JP2001185443A - Thin-film capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin-film capacitor wherein copper and its oxide that are inexpensive and have high conductivity are used for electrode material and stress in the manufacturing process is relaxed. SOLUTION: In a thin-film capacitor wherein an electrode 11, a dielectric layer 21 and an electrode 12 are laminated on a substrate 1, a composite material of copper and cuprous oxide is used for the electrodes 11 and 12. As a result, the stresses generated in the manufacturing process between the substrate 1 and the electrode 11 and between the electrodes 11 and 12 and the dielectric layer 21 are relaxed and the generation of cracks and peelings and the like can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin film capacitor mounted on an electronic device or the like.

[0002]

2. Description of the Related Art In recent years, the development of electronic devices such as computers has been remarkable, and the speed, size, and capacity have been steadily increasing. As the data volume of digital signals handled by these electronic devices increases and the signal switching frequency increases,
The fluctuation of the power supply voltage, that is, the power supply noise increases. If the power supply noise becomes extremely large, malfunction of the device may occur, so that measures such as noise reduction are required.

In order to reduce power supply noise, it is effective to reduce the impedance when the power supply is viewed from a noise source such as an LSI. To reduce the power supply impedance, it is useful to arrange a large-capacity, low-resistance capacitor in the immediate vicinity of the noise source. As a capacitor used for this purpose, a thin film capacitor formed on a module substrate on which an LSI is mounted has recently attracted attention.

As a material for a thin film capacitor, the electrode is C
It is desirable to use a low-resistance metal such as u or Au, and to use a ferroelectric ceramic material having a high dielectric constant such as a perovskite compound for the dielectric layer. Further, ceramic materials such as alumina are often used for the module substrate from the viewpoint of mechanical strength.

However, the difference between the coefficient of thermal expansion of a metal material and the coefficient of thermal expansion of a ceramic material is large, and a stress is generated at the interface between the two materials due to thermal expansion and thermal contraction. Therefore, there has been a problem that cracks are generated in the electrodes and the dielectric layer due to the heat treatment during the formation of the thin film capacitor, which causes an electric short circuit. In addition, peeling occurs between the substrate and the electrode or between the electrode and the dielectric layer, which causes problems such as a decrease in the capacity of the capacitor and a decrease in the yield.

As a solution to this, there is known a method of providing a metal layer having a coefficient of thermal expansion intermediate between the electrode and the dielectric layer to solve the problem.

As an example, FIG. 7 shows a thin film capacitor disclosed in Japanese Patent Application Laid-Open No. H11-243032. An electrode 11, a dielectric layer 21, and an electrode 12 are sequentially laminated on a substrate 1,
Between the substrate 1 and the electrode 11 and / or the electrodes 11, 12
Stress relaxation layers 31, 32, 33 made of Nb and / or Ta are formed between
From room temperature to 500 ° C for substrate, electrode, dielectric layer and stress relaxation layer
When α ₁ , α ₂ , α ₃ , and α ₄ are the thermal expansion coefficients of α ₁ , α ₁ <α ₄ <α ₂ and / or α ₃ <α ₄ <α ₂ , respectively. When this method is used, the thermal stress at the interface between the substrate and the electrode and the interface between the electrode and the dielectric layer is relaxed as compared with the case where there is no Nb or Ta stress relaxation layer. It can be expected to suppress the occurrence.

[0008]

In the thin film capacitor disclosed in Japanese Patent Application Laid-Open No. H11-243032, the electrode material is
It is stated that at least one of Au, Ag, Pt, and Cu is desirable. On the other hand, a material different from the electrode, such as Nb or Ta, is used for the stress relaxation layer. Therefore, there is a problem that the material cost of Nb and Ta is increased as compared with the case where the stress relaxation layer is not used, and the number of steps of the forming process is increased, which causes an increase in manufacturing cost.

The conductivity of Nb and Ta at room temperature is about 14% IACS, and Cu (1
There is a problem that the resistance of the electrode part is increased because the conductivity is 1/7 to 1/5 of that of the conductivity of 00% IACS or Au (78% IACS).

