U.S. patent application number 11/214740 was filed with the patent office on 2006-03-09 for ceramic film and method of manufacturing the same, ferroelectric capacitor, semiconductor device, and other element.
This patent application is currently assigned to SEIKO EPSON CORPORATION. Invention is credited to Koichi Furuyama, Takeshi Kijima, Eiji Natori, Yuzo Tasaki.
Application Number | 20060051601 11/214740 |
Document ID | / |
Family ID | 27346927 |
Filed Date | 2006-03-09 |
United States Patent
Application |
20060051601 |
Kind Code |
A1 |
Natori; Eiji ; et
al. |
March 9, 2006 |
Ceramic film and method of manufacturing the same, ferroelectric
capacitor, semiconductor device, and other element
Abstract
A method of manufacturing a ceramic film includes forming the
ceramic film by crystallizing a ceramic raw material liquid which
includes a first raw material liquid and a second raw material
liquid. The first raw material liquid and the second raw material
liquid are different types of liquids, the first raw material
liquid is a raw material liquid for producing a ferroelectric, the
second raw material liquid is a raw material liquid for producing
an oxide such as an ABO-type oxide, a solvent included in the first
raw material liquid and a solvent included in the second raw
material liquid have different polarities, and the ceramic film is
formed in a state in which the first raw material liquid and the
second raw material liquid are phase separated so that first
crystals formed of the first raw material liquid are intermittently
formed in a surface direction of the ceramic film and second
crystals formed of the second raw material liquid are formed so as
to interpose between the first crystals.
Inventors: |
Natori; Eiji; (Chino-shi,
JP) ; Kijima; Takeshi; (Matsumoto-shi, JP) ;
Furuyama; Koichi; (Sayama-shi, JP) ; Tasaki;
Yuzo; (Hachioji-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
SEIKO EPSON CORPORATION
TOKYO
JP
|
Family ID: |
27346927 |
Appl. No.: |
11/214740 |
Filed: |
August 31, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10166781 |
Jun 12, 2002 |
|
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11214740 |
Aug 31, 2005 |
|
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Current U.S.
Class: |
428/469 ;
257/E21.272; 257/E21.664; 361/321.4 |
Current CPC
Class: |
C04B 35/4521 20130101;
C04B 2235/3232 20130101; H01L 41/1878 20130101; C04B 35/465
20130101; C04B 2235/3418 20130101; C04B 2235/3296 20130101; C04B
35/493 20130101; C04B 2235/3454 20130101; H01L 21/02282 20130101;
H01L 21/31691 20130101; C04B 35/624 20130101; C04B 2235/3215
20130101; C04B 2235/3427 20130101; C04B 35/6264 20130101; C04B
35/42 20130101; C04B 2235/3244 20130101; C04B 2235/3258 20130101;
C04B 2235/80 20130101; C04B 35/64 20130101; C23C 16/40 20130101;
C04B 2235/3205 20130101; C23C 18/1225 20130101; C04B 35/495
20130101; C04B 2235/3227 20130101; C04B 35/472 20130101; C04B
2235/3256 20130101; C04B 35/62645 20130101; C23C 16/409 20130101;
C04B 2235/3445 20130101; C23C 18/1208 20130101; C04B 35/497
20130101; C04B 2235/3213 20130101; C04B 35/457 20130101; C04B
35/475 20130101; C04B 2235/3287 20130101; C04B 35/16 20130101; C04B
35/01 20130101; H01L 21/02197 20130101; C04B 2235/3463 20130101;
H01L 27/11502 20130101; C04B 2235/3208 20130101; C04B 2235/3251
20130101; C04B 2235/3298 20130101; C04B 2235/76 20130101; C04B
35/491 20130101; C23C 14/08 20130101; C04B 2235/664 20130101; H01L
41/318 20130101; H01L 27/11507 20130101; C04B 2235/3224 20130101;
C04B 2235/3436 20130101 |
Class at
Publication: |
428/469 ;
361/321.4 |
International
Class: |
B32B 15/04 20060101
B32B015/04; H01G 4/06 20060101 H01G004/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 13, 2001 |
JP |
JP 2001-178840 |
Jun 26, 2001 |
JP |
JP 2001-193048 |
Mar 26, 2002 |
JP |
JP 2002-086139 |
Claims
1-37. (canceled)
38. A ferroelectric ceramic film, comprising: a stack in which a
first crystal layer and a second crystal layer are sequentially
layered, the second crystal layer having a melting point lower than
a melting point of the first crystal layer, the first crystal layer
having a PZT-based perovskite structure, and the second crystal
layer having ABO-type oxides in which Pb is provided in an
A-site.
39. A ferroelectric ceramic film, comprising: a crystal stack in
which a first crystal layer, a second crystal layer, and a third
crystal layer are sequentially layered, the second crystal layer
having a melting point lower than melting points of the first
crystal layer and the third crystal layer, the first crystal layer
having a PZT-based perovskite structure, and the second crystal
layer having ABO-type oxides in which Pb is provided in an
A-site.
40. A ferroelectric ceramic film, comprising: a stack in which a
first crystal layer and a second crystal layer are sequentially
layered, the second crystal layer having a melting point higher
than a melting point of the first crystal layer, the first crystal
layer having a PZT-based perovskite structure, and the second
crystal layer having ABO-type oxides in which Pb is provided in an
A-site.
41. A ferroelectric ceramic film, comprising: a stack in which a
first crystal layer and a second crystal layer are sequentially
layered, the second crystal layer having a melting point lower than
a melting point of the first crystal layer, the first crystal layer
having a PZT-based perovskite structure, and the second crystal
layer having ABO-type oxides in which Si is provided in a
B-site.
42. A ferroelectric ceramic film, comprising: a crystal stack in
which a first crystal layer, a second crystal layer, and a third
crystal layer are sequentially layered, the second crystal layer
having a melting point lower than melting points of the first
crystal layer and the third crystal layer, the first crystal layer
having a PZT-based perovskite structure, and the second crystal
layer having ABO-type oxides in which Si or Ge is provided in a
B-site.
43. A ferroelectric ceramic film, comprising: a stack in which a
first crystal layer and a second crystal layer are sequentially
layered, the second crystal layer having a melting point higher
than a melting point of the first crystal layer, the first crystal
layer having a PZT-based perovskite structure, and the second
crystal layer having ABO-type oxides in which Si or Ge is provided
in a B-site.
44. The ferroelectric ceramic film as defined in claim 38, a
constituent metal element of the first crystal layer and a
constituent metal element of the second crystal layer being mixed
in an interface region between the first crystal layer and the
second crystal layer.
45. The ferroelectric ceramic film as defined in claim 38, the
first crystal layer being formed on a base with a third crystal
layer interposed therebetween, and the third crystal layer having a
melting point lower than a melting point of the first crystal
layer.
Description
[0001] This is a Divison of U.S. patent application Ser. No.
10/166,781 filed Jun. 12, 2002. The entire disclosure of the prior
application is hereby incorporated by reference herein in its
entirety. The invention claims priority to Japanese patent
applications Nos. JP 2001-178840 filed on Jun. 13, 2001, JP
2001-193048 filed Jun. 26, 2001 and JP 2002-086139 filed Mar. 26,
2002. The entire disclosures of the prior applications are hereby
incorporated by reference herein in their entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a ceramic film and a method
of manufacturing the same, a ferroelectric capacitor, a
semiconductor device, and other elements.
[0003] As a ferroelectric film applied to semiconductor devices
(ferroelectric memory (FeRAM), for example), ferroelectric films
having a layered perovskite structure (BiLaTiO-based, BiTiO-based,
and SrBiTaO-based ferroelectric films, for example) have been
proposed. The ferroelectric film having a layered perovskite
structure is generally formed by crystal growth from an amorphous
state.
[0004] In the case of forming a ferroelectric film having a layered
perovskite structure by using this formation method, the crystal
growth rate in the c-axis direction becomes lower than that in the
a-axis direction and the b-axis direction due to the crystal
structure of the ferroelectric film. Specifically, crystals tend to
be grown in the a-axis direction and the b-axis direction.
Therefore, a ferroelectric film having a layered perovskite
structure formed by using the above method has rough surface
morphology. Specifically, openings (holes or grooves, for example)
are formed between crystals in the resulting ferroelectric
film.
BRIEF SUMMARY OF THE INVENTION
[0005] The present invention may provide a method of manufacturing
a ceramic film capable of improving the surface morphology of the
ceramic film.
[0006] The present invention may also provide a ceramic film
obtained by the method of manufacturing a ceramic film of the
present invention.
[0007] The present invention may further provide a semiconductor
device and a piezoelectric device to which the ceramic film of the
present invention is applied.
[0008] In a ceramic film according to one aspect of the present
invention, first crystals are intermittently formed in a surface
direction of the ceramic film, and second crystals are interposed
between the first crystals.
[0009] A ferroelectric capacitor according one aspect to the
present invention comprises:
[0010] a lower electrode, a ceramic film which is formed on the
lower electrode and includes first crystals and second crystals,
and an upper electrode formed on the ceramic film,
[0011] wherein the first crystals are intermittently formed in a
surface direction of the ceramic film, and the second crystals are
formed so as to interpose between the first crystals.
[0012] A method of manufacturing a ceramic film according one
aspect to the present invention comprises:
[0013] forming the ceramic film by crystallizing a ceramic raw
material liquid which includes a first raw material liquid and a
second raw material liquid,
[0014] wherein the first raw material liquid and the second raw
material liquid are different types of liquids,
[0015] wherein the first raw material liquid is a raw material
liquid for producing a ferroelectric,
[0016] wherein the second raw material liquid is a raw material
liquid for producing an ABO-type oxide, and
[0017] wherein the ceramic film is formed in a state in which the
first raw material liquid and the second raw material liquid are
phase separated so that first crystals formed of the first raw
material liquid are intermittently formed in a surface direction of
the ceramic film, and second crystals formed of the second raw
material liquid are formed so as to interpose between the first
crystals.
[0018] The state in which the first raw material liquid and the
second raw material liquid are phase separated is obtained by the
following techniques.
[0019] (1) In the case where the phase separated state occurs in a
liquid state after mixing due to differences in polarity, molecular
weight, and the like between the first raw material liquid and the
second raw material liquid, the phase separated state is obtained
by depositing the mixed liquid by spin coating, dipping, an LSMCD
method, or the like. In particular, the phase separated state is
significantly easily obtained when the percentage of the second raw
material liquid is greater than that of the first raw material
liquid.
[0020] (2) In the case of using raw material liquids which are not
phase separated in a mixed state, the phase separated state can be
obtained by separately misting the first raw material liquid and
the second raw material liquid, and supplying the mist of the first
raw material liquid and the mist of the second raw material liquid
at the same time by using the LSMCD method.
[0021] (3) The phase separated state can be obtained by depositing
one of the first raw material liquid and the second raw material
liquid by using a deposition method which enables the raw material
liquid to be grown in the shape of islands, and depositing the
other raw material liquid so as to interpose between the
islands.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0022] FIGS. 1A to 1C are cross-sectional views schematically
showing manufacturing steps of a ceramic film using a ceramic raw
material liquid according to an embodiment.
[0023] FIG. 2 is a cross-sectional view schematically showing a
ferroelectric memory device.
[0024] FIG. 3 is a cross-sectional view schematically showing an
apparatus for forming a raw material body on a base by using an
LSMCD method.
[0025] FIGS. 4A and 4B are conceptual views schematically showing a
raw material body obtained by using the apparatus shown in FIG.
3.
[0026] FIGS. 5A to 5C are conceptual views schematically showing
manufacturing steps of a first multilayer ceramic film.
[0027] FIGS. 6A to 6C are conceptual views schematically showing
manufacturing steps of a second multilayer ceramic film.
[0028] FIGS. 7A to 7C are conceptual views schematically showing
manufacturing steps of a third multilayer ceramic film.
[0029] FIGS. 8A and 8B are conceptual views schematically showing
manufacturing steps of a fourth multilayer ceramic film.
[0030] FIG. 9 is a flowchart of a deposition process.
