CN111971423A - Co anode and Co electroplating method using the same - Google Patents

Abstract

The present invention provides a novel electroplating anode which can replace the Cu anode and which can suppress poor plating. The anode is a Co anode having a particle size of 0.5 μm or more and the number of particles/g or less as measured by JIS B 9925 after dissolving in dilute nitric acid having a nitric acid concentration of 20 mass %, using a liquid particle counter.

Description

Co anode and Co electroplating method using Co anode

technical field

The present invention relates to a Co anode and a Co electroplating method using the Co anode.

Background technique

In general, Cu electroplating is used for the formation of Cu wirings of PWBs (printed wiring boards) and the like, but recently, it is also used for the formation of Cu wirings of semiconductors. As the anode for Cu electroplating for forming Cu wiring, a pure Cu anode or a phosphorus-containing Cu anode can be used.

The pure Cu anode or phosphorus-containing Cu anode used for Cu electroplating is described in, for example, Patent Document 1, and it is described that by controlling the purity to a predetermined range and controlling the content of impurities to a predetermined value or less, adhesion of fine particles can be suppressed. The pure Cu anode or the phosphorous-containing Cu anode is fabricated as a semiconductor wafer.

Furthermore, as a technique for preventing particles from adhering to a semiconductor wafer also manufactured using a phosphorous-containing Cu anode, Patent Document 2 describes a technique in which, when the semiconductor wafer is subjected to Cu electroplating, the phosphorous-containing Cu anode is formed on the surface of the phosphorous-containing Cu anode in advance. A fine crystal layer whose crystal grain size is controlled within a predetermined range.

Background Art Documents

Patent Literature

Patent Document 1: Patent No. 5066577

Patent Document 2: Patent No. 4076751.

SUMMARY OF THE INVENTION

[Problems to be Solved by Invention]

In recent years, higher performance and lower power consumption of semiconductor devices have been gradually demanded, and along with progress in miniaturization of wiring, measures for degradation of electromigration (EM) that affect the reliability of wiring, or wiring that causes signal delays The reduction of the line resistance has become a problem. The technology described in Patent Document 1 or Patent Document 2 is a technology that can improve the plating defects by suppressing fine particles generated when forming Cu wirings etc. by Cu electroplating as described above, and can obtain Cu wirings etc. which are advantageous for fine wirings. However, in the conventional electroplating using a Cu anode, there is still room for improvement in terms of EM resistance and reduction of wiring resistance. Therefore, the development of a novel electroplating anode which can replace the Cu anode and can further suppress the plating defect, which is a conventional problem, has been expected.

Therefore, the embodiment of the present invention aims to provide a novel electroplating anode which can suppress plating defects in place of the Cu anode.

[Technical means to solve the problem]

As a result of various studies conducted by the present inventors to solve the above-mentioned problems, in the technical field of forming fine wirings, it has been found that in the technical field of forming fine wirings, it is necessary to replace Cu from Cu in the frontmost partial wirings, etc. where narrow wirings are relatively short and wiring distances are relatively short. Wiring for Co. It was found that the Co wiring has better EM resistance than the Cu wiring, and when the wiring distance is shortened according to the thinning amount of the barrier metal layer, the wiring resistance can be suppressed from being lower than that of the Cu wiring.

Therefore, it has been found that a plated anode capable of suppressing plating defects can be obtained by producing a Co anode instead of the conventional Cu anode and controlling the number of particles having a predetermined particle size or larger in the Co anode.

One aspect of an embodiment of the present invention completed based on the above findings is a Co anode having a particle diameter of 0.5 as measured by a liquid particle counter based on JIS B 9925 after being dissolved in dilute nitric acid having a nitric acid concentration of 20 mass %. The number of microparticles of μm or more is 6000 particles/g or less.

Also, another aspect of an embodiment of the present invention is a Co electroplating method using the Co anode of an embodiment of the present invention.

[Effect of invention]

According to the embodiment of the present invention, it is possible to provide a novel electroplating anode which can suppress poor plating in place of the Cu anode.

