JP6597430B2 - Ferroelectric film and manufacturing method thereof - Google Patents

Description

  The present invention relates to a ferroelectric film with improved lifetime reliability and a method for manufacturing the same.

  A perovskite structure PLZT film containing Pb, La, Zr and Ti as a ferroelectric film used in infrared sensors, piezoelectric filters, vibrators, laser modulation elements, optical shutters, capacitor films, nonvolatile memories, etc. Is used. For example, Patent Document 1 discloses a PLZT film in which the contents of Li, Na, and K are reduced and the leakage current is suppressed.

Japanese Patent No. 2956356

  If the contents of Li, Na, and K are reduced as described in Patent Document 1, the leakage current of the PLZT film can be reduced, but sufficient characteristics may not be obtained from the viewpoint of lifetime reliability.

  An object of the present invention is to provide a ferroelectric film having excellent lifetime reliability and a method for manufacturing the same.

A first aspect of the present invention is a ferroelectric film made of a plurality of fired films, made of a metal oxide having a perovskite structure containing Pb, Zr and Ti, and has a total content of Li, Na and K 1 mass ppm or more and 3 mass ppm or less, and the total content of Li, Na, and K on one surface of each fired film constituting the plurality of fired films is the total content of Li, Na, and K on the other surface It is a ferroelectric film characterized by being 5 to 12 times the amount.

  A second aspect of the present invention is the invention based on the first aspect, wherein in each of the fired films, the total content of Li, Na, and K is between the one surface and the other surface. A ferroelectric film that forms a constant concentration gradient in the film thickness direction.

  3rd viewpoint of this invention is invention based on 2nd viewpoint, Comprising: Arbitrary adjacent pairs of baking films are defined as the 1st baking film and the 2nd baking film among these baking films The other surface of the first fired film (the surface on the side where the concentration of Li etc. is low) is adjacent to the one surface (the surface on the side where the concentration of Li etc. is high) of the second fired film. It is a membrane.

4th viewpoint of this invention is invention based on 3rd viewpoint, Comprising: Total content of Li, Na, and K in said one side (surface with high density | concentrations, such as Li) of said 2nd baking film | membrane The amount is a ferroelectric film that is not less than 5 times and not more than 12 times the total content of Li, Na, and K on the other surface of the first fired film (the surface on the side where the concentration of Li or the like is low).

According to a fifth aspect of the present invention, there is provided a coating process in which a ferroelectric film forming liquid composition containing Pb, Zr and Ti is coated on a substrate to form a precursor film, and the precursor film is heated. A ferroelectric that performs at least three times each of a calcining step of converting to a composite oxide and forming a calcined film, and a calcining step of firing and crystallizing the calcined film to form a calcined film In the method for producing a film, the liquid composition for forming a ferroelectric film contains Li, Na, and K in a total amount of 3 mass ppm to 10 mass ppm, and in the calcining step, 10 mm from the upper surface of the substrate. A method for producing a ferroelectric film, characterized in that a carrier gas wind speed at a height is set to 0.1 m / second or more and 1.0 m / second or less.

  A sixth aspect of the present invention is an electronic component having a ferroelectric film based on any one of the first to fourth aspects.

In the ferroelectric film according to the first aspect of the present invention, the total content of Li, Na, and K is 1 mass ppm or more and 3 mass ppm or less, and on one surface of each of the fired films constituting the plurality of fired films. Since the total content of Li, Na and K is not less than 5 times and not more than 12 times the total content of Li, Na and K in the other surface, excellent lifetime reliability is provided. That is, in such a ferroelectric film of the present invention, each fired film contains a predetermined amount of Li, Na, and K, and at the interface between one fired film and the adjacent fired film, Li, Na, and K The content changes rapidly, causing a concentration gradient. This sudden change in the content of Li or the like at the interface of the fired film suppresses the movement of oxygen defects in the film thickness direction and contributes to the improvement of the lifetime of the ferroelectric film.

