Spectroscopic imaging ellipsometry for two-dimensional thin film thickness measurement using a digital light processing projector

An improved version of spectroscopic imaging ellipsometry is described for accurate reconstruction of two-dimensional thin film thickness. A digital light processing projector enables a selected area of the back focal plane of the objective lens to be illuminated so that the angle of incidence and the polarization state of the light source vary depending on the area of the back focal plane being illuminated. By combining multiple images of the object plane obtained at different polarization states, every pixel in the field of view has its own ellipsometric parameters; therefore a reconstruction of two-dimensional thin film thickness is possible. Because the proposed ellipsometry system has a co-axial optical structure in which the objective lens is arranged in the normal direction to the measurement target, the spatial resolution is improved due to the application of a high-magnitude objective lens. In addition, spectroscopic analysis can be conducted using a number of band-pass filters which each have a central wavelength. The effect of the proposed method on thin film thickness measurement was evaluated by comparing the experimental results with a topographic profile obtained using a commercial atomic force microscope.