JP2002016235A - Ferroelectric capacitor and method of manufacturing the same, and semiconductor device provided with the ferroelectric capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a capacitor, provided with a tantalic acid strontium bismuth film which has large spontaneous polarization in the film direction, and to provide a method of manufacturing the dielectric film of the capacitor. SOLUTION: The ferroelectric capacitor 30 is provided with the tantalic acid strontium bismuth ferroelectric film 35, formed between a pair of electrodes 36, 34. An X-ray diffraction image formed in the thickness direction using a CuKα beam, has more crystal orientation components with an inter-plane spacing of 32.45 Å(±0.2 Å) in a region near an electrode 36 than in a region near an electrode 34 on the substrate 31 side, which faces the electrode 36.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric capacitor using a ferroelectric film, and more particularly, to strontium / bismuth tantalate, strontium / bismuth niobate, which are preferably used as a memory material.
Alternatively, the present invention relates to a ferroelectric capacitor using a solid solution material thereof and a method for manufacturing the same.

[0002]

2. Description of the Related Art A ferroelectric thin film has a spontaneous polarization, a high dielectric constant,
Since it has many functions such as an electro-optic effect, a piezoelectric effect, and a pyroelectric effect, it is applied to a wide range of device development. For example, it is used for an infrared linear ray sensor utilizing its pyroelectricity. Further, 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, by utilizing its high dielectric property, it is used in various fields such as DRAM and MMIC capacitors.

[0003] Among these widespread application device developments, with the development of thin film forming technology in recent years, a combination of a semiconductor memory technology and a ferroelectric nonvolatile memory (FRAM) operating at high density and high speed have been developed. Development is active.

A non-volatile memory using a ferroelectric thin film is:
Due to its characteristics such as high-speed write / read, low-voltage operation, and high write / read durability, it is not only possible to replace the conventional non-volatile memory, but also as a memory that can be replaced with SRAM or DRAM. R & D is actively conducted.

[0005] Such device development requires remanent polarization.
It is necessary to use a material having a large (P _r ), a small coercive electric field (E _c ), a low leakage current, and a large resistance to repetition of polarization reversal. Further, in forming a thin film, it is preferable that the film formation time is short in order to improve the throughput.

Conventionally, ferroelectric materials used for these purposes include PZT (lead zirconate titanate, Pb (T
oxide material _{i X, Zr 1-X)} O 3) perovskite structure represented by is the mainstream. However, a material containing lead as its constituent element, such as PZT, has a high vapor pressure of lead and its oxide, so that lead evaporates during film formation.
Defects were generated in the film, and in severe cases, pinholes were formed. As a result, there has been a defect that, when the leakage current increases or when the polarization reversal is further repeated, a fatigue phenomenon in which the magnitude of spontaneous polarization decreases occurs.

In particular, regarding the fatigue phenomenon, considering replacement of a DRAM with a ferroelectric nonvolatile memory, it is necessary to guarantee that there is no change in characteristics even after 10 ¹⁵ times of polarization reversal. The development of a dielectric thin film has been desired.

On the other hand, in recent years, as a ferroelectric material for FRAM, research and development of a bismuth layer structure compound material has been carried out. Bismuth layered structure compound material was
Discovered by Smolenskii et al. (GA Smolenskii,
VA Isupov and A. I. Agranovskaya, Soviet
Phys. Solid State, 1, 149 (1959)), followed by a detailed study by Subbarao (E.C.S.
ubbarao, J. Phys. Chem. Solids, 23, 665 (19
62)).

[0009] Recently, Carlos A. Paz de Araujo et al., The bismuth layer structure compound thin film, and found that is suitable for application to ferroelectric and high dielectric integrated circuit, in particular, of more than 10 ¹² times It reports excellent fatigue properties in which no change is observed in the properties even after polarization reversal (International Publication No. WO93 / 10542, Japanese Translation of PCT International Publication No. 7-502149).
Publication).

The bismuth layer structure compound has a chemical formula B
i ₂ A _m-1 B _m O _{3m + 3} (A is Na, K, Pb, C
a, Sr, Ba, Bi, where B is Fe, Ti, Nb,
Ta, W, and Mo, where m is a natural number). The crystal structure of the bismuth layered compound is a structure in which (Bi ₂ O ₂ ) 2+ layers and (A _{m-1 Bm} O _{3m + 1} ) 2- layers are alternately stacked. That is, the basis of the crystal structure is that a perovskite layer composed of (m-1) ABO ₃ perovskite lattices is arranged above and below.
It has a structure in which a (Bi ₂ O ₂ ) 2+ layer is interposed.
Here, the selection of A and B is not limited to a single one.

A typical example of such a bismuth layer structure compound material is strontium bismuth tantalate. Methods for producing these films include physical methods such as vacuum evaporation, sputtering, and laser ablation, and sol-gel methods that use organic metal compounds as starting materials and thermally decompose and oxidize them to obtain oxide ferroelectrics. Or MOD (Metal Organic Decomposition) method, M
OCVD (Metal Organic Chemical Vapor Deposit)
A chemical method such as the ion method is used.

[0012] Among the above film forming methods, the MOCVD method is excellent in step coverage, and has a possibility of forming a film at a low temperature. R & D is becoming active.

On the other hand, the sol-gel method or the MOD method can use a raw material solution capable of being homogeneously mixed at the atomic level, so that the composition can be easily controlled and the reproducibility is excellent. It is widely used because of its advantages such as being able to form a large area film and being industrially low cost. In particular, the MOD method is used as a preferable film forming method of the strontium bismuth tantalate film.

[0014]

The conventional strontium-bismuth tantalate film is randomly oriented in the film thickness direction, and its ferroelectricity shows a remarkable anisotropy, so that it does not have a large spontaneous polarization. There are drawbacks. That is,
The strontium bismuth tantalate film has a characteristic that it 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 non-volatile memory that stores information 1,0 depending on the amount of spontaneous polarization.

As a solution to the above problem, Japanese Patent No. 265
No. 8878 proposes the following film forming process using a conventional MOD method.

(1) An alkoxide or an organic metal salt is spin-coated on a substrate.

(2) Dry at 250 ° C. for 10 minutes. The film thickness after drying is about 20 to 80 nm.

(3) 600 to 850 ° C. in an oxygen atmosphere
Heat treatment and crystallization for 10 minutes.

This heat treatment step may be performed by a rapid heat treatment other than the usual heat treatment method.

In order to obtain a desired film thickness, (1) to (3)
Is repeated several times. At this time, since crystallization occurs from the interface with the substrate, the crystal grows epitaxially, and <1
It is stated that a film oriented in the 05> axis can be obtained.

However, if high ferroelectric properties are desired in the strontium bismuth tantalate film, it is necessary to reduce the c-axis component as much as possible in the film thickness direction and obtain a film strongly oriented in the a and b-axis orientation components. preferable.

Japanese Patent Application Laid-Open No. 8-249876 discloses that, in a ferroelectric device having a memory cell, a ferroelectric thin film sandwiched between a pair of electrodes, the ferroelectric thin film has two substantially equivalent ferroelectric thin films. A third crystal having a different symmetry from the first and second crystal axes and a symmetry having the first and second crystal axes as symmetry axes in directions different from the first and second crystal axes; And wherein the third crystal axis is oriented in a direction substantially perpendicular to the electric field applied by the pair of electrodes. A dielectric device or "+/- 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," Oriented within a predetermined direction in a plane perpendicular to the electric field Offering the third and direction of projection onto a plane perpendicular to the electric field of the crystal axis, characterized in that an angle of within plus or minus 30 degrees "ferroelectric device. Furthermore, it states that "the ratio of the crystal grains is 60% or more".

However, in the prior art, in a strontium-bismuth tantalate film, a c-axis component (the above-mentioned first element) is formed on a noble metal electrode such as platinum, which is preferably used as an electrode material, in the thickness direction (electric field). It is very difficult to grow crystal grains in the vertical direction or in a direction within plus or minus 30 degrees with respect to the vertical plane, mainly, or more than 60%. It is usually the case.

Hu et al. (APLLIED PHYSICS LET)
TERS, VOLUME74, NUMBER9, p.1221)
In the OD method, the atomic composition ratio is Sr: Bi: Ta = 1.
Using a raw material solution of 0:24:20, RTA was applied to each layer.
By performing crystal heating treatment by the (rapid thermal annealing) method, a strontium / bismuth tantalate tantalate film having a high a-axis orientation strength can be obtained because the lower layer is always a seed layer, and the orientation strength reaches RTA. It states that it is controlled by temperature.

However, this manufacturing method is basically the same as that of the aforementioned Japanese Patent No. 2,658,878.
It is very difficult to produce an axially oriented film. Therefore, they have realized lower temperature and higher a-axis orientation strength by using bismuth titanate as a seed layer (AP
LLIED PHYSICS LETTERS, VOLUME74, NUMBER24,
P. 3711). However, the use of another material in the same capacitor complicates the process and may cause a loss of reliability due to the diffusion of components. Therefore, it is desired to form the capacitor using the same material.

Therefore, the present invention has been made to solve the above-mentioned problems, and when the MOD method is used to stack only a plurality of layers, the first layer having a random orientation formed on the electrode and having a random orientation is formed. Provided is a ferroelectric film capacitor comprising a strontium bismuth tantalate film in which a <110> axis (plane spacing of 32.45 °) component having preferentially high ferroelectric characteristics in the film thickness direction is grown, and a method of manufacturing the same The purpose is to:

[0027]

To achieve the above object, a ferroelectric capacitor according to the present invention is a ferroelectric capacitor having at least a pair of electrodes on a substrate and a ferroelectric film. In the X-ray diffraction image using CuKα radiation, the ferroelectric film formed between the pair of electrodes has a plane spacing of 29.02Å ± 0.2Å and a plane spacing of 32.4 in the film thickness direction.
SrBi ₂ (Ta _X N) showing a peak value at 5 ° ± 0.2 °
b _1-X ) ₂ O ₉ (x = 0 to 1) is a ferroelectric film.

According to the structure of the ferroelectric capacitor of the present invention, a large ferroelectric characteristic can be obtained.
It can be suitably used as a part of an integrated circuit element formed on a substrate.

In one embodiment of the present invention, in the ferroelectric film, the peak intensity of the ferroelectric film in an X-ray diffraction image using CuKα rays is 29.02Å ± 0.2 in the film thickness direction.
Assuming that the peak value of 2 ％ is 100%, the surface spacing is 32.4.
Sr with a peak value of 5 ± 0.2% of 80-300%
Bi ₂ (Ta _X Nb ₁ -x) ₂ O ₉ (x = 0 to 1) is a ferroelectric film.

According to the ferroelectric capacitor of this embodiment, larger ferroelectric characteristics can be obtained.

Further, another embodiment of the ferroelectric capacitor
Then, the ferroelectric film is made of SrBi _Two(Ta_XNb_1-X)_TwoO
₉(x = 0 to 1) is a columnar structure.

According to the ferroelectric capacitor of this embodiment, larger ferroelectric characteristics can be obtained.

In one embodiment, a method of manufacturing a ferroelectric film includes a step of forming a metal film on a substrate, an alkoxide or an organic metal salt of two elements of strontium and bismuth and at least one of tantalum and niobium. A step of preparing a raw material solution, a step of applying the solution to a metal film on the substrate, a step of drying the solution applied to the metal film on the substrate, and a step of drying the solution at a crystallization temperature or higher. Heating the solution, and 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, so that SrBi ₂ (Ta _X Nb
_1-X ) ₂ O ₉ (x = 0 to 1) A method for manufacturing a ferroelectric capacitor for forming a ferroelectric film, wherein the solution is heated to a temperature of 550 to 650 ° C. in a step of heating the solution to a crystallization temperature or higher. SrBi ₂ (Ta _X Nb _{1 -X} ) ₂ O ₉ (x = 0 to ₁ ) by adjusting at least one of the rate of temperature rise in the temperature region and the composition ratio of bismuth in the raw material solution. The magnitude of the orientation components of the a and b axes of the ferroelectric film is controlled.

In the manufacturing method of this embodiment, SrBi
_{The 2} (Ta _X Nb _1-x ) ₂ O ₉ (x = 0 to 1) film is a conventional film which is said to have the highest a- and b-axis components, for example, <110> -axis orientation strength, at which high ferroelectric properties can be obtained. In this case, a structure that could not be seen was shown, and the ferroelectric characteristics of the capacitor using the structure were higher than those of the conventional one.

In the method for manufacturing a ferroelectric capacitor according to another embodiment, the rate of temperature rise in the temperature range of 550 to 650 ° C. is in the range of 5 to 200 ° C./sec.

In this embodiment, high ferroelectric characteristics can be obtained while suppressing warpage of the substrate.

In one embodiment of the method of manufacturing a ferroelectric capacitor, in the step of applying the solution to the substrate, the solution applied to the substrate has an atomic composition ratio of (tantalum + niobium) of 20. And the atomic composition ratio of bismuth is 20 to 2
In the step of preparing the raw material solution, the atomic composition ratio of bismuth is adjusted so as to be 4.

In this embodiment, particularly, high ferroelectric characteristics were obtained.

According to another embodiment of the present invention, there is provided a method of manufacturing a ferroelectric capacitor, wherein the metal film formed on the substrate has a thickness of 35 nm after crystallization.
The raw material solution is applied on the substrate as described below.

In this embodiment, since the thickness of the metal film formed on the substrate after crystallization is set to 35 nm or less, the ferroelectric characteristics increase as the film thickness increases.

In one embodiment of the present invention, in the method for manufacturing a ferroelectric capacitor, the top of the metal film formed on the substrate is a platinum layer.

In this embodiment, since the uppermost part of the metal film formed on the substrate is a platinum layer, particularly high ferroelectric characteristics are obtained.

In a semiconductor device according to another embodiment, the ferroelectric capacitor is used as a part of an integrated circuit element formed on a substrate.

Since the semiconductor device of this embodiment uses the above-mentioned capacitor having high ferroelectric characteristics, high integration is possible.

A ferroelectric capacitor according to one embodiment is a ferroelectric capacitor having at least a pair of electrodes and a ferroelectric film on a substrate, wherein the ferroelectric capacitor is formed between the pair of electrodes. The film is made of strontium tantalate
It is a ferroelectric film of bismuth, strontium / bismuth niobate, or a solid solution thereof, and the ferroelectric film has a CuKα line in the other counter electrode side region compared to the substrate side electrode side region. In the X-ray diffraction image in the film thickness direction using the above, a crystal orientation component having a plane spacing of 32.45 ° ± 0.2 ° is large.

The capacitor of this embodiment has many crystal components oriented in the direction of the polarization axis, and can exhibit high ferroelectric characteristics. Therefore, it can be suitably used as a part of an integrated circuit element formed on a substrate.

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 capacitor is formed between the pair of electrodes. The body membrane is made of strontium tantalate
A ferroelectric film of bismuth, strontium / bismuth niobate, or a solid solution thereof, having a thickness of 90
270 nm, and the peak intensity in an X-ray diffraction image using CuKα radiation was 29.02 ° in the film thickness direction.
When the peak value of ± 0.2% is 100%,
The peak value of 2.45 ° ± 0.2 ° is in the range of 80 to 230%.

The capacitor of this embodiment has many crystal components oriented in the direction of the polarization axis, and can exhibit high ferroelectric characteristics. Furthermore, mass productivity is high.

In one embodiment, a method of manufacturing a ferroelectric film includes a step of forming a metal film on a substrate, an alkoxide or an organic metal salt of two elements of strontium and bismuth and at least one of tantalum and niobium. A step of preparing a raw material solution, a step of applying the solution to a substrate, a step of drying the solution applied to the substrate, and the substrate
Heating the crystallization temperature of the raw material solution or higher, and repeating the steps from the solution application to the substrate heating until the film made of the raw material solution reaches a predetermined thickness, thereby forming a film on the substrate. A method for producing a ferroelectric capacitor for forming a ferroelectric film of strontium bismuth tantalate, strontium bismuth niobate, or a solid solution thereof, wherein the atomic composition ratio in the raw material solution in the step of preparing the raw material solution Adjustment, adjustment of the rate of temperature rise in the temperature range of 550 to 650 ° C. in the step of heating above the crystallization temperature, and adjustment of the film thickness formed in one step from the solution application to the substrate heating By adjusting at least one of the above, the size of the orientation component of the ferroelectric film having a plane spacing of 32.45 ° ± 0.2 ° 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 direction of the polarization axis from the random oriented first layer has priority. It can be made to grow.