[0031] FIG. 10 is a micrograph of a ferroelectric film obtained
from a mixed liquid of a main liquid and a secondary liquid
according to Example 1.
[0032] FIG. 11 is a micrograph of a ferroelectric film according to
a comparative example.
[0033] FIG. 12 is a plan view schematically showing a manufacturing
step of a ceramic film according to an embodiment.
[0034] FIG. 13 is a cross-sectional view schematically showing a
ceramic film according to an embodiment.
DETAILED DESCRIPTION OF THE EMBODIMENT
Method of Manufacturing Ceramic Film
[0035] The meaning of the term "the first raw material liquid and
the second raw material liquid are different types of liquids" in
the present invention is described below.
[0036] (A) A first method of manufacturing a ceramic film of the
present invention comprises:
[0037] forming a ceramic film by crystallizing a raw material
body,
[0038] wherein the raw material body includes different types of
raw materials in a mixed state, and
[0039] wherein the different types of raw materials differ from one
another in at least one of a crystal growth condition and a crystal
growth mechanism in the crystallization of the raw materials.
[0040] The different types of raw materials differ from one another
in at least one of the crystal growth condition and the crystal
growth mechanism. Specifically, the raw materials are judged to be
different depending upon whether or not the raw materials differ
from one another in at least one of the crystal growth condition
and the crystal growth mechanism.
[0041] As examples of the crystal growth condition and the crystal
growth mechanism in the crystallization of the raw materials, a
crystallization temperature, crystal nucleus formation temperature,
crystal growth temperature, crystal growth rate, crystal nucleus
formation rate, size of crystal nuclei, crystallization method, and
the like can be given.
[0042] In the present invention, the raw material body includes the
different types of raw materials. Specifically, the raw material
body includes at least two types of raw materials. The different
types of raw materials differ from one another in at least one of
the crystal growth condition and the crystal growth mechanism in
the crystallization of the raw materials. Therefore, one of the raw
materials can be crystallized before the other raw material, and
the other raw material can be crystallized in openings between
crystals produced from the first crystallized raw material by
controlling various conditions, for example. Specifically, the
openings between crystals produced from one of the raw materials
can be filled with crystals produced from the other raw material.
Therefore, surface morphology of the ceramic film can be
improved.
[0043] The different types of raw materials may be crystallized at
the same time by controlling various conditions. For example, the
crystallization temperature can be adjusted by replacing a metal
element of the raw material with another element. This enables the
crystallization temperatures of the different types of raw
materials to be approximately the same. The different types of raw
materials can be crystallized at the same time if the
crystallization temperatures of the different types of raw
materials are approximately the same.
[0044] (B) A second method of manufacturing a ceramic film of the
present invention comprises:
[0045] forming a ceramic film by crystallizing a raw material
body,
[0046] wherein the raw material body includes different types of
raw materials in a mixed state, and
[0047] wherein the different types of raw materials differ from one
another in a crystal structure of crystals obtained from the raw
materials.
[0048] The different types of raw materials differ from one another
in the crystal structure of crystals obtained from the raw
materials. Specifically, the raw materials are judged to be
different when the raw materials differ from one another in the
crystal structure of crystals obtained from the raw materials.
[0049] When crystals obtained from the raw materials are expressed
as (Bi.sub.2O.sub.2).sup.2+(A.sub.m-B.sub.mO.sub.3m+1).sup.2-,
crystals having different crystal structures have different values
for m, for example.
[0050] In the present invention, the different types of raw
materials differ from one another in the crystal structure of
crystals obtained from the raw materials. If the raw materials
differ from one another in the crystal structure of crystals
obtained from the raw materials, the raw materials differ from one
another in the crystal growth condition and the crystal growth
mechanism of the raw materials. Therefore, effects the same as in
the first method of manufacturing a ceramic film of the present
invention can be obtained.
[0051] (C) A third method of manufacturing a ceramic film of the
present invention comprises:
[0052] forming a ceramic film by crystallizing a raw material
body,
[0053] wherein the raw material body includes different types of
raw materials in a mixed state, and
[0054] wherein the different types of raw materials are
individually crystallized at least at an initial stage of
crystallization.
[0055] The different types of raw materials are individually
crystallized at least at an initial stage of crystallization.
[0056] In the third method of manufacturing a ceramic film of the
present invention, the different types of raw materials are
individually crystallized at least at an initial stage of
crystallization. Therefore, crystals produced from one of the raw
materials can be grown in the openings between crystals produced
from the other raw material. As a result, formation of the openings
between the crystals can be prevented, whereby the surface
morphology is improved.
[0057] The first to third methods of manufacturing a ceramic film
of the present invention may have at least any of the following
features.
[0058] (a) The ceramic film may be a ferroelectric.
[0059] (b) The ceramic film may be a paraelectric.
[0060] (c) The ceramic film may include a ferroelectric and a
paraelectric in a mixed state.
[0061] (d) At least two of the different types of raw materials may
differ from each other in crystallization temperature in the
crystallization of the raw materials.
[0062] (e) At least two of the different types of raw materials may
differ from each other in crystal nucleus formation temperature in
the crystallization of the raw materials.
[0063] (f) At least two of the different types of raw materials may
differ from each other in crystal growth temperature in the
crystallization of the raw materials.
[0064] (g) At least two of the different types of raw materials may
differ from each other in crystal growth rate in the
crystallization of the raw materials.
[0065] (h) At least two of the different types of raw materials may
differ from each other in crystal nucleus formation rate in the
crystallization of the raw materials.
[0066] (i) At least two of the different types of raw materials may
differ from each other in the size of crystal nuclei in the
crystallization of the raw materials.
[0067] (j) At least two of the different types of raw materials may
differ from each other in crystallization method in the
crystallization of the raw materials.
[0068] (k) There may be a time lag between the crystallization of
the different types of raw materials.
[0069] (1) There maybe a time lag between the formation of crystal
nuclei in the crystallization of the raw materials.
[0070] (m) The different types of raw materials may be crystallized
at the same time.
[0071] When crystallizing the different types of raw materials at
the same time, crystals produced from one of the raw materials
interrupt the growth of crystals produced from the other raw
material. As a result, the resulting crystals can be
microcrystallized. This causes the openings between the crystals to
become narrow, whereby the surface morphology is improved.
[0072] When crystallizing the different types of raw materials at
the same time, it is preferable to use raw materials from which
ceramics having different crystal structures are obtained. This
enables the crystal growth condition and the crystal growth
mechanism during crystallization of the raw materials to be changed
at the same time.
[0073] (n) When ceramics obtained from the raw materials are
expressed as
(Bi.sub.2O.sub.2).sup.2+(A.sub.m-,B.sub.mO.sub.3m+1).sup.2-, the
different types of raw materials may have different values for
m.
[0074] (o) The raw material body may be formed on a base by the
liquid source misted chemical deposition (LSMCD) method.
[0075] In the case of forming the raw material body on the base by
using the LSMCD method, the raw material body is provided to the
base in the form of a mist by ultrasonic waves.
[0076] The raw material body may be formed on a base by separately
providing the different types of raw materials.
[0077] The raw material body may be formed on a base by providing
the different types of raw materials at the same time.
[0078] (p) The raw material body may be formed on a base by spin
coating or dipping.
[0079] (q) The raw materials may be at least one of a sol-gel raw
material and an MOD raw material.
[0080] (r) The raw material body may include a sol-gel raw material
and an MOD raw material.
[0081] In the above (p) and (q), the sol-gel raw material may be
polycondensed by hydrolysis.
[0082] The sol-gel raw material may have a crystal structure
similar to the crystal structure of crystals obtained by
crystallizing the raw material. This enables the sol-gel raw
material to be easily crystallized.
[0083] The MOD raw material may be a polynuclear complex raw
material.
[0084] (s) The raw material body may include different types of
sol-gel raw materials, wherein the different types of sol-gel raw
materials may differ from one another in the degree of
polycondensation or metal element composition.
[0085] (D) A fourth method of manufacturing a ceramic film of the
present invention comprises:
[0086] forming a ceramic film by crystallizing a raw material
body,
[0087] wherein the raw material body is crystallized so that a
plurality of phases is formed.
[0088] The ceramic film may have any of the following features.
[0089] (a) The ceramic film may be a ferroelectric.
[0090] (b) The ceramic film may be a paraelectric.
[0091] (c) The ceramic film may include a ferroelectric and a
paraelectric in a mixed state.
[0092] (E) A fifth method of manufacturing a ceramic film of the
present invention comprises:
[0093] forming a ceramic film by crystallizing a ceramic raw
material liquid which includes a first raw material liquid and a
second raw material liquid,
[0094] wherein the first raw material liquid and the second raw
material liquid are different types of liquids,
[0095] wherein the first raw material liquid is a raw material
liquid for producing a ferroelectric having a Bi-type layered
perovskite structure, and
[0096] wherein the second raw material liquid is a raw material
liquid for producing an ABO-type oxide in which Bi is provided in
the A site.
[0097] A ferroelectric film having predetermined characteristics at
a low temperature can be formed by forming a ceramic film using the
ceramic raw material liquid of the present invention. A ceramic
film obtained by using the ceramic raw material liquid of the
present invention excels in surface morphology.
[0098] The molar ratio of the ferroelectric produced from the first
raw material liquid to the ABO-type oxide produced from the second
raw material liquid is preferably from 100:20 to 100:100. This
enables a ferroelectric film having predetermined characteristics
to be formed at a lower temperature more reliably.
[0099] (F) A sixth method of manufacturing a ceramic film of the
present invention comprises:
[0100] forming a ceramic film by crystallizing a ceramic raw
material liquid which includes a third raw material liquid and a
fourth raw material liquid,
[0101] wherein the third raw material liquid and the fourth raw
material liquid are different types of liquids,
[0102] wherein the third raw material liquid is a raw material
liquid for producing a PZT-type ferroelectric, and
[0103] wherein the fourth raw material liquid is a raw material
liquid for producing an ABO-type oxide in which Pb is provided in
the A site.
[0104] Effects the same as in the fifth method of manufacturing a
ceramic film of the present invention can be obtained by forming a
ceramic film using the ceramic raw material liquid of the present
invention, for example.
[0105] The molar ratio of the ferroelectric produced from -the
third raw material liquid to the ABO-type oxide produced from the
fourth raw material liquid is preferably from 100:20 to 100:100.
This enables a ferroelectric film having predetermined
characteristics to be formed at a lower temperature more
reliably.
[0106] The third raw material liquid may be a liquid in which a
metal compound or a metal-inorganic compound of a metal element for
the ferroelectric is dissolved in a solvent, and the fourth raw
material liquid may be a liquid in which a metal compound or a
metal-inorganic compound of a metal element for the ABO-type oxide
is dissolved in a solvent.
[0107] (G) A seventh method of manufacturing a ceramic film of the
present invention comprises:
[0108] forming a ceramic film by crystallizing a ceramic raw
material liquid which includes a fifth raw material liquid and a
sixth raw material liquid,
[0109] wherein the fifth raw material liquid is a raw material
liquid for producing a ferroelectric having a Bi-type layered
perovskite structure or a PZT-type ferroelectric, and
[0110] wherein the sixth raw material liquid is a raw material
liquid for producing an ABO-type oxide in which Ge or Si is
provided in the B site.
[0111] Effects the same as in the fifth method of manufacturing a
ceramic film of the present invention can be obtained by forming a
ceramic film using the ceramic raw material liquid of the present
invention, for example.
[0112] The molar ratio of the ferroelectric produced from the fifth
raw material liquid to the ABO-type oxide produced from the sixth
raw material liquid is preferably from 100:20 to 100:100. This
enables a ferroelectric film having predetermined characteristics
to be formed at a lower temperature more reliably.
[0113] (H) An eighth method of manufacturing a ceramic film of the
present invention comprises:
[0114] forming a raw material body layer in which a plurality of
raw material layers is layered, and
[0115] forming a ceramic film by crystallizing the raw material
body layer,
[0116] wherein an uppermost raw material layer in the raw material
body layer has a crystallization temperature lower than the
crystallization temperature of a lower raw material layer which is
in contact with the uppermost raw material layer.
