Removal of post-etch photoresist and sidewall residues using organic solvent and additive combined with physical forces

The effect of tetramethyl ammonium hydroxide (TMAH) used as additive in organic solvent (N-methyl pyrrolidone, NMP) on removal efficiency of post-etch photoresist was investigated on both blanket substrate and single damascene structures. In contrast to plasma ashing, photoresist removal using NMP/TMAH combined with megasonics showed no carbon depletion and no significant change in k-value. Mixing TMAH with NMP enhanced photoresist removal efficiency with respect to pure NMP. Photoresist removal using NMP/TMAH resulted in lower low-k capacitance (lower k-value) compared with that of plasma ashing process, due to the removal of the damaged layer generated during plasma etching. As a consequence of the removal of the damaged layer, a CD change was observed. The CD loss was estimated to be about 7 nm for 1% TMAH, and became negligible for 0.1% TMAH. Analysis of low-k sidewall using angle-resolved X-ray photoelectron spectroscopy showed that solvent mixture containing TMAH also removed sidewall residues generated by the etch plasma.