In the method of manufacturing a ferroelectric capacitor according to another embodiment, the heating rate in the adjustment of the heating rate in the temperature range of 550 to 650 ° C. is set in the range of 5 to 300 ° C./sec. .

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 direction of the polarization axis from the random oriented first layer has priority. It can be made to grow.

In one embodiment of the method of manufacturing a ferroelectric capacitor, the atomic composition ratio Sr: B
i: (Ta + Nb) = X: Y: Z is 1.4 <(X + Y) /
Z <1.6.

According to the manufacturing method of this embodiment, a crystal component oriented in the polarization axis direction can be preferentially grown from the random oriented first layer.

In the method of manufacturing a ferroelectric capacitor according to another embodiment, the step of applying the raw material solution to the substrate is such that the film thickness after crystallization is 25 to 25 in one application step.
The raw material solution is applied so as to have a thickness of 50 nm.

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.

In one embodiment of the present invention, 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.

In another embodiment, the ferroelectric capacitor is used as a part of an integrated circuit element formed on a substrate.

Since the semiconductor device of this embodiment uses a capacitor having a high ferroelectric characteristic, high integration is possible.

[0061]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows that SrBi ₂ (Ta _X Nb ₁ -x) ₂ O ₉ (x = 0) formed according to the present invention.
1) A schematic sectional view of a capacitor using a ferroelectric film. 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,
On top of that, a titanium oxide film 3 (adhesion layer) having a thickness of about 20 nm
A platinum film 4 (lower electrode layer) having a thickness of about 200 nm is formed, and a ferroelectric thin film 5 and an upper electrode layer 6 are formed as described later.

The ferroelectric thin film 5 is formed by using a ferroelectric
MOD method including film forming process using precursor solution of material
Was used. In the synthesis of the precursor material solution of the MOD method, the starting material is used.
Niobium ethoxide (Nb (OC_TwoH_Five)_Five), Tongue
Talethoxide (Ta (OC_TwoH _Five)_Five), Bismuth 2-ethyl
Hexanate (Bi (C₇H_FifteenCOO)_Two), And stron
Titanium 2-ethyl hexanate (Sr (C₇H_FifteenCOO)_Two)
used.

First, SrBi ₂ (Ta _X Nb _{1 -X} ) ₂ O ₉ (x =
0-1) Synthesis of a precursor raw material solution used for forming the ferroelectric thin film 5 will be described. Weigh niobium ethoxide and tantalum ethoxide. This was dissolved in 2-ethylhexanate and stirred for 30 minutes while heating from 100 ° C. to a maximum temperature of 120 ° C. to promote the reaction. Thereafter, ethanol and water generated by the reaction at 120 ° C. were removed. 20ml to 30m in the solution
strontium 2-ethylhexanate dissolved in 1 xylene was added, and 125 ° C. to 140 ° C.
The mixture was heated and stirred for 0 minutes. Thereafter, bismuth 2-ethylhexanate dissolved in 10 ml of xylene was added to this solution, and the mixture was heated with stirring at 130 ° C. to a maximum temperature of 150 ° C. for 10 hours.

Next, in order to remove low molecular weight alcohol, water and xylene used as a solvent from the solution, distillation was conducted at a temperature of 130 ° C. to 150 ° C. for 5 hours. In order to remove dust from the solution, the solution was filtered with a 0.45 μm filter. Then, the solution SrBi ₂ (Ta _X N
The concentration of b _1-X ) ₂ O ₉ (x = 0 to 1) was adjusted to 0.1 mol / l, and this was used as a precursor solution. In the above process,
It was adjusted so that the ratio of strontium: bismuth: (tantalum + niobium) was 8:22:20. Further, these raw materials are not limited to those described above, and the solvent may be any solvent as long as the above-mentioned starting materials can be sufficiently dissolved.

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.

Step 1: A titanium film 3 (adhesive layer) having a thickness of about 20 nm as an adhesive layer is formed on a silicon single crystal (100) plane substrate 1 on which a silicon thermal oxide film 2 having a thickness of 200 nm is formed by a sputtering method. Is formed.

Step 2: A stable titanium oxide film is formed by heat-treating the titanium film in oxygen.

Step 3: Pt film 4 having a thickness of about 200 nm
(Lower electrode layer) is formed by a sputtering method.

Step 4: A raw material solution for the ferroelectric film is applied by spin coating.

Step 5: Install and dry on a hot plate set at 270 ° C. for 4 minutes under atmospheric pressure.

Step 6: RTA (Rapid Thermal Anneal)
The crystallization is performed by heating at a temperature of 750 ° C. in an oxygen atmosphere using the ing) method.

Step 7: The steps from the application of the solution are repeated seven times until the film made of the raw material solution has a desired thickness to form a thin film having a thickness of about 200 nm. Hold.

Step 8: SrBi ₂ (Ta _X Nb ₁ -x) ₂ O ₉ (x
= 0 to 1) Pt is formed as an upper electrode on the film by a sputtering method.

Step 9: After forming the upper electrode, in an oxygen atmosphere,
A heat treatment is performed at 800 ° C. for 10 minutes.

In the above process, a ferroelectric film was formed while paying attention to the following points. In particular, in step 6, 500
Conditions such as raising the temperature in the temperature range from about 40 ° C. to about 700 ° C. at a rate of about 40 ° C./sec, and maintaining the 750 ° C. after the temperature rise at 300 seconds were required. The heat treatment in the final step 9 is performed to stabilize the interface between the ferroelectric and the electrode.

Here, the sputtering method is used for forming the titanium film in the step 1 and the platinum film in the steps 3 and 7. However, the present invention is not limited to this. For example, a CVD method (chemical vapor deposition method) or a vapor deposition method may be used. The thickness of each film is not limited. Step 4
The spin coating method of the present invention does not limit the present invention. For example, dip coating method, LSMCD method (electrodeposition atomization method)
Any method can be used as long as it can control the film thickness of the solution and can apply the solution on the substrate.

Next, FIG. 3 shows the result of measurement of X-ray diffraction (using CuKα ray) of the ferroelectric film formed by the above method. From FIG. 3, it can be seen that the angle is about 29 degrees (inter-plane spacing 29.0
For the peak of the <105> axis of 2Å (± 0.2Å), 3
<110> at around 3 degrees (surface spacing 32.45 ° (± 0.2 °))
It can be seen that the axis peak is more than 1.5 times stronger.

Further, powder SrBi ₂ (Ta _X Nb _{1 -X} ) ₂ O
FIG. 4 shows the result of obtaining the orientation component ratio of the ferroelectric film obtained according to the present embodiment from the peak intensity ratio of the X-ray diffraction image of ₉ (x = 0 to 1). From the figure, <110> axis, <200>
It was found that about 50% of crystal grains containing no c-axis component such as the axis existed.

Next, the result of measuring the ferroelectric characteristics of the ferroelectric film will be described. The ferroelectric characteristics were measured by the Sawyer tower method, and were measured by applying a voltage of 5 V to the ferroelectric capacitor shown in FIG. 1 using the Sawyer tower circuit shown in FIG. In this embodiment, a hysteresis curve is displayed by an oscilloscope using the Sawyer tower bridge shown in FIG.

FIG. 5 will be described in detail. The capacitor C of the reference capacitor connected in series with the ferroelectric capacitor
_R is 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, assuming that the polarization surface charge density of the ferroelectric thin film is P and the true charge surface density is D, (P + ε ₀ E) × A, ie, D ×
A (A is the electrode area) and the charge C stored in the reference capacitor
_Since both _R V _Y are equal to Q, a voltage V _Y = (D × A / C _R ) proportional to D is input to the vertical axis terminal.

In the ferroelectric film, since P is sufficiently larger than εE, it can be considered that D = P. The film thickness of the V _Y -V _X curve is a known quantity, the partial pressure ratio and the electrode area (A), if able to re scale with the capacitance of the reference capacitor (C _R), P
-E (residual spontaneous polarization-electric field) hysteresis curve, or D
-E (accumulated charge-electric field) hysteresis curve was obtained. From this, residual spontaneous polarization (Pr), coercive electric field (Ec), accumulated electric charge
Each value of (ΔQ) can be read.

