Sub-Nanometer Microscopy the Easy Way: An Underutilzed Tool for Reliability Assurance

Scanning electron microscopy (SEM) is a frequently used tool for establishing reliability where potential causes of failure are related to structural aspects that show up on a submicron scale. Conventional SEMs, however, even those equipped with field emission sources, can provide high-quality photomicrographs only up to a magnification of about 100,000×. For many purposes greater resolution (several nanometers or below) is required, in which case the usual alternative is to turn to transmission electron microscopy (TEM), in spite of the laborious sample preparation required and limited plan-view images obtained. We describe here an underutilized alternative to TEM for many applications. The in-lens field emission SEM (ILFESEM) can provide pictures above 500,000× magnification with sub-nanometer resolution, with the simple sample preparation and surface viewing advantages of the SEM. Magnification in this range is necessary to verify modern day tolerances on surface morphology and roughness, oxide and thin film structure, thickness, and step coverage, and pore sizes in adhesion layers or diffusion membranes.