JP2010157529A - Method of manufacturing dielectric thin-film element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a dielectric thin-film element capable of sufficiently increasing insulation resistance while preventing oxidation of metal foil. <P>SOLUTION: This method of manufacturing the dielectric thin-film element includes: a baking process S3 of heating a dielectric thin film 12 formed on the metal foil 11 to 400-1,200°C in a vacuum atmosphere or reductive atmosphere; a reductive annealing process S4 of executing an annealing process in a reductive atmosphere after the baking process S3. Thereby, leak current can be reduced while preventing oxidation of the metal foil, and insulation resistance can be sufficiently increased. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a dielectric thin film element.

  Dielectrics based on barium titanate are widely used as material for chip capacitors. In recent years, electronic parts have been made thinner and rapidly, and the dielectric layer is close to the limit of thickness reduction by the conventional method of sintering powder. Therefore, there is an increasing demand for electronic parts using a dielectric thin film. For example, there is a need for a thin film capacitor in which a dielectric thin film is formed on a metal foil serving as a substrate and a lower electrode, and an upper electrode is formed on the dielectric thin film. Is growing.

Since passive components such as capacitors are premised on low cost, it is desirable to use inexpensive base metals for the metal foil and electrode materials. In this case, since the base metal is susceptible to oxidation, it is necessary to fire a dielectric thin film based on barium titanate in a vacuum atmosphere in order to suppress a decrease in conductivity due to oxidation of the metal foil (for example, Patent Documents). 1).
JP 2007-66754 A

  However, when the dielectric thin film is baked in vacuum as in Patent Document 1, although the metal foil can be prevented from being oxidized and reduced in conductivity, defects (such as oxygen defects) enter the dielectric thin film. Due to the generated charged elements (electrons and holes), there is a problem that leakage current is generated and the insulation resistance cannot be sufficiently high.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing a dielectric thin film element that can sufficiently increase an insulation resistance while preventing oxidation of a metal foil.

  In order to solve the above problems, the method for manufacturing a dielectric thin film element according to the present invention heats the dielectric thin film formed on the metal foil to 400 to 1200 ° C. in a vacuum atmosphere or a reducing atmosphere. And a reduction annealing step of performing an annealing process in a reducing atmosphere after the firing step.

  According to such a method for manufacturing a dielectric thin film element, a leakage current can be reduced by further annealing the dielectric thin film fired in a vacuum atmosphere or a reducing atmosphere to prevent oxidation of the metal foil in a reducing atmosphere. The insulation resistance can be made sufficiently high.

  Here, the reduction annealing temperature in the reduction annealing step is preferably 280 to 480 ° C., and the reduction annealing temperature is more preferably 300 to 460 ° C. Thereby, the leakage current can be further reduced and the insulation resistance can be further increased.

  The reduction annealing time in the reduction annealing step is preferably 20 to 740 minutes, and more preferably the reduction annealing time is 30 to 720 minutes. Thereby, the leakage current can be further reduced and the insulation resistance can be further increased.

  In addition, it is preferable that the reduction annealing step includes a temperature raising step and a temperature lowering step, in which the reducing atmosphere is started and the reducing atmosphere is ended in the temperature lowering step. It is preferable that the reducing atmosphere is started from room temperature in the temperature raising step and the reducing atmosphere is ended at room temperature in the temperature lowering step. Similarly, it is preferable that the reducing atmosphere is started at 220 ° C. or lower in the temperature raising step and the reducing atmosphere is ended at 220 ° C. or lower in the temperature lowering step. Thereby, the leakage current can be further reduced and the insulation resistance can be further increased.

  According to the method for manufacturing a dielectric thin film element according to the present invention, the insulation resistance can be sufficiently increased while preventing the metal foil from being oxidized.

  Hereinafter, preferred embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments. In addition, the same code | symbol is attached | subjected about the same or equivalent element, and the description is abbreviate | omitted when description overlaps.

  FIG. 1 is a schematic sectional view showing the structure of a dielectric thin film element 10 according to an embodiment of the present invention. The dielectric thin film element 10 includes a metal foil 11, a dielectric thin film 12 provided on the metal foil 11, and an upper electrode 13 provided on the dielectric thin film 12.

