Imaging Overlay Metrology Target with Nested Self-Symmetric Structures
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Solution Overview
Problem
Current overlay metrology targets require significant space for multi-directional measurements, leading to inefficiencies in semiconductor wafer processing due to the need for multiple target structures and increased area usage, which complicates the alignment of layers and increases the risk of optical information contamination between inner and outer target structures.
Innovation Solution
The development of an imaging overlay metrology target with overlapping self-symmetric and additional target structures, where the additional structures are contained within the boundaries of the self-symmetric ones, allowing for a composite exterior region of interest to be defined by removing exclusion zones, enabling efficient measurement of overlay errors while maintaining rotational invariance and reducing the overall space required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple separate target structures are used for multi-directional overlay measurements, then measurement capability in both X and Y directions is achieved, but the overall area required for the metrology target increases significantly
Solution Approach 1:
The patent combines multiple target structures (first target structure with segmentation lines for X-direction measurement and second target structure with segmentation lines for Y-direction measurement) into a single integrated metrology target. Both target structures share a common center of symmetry and are positioned to overlap, allowing simultaneous multi-directional overlay measurements without requiring separate target areas.
Solution Approach 2:
The patent positions the first and second target structures such that they overlap and share a common center of symmetry. The target structures are nested within each other's spatial footprint, with each structure's pattern elements contained within or overlapping the boundary defined by the other structure, thereby maximizing space utilization.
2Ease of manufacture
If segmented pattern elements are used to meet process design rules, then manufacturing compliance is achieved, but overlay measurement becomes reliable in only one direction perpendicular to the segmentation lines
Solution Approach 1:
The patent employs target structures with different segmentation orientations - the first target structure has segmentation lines extending in a first direction (e.g., horizontal for X-overlay), while the second target structure has segmentation lines extending in a second direction orthogonal to the first (e.g., vertical for Y-overlay). This asymmetric arrangement of segmented elements enables reliable overlay measurements in both orthogonal directions simultaneously.
3Area of stationary object
If multiple target structures are placed close together to reduce area, then space efficiency is improved, but optical information contamination between inner and outer target structures increases
Solution Approach 1:
The patent extracts or removes portions of the region of interest (ROI) that would otherwise include optical information from both the inner and outer target structures. By defining the ROI to exclude the inner target structure when measuring the outer structure, and vice versa, the patent eliminates optical contamination while maintaining the compact overlapping geometry of the combined target structures.
Data Source
AI summary
An exclusion region of interest imaging overlay target includes a self-symmetric target structure including two or more pattern elements, and an additional target structure including two or more pattern elements, wherein each of pattern elements of the additional target structure is contained within a boundary defined by one of the pattern elements of the self-symmetric target structure, wherein the self-symmetric target structure is characterized by a composite exterior region of interest, wherein the composite exterior region of interest is formed by removing two or more exclusion zones corresponding with the pattern elements of the additional target structure from an exterior region of interest encompassing the self-symmetric target structure, wherein each of the pattern elements of the additional target structure is characterized by an interior region of interest, wherein the self-symmetric target structure and the additional target structure are configured to have a common center of symmetry upon alignment.