Evaluation of the Disadvantage of Radio Frequency Plasma Treatment on Polymer using Equivalent Circuit Model of Capacitor

Abstract

The surface modification by plasma treatment is recently preferred to improve adhesion of metal on polymer. However, it may degrade the electrical or dielectric properties. To verify the drawbacks of surface modification, we compared biphenyldianhydride phenylenediamine (BPDA-PDA) polyimide after radio frequency (RF) Ar plasma treatments with as-baked polyimide. The confirmation of degrading the electrical properties of which surface is modified was attempted by means of equivalent circuit model of capacitor. Judging from that theory, we hypothesized that the electrical degradation can be easily checked out only by measuring resonance frequency. Capacitor before RF Ar plasma treatments showed the resonance frequency of 40.5 MHz (estimated). RF Ar plasma treatments for improving adhesion of metal on polyimide, however, lowered resonance frequency of polyimide to 34–35 MHz. From X-ray photoelectron spectroscopy (XPS) analysis, we certified that the degradation of electrical properties is derived out from the accumulated carbon atoms on the destroyed surface of polyimide layer. We deduced that although plasma treatments definitely did not affect the bulk dielectric constant of polyimide, it degraded the electrical properties of polyimide by lowering resonance frequency. Consequently, just measuring resonance frequency of capacitor can estimate the degradation of the electrical properties.