Overlay Error Determination via Target Image Asymmetry
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Solution Overview
Problem
Current overlay metrology techniques struggle to accurately measure alignment errors between increasingly smaller semiconductor device layers, as existing optical systems lack the resolution to detect features within small targets, and modifying these systems is costly and time-consuming.
Innovation Solution
The method involves calculating overlay error based on asymmetry or symmetry in image profiles, using existing measurement tools and systems, by defining a region of interest, scanning image lines, and calculating symmetry values to determine the center point and overlay error, which can be applied to very small in-chip targets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing optical measurement systems are used to measure small targets, then measurement speed is maintained, but measurement precision deteriorates due to insufficient optical resolution
Solution Approach 1:
The patent applies asymmetry by measuring the asymmetry of image profiles rather than directly measuring symmetric target features. The method calculates asymmetry values from image intensities at different positions, and uses these asymmetry measurements to determine overlay error. This transforms the measurement approach from direct feature resolution to asymmetry-based calculation, enabling precise measurements with existing optical resolution capabilities
Solution Approach 2:
The patent changes the measurement parameter from direct spatial position measurement to asymmetry parameter measurement. By transforming the measurement quantity from physical dimension to derived parameter (asymmetry ratio), the system can achieve higher measurement precision without improving optical resolution. The asymmetry parameter is calculated from intensity ratios, which maintains sensitivity to small displacements while being compatible with existing optical systems
2Measurement precision
If optical systems are modified to improve resolution for smaller targets, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The patent changes the measurement parameter from direct spatial position to asymmetry ratio, allowing existing optical systems to measure smaller targets without modification. The asymmetry calculation method transforms the measurement problem into one that can be solved with current optical resolution, avoiding the need for complex system changes while maintaining measurement precision for reduced-size targets
Solution Approach 2:
The patent replaces direct optical measurement of physical features with a computational approach based on image intensity analysis. Instead of relying on mechanical or optical system improvements, the solution uses software-based asymmetry calculation to achieve the required measurement precision, substituting physical system complexity with algorithmic processing
3Measurement precision
If direct measurement of misregistration between patterns is used, then overlay error is quantified, but measurement time increases for repeated measurements
Solution Approach 1:
The patent performs preliminary action by establishing the asymmetry measurement methodology and calibration in advance. The asymmetry calculation framework is set up beforehand, allowing rapid repeated measurements without requiring complex image processing or analysis for each measurement. The pre-established asymmetry parameters enable quick overlay error determination while maintaining precision
Data Source
AI summary
In systems and methods measure overlay error in semiconductor device manufacturing based on target image asymmetry. As a result, the advantages of using very small in-chip targets can be achieved, while their disadvantages are reduced or eliminated. Methods for determining overlay error based on measured asymmetry can be used with existing measurement tools and systems. These methods allow for improved manufacturing of semiconductor devices and similar devices formed from layers.