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Caro's Acid Stripping Bath for Resist Removal

IP.com Disclosure Number: IPCOM000085019D
Original Publication Date: 1976-Feb-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Kaplan, LH: AUTHOR [+2]

Abstract

Caro's acid is a solution of peroxymonosulfuric acid in sulfuric acid. For stripping resists it is normally made by an admixture of highly concentrated hydrogen peroxide with concentrated sulfuric acid. The peroxide oxidizes a small portion of the sulfuric acid to form peroxymonosulfuric acid, H(2)SO(5), which is then available for controlled oxidation and removal of the resists.

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Caro's Acid Stripping Bath for Resist Removal

Caro's acid is a solution of peroxymonosulfuric acid in sulfuric acid. For stripping resists it is normally made by an admixture of highly concentrated hydrogen peroxide with concentrated sulfuric acid. The peroxide oxidizes a small portion of the sulfuric acid to form peroxymonosulfuric acid, H(2)SO(5), which is then available for controlled oxidation and removal of the resists.

It is found that the amount of water must be carefully controlled in order to maintain the effectiveness of the solution. This requires the use of the highly concentrated hydrogen peroxide which represents an explosion hazard.

Caro's acid is formed in situ in a working resist stripping bath by the use of electrolysis. As illustrated in the drawing, stripping tank 1 is fitted with a pair of inert metal electrodes 2 and 3 (e.g., gold or platinum) which are connected to a constant-voltage power supply 4 (e.g., 0 to 9 V DC with concentrated sulfuric acid 5 being placed in the tank 1.

Other highly oxidized species can be created in the sulfuric acid medium to give a stripper with optimized properties for a given type of resist. For example, the incorporation of small amounts of fuming nitric acid into the sulfuric acid both causes the electrolytic creation of peroxidized nitrogen species.

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