Improved deep-etched multilayer grating reconstruction by considering etching anisotropy and abnormal errors in optical scatterometry

Accurate, fast, and nondestructive reconstruction of the etched nanostructures is important for etching process control to achieve good fidelity, as well as high manufacturing yield. In this work, we have demonstrated the improved deep-etched multilayer grating reconstruction by simultaneously considering the model error of nonuniform side-wall angle (SWA) because of different etching anisotropies of various materials and by suppressing the abnormally distributed measurement errors using a robust statistics based method in optical scatterometry. More specifically, we introduce an additional parameter to perfect the profile model under measurement, and use a robust estimation procedure at the end of each iteration of the Gauss-Newton (GN) method to obtain the more accurate parameter departure vector. By applying the proposed methods, more accurate reconstructed results can be achieved.