JP2001127266A - Method for manufacturing ferroelectrics thin film, ferroelectrics capacitor, ferroelectrics memory cell and manufacturing method for ferroelectrics memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a laminar ferroelectrics thin film of non-c-axis orientation. SOLUTION: The manufacturing method for a ferroelectrics thin film comprises a process where a ferroelectrics thin film 13 having a laminar structure of random orientation is formed on the surface of a conductive layer 12 where at least a surface comprises a globular crystal structure. The ferroelectrics thin film is formed by providing, on its surface, a precursor solution containing an organic metal compound which comprises a small amount of at least one element among Mn, La, Ce, and Dy before sintered at 700 deg.C or below. The thin film is formed on a lower part electrode having a globular crystal structure at its surface to form a ferroelectrics capacitor or ferroelectrics memory.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ferroelectric thin film, and to a ferroelectric capacitor and a ferroelectric memory cell. In particular, the present invention relates to a method for manufacturing a ferroelectric thin film used as a capacitance insulating film of a ferroelectric memory.

[0002]

2. Description of the Related Art In recent years, research and development on ferroelectric thin films having spontaneous polarization characteristics have been actively conducted in order to realize a non-volatile memory capable of low-voltage operation and high-speed writing. Among ferroelectric materials, low melting point metal oxides containing lead or bismuth have been generally studied, and a layered structure ferroelectric, particularly, a bismuth layered structure ferroelectric has attracted attention.

The basic structure of a layered structure ferroelectric is represented by the following formula (I)
Shown in

(S ₂ O ₂ ) ₂ + (A _{m -1} B _m O _{3m +1} ) ₂ -Formula (I) A layered structure such as Bi or Tl is formed at the S site in Formula (I). Contains a trivalent cation or a combination thereof. On the other hand, site A contains Na, Sr, Pb, Bi,
Monovalent to trivalent cations such as Ba, Ca, La and the like or a combination thereof are included. Site B contains Ti, T
A tetravalent or pentavalent cation such as a, Nb, Zr, Mo, W, or a combination thereof is included. m is typically an integer from 1 to 5. However, the characteristics may be improved by intentionally combining compositions having different m values arbitrarily. For example, by combining the composition of m = 1 with the composition of m = 1, the distance between layers can be arbitrarily changed.

Since such a layered structure ferroelectric has a layered structure, it is less likely to be degraded due to polarization reversal, and can operate at a low voltage, and therefore has excellent characteristics as a memory capacitor film. Have. In particular, a bismuth layered structure ferroelectric containing Bi at the S site can be formed at a relatively low temperature because of the presence of a low melting point metal bismuth. For example, 800 ° C. is used for SrBi ₂ Ta ₂ O _9.
A degree of heat treatment is usually performed. However, in order to realize a more miniaturized semiconductor process, it is required to further lower the temperature of the heat treatment. For example, in order to realize a highly integrated memory of megabits or more, realization of a stacked memory cell structure is indispensable. When this stacked memory cell structure is executed, a reaction between an electrode and a plug is prevented. From the viewpoint of the heat resistance of the barrier layer (for example, an iridium oxide layer), it is essential to perform a heat treatment at a low temperature of 650 to 700 ° C.

As a method of forming a ferroelectric thin film, generally, a spin coating method using a thermal decomposition method or a sol-gel method is widely used. The law is promising. The sol-gel method is
Since a thin film is formed by using a solution containing a highly reactive metal alkoxide and causing crystallization via a condensation polymerization reaction by hydrolysis, low-temperature formation is possible.

[0007]

However, when a bismuth layer-structured ferroelectric thin film is formed by using the above-mentioned conventional sol-gel method, most of the obtained film is finally oriented along the c-axis. A bismuth layered structure ferroelectric thin film usually has a polarization component in the a-axis and b-axis planes, and has only zero or a small polarization component in the c-axis direction. Therefore, this c
When a capacitor (ferroelectric capacitor) is manufactured using a ferroelectric thin film oriented in an axis, a spontaneous polarization sufficient to guarantee the operation as a nonvolatile memory cannot be obtained.

The present invention has been made in view of the above points, and a main object of the present invention is to provide a method for producing a non-c-axis oriented layered structure ferroelectric thin film using a sol-gel method.

