Semispherical Lens With Truncated Cone Aperture for Lithography
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Solution Overview
Problem
In lithography processes, the reduction in wavelength of exposure light and increase in numerical aperture of the projection optical system lead to a decrease in depth of focus, making it challenging to maintain a constant focal distance between the two-dimensional light-modulating nano/micro aperture array and the recording medium, resulting in inconsistent exposure patterns.
Innovation Solution
A lens structure with a semispherical shape and a truncated-cone protruding portion, featuring a thin metal film with a nanometer-diameter aperture and an immersion layer of higher refractive index than air, which maintains a constant distance from the recording medium, ensuring consistent exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the wavelength of exposure light is shortened and the numerical aperture of the projection optical system is increased to improve resolution, then the resolution increases, but the depth of focus decreases
Solution Approach 1:
The patent divides the aperture array into multiple independent aperture elements arranged in a two-dimensional pattern. Each aperture acts as an independent light-modulating unit, allowing the system to maintain a larger effective aperture for high resolution while the segmented structure helps manage the depth of focus challenge through distributed light modulation
Solution Approach 2:
The patent transitions from a one-dimensional aperture arrangement to a two-dimensional light-modulating aperture array. This dimensional change allows the system to achieve high resolution in both lateral directions simultaneously while maintaining a constant focal distance, effectively addressing the depth of focus limitation that arises from high numerical aperture configurations
2Manufacturing precision
If a two-dimensional light-modulating nano/micro aperture array is used to improve resolution and depth of focus, then the resolution and lithography characteristics improve, but it becomes difficult to maintain a constant distance between the aperture array and the recording medium
Solution Approach 1:
The patent incorporates an immersion layer between the aperture array and the recording medium to pre-establish a constant focal distance. This preliminary structural arrangement ensures that the distance is maintained constant during the exposure process, eliminating the need for real-time adjustment and ensuring consistent exposure patterns
Solution Approach 2:
The immersion layer acts as an intermediary element between the aperture array and the recording medium. This intermediate layer with higher refractive index than air serves multiple functions: maintaining constant focal distance, enabling evanescent field coupling for improved resolution, and ensuring stable exposure conditions throughout the lithography process
3Ease of manufacture
If the distance between the aperture array and the recording medium is not kept constant, then the system becomes easier to manufacture, but different exposure patterns are formed even with light of the same intensity
Solution Approach 1:
The immersion layer with its specific refractive index and thickness is designed to self-maintain the constant focal distance between the aperture array and the recording medium. This self-service mechanism ensures that the system automatically maintains the required distance without complex external control mechanisms, achieving both ease of manufacture and exposure pattern consistency
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 allows for a more stable and consistent focal distance, enhancing the reliability of the lithography process by maintaining a constant distance between the lens and the recording medium, thereby improving the depth of focus and reducing manufacturing costs.
Implementation Method 1
an immersion layer which is formed with a constant thickness on an upper surface of the protruding portion
Implementation Method 2
a thin metal film that is formed on a surface of the protruding portion, and has an aperture formed at a position corresponding to a center of an upper surface of the protruding portion
Data Source
AI summary
Disclosed are a lens structure, an optical system including the same, and a lithography method using the optical system. The disclosed lens structure includes: a lens that has a substantially semispherical shape and includes a protruding portion having a truncated cone shape that is provided on its aspherical surface; a thin metal film that is formed on the surface of the protruding portion, and has an aperture formed at a position corresponding to the center of an upper surface of the protruding portion; and an immersion layer that is formed with a constant thickness on the upper surface of the protruding portion.