Dynamic Wavefront Control for Frequency Converted Laser Systems
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Solution Overview
Problem
Current frequency converted light sources for semiconductor and photomask inspection systems lack stability and efficiency, particularly in maintaining a consistent wavefront over time due to degradation in optics and nonlinear crystals, which affects the performance and lifespan of deep ultraviolet (DUV) lasers.
Innovation Solution
A laser system incorporating a beam sampling device, diagnostics system, and correction system that samples a portion of the emitted light, measures current wavefront parameters, and provides real-time corrections to maintain a desired wavefront state, using techniques such as moving or adjusting optical elements, changing their temperature, and altering their shape to compensate for degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If frequency conversion is used to generate DUV light, then the laser can operate at higher powers and longer wavelengths, but the wavefront stability degrades over time due to optical element degradation
Solution Approach 1:
The patent implements a feedback control system that continuously monitors wavefront parameters using a beam diagnostics system and automatically adjusts optical elements (lens, mirror, or spatial light modulator) to compensate for wavefront degradation. The system measures current wavefront state, compares it to desired state, and applies corrections through actuators to maintain stable wavefront quality over time despite optical element degradation.
Solution Approach 2:
The patent introduces dynamic adjustability to the optical system by incorporating movable or reconfigurable optical elements (lens, mirror, or spatial light modulator) that can be real-time adjusted based on measured wavefront conditions. This dynamic capability allows the system to adapt to changing optical conditions and maintain optimal wavefront performance throughout the laser's operational life.
2Temperature
If optical elements are used for frequency conversion, then the laser can generate the required wavelength, but the optics and nonlinear crystals degrade over time affecting performance
Solution Approach 1:
The patent applies preliminary correction by proactively monitoring wavefront parameters and applying compensatory adjustments before significant performance degradation occurs. The system continuously measures wavefront quality and applies corrections to optical elements to prevent degradation from affecting inspection system performance, thereby extending the effective operational lifespan of the laser system.
Solution Approach 2:
The feedback control system continuously monitors the impact of optical element degradation on wavefront quality and automatically adjusts optical parameters to compensate for aging effects. This closed-loop control maintains inspection system performance despite the gradual degradation of frequency conversion optics and nonlinear crystals over time.
3Measurement precision
If a beam sampling device is introduced to monitor wavefront, then wavefront control is enabled, but the system complexity increases
Solution Approach 1:
The patent extracts a small portion of the laser beam using a beam sampling device (such as a partially transmitting mirror or holographic beam sampler) to create a measurement copy that can be analyzed by the diagnostics system without significantly impacting the main beam quality or intensity. This extraction approach enables wavefront monitoring while minimizing interference with the primary laser function.
Solution Approach 2:
The patent introduces an intermediary measurement system that indirectly monitors wavefront parameters by analyzing a sampled portion of the beam. The beam diagnostics system acts as an intermediary that measures wavefront properties (such as M-squared ratio or wavefront curvature) without requiring direct interference with the main laser path, thereby enabling monitoring while maintaining system functionality.
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 system ensures stable and long-lasting wavefront output with minimal impact on photocontamination, enhancing the performance and lifespan of frequency converted lasers by continuously monitoring and correcting wavefront changes, thereby improving the throughput and resolution of inspection systems.
Implementation Method 1
The beam sampling device may be a substrate having a first surface, which may be a partially (low) reflecting, light sampling surface
Implementation Method 2
The angle of incidence for the low transmitting mirror may be less than twenty degrees
Implementation Method 3
the beam diagnostics system being configured for receiving the sampled portion of the emitted light and measuring a current state of a wavefront parameter of the sampled portion of the emitted light
Implementation Method 4
the beam correction system including at least one of: a lens or a mirror element, the beam correction system being configured for: obtaining the measured state from the beam diagnostics system; comparing the measured state of the wavefront parameter against a desired state
Implementation Method 5
the lens or mirror element may be moved from a first position to a second position when the correction is provided for obtaining a desired wavefront
Data Source
AI summary
The present invention is directed to a laser system in which a current laser wavefront performance of the laser system may be monitored. Further, the laser system embodiments disclosed herein may be configured for correcting the laser wavefront internally via correction system(s) within the laser system. Still further, the correction system(s) disclosed herein may provide a long lifetime of performance and may be configured for having a minimal impact on photocontamination.