[0009]

According to a method of manufacturing a ferroelectric thin film according to the present invention, a ferroelectric thin film having a layer structure of random orientation is formed on at least the surface of a conductive layer having a spherical crystal structure. The step of performing

It is preferable that the step of forming the ferroelectric thin film includes a step of applying a precursor solution containing an organometallic compound on the surface of the conductive layer and firing the conductive layer.

The organometallic compound is preferably an organometallic compound containing two or more metal atoms in one molecule.

In the step of forming the ferroelectric thin film, 70
It is preferable to perform the process at a temperature of 0 ° C. or lower. 650 ° C
It is more preferred that:

The ferroelectric thin film having the layered structure is preferably a ferroelectric thin film having a bismuth layered structure.

[0014] The ferroelectric thin film having a bismuth layer structure may contain a small amount of at least one element selected from the group consisting of Mn, La, Ce and Dy.

A ferroelectric capacitor according to the present invention comprises: a lower electrode having at least a surface having a spherical crystal structure; and a capacitance insulating film formed on the surface of the lower electrode.
The capacitor insulating film has a layer structure of random orientation obtained by applying a precursor solution containing an organometallic compound containing two or more metal atoms in one molecule on the surface of the lower electrode and firing the solution. And a ferroelectric thin film.

Another ferroelectric capacitor according to the present invention comprises:
A lower electrode having at least a surface having a spherical crystal structure; and a capacitive insulating film formed on the surface of the lower electrode, wherein the capacitive insulating film has a temperature of the lower electrode of 700 ° C.
It is formed of a ferroelectric thin film formed in the following state and having a layer structure of random orientation.

A ferroelectric memory according to the present invention includes a substrate on which a semiconductor integrated circuit is formed, and a ferroelectric capacitor formed on the substrate.
The ferroelectric capacitor includes a lower electrode having at least a surface having a spherical crystal structure, and a capacitor insulating film formed on the surface of the lower electrode and formed of a ferroelectric thin film having a layer structure of random orientation. And the ferroelectric capacitor has a stack type structure.

The method for manufacturing a ferroelectric memory according to the present invention includes a step of forming a ferroelectric thin film having a layer structure of random orientation on the surface of the conductive layer having at least a surface having a spherical crystal structure.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors surprisingly found that when a bismuth layered structure ferroelectric thin film was formed on a platinum electrode having a spherical crystal structure by a sol-gel method, the c-axis orientation was not achieved. The present inventors have found that a ferroelectric thin film having a bismuth layer structure having a random orientation can be obtained, and have arrived at the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, components having substantially the same function are denoted by the same reference numeral for the sake of simplicity. Note that the present invention is not limited to the following embodiments. (Embodiment 1) Embodiment 1 according to the present invention will be described with reference to FIGS. 1 (a) to 1 (c). FIG. 1 (a)-
(C) is a step sectional view for illustrating the method for manufacturing a ferroelectric thin film in the present embodiment.

First, as shown in FIG. 1A, a support substrate 11 is prepared. In this embodiment, as a supporting substrate, a thermal oxide layer (100 nm) and a titanium oxide layer (1
00 nm) is sequentially formed.

Next, as shown in FIG. 1B, a platinum electrode (conductive layer) 12 is formed by a sputtering method.
The platinum electrode 12 is a conductive layer having a spherical crystal structure at least on the surface (typically, a conductive layer having a spherical crystal structure as a whole).

The sputtering for forming the platinum electrode 12 is typically performed in an argon gas atmosphere.
In this embodiment, in an active gas atmosphere in which 4% oxygen is added to argon gas, 12 mTorr (1.6 P
The sputtering was performed at the gas pressure of a) and the substrate temperature of room temperature. By performing sputtering under such conditions, a platinum electrode 12 having a spherical crystal structure can be obtained. That is, if oxygen is used during the formation of the platinum electrode 12, oxygen is taken into the platinum electrode 12 and precipitates at the grain boundaries,
Platinum columnar crystal growth is inhibited, resulting in small crystals with an average particle size of 20 nm or less. Platinum electrode 12 in this embodiment
Is about 10 nm, and the thickness of the platinum electrode 12 is about 300 nm.

