Overlay Metrology Using Amplitude Asymmetry Across Diffraction Orders
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Solution Overview
Problem
Existing overlay metrology techniques face challenges in accurately measuring and correcting for amplitude asymmetries in overlay targets due to the increasing complexity of feature sizes and pitches in modern devices, leading to reduced contrast and signal-to-noise ratios, and potential errors in overlay measurements.
Innovation Solution
A metrology system that generates multiple images of overlay targets under different measurement conditions, such as varying focal distances or diffraction orders, to calculate amplitude asymmetry and generate quality metrics, which are used to correct overlay measurements and improve process control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the size and pitch of device features are scaled down to meet market demands, then device density and integration are improved, but contrast and signal-to-noise ratios during optical measurements deteriorate
Solution Approach 1:
The overlay target is segmented into multiple periodic features with different pitches and orientations. By using multiple diffraction orders from these segmented features, the system can maintain measurement contrast even as individual feature sizes are reduced, since different pitch values produce different diffraction patterns that can be combined to improve signal quality.
Solution Approach 2:
The invention transitions from measuring only overlay displacement to also measuring amplitude asymmetry in the diffraction pattern. By utilizing the amplitude dimension of the diffraction orders in addition to positional information, the system can correct for target deformations and maintain measurement accuracy despite reduced feature contrast.
2Measurement precision
If overlay targets are designed to facilitate visible light characterization, then measurement capability is improved, but process compatibility deteriorates
Solution Approach 1:
The system measures amplitude asymmetry as a quality metric and uses this information to correct overlay measurements. By providing feedback on target deformation through the amplitude asymmetry measurement, the system can compensate for process incompatibility effects and maintain reliable measurements even when target design priorities conflict.
Solution Approach 2:
The invention changes the measurement parameters from solely positional analysis to include amplitude analysis of diffraction orders. By monitoring amplitude asymmetry as an additional parameter, the system can detect and correct for target deformations caused by process incompatibility, thereby maintaining measurement reliability across different target designs.
3Reliability
If process compatibility is emphasized in overlay target design, then fabrication integration is improved, but measurement accuracy deteriorates due to decreased contrast
Solution Approach 1:
The overlay target uses multiple periodic features with different pitches segmented across the target structure. This segmentation allows the target to maintain process compatibility while providing multiple diffraction orders that can be analyzed for both position and amplitude, thereby maintaining measurement accuracy despite the constraints of process-compatible design.
Solution Approach 2:
The system adds amplitude asymmetry measurement as an additional dimension to the overlay measurement process. This extra measurement dimension allows correction of accuracy losses that occur when target design is optimized for process compatibility rather than measurement contrast, since amplitude information provides independent verification and correction capability.
4Measurement precision
If multiple images are generated with different measurement conditions to calculate amplitude asymmetry, then measurement accuracy is improved, but measurement time and system complexity increase
Solution Approach 1:
The system merges multiple measurement conditions into a single integrated measurement process. By capturing images under different focal distances or diffraction order configurations and processing them together to calculate amplitude asymmetry, the system achieves improved accuracy without requiring separate measurement cycles, thereby minimizing time loss.
Solution Approach 2:
The measurement process maintains continuity by using multiple images taken under different conditions as complementary data rather than sequential measurements. The amplitude asymmetry calculation continuously processes information from all images simultaneously, ensuring that the useful measurement action continues without interruption and time is not lost to repeated measurements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances the accuracy of overlay measurements by mitigating amplitude asymmetries, providing a metric for process control and enabling feedback and feed-forward corrections to improve fabrication processes.
Implementation Method 1
calculating an amplitude asymmetry associated of opposing diffraction orders of the illumination by the overlay target
Data Source
AI summary
A metrology system may include a controller to receive two or more images of the overlay target from one or more detectors of an optical sub-system, the overlay target including first and second periodic features generated with different measurement conditions, each measurement condition associated with at least one of a sample focal distance or a configuration of diffraction orders of the illumination by the overlay target that contributes to the associated image. The controller may further calculate an amplitude asymmetry associated of opposing diffraction orders of the illumination by the overlay target based on the two or more images and one or more quality metrics associated with the overlay target based on the amplitude asymmetry.