Reflective Mask Blank Multilayer Stack for Lower EUV 3D Effect
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Solution Overview
Problem
The 3D effect in EUV lithography causes positional and dimensional deviations in transferred patterns due to the shadowing effect of absorber patterns, and conventional multilayer reflection films in reflective masks do not effectively reduce this effect while maintaining high reflectance.
Innovation Solution
A reflective mask blank with a multilayer reflection film comprising a periodically laminated structure of high, low, and medium refractive index layers, including an intermediate layer to prevent interdiffusion, is used, with ruthenium (Ru) as the low refractive index layer, and formed using a sputtering apparatus with multiple targets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional multilayer reflection film is used, then high reflectance is achieved, but the 3D effect increases causing positional and dimensional deviations
Solution Approach 1:
The patent changes the optical parameters of the multilayer reflection film by introducing a medium refractive index layer between the high and low refractive index layers. This parameter change in the refractive index distribution modifies the reflection characteristics to reduce the 3D effect while maintaining high reflectance, thereby improving pattern transfer accuracy.
Solution Approach 2:
The patent uses a composite multilayer structure combining materials with different refractive indices (high, medium, and low) to create a reflection film that simultaneously achieves high reflectance and reduced 3D effect. The composite structure allows optimization of both optical performance and pattern fidelity.
2Manufacturing precision
If the absorber pattern thickness is reduced to minimize the 3D effect, then pattern accuracy improves, but the reflectance may be compromised
Solution Approach 1:
The patent applies preliminary action by optimizing the multilayer reflection film structure before forming the absorber pattern. The medium refractive index layer is introduced in advance to control the optical path and reduce the 3D effect, allowing the use of thinner absorber patterns without sacrificing reflectance, thus improving pattern accuracy.
3Illumination intensity
If reflections at deeper positions in the multilayer film are increased, then reflectance is enhanced, but the 3D effect increases
Solution Approach 1:
The patent applies local quality by creating a specific refractive index distribution within the multilayer film structure. The medium refractive index layer is positioned at a specific depth to locally control the reflection characteristics, ensuring that reflections contribute to high reflectance without exacerbating the 3D effect.
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 multilayer reflection film reduces the 3D effect and maintains high reflectance, enabling precise pattern transfer with improved accuracy in EUV lithography.
Implementation Method 1
The reflection of EUV light, which is exposure light, by the multilayer reflection film is caused by overlapping of reflections occurred at respective interfaces of layers inside the multilayer reflection film
Implementation Method 2
a patterned absorber film that absorbs EUV light is formed on the multilayer reflection film
Implementation Method 3
formed using a sputtering apparatus with multiple targets
Data Source
Figure 1~2
Figure 3~4
AI summary
A reflective mask blank including a substrate, a multilayer reflection film that is formed on one main surface of the substrate and reflects exposure light is provided. The multilayer reflection film has a periodically laminated structure in which repeating units are multiply stacked, the repeating unit includes one each of a high refractive index layer, a low refractive index layer, and a medium refractive index layer having a refractive index lower than a refractive index of the high refractive index layer and higher than a refractive index of the low refractive index layer, and in the repeating unit, the high refractive index layer and the medium refractive index layer are disposed at the substrate side and the side remote from the substrate, respectively, with respect to the low refractive index layer.