JP2006128718A - Oxide dielectric element - Google Patents

Abstract

An oxide dielectric device including an oxide dielectric thin film having a high dielectric constant and a low leakage current density is provided.
The oxide dielectric element of the present invention forms an oxide dielectric thin film in an oxygen concentration atmosphere lower than that of the prior art, so the formation temperature can be lowered, and the oxide dielectric thin film has a polarization axis. Highly spontaneous because it has a crystal structure preferentially oriented in the plane orientation in the vertical direction, there is no reaction between the oxide dielectric thin film and the electrode material, and it controls the growth of crystal grains in the oxide dielectric thin film. It has polarization and a small coercive field, and has a small leakage current density.
[Selection] Figure 1

Description

  The present invention relates to an oxide dielectric element, a manufacturing method thereof, a memory and a semiconductor device using the same.

In recent years, semiconductor memories include non-volatile ROM (Read Only Memory) that retains data even when the power is off, but there are problems such as a significant limitation on the number of rewrites and slow rewrite speed. ing. In addition, there is a RAM (Random Access Memory) having an advantage that data can be rewritten at high speed. Among them, there are a DRAM using a high dielectric and a nonvolatile RAM using a ferroelectric. First, a nonvolatile RAM using a ferroelectric has non-volatility by using the hysteresis effect of the ferroelectric, and the number of rewrites is 10 10 to 10 12. . In addition, the rewriting speed is as fast as μs (parts per millionth of a second) compared to other methods, and is attracting attention as an ideal memory for the next generation. Developments have been made to realize such large-capacity, non-volatile, and high-speed nonvolatile RAMs. However, film fatigue such as a decrease in spontaneous polarization (Pr) of the ferroelectric as the number of times of writing occurs as a major problem. In order to increase the capacity and durability, it is well known that (1) a ferroelectric material having a large spontaneous polarization (Pr) is employed, and (2) a ferroelectric material that is resistant to film fatigue is employed. As these materials, oxides having a perovskite structure are widely used. Among these, Bi layered ferroelectric SrBi ₂ Ta ₂ O ₉ having a crystal structure in which a plurality of perovskite single lattices are overlapped is known. For this material, Pr has crystal anisotropy only in the direction perpendicular to the c-axis. Also, although the Pr value is not necessarily large, examples of using this material are disclosed in Patent Document 1 and Patent Document 2 because of excellent film fatigue characteristics.

On the other hand, DRAMs using high dielectric materials are entering an era of large capacity of 16M and 64M bits with the progress of high density and high integration technology. For this reason, miniaturization of circuit constituent elements is required, and in particular, miniaturization of capacitors for storing information has been performed. Among these, miniaturization of capacitors includes thinning of a dielectric material, adoption of a material having a high dielectric constant, flattening and flattening of a structure composed of upper and lower electrodes and a dielectric. Among these, as a material having a high dielectric constant, BST ((Ba / Sr) TiO ₃ ), which is a single lattice having a perovskite crystal structure, has a large dielectric constant (ε) compared to conventional SiO ₂ / Si ₃ N _4. ). An example of using this high dielectric material is reported in Non-Patent Document 1.

Patent WO93 / 12542 (PCT / US92 / 10627) Japanese Patent Laid-Open No. 5-24994 International Electron Device Meeting Technical Digest 1991, page 823 (IEDM Tech. Dig. 823, 1991)

  The present invention relates to a method for manufacturing an oxide dielectric element, a memory and a semiconductor device using the same, and more particularly, a high dielectric element such as a DRAM using a high dielectric constant and a low leakage current density, and a high spontaneous polarization / low The present invention can be used for a ferroelectric element such as a nonvolatile RAM using a coercive electric field, a memory using a high dielectric element or a ferroelectric element, and a semiconductor device.

In this case, the ferroelectric thin film and about 650 ° C. temperature to form a high dielectric thin film by _{Pb (Zr / Ti) O 3} , (Ba / Sr) TiO 3 at about 600 ° C., in SrBi ₂ Ta ₂ O ₉ is It was necessary to raise the temperature to about 800 ° C. In the formation of a thin film having a perovskite structure as described above, a high temperature of 600 ° C. or higher is required to promote crystallization. However, raising the temperature causes various problems. For example, in the vapor phase method, the lower electrode is peeled off by experiencing an oxidizing atmosphere at a high temperature in the initial stage of film formation. Furthermore, in the case of SrBi ₂ Ta ₂ O ₉ , when forming at a conventional high temperature of 800 ° C., Bi evaporates and a composition shift occurs, so it is necessary to make the starting Bi composition excessive. As a result, after the high temperature formation, surplus Bi exists as a heterogeneous phase containing a large amount of Bi at the grain boundary of the ferroelectric layer. A transition layer was formed by the diffusion reaction of the elements, the spontaneous polarization (Pr) was lowered, the original characteristics were hardly obtained, the coercive electric field (Ec) was increased, and film fatigue was caused. For this reason, the number of times of writing performed by reversing the electric field is greatly limited. Furthermore, by raising the temperature, problems such as (a) the formation of the reaction layer reduces the dielectric constant and spontaneous polarization, and (b) the crystal grains grow and the leakage current density increases. However, this increases the operating voltage and makes it difficult to achieve high integration of elements.

