JP2010171397A - Method for manufacturing thin-film capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a thin-film capacitor capable of improving the leakage characteristics. <P>SOLUTION: The method for manufacturing the thin-film capacitor includes an annealing step S2 for annealing metal foil 11 at a temperature of 800°C or higher; a dielectric thin film formation step S3 for forming a dielectric thin film 12 on the metal foil 11 so that the ratio D0/t of a crystal grain size D0 of the annealed metal foil 11 to a film thickness t of the dielectric thin film becomes 104 to 560; a sintering step S4 for sintering the dielectric thin film 12, by heating the metal foil 11 and the dielectric thin film 12; and an upper electrode formation step S5 for forming an upper electrode 13 on the sintered dielectric thin film 12. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  In recent years, thinning of electronic components has been progressing rapidly. For example, there is an increasing 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. ing. In order to increase the dielectric constant of the thin film capacitor, it is essential to perform a sintering process in which a dielectric thin film is formed on a metal foil and then heated at a high temperature to sinter the dielectric.

  In this sintering process, if the hardness of the metal foil is large, excessive strain is applied to the dielectric thin film, and cracks may occur in the dielectric thin film. In this case, the leakage current of the thin film capacitor increases and the leakage characteristics deteriorate. Therefore, in order to suppress the generation of cracks in the sintering process, for example, Patent Document 1 below describes that the metal foil is annealed before forming the dielectric thin film.

JP 2007-110127 A

  However, even if the metal foil is annealed before dielectric film formation as in Patent Document 1, cracks still occur in the dielectric thin film depending on the annealing and sintering conditions such as heating temperature, and leakage characteristics Sometimes deteriorated.

  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 thin film capacitor capable of improving leakage characteristics.

  As a result of extensive research, it has been found that the relationship between the crystal grain size of the metal foil after annealing the metal foil and the thickness of the dielectric thin film greatly affects the occurrence of cracks.

  Therefore, in order to solve the above problems, the method of manufacturing a thin film capacitor according to the present invention includes an annealing process in which the metal foil is annealed at a temperature of 800 ° C. or higher, a crystal grain size D0 of the annealed metal foil, and a dielectric. A dielectric thin film forming step of forming a dielectric thin film on the metal foil so that a ratio D0 / t to the thin film thickness t is 104 to 560, and heating the metal foil and the dielectric thin film to form the dielectric thin film It comprises a sintering step for sintering and an upper electrode forming step for forming an upper electrode on the sintered dielectric thin film.

  According to such a method of manufacturing a thin film capacitor, the metal foil is annealed at a temperature of 800 ° C. or higher, and the ratio D0 / t between the crystal grain size D0 of the annealed metal foil and the film thickness t of the dielectric thin film. By forming the dielectric thin film on the metal foil so that becomes 104 to 560, the leakage characteristics of the thin film capacitor can be improved.

  In addition, in the annealing step, it is preferable to anneal the metal foil so that the crystal grain size D0 of the metal foil grows up to a foil thickness H or more. By performing the annealing process so that the crystal grain size D0 of the metal foil grows to the foil thickness H or more in this way, the grain growth of the metal foil due to heating in the sintering process is suppressed, and the leakage characteristics of the thin film capacitor are improved. be able to.

  Here, it is preferable that the ratio D1 / D0 between the crystal grain size D0 of the metal foil before the dielectric thin film forming step and the crystal grain size D1 of the metal foil after the sintering step is 1.50 or less. More preferably, it is 1.22 or less. Thereby, the grain growth of the metal foil due to high-temperature heating in the sintering process is further suppressed, and the occurrence of cracks can be further suppressed to further improve the leak characteristics.

  Here, in the dielectric thin film forming step, the dielectric thin film is formed on the metal foil so that the ratio D0 / t of the crystal grain size D0 of the annealed metal foil and the film thickness t of the dielectric thin film is 144 to 400. It is preferable to form. Thereby, the leak characteristic can be further improved.

  According to the method for manufacturing a thin film capacitor according to the present invention, the leakage characteristics can be improved.

