Quantitative Analysis of Laser Interferometer Waveforms Obtained during Oxygen Reactive-Ion Etching of Thin Polymer Films

摘要

Continuous laser interferometry, especially of inorganic materials, during reactive ion etching often has been used as an end-point detection method. However, the detailed patterns obtained during etching of thin organic polymer films have not been fully exploited. The sinusoidal oscillations in reflected light intensity often exhibit almost uniform amplitudes. In addition to variations in the rate of etching with time or depth, a rigorous analysis of the waveform yields an in situ measure of the refractive index of the film. A reduction factor for the medium/polymer interface Fresnel coefficient is used to account for the diffuseness arising from 'roughening' of the film. Ion bombardment causes the roughening and necessitates the correction which is not usually the case when interferometry is used in solvent dissolution studies. The analysis, an iterative procedure for its use, and the application to oxygen/RIE of several polymers will be described. Keywords: Plasma, Resist, Microlithography. (aw)