[0117] According to the present invention, crystals produced from
the uppermost raw material layer function as a seed layer during
crystallization of the lower raw material layer.
[0118] The lower raw material layer which is in contact with the
uppermost raw material layer may be formed on a base with a first
raw material layer interposed therebetween, wherein the first raw
material layer may have a crystallization temperature lower than
the crystallization temperature of the lower raw material layer
which is in contact with the uppermost raw material layer.
Therefore, crystals produced from the first raw material layer
function as a seed layer during crystallization of the lower raw
material layer which is in contact with the uppermost raw material
layer.
[0119] (I) A ninth method of manufacturing a ceramic film of the
present invention comprises:
[0120] forming a raw material body layer which includes a raw
material stack in which a first raw material layer, a second raw
material layer, and a third raw material layer are sequentially
layered, and
[0121] forming a ceramic film by crystallizing the raw material
body layer,
[0122] wherein the second raw material layer has a crystallization
temperature lower than the crystallization temperatures of the
first raw material layer and the third raw material layer.
[0123] According to the present invention, crystals produced from
the second raw material layer function as a stopper for preventing
the growth of crystals in the first raw material layer and the
third raw material layer. Therefore, the grain size of the crystals
produced from the first raw material layer and the third raw
material layer can be decreased.
[0124] A fourth raw material layer may be further layered on the
third raw material layer, wherein the fourth raw material layer may
have a crystallization temperature lower than the crystallization
temperature of the third raw material layer. In this case, crystals
produced from the fourth raw material layer function as a seed
layer during crystallization of the third raw material layer.
[0125] (J) A tenth method of manufacturing a ceramic film of the
present invention comprises:
[0126] forming a raw material body layer in which a plurality of
raw material layers is layered, and
[0127] forming a ceramic film by crystallizing the raw material
body layer,
[0128] wherein an uppermost raw material layer in the raw material
body layer has a crystallization temperature higher than the
crystallization temperature of a lower raw material layer which is
in contact with the uppermost raw material layer.
[0129] According to the present invention, crystals produced from
the uppermost raw material layer can be formed to cover crystals
produced from the lower raw material layer.
[0130] Crystals obtained from the uppermost raw material layer in
the raw material body layer preferably have no layered structure.
This enables the surface morphology of the ceramic film to be
improved.
[0131] In the first to tenth methods of manufacturing a ceramic
film of the present invention, the step of forming a ceramic film
by crystallizing the raw material body may be performed two or more
times.
Ceramic Film
[0132] A ceramic film of the present invention is obtained by the
method of manufacturing a ceramic film of the present
invention.
[0133] A ceramic film of the present invention comprises:
[0134] a stack in which a first crystal layer and a second crystal
layer are sequentially layered,
[0135] wherein the second crystal layer has a melting point lower
than a melting point of the first crystal layer.
[0136] In the present invention, a constituent metal element of the
first crystal layer and a constituent metal element of the second
crystal layer may be mixed in a region around an interface between
the first crystal layer and the second crystal layer.
[0137] In the present invention, the first crystal layer may be
formed on a base with a third crystal layer interposed
therebetween, and the third crystal layer may have a melting point
lower than a melting point of the first crystal layer.
[0138] A ceramic film of the present invention comprises:
[0139] a crystal stack in which a first crystal layer, a second
crystal layer, and a third crystal layer are sequentially
layered,
[0140] wherein the second crystal layer has a melting point lower
than melting points of the first crystal layer and the third
crystal layer.
[0141] In the present invention, a constituent metal element of the
first crystal layer and a constituent metal element of the second
crystal layer may be mixed in a region around an interface between
the first crystal layer and the second crystal layer, and a
constituent metal element of the second crystal layer and a
constituent metal element of the third crystal layer may be mixed
in a region around an interface between the second crystal layer
and the third crystal layer.
[0142] In the present invention, a fourth crystal layer may be
further provided on the third crystal layer, the fourth crystal
layer may have a melting point lower than a melting point of the
third crystal layer, and a constituent metal element of the third
crystal layer and a constituent metal element of the fourth crystal
layer may be mixed in a region around an interface between the
third crystal layer and the fourth crystal layer.
[0143] A ceramic film of the present invention comprises:
[0144] a stack in which a first crystal layer and a second crystal
layer are sequentially layered,
[0145] wherein the second crystal layer has a melting point higher
than a melting point of the first crystal layer.
[0146] In the present invention, a constituent metal element of the
first crystal layer and a constituent metal element of the second
crystal layer may be mixed in a region around an interface between
the first crystal layer and the second crystal layer.
Application Example of Ceramic Film
[0147] A semiconductor device of the present invention comprises a
capacitor including the ceramic film of the present invention.
[0148] The ceramic film of the present invention may be applied to
various types of devices, other than a semiconductor device, such
as a piezoelectric of a piezoelectric device.
[0149] The present invention may further provide a ferroelectric
capacitor and a method of manufacturing a ceramic film given
below.
[0150] A ferroelectric capacitor of the present invention
comprises:
[0151] a lower electrode, a ceramic film which is formed on the
lower electrode and includes first crystals and second crystals,
and an upper electrode formed on the ceramic film,
[0152] wherein the first crystals have a Bi-based layered
perovskite structure,
[0153] wherein the second crystals are ABO-type oxides in which Bi
is provided in an A site, and
[0154] wherein the first crystals are intermittently formed in a
surface direction of the ceramic film, and the second crystals are
formed so as to interpose between the first crystals.
[0155] The ceramic film which makes up this ferroelectric capacitor
may be formed by a first method given below.
[0156] The first method comprises:
[0157] forming the ceramic film by crystallizing a ceramic raw
material liquid which includes a first raw material liquid and a
second raw material liquid,
[0158] wherein the first raw material liquid and the second raw
material liquid are different types of liquids,
[0159] wherein the first raw material liquid is a raw material
liquid for producing a ferroelectric having a Bi-based layered
perovskite structure, and the second raw material liquid is a raw
material liquid for producing an ABO-type oxide in which Bi is
provided in an A site,
[0160] wherein a solvent included in the first raw material liquid
and a solvent included in the second raw material liquid have
different polarities, and
[0161] wherein the ceramic film is formed in a state in which the
first raw material liquid and the second raw material liquid are
phase separated so that first crystals formed of the first raw
material liquid are intermittently formed in a surface direction of
the ceramic film, and second crystals formed of the second raw
material liquid are formed so as to interpose between the first
crystals.
[0162] The ceramic film which makes up the ferroelectric capacitor
may be formed by a second method given below.
[0163] The second method comprises:
[0164] forming the ceramic film by crystallizing a ceramic raw
material liquid which includes a first raw material liquid and a
second raw material liquid,
[0165] wherein the first raw material liquid and the second raw
material liquid are different types of liquids,
[0166] wherein the first raw material liquid is a raw material
liquid for producing a ferroelectric having a Bi-based layered
perovskite structure, and the second raw material liquid is a raw
material liquid for producing an ABO-type oxide in which Bi is
provided in an A site,
[0167] wherein a solvent included in the first raw material liquid
and a solvent included in the second raw material liquid have
different polarities, and
[0168] wherein a mist produced from the first raw material liquid
is formed so as to be dispersed on a base and then a film of the
second raw material liquid is formed on the base so that first
crystals formed of the first raw material liquid are intermittently
formed in a surface direction of the ceramic film, and second
crystals formed of the second raw material liquid are formed so as
to interpose between the first crystals.
[0169] In the second method, as the method of forming the film of
the second raw material liquid on the base on which the mist of the
first raw material liquid is dispersed, a method of forming the
film of the second raw material liquid by misting the second raw
material liquid, or a method of forming the film of the second raw
material liquid by spin coating may be used. These methods also
apply to a second method described later. The phase separation
effect is increased if the film of the first raw material liquid is
formed in the shape of islands.
[0170] The first and second methods may have the following
features. These features also apply to first and second methods
described later.
[0171] (a) One of the solvents included in the first raw material
liquid and the second raw material liquid may be soluble in water,
and the other of the solvents may be insoluble in water.
[0172] (b) The molar ratio of the ferroelectric produced from the
first raw material liquid to the ABO-type oxide produced from the
second raw material liquid may be from 100:20 to 100:100.
[0173] A ferroelectric capacitor of the present invention
comprises:
[0174] a lower electrode, a ceramic film which is formed on the
lower electrode and includes first crystals and second crystals,
and an upper electrode formed on the ceramic film,
[0175] wherein the first crystals have a PZT-type perovskite
structure,
[0176] wherein the second crystals are ABO-type oxides in which Pb
is provided in an A site, and
[0177] wherein the first crystals are intermittently formed in a
surface direction of the ceramic film, and the second crystals are
formed so as to interpose between the first crystals.
[0178] The ceramic which makes up this ferroelectric capacitor may
be formed by a method similar to the above first and second
methods.
[0179] Specifically, a first method comprises:
[0180] forming the ceramic film by crystallizing a ceramic raw
material liquid which includes a first raw material liquid and a
second raw material liquid,
[0181] wherein the first raw material liquid and the second raw
material liquid are different types of liquids,
[0182] wherein the first raw material liquid is a raw material
liquid for producing a PZT-type ferroelectric,
[0183] wherein the second raw material liquid is a raw material
liquid for producing an ABO-type oxide in which Pb is provided in
an A site,
[0184] wherein a solvent included in the first raw material liquid
and a solvent included in the second raw material liquid have
different polarities, and
[0185] wherein the ceramic film is formed in a state in which the
first raw material liquid and the second raw material liquid are
phase separated so that first crystals formed of the first raw
material liquid are intermittently formed in a surface direction of
the ceramic film, and second crystals formed of the second raw
material liquid are formed so as to interpose between the first
crystals.
[0186] A second method comprises:
[0187] forming the ceramic film by crystallizing a ceramic raw
material liquid which includes a first raw material liquid and a
second raw material liquid,
[0188] wherein the first raw material liquid and the second raw
material liquid are different types of liquids,
[0189] wherein the first raw material liquid is a raw material
liquid for producing a PZT-type ferroelectric,
[0190] wherein the second raw material liquid is a raw material
liquid for producing an ABO-type oxide in which Pb is provided in
an A site,
[0191] wherein a solvent included in the first raw material liquid
and a solvent included in the second raw material liquid have
different polarities, and
[0192] wherein a mist produced from the first raw material liquid
is formed so as to be dispersed on a base and then a film of the
second raw material liquid is formed on the base so that first
crystals formed of the first raw material liquid are intermittently
formed in a surface direction of the ceramic film, and second
crystals formed of the second raw material liquid are formed so as
to interpose between the first crystals.
[0193] In the second method, as the method of forming the film of
the second raw material liquid on the base on which the mist of the
first raw material liquid is dispersed, a method of forming the
film of the second raw material liquid by misting the second raw
material liquid, or a method of forming the film of the second raw
material liquid by spin coating may be used. The phase separation
effect is increased if the film of the first raw material liquid is
formed in the shape of islands.
[0194] The above first and second methods may have the following
features.
[0195] (a) One of the solvents included in the first raw material
liquid and the second raw material liquid may be soluble in water,
and the other of the solvents may be insoluble in water.
[0196] (b) The molar ratio of the ferroelectric produced from the
first raw material liquid to the ABO-type oxide produced from the
second raw material liquid may be from 100:20 to 100:100.
[0197] A ferroelectric capacitor of the present invention
comprises:
[0198] a lower electrode, a ceramic film which is formed on the
lower electrode and includes first crystals and second crystals,
and an upper electrode formed on the ceramic film,
[0199] wherein the first crystals are intermittently formed in a
surface direction of the ceramic film, and the second crystals are
formed so as to interpose between the first crystals.
