Pulsed high rate plasma etching with variable Si/SiO2 selectivity and variable Si etch profiles

Very high etch rates of Si in SF6 have been obtained in a low-pressure resonant rf discharge. By pulsing the discharge the etch selectivity between Si and SiO2 can be varied from greater than 100 at high repetition rates to around 6 at low repetition rates or continuous operation. A ‘‘lifetime’’ of atomic fluorine has been derived which is in agreement with previous measurements. With a biased substrate the etch profile can be varied from isotropic at high repetition rates to anisotropic with continuous operation.