JPH07220921A - Soft magnet thin film, its manufacture and electroless plating bath - Google Patents

Abstract

PURPOSE:To provide a plating bath for electroless plating with excellent mass- producibility which shows good soft magnetic characteristics, has good uniformity in composition distribution and thickness distribution, and is easily managing and controlling the soft magnetic thin film having a high saturated magnetic flux density and a good heat resistance. CONSTITUTION:Co, Fe and B are contained and content of Fe is 8 to 15 atomic percentage; and an electroless plating bath is used which has Co ion, Fe ion, a boron contained reducing agent and phosphorous acid ion with the concentration of the phosphorous acid ion of more than 0.01mol/liter when forming a soft magnetic thin film having a coercive force of less than 20e by electroless plating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soft magnetic thin film used for magnetic head materials, sensor materials, magnetic cores for transformers, choke coils, supersaturated reactors, noise filters, etc., and a method for producing this soft magnetic thin film. , An electroless plating bath used in this manufacturing method.

[0002]

2. Description of the Related Art In the field of magnetic recording, the coercive force of magnetic recording media has been increased to achieve high density recording. For a magnetic recording medium having a high coercive force, a recording head having a high saturation magnetic flux density and a high magnetic permeability is required. Therefore, a thin film using a soft magnetic thin film having a high saturation magnetic flux density and a high magnetic permeability is usually used. Type and metal-in-gap type recording heads are used. In addition, high saturation magnetic flux density and high magnetic permeability are also required for soft magnetic thin films used for magnetic cores of thin film transformers.

Conventionally, the soft magnetic thin film used for these purposes is produced by a vacuum film forming method such as a sputtering method or an electroplating method, and permalloy or the like is generally used as a composition. However, since the Fe / Co ratio range in which permalloy exhibits good soft magnetic characteristics is narrow, composition control during film formation is difficult. Further, the sputtering method is poor in mass productivity, and it is difficult to uniformly form a large-area film. On the other hand, when the electroplating method is used, there arise problems such as oxidation of divalent iron and nonuniform composition distribution due to current density distribution.

The permalloy film formed by the electroless plating method is described in Kojima et al. (Tohoku University Institute of Science Report Vol. 33, No. 1).
No. P1-13 1984) and Takano et al. (Abstracts of the 74th Lecture Meeting of the Japan Metal Surface Technology Association 16A-11), but it is also difficult to control the composition and the Fe / Ni range showing good characteristics is reproducible. It is difficult to get well. Further, although the electroless plating Co-P thin film has been studied by Kojima et al., The coercive force is reduced to 5 Oe at most, and sufficient soft magnetic characteristics have not been obtained.

An electroplating film of Co--Fe has been proposed as a soft magnetic thin film which is excellent in mass productivity and whose composition can be easily controlled. However, since the electroplating method is used, the composition distribution and There is a problem that non-uniformity of thickness distribution occurs, and there is a limitation that only a conductive substrate can be used.

Under these circumstances, Japanese Patent Application Laid-Open No. 4-1964
No. 02 publication proposes a Fe-Co-B ternary soft magnetic thin film. This soft magnetic thin film can be formed by an electroless plating method that can obtain a film having excellent uniformity in composition distribution and thickness distribution, and management and control during film formation are easy. However, the soft magnetic thin film described in the above publication has an Fe content of 7 atomic% or less in order to reduce the coercive force, and therefore has an insufficient saturation magnetic flux density. Further, this soft magnetic thin film has low heat resistance, and when heated to, for example, 400 ° C., the coercive force increases to 5 Oe or more. Since the soft magnetic thin film is heated during core joining when manufacturing a magnetic head,
This soft magnetic thin film may deteriorate the soft magnetic characteristics.