Description of drawings

(a) of FIG. 1 is an SEM image of Example 5 (purity: 3N; magnification: 300 times), (b) is an SEM image of Example 3 (purity: 4N; magnification: 300 times), and (c) is an implementation SEM image of Example 1 (purity: 5N; magnification: 300 times).

(a) of FIG. 2 is an SEM image of Example 5 (purity: 3N; magnification: 15,000 times), (b) is an SEM image of Example 3 (purity: 4N; magnification: 30,000 times), and (c) is an implementation SEM image of Example 1 (purity: 5N; magnification: 15000 times).

FIG. 3( a ) is an EDX spectrogram of Example 5. FIG.

FIG. 3(b) is the EDX spectrum of Example 3. FIG.

FIG. 3( c ) is an EDX spectrogram of Example 1. FIG.

Detailed ways

[Constitution of Co anode]

The Co anode, which is an embodiment of the present invention, was dissolved in dilute nitric acid having a nitric acid concentration of 20% by mass, and the number of particles having a particle diameter of 0.5 μm or more was measured by a liquid particle counter according to JIS B 9925 to be 6,000. pcs/g or less. The Co anode has better EM resistance than the Cu anode, and when the wiring distance is shortened according to the thinning amount of the barrier metal layer, the wiring resistance can 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 be 6000 particles/g or less, when electroplating using a Co anode, the occurrence of abnormal precipitation in plating can be suppressed, and as a result, plating defects can be suppressed favorably.

The particles are solid inclusions present in the structure of the Co anode, and refer to substances that do not dissolve in dilute nitric acid during the implementation of the liquid particle counter described later. As an impurity of the Co anode, a substance soluble in dilute nitric acid (for example, a metal having a strong ionization tendency) is also included. However, even if such substances exist in the Co anode in the form of a coarse structure, they are ionized during the electroplating process, so they are incorporated into the coating film in a very fine form on the ionic level. On the other hand, the inclusions (fine particles) that are not dissolved in dilute nitric acid are electrochemically stable, and therefore, are taken into the plated film while maintaining a form close to that when they exist in the Co anode. Therefore, even if it is a Co anode with the same purity, the size of the impurity incorporated into the plating film increases in the one with the larger proportion of the particles in the impurity, and plating defects are likely to occur. In view of this point, the present invention provides a Co anode in which the number of particles having a predetermined particle diameter or more of fine particles that are inclusions in a solid form that are not dissolved in dilute nitric acid is controlled.

The fine particles are mainly caused by impurities contained in the Co raw material, or impurities or products mixed in the production process. The fine particles are, for example, one or more selected from metals, metal oxides, carbon, carbon compounds, and chlorine compounds. In addition, the fine particles may be one or more metals selected from Fe, Mg, Cr, Ni, Si, and Al or their oxides (including cobalt oxides).

In particular, the present inventors have found that fine particles having a particle diameter of 0.5 μm or more are not dissolved in the electrolyte, but are absorbed into the plating film and become prone to abnormal precipitation of the plating. The number density of particles having a particle size, and by controlling the number density to 6,000 particles/g or less, the generation of particles in the plated film produced by electroplating can be extremely well controlled, and it was found that the occurrence of the plated particles can be suppressed. The occurrence of abnormal precipitation. In addition, comparing the case where the impurities as fine particles were not detected and the case where the impurities as fine particles were detected, it was found that the one where the fine particles were detected had an adverse effect on the plating process, especially the Co wiring formed by the Co anode. It is often used for fine wiring, and such adverse effects become conspicuous. From this viewpoint, the number of fine particles having a particle diameter of 0.5 μm or more is also controlled. In the Co anode of the embodiment of the present invention, the number of fine particles having a particle diameter of 0.5 μm or more is preferably 5000 particles/g or less, and more preferably 4000 particles/g or less.

The particle diameter of the fine particles can be measured by a "light-scattering automatic particle counter for liquids" (manufactured by Kyushu RION Co., Ltd.). This measurement method is based on JISB 9925, which separates particles of various sizes in a liquid and measures the particle concentration and particle number (this measurement is referred to as a "liquid particle counter" in the present invention).

