Optical Actuator Control for Repetition-Rate Wavelength Errors
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Solution Overview
Problem
Current radiation systems in lithographic apparatuses face challenges in accurately controlling wavelength on a pulse-to-pulse basis due to deviations in pulse repetition rates, leading to errors in wavelength stability, which is critical for achieving precise feature sizes in advanced semiconductor manufacturing, especially in 3D NAND lithography where depth of focus and uniformity are paramount.
Innovation Solution
A radiation system that includes an optical element and an actuator controlled by a signal adjusted based on pulse information, specifically using a correction factor to account for differences between reference and operational pulse repetition rates, thereby minimizing wavelength errors by modifying the control signal's magnitude rather than phase to maintain synchronization with the actuator's dynamics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the control signal phase is adjusted to compensate for repetition rate deviation, then wavelength accuracy is improved, but system complexity and potential for transient oscillation increase
Solution Approach 1:
The patent changes the control parameter from phase adjustment to magnitude adjustment. The feed-forward compensator modifies the magnitude of the control signal based on the repetition rate deviation, avoiding the complexity and instability issues associated with phase adjustment while achieving the same wavelength compensation goal
Solution Approach 2:
The patent implements a feed-forward compensation mechanism that uses the known repetition rate deviation to pre-adjust the control signal magnitude. This feedback-based approach compensates for wavelength errors before they occur, improving wavelength accuracy without requiring complex real-time phase detection and adjustment systems
2Stability of the object's composition
If wavelength control is maintained during repetition rate changes, then wavelength stability is improved, but pulse synchronization accuracy deteriorates
Solution Approach 1:
The patent applies preliminary action by calculating and applying the magnitude adjustment to the control signal before the repetition rate deviation affects wavelength. The compensator uses the known deviation to pre-adjust the control signal, maintaining both wavelength stability and pulse synchronization without the trade-off
3Measurement precision
If settling time is increased to allow wavelength stabilization, then wavelength accuracy is improved, but productivity decreases
Solution Approach 1:
The patent eliminates the need for settling time by applying preliminary compensation through magnitude adjustment. The feed-forward compensator prepares the control signal in advance based on the repetition rate deviation, allowing immediate accurate wavelength control without requiring extended settling periods, thus maintaining high pulse rates
Solution Approach 2:
The patent skips the traditional settling phase by using feed-forward compensation. The magnitude-adjusted control signal immediately compensates for repetition rate deviations, allowing the system to rush through what would normally be a settling period and achieve accurate wavelength control at the full pulse rate
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.