Lateral movement and angular illuminating non-uniformity corrected TSOM image using Fourier transform.

Area of Science:

• Optical Metrology
• Nanoscale Measurement
• Semiconductor Inspection

Background:

• Through-focus scanning optical microscopy (TSOM) is a cost-effective, non-destructive technique for nanoscale semiconductor metrology.
• Instability from target movement and illumination non-uniformity limits TSOM's precision and applications.
• Current TSOM methods require extensive optical alignment and post-acquisition image correction.

Purpose of the Study:

• To introduce an improved TSOM method utilizing Fourier transforms for enhanced accuracy.
• To address and correct image instability issues inherent in traditional TSOM.
• To improve the precision and repeatability of nanoscale measurements using TSOM.

Main Methods:

• Collected a series of experimental through-focus (TF) images by scanning the optical microscopy objective.
• Generated ideally simulated TF images using a full-vector formulation.
• Aligned experimental images to simulated counterparts before constructing the corrected TSOM image via Fourier transform.

Main Results:

• The improved TSOM method effectively corrects for lateral target movement and illumination non-uniformity.
• Demonstrated significant improvements in measurement precision and repeatability compared to standard TSOM.
• Validated the method's capability to enhance TSOM performance for nanoscale targets.

Conclusions:

• The presented Fourier transform-based TSOM correction method significantly enhances measurement accuracy.
• This improved technique holds promise for reliable online and in-machine nanoscale measurements in semiconductor manufacturing.
• Further development could expand TSOM's applicability in demanding industrial metrology settings.