Computational Adaptive Optics for HAR Hybrid Trench Array Topography Measurement by Utilizing Coherence Scanning...

Area of Science:

• Optical Metrology
• Nanotechnology
• Computational Imaging

Background:

• Coherence scanning interferometry (CSI) struggles with aberrations from high aspect ratio (HAR) samples, hindering accurate topography measurement of microstructures.
• Existing aberration correction methods using deformable mirrors are insufficient for shift-variant aberrations in hybrid trench arrays with varying parameters.

Purpose of the Study:

• To develop a novel computational aberration correction method for precise topography measurement of HAR structures using CSI.
• To address the limitations of previous methods in compensating for shift-variant aberrations in complex hybrid trench arrays.

Main Methods:

• A computational aberration correction method employing the particle swarm optimization (PSO) algorithm is proposed, eliminating the need for databases or prior knowledge.
• A spatial frequency domain phase filter is constructed to restore interference signals distorted by shift-variant aberrations.
• A multi-channel aberration correction scheme using virtual phase filters, based on isoplanatic region segmentation, is established for hybrid trench array samples.

Main Results:

• The PSO algorithm successfully derives optimal Zernike polynomial coefficients for the phase filter, using interference fringe contrast as the optimization criterion.
• A window function derived from the 3D transfer function (3D-TF) bandwidth is used to preprocess interferograms, filtering out extraneous signals.
• Experimental validation on single and hybrid trench samples (depths 100-300 μm, widths 10-30 μm) confirms the method's effectiveness and accuracy.

Conclusions:

• The proposed computational aberration correction method accurately measures HAR structure topography, even in challenging hybrid trench arrays.
• The isoplanatic region segmentation and PSO-based virtual phase filtering offer a robust solution for shift-variant aberration compensation in CSI.