Radiation Pulse Control for Repetition-Rate Wavelength Compensation
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Solution Overview
Problem
Existing radiation systems struggle to accurately control wavelength changes on a pulse-to-pulse basis, leading to errors and reduced accuracy in lithographic processes, particularly in 3D NAND lithography, due to the challenges of rapid wavelength transitions and the limitations of current feedback and feed-forward compensators.
Innovation Solution
A radiation system with an optical element and actuator controlled by a controller that adjusts the control signal based on pulse repetition rate information, using a correction factor to minimize wavelength errors by altering the magnitude of the control signal, thereby improving synchronization and reducing transient oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If feedback and feed-forward compensators are used to control wavelength, then wavelength stability is improved, but the system cannot achieve rapid pulse-to-pulse wavelength changes due to settling time requirements
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal control signals for different wavelength set points in a lookup table before operation. When a wavelength change is commanded, the system retrieves the pre-computed control signal immediately without requiring settling time, enabling pulse-to-pulse wavelength changes while maintaining stability through the pre-optimized control parameters.
Solution Approach 2:
The system transitions from static feedback compensators to a dynamic lookup table approach where control parameters are selected based on real-time wavelength commands. This allows the system to adapt rapidly to changing wavelength requirements by switching between pre-optimized control signals, achieving both stability and speed.
2Reliability
If wavelength control systems use traditional feedback compensators, then transient disturbances are rejected, but pulse-to-pulse wavelength tracking performance is insufficient due to 100 ms settling time
Solution Approach 1:
The lookup table stores pre-calculated control signals that account for transient disturbance characteristics. When a wavelength change is commanded, the appropriate pre-computed signal is retrieved immediately, providing both transient disturbance rejection and accurate pulse-to-pulse wavelength tracking without the 100 ms settling time limitation of traditional feedback compensators.
Solution Approach 2:
The patent replaces the mechanical feedback compensator system with a computational lookup table approach. This substitution eliminates the inherent settling time limitation of analog feedback systems by using pre-computed digital control signals that can be retrieved and applied instantaneously, achieving both reliability and manufacturing precision.
3Stability of the object's composition
If multiple exposure passes are made with different wavelengths for 3D NAND lithography, then depth of focus is improved, but wavelength control accuracy deteriorates due to repetition rate deviations
Solution Approach 1:
The system dynamically changes control parameters based on the commanded wavelength set point. The lookup table stores control signals optimized for different wavelength values and pulse repetition rates. When operating at different wavelengths for multi-pass 3D NAND lithography, the system retrieves the appropriate pre-optimized control signal, maintaining wavelength control accuracy despite repetition rate deviations that would otherwise degrade precision.
4Manufacturing precision
If the control signal magnitude is adjusted to account for repetition rate deviations, then wavelength error is reduced, but system complexity increases
Solution Approach 1:
Instead of implementing complex real-time calculations to adjust control signal magnitude for repetition rate deviations, the system uses preliminary action by pre-calculating these adjustments and storing them in a lookup table. The controller simply retrieves the appropriate pre-computed control signal based on the commanded wavelength and repetition rate, reducing wavelength error while avoiding the complexity of real-time adjustment mechanisms.
Data Source
AI summary
A radiation system for controlling pulses of radiation comprising an optical element configured to interact with the pulses of radiation to control a characteristic of the pulses of radiation, an actuator configured to actuate the optical element according to a control signal received from a controller, the control signal at least partially depending on a reference pulse repetition rate of the radiation system and, a processor configured to receive pulse information from the controller and use the pulse information to determine an adjustment to the control signal. The radiation system may be used to improve an accuracy of a lithographic apparatus operating in a multi-focal imaging mode.