  The metal foil 11 is preferably made of a base metal such as inexpensive Ni, Cu, Al or the like, or an alloy thereof, stainless steel, or Inconel for reducing the cost, and particularly preferably Ni foil. The thickness of the metal foil 11 is preferably 5 to 500 μm. In the present embodiment, the metal foil 11 has both a function as a holding member that holds the dielectric thin film 12, a function as a lower electrode, and a function as a substrate on which the dielectric thin film is formed.

The dielectric thin film 12 is made of a perovskite oxide such as BT, that is, barium titanate BaTiO ₃ , BST, that is, barium strontium titanate (BaSr) TiO ₃ , strontium titanate SrTiO ₃ , (BaSr) (TiZr) O ₃ , BaTiOZrO _3. Preferably used. The dielectric thin film 12 may contain one or more of these oxides. The film thickness of the dielectric thin film 12 is preferably about 30 nm to 5 μm.

The upper electrode 13 is preferably composed of an inexpensive base metal material as a main component for cost reduction, and particularly preferably composed of Cu as a main component. The upper electrode 13 is made of, for example, at least one of Ni, Pt, Pd, Ir, Ru, Rh, Re, Os, Au, Ag, Cu, IrO ₂ , RuO ₂ , SrRuO ₃ , and LaNiO _3. You may comprise so that it may be included.

  Next, a manufacturing method of the dielectric thin film element 10 will be described with reference to FIG.

  First, the metal foil 11 is prepared as a base for forming a dielectric thin film (S1), and a precursor layer made of a dielectric material such as BT is formed on the metal foil 11 (S2). For example, a sputtering method, a CSD method, or the like is used to form the precursor layer. In the precursor layer after film formation, the dielectric is generally in an amorphous state.

  Next, the precursor layer formed on the metal foil 11 is heated in a vacuum atmosphere or a reducing atmosphere, and the crystallization of the dielectric proceeds to obtain the dielectric thin film 12 having a high dielectric constant ( S3: Firing step). Particularly in the present embodiment, the firing temperature is preferably 400 to 1200 ° C, more preferably 700 to 900 ° C.

Here, the “vacuum atmosphere” in the present embodiment is a reduced pressure atmosphere in which the pressure is 1 × 10 ⁻⁹ to 1 × 10 ³ Pa, and is generally 1 × 10 ⁻⁵ to 1 × 10. ² Pa is preferable, and 1 × 10 ^{−3 to} 10 Pa is more preferable. In particular, when the metal foil 11 is mainly made of Ni, the pressure is preferably 2 × 10 ⁻³ to 8 × 10 ⁻¹ Pa. When the metal foil 11 is mainly made of Cu, the pressure is 4 × is preferably ¹⁰ -1 ^~8 × ¹⁰ -1 Pa. The “reducing atmosphere” is an atmosphere composed of an inert gas such as nitrogen, helium, and argon and hydrogen gas, and preferably contains 4 vol% or less of hydrogen in the inert gas. By performing the heat treatment under such conditions, the oxidation of the metal foil 11 such as the Ni foil is suppressed.

  Next, the dielectric thin film 12 formed on the metal foil 11 is annealed in a reducing atmosphere (S4: reduction annealing step). Particularly in the present embodiment, the “reduction annealing temperature”, which is a temperature maintained in the vicinity of the workpiece during the annealing treatment, is preferably 280 to 480 ° C., more preferably 300 to 460 ° C., More preferably, it is 340-420 degreeC. Further, the “reduction annealing time” that is the time for continuing the reduction annealing temperature is preferably 20 to 740 minutes, more preferably 30 to 720 minutes, and more preferably 90 to 600 minutes, More preferably, it is 160 to 480 minutes. The “reducing atmosphere” is an atmosphere composed of an inert gas such as nitrogen, helium, and argon and hydrogen gas, and preferably contains 4 vol% or less of hydrogen in the inert gas.

  In this embodiment, the reduction annealing step includes a temperature raising step for raising the internal temperature of the annealing furnace from room temperature (about 25 ° C.) to the reduction annealing temperature, a maintenance step for maintaining the reduction annealing temperature for the reduction annealing time, and reduction annealing. And a temperature lowering step for lowering the temperature from room temperature to room temperature. When a predetermined temperature is reached from room temperature in this temperature raising step, a reducing atmosphere gas is introduced into the annealing furnace, the atmosphere in the annealing furnace is switched to a reducing atmosphere, and a reducing atmosphere is started. Similarly, when a predetermined temperature is reached from the reduction annealing temperature in the temperature lowering step, the introduction of the reducing atmosphere gas into the annealing furnace is stopped and the reducing atmosphere is ended. The predetermined temperature for starting and ending the reducing atmosphere is preferably 220 ° C. or lower, and can be set to room temperature, 80, 100, 180, 200, 220 ° C., or the like.

