Microlithography Illumination System Using Dual Raster Plates
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Solution Overview
Problem
Current microlithographic projection exposure apparatus illumination systems face challenges in producing flexible and homogeneous illumination settings without increasing system complexity and cost, particularly when dealing with small light spots and multiple illumination settings.
Innovation Solution
The use of two optical raster plates with separate Fourier optics to independently control the irradiance distribution on different portions of the illuminated field, allowing for distinct illumination settings by varying the focal lengths of the Fourier optics and employing a spatial light modulator to adjust the irradiance distribution on each raster plate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single optical raster plate is used to illuminate the mask, then the system structure is simple, but it cannot provide different illumination settings for different portions of the mask
Solution Approach 1:
The patent divides the mask illumination into multiple portions, with each portion having its own optical raster plate and Fourier optics system. This segmentation allows different illumination settings (e.g., annular, dipole, quadrupole) to be independently applied to different mask regions, providing versatility without requiring a single complex reconfigurable system
Solution Approach 2:
Each optical raster plate is designed to be multifunctional, capable of producing various illumination patterns (conventional, annular, dipole, quadrupole) by adjusting the irradiance distribution on the plate. This universal design allows the same hardware structure to serve multiple illumination purposes
2Adaptability or versatility
If multiple optical raster plates are used to provide different illumination settings, then illumination flexibility is improved, but optical cross-talk between plates may occur
Solution Approach 1:
The patent applies different irradiance distributions to different regions of each optical raster plate, with each local region optimized for a specific illumination pattern. The Fourier optics systems are configured to direct light from specific plate regions to corresponding mask portions, ensuring that illumination settings are locally optimized without interfering with adjacent regions
Solution Approach 2:
The Fourier optics system acts as an intermediary between the optical raster plates and the mask, spatially separating the light paths from different plates. This intermediary optical system ensures that light from one plate does not reach unintended mask regions, preventing cross-talk while maintaining the ability to provide multiple illumination settings
3Adaptability or versatility
If the irradiance distribution is adjusted to achieve different angular light distributions, then the illumination adaptability is improved, but the control complexity increases
Solution Approach 1:
The patent changes the irradiance distribution parameter on the optical raster plate to achieve different angular light distributions. By varying the spatial intensity profile on the plate (e.g., concentrating light in different regions or patterns), the system can produce conventional, annular, dipole, or quadrupole illumination settings without adding complex control mechanisms
Solution Approach 2:
The optical raster plate system is designed to automatically produce the desired angular light distribution based on the irradiance distribution applied to it. The Fourier optics system self-adjusts the light paths according to the plate's irradiance pattern, reducing the need for external active control elements
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 approach enables the production of different illumination settings on distinct portions of the mask without significantly increasing system complexity, maintaining homogeneity and flexibility, while preventing optical cross-talk between the raster plates.
Implementation Method 1
Each optical raster element has the property that it directs impinging light into one or a plurality of directions
Implementation Method 2
an optical integrator formed by an optical raster element
Implementation Method 3
first Fourier optics that establish a Fourier relationship between a first pupil plane, which intersects, or is arranged in close proximity to, the first optical raster plate, and the first portion of the illuminated field
Implementation Method 4
a spatial light modulator that modifies an irradiance distribution of projection light on the optical raster plates
Data Source
AI summary
An illumination system of a microlithographic projection exposure apparatus includes first and second optical raster plates. An irradiance distribution of projection light on the first and second optical raster plates determines an angular light distribution of the projection light exclusively at a first portion and a second portion, respectively, of an illuminated field. The second portion is distinct from and arranged adjacent to the first portion. It is possible to produce different illumination settings in different adjacent portions on the mask. First and second Fourier optics establish a Fourier relationship between the first and second optical raster plates one the one hand and the first and second portion on the other hand. The first and second Fourier optics have a first and second focal length, respectively, that are variable in response to a focal length change command signal from a control unit.