[0200] A first method for forming the ceramic film which makes up
this ferroelectric capacitor comprises:
[0201] forming the ceramic film by crystallizing a ceramic raw
material liquid which includes a first raw material liquid and a
second raw material liquid,
[0202] wherein the first raw material liquid and the second raw
material liquid are different types of liquids,
[0203] wherein the first raw material liquid is a raw material
liquid for producing a ferroelectric,
[0204] wherein the second raw material liquid is a raw material
liquid for producing an ABO-type oxide,
[0205] wherein a solvent included in the first raw material liquid
and a solvent included in the second raw material liquid have
different polarities, and
[0206] wherein the ceramic film is formed in a state in which the
first raw material liquid and the second raw material liquid are
phase separated so that first crystals formed of the first raw
material liquid are intermittently formed in a surface direction of
the ceramic film, and second crystals formed of the second raw
material liquid are formed so as to interpose between the first
crystals.
[0207] A second method for forming the ceramic film which makes up
the ferroelectric capacitor comprises:
[0208] forming a ceramic film by crystallizing a ceramic raw
material liquid which includes a first raw material liquid and a
second raw material liquid,
[0209] wherein the first raw material liquid and the second raw
material liquid are different types of liquids,
[0210] wherein the first raw material liquid is a raw material
liquid for producing a ferroelectric,
[0211] wherein the second raw material liquid is a raw material
liquid for producing an ABO-type oxide,
[0212] wherein a solvent included in the first raw material liquid
and a solvent included in the second raw material liquid have
different polarities, and
[0213] wherein a mist produced from the first raw material liquid
is formed so as to be dispersed on a base and then a film of the
second raw material liquid is formed on the base so that first
crystals formed of the first raw material liquid are intermittently
formed in a surface direction of the ceramic film, and second
crystals formed of the second raw material liquid are formed so as
to interpose between the first crystals.
[0214] There are no specific limitations to the first raw material
liquid and the second raw material liquid insofar as the liquids
have the above configuration, and various types of combinations are
possible. Specifically, these manufacturing methods may be applied
not only to the case of the ferroelectric having a Bi-based layered
perovskite structure or a PZT-type perovskite structure, but also
to the case where the first raw material liquid is a raw material
liquid for producing a ferroelectric having a Bi-based layered
perovskite structure or a PZT-type ferroelectric, and the second
raw material liquid is a raw material liquid for producing an
ABO-type oxide in which Ge, Si, or Sn, or combination of these is
provided in the B site.
[0215] According to the first and second methods, first crystals
produced from the first or third raw material liquid are
intermittently formed, and second crystals produced from the second
or fourth raw material liquid are formed so as to interpose between
the first crystals. As a result, the second crystals (paraelectric,
for example) are disposed to surround the first crystals
(ferroelectric, for example). In such a structure, occurrence of
domains in the direction at an angle of 90.degree. with respect to
the direction of the thickness of the ferroelectric film of the
ferroelectric capacitor consisting of the upper and lower
electrodes and the ferroelectric (generally called 90.degree.
domains) can be prevented. As a result, squareness of the
hysteresis characteristics of the ferroelectric capacitor can be
improved.
[0216] The above-described first and second methods may be applied
not only to the case of forming a ceramic film of a ferroelectric
capacitor but also to the case of forming a ceramic film used for
other applications.
[0217] Embodiments of the present invention are described below in
more detail with reference to the drawings.
First Embodiment
Method of Manufacturing Ceramic Film
[0218] A method of manufacturing a ceramic film according to the
present embodiment is described below. FIG. 1 is a cross-sectional
view schematically showing manufacturing steps of a ceramic film
according to the present embodiment. FIG. 1B is a conceptual view
showing a concept of a crystallization mechanism.
[0219] (1) As shown in FIG. 1A, a raw material body 20 is formed on
a base 10. As a method for forming the raw material body 20 on the
base 10, a coating method, an LSMCD method, and the like can be
given. As examples of the coating method, spin coating and dipping
can be given. The raw material body 20 includes a sol-gel raw
material and an MOD raw material. As the sol-gel raw material, a
raw material having a crystallization temperature lower than that
of the MOD raw material and a crystal nucleus formation rate and a
crystal growth rate higher than those of the MOD raw material is
selected.
[0220] The sol-gel raw material may be prepared as described below.
Metal alkoxides having four or less carbon atoms are mixed and
subjected to hydrolysis and polycondensation. A strong M-O-M-O . .
. bond is formed by hydrolysis and polycondensation. The resulting
M-O-M bond has a structure similar to the crystal structure of a
ceramic (perovskite structure). M represents a metal element (Bi,
Ti, La, Pb, for example), and O represents oxygen. Metal elements
and the ratio of the metal elements are appropriately determined
depending on a desired ceramic. Taking a BiLaTiO-based (hereinafter
called "BLT") ceramic as an example, the ratio is expressed as
Bi.sub.3.25La.sub.0.75Ti.sub.3O.sub.X. The value X for O is not a
final value. A solvent is added to the product obtained by
hydrolysis and polycondensation to obtain a raw material. The
sol-gel raw material is prepared in this manner.
[0221] As examples of the MOD raw material, a polynuclear metal
complex raw material in which constituent elements for a ceramic
are continuously connected to each other either directly or
indirectly can be given. As examples of the MOD raw material, metal
salts of carboxylic acids can be given. As examples of carboxylic
acids, acetic acid, 2-ethylhexanoic acid, and the like can be
given. As examples of metals, Bi, Ti, La, and Pb can be given. The
MOD raw material (polynuclear metal complex raw material) has an
M-O bond in the same manner as in the sol-gel raw material.
However, the M-O bond is not a continuous bond as in the case of
the sol-gel raw material obtained by polycondensation. The bond
structure of the M-O bond is similar to a linear structure, and
completely differs from the perovskite structure.
[0222] The raw material body 20 is optionally dried.
[0223] (2) The raw material body 20 is crystallized by subjecting
the raw material body 20 to a thermal treatment, thereby forming a
ceramic film 30 as shown in FIG. 1C. The raw material body 20 is
crystallized under conditions whereby the sol-gel raw material and
the MOD raw material are individually crystallized at least at an
initial stage of the crystal growth so that first crystals 42 are
produced from the sol-gel raw material and second crystals 52 are
produced from the MOD raw material.
[0224] An example of the crystallization mechanism of the sol-gel
raw material and the MOD raw material is described below. The
sol-gel raw material has a crystallization temperature lower than
that of the MOD raw material. The crystal nucleus formation rate
and the crystal growth rate of the sol-gel raw material are higher
than those of the MOD raw material. Therefore, the sol-gel raw
material can be crystallized before the MOD raw material by
controlling the temperature and the like. Since the sol-gel raw
material is crystallized before the MOD raw material, the MOD raw
material remains in the openings between the first crystals 42
produced from the sol-gel raw material, as shown in FIG. 1B.
Therefore, the second crystals 52 produced from the MOD raw
material are grown in the openings between the first crystals 42
produced from the sol-gel raw material. The first crystals 42 and
the second crystals 52 are individually grown in this manner.
Specifically, the second crystals 52 are grown so that the openings
between the first crystals 42 are filled with the second crystals
52. Moreover, the sol-gel raw material and the MOD raw material
differ from each other in a direction in which the crystals tend to
be oriented. Therefore, the first crystals 42 and the second
crystals 52 interrupt the growth of the other, whereby the crystals
are easily microcrystallized. If the crystals are
microcrystallized, openings between the crystals are reduced. As a
result, the ceramic film 30 with improved surface morphology can be
formed.
[0225] Specific crystallization conditions for the raw material
body are described below.
[0226] As the thermal treatment method, a method of annealing the
raw material body by rapid thermal annealing (RTA) and furnace
annealing (FA) in an oxygen atmosphere can be given.
[0227] More specific crystallization conditions for the raw
material body are described below. The raw material body is
annealed at a temperature of 500 to 650.degree. C. for a short
period of time (5 to 30 seconds) by RTA, whereby microcrystal
nuclei are produced. At this time, crystal nuclei are first
produced from the sol-gel raw material. During the growth of the
crystals produced from the sol-gel raw material, crystal nuclei
produced from the MOD raw material are grown around the crystals
produced from the sol-gel raw material. Crystallization is promoted
by FA at 600 to 650.degree. C. for 10 to 30 minutes to obtain the
ceramic film 30.
Modification
[0228] The following modifications are applicable to the method of
manufacturing a ceramic film according to the above embodiment.
[0229] (1) The combination of the raw materials is not limited to
the above embodiment. For example, combinations given below may be
employed.
[0230] 1) A plurality of sol-gel raw materials with different
degrees of polycondensation may be used in combination. If the
degrees of polycondensation differ, directions in which the crystal
growth tends to proceed generally differ even if the compositions
are the same. Therefore, if the raw materials with different
degrees of polycondensation are mixed, the raw materials interrupt
the crystal growth of the other since the directions in which the
crystal growth tends to proceed differ. As a result, the crystals
are microcrystallized.
[0231] 2) Raw materials having compositions for different crystal
structures may be used in combination. For example, raw materials
which have the following relation may be used.
[0232] When ceramics obtained from the raw materials are expressed
as (Bi.sub.2O.sub.2).sup.2+(A.sub.m-1B.sub.mO.sub.3m+1).sup.2-, raw
materials having different values for m may be used. As an example
of compounds in which m=1, Bi.sub.2WO.sub.6 can be given. As an
example of compounds in which m=2, Bi.sub.3TiNbO.sub.9 can be
given. As an example of compounds in which m=3,
Bi.sub.4Ti.sub.3O.sub.12 can be given. These compounds are all
ferroelectrics, but have different crystal structures.
Specifically, although there are small differences in length in the
a-axis direction and the b-axis direction, the length in the c-axis
direction is 16.4 angstroms (1.64 nm) when m=1, 25.0 angstroms
(2.50 nm) when m=2, and 32.8 angstroms (3.28 nm) when m=3. Since
these compounds have different crystal structures, the raw
materials which produce these crystals differ from one another in
the crystal growth condition and the crystal growth mechanism.
[0233] In the case of using raw materials having compositions for
different crystal structures, it is preferable that an element in
the B site be common between the different raw materials for the
following reasons. Specifically, even if the different raw
materials are individually crystallized by allowing the crystal
growth condition and the crystal growth mechanism to be different,
interdiffusion occurs to a large extent near the crystal grain
boundary during the subsequent long annealing step. In this case,
if an element in the B site is replaced, characteristics of the
ceramics tend to deteriorate.
[0234] 3) A raw material which produces crystals having the crystal
structure Bi.sub.4Ti.sub.3O.sub.9 (hereinafter called "BTO raw
material") and a raw material which produces crystals having the
crystal structure PbTiO.sub.3 (hereinafter called "PTO raw
material") may be used in combination. PbTiO.sub.3 is a perovskite
having a tetragonal structure. However, since PTO has a small
difference in length between the a-axis and the c-axis, PTO has a
small degree of crystal growth anisotropy caused by the crystal
structure. Moreover, crystal nuclei are easily produced from the
PTO raw material at a comparatively low temperature. Therefore, in
the case of mixing the BTO raw material with the PTO raw material
at a lower ratio (about 10:1, for example) and allowing the
crystals to be grown, these materials interrupt the crystal growth
of the other. This causes the resulting crystals to be
microcrystallized. This effect is more significant than in the case
of crystals having the same layered perovskite structure.
[0235] 4) A raw material which produces ferroelectric crystals and
a raw material which produces paraelectric crystals may be used in
combination. The amount of raw materials to be mixed is determined
depending on the characteristics of the desired ceramic film.
[0236] 5) A sol-gel raw material and an MOD raw material may be
used in combination so that crystals having different crystal
structures are produced from the raw materials.
[0237] 6) Sol-gel raw materials with different degrees of
polycondensation may be used in combination so that crystals having
different crystal structures are produced from the raw
materials.
[0238] (2) A ceramic film may be formed by repeatedly performing
the method of manufacturing a ceramic film according to the present
invention two or more times. A ceramic film may be formed by
combining the method of manufacturing a ceramic -film according to
the present invention and a conventional method of manufacturing a
ceramic film.
[0239] (3) As a method for forming the raw material body on the
base by using the LSMCD method, the following method can be given.
FIG. 3 is a cross-sectional view schematically showing an apparatus
200 for forming the raw material body on the base by using the
LSMCD method.
