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New Product: Toshiba & partners use electrolyzed sulfuric acid for resist stripping

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ToshibaProduct Briefing Outline: Toshiba Corporation, Shibaura Mechatronics Corporation and Chlorine Engineers Corp. have co-developed an innovative semiconductor resist stripping technology that employs electrolyzed sulfuric acid. It is the first time that electrolyzed sulfuric acid has been applied to resist stripping, according to the companies. The partners have already developed a single-wafer resist-stripping system that will be integrated into the resist-stripping process at Toshiba's Yokkaichi Operations in April 2007.

Problem: Once circuits are etched, the resist must be removed, which is typically done with peroxymonosulfuric acid, produced by mixing sulfuric acid with hydrogen peroxide. However, once the process is completed, it is difficult to recycle the sulfuric acid because of dilution by the water released as a by-product of the breakdown of the hydrogen peroxide in the mixture. The new technology allows sulfuric acid to be recycled, as electrolyzing sulfuric acid generates peroxymonosulfuric acid without producing water.

Solution: The new technology was developed as a substitute for the current sulfuric acid hydrogen peroxide Mixture (SPM) technology applied to the "wet process" of resist stripping. The new technology reduces the volume of sulfuric acid used in resist stripping by 70 percent and totally eliminates use of hydrogen peroxide. As a result, it reduces the overall environmental burden of the semiconductor wet process and adds to the efficiency of wastewater treatment. The new process is also more efficient, and contributes to improved productivity by shortening resist stripping time by 20%.

Applications: Photoresist stripping

Platform: Impact on resist-stripping process (pattern rework process): sulfuric acid use reduced by approximately 70%; hydrogen peroxide use reduced to zero

Availability: February 2007 onwards.

The new technology achieves the same reaction and result as SPM, but uses electrolyzed sulfuric acid. This is achieved by exciting the acid, as shown below.


The new method allows reuse of sulfuric acid, as the water is also electrolyzed and does not dilute the sulfuric acid.


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