Critical-dimension scanning electron microscope characterization of smoothly varying wave structures with a Monte Carlo simulation

Scanning electron microscopy (SEM) characterization of a smoothly varying nanograting structure (a Pt-coated Cr grid on a Si substrate) with a sinusoidal waveform has been carried out by a Monte Carlo (MC) simulation technique. Previous studies with critical-dimension (CD) SEM (CD-SEM) have mostly concerned line structures with sharp edges so that there is an obvious edge bloom in the linescan profile of secondary electrons. In contrast, the present grating structures prepared by a laser-focused atomic deposition technique have a smoothly varying waveform in the cross-sectional profile, which pose greater difficulty for quantitative structural characterization by SEM. The grating structure, with a fixed pitch of lambda/2 as the period of the standing-wave laser light field, where lambda is the wavelength of the corresponding laser light, can be used as an ideal nanoscale metrological length tool; therefore, it is important to characterize its structural features over a large deposited area by SEM imaging for quality control, with the aim of mass reproduction. The present work extends the CD characterization of MC simulation methods to more complex structures. Taking into account different experimental factors, i.e. primary electron beam parameters, geometrical parameters and material properties, the unknown geometrical parameters (i.e. base height, peak height, linewidth shrinkage and peak tilt angle) of the grating lines have been successfully extracted from the experimental linescan profiles of SEM images.