APC Control Strategies for Lithography Overlay Error Reduction
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Solution Overview
Problem
In microstructure fabrication, particularly for integrated circuits, existing lithography processes face challenges in achieving precise alignment and pattern placement accuracy due to tool and reticle imperfections, leading to overlay errors and pattern placement errors, which are exacerbated by limited measurement data coverage and reliance on corner overlay marks.
Innovation Solution
The approach involves generating measurement data with high spatial coverage for lithography tool and reticle combinations to estimate complex interactions, allowing for improved overlay error reduction by encoding tool-specific and reticle-specific characteristics into the measurement data, enabling more accurate alignment control across multiple substrates without complicating the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If measurement data is obtained from only a few positions (e.g., corner overlay marks) to simplify the measurement process, then the measurement process is faster and easier, but the overlay accuracy and representation of the entire exposure field deteriorates
Solution Approach 1:
The system performs preliminary characterization of the exposure field by obtaining measurement data from multiple positions across the entire exposure field before actual production. This pre-acquired data is stored and used to create correction maps that compensate for systematic errors, allowing fast corner-mark-based measurements during production to be corrected with high-precision full-field data, thus resolving the contradiction between speed and accuracy
Solution Approach 2:
The patent introduces an intermediary correction mechanism where full-field measurement data acts as a mediator between the simple corner mark measurements and the actual overlay accuracy. The correction data, acquired comprehensively across the exposure field, mediates the relationship between fast but inaccurate corner measurements and the need for high precision, allowing the system to use simple measurements while achieving accurate results through correction
2Measurement precision
If overlay measurement is performed at multiple positions across the exposure field to improve accuracy, then overlay accuracy improves, but the measurement process becomes more complex and time-consuming
Solution Approach 1:
The measurement process is segmented into two distinct phases: a characterization phase where comprehensive multi-position measurements are performed to build correction models, and a production phase where only simple corner mark measurements are performed. This segmentation allows the complex full-field measurements to be performed only once during setup, while production measurements remain simple and fast, resolving the contradiction between accuracy and complexity
Solution Approach 2:
The system performs the complex multi-position measurements in advance during a characterization phase, before actual production begins. The results are stored as correction data that can be applied during production without requiring repeated complex measurements. This preliminary action eliminates the need for complex measurements during production while maintaining high accuracy
3Ease of operation
If corner overlay marks are used for overlay measurement to simplify the process, then the measurement process is simpler and faster, but the overlay error control within the exposure field deteriorates
Solution Approach 1:
The patent uses full-field correction data as an intermediary that bridges the gap between simple corner mark measurements and accurate overlay control. The corner marks provide easy measurements, while the correction data (acquired through comprehensive full-field characterization) mediates to achieve accurate overlay control throughout the exposure field, resolving the contradiction between ease of operation and manufacturing precision
Solution Approach 2:
The system implements a feedback mechanism where comprehensive full-field measurement data is used to create correction models that feed back into the overlay measurement process. This feedback allows the simple corner mark measurements to be corrected based on patterns observed in full-field data, maintaining ease of operation while improving manufacturing precision through the feedback correction
Data Source
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 be significantly 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.