Extracting interface locations in multilayer polymer waveguide films using scanning angle Raman spectroscopy

There is an increasing demand for nondestructive in situ techniques that measure chemical content, total thickness, and interface locations for multilayer polymer films, and scanning angle (SA) Raman spectroscopy in combination with appropriate data models can provide this information. A SA Raman spectroscopy method was developed to measure the chemical composition of multilayer polymer waveguide films and to extract the location of buried interfaces between polymer layers with 7- to 80-nm axial spatial resolution. The SA Raman method acquires Raman spectra as the incident angle of light upon a prism-coupled thin film is scanned. Six multilayer films consisting of poly(methyl methacrylate)/polystyrene or poly(methyl methacrylate)/polystyrene/poly(methyl methacrylate) were prepared with total thicknesses ranging from 330 to 1,260nm. The interface locations were varied by altering the individual layer thicknesses between 140 and 680nm. The Raman amplitude ratio of the 1,605-cm(-1) peak for polystyrene and 812-cm(-1) peak for poly(methyl methacrylate) was used in calculations of the electric field intensity within the polymer layers to model the SA Raman data and extract the total thickness and interface locations. There is an average 8% and 7% difference in the measured thickness between the SA Raman and profilometry measurements for bilayer and trilayer films, respectively.