JP5560460B2 - Method for forming dielectric thin film - Google Patents

Description

The present invention, when used in a thin film capacitor or the like, about the formation how the dielectric thin film capable of expressing high tunability and a high dielectric constant. In this specification, “tunable” means that the capacitance can be changed by changing the applied voltage, and “tunability” means variability or change in capacitance. Say rate.

High-frequency tunable devices such as high-frequency filters, high-frequency antennas, and phase shifters are composed of upper and lower electrodes and a dielectric layer formed between both electrodes as variable capacitance elements (tunable elements). A thin film capacitor or the like is incorporated. The thin film capacitor functions as a capacitor that changes its capacitance according to a change in voltage applied between both electrodes. The dielectric layer constituting such a thin film capacitor has perovskite such as strontium titanate (SrTiO ₃ ), barium strontium titanate (hereinafter referred to as “BST”), barium titanate (BaTiO ₃ ), etc. having a high dielectric constant. A dielectric thin film formed using a type oxide is used. As a method for forming a dielectric thin film, in addition to a physical vapor deposition method such as a vacuum deposition method, a sputtering method, a laser ablation method, or a chemical vapor deposition method such as a CVD (Chemical Vapor Deposition) method, a sol-gel method is used. The chemical solution method is used (see, for example, Patent Document 1 and Non-Patent Document 1).

And, the thin film capacitor incorporated in the high frequency tunable device requires the variability of the electrostatic capacity with respect to the applied voltage (tunability), and the width of the electrostatic capacity that can be controlled when the voltage is applied is larger. That is, high tunability is desired. The reason is that the higher the tunability, the wider the resonance frequency band can be accommodated with a smaller voltage change. Specifically, the tunability is as _{follows: Tunability} = (C _0V −C _tV ), where C _0V is the capacitance before the voltage is applied and C _tV is the capacitance after the voltage of tV is applied. / C _0V × 100%. For example, as shown in FIG. 8, when a voltage of 5V is applied, the capacitance changes from C _0V to C _5V when there is no applied voltage. At this time, if the width from C _0V to C _5V is large, It can be said that the larger the size, the higher the tunability and the higher the tunability of the thin film capacitor. As a technique for enhancing such tunability, a tunable capacitor that can ensure high tunability using a material having a high dielectric constant while maintaining a desired impedance when used in a high frequency band is disclosed (for example, a patent). Reference 2). The tunable capacitor disclosed in Patent Document 2 includes a second dielectric layer having a dielectric constant lower than that of the first dielectric layer between the first dielectric layer and the upper surface electrode. By forming so as to cover a part of the main surface of the dielectric layer, low capacity and high tunability are ensured.

JP-A-60-236404 (page 6, upper right column, line 10 to lower left column, line 3) JP 2008-53563 A (paragraph [0004], paragraph [0008])

T.Hosokura, A.Ando, Y.Sakabe, Key Engineering Materials Vol.320 (2006) pp81-84

  However, many thin film capacitors currently on the market are still about 40 to 50% even if their tunability is relatively high, and it cannot be said that they are sufficient. Various thin film capacitors for improving tunable characteristics from various directions Has been studied.

  Therefore, the present inventors paid attention to the firing conditions when forming the dielectric thin film, and from the viewpoint of improving this material, the present inventors developed high tunability and also the dielectric constant, which is a basic characteristic of thin film capacitors and the like. The present invention has been improved.

An object of the present invention, when used in thin film capacitors, etc., may be expressed high tunability and high dielectric constant to provide a way of forming a dielectric thin film.

As shown in FIG. 1, the first aspect of the present invention is that the composition having a predetermined thickness is obtained by repeatedly applying and drying a dielectric thin film forming composition on a lower electrode on a heat resistant substrate. In the method of forming a dielectric thin film by firing the green film formed on the lower electrode after obtaining the green film , and subsequently forming the upper electrode on the dielectric thin film Is a thin film containing a perovskite oxide as a main component, the firing of the unsintered film formed on the lower electrode before forming the upper electrode is rapidly heated at a temperature increase rate of 60 to 6000 ° C./min. The first firing is performed at a temperature of 375 to 550 ° C. for 1 to 60 minutes, and the temperature is increased at a low rate of 0.5 to 30 ° C./minute and heated at a temperature of 600 to 900 ° C. for 10 to 1500 minutes . Secondary firing is included at least in this order.

