Ryu Shimizu

Effect of iodotrifluoromethane plasma for reducing ultraviolet light irradiation damage in dielectric film etching processes

Iodotrifluoromethane (CF3I) gas is one of the environmentally conscious perfluorocarbon gases because it has a very low global warming potential. The authors have found that CF3I gas plasma drastically reduces ultraviolet (UV) photon irradiation of ∼4.0 eV, which corresponds to the excitation energy at silicon dioxide (SiO2)/silicon (Si) interfaces, in comparison with octafluorocyclobutane (C4F8) gas. This results in reducing UV irradiation damage in dielectric film etching processes, which was experimentally confirmed by evaluating charge-pumping currents in metal insulator semiconductor field effect transistors fabricated by using CF3I gas etching. They have also demonstrated that a novel etching method using pulse-time modulation of CF3I gas plasma for the first time further reduced UV light irradiation damage.

Mechanism of increase in charge-pumping current of metal-nitride-oxide-silicon-field effect transistors during thick dielectric film etching using fluorocarbon gas plasma

Plasma irradiation damage to metal-insulator-semiconductor (MIS) devices can cause serious problems, such as an increase in the charge-pumping current and interface state density between SiO2 and Si during the dielectric film etching process using perfluorocarbon gas. The increase in a charge-pumping current was observed as a result of increasing the substrate rf bias for accelerating ions during plasma etching for thick dielectric film. The authors found that the current increase was caused by combination of E′ centers and Pb centers. That is, the generated electrons (E′ center) in the dielectric film surface by ion bombardment are trapped at the Si dangling bonds of the SiO2/Si interface (Pb centers). These Pb centers are generated by the penetration of UV photons. Control of both UV photons and ion bombardment is therefore crucial to eliminate damage at the SiO2/Si interface in MIS devices.