When the characteristics of the ferroelectric film according to the present invention were evaluated using the Sawyer tower method, a hysteresis curve as shown by a circle in FIG. 6 was obtained (Bi22 line). 5V
Was ² μC / cm ² or more, 2Ec was 132 kV / cm or more, and ΔQ was 28 μC / cm ² or more.

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. When the film was formed by the same process as that of the embodiment, the peak intensity of the <110> axis was <10.
5> It was found that the peak intensity was weaker than the axis. It was also found that the c-axis components such as the <006> axis and the <0010> axis were strong.

Thus, the effect of the difference in the orientation component between the present 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 μm.
C / cm ² or less, 2Ec is 125 kV / cm or more, Δ
Q is 23 μC / cm ² or less.
It was found that the characteristics were lower than those in the case of (1).

From further detailed examination, it was found that the <110> axial strength / <105> when the bismuth composition was changed.
It was found that the axial strength ratio was high when the bismuth composition ratio was between 20 and 24, and especially the highest around 21 and 23. Also,
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.

Next, without adding niobium, the sintering conditions were as follows: the temperature reached in step 6 was 800 ° C., the maintenance time was 12 seconds,
When the maintenance time of the uppermost layer at 800 ° C. is 8 minutes, the film thickness is 1
FIG. 7 shows the speed dependence of the <110> axis strength / <105> axis strength ratio when the temperature range from 500 ° C. to 700 ° C. was heated at a rate of 1 to 40 ° C./sec under the condition of 50 nm. FIG. 8 shows the speed dependence of ΔQ. With these, the <110> axis /
It was found that the <105> axial strength ratio was high, and that ΔQ increased with the temperature increase rate.

FIG. 9 shows the dependence of the signal-to-noise ratio and Ec on the heating rate. From this, it was found that the signal-to-noise ratio increased and Ec decreased as the heating rate increased. In other words, it can be said that when the temperature rise rate is increased, when the capacitor of the present invention is used for a semiconductor device, low-voltage driving can be performed.

Further, from a more detailed study, it is
It has been found important to pass through a temperature range around 650 ° C. at a speed higher than 5 ° C./sec. However, when the substrate was heated at a very high temperature rising rate, for example, 200 ° C./sec or more, warpage of the substrate due to thermal shock was observed, and it was found that the region where a good film could be obtained was 5 to 200 ° C./sec. Was.

In the above embodiment, the film thickness after crystallization for each coating was reduced to less than 30 nm, but this film thickness was gradually increased to a thickness of about 37 to 39 nm.
(The other conditions were the same), the peak intensity on the <110> axis decreased. FIG. 10 shows the X-ray diffraction image. FIG. 10 clearly shows that the peak of the <110> axis has decreased. Conversely, the intensity of the <00 10 > axis, which is the c-axis component around 36 degrees, increased.
Accordingly, ΔQ also became a low value of about 19 μC / cm ² .

Next, platinum is directly placed on the titanium substrate.
In the formed one, SrBi_TwoTa_TwoO ₉Shape the membrane in the manner described above
As a result, the peak component of the <110> axis decreases, and 2P
r also became a low value.

Further, SrBi ₂ (Ta _X Nb _{1 -X} ) ₂ O ₉ (x =
0-1) The metal film between the film and the Si oxide film is Ir / TaSi
The peak component of <110> was reduced even when other materials such as N and Ir / TiN were used. However, it exhibited better ferroelectric characteristics than the conventional film forming method. For example, when the film forming method according to the present invention was formed on Ir / TaSiN at a low temperature of 700 ° C., the <110> peak component was reduced as compared with that on platinum, but a good ΔQ of 17 μC / cm ² or more was obtained. Could be obtained.

From the above results, SrBi_Two(Ta_XN
b_1-X)_TwoO₉(x = 0 to 1) The film thickness is controlled by controlling the orientation component of the film.
In order to grow the a and b axis components in the directions, SrBi
_Two(Ta_XNb _1-X)_TwoO₉(x = 0 to 1) is preferably
It is formed on a substrate on which tin and platinum are stacked.

SrBi ₂ (Ta _X Nb _{1 -X} ) ₂ O ₉ (x = 0 to 0)
A solution prepared by using strontium, bismuth, tantalum, niobium alkoxide or an organic metal salt as a raw material solution component of 1), and adjusting (tantalum + niobium) to 20 so that bismuth becomes an excess of 20 to 24 is used. Make it. The above-mentioned raw material solution is applied so that the film thickness of SrBi ₂ (Ta _X Nb ₁ -x) ₂ O ₉ (x = 0 to 1) after crystallization becomes 35 nm or less.

After coating, a drying step, SrBi ₂ (Ta _X
When Nb _1-X ) ₂ O ₉ (x = 0 to 1) is heated and crystallized, 55
Including all steps such as raising the temperature in a temperature range of 0 to 650 ° C. at a rate of 10 ° C./sec or more, SrBi ₂ (Ta _X N
It has been found that it is important to repeat the steps from the solution application until b _1-X ) ₂ O ₉ (x = 0 to 1) has a desired film thickness.

As described above, according to the present embodiment, SrBi ₂ (Ta _X Nb ₁ -x) ₂ O ₉ (x = 0) according to the formation method of the present invention.
~ 1) The film shows a structure not obtained in the prior art, which is said to have the highest a and b axis components, for example, <110> axis orientation strength, from which a high ferroelectric property can be obtained. Was also higher than the conventional one.

Next, a sectional view of an example of a nonvolatile memory having a planar structure in which a ferroelectric thin film formed according to the present invention is applied to a ferroelectric capacitor according to the present invention as shown in FIG. 11 is shown.

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. MIS transistor (insulated gate field effect transistor) 8 is formed between drain regions 9 and 10. Further, an interlayer insulating layer 11 made of, for example, SiO ₂ or BPSG (boron phosphorus silicate glass) is formed on the MIS transistor 8.

Then, the buffer layer 3 is formed on the interlayer insulating layer 11 on the element isolation insulating layer 7. This buffer layer 3 is constituted by a titanium oxide layer. The SrBi ₂ formed according to the present invention on the lower electrode 4
A Ta ₂ O ₉ ferroelectric layer 5 is formed, and a platinum upper electrode 6 is formed thereon. Thus, a large-capacity ferroelectric capacitor is formed by the lower electrode 4, the ferroelectric layer 5, and the upper electrode 6.

Further, an upper insulating layer 12 is formed on the entire surface including the upper electrode 6, and contact holes are formed in the upper insulating layer 12, for example, on the upper electrode 6 and on the source region 9 of the interlayer insulating layer 11. 13 are formed, and the upper electrode 6 and the source region 9 are in contact with each other by the wiring 14 through the contact holes 13.

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. In addition, since the semiconductor device has a high signal-to-noise ratio and a saturation characteristic, the semiconductor device has low power consumption.

Here, the formed substrate is not particularly limited as long as it can be used as a substrate of a semiconductor device or an integrated circuit. For example, a semiconductor substrate such as silicon, a compound semiconductor substrate such as GaAs, MgO
It can be selected depending on the type and use of the element to be formed, such as an oxide crystal substrate such as a glass substrate, a glass substrate, etc. Among them, a silicon substrate is preferable.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
Embodiments will be described with reference to the drawings. Figure 1
FIG. 2 is a schematic cross-sectional view of a ferroelectric capacitor 30 having a strontium-bismuth tantalate-bismuth ferroelectric film 35 formed according to an embodiment of the present invention.

As shown in FIG. 12, a 200 nm-thick silicon thermal oxide film 32 is formed on the surface of a silicon single crystal substrate 31.
Is formed thereon, and a titanium oxide film 33 (adhesive layer) having a thickness of about 20 nm and a platinum film 34 having a thickness of about 200 nm are formed thereon.
(Lower electrode layer) is formed, and a ferroelectric thin film 35 and an upper electrode layer 36 are formed as described below.

