JP5018581B2 - Etching method of transparent conductive film using etching solution - Google Patents

Description

  The present invention relates to an etching solution which is an aqueous solution of hydrochloric acid and ferric chloride, a method for etching a transparent conductive film using the etching solution, and a substrate to be etched on which a circuit pattern is formed by etching.

  Hydrochloric acid and ferric chloride are used as etching solutions for etching various substrates. Examples of materials to be etched (hereinafter referred to as materials to be etched) include iron, copper, nickel, aluminum, iron alloys (various stainless steels, iron nickel alloys such as 42 nickel-iron, 36 nickel-iron), Examples include copper alloys (copper-zinc copper-tin copper-nickel), transparent conductive films (ITO, IZO, GZO, tin oxide, indium oxide, zinc oxide, titanium oxide, tantalum compounds, conductive polymers). Materials to be etched or substrates combined with a substrate such as glass (hereinafter referred to as etched substrate) include printed wiring boards, electromagnetic shielding materials, lead frames, shadow masks, transparent electrodes, heating elements, etc. Over. Among these, in recent years, a method for forming a transparent electrode pattern by etching a transparent conductive film has attracted attention.

The transparent electrode is used for a pixel electrode such as an LCD, and is an important component of the LCD. As the transparent electrode, a metal oxide such as ITO (indium tin oxide) is preferably used.
There are crystalline and non-crystalline ITO depending on the temperature at the time of film formation. Among these, amorphous ITO has an advantage that it can be etched with oxalic acid which is a weak acid, but crystalline ITO is widely used because there is a problem that a residue remains after etching rather than complete amorphous.

Flat displays such as LCDs and PDPs are widely used as devices for recognizing images and characters with the eyes such as televisions, industrial monitors, touch panels, calculators, wrist watches, and instrument panels of automobiles. Brightness is progressing.
In order to increase the definition, the number of pixels must be increased, and in order to increase the luminance, it is necessary to increase the aperture ratio, and the space between each pixel and the wiring portion must be reduced.
Each pixel has a circuit pattern formed by photolithography using a resist, and then wet etching the material to be etched. In order to achieve high definition, dimensional stability after etching is strongly required, and it is necessary to reduce the undercut that most affects dimensional accuracy.

Hydrochloric acid and ferric chloride have so far been added with an aqueous solution of hydrochloric acid and ferric chloride containing 18% or more of free acid (Patent Document 1) and ferric chloride in a ratio of twice or less by weight of hydrochloric acid. An aqueous solution (Patent Document 2) is known.
These etchants are frequently used because of their high etching rates, but the concentration of hydrochloric acid is high, so the working environment is deteriorated by the acidic odor of hydrogen chloride, and the surrounding measuring instruments and buildings are corroded. was there.
In addition, the mixed solution of hydrochloric acid and ferric chloride has the biggest problem that the undercut is larger than that of an etching solution called aqua regia.
On the other hand, the aqua regia type etching solution is excellent in undercut, but there is a problem that the corrosion of titanium used for the members of the etching apparatus is severe and the durability of the apparatus is lowered.
Etching of other transparent electrodes includes hydroiodic acid and hydrobromic acid-based etchants, which excel in undercutting, but are more expensive than hydrochloric acid and are not economical and are actually used. Not.

JP-A 61-199080 Japanese Patent Laid-Open No. 07-130701 JP 05-005899 A

  Provided are an etching solution, an etching method, and a substrate to be etched, which have less acidic odor of hydrogen chloride, less undercut of a transparent conductive film, and less corrosion of titanium used in an etching apparatus.

As a result of intensive studies to achieve the above-mentioned problems, the present inventor completed the present invention.
[1] An aqueous solution of hydrochloric acid and ferric chloride, the concentrations of 4A + B ≧ 50 and 2A + B ≦ 53, −A + 0.39B ≧ −7.5, and B ≦ 40 (where A is the concentration of hydrochloric acid ( (Mass%) and B are etching solutions shown in the range of ferric chloride concentration (mass%).
[2] The method for etching a transparent conductive film using the etching solution according to [1], wherein the temperature of the etching solution is 30 to 60 ° C. and the etching time is 0.2 to 30 minutes.
[3] The etching method according to [2], wherein the transparent conductive film is a metal oxide.
[4] A substrate to be etched having a circuit pattern formed by the etching method [5] [2] to [4] according to [3], wherein the metal oxide is ITO (indium tin oxide).
It is.

  According to the present invention, there is no acidic odor of hydrogen chloride unique to an etching solution comprising conventional hydrochloric acid and ferric chloride, there is little undercut of the transparent conductive film, and there is little corrosion of titanium used in the etching apparatus. An etching solution and an etching method are provided.

  The inventor has studied an etching solution having a low hydrochloric acid concentration in order to solve the generation of the odor of hydrogen chloride. In addition to suppressing the odor of hydrogen chloride at a specific concentration, the undercut of the transparent conductive film It was found that the interface between the transparent conductive film and the resist film as the mask material does not peel off.

