Lithographic Support Structure Control via Coordinate Conversion
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Solution Overview
Problem
In lithographic apparatuses, achieving precise positioning of substrates and masks with sub-nanometer accuracy is challenging due to vibrations caused by increased accelerations and decelerations, leading to instability in alignment and overlay errors.
Innovation Solution
A control system comprising a first measurement system, a second measurement system, and a controller that measures and converts positions between coordinate systems, using a position error signal to dampen relative movements and improve alignment accuracy by adjusting the support structure's position based on the error signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If increased accelerations and decelerations are used to maintain productivity, then throughput is improved, but vibrations increase causing alignment instability and overlay errors
Solution Approach 1:
The system uses measurement systems to detect the actual positions of the support structure and object, converts these measurements between coordinate systems, and feeds back position error signals to actuators that adjust the support structure position, thereby maintaining alignment stability during high-speed operations
Solution Approach 2:
The patent replaces purely mechanical positioning systems with a hybrid system that uses optical or electromagnetic measurement systems and electronic control to achieve precise positioning, allowing high-speed movement without mechanical vibration-induced errors
2Manufacturing precision
If sub-nanometer positioning accuracy is achieved through fine positioning module, then manufacturing precision is improved, but device complexity increases due to cascaded coarse and fine positioning modules
Solution Approach 1:
The measurement system performs multiple functions: it measures positions in different coordinate systems, provides feedback for positioning control, and enables coordinate transformation, thereby reducing the need for separate dedicated systems for each function
Solution Approach 2:
The controller acts as an intermediary that receives measurements from the measurement system, performs coordinate system conversions using the presumed position information, and generates control signals for actuators, simplifying the overall control architecture
3Ease of manufacture
If optical encoders are used for coarse positioning, then ease of manufacture is improved, but measurement precision is insufficient for sub-nanometer accuracy requirements
Solution Approach 1:
The positioning measurement function is segmented into two parts: the measurement system provides high-precision measurements, while the presumed position information provides the transformation context, with each part optimized for its specific function
Solution Approach 2:
The system adds the dimension of coordinate system transformation by maintaining presumed position information that maps between different reference frames, enabling the same measurement data to serve multiple positioning requirements with different precision levels
Data Source
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AI summary
A control system is provided for controlling a support structure in a lithographic apparatus. The control system includes a first measurement system arranged to measure the position of a substrate supported by the support structure, the position being measured in a first coordinate system. The control system further includes a second measurement system for measuring the position of the support structure in a second coordinate system, the first measurement system having a presumed position in the second coordinate system. The control system further comprises a controller configured to control the position of the support structure based on measurements by the second measurement system, to convert the measured position of the substrate into a converted position of the support structure in the second coordinate system, to position the support structure based on the converted position, to receive a position error signal indicative of a difference between the presumed position and an actual position of the first measurement system in the second coordinate system, and to position the support structure in a manner dependent upon the position error signal.