Single-Cell Scatterometry Overlay Targets for In-Die Metrology
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing scatterometry overlay (SCOL) metrology methods require large targets with multiple cells and complex illumination conditions, leading to increased target size and reduced measurement efficiency.
Innovation Solution
Utilizing a single cell SCOL target with small illumination spots and varying illumination parameters to generate a signal matrix, allowing for efficient measurement of overlay using interference signals from zeroth and first diffraction orders, reducing target size and improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple cells with multiple periodic structures are used in SCOL metrology, then measurement accuracy can be maintained, but target size increases and measurement efficiency decreases
Solution Approach 1:
The invention divides the measurement task into multiple independent measurements at different spot locations and illumination parameters, rather than requiring multiple cells in a single target. Each measurement contributes to the overall overlay determination through differential signal analysis, allowing the same accuracy with a smaller target area.
Solution Approach 2:
The invention transitions from spatial segmentation (multiple cells in different locations) to parameter segmentation (multiple measurements at different illumination parameters and spot locations). This dimensional change allows the same measurement information to be obtained from a single cell by varying measurement parameters rather than target geometry.
2Measurement precision
If multiple cells with multiple periodic structures are used, then overlay can be derived from differential signals, but device complexity increases
Solution Approach 1:
The invention extracts the essential measurement function from the complex multi-cell structure and concentrates it into a single cell measured at multiple parameters. The differential signal analysis is performed computationally rather than requiring physical differential structures, simplifying the target design while maintaining measurement capability.
Solution Approach 2:
A single cell structure serves multiple measurement functions by being measured at different spot locations and illumination parameters. This multi-functional single cell replaces what would traditionally require multiple specialized cells, reducing structural complexity while maintaining comprehensive measurement capability.
3Measurement precision
If large targets with multiple cells are used, then measurement accuracy is maintained, but measurement efficiency decreases
Solution Approach 1:
The invention performs preliminary measurements at multiple spot locations and illumination parameters before final overlay calculation. These preliminary measurements capture the necessary signal variations that enable accurate overlay determination from a single cell, improving measurement efficiency by avoiding the need to scan large multi-cell targets.
Solution Approach 2:
Instead of physically copying multiple cells in different locations, the invention creates virtual copies through computational analysis of a single cell measured at multiple parameters. The differential signal analysis computationally reconstructs the measurement information that would otherwise require physical multiple cells, significantly improving measurement efficiency.
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
The single cell approach enables smaller targets, enhancing measurement accuracy and fidelity, and allows for in-die metrology, reducing the real estate required for metrology targets while maintaining measurement speed and accuracy.
Implementation Method 1
measuring interference signals of zeroth and first diffraction orders
Implementation Method 2
measuring interference signals of zeroth and first diffraction orders
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
Scatterometry overlay (SCOL) measurement methods, systems and targets are provided to enable efficient SCOL metrology with in-die targets. Methods comprise generating a signal matrix by: illuminating a SCOL target at multiple values of at least one illumination parameter, and at multiple spot locations on the target, wherein the illumination is at a NA (numerical aperture) >1/3 yielding a spot diameter < 1µ, measuring interference signals of zeroth and first diffraction orders, and constructing the signal matrix from the measured signals with respect to the illumination parameters and the spot locations on the target; and deriving a target overlay by analyzing the signal matrix. The SCOL targets may be reduced to be a tenth in size with respect to prior art targets, as less and smaller target cells are required, and be easily set in-die to improve the accuracy and fidelity of the metrology measurements.