  The present invention is directed to an excellent oxide dielectric element, particularly a ferroelectric element having high spontaneous polarization and a low coercive electric field, or a high dielectric element excellent in high dielectric constant and withstand voltage characteristics. An object is to propose a memory and a semiconductor device using the same.

  The present invention is directed to an oxide dielectric element, particularly a ferroelectric element having high spontaneous polarization and a low coercive electric field, or a high dielectric element having high dielectric constant and excellent withstand voltage characteristics. One feature is that the formation of the dielectric thin film and the high dielectric thin film is performed in a low oxygen concentration atmosphere, and the forming temperature is 650 ° C. or lower for a ferroelectric thin film and 600 ° C. or lower for a high dielectric thin film. In this case, the oxygen concentration in which the perovskite structure is most formed as the low oxygen concentration atmosphere, and the oxygen concentration at which high electrical characteristics can be easily obtained is preferably in the range of more than 0.1% and less than 5.0%.

  Another feature of the present invention is that it is possible to produce a low oxygen concentration atmosphere by adjusting the mixing ratio of oxygen and inert gas, and is a very simple method because it is at atmospheric pressure.

Another feature of the present invention is that the ferroelectric thin film and the high dielectric thin film formed by the above manufacturing method are heat-treated again in an activated oxygen atmosphere such as O ₃ , N ₂ O, radical oxygen, etc. High quality ferroelectric thin films and high dielectric thin films are formed.

Next, in the present invention, the ferroelectric thin film is
(AO) ²⁺ (BCO) ^2-
A = Bi, Tl, Hg, Pb, Sb, As
B = Pb, Ca, Sr, Ba, at least one or more of rare earth elements C = Ti, Nb, Ta, W, Mo, Fe, Co, Cr at least one or more, and
(Pb / A) (Zr / Ti) O ₃
A = La, Ba, Nb
It is represented by the following chemical structural formula.

High dielectric thin film
(Ba / Sr) TiO ₃
It is represented by the following chemical structural formula.

The high dielectric thin film obtained by the present invention is characterized by having a dielectric constant larger than that of Ta ₂ O ₅ obtained conventionally.

Further, when metals are used as the upper and lower electrode materials used in the present invention, they are at least one of Pt, Au, Al, Ni, Cr, Ti, Mo, and W. In the case of a conductive oxide composed of a single element, it is at least one oxide of Ti, V, Eu, Cr, Mo, W, Ph, Os, Ir, Pt, Re, Ru, and Sn. It is characterized by that. Further, in the case of a conductive oxide having a perovskite structure, ReO ₃ , SrReO ₃ , BaReO ₃ , LaTiO ₃ , SrVO ₃ , CaCrO ₃ , SrCrO ₃ , SrFeO ₃ , La _1-x Sr _x CoO ₃ (0 <x < 0.5), at least one of LaNiO ₃ , CaRuO ₃ , SrRuO ₃ , SrTiO ₃ , and BaPbO ₃ , and is a conductive oxide composed of a single element in order to have a function as an electrode material When a conductive oxide having a perovskite structure is used, the resistivity is 1 mΩ · cm or less.

  The method for producing a ferroelectric thin film and a high dielectric thin film according to the present invention is characterized in that it is produced using a sputtering method, a laser deposition method, or an MOCVD method in a mixed gas atmosphere of oxygen and an inert gas. Alternatively, it may be produced by a spin coating method or a dip coating method using a metal alkoxide or an organic acid salt as a starting material in a mixed gas atmosphere of oxygen and inert gas at normal pressure.

  In the manufacturing method of the ferroelectric thin film and the high dielectric thin film of the present invention, the reheat treatment is performed by a reheat treatment using a sputtering method equipped with ECR oxygen plasma, a laser deposition method, or a MOCVD method. And Further, re-heat treatment may be performed using a spin coating method or a dip coating method using a metal alkoxide or an organic acid salt as a starting material while irradiating light in the ultraviolet region.

  The present invention can be applied to highly integrated ferroelectric elements, high dielectric elements, and semiconductor devices.

