Influence Of Structure On The Dielectric Properties Of PECVD Polymer Films
Polymer dielectric films fabricated by plasma enhanced chemical vapor deposition (PECVD) have inherent superiority due to their smooth surface, pin-hole free morphology, and dense crosslinked bulk structure. These spatially uniform films also exhibit good adhesion to a variety of substrates, excellent chemical inertness, high thermal resistance, and are formed from a rapid, inexpensive, solvent-free, room temperature process. In this work, we describe PECVD polymer dielectric films prepared from three precursors including benzene, octafluorocyclobutane (OFCB) and hexamethyldisiloxane (HMDS) using two different feed locations including in the plasma zone center and in the downstream region. The chemical structure of the PECVD films was determined by XPS, FTIR and ESR. The dielectric constant and dissipation of the films were studied over a range of frequencies up to 1 MHz, and the dielectric strength was characterized by the current-voltage method. Spectroscopic ellipsometry was performed to determine the thickness and refractive index of the resultant films. The PP-benzene films showed strong aromatic characteristics, PP-OFCB films maintained a high F/C ratio with a variety of fluorine moieties, and PP-HMDS retained a large fraction of Si-O bonds. All the PECVD films showed higher dielectric constants than those of corresponding conventional polymers. There is a small sharp drop in dielectric constant at low frequencies for all the PECVD films, attributed to the orientational polarization caused by trapped free radicals, oxygenated groups (C=O), and unsaturated moieties. The largest drop occurred for the PP-HMDS films. All films exhibit a continuous increase in dielectric loss as a function of frequency. Among all the PECVD films, the PP-benzene exhibited high breakdown strength. These variations in the dielectric properties are closely associated with the unique structure features of PECVD films.