The average of the irregularities on the surface of the platinum electrode 12 in this embodiment is about 3 nm. This average is
When the gas pressure in the conventional sputtering method to which oxygen is not added is 8 mTorr, the value is the same as that when forming a platinum electrode. Therefore, the irregularities (about 3 nm on average) on the surface of the platinum electrode 12 in the present embodiment do not pose a practical problem from the viewpoint of the withstand voltage.
Another layer can be favorably formed on the surface of No. 2. On the other hand, the gas pressure in the conventional sputtering method is usually 8 m
When the pressure is increased from Torr to 20 mTorr, it is possible to obtain a platinum electrode having columnar crystals (not spherical crystals) having irregularities on the surface. In this case, the average of the irregularities on the surface is about 6 nm. This is a practical problem from the viewpoint of the withstand voltage.

Next, as shown in FIG. 1C, a ferroelectric thin film 13 is formed by applying a precursor solution containing an organometallic compound on the surface of the platinum electrode 12 and firing it. That is, the ferroelectric thin film 1 is formed using the sol-gel method.
Form 3 Since the sol-gel method is used, the ferroelectric thin film 13 can be formed in a state where the substrate temperature (or the temperature of the platinum electrode 12) is 700 ° C. or less. The organometallic compound contained in the precursor solution used in the sol-gel method is preferably an organometallic compound containing two or more metal atoms in one molecule from the viewpoint of low-temperature crystallization. In the present embodiment, Sr, Bi, T
After applying and drying a metal alkoxide solution (precursor solution) of a, a heat treatment is performed at a substrate temperature of 650 ° C. to form a bismuth layered structure ferroelectric thin film 13. As the metal alkoxide solution, for example, a solution containing a complex alkoxide of Sr—Bi—Ta can be used. As a solution containing a complex alkoxide of Sr-Bi-Ta, JP-A-11-8
No. 0181 can be used. In the present embodiment, Sr alkoxides (for example, Sr alkoxides) can be used.
(OC ₂ H ₄ OCH ₃ ) ₂ )) in an alcohol (eg, methoxyethanol) with a Bi alkoxide (eg, Bi)
(OC ₂ H _{5) 2)} and is reacted, Sr-Bi double alkoxide _{(e.g., Sr [Bi (OR) 4} ] 2) is generated and then, this and Ta alkoxide (e.g., Ta (OC ₂ H
₅ ) A solution of a complex alkoxide of Sr—Bi—Ta obtained by reacting with ₅ ) is used.

Next, the result of examining the degree of c-axis orientation of the bismuth layered structure ferroelectric thin film 13 obtained by the manufacturing method of this embodiment by X-ray diffraction will be described. In order to simply express the c-axis orientation, the reflection intensity I (0010) of the plane (0010) parallel to the c-axis and the reflection intensity I of the densest plane (115) are determined.
The intensity ratio I (0010) / (115) with (115) was examined. Table 1 below shows intensity ratios (and various conditions) comparing this embodiment with the conventional technology.

[0027]

[Table 1] From Table 1, in the case of the prior art, the intensity ratio I was 30.
%, Indicating that a considerable portion is c-axis oriented. Therefore, even if a ferroelectric thin film manufactured by a conventional method is used, only a small hysteresis can be obtained. On the other hand, in the case of the present invention, the intensity ratio I was 8%. Since this value is almost the same as the data of the powder, the ferroelectric thin film 13 manufactured according to the present embodiment is used.
Was randomly oriented and found to be a non-c-axis oriented film. Therefore, the ferroelectric thin film 1 according to the present embodiment
By using No. 3, it can be understood that a large hysteresis can be obtained even when a low-temperature treatment (for example, 700 ° C. or lower) is performed.

FIG. 2 shows a hysteresis curve of the bismuth layer-structured ferroelectric thin film 13 according to the present embodiment.
The black circles in the figure represent the characteristics using the bismuth layered structure ferroelectric thin film 13 of the present embodiment as a substrate, and the white circles compare the characteristics using the conventional bismuth layered structure ferroelectric thin film as a substrate. This is shown as an example. As can be seen from FIG. 2, when the substrate of the related art is used (open circles), the remanent polarization (2Pr) is reduced due to the influence of the C-axis oriented crystal that does not contribute to the polarization. In the case of using (black circles), a large remanent polarization (2Pr) can be obtained because it is not affected by the C-axis oriented crystal.

