Retroreflex ellipsometry for isotropic three-phase systems with nonplanar surfaces

Ellipsometry is a long-established and highly-accurate method for characterizing materials and thin films in the semiconductor, optical coating and biology industry. However, the geometric shape of samples is usually limited to flat samples for conventional ellipsometers because the operation must fulfill the condition of the law of reflection. The retroreflex ellipsometer developed at Fraunhofer IOSB can overcome the shape constraints without realignment of the sample but information on surface inclinations is still necessary. In this work, the polarization model of nonplanar surfaces is analyzed by polarization ray tracing and a numerical inverse method is proposed to calculate the angle of incidence for isotropic three-phase systems with known refractive indices and ellipsometric parameters (Ψ,Δ). The experiments show excellent accuracy for the measurements of the incident and tilt angles and prove that the method is capable of measuring the film thickness of nonplanar surfaces.