Linear Motor Feedforward Control for Lithography Vibration
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Solution Overview
Problem
Lithographic apparatuses face challenges in achieving high speed and acceleration while minimizing vibrations, which are exacerbated by dual stroke stages as production capacity and alignment/focus performance demands increase.
Innovation Solution
A linear motor design with a stationary part comprising multiple phase coil assemblies and a movable part with permanent magnets, incorporating a feedforward device to compensate for unbalanced back electromotive forces and edge effects, along with a system identification method to optimize feedforward parameters, is implemented to reduce vibrations and enhance positioning accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the speed and acceleration of the substrate support and patterning device support are increased to increase production capacity, then productivity is improved, but vibrations generated by the dual stroke stage increase which deteriorates manufacturing precision
Solution Approach 1:
The feedforward device pre-calculates and applies compensation signals based on the commanded motion trajectory before vibrations occur. By anticipating the unbalanced back electromotive forces that will arise during acceleration and deceleration, the system proactively counteracts these forces, preventing vibrations rather than reacting to them after they occur.
Solution Approach 2:
The system uses feedback from position measurements to adjust the feedforward compensation parameters. The feedforward device is configured to provide compensation signals based on the commanded motion, and this compensation is continuously refined using feedback information about actual position and vibration characteristics, creating a closed-loop system that improves precision while maintaining high speed.
2Length of moving object
If a long stroke linear motor is used to move the long stroke stage over a large movement range with low accuracy, then the movement range is improved, but positioning precision deteriorates
Solution Approach 1:
The positioning system is segmented into two independent stages: a long stroke stage for coarse positioning over large ranges and a short stroke stage for fine positioning with high precision. The feedforward device applies different compensation strategies to each stage based on their respective characteristics, allowing the long stroke stage to operate over large ranges while the short stroke stage provides the necessary positioning accuracy.
3Measurement precision
If a short stroke stage is used to position accurately over a small movement range, then positioning precision is improved, but the movement range is limited
Solution Approach 1:
The short stroke stage is nested on top of the long stroke stage, with the short stroke stage positioned on the long stroke stage. This nested configuration allows the short stroke stage to provide high-precision positioning within its limited range while the long stroke stage provides the extended movement range, effectively combining both capabilities in a compact structure.
4Power
If coil assemblies are only partly aligned with permanent magnets to generate driving force, then the motor can operate, but unbalanced back electromotive forces are generated causing vibrations
Solution Approach 1:
The feedforward device takes the harmful unbalanced back electromotive forces and converts them into a beneficial compensation signal. By calculating the expected unbalanced back EMF based on the commanded motion and coil-magnet alignment, the system generates a compensating signal that cancels out the harmful vibrations, turning the problem of partial alignment into an opportunity for active vibration control.
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 solution allows for high-speed and high-acceleration operations with significantly reduced vibrations, improving the focus and alignment of the patterned radiation beam on the substrate, thus increasing production capacity and performance in lithographic processes.
Implementation Method 1
the coil assemblies are arranged to interact with permanent magnets aligned with the coil assemblies to generate a driving force
Implementation Method 2
the feedforward device is configured to provide a current amplifier feedforward signal on the basis of the set-point signal, or a derivative thereof, wherein the current amplifier feedforward signal is provided to the at least one current amplifier to compensate for unbalanced back electromotive forces
Data Source
AI summary
The invention relates to a motor (LD) comprising: a stationary part (STP), comprising: a row of coil assemblies (UCA,LCA), the coil assemblies having multiple phases, a movable part (MP), comprising: a row of permanent magnets (UPM,LPM), wherein the row of coil assemblies has a first length and the row of permanent magnets has a second length, wherein the second length is smaller than the first length, wherein the coil assemblies are arranged to interact with permanent magnets aligned with the coil assemblies to generate a driving force, a comparator to compare a position measurement signal representative for an actual position of the movable part with a set-point signal representative for a desired position of the movable part to provide an error signal; a motion feedback controller configured to provide a control signal on the basis of the error signal; at least one current amplifier configured to provide an actuation signal to the coil assemblies on the basis of the control signal, wherein the motor comprises a feedforward device, wherein the feedforward device is configured to provide a current amplifier feedforward signal on the basis of the set-point signal, or a derivative thereof, wherein the current amplifier feedforward signal is provided to the at least one current amplifier to compensate for unbalanced back electromotive forces on one or more of the coil assemblies due to the one or more coil assemblies being only partly aligned with the permanent magnets.