JPH08138934A - Soft magnetic thin film and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide a method of manufacturing a soft magnetic thin film which is suitable for a magnetic core material used for an inductor or a transformer which is operable in a high-frequency range. CONSTITUTION: A polycrystalline soft magnetic ferrite layer of Ni-Zn ferrite or Mn-Zn ferrite is formed on a polycrystalline MgO layer or a polycrystalline soft magnetic ferrite and a polycrystalline MgO layer are formed for the formation of a soft magnetic thin film through a plasma MOCVD method.

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 suitable for a magnetic core material such as an inductor and a transformer used in a high frequency range, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Since other crystalline soft magnetic ferrite materials such as Ni-Zn ferrite and Mn-Zn ferrite have higher resistance than metallic soft magnetic materials, they are excellent in soft magnetic characteristics in a high frequency region. Since there is little magnetic loss,
Used in magnetic core materials for transformers and inductors.
Further, since it also has good wear resistance, it is used as a magnetic recording head material in addition to the above applications.

In recent years, with the trend toward smaller and lighter electronic devices and higher frequencies, there has been a demand for thin film transformers and thin film inductors having excellent characteristics in the high frequency region. Research on thinning soft magnetic ferrite materials such as Ni-Zn ferrite and Mn-Zn ferrite, which are promising materials as soft magnetic materials for magnetic cores, has been studied by vacuum deposition method, M
Various film forming film methods such as the OCVD method and the plating method are widely used (for example, Nobuyuki Hiratsuka et al .: Powder belt and powder metallurgy 39 (1992) 152, Hideaki Ito et al .: Ceramic Society Journal 95 (1987). 60, Masanori Abe et al .: Metal Surface Technology 38 (1987) 416).

Among the above film forming methods, the MOCVD method is
It has features such as large-area film formation, easy composition control, and excellent step coverage when manufacturing oxide thin films such as ferrite. Furthermore, the plasma MOCVD method, in which plasma is applied during film formation, allows the starting material to be decomposed / excited by active plasma, thereby enabling film formation at low temperatures and high-speed film formation in addition to the features of the MOCVD method. (For example, Hideo Torii et al .: The 6th International Ferrite Conference Proceedings (1992) 464, Atsushi Tomozawa et al .: Journal of Japan Society for Applied Magnetics 17 (1993) 319).

[0005]

However, when a soft magnetic ferrite thin film is formed on a substrate by the plasma MOCVD method, a layer having poor crystallinity (initial layer) exists at the early stage of film growth, and soft magnetic characteristics are Lower.

The present invention solves the above-mentioned conventional problems, and when a soft magnetic ferrite thin film is formed on a substrate by the plasma MOCVD method, the soft magnetic layer is formed by an initial layer which does not have excellent crystallinity at the initial stage of film growth. The purpose is to eliminate the problem of characteristic deterioration.

[0007]

In order to solve the above-mentioned problems, the present invention uses a soft magnetic thin film as Ni--Zn ferrite or Mn.
-A polycrystalline soft magnetic ferrite layer such as Zn ferrite is N
The structure is formed on a polycrystalline oxide layer having an aCl type crystal structure. Further, the soft magnetic thin film has a structure in which a polycrystalline soft magnetic ferrite layer such as Ni-Zn ferrite or Mn-Zn ferrite and a polycrystalline oxide layer having a NaCl type crystal structure are laminated. Further, the polycrystalline soft magnetic ferrite layer such as Ni-Zn ferrite or Mn-Zn ferrite in the soft magnetic thin film having the above-mentioned structure is manufactured by plasma MOCVD method.

[0008]

According to the present invention, a polycrystalline soft magnetic ferrite such as Ni--Zn ferrite or Mn--Zn ferrite (100) is epitaxially formed on a MgO thin film having a NaCl type crystal structure exhibiting good crystallinity and (100) orientation. ) A soft magnetic thin film with an orientation film formed, and soft magnetic properties due to an initial layer with poor crystallinity that exists in the initial stage of film growth compared to the case where a polycrystalline soft magnetic ferrite film is formed directly on the underlying substrate. It is possible to improve the soft magnetic characteristics by eliminating the problem of decrease in the magnetic field. Further, the composition is a MgO thin film having a NaCl type crystal structure showing a (100) orientation and a (100)
By forming a laminated film of oriented polycrystalline soft magnetic ferrite, by further improving the crystallinity of the polycrystalline soft magnetic ferrite, it becomes a soft magnetic thin film exhibiting excellent soft magnetic characteristics. Further, by using the plasma MOCVD method as the manufacturing method, MgO having a NaCl type crystal structure exhibiting good crystallinity and (100) orientation regardless of the type of the underlying substrate.
A thin film can be easily obtained (for example, Eiji Fujii et al .: Japanese Journal of Applied Physics 32 (199
3) 1448), and polycrystalline soft magnetic ferrite and M
It is also possible to reduce the cost by enabling low-temperature and high-speed film formation of the gO film.

