Plasma etching behavior of iridium in CF4- and Cl2-based chemistries

Iridium (Ir) is a chemically stable noble metal that remains difficult to etch with high controllability under plasma processing conditions due to its low volatility and limited chemical reactivity. In this work, Ir plasma etching under fluorine- and chlorine-based chemistries is systematically investigated to examine the distinct ion–surface interaction behaviors governing material removal under different plasma conditions. Variations in transformer-coupled plasma (TCP) power and substrate bias voltage reveal markedly different etch-rate scaling characteristics for CF4/O2 and Cl2/O2/Ar plasmas, particularly with respect to substrate bias. In CF4-based plasmas, the Ir etch rate increases monotonically with both TCP power and bias voltage, consistent with a sustained ion-assisted etching response. In contrast, Cl2-based plasmas exhibit progressively reduced etch-rate sensitivity to substrate bias at higher voltages. Gas composition further modifies the etching characteristics through the contrasting role of oxygen in the two plasma chemistries. In CF4-based plasmas, O2 suppresses fluorocarbon accumulation and sustains Ir removal, whereas in Cl2-based plasmas, increasing O2 content reduces the etch rate and promotes surface-constrained etching conditions. X-ray photoelectron spectroscopy reveals distinct surface chemical states for CF4- and Cl2-based plasmas, while transmission electron microscopy shows substantially more aggressive material removal under CF4-based conditions. Overall, the results demonstrate that Ir etching is governed by the interplay between ion-assisted removal and chemistry-dependent surface limitations in fluorine- and chlorine-based plasmas.