JP2942128B2 - Thin film capacitor and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin-film capacitor and a method of manufacturing the same, which aims at increasing the capacitance per unit area while preventing a reaction between a ferroelectric phase and a lower electrode.

[0002]

2. Description of the Related Art As shown in FIG.
Each thin film of a lower electrode 12, a ferroelectric phase 14, and an upper electrode 16 is sequentially laminated on a substrate 10 of MgO single crystal or the like. In forming such a thin film capacitor, when the ferroelectric phase 14 is formed, the ferroelectric material reacts with the lower electrode 12 due to heat (the metal forming the lower electrode 12 diffuses into the ferroelectric phase 14). 3.) The ferroelectric phase 14 has semiconductor characteristics, and ferroelectric characteristics cannot be obtained. In order to prevent this reaction, it is conceivable to use Pt or the like having low reactivity as the lower electrode 12, but there is a problem that the cost increases.

In order to solve such a problem and to prevent the reaction between the ferroelectric material and the lower electrode by using an inexpensive electrode material, there is one disclosed in Japanese Patent Application Laid-Open No. Hei 3-276615. . As shown in FIG. 3, the lower electrode 12 is formed by using a Ni-Al-based alloy or a Ni-Cr-Al-based alloy, and then the surface of the lower electrode 12 is heated in an oxidizing atmosphere. Al on the surface of 12
The ₂ O ₃ (alumina) layer 18 formed by deposition, the Al ₂ O
_The ferroelectric phase 14 is formed on the _three layers 18 by the PVD method. According to such a configuration, the Al ₂ O ₃ layer 18
Is stable and the ferroelectric material hardly reacts with the Al ₂ O ₃ layer 18 during the formation of the ferroelectric phase 14, so that ferroelectric characteristics can be obtained while using an inexpensive material for the lower electrode 12. .

[0004]

[SUMMARY OF THE INVENTION In the structure having the Al ₂ O ₃ layer 18 as a reaction preventing layer as a thin film capacitor 20 of FIG. 3, in addition to Al ferroelectric phase 14 between the electrodes 12, 16 _The paraelectric phase composed of the ₂ O ₃ layer 18 is configured in series. Therefore, as shown in an equivalent circuit in FIG. 4, the capacitance of the ferroelectric phase 14 is changed to Cf and the Al ₂ O ₃ layer 18.
Is defined as Cp (Cf >> Cp), the thin film capacitor 2
0, the total capacitance C is reduced to a value obtained by (1 / C) = (1 / Cf) + (1 / Cp), and it is possible to realize a large-capacity thin film capacitor having a small capacitance per unit area. could not.

The present invention solves the above-mentioned problems in the prior art and prevents a reaction between a ferroelectric phase and a lower electrode while increasing the capacitance per unit area, and a method of manufacturing the same. It is intended to provide.

[0006]

A thin film capacitor according to the present invention comprises a Ni—Al alloy or Ni laminated on a substrate.
A lower electrode made of a Cr-Al-based alloy, and laminated on this lower electrode with no or almost no Al ₂ O ₃ layer, with Al ₂ O ₃ mixed therein and constituting the lower electrode The ceramic ferroelectric phase comprises a ceramic ferroelectric phase having a composition in which no or almost no metal is mixed, and an upper electrode laminated on the ceramic ferroelectric phase.

Further, the method for manufacturing a thin film capacitor according to the present invention is characterized in that a Ni-Al alloy or Ni-Cr-A
forming a lower electrode made of an l-based alloy; and heat-treating the lower electrode in an oxidizing atmosphere to form an Al layer on the lower electrode.
Forming a ₂ O ₃ layer, a solution containing a ferroelectric component to the the Al ₂ O ₃ layer on the coating, dried, by heat treatment, the ferroelectric said the Al ₂ O ₃ layer The method comprises the steps of forming a dielectric phase while taking in the body constituents, and forming an upper electrode on the ferroelectric phase.

[0008]

The manufacturing method of the present invention uses a so-called sol-gel method for forming a ferroelectric phase. According to experiments by the inventors, Al ₂ O 3 formed on the surface of the lower electrode _Three
It was found that the layer was gradually incorporated into the ferroelectric constituents during the drying and heat treatment of the sol-gel method. In addition, it was found that when Al ₂ O ₃ was taken into the ferroelectric constituent components, it did not form a paraelectric phase, and a decrease in the relative dielectric constant was prevented. Therefore, according to the present invention, during formation of the ferroelectric phase, Al ₂ O according with the reaction between the lower electrode and the ferroelectric material is prevented by the Al ₂ O ₃ layer, a ferroelectric phase is formed _Three
The reduction of the layers and ultimately the disappearance of all or almost no paraelectric phase prevents a decrease in the relative dielectric constant. This allows
A thin film capacitor with a large capacity per unit area can be obtained.
A large-capacity thin-film capacitor can be easily obtained. Further, according to the thin film capacitor of the present invention, the ceramic ferroelectric phase is formed on the lower electrode without any or almost no Al ₂ O _3, and the metal forming the lower electrode is completely absent in the ceramic ferroelectric phase. Alternatively, since they are hardly mixed, a high relative dielectric constant can be obtained. Thus, a thin film capacitor having a large capacity per unit area can be obtained, and a large capacity thin film capacitor can be easily obtained.