It is a schematic sectional drawing which shows the structure of the thin film capacitor which concerns on one Embodiment of this invention. It is a flowchart which shows the manufacturing method of the thin film capacitor which concerns on this embodiment. It is a figure which shows the outline of the grain growth of the crystal grain in metal foil.

  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 thin film capacitor 10 according to an embodiment of the present invention. The thin film capacitor 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 a Ni foil, Cu foil, Al foil, Pt foil, or an alloy thereof, and Ni foil is particularly preferable. In addition, as a method for producing the metal foil 11, there are an electrolytic method (plating method, sputtering method, vapor deposition method, CVD method, etc.) and a rolling method, but a metal foil produced by an electrolytic method that does not include processing strain in the manufacturing process is used. In particular, a metal foil produced by a plating method is preferably used because it is less contaminated with impurities and has a high purity (99.99% or more). The foil 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. In particular, in the present embodiment, it is preferable to appropriately adjust a suitable range based on the crystal grain size of the metal foil 11. A method of determining the film thickness of the dielectric thin film 12 in this embodiment will be described later.

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 method for manufacturing the thin film capacitor 10 will be described with reference to FIG.

  First, the metal foil 11 is prepared as a substrate for forming a dielectric thin film (S1), and is subjected to an annealing treatment in a reducing atmosphere or a vacuum atmosphere (S2: annealing process). The annealing temperature is high enough to cause crystal grain growth in the metal foil 11, may be 800 ° C or higher, more preferably 900 ° C to 1300 ° C, and further preferably 1000 ° C to 1300 ° C. The annealing time is preferably 1 minute to 4 hours. This annealing process is performed in order to relieve strain in the foil of the metal foil 11. The strain in the foil of the metal foil can be controlled by the annealing temperature and the annealing time, and the strain in the crystal can be relaxed in a shorter time as the high temperature annealing is performed. Specifically, the state in which the in-foil strain of the metal foil 11 is relaxed is preferably that the Vickers hardness of the metal foil 11 is smaller than about 100 HV. Regarding the relationship between the annealing temperature and the annealing time, the annealing time can be shortened as the annealing temperature becomes higher.

The “vacuum atmosphere” in the present embodiment is a reduced pressure atmosphere in which the pressure is 1 × 10 ³ Pa or less, and is generally preferably 1 × 10 ⁻⁵ to 1 × 10 ² Pa. It is more preferable that it is 1 × 10 ^{−3 to} 10 Pa. 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 a mixed gas of nitrogen, hydrogen and water vapor, and preferably contains 4 vol% or less of hydrogen in the nitrogen. By performing the heat treatment under such conditions, the oxidation of the metal foil 11 such as the Ni foil is suppressed.

  Here, “grain growth” will be described. In this embodiment, “grain growth” means that a metal foil having a fine polycrystalline structure is initially heat-treated to move the grain boundary of each fine crystal, while eroding adjacent crystal grains. The process. For example, as shown in FIG. 3A, the metal foil 11 has a multilayer structure with respect to the direction of the foil thickness H due to fine crystals of various sizes having a grain size of about 20 nm to 60 nm. It has become. Then, as the grain growth proceeds, as shown in FIGS. 3B and 3C, each crystal grain becomes larger until the crystal grain size becomes equal to or larger than the foil thickness H. Become. The “crystal grain size” indicates the size of the crystal grain, and is specifically an average particle size calculated by a “code method” described later. The size of the crystal grain size can be controlled by the impurities inside the metal foil, the annealing temperature, and the annealing time.

  Further, as shown in FIG. 3C, when the grain growth proceeds and the crystal grain size is increased to a certain extent, the grain growth is saturated and the grain size does not increase any more. The particle size at this time is called “saturated particle size”. The saturated particle diameter is approximately 2.5 times the foil thickness of the metal foil. That is, the saturated particle diameter of the metal foil 11 is mainly determined by the foil thickness H.