[0009]

EXAMPLE A soft magnetic thin film having a structure in which a polycrystalline ferrite magnetic layer having a spinel type crystal structure is formed on a polycrystalline oxide layer having a NaCl type crystal structure will be described below with reference to the manufacturing method and the drawings. To do.

(Example 1) FIG. 1 is a schematic configuration diagram of a plasma MOCVD apparatus for producing a MgO film as a NaCl type oxide thin film and a Ni-Zn ferrite thin film having a spinel type crystal structure in a soft magnetic thin film of the present invention. Is. FIG.
In the reaction chamber 1, a substrate heating heater 2 with a substrate rotating mechanism, an electrode 3 incorporated therein, and a high frequency power source (1
3.56MHz)) 5 electrodes are connected to each other,
The electrode 3 is installed, and a base substrate (Si) 6 is installed below the electrode 3. Further, an exhaust system 7 for keeping the reaction chamber 1 at a low pressure is provided on the side surface of the reaction chamber 1.

On the other hand, vaporizers 8, 9, 10 containing the raw materials
11 is an electrode 3 via valves 12, 13, 14, and 15.
The pipes connected to the base substrate 6 and the electrode 4 which are arranged in the above are introduced into the vaporizers 8, 9, 10, 11 respectively.
The carrier gas is connected to the argon cylinder 20 via 9 and the introduction of the source gas and the carrier gas into the reaction chamber 1 is controlled by opening and closing the valves 16, 17, 18, and 19. The oxygen cylinder 21 is used as the base substrate 6.
Is connected to a pipe opening between the electrode 4 and the electrode 4.

Here, a method of manufacturing the soft magnetic thin film in the embodiment will be described. As a starting material, magnesium acetylacetonate [Mg (C ₅ H ₇
O ₂ ) ₂ ], nickel acetylacetonate [Ni (C ₅
H ₇ O ₂ ) ₂ · xH ₂ O], zinc acetylacetonate [Z
n (C ₅ H ₇ O ₂ ) ₂ xH ₂ O] and iron acetylacetonate [Fe (C ₅ H ₇ O ₂ ) ₃ ] were used.

Magnesium acetylacetonate is used for the vaporizer 8 and vaporizers 9 and 1 in the plasma CVD apparatus of FIG.
0 to vacuum (1 Torr) at 90 ℃ dehydrated nickel acetylacetonate and zinc acetylacetonate, vaporizer 11 put iron acetylacetonate, 220 ℃, 160 ℃, 65 ℃, heated to 125 ℃ respectively And keep it. The valves 12 and 16 are opened, and the vapor of magnesium acetylacetonate and oxygen as a reaction gas (flow rate 3 SCCM) are introduced into the reaction chamber 1 whose pressure is reduced by the exhaust system 7 together with the nitrogen carrier (flow rate 25 SCCM) to generate plasma (electric power). 1.4 W / cm ² ) and the reaction was performed under reduced pressure (0.1 Torr) for 2 minutes, and a MgO film was formed on the base substrate (120 revolutions / minute) 6 heated to 500 ° C., and the valves 12, 16 were used. Closed.

Further, the valve 1 is continued without breaking the vacuum.
3, 14, 15, 16, 17, 18 are opened, and carrier gas (flow rates of 15 SCCM, 6 for vaporizers 9, 10, 11 respectively)
SCCM, 25SCCM) to convert nickel acetylacetonate, zinc acetylacetonate, and iron acetylacetonate vapor into reaction gas oxygen (flow rate 15 SCCM).
Introduced into the reaction chamber 1 together with it, reacted in plasma (power 1.4 W / cm ² ) under reduced pressure (0.2 Torr) for 60 minutes to form a Ni—Zn ferrite film on the MgO film, -Zn ferrite / MgO bilayer film was prepared. For comparison, a single-layer film was also formed by directly forming a Ni—Zn ferrite film on the Si substrate by the plasma CVD method under the above film forming conditions without forming the MgO film.

