Highly Selective SiO2/Si Etching and Related Kinetics in Time-Modulated Helicon Wave Plasma

Highly selective SiO2/Si etching has been achieved by using time-modulated helicon wave plasma (HWP) employing C4F8/H2 mixture. Time modulation of less than 5 µ s. effectively controlled the electron energy, suppressing redissociation of HF. The selectivity window for H2 concentration was widened by synchronizing the phase of 100 kHz self-bias to the phase of 100 kHz time-modulated HWP. This is performed by extension of the polymer point to higher H2 concentration due to bombardment of more ions. Measurements of AMS of radicals and XPS of polymer formed on the Si surface suggest that CF1 radicals contribute to the polymer formation and produce carbon-rich film in the presence of hydrogen in the case of the pulse discharge in which electron energy is controlled and dissociation is suppressed. Measurement of CF1/F ratio also supported this conclusion.