[0007]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a soft magnetic thin film which exhibits good soft magnetic properties, good composition distribution and thickness distribution uniformity, and high saturation magnetic flux density and good heat resistance. Another object is to provide a method for forming such a soft magnetic thin film by an electroless plating method that is easy to manage and control and is excellent in mass productivity, and another object is to provide The purpose is to provide a plating bath used in such an electroless plating method.

[0008]

These objects are achieved by the following constitutions (1) to (8). (1) Co, Fe and B are contained, and the Fe content is 8
A soft magnetic thin film having a coercive force of 2 to 15 atomic% and a coercive force of 2 Oe or less and formed by an electroless plating method. (2) The soft magnetic thin film according to (1) above, wherein the B content is 1 to 7 atomic%. (3) The soft magnetic thin film according to (1) or (2) above, wherein the crystalline material contained is substantially a face-centered cubic single phase. (4) Containing Co ion, Fe ion, boron-containing reducing agent and phosphite ion, and having a phosphite ion concentration of 0.01
An electroless plating bath characterized by a mol / liter or more. (5) The electroless plating bath according to (4) above, wherein the concentration of phosphite ions is 1 mol / liter or less. (6) The electroless plating bath according to the above (4) or (5), which contains tartrate ions and / or citrate ions as complexing agent ions. (7) A method for producing a soft magnetic thin film, which comprises forming the soft magnetic thin film using the electroless plating bath according to any one of (4) to (6). (8) The method for producing a soft magnetic thin film according to (7) above, wherein the soft magnetic thin film according to any one of (1) to (3) above is formed.

[0009]

In the present invention, since the electroless plating method is used in forming the soft magnetic thin film containing Co, Fe and B, a film having a good composition distribution and a uniform thickness distribution can be obtained. The property is also good.

In the present invention, since the Fe content in the soft magnetic thin film is set to 8 atomic% or more, a high saturation magnetic flux density can be obtained. By using an electroless plating bath containing Co ions, Fe ions, and a boron-containing reducing agent in addition to a phosphite ion, a soft magnetic thin film having a remarkably low coercive force can be obtained even when the Fe content is 8 atomic% or more. Easily obtained.
Moreover, this soft magnetic thin film has good heat resistance,
The coercive force only slightly increases even after heating to about ℃. When using an electroless plating bath containing phosphite ions,
It is considered that a very small amount of P is co-deposited in the film to affect the fine structure of the film to improve the soft magnetic properties and heat resistance, but the detailed function is not well understood.

In the electroplating method, it is known to add hypophosphite ions or phosphite ions to the plating bath for the purpose of positively co-depositing P in the film.
However, conventionally, P is co-deposited in the electroplating method in order to improve the corrosion resistance and the magnetic properties by making it amorphous, and the P content rate greatly exceeds 1%. On the other hand, in the present invention, as will be described later, the amount of P contained in the film is extremely small.

Further, in the electroless plating method, it is known to add hypophosphorous acid as a reducing agent to the plating bath.
However, hypophosphorous acid used in a general electroless plating method is indispensable as a reducing agent during film formation. on the other hand,
In the present invention, it is considered that the action as a reducing agent is not so important, as is clear from the fact that a sufficient effect can be obtained even with phosphorous acid having a small reducing power. In fact, even if the phosphite ion is removed from the electroless plating bath used in the present invention, the film forming reaction occurs.

By the way, Co containing 8 atomic% or more of Fe
Although it has been reported that the -Fe-B alloy is manufactured by the quenching method, the amorphous quenching alloy has insufficient heat resistance. However, since the B content must be increased in order to crystallize, good soft magnetic characteristics cannot be obtained, and the coercive force becomes large, for example, 5 Oe or more. Also,
Quenched alloys are virtually impossible to thin and pattern.

In the above-mentioned Japanese Patent Laid-Open No. 4-196402, an electroless plated film containing 9.2 atomic% Fe is described as a comparative example. Since this film is formed by using an electroless plating bath containing no phosphite ion, the coercive force reaches 25.3 Oe and cannot be used as a soft magnetic thin film.

