Efficient Wet Stripping of Photo Resist by UV Flood-Exposure

Wet stripping of bulk PR in general is difficult and getting a cleaner wafer without residues is even harder. This difficulty is amplified in the case of thick PR (used to create tall pillars in RDL). In this report we show that re-exposing the PR coated wafers to UV before wet stripping not only makes PR stripping easier but also provides cleaner surface using less solvent with a short process time. The impact of UV re-exposure on the ease of PR wet strip was studied in 2 phases. 1) Lab experiments were conducted on coupons in a beaker. The PR removal efficiency was established a) by visually b) using water contact angle and c) FTIR spectroscopy. 2) FAB tool tests were conducted on Waferstorm using TMAH based solvent. The PR removal efficiency was established using a) SP3 and b) water contact angle.