  Hereinafter, the details of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

1 shows an embodiment of the present invention. The characteristics of the present invention will be described in more detail. By controlling the atmosphere for forming the ferroelectric thin film and the high dielectric thin film in the above means to a low oxygen concentration, the ratio of the formation of the perovskite structure in the thin film increases. be able to. In the case of SrBi ₂ Ta ₂ O ₉ ferroelectrics, the formation of a melt accompanying the decomposition reaction of the oxide is promoted even at a low temperature by using a low oxygen concentration. it can. Further, since the formation temperature can be lowered, reaction with the upper and lower electrodes can be prevented.

The ferroelectric thin film used in this example has a chemical structural formula of (AO) ²⁺ (BCO) ²⁻ , and the manufacturing method in the case of A = Bi element, B = Sr element, C = Ta element is as follows. Show. FIG. 2 shows a dielectric element structure according to this example. A lower electrode is formed on the base substrate, and a ferroelectric thin film is formed on the lower electrode. Further, the upper electrode is arranged on the ferroelectric thin film. Reference numeral 24 denotes a base substrate. First, a substrate on which the surface of Si was thermally oxidized to form SiO ₂ was used as the base substrate. Next, a lower electrode 23 (Pt) was formed on the base substrate 24 with a thickness of 2000 mm by sputtering at room temperature. In order to form the ferroelectric thin film 22 on the lower electrode 23, a metal alkoxide solution prepared with a composition of Bi: Sr: Ta = 2: 1: 2 is spin-coated at 3000 rpm (the number of revolutions per minute) for 30 seconds. did. Thereafter, after drying at 150 ° C. for 10 minutes, a pre-heat treatment was further performed in air or oxygen at 500 ° C., which is lower than the crystallization temperature of the ferroelectric thin film, for 15 minutes. The above operation was repeated three times to produce a precursor thin film having a thickness of 2400 mm. Finally, heat treatment was performed by changing the oxygen concentration atmosphere at 650 ° C. × 1 hour to produce a ferroelectric thin film. The crystal structure of the ferroelectric thin film was identified by X-ray diffraction.

  FIG. 1 shows a change in the proportion of the perovskite structure in the crystal with respect to the oxygen concentration of the atmospheric gas. By making the oxygen concentration low, the ratio of the perovskite structure is increased. Furthermore, since the increase in the formation ratio of the perovskite structure becomes the highest when the oxygen concentration is in the range of 0.2 to 3.0%, the oxygen concentration of the atmosphere gas to be formed is greater than 0.1% and less than 5.0%. A range of is desirable. Further, when the oxygen concentration is 0.1% or less, the amount of oxygen necessary to form the perovskite structure is insufficient, making it difficult to form the perovskite structure. In addition, at an oxygen concentration of 5.0% or more, no significant difference was observed in the formation of the perovskite structure. Further, FIG. 1 shows a change in the ratio of the perovskite structure in the crystal to the oxygen concentration in the atmosphere when the formation temperature is changed from 600 to 700 ° C. The effect of the low oxygen concentration is more effective as the forming temperature becomes lower. In this embodiment, it is desirable that the ferroelectric thin film is 650 ° C. or lower, the high dielectric thin film is 600 ° C. or lower, and further 400 ° C. or higher. Even if heat treatment is performed at a temperature lower than this temperature range, the perovskite structure is hardly formed.

FIG. 8 shows the relationship between the orientation of the (105) plane of the perovskite structure and the oxygen concentration. The peak intensity on the (105) plane with respect to all peak intensities identified by X-ray diffraction is shown. When the oxygen concentration is lower than 5%, the degree of orientation of the (105) plane increases, so that the crystal structure of the SrBi ₂ Ta ₂ O ₉ ferroelectric thin film formed at a low oxygen concentration has a strong (105) plane orientation. There are features. This is because a low oxygen concentration generates a melt accompanying the decomposition reaction of the oxide of each constituent element, and crystal growth from the melt facilitates preferential growth of the (105) plane. . This has the effect of facilitating (105) plane orientation. The SrBi ₂ Ta ₂ O ₉ ferroelectric thin film has a layered perovskite structure and has crystal anisotropy in which the polarization axis shows only the direction parallel to the Bi—O layer (perpendicular to the c-axis) due to crystal symmetry. . Therefore, a thin film having excellent characteristics can be formed by preferentially orienting the (105) plane. Even when another ferroelectric material is used, it can be preferentially oriented in the plane orientation that the polarization axis has in the vertical direction.

Next, on the ferroelectric thin film 22 ((BiO) ²⁺ (SrTaO) ²⁻ ), a metal Pt having a thickness of 2000 mm is formed at room temperature by sputtering, and the upper electrode 21 is fabricated. 25 was obtained. Table 1 shows the results obtained by measuring spontaneous polarization (Pr) and coercive electric field (Ec) of the obtained ferroelectric element at room temperature.

