Optimization of O2/N2 inductively coupled plasma ashing: Role of total gas flow rate and nitrogen addition on uniformity and rate

In advanced semiconductor manufacturing, achieving ultrahigh ashing uniformity is critical. This study systematically investigated the combined effects of the total gas flow rate and nitrogen addition in an inductively coupled plasma ashing process. A two-dimensional axisymmetric fluid model was integrated with experimental diagnostics. The results revealed that within a flow rate range of 200–1000 SCCM, the expanding separation vortex and enhanced convective transport synergistically homogenized the spatial distribution of reactive species, resulting in uniform ashing across the wafer. Furthermore, the performance improvement observed with the 10% N2 addition is primarily driven by the “NO poisoning,” which suppresses O atom loss at the surface through a marked significance in the sticking coefficient. This mechanism effectively resolves the conventional trade-off between the ashing rate and uniformity. An optimized process window of 500–1000 SCCM with 10% N2 consistently delivered a high ashing rate (>500 nm/min) and excellent within-wafer uniformity (<3%).