Reflective Mask Blank Absorber Stack for Low Stress and Roughness
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Solution Overview
Problem
Conventional reflective mask blanks for EUV lithography suffer from film stress and surface roughness issues, which affect pattern transfer accuracy and defect inspection sensitivity.
Innovation Solution
A reflective mask blank with an absorber film composed of multiple layers of tantalum (Ta) and nitrogen (N), including low and high nitrogen content layers, to achieve low film stress and surface roughness, enhancing pattern transfer performance and defect inspection sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer absorber film is used, then the manufacturing process is simple, but the film stress is large causing substrate deformation
Solution Approach 1:
The absorber film is divided into multiple layers with different nitrogen contents (low nitrogen content layer and high nitrogen content layer). This segmentation allows each layer to contribute differently to stress management, reducing overall film stress and preventing substrate deformation while maintaining manufacturing feasibility.
2Device complexity
If a single-layer absorber film is used, then the manufacturing process is simple, but the surface roughness is high reducing defect detection sensitivity
Solution Approach 1:
The absorber film is segmented into multiple layers with different nitrogen contents. The high nitrogen content layer specifically contributes to reducing surface roughness, thereby improving defect detection sensitivity, while the low nitrogen content layer maintains appropriate stress characteristics.
Solution Approach 2:
Different layers of the absorber film are assigned different nitrogen contents to achieve different local properties. The high nitrogen content layer provides smooth surface quality for defect detection, while the low nitrogen content layer manages stress, creating optimal local characteristics in each layer.
3Measurement precision
If high nitrogen content is used in absorber film, then surface roughness is reduced, but film stress increases causing substrate deformation
Solution Approach 1:
The absorber film is divided into layers with different nitrogen contents. The high nitrogen content layer reduces surface roughness, while the low nitrogen content layer compensates for stress, allowing each layer to optimize its function without compromising the other.
Solution Approach 2:
Different nitrogen content levels are assigned to different layers based on their specific functions. The high nitrogen content layer locally optimizes surface smoothness, while the low nitrogen content layer locally manages stress, achieving overall balance.
4Manufacturing precision
If low nitrogen content is used in absorber film, then film stress is reduced, but surface roughness increases reducing defect detection sensitivity
Solution Approach 1:
The absorber film is segmented into layers with different nitrogen contents. The low nitrogen content layer manages film stress to prevent substrate deformation, while the high nitrogen content layer ensures smooth surface for defect detection.
Solution Approach 2:
Different nitrogen content levels are assigned to different layers based on their specific functions. The low nitrogen content layer locally optimizes stress characteristics, while the high nitrogen content layer locally optimizes surface smoothness, achieving overall balance.
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 film with a specific nitrogen content distribution reduces substrate deformation and improves sensitivity in pattern defect inspection, ensuring high accuracy in pattern transfer.
Implementation Method 1
a multilayer reflection film that reflects EUV light is formed on one of the two main surfaces of the substrate
Implementation Method 2
an absorber film that absorbs EUV light and is formed thereon
Data Source
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AI summary
A reflective mask blank including a substrate, a multilayer reflection film that is formed on the substrate and reflects exposure light, a protection film that is formed on the multilayer reflection film, and an absorber film that is formed in contact with the protection film and absorbs the exposure light is provided. The reflective mask blank is a material for a reflective mask used in EUV lithography using EUV light as the exposure light. The absorber film includes a main region that occupies not less than 94 % of a thickness of the absorber film, the main region consists of tantalum and nitrogen and is constituted of multiple layers that include at least one low nitrogen content layer having a nitrogen content of not more than 20 at%, and at least one high nitrogen content layer having a nitrogen content of 40 at% to 60 at%.