Initiated chemical vapor deposition of functional polyacrylic thin films

Abstract

Initiated chemical vapor deposition (iCVD) was explored as a novel method for synthesis of functional polyacrylic thin films. The process introduces a peroxide initiator, which can be decomposed at low temperatures (<200⁰C) and initialize addition reaction of monomer species. The use of low temperatures limits the decomposition chemistry to the bond scission of initiator, while retaining functional groups of monomers, which has been confirmed in the infrared spectroscopy, nuclear magnetic resonance, and x-ray photoelectron spectroscopy of iCVD poly(glycidyl methacrylate) (PGMA) thin films. Studies of PGMA iCVD deposition kinetics and molecular weights indicate a free radical polymerization mechanism and provide guide for vapor-phase synthesis of other vinyl monomers. The retained epoxy groups can crosslink under e-beam irradiation, resulting in e-beam patterning of iCVD PGMA thin films with 80 nm negative-tone features achieved. iCVD copolymerization was also investigated to further tune film composition and properties. A surface propagation mechanism was proposed based on the study of the monomer reactivity ratios and the copolymer molecular weights during iCVD copolymerization.

(cont.) The synthesized acrylic copolymers have been investigated in applications as positive-tone e- beam resists, CO₂-developable resists, and low surface energy coatings with improved mechanical properties. The process of iCVD polymerization is extendable to vapor-phase polymerization of other vinyl monomers and creates new opportunities for the application of functional polymer thin films.