  According to the method for manufacturing a ferroelectric film of the fifth aspect of the present invention, a ferroelectric film forming liquid composition (hereinafter referred to as a liquid composition) containing Li and the like in a total amount of 3 mass ppm to 10 mass ppm. In the calcination step, the carrier gas wind speed at a height of 10 mm from the upper surface of the substrate is set to 0.1 m / second or more and 1.0 m / second or less, so that it contains Li or the like with a predetermined content. The concentration is inclined, and a ferroelectric film having excellent lifetime reliability can be obtained.

  Since the electronic component according to the sixth aspect of the present invention has the ferroelectric film described above, it has excellent lifetime reliability.

It is a cross-sectional schematic diagram of the ferroelectric film of the embodiment of the present invention. It is a graph which shows density | concentration changes, such as Li in the thickness direction of the ferroelectric film of this invention embodiment. It is principal part sectional drawing of the hotplate apparatus used for the calcination process of this invention embodiment.

  Next, an embodiment for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the configuration of the present embodiment.

[Ferroelectric film]
As shown in FIG. 1, the ferroelectric film 10 of this embodiment is composed of a five-layered fired film 101 formed on the lower electrode 11 of a substrate 12 having a lower electrode 11. The ferroelectric film 10 is made of a metal oxide having a perovskite structure containing Pb, Zr and Ti, and the total content of Li, Na and K is 1 mass ppm or more and 3 mass ppm or less. Then, as shown in FIG. 2, the total content of Li, Na and K (hereinafter abbreviated as Li etc.) on one surface of each fired film 101 is the sum of Li, Na and K on the other surface. It is 5 to 12 times the content. The ferroelectric film 10 may contain La in addition to Pb, Zr and Ti.

(1) Total content of Li etc. Since the total content of Li etc. of the ferroelectric film 10 is 3 mass ppm or less, there is little segregation of an impurity at the grain boundary in a film | membrane, and it is hard to produce a leak current. Thereby, even if time passes, a dielectric breakdown does not produce easily and it is excellent in lifetime stability. Incidentally, when the total content of such Li is less than 1 mass ppm, since the preferred concentration gradient of Li or the like is difficult to obtain, the total content of such Li is shall be the one or more mass ppm. On the other hand, if the total content of Li, Na and K exceeds 3 ppm by mass, the leakage current becomes excessive, resulting in a shortened life. In addition, when the total content of Li and the like on one surface of each fired film is less than 5 times the total content of Li and the like on the other surface, the concentration gradient of Li and the like in the thickness direction of the fired film is small. The change in the content of Li or the like at the interface of the fired film is reduced, the function of suppressing the movement of oxygen defects is insufficient, and the life is shortened. The total content of such Li is Ru der 3 ppm by mass or more 1 mass ppm.

(2) Concentration gradient in fired film such as Li The total content of Li etc. on one side of each fired film 101 is more than 5 times the total content of Li etc. on the other side. The concentration gradient of Li or the like in the thickness direction is sufficient, and this fired film interface suppresses oxygen defect migration due to a rapid change in the content of Li or the like at the fired film interface. As a result, the ferroelectric film of this embodiment is excellent in life stability. In order to increase the concentration gradient of Li or the like, it is necessary to increase the total content of Li or the like, but for the above-mentioned reason, the total content of Li or the like must be 3 mass ppm or less. Therefore, the concentration gradient in the baked film of Li such shall be the 12 times or less. This concentration gradient is more preferably 5 times or more and 10 times or less, and further preferably 5 times or more and 9 times or less.

  This concentration gradient is preferably a constant concentration gradient from the maximum value to the minimum value. However, if the tendency of concentration change is maintained in one direction (decrease direction or increase direction), it may deviate locally by about ± 20% from this ideal constant concentration gradient (mass ppm / nm). .

(3) Number of Layers of Fired Film The ferroelectric film 10 is preferably composed of a fired film 101 having two to 23 layers. By laminating a plurality of fired films 101, an interface is introduced into the ferroelectric film 10. This interface serves as a trap for suppressing the movement of oxygen vacancies and contributes to a decrease in the mobility of oxygen vacancies. As a result, the lifetime reliability of the ferroelectric film 10 can be further improved. The reason why the number of layers of the fired film 101 is 2 or more and 23 or less is that if the interface is not introduced into the ferroelectric film 10 below the lower limit, further improvement in lifetime reliability cannot be achieved, and the upper limit This is because if the value is exceeded, the production takes time. The number of layers of the fired film 101 is more preferably 2 or more and 6 or less, and further preferably 2 or more and 3 or less.