[0240] A first raw material 210 is sent to a mesh 240 through an
atomizer 230. The first raw material 210 passing through the mesh
240 forms a mist 250 and is supplied to the base 10. A second raw
material 220 is sent to the mesh 240 through an atomizer 232. The
second raw material 220 passing through the mesh 240 forms the mist
250 and is supplied to the base 10. A raw material body is formed
by allowing the mist 250 to be repeatedly deposited on the base 10.
The diameter of droplets of the mist 250 is 10 to 200 nm, for
example.
[0241] The first raw material 210 and the second raw material 220
may be supplied to the base 10 at the same time. The first raw
material 210 and the second raw material 220 may be supplied
alternately.
[0242] In the case of supplying the first raw material 210 and the
second raw material 220 to the base 10 at the same time, the
resulting raw material body has a structure in which first mist
droplets 210a produced from the first raw material 210 and second
mist droplets 220a produced from the second raw material 220 are
mixed as shown in FIG. 4A, for example.
[0243] In the case of alternately supplying the first raw material
210 and the second raw material 220, the resulting raw material
body has a structure in which each of the first mist droplets 210a
produced from the first raw material 210 and the second mist
droplets 220a produced from the second raw material 220 makes up
one layer, as shown in FIG. 4B, for example. In other words, each
layer is formed by the mist droplets produced from the same raw
material.
[0244] In the case of alternately supplying the first raw material
liquid 210 and the second raw material liquid 220, different
crystal structures can be formed in a single layer from the mist
droplets produced from different raw materials by using the
following method.
[0245] As shown in FIGS. 3 and 12, after supplying the first mist
droplets 210a produced from the first raw material liquid 210 to
the base 10 so as to be dispersed on the base 10, the first mist
droplets 210a are heated so that a solvent contained in the first
mist droplets 210a is evaporated. The first mist droplets 210a are
dispersed on the base 10 at this stage.
[0246] The second mist droplets 220a can be interposed between the
first mist droplets 210a by supplying the second mist droplets 220a
produced from the second raw material liquid 220 in this state.
[0247] The first mist droplets 210a and the second mist droplets
220a are crystallized by a thermal treatment to form the ceramic
film 30. As shown in FIG. 13, the ceramic film 30 consists of first
crystals 42 produced from the first mist droplets 210a and second
crystals 52 produced from the second mist droplets 220a. This
enables a ceramic film in which at least first crystal phases are
intermittently provided in the surface direction of the ceramic
film to be easily obtained.
[0248] The second raw material liquid may be interposed between the
first mist droplets 210a by applying the second raw material liquid
by spin coating in a state in which the first mist droplets 210a
are dispersed on the base 10 instead of forming the second mist
droplets 220a. This method also enables a ceramic film in which at
least first crystal phases are intermittently provided in the
surface direction of the ceramic film to be easily obtained.
[0249] (4) In the case of using the combination of the raw
materials described in the first embodiment or any of the
combinations 1) to 6) of the raw materials described in the
modification of the first embodiment, solvents in which the raw
materials are dissolved may have different polarities. In this
case, since the raw materials are easily phase separated, crystals
produced from the different raw materials are easily intermittently
formed in the surface direction of the ceramic film.
[0250] For example, one of the solvents may be soluble in water,
and the other solvent may be insoluble in water. As a solvent
soluble in water, acetate, nitrate, and the like can be given. As a
solvent insoluble in water, butanol and the like can be given.
Second Embodiment
First Ceramic Raw Material Liquid
[0251] A first ceramic raw material liquid is used by mixing a
first raw material liquid and a second raw material liquid. The
first ceramic raw material liquid may be a raw material liquid from
which a ceramic film is obtained by pyrolysis. The first raw
material liquid and the second raw material liquid produce
different types of materials. The first and second raw material
liquids may be: 1) a liquid in which a metal organic compound
(metal alkoxide, metal carboxylate, for example) or a metal
inorganic compound (metal nitrate, metal chloride, for example) is
dissolved in a solvent (water, alcohol, ester, aliphatic
hydrocarbon, aromatic hydrocarbon, ketone, ether, mixture of these,
for example); 2) a liquid obtained by subjecting a metal compound
to hydrolysis, condensation, and the like in a solvent; or 3) a
sol-gel liquid obtained by hydrolysis of a metal alkoxide.
[0252] The first raw material liquid and the second raw material
liquid are described below in detail.
[0253] The first raw material liquid is a raw material liquid for
producing a ferroelectric having a Bi-based layered perovskite
structure. As examples of ferroelectrics having a Bi-based layered
perovskite structure, SrBiTaO-based ferroelectrics
(SrBi.sub.2Ta.sub.2O.sub.9, for example), BiLaTiO-based
ferroelectrics (Bi.sub.3.25La.sub.0.75Ti.sub.3O.sub.12, for
example), and BiTiO-based ferroelectrics (Bi.sub.4Ti.sub.3O.sub.12,
for example) can be given. The first raw material liquid contains
metal elements which make up a ferroelectric. The amount of
constituent metal elements for a ferroelectric contained in the
first raw material liquid is determined taking into consideration
the amount of a desired ferroelectric and the ratio of the number
of atoms of constituent metal elements in the desired
ferroelectric.
[0254] As examples of the first raw material liquid, in the case of
SrBiTaO-based ferroelectrics, a liquid in which solutions of an
alkoxide of strontium, an alkoxide of bismuth, and an alkoxide of
tantalum are mixed in 2-methoxyethanol can be given. The
concentration of an alkoxide of strontium, an alkoxide of bismuth,
and an alkoxide of tantalum in the first raw material liquid maybe
0.05 mol/l, 0.1 mol/l, and 1.0 mol/l, respectively. Specifically,
the concentration may be set so that 0.05 mol of an
SrBi.sub.2Ta.sub.2O.sub.9 ferroelectric is produced per liter of
the first raw material liquid.
[0255] The second raw material liquid is a raw material liquid for
producing an ABO-type oxide in which Bi is provided in the A site.
If Bi is not provided in the A site, an element other than Bi may
be positioned at the site of the Bi-type layered perovskite
structure at which Bi should be positioned, whereby the
characteristics of the ferroelectric film may be adversely
affected. As examples of the ABO-type oxide in which Bi is provided
in the A site, BiGeO-based oxides (Bi.sub.4Ge.sub.3O.sub.12, for
example), BiMoO-based oxides (Bi.sub.2MoO.sub.6), BiVO-based oxides
(Bi.sub.2VO.sub.6), BiCrO-based oxides (Bi.sub.2CrO.sub.6),
BiSiO-based oxides (Bi.sub.4Si.sub.3O.sub.12), and BiWO-based
oxides (Bi.sub.4W.sub.3O.sub.12) can be given. These oxides may be
used individually or in combination of two or more. The
crystallization temperature of the crystals produced from the
second raw material liquid can be changed by changing an element in
the B site of the ABO-type oxide. The ABO-type oxide may be either
a ferroelectric or a paraelectric. In the case of a paraelectric,
an element in the B site is preferably either Si or Ge.
[0256] The second raw material liquid contains metal elements which
make up the ABO-type oxide. The amount of constituent metal
elements for the ABO-type oxide contained in the second raw
material liquid is determined taking into consideration the amount
of a desired ABO-type oxide and the ratio of the number of atoms of
constituent metal elements in the desired ABO-type oxide.
[0257] As examples of the second raw material liquid, in the case
of a BiGeO-based oxide, a liquid in which solutions of an alkoxide
of bismuth and an alkoxide of germanium are mixed in
2-methoxyethanol can be given. The concentration of an alkoxide of
bismuth and an alkoxide of germanium in the second raw material
liquid may be 0.20 mol/l and 0.15 mol/l, respectively.
Specifically, the concentration of an alkoxide of bismuth and an
alkoxide of germanium may be set so that 0.05 mol of a
Bi.sub.4Ge.sub.3O.sub.12 oxide is produced per liter of the second
raw material liquid.
[0258] The first raw material liquid and the second raw material
liquid are preferably mixed so that the molar ratio of the
ferroelectric produced from the first raw material liquid to the
ABO-type oxide produced from the second raw material liquid is from
100:20 to 100:100. The reasons therefor are described in the
description of examples.
Example of Manufacture of Ceramic Film
[0259] A ceramic film can be formed by using the ceramic raw
material liquid of the present embodiment as described below, for
example. The manufacturing process for a ceramic film is described
below with reference to FIG. 1 which is a cross-sectional view
schematically showing the manufacturing steps for a ceramic film in
the same manner as in the first embodiment.
[0260] (a) The base 10 is subjected to a thermal treatment. This
thermal treatment is performed for removing moisture present on the
surface of the base 10. The thermal treatment temperature is
180.degree. C., for example.
[0261] (b) The ceramic raw material liquid is applied to the base
10, thereby forming the ceramic raw material body layer 20. As the
formation method, spin coating, dipping, and LSMCD can be
given.
[0262] (c) A solvent present in the ceramic raw material body layer
20 is evaporated by a dry thermal treatment. The solvent may be
evaporated in a nitrogen atmosphere. The temperature of dry thermal
treatment is 160.degree. C., for example.
[0263] (d) The ceramic raw material body layer 20 is subjected to a
pyrolizing. Organic substances present in the ceramic raw material
body layer 20 are decomposed by this thermal treatment. The organic
substances may be decomposed in a nitrogen atmosphere. The thermal
treatment temperature is 260.degree. C., for example.
[0264] (e) The ceramic raw material body layer 20 is calcined.
Crystal nuclei are formed during the calcining. Calcining may be
performed by RTA in an oxygen atmosphere, for example.
[0265] (f) The ceramic raw material body layer 20 is sintered.
Sintering may be performed by FA in an oxygen atmosphere, for
example.
[0266] A cycle consisting of the steps (a) to (e) may be repeated
two or more times.
Effect
[0267] Effects obtained by depositing a ceramic film using the
ceramic raw material liquid according to the second embodiment are
described below.
[0268] (1) In the case of forming a ferroelectric (SBT) film by
sintering the ceramic raw material liquid consisting only of the
first raw material liquid, desired characteristics (remanent
polarization, for example) required for the ferroelectric film
cannot be obtained at a sintering temperature of less than about
700.degree. C.
[0269] However, in the case of forming a ceramic film by sintering
the first ceramic raw material liquid in which the first raw
material liquid and the second raw material liquid are mixed,
desired characteristics required for the ferroelectric film can be
obtained even at a sintering temperature of about 500.degree. C. as
described later. In other words, according to the present
embodiment, a ferroelectric film having desired characteristics can
be formed at a lower temperature.
[0270] (2) A material produced from the first raw material liquid
differs from a material produced from the second raw material
liquid. Therefore, a crystallization temperature at which the first
raw material liquid is crystallized differs from a crystallization
temperature at which the second raw material liquid is
crystallized, for example. As a result, one of the raw material
liquids can be crystallized prior to the other raw material liquid.
Because of this, the crystals 52 produced from one of the raw
material liquids can be grown between the crystals 42 produced from
the other raw material liquid, as shown in FIG. 1B. Specifically,
the crystals 42 produced from one of the raw material liquids and
the crystals 52 produced from the other raw material liquid are
individually grown so that the openings between the crystals 42 are
filled with the crystals 52. As a result, a ceramic film with
improved surface morphology can be formed.
[0271] (3) If the direction in which the crystals produced from the
second raw material liquid tend to be oriented differs from the
direction in which the crystals produced from the first raw
material liquid tend to be oriented, crystal growth of the crystals
produced from one of the raw material liquids is interrupted by the
crystal growth of the other crystals. Therefore, crystals in the
resulting ceramic film can be microcrystallized. As a result, a
ceramic film with improved surface morphology can be formed.
Modification
[0272] The following modifications are applicable to the second
embodiment.
[0273] (1) A ceramic film may be formed by repeatedly performing
the above manufacturing steps of a ceramic film two or more times.
A ceramic film may be formed by combining the above manufacturing
steps of a ceramic film and manufacturing steps of a ceramic film
using a conventional ceramic raw material.