The ferroelectric thin film 35 is formed by ferroelectric
MOD including film forming process using precursor material solution of body material
(Metal organic deposition) method was used. This
In the precursor raw material solution of the MOD method of
Nthalethoxide (Ta (OC _TwoH_Five)_Five), 2-ethylhexa
Bismuth acid (Bi (C₇H_FifteenCOO)_Two), And 2-ethyl
Strontium hexanoate (Sr (C₇H_FifteenCOO)_Two)
And synthesized this.

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.

Step 1: Silicon single crystal (100) plane substrate 3
On the substrate 1, a silicon thermal oxide film 32, a titanium oxide film 33, and a platinum electrode 34 are sequentially formed.

Step 2: A raw material solution for the ferroelectric film 35 is applied on the platinum electrode 34 on the substrate 31 by spin coating.

Step 3: The substrate 31 is placed on a hot plate set at a temperature of 250 ° C. under atmospheric pressure for 4 minutes and dried.

Step 4: RTA (Rapid Thermal Anneal)
The substrate 31 is crystallized by heating the substrate 31 in an oxygen atmosphere at a temperature of 800 ° C. for 30 seconds using the ing) method.

Step 5: Steps 2 to 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.

Step 6: Platinum is formed as the upper electrode 36 on the ferroelectric film 35 made of a strontium bismuth tantalate film.

Step 7: After forming the upper electrode 36, heat treatment is performed at 800 ° C. for 10 minutes in an oxygen atmosphere.

The heat treatment in the final step 7 is performed to stabilize the interface between the ferroelectric film 35 and the upper electrode 36.

The coating in the above step 2 is not limited to the spin coating method. For example, the thickness of the solution can be controlled by a dip coating method, an LSMCD method (electrodeposition atomization method), and the like. Any method can be used as long as it can be applied on the surface 31. Further, the heat treatment temperature and time in the above steps 3, 4, 5, and 7 are not limited to the above-mentioned values, and may be any values as long as the purpose of each step can be satisfied.

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 the step 2 was changed so that the ratio of strontium: bismuth: tantalum was 8:
The adjustment was made to be 22:20. In the spin coating in the step 2, the thickness of one layer after crystallization is set to 3
It was adjusted to be about 0 nm. Steps 4 and 5
In the heat treatment step, the heating rate in a temperature region from 550 ° C. to 650 ° C. where crystallization is considered to be started was adjusted to 40 ° C./sec.

The results of measurement of X-ray diffraction images (using CuKα rays) of the first, fifth, and ninth layers of the strontium-bismuth tantalate film 35 thus formed are shown in FIG. FIG.

In FIG. 13, for easy viewing,
The intensity of the diffraction image when the number of layers is the first layer is tripled. In the first layer, the peak intensity on the <110> axis was 50% or less of the peak intensity on the <105> axis, and a diffraction image similar to that of the conventional random-oriented strontium-bismuth tantalate film was shown. .

However, as the number of layers increases, <110>
It was found that the peak of the axis increased preferentially, and in the ninth layer, the peak of the <110> axis increased more than twice the peak of the <105> axis.
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> -axis dominant as the film thickness increases. .

FIG. 15 shows that the angle is around 33 degrees (the surface interval is 32.degree.).
The peak intensity of the <110> axis at 45 ° (± 0.2 °)
The axis peak intensity ratio divided by the <105> axis peak intensity near the degree (plane spacing 29.02Å (soil 0.2Å)) is calculated as follows: the number of stacked strontium / bismuth tantalate films 35 is 1 to 9 The following is shown. It can be seen that the axial peak intensity ratio increases sequentially as the number of layers increases.

Next, FIG. 26 shows a cross-sectional photograph of the strontium-bismuth tantalate film 35 formed by the film forming method of this embodiment, taken by a scanning electron microscope. In the film 35, there are many crystal grains whose grain size increases from the center of the photograph toward the upper side in the film thickness direction on the left side. From further detailed analysis, such crystal grains are found to be <110. > It was found that they were axially oriented. In other words, the strontium-bismuth tantalate film 35 included in the capacitor of this embodiment has more crystal orientation components having the <110> axis orientation in the vicinity of the other electrode 36 that is opposed to the vicinity of the substrate 31 side electrode. There is a feature.

Next, the result of measuring the ferroelectric characteristics of the strontium bismuth tantalate film 35 according to this embodiment will be described. This ferroelectric characteristic was measured by the Sawyer tower method, and was measured by applying a voltage to the ferroelectric capacitor 30 shown in FIG. 12 using a Sawyer tower bridge circuit shown in FIG. . In this embodiment, using the Sawyer tower bridge circuit,
The hysteresis curve was displayed on an oscilloscope.

[0123] Sawyer tower bridge circuit shown in FIG. 17, a capacitor C _R of the ferroelectric capacitor 30 and reference capacitor 71 connected in series are capacitor serving as a reference, the horizontal axis pin 73 of the oscilloscope, the ferroelectric voltage V _X obtained by dividing the applied voltage V to the ferroelectric capacitor 30 is the body thin film device is inputted.

Here, assuming that the polarization surface charge density of the ferroelectric thin film 35 is P and the true charge surface density is D, (P + ε
_o E) × A, that is, D × A (A is an electrode area) and the electric charge C _R V _Y stored in the reference capacitor 71 have the same electric charge amount Q. Therefore, a voltage V _Y = (D × A / C _R ) proportional to D is input to the vertical axis terminal 72.

In the ferroelectric film 35, since P is sufficiently larger than εE, it can be considered that true charge surface density D = polarized surface charge density P. The V _Y -V _X curve, with a thickness which is a known quantity, the partial pressure ratio, the electrode area (A), the capacitance of the reference capacitor (C _R), if fix it graduation, P-E (residual spontaneous Polarization-electric field) hysteresis curve or DE (accumulated charge-
An electric field) hysteresis curve is obtained. From this hysteresis curve, residual spontaneous polarization (P _r ), coercive electric field (E _c ), and accumulated charge
Each value of (ΔQ) can be read.

When the characteristics of the nine-layered ferroelectric film 35 according to this embodiment were evaluated using the Sawyer tower method, a hysteresis curve as shown in FIG. 18 was obtained.
In other words, 2P _r in the electric field intensity 330kV / cm 30
At ² μC / cm ² or more, 2E _c was 112 kV / cm or more, and the accumulated charge ΔQ was 28 μC / cm ² or more.

Also, FIG._rDependence on the number of layers
Show. The number of layers is less than three, that is, the film thickness is 90 nm
If it is thinner, the leakage current density is higher and the hysteresis
Measurement was not possible. However, when the number of layers is three, two
P_rIs 24.6 μC / cm ^TwoAnd the number of layers
It was found that there was an increasing trend with the increase of. Also before
As shown in FIG. 15 described above, even if the number of layers is 10 or more, it is high <110.
> Axial peak intensity is known, but productivity is
Due to low thickness and thick film, cracks occur in the film during the process
It became easier.

From the characteristics shown in FIG. 15 and FIG. 16, when the productivity and the 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 film thickness was in the range of 90 to 270 nm (3 to 9 layers). The peak intensity ratio is defined as the peak intensity of the <110> axis near 33 degrees (plane spacing of 32.45 ° (± 0.2 °)) and 29 degrees (plane spacing of 29.02 ° (± 0.2 °)).
Å)) divided by <105> axis peak intensity.

Next, the strontium / bismuth tantalate film 35 having a thickness of 150 nm (five layers) is formed from 550 ° C. to 650 ° C. in the heat treatment steps 6 and 7 by using the film forming method according to this embodiment. It was prepared by changing the temperature rising rate in a nearby temperature range from 1 to 40 ° C./sec. 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 was 30.
nm.

The prepared strontium tantalate.
The <110> axis intensity / <105> axis intensity ratio of the heating rate dependence of the bismuth films 35, shown in FIG. 21, showing a heating rate dependence of the 2P _r in FIG. 22. From these characteristics, it was found that the intensity ratio of the <110> axis / <105> axis was high in the region where the heating rate was 5 ° C./sec or more, and 2P _r increased with the heating rate. However, a very high heating rate (300 ° C. /
(Seconds), the substrate was warped due to thermal shock. As a result, the temperature rising rate region in which a good strontium bismuth tantalate film can be obtained is 5
３００300 ° C./sec.

