Predicting Thermally Induced Aberrations in EUV Projection Systems
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Solution Overview
Problem
Lithographic apparatuses face challenges in predicting and mitigating thermally induced aberrations caused by mirror heating, leading to imaging errors and reduced productivity due to the need for frequent calibrations and sensitivity to thermal drift and modeling errors.
Innovation Solution
A method and system for predicting thermally induced aberrations by calculating irradiance profiles, estimating temperature distributions, and using thermal expansion maps to calculate aberrations, which includes feedback correction using temperature measurements to adapt the projection system, thereby improving imaging accuracy and reducing the need for frequent calibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If physical modeling methods are used to predict thermally induced aberrations, then modeling accuracy and reliability are improved, but computational complexity and device complexity increase
Solution Approach 1:
The prediction method is segmented into distinct sequential steps: irradiance profile calculation, temperature distribution estimation, and aberration calculation. Each step processes specific parameters and produces intermediate results that feed into the next step, making the complex physical modeling process more manageable and implementable while maintaining high prediction accuracy through systematic decomposition of the thermal-aberration relationship
Solution Approach 2:
The system performs preliminary calculation of irradiance profiles and temperature distributions before actual lithographic exposure. By pre-computing thermal effects and their corresponding aberrations, the system prepares correction data in advance, allowing real-time compensation without adding significant computational burden during the actual imaging process
2Manufacturing precision
If comprehensive thermal modeling is implemented to improve imaging performance, then manufacturing precision is improved, but calculation time and productivity are reduced
Solution Approach 1:
The comprehensive thermal modeling and aberration prediction are performed periodically at key moments: before lithographic exposure begins and when thermal conditions change significantly. This periodic execution strategy ensures high imaging precision through accurate aberration compensation while avoiding continuous computation that would reduce productivity, thereby balancing precision requirements with production throughput
3Manufacturing precision
If frequent calibration is performed to maintain imaging quality, then imaging precision is improved, but loss of time and productivity are reduced
Solution Approach 1:
The system implements feedback correction using temperature measurements from sensors positioned on optical elements. Measured temperatures are fed back into the thermal model to validate and adjust predictions, enabling continuous monitoring and correction without frequent manual calibration. This feedback mechanism maintains imaging quality by dynamically compensating for thermal drift while minimizing time loss through automated real-time adjustment rather than periodic recalibration
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
The method enhances the accuracy of predicting thermally induced optical aberrations, improving imaging, overlay, and focus performance while reducing the requirement for calibration after each customer application, thus increasing productivity and robustness against thermal drift.
Implementation Method 1
a significant part of EUV (but also out-of-band) energy is absorbed in the mirrors and transformed into heat
Implementation Method 2
This heating causes thermal stresses in the material of the mirrors leading to deformations of the optical surfaces
Data Source
AI summary
A method of predicting thermally induced aberrations of a projection system for projecting a radiation beam, the method comprising: calculating an irradiance profile for at least one optical element of the projection system from a power and illumination source pupil of the radiation beam, estimating a temperature distribution as a function of time in the at least one optical element of the projection system using the calculated irradiance profile for the at least one optical element of the projection system; calculating the thermally induced aberrations of the projection system based on the estimated temperature distribution and a thermal expansion parameter map associated with the at least one optical element of the projection system, wherein the thermal expansion parameter map is a spatial map indicating spatial variations of thermal expansion parameters in the at least one optical element of the projection system or a uniform map.