Motion-free all optical inspection system for nanoscale topology control

We present a novel all optical method for nanoscale pattern inspection. This method uses the chromatic aberration in an imaging optical system and a tunable light source. Such an approach allows stable and precise inspection of nanoscale objects based on an analysis of their defocused diffraction patterns without any external mechanical influence on the sample or optical system. We demonstrate the efficiency of a low cost light source tunable in the range of a light emitting diode bandwidth of ~30 nm (FWHM) for providing the required defocusing. The proposed method is tested using calibrated lines (height 50 nm, length 100 μm, critical dimension (СD) value range 40-150 nm with 10 nm steps) on a monocrystalline silicon substrate with demonstrated measurement accuracy better than 10 nm. A comparison of this all optical method with a mechanical scanning inspection system is discussed.