  The second aspect of the present invention is an invention based on the first aspect, wherein the primary firing is performed by rapid heating at 300 to 6000 ° C./min, and the secondary firing is 0.5 to It is characterized by being carried out by low-temperature heating at 5 ° C./min.

A third aspect of the present invention is an invention based on the first aspect, wherein the perovskite oxide is Ba _1-x Sr _x Ti _y O ₃ (where 0 ≦ x ≦ 1, 0.9 ≦ y ≦ 1.1).

A fourth aspect of the present invention is a thin film capacitor having a dielectric thin film formed by a method based on the first to third aspects , a capacitor, an IPD (Integrated Passive Device), a DRAM memory capacitor, a multilayer capacitor, and a gate of a transistor. This is a method of manufacturing a composite electronic component of an insulator, nonvolatile memory, pyroelectric infrared detection element, piezoelectric element, electro-optical element, actuator, resonator, ultrasonic motor, or LC noise filter element.

A fifth aspect of the present invention is a thin film capacitor having a dielectric thin film, a capacitor, an IPD (Integrated Passive Device), which corresponds to a frequency band of 100 MHz or more , formed by a method based on the first to third aspects . DRAM memory capacitor, multilayer capacitor, transistor gate insulator, non-volatile memory, pyroelectric infrared detector, piezoelectric element, electro-optic element, actuator, resonator, ultrasonic motor, or LC noise filter element composite electronic component It is a manufacturing method .

In the forming method according to the first aspect of the present invention, when the dielectric thin film is a thin film containing a perovskite oxide as a main component, firing of the unfired film formed on the lower electrode before forming the upper electrode is performed. 60 to 6000 ° C. / and the primary firing heating for 1 to 60 minutes at a minute temperature rapidly raised 375 to 550 ° C. at a heating rate, a slow heating at a heating rate of 0.5 to 30 ° C. / min And secondary firing that is heated at a temperature of 600 to 900 ° C. for 10 to 1500 minutes . By forming in this way, a dielectric thin film that is dense and has no cracks on the surface can be obtained. Thereby, high tunability and a high dielectric constant can be expressed in a thin film capacitor or the like formed using this dielectric thin film.

It is process drawing of the formation method of the dielectric material thin film of this invention. FIG. 4 is a diagram showing tunability characteristics in the thin film capacitor of Example 1. 2 is a surface and cross-sectional SEM image of a dielectric thin film of Example 1. FIG. 6 is a diagram showing tunability characteristics in the thin film capacitor of Comparative Example 1. FIG. 2 is a surface and cross-sectional SEM image of a dielectric thin film of Comparative Example 1. It is a figure which shows the tunability characteristic in the thin film capacitor of the comparative example 2. 4 is a surface and cross-sectional SEM image of a dielectric thin film of Comparative Example 2. It is explanatory drawing which shows the change of the electrostatic capacitance accompanying the change of the applied voltage in a variable capacitance element.

  Next, the form for implementing this invention is demonstrated.

  The method for forming a dielectric thin film according to the present invention includes a step of repeatedly applying a dielectric thin film forming composition to a heat resistant substrate and drying it to obtain a green film of a composition having a desired thickness. The unfired film formed in the above is fired.

The dielectric thin film to be formed has a composition of perovskite type oxide, specifically, Ba _1-x Sr _x Ti _y O ₃ (where 0 ≦ x ≦ 1, 0.9 ≦ y ≦ 1.1). Examples include thin films as components.

  A conventionally known composition can be used as the dielectric thin film forming composition.

  For example, if it is a composition for BST thin film formation, it prepares by melt | dissolving an organic barium compound, an organic strontium compound, and an organic titanium compound in an organic solvent in a predetermined ratio.

