High-energy scanning electron microscope for the observation of subsurface structures

We propose a technique using high-energy scanning electron microscope (SEM), which has the advantage of measuring 3-D structures and underlayer structures when compared to conventional low-energy SEM, to meet future metrology requirements. At first, we demonstrate that a technique using high-energy SEM has the advantages of measuring gate structures with a spatial resolution of a few nanometers. For example, a notched gate structure was most clearly visible when the beam energy is at 200 keV. Another example of a polyside gate with a sidewall spacer was most clearly visible at 100 keV. In addition, we studied the relationship between the thickness of the upper layer and beam energy at which the structure of the underlayers can be observed. The beam energy should be high enough to pass through the upper layer without the incident beam becoming broader, but low enough for the incident electrons to be backscattered at the structures in the underlayer. We could observe the line structures at a depth of 800 nm or less using an incident beam with energy from 50 to 100 keV. (c) 2005 Society of Photo-Optical Instrumentation Engineers.