a vacuum or an inert gas. 5. The method according to claim 1, wherein the copper material is oxygen (O), nitrogen (N),
And a purity of 9 excluding gas components of carbon (C) and hydrogen (H).
The sputtering target according to claim 4, wherein the sputtering target is made of 9.9999% by weight or more of copper. 6. A semiconductor element formed by using the sputtering target according to claim 1. 7. A method for producing a sputtering target containing copper as a main component, comprising: oxygen (O), nitrogen (N), carbon (C) and hydrogen (H).
A dissolving step of dissolving the base metal in an atmosphere having an oxygen concentration of 0.1 vol ppm or less, using copper having a purity of 99.9999 wt% or more excluding the gas component of A solidifying step of solidifying the dissolved base metal in the atmosphere of (1).