Evolution of Roughness and Wavelength Selection during Fluorocarbon Plasma Etching of Nanoporous Silica

Nanoporous silica is a technologically appealing candidate as a low-k dielectric material for high speed nano device applications. A crucial issue during plasma pattern transferring processes is the stability of the plasma/NPS interface. Induced surface/interface roughness may ultimately limit the minimum feature sizes attainable in devices using this material. Our results show a monotonic increase with porosity in the roughening rate, and pronounced disagreement with the predictions of simple models based upon self-affine behavior. In addition we find direct evidence for spontaneous pattern formation during etching.