An object of the present invention is to provide a thin-film capacitor which is inexpensive and has high conductivity and which can alleviate stress in the manufacturing process only by using an electrode material mainly composed of Cu and its oxide.

[0011]

To achieve the above object, the present invention uses the following means (1) to (4).

(1) At least one of the electrodes is a first electrode mainly composed of a composite material of copper and cuprous oxide.

(2) At least one of the electrodes is a second electrode containing copper as a main component, and the second electrode has a porous structure. (3) The first electrode and / or the second electrode exist in a state where a composite material of copper and cuprous oxide is a main component during a capacitor forming process, and the first electrode and / or the second electrode are made of cuprous oxide by a reduction treatment. Is reduced. (4) The conductivity at 20 ° C. of the first electrode and / or the second electrode is 15% IACS or more.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A thin film capacitor according to the present invention comprises electrodes and dielectric layers alternately laminated on a substrate.
This includes a single-layer type capacitor having only one dielectric layer and a laminated type thin-film capacitor having a plurality of dielectric layers. Also,
It also includes a single-sided type in which a capacitor is formed on only one side of the substrate and a double-sided type in which a capacitor is formed on both sides of the substrate. Hereinafter, the present invention will be described using a single-sided single-layer type thin film capacitor as an example.

FIG. 1 is a sectional view of a single-sided single-layer type thin-film capacitor. An electrode 11 and a dielectric layer 2 are provided on the upper surface of a substrate 1.
1, electrodes 12 are sequentially laminated.

As the substrate 1, for example, a ceramic mainly composed of alumina is used. The thermal expansion coefficient of this material near room temperature is 7.7 × 10 ⁻⁶ / K.

As the dielectric layer 21, for example, P
A ceramic mainly composed of b (Mg _1/3 Nb _2/3 ) O ₃ (hereinafter referred to as PMN) is used. The thermal expansion coefficient of this dielectric material near room temperature is 7.4 × 10 ⁻⁶ / K.

Here, composite materials of Cu and Cu ₂ O are used for the electrodes 11 and 12. This copper composite is very inexpensive. The thermal expansion coefficient, Young's modulus, and conductivity can be adjusted as shown in Table 1 depending on the composition ratio of Cu ₂ O. Here, the composition ratio of Cu ₂ O is adjusted to, for example, 55% by volume or more so that the coefficients of thermal expansion of the electrodes 11 and 12 are close to the coefficients of thermal expansion of alumina and PMN to form a thin film capacitor. By doing, for example, Cu
The process stress between the substrate and the electrode and between the electrode and the dielectric layer can be reduced as compared with the case where is used as the electrode material.

[0019]

[Table 1]

Further, since the Young's modulus of the copper composite material is reduced by increasing the composition ratio of Cu ₂ O, the stress is reduced even when there is a difference in the thermal expansion coefficient between the electrode and the substrate or between the dielectric layers. Due to these stress reduction effects, it is possible to suppress the occurrence of peeling and the generation of cracks at the interface.

If the ratio of Cu ₂ O is increased in order to reduce the coefficient of thermal expansion and Young's modulus of the electrode, the conductivity of the electrode is reduced and the resistance component of the thin film capacitor is increased. Therefore, when it is necessary to improve the conductivity,
It is very useful to reduce the copper composite material by annealing at, for example, about 200 ° C. for about 2 minutes in a reducing atmosphere such as hydrogen after forming the thin film capacitor.

By the reduction, the ratio of Cu ₂ O in the copper composite material is reduced or becomes zero, and the conductivity of the electrode is increased.
In this case, since the reduction treatment is performed at a temperature lower than the temperature required for forming the dielectric layer (about 600 ° C.), the increase in the difference in thermal expansion coefficient between the copper composite material and the ceramic material due to the reduction does not matter so much. . In addition, when the copper composite material is reduced, the O ₂ component is released, resulting in a porous structure.
The Young's modulus is lower than that of the non-reduced copper composite material having the same Cu ₂ O ratio, and the effect of reducing the stress can be expected.