The inventor of the present application has inferred the reason why the bismuth layered structure ferroelectric thin film 13 of the present embodiment has a random orientation as follows. FIG. 3A schematically shows a crystal growth mechanism according to the related art, and FIG. 3B schematically shows a crystal growth mechanism according to the present invention. In addition,
In the figure, a thin film 20 formed on a platinum electrode represents a film formed from a precursor solution (metal alkoxide solution).

In general, when a sol-gel method is used, a thin film is crystallized by an interfacial crystal growth in which crystallization proceeds from a nucleus 21 generated at the interface and a film in which crystallization proceeds from a nucleus 22 generated in the film. There are two types of medium crystal growth.

As shown in FIG. 3A, in the case of the prior art, a ferroelectric thin film is typically formed on a large columnar crystal platinum electrode 12a having an average particle diameter of 100 nm or more. Therefore, first, ferroelectric nuclei 21 are generated on a flat portion of the platinum crystal at the electrode interface, and crystallization of the ferroelectric proceeds based on the nuclei 21. Therefore, the interface crystal growth mechanism is mainly used. Since the crystal nuclei 21 of the bismuth layer generated in the flat portion of the platinum crystal tend to have c-axis orientation parallel to the substrate, most of the finally obtained film has c-axis orientation.

On the other hand, as shown in FIG. 3B, in the case of the present embodiment, a ferroelectric thin film is formed on a platinum electrode 12b having a spherical crystal structure with an average crystal grain size of 20 nm or less.
In this case, since the area of the flat portion of the platinum crystal 12b at the electrode interface is small, the nucleus of the ferroelectric hardly occurs.
Therefore, crystal growth in the film is mainly performed. Since the crystal nuclei 22 generated in the film are randomly oriented, the finally obtained film is also randomly oriented.

In the present embodiment, since the ferroelectric thin film is formed on the platinum electrode (conductive layer) 12 having a spherical crystal structure by using the sol-gel method, a bismuth layered structure ferroelectric thin film having a randomly oriented layered structure is formed. 13 can be manufactured.

In this embodiment, argon is used as the inert gas in the sputtering of platinum, but another inert gas such as helium may be used. Further, the oxygen partial pressure ratio under the sputtering conditions is set to 4%, but may be at least 1% or more. The substrate temperature was room temperature,
More than that. However, the temperature is preferably about 200 ° C. or less. The reason is that, when the temperature exceeds 200 ° C., oxygen is easily removed from the grain boundaries to form columnar crystals.

The gas pressure is 12 mTorr (1.6 P
a), but from 1 mTorr to 20 mTorr (0.1
It should be about 3 to 2.7 Pa). If it is 1 mTorr or more, it is possible to prevent spatter damage from being applied to the substrate. .

In the present embodiment, the layered structure ferroelectric 13
As an example, SrBi_TwoTa_TwoO₉Was explained using
Of course, other layered ferroelectrics may be used. For example, SrBi
_TwoNb_TwoO₉, SrBi_TwoTi_TwoO₉, SrBi_Two(Ta_xNb
_(1-x))_TwoO₉, Bi_FourTi_ThreeO ₁₂And the like. What
In addition, polarization characteristics and leakage characteristics can be improved and more effectively
For the purpose of enabling low-temperature film formation, a small amount of
Mn, La, Ce, Dy, etc. may be added.

Further, in this embodiment, the sol-gel method is used in the step of forming the ferroelectric thin film 13 in order to explain that the problem of the sol-gel method having a large degree of c-axis orientation can be solved. Alternatively, an organic metal thermal decomposition method using a metal solution or the like may be used. Even when the organometallic thermal decomposition method is used, a randomly oriented ferroelectric thin film 13 can be obtained in the same manner. (Embodiment 2) Embodiment 2 according to the present invention will be described with reference to FIGS. In order to simplify the description of the present embodiment, points different from the first embodiment will be mainly described, and description of the same points as the first embodiment will be omitted or simplified.

