Composite EUV Mask Absorber Layers for Reduced 3D Effects
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Solution Overview
Problem
EUV lithography masks face challenges such as mask 3D effects (M3D) that result in reduced contrast and quality of photoresist profiles, due to shadowing and reflection issues, especially as feature sizes shrink, and defects in absorber layers are costly to repair and may not perform as well as defect-free masks.
Innovation Solution
The use of a patterned absorber layer comprising two different materials with specific EUV refractive indices and extinction coefficients, either in separate layers or as an alloy, to reduce M3D effects and enhance phase shifting, thereby improving image quality and reducing focus shifts and pattern placement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-material absorber layer is used, then the mask structure is simple and manufacturing is easier, but M3D effects increase and image quality deteriorates
Solution Approach 1:
The patent employs composite absorber layers comprising multiple materials (e.g., Mo, Ru, Pd, Pt, Ir) with different optical properties to reduce M3D effects. The composite structure allows optimization of phase shifting and reflection characteristics, thereby improving photoresist profile quality while managing the increased structural complexity through systematic material selection and layer configuration.
2Ease of manufacture
If absorber layer defects are present, then manufacturing costs increase due to repair requirements, but defect-free masks are more expensive to produce
Solution Approach 1:
The patent utilizes specific material parameter combinations (refractive index n and extinction coefficient k) for the absorber layer materials to optimize performance. By selecting materials with particular optical properties and controlling their thickness and arrangement, the patent achieves effective defect repair capability while maintaining high mask performance, balancing manufacturing cost and reliability.
3Productivity
If feature sizes are reduced, then production efficiency increases and costs decrease, but M3D effects become more severe and image quality deteriorates
Solution Approach 1:
The patent implements local quality variations in the absorber layer structure by using different materials with distinct optical properties at different locations or depths. This localized optimization of material properties allows the mask to maintain high image contrast and reduce M3D effects even as feature sizes are reduced for increased production efficiency.
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 absorber layer design effectively minimizes M3D effects, enhances image contrast, and maintains photoresist profile quality, while also addressing defects by providing materials that can repair existing defects, thus improving overall mask performance.
Implementation Method 1
The absorber layer includes a first material and a second material, wherein the first material has an EUV refractive index (n) between 0.855-0.890 and an EUV extinction coefficient (k) between 0.035-0.075 and wherein the second material has an EUV refractive index (n) between 0.920-0.970 and an EUV extinction coefficient (k) between 0-0.035
Implementation Method 2
EUV lithography masks face challenges such as mask 3D effects (M3D) that result in reduced contrast and quality of photoresist profiles, due to shadowing and reflection issues
Data Source
AI summary
An EUV lithography mask including a substrate, a patterned absorber layer including a first material and a second material. In some embodiments, the first material is a second row transition metal and the second material is a first row transition metal or second row transition metal. The disclosed EUV lithography masks reduce undesirable mask 3D effects.