Wet Surface Treatment for Preventing Pattern Collapse of Dry-Film Photoresist in Panel-Level Redistribution Layer Interposer Fabrication

Dry-film photoresists (DFRs) are susceptible to pattern collapse arising from hydrophilic water–DFR interactions after the development process. Although wet surface treatment (rinsing) has been proposed to increase the hydrophobicity and prevent collapse, the associated surface chemical and mechanical changes remain insufficiently understood. In this study, the effects of these changes on pattern collapse were systematically analyzed using rinses containing tetramethylammonium chloride (TMAC), cetyltrimethylammonium chloride (CTAC), or BHA hydrochloride (BHAC). The surface free energy decreased after rinsing, confirming the increased hydrophobicity. During photolithography, pattern collapse was worsened by TMAC or CTAC but prevented by BHAC. The mechanical strength was degraded by TMAC or CTAC but enhanced by BHAC, as observed by nanoindentation. Diffusion of cations into the DFR was confirmed by confocal Raman microscopy, while changes in the chemical structure and apparent crosslink density arising from cation–DFR interactions were evaluated by Fourier transform infrared spectroscopy and swelling tests, respectively. In particular, BHAC treatment enhanced hydrogen-bonding in the DFR, which was associated with a higher apparent crosslink density and improved mechanical robustness. Finally, the BHAC-containing rinse was selected as the optimal rinse and used to fabricate a panel-level redistribution layer interposer. The interposer was successfully fabricated, exhibiting an insertion loss magnitude below 1.4 dB over 0–40 GHz. These results highlight that pattern collapse of the DFR can be effectively prevented using a BHAC-containing rinse during fine patterning.