  When laminating the fired film 101, if a pair of adjacent fired films among a plurality of fired films is defined as a first fired film and a second fired film, the other surface of the first fired film (Li or the like) Are laminated in a direction adjacent to one surface of the second fired film (surface having a high concentration of Li or the like). Thereby, content, such as Li, can be changed abruptly in a baking film interface.

  The total content of Li and the like on one side of the second fired film (the surface on the side where the concentration of Li etc. is high) is Li and the like on the other side of the first fired film (the side on the side where the concentration of Li etc. is low) The total content is preferably 5 times or more. The abrupt change in the total content of Li and the like at the sintered film interface is preferably 5 to 10 times, more preferably 5 to 9 times. However, the present invention is not particularly limited to these preferred ranges.

(4) Film thickness of fired film The film thickness t of each fired film 101 is preferably in the range of 45 nm to 500 nm. This is because if it is less than the lower limit, it is difficult to obtain a uniform continuous film, and if it exceeds the upper limit, cracks may occur. The thickness t is more preferably 45 nm or more and 135 nm or less, and further preferably 60 nm or more and 120 nm or less. The film thickness T of the ferroelectric film 10 is preferably in the range of 150 nm to 5000 nm. If it is less than the lower limit value, a film with poor productivity may be formed, and defects in characteristics such as an increase in leakage current density may occur. On the other hand, if the upper limit is exceeded, cracks may occur. The film thickness T is more preferably 200 nm or more and 4000 nm or less, and further preferably 250 nm or more and 3000 nm or less.

(5) Metal atomic ratio The ferroelectric film 10 has a metal atomic ratio Pb: La: Zr: Ti of (0.95 to 1.25) :( 0 to 0.05) :( 0.40 to 0.55). ): (0.45 to 0.60) is preferable. The reason for this metal atomic ratio is that it has a high relative dielectric constant and has excellent characteristics as a ferroelectric. Metal atomic ratio Pb: La: Zr: Ti is (1.00-1.15) :( 0-0.03) :( 0.50-0.55) :( 0.45-0.50). More preferably, (1.05 to 1.10): (0.01 to 0.03): (0.51 to 0.53): (0.47 to 0.49) is more preferable. .

(6) Ferroelectric film substrate and lower electrode As the substrate 12 on which the ferroelectric film 10 is formed, for example, a heat-resistant substrate such as a silicon substrate, a SiO ₂ / Si substrate or a sapphire substrate is used. For the lower electrode 11, for example, a material having conductivity such as Pt, Ir, Ru, or the like that does not react with the ferroelectric film 10 is used.

[Liquid composition for forming a ferroelectric film]
The liquid composition for forming a ferroelectric film (hereinafter abbreviated as “liquid composition”) is a raw material solution for forming the ferroelectric film 10, and a precursor for forming a metal oxide having a perovskite structure. Is dissolved in a solvent at a desired ratio and adjusted to a concentration suitable for coating.

(1) Total content of Li and the like The liquid composition contains Li and the like in a total amount of 3 mass ppm to 10 mass ppm. Since the total content of Li and the like is 3 mass ppm or more, a fired film 101 having a sufficient concentration gradient can be obtained, and since it is 10 mass ppm or less, Li or the like contained in the obtained ferroelectric film 10 The total concentration of can be kept low. The total content of Li and the like is more preferably 3 mass ppm or more and 5 mass ppm or less. The total content of Li and the like in the liquid composition is adjusted by, for example, a method described in Patent Document 1 in which each metal component is repeatedly distilled, sublimated, and recrystallized in the form of a metal organic compound, or a combination thereof. be able to.

