Comparison of Electron Imaging Modes for Dimensional Measurements in the Scanning Electron Microscope

Area of Science:

• Materials Science
• Electron Microscopy
• Metrology

Background:

• Accurate dimensional measurements are crucial in electron microscopy.
• Secondary electron (SE), backscattered electron (BSE), and low-loss electron (LLE) imaging techniques are commonly used.
• Discrepancies in measurements between SE and BSE/LLE images have been reported.

Purpose of the Study:

• To investigate the reasons for dimensional measurement differences between SE, BSE, and LLE images.
• To explain nanometer-scale discrepancies observed in simultaneous SE, BSE, and LLE imaging.
• To reconcile larger discrepancies reported in previous studies.

Main Methods:

• Comparison of dimensional measurements from SE, BSE, and LLE images using a 50% threshold criterion.
• Simulations using JMONSEL electron microscope simulator.
• Modeling of convolution effects and sidewall angle influences.

Main Results:

• Lines consistently appeared larger in SE images compared to BSE and LLE images.
• Nanometer-scale differences were explained by the convolution effects of a finite beam size on signals with different symmetry.
• Larger discrepancies (>100 nm) in previous studies were attributed to larger sidewall angles and differential signal responses.

Conclusions:

• The observed dimensional differences in electron microscopy are influenced by the interplay between signal symmetry and beam convolution.
• SE imaging inherently leads to larger measurements due to its signal characteristics.
• Sidewall angles significantly impact measurement discrepancies, especially in conjunction with differing SE and BSE/LLE responses.