Surface Resistivity Modification of Polyimide Film by Plasma Process

Abstract

Plasma-based ion implantation (PBII) is known an effective technique to modify the material surface among various ion implantation methods. The ballistic-mode PBII was developed to modify the surface resistivity of polymer. Repetitive high-voltage pulses are applied to the grid a few centimeters from a polyimide (PI) film in the ballistic-mode PBII. The high-voltage pulse applied to the grid has the peak values of -20 ~ -30 kV, width of a few µs, rise time of 1.5 µs and fall time of 0.5 or 40 µs. The surface resistivity of PI film was improved by the argon gas ballistic-mode PBII technique for Electrostatic Dissipation (ESD) application. The surface resistivity of PI film was changed from 1016 Ω/square to ESD range of 106 ~ 109 Ω/square by the ballistic-mode PBII. The PI film treated by the ballistic-mode PBII maintains the surface resistivity of ESD range after many days, acetone test and at the high temperature of 200 ̊C. Many ion dose and high ion energy show a good performance to modify the material surface. In this process, the efficiency of surface resistivity modification depends on the fall time of the pulse applied to the grid immersed in plasma.In-line process system was developed based on experimental results performed in the prototype system of the ballistic-mode PBII. The plasma was produced by the 13.56 MHz RF discharge in the vacuum chamber with Ar gas pressure of 10-3 ~ 10-4 Torr. Electron density measured by cutoff probe was in the order of 109 cm-3. The surface resistivity of ~108 Ω/square was achieved in the continuous process for the ESD PI film rolls having 514 mm width and 300 m length. The properties of the PI film untreated and treated by a ballistic-mode PBII were nearly same except the surface roughness.