Refined extreme ultraviolet mask stack model.

Area of Science:

• Materials Science
• Optical Engineering
• Semiconductor Manufacturing

Background:

• Accurate modeling of extreme ultraviolet (EUV) mask stacks is crucial for advanced photo-lithography.
• Existing models may not fully capture the complex optical properties of multilayer and absorber layers.
• High-numerical aperture (high-NA) EUV lithography (EUVL) demands precise simulation tools.

Purpose of the Study:

• To develop a refined model of an EUV mask stack for accurate performance simulations in high-NA EUVL.
• To improve the description of optical constants and layer interfaces within the mask stack.
• To create both high-resolution and computationally efficient low-resolution models for simulation.

Main Methods:

• Combined analysis of measured EUV and X-ray reflectivity of a mask blank.
• Utilized a "free-form analysis" procedure to determine optical constant depth profiles and layer interface shapes experimentally.
• Developed a high-resolution model (sublayers as thin as 0.25 nm) and derived a low-resolution model (sublayers > 2 nm) for simulation efficiency.

Main Results:

• The refined model provides a more accurate description of reflectivity compared to models based solely on EUV reflectivity.
• The free-form analysis yielded high-resolution optical constant depth profiles.
• A low-resolution model was successfully derived from the high-resolution model for reduced simulation effort.

Conclusions:

• The developed EUV mask model accurately represents industry-standard mask blanks.
• The model facilitates more reliable performance simulations for high-NA EUVL.
• This work advances the accuracy and efficiency of EUV lithography modeling.