Incorporating mask topography edge diffraction in photolithography simulations

Area of Science:

• Semiconductor manufacturing
• Optical lithography
• Computational physics

Background:

• Conventional deep ultraviolet (DUV) lithography simulations use Kirchhoff's boundary conditions, leading to a "thin-mask" approximation.
• This thin-mask approximation is insufficient for subwavelength lithography, as it neglects crucial topographical or "thick-mask" effects.

Purpose of the Study:

• To develop a novel simulation model for DUV lithography that accurately incorporates thick-mask effects.
• To improve the precision of aerial image simulations in photolithography.

Main Methods:

• The new model is theoretically grounded in the physical theory of diffraction.
• Diffraction effects are modeled as an intrinsic edge property using two parameters: boundary layer width and transmission coefficient.
• A locally determined boundary layer is applied to each chrome edge.

Main Results:

• The proposed model accurately captures the impact of thick-mask topography on optical fields.
• It significantly enhances the accuracy of aerial image simulations compared to conventional methods.
• The model achieves improved accuracy while maintaining manageable computational costs.

Conclusions:

• The new diffraction-based model offers a more accurate representation of mask topography in lithography simulations.
• This advancement is crucial for precise aerial image prediction in advanced photolithography processes.
• The model provides a computationally efficient solution for accounting for thick-mask effects.