(2) Precursor As a precursor to be blended in the liquid composition, an organometallic compound in which an organic group is bonded to each metal element of Pb, La, Zr, or Ti via its oxygen or nitrogen atom is used. be able to. For example, from the group consisting of metal alkoxide, its partial hydrolyzate, metal diol complex, metal triol complex, metal carboxylate, metal β-diketonate complex, metal β-diketoester complex, metal β-iminoketo complex and metal amino complex One type or two or more types selected can be used. Particularly preferred compounds are metal alkoxides, partial hydrolysates thereof, and metal carboxylates.

The liquid composition contains these precursors in proportions that provide the desired metal atomic ratio.
For example, the metal atomic ratio Pb: La: Zr: Ti is (0.95 to 1.25) :( 0 to 0.05) :( 0.40 to 0.55) :( 0.45 to 0.60). The ratio is preferably Thereby, the ferroelectric film 10 having a preferable metal atomic ratio as described above can be obtained. Among these, the metal atomic ratio Pb: La: Zr: Ti is (1.00-1.15) :( 0-0.03) :( 0.50-0.55) :( 0.45-0.50). More preferably, (1.05 to 1.10): (0.01 to 0.03): (0.51 to 0.53): (0.47 to 0.49) Is more preferable.

  The proportion of the precursor in 100% by mass of the liquid composition is preferably 10% by mass to 35% by mass in terms of oxide. If it is less than the lower limit, it is difficult to obtain a sufficient film thickness by one coating, and if it exceeds the upper limit, cracks may occur in the ferroelectric film. The proportion of the precursor is more preferably 10% by mass or more and 20% by mass or less, and further preferably 12% by mass or more and 17% by mass or less. The ratio in terms of oxide means the ratio of the metal oxide in 100% by mass of the liquid composition when it is assumed that all the metal elements contained in the liquid composition are converted into oxides.

(3) Solvent The solvent used for the preparation of the liquid composition is appropriately determined according to the raw material used. For example, carboxylic acids, alcohols, esters, ketones, ethers, cycloalkanes, aromatics, other tetrahydrofuran, or a mixed solvent of two or more of these can be used.

(4) Polymer compound The liquid composition may contain a polymer compound such as polyvinyl pyrrolidone (PVP) or polyethylene glycol in order to adjust the liquid viscosity. The ratio of the polymer compound is preferably in the range of 0.15 mol or more and 0.50 mol or less in terms of monomer with respect to 1 mol of the precursor. If it is less than the lower limit, cracks may occur, and if it exceeds the upper limit, pores may occur.

(5) Stabilizers Further, as stabilizers, β-diketones, β-ketone acids, β-ketoesters, oxyacids, lower alkyl esters of the above oxyacids, oxyketones, diols, triols, higher carboxylic acids Further, alkanolamines, polyvalent amines, etc. may be added in a range of about 0.2 to 3 in terms of (stabilizer molecule number) / (metal atom number). In particular, it is preferable to add β-diketones and polyhydric alcohols. It is preferable to add acetylacetone as the β-diketone and propylene glycol as the polyhydric alcohol.

[Method for producing liquid composition]
In order to prepare the liquid composition, first, the precursor described above is weighed so as to give a desired metal atomic ratio. The precursor and the solvent are put into a reaction vessel and mixed, and are preferably refluxed and reacted at a temperature of 150 ° C. to 160 ° C. for 30 minutes to 3 hours in a nitrogen atmosphere. Subsequently, the solvent is removed by a method such as distillation or evaporation. In the case of adding a stabilizer such as acetylacetone, the stabilizer is added to the synthesis solution after desolvation, and reflux is performed again under the same conditions as above. Furthermore, a solvent is added for dilution, and the concentration of each component in the liquid composition is adjusted to the desired concentration described above. If necessary, a polymer compound is added to a desired ratio, and the mixture is stirred and dispersed uniformly at a temperature close to room temperature for 30 minutes to 3 hours. Thereby, a liquid composition is obtained.

[Manufacturing method of ferroelectric film]
In the method for manufacturing a ferroelectric film according to the present embodiment, the above-described liquid composition containing Li and the like in total of 3 mass ppm to 10 mass ppm is used, and a carrier gas at a height of 10 mm from the upper surface of the substrate in the calcining step. The wind speed is set to 0.1 m / second or more and 1.0 m / second or less. Thereby, the ferroelectric film of this embodiment containing Li or the like with a predetermined content and concentration gradient can be obtained. The wind speed of the carrier gas is the wind speed on the outermost precursor film 10a in a direction parallel to the outermost precursor film 10a, and is a point at a height of 10 mm from the upper surface of the substrate 12 (see FIG. 3). It means the wind speed of the carrier gas at point P).

