Minimization of plasma ashing damage to OSG low-k dielectrics

This paper investigated the plasma ashing damage to patterned porous low k structures with the objective to minimize the plasma damage by optimizing the low-k structural geometry and plasma chemistry. We first extended the plasma altered layer model to formulate the transport kinetics of the plasma process in patterned low-k structures. This enabled us to analyze the effects of the hardmask thickness, trench width and trench length on the plasma interaction with the trench sidewall. Then CO/O₂ and CO₂/N₂ plasmas were used to replace O₂ plasma for ashing process to examine their potential for reducing plasma ashing damage to porous low k patterned structures. With increasing CO in CO/O₂ plasma, the extent of plasma induced damages was found to decrease. Similarly, with increasing N₂ in CO₂/N₂ plasma, the plasma induced damages were also found to decrease. On the basis of the Knudsen diffusivity difference among C, N, and O, the reduction of plasma induced damage was ascribed to the formation of C- and N- rich passivation layer on the sidewall and pore surface of the patterned low-k structure.