Optical characterization of sub-wavelength photonic structures (Invited)

Optical techniques provide highly desirable non-invasive, non-de- structive, fast, and contactless characterization capabilities of use for materials characterization and sensing. Spectroscopic ellipsometry (SE) achieves extreme sensitivity because it is a phase sensitive and self-referenced technique akin to a “single beam interferometry”. The power of SE to provide non-imaging subwavelength scale infor- mation in semiconductor and dielectric 1D gratings is well know in the semiconductor industry where it has been used to determine optical critical dimension (OCD) characterization of purposely made 1D gratings using the Rigorous Coupled-Wave Analysis (RCWA) technique. However, RCWA presents difficulties for the modeling of 2D and plasmonic structures. Our group has provided the first systematic demonstration of a suitable alternative to RCWA for the optical characterization of such complex samples by SE using the Finite-Difference Time-Domain (FDTD) method. This approach provide numerical results with precision equivalent to ~ 1/2-mono- layer thickness sensitivity and provide an alterative computational technique that can extend the application of SE to provide detailed information on complex samples including photonic and plas- monic subwavelength structures of interest for sensing and energy applications. Financial support from the RGC of the HKSAR, China (Project CityU- 122812) is acknowledged.