An environment friendly wet strip process for 193 nm lithography patterning in BEOL applications

In semiconductor Back-End-of-Line (BEOL) processing, wet organic strippers have gained a renewed interest for removal of etched photoresist (PR) layers to replace plasma strip, which degrades porous low-k dielectrics. In this study we show how the characterization of 193-nm PR degradation by etch plasmas led to the development of an environment friendly wet strip using aqueous ozone solutions. Characterization of post-etch PR films have shown that degradation was similar to that of poly(methyl acrylate/methacrylate) (PMA/PMMA) by UV light, with formation of single and conjugated CC bonds in PR chains. However little removal was obtained with O3/H2O strips without an organic solvent rinse, indicating reactions fragments were too long for a complete dissolution in water. In turn known effects of UV on PMA/PMMA were used to develop an optimized UV pre-treatment enabling a fully aqueous O3 strip. This process was shown to efficiently remove PR in a dual damascene application. Also we shortly discuss the impact of materials selection on process efficiency, improvement in low-k compatibility and transfer to a production environment.

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