  Here, if Li etc. contained in the liquid composition is less than 3 ppm, a fired film having a sufficient concentration gradient cannot be obtained, and if it exceeds 10 mass ppm, it is included in the obtained ferroelectric film. This is not preferable because the total concentration of Li and the like increases excessively. In addition, when the wind speed of the carrier gas is less than 0.1 m / second, the volatilization of Li and the like during the heat treatment is insufficient, the total concentration of Li and the like remaining in the film becomes excessive, and the firing has an appropriate concentration gradient. If the film cannot be obtained, and if it exceeds 1.0 m / sec, the material removal speed from the precursor film is too high, and cracks are generated in the obtained fired film, which is not preferable.

  As shown in FIG. 3, in the method for manufacturing the ferroelectric film 10 of the present embodiment, a ferroelectric film forming liquid composition containing Pb, Zr and Ti, and optionally La is applied on the substrate 12. The precursor film 10a is formed by a coating process, the precursor film 10a is heated to be converted into a composite oxide, the calcined film 10b is formed, and the calcined film 10b is fired and crystallized. And the firing step of forming the fired film 101 is performed at least once. When a plurality of layers of the fired film 101 are provided, the coating process, the calcination process, and the firing process are appropriately repeated.

(1) Application Step In the application step, as shown in FIG. 3, a liquid composition is applied on the lower electrode 11 (see FIG. 1) formed on the surface of the substrate 12 to form a precursor film 10a. Note that the lower electrode is not shown in FIG. The application amount of the liquid composition at this time is set so that the film thickness of the fired film 101 after baking is not less than 45 nm and not more than 500 nm, as described above. The coating method is not particularly limited, and examples thereof include spin coating, dip coating, LSMCD (Liquid Source Misted Chemical Deposition) method, and spin spray method.

(2) Drying step After the coating step, a drying step of heating the precursor film 10a may be performed in order to remove the low boiling point solvent and the adsorbed water molecules. Although heating temperature changes also with the kind of solvent, it is about 50 to 200 degreeC normally, and the range of 65 to 75 degreeC is more preferable. However, since the low boiling point solvent and the like can be removed during the heating of the next calcining step, the drying step may be omitted and the low boiling point solvent and the like may be removed in the calcining step.

(3) Calcination Step In the calcination step, the precursor film 10a is heated to be converted into a composite oxide, thereby forming the calcination film 10b. The calcining step and the drying step described above are performed using, for example, a hot plate device 15 shown in FIG. The hot plate apparatus 15 includes a chamber 16, a susceptor 17 having a horizontal upper surface, and a heater 18 embedded in the susceptor. A supply port 16a for supplying the carrier gas G into the hot plate apparatus is provided at the upper center of the chamber 16, and discharge ports 16b for discharging the carrier gas G are provided on both sides of the susceptor 17 below the hot plate apparatus. . A heater power supply device with a temperature control mechanism (not shown) is connected to the heater 18. On the upper surface of the susceptor 17, the substrate 12 having the precursor film 10a is placed. In the hot plate apparatus 15, the carrier gas G introduced from the supply port 16 a of the chamber 16 moves toward the center of the substrate 11, then flows along the upper surface of the substrate 11, and is discharged from the discharge port 16 b at the lower part of the chamber 16. It has become so. The wind speed of the carrier gas G can be controlled by adjusting an exhaust mechanism (not shown).

