CN111971423A

CN111971423A - Co anode and Co electroplating method using the same

Info

Publication number: CN111971423A
Application number: CN201880091917.3A
Authority: CN
Inventors: 村田周平; 小井土由将; 浅野孝幸; 神永贤吾
Original assignee: JX Nippon Mining and Metals Corp
Current assignee: JX Nippon Mining and Metals Corp
Priority date: 2018-03-28
Filing date: 2018-10-03
Publication date: 2020-11-20
Also published as: US20210010149A1; TW201942423A; JP2019173104A; TWI683040B; KR20200128097A; JP6960363B2; SG11202009378RA; WO2019187250A1; KR102435667B1

Abstract

The invention provides a novel anode for electroplating, which can replace a Cu anode and inhibit poor plating. The anode was a Co anode in which the number of fine particles having a particle diameter of 0.5 μm or more was 6000 particles/g or less, as measured by a liquid fine particle counter in accordance with JIS B9925 after dissolving the anode in dilute nitric acid having a nitric acid concentration of 20 mass%.

Description

Co anode and Co electroplating method using the same

Technical Field

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

Background

In general, Cu plating is used for forming Cu wiring for PWBs (printed wiring boards) and the like, but recently, Cu wiring for semiconductors is also used. As an anode for Cu plating for forming Cu wiring, a pure Cu anode or a phosphorus-containing Cu anode may be used.

For example, patent document 1 discloses a pure Cu anode or a phosphorus-containing Cu anode for Cu plating, and discloses: by controlling the purity to be within a predetermined range and the content of impurities to be equal to or less than a predetermined value, it is possible to suppress the adhesion of particles to a semiconductor wafer manufactured using the pure Cu anode or the phosphorus-containing Cu anode.

As a technique for suppressing the adhesion of particles to a semiconductor wafer manufactured by using a phosphorus-containing Cu anode, patent document 2 describes the following technique: when Cu plating is performed on a semiconductor wafer, a fine crystal layer in which the grain size is controlled within a predetermined range is formed on the surface of a phosphorus-containing Cu anode in advance.

Background of the invention

Patent document

Patent document 1: japanese patent No. 5066577

Patent document 2: patent No. 4076751.

Disclosure of Invention

[ problems to be solved by the invention ]

In recent years, high performance and low power consumption of semiconductor devices have been increasingly demanded, and with the progress of miniaturization of wiring, measures against deterioration of Electromigration (EM) which affects the reliability of wiring, and reduction in resistance of wiring which causes signal delay have been becoming problems. As described above, the techniques described in patent document 1 and patent document 2 are techniques for obtaining a Cu wiring or the like advantageous for fine wiring by suppressing fine particles generated when forming a Cu wiring or the like by Cu plating, but there is room for improvement in EM resistance and reduction in wiring resistance in such plating using a Cu anode as in the past. Therefore, development of a novel electroplating anode capable of replacing the Cu anode and further suppressing the plating failure, which is a conventional problem, has been desired.

Accordingly, an object of the present invention is to provide a novel electroplating anode capable of suppressing plating failure in place of a Cu anode.

[ means for solving problems ]

As a result of various studies to solve the above-described problems, the present inventors have found that, in the field of fine wiring formation, a Cu wiring is replaced with a Co wiring in a frontmost partial wiring or the like having a narrow wiring and a relatively short wiring distance. It is found that the Co wiring has good EM resistance compared with the Cu wiring, and the wiring resistance is suppressed to be lower than that of the Cu wiring when the wiring distance is shortened by the thinning amount of the barrier metal layer.

Therefore, it has been found that an anode capable of suppressing plating failure can be obtained by forming a Co anode in place of the Cu anode and controlling the number of fine particles having a predetermined particle diameter or more in the Co anode.