[0015]

Specific Structure The specific structure of the present invention will be described in detail below.

<Soft Magnetic Thin Film> The soft magnetic thin film of the present invention is C
It contains o, Fe and B. Fe content is 8 to 1
It is 5 atom%. If the Fe content is too small, a high saturation magnetic flux density cannot be obtained, and if the Fe content is too large, body-centered cubic crystals are precipitated, resulting in poor soft magnetic properties. The B content is preferably 1 to 7 atomic%,
More preferably, it is 2 to 5 atom%. If the amount of B is too large, the Co-B alloy or the Co-Fe-B alloy becomes the main component, and if the amount of B is too small, Co or Co-Fe.
Crystals are the main component, and in any case, it becomes difficult to obtain preferable soft magnetic characteristics. The rest of the soft magnetic thin film is substantially C
Although formed from o, Ni, W, Mo, Cu, Zn, S
At least one selected from n, S, Ca and the like may be contained. However, the total content of these elements is preferably 5 atomic% or less.

By forming the soft magnetic thin film of the present invention by an electroless plating method using a plating bath containing phosphite ions as described later, good soft magnetic characteristics can be easily obtained. However, when the addition amount of phosphite ions was set to a range where good soft magnetic characteristics were obtained, P derived from phosphite ions could not be detected by fluorescent X-ray analysis. Therefore, the P content is at most 1 atom%, and is usually considered to be 0.2 atom% or less. It is considered that P derived from the phosphite ion segregates at the crystal grain boundaries and contributes to the improvement of the soft magnetic properties, but it has not been confirmed.

When such a soft magnetic thin film has an amorphous-like structure having fine crystal grains, extremely good soft magnetic characteristics can be obtained. Amorphous analog structure is X
It has a structure showing a broad peak in line diffraction, and is considered to be composed of, for example, a crystalline substance estimated to have an average particle size of about 100 A or less. In the soft magnetic thin film of the present invention, broad peaks are recognized as face-centered cubic (1
Since it is a peak corresponding to the 11) plane, it is considered that the crystalline material contained in the soft magnetic thin film is substantially composed of the face-centered cubic single phase. However, since the composition range in which the coercive force is small is adjacent to the composition range in which the body-centered cubic crystal phase is co-deposited, it is possible that a very small amount of body-centered cubic crystal is locally segregated. Therefore, “substantially consisting of a face-centered cubic single phase” is an evaluation result when a general-purpose X-ray diffractometer is used,
The concept also includes the case where an extremely small amount of body-centered cubic crystal that cannot be detected by such a device is included.

As a Co-B type alloy, Co ₂ B is used.
(33.3 atom%, that is, 841 wt% B) and Co
B (50 atomic%, that is, 15.51 wt% B) and the like are known, but the soft magnetic thin film of the present invention is completely different from them. That is, the B content of the soft magnetic thin film of the present invention is at most about 7 atom%.

The soft magnetic thin film of the present invention has good soft magnetic characteristics. That is, the coercive force immediately after film formation is usually 1.0
Since it is less than Oe and has good heat resistance, it is 5
It shows a low coercive force of 2 Oe or less even after heating to about 00 ° C. Also, the magnetic permeability is high, for example, 1000 at 5MHz.
The above magnetic permeability is shown. Further, the soft magnetic thin film of the present invention has a high saturation magnetic flux density, and usually shows a value of 1550 emu / cc or more.

The thickness of the soft magnetic thin film of the present invention is not particularly limited, but it is preferably 0.05 μm or more in order to form a uniform film. The thicker the film, the easier it is to form a giant crystal structure. Therefore, the thickness is preferably 10 μm or less, more preferably 5 μm or less.