  In the calcination step, the substrate 12 is placed on the susceptor 17 and heated while flowing the carrier gas G into the hot plate apparatus 15. Here, the wind speed of the carrier gas G at the point P at a height h of 10 mm from the upper surface of the substrate 12 is set to 0.1 m / second or more and 1.0 m / second or less. The flow of the carrier gas G removes impurities including Li and the like contained in the precursor film 10a together with a solvent, a decomposition product of the precursor, and the like, but the wind speed is set to 0.1 m / second or more. The amount of impurities removed from the surface side of the film becomes larger than the amount of impurities removed from the bottom surface side of the precursor film 10a, and the fired film 101 having a sufficient concentration gradient can be obtained. Further, since the wind speed is set to 1.0 m / second or less, it is possible to prevent the fired film 101 from being cracked due to the speed of material removal from the precursor film 10a being too fast. The wind speed is more preferably 0.4 m / sec or more and 0.6 m / sec or less. The observation point of the wind speed is set to a height h of 10 mm from the upper surface of the substrate 12 in order to accurately grasp the influence on the material removal from the upper surface of the calcined film 10b.

  The calcination step is preferably performed, for example, under conditions of 150 ° C. or more and 450 ° C. or less and 1 minute or more and 10 minutes or less, and the calcination temperature is more preferably 200 ° C. or more and 400 ° C. or less, and 300 ° C. or more and 375 ° C. or less. Further preferred. The calcining time is more preferably 2 minutes or more and 5 minutes or less. Since the calcination step is performed to remove the solvent and convert the precursor into a composite oxide by thermal decomposition or hydrolysis, it may be performed in air, in an oxidizing atmosphere, or in a steam-containing atmosphere. preferable. For this reason, as the carrier gas G, for example, air, water vapor, nitrogen gas containing water vapor, or the like can be used. In addition, although an application process and a calcination process may each be implemented once, after repeating a coating process and a calcination process in multiple times so that the calcined film 10b may become a desired film thickness, the following is carried out. You may implement a baking process.

(4) Firing step In the firing step, the calcined film 10b is fired and crystallized to form the fired film 101. For example, the firing is preferably performed at 600 ° C. to 800 ° C. for 1 minute to 5 minutes, and the firing time is more preferably 650 ° C. to 750 ° C. Firing can be performed by rapid temperature raising and lowering heat treatment (RTA treatment) by infrared lamp heating using an RTA (Rapid Thermal Annealing) apparatus. When firing by RTA treatment, the rate of temperature rise is preferably, for example, 2.5 ° C./second or more and 100 ° C./second or less, and more preferably 20 ° C./second or more and 100 ° C./second or less. The firing atmosphere is preferably, for example, oxygen, nitrogen or a mixed gas thereof. By performing the above-described coating process, calcination process, and firing process at least three times , the ferroelectric film 10 composed of a plurality of fired films 101 is obtained.

[Electronic parts]
The electronic component of the present embodiment includes, for example, 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. An electronic component such as a resonator, an ultrasonic motor, an electric switch, an optical switch, or a composite electronic component of an LC noise filter element, which has the ferroelectric film 10 described above. Since these electronic components have the ferroelectric film 10 described above, they have excellent lifetime reliability.

Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
For reagent-grade lead acetate trihydrate (Pb source), lanthanum acetate (La source), tetratitanium isopropoxide (Ti source), tetrazirconium butoxide (Zr source), the method described in Patent Document 1 Recrystallization from pure water was repeated twice to obtain a high purity product. The precursors were weighed so that the metal atomic ratio Pb / La / Zr / Ti was 110/3/52/48, and these were added to propylene glycol in the reaction vessel to prepare a synthesis solution. The synthesis solution was refluxed for 60 minutes at a temperature of 150 ° C. in a nitrogen atmosphere, and then the solvent was removed by distillation. Thereafter, acetylacetone was added as a stabilizer and refluxed at 150 ° C. for 60 minutes.

  Next, it diluted until the total density | concentration of the precursor became 35 mass% in conversion of an oxide by adding propylene glycol to the said synthetic liquid. Furthermore, ethanol was added, and the total concentration of the precursor was diluted to 25% by mass in terms of oxide. Next, polyvinyl pyrrolidone (k value = 30) is added so as to be 0.025 mol with respect to 1 mol of the precursor, and stirred at room temperature for 24 hours to obtain a liquid composition for forming a ferroelectric film. It was. When the concentration of Li, Na and K in the liquid composition was measured using ICP (manufactured by Thermo Fisher Scientific), the total concentration was 10 mass ppm.