The concentration of the etching solution in the present invention is as follows.
4A + B ≧ 50, 2A + B ≦ 53, −A + 0.39B ≧ −7.5, B ≦ 40
However, A: Concentration (mass%) of hydrochloric acid, B: Concentration of ferric chloride (mass%)
Here, if the concentration of hydrochloric acid and / or ferric chloride is lower than 4A + B ≧ 50, a sufficient etching rate cannot be obtained.
If the concentration of hydrochloric acid and / or ferric chloride is higher than 2A + B ≦ 53, the odor of hydrogen chloride is severe and the working environment is deteriorated.
If the concentration of hydrochloric acid and / or ferric chloride is higher than −A + 0.39B ≧ −7.5, the undercut of the transparent conductive film when etched becomes large. In addition to undercut, the odor of hydrogen chloride is severe and the working environment deteriorates.
If the concentration of ferric chloride is higher than B ≦ 40, a sufficient etching rate cannot be obtained.

Preferably, the region satisfies the following conditions.
4A + B ≧ 53, 2A + B ≦ 50, −A + 0.39B ≧ −1.2, B ≦ 36
A region that satisfies the following conditions is more preferable.
4A + B ≧ 56, 2A + B ≦ 49, −A + 0.39B ≧ −1.1, B ≦ 34
A region that satisfies the following conditions is particularly preferable.
4A + B ≧ 60, 2A + B ≦ 48, −A + 0.39B ≧ 0.4, B ≦ 32
Most preferably, the region satisfies the following conditions.
4A + B = 62 ± 1, 2A + B = 46 ± 1, −A + 0.39B = 3.7 ± 1.4, and B = 30 ± 1. This corresponds to 7-9 (mass%) hydrochloric acid and 29-31 (mass%) ferric chloride.

The material to be etched in the present invention is a transparent conductive film, preferably a metal oxide transparent conductive film, and more preferably ITO (indium tin oxide). In the ITO, indium oxide is preferably 70% by mass or more, and more preferably indium oxide is 80% or more.
The film thickness of the transparent conductive film is preferably 20 nm to 10 μm, more preferably 50 nm to 1 μm, and most preferably 100 nm to 500 nm.

  The etching solution temperature when using the etching solution of the present invention is preferably 30 to 60 ° C. If it is less than 30 ° C., the etching rate is slow, and if it exceeds 60 ° C., the odor of hydrogen chloride is severe and the atmosphere becomes acidic. A more preferable liquid temperature is 30 to 55 ° C, and a most preferable temperature is 35 to 50 ° C. In the etching solution of the present invention, when the solution temperature is in the above range, the etching processing ability and working environment are excellent.

  The etching time when using the etching solution of the present invention is preferably 0.2 to 30 minutes, more preferably 0.3 to 20 minutes, further preferably 0.4 to 10 minutes, and 0.5 to 5 minutes. Most preferred. In the etching solution of the present invention, when the etching time is in the above range, there is little damage to the substrate material in the etching process. Furthermore, peeling of the interface between the transparent conductive film and the resist film as the mask material does not occur.

There is no restriction | limiting in particular as a base material with which the transparent conductive film in this invention forms into a film, According to a use application, it can select. Specifically, glass (including those having a SiO2 film on the surface), quartz, polyester (for example, polyethylene terephthalate, polyethylene naphthalate, etc.), polyolefin (for example, polyethylene, polypropylene, polystyrene, etc.), polyimide, polyacrylate, methacrylate Etc. Glass, silicon, PP, PE, and PET are preferred. More preferably, glass, quartz, PP, PE, and PET are used. The most preferred substrate is glass or quartz glass.
Moreover, you may perform surface treatment in order to improve the adhesiveness of these base materials and a transparent conductive film. For example, another material having excellent adhesion between the base material and the transparent conductive film may be formed, or the surface roughness of the base material may be adjusted.

  As the patterning method using the etching solution of the present invention, either an immersion method or a spray method can be used.

  The concentration of the etching solution of the present invention can be controlled by using a redox potential, pH, electrical conductivity, specific gravity, or the like, or a combination thereof.

The resist used in the present invention is preferably a photoresist, more preferably a roll-shaped dry film resist and a liquid liquid resist, and particularly preferably a dry film resist.
Further, in order to improve the adhesion between these resists and the transparent conductive film, heating after development called surface treatment or post-baking may be performed. As an example of the surface treatment, there is an example in which chemical treatment such as HMDS (hexamethyldisilazane) is performed.