Pr is the amount of polarization obtained at the maximum positive and negative applied voltage with Pr-V hysteresis. In particular, when the oxygen concentration was in the range of 0.2 to 3.0%, Pr was high and showed a low Ec value, reflecting the result of X-ray diffraction. In particular, the ferroelectric element having an oxygen concentration of 0.7% showed values of ²⁰ μC / cm ² and 45 kV / cm, respectively. Of the results obtained by inverting the voltage of 136 kV / cm and measuring the number of repetitions, FIG. 11 shows a measurement result with an oxygen concentration of 0.7% as a representative example. None of the thin films produced at an oxygen concentration of 0.15 to 3.0% showed any deterioration in Pr characteristics up to 10 14 times.

In addition, in the chemical structural formula of (AO) ²⁺ (Sr, TaO) ²⁻ , even when any one of Tl, Hg, Pb, Sb, and As is used as the A site element, the same production as described above is performed. As a result of measuring Pr and Ec of the ferroelectric element obtained by performing the above, values of Pr = 19 to 21 μC / cm ² and Ec = 44 to 48 kV / cm were obtained.

Further, in the chemical structural formula of (BiO) ²⁺ (BTaO) ²⁻ , even when any one of Pb, Ca and Ba was used as the B site element, it was obtained in the same manner as described above. As a result of measuring Pr and Ec of the ferroelectric element, values of Pr = 18 to 22 μC / cm ² and Ec = 43 to 47 kV / cm were obtained.

In addition, in the chemical structural formula of (BiO) ²⁺ (SrCO) ²⁻ , the same applies as described above even when any one of Ti, Nb, W, Mo, Fe, Co, and Cr is used as the C site element. As a result of measuring Pr and Ec of the ferroelectric element obtained by making the above, values of Pr = 17 to 22 μC / cm ² and Ec = 42 to 49 kV / cm were obtained.

  Further, in Example 1 above, since formation at a low temperature can be performed by using a low oxygen concentration, there is no problem such as formation of a transition layer or element diffusion, and a diffusion prevention layer is omitted between the base substrate and the substrate. The structure of providing may be sufficient.

In the ferroelectric thin film having the chemical structural formula of (Pb / A) (Zr / Ti) O ₃ used in this example, a manufacturing method in the case where A = La element is shown below. In the cross-sectional view of the ferroelectric element shown in FIG. First, as a base substrate, a substrate in which the surface of Si was thermally oxidized to form SiO ₂ was used. Next, the lower electrode 23 was formed on the base substrate 24. On the base substrate 24, a metal Pt having a thickness of 2500 mm was formed by sputtering in a vacuum at room temperature. In order to form the high dielectric thin film 22 on the lower electrode 23, a metal alkoxide solution prepared with a composition of Pb: La: Zr: Ti = 0.95: 0.05: 0.52: 0.48 is 2500 rpm. And spin coated for 30 seconds. Thereafter, the film was dried at 140 ° C. for 13 minutes, and further pre-heated in air or oxygen at 450 ° C. for 20 minutes, which is lower than the crystallization temperature of the ferroelectric thin film. The above operation was made into 1 cycle, and the precursor thin film of thickness 1700mm was produced by repeating a cycle 3 times. Then, a ferroelectric thin film ((Pb / La) (Zr / Ti) O ₃ ) was obtained by heat treatment at 550 ° C. at a low oxygen concentration. The crystal structure of the ferroelectric thin film was examined by X-ray diffraction. As a result, the proportion of the perovskite structure in the crystal tended to increase rapidly in the range of 0.2 to 3.0% as in Example 1. Next, the upper electrode 21 was formed on the ferroelectric thin film 22. The upper electrode 21 is made of a metal Pt having a thickness of 2000 mm on the (Pb / La) (Zr / Ti) O ₃ , which is the ferroelectric thin film 22, in a vacuum at room temperature by sputtering. The body element 25 was produced. Pr and coercive electric field (Ec) of the ferroelectric element were measured. As a result, the oxygen concentrations were 0.7% and 20 μC / cm ² and 50 kV / cm, respectively. Table 2 shows the results of measuring the dielectric constant (ε) at room temperature.

When the oxygen concentration was 0.7%, a value of 1590 was shown. Further, as a result of investigating the relationship between the voltage and the leakage current density, it was found that the voltage resistance was very excellent at 3 V, 1 × 10 ⁻⁷ A / cm ² or less.

Further, in a ferroelectric thin film having a chemical structural formula of (Pb / A) (Zr / Ti) O ₃ , a high-dielectric element having A = Ba and A = Nb is produced using the same production method as described above. When Pr and Ec were measured, they showed values of Pr = 20 μC / cm ² and Ec = 51 kV / cm, and the dielectric constant was evaluated at room temperature. As a result, when the oxygen concentration was 0.2 to 3.0% It was found that a high value of dielectric constant = 1590-1610 was obtained.