  As the organic barium compound, the organic strontium compound, and the organic titanium compound, a compound in which an organic group is bonded to each metal element of Ba, Sr, and Ti through an oxygen or nitrogen atom thereof is preferable. For example, one kind selected from the group consisting of metal alkoxide, metal diol complex, metal triol complex, metal carboxylate, metal β-diketonate complex, metal β-diketoester complex, metal β-iminoketo complex, and metal amino complex Or 2 or more types are illustrated. Particularly suitable compounds are metal alkoxides, partial hydrolysates thereof, and organic acid salts.

  Specifically, examples of the organic barium compound include carboxylates such as barium 2-ethylbutyrate, barium 2-ethylhexanoate, barium acetate, and metal alkoxides such as barium diisopropoxide and barium dibutoxide. . Examples of organic strontium compounds include carboxylates such as strontium 2-ethylbutyrate, strontium 2-ethylhexanoate, and strontium acetate, and metal alkoxides such as strontium diisopropoxide and strontium dibutoxide. Examples of the organic titanium compound include metal alkoxides such as titanium tetraethoxide, titanium tetraisopropoxide, titanium tetrabutoxide, and titanium dimethoxydiisopropoxide. Although the metal alkoxide may be used as it is, a partially hydrolyzed product thereof may be used in order to promote decomposition.

  Since the metal molar ratio in the composition is reflected in the metal molar ratio in the dielectric thin film after formation, these raw materials correspond to the desired dielectric thin film composition to prepare the dielectric thin film forming composition. To a concentration suitable for coating.

  The solvent of the dielectric thin film forming composition used here is appropriately determined according to the raw material used, but in general, carboxylic acid, alcohol, ester, ketones (for example, acetone, methyl ethyl ketone), ethers (E.g., dimethyl ether, diethyl ether), cycloalkanes (e.g., cyclohexane, cyclohexanol), aromatics (e.g., benzene, toluene, xylene), other tetrahydrofuran, or a mixture of two or more of these Can do.

  Specific examples of the carboxylic acid include n-butyric acid, α-methylbutyric acid, i-valeric acid, 2-ethylbutyric acid, 2,2-dimethylbutyric acid, 3,3-dimethylbutyric acid, 2,3-dimethylbutyric acid, 3-methylpentanoic acid, 4-methylpentanoic acid, 2-ethylpentanoic acid, 3-ethylpentanoic acid, 2,2-dimethylpentanoic acid, 3,3-dimethylpentanoic acid, 2,3-dimethylpentanoic acid, 2- It is preferable to use ethylhexanoic acid or 3-ethylhexanoic acid.

  As the ester, ethyl acetate, propyl acetate, n-butyl acetate, sec-butyl acetate, tert-butyl acetate, isobutyl acetate, n-amyl acetate, sec-amyl acetate, tert-amyl acetate, isoamyl acetate are used. As the alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, iso-butyl alcohol, 1-pentanol, 2-pentanol, 2-methyl-2-pentanol, 2-methoxy It is preferred to use ethanol.

  The total concentration of the organometallic compound in the organometallic compound solution of the dielectric thin film forming composition is preferably about 0.1 to 20% by mass in terms of metal oxide.

  In this organometallic compound solution, β-diketones (for example, acetylacetone, heptafluorobutanoylpivaloylmethane, dipivaloylmethane, trifluoroacetylacetone, benzoylacetone, etc.) are used as stabilizers as necessary. , Β-ketone acids (for example, acetoacetic acid, propionylacetic acid, benzoylacetic acid, etc.), β-ketoesters (for example, lower alkyl esters such as methyl, propyl, and butyl of the above ketone acids), oxyacids (for example, lactic acid, Glycolic acid, α-oxybutyric acid, salicylic acid, etc.), lower alkyl esters of the above oxyacids, oxyketones (eg, diacetone alcohol, acetoin, etc.), diols, triols, higher carboxylic acids, alkanolamines (eg, diethanolamine, Triethanolamine, Roh ethanolamine), a polyvalent amine or the like, may be added from 0.2 to 3 approximately at (stabilizer number of molecules) / (number of metal atoms).

  Particles are removed from the prepared organometallic compound solution by filtration or the like, and the number of particles having a particle size of 0.5 μm or more (especially 0.3 μm or more, especially 0.2 μm or more) is 50 / mL per 1 mL of the solution. The following is preferable.

