JP2006199976A - Method for etching aluminum-based material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for etching an aluminum-based material into an aluminum thin line having a width of 30 μm. <P>SOLUTION: The method for etching the aluminum-based material includes etching the aluminum-based material having a resist pattern mask formed on its surface with an etching solution containing at least ferric chloride and ammonium chloride. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an etching method for an aluminum-based material, and more particularly to an etching method for forming fine fine lines on the surface of an aluminum-based material.

Aluminum has been used as a wiring material because it has a relatively low electrical resistance, a high-purity raw material is obtained, film formation is easy, and it can be processed at low temperatures.
High-density mounting is being promoted on printed circuit boards, and accordingly, circuit thinning is required. In a circuit using aluminum as a wiring material, a desired pattern is drawn using a photoresist on an aluminum foil on a substrate, and aluminum wiring is formed by etching. As etching, dry etching using plasma or the like requires expensive equipment, and cheaper wet etching is preferably used. As an etchant used for wet etching, hydrochloric acid, sulfuric acid, nitric acid, or the like is used.

However, aluminum is easily oxidized, and when an oxide film is formed on the surface, the aluminum oxide portion is difficult to be etched, so that the aluminum oxide portion is likely to remain without being etched. For this reason, uniform thinning becomes difficult, and the resist resin is also damaged when etching is strengthened. Therefore, it is difficult to form a uniform thin line with an etching solution that has been conventionally used, and a thin line having a width of 200 μm is the limit in the chemical etching of aluminum.
In recent years, higher density mounting has been demanded, and it has been strongly demanded to form thinner fine wires of aluminum.
An object of the present invention is to provide an etching method capable of forming a 30 μm thin aluminum wire.

  The method for etching an aluminum material of the present invention is characterized in that an aluminum material having a resist pattern mask formed on the surface thereof is etched with an etching solution containing at least ferric chloride and ammonium chloride.

  According to the present invention, it is possible to form a thin line having a width of 30 μm, which has been conventionally difficult.

In the present invention, the aluminum-based material to be etched has a resist pattern mask formed on the surface.
Examples of the aluminum-based material include aluminum and aluminum alloys, but the aluminum-based material preferably has an aluminum purity of 99.5% by mass or more, and more preferably 99.9% by mass or more. Examples of the aluminum-based material include printed circuit boards, micromachine-related devices, holograms, aluminum crafts using fine patterns, etc., having aluminum foil for circuits or aluminum foil for heat sinks on the surface. However, the present invention is not limited to these as long as it can form a fine pattern.

  The resist material for forming the resist pattern mask is not particularly limited, but dry film resist (DFR) is preferably used. Of course, a liquid resist may be applied to form a resist pattern mask. The resist pattern mask is formed with a pattern for forming a fine line having a predetermined shape by photolithography.

  Since aluminum is very easily oxidized, the surface of aluminum is always covered with an oxide film at room temperature. When etching for forming fine wires, if there is oil or fat on the surface of the aluminum-based material, the etching at that location will be hindered and the accuracy of the fine wire formed by etching will be reduced, so oil and fat will be removed before etching It is preferable to perform a degreasing treatment to perform and an activation treatment to remove the oxide film from the surface.

  As the degreasing treatment, an immersion treatment with a surfactant aqueous solution can be employed. The surfactant is preferably a neutral surfactant, and examples thereof include higher alkyl sulfonates such as alkyl benzene sulfonates.

The aluminum material subjected to the degreasing treatment is subjected to the activation treatment as it is without being washed with water.
Activation of the degreased aluminum-based material is a treatment to remove the purified oxide film on the exposed surface, and acids such as hydrochloric acid, sulfuric acid, and nitric acid can be used. It is preferable to use an aqueous phosphoric acid solution because the oxide film can be removed well without peeling off the resist. This phosphoric acid aqueous solution may be composed only of phosphoric acid, and an organic acid, a chelating agent or the like may be added as necessary. Examples of the organic acid include gluconic acid, and examples of the chelating agent include EDTA, sodium gluconate, sodium citrate, urea, ammonium carboxylate, ammonium citrate, ammonium gluconate, and Rochelle salt.