  In particular, in this embodiment, in order to reduce grain growth of the metal foil 11 due to heating in the dielectric thin film sintering process described later, the crystal grain size of the metal foil 11 after the annealing process is the foil thickness of the metal foil 11. It is preferable to perform the annealing treatment so that the metal foil 11 has a single layer structure, and it is more preferable that the crystal grain size after the annealing treatment is larger than 1.4 times the foil thickness. Furthermore, if the annealing process is performed on the metal foil 11 so that the crystal grain size grows to a saturated grain size, grain growth of the metal foil does not occur in the sintering process of the dielectric thin film described later. It is particularly preferable that the crystal grain size is not less than the foil thickness H and the saturated grain size. Accordingly, as long as the metal foil is not damaged by oxidation or the like, the annealing process may be performed in a low oxygen partial pressure state such as a reducing atmosphere or a vacuum atmosphere.

  Next, a precursor layer made of a dielectric material such as BST is formed on the annealed metal foil 11 (S3: dielectric thin film forming step). For the formation of the precursor layer, for example, a sputtering method, a CSD method (chemical solution method), a CVD method, or the like is used. In the case of the CSD method or the like, after applying the solution to the substrate, heat is applied to such an extent that the substance in the chemical solution is decomposed to some extent so as not to cause crystallization. A layer which is decomposed to some extent by applying this heat and is not crystallized is referred to herein as a precursor layer when a chemical solution method is used. In general, the precursor layer in such a state has an amorphous dielectric state.

  Here, particularly in the present embodiment, the precursor layer is a metal foil 11 annealed in the annealing step of step S2 in order to avoid the generation of cracks due to distortion applied to the dielectric in the sintering process of the dielectric thin film described later. It is preferable that the ratio D0 / t between the crystal grain size D0 and the film thickness t of the precursor layer (dielectric thin film) be 104 to 560. Considering further reduction of the leakage current of the dielectric, D0 / t is more preferably 144 to 400.

  In the dielectric thin film forming step, by forming the dielectric thin film 12 under such conditions, generation of cracks is suppressed in the sintering process described later. In the present embodiment, the crystal grain size of the metal foil 11 grows to a thickness equal to or greater than the foil thickness, preferably the saturated grain size, by the annealing process in step S2, and individual crystals of the metal foil 11 are enlarged when the dielectric thin film 12 is formed. For this reason, on the surface of the metal foil 11, the level difference at the boundary (grain boundary) between adjacent crystal grains becomes large. For this reason, when the film thickness of the dielectric thin film 12 is excessively small with respect to the crystal grain size of the metal foil 11, that is, when D0 / t is excessively large, in the sintering process described later, the dielectric is crystallized. When stress is generated in the dielectric thin film 12, there is a possibility that cracks may occur in the dielectric due to the step of the grain boundary. In the present embodiment, by forming the dielectric thin film 12 with D0 / t of 104 to 560, more preferably 144 to 400, the film of the dielectric thin film 12 according to the crystal grain size and foil thickness of the metal foil 11. It is considered that the thickness is set in a suitable range, and as a result, generation of cracks in the sintering process is suppressed.

  Further, in the dielectric thin film forming step, by forming the dielectric thin film 12 under such conditions, warping of the metal foil 11 and the dielectric thin film 12 is suppressed in the sintering process described later. When the film thickness of the dielectric thin film 12 is excessively large with respect to the crystal grain size of the metal foil 11, that is, when D0 / t is excessively small, in the sintering process described later, The stress and strain generated in the body thin film 12 are excessive. For this reason, the balance of force at the contact surface with the metal foil 11 is lost, the metal foil 11 cannot suppress the deformation of the dielectric thin film 12, and the metal foil 11 and the dielectric 12 may be warped. . In the present embodiment, by forming the dielectric thin film 12 with D0 / t of 104 to 560, more preferably 144 to 400, the film of the dielectric thin film 12 according to the crystal grain size and foil thickness of the metal foil 11. It is considered that the thickness is set in a suitable range, and as a result, warpage of the metal foil 11 and the dielectric thin film 12 in the sintering process is suppressed.

