OPTICAL INVERSE SCATTERING PHASE RETRIEVAL ALGORITHM FOR SURFACE TOPOGRAPHY MEASUREMENT BY OPTICAL FREQUENCY COMB SCATTERING SPECTROSCOPY

抄録

We have been developing a surface topography measurement system using laser inverse scattering with an optical frequency comb as a light source to measure microtopography of several nanometers to several micrometers in size with high accuracy and over a large area. The laser inverse scattering measures the surface topography by retrieving the phase distribution of the scattering light when a plane wave is incident on the sample surface. However, the dynamic range of this measurement is limited to sub-wavelength order. We propose a method to extend the dynamic range of the laser inverse scattering by using the retrieved phase at several different wavelengths. The method estimates the surface topography from the inversely proportional relationship between the phase and wavelength of light propagating in a fixed optical path. The phase distribution at several different wavelengths can be obtained by using an optical frequency comb as the light source of the laser inverse scattering.

We analyzed the scattering electric field at a sine wave shape surface with a height of 100 to 1000 nm, and simulated the surface topography measurement using the retrieved phase distribution at each wavelength. The simulation results show good agreement with the surface topography of the measurement target, confirming the accurate surface topography measurement and dynamic range extension with the proposed algorithm.