Through-focus technique for nano-scale grating pitch and linewidth analysis.

Area of Science:

• Optical Metrology
• Nanotechnology
• Microscopy

Background:

• Accurate measurement of sub-wavelength features is crucial for advanced manufacturing and research.
• Traditional optical methods face limitations in resolving dimensions below the diffraction limit.
• Developing accessible techniques for sub-wavelength metrology remains a significant challenge.

Purpose of the Study:

• To present and validate a through-focus method for sub-wavelength feature dimension measurement.
• To demonstrate the linearization of focus indicator derivatives for pitch determination.
• To show the applicability of the method using standard optical microscopes.

Main Methods:

• Experimental investigation of a novel through-focus technique.
• Linearization of focus indicator partial derivative values.
• Analysis of through-focus curves derived from images at various focal positions.
• Evaluation of responses to sub-resolution changes in grating structures.

Main Results:

• The through-focus method successfully linearizes focus indicator derivatives.
• Pitch determination is achieved using a classical linear method.
• Through-focus curves exhibit sensitivity to sub-resolution grating structure variations.
• The method demonstrates a response to sub-wavelength changes.

Conclusions:

• Sub-wavelength feature dimensions can be reliably evaluated using the proposed through-focus method.
• Regular optical microscopes are sufficient for implementing this advanced metrology technique.
• The method offers a practical approach for high-resolution dimensional analysis.