Coating processes – Coating by vapor – gas – or smoke
Reexamination Certificate
2001-07-27
2004-10-12
Barr, Michael (Department: 1762)
Coating processes
Coating by vapor, gas, or smoke
C427S226000, C427S327000, C427S294000, C427S350000, C427S377000, C427S379000, C427S376200, C427S419300, C427S421100, C427S126300
Reexamination Certificate
active
06803074
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a complex oxide thin-film and an apparatus for producing the complex oxide thin-film, and more particularly, to a method of producing a complex oxide thin-film for use in electronic devices such as a thin-film capacitor capable of presenting a large capacitance even if the capacitor has a small area, and so forth, and an apparatus for producing the complex oxide thin film.
2. Description of the Related Art
Recently, development of high density circuits for electronic parts have been made. Regarding electronic devices such as monolithic ceramic capacitors and so forth, it has been increasingly required that the sizes are further reduced and the performances are more enhanced.
Ordinarily, monolithic ceramic capacitors are produced by the following method.
(1) First, electrode paste is printed on a ceramic green sheet cut to a predetermined size and dried.
(2) Then, the green sheets each having the electrode paste printed and dried are laminated, and bonded under pressure to produce a laminated, press-bonded block.
(3) The laminated, press-bonded block is cut in predetermined positions and separated into individual elements.
(4) The elements individually separated are fired under predetermined conditions.
(5) An external electrode paste is applied to a predetermined location of the fired element, and is baked to form the external electrode. Thereby, a monolithic ceramic capacitor is obtained as the product.
When the monolithic ceramic capacitor is produced by the above-described conventional method, the thickness of the dielectric layer thereof can not be reduced to be smaller than the grain size of ceramic raw material powder. Even if the thickness is larger than the grain size of the ceramic raw material powder, there will arise the problem that for a dielectric layer having an excessively small thickness, short-circuits and electrode-intersections are readily caused due to deficiencies in the dielectric layer. Thus, at present, it is difficult to produce monolithic ceramic capacitors having a dielectric layer with a thickness below about 1 &mgr;m. Development of such capacitors having a reduced size and increased capacitance is thus limited.
To solve such problems and produce monolithic ceramic capacitors having a dielectric layer with a thickness of up to 1 &mgr;m, thin-film manufacturing processes such as a CVD method, a sol-gel method, a PVD method, and so forth have been investigated as methods of producing dielectrics.
Of these methods, the CVD method in which a raw material gas is introduced into a film-forming chamber and is formed into a film on a heated substrate is characterized in that a film with a good crystallinity and a high dielectric constant can be obtained. However, if many constitutional elements are employed, the apparatus becomes very complicated, increasing the cost.
If dielectric materials such as BaTiO
3
, SrTiO
3
, (Ba, Sr)TiO
3
, PbTiO
3
, Pb(Zr, Ti)O
3
, (Pb, La)TiO
3
, (Pb, La)(Zr, Ti)O
3
, Pb(Mg, Nb)O
3
or the like, which present a high dielectric constant, are used, it is necessary to heat the materials under reduced pressure for vaporization or sublimation since the raw materials are solid or liquid at ordinary temperature and pressure.
Moreover, the materials need to have a sufficient vapor pressure for vaporization or sublimation of the materials. Furthermore, it is required for production of a complex oxide film that the temperature at which a material having the highest gasification temperature is lower than the decomposition temperature of a material having the lowest decomposition temperature. Therefore, the selection range for the materials becomes very narrow. Thus, in general, there arises the problem that the use of expensive materials becomes necessary.
Generally, it is needed to heat a raw material for gasification. Accordingly, there arise the problems that chemical reactions such as polymerization or the like of the material itself occurs to modify the material, the gasification quantity can not be stably obtained, and it is difficult to control the composition.
To solve such problems, there has been proposed a method in which a CVD raw material, dissolved in THF (tetrahydrofuran: C
4
H
8
O), is fed to a heated carburetor, in which the solution is atomized and gasified. The material, in the gasified state, is carried to a film-forming chamber to be film-formed (Japanese Unexamined Patent Application Publication No. 9-219497).
In this method, it is not required to heat the material in the process prior to the gasification. Thus, modification of the material can be inhibited. On the other hand, the gasified material needs to be carried to the film-forming chamber. Accordingly, it is necessary to select the raw material as to cause no condensation, solidification, decomposition and so forth, in the transportation process. This method is thus similar to the ordinary CVD method in the respect of the fact that the selection range for the raw material is limited.
Moreover, Japanese Unexamined Patent Application Publication No. 9-213643 discloses a method in which a raw material solution is atomized by means of a supersonic atomizer, and the formed droplets are carried to a chamber maintained under a pressure of 200 to 700 Torr and are vapor-deposited on a substrate held in the chamber, and thereafter, the vapor deposition film is heat-treated at a temperature of 550 to 850° C., whereby a dielectric thin-film is obtained. In this method, the film-forming process by the MOD or sol-gel method is carried out by use of atomized droplets. Characteristically, raw materials excluding the above-described CVD raw materials can be used, and moreover, vapor deposition can be performed nearly at ordinary temperature.
However, the film-forming in this method is carried out at nearly room temperature and under a relatively high pressure. Therefore, organic components contained as droplets in the film remain there. Thus, reduction in pressure and drying after the film-forming, and a heat treatment thereafter are indispensable. Thus, there arises the problem that cracking or the like is readily caused in the processes of drying and heat treatment. This problem is similar to that of the sol-gel method. Accordingly, even if formation of a dielectric film having no cracks is attempted by this method, reduction in pressure, drying and heat treatment after the film-formation can not be sufficiently carried out. There arise the problems that organic components remain in the film, sufficient crystallization can not be performed and a high dielectric constant can only be attained with difficulty.
SUMMARY OF THE INVENTION
To solve the above problems, the present invention has been devised. It is an object of the present invention to provide a method of producing a complex oxide thin-film in which a complex oxide thin-film having a high dielectric constant and a good reliability can be efficiently produced by use of an inexpensive raw material, without need of a complicated process, and to provide an apparatus for producing the complex oxide thin film.
To achieve the above object, according to the present invention, there is provided a method of producing a complex oxide thin-film which comprising the steps of (a) dissolving at least two kinds of metal compounds in a solvent to prepare a metal compound solution, (b) putting the metal compound solution into an atomized state by means of a two-fluid nozzle, and directly introducing the atomized solution into a film-forming chamber of which the pressure is kept at about 100 Torr or lower, and (c) forming a complex oxide thin-film on a substrate placed in the film-forming chamber and heating to a temperature equal to or higher than the boiling point of the solvent.
Since the metal compound solution is put into an atomized state by means of the two-fluid nozzle, and the atomized solution is introduced into the film-forming chamber of which the pressure is kept at about 100 Torr or lower, it is not necessary tha
Barr Michael
Dickstein Shapiro Morin & Oshinsky LLP.
Murata Manufacturing Co. Ltd
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