Optical scatterometry with relaxed model constraints

Area of Science:

• Nanotechnology
• Optical Metrology
• Computational Physics

Background:

• Optical scatterometry is crucial for nanostructure characterization.
• Current methods rely on strict models that may oversimplify details.
• Solving optical inverse problems (OIPs) often requires extensive prior information.

Purpose of the Study:

• To develop a novel optical scatterometry strategy with relaxed model constraints.
• To enhance the accuracy and efficiency of nanostructure property extraction.
• To address the limitations of oversimplified structural models in OIPs.

Main Methods:

• Integration of automatic differentiation for inverse design-inspired optimization (IDO-OS).
• Implementation of relaxed model constraints to expand the solution space.
• Combination with hybrid metrology and thin plate splines for experimental validation.

Main Results:

• Achieved an optimized spectral goodness-of-fit of 0.99 in numerical simulations.
• Demonstrated high consistency between reconstructed and target nanostructures.
• Experimental results showed excellent agreement with transmission electron microscopy measurements.

Conclusions:

• The proposed IDO-OS strategy offers a new approach to solving OIPs in optical scatterometry.
• Relaxed model constraints lead to enhanced structural reconstruction capabilities.
• The method maintains computational efficiency while improving accuracy.