Extreme Chemical Reduction on Photoresist Stripping Process by Using Sulfuric Acid Ozone Mixture in Liquid Film

Sulfuric acid (H 2 SO 4 ) and hydrogen peroxide (H 2 O 2 ) mixture (SPM) has been widely used in the photoresist (PR) stripping process of semiconductor manufacturing. However, the consumption of H 2 SO 4 and H 2 O 2 increases environmental burden such as water pollution. To reduce SPM consumption, one of the ideas was that SPM was supplied to the wafer until liquid film was formed and stopped during stripping process instead of continuous dispensing. It was concerned that chemical species in SPM became inactive while SPM was stopped. Therefore, in this work, H 2 SO 4 liquid film was formed on the wafer and then exposed to ozone (O 3 ) atmosphere so that chemical species remained active. Generation of peroxydisulfate ion (S 2 O 8 2− ) by reacting hydrogen sulfate (HSO 4 − ) with O 3 was the key to achieve PR stripping (1, 2). Results showed sulfuric acid ozone mixture (SOM) in liquid film was comparable to conventional SPM even though chemical consumption of SOM was extremely reduced.