Measurement of asymmetric side wall angles by coherent scanning Fourier scatterometry

We propose a measurement technique which enables the precise determination of side wall angles (SWAs) with absolute values below 1°. Our simulations show that a differentiation between asymmetric SWAs is also possible. The grating structure under investigation has a grating period on the order of a few micrometers. Each grating line consists of a fine sub-grating with 40 nm period and 20 nm critical dimension. Our approach is based on coherent high-NA Fourier scatterometry, extended by a lateral scan over the sample. Additionally, a 180°-shearing element allows for coherent superposition of the higher diffraction orders.