SoC Profile Control for BEOL Tri-Layer Patterning Scheme

A tri-layer mask scheme consisting of photoresist (PR), Si-based anti-reflection coating (SiARC) and spin-on-carbon (SOC) is widely used to transfer initial PR pattern to the underneath patterning layer (PL). To perform desired pattern transfer, it is critical to achieve a vertical SOC profile after the SOC etch step. The spacing CD is primarily determined by the selectivity to SiARC during etching of SOC while the profile of SOC requires sidewall passivation from the etch chemistry. However, for most BEOL applications, the use of sulfur-based passivation gases is limited, resulting in weak sidewall and top protection, which poses significant challenges to achieve desired SOC profile. In this work, we propose a solution for SOC profile control for BEOL applications requiring small CD and vertical profiles. In our approach, the SOC etch step consists of recipe A (oxygen based, higher selectivity to SiARC) and recipe B (non-oxygen based, lower selectivity but less lateral etching). This work discusses the strategy for the combination of recipe A and recipe B.