A method for producing a high dielectric thin film having a composition ratio of (Ba _0.5 Sr _0.5 ) TiO ₃ used in this example will be described below. In the cross-sectional view of the high dielectric element shown in FIG. 3, reference numeral 34 denotes a base substrate. First, the same Si as in Example 2 was used for the base substrate. Next, the lower electrode 33 was formed on the base substrate 34. A metal Pt having a thickness of 2000 mm was formed on the base substrate 34 by sputtering under the conditions of room temperature and vacuum atmosphere. In order to form the high dielectric thin film 32 on the lower electrode 33, a precursor thin film having a thickness of 100 nm was produced under the conditions of a temperature of 600 ° C., a pressure of 0.55 Pa, and a mixed gas of oxygen and argon. Next, in order to form a perovskite structure, a high dielectric thin film ((Ba _0.5 Sr _0.5 ) TiO ₃ ) was obtained by performing a heat treatment at 500 ° C. in a low oxygen concentration atmosphere. The crystal structure of the high dielectric thin film was examined by X-ray diffraction. As a result, as in Example 1, when the oxygen concentration was made smaller than 5%, the ratio of the perovskite structure in the total crystal phase started to increase, and the ratio was highest in the range of 0.2 to 3.0%. The tendency to become was seen. Next, the upper electrode 31 was formed on the high dielectric thin film 32. The upper electrode 31 was made of the high dielectric thin film 32 ((Ba _0.5 Sr _0.5 ) TiO ₃ ), and a metal Pt having a thickness of 2000 mm was produced by sputtering in a vacuum at room temperature. Table 3 shows the results of measuring the dielectric constant (ε) of the obtained high dielectric element 35 at room temperature.

  A high value of dielectric constant = 480 to 520 was exhibited when the oxygen concentration was in the range of 0.2 to 3.0%.

The ferroelectric thin film used in this example is a chemical structural formula of (AO) ²⁺ (BCO) ²⁻ , and the manufacturing method in the case of A = Bi element, B = Sr element, C = Nb element is as follows. Show. First, in the cross section of the ferroelectric element shown in FIG. 4, a substrate on which the surface of Si was thermally oxidized to form SiO ₂ was used as the base substrate 44. Next, the lower electrode 43 was formed on the base substrate 44. A single element conductive oxide RuO having a thickness of 1700 mm was formed on the base substrate 44 by sputtering while heating at 450 ° C. in an oxygen gas atmosphere. In order to form a ferroelectric thin film on the lower electrode 43, a metal alkoxide solution of Bi, Sr, and Nb elements was spin-coated at 3000 rpm for 25 seconds. Then, it was dried at 150 ° C. for 10 minutes, and further pre-heated at 450 ° C. for 10 minutes in air or oxygen. The above operation was taken as one cycle, and the cycle was repeated three times to produce a precursor thin film having a thickness of 2300 mm. Finally, (BiO) ²⁺ (SrNbO) ²⁻ which is a ferroelectric thin film 42 having a perovskite structure is obtained by heating at 600 ° C. in an atmosphere of low oxygen concentration of argon gas + 0.7% oxygen. Obtained. An upper electrode 41 was formed on the ferroelectric thin film 42. For the upper electrode 41, a ferroelectric element 45 was produced by producing a single-element conductive oxide RuO having a thickness of 1700 mm by sputtering while heating at 450 ° C. in an oxygen gas atmosphere. Pr and coercive electric field (Ec) of the obtained ferroelectric element 45 were measured at room temperature. As a result, values of 19 μC / cm ² and 46 kV / cm, respectively, were shown.

Similarly to the above, when any one of TiO _x , VO _x , EuO, CrO ₂ , MoO ₂ , WO ₂ , PhO, OsO, IrO, PtO, ReO ₂ , RuO ₂ , SnO ₂ is used as the electrode material. The characteristics of the ferroelectric element obtained by performing the same fabrication as described above showed values of Pr = 18 to 22 μC / cm ² and Ec = 44 to 48 kV / cm. As described above, as the upper and lower electrode materials used in this embodiment, a conductive oxide and perovskite composed of a single element having a resistivity of 1 mΩ · cm or less in order to have a function as a metal or an electrode material. By using one type of conductive oxide having a structure, an oxide dielectric element having excellent electrical characteristics can be manufactured.