Hereinafter, the implementation procedure of the liquid particle counter will be described in detail. That is, 1 g of the sample is sampled, slowly dissolved in 150 ml of dilute nitric acid (aqueous solution with a nitric acid concentration of 20 mass %) so that the particles do not dissolve, and after standing for 24 hours, it is further diluted with pure water. It was 500ml, and 10ml was taken and measured using the above-mentioned liquid particle counter. For example, when the number of microparticles is 1,000/ml, 0.02 g of the sample is measured in 10 ml, so the number of microparticles is 500,000/g.

Furthermore, the number of particles is not limited to the measurement using a liquid particle counter, and other means may be used as long as the same number can be measured.

The purity of the Co anode in the embodiment of the present invention is preferably 3N or more. When the purity of the Co anode is 3N (purity of 99.9 mass %) or more, the generation of particles in the plating film produced by the electroplating using the Co anode can be suppressed more favorably, and as a result, abnormal precipitation of the plating can be further suppressed. produce. The purity of the Co anode of the embodiment of the present invention is more preferably 4N (purity of 99.99 mass %) or more, and still more preferably 5N (purity of 99.999 mass %) or more. In addition, regarding the "purity" in the present invention, for example, the purity of 5N (99.999%) is defined as an element below the detection limit by analyzing the dissolved Co ingot by Glow Discharge Mass Spectrometry (GDMS: Glow Discharge Mass Spectrometry). And all metal 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 , the total value of Sn, Sb, Hg, Pb, Bi, Th, and U was less than 10 ppm.

Furthermore, as shown in the Examples and Comparative Examples to be described later, as long as it is "highly pure", the relationship that the number of particles is small does not necessarily hold, and there are also Co anodes with higher purity than Co anodes with lower purity. if the number of particles shown is higher.

In the Co anode of the embodiment of the present invention, it is preferable that the Fe concentration is controlled to be 10 ppm or less. Fe is not easily dissolved in an acidic solution, and therefore, when Fe is mixed into the Co anode, it becomes easy to form fine particles. When compared between Co anodes with the same degree of purity, the number of particles generated in the coating film of the Co anode with the Fe concentration controlled to 10 ppm or less is smaller than that of the Co anode with the Fe concentration exceeding 10 ppm. As a result, the occurrence of abnormal precipitation in plating can be further suppressed. The Fe concentration of the Co anode of the embodiment of the present invention is controlled to be 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, still more preferably 0 ppm.

[Manufacturing method of Co anode]

The manufacturing method of the Co anode in the embodiment of the present invention will be described in detail. First, Co, which is a raw material, is melted in a predetermined container. As the Co raw material used, for example, Co having a purity of 3N (purity of 99.9 mass %) or more can be used.

As described above, the particles that are problematic in electroplating are particles of compounds such as Fe, Mg, Cr, Ni, Si, and Al, and these particles cause particles to be generated in the plating film. In order to control that these particles are not mixed into the Co anode, the surface roughness of the part in contact with the Co raw material in the container, the piping, and the mold can also be controlled. In addition, from the knowledge that these particles tend to float on the slag side, it is also possible to increase the stirring time of the melt to distribute particles of Fe, Mg, Cr, Ni, Si, and Al compounds with a particle size exceeding 0.5 μm to the melt. Slag side.

Next, after supplying the melted Co raw material to a mold and performing forging, rolling, heat treatment, and further surface cutting are performed to produce a Co anode.

[Co plating method]

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

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

In addition, although a plating bath temperature of 25 to 60° C., a cathode current density of 0.5 to 10 A/dm ² , and an anode current density of 0.5 to 10 A/dm ² may be used, these conditions are not necessarily limited. A glossing agent, a complexing agent, a pH value buffer, a surfactant, etc. may also be included in the plating bath.

[Example]

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

[Production of Co anode]

As Examples 1 to 5 and Comparative Example 1, Co raw materials of predetermined purity were vacuum-melted, and then ingots were prepared and melted. In addition, a commercially available cobalt material was used as the Co raw material with a purity of 3N, and the Co raw materials with a purity of 4N and 5N were obtained by electrolytic purification.