  In the reduction annealing step, the leakage current in the dielectric thin film element 10 is reduced by annealing the dielectric thin film 12 under such conditions. This is because a vacuum-fired or reduction-fired dielectric contains a large number of holes as carriers, so oxygen defects are generated. However, when hydrogen is doped by reduction annealing, holes are reduced and the generated oxygen defects are alleviated. It is considered that the leakage current is reduced.

  Then, the upper electrode 13 is formed on the dielectric thin film 12 subjected to the reduction annealing process (S5). Examples of a method for forming the upper electrode 13 include a sputtering method. After the upper electrode 13 is formed, recovery annealing is performed for a predetermined time in an oxygen atmosphere or a reduced pressure atmosphere as required (S6).

  Note that the reduction annealing process in step S4 may be performed after the formation of the upper electrode 13 in step S5.

  As described above, according to the method for manufacturing the dielectric thin film element 10 according to this embodiment, the dielectric thin film 12 baked in a vacuum atmosphere or a reducing atmosphere to prevent oxidation of the metal foil 11 is further annealed in a reducing atmosphere. Therefore, the leakage current can be reduced and the insulation resistance can be sufficiently increased.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

(Example)
On the Ni foil as the lower electrode whose surface was mirror-polished, a BT thin film as a precursor layer was formed by sputtering under the following conditions.
-Substrate (Ni foil) temperature: 24 ° C
・ Input power: 1.8W / cm2
・ Atmosphere: Ar + O2 (33% by volume)
-Film formation time: 120 minutes-Film thickness: 300 nm

Next, the obtained BT thin film was passed through a vacuum atmosphere (pressure 4 × 10 ⁻² Pa) or a reducing atmosphere (nitrogen-hydrogen mixed gas (hydrogen 0.1%)), and oxygen partial pressure 1 × using a 35 ° C. wetter. The dielectric thin film in which BT crystallization progressed was formed by heating at a firing temperature of 400, 700, 800, 900, and 1200 ° C. under a control of 10 ⁻¹⁴ MPa.

Then, reduction annealing is performed on the dielectric thin film formed on the Ni foil by combining the following conditions as shown in Table 1 under a reducing atmosphere in which a mixed gas of 3 vol% hydrogen (remaining nitrogen) flows at 500 cc per minute. Processed.
Reduction annealing temperature: 280, 300, 340, 380, 420, 460, 480 ° C
Reduction annealing time: 20, 30, 90, 160, 200, 480, 600, 720, 740 minutes Reduction atmosphere start temperature and end temperature (minimum temperature for holding the reduction atmosphere): Room temperature (RT), 80, 100, 180, 200, 220 ° C

  Thereafter, a Cu film is formed on the dielectric thin film by sputtering without heating the substrate, an electrode having a thickness of 1 mmΦ and a thickness of 200 nm is formed using a metal mask, an upper electrode is formed, and the heating temperature is 350 ° C. in a vacuum furnace. Recovery annealing was performed under the condition of a heating time of 1 hour. About the produced dielectric thin film element, the leak characteristic was measured.

As the leakage characteristics, the leakage current density (A / A) obtained by dividing the leakage current value measured by applying a DC voltage of 4 V between the dielectric thin film element (Ni foil) and the upper electrode at room temperature by the electrode area cm ² ) was calculated.

(Comparative Example 1)
The BT thin film formed on the Ni foil in the same manner as in the example was baked at an atmospheric temperature and a baking temperature of 800 ° C., and was subjected to reduction annealing at a reduction annealing temperature of 380 ° C., a reduction annealing time of 200 minutes, and a reduction atmosphere start temperature of 80 ° C. Subsequent processing was performed in the same manner as in the example. About the produced dielectric thin film element, the leak characteristic was measured like the Example.

