Transition between kinetic and mass transfer regimes in the initiated chemical vapor deposition from ethylene glycol diacrylate

Abstract

In this work, initiated chemical vapor deposition (iCVD) of the poly(ethylene glycol diacrylate) is reported and the effects of process parameters on the deposition rates are investigated. The systematic studies of depositions performed at different filament temperatures showed that the deposition rates increased with the temperature due to the increase in the radical concentration which was monitored with a gas-phase Fourier transform infrared spectroscopy. For temperatures below 242±3 and 224±2°C for 2 and 1SCCM (SCCM denotes cubic centimeter per minute at STP) of monomer flowrates, respectively, a reaction-kinetics limited regime was observed, where the deposition kinetics was limited by the decomposition of the radicals. In this regime, the deposition rates were highly dependent on the filament temperature and the apparent activation energy was found to be 166±5kJ∕mol, consistent with the cleavage of the O–O bond in the tert-butyl peroxide initiator as the rate limiting reaction in the deposition mechanism. Above these temperatures, transition to a mass transfer limited regime was observed where the deposition rates were less dependent on the filament temperature. In the studies performed at different substrate temperatures, on the other hand, an inverse relation between the deposition rate and the substrate temperature was observed which indicated an adsorption limited regime. The studies presented in this work demonstrate the dependence of the deposition kinetics on the process temperatures, which can also be applied to other iCVD systems to achieve higher deposition rates and better conformality.