Evaluating a Multilayer Polymer Film by Raman Microscopy

Abstract

Multilayer polymer films are engineered to accommodate a variety of requirements where polymer layers are fused together, with each polymer selected for a specific purpose. Specific analysis approaches can troubleshoot a defective film or allow us to reverse-engineer a film of unknown composition. Since the inception of Raman microscopy in the mid-1970s, it has been argued that a well designed confocal Raman microscope can analyze the composition of a multilayer film non-destructively. This is a powerful capability because it has the potential to provide information with optical resolution (better than 1 μm) below sample surfaces non-destructively. However, because standard microscope optics do not maintain focus inside of a material with a finite index of refraction, and the errors become greater with increasing numerical aperture and increasing depth, we wanted to determine the quality of the information achieved by comparing a depth profile with a two dimensional map of a cross-section. In this article, we show a cross-sectional map of a film compared to a depth profile to evaluate the quality of depth profile measurements.