  A light scattering particle counter is used for measuring the number of particles in the organometallic compound solution.

  If the number of particles having a particle size of 0.5 μm or more in the organometallic compound solution exceeds 50 particles / mL, the long-term storage stability becomes poor. The smaller the number of particles having a particle size of 0.5 μm or more in this organometallic compound solution, the more preferable, and particularly preferably 30 particles / mL or less.

  The method for treating the organometallic compound solution after preparation so as to achieve the number of particles is not particularly limited, and examples thereof include the following method. The first method is a filtration method in which a commercially available membrane filter having a pore size of 0.2 μm is used and pressure-fed with a syringe. The second method is a pressure filtration method in which a commercially available membrane filter having a pore size of 0.05 μm and a pressure tank are combined. The third method is a circulation filtration method in which the filter used in the second method and the solution circulation tank are combined.

  In any method, the particle capture rate by the filter varies depending on the solution pressure. It is generally known that the lower the pressure, the higher the capture rate. In particular, in the first method and the second method, the number of particles having a particle size of 0.5 μm or more is set to 50 or less. In order to achieve, it is preferable to pass the solution through the filter very slowly at low pressure.

  Next, the dielectric thin film forming composition is applied onto a heat-resistant substrate by a coating method such as spin coating, dip coating, or LSMCD (Liquid Source Misted Chemical Deposition), and dried (pre-baked). A green film having a thickness is formed.

As a specific example of the heat-resistant substrate to be used, a single crystal Si, polycrystalline Si, Pt, Pt (uppermost layer) / Ti, Pt (uppermost layer) / Ta, Ru, RuO ₂ , Ru ( Top layer) / RuO ₂ , RuO ₂ (top layer) / Ru, Ir, IrO ₂ , Ir (top layer) / IrO ₂ , Pt (top layer) / Ir, Pt (top layer) / IrO ₂ , SrRuO ₃ or _{(La x Sr (1-x} )) is a substrate with CoO ₃ perovskite-type conductive oxide such like, but not limited thereto.

  In general, since a desired film thickness cannot be obtained by one application, an unfired film having a desired thickness is obtained by repeatedly applying and drying a plurality of times. In addition, the film is sintered in the subsequent firing, and the film thickness changes between the unfired film and the dielectric thin film after the firing. The film thickness is adjusted. For example, in the case of high-capacity density thin film capacitor applications, the thickness of the dielectric thin film after the main firing is preferably in the range of 50 to 500 nm, and the thickness of the unfired film is adjusted so as to be in this range. .

  In addition, drying (preliminary firing) is performed in order to remove the solvent and thermally decompose or hydrolyze the organic metal compound or organic compound to convert it into a composite oxide. Perform in an atmosphere. Even in heating in the air, the moisture required for hydrolysis is sufficiently secured by the humidity in the air. Drying (preliminary firing) is performed by holding at a temperature of 200 to 450 ° C. for 1 to 20 minutes. In addition, drying (preliminary firing) may be performed in two stages: low-temperature heating for removing the solvent and high-temperature heating for decomposing the organometallic compound or organic compound.

  Subsequently, the unfired film after drying (preliminary firing) is subjected to main firing at a temperature equal to or higher than the crystallization temperature to obtain a dielectric thin film. The characteristic structure in the method for forming a dielectric thin film of the present invention is that the unsintered film is subjected to primary firing by rapid heating at 60 to 6000 ° C./min, and 0.5 to 30 ° C./min. And secondary firing by slow heating at a low temperature in this order.

Initial crystal nuclei are generated by the primary firing by this rapid heating. The reason why the temperature increase rate of the primary firing is within the above range is that the effect of the primary firing is insufficient and the tunability is not improved below the lower limit, and when the upper limit is exceeded, initial crystal nuclei are generated. This is because the density is increased and each crystal cannot sufficiently grow during the secondary firing, and the tunability is not improved. The primary firing is performed by raising the temperature at the above-mentioned temperature rise rate and holding at a temperature of 375 to 550 ° C., preferably 450 to 550 ° C. for 1 to 60 minutes, preferably 1 to 5 minutes. The atmosphere in the primary firing is preferably O ₂ , N ₂ , Ar, N ₂ O, H _2, or a mixed gas thereof. For the rapid heating at the first firing, a rapid heating treatment (RTA) apparatus using an incandescent lamp, a halogen lamp, an arc lamp, a graphite heater or the like as a heating source, a hot plate, or the like can be used.