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

[Evaluation]

(Evaluation of Particles)

The particle diameter and the number of fine particles were measured by a "light-scattering automatic particle counter for liquids" (manufactured by Kyushu RION Co., Ltd.). Specifically, 1 g of Co anode was sampled, slowly dissolved in 150 ml of dilute nitric acid (aqueous solution with a nitric acid concentration of 20 mass %) so that the particles were not dissolved, and after standing for 24 hours, it was further diluted with pure water to 500 ml, and 10 ml was taken, The measurement is performed using the above-mentioned liquid particle counter. The average value obtained by repeating the above operation three times was taken as the number of fine particles. In addition, the particle diameter of the microparticles was evaluated using an SEM image. 1(a) shows the SEM image of Example 5 (purity: 3N; magnification: 300 times), (b) shows the SEM image of Example 3 (purity: 4N; magnification: 300 times), and (c) The SEM image of Example 1 (purity: 5N; magnification: 300 times) is shown in the middle. 2 (a) shows the SEM image of Example 5 (purity: 3N; magnification: 15,000 times), (b) shows the SEM image of Example 3 (purity: 4N; magnification: 30,000 times), ( In c), the SEM image of Example 1 (purity: 5N; magnification: 15000 times) is shown. In addition, in FIG. 1, the microparticles|fine-particles (inclusions) whose particle diameters are 0.5 micrometer or more are shown by a wire frame.

(Evaluation of Fe concentration)

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

(Evaluation of the number of abnormal electrodepositions)

On a wafer with a diameter of 300 mm, the Co anodes of Examples 1 to 5 and Comparative Example 1 were used to perform Co plating under the same conditions to form a Co plated film with a thickness of 10 nm. The number of defects (number of abnormal electrodepositions) was evaluated.

The results of each of the above Examples and Comparative Examples are shown in Table 1.

[Table 1]

(Evaluation results)

In Examples 1 to 5, Co anodes having a particle diameter of 0.5 μm or more and the number of particles of 6000 particles/g or less were produced. On the other hand, in Comparative Example 1, the number of particles having a particle diameter of 0.5 μm or more exceeded 6000 particles/g.

In addition, Co anodes with the same purity were used in Example 1 and Example 2, Example 3 and Example 4, and Example 5 and Comparative Example 1, but the number of particles with a particle diameter of 0.5 μm or more existed due to the difference in Fe concentration. difference. From this result, it can be seen that, when the purity is the same, the number of particles having a particle diameter of 0.5 μm or more can be reduced more as the Fe concentration is smaller.

In addition, compared with Example 5 of purity 3N, Example 4 of purity 4N has a larger number of microparticles|fine-particles whose particle diameter is 0.5 micrometer or more. Thus, as long as it is "high purity", the relationship that the number of microparticles is small does not necessarily hold, and the number of microparticles shown in the present invention may be larger in a Co anode having a higher purity than a Co anode having a lower purity.

In addition, the number of abnormal electrodepositions of the Co plating films formed using the Co anodes of Examples 1 to 5 was 0, and plating defects were suppressed favorably. In the Co plated film formed using the Co anode of Comparative Example 1, abnormal electrodeposition was observed, resulting in poor plating.

Claims (7)

1. A Co anode, which is dissolved in dilute nitric acid having a nitric acid concentration of 20 mass %, and the number of particles having a particle diameter of 0.5 μm or more measured by a liquid particle counter according to JIS B 9925 is 6000 particles/g or less . 2 . The Co anode according to claim 1 , wherein the number of fine particles having a particle diameter of 0.5 μm or more is 5000 particles/g or less. 3 . 3. The Co anode according to claim 1 or 2, having a purity of 3N or more. 4. The Co anode according to claim 3, having a purity of 4N or more. 5. The Co anode according to claim 3 or 4, 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. 7. A Co electroplating method using the Co anode according to any one of claims 1 to 6.

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