KR102435667B1 - Electroco plating method using Co anode and Co anode - Google Patents

Abstract

Provided is an anode that is a novel electroplating anode replacing the Cu anode and capable of suppressing plating failure. After dissolving in diluted nitric acid having a nitric acid concentration of 20% by mass, the number of particles having a particle size of 0.5 µm or more, as measured by a particle counter in the liquid according to JIS B 9925, is 6000 particles/g or less.

Description

Electroco plating method using Co anode and Co anode

The present invention relates to a Co anode and an electrolytic Co plating method using a Co anode.

Generally, although electric Cu plating is used for Cu wiring formation in PWB (printed wiring board) etc., it is also used also for Cu wiring formation of a semiconductor in recent years. A pure Cu anode or a phosphorus-containing Cu anode is used as an anode for electro-Cu plating for forming Cu wirings.

About the pure Cu anode or phosphorus containing Cu anode used for electric Cu plating, it describes in patent document 1, for example, By controlling purity to a predetermined range, and controlling content of an impurity to below predetermined value, the said It is described that adhesion of particles to semiconductor wafers prepared using pure Cu anodes or phosphorus-containing Cu anodes can be suppressed.

In addition, as a technique for suppressing the adhesion of particles to a semiconductor wafer produced by using a phosphorus-containing Cu anode similarly, Patent Document 2 discloses a crystal grain size on the surface of the phosphorus-containing Cu anode in advance when performing electric Cu plating on a semiconductor wafer. A technique for forming a microcrystalline layer controlled in this predetermined range is described.

Japanese Patent Publication No. 5066577 Japanese Patent No. 4076751

In recent years, high performance and low power consumption of semiconductor devices are demanded, and as wiring miniaturization progresses, countermeasures against deterioration of electromigration (EM) that affect wiring reliability and low resistance of wiring resistance that cause signal delay are a challenge is becoming The technique described in Patent Document 1 and Patent Document 2, as described above, suppresses particles generated when Cu wiring or the like is formed by electric Cu plating, thereby improving plating defects, and providing Cu wiring useful for fine wiring. Although this is an object to be obtained, in electroplating using such a conventional Cu anode, there is room for improvement in terms of EM resistance and low resistance of wiring resistance. Therefore, the development of the anode which is a new electroplating anode instead of Cu anode, and can suppress the plating defect which is a conventional subject is awaited.

Then, embodiment of this invention makes it a subject to provide the anode which is a novel electroplating anode which replaces a Cu anode, and can suppress plating defect.

As a result of various studies conducted by the present inventors in order to solve this problem, in the technical field of fine wiring formation, in the case of narrow wiring and state-of-the-art local wiring with a relatively short wiring distance, the replacement of Cu to Co wiring is about to be performed. focused on It turns out that Co wiring has favorable EM resistance compared with Cu wiring, and wiring resistance can also be suppressed lower than Cu wiring when a wiring distance is short as much as a barrier metal layer can be made thin.

Therefore, it was discovered that an electroplating anode capable of suppressing plating failure was obtained by producing a Co anode instead of the conventional Cu anode and controlling the number of particles having a predetermined particle size or more in the Co anode. .

In one aspect, the embodiment of the present invention completed based on the above findings is a particle having a particle size of 0.5 µm or more, which is measured based on JIS B 9925 by a particle counter in a liquid after dissolving in dilute nitric acid having a nitric acid concentration of 20 mass%. The number of is a Co anode of 6000 pieces/g or less.

Further, an embodiment of the present invention is another aspect, an electrolytic Co plating method using the Co anode according to the embodiment of the present invention.

ADVANTAGE OF THE INVENTION According to embodiment of this invention, it is an anode of the new electroplating replacing a Cu anode, and the anode which can suppress plating defect can be provided.

1 (a), Example 5 (purity: 3N, magnification: 300 times), (b) Example 3 (purity: 4N, magnification: 300 times), (c) Example 1 (purity: 5N, Magnification: 300 times) SEM image.
2 (a) is, Example 5 (purity: 3N, magnification: 15000 times), (b) Example 3 (purity: 4N, magnification: 30000 times), (c) Example 1 (purity: 5N, Magnification: 15000 times) SEM image.
Fig. 3(a) is a graph of the EDX spectrum of Example 5;
Fig. 3(b) is a graph of the EDX spectrum of Example 3.
Fig. 3(c) is a graph of the EDX spectrum of Example 1.