  Next, the precursor layer formed on the metal foil 11 is heated in a vacuum atmosphere or a reducing atmosphere, and the dielectric thin film 12 having a high dielectric constant is sintered by progressing crystallization of the dielectric. Obtained (S4: sintering step). The heating temperature for the sintering treatment is preferably about 300 to 1300 ° C. The heating time is preferably 10 to 90 minutes. A high dielectric constant can be obtained by this sintering process.

  Here, particularly in this embodiment, in order to suppress grain growth and deformation of the metal foil 11 due to heating during the sintering process, the crystal grain size D1 of the metal foil 11 after the sintering process, and after the annealing process and Sintering is preferably performed so that the ratio D1 / D0 to the crystal grain size D0 of the metal foil 11 before the precursor layer forming treatment is 1.5 or less, more preferably 1.22 or less. .

  Then, the upper electrode 13 is formed on the sintered dielectric thin film 12 (S5). Examples of a method for forming the upper electrode 13 include a sputtering method.

  Thus, according to the method for manufacturing the thin film capacitor 10 according to the present embodiment, the metal foil 11 is annealed at a temperature of 800 ° C. or more, and the crystal grain size D0 of the annealed metal foil 11 and the dielectric thin film 12 are increased. By forming the dielectric thin film 12 on the metal foil 11 so that the ratio D0 / t to the film thickness t is 104 to 560, more preferably 144 to 400, the leakage characteristics of the thin film capacitor 10 are improved. Can be improved.

  Also, in the annealing step S2, by annealing the metal foil such that the crystal grain size D0 of the metal foil 11 grows to a foil thickness H or more, grain growth of the metal foil 11 due to heating in the sintering step S4 is suppressed, The leakage characteristics of the thin film capacitor 10 can be improved.

  Further, the ratio D1 / D0 between the crystal grain size D0 of the metal foil 11 after the annealing step S2 and before the dielectric thin film forming step S3 and the crystal grain size D1 of the metal foil after the sintering step S4 is 1.50 or less. More preferably, since it is 1.22 or less, grain growth of the metal foil 11 due to high-temperature heating in the sintering step S4 can be further suppressed, crack generation can be further suppressed, and leakage characteristics can be improved.

と表される。これは、インダクタンスＬを大きく、キャパシタンスＣを小さく、又は直列抵抗Ｒを小さくするほどＱが大きくなることを示すものである。従って、本実施形態の薄膜コンデンサ１０のＱ値を高くするためには、金属抵抗、すなわち金属箔１１の抵抗値を小さくすることが好ましい。 Here, advantages of the metal foil 11 having a single layer structure will be described. Generally, it is desirable that the Q value is high in a vibrator or an electric circuit. In the field of electronics, the definition of the Q value is the case of a series resonant circuit using a coil and a capacitor.

It is expressed. This indicates that Q increases as inductance L increases, capacitance C decreases, or series resistance R decreases. Therefore, in order to increase the Q value of the thin film capacitor 10 of the present embodiment, it is preferable to decrease the metal resistance, that is, the resistance value of the metal foil 11.

  In general, when charge moves through a metal, if the charge passes through the boundary (grain boundary) between adjacent particles, the crystal is discontinuous at the grain boundary, so the flow of charge is scattered and the metal resistance is high. Become. Therefore, the resistance value increases as the fine crystal contains more grain boundaries through which charges pass. In this embodiment, when the metal foil 11 is annealed to form a single layer structure, each crystal grain erodes adjacent crystals and coarsely crystallizes, so that there are few grain boundaries inside the metal foil. Thus, it is considered that an increase in resistance due to the metal grain boundary can be suppressed.

  Thus, according to the manufacturing method of the thin film capacitor according to the present embodiment, the metal foil 11 has a single layer structure with a crystal grain size equal to or larger than the foil thickness, thereby reducing the electrical resistance of the metal foil 11 and reducing the Q value. A thin film capacitor having a high thickness can be obtained.