An aspect of the embodiment of the present invention completed based on the above-described findings is a Co anode in which the number of fine particles having a particle diameter of 0.5 μm or more, measured by a liquid fine particle counter according to JIS B9925 after dissolution with dilute nitric acid having a nitric acid concentration of 20 mass%, is 6000 pieces/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 the invention ]

According to the embodiment of the present invention, a novel electroplating anode capable of suppressing poor plating in place of a Cu anode can be provided.

Drawings

FIG. 1 (a) 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 SEM image of example 1 (purity: 5N; magnification: 300 times).

FIG. 2 (a) is an SEM image of example 5 (purity: 3N; magnification: 15000 times), (b) is an SEM image of example 3 (purity: 4N; magnification: 30000 times), and (c) is an SEM image of example 1 (purity: 5N; magnification: 15000 times).

FIG. 3(a) is an EDX spectrum of example 5.

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

FIG. 3(c) is the EDX spectrum of example 1.

Detailed Description

[ constitution of Co Anode ]

The Co anode according to the embodiment of the present invention has a number of particles having a particle diameter of 0.5 μm or more, measured in accordance with JIS B9925 using a liquid particle counter after being dissolved in dilute nitric acid having a nitric acid concentration of 20 mass%, of 6000 particles/g or less. The Co anode has good EM resistance compared with the Cu anode, and the wiring resistance can be suppressed to be lower than that of the Cu wiring when the wiring distance is shortened according to the thinning amount of the barrier metal layer. Further, since the number of fine particles having a particle size of 0.5 μm or more is controlled to 6000 particles/g or less, the occurrence of abnormal deposition of plating can be suppressed when electroplating is performed using a Co anode, and as a result, plating failure can be favorably suppressed.

The particles are solid inclusions existing in the structure of the Co anode, and are not dissolved in dilute nitric acid in the implementation of the liquid particle counter described later. As the impurities 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 a substance exists in the form of a coarse structure in the Co anode, it is ionized in the plating process, and thus, it is taken into the plating film in a very fine form of an ion grade. On the other hand, the inclusions (fine particles) that do not dissolve in the dilute nitric acid are electrochemically stable, and thus remain in the form close to that when present in the Co anode and are taken into the plating film. Therefore, even in the case of a Co anode having the same purity, the size of the impurity to be incorporated into the plating film becomes large in the case where the proportion of fine particles in the impurity is large, and thus plating failure is likely to occur. In view of this, the present invention provides a Co anode in which the number of particles having a predetermined particle diameter or more, which are solid inclusions insoluble in dilute nitric acid, is controlled.

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

The present inventors have found that, particularly, fine particles having a particle size of 0.5 μm or more are not dissolved in an electrolyte and are taken up into a plating film, and abnormal deposition of plating is likely to occur, and therefore, focusing on the number density of fine particles having such a particle size, and controlling the number density to 6000 particles/g or less, the generation of fine particles in the plating film produced by electroplating can be excellently controlled, and as a result, it has been found that the generation of abnormal deposition of plating can be suppressed. Further, when the impurity as fine particles is not detected or when the impurity as fine particles is detected, it is found that one side in which the fine particles are detected has an adverse effect on the plating process, and particularly, the Co wiring formed by the Co anode is frequently used as fine wiring, and such an adverse effect becomes remarkable, and from this viewpoint, the number of fine particles having a particle diameter of 0.5 μm or more is also controlled. The number of fine particles having a particle diameter of 0.5 μm or more in the Co anode according to the embodiment of the present invention is preferably 5000 pieces/g or less, and more preferably 4000 pieces/g or less.

The particle diameter of the fine particles can be measured by a "light scattering type automatic particle counter for liquids" (manufactured by Jiuzhou RION Co., Ltd.). This measurement method is a method of distinguishing particles of various sizes in a liquid and measuring the particle concentration and the number of particles, and is based on JIS B9925 (in the present invention, this measurement is referred to as a "liquid particle counter").