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

[Example 1]
An etching solution containing 8% by mass of hydrochloric acid and 30% by mass of ferric chloride was prepared using reagent-grade 35% hydrochloric acid, ferric chloride hexahydrate and ion-exchanged water. Using a 10% by mass target having a density of 70%, sputtering is performed on a glass substrate by a DC magnetron sputtering method (substrate temperature: 350 ° C.), so that crystalline ITO (90% by mass of indium oxide) having a thickness of 250 nm is obtained. And 10% by mass of tin oxide). On top of that, a novolac-based photoresist (TFR-H manufactured by Tokyo Ohka Kogyo Co., Ltd.) was formed to a thickness of 2 μm. Subsequently, the substrate was exposed to 40 mJ ultraviolet light and developed with a TMAH (tetramethylammonium hydroxide) 2.38% developer at 25 ° C. for 40 seconds to obtain a test substrate.
An etching solution was sprayed onto this test substrate from an Ikeuchi-made full cone nozzle (product name: 1 / 4MJXP040HTPVC) at a spraying pressure of 0.18 MPa at a temperature of 40 ° C. for 3 minutes and 50 seconds. Immediately after the spraying was completed, the etching solution was washed away with ion-exchanged water, the resist was peeled off with acetone, washed with ion-exchanged water, and then dried to prepare an etching substrate.
This substrate was observed with a surface shape observation microscope (product number: VF-7510) manufactured by Keyence Corporation to obtain an undercut.

As shown in FIG. 1, the undercut width was obtained from the distance between the edge of the photoresist and the edge of ITO on the substrate.
Further, the etching time was set to the time when there was no etching residue on a portion of the glass substrate that was not protected by the resist by preparing test substrates with different etching times and observing with the same microscope.
The etching rate was determined by dividing the film thickness by the etching time.
The above results are shown in Table 1 together with the odor of the etching solution.

[Odor determination]
Etching solution was taken into a test tube, smelled at a temperature suitable for etching, and judged by the intensity of an irritating acidic odor.
○: Almost no irritation even when looking up with hand △: Slight irritation when looking up with hand ×: Intense irritation even without looking up with hand

[ Comparative Reference Examples 2 to 10 ]
The same operation as in Example 1 was carried out except that the concentrations of hydrochloric acid and ferric chloride were changed to Table 1. The results are shown in Table 1.

[Comparative Example 1]
The same operation as in Example 1 except that the etching solution was aqua regia type etching solution (hydrochloric acid 18% by mass, nitric acid 3% by mass, the balance being water) using reagent-grade 35% hydrochloric acid, 60% nitric acid and ion-exchanged water. To do. The results are shown in Table 1.

[Comparative Examples 2 to 6]
The same operation as in Example 1 was carried out except that the concentrations of hydrochloric acid and ferric chloride were changed to Table 1. The results are shown in Table 1.

[ Comparative Reference Examples 11 and 14, Examples 12 and 13 ]
The same operation as in Example 1 was performed except that the etching temperature was changed to Table 1. The results are shown in Table 1.

[ Comparative Reference Examples 16 to 24, 26 to 34, Examples 15 and 25 ]
The same operation as in Example 1 was performed except that the concentrations and temperatures of hydrochloric acid and ferric chloride were changed to those shown in Table 1. The results are shown in Table 2.

[Reference Example 1]
In order to investigate the influence of the etching solution on the corrosion of the etching apparatus, the corrosion rate for titanium which is the material of the etching apparatus was obtained.
A 0.5 mm thick titanium plate of JIS type 1 (TP 270) was immersed in the etching solution of Example 1 and held at 55 ° C. for 2 weeks. From the weight difference before and after immersion, the surface area of the titanium plate, the density of titanium and the immersion time, the corrosion distance converted to one year was determined, and the corrosion rate was determined by the following equation. The results are shown in Table 3.
Titanium corrosion rate = weight difference (g) / surface area (square mm) / specific gravity (g / legal mm) / immersion time (year)

[Reference Examples 2 to 5]
The same operation as in Reference Example 1 was performed except that the concentrations of hydrochloric acid and ferric chloride were changed to Table 3. The results are shown in Table 3.

[Comparative Reference Example 1]
The same operation as in Reference Example 1 except that the etching solution was an aqua regia type etching solution (hydrochloric acid 18% by mass, nitric acid 3% by mass, the balance being water) using reagent-grade 35% hydrochloric acid, 60% nitric acid and ion-exchanged water. I did it. The results are shown in Table 3.

  According to the present invention, low undercutting and further less odor, the workability is good, and the etching apparatus does not corrode. Therefore, etching with excellent safety and productivity is possible, and the transparent conductive film is patterned. The manufactured substrate can be manufactured inexpensively and efficiently. Therefore, it is suitable for the production of highly integrated semiconductors and miniaturized devices.

It is the figure which showed the state of the undercut.

Explanation of symbols

1 Photoresist 2 ITO film 3 Glass substrate 4 Undercut width

Claims (2)

An aqueous solution of hydrochloric acid and ferric chloride, the concentrations being 4A + B = 62 ± 1 and 2A + B = 46 ± 1 , −A + 0.39B = 3.7 ± 1.4 and B = 30 ± 1 A is an etching solution having a hydrochloric acid concentration (mass%) and B is a ferric chloride concentration (mass%). The etching liquid temperature is 30 to 60 ° C., and the etching time is Etching method of ITO (indium tin oxide) transparent conductive film for 0.2 to 30 minutes. The circuit pattern is formed by etching a transparent conductive film formed in a film thickness of 20 nm to 10 μm on a substrate selected from glass, quartz, polyester, polyolefin, polyimide, polyacrylate, and methacrylate. 2. The method for etching an ITO (indium tin oxide) transparent conductive film according to 1.

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