EUV Mask Blank Absorbent Layer UV Reflectance
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Solution Overview
Problem
Current masks for EUV exposure face challenges in achieving sufficient contrast during ultraviolet inspection due to the reflectance characteristics, especially as line and space patterns narrow to the order of the inspection wavelength, leading to decreased inspection performance.
Innovation Solution
A mask blank and mask design featuring a substrate with a reflecting layer and an absorbent layer, where the reflectance of ultraviolet light at 150-300 nm is greater at the absorbent layer than the reflecting layer, enhancing contrast and inspection performance by optimizing the layer structures and materials used.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an antireflection layer with respect to ultraviolet is provided above the absorbent layer, then the contrast at inspection is improved, but the contrast remarkably decreases when the line and space of the pattern get narrow as the same order as the wavelength order of the inspection light
Solution Approach 1:
The patent changes the optical parameters of the mask layers by making the absorbent layer transparent to ultraviolet inspection light while maintaining its EUV absorption function. This parameter change allows the absorbent layer itself to provide high reflectance at UV wavelengths, eliminating the need for a separate antireflection layer and maintaining contrast for narrow patterns.
Solution Approach 2:
The absorbent layer is designed to serve multiple functions: absorbing EUV light for pattern formation during exposure and simultaneously providing high reflectance for UV inspection light. This multi-functionality eliminates the need for a separate antireflection layer and maintains inspection contrast even for narrow patterns.
2Reliability
If the space part of the pattern approaches the wavelength order of the inspection light, then the inspection light is hardly reflected at the space part, but the difference between reflectance values decreases
Solution Approach 1:
The patent changes the optical parameters of the absorbent layer to make it transparent to UV inspection light while maintaining EUV absorption. This allows the absorbent layer to reflect UV light effectively, maintaining contrast even when pattern dimensions approach the UV wavelength.
3Reliability
If a reflecting layer is provided to reflect EUV light, then EUV reflection characteristics are improved, but reflectance at UV wavelengths is low
Solution Approach 1:
The patent applies different optical properties to different layers: the reflecting layer maintains high EUV reflectance while the absorbent layer is designed to be transparent to UV light and provide high UV reflectance. This local differentiation of optical properties allows simultaneous optimization for both EUV exposure and UV inspection.
Solution Approach 2:
The mask uses composite material structure with a reflecting layer (Mo/Si multilayer) for EUV reflection and an absorbent layer (Cr, Ta, W, or Ru) that is transparent to UV. This composite structure achieves both high EUV reflection and high UV reflectance from the absorbent layer.
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 design improves inspection accuracy and performance by maintaining contrast even at small pattern pitches, effectively addressing the limitations of previous masks by ensuring higher reflectance at the absorbent layer and reduced reflectance at the reflecting layer during ultraviolet inspection.
Implementation Method 1
a reflecting layer which is provided on the substrate and reflects EUV light
Implementation Method 2
an absorbent layer which is provided on the reflecting layer and absorbs EUV light
Implementation Method 3
reflectance of light at a wavelength between 150 nm and 300 nm is greater at the absorbent layer than reflectance at the reflecting layer
Data Source
AI summary
Provided are a mask for EUV exposure and a mask blank for EUV exposure for manufacturing the same, so as to improve the contrast of ultraviolet inspection light and improve the inspection performance for the mask. This mask blank for EUV exposure includes a substrate, a reflecting layer which is provided on the substrate and reflects EUV light, and an absorbent layer which is provided on the reflecting layer and absorbs EUV light. Reflectance of light at a wavelength between 150 nm and 300 nm is greater at the absorbent layer than that of the reflecting layer. The mask for EUV exposure can be manufactured by processing this mask blank for EUV exposure.