Etching and structural changes in nitrogen plasma immersion ion implanted polystyrene films

Plasma immersion ion implantation (PIII), with nitrogen ions of energy 20 keV in the fluence range of 5 × 1014–2 × 1016 ions cm−2, is used to modify 100 nm thin films of polystyrene on silicon wafer substrates. Ellipsometry is used to study changes in thickness with etching and changes in optical constants. Two distinctly different etch rates are observed as the polymer structure is modified. FTIR spectroscopy data reveals the structural changes, including changes in aromatic and aliphatic groups and oxidation and carbonisation processes, occurring in the polystyrene film as a function of the ion fluence. The transformation to a dense amorphous carbon-like material was observed to progress through an intermediate structural form containing a high concentration of CC and CO bonds.