Use of a Thermally Degradable Chemical Vapor Deposited Polymer Film for Low Damage Plasma Processing of Highly Porous Dielectrics

Nanoporous materials show a large surface area and co-continuous topology, leading to a high sensitivity to chemically active components over macroscopic length scales. The processing of nanoporous systems can be complex, causing modifications of the original material, or appearance of unwanted contaminants. The present work reports on a protection method based on temporary filling by a sacrificial template polymer, forming in situ a reversible urea linkage. Microporous organo-silicate low-k dielectric thin films are used as demonstrators, exposed to aggressive plasma discharges. Depending on the studied material, the fraction of filled pore volume varies between 29% and 66%, with a homogeneous spatial distribution. The filling component is formed by a blend of urea-linked polymer and isocyanate-terminated monomers, is stable during plasma processing, and can be fully removed by annealing above 300 °C. This sacrificial filler protects the internal structure of the porous dielectric from the plasma, reducing chemical damage and leading to better electrical characteristics.