The procedure of carrying out the liquid particle counter will be specifically described below, namely, 1g of the sample is slowly dissolved by 150ml of dilute nitric acid (aqueous solution of nitric acid concentration 20 mass%) so as to insolubilize the particles, and after leaving for 24 hours, the sample is further diluted to 500ml with pure water, and 10ml of the solution is taken out and measured by the liquid particle counter. For example, when the number of fine particles was 1000 particles/ml, the number of fine particles was 500000 particles/g because 0.02g of the sample was measured in 10 ml.

The number of particles is not limited to the number measured by the liquid particle counter, and may be measured by other means 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 99.9 mass%) or more, the generation of fine particles in the plating film produced by electroplating using the Co anode can be more favorably suppressed, and as a result, the generation of abnormal deposition of plating can be more favorably suppressed. The purity of the Co anode according to the embodiment of the present invention is more preferably 4N (purity 99.99 mass%) or more, and still more preferably 5N (purity 99.999 mass%) or more. The term "purity" As used herein, for example, purity 5N (99.999%) is defined As the total value of elements not more than the lower limit of detection and all metal elements other than Co, for example 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, which are analyzed by Glow Discharge Mass Spectrometry (GDMS).

As shown in examples and comparative examples described later, the relationship that the number of fine particles is small is not necessarily satisfied as long as "high purity" is concerned, and the number of fine particles shown in the present invention may be larger in a Co anode having high purity than in a Co anode having low purity.

The Co anode of the embodiment of the present invention is preferably controlled to have an Fe concentration of 10ppm or less. Fe is not easily dissolved in an acidic solution, and therefore, if Fe is mixed into a Co anode, fine particles are easily formed. When a comparison is made between Co anodes having the same degree of purity, the number of fine particles generated in the plating film of one of the Co anodes in which the Fe concentration is controlled to 10ppm or less is smaller than that of a Co anode in which the Fe concentration exceeds 10ppm, and as a result, the generation of abnormal deposition in the plating can be further suppressed. The Fe concentration of the Co anode according to the embodiment of the present invention is controlled to be more preferably 8ppm or less, still more preferably 5ppm or less, still more preferably 3ppm or less, still more preferably 1ppm or less, and still more preferably 0 ppm.

[ method for producing Co Anode ]

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

As described above, fine particles that are problematic in electroplating are particles of compounds such as Fe, Mg, Cr, Ni, Si, and Al, and these particles are responsible for the generation of fine particles in the plating film. In order to prevent these particles from being mixed into the Co anode, the surface roughness of the portion of the container, piping, and mold that contacts the Co raw material may be controlled. From the viewpoint that these particles are likely to float on the slag side, the molten metal may be stirred for a longer period of time to distribute particles having a particle size of the compound of Fe, Mg, Cr, Ni, Si or Al of more than 0.5 μm on the slag side.

Then, the melted Co raw material is supplied to a mold and forged, followed by rolling, heat treatment, and surface cutting, thereby producing a Co anode.

[ Co electroplating method ]

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

In the Co electroplating method according to the embodiment of the present invention, there is no particular limitation, and, for example, as the plating solution, cobalt sulfate: 10-30 g/L of (Co), or 5-15 g/L of cobalt chloride. The pH value is set to 2.5-3.5.

Further, the plating bath temperature is 25 to 60 ℃, and the cathode current density is 0.5 to 10A/dm²The anode current density is 0.5 to 10A/dm²But is not necessarily limited to these conditions. The plating bath may also contain a gloss agent, a complexing agent, a pH buffer, a surfactant, and the like.

[ examples ]

Hereinafter, examples are provided to better understand 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, a Co raw material having a predetermined purity was vacuum-melted to prepare an ingot, and the ingot was melted. The Co raw material having a purity of 3N was obtained by using a commercially available cobalt material, and the Co raw materials having purities of 4N and 5N were obtained by electrolytic purification.

Then, the melted Co raw material is supplied to a mold and forged, then rolled at a rolling rate of 30 to 50%, then heat-treated at 300 to 600 ℃, and further subjected to surface cutting, thereby producing a Co anode.