From these results, it was found that 550 ° C. to 650 ° C.
The heating rate of the temperature region near, can control the orientation strength of <110> axis was found to be controlled also the value of the residual polarization P _r therewith.

Next, by using the film forming method according to this embodiment, a strontium bismuth tantalate film having a thickness of 150 nm was formed by changing the atomic composition ratio of Bi (bismuth) in the precursor raw material solution from 20 to 24 in increments of 1 from 20. It was made by changing. At this time, the rate of temperature rise in a temperature range from 550 ° C. to 650 ° C. was set to 40 ° C./sec, and the film thickness after crystallization for each coating was set to 30 nm. <110> axial strength / <105> of the prepared strontium bismuth tantalate film
FIG. 19 shows the relationship between the axial strength ratio and the Bi composition ratio in the raw material solution. As shown in FIG. 19, when the atomic composition ratio of Bi is 22, the film has the strongest <110> axis / <10
5> axial strength ratio.

FIG. 20 shows the strontium tantalate.
2P of each sample of Tb / Bm film _rShows the value of this
FIG. 20 shows that the <110> axis strength / <105> axis strength
The sample having a strong Bi composition ratio of 22 has the highest 2P_rThe value
You can see that it is getting. The details are shown here.
Not to change the atomic composition ratio of Bi from 20 to 24
Investigation of the effect of the heating rate revealed that the atomic composition ratio of Bi was 2
At 0, 2P_rAlthough the value increases with the heating rate,
<110> axis strength / <105> axis strength ratio shows change
Was not.

In the X-ray diffraction image, weak fluorite and pyrochlore peaks were observed. Further, B
In the Bi composition ratio 24 where i is excessive, <110> axial strength / <
105> The rate of increase of the axial intensity ratio with the heating rate is lower than in the case where the Bi composition ratio is 22, and in the X-ray diffraction image, a strong bismuth platinum peak is observed, and diffusion of Bi to the platinum electrode is confirmed. Was done.

Although not described in detail here, it was found that when the atomic composition ratio of Sr was changed from 8, the optimum value of the atomic composition ratio of Bi also changed.

For the above reasons, the conditions for obtaining a good film are as follows: the atomic composition ratio Sr: Bi: Ta in the raw material solution
When expressed as X: Y: Z, 1.4 <(X + Y) / Z <1.6.
It turned out that there was a relationship.

[0137] From these results, by controlling the composition ratio of bismuth, it can control the orientation strength of <110> axis, it was found that it is possible to control the value of the residual polarization P _r therewith.

Next, a strontium / bismuth tantalate / tantalate film 35 having a film thickness of 200 nm (± 10 nm) is applied to the film after crystallization for each single-layer coating in Steps 2 to 4 by using the film forming method according to this embodiment. The thickness was changed from 25 nm to slightly less than 50 nm. At this time, 550 ° C to 650 ° C
The heating rate in the vicinity of the temperature range was set to 40 ° C./sec, and the composition ratio of Bi in the precursor raw material solution was set to 22. The dependence on each film thickness of <110> axis intensity / <105> axis intensity ratio of this time, shown in Figure 23, the dependence on each film thickness of the 2P _r, shown in Figure 24.

From FIG. 23, it can be seen that the <110> axis / <105> axis intensity ratio increases as the film thickness of each layer decreases. Further, from FIG. 24, with each layer thickness is decreased, 2P _r also can be seen that increasing. However, it was found that when the film thickness of each layer was smaller than 25 nm, the leak characteristics were reduced. It is considered that the reason for this decrease is that the initial layer grows in a stripe shape.

On the other hand, when the film thickness of each layer was larger than 50 nm, the leak characteristics also deteriorated. It is considered that the reason for the decrease is that crystal nuclei are generated in each layer, and the denseness in the film thickness direction is reduced.
Therefore, a region where a good film can be obtained has a thickness of 25% for each layer.
It was found to be in the range of ５０50 nm.

[0141] From these results, by controlling the thickness of each layer, can control the orientation strength of <110> axis was found to be controlled also the value of the residual polarization P _r therewith.

In the second embodiment, the MO
Even when a strontium-bismuth niobate film was formed by using niobium ethoxide as the starting material in method D and replacing all tantalum with niobium, the same effects as in the above embodiment were obtained. Further, even when a strontium bismuth tantalate niobate film is formed by using niobium ethoxide as a starting material in the MOD method and substituting a part of tantalum with niobium,
The same effect as the above embodiment was obtained.

As described above, according to the method of forming a strontium-bismuth tantalate film of this embodiment, a high ferroelectric property can be obtained from the random-oriented initial layer (first layer). It is possible to preferentially increase the component (eg, <110> axis orientation component). Also,
The component ratio can be controlled by the temperature rise 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 was higher than that.

Next, FIG. 25 shows a cross section of a nonvolatile memory having a planar structure having a ferroelectric capacitor having a ferroelectric thin film formed according to the above embodiment.

This non-volatile memory includes a semiconductor substrate 51,
An element isolation insulating layer 57 formed by local oxidation, so-called LOCOS, is formed, and a source region 59 and a drain region 60 are formed in the region thus separated. An MIS transistor is formed between the source region 59 and the drain region 60. (Insulated gate field effect transistor) 58 is formed. Further, on this MIS transistor 58, for example, SiO ₂ or BPSG (boron
An interlayer insulating layer 61 made of phosphorus silicate glass or the like is formed.

Then, the buffer layer 53 is formed on the interlayer insulating layer 61 on the element isolation insulating layer 57. This buffer layer 53 is composed of a titanium oxide layer. Then, on the lower electrode 54, the strontium bismuth tantalate-bismuth ferroelectric layer 55 formed according to the above embodiment is formed.
Is formed, and a platinum upper electrode 56 is formed on the ferroelectric layer 55.
To form Thereby, the lower electrode 54 and the ferroelectric layer 5
5 and a large-capacity ferroelectric capacitor 5 composed of an upper electrode 56
0 is configured.

Further, an upper insulating layer 62 is formed on the entire surface including the upper electrode 56, and, for example, the source region 5 of the upper insulating layer 62 on the upper electrode 56 and the interlayer insulating layer 61 is formed.
9, a contact hole 63 is formed, and the upper electrode 56 and the source region 59 are in contact with each other by a wiring 64 through the contact holes 63.

The nonvolatile memory manufactured in this manner uses a ferroelectric capacitor having a high accumulated charge amount ΔQ, so that the capacitor area can be reduced. Therefore, it is advantageous for high integration. Further, since the semiconductor device has a high signal-to-noise ratio and a saturation characteristic, the semiconductor device has low power consumption.

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, an integrated circuit, or the like. For example, a semiconductor substrate such as silicon, a compound semiconductor substrate such as GaAs, an oxide crystal substrate such as MgO, a glass substrate, and the like can be selected according to the type and use of the element to be formed. Among them, a silicon substrate is preferable.

[0150]

As is clear from the above, in the ferroelectric capacitor of the present invention, the ferroelectric film formed between the pair of electrodes has a thickness direction in the X-ray diffraction image using CuKα ray. Mainly, surface spacing 29.02Å (± 0.2Å) and surface spacing 3
SrBi ₂ (Ta having a peak value at 2.45 ° (± 0.2 °)
_{X Nb 1-X) 2 O} 9 (x = 0~1) is a ferroelectric film. With a configuration like the ferroelectric capacitor of the present invention, it is possible to obtain a large ferroelectric characteristic, and it can be suitably used as a part of an integrated circuit element formed on a substrate.

In one embodiment of the ferroelectric capacitor, the ferroelectric film has a peak intensity in an X-ray diffraction image using CuKα radiation of 29.02 ° (±
When the peak value of 0.2%) is taken as 100%, the surface spacing is 3
This is a SrBi ₂ (Ta _X Nb ₁ -x) ₂ O ₉ (x = 0 to 1) ferroelectric film having a peak value of 2.45 ° (± 0.2 °) of 80 to 300%. According to the ferroelectric capacitor of the second aspect, it is possible to obtain a larger ferroelectric characteristic.

Further, a ferroelectric capacitor of another embodiment
Then, the ferroelectric film is made of SrBi _Two(Ta_XNb_1-X)_TwoO
₉(x = 0 to 1) is a columnar structure. Invitation of this embodiment
According to the electric capacitor, a larger ferroelectric property is obtained.
be able to.

