Localized Etching of a Polyimide Film by an Atmospheric-Pressure Radio Frequency Microplasma Excited by a 100-μm-$\phi$ Metal Pipe Electrode

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Atmospheric-pressure He and Ar microplasmas (μ-plasmas) have been generated by a 14 MHz radio-frequency (RF) discharge using a metal narrow pipe electrode with an outer diameter of 100 μm. The metal pipe acts as both a powered electrode and a gas nozzle. The discharge mode changed from a corona discharge to a glow discharge and finally to a thermal spot arc discharge with decreasing discharge gap between the pipe electrode and the grounded plate as well as with increasing RF power. The Ar glow μ-plasma was applied to the localized etching of a polyimide film with a thickness of 0.025 mm in air ambient. The etched spot showed an isotropic profile having a gradual slope with a full width at half maximum of approximately 170 μm. The etching rate was approximately 3 μm/s at an RF power of 1.5 W. The optical emission spectrum exhibited second-positive N2 molecular bands and atomic oxygen lines (777 and 845 nm) as well as many Ar atomic lines. It appears that the energetic N2 molecules and UV photons radiated from the excitation states of N2 broke C–C and C–H bonds and then O radicals reacted with the hydrocarbon fragments to produce CO2 and H2O. Consequently, isotropic chemical etching was achieved.
2010-08-25