Model-assisted measuring method for periodical sub-wavelength nanostructures.

Area of Science:

• Optical metrology
• Nanotechnology
• Materials science

Background:

• Current methods for grating characterization involve complex in situ measurements.
• Sub-wavelength sinusoidal gratings are crucial in roll-to-roll manufactured transparent foils.
• Accurate and efficient characterization is needed for in-line process control.

Purpose of the Study:

• To investigate a scatterometry approach for in-line characterization of sub-wavelength gratings.
• To determine the feasibility of using single measurements of diffraction maxima for grating height determination.
• To optimize measurement parameters and evaluate uncertainties for roll-to-roll production.

Main Methods:

• Light scattering simulations were used to establish the relationship between diffraction maxima power and grating height.
• The inverse problem was solved to extract dimensional information from scattered light.
• Simulations identified optimal setup parameters for grating heights between 100 nm and 300 nm.

Main Results:

• A single measurement of first diffraction maxima can accurately determine sub-wavelength grating height.
• Measurement uncertainty is dominated by systematic contributions, estimated at ≤12 nm, with potential for <4 nm.
• The method demonstrated sensitivity to local surface variations, verified by atomic force microscopy.

Conclusions:

• The developed scatterometry approach enables accurate, in-line characterization of sub-wavelength gratings in roll-to-roll processes.
• High sampling rates (MHz range) are feasible, meeting production requirements.
• This technique offers a significant improvement over existing methods for grating metrology.