[0009]

FIG. 1 shows an embodiment of the present invention in the order of steps.
Each step will be described. (1) Formation of Lower Electrode On a glass substrate 10, a Ni alloy is sputtered under the following conditions to form a lower electrode 12 of a Ni-Al-based alloy or a Ni-Cr-Al-based alloy. (Sputtering conditions)-Ni alloy target In the case of a Ni-Al alloy: Ni = 91% by weight, Al =
4.5% by weight, trace elements such as Fe = 4.5% by weight In the case of Ni-Cr-Al alloy: Ni = 74.5% by weight, Cr = 16% by weight, Fe = 3.5% by weight, Al =
4.5 wt%, other trace elements 1.5 wt% ・ Substrate temperature Ts: 400 ° C. ・ Sputtering gas: pure Ar ・ Sputtering gas pressure: 3.0 × 10 ^-3 Torr ・ RF power: 400 W / diameter 2 inches (2) Al ₂ O ₃ layer deposition The substrate 10 on which the lower electrode 12 was formed was heat-treated at 400 ° C. for 1 hour in an atmosphere of an oxidizing atmosphere to form the lower electrode 12.
An Al ₂ O ₃ layer 18 is formed to a thickness of about 20 nm. (3) Applying Alcoholate The substrate temperature Ts is returned to room temperature, and an alcoholate 22 containing Ba and Ti (Ba: Ti = 1: 1) as ferroelectric components is applied to the lower electrode 12 by a dip method or a spin-on method. I do. It should be noted that a material composed of a lead-based perovskite component may be used instead of Ba and Ti. (4) Drying The substrate temperature Ts is raised from room temperature to 400 ° C. to dry the alcoholate solution. (5) Heat treatment Heat treatment is performed by increasing the substrate temperature Ts from 400 ° C. to 600 ° C. By undergoing drying and heat treatment, the precursor compound 24 composed of a ferroelectric component is crystallized through polycondensation and amorphization, whereby the ferroelectric phase 14 is formed. (6) Upper electrode formation The upper electrode 16 is formed on the ferroelectric phase 14 with Au or the like. Since the upper electrode 16 can be formed at a relatively lower temperature than the ferroelectric phase 14 even by using a sputtering method or the like, the reaction with the ferroelectric phase 14 can be prevented even if a metal other than Au is used. After the upper electrode 16 is formed, the conductive portions for connection are connected to the upper and lower electrodes 16 and 12, respectively, and the entire surface is covered with a protective layer to complete the thin film capacitor 30.

According to the above steps, steps (3) to (5)
Al ₂ O between when forming a ferroelectric phase, and the precursor compound 24 consisting of the lower electrode 12 and the ferroelectric component
_{Since the three} layers 14 are interposed, the reaction between the lower electrode 12 and the precursor compound 24 (Ba and Ti) composed of a ferroelectric component is prevented. At this time, since the Al ₂ O ₃ layer 18 is gradually taken into the ferroelectric component, the Al ₂ O ₃ layer 18 gradually decreases as shown in FIG. In this case, the amount of Al ₂ O ₃ incorporated in the precursor compound 24 composed of the ferroelectric component is much smaller than the amount of the finally obtained ferroelectric compound BaTiO ₃ , and Al ₂ O ₃ becomes conductive. Since it does not have the property, the dielectric properties of the ferroelectric phase 14 are not affected. In this way, when the formation of the ferroelectric phase 14 is completed in Step 5, the paraelectric Al ₂ O ₃ layer 18 is almost eliminated (in other words, when the formation of the ferroelectric phase 14 is completed, Al ₂ O
The thickness of the Al ₂ O ₃ layer 18 is formed so that the _three layers 18 are almost or completely eliminated. ). Therefore, a high relative dielectric constant between the upper and lower electrodes 12 and 16 can be secured, and the completed thin film capacitor 30
Has a large capacitance per unit area, and a large-capacity capacitor can be easily obtained. If the formation of the ferroelectric phase 14 is completed and the substrate temperature Ts is lowered, no reaction occurs between the ferroelectric phase 14 and the lower electrode 12 even if they are in direct contact.