  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 1
An Ni foil (foil thickness H: 50 μm, purity 99.99% or more) produced by plating is subjected to an annealing treatment under the following conditions, and the Vickers hardness and crystal grain size D0 of the metal foil after the annealing treatment are measured. did.
・ Annealing temperature: 1300 ℃
・ Annealing holding time: 1 hour ・ Temperature rising temperature: 5 ° C./min ・ Annealing atmosphere: reducing atmosphere (H ₂ + N ₂ mixed gas (H ₂ = 3 vol%) + water vapor, flow rate 1 L / min, set oxygen content Pressure pO2 = 2.3 × 10 ⁻¹¹ atm)

Next, after polishing and washing the annealed Ni foil, a dielectric thin film was deposited on the Ni foil by a sputter deposition method (ULVAC MPS-3000-C1-S) under the following conditions.
Target composition: (Ba + Sr) 1.02TiO ₃ (Ba / Sr = 70/30)
-Substrate temperature: 200 ° C
Atmosphere: Ar: O ₂ = 3: 1 (vol%)
・ Vacuum degree: 1.7 Pa,
・ Deposition film thickness: 500 nm

Next, the sample was sintered in an infrared lamp annealing furnace (RTA-3000) at a vacuum atmosphere (<10 ⁻² Pa), a heating temperature of 800 ° C., a temperature rising rate of 100 ° C./min, and a holding time of 30 minutes. The dielectric film thickness was measured using an optical film thickness meter (F20 manufactured by Filmmetrics).

  Thereafter, an electrode having a diameter of 1 mm containing Cu as a main component was deposited on the dielectric thin film by sputtering. The manufactured thin film capacitor was measured and observed for leakage characteristics, substrate warpage, and Ni foil crystal grain size D1.

The crystal grain sizes D0 and D1 of the metal foil were measured using a code method. In the code method, the surface is observed with an optical microscope, a straight line L is arbitrarily drawn on the observation surface, the intersection N with the grain boundary is counted, and L is divided by N as shown in the equation (1). The average length l between the grain boundaries is obtained and multiplied by a certain statistical numerical value k (here, K = 1.7776) to obtain an average particle diameter D (references: "Ceramic characterization technology" Japan Ceramics Association p7).
D = k × (L / N) (1)

The Vickers hardness of the metal foil was measured with a Vickers hardness meter (AKASHI MVK-03). After pushing the Vickers indenter of diamond regular square pyramid (face angle θ = 136 degrees) into the surface of the Ni foil with a predetermined load F (1 to 50 gf (changed depending on the main component of the sample)) for 20 seconds and removing the load The average value d (μm) of the diagonal distance of the indentation remaining on the surface of the holding member was measured. And based on the average value d of this diagonal distance, and the load F, Vickers hardness HV was computed by (2) Formula.
HV = 2Fsin (θ / 2) / d ² = 1854.4F / d ² (kgf / mm ² ) (2)

As the leakage characteristics, the leakage current density (A / cm ² ) obtained by dividing the leakage current value measured by applying a DC voltage of 4 V between the Ni foil and the upper electrode at room temperature by the electrode area was calculated. . The leakage current value was measured with an Agilent 4156C semiconductor parameter analyzer.

  Furthermore, D0 / t, D1 / D0, and D0 / H were calculated using the measured crystal grain diameters D0 and D1, the film thickness t, and the foil thickness H.

(Example 2)
A thin film capacitor was fabricated under the same conditions as in Example 1 except that the annealing temperature was 1100 ° C. and the oxygen partial pressure pO2 for annealing was 1.0 × 10 ⁻¹³ atm. Similarly, the Vickers hardness and crystal grain size D0 of the metal foil after the annealing treatment, the crystal grain size D1 of the metal foil after the sintering treatment, the leakage characteristics, and the warp of the substrate were measured and observed.

(Example 3)
A thin film capacitor was fabricated under the same conditions as in Example 1 except that the annealing temperature was set to 1000 ° C. and the oxygen partial pressure pO2 for annealing was set to 3.5 × 10 ⁻¹⁵ atm. Similarly, the Vickers hardness and crystal grain size D0 of the metal foil after the annealing treatment, the crystal grain size D1 of the metal foil after the sintering treatment, the leakage characteristics, and the warp of the substrate were measured and observed.