[Composition of Co anode]

After dissolving the Co anode according to the embodiment of the present invention in dilute nitric acid having a nitric acid concentration of 20% by mass, the number of particles having a particle diameter of 0.5 µm or more, measured based on JIS B9925 by a particle counter in the liquid, is 6000 pieces/g is below. The Co anode has good EM resistance to the Cu anode, so that the barrier metal layer can be made thin, and when the wiring distance is short, the wiring resistance can also be suppressed to be lower than that of the Cu wiring. In addition, since the number of particles having a particle diameter of 0.5 µm or more is controlled to 6000 particles/g or less, when electroplating using a Co anode, the occurrence of abnormal precipitation in plating is suppressed, and as a result, poor plating is suppressed. can do.

Particles are solid inclusions present in the structure of the Co anode, meaning that they do not dissolve in dilute nitric acid in the implementation of a particle counter in a liquid to be described later. As impurities of the Co anode, substances soluble in dilute nitric acid (eg, metals with strong ionization tendency) are also included. However, even if such a substance exists as a coarse structure in the Co anode, for example, since it is ionized in the process of electroplating, it is introduced into the plating film in a very fine ion level form. On the other hand, inclusions (particles) that do not dissolve in dilute nitric acid are introduced into the plating film while maintaining a form close to that when present in the Co anode because they are electrochemically stable. For this reason, even for a Co anode of the same purity, the larger the proportion of particles in the impurities, the larger the size of the impurities introduced into the plating film, and the plating failure tends to occur. The present invention pays attention to this point and provides a Co anode in which the number of particles having a predetermined particle size or larger is controlled for particles that are solid inclusions that do not dissolve in dilute nitric acid.

Particles are mainly due to impurities contained in the Co raw material, impurities or products mixed in during the manufacturing process. Particles are, for example, at least one selected from the group consisting of metals, metal oxides, carbon, carbon compounds, and chlorine compounds. Further, the particles may be one or more metals selected from the group consisting of Fe, Mg, Cr, Ni, Si, and Al, or oxides thereof (including cobalt oxides).

In addition, the present inventors pay attention to the number density of particles having such a particle size, especially since particles having a particle size of 0.5 µm or more do not dissolve in the electrolyte and are easily introduced into the plating film to cause abnormal precipitation of the plating. It was found that by controlling the number density to 6000 pieces/g or less, generation of particles in a plating film produced by electroplating can be extremely well suppressed, and as a result, occurrence of abnormal precipitation of plating can be suppressed. In addition, comparing the case where the impurity is not detected as a particle and the case where it is detected, the detected particle adversely affects the plating process, especially the case where the Co wiring formed using a Co anode is used as a fine wiring It has been found that many of these adverse effects become significant, and the number of particles having a particle size of 0.5 µm or more is controlled from such a viewpoint. In the Co anode according to the embodiment of the present invention, the number of particles having a particle size of 0.5 µm or more is preferably 5000/g or less, and more preferably 4000/g or less.

The particle size of the particle is obtained by measuring with a "liquid light scattering type automatic particle counter" (manufactured by Lyon, Kyushu). This measurement method is based on JIS B 9925 by selecting the size of particles in the liquid and measuring the particle concentration and number of particles (in the present invention, this measurement is called "particle counter in liquid").

Specifically, the procedure for the particle counter in the solution is to sample 1 g, dissolve slowly in 150 ml of dilute nitric acid (aqueous solution of 20 mass% nitric acid concentration of 20 mass%) so that the particles do not dissolve, and after standing for 24 hours, 500 ml of this As much as possible, dilute with pure water, take 10 ml, and measure with a particle counter in the liquid. For example, in the case where the number of particles is 1000/ml, since 0.02 g of a sample is measured in 10 ml, the number of particles is 500,000/g.

In addition, the number of particles is not limited to measurement by a particle counter in the liquid, and as long as the same number of particles can be measured, other means may be used for measurement.