Using the same manufacturing method as in Example 1, a lower electrode (Pt) was formed on the base substrate. On the lower electrode, the chemical structural formula of (AO) ²⁺ (BCO) ² -is composed of A = Bi element, B = Sr element, C = Ta element, and prepared in the same composition ratio as in Example 1. The metal alkoxide solution was spin coated at 3000 rpm for 35 seconds. Then, it was dried at 150 ° C. for 10 minutes, and further pre-heated at 400 ° C. for 10 minutes in air or oxygen. The above operation was taken as one cycle, and the cycle was repeated twice to produce a precursor thin film having a thickness of 1100 mm. Then, a ferroelectric thin film was produced by heating at 630 ° C. in a low oxygen concentration atmosphere. For comparison, a lower electrode is formed on a base substrate using the same method as described above, a ferroelectric thin film having the same composition is formed in low oxygen, and further heated at 400 ° C. in ECR oxygen plasma. A ferroelectric thin film was prepared. An upper electrode (Pt) was formed on each ferroelectric thin film in the same manner as in Example 1 to produce a ferroelectric element having a cross-sectional structure shown in FIG. Table 4 shows the results of measuring the Pr and coercive electric field (Ec) of each ferroelectric element at room temperature.

The ferroelectric element heated in ECR oxygen plasma showed higher values for both spontaneous polarization and coercive electric field. In addition, even when re-heat treatment was performed using O ₃ , radical oxygen, and N ₂ O (nitrous oxide) in the same manner as described above, both spontaneous polarization and coercive electric field showed the same value. As described above, by performing the heat treatment again in an activated oxygen atmosphere having a strong oxidizing power, a perovskite structure free from oxygen vacancies was obtained, and as a result, the electrical characteristics were greatly improved. This reheat treatment is desirably performed at a temperature lower than the crystallization heat treatment temperature at a low oxygen concentration.

A lower electrode (Pt) was formed on the base substrate using the same method as in Example 1. On the lower electrode, the chemical structural formula of (AO) ²⁺ (BCO) ^2- consists of A: Bi, B: Sr, C: Ta, and Bi: Sr: Ta = 2.2: 1: 2 composition. The metal alkoxide solution prepared in the above was spin-coated at 3500 rpm for 25 seconds. Then, after drying at 170 ° C. for 10 minutes, pre-heat treatment was performed at 450 ° C. for 10 minutes. The above operation was repeated three times to produce a precursor thin film having a thickness of 2200 mm. Then, heat treatment was performed in a 0.7% oxygen atmosphere at 650 ° C. for 1 hour to produce a ferroelectric thin film. For comparison, a precursor thin film was prepared by using the same method as described above, and a ferroelectric thin film was also heat-treated in a 100% oxygen atmosphere at 650 ° C. for 1 hour and 5 hours. On the obtained ferroelectric thin film, an upper electrode (Pt) was formed in the same manner as in Example 1 to produce a ferroelectric element having a cross-sectional structure shown in FIG. Pr of each ferroelectric element was measured at room temperature. As a result, the ferroelectric element formed with an oxygen concentration of 0.7% has Pr = 22 μC / cm ² , whereas the result of the ferroelectric element formed with an oxygen concentration of 100% is 1 hour. No polarization hysteresis curve was observed, and the value was as low as Pr = 10 μC / cm ^{2 in} 5 hours. In this way, the heat treatment time can be shortened by reducing the oxygen concentration. This is because, as previously described, the rate of crystal growth from the melt due to the decomposition reaction of the oxides of the constituent elements is promoted by the low oxygen concentration, so it is lower than the conventional thin film formed with an oxygen concentration of 100%. A thin film formed at an oxygen concentration forms a perovskite structure in about 1/5 of the time, and high electrical characteristics can be obtained.

Furthermore, as a result of the compositional analysis of each ferroelectric thin film, the thin film heat-treated in the low oxygen concentration atmosphere has a stoichiometric composition of Sr: Bi: Ta = 1: 2: 2. The thin film heat-treated in a 100% oxygen atmosphere had a composition with a large amount of Bi, with Sr: Bi: Ta = 1: 2.2: 2. Since this example is formed at a low temperature and a low oxygen concentration, for example, in the case of a SrBi ₂ Ta ₂ O ₉ ferroelectric thin film, the composition ratio after the formation is stoichiometric regardless of the starting Bi composition. A thin film having a composition can be formed. Therefore, it is not necessary to make the starting Bi composition excessive, and even if it is excessive, the generation of a heterogeneous phase containing a large amount of Bi at the grain boundary of the formed ferroelectric layer can be suppressed, and the withstand voltage characteristics are excellent. There is no reaction with the upper and lower electrodes, and a thin film having a high dielectric constant can be formed.

In the above-described embodiment 6, the SrBi ₂ Ta ₂ O ₉ ferroelectric thin film has been described. However, in the case of an oxide dielectric thin film such as Pb (Zr / Ti) O ₃ or (Ba / Sr) TiO _3. However, it is possible to shorten the heat treatment time.