The magnetic properties of the Ni-Zn ferrite / MgO bilayer film and the Ni-Zn ferrite single layer film thus produced are shown in B.
-Measured using an H-curve tracer and a vibrating sample magnetometer. As a result, the values of coercive force and saturation magnetization of the film were 4 Oe and 340 emu / cc for the bilayer film and 3 Oe for the monolayer film, respectively.
It was 230 emu / cc. The initial permeability (μ _i ) was measured with a vector impedance meter. 1 to 10 in FIG.
The frequency characteristic of the initial magnetic permeability at 0 MHz is shown. Ni-
Compared with the Zn ferrite single-layer film, the Ni—Zn ferrite / MgO bilayer film had a larger initial permeability value in the measured frequency region.

The surface and fracture surface were observed using a high resolution scanning electron microscope. As a result, each of the sample films was a very dense polycrystalline film and had a grain size of about 0.4 μm. The film thickness of the Ni-Zn ferrite / MgO bilayer film is 5.70μ.
m, the Ni-Zn ferrite single layer film was 5.68 μm. Ni-Z by electron beam microanalyzer
Analysis of the composition of the n-ferrite film revealed that Ni _0.65 Zn
_{It was 0.35} Fe ₂ O ₄ .

Then, only the MgO film was formed on the Si substrate under the above-mentioned film forming conditions in the present film forming method to prepare a sample film, and the Ni-Zn ferrite / MgO bilayer film and the Ni-Zn film were formed.
The crystal structure and crystal orientation were analyzed by reflection high-energy electron diffraction (RHEED) and X-ray diffraction together with the Zn ferrite single layer film. As a result, the MgO film was polycrystalline and oriented in (100). Then, by using a NiO (100) orientation film as the base film, Ni-
The Ni-Zn ferrite layer in the Zn ferrite / MgO bilayer film exhibits stronger (100) orientation and better crystallinity as compared with the case where the Ni-Zn ferrite film is directly formed on the substrate. Had.

From the above results, Ni-Zn ferrite /
The MgO bilayer film exhibits soft magnetic characteristics superior to that of the Ni-Zn ferrite single layer film because of the influence of the (100) -oriented MgO underlayer film, and the Ni-Zn ferrite film is high (1
This is because the (00) orientation is exhibited and the crystallinity is good.

Further, the formation of a two-layer film with the MgO film is performed by Mn-Z
Even in the case of n-ferrite film, it is effective for improving soft magnetic characteristics.
Was. Instead of nickel acetylacetonate as the starting material
The same β-diketone metal complex manganese acetyl acetate
Setonate [Mn (C_FiveH₇O ₂)₂] (0.1 Torr, 90
Mn-Zn ferra prepared by using
Ito (Mn_0.78Zn_0.22Fe₂O_Four) / MgO polycrystalline double layer
0.1% of the film and Mn-Zn ferrite polycrystalline single layer film
Figure 3 shows the frequency characteristics of initial permeability at 10MHz.
You. Similar to the case of Ni-Zn ferrite, the initial permeability
The value increased in the measured frequency range.

Incidentally, Ni-Zn ferrite and Mn-
When the composition of Zn ferrite shows values other than the above,
Even in the case of a composition containing copper, lithium, magnesium, etc. as an additive, it was also effective in improving the soft magnetic characteristics by forming a two-layer film with the MgO film.

Further, the same NaC is used instead of the MgO film.
The soft magnetic properties were also improved when a polycrystalline NiO film or CoO film having an l-type crystal structure with preferential orientation on the (100) plane was used. Generated a low resistance of about 10 Ω · cm. Since this low resistance layer is considered to be an obstacle when applying the soft magnetic thin film to various devices, in the present invention,
High resistance MgO oxide layer of NaCl type crystal structure
It was limited to a film (specific resistance ≧ 10 ⁸ Ω · cm).

(Embodiment 2) A soft magnetic thin film in which a polycrystalline ferrite magnetic layer having a spinel type crystal structure and a polycrystalline oxide thin film layer having a NaCl type crystal structure are alternately laminated will be described below along with a method of manufacturing the same. A description will be given with reference to the drawings.

As the starting material, magnesium acetylacetonate [Mg (C ₅ H
₇ O ₂ ) ² ], manganese acetylacetonate [Mn (C ₅
H ₇ O ₂ ) ₂ · xH ₂ O], zinc acetylacetonate [Z
n (C ₅ H ₇ O ₂ ) ₂ xH ₂ O] and iron acetylacetonate [Fe (C ₅ H ₇ O ₂ ) ₃ ] were used.

