Tin Oxide Light Absorbing Layer for EUV Photomask Shadowing
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Solution Overview
Problem
In EUV lithography, the optical axis inclination causes a shadowing effect, leading to reduced contrast and increased line edge roughness in transferred patterns, and existing EUV mask blanks lack sufficient cleaning resistance, hindering the miniaturization of semiconductor devices.
Innovation Solution
A reflective photomask blank with a substrate, a reflective layer, and a light absorbing layer composed of a tin oxide film with an atomic ratio of oxygen to tin between 1.50 and 2.0 and a film thickness of 25 nm to 45 nm, which reduces the shadowing effect and enhances cleaning resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a light absorbing layer with thickness of 60 to 90 nm mainly containing tantalum is used, then sufficient EUV absorption is achieved, but the shadowing effect increases causing reduced contrast and increased line edge roughness
Solution Approach 1:
The patent changes the material composition parameter by using tin oxide instead of tantalum, and optimizes the film thickness parameter to 25-45 nm. This parameter change reduces the shadowing effect while maintaining sufficient EUV absorption, thereby improving line edge roughness and manufacturing precision
Solution Approach 2:
The patent employs a composite structure by forming a tin oxide film with specific oxygen to tin atomic ratio (1.50 < O/Sn ≤ 2.00) on top of the reflective layer. This composite material approach provides both sufficient EUV absorption and reduced shadowing effect compared to conventional tantalum layers
2Manufacturing precision
If the light absorbing layer thickness is reduced to suppress shadowing effect, then line edge roughness improves, but cleaning resistance decreases
Solution Approach 1:
The patent optimizes the film thickness parameter to a specific range (25-45 nm) and controls the compositional parameter (O/Sn atomic ratio between 1.50 and 2.00). This parameter optimization achieves the right balance between reducing shadowing effect and maintaining adequate cleaning resistance
Solution Approach 2:
The patent applies local quality by creating a tin oxide film with specific compositional characteristics (controlled O/Sn ratio) that provides different properties than bulk tin oxide. This localized compositional control ensures both good shadowing effect suppression and sufficient cleaning resistance
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 use of a tin oxide film as a light absorbing layer in EUV photomasks suppresses the shadowing effect, improving pattern transfer performance and line edge roughness while maintaining sufficient EUV absorbency and thermal stability.
Implementation Method 1
a light absorbing layer which includes a tin oxide film with an atomic ratio (O/Sn) of oxygen (O) to tin (Sn) being more than 1.50 and equal to or less than 2.00, and with a film thickness of 25 nm or more and 45 nm or less
Data Source
AI summary
A reflective photomask blank (10) of a first aspect includes a substrate (1); a reflective layer (2) formed on the substrate (1); and a light absorbing layer (4) formed on the reflective layer (2). The light absorbing layer (4) includes a tin oxide film with an atomic ratio (O/Sn) of oxygen (O) to tin (Sn) being more than 1.50 and equal to or less than 2.0, and with a film thickness of 25 nm or more and 45 nm or less. Consequently, the shadowing effect of a reflective photomask for pattern transfer using extreme ultraviolet light as a light source is suppressed or reduced to improve the performance of transfer to a semiconductor substrate, and further, the cleaning resistance of the light absorbing layer is improved.