JP3764650B2 - Ferroelectric capacitor, method for manufacturing the same, and semiconductor device including the ferroelectric capacitor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a ferroelectric capacitor using a ferroelectric film, and in particular, strontium bismuth tantalate, strontium bismuth niobate, or a solid solution material thereof, which is preferably used as a memory material. The present invention relates to a ferroelectric capacitor and a manufacturing method thereof.
[0002]
[Prior art]
  Ferroelectric thin films have many functions such as spontaneous polarization, high dielectric constant, electro-optic effect, piezoelectric effect, pyroelectric effect and the like, and thus are applied to a wide range of device development. For example, it is used for an infrared linear ray sensor utilizing its pyroelectricity. In addition, it is used for an ultrasonic sensor utilizing its piezoelectricity, and is used for a waveguide type optical modulator utilizing its electro-optic effect. Further, it is used in various fields such as DRAM and MMIC capacitors by utilizing its high dielectric property.
[0003]
  Among these wide-ranging application device developments, along with the progress of thin film formation technology in recent years, development of ferroelectric non-volatile memory (FRAM) that operates at high density and high speed in combination with semiconductor memory technology is prosperous. It is.
[0004]
  Non-volatile memories using ferroelectric thin films are not only used for replacing conventional non-volatile memories but also for SRAMs and DRAMs because of their high-speed writing / reading, low-voltage operation, and high writing / reading resistance. As a replaceable memory, research and development for the practical use is actively conducted.
[0005]
  For such device development, residual polarization (P_r) Is large and the coercive electric field (E_c) Is small, has a low leakage current, and requires a material having a high resistance to repeated polarization inversion. In addition, when forming a thin film, it is preferable that the film formation time is short in order to improve throughput.
[0006]
  Conventionally, as a ferroelectric material used for these applications, PZT (lead zirconate titanate, Pb (Ti_X, Zr_1-X) O_ThreeOxide materials with a perovskite structure typified by However, a material containing lead as its constituent element, such as PZT, has a high vapor pressure of lead or its oxide, so that lead evaporates during film formation, causing defects in the film, Has formed a pinhole. As a result, there is a drawback that a fatigue phenomenon occurs in which the magnitude of spontaneous polarization decreases when the leakage current increases or the polarization inversion is repeated.
[0007]
  In particular, regarding the fatigue phenomenon, considering replacement of a DRAM with a ferroelectric nonvolatile memory, 10¹⁵Since it has to be ensured that there is no change in characteristics even after polarization reversal, the development of a ferroelectric thin film without fatigue has been desired.
[0008]
  On the other hand, in recent years, research and development of bismuth layered structure compound materials have been conducted as ferroelectric materials for FRAM. Bismuth layered structure compound material was discovered in 1959 by Smolenskii et al. (G. A. Smolenskii, V. A. Isupov and A. I. Agranovskaya, Soviet Phys. Solid State, 1, 149 (1959)). Detailed studies were made by Subbarao (E. C. Subbarao, J. Phys. Chem. Solids, 23,665 (1962)).
[0009]
  Recently, Carlos A. Paz de Araujo et al. Found that this bismuth layered structure compound thin film is suitable for application to ferroelectric and high-dielectric integrated circuits.¹²It has reported excellent fatigue characteristics in which no change in the characteristics is observed even after polarization reversal over and over (International Publication No. WO93 / 10542, JP 7-502149A).
[0010]
  This bismuth layered structure compound has the chemical formula Bi₂A_m-1B_mO_{3m + 3}(A is selected from Na, K, Pb, Ca, Sr, Ba, Bi, B is selected from Fe, Ti, Nb, Ta, W, Mo, and m is a natural number. ). The crystal structure of the bismuth layered structure compound is (Bi₂O₂) 2+ layer and (A_m-1B_mO_{3m + 1}) It is a structure in which 2-layers are stacked alternately. That is, the basis of the crystal structure is (m−1) ABOs._ThreeThe upper and lower sides of the layered perovskite layer (Bi)₂O₂) A structure in which 2+ layers are sandwiched. In addition, what is selected as A and B here is not necessarily single.
[0011]
  A typical example of such a bismuth layered structure compound material is strontium bismuth tantalate. The methods for producing these films include physical methods such as vacuum deposition, sputtering, and laser ablation, and sol-gel methods in which organometallic compounds are used as starting materials, and these are pyrolyzed and oxidized to obtain oxide ferroelectrics. Alternatively, a chemical method such as a MOD (Metal Organic Deposition) method or a MOCVD (Metal Organic Chemical Vapor Deposition) method is used.
[0012]
  Among the above film formation methods, the MOCVD method is excellent in step coverage and has the possibility of low-temperature film formation. Therefore, it is promising particularly in the case of high integration of FRAM. It is getting popular.
[0013]
  On the other hand, the sol-gel method or the MOD method can use a raw material solution capable of homogeneous mixing at the atomic level, so that the composition control is easy and the reproducibility is excellent. It is widely used because of its advantages such as that it can be formed and industrially low cost. In particular, the MOD method is used as a suitable method for forming the strontium bismuth tantalate film.
[0014]
[Problems to be solved by the invention]
  The conventional strontium bismuth tantalate film is randomly oriented in the film thickness direction and has a drawback that it does not have a large spontaneous polarization because its ferroelectricity exhibits significant anisotropy. That is, the strontium tantalate bismuth film has a large spontaneous polarization in the a-axis or b-axis direction, but has a very small spontaneous polarization in the c-axis direction. This is a serious obstacle to realizing a nonvolatile memory that stores 1 and 0 of information according to the amount of spontaneous polarization.
[0015]
  As a solution to the above problem, Japanese Patent No. 2658878 proposes a film formation process described below using a conventional MOD method.
[0016]
    (1) Spin coat alkoxide or organometallic salt on the substrate.
[0017]
    (2) Dry at 250 ° C. for 10 minutes. The film thickness after drying is about 20 to 80 nm.
[0018]
    (3) Heat treatment and crystallization at 600 to 850 ° C. for 10 minutes in an oxygen atmosphere.
[0019]
  This heat treatment step may be performed by a rapid heat treatment other than a normal heat treatment method.
[0020]
  In order to obtain a desired film thickness, the steps (1) to (3) are repeated several times. At this time, since crystallization occurs from the interface with the substrate, the crystal grows epitaxially, and a film oriented along the <105> axis can be obtained.
[0021]
  However, if high ferroelectric properties are desired in the strontium bismuth tantalate film, it is preferable to obtain a film in which the c-axis component is reduced as much as possible in the film thickness direction and is strongly oriented in the a and b-axis alignment components.
[0022]
  Therefore, in Japanese Patent Laid-Open No. 8-249876, “in a ferroelectric device having a memory cell with a ferroelectric thin film sandwiched between a pair of electrodes, the ferroelectric thin film has two substantially equivalent first and second A second crystal axis and a third crystal axis having a symmetry different from that of the first and second crystal axes in a direction different from the first and second crystal axes. The ferroelectric device is characterized in that the third crystal axis is oriented in a direction substantially perpendicular to the electric field applied by the pair of electrodes. Or, “the third crystal axis is oriented within plus or minus 30 degrees in a plane including the electric field and the third crystal axis with respect to a direction perpendicular to the electric field applied by the pair of electrodes. A predetermined direction in a plane perpendicular to the electric field and the third The direction of projection onto a plane perpendicular to the electric field Akirajiku is providing characterized "ferroelectric device that forms an angle within ± 30 degrees. Furthermore, it is described as “characterized in that the proportion of the crystal grains is 60% or more”.
[0023]
  However, in the conventional technology, in the strontium tantalate bismuth film, platinum or the like that is suitably used as an electrode material, the c-axis component (the third crystal) with respect to the film thickness direction (electric field) on the noble metal electrode. It is very difficult to grow crystal grains mainly in the vertical direction or in the direction within plus or minus 30 degrees with respect to a vertical plane, or more than 60%, and generally it is random orientation. It is normal.
[0024]
  In addition, Hu et al. (APLLIED PHYSICS LETTERS, VOLUME74, NUMBER9, P.1221) use a raw material solution having an atomic composition ratio of Sr: Bi: Ta = 10: 24: 20 in each MOD method in each MOD method. When crystal heating treatment by the RTA (Rapid Thermal Annealing) method is performed, a strontium bismuth tantalate film having a high a-axis orientation strength can be obtained by always making the lower layer a seed layer, and the orientation strength is that of RTA It states that it is controlled by the ultimate temperature.
[0025]
  However, this manufacturing method is basically the same method as the above-mentioned Japanese Patent No. 2658878, and it is very difficult to produce a film having an a-axis orientation directly on the electrode. Therefore, they have realized low temperature and high orientation strength of the a-axis by using bismuth titanate as a seed layer (APLLIED PHYSICS LETTERS, VOLUME74, NUMBER24, P.3711). However, the use of other materials in the same capacitor complicates the process and further may result in lack of reliability due to diffusion of components, and it is desirable to configure a capacitor with the same material.
