Reflective Mask Blank Mo Sublayers for Low-Background EUV Inspection
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Solution Overview
Problem
Existing reflective mask blanks face challenges in detecting and correcting phase defects due to increased background levels during defect inspection, which are difficult to address after forming the absorber film, especially when molybdenum layers coarsen, leading to roughness and reduced reflectance.
Innovation Solution
A reflective mask blank with a multilayer reflection film structure that includes low and high refractive index layers alternately laminated, where the low refractive index layers have a two-layered structure of molybdenum with added nitrogen, carbon, boron, silicon, or hydrogen, and a second sublayer of pure molybdenum, maintaining high reflectance and reducing background levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional multilayer reflection film is used, then the structure is simple and easy to manufacture, but the background level during defect inspection increases and detectability decreases
Solution Approach 1:
The low refractive index layer is divided into two sublayers: a first sublayer containing molybdenum and additive elements (nitrogen, carbon, boron, silicon, or hydrogen) to reduce background level, and a second sublayer of substantially pure molybdenum to maintain high reflectance. This segmentation allows each sublayer to perform its specific function optimally.
Solution Approach 2:
Different regions of the low refractive index layer are given different compositions: the first sublayer has additive elements for background reduction, while the second sublayer has high purity molybdenum for reflectance. This local quality differentiation resolves the contradiction between detection precision and structural simplicity.
2Reliability
If molybdenum layers are made thick to maintain structural stability, then reliability improves, but crystal grain coarsening occurs leading to increased surface roughness and reduced reflectance
Solution Approach 1:
The low refractive index layer uses a composite structure with two sublayers having different compositions. The first sublayer contains molybdenum with additive elements to suppress grain growth, while the second sublayer provides high reflectance. This composite approach maintains both structural stability and surface quality.
Solution Approach 2:
The invention changes the compositional parameters of the molybdenum layer by introducing additive elements in the first sublayer to control crystal grain growth, while maintaining high molybdenum content in the second sublayer to preserve reflectance properties.
3Measurement precision
If additive elements are added to molybdenum to reduce background level, then defect detection precision improves, but reflectance decreases
Solution Approach 1:
The low refractive index layer is segmented into two sublayers: the first sublayer contains additive elements to reduce background level for improved defect detection, while the second sublayer consists of substantially pure molybdenum to maintain high reflectance. This segmentation resolves the contradiction between detection precision and reflectance.
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 solution provides a reflective mask blank with a low background level and high reflectance, effectively detecting and correcting phase defects, ensuring high-quality pattern transfer in EUV lithography.
Implementation Method 1
a multilayer reflection film that is formed on a substrate and reflects EUV light
Implementation Method 2
a multilayer reflection film in which molybdenum (Mo) films and silicon (Si) films are alternately laminated to obtain a necessary reflectance for EUV light
Implementation Method 3
a patterned absorber film that is formed on the multilayer reflection film and absorbs EUV light
Data Source
AI summary
A reflective mask blank including a substrate, a multilayer reflection film formed on one main surface of the substrate and reflects exposure light. The multilayer reflection film has a periodically laminated structure portion in which low refractive index layers and high refractive index layers are alternately laminated, and at least one of the low refractive index layer has a two-layered structure consisting of one layer containing molybdenum, and at least one additive element selected from the group consisting of nitrogen, carbon, boron, silicon and hydrogen, and the other layer containing molybdenum and substantively free of other elements other than molybdenum.