Here, the results of measuring the characteristics of the thin film capacitor manufactured by the process of FIG. 1 and the thin film capacitor manufactured by another method are shown in the following table.

[0012] Here, the contents of each of the above-mentioned production methods A, B, and C are as follows. A: A BaTiO ₃ ferroelectric phase is formed by sputtering on a lower electrode made of Pt formed by sputtering. B: After an Al ₂ O ₃ layer is formed on a lower electrode made of a Ni—Al alloy formed by sputtering. BaTiO _{3 by} sputtering
Formation of ferroelectric phase C: An Al ₂ O ₃ layer is formed on a lower electrode made of a Ni—Al alloy prepared by a sputtering method, and then BaTiO is formed by a sol-gel method.
₍₃ ) Form ferroelectric phase (method of FIG. 1) The above measurement results were obtained when the thickness of the BaTiO ₃ thin film was 1 μm, the upper and lower electrodes were 4 mm square, and the number of measurement was 20. It is each average value.

According to the above measurement results, the thin film capacitor prepared by the method (method C) of the present invention has a relative dielectric constant equivalent to that of method A using Pt as an electrode, and also has a tan δ. At the same time, it has been improved, and it has been found that the thin film capacitor has excellent characteristics.

In the above embodiment, the case where the ceramic ferroelectric phase of BaTiO ₃ is constituted by using Ba and Ti as the ferroelectric compound has been described, but other materials may be used. An example is shown below.

Ferroelectric constituents Ferroelectric phase generated Mg, Ba, Ti (Mg, Ba) TiO ₃ Ba, Sr, Ti (Ba, Sr) TiO ₃ Pb, Fe, Ni Pb (Fe, Ni) O ₃

[0016]

As described above, according to the present invention, during the formation of the ferroelectric phase, the reaction between the lower electrode and the ferroelectric material is prevented by the Al ₂ O ₃ layer.
Since the Al ₂ O ₃ layer decreases as the ferroelectric phase is formed, a decrease in the relative dielectric constant is finally prevented. Thus, a thin film capacitor having a large capacity per unit area can be obtained, and a large capacity thin film capacitor can be easily obtained. Further, according to the thin film capacitor of the present invention, the ceramic ferroelectric phase is formed on the lower electrode without any or almost no Al ₂ O _3, and the metal forming the lower electrode is completely absent in the ceramic ferroelectric phase. Alternatively, since they are hardly mixed, a high relative dielectric constant can be obtained. Thus, a thin film capacitor having a large capacity per unit area can be obtained, and a large capacity thin film capacitor can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a process chart showing one embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a general configuration of a thin film capacitor.

FIG. 3 is a cross-sectional view showing a thin-film capacitor manufactured by a conventional method.

FIG. 4 is an equivalent circuit diagram of the thin film capacitor of FIG.

FIG. 5 is a diagram showing how the Al ₂ O ₃ layer gradually decreases in the process of FIG. 1;

[Explanation of symbols]

10 substrate 12 precursor compound 30 thin-film capacitor comprising a lower electrode 14 ferroelectric phase 16 upper electrode 18 Al ₂ O ₃ layer 24 ferroelectric component

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Osamu Sugiyama 2449 Takamatsu, Shizuoka City, Shizuoka Prefecture (72) Inventor Atsushi Kondo 1227-1 Hofukushima, Yaizu City, Shizuoka Prefecture (72) Inventor Takuo Mochizuka Gold, Shizuoka Prefecture 143 Tanimachi Shidoro (72) Inventor Hideaki Masuda 1-7-5 203 Surugadai, Fujieda-shi, Shizuoka Prefecture (56) References JP-A-3-276615 (JP, A) JP-A-3-1515 (JP, A (58) Fields surveyed (Int. Cl. ⁶ , DB name) H01G 4/00-4/40

Claims (2)

(57) [Claims] And 1. A lower electrode made of Ni-Al alloy or Ni-Cr-Al alloy stacked on a substrate, are stacked without interposing no or little the Al ₂ O ₃ layer on the lower electrode, A ceramic ferroelectric phase having a composition in which Al ₂ O ₃ is mixed therein and the metal constituting the lower electrode is mixed at all or almost not; and an upper electrode laminated on the ceramic ferroelectric phase. Thin film capacitor. 2. A Ni-Al based alloy or Ni-C
forming a lower electrode made of r-Al-based alloy, a step of forming an Al ₂ O ₃ layer on the lower electrode by heat-treating the lower electrode in an oxidizing atmosphere, the the Al ₂ O ₃ layer on the the solution containing the ferroelectric component is coated, dried, by heat treatment, Al ₂
A method for manufacturing a thin film capacitor, comprising: a step of forming a ferroelectric phase while incorporating an O ₃ layer into the ferroelectric component; and a step of forming an upper electrode on the ferroelectric phase.