Lithographic Controller Transfer Function Switching
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Solution Overview
Problem
Conventional lithographic apparatus controllers face a compromise between achieving fast response and maximizing disturbance rejection, with optimizing for one often deteriorating the other.
Innovation Solution
A controller with a selector that chooses between two distinct transfer functions based on the state of the movable part, allowing for optimal disturbance rejection in stationary states and fast response in non-stationary states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the controller is optimized for high disturbance rejection, then disturbance rejection is maximized, but the response speed deteriorates
Solution Approach 1:
The controller dynamically switches between two different transfer functions based on the operational state of the movable part. During stationary states, the first transfer function is applied for optimal disturbance rejection. During non-stationary states (movement, acceleration, deceleration), the second transfer function is applied for faster response. This dynamic adaptation resolves the contradiction by allowing the controller to optimize for disturbance rejection when needed while prioritizing response speed during movement phases.
2Loss of time
If the controller is dimensioned for high speed response, then settling time is reduced, but disturbance rejection becomes marginal
Solution Approach 1:
The controller employs two distinct transfer functions with different characteristics. The first transfer function is optimized for disturbance rejection during stationary periods, while the second transfer function is optimized for fast response and reduced settling time during movement. The selector dynamically switches between these functions based on whether the movable part is in a stationary or non-stationary state, thereby achieving both fast settling time and adequate disturbance rejection at different operational phases.
3Device complexity
If a single controller transfer function is used, then device complexity is reduced, but the controller cannot optimize for both disturbance rejection and response speed simultaneously
Solution Approach 1:
The controller is segmented into two distinct transfer functions, each optimized for specific operational conditions. The first transfer function handles stationary states with optimal disturbance rejection parameters, while the second transfer function handles non-stationary states with optimized response speed parameters. This segmentation allows the controller to achieve superior overall performance compared to a single transfer function, while the added complexity is justified by the significant improvement in adaptability and control precision.
Data Source
AI summary
A lithographic apparatus includes a movable part and a controller to control a position quantity of the movable part. The controller includes a first controller transfer function and a second controller transfer function. A selector selects the first controller transfer function or the second controller transfer function depending on a state of the movable part. The first controller transfer function may be chosen in a substantially stationary state of the movable part, while in a substantially non-stationary state of the movable part, the second controller transfer function may be chosen.