Low-k protection from F radicals and VUV photons using a multilayer pore grafting approach

Abstract

Polymer grafting was studied in porous low-k SiCOH films as a protection against plasma damage. Pores of low-k films were covered by a plasma damage management polymer. A multistep deposition approach was applied to increase the polymer layer thickness that helped avoid pore stuffing, nonuniform deposition and polymer overburden. To study polymer protection, low-k films were exposed to F radicals and VUV photons, separately and simultaneously, at temperatures from −45 °C to +10 °C. Effective polymer protection at room temperatures was demonstrated. Lowering the temperature decreases degradation by F radicals while VUV damage, which is temperature independent, became dominant. Low-k damage protection was also significant under simultaneous exposure to F radicals and VUV photons. In the tested temperature range damage under simultaneous exposure to F radicals and VUV photons was higher than the sum of separate F and VUV damage due to a synergistic effect. To decrease the material k-value after etching, the polymer was removed from the pore walls using UV cure. It was shown that almost complete polymer removal was achieved after UV treatment. The described approach was applied to low-k etching in RF CCP CF4, CF4/Ar plasmas and exposure to Ar plasma. Significant improvement of the film k-value after the plasma treatment was confirmed.