The Co anode according to the embodiment of the present invention preferably has a purity of 3N or more. When the purity of the Co anode is 3N (purity 99.9% by mass) or more, the generation of particles in the plating film produced by electroplating using the Co anode can be better suppressed, and as a result, the occurrence of abnormal precipitation of the plating is further suppressed can do. As for the Co anode which concerns on embodiment of this invention, it is more preferable that it is 4N (purity 99.99 mass %) or more, and, as for the purity, it is still more preferable that it is 5N (purity 99.999 mass %) or more. In addition, with respect to "purity" in the present invention, for example, a purity of 5N (99.999%) is analyzed by Glow Discharge Mass Spectrometry (GDMS) of a Co ingot after dissolution, and an element below the lower limit of detection. and all metallic elements other than Co, such as Be, Na, Mg, Al, Si, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Zr, Mo , Cd, Sn, Sb, Hg, Pb, Bi, Th, and U mean less than 10 ppm.

In addition, as shown in Examples and Comparative Examples to be described later, there is not necessarily a relationship that the number of particles is small if "high purity" is there, and Co anode with high purity is more purified than Co anode with low purity of particles shown in the present invention. Sometimes there are many.

In the Co anode according to the embodiment of the present invention, it is preferable that the Fe concentration is controlled to 10 ppm or less. Since Fe is difficult to dissolve in an acidic solution, it becomes easy to form particles when Fe is incorporated in the Co anode. Comparing between Co anodes of the same purity, the number of particles generated in the plating film is smaller for the Co anode whose Fe concentration is controlled to 10 ppm or less than the Co anode whose Fe concentration exceeds 10 ppm. As a result, the plating Generation|occurrence|production of abnormal precipitation can be suppressed more. The Co anode according to the embodiment of the present invention has an Fe concentration of more preferably 8 ppm or less, still more preferably 5 ppm or less, still more preferably 3 ppm or less, still more preferably 1 ppm or less, even more preferably is controlled to 0ppm.

[Method for producing Co anode]

A method for manufacturing a Co anode according to an embodiment of the present invention will be described in detail. First, Co, which is a raw material, is dissolved in a predetermined container. As the Co raw material to be used, for example, Co having a purity of 3N (purity 99.9% by mass) or higher can be used.

As described above, particles that cause problems during electroplating are particles of compounds such as Fe, Mg, Cr, Ni, Si, and Al, and these particles cause particles generated in the plating film. In order to control so that these particles do not mix into the Co anode, the surface roughness of the portion in contact with the Co raw material may be controlled in the container, the pipe, and the mold. In addition, from the knowledge that these particles tend to float on the slag side, by increasing the stirring time of the molten metal, particles exceeding 0.5 µm in particle diameter of compounds of Fe, Mg, Cr, Ni, Si, and Al may be distributed to the slag side. .

Next, the melted Co raw material is supplied to a mold for forging, then rolling and heat treatment are performed, and further surface cutting is performed to produce a Co anode.

[Electric Co plating method]

By electroplating Co using the Co anode according to the embodiment of the present invention, generation of particles in the produced plated film can be extremely well suppressed, and as a result, occurrence of abnormal precipitation in the plating can be suppressed.

In the electrolytic Co plating method according to the embodiment of the present invention, although it is not particularly limited, for example, as the plating solution, cobalt sulfate: 10 to 30 g/L (Co), or 5 to 15 g/L of cobalt chloride can be used in an appropriate amount. . The pH is set to 2.5 to 3.5.

Alternatively, the plating bath may be 25 to 60° C., a cathode current density of 0.5 to 10 A/dm 2 , an anode current density of 0.5 to 10 A/dm 2 , but it is not necessarily limited to these conditions. The plating bath may contain a brightening agent, a complexing agent, a pH buffer, a surfactant, and the like.

Example

Hereinafter, examples are provided for better understanding of the present invention and its advantages, but the present invention is not limited to these examples.

[Production of Co anode]

As Examples 1 to 5 and Comparative Example 1, a Co raw material having a predetermined purity was vacuum melted to prepare an ingot and melted. A commercially available cobalt material was used for the Co raw material having a purity of 3N, and the Co raw material having a purity of 4N and 5N was obtained by electrolytic refining.

