Lithography Overlay Error Correction via APC Control Strategies
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Solution Overview
Problem
Current lithography processes face challenges in achieving accurate alignment and overlay precision due to tool and reticle specific imperfections, leading to increased overlay errors and pattern placement errors, especially when using multiple lithography tools and reticles in complex manufacturing environments.
Innovation Solution
The method involves obtaining additional measurement data with increased spatial coverage for tool/reticle combinations, which are more stable over time, to modify the control algorithm and correct alignment parameter values, thereby improving overlay accuracy across the entire exposure field, even with limited feedback measurement data from dedicated overlay measurement marks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple lithography tools and reticles are used in complex manufacturing environments, then productivity is improved, but overlay accuracy and pattern placement precision deteriorate due to tool and reticle specific imperfections
Solution Approach 1:
The patent implements a feedback mechanism where overlay measurement data from previously processed substrates is fed back into the control algorithm. The system measures overlay errors at multiple positions within the exposure field, uses this measurement data to update the control algorithm, and applies the updated algorithm to subsequent substrates. This closed-loop feedback enables continuous improvement of overlay accuracy while maintaining high productivity through automated correction of tool and reticle specific imperfections.
Solution Approach 2:
The patent dynamically adjusts alignment parameter values based on measured overlay errors. The control algorithm modifies parameters such as overlay correction values, alignment offsets, and positioning corrections in response to measured deviations. By changing these parameters adaptively, the system compensates for tool and reticle specific imperfections, maintaining high overlay accuracy across multiple lithography tools and reticles used in parallel manufacturing operations.
2Loss of time
If overlay measurement data is collected from limited positions, then measurement time is reduced, but measurement precision and representation of the entire exposure field deteriorate
Solution Approach 1:
The patent employs a partial measurement strategy where overlay errors are measured at a selected number of specific positions within the exposure field rather than comprehensively across all areas. The control algorithm is designed to infer and correct errors across the entire exposure field based on this partial measurement data. This approach achieves adequate measurement precision for process control while significantly reducing measurement time and maintaining high productivity.
Solution Approach 2:
The system uses the measured overlay data from limited positions to automatically update and refine its own control algorithm. The control algorithm learns from the measurement data and improves its ability to predict and correct overlay errors across the entire exposure field. This self-improving mechanism enables the system to achieve high measurement precision through iterative refinement without requiring comprehensive measurements at every step.
3Speed
If alignment parameter values are not corrected, then process speed is maintained, but overlay errors and pattern placement errors increase
Solution Approach 1:
The patent applies preliminary corrections to alignment parameter values based on overlay measurement data from previously processed substrates. The control algorithm pre-calculates correction values and applies them before subsequent lithography operations. This preliminary action prevents overlay errors from accumulating and ensures high pattern placement precision is maintained throughout the manufacturing process without requiring slow re-measurement and re-adjustment cycles.
Data Source
Figure 1a
Figure 1b~1d
Figure 1e~1f
AI summary
By taking into consideration tool specific distortion signatures and reticle specific placement characteristics in an alignment control system the control quality of sophisticated APC strategies may significantly be enhanced. Respective correction data may be established on the basis of any combinations of tool/reticles and layers to be aligned to each other, which may modify the respective target values of alignment parameters used for controlling the alignment process on the basis of standard overlay measurement data obtained from dedicated overlay marks.