[0026]
  Therefore, the present invention has been made to solve the above-described problems, and when the plurality of layers are stacked by the MOD method, the present invention is given priority from the first layer showing the random orientation formed on the electrode. An object of the present invention is to provide a ferroelectric film capacitor composed of a strontium bismuth tantalate film grown with a <110> axis (plane spacing of 32.45 mm) component having high ferroelectric characteristics in the film thickness direction, and a method for manufacturing the same. And
[0027]
[Means for Solving the Problems]
  To achieve the above object, a ferroelectric capacitor of the present invention is a ferroelectric capacitor comprising at least a pair of electrodes and a ferroelectric film on a substrate,
  The ferroelectric film formed between the pair of electrodes has an interplanar spacing of 29.02Å ± 0.2 が and an interplanar spacing of 32.45Å ± 0.2Å in the X-ray diffraction image using CuKα rays. And SrBi indicating the peak value₂(Ta_XNb_1-X)₂O₉(x = 0-1) Ferroelectric filmThe
  The ferroelectric film is
  The peak intensity in the X-ray diffraction image using the CuKα ray has a surface separation of 29 in the film thickness direction. . 02Å ± 0 . When the peak value of 2 mm is 100%, the surface separation is 32. . 45Å ± 0 . SrBi with a peak value of 2% being 80-300% ₂ ( Ta _X Nb _1-X ) ₂ O ₉ ( x = 0-1 ) A ferroelectric film,
  The ferroelectric film is formed on a platinum film that is a base electrode layer formed on the substrate.It is characterized by that.
[0028]
  With the configuration of the ferroelectric capacitor of the present invention, a large ferroelectric characteristic can be obtained, and it can be suitably used as a part of an integrated circuit element formed on a substrate.
[0029]
  In another embodiment of the ferroelectric capacitor, the ferroelectric film is SrBi.₂(Ta_XNb_1-X)₂O₉(x = 0 to 1) is a columnar structure.
[0030]
  According to the ferroelectric capacitor of this embodiment, larger ferroelectric characteristics can be obtained.
[0031]
  In addition, a method for manufacturing a ferroelectric film according to an embodiment includes the above-described method.A method of manufacturing a ferroelectric capacitor, comprising:
  Forming a metal film on the substrate;
  Producing a raw material solution of an alkoxide or organometallic salt of two elements of strontium and bismuth and at least one of tantalum and niobium;
  Applying the solution to the metal film on the substrate;
  Drying the solution applied to the metal film on the substrate;
  Heating the solution above the crystallization temperature,
  By repeating the steps from the application of the solution to the heating of the solution until the film made of the solution has a predetermined thickness, SrBi is formed on the substrate.₂(Ta_XNb_1-X)₂O₉(x = 0 to 1) A method for manufacturing a ferroelectric capacitor for forming a ferroelectric film.The
  By adjusting at least one of the temperature increase rate in the temperature range of 550 to 650 ° C. in the step of heating the above solution to the crystallization temperature or the composition ratio of bismuth in the raw material solution, SrBi₂(Ta_XNb_1-X)₂O₉(x = 0 to 1) Controls the size of the orientation components of the a and b axes of the ferroelectric film.
[0032]
  In the manufacturing method of this embodiment, SrBi₂(Ta_XNb_1-X)₂O₉The film (x = 0 to 1) shows a structure that has not been seen in the past, such as the highest a and b axis components, for example, <110> axis orientation strength, at which high ferroelectric characteristics can be obtained. The ferroelectric characteristics of the capacitor were also higher than the conventional one.
[0033]
  Moreover, in the manufacturing method of the ferroelectric capacitor of other embodiment, the temperature increase rate of the temperature range of 550-650 degreeC is made into the range of 5-200 degreeC / sec.
[0034]
  In this embodiment, high ferroelectric characteristics can be obtained while suppressing warping of the substrate.
[0035]
  In one embodiment of the method for manufacturing a ferroelectric capacitor, in the step of applying the solution to the substrate, when the solution applied to the substrate has an atomic composition ratio of (tantalum + niobium) of 20, bismuth In the raw material solution preparation step, the atomic composition ratio of bismuth is adjusted so that the atomic composition ratio is 20 to 24.
[0036]
  In this embodiment, particularly high ferroelectric characteristics were obtained.
[0037]
  Further, a method for manufacturing a ferroelectric film according to another embodiment is the same as the method for manufacturing a ferroelectric capacitor according to the present invention, after the crystallization formed on the substrate.FerroelectricThe raw material solution is applied onto the substrate so that the film thickness is 35 nm or less.
[0038]
  In this embodiment, the thickness of the metal film after crystallization formed on the substrate is set to 35 nm or less, so that the ferroelectric characteristics increased as the film thickness increased.
[0039]
  In one embodiment of the method for manufacturing a ferroelectric film, the uppermost portion of the metal film formed on the substrate is a platinum layer in the method for manufacturing a ferroelectric capacitor.
[0040]
  In this embodiment, since the uppermost portion of the metal film formed on the substrate is a platinum layer, particularly high ferroelectric characteristics were obtained.
[0041]
  The semiconductor device of another embodiment uses the ferroelectric capacitor as a part of an integrated circuit element formed on a substrate.
[0042]
  Since the semiconductor device of this embodiment uses the capacitor having high ferroelectric characteristics, it can be highly integrated.
[0043]
  The ferroelectric capacitor of one embodiment is a ferroelectric capacitor comprising at least a pair of electrodes and a ferroelectric film on a substrate,
  The ferroelectric film formed between the pair of electrodes is a ferroelectric film of strontium bismuth tantalate, strontium bismuth niobate, or a solid solution thereof,
  This ferroelectric film is
  Compared with the region on the electrode side on the substrate side, the region on the other counter electrode side has a crystal orientation component having an interplanar spacing of 32.45Å ± 0.2Å in the X-ray diffraction image in the film thickness direction using CuKα rays. GrowsAnd
The ferroelectric film is formed on a platinum film that is a base electrode layer formed on the substrate..
[0044]
  The capacitor of this embodiment has many crystal components oriented in the polarization axis direction and can exhibit high ferroelectric characteristics. Therefore, it can be suitably used as a part of an integrated circuit element formed on a substrate.
[0045]
  A ferroelectric capacitor according to another embodiment is a ferroelectric capacitor including at least a pair of electrodes and a ferroelectric film on a substrate,
  The ferroelectric film formed between the pair of electrodes is a ferroelectric film of strontium bismuth tantalate, strontium bismuth niobate, or a solid solution thereof, and has a thickness in the range of 90 to 270 nm. ,
  The peak intensity in the X-ray diffraction image using CuKα rays is a peak value of 32.45 mm ± 0.2 mm of the plane distance when the peak value of the plane distance of 29.02 mm ± 0.2 mm is 100% in the film thickness direction. Is in the range of 80-230%The
  The ferroelectric film is formed on a platinum film that is a base electrode layer formed on the substrate..
[0046]
  The capacitor of this embodiment has many crystal components oriented in the polarization axis direction and can exhibit high ferroelectric characteristics. Furthermore, mass productivity is high.
[0047]
  In addition, a method for manufacturing a ferroelectric film according to an embodiment includes:A method of manufacturing the ferroelectric capacitor, comprising:
  Forming a metal film on the substrate;
  A step of preparing a raw material solution of an alkoxide or organometallic salt of two elements of strontium and bismuth and at least one of tantalum and niobium,
  Applying the solution to a substrate;
  Drying the solution applied to the substrate;
  Heating the substrate above the crystallization temperature of the raw material solution,
  By repeating the steps from applying the solution to heating the substrate until the film made of the raw material solution has a predetermined thickness, strontium bismuth tantalate, strontium bismuth niobate, or a solid solution thereof is formed on the substrate. A method of manufacturing a ferroelectric capacitor for forming a ferroelectric film ofThe
  Adjustment of the atomic composition ratio in the raw material solution in the step of preparing the raw material solution, adjustment of the temperature increase rate in the temperature range of 550 to 650 ° C. in the step of heating to the crystallization temperature or higher, and from the solution coating to the substrate By adjusting at least one of the adjustments of the film thickness formed in a single process until heating, the size of the orientation component of the surface spacing of 32.45Å ± 0.2Å of the ferroelectric film is adjusted. Control.
[0048]
  According to the manufacturing method of this embodiment, in the ferroelectric film formed by applying, drying and heating the raw material solution, the crystal component oriented in the polarization axis direction is preferentially grown from the randomly oriented first layer. Can be made.
[0049]
  In another embodiment of the method for manufacturing a ferroelectric capacitor, the temperature rising rate in adjusting the temperature rising rate in the temperature range of 550 to 650 ° C.200Set in the range of ° C / sec.
[0050]
  According to the manufacturing method of this embodiment, in the ferroelectric film formed by applying, drying and heating the raw material solution, the crystal component oriented in the polarization axis direction is preferentially grown from the randomly oriented first layer. Can be made.
[0051]
  In one embodiment of the method for manufacturing a ferroelectric capacitor, the atomic composition ratio Sr: Bi: (Ta + Nb) = X: Y: Z in the raw material solution is 1.4 <(X + Y) / Z <1.6. is there.
