Lithographic Substrate Table Actuator Control for Positioning Accuracy
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Solution Overview
Problem
Current lithographic apparatuses face challenges in maintaining accurate dynamic positioning of substrates during scanning exposures, leading to increased overlay and focus errors as feature sizes decrease and substrate sizes increase, making it difficult to manage compliant dynamics effectively.
Innovation Solution
The implementation of a lithographic apparatus with a substrate table having compliant dynamics, equipped with over-determined actuators and sensors, utilizing a transformation matrix to generate controller output signals that do not excite or observe the compliant dynamics in at least one degree of freedom, thereby improving positioning accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If scanning mode is used to maximize exposable field size and throughput, then productivity is improved, but positioning accuracy deteriorates due to dynamic positioning errors
Solution Approach 1:
The patent applies dynamics by making the substrate table actively controllable with multiple actuators that can dynamically adjust positioning during scanning. The table transitions from a static support to an active platform with compliant dynamics that can be controlled in real-time to maintain positioning accuracy while moving at high speeds
Solution Approach 2:
The patent changes the mechanical parameters of the substrate table by introducing compliant dynamics through multiple actuators. The system modifies the stiffness and mass distribution parameters to create a controllable flexible structure that can maintain precision during dynamic scanning operations
2Productivity
If substrate size is increased to accommodate more target portions, then productivity is improved, but positioning control difficulty increases
Solution Approach 1:
The patent segments the positioning control into multiple independent actuator systems, each controlling specific degrees of freedom. This segmentation allows the large substrate table to be controlled through distributed actuation points rather than requiring monolithic control of the entire structure
Solution Approach 2:
The substrate table is designed with multi-functionality by incorporating multiple actuators that can perform different positioning functions simultaneously. The same table structure handles both large-scale substrate support and fine-positioning adjustments through its compliant dynamics
3Manufacturing precision
If over-determined actuators are used to improve positioning accuracy, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent implements feedback control by using the compliant dynamics model to continuously adjust actuator commands based on desired positioning. The feedback mechanism uses the known dynamic characteristics to predict and correct positioning errors in real-time, reducing the need for excessive actuator complexity
4Manufacturing precision
If compliant dynamics are managed to reduce overlay errors, then manufacturing precision is improved, but control system complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-characterizing the compliant dynamics of the substrate table before operation. The dynamic model is established in advance and used to generate compensating control signals, allowing the system to proactively counteract positioning errors rather than reacting to them after they occur
Data Source
AI summary
A lithographic apparatus includes a driven object having compliant dynamics; a plurality of actuators configured to act on the driven object, wherein the plurality of actuators are over-determined in an actuator degree of freedom; a control system including a transformation matrix configured to generate controller output signals for each of the plurality of actuators in response to a setpoint, wherein the transformation matrix is configured such that the controller output signals do not excite the compliant dynamics of the driven object in at least one degree of freedom.