Reflective Mask Blank Multilayers for Low-Background EUV Inspection
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Solution Overview
Problem
Existing reflective mask blanks for EUV lithography face challenges in detecting phase defects due to high background levels during defect inspection, which are exacerbated by the use of additive elements in molybdenum layers, leading to reduced reflectance and increased background noise.
Innovation Solution
A reflective mask blank with a multilayer reflection film structure that includes low-refractive index layers composed of molybdenum and specific additive elements like nitrogen, carbon, or boron, and an amorphous structure to maintain high reflectance while reducing background levels, achieved by controlling the thickness and composition of these layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If additive elements (nitrogen, carbon, boron) are incorporated into molybdenum layers to reduce background levels, then background level is reduced, but reflectance decreases
Solution Approach 1:
The low-refractive index layer is segmented into multiple sublayers with different compositions and thicknesses. The first sublayer contains molybdenum with additive elements (nitrogen, carbon, or boron) to reduce background level, while the second sublayer is optimized for reflectance. This segmentation allows each sublayer to perform its specific function, resolving the contradiction between reducing background level and maintaining reflectance.
Solution Approach 2:
Different regions of the low-refractive index layer have different compositions and properties. The first sublayer has higher additive element content for background reduction, while the second sublayer has optimized composition for reflectance. This local quality variation allows the structure to simultaneously achieve both low background level and high reflectance.
2Measurement precision
If molybdenum layers contain additive elements to control structure, then phase defect detection is improved, but manufacturing complexity increases
Solution Approach 1:
The low-refractive index layer is divided into multiple sublayers with specific thickness ranges (first sublayer: 2.0-4.0 nm, second sublayer: 0.5-2.0 nm). This segmentation provides a systematic approach to controlling the structure for phase defect detection while keeping the total thickness and composition manageable for manufacturing.
Solution Approach 2:
The invention specifies precise parameter ranges for composition (additive element content: 0.1-5.0 at%) and thickness (first sublayer: 2.0-4.0 nm, second sublayer: 0.5-2.0 nm) to optimize phase defect detection. By controlling these parameters within defined ranges, the invention achieves improved detection precision while maintaining manufacturability.
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 high reflectance for EUV light and controlled low background levels, effectively reducing phase defects and enhancing defect detection sensitivity.
Implementation Method 1
a multilayer reflection film that is formed on one main surface of the substrate and reflects the exposure light
Implementation Method 2
the multilayer reflection film has a periodically laminated structure in which low-refractive index layers composed of a material containing molybdenum (Mo) and high-refractive index layers are alternately laminated
Implementation Method 3
an absorber film that is formed on the protection film and absorbs the exposure light
Data Source
Figure 1
AI summary
With respect to a reflective mask blank for a reflective mask used in EUV lithography using EUV light, the reflective mask blank including a substrate, a multilayer reflection film having a periodically laminated structure in which low-refractive index layers composed of a material containing molybdenum and high-refractive index layers are alternately laminated, a protection film, and an absorber film is provided. The low-refractive index layer consists of one or more of first low-refractive index sublayers, and one or more of second low-refractive index sublayers that have a different composition from a composition of the first low-refractive index sublayer.