[0052]
  According to the manufacturing method of this embodiment, the crystal component oriented in the polarization axis direction can be preferentially grown from the randomly oriented first layer.
[0053]
  In the method of manufacturing a ferroelectric capacitor according to another embodiment,
  The step of applying the raw material solution to the substrate includes:
  In one application step, the raw material solution is applied so that the film thickness after crystallization is 25 to 50 nm.
[0054]
  According to the manufacturing method of this embodiment, the crystal component oriented in the direction of the polarization axis can be preferentially grown from the randomly oriented first layer.
[0055]
  In one embodiment of the method for manufacturing a ferroelectric capacitor, the main component of the metal film formed on the substrate is platinum.
[0056]
  According to the manufacturing method of this embodiment, the crystal component oriented in the direction of the polarization axis can be preferentially grown from the randomly oriented first layer.
[0057]
  The semiconductor device of another embodiment uses the ferroelectric capacitor as a part of an integrated circuit element formed on a substrate.
[0058]
  Since the semiconductor device of this embodiment uses a capacitor having high ferroelectric characteristics, it can be highly integrated.
[0059]
DETAILED DESCRIPTION OF THE INVENTION
  Embodiments of the present invention will be described below with reference to the drawings.
[0060]
        (First embodiment)
  FIG. 1 shows the SrBi formed according to the present invention.₂(Ta_XNb_1-X)₂O₉1 is a schematic cross-sectional view of a capacitor using a ferroelectric film (x = 0 to 1). FIG. As shown in FIG. 1, a silicon thermal oxide film 2 having a thickness of 200 nm is formed on the surface of a silicon single crystal substrate 1, and a titanium oxide film 3 (adhesion layer) having a thickness of about 20 nm and a film thickness of 200 nm are formed thereon. A platinum film 4 (lower electrode layer) is formed, and a ferroelectric thin film 5 and an upper electrode layer 6 are formed as described later.
[0061]
  For the formation of the ferroelectric thin film 5, a MOD method including a film forming process using a precursor raw material solution of a ferroelectric material was used. In the synthesis of the precursor raw material solution of the MOD method, niobium ethoxide (Nb (OC₂H_Five)_Five), Tantalum ethoxide (Ta (OC₂H_Five)_Five), Bismuth 2-ethylhexanate (Bi (C₇H₁₅(COO)₂), And strontium 2-ethylhexanate (Sr (C₇H₁₅(COO)₂)It was used.
[0062]
  First, SrBi₂(Ta_XNb_1-X)₂O₉(x = 0 to 1) The synthesis of the precursor raw material solution used for forming the ferroelectric thin film 5 will be described. Weigh niobium ethoxide and tantalum ethoxide. In order to dissolve this in 2-ethylhexanate and to accelerate the reaction, the mixture was stirred while heating from 100 ° C. to the maximum temperature of 120 ° C. and reacted for 30 minutes. Thereafter, ethanol and water produced by the reaction at 120 ° C. were removed. Strontium 2-ethylhexanate dissolved in 20 ml to 30 ml of xylene was added to the solution, and the mixture was heated and stirred from 125 ° C. to the maximum temperature of 140 ° C. for 30 minutes. Thereafter, bismuth 2-ethylhexanate dissolved in 10 ml of xylene was added to this solution, and the mixture was heated and stirred from 130 ° C. to a maximum temperature of 150 ° C. for 10 hours.
[0063]
  Next, in order to remove low molecular weight alcohol, water, and xylene used as a solvent from this solution, it was distilled at a temperature of 130 ° C. to 150 ° C. for 5 hours. In order to remove dust from this solution, it was filtered with a 0.45 μm diameter filter. Then, SrBi of the solution₂(Ta_XNb_1-X)₂O₉The concentration of (x = 0 to 1) is adjusted to 0.1 mol / l, and this is used as a precursor solution. In the above process, the ratio of strontium: bismuth: (tantalum + niobium) was adjusted to 8:22:20. Further, these raw materials are not limited to those described above, and any solvent may be used as long as the above starting materials are sufficiently dissolved.
[0064]
  The film forming method of the present invention when this raw material solution is used as a precursor solution will be described with reference to FIG.
[0065]
    Step 1: A titanium film 3 (adhesion layer) having a thickness of about 20 nm is formed as a bonding layer on the silicon single crystal (100) surface substrate 1 on which the silicon thermal oxide film 2 having a thickness of 200 nm is formed by sputtering. .
[0066]
    Step 2: The titanium film is heat treated in oxygen to form a stable titanium oxide film.
[0067]
    Step 3: A Pt film 4 (lower electrode layer) having a thickness of about 200 nm is formed by sputtering.
[0068]
    Step 4: A ferroelectric film raw material solution is applied by spin coating.
[0069]
    Step 5: Place and dry on a hot plate set at 270 ° C. for 4 minutes under atmospheric pressure.
[0070]
    Step 6: Crystallization is performed by heating at an ultimate temperature of 750 ° C. in an oxygen atmosphere using RTA (Rapid Thermal Annealing) method.
[0071]
    Step 7: Until the film made of the raw material solution has a desired film thickness, the process from the solution application is repeated seven times to form a thin film having a thickness of about 200 nm, and the uppermost layer is kept at 800 ° C. for 30 minutes at a high temperature.
[0072]
    Process 8: SrBi₂(Ta_XNb_1-X)₂O₉(x = 0 to 1) Pt is formed as an upper electrode on the film by sputtering.
[0073]
    Step 9: After forming the upper electrode, heat treatment is performed at 800 ° C. for 10 minutes in an oxygen atmosphere.
[0074]
  In the above process, the ferroelectric film was formed while paying attention to the following points. In particular, in Step 6, conditions such as raising the temperature range from 500 ° C. to 700 ° C. at a rate of about 40 ° C./second and maintaining the 750 ° C. maintenance time after the temperature rise to 300 seconds are required. . Further, the heat treatment step in the final step 9 is performed to stabilize the interface between the ferroelectric and the electrode.
[0075]
  Here, the sputtering method is used for forming the titanium film in step 1 and the platinum film in steps 3 and 7, but the present invention is not limited to this, and other film forming methods such as CVD are used. Alternatively, a chemical vapor deposition method or a vapor deposition method may be used. Moreover, each film thickness is not limited. In addition, the spin coating method in step 4 is not intended to limit the present invention. For example, a method capable of controlling the film thickness of the solution such as a dip coating method, an LSMCD method (electrodeposition atomization method), and the like, which can be applied onto the substrate If it is good.
[0076]
  Next, FIG. 3 shows the results of measurement of X-ray diffraction (using CuKα rays) of the ferroelectric film formed by the above method. FIG. 3 shows that the peak of the <105> axis near 29 degrees (plane spacing 29.02 mm (± 0.2 mm)) is <110 near 33 degrees (plane spacing 32.45 mm (± 0.2 mm)). > It can be seen that the peak of the axis is 1.5 times or more strong.
[0077]
  In addition, powder SrBi₂(Ta_XNb_1-X)₂O₉FIG. 4 shows the result of obtaining the orientation component ratio of the ferroelectric film obtained by the present embodiment from the peak intensity ratio of the X-ray diffraction image of (x = 0 to 1). From the figure, it was found that about 50% of the crystal grains such as the <110> axis and the <200> axis do not contain any c-axis component.
[0078]
  Next, the result of measuring the ferroelectric characteristics of this ferroelectric film will be described. The ferroelectric characteristics were measured by the Soya tower method, and were measured by applying a voltage of 5 V to the ferroelectric capacitor shown in FIG. 1 using the Soya tower circuit shown in FIG. In the present embodiment, a hysteresis curve is displayed with an oscilloscope using the Soya Tower Bridge shown in FIG.
[0079]
  Referring to FIG. 5 in detail, the capacitor C of the reference capacitor connected in series with the ferroelectric capacitor._RIs a reference capacitor, and a voltage Vx obtained by dividing a voltage V applied to a ferroelectric capacitor, which is a ferroelectric thin film element, is input to a horizontal axis terminal of the oscilloscope. Here, when the polarization surface charge density of the ferroelectric thin film is P and the true charge surface density is D, (P + ε₀E) × A, that is, D × A (A is the electrode area) and the charge C stored in the reference capacitor_RV_YIs equal to Q, so the vertical axis terminal has a voltage V proportional to D._Y= (D × A / C_R) Is entered.
[0080]
  In the ferroelectric film, since P is sufficiently larger than εE, it can be regarded that D = P. This V_Y-V_XThe curve is a known amount of film thickness, voltage division ratio, electrode area (A), reference capacitor capacitance (C_R) To obtain a PE (residual spontaneous polarization-electric field) hysteresis curve or a DE (accumulated charge amount-electric field) hysteresis curve, from which residual spontaneous polarization (Pr), coercive electric field ( Each value of Ec) and accumulated charge amount (ΔQ) can be read.
[0081]
  When the characteristics of the ferroelectric film according to the present invention were evaluated using this Soya tower method, a hysteresis curve as shown by a circle in FIG. 6 was obtained (line Bi22). 5 V remanent polarization 2Pr is 29 μC / cm²2Ec is 132 kV / cm or more, and ΔQ is 28 μC / cm.²That was all.
