RFEA-Derived Ion-Energy Descriptors for Preliminary Process-Window Evaluation in Dual-Beam Soft Plasma Etching of Organic Semiconductor Films

Low-damage plasma processing of organic semiconductor films requires a consistent way to relate plasma diagnostics to material responses. This study presents a retarding-field energy analyser (RFEA)-guided workflow for preliminary evaluation of seven nominal single- and dual-beam settings. A selectivity-ratio (SR) screening index was calculated as the ratio of integrated ion-energy-distribution intensity in fixed 4–6 eV and 6–8 eV windows. The seven recorded scores range from 1.32 to 7.58, with the 50 + 100 condition label giving the highest window ratio. The index describes the relative spectral weight of the two intervals under an assumed activation-versus-damage interpretation. A published effective-energy model provides separate physical context. Time-resolved optical measurements and baseline electrical characterisation were complemented by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). At 100 Pa for 100 s, dual-beam treatment showed higher mean surface O/C while retaining mean roughness close to the unetched films. Additional stylus profilometry comprised 42 scans from 14 specimens. At 50 Pa for 180 s, treated-group mean apparent step heights ranged from 160.7 to 205.9 nm, without a uniform increase under source superposition. These within-protocol measurements provide complementary criteria for assessing candidate conditions. The workflow combines an explicit spectral ranking with measured film responses for preliminary process-window evaluation; SR is interpreted as a screening index rather than a measured molecular etch-rate ratio.