Then, the initial crystal nuclei generated by the primary firing are grown by secondary firing by low-temperature heating and subsequent to the primary firing. In addition, although the crack may arise in the film | membrane surface after primary baking, the crack is filled up by the grain growth by this secondary baking. The reason why the temperature increase rate of the secondary firing is within the above range is that if it is less than the lower limit value, the crystal grains are coarsened to form a film with many voids, which adversely affects the electrical characteristics. This is because growth is insufficient and tunability is not improved. The secondary firing is performed by raising the temperature at the above temperature rise rate and holding at a temperature of 600 to 900 ° C., preferably 700 to 900 ° C. for 10 to 1500 minutes, preferably 30 to 120 minutes. The atmosphere in the secondary firing is preferably O ₂ , N ₂ , Ar, N ₂ O, H _2, or a mixed gas thereof. For example, a muffle furnace or the like can be used for the slow temperature heating in the second firing.

  Among these, it is preferable that the primary firing is performed by rapid heating at 300 to 6000 ° C./min, and the secondary firing is performed by slow heating at 0.5 to 5 ° C./min.

  In this embodiment, the firing of the unsintered film has been described by the primary firing and the secondary firing. For example, in order to improve the adhesion of the upper electrode, oxygen vacancies in the perovskite oxide are formed. In order to compensate, the heat treatment step can be further increased as necessary, such as further heat-treating the film after the secondary baking. Moreover, a primary baking process and a secondary baking process can be continuously performed using a single heating apparatus.

  The dielectric thin film of the present invention thus formed is dense and free of cracks on the surface, and can exhibit high tunability and high dielectric constant in a thin film capacitor or the like provided with this thin film. The dielectric thin film of the present invention is also excellent in basic characteristics as an IPD.

  The dielectric thin film of the present invention includes a thin film capacitor, a capacitor, an IPD, a DRAM memory capacitor, a multilayer capacitor, a transistor gate insulator, a nonvolatile memory, a pyroelectric infrared detection element, a piezoelectric element, an electro-optical element, and an actuator. It can be used as a constituent material in a composite electronic component of a resonator, an ultrasonic motor, or an LC noise filter element. Among these, it can also be used especially for the thing corresponding to the frequency band of 100 MHz or more.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1>
First, solution stabilization of barium 2-ethylbutyrate as the organic barium compound, strontium 2-ethylbutyrate as the organic strontium compound, titanium tetraisopropoxide as the organic titanium compound, and isoamyl acetate sufficiently dehydrated as the organic solvent Acetylacetone was prepared as a stabilizer for each.

  Next, an organic barium compound and an organic strontium compound are dissolved in an organic solvent so that the molar ratio of Ba: Sr is 70:30, and the molar ratio of Ba: Sr: Ti is 70: It added so that it might be set to 30: 100. Moreover, 1 time mole was added with respect to the metal total amount, and the composition for thin film formation whose metal oxide conversion density | concentration was 7 mass% was prepared.

Next, a thin film was formed by the CSD method (chemical solution deposition method) using the prepared thin film forming composition. That is, a substrate (Pt / TiO ₂ / SiO ₂ / (100) Si) having a Pt lower electrode film formed by sputtering on the surface of a 6-inch silicon substrate having an adhesion layer laminated on an insulator film is prepared. The thin film-forming composition prepared above was applied on the Pt lower electrode film of this substrate by spin coating at 500 rpm for 3 seconds and then at 2000 rpm for 15 seconds to form a coating film. Subsequently, using a hot plate, the substrate having the coating film was dried by holding at a temperature of 350 ° C. for 10 minutes. This coating and drying process was repeated four times to obtain a green film having a thickness of 580 nm.

