Electron Reflectometry for Measuring Nanostructures on Opaque Substrates.

Here, we present a method for measuring dimensions of nanostructures using specular reflection of electrons from an electronically opaque surface. Development of this method has been motivated by measurement needs of the semiconductor industry1-4, and it can also be more broadly applicable to any periodic, pseudo-periodic or statistically stationary nanostructures or nanopattern on an opaque substrate. In prior work5,6, it was demonstrated through the presentation of proof of concept experiments and simulated examples that Reflective Small Angle Electron Scattering (RSAES) can meet certain dimensional metrology requirements of the semiconductor industry. In RSAES, an entire reflected scattering pattern is measured, with the scattered electrons being of primary interest. Later, in the process of further simulating RSAES, it was serendipitously discovered that dimensional measurement using reflected electrons might be greatly simplified by Electron Reflectometry (ER), whereby the intensity of the specularly reflected electron beam is measured and the scattered beams ignored.7 This innovation may allow faster and cheaper development and deployment or at the very least provide an alternate pathway to exploit the phenomenon of reflected electrons for dimensional measurement. Here we discuss how ER complements existing dimensional measurement techniques, show simulated applications with an emphasis an defect detection and line-width measurements.