Hydrofluoroethane plasma etching of SiN, SiO2, and poly-Si films with CHF2CF3, CF3CH3, and CHF2CH3

Plasmas containing hydrofluorocarbon gases (CHF2CF3, CF3CH3, and CHF2CH3) are used for the selective removal of SiN, SiO2, and poly-Si films when manufacturing large-scale integrated circuits. Understanding the plasma chemistry of hydrofluorocarbons is important for gaining insight into the mechanisms of these selective-etching processes. The fragmental reactants produced by the reactive plasma are essential for evaluating and controlling highly accurate selective etching. This study examined such fragments using a primary dissociation ionization threshold quadrupole mass spectrometer at an electron energy of 20 eV. Their primary dissociative ionization thresholds were identified using photoelectron-photoion coincidence spectroscopy, with photon energies ranging from 10 to 28 eV. The results showed the following: (i) the CHF2CF3 molecule dissociated into ions such as CHF2+ and C2HF4+, which formed secondary ions, such as CF3+ and CF2+. The F-rich reactants effectively enhanced the etching of both SiO2 and SiN; (ii) the CF3CH3 molecule dissociated into ions such as C2H2F+ and C2H2F2+, while the dominant CF3+ remained as a crucial fragment for the primary etching of SiO2; (iii) the CHF2CH3 molecule predominantly yielded ions such as CHF2+, CF2CH3+ and CxHy+, promoting polymer film deposition on the surfaces of SiO2 and poly-Si.