SEM linewidth measurements of anisotropically etched silicon structures smaller than 0.1 µm

Abstract

Scanning electron microscopy (SEM) is a standard method for linewidth (CD) metrology. For structure sizes smaller than 0.1 µm the information volume of the scanning electron probe is of the same order of magnitude as the structure size and the resulting SEM signal profile is a superposition of structural information from the whole structure. Evaluation of top and bottom linewidths needs to take into account the electron diffusion in the solid state. SEM linewidth measurements at anisotropically etched silicon structures with an exact edge slope angle of 54.7° and a top linewidth smaller than 0.1 µm were performed by a low-voltage SEM metrology system. Different algorithms were applied for linewidth evaluation which were especially adapted for measurements at small structures. The results of SEM linewidth evaluation were compared among each other and to AFM measurements performed by a large-range scanning probe microscope.