February 21, 2007 – Toshiba Corp., Shibaura Mechatronics Corp., and Chlorine Engineers Corp. Ltd. have devised a new semiconductor resist strip technology that utilizes electrolyzed sulfuric acid to reduce the volume of sulfuric acid used in the process by 70%, and entirely eliminate the need for hydrogen peroxide.
The technology utilizes Toshiba’s process technology for stripping resist with electrolyzed sulfuric acid, Shibaura Mechatronics’ manufacturing equipment (system technology for the new process and electrolytic tank), and Chlorine Engineers’ high-durability electrolyzer technology for direct electrolysis of concentrated sulfuric acid.
Peroxymonosulfuric acid (a mix of sulfuric acid and hydrogen peroxide) is used to strip photoresists following the etch process in semiconductor manufacturing, but the hydrogen peroxide is not easily recycled due to dilution by water releases as a byproduct of the breakdown of hydrogen peroxide. With this new process, electrolyzing sulfuric acid generates peroxymonosulfuric acid, but the water is also electrolyzed and does not dilute the mixture, so the sulfuric acid can be reused.
The end result is a 70% reduction in the volume of sulfuric acid used in resist stripping, and elimination of use of hydrogen peroxide. And the companies say the new process is more efficient, shortening resist stripping time by 20%.
A single-wafer resist-stripping system has already been developed, and will be integrated into Toshiba’s Yokkaichi operations in April. Shibaura Mechatronics and Chlorine Engineers plan to market the tool as well as an electrolyzed sulfuric acid generation unit.
Typical sulfuric acid-hydrogen peroxide mixture (SPM) chemical reaction process:
H2SO4 (sulfuric acid) + H2O2 (hydrogen peroxide) –> H2SO5 (peroxymonosulfuric acid) + H2O (water)
* peroxymonosulfuric acid is activated sulfuric acid, a strong oxidizer that facilitates resist stripping
New chemical reaction process:
H2SO4 (sulfuric acid) + H2O (water) –> H2O2 (hydrogen peroxide) + 2H+ (hydrogen ion) + 2e– (electron)
* peroxymonosulfuric acid production and resist stripping match that of SPM