Exposure Apparatus Focus Calibration via Through-The-Lens Detection
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Solution Overview
Problem
In photolithography processes, the accuracy of exposure apparatuses is compromised due to changes in the best focus position over time caused by air fluctuations and positional deviations within the projection optical system, leading to decreased productivity from frequent focus recalibrations.
Innovation Solution
An exposure apparatus with a detection system that measures light quantity distributions through specific marks on the mask and substrate, allowing for real-time adjustment of the relative positions of the mask and substrate to maintain optimal focus without moving the substrate stage, thereby reducing the need for frequent recalibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If focus calibration is performed frequently to maintain exposure accuracy, then manufacturing precision is improved, but productivity deteriorates due to time loss from recalibration operations
Solution Approach 1:
The patent performs focus calibration in advance using a through-the-lens method before actual substrate exposure. By determining the best focus position beforehand using calibration marks and storing this information, the system eliminates the need for frequent recalibration during production, thus maintaining exposure accuracy while preserving productivity
Solution Approach 2:
The patent uses calibration marks that replicate the optical path characteristics of actual substrate marks. By measuring focus using these copied marks through the projection optical system, the system obtains accurate focus data without requiring actual substrate processing, enabling separate calibration and production operations
2Manufacturing precision
If substrate stage is moved frequently for focus calibration, then focus accuracy is improved, but productivity worsens due to increased calibration time
Solution Approach 1:
The system determines the best focus position in advance by moving the substrate stage during an initial calibration phase. This best focus position information is then stored and used for subsequent exposures without requiring repeated stage movements, thus achieving accurate focus while minimizing time loss
Solution Approach 2:
The patent replaces repeated mechanical substrate stage movements with a computational approach. By calculating and storing the best focus position based on light quantity measurements from calibration marks, the system eliminates the need for continuous mechanical adjustment during production, reducing both time loss and mechanical wear
3Manufacturing precision
If best focus position is adjusted in real-time to compensate for air fluctuations and heat, then manufacturing precision is improved, but device complexity increases due to additional detection and control systems
Solution Approach 1:
The patent makes the projection optical system serve multiple functions: it is used both for actual substrate exposure and for focus calibration through the through-the-lens method. By utilizing the same optical path for both purposes, the system avoids adding separate detection optics, thereby maintaining focus stability without significantly increasing device complexity
Solution Approach 2:
The system uses itself to perform focus calibration - the projection optical system calibrates its own focus by measuring light quantity through calibration marks positioned in its optical path. This self-calibration capability eliminates the need for external focus detection devices, maintaining precision while minimizing added complexity
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 enhances exposure accuracy and productivity by allowing continuous monitoring and adjustment of focus and alignment, minimizing downtime for recalibration and maintaining high precision without the need for frequent substrate stage movements.
Implementation Method 1
a detection system configured to detect a light quantity distribution of illumination light having passed through a first mark disposed on an object surface of the projection system, the projection system, and a second mark disposed on an image plane of the projection system
Data Source
AI summary
The control unit controls the relative position in an optical axis direction of the projection system and the relative position in a direction perpendicular to an optical axis direction at a third timing after a second timing based on a first distribution of illumination light detected by the detection system at a first timing and a second distribution of illumination light detected by the detection system at the second timing after the first timing, the illumination light detected at the first and second timings having passed through the first and second marks.