Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Insulative material deposited upon semiconductive substrate
Reexamination Certificate
2003-01-10
2004-11-30
Fourson, George (Department: 2823)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Insulative material deposited upon semiconductive substrate
C438S781000
Reexamination Certificate
active
06825131
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods for forming a dielectric thin film, and more particularly to a method for forming a dielectric thin film using a solution containing starting materials.
2. Description of the Related Art
In order to form a dielectric thin film, using a material solution, the following methods have been applied:
(1) Liquid Source CVD (LSCVD): a solution in which organic metal materials are uniformly dissolved is vaporized to react with the surface of a substrate, thus forming an oxide thin film.
(2) Metal Organic Deposition (MOD): a solution in which organic metal materials are uniformly dissolved is applied, dried, calcined, and fired to form an oxide thin film.
(3) A spray method: a material solution is sprayed onto the surface of a substrate, followed by drying and firing to form an oxide thin film (for example, a solution is sprayed onto a substrate by ultrasonic waves, and is subsequently heated to dry and heat-treated to form a thin film, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 9-213643).
However, the LSCVD method described as method (1) above, requires the use of expensive compounds having a high vapor pressure as raw materials because the raw materials must be in a gas form to be applied onto a substrate. Thus, LSCVD has disadvantage in that it is very expensive.
On the other hand, the MOD method described as method (2), and the spray method, described as method (3), have no vapor pressure requirement because a solution containing raw materials is applied in a liquid form onto a substrate. However, the vaporized solvent passes through the deposited film during drying to form cavities which are likely to cause a short circuit between electrodes disposed on both surfaces of the resulting film if the film thickness is small. It is thus difficult to form a reliable dielectric thin film.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a method for forming a dielectric thin film having high reliability, and provide a dielectric thin film formed by the novel method.
According to a preferred embodiment of the present invention, a method for forming a dielectric thin film includes the steps of (a) spraying a material solution including a starting material and a solvent onto a heated substrate under a reduced pressure by a two-fluid technique using an inert gas to deposit a thin film, and (b) subjecting the thin film to heat treatment in an oxidizing atmosphere.
By performing this film deposition step, the steps of drying and calcining the deposited film, which are necessary in known methods, such as the MOD method and the spray method, can be eliminated. Thus, the vaporization of the solvent from the deposited film is prevented and the occurrence of cavities (loopholes of solvent vapor) is reliably prevented in the thin film. Consequently, a short circuit between electrodes disposed on both surfaces of the film is reliably prevented. Thus, a reliable dielectric thin film can be provided.
In the method of preferred embodiments of the present invention, characteristics of the resulting dielectric thin film depend on conditions for film deposition before heat treatment rather than on heat treatment conditions. Therefore, by selecting the conditions for film deposition, a reliable dielectric thin film can be efficiently formed.
Also, by heat-treating the deposited thin film in an oxidizing atmosphere, organic constituents of organic metal compounds in the material solution are surely burned and removed. Thus, a reliable, precise dielectric thin film can be provided.
More specifically, in the method of preferred embodiments of the present invention, the solvent in the sprayed material solution is rapidly vaporized to be removed immediately after reaching the surface of the heated substrate. Thus, a film hardly including any of the solvent can be deposited on the substrate.
Thus, the vaporization of the solvent from the deposited film can be prevented and, thus, the occurrence of cavities in the resulting thin film is prevented. Consequently, a reliable dielectric thin film can be achieved in which short circuits do not occur between electrodes, even if the electrodes are disposed on both surfaces of the film.
Preferably, the material solution is sprayed under conditions that a major portion of the solvent vaporize immediately soon after the solvent reaches a surface of the substrate.
By spraying the material solution under conditions allowing a major portion of the solvent to vaporize immediately, the vaporization of the solvent is prevented in the deposited thin film and the occurrence of cavities in the resulting thin film is reliably prevented and minimized. Thus, a reliable dielectric thin film can be provided.
Preferably, the film deposition step and the heat treatment step are performed two or more times.
By subjecting one substrate to the film deposition and heat treatment steps two or more times, a reliable, precise dielectric thin film in which short circuits do not occur can be provided.
If the material solution includes an organic metal compound, very few cavities or voids are inevitably formed in the thin film when the organic constituents of the organic metal compound are removed, even if the solvent can be efficiently removed in the film deposition step. However, by repeating the film deposition step and the heat treatment step, the cavities or voids, which are likely to cause short circuits, are filled, so that the occurrence of short circuits can be reliably prevented.
Preferably, the material solution includes at least one metallic element in a total concentration of approximately 0.01 mol/L or less.
By using a material solution including approximately 0.01 mol/L or less of the metallic element, the size of lumps formed by the solidification of drops of the sprayed material solution can be reduced and, thus, a dielectric thin film having a uniform, small thickness can be achieved.
Since the substrate is heated in the method of preferred embodiments of the present invention, a material solution having an excessively high concentration is likely to result in lumps having a grain size as large as several micrometers. This makes it difficult to form a dielectric thin film having a thickness as small as a submicron. Also, the surface morphology is significantly degraded due to the resulting rough surface.
The inventors conducted an experiment to determine a suitable concentration of the material solution for forming a film having an adequately small thickness. As a result, it has been discovered and shown that, by using a material solution having a metallic element concentration of approximately 0.01 mol/L or less, the size of lumps formed on the surface of the substrate can be reduced so that the thickness of the dielectric thin film becomes uniform and small. Therefore, it is preferable to use a material solution having a metallic element concentration of approximately 0.01 mol/L or less.
According to another preferred embodiment of the present invention, a method for forming a dielectric thin film includes the steps of (a) spraying a material solution including a starting material and a solvent onto a heated substrate under a reduced pressure by a two-fluid technique using an inert gas to deposit a thin film, (b) stopping the supply of the material solution and vaporizing the solvent remaining in the thin film, and (c) subjecting the thin film to heat treatment in an oxidizing atmosphere.
The heat treatment step is performed after the film deposition step and the solvent vaporization step is preferably repeated once or more times. Also, the material solution is supplied at a rate that is greater than the vaporization rate of the solvent in the film deposited on the substrate.
By supplying the material solution at a rate that is greater than the vaporization rate of the solvent in the film to deposit a thin film, then vaporizing the solvent remaining in the film with
Nishida Koichi
Shibuya Koki
Takeshima Yutaka
Estrada Michelle
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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