  Next, the substrate having the unsintered film was subjected to primary firing using an RTA apparatus and raising the temperature in the air atmosphere at a rate of 600 ° C./min and holding at a temperature of 550 ° C. for 1 minute. Subsequently, a BST dielectric thin film having a film thickness of 350 nm is obtained by performing secondary firing using a muffle furnace, raising the temperature at a rate of 5 ° C./min in an air atmosphere and holding the temperature at 700 ° C. for 60 minutes. It was. Thereafter, using a metal mask, an approximately 250 × 250 μm square Pt upper electrode was formed on the surface by a sputtering method to obtain a thin film capacitor.

<Example 2>
A BST dielectric thin film was formed in the same manner as in Example 1 except that the rate of temperature increase in the second firing was 0.5 ° C./min, and a thin film capacitor was obtained.

<Example 3>
A thin film capacitor was obtained by forming a BST dielectric thin film in the same manner as in Example 1 except that the ultimate temperature in the primary firing was 500 ° C.

<Example 4>
A BST dielectric thin film was formed in the same manner as in Example 1 except that the ultimate temperature in the primary firing was 450 ° C., and a thin film capacitor was obtained.

<Example 5>
A BST dielectric thin film was formed in the same manner as in Example 1 except that a hot plate was used for the primary firing, the heating rate was 2000 ° C./min, the ultimate temperature was 450 ° C., and the holding time was 5 minutes. A thin film capacitor was obtained.

<Example 6>
A BST dielectric thin film was formed in the same manner as in Example 1 except that a hot plate was used for the primary firing, the heating rate was 2000 ° C./min, the ultimate temperature was 425 ° C. and the holding time was 5 minutes, A thin film capacitor was obtained.

<Example 7>
A BST dielectric thin film was formed in the same manner as in Example 1 except that a hot plate was used for the primary firing, the heating rate was 2000 ° C./min, the ultimate temperature was 400 ° C., and the holding time was 5 minutes. A thin film capacitor was obtained.

<Example 8>
A BST dielectric thin film was formed in the same manner as in Example 1 except that a hot plate was used for the primary firing, the heating rate was 2000 ° C./min, the ultimate temperature was 375 ° C. and the holding time was 5 minutes, A thin film capacitor was obtained.

<Example 9>
A BST dielectric thin film was formed in the same manner as in Example 1 except that the rate of temperature increase in the second firing was 0.5 ° C./min and the ultimate temperature was 900 ° C., to obtain a thin film capacitor.

<Example 10>
A BST dielectric thin film was formed in the same manner as in Example 1 except that the temperature increase rate in the primary firing was set to 6000 ° C./min to obtain a thin film capacitor.

<Comparative Example 1>
A BST dielectric thin film was formed in the same manner as in Example 1 except that the primary firing was not performed to obtain a thin film capacitor.

<Comparative example 2>
A BST dielectric thin film was formed in the same manner as in Example 1 except that the ultimate temperature in the primary firing was 700 ° C., the holding time was 5 minutes, and the secondary firing was not performed, and a thin film capacitor was obtained.

<Comparative Example 3>
A BST dielectric thin film was formed in the same manner as in Example 1 except that the temperature increase rate in the primary firing was 50 ° C./min, and a thin film capacitor was obtained.

<Comparative Example 4>
A BST dielectric thin film was formed in the same manner as in Example 1 except that the temperature increase rate in the primary firing was 6600 ° C./min, and a thin film capacitor was obtained.

<Comparative Example 5>
A BST dielectric thin film was formed in the same manner as in Example 1 except that the rate of temperature increase in the second firing was 0.3 ° C./min and the ultimate temperature was 900 ° C., to obtain a thin film capacitor.

<Comparative Example 6>
A BST dielectric thin film was formed in the same manner as in Example 1 except that the rate of temperature increase in the second firing was 35 ° C./min, and a thin film capacitor was obtained.

<Comparison test and evaluation>
For the thin film capacitors obtained in Examples 1 to 10 and Comparative Examples 1 to 6, the capacity density, tunability, dielectric constant, and film thickness of the dielectric thin film were evaluated. These results are shown in Table 2 below. The tunability characteristic diagrams of the thin film capacitors of Example 1 and Comparative Examples 1 and 2 are shown in FIGS. 2, 4 and 6, and the surface and cross-sectional SEM images of the dielectric thin films of Example 1 and Comparative Examples 1 and 2 are shown. 3, 5, and 7, respectively.

