3-D Materials Characterization Using Structured Illumination in the SEM

Microscopic measurement of surface topography is a continuing need in microfabrication technology and materials research. The aim of this research is to adapt the scanning electron microscope (SEM) to the quantitative measurement of a wide range of surface structures. The SEM is a widely used measurement tool in materials science and semiconductor fabrication. The SEM's strength is that it provides high resolution images which often have a three dimensional appearance. Its weakness is that highly precise three dimensional measurements are difficult or impossible even with stereo techniques. In addition the accuracy of two dimensional measurement is degraded by the reliance of intensity profiles to determine the location of edges.

The proposed research will examine the feasibility of using structured illumination to generate SEM images that provide purely topographical information while maintaining the conditions useful for normal viewing as well. In this technique the SEM projects a known pattern on the specimen. The beam either etches the surface or promotes a deposition process. The patterned surface is viewed in the SEM from a different angle of incidence. The detected pattern is a direct measure of the topography of the specimen surface. The accuracy of the measurement depends only on the quality of the generated pattern and the SEM image. As long as the pattern is detectable, accuracy is independent of composition and the multitude of contrast mechanisms in the SEM. In addition, the proposed device would be cost effective and provide easily interpretable data that would make it suitable for widespread use.