Using the same manufacturing method as in Example 1, 2000 Pt lower electrodes were formed on a base substrate in which SiO ₂ was formed on a Si substrate. In order to form a ferroelectric thin film on the Pt lower electrode, a metal alkoxide solution prepared with a composition of Bi: Sr: Ta = 2: 1: 2 was spin-coated at 2000 rpm for 30 seconds. Then, it dried at 150 degreeC for 15 minutes, and also pre-heat-treated in air at 450 degreeC for 20 minutes. The above operation was repeated 5 times to produce a precursor thin film having a film pressure of 2000 kg. Next, heat treatment was performed at 650 ° C. for 1 hour in an atmosphere of 0.7% oxygen to form a ferroelectric thin film. As a comparison, a ferroelectric thin film that was heat-treated in 100% oxygen for 1 hour at 800 ° C. and 720 ° C. was produced. Using the sputtering method, 2000 Pt upper electrodes were formed on the surface of each ferroelectric thin film, and withstand voltage characteristics were measured. The measurement results are shown in FIG. A ferroelectric element manufactured at 650 ° C. with an oxygen concentration of 0.7% shows a leak current density of 3.0 × 10 ⁻⁹ A / cm ² even at a voltage of 5 V, and is 800 ° C. and 720 ° C. It was found that the withstand voltage characteristic was superior to the ferroelectric element fabricated at a high temperature of.

FIG. 5 shows a schematic diagram of the microstructure of the SrBi ₂ Ta ₂ O ₉ ferroelectric obtained in this example. It was found that the crystal grains of the ferroelectric thin film formed at a low oxygen concentration and a low temperature had a particle size of about 70 nm or less, which was smaller and denser than the thin film formed at a high temperature. Therefore, a ferroelectric thin film having a small leakage current density and excellent withstand voltage characteristics can be formed.

In addition, as a result of measuring the withstand voltage of the high dielectric thin film ((Ba _0.5 Sr _0.5 ) TiO ₃ ) prepared in Example 3, the withstand voltage characteristics at a leak current density of 5.0 × 10 ⁻⁷ A / cm ^2. It turned out to be excellent.

FIG. 6 is a cross section of a ferroelectric memory using the ferroelectric element according to this example. A ferroelectric transistor shown in FIG. 2 is formed on a MOS transistor and a capacitor in which an oxide layer, a metal layer, and an insulator layer are formed on a semiconductor field transistor structure. A manufacturing method is shown below. First, Si64 having a source portion 65 and a drain portion 66 was used as a substrate, and this was surface oxidized to form a SiO ₂ film having a thickness of 260 mm. A convex SiO ₂ film 68 was produced in the center of the substrate by mask patterning. Next, polycrystal Si67 having a film thickness of 4500 mm was formed on the obtained convex portion by CVD. On this, a ferroelectric element having a structure composed of the upper electrode 61, the ferroelectric thin film, and the lower electrode 63 manufactured in Example 1 is formed, thereby obtaining a ferroelectric memory using the ferroelectric element. It was. As a result, the advantage that the difference in capacitance due to the electric field reversal can be detected in a double size is obtained.

FIG. 7 is a cross-sectional view of a high-dielectric memory using the high-dielectric element according to this example, and the manufacturing method will be described below. First, Si74 having a source portion 75 and a drain portion 76 was used as a substrate, and this was surface oxidized to form a SiO ₂ film having a thickness of 270 mm. A convex SiO ₂ film 78 was produced in the center of the substrate by mask patterning. Next, a polycrystal Si 79 having a thickness of 4600 を was formed by CVD on the obtained convex portion, and the surface was oxidized to form a SiO ₂ film 77 having a thickness of 250 し た, thereby producing a MOS transistor. By forming a high dielectric element having a structure composed of the upper electrode 71, the high dielectric thin film 72, and the lower electrode 73 manufactured in Example 3 on the obtained capacitor portion facing the semiconductor MOS portion, A high dielectric memory using a dielectric element was obtained. The obtained high dielectric memory can be detected by a change in the storage electric capacity obtained at a voltage of 3V.

FIG. 10A shows a non-contact type semiconductor device 1001, and FIG. 10B shows a structure of a ferroelectric element incorporated in the non-contact type semiconductor device. In the ferroelectric element, Si 1002 having a diffusion layer 1003 was used as a substrate, an SiO ₂ gate film 1004 was formed on the substrate, and mask patterning was performed to form a gate electrode 1005. The ferroelectric capacitor includes a Pt lower electrode 1006, an SrBi ₂ Ta ₂ O ₉ ferroelectric thin film 1007 formed at a low oxygen concentration, and a Pt upper electrode 1008. In order to separate the transistor and the capacitor, SiO ₂ insulating layers 1009 and 1010 are formed, and the upper electrode 1008 and the diffusion layer 1003 are connected by the aluminum wiring 1011. The non-contact type configuration includes a controller, a memory, a responder with a built-in communication function, an IC card, and the like. In this system, a signal is transmitted from the controller unit to the IC card, and the IC card returns necessary information to the controller in response to the command. By using a nonvolatile RAM for the memory element, the inversion time of the ferroelectric itself becomes 1 nanosecond or less. For this reason, many excellent performances such as equidistant reading and writing of information, high-speed data transfer, and extremely small errors during writing can be obtained.

