Etching solution

Details Etching solution Etching solution

1992-12-22

1995-10-31

Dang, Thi

Etching a substrate: processes

Nongaseous phase etching of substrate

Etching inorganic substrate

252 792, 252 794, 252 795, 216108, C09K 1300, C23F 100

Patent

active

054626404

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to an etching solution for etching away a metal layer from a substrate which includes a hydrogen containing compound that dissolves the metal per se while developing hydrogen, and a nitrosubstituted organic compound, to a method for etching away a metal layer from a substrate wherein the substrate coated with the metal is immersed into an etching solution which contains a hydrogen containing compound that dissolves the metal per se while developing hydrogen, and includes a nitro substituted organic compound, preamble of the eighth claim and to the use of a water soluble, easily hydratable organic nitro compound as an addition to the aqueous solution of an acid or a highly basic metal hydroxide in order to prevent the release of hydrogen gas when metal is dissolved in the solution.
2. Description of the Related Art
An etching solution and a process of this type are disclosed in DE 3,248,006.A1. One subject of this publication is an agent for the selective removal of hard metal surface coatings, particularly ceramics, cermets and mixtures based on nickel from high strength, high temperature resistant substrates. This agent is characterized by approximately 90 to 450 g/l H.sub.2 SO.sub.4, approximately 20 to 240 g/l of a water soluble, nitrosubstituted aromatic compound, the remainder water. The publication further relates to a process for removing hard metal surface coatings by employing this agent.
The water soluble, nitrosubstituted aromatic compound is preferably composed of m-nitrobenzene sodium sulfonate or m-nitrobenzene sodium sulfonic acid or the corresponding alkali or earth alkali metal nitrobenzene sulfonates; however, the other organic nitro compounds mentioned in U.S. Pat. No. 2,698,781, which will be discussed below, can also be employed.
The etching solution may additionally include hydrofluoric acid, fluoboric acid HBF.sub.4 and surfactants as wetting agents.
The publication does not reveal the manner in which the described etching solution works. The nitroaromatic compound is merely called an oxidation agent.
During practical tests with the prior art etching solution employing a sulfuric acid concentration of (i) 90 g/l, (ii) 300 g/l and (iii) 450 g/l, together in each case with 240 g/l m-nitrobenzene sodium sulfonate, it was found that hydrogen developed and was released. The etching solution was very viscous and could be employed only at an elevated temperature. Accordingly, the etching process disclosed in the publication is implemented at a temperature between about 49.degree. C. and 82.degree. C.
Another etching solution of the above-mentioned type is disclosed in the already cited U.S. Pat. No. 2,698,781. In the simplest case, this etching solution is composed of an acid and a nitrosubstituted aromatic compound whose potential under special conditions mentioned in the publication lies between 0.50 Volt and 0.90 Volt. In this etching solution, the nitrosubstituted aromatic compound is not used up during the etching process or only to a slight extent; it acts as an activator or catalyst for the etching reaction. Thus--although this is not explicitly mentioned in the publication--hydrogen has to form during the etching process. Due to the condition that the potential of the nitrosubstituted aromatic compound is to lie in the stated range, it is obvious that the compounds selected from this class of compounds are those which, after the etching process, form a reaction product neither with the metal nor with the developing hydrogen. The m-nitrobenzene sulfonic acid specially preferred in the above-mentioned DE 3,248,006.A1 is mentioned as one of the nitrosubstituted aromatic compounds that have such a potential.
Further etching solutions containing additional components are disclosed, for example in the publications CH 394,761, DE 2,635,295.C2, DE 2,536,404.C2 and DE-OS [Unexamined Published Patent Application] 2,143,785.
CH 394,761 relates to a mixture for the selective dissolution of a metal in the presence of a

REFERENCES:
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patent: 4687545 (1987-08-01), William et al.
patent: 5035749 (1991-07-01), Haruta et al.
Sensors and Actuators A, 25-27 (1991), 559, 563 C. Burbaum et al.: "Fabrication of Captive . . . ".
S. Hirsch et al.: "Stripping Metallic Coatings".

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