JPS5830252B2 - Method for manufacturing tantalum oxide film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a tantalum oxide film, and more particularly to a method for producing a tantalum oxide film by applying a coating composition to a substrate.

Tantalum oxide thin films have excellent physical and chemical stability, refractive index, and transmittance, so they are used as antireflection coatings for photoelectric conversion elements (solar cells), lenses, mirrors, etc.
Used as an anti-reflection coating for optical equipment such as optical filters.

Tantalum oxide thin films also have high dielectric constants and dielectric strength, so they are used for semiconductor surface treatments and thin film capacitors.

Conventionally, these tantalum oxide thin films have been deposited by heating tantalum oxide using resistance heating, electron beam heating, etc.
It is manufactured by a reactive sputtering method, a gas phase reaction method, an anodic oxidation method, or the like.

However, all of these methods have drawbacks such as requiring large-scale equipment and laborious operations, resulting in poor workability.

Further, the deposition rate of the tantalum oxide thin film by these methods is typically about 100 persons/min, and there is also a drawback that there is a limit to the temporal capacity in the case of mass production.

For example, the reactive sputtering method uses glow discharge or superimposition of a high-frequency electric field on it, but there are many influencing factors such as ion energy, ion density, and introduced gas, and requires skilled work.

Further, the deposition rate is about 100 persons/min at maximum.

The present invention solves the above conventional problems and provides a method for producing tantalum oxide thin films using simple equipment, in a very simple manner, and in a very short time.

The tantalum oxide thin film body according to the invention is prepared by mixing one volume of a tantalum alkoxide, such as tantrium ethylate, with one volume or less of a carboxylic acid, such as glacial acetic acid, in one or more volumes of a suitable solvent, such as alcohol. It is obtained by forming a coating composition containing the derivative tantalic acid and a solvent, applying the coating composition to a substrate, and further heating.

More specifically, tantalic acid is formed as a derivative from one volume of tanchloric alkoxide, such as tantrium ethylate, and one or less volumes of a carboxylic acid, such as glacial acetic acid.

The coating composition contains quintaric acid, a solvent, and esters resulting from their mutual reaction.

This is applied to substrates of semiconductor materials, optical equipment, etc.

The coating method is carried out by a simple method such as spin coating, spraying, or dipping.

By heating the coated substrate, it becomes a tantalum thin film.

At the same time, the solvent or esters evaporate.

The present invention will be explained in detail below.

Example A coating composition was prepared by mixing 1 volume of tantalum ethylate, 1 volume of glacial acetic acid, and 8 volumes of ethyl alcohol.

In this coating composition, tantalum ethylate and glacial acetic acid react to produce tantalic acid.

This is coated onto a silicon substrate using a spin coater.

The coated silicon substrate is heated to the desired temperature in nitrogen.

The thickness of the produced tantalum oxide thin film is approximately determined by the amount of tantalum ethylene added initially and the rotation speed of the substrate, but if the film is too thick, cracks will occur during heating and it will peel off from the substrate.

Table 1 shows the refractive index results of tantalum oxide thin films coated at 5,000 revolutions per minute for 10 seconds and then heated at various temperatures for 30 minutes.

As the heating temperature increases, the film becomes more dense and the refractive index increases.

According to this method, a desired refractive index can be appropriately selected by selecting the heating temperature.

In the conventional tantalum oxide thin film manufacturing method described above,
Only a constant refractive index can be obtained, and it has been almost impossible to select the refractive index.

When light enters a single-layer film from the air perpendicularly, there is no reflection when the following equation holds.

n-nn ・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・(1) λ n1d= / ・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・(2) Here n.

is the refractive index of air, nl is the refractive index of the single layer film, n2 is the refractive index of the substrate, λ is the wavelength of light, and d is the thickness of the single layer film.

As is well known, this is the principle of an antireflection film when a single-layer interference film is used.

By forming the above-mentioned Kuntal oxide thin film under conditions close to formulas (1) and (2), it can be used as an antireflection film.

In particular, as an antireflection film for a photoelectric conversion element, such as a solar cell element, it is easy to approximate the formulas (1) and (2) and is suitable.

Next, an example of application to solar cells will be described.

A tantalum oxide thin film was formed on a silicon solar cell having dimensions of 2CWl x 2crr1 by the above method.

The refractive index was 1.95, and the film thickness was approximately 700 mm.

Figure 1 shows the relationship between the wavelength of irradiation light and reflectance.

In the figure, curve 1 is the measured value of a silicon solar cell without an antireflection film, and curve 2 is the measured value of a silicon solar cell coated with the antireflection film according to the present invention.

FIG. 2 shows the current-voltage characteristics when sunlight is vertically incident on a silicon solar cell.

The element temperature was 28℃, and the incident energy was 139.6mV/
CI? The L incident spectrum is AMO.

In the figure, curve 3 is the measured value of a solar cell without a tantalum oxide thin film, and curve 4 is the measured value of a solar cell with a tantalum oxide thin film according to the present invention.

The short circuit current increased by 30% due to the presence of the anti-reflection coating.

It has been confirmed that this is equivalent to that of the tantalum oxide antireflection film obtained by the conventional method.

As explained above, according to the present invention, a tantalum oxide thin film can be obtained by simply applying a coating material made of a simple composition onto a substrate and heating it, which is much simpler and faster to form than conventional methods. It is suitable for rapid mass production and has great economic effects.

Antireflection coatings and dielectric materials for photoelectric conversion elements, optical equipment, etc.
A tantalum oxide thin film serving as an insulating material can be easily obtained, and the productivity of the tantalum oxide thin film can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between light wavelength and reflectance of a silicon solar cell, and FIG. 2 is a current-voltage characteristic diagram of the silicon solar cell. 1.3: Measured value of silicon solar cell without anti-reflection film,
2, 4: Measured values of a silicon solar cell with a tantalum oxide antireflection film according to the present invention.

Claims (1)

[Scope of Claims] 1. A coating composition is prepared by mixing one volume of quintal alkoxide and one volume of carboxylic acid, or less, in one volume or more of a solvent, and the coating composition is A method for producing a tantalum oxide film, which comprises applying the film onto a substrate and then heating it. 2 The heating temperature of the coating composition on the substrate is 200°C.
The method for producing a tantalum oxide film according to claim 1, wherein the temperature is 800°C.