Wafer Overlay Control via Feedforward Feedback Segmentation
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Solution Overview
Problem
Conventional overlay control systems in semiconductor manufacturing face challenges in achieving tight overlay control, particularly with the shrinking dimensions of semiconductor devices and the increased complexity of multiple patterning techniques, which require more precise alignment and correction across multiple lithography steps, but often rely on static feedforward corrections and extensive metrology, leading to increased time and costs.
Innovation Solution
An overlay control system that combines wafer-by-wafer feedforward and lot-by-lot feedback control, utilizing a controller to acquire feedback and feedforward measurements, generate reference and artificial overlay maps, and produce control signals to adjust lithography tools for improved alignment, reducing overlay errors and metrology time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple patterning techniques are used to shrink device dimensions, then manufacturing precision is improved, but device complexity increases and overlay control becomes more critical
Solution Approach 1:
The overlay control process is segmented into distinct feedforward and feedback control stages. Feedforward control measures overlay errors on first layers before second layer fabrication, while feedback control measures overlay errors on second layers after fabrication. This segmentation allows each control mechanism to be optimized independently, managing the complexity of multiple patterning processes.
Solution Approach 2:
The system performs preliminary overlay measurements and corrections on first layers before fabricating second layers. By measuring and correcting overlay errors in advance (feedforward control), the system prevents error propagation to subsequent layers, thereby improving final overlay precision without requiring complex real-time adjustments during multi-step lithography.
2Manufacturing precision
If conventional feedback control alone is used, then implementation is simple, but overlay control precision is insufficient for multiple patterning
Solution Approach 1:
The system merges feedforward control and feedback control into a unified overlay control architecture. Feedforward control provides preliminary corrections based on measurements from first layers, while feedback control provides final corrections based on measurements from second layers. This combination achieves high overlay precision for multiple patterning without requiring overly complex individual control mechanisms.
Solution Approach 2:
The system implements feedback control by measuring overlay errors on second layers after fabrication and using these measurements to generate corrections for subsequent lots. This closed-loop feedback mechanism continuously improves overlay precision across production lots, enabling the system to meet the stringent requirements of multiple patterning processes.
3Measurement precision
If extensive metrology is performed to achieve tight overlay control, then overlay measurement precision is improved, but processing time and costs increase
Solution Approach 1:
Metrology measurements are segmented into feedforward measurements on first layers and feedback measurements on second layers. This segmentation allows overlay control to be performed at different stages with appropriate measurement densities, achieving necessary precision without requiring exhaustive measurements at every stage, thereby maintaining productivity.
Solution Approach 2:
The system performs preliminary overlay measurements on first layers before second layer fabrication. By identifying and correcting overlay errors early in the process (feedforward control), the system reduces the need for extensive corrective measurements and rework later, thereby improving both measurement efficiency and throughput while maintaining precision.
Data Source
AI summary
An overlay control system is disclosed. In embodiments, the system may include a controller configured to: acquire a set of feedback overlay measurements based on a plan of record (POR) sampling map on a second layer of samples of at least one previous lot of samples; generate a reference wafer overlay map based on the set of feedback overlay measurements; acquire a set of feedforward overlay measurements based on a feedforward sampling map on a first layer of a set of samples of a current lot of samples; generate a set of artificial overlay vector maps for the set of samples of the current lot of samples based on the set of feedforward overlay measurements; and cause a lithography tool to fabricate a second layer of samples of the current lot of samples based on the reference wafer overlay map and the set of artificial overlay vector maps.