Lithographic Position Control with Compliance Compensation
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Solution Overview
Problem
Conventional lithographic apparatus position control systems face challenges in maintaining accuracy and response time due to temporary deformations of the substrate support during acceleration and deceleration, leading to focus errors and overlay offsets, which are exacerbated by the need to switch between different sets of encoder heads for position measurement.
Innovation Solution
A position control system incorporating a position measurement system with redundant encoder heads, a comparator, controller, feed-forward device, and compliance compensator to provide accurate position control by compensating for internal deformations and optimizing actuator signals based on set-point and measured position signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the stiffness of the substrate support is increased to reduce deformations, then focus errors and overlay offsets are reduced, but the weight and complexity of the substrate support increase
Solution Approach 1:
The patent changes the physical state of the substrate support from rigid to flexible, allowing controlled elastic deformations. Instead of increasing stiffness, the system accepts and compensates for deformations by measuring encoder head positions and calculating equivalent rigid body motion parameters, thereby achieving accurate positioning without the weight penalty of a stiffer support structure.
2Adaptability or versatility
If encoder heads are switched between different sets during substrate support movement, then position measurement coverage is improved, but discontinuities and servo errors increase
Solution Approach 1:
The patent implements a feedback mechanism where the position measurement system continuously monitors encoder head positions and provides feedback to the control system. The controller uses this feedback to determine when switching between encoder head sets is necessary and calculates the equivalent rigid body motion parameters to maintain continuous, discontinuity-free position measurements throughout the substrate support's range of motion.
3Manufacturing precision
If level actuations are performed during expose phase to position the substrate, then orientation accuracy is improved, but temporary deformations of the substrate support occur
Solution Approach 1:
The patent applies preliminary action by measuring and recording the positions of encoder heads before and during level actuations. The control system uses these measurements to calculate the equivalent rigid body motion parameters and compensates for the temporary deformations caused by level actuations, ensuring that the substrate orientation accuracy is maintained without being adversely affected by the support's elastic deformations.
Data Source
AI summary
A position control system configured to control the position of a movable object, includes: a position measurement system configured to determine a position of a sensor or sensor target on the movable object, a comparator configured to provide an error signal by comparing a set-point position and a position feed-back signal based on the measured position, a controller to provide a control signal based on the error signal, a feed-forward device to provide a feed-forward signal on the basis of a first signal related to the desired position, and one or more actuators configured to act on the movable object based on the control signal and the feed-forward signal, wherein the position control system further includes a compliance compensation device providing a compliance compensation signal, wherein the compliance compensation signal is subtracted from a measured position of the position measurement system to obtain the feed-back position signal.