Lithography Mark Detection for Overlay Accuracy
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Solution Overview
Problem
Current lithography systems face challenges in achieving high overlay accuracy due to distortion in the arrangement of shot areas on wafers caused by processing steps like resist coating, development, etching, and CMP, making it difficult to detect a sufficient number of marks without reducing throughput.
Innovation Solution
A measurement device that includes a base member, a movable stage, a drive system, and position measurement systems to accurately measure and correct the position of multiple marks on a substrate, integrated with an exposure apparatus to enhance alignment precision and correct nonlinear distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of sample shot areas is increased to improve overlay accuracy, then measurement precision is improved, but productivity is reduced due to longer detection time
Solution Approach 1:
The patent divides the wafer surface into multiple shot areas and further segments the detection process by selecting specific sample shot areas for detailed mark detection. This segmentation allows the system to measure marks in a distributed manner across different regions, improving overlay accuracy through multiple measurement points while maintaining throughput by not requiring exhaustive detection of every shot area.
Solution Approach 2:
The patent implements partial action by detecting marks in only a selected subset of shot areas (sample shot areas) rather than all shot areas on the wafer. This partial detection approach provides sufficient statistical data for accurate overlay measurement and grid correction while significantly reducing the total detection time compared to exhaustive measurement, thus balancing precision and productivity.
2Manufacturing precision
If grid correction function is applied to correct nonlinear components of shot arrangement, then manufacturing precision is improved, but device complexity is increased
Solution Approach 1:
The patent implements a feedback mechanism where mark position detection results from sample shot areas are used to calculate actual shot arrangement deviations, which then feed into grid correction functions. This feedback loop enables the system to dynamically adjust and correct nonlinear arrangement errors, improving overlay accuracy while managing complexity through iterative correction based on measured data.
Solution Approach 2:
The patent applies parameter changes by modifying the shot arrangement parameters through grid correction based on detected mark positions. The system calculates correction parameters from measured deviations and applies these parameter changes to compensate for nonlinear distortions, thereby improving manufacturing precision without requiring fundamental changes to the exposure apparatus structure.
3Measurement precision
If more marks are detected on the wafer to achieve higher overlay accuracy, then measurement precision is improved, but loss of time increases due to extended detection duration
Solution Approach 1:
The patent applies preliminary action by pre-selecting sample shot areas that will be used for mark detection before the actual measurement process begins. This pre-selection is based on statistical considerations and wafer characteristics, allowing the system to prepare an optimal set of measurement points in advance. During execution, marks are detected only in these predetermined sample areas, achieving high measurement precision with reduced detection time compared to random or exhaustive selection.
Data Source
AI summary
A measurement device is equipped with a surface plate, a slider which holds a substrate and which is movable relative to the surface plate, a drive system that moves the slider, a first position measurement system which measures the slider's first position information relative to the surface plate, a measurement unit having a mark detection system that detects a mark on a substrate, a second position measurement system which measures a relative second position information between the mark detection system and substrate, and a controller which obtains the first position information from the first position measurement system and second position information from the second position measurement system while controlling the slider's movement by the drive system, and obtains position information of a plurality of marks based on detection signals of the mark detection system having detected marks on the substrate, the first position information, and the second position information.