Practical Application of Industry's First Electrolyzed Sulfuric Acid Method

Toshiba Corporation, Shibaura Mechatronics Corporation and Chlorine Engineers Corp., Ltd. has code-veloped an innovative semiconductor resist st- ripping technology that employs electrolyzed sulfuric acid. The technology draws on Toshiba's cutting-edge semiconductor process technology, Shibaura Mechatronics' expertise in semiconductor manufacturing equipment and Chlorine Engineers' know-how in high durability electrolyzer technology for high-purity chemicals. It is the first time that electrol-yzed sulfuric acid has been applied to resist stripping.

Resist is a masking material used in the lithographic process that forms semiconductor circuits on a chip substrate. 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 peroxymono sulfuric acid without producing water.

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 pro- ductivity by shortening resist stripping time by 20%.

Toshiba, Shibaura Mechatronics and Chlorine Engineers have already developed a single-wafer resist-stripping system that will be integrated into the resiststripping process at Toshiba's Yokkaichi Operations in April. Shibaura Mechatronics Corporation and Chlorine Engineers Corp., Ltd. also plan to market the overall system and an electrolyzed sulfuric acid generation unit that can be integrated into the current resist stripping process. The new technology can be applied to overall process of circuit formation on wafers, and the companies intend to promote such application.