$CF_4/O_2$ gas chemistry에 의한 Ru 박막의 식각 특성

Etching characteristics of Ru thin films with $CF_4/O_2$ gas chemistry

Ferroelectric Random Access Memory(FRAM) and MEMS applications require noble metal or refractory metal oxide electrodes. In this study, Ru thin films were etched using $O_2$+10% $CF_4$ plasma in an inductively coupled plasma(ICP) etching system. The etch rate of Ru thin films was examined as function of rf power, DC bias applied to the substrate. The enhanced etch rate can be obtained not only with increasing rf power and DC bias voltage, but also with small addition $CF_4$ gas. The selectivity of $SiO_2$ over Ru are 1.3. Radical densities of oxygen and fluorine in $CF_4/O_2$ plasma have been investigated by optical emission spectroscopy(OES). The etching profiles of Ru films with an photoresist pattern were measured by a field emission scanning electron microscope (FE-SEM). The additive gas increases the concentration of oxygen radicals, therefore increases the etch rate of the Ru thin films and enhances the etch slope. In $O_2$+10% $CF_4$ plasma, the etch rate of Ru thin films increases up to 10% $CF_4$ but decreases with increasing $CF_4$ mixing ratio.