As described in the above embodiment, the description is made using the structure including the Pt upper electrode 1008, the SrBi ₂ Ta ₂ O ₉ ferroelectric thin film 1007, and the lower electrode 1006, but the structure including the upper electrode, the high dielectric thin film, and the lower electrode. Alternatively, a high dielectric element may be formed. The obtained semiconductor device of a high dielectric element is a semiconductor device having a 30 fF accumulated charge capacity at a voltage of 3V. Thus, an excellent non-contact semiconductor device could be manufactured by using the ferroelectric element of this example.

  As described above, when the atmosphere in which the oxide ferroelectric thin film and the oxide high dielectric thin film are formed is performed at a low oxygen concentration, a melt accompanying the decomposition reaction of the constituent element oxide is generated, and Since the crystal growth from the liquid is promoted, the ferroelectric thin film can be formed at 650 ° C. or lower, and the high dielectric thin film can be formed at 600 ° C. or lower at a temperature lower than the conventional temperature, and the heat treatment time can be shortened. As a result, the thin film produced by the present invention has a crystal structure preferentially oriented in the plane orientation that the polarization axis has in the vertical direction, controls the crystal grain size to an optimum size, and prevents reaction with the electrode. As a result, an oxide dielectric element having a high dielectric constant, spontaneous polarization, and a small coercive electric field could be produced. Furthermore, by incorporating the ferroelectric element into a semiconductor field transistor structure and incorporating the high dielectric element into a semiconductor MOS structure, a ferroelectric memory and a high dielectric memory that detect reading and writing can be manufactured. It was. In addition, a semiconductor device using the ferroelectric memory and the high dielectric memory as a contactless read or write memory can be manufactured.

It is a figure which shows the change of the crystal structure of the ferroelectric thin film by the oxygen concentration in the atmosphere of this invention. It is sectional drawing which shows the ferroelectric element of this invention. It is sectional drawing which shows the high dielectric material element of this invention. It is sectional drawing which shows the ferroelectric element which used the electroconductive oxide of this invention for the electrode. It is a schematic diagram of the microstructure of the ferroelectric thin film of the present invention. 1 is a cross-sectional view showing a ferroelectric memory of the present invention. It is sectional drawing which shows the high dielectric material memory of this invention. It is a figure which shows the orientation degree of the (105) plane in the crystal structure by the oxygen concentration in the atmosphere of this invention. It is a figure which shows the relationship between the voltage of this invention, and a leak current density. A non-contact type semiconductor device using the ferroelectric element of the present invention. It is a figure which shows the result of having measured the repetition frequency of the ferroelectric element of this invention.

Explanation of symbols

21, 31, 61, 71, 1008 ... upper electrode, 22, 32, 42, 62, 72, 1007 ... ferroelectric thin film, 23, 33, 63, 73, 1006 ... lower electrode, 24, 34, 44 ... underlayer Substrate, 25, 45 ... Ferroelectric element, 35 ... High dielectric element, 41 ... Upper electrode (conductive oxide), 43 ... Lower electrode (conductive oxide), 64, 74, 1002 ... Si, 65, 75 ... source unit, 66 and 76 ... drain part, 67,79 ... polycrystal _{Si, 68,77,78 ... SiO 2, 1001} ... non-contact type semiconductor device, 1003 ... diffusion layer, 1004 ... SiO ₂ gate - DOO film , 1005... Gate electrode, 1009, 1010... SiO ₂ insulating layer, 1011.

Claims (3)

In an oxide dielectric element composed of an upper electrode, an oxide dielectric thin film, and a lower electrode,
The lower electrode is a Pt electrode formed on a base substrate in which SiO ₂ is formed on a Si substrate,
The oxide dielectric thin film formed on the Pt electrode was formed at a temperature of 650 ° C. or less in an atmosphere having an oxygen concentration of 0.1% to 5% after forming the precursor (Pb / A) (Zr / Ti) O ₃ (where A = La, Ba, Nb). The oxide dielectric thin film has a leakage current density of 3 × 10 ⁻⁶ A / cm at an applied voltage of 3 V. An oxide dielectric element characterized by being ² or less. 2. The oxide dielectric device according to claim 1, wherein the oxide dielectric thin film is formed in an atmosphere having an oxygen concentration of 0.2% to 3% after the precursor is formed, and the oxide dielectric thin film leaks. An oxide dielectric element characterized by having a current density of 4 × 10 ⁻⁷ A / cm ² or less at an applied voltage of 3 V. 2. The oxide dielectric device according to claim 1, wherein the oxide dielectric thin film is (111) -oriented.

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