Below-Wafer Second Facet Mirror Layout for Thermal Load Control
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Solution Overview
Problem
Existing projection exposure apparatuses face challenges in optimizing the arrangement of facet mirrors, particularly the second facet mirror, which affects thermal load, switching angles, and installation space utilization in the illumination optical unit.
Innovation Solution
The second facet mirror is positioned at a significant distance from the object plane, typically at least 1500 mm, with a distance ratio to the first facet mirror greater than 3, and arranged below the wafer plane, reducing thermal load and switching angles while maximizing installation space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the second facet mirror is positioned closer to the object plane, then the installation space is reduced, but the thermal load on the mirror increases
Solution Approach 1:
The patent positions the second facet mirror in the vertical dimension (below the wafer plane) rather than only adjusting its horizontal position, utilizing the z-dimension to achieve both thermal management and space optimization. This dimensional approach allows the mirror to be far from the heat source while maintaining compact overall footprint.
Solution Approach 2:
The patent changes the positional parameter of the second facet mirror, specifying it should be located at a distance of at least 1500 mm from the object plane. This parameter modification directly reduces the thermal load on the mirror while the overall system design ensures compact installation space utilization.
2Temperature
If the second facet mirror is positioned farther from the object plane, then the thermal load is reduced, but the installation space increases
Solution Approach 1:
The patent utilizes the vertical dimension by positioning the second facet mirror below the wafer plane, allowing the mirror to be far from the heat source in the z-direction while maintaining a compact horizontal footprint. This dimensional strategy reduces thermal load without proportionally increasing the overall installation volume.
Solution Approach 2:
The illumination optical unit is designed to fit within the existing space constraints of the projection exposure apparatus, with the second facet mirror nested in the available volume below the wafer plane. This nesting approach maximizes space utilization while maintaining the required mirror-to-object-plane distance.
3Ease of operation
If the distance between facet mirrors is increased, then the switching angles are minimized, but the device complexity increases
Solution Approach 1:
The patent modifies the geometric parameter of the mirror arrangement by specifying that the second facet mirror should be positioned at least 1500 mm from the object plane, creating a distance ratio greater than 3 compared to the first facet mirror. This parameter change reduces the switching angles required for operation.
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 arrangement reduces thermal stress on mirrors, minimizes switching angles, and optimizes the use of available space, enhancing the performance and efficiency of the illumination optical unit.
Implementation Method 1
a first facet mirror (13) and a second facet mirror (14) in a beam path of an illumination optical unit (4)
Data Source
AI summary
A microlithographic projection exposure apparatus in which the second facet mirror of the illumination optical unit is in the region of the wafer plane, such as below the wafer plane.