Laser Firing Timing Control for Lithography Bandwidth Stability
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Solution Overview
Problem
Laser systems used in semiconductor photolithography face challenges with bandwidth resonance issues when switching between different repetition rates, leading to transient disturbances that can drive bandwidth metrics out of specification, and existing fast bandwidth actuators have limited range and can saturate, making it difficult to maintain control.
Innovation Solution
A feedforward model is implemented using a lookup table of MOPA timing values correlated with repetition rates, allowing for pre-calibrated adjustments to prevent transients and maintain bandwidth control, and active spectral control is used to adjust bandwidth offsets based on actual MOPA timing and user-defined firing patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fast bandwidth actuator is used to control bandwidth disturbances, then bandwidth control is improved, but the actuator can saturate when switching between repetition rates, reducing control effectiveness
Solution Approach 1:
The patent applies preliminary action by implementing a feedforward control mechanism that anticipates bandwidth disturbances caused by repetition rate changes. The system pre-calculates the required MOPA timing adjustments based on the target repetition rate and applies these adjustments before the actual rate change occurs. This prevents the fast bandwidth actuator from needing to respond to large transients, avoiding saturation and maintaining control effectiveness across different repetition rates.
2Manufacturing precision
If MOPA timing is adjusted to compensate for bandwidth offsets, then bandwidth metrics are maintained, but the actuator range is limited and can saturate at extreme offsets
Solution Approach 1:
The patent applies dynamics by making the MOPA timing adjustment dynamic and adaptive rather than fixed. The system continuously monitors the actual bandwidth metrics and repetition rate, and dynamically adjusts the MOPA timing within its available range. When approaching saturation limits, the system adapts by modifying the feedforward parameters or using alternative control strategies, allowing the actuator to operate effectively across a wider range of conditions without physical saturation.
3Measurement precision
If feedback control is used to respond to bandwidth disturbances, then control accuracy is improved, but response time is delayed until after disturbance occurs
Solution Approach 1:
The patent implements feedback control by continuously monitoring the actual bandwidth metrics and repetition rate, and using this information to adjust the MOPA timing. The feedback mechanism provides real-time correction to compensate for any deviations from the desired bandwidth, ensuring high control accuracy. The system combines this feedback with feedforward prediction to minimize response delay, creating a hybrid control approach that leverages both the accuracy of feedback and the responsiveness of feedforward control.
Data Source
AI summary
Methods and apparatus for controlling laser firing timing and hence bandwidth in a laser capable of operating at any one of multiple repetition rates.