Subsequently, an application process was performed. The liquid composition was dropped onto a Pt / TiO ₂ / SiO ₂ / Si substrate set on a spin coater and spin-coated at a rotational speed of 3000 rpm for 30 seconds to form a precursor film on the substrate. The rotation speed and time of the spin coater are set so that the thickness of the fired film obtained in one firing process is 90 nm.

  Next, a calcination step was performed. A substrate having a precursor film is placed on a susceptor of a hot plate apparatus, and a carrier gas (dry air) is flowed so that the wind speed at a height of 10 mm from the upper surface of the substrate is 1 m / second, at 300 ° C. for 5 minutes. By holding, the precursor was converted into a complex oxide to form a calcined film. The wind speed was measured with a hot wire anemometer (manufactured by Custom, model CW-60).

  Then, the baking process was implemented. Using an RTA apparatus, the temperature was raised to 700 ° C. at a rate of temperature rise of 30 ° C./second in an atmosphere in which oxygen gas was supplied at 2 liters per minute and held for 1 minute. Thereby, a fired film having a thickness of 90 nm was formed on the lower electrode of the substrate. By repeating the process from the coating step to the firing step three times, a ferroelectric film having a three-layered fired film 101 and a film thickness of 270 nm was obtained. The film thickness was measured with a scanning electron microscope (HITACHI s4300). The metal atomic ratio Pb: La: Zr: Ti of the ferroelectric film was measured using ICP (manufactured by Thermo Fisher Scientific) and found to be 103/3/52/48.

<Examples 2-9, Comparative Examples 1-4>
As shown in Table 1, a ferroelectric film was formed in the same manner as in Example 1 except that various conditions were changed. Specifically, in some examples, the film thickness of the fired film was changed by adjusting the rotation speed and time of the spin coater. In some examples, the number of process repetitions (firing times) and the thickness of the ferroelectric film were changed. In some examples and comparative examples, liquid compositions having different concentrations such as Li were used by changing the number of times of purification by recrystallization. In some comparative examples, the wind speed in the calcination step was changed. In Example 9, the metal atomic ratio Pb / La / Zr / Ti of the precursor was 110/0/52/48.

<Evaluation>
About the ferroelectric film formed in the Example and the comparative example, the following method evaluated the total density | concentration of Li etc. in a film | membrane, density | concentration gradient, and lifetime reliability. These results are shown in Table 1 below.

(1) Total concentration of Li and the like The total concentration of Li and the like was measured using ICP (manufactured by Thermo Fisher Scientific).

(2) Concentration gradient of Li and the like The concentration distribution of Li and the like in the film thickness direction as shown in FIG. 2 was measured using AES (manufactured by ULVAC) with a concentration gradient of Li and the like. Table 1 shows numerical values obtained by dividing the concentration of Li or the like on one surface of each fired film by the concentration of Li or the like on the other surface to obtain a concentration gradient, and averaging the concentration gradient of all the fired films.

(3) Life Reliability Lifetime property evaluation was performed by an accelerated test (HALT) exposed to a higher load (high temperature / high voltage) environment than a normal use condition. On each ferroelectric thin film of each of Examples and Comparative Examples, a dot-shaped (area: 3.5 × 10 ⁻² mm ² ) platinum thin film was formed by sputtering to form an upper Pt electrode, and the same substrate After forming a plurality of capacitor structures on top, it was reheated at 700 ° C. for 1 minute in an oxygen atmosphere to obtain an evaluation sample.

  The upper Pt electrode and the lower Pt electrode of the thin film capacitor are electrically connected, a voltage of 10 to 20 V is applied in a state where the thin film capacitor is heated to 125 to 205 ° C., and the voltage application time and the leak current value flowing through each capacitor Was measured. As time passes, dielectric breakdown accompanying capacitor deterioration occurs, and it is confirmed that the leakage current increases rapidly. Therefore, the time until each capacitor reaches dielectric breakdown was read from this measurement data (TDDB (time-dependent). (dielectric breakdown, dielectric breakdown over time) evaluation). Specifically, it is considered that dielectric breakdown has occurred when the leak current value exceeds 100 μA, and statistical processing is performed on a plurality of dielectric breakdown time data by Weibull distribution analysis, and 63.2% of the total number of capacitors is dielectric breakdown. The time taken was defined as the mean time to failure (hereinafter referred to as MTF). The following empirical formula (1) is known for bulk capacitors.