In one embodiment, a method of manufacturing a ferroelectric film includes a step of forming a metal film on a substrate, an alkoxide or an organic metal salt of two elements of strontium and bismuth and at least one of tantalum or niobium. Preparing a raw material solution, applying the solution to a substrate, applying the solution to the substrate, drying the solution, and heating the solution to a crystallization temperature or higher. Is repeated until the metal film on the substrate has a predetermined thickness, so that SrBi ₂ (Ta _X Nb _{1 -X} ) ₂ O ₉ (x = 0-1)
A method for forming a ferroelectric film, wherein the step of heating the solution to a temperature higher than the crystallization temperature includes adjusting a heating rate in a temperature region around 550 to 650 ° C. and adjusting a composition ratio of bismuth in the raw material solution. By performing at least one adjustment, the orientation components of the a and b axes of the SrBi ₂ (Ta _X Nb ₁ -x) ₂ O ₉ (x = 0 to 1) ferroelectric film are controlled.

In the manufacturing method of this embodiment, SrBi
_{The 2} (Ta _X Nb _1-x ) ₂ O ₉ (x = 0 to 1) film is a conventional film which is said to have the highest a- and b-axis components, for example, <110> -axis orientation strength, at which high ferroelectric properties can be obtained. In this case, a structure that could not be seen was shown, and the ferroelectric characteristics of the capacitor using the structure were higher than those of the conventional one.

In the method of manufacturing a ferroelectric film according to another embodiment, the temperature rise rate in the temperature range around 550 to 650 ° C. is adjusted within a range of 5 to 200 ° C./sec. In this embodiment, high ferroelectric characteristics can be obtained while suppressing warpage of the substrate.

In one embodiment of the method of manufacturing a ferroelectric film, in the step of applying the solution to the substrate, when the solution applied to the substrate is (tantalum + niobium) = 20, the bismuth is 20 to In the step of preparing the raw material solution, the composition ratio of bismuth is adjusted so that 24 is excessive. In this embodiment, particularly, high ferroelectric characteristics were obtained.

In the method of manufacturing a ferroelectric film according to another embodiment, the raw material solution is applied to the substrate such that the metal film thickness after crystallization formed on the substrate is 35 nm or less. . In this embodiment, when the thickness of the metal film formed on the substrate after crystallization is 35 nm or less, the ferroelectric characteristics increase as the film thickness increases.

In one embodiment of the method of manufacturing a ferroelectric film, the uppermost part of the metal film formed on the substrate is a platinum layer. In this embodiment, particularly high ferroelectric characteristics were obtained because the platinum layer was the uppermost part of the metal film formed on the substrate.

In the semiconductor device according to another embodiment, the capacitor is used as a part of an integrated circuit element formed on a substrate. Since the semiconductor device of this embodiment uses the above-described capacitor having high ferroelectric characteristics, high integration is possible.

The ferroelectric capacitor of one embodiment is a ferroelectric capacitor having at least a pair of electrodes and a ferroelectric film on a substrate, wherein the ferroelectric capacitor formed between the pair of electrodes is provided. The X-ray diffraction image of the film in the thickness direction using CuKα radiation in the vicinity of the other electrode opposed to the vicinity of the substrate-side electrode showed a surface spacing of 32.45 ° (± 0.
2Å) strontium bismuth tantalate, strontium bismuth niobate having a crystal orientation component,
Or a ferroelectric film of a solid solution thereof. The capacitor of this embodiment has many crystal components oriented in the direction of the polarization axis, and can exhibit high ferroelectric characteristics. Therefore, it can be suitably used as a part of an integrated circuit element formed on a substrate.

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 capacitor is formed between the pair of electrodes. When the body film has a peak intensity in the X-ray diffraction image using CuKα radiation of 29.02 ° (±
When the peak value of 0.2%) is set to 100%, the surface spacing is 3
Strontium bismuth tantalate, strontium bismuth niobate, or a solid solution thereof having a peak value of 2.45 ° (± 0.2 °) in the range of 80 to 230% and a film thickness of 90 to 270 nm. It is a dielectric film. The capacitor of this embodiment has many crystal components oriented in the direction of the polarization axis, and can exhibit high ferroelectric characteristics. Furthermore, mass productivity is high.

In one embodiment of the present invention, a method of manufacturing a ferroelectric film includes a step of forming a metal film on a substrate, an alkoxide or an organic metal salt of two elements of strontium and bismuth and at least one of tantalum and niobium. A step of preparing a raw material solution, a step of applying the solution to the substrate, and a step of drying the substrate after the application, and at a crystallization temperature or higher,
Heating the substrate, the steps from the solution application to the substrate heating, by repeating until the metal film on the substrate has a predetermined thickness, strontium bismuth tantalate on the substrate, A method for forming a ferroelectric film of strontium bismuth niobate or a solid solution thereof, wherein the step of heating to a temperature equal to or higher than the above-mentioned crystallization temperature adjusts the atomic composition ratio in the raw material solution;
By adjusting at least one of the adjustment of the temperature rising rate in the temperature region near 50 ° C. and the adjustment of the film thickness formed in one process, the orientation of the plane spacing of 32.45 ° (± 0.2 °) is achieved. Control the ingredients. According to the manufacturing method of this embodiment, in the ferroelectric film formed by applying, drying, and heating the raw material solution, a crystal component oriented in the polarization axis direction is preferentially grown from the randomly oriented first layer. Can be done.

In the method of manufacturing a ferroelectric film according to another embodiment, the temperature rise rate in the temperature range around 550 to 650 ° C. is adjusted to a range of 5 to 300 ° C./sec. According to the manufacturing method of this embodiment, in the ferroelectric film formed by applying, drying and heating the raw material solution,
Crystal components oriented in the polarization axis direction can be preferentially grown from the randomly oriented first layer.

In one embodiment of the method for manufacturing a ferroelectric film, the atomic composition ratio Sr: Bi: (Ta
+ Nb) = X: Y: Z, where 1.4 <(X + Y) / Z <1.6
It is. According to this embodiment, a crystal component oriented in the polarization axis direction can be preferentially grown from the random oriented first layer.

In the method of manufacturing a ferroelectric film according to another embodiment, the step of applying the raw material solution to the substrate is such that the thickness after crystallization is 25 to 50 nm in one application step. Then, the above-mentioned raw material solution is applied. This claim 15
According to the manufacturing method of (1), the crystal component oriented in the polarization axis direction can be preferentially grown from the randomly oriented first layer.

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 polarization axis direction can be preferentially grown from the randomly oriented first layer.

In a semiconductor device according to another embodiment, the ferroelectric capacitor is used as a part of an integrated circuit element formed on a substrate. The semiconductor device according to this embodiment includes:
Since a capacitor having high ferroelectric characteristics is used, high integration is possible.

As described above, according to the present invention, SrBi ₂ (Ta _X
Since the <110> axis of Nb _1-X ) ₂ O ₉ (x = 0 to 1) is preferentially oriented in the film thickness direction, high ferroelectric characteristics can be obtained when a capacitor is formed. Further, a semiconductor device using this capacitor, for example, a non-volatile memory can be highly integrated and driven at a low voltage.

[Brief description of the drawings]

FIG. 1 is a schematic 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 the 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 an orientation component ratio of the ferroelectric film according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a Sawyer tower bridge used for measuring 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 diagram showing a heating rate dependency of a <110> intensity and a <105> intensity ratio in the first embodiment.

FIG. 8 is a diagram showing a temperature rise rate dependency of an accumulated charge amount ΔQ in the first embodiment.

FIG. 9 is a diagram showing the dependency of the signal-to-noise ratio and the coercive electric field Ec on the heating rate in the first embodiment.

FIG. 10 is an X-ray diffraction image of the ferroelectric film of the embodiment according to the present invention and a ferroelectric film of a comparative example.

FIG. 11 is a fragmentary cross-sectional view showing a schematic structure of the semiconductor device of the embodiment.

FIG. 12 is a schematic sectional view of a main 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 the ferroelectric film according to the second embodiment of the present invention.

FIG. 14 is a process chart illustrating a process of manufacturing a ferroelectric film according to a second embodiment of the present invention.