[0082]
  Next, as a comparative example for evaluating the above measurement results, the composition of the raw material liquid was adjusted so that the ratio of strontium: bismuth: (tantalum + niobium) was 8:24:20, which is completely the same as that of the present embodiment. When a film was formed by the same process, it was found that the peak intensity of the <110> axis was weaker than the peak intensity of the <105> axis. It was also found that c-axis components such as the <006> axis and the <0010> axis were strong.
[0083]
  Therefore, the influence of the difference in orientation components between this embodiment and the comparative example on the ferroelectric characteristics was examined. As a result, the characteristics of this thin film element show a hysteresis curve as shown by Bi24 in FIG. 6, and the residual polarization 2Pr of 5V is 25 μC / cm.²In the following, 2Ec is 125 kV / cm or more, and ΔQ is 23 μC / cm.²It was as follows, and it was found that the characteristics were lower than when the Bi composition was set to 22.
[0084]
  Further, from further detailed examination, the <110> axial strength / <105> axial strength ratio when the bismuth composition is changed is high when the bismuth composition ratio is between 20 and 24, and most particularly around 21 to 23. I found it expensive. At the same time, the value of ΔQ showed the same behavior. That is, it was found that the orientation strength of the <110> axis can be controlled by the composition ratio of bismuth.
[0085]
  Next, without adding niobium, the firing conditions were the same as in step 6 above, in which the ultimate temperature was 800 ° C., the maintenance time was 12 seconds, the top layer 800 ° C. maintenance time was 8 minutes, and the film thickness was 150 nm. FIG. 7 shows the speed dependency of the <110> axial strength / <105> axial strength ratio when a temperature range from 500 ° C. to 700 ° C. is heated at a rate of 1 to 40 ° C./sec. The dependency is shown in FIG. As a result, it was found that the <110> axis / <105> axis strength ratio was high in the region where the rate of temperature increase was 5 ° C./second or more, and ΔQ increased with the rate of temperature increase.
[0086]
  Further, FIG. 9 shows the dependence of the signal noise ratio and Ec on the temperature rise rate. From this, it was found that the signal noise ratio was improved and Ec was lowered as the temperature rise rate was increased. That is, it can be said that the increase in the temperature rising rate enables low voltage driving when the capacitor of the present invention is used in a semiconductor device.
[0087]
  Further, it was found from a more detailed examination that it is particularly important to pass through a temperature region near 550 to 650 ° C. at a speed higher than 5 ° C./second. However, when heated at a very high temperature increase rate, for example, 200 ° C./second or more, it was found that the region where a good film can be obtained is 5 to 200 ° C./second because the substrate was warped by thermal shock. It was.
[0088]
  Further, in the above embodiment, the film thickness after crystallization for each coating is made slightly less than 30 nm, but when this film thickness is gradually increased to a film thickness of about 37 to 39 nm (other conditions are the same) ), <110> axis peak intensity decreased. FIG. 10 shows the X-ray diffraction image. FIG. 10 clearly shows that the peak of the <110> axis has decreased. Conversely, the c-axis component around 36 degrees is <00.10> The strength of the shaft increased. Accordingly, ΔQ is 19 μC / cm.²The value was low.
[0089]
  Next, the substrate is formed by directly forming platinum on titanium.₂Ta₂O₉As a result of forming the film by the above-described method, the peak component of the <110> axis was lowered and 2Pr was also low.
[0090]
  SrBi₂(Ta_XNb_1-X)₂O₉Even when the metal film between the (x = 0 to 1) film and the Si oxide film was changed to other materials such as Ir / TaSiN and Ir / TiN, the peak component of <110> decreased. However, it showed good ferroelectric properties compared with the conventional film forming method. For example, when the film forming method according to the present invention is formed on Ir / TaSiN at a low temperature of 700 ° C., the <110> peak component is reduced as compared with that on platinum, but ΔQ is 17 μC / cm.²The above good values could be obtained.
[0091]
  From the above results, SrBi₂(Ta_XNb_1-X)₂O₉(x = 0 to 1) In order to control the orientation component of the film and grow the a and b axis components in the film thickness direction, SrBi₂(Ta_XNb_1-X)₂O₉(x = 0 to 1) is preferably formed on a substrate on which titanium oxide and platinum are stacked.
[0092]
  SrBi₂(Ta_XNb_1-X)₂O₉When strontium, bismuth, tantalum, niobium alkoxide or organometallic salt is used as a raw material solution component of (x = 0 to 1), and (tantalum + niobium) is 20, so that bismuth is in excess of 20-24. A solution adjusted to the above is prepared. SrBi₂(Ta_XNb_1-X)₂O₉The raw material solution is applied so that the film thickness after crystallization of (x = 0 to 1) is 35 nm or less.
[0093]
  Step of drying after application, SrBi₂(Ta_XNb_1-X)₂O₉including all steps such as increasing the temperature in the vicinity of 550 to 650 ° C. at a rate of 10 ° C./second or more when crystallization of (x = 0 to 1) by heating, SrBi₂(Ta_XNb_1-X)₂O₉It turned out that it is important to repeat the process from the said solution application | coating until (x = 0-1) becomes a desired film thickness.
[0094]
  As described above, according to the present embodiment, SrBi by the formation method of the present invention.₂(Ta_XNb_1-X)₂O₉The film (x = 0 to 1) shows a structure that is not seen in the prior art and has the highest a and b axis components, for example, <110> axis orientation strength, with which high ferroelectric characteristics can be obtained, and a capacitor using the same The ferroelectric properties of this were also higher than the conventional ones.
[0095]
  Next, a cross-sectional view of an example of a planar type nonvolatile memory in which the ferroelectric thin film formed according to the present invention is applied to the ferroelectric capacitor according to the present invention as shown in FIG. 11 is shown.
[0096]
  In this nonvolatile memory, an element isolation insulating layer 7 formed by local oxidation so-called LOCOS is formed on a semiconductor substrate 1, and a source region 9 and a drain region 10 are formed in regions separated by this, and these source and drain regions are formed. An MIS transistor (insulated gate field effect transistor) 8 is formed between 9 and 10. Furthermore, on this MIS transistor 8, for example, SiO 2₂Then, an interlayer insulating layer 11 made of BPSG (boron, phosphorus, silicate glass) or the like is formed.
[0097]
  Then, the buffer layer 3 is formed on the interlayer insulating layer 11 on the element isolation insulating layer 7. The buffer layer 3 is composed of a titanium oxide layer. Then, SrBi formed on the lower electrode 4 according to the present invention.₂Ta₂O₉A ferroelectric layer 5 is formed, and a platinum upper electrode 6 is formed thereon. Thereby, a large-capacity ferroelectric capacitor is constituted by the lower electrode 4, the ferroelectric layer 5 and the upper electrode 6.
[0098]
  Further, an upper insulating layer 12 is formed on the entire surface including the upper electrode 6, and contact holes 13 are formed in the upper insulating layer 12, for example, on the upper electrode 6 and the source region 9 of the interlayer insulating layer 11. The upper electrode 6 and the source region 9 are in contact with each other through the contact hole 13 by the wiring 14.
[0099]
  Since the nonvolatile memory manufactured in this manner uses a ferroelectric capacitor having a high ΔQ, the capacitor area can be reduced, which is advantageous for high integration. Further, since it has a high signal-to-noise ratio and saturation characteristics, it becomes a low power consumption semiconductor device.
[0100]
  Here, the substrate on which the film is formed is not particularly limited as long as it can be used as a substrate for a semiconductor device or an integrated circuit. For example, a semiconductor substrate such as silicon, a compound semiconductor substrate such as GaAs, an oxide crystal substrate such as MgO, and a glass substrate can be selected depending on the type and application of the element to be formed. .
[0101]
      (Second embodiment)
  Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 12 is a schematic cross-sectional view of a ferroelectric capacitor 30 having a strontium bismuth tantalate ferroelectric film 35 formed according to an embodiment of the present invention.
[0102]
  As shown in FIG. 12, a silicon thermal oxide film 32 with a film thickness of 200 nm is formed on the surface of a silicon single crystal substrate 31, and a titanium oxide film 33 (adhesion layer) with a film thickness of about 20 nm and a film thickness of 200 nm are formed thereon. An approximately platinum film 34 (lower electrode layer) is formed, and a ferroelectric thin film 35 and an upper electrode layer 36 are formed as described below.
[0103]
  For the formation of the ferroelectric thin film 35, a MOD (Metal Organic Deposition) method including a film forming process using a precursor raw material solution of a ferroelectric material was used. In the precursor raw material solution of this MOD method, tantalum ethoxide (Ta (OC₂H_Five)_Five) Bismuth 2-ethylhexanoate (Bi (C₇H₁₅(COO)₂), And strontium 2-ethylhexanoate (Sr (C₇H₁₅(COO)₂) To synthesize this.
[0104]
  A film forming method according to an embodiment of the present invention using this raw material solution as a precursor solution will be described in the order of step 1 to step 7 with reference to FIG.
