The Effect of Deposition Conditions on the Properties of Vapor-Deposited Parylene AF-4 Films

Abstract

One potential low dielectric constant material for ULSI multilevel interconnect applications is parylene AF-4, an organic polymer more formally known as Poly (α, α, α’, α’ - tetrafluoro-p-xylylene). In this study parylene AF-4 films were vapor-deposited on silicon wafers by pyrolytic decomposition of the cyclic dimer, cyclodi(α, α, α’, α’ - tetrafluoro-p-xylylene) using four different deposition conditions. Two different wafer temperatures and two different vaporizer temperatures were used, while the chamber pressure was kept constant. High vaporizer temperature and low wafer temperature give the highest deposition rates. It was found that the surface roughness of films of similar thickness showed a dependence on the deposition conditions. The films deposited at a low vaporizer temperature exhibit a smooth surface (RMS ∼ 4 nm) while those deposited at high vaporizer temperature have a rougher surface (RMS ∼ 16 nm). However, other properties of the films remained very similar. The FTIR spectra and refractive indices, both TE and TM, were measured for the films deposited using the four different deposition processes and showed no dependence on deposition conditions. These results indicate that the change in surface roughness is not due to a large difference in the chemical bonding among the films deposited using the four processes. Also, both weight loss and thickness loss of the films were measured after thermal cycling the films to 450°C and no significant differences were observed. This result indicates that the observed increase in surface roughness with increased vaporizer temperature cannot be related to a change in dimer incorporation in the films. Further experiments are planned to investigate the role of the initiation stage of the polymerization on film surface morphology.