Wavefront Correction Device for Microlithography
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Solution Overview
Problem
Current microlithographic projection exposure apparatuses face challenges in quickly changing and correcting high spatial frequency phase variations due to rotationally asymmetric aberrations, which are caused by non-uniform heating and material changes in optical elements under high-energy projection light, limiting their ability to produce small structures with high integration densities.
Innovation Solution
A method and apparatus using a wavefront correction device with a first refractive optical element made of material with a negative temperature-dependent refractive index and a second element with a positive temperature-dependent refractive index, allowing for independent temperature distribution control using separate heating devices to quickly change phase variations and correct aberrations, leveraging the high thermal conductivity of materials like fluorite to rapidly adjust optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a single refractive optical element is used for wavefront correction, then the device complexity is low, but the ability to quickly change phase variations with high spatial frequencies is limited
Solution Approach 1:
The wavefront correction device is segmented into multiple refractive optical elements (at least two), each capable of independent temperature control. This segmentation allows different regions of the wavefront to be corrected independently and simultaneously, enabling rapid changes in phase variations with high spatial frequencies without requiring a single complex adjustable element.
Solution Approach 2:
The patent introduces dynamic temperature control of refractive optical elements using heating devices. By dynamically adjusting the temperature of each element, the refractive index can be changed in real-time, allowing rapid modification of phase variations. This dynamic control transforms a static correction system into an adaptive one that can respond quickly to changing aberration conditions.
2Manufacturing precision
If heating devices are used to change refractive index for aberration correction, then phase variations can be adjusted, but heat-induced material changes and thermal damage may occur
Solution Approach 1:
The patent changes the physical parameter (temperature) of the refractive optical elements to modify their refractive index and correct aberrations. By controlling temperature variations within safe limits, the system achieves precise wavefront correction while avoiding excessive heating that would cause material damage. This parameter-based control allows fine-tuning of optical properties without crossing into harmful thermal regimes.
Solution Approach 2:
The refractive optical elements act as intermediaries between the heating devices and the projection light path. The heating devices indirectly affect the optical system by modifying the temperature and refractive index of these intermediate elements, rather than directly heating the projection light or mask. This intermediary approach allows precise control of wavefront correction while isolating the sensitive optical components from direct thermal exposure.
3Manufacturing precision
If multiple refractive optical elements with independent temperature control are used, then high spatial frequency phase variations can be corrected quickly, but the device complexity increases
Solution Approach 1:
The correction system is divided into multiple independently controllable refractive optical elements, each with its own heating device. This segmentation enables localized correction of different spatial frequency components of wavefront aberrations. By distributing the correction function across multiple simple elements rather than one complex element, the system achieves high precision while keeping individual components manageable.
Solution Approach 2:
Multiple refractive optical elements with identical or similar structures perform the same basic function (wavefront correction) but can be independently controlled to address different aspects of aberration. This universality allows the use of standardized, simpler components that can be replicated and controlled in parallel, reducing the complexity of individual elements while achieving sophisticated overall 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
Enables rapid and effective correction of aberrations with high spatial frequencies, improving the ability to produce small structures and maintain high integration densities by quickly adjusting phase variations and reducing heat-induced distortions, thus enhancing the performance of microlithographic processes.
Implementation Method 1
a first refractive optical element that comprises a first optical material having, for an operating wavelength of the apparatus, an index of refraction that decreases with increasing temperature
Implementation Method 2
a second refractive optical element that comprises a second optical material having, for the operating wavelength of the apparatus, an index of refraction that increases with increasing temperature
Implementation Method 3
leveraging the high thermal conductivity of materials like fluorite to rapidly adjust optical properties
Data Source
AI summary
A projection objective of a microlithographic projection exposure apparatus has a wavefront correction device including a first refractive optical element and a second refractive optical element. The first refractive optical element includes a first optical material having, for an operating wavelength of the apparatus, an index of refraction that decreases with increasing temperature. The second refractive optical element includes a second optical material having, for an operating wavelength of the apparatus, an index of refraction that increases with increasing temperature. In a correction mode of the correction device, a first heating device produces a non-uniform and variable first temperature distribution in the first optical material, and a second heating device produces a non-uniform and variable second temperature distribution in the second optical material.