Lithographic Aberration Correction via Adaptive Averaging
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Solution Overview
Problem
Lithographic apparatuses face challenges in correcting aberrations introduced by their projection systems, which affect the accuracy of pattern transfer onto substrates, particularly due to rapid changes in aberrations following machine state changes such as illumination mode changes or interruptions.
Innovation Solution
A method that uses a sensor to measure aberrations and determines whether to average these measurements based on the history of the lithographic apparatus' operation since a machine state change, applying corrections calculated from either immediate or averaged measurements to adjust the projection system, with options to cease corrections when aberrations stabilize or a predetermined number of substrates are exposed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If aberration measurements are averaged continuously, then measurement precision is improved, but the system cannot respond quickly to rapid aberration changes after machine state changes
Solution Approach 1:
The patent applies dynamics by making the aberration correction system adaptive rather than static. The system dynamically adjusts between using individual measurements and averaged measurements based on the current operational context. Specifically, the controller monitors machine state changes and automatically switches correction strategies: using individual immediate corrections when rapid changes are detected, and using averaged corrections when stability is achieved, thereby optimizing both precision and responsiveness across different operational phases
Solution Approach 2:
The patent changes the parameter of correction data selection from fixed to variable. The system monitors parameters such as machine state stability and temporal distance since last correction, and based on these parameter values, dynamically selects whether to apply individual or averaged aberration measurements. This parameter-based decision-making allows the system to optimize correction precision while maintaining adaptability to changing conditions
2Manufacturing precision
If corrections are applied continuously, then manufacturing precision is improved, but productivity decreases due to frequent measurement and correction cycles
Solution Approach 1:
The patent implements periodic action by establishing rhythm in the correction process. Instead of continuous corrections after every single substrate, the system performs aberration measurements and corrections periodically based on monitored conditions. The controller evaluates whether corrections are needed by checking for machine state changes and time elapsed since last correction, creating a periodic correction cycle that maintains precision while avoiding unnecessary interruptions to substrate processing
Solution Approach 2:
The patent applies partial action by selectively applying corrections only when and where needed. Rather than continuously correcting after every substrate exposure, the system determines partial correction cycles based on machine state stability and operational context. This allows the system to maintain manufacturing precision during critical phases while reducing correction frequency during stable periods, thereby improving overall productivity without sacrificing necessary precision
3Adaptability or versatility
If individual aberration measurements are used immediately, then adaptability to current conditions is improved, but measurement precision decreases due to noise and variability
Solution Approach 1:
The patent applies preliminary action by preparing averaged aberration correction data in advance during stable operational periods. The system accumulates and averages multiple aberration measurements when machine state is stable, creating pre-computed correction values that are ready for immediate use when rapid corrections are needed. This preliminary preparation of correction data ensures both precision (through averaging) and adaptability (through pre-computation) without requiring real-time processing during critical correction moments
Data Source
AI summary
A method of correcting aberrations caused by a projection system of a lithographic apparatus, the method including performing a measurement of an aberration caused by the projection system using a sensor located in the lithographic apparatus, determining, based on a history of operation of the lithographic apparatus since a change of machine state, whether to average the measured aberration with one or more aberration measurements previously obtained using the sensor, calculating a correction to be applied to the lithographic apparatus using the measured aberration if it is determined that averaging should not be performed, calculating a correction to be applied to the lithographic apparatus using an averaged aberration measurement if it is determined that averaging should be performed, and applying the calculated correction to the lithographic apparatus.