Lithographic Encoder Compensation for Thermal Deformation
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Solution Overview
Problem
Conventional measurement systems in lithographic apparatuses face accuracy issues due to disturbances caused by movements and deformations of the substrate stage, which are exacerbated by the flexibility introduced by flexure elements in the mounting device, leading to reduced measurement precision.
Innovation Solution
An encoder-type measurement system with a compensation device that partially compensates for movements and deformations of the sensor target object with respect to the stationary frame, using a damping device and feedback position control system to maintain measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flexure elements are used in the mounting device to compensate for shape changes of the metro-frame, then the measurement system can accommodate thermal deformations, but the flexibility introduced reduces measurement precision
Solution Approach 1:
The patent extracts the harmful flexibility from the mounting device by replacing flexure elements with a rigid mounting structure. The compensation function is separated into a dedicated active compensation device that uses sensors and actuators to counteract deformations, rather than relying on passive flexure elements that inherently reduce precision.
Solution Approach 2:
The patent implements a feedback-based active compensation system where sensors detect the actual position and deformations of the sensor target object, and actuators apply corrective forces to counteract these deformations. This closed-loop feedback mechanism maintains measurement precision while compensating for thermal and mechanical disturbances.
2Measurement precision
If the sensor target object is rigidly mounted to the stationary frame, then measurement precision is maximized, but the system cannot compensate for movements and deformations of the stationary frame
Solution Approach 1:
The patent introduces an active compensation device as an intermediary between the stationary frame and the sensor target object. This compensation device includes sensors that detect frame movements and actuators that apply corrective forces, serving as a mediator that maintains the rigid connection while actively counteracting frame deformations.
Solution Approach 2:
The patent dynamically changes the physical state and positioning parameters of the sensor target object using active actuators. By adjusting position, orientation, and shape parameters in real-time based on sensor feedback, the system maintains measurement precision even when the stationary frame undergoes thermal or mechanical deformations.
3Measurement precision
If the grid plate is made more rigid to reduce deformations, then measurement accuracy improves, but the mounting device becomes more sensitive to disturbances from substrate stage movements
Solution Approach 1:
The patent applies preliminary anti-action by using sensors to detect disturbances from substrate stage movements before they significantly affect measurements, and actuators to apply counteracting forces to the sensor target object. This proactive compensation prevents disturbances from degrading measurement accuracy.
Solution Approach 2:
The patent employs composite structural approaches where the mounting device combines rigid components for stable mounting with active compensation mechanisms. The sensor target object itself may use composite materials or structures that provide both rigidity for precision and controlled flexibility for disturbance isolation.
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
The system effectively suppresses displacements and deformations, particularly in resonance frequencies, thereby enhancing the measurement accuracy and reducing the impact of external disturbances on the measurement system.
Implementation Method 1
The measurement system includes a damping device configured to damp vibrations of the sensor target object with respect to the stationary frame, in particular at resonance frequencies
Implementation Method 2
The measurement system includes a feedback position control system configured to suppress position dependent signal deviations caused by movements and/or deformations of the sensor target object with respect to the stationary frame
Data Source
AI summary
An encoder-type measurement system is configured to measure a position dependent signal of a movable object, the measurement system including at least one sensor mountable on the movable object a sensor target object mountable on a substantially stationary frame, and a mounting device configured to mount the sensor target object on the substantially stationary frame. The measurement system further includes a compensation device configured to compensate movements and/or deformations of the sensor target object with respect to the substantially stationary frame. The compensation device may include a passive or an active damping device and/or a feedback position control system. In an alternative embodiment, the compensation device includes a gripping device which fixes the position of the sensor target object during a high accuracy movement of the movable object.