[ evaluation ]

(evaluation of Fine particles)

The particle diameter and number of fine particles were measured by a "liquid light scattering type automatic particle counter" (manufactured by Jiuzhou RION Co., Ltd.). Specifically, 1g of the Co anode was sampled and slowly dissolved in 150ml of dilute nitric acid (aqueous solution of nitric acid concentration 20 mass%) so as to insolubilize the fine particles, and after leaving for 24 hours, the sample was further diluted with pure water to 500ml and 10ml of the solution was taken out and measured by the liquid particle counter. The number of fine particles was determined as an average value obtained by repeating the above operation 3 times. The particle size of the fine particles was evaluated by SEM image. FIG. 1 (a) shows an SEM image of example 5 (purity: 3N; magnification: 300 times), (b) shows an SEM image of example 3 (purity: 4N; magnification: 300 times), and (c) shows an SEM image of example 1 (purity: 5N; magnification: 300 times). FIG. 2 (a) shows an SEM image of example 5 (purity: 3N; magnification: 15000 times), (b) shows an SEM image of example 3 (purity: 4N; magnification: 30000 times), and (c) shows an SEM image of example 1 (purity: 5N; magnification: 15000 times). In FIG. 1, fine particles (inclusions) having a particle size of 0.5 μm or more are indicated by a line frame.

(evaluation of Fe concentration)

The Fe concentration contained in the Co anode was evaluated by GDMS. The particulate component remaining on the filter when the particle size and number of the particulates were measured was evaluated by Energy Dispersive X-ray analysis (EDX). 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 electrodeposition)

Co electroplating was performed on a Wafer (Wafer) having a diameter of 300mm under the same conditions using the Co anodes of examples 1 to 5 and comparative example 1, to form a Co plating film having a thickness of 10nm, and the number of defects (the number of abnormal depositions) generated in the Co plating film was evaluated.

The results of the above examples and comparative examples are shown in table 1.

[ Table 1]

(evaluation results)

In examples 1 to 5, Co anodes having particle diameters of 0.5 μm or more and a particle number of 6000 particles/g or less were produced. On the other hand, in comparative example 1, the number of fine particles having a particle diameter of 0.5 μm or more was more than 6000 particles/g.

In addition, although Co anodes having the same purity were used in examples 1 and 2, examples 3 and 4, and examples 5 and comparative example 1, the number of fine particles having a particle diameter of 0.5 μm or more was different depending on the Fe concentration. From the results, it is understood that the smaller the Fe concentration, the smaller the number of fine particles having a particle diameter of 0.5 μm or more, the higher the purity.

In example 4 with a purity of 4N, the number of fine particles having a particle diameter of 0.5 μm or more was larger than that in example 5 with a purity of 3N. As described above, the relationship that the number of fine particles is small is not necessarily satisfied as long as "high purity" is satisfied, and the number of fine particles shown in the present invention may be larger in one of high-purity Co anodes than in a Co anode having low purity.

In addition, the Co plating films formed by using the Co anodes of examples 1 to 5 showed 0 number of abnormal electrodeposition, and thus the plating failure was favorably suppressed. Abnormal electrodeposition was observed in the Co plating film formed using the Co anode of comparative example 1, and plating failure occurred.

Claims

1. A Co anode, which is dissolved by dilute nitric acid with 20 mass percent of nitric acid concentration, wherein the number of particles with the particle diameter of more than 0.5 μm measured by a liquid particle counter according to JIS B9925 is less than 6000/g.

2. The Co anode of claim 1, wherein the number of the fine particles having a particle size of 0.5 μm or more is 5000 pieces/g or less.

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 of claim 3 or 4, wherein the Fe concentration is 10ppm or less.

6. The Co anode of claim 5, wherein the Fe concentration is 5ppm or less.

7. A Co electroplating method using the Co anode according to any one of claims 1 to 6.