Lithography Overlay Error Measurement Using Scatterometry
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Solution Overview
Problem
Current methods for calculating overlay error in lithographic processes require a large area of the substrate for multiple targets, which reduces the usable space for pattern formation in integrated circuits.
Innovation Solution
A method and apparatus that project a beam of radiation onto multiple targets at various positions on the substrate, using a scatterometer to measure reflected radiation and calculate overlay error, assuming a constant proportion of error due to asymmetry across all targets, thereby reducing the number of targets needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large number of targets are used to account for different parameters (linear displacement, rotation, magnification, asymmetry), then measurement precision is improved, but substrate area occupied increases
Solution Approach 1:
The patent changes the parameter of target quantity from many to few (specifically to 4 targets), and compensates by enhancing the measurement method to account for multiple parameters (linear displacement, rotation, magnification, asymmetry) through mathematical modeling and calculation, thus maintaining measurement precision while reducing substrate area occupation
Solution Approach 2:
The patent explicitly addresses asymmetry as one of the four parameters to be accounted for in the overlay error calculation. By incorporating asymmetry correction into the measurement model, the system can achieve accurate measurements with fewer targets, as the asymmetry parameter is mathematically compensated rather than requiring additional symmetric target pairs
2Reliability
If multiple sets of targets are etched for each pattern layer, then overlay error monitoring reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent makes the 4-target configuration universal for measuring overlay error across multiple pattern layers. The same 4-target structure serves all measurement needs by incorporating mathematical models that account for all relevant parameters (displacement, rotation, magnification, asymmetry), eliminating the need to create different target configurations for different layers
Solution Approach 2:
The patent performs preliminary mathematical modeling and parameter analysis to establish a comprehensive measurement model before actual measurement. By pre-calculating the relationships between the 4 targets and all relevant error parameters, the system ensures reliable measurement without needing to add complex target structures for each new measurement scenario
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 minimizes the substrate area required for target placement, increasing the usable space for pattern formation and improving manufacturing efficiency by reducing the number of targets needed from 20 to 8, or potentially 4 with 2D targets, thus optimizing scribe lane usage.
Implementation Method 1
measuring radiation reflected from each of the plurality of targets on the substrate using a scatterometer
Data Source
AI summary
Radiation is projected onto a plurality of targets on a substrate. By assuming that the overlay error derivable from asymmetry varies smoothly across the substrate, the number of targets measured can be reduced. This may result in a smaller area of the scribe lane being used by targets for each layer of the substrate.