JPH04223335A - Manufacture of dielectric thin film - Google Patents

Abstract

PURPOSE:To easily form the title dielectric thin film having a large area at low cost by a method wherein a laminated metallic thin film of two or more layers having a tantalum metal on the topmost layer is oxidized by anode- oxidization step. CONSTITUTION:A multilayer structure formed by anode oxidization step is composed of four layers comprising a tantalum oxide thin film 1, the other element oxide thin film 2, another tantalum oxide thin film 3 and the other element oxide thin film 4. In such a constitution, after evaporating gold/chrome thin films 6, 7 used as electrodes on a glass substrate 5, the constituent metals are successively laminated by multielement high-frequency magnetron sputter step specifying the tantalum metal as the fourth layer. In general, the volume of a metal is to be expanded for increasing the film thickness when it is anode- oxidized. After performing the four layer lamination step, oxalic acid is used as a chemical-conversing solution to form all of the layers into oxides excluding gold/chrome electrodes. After drying-up step, aluminum electrodes 7 are evaporated to form capacitors.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing dielectric thin films for LSI transistors and capacitors and electronic devices, such as EL display panels and liquid crystal display panels, which are constructed of thin films.

0002

[Prior Art] Tantalum oxide thin films have conventionally been used as capacitor dielectric materials for discrete and hybrid ICs, and recently, the development of gate insulating films for MOS transistors and MOS capacitors has been progressing for application to LSIs. . Furthermore, it has been applied as a TFT gate insulating film for liquid crystal display devices and an insulating film for MIM diodes. In addition to anodic oxidation, its manufacturing methods include metal thermal oxidation, sputtering, and CVD using chlorides.
MOCVD methods and MOCVD methods using organometallic compounds have been developed. Among these, the anodic oxidation method is the most excellent method from the viewpoints of ease of manufacture, productivity, and cost, and is suitable for forming a film over a large area. The produced thin film has fewer defects such as pinholes.

0003

[Problems to be Solved by the Invention] The tantalum oxide thin film manufactured by the anodic oxidation method described in the prior art has a dielectric constant of 25,
Dielectric loss 0.5%, dielectric strength voltage 4 to 5 MV/cm, and leakage current 5 x 10-8 A/cm2 (electric field strength 0.5
MV/cm). Immediately after anodizing, tantalum oxide exhibits a very small leakage current as described above, but when subjected to vacuum heat treatment at 300°C, the leakage current decreases to 5 x 10-4.
It has the disadvantage of increasing A/cm2.

[0004]Currently, as already explained, anodic oxidation is a very advantageous method for dielectric thin films of various electronic devices and semiconductor devices from the viewpoint of productivity and cost. A material with better electrical properties than tantalum is desired. For example, AC thin film EL display devices require even higher dielectric constant and dielectric strength. A gate insulating film for a TFT liquid crystal display device is required to have a high dielectric constant and high heat resistance without defects. In order to maintain compatibility with other processes, the higher the heat resistance, the better in general, not only for liquid crystal devices. Until now, in order to improve heat resistance and reduce leakage current, for example, in reactive sputtering, we have improved the purity of the tantalum metal target and flattened the electrodes, and in CVD, we have lowered the substrate temperature and reduced oxygen defects by annealing, and applied plasma. It has been made. By oxidizing the Ta2O5/Si interface, S
An interfacial oxidation method to iO2 was also developed to increase heat resistance. On the other hand, it is preferable for the MIM diode of a liquid crystal display device to have a large leakage current and stable characteristics.

The present invention was made in view of the above problems, and an object of the present invention is to provide a method for easily producing a thin film having properties superior to tantalum oxide in various properties.

[0006]

[Means for Solving the Problem] In order to solve this problem, the gist of the present invention is to oxidize a laminated metal thin film of two or more layers with tantalum metal as the outermost surface by an anodic oxidation method. .

To further explain the present invention, a laminated film having tantalum metal as the outermost surface and having a predetermined metal type and film thickness is formed using a multi-dimensional electron beam heating method or the like. Metals other than tantalum metal that can form a film by anodizing are selected. Subsequently, tantalum metal is chemically converted under anodizing conditions suitable for tantalum metal to form a composite oxide laminated film. Since tantalum metal is used as the top surface, no matter what kind of other metals are used in the composite,
It has the feature of being able to produce a laminated oxide film by performing chemical conversion under the conditions of anodic oxidation of tantalum metal.

[0008]