  As this phosphoric acid aqueous solution, a 2 to 30 mass% aqueous solution is preferable. When using a low-concentration phosphoric acid aqueous solution, it is preferable to add hydrochloric acid or sulfuric acid to bring the pH of the aqueous solution to 1 or less. In the case of activation with an aqueous phosphoric acid solution, the temperature of the aqueous solution is preferably 30 to 70 ° C, more preferably 40 to 60 ° C, and even more preferably 50 to 55 ° C. When the aluminum-based material is immersed in such an aqueous solution, hydrogen gas is generated from the entire surface, and the oxide is removed from the surface of the aluminum-based material. The treatment time is appropriately selected according to the phosphoric acid concentration and temperature, but is usually 30 seconds to 3 minutes, more preferably 1 to 1.5 minutes.

  The aluminum-based material activated with the phosphoric acid aqueous solution may be subjected to the etching process as it is, but may be further activated with a hydrochloric acid aqueous solution. As the aqueous hydrochloric acid solution, an aqueous solution of 10 to 30% by mass is preferably used, and when a heated aqueous hydrochloric acid solution is used, the reaction is intense and the resist may be easily peeled off. The treatment time is preferably about 5 to 15 seconds.

The aluminum-based material thus activated is immersed in an etching solution without being washed with water and etched.
In the present invention, an etching solution containing ferric chloride and ammonium chloride is used. The concentration of ferric chloride in the etching solution is preferably 20 to 40% by mass, and the ammonium chloride concentration is preferably 5 to 15% by mass. By using this solution, the fine wire process is stabilized, and therefore, it is possible to form a fine wire of 100 μm or less, which has been difficult in the past. Further, the etching can be performed at a high rate of 8 μm / min or more.
This etching solution may further contain an inorganic acid such as hydrochloric acid or sulfuric acid. Although an organic acid can be added, it tends to weaken the adhesion of the resist, and care must be taken when adding it. Furthermore, the addition of chelating agents such as ethylenediaminetetraacetic acid (EDTA), sodium gluconate, sodium citrate, urea, ammonia carboxylate, ammonium citrate, ammonium gluconate, and Rochelle salt stabilizes the formation of fine wires. preferable. The concentration of the chelating agent is preferably 3 to 15% by mass.

  As an example of a preferable composition of this etching solution, 20-40 mass% ferric chloride, 5-30 mass% hydrochloric acid, 1-10 mass% sulfuric acid, 5-15 mass% ammonium chloride, 3-15% EDTA can be exemplified. The temperature of the etching solution is preferably 30 to 60 ° C, more preferably 45 to 50 ° C. The etching treatment time is preferably 5 to 20 seconds, more preferably 8 to 15 seconds, although it depends on the thickness of the fine line to be formed and the etching depth.

  After the etching treatment, after washing with water, a black oxide film is formed on the surface of the exposed portion of the aluminum-based material at the time of etching, so that it is removed. At this stage, since the etching is completed, there is no need to worry about peeling off the resist. Therefore, any liquid that is usually used for removing the oxide film can be used. An example of such a liquid is a 20-40% nitric acid aqueous solution. A processing time of about 10 to 20 seconds is sufficient.

  Next, the resist is stripped from the aluminum-based material after completion of etching. Conventionally, alkali has been used for resist stripping. However, since alkali may damage the surface of the aluminum-based material, it is preferable to use acetic acid or acetate as the stripping material. Examples of acetate esters include methyl acetate, ethyl acetate, propyl acetate and the like.

  This resist peeling treatment can be performed at room temperature, and can be performed in 1 to 5 minutes.