Example 4
A thin film capacitor was fabricated under the same conditions as in Example 1 except that the annealing temperature was set to 900 ° C. and the oxygen partial pressure pO2 for annealing was set to 7.0 × 10 ⁻¹⁷ atm. In addition, the Vickers hardness and crystal grain size D0 of the metal foil after the annealing treatment, the crystal grain size D1 of the metal foil after the sintering treatment, the leakage characteristics, and the warpage of the substrate were measured and observed.

(Example 5)
A thin film capacitor was fabricated under the same conditions as in Example 1 except that the annealing temperature was set to 800 ° C. and the oxygen partial pressure pO2 for annealing was set to 6.5 × 10 ⁻¹⁹ atm. In addition, the Vickers hardness and crystal grain size D0 of the metal foil after the annealing treatment, the crystal grain size D1 of the metal foil after the sintering treatment, the leakage characteristics, and the warpage of the substrate were measured and observed.

(Comparative Example 1)
A thin film capacitor was fabricated under the same conditions as in Example 1 except that the annealing temperature was 600 ° C. and the oxygen partial pressure pO2 of the annealing treatment was 2.4 × 10 ⁻²⁴ atm. In addition, the Vickers hardness and crystal grain size D0 of the metal foil after the annealing treatment, the crystal grain size D1 of the metal foil after the sintering treatment, the leakage characteristics, and the warpage of the substrate were measured and observed.

(Comparative Example 2)
A thin film capacitor was fabricated under the same conditions as in Example 1 except that the annealing temperature was 400 ° C. and the oxygen partial pressure pO2 of the annealing treatment was 5.0 × 10 ⁻³³ atm. In addition, the Vickers hardness and crystal grain size D0 of the metal foil after the annealing treatment, the crystal grain size D1 of the metal foil after the sintering treatment, the leakage characteristics, and the warpage of the substrate were measured and observed.

(Comparative Example 3)
A thin film capacitor was produced under the same conditions as in Example 1 except that the annealing treatment was not performed, and the Vickers hardness and crystal grain size D0 of the metal foil after the annealing treatment, the metal after the sintering treatment, as in Example 1. The crystal grain size D1 of the foil, the leakage characteristics, and the warpage of the substrate were measured and observed.

For Examples 1 to 5 and Comparative Examples 1 to 3 described above, the foil thickness H of the Ni foil, the Ni foil preparation method, the annealing atmosphere, the annealing temperature, the crystal grain size D0 of the annealed metal foil, the metal after the annealing treatment Table 1 shows the Vickers hardness of the foil, the thickness t, D0 / t of the dielectric thin film, the crystal grain size D1, D1 / D0, the leakage current density, the warp of the substrate, and D0 / H of the sintered metal foil. .

As shown in Table 1, the capacitor of the example using the Ni foil annealed at 800 ° C. or higher had a Vickers hardness of 102 HV or less at the maximum after annealing, and the Ni foil annealed at 900 ° C. or higher. The capacitor of the example using this is 90 HV or less. As can be seen from Table 1, the thin film capacitor of the example is softer than that of the comparative example. Furthermore, the thin film capacitor of the example has no warping of the substrate after the thin film is formed. Further, when the leakage current characteristics are evaluated, the leakage current density of Example 5 at an annealing temperature of 800 ° C. is 1 × 10 ⁻⁵ A / cm ² , and the leakage current density of Examples 1 to 4 at an annealing temperature of 900 ° C. or more is as follows. It was 1 × 10 ⁻⁶ A / cm ² , and the thin film capacitor of the example was found to have a relatively low leakage current density.

The ratio D0 / t between the crystal grain size D0 of the annealed metal foil and the film thickness t of the dielectric thin film is 104 in Example 5 where the leakage current density is 1 × 10 ⁻⁵ A / cm ^2. In Examples 1-4 where the leakage current density is 1 × 10 ⁻⁶ A / cm ² , the leakage current density is 144 or more. That is, the leakage current density is reduced when D0 / t is 104 or more, more preferably 144 or more.

