Tin Oxide Light Absorbing Layer for EUV Photomask Shadowing
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Solution Overview
Problem
In EUV lithography, the inclined optical axis causes a shadowing effect, leading to reduced contrast and increased line edge roughness in transferred patterns, and pattern collapse during photomask cleaning, due to the limitations of current reflective photomasks with tantalum-based light absorbing layers.
Innovation Solution
A reflective photomask blank and photomask using a tin oxide film with a thickness of 17 nm to 25.0 nm as the light absorbing layer, which provides improved EUV absorbency and resistance to heat and cleaning solutions, reducing the shadowing effect and pattern collapse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a tantalum-based light absorbing layer with film thickness of 60 to 90 nm is used in a reflective photomask, then the EUV light absorption is sufficient, but the shadowing effect increases causing reduced contrast and increased line edge roughness in transferred patterns
Solution Approach 1:
The patent changes the material composition of the light absorbing layer from tantalum-based to tin oxide-based, and optimizes the film thickness parameter to 15-30 nm. This parameter change reduces the shadowing effect while maintaining sufficient EUV light absorption, thereby improving line edge roughness and pattern transfer precision
Solution Approach 2:
The patent uses tin oxide as a composite material for the light absorbing layer, which provides both sufficient EUV absorption and reduced shadowing effect compared to conventional tantalum-based materials. The composite material approach allows optimization of optical properties while minimizing harmful shadowing effects
2Ease of operation
If the optical axis is inclined at 6 degrees for EUV exposure, then the reflective optical system can be used, but the shadowing effect occurs due to the inclined incident light
Solution Approach 1:
The patent changes the material properties of the light absorbing layer to tin oxide with optimized thickness, which reduces the shadowing effect caused by the 6-degree inclined optical axis. This material parameter change allows the reflective optical system to operate effectively while minimizing shadowing artifacts
3Ease of manufacture
If a conventional light absorbing layer is used, then the photomask can be manufactured, but pattern collapse occurs during cleaning processes
Solution Approach 1:
The patent employs tin oxide as a composite material for the light absorbing layer that provides both manufacturability and enhanced reliability. The tin oxide material resists pattern collapse during cleaning processes while allowing standard photomask manufacturing procedures to be used
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 with specific thickness and composition in the reflective photomask significantly reduces the shadowing effect, enhancing pattern transfer performance and preventing pattern collapse during cleaning, thereby improving line edge roughness and resolution.
Implementation Method 1
a light absorbing layer formed on the reflective layer, the light absorbing layer including a tin oxide film with a film thickness of 17 nm or more and less than 25.0 nm
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) and including a tin oxide film with a film thickness of 17 nm or more and less than 25.0 nm. 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, pattern collapse due to cleaning of the reflective photomask is suppressed.