Angle-Resolved Antisymmetric Scatterometry for Overlay Offset
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Solution Overview
Problem
Current scatterometry methods for measuring overlay offset in semiconductor wafers are slow and require detailed modeling, making them inefficient for accurately measuring complex profiles and asymmetry, especially when dealing with structures like two gratings separated by a layered non-flat film.
Innovation Solution
The method involves obtaining anti-symmetric differential signals from multiple scatterometry cells with programmed offsets, allowing for the computation of overlay offset without relying on simulated reference signals, thereby reducing the need for large libraries of simulated data and enabling faster measurement through the use of fewer cells and specific optical configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If detailed modeling is used to measure overlay offset, then measurement precision is improved, but measurement time increases and productivity decreases
Solution Approach 1:
The patent extracts the essential measurement function from complex detailed modeling by using anti-symmetric differential signals that directly encode overlay information. The method takes only the necessary asymmetric signal components and processes them to obtain overlay offset, eliminating the need for full detailed modeling while maintaining accuracy.
Solution Approach 2:
The patent performs preliminary signal processing by pre-computing anti-symmetric differential signals from measured scatterometry data. This preliminary extraction of asymmetric components before final overlay calculation enables faster measurement without requiring time-consuming detailed modeling during the actual measurement process.
2Measurement precision
If detailed modeling is used to measure complex profiles, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts only the anti-symmetric differential signal components that contain overlay information, separating this essential information from the complex full signal model. This extraction approach maintains measurement precision for complex profiles while significantly reducing the complexity of the measurement device and processing requirements.
Solution Approach 2:
The patent segments the scatterometry signal into symmetric and anti-symmetric components, focusing only on the anti-symmetric differential signals for overlay measurement. This segmentation simplifies the measurement system by ignoring symmetric components that do not contribute to overlay information, reducing device complexity while maintaining precision.
3Measurement precision
If more scatterometry cells are used to measure overlay offset, then measurement precision is improved, but device complexity and measurement time increase
Solution Approach 1:
The patent makes each scatterometry cell multi-functional by programming them with different offset values that can measure overlay in different directions. The same cell structure serves multiple measurement purposes through different offset configurations, reducing the total number of cells needed while maintaining comprehensive measurement capability.
Solution Approach 2:
The patent utilizes anti-symmetric differential signals generated by asymmetric offset programming in the scatterometry cells. This asymmetry in the signal characteristics enables precise overlay measurement with fewer cells, as the asymmetric signals provide directional information that reduces the need for multiple symmetric measurement configurations.
4Measurement precision
If conventional scatterometry methods are used, then measurement precision is maintained, but loss of time increases due to slow measurement speed
Solution Approach 1:
The patent extracts anti-symmetric differential signals that directly contain overlay information, eliminating the need for time-consuming detailed modeling. This extraction approach maintains measurement precision while significantly reducing measurement time by processing only the essential asymmetric signal components.
Solution Approach 2:
The patent performs preliminary extraction of anti-symmetric signal components before final overlay calculation, preparing the data in advance. This preliminary action reduces the computational burden during actual measurement, maintaining precision while cutting measurement time through efficient signal processing.
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 simplifies the measurement process by relying on symmetry characteristics of the signals, reducing the complexity and time required for overlay offset determination, and allows for accurate measurement of overlay offsets in both x and y directions using fewer cells, enhancing the efficiency of scatterometry metrology.
Implementation Method 1
obtaining a first anti-symmetric differential signal (ΔS1) associated with a first scatterometry cell; obtaining a second anti-symmetric differential signal (ΔS2) associated with a second scatterometry cell
Data Source
AI summary
A method for determining an overlay offset may include, but is not limited to: obtaining a first anti-symmetric differential signal (ΔS1) associated with a first scatterometry cell; obtaining a second anti-symmetric differential signal (ΔS2) associated with a second scatterometry cell and computing an overlay offset from the first anti-symmetric differential (ΔS1) signal associated with the first scatterometry cell and the second anti-symmetric differential signal (ΔS2) associated with the second scatterometry cell.