When it is desired to form a thicker film, the film can be laminated via an intermediate layer such as another electroless plating layer. Other electroless plating layers include non-magnetic layers such as Ni-P.
Layers and Cu layers. That is, it is also possible to preferably form a non-magnetic layer as an intermediate layer and form Co—Fe—B layers above and below it. Further, it is possible to increase the number of intermediate layers and stack any number of layers. This is Co-Fe-
When the structure of the B film changes depending on the thickness, it is useful for stacking a number of thin films to obtain a desired thickness. The intermediate layer may be a magnetic layer, but a nonmagnetic plating layer is particularly preferable. When stacking in this way, C
It is preferable that the o-Fe-B layer has a thickness of about 0.05 to 2 μm and the intermediate layer has a thickness of about 5 to 30% thereof. Ni-P used as the intermediate layer has a P content of 5 to 1
The composition is preferably about 8% by weight. In addition, the intermediate layer is made of Co-P or Co-Ni-P having a thickness of 0.01 μm or less
May be

The soft magnetic thin film of the present invention is a magnetic pole material of a thin film magnetic head, a soft magnetic thin film of a metal-in-gap type magnetic head, a soft magnetic underlayer of a perpendicular magnetic recording medium, a magnetic sensor, a distance sensor, and an orientation sensor. It is useful as a sensor thin film such as an inclination sensor, a transformer, a choke coil, a noise filter, a thin film magnetic core such as a supersaturated reactor, a magnetic shield thin film, and the like.

<Manufacturing Method> The soft magnetic thin film described above is Co
By an electroless plating method using a plating bath containing ions, Fe ions, a boron-containing reducing agent and phosphite ions,
It can be easily formed.

The Co ion concentration and the Fe ion concentration in the plating bath may be appropriately determined according to the intended film composition and the required film formation rate, but usually Co
The ion concentration is 0.05 to 3.0 mol / liter, and F
e ion / Co ion (molar ratio), preferably 0.0
It is set to 05 to 0.3, and more preferably 0.01 to 0.2. The source of these metal ions is preferably selected from water-soluble salts such as sulfates, sulfamic acid salts, acetates and nitrates, and sulfates are particularly preferable because they are inexpensive. In addition, the metal may be immersed in a plating bath to spontaneously dissolve it, or the anode may be dissolved and supplied by electrolysis.

A boron-containing reducing agent is used as the source of B.
As the boron-containing reducing agent, dimethylamine borane, trimethylamine borane, sodium borohydride and the like are preferable, and dimethylamine borane is particularly preferable. The concentration of the boron-containing reducing agent is preferably 0.01 to 0.10 mol / liter.

The concentration of phosphite ions is preferably 0.01 mol / liter or more. By using the electroless plating bath containing phosphite ions, the coercive force of the above-mentioned soft magnetic thin film having a high Fe content can be lowered, and the heat resistance of the film also becomes good. If the concentration of phosphite ions is low,
It becomes difficult to obtain a film having a low coercive force. Although there is no particular upper limit to the concentration of phosphite ions, a sufficient effect can be obtained at a concentration of about 0.1 mol / liter, and even if the concentration exceeds 1 mol / liter, the effect is not improved. Considering the solubility limit, it is preferably 1 mol / liter or less. As a source of phosphite ions, phosphorous acid or a salt thereof, such as sodium phosphite and potassium phosphite, can be used.

The plating bath preferably contains complexing agent ions. The complexing agent ion is preferably an organic acid ion, and specifically, tartaric acid, citric acid, succinic acid,
It is preferable to add malonic acid, malic acid, gluconic acid or a salt thereof as a complexing agent to the plating bath, particularly tartaric acid or a salt thereof and / or citric acid or a salt thereof, particularly sodium tartarate and / or sodium citrate. Is preferably used. The concentration of the complexing agent ion is preferably 0.05 mol / liter or more, more preferably 0.1 to 1 mol / liter. By adding a complexing agent to the plating bath, a microstructure structure is stably formed and soft magnetic properties are improved.

