JPH084084B2 - Etching method of aluminum film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an aluminum (hereinafter referred to as Al) film that contacts an ITO film that is widely used as a transparent electrode in a light receiving element, a light emitting element, a display element, or the like. Processing method.

[Conventional technology]

Since the ITO film is transparent and has excellent electric conductivity, it is widely used as a transparent electrode in a light receiving element, a light emitting element, a display element, or the like. Usually, an Al wiring having a small resistance value is used for electrical connection between the transparent electrode and another electrode in the element, such as a TFT source electrode in a display element. Therefore, an etching process of an Al film in contact with the ITO film, that is, an Al film formed on the ITO film is required to manufacture the light receiving element, the light emitting element, the display element, or the like. As the conventional etching method for the Al film on the ITO film, the following two methods, which are widely known as Al etching methods, have been used.

The first method is under atmospheric pressure (hereinafter referred to as atmospheric pressure method).
The method is usually performed by keeping the etching liquid at about 40 ° C in a constant temperature bath. As the etching liquid, a mixed liquid containing phosphoric acid as a main component and containing nitric acid, acetic acid and water is used. Here, nitric acid has the effect of promoting the reaction between phosphoric acid and Al to increase the etching rate, and acetic acid and water have the effect of suppressing the irregularities that are likely to occur in the pattern edges. In the atmospheric method, only a simple thermostatic bath is required as the required equipment, and the etching time is as short as several minutes, which is a very simple method. However, this method has the drawbacks of poor uniformity and difficulty in etching high density patterns. Both of these defects are due to hydrogen gas generated in the reaction process between Al and the etching liquid during etching of the Al film. That is, when hydrogen gas adheres to the substrate surface in the form of bubbles,
The etching liquid cannot be supplied to that portion, and the etching progresses until the bubbles disappear. Since the rate of generation and disappearance of such bubbles is not uniform on the surface of the substrate, it is difficult to perform uniform etching particularly on a large-area substrate used for a display element or the like. In addition, hydrogen gas is likely to adhere between the patterns having a particularly small interval, which causes etching residue of Al and causes shortage between patterns, which makes it difficult to achieve high density.

The second method is to perform under reduced pressure of several tens Torr (hereinafter,
It is called a decompression method), and has been used as a method for overcoming the drawbacks of the above atmospheric pressure method. In the depressurization method, only phosphoric acid is used in the etching solution, and nitric acid is not contained.
The reason for this is that the use of a high vapor pressure acid such as nitric acid damages the vacuum pump for decompression. FIG. 2 shows an etching apparatus used in the depressurization method. That is, FIG. 2 is a schematic configuration diagram of an etching device used in a conventional decompression method. In FIG. 2, 1 is an etching liquid, 2 is a constant temperature tank, 3 is a vacuum tank, 4 is a vacuum pump, 5 is a substrate holder,
Reference numeral 6 is a substrate, and 7 is a heater. Etching liquid 1
The constant temperature chamber 2 containing the above is contained in the vacuum chamber 3, and the inside of the vacuum chamber 3 is decompressed by the vacuum pump 4. In this method, hydrogen bubbles generated by depressurization are quickly removed from the substrate surface to overcome the drawbacks of the atmospheric method. Therefore, it has excellent uniformity and is suitable for etching high density patterns.

[Problems to be solved by the invention]

However, when etching the Al film in contact with the ITO film by the depressurization method, the ITO film is severely eroded, and there is a problem that the ITO film disappears before the etching of the Al film. It couldn't be used for.

An object of the present invention is to solve the above-mentioned drawbacks in the conventional Al film etching method on an ITO film.
An object of the present invention is to provide a method for uniformly etching an Al film without damaging the film.

[Means for solving problems]

Briefly describing the present invention, the present invention is an invention relating to an etching method for an Al film, wherein in the vacuum etching of an Al film in contact with an ITO film, a solution obtained by adding a nitrate to phosphoric acid is used as an etching solution. To do.

Focusing on the fact that the erosion of the ITO film does not occur in the atmospheric pressure method as described above, it is considered that one of the components of the etching liquid used in the atmospheric pressure method has an effect of inhibiting the erosion of the ITO film, and each component As a result of examining the presence or absence of the ITO film erosion inhibition effect, it was found that nitric acid has an effect of inhibiting the ITO film erosion. Nitric acid has the above effect because IT
It is considered that the erosion of the O film is due to the reducing action of hydrogen ions generated in the reaction process of phosphoric acid and Al, and the oxidizing power of nitric acid suppresses this reducing action. When the hydrogen peroxide solution was examined, it was found to have the same effect.

