EUV Lithography Diffractive Microlens Aberration Correction
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Solution Overview
Problem
EUV lithography systems face challenges with high cost, limited throughput, and optical inefficiency due to the need for complex and expensive six-mirror projection systems, which are also limited by optical shadowing and chromatic aberration issues in mask-projection systems, while maskless EUV lithography offers higher throughput but struggles with chromatic aberration in diffractive microlenses.
Innovation Solution
A new EUV maskless lithography design using binary-optic zone-plate lenses with a diffractive projection mirror to neutralize chromatic aberration, allowing for simpler optics and higher optical efficiency, and the option to transform the microlens array into a holographic transmission mask for full-field imaging without scanning, enabling larger field exposure and reduced manufacturing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a six-mirror projection system is used in mask-projection EUV lithography, then imaging quality and resolution are improved, but device complexity and manufacturing cost increase significantly
Solution Approach 1:
The patent extracts and removes the complex six-mirror projection system from the EUV lithography setup, replacing it with a simplified optical system that uses diffractive microlenses. This extraction eliminates the need for multiple precision mirrors while maintaining the essential imaging function through the diffractive optical element.
Solution Approach 2:
The patent replaces the mechanical optical system (six mirrors) with a diffractive optical system (microlenses). This substitution transitions from a reflection-based mechanical optical path to a diffraction-based system that achieves similar imaging functionality with fewer components and lower manufacturing complexity.
2Manufacturing precision
If a six-mirror projection system is used, then imaging performance is improved, but manufacturing cost increases to approximately $250 million per system
Solution Approach 1:
The patent employs diffractive microlenses that can be manufactured more economically compared to six-mirror systems. These microlenses represent a simpler, less expensive optical component that achieves the required imaging performance at a lower manufacturing cost, potentially reducing system costs from $250 million to more affordable levels.
Solution Approach 2:
By extracting and removing the expensive six-mirror projection system, the patent eliminates the primary driver of high manufacturing costs. The simplified diffractive optical system requires significantly fewer precision components, thereby reducing overall system manufacturing cost while maintaining imaging performance.
3Productivity
If mask-projection EUV lithography is used, then throughput is limited by optical efficiency, but increasing exposure dose requires further throughput reduction
Solution Approach 1:
The patent replaces the six-mirror projection system with a diffractive microlens system that has superior optical efficiency. This substitution reduces energy loss in the optical path, allowing for higher exposure doses without requiring proportional increases in throughput time, thereby improving overall productivity.
Solution Approach 2:
The patent changes the optical system parameters by using diffractive microlenses instead of mirrors. This parameter change results in improved optical efficiency and reduced energy loss, enabling the system to achieve adequate exposure doses with better throughput performance.
4Ease of operation
If oblique illumination is used on the mask, then incident and reflected light paths are separated, but optical shadowing and 3-D effects occur
Solution Approach 1:
The patent extracts and eliminates the mask component that causes optical shadowing and 3-D effects. By using a maskless approach with diffractive microlenses, the system avoids the problematic oblique illumination geometry entirely, replacing it with a direct transmission-based imaging method that does not suffer from these harmful optical effects.
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
This design significantly reduces manufacturing costs, increases optical efficiency, and allows for larger field exposure without scanning, addressing chromatic aberration and optical shadowing issues, thereby improving throughput and print quality.
Implementation Method 1
A new EUV maskless lithography design uses a diffractive microlens array to focus EUV illumination onto a corresponding array of focal spots
Implementation Method 2
at least one projection mirror in the projection system can be constructed as a diffractive element, operating to neutralize chromatic aberrations in the microlens array
Data Source
AI summary
A maskless, extreme ultraviolet (EUV) lithography scanner uses an array of microlenses, such as binary-optic, zone-plate lenses, to focus EUV radiation onto an array of focus spots (e.g. about 2 million spots), which are imaged through projection optics (e.g., two EUV mirrors) onto a writing surface (e.g., at 6× reduction, numerical aperture 0.55). The surface is scanned while the spots are modulated to form a high-resolution, digitally synthesized exposure image. The projection system includes a diffractive mirror, which operates in combination with the microlenses to achieve point imaging performance substantially free of geometric and chromatic aberration. Similarly, a holographic EUV lithography stepper can use a diffractive photomask in conjunction with a diffractive projection mirror to achieve substantially aberration-free, full-field imaging performance for high-throughput, mask-projection lithography. Maskless and holographic EUV lithography can both be implemented at the industry-standard 13.5-nm wavelength, and could potentially be adapted for operation at a 6.7-nm wavelength.