On the other hand, in Comparative Examples 1 and 2 in which annealing treatment was performed at 600 ° C. or less and in Comparative Example 3 in which annealing treatment was not performed, D0 / t was smaller than 104, and the leakage current density was 1 × 10 ⁻³ A / cm. ² , which was significantly larger than the example.

It can also be seen that the ratio D0 / H between the crystal grain size D0 and the foil thickness H of the annealed metal foil is 1 or more times in the examples. That is, in the thin film capacitor of the example, after the annealing treatment, the crystal grain size of the metal foil becomes equal to or greater than the foil thickness and has a single layer structure. Furthermore, in Examples 1 to 4 where the leakage current density is 1 × 10 ⁻⁶ A / cm ² , D0 / H is 1.44 times or more. On the other hand, D0 / H of the comparative example is smaller than 1, and the thin film capacitor of the comparative example still has a multilayer structure even after the annealing treatment.

It can also be seen that the change rate D1 / D0 of the Ni particle diameter before and after the dielectric precursor is crystallized is 1.50 or less in the examples. In Examples 1 to 4 further leakage current density is ^{1 × 10 -6 A / cm 2} , D1 / D0 is in a 1.22 or less. In contrast, D1 / D0 of the comparative example is larger than that of the example. In the thin film capacitor of the example, it can be seen that regrown growth due to recrystallization of Ni is suppressed at the time of dielectric crystallization annealing as compared with the comparative example.

  That is, the thin film capacitor of the example can reduce the leakage current density from about 1/100 to 1/1000 times that of the comparative example, and can improve the leakage characteristics. Thus, according to the present invention, it was confirmed that the leakage characteristics can be improved.

  For a thin film capacitor on a metal foil, heat is applied to the metal foil along with the crystallization of the thin film at the time of forming the thin film, and the metal foil also causes recrystallization and particle growth due to the heat. Therefore, when heat treatment as in the present application is performed in advance, grain growth of the metal foil during thin film formation is suppressed, generation of cracks in the film accompanying movement of the metal foil is suppressed, and leakage current of the thin film is improved. Conceivable. As a result, as a thin film capacitor on a metal foil, there is a relationship satisfying the above relationship between the thickness of the dielectric and the thickness of the metal foil and the particle diameter of the metal foil, and a thin film capacitor having good electrical characteristics has been completed. it is conceivable that.

  Next, measurement and observation similar to the above were performed by changing the metal foil thickness and the dielectric film thickness. In the following examples and comparative examples, the annealing temperatures of the metal foils were all 1100 ° C., and the annealing conditions were the same as in Example 2 above.

(Example 6)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 30 μm and the thickness of the dielectric thin film was 400 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 7)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 30 μm and the thickness of the dielectric thin film was 350 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 8)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 30 μm and the thickness of the dielectric thin film was 300 nm, and the same measurement and observation as in Example 2 were performed. .

Example 9
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 50 μm and the thickness of the dielectric thin film was 500 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 10)
A thin film capacitor was produced under the same conditions as in Example 2 except that the thickness of the metal foil was 50 μm and the thickness of the dielectric thin film was 450 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 11)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 30 μm and the thickness of the dielectric thin film was 250 nm, and the same measurement and observation as in Example 2 were performed. .

Example 12
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 50 μm and the thickness of the dielectric thin film was 400 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 13)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 70 μm and the thickness of the dielectric thin film was 500 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 14)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 50 μm and the thickness of the dielectric thin film was 350 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 15)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 30 μm and the thickness of the dielectric thin film was 200 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 16)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 70 μm and the thickness of the dielectric thin film was 450 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 17)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 50 μm and the thickness of the dielectric thin film was 300 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 18)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 70 μm and the thickness of the dielectric thin film was 400 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 19)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 50 μm and the thickness of the dielectric thin film was 250 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 20)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was set to 70 μm and the thickness of the dielectric thin film was set to 350 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 21)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 70 μm and the thickness of the dielectric thin film was 330 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 22)
A thin film capacitor was produced under the same conditions as in Example 2 except that the thickness of the metal foil was 70 μm and the thickness of the dielectric thin film was 300 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 23)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 50 μm and the thickness of the dielectric thin film was 200 nm, and the same measurement and observation as in Example 2 were performed. .