[0105]
    Step 1: A silicon thermal oxide film 32, a titanium oxide film 33, and a platinum electrode 34 are sequentially formed on a silicon single crystal (100) surface substrate 31.
[0106]
    Step 2: A raw material solution of the ferroelectric film 35 is applied onto the platinum electrode 34 on the substrate 31 by a spin coating method.
[0107]
    Step 3: Under the atmospheric pressure, the substrate 31 is placed on a hot plate set at 250 ° C. for 4 minutes and dried.
[0108]
    Step 4: Using the RTA (Rapid Thermal Annealing) method, the substrate 31 is crystallized by heating it for 30 seconds at an ultimate temperature of 800 ° C. in an oxygen atmosphere.
[0109]
    Step 5: The steps from Step 2 to Step 4 of the solution application are repeated until the ferroelectric film 35 has a desired thickness. The uppermost layer of the ferroelectric film 35 is heated at 800 ° C. for 8 minutes in order to improve the overall crystallinity.
[0110]
    Step 6: Platinum is formed as the upper electrode 36 on the ferroelectric film 35 made of a strontium tantalate / bismuth film.
[0111]
    Step 7: After forming the upper electrode 36, heat treatment is performed in an oxygen atmosphere at 800 ° C. for 10 minutes.
[0112]
  The heat treatment step in the final step 7 is performed to stabilize the interface between the ferroelectric film 35 and the upper electrode 36.
[0113]
  In addition, the coating in the above step 2 is not limited to the spin coating method, and the film thickness of the solution can be controlled by, for example, dip coating method, LSMCD method (electrodeposition atomization method), etc. Any method that can be applied is acceptable. Furthermore, the heat treatment temperature and time in Step 3, Step 4, Step 5, and Step 7 are not limited to the above-described values, and may satisfy the purpose of each step.
[0114]
  In the above film forming method, the strontium bismuth tantalate film 35 was formed while paying attention to the following points. That is, the atomic composition of the raw material solution in Step 2 was adjusted so that the ratio of strontium: bismuth: tantalum was 8:22:20. In the spin coating in step 2, the thickness after crystallization per layer was adjusted to about 30 nm. Furthermore, in the heat treatment steps in Steps 4 and 5, the temperature increase rate in the temperature region near 550 ° C. to 650 ° C. where crystallization is considered to start is adjusted to 40 ° C./second.
[0115]
  FIG. 13 shows the results of measurement of the X-ray diffraction images (using CuKα rays) of the first, fifth and ninth layers of the strontium tantalate / bismuth film 35 thus formed. .
[0116]
  In FIG. 13, in order to make it easy to see, the intensity of the diffraction image in the first layer is enlarged three times. In the first layer, the peak intensity of the <110> axis was 50% or less with respect to the peak intensity of the <105> axis, and a diffraction image similar to that of the conventional randomly oriented strontium bismuth tantalate film was shown. .
[0117]
  However, as the number of layers increases, the <110> axis peak preferentially increases, and in the ninth layer, the <110> axis peak is more than twice the peak of the <105> axis. It turned out to increase. That is, according to the film forming method of this embodiment, it was found that the orientation of the strontium bismuth tantalate film 35 can be changed from random to <110> axial dominant as the film thickness increases. .
[0118]
  FIG. 15 shows the <110> axis peak intensity around 33 degrees (plane spacing 32.45 mm (± 0.2 mm)) and <105 near 29 degrees (plane spacing 29.02 mm (soil 0.2 mm)). The axial peak intensity ratio divided by the axial peak intensity is shown for the number of stacked layers of the strontium tantalate / bismuth tantalum film 35 from the first layer to the ninth layer. It can be seen that the axial peak intensity ratio increases sequentially as the number of layers increases.
[0119]
  Next, FIG. 26 shows a cross-sectional photograph obtained by photographing the strontium tantalate / bismuth film 35 by the film forming method of this embodiment with a scanning electron microscope. In the film 35, many crystal grains having a grain size that increases from the center of the photograph toward the upper side in the film thickness direction on the left hand side are observed. From further detailed analysis, such crystal grains are <110. > Axis orientation was found. In other words, the strontium tantalate / bismuth film 35 of the capacitor of this embodiment has a larger amount of crystal orientation component that is <110> axial orientation in the vicinity of the other electrode 36 facing the substrate 31 than in the vicinity of the substrate 31 side electrode. There is a feature.
[0120]
  Next, the result of measuring the ferroelectric characteristics of the strontium tantalate bismuth film 35 according to this embodiment will be described. This ferroelectric characteristic was measured by the Soya tower method, and was measured by applying a voltage to the ferroelectric capacitor 30 shown in FIG. 12 using the Soya tower bridge circuit shown in FIG. . In this embodiment, the hysteresis curve was displayed with an oscilloscope using the Soya Tower Bridge circuit.
[0121]
  17 is the capacitor C of the reference capacitor 71 connected in series with the ferroelectric capacitor 30._RIs a reference capacitor, and the horizontal axis terminal 73 of the oscilloscope has a voltage V obtained by dividing the voltage V applied to the ferroelectric capacitor 30 which is a ferroelectric thin film element._XIs entered.
[0122]
  Here, when the polarization surface charge density of the ferroelectric thin film 35 is P and the true charge surface density is D, (P + ε_oE) × A, that is, D × A (A is an electrode area), and electric charge C stored in the reference capacitor 71_RV_YBoth have the same charge amount Q. Therefore, the vertical terminal 72 has a voltage V proportional to D._Y= (D × A / C_R) Is entered.
[0123]
  In the ferroelectric film 35, since P is sufficiently larger than εE, it can be regarded that true charge surface density D = polarized surface charge density P. This V_Y-V_XThe curve is a known amount of film thickness, voltage division ratio, electrode area (A), reference capacitor capacitance (C_R), A PE (residual spontaneous polarization-electric field) hysteresis curve or a DE (accumulated charge amount-electric field) hysteresis curve is obtained. From this hysteresis curve, residual spontaneous polarization (P_r), Coercive electric field (E_c), Each value of the accumulated charge amount (ΔQ) can be read.
[0124]
  When the characteristics of the nine-layered ferroelectric film 35 according to this embodiment were evaluated using this Soya tower method, a hysteresis curve as shown in FIG. 18 was obtained. That is, 2P at an electric field strength of 330 kV / cm_rIs 30μC / cm²2E_cIs 112 kV / cm or more, and the accumulated charge amount ΔQ is 28 μC / cm.²That was all.
[0125]
  Also, in FIG._rThis shows the dependence of the number of layers. When the number of stacked layers is less than 3, that is, when the film thickness is thinner than 90 nm, the leakage current density is high and hysteresis measurement is impossible. However, if the number of stacked layers is 3, 2P_rThe value is 24.6 μC / cm²It was found that the value increased with increasing number of layers. In addition, as shown in FIG. 15 described above, it has been found that even at 10 layers or more, a high <110> axis peak intensity is exhibited, but the productivity is low, and the film is cracked during the process due to the thick film. It became easy to occur.
[0126]
  From the characteristics shown in FIG. 15 and FIG. 16, when the productivity and mechanical strength are taken into consideration, the condition for obtaining good ferroelectric characteristics is that the peak intensity ratio is in the range of 80 to 230%. It was found that the thickness was in the range of 90 to 270 nm (3 to 9 layers). The peak intensity ratio is the <110> axis peak intensity around 33 degrees (plane spacing 32.45 mm (± 0.2 mm)), and the peak intensity ratio near 29 degrees (plane spacing 29.02 mm (± 0.2 mm)) < 105> A value divided by the axial peak intensity.
[0127]
  Next, using the film formation method according to this embodiment, the strontium bismuth tantalate film 35 having a film thickness of 150 nm (5 layers) is heated to a temperature in the vicinity of 550 ° C. to 650 ° C. in the heat treatment step in the steps 6 and 7. It was produced by changing the temperature rising rate of the region to 1 to 40 ° C./second. At this time, the atomic composition ratio of Bi (bismuth) in the precursor raw material solution was set to 22, and the film thickness after crystallization for each coating layer was set to 30 nm.
[0128]
  The temperature rise rate dependence of the <110> axial strength / <105> axial strength ratio of the produced strontium tantalate bismuth film 35 is shown in FIG._rFIG. 22 shows the temperature rise rate dependency of. From these characteristics, the <110> axis / <105> axis strength ratio is high in the region where the temperature rising rate is 5 ° C./second or more, and 2P along with the temperature rising rate._rI also found that it was rising. However, when heated at a very high rate of temperature rise (greater than 300 ° C./second), warping of the substrate due to thermal shock was observed. Thereby, it turned out that the temperature increase rate area | region which can obtain a favorable strontium tantalate bismuth film | membrane is 5-300 degreeC / sec.
[0129]
  From these results, the orientation intensity of the <110> axis can be controlled by the rate of temperature increase in the temperature range from 550 ° C. to 650 ° C., along with the residual polarization P_rIt was found that the value of can also be controlled.
