Lithographic Substrate Support Stiffness Compensation
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Solution Overview
Problem
Lithographic apparatuses face challenges in maintaining accurate positioning of substrates due to temporary deformations caused by external forces, such as those from the liquid confinement system, which can result in focus errors and overlay offsets, and increasing stiffness without compromising weight or performance is limited.
Innovation Solution
A position control system that includes a stiffness compensation model, which relates forces exerted on the substrate support to resulting position errors, allowing for real-time correction of the substrate's position during pattern projection, using a combination of position measurement systems, controllers, and actuators to account for the substrate's flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the stiffness of the substrate support is increased to reduce deformations, then positioning accuracy is improved, but weight increases and further stiffening becomes difficult
Solution Approach 1:
The patent changes the physical state of the substrate support from rigid to flexible, allowing it to deform elastically under external forces. By introducing a flexibility model that characterizes the support's deformation behavior, the system can predict and compensate for position errors caused by forces from the liquid confinement system, thereby maintaining positioning accuracy without requiring increased stiffness or weight
Solution Approach 2:
The patent implements a feedback mechanism where the flexibility model continuously predicts position errors based on measured or estimated external forces, and the control system adjusts the positioning accordingly. This closed-loop approach allows the system to compensate for deformations in real-time, achieving accurate positioning despite the flexible nature of the substrate support
2Manufacturing precision
If the stiffness of the substrate support is increased to reduce deformations, then positioning accuracy is improved, but device complexity increases
Solution Approach 1:
The patent transforms the substrate support from a rigid structure to a flexible one, fundamentally changing its mechanical parameters. The flexibility model captures the deformation characteristics, allowing the control system to compensate for position errors without requiring complex structural modifications or additional stiffening mechanisms
Solution Approach 2:
The patent replaces mechanical stiffening solutions with a computational approach. Instead of adding more mechanical elements to increase stiffness, the system uses a flexibility model and control algorithms to predict and compensate for deformations, substituting mechanical complexity with computational compensation
3Manufacturing precision
If level actuations are performed to position the substrate surface correctly, then orientation accuracy is improved, but temporary deformations occur causing focus errors and overlay offset
Solution Approach 1:
The patent applies preliminary action by predicting the position errors caused by level actuations before they occur. The flexibility model is used to calculate the expected deformations from the actuation forces, and the control system pre-compensates for these errors by adjusting the positioning, thereby preventing focus errors and overlay offset before they manifest
Solution Approach 2:
The patent applies preliminary anti-action by introducing counteracting adjustments based on the flexibility model. The system predicts the deformations that will result from level actuations and applies compensating forces or position adjustments in advance, effectively canceling out the harmful effects before they occur
Data Source
AI summary
A position control system for a substrate support of a lithographic apparatus includes a position measurement system configured to determine a position of a sensor or sensor target on the substrate support, a controller configured to provide a control signal based on a desired position of a target portion of the substrate and the determined position, and one or more actuators configured to act on the substrate support. The position control system includes a stiffness compensation model of the substrate support, the stiffness compensation model including a relation between a difference in a change in position of the target portion and a change in position of the sensor or sensor target as a result of a force exerted on the substrate support. The position control system is configured to substantially correct at least during projection of a patterned radiation beam on the target portion, the position of the target portion using the stiffness compensation model.