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-modul ated helicon wave plasma (HWP) employing C4F8/H-2 mixture. Time modula tion of less than 5 mu s. effectively controlled the electron energy, suppressing redissociation of HF. The selectivity window for H-2 conce ntration was widened by synchronizing the phase of 100 kHz self-bias t o the phase of 100 kHz time-modulated HWP. This is performed by extens ion of the polymer point to higher H-2 concentration due to bombardmen t of more ions. Measurements of AMS of radicals and XPS of polymer for med on the Si surface suggest that CF1 radicals contribute to the poly mer formation and produce carbon-rich film in the presence of hydrogen in the case of the pulse discharge in which electron energy is contro lled and dissociation is suppressed. Measurement of CF1/F ratio also s upported this conclusion.