(1) Capacitance density: 5 V bias voltage applied at 10 MHz between the Pt upper electrode and Pt lower electrode of the thin film capacitor, and the capacitance C _{0 V} when no bias voltage is applied, and the area of the thin film capacitor From S, the electrostatic capacity (capacity density) per 1 cm ² was calculated. The capacitance C _0V was measured using an impedance material analyzer (manufactured by Hewlett-Packard Company: HP4291A).

(2) Tunability: A bias voltage of 5 V is applied between the Pt upper electrode and the Pt lower electrode of the thin film capacitor at 10 MHz, and the capacitance C _{0 V} when no bias voltage is applied and when 5 V is applied. From C _{5 V} , the change rate T (%) of capacitance calculated from the following equation (1) was calculated. The capacitance change rate T (%) was measured by using an impedance material analyzer (manufactured by Hewlett-Packard Company: HP4291A).

T = (C _0V −C _5V ) / C _0V × 100 (1)
(3) Dielectric constant: From the capacitance C _0V when a bias voltage of 0 V is applied at 10 MHz between the Pt upper electrode and the Pt lower electrode of a thin film capacitor having a thickness d and an area S, the following equation (2 ) To calculate the dielectric constant ε. The dielectric constant of vacuum was 8.854 × 10 ⁻¹² (F / m). The capacitance C _0V was measured using an impedance material analyzer (manufactured by Hewlett-Packard Company: HP4291A).

ε = C _0V × d / S / 8.854 × 10 ⁻¹² (2)
(4) Film thickness: Film thickness was determined by cross-sectional SEM observation.

As is clear from Table 2, FIG. 4 and FIG. 6, Comparative Example 1 with only slow heating and heating has a low capacity density and dielectric constant, and Comparative Example 2 with only rapid heating and heating has low tunability. It was. In the surface and cross-sectional SEM image of Comparative Example 1 shown in FIG. 5, the crystal grains are rough, the crystal grains are spaced from each other, and a gap is generated at the interface between the Pt thin film and the dielectric thin film. . Moreover, although it can confirm that the precise | minute film | membrane was obtained from the surface and cross-sectional SEM image of the comparative example 2 shown in FIG. 7, the surface has cracked.

  On the other hand, as is clear from Table 2 and FIG. 2, in Examples 1 to 4, 9, and 10, the results of high dielectric constant and high tunability were obtained compared to Comparative Examples 1 and 2. It was. Moreover, in Examples 5-8, the result which is high tunability compared with the comparative examples 1 and 2 and high dielectric constant compared with the comparative example 1 was obtained. From the surface and cross-sectional SEM images of Example 1 shown in FIG. 3, it was confirmed that a dense film was obtained.

  In addition, from each result of Examples 1, 3, and 4 in which only the ultimate temperature of the primary firing is different using an RTA apparatus, a film having superior characteristics can be obtained as the ultimate temperature of the primary firing is higher. There was a tendency to obtain a dense film because the film thickness was thin. Further, from the results of Examples 1 and 10 in which only the temperature increase rate of the primary firing was different, there was a tendency that the characteristics were inferior when the temperature increase rate of the primary firing was too high. Further, from the results of Examples 1 and 2 in which only the temperature increase rate of the secondary firing was different, there was a tendency that a film having superior characteristics was obtained as the temperature increase rate of the secondary firing was lower. In addition, from the results of Examples 2 and 9 in which only the ultimate temperature of secondary firing was different, there was a tendency that a film having superior characteristics was obtained as the ultimate temperature of secondary firing was higher.

  Similarly, from the results of Examples 5 to 8 in which only the ultimate temperature of primary firing is different using a hot plate, a film having superior characteristics can be obtained as the ultimate temperature of primary firing is higher. There was a tendency to obtain a dense film because the thickness was reduced.