[Operation] The present invention forms a composite laminated film in which tantalum oxide and other formable metal oxides are laminated alternately by the above-described means, and the various properties of tantalum oxide are changed by the combined effect, so that the properties of each tantalum oxide are changed. Dielectric thin films suitable for thin film devices can be easily manufactured. The combined effect of stacking averages the dielectric constant and dielectric strength, but the figure of merit (maximum stored charge) maintains the value of the higher thin film material. The dielectric strength voltage is not necessarily averaged, and depending on the combination of thin film materials, the dielectric strength voltage may be higher than that of each constituent thin film alone having the same thickness. Furthermore, the number of defects that are likely to cause dielectric breakdown is minimized, making it possible to change the dielectric breakdown mode. Furthermore, properties related to the device fabrication process, such as heat resistance, adhesion, and chemical resistance, can be adjusted. The manufacturing method using anodic oxidation is an industrially advantageous method that allows a thin film without defects or dust to be easily manufactured over a large area at low cost.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. First, to explain the first example,
In Figure 1, the structure of the laminated film formed by anodic oxidation is as follows.
The four layers of tantalum oxide thin film 1, other oxide thin film 2, tantalum oxide thin film 3, and other oxide thin film 4 were designed in advance so that the film thickness of each layer was 50 nm and the total film thickness was 200 nm. Therefore, after depositing gold/chromium thin films 6 and 7 to be used as electrodes on the glass substrate 5, the constituent metals were sequentially stacked using a multi-element high-frequency magnetron sputtering method.
The fourth layer was always made of tantalum metal. When anodized, the metal generally expands in volume and increases in film thickness. For example, since tantalum metal expands 2.5 times, the metal film thickness was set to 20 nm. The results of laminating titanium oxide as another type of oxide are shown below. After laminating four layers, 0.1N oxalic acid at 50° C. was used as a chemical liquid. Current 0.3m
A/cm2 and chemical conversion was performed at 120 V for 60 minutes to convert everything except the gold/chromium electrode into oxide. After drying at 150° C., an aluminum electrode 7 with a diameter of 2 mm was deposited to form a capacitor, and the electrical properties were measured. As a result, the dielectric constant was 35, and the dielectric breakdown field strength was 4 to 5 MV/
cm and leakage current as 4×10-8A/cm2
(Electric field: 0.5 MV/cm) characteristics were obtained. A thin film was obtained whose breakdown voltage and leakage current were almost the same as those of the tantalum oxide thin film, and whose dielectric constant was slightly more than twice as high. A thin film with such characteristics is suitable as a dielectric thin film for an AC thin film EL display device driven at a low voltage. It is clear in principle that a higher dielectric constant can be obtained by increasing the film thickness ratio of titanium oxide to more than 50% of the above example.

Next, the second embodiment will be described. It has exactly the same dimensions and structure as the first embodiment, but aluminum oxide is used instead of titanium oxide. The manufacturing conditions were almost the same, but phosphoric acid was used instead of oxalic acid. When obtaining a dense barrier-type aluminum oxide anodic oxide film, a neutral solution that does not easily corrode aluminum is basically used. However, it was possible to form a dense barrier-type aluminum oxide using the above-mentioned phosphoric acid solution, which is commonly used in anodizing tantalum, probably because tantalum metal was placed on the outermost surface and corrosion was prevented. As a result, the dielectric constant is 1
4. Breakdown electric field strength 9MV/cm, leakage current 4×1
Although the dielectric constant was 0-9 A/cm2, which was somewhat lower than that of tantalum oxide, a laminated thin film with better withstand voltage characteristics was obtained. When further heated in a vacuum at 300 DEG C., a leak current of 6.times.10@-8 A/cm@2 and extremely excellent heat resistance properties were obtained. A thin film with such characteristics is suitable as a TFT gate insulating film of a liquid crystal display device or a dielectric thin film of a thin film EL display device.

Next, the third embodiment will be described. It has the same dimensions and structure as the first embodiment, but uses niobium oxide instead of titanium oxide. The manufacturing conditions were almost the same, but phosphoric acid was used instead of oxalic acid. As a result, the dielectric constant was 32, the dielectric breakdown field strength was 6 MV/cm, and the leakage current was 2 x 10-8 A.
/cm2, and properties very similar to those of titanium oxide were obtained. A thin film with such characteristics is suitable as a dielectric thin film for a thin film EL display device.

Next, the fourth embodiment will be described. It has exactly the same dimensions and structure as the first embodiment, but uses zirconium oxide instead of titanium oxide. The manufacturing conditions were almost the same, but boric acid was used instead of oxalic acid. As a result, the dielectric constant 2
5. Breakdown electric field strength 8MV/cm, leakage current 3×1
A laminated thin film having a dielectric constant of 0-9 A/cm2, which is almost the same as that of tantalum oxide, and a much superior dielectric strength property was obtained. Furthermore, when heated in a vacuum at 300 °C,
The leakage current was 1 x 10-9 A/cm2, and the heat resistance was also excellent. A thin film with such characteristics is suitable as a TFT gate insulating film of a liquid crystal display device or a dielectric material of a MOS capacitor of an LSI.

Further describing the fifth embodiment, the first
The dimensions and structure were exactly the same as in the example, but tungsten oxide was used instead of titanium oxide. The manufacturing conditions were almost the same, but dilute sulfuric acid was used instead of oxalic acid. As a result, the dielectric constant was 28, the dielectric breakdown field strength was 3MV/cm, and the leakage current was 9×
A laminated thin film having a dielectric constant of 10-8 A/cm2, which is almost the same as that of tantalum oxide, and a high leakage current in terms of withstand voltage characteristics was obtained. A thin film with such characteristics is suitable as an insulating film for an MIM diode in a liquid crystal display device.

The above example shows a typical four-layer laminated structure in which titanium oxide, aluminum oxide, niobium oxide, zirconium oxide, and tungsten oxide are laminated on tantalum oxide. It is clear from the above examples that various characteristic laminated thin films can be created by combining oxides that can be chemically formed. As for the structure, the number of layers can be increased or the film thickness ratio can be changed. In addition to the examples, oxides of yttrium, hafnium, chromium, molybdenum, bismuth, magnesium, germanium, vanadium, and silicon can be used as oxides. It is also possible to use not only one type of these but also a combination of two or more types.

[0015]

As explained above, according to the present invention, dielectric thin films useful for various electronic devices can be easily manufactured over a large area at low cost, and the practical effects thereof are significant.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a dielectric thin film in one embodiment of the present invention.

[Explanation of symbols]

1 Tantalum oxide thin film 2 Other oxide thin films 3 Tantalum oxide thin film 4 Other oxide thin films 5 Glass substrate 6　　　　Gold/Chromium thin film 7 Aluminum electrode

Claims (1)

[Claims] 1. A method for producing a dielectric thin film, which comprises oxidizing a laminated metal thin film of two or more layers with tantalum metal as the outermost surface by an anodic oxidation method.