Hybrid Overlay Metrology for Device-Relevant Accuracy
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Solution Overview
Problem
Existing overlay metrology systems face challenges in achieving device-relevant accuracy while balancing throughput requirements, as they often introduce errors due to differences in size, orientation, and location between overlay targets and device features, and may damage device features during measurement.
Innovation Solution
The system employs a hybrid overlay metrology approach combining optical metrology tools for high-throughput measurements with particle-beam metrology tools to resolve device-scale features, using a controller to generate device-relevant corrections and provide feedback for fabrication tools, thereby compensating for errors and maintaining overlay within tight tolerances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If optical metrology tools are used for overlay measurements, then throughput is improved, but measurement precision deteriorates due to susceptibility to errors from target-feature mismatches
Solution Approach 1:
The system measures overlay at both overlay targets and device features, then uses the device feature measurements to generate adjustments that are applied to correct the overlay measurements. This feedback loop compensates for the inherent errors in optical metrology of overlay targets, maintaining measurement precision while preserving high throughput capability.
Solution Approach 2:
The system changes the measurement parameters by using multiple measurement locations (both overlay targets and device features) and combining their results. By measuring at device features which have the same scale and properties as the actual device structures, the system obtains more accurate overlay data that can be used to correct measurements from the overlay targets.
2Measurement precision
If particle-beam metrology tools are used to measure device-scale features, then measurement precision is improved, but productivity deteriorates due to limited throughput
Solution Approach 1:
The system applies particle-beam metrology selectively only to device features for generating correction adjustments, rather than using it for all overlay measurements. This partial application maintains high measurement precision where needed while preserving overall throughput by relying on faster optical metrology for routine measurements.
Solution Approach 2:
The system uses device features as an intermediary to transfer the high-precision measurement capability from particle-beam metrology to the overall overlay measurement process. The device feature measurements serve as a reference that corrects the optical overlay target measurements, enabling accurate device-relevant overlay without requiring particle-beam metrology for every measurement.
3Measurement precision
If overlay targets with device-scale features are used, then measurement precision is improved, but device complexity increases due to target design requirements
Solution Approach 1:
The system makes device features serve multiple functions: they act as both the actual device structures to be fabricated and as metrology targets for overlay measurement. This eliminates the need for separate, complex overlay target designs with device-scale features, as the device features themselves provide the necessary measurement reference.
Data Source
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AI summary
An overlay metrology system may include a controller to generate optical tool error adjustments for a hybrid overlay target including optically-resolvable features and device-scale features by measuring a difference between an optical overlay measurement based on the optically-resolvable features and a device-scale overlay measurement based on the device-scale features, generate target-to-device adjustments for the hybrid overlay target based on positions of features within the device area, determine device-relevant overlay measurements for one or more locations in the device area based on at least one of the optical overlay measurement, the optical tool error adjustments, or the target-to-device adjustments, and provide overlay correctables for the device area to a lithography tool to modify exposure conditions for at least one subsequent exposure based on the device-relevant overlay measurements.