DUV Laser Wavelength Control via Pulse-by-Pulse Prism Adjustment
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Solution Overview
Problem
Current laser light sources and stepper-scanners in semiconductor photolithography face challenges in accurately generating laser light at specified wavelengths due to disturbances, which affect precision and speed, and existing feedback operations do not adequately address these issues.
Innovation Solution
A system and method for controlling laser pulse wavelength on a pulse-by-pulse basis using a change in wavelength target based on measured wafer positional error, incorporating both feed-forward and feedback operations to adjust the prism position in the laser system, ensuring stable and precise laser light generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback operations are used to address disturbances in the laser light source, then wavelength stability is improved, but response speed is limited due to the delayed nature of feedback
Solution Approach 1:
The patent applies preliminary action by using feed-forward control to predict and compensate for wafer stage position errors before they affect the laser wavelength. The controller receives wafer stage position information and proactively adjusts the laser wavelength to prevent errors, rather than waiting for feedback after the error occurs. This resolves the contradiction by providing immediate correction without the delay inherent in feedback systems.
2Manufacturing precision
If pulse-by-pulse wavelength adjustment is implemented, then manufacturing precision is improved, but device complexity increases due to real-time control requirements
Solution Approach 1:
The patent merges the feed-forward control path (using wafer stage position information) with the existing feedback control path (using wavelength error signals) into a unified controller. This combination allows pulse-by-pulse wavelength adjustment to achieve high manufacturing precision while managing device complexity by integrating multiple control functions into a single system rather than adding separate independent control mechanisms.
3Manufacturing precision
If feed-forward operation is used to compensate for wafer stage movement, then precision is improved, but measurement precision requirements increase for accurate error compensation
Solution Approach 1:
The patent uses feedback to compensate for the increased measurement precision requirements of feed-forward control. By combining feed-forward (using wafer stage position) with feedback (using actual wavelength measurements), the system can tolerate moderate measurement precision in the feed-forward path because the feedback path corrects residual errors. This resolves the contradiction by making the overall system robust to measurement precision limitations while still achieving high wavelength accuracy.
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
This approach enables continuous adjustment of laser light wavelength during a burst of pulses to compensate for wafer stage movement, improving precision and stability by combining feed-forward and feedback operations, thus addressing disturbances in both the laser system and stepper-scanner.
Implementation Method 1
a piezoelectric transducer and drive electronics
Implementation Method 2
a line narrowing module including a prism
Data Source
AI summary
Wafer positioning errors in stepper-scanners contribute to imaging defects. Changing the wavelength of the light source's generated light can compensate for wafer positional errors in the Z-direction. The wafer's real-time z-position is determined and a change in wavelength target to offset this error is communicated to the light source. The light source uses this change in wavelength target in a feed-forward operation and, in an embodiment, in combination with existing feedback operations, on a pulse-by-pulse basis for subsequent pulses in a current burst of pulses in addition to receiving the newly-specified laser wavelength target for a subsequent burst of laser pulses.