Three-Index Reflective Mask Blank 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, which is exacerbated by the structure of the multilayer reflection film in reflective masks, necessitating a solution to 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 and enhance surface reflections, is developed, utilizing materials like Ru/Si for improved reflectance and reduced 3D effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional Mo/Si multilayer reflection film is used, then high reflectance can be achieved, but the 3D effect increases due to deeper reflection contributions
Solution Approach 1:
The patent changes the refractive index parameters of the multilayer reflection film by introducing a medium refractive index layer between the high and low refractive index layers. This parameter modification alters the reflection characteristics to reduce 3D effect while maintaining high reflectance through optimized optical path control.
Solution Approach 2:
The patent creates a composite multilayer structure combining three distinct refractive index layers (high, medium, and low) in a periodic arrangement. This composite material approach enables simultaneous optimization of reflectance and 3D effect reduction by leveraging the complementary optical properties of each layer type.
2Manufacturing precision
If the absorber pattern thickness is reduced to minimize 3D effect, then positional and dimensional deviations decrease, but the absorber pattern becomes more difficult to manufacture with sufficient precision
Solution Approach 1:
The patent applies preliminary anti-action by modifying the multilayer reflection film structure beforehand to reduce the 3D effect. This pre-compression of the shadowing effect allows for thinner absorber patterns while maintaining manufacturability, as the reduced 3D effect compensates for the decreased pattern thickness margin.
3Illumination intensity
If a multilayer reflection film with deeper reflection contributions is used, then high reflectance is achieved, but the 3D effect is exacerbated
Solution Approach 1:
The patent applies local quality by creating spatial variation in refractive index throughout the multilayer structure. The medium refractive index layer is strategically positioned to locally control reflection contributions, ensuring that reflections from shallower interfaces are enhanced while deeper interface contributions are suppressed, thereby reducing 3D effect locally at critical interfaces.
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 results in a reflective mask blank with reduced 3D effect and high reflectance, enabling precise pattern transfer 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
forming the multilayer reflection film by sputtering using a sputtering apparatus
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.