Coating processes – Direct application of electrical – magnetic – wave – or... – Electromagnetic or particulate radiation utilized
Reexamination Certificate
2000-02-25
2003-06-10
Beck, Shrive P. (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Electromagnetic or particulate radiation utilized
C427S596000, C427S595000, C427S492000, C427S554000, C427S556000, C427S508000
Reexamination Certificate
active
06576302
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing a metal oxide. The present invention also relates to a method for forming a minute pattern.
BACKGROUND OF THE INVENTION
Formation of a thin film made up of a metal film, a metal oxide film, or a composite oxide film on a substrate, is actively performed in the field of the semiconductor production technology. In forming the metal film, the metal oxide film, or the composite oxide film on the substrate, a method of using a metal organic compound containing the metal species as a raw material, applying a homogeneous solution, obtained by dissolving the compound in a solvent, onto the substrate, heating, and baking, has been usually utilized.
However, in general, according to the method, in producing a metal oxide by heating and baking after application, metal ions which can be the cores aggregate together, to cause crystal growth and powdering. In order to eliminate this problem, it is considered necessary to take a measure to prevent contact of the metal ions with each other; that is, a means to isolate the metal ions by utilizing the steric hindrance effect. As such a means, specifically, separation of the metal ions by a large organic group can be considered.
Based on the idea, if an organic group bonding metal is selected and is thermally decomposed, core formation and crystal growth are restrained. As a result, a metal oxide can be obtained in the amorphous state, and the same will further be crystallized. Accordingly, when the desired metal oxide is to be in a film state, since it is provided via the amorphous state, a film with an improved film formation property can be obtained, and thus it became known that the film formation itself is not difficult. The above method is called the application thermal decomposition method, and it was extensively studied by Toru Matsushita et al. in the 1970s. The application thermal decomposition method is aimed at forming a metal oxide film or a composite oxide film by applying a homogeneous film of good quality on a substrate, and a heat-baking treatment. T. Matsushita et al. pointed out that an organic group bonding metal compound having a metal-oxygen-carbon bond is suitable as a raw material, and they mainly studied particularly a metal organic acid salt having a large organic group (Ceramics, 21, 236 (1986)).
As a raw material for the above operation, originally, a method of using a metal acetylacetonato complex for forming a metal oxide film on a substrate, by decomposing the metal acetylacetonato, was developed. Specifically, a method of forming a highly functional oxide film by only applying a raw material solution on a substrate, and applying a heat treatment thereto, was proposed, which attracted attention (U.S. Patent by American inventors concerning In
2
O
3
film (transparent conductive film) in 1956 (M. S. Jaffy et al., JP-B-31-3282 (1956) (“JP-B” means examined Japanese patent publication))).
Studies have been done since then on the methods of using a metal acetylacetonato complex as a raw material. However, as mentioned below, a problem is involved, in that disadvantages of applying heat cannot be avoided.
In contrast, general decomposition or reaction by radiating light onto a metal acetylacetonato complex has been performed since long ago (N. Filipescu et al., Inorg. Chem. 8 1863 (1969)) (H. D. Gafney et al., Inorg. Chem. 9 1728 (1970)) (H. D. Gafney et al., J. Am. Chem. Soc. 93 1623 (1971)).
However, products obtained by these methods so far were not metal oxides; rather, they consisted of a metal or a composition with the valence of the metal ion changed, and no oxide was really obtained.
Meantime, according to the superconductivity fever of the mid 1980s, superconductive epitaxial films, using various kinds of single crystal substrates, were synthesized for the first time by the application thermal decomposition method, using a metal organic acid salt as the raw material (Susumu Mizuta et al., Nihon Kagakukaishi (Journal of the Chemical Society of Japan) 1997, (1) 11-23 (1997); S. Mizuta et al., Japanese Patent Registration No. 1778693; S. Mizuta et al., Japanese Patent Registration No. 1778694; Toshiya Kumagai et al., JP-A-5-14794 (“JP-A” means unexamined published Japanese patent application), and T. Kumagai et al., JP-A-5-9022).
Furthermore, from the 1990s, studies on synthesis of an epitaxial film for production of a ferroelectric substance, such as Pb(Zr)TiO
3
(K. Hwang et al., Jpn. J. Appl. Phys. Vol. 36, Part 1, No. 8, pp. 5221-5225 (1997)), BaTiO
3
(S. Kim et al., Trans. Mater. Res. Soc. Jpn., 20, p. 636-639 (1996)), La(Sr)MnO
3
(T. Manabe et al., J. Mater. Res., 12(2), p. 541-545 (1997)), and LiNbO
3
(T. Manabe et al., Trans. Mater. Res. Soc. Jpn., 20, p.599-602 (1996)), have been pursued.
According to a method of producing a metal oxide using a metal acetylacetonato complex, in general, treatment at a high temperature of 500° C. or more is required for decomposing the metal acetylacetonato. According to a recent method (K. Shinmou et al., Jpn. J. Appl. Phys. 33 L1181 (1994)), patterning is performed by adding acetylacetone to a metal alkoxide and radiating with ultraviolet rays, to make the film insoluble. However, a metal oxide cannot be obtained by this method. In order to obtain an oxide, heat treatment is finally necessitated.
Moreover, in the case of using a metal organic acid salt as the raw material, decomposition at 500° C. or more is inevitable, but it is pointed out that such a high temperature thermal decomposition causes several harmful effects on electronics devices.
For example, in the case of using a silicon, it is known that deterioration is caused and laminated films react with each other. In order to prevent deterioration of silicon or reaction among the laminated films, it is said that the heat treatment temperature should be 650° C. or less, desirably 300° C. or less.
As mentioned above, decomposition at a high temperature close to 500° C. is too high for electronics devices, and harmful influences thereby are pointed out. For example, in the case of PZT, which is expected as a dielectric memory, the PbO component thereof reacts with a silicon substrate, to lower the dielectric characteristics. Moreover, for a transparent conductive film made, for example, of indium oxide, which is used as an electrode of photonics, or electronics devices related to a light, such as a liquid crystal display board, a plasma display panel, and a solar battery, a high-temperature heat treatment of the above-mentioned degree is not preferable. In particular, in the case of a color liquid crystal display board, since a film needs to be formed on an organic compound resin color filter, a low-temperature film formation, preferably in the range of 150 to 170° C., is desired. However, there has been no case of converting a metal acetylacetonato complex to an oxide film in 100%-yield by treatment at a relatively low temperature.
Accordingly, a specific example of decomposition at 200° C. or less has not been known so far either in the case of acetylacetonato or a metal organic acid salt. As a heating means, use of various kinds of heat sources are conceivable, but the use of new means has not been known.
As a heating means, radiation by an excimer laser, which radiates ultraviolet rays having a high heating effect and high-level energy, without containing a wavelength at the infrared part, is expected; however, a specific example of producing an oxide using the excimer laser has not been reported so far.
That is, it has been considered to be difficult to decompose a metal acetylacetonato or a metal organic acid salt for synthesizing an oxide directly since both of these are known to be stable. Furthermore, there are no reports on decomposition using a metal alkoxide having an organic group with 6 or more carbon atoms as the raw material. Direct synthesis of an oxide film using an organic group with 5 or less carbon groups, for example, decomposition of an alkoxide comprising i-propoxide as an organic group with 5 or less carbon at
Imai Yoji
Kumagai Toshiya
Manabe Takaaki
Mizuta Susumu
Niino Hiroyuki
Agency of Industrial Science and Technology
Beck Shrive P.
Fuller Eric B
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