Where t is the MTF, T is the test temperature, V is the DC applied voltage, E _a is the activation energy, N is the voltage acceleration coefficient, k _B is the Boltzmann constant, and the subscripts 1 and 2 are for the temperature and the applied voltage. Represents any condition. From the above formula (1), it can be seen that the temperature T and the applied voltage V affect the lifetime of the capacitor. This time, the above relational expression was applied to a thin film capacitor. When the voltage V is constant (V ₁ = V ₂ ) in the above formula (1),

(Where _KV is a constant with respect to temperature), and the inverse of temperature and the logarithmic display of MTF have a linear relationship. This can be used to estimate the activation energy E _a is an acceleration factor for temperature. Similarly, when the temperature T is constant (T ₁ = T ₂ ) in the above equation (1),

(Where _KT is a constant for the applied voltage), and the voltage acceleration coefficient N, which is an acceleration factor for the voltage, can be estimated. Using the values of these two acceleration factors E _a and N, the MTF in a state where a voltage of 5 V was applied after heating to 85 ° C. was extrapolated, and this value was estimated as the predicted life. The obtained results are shown in Table 1 below.

  From Table 1, the ferroelectric film of the example formed within the range of the manufacturing method of the present invention and having a total concentration and concentration gradient of Li or the like in a predetermined range has a long predicted life and has excellent life reliability. I found out. The ferroelectric film of Comparative Example 1 using a liquid composition having a low total concentration such as Li had a small concentration gradient and a predicted life shorter than that of the example. The ferroelectric film of Comparative Example 2 in which the wind speed in the calcination process was reduced had a high total concentration of Li and the like, a large concentration gradient, and a predicted life shorter than that of the Example. In the ferroelectric film of Comparative Example 3 in which the wind speed in the calcination step was increased, cracks that could be visually confirmed occurred. The ferroelectric film of Comparative Example 4 using a liquid composition having a high total concentration such as Li had a high total concentration of Li and the like, and the predicted life was shorter than that of the example.

  The ferroelectric 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, an actuator, It can be used for electronic components such as resonators, ultrasonic motors, electrical switches, optical switches, or composite electronic components of LC noise filter elements.

Claims (6)

A ferroelectric film composed of a plurality of fired films,
A metal oxide having a perovskite structure containing Pb, Zr and Ti,
The total content of Li, Na and K is 1 mass ppm or more and 3 mass ppm or less,
The total content of Li, Na, and K on one surface of each fired film constituting the plurality of fired films is not less than 5 times and not more than 12 times the total content of Li, Na, and K on the other surface. A ferroelectric film characterized by   2. The ferroelectric according to claim 1, wherein in each of the fired films, the total content of Li, Na, and K forms a constant concentration gradient in the film thickness direction between the one surface and the other surface. film.   Of the plurality of fired films, when a pair of adjacent fired films is defined as a first fired film and a second fired film, the other surface of the first fired film is the one of the second fired films. The ferroelectric film according to claim 2, which is adjacent to the surface. The total content of Li, Na, and K on the one surface of the second fired film is 5 to 12 times the total content of Li, Na, and K on the other surface of the first fired film. The ferroelectric film according to claim 3. A coating step of coating a ferroelectric film-forming liquid composition containing Pb, Zr and Ti on a substrate to form a precursor film;
A calcining step of heating the precursor film to convert it into a composite oxide to form a calcined film;
A method of manufacturing a ferroelectric film, wherein the calcined film is fired and crystallized to form a fired film at least three times ;
The ferroelectric film forming liquid composition contains Li, Na, and K in a total of 3 mass ppm to 10 mass ppm,
In the calcining step, the wind speed of the carrier gas at a height of 10 mm from the upper surface of the substrate is 0.1 m / second or more and 1.0 m / second or less.   An electronic component having the ferroelectric film according to claim 1.

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