The layered ferroelectric thin film 13 obtained by the manufacturing method of the first embodiment is used as a capacitor insulating film, and the platinum electrode 12
Is used as a lower electrode, and an upper electrode is provided on the capacitor insulating film, whereby a ferroelectric capacitor can be obtained.
If a substrate on which a semiconductor integrated circuit is formed is used as a support substrate for the ferroelectric capacitor, a ferroelectric memory can be formed. The ferroelectric capacitor and the ferroelectric memory can be manufactured by using a known method except for the step of forming the layered structure ferroelectric 13 functioning as a capacitor insulating film.

The ferroelectric capacitor shown in FIG. 4A is a ferroelectric capacitor 10 having a stack type structure.
0 is schematically shown. Ferroelectric capacitor 100
Constitutes a part of a ferroelectric memory, and is formed on a substrate 50 (for example, a silicon substrate) on which a semiconductor integrated circuit is formed. The ferroelectric capacitor 100 includes a lower electrode (barrier layer) 32, a capacitance insulating film 33 composed of the ferroelectric thin film 13 of the first embodiment, and an upper electrode 34.
Are sequentially laminated. The lower electrode (barrier layer) 32 is electrically connected to a transistor 40 (diffusion layer 42) via a plug 35 made of, for example, polysilicon, and the transistor 40 is electrically connected to a wiring 44. I have. An element isolation oxide film (field oxide film) 52 is formed on a part of the surface of the substrate 50, and an insulating film 46 is formed on the substrate 50 so as to cover the ferroelectric capacitor 100 and the transistor 40. ing.

The ferroelectric capacitor 100 of the present embodiment
Is a ferroelectric thin film 13 having a layer structure of random orientation despite being formed by the sol-gel method.
, And has a spontaneous polarization sufficient to guarantee the operation as a nonvolatile memory. Also, the ferroelectric capacitor 100
Since it is manufactured in a low-temperature heat treatment state of 0 ° C. or less (for example, about 700 ° C. to 650 ° C., and preferably about 650 ° C.), a stacked memory cell structure can be favorably realized. That is, in the case of a stacked memory cell structure, heat treatment is required at a low temperature of 650 to 700 ° C. from the viewpoint of heat resistance of the barrier layer 32 (for example, an iridium oxide layer). 10
Since the zero capacity insulating film 33 can be manufactured under a heat treatment condition of about 650 ° C., a stack type memory cell structure can be favorably realized.

In this structure, as shown in FIG. 4B, the average crystal grain size is 2
After forming a platinum layer (thickness: for example, 50 nm) having a spherical crystal structure of 0 nm or less, and forming a ferroelectric thin film on this platinum layer as described above, the ferroelectric thin film 1
3 can be obtained.
The lower electrode (barrier layer) 32 in the present embodiment has a double barrier structure including a first barrier layer 66 and a second barrier layer 68, and the first barrier layer 66 is made of Ti.
The second barrier layer 68 is composed of an Ir layer 63, an IrO ₂ layer 64, and a Pt layer 65 having a spherical crystal structure.
That is, the lower electrode 32 is formed of the Ti layer 61 in order from the lower layer.
/ TiAlN layer 62 / Ir layer 63 / IrO ₂ layer 64 / P
It has a laminated structure composed of the t layer 65. The Ti layer 61 of the first barrier layer 66 is a layer for making a contact by being silicided, and the TiAlN layer 62 is formed of Ir and S
This is a layer for preventing silicidation due to reaction with i.
On the other hand, the Ir layer 63 of the second barrier layer 68 and the IrO ₂
The layer 64 is a layer for a diffusion barrier of oxygen, and the Pt layer 65 is a layer functioning as an electrode.

On the other hand, in the case of a planar structure as shown in FIG. 5, a heat treatment temperature of about 800 ° C. can be applied. Is not required, but even in this case, the ferroelectric capacitor 2
It is possible to manufacture 00.

In the present embodiment, the heat treatment temperature of the ferroelectric memory cell is set at 650 ° C. However, it is needless to say that the temperature range may be 400 ° C. or more at which the layered ferroelectric can be crystallized. .

