Projection Exposure Tool Lens Heating Compensation
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Solution Overview
Problem
Projection exposure tools for microlithography face challenges in maintaining optimal performance due to radiation-induced changes in optical properties of lenses, leading to aberrations and reduced throughput, as existing methods for correcting these changes are time-consuming and require significant computing resources.
Innovation Solution
A method and control apparatus that classify object structures on a mask, calculate the changes in optical properties of the projection objective, and adjust the imaging behavior to compensate for radiation-induced effects, using thermal eigenmodes and approximation techniques to reduce computing requirements and enable real-time compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high radiation intensities are used to achieve high throughput rate, then productivity is improved, but radiation-induced changes in optical properties of the projection objective worsen
Solution Approach 1:
The patent implements a feedback mechanism where the actual radiation dose delivered to the projection objective is measured and monitored. Based on this feedback, the control system dynamically adjusts exposure parameters to compensate for radiation-induced optical property changes, thereby maintaining image quality while operating at high throughput rates
Solution Approach 2:
The patent changes operational parameters such as radiation intensity, exposure time, and wavelength based on the accumulated radiation dose. By dynamically adjusting these parameters, the system compensates for lens heating and other radiation-induced effects, allowing sustained high productivity without degradation of optical performance
2Measurement precision
If full chip simulation using finite element method is performed to calculate temperature distribution, then measurement precision is improved, but loss of time and computing resources worsen
Solution Approach 1:
The patent segments the mask layout into representative regions or uses simplified geometric models that capture the essential thermal characteristics. This segmentation allows temperature distribution to be calculated using reduced-order models that are computationally efficient while maintaining sufficient accuracy for compensation purposes
Solution Approach 2:
The patent creates simplified thermal models or lookup tables that replicate the behavior of the full finite element model. These pre-computed models can be queried rapidly during operation, providing accurate temperature estimates without the computational burden of real-time full-chip simulation
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 allows for precise compensation of radiation-induced changes, maintaining image quality and throughput by adjusting the imaging behavior of the projection exposure tool, reducing aberrations and lens heating effects within a narrow range, and enabling faster calculation of temperature distributions for improved operational efficiency.
Implementation Method 1
a projection objective for imaging object structures on a mask into an image plane using electromagnetic radiation
Implementation Method 2
absorbed radiation in a lens can have the effect of a localized temperature change in the lens
Implementation Method 3
This effect is a reversible, short-term effect and known as 'lens heating'
Data Source
AI summary
A method of operating a projection exposure tool for microlithography is provided. The projection exposure tool has a projection objective for imaging object structures on a mask into an image plane using electromagnetic radiation, during which imaging the electromagnetic radiation causes a change in optical properties of the projection objective. The method comprises the steps of: providing the layout of the object structures on the mask to be imaged and classifying the object structures according to their type of structure, calculating the change in the optical properties of the projection objective effected during the imaging process on the basis of the classification of the object structures, and using the projection exposure tool for imaging the object structures into the image plane, wherein the imaging behavior of the projection exposure tool is adjusted on the basis of the calculated change of the optical properties in order to at least partly compensate for the change of the optical properties of the projection objective caused by the electromagnetic radiation during the imaging process.