Next, after supplying the melted Co raw material to the mold and forging, rolling is performed at a reduction ratio of 30 to 50%, then heat treatment at 300° C. to 600° C. is performed, and further cutting the surface of the Co anode was produced.

〔evaluation〕

(Evaluation of particles)

The particle size and number of particles were measured with a "liquid light scattering type automatic particle counter" (manufactured by Lyon, Kyushu). Specifically, 1 g of Co anode is sampled, and it is slowly dissolved with 150 ml of diluted nitric acid (aqueous solution of 20 mass% nitric acid concentration) so that particles are not dissolved, and after standing for 24 hours, this is further diluted with pure water to 500 ml, 10 ml was taken and measured with a particle counter in the liquid. The average value of repeating this three times was taken as the number of particles. In addition, the particle size of the particle was evaluated by SEM image. 1 (a) in Example 5 (purity: 3N, magnification: 300 times), (b) in Example 3 (purity: 4N, magnification: 300 times), (c) in Example 1 (purity: 5N) , magnification: 300 times) shows the SEM image. In addition, in (a) of Figure 2, Example 5 (purity: 3N, magnification: 15000 times), (b) in Example 3 (purity: 4N, magnification: 30000 times), (c) in Example 1 (purity) : 5N, magnification: 15000 times) SEM image is shown. Also, in FIG. 1 , particles (inclusions) having a particle diameter of 0.5 μm or more are shown surrounded by an outline.

(Evaluation of Fe concentration)

The Fe concentration contained in the Co anode was evaluated by GDMS. In addition, when the particle size and number of particles were measured, the particle component remaining on the filter was evaluated using Energy Dispersive X-ray Spectrometry (EDX). The graphs of the EDX spectrum of Example 5 in (a) of FIG. 3, Example 3 in (b), and Example 1 in (c) are respectively shown.

(Evaluation of the number of abnormal electrodepositions)

On a wafer having a diameter of 300 mm, using the Co anodes of Examples 1 to 5 and Comparative Example 1, electrolytic Co plating was performed under the same conditions, respectively, and a Co plating film having a thickness of 10 nm was formed, which was generated in the Co plating film. The number of defects (number of abnormal electrodepositions) was evaluated.

Table 1 shows the results of each of the above Examples and Comparative Examples.

(Evaluation results)

In Examples 1 to 5, Co anodes having a particle size of 0.5 µm or more and a number of particles of 6000/g or less could be produced. On the other hand, in Comparative Example 1, a Co anode having a particle size of 0.5 µm or more and a number of particles exceeding 6000/g was obtained.

In addition, in Example 1 and Example 2, Example 3 and Example 4, Example 5 and Comparative Example 1, although Co anodes of the same purity are used, respectively, since the Fe concentration is different, particles having a particle size of 0.5 µm or more There is a difference in number. From this result, it turns out that when the purity is the same, the number of particles with a particle diameter of 0.5 micrometer or more can be reduced more when the Fe concentration is smaller.

In Example 4 having a purity of 4N, the number of particles having a particle size of 0.5 µm or more was greater than that of Example 5 having a purity of 3N. As described above, there is not necessarily a relationship that the number of particles is small if "high purity" is applied. In some cases, the number of particles shown in the present invention is greater for a Co anode with high purity than for a Co anode with low purity.

In the Co plating films formed using the Co anodes of Examples 1 to 5, the number of abnormal electrodepositions was 0, and poor plating was well suppressed. In the Co plating film formed using the Co anode of Comparative Example 1, abnormal electrodeposition was confirmed and plating failure occurred.

Claims (9)

Co anode for electroplating in which the number of particles having a particle size of 0.5 µm or more, as measured according to JIS B 9925 by a particle counter in a liquid, after dissolving in dilute nitric acid having a nitric acid concentration of 20% by mass, is 6000 particles/g or less. The Co anode according to claim 1, wherein the number of particles having a particle diameter of 0.5 µm or more is 5000/g or less. The Co anode of claim 1 having a purity of at least 3N. The Co anode according to claim 3, wherein the purity is at least 4N. The Co anode according to claim 3, wherein the Fe concentration is 10 ppm or less. 6. The Co anode according to claim 5, wherein the Fe concentration is 5 ppm or less. The electroplating method of Co using the Co anode in any one of Claims 1-6. delete delete

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