Laser confocal feedback tomography and nano-step height measurement

Area of Science:

• Optical Metrology
• Microscopy
• Nanoscale Measurement

Background:

• Accurate imaging and dimensional measurement of micro-scale devices and biological samples are crucial in various scientific fields.
• Traditional methods face challenges in highly scattered mediums and achieving sub-nanometer resolution.

Purpose of the Study:

• To develop and validate a new method for high-resolution tomography and step height measurement.
• To demonstrate the capability of imaging in highly scattered mediums and achieving precise axial measurements.

Main Methods:

• Integration of a frequency-shifted feedback laser with confocal microscopy.
• Demodulation of feedback-induced intensity modulation signals to extract amplitude and phase information.
• Utilizing amplitude for cross-sectional imaging and both amplitude and phase for axial measurements.

Main Results:

• Successful cross-sectional imaging of micro devices and biological samples in highly scattered mediums.
• Achieved axial high resolution (better than 2 nm) for nano-step height measurement on a glass-substrate grating.
• Demonstrated a non-ambiguous measurement range of approximately ten microns.

Conclusions:

• The proposed method offers a promising approach for advanced tomography and high-resolution step height metrology.
• The technique provides accurate imaging in challenging scattered environments and precise nanoscale dimensional analysis.