[0044]

According to the present invention, the step of forming a ferroelectric thin film having a layer structure of random orientation on the surface of a conductive layer having at least a surface having a spherical crystal structure is performed, so that it operates as a nonvolatile memory. It is possible to manufacture a ferroelectric thin film having a spontaneous polarization sufficient to guarantee the following.
Further, a ferroelectric capacitor and a ferroelectric memory can be provided by using the ferroelectric thin film.

[Brief description of the drawings]

1 (a) to 1 (c) show Embodiment 1 according to the present invention.
FIG. 4 is a process cross-sectional view for describing the method of manufacturing the ferroelectric thin film of FIG.

FIG. 2 is a graph for comparing characteristics of a ferroelectric thin film 13 of the present embodiment and a ferroelectric thin film of a conventional technique.

FIGS. 3A and 3B are schematic diagrams for explaining crystal growth of a ferroelectric thin film.

4A is a cross-sectional view schematically illustrating a stacked memory cell structure, and FIG. 4B is an enlarged view of a peripheral portion of a barrier layer 32. FIG.

FIG. 5 is a cross-sectional view schematically showing a configuration of a planar type ferroelectric capacitor.

[Explanation of symbols]

 Reference Signs List 11 support substrate 12 platinum electrode (conductive layer) 13 layered ferroelectric thin film 20 film formed from precursor solution 21 nucleus generated at interface 22 nucleus generated in film 32 lower electrode (barrier layer) 33 capacitance insulating film 34 Upper electrode 35 Plug 40 Transistor 42 Diffusion layer 44 Wiring 43 Insulating film 50 Substrate 52 Element isolation oxide film (field oxide film) 66 First barrier layer 68 Second barrier layer 100 Ferroelectric capacitor (stack type) 200 Strong Dielectric capacitor (planar type)

Claims (10)

[Claims] 1. A method for producing a ferroelectric thin film, comprising the step of forming a ferroelectric thin film having a layer structure with random orientation on the surface of a conductive layer having at least a surface having a spherical crystal structure. 2. The method according to claim 1, wherein the step of forming the ferroelectric thin film includes a step of applying a precursor solution containing an organometallic compound on the surface of the conductive layer and firing the conductive layer. A method for manufacturing a ferroelectric thin film. 3. The method according to claim 2, wherein the organometallic compound is an organometallic compound containing two or more metal atoms in one molecule. 4. The step of forming the ferroelectric thin film comprises the steps of:
The method for producing a ferroelectric thin film according to claim 1, wherein the method is performed at a temperature of 00 ° C. or lower. 5. The ferroelectric thin film having a layered structure,
The method for producing a ferroelectric thin film according to claim 1, wherein the ferroelectric thin film has a bismuth layered structure. 6. The ferroelectric thin film according to claim 5, wherein the ferroelectric thin film having a bismuth layered structure contains a small amount of at least one element selected from the group consisting of Mn, La, Ce, and Dy. Manufacturing method. 7. A lower electrode having at least a surface having a spherical crystal structure, and a capacitor insulating film formed on the surface of the lower electrode, wherein the capacitor insulating film has two or more metal atoms in one molecule. A ferroelectric thin film having a layered structure of random orientation obtained by applying a precursor solution containing an organometallic compound containing on the surface of the lower electrode and baking the precursor solution, . 8. A lower electrode having at least a surface having a spherical crystal structure, and a capacitance insulating film formed on the surface of the lower electrode, wherein the temperature of the lower electrode is 700 ° C. or less. And a ferroelectric thin film formed of a ferroelectric thin film having a layered structure of random orientation. 9. A ferroelectric memory comprising: a substrate on which a semiconductor integrated circuit is formed; and a ferroelectric capacitor formed on the substrate, wherein the ferroelectric capacitor has at least a spherical crystal surface. A lower electrode having a structure, and a capacitor insulating film formed on the surface of the lower electrode and formed of a ferroelectric thin film having a layer structure of random orientation, wherein the ferroelectric capacitor is A ferroelectric memory having a stack type structure. 10. A method for manufacturing a ferroelectric memory, comprising a step of forming a ferroelectric thin film having a layer structure with random orientation on the surface of a conductive layer having at least a surface having a spherical crystal structure.