An ammonia source is preferably contained in the plating bath. Examples of the ammonia source include ammonium sulfate and ammonium chloride. The addition of the ammonia source also stabilizes the fine structure of the film and improves the soft magnetic properties. The concentration of the ammonia source is preferably 0.1 mol / liter or more, more preferably 0.2 to 0.4 mol / liter.

In addition to this, a buffering agent such as boric acid may be added to the plating bath, if necessary.

The pH of the plating bath is preferably 7-10. If the pH is too low, the deposition rate will be slow, and if it is too high, the bath will be unstable and separation will be easy. The pH adjuster is not particularly limited, but sodium hydroxide or the like may be used to keep the amount of ammonium ions in the bath constant.

The temperature of the plating bath is preferably 40 to 95.
C., more preferably 70 to 90.degree. If the bath temperature is too high, the bath becomes unstable and separation tends to occur, and if it is too low, the deposition rate becomes slow. Note that the bath is likely to become unstable at a high temperature close to the boiling point in the atmosphere, and in such a case, the film formation may be performed under pressure.

The plating time is preferably 2 to 60 minutes,
It is more preferable in view of the process that the film thickness is set to 10 to 20 minutes.

If the film needs to be thickened,
It is possible to obtain a thick film in a short time by using electroplating together or activating electroless deposition by alternating current electrolysis. Further, these electrolysis techniques can be performed only during a certain period during plating. For example, use electroless plating alone to form a film with a thickness of 0.5 μm and then use electrolysis together, or use electroless plating for 5 minutes and electroplating together 5
It is also possible to alternate between minutes and. The current density of the electrolytic plating combination which is preferably in the 0.5~3A / dm ² about, alternating current electrolysis is preferably carried out at a frequency of about 1~1000Hz at a current density of 0.1~1A / dm ^2.

When it is desired to impart a suitable magnetic anisotropy to the soft magnetic thin film, it is preferable to apply an orthogonal magnetic field during plating. For example, a magnetic field strength of 800 in the direction of the axis of easy magnetization.
After applying Oe for 10 seconds, 200 Oe is applied for 5 seconds in the desired direction of the hard axis, and this is repeated during film formation. Alternatively, the same effect can be obtained by rotating the substrate in a DC magnetic field. In this way, by applying magnetic fields from different directions alternately or forming a film while applying a rotating magnetic field, a suitable magnetic anisotropy is imparted. The magnetic field applied in the in-plane easy axis direction is preferably about 50 to 1000 Oe, and the magnetic field applied in the in-plane hard axis direction is preferably about 50 to 1000 Oe. The period of application of such alternating or rotating magnetic field may be generally about 0.1 to 200 seconds.

In the present invention, as described above, a multi-layer structure in which a non-magnetic intermediate layer is sandwiched between soft magnetic thin films can be used.
When a Ni—P layer is provided as the non-magnetic intermediate layer, sodium hypophosphite or the like may be used as the P supply source.
As the i supply source, nickel sulfate, nickel chloride or the like may be used.

The base material carrying the soft magnetic thin film may be appropriately selected depending on the application, and may be rigid or flexible. The substrate may be subjected to various known activation treatments such as electroless plating before forming the soft magnetic thin film.

If necessary, the soft magnetic thin film may be peeled off from the substrate after use.

[0039]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

<Examples 1 and 2, Comparative Examples 1 to 3> As a substrate, a glass plate having a thickness of 0.7 mm on which a Cu film having a thickness of 500 A was formed by a sputtering method (Corning product number 705)
9) was prepared. This substrate was immersed in a 5% sodium hydroxide solution (room temperature) for 30 seconds for degreasing treatment. Then, after rinsing with water, activation treatment was carried out by immersing in a 10% hydrochloric acid solution (room temperature) for 30 seconds. Electroless plating was performed on this substrate for 10 minutes using the plating bath shown in Table 1 and Table 2
The thin film shown in was formed.

