JPH0431034B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Field of Industrial Application The present invention relates to a method for forming a fine conductor coil, which is a component of an electromagnetic transducer such as a thin film magnetic head, by electroplating. (b) Prior art Electromagnetic transducers such as thin-film magnetic heads are usually composed of a magnetic circuit and a conductive coil, and this conductive coil is formed using a fine pattern several μm in width formed using semiconductor lithography technology. It is often formed by electroplating in a copper sulfate bath. Compared to sputtering methods and the like, this plating method has the advantage that it can be processed at room temperature, thereby avoiding an increase in the temperature of the substrate, and that the processing time is short. Further, performing copper plating using a copper sulfate bath is advantageous in that the burden of waste liquid treatment can be reduced compared to using a copper cyanide bath or a pyrophosphoric acid bath. For information on how to perform copper plating in a copper sulfate bath,
"Metting Technology Handbook" (published by Nikkan Kogyo Shimbun, July 1973), "Practical Electrical Mitsuki" (Nikkan Kogyo Shimbun, published in 1972)
As is clear from publications such as ``Copper Sulfate Plating Bath'', copper sulfate, sulfuric acid, and a small amount of chlorine ion (C ^- ) are said to be essential in the composition of the copper sulfate plating bath, which makes the plated film glossy and uniform. Small amounts of surfactants (nonionic polymers) and sulfur-based organic compounds are usually added as plating bath additives to improve electrodeposition properties. (c) Problems to be solved by the invention However, according to the experience of the inventors, a phenomenon occurs when copper plating is applied to fine grooves with a width of 2 to 8 μm patterned with organic polymer using lithography technology. It was found that when an organic additive is included, the cross-sectional shape of the conductor coil becomes mountain-shaped. That is, as shown in FIG. 2, in the electromagnetic transducer 1 provided on the ceramic substrate 2, the cross-sectional shape of the conductor 5 formed by copper plating on the upper part of the lower magnetic film 3 through the gap 4 is chevron-shaped. In the next step, the upper magnetic film 7 formed on the conductive coil cannot be made flat even by normal means for eliminating steps, resulting in a wavy state. There was a problem in that the magnetic properties of the magnetic film deteriorated due to stress. (d) Means and action for solving the problem Therefore, the present inventors conducted studies from the viewpoint that it is extremely important for the top surface of the conductor to be flat in order to obtain a magnetoelectric transducer with good performance. As a result, we discovered that a matting bath with bromide ions or iodide ions added instead of the chlorine ions without adding the above-mentioned organic additives could yield a smooth plated film with a flat top surface. The invention was completed. FIG. 1 is a sectional view showing a magnetic head having a conductive coil plated with copper using the method of the present invention, in which the conductive coil is formed on the upper part of the lower magnetic film 3 of the electromagnetic transducer 1. The upper surfaces of the coils 5 are all flat, and therefore the upper magnetic film 7 formed above the coil also has a flat cross-sectional shape without any undulations. Table 1 shows the compositions of conventionally used general copper plating baths and the plating bath used in the method of the present invention.

【table】

[Table] In general, plating baths with a high ratio of sulfuric acid concentration (for example, 0.5 mol) to copper sulfate concentration (for example, 0.8 mol) have better uniform electrodeposition (responsiveness to unevenness). In the present invention, the sulfuric acid concentration is higher than the copper sulfate concentration, preferably a ratio of 3 to 8 is used. This is because if the copper sulfate concentration exceeds the range shown in the table above, problems will arise in the durability of the plating bath. In conventional copper sulfate plating baths, surfactants and organic compounds containing sulfur are added in millimole order to improve the gloss and leveling of the plated surface. The attached film becomes chevron-shaped. It is assumed that this is because the organic substances in the plating bath are adsorbed on the walls of the resist, which is the material of the lithographic pattern, and have an adverse effect on the deposition of copper, which is the plating metal. In addition, the presence of a very small amount of chlorine ions is essential in conventional plating baths, and the aforementioned ``Practical Electroplating'' also states that ``a very small amount of C ^- ions is effective in leveling copper plating.'' It is believed that this is because C ^- ions act on intermediates of anode dissolution reactions and cathode reactions, contributing to glossiness and leveling. However, according to the inventors' experiments, copper sulfate, sulfuric acid and C
^- When copper plating was performed on a fine pattern using a plating bath consisting of ions, the surface of the copper plating film was so uneven that it could not be put to practical use. Therefore, in the method of the present invention, the sulfuric acid concentration is higher than the copper sulfate concentration, preferably at a concentration ratio of 3 to 8, and without adding the above-mentioned organic additives.
The bath composition is such that Br ^- ions or I ^- ions are added instead of C ^- ions. The ions to be added can be used alone or in combination, and if the ion concentration is less than 0.1 mmol, the desired effect will not be obtained, while if it is added in excess of 2 mmol, the durability of the bath will deteriorate, so they should not be added. should
The range of Br ^- or I ^- ion concentration was determined to be 0.1-2 mmol. When copper plating is performed by the method of the present invention, as shown in FIG. 3, the flatness of the upper surface of the copper plating film 5 plated between the patterned resist frames 8 is ensured, and Since a coil with a high aspect ratio (large aspect ratio) can be formed, electromagnetic conversion efficiency can be increased. It is also extremely effective when forming a coil in multiple layers to increase the number of coil turns. Therefore, it will be obvious to those skilled in the art that the method of the present invention can be applied not only to magnetic heads but also to the production of other fine coils, wiring, etc. Next, the present invention will be further explained by examples. Example For the purpose of preparing a magnetoelectric transducer for a magnetic head,
After patterning fine grooves approximately 5 μm wide on the resist by lithography, copper plating was performed using the plating bath composition shown in Table 2.

[Table] The upper surface of the obtained copper-plated film was flat, and the third
It had a cross-sectional structure as shown in the figure. Note that copper plating was similarly attempted by changing the additive ions to iodide ions, but the same results as in the case of bromide ions were obtained. Effects of the Invention As described above, according to the present invention, in addition to obtaining a conductive coil with a flat top surface, it is also possible to form a plated film having a high aspect ratio, thereby increasing electromagnetic conversion efficiency. FIG. 4 shows the frequency characteristics of the magnetic transducer. Therefore, a copper plating method is provided that is extremely effective compared to conventional methods.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a magnetic head having a conductive coil plated with copper by the method of the present invention, and FIG. 2 is a schematic sectional view of a magnetic head using a conventional copper sulfate plating bath. FIG. 3 is a cross-sectional view illustrating a copper-plated film obtained by the method of the present invention. Fourth
The figure is a diagram showing the frequency characteristics of magnetic transducer elements obtained by the method of the present invention and the conventional method. 1... Magnetic head, 2... Ceramic substrate, 3
... lower magnetic film, 4 ... gap, 5 ... copper-plated conductor, 6 ... resist, 7 ... upper magnetic film,
8...Regist frame.

Claims (1)

[Scope of Claims] 1. An electromagnetic transducer comprising a conductor and a magnetic film provided on a ceramic substrate, wherein the conductor is made of copper containing at least one of bromine and iodine. . 2. In a copper plating bath for forming a conductor of an electromagnetic conversion element on a ceramic substrate by plating, the copper plating bath is made of a copper sulfate bath containing at least one of bromine ions and iodine ions. Copper plating bath for producing conductors for electromagnetic conversion elements. 3. The copper plating bath for producing a conductor of an electromagnetic conversion element according to claim 2, wherein the ion concentration of at least one of the bromine ions and iodine ions is in the range of 0.12 mmol.