Scatterometry Overlay Target Cell Segmentation for Error Discrimination
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Solution Overview
Problem
Existing scatterometry overlay metrology techniques face challenges in accurately measuring overlays between layers in integrated circuits due to process-related and illumination-related errors, which affect the precision and reliability of measurements.
Innovation Solution
The implementation of scatterometry overlay targets with at least three cells associated with a measurement direction, where two cells have periodic structures at different target layers with the same pitch and opposite offsets, and a third cell with a periodic structure at only one layer, allows for the detection of irregularities, enhances metrology simulations, and mitigates errors by incorporating scatterometry measurements in the additional cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional scatterometry overlay targets with two cells are used, then the measurement process is simple, but process-related and illumination-related errors reduce measurement precision
Solution Approach 1:
The target is segmented into three separate cells, each with specific periodic structures. Cell 1 has a first periodic structure, cell 2 has a second periodic structure, and cell 3 has a third periodic structure. This segmentation allows independent measurement of different error sources, enabling precise separation of overlay errors from process and illumination errors through comparative analysis of the scattered light signals from each cell.
Solution Approach 2:
Each cell is designed with specific local structural characteristics: cell 1 contains a first periodic structure with specific pitch and orientation, cell 2 contains a second periodic structure with different pitch or orientation, and cell 3 contains a third periodic structure serving as a reference. This local quality differentiation enables each cell to respond differently to overlay errors versus process/illumination errors, allowing error discrimination through signal comparison.
2Reliability
If additional cells are added to detect irregularities and mitigate errors, then measurement reliability improves, but wafer space and measurement time increase
Solution Approach 1:
The target combines multiple functional cells into a single integrated structure that can be measured simultaneously in one measurement process. Cell 1, cell 2, and cell 3 are arranged in close proximity with shared support structures, allowing the scatterometry system to collect data from all three cells during a single measurement pass, thereby improving reliability without proportionally increasing measurement time.
Solution Approach 2:
The additional cell (cell 3) serves multiple functions: it provides a reference measurement for illumination non-uniformity correction, enables process error detection through comparison with cells 1 and 2, and contributes to overlay measurement. This multi-functionality ensures that the added structural complexity yields multiple measurement benefits simultaneously, improving reliability while minimizing the penalty in measurement time and wafer space.
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 enhances the accuracy and quality control of metrology measurements, provides additional data, and minimizes errors, while using minimal wafer space and measurement time, enabling robust and efficient detection of process defects and illumination non-uniformities.
Implementation Method 1
scatterometry overlay metrology is used to estimate overlays between layers in produced integrated circuits, by measurements of scatterometry targets and analysis of measured diffraction signals between periodic structures in different target layers
Data Source
AI summary
Scatterometry overlay targets and measurement methods are provided, which are configured to detect and eliminate process-related errors and illumination-related errors from overlay measurements of the targets. Targets comprise at least three cells associated with a measurement direction, wherein at least two of the cells comprise periodic structures at different target layers, having a same pitch and opposite offsets between the two cells, and at least an additional cell comprises a periodic structure with the same pitch at only one of the target layers. The additional cell(s) are used to detect irregularities in the respective periodic structure(s), enable estimation of process quality, provide reference images, enhance metrology simulations and provide mitigation of errors in critical process steps. Measurement methods incorporate scatterometry measurements ion the additional cell(s) for these purposes.