[0130]
  Next, by using the film formation method according to this embodiment, the atomic composition ratio of Bi (bismuth) in the precursor raw material solution is changed from 20 to 24 by 1 for a 150 nm-thick strontium tantalate bismuth film. Produced. At this time, the rate of temperature increase in the temperature range from 550 ° C. to about 650 ° C. was 40 ° C./second, and the film thickness after crystallization for each coating was 30 nm. FIG. 19 shows the relationship between the <110> axial strength / <105> axial strength ratio of the produced strontium bismuth tantalate film and the composition ratio of Bi in the raw material solution. As shown in FIG. 19, when the atomic composition ratio of Bi was 22, the film exhibited the strongest <110> axis / <105> axis intensity ratio.
[0131]
  Next, FIG. 20 shows 2P of each sample of the strontium tantalate bismuth film._rIndicates the value of. From FIG. 20, the sample with Bi composition ratio 22 having the strongest <110> axial strength / <105> axial strength ratio is the highest 2P._rIt can be seen that the value is obtained. Further, although details are not shown here, when the Bi atomic composition ratio is changed from 20 to 24 and the influence of the heating rate is examined, when the Bi atomic composition ratio is 20, 2P_rThe value of increases with the rate of temperature increase, but no change was observed in the <110> axial strength / <105> axial strength ratio.
[0132]
  In the X-ray diffraction image, weak fluorite and pyrochlore peaks were observed. Furthermore, at the Bi composition ratio 24 in which Bi is excessive, the rate of increase of the <110> axial strength / <105> axial strength ratio due to the heating rate is lower than that when the Bi composition ratio is 22, and in the X-ray diffraction image A strong bismuth platinum peak was observed, and diffusion of Bi into the platinum electrode was confirmed.
[0133]
  Although details are not shown here, it has been found that when the atomic composition ratio of Sr is changed from 8, the optimum value of the atomic composition ratio of Bi also changes.
[0134]
  For the above reasons, the condition for obtaining a good film is that the atomic composition ratio Sr: Bi: Ta in the raw material solution is expressed as X <Y: Z: 1.4 <(X + Y) / Z <1.6. I found out that there was a relationship.
[0135]
  From these results, by controlling the composition ratio of bismuth, it is possible to control the orientation strength of the <110> axis and the residual polarization P_rIt was found that the value of can also be controlled.
[0136]
  Next, using the film forming method according to this embodiment, the strontium bismuth tantalate film 35 having a film thickness of 200 nm (± 10 nm) is formed to a film thickness of 25 nm after crystallization for each coating in steps 2 to 4. It was made to change to less than ˜50 nm. At this time, the rate of temperature increase in the temperature range from 550 ° C. to about 650 ° C. was 40 ° C./second, and the composition ratio of Bi in the precursor raw material solution was 22. The dependency of the <110> axial strength / <105> axial strength ratio on the film thickness of each layer at this time is shown in FIG._rFIG. 24 shows the dependence of each on the thickness of each layer.
[0137]
  From FIG. 23, it can be seen that as the film thickness of each layer decreases, the <110> axis / <105> axis intensity ratio increases. Furthermore, from FIG. 24, each layer thickness decreases and 2P_rIt can be seen that there is an increasing trend. However, it was found that when the thickness of each layer was smaller than 25 nm, the leak characteristics were lowered. The reason for this decrease is thought to be that the initial layer grows in a strip shape.
[0138]
  On the other hand, when the thickness of each layer was thicker than 50 nm, the leak characteristics were deteriorated. The reason for the decrease is considered to be that the denseness in the film thickness direction decreases due to the generation of crystal nuclei for each layer. Therefore, it was found that a region where a good film can be obtained has a thickness of each layer in the range of 25 to 50 nm.
[0139]
  From these results, it is possible to control the orientation intensity of the <110> axis by controlling the film thickness of each layer, and the residual polarization P_rIt was found that the value of can also be controlled.
[0140]
  In the second embodiment described above, even when a strontium / bismuth niobate film is formed by using niobium ethoxide as a starting material in the MOD method and replacing all tantalum with niobium, the same as in the above embodiment. The effect of was obtained. In addition, even when a strontium bismuth tantalate niobate film is formed by using niobium ethoxide as a starting material in the MOD method and substituting part of tantalum with niobium, the same effect as in the above embodiment can be obtained. It was.
[0141]
  As described above, according to the method for forming a strontium bismuth tantalate film of this embodiment, high ferroelectric characteristics can be obtained from a randomly oriented initial layer (first layer) (for example, a and b axis components (for example, , <110> axial orientation component) can be preferentially increased. The component ratio can be controlled by the temperature rising rate in the temperature range from 550 ° C. to 650 ° C., the atomic composition of the raw material solution, and the film thickness of each layer. It became high compared with the one.
[0142]
  Next, FIG. 25 shows a cross section of a non-volatile memory having a planar structure provided with a ferroelectric capacitor having a ferroelectric thin film formed according to the above embodiment.
[0143]
  In this nonvolatile memory, an element isolation insulating layer 57 formed by local oxidation, so-called LOCOS, is formed on a semiconductor substrate 51, and a source region 59 and a drain region 60 are formed in regions separated by this, and these source regions 59 are formed. An MIS transistor (insulated gate field effect transistor) 58 is formed between the drain region 60 and the drain region 60. Further, on this MIS transistor 58, for example, SiO₂Then, an interlayer insulating layer 61 made of BPSG (boron, phosphorus, silicate glass) or the like is formed.
[0144]
  Then, the buffer layer 53 is formed on the interlayer insulating layer 61 on the element isolation insulating layer 57. The buffer layer 53 is composed of a titanium oxide layer. Then, the strontium bismuth tantalate ferroelectric layer 55 formed according to the above embodiment is formed on the lower electrode 54, and the platinum upper electrode 56 is formed on the ferroelectric layer 55. Thus, a large-capacity ferroelectric capacitor 50 is constituted by the lower electrode 54, the ferroelectric layer 55, and the upper electrode 56.
[0145]
  Further, an upper insulating layer 62 is formed on the entire surface including the upper electrode 56, and contact holes 63 are formed in the upper insulating layer 62, for example, on the upper electrode 56 and on the source region 59 of the interlayer insulating layer 61. The upper electrode 56 and the source region 59 are in contact with each other via the wiring 64 through the contact holes 63.
[0146]
  Since the nonvolatile memory manufactured in this way uses a ferroelectric capacitor having a high accumulated charge amount ΔQ, the capacitor area can be reduced. Therefore, it is advantageous for high integration. Further, since it has a high signal-to-noise ratio and saturation characteristics, it becomes a low power consumption semiconductor device.
[0147]
  Here, the substrate on which the film is formed is not particularly limited as long as it can be used as a substrate for a semiconductor device or an integrated circuit. For example, a semiconductor substrate such as silicon, a compound semiconductor substrate such as GaAs, an oxide crystal substrate such as MgO, and a glass substrate can be selected depending on the type and application of the element to be formed. Among these, a silicon substrate is preferable.
[0148]
【The invention's effect】
  As apparent from the above, in the ferroelectric capacitor of the present invention, the ferroelectric film formed between the pair of electrodes has an interplanar spacing mainly in the film thickness direction in an X-ray diffraction image using CuKα rays. SrBi showing peak values at 29.02 mm (± 0.2 mm) and a surface interval of 32.45 mm (± 0.2 mm)₂(Ta_XNb_1-X)₂O₉(x = 0 to 1) Ferroelectric film. With the configuration of the ferroelectric capacitor of the present invention, a large ferroelectric characteristic can be obtained, and it can be suitably used as a part of an integrated circuit element formed on a substrate.
[0149]
  Also,This inventionIn the above ferroelectric capacitor, the ferroelectric film has a peak intensity in an X-ray diffraction image using CuKα rays of 100% of the peak value with a surface interval of 29.02 mm (± 0.2 mm) in the film thickness direction. SrBi having a peak value of a surface spacing of 32.45 mm (± 0.2 mm) is 80 to 300%.₂(Ta_XNb_1-X)₂O₉(x = 0 to 1) Ferroelectric film. ThisDepartureAccording to the bright ferroelectric capacitor, larger ferroelectric characteristics can be obtained.
[0150]
  In another embodiment of the ferroelectric capacitor, the ferroelectric film is SrBi.₂(Ta_XNb_1-X)₂O₉(x = 0 to 1) is a columnar structure. According to the ferroelectric capacitor of this embodiment, larger ferroelectric characteristics can be obtained.
[0151]
  Also, a method of manufacturing a ferroelectric film according to an embodiment includes a step of forming a metal film on a substrate, and a raw material solution of an alkoxide or an organometallic salt of two elements of strontium and bismuth and at least one of tantalum or niobium A step of applying the solution to a substrate, a step of drying the solution after applying the solution to the substrate, and a step of heating the solution to a temperature equal to or higher than the crystallization temperature. By repeating the process until the solution is heated until the metal film on the substrate reaches a predetermined thickness, SrBi is formed on the substrate.₂(Ta_XNb_1-X)₂O₉(x = 0 to 1) A method of forming a ferroelectric film, wherein the solution is heated to a temperature higher than the crystallization temperature, the temperature rise rate is adjusted in the temperature range near 550 to 650 ° C. By adjusting at least one of the adjustment of the composition ratio of bismuth, SrBi₂(Ta_XNb_1-X)₂O₉(x = 0 to 1) Controls the orientation components of the a and b axes of the ferroelectric film.
