Microlithography Wavefront Correction via Thermal Rim Heating
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Solution Overview
Problem
Current microlithographic projection exposure apparatuses face challenges in correcting higher-order wavefront errors due to heat-induced image errors, particularly rotationally asymmetric aberrations, which are difficult to address with existing deformation-based correction methods that are complex and prone to scattering losses or require costly structures.
Innovation Solution
A wavefront correction device is introduced that uses heating light directed onto the circumferential rim surface of a refractive optical element, creating a refractive index distribution to correct wavefront errors, with a focusing optical element and spatial light modulator to control the heating light beams for precise temperature distribution and absorption, minimizing scattering and complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If deformation-based correction methods are used to correct wavefront errors, then correction capability is improved, but device complexity increases and scattering losses occur
Solution Approach 1:
The patent replaces mechanical deformation-based correction with a thermal-optical system. Heating elements generate temperature distributions within the optical element, which create refractive index variations that correct wavefront errors. This substitution eliminates complex mechanical deformation mechanisms and reduces scattering losses associated with physical deformation.
Solution Approach 2:
The patent changes the physical state parameters of the optical element by introducing controlled temperature distributions. By varying temperature spatially within the optical element, refractive index parameters are modified to correct wavefront errors, providing a simpler alternative to mechanical deformation while maintaining correction effectiveness.
2Manufacturing precision
If heating light is directed onto the rim surface of a refractive optical element, then wavefront correction is achieved, but temperature distribution control becomes critical
Solution Approach 1:
The patent applies heating light selectively to different regions of the rim surface to create localized temperature variations. By controlling which portions of the rim receive heating light, specific spatial patterns of temperature and refractive index are generated within the optical element, enabling precise wavefront correction while managing temperature distribution.
Solution Approach 2:
The patent uses the refractive optical element itself as an intermediary medium. The heating light does not directly correct the wavefront; instead, it creates temperature distributions within the optical element, which in turn create refractive index variations that correct the wavefront. This intermediary approach decouples the heating mechanism from the correction function, simplifying control.
3Manufacturing precision
If complex deformation-based correction structures are used, then wavefront correction capability is improved, but scattering losses increase
Solution Approach 1:
The patent replaces mechanical deformation structures with a thermal-optical correction mechanism. By using temperature-induced refractive index changes instead of physical deformation, the system achieves wavefront correction without the scattering losses inherent in mechanical deformation methods, while maintaining correction capability.
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 effectively corrects wavefront errors, including higher-order aberrations, while maintaining a simple construction and reducing scattering issues, enhancing the accuracy and efficiency of microlithographic processes.
Implementation Method 1
A temperature distribution caused by a partial absorption of the first and the second heating light results in a refractive index distribution inside the refractive optical element that changes
Implementation Method 2
A temperature distribution caused by a partial absorption of the first and the second heating light results in a refractive index distribution inside the refractive optical element that changes
Implementation Method 3
At least the first optical system comprises a focusing optical element that is configured to focus the first heating light in a focal area such that the first heating light emerging from the focal area impinges on the first portion of the rim surface
Implementation Method 4
a refractive optical element (44) that has two opposite optical surfaces (46, 48), through which projection light passes when the mask (16) is imaged on the light sensitive surface (22)
Data Source
AI summary
A projection objective of a microlithographic projection exposure apparatus includes a wavefront correction device including a refractive optical element that has two opposite optical surfaces, through which projection light passes, and a circumferential rim surface extending between the two optical surfaces. A first and a second optical system are configured to direct first and second heating light to different portions of the rim surface such that at least a portion of the first and second heating light enters the refractive optical element. A temperature distribution caused by a partial absorption of the heating light results in a refractive index distribution inside the refractive optical element that corrects a wavefront error. At least the first optical system includes a focusing optical element that focuses the first heating light in a focal area such that the first heating light emerging from the focal area impinges on the rim surface.