High density plasma etching of low k dielectric polymers in oxygen-based chemistries

We have studied the etching of low dielectric constant polymers in halogen- and sulfur-free chemistries under various plasma operating conditions. The polymer graphitization phenomenon, which corresponds to the transformation of the aromatic hydrocarbon network into an amorphous carbon backbone, has been fully investigated under several plasma conditions by in situ mass sp ectrometry and quasi-in situ x-ray photoelectron spectroscopy (XPS). Profil e control in high aspect ratio contact holes is obtained thanks to the form ation of a passivation layer on the polymer sidewalls preventing the sponta neous chemical attacks by the oxygen reactive species of the plasma. XPS st udies show that the passivation layer only forms under conditions where the plasma induces a polymer graphitization. Strong correlations are observed between plasma conditions leading to the polymer graphitization, the presen ce of heavy carbon byproducts detected in the plasma gas phase, and the pas sivation layer formation. (C) 2001 American Vacuum Society.