An alternating orthogonal magnetic field was applied to the substrate being plated. That is, a direct-current magnetic field was obtained by facing two permanent magnets in pairs, and the positions of these permanent magnets were periodically changed with respect to the substrate to form an alternating orthogonal magnetic field. The magnetic field strength is 600 Oe in the easy axis of magnetization,
The magnetization direction was set to 300 Oe in the hard axis direction, and the application direction was changed every 20 seconds.

For each thin film, the thickness was measured with a step gauge, the saturation magnetic flux density (Bs) and the coercive force (Hc) were measured with VSM, and the magnetic permeability (μ) was measured with the figure eight coil method. Further, after dissolving each thin film with nitric acid, plasma emission analysis was performed to quantify the Fe content rate and the B content rate in the film. The results are shown in Table 2.

[0043]

[Table 1]

[0044]

[Table 2]

From the results shown in Table 1 and Table 2, the effect of the present invention is clear. That is, Examples 1 and 2
Then, using an electroless plating bath containing phosphite ions, Fe
Since the film having the content in the range of 8 to 15 atomic% is formed, a high saturation magnetic flux density is obtained, and the coercive force is low and the magnetic permeability is high. On the other hand, in Comparative Example 1, the Fe content was 8 using the plating bath containing no phosphite ion.
The coercive force is significantly increased because the film is formed in an atomic percentage of at least. In Comparative Example 2, the Fe content exceeds 15 atom%, so that the coercive force is high and the magnetic permeability is low. In Comparative Example 3, a plating bath containing no phosphite ion is used, but since the Fe content is suppressed to 7 atom% or less as in the above-mentioned JP-A-4-196402, good soft magnetic characteristics are obtained. Has been obtained. However, since the Fe content is low, the saturation magnetic flux density is insufficient.

As a result of X-ray diffraction, the Fe content was 15
In the film of Comparative Example 2 in which the atomic percentage exceeds, the face-centered cubic (11
In addition to the broad peak corresponding to the 1) plane, a broad peak corresponding to the (110) plane of the body-centered cubic crystal was observed, but in the films of Examples 1 and 2 and Comparative Examples 1 and 3, Only cubic peaks were observed.

Example 3 The soft magnetic thin film formed in Example 1 was heat-treated for 1 hour, and the coercive force was measured after the heat treatment.
As a result, when the holding temperature during heat treatment was 300 ° C.
84 Oe, 1.00 Oe at 400 ° C., 1.04 Oe at 500 ° C., and it was confirmed that the heat resistance was extremely good.

Example 4 A soft magnetic thin film was formed in the same manner as in Example 1 except that the film thickness was changed by changing the plating time. As a result, the coercive force was 0.7 Oe when the film thickness was 2.2 μm and 0.7 Oe when the film thickness was 3.4 μm, and a sufficiently low coercive force was obtained in each case.

From the results of the above examples, the effect of the present invention is clear.

Claims (8)

[Claims] 1. It is characterized by containing Co, Fe and B, having a Fe content of 8 to 15 atom%, a coercive force of 2 Oe or less, and being formed by an electroless plating method. Soft magnetic thin film. 2. The soft magnetic thin film according to claim 1, wherein the B content is 1 to 7 atomic%. 3. The soft magnetic thin film according to claim 1, wherein the crystalline substance contained is substantially a face-centered cubic single phase. 4. An electroless plating bath containing Co ions, Fe ions, a boron-containing reducing agent, and phosphite ions, and having a phosphite ion concentration of 0.01 mol / liter or more. 5. The electroless plating bath according to claim 4, wherein the concentration of phosphite ion is 1 mol / liter or less. 6. The electroless plating bath according to claim 4, which contains tartrate and / or citrate as complexing agent ions. 7. A method for producing a soft magnetic thin film, which comprises forming the soft magnetic thin film using the electroless plating bath according to claim 4. 8. The method of manufacturing a soft magnetic thin film according to claim 7, wherein the soft magnetic thin film according to claim 1 is formed.