(Comparative Example 2)
Similar to the example, the BT thin film formed on the Ni foil was fired at a firing temperature of 800 ° C. in a vacuum atmosphere and a reducing atmosphere, and Cu was formed on the dielectric thin film by sputtering without performing a reduction annealing treatment. An upper electrode containing as a main component was formed, and recovery annealing was performed. About the produced dielectric thin film element, the leak characteristic was measured like the Example.

(Comparative Example 3)
The BT thin film formed on the Ni foil was fired at a firing temperature of 380 ° C. in a vacuum atmosphere and a reducing atmosphere in the same manner as in the example, the reducing annealing temperature was 380 ° C., the reducing annealing time was 200 minutes, and the reducing atmosphere starting temperature was 80 ° C. Then, reduction annealing was performed, and the subsequent treatment was performed in the same manner as in the example. About the produced dielectric thin film element, the leak characteristic was measured like the Example.

(Comparative Example 4)
The BT thin film formed on the Ni foil was fired at a firing temperature of 1250 ° C. in a vacuum atmosphere and a reducing atmosphere in the same manner as in the example, a reducing annealing temperature of 380 ° C., a reducing annealing time of 200 minutes, and a reducing atmosphere start temperature of 80 ° C. Then, reduction annealing was performed, and the subsequent treatment was performed in the same manner as in the example. About the produced dielectric thin film element, the leak characteristic was measured like the Example.

Table 1 shows the firing atmosphere, firing temperature, reduction annealing temperature, reduction annealing time, reducing atmosphere start temperature, and leakage current density for the above Examples and Comparative Examples 1 to 4.

  As shown in Table 1, firing is performed at a firing temperature of 400 to 1200 ° C. in a reducing or vacuum atmosphere, and reduction annealing is performed under conditions of a reduction annealing temperature of 280 to 480 ° C., a reduction annealing time of 20 to 740 minutes, and a reducing atmosphere start temperature of 220 or less. It was confirmed that the dielectric thin film element of the example manufactured by performing the above has a sufficiently low leakage current density. On the other hand, Comparative Example 1 which was fired in an air atmosphere, Comparative Example 2 which was not subjected to reduction annealing after vacuum or reduction firing, Comparative Example 3 whose firing temperature was 380 ° C., and Comparative Example 4 whose firing temperature was 1250 ° C. The leakage current density was significantly larger than that of the example. That is, the dielectric thin film element of the example can reduce the leakage current density from about 1/10 to 1 / 10,000 times that of the comparative example, and can improve the leakage characteristics. Thus, according to the present invention, it was confirmed that a dielectric thin film element capable of reducing the leakage current and sufficiently increasing the insulation resistance while preventing oxidation of the metal foil is provided.

It is a schematic sectional drawing which shows the structure of the dielectric thin film element concerning one Embodiment of this invention. It is a flowchart which shows the manufacturing method of the dielectric thin film element concerning this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Dielectric thin film element, 11 ... Metal foil, 12 ... Dielectric thin film, 13 ... Upper electrode

Claims (8)

A firing step of heating the dielectric thin film formed on the metal foil to 400 to 1200 ° C. in a vacuum atmosphere or a reducing atmosphere;
And a reduction annealing step in which annealing treatment is performed in a reducing atmosphere after the firing step.   The method for manufacturing a dielectric thin film element according to claim 1, wherein a reduction annealing temperature in the reduction annealing step is 280 to 480 ° C.   The method of manufacturing a dielectric thin film element according to claim 2, wherein the reduction annealing temperature is 300 to 460 ° C.   The method for manufacturing a dielectric thin film element according to any one of claims 1 to 3, wherein a reduction annealing time in the reduction annealing step is 20 to 740 minutes.   The method of manufacturing a dielectric thin film element according to claim 4, wherein the reduction annealing time is 30 to 720 minutes.   6. The reduction annealing process includes a temperature raising step and a temperature lowering step, wherein a reducing atmosphere is started in the temperature raising step, and the reducing atmosphere is terminated in the temperature lowering step. A method for producing a dielectric thin film element according to 1.   7. The method for manufacturing a dielectric thin film element according to claim 6, wherein the reducing atmosphere is started at room temperature in the temperature raising step, and the reducing atmosphere is ended at room temperature in the temperature lowering step. 8. The method for manufacturing a dielectric thin film element according to claim 7, wherein the reducing atmosphere is started at 220 [deg.] C. or lower in the temperature raising step, and the reducing atmosphere is ended at 220 [deg.] C. or lower in the temperature lowering step.

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