  In Comparative Example 3 where the temperature increase rate of the primary firing is low, there is no improvement in tunability compared to Comparative Example 1, and in Comparative Example 4 where the temperature increase rate of the primary firing is high, Comparative Example 1 and Although it was denser and had a higher capacity density, there was no improvement in tunability. In Comparative Example 5 where the temperature increase rate of the secondary firing is low, the characteristics are adversely affected, and in Comparative Example 6 where the temperature increase rate of the primary firing is high, the tunability is improved as compared with Comparative Example 1. There wasn't. From these results, it was confirmed that there is an appropriate range in which the characteristics of the dielectric thin film can be improved in the heating rate in the primary firing and the secondary firing.

  From these results, when forming a dielectric thin film containing a perovskite oxide such as BST as a main component by using a coating method, by applying the forming method of the present invention, the dielectric thin film having no cracks on the surface can be obtained. It has been found that a dielectric thin film can be formed, and the obtained dielectric thin film can exhibit high tunability and high dielectric constant when used in a thin film capacitor or the like.

  Although not illustrated, a dielectric thin film was formed under the same conditions except that the thin film forming composition was changed to BT and ST for the BT thin film and ST thin film as the dielectric thin film, and the obtained thin film capacitor On the other hand, when the same evaluation was performed, the same tendency as the evaluation result obtained with the BST thin film was observed. In other words, compared to firing only at low temperature heating or only rapid heating, the dielectric material is dense and has no cracks on the surface by firing in a combination of rapid heating and slow heating in this order. A thin film could be formed, and when the obtained dielectric thin film was used for a thin film capacitor or the like, high tunability and high dielectric constant could be expressed. From this, it was confirmed that the forming method of the present invention is effective not only for forming the BST thin film but also for forming the BT thin film and the ST thin film.

  The dielectric thin film obtained by the forming method of the present invention can be used for a thin film capacitor having a high dielectric constant and high tunability.

Claims (5)

After forming the dielectric thin film forming composition on the lower electrode on the heat-resistant substrate and drying it repeatedly to obtain an unsintered film of the composition having a predetermined thickness, it was formed on the lower electrode . In a method of forming a dielectric thin film by firing an unfired film , and subsequently forming an upper electrode on the dielectric thin film ,
When the dielectric thin film to be formed is a thin film containing a perovskite oxide as a main component,
Firing of the unsintered film formed on the lower electrode before forming the upper electrode is rapidly heated at a temperature increase rate of 60 to 6000 ° C./min and heated at a temperature of 375 to 550 ° C. for 1 to 60 minutes. It includes at least a first firing and a second firing that is heated at a low temperature of 0.5 to 30 ° C./min and heated at a temperature of 600 to 900 ° C. for 10 to 1500 minutes in this order. A method for forming a dielectric thin film.   2. The dielectric according to claim 1, wherein the first firing is performed by rapid heating at 300 to 6000 ° C./min, and the second firing is performed at low heating at 0.5 to 5 ° C./min. Method for forming a thin film. Said perovskite oxide is _{Ba 1-x Sr x Ti y} O 3 ( where, 0 ≦ x ≦ 1,0.9 ≦ y ≦ 1.1) the method of forming the dielectric thin film of claim 1 having a composition of . A thin film capacitor having a dielectric thin film formed by the method according to any one of claims 1 to 3 , a capacitor, an IPD (Integrated Passive Device), a DRAM memory capacitor, a multilayer capacitor, a gate insulator of a transistor, a non-volatile Of manufacturing a composite electronic component of a volatile memory, a pyroelectric infrared detection element, a piezoelectric element, an electro-optical element, an actuator, a resonator, an ultrasonic motor, or an LC noise filter element. A thin film capacitor having a dielectric thin film, a capacitor, an IPD (Integrated Passive Device), a DRAM memory capacitor, which is formed by the method according to any one of claims 1 to 3 and corresponds to a frequency band of 100 MHz or more, A method of manufacturing a composite electronic component of a multilayer capacitor, a transistor gate insulator, a nonvolatile memory, a pyroelectric infrared detection element, a piezoelectric element, an electro-optical element, an actuator, a resonator, an ultrasonic motor, or an LC noise filter element .