(Example 24)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 70 μm and the thickness of the dielectric thin film was 250 nm, and the same measurement and observation as in Example 2 were performed. .

(Comparative Example 4)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 70 μm and the thickness of the dielectric thin film was 240 nm, and the same measurement and observation as in Example 2 were performed. .

(Comparative Example 5)
A thin film capacitor was fabricated under the same conditions as in Example 2 except that the thickness of the metal foil was 70 μm and the thickness of the dielectric thin film was 200 nm, and the same measurement and observation as in Example 2 were performed. .

表２に示すように、実施例６〜２４の薄膜コンデンサでは、焼鈍処理後の金属箔の結晶粒径Ｄ０と誘電体薄膜の膜厚ｔとの比Ｄ０／ｔが５６０以下となり、リーク電流密度が１×１０^−５Ａ／ｃｍ^２以下であることがわかる。さらに、Ｄ０／ｔが４００以下となる実施例６〜２０では、リーク電流密度が１×１０^−６Ａ／ｃｍ^２となった。 About the above-mentioned Examples 6-24 and Comparative Examples 4 and 5, foil thickness H of metal foil, Ni foil preparation method, annealing atmosphere, annealing temperature, crystal grain size D0 of metal foil after annealing, metal after annealing Table 2 shows the Vickers hardness of the foil, the thickness t, D0 / t of the dielectric thin film, the crystal grain size D1, D1 / D0, the leakage current density, the warp of the substrate, and D0 / H of the sintered metal foil. .

As shown in Table 2, in the thin film capacitors of Examples 6 to 24, the ratio D0 / t between the crystal grain size D0 of the annealed metal foil and the film thickness t of the dielectric thin film was 560 or less, and the leakage current density Is 1 × 10 ⁻⁵ A / cm ² or less. Furthermore, in Examples 6 to 20 in which D0 / t was 400 or less, the leakage current density was 1 × 10 ⁻⁶ A / cm ² .

On the other hand, in the thin film capacitors of Comparative Examples 4 and 5, D0 / t was larger than 560, and the leakage current density was 1 × 10 ⁻² A / cm ² or more, which was significantly larger than that of the example.

  That is, the thin film capacitors of Examples 6 to 24 can also reduce the leakage current density and improve the leakage characteristics as compared with Comparative Examples, as in Examples 1 to 5. Thus, according to the present invention, it was confirmed that the leakage characteristics can be improved.

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

Claims (5)

An annealing step of annealing the metal foil at a temperature of 800 ° C. or higher;
A dielectric thin film forming step of forming the dielectric thin film on the metal foil such that a ratio D0 / t of a crystal grain size D0 of the annealed metal foil and a film thickness t of the dielectric thin film is 104 to 560. When,
A sintering step of sintering the dielectric thin film by heating the metal foil and the dielectric thin film;
Forming an upper electrode on the sintered dielectric thin film; and
A method of manufacturing a thin film capacitor, comprising:   2. The method of manufacturing a thin film capacitor according to claim 1, wherein in the annealing step, the metal foil is annealed so that the crystal grain size D0 of the metal foil grows to a foil thickness H or more.   A ratio D1 / D0 between a crystal grain size D0 of the metal foil before the dielectric thin film forming step and a crystal grain size D1 of the metal foil after the sintering step is 1.50 or less, The method of manufacturing a thin film capacitor according to claim 1 or 2.   The ratio D1 / D0 between the crystal grain size D0 of the metal foil before the dielectric thin film forming step and the crystal grain size D1 of the metal foil after the sintering step is 1.22 or less, The method of manufacturing a thin film capacitor according to claim 3. In the dielectric thin film forming step, the dielectric thin film is formed on the metal foil such that a ratio D0 / t between the crystal grain size D0 of the annealed metal foil and the film thickness t of the dielectric thin film is 144 to 400. The method of manufacturing a thin film capacitor according to claim 1, wherein the thin film capacitor is formed.

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