Flexible Sparse Metrology Sampling for Semiconductor Overlay Control
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Solution Overview
Problem
Conventional semiconductor wafer metrology relies on static sampling plans, which are time-consuming and less effective for irregular overlay signatures, especially as device dimensions decrease, necessitating improved metrology capabilities for accurate process control.
Innovation Solution
A system generates flexible sparse sampling plans based on metrology measurements, forming a virtual dense map to calculate process tool correctables, reducing noise and optimizing sampling by selecting a subset of targets that represent the full set of metrology signals, allowing for field-by-field corrections without periodic dense map measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If static sampling plans are used for metrology measurements, then measurement completeness is improved, but measurement time and processing duration increase
Solution Approach 1:
The patent transitions from static sampling plans to dynamic adaptive sampling plans that adjust the number and locations of measurement targets based on process conditions, wafer characteristics, and measurement objectives. This dynamic approach allows the system to use fewer measurements when process variability is low while increasing measurement density when variability increases, thereby reducing overall measurement time while maintaining measurement completeness when needed.
Solution Approach 2:
The system changes sampling parameters (number of targets, spatial distribution, measurement locations) based on process conditions and wafer characteristics. By dynamically adjusting these parameters rather than using fixed static plans, the system optimizes the balance between measurement completeness and measurement time, using minimal measurements when sufficient and comprehensive sampling when necessary.
2Stability of the object's composition
If static sampling plans are used for metrology measurements, then sampling consistency is improved, but adaptability to irregular overlay signatures deteriorates
Solution Approach 1:
The patent implements dynamic adaptive sampling plans that automatically adjust based on detected process conditions and wafer characteristics. When irregular overlay signatures are detected, the system increases measurement density in affected regions and modifies sampling locations accordingly. This dynamic adaptation maintains sampling consistency for regular processes while providing the flexibility needed to capture irregular overlay patterns effectively.
Solution Approach 2:
The system uses feedback from preliminary measurements and process data to adjust subsequent sampling plans. By analyzing overlay signature patterns and process variability, the system determines whether to use standard sampling density or increase measurements in specific regions, thereby adapting to irregular overlay signatures while maintaining consistency for normal processes.
3Measurement precision
If dense map measurements are performed periodically, then overlay correction accuracy is improved, but productivity and throughput decrease
Solution Approach 1:
Instead of performing complete dense map measurements on every wafer, the system applies partial dense mapping only when and where needed based on detected process conditions. For wafers with regular overlay signatures, standard sampling suffices. For wafers exhibiting irregular patterns or high variability, the system selectively increases measurement density in affected regions, thereby maintaining correction accuracy while minimizing the impact on throughput.
Solution Approach 2:
The patent applies different sampling densities to different regions of the wafer based on local overlay signature characteristics. Rather than uniformly increasing measurements across the entire wafer, the system concentrates additional measurements only in regions exhibiting irregular patterns or high variability, thereby achieving accurate local corrections without sacrificing overall productivity.
4Loss of time
If extrapolation techniques are used for field-by-field corrections, then measurement time is reduced, but accuracy for irregular overlay signatures deteriorates
Solution Approach 1:
The system uses feedback from the sparse sampling measurements to determine when extrapolation is sufficient and when direct measurement is needed. By analyzing the quality and characteristics of the sparse measurements, the system identifies regions where extrapolation from neighboring fields is reliable versus regions where direct measurement is necessary to capture irregular patterns accurately, thereby optimizing the balance between measurement time and accuracy.
Solution Approach 2:
The patent dynamically switches between extrapolation-based corrections and direct measurement-based corrections based on process conditions and detected overlay signature characteristics. For regular, predictable patterns, extrapolation provides accurate corrections with minimal measurements. For irregular patterns, the system dynamically increases measurement density in affected regions to provide sufficient data for accurate direct modeling, thereby maintaining accuracy while minimizing measurement time.
Data Source
AI summary
The generation of flexible sparse metrology sample plans includes receiving a full set of metrology signals from one or more wafers from a metrology tool, determining a set of wafer properties based on the full set of metrology signals and calculating a wafer property metric associated with the set of wafer properties, calculating one or more independent characterization metrics based on the full set of metrology signals, and generating a flexible sparse sample plan based on the set of wafer properties, the wafer property metric, and the one or more independent characterization metrics. The one or more independent characterization metrics of the one or more properties calculated with metrology signals from the flexible sparse sampling plan is within a selected threshold from one or more independent characterization metrics of the one or more properties calculated with the full set of metrology signals.