EUV Reflective Mask Blank Phase Optimization
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Solution Overview
Problem
Existing reflective masks for EUV lithography face challenges in achieving high dimension accuracy for fine line-like patterns due to shadowing effects and limitations in optimizing reflectance and phase difference based on exposure conditions and pattern complexity.
Innovation Solution
A reflective mask blank with a multi-layer reflection film and an absorption layer, where the absorption layer has a refractive index of 0.930 or less and an extinction coefficient of 0.025 or more, and a phase difference of 220 to 280°, is used to enhance the reflectance and phase shift properties, thereby improving the accuracy of fine line-like patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the thickness of the absorption layer is increased to improve phase shift effect, then the phase difference increases, but dimension error due to shadowing increases
Solution Approach 1:
The patent changes the optical parameters (refractive index and extinction coefficient) of the absorption layer material to achieve the desired phase difference while maintaining thin thickness. By selecting materials with specific optical properties, the phase shift effect is enhanced without increasing thickness, thereby avoiding shadowing effects.
Solution Approach 2:
The patent uses composite material structures combining the multi-layer reflection film with the absorption layer having specific optical properties. This composite structure achieves both high reflectance and appropriate phase difference while keeping the absorption layer thin to minimize shadowing.
2Object-affected harmful factors
If the absorption layer thickness is decreased to suppress shadowing, then shadowing effect is reduced, but phase difference decreases
Solution Approach 1:
The patent compensates for reduced thickness by carefully selecting materials with optimized refractive index and extinction coefficient values. This allows the thin absorption layer to still produce the necessary phase difference for high dimension accuracy while maintaining thinness to suppress shadowing.
3Manufacturing precision
If the phase difference is optimized for 180° or 216° based on conventional designs, then transmissive mask performance is improved, but reflective mask performance for oblique incidence is insufficient
Solution Approach 1:
The patent adjusts the target phase difference parameter from conventional 180° or 216° to approximately 252° specifically for oblique incidence conditions in reflective masks. This parameter change optimizes the interference pattern for the specific application, achieving high transfer accuracy for reflective EUV lithography.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed solution enables the formation of transfer patterns with high dimension accuracy for fine line-like patterns, effectively addressing the limitations of existing technologies by optimizing the reflectance and phase difference within the absorption layer.
Implementation Method 1
an absorption layer that absorbs EUV light
Implementation Method 2
reflect light such that it differs in phase from reflected light from a multi-layer reflection film
Implementation Method 3
a multi-layer reflection film that reflects EUV light
Implementation Method 4
a substance or shape different in refractive index and transmittance from the transmission portion is added to change the phase of the transmitted light
Data Source
AI summary
A reflective mask blank 10 for EUV lithography in which a multi-layer reflection film 2 that reflects EUV light and an absorption layer 3 that absorbs EUV light are laminated on a substrate 1 in the stated order from the substrate 1 side, wherein the absorption layer 3 has a refractive index of 0.930 or less and an extinction coefficient of 0.025 or more for EUV light having a wavelength of 13.5 nm, and a phase difference between reflected light from a surface of the multi-layer reflection film and reflected light from a surface of the absorption layer with respect to an incident ray of the EUV light having a wavelength of 13.5 nm is 220 to 280°, and a reflective mask in which a mask pattern is formed on the absorption layer 3.