Facet Mirror Positioning Model for EUV Lithography
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Solution Overview
Problem
Existing methods for positioning individual mirrors in EUV lithography apparatuses fail to accurately account for interactions between control loops, leading to deviations in relative angular positions due to electromagnetic signal crosstalk, mechanical stresses, and other interferences, which are exacerbated by the large number of possible illumination settings and unknown user settings.
Innovation Solution
A method is developed to generate a mathematical model for positioning individual mirrors in a facet mirror system, using a measuring device outside the optical system to capture accurate measurement positions, and a controller unit to provide manipulated variables based on intended positions and sensor actual positions, considering interactions between components like actuators, sensors, and optical connections, to predict and correct deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If control loops for positioning facets are implemented, then relative angular positions can be adjusted, but electromagnetic signal crosstalk and reciprocal interference cause deviations between actual and intended positions
Solution Approach 1:
A mathematical model is introduced as an intermediary between the control loops and the actual positioning system. This model predicts the deviations caused by electromagnetic signal crosstalk and reciprocal interference, allowing the control system to compensate for these effects and achieve accurate positioning despite the interfering factors
Solution Approach 2:
The system implements feedback by continuously monitoring the actual positions of facets and comparing them with intended positions. The mathematical model uses this feedback information to predict deviations and adjust control signals, creating a closed-loop control system that compensates for electromagnetic interference and maintains positioning accuracy
2Adaptability or versatility
If multiple illumination settings are supported, then system versatility increases, but the number of possible deviations increases making control more difficult
Solution Approach 1:
The mathematical model is designed with universal applicability across all illumination settings. By establishing general relationships between control parameters and positioning deviations that hold across different operating conditions, the model can predict and correct deviations for any illumination setting without requiring setting-specific calibration, thus managing complexity while supporting versatility
3Manufacturing precision
If sensors and actuators are used for closed-loop control, then positioning accuracy can be maintained, but mechanical stresses and deformations cause additional deviations
Solution Approach 1:
The mathematical model predicts deviations caused by mechanical stresses and deformations before they affect positioning accuracy. By calculating expected deviations based on the current state of the system and compensating for them in advance, the control system can maintain positioning accuracy despite the presence of mechanical interfering factors
Data Source
AI summary
A method for generating a mathematical model (MM) for positioning individual mirrors (204, 204′) of a facet mirror (200) in an optical system (500), e.g. in a lithography apparatus (100A, 100B). The method includes: a) providing (S701) target positions (SP) of the individual mirrors (204, 204′) with an adjustment unit (502), b) capturing (S702) actual measurement positions (MI) of the individual mirrors (204, 204′) with a measuring device (508), which is embodied as an interferometer, deflectometer and/or camera, and c) generating (S705) a mathematical model (MM) for positioning the individual mirrors (204, 204′) based on the captured actual measurement positions (MI) and the target positions (SP). In step c), a difference (EA) is formed (S703) between a respective actual measurement position (MI) and a respective target position (SP) and the mathematical model (MM) is generated (S705) based on the difference (EA) formed.