From the above, it was clarified that the addition of chemicals with oxidizing power to phosphoric acid is effective in preventing ITO erosion. However, use of an acid having a high vapor pressure such as nitric acid cannot be used because it damages the vacuum pump for pressure reduction. Therefore, in order to avoid pump damage, we focused on salts with low vapor pressure, picked up nitrates that can be expected to have a strong oxidizing action by nitrate ions, and investigated their effects. As a result, it was found that even in the case of nitrate, the corrosion of ITO can be prevented as well as nitric acid. The effect of nitrate on ITO erosion was dependent on nitrate ion, so it was effective regardless of the type of nitrate.

As described above, in the decompression etching method for the Al film according to the present invention, the solution obtained by adding the nitrate to phosphoric acid is used as the etching solution. The addition of nitrate enabled etching of Al film on ITO film, which was not possible with the conventional decompression method. Further, in the present invention, since etching is carried out under reduced pressure, it is excellent in uniformity as compared with the conventional atmospheric pressure method, and it is possible to etch a high density pattern.

Examples of nitrates used in the present invention include ammonium nitrate and potassium nitrate, with ammonium nitrate being particularly preferred. When ammonium nitrate is used, the amount is preferably 20 g or more of ammonium nitrate per phosphoric acid.

〔Example〕

Hereinafter, details of the present invention will be described with reference to examples, but the present invention is not limited to these examples.

Example 1 In this example, ammonium nitrate was used as the nitrate added to phosphoric acid. The etching apparatus used was the same as the etching apparatus used in the conventional decompression method shown in FIG. The sample used was an ITO film of about 500 nm and an Al film of about 1 μm deposited on a large area substrate of about 30 × 20 cm ² , and a resist pattern was formed at a high density on the Al film. . The Al film etching was performed by reducing the pressure in the vacuum chamber to 50 Torr with a vacuum pump and maintaining the temperature of the etching liquid at 40 ° C. When a number of etchings were carried out by changing the amount of ammonium nitrate added to phosphoric acid, the ITO film was severely eroded during etching with the etching solution containing only phosphoric acid containing no ammonium nitrate, and the Al film was completely disappeared at the end of etching. On the other hand, by adding a few g of ammonium nitrate per phosphoric acid, the ITO film erosion rate is remarkably slowed and the ITO film is present even after the etching is completed. Furthermore, it was found that if 20 g or more of ammonium nitrate was added per 1 part of phosphoric acid, the ITO film was not corroded at all during etching of the Al film. Also, phosphoric acid 1
It was confirmed that the vacuum pump for depressurization did not deteriorate even if 20 g or more of ammonium nitrate was added. From the above, in the Al film etching on the ITO film according to the present invention, it is desirable to add 20 g or more of ammonium nitrate per 1 phosphoric acid.

These points will be further described with reference to FIG. That is, FIG. 1 shows the amount of ammonium nitrate added per g of phosphoric acid (g, horizontal axis) and the etching time (min,
It is a graph which shows the relationship with (vertical axis). According to FIG.
When the etching solution is only phosphoric acid, that is, it takes about 20 minutes to etch an Al film with a thickness of 1 μm used for wiring in the conventional decompression method, whereas phosphoric acid and ammonium nitrate are used as the etching solution. In the present invention using the liquid added with, the etching time is reduced to a few times, which is about 3 minutes.

The etching uniformity was extremely good because the etching was performed under reduced pressure, and the etching residue of Al did not occur even in the narrow portion where the pattern interval was about 2 to 3 μm, and the etching of the high density pattern was also good.

Although ammonium nitrate was selected as the nitrate in this embodiment, the etching of the Al film on the ITO film can be similarly performed by using other nitrates.

〔The invention's effect〕

As described above, in the etching method of the Al film on the ITO film according to the present invention, the Al film is not eroded at all in the Al film.
It is possible to etch the membrane. Further, since the etching is performed under reduced pressure, it has excellent uniformity and can process a high density pattern. Furthermore, the addition of ammonium nitrate has the effect of shortening the etching time as shown in FIG.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of ammonium nitrate added and the time taken for etching an Al film of 1 μm in an etching liquid in which ammonium nitrate is added to phosphoric acid used in the present invention, and FIG. 2 is used in a conventional decompression method. It is a schematic block diagram of the etching device which exists. 1 ... Etching liquid, 2 ... Constant temperature bath, 3 ... Vacuum bath, 4
...... Vacuum pump, 5 ... Substrate holder, 6 ... Substrate, 7
...... Heating heater

Claims (1)

[Claims] 1. A method for etching an aluminum film, wherein a solution obtained by adding a nitrate to phosphoric acid is used as an etching solution in the vacuum etching of an aluminum film in contact with an ITO film.