Drive System Resonance Control Using Dual Interferometer Feedback
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Solution Overview
Problem
The increasing size of substrates in lithography processes leads to resonance issues in substrate stages, compromising the accurate and stable control required for high overlay accuracy in electronic device manufacturing, particularly due to low resonance frequencies and the trade-off between bandwidth and robustness in existing control systems.
Innovation Solution
A driving system and method that employs a single-input two-output feedback control system, utilizing two interferometers to measure and synthesize position data from both the plate table and carriage, allowing for robust control by canceling out resonance modes and maintaining high bandwidth, thereby stabilizing the plate stage movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the substrate stage size is increased to accommodate larger substrates, then the exposure area is improved, but resonance frequency decreases causing control instability
Solution Approach 1:
The substrate stage is divided into two independent measurement sections: the carriage section and the plate table section. Each section is measured by a separate interferometer, allowing independent measurement and control of each segment's position and vibration characteristics. This segmentation enables the control system to address resonance issues in each section separately while maintaining overall system stability.
Solution Approach 2:
The patent implements a feedback control system that uses measurement results from both interferometers to generate control inputs. The control system continuously monitors the positions of the carriage and plate table, compares them with target positions, and adjusts the drive mechanism to eliminate deviations. This feedback mechanism compensates for resonance-induced position errors and maintains control stability despite the large stage size.
2Device complexity
If a single-input single-output control system is used, then the control structure is simple, but bandwidth and robustness are limited due to resonance
Solution Approach 1:
The control system transitions from a single-input single-output structure to a single-input two-output structure. The single control input (drive mechanism command) now controls two independent output measurements (carriage position and plate table position). This dimensional expansion allows the system to account for resonance effects in both sections simultaneously while maintaining a relatively simple single-input control architecture.
Solution Approach 2:
The patent changes the control parameters by using measurement results from two different interferometers positioned at different locations on the substrate stage. By incorporating position data from both the carriage section and the plate table section, the control system gains more information about the system's dynamic behavior, enabling it to compensate for resonance effects and achieve higher overlay accuracy.
3Measurement precision
If two interferometers are used to measure both carriage and plate table positions, then measurement precision is improved, but device complexity increases
Solution Approach 1:
Both interferometers serve multiple functions: they measure the absolute positions of their respective sections (carriage and plate table) relative to the reference coordinate system, and they provide data for the feedback control system. This multi-functionality justifies the addition of the second interferometer, as each device contributes to both measurement accuracy and control stability.
Solution Approach 2:
The patent introduces a reference coordinate system as an intermediary framework that both interferometers reference. This common reference allows the measurement data from the two interferometers to be integrated and processed together in the control system, simplifying the coordination between the two measurement devices and reducing the complexity of data fusion.
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 enables precise and stable driving of the substrate stage, enhancing exposure accuracy and overlay precision by eliminating resonance-related instability and maintaining high bandwidth control.
Implementation Method 1
utilizing two interferometers to measure and synthesize position data
Data Source
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AI summary
A synthetic controlled variable (Xmix=F1 (Xc)+F2 (X2, X1)) is obtained by obtaining a synthetic quantity (Xc=αX2+βX1) using measurement results (X2, X1) of a first and a second measuring instruments and corresponding gains (or transfer function) (α, β) and synthesizing the synthetic quantity (Xc) and one of the measurement results (X2, X1) of the first and the second measuring instruments, respectively, via a high pass filter (F1) and a low pass filter (F2). A feedback control system is structured that obtains a control input (U) using a synthetic controlled variable (Xmix) and a desired value (R), and gives a plant the control input (U). This makes adding of a high pass filter for removing offset of installation position of the first and the second measuring instruments no longer necessary, and allows a driving system which controls robust driving in a high bandwidth of a plate stage (PST) regardless of bandwidth in which resonance appears to be designed.