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This study investigates the etching behavior of silicon nitride (SiN), silicon dioxide (SiO₂), and poly-Si films using CHF₂CF₃, CF₃CH₃, and CHF₂CH₃ hydrofluorocarbon plasmas. The dissociation of fragments and reactants from the parent gas was analyzed to achieve controllable changes in the etching process through the etchant composition. Fragment species of these gases was conducted using quadrupole mass spectrometry (QMS) under plasma and non-plasma conditions. The electron impact energy (EI) for the QMS analysis was fixed at 20 eV. Photoelectron-photoion coincidence (PEPICO) spectroscopy was employed to identify primary dissociation fragments generated by photons with energies ranging from 10 to 28 eV and compare with QMS results. The appearance energies of the fragments obtained from PEPICO were compared to the calculated vertical potentials predicted by computational chemistry. CHF₂CF₃ dissociates CHF₂⁺ and C₂HF₄⁺ ions, enhancing SiN etching. CF₃⁺ and CF₂⁺ ions, generated during the process, effectively etch SiO₂. In the case of CF₃CH₃, while CF₃⁺ remains a crucial fragment, the presence of C₂H₂F⁺ and C₂H₂F₂⁺ ions are also significant. C_xH_yF_z⁺ exhibits a strong propensity for SiN etching, while CF₃⁺ primarily etches SiO₂. CHF₂CH₃ fragments predominantly yield CHF₂⁺ and CF₂CH₃⁺ ions, promoting the deposition on the surfaces of SiO₂ and poly-Si.