Gaussian beam incident on the one-dimensional diffraction gratings with the high-K metal gate stack structures

Area of Science:

• Nanotechnology
• Optical Engineering
• Computational Physics

Background:

• Optical scatterometry is vital for nanolithography pattern analysis due to shrinking device sizes and complex structures.
• Rigorous Coupled-Wave Analysis (RCWA) is standard but has limitations with metallic gratings and TM waves.
• High-k metal gate (HKMG) processes present unique challenges for accurate geometric characterization.

Purpose of the Study:

• To apply the Finite-Difference Time-Domain (FDTD) method with Gaussian beam excitation for analyzing diffraction efficiency in HKMG nanolithography patterns.
• To compare the FDTD method's results with plane wave excitation and identify numerical discrepancies.
• To investigate the impact of various parameters (CDs, SWAs, incident angles, pitches, polarization) on diffraction efficiency and phase.

Main Methods:

• Utilized the FDTD method with a Gaussian beam excitation source for numerical simulations.
• Modeled 1D surface relief gratings representing line/space nanolithography patterns in HKMG stacks (45 nm node).
• Analyzed the 0th order diffraction efficiency and phase as functions of grating parameters and incident wave properties.

Main Results:

• The FDTD method with Gaussian beam excitation provides accurate analysis of diffraction efficiency for HKMG gratings.
• Verified numerical discrepancies between Gaussian beam and plane wave excitation methods.
• Demonstrated the significant impact of incident wave polarization and grating parameters (CDs, SWAs, pitch) on diffraction efficiency.
• Illustrated the effect of SWAs on the phase of the 0th diffraction order.

Conclusions:

• The FDTD method is a viable and effective alternative to RCWA for optical scatterometry of metallic nanostructures.
• Determined the minimum Gaussian beam radius required to achieve convergence with plane wave results.
• Provides insights into optimizing scatterometry techniques for advanced semiconductor process control and metrology.