After channel dry etching of High Aperture Advanced Super Dimensional Switching（HADS）array substrate， the edge of source/drain electrode line was prone to form Photo Resist（PR）remain， leading to passivation microcracks and channel contamination. In order to improve PR remain and TFT leakage current， the formation mechanism of PR remain and effect of PR ashing process on PR undercut were studied. Then， the relationship between PR undercut， channel tail and TFT leakage current at different ashing time was explained. Effect of post-treatment on TFT leakage current was studied by a full factor experiment. The results showed that PR undercut and by-product were formed in enhanced capacitive coupled plasma etching， which together caused PR remain. PR undercut was significantly improved by increasing bias power and reducing pressure in PR ashing process， with PR coverage source/drain distance d>0. But as the distance d increased， the channel tail grew， causing an increase of TFT leakage current. Post-treatment optimization further reduced channel contamination to reduce back-channel leakage current. With post-treatment of bias power 1 kW， pressure 4 Pa， O₂/SF₆ 10， the leakage current was reduced by 18% compared to the mass production， and no PR remain occurred. This work could provide a reference for process research， PR morphology optimization and TFT leakage current improvement in different modes of channel dry etching.