Pupil Phase Analysis for Semiconductor Overlay Metrology
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Solution Overview
Problem
Conventional overlay metrology in semiconductor manufacturing primarily relies on intensity-based optical systems, which do not effectively utilize phase information for measuring overlay errors between multiple layers, limiting the accuracy and precision of alignment measurements.
Innovation Solution
A method and system that measures phase distributions across the pupil plane of semiconductor wafers with intentionally offset overlay targets to determine phase tilts, allowing for calibration and quantification of overlay errors using pupil phase information, thereby enhancing measurement sensitivity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If intensity-based optical systems are used for overlay metrology, then the system is simpler to implement, but measurement precision is limited
Solution Approach 1:
The patent transitions from intensity-based measurement (single dimension) to phase-based measurement (adding phase dimension). By measuring phase distributions across the pupil plane and calculating phase tilts, the system extracts additional dimensional information from the optical field, enabling more precise overlay error measurement without proportionally increasing system complexity
Solution Approach 2:
The patent changes the measurement parameter from intensity to phase. By utilizing phase information contained in the reflected illumination and measuring phase distributions across different pupil plane locations, the system achieves higher measurement precision. The phase tilt calculations provide sensitive indicators of overlay errors that are not accessible through intensity measurements alone
2Measurement precision
If phase information is utilized for overlay measurement, then measurement sensitivity improves, but system complexity increases
Solution Approach 1:
The patent segments the pupil plane into multiple measurement locations and measures phase distributions at each location separately. This segmentation approach allows the complex phase measurement task to be broken down into manageable components, where phase tilts are calculated independently for each pupil location and then combined to determine overlay errors, reducing overall system complexity
Solution Approach 2:
The patent introduces phase tilt calculations as an intermediary parameter between raw phase measurements and final overlay error determination. By first calculating phase tilts from phase distributions and then using these tilts to determine overlay errors, the system creates a simplified intermediate representation that reduces computational complexity while maintaining measurement sensitivity
3Measurement precision
If multiple overlay targets with intentional overlays are measured, then calibration accuracy improves, but measurement time increases
Solution Approach 1:
The patent performs preliminary measurements on multiple overlay targets with known intentional overlays to establish calibration data before measuring unknown overlay errors. By pre-measuring and storing the relationship between phase tilts and known overlay values, the system creates a calibration model that accelerates subsequent measurements, reducing the time penalty of measuring multiple targets
Solution Approach 2:
The patent combines measurements from multiple overlay targets with different intentional overlays to create a comprehensive calibration dataset. By merging the phase tilt information from targets with opposite intentional overlays, the system establishes a more accurate calibration model that accounts for various overlay conditions, improving calibration accuracy while efficiently utilizing measurement data
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 enables more precise measurement of overlay errors by leveraging phase information, improving the alignment accuracy between multiple layers and reducing the impact of aberrations and focus errors, allowing for lower-cost optical components and more accurate calibration of phase tilt versus overlay data.
Implementation Method 1
In addition to intensity information, the illumination reflected from the surface of a given set of overlay targets of a semiconductor wafer also includes phase information
Data Source
AI summary
The present invention may include measuring a first phase distribution across a pupil plane of a portion of illumination reflected from a first overlay target of a semiconductor wafer, wherein the first overlay target is fabricated to have a first intentional overlay, measuring a second phase distribution across the pupil plane of a portion of illumination reflected from a second overlay target, wherein the second overlay target is fabricated to have a second intentional overlay in a direction opposite to and having the same magnitude as the first intentional overlay, determining a first phase tilt associated with a sum of the first and second phase distributions, determining a second phase tilt associated with a difference between the first and second phase distributions, calibrating a set of phase tilt data, and determining a test overlay value associated with the first and second overlay target.