FIG. 15 is a diagram showing the dependence of the <110> intensity and <105> intensity ratio on the number of layers in the second embodiment.

[16] In the second embodiment, showing the stacking number dependence of the 2P _r.

FIG. 17 is a diagram showing a Sawyer tower bridge circuit used for measuring 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 dependency of the <110> intensity / <105> intensity ratio in the second embodiment.

[20] In the second embodiment, the 2P _r Bi
It is a figure which shows a composition ratio dependency.

FIG. 21 is a diagram showing a heating rate dependency of a <110> intensity / <105> intensity ratio in the second embodiment.

[22] In the second embodiment, showing a heating rate dependence of the 2P _r.

FIG. 23 is a diagram showing the dependence of <110> intensity / <105> intensity ratio on each layer thickness in the second embodiment.

FIG. 24 is a diagram showing the dependency of 2P _r on each layer thickness in the second embodiment.

FIG. 25 is a fragmentary cross-sectional view showing a schematic structure of a semiconductor device having the second embodiment.

FIG. 26 is a cross-sectional photograph of the ferroelectric film according to the second embodiment of the present invention taken by a scanning electron microscope.

[Explanation of symbols]

DESCRIPTION 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, 3
0,50: 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, 5
DESCRIPTION OF SYMBOLS 1 ... 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.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F038 AC05 AC15 AC17 AC18 EZ14 EZ17 EZ20 5F083 AD14 FR02 GA12 JA13 JA17 JA35 JA38 JA39 JA40 PR23 PR33 PR34

Claims (17)

[Claims] 1. 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 CuKα.
In the X-ray diffraction image using X-rays,
SrBi ₂ (Ta _X Nb _{1 -X} ) ₂ O ₉ (x = ₁₀ ) showing peak values at 9.02 {± 0.2} and at a spacing of 32.45 ± 0.2 °
0-1) A ferroelectric capacitor characterized by being a ferroelectric film. 2. The ferroelectric capacitor according to claim 1, wherein the ferroelectric film has a peak intensity in an X-ray diffraction image using CuKα radiation of 29.02Å ± 0 in a film thickness direction. .2Å peak value of 100
%, SrBi ₂ (Ta _X Nb ₁ -x) ₂ O having a peak value of 80 to 300% at a spacing of 32.45 ° ± 0.2 °.
₉ (x = 0-1) Ferroelectric capacitor characterized by being a ferroelectric film. 3. The ferroelectric capacitor according to claim 1, wherein the ferroelectric film is made of SrBi ₂ (Ta _X Nb ₁ -x) ₂ O ₉ (x =
A ferroelectric capacitor wherein 0-1) has a columnar structure. 4. A step of forming a metal film on a substrate; a step of forming a raw material solution of an alkoxide or an organic metal salt of two elements of strontium and bismuth and at least one of tantalum and niobium; A step of coating the metal film on the substrate; a step of drying the solution applied to the metal film on the substrate; and a step of heating the solution to a crystallization temperature or higher. Are repeated until the film made of the solution reaches a predetermined film thickness, so that SrBi ₂ (Ta _X Nb ₁ -x) ₂ O ₉ (x = 0 to ₁ ) is formed on the substrate.
A method of manufacturing a ferroelectric capacitor for forming a ferroelectric film, comprising: a step of heating the solution to a temperature equal to or higher than a crystallization temperature;
By adjusting at least one of the rate of temperature rise in the temperature range of 650 ° C. and / 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 manufacturing a ferroelectric capacitor, comprising controlling the magnitude of the orientation components of the a and b axes of the ferroelectric film. 5. The method for manufacturing a ferroelectric capacitor according to claim 4, wherein the temperature increase rate in the adjustment of the temperature increase rate in the temperature range of 550 to 650 ° C. is in the range of 5 to 200 ° C./sec. A method for manufacturing a ferroelectric capacitor, comprising: 6. The method for manufacturing a ferroelectric capacitor according to claim 4, wherein in the step of applying the solution to the substrate, the solution applied to the substrate has an atomic composition ratio of (tantalum + niobium) of 20. A method of manufacturing a ferroelectric capacitor, comprising adjusting the atomic composition ratio of bismuth in the step of preparing the raw material solution so that the atomic composition ratio of bismuth is 20 to 24. 7. The method of manufacturing a ferroelectric capacitor according to claim 4, wherein the metal film formed on the substrate after crystallization has a thickness of 35 n.
m. The method of manufacturing a ferroelectric capacitor, wherein the raw material solution is applied onto the substrate so that the thickness is equal to or less than m. 8. The method for manufacturing a ferroelectric capacitor according to claim 4, wherein an uppermost part of the metal film formed on the substrate is a platinum layer. A method for manufacturing a dielectric capacitor. 9. A semiconductor device using the ferroelectric capacitor according to claim 1, as a part of an integrated circuit element formed on a substrate. 10. A ferroelectric capacitor comprising at least a pair of electrodes and a ferroelectric film on a substrate, wherein the ferroelectric film formed between the pair of electrodes comprises strontium bismuth tantalate, niobium. It is a ferroelectric film of strontium bismuth acid or a solid solution thereof. The ferroelectric film is formed by using CuKα radiation in a region on the other counter electrode side compared to a region on the substrate side electrode side. A ferroelectric capacitor characterized in that, in an X-ray diffraction image in a film thickness direction, a crystal orientation component having a plane spacing of 32.45 ° (± 0.2 °) is large. 11. A ferroelectric capacitor comprising at least a pair of electrodes and a ferroelectric film on a substrate, wherein the ferroelectric film formed between the pair of electrodes comprises strontium bismuth tantalate, niobium. It is a ferroelectric film of strontium bismuth acid or a solid solution thereof, the thickness of which is in the range of 90 to 270 nm, and the peak intensity in an X-ray diffraction image using CuKα radiation is represented by a plane spacing in the film thickness direction. The peak value of 29.02Å ± 0.2Å is 100
%, Wherein the peak value at a plane spacing of 32.45 ° ± 0.2 ° is in the range of 80 to 230%. 12. A step of forming a metal film on a substrate; a step of preparing a raw material solution of an alkoxide or an organic metal salt of two elements of strontium and bismuth and at least one of tantalum and niobium; And a step of drying the solution applied to the substrate, and a step of heating the substrate to a temperature equal to or higher than the crystallization temperature of the raw material solution. The steps from the solution application to the substrate heating, A ferroelectric capacitor for forming a ferroelectric film of strontium-bismuth tantalate, strontium-bismuth niobate, or a solid solution thereof on the substrate by repeating until the film made of the raw material solution has a predetermined thickness. Adjusting the atomic composition ratio in the raw material solution in the step of preparing the raw material solution, and adjusting the atomic composition ratio to not less than the crystallization temperature. At least one of the adjustment of the heating rate in the temperature range of 550 to 650 ° C. in the heating step and the adjustment of the film thickness formed in one step from the solution application to the substrate heating is performed. As a result, the surface spacing of the ferroelectric film is 32.45 ° (± 0.4 mm).
2)) A method for manufacturing a ferroelectric capacitor, wherein the magnitude of the orientation component is controlled. 13. The method for manufacturing a ferroelectric capacitor according to claim 12, wherein the rate of temperature rise in the temperature range of 550 to 650 ° C. is 5 to 3.
A method for producing a ferroelectric material, wherein the temperature is set in the range of 00 ° C./sec. 14. The method for manufacturing a ferroelectric capacitor according to claim 12, wherein the atomic composition ratio Sr: Bi: (Ta + Nb) in the raw material solution.
= X: Y: Z satisfies 1.4 <(X + Y) / Z <1.6. 15. The method for manufacturing a ferroelectric capacitor according to claim 12, wherein the step of applying the raw material solution to the substrate is such that the film thickness after crystallization is 25 to 50 in one application step.
A method for manufacturing a ferroelectric capacitor, which comprises applying the raw material solution so as to have a thickness of nm. 16. The method for manufacturing a ferroelectric capacitor according to claim 12, wherein a main component of the metal film formed on the substrate is platinum. 17. A semiconductor device, wherein the ferroelectric capacitor according to claim 10 is used as a part of an integrated circuit element formed on a substrate.