[0152]
  In the manufacturing method of this embodiment, SrBi₂(Ta_XNb_1-X)₂O₉The film (x = 0 to 1) shows a structure that has not been seen in the past, such as the highest a and b axis components, for example, <110> axis orientation strength, at which high ferroelectric characteristics can be obtained. The ferroelectric characteristics of the capacitor were also higher than the conventional one.
[0153]
  In the method of manufacturing a ferroelectric film according to another embodiment, the temperature rising rate in adjusting the temperature rising rate in the temperature region near 550 to 650 ° C. is set to a range of 5 to 200 ° C./second. In this embodiment, high ferroelectric characteristics can be obtained while suppressing warping of the substrate.
[0154]
  In the method of manufacturing a ferroelectric film according to an embodiment, in the step of applying the above solution to the substrate, when the solution applied to the substrate is 20 (tantalum + niobium), bismuth is 20 to 24 excess. The composition ratio of bismuth is adjusted in the above raw material solution preparation step. In this embodiment, particularly high ferroelectric characteristics were obtained.
[0155]
  In the method for manufacturing a ferroelectric film according to another embodiment, the raw material solution is applied to the substrate so that the metal film after crystallization formed on the substrate has a thickness of 35 nm or less. In this embodiment, if the metal film thickness after crystallization formed on the substrate is 35 nm or less, the ferroelectric characteristics increase as the film thickness increases.
[0156]
  In one embodiment of the method for manufacturing a ferroelectric film, the uppermost part of the metal film formed on the substrate is a platinum layer. In this embodiment, since the uppermost portion of the metal film formed on the substrate is a platinum layer, particularly high ferroelectric characteristics were obtained.
[0157]
  In addition, the semiconductor device of another embodiment uses the capacitor as a part of an integrated circuit element formed on a substrate. Since the semiconductor device of this embodiment uses the capacitor having high ferroelectric characteristics, it can be highly integrated.
[0158]
  The ferroelectric capacitor according to an embodiment is a ferroelectric capacitor including at least a pair of electrodes and a ferroelectric film on a substrate, and the ferroelectric film formed between the pair of electrodes includes: An X-ray diffraction image in the film thickness direction using CuKα rays has a crystal orientation component having a surface spacing of 32.45 mm (± 0.2 mm) in the vicinity of the other electrode opposite to the vicinity of the substrate side electrode. It is a ferroelectric film of strontium bismuth tantalate, strontium bismuth niobate, or a solid solution thereof. The capacitor of this embodiment has many crystal components oriented in the polarization axis direction and can exhibit high ferroelectric characteristics. Therefore, it can be suitably used as a part of an integrated circuit element formed on a substrate.
[0159]
  A ferroelectric capacitor according to another embodiment is a ferroelectric capacitor having at least a pair of electrodes and a ferroelectric film on a substrate, wherein the ferroelectric film formed between the pair of electrodes is The peak intensity in the X-ray diffraction image using the CuKα ray is 32.45 mm (± 0.00 mm) when the peak value of the surface distance 29.02 mm (± 0.2 mm) is 100% in the film thickness direction. 2) is a ferroelectric film of strontium bismuth tantalate, strontium bismuth niobate, or a solid solution thereof having a film thickness in the range of 90 to 270 nm. The capacitor of this embodiment has many crystal components oriented in the polarization axis direction and can exhibit high ferroelectric characteristics. Furthermore, mass productivity is high.
[0160]
  Also, a method of manufacturing a ferroelectric film according to an embodiment includes a step of forming a metal film on a substrate, a raw material solution of an alkoxide or an organometallic salt of two elements of strontium and bismuth, and at least one of tantalum and niobium A step of applying the solution to the substrate, a step of drying the substrate after the application, and a step of heating the substrate above the crystallization temperature. By repeating the above steps until the metal film on the substrate reaches a predetermined film thickness, a ferroelectric film of strontium bismuth tantalate, strontium bismuth niobate, or a solid solution thereof is formed on the substrate. In the step of heating above the crystallization temperature, the adjustment of the atomic composition ratio in the raw material solution, the temperature increase rate in the temperature range near 550 to 650 ° C. By adjusting at least one of the adjustment and the adjustment of the film thickness formed in a single step, the orientation component having a surface spacing of 32.45 mm (± 0.2 mm) is controlled. According to the manufacturing method of this embodiment, in the ferroelectric film formed by applying, drying and heating the raw material solution, the crystal component oriented in the polarization axis direction is preferentially grown from the randomly oriented first layer. Can be made.
[0161]
  Further, in the method of manufacturing a ferroelectric film according to another embodiment, the temperature increase rate in the adjustment of the temperature increase rate in the temperature range near 550 to 650 ° C. is set to 5 to 5.200Set to the range of ° C / second. According to the manufacturing method of this embodiment, in the ferroelectric film formed by applying, drying and heating the raw material solution, the crystal component oriented in the polarization axis direction is preferentially grown from the randomly oriented first layer. Can be made.
[0162]
  In the method of manufacturing a ferroelectric film according to an embodiment, the atomic composition ratio Sr: Bi: (Ta + Nb) = X: Y: Z in the raw material solution is 1.4 <(X + Y) / Z <1.6. is there. According to this embodiment, the crystal component oriented in the polarization axis direction can be preferentially grown from the randomly oriented first layer.
[0163]
  In the method of manufacturing a ferroelectric film of another embodiment, the step of applying the raw material solution to the substrate is performed so that the film thickness after crystallization is 25 to 50 nm in one application step. Apply the raw material solution. According to the manufacturing method of the fifteenth aspect, the crystal component oriented in the polarization axis direction can be preferentially grown from the randomly oriented first layer.
[0164]
  In one embodiment of the method for manufacturing a ferroelectric film, the main component of the metal film formed on the substrate is platinum. According to the manufacturing method of this embodiment, the crystal component oriented in the direction of the polarization axis can be preferentially grown from the randomly oriented first layer.
[0165]
  The semiconductor device of another embodiment uses the ferroelectric capacitor as a part of an integrated circuit element formed on a substrate. Since the semiconductor device of this embodiment uses a capacitor having high ferroelectric characteristics, it can be highly integrated.
[0166]
  As described above, according to the present invention, SrBi₂(Ta_XNb_1-X)₂O₉In (x = 0 to 1), since the <110> axis is preferentially oriented in the film thickness direction, high ferroelectric characteristics can be obtained when the capacitor is formed. A semiconductor device using this capacitor, for example, a nonvolatile memory, can be highly integrated and driven at a low voltage.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a main part of a ferroelectric thin film element according to a first embodiment of the present invention.
FIG. 2 is a process diagram illustrating a manufacturing process of a ferroelectric film according to the first embodiment of the present invention.
FIG. 3 is an X-ray diffraction image of the ferroelectric film according to the first embodiment of the present invention.
FIG. 4 is a diagram showing the orientation component ratio of the ferroelectric film according to the first embodiment of the present invention.
FIG. 5 is a diagram showing a Soya tower bridge used for measurement of ferroelectric characteristics in the first embodiment.
FIG. 6 is a characteristic diagram showing a hysteresis curve according to the first embodiment and a hysteresis curve of a comparative example.
FIG. 7 is a graph showing temperature rise rate dependence of <110> intensity and <105> intensity ratio in the first embodiment.
FIG. 8 is a graph showing temperature rise rate dependence of accumulated charge amount ΔQ in the first embodiment.
FIG. 9 is a diagram illustrating the temperature rise rate dependency of the signal-to-noise ratio and the coercive electric field Ec in the first embodiment.
FIG. 10 is an X-ray diffraction image of the ferroelectric film of the embodiment and the ferroelectric film of the comparative example according to the present invention.
FIG. 11 is a fragmentary cross-sectional view showing a schematic structure of the semiconductor device of the embodiment.
FIG. 12 is a schematic cross-sectional view of an essential part of a ferroelectric thin film element according to a second embodiment of the present invention.
FIG. 13 is an X-ray diffraction image of a ferroelectric film according to a second embodiment of the present invention.
FIG. 14 is a process diagram illustrating a manufacturing process of a ferroelectric film according to a second embodiment of the invention.
FIG. 15 is a diagram showing the number-of-stack dependency of <110> strength and <105> strength ratio in the second embodiment.
FIG. 16 shows 2P in the second embodiment._rIt is a figure which shows the lamination number dependence.
FIG. 17 is a diagram showing a Soya tower bridge circuit used for measurement of ferroelectric characteristics in the second embodiment.
FIG. 18 is a diagram showing a hysteresis curve according to the second embodiment.
FIG. 19 is a diagram showing the Bi composition ratio dependence of the <110> strength / <105> strength ratio in the second embodiment.
FIG. 20 shows 2P in the second embodiment._rIt is a figure which shows Bi composition ratio dependence.