Magnesium acetylacetonate is used for the vaporizer 8 and vaporizers 9 and 1 in the plasma CVD apparatus of FIG.
Manganese acetylacetonate and zinc acetylacetonate dehydrated at 0 ° C in vacuum (1 Torr), iron acetylacetonate in vaporizer 11 and heated to 200 ° C, 230 ° C, 75 ° C and 125 ° C, respectively. And keep it. The valves 12 and 16 are opened, and the vapor of magnesium acetylacetonate and oxygen as a reaction gas (flow rate 1 SCCM) are introduced into the reaction chamber 1 whose pressure is reduced by the exhaust system 7 together with the nitrogen carrier (flow rate 20 SCCM) to generate plasma (electric power). 1.4 W / cm ² ) and the reaction was performed under reduced pressure (0.1 Torr) for 1 minute to form a MgO film on a base substrate (120 revolutions / minute) 6 heated to 500 ° C. and the valves 12, 16 Closed. Then, without breaking the vacuum, the valves 13, 14, 15, 16, 17, and 18 are opened, and nickel acetylacetonate and zinc acetyl are used by the carrier gas (flow rates 25 SCCM, 6 SCCM, and 25 SCCM for the vaporizers 9, 10 and 11 respectively). Vapors of acetonate and iron acetylacetonate were introduced into the reaction chamber 1 together with oxygen as a reaction gas (flow rate 25 SCCM), and the pressure was reduced (0.2 Torr) in plasma (electric power 1.4 W / cm ² ) for 3 minutes. The reaction is carried out with Mn-Zn on the MgO film.
A ferrite film was formed.

Further, subsequently, the above operation was repeated 49 times to prepare a laminated film of Mn—Zn ferrite / MgO (the number of times of lamination was 50 times). For comparison, M
A single layer film in which only the n-Zn ferrite film was similarly formed by the plasma CVD method under the above film forming conditions was prepared.

The magnetic properties of the produced Mn-Zn ferrite / MgO laminated film and Mn-Zn ferrite single-layer film are shown in B.
-Measured using an H-curve tracer and a vibrating sample magnetometer. As a result, the values of coercive force and saturation magnetization of the film are 1 Oe and 410 emu / cc for the multilayer film and 2 Oe for the single layer film,
It was 390 emu / cc. The initial permeability (μ _i ) was measured with a vector impedance meter. 0.1 to Figure 4
The frequency characteristic of the initial magnetic permeability at 10 MHz is shown. Mn
By using the Mn-Zn ferrite / MgO bilayer film as compared with the -Zn ferrite single layer film, the value of the initial magnetic permeability was increased in the frequency region of 0.5 MHz or higher.

The surface and the fracture surface were observed using a high resolution scanning electron microscope and a transmission electron microscope. As a result, each of the sample films was a very dense polycrystalline film and had a grain size of about 0.4 μm. The thickness of the Mn—Zn ferrite / MgO multilayer film is 5.42 μm, and the thicknesses of the Mn—Zn ferrite layer and the MgO layer are about 100 nm and about 1 respectively.
It was 0 nm. The thickness of the Mn—Zn ferrite single layer film was 4.90 μm. Further, the composition of the Mn-Zn ferrite film was analyzed by an electron beam microanalyzer to find that it was Mn _0.72 Zn _0.38 Fe ₂ O ₄ .

Next, reflection high-energy electron diffraction (RHEED)
The crystal structure and crystal orientation were analyzed by and X-ray diffraction. As a result, the Mn-Zn ferrite / MgO multilayer film showed stronger (100) orientation and more favorable crystallinity than the Mn-Zn ferrite single layer film.

Further, the specific resistance of the film was measured. Mn-Zn
The specific resistances of the ferrite / MgO multilayer film and the Mn-Zn ferrite single layer film were 10 ³ Ω · cm and 10 ⁵ Ω · cm, respectively.

From the above results, Mn-Zn ferrite /
The reason why the MgO multilayer film exhibits soft magnetic characteristics superior to that of the Mn-Zn ferrite single layer film in the high frequency region is that the crystallinity of the film is improved and the specific resistance of the film is increased due to the multilayer film. It is thought that the cause is.

In addition, the formation of a multilayer film with the MgO film is performed by Ni--Z
Even in the case of n-ferrite film, it is effective for improving soft magnetic characteristics.
Was. Instead of nickel acetylacetonate as the starting material
The same β-diketone metal complex manganese acetyl acetate
Setonate [Ni (C_FiveH₇O ₂)²] (0.1 Torr, 90
Ni-Zn ferrite prepared by using
To (Ni_0.64Zn_0.36Fe₂O_Four) / MgO multilayer film and
Ni-Zn ferrite single layer film at 1 to 100 MHz
FIG. 5 shows the frequency characteristics of the initial magnetic permeability. Mn-Zn Fe
As with the light, the value of initial permeability is in the high frequency range.
And was getting bigger.

