Depth Profiling in Thin Films via Waveguide Spectroscopy

218 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.A novel optical depth profiling technique is developed to depth profile thin optically transparent films which can be fabricated in the form of an asymmetric slab optical waveguide. Various methods for depth profiling thin dielectric films are also reviewed in a manner which illustrates the utility and limitations of depth profiling. The general theory of wave-guiding is also reviewed and then extended to develop the theory of depth profiling in homogeneous waveguides. Depth profiling is achieved by observing Raman spectroscopic signals due to the dopant from different waveguide modes. These signals contain information on the dopant distribution because the excitation spatial distribution is different from each mode.Two general approaches are considered. In the simpler approach the functional form of the dopant distribution is assumed a priori. The interface position of composite polystyrene and poly-4-vinylpyridine films (total thickness approx. 2.5$\mu$m) were determined typically within 50nm of the physically measured position. A second approach involved depth profiling without explicit functional form assumptions of the dopant distribution. Calculations indicated that this approach, with singly excited modes, is feasible only if the dopant is restricted to a fractional region of the total film thickness. A profile generated by diffusion of deuterated polystyrene-d$\sb8$ into normal polystyrene was measured with approximately.2$\mu$m resolution. Although the distribution obtained is in general agreement with expectations, subtle discrepancies were present. These were attributed to excessive error in the data due to weak Raman intensities observed for the lower order modes of the sample.Further calculations predict that depth profiling the entire film thickness region is possible if quantitative mode mixing can be achieved experimentally. Resolution of approximately.12$\mu$m is predicted for a 2.5$\mu$m polystyrene film.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD