Multi-Layer Calibration Targets for In-Device Overlay Measurement
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Solution Overview
Problem
Existing overlay metrology methods struggle to accurately measure the alignment of multiple patterns in semiconductor devices, particularly at submicrometer scales, due to the limitations of scribe line measurements and the influence of underlying layers, leading to increased measurement uncertainty and reduced throughput.
Innovation Solution
The use of multi-layer calibration targets with known overlay shifts, located in the scribe line, product area, or on a separate calibration wafer, to determine the overlay error directly on the device by analyzing the signal response from these targets and the device itself, using optical metrology techniques like spectroscopic ellipsometry and Mueller matrix analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate sets of targets are generated for each individual overlay error measurement, then measurement accuracy for multiple patterns is improved, but device complexity and measurement time increase
Solution Approach 1:
The patent combines multiple overlay error measurements into a single calibration target structure. The calibration target includes multiple patterns corresponding to different patterning steps, allowing simultaneous measurement of multiple overlay errors (e.g., between first and second patterns, second and third patterns) using one target instead of requiring separate targets for each measurement pair.
Solution Approach 2:
The calibration target is designed to serve multiple measurement functions simultaneously. A single calibration target structure can be used to calibrate and measure overlay errors across multiple pattern layers and different patterning steps, making the measurement system more efficient by eliminating the need for multiple specialized targets.
2Measurement precision
If separate measurements are performed for each overlay error, then measurement accuracy is maintained, but productivity decreases
Solution Approach 1:
The patent merges multiple separate overlay measurements into a single integrated measurement process. By incorporating multiple patterns and their relationships into one calibration target, the system can extract multiple overlay error values simultaneously from a single measurement, thereby increasing throughput without compromising accuracy.
Solution Approach 2:
The measurement process continues efficiently by obtaining multiple overlay error measurements in one continuous measurement action rather than performing sequential separate measurements. The single calibration target enables continuous extraction of multiple overlay parameters without interrupting the measurement flow.
3Measurement precision
If a large number of calibration targets are used to measure multiple overlay errors, then measurement completeness is improved, but the footprint required increases
Solution Approach 1:
The patent merges multiple calibration functions into a single compact calibration target structure. Instead of requiring separate physical targets for each overlay error measurement, the integrated target contains all necessary patterns and relationships to enable complete multi-layer overlay measurement within a smaller area.
Solution Approach 2:
The calibration target structure employs a nested arrangement where multiple patterns and measurement features are embedded within a single target geometry. This nested design allows multiple overlay error measurements to be contained within one compact structure, reducing the overall footprint while maintaining measurement completeness.
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
This approach allows for precise, non-destructive overlay measurements that account for all patterning steps, reducing measurement uncertainty and increasing throughput by directly measuring overlay errors on the device, thereby improving alignment accuracy and process control.
Implementation Method 1
a light source that produces light that is incident on and reflected by a sample
Implementation Method 2
using optical metrology techniques like spectroscopic ellipsometry and Mueller matrix analysis
Data Source
AI summary
Overlay is determined for a device using signals measured from the device and a signal response to overlay determined from a plurality of calibration targets. Each calibration target has the same design as the device, but includes a known overlay shift. The calibration targets may be located in a scribe line, within a product area on the wafer, or on a separate calibration wafer. Each calibration target may have a different overlay shift, including zero overlay shift. The device may serve as a calibration target with zero overlay shift. The overlay shift may be in two orthogonal directions. The signal response to overlay may be determined based on a set of signals obtained from the calibration targets. A second set of signals may then be obtained from the device and the overlay determined based on the second set of signals and the determined signal response to overlay.