Tunable Conformality of Polymer Coatings on High Aspect Ratio Features

In this work we demonstrate that the concentration of vinyl bonds present in monomers adsorbed onto the surface determines the degree of conformality achieved by polymeric films grown over substrate topology by initiated (i)CVD. For microtrenches of varying aspect ratio, a ballistic model correlates the observed step coverage to a range of sticking coefficients of the initiating radicals, gamma, between 0.01 and 0.05. Increasing the surface concentration of the monomer results in higher values of gamma. In the deposition regime studied, gamma is independent of the concentration of radical initiators. Furthermore, gamma is insensitive to substrate temperature if the surface concentration of monomer is fixed. Using this knowledge, conformal coverage on microtrenches is demonstrated from both ethylene glycol diacrylate (EGDA) and neopentyl methacrylate (npMA). Additionally, the conformality permits templating of nanotubes of the mechanically robust and solvent-resistant iCVD-produced p(EGDA) crosslinked polymer.