  If the aluminum-based material is etched by the above-described method, even if the aluminum substrate is formed with a resist mask having a 30 μm line-and-space pattern, the line is not cut off and adjacent lines are not connected. A clean 30 μm line pattern can be formed on the aluminum substrate.

  The present invention will be further described below with reference to examples.

Example 1
A mask pattern for forming a line pattern having a width and a distance of 30 μm was formed by photolithography using a dry film resist (AQ2075; manufactured by Asahi Kasei Co., Ltd.) on a substrate obtained by laminating an aluminum foil having a thickness of 12 μm on a polyimide substrate. .

  This substrate was immersed in an ultrasonic bath of 40% neutral surfactant mass 1% aqueous solution for 10 minutes, degreased, pulled up, and then immersed in a 20 mass% phosphoric acid aqueous solution at 50 ° C. for activation treatment. However, hydrogen gas was generated from the front surface of the aluminum foil surface on which the mask pattern of the substrate was mounted. After dipping for 80 seconds, it was pulled up and immersed in a 20% aqueous hydrochloric acid solution at room temperature for further activation. Hydrogen gas was generated more intensely. No resist lift or the like was observed on the substrate after immersion in the phosphoric acid aqueous solution and after immersion in the hydrochloric acid aqueous solution.

After 8 seconds of immersion, the film was pulled up and immersed in an etching solution at 48 ° C. The composition of the etching solution was 30% ferric chloride, 10% hydrochloric acid, 5% sulfuric acid, 10% ammonium chloride, 5% EDTA. After being immersed in the etching solution for 10 seconds, it was pulled up and washed with water to wash away the etching solution.
The exposed portions of the zinc foil between the line patterns of the resist were etched, and a black aluminum oxide film was formed on the surface.

  This substrate was immersed in a 30% by mass nitric acid aqueous solution at 35 ° C. for 15 seconds to remove the aluminum oxide film, washed with water, then immersed in a 30% acetic acid aqueous solution to peel the resist, sufficiently washed with water, and dried. When the obtained substrate was examined, a clean line-and-space pattern of 30 μm was formed, there was no disconnection of the aluminum thin wires, no short circuit of the adjacent aluminum wires, and no disturbance in the line width and spacing was observed throughout. It was a thing.

(Comparative Example 1)
A mask pattern was formed in the same manner as in Example 1 except that a mask pattern for a line pattern having a width and interval of 100 μm was formed on the same substrate as that used in Example 1.

This substrate was degreased in the same manner as in Example 1 and then immersed in an etching solution at 42 ° C. The composition of the etching solution was 39.5% ferric chloride and 5% hydrochloric acid. After being immersed in the etching solution for 40 seconds, it was pulled up and washed with water to wash away the etching solution. Finally, the resist was peeled off, sufficiently washed with water and dried.
When the obtained etching pattern was examined, the aluminum fine wire was unsuitable as a circuit pattern because it was broken, the wire width was greatly disturbed, and adjacent fine wires were short-circuited.

  From the above, it can be seen that according to the method of the present invention, although it has been conventionally difficult to form an aluminum fine wire of 200 μm or less by chemical etching, a fine wire of 30 μm much finer than this can be formed.

The present invention enables the production of circuit boards with high-density mounting, enables further miniaturization of micromachines, and enables fine patterning, thereby developing various fields such as the production of various aluminum crafts. It is useful as a technology that can contribute to

Claims (4)

  A method of etching an aluminum-based material, comprising: etching an aluminum-based material having a resist pattern mask formed on a surface thereof with an etching solution containing at least ferric chloride and ammonium chloride.   2. The method for etching an aluminum-based material according to claim 1, wherein the etching solution further contains a chelating agent.   3. The method for etching an aluminum-based material according to claim 1, wherein an aluminum-based material having a resist pattern mask formed on the surface is pretreated with a phosphoric acid aqueous solution. The method for etching an aluminum-based material according to any one of claims 1 to 3, wherein the resist of the aluminum-based material after the etching treatment is removed with an acetic acid aqueous solution.