Incidentally, Mn-Zn ferrite and Ni-
When the composition of Zn ferrite shows values other than the above,
Even in the case of a composition containing copper, lithium, magnesium, etc. as an additive, it was also effective in improving the soft magnetic characteristics by forming a multilayer film with MgO.

[0033]

As is apparent from the above embodiments, the present invention provides a polycrystalline ferrite magnetic layer having a spinel type crystal structure,
A soft magnetic thin film having a structure formed on a polycrystalline oxide layer having a NaCl type crystal structure, or a polycrystalline ferrite magnetic layer having a spinel type crystalline structure and a polycrystalline oxide thin film layer having a NaCl type crystalline structure are alternately laminated. Since it is a soft magnetic thin film having a constitution and the soft magnetic thin film is produced by a plasma CVD method, it has an effect that a soft magnetic thin film exhibiting excellent soft magnetic characteristics can be easily obtained.

[Brief description of drawings]

FIG. 1 is a plasma MOCVD used in an embodiment of the present invention.
Schematic configuration diagram of the device

FIG. 2 is a diagram showing the relationship between the frequency and the initial permeability of the soft magnetic thin film using Ni—Zn ferrite in the first embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between frequency and initial magnetic permeability of a soft magnetic thin film using Mn-Z ferrite in the first example of the present invention.

FIG. 4 is a diagram showing the relationship between frequency and initial permeability of a soft magnetic thin film using Ni—Zn ferrite in the second embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between frequency and initial magnetic permeability of a soft magnetic thin film using Mn-Z ferrite according to a second embodiment of the present invention.

[Explanation of symbols]

 1 Reaction Chamber 2 Substrate Heating Heater 3 Electrode 4 Electrode 5 High Frequency Power Supply 6 Si Substrate 7 Exhaust System 8 Vaporizer 9 Vaporizer 10 Vaporizer 11 Vaporizer 12 Raw Material Gas Supply Valve 13 Raw Material Gas Supply Valve 14 Raw Material Gas Supply Valve 15 Raw Material Gas Supply valve 16 Carrier gas supply valve 17 Carrier gas supply valve 18 Carrier gas supply valve 19 Carrier gas supply valve 20 Nitrogen cylinder 21 Oxygen cylinder

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01F 41/22

Claims (8)

[Claims] 1. A soft magnetic thin film having a structure in which a polycrystalline ferrite magnetic layer having a spinel type crystal structure is formed on a polycrystalline oxide layer having a NaCl type crystal structure. 2. A soft magnetic thin film having a structure in which a polycrystalline ferrite magnetic layer having a spinel type crystal structure and a polycrystalline oxide thin film layer having a NaCl type crystal structure are alternately laminated. 3. A method for producing a soft magnetic thin film, wherein a polycrystalline ferrite magnetic layer having a spinel type crystal structure is formed on a polycrystalline oxide layer having a NaCl type crystal structure, the polycrystalline ferrite magnetic layer having a spinel type crystal structure. A method of manufacturing a soft magnetic thin film, which comprises forming a magnetic layer and a polycrystalline oxide layer having a NaCl type crystal structure by a plasma CVD method. 4. A method of manufacturing a soft magnetic thin film in which a polycrystalline ferrite magnetic layer having a spinel type crystal structure and a polycrystalline oxide thin film layer having a NaCl type crystal structure are alternately laminated, wherein the polycrystal having a spinel type crystal structure is used. Ferrite magnetic layer and NaCl
A method of manufacturing a soft magnetic thin film, which comprises forming a polycrystalline oxide layer having a type crystal structure by a plasma CVD method. 5. A polycrystalline ferrite magnetic layer having a spinel type crystal structure and a polycrystalline oxide layer having a NaCl type crystal structure are perpendicular to a substrate surface holding them (100).
The soft magnetic thin film according to claim 1, which is preferentially oriented in the plane. 6. The method according to claim 1 or 2, wherein the polycrystalline ferrite magnetic layer having a spinel type crystal structure contains nickel zinc ferrite or manganese zinc ferrite as a main component, and the polycrystalline oxide layer having a NaCl type crystal structure is magnesium oxide. The soft magnetic thin film described. 7. A polycrystalline ferrite magnetic layer having a spinel type crystal structure and a polycrystalline oxide layer having a NaCl type crystal structure are perpendicular to a surface of a substrate holding them (100).
The method for producing a soft magnetic thin film according to claim 3, wherein the surface is preferentially oriented. 8. The method according to claim 3, wherein the polycrystalline ferrite magnetic layer having a spinel type crystal structure contains nickel zinc ferrite or manganese zinc ferrite as a main component, and the polycrystalline oxide layer having a NaCl type crystal structure is magnesium oxide. A method for producing the soft magnetic thin film described.