As described above, by controlling the Cu ₂ O ratio in the capacitor electrode, Nb can be reduced while reducing the stress.
It is possible to form the electrode with a copper composite material having a conductivity higher than that of Ta and Ta.

In the above embodiment, a single-sided single-layer type thin film capacitor is taken as an example. However, the present invention is not limited to this. For example, a single-sided layer type (FIG. 2) and a double-sided single-layer type (FIG. 3) ), Double-sided lamination type (FIG. 4) and the like. Also, as for the structure, not only the planar type shown in FIGS. 1 to 4 but also a trench type (FIG. 5) in which a groove is dug in the substrate and the surface thereof is a capacitor, or a capacitor having a three-dimensional structure is formed on the substrate. It can also be applied to a stacked type (FIG. 6).

As a substrate material, besides alumina, S
Application to i, glass, glass ceramics, etc. is also conceivable.

As a dielectric used for a thin film capacitor,
The present invention is not limited to the above PMN. For example, Pb (Z
r, Ti) O ₃ , BaTiO ₃ , SrTiO ₃ , (Ba,
Sr) TiO ₃ , tantalum oxide and the like are also applicable.

In the above embodiment, a copper composite material is used for both the upper electrode and the lower electrode. However, a copper composite material may be applied to only a part of the electrodes, or there is an electrode that does not use a copper composite material. You may. Regarding the composition of the electrode using the copper composite material, not only the composite of copper and cuprous oxide, but also the mixture of copper and cuprous oxide, for example, even when cupric oxide (CuO) and other impurities are mixed. Any material containing a composite as a main component can be an object of the present invention.

The method for manufacturing the thin film capacitor of the present invention is not particularly limited. For example, after forming a substrate, a capacitor may be formed by using a sputtering method, a CVD method, or the like in the order of an electrode, a dielectric layer, and an electrode. When a green sheet is used as the substrate material, the substrate and the lower electrode may be simultaneously formed by printing a conductive paste mainly composed of a copper composite material on the green sheet as an electrode of the capacitor, followed by firing.

[0029]

According to the present invention, it is possible to provide a thin-film capacitor which is inexpensive and has high conductivity, and which can alleviate the stress in the manufacturing process using only an electrode material mainly composed of Cu and its oxide.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a single-sided single-layer thin-film capacitor according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a single-layered thin-film capacitor according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a double-sided single-layer thin film capacitor according to an embodiment of the present invention.

FIG. 4 is a sectional view of a double-sided laminated thin-film capacitor according to an embodiment of the present invention.

FIG. 5 is a sectional view of a trench capacitor according to an embodiment of the present invention.

FIG. 6 is a sectional view of a stacked capacitor according to an embodiment of the present invention.

FIG. 7 is a cross-sectional view of a conventional single-sided single-layer thin-film capacitor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 11, 12, 13, 14, 15, 16 ... Electrode 21, 22, 23, 24 ... Dielectric layer, 31, 32, 33
... Stress relaxation layer.

Claims (4)

[Claims] 1. A thin film capacitor comprising an electrode and a dielectric layer alternately laminated on a substrate, wherein at least one of said electrodes is composed of a first material mainly composed of a composite material of copper and cuprous oxide. A thin film capacitor characterized by being an electrode. 2. A thin film capacitor comprising an electrode and a dielectric layer alternately stacked on a substrate, wherein at least one of said electrodes is a second electrode mainly composed of copper.
Wherein the electrode has a porous structure. 3. The method according to claim 1, wherein the first electrode and / or the second electrode are present in a state where a composite material of copper and cuprous oxide is a main component during a capacitor forming process, and then oxidized by a reduction treatment. 3. The thin film capacitor according to claim 1, wherein the content of cuprous copper is reduced. 4. The thin film capacitor according to claim 1, wherein the conductivity of the first electrode and / or the second electrode at 20 ° C. is 15% IACS or more.