FIG. 21 is a diagram showing the temperature increase rate dependency of the <110> intensity / <105> intensity ratio in the second embodiment.
FIG. 22 shows 2P in the second embodiment._rIt is a figure which shows the temperature increase rate dependence.
FIG. 23 is a diagram showing the dependency of <110> intensity / <105> intensity ratio on the thickness of each layer in the second embodiment.
24 shows 2P in the second embodiment. FIG._rIt is a figure which shows each layer film thickness dependence.
FIG. 25 is a fragmentary cross-sectional view showing a schematic structure of a semiconductor device including the second embodiment.
FIG. 26 is a cross-sectional photograph taken with a scanning electron microscope of the ferroelectric film according to the second embodiment of the present invention.
[Explanation of symbols]
  1 ... substrate, 2 ... thermal oxide film, 3 ... buffer layer (titanium oxide film),
  4 ... Lower electrode layer, 5 ... Ferroelectric thin film, 6 ... Upper electrode layer,
  7 ... element isolation insulating layer, 8 ... MIS transistor-impurity diffusion region,
  9 ... Source region-contact hole, 10 ... Drain region,
  11 ... interlayer insulating film, 12 ... upper insulating layer, 13 ... contact hole,
  14 ... wiring,
  30, 50: Ferroelectric capacitor, 31: Substrate, 32: Thermal oxide film,
  33 ... Buffer layer (titanium oxide film), 34 ... Lower electrode layer,
  35 ... Ferroelectric thin film, 36 ... Upper electrode layer,
  51 ... Semiconductor substrate, 53 ... Buffer layer, 54 ... Lower electrode,
  55 ... Ferroelectric layer, 56 ... Upper electrode, 57 ... Element isolation insulating layer,
  58 ... MIS transistor, 59 ... source region, 60 ... drain region,
  61 ... interlayer insulating layer, 62 ... upper insulating layer, 63 ... contact hole,
  64: Wiring.

Claims (16)

A ferroelectric capacitor comprising at least a pair of electrodes and a ferroelectric film on a substrate,
The ferroelectric film formed between the pair of electrodes has an interplanar spacing of 29.02Å ± 0.2 が and an interplanar spacing of 32.45Å ± 0.2Å in the X-ray diffraction image using CuKα rays. DOO in, SrBi ₂ showing a peak value _{(Ta X Nb 1-X)} 2 O 9 (x = 0~1) ferroelectric film der is,
The ferroelectric film is
Peak intensity of X-ray diffraction pattern using a CuKα line, plane spacing in the film thickness direction 29. 02Å ± 0. When the peak value of 2Å was 100%, the surface spacing 32. 45Å ± 0. 2Å peak value Is a SrBi ₂ ( Ta _x Nb _1-x ) ₂ O ₉ ( x = 0 to 1 ) ferroelectric film having a thickness of 80 to 300% ,
The ferroelectric capacitor, wherein the ferroelectric film is formed on a platinum film which is a base electrode layer formed on the substrate . The ferroelectric capacitor according to claim 1,
The ferroelectric capacitor is characterized in that SrBi ₂ (Ta _x Nb _1-x ) ₂ O ₉ (x = 0 to 1) has a columnar structure. A method of manufacturing the ferroelectric capacitor according to claim 1, comprising:
Forming a metal film on the substrate;
A step of preparing a raw material solution of an alkoxide or organometallic salt of two elements of strontium and bismuth and at least one of tantalum and niobium,
Applying the solution to the metal film on the substrate;
Drying the solution applied to the metal film on the substrate;
Heating the solution above the crystallization temperature,
SrBi ₂ (Ta _x Nb _1-x ) ₂ O ₉ (x = 0) is formed on the substrate by repeating the steps from the solution application to the solution heating until the film made of the solution has a predetermined thickness. ~ 1) Ri manufacturing method der ferroelectric capacitor to form a ferroelectric film,
By adjusting at least one of the temperature increase rate in the temperature range of 550 to 650 ° C. in the step of heating the solution to the crystallization temperature or higher or the composition ratio of bismuth in the raw material solution, SrBi ₂ (Ta _x Nb _1-x ) ₂ O ₉ (x = 0 to 1) A method for producing a ferroelectric capacitor, wherein the size of the orientation components of the a and b axes of the ferroelectric film is controlled. In the manufacturing method of the ferroelectric capacitor according to claim 3 ,
A method for manufacturing a ferroelectric capacitor, characterized in that a temperature rising rate in adjusting a temperature rising rate in a temperature range of 550 to 650 ° C. is in a range of 5 to 200 ° C./second. In the manufacturing method of the ferroelectric capacitor according to claim 3 ,
In the step of applying the solution to the substrate, the solution applied to the substrate is such that the atomic composition ratio of tantalum + niobium is 20 and the atomic composition ratio of bismuth is 20-24. A method of manufacturing a ferroelectric capacitor, wherein the atomic composition ratio of bismuth is adjusted in the manufacturing step. The method for manufacturing a ferroelectric capacitor according to any one of claims 3 to 5 ,
A method for producing a ferroelectric capacitor, wherein the raw material solution is applied onto the substrate such that a film thickness of the ferroelectric film after crystallization formed on the substrate is 35 nm or less. The method for manufacturing a ferroelectric capacitor according to any one of claims 3 to 5 ,
A method of manufacturing a ferroelectric capacitor, wherein the uppermost portion of the metal film formed on the substrate is a platinum layer. 3. A semiconductor device using the ferroelectric capacitor according to claim 1 as a part of an integrated circuit element formed on a substrate. A ferroelectric capacitor comprising at least a pair of electrodes and a ferroelectric film on a substrate,
The ferroelectric film formed between the pair of electrodes is a ferroelectric film of strontium bismuth tantalate, strontium bismuth niobate, or a solid solution thereof,
This ferroelectric film is
Compared with the electrode side region on the substrate side, the region on the other counter electrode side has a crystal spacing of 32.45 mm (± 0.2 mm) in the X-ray diffraction image in the film thickness direction using CuKα rays. The orientation component is larger ,
The ferroelectric capacitor, wherein the ferroelectric film is formed on a platinum film which is a base electrode layer formed on the substrate . A ferroelectric capacitor comprising at least a pair of electrodes and a ferroelectric film on a substrate,
The ferroelectric film formed between the pair of electrodes is a ferroelectric film of strontium bismuth tantalate, strontium bismuth niobate, or a solid solution thereof, and has a thickness in the range of 90 to 270 nm. ,
The peak intensity in the X-ray diffraction image using CuKα rays is a peak value of 32.45 mm ± 0.2 mm of the plane distance when the peak value of the plane distance of 29.02 mm ± 0.2 mm is 100% in the film thickness direction. There Ri range near of 80 to 230 percent,
The ferroelectric capacitor, wherein the ferroelectric film is formed on a platinum film which is a base electrode layer formed on the substrate . A method for manufacturing the ferroelectric capacitor according to claim 9, comprising:
Forming a metal film on the substrate;
A step of preparing a raw material solution of an alkoxide or organometallic salt of two elements of strontium and bismuth and at least one of tantalum and niobium,
Applying the solution to a substrate;
Drying the solution applied to the substrate;
Heating the substrate above the crystallization temperature of the raw material solution,
By repeating the steps from applying the solution to heating the substrate until the film made of the raw material solution has a predetermined thickness, strontium bismuth tantalate, strontium bismuth niobate, or a solid solution thereof is formed on the substrate. production method der ferroelectric capacitor forming a ferroelectric film is,
Adjustment of the atomic composition ratio in the raw material solution in the step of preparing the raw material solution, adjustment of the temperature increase rate in the temperature range of 550 to 650 ° C. in the step of heating to the crystallization temperature or higher, and from the solution coating to the substrate By adjusting at least one of the adjustments of the film thickness formed in a single process until heating, the orientation component size of 32.45 mm (± 0.2 mm) of the ferroelectric film is increased. A method of manufacturing a ferroelectric capacitor, characterized by controlling the thickness. In the manufacturing method of the ferroelectric capacitor according to claim 11 ,
A method for manufacturing a ferroelectric capacitor , wherein a temperature rising rate in the temperature range of 550 to 650 ° C. is set in a range of 5 to 200 ° C./second. In the manufacturing method of the ferroelectric capacitor according to claim 11 ,
A method of manufacturing a ferroelectric capacitor, wherein the atomic composition ratio Sr: Bi: (Ta + Nb) = X: Y: Z in the raw material solution is 1.4 <(X + Y) / Z <1.6. In the manufacturing method of the ferroelectric capacitor according to claim 11 ,
The step of applying the raw material solution to the substrate includes:
A method for manufacturing a ferroelectric capacitor, wherein the raw material solution is applied so that the film thickness after crystallization is 25 to 50 nm in a single application step. In the manufacturing method of the ferroelectric capacitor according to claim 11 ,
A manufacturing method of a ferroelectric capacitor, wherein a main component of a metal film formed on the substrate is platinum. The semiconductor device, which comprises using a ferroelectric capacitor according to claim 9 or 10, as part of an integrated circuit device formed on a substrate.

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