Using scattered-light modeling for semiconductor critical dimension metrology and calibration

Quantitative methods are developed to use optical scatter to measure the critical dimensions of gratings etched into bulk Si and developed photoresist patterns on silicon substrates. Previous work either classified microstructures qualitatively or employed a 'chi-by-eye' method to find that structures were similar or dissimilar. A single detector scanning scatterometer is used to measure large 32 micrometers pitch structures while another instrument that varies the angle of incidence and tracks diffracted orders via the grating equation is used to measure 2 micrometers pitch structures. A rigorous coupled wave light scatter model is used to simulate diffraction from a set of test wafers. Partial least squares and neural network analysis techniques are then employed to use correlations between the simulated diffraction and the critical dimensions of the modeled structures to produce a capability to measure the critical dimensions from scattered light measurements. The marriage of rigorous coupled wave diffraction modeling and optical scatterometry directly addresses the needs of the industry for a rapid and nondestructive metrology tool.