EPR investigation of plasma-chemical resist etching in O2 and O2/CF4 discharges

During the etching of AZ 1350 photoresist in O₂ and O₂/CF₄ discharges, ground-state concentrations of atoms (O, F, and H), and small radicals (OH, HO₂, RO₂) were measured in the discharge afterglow by EPR spectroscopy. In the case of CF₄/O₂ discharges, the dependence of O and F atom concentrations on the etch time reflects both surfäce oxidation and fluorination reactions in accordance with existing etch models. In the case of high-rate resist etching in pure O₂ discharges, high concentrations of product radicals (H, OH and HO₂) were detected and compared with resist free O₂/H₂O discharges. Kinetic modeling of the afterglow reactions reveals that the mean lifetime and, accordingly, the diffusion length of the etchant species O(³P) is drastically reduced in rapid reactions with OH and HO₂. The results are used to simulate both etch homogeneity and the loading effect in a simple etch model.