SEM characterization of multilayer structures

Abstract

Multilayer stuctures are now widely used in numerous fields of technology, therefore the development of techniques for non-destuctive characterization of these stuctures is of great importance. The thickness of layers in multilayer stuctures can range from 1 nm to some μm, thus in order to measure their parameters it is necessary to develop different techniques with an appropriate spatial resolution. Very promising for these purposes are the methods based on the scanning electron microscopy (SEM) measurements. In principle, the SEM techniques allow one to achieve a high spatial resolution but usually the resolution degrades due to large enough dimensions of the signal 'formation region. Therefore, in order to realize the high spatial resolution, some special methods or image processing procedures should be developed [1-3]. In the case of a non-destuctive characterization of planar multilayer structures the electron beam is directed perpendicular to the stucture plane while the main parameters change as a function of depth. Therefore a third variable for the reconstuction of the parameter distribution should be used. As the third variable an electron beam energy Eb is usually used, which determines the primary electron penetration depth, i.e. a set of images with Eb as a parameter is obtained and the property distribution is reconstructed on the base of such measurements.