[0274] (2) As an example of a method for forming the raw material
body on the base by using the LSMCD method, the following method
can be given. FIG. 3 is a cross-sectional view schematically
showing the apparatus 200 for forming the raw material body on the
base by using the LSMCD method.
[0275] The first raw material liquid 210 is sent to the mesh 240
through the atomizer 230. The first raw material liquid 210 passing
through the mesh 240 forms the mist 250 and is supplied to the base
10. The second raw material liquid 220 is sent to the mesh 240
through the atomizer 232. The second raw material liquid 220
passing through the mesh 240 forms the mist 250 and is supplied to
the base 10. The raw material body is formed by allowing the mist
250 to be repeatedly deposited on the base 10. The diameter of
droplets of the mist 250 is 10 to 200 nm, for example.
[0276] The first raw material liquid 210 and the second raw
material liquid 220 may be supplied to the base 10 at the same
time. The first raw material liquid 210 and the second raw material
liquid 220 may be alternately supplied.
[0277] In the case of supplying the first raw material liquid 210
and the second raw material liquid 220 to the base 10 at the same
time, the resulting raw material body has a structure in which the
first mist droplets 210a produced from the first raw material
liquid 210 and the second mist droplets 220a produced from the
second raw material liquid 220 are mixed, as shown in FIG. 4A, for
example.
[0278] In the case of alternately supplying the first raw material
liquid 210 and the second raw material liquid 220, the resulting
raw material body may have a structure in which each of the first
mist droplets 210a produced from the first raw material liquid 210
and the second mist droplets 220a produced from the second raw
material liquid 220 makes up one layer, as shown in FIG. 4B, for
example. In other words, each layer is formed by the mist droplets
produced from the same raw material.
[0279] In the case of alternately supplying the first raw material
210 and the second raw material 220, different crystal structures
can be formed in a single layer from the mist droplets produced
from different raw materials by using the following method.
[0280] As shown in FIGS. 3 and 12, after supplying the first mist
droplets 210a produced from the first raw material liquid 210 to
the base 10 so as to be dispersed on the base 10, the first mist
droplets 210a are heated so that a solvent contained in the first
mist droplets 210a is evaporated. The first mist droplets 210a are
dispersed on the base 10 at this stage.
[0281] The second mist droplets 220a can be interposed between the
first mist droplets 210a by supplying the second mist droplets 220a
produced from the second raw material liquid 220 in this state.
[0282] The first mist droplets 210a and the second mist droplets
220a are crystallized by a thermal treatment, whereby the ceramic
film 30 is formed. As shown in FIG. 13, the ceramic film 30
consists of the first crystals 42 produced from the first mist
droplets 210a and the second crystals 52 produced from the second
mist droplets 220a. This enables a ceramic film in which at least
first crystal phases are intermittently provided in the surface
direction of the ceramic film to be easily obtained.
[0283] The second raw material liquid may be interposed between the
first mist droplets 210a by applying the second raw material liquid
by spin coating in a state in which the first mist droplets 210a
are dispersed on the base 10 instead of forming the second mist
droplets 220a. This method also enables a ceramic film in which at
least first crystal phases are intermittently provided in the
surface direction of the ceramic film to be easily obtained.
[0284] (3) In the case of using the combination of the raw
materials described in the second embodiment, solvents in which the
raw materials are dissolved may have different polarities. In this
case, since the raw materials are easily phase separated, crystals
produced from the different raw materials are easily intermittently
formed in the surface direction of the ceramic film.
[0285] For example, one of the solvents may be soluble in water,
and the other solvent may be insoluble in water. As a solvent
soluble in water, acetate, nitrate, and the like can be given. As a
solvent insoluble in water, butanol and the like can be given.
Third Embodiment
Second Ceramic Raw Material Liquid
[0286] A second ceramic raw material liquid is used by mixing a
third raw material liquid and a fourth raw material liquid. The
second ceramic raw material liquid may be a raw material liquid
from which a ceramic film is obtained by pyrolysis. The third raw
material liquid and the fourth raw material liquid produce
different types of materials. The third and fourth raw material
liquids may be: 1) a liquid in which a metal organic compound
(metal alkoxide, metal carboxylate, for example) or a metal
inorganic compound (metal nitrate, metal chloride, for example) is
dissolved in a solvent (water, alcohol, ester, aliphatic
hydrocarbon, aromatic hydrocarbon, ketone, ether, mixture of these,
for example); 2) a liquid obtained by subjecting a metal compound
to hydrolysis, condensation, and the like in a solvent; or 3) a
sol-gel liquid obtained by hydrolysis of a metal alkoxide.
[0287] The third raw material liquid and the fourth raw material
liquid are described below in detail.
[0288] The third raw material liquid is a raw material liquid for
producing a PZT-type ferroelectric. As examples of PZT-type
ferroelectrics, PbZrTiO-based ferroelectrics
(PbZr.sub.yTi.sub.1-yO.sub.3, for example) and PbLaZrTiO-based
ferroelectrics (Pb.sub.1-xLa.sub.xZr.sub.yTi.sub.1-yO.sub.3, for
example) can be given. The third raw material liquid contains metal
elements which make up a ferroelectric. The amount of constituent
metal elements for a ferroelectric contained in the third raw
material liquid is determined taking into consideration the amount
of the desired ferroelectric and the ratio of the number of atoms
of constituent metal elements in the desired ferroelectric.
[0289] As examples of the third raw material liquid, taking a
PbZrTiO-based ferroelectric as an example, a liquid in which lead
acetate trihydrate, zirconium butoxide, and titanium isopropoxide
are mixed in 1-methoxy-2-propanol can be given. The amount of lead
acetate trihydrate, zirconium butoxide, and titanium isopropoxide
is determined taking into consideration the ratio of the number of
atoms of the constituent metal elements in the desired
ferroelectric and the amount of the desired ferroelectric.
[0290] The fourth raw material liquid is a raw material liquid for
producing an ABO-type oxide in which Pb is provided in the A site.
If Pb is not provided in the A site, an element other than Pb may
be positioned at the site of the PZT-type oxide at which Pb should
be positioned, whereby the characteristics of the ferroelectric
film may be adversely affected. As examples of the ABO-type oxide
in which Pb is provided in the A site, PbGeO-based oxides
(Pb.sub.5Ge.sub.3O.sub.1l), PbMoO-based oxides (Pb.sub.2MoO.sub.5),
PbVO-based oxides (Pb.sub.2VO.sub.5), PbCrO-based oxides
(Pb.sub.2CrO.sub.5), PbSiO-based oxides (Pb.sub.5Si.sub.3O.sub.1l),
PbWO-based oxides (Pb.sub.2WO.sub.5), PbSnO-based oxides
(PbSnO.sub.3), and PbGeSiO-based oxides
(Pb.sub.5Ge.sub.2SiO.sub.11) can be given. These oxides may be used
individually or in combination of two or more. The crystallization
temperature of the crystals produced from the second raw material
liquid can be changed by changing an element in the B site of the
ABO-type oxide. The ABO-type oxide may be either a ferroelectric or
a paraelectric. In the case of a paraelectric, an element in the B
site is preferably one of Ge, Si, and Sn, or combination of these
elements.
[0291] As examples of the fourth raw material liquid, taking a
PbGeO-based oxide as an example, a liquid in which germanium
ethoxide and lead butoxide are mixed in 1-methoxy-2-propanol can be
given. The amount of germanium ethoxide and lead butoxide is
determined taking into consideration the ratio of the number of
atoms of constituent metal elements in the desired oxide and the
amount of the desired oxide.
[0292] The third raw material liquid and the fourth raw material
liquid are preferably mixed so that the molar ratio of the
ferroelectric obtained from the third raw material liquid to the
ABO-type oxide obtained from the fourth raw material liquid is from
100:20 to 100:100.
Second Example of Manufacture of Ceramic Film
[0293] A method of manufacturing a ceramic film using the second
ceramic raw material liquid may be the method of manufacturing a
ceramic film using the first ceramic raw material liquid.
Effect
[0294] Effects obtained by depositing a ceramic film using the
ceramic raw material liquid according to the third embodiment are
described below.
[0295] (1) According to the ceramic raw material liquid according
to the present embodiment, a ferroelectric film having specific
characteristics can be obtained at a sintering temperature lower
than a sintering temperature necessary for providing the specific
characteristics when forming a ferroelectric film by sintering only
the third raw material liquid. In other words, according to the
present embodiment, a ferroelectric film having the desired
characteristics can be formed at a lower temperature.
[0296] (2) A material produced from the third raw material liquid
differs from a material produced from the fourth raw material
liquid. Therefore, a crystallization temperature at which the third
raw material liquid is crystallized differs from a crystallization
temperature at which the fourth raw material liquid is
crystallized, for example. As a result, a ceramic film with
improved surface morphology can be formed in the same manner as in
the second embodiment.
[0297] The modifications illustrated in the second embodiment are
also applicable to the third embodiment.
Fourth Embodiment
Third Ceramic Raw Material Liquid
[0298] A third ceramic raw material liquid is used by mixing a
fifth raw material liquid and a sixth raw material liquid. The
fifth ceramic raw material liquid may be a raw material liquid from
which a ceramic film is obtained by pyrolysis. The fifth raw
material liquid and the sixth raw material liquid produce different
types of materials. The fifth and sixth raw material liquids may
be: 1) a liquid in which a metal organic compound (metal alkoxide,
metal carboxylate, for example) or a metal inorganic compound
(metal nitrate, metal chloride, for example) is dissolved in a
solvent (water, alcohol, ester, aliphatic hydrocarbon, aromatic
hydrocarbon, ketone, ether, mixture of these, for example); 2) a
liquid obtained by subjecting a metal compound to hydrolysis,
condensation, and the like in a solvent; or 3) a sol-gel liquid
obtained by hydrolysis of a metal alkoxide.
[0299] The fifth raw material liquid and the sixth raw material
liquid are described below in more detail.
[0300] The fifth raw material liquid is a raw material liquid for
producing a ferroelectric having a Bi-based layered perovskite
structure or a PZT-type ferroelectric. As a ferroelectric having a
Bi-based layered perovskite structure, ferroelectrics illustrated
for the first ceramic raw material liquid can be given. As a
PZT-type ferroelectric, PZT-type ferroelectrics illustrated for the
first ceramic raw material liquid can be given. As examples of the
fifth raw material liquid, in the case of a ferroelectric having a
Bi-based layered perovskite structure, examples illustrated for the
first raw material liquid (second embodiment) can be given. In the
case of a PZT-type ferroelectric, examples illustrated for the
third raw material liquid (third embodiment) can be given.
[0301] The sixth raw material liquid is a raw material liquid for
producing an AGeO-based oxide. An oxide in which Ge is provided in
the B site has a low melting point of about 700.degree. C., whereby
the process temperature can be decreased. As examples of an element
in the A site of the AGeO-based oxide, alkaline earth metals, rare
earth elements (Ce, in particular), Zr, Sr, and Bi can be given. As
examples of a ZrGeO-based oxide, ZrGeO.sub.4 can be given. As
examples of an SrGeO-based oxide, Sr.sub.5Ge.sub.3O.sub.11 can be
given. As examples of the sixth raw material liquid, in the case of
a BiGeO-based oxide, examples illustrated for the second raw
material liquid (second embodiment) can be given. The AGeO-based
oxide may be either a paraelectric or a ferroelectric.
[0302] The fifth raw material liquid and the sixth raw material
liquid are preferably mixed so that the molar ratio of the
ferroelectric obtained from the fifth raw material liquid to the
ABO-type oxide obtained from the sixth raw material liquid is from
100:20 to 100:100.
Third Example of Manufacture of Ceramic Film
[0303] The method of manufacturing a ceramic film using the third
ceramic raw material liquid may be the method of manufacturing a
ceramic film using the first ceramic raw material liquid.
Effect
[0304] Effects obtained by depositing a ceramic film using the
ceramic raw material liquid according to the fourth embodiment are
described below.
[0305] (1) According to the ceramic raw material liquid of the
present embodiment, a ferroelectric film having specific
characteristics can be obtained at a sintering temperature lower
than a sintering temperature necessary for providing the specific
characteristics when forming a ferroelectric film by sintering only
the fifth raw material liquid. In other words, according to the
present embodiment, a ferroelectric film having the desired
characteristics can be formed at a lower temperature.
[0306] (2) A material produced from the fifth raw material liquid
differs from a material produced from the sixth raw material
liquid. Therefore, a crystallization temperature at which the fifth
raw material liquid is crystallized differs from a crystallization
temperature at which the sixth raw material liquid is crystallized,
for example. As a result, a ceramic film with improved surface
morphology can be formed in the same manner as in the second
embodiment.
[0307] (3) If the direction in which the crystals produced from the
sixth raw material liquid tend to be oriented differs from the
direction in which the crystals produced from the fifth raw
material liquid tend to be oriented, the crystal growth of the
crystals produced from one of the raw material liquids is
interrupted by the crystal growth of the other crystals. Therefore,
crystals in the resulting ceramic film can be microcrystallized. As
a result, a ceramic film with improved surface morphology can be
formed.
[0308] The modifications illustrated in the second embodiment are
also applicable to the fourth embodiment.
Fifth Embodiment
[0309] An example of the manufacture of a multilayer ceramic film
according to a fifth embodiment is described below.
Example of Manufacture of First Multilayer Ceramic Film
[0310] An example of the manufacture of a first multilayer ceramic
film is described below. FIG. 5 is a cross-sectional view
schematically showing the manufacturing process for the first
multilayer ceramic film.
[0311] A main liquid layer 312 for producing a ferroelectric is
formed on the base 10 by using a coating method, as shown in FIG.
5A. As the material for the main liquid layer 312, the first raw
material liquid in the second embodiment and the third raw material
liquid in the third embodiment can be given.
[0312] A secondary liquid layer 322 for producing either a
ferroelectric or a paraelectric is formed on the main liquid layer
312. As the material for the secondary liquid layer 322, a material
having a crystallization temperature lower than that of the
material for the main liquid layer 312 is selected. In addition, a
material from which an oxide having no layered structure is
produced after crystallization is selected as the material for the
secondary liquid layer 322. The material for the secondary liquid
layer 322 differs depending upon the material for the main liquid
layer 312. In the case where an SBT-type ferroelectric is formed by
crystallizing the main liquid layer 312, the material for the
secondary liquid layer 322 is a BiGeO-based material, BiSiO-based
material, or SrGeO-based material, for example.
[0313] The main liquid layer 312 and the secondary liquid layer 322
are crystallized by performing a thermal treatment as shown in FIG.
5C, thereby forming a ceramic film 300 consisting of a main crystal
layer 310 and a secondary crystal layer 320.
[0314] According to this example of the manufacture of the first
multilayer ceramic film, the following effects are obtained.
[0315] As the material for the secondary liquid layer 322, a
material having a crystallization temperature lower than that of
the main liquid layer 312 is selected. Therefore, the secondary
liquid layer 322 is crystallized before the main liquid layer 312
at an initial stage of crystallization, as shown in FIG. 5B. As a
result, crystals produced in the secondary liquid layer 322
function as seeds during the crystallization of the main liquid
layer 312. Therefore, crystallization of the main liquid layer 312
proceeds in the direction from the secondary liquid layer 322 and
from the base 10. This enables the grain size of crystals produced
in the main liquid layer 312 to be decreased.
[0316] A material from which an oxide having no layered structure
is produced after crystallization is used as the material for the
secondary liquid layer 322. Therefore, crystals are isotropically
grown in the secondary liquid layer 322. As a result, a secondary
crystal layer 320 with a flat surface is formed, whereby the
surface morphology of the ceramic film 300 can be improved.
[0317] The ceramic film 300 consisting of the main crystal layer
310 and the secondary crystal layers 320 and 330 may be formed by
allowing a secondary liquid layer 332 to be interposed between the
base 10 and the main liquid layer 312, as shown in FIG. 6A.
Example of Manufacture of Second Multilayer Ceramic Film
[0318] An example of the manufacture of a second multilayer ceramic
film is described below. FIG. 7 is a cross-sectional view
schematically showing the manufacturing process for the second
multilayer ceramic film.
[0319] The example of the manufacture of the second multilayer
ceramic film differs from the example of the manufacture of the
first multilayer ceramic film in that a secondary liquid layer 422
is interposed between main liquid layers 412 and 432.
[0320] Specifically, the main liquid layer 412, secondary liquid
layer 422, main liquid layer 432, and secondary liquid layer 442
are layered on the base 10 in that order. A ceramic film 400
consisting of main crystal layers 410 and 430 and secondary crystal
layers 420 and 440 are formed by crystallizing these layers.
[0321] As the material for the secondary liquid layers 422 and 442,
a material having a crystallization temperature lower than that of
the main liquid layers 412 and 432 is selected in the same manner
as in the example of the manufacture of the first multilayer
ceramic film.
[0322] Crystals produced in the secondary liquid layer 422 function
as a stopper for preventing crystal growth in the main liquid
layers 412 and 432 by allowing the secondary liquid layer 422 to be
interposed between the main liquid layers 412 and 432. Therefore,
the grain size of crystals in the main crystal layers 410 and 430
formed on opposite sides of the secondary crystal layer 420 can be
decreased.
Example of Manufacture of Third Multilayer Ceramic Film
[0323] An example of the manufacture of a third multilayer ceramic
film is described below. FIG. 8 is a cross-sectional view
schematically showing the manufacturing process for the third
multilayer ceramic film.
[0324] The example of the manufacture of the third multilayer
ceramic film differs from the example of the manufacture of the
first multilayer ceramic film in that a material for a main liquid
layer 512 has a crystallization temperature lower than that of the
material for a secondary liquid layer 522.
[0325] As the material for the main liquid layer 512, the first raw
material liquid in the second embodiment and the third raw material
liquid in the third embodiment can be given. In the case where the
material for the main liquid layer 512 produces a PZT-type
ferroelectric, the material for the secondary liquid layer 522 may
be a PbWO-based material or a PbMoO-based material.
[0326] A ceramic film with improved surface morphology can be
formed by crystallizing the main liquid layer 512 and the secondary
liquid layer 522. The reasons therefor are as follows. The material
for the main liquid layer 512 has a crystallization temperature
lower than that of the material for the secondary liquid layer 522.
Therefore, crystallization of the secondary liquid layer 522
proceeds after the crystallization of the main liquid layer 512,
whereby the crystals produced from the secondary liquid layer 522
are grown to cover a main crystal layer 510 produced from the main
liquid layer 512. Since the crystals produced from the secondary
liquid layer 522 do not have a layered structure, crystals produced
from the secondary liquid layer 522 are isotropically grown.
Therefore, a secondary crystal layer 520 with a flat surface is
formed. This decreases unevenness on the surface of a ceramic film
500, whereby the surface morphology of the ceramic film 500 can be
improved.
[0327] In the above examples of the manufacture of the first to
third multilayer ceramic films, crystal grains produced from the
main liquid layer and crystal grains produced from the secondary
liquid layer may be diffused into different crystal layers.
Moreover, a constituent metal element of the main liquid layer may
be diffused into the secondary liquid layer, or a constituent metal
element of the secondary liquid layer may be diffused into the main
liquid layer. Therefore, there may be a case where the interface
between the main crystal layer produced from the main liquid layer
and the secondary crystal layer produced from the secondary liquid
layer is not distinguishable.
[0328] Generally, the crystallization temperature has a correlation
with the melting point. Specifically, in the case where one of the
crystals has a crystallization temperature higher than that of the
other crystal, the crystal having a higher crystallization
temperature generally has a melting point higher than that of the
other crystal.
Sixth Embodiment
Semiconductor Device
[0329] A semiconductor device to which a ceramic film obtained by
using the method of manufacturing a ceramic film of the present
invention is applied is described below. The present embodiment
illustrates a ferroelectric memory device as an example of the
semiconductor device. FIG. 2 is a cross-sectional view
schematically showing a ferroelectric memory device.
[0330] A ferroelectric memory device 5000 includes a CMOS region
R1, and a capacitor region R2 formed on the CMOS region R1. The
CMOS region R1 includes a semiconductor substrate 1, an element
isolation region 2 and a MOS transistor 3 which are formed on the
semiconductor substrate 1, and an interlayer dielectric 4. The
capacitor region R2 includes a capacitor C100 consisting of a lower
electrode 5, a ferroelectric film 6, and an upper electrode 7, an
interconnect layer 8a connected with the lower electrode 5, an
interconnect layer 8b connected with the upper electrode 7, and an
insulating layer 9. The ferroelectric film 6 in the capacitor C100
is formed by using the method of manufacturing a ceramic film of
the present invention. An impurity diffusion layer 3a of the MOS
transistor 3 and the lower electrode 5 which makes up the capacitor
are connected by a contact layer 11 formed of polysilicon or
tungsten.
[0331] Effects of the ferroelectric device are described below.
[0332] (1) When forming a ferroelectric film, the thickness of the
ferroelectric film must be increased in order to prevent occurrence
of a short circuit between the upper electrode and the lower
electrode, taking into consideration formation of grooves or holes.
A short circuit between the upper electrode and the lower electrode
occurs considerably when the upper electrode is formed of an
iridium-based material (Ir, IrO.sub.2). However, in the present
embodiment, the ferroelectric film 6 of the ferroelectric device
5000 is formed by using the method of manufacturing a ceramic film
of the present invention. Therefore, the ferroelectric film 6 has
improved surface morphology. As a result, the thickness of the
ferroelectric film 6 can be decreased to such an extent that the
surface morphology of the ferroelectric film 6 is improved.
Therefore, according to the ferroelectric memory device 5000, a
higher degree of integration can be achieved. Moreover, since the
crystals of the ferroelectric material and the crystals of the
paraelectric material are intermittently dispersed in the surface
direction of the ceramic film as shown in FIG. 13, hysteresis
characteristics with good squareness can be obtained. This
increases the SN ratio of a ferroelectric memory device in which
this ceramic film is used as the capacitor film, whereby an
increase in speed can be achieved.
[0333] According to the present embodiment, the range of the
thickness of the ferroelectric film 6 for which an iridium-based
material is used as the material for the upper electrode 7 can be
increased. Specifically, the lower limit for the thickness of the
ferroelectric film 6 for which an iridium-based material is used as
the material for the upper electrode 7 can be decreased.
[0334] An iridium-based material has an advantage of having
superior hydrogen barrier characteristics and fatigue
characteristics in comparison with platinum (Pt).
[0335] (2) If the ferroelectric film is etched in a state in which
unevenness is formed on the surface of the ferroelectric film, the
unevenness formed on the surface of the ferroelectric film is
transferred to the surface of the lower electrode, which is an
underlay for the ferroelectric film. This causes the surface
morphology of the lower electrode to deteriorate. If the surface
morphology of the lower electrode deteriorates, a contact failure
may occur between the interconnect layer to be connected to the
lower electrode and the lower electrode.
[0336] However, the surface morphology of the ferroelectric film 6
is improved in the present embodiment. Therefore, deterioration of
the surface morphology of the lower electrode 5 after etching the
ferroelectric film 6 can be prevented. As a result, the
interconnect layer 8a can be electrically connected to the lower
electrode 9 reliably.
Modification
[0337] The ceramic film obtained by using the method of
manufacturing a ceramic film of the present invention can be
applied not only to the ferroelectric memory, but also to various
types of semiconductor devices such as a DRAM. Specifically, the
ceramic film of the present invention may be applied to a
dielectric film for a capacitor of a DRAM. In this case, the
dielectric film maybe formed of a paraelectric having a high
dielectric constant, such as BST, from the viewpoint of an increase
in capacitance of the capacitors.
[0338] The ceramic film obtained by using the method of
manufacturing a ceramic film of the present invention may be
applied not only to semiconductor devices, but also to other
applications such as a piezoelectric for piezoelectric devices used
for actuators.
[0339] The present invention is described below in more detail by
examples. The present invention is not limited to the following
examples, and other examples are possible within the scope of the
present invention.
EXAMPLE 1
[0340] A main liquid was obtained as follows. 1100 ml of a toluene
solution of bismuth 2-ethylhexanoate at a concentration of 0.1
mol/l, 400 ml of a toluene solution of strontium 2-ethylhexanoate
at a concentration of 0.1 mol/l, 1000 ml of a toluene solution of
tantalum ethoxide at a concentration of 0.1 mol/l, and 100 g of
2-ethylhexanoic acid were mixed to prepare a mixed liquid. After
refluxing the mixture while heating at 120.degree. C. for one hour
in a nitrogen atmosphere, the solvent was evaporated at atmospheric
pressure. Toluene was added to the mixture so that the oxide
concentration as Sr.sub.0.8Bi.sub.2.2Ta.sub.2O.sub.X (SBT) was 0.1
mol/l to obtain a main liquid.
[0341] A secondary liquid was obtained as follows. 2000 ml of a
toluene solution of bismuth 2-ethylhexanoate at a concentration of
0.1 mol/l, 1500 ml of a toluene solution of germanium ethoxide at a
concentration of 0.1 mol/l, and 100 g of 2-ethylhexanoic acid were
mixed. After refluxing the mixture while heating at 120.degree. C.
for one hour in a nitrogen atmosphere, the solvent was evaporated
at atmospheric pressure. Toluene was added to the mixture so that
the oxide concentration as Bi.sub.4Ge.sub.3O.sub.12 was 0.1 mol/l
to obtain a secondary liquid.
[0342] The main liquid and the secondary liquid thus obtained were
mixed to obtain seven types of mixed liquids with different volume
mixing ratios. The volume mixing ratios of the main liquid to the
secondary liquid were 100:1, 100:10, 100:20, 100:50, 100:100,
100:150, and 100:200.
[0343] Ferroelectric films were formed from each of these seven
types of mixed liquids and a solution containing only the main
liquid.
[0344] The deposition method is shown in FIG. 9. A series of steps
consisting of a pretreatment heating step, a solution coating step,
a dry thermal treatment step, a pyrolizing step, and a calcining
step was performed two times. The calcined product was sintered to
form a film. Specific conditions are given below. The pretreatment
heating step was performed at 180.degree. C. for 30 seconds. The
mixed liquid was applied for 30 seconds using a spin coater (2100
rpm). The dry thermal treatment step was performed at 160.degree.
C. for one minute in a nitrogen atmosphere. The pyrolizing step was
performed at 260.degree. C. for four minutes in a nitrogen
atmosphere. Calcining was performed for 30 seconds in an oxygen
atmosphere. The calcining temperature is shown in Table 1.
Sintering was performed for 60 minutes in an oxygen atmosphere. The
sintering temperature is shown in Table 1. The thickness of the
deposited film was 50 nm.
[0345] The Pr (remanent polarization) of each ferroelectric film
was measured. The measurement results for the Pr are shown in Table
1. The unit for Pr is .mu.C/cm.sup.2. TABLE-US-00001 TABLE 1 Volume
mixing ratio (Main liquid: Sintering temperature secondary liquid)
400.degree. C. 450.degree. C. 500.degree. C. 600.degree. C.
700.degree. C. Only main liquid ND ND ND ND 8 100:1 ND ND ND ND 9
100:10 ND 1 2 3 8 100:20 ND 3 7 9 9 100:50 ND 5 8 8 9 100:100 ND 3
7 9 8 100:150 ND 3 2 3 5 100:200 ND 2 3 3 4 ND: Not detectable
[0346] When manufacturing a ferroelectric memory device in which
the ferroelectric is SBT, it is difficult to manufacture a
ferroelectric memory device with a certain degree of integration if
the sintering temperature is more than 600.degree. C. In a
ferroelectric memory device, the Pr of the ferroelectric capacitor
is preferably 7 or more. In Table 12, the volume mixing ratio (main
liquid:secondary liquid) at which a Pr of 7 or more was obtained at
a sintering temperature of 600.degree. C. or less is between 100:20
and 100:100. Therefore, the volume mixing ratio of the main liquid
to the secondary liquid is preferably in the range from 100:20 to
100:100.
[0347] The main liquid was prepared so that 0.1 mol of
Sr.sub.0.8Bi.sub.2.2Ta.sub.2O.sub.X was produced per liter of the
main liquid. The secondary liquid was prepared so that 0.1 mol of
Bi.sub.4Ge.sub.3O.sub.12 was produced per liter of the secondary
liquid. Therefore, the volume mixing ratio of the main liquid to
the secondary liquid shows the molar ratio of
Sr.sub.0.8Bi.sub.2.2Ta.sub.2O.sub.X produced from the main liquid
to Bi.sub.4Ge.sub.3O.sub.12 produced from the secondary liquid.
Therefore, the main liquid and the secondary liquid are preferably
mixed so that the molar ratio of
Sr.sub.0.8Bi.sub.2.2Ta.sub.2O.sub.X produced from the main liquid
to Bi.sub.4Ge.sub.3O.sub.12 produced from the secondary liquid is
from 100:20 to 100:100.
[0348] In the case of a solution containing only the main liquid,
specific characteristics relating to the Pr were not obtained at a
sintering temperature of less than 700.degree. C. On the contrary,
in the case of mixing the secondary liquid with the main liquid,
specific characteristics relating to the Pr were obtained even at a
sintering temperature of about 500.degree. C. This shows that the
process temperature can be decreased by depositing a ferroelectric
film by mixing the secondary liquid with the main liquid.
EXAMPLE 2
[0349] A main liquid was obtained as follows. 85.3 g of titanium
isopropoxide and 139.2 g of bismuth butoxide were added to 1000 ml
of 2-methoxyethanol. After refluxing the mixture while heating at
125.degree. C. for one hour in a nitrogen atmosphere, the mixture
was cooled to room temperature. After the addition of 23.7 g of
lanthanum isopropoxide, the mixture was stirred at room temperature
for two hours. After the addition of 1.3 g of water, the mixture
was stirred at room temperature for one hour. 2-Methoxyethanol was
added to the mixture so that the oxide concentration as
Bi.sub.3.25La.sub.0.75Ti.sub.3O.sub.12 was 0.07 mol/l to obtain a
main liquid.
[0350] A secondary liquid was obtained as follows. 75.9 g of
germanium ethoxide and 171.3 g of bismuth butoxide were added to
1000 ml of 2-methoxyethanol. After refluxing the mixture while
heating at 125.degree. C. for one hour in a nitrogen atmosphere,
the mixture was cooled to room temperature. After the addition of
1.3 g of water, the mixture was stirred at room temperature for one
hour. 2-Methoxyethanol was added to the mixture so that the oxide
concentration as Bi.sub.4Ge.sub.3O.sub.12 was 0.07 mol/l to obtain
a secondary liquid.
[0351] The main liquid and the secondary liquid thus obtained were
mixed to obtain seven types of mixed liquids with different mixing
ratios. The mixing ratios of the main liquid to the secondary
liquid were 100:1, 100:10, 100:20, 100:50, 100:100, 100:150, and
100:200.
[0352] Ferroelectric films were formed from each of these seven
types of mixed liquids and a solution containing only the main
liquid. The deposition method was the same as in Example 1.
[0353] In Example 2, the same tendency as in Example 1 was observed
relating to the Pr.
EXAMPLE 3
[0354] A main liquid was obtained as follows. 81.2 g of tantalum
ethoxide and 170 g of 2-ethylhexanoic acid were added to 100 ml of
xylene. After the addition of 20.6 g strontium isopropoxide, the
mixture was stirred at 120.degree. C. for two hours. Xylene, the
resulting alcohols, and excess 2-ethylhexanoic acid were evaporated
at 180.degree. C. under atmospheric pressure. 200 ml of a xylene
solution of bismuth 2-ethylhexanoate at a concentration of 1.0
mol/l was added to the mixture. Xylene was added to the mixture so
that the oxide concentration as SrBi.sub.2Ta.sub.2O.sub.X was 0.2
mol/l. Then, butyl acetate was added to the mixture so that the
oxide concentration as SrBi.sub.2Ta.sub.2O.sub.x was 0.1 mol/l to
obtain a main liquid.
[0355] A secondary liquid was obtained as follows. 500 ml of a
xylene solution of tungsten ethoxide at a concentration of 0.1
mol/l and 100 g of 2-ethylhexanoic acid were mixed with 1000 ml of
a xylene solution of bismuth 2-ethylhexanoate at a concentration of
0.1 mol/l. After refluxing the mixture while heating at 120.degree.
C. for one hour in a nitrogen atmosphere, the solvent was
evaporated at atmospheric pressure. Xylene was added to the mixture
so that the oxide concentration as Bi.sub.2WO.sub.6 was 0.1 mol/l
to obtain a secondary liquid.
[0356] The main liquid and the secondary liquid thus obtained were
mixed to obtain seven types of mixed liquids with different volume
mixing ratios. The volume mixing ratios of the main liquid to the
secondary liquid were 100:1, 100:10, 100:20, 100:50, 100:100,
100:150, and 100:200.
[0357] Ferroelectric films were formed from each of these seven
types of mixed liquids and a solution containing only the main
liquid. The deposition method was the same as in Example 1.
[0358] In Example 3, the same tendency as in Example 1 was observed
relating to the Pr.
EXAMPLE 4
[0359] A main liquid was obtained as follows. 37.93 g of lead
acetate trihydrate, 19.95 g of zirconium butoxide, and 13.64 g of
titanium isopropoxide were added to 100 ml of 1-methoxy-2-propanol.
The mixture was refluxed while heating at 120.degree. C. for one
hour in a nitrogen atmosphere. After the addition of 4.5 g of
acetylacetone and 1.1 g of water, the solvent was evaporated at
atmospheric pressure. 1-Methoxy-2-propanol was added to the mixture
so that the oxide concentration as Pb(Zr.sub.0.52Ti0.48)O.sub.3 was
0.3 mol/l to obtain a main liquid.
[0360] A secondary liquid was obtained as follows. 200 ml of a
1-methoxy-2-propanol solution of germanium ethoxide at a
concentration of 0.5 mol/l and 250 ml of a 1-methoxy-2-propanol
solution of lead butoxide at a concentration of 0.5 mol/l were
mixed. After refluxing the mixture while heating at 120.degree. C.
for one hour in a nitrogen atmosphere, the mixture was cooled to
room temperature. After the addition of 4.1 g of acetylacetone and
1.0 g of water, the solvent was evaporated at atmospheric pressure.
1-Methoxy-2-propanol was added to the mixture so that the oxide
concentration as Pb.sub.5Ge.sub.3O.sub.12 was 0.15 mol/l to obtain
a secondary liquid.
[0361] The main liquid and the secondary liquid thus obtained were
mixed to obtain seven types of mixed liquids with different volume
mixing ratios. The volume mixing ratios of the main liquid to the
secondary liquid were 100:1, 100:10, 100:20, 100:50, 100:100,
100:150, and 100:200.
[0362] Ferroelectric films were formed from each of these seven
types of mixed liquids and a solution containing only the main
liquid. The deposition method was the same as in Example 1.
[0363] In Example 4, the same tendency as in Example 1 was observed
relating to the Pr.
Experimental Example Relating to Surface Morphology
[0364] Experimental results for surface morphology are described
below.
[0365] FIG. 10 is a micrograph of the ferroelectric film obtained
from the mixed liquid of the main liquid and the secondary liquid
according to Example 1. FIG. 11 is a micrograph of a ferroelectric
film according to a comparative example.
[0366] The ferroelectric film according to Example 1 shown in FIG.
10 is a ferroelectric film in which the volume mixing ratio of the
main liquid to the secondary liquid is 100:100. The ferroelectric
film according to the comparative example was obtained by
depositing a solution containing only the main liquid illustrated
in Example 1 using the deposition method of Example 1. The
thickness of the ferroelectric films was 50 nm in both Examples and
comparative example.
[0367] As shown in FIGS. 10 and 11, the surface morphology of the
ferroelectric film according to Example was significantly improved
in comparison with the ferroelectric